FEDERAL EMERGENCY MANAGEMENT AGENCY FEMA 356/November 2000

PRESTANDARD AND COMMENTARY FOR THE

SEISMIC REHABILITATION OF BUILDINGS

FEDERAL EMERGENCY MANAGEMENT AGENCY FEMA 356/November 2000

PRESTANDARD AND COMMENTARY FOR THE

SEISMIC REHABILITATION OF BUILDINGS
NOTICE: This report was prepared under a cooperative agreement between the Federal Emergency Management 

Agency and the American Society of Civil Engineers.

Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the 

views of the Federal Emergency Management Agency (FEMA) or the American Society of Civil Engineers (ASCE). 

Additionally, neither FEMA, ASCE, nor any of their employees make any warranty, expressed or implied, nor 

assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product, or process included in this publication. Users of information from this publication assume all liability arising 

from such use.

For further information concerning this document or the activities of the ASCE, contact the American Society of 

Civil Engineers, 1801 Alexander Bell Drive, Reston, Virginia, 20191, (703) 295-6000.
FEDERAL EMERGENCY MANAGEMENT AGENCY FEMA 356/November 2000

PRESTANDARD AND COMMENTARY FOR THE

SEISMIC REHABILITATION OF BUILDINGS

Prepared by

AMERICAN SOCIETY OF CIVIL ENGINEERS

Reston, Virginia

Prepared for

FEDERAL EMERGENCY MANAGEMENT AGENCY

Washington, D.C.

November 2000

Federal Emergency Management Agency

Washington, D.C.
ASCE Standards Program and the Structural Engineering Institute

The Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) was created in 1996 as a semiautonomous organization within ASCE to focus on serving the needs of the broad structural engineering community. The mission of SEI is to advance the profession of structural engineering by enhancing and sharing knowledge, supporting research, and

improving business and professional practices. SEI is comprised of three divisions: Technical Activities, Business and Professional Activities, and Codes and Standards Activities.

The standards activities of SEI operate under the umbrella of ASCE’s standards program. ASCE has over 125,000 members 

worldwide. More than 7,000 of these members participate on over 500 technical committees, 44 of which are active Standards 

Committees that have resulted in over 30 published standards, to date. In addition to individual participation, ASCE's standards 

program actively encourages participation by representatives of affected organizations, thereby expanding the input into the standards developing process well beyond ASCE’s 125,000 members to ensure a high level of exposure and participation.

ASCE’s standards program, and hence SEI’s activities, are governed by the Rules for Standards Committees (referred to herein 

as ASCE Rules). These Rules are reviewed and approved by the American National Standards Institute (ANSI), which accredits 

ASCE as a standards developing organization (SDO). Membership and participation in ASCE's standards program is open to 

both members and non-members of ASCE. Standards committees are required to publicize their activities through ASCE News 

and to distribute meeting agendas at least 30 days in advance, to afford all interested parties the opportunity to participate. To further extend beyond its membership, ASCE distributes press releases on new standards activities, and to announce when a standard progresses into the public ballot phase. ASCE’s Public Relations Department maintains a list of over 400 civil engineering

related publications, and it is common for 40 to 50 press releases to be distributed, thereby notifying and soliciting comments

from several hundred thousand individuals.

An ASCE standards committee must have a minimum of 12 members, though, current committees range in size from 12 to over 

200 members. To join a standards committee, an application must be completed which describes the individual’s qualifications 

and interest in the respective subject. However, acceptance of an applicant is not based solely on technical qualifications. During 

the initial formation of a standards committee, membership is open to any interested party, provided they can demonstrate that 

they are directly or indirectly affected by the activity.

As the committee begins its work to bring the standard into suitable condition for balloting, the committee also must ensure that 

its membership is “balanced.” ASCE Rules define a balanced committee and require that members be classified into one of three 

categories: Producer, Consumer, or General Interest. For standards of regulatory interest, a subclass of General Interest is established for Regulators. Each of the three categories must compose from 20 to 40 percent of the total committee membership. 

When the subclass of Regulators is established, they must compose 5 to 15 percent of the total membership.

Producers include representatives of manufacturers, distributors, developers, contractors and subcontractors, construction labor 

organizations, associations of these groups, and professional consultants to these groups. Consumers include representatives of

owners, owner's organizations, designers, consultants retained by owners, testing laboratories retained by owners, and insurance 

companies serving owners. General Interest members include researchers from private, state and federal organizations, representatives of public interest groups, representatives of consumer organizations, and representatives of standards and model code 

organizations. Regulators include representatives of regulatory organizations at local, state, or federal levels of government.

Recognizing that committee members are volunteers whose time and travel budgets are limited, ASCE's Rules are designed to 

allow members to fully participate in the work of the standards committee without attending committee meetings. Responding in 

writing to letter ballots is a proven and effective means of participation. 

ASCE’s ANSI accreditation ensures that all standards developed for the civil engineering profession that are intended to become

part of the laws which govern the profession have been developed through a process that is fully open, allows for the participation of all interested parties, and provides participants with due process. Standards resulting from this ANSI process are true

national voluntary consensus standards which serve and benefit the general public.
FEMA 356 Seismic Rehabilitation Prestandard v

Participants

Project Managers

Ugo Morelli, FEMA Project Officer

Thomas R. McLane, ASCE Project Manager

Project Team

Chris D. Poland, Principal Investigator

Jon A. Heintz, Author

Ashvin Shah, Author

Vicky Vance May, Author

Melvyn Green

Ronald O. Hamburger

William T. Holmes

Jack P. Moehle

Mike Mehrain

Lawrence D. Reaveley

Christopher Rojahn

Jim Rossberg

Daniel Shapiro

Diana Todd

Project Advisory Committee

John R. Baals, Chair

James Cagley

Edwin T. Dean

S.K. Ghosh

James O. Jirsa

Patrick J. Lama

Michael Valley

Richard A. Vognild

Eugene Zeller

Special Study Participants

Daniel P. Abrams

John M. Coil

Craig D. Comartin

W. Paul Grant

Darrick B. Hom

John Hooper

Brian Kehoe

Peter Somers

Desktop Publishing

Kris Ingle
vi Seismic Rehabilitation Prestandard FEMA 356
FEMA 356 Seismic Rehabilitation Prestandard vii

Foreword

The preparation of this prestandard was originally 

undertaken with two principal and complementary 

objectives. The first was to encourage the wider 

application of the NEHRP Guidelines for the Seismic 

Rehabilitation of Buildings, FEMA 273, by converting 

it into mandatory language. Design professionals and 

building officials thus would have at their disposal a 

more specific reference document for making buildings 

more resistant to earthquakes. This volume fully meets 

this first objective.

The second objective was to provide a basis for a 

nationally recognized, ANSI-approved standard that 

would further help in disseminating and incorporating 

the approaches and technology of the prestandard into 

the mainstream of design and construction practices in 

the United States. How successfully this volume 

achieves the second objective will become apparent 

with the passage of time, as this prestandard goes 

through the balloting process of the American Society 

of Civil Engineers.

Several additional related efforts were ongoing during 

the development of this prestandard. A concerted effort 

was made to gather any new information produced by 

these endeavors. Topics varied considerably, but 

typically covered approaches, methodologies, and 

criteria. Whenever an analysis of the new information 

disclosed significant advances or improvements in the 

state-of-the-practice, they were included in this volume. 

Thus, maintaining FEMA 273 as a living document—a 

process to which FEMA is strongly committed—is 

continuing.

FEMA and the Project Officer are deeply thankful to 

the members of the Project Team and consultants, the 

Project Advisory Committee, and the staff of the 

American Society of Civil Engineers for their dedicated 

efforts in completing this prestandard, which is a 

significant addition to the bibliography on seismic 

safety of existing buildings.

The Federal Emergency Management Agency
viii Seismic Rehabilitation Prestandard FEMA 356
FEMA 356 Seismic Rehabilitation Prestandard ix

Preface

The title of this document, FEMA 356 Prestandard and 

Commentary for the Seismic Rehabilitation of 

Buildings, incorporates a word that not all users may be 

familiar with. That word—prestandard—has a special 

meaning within the ASCE Standards Program in that it 

signifies the document has been accepted for use as the 

start of the formal standard development process, 

however, the document has yet to be fully processed as 

a voluntary consensus standard.

Users of this prestandard should be aware that the 

ASCE Standards Committee on Seismic Rehabilitation 

of Buildings is currently reviewing, discussing, and 

potentially revising the document prior to issuing it as a 

voluntary consensus standard. The Standards 

Committee, with over 150 members, has voted to accept 

this prestandard as the initial draft for their standard 

which, upon completion, will be suitable for adoption 

by building codes and inclusion in contracts. In early 

2001, the Standards Committee will begin committee 

balloting on this document to be followed by an open 

public ballot period. The process the Standards 

Committee will follow will be in accordance with the 

ASCE Rules for Standards Committees. These rules 

have been approved by the ASCE Board of Direction 

and by the American National Standards Institute 

(ANSI). A copy of these rules may be found in the 

ASCE Official Register.

If you would like to participate in the formal standard 

development process either as a member of the 

Standards Committee or as part of the public ballot 

process, please contact ASCE's Standards Coordinator, 

Kim Brubaker, ASCE, 1801 Alexander Bell Drive, 

Reston, VA 20191. 

American Society of Civil Engineers
x Seismic Rehabilitation Prestandard FEMA 356
FEMA 356 Seismic Rehabilitation Prestandard xi

Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

1. Rehabilitation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.3 Seismic Rehabilitation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1.3.1 Review Initial Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

1.3.2 Select Rehabilitation Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.3.3 Obtain As-Built Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.3.4 Select Rehabilitation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.3.5 Perform Rehabilitation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.3.6 Verify Rehabilitation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.4 Rehabilitation Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

1.4.1 Basic Safety Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

1.4.2 Enhanced Rehabilitation Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

1.4.3 Limited Rehabilitation Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

1.5 Target Building Performance Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

1.5.1 Structural Performance Levels and Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

1.5.2 Nonstructural Performance Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17

1.5.3 Designation of Target Building Performance Levels . . . . . . . . . . . . . . . . . . . . . 1-23

1.6 Seismic Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-26

1.6.1 General Procedure for Hazard Due to Ground Shaking . . . . . . . . . . . . . . . . . . . 1-27

1.6.2 Site-Specific Procedure for Hazard Due to Ground Shaking . . . . . . . . . . . . . . 1-34

1.6.3 Zones of Seismicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-35

2. General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.2 As-Built Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.2.1 Building Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.2.2 Component Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.2.3 Site Characterization and Geotechnical Information . . . . . . . . . . . . . . . . . . . . . . 2-2

2.2.4 Adjacent Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.2.5 Primary and Secondary Elements and Components . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.2.6 Data Collection Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.3 Rehabilitation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.3.1 Simplified Rehabilitation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.3.2 Systematic Rehabilitation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2.4 Analysis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.4.1 Linear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.4.2 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

2.4.3 Alternative Rational Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

2.4.4 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
xii Seismic Rehabilitation Prestandard FEMA 356

2.5 Rehabilitation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-17

2.5.1 Local Modification of Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-17

2.5.2 Removal or Lessening of Existing Irregularities . . . . . . . . . . . . . . . . . . . . . . . . .2-18

2.5.3 Global Structural Stiffening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-18

2.5.4 Global Structural Strengthening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-19

2.5.5 Mass Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-19

2.5.6 Seismic Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-19

2.5.7 Supplemental Energy Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6 General Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.1 Multidirectional Seismic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.2 P-∆ Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.3 Horizontal Torsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.4 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.5 Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-20

2.6.6 Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-21

2.6.7 Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-22

2.6.8 Nonstructural Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-23

2.6.9 Structures Sharing Common Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-23

2.6.10 Building Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-23

2.6.11 Vertical Seismic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-24

2.7 Construction Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-24

2.7.1 Construction Quality Assurance Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-25

2.7.2 Construction Quality Assurance Requirements . . . . . . . . . . . . . . . . . . . . . . . . . .2-25

2.7.3 Responsibilities of the Code Official . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-26

2.8 Alternative Modeling Parameters and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . .2-27

2.8.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-27

2.8.2 Data Reduction and Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-27

2.8.3 Design Parameters and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-28

3. Analysis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

3.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

3.2 General Analysis Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

3.2.1 Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

3.2.2 Mathematical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

3.2.3 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

3.2.4 Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

3.2.5 P-∆ Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5

3.2.6 Soil-Structure Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6

3.2.7 Multidirectional Seismic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7

3.2.8 Component Gravity Loads for Load Combinations . . . . . . . . . . . . . . . . . . . . . . .3-8

3.2.9 Verification of Design Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

3.2.10 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-9

3.3 Analysis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-10

3.3.1 Linear Static Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-10

3.3.2 Linear Dynamic Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-16

3.3.3 Nonlinear Static Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-18

3.3.4 Nonlinear Dynamic Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-24
FEMA 356 Seismic Rehabilitation Prestandard xiii

3.4 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.4.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.4.2 Linear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.4.3 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

4. Foundations and Geologic Site Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2 Site Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2.1 Foundation Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2.2 Seismic Geologic Site Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.3 Mitigation of Seismic-Geologic Site Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4.4 Foundation Strength and Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

4.4.1 Expected Capacities of Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.4.2 Load-Deformation Characteristics for Foundations . . . . . . . . . . . . . . . . . . . . . . 4-15

4.4.3 Foundation Acceptability Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

4.5 Seismic Earth Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

4.6 Foundation Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

5. Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2 Material Properties Based on Historical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.3 Material Properties and Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.3.2 Properties of In-Place Materials and Components . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5.3.3 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

5.3.4 Knowledge Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9

5.4 General Assumptions and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.4.1 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.4.2 Design Strengths and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.4.3 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.5 Steel Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5.5.2 Fully Restrained Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

5.5.3 Partially Restrained Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

5.6 Steel Braced Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

5.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

5.6.2 Concentric Braced Frames (CBF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

5.6.3 Eccentric Braced Frames (EBF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30

5.7 Steel Plate Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.7.2 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.7.3 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.7.4 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33

5.7.5 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33

5.8 Steel Frames with Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-34

5.9 Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-45

5.9.1 Bare Metal Deck Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-45
xiv Seismic Rehabilitation Prestandard FEMA 356

5.9.2 Metal Deck Diaphragms with Structural Concrete Topping . . . . . . . . . . . . . . . .5-46

5.9.3 Metal Deck Diaphragms with Nonstructural Concrete Topping . . . . . . . . . . . . .5-48

5.9.4 Horizontal Steel Bracing (Steel Truss Diaphragms) . . . . . . . . . . . . . . . . . . . . . .5-49

5.9.5 Archaic Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-51

5.9.6 Chord and Collector Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-52

5.10 Steel Pile Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-53

5.10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-53

5.10.2 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-53

5.10.3 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-53

5.10.4 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-53

5.10.5 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-54

5.11 Cast and Wrought Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-54

5.11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-54

5.11.2 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-54

5.11.3 Strength and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-54

6. Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

6.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

6.2 Material Properties Based on Historical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

6.3 Material Properties and Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-4

6.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-4

6.3.2 Properties of In-Place Materials and Components . . . . . . . . . . . . . . . . . . . . . . . .6-4

6.3.3 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-9

6.3.4 Knowledge Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-11

6.4 General Assumptions and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-11

6.4.1 Modeling and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-11

6.4.2 Strength and Deformability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-14

6.4.3 Flexure and Axial Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-15

6.4.4 Shear and Torsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-16

6.4.5 Development and Splices of Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-17

6.4.6 Connections to Existing Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-18

6.4.7 Rehabilitation—General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-18

6.5 Concrete Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-19

6.5.1 Types of Concrete Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-19

6.5.2 Reinforced Concrete Beam-Column Moment Frames . . . . . . . . . . . . . . . . . . . .6-20

6.5.3 Post-Tensioned Concrete Beam-Column Moment Frames . . . . . . . . . . . . . . . . .6-29

6.5.4 Slab-Column Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-30

6.6 Precast Concrete Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-34

6.6.1 Types of Precast Concrete Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-34

6.6.2 Precast Concrete Frames that Emulate Cast-in-Place Moment Frames . . . . . . .6-35

6.6.3 Precast Concrete Moment Frames Constructed with Dry Joints . . . . . . . . . . . . .6-36

6.6.4 Precast Concrete Frames Not Expected to Resist Lateral Loads Directly . . . . .6-37

6.7 Concrete Frames with Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-37

6.7.1 Types of Concrete Frames with Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-37

6.7.2 Concrete Frames with Masonry Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-38

6.7.3 Concrete Frames with Concrete Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-41
FEMA 356 Seismic Rehabilitation Prestandard xv

6.8 Concrete Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-43

6.8.1 Types of Concrete Shear Walls and Associated Components . . . . . . . . . . . . . . 6-43

6.8.2 Reinforced Concrete Shear Walls, Wall Segments, Coupling Beams, and 

RC Columns Supporting Discontinuous Shear Walls . . . . . . . . . . . . . . . . . . . . . 6-46

6.9 Precast Concrete Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56

6.9.1 Types of Precast Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56

6.9.2 Precast Concrete Shear Walls and Wall Segments . . . . . . . . . . . . . . . . . . . . . . . 6-57

6.10 Concrete-Braced Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-60

6.10.1 Types of Concrete-Braced Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-60

6.10.2 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-60

6.10.3 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-60

6.10.4 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.10.5 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.10.6 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.11 Cast-in-Place Concrete Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.11.1 Components of Concrete Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61

6.11.2 Analysis, Modeling, and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . 6-62

6.11.3 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63

6.12 Precast Concrete Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63

6.12.1 Components of Precast Concrete Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63

6.12.2 Analysis, Modeling, and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63

6.12.3 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-64

6.13 Concrete Foundation Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-64

6.13.1 Types of Concrete Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-64

6.13.2 Analysis of Existing Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-65

6.13.3 Evaluation of Existing Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-65

6.13.4 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-65

7. Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.2 Historical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.3 Material Properties and Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.3.2 Properties of In-Place Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.3.3 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7.3.4 Knowledge Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.4 Engineering Properties of Masonry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.4.1 Types of Masonry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

7.4.2 Unreinforced Masonry Walls and Piers In-Plane . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7.4.3 Unreinforced Masonry Walls Out-of-Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.4.4 Reinforced Masonry Walls and Piers In-Plane . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

7.4.5 Reinforced Masonry Walls Out-of-Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-23

7.5 Engineering Properties of Masonry Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-23

7.5.1 Types of Masonry Infills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-24

7.5.2 Masonry Infills In-Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-25

7.5.3 Masonry Infills Out-of-Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-29

7.6 Anchorage to Masonry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-30
xvi Seismic Rehabilitation Prestandard FEMA 356

7.6.1 Types of Anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-30

7.6.2 Analysis of Anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-31

7.7 Masonry Foundation Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-31

7.7.1 Types of Masonry Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-31

7.7.2 Analysis of Existing Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-31

7.7.3 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-31

8. Wood and Light Metal Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-1

8.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-1

8.2 Historical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-1

8.3 Material Properties and Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-2

8.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-2

8.3.2 Properties of In-Place Materials and Components . . . . . . . . . . . . . . . . . . . . . . . .8-3

8.3.3 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-10

8.3.4 Knowledge Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-12

8.4 General Assumptions and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-12

8.4.1 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-12

8.4.2 Strength and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-13

8.4.3 Connection Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-13

8.4.4 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-14

8.5 Wood and Light Frame Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-14

8.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-14

8.5.2 Types of Wood Frame Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-15

8.5.3 Types of Light Gage Metal Frame Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . .8-19

8.5.4 Single Layer Horizontal Lumber Sheathing or Siding Shear Walls . . . . . . . . . .8-20

8.5.5 Diagonal Lumber Sheathing Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-27

8.5.6 Vertical Wood Siding Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-27

8.5.7 Wood Siding over Horizontal Sheathing Shear Walls . . . . . . . . . . . . . . . . . . . .8-28

8.5.8 Wood Siding over Diagonal Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-28

8.5.9 Wood Structural Panel Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-29

8.5.10 Stucco on Studs, Sheathing, or Fiberboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-30

8.5.11 Gypsum Plaster on Wood Lath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-31

8.5.12 Gypsum Plaster on Gypsum Lath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-31

8.5.13 Gypsum Wallboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-32

8.5.14 Gypsum Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-32

8.5.15 Plaster on Metal Lath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-33

8.5.16 Horizontal Lumber Sheathing with Cut-In Braces or Diagonal Blocking . . . . .8-33

8.5.17 Fiberboard or Particleboard Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-34

8.5.18 Light Gage Metal Frame Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-34

8.6 Wood Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-35

8.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-35

8.6.2 Types of Wood Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-35

8.6.3 Single Straight Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-39

8.6.4 Double Straight Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-40

8.6.5 Single Diagonal Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-40

8.6.6 Diagonal Sheathing with Straight Sheathing or Flooring Above . . . . . . . . . . . .8-41

8.6.7 Double Diagonal Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-41
FEMA 356 Seismic Rehabilitation Prestandard xvii

8.6.8 Wood Structural Panel Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-42

8.6.9 Wood Structural Panel Overlays on Straight or Diagonal Sheathing . . . . . . . . . 8-43

8.6.10 Wood Structural Panel Overlays on Existing Wood Structural Panel Sheathing 8-44

8.6.11 Braced Horizontal Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

8.7 Wood Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

8.7.1 Types of Wood Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

8.7.2 Analysis, Strength, and Acceptance Criteria of Wood Foundations . . . . . . . . . . 8-45

8.7.3 Rehabilitation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-45

8.8 Other Wood Elements and Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46

8.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46

8.8.2 Components Supporting Discontinuous Shear Walls . . . . . . . . . . . . . . . . . . . . . 8-46

9. Seismic Isolation and Energy Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.2 Seismic Isolation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

9.2.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

9.2.2 Mechanical Properties and Modeling of Seismic Isolation Systems . . . . . . . . . . 9-4

9.2.3 General Criteria for Seismic Isolation Design . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15

9.2.4 Linear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-17

9.2.5 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19

9.2.6 Nonstructural Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20

9.2.7 Detailed System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20

9.2.8 Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-22

9.2.9 Isolation System Testing and Design Properties . . . . . . . . . . . . . . . . . . . . . . . . . 9-22

9.3 Passive Energy Dissipation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25

9.3.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25

9.3.2 Implementation of Energy Dissipation Devices . . . . . . . . . . . . . . . . . . . . . . . . . 9-26

9.3.3 Modeling of Energy Dissipation Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26

9.3.4 Linear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28

9.3.5 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31

9.3.6 Detailed Systems Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33

9.3.7 Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-34

9.3.8 Required Tests of Energy Dissipation Devices . . . . . . . . . . . . . . . . . . . . . . . . . . 9-34

9.4 Other Response Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37

10. Simplified Rehabilitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

10.3 Correction of Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9

11. Architectural, Mechanical, and Electrical Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

11.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

11.2 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

11.2.1 Condition Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

11.2.2 Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
xviii Seismic Rehabilitation Prestandard FEMA 356

11.3 Historical and Component Evaluation Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-6

11.3.1 Historical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-6

11.3.2 Component Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-10

11.4 Rehabilitation Objectives and Performance Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-11

11.5 Structural-Nonstructural Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-12

11.5.1 Response Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-12

11.5.2 Base Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-12

11.6 Classification of Acceleration-Sensitive and Deformation-Sensitive Components . . . . .11-12

11.7 Evaluation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14

11.7.1 Analytical Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14

11.7.2 Prescriptive Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14

11.7.3 Force Analysis: Default Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15

11.7.4 Force Analysis: General Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15

11.7.5 Deformation Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-16

11.7.6 Other Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-16

11.8 Rehabilitation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-19

11.9 Architectural Components: Definition, Behavior, and Acceptance Criteria . . . . . . . . . . .11-20

11.9.1 Exterior Wall Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-20

11.9.2 Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-25

11.9.3 Interior Veneers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-26

11.9.4 Ceilings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-27

11.9.5 Parapets and Appendages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-28

11.9.6 Canopies and Marquees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-29

11.9.7 Chimneys and Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-29

11.9.8 Stairs and Stair Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-30

11.10 Mechanical, Electrical, and Plumbing Components: Definition, Behavior, and 

Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-30

11.10.1 Mechanical Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-30

11.10.2 Storage Vessels and Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-32

11.10.3 Pressure Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-33

11.10.4 Fire Suppression Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-34

11.10.5 Fluid Piping other than Fire Suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-34

11.10.6 Ductwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-36

11.10.7 Electrical and Communications Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . .11-36

11.10.8 Electrical and Communications Distribution Components . . . . . . . . . . . . . . . .11-37

11.10.9 Light Fixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-38

11.11 Furnishings and Interior Equipment: Definition, Behavior, and Acceptance Criteria . . . .11-39

11.11.1 Storage Racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-39

11.11.2 Bookcases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-39

11.11.3 Computer Access Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-40

11.11.4 Hazardous Materials Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-41

11.11.5 Computer and Communication Racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-41

11.11.6 Elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-42

11.11.7 Conveyors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-43
FEMA 356 Seismic Rehabilitation Prestandard xix

A. Use of this Standard for Local or Directed Risk Mitigation Programs . . . . . . . . . . . . . . . . . . . A-1

A.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

A.2 Initial Considerations for Mitigation Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

A.2.1 Potential Costs of Local or Directed Programs . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

A.2.2 Timetables and Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

A.2.3 Historic Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

A.3 Use in Passive Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

A.3.1 Selection of Seismic Rehabilitation Triggers . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

A.3.2 Selection of Passive Seismic Rehabilitation Standards . . . . . . . . . . . . . . . . . . . A-3

A.4 Use in Active or Mandated Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

A.4.1 Selection of Buildings to be Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

A.4.2 Selection of Active Seismic Rehabilitation Standards . . . . . . . . . . . . . . . . . . . . A-3

A.5 Social, Economic, and Political Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

A.5.1 Construction Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.5.2 Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.5.3 Impacts on Lower-Income Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.5.4 Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.5.5 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.5.6 Community Revitalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.6 Considerations for Historic Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.6.1 Secretary of Interior’s Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.6.2 Application of Building Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

A.6.3 Rehabilitation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

A.6.4 Rehabilitation Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Symbols-1

Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acronyms-1

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Definitions-1

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .References-1

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index-1
xx Seismic Rehabilitation Prestandard FEMA 356
FEMA 356 Seismic Rehabilitation Prestandard xxi

List of Figures

Figure C1-1 Rehabilitation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Figure C1-2 Target Building Performance Levels and Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-23

Figure 1-1 General Horizontal Response Spectrum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-34

Figure 2-1 In-Plane Discontinuity in Lateral System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Figure 2-2 Typical Building with Out-of-Plane Offset Irregularity. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Figure 2-3 Component Force Versus Deformation Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

Figure C2-1 Generalized Component Force-Deformation Relations for Depicting Modeling and 

Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15

Figure 2-4 Backbone Curve for Experimental Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29

Figure 2-5 Alternative Force-Deformation Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29

Figure C3-1 Plausible Force Distribution in a Flexible Diaphragm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

Figure C3-2 Diaphragm and Wall Displacement Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

Figure 3-1 Idealized Force-Displacement Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

Figure 4-1 Presumptive Expected Capacities of Piles or Piers in Granular Soils . . . . . . . . . . . . . . . . . 4-12

Figure 4-2 Presumptive Expected Capacities of Piles or Piers in Cohesive Soils . . . . . . . . . . . . . . . . 4-13

Figure C4-1 Outline Procedure for Consideration of Rocking Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

Figure 4-3 (a) Idealized Elasto-Plastic Load-Deformation Behavior for Soils

(b) Uncoupled Spring Model for Rigid Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

Figure 4-4 Elastic Solutions for Rigid Footing Spring Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

Figure C4-2 (a) Foundation Shape Effect

(b) Foundation Embedment Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

Figure 4-5 Vertical Stiffness Modeling for Shallow Bearing Footings . . . . . . . . . . . . . . . . . . . . . . . . 4-23

Figure 4-6 Passive Pressure Mobilization Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

Figure C4-3 Idealized Concentration of Stress at Edge of Rigid Footings Subjected to 

Overturning Moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

Figure 5-1 Generalized Force-Deformation Relation for Steel Elements or Components . . . . . . . . . . 5-13

Figure 5-2 Definition of Chord Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

Figure 5-3 Top and Bottom Clip Angle Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

Figure 5-4 Double Split Tee Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

Figure 5-5 Bolted Flange Plate Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

Figure 5-6 Bolted End Plate Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

Figure 6-1 Generalized Force-Deformation Relations for Concrete Elements or Components . . . . . . 6-13

Figure C6-1 Identification of Component Types in Concrete Shear Wall Elements . . . . . . . . . . . . . . . 6-44

Figure 6-2 Plastic Hinge Rotation in Shear Wall where Flexure Dominates Inelastic Response . . . . . 6-48

Figure 6-3 Story Drift in Shear Wall where Shear Dominates Inelastic Response . . . . . . . . . . . . . . . . 6-48

Figure 6-4 Chord Rotation for Shear Wall Coupling Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-48

Figure 7-1 Generalized Force-Deformation Relation for Masonry Elements or Components . . . . . . . 7-11

Figure C7-1 Effective Height and Differential Displacement of Wall Components . . . . . . . . . . . . . . . . 7-12

Figure C7-2 Compression Strut Analogy–Concentric Struts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-26

Figure C7-3 Compression Strut Analogy–Eccentric Struts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-26
xxii Seismic Rehabilitation Prestandard FEMA 356

Figure C7-4 Compression Strut Analogy–Perforated Infills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-26

Figure 8-1 Generalized Force-Deformation Relation for Wood Elements or Components . . . . . . . . .8-12

Figure C9-1 Idealized Hysteretic Force-Displacement Relation of a Lead-Rubber Bearing . . . . . . . . . . .9-5

Figure C9-2 Force-Displacement Loops of a High-Damping Rubber Bearing . . . . . . . . . . . . . . . . . . . . .9-6

Figure C9-3 Tangent Shear Modulus and Effective Damping Ratio of High-Damping Rubber Bearing .9-7

Figure C9-4 Analytical Force-Displacement Loops of High-Damping Rubber Bearing . . . . . . . . . . . . . .9-8

Figure C9-5 Idealized Force Displacement Loops of Sliding Bearings . . . . . . . . . . . . . . . . . . . . . . . . . .9-10

Figure C9-6 Coefficient of Friction of PTFE-based Composite in Contact with Polished Stainless 

Steel at Normal Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-11

Figure C9-7 Definition of Effective Stiffness of Seismic Isolation Devices . . . . . . . . . . . . . . . . . . . . . .9-12

Figure C9-8 Idealized Force-Displacement Loops of Energy Dissipation Devices with Recentering 

Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-28

Figure 9-1 Calculation of Secant Stiffness, Ks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-32
FEMA 356 Seismic Rehabilitation Prestandard xxiii

List of Tables

Table C1-1 Rehabilitation Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

Table C1-2 Damage Control and Building Performance Levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13

Table C1-3 Structural Performance Levels and Damage—Vertical Elements . . . . . . . . . . . . . . . . . . . 1-14

Table C1-4 Structural Performance Levels and Damage—Horizontal Elements . . . . . . . . . . . . . . . . . 1-17

Table C1-5 Nonstructural Performance Levels and Damage—Architectural Components . . . . . . . . . . 1-20

Table C1-6 Nonstructural Performance Levels and Damage—Mechanical, Electrical, and 

Plumbing Systems/Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21

Table C1-7 Nonstructural Performance Levels and Damage—Contents . . . . . . . . . . . . . . . . . . . . . . . . 1-22

Table C1-8 Target Building Performance Levels and Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-25

Table 1-1 Values of Exponent n for Determination of Response Acceleration Parameters at 

Earthquake Hazard Levels between 10%/50 years and 2%/50 years; Sites where 

Mapped BSE-2 Values of SS ≥1.5g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-32

Table 1-2 Values of Exponent n for Determination of Response Acceleration Parameters at 

Probabilities of Exceedance Greater than 10%/50 years; Sites where Mapped BSE-2 

Values of SS < 1.5g. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-33

Table 1-3 Values of Exponent n for Determination of Response Acceleration Parameters at 

Probabilities of Exceedance Greater than 10%/50 years; Sites where Mapped BSE-2 

Values of SS ≥1.5g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-33

Table 1-4 Values of Fa as a Function of Site Class and Mapped Short-Period Spectral Response 

Acceleration SS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-33

Table 1-5 Values of Fv as a Function of Site Class and Mapped Spectral Response Acceleration at 

One-Second Period S1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-33

Table 1-6 Damping Coefficients BS and B1 as a Function of Effective Damping β . . . . . . . . . . . . . . 1-34

Table 2-1 Data Collection Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Table C2-1 Examples of Possible Deformation-Controlled and Force-Controlled Actions. . . . . . . . . . 2-14

Table 2-2 Calculation of Component Action Capacity—Nonlinear Procedures . . . . . . . . . . . . . . . . . 2-17

Table 2-3 Calculation of Component Action Capacity—Linear Procedures . . . . . . . . . . . . . . . . . . . . 2-17

Table 2-4 Coefficient χ for Calculation of Out-of-Plane Wall Forces . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

Table 3-1 Values for Effective Mass Factor Cm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

Table 3-2 Values for Modification Factor C0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22

Table 3-3 Values for Modification Factor C2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22

Table 4-1 Estimated Susceptibility to Liquefaction of Surficial Deposits During Strong 

Ground Shaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Table 4-2 Parameters for Calculating Presumptive Expected Foundation Load Capacities of 

Spread Footings and Mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

Table 4-3 Typical Pile and Pier Capacity Parameters: Bearing Capacity Factors, Nq . . . . . . . . . . . . . 4-14

Table 4-4 Typical Pile and Pier Capacity Parameters: Effective Horizontal Stress Factors, 

Fdi and Fui. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

Table 4-5 Typical Pile and Pier Capacity Parameters: Friction Angle, δ (degrees) . . . . . . . . . . . . . . . 4-14

Table 4-6 Typical Pile and Pier Capacity Parameters: Cohesion, ct

, and Adhesion, ca (psf). . . . . . . . 4-15
xxiv Seismic Rehabilitation Prestandard FEMA 356

Table 4-7 Effective Shear Modulus Ratio(G/G0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-18

Table 5-1 Default Lower-Bound Material Strengths for Archaic Materials . . . . . . . . . . . . . . . . . . . . . .5-5

Table 5-2 Default Lower-Bound Material Strengths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-6

Table 5-3 Factors to Translate Lower-Bound Steel Properties to Expected-Strength Steel Properties .5-7

Table 5-4 Steel Moment Frame Connection Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-11

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components. . . . . . . . . . . . .5-35

Table 5-6 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—

Structural Steel Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-40

Table 5-7 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—

Structural Steel Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-44

Table 6-1 Default Lower-Bound Tensile and Yield Properties of Reinforcing Bars for 

Various Periods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-2

Table 6-2 Default Lower-Bound Tensile and Yield Properties of Reinforcing Bars for Various 

ASTM Specifications and Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-3

Table 6-3 Default Lower-Bound Compressive Strength of Structural Concrete . . . . . . . . . . . . . . . . . .6-4

Table 6-4 Factors to Translate Lower Bound Material Properties to Expected Strength

Material Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-4

Table 6-5 Effective Stiffness Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-12

Table 6-6 Component Ductility Demand Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-15

Table 6-7 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Reinforced Concrete Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-21

Table 6-8 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Reinforced Concrete Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-22

Table 6-9 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Reinforced Concrete Beam-Column Joints. . . . . . . . . . . . . . . . . . . . . . . . . . .6-23

Table 6-10 Values of γ for Joint Strength Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-24

Table 6-11 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete Beams . . . .6-26

Table 6-12 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete Columns . .6-27

Table 6-13 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete

Beam-Column Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-28

Table 6-14 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Two-way Slabs and Slab-Column Connections . . . . . . . . . . . . . . . . . . . . . . .6-33

Table 6-15 Numerical Acceptance Criteria for Linear Procedures—Two-way Slabs and

Slab-Column Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-34

Table 6-16 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Reinforced Concrete Infilled Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-40

Table 6-17 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete

Infilled Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-41

Table C6-1 Reinforced Concrete Shear Wall Component Types (from FEMA 306) . . . . . . . . . . . . . . .6-45

Table 6-18 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Members Controlled by Flexure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-51

Table 6-19 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Members Controlled by Shear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-52

Table 6-20 Numerical Acceptance Criteria for Linear Procedures—Members Controlled by Flexure .6-53
FEMA 356 Seismic Rehabilitation Prestandard xxv

Table 6-21 Numerical Acceptance Criteria for Linear Procedures—Members Controlled by Shear . . 6-54

Table 7-1 Default Lower-Bound Masonry Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Table 7-2 Factors to Translate Lower-Bound Masonry Properties to Expected Strength 

Masonry Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Table 7-3 Linear Static Procedure—m-factors for URM In-Plane Walls and Piers. . . . . . . . . . . . . . . 7-16

Table 7-4 Nonlinear Static Procedure—Simplified Force-Deflection Relations for URM 

In-Plane Walls and Piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

Table 7-5 Permissible h/t Ratios for URM Out-of-Plane Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

Table 7-6 Acceptance Criteria for Linear Procedures—Reinforced Masonry In-Plane Walls . . . . . . 7-21

Table 7-7 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—

Reinforced Masonry In-plane Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-22

Table 7-8 Linear Static Procedure—m-factors for Masonry Infill Panels . . . . . . . . . . . . . . . . . . . . . . 7-28

Table 7-9 Nonlinear Static Procedure—Simplified Force-Deflection Relations for Masonry 

Infill Panels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-29

Table 7-10 Maximum hinf /tinf Ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-29

Table 7-11 Values of λ2 for Use in Equation (7-21) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-30

Table 8-1 Default Expected Strength Values for Wood and Light Frame Shear Walls . . . . . . . . . . . . . 8-7

Table 8-2 Default Expected Strength Values for Wood Diaphragms. . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

Table 8-3 Numerical Acceptance Factors for Linear Procedures—Wood Components . . . . . . . . . . . 8-21

Table 8-4 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear 

Procedures—Wood Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24

Table C9-1 Applicability of Isolation and Energy Dissipation Systems. . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

Table 10-1 Limitations on Use of the Simplified Rehabilitation Method . . . . . . . . . . . . . . . . . . . . . . . 10-4

Table 10-2 Description of Model Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6

Table C10-1 W1: Wood Light Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Table C10-2 W1A: Multistory, Multi-Unit, Wood Frame Construction . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Table C10-3 W2: Wood, Commercial, and Industrial. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19

Table C10-4 S1 and S1A: Steel Moment Frames with Stiff or Flexible Diaphragms . . . . . . . . . . . . . . 10-20

Table C10-5 S2 and S2A: Steel Braced Frames with Stiff or Flexible Diaphragms. . . . . . . . . . . . . . . . 10-20

Table C10-6 S3: Steel Light Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20

Table C10-7 S4: Steel Frames with Concrete Shear Walls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20

Table C10-8 S5, S5A: Steel Frames with Infill Masonry Shear Walls and Stiff or Flexible 

Diaphragms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21

Table C10-9 C1: Concrete Moment Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-21

Table C10-10 C2, C2A: Concrete Shear Walls with Stiff or Flexible Diaphragms . . . . . . . . . . . . . . . . . 10-22

Table C10-11 C3, C3A: Concrete Frames with Infill Masonry Shear Walls and Stiff or Flexible 

Diaphragms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22

Table C10-12 PC1: Precast/Tilt-up Concrete Shear Walls with Flexible Diaphragms. . . . . . . . . . . . . . . 10-23

Table C10-13 PC1A: Precast/Tilt-up Concrete Shear Walls with Stiff Diaphragms . . . . . . . . . . . . . . . . 10-23

Table C10-14 PC2: Precast Concrete Frames with Shear Walls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24

Table C10-15 PC2A: Precast Concrete Frames Without Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24

Table C10-16 RM1: Reinforced Masonry Bearing Wall Buildings with Flexible Diaphragms. . . . . . . . 10-25
xxvi Seismic Rehabilitation Prestandard FEMA 356

Table C10-17 RM2: Reinforced Masonry Bearing Wall Buildings with Stiff Diaphragms . . . . . . . . . . .10-25

Table C10-18 URM: Unreinforced Masonry Bearing Wall Buildings with Flexible Diaphragms . . . . . .10-25

Table C10-19 URMA: Unreinforced Masonry Bearing Walls Buildings with Stiff Diaphragms. . . . . . .10-25

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 Deficiency

Reference Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-26

Table 11-1 Nonstructural Components: Applicability of Hazards Reduced, Life Safety and 

Immediate Occupancy Requirements and Methods of Analysis . . . . . . . . . . . . . . . . . . . . .11-3

Table C11-1 Nonstructural Architectural Component Seismic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . .11-9

Table C11-2 Mechanical And Electrical Equipment Seismic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . .11-9

Table C11-3 Nonstructural Components: Response Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-13

Table 11-2 Nonstructural Component Amplification and Response Modification Factors . . . . . . . . .11-17
FEMA 356 Seismic Rehabilitation Prestandard 1-1

1. Rehabilitation Requirements

1.1 Scope

This Prestandard for the Seismic Rehabilitation of 

Buildings, referred to herein as “this standard,” 

specifies nationally applicable provisions for the 

rehabilitation of buildings to improve seismic 

performance. It is intended for use by code officials in 

directed seismic rehabilitation programs, or for 

reference by building owners and design professionals 

in voluntary rehabilitation efforts.

This chapter sets forth requirements for selecting a 

Rehabilitation Objective and conducting the seismic 

rehabilitation process. 

Symbols, acronyms, definitions, and references used 

throughout this standard are cited separately in sections 

located at the end of this standard. 

C1.1 Scope

This standard is intended to serve as a nationally 

applicable tool for design professionals, code officials, 

and building owners undertaking the seismic 

rehabilitation of existing buildings. It consists of two 

parts: provisions, which contain the technical 

requirements, and commentary, intended to explain the 

provisions. Commentary for a given section is located 

in a shaded box immediately following the section, and 

is identified by the same section number preceded by 

the letter “C.”

It is expected that most buildings rehabilitated in 

accordance with this standard would perform within 

the desired levels when subjected to the design 

earthquakes. However, compliance with the standard 

does not guarantee such performance. The practice of 

earthquake engineering is rapidly evolving, and both 

our understanding of the behavior of buildings 

subjected to strong earthquakes and our ability to 

predict this behavior are advancing. In the future, new 

knowledge and technology will provide more reliable 

methods of accomplishing these goals.

The procedures contained in this standard are 

specifically applicable to the rehabilitation of existing 

buildings and are, in general, more appropriate for that 

purpose than are new building codes. New building 

codes are primarily intended to regulate the design and 

construction of new buildings; as such, they include 

many provisions that encourage the development of 

designs with features important for good seismic 

performance, including regular configuration, 

structural continuity, ductile detailing, and materials of 

appropriate quality. Many existing buildings were 

designed and constructed without these features and 

contain characteristics such as unfavorable 

configuration and poor detailing that preclude 

application of building code provisions for their 

seismic rehabilitation. 

While it is intended to be used as a follow-up to a 

previous seismic evaluation, this standard can also be 

used as an evaluation tool that ascertains compliance 

with a selected rehabilitation objective. A FEMA 310, 

Tier 3 evaluation is an example of this use. It should be 

noted, however, that an evaluation using this standard 

may be more stringent than other evaluation 

methodologies because the provisions have been 

calibrated for use in design. Historically, criteria for 

evaluation have been set lower than those for design to 

minimize the need to strengthen buildings that would 

otherwise have only modest deficiencies.

The expertise of the design professional in earthquake 

engineering is an important prerequisite for the 

appropriate use of this standard in assisting a building 

owner to select voluntary seismic criteria or to design 

and analyze seismic rehabilitation projects.

This standard is intended to be generally applicable to 

seismic rehabilitation of all buildings—regardless of 

importance, occupancy, historic status, or other 

classifications of use. However, application of these 

provisions should be coordinated with other 

requirements that may be in effect, such as ordinances 

governing historic structures or hospital construction. 

In addition to the direct effects of ground shaking, this 

standard also considers the effects of local geologic 

site hazards such as liquefaction.
1-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.2 Design Basis

Seismic rehabilitation of buildings shall comply with 

the design criteria and procedures of this standard for 

achieving the performance-based Rehabilitation 

Objectives defined in Section 1.4. The use of alternative 

performance-based criteria and procedures shall be 

permitted as approved by the code official.

This standard applies to the seismic rehabilitation of 

both the overall structural system of a building and its 

nonstructural components including ceilings, 

partitions, mechanical, electrical, and plumbing 

systems.

With careful extrapolation, the procedures of this 

standard may also be applied to many nonbuilding 

structures such as pipe racks, steel storage racks, 

structural towers for tanks and vessels, piers, wharves, 

and electrical power generating facilities. However, the 

applicability of these procedures has not been fully 

examined for every type of structure, particularly those 

that have generally been covered by specialized codes 

or standards, such as bridges and nuclear power plants.

In addition to techniques for increasing the strength 

and ductility of systems, this standard provides 

techniques for reducing seismic demand, such as the 

introduction of isolation or damping devices. Design of 

new buildings and evaluation of components for 

gravity and wind forces in the absence of earthquake 

demands are beyond the scope of this standard.

This standard does not explicitly address the 

determination of whether or not a rehabilitation project 

should be undertaken for a particular building. 

Guidance on the use of this standard in voluntary or 

directed risk-mitigation programs is provided in 

Appendix A. Determining when these provisions 

should be required or desired is beyond the scope of 

this standard. Once the decision to rehabilitate a 

building has been made, this standard can be 

referenced for detailed engineering guidance on how to 

conduct a seismic rehabilitation analysis and design.

Featured in this standard are descriptions of damage 

states in relation to specific performance levels. These 

descriptions are intended to aid design professionals 

and owners in selecting appropriate performance levels 

for rehabilitation design. They are not intended to be 

used for condition assessment of earthquake-damaged 

buildings. Although there may be similarities between 

these damage descriptions and those used for postearthquake damage assessment, many factors enter 

into the processes of assessing seismic performance. 

No single parameter in this standard should be cited as 

defining either a performance level or the safety or 

usefulness of an earthquake-damaged building.

Techniques for repair of earthquake- damaged 

buildings are not included in this standard, but are 

referenced in the commentary of Chapters 5 through 8 

when such guidelines exist. If the mechanical 

properties of repaired components are known, 

acceptability criteria for use with this standard can be 

either deduced by comparison with other similar 

components, or derived. Any combination of repaired 

elements, undamaged existing elements, and new 

elements can be modeled using this standard, and each 

checked against performance level acceptance criteria.

C1.2 Design Basis

Provisions of this standard for seismic rehabilitation 

are based on a performance-based design methodology 

that differs from seismic design procedures for the 

design of new buildings currently specified in national 

building codes and standards.

The framework in which these requirements are 

specified is purposefully broad so that Rehabilitation 

Objectives can accommodate buildings of different 

types, that satisfy a variety of performance levels, and 

consider the variation of seismic hazards across the 

United States and Territories.

The provisions and commentary of this standard are 

primarily based on the FEMA 273 Guidelines with 

limited material taken from the FEMA 274 

Commentary. This standard is intended to supersede 

FEMA 273, but FEMA 274 remains a valid explanation 

for the provisions in this standard unless indicated 

otherwise in the relevant commentary of this standard. 

For this reason, section numbers in this standard 

remain essentially the same as in FEMA 273, with the 

exception of Chapters 1 and 2, which were reorganized 

for clarity.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-3

FEMA 273 was developed by a large team of 

specialists in earthquake engineering and seismic 

rehabilitation. The most advanced analytical 

techniques considered practical for production use 

have been incorporated. The acceptance criteria have 

been specified using actual laboratory test results, 

where available, supplemented by the engineering 

judgment of various development teams. Certain 

buildings damaged in the 1994 Northridge earthquake 

and a limited number of designs using codes for new 

buildings have been checked using the procedures of 

FEMA 273. A comprehensive program of case studies 

was undertaken by FEMA in 1998 to test more 

thoroughly the various analysis techniques and 

acceptability criteria. The results of this study are 

reported in FEMA 343, Case Studies: An Assessment 

of the NEHRP Guidelines for the Seismic 

Rehabilitation of Buildings. The results of the 

FEMA 343 case studies have been incorporated in the 

provisions of this standard, where possible. Similarly, 

information from FEMA 350, FEMA 351, and other 

reports published by the SAC Joint Venture project, 

formed as a result of the Northridge steel moment 

frame damage, has been incorporated where 

applicable. Engineering judgment should be exercised 

in determining the applicability of various analysis 

techniques and material acceptability criteria in each 

situation.

The commentary to this standard contains specific 

references to many other documents. In addition, this 

standard is also related generically to the following 

publications.

1. FEMA 222A and 223A, NEHRP Recommended 

Provisions for Seismic Regulations for New 

Buildings, 1994 Edition. For the purposes of the 

design of new components, this standard has been 

designed to be as compatible as possible with the 

companion Provisions for new buildings and its 

reference design documents. Detailed references to 

the use of specific sections of the Provisions 

document will be found in subsequent sections of 

this standard.

2. FEMA 302 and 303, 1997 NEHRP Recommended 

Provisions for Seismic Regulations for New 

Buildings and Other Structures referred to herein as 

the 1997 NEHRP Recommended Provisions.

3. FEMA 237, Development of Guidelines for Seismic 

Rehabilitation of Buildings, Phase I: Issues 

Identification and Resolution, which underwent an 

American Society of Civil Engineers (ASCE) 

consensus approval process, provided policy 

direction for this standard.

4. ATC-28-2, Proceedings of the Workshop to Resolve 

Seismic Rehabilitation Sub-issues provided 

recommendations to the writers of this standard on 

more detailed sub-issues.

5. FEMA 172, NEHRP Handbook of Techniques for 

the Seismic Rehabilitation of Existing Buildings, 

originally produced by URS/Blume and reviewed 

by BSSC, contains construction techniques for 

implementing engineering solutions to the seismic 

deficiencies of existing buildings.

6. FEMA 178, NEHRP Handbook for the Seismic 

Evaluation of Existing Buildings, which was 

originally developed by ATC and underwent the 

consensus approval process of the BSSC, covered 

the subject of evaluating existing buildings to 

determine if they are seismically deficient in terms 

of life safety. This document has been updated by 

FEMA as a prestandard, FEMA 310, Handbook for 

the Seismic Evaluation of Existing Buildings, which 

underwent an ASCE consensus approval process. 

(The model building types and other information 

from FEMA 310 are used or referred to extensively 

in this standard in Chapter 10.)

7. FEMA 156 and 157, Typical Costs for Seismic 

Rehabilitation of Existing Buildings, Second 

Edition, reports statistical analysis of the costs of 

rehabilitation of over 2,000 buildings based on 

construction costs or detailed studies. Several 

different seismic zones and performance levels are 

included in the data. Since the data were developed 

in 1994, none of the data are based on buildings 

rehabilitated specifically in accordance with the 

FEMA 273 Guidelines document. Performance 

Levels defined in this standard are not intended to 

be significantly different from parallel levels used 

previously, and costs still should be reasonably 

representative.

8. FEMA 275, Planning for Seismic Rehabilitation: 

Societal Issues, discusses societal and 

implementation issues associated with 

rehabilitation and describes several case histories.
1-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.3 Seismic Rehabilitation Process

Seismic rehabilitation of an existing building shall be 

conducted in accordance with the process outlined in 

Sections 1.3.1 through 1.3.6. Before embarking on a 

rehabilitation design, seismic deficiencies shall have 

been identified through a prior seismic evaluation 

performed using an evaluation methodology 

considering a combination of building performance and 

seismic hazard. 

9. FEMA 276, Guidelines for the Seismic 

Rehabilitation of Buildings: Example Applications,

intended as a companion document to FEMA 273

and FEMA 274, describes examples of buildings 

that have been seismically rehabilitated in various 

seismic regions and for different Rehabilitation 

Objectives. Costs of the work are given and 

references made to FEMA 156 and 157. Because 

this document is based on previous case histories, 

none of the examples was rehabilitated specifically 

in accordance with this standard. However, 

Performance Levels defined in this standard are not 

intended to be significantly different from parallel 

levels used previously, and the case studies are 

therefore considered representative.

10.ATC 40, Seismic Evaluation and Retrofit of 

Concrete Buildings, incorporates performance 

levels almost identical to those shown in Table 

C1-8 and employs “pushover” nonlinear analysis 

techniques. The capacity spectrum method for 

determining the displacement demand is treated in 

detail. This document covers only concrete 

buildings.

C1.3 Seismic Rehabilitation Process

The steps are presented in this section in the order in 

which they would typically be followed in the 

rehabilitation process. However, the criteria for 

performing these steps are presented in a somewhat 

different order to facilitate presentation of the 

concepts.

Figure C1-1 depicts the rehabilitation process specified 

in this standard and shows specific chapter references 

in parentheses at points where input from this standard 

is to be obtained.

This standard requires the building owner or the code 

official to select a Rehabilitation Objective for a 

building that has been previously identified as needing 

seismic rehabilitation.

Prior to embarking on a rehabilitation program, an 

evaluation should be performed to determine whether 

the building, in its existing condition, has the desired 

seismic performance capability. FEMA 310 is an 

example of an evaluation methodology that may be 

used for this purpose. It should be noted, however, that 

a building may meet certain performance objectives 

using the methodology of FEMA 310, but may not 

meet those same performance objectives when an 

evaluation is performed using the procedures of this 

standard. This is largely because FEMA 310 is 

specifically intended to accept somewhat greater levels 

of damage within each performance level than 

permitted by this standard, which is consistent with the 

historic practice of evaluating existing buildings for 

slightly lower criteria than those used for design of 

new buildings. FEMA 310 quantifies this difference 

with the use of a 0.75 factor on demands when using 

this standard in a Tier 3 evaluation. This essentially 

lowers the reliability of achieving the selected 

performance level from about 90% to 60%. This 

practice minimizes the need to rehabilitate structures 

with relatively modest deficiencies relative to the 

desired performance level.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-5

Figure C1-1 Rehabilitation Process

6.2A Section 1.3.6.2: Prepare 

Construction Documents of 

Acceptable Rehabilitation

• Develop construction 

documents

• Begin rehabilitation

• Exercise quality control

4A Simplified Rehabilitation (Chapters 2, 10 

and 11)

• Identify building model type 

• Consider deficiencies

• Select full or partial rehabilitation

(Note: Simplified Rehabilitation shall be used 

for Limited Objectives only.)

4B Systematic Rehabilitation (Chapters 2 through 9 and 11)

• Consider deficiencies

• Select rehabilitation strategy (Chapter 2)

• Select analysis procedure (Chapters 2 and 3)

• Consider general requirements (Chapter 2)

4C Other Choices 

(not in this standard)

• Reduce occupancy

• Demolish

5A Section 1.3.5:

Perform Rehabilitation Design

• Determine and design 

rehabilitation measures to meet 

applicable FEMA 310 

requirements

6A Section 1.3.6:

Verify Rehabilitation Design

• Reevaluate building to assure 

that rehabilitation measures 

remove all deficiencies without 

creating new ones

• Review for economic acceptability

6B Section 1.3.6:

Verify Rehabilitation Design

• Apply component acceptance criteria (Chapters 2 through 9 

and 11)

• Review for conformance with requirements of Chapter 2

• Review for economic acceptability

6.1B Section 1.3.6.1: Redesign 

Unacceptable 

Rehabilitation

• Return to 4B to revise 

analysis and design or to 

2 to reconsider 

Rehabilitation Objective

6.2B Section 1.3.6.2: Prepare 

Construction Documents 

of Acceptable 

Rehabilitation

• Develop construction 

documents

• Begin rehabilitation

• Exercise quality control

6.1A Section 1.3.6.1: Redesign 

Unacceptable 

Rehabilitation

• Return to 4A to 

reconsider 

Rehabilitation Objective 

or to 5A to revise 

corrective measures

5B Section 1.3.5: Perform Rehabilitation Design

• Develop mathematical model (Chapters 3 through 9 for stiffness 

and strength)

• Perform force and deformation response evaluation 

(Chapters 2 through 9 and 11)

• Size elements, components, and connections

(Chapters 2, 5 through 9, and 11)

4 Section 1.3.4: Select Rehabilitation Method

3 Section 1.3.3: Obtain As-Built Information (Chapter 2)

Interest in reducing seismic risk

1 Section 1.3.1: Review Initial Considerations

• Structural characteristics (Chapter 2)

• Site seismic hazards (Chapters 1 and 4)

• Results from prior seismic evaluations (Section 1.2)

• Occupancy (not considered in this standard)

• Historic status (Appendix A)

• Economic considerations (Section C1.2.6.2)

• Societal issues: (Appendix A)

• Local jurisdictional requirements (not considered in this standard)

2 Section 1.3.2: Select Rehabilitation Objective

• Target Building Performance level (Section 1.5)

• Seismic Hazard (Section 1.6)

Prior Seismic Evaluation (Section 1.2)
1-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.3.1 Review Initial Considerations

The design professional shall review initial 

considerations with the building owner or code official 

to determine any restrictions that exist on the design of 

rehabilitation measures. Initial considerations shall 

include structural characteristics of the building, 

seismic hazards including geologic site hazards known 

to be present at the site, results of prior seismic 

evaluations, building use and occupancy requirements, 

historic status, economic considerations, societal issues, 

and local jurisdictional requirements.

C1.3.1 Review Initial Considerations

The process of building rehabilitation will be 

simplified and made more efficient if information that 

significantly affects the rehabilitation design is 

obtained and considered prior to beginning the process. 

Rehabilitation requirements mandated by local 

jurisdictions would be particularly important to 

determine in the initial stages of a project.

The building owner should be aware of the range of 

costs and impacts of rehabilitation, including both the 

variation associated with different Rehabilitation 

Objectives and the potential additional costs often 

associated with seismic rehabilitation, such as other 

life safety upgrades, hazardous material removal, work 

associated with the Americans with Disabilities Act, 

and nonseismic building remodeling. Also to be 

considered are potential federal tax incentives for the 

rehabilitation of historic buildings and for some other 

older nonresidential buildings.

Seismic hazards other than ground shaking may exist 

at the building site. The risk and possible extent of 

damage from geologic site hazards identified in 

Section 4.2.2 should be considered before undertaking 

a rehabilitation aimed solely at reducing damage due to 

shaking. In some cases it may be feasible to mitigate 

the site hazard or rehabilitate the building and still 

meet the selected performance level. In other cases the 

risk due to site hazards may be so extreme and difficult 

to control that rehabilitation is neither cost-effective 

nor feasible.

The use of the building must be considered in weighing 

the significance of potential temporary or permanent 

disruptions associated with various risk mitigation 

schemes. Other limitations on modifications to the 

building due to historic or aesthetic features must also 

be understood. The historic status of every building at 

least 50 years old should be determined (see Appendix 

A, Section A.6, Considerations for Historic Buildings). 

This determination should be made early as it could 

influence the choices of rehabilitation approaches and 

techniques.

There are many ways to reduce seismic risk, whether 

the risk is to property, life safety, or post- earthquake 

use of the building. The occupancy of vulnerable 

buildings can be reduced, redundant facilities can be 

provided, and nonhistoric buildings can be demolished 

and replaced. The risks posed by nonstructural 

components and contents can be reduced. Seismic site 

hazards other than shaking can be mitigated.

Most often, however, when all alternatives are 

considered, the options of modifying the building to 

reduce the risk of damage should be studied. Such 

corrective measures include stiffening or strengthening 

the structure, adding local elements to eliminate 

irregularities or tie the structure together, reducing the 

demand on the structure through the use of seismic 

isolation or energy dissipation devices, and reducing 

the height or mass of the structure. Rehabilitation 

strategies are discussed in Chapter 2.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-7

1.3.2 Select Rehabilitation Objective

The building owner or code official shall select a 

seismic Rehabilitation Objective for the building as 

specified in Section 1.4. The selection of a 

Rehabilitation Objective shall consist of the selection of 

a target Building Performance Level from a range of 

performance levels defined in Section 1.5 and on the 

selection of an anticipated Earthquake Hazard Level 

from a range of seismic hazards defined in 

Section 1.6.

1.3.3 Obtain As-Built Information

Available as-built information for the building shall be 

obtained and a site visit shall be conducted as specified 

in Section 2.2.

1.3.4 Select Rehabilitation Method

An applicable rehabilitation method shall be determined 

in accordance with Section 2.3.

1.3.5 Perform Rehabilitation Design

Rehabilitation measures shall be designed using the 

applicable rehabilitation method.

1.3.6 Verify Rehabilitation Design

The rehabilitation design shall be verified to meet the 

requirements of this standard through an analysis of the 

building, including rehabilitation measures. The 

analysis shall be consistent with the procedures for the 

applicable rehabilitation method specified in 

Section 2.3. A separate analytical evaluation shall be 

performed for each combination of building 

performance and seismic hazard specified in the 

selected Rehabilitation Objective.

1.3.6.1 Redesign Unacceptable 

Rehabilitation

If the rehabilitation design fails to comply with the 

acceptance criteria for the selected Rehabilitation 

Objective, the rehabilitation measures shall be 

redesigned or an alternative rehabilitation strategy shall 

be implemented. This process shall be repeated until the 

design is in compliance with the acceptance criteria for 

the selected Rehabilitation Objective.

C1.3.2 Select Rehabilitation Objective

The concepts and terminology of performance-based 

design are new and should be carefully studied and 

discussed with building owners before use. The 

terminology used for target Building Performance 

Levels is intended to represent goals of design. The 

actual ground motion will seldom be comparable to 

that specified in the Rehabilitation Objective, so in 

most events, designs targeted at various damage states 

may only determine relative performance. Even given 

a ground motion similar to that specified in the 

Rehabilitation Objective and used in design, variations 

from stated performance objectives should be expected 

and compliance with this standard should not be 

considered a guarantee of performance. Variations in 

actual performance could be associated with unknown 

geometry and member sizes in existing buildings, 

deterioration of materials, incomplete site data, 

variation of ground motion that can occur within a 

small area, and incomplete knowledge and 

simplifications related to modeling and analysis. 

Information on the expected reliability of achieving 

various target Building Performance Levels when the 

requirements are followed can be found in Chapter 2 of 

FEMA 274.

C1.3.4 Select Rehabilitation Method

Rehabilitation can consist of the Simplified 

Rehabilitation Method or the Systematic 

Rehabilitation Method. These methods are defined in 

Section 2.3 and further explained in the associated 

commentary of that section.
1-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.3.6.2 Prepare Construction Documents of 

Acceptable Rehabilitation

If the rehabilitation design meets the acceptance criteria 

for the selected Rehabilitation Objective, and the 

decision is made to proceed with the rehabilitation, 

construction documents shall be prepared and shall 

include requirements for construction quality assurance 

in accordance with Section 2.7.

1.4 Rehabilitation Objectives

A seismic Rehabilitation Objective shall be selected for 

the building, consisting of one or more rehabilitation 

goals. Each goal shall consist of a target Building 

Performance Level defined in Section 1.5 and an 

Earthquake Hazard Level defined in Section 1.6. Goals 

shall be selected considering basic, enhanced, or limited 

objectives defined in Sections 1.4.1 through 1.4.3. 

C1.3.6.2 Prepare Construction Documents of 

Acceptable Rehabilitation

At this stage, a cost estimate can be made to review the 

economic acceptability of the design. Cost estimating 

or reviewing economic acceptability of the 

rehabilitation design is not included in the standard, 

but is an essential part of the rehabilitation process 

shown in Figure C1-1.

Construction costs are discussed in Example 

Applications, FEMA 276 and Typical Costs for 

Seismic Rehabilitation, FEMA 156 and 157.

If the design proves uneconomical or otherwise not 

feasible, further refinement may be considered in 

analysis, a different rehabilitation scheme may be 

designed or a different Rehabilitation Objective may 

be considered.

Section 2.7 specifies provisions for a quality assurance 

program during the construction or implementation of 

the rehabilitation design. Other aspects of the 

implementation process, including details of the 

preparation of construction documents, obtaining a 

building permit, selection of a contractor, details of 

historic preservation techniques for particular kinds of 

materials, and financing are not covered in this 

standard.

C1.4 Rehabilitation Objectives

Recommendations regarding the selection of a 

Rehabilitation Objective for any building are beyond 

the scope of this standard. FEMA 274 discusses issues 

to consider when combining various performance and 

seismic hazard levels. It should be noted that not all 

combinations constitute reasonable or cost-effective 

Rehabilitation Objectives. This standard is written 

under the premise that greater flexibility is required in 

seismic rehabilitation than in the design of new 

buildings. However, given that flexibility, once a 

Rehabilitation Objective is selected, this standard 

provides internally consistent procedures with the 

necessary specificity to perform a rehabilitation 

analysis and design.

Building performance can be described qualitatively in 

terms of the safety afforded building occupants during 

and after the event; the cost and feasibility of restoring 

the building to pre-earthquake condition; the length of 

time the building is removed from service to effect 

repairs; and economic, architectural, or historic 

impacts on the larger community. These performance 

characteristics are directly related to the extent of 

damage that would be sustained by the building.

In this standard, the extent of damage to a building is 

categorized as a Building Performance Level. A broad 

range of target Building Performance Levels may be 

selected when determining Rehabilitation Objectives.

Probabilistic Earthquake Hazard Levels frequently 

used in this standard and their corresponding mean 

return periods (the average number of years between 

events of similar severity) are as follows:

These mean return periods are typically rounded to 75, 

225, 500, and 2,500 years, respectively.

Earthquake Having 

Probability of Exceedance

Mean Return 

Period (years)

50%/50 year 72

20%/50 year 225

10%/50 year 474

2%/50 year 2,475
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-9

1.4.1 Basic Safety Objective

The Basic Safety Objective (BSO) is a Rehabilitation 

Objective that achieves the dual rehabilitation goals of 

Life Safety Building Performance Level (3-C) for the 

BSE-1 Earthquake Hazard Level and Collapse 

Prevention Building Performance Level (5-E) for the 

BSE-2 Earthquake Hazard Level.

1.4.2 Enhanced Rehabilitation Objectives

Rehabilitation that provides building performance 

exceeding that of the BSO is termed an Enhanced 

Objective. Enhanced Rehabilitation Objectives shall be 

achieved using one or a combination of the following 

two methods:

1. By designing for target Building Performance 

Levels that exceed those of the BSO at either the 

BSE-1 or BSE-2 hazard levels, or both.

2. By designing for the target Building Performance 

Levels of the BSO using an Earthquake Hazard 

Level that exceeds either the BSE-1 or BSE-2 

hazard levels, or both.

The Rehabilitation Objective selected as a basis for 

design will determine, to a great extent, the cost and 

feasibility of any rehabilitation project, as well as the 

benefit to be obtained in terms of improved safety, 

reduction in property damage, and interruption of use 

in the event of future earthquakes. Table C1-1 indicates 

the range of Rehabilitation Objectives that may be used 

in this standard. 

Table C1-1 Rehabilitation Objectives

Target Building Performance 

Levels

Operational Performance Level (1-A)Immediate Occupancy Performance Level (1-B)Life Safety Performance Level (3-C)Collapse Prevention Performance Level (5-E)

Earthquake Hazard Level

50%/50 year a b c d

20%/50 year e f g h

BSE-1

(~10%/50 year)

i j k l

BSE-2

(~2%/50 year)

m n o p

Notes:

1. Each cell in the above matrix represents a discrete Rehabilitation 

Objective.

2. The Rehabilitation Objectives in the matrix above may be used to 

represent the three specific Rehabilitation Objectives defined in 

Sections 1.4.1, 1.4.2, and 1.4.3, as follows: 

k + p = Basic Safety Objective (BSO)

k + p + any of a, e, i, b, f, j, or n = Enhanced Objectives

o alone or n alone or m alone = Enhanced Objective

k alone or p alone = Limited Objectives

c, g, d, h, l = Limited Objectives

C1.4.1 Basic Safety Objective

The BSO is intended to approximate the earthquake 

risk to life safety traditionally considered acceptable in 

the United States. Buildings meeting the BSO are 

expected to experience little damage from relatively 

frequent, moderate earthquakes, but significantly more 

damage and potential economic loss from the most 

severe and infrequent earthquakes that could affect 

them. The level of damage and potential economic 

loss experienced by buildings rehabilitated to the BSO 

may be greater than that expected in properly designed 

and constructed new buildings.

C1.4.2 Enhanced Rehabilitation Objectives

Enhanced Rehabilitation Objectives can be obtained 

by designing for higher target Building Performance 

Levels (method 1) or by designing using higher 

Earthquake Hazard Levels (method 2) or any 

combination of these two methods.
1-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.4.3 Limited Rehabilitation Objectives

Rehabilitation that provides building performance less 

than that of the BSO is termed a Limited Objective. 

Limited Rehabilitation Objectives shall be achieved 

using Reduced Rehabilitation specified in 

Section 1.4.3.1 or Partial Rehabilitation specified in 

Section 1.4.3.2, and shall comply with the following 

conditions:

1. The rehabilitation measures shall not result in a 

reduction in the performance level of the existing 

building;

2. The rehabilitation measures shall not create a new 

structural irregularity or make an existing structural 

irregularity more severe;

3. The rehabilitation measures shall not result in an 

increase in the seismic forces to any component that 

is deficient in capacity to resist these forces;

4. All new or rehabilitated structural components and 

elements shall be detailed and connected to the 

existing structure in compliance with the 

requirements of this standard.

1.4.3.1 Reduced Rehabilitation Objective

Rehabilitation that addresses the entire building 

structural and nonstructural systems, but uses a lower 

seismic hazard or lower target Building Performance 

Level than the BSO, is termed Reduced Rehabilitation 

Objective. Reduced Rehabilitation shall be designed for 

one or more of the following objectives:

1. Life Safety Building Performance Level (3-C) for 

earthquake demands that are less severe (more 

probable) than the BSE-1;

2. Collapse Prevention Building Performance Level 

(5-E) for earthquake demands that are less severe 

(more probable) than the BSE-2;

3. Building Performance Levels 4-C, 4-D, 4-E, 5-C, 

5-D, 5-E, 6-D, or 6-E for BSE-1 or less severe (more 

probable) earthquake demands.

1.4.3.2 Partial Rehabilitation Objective

Rehabilitation that addresses a portion of the building 

without rehabilitating the complete lateral-forceresisting system is termed Partial Rehabilitation. A 

Partial Rehabilitation shall be designed and constructed 

considering future completion of a Rehabilitation 

Objective intended to improve the performance of the 

entire structure.

1.5 Target Building Performance 

Levels

A target Building Performance Level shall consist of a 

combination of a Structural Performance Level selected 

from the levels specified in Section 1.5.1 and a 

Nonstructural Performance Level selected from the 

levels specified in Section 1.5.2. The target Building 

Performance Level shall be designated 

alphanumerically in accordance with Section 1.5.3. 

C1.5 Target Building Performance 

Levels

Building performance is a combination of the 

performance of both structural and nonstructural 

components. Table C1-2 describes the approximate 

limiting levels of structural and nonstructural damage 

that may be expected of buildings rehabilitated to the 

levels defined in the standard. On average, the 

expected damage would be less. For comparative 

purposes, the estimated performance of a new building 

subjected to the BSE-1 level of shaking is indicated. 

Performance descriptions in Table C1-2 are estimates 

rather than precise predictions, and variation among 

buildings of the same target Building Performance 

Level must be expected.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-11

1.5.1 Structural Performance Levels and 

Ranges

The Structural Performance Level of a building shall be 

selected from four discrete Structural Performance 

Levels and two intermediate Structural Performance 

Ranges defined in this section.

The discrete Structural Performance Levels are 

Immediate Occupancy (S-1), Life Safety (S-3), 

Collapse Prevention (S-5), and Not Considered (S-6). 

Design procedures and acceptance criteria 

corresponding to these Structural Performance Levels 

shall be as specified in Chapters 4 through 10.

The intermediate Structural Performance Ranges are the 

Damage Control Range (S-2) and the Limited Safety 

Range (S-4). Acceptance criteria for performance 

within the Damage Control Structural Performance 

Range shall be obtained by interpolating the acceptance 

criteria provided for the Immediate Occupancy and Life 

Safety Structural Performance Levels. Acceptance 

criteria for performance within the Limited Safety 

Structural Performance Range shall be obtained by 

interpolating the acceptance criteria provided for the 

Life Safety and Collapse Prevention Structural 

Performance Levels.

1.5.1.1 Immediate Occupancy Structural 

Performance Level (S-1)

Structural Performance Level S-1, Immediate 

Occupancy, shall be defined as the post-earthquake 

damage state that remains safe to occupy, essentially 

retains the pre-earthquake design strength and stiffness 

of the structure, and is in compliance with the 

acceptance criteria specified in this standard for this 

Structural Performance Level.

Building performance in this standard is expressed in 

terms of target Building Performance Levels. These 

target Building Performance Levels are discrete 

damage states selected from among the infinite 

spectrum of possible damage states that buildings 

could experience during an earthquake. The particular 

damage states identified as target Building 

Performance Levels in this standard have been selected 

because they have readily identifiable consequences 

associated with the post-earthquake disposition of the 

building that are meaningful to the building 

community. These include the ability to resume normal 

functions within the building, the advisability of postearthquake occupancy, and the risk to life safety. 

Due to inherent uncertainties in prediction of ground 

motion and analytical prediction of building 

performance, some variation in actual performance 

should be expected. Compliance with this standard 

should not be considered a guarantee of performance. 

Information on the reliability of achieving various 

Performance Levels can be found Chapter 2 of 

FEMA 274).

C1.5.1 Structural Performance Levels and 

Ranges

A wide range of structural performance requirements 

could be desired by individual building owners. The 

four Structural Performance Levels defined in this 

standard have been selected to correlate with the most 

commonly specified structural performance 

requirements. The two Structural Performance Ranges 

permit users with other requirements to customize their 

building Rehabilitation Objectives.

Table C1-3 relates these Structural Performance Levels 

to the limiting damage states for common vertical 

elements of lateral-force-resisting systems. Table C1-4 

relates these Structural Performance Levels to the 

limiting damage states for common horizontal 

elements of building lateral-force-resisting systems. 

Later sections of this standard specify design 

parameters (such as m-factors, component capacities, 

and inelastic deformation demands) specified as 

limiting values for attaining these Structural 

Performance Levels for a known earthquake demand.

The drift values given in Table C1-3 are typical values 

provided to illustrate the overall structural response 

associated with various Structural Performance Levels. 

They are not provided in these tables as drift limit 

requirements for this standard, and do not supersede 

component or element deformation limits that are 

specified in Chapters 4 through 9, and 11.

The expected post-earthquake state of the buildings 

described in these tables is for comparative purposes 

and should not be used in the post-earthquake safety 

evaluation process.
1-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.5.1.2 Damage Control Structural 

Performance Range (S-2)

Structural Performance Range S-2, Damage Control, 

shall be defined as the continuous range of damage 

states between the Life Safety Structural Performance 

Level (S-3) and the Immediate Occupancy Structural 

Performance Level (S-1).

1.5.1.3 Life Safety Structural Performance 

Level (S-3)

Structural Performance Level S-3, Life Safety, shall be 

defined as the post-earthquake damage state that 

includes damage to structural components but retains a 

margin against onset of partial or total collapse in 

compliance with the acceptance criteria specified in this 

standard for this Structural Performance Level.

1.5.1.4 Limited Safety Structural 

Performance Range (S-4)

Structural Performance Range S-4, Limited Safety, 

shall be defined as the continuous range of damage 

states between the Life Safety Structural Performance 

Level (S-3) and the Collapse Prevention Structural 

Performance Level (S-5).

1.5.1.5 Collapse Prevention Structural 

Performance Level (S-5)

Structural Performance Level S-5, Collapse Prevention, 

shall be defined as the post-earthquake damage state 

that includes damage to structural components such that 

the structure continues to support gravity loads but 

retains no margin against collapse in compliance with 

the acceptance criteria specified in this standard for this 

Structural Performance Level.

C1.5.1.1 Immediate Occupancy Structural 

Performance Level (S-1)

Structural Performance Level S-1, Immediate 

Occupancy, means the post-earthquake damage state in 

which only very limited structural damage has 

occurred. The basic vertical- and lateral-force-resisting 

systems of the building retain nearly all of their preearthquake strength and stiffness. The risk of lifethreatening injury as a result of structural damage is 

very low, and although some minor structural repairs 

may be appropriate, these would generally not be 

required prior to reoccupancy.

C1.5.1.2 Damage Control Structural 

Performance Range (S-2)

Design for the Damage Control Structural Performance 

Range may be desirable to minimize repair time and 

operation interruption, as a partial means of protecting 

valuable equipment and contents, or to preserve 

important historic features when the cost of design for 

immediate occupancy is excessive.

C1.5.1.3 Life Safety Structural Performance 

Level (S-3)

Structural Performance Level S-3, Life Safety, means 

the post-earthquake damage state in which significant 

damage to the structure has occurred, but some margin 

against either partial or total structural collapse 

remains. Some structural elements and components are 

severely damaged, but this has not resulted in large 

falling debris hazards, either within or outside the 

building. Injuries may occur during the earthquake; 

however, the overall risk of life-threatening injury as a 

result of structural damage is expected to be low. It 

should be possible to repair the structure; however, for 

economic reasons this may not be practical. While the 

damaged structure is not an imminent collapse risk, it 

would be prudent to implement structural repairs or 

install temporary bracing prior to reoccupancy.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-13

1.5.1.6 Structural Performance Not 

Considered (S-6)

A building rehabilitation that does not address the 

performance of the structure shall be classified as 

Structural Performance Not Considered (S-6). 

C1.5.1.5 Collapse Prevention Structural 

Performance Level (S-5)

Structural Performance Level S-5, Collapse 

Prevention, means the post-earthquake damage state in 

which the building is on the verge of partial or total 

collapse. Substantial damage to the structure has 

occurred, potentially including significant degradation 

in the stiffness and strength of the lateral-forceresisting system, large permanent lateral deformation 

of the structure, and—to a more limited extent—

degradation in vertical-load-carrying capacity. 

However, all significant components of the gravityload-resisting system must continue to carry their 

gravity load demands. Significant risk of injury due to 

falling hazards from structural debris may exist. The 

structure may not be technically practical to repair and 

is not safe for reoccupancy, as aftershock activity 

could induce collapse.

C1.5.1.6 Structural Performance Not 

Considered (S-6)

Some owners may desire to address certain 

nonstructural vulnerabilities in a rehabilitation 

program—for example, bracing parapets, or anchoring 

hazardous materials storage containers—without 

addressing the performance of the structure itself. Such 

rehabilitation programs are sometimes attractive 

because they can permit a significant reduction in 

seismic risk at relatively low cost.

Table C1-2 Damage Control and Building Performance Levels

Target Building Performance Levels

Collapse Prevention 

Level (5-E)

Life Safety

Level (3-C)

Immediate Occupancy

Level (1-B)

Operational

Level (1-A)

Overall Damage Severe Moderate Light Very Light

General Little residual stiffness 

and strength, but loadbearing columns and 

walls function. Large 

permanent drifts. Some 

exits blocked. Infills and 

unbraced parapets 

failed or at incipient 

failure. Building is near 

collapse.

Some residual strength 

and stiffness left in all 

stories. Gravity-loadbearing elements 

function. No out-ofplane failure of walls or 

tipping of parapets. 

Some permanent drift. 

Damage to partitions. 

Building may be beyond 

economical repair.

No permanent drift. 

Structure substantially 

retains original strength 

and stiffness. Minor 

cracking of facades, 

partitions, and ceilings 

as well as structural 

elements. Elevators can 

be restarted. Fire 

protection operable.

No permanent drift. 

Structure substantially 

retains original strength 

and stiffness. Minor 

cracking of facades, 

partitions, and ceilings 

as well as structural 

elements. All systems 

important to normal 

operation are functional.

Nonstructural 

components

Extensive damage. Falling hazards 

mitigated but many 

architectural, 

mechanical, and 

electrical systems are 

damaged.

Equipment and contents 

are generally secure, 

but may not operate due 

to mechanical failure or 

lack of utilities.

Negligible damage 

occurs. Power and 

other utilities are 

available, possibly from 

standby sources.

Comparison with 

performance intended 

for buildings designed 

under the NEHRP 

Provisions, for the 

Design Earthquake 

Significantly more 

damage and greater 

risk.

Somewhat more 

damage and slightly 

higher risk.

Less damage and lower 

risk.

Much less damage and 

lower risk.
1-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

Table C1-3 Structural Performance Levels and Damage1, 2, 3—Vertical Elements

Elements Type

Structural Performance Levels

Collapse Prevention 

S-5

Life Safety 

S-3

Immediate Occupancy 

S-1

Concrete Frames Primary Extensive cracking and 

hinge formation in ductile 

elements. Limited cracking 

and/or splice failure in 

some nonductile columns. 

Severe damage in short 

columns.

Extensive damage to 

beams. Spalling of cover 

and shear cracking (<1/8" 

width) for ductile columns. 

Minor spalling in nonductile 

columns. Joint cracks

<1/8" wide.

Minor hairline cracking. 

Limited yielding possible at 

a few locations. No 

crushing (strains below 

0.003).

Secondary Extensive spalling in 

columns (limited 

shortening) and beams. 

Severe joint damage. Some 

reinforcing buckled.

Extensive cracking and 

hinge formation in ductile 

elements. Limited cracking 

and/or splice failure in 

some nonductile columns. 

Severe damage in short 

columns.

Minor spalling in a few 

places in ductile columns 

and beams. Flexural 

cracking in beams and 

columns. Shear cracking in 

joints <1/16" width.

Drift 4% transient

or permanent

2% transient;

1% permanent

1% transient; 

negligible permanent

Steel Moment Frames Primary Extensive distortion of 

beams and column panels. 

Many fractures at moment 

connections, but shear 

connections remain intact.

Hinges form. Local buckling 

of some beam elements. 

Severe joint distortion; 

isolated moment 

connection fractures, but 

shear connections remain 

intact. A few elements may 

experience partial fracture.

Minor local yielding at a few 

places. No fractures. Minor 

buckling or observable 

permanent distortion of 

members.

Secondary Same as primary. Extensive distortion of 

beams and column panels. 

Many fractures at moment 

connections, but shear 

connections remain intact.

Same as primary.

Drift 5% transient 

or permanent

2.5% transient;

1% permanent

0.7% transient; 

negligible permanent

Braced Steel Frames Primary Extensive yielding and 

buckling of braces. Many 

braces and their 

connections may fail.

Many braces yield or buckle 

but do not totally fail. Many 

connections may fail.

Minor yielding or buckling of 

braces.

Secondary Same as primary. Same as primary. Same as primary.

Drift 2% transient

or permanent

1.5% transient; 

0.5% permanent

0.5% transient; 

negligible permanent
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-15

Concrete Walls Primary Major flexural and shear 

cracks and voids. Sliding at 

joints. Extensive crushing 

and buckling of 

reinforcement. Failure 

around openings. Severe 

boundary element damage. 

Coupling beams shattered 

and virtually disintegrated.

Some boundary element 

stress, including limited 

buckling of reinforcement. 

Some sliding at joints. 

Damage around openings. 

Some crushing and flexural 

cracking. Coupling beams: 

extensive shear and 

flexural cracks; some 

crushing, but concrete 

generally remains in place.

Minor hairline cracking of 

walls, <1/16" wide. 

Coupling beams 

experience cracking 

<1/8" width.

Secondary Panels shattered and 

virtually disintegrated.

Major flexural and shear 

cracks. Sliding at joints. 

Extensive crushing. Failure 

around openings. Severe 

boundary element damage. 

Coupling beams shattered 

and virtually disintegrated.

Minor hairline cracking of 

walls. Some evidence of 

sliding at construction 

joints. Coupling beams 

experience cracks <1/8" 

width. Minor spalling.

Drift 2% transient

or permanent

1% transient; 

0.5% permanent

0.5% transient; 

negligible permanent

Unreinforced Masonry 

Infill Walls

Primary Extensive cracking and 

crushing; portions of face 

course shed.

Extensive cracking and 

some crushing but wall 

remains in place. No falling 

units. Extensive crushing 

and spalling of veneers at 

corners of openings.

Minor (<1/8" width) 

cracking of masonry infills 

and veneers. Minor spalling 

in veneers at a few corner 

openings.

Secondary Extensive crushing and 

shattering; some walls 

dislodge.

Same as primary. Same as primary.

Drift 0.6% transient

or permanent

0.5% transient; 

0.3% permanent

0.1% transient; 

negligible permanent

Unreinforced

Masonry (Noninfill) 

Walls

Primary Extensive cracking; face 

course and veneer may 

peel off. Noticeable inplane and out-of-plane 

offsets.

Extensive cracking. 

Noticeable in-plane offsets 

of masonry and minor outof-plane offsets.

Minor (<1/8" width) 

cracking of veneers. Minor 

spalling in veneers at a few 

corner openings. No 

observable out-of-plane 

offsets.

Secondary Nonbearing panels 

dislodge.

Same as primary. Same as primary.

Drift 1% transient

or permanent

0.6% transient; 

0.6% permanent

0.3% transient; 

0.3% permanent

Table C1-3 Structural Performance Levels and Damage1, 2, 3—Vertical Elements (continued)

Elements Type

Structural Performance Levels

Collapse Prevention 

S-5

Life Safety 

S-3

Immediate Occupancy 

S-1
1-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

Reinforced Masonry 

Walls

Primary Crushing; extensive 

cracking. Damage around 

openings and at corners. 

Some fallen units.

Extensive cracking 

(<1/4") distributed 

throughout wall. Some 

isolated crushing.

Minor (<1/8" width) 

cracking. No out-of-plane 

offsets.

Secondary Panels shattered and 

virtually disintegrated.

Crushing; extensive 

cracking; damage around 

openings and at corners; 

some fallen units.

Same as primary.

Drift 1.5% transient 

or permanent

0.6% transient; 

0.6% permanent

0.2% transient; 

0.2% permanent

Wood Stud Walls Primary Connections loose. Nails 

partially withdrawn. Some 

splitting of members and 

panels. Veneers dislodged.

Moderate loosening of 

connections and minor 

splitting of members.

Distributed minor hairline 

cracking of gypsum and 

plaster veneers.

Secondary Sheathing sheared off. 

Let-in braces fractured and 

buckled. Framing split and 

fractured.

Connections loose. Nails 

partially withdrawn. Some 

splitting of members and 

panels.

Same as primary.

Drift 3% transient 

or permanent

2% transient; 

1% permanent

1% transient; 

0.25% permanent

Precast Concrete 

Connections

Primary Some connection failures 

but no elements dislodged.

Local crushing and spalling 

at connections, but no 

gross failure of 

connections.

Minor working at 

connections; cracks 

<1/16" width at 

connections.

Secondary Same as primary. Some connection failures 

but no elements dislodged.

Minor crushing and spalling 

at connections.

Foundations General Major settlement and tilting. Total settlements <6" and 

differential settlements 

<1/2" in 30 ft.

Minor settlement and 

negligible tilting.

1. Damage states indicated in this table are provided to allow an understanding of the severity of damage that may be sustained by various structural elements 

when present in structures meeting the definitions of the Structural Performance Levels. These damage states are not intended for use in post-earthquake 

evaluation of damage or for judging the safety of, or required level of repair to, a structure following an earthquake.

2. Drift values, differential settlements, crack widths, and similar quantities indicated in these tables are not intended to be used as acceptance criteria for 

evaluating the acceptability of a rehabilitation design in accordance with the analysis procedures provided in this standard; rather, they are indicative of the 

range of drift that typical structures containing the indicated structural elements may undergo when responding within the various Structural Performance 

Levels. Drift control of a rehabilitated structure may often be governed by the requirements to protect nonstructural components. Acceptable levels of 

foundation settlement or movement are highly dependent on the construction of the superstructure. The values indicated are intended to be qualitative 

descriptions of the approximate behavior of structures meeting the indicated levels.

3. For limiting damage to frame elements of infilled frames, refer to the rows for concrete or steel frames.

Table C1-3 Structural Performance Levels and Damage1, 2, 3—Vertical Elements (continued)

Elements Type

Structural Performance Levels

Collapse Prevention 

S-5

Life Safety 

S-3

Immediate Occupancy 

S-1
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-17

1.5.2 Nonstructural Performance Levels

The Nonstructural Performance Level of a building 

shall be selected from five discrete Nonstructural 

Performance Levels, consisting of Operational (N-A), 

Immediate Occupancy (N-B), Life Safety (N-C), 

Hazards Reduced (N-D), and Not Considered (N-E). 

Design procedures and acceptance criteria for 

rehabilitation of nonstructural components shall comply 

with the requirements of Chapters 10 and 11.

Table C1-4 Structural Performance Levels and Damage1, 2—Horizontal Elements

Element

Structural Performance Levels

Collapse Prevention 

S-5

Life Safety 

S-3

Immediate Occupancy 

S-1

Metal Deck Diaphragms Large distortion with buckling 

of some units and tearing of 

many welds and seam 

attachments.

Some localized failure of 

welded connections of deck to 

framing and between panels. 

Minor local buckling of deck.

Connections between deck 

units and framing intact. Minor 

distortions.

Wood Diaphragms Large permanent distortion 

with partial withdrawal of nails 

and extensive splitting of 

elements.

Some splitting at connections. 

Loosening of sheathing. 

Observable withdrawal of 

fasteners. Splitting of framing 

and sheathing.

No observable loosening or 

withdrawal of fasteners. No 

splitting of sheathing or 

framing.

Concrete Diaphragms Extensive crushing and 

observable offset across many 

cracks.

Extensive cracking (<1/4" 

width). Local crushing and 

spalling.

Distributed hairline cracking. 

Some minor cracks of larger 

size (<1/8” width).

Precast Diaphragms Connections between units 

fail. Units shift relative to each 

other. Crushing and spalling at 

joints.

Extensive cracking (<1/4”

width). Local crushing and 

spalling.

Some minor cracking along 

joints.

1. Damage states indicated in this table are provided to allow an understanding of the severity of damage that may be sustained by various structural elements 

when present in structures meeting the definitions of the Structural Performance Levels. These damage states are not intended for use in post-earthquake 

evaluation of damage or for judging the safety of, or required level of repair to, a structure following an earthquake.

2. Drift values, differential settlements, crack widths, and similar quantities indicated in these tables are not intended to be used as acceptance criteria for 

evaluating the acceptability of a rehabilitation design in accordance with the analysis procedures provided in this standard; rather, they are indicative of the 

range of drift that typical structures containing the indicated structural elements may undergo when responding within the various Structural Performance 

Levels. Drift control of a rehabilitated structure may often be governed by the requirements to protect nonstructural components. Acceptable levels of 

foundation settlement or movement are highly dependent on the construction of the superstructure. The values indicated are intended to be qualitative 

descriptions of the approximate behavior of structures meeting the indicated levels.

C1.5.2 Nonstructural Performance Levels

Nonstructural Performance Levels other than Not 

Considered (N-E) are summarized in Table 

C1-5 through C1-7. Nonstructural components 

addressed in this standard include architectural 

components such as partitions, exterior cladding, and 

ceilings; and mechanical and electrical components, 

including HVAC systems, plumbing, fire suppression 

systems, and lighting. Occupant contents and 

furnishings (such as inventory and computers) are 

included in these tables for some levels but are 

generally not covered with specific requirements.
1-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.5.2.1 Operational Nonstructural 

Performance Level (N-A)

Nonstructural Performance Level N-A, Operational, 

shall be defined as the post-earthquake damage state in 

which the nonstructural components are able to support 

the pre-earthquake functions present in the building.

1.5.2.2 Immediate Occupancy Nonstructural 

Performance Level (N-B)

Nonstructural Performance Level N-B, Immediate 

Occupancy, shall be defined as the post-earthquake 

damage state that includes damage to nonstructural 

components, but building access and life safety 

systems—including doors, stairways, elevators, 

emergency lighting, fire alarms, and suppression 

systems—generally remain available and operable, 

provided that power is available.

1.5.2.3 Life Safety Nonstructural 

Performance Level (N-C)

Nonstructural Performance Level N-C, Life Safety, 

shall be defined as the post-earthquake damage state 

that includes damage to nonstructural components but 

the damage is non-life threatening.

C1.5.2.1 Operational Nonstructural 

Performance Level (N-A)

At this level, most nonstructural systems required for 

normal use of the building—including lighting, 

plumbing, HVAC, and computer systems—are 

functional, although minor cleanup and repair of some 

items may be required. This Nonstructural 

Performance Level requires considerations beyond 

those that are normally within the sole province of the 

structural engineer. In addition to assuring that 

nonstructural components are properly mounted and 

braced within the structure, it is often necessary to 

provide emergency standby utilities. It also may be 

necessary to perform rigorous qualification testing of 

the ability of key electrical and mechanical equipment 

items to function during or after strong shaking.

Specific design procedures and acceptance criteria for 

this Nonstructural Performance Level are not included 

in this standard. Users wishing to design for this 

Nonstructural Performance Level will need to refer to 

appropriate criteria from other sources (such as 

equipment manufacturers’ data) to ensure the 

performance of mechanical and electrical systems.

C1.5.2.2 Immediate Occupancy Nonstructural 

Performance Level (N-B)

Minor window breakage and slight damage could 

occur to some components. Presuming that the 

building is structurally safe, occupants could safely 

remain in the building, although normal use may be 

impaired and some cleanup and inspection may be 

required. In general, components of mechanical and 

electrical systems in the building are structurally 

secured and should be able to function if necessary 

utility service is available. However, some components 

may experience misalignments or internal damage and 

be nonoperable. Power, water, natural gas, 

communications lines, and other utilities required for 

normal building use may not be available. The risk of 

life-threatening injury due to nonstructural damage is 

very low.

C1.5.2.3 Life Safety Nonstructural 

Performance Level (N-C)

Nonstructural Performance Level C, Life Safety, is the 

post-earthquake damage state in which potentially 

significant and costly damage has occurred to 

nonstructural components but they have not become 

dislodged and fallen, threatening life safety either 

inside or outside the building. Egress routes within the 

building are not extensively blocked, but may be 

impaired by lightweight debris. HVAC, plumbing, and 

fire suppression systems may have been damaged, 

resulting in local flooding as well as loss of function. 

While injuries may occur during the earthquake from 

the failure of nonstructural components, overall, the 

risk of life-threatening injury is very low. Restoration 

of the nonstructural components may take extensive 

effort.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-19

1.5.2.4 Hazards Reduced Nonstructural 

Performance Level (N-D)

Nonstructural Performance Level N-D, Hazards 

Reduced, shall be defined as the post-earthquake 

damage state that includes damage to nonstructural 

components that could potentially create falling 

hazards, but high hazard nonstructural components 

identified in Table 11-1 are secured and will not fall into 

areas of public assembly. Preservation of egress, 

protection of fire suppression systems, and similar lifesafety issues are not addressed in this Nonstructural 

Performance Level.

1.5.2.5 Nonstructural Performance Not 

Considered (N-E)

A building rehabilitation that does not address 

nonstructural components shall be classified as 

Nonstructural Performance Not Considered (N-E).

C1.5.2.4 Hazards Reduced Nonstructural 

Performance Level (N-D)

Nonstructural Performance Level D, Hazards Reduced, 

represents a post-earthquake damage state in which 

extensive damage has occurred to nonstructural 

components, but large or heavy items that pose a high 

risk of falling hazard to a large number of people—

such as parapets, cladding panels, heavy plaster 

ceilings, or storage racks—are prevented from falling. 

The hazards associated with exterior elements along 

portions of the exterior of the building that are 

available for public occupancy have been reduced. 

While isolated serious injury could occur from falling 

debris, failures that could injure large numbers of 

persons—either inside or outside the structure—should 

be avoided.

Nonstructural components that are small, lightweight, 

or close to the ground may fall, but should not cause 

serious injury. Larger nonstructural components in 

areas that are less likely to be populated may also fall.

The intent of the Hazards Reduced Performance Level 

is to address significant nonstructural hazards without 

needing to rehabilitate all of the nonstructural 

components in a building. When using this 

performance level, it will generally be appropriate to 

consider Hazards Reduced Performance as equivalent 

to Life Safety Performance for the most hazardous, 

highest risk subset of the nonstructural components in 

the building.

C1.5.2.5 Nonstructural Performance Not 

Considered (N-E)

In some cases, the decision to rehabilitate the structure 

may be made without addressing the vulnerabilities of 

nonstructural components. It may be desirable to do 

this when rehabilitation must be performed without 

interruption of building operation. In some cases, it is 

possible to perform all or most of the structural 

rehabilitation from outside occupied building areas. 

Extensive disruption of normal operation may be 

required to perform nonstructural rehabilitation. Also, 

since many of the most severe hazards to life safety 

occur as a result of structural vulnerabilities, some 

municipalities may wish to adopt rehabilitation 

ordinances that require structural rehabilitation only.
1-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

Table C1-5 Nonstructural Performance Levels and Damage1—Architectural Components

Component

Nonstructural Performance Levels

Hazards Reduced2

N-D

Life Safety 

N-C

Immediate Occupancy 

N-B

Operational 

N-A

Cladding Severe distortion in 

connections. Distributed 

cracking, bending, 

crushing, and spalling of 

cladding elements. 

Some fracturing of 

cladding, but panels do 

not fall in areas of public 

assembly.

Severe distortion in 

connections. Distributed 

cracking, bending, 

crushing, and spalling of 

cladding elements. 

Some fracturing of 

cladding, but panels do 

not fall.

Connections yield; 

minor cracks (<1/16" 

width) or bending in 

cladding.

Connections yield; 

minor cracks (<1/16" 

width) or bending in 

cladding.

Glazing General shattered glass 

and distorted frames in 

unoccupied areas. 

Extensive cracked 

glass; little broken glass 

in occupied areas.

Extensive cracked 

glass; little broken 

glass.

Some cracked panes; 

none broken.

Some cracked panes; 

none broken.

Partitions Distributed damage; 

some severe cracking, 

crushing, and racking in 

some areas.

Distributed damage; 

some severe cracking, 

crushing, and racking in 

some areas.

Cracking to about 

1/16" width at openings. 

Minor crushing and 

cracking at corners.

Cracking to about 

1/16" width at openings. 

Minor crushing and 

cracking at corners.

Ceilings Extensive damage. 

Dropped suspended 

ceiling tiles. Moderate 

cracking in hard 

ceilings.

Extensive damage. 

Dropped suspended 

ceiling tiles. Moderate 

cracking in hard 

ceilings.

Minor damage. Some 

suspended ceiling tiles 

disrupted. A few panels 

dropped. Minor cracking 

in hard ceilings.

Generally negligible 

damage. Isolated 

suspended panel 

dislocations, or cracks 

in hard ceilings.

Parapets & 

Ornamentation

Extensive damage; 

some falling in 

unoccupied areas.

Extensive damage; 

some falling in 

unoccupied areas.

Minor damage. Minor damage.

Canopies & Marquees Moderate damage. Moderate damage. Minor damage. Minor damage.

Chimneys & Stacks Extensive damage. No 

collapse.

Extensive damage. No 

collapse.

Minor cracking. Negligible damage.

Stairs & Fire Escapes Extensive racking. Loss 

of use.

Some racking and 

cracking of slabs. 

Usable.

Minor damage. Negligible damage.

Doors Distributed damage. 

Many racked and 

jammed doors.

Distributed damage. 

Some racked and 

jammed doors.

Minor damage. Doors 

operable.

Minor damage. Doors 

operable.

1. Damage states indicated in this table are provided to allow an understanding of the severity of damage that may be sustained by various nonstructural 

elements meeting the Nonstructural Performance Levels defined in this standard. These damage states are not intended for use in post-earthquake evaluation 

of damage or for judging the safety or required level of repair following an earthquake.

2. For the Hazards Reduced Performance Level, high hazard nonstructural components evaluated or rehabilitated to the Life Safety criteria will have Hazards 

Reduced performance identical to that expected for the Life Safety Performance Level.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-21

Table C1-6 Nonstructural Performance Levels and Damage1—Mechanical, Electrical, and Plumbing 

Systems/Components

System/Component

Nonstructural Performance Levels

Hazards Reduced2

N-D

Life Safety

N-C

Immediate Occupancy 

N-B

Operational

N-A

Elevators Elevators out of service; 

counterweights off rails.

Elevators out of service; 

counterweights do not 

dislodge.

Elevators operable; can 

be started when power 

available.

Elevators operate.

HVAC Equipment Most units do not 

operate; many slide or 

overturn; some 

suspended units fall.

Units shift on supports, 

rupturing attached 

ducting, piping, and 

conduit, but do not fall.

Units are secure and 

most operate if power 

and other required 

utilities are available.

Units are secure and 

operate. Emergency 

power and other utilities 

provided, if required.

Manufacturing 

Equipment

Units slide and overturn; 

utilities disconnected. 

Heavy units require 

reconnection and 

realignment. Sensitive 

equipment may not be 

functional.

Units slide, but do not 

overturn; utilities not 

available; some 

realignment required to 

operate.

Units secure, and most 

operable if power and 

utilities available.

Units secure and 

operable; power and 

utilities available.

Ducts Ducts break loose of 

equipment and louvers; 

some supports fail; 

some ducts fall.

Ducts break loose of 

equipment and louvers; 

some supports fail; 

some ducts fall.

Minor damage at joints, 

but ducts remain 

serviceable.

Negligible damage.

Piping Some lines rupture. 

Some supports fail. 

Some piping falls.

Minor damage at joints, 

with some leakage. 

Some supports 

damaged, but systems 

remain suspended.

Minor leaks develop at a 

few joints. 

Negligible damage.

Fire Sprinkler Systems Some sprinkler heads 

damaged by collapsing 

ceilings. Leaks develop 

at couplings. Some 

branch lines fail.

Some sprinkler heads 

damaged by swaying 

ceilings. Leaks develop 

at some couplings.

Minor leakage at a few 

heads or pipe joints. 

System remains 

operable.

Negligible damage.

Fire Alarm Systems Ceiling mounted 

sensors damaged. May 

not function.

Ceiling mounted 

sensors damaged. May 

not function.

System is functional. System is functional.

Emergency Lighting Some lights fall. Power 

may not be available.

Some lights fall. Power 

may be available from 

emergency generator.

System is functional. System is functional.

Electrical Distribution 

Equipment

Units slide and/or 

overturn, rupturing 

attached conduit. 

Uninterruptable Power 

Source systems fail. 

Diesel generators do 

not start.

Units shift on supports 

and may not operate. 

Generators provided for 

emergency power start; 

utility service lost.

Units are secure and 

generally operable. 

Emergency generators 

start, but may not be 

adequate to service all 

power requirements.

Units are functional. 

Emergency power is 

provided, as needed.

Light Fixtures Many broken light 

fixtures. Falling hazards 

generally avoided in 

heavier fixtures (>20 

pounds) in areas of 

public assembly.

Many broken light 

fixtures. Falling hazards 

generally avoided in 

heavier fixtures (> 20 

pounds).

Minor damage. Some 

pendant lights broken.

Negligible damage.
1-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

Plumbing Some fixtures broken; 

lines broken; mains 

disrupted at source.

Some fixtures broken, 

lines broken; mains 

disrupted at source.

Fixtures and lines 

serviceable; however, 

utility service may not 

be available.

System is functional. 

On-site water supply 

provided, if required.

1. Damage states indicated in this table are provided to allow an understanding of the severity of damage that may be sustained by various nonstructural 

elements meeting the Nonstructural Performance Levels defined in this standard. These damage states are not intended for use in post-earthquake evaluation 

of damage or for judging the safety or required level of repair following an earthquake.

2. For the Hazards Reduced Performance Level, high hazard nonstructural components evaluated or rehabilitated to the Life Safety criteria will have Hazards 

Reduced performance identical to that expected for the Life Safety Performance Level.

Table C1-7 Nonstructural Performance Levels and Damage1—Contents

Contents

Nonstructural Performance Levels

Hazards Reduced2

N-D

Life Safety 

N-C

Immediate Occupancy

N-B

Operational

N-A

Computer Systems Units roll and overturn, 

disconnect cables. 

Raised access floors 

collapse. Power not 

available.

Units shift and may 

disconnect cables, but 

do not overturn. Power 

not available.

Units secure and 

remain connected. 

Power may not be 

available to operate, 

and minor internal 

damage may occur.

Units undamaged and 

operable; power 

available.

Desktop Equipment Some equipment slides 

off desks.

Some equipment slides 

off desks.

Some equipment slides 

off desks.

Equipment secured to 

desks and operable.

File Cabinets Cabinets overturn and 

spill contents.

Cabinets overturn and 

spill contents.

Drawers slide open, but 

cabinets do not tip.

Drawers slide open, but 

cabinets do not tip.

Book Shelves Shelves overturn and 

spill contents.

Books slide off shelves. Books slide on shelves. Books remain on 

shelves.

Hazardous Materials Minor damage; 

occasional materials 

spilled; gaseous 

materials contained.

Minor damage; 

occasional materials 

spilled; gaseous 

materials contained.

Negligible damage; 

materials contained.

Negligible damage; 

materials contained.

Art Objects Objects damaged by 

falling, water, dust.

Objects damaged by 

falling, water, dust.

Some objects may be 

damaged by falling.

Objects undamaged.

1. Damage states indicated in this table are provided to allow an understanding of the severity of damage that may be sustained by various nonstructural 

elements meeting the Nonstructural Performance Levels defined in this standard. These damage states are not intended for use in post-earthquake evaluation 

of damage or for judging the safety or required level of repair following an earthquake.

2. For the Hazards Reduced Performance Level, high hazard nonstructural components evaluated or rehabilitated to the Life Safety criteria will have Hazards 

Reduced performance identical to that expected for the Life Safety Performance Level.

Table C1-6 Nonstructural Performance Levels and Damage1—Mechanical, Electrical, and Plumbing 

Systems/Components (continued)

System/Component

Nonstructural Performance Levels

Hazards Reduced2

N-D

Life Safety

N-C

Immediate Occupancy 

N-B

Operational

N-A
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-23

1.5.3 Designation of Target Building 

Performance Levels

A target Building Performance Level shall be 

designated alphanumerically with a numeral 

representing the Structural Performance Level and a 

letter representing the Nonstructural Performance Level 

(e.g., 1-B, 3-C). If a Structural Performance Level 

other than Immediate Occupancy (S-1), Life Safety

(S-3), or Collapse Prevention (S-5) is selected, the 

numerical designation shall represent the extent of 

structural damage expected in the selected Structural 

Performance Range.

C1.5.3 Designation of Target Building 

Performance Levels

Several common target Building Performance Levels 

described in this Section are shown in Figure C1-2. 

Many combinations are possible as structural 

performance can be selected at any level in the two 

Structural Performance Ranges. Table C1-8 indicates 

the possible combinations of target Building 

Performance Levels and provides names for those most 

likely to be selected as the basis for design.

Figure C1-2 Target Building Performance Levels 

and Ranges

Operational (1-A)

Backup utility services maintain 

functions; very little damage. 

(S1+NA)

Immediate Occupancy (1-B)

The building remains safe to 

occupy; any repairs are minor. 

(S1+NB)

Life Safety (3-C)

Structure remains stable and 

has significant reserve 

capacity; hazardous 

nonstructural damage is 

controlled. (S3+NC)

Collapse Prevention (5-E)

The building remains standing, 

but only barely; any other 

damage or loss is acceptable. 

(S5 + NE)

lower performance

more loss

higher performance

less loss

Expected Post-Earthquake 

Damage State
1-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.5.3.1 Operational Building Performance 

Level (1-A) 

To attain the Operational Building Performance Level 

(1-A), the structural components of the building shall 

meet the requirements of Section 1.5.1.1 for the 

Immediate Occupancy Structural Performance Level 

(S-1) and the nonstructural components shall meet the 

requirements of Section 1.5.2.1 for the Operational 

Nonstructural Performance Level (N-A).

1.5.3.2 Immediate Occupancy Building 

Performance Level (1-B)

To attain the Immediate Occupancy Building 

Performance Level (1-B), the structural components of 

the building shall meet the requirements of 

Section 1.5.1.1 for the Immediate Occupancy Structural 

Performance Level (S-1) and the nonstructural 

components of the building shall meet the requirements 

of Section 1.5.2.2 for the Immediate Occupancy 

Nonstructural Performance Level (N-B).

1.5.3.3 Life Safety Building Performance 

Level (3-C)

To attain the Life Safety Building Performance Level 

(3-C), the structural components of the building shall 

meet the requirements of Section 1.5.1.3 for the Life 

Safety Structural Performance Level (S-3) and the 

nonstructural components shall meet the requirements 

of Section 1.5.2.3 for the Life Safety Nonstructural 

Performance Level (N-C).

C1.5.3.1 Operational Building Performance 

Level (1-A)

Buildings meeting this target Building Performance 

Level are expected to sustain minimal or no damage to 

their structural and nonstructural components. The 

building is suitable for its normal occupancy and use, 

although possibly in a slightly impaired mode, with 

power, water, and other required utilities provided 

from emergency sources, and possibly with some nonessential systems not functioning. Buildings meeting 

this target Building Performance Level pose an 

extremely low risk to life safety.

Under very low levels of earthquake ground motion, 

most buildings should be able to meet or exceed this 

target Building Performance Level. Typically, 

however, it will not be economically practical to 

design for this target Building Performance Level for 

severe ground shaking, except for buildings that house 

essential services.

C1.5.3.2 Immediate Occupancy Building 

Performance Level (1-B)

Buildings meeting this target Building Performance 

Level are expected to sustain minimal or no damage to 

their structural elements and only minor damage to 

their nonstructural components. While it would be safe 

to reoccupy a building meeting this target Building 

Performance Level immediately following a major 

earthquake, nonstructural systems may not function, 

either because of the lack of electrical power or 

internal damage to equipment. Therefore, although 

immediate reoccupancy of the building is possible, it 

may be necessary to perform some cleanup and repair 

and await the restoration of utility service before the 

building can function in a normal mode. The risk to life 

safety at this target Building Performance Level is very 

low.

Many building owners may wish to achieve this level 

of performance when the building is subjected to 

moderate earthquake ground motion. In addition, some 

owners may desire such performance for very 

important buildings under severe earthquake ground 

shaking. This level provides most of the protection 

obtained under the Operational Building Performance 

Level without the cost of providing standby utilities 

and performing rigorous seismic qualification of 

equipment performance.

C1.5.3.3 Life Safety Building Performance 

Level (3-C)

Buildings meeting this level may experience extensive 

damage to structural and nonstructural components. 

Repairs may be required before reoccupancy of the 

building occurs, and repair may be deemed 

economically impractical. The risk to life safety in 

buildings meeting this target Building Performance 

Level is low.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-25

1.5.3.4 Collapse Prevention Building 

Performance Level (5-E)

To attain the Collapse Prevention Building Performance 

Level (5-E), the structural components of the building 

shall meet the requirements of Section 1.5.1.5 for the 

Collapse Prevention Structural Performance Level 

(S-5). Nonstructural components are not considered.

This target Building Performance Level entails 

somewhat more damage than anticipated for new 

buildings that have been properly designed and 

constructed for seismic resistance when subjected to 

their design earthquakes. Many building owners will 

desire to meet this target Building Performance Level 

for severe ground shaking.

C1.5.3.4 Collapse Prevention Building 

Performance Level (5-E)

Buildings meeting this target Building Performance 

Level may pose a significant hazard to life safety 

resulting from failure of nonstructural components. 

However, because the building itself does not collapse, 

gross loss of life may well be avoided. Many buildings 

meeting this level will be complete economic losses.

This level has been sometimes selected as the basis for 

mandatory seismic rehabilitation ordinances enacted 

by municipalities, as it results in mitigation of the most 

severe life-safety hazards at relatively low cost.

Table C1-8 Target Building Performance Levels and Ranges

Nonstructural 

Performance 

Levels

Structural Performance Levels and Ranges

S-1

Immediate 

Occupancy

S-2 

Damage 

Control Range

S-3 

Life 

Safety

S-4 

Limited 

Safety Range

S-5 

Collapse 

Prevention

S-6 

Not 

Considered

N-A 

Operational

Operational 1-A 2-A Not 

recommended

Not 

recommended

Not 

recommended

Not 

recommended

N-B 

Immediate 

Occupancy

Immediate 

Occupancy 1-B

2-B 3-B Not 

recommended

Not 

recommended

Not 

recommended

N-C 

Life Safety

1-C 2-C Life Safety 3-C 4-C 5-C 6-C

N-D 

Hazards 

Reduced 

Not 

recommended

2-D 3-D 4-D 5-D 6-D

N-E 

Not Considered

Not 

recommended

Not 

recommended

Not 

recommended

4-E Collapse 

Prevention 5-E

No rehabilitation
1-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.6 Seismic Hazard

Seismic hazard due to ground shaking shall be based on 

the location of the building with respect to causative 

faults, the regional and site-specific geologic 

characteristics, and a selected Earthquake Hazard 

Level. Assessment of seismic hazard due to earthquakeinduced geologic site hazards shall be performed in 

accordance with Chapter 4.

Seismic hazard due to ground shaking shall be defined 

as acceleration response spectra or acceleration timehistories on either a probabilistic or deterministic basis. 

Acceleration response spectra shall be developed in 

accordance with either the General Procedure of 

Section 1.6.1 or the Site-Specific Procedure of 

Section 1.6.2. Acceleration time-histories shall be 

developed in accordance with Section 1.6.2.2. The 

seismic zone of the building shall be determined as 

specified in Section 1.6.3.

Unless otherwise approved, the site-specific procedure 

shall be used where any of the following conditions 

apply.

1. The building is located on Type E soils (as defined 

in Section 1.6.1.4) and the mapped BSE-2 spectral 

response acceleration at short periods (SS) exceeds 

2.0g.

2. The building is located on Type F soils as defined in 

Section 1.6.1.4.

Exception: Where SS determined in accordance with 

Section 1.6.1.1 is less than 0.20g, use of a Type E 

soil profile shall be permitted.

3. A time-history response analysis of the building will 

be performed as part of the design. 

C1.6 Seismic Hazard

The analysis and design procedures of this standard are 

primarily aimed at improving performance of 

buildings under loads and deformations imposed by 

seismic shaking. However, other seismic hazards could 

exist at the building site that could damage the building 

regardless of its ability to resist ground shaking. These 

hazards include fault rupture, liquefaction or other 

shaking-induced soil failures, landslides, and 

inundation from offsite effects such as dam failure or 

tsunami.

This standard requires hazards due to earthquake 

shaking to be defined on either a probabilistic or 

deterministic basis. Probabilistic hazards are defined in 

terms of the probability that more severe demands will 

be experienced (probability of exceedance) in a 50-

year period. Deterministic demands are defined within 

a level of confidence in terms of a specific magnitude 

event on a particular major active fault.

This standard defines two basic Earthquake Hazard 

Levels: Basic Safety Earthquake 1 (BSE-1) and Basic 

Safety Earthquake 2 (BSE-2).

In addition to the BSE-1 and BSE-2 Earthquake 

Hazard Levels, Rehabilitation Objectives may be 

formed considering ground shaking due to Earthquake 

Hazard Levels with any defined probability of 

exceedance, or based on any deterministic event on a 

specific fault.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-27

1.6.1 General Procedure for Hazard Due to 

Ground Shaking

The seismic hazard due to ground shaking shall be 

defined for any Earthquake Hazard Level using 

approved spectral response acceleration contour maps 

of 5%-damped response spectrum ordinates for shortperiod (0.2 second) and long-period (1 second) 

response. 

The short-period response acceleration parameter, SS, 

and the long-period response acceleration parameter, 

S1, shall be determined as follows:

1. If the desired Earthquake Hazard Level corresponds 

with one of the mapped Earthquake Hazard Levels, 

obtain spectral response acceleration parameters 

directly from the maps. Values between contour 

lines shall be interpolated in accordance with the 

procedure in Section 1.6.1.1.

2. If the desired Earthquake Hazard Level does not 

correspond with the mapped levels of hazard, then 

obtain the spectral response acceleration parameters 

from the available maps, and modify them to the 

desired hazard level, either by logarithmic 

interpolation or extrapolation, in accordance with 

Section 1.6.1.3.

3. Obtain design spectral response acceleration 

parameters by adjusting the mapped or modified 

spectral response acceleration parameters for site 

class effects, in accordance with Section 1.6.1.4.

4. If the desired Earthquake Hazard Level is the Basic 

Safety Earthquake 2 (BSE-2), obtain spectral 

response acceleration parameters in accordance with 

Section 1.6.1.1.

5. If the desired Earthquake Hazard Level is the Basic 

Safety Earthquake 1 (BSE-1), obtain the spectral 

response acceleration parameters in accordance with 

Section 1.6.1.2.

6. Using the design spectral response acceleration 

parameters that have been adjusted for site class 

effects, develop the general response spectrum in 

accordance with Section 1.6.1.5.

C1.6.1 General Procedure for Hazard Due to 

Ground Shaking

This standard uses the latest national earthquake 

hazard maps developed by the United States 

Geological Survey (USGS) as part of a joint effort with 

the Building Seismic Safety Council, known as Project 

97. National probabilistic maps were developed for 

ground motions with a 10% chance of exceedance in 

50 years, a 10% chance of exceedance in 100 years 

(which can also be expressed as a 5% chance of 

exceedance in 50 years) and a 10% chance of 

exceedance in 250 years (which also can be expressed 

as a 2% chance of exceedance in 50 years). These 

probabilities correspond to motions that are expected 

to occur, on average, about once every 500, 1,000, and 

2,500 years. In addition, local ground motions in 

regions with well-defined earthquake sources, known 

as deterministic motions, were used to develop 

Maximum Considered Earthquake (MCE) maps.

The Rehabilitation Objective options featured in this 

standard allow consideration of any ground motion that 

may be of interest. However, for defining BSE-1 and 

BSE-2 Earthquake Hazard Levels, and for convenience 

in defining the ground motion for other Earthquake 

Hazard Levels, the 10%/50-year probabilistic maps 

and the MCE maps developed in Project 97 are 

referenced in this standard. This collection of maps, 

referred to as the National Earthquake Hazards 

Reduction Program (NEHRP) design map set (Maps 1 

through 32), is available from the FEMA Distribution 

Center at 1-800-480-2520, online at 

http://geohazards.cr.usgs.gov/eq, or on CD-ROM from 

the USGS.
1-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.6.1.1 BSE-2 Response Acceleration 

Parameters

The design short-period response acceleration 

parameter, SXS, and design response acceleration 

parameter at a one-second period, SX1, for the BSE-2 

Earthquake Hazard Level shall be determined using 

values of SS and S1 taken from approved MCE spectral 

response acceleration contour maps and modified for 

site class in accordance with Section 1.6.1.4.

Parameters SS and S1 shall be obtained by interpolating 

between the values shown on the map for the response 

acceleration contour lines on either side of the site, or 

by using the value shown on the map for the higher 

contour adjacent to the site.

The MCE ground motion maps, were developed by the 

USGS in conjunction with the Seismic Design 

Procedure Group (SDPG) appointed by BSSC. The 

effort utilized the latest seismological information to 

develop design response acceleration parameters with 

the intent of providing a uniform margin against 

collapse in all areas of the United States. The MCE 

ground motion maps are based on seismic hazard 

maps, which are (1) 2%/50 year earthquake ground 

motion hazard maps for regions of the United States 

that have different ground motion attenuation 

relationships, and (2) deterministic ground motion 

maps in regions of high seismicity with the appropriate 

ground motion attenuation relationships for each 

region. The deterministic maps are used in regions of 

high seismicity where frequent large earthquakes are 

known to occur, and the rare earthquake ground 

motions corresponding to the 2%/50 year hazard are 

controlled by the large uncertainties in the hazard 

studies, which results in unusually high ground 

motions. These high ground motions were judged by 

the Seismic Design Procedure Group to be 

inappropriate for use in design. The use of these 

different maps to develop the MCE maps required the 

Seismic Design Procedure Group to define guidelines 

for integrating the maps into the design ground motion 

maps.

The most rigorous guideline developed was for 

integrating the probabilistic and the deterministic 

maps. To integrate the probabilistic maps and the 

deterministic map, a transition zone set at 150% of the 

level of the 1994 NEHRP Provisions was used and is 

extensively discussed in the 1997 NEHRP Provisions

Commentary. The goal of this guideline was to not 

exceed the deterministic ground motion in these areas 

of high seismicity where earthquake faults and 

maximum magnitudes are relatively well defined. The 

remaining guidelines were more subjective, and were 

related to smoothing irregular contours, joining 

contours in areas where closely spaced contours of 

equal values occurred (particularly in areas where 

faults are known to exist, but the hazard parameters are 

not well defined), increasing the response acceleration 

parameters in small areas surrounded by higher 

parameters, etc.

Based on the process used to develop the MCE maps, 

there are some locations where the mapped 

acceleration response parameters in the MCE maps 

exceed the probabilistic 2%/50-years seismic hazard 

maps. These locations occur primarily in the New 

Madrid, Missouri, area; the Salt Lake City, Utah, area; 

coastal California; and the Seattle, Washington, area. 

This is an intended result of the process and the 

mapped values represent the appropriate values as 

determined by the Seismic Design Procedure Group.

This standard requires earthquake shaking demands to 

be expressed in terms of ground motion response 

spectra or suites of ground motion time histories, 

depending on the analysis procedure selected. While 

the maps provide a ready source for this type of 

information, this standard may be used with approved 

seismic hazard data from any source, as long as it is 

expressed as a response spectrum.
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-29

1.6.1.2 BSE-1 Response Acceleration 

Parameters

The design short-period response acceleration 

parameter, SXS, and design response acceleration 

parameter at a one-second period, SX1, for the BSE-1 

Earthquake Hazard Level shall be taken as the smaller 

of the following:

1. The values of SS and S1 taken from approved 

10%/50 year spectral response acceleration contour 

maps and modified for site class in accordance with 

Section 1.6.1.4. Values between contour lines shall 

be interpolated in accordance with the procedure in 

Section 1.6.1.1.

2. Two-thirds of the values of the parameters for the 

BSE-2 earthquake hazard level, determined in 

accordance with Section 1.6.1.1.

1.6.1.3 Adjustment of Mapped Response 

Acceleration Parameters for Other 

Probabilities of Exceedance

Acceleration response spectra for earthquake hazard 

level corresponding to probabilities of exceedance other 

than 2%/50 years and 10%/50 years shall be determined 

using the following procedures specified in Sections 

1.6.1.3.1 or 1.6.1.3.2.

1.6.1.3.1 Probabilities of Exceedance Between 

2%/50 Years and 10%/50 Years

 For probabilities of exceedance, PEY, between 2%/50 

years and 10%/50 years, when the mapped BSE-2 

short-period response acceleration parameter, SS, is less 

than 1.5g, the modified mapped short-period response 

acceleration parameter, SS, and modified mapped 

response acceleration parameter at a one-second period, 

S1, shall be determined from Equation (1-1):

1n(Si

) = 1n(Si10/50) + [1n(SiBSE-2) – 1n(Si10/50)]

[0.606 1n(PR) – 3.73] (1-1)

C1.6.1.1 BSE-2 Response Acceleration 

Parameters

The latest MCE contour maps are contained in Maps 1 

through 24 of the NEHRP design map set. 

The BSE-2 Earthquake Hazard Level is consistent with 

MCE in FEMA 302. In most areas of the United States, 

the BSE-2 Earthquake Hazard Level has a 2% 

probability of exceedance in 50 years (2%/50 year). In 

regions close to known faults with significant slip rates 

and characteristic earthquakes with magnitudes in 

excess of about 6.0, the BSE-2 Earthquake Hazard 

Level is limited by a deterministic estimate of ground 

motion based on 150% of the median attenuation of the 

shaking likely to be experienced as a result of such a 

characteristic event. Ground shaking levels determined 

in this manner will typically correspond to a 

probability of exceedance greater than 2% in 50 years.

C1.6.1.2 BSE-1 Response Acceleration 

Parameters

The latest 10%/50 year contour maps are contained in 

Maps 25 through 30 of the NEHRP design map set. In 

determining BSE-1 parameters, the modification for 

site class shall be made prior to application of the twothirds factor on BSE-2 parameters. 

This standard has not directly adopted the concept of a 

design earthquake solely based on 2/3 of the MCE 

level as in FEMA 302. This design earthquake would 

have a different probability of exceedance throughout 

the nation, depending on the seismicity of the 

particular region, which would be inconsistent with the 

intent of this standard to permit design for specific 

levels of performance for hazards that have specific 

probabilities of exceedance. The BSE-1 Earthquake 

Hazard Level is similar, but not identical to the concept 

of the FEMA 302 design earthquake. It is defined as 

ground shaking having a 10% probability of 

exceedance in 50 years (10%/50 year), but not 

exceeding values used for new buildings taken as 2/3 

of the BSE-2 motion (i.e., 2/3 MCE).
1-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

where:

and the mean return period, PR, at the desired 

exceedance probability shall be calculated from 

Equation (1-2):

(1-2)

where PEY is the probability of exceedance (expressed 

as a decimal) in time Y (years) for the desired 

earthquake hazard level.

When the mapped BSE-2 short-period response 

acceleration parameter, SS, is greater than or equal to 

1.5g, the modified mapped short-period response 

acceleration parameter, SS, and modified mapped 

response acceleration parameter at a one-second period, 

S1, for probabilities of exceedance between 2%/50 

years and 10%/50 years shall be determined from 

Equation (1-3):

(1-3)

where Si

, Si10/50 and PR are as defined above and n shall 

be obtained from Table 1-1.

1.6.1.3.2 Probabilities of Exceedance Greater than 

10%/50 Years

For probabilities of exceedance greater than 10%/50 

years and when the mapped short-period response 

acceleration parameter, SS, is less than 1.5g, the 

modified mapped short-period response acceleration 

parameter, SS, and modified mapped response 

acceleration parameter at a one-second period, S1, shall 

be determined from Equation (1-3), where the exponent 

n is obtained from Table 1-2.

For probabilities of exceedance greater than 10%/50 

years and when the mapped short-period response 

acceleration parameter, SS, is greater than or equal to 

1.5g, the modified mapped short-period response 

acceleration parameter, SS, and modified mapped 

response acceleration parameter at a one-second period, 

S1, shall be determined from Equation (1-3), where the 

exponent n is obtained from Table 1-3.

1.6.1.4 Adjustment for Site Class

The design short-period spectral response acceleration 

parameter, SXS, and the design spectral response 

acceleration parameter at one-second, SX1, shall be 

obtained from Equations (1-4) and (1-5), respectively, 

as follows:

(1-4)

(1-5)

where Fa and Fv are site coefficients determined 

respectively from Tables 1-4 and 1-5, based on the site 

class and the values of the response acceleration 

parameters SS and S1 for the selected return period.

1n(Si

) = Natural logarithm of the spectral 

acceleration parameter (“i” = “s” for 

short-period or “i” = 1 for 1 second 

period) at the desired probability of 

exceedance

1n(Si10/50) = Natural logarithm of the spectral 

acceleration parameter (“i” = “s” for 

short-period or “i” = 1 for 1 second 

period) at a 10%/50 year exceedance 

rate

1n(SiBSE-2) = Natural logarithm of the spectral 

acceleration parameter (“i” = “s” for 

short-period or “i” = 1 for 1 second 

period) for the BSE-2 hazard level

1n(PR) = Natural logarithm of the mean return 

period corresponding to the 

exceedance probability of the desired 

earthquake hazard level

PR

–Y

1 PEY ln( ) – = ----------------------------

C1.6.1.3.1 Probabilities of Exceedance Between 

2%/50 Years and 10%/50 Years

Tables 1-1 through 1-3 specify five regions, three of 

which are not yet specifically defined, namely 

Intermountain, Central US, and Eastern US.

Si Si10 50 ⁄

PR

475

--------     n

=

SXS Fa SS =

SX1 Fv S1 =
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-31

1.6.1.4.1 Site Classes

Site classes shall be defined as follows:

1. Class A: Hard rock with average shear wave 

velocity, > 5,000 ft/sec

2. Class B: Rock with 2,500 ft/sec < < 5,000 ft/sec

3. Class C: Very dense soil and soft rock with 

1,200 ft/sec < ≤ 2,500 ft/sec or with either 

standard blow count > 50 or undrained shear 

strength > 2,000 psf

4. Class D: Stiff soil with 600 ft/sec < ≤

1,200 ft/sec or with 15 < ≤ 50 or 1,000 psf ≤ 

< 2,000 psf

5. Class E: Any profile with more than 10 feet of 

soft clay defined as soil with plasticity index PI > 

20, or water content w > 40 percent, and < 500 

psf or a soil profile with < 600 ft/sec.

6. Class F: Soils requiring site-specific evaluations:

6.1. Soils vulnerable to potential failure or collapse 

under seismic loading, such as liquefiable 

soils, quick and highly-sensitive clays, 

collapsible weakly-cemented soils

6.2. Peats and/or highly organic clays (H > 10 feet 

of peat and/or highly organic clay, where H = 

thickness of soil)

6.3. Very high plasticity clays (H > 25 feet with PI 

> 75)

6.4. Very thick soft/medium stiff clays (H > 120 

feet).

The parameters , , and are, respectively, the 

average values of the shear wave velocity, Standard 

Penetration Test (SPT) blow count, and undrained shear 

strength of the upper 100 feet of soils at the site. These 

values shall be calculated from Equation (1-6), below:

(1-6)

where: 

and

(1-7)

Where vs data are available for the site, such data shall 

be used to classify the site. If such data are not 

available, N data shall be used for cohesionless soil sites 

(sands, gravels), and su data for cohesive soil sites 

(clays). For rock in profile classes B and C, 

classification shall be based either on measured or 

estimated values of vs. Classification of a site as Class 

A rock shall be based on measurements of vs either for 

material at the site itself, or for rock having the same 

formation adjacent to the site; otherwise, Class B rock 

shall be assumed. Class A or B profiles shall not be 

assumed to be present if there is more than 10 feet of 

soil between the rock surface and the base of the 

building.

1.6.1.4.2 Default Site Class

If there is insufficient data available to classify a soil 

profile as Class A through C, and there is no evidence 

of soft clay soils characteristic of Class E in the vicinity 

of the site, the default site class shall be taken as Class 

D. If there is evidence of Class E soils in the vicinity of 

the site, and no other data supporting selection of Class 

A through D, the default site class shall be taken as 

Class E.

vs

vs

vs

N

su

vs

N su

su

vs

vs N su

Ni = SPT blow count in soil layer “i”

n = Number of layers of similar soil materials for 

which data is available

di = Depth of layer “i”

sui = Undrained shear strength in layer “i”

= Shear wave velocity of the soil in layer “i”

vs N su , ,

di

i = 1

n

∑

di

vsi

------ di

Ni

----- di

sui

, , ------

n

∑

= -----------------------------------

νsi

di

i = 1

n

∑ = 100 ft
1-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.6.1.5 General Response Spectrum

A general response spectrum shall be developed as 

specified in Sections 1.6.1.5.1 through 1.6.1.5.3.

1.6.1.5.1 General Horizontal Response Spectrum

A general horizontal response spectrum as shown in 

Figure 1-1 shall be developed using Equations (1-8), 

(1-9), and (1-10) for spectral response acceleration, Sa,

versus structural period, T, in the horizontal direction.

(1-8)

, and

, and (1-9)

(1-10)

where TS and T0 are given by Equations (1-11) and 

(1-12)

(1-11)

(1-12)

and where BS and B1 shall be taken from Table 1-6.

Use of spectral response accelerations calculated using 

Equation (1-8) in the extreme short period range (T < 

T0) shall only be permitted in dynamic analysis 

procedures and only for modes other than the 

fundamental mode.

1.6.1.5.2 General Vertical Response Spectrum

Where a vertical response spectrum is required, it shall 

be developed by taking two-thirds of the spectral 

ordinates, at each period, obtained for the horizontal 

response spectrum.

1.6.1.5.3 Damping Ratios

A 5% damped response spectrum shall be used for the 

rehabilitation design of all buildings and structural 

systems except those meeting the following criteria:

1. For structures without exterior cladding, an effective 

viscous damping ratio, β, equal to 2% of critical 

damping shall be assumed.

2. For structures with wood diaphragms and interior 

partitions and cross walls that interconnect the 

diaphragm levels at a maximum spacing of 40 feet 

on center transverse to the direction of motion, an 

effective viscous damping ratio, β, equal to 10% of 

critical damping shall be permitted.

3. For structures rehabilitated using seismic isolation 

technology or enhanced energy dissipation 

technology, an equivalent effective viscous damping 

ratio, β, shall be calculated using the procedures 

specified in Chapter 9. 

Sa SXS

5

BS

----- – 2     T

TS

= ----- + 0.4

for 0 T T0 < <

Sa SXS BS ⁄ for T TS = ( ) <

Sa SX1 B1 ( ) ⁄ ( ) T for T TS = >

TS SX1BS ( ) SXSB1 = ⁄ ( )

T0 0.2TS =

Table 1-1 Values of Exponent n for 

Determination of Response 

Acceleration Parameters at 

Earthquake Hazard Levels between 

10%/50 years and 2%/50 years;

Sites where Mapped BSE-2 Values 

of SS ≥1.5g

Values of Exponent n for

Region SS S1

California 0.29 0.29

Pacific Northwest 0.56 0.67

Intermountain 0.50 0.60

Central US 0.98 1.09

Eastern US 0.93 1.05
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-33

Table 1-2 Values of Exponent n for 

Determination of Response 

Acceleration Parameters at 

Probabilities of Exceedance Greater 

than 10%/50 years;

Sites where Mapped BSE-2 Values 

of SS < 1.5g

Values of Exponent n for

Region SS S1

California 0.44 0.44

Pacific Northwest and 

Intermountain

0.54 0.59

Central and Eastern US 0.77 0.80

Table 1-3 Values of Exponent n for 

Determination of Response 

Acceleration Parameters at 

Probabilities of Exceedance Greater 

than 10%/50 years;

Sites where Mapped BSE-2 Values 

of SS ≥1.5g

Values of Exponent n for

Region SS S1

California 0.44 0.44

Pacific Northwest 0.89 0.96

Intermountain 0.54 0.59

Central US 0.89 0.89

Eastern US 1.25 1.25

Table 1-4 Values of Fa as a Function of Site 

Class and Mapped Short-Period 

Spectral Response Acceleration SS

Site 

Class

Mapped Spectral Acceleration at Short-Periods 

SS

SS ≤

0.25

SS = 

0.50

SS = 

0.75

SS = 

1.00

SS ≥

1.25

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F ∗∗ ∗ ∗ ∗

NOTE: Straight-line interpolation shall be used for intermediate values of 

SS.

* Site-specific geotechnical investigation and dynamic site response 

analyses shall be performed.

Table 1-5 Values of Fv as a Function of Site 

Class and Mapped Spectral 

Response Acceleration at 

One-Second Period S1

Site 

Class

Mapped Spectral Acceleration at One-Second 

Period S1

S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥ 0.50

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.7 1.6 1.5 1.4 1.3

D 2.4 2.0 1.8 1.6 1.5

E 3.5 3.2 2.8 2.4 2.4

F ∗∗ ∗ ∗ ∗

NOTE: Straight-line interpolation shall be used for intermediate values of 

S1.

* Site-specific geotechnical investigation and dynamic site response 

analyses shall be performed.
1-34 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.6.2 Site-Specific Procedure for Hazard 

Due to Ground Shaking 

Where site-specific ground shaking characterization is 

selected or required by the code official as the basis of 

rehabilitation design, the characterization shall be 

developed in accordance with this section.

1.6.2.1 Site-Specific Response Spectra

Development of site-specific response spectra shall be 

based on the geologic, seismologic, and soil 

characteristics associated with the specific site and as 

specified in Sections 1.6.2.1.1 through 1.6.2.1.4.

1.6.2.1.1 Damping Ratios

Response spectra shall be developed for an effective 

viscous damping ratio of 5% of critical damping and for 

other damping ratios appropriate to the indicated 

structural behavior, as discussed in Section 1.6.1.5.

1.6.2.1.2 Minimum Spectral Amplitude

The 5% damped site-specific spectral amplitudes in the 

period range of greatest significance to the structural 

response shall not be specified less than 70 percent of 

the spectral amplitudes of the General Response 

Spectrum.

1.6.2.1.3 Basis of the Response Spectra

Probabilistic site-specific spectra that represent the 

BSE-1 Earthquake Hazard Level shall be mean spectra 

at the 10%/50 year probability of exceedance. 

Probabilistic site-specific spectra that represent the 

BSE-2 Earthquake Hazard Level shall be mean spectra 

at the 2%/50 year probability of exceedance. 

Deterministic BSE-2 site-specific spectra shall be taken 

as 150% of the median spectra for the characteristic 

event on the controlling fault.

1.6.2.1.4 Site-Specific Response Acceleration 

Parameters and Construction of 

Response Spectra

The design response acceleration parameters, SXS, SX1, 

and TS shall be obtained using the site-specific response 

spectra in accordance with this section. Values of the 

design response acceleration parameter at short-periods, 

SXS, shall be taken as the response acceleration obtained 

from the site-specific spectra at a period of 0.2 seconds, 

except that it shall not be taken as less than 90% of the 

peak response acceleration at any period. In order to 

obtain values for the design spectral response 

acceleration parameter SX1, a curve of the form Sa = 

SX1/T shall be graphically overlaid on the site-specific 

spectra such that at any period, the value of Sa obtained 

from the curve is not less than 90% of that which would 

be obtained directly from the spectra. The value of TS

shall be determined in accordance with Equation (1-13).

(1-13)

Table 1-6 Damping Coefficients BS and B1 as a 

Function of Effective Damping β

Effective Viscous Damping β

(percentage of critical 

damping)1 BS B1

< 2 0.8 0.8

5 1.0 1.0

10 1.3 1.2

20 1.8 1.5

30 2.3 1.7

40 2.7 1.9

> 50 3.0 2.0

1. Damping coefficients shall be based on linear interpolation for 

effective viscous damping values other than those given. 

Figure 1-1 General Horizontal Response Spectrum

TS SX1 SXS = ⁄
 Chapter 1: Rehabilitation Requirements

FEMA 356 Seismic Rehabilitation Prestandard 1-35

1.6.2.1.5 Site-Specific BSE-2 Response 

Acceleration Parameters

The site-specific response acceleration parameters for 

the BSE-2 Earthquake Hazard Level shall be taken as 

the smaller of the following:

1. The values of the parameters from mean 

probabilistic site-specific spectra at the 2%/50 year 

probability of exceedance.

2. The values of the parameters from 150% of median 

deterministic site-specific spectra.

1.6.2.1.6 Site-Specific BSE-1 Response 

Acceleration Parameters

The site-specific response acceleration parameters for 

the BSE-1 Earthquake Hazard Level shall be taken as 

the smaller of the following:

1. The values of the parameters from mean 

probabilistic site-specific spectra at the 10%/50 year 

probability of exceedance.

2. Two-thirds of the values of the parameters 

determined for the BSE-2 Earthquake Hazard 

Level.

1.6.2.2 Acceleration Time Histories

Time history analysis shall be performed with no fewer 

than three data sets (each containing two horizontal 

components or, if vertical motion is to be considered, 

two horizontal components and one vertical 

component) of ground motion time histories that shall 

be selected and scaled from no fewer than three 

recorded events. Time histories shall have magnitude, 

fault distances, and source mechanisms that are 

equivalent to those that control the design earthquake 

ground motion. Where three recorded ground-motion 

time history data sets having these characteristics are 

not available, simulated time history data sets having 

equivalent duration and spectral content shall be used to 

make up the total number required. For each data set, 

the square root of the sum of the squares (SRSS) of the 

5%-damped site-specific spectrum of the scaled 

horizontal components shall be constructed. The data 

sets shall be scaled such that the average value of the 

SRSS spectra does not fall below 1.4 times the 5%-

damped spectrum for the design earthquake for periods 

between 0.2T seconds and 1.5T seconds (where T is the 

fundamental period of the building).

Where three time history data sets are used in the 

analysis of a structure, the maximum value of each 

response parameter (e.g., force in a member, 

displacement at a specific level) shall be used to 

determine design acceptability. Where seven or more 

time history data sets are employed, the average value 

of each response parameter shall be permitted to 

determine design acceptability.

1.6.3 Zones of Seismicity

The zone of seismicity shall be defined as High, 

Moderate, or Low as specified in Sections 1.6.3.1, 

1.6.3.2, and 1.6.3.3, respectively.

1.6.3.1 Zones of High Seismicity

Buildings shall be considered to be located within zones 

of high seismicity where the 10%/50 year, design shortperiod response acceleration, SXS, and the 10%/50 year 

design one-second period response acceleration, SX1, 

are as specified in Equation (1-14):

SXS ≥ 0.5g and

SX1 ≥ 0.2g (1-14)

C1.6.2.1 Procedure for Site-Specific 

Response Spectrum

The code official should consider an independent thirdparty review of the site-specific spectra by an 

individual with expertise in the evaluation of ground 

motion.
1-36 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 1: Rehabilitation Requirements

1.6.3.2 Zones of Moderate Seismicity

Buildings shall be considered to be located within zones 

of moderate seismicity where the 10%/50 year, design 

short-period response acceleration, SXS, and the 10%/

50 year, design one-second period response 

acceleration, SX1, are as specified in Equation (1-15):

0.167 ≤ SXS < 0.5g or

0.067 ≤ SX1 < 0.2g (1-15)

1.6.3.3 Zones of Low Seismicity

Buildings shall be considered to be located within zones 

of low seismicity where the 10%/50 year, design shortperiod response acceleration, SXS, and the 10%/50 year, 

design one-second period response acceleration, SX1, 

are as specified in Equation (1-16): 

SXS < 0.167g and

SX1 < 0.067g (1-16)
FEMA 356 Seismic Rehabilitation Prestandard 2-1

2. General Requirements

2.1 Scope

This chapter sets forth general requirements for data 

collection, analysis procedures, methods, and strategies 

for the design of seismic rehabilitation projects.

Section 2.2 specifies data collection procedures for 

obtaining required as-built information on buildings. 

Section 2.3 outlines the Simplified and Systematic 

Methods for seismic rehabilitation of buildings. 

Section 2.4 specifies limitations on selecting analysis 

procedures, and defines component behavior types and 

corresponding acceptance criteria. Section 2.5 identifies 

acceptable rehabilitation strategies. Section 2.6 contains 

general design requirements for rehabilitation designs. 

Section 2.7 specifies construction quality assurance 

requirements. Section 2.8 specifies procedures for 

developing alternative modeling parameters and 

acceptance criteria. 

2.2 As-Built Information

The configuration of the structural system, as well as 

the type, detailing, connectivity, material strength and 

condition of the structural elements comprising the 

building shall be determined in accordance with this 

section. Data shall also be obtained for all nonstructural 

elements of the building that affect the forces and 

deformations experienced by the structural elements 

during response to earthquake ground motion. This data 

shall be obtained from available drawings, 

specifications, and other documents for the existing 

construction, and shall be supplemented and verified by 

on-site investigations including nondestructive 

examination and testing of building materials and 

components as required in Section 2.2.6.

At least one site visit shall be made to observe exposed 

conditions of building configuration, building 

components, site and foundation conditions, and 

adjacent structures, and to verify that as-built 

information obtained from other sources is 

representative of the existing conditions.

C2.2 As-Built Information

Existing building characteristics pertinent to seismic 

performance should be obtained from the following 

sources, as appropriate:

1. Field observation of exposed conditions and 

configuration.

2. Construction documents, engineering analyses, 

reports, soil borings and test logs, maintenance 

histories, and manufacturers’ literature and test data 

available from the owner and/or the code official.

3. Reference standards and codes from the period of 

construction as cited in Chapters 5 through 8.

4. Destructive and nondestructive examination and 

testing of selected building materials and 

components as specified in Section 2.2.6.

5. Interviews with building owners, tenants, 

managers, the original architect and engineer, 

contractor(s), and the local building official as 

arranged by the code official.

The information required for an existing building may 

also be available from a previously conducted seismic 

evaluation of the building. For situations where 

seismic rehabilitation has been mandated according to 

building construction classification, familiarity with 

the building type and typical seismic deficiencies is 

recommended. Such information is available from 

several sources, including FEMA 310. Such 

information may be sufficient for Simplified 

Rehabilitation. Additional as-built information may be 

needed for Systematic Rehabilitation.

When a destructive and nondestructive testing program 

is necessary to obtain as-built information, it is prudent 

to perform preliminary calculations to select key 

locations or parameters prior to establishing a detailed 

testing program. These obtain knowledge at a 

reasonable cost and with as little disruption as possible 

of construction features and materials properties at 

concealed locations.
2-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.2.1 Building Configuration

The as-built building configuration information shall 

include data on the type and arrangement of existing 

structural elements and components of the gravity- and 

lateral-load-resisting systems, and the nonstructural 

components of the building that affect either the 

stiffness or strength of the structural elements, or the 

structural load path. The structural elements and 

components shall be identified and categorized as either 

primary or secondary, using the criteria described in 

Section 2.4.4.2.

The as-built building configuration shall be examined to 

identify the gravity and lateral load paths. These load 

paths shall be evaluated to identify seismic deficiencies 

prior to conducting a detailed rehabilitation design.

2.2.2 Component Properties

Sufficient as-built information shall be collected on 

component properties and their interconnection with 

other components to permit computation of strengths 

and deformation capacities. To account for any 

uncertainty associated with component as-built 

information, a knowledge factor κ shall be used in the 

capacity evaluation as specified in Section 2.2.6.4.

2.2.3 Site Characterization and 

Geotechnical Information

Data on foundation configuration and soil surface and 

subsurface conditions at the site shall be obtained from 

existing documentation, visual site reconnaissance, or a 

program of site-specific subsurface investigation in 

accordance with Chapter 4. A site-specific subsurface 

investigation shall be performed when Enhanced 

Rehabilitation Objectives are selected, or when 

insufficient data are available to quantify foundation 

capacities or determine the presence of geologic site 

hazards identified in Section 4.2.2. When historic 

information indicates geologic site hazards have 

occurred in the vicinity of the site, a site-specific 

subsurface investigation shall be performed to 

investigate the potential for geologic site hazards at the 

site. Use of applicable existing foundation capacity or 

geologic site hazard information available for the site 

shall be permitted.

If the building is a historic structure, it is also 

important to identify the locations of historically 

significant features and fabric which should be 

thoroughly investigated. Care should be taken in the 

design and investigation process to minimize the 

impact of work on these features. Refer to the 

Secretary of the Interior’s Standards for the Treatment 

of Historic Properties as discussed in Appendix A. The 

services of a historic preservation expert may be 

necessary.

C2.2.1 Building Configuration

Identifying the building configuration will identify 

both the intended load-resisting elements and effective 

load-resisting elements. Effective load-resisting 

elements may include structural elements and 

nonstructural elements that participate in resisting 

lateral loads, whether or not they were intended to do 

so by the original designers. Potential seismic 

deficiencies in intended and effective load resisting 

elements may include discontinuities in the load path, 

weak links, irregularities and inadequate strength and 

deformation capacities.

FEMA 310 is one example of a seismic evaluation tool 

that offers guidance on building configuration.

C2.2.2 Component Properties

Meaningful structural analysis of a building’s probable 

seismic behavior and reliable design of rehabilitation 

measures requires good understanding of the existing 

components (e.g., beams, columns, diaphragms), their 

interconnection, and their material properties (strength, 

deformability, and toughness). The strength and 

deformation capacity of existing components should 

be computed, as specified in Chapters 4 through 9 and 

11, based on derived material properties and detailed 

component knowledge. Existing component action 

strengths must be determined for two basic purposes: 

to allow calculation of their ability to deliver load to 

other elements and components, and to allow 

determination of their capacity to resist forces and 

deformations.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-3

A site reconnaissance shall be performed to observe 

variances from existing building drawings, foundation 

modifications not shown on existing documentation, the 

presence of adjacent development or grading activities, 

and evidence of poor foundation performance. 

2.2.4 Adjacent Buildings

Sufficient data shall be collected on the configuration of 

adjacent structures to permit analysis of the interaction 

issues identified in Section 2.2.4.1 through 2.2.4.3. If 

the necessary information on adjacent structures is not 

available, the building owner shall be informed of the 

potential consequences of the interactions which are not 

being evaluated.

2.2.4.1 Building Pounding

Data shall be collected to permit investigation of the 

effects of building pounding in accordance with 

Section 2.6.10, whenever a portion of an adjacent 

structure is located within 4% of the height above grade 

at the location of potential impact. 

2.2.4.2 Shared Element Condition

Data shall be collected on adjacent structures that share 

common vertical or lateral load-resisting elements with 

the building to permit investigation in accordance with 

Section 2.6.9. 

2.2.4.3 Hazards from Adjacent Buildings 

Data on adjacent buildings shall be collected to permit 

consideration of the potential for damage due to hazards 

such as falling debris, aggressive chemical leakage, fire, 

or explosion that might occur as a result of an 

earthquake. If the potential for such hazards exists, the 

building owner shall be notified of the potential impact 

on the ability to meet the selected Rehabilitation 

Objective.

C2.2.3 Site Characterization and 

Geotechnical Information

Sources of applicable existing geotechnical 

information include original design information, 

foundation capacity information included on the 

drawings, and previous geotechnical reports located at, 

or in the immediate vicinity, of the site.

Adjacent building development or grading activities 

that impose loads or reduce the lateral support of the 

structure can affect building performance in a future 

earthquake. Evidence of poor foundation performance 

can include settlement of building floor slabs and 

foundations, or differential movement visible at 

adjacent exterior sidewalks or other miscellaneous site 

construction.

C2.2.4.1 Building Pounding

Building pounding can alter the basic response of the 

building to ground motion and impart additional 

inertial loads and energy to the building from the 

adjacent structure. Of particular concern is the 

potential for extreme local damage to structural 

elements at the zones of impact.

C2.2.4.2 Shared Element Condition

Buildings sharing common elements, such as party 

walls, have several potential problems. If the buildings 

attempt to move independently, one building may pull 

the shared element away from the other, resulting in a 

partial collapse. If the buildings behave as an integral 

unit, the additional mass and inertial loads of one 

structure may result in extreme demands on the lateralforce-resisting system of the other.

C2.2.4.3 Hazards from Adjacent Buildings

Hazards from adjacent buildings that may impact 

building performance or the operation of the building 

after an earthquake should be considered and discussed 

with the building owner. Consideration should be 

given to hardening those portions of the building that 

may be impacted by debris or other hazards from 

adjacent structures. Where Immediate Occupancy of 

the building is desired and ingress to the building may 

be impaired by such hazards, consideration should be 

given to providing suitably resistant access to the 

building. Sufficient information should be collected on 

adjacent structures to allow preliminary evaluation of 

the likelihood and nature of hazards such as potential 

falling debris, fire, and blast pressures. Evaluations 

similar to those in FEMA 154 may be adequate for this 

purpose.
2-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.2.5 Primary and Secondary Elements and 

Components

Data shall be collected to classify elements and 

components as primary or secondary in accordance with 

Section 2.4.4.2. Data on primary and secondary 

elements and components shall be collected in 

sufficient detail to permit modeling and analysis of such 

components in accordance with the requirements of this 

standard.

2.2.6 Data Collection Requirements

Data on the as-built condition of the structure, 

components, site, and adjacent buildings shall be 

collected in sufficient detail to perform the selected 

analysis procedure. The extent of data collected shall be 

consistent with minimum, usual, or comprehensive 

levels of knowledge as specified in Sections 2.2.6.1, 

2.2.6.2, or 2.2.6.3. The required level of knowledge 

shall be determined considering the selected 

Rehabilitation Objective and analysis procedure in 

accordance with Table 2-1.

2.2.6.1 Minimum Data Collection 

Requirements

As a minimum, collection of as-built information shall 

consist of the following:

1. Information shall be obtained from design drawings 

with sufficient information to analyze component 

demands and calculate component capacities. For 

minimum data collection, design drawings need not 

be complete, but shall communicate the 

configuration of the gravity and lateral-forceresisting system and typical connections with 

sufficient detail to carry out linear analysis 

procedures. When design drawings are available, 

information shall be verified by a visual condition 

assessment in accordance with Chapters 5 through 8. 

2. In the absence of sufficient information from design 

drawings, incomplete or non-existent information 

shall be supplemented by a comprehensive condition 

assessment including destructive and nondestructive 

investigation in accordance with Chapters 5 

through 8.

3. In the absence of material test records and quality 

assurance reports, use of default material properties 

in accordance with Chapters 5 through 8 shall be 

permitted.

Table 2-1 Data Collection Requirements

Data

Level of Knowledge

Minimum Usual Comprehensive

Rehabilitatio

n Objective

BSO or Lower BSO or Lower Enhanced Enhanced

Analysis 

Procedures

LSP, LDP All All All

Testing No Tests Usual Testing Usual Testing Comprehensive Testing

Drawings Design

Drawings

Or

Equivalent

Design

Drawings

Or

Equivalent

Design

Drawings

Or

Equivalent

Construction 

Documents

Or 

Equivalent

Condition 

Assessment

Visual ComprehensiveVisual ComprehensiveVisual ComprehensiveVisual Comprehensive

Material 

Properties

From 

Drawings 

or Default 

Values

From 

Default 

Values

From 

Drawings 

and Tests

From 

Usual 

Tests

From 

Drawings 

and Tests

From 

Usual 

Tests

From 

Documents 

and Tests

From 

Comprehensive 

Tests

Knowledge 

Factor (κ)

0.75 0.75 1.00 1.00 0.75 0.75 1.00 1.00
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-5

4. Information needed on adjacent buildings, 

referenced in Section 2.2.4, shall be gained through 

field surveys and research of available as-built 

information.

5. Information on foundation and site related concerns 

shall be collected in accordance with Section 2.2.3.

2.2.6.2 Usual Data Collection Requirements

Usual collection of as-built information shall consist of 

the following:

1. Information shall be obtained from design drawings 

with sufficient information to analyze component 

demands and calculate component capacities. For 

usual data collection, design drawings need not be 

complete, but shall communicate the configuration 

of the gravity and lateral-force-resisting system and 

typical connections with sufficient detail to carry out 

any analysis procedure. When design drawings are 

available, information shall be verified by a visual 

condition assessment in accordance with Chapters 5 

through 8. 

2. In the absence of sufficient information from design 

drawings, incomplete or non-existent information 

shall be supplemented by a comprehensive condition 

assessment including destructive and nondestructive 

investigation in accordance with Chapters 5 through 

8. 

3. In the absence of material test records and quality 

assurance reports, material properties shall be 

determined by usual materials testing in accordance 

with Chapters 5 through 8.

4. Information needed on adjacent buildings, 

referenced in Section 2.2.4, shall be gained through 

field surveys and research of available as-built 

information.

5. Information on foundation and site related concerns 

shall be collected in accordance with Section 2.2.3.

2.2.6.3 Comprehensive Data Collection 

Requirements

Comprehensive collection of as-built information shall 

consist of the following:

1. Information shall be obtained from construction 

documents including design drawings, 

specifications, material test records, and quality 

assurance reports covering original construction and 

subsequent modifications to the structure. When 

construction documents are available, information 

shall be verified by a visual condition assessment in 

accordance with Chapters 5 through 8.

2. If construction documents are incomplete, missing 

information shall be supplemented by a 

comprehensive condition assessment including 

destructive and nondestructive investigation in 

accordance with Chapters 5 through 8. 

3. In the absence of material test records and quality 

assurance reports, material properties shall be 

determined by comprehensive materials testing in 

accordance with Chapters 5 through 8. The 

coefficient of variation in material test results shall 

be less than 20%.

4. Information needed on adjacent buildings, 

referenced in Section 2.2.4, shall be gained through 

field surveys and research of available as-built 

information.

5. Information on foundation and site related concerns 

shall be collected in accordance with Section 2.2.3.
2-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.2.6.4 Knowledge Factor

2.2.6.4.1 General

To account for uncertainty in the collection of as-built 

data, a knowledge factor, κ, shall be selected from 

Table 2-1 considering the selected Rehabilitation 

Objective, analysis procedure, and data collection 

process. Knowledge factors shall be applied on a 

component basis as determined by the level of 

knowledge obtained for individual components during 

data collection. 

2.2.6.4.2 Linear Procedures

When linear procedures are used, data collection 

consistent with the minimum level of knowledge shall 

be permitted.

2.2.6.4.3 Nonlinear Procedures

When nonlinear procedures are used, data collection 

consistent with either the usual or comprehensive levels 

of knowledge shall be performed.

2.2.6.4.4 Assumed values of Knowledge Factor

Selected κ values shall be supported by data collection 

performed at any time prior to implementation of a 

rehabilitation strategy. It shall be permitted to perform 

an analysis in advance of the data collection process 

using an assumed value of κ, provided the value of κ is 

substantiated by data collection in accordance with the 

requirements of Section 2.2.6 prior to implementation 

of the rehabilitation strategies.

If the assumed value of κ is not supported by 

subsequent data collection, the analysis shall be revised 

to include a revised κ consistent with the data collected 

in accordance with the requirements of Section 2.2.6.

If an analysis using an assumed value of κ will result in 

no required rehabilitation of the structure, the value of κ

shall be substantiated by data collection in accordance 

with the requirements of Section 2.2.6 before the 

analysis is finalized.

2.3 Rehabilitation Methods

Seismic rehabilitation of the building shall be 

performed to achieve the selected Rehabilitation 

Objective in accordance with the requirements of the 

Simplified Rehabilitation Method of Section 2.3.1 or 

the Systematic Rehabilitation Method of Section 2.3.2. 

2.3.1 Simplified Rehabilitation Method

The Simplified Rehabilitation Method shall be 

permitted for buildings that conform to one of the 

Model Building Types contained in Table 10-1, and all 

limitations in that table with regard to building size and 

seismic zone. 

Use of the Simplified Rehabilitation Method shall be 

restricted to Limited Rehabilitation Objectives 

consisting of the Life Safety Building Performance 

Level (3-C) at the BSE-1 Earthquake Hazard Level, or 

Partial Rehabilitation as defined in Section 1.4.3.2.

The Simplified Rehabilitation Method shall be 

performed in accordance with the requirements of 

Chapters 2, 10, and 11. 

C2.2.6.4.1 General

The κ factor is used to express the confidence with 

which the properties of the building components are 

known, when calculating component capacities. The 

value of the factor is established from the knowledge 

obtained based on access to original construction 

documents, or condition assessments including 

destructive or nondestructive testing of representative 

components. The values of the factor have been 

established, indicating whether the level of knowledge 

is “minimum,” “usual,” or “comprehensive.”

C2.3.1 Simplified Rehabilitation Method

Simplified Rehabilitation may be applied to certain 

buildings of regular configuration that do not require 

advanced analytical procedures. The primary intent of 

Simplified Rehabilitation is to reduce seismic risk 

efficiently, where possible and appropriate, by seeking 

Limited Objectives. Partial Rehabilitation measures, 

which target high-risk building deficiencies such as 

parapets and other exterior falling hazards, are 

included as Simplified Rehabilitation techniques.

The Simplified Rehabilitation Method is less 

complicated than the complete analytical rehabilitation 

design procedures found under Systematic 

Rehabilitation. In many cases, Simplified 

Rehabilitation represents a cost-effective improvement 

in seismic performance, and often requires less 

detailed evaluation or partial analysis to qualify for a 

specific performance level.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-7

2.3.2 Systematic Rehabilitation Method

If the Simplified Rehabilitation Method is not 

applicable, the Systematic Rehabilitation Method shall 

be used as specified below:

1. An analysis procedure shall be selected in 

accordance with the requirements and limitations of 

Section 2.4.

2. A preliminary rehabilitation scheme shall be 

developed using one or more of the rehabilitation 

strategies defined in Section 2.5.

3. An analysis of the building, including rehabilitation 

measures, shall be performed, and the results of the 

analysis shall be evaluated in accordance with the 

requirements of Chapters 2 through 9 and 11 to 

verify the rehabilitation design meets the selected 

Rehabilitation Objective.

C2.3.2 Systematic Rehabilitation Method

Systematic Rehabilitation may be applied to any 

building and involves thorough checking of each 

existing structural element or component, the design of 

new ones, and verification of acceptable overall 

performance represented by expected displacements 

and internal forces. The Systematic Rehabilitation 

Method focuses on the nonlinear behavior of structural 

response, and employs procedures not previously 

emphasized in seismic codes.

The Systematic Rehabilitation Method is intended to 

be complete and contains all requirements to reach any 

specified performance level. Systematic Rehabilitation 

is an iterative process, similar to the design of new 

buildings, in which modifications of the existing 

structure are assumed for the purposes of a preliminary 

design and analysis, and the results of the analysis are 

verified as acceptable on an element and component 

basis. If either new or existing components or elements 

still prove to be inadequate, the modifications are 

adjusted and, if necessary, a new analysis and 

verification cycle is performed. A preliminary design 

is needed to define the extent and configuration of 

corrective measures in sufficient detail to estimate the 

interaction of the stiffness, strength, and post-yield 

behavior of all new, modified, or existing elements to 

be used for lateral force resistance. The designer is 

encouraged to include all elements with significant 

lateral stiffness in a mathematical model to assure 

deformation capability under realistic seismic drifts. 

However, just as in the design of new buildings, it may 

be determined that certain components or elements will 

not be considered part of the lateral-force-resisting 

system, as long as deformation compatibility checks 

are made on these components or elements to assure 

their adequacy.

A mathematical model, developed for the preliminary 

design, must be constructed in connection with one of 

the analysis procedures defined in Chapter 3. These are 

the linear procedures (Linear Static and Linear 

Dynamic) and the nonlinear procedures (Nonlinear 

Static and Nonlinear Dynamic). With the exception of 

the Nonlinear Dynamic Procedure, this standard 

defines the analysis and rehabilitation design 

procedures sufficiently that compliance can be checked 

by a building department in a manner similar to design 

reviews for new buildings. Modeling assumptions to 

be used in various situations are given in Chapters 4 

through 9, and in Chapter 11 for nonstructural 

components. Requirements for seismic demand are 

given in Chapter 1. Requirements are specified for use 

of the Nonlinear Dynamic Procedure; however, 

considerable judgment is required in its application. 

Criteria for applying ground motion for various 

analysis procedures is given, but definitive rules for 

developing ground motion input are not included in 

this standard.
2-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.4 Analysis Procedures

An analysis of the building, including rehabilitation 

measures, shall be conducted to determine the forces 

and deformations induced in components of the 

building by ground motion corresponding to the 

selected Earthquake Hazard Level, or by other seismic 

geologic site hazards specified in Section 4.2.2.

The analysis procedure shall comply with one of the 

following:

1. Linear analysis subject to limitations specified in 

Section 2.4.1, and complying with the Linear Static 

Procedure (LSP) in accordance with Section 3.3.1, 

or the Linear Dynamic Procedure (LDP) in 

accordance with Section 3.3.2. 

2. Nonlinear analysis subject to limitations specified in 

Section 2.4.2, and complying with the Nonlinear 

Static Procedure (NSP) in accordance with 

Section 3.3.3, or the Nonlinear Dynamic Procedure 

(NDP) in accordance with Section 3.3.4. 

3. Alternative rational analysis in accordance with 

Section 2.4.3.

The analysis results shall comply with the applicable 

acceptance criteria selected in accordance with 

Section 2.4.4.

This standard specifies acceptance criteria for stiffness, 

strength, and ductility characteristics of structural 

elements and components for three discrete structural 

performance levels in Chapters 4 though 8 for use in 

the Systematic Rehabilitation Method, and acceptance 

criteria for the performance of nonstructural 

components or architectural, mechanical, and electrical 

components in Chapter 11 for use in Systematic and 

Simplified Rehabilitation Methods.

Inherent in the concept of performance levels and 

ranges is the assumption that performance can be 

measured using analytical results such as story drift 

ratios or strength and ductility demands on individual 

components or elements. To enable structural 

verification at the selected performance level, stiffness, 

strength, and ductility characteristics of many common 

elements and components have been derived from 

laboratory tests and analytical studies and are 

presented in a standard format in Chapters 4 through 8 

of this standard.

This standard specifies two new technologies in 

Chapter 9: seismic isolation and energy dissipation, for 

use in seismic rehabilitation of buildings using the 

Systematic Rehabilitation Method.

It is expected that testing of existing materials and 

elements will continue and that additional corrective 

measures and products will be developed. It is also 

expected that systems and products intended to modify 

structural response beneficially will be advanced. The 

format of the analysis techniques and acceptability 

criteria of this standard allows rapid incorporation of 

such technology. Section 2.8 gives specific 

requirements in this regard. It is expected that this 

standard will have a significant impact on testing and 

documentation of existing materials and systems as 

well as on new products.

C2.4 Analysis Procedures

The linear procedures maintain the traditional use of a 

linear stress-strain relationship, but incorporate 

adjustments to overall building deformations and 

material acceptance criteria to permit better 

consideration of the probable nonlinear characteristics 

of seismic response. The Nonlinear Static Procedure, 

often called “pushover analysis,” uses simplified 

nonlinear techniques to estimate seismic structural 

deformations. The Nonlinear Dynamic Procedure, 

commonly known as nonlinear time history analysis, 

requires considerable judgment and experience to 

perform, and may be used only within the limitations 

described in Section 2.4.2.2 of this standard.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-9

2.4.1 Linear Procedures

Linear procedures shall be permitted for buildings 

which do not have an irregularity defined in 

Section 2.4.1.1. For buildings that have one or more of 

the irregularities defined in Section 2.4.1.1, linear 

procedures shall not be used unless the earthquake 

demands on the building comply with the demand 

capacity ratio (DCR) requirements in Section 2.4.1.1. 

For buildings incorporating base isolation systems or 

supplemental energy dissipation systems, the additional 

limitations of Section 9.2.4 or Section 9.3.4 shall apply.

2.4.1.1 Method to Determine Limitations on 

Use of Linear Procedures

The methodology presented in this section shall be used 

to determine the applicability of linear analysis 

procedures based on four conditions of irregularity 

defined in Section 2.4.1.1.1 through Section 2.4.1.1.4. 

The determination of irregularity shall be based on the 

configuration of the rehabilitated structure. A linear 

analysis to determine irregularity shall be performed by 

either an LSP in accordance with Section 3.3.1 or an 

LDP in accordance with Section 3.3.2. The results of 

this analysis shall be used to identify the magnitude and 

uniformity of distribution of inelastic demands on the 

primary elements and components of the lateral-forceresisting system.

The magnitude and distribution of inelastic demands for 

existing and added primary elements and components 

shall be defined by demand-capacity ratios (DCRs) and 

computed in accordance with Equation (2-1):

(2-1)

where:

DCRs shall be calculated for each action (such as axial 

force, moment, shear) of each primary component. The 

critical action for the component shall be the one with 

the largest DCR. The DCR for this action shall be 

termed the critical component DCR. The largest DCR 

for any element at a particular story is termed the 

critical element DCR at that story. If an element at a 

particular story is composed of multiple components, 

then the component with the largest computed DCR 

shall define the critical component for the element at 

that story.

The applicability of linear procedures shall be 

determined as follows:

1. If all component DCRs < 2.0, then linear procedures 

are applicable.

2. If one or more component DCRs exceed 2.0, and no 

irregularities described in Sections 2.4.1.1.1 through 

2.4.1.1.4 are present, then linear procedures are 

applicable.

3. If one or more component DCRs exceed 2.0 and any 

irregularity described in Section 2.4.1.1.1 through 

Section 2.4.1.1.4 is present, then linear procedures 

are not applicable, and shall not be used.

C2.4.1 Linear Procedures

The results of the linear procedures can be very 

inaccurate when applied to buildings with highly 

irregular structural systems, unless the building is 

capable of responding to the design earthquake(s) in a 

nearly elastic manner. The procedures of 

Section 2.4.1.1 are intended to evaluate whether the 

building is capable of nearly elastic response.

QUD = Force due to the gravity and earthquake 

loads calculated in accordance with 

Section 3.4.2.

QCE = Expected strength of the component or 

element, calculated as specified in 

Chapters 5 through 8.

DCR

QUD

QCE

= -----------
2-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.4.1.1.1 In-Plane Discontinuity Irregularity

An in-plane discontinuity irregularity shall be 

considered to exist in any primary element of the 

lateral-force-resisting system whenever a lateral-forceresisting element is present in one story, but does not 

continue, or is offset within the plane of the element, in 

the story immediately below. Figure 2-1 depicts such a 

condition.

2.4.1.1.2 Out-of-Plane Discontinuity Irregularity

An out-of-plane discontinuity irregularity shall be 

considered to exist in any primary element of the 

lateral-force-resisting system when an element in one 

story is offset out-of-plane relative to that element in an 

adjacent story, as depicted in Figure 2-2. 

2.4.1.1.3 Severe Weak Story Irregularity

A severe weak story irregularity shall be considered to 

exist in any direction of the building if the ratio of the 

average shear DCR of any story to that of an adjacent 

story in the same direction exceeds 125%. The average 

DCR of a story shall be calculated by Equation (2-2):

(2-2)

C2.4.1.1 Method to Determine Limitations on 

Use of Linear Procedures

The magnitude and distribution of inelastic demands 

are indicated by demand-capacity ratios (DCRs). Note 

that these DCRs are not used to determine the 

acceptability of component behavior. The adequacy of 

structural components and elements must be evaluated 

using the procedures contained in Chapter 3 along with 

the acceptance criteria provided in Chapters 4 through 

8. DCRs are used only to determine a structure’s 

regularity. It should be noted that for complex 

structures, such as buildings with perforated shear 

walls, it may be easier to use one of the nonlinear 

procedures than to ensure that the building has 

sufficient regularity to permit use of linear procedures.

If all of the computed controlling DCRs for a 

component are less than or equal to 1.0, then the 

component is expected to respond elastically to the 

earthquake ground shaking being evaluated. If one or 

more of the computed DCRs for a component are 

greater than 1.0, then the component is expected to 

respond inelastically to the earthquake ground shaking.

Figure 2-1 In-Plane Discontinuity in Lateral System

Figure 2-2 Typical Building with Out-of-Plane Offset 

Irregularity

DCR

DCRi

Vi

1

n

∑

Vi

1

n

∑

= --------------------------
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-11

where:

For buildings with flexible diaphragms, each line of 

framing shall be independently evaluated.

2.4.1.1.4 Severe Torsional Strength Irregularity

A severe torsional strength irregularity shall be 

considered to exist in any story if the diaphragm above 

the story under consideration is not flexible and, for a 

given direction, the ratio of the critical element DCRs 

for primary elements on one side of the center of 

resistance of a story, to those on the other side of the 

center of resistance of the story, exceeds 1.5.

2.4.1.2 Limitations on Use of the Linear Static 

Procedure

The Linear Static Procedure shall not be used for a 

building with one or more of the following 

characteristics:

1. The fundamental period of the building, T, is greater 

than or equal to 3.5 times Ts.

2. The ratio of the horizontal dimension at any story to 

the corresponding dimension at an adjacent story 

exceeds 1.4 (excluding penthouses).

3. The building has a severe torsional stiffness 

irregularity in any story. A severe torsional stiffness 

irregularity exists in a story if the diaphragm above 

the story under consideration is not flexible and the 

results of the analysis indicate that the drift along 

any side of the structure is more than 150% of the 

average story drift.

4. The building has a severe vertical mass or stiffness 

irregularity. A severe vertical mass or stiffness 

irregularity exists when the average drift in any story 

(except penthouses) exceeds that of the story above 

or below by more than 150%.

5. The building has a nonorthogonal lateral-forceresisting system.

For buildings in which linear procedures are applicable, 

but the Linear Static Procedure is not permitted, use of 

the Linear Dynamic Procedure shall be permitted. 

2.4.2 Nonlinear Procedures

Nonlinear procedures shall be permitted for any of the 

rehabilitation strategies contained in Section 2.5. 

Nonlinear procedures shall be used for analysis of 

buildings when linear procedures are not permitted. 

Data collection for use with nonlinear procedures shall 

be in accordance with Section 2.2.6.

2.4.2.1 Nonlinear Static Procedure

The NSP shall be permitted for structures in which 

higher mode effects are not significant, as defined in 

this section. To determine if higher modes are 

significant, a modal response spectrum analysis shall be 

performed for the structure using sufficient modes to 

capture 90% mass participation. A second response 

spectrum analysis shall also be performed, considering 

only the first mode participation. Higher mode effects 

shall be considered significant if the shear in any story 

resulting from the modal analysis considering modes 

required to obtain 90% mass participation exceeds 

130% of the corresponding story shear considering only 

the first mode response.

DCR = Average DCR for the story

DCRi = Critical action DCR for element i of the 

story

Vi = Total calculated lateral shear force in an 

element i due to earthquake response, 

assuming that the structure remains 

elastic

n = Total number of elements in the story

C2.4.1.2 Limitations on Use of the Linear 

Static Procedure

For buildings that have irregular distributions of mass 

or stiffness, irregular geometries, or nonorthogonal 

lateral-force-resisting systems, the distribution of 

demands predicted by an LDP analysis will be more 

accurate than those predicted by the LSP. Either the 

response spectrum method or time history method may 

be used for evaluation of such structures.
2-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

If higher mode effects are significant, the NSP shall be 

permitted if an LDP analysis is also performed to 

supplement the NSP. Buildings with significant higher 

mode effects must meet the acceptance criteria of this 

standard for both analysis procedures, except that an 

increase by a factor of 1.33 shall be permitted in the 

LDP acceptance criteria for deformation-controlled 

actions (m-factors) provided in Chapters 5 through 9. A 

building analyzed using the NSP, with or without a 

supplementary LDP evaluation, shall meet the 

acceptance criteria for nonlinear procedures specified in 

Section 3.4.3. 

2.4.2.2 Nonlinear Dynamic Procedure

The NDP shall be permitted for all structures. An 

analysis performed using the NDP shall be reviewed 

and approved by an independent third-party engineer 

with experience in seismic design and nonlinear 

procedures. 

2.4.3 Alternative Rational Analysis

Nothing in this standard shall be interpreted as 

preventing the use of any approved alternative analysis 

procedure that is rational and based on fundamental 

principles of engineering mechanics and dynamics. 

Such alternative analyses shall not adopt the acceptance 

criteria contained in this standard without first 

determining their applicability. All projects using 

alternative rational analysis procedures shall be 

reviewed and approved by an independent third-party 

engineer with experience in seismic design.

2.4.4 Acceptance Criteria

2.4.4.1 General

The acceptability of force and deformation actions shall 

be evaluated for each component in accordance with the 

requirements of Section 3.4. Prior to selecting 

component acceptance criteria for use in Section 3.4, 

each component shall be classified as primary or 

secondary in accordance with Section 2.4.4.2, and each 

action shall be classified as deformation-controlled 

(ductile) or force-controlled (nonductile) in accordance 

with Section 2.4.4.3. Component strengths, material 

properties, and component capacities shall be 

determined in accordance with Sections 2.4.4.4, 2.4.4.5, 

and 2.4.4.6, respectively. Component acceptance 

criteria not presented in this standard shall be 

determined by qualification testing in accordance with 

Section 2.8.

The rehabilitated building shall be provided with at 

least one continuous load path to transfer seismic 

forces, induced by ground motion in any direction, from 

the point of application to the final point of resistance. 

All primary and secondary components shall be capable 

of resisting force and deformation actions within the 

applicable acceptance criteria of the selected 

performance level. 

2.4.4.2 Primary and Secondary Elements and 

Components

Elements and components that affect the lateral 

stiffness or distribution of forces in a structure, or are 

loaded as a result of lateral deformation of the structure, 

shall be classified as primary or secondary, even if they 

are not part of the intended lateral-force-resisting 

system.

2.4.4.2.1 Primary Elements and Components

Elements and components that provide the capacity of 

the structure to resist collapse under seismic forces 

induced by ground motion in any direction shall be 

classified as primary.

C2.4.2.1 Nonlinear Static Procedure

The NSP is generally a more reliable approach to 

characterizing the performance of a structure than are 

linear procedures. However, it is not exact, and cannot 

accurately account for changes in dynamic response as 

the structure degrades in stiffness or account for higher 

mode effects. When the NSP is utilized on a structure 

that has significant higher mode response, the LDP is 

also employed to verify the adequacy of the design. 

When this approach is taken, less restrictive criteria are 

permitted for the LDP, recognizing the significantly 

improved knowledge that is obtained by performing 

both analysis procedures.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-13

2.4.4.2.2 Secondary Elements and Components

Other elements and components shall be classified as 

secondary. 

2.4.4.3 Deformation- and Force-Controlled 

Actions

All actions shall be classified as either deformationcontrolled or force-controlled using the component 

force versus deformation curves shown in Figure 2-3.

Figure 2-3 Component Force Versus Deformation Curves

C2.4.4.2 Primary and Secondary Elements 

and Components

In a typical building, nearly all elements, including 

many nonstructural components, will contribute to the 

building’s overall stiffness, mass, and damping, and 

consequently its response to earthquake ground 

motion. However, not all of these elements are critical 

to the ability of the structure to resist collapse when 

subjected to strong ground shaking.

The secondary designation typically will be used when 

a component or element does not contribute 

significantly or reliably in resisting earthquake effects 

because of low lateral stiffness, strength, or 

deformation capacity.

For example, exterior cladding and interior partitions 

can add substantial initial stiffness to a structure, yet 

this stiffness is not typically considered in the design of 

new buildings because the lateral strength of these 

elements is often small. Similarly, the interaction of 

floor framing systems and columns in shear wall 

buildings can add some stiffness, although designers 

typically neglect such stiffness when proportioning the 

building’s shear walls.

The concept of primary and secondary elements 

permits the engineer to differentiate between the 

performance required of elements that are critical to 

the building’s ability to resist collapse and of those that 

are not. For a given performance level, acceptance 

criteria for primary elements and components will 

typically be more restrictive than those for secondary 

elements and components.

Use of the secondary classification will allow certain 

components to experience greater damage and larger 

displacements than would otherwise be permitted for 

primary elements, as explained below.

1. Although damage to the primary elements and 

some degradation of their stiffness may be 

permitted to occur, the overall function of these 

elements in resisting structural collapse should not 

be compromised.

2. For some structural performance levels, substantial 

degradation of the lateral-force-resisting stiffness 

and strength of secondary elements and 

components is permissible. However, the ability of 

these secondary elements and components to 

support gravity loads under the maximum induced 

deformations must be preserved.
2-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.4.4.3.1 Deformation-Controlled and ForceControlled Behavior

The Type 1 curve depicted in Figure 2-3 is 

representative of ductile behavior where there is an 

elastic range (point 0 to point 1 on the curve) followed 

by a plastic range (points 1 to 3) with non-negligible 

residual strength and ability to support gravity loads at 

point 3. The plastic range includes a strain hardening or 

softening range (points 1 to 2) and a strength-degraded 

range (points 2 to 3). Primary component actions 

exhibiting this behavior shall be classified as 

deformation-controlled if the strain-hardening or strainsoftening range is such that e > 2g; otherwise, they shall 

be classified as force-controlled. Secondary component 

actions exhibiting Type 1 behavior shall be classified as 

deformation-controlled for any e/g ratio.

The Type 2 curve depicted in Figure 2-3 is 

representative of ductile behavior where there is an 

elastic range (point 0 to point 1 on the curve) and a 

plastic range (points 1 to 2) followed by loss of strength 

and loss of ability to support gravity loads beyond 

point 2. Primary and secondary component actions 

exhibiting this type of behavior shall be classified as 

deformation-controlled if the plastic range is such that e

> 2g; otherwise, they shall be classified as forcecontrolled.

The Type 3 curve depicted in Figure 2-3 is 

representative of a brittle or nonductile behavior where 

there is an elastic range (point 0 to point 1 on the curve) 

followed by loss of strength and loss of ability to 

support gravity loads beyond point 1. Primary and 

secondary component actions displaying Type 3 

behavior shall be classified as force-controlled 

C2.4.4.3.1 Deformation-Controlled and ForceControlled Behavior

Acceptance criteria for primary components that 

exhibit Type 1 behavior are typically within the elastic 

or plastic ranges between points 0 and 2, depending on 

the performance level. Acceptance criteria for 

secondary elements that exhibit Type 1 behavior can be 

within any of the performance ranges.

Acceptance criteria for primary and secondary 

components exhibiting Type 2 behavior will be within 

the elastic or plastic ranges, depending on the 

performance level.

Acceptance criteria for primary and secondary 

components exhibiting Type 3 behavior will always be 

within the elastic range.

Table C2-1 provides some examples of possible 

deformation- and force-controlled actions in common 

framing systems. Classification of force- or 

deformation-controlled actions are specified for 

foundation and framing components in Chapters 4 

through 8.

A given component may have a combination of both 

force- and deformation-controlled actions.

Classification as a deformation-controlled action is not 

up to the discretion of the user. Deformation-controlled 

actions have been defined in this standard by the 

designation of m-factors or nonlinear deformation 

capacities in Chapters 4 through 8. In the absence of 

component testing justifying Type 1 or Type 2 

behavior, all other actions are to be taken as forcecontrolled.

Table C2-1 Examples of Possible 

Deformation-Controlled and 

Force-Controlled Actions

Component

DeformationControlled 

Action

ForceControlled 

Action

Moment Frames

• Beams

• Columns

• Joints

Moment (M)

M

--

Shear (V)

Axial load (P), V

V1

Shear Walls M, V P

Braced Frames

• Braces

• Beams

• Columns

• Shear Link

P

--

--

V

--

P

P

P, M

Connections P, V, M3 P, V, M

Diaphragms M, V2 P, V, M

1. Shear may be a deformation-controlled action in steel moment frame 

construction.

2. If the diaphragm carries lateral loads from vertical seismic resisting 

elements above the diaphragm level, then M and V shall be 

considered force-controlled actions.

3. Axial, shear, and moment may be deformation-controlled actions for 

certain steel and wood connections.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-15

Figure C2-1 shows the generalized force versus 

deformation curves used throughout this standard to 

specify component modeling and acceptance criteria 

for deformation-controlled actions in any of the four 

basic material types. Linear response is depicted 

between point A (unloaded component) and an 

effective yield point B. The slope from B to C is 

typically a small percentage (0-10%) of the elastic 

slope, and is included to represent phenomena such as 

strain hardening. C has an ordinate that represents the 

strength of the component, and an abscissa value equal 

to the deformation at which significant strength 

degradation begins (line CD). Beyond point D, the 

component responds with substantially reduced 

strength to point E. At deformations greater than point 

E, the component strength is essentially zero.

The sharp transition as shown on idealized curves in 

Figure C2-1 between points C and D can result in 

computational difficulty and an inability to converge 

when used as modeling input in nonlinear 

computerized analysis software. In order to avoid this 

computational instability, a small slope may be 

provided to the segment of these curves between points 

C and D.

For some components it is convenient to prescribe 

acceptance criteria in terms of deformation (e.g., θ or

∆), while for others it is more convenient to give 

criteria in terms of deformation ratios. To 

accommodate this, two types of idealized force vs. 

deformation curves are used in Figures C2-1 (a) and 

(b). Figure C2-1(a) shows normalized force (Q/QCE) 

versus deformation (θ or ∆) and the parameters a, b, 

and c. Figure C2-1(b) shows normalized force (Q/

QCE) versus deformation ratio (θ/θy, ∆/∆y, or ∆/h) and 

the parameters d, e, and c. Elastic stiffnesses and 

values for the parameters a, b, c, d, and e that can be 

used for modeling components are given in Chapters 5 

through 8. Acceptance criteria for deformation or 

deformation ratios for primary members (P) and 

secondary members (S) corresponding to the target 

Building Performance Levels of Collapse Prevention 

(CP), Life Safety (LS), and Immediate Occupancy (IO) 

as shown in Figure 2-1(c) are given in Chapters 5 

through 8.

Figure C2-1 Generalized Component ForceDeformation Relations for Depicting 

Modeling and Acceptance Criteria
2-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.4.4.4 Expected and Lower-Bound Strength

In Figure 2-3, Qy represents the yield strength of the 

component. When evaluating the behavior of 

deformation-controlled actions, the expected strength, 

QCE, shall be used. QCE is defined as the statistical 

mean value of yield strengths, Qy, for a population of 

similar components, and includes consideration of 

strain hardening and plastic section development. When 

evaluating the behavior of force-controlled actions, a 

lower bound estimate of the component strength, QCL, 

shall be used. QCL is defined as the statistical mean 

minus one standard deviation of the yield strengths, Qy, 

for a population of similar components. 

2.4.4.5 Material Properties

Expected material properties shall be based on mean 

values of tested material properties. Lower bound 

material properties shall be based on mean values of 

tested material properties minus one standard deviation 

(σ).

Nominal material properties, or properties specified in 

construction documents, shall be taken as lower bound 

material properties unless otherwise specified in 

Chapters 5 through 8. Corresponding expected material 

properties shall be calculated by multiplying lowerbound values by appropriate factors specified in 

Chapters 5 through 8 to translate from lower bound to 

expected values.

2.4.4.6 Component Capacities

2.4.4.6.1 General

Detailed criteria for calculation of individual 

component force and deformation capacities shall 

comply with the requirements in individual materials 

chapters as follows: 

1. Foundations—Chapter 4.

2. Elements and components composed of steel or cast 

iron—Chapter 5.

3. Elements and components composed of reinforced 

concrete—Chapter 6.

4. Elements and components composed of reinforced 

or unreinforced masonry—Chapter 7.

5. Elements and components composed of timber, light 

metal studs, gypsum, or plaster products—

Chapter 8.

6. Seismic isolation systems and energy dissipation 

systems—Chapter 9.

7. Nonstructural (architectural, mechanical, and 

electrical) components—Chapter 11.

8. Elements and components comprising combinations 

of materials are covered in the Chapters associated 

with each material.

2.4.4.6.2 Nonlinear Procedures

If nonlinear procedures are used, component capacities 

for deformation-controlled actions shall be taken as 

permissible inelastic deformation limits, and 

component capacities for force-controlled actions shall 

be taken as lower-bound strengths, QCL, as summarized 

in Table 2-2.

2.4.4.6.3 Linear Procedures

If linear procedures are used, capacities for 

deformation-controlled actions shall be defined as the 

product of m-factors and expected strengths, QCE. 

Capacities for force-controlled actions shall be defined 

as lower-bound strengths, QCL, as summarized in 

Table 2-3. 

C2.4.4.4 Expected and Lower-Bound Strength

In Figure 2-3, the yield strength of the component, Qy,

will vary because of inherent variability in the material 

strength comprising the individual elements as well as 

differences in workmanship and physical condition. 

See Chapters 5 through 8 for specific direction 

regarding the calculation of expected and lower-bound 

strengths of components.

C2.4.4.5 Material Properties

When calculations are used to determine expected or 

lower-bound strengths of components, expected or 

lower-bound materials properties, respectively, shall be 

used.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-17

2.5 Rehabilitation Strategies

A Rehabilitation Objective shall be achieved by 

implementing rehabilitation measures based on a 

strategy of addressing deficiencies identified by a prior 

seismic evaluation. Each rehabilitation measure shall be 

evaluated in conjunction with other rehabilitation 

measures, and the existing structure as a whole, to 

assure that the complete rehabilitation scheme achieves 

the target Building Performance Level for the selected 

Earthquake Hazard Level. The effects of rehabilitation 

on stiffness, strength, and deformability shall be taken 

into account in an analytical model of the rehabilitated 

structure. The compatibility of new and existing 

components and elements shall be checked at 

displacements consistent with the demands produced by 

the selected Earthquake Hazard Level and geologic site 

hazards present at the site.

2.5.1 Local Modification of Components

Local modification of deficient components shall be 

permitted as an applicable rehabilitation strategy.

Table 2-2 Calculation of Component Action 

Capacity—Nonlinear Procedures

Parameter

DeformationControlled Force-Controlled

Deformation 

Capacity—

Existing 

Component

κ · deformation 

limit

N/A

Deformation 

Capacity—

New Component

deformation limit N/A

Strength 

Capacity—

Existing 

Component

N/A κ · QCL

Strength 

Capacity—

New Component

N/A QCL

Note: Capacity reduction (φ) factors shall be taken as unity in the evaluation 

of capacities.

Table 2-3 Calculation of Component Action 

Capacity—Linear Procedures

Parameter

DeformationControlled Force-Controlled

Existing Material 

Strength

Expected mean 

value with 

allowance for 

strain hardening

Lower-bound 

value 

(approximately 

mean value -1σ

level)

Existing Action 

Capacity

κ · QCE κ · QCL

New Material 

Strength

Expected material 

strength

Specified material 

strength

New Action 

Capacity

QCE QCL

Note: Capacity reduction (φ) factors shall be taken as unity in the evaluation 

of capacities.

C2.5 Rehabilitation Strategies

Although not specifically required by any of the 

strategies, it is very beneficial for the rehabilitated 

lateral-force-resisting system to have an appropriate 

level of redundancy, so that any localized failure of a 

few elements of the system will not result in local 

collapse or an instability. This should be considered 

when developing rehabilitation designs.

C2.5.1 Local Modification of Components

Some existing buildings have substantial strength and 

stiffness, but some of their components may not have 

adequate strength, toughness, or deformation capacity 

to satisfy the Rehabilitation Objectives. An appropriate 

strategy for such structures may be to perform local 

modifications of components that are inadequate while 

retaining the basic configuration of the building’s 

lateral-force-resisting system. Local modifications that 

can be considered include improvement of component 

connectivity, component strength, and/or component 

deformation capacity. This strategy tends to be the 

most economical rehabilitation approach when only a 

few of the building’s components are inadequate.
2-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.5.2 Removal or Lessening of Existing 

Irregularities

Removal or lessening of existing irregularities shall be 

permitted as an applicable rehabilitation strategy.

2.5.3 Global Structural Stiffening

Global stiffening of the structure shall be permitted as 

an applicable rehabilitation strategy. 

Local strengthening allows one or more under-strength 

elements or connections to resist the strength demands 

predicted by the analysis without affecting the overall 

response of the structure. This could include measures 

such as cover plating steel beams or columns, or 

adding plywood sheathing to an existing timber 

diaphragm. Such measures increase the strength of the 

element or component and allow it to resist more 

earthquake-induced force before the onset of damage.

Local corrective measures that improve the 

deformation capacity or ductility of a component allow 

it to resist large deformation levels with reduced 

amounts of damage, without necessarily increasing the 

strength. One such measure is placement of a 

confinement jacket around a reinforced concrete 

column to improve its ability to deform without 

spalling or degrading reinforcement splices. Another 

measure is reduction of the cross-section of selected 

structural components to increase their flexibility and 

response displacement capacity.

C2.5.2 Removal or Lessening of Existing 

Irregularities

Removal or lessening of existing irregularities may be 

an effective rehabilitation strategy if a seismic 

evaluation shows that the irregularities result in the 

inability of the building to meet the selected Structural 

Performance Level.

The results of analysis should be reviewed to detect 

existing irregularities. Stiffness, mass, and strength 

irregularities may be detected either by reviewing the 

results of a linear analysis, examining the distribution 

of structural displacements and DCRs, or reviewing 

the results of a nonlinear analysis by examining the 

distribution of structural displacements and inelastic 

deformation demands. If the distribution of values of 

structural displacements, DCRs, or inelastic 

deformation demands predicted by the analysis is 

nonuniform with disproportionately high values within 

one story relative to the adjacent story, or at one side of 

a building relative to the other, then an irregularity 

exists.

Such irregularities are often, but not always, caused by 

the presence of a discontinuity in the structure, as for 

example, termination of a perimeter shear wall above 

the first story. Simple removal of the irregularity may 

be sufficient to reduce demands predicted by the 

analysis to acceptable levels. However, removal of 

discontinuities may be inappropriate in the case of 

historic buildings, and the effect of such alterations on 

important historic features should be considered 

carefully.

Effective corrective measures for removal or reduction 

of irregularities, such as soft or weak stories, include 

the addition of braced frames or shear walls within the 

soft or weak story. Torsional irregularities can be 

corrected by the addition of moment frames, braced 

frames, or shear walls to balance the distribution of 

stiffness and mass within a story. Discontinuous 

components such as columns or walls can be extended 

through the zone of discontinuity.

Partial demolition can also be an effective corrective 

measure for irregularities, although this obviously has 

significant impact on the appearance and utility of the 

building, and this may not be an appropriate alternative 

for historic structures. Portions of the structure that 

create the irregularity, such as setback towers or side 

wings, can be removed. Expansion joints can be 

created to transform a single irregular building into 

multiple regular structures; however, care must be 

taken to avoid the potential problems associated with 

pounding.

C2.5.3 Global Structural Stiffening

Global stiffening of the structure may be an effective 

rehabilitation strategy if the results of a seismic 

evaluation show deficiencies attributable to excessive 

lateral deflection of the building, and critical 

components do not have adequate ductility to resist the 

resulting deformations.

Construction of new braced frames or shear walls 

within an existing structure are effective measures for 

adding stiffness.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-19

2.5.4 Global Structural Strengthening

Global strengthening of the structure shall be permitted 

as an applicable rehabilitation strategy. 

2.5.5 Mass Reduction

Reduction of mass in the building shall be permitted as 

an applicable rehabilitation strategy. 

2.5.6 Seismic Isolation

Seismic isolation of the building shall be permitted as 

an applicable rehabilitation strategy in accordance with 

Chapter 9. 

C2.5.4 Global Structural Strengthening

Global strengthening of the structure may be an 

effective rehabilitation strategy if the results of a 

seismic evaluation show unacceptable performance 

attributable to a global deficiency in structural 

strength. This can be identified when the onset of 

global inelastic behavior occurs at levels of ground 

shaking that are substantially less than the selected 

level of ground shaking or large DCRs (or inelastic 

deformation demands) are present throughout the 

structure. By providing supplemental strength to such a 

lateral-force-resisting system, it is possible to raise the 

threshold of ground motion at which the onset of 

damage occurs. Shear walls and braced frames are 

effective elements for this purpose, but they may be 

significantly stiffer than the structure to which they are 

added, which requires their design to provide nearly all 

of the structure’s lateral resistance. Moment-resisting 

frames, being more flexible, may be more compatible 

with existing elements in some structures; however, 

such flexible elements may not become effective in the 

building’s response until existing brittle elements have 

already been damaged.

C2.5.5 Mass Reduction

Mass reduction may be an effective rehabilitation 

strategy if the results of a seismic evaluation show 

deficiencies attributable to excessive building mass, 

global structural flexibility, or global structural 

weakness. Mass and stiffness control the amount of 

force and deformation induced in a structure by ground 

motion. Reductions in mass can result in direct 

reductions in both the amount of force and deformation 

demand produced by earthquakes and, therefore, can 

be used in lieu of structural strengthening and 

stiffening. Mass can be reduced through demolition of 

upper stories, replacement of heavy cladding and 

interior partitions, or removal of heavy storage and 

equipment loads.

C2.5.6 Seismic Isolation

Seismic isolation may be an effective rehabilitation 

strategy if the results of a seismic evaluation show 

deficiencies attributable to excessive seismic forces or 

deformation demands, or if it is desired to protect 

important contents and nonstructural components from 

damage. When a structure is seismically isolated, 

compliant bearings are inserted between the 

superstructure and its foundations. This produces a 

system (structure and isolation bearings) with a nearly 

rigid body translation of the structure above the 

bearings. Most of the deformation induced in the 

isolated system by the ground motion occurs within the 

compliant bearings, which are specifically designed to 

resist these concentrated displacements. Most bearings 

also have excellent energy dissipation characteristics 

(damping). Together, this results in greatly reduced 

demands on the existing elements of the structure, 

including contents and nonstructural components. For 

this reason, seismic isolation is often an appropriate 

strategy to achieve Enhanced Rehabilitation Objectives 

that include the protection of historic fabric, valuable 

contents, and equipment, or for buildings that contain 

important operations and functions. This technique is 

most effective for relatively stiff buildings with low 

profiles and large mass. It is less effective for light, 

flexible structures.
2-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.5.7 Supplemental Energy Dissipation

Installation of supplemental energy dissipation devices 

shall be permitted as an applicable rehabilitation 

strategy in accordance with Chapter 9. 

2.6 General Design Requirements

The requirements of this section shall apply to all 

buildings for which the systematic rehabilitation 

method is selected for any target Building Performance 

Level and any selected seismic hazard unless specified 

otherwise.

2.6.1 Multidirectional Seismic Effects

Elements and components shall be designed to resist 

seismic forces acting in any horizontal direction. 

Seismic forces in the vertical direction shall be 

considered when required by Section 2.6.11. 

Multidirectional seismic effects shall be considered in 

the analysis as specified in Section 3.2.7.

2.6.2 P-∆ Effects

Elements and components of buildings shall be 

designed for P-∆ effects, defined as the combined 

effects of gravity loads acting in conjunction with 

lateral drifts due to seismic forces, as specified in 

Section 3.2.5.

2.6.3 Horizontal Torsion

Elements and components of buildings shall be 

designed to resist the effects of horizontal torsion as 

specified in Section 3.2.2.2.

2.6.4 Overturning

Elements and components of buildings shall be 

designed to resist the effects of overturning at each 

intermediate level as well as the base of the structure. 

Stability against overturning shall be evaluated as 

specified in Section 3.2.10. Effects of overturning on 

foundations shall be evaluated as specified in 

Section 4.4.

2.6.5 Continuity

All elements and components shall be tied together to 

form a complete load path for the transfer of inertial 

forces generated by the dynamic response of portions of 

the structure to the rest of the structure. Inertial forces 

specified in this section shall be considered forcecontrolled.

1. Smaller portions of a structure, such as an 

outstanding wing, shall be connected to the structure 

as a whole. Component connections shall be capable 

of resisting horizontal force in any direction 

calculated using Equation (2-3). These connections 

are not required if the individual portions of the 

structure are self-supporting and are separated by a 

seismic joint permitting independent movement 

during dynamic response.

(2-3)

C2.5.7 Supplemental Energy Dissipation

)Installation of supplemental energy dissipation 

devices may be an effective rehabilitation strategy if 

the results of a seismic evaluation show deficiencies 

attributable to excessive deformations due to global 

structural flexibility in a building. Many available 

technologies allow the energy imparted to a structure 

by ground motion to be dissipated in a controlled 

manner through the action of special devices—fluid 

viscous dampers (hydraulic cylinders), yielding plates, 

or friction pads—resulting in an overall reduction in 

the displacements of the structure. The most 

commonly used devices dissipate energy through 

frictional, hysteretic, or viscoelastic processes. In order 

to dissipate substantial energy, dissipation devices 

must typically undergo significant deformation (or 

stroke), which requires that the structural experience 

substantial lateral displacements. Therefore, these 

systems are most effective in structures that are 

relatively flexible and have some inelastic deformation 

capacity. Energy dissipaters are most commonly 

installed in structures as components of braced frames. 

Depending on the characteristics of the device, either 

static or dynamic stiffness is added to the structure as 

well as energy dissipation capacity (damping). In some 

cases, although the structural displacements are 

reduced, the forces delivered to the structure can 

actually be increased.

Fp 0.133S = XS W
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-21

where:

2. Components shall be connected to the structure to 

resist a horizontal force in any direction calculated 

using Equation (2-4) unless specified otherwise in 

Sections 2.6.6 and 2.6.7.

(2-4)

where:

exceptions:

1. For discrete connections resisting 

concentrated forces, Fp shall not be less 

than 1120 pounds.

2. For continuous connections, Fp shall not 

be less than 280 pounds per lineal foot.

3. Where a sliding support is provided at the end(s) of a 

component, the bearing length shall be sufficient to 

accommodate the expected differential displacement 

between the component and the support.

2.6.6 Diaphragms

 Diaphragms shall be defined as horizontal elements 

that transfer earthquake-induced inertial forces to 

vertical elements of the lateral-force-resisting systems 

through the collective action of diaphragm components 

including chords, collectors, and ties.

Diaphragms shall be provided at each level of the 

structure as necessary to connect building masses to the 

primary vertical elements of the lateral-force-resisting 

system. The analytical model of the building shall 

account for the behavior of the diaphragms as specified 

in Section 3.2.4.

Diaphragms and their connections to vertical elements 

providing lateral support shall comply with the design 

requirements specified in Section 5.9 for metal 

diaphragms, Section 6.11 for concrete diaphragms, 

Section 6.12 for precast concrete diaphragms, and 

Section 8.6 for wood diaphragms.

2.6.6.1 Diaphragm Chords

Except for diaphragms evaluated as “unchorded” as 

specified in Chapter 8, a component shall be provided 

to develop horizontal shear stresses at each diaphragm 

edge (either interior or exterior). This component shall 

consist of either a continuous diaphragm chord, a 

continuous wall or frame element, or a continuous 

combination of wall, frame, and chord elements. The 

forces accumulated in these components and elements 

due to their action as diaphragm boundaries shall be 

considered. At re-entrant corners in diaphragms, and at 

the corners of openings in diaphragms, diaphragm 

chords shall be extended a distance sufficient to develop 

the accumulated diaphragm boundary stresses into the 

diaphragm beyond the corner.

2.6.6.2 Diaphragm Collectors

At each vertical element a diaphragm collector shall be 

provided to transfer to the element accumulated 

diaphragm forces that are in excess of the forces 

transferred directly to the element in shear. The 

diaphragm collector shall be extended beyond the 

element and attached to the diaphragm to transfer the 

accumulated forces.

2.6.6.3 Diaphragm Ties

Diaphragms shall be provided with continuous tension 

ties between chords or boundaries. Ties shall be spaced 

at a distance not exceeding three times the length of the 

tie. At a minimum, ties shall be designed for an axial 

tensile force calculated using Equation (2-5) as a forcecontrolled action.

(2-5)

Fp = Horizontal force in any direction for the 

design of connections between two portions 

of a structure

SXS = Spectral response acceleration parameter at 

short periods for the selected Earthquake 

Hazard Level and damping, adjusted for site 

class

W = Weight of the smaller portion of the structure

Fp = Horizontal force in any direction for the 

design of component connections to the 

structure

SXS = Spectral response acceleration parameter for 

short periods for the selected Earthquake 

Hazard Level and damping adjusted for site 

class

W = Weight of the component

Fp 0.08S = XS W

Fp 0.4S = XS W
2-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

where:

Where diaphragms of timber, gypsum, or metal deck 

construction provide lateral support for walls of 

masonry or concrete construction, ties shall be designed 

for the wall anchorage forces specified in Section 2.6.7 

for the area of wall tributary to the diaphragm tie.

2.6.7 Walls

Walls shall be evaluated for out-of-plane inertial forces 

as required by this section and as further required for 

specific structural systems in Chapters 5 through 8. 

Forces specified in this section shall be considered 

force-controlled actions.

2.6.7.1 Out-of-Plane Anchorage to 

Diaphragms

Walls shall be positively anchored to all diaphragms 

that provide lateral support for the wall or are vertically 

supported by the wall. Walls shall be anchored to 

diaphragms at horizontal distances not exceeding eight 

feet, unless it can be demonstrated that the wall has 

adequate capacity to span horizontally between the 

supports for greater distances. Anchorage of walls to 

diaphragms shall be designed for forces calculated 

using Equation (2-6), which shall be developed in the 

diaphragm. If sub-diaphragms are used, each subdiaphragm shall be capable of transmitting the shear 

forces due to wall anchorage to a continuous diaphragm 

tie. Sub-diaphragms shall have length-to-depth ratios 

not exceeding 3:1. Where wall panels are stiffened for 

out-of-plane behavior by pilasters or similar elements, 

anchors shall be provided at each such element and the 

distribution of out-of-plane forces to wall anchors and 

diaphragm ties shall consider the stiffening effect and 

accumulation of forces at these elements. Wall anchor 

connections shall be considered force-controlled.

(2-6)

where:

exceptions:

1. Fp shall not be less than the minimum of 

400 lb/ft or 400 SXS (lbs/foot).

2.6.7.2 Out-of-Plane Strength

Wall components shall have adequate strength to span 

between locations of out-of-plane support when 

subjected to out-of-plane forces calculated using 

Equation (2-7).

(2-7)

where:

Fp = Axial tensile force for the design of ties 

between the diaphragm and chords or 

boundaries

SXS = Spectral response acceleration parameter at 

short periods for the selected hazard level and 

damping adjusted for site class

W = Weight tributary to that portion of the 

diaphragm extending half the distance to each 

adjacent tie or diaphragm boundary

Fp χS = XS W

Fp = Design force for anchorage of walls to 

diaphragms

χ = Factor from Table 2-4 for the selected 

Structural Performance Level. Increased 

values of χ shall be used when anchoring to 

flexible diaphragms

SXS = Spectral response acceleration parameter at 

short periods for the selected hazard level and 

damping adjusted for site class

W = Weight of the wall tributary to the anchor

Table 2-4 Coefficient χ for Calculation of 

Out-of-Plane Wall Forces

Structural 

Performance Level

χ1

1. Values of χ for flexible diaphragms need not be applied to out-of-plane 

strength of walls in Section 2.6.7.2.

Flexible 

Diaphragms

Other 

Diaphragms

Collapse Prevention 0.9 0.3

Life Safety 1.2 0.4

Immediate Occupancy 1.8 0.6

Fp = Out-of-plane force per unit area for design of a 

wall spanning between two out-of-plane 

supports

χ = Factor from Table 2-4 for the selected 

performance level. Values of χ for flexible 

diaphragms need not be applied to out-of-plane 

strength of wall components

Fp χS = XS W
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-23

2.6.8 Nonstructural Components

Nonstructural components, including architectural, 

mechanical and electrical components, shall be 

anchored and braced to the structure in accordance with 

the provisions of Chapter 11.

2.6.9 Structures Sharing Common Elements

Buildings sharing common vertical or lateral loadresisting elements shall be rehabilitated considering 

interconnection of the two structures, or they shall be 

separated as specified in this section.

2.6.9.1 Interconnection

Buildings sharing common elements, other than 

foundation elements, shall be thoroughly tied together 

so as to behave as an integral unit. Ties between the 

structures at each level shall be designed for the forces 

specified in Section 2.6.5. Analyses of the combined 

response of the buildings shall account for the 

interconnection of the structures and shall evaluate the 

structures as one integral unit.

If the shared common elements are foundation 

elements, and the superstructures meet the separation 

requirements of Section 2.6.10, the structures need not 

be tied together. Shared foundation elements shall be 

designed considering an analysis of the combined 

response of the two buildings.

2.6.9.2 Separation

Buildings sharing common elements shall be 

completely separated by introducing seismic joints 

between the structures meeting the requirements of 

Section 2.6.10. Independent lateral-force-resisting 

systems shall be provided for each structure. 

Independent vertical support shall be provided on each 

side of the seismic joint, unless slide bearings are used 

and adequate bearing length is provided to 

accommodate the expected independent lateral 

movement of each structure. It shall be assumed for 

such purposes that the structures move out of phase 

with each other in opposite directions simultaneously. 

The original shared element shall be either completely 

removed, or anchored to one of the structures in 

accordance with the applicable requirements of 

Section 2.6.5.

2.6.10 Building Separation 

2.6.10.1 Minimum Separation

Buildings shall be separated from adjacent structures to 

prevent pounding by a minimum distance si at any level 

i given by Equation (2-8) unless exempted as specified 

in Section 2.6.10.2.

(2-8)

where:

The value of si need not exceed 0.04 times the height of 

the level under consideration above grade at the 

location of potential impact.

SXS = Spectral response acceleration at short periods 

for the selected hazard level and damping 

adjusted for site class

W = Weight of the wall per unit area

∆i1 = Lateral deflection of the building under 

consideration, at level i, relative to the ground, 

calculated in accordance with the provisions of 

this standard for the selected hazard level

∆i2 = Lateral deflection of an adjacent building, at 

level i, relative to the ground, estimated using 

the provisions of this standard or other 

approved approximate procedure. 

Alternatively, it shall be permitted to assume 

∆i2 = (0.03) (hi

) for any structure in lieu of a 

more detailed analysis, where hi

 is the height 

of level i above grade

si ∆i1

2 ∆i22 = +
2-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.6.10.2 Exceptions

For Structural Performance Levels of life safety or 

lower, buildings adjacent to structures that have 

diaphragms located at the same elevation, and differ in 

height by less than 50% of the height of the shorter 

building, need not meet the minimum separation 

distance specified in Section 2.6.10.1.

Buildings rehabilitated using an approved analysis 

procedure that accounts for the change in dynamic 

response of the structures due to impact need not meet 

the minimum separation distance specified in 

Section 2.6.10.1. Such an analysis shall demonstrate 

that:

1. The structures are capable of transferring forces 

resulting from impact when diaphragms are located 

at the same elevation; or

2. The structures are capable of resisting all required 

vertical and lateral forces considering the loss of any 

elements or components damaged by impact of the 

structures.

2.6.11 Vertical Seismic Effects

The effects of the vertical response of a structure to 

earthquake ground motion shall be considered for the 

following cases:

1. Cantilever elements and components of structures.

2. Pre-stressed elements and components of structures.

3. Structural components in which demands due to 

gravity loads specified in Section 3.2.8 exceed 80% 

of the nominal capacity of the component.

2.7 Construction Quality Assurance

Construction of seismic rehabilitation work shall be 

checked for quality of construction and general 

compliance with the intent of the plans and 

specifications of the rehabilitation design. Construction 

quality assurance shall conform to the requirements of 

this section and the additional testing and inspection 

requirements of the building code and reference 

standards of Chapters 5 through 11.

C2.6.10.2 Exceptions

This standard permits rehabilitated buildings to 

experience pounding as long as the effects are 

adequately considered by analysis methods that 

account for the transfer of momentum and energy 

between the structures as they impact.

Approximate methods of acounting for these effects 

can be obtained by performing nonlinear time history 

analyses of both structures (Johnson 1992). 

Approximate elastic methods for evaluating these 

effects have also been developed and are presented in 

the literature (Kasai 1990).

Buildings that are likely to experience significant 

pounding should not be considered capable of meeting 

Enhanced Rehabilitation Objectives. This is because 

signficant local crushing of building components is 

likely to occur at points of impact. Further, the very 

nature of the impact is such that high frequency shocks 

can be transmitted through the structures and 

potentially be very damaging to architectural elements, 

and mechanical and electrical systems. Such damage 

is not consistent with the performance expected of 

buildings designed to Enhahced Rehabilitation 

Objectives.

C2.7 Construction Quality Assurance

The design professional responsible for the seismic 

rehabilitation of a specific building may find it 

appropriate to specify more stringent or more detailed 

requirements. Such additional requirements may be 

particularly appropriate for those buildings having 

Enhanced Rehabilitation Objectives.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-25

2.7.1 Construction Quality Assurance Plan

A Quality Assurance Plan (QAP) shall be prepared by 

the design professional and approved by the code 

official. The QAP shall identify components of the 

work that are subject to quality assurance procedures 

and identify special inspection, testing, and observation 

requirements to confirm construction quality. The QAP 

shall also include a process for modifying the 

rehabilitation design to reflect unforeseen conditions 

discovered during construction.

2.7.2 Construction Quality Assurance 

Requirements

2.7.2.1 Requirements for the Design 

Professional

The design professional shall be responsible for 

preparing the QAP applicable to the portion of the work 

for which they are in responsible charge, overseeing the 

implementation of the plan, and reviewing special 

inspection and testing reports.

The design professional shall be responsible for 

performing periodic structural observation of the 

rehabilitation work. Structural observation shall be 

performed at significant stages of construction, and 

shall include visual observation of the work for 

substantial conformance with the construction 

documents and confirmation of conditions assumed 

during design. Structural observation shall be 

performed in addition to any special inspection and 

testing that is otherwise required for the work.

The design professional shall be responsible for 

modifying the rehabilitation design to reflect conditions 

discovered during construction.

2.7.2.2 Special Inspection

The owner shall engage the services of a special 

inspector to observe construction of the following 

rehabilitation work:

1. Items designated in Section A.9.3.3 of Appendix A 

of ASCE 7

2. All other elements and components designated for 

such special inspection by the design professional.

2.7.2.3 Testing

The special inspector shall be responsible for verifying 

that special test requirements, as described in the QAP, 

are performed by an approved testing agency for the 

following rehabilitation work:

1. All work described in Section A.9.3.4 of Appendix 

A of ASCE 7

2. Other work designated for such testing by the design 

professional.

C2.7.1 Construction Quality Assurance Plan

The QAP should, as a minimum, include the following:

1. Required contractor quality control procedures.

2. Required design professional construction quality 

assurance services, including but not limited to the 

following:

2.1. Review of required contractor submittals.

2.2. Monitoring of required inspection reports and 

test results.

2.3. Construction consultation as required by the 

contractor on the intent of the construction 

documents.

2.4. Construction observation in accordance with 

Section 2.7.2.1.

C2.7.2.1 Requirements for the Design 

Professional

Following structural observations, the design 

professional should report any observed deficiencies in 

writing to the owner’s representative, the special 

inspector, the contractor, and the code official. Upon 

completion of the work, the design professional should 

submit to the code official a written statement attesting 

that the site visits have been made, and identifying any 

reported deficiencies that, to the best of the structural 

construction observer’s knowledge, have been resolved 

or rectified.
2-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.7.2.4 Reporting and Compliance 

Procedures

The special inspector shall furnish copies of progress 

reports to the owner’s representative and the design 

professional, noting any uncorrected deficiencies and 

corrections of previously reported deficiencies. All 

observed deficiencies shall be brought to the immediate 

attention of the contractor for correction.

Upon completion of construction, the special inspector 

shall submit a final report to the owner’s representative 

and the design professional, indicating the extent to 

which inspected work was completed in accordance 

with approved construction documents. Non-compliant 

work shall have been corrected prior to completion of 

construction.

2.7.3 Responsibilities of the Code Official

The code official shall be responsible for reviewing and 

approving the QAP and specifying minimum special 

inspection, testing, and reporting requirements.

C2.7.3 Responsibilities of the Code Official

The code official should act to enhance and encourage 

the protection of the public that is represented by such 

rehabilitation. These actions should include those 

described in the following subsections.

1. Construction Document Submittals— Permitting

As part of the permitting process, the code official 

should require that construction documents be 

submitted for a permit to construct the proposed 

seismic rehabilitation measures. The documents should 

include a statement of the design basis for the 

rehabilitation, drawings (or adequately detailed 

sketches), structural/seismic calculations, and a QAP 

as recommended by Section 2.7.1. Appropriate 

structural construction specifications are also 

recommended, if structural requirements are not 

adequately defined by notes on drawings.

The code official should require that it be demonstrated 

(in the design calculations, by third-party review, or by 

other means) that the design of the seismic 

rehabilitation measures has been performed in 

conformance with local building regulations, the stated 

design basis, the intent of this standard, and/or 

accepted engineering principles. The code official 

should be aware that compliance with the building 

code provisions for new structures is often not possible 

and is not required by this standard. It is not intended 

that the code official assure compliance of the 

submittals with the structural requirements for new 

construction.

The code official should maintain a permanent public 

file of the construction documents submitted as part of 

the permitting process for construction of the seismic 

rehabilitation measures.

2. Construction Phase Role

The code official should monitor the implementation 

of the QAP. In particular, the following actions should 

be taken.

2.1 Files of inspection reports should be maintained 

for a defined length of time following 

completion of construction and issuance of a 

certificate of occupancy. These files should 

include both reports submitted by special 

inspectors employed by the owner, as in 

Section 2.7.2.2, and those submitted by 

inspectors employed by the code official.

2.2 Prior to issuance of certificates of occupancy, the 

code official should ascertain that either all 

reported noncompliant aspects of construction 

have been rectified, or such noncompliant 

aspects have been accepted by the design 

professional in responsible charge as acceptable 

substitutes that are consistent with the general 

intent of the construction documents.

2.3 Files of test reports prepared in accordance with 

Section 2.7.2.4 should be maintained for a 

defined length of time following completion of 

construction and issuance of a certificate of 

occupancy.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-27

2.8 Alternative Modeling Parameters 

and Acceptance Criteria

For elements, components, systems, and materials for 

which structural modeling parameters and acceptance 

criteria are not provided in this standard, it shall be 

permitted to derive the required parameters and 

acceptance criteria using the experimentally obtained 

cyclic response characteristics of the assembly, 

determined in accordance with this section. Approved 

independent review of this process shall be conducted.

2.8.1 Experimental Setup

When relevant data on the inelastic force-deformation 

behavior for a structural subassembly (elements or 

components) are not available, such data shall be 

obtained from experiments consisting of physical tests 

of representative subassemblies as specified in this 

section. Each subassembly shall be an identifiable 

portion of the structural element or component, the 

stiffness of which is required to be modeled as part of 

the structural analysis process. The objective of the 

experiment shall be to estimate the lateral-forcedisplacement relationships (stiffness) for the 

subassemblies at different loading increments, together 

with the strength and deformation capacities for the 

desired Structural Performance Levels. These properties 

shall be used in developing an analytical model of the 

structure to calculate its response to earthquake ground 

shaking and other hazards, and in developing 

acceptance criteria for strength and deformations. The 

limiting strength and deformation capacities shall be 

determined from the experimental program using the 

average values of a minimum of three tests performed 

for the same design configuration and test conditions.

The experimental setup shall replicate the construction 

details, support and boundary conditions, and loading 

conditions expected in the building. The loading shall 

consist of fully reversed cyclic loading at increasing 

displacement levels with the number of cycles and 

displacement levels based on expected response of the 

structure to the design earthquake. Increments shall be 

continued until the subassembly exhibits complete 

failure, characterized by the loss of lateral- and gravityload resistance.

2.8.2 Data Reduction and Reporting

A report shall be prepared for each experiment. The 

report shall include the following:

1. Description of the subassembly being tested.

2. Description of the experimental setup, including:

2.1. Details on fabrication of the subassembly,

2.2. Location and date of experiment,

2.3. Description of instrumentation employed,

2.4. Name of the person in responsible charge of 

the test, and

2.5. Photographs of the specimen, taken prior to 

testing.

3. Description of the loading protocol employed, 

including:

3.1. Increment of loading (or deformation) applied,

3.2. Rate of loading application, and

3.3. Duration of loading at each stage.

4. Description, including photographic documentation, 

and limiting deformation value for all important 

behavior states observed during the test, including 

the following, as applicable:

4.1. Elastic range with effective stiffness reported,

4.2. Plastic range,

4.3. Onset of visible damage,

4.4. Loss of lateral-force-resisting capacity,

4.5. Loss of vertical-load-carrying capacity,

4.6. Force-deformation plot for the subassembly 

(noting the various behavior states), and

4.7. Description of limiting behavior states defined 

as the onset of specific damage mode, change 

in stiffness or behavior (e.g., initiation of 

cracking or yielding) and failure modes.
2-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements

2.8.3 Design Parameters and Acceptance 

Criteria

The following procedure shall be followed to develop 

structural modeling parameters and acceptance criteria 

for subassemblies based on experimental data.

1. An idealized lateral-force-deformation pushover 

curve shall be developed from the experimental data 

for each experiment and for each direction of 

loading with unique behavior. The curve shall be 

plotted in a single quadrant (positive force versus 

positive deformation, or negative force versus 

negative deformation). The curve shall be 

constructed as follows:

1.1. The appropriate quadrant of data from the 

lateral-force-deformation plot from the 

experimental report shall be taken.

1.2. A smooth “backbone” curve shall be drawn 

through the intersection of the first cycle curve 

for the (i)th deformation step with the second 

cycle curve of the (i-1)th deformation step, for 

all i steps, as indicated in Figure 2-4. 

1.3. The backbone curve so derived shall be 

approximated by a series of linear segments, 

drawn to form a multi-segmented curve 

conforming to one of the types indicated in 

Figure 2-3. 

2. The multilinear curves derived for all experiments 

involving the subassembly shall be compared and an 

average multilinear representation of the 

subassembly behavior shall be derived based on 

these curves. Each segment of the composite curve 

shall be assigned the average stiffness (either 

positive or negative) of the similar segments in the 

multilinear curves for the various experiments. Each 

segment on the composite curve shall terminate at 

the average of the deformation levels at which the 

similar segments of the multilinear curves for the 

various experiments terminate.

3. The stiffness of the subassembly for use in linear 

procedures shall be taken as the slope of the first 

segment of the composite curve.

4. For the purpose of determining acceptance criteria, 

assemblies shall be classified as being either forcecontrolled or deformation-controlled. Assemblies 

shall be classified as force-controlled unless any of 

the following apply.

4.1. The composite multilinear force-deformation 

curve for the assembly, determined in 

accordance with requirements in paragraph 2 

above, conforms to either Type 1 or Type 2, as 

indicated in Figure 2-3, and the deformation 

parameter e, as indicated in Figure 2-3, is at 

least twice the deformation parameter g, as 

indicated in Figure 2-3.

4.2. The composite multilinear force-deformation 

curve for the assembly determined in 

accordance with requirements in paragraph 2 

above, conforms to Type 1, as indicated in 

Figure 2-3, and the deformation parameter e is 

less than twice the deformation parameter g, 

but the deformation parameter d is at least 

twice the deformation parameter g. In this case 

the assembly shall be either classified as forcecontrolled, or classified as deformationcontrolled but with acceptance criteria 

determined by redrawing the forcedeformation curve as a Type 2 curve, with that 

portion of the original curve between points 2 

and 3 extended back to intersect the first linear 

segment at point 1′ as indicated in Figure 2-5. 

The parameters a′ and Q′y and points 1′ and 2′

shall be taken as shown in Figure 2-5 and shall 

be used in place of parameters a and Qy1 and 

points 1 and 2 in Figure 2-3.

5. The strength capacity, QCL, for force-controlled 

elements evaluated using either the linear or 

nonlinear procedures shall be taken as follows for 

any Structural Performance Level or Range, the 

lowest strength Qy determined from the series of 

representative assembly tests.

6. The acceptance criteria for deformation-controlled 

assemblies used in nonlinear procedures shall be the 

deformations corresponding with the following 

points on the curves of Figure 2-3:

6.1. Primary Elements

- 6.1.1 Immediate Occupancy: the deformation 

at which permanent, visible damage occurred 

in the experiments but not greater than 0.67 

times the deformation limit for Life Safety 

specified in 6.1.2.

- 6.1.2 Life Safety: 0.75 times the deformation 

at point 2 on the curves.

- 6.1.3 Collapse Prevention: The deformation at 

point 2 on the curves but not greater than 0.75 

times the deformation at point 3.
 Chapter 2: General Requirements

FEMA 356 Seismic Rehabilitation Prestandard 2-29

6.2. Secondary Elements

- 6.2.1 Immediate Occupancy: the deformation 

specified in 6.1.1.

- 6.2.2 Life Safety: 75% of the deformation at 

point 3.

- 6.2.3 Collapse Prevention: 100% of the 

deformation at point 3 on the curve.

7. The m-factors used as acceptance criteria for 

deformation-controlled assemblies in linear 

procedures shall be determined as follows: (a) obtain 

the deformation acceptance criteria given in 

paragraph 6 above; (b) then obtain the ratio of this 

deformation to the deformation at yield, represented 

by the deformation parameter g in the curves shown 

in Figure 2-3; (c) then multiply this ratio by a factor 

0.75 to obtain the acceptable m-factor. 

Figure 2-4 Backbone Curve for Experimental Data 

Figure 2-5 Alternative Force-Deformation Curve
2-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 2: General Requirements
FEMA 356 Seismic Rehabilitation Prestandard 3-1

3. Analysis Procedures

3.1 Scope

This chapter sets forth requirements for analysis of 

buildings using the Systematic Rehabilitation Method. 

Section 3.2 specifies general analysis requirements for 

the mathematical modeling of buildings including basic 

assumptions, consideration of torsion, diaphragm 

flexibility, P-∆ effects, soil-structure interaction, 

multidirectional effects, and overturning. Section 3.3 

defines four analysis procedures included in this 

standard. Section 3.4 defines component acceptance 

criteria. 

Analysis of buildings with seismic isolation or energy 

dissipation systems shall comply with the requirements 

of Chapter 9. Analysis of buildings using the Simplified 

Rehabilitation Method shall comply with the 

requirements of Chapter 10.

3.2 General Analysis Requirements

An analysis of the building, as specified in Section 2.4, 

shall be conducted in accordance with the requirements 

of this section and Section 2.6.

3.2.1 Analysis Procedure Selection

An analysis of the building shall be performed using the 

Linear Static Procedure (LSP), Linear Dynamic 

Procedure (LDP), Nonlinear Static Procedure (NSP), or 

Nonlinear Dynamic Procedure (NDP) selected based on 

the limitations specified in Section 2.4. Use of 

alternative rational analysis procedures as described in 

Section 2.4.3 shall also be permitted.

C3.1 Scope

The relationship of the analysis procedures described 

in this chapter with specifications in other chapters of 

this standard is as follows.

• Information on Rehabilitation Objectives, including 

Earthquake Hazard Levels and target Building 

Performance Levels, is provided in Chapter 1.

• The provisions set forth in this chapter are intended 

for Systematic Rehabilitation. Provisions for 

Simplified Rehabilitation are presented in 

Chapter 10. 

• Guidelines for selecting an appropriate analysis 

procedure are provided in Chapter 2. Chapter 3 

describes the loading requirements, mathematical 

model, and detailed analytical procedures required 

to estimate seismic force and deformation demands 

on elements and components of a building. 

Information on the calculation of appropriate 

stiffness and strength characteristics for 

components and elements is provided in Chapters 4 

through 9.

• General design requirements are specified in 

Section 2.6 for multidirectional excitation effects, 

P-∆ effects, horizontal torsion, overturning, 

continuity of the framing system, diaphragms, 

walls, nonstructural components, building 

separation, structures sharing common components, 

and vertical seismic effects.

• Component strength and deformation demands 

obtained from analysis using procedures described 

in this chapter, based on component acceptance 

criteria outlined in this chapter, are compared with 

permissible values provided in Chapters 4 through 

9 for the desired performance level.

• Design methods for walls subjected to out-of-plane 

seismic forces are addressed in Chapter 2. Analysis 

and design methods for nonstructural components 

and mechanical and electrical equipment are 

presented in Chapter 11.

C3.2.1 Analysis Procedure Selection

Four procedures are presented for seismic analysis of 

buildings: two linear procedures, and two nonlinear 

procedures. The two linear procedures are termed the 

Linear Static Procedure (LSP) and the Linear Dynamic 

Procedure (LDP). The two nonlinear procedures are 

termed the Nonlinear Static Procedure (NSP) and 

Nonlinear Dynamic Procedure (NDP).
3-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.2.2 Mathematical Modeling 

3.2.2.1 Basic Assumptions

A building shall be modeled, analyzed, and evaluated as 

a three-dimensional assembly of elements and 

components. Alternatively, use of a two-dimensional 

model shall permitted if the building meets one of the 

following conditions:

1. The building has rigid diaphragms as defined in 

Section 3.2.4 and horizontal torsion effects do not 

exceed the limits specified in Section 3.2.2.2, or 

horizontal torsion effects are accounted for as 

specified in Section 3.2.2.2.

2. The building has flexible diaphragms as defined in 

Section 3.2.4.

If two-dimensional models are used, the threedimensional nature of components and elements shall 

be considered when calculating stiffness and strength 

properties.

If the building contains out-of-plane offsets in vertical 

lateral-force-resisting elements, the model shall 

explicitly account for such offsets in the determination 

of diaphragm demands.

Modeling stiffness of structural components shall be 

based on the stiffness requirements of Chapters 4 

through 8.

For nonlinear procedures, a connection shall be 

explicitly modeled if the connection is weaker, has less 

ductility than the connected components, or the 

flexibility of the connection results in a change in the 

connection forces or deformations greater than 10%.

3.2.2.2 Horizontal Torsion

The effects of horizontal torsion shall be considered in 

accordance with this section. Torsion need not be 

considered in buildings with flexible diaphragms as 

defined in Section 3.2.4.

Either the linear procedures of Section 3.3.1 and 

Section 3.3.2 or the nonlinear procedures of 

Sections 3.3.3 and 3.3.4 may be used to analyze a 

building, subject to the limitations set forth in 

Section 2.4.

Linear procedures are appropriate when the expected 

level of nonlinearity is low. This is measured by 

component demand to capacity ratios (DCRs) of less 

than 2.0.

Static procedures are appropriate when higher mode 

effects are not significant. This is generally true for 

short, regular buildings. Dynamic procedures are 

required for tall buildings, buildings with torsional 

irregularities, or non-orthogonal systems.

The Nonlinear Static Procedure is acceptable for most 

buildings, but should be used in conjunction with the 

Linear Dynamic Procedure if mass participation in the 

first mode is low.

The term “linear” in linear analysis procedures implies 

“linearly elastic.” The analysis procedure, however, 

may include geometric nonlinearity of gravity loads 

acting through lateral displacements and implicit 

material nonlinearity of concrete and masonry 

components using properties of cracked sections. The 

term “nonlinear” in nonlinear analysis procedures 

implies explicit material nonlinearity or inelastic 

material response, but geometric nonlinearity may also 

be included.

C3.2.2.1 Basic Assumptions

For two-dimensional models, the three-dimensional 

nature of components and elements should be 

recognized in calculating their stiffness and strength 

properties. For example, shear walls and other bracing 

systems may have “L” or “T” or other threedimensional cross-sections where contributions of both 

the flanges and webs should be accounted for in 

calculating stiffness and strength properties.

In this standard, component stiffness is generally taken 

as the effective stiffness based on the secant stiffness to 

yield level forces. Specific direction on calculating 

effective stiffness is provided in each material chapter 

for each type of structural system.

Examples of where connection flexibility may be 

important to model include the panel zone of steel 

moment-resisting frames and the “joint” region of 

perforated masonry or concrete walls.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-3

3.2.2.2.1 Total Torsional Moment

The total horizontal torsional moment at a story shall be 

equal to the sum of the actual torsional moment and 

accidental torsional moment calculated as follows:

1. The actual torsional moment at a story shall be 

calculated by multiplying the seismic story shear 

force by the eccentricity between the center of mass 

and the center of rigidity measured perpendicular to 

the direction of the applied load. The center of mass 

shall be based on all floors above the story under 

consideration. The center of rigidity of a story shall 

include all vertical seismic elements in the story.

2. The accidental torsion moment at a story shall be 

calculated as the seismic story shear force multiplied 

by a distance equal to 5% of the horizontal 

dimension at the given floor level measured 

perpendicular to the direction of the applied load.

3.2.2.2.2 Consideration of Torsional Effects

Effects of horizontal torsion shall be considered in 

accordance with the following requirements:

1. Increased forces and displacements due to actual 

torsion shall be calculated for all buildings.

2. The displacement multiplier, η, at each floor shall be 

calculated as the ratio of the maximum displacement 

at any point on the floor diaphragm to the average 

displacement (δmax/δavg). Displacements shall be 

calculated for the applied loads.

3. Increased forces and displacements due to accidental 

torsion shall be considered unless the accidental 

torsional moment is less than 25 percent of the 

actual torsional moment, or the displacement 

multiplier η due to the applied load and accidental 

torsion is less than 1.1 at every floor.

4. For linear analysis procedures, forces and 

displacements due to accidental torsion shall be 

amplified by a factor, Ax, as defined by Equation 

(3-1), when the displacement multiplier η due to 

total torsional moment exceeds 1.2 at any level.

(3-1)

5. If the displacement modifier η due to total torsional 

moment at any floor exceeds 1.50, two-dimensional 

models shall not be permitted and three-dimensional 

models that account for the spatial distribution of 

mass and stiffness shall be used.

6. When two-dimensional models are used, the effects 

of horizontal torsion shall be calculated as follows.

6.1. For the LSP and the LDP, forces and 

displacements shall be amplified by the 

maximum value of η calculated for the 

building.

6.2. For the NSP, the target displacement shall be 

amplified by the maximum value of η

calculated for the building.

6.3. For the NDP, the amplitude of the ground 

acceleration record shall be amplified by the 

maximum value of η calculated for the 

building.

7. The effects of accidental torsion shall not be used to 

reduce force and deformation demands on 

components and elements.

Ax

ηx

1.2

-------     2

= 3.0 ≤

C3.2.2.2 Horizontal Torsion

Actual torsion is due to the eccentricity between 

centers of mass and stiffness. Accidental torsion is 

intended to cover the effects of the rotational 

component of the ground motion, differences between 

computed and actual stiffness, and unfavorable 

distributions of dead and live load masses.

The 10% threshold on additional displacement due to 

accidental torsion is based on judgment. The intent is 

to reward those building frames that are torsionally 

redundant and possess high torsional stiffness. Such 

structures are likely to be much less susceptible to 

torsional response than those framing systems 

possessing low redundancy and low torsional stiffness.
3-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.2.2.3 Primary and Secondary Elements and 

Components

Elements and components shall be classified as primary 

or secondary as defined in Section 2.4.4.2. Primary 

elements and components shall be evaluated for 

earthquake-induced forces and deformations in 

combination with gravity load effects. Secondary 

elements and components shall be evaluated for 

earthquake-induced deformations in combination with 

gravity load effects.

Mathematical models for use with linear analysis 

procedures shall include the stiffness and resistance of 

only the primary elements and components. If the total 

lateral stiffness of secondary elements exceeds 25% of 

the total initial stiffness of primary elements, some 

secondary elements shall be reclassified as primary to 

reduce the total stiffness of secondary elements to less 

than 25% of primary. If the exclusion of a secondary 

element will reduce the force or deformation demands 

on a primary element, the secondary element shall be 

included in the model.

Mathematical models for use with nonlinear procedures 

shall include the stiffness and resistance of primary and 

secondary elements and components. The strength and 

stiffness degradation of primary and secondary 

elements and components shall be explicitly modeled. 

For the simplified NSP of Section 3.3.3.2.1, only 

primary elements and components shall be included in 

the model and degradation shall not be modeled.

Nonstructural components shall be included in 

mathematical models if their lateral stiffness exceeds 

10% of the total initial lateral stiffness of a story.

Components and elements shall not be selectively 

designated primary or secondary to change the 

configuration of a building from irregular to regular.

3.2.2.4 Stiffness and Strength Assumptions

Stiffness and strength properties of components and 

elements shall be determined in accordance with the 

requirements of Chapters 4 through 9, and 11.

3.2.2.5 Foundation Modeling

The foundation system shall be modeled considering 

the degree of fixity provided at the base of the structure. 

Rigid or flexible base assumptions shall be permitted in 

accordance with the requirements of Section 4.4.3. The 

foundation modeling shall consider movement due to 

geologic site hazards specified in Section 4.2.2.

3.2.3 Configuration

Building irregularities defined in Section 2.4.1.1 shall 

be based on the plan and vertical configuration of the 

rehabilitated structure. A structure defined as regular 

shall not have any irregularity defined in 

Section 2.4.1.1, both with and without the contribution 

of secondary components.

3.2.4 Diaphragms

3.2.4.1 General

Diaphragms shall be classified as either flexible, stiff, 

or rigid in accordance with Section 3.2.4.2.

C3.2.2.3 Primary and Secondary Elements 

and Components

In linear analysis procedures, the 25% limit for the 

lateral stiffness of the secondary components and 

elements can be checked by initially including the 

secondary components and elements in the 

mathematical model and examining their stiffness 

contribution.

C3.2.3 Configuration

One objective of seismic rehabilitation should be the 

improvement of the regularity of a building through the 

judicious placement of new framing elements.

Adding seismic framing elements at certain locations 

will improve the regularity of the building and should 

be considered as a means to improve seismic 

performance of the building.

Secondary components can lose significant strength 

and stiffness after initial earthquake shaking and may 

no longer be effective. Therefore, regularity of the 

building should be determined independent of the 

contribution of secondary components.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-5

3.2.4.2 Classification of Diaphragms

Diaphragms shall be classified as flexible when the 

maximum horizontal deformation of the diaphragm 

along its length is more than twice the average 

interstory drift of the vertical lateral-force-resisting 

elements of the story immediately below the 

diaphragm. For diaphragms supported by basement 

walls, the average interstory drift of the story above the 

diaphragm shall be used.

Diaphragms shall be classified as rigid when the 

maximum lateral deformation of the diaphragm is less 

than half the average interstory drift of the vertical 

lateral-force-resisting elements of the associated story.

Diaphragms that are neither flexible nor rigid shall be 

classified as stiff.

For the purpose of classifying diaphragms, interstory 

drift and diaphragm deformations shall be calculated 

using the pseudo lateral load specified in Equation 

(3-10). The in-plane deflection of the diaphragm shall 

be calculated for an in-plane distribution of lateral force 

consistent with the distribution of mass, and all in-plane 

lateral forces associated with offsets in the vertical 

seismic framing at that diaphragm level.

3.2.4.3 Mathematical Modeling

Mathematical modeling of buildings with rigid 

diaphragms shall account for the effects of horizontal 

torsion as specified in Section 3.2.2.2. Mathematical 

models of buildings with stiff or flexible diaphragms 

shall account for the effects of diaphragm flexibility by 

modeling the diaphragm as an element with an in-plane 

stiffness consistent with the structural characteristics of 

the diaphragm system. Alternatively, for buildings with 

flexible diaphragms at each floor level, each lateralforce-resisting element in a vertical plane shall be 

permitted to be designed independently, with seismic 

masses assigned on the basis of tributary area. 3.2.5 P-∆ Effects

Buildings shall be evaluated for static P-∆ effects and 

dynamic P-∆ effects as specified in this section.

3.2.5.1 Static P-∆ Effects

Static P-∆ effects shall be included in linear or 

nonlinear analysis procedures as specified in 

Sections 3.2.5.1.1 and 3.2.5.1.2, respectively.

C3.2.4 Diaphragms

Evaluation of diaphragm demands should be based on 

the likely distribution of horizontal inertia forces. For 

flexible diaphragms, such a distribution may be given 

by Equation (C3-1) and illustrated in Figure C3-1 

below.

(C3-1)

where:

fd = Inertial load per foot

Fd = Total inertial load on a flexible diaphragm

x = Distance from the center line of flexible diaphragm

Ld = Distance between lateral support points for diaphragm

Figure C3-1 Plausible Force Distribution in a 

Flexible Diaphragm

fd

1.5Fd

Ld

------------- 1 2x

Ld

-----     2

= –
3-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.2.5.1.1 Linear Procedures

For linear procedures, the stability coefficient θ shall be 

evaluated for each story in the building and for each 

direction of response using Equation (3-2).

(3-2)

where:

When the stability coefficient θi

 is less than 0.1 in all 

stories, the P-∆ effects need not be considered. If the 

stability coefficient lies between 0.1 and 0.33, seismic 

forces and deformations in story i shall be increased by 

the factor 1/(1– θi

). When the stability coefficient θi

exceeds 0.33, the structure shall be considered unstable 

and the rehabilitation design modified to reduce the 

computed lateral deflections in the story to comply with 

this limitation.

3.2.5.1.2 Nonlinear Procedures

For nonlinear procedures, static P-∆ effects shall be 

incorporated in the analysis by including in the 

mathematical model the nonlinear force-deformation 

relationship of all elements and components subjected 

to axial forces.

3.2.5.2 Dynamic P-∆ Effects

Dynamic P-∆ effects shall be included using the 

coefficient C3 defined for linear procedures in 

Section 3.3.1.3.1 or for the NSP in Section 3.3.3.3.2.

3.2.6 Soil-Structure Interaction

The effects of soil-structure interaction (SSI) shall be 

evaluated for those buildings in which an increase in 

fundamental period due to SSI effects will result in an 

increase in spectral accelerations. For other buildings, 

the effects of SSI need not be evaluated.

Pi = Portion of the total weight of the structure 

including dead, permanent live, and 25% of 

transient live loads acting on the columns 

and bearing walls within story level i

Vi = The total calculated lateral shear force in the 

direction under consideration at story i due to 

earthquake response to the selected ground 

shaking level, as indicated by the selected 

linear analysis procedure

hi = Height of story i, which shall be taken as the 

distance between either the centerline of 

floor framing at each of the levels above and 

below, or the top of floor slabs at each of the 

levels above and below (or other common 

points of reference)

δi = Lateral drift in story i, in the direction under 

consideration, at its center of rigidity, using 

the same units as for measuring hi

θi

Piδi

Vihi

= --------- C3.2.5 P-∆ Effects

Static P-∆ effects are caused by gravity loads acting 

through the deformed configuration of a building and 

result in an increase in lateral displacements. 

A negative post-yield stiffness may significantly 

increase interstory drift and the target displacement. 

Dynamic P-∆ effects are introduced to consider this 

additional drift. The degree by which dynamic P-∆

effects increase displacements depends on the 

following:

1. The ratio α of the negative post-yield stiffness to 

the effective elastic stiffness;

2. The fundamental period of the building;

3. The strength ratio, R;

4. The hysteretic load-deformation relations for each 

story;

5. The frequency characteristics of the ground motion; 

and

6. The duration of the strong ground motion.

Because of the number of parameters involved, it is 

difficult to capture dynamic P-∆ effects with a single 

modification factor. Coefficient C3 represents a 

substantial simplification and interpretation of much 

analysis data. Dynamic P-∆ effects are automatically 

captured in the NDP. 
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-7

SSI effects shall be calculated in accordance with this 

section, or other approved rational procedure. The 

simplified procedure shall be permitted only when the 

LSP is used. The explicit modeling procedure shall be 

used when the LDP, NSP, or NDP are used. It shall be 

permitted to ignore the effects of damping in the 

calculation of SSI when SSI effects are not required to 

be evaluated.

3.2.6.1 Simplified Procedure

Calculation of SSI effects using the simplified 

procedure shall comply with the procedure in ASCE 7

utilizing the effective fundamental period and effective 

fundamental damping ratio of the foundation-structure 

system.

When the simplified procedure is used to evaluate SSI 

effects, reduction in seismic demands on elements and 

components shall not exceed 25% of the demands 

calculated without SSI effects.

3.2.6.2 Explicit Modeling Procedure

Calculation of SSI effects using the explicit modeling 

procedure shall explicitly model the stiffness and 

damping of individual foundation elements. Foundation 

stiffness parameters shall comply with the requirements 

of Section 4.4.2. In lieu of explicitly modeling 

damping, the effective damping ratio, β, of the 

structure-foundation system shall be permitted to be 

calculated using the simplified procedure. The damping 

ratio used for individual foundation elements shall not 

exceed the value used for the elastic superstructure. For 

the NSP, the effective damping ratio of the foundationstructure system shall be used to calculate the spectral 

demands. If the simplified procedure is used to 

calculate the effective damping ratio, reduction in 

seismic demands shall not exceed 25% of the demands 

calculated without SSI effects.

3.2.7 Multidirectional Seismic Effects

Buildings shall be designed for seismic motion in any 

horizontal direction. Multidirectional seismic effects 

shall be considered to act concurrently as specified in 

Section 3.2.7.1for buildings meeting the following 

criteria:

1. The building has plan irregularities as defined in 

Section 2.4.1.1; or

2. The building has one or more primary columns 

which form a part of two or more intersecting frame 

or braced frame elements.

All other buildings shall be permitted to be designed for 

seismic motions acting nonconcurrently in the direction 

of each principal axis of the building.

3.2.7.1 Concurrent Seismic Effects

When concurrent multidirectional seismic effects must 

be considered, horizontally oriented orthogonal X and 

Y axes shall be established. Elements and components 

of the building shall be designed for combinations of 

forces and deformations from separate analyses 

performed for ground motions in X and Y directions as 

follows:

1. Where the LSP or LDP are used as the basis for 

design, elements and components shall be designed 

for (a) forces and deformations associated with 

100% of the design forces in the X direction plus the 

forces and deformations associated with 30% of the 

design forces in the perpendicular horizontal Y 

direction, and for (b) forces and deformations 

associated with 100% of the design forces in the Y 

direction plus the forces and deformations 

associated with 30% of the design forces in the X 

direction. Other combination rules shall be permitted 

where verified by experiment or analysis.

C3.2.6 Soil-Structure Interaction

Soil-structure interaction (SSI) may modify the seismic 

demand on a building.

For those rare cases (such as near-field and soft soil 

sites) in which the increase in period due to SSI 

increases spectral accelerations, the effects of SSI on 

building response must be evaluated.
3-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

2. Where the NSP or NDP are used as the basis for 

design, elements and components of the building 

shall be designed for (a) forces and deformations 

associated with 100% of the design displacement in 

the X direction plus the forces (not deformations) 

associated with 30% of the design displacements in 

the perpendicular horizontal Y direction, and for (b) 

forces and deformations associated with 100% of the 

design displacements in the Y direction plus the 

forces (not deformations) associated with 30% of the 

design displacements in the X direction. Other 

combination rules shall be permitted where verified 

by experiment or analysis.

3.2.7.2 Vertical Seismic Effects

For components in which Section 2.6.11 requires 

consideration of vertical seismic effects, the vertical 

response of a structure to earthquake ground motion 

need not be combined with the effects of the horizontal 

response.

3.2.8 Component Gravity Loads for Load 

Combinations

The following component gravity forces, , shall be 

considered for combination with seismic loads.

When the effects of gravity and seismic loads are 

additive, the gravity loads shall be obtained in 

accordance with Equation (3-3).

 (3-3)

When the effects of gravity and seismic loads are 

counteracting, the gravity loads shall be obtained in 

accordance with Equation (3-4).

 (3-4)

where:

3.2.9 Verification of Design Assumptions

Each component shall be evaluated to determine that 

assumed locations of inelastic deformations are 

consistent with strength and equilibrium requirements 

along the component length to verify that locations of 

potential inelastic action have been properly accounted 

for in the analysis. Each component shall also be 

evaluated for post-earthquake residual gravity load 

capacity by an approved rational analysis procedure that 

accounts for potential redistribution of gravity loads and 

reduction of strength or stiffness caused by earthquake 

damage to the structure.

QD = Dead-load (action).

QL = Effective live load (action), equal to 25% of 

the unreduced design live load, but not less 

than the actual live load.

QS = Effective snow load (action) contribution to 

W, specified in Section 3.3.1.3.1.

QG

QG= 1.1 QD + QL QS ( ) +

QG 0.9QD =

C3.2.8 Component Gravity Loads for Load 

Combinations

Evaluation of components for gravity and wind forces, 

in the absence of earthquake forces, is beyond the 

scope of this document.

C3.2.9 Verification of Design Assumptions

It is important that assumptions about locations of 

potential inelastic activity in the structure are verified. 

In linear procedures, the potential for inelastic flexural 

action is restricted to the beam ends because flexural 

yielding along the span length can lead to 

unconservative results. In nonlinear procedures, 

potential inelastic activity should only occur where 

specifically modeled. Where demands due to gravity 

load combinations of Section 3.2.8 exceed 50 percent 

of the capacity of the component at any location along 

its length, the potential for inelastic activity exists and 

should be investigated. Sample procedures for 

verifying design assumptions are contained in 

Section C3.2.9 of FEMA 274.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-9

3.2.10 Overturning

Structures shall be designed to resist overturning effects 

caused by seismic forces. Each vertical-force-resisting 

element receiving earthquake forces due to overturning 

shall be investigated for the cumulative effects of 

seismic forces applied at and above the level under 

consideration. The effects of overturning shall be 

evaluated at each level of the structure as specified in 

Section 3.2.10.1 for linear procedures, or 

Section 3.2.10.2 for nonlinear procedures. The effects 

of overturning on foundations and geotechnical 

components shall be considered in the evaluation of 

foundation strength and stiffness as specified in 

Chapter 4. 

3.2.10.1 Linear Procedures

When linear procedures are used, overturning effects 

shall be resisted through the stabilizing effect of dead 

loads acting alone or in combination with positive 

connection of structural components to elements or 

components below the level under consideration.

Where dead loads alone are used to resist the effects of 

overturning, Equation (3-5) shall be satisfied:

(3-5)

C3.2.10 Overturning

Response to earthquake ground motion results in a 

tendency for structures and individual vertical 

elements of structures to overturn about their bases. 

Although actual overturning failure is very rare, 

overturning effects can result in significant stresses, as 

demonstrated in some local and global failures. In new 

building design, earthquake effects, including 

overturning, are evaluated for lateral forces that are 

significantly reduced (by an R-factor) from those that 

may actually develop in the structure.

For elements with positive attachment between levels 

that behave as single units—such as reinforced 

concrete walls—the overturning effects are resolved 

into component forces (e.g., flexure and shear at the 

base of the wall). The element is then proportioned 

with adequate strength using m-factors, where 

appropriate, to resist overturning effects resulting from 

these force levels.

Some elements, such as wood shear walls and 

foundations, may not be designed with positive 

attachment between levels. An overturning stability 

check is typically performed for such elements when 

designed using codes for new buildings. If the element 

has sufficient dead load to remain stable under the 

overturning effects of the design lateral forces and 

sufficient shear connection to the level below, then the 

design is deemed adequate. However, if dead load is 

inadequate to provide stability, then hold-downs, piles, 

or other types of uplift anchors are provided to resist 

the residual overturning caused by the design forces.

In the linear and nonlinear procedures of this standard, 

lateral forces are not reduced by an R-factor, as they 

are for new buildings, so computed overturning effects 

are larger than typically calculated for new buildings. 

Although the procedure used for new buildings is not 

completely rational, it has resulted in successful 

performance. Therefore, it may not be appropriate to 

require that structures and elements of structures 

remain stable for the pseudo lateral forces used in the 

linear procedures in this standard. Instead, the designer 

must determine if positive direct attachment will be 

used to resist overturning effects or if dead loads will 

be used. If positive direct attachment will be used, then 

this attachment is treated just as any other element or 

component action.

However, if dead loads alone are used to resist 

overturning, then overturning is treated as a forcecontrolled behavior and the overturning demands are 

reduced to an estimate of the real overturning demands 

that can be transmitted to the element, considering the 

overall limiting strength of the structure.

There is no simple rational method available, shown to 

be consistent with observed behavior, to design or 

evaluate elements for overturning effects. The method 

described in this standard is rational, but inconsistent 

with procedures used for new buildings. To improve 

damage control, the full lateral forces used in the linear 

procedures of this standard are required for checking 

acceptability for performance levels higher than life 

safety.

Additional studies are needed on the parameters that 

control overturning in seismic rehabilitation.

MST MOT C1C2C3 > ⁄ ( ) J
3-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

where:

MOT = Total overturning moment induced 

on the element by seismic forces 

applied at and above the level 

under consideration

MST = Stabilizing moment produced by 

dead loads acting on the element

C1, C2, and C3 = Coefficients defined in 

Section 3.3.1.3

J =Coefficient defined in Section 3.4.2.1.2The quantity 

MOT / (C1C2C3J) need not exceed the overturning 

moment on the element, as limited by the expected 

strength of the structure. The element shall be evaluated 

for the effects of increased compression at the end about 

which it is being overturned. For this purpose, 

compression at the end of the element shall be 

considered a force-controlled action.

Alternatively, the load combination represented by 

Equation (3-6) shall be permitted for evaluating the 

adequacy of dead loads alone to resist the effects of 

overturning.

(3-6)

where:

When Equations (3-5) or (3-6) for dead load stability 

against the effects of overturning are not satisfied, 

positive attachment between elements of the structure 

above and below the level under consideration shall be 

provided. If the level under consideration is the base of 

the structure, positive attachment shall be provided 

between the structure and the supporting soil, unless 

nonlinear procedures are used to rationalize overturning 

stability. Positive attachments shall be capable of 

resisting earthquake forces in combination with gravity 

loads as force- or deformation-controlled actions in 

accordance with Equations (3-18) or (3-19) and 

applicable acceptance criteria of Equations (3-20) or 

(3-21).

3.2.10.2 Nonlinear Procedures

When nonlinear procedures are used, the effects of 

earthquake-induced uplift on the tension side of an 

element, or rocking, shall be included in the analytical 

model as a nonlinear degree of freedom. The adequacy 

of elements above and below the level at which uplift or 

rocking occurs, including the foundations, shall be 

evaluated for any redistribution of forces or 

deformations that occurs as a result of this rocking.

3.3 Analysis Procedures

Selection of an appropriate analysis procedure shall 

comply with Section 3.2.1.

3.3.1 Linear Static Procedure

3.3.1.1 Basis of the Procedure

If the Linear Static Procedure (LSP) is selected for 

seismic analysis of the building, the design seismic 

forces, their distribution over the height of the building, 

and the corresponding internal forces and system 

displacements shall be determined using a linearly 

elastic, static analysis in accordance with this section.

ROT = 10.0 for Collapse Prevention

= 8.0 for Life Safety

= 4.0 for Immediate Occupancy.

0.9MST MOT C1C2C3ROT > ⁄ ( )

C3.2.10.1 Linear Procedures

For evaluating the adequacy of dead loads to provide 

stability against overturning, the alternative procedure 

of Section 3.2.10.1 is intended to provide a method that 

is consistent with prevailing practice specified in 

current codes for new buildings.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-11

Buildings shall be modeled with linearly elastic 

stiffness and equivalent viscous damping values 

consistent with components responding at or near yield 

level, as defined in Section 2.4.4. The pseudo lateral 

load defined in Section 3.3.1.3 shall be used to calculate 

internal forces and system displacements due to the 

design earthquake.

Results of the LSP shall be checked using the 

acceptance criteria of Section 3.4.2.

3.3.1.2 Period Determination

The fundamental period of a building shall be 

calculated for the direction under consideration using 

one of the following analytical, empirical, or 

approximate methods specified in this section.

3.3.1.2.1 Method 1—Analytical

Eigenvalue (dynamic) analysis of the mathematical 

model of the building shall be performed to determine 

the fundamental period of the building.

3.3.1.2.2 Method 2—Empirical

The fundamental period of the building shall be 

determined in accordance with Equation (3-7):

(3-7)

where: 

3.3.1.2.3 Method 3—Approximate

1. For any building, use of the Rayleigh-Ritz method to 

approximate the fundamental period shall be 

permitted.

2. For one-story buildings with single span flexible 

diaphragms, use of Equation (3-8) to approximate 

the fundamental period shall be permitted.

(3-8)

Where ∆w and ∆d are in-plane wall and diaphragm 

displacements in inches, due to a lateral load in the 

direction under consideration, equal to the weight of 

the diaphragm.

C3.3.1.1 Basis of the Procedure

The magnitude of the pseudo lateral load has been 

selected with the intention that, when applied to the 

linearly elastic model of the building, it will result in 

design displacement amplitudes approximating 

maximum displacements expected during the design 

earthquake. The procedure is keyed to the 

displacement response of the building because 

displacements are a better indicator of damage in the 

nonlinear range of building response than are forces. In 

this range relatively small changes in force demand 

correspond to large changes in displacement demand. 

If the building responds essentially elastically to the 

design earthquake, the calculated internal forces will 

be reasonable approximations of those expected during 

the design earthquake. If the building responds 

inelastically to the design earthquake, as commonly 

will be the case, the actual internal forces that would 

develop in the yielding building will be less than the 

internal forces calculated using a pseudo lateral load.

Calculated internal forces typically will exceed those 

that the building can develop because of anticipated 

inelastic response of components and elements. These 

design forces are evaluated through the acceptance 

criteria of Section 3.4.2, which include modification 

factors and alternative analysis procedures to account 

for anticipated inelastic response demands and 

capacities.

= Fundamental period (in seconds) in the 

direction under consideration

= 0.035 for steel moment-resisting frame 

systems

= 0.018 for concrete moment-resisting frame 

systems

= 0.030 for steel eccentrically-braced frame 

systems

= 0.060 for wood buildings (Types 1 and 2 in 

Table 10-2)

= 0.020 for all other framing systems

= Height (in feet) above the base to the roof level

= 0.80 for steel moment-resisting frame systems

= 0.90 for concrete moment-resisting frame 

systems

= 0.75 for all other framing systems

T Ct

hn

β =

T

Ct

hn

β

T 0.1∆w 0.078∆d ( ) +

0.5 =
3-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3. For one-story buildings with multiple-span 

diaphragms, use of Equation (3-8) shall be permitted 

as follows: a lateral load equal to the weight 

tributary to the diaphragm span under consideration 

shall be applied to calculate a separate period for 

each diaphragm span. The period that maximizes the 

pseudo lateral load shall be used for design of all 

walls and diaphragm spans in the building.

4. For unreinforced masonry buildings with single span 

flexible diaphragms, six stories or less in height, use 

of Equation (3-9) to approximate the fundamental 

period shall be permitted.

(3-9)

where ∆d is the maximum in-plane diaphragm 

displacement in inches, due to a lateral load in the 

direction under consideration, equal to the weight 

tributary to the diaphragm.

C3.3.1.2 Period Determination

C3.3.1.2.1 Method 1—Analytical

For many buildings, including multistory buildings 

with well-defined framing systems, the preferred 

approach to obtaining the period for design is Method 

1. By this method, the building is modeled using the 

modeling procedures of Chapters 4 through 8 and 11, 

and the period is obtained by Eigenvalue analysis. 

Flexible diaphragms may be modeled as a series of 

lumped masses and diaphragm finite elements.

Contrary to procedures in codes for new buildings, 

there is no maximum limit on period calculated using 

Method 1. This omission is intended to encourage the 

use of more advanced analyses. It is felt that sufficient 

controls on analyses and acceptance criteria are present 

within this standard to provide appropriately 

conservative results using calculated periods.

T 0.078∆d ( )0.5 =

C3.3.1.2.2 Method 2—Empirical

Empirical equations for period, such as that used in 

Method 2, intentionally underestimate the actual 

period and will generally result in conservative 

estimates of pseudo lateral load. Studies have shown 

that depending on actual mass or stiffness distributions 

in a building, the results of Method 2 may differ 

significantly from those of Method 1. The Ct

 values 

specified for Method 2 are generally consistent with 

FEMA 302 but have been modified based on recent 

published research on measured building response to 

earthquakes. The Ct

 value for wood buildings is not 

substantiated by field measurements and is based on 

engineering judgment.

C3.3.1.2.3 Method 3—Approximate

Method 3 is appropriate for systems with rigid vertical 

elements and flexible diaphragms in which the 

dynamic response of the system is concentrated in the 

diaphragm. Use of Method 2 on these systems to 

calculate the period based on the stiffness of the 

vertical elements will substantially underestimate the 

period of actual dynamic response and overestimate 

the pseudo lateral load.

Equation (3-9) is a special case developed specifically 

for URM buildings. In this method, wall deformations 

are assumed negligible compared to diaphragm 

deflections.

For illustration of wall and diaphragm displacements 

see Figure C3-2. When calculating diaphragm 

displacements for the purpose of estimating period 

using Equations (3-8) or (3-9), the diaphragm shall be 

considered to remain elastic under the prescribed 

lateral loads.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-13

3.3.1.3 Determination of Forces and 

Deformations

Forces and deformations in elements and components 

shall be calculated for the psuedo lateral load of 

Section 3.3.1.3.1, using component stiffnesses 

calculated in accordance with Chapters 4 through 8. 

Pseudo lateral loads shall be distributed throughout the 

building in accordance with Sections 3.3.1.3.2 through 

3.3.1.3.4. Alternatively, for unreinforced masonry 

buildings in which the fundamental period is calculated 

using Equation (3-9), pseudo lateral loads shall be 

permitted to be distributed in accordance with 

Section 3.3.1.3.5. Actions and deformations shall be 

modified to consider the effects of horizontal torsion in 

accordance with Section 3.2.2.2.

3.3.1.3.1 Pseudo Lateral Load

The pseudo lateral load in a given horizontal direction 

of a building shall be determined using Equation (3-10). 

This load shall be used to design the vertical elements 

of the lateral-force-resisting system.

(3-10)

where: 

Figure C3-2 Diaphragm and Wall Displacement 

Terminology

V C1C2C3CmSa = W

= Pseudo lateral load.

= Modification factor to relate expected 

maximum inelastic displacements to 

displacements calculated for linear elastic 

response, calculated either using the 

procedure indicated in Section 3.3.3.3 with 

the elastic base shear capacity substituted for 

shear yield strength Vy in Equation (3-16) or 

calculated as follows:

= 1.5 for second.

= 1.0 for second.

Linear interpolation shall be used to calculate 

 for intermediate values of .

 = Fundamental period of the building in 

the direction under consideration, calculated 

in accordance with Section 3.3.1.2, including 

modification for SSI effects of Section 3.2.6, 

if applicable.

 = Characteristic period of the response 

spectrum, defined as the period associated 

with the transition from the constant 

acceleration segment of the spectrum to the 

constant velocity segment of the spectrum in 

accordance with Sections 1.6.1.5 and 1.6.2.1.

= Modification factor to represent the effects of 

pinched hysteresis shape, stiffness 

degradation, and strength deterioration on 

maximum displacement response. For linear 

procedures C2 shall be taken as 1.0.

= Modification factor to represent increased 

displacements due to dynamic P-∆ effects 

specified in Section 3.2.5.2. For values of the 

stability coefficient θi

 per Equation (3-2) less 

than 0.1 in all stories, C3 shall be set equal to 

1.0, otherwise C3 shall be calculated as 

1+5 (θ − 0.1)/T using θ equal to the 

maximum value of θi

 of all stories.

= Effective mass factor to account for higher 

mode mass participation effects obtained 

from Table 3-1. Cm shall be taken as 1.0 if the 

fundamental period, T, is greater than 1.0 

second.

V

C1

C1 T < 0.10

C1 T TS ≥

C1 T

T

TS

C2

C3

Cm
3-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

= Response spectrum acceleration, at the 

fundamental period and damping ratio of the 

building in the direction under consideration. 

The value of shall be obtained from the 

procedure specified in Section 1.6.

W = Effective seismic weight of the building 

including the total dead load and applicable 

portions of other gravity loads listed below:

1. In areas used for storage, a minimum 25% 

of the floor live load shall be applicable. 

The live load shall be permitted to be 

reduced for tributary area as approved by 

the code official. Floor live load in public 

garages and open parking structures is not 

applicable.

2. Where an allowance for partition load is 

included in the floor load design, the 

actual partition weight or a minimum 

weight of 10 psf of floor area, whichever 

is greater, shall be applicable.

3. Total operating weight of permanent 

equipment.

4. Where the design flat roof snow load 

calculated in accordance with ASCE 7 

exceeds 30 psf, the effective snow load 

shall be taken as 20% of the design snow 

load. Where the design flat roof snow load 

is less than 30 psf, the effective snow load 

shall be permitted to be zero.

Sa

Sa

C3.3.1.3.1 Pseudo Lateral Load

Coefficient C1. This modification factor is to account 

for the difference in maximum elastic and inelastic 

displacement amplitudes in structures with relatively 

stable and full hysteretic loops. The values of the 

coefficient are based on analytical and experimental 

investigations of the earthquake response of yielding 

structures. The quantity, R, is the ratio of the required 

elastic strength to the yielding strength of the structure. 

Where the quantity R is defined, it is preferable to use 

the appropriate value of C1 given by the equations in 

Section 3.3.3.3. Where the quantity R is not defined, as 

permitted for the LSP, the coefficient C1 may be read 

from the expressions given in Section 3.3.1.3.1.

Coefficient C2. This coefficient adjusts design values 

based on component hysteresis characteristics, 

stiffness degradation, and strength deterioration. See 

Section C3.3.3.3.2 and FEMA 274 for additional 

discussion.

Coefficient C3. For framing systems that exhibit 

negative post-yield stiffness, dynamic P-∆ effects may 

lead to significant amplification of displacements. 

Such effects cannot be explicitly addressed with linear 

procedures. No measure of the degree of negative postyield stiffness can be explicitly included in a linear 

procedure.

Table 3-1 Values for Effective Mass Factor Cm1

No. of 

Stories

Concrete 

Moment 

Frame

Concrete 

Shear

Wall

Concrete 

Pier-Spandrel

Steel 

Moment 

Frame

Steel 

Concentric 

Braced Frame

Steel 

Eccentric 

Braced Frame Other

1–2 1.0 1.0 1.0 1.0 1.0 1.0 1.0

3 or more 0.9 0.8 0.8 0.9 0.9 0.9 1.0

1. Cm shall be taken as 1.0 if the fundamental period, T, is greater than 1.0 second.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-15

3.3.1.3.2 Vertical Distribution of Seismic Forces

The vertical distribution of the pseudo lateral load shall 

be as specified in this section for all buildings except 

unreinforced masonry buildings for which the pseudo 

lateral loads shall be permitted to be distributed in 

accordance with Section 3.3.1.3.5. The lateral load 

applied at any floor level x shall be determined in 

accordance with Equation (3-11) and Equation (3-12):

(3-11)

(3-12)

where:

3.3.1.3.3 Horizontal Distribution of Seismic Forces

The seismic forces at each floor level of the building 

calculated using Equation (3-11) shall be distributed 

according to the distribution of mass at that floor level.

3.3.1.3.4 Diaphragms

Diaphragms shall be designed to resist the combined 

effects of the inertial force, , calculated in 

accordance with Equation (3-13), and horizontal forces 

resulting from offsets in or changes in the stiffness of 

the vertical seismic framing elements above and below 

the diaphragm. Forces resulting from offsets in or 

changes in the stiffness of the vertical seismic framing 

elements shall be taken as the forces due to the pseudo 

lateral load of Equation (3-10) without reduction, unless 

smaller forces are justified by a limit-state or other 

rational analysis, and shall be added directly to the 

diaphragm inertial forces.

(3-13)

where:

The seismic load on each flexible diaphragm shall be 

distributed along the span of that diaphragm, 

proportional to its displaced shape.

Diaphragms receiving horizontal forces from 

discontinuous vertical elements shall be taken as forcecontrolled. Actions on other diaphragms shall be 

considered force- or deformation-controlled as 

specified for diaphragm components in Chapters 5 

through 8.

= Vertical distribution factor

= 2.0 for seconds

= 1.0 for seconds

Linear interpolation shall be used to calculate 

values of for intermediate values of 

= Pseudo lateral load from Equation (3-10)

= Portion of the total building weight W

located on or assigned to floor level i

= Portion of the total building weight W

located on or assigned to floor level x

= Height (in ft) from the base to floor level i

= Height (in ft) from the base to floor level x

Fx

Fx = CvxV

Cvx

wxhx

k

wihi

k

i = 1

n

∑

= --------------------

Cvx

k T ≥ 2.5

T ≤ 0.5

k T

V

wi

wx

hi

hx

= Total diaphragm inertial force at level x

= Lateral load applied at floor level i given by 

Equation (3-11)

= Portion of the effective seismic weight W

located on or assigned to floor level i

= Portion of the effective seismic weight W

located on or assigned to floor level x

Fpx

Fpx Fi

i x =

n

∑

wx

wi

i x =

n

∑

= --------------

Fpx

Fi

wi

wx
3-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.3.1.3.5 Distribution of Seismic Forces for 

Unreinforced Masonry Buildings with 

Flexible Diaphragms

For unreinforced masonry buildings with flexible 

diaphragms for which the fundamental period is 

calculated using Equation (3-9), it shall be permitted to 

calculate and distribute the pseudo lateral loads as 

follows:

1. For each span of the building and at each level, 

calculate period from Equation (3-9).

2. Using Equation (3-10), calculate pseudo lateral load 

for each span.

3. Apply the lateral loads calculated for all spans and 

calculate forces in vertical seismic-resisting 

elements using tributary loads.

4. Diaphragm forces for evaluation of diaphragms shall 

be determined from the results of step 3 above and 

distributed along the diaphragm span considering its 

deflected shape.

5. Diaphragm deflection shall not exceed 6 inches for 

this method of distribution of pseudo lateral loads to 

be applicable.

3.3.2 Linear Dynamic Procedure

3.3.2.1 Basis of the Procedure

If the Linear Dynamic Procedure (LDP) is selected for 

seismic analysis of the building, the design seismic 

forces, their distribution over the height of the building, 

and the corresponding internal forces and system 

displacements shall be determined using a linearlyelastic, dynamic analysis in compliance with the 

requirements of this section. 

Buildings shall be modeled with linearly elastic 

stiffness and equivalent viscous damping values 

consistent with components responding at or near yield 

level, as defined in Section 2.4.4. Modeling and 

analysis procedures to calculate forces and 

deformations shall be in accordance with 

Section 3.3.2.2.

Results of the LDP shall be checked using the 

acceptance criteria of Section 3.4.2.

3.3.2.2 Modeling and Analysis 

Considerations

3.3.2.2.1 General

The ground motion characterized for dynamic analysis 

shall comply with the requirements of Section 3.3.2.2.2. 

The dynamic analysis shall be performed using the 

response spectrum method in accordance with 

Section 3.3.2.2.3 or the time-history method in 

accordance with Section 3.3.2.2.4.

3.3.2.2.2 Ground Motion Characterization

The horizontal ground motion shall be characterized for 

design by the requirements of Section 1.6 and shall be 

one of the following:

1. A response spectrum as specified in Section 1.6.1.5.

2. A site-specific response spectrum as specified in 

Section 1.6.2.1.

3. Ground acceleration time histories as specified in 

Section 1.6.2.2.

C3.3.2.1 Basis of the Procedure

Modal spectral analysis is carried out using linearlyelastic response spectra that are not modified to 

account for anticipated nonlinear response. As with the 

LSP, it is expected that the LDP will produce 

displacements that approximate maximum 

displacements expected during the design earthquake, 

but will produce internal forces that exceed those that 

would be obtained in a yielding building.

Calculated internal forces typically will exceed those 

that the building can sustain because of anticipated 

inelastic response of components and elements. These 

design forces are evaluated through the acceptance 

criteria of Section 3.4.2, which include modification 

factors and alternative analysis procedures to account 

for anticipated inelastic response demands and 

capacities.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-17

3.3.2.2.3 Response Spectrum Method

Dynamic analysis using the response spectrum method 

shall calculate peak modal responses for sufficient 

modes to capture at least 90% of the participating mass 

of the building in each of two orthogonal principal 

horizontal directions of the building. Modal damping 

ratios shall reflect the damping in the building at 

deformation levels less than the yield deformation.

Peak member forces, displacements, story forces, story 

shears, and base reactions for each mode of response 

shall be combined by either the SRSS (square root sum 

of squares) rule or the CQC (complete quadratic 

combination) rule.

Multidirectional seismic effects shall be considered in 

accordance with the requirements of Section 3.2.7.

3.3.2.2.4 Time History Method

Dynamic analysis using the time history method shall 

calculate building response at discrete time steps using 

discretized recorded or synthetic time histories as base 

motion. The damping matrix associated with the 

mathematical model shall reflect the damping in the 

building at deformation levels near the yield 

deformation.

Response parameters shall be calculated for each time 

history analysis. If three or more time history analyses 

are performed, the maximum response of the parameter 

of interest shall be used for design. If seven or more 

consistent pairs of horizontal ground motion records are 

used for time history analysis, use of the average of all 

responses of the parameter of interest shall be permitted 

for design.

Multidirectional seismic effects shall be considered in 

accordance with the requirements of Section 3.2.7. 

Alternatively, an analysis of a three-dimensional 

mathematical model using simultaneously imposed 

consistent pairs of earthquake ground motion records 

along each of the horizontal axes of the building shall 

be permitted.

3.3.2.3 Determination of Forces and 

Deformations

3.3.2.3.1 Modification of Demands

All forces and deformations calculated using either the 

Response Spectrum or Time History Analysis Methods 

shall be multiplied by the product of the modification 

factors C1, C2, and C3 defined in Section 3.3.1.3, and 

further modified to consider the effects of torsion in 

accordance with Section 3.2.2.2.

3.3.2.3.2 Diaphragms

Diaphragms shall be designed to resist simultaneously 

(1) the seismic forces calculated by the LDP, and (2) the 

horizontal forces resulting from offsets in, or changes in 

stiffness of, the vertical seismic framing elements above 

and below the diaphragm. The seismic forces calculated 

by the LDP shall be taken as not less than 85% of the 

forces calculated using Equation (3-13). Forces 

resulting from offsets in, or changes in stiffness of, the 

vertical seismic framing elements shall be taken to be 

equal to the elastic forces without reduction, unless 

smaller forces are justified by an approved rational 

analysis. Diaphragm actions need not be multiplied by 

the product of the modification factors C1, C2, and C3.

C3.3.2.2 Modeling and Analysis 

Considerations

The LDP includes two analysis methods, namely, the 

Response Spectrum Method and the Time History 

Method. The Response Spectrum Method uses peak 

modal responses calculated from dynamic analysis of a 

mathematical model. Only those modes contributing 

significantly to the response need to be considered. 

Modal responses are combined using rational methods 

to estimate total building response quantities. The 

Time History Method (also termed Response-History 

Analysis) involves a time-step-by-time-step evaluation 

of building response, using discretized recorded or 

synthetic earthquake records as base motion input. 

Pairs of ground motion records for simultaneous 

analysis along each horizontal axis of the building 

should be consistent. Consistent pairs are the 

orthogonal motions expected at a given site based on 

the same earthquake.
3-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.3.3 Nonlinear Static Procedure

3.3.3.1 Basis of the Procedure

If the Nonlinear Static Procedure (NSP) is selected for 

seismic analysis of the building, a mathematical model 

directly incorporating the nonlinear load-deformation 

characteristics of individual components and elements 

of the building shall be subjected to monotonically 

increasing lateral loads representing inertia forces in an 

earthquake until a target displacement is exceeded. 

Mathematical modeling and analysis procedures shall 

comply with the requirements of Section 3.3.3.2. The 

target displacement shall be calculated by the procedure 

in Section 3.3.3.3.

Calculated displacements and internal forces shall meet 

the acceptance criteria specified in Section 3.4.3. 

3.3.3.2 Modeling and Analysis 

Considerations

3.3.3.2.1 General

The selection of a control node, the selection of lateral 

load patterns, the determination of the fundamental 

period, and analysis procedures shall comply with the 

requirements of this section.

The relation between base shear force and lateral 

displacement of the control node shall be established for 

control node displacements ranging between zero and 

150% of the target displacement, δt

. 

The component gravity loads shall be included in the 

mathematical model for combination with lateral loads 

as specified in Section 3.2.8. The lateral loads shall be 

applied in both the positive and negative directions, and 

the maximum seismic effects shall be used for design.

The analysis model shall be discretized to represent the 

load-deformation response of each component along its 

length to identify locations of inelastic action.

All primary and secondary lateral-force-resisting 

elements shall be included in the model, as specified in 

Section 3.2.2.3.

The force-displacement behavior of all components 

shall be explicitly included in the model using full 

backbone curves that include strength degradation and 

residual strength, if any.

Alternatively, the use of a simplified NSP analysis shall 

be permitted. In a simplified NSP analysis only primary 

lateral force resisting elements are modeled, the forcedisplacement characteristics of such elements are 

bilinear, and the degrading portion of the backbone 

curve is not explicitly modeled. The simplified NSP 

analysis shall only be used in conjunction with the 

acceptance criteria of Section 3.4.3.2.2. Elements not 

meeting the acceptance criteria for primary components 

shall be designated as secondary, and removed from the 

mathematical model.

3.3.3.2.2 Control Node Displacement

The control node shall be located at the center of mass 

at the roof of a building. For buildings with a penthouse, 

the floor of the penthouse shall be regarded as the level 

of the control node. The displacement of the control 

node in the mathematical model shall be calculated for 

the specified lateral loads.

C3.3.3.1 Basis of the Procedure

The target displacement is intended to represent the 

maximum displacement likely to be experienced 

during the design earthquake. Because the 

mathematical model accounts directly for effects of 

material inelastic response, the calculated internal 

forces will be reasonable approximations of those 

expected during the design earthquake.

C3.3.3.2.1 General

When using the simplified NSP analysis, care should 

be taken to make sure that removal of degraded 

elements from the model does not result changes in the 

regularity of the structure that would significantly alter 

the dynamic response. In pushing with a static load 

pattern, the NSP does not capture changes in the 

dynamic characteristics of the structure as yielding and 

degradation take place.

In order to explicitly evaluate deformation demands on 

secondary elements that are to be excluded from the 

model, one might consider including them in the 

model, but with negligible stiffness, to obtain 

deformations demands without significantly affecting 

the overall response.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-19

3.3.3.2.3 Lateral Load Distribution

Lateral loads shall be applied to the mathematical 

model in proportion to the distribution of inertia forces 

in the plane of each floor diaphragm. For all analyses, at 

least two vertical distributions of lateral load shall be 

applied. One pattern shall be selected from each of the 

following two groups:

1. A modal pattern selected from one of the following:

1.1. A vertical distribution proportional to the 

values of Cvx given in Equation (3-12). Use of 

this distribution shall be permitted only when 

more than 75% of the total mass participates in 

the fundamental mode in the direction under 

consideration, and the uniform distribution is 

also used.

1.2. A vertical distribution proportional to the 

shape of the fundamental mode in the direction 

under consideration. Use of this distribution 

shall be permitted only when more than 75% 

of the total mass participates in this mode.

1.3. A vertical distribution proportional to the story 

shear distribution calculated by combining 

modal responses from a response spectrum 

analysis of the building, including sufficient 

modes to capture at least 90% of the total 

building mass, and using the appropriate 

ground motion spectrum.This distribution shall 

be used when the period of the fundamental 

mode exceeds 1.0 second.

2. A second pattern selected from one of the following:

2.1. A uniform distribution consisting of lateral 

forces at each level proportional to the total 

mass at each level.

2.2. An adaptive load distribution that changes as 

the structure is displaced. The adaptive load 

distribution shall be modified from the original 

load distribution using a procedure that 

considers the properties of the yielded 

structure.

3.3.3.2.4 Idealized Force-Displacement Curve

The nonlinear force-displacement relationship between 

base shear and displacement of the control node shall be 

replaced with an idealized relationship to calculate the 

effective lateral stiffness, , and effective yield 

strength, , of the building as shown in Figure 3-1. 

This relationship shall be bilinear, with initial slope Ke

and post-yield slope α. Line segments on the idealized 

force-displacement curve shall be located using an 

iterative graphical procedure that approximately 

balances the area above and below the curve. The 

effective lateral stiffness, , shall be taken as the 

secant stiffness calculated at a base shear force equal to 

60% of the effective yield strength of the structure. The 

post-yield slope, α, shall be determined by a line 

segment that passes through the actual curve at the 

calculated target displacement. The effective yield 

strength shall not be taken as greater than the maximum 

base shear force at any point along the actual curve. 

C3.3.3.2.3 Lateral Load Distribution

The distribution of lateral inertial forces determines 

relative magnitudes of shears, moments, and 

deformations within the structure. The distribution of 

these forces will vary continuously during earthquake 

response as portions of the structure yield and stiffness 

characteristics change. The extremes of this 

distribution will depend on the severity of the 

earthquake shaking and the degree of nonlinear 

response of the structure. Use of more than one lateral 

load pattern is intended to bound the range of design 

actions that may occur during actual dynamic 

response.

In lieu of using the uniform distribution to bound the 

solution, changes in the distribution of lateral inertial 

forces can be investigated using adaptive load patterns 

that change as the structure is displaced to larger 

amplitudes. Procedures for developing adaptive load 

patterns include the use of story forces proportional to 

the deflected shape of the structure (Fajfar and 

Fischinger), the use of load patterns based on mode 

shapes derived from secant stiffnesses at each load step 

(Eberhard and Sozen), and the use of load patterns 

proportional to the story shear resistance at each step 

(Bracci et al.). Use of an adaptive load pattern will 

require more analysis effort, but may yield results that 

are more consistent with the characteristics of the 

building under consideration.

Ke

Vy

Ke
3-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.3.3.2.5 Period Determination

The effective fundamental period in the direction under 

consideration shall be based on the idealized forcedisplacement curve defined in Section 3.3.3.2.4. The 

effective fundamental period, , shall be calculated in 

accordance with Equation (3-14):

(3-14)

where: 

3.3.3.2.6 Analysis of Mathematical Models

Separate mathematical models representing the framing 

along two orthogonal axes of the building shall be 

developed for two-dimensional analysis. A 

mathematical model representing the framing along two 

orthogonal axes of the building shall be developed for 

three-dimensional analysis.

The effects of horizontal torsion shall be evaluated in 

accordance with Section 3.2.2.2.

Independent analysis along each of the two orthogonal 

principal axes of the building shall be permitted unless 

concurrent evaluation of multidirectional effects is 

required by Section 3.2.7.

3.3.3.3 Determination of Forces and 

Deformations

3.3.3.3.1 General

For buildings with rigid diaphragms at each floor level, 

the target displacement, δt, shall be calculated in 

accordance with Equation (3-15) or by an approved 

procedure that accounts for the nonlinear response of 

the building.

For buildings with non-rigid diaphragms at each floor 

level, diaphragm flexibility shall be explicitly included 

in the model. The target displacement shall be 

calculated as specified for rigid diaphragms, except that 

it shall be amplified by the ratio of the maximum 

displacement at any point on the roof to the 

displacement at the center of mass of the roof (δmax/

δcm). δmax and δcm shall be based on a response 

spectrum analysis of a three-dimensional model of the 

building. The target displacement so calculated shall be 

no less than that displacement given by Equation 

(3-15). No line of vertical seismic framing shall be 

evaluated for displacements smaller than the target 

displacement.

Figure 3-1 Idealized Force-Displacement Curves

Te

Te Ti

Ki

Ke

= ------

= Elastic fundamental period (in seconds) in 

the direction under consideration calculated 

by elastic dynamic analysis

= Elastic lateral stiffness of the building in the 

direction under consideration

= Effective lateral stiffness of the building in 

the direction under consideration

Ti

Ki

Ke
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-21

Alternatively, for buildings with flexible diaphragms at 

each floor level, a target displacement shall be 

calculated for each line of vertical seismic framing. The 

target displacement for an individual line of vertical 

seismic framing shall be as specified for buildings with 

rigid diaphragms, except that the masses shall be 

assigned to each line on the basis of tributary area.

Forces and deformations corresponding to the control 

node displacement equaling or exceeding the target 

displacement shall comply with acceptance criteria of 

Section 3.4.3.

3.3.3.3.2 Target Displacement

The target displacement, δt, at each floor level shall be 

calculated in accordance with Equation (3-15) and as 

specified in Section 3.3.3.3.1.

g (3-15)

where: 

The strength ratio R shall be calculated in accordance 

with Equation (3-16):

(3-16)

= Modification factor to relate spectral 

displacement of an equivalent SDOF system 

to the roof displacement of the building 

MDOF system calculated using one of the 

following procedures:

• The first modal participation factor at the 

level of the control node;

• The modal participation factor at the level 

of the control node calculated using a 

shape vector corresponding to the deflected 

shape of the building at the target 

displacement. This procedure shall be used 

if the adaptive load pattern defined in 

paragraph 2.2 of Section 3.3.3.2.3 is used; 

or

• The appropriate value from Table 3-2.

= Modification factor to relate expected 

maximum inelastic displacements to 

displacements calculated for linear elastic 

response:

= 1.0 for 

= for 

δt C0C1C2C3Sa

Te

2

4π

2 = --------

C0

C1

Te TS ≥

1.0 ( ) R – 1 TS Te [ ] + ⁄ ⁄ R Te TS <

but not greater than the values given in 

Section 3.3.1.3 nor less than 1.0.

= Effective fundamental period of the building 

in the direction under consideration, sec.

= Characteristic period of the response 

spectrum, defined as the period associated 

with the transition from the constant 

acceleration segment of the spectrum to the 

constant velocity segment of the spectrum per 

Sections 1.6.1.5 and 1.6.2.1.

= Ratio of elastic strength demand to calculated 

yield strength coefficient calculated by 

Equation (3-16).

= Modification factor to represent the effect of 

pinched hysteretic shape, stiffness degradation 

and strength deterioration on maximum 

displacement response. Values of for 

different framing systems and Structural 

Performance Levels shall be obtained from 

Table 3-3. Alternatively, use of C2 = 1.0 shall 

be permitted for nonlinear procedures.

= Modification factor to represent increased 

displacements due to dynamic P-∆ effects. For 

buildings with positive post-yield stiffness, 

shall be set equal to 1.0. For buildings with 

negative post-yield stiffness, values of 

shall be calculated using Equation (3-17) but 

not to exceed the values set forth in 

Section 3.3.1.3.

= Response spectrum acceleration, at the 

effective fundamental period and damping 

ratio of the building in the direction under 

consideration, g, as calculated in 

Sections 1.6.1.5 and 1.6.2.1.

g = acceleration of gravity

Te

TS

R

C2

C2

C3

C3

C3

Sa

R

Sa

Vy ⁄ W -------------- Cm = ⋅
3-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

where is defined above, and: 

Coefficient shall be calculated in accordance with 

Equation (3-17) if the relation between base shear force 

and control node displacement exhibits negative postyield stiffness.

(3-17)

where and are as defined above, and:

= Yield strength calculated using results of the 

NSP for the idealized nonlinear forcedisplacement curve developed for the building 

in accordance with Section Section 3.3.3.2.4

= Effective seismic weight, as calculated in 

Section 3.3.1.3.1

= Effective mass factor from Table 3-1. 

Alternatively, Cm taken as the effective model 

mass calculated for the fundamental mode 

using an Eigenvalue analysis shall be 

permitted

Sa

Vy

W

m

C3

α = Ratio of post-yield stiffness to effective 

elastic stiffness, where the nonlinear forcedisplacement relation shall be characterized 

by a bilinear relation as shown in Figure 3-1

C3 1.0 α ( ) R – 1 3 2/

Te

= + -------------------------------

R Te

Table 3-2 Values for Modification Factor 1

Shear Buildings2 Other Buildings

Number of Stories

Triangular Load Pattern 

(1.1, 1.2, 1.3)

Uniform Load Pattern

(2.1) Any Load Pattern

1 1.0 1.0 1.0

2 1.2 1.15 1.2

3 1.2 1.2 1.3

5 1.3 1.2 1.4

10+ 1.3 1.2 1.5

1. Linear interpolation shall be used to calculate intermediate values.

2. Buildings in which, for all stories, interstory drift decreases with increasing height.

Table 3-3 Values for Modification Factor 

Structural Performance Level

 second3 second3

Framing 

Type 11

Framing 

Type 22

Framing 

Type 11

Framing 

Type 22

Immediate Occupancy 1.0 1.0 1.0 1.0

Life Safety 1.3 1.0 1.1 1.0

Collapse Prevention 1.5 1.0 1.2 1.0

1. Structures in which more than 30% of the story shear at any level is resisted by any combination of the following components, elements, or frames: 

ordinary moment-resisting frames, concentrically-braced frames, frames with partially-restrained connections, tension-only braces, unreinforced masonry 

walls, shear-critical, piers, and spandrels of reinforced concrete or masonry. 

2. All frames not assigned to Framing Type 1.

3. Linear interpolation shall be used for intermediate values of T.

C0

C2

T ≤ 0.1 T TS ≥
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-23

C3.3.3.3.2 Target Displacement

Calculation Method. This standard presents the 

Coefficient Method for calculating target 

displacement. Other procedures can also be used. 

Section C3.3.3.3 of FEMA 274 presents additional 

background information on the Coefficient Method 

and another acceptable procedure referred to as the 

Capacity Spectrum Method.

Coefficient C0. This coefficient accounts for the 

difference between the roof displacement of an MDOF 

building and the displacement of the equivalent SDOF 

system. Using only the first mode shape (φ1) and 

elastic behavior, coefficient C0 is equal to the firstmode participation factor at the roof (control node) 

level. If the absolute value of the roof (control node) 

ordinate of each mode shape is set equal to unity, the 

value of coefficient C0 is equal to the first mode mass 

participation factor.

Explicit calculation of C0 using the actual deflected 

shape is more accurate and may be beneficial in terms 

of lower amplification of target displacement. The 

actual shape vector may take on any form, particularly 

since it is intended to simulate the time-varying 

deflection profile of the building responding 

inelastically to the ground motion. Based on past 

studies, the use of a shape vector corresponding to the 

deflected shape at the target displacement level may be 

more appropriate. This shape will likely be different 

from the elastic first-mode shape. While the use of 

such a deflected shape vector in the estimation of C0 is 

preferred, the choice of the elastic first-mode shape 

vector is a simpler alternative that takes into account at 

least the relative mass distribution over the height of 

the structure.

The use of the tabulated values, which are based on a 

straight-line vector with equal masses at each floor 

level, is approximate, particularly if masses vary much 

over the height of the building, and may be overly 

conservative.

Coefficient C1. This coefficient accounts for the 

observed difference in peak displacement response 

amplitude for nonlinear response as compared with 

linear response, as observed for buildings with 

relatively short initial vibration periods. For use with 

the NSP, it is recommended to calculate the value of 

this coefficient using the strength ratio, R, given by 

Equation (3-16). Additional discussion of this 

coefficient is in the commentary to Section 3.3.1.3.1.

Recent studies suggest that maximum elastic and 

inelastic displacement amplitudes may differ 

considerably if either the strength ratio R is large or the 

building is located in the near field of the causative 

fault. Specifically, the inelastic displacements will 

exceed the elastic displacement. If the strength ratio 

exceeds five, it is recommended that a displacement 

larger than the elastic displacement be used as the basis 

for calculating the target displacement.

Coefficient C2. If the hysteresis loops exhibit 

significant pinching or stiffness deterioration, the 

energy absorption and dissipation capacities decrease, 

and larger displacement excursions should be 

expected. This effect is important for short-period, 

low-strength structures with very pinched hysteresis 

loops. Framing Types 1 and 2 are introduced for the 

purpose of cataloguing systems prone to exhibit 

pinching and strength degradation—that is, Type 1. 

Type 2 systems are those not specifically identified as 

Type 1. Values for C2 are reduced for smaller levels of 

damage; that is, the values for C2 are smaller for the 

Immediate Occupancy Structural Performance Level 

(little to no damage) than for the Collapse Prevention 

Structural Performance Level (moderate to major 

damage). However, the selected performance level is 

not a direct measure of the extent of inelastic behavior 

that a building will experience, particularly in zones of 

moderate and low seismicity. If, for example, the 

structure meets a performance level superior to the 

selected performance level, use of a lower value of C2

corresponding to the actual performance level achieved 

would be justified. This may be done by interpolation 

between the C2 values specified for the performance 

levels above and below the level achieved. The values 

for C2 given in Table 3-3 are intended to account for 

both stiffness degradation and strength deterioration, 

and are based on judgment at the time this standard 

was written.
3-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.3.3.3.3 Modification of Demands

The target displacement shall be modified to consider 

the effects of horizontal torsion in accordance with 

Section 3.2.2.2.

3.3.3.3.4 Diaphragms

Diaphragms shall be designed to resist the combined 

effects of the horizontal forces resulting from offsets in, 

or changes in stiffness of, the vertical seismic framing 

elements above and below the diaphragm, and the 

diaphragm forces determined using either

Section 3.3.1.3.4 or Section 3.3.2.3.2.

3.3.4 Nonlinear Dynamic Procedure

3.3.4.1 Basis of the Procedure

If the Nonlinear Dynamic Procedure (NDP) is selected 

for seismic analysis of the building, a mathematical 

model directly incorporating the nonlinear loaddeformation characteristics of individual components 

and elements of the building shall be subjected to 

earthquake shaking represented by ground motion time 

histories in accordance with Section 1.6.2.2 to obtain 

forces and displacements.

Calculated displacements and internal forces shall be 

compared directly with acceptance criteria specified in 

Section 3.4.3. 

3.3.4.2 Modeling and Analysis 

Considerations

3.3.4.2.1 General

The modeling and analysis requirements specified in 

Section 3.3.3.2 for the NSP shall apply to the NDP, 

excluding considerations of control node and target 

displacements.

3.3.4.2.2 Ground Motion Characterization

For the NDP, earthquake shaking shall be characterized 

by discretized recorded or synthetic earthquake records 

as base motion meeting the requirements of 

Section 1.6.2.2.

While single-degree-of-freedom systems with pinched 

hysteretic behavior do experience amplified 

displacements, some recent research has shown that 

the displacement response of multiple-degree-offreedom building structures is not significantly 

affected by the pinched hysteretic behavior of 

individual elements. These new results are not yet 

entirely conclusive. At present, Table 3-3 has been 

retained in this standard, but the use of C2 = 1.0 is 

permitted.

Coefficient C3. P-∆ effects caused by gravity loads 

acting through the deformed configuration of a 

building will always result in an increase in lateral 

displacements. Static P-∆ effects can be captured using 

procedures set forth in Section 3.2.5. If P-∆ effects 

result in a negative post-yield stiffness in any one story, 

such effects may significantly increase the interstory 

drift and the target displacement. The degree by which 

dynamic P-∆ effects increase displacements depends 

on (1) the ratio α of the negative post-yield stiffness to 

the effective elastic stiffness, (2) the fundamental 

period of the building, (3) the strength ratio, (4) the 

hysteretic load-deformation relations for each story, (5) 

the frequency characteristics of the ground motion, and 

(6) the duration of the strong ground motion. Because 

of the number of parameters involved, it is difficult to 

capture dynamic P- ∆ effects with a single 

modification factor. Coefficient C3, calculated only for 

those buildings that exhibit negative post-yield 

stiffness, given by Equation (3-17), represents a 

substantial simplification and interpretation of much 

analysis data.

C3.3.4.1 Basis of the Procedure

The basis, modeling approaches, and acceptance 

criteria of the NDP are similar to those for the NSP. 

The main exception is that the response calculations 

are carried out using Time History Analysis. With the 

NDP, the design displacements are not established 

using a target displacement, but instead are determined 

directly through dynamic analysis using ground motion 

time histories. Calculated response can be highly 

sensitive to characteristics of individual ground 

motions; therefore, the analysis should be carried out 

with more than one ground motion record. Because the 

numerical model accounts directly for effects of 

material inelastic response, the calculated internal 

forces will be reasonable approximations of those 

expected during the design earthquake.
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-25

3.3.4.2.3 Time History Method

For the NDP, Time History Analysis shall be performed 

using horizontal ground motion time histories prepared 

according to the requirements of Section 1.6.2.2. 

Multidirectional seismic effects shall be accounted for 

in accordance with Section 3.2.7. Alternatively, an 

analysis of a three-dimensional mathematical model 

using simultaneously imposed consistent pairs of 

earthquake ground motion records along each of the 

horizontal axes of the building shall be permitted.

3.3.4.3 Determination of Forces and 

Deformations

Forces and deformations shall be determined in 

accordance with Section 3.3.2.2.4.

3.3.4.3.1 Modification of Demands

The effects of torsion shall be considered in accordance 

with Section 3.2.2.2.

3.3.4.3.2 Diaphragms

Diaphragms shall be designed to resist the effects of the 

seismic forces calculated by dynamic analysis including 

the effects of the horizontal forces resulting from offsets 

in, or changes in stiffness of, the vertical seismic 

framing elements above and below the diaphragm.

3.4 Acceptance Criteria

3.4.1 General Requirements

Components and elements analyzed using the linear 

procedures of Section 3.3.1 and Section 3.3.2 shall 

satisfy the requirements of Section 3.4.2. Components 

and elements analyzed using the nonlinear procedures 

of Section 3.3.3 and Section 3.3.4 shall satisfy the 

requirements of Section 3.4.3.

Prior to selecting component acceptance criteria, 

components shall be classified as primary or secondary, 

and actions shall be classified as deformation-controlled 

or force-controlled, as defined in Section 2.4.4.

Foundations shall satisfy the criteria specified 

in Chapter 4.

3.4.2 Linear Procedures

3.4.2.1 Design Forces and Deformations

Component design forces and deformations shall be 

calculated in accordance with linear analysis procedures 

of Sections 3.3.1 or 3.3.2.

3.4.2.1.1 Deformation-Controlled Actions

Deformation-controlled design actions shall be 

calculated in accordance with Equation (3-18):

(3-18)

where: 

3.4.2.1.2 Force-Controlled Actions

Force-controlled design actions, QUF, shall be 

calculated using one of the following methods:

1. QUF shall be taken as the maximum action that can 

be developed in a component based on a limit-state 

analysis considering the expected strength of the 

components delivering load to the component under 

consideration, or the maximum action developed in 

the component as limited by the nonlinear response 

of the building.

2. Alternatively, QUF shall be calculated in accordance 

with Equation (3-19). 

= Action due to design earthquake loads 

calculated using forces and analysis models 

described in either Section 3.3.1 or 

Section 3.3.2

= Action due to design gravity loads as 

defined in Section 3.2.8

= Deformation-controlled design action due to 

gravity loads and earthquake loads

C3.4.2.1.1 Deformation-Controlled Actions 

Because of possible anticipated nonlinear response of 

the structure, the design actions as represented by 

Equation (3-18) may exceed the actual strength of the 

component or element to resist these actions. The 

acceptance criteria of Section 3.4.2.2.1 take this 

overload into account through use of a factor, m, which 

is an indirect measure of the nonlinear deformation 

capacity of the component or element.

QUD

QUD QG QE = ±

QE

QG

QUD
3-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

(3-19)

where: 

3.4.2.2 Acceptance Criteria for Linear 

Procedures

3.4.2.2.1 Deformation-Controlled Actions

Deformation-controlled actions in primary and 

secondary components and elements shall satisfy 

Equation (3-20).

(3-20)

where: 

QCE, the expected strength, shall be determined 

considering all coexisting actions on the component 

under the design loading condition by procedures 

specified in Chapters 4 through 8.

= Force-controlled design action due to gravity 

loads in combination with earthquake loads

= Force-delivery reduction factor, greater than 

or equal to 1.0, taken as the smallest DCR of 

the components in the load path delivering 

force to the component in question, calculated 

in accordance with Equation (2-1).

Alternatively, values of J equal to 2.0 in 

Zones of High Seismicity, 1.5 in Zones of 

Moderate Seismicity, and 1.0 in Zones of Low 

Seismicity shall be permitted when not based 

on calculated DCRs. J shall be taken as 1.0 for 

the Immediate Occupancy Structural 

Performance Level. In any case where the 

forces contributing to QUF are delivered by 

components of the lateral force resisting 

system that remain elastic, J shall be taken as 

1.0.

C3.4.2.1.2 Force-Controlled Actions

The basic approach for calculating force-controlled 

actions for design differs from that used for 

deformation-controlled actions because nonlinear 

deformations associated with forced-controlled actions 

are not permitted. Therefore, force demands for forcecontrolled actions should not exceed the force capacity 

(strength).

Ideally, an inelastic mechanism for the structure will be 

identified, and the force-controlled actions, QUF, for 

design will be determined by limit analysis using that 

mechanism. This approach will always produce a 

conservative estimate of the design actions, even if an 

incorrect mechanism is selected. Where it is not 

possible to use limit (or plastic) analysis, or in cases 

where design forces do not produce significant 

nonlinear response in the building, it is acceptable to 

determine the force-controlled actions for design using 

Equation (3-19).

QUF QG

QE

C1C2C3J = ± ---------------------- 

QUF

J

Coefficients C1, C2, and C3 were introduced in 

Equation (3-10) to amplify the design base shear to 

achieve a better estimate of the maximum 

displacements expected for buildings responding in the 

inelastic range. Displacement amplifiers, C1, C2, and 

C3 are divided out of Equation (3-19) when seeking an 

estimate of the force level present in a component 

when the building is responding inelastically.

Since J is included for force-controlled actions, it may 

appear to be more advantageous to treat an action as 

force-controlled when m-factors are less than J. 

However, proper application of force-controlled 

criteria requires a limit state analysis of demand and 

lower bound calculation of capacity that will yield a 

safe result whether an action is treated as force- or 

deformation-controlled.

m = Component or element demand modifier 

(factor) to account for expected ductility 

associated with this action at the selected 

Structural Performance Level. m-factors are 

specified in Chapters 4 through 8

= Expected strength of the component or 

element at the deformation level under 

consideration for deformation-controlled 

actions

κ = Knowledge factor defined in Section 2.2.6.4

mκQCE QUD ≥

QCE
 Chapter 3: Analysis Procedures

FEMA 356 Seismic Rehabilitation Prestandard 3-27

3.4.2.2.2 Force-Controlled Actions

Force-controlled actions in primary and secondary 

components and elements shall satisfy Equation (3-21):

(3-21)

where: 

QCL, the lower-bound strength, shall be determined 

considering all coexisting actions on the component 

under the design loading condition by procedures 

specified in Chapters 5 through 8.

3.4.2.2.3 Verification of Design Assumptions

In addition to the requirements in Section 3.2.9, the 

following verification of design assumptions shall be 

made.

Where moments due to gravity loads in horizontally 

spanning primary components exceed 75% of the 

expected moment strength at any location, the 

possibility for inelastic flexural action at locations other 

than member ends shall be specifically investigated by 

comparing flexural actions with expected member 

strengths.

3.4.3 Nonlinear Procedures

3.4.3.1 Design Forces and Deformations

Component design forces and deformations shall be 

calculated in accordance with nonlinear analysis 

procedures of Sections 3.3.3 or 3.3.4.

3.4.3.2 Acceptance Criteria for Nonlinear 

Procedures

3.4.3.2.1 Deformation-Controlled Actions

Primary and secondary components shall have expected 

deformation capacities not less than maximum 

deformation demands calculated at the target 

displacement. Primary and secondary component 

demands shall be within the acceptance criteria for 

secondary components at the selected Structural 

Performance Level. Expected deformation capacities 

shall be determined considering all coexisting forces 

and deformations in accordance with Chapters 4 

through 8.

The base shear at the target displacement, Vt

, shall not 

be less than 80% of the effective yield strength of the 

structure, Vy, defined in Section 3.3.3.2.4.

Acceptance criteria for the simplified NSP analysis of 

Section 3.3.3.2.1 shall be as specified in 

Section 3.4.3.2.2.

3.4.3.2.2 Deformation-Controlled Actions for the 

Simplified Nonlinear Static Analysis

Primary and secondary components modeled using the 

alternative simplified NSP analysis of Section 3.3.3.2.1 

shall meet the requirements of this section. Expected 

deformation capacities shall not be less than maximum 

deformation demands calculated at the target 

displacement. Primary component demands shall be 

within the acceptance criteria for primary components 

at the selected Structural Performance Level. Demands 

on other components shall be within the acceptance 

criteria for secondary components at the selected 

Structural Performance Level. Expected deformation 

capacities shall be determined considering all 

coexisting forces and deformations by procedures 

specified in Chapters 4 through 8.

= Lower-bound strength of a component or 

element at the deformation level under 

consideration for force-controlled actions

κQCL QUF ≥

QCL

C3.4.3.2.1 Deformation-Controlled Actions

When all components are explicitly modeled with full 

backbone curves, the NSP can be used to evaluate the 

full contribution of all components to the lateral force 

resistance of the structure as they degrade to residual 

strength values. When degradation is explicitly 

evaluated in the NSP, components can be relied upon 

for lateral-force resistance out to the secondary 

component limits of response. As components degrade, 

the post-yield slope of the force-displacement curve 

becomes negative, and the target displacement begins 

to grow. The procedure is self-limiting in that small 

negative post-yield slopes will result in large 

amplifications of the target displacement through the 

C3 coefficient, quickly causing nonconvergence of the 

solution. As an additional control on the extent of 

degradation, Vt

 is limited to not less than 80% of Vy.
3-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 3: Analysis Procedures

3.4.3.2.3 Force-Controlled Actions

Primary and secondary components shall have lowerbound strengths not less than the maximum design 

forces. Lower-bound strengths shall be determined 

considering all coexisting forces and deformations by 

procedures specified in Chapters 4 through 8.

3.4.3.2.4 Verification of Design Assumptions

In addition to the requirements in Section 3.2.9, the 

following verification of design assumptions shall be 

made.

Flexural plastic hinges shall not form away from 

component ends unless they are explicitly accounted for 

in modeling and analysis.

C3.4.3.2.2 Deformation-Controlled Actions for the 

Simplified Nonlinear Static Analysis

In the simplified NSP analysis, primary components 

are not modeled with full backbone curves. 

Degradation cannot be explicitly evaluated and 

degraded elements cannot be reliably used to the 

secondary component limits of response. For this 

reason, the lateral-force-resistance of the structure 

consists of primary components measured against 

primary component acceptance criteria.
FEMA 356 Seismic Rehabilitation Prestandard 4-1

4. Foundations and Geologic Site Hazards

4.1 Scope

This chapter sets forth general requirements for 

consideration of foundation load-deformation 

characteristics, seismic rehabilitation of foundations, 

and mitigation of geologic site hazards in the 

Systematic Rehabilitation of buildings.

Section 4.2 specifies data collection for site 

characterization and defines geologic site hazards. 

Section 4.3 outlines procedures for mitigation of 

geologic site hazards. Section 4.4 provides soil strength 

and stiffness parameters for consideration of foundation 

load-deformation characteristics. Section 4.5 specifies 

seismic earth pressures on building walls. Section 4.6 

specifies requirements for seismic rehabilitation of 

foundations. 

4.2 Site Characterization

Site characterization shall include collection of 

information on the building foundation as specified in 

Section 4.2.1, and on seismic geologic site hazards as 

specified in Section 4.2.2.

4.2.1 Foundation Information

Information on the foundation supporting the building 

to be rehabilitated, nearby foundation conditions, 

design foundation loads, and load-deformation 

characteristics of the foundation soils shall be obtained 

as specified in Sections 4.2.1.1 through 4.2.1.3.

4.2.1.1 Foundation Conditions

4.2.1.1.1 Structural Foundation Information

The following structural information shall be obtained 

for the foundation of the building to be rehabilitated:

1. Foundation type.

2. Foundation configuration, including dimensions, 

locations, depth of embedment of shallow 

foundations, pile tip elevations, and variations in 

cross-section along the length of pile or belled 

caissons.

3. Material composition and details of construction.

4.2.1.1.2 Subsurface Soil Conditions

The following information on subsurface soil 

conditions shall be obtained as required by the selected 

performance level:

C4.1 Scope

This chapter provides geotechnical engineering 

provisions for building foundations and seismicgeologic site hazards. Acceptability of the behavior of 

the foundation system and foundation soils for a given 

performance level cannot be determined apart from the 

context of the behavior of the superstructure.

Geotechnical requirements for buildings that are 

suitable for Simplified Rehabilitation are included in 

Chapter 10. Structural engineering issues of foundation 

systems are discussed in the chapters on Steel and Cast 

Iron (Chapter 5), Concrete (Chapter 6), Masonry 

(Chapter 7), and Wood and Light Metal Framing 

(Chapter 8).

C4.2 Site Characterization

The guidance of the State Historic Preservation Officer 

should be obtained if historic or archeological 

resources are present at the site.

C4.2.1.1.1 Structural Foundation Information

Foundation types may consist of shallow isolated or 

continuous spread footings, mat foundations, deep 

foundations of driven piles, or cast-in-place concrete 

piers or drilled shafts of concrete.

Foundation material types include concrete, steel, and 

wood. Foundation installation methods include cast-inplace and open/closed-end driving.

With this minimum amount of information, 

presumptive or prescriptive procedures may be used to 

determine the ultimate bearing capacity of the 

foundations. However, additional information is 

required for site-specific assessments of foundation 

bearing capacity and stiffness. Acquiring this 

additional information involves determining unit 

weights, shear strength, friction angle, compressibility 

characteristics, soil moduli, and Poisson’s ratio.
4-2 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

1. For Collapse Prevention and Life Safety 

Performance Levels, the type, composition, 

consistency, relative density, and layering of soils 

shall be determined to a depth at which the stress 

imposed by the building is less than or equal to 10% 

of the building weight divided by the total 

foundation area. For buildings with friction piles, the 

depth so calculated shall be increased by two-thirds 

of the pile length. For end bearing piles, the depth of 

investigation shall be the pile length plus 10 feet.

2. The location of the water table and its seasonal 

fluctuations beneath the building shall be 

determined.

3. For enhanced rehabilitation objectives, the soil unit 

weight, γ; soil cohesion, c; soil friction angle, φ; soil 

compressibility characteristics, soil shear modulus, 

G; and Poisson’s ratio, ν, for each type, shall be 

determined.

4.2.1.2 Design Foundation Loads

Information on the design foundation loads shall be 

obtained including separate information on dead loads 

and live loads.

4.2.1.3 Load-Deformation Characteristics 

Under Seismic Loading

Load-deformation characteristics of foundations shall 

be obtained from geotechnical reports, or shall be 

determined in accordance with the requirements of 

Section 4.4.

4.2.2 Seismic Geologic Site Hazards

Seismic rehabilitation shall include an assessment of 

earthquake-induced hazards at the site due to fault 

rupture, liquefaction, differential compaction, 

landsliding, and an assessment of earthquake-induced 

flooding or inundation in accordance with 

Sections 4.2.2.1 through 4.2.2.5.

If the resulting ground movements cause unacceptable 

performance in the building for the selected 

performance level, then the hazards shall be mitigated 

in accordance with Section 4.3.

4.2.2.1 Fault Rupture

A geologic fault shall be defined as a plane or zone 

along which earth materials on opposite sides have 

moved differentially in response to tectonic forces.

Geologic site information shall be obtained to 

determine if an active geologic fault is present under the 

building foundation. If a fault is present, the following 

information shall be obtained:

C4.2.1.1.2 Subsurface Soil Conditions

Specific foundation information developed for an 

adjacent or nearby building may be useful if subsurface 

soils and ground water conditions in the site region are 

known to be uniform. However, less confidence will 

result if subsurface data are developed from anywhere 

but the site of the building being rehabilitated. 

Adjacent sites where construction has been done 

recently may provide a guide for evaluation of 

subsurface conditions at the site being considered.

Design drawings may indicate information regarding 

the allowable bearing capacity of the foundation 

elements. This information can be used directly in a 

presumptive or prescriptive evaluation of the 

foundation capacity. Construction records may also be 

available indicating ultimate pile capacities if load tests 

were performed. Information on the existing loads on 

the structure is relevant to determining the amount of 

overload that the foundations may be capable of 

resisting during an earthquake.

C4.2.1.3 Load-Deformation Characteristics 

Under Seismic Loading

Traditional geotechnical engineering treats loaddeformation characteristics for long-term dead loads 

plus frequently applied live loads only. In most cases, 

long-term settlement governs foundation design. 

Short-term (earthquake) load-deformation 

characteristics have not traditionally been used for 

design; consequently, such relationships are not 

generally found in the geotechnical reports for existing 

buildings.
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-3

1. The degree of activity based on the age of most 

recent movement.

2. The fault type; whether it is a strike-slip, normalslip, reverse-slip, or thrust fault.

3. The sense of slip with respect to building geometry.

4. Magnitudes of vertical and/or horizontal 

displacements consistent with the selected 

earthquake hazard level.

5. The width and distribution of the fault-rupture zone. 

4.2.2.2 Liquefaction

Liquefaction shall be defined as an earthquake-induced 

process in which saturated, loose, granular soils lose 

shear strength and liquefy as a result of an increase in 

pore-water pressure during earthquake shaking.

Subsurface soil and ground water information shall be 

obtained to determine if liquefiable materials are 

present under the building foundation. If liquefiable 

soils are present, the following information shall be 

obtained: soil type, soil density, depth to water table, 

ground surface slope, proximity of free-face conditions, 

and lateral and vertical differential displacements. 

A site shall be regarded as free from liquefaction hazard 

if the site soils, or similar soils in the site vicinity, have 

not experienced historical liquefaction, and if any of the 

following criteria are met:

1. The geologic materials underlying the site are either 

bedrock or have a very low liquefaction 

susceptibility according to the relative susceptibility 

ratings based upon the type of deposit and geologic 

age of the deposit, as shown in Table 4-1.

2. The soils underlying the site are stiff clays or clayey 

silts.

3. The soils are not highly sensitive, based on local 

experience.

4. The soils are cohesionless with a minimum 

normalized Standard Penetration Test (SPT) 

resistance, N1 60, value of 30 blows/foot as defined 

in ASTM D1586-99, for depths below the ground 

water table, or with clay content greater than 20%.

5. The ground water table is at least 35 feet below the 

deepest foundation depth, or 50 feet below the 

ground surface, whichever is shallower, including 

considerations for seasonal and historic groundwater level rises, and any slopes or free-face 

conditions in the site vicinity do not extend below 

the ground water elevation at the site.

If a liquefaction hazard is determined to exist at the site, 

then a more detailed evaluation of potential ground 

movements due to liquefaction shall be performed using 

approved procedures.

C4.2.2.1 Fault Rupture

Buildings found to straddle active faults should be 

assessed to determine if any rehabilitation is 

warranted, possibly to reduce the collapse potential of 

the structure given the likely amount and direction of 

fault displacement.
4-4 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Table 4-1 Estimated Susceptibility to Liquefaction of Surficial Deposits During Strong Ground Shaking

Type of Deposit

General Distribution 

of Cohesionless

Sediments in

Deposits

Likelihood that Cohesionless Sediments, When Saturated,

Would be Susceptible to Liquefaction (by Age of Deposit)

Modern

< 500 yr.

Holocene

< 11,000 yr.

Pleistocene

< 2 million yr.

Pre-Pleistocene

> 2 million yr.

(a) Continental Deposits

River channel

Flood plain

Alluvial fan, plain

Marine terrace

Delta, fan delta

Lacustrine, playa

Colluvium

Talus

Dune

Loess

Glacial till

Tuff

Tephra

Residual soils

Sebka

Locally variable

Locally variable

Widespread

Widespread

Widespread

Variable

Variable

Widespread

Widespread

Variable

Variable

Rare

Widespread

Rare

Locally variable

Very high

High

Moderate

—

High

High

High

Low

High

High

Low

Low

High

Low

High

High

Moderate

Low

Low

Moderate

Moderate

Moderate

Low

Moderate

High

Low

Low

Low

High

Moderate

Low

Low

Low

Very low

Low

Low

Low

Very low

Low

High

Very low

Very low

Unknown

Very low

Low

Very low

Very low

Very low

Very low

Very low

Very low

Very low

Very low

Very low

Unknown

Very low

Very low

Unknown

Very low

Very low

(b) Coastal Zone Deposits

Delta

Esturine

Beach, high energy

Beach, low energy

Lagoon

Foreshore

Widespread

Locally variable

Widespread

Widespread

Locally variable

Locally variable

Very high

High

Moderate

High

High

High

High

Moderate

Low

Moderate

Moderate

Moderate

Low

Low

Very low

Low

Low

Low

Very low

Very low

Very low

Very low

Very low

Very low

(c) Fill Materials

Uncompacted fill

Compacted fill

Variable

Variable

Very high

Low

—

—

—

—

—

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Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-5

C4.2.2.2 Liquefaction

Soil liquefaction is a phenomenon in which a soil 

below the ground-water table loses a substantial 

amount of strength due to strong earthquake ground 

shaking. Recently deposited (i.e., geologically young) 

and relatively loose natural soils and uncompacted or 

poorly compacted fill soils are potentially susceptible 

to liquefaction. Loose sands and silty sands are 

particularly susceptible; loose silts and gravels also 

have potential for liquefaction. Dense natural soils and 

well-compacted fills have low susceptibility to 

liquefaction. Clay soils are generally not susceptible, 

except for highly sensitive clays found in some 

geographic regions.

The following information may be necessary for 

evaluating the liquefaction potential of soils.

1. Soil type: Whether liquefiable soils—i.e., granular 

(sand, silty sand, nonplastic silt) soils—are present.

2. Soil density: Whether liquefiable soils are loose to 

medium dense.

3. Depth to water table: Whether liquefiable soils are 

saturated at any time during seasonal fluctuations of 

the water table.

4. Ground surface slope and proximity of free-face 

conditions: Whether liquefiable soils are at a 

gently sloping site or in the proximity of freesurface conditions.

5. Lateral and vertical differential displacement: 

Amount and direction at the building foundation 

should be calculated.

Seed-Idriss Procedure for Evaluating Liquefaction 

Potential The potential for liquefaction to occur may 

be assessed by a variety of available approaches 

(National Research Council). The most commonly 

utilized approach is the Seed-Idriss simplified 

empirical procedure—presented by Seed and Idriss 

(1971, 1982) and updated by Seed et al. (1985) and 

Seed and Harder (1990)—that utilizes SPT blow count 

data. Using SPT data to assess liquefaction potential 

due to an earthquake is considered a reasonable 

engineering approach (Seed and Idriss, 1982; Seed et 

al., 1985; National Research Council), because many 

of the factors affecting penetration resistance affect the 

liquefaction resistance of sandy soils in a similar way, 

and because these liquefaction potential evaluation 

procedures are based on actual performance of soil 

deposits during worldwide historical earthquakes. 

More guidance for evaluating liquefaction potential is 

contained in Section C4.2.2.2 of FEMA 274.

Evaluating Potential for Lateral Spreading. Lateral 

spreads are ground-failure phenomena that can occur 

on gently sloping ground underlain by liquefied soil. 

Earthquake ground shaking affects the stability of 

sloping ground containing liquefiable materials by 

seismic inertia forces within the slope and by shakinginduced strength reductions in the liquefiable 

materials. Temporary instability due to seismic inertia 

forces is manifested by lateral “downslope” movement 

that can potentially involve large land areas. For the 

duration of ground shaking associated with moderate 

to large earthquakes, there could be many such 

occurrences of temporary instability, producing an 

accumulation of “downslope” movement. The 

resulting movements can range from a few inches or 

less to tens of feet, and are characterized by breaking 

up of the ground and horizontal and vertical offsets.
4-6 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Various relationships for estimating lateral spreading 

displacement have been proposed, including the 

Liquefaction Severity Index (LSI) by Youd and 

Perkins (1978), a relationship incorporating slope and 

liquefied soil thickness by Hamada et al. (1986), a 

modified LSI approach presented by Baziar et al. 

(1992), and a relationship by Bartlett and Youd (1992), 

in which they characterize displacement potential as a 

function of earthquake and local site characteristics 

(e.g., slope, liquefaction thickness, and grain size 

distribution). The relationship of Bartlett and Youd 

(1992), which is empirically based on analysis of case 

histories where lateral spreading did and did not occur, 

is relatively widely used, especially for initial 

assessments of the hazard. More site-specific analyses 

can also be made based on slope stability and 

deformation analysis procedures using undrained 

residual strengths for liquefied sand (Seed and Harder, 

1990; Stark and Mesri, 1992), along with either 

Newmark-type simplified displacement analyses 

(Newmark, 1965; Franklin and Chang, 1977; Makdisi 

and Seed, 1978; Yegian et al., 1991) or more complex 

deformation analysis approaches.

Evaluating Potential for Flow Slides. Flow generally 

occurs in liquefied materials found on steeper slopes 

and may involve ground movements of hundreds of 

feet or more. As a result, flow slides can be the most 

catastrophic of the liquefaction-related ground-failure 

phenomena. Fortunately, flow slides occur much less 

commonly than lateral spreads. Whereas lateral 

spreading requires earthquake inertia forces to create 

instability for movement to occur, flow movements 

occur when the gravitational forces acting on a ground 

slope exceed the strength of the liquefied materials 

within the slope. The potential for flow sliding can be 

assessed by carrying out static slope stability analyses 

using undrained residual strengths for the liquefied 

materials.

Evaluating Potential for Bearing Capacity Failure. 

The occurrence of liquefaction in soils supporting 

foundations can result in bearing capacity failures and 

large plunging-type settlements. In fact, the buildup of 

pore water pressures in a soil to less than a complete 

liquefaction condition will still reduce soil strength and 

may threaten bearing capacity if the strength is reduced 

sufficiently.

The potential for bearing capacity failure beneath a 

spread footing depends on the depth of the liquefied (or 

partially liquefied) layer below the footing, the size of 

the footing, and the load. If lightly loaded small 

footings are located sufficiently above the depth of 

liquefied materials, bearing capacity failure may not 

occur. The foundation bearing capacity for a case 

where a footing is located some distance above a 

liquefied layer can be assessed by evaluating the 

strength of the liquefied (excess pore pressure ratio = 

1.0), partially liquefied and nonliquefied strata, then 

applying bearing capacity formulations for layered 

systems (Meyerhof, 1974; Hanna and Meyerhof, 1980; 

Hanna, 1981). The capacity of friction pile or pier 

foundations can be similarly assessed, based on the 

strengths of the liquefied, partially liquefied, and 

nonliquefied strata penetrated by the foundations.

Evaluating Potential for Liquefaction-Induced 

Settlements. Following the occurrence of liquefaction, 

over time the excess pore water pressures built up in 

the soil will dissipate, drainage will occur, and the soil 

will densify, manifesting at the ground surface as 

settlement. Differential settlements occur due to lateral 

variations in soil stratigraphy and density. Typically, 

such settlements are much smaller and tend to be more 

uniform than those due to bearing capacity failure. 

They may range from a few inches to a few feet at the 

most where thick, loose soil deposits liquefy.

One approach to estimating the magnitude of such 

ground settlement, analogous to the Seed-Idriss 

simplified empirical procedure for liquefaction 

potential evaluation (i.e., using SPT blow count data 

and cyclic stress ratio), has been presented by 

Tokimatsu and Seed (1987). Relationships presented 

by Ishihara and Yoshimine (1992) are also available 

for assessing settlement.

Evaluating Increased Lateral Earth Pressures on 

Building Walls. Liquefaction of soils adjacent to 

building walls increases lateral earth pressures which 

can be approximated as a fluid pressure having a unit 

weight equal to the saturated unit weight of the soil 

plus the inertial forces on the soil equal to the 

hydrodynamic pressure.
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-7

4.2.2.3 Differential Compaction

Differential compaction shall be defined as an 

earthquake-induced process in which foundation soils 

compact and the foundation settles in a nonuniform 

manner across a site.

Subsurface soil information shall be obtained to 

determine if soils susceptible to differential compaction 

are present under the building foundation.

A site shall be regarded as free of a differential 

compaction hazard if the soil conditions meet both of 

the following criteria:

1. Geologic materials below the ground water table do 

not pose a liquefaction hazard, based on the criteria 

in Section 4.2.2.2.

2. Geologic deposits above the ground water table are 

either Pleistocene in geologic age (older than 11,000 

years), stiff clays or clayey silts, or cohesionless 

sands, silts, and gravels with a minimum (N I)60 of 

20 blows/0.3 m (20 blows/foot).

If a differential compaction hazard is determined to 

exist at the site, then a more detailed evaluation shall be 

performed using approved procedures.

4.2.2.4 Landsliding

A landslide shall be defined as the down-slope mass 

movement of earth resulting from any cause. 

Subsurface soil information shall be obtained to 

determine if soils susceptible to a landslide that will 

cause differential movement of the building foundation 

are present at the site.

Slope stability shall be evaluated at sites with:

1. Existing slopes exceeding 18 degrees (three 

horizontal to one vertical).

2. Prior histories of instability (rotational or 

translational slides, or rock fall).

Use of pseudo-static analyses shall be permitted to 

determine slope stability if the soils are not susceptible 

to liquefaction based on Section 4.2.2.2 or otherwise 

expected to lose shear strength during deformation. If 

soils are susceptible to liquefaction based on 

Section 4.2.2.2 or otherwise expected to lose shear 

strength during deformation, dynamic analyses shall be 

performed to determine slope stability.

Evaluating Potential for Flotation of Buried 

Structures. A common phenomenon accompanying 

liquefaction is the flotation of tanks or structures that 

are embedded in liquefied soil. A building with a 

basement surrounded by liquefied soil can be 

susceptible to either flotation or bearing capacity 

failure, depending on the building weight and the 

structural continuity (i.e., whether the basement acts as 

an integral unit). The potential for flotation of a buried 

or embedded structure can be evaluated by comparing 

the total weight of the buried or embedded structure 

with the increased uplift forces occurring due to the 

buildup of liquefaction-induced pore water pressures.

C4.2.2.3 Differential Compaction

Differential compaction or densification of soils may 

accompany strong ground shaking. The resulting 

differential settlements can be damaging to structures. 

Types of soil susceptible to liquefaction (that is, 

relatively loose natural soils, or uncompacted or poorly 

compacted fill soils) are also susceptible to 

compaction. Compaction can occur in soils above and 

below the ground-water table.

Situations most susceptible to differential compaction 

include heavily graded areas where deep fills have 

been placed to create building sites for development. If 

the fills are not well compacted, they may be 

susceptible to significant settlements, and differential 

settlements may occur above variable depths of fill 

placed in canyons and near the transitions of cut and 

filled areas.
4-8 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Pseudo-static analyses shall use a seismic coefficient 

equal to SXS /5, to approximate one-half the peak 

ground acceleration at the site associated with the 

selected Rehabilitation Objective. Sites with a static 

factor of safety equal to or greater than 1.0 shall be 

judged to have adequate stability, and require no further 

stability analysis.

A sliding-block displacement analysis shall be 

performed for sites with a static factor of safety of less 

than 1.0. The displacement analysis shall determine the 

magnitude of ground movement and its effect upon the 

performance of the structure.

In addition to the effects of landslides that directly 

undermine the building foundation, the effects of rock 

fall or slide debris from adjacent slopes shall be 

evaluated using approved procedures.

4.2.2.5 Flooding or Inundation

For seismic rehabilitation of buildings for performance 

levels higher than Life Safety, site information shall be 

obtained to determine if the following sources of 

earthquake-induced flooding or inundation are present:

1. Dams located upstream, subject to damage by 

earthquake shaking or fault rupture.

2. Pipelines, aqueducts, and water storage tanks 

located upstream, subject to damage by fault 

rupture, earthquake-induced landslides, or strong 

shaking.

3. Coastal areas within tsunami zones or areas adjacent 

to bays or lakes, subject to seiche waves.

4. Low-lying areas with shallow ground water, subject 

to regional subsidence and surface ponding of water, 

resulting in inundation of the site.

Damage to buildings from earthquake-induced flooding 

or inundation shall be evaluated for its effect upon the 

performance of the structure.

In addition to the effects of earthquake-induced 

flooding or inundation, scour of building foundation 

soils from swiftly flowing water shall be evaluated 

using approved procedures.

4.3 Mitigation of Seismic-Geologic 

Site Hazards

Mitigation of seismic-geologic hazards identified in 

Section 4.2 shall be accomplished through modification 

of the structure, foundation, soil conditions, or other 

approved methods. 

C4.2.2.4 Landsliding

If no blocks of rock are present at the site but a cliff or 

steep slope is located nearby, then the likely 

performance of the cliff under earthquake loading 

should be evaluated. The earthquake loading condition 

for cliff performance must be compatible with the 

earthquake loading condition selected for the 

Rehabilitation Objective for the building.

Some sites may be exposed to hazards from major 

landslides moving onto the site from upslope, or 

retrogressive removal of support from downslope. 

Such conditions should be identified during site 

characterization, and may pose special challenges if 

adequate investigation requires access to adjacent 

property.

C4.3 Mitigation of Seismic-Geologic 

Site Hazards

Opportunities exist to improve seismic performance 

under the influence of some site hazards at reasonable 

cost; however, some site hazards may be so severe that 

they are economically impractical to include in riskreduction measures. The discussions presented in this 

section are based on the concept that the extent of site 

hazards is discovered after the decision for seismic 

rehabilitation of a building has been made; however, 

the decision to rehabilitate a building and the selection 

of a Rehabilitation Objective may have been made 

with full knowledge that significant site hazards exist 

and must be mitigated as part of the rehabilitation.

Possible mitigation strategies for seismic geologic site 

hazards are presented in the following sections.
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-9

1. Fault Rupture. If the structural performance of a 

building evaluated for the calculated ground movement 

due to fault rupture during earthquake fails to comply 

with the requirements for the selected performance 

level, mitigation schemes should be employed that 

include one or more of the following measures to 

achieve acceptable performance: stiffening of the 

structure and/or its foundation; strengthening of the 

structure and/or its foundation; and modifications to 

the structure and/or its foundation to distribute the 

effects of differential vertical movement over a greater 

horizontal distance to reduce angular distortion.

Large movements caused by fault rupture generally 

cannot be mitigated economically. If the structural 

consequences of the estimated horizontal and vertical 

displacements are unacceptable for any performance 

level, either the structure, its foundation, or both, might 

be stiffened or strengthened to reach acceptable 

performance. Measures are highly dependent on 

specific structural characteristics and inadequacies. 

Grade beams and reinforced slabs are effective in 

increasing resistance to horizontal displacement. 

Horizontal forces are sometimes limited by sliding 

friction capacity of spread footings or mats. Vertical 

displacements are similar in nature to those caused by 

long-term differential settlement.

2. Liquefaction. If the structural performance of a 

building evaluated for the calculated ground movement 

due to liquefaction during an earthquake fails to 

comply with the requirements for the selected 

performance level, then one or more of the following 

mitigation measures should be implemented to achieve 

acceptable performance.

2.1 Modification of the Structure. The structure should 

be strengthened to improve resistance against the 

predicted liquefaction-induced ground deformation.

This solution may be feasible for small ground 

deformations.

2.2 Modification of the Foundation. The foundation 

system should be modified to reduce or eliminate the 

differential foundation displacements by underpinning 

existing shallow foundations to achieve bearing on 

deeper, nonliquefiable strata or by stiffening a shallow 

foundation system by a system of grade beams 

between isolated footings, or any other approved 

method.

2.3 Modification of the Soil Conditions. One or more 

of the following ground improvement techniques 

should be implemented to reduce or eliminate the 

liquefaction under existing buildings: soil grouting 

(either throughout the entire liquefiable strata beneath 

a building, or locally beneath foundation elements); 

installation of drains; or installation of permanent 

dewatering systems.

Other types of ground improvement widely used for 

new construction are less applicable to existing 

buildings because of the effects of the procedures on 

the building. Thus, removal and replacement of 

liquefiable soil or in-place densification of liquefiable 

soil by various techniques are not applicable beneath 

an existing building.

2.4 Mitigation of the Lateral Spreading. Large soil 

volumes should be stabilized and/or buttressing 

structures should be constructed.

If the potential for significant liquefaction-induced 

lateral spreading movements exists at a site, then the 

mitigation of the liquefaction hazard may be more 

difficult. This is because the potential for lateral 

spreading movements beneath a building may depend 

on the behavior of the soil mass at distances well 

beyond the building as well as immediately beneath it.

3. Differential Compaction. If the structural 

performance of a building evaluated for the calculated 

differential compaction during earthquake fails to 

comply with the requirements for the selected 

performance level, then one or more mitigation 

measures similar to those recommended for 

liquefaction should be implemented to achieve 

acceptable performance.

4. Landslide. If the structural performance of a 

building evaluated for the calculated ground movement 

due to landslide during earthquake fails to comply with 

the requirements for the selected performance level, 

then one or more of the following mitigation measures 

should be implemented to achieve acceptable 

performance:

1. Regrading.

2. Drainage.

3. Buttressing.
4-10 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

4.4 Foundation Strength and 

Stiffness

Foundation strength and stiffness shall be determined in 

accordance with this section.

4. Structural Improvements:

a. Gravity walls.

b. Tieback/soil nail walls.

c. Mechanically stabilized earth walls.

d. Barriers for debris torrents or rock fall.

e. Building strengthening to resist deformation.

f. Grade beams.

g. Shear walls.

5. Soil Modification/Replacement:

a. Grouting.

b. Densification.

5. Flooding or Inundation. If the structural 

performance of a building evaluated for the effects of 

earthquake-induced flooding and inundation fails to 

comply with the requirements for the selected 

performance level, then one or more of the following 

mitigating measures should be implemented to achieve 

acceptable performance:

1. Improvement of nearby dam, pipeline, or aqueduct 

facilities independent of the rehabilitated building.

2. Diversion of anticipated peak flood flows.

3. Installation of pavement around the building to 

reduce scour.

4. Construction of sea wall or breakwater for tsunami 

or seiche protection.

C4.4 Foundation Strength and 

Stiffness

It is assumed that foundation soils are not susceptible 

to significant strength loss due to earthquake loading. 

In general, soils have considerable ductility unless they 

degrade significantly in stiffness and strength under 

cyclic loading. With this assumption, the provisions of 

this section provide an overview of the requirements 

and procedures for evaluating the ability of 

foundations to withstand the imposed seismic loads 

without excessive deformations.

The amount of acceptable deformations for 

foundations in such soils depends primarily on the 

effect of the deformation on the structure, which in 

turn depends on the desired Structural Performance 

Level. However, foundation yield associated with 

mobilization at upper bound expected capacity during 

earthquake loading may be accompanied by 

progressive permanent foundation settlement during 

continued cyclic loading, albeit in most cases this 

settlement probably would be less than a few inches. In 

general, if the real loads transmitted to the foundation 

during earthquake loading do not exceed upper bound 

expected soil capacities, it can be assumed that 

foundation deformations will be relatively small.

Parametric analyses to cover uncertainties in soil loaddeformation characteristics are required. One 

alternative is to perform the NSP or NDP because the 

nonlinear load-deformation characteristics of the 

foundations can be directly incorporated in these 

analyses (Section 4.4.2). In static analyses, a somewhat 

conservative interpretation of the results is 

recommended because cyclic loading effects cannot be 

incorporated directly.
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-11

4.4.1 Expected Capacities of Foundations

The expected capacity of foundation components shall 

be determined by presumptive, prescriptive, or sitespecific methods as specified in Sections 4.4.1.1 

through 4.4.1.3. Capacities shall be based on foundation 

information obtained as specified in Section 4.2.1.

4.4.1.1 Presumptive Capacities

4.4.1.1.1 Presumptive Capacities of Shallow 

Foundations

Calculation of presumptive expected capacities for 

spread footings and mats shall be permitted using the 

parameters specified in Table 4-2.

4.4.1.1.2 Presumptive Capacities of Deep 

Foundations

1. Capacities of Piles or Piers in Granular Soils

Calculation of presumptive expected capacities of piles 

or piers in granular soils shall be permitted using the 

procedure shown in Figure 4-1.

2. Capacities of Piles or Piers in Cohesive Soils

Calculation of presumptive expected capacities of piles 

or piers in cohesive soils shall be permitted using the 

procedure shown in Figure 4-2. 

C4.4.1 Expected Capacities of Foundations

Design values recommended by geotechnical 

engineers are generally consistent with lower bound 

values. It is important to obtain information on the 

actual factor of safety applied to arrive at design values 

so that ultimate soil capacities are understood and 

expected values can be properly derived.

C4.4.1.1.2 Presumptive Capacities of Deep 

Foundations

The calculation procedures for presumptive expected 

capacities of piles or piers specified in this section are 

adapted from ATC-40 and NAVFAC (1986a and 

1986b).

Table 4-2 Parameters for Calculating Presumptive Expected Foundation Load Capacities of 

Spread Footings and Mats

Class of Materials2

Vertical Foundation

Pressure3

Lbs/Sq. Ft. (qc)

Lateral Bearing 

Pressure 

Lbs/Sq. Ft./Ft of

Depth Below 

Natural Grade4

Lateral Sliding1

Coefficient5 Resistance6

Lbs/Sq. Ft

Massive Crystalline Bedrock 8000 2400 0.80 —

Sedimentary and Foliated Rock 4000 800 0.70 —

Sandy Gravel and/or Gravel (GW 

and GP)

4000 400 0.70 —

Sand, Silty Sand, Clayey Sand, Silty 

Gravel, and Clayey Gravel (SW, SP, 

SM, SC, GM, and GC)

3000 300 0.50 —

Clay, Sandy Clay, Silty Clay, and 

Clayey Silt (CL, ML, MH, and CH) 20007 200 — 260

1. Lateral bearing and lateral sliding resistance shall be permitted to be combined.

2. For soil classifications OL, OH, and PT (i.e., organic clays and peat), a foundation investigation shall be required.

3. All values of expected bearing capacities are for footings having a minimum width of 12 inches and a minimum depth of 12 inches into natural grade. 

Except where Footnote 7 applies, an increase of 20% is allowed for each additional foot of width or depth to a maximum value of three times the designated 

value.

4. Shall be permitted to be increased by the amount of the designated value for each additional foot of depth to a maximum of 15 times the designated value.

5. Coefficient applied to the dead load.

6. Lateral sliding resistance value to be multiplied by the contact area. In no case shall the lateral sliding resistance exceed one-half of the dead load.

7. No increase for width shall be permitted.
4-12 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Downward Capacity

Qc (-) = 

Upward Capacity

Qc (+) = 

where:

B = Pile or pier diameter

L0 = 3B for use with high values of Fdi or Fui

= 5B for use with low values of Fdi or Fui

Pi = Effective vertical stress at depth i

Pc = Effective vertical stress Pi

 at depth L0 + 20B

Pt = Effective vertical stress Pi

 at tip or at i=t

Nq = Bearing capacity factor (see Table 4-3)

At = Bearing area at tip

Fdi = Effective horizontal stress factor for downward load (see Table 4-4)

Fui = Effective horizontal stress factor for upward load (see Table 4-4)

δi = Friction angle between pile/pier at soil depth i (see Table 4-5)

as = Surface area of pile/pier per unit length

Figure 4-1 Presumptive Expected Capacities of Piles or Piers in Granular Soils

PtNqAt FdiPi δiasLi tan

i = 1

t – 1

+ ∑

FuiPi δiasLi tan

i = 1

t – 1

∑

Pi Ljγj Pc ≤

j = 0

i

= ∑
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-13

Downward Capacity

Qc (-) = 

Upward Capacity

Qc (+) = 

where:

B = Pile or pier diameter

L0 = 4B

ct = Cohesion strength of soil at tip (see Table 4-6)

Nc = Bearing capacity factor = 9.0 for L > 4B

= 9L/4B for L < L0

At = Bearing area at tip

cai = Adhesion strength of soil (see Table 4-6) at depth i

as = Surface area of pile/pier per unit length

Figure 4-2 Presumptive Expected Capacities of Piles or Piers in Cohesive Soils

ctNcAt caiasLi

i = 1

t

+ ∑

caiasLi

i = 1

t

∑
4-14 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

4.4.1.2 Prescriptive Expected Capacities

Prescriptive expected capacities shall be used when 

construction documents or previous geotechnical 

reports for the existing building are available and 

provide information on foundation soil design 

parameters. Calculation of prescriptive expected 

capacities by the following methods shall be permitted.

1. The prescriptive expected bearing capacity, qc, for a 

spread footing shall be calculated using Equation 

(4-1).

(4-1)

where:

2. For deep foundations, the prescriptive expected 

vertical capacity, Qc, of individual piles or piers 

shall be calculated using Equation (4-2).

(4-2)

where:

3. Alternatively, the prescriptive expected capacity, qc

or Qc, of any foundation, shallow or deep, shall be 

calculated using Equation (4-3).

(4-3)

where QG = gravity load action as specified in 

Section 3.2.8, expressed in terms of pressure or load.

Table 4-3 Typical Pile and Pier Capacity Parameters: Bearing Capacity Factors, Nq

Placement

Angle of Shearing Resistance for Soil, φ (degrees)

26 28 30 31 32 33 34 35 36 37 38 39 40+

Driven pile 10 15 21 24 29 35 42 50 62 77 86 120 145

Drilled pier 5 8 10 12 14 17 21 25 30 38 43 60 72

Table 4-4 Typical Pile and Pier Capacity 

Parameters: Effective Horizontal 

Stress Factors, Fdi and Fui

Pile or Pier Type

Downward Fdi Upward Fui

low high low high

Driven H-pile 0.5 1.0 0.3 0.5

Driven straight 

prismatic pile

1.0 1.5 0.6 1.0

Driven tapered pile 1.5 2.0 1.0 1.3

Driven jetted pile 0.4 0.9 0.3 0.6

Drilled pier 0.7 0.7 0.4 0.4

Table 4-5 Typical Pile and Pier Capacity 

Parameters: Friction Angle, 

δ (degrees)

Pile or Pier Material δ

Steel 20

Concrete 0.75 φ

Timber 0.75 φ

qallow = Allowable bearing pressure specified in 

available documents for the gravity load 

design of shallow foundations (dead plus 

live loads)

Qallow = Allowable vertical capacity specified in 

available documents for the gravity load 

design of deep foundations (dead plus live 

loads)

qc 3qallow =

Qc 3Qallow =

qc or Qc 1.5QG =
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-15

4.4.1.3 Site-Specific Capacities

For buildings where the methods specified in 

Sections 4.4.1.1 and 4.4.1.2 do not apply, a subsurface 

geotechnical investigation shall be conducted to 

determine expected ultimate foundation capacities 

based on the specific characteristics of the building site.

4.4.2 Load-Deformation Characteristics for 

Foundations

If building foundations are explicitly modeled in the 

mathematical model of the building, the loaddeformation characteristics shall be calculated in 

accordance with Section 4.4.2.1 for shallow bearing 

foundations, Section 4.4.2.2 for pile foundations, and 

Section 4.4.2.3 for drilled shafts.

For explicit modeling of other types of foundations, 

load deformation characteristics shall be calculated by 

an approved method.

Nonlinear behavior of foundations shall be represented 

by an equivalent elasto-plastic load-deformation 

relationship unless another approved relationship is 

available.

Building analyses, including load-deformation 

characteristics of foundations, shall be bounded by 

upper and lower bound assumptions of stiffness and 

capacity as illustrated in Figure 4-3a and defined in this 

section. In lieu of an explicit evaluation of uncertainties 

of the foundation characteristics, it shall be permitted to 

take the respective upper and lower bound stiffness and 

strength values as twice-and-one-half the values given 

in this section. 

Table 4-6 Typical Pile and Pier Capacity Parameters: Cohesion, ct, and Adhesion, ca (psf)

Pile Material

Consistency of Soil

(approximately STP blow count)

Cohesion, ct Adhesion, ca

low high low high

Timber and Concrete Very soft (<2) 0 250 0 250

Soft (2–4) 250 500 250 480

Medium stiff (4–8) 500 1000 480 750

Stiff (8–15) 1000 2000 750 950

Very stiff (>15) 2000 4000 950 1300

Steel Very soft (<2) 0 250 0 250

Soft (2–4) 250 500 250 460

Medium stiff (4–8) 500 1000 460 700

Stiff (8–15) 1000 2000 700 720

Very stiff (>15) 2000 4000 720 750

C4.4.2 Load-Deformation Characteristics 

for Foundations

Load-deformation characteristics are required where 

the effects of foundations are to be taken into account 

in Linear Static or Dynamic Procedures (LSP or 

LDP), Nonlinear Static (pushover) Procedures (NSP), 

or Nonlinear Dynamic (time-history) Procedures 

(NDP). Foundation load-deformation parameters 

characterized by both stiffness and capacity can have 

a significant effect on both structural response and 

load distribution among structural elements.

While it is recognized that the load-deformation 

behavior of foundations is nonlinear, an equivalent 

elasto-plastic representation of load-deformation 

behavior is recommended because of the difficulties 

in determining soil properties and the likely 

variability of soils supporting foundations. In 

addition, to allow for such variability or uncertainty, 

an upper and lower bound approach to defining 

stiffness and capacity is required to evaluate the 

sensitivity of the structural response to these 

parameters.
4-16 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

The sources of this uncertainty include variations due 

to rate of loading, assumed elasto-plastic soil 

behavior, level of strain, cyclic loading, and 

variability of soil properties. These sources of 

variability produce results that are generally within a 

factor of two above or below the expected value. It is 

conceivable that certain conditions will fall outside 

the bounds prescribed in this standard. However, it is 

not the objective to guarantee that the answer is 

always within the applied factor. Instead, the intent is 

that 1) solution sensitivity be identified, and 2) that 

the bounds, considered reasonably, capture the 

expected behavior. Current practice (both 

conventional and within the nuclear industry) has 

suggested that variation by a factor of two is generally 

appropriate. Geotechnical engineers often use a safety 

factor of two to establish lower bound values for use 

in design. Consistent with the approach taken in 

ASCE 4, if additional testing is performed, the range 

could be narrowed to that defined by multiplying and 

dividing by (1+Cv), where the coefficient of variation, 

Cv , is defined as the standard deviation divided by the 

mean. In no case should Cv be taken to be less than 

0.5.

It is important that geotechnical engineers report the 

average results obtained and the actual factor of safety 

applied to arrive at design values. The design values 

recommended by geotechnical engineers are generally 

consistent with the lower bound. If such reduced 

values were used by the structural engineer as 

expected values, the application of the prescribed 

upper and lower bound variations would not achieve 

the intended aim.

1. Consideration of Foundation Rocking: Buildings 

may rock on their foundations in an acceptable 

manner provided the structural components can 

accommodate the resulting displacements and 

deformations. Consideration of rocking can be used to 

limit the force input to a building; however, rocking 

should not be considered simultaneously with the 

effects of soil flexibility.

The design professional is directed to FEMA 274 and 

the work of Yim and Chopra (1985), Housner (1963), 

Makris and Roussos (1998), and Priestly and Evison 

(1978) for additional information on rocking behavior.

A possible procedure for considering rocking is 

outlined in Figure C4-1. The procedure involves the 

following steps:

• Calculation of the mass, weight, and center of 

gravity for the rocking system (or subsystem);

• Calculation of the soil contact area, center of 

contact, and rocking system dimension, R;

• Determination of whether rocking will initiate;

• Calculation of the effective viscious damping of 

the rocking system (and the corresponding design 

displacement spectrum);

• Calculation (graphically or iteratively) of the 

period and amplitude of rocking (the solution will 

not converge if overturning will occur—that is, 

when . θ α >
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-17

,

Figure C4-1 Outline Procedure for Consideration of Rocking Behavior

Mass, weight, and center of gravity

Note that, in general, the mass and weight will not be consistent with each 

other. The mass, M, is the total seismic mass tributary to the wall. The weight, 

W, is the vertical gravity load reaction. For the purposes of these calculations, 

the vertical location of the center of gravity is taken at the vertical center of the 

seismic mass and the horizontal location of the center of gravity is taken at the 

horizontal center of the applied gravity loads.

Soil contact area and center of contact

The soil contact area is taken as W/qc. The wall rocks about point O located at 

the center of the contact area.

Wall rocking potential

Determine whether the wall will rock by comparing the overturning moment to 

the restoring moment. For this calculation, Sa is based on the fundamental, 

elastic (no-rocking) period of the wall. The wall will rock if 

Sa > (W/Mg)tan α. If rocking is not indicated, discontinue these calculations.

Rocking calculations

Calculate IO, the mass moment of inertia of the rocking system about point O.

Calculate the effective viscous damping, β, of the rocking system as follows:

 where 

Construct the design response spectrum at this level of effective damping using the procedure defined in 

Section 1.6.1.5. By iteration or graphical methods, solve for the period and displacement that simultaneously 

satisfy the design response spectrum and the following rocking period equation:

 where 

Also recall that 

At the desired solution, 

β = 0.4( ) 1 – r r 1 MR2

IO

– -----------( ) 1 2 – cos( ) α

2

=

T 4

WR

IO

--------

------------- –1 cosh 1

1 θ

α– ---

------------

       

= θ

δrocking

Rcosα = -------------------

Sd Sag

T2

4π

2 = --------

δrocking Sd =
4-18 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

4.4.2.1 Shallow Bearing Foundations

4.4.2.1.1 Stiffness Parameters

The initial shear modulus, Go, shall be calculated in 

accordance with Equation (4-4) or (4-5) where vs is the 

shear wave velocity at low strains, γ is the weight 

density of the soil, and g is the acceleration due to 

gravity.

(4-4)

(4-5)

where:

Go in Equation (4-5) is expressed in pounds per square 

foot, as is .

The effective shear modulus, G, shall be calculated in 

accordance with Table 4-7. 

Based on relative stiffnesses of the foundation structure 

and the supporting soil, the foundation stiffness shall be 

calculated using one of the following three methods.

= Standard Penetration Test blow count 

normalized for an effective stress of 1.0 

ton per square foot confining pressure and 

corrected to an equivalent hammer energy 

efficiency of 60%

= Effective vertical stress in psf

=

γt = Total unit weight of soil

γw = Unit weight of water

d = Depth to sample

dw = Depth to ground-water level

Go

γvs

2

g = -------

Go 20 000 N1 ( )60

1 3⁄ σ ′o ≅ ,

N1 ( )60

σ ′o

σ ′o γtd γw d dw – ( ) –

σ ′o

Table 4-7 Effective Shear Modulus Ratio

(G/G0)

Site Class

Effective Peak Acceleration, SXS/2.5

SXS/2.5

=0

SXS/2.5

=0.1

SXS/2.5

=0.4

SXS/2.5

=0.8

A 1.00 1.00 1.00 1.00

B 1.00 1.00 0.95 0.90

C 1.00 0.95 0.75 0.60

D 1.00 0.90 0.50 0.10

E 1.00 0.60 0.05 *

F ****

Note: Use straight-line interpolation for intermediate values of SXS/2.5.

* Site-specific geotechnical investigation and dynamic site response 

analyses shall be performed.

C4.4.2.1.1 Stiffness Parameters

Table 4-7 is consistent with the site classification 

Tables 1-4 and 1-5 in that the layout and level of 

complexity is identical, and the indication of problem 

soils that require site-specific investigation (Site Class 

F) is consistent. The following observations on the 

relationship between shear modulus reduction and 

peak ground acceleration can be made:

1. As the peak ground acceleration approaches zero, 

the modulus reduction factor approaches unity,

2. Modulus reduction effects are significantly more 

pronounced for softer soils, and

3. The modulus reduction factors given in both 

FEMA 273 and the FEMA 302 NEHRP 

Recommended Provisions overestimate the 

modulus reduction effects for Site Classes A, B, 

and C.
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-19

4.4.2.1.2 Method 1

For shallow bearing footings that are rigid with respect 

to the supporting soil, an uncoupled spring model, as 

shown in Figure 4-3(b), shall represent the foundation 

stiffness.

The equivalent spring constants shall be calculated as 

specified in Figure 4-4. 

The shears and moments in foundation elements are 

conservative when such elements are considered rigid. 

However, soil pressures may be significantly 

underestimated when foundation flexibility is ignored. 

The flexibility and nonlinear response of soil and of 

foundation structures should be considered when the 

results would change.

For beams on elastic supports (for instance, strip 

footings and grade beams) with a point load at 

midspan, the beam may be considered rigid when:

(C4-1)

The above equation is generally consistent with 

traditional beam-on-elastic foundation limits 

(NAVFAC, 1986b; Bowles, 1988). The resulting soil 

bearing pressures are within 3% of the results, 

including foundation flexibility.

For rectangular plates (with plan dimensions L and B, 

and thickness t, and mechanical properties Ef and vf) on 

elastic supports (for instance, mat foundations or 

isolated footings) subjected to a point load in the 

center, the foundation may be considered rigid when:

(C4-2)

where:

 (C4-3)

The above equation is based on Timoshenko’s 

solutions for plates on elastic foundations 

(Timoshenko, 1959). The general solution has been 

simplified by restriction to a center load. Only the first 

five values of m and n (in the infinite series) are 

required to achieve reasonable accuracy.

EI

L4 ----- 2

3

--ksv > B

4ksv

m = 1

5

∑

sin 2 m ⋅ π

2 -----------     sin 2 n ⋅ π2

----------    

π

4

Df

m2

L2 ------ n

2

B2 + -----

      2

ksv +

-------------------------------------------------------------- < 0.03

n = 1

5

∑

Df

Ef t

3

12 1 νf ( ) – 2 = ------------------------------

Figure 4-3 (a) Idealized Elasto-Plastic LoadDeformation Behavior for Soils

(b) Uncoupled Spring Model for 

Rigid Footings
4-20 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Figure 4-4 Elastic Solutions for Rigid Footing Spring Constraints

Degree of Freedom Stiffness of Foundation at Surface Note

Translation along x-axis

Orient axes such that L > B

Translation along y-axis

Translation along z-axis

Rocking about x-axis

Rocking about y-axis

Torsion about z-axis

Kx sur ,

GB

2 – v ----------- 3.4 L

B

---     0.65

= + 1.2

Ky sur ,

GB

2 – v ----------- 3.4 L

B

---     0.65

0.4L

B = + + --- 0.8

Kz sur ,

GB

1 – v ----------- 1.55 L

B

---     0.75

= + 0.8

Kxx sur ,

GB3

1 – v ----------- 0.4 L

B

---     = + 0.1

Kyy sur ,

GB3

1 – v ----------- 0.47 L

B

---     2.4

= + 0.034

Kzz sur , GB3 0.53 L

B

---     2.45

= + 0.51

Degree of Freedom Correction Factor for Embedment Note

Translation along x-axis

d = height of effective sidewall 

contact (may be less than total 

foundation height)

h = depth to centroid of effective 

sidewall contact

For each degree of freedom, 

calculate 

Kemb = Ksur

Translation along y-axis

Translation along z-axis

Rocking about x-axis

Rocking about y-axis

Torsion about z-axis

βx 1 0.21 D

B

+ ---     1 1.6 hd B L ( ) +

BL2 ------------------------     0.4

= ⋅ +

β

βy βx =

βz 1 1

21

-----D

B

--- 2 2.6B

L

+ ---     + 1 0.32 dB L ( ) +

BL ---------------------     2 3⁄

= ⋅ +

βxx 1 2.5 d

B

--- 1 2d

B

----- d

D

---     –0.2 B

L = + + ---

βyy 1 1.4 d

L

--     0.6

1.5 3.7 d

L

--     1.9 d

D

---     –0.6

= + +

βzz 1 2.6 1 B

L

+ ---     d

B

---     0.9

= +
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-21

C4.4.2.1.2 Method 1

Researchers have developed spring stiffness solutions 

that are applicable to any solid basemat shape on the 

surface of, or partially or fully embedded in, a 

homogeneous halfspace (Gazetas). Rectangular 

foundations are most common in buildings. Therefore, 

the general spring stiffness solutions were adapted to 

the general rectangular foundation problem, which 

includes rectangular strip footings.

Using Figure 4-4, a two step calculation process is 

required. First, the stiffness terms are calculated for a 

foundation at the surface. Then, an embedment 

correction factor is calculated for each stiffness term. 

The stiffness of the embedded foundation is the 

product of these two terms. Figure C4-2 illustrates the 

effects of foundation aspect ratio and embedment.

According to Gazetas, the height of effective sidewall 

contact, d, should be taken as the average height of the 

sidewall that is in good contact with the surrounding 

soil. It should, in general, be smaller than the nominal 

height of contact to account for such phenomena as 

slippage and separation that may occur near the ground 

surface. Note that d will not necessarily attain a single 

value for all modes of oscillation. When d is taken 

larger than zero, the resulting stiffness includes 

sidewall friction and passive pressure contributions

Although frequency-dependent solutions are available, 

results are reasonably insensitive to loading 

frequencies within the range of parameters of interest 

for buildings subjected to earthquakes. It is sufficient 

to use static stiffnesses as representative of repeated 

loading conditions. Other formulations incorporating a 

wider range of variables may be found in Gazetas and 

Lam, et al.
4-22 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Figure C4-2 (a) Foundation Shape Effect

(b) Foundation Embedment Effect

Embedment Effect

(L/B = 2; d = D/2)

1.0

1.5

2.0

2.5

3.0

3.5

0 0.2 0.4 0.6 0.8 1

D/B

β

x, y

z

xx

yy

zz

Shape Effect

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1 2 3 4 5 6 7 8 9 10

L/B

Normalized Stiffness

x

y

z

xx

yy

zz
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-23

4.4.2.1.3 Method 2

For shallow bearing foundations that are not rigid with 

respect to the supporting soils, a finite element 

representation of linear or nonlinear foundation 

behavior using Winkler models shall be used. 

Distributed vertical stiffness properties shall be 

calculated by dividing the total vertical stiffness by the 

area. Uniformly distributed rotational stiffness 

properties shall be calculated by dividing the total 

rotational stiffness of the footing by the moment of 

inertia of the footing in the direction of loading. Vertical 

and rotational stiffnesses shall be decoupled for a 

Winkler model. It shall be permitted to use the 

procedure illustrated in Figure 4-5 to decouple these 

stiffnesses.

C4.4.2.1.3 Method 2

The stiffness per unit length in these end zones is based 

on the vertical stiffness of a B x B/6 isolated footing. 

The stiffness per unit length in the middle zone is 

equivalent to that of an infinitely long strip footing.

Figure 4-5 Vertical Stiffness Modeling for Shallow Bearing Footings

y

x

y

x

Plan

L

(length)

B

(width)

B/6 End zone each side

Soil components

K1

l

1 l

5 l4 l

3 l

2

K5

K2 K3 K4

Component stiffnesses:

Ki = l

i k

where k is the appropriate

stiffness per unit length for

the end zone or middle zone

Stiffness per unit length:

kend = for B/6 end zones

kmid = for middle zone

Section

kmid kend kend

End zone Middle zone End zone

0.73 G

1 -

6.83 G

1 -
4-24 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

4.4.2.1.4 Method 3

For shallow bearing foundations that are flexible 

relative to the supporting soil, based on approved 

theoretical solutions for beams or plates on elastic 

supports, the foundation stiffness shall be permitted to 

be calculated by a decoupled Winkler model using a 

unit subgrade spring coefficient. For flexible foundation 

systems, the unit subgrade spring coefficient, ksv , shall 

be calculated by Equation (4-6).

(4-6)

where:

4.4.2.1.5 Capacity Parameters

The vertical expected capacity of shallow bearing 

foundations shall be determined using the procedures of 

Section 4.4.1.

In the absence of moment loading, the expected vertical 

load capacity, Qc, of a rectangular footing shall be 

calculated by Equation (4-7).

(4-7)

where:

The moment capacity of a rectangular footing shall be 

calculated by Equation (4-8):

(4-8)

where:

The lateral capacity of shallow foundations shall be 

calculated using established principles of soil 

mechanics and shall include the contributions of 

traction at the bottom and passive pressure resistance on 

the leading face. Mobilization of passive pressure shall 

be calculated using Figure 4-6. 

G = Shear modulus

B = Width of footing

= Poisson’s ratio

qc = Expected bearing capacity determined in 

Section 4.4.1

B = Width of footing

L = Length of footing

P = Vertical load on footing

q = = vertical bearing pressure

ksv

1.3G

B( ) 1 – ν = --------------------

ν

Qc qc = BL

Mc

LP

2

------- 1 q

qc

– ----     =

P

BL

------

B = Width of footing (parallel to the axis of 

bending)

L = Length of footing in the direction of bending

qc = Expected bearing capacity determined in 

Section 4.4.1

C4.4.2.1.5 Capacity Parameters

For rigid footings subject to moment and vertical load, 

contact stresses become concentrated at footing edges, 

particularly as uplift occurs. The ultimate moment 

capacity, Mc, is dependent upon the ratio of the vertical 

load stress, q, to the expected bearing capacity, qc. 

Assuming that contact stresses are proportional to 

vertical displacement and remain elastic up to the 

expected bearing capacity, qc, it can be shown that 

uplift will occur prior to plastic yielding of the soil 

when q/qc is less than 0.5. If q/qc is greater than 0.5, 

then the soil at the toe will yield prior to uplift. This is 

illustrated in Figure C4-3.

For footings subjected to lateral loads, the base traction 

strength is given by V = C + N ; where C is the 

effective cohesion force (effective cohesion stress, c, 

times footing base area), N is the normal (compressive) 

force and μ is the coefficient of friction. If included, 

side traction is calculated in a similar manner. The 

coefficient of friction is often specified by the 

geotechnical consultant. In the absence of such a 

recommendation, may be based on the minimum of 

the effective internal friction angle of the soil and the 

friction coefficient between soil and foundation from 

published foundation references. The ultimate passive 

pressure strength is often specified by the geotechnical 

consultant in the form of passive pressure coefficients 

or equivalent fluid pressures. The passive pressure 

problem has been extensively investigated for more 

than 200 years. As a result, countless solutions and 

recommendations exist. The method used should, at a 

minimum, include the contributions of internal friction 

and cohesion, as appropriate.

μ

μ
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-25

4.4.2.2 Pile Foundations

A pile foundation shall be defined as a deep foundation 

system composed of one or more driven or cast-in-place 

piles and a pile cap cast-in-place over the piles, which 

together form a pile group supporting one or more loadbearing columns, or a linear sequence of pile groups 

supporting a shear wall.

The requirements of this section shall apply to piles less 

than or equal to 24 inches in diameter. The stiffness 

characteristics of single large-diameter piles or drilled 

shafts larger than 24 inches in diameter shall comply 

with the requirements of Section 4.4.2.3.

4.4.2.2.1 Stiffness Parameters

The uncoupled spring model shown in Figure 4-3(b) 

shall be used to represent the stiffness of a pile 

foundation where the footing in the figure represents the 

pile cap. In calculating the vertical and rocking springs, 

the contribution of the soil immediately beneath the pile 

cap shall be neglected. The total lateral stiffness of a 

pile group shall include the contributions of the piles 

(with an appropriate modification for group effects) and 

the passive resistance of the pile cap. The lateral 

stiffness of piles shall be based on classical methods or 

on analytical solutions using approved beam-column 

pile models. The lateral stiffness contribution of the pile 

cap shall be calculated using the passive pressure 

mobilization curve in Figure 4-6.

Pile group axial spring stiffness values, ksv, shall be 

calculated using Equation (4-9).

(4-9)

where: 

The rocking spring stiffness values about each 

horizontal pile cap axis shall be computed by modeling 

each pile axial spring as a discrete Winkler spring. The 

rotational spring constant, ksr , (moment per unit 

rotation) shall be calculated using Equation (4-10).

(4-10)

where: 

4.4.2.2.2 Capacity Parameters

The axial load capacity of piles in compression and 

tension shall be determined using the procedures in 

Section 4.4.1. The axial capacity in tension shall not 

exceed the tensile load capacity of the pile cap and 

splice connections.

As shown in Figure 4-6, the force-displacement 

response associated with passive pressure resistance is 

highly nonlinear. However, for shallow foundations, 

passive pressure resistance generally accounts for 

much less than half of the total strength. Therefore, it is 

adequate to characterize the nonlinear response of 

shallow foundations as elastic-perfectly plastic using 

the initial, effective stiffness and the total expected 

strength. The actual behavior is expected to fall within 

the upper and lower bounds prescribed in this standard.

ksv

A E

L

---------

n = 1

N

= ∑

A = Cross-sectional area of a pile

E = Modulus of elasticity of piles

L = Length of piles

N = Number of piles in group

kvn = Axial stiffness of the nth pile

Sn = Distance between nth pile and axis of rotation.

C4.4.2.2.1 Stiffness Parameters

As the passive pressure resistance may be a significant 

part of the total strength, and deep foundations often 

require larger lateral displacements than shallow 

foundations to mobilize the expected strength, it may 

not be appropriate to base the force-displacement 

response on the initial, effective stiffness alone. 

Instead, the contribution of passive pressure should be 

based on the passive pressure mobilization curve 

provided in Figure 4-6.

Although the effects of group action and the influence 

of pile batter are not directly accounted for in the form 

of the above equations, it can be reasonably assumed 

that the latter effects are accounted for in the range of 

uncertainties that must be considered in accordance 

with Section 4.4.1.

ksr kvnSn

2

n = 1

N

= ∑
4-26 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

The moment capacity of a pile group shall be 

determined assuming a rigid pile cap. Lower-bound 

moment capacity shall be based on triangular 

distribution of axial pile loading and lower-bound axial 

capacity of the piles. Upper-bound moment capacity 

shall be based on a rectangular distribution of axial pile 

load using full, upper-bound axial capacity of the piles.

The lateral capacity of a pile group shall include the 

contributions of the piles (with an appropriate 

modification for group effects) and the passive 

resistance of the pile cap. The lateral capacity of the 

piles shall be calculated using the same method used to 

calculate the stiffness. The lateral capacity of the pile 

cap, due to passive pressure, shall be calculated using 

established principles of soil mechanics. Passive 

pressure mobilization shall be calculated using Figure 

4-6. 

C4.4.2.2.2 Capacity Parameters

The lateral capacity of a pile cap should be calculated 

in the same way that the capacity of a shallow 

foundation is computed, except that the contribution of 

base traction should be neglected. Section C4.4.2.1.5 

provides a more detailed description of the calculation 

procedure.

Figure 4-6 Passive Pressure Mobilization Curve

Passive Pressure Mobilization Curve

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.00 0.01 0.02 0.03 0.04 0.05 0.06

δ/H

P/Pult

Based on NAVFAC, 1986b.

P = Mobilized Passive Pressure

Pult =Ultimate Passive Pressure

 = Lateral displacement

H = Thickness of Footing

δ
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-27

4.4.2.3 Drilled Shafts

The stiffness and capacity of drilled shaft foundations 

and piers of diameter less than or equal to 24 inches 

shall be calculated using the requirements for pile 

foundations specified in 4.4.2.2. For drilled shaft 

foundations and piers of diameter greater than 24 

inches, the capacity shall be calculated based on the 

interaction of the soil and shaft where the soil shall be 

represented using Winkler type models specified in 

Section 4.4.2.2. 

4.4.3 Foundation Acceptability Criteria

The foundation soil shall comply with the acceptance 

criteria specified in this section. The structural 

components of foundations shall meet the appropriate 

requirements of Chapters 5 through 8. The foundation 

soil shall be evaluated to support all actions, including 

vertical loads, moments, and lateral forces applied to 

the soil by the foundation.

4.4.3.1 Simplified Rehabilitation

The foundation soil of buildings for which the 

Simplified Rehabilitation Method is selected in 

accordance with Section 2.3.1 shall comply with the 

requirements of Chapter 10.

4.4.3.2 Linear Procedures

The acceptance criteria for foundation soil analyzed by 

linear procedures shall be based on the modeling 

assumptions for the base of the structure specified in 

Section 4.4.3.2.1 or 4.4.3.2.2.

4.4.3.2.1 Fixed Base Assumption

If the base of the structure is assumed to be completely 

rigid, the geotechnical components shall be classified as 

deformation-controlled. Component actions shall be 

determined by Equation (3-18). Acceptance criteria 

shall be based on Equation (3-20), m-factors for 

geotechnical components shall not exceed 3, and the 

use of upper-bound component capacities shall be 

permitted. A fixed base assumption shall not be used for 

buildings being rehabilitated to the Immediate 

Occupancy Performance Level that are sensitive to base 

rotations or other types of foundation movement.

Figure C4-3 Idealized Concentration of Stress at Edge of Rigid Footings Subjected to Overturning Moment

P

P

P

P

P

P

q

q

qc

qc

qc

qc

< 0.5 q

cq

> 0.5 q

cq

M

M

M c

M c

C4.4.2.3 Drilled Shafts

When the diameter of the shaft becomes large (> 24 

inches), the bending and the lateral stiffness and 

strength of the shaft itself may contribute to the overall 

capacity. This is obviously necessary for the case of 

individual shafts supporting isolated columns.
4-28 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

If the alternative overturning method described in 

Section 3.2.10.1 is used, the geotechnical components 

shall be classified as force-controlled. Component 

actions shall not exceed the calculated capacities and 

upper-bound component capacities shall not be used.

4.4.3.2.2 Flexible Base Assumption

If the base of the structure is assumed to be flexible and 

modeled using linear geotechnical components, then the 

geotechnical components shall be classified as 

deformation-controlled. Component actions shall be 

determined by Equation (3-18). Soil strength need not 

be evaluated. Acceptability of soil displacements shall 

be based on the ability of the structure to accommodate 

these displacements within the acceptance criteria for 

the selected Rehabilitation Objective.

4.4.3.3 Nonlinear Procedures

The acceptance criteria for geotechnical components 

analyzed by nonlinear procedures shall be based on the 

modeling assumptions for the base of the structure 

specified in Section 4.4.3.3.1 or 4.4.3.3.2.

4.4.3.3.1 Fixed Base Assumption

If the base of the structure is assumed to be completely 

rigid, then the base reactions for all geotechnical 

components shall be classified as force-controlled, as 

determined by Equation (3-19), and shall not exceed 

upper-bound component capacities. A fixed base 

assumption shall not be used for buildings being 

rehabilitated for the Immediate Occupancy 

Performance Level that are sensitive to base rotations or 

other types of foundation movement.

4.4.3.3.2 Flexible Base Assumption

If the base of the structure is assumed to be flexible and 

modeled using flexible nonlinear geotechnical 

components, then the geotechnical components shall be 

classified as deformation-controlled and the 

displacements at the base of the structure shall not 

exceed the acceptance criteria of this section. For the 

Life Safety and Collapse Prevention Structural 

Performance Levels, acceptability of soil displacements 

shall be based on the ability of the structure to 

accommodate these displacements within the 

acceptance criteria for the selected Rehabilitation 

Objective. For the Immediate Occupancy Structural 

Performance Level, the permanent, nonrecoverable 

displacement of the geotechnical components shall be 

calculated by an approved method based on the 

maximum total displacement, foundation and soil type, 

thickness of soil layers, and other pertinent factors. The 

acceptability of these displacements shall be based upon 

the ability of the structure to accommodate them within 

the acceptance criteria for the Immediate Occupancy 

Structural Performance Level.

4.5 Seismic Earth Pressure

Building walls retaining soil shall be evaluated to resist 

additional earth pressure due to seismic forces. Unless 

otherwise determined from a site-specific geotechnical 

investigation, the seismic earth pressure acting on a 

building wall retaining nonsaturated, level soil above 

the ground water table shall be calculated using 

Equation (4-11):

(4-11)

where:

∆p = Additional earth pressure due to seismic 

shaking, which is assumed to be a uniform 

pressure

kh = Horizontal seismic coefficient in the soil, 

which may be assumed equal to SXS /2.5

γt = Total unit weight of soil

Hrw = Height of the retaining wall

SXS = Spectral response acceleration parameter as 

specified in Section 1.6

∆p 0.4khγtHrw =
Chapter 4: Foundations and Geologic 

Site Hazards

FEMA 356 Seismic Rehabilitation Prestandard 4-29

The seismic earth pressure shall be added to the 

unfactored static earth pressure to obtain the total earth 

pressure on the wall. The wall shall be evaluated as a 

force-controlled component using acceptance criteria 

based on the type of wall construction and approved 

methods.

4.6 Foundation Rehabilitation

Foundation rehabilitation schemes shall be evaluated in 

conjunction with any rehabilitation of the superstructure 

and according to the general principles and 

requirements of this standard to assure that the complete 

rehabilitation achieves the selected building 

performance level for the selected earthquake hazard 

level. When new rehabilitation elements are used in 

conjunction with existing elements, the effects of 

differential foundation stiffness on the modified 

structure shall be demonstrated to meet the acceptance 

criteria. If existing loads are not redistributed to all the 

elements of rehabilitated foundation by shoring and/or 

jacking, the effects of differential strengths and 

stiffnesses among individual foundation elements shall 

be included in the analysis of the rehabilitated 

foundation. The effects of rehabilitation on stiffness, 

strength, and deformability shall be taken into account 

in an analytical model of the rehabilitated structure. The 

compatibility of new and existing components and/or 

elements shall be checked at displacements consistent 

with the performance level chosen. 

C4.5 Seismic Earth Pressure

Past earthquakes have not caused extensive damage to 

building walls below grade. In some cases, however, it 

is advisable to verify the adequacy of retaining walls to 

resist increased pressure due to seismic loading. These 

situations include walls of poor construction quality, 

unreinforced or lightly reinforced walls, walls of 

archaic materials, unusually tall or thin walls, damaged 

walls, or other conditions implying a sensitivity to 

increased loads.

The expression in Equation (4-11) is a simplified 

approximation of the Mononobe-Okabe formulation. 

The actual magnitude and distribution of pressure on 

walls during earthquakes is very complex. If walls do 

not have the apparent capacity to resist the pressures 

estimated from the above approximate procedures, 

detailed investigation by a qualified geotechnical 

engineer is recommended.

Seismic earth pressures calculated in accordance with 

this section are intended for use in checking 

acceptability of local wall components and should not 

be used to increase total base shear on the building.

C4.6 Foundation Rehabilitation

Guidance for modification of foundations to improve 

seismic performance is provided below.

1. Soil Material Improvements. Improvement in 

existing soil materials may be effective in the 

rehabilitation of foundations by achieving one or more 

of the following results: (a) improvement in vertical 

bearing capacity of footing foundations, (b) increase in 

the lateral frictional resistance at the base of footings, 

(c) and increase in the passive resistance of the soils 

adjacent to foundations or grade beams.
4-30 Seismic Rehabilitation Prestandard FEMA 356

Chapter 4: Foundations and Geologic 

Site Hazards

Soil improvement options to increase the vertical 

bearing capacity of footing foundations are limited. 

Soil removal and replacement and soil vibratory 

densification usually are not feasible because they 

would induce settlements beneath the footings or be 

expensive to implement without causing settlement. 

Grouting may be considered to increase bearing 

capacity. Different grouting techniques are discussed 

in FEMA 274 Section C4.3.2. Compaction grouting 

can achieve densification and strengthening of a 

variety of soil types and/or extend foundation loads to 

deeper, stronger soils. The technique requires careful 

control to avoid causing uplift of foundation elements 

or adjacent floor slabs during the grouting process. 

Permeation grouting with chemical grouts can achieve 

substantial strengthening of sandy soils, but the more 

fine-grained or silty the sand, the less effective the 

technique becomes. Jet grouting could also be 

considered. These same techniques also may be 

considered to increase the lateral frictional resistance at 

the base of footings.

Soil improvement by the following methods may be 

effective in increasing the passive resistance of soils 

adjacent to foundations or grade beams; removal and 

replacement of existing soils with stronger, wellcompacted soils or with treated (e.g., cementstabilized) soils; in-place mixing of existing soils with 

strengthening materials (e.g., cement); grouting, 

including permeation grouting and jet grouting; and inplace densification by impact or vibratory compaction. 

In-place densification by impact or vibratory 

compaction should be used only if the soil layers to be 

compacted are not too thick and vibration effects on 

the structure are tolerable.

2. Shallow Foundation Rehabilitation. The following 

measures may be effective in the rehabilitation of 

shallow foundations:

2.1 New isolated or spread footings may be added to 

existing structures to support new structural elements 

such as shear walls or frames.

2.2 Existing isolated or spread footings may be 

enlarged to increase bearing or uplift capacity. 

Consideration of existing contact pressures on the 

strength and stiffness of the modified footing may be 

required unless uniform distribution is achieved by 

shoring and/or jacking.

2.3 Existing isolated or spread footings may be 

underpinned to increase bearing or uplift capacity. 

Underpinning improves bearing capacity by lowering 

the contact horizon of the footing. Consideration of the 

effects of jacking and load transfer may be required.

2.4 Uplift capacity may be improved by increasing the 

resisting soil mass above the footing.

2.5 Mitigation of differential lateral displacement of 

different portions of a building foundation may be 

carried out by provision of interconnection with grade 

beams, reinforced grade slab or ties.

3. Deep Foundation Rehabilitation. The following 

measures may be effective in the rehabilitation of deep 

foundation consisting of driven piles made of steel, 

concrete, or wood, or cast-in-place concrete piers, or 

drilled shafts of concrete.

3.1 Shallow foundation of spread footings or mats may 

be provided to support new shear walls or frames or 

other new elements of the lateral force-resisting 

system, provided the effects of differential foundation 

stiffness on the modified structure are analyzed and 

meet the acceptance criteria.

3.2 New wood piles may be provided for an existing 

wood pile foundation. A positive connection should be 

provided to transfer the uplift forces from the pile cap 

or foundation above to the new wood piles. Existing 

wood piles should be inspected for deterioration 

caused by decay, insect infestation, or other signs of 

distress prior to undertaking evaluation of existing 

wood pile foundation.

3.3 Driven piles made of steel, concrete, or wood, or 

cast-in-place concrete piers or drilled shafts of 

concrete, may be provided to support new structural 

elements such as shear walls or frames.

3.4 Driven piles made of steel, concrete, or wood, or 

cast-in-place concrete piers or drilled shafts of 

concrete, may be provided to supplement the vertical 

and lateral capacities of existing pile and pier 

foundation groups.
FEMA 356 Seismic Rehabilitation Prestandard 5-1

5. Steel

5.1 Scope

This chapter sets forth requirements for the Systematic 

Rehabilitation of steel lateral-force-resisting elements 

within a building. The requirements of this chapter shall 

apply to existing steel components of a building system, 

rehabilitated steel components of a building system, and 

new steel components added to an existing building 

system.

Sections 5.2 and 5.3 specify data collection procedures 

for obtaining material properties and performing 

condition assessments. Section 5.4 specifies general 

requirements. Sections 5.5, 5.6, 5.7, and 5.8 provide 

modeling procedures, component strengths, acceptance 

criteria, and rehabilitation measures for steel momentresisting frame, steel braced frame, steel plate shear 

wall, and steel frame with infill structures. Section 5.9 

provides modeling procedures, strengths, acceptance 

criteria, and rehabilitation measures for diaphragms 

used in steel structures. Section 5.11 specifies 

requirements for steel piles. Section 5.11 specifies 

requirements for components of cast or wrought iron. 

5.2 Material Properties Based on 

Historical Information

Available construction documents and as-built 

information shall be obtained as specified in 

Section 2.2. Use of material properties based on 

historical information as default values shall be 

permitted as specified in Section 5.3.2.5.

5.3 Material Properties and 

Condition Assessment

5.3.1 General

Mechanical properties for steel materials and 

components shall be based on available construction 

documents and as-built conditions for the particular 

structure. Where such information fails to provide 

adequate information to quantify material properties or 

document the condition of the structure, such 

information shall be supplemented by material tests and 

assessments of existing conditions as required in 

Section 2.2.6.

Material properties of existing steel components shall 

be determined in accordance with Section 5.3.2. A 

condition assessment shall be conducted in accordance 

with Section 5.3.3. The extent of materials testing and 

condition assessment performed shall be used to 

determine the knowledge factor as specified in 

Section 5.3.4.

C5.1 Scope

Techniques for repair of earthquake-damaged steel 

components are not included in this standard. The 

design professional is referred to SAC publications 

FEMA 351 and FEMA 353 for information on design, 

evaluation, and repair of damaged steel moment 

resisting frame structures.

C5.2 Material Properties Based on 

Historical Information

Steel components of buildings include columns, 

beams, braces, connections, link beams, and 

diaphragms. Columns, beams, and braces may be built 

up with plates, angles, and/or channels connected 

together with rivets, bolts, or welds. The material used 

in older construction is likely to be mild steel with a 

specified yield strength between 30 ksi and 36 ksi. Cast 

iron was often used for columns in much older 

construction (before 1900). Cast iron was gradually 

replaced by wrought iron and then by steel. The 

connectors in older construction were usually mild 

steel rivets or bolts. These were later replaced by highstrength bolts and welds. The seismic performance of 

these components will depend heavily on the condition 

of the in-place material. A more detailed historical 

perspective is given in Section C5.2 of FEMA 274.

Great care should be exercised in selecting the 

appropriate rehabilitation approaches and techniques 

for application to historic buildings in order to preserve 

their unique characteristics.
5-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Use of default material properties shall be permitted in 

accordance with Section 5.3.2.5. 

5.3.2 Properties of In-Place Materials and 

Components

5.3.2.1 Material Properties

5.3.2.1.1 General

The following component and connection material 

properties shall be obtained for the as-built structure:

1. Yield and tensile strength of the base material.

2. Yield and tensile strength of the connection material.

3. Carbon equivalent of the base and connection 

material.

Structural steel components constructed after 1900 shall 

be classified based on ASTM specification and material 

grade and, if applicable, shape group in accordance with 

Table 5-2. Lower bound material properties shall be 

taken in accordance with Table 5-2 for material 

conforming to the specifications listed therein. For 

material grades not listed in Table 5-2, lower bound 

material properties shall be taken as nominal or 

specified properties, or shall be based on tests when the 

material grade or specified value is not known.

When materials testing is required by Section 2.2.6, test 

methods to determine ASTM designation and material 

grade or to quantify material properties shall be as 

specified in Section 5.3.2.3.

The minimum number of tests shall comply with the 

requirements of Section 5.3.2.4.

The carbon equivalent of the existing components shall 

be determined unless it is confirmed that the existing 

material provides suitable characteristics of weldability, 

by virtue of their conformance with a weldable material 

specification, or welding to existing components will 

not be performed as part of the rehabilitation. The 

welding procedures shall be determined based on the 

chemistry of the base material and filler material as 

specified in Section 8 of AWS D1.1. Material 

conforming to ASTM A36/A36M-00, ASTM A242/

A242M-00, ASTM A307-00, ASTM A572/572M-00, 

ASTM A913/A913M-00, and ASTM A972/A972M-00

shall be deemed to be weldable.

5.3.2.1.2 Nominal Properties

Nominal material properties, or properties specified in 

construction documents, shall be taken as lower bound 

material properties. Corresponding expected material 

properties shall be calculated by multiplying lowerbound values by an appropriate factor taken from Table 

5-3 to translate from lower bound to expected values.

Where construction documents indicate the ultimate 

tensile strength of weld metal, the lower-bound strength 

of welds shall be taken as indicated in AWS D1.1. For 

construction pre-dating 1970, use of a nominal ultimate 

tensile strength of 60 ksi shall be permitted. 

5.3.2.2 Component Properties

The following properties of components and their 

connections shall be obtained for the structure: 

1. Size and thickness of connected materials, including 

cover plates, bracing, and stiffeners.

C5.3.1 General

The extent of in-place materials testing and condition 

assessment that must be accomplished is related to 

availability and accuracy of construction and as-built 

records, the quality of materials used and construction 

performed, and the physical condition of the structure. 

Data such as the properties and grades of material used 

in component and connection fabrication may be 

effectively used to reduce the amount of in-place 

testing required. The design professional is encouraged 

to research and acquire all available records from 

original construction.

C5.3.2.1 Material Properties

Mechanical properties of component and connection 

material dictate the structural behavior of the 

component under load. Mechanical properties of 

greatest interest include the expected and lower bound 

estimates of yield (Fye) and tensile (Fte) strengths of 

base and connection material, modulus of elasticity, 

ductility, toughness, elongational characteristics, and 

weldability.

Expected material properties should be used for 

deformation-controlled actions. Lower bound material 

properties should be used for force-controlled actions 

in lieu of nominal strengths specified in the AISC

(1993) LRFD Specifications. 
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-3

2. Cross-sectional area, section moduli, moments of 

inertia, and torsional properties of components at 

critical sections.

3. As-built configuration of intermediate, splice, and 

end connections.

4. Current physical condition of base metal and 

connector materials, including presence of 

deformation and extent of deterioration.

Review of available construction documents shall be 

performed to identify primary vertical- and lateral-loadcarrying elements and systems, critical components and 

connections, and any modifications to components or 

overall configuration of the structure.

In the absence of deterioration, use of the nominal 

cross-sectional dimensions of components published by 

the American Institute of Steel Construction (AISC), 

the American Iron and Steel Institute (AISI), and other 

approved trade associations shall be permitted.

5.3.2.3 Test Methods to Quantify Properties

Laboratory testing of samples to determine in-place 

mechanical properties of materials and components 

shall be performed in compliance with consensus 

standards published by ASTM, the American National 

Standards Institute (ANSI), and other approved 

organizations.

The extent of in-place materials testing required to 

determine material properties shall be based on the 

availability of original and updated construction 

documents, original quality of construction, 

accessibility, and condition of materials.

The determination of material properties shall be 

accomplished through removal of samples and 

laboratory testing. Sampling shall take place in regions 

of reduced stress. If a connector such as a bolt or rivet is 

removed for testing, a comparable bolt shall be 

reinstalled at the time of sampling. Destructive removal 

of a welded connection sample shall be accompanied by 

repair of the connection.

Expected material properties shall be based on mean 

test values. Lower bound material properties shall be 

based on mean test values minus one standard deviation 

except that where the material is positively identified as 

conforming to a defined standard material specification, 

lower-bound properties need not be taken less than the 

nominal properties for that specification.

C5.3.2.3 Test Methods to Quantify Properties

FEMA 274 provides information and references for 

several test methods.

Sampling should take place in regions of reduced 

stress—such as flange tips at beam ends and external 

plate edges—to minimize the effects of reduced area.

Of greatest interest to steel building system 

performance are the expected yield and tensile strength 

of the installed materials. Notch toughness of structural 

steel and weld material is also important for 

connections that undergo cyclic loadings and 

deformations during earthquakes. Chemical and 

metallurgical properties can provide information on 

properties such as compatibility of welds with parent 

metal and potential lamellar tearing due to throughthickness stresses. Virtually all steel component elastic 

and inelastic limit states are related to yield and tensile 

strengths. Past research and accumulation of data by 

industry groups have resulted in published material 

mechanical properties for most primary metals and 

their date of fabrication. Section 5.3.2.5 provides 

default properties. This information may be used, 

together with tests from recovered samples, to rapidly 

establish expected strength properties for use in 

component strength and deformation analyses.

Review of other properties derived from laboratory 

tests—such as hardness, impact, fracture, and 

fatigue—is generally not needed for steel component 

capacity determination, but may be required for 

archaic materials and connection evaluation. These 

properties may not be needed in the analysis phase if 

significant rehabilitative measures are already known 

to be required.
5-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.3.2.4 Minimum Number of Tests

Materials testing is not required if material properties 

are available from original construction documents that 

include material test records or material test reports. If 

such properties differ from default material properties 

given in Tables 5-1 and 5-2, material properties for 

rehabilitation shall be selected such that the largest 

demands on components and connections are generated.

5.3.2.4.1 Usual Testing

The minimum number of tests to determine the yield 

and tensile strengths of steel materials for usual data 

collection shall be based on the following criteria:

1. If design drawings are incomplete or not available, 

at least one strength coupon from each steel 

component type shall be removed for testing, and 

one weld metal sample shall be obtained for testing.

2. If design drawings containing ASTM specification 

and material grade information are available, use of 

Table 5-2 to determine material properties shall be 

permitted without additional testing.

3. If design drawings containing material property 

information are available but the material properties 

are not listed in Table 5-2, use of nominal or 

specified material properties shall be permitted 

without additional testing.

5.3.2.4.2 Comprehensive Testing

The minimum number of tests to determine the yield 

and tensile strengths of steel materials for 

comprehensive data collection shall be based on the 

following criteria:

1. If original construction documents defining material 

properties are inconclusive or do not exist, but the 

date of construction is known and the material used 

is confirmed to be carbon steel, at least three 

strength coupons and three bolts and rivets shall be 

randomly removed from each component type. 

2. If no knowledge of the structural system and 

materials used exists, at least two tensile strength 

coupons and two bolts and rivets shall be removed 

from each component type for every four floors. If it 

is determined from testing that more than one 

material grade exists, additional sampling and 

testing shall be performed until the extent of each 

grade in component fabrication has been established.

3. In the absence of construction records defining 

welding filler metals and processes used, at least one 

weld metal sample for each construction type shall 

be obtained for laboratory testing. The sample shall 

consist of both local base and weld metal to 

determine composite strength of the connection.

4. For archaic materials, at least three strength coupons 

shall be extracted for each component type for every 

four floors of construction. If initial tests provide 

material properties that are consistent with 

properties given in Table 5-1, tests shall be required 

for every six floors of construction only. If these 

tests provide material properties that are 

nonuniform, additional tests shall be performed until 

the extent of different materials is established.

For other material properties, a minimum of three tests 

shall be conducted.

The results of any material testing performed shall be 

compared to the default values in Tables 5-1 and 5-2 for 

the particular era of building construction. The amount 

of testing shall be doubled if the expected and lowerbound yield and tensile strengths determined from 

testing are lower than the default values.

To quantify material properties and analyze the 

performance of welded moment connections, more 

extensive sampling and testing may be necessary. This 

testing may include base and weld material chemical 

and metallurgical evaluation, expected strength 

determination, hardness, and charpy V-notch testing of 

the heat-affected zone and neighboring base metal, and 

other tests depending on connection configuration.

Recommendations given in FEMA 351 may also be 

followed to select welding procedures for welding of 

rehabilitative measures to existing components.

C5.3.2.4 Minimum Number of Tests

In order to quantify expected strength and other 

properties accurately, a minimum number of tests may 

be required to be conducted on representative 

components.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-5

5.3.2.5 Default Properties

The default lower bound material properties for steel 

components shall be as specified in Tables 5-1 and 5-2. 

Default expected strength material properties shall be 

determined by multiplying lower-bound values by an 

appropriate factor taken from Table 5-3.

Use of default material properties to determine 

component and connection strengths shall be permitted 

in conjunction with the linear analysis procedures of 

Chapter 3. 

Material properties of structural steel vary much less 

than those of other construction materials. In fact, the 

expected yield and tensile stresses are usually 

considerably higher than the nominal specified values. 

As a result, testing for material properties of structural 

steel may not be required. The properties of wrought 

iron are more variable than those of steel. The strength 

of cast iron components cannot be determined from 

small sample tests, since component behavior is 

usually governed by inclusions and other 

imperfections.

If ductility and toughness are required at or near the 

weld, the design professional may conservatively 

assume that no ductility is available, in lieu of testing. 

In this case the joint would have to be modified if 

inelastic demands are anticipated and the possibility of 

fractures cannot be tolerated. Special requirements for 

welded moment frames are given in FEMA 351.

If a higher degree of confidence in results is desired, 

either the sample size shall be determined using ASTM 

E22 criteria, or the prior knowledge of material grades 

from Section 5.3.2.5 should be used in conjunction 

with approved statistical procedures.

Design professionals may consider using Bayesian 

statistics and other statistical procedures contained in 

FEMA 274 to gain greater confidence in the test results 

obtained from the sample sizes specified in this 

section.

Table 5-1 Default Lower-Bound Material Strengths for Archaic Materials1

Properties based on tables of allowable loads as published in mill catalogs

Year Material

Lower-Bound Yield 

Strength, ksi

Lower-Bound Tensile 

Strength, ksi

pre-1900 cast iron 18 —

pre-1900 steel 24 36

1. Modified from unit stress values in AISC “Iron and Steel Beams from 1873 to 1952.”
5-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Table 5-2 Default Lower-Bound Material Strengths1

Properties based on ASTM and AISC Structural Steel Specification Stresses

Date Specification Remarks Tensile Strength2, ksi

Yield Strength2, ksi

1900 ASTM, A9

Buildings

Rivet Steel

Medium Steel

50

60

30

35

1901–1908 ASTM, A9

Buildings

Rivet Steel

Medium Steel

50

60

25

30

1909–1923 ASTM, A9

Buildings

Structural Steel

Rivet Steel

55

46

28

23

1924–1931 ASTM, A7 Structural Steel 55 30

Rivet Steel 46 25

ASTM, A9 Structural Steel 55 30

Rivet Steel 46 25

1932 ASTM, A140-32T issued as a 

tentative revision to ASTM, A9 

(Buildings)

Plates, Shapes, Bars 60 33

Eyebar flats unannealed 67 36

1933 ASTM, A140-32T discontinued 

and ASTM, A9 (Buildings) 

revised Oct. 30, 1933

Structural Steel 55 30

ASTM, A9 tentatively revised to 

ASTM, A9-33T (Buildings)

Structural Steel 60 33

ASTM, A141-32T adopted as a 

standard 

Rivet Steel 52 28

1934 on ASTM, A9 Structural Steel 60 33

ASTM, A141 Rivet Steel 52 28

1961 – 1990 ASTM, A36/A36M-00

Group 1

Group 2

Group 3

Group 4

Group 5

Structural Steel

62

59

60

62

70

44

41

39

37

41

1961 on ASTM, A572, Grade 50

Group 1

Group 2

Group 3

Group 4

Group 5

Structural Steel

65

66

68

72

77

50

50

51

50

50

1990 on A36/A36M-00 & Dual Grade

Group 1

Group 2

Group 3

Group 4

Structural Steel

66

67

70

70

49

50

52

49

1. Lower-bound values for material prior to 1960 are based on minimum specified values. Lower-bound values for material after 1960 are mean minus one 

standard deviation values from statistical data.

2. The indicated values are representative of material extracted from the flanges of wide flange shapes.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-7

Table 5-3 Factors to Translate Lower-Bound Steel Properties to Expected-Strength Steel Properties

Property Year Specification Factor

Tensile Strength Prior to 1961 1.10

Yield Strength Prior to 1961 1.10

Tensile Strength 1961-1990 ASTM A36/A36M-00 1.10

1961-present ASTM A572/A572M-89, Group 1 1.10

ASTM A572/A572M-89, Group 2 1.10

ASTM A572/A572M-89, Group 3 1.05

ASTM A572/A572M-89, Group 4 1.05

ASTM A572/A572M-89, Group 5 1.05

1990-present ASTM A36/A36M-00 & Dual Grade, 

Group 1

1.05

ASTM A36/A36M-00 & Dual Grade, 

Group 2

1.05

ASTM A36/A36M-00 & Dual Grade, 

Group 3

1.05

ASTM A36/A36M-00 & Dual Grade, 

Group 4

1.05

Yield Strength 1961-1990 ASTM A36/A36M-00 1.10

1961-present ASTM A572/A572M-89, Group 1 1.10

ASTM A572/A572M-89, Group 2 1.10

ASTM A572/A572M-89, Group 3 1.05

ASTM A572/A572M-89, Group 4 1.10

ASTM A572/A572M-89, Group 5 1.05

1990-present ASTM A36/A36M-00, Rolled Shapes 1.50

ASTM A36/A36M-00, Plates 1.10

Dual Grade, Group 1 1.05

Dual Grade, Group 2 1.10

Dual Grade, Group 3 1.05

Dual Grade, Group 4 1.05

Tensile Strength All Not Listed 1 1.10

Yield Strength All Not Listed 1 1.10

1. For materials not conforming to one of the listed specifications.
5-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.3.3 Condition Assessment

5.3.3.1 General

A condition assessment of the existing building and site 

shall be performed as specified in this section. A 

condition assessment shall include the following:

1. Examination of components that will receive 

earthquake-induced forces or deformations to 

identify the presence of degradation due to 

environmental or loading effects.

2. Verification of the presence and configuration of 

structural elements and components and their 

connections, and the continuity of load paths 

between components, elements, and systems.

3. Identification of other conditions including the 

presence of nonstructural components that influence 

building performance and impose limitations on 

rehabilitation.

4. Characterization of soil and foundation conditions as 

specified in Section 2.2.3.

5. Identification of adjacent buildings as specified in 

Section 2.2.4. 

5.3.3.2 Scope and Procedures

The condition assessment shall include visual 

inspection of accessible structural elements and 

components involved in lateral-load resistance to verify 

information shown on available documents.

If coverings or other obstructions exist, either indirect 

visual inspection through use of drilled holes and a 

fiberscope shall be used, or direct visual inspection 

shall be performed by local removal of covering 

materials. When required by Section 2.2.6, visual and 

comprehensive condition assessments shall include the 

following:

1. If detailed design drawings exist, at least one 

connection of each connection type shall be 

exposed. If no deviations from the drawings exist, 

the sample shall be considered representative. If 

deviations from the existing drawings exist, then 

removal of additional coverings from connections of 

that type shall be done until the extent of deviations 

is determined. 

2. In the absence of construction drawings, at least 

three primary connections of each connection type 

shall be exposed. If no deviations within a 

connection group are observed, the sample shall be 

considered representative. If deviations within a 

connection group are observed, then additional 

connections shall be exposed until the extent of 

deviations is determined.

C5.3.3.1 General

The physical condition of existing components and 

elements and their connections must be examined for 

degradation. Degradation may include environmental 

effects (e.g., corrosion, fire damage, chemical attack) or 

past/current loading effects (e.g., overload, damage 

from past earthquakes, fatigue, fracture). The condition 

assessment should also examine for configurational 

problems observed in recent earthquakes, including 

effects of discontinuous components, improper 

welding, and poor fit-up.

Component orientation, plumbness, and physical 

dimensions should be confirmed during an assessment. 

Connections in steel components, elements, and 

systems require special consideration and evaluation. 

The load path for the system must be determined, and 

each connection in the load path(s) must be evaluated. 

This includes diaphragm-to-component and 

component-to-component connections. FEMA 351 

provides recommendations for inspection of welded 

steel moment frames.

The condition assessment also affords an opportunity to 

review other conditions that may influence steel 

elements and systems and overall building 

performance. Of particular importance is the 

identification of other elements and components that 

may contribute to or impair the performance of the steel 

system in question, including infills, neighboring 

buildings, and equipment attachments. Limitations 

posed by existing coverings, wall and ceiling space, 

infills, and other conditions shall also be defined such 

that prudent rehabilitation measures may be planned.

C5.3.3.2 Scope and Procedures

For steel elements encased in concrete, it may be more 

cost effective to provide an entirely new lateral-loadresisting system than undertaking a visual inspection by 

removal of concrete encasement and repair.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-9

5.3.3.3 Basis for the Mathematical Building 

Model

The results of the condition assessment shall be used to 

create a mathematical building model.

If no damage, alteration, or degradation is observed in 

the condition assessment, component section properties 

shall be taken from design drawings. If some sectional 

material loss or deterioration has occurred, the loss shall 

be quantified by direct measurement and section 

properties shall be reduced accordingly using principles 

of structural mechanics.

5.3.4 Knowledge Factor

A knowledge factor (κ) for computation of steel 

component capacities and permissible deformations 

shall be selected in accordance with Section 2.2.6.4 

with the following additional requirements specific to 

steel components.

A knowledge factor of 0.75 shall be used if the 

components and their connectors are composed of cast 

or wrought iron.

5.4 General Assumptions and 

Requirements

5.4.1 Stiffness

Component stiffnesses shall be calculated in accordance 

with Sections 5.5 through 5.11.

5.4.2 Design Strengths and Acceptance 

Criteria

5.4.2.1 General

Classification of steel component actions as 

deformation- or force-controlled, and calculation of 

design strengths, shall be as specified in Sections 5.5 

through 5.10.

5.4.2.2 Deformation-Controlled Actions

Design strengths for deformation-controlled actions, 

QCE, shall be taken as expected strengths obtained 

experimentally or calculated using accepted principles 

of mechanics. Expected strength shall be defined as the 

mean maximum resistance expected over the range of 

deformations to which the component is likely to be 

subjected. When calculations are used to determine 

mean expected strength, expected material properties 

(including strain hardening) shall be used. Unless other 

procedures are specified in this standard, procedures 

contained in AISC (1993) LRFD Specifications to 

calculate design strength shall be permitted, except that 

the strength reduction factor, φ, shall be taken as unity. 

Deformation capacities for acceptance of deformationcontrolled actions shall be as specified in Sections 5.5 

through 5.11.

5.4.2.3 Force-Controlled Actions

Design strengths for force-controlled actions, QCL, shall 

be taken as lower-bound strengths obtained 

experimentally or calculated using established 

principles of mechanics. Lower-bound strength shall be 

defined as mean strength minus one standard deviation. 

When calculations are used to determine lower-bound 

strength, lower bound material properties shall be used. 

Unless other procedures are specified in this standard, 

procedures contained in AISC (1993) LRFD 

Specifications to calculate design strength shall be 

permitted, except that the strength reduction factor, φ, 

shall be taken as unity. Where alternative definitions of 

design strength are used, they shall be justified by 

experimental evidence.

5.4.3 Rehabilitation Measures

Upon determining that steel elements in an existing 

building are deficient for the selected Rehabilitation 

Objective, these elements shall be rehabilitated or 

replaced so they are no longer deficient. If replacement 

of the element is selected, the new element shall be 

designed in accordance with an approved building code.

Physical condition of components and connectors may 

also dictate the use of certain destructive and 

nondestructive test methods. If steel elements are 

covered by well-bonded fireproofing materials or 

encased in durable concrete, it is likely that their 

condition will be suitable. However, local removal of 

these materials at connections should be performed as 

part of the assessment. The scope of this removal effort 

is dictated by the component and element design. For 

example, in a braced frame, exposure of several key 

connections may suffice if the physical condition is 

acceptable and the configuration matches the design 

drawings. However, for moment frames, it may be 

necessary to expose more connection points because of 

varying designs and the critical nature of the 

connections. See FEMA 351 for inspection of welded 

moment frames.
5-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.5 Steel Moment Frames

5.5.1 General

The behavior of steel moment-resisting frames is 

generally dependent on the connection configuration 

and detailing. Table 5-4 identifies the various 

connection types for which acceptance criteria are 

provided. Modeling procedures, acceptance criteria, 

and rehabilitation measures for Fully Restrained (FR) 

Moment Frames and Partially Restrained (PR) Moment 

Frames shall be as defined in Sections 5.5.2 and 5.5.3, 

respectively. 

C5.5.1 General

Steel moment frames are those frames that develop 

their seismic resistance through bending of steel beams 

and columns, and moment-resisting beam-column 

connections. A moment-resisting beam-column 

connection is one that is designed to develop moment 

resistance at the joint between the beam and the 

column and also designed to develop the shear 

resistance at the panel zone of the column. Beams and 

columns consist of either hot-rolled steel sections or 

cold-formed steel sections or built-up members from 

hot-rolled or cold-formed plates and sections. Built-up 

members are assembled by riveting, bolting, or 

welding. The components are either bare steel or steel 

with a nonstructural coating for protection from fire or 

corrosion or both, or steel with either concrete or 

masonry encasement.

Following the 1994 Northridge Earthquake, the SAC 

Joint Venture undertook a major program to address 

the issue of the seismic performance of momentresisting steel frame structures. This program produced 

several documents which provide recommended 

criteria for the evaluation and upgrade of this building 

type. However, the design professional should be 

cautioned that there are some differences in the 

methodologies and specifics of this standard and the 

SAC procedures. While both methodologies utilize 

similar analysis procedures, there are some variations 

in the factors used to compute the pseudo lateral load 

in the LSP and NSP. When using the acceptance 

criteria of this section, the design professional should 

follow the procedures set forth in Chapter 3 of this 

standard without modification. The procedures in this 

standard and the SAC procedures are judged to result 

in comparable levels of drift demand.

Connections between the members shall be classified 

as fully restrained (FR) or partially restrained (PR), 

based on the strength and stiffness of the connection 

assembly. The connection types and definitions 

contained in Table 5-4, as well as the acceptance 

criteria for these connections, has been adopted from 

the referenced SAC documents, FEMA 350, 351, 

355D, and 355F. The number of connections identified 

is based on research that has shown behavior to be 

highly dependent on connection detailing. The design 

professional should refer to those guidelines for more 

detailed descriptions of these connections as well as a 

methodology for determining acceptance criteria for 

other connection types not included in this standard.

FEMA 351 provides an alternate methodology for 

determining column demands that has not been 

adopted into this standard.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-11

Table 5-4 Steel Moment Frame Connection Types

Connection Description1, 2 Type

Welded Unreinforced Flange 

(WUF)

Full-penetration welds between beam and columns, flanges, bolted or 

welded web, designed prior to code changes following the Northridge 

earthquake

FR

Bottom Haunch in WUF 

w/Slab

Welded bottom haunch added to existing WUF connection with 

composite slab3

FR

Bottom Haunch in WUF w/o 

Slab

Welded bottom haunch added to existing WUF connection without 

composite slab3

FR

Welded Cover Plate in WUF Welded cover plates added to existing WUF connection3 FR

Improved WUF-Bolted Web Full-penetration welds between beam and column flanges, bolted 

web4

FR

Improved WUF-Welded Web Full-penetration welds between beam and column flanges, welded 

web4

FR

Free Flange Web is coped at ends of beam to separate flanges, welded web tab 

resists shear and bending moment due to eccentricity due to coped 

web4

FR

Welded Flange Plates Flange plate with full-penetration weld at column and fillet welded to 

beam flange4

FR

Reduced Beam Section Connection in which net area of beam flange is reduced to force 

plastic hinging away from column face4

FR

Welded Bottom Haunch0 Haunched connection at bottom flange only4 FR

Welded Top and Bottom0

Haunches

Haunched connection at top and bottom flanges4 FR

Welded Cover-Plated0

Flanges

Beam flange and cover-plate are welded to column flange4 FR

Top and Bottom Clip Angles Clip angle bolted or riveted to beam flange and column flange PR

Double Split Tee Split tees bolted or riveted to beam flange and column flange PR

Composite Top and Clip 

Angle Bottom

Clip angle bolted or riveted to column flange and beam bottom flange 

with composite slab

PR

Bolted Flange Plates Flange plate with full-penetration weld at column and bolted to beam 

flange4

PR5

Bolted End Plate Stiffened or unstiffened end plate welded to beam and bolted to 

column flange 

PR5

Shear Connection w/ Slab Simple connection with shear tab, composite slab PR

Shear Connection w/o Slab Simple connection with shear tab, no composite slab PR

1. Where not indicated otherwise, definition applies to connections with bolted or welded web.

2. Where not indicated otherwise, definition applies to connections with or without composite slab.

3. Full-penetration welds between haunch or cover plate to column flange conform to the requirements of the AISC (1997) Seismic Provisions.

4. Full-penetration welds conform to the requirements of the AISC (1997) Seismic Provisions.

5. For purposes of modeling, the connection may be considered FR if it meets the strength and stiffness requirements of Section 5.5.2.1.
5-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.5.2 Fully Restrained Moment Frames

5.5.2.1 General

Fully restrained (FR) moment frames shall be those 

moment frames with connections identified as FR in 

Table 5-4. 

Moment frames with connections not included in Table 

5-4 shall be defined as FR if the joint deformations (not 

including panel zone deformation) do not contribute 

more than 10% to the total lateral deflection of the 

frame, and the connection is at least as strong as the 

weaker of the two members being joined. If either of 

these conditions is not satisfied, the frame shall be 

characterized as partially restrained.

Fully restrained moment frames encompass both 

Special Moment Frames and Ordinary Moment Frames, 

defined in AISC (1997) Seismic Provisions. These 

terms are not used in this standard, but the requirements 

for these systems and for general or seismic design of 

steel components specified in AISC (1993) LRFD 

Specifications or ASCE 7 shall be followed for new 

elements designed as part of the seismic rehabilitation, 

unless superseded by provisions in this standard.

5.5.2.2 Stiffness 

5.5.2.2.1 Linear Static and Dynamic Procedures

The stiffness of steel members (columns and beams) 

and connections (joints and panel zones used with the 

linear procedures of Chapter 3) shall be based on 

principles of structural mechanics and as specified in 

the AISC (1993) LRFD Specifications unless 

superseded by provisions of this section.

1. Axial Area and Shear Area: [For elements fully 

encased in concrete, calculation of the stiffness using 

full composite action shall be permitted if confining 

reinforcement is provided to allow the concrete to 

remain in place during an earthquake. Concrete 

enclosed on at least three sides, or over 75% of its 

perimeter, by elements of the structural steel member 

shall be permitted to be considered adequately confined 

to provide composite action.

2. Moment of Inertia: [For components encased in 

concrete, the stiffness shall include composite action, 

but the width of the composite section shall be taken as 

equal to the width of the flanges of the steel member 

and shall not include parts of the adjoining floor slab, 

unless there is an identifiable shear transfer mechanism 

between the concrete and the steel which is shown to 

meet the applicable acceptance criteria for the selected 

performance level.

3. Panel Zone Modeling: [Inclusion of panel zones 

flexibility shall be permitted in a frame analysis by 

adding a panel zone element to the mathematical model. 

Alternatively, adjustment of the beam flexural stiffness 

to account for panel zone flexibility shall be permitted. 

Where the expected shear strength of panel zones 

exceeds the flexural strength of the beams at a beamcolumn connection, and the stiffness of the panel zone 

is at least 10 times larger than the flexural stiffness of 

the beam, direct modeling of the panel zone shall not be 

required. In such cases, rigid offsets from the center of 

the column shall be permitted to represent the effective 

span of the beam. Use of center line analysis shall be 

permitted for other cases.

4. Joint Modeling: Modeling of connection stiffness for 

FR moment frames shall not be required except for 

joints that are intentionally reinforced to force 

formation of plastic hinges within the beam span, 

remote from the column face. For such joints, rigid 

elements shall be used between the column and the 

beam to represent the effective span of the beam.

5. Connections: Requirements of this section shall 

apply to connections identified as FR in Table 5-4 and 

those meeting the requirements of Section 5.5.2.1.

C5.5.2.1 General

FEMA 351 identifies two types of connections—Type 

1 (ductile) and Type 2 (brittle). These definitions are 

not used in this standard since the distinction is 

reflected in the acceptance criteria for the connections. 

The most common beam-to-column connection used in 

steel FR moment frames since the late 1950s required 

the beam flange to be welded to the column flange 

using complete joint penetration groove welds. Many 

of these connections have fractured during recent 

earthquakes. The design professional is referred to 

FEMA 274 and to FEMA 351.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-13

5.5.2.2.2 Nonlinear Static Procedure

If the Nonlinear Static Procedure of Chapter 3 is used, 

the following criteria shall apply:

1. Elastic component properties shall be modeled as 

specified in Section 5.5.2.2.1.

2. Plastification shall be represented by nonlinear 

moment-curvature and interaction relationships for 

beams and beam-columns derived from experiment 

or analysis.

3. Linear or nonlinear behavior of panel zones shall be 

included in the mathematical model except as 

indicated in Section 5.5.2.2.1, Item 3.

In lieu of relationships derived from experiment or 

analysis, the generalized load-deformation curve shown 

in Figure 5-1, with parameters a, b, c, as defined in 

Tables 5-6 and 5-7, shall be used for components of 

steel moment frames. Modification of this curve shall 

be permitted to account for strain-hardening of 

components as follows: (a) a strain-hardening slope of 

3% of the elastic slope shall be permitted for beams and 

columns unless a greater strain-hardening slope is 

justified by test data; and (b) where panel zone yielding 

occurs, a strain-hardening slope of 6% shall be used for 

the panel zone unless a greater strain-hardening slope is 

justified by test data. 

The parameters Q and QCE in Figure 5-1 are 

generalized component load and generalized 

component expected strength, respectively. For beams 

and columns, θ is the total elastic and plastic rotation of 

the beam or column, θy is the rotation at yield, ∆ is total 

elastic and plastic displacement, and ∆y is yield 

displacement. For panel zones, θy is the angular shear 

deformation in radians. Figure 5-2 defines chord 

rotation for beams. The chord rotation shall be 

calculated either by adding the yield rotation, θy, to the 

plastic rotation or taken to be equal to the story drift. 

Use of Equations (5-1) and (5-2) to calculate the yield 

rotation, θy, where the point of contraflexure is 

anticipated to occur at the mid-length of the beam or 

column, respectively, shall be permitted. 

Beams: (5-1)

Columns: (5-2)

Figure 5-1 Generalized Force-Deformation Relation 

for Steel Elements or Components

Figure 5-2 Definition of Chord Rotation

θy

ZFyel

b

6EIb

= ----------------

θy

ZFyel

c

6EIc

---------------- 1 P

Pye

– --------     =
5-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Q and QCE are the generalized component load and 

generalized component expected strength, respectively. 

For flexural actions of beams and columns, QCE refers 

to the plastic moment capacity, which shall be 

calculated using Equations (5-3) and (5-4): 

Beams:

(5-3)

Columns:

(5-4)

For panel zones, QCE refers to the plastic shear capacity 

of the panel zone, which shall be calculated using 

Equation (5-5):

Panel Zones:

(5-5)

where: 

5.5.2.2.3 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be determined experimentally. 

5.5.2.3 Strength

5.5.2.3.1 General

Component strengths shall be computed in accordance 

with the general requirements of Section 5.4.2 and the 

specific requirements of this section.

5.5.2.3.2 Linear Static and Dynamic Procedures

1. Beams: The strength of elements of structural steel 

under flexural actions with negligible axial load present 

shall be calculated in accordance with this section. 

These actions shall be considered 

deformation-controlled. 

The expected flexural strength, QCE, of beam 

components shall be determined using equations for 

design strength, Mp, given in AISC (1997) Seismic 

Provisions, except that φ shall be taken as 1.0 and Fye

shall be substituted for Fy. The component expected 

strength, QCE, of beams and other flexural 

deformation-controlled members shall be the lowest 

value obtained for the limit states of yielding, 

lateral-torsional buckling, local flange buckling, or 

shear yielding of the web. 

dc = Column depth

E = Modulus of elasticity

Fye = Expected yield strength of the material

I = Moment of inertia

lb = Beam length

lc = Column length

MCE = Expected flexural strength

P = Axial force in the member at the target 

displacement for nonlinear static analyses, or 

at the instant of computation for nonlinear 

dynamic analyses. For linear analyses, P shall 

be taken as QUF, calculated in accordance with 

Section 3.4.2.1.2

Pye = Expected axial yield force of the member = 

AgFye

Q = Generalized component load

QCE = Generalized component expected strength

QCE MCE ZFye = =

QCE MCE 1.18ZFye 1 P

Pye

– --------     ZFye = = ≤

QCE VCE 0.55Fyedct

p = =

tp = Total thickness of panel zone including 

doubler plates

θ = Chord rotation

θy = Yield rotation

VCE = Expected shear strength

Z = Plastic section modulus

C5.5.2.2.2 Nonlinear Static Procedure

Strain hardening should be considered for all 

components. The design professional is directed to 

FEMA 355D for information concerning nonlinear 

behavior of various tested connection configurations.

C5.5.2.2.3 Nonlinear Dynamic Procedure

The design professional is directed to FEMA 355D for 

information concerning nonlinear behavior of various 

tested connection configurations.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-15

For fully concrete-encased beams where confining 

reinforcement is provided to allow the concrete to 

remain in place during the earthquake, the values of 

bf = 0 and Lp = 0 shall be permitted to be used. For bare 

beams bent about their major axes and symmetric about 

both axes, satisfying the requirements of compact 

sections, and Lb < Lp, QCE shall be computed in 

accordance with Equation (5-6):

QCE = MCE = MpCE = ZFye (5-6)

where: 

The limit states of local and lateral torsional buckling 

shall not be considered for components either subjected 

to bending about their minor axes or fully encased in 

concrete where confining reinforcement is provided to 

allow the concrete to remain in place during an 

earthquake.

If the beam strength is governed by the shear strength of 

the unstiffened web and , then VCE shall be 

calculated in accordance with Equation (5-7): 

(5-7)

where:

If , then the value of VCE shall be calculated 

from AISC (1997) Seismic Provisions.

2. Columns: This section shall be used to evaluate 

flexural and axial strengths of structural steel elements 

with non-negligible axial load present. These actions 

shall be considered force-controlled.

The lower-bound strength, QCL, of steel columns under 

axial compression shall be the lowest value obtained for 

the limit states of column buckling, local flange 

buckling, or local web buckling. The effective design 

strength or the lower-bound axial compressive strength, 

PCL, shall be calculated in accordance with AISC

(1997) Seismic Provisions, taking φ=1.0 and using the 

lower-bound strength, FyLB, for yield strength.

The expected axial strength of a column in tension, 

QCE, shall be computed in accordance with Equation 

(5-8):

(5-8)

where:

3. Panel Zone: The strength of the panel zone shall be 

calculated using Equation (5-5).

4. FR Beam-Column Connections: The strength of 

connections shall be based on the controlling 

mechanism considering all potential modes of failure.

bf = Width of the compression flange

Lb = Length of beam

Lp = Limiting lateral unbraced length for full 

plastic bending capacity for uniform bending 

from AISC (1993) LRFD Specifications

MpCE = Expected plastic moment capacity

Fye = Expected yield strength determined in 

accordance with Section 5.3.2.3

VCE = Expected shear strength

Aw = Nominal area of the web = dbtw

tw = Web thickness

h = Distance from inside of compression flange to 

inside of tension flange

h

t

w

---- 418

Fy

≤ ---------

CE CE ye w Q = V = 0.6F A

Fy = Yield strength; must be in ksi when used in 

Equation (5-7)

Ac = Area of column

Fye = Expected yield strength of column

TCE = Expected tensile strength of column

C5.5.2.3.2 Linear Static and Dynamic Procedures

4. FR Beam-Column Connections: The design 

professional is directed to FEMA 351 for guidance in 

determining the strength of various FR connection 

configurations.

h

t

w

---- 418

Fy

> ---------

QCE TCE AcFye = =
5-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5. Column Base Plate to Concrete Pile Caps or Footings: 

The strength of connections between columns and 

concrete pile caps or footings shall be the lowest value 

obtained for the limit states of the strength of the 

columns, the strength of the base plates, and the 

strength of the anchor bolts. The strength of the base 

plate shall be the lowest value based on the following 

limit states: expected strength of the welds or bolts, 

expected bearing stress of the concrete, and expected 

yield strength, Fye, of the base plate.

The strength of the anchor bolt connection between the 

base plate and the concrete shall be the lowest value 

based on the following limit states: shear or tension 

yield strength of the anchor bolts, loss of bond between 

the anchor bolts and the concrete, or failure of the 

concrete. Anchor bolt strengths for each failure type or 

limit state shall be calculated in accordance with IBC, 

Section 1913, using φ=1.0, or other approved 

procedure.

5.5.2.3.3 Nonlinear Static Procedure

The complete load-deformation relationship of each 

component as depicted in Figure 5-1 shall be 

determined in accordance with Section 5.5.2.2.2. The 

values for expected strength, QCE, shall be the same as 

those used for linear procedures as specified in 

Section 5.5.2.3.2.

5.5.2.3.4 Nonlinear Dynamic Procedures

The complete hysteretic behavior of each component 

shall be determined experimentally.

5.5.2.4 Acceptance Criteria

5.5.2.4.1 General

Component acceptance criteria shall be computed in 

accordance with the general requirements of 

Section 5.4.2 and the specific requirements of this 

section.

5.5.2.4.2 Linear Static and Dynamic Procedures

1. Beams: The acceptance criteria of this section shall 

apply to flexural actions of elements of structural steel 

with negligible axial load. Beam flexure and shear shall 

be considered deformation-controlled.

For built-up shapes, the adequacy of lacing plates shall 

be evaluated using the provisions for tension braces in 

Section 5.6.2.4.

Values for the m-factor used in Equation (3-20) shall be 

as specified in Table 5-5. For fully concrete-encased 

beams where confining reinforcement is provided to 

allow the concrete to remain in place during an 

earthquake, the values of bf = 0 and Lp = 0 shall be used 

for the purpose of determining m. If QCE < MpCE due to 

lateral torsional buckling, then m in Equation (3-20) 

shall be replaced by me, calculated in accordance with 

Equation (5-9): 

(5-9)

where:

C5.5.2.3.4 Nonlinear Dynamic Procedures

The design professional is directed to FEMA 355D for 

information concerning nonlinear behavior of various 

tested connection configurations.

C5.5.2.4.1 General

The strength and behavior of steel moment-resisting 

frames is typically governed by the connections. The 

design professional is urged to determine the 

controlling limit state of the system when selecting the 

corresponding acceptance criterion.

Lb = Distance between points braced against lateral 

displacement of the compression flange, or 

between points braced to prevent twist of the 

cross-section, AISC (1993) LRFD Specifications

Lp = Limiting unbraced length between points of 

lateral restraint for the full plastic moment 

capacity to be effective, AISC (1993) LRFD 

Specifications

Lr = Limiting unbraced length between points of 

lateral support beyond which elastic lateral 

torsional buckling of the beam is the failure 

mode, AISC (1993) LRFD Specifications

m = Value of m given in Table 5-5

me = Effective m computed in accordance with 

Equation (5-9)

Cb = Coefficient to account for effect of nonuniform 

moment, AISC (1993) LRFD Specifications

me Cb m m( ) – 1

Lb Lp –

Lr Lp – = – -----------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-17

For built-up shapes, where the strength is governed by 

the strength of the lacing plates that carry component 

shear, the m-factor shall be taken as 0.5 times the 

applicable value in Table 5-5, unless larger values are 

justified by tests or analysis; however, m need not be 

taken less than 1.0. For built-up laced beams and 

columns fully encased in concrete, local buckling of the 

lacing need not be considered where confining 

reinforcement is provided to allow the encasement to 

remain in place during a design earthquake.

2. Columns: For steel columns under combined axial 

compression and bending stress, where the axial 

column load is less than 50% of the lower-bound axial 

column strength, PCL, the column shall be considered 

deformation-controlled for flexural behavior and forcecontrolled for compressive behavior and the combined 

strength shall be evaluated by Equation (5-10) or (5-11).

For 

(5-10)

For 

(5-11)

where: 

Steel columns with axial compressive forces exceeding 

50% of the lower-bound axial compressive strength, 

PCL, shall be considered force-controlled for both axial 

loads and flexure and shall be evaluated using Equation 

(5-12):

(5-12)

where: 

Flexural strength shall be calculated in accordance with 

AISC (1997) Seismic Provisions taking φ=1.0 and using 

the lower-bound value for yield strength.

For columns under combined compression and bending, 

lateral bracing to prevent torsional buckling shall be 

provided as required by the AISC (1993) LRFD 

Specifications.

Steel columns under axial tension shall be considered 

deformation-controlled and shall be evaluated using 

Equation (3-20).

Steel columns under combined axial tension and bending stress shall be considered deformation-controlled 

and shall be evaluated using Equation (5-13):

(5-13)

PUF = Axial force in the member computed in 

accordance with Section 3.4.2.1.2

PCL = Lower-bound compression strength of the 

column

Mx = Bending moment in the member for the 

x-axis computed in accordance with 

Section 3.4.2.1.1

My = Bending moment in the member for the 

y-axis computed in accordance with 

Section 3.4.2.1.1

MCEx = Expected bending strength of the column 

for the x-axis

MCEy = Expected bending strength of the column 

for the y-axis

0.2

PUF

PCL

≤ ≤ ---------- 0.5

PUF

PCL

---------- 8

9

-- Mx

mxMCEx

-------------------- My

myMCEy

+ + -------------------- ≤ 1.0

PUF

PCL

---------- < 0.2

PUF

2PCL

------------ Mx

mxMCEx

-------------------- My

myMCEy

+ + -------------------- ≤ 1.0

mx = Value of m for the column bending about 

the x-axis in accordance with Table 5-5

my = Value of m for the column bending about 

the y-axis in accordance with Table 5-5

PUF = Axial load in the member, calculated in 

accordance with Section 3.4.2.1.2

MUFx = Bending moment in the member about the 

x-axis, calculated in accordance with 

Section 3.4.2.1.2

MUFy = Bending moment in the member about the 

y-axis, calculated in accordance with 

Section 3.4.2.1.2

MCLx = Lower-bound flexural strength of the 

member about the x-axis

MCLy = Lower-bound flexural strength of the 

member about the y-axis

PUF

PCL

---------- MuFx

MCLx

------------- MuFy

MCLy

+ + ------------- ≤ 1

T

mt

TCE

--------------- Mx

mxMCEx

-------------------- My

myMCEy

+ + -------------------- ≤ 1.0
5-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

where:

3. Panel Zone: Shear behavior of panel zones shall be 

considered deformation-controlled and shall be 

evaluated using Equation (3-20), with the expected 

panel zone shear strength, QCE, calculated according to 

Equation (5-5) and m-factors taken from Table 5-5.

4. FR Beam-Column Connections: FR connections 

identified in Table 5-4 shall be considered 

deformation-controlled and evaluated in accordance 

with Equation (3-20), with QUD and QCE taken as the 

computed demand and capacity of the critical 

connection component respectively, and m-factors taken 

from Table 5-5 as modified below.

Connection acceptance criteria are dependent on the 

detailing of continuity plates (column stiffeners that 

align with the beam flanges), the strength of the panel 

zone, the beam span-to-depth ratio, and the slenderness 

of the beam web and flanges. Tabulated m-factors in 

Table 5-5 shall be modified as determined by the 

following four conditions. The modifications shall be 

cumulative, but m-factors need not be taken as less than 

1.0.

1. If one of the following conditions is not met, the 

tabulated m-factors in Table 5-5 shall be multiplied 

by 0.8.

or

 and continuity plates with 

or

 and continuity plates with 

2. If one of the following conditions is not met, the 

tabulated m-factors in Table 5-5 shall be multiplied 

by 0.8.

where Vy = 0.55Fye(col)dctcw and VPZ is the 

computed panel zone shear at the development of a 

hinge at the critical location of the connection. For 

Mye at the face of the column, 

3. If the clear span-to-depth ratio, L/d, is greater than 

10, the tabulated m-factors in Table 5-5 shall be 

multiplied by 

4. If the beam flange and web meet the following 

conditions, the tabulated m-factors in Table 5-5 need 

not be modified for flange and web slenderness. 

and 

If the beam flange or web slenderness values exceed 

either of the following limits, the tabulated 

m-factors in Table 5-5 shall be multiplied by 0.5.

or 

Mx = Bending moment in the member for the 

x-axis.

My = Bending moment in the member for the 

y-axis

MCEx = Expected bending strength of the column for 

the x-axis

MCEy = Expected bending strength of the column for 

the y-axis

 mt = Value of m for the column in tension based 

on Table 5-5

 mx = Value of m for the column bending about the 

x-axis based on Table 5-5

 my = Value of m for the column bending about the 

y-axis based on Table 5-5

T = Tensile load in column

TCE = Expected tensile strength of column 

computed in accordance with Equation (5-8)

t

cf

bbf

5.2 ≥ -------

bbf

7

------ t

cf

bbf

5.2 ≤ < ------- t

t

bf

2 ≥ -----

t

cf

bbf

7 < ------ t

t

bf

2 ≥ -----

0.6

VPZ

Vy

≤ ≤ --------- 0.9

VPZ

My ∑ beam

db

= --------------------------- L

L dc – --------------     h db –

h --------------    

1.4 0.04L

d – --

bf

2t

f

------ 52

Fye

< ------------ h

t

w

---- 418

Fye

< ------------

bf

2t

f

------ 65

Fye

> ------------ h

t

w

---- 640

Fye

> ------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-19

Straight line interpolation, based on the case that 

results in the lower modifier, shall be used for 

intermediate values of beam flange or web 

slenderness.

Type FR connections designed to promote yielding 

of the beam remote from the column face shall be 

considered force-controlled and shall be designed 

using Equation (5-14):

(5-14)

where:

5. Column Base Plate to Concrete Pile Caps or Footings: 

For column base plate yielding, bolt yielding, and weld 

failure, the use of m-factors from Table 5-5, based on 

the respective limit states for partially restrained end 

plates, shall be permitted. Column-base connection 

limit states controlled by anchor bolt failure modes 

governed by the concrete shall be considered forcecontrolled.

5.5.2.4.3 Nonlinear Static and Dynamic Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3. Maximum permissible 

inelastic deformations shall be taken from Tables 5-6 

and 5-7.

1. Beams: Flexural actions of beams shall be considered 

deformation-controlled. Permissible plastic rotation 

deformation shall be as indicated in Tables 5-6 and 5-7, 

where θy shall be calculated in accordance with 

Section 5.5.2.2.2.

2. Columns: Axial compressive loading of columns 

shall be considered force-controlled, with the lowerbound axial compression capacity, PCL, computed in 

accordance with Section 5.5.2.4.2.

Flexural loading of columns, with axial loads at a target 

displacement less than 50% of PCL, computed in 

accordance with Section 5.5.2.4.2, shall be considered 

deformation-controlled and maximum permissible 

plastic rotation demands on columns, in radians, shall 

be as indicated in Tables 5-6 and 5-7, dependent on the 

axial load present and the compactness of the section.

Flexural loading of columns, with axial loads at the 

target displacement greater than or equal to 50% of PCL, 

computed in accordance with Section 5.5.2.4.2, shall be 

considered force-controlled and shall conform to 

Equation (5-11).

QCLc = The lower-bound strength of the connection

QCEb = Expected bending strength of the beam

C5.5.2.4.2 Linear Static and Dynamic Procedures

4. FR Beam-Column Connections. The continuity 

plate modifier is based on recommendations 

FEMA 355F for continuity plate detailing in 

relationship to column flange thickness.

The panel zone modifier is based on research in 

FEMA 355F indicating that connection performance is 

less ductile when the strength of the panel zone is 

either too great or too small compared to the flexural 

strength of the beam. The panel zone range between 60 

percent to 90 percent of the beam strength is 

considered to provide balanced yielding between the 

beam and panel zone, which results in more desirable 

performance.

QCLc QCEb ≥

The clear span-to-depth ratio modifier for linear 

acceptance criteria reflects the decreased apparent 

ductility that arises due to increased elastic rotations 

for longer beams. The decreased plastic rotation 

capacity of beams with very small L/d ratios is not 

reflected directly. However, the modifier for linear 

criteria was developed so that it would be appropriate 

for the predominant case of L/d ratios greater than 

about 5.

The beam flange and web slenderness modifier is 

based on the same modifications to beam acceptance 

criteria contained in Table 5-5. While not an aspect of 

the connection itself, beam flange and web slenderness 

affect the behavior of the connection assembly.

Type FR connections designed to promote yielding of 

the beam in the span, remote from the column face, are 

discussed in FEMA 350.
5-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

3. FR Connection Panel Zones: Plastic rotation demands 

on panel zones, shall be evaluated using the acceptance 

criteria provided in Tables 5-6 and 5-7.

4. FR Beam-Column Connections: FR connections 

identified in Table 5-4 shall be considered deformationcontrolled and the plastic rotation predicted by analysis 

shall be compared with the acceptance criteria in 

Tables 5-6 and 5-7 as modified below. Connection 

acceptance criteria are dependent on the detailing of 

continuity plates, the strength of the panel zone, the 

beam span-to-depth ratio, and the slenderness of the 

beam web and flanges as determined by the following 

four conditions. The modifications shall be cumulative.

1. If one of the following conditions is not met, the 

tabulated plastic rotation in Tables 5-6 and 5-7 shall 

be multiplied by 0.8.

or

 and continuity plates with 

or

 and continuity plates with 

2. If the following condition is not met, the tabulated 

plastic rotations in Tables 5-6 and 5-7 shall be 

multiplied by 0.8.

where Vy = 0.55Fye(col)dctcw and VPZ is the 

computed panel zone shear at the development of a 

hinge at the critical location of the connection. For 

Mye at the face of the column, 

3. If the clear span-to-depth ratio, L/d, is less than 8, 

the tabulated plastic rotations in Tables 5-6 and 5-7 

shall be multiplied by 

4. If the beam flange and web meet the following 

conditions, the tabulated plastic rotations in 

Tables 5-6 and 5-7 need not be modified for flange 

and web slenderness.

and 

If the beam flange or web slenderness values exceed 

either of the following limits, the tabulated plastic 

rotations Tables 5-6 and 5-7 shall be multiplied by 

0.5.

or 

Straight line interpolation, based on the case that 

results in the lower modifier, shall be used for 

intermediate values of beam flange or web 

slenderness.

Type FR connections designed to promote yielding of 

the beam in the span remote from the column face, shall 

be considered force-controlled and shall be evaluated to 

assure that the lower-bound strength of the connection 

exceeds the expected flexural strength of the beam at 

the connection. 

t

cf

bbf

5.2 ≥ -------

bbf

7

------ t

cf

bbf

5.2 ≤ < ------- t

t

bf

2 ≥ -----

t

cf

bbf

7

< ------ t tbf ≥

0.6

VPZ

Vy

≤ ≤ --------- 0.9

VPZ

My ∑ beam

db

= ---------------------------- L

L dc – --------------     h db –

h --------------    

C5.5.2.4.3 Nonlinear Static and Dynamic 

Procedures

4. FR Beam-Column Connections: The continuity plate 

modifier is based on recommendations in FEMA 355F

for continuity plate detailing in relationship to column 

flange thickness.

The panel zone modifier is based on research in 

FEMA 355F indicating that connection performance is 

less ductile when the strength of the panel zone is 

either too great or too small compared to the flexural 

strength of the beam. The panel zone range between 60 

percent to 90 percent of the beam strength is 

considered to provide balanced yielding between the 

beam and panel zone, which results in more desirable 

performance.

( ) 0.5 8 – L d⁄

3 ------------------

bf

2t

f

------ 52

Fye

< ------------ h

t

w

---- 418

Fye

< ------------

bf

2t

f

------ 65

Fye

> ------------ h

t

w

---- 640

Fye

> ------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-21

5.5.2.5 Rehabilitation Measures

FR moment frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 5.4.3 

and other provisions of this standard.

The clear span-to-depth ratio modifier for nonlinear 

modeling and acceptance criteria reflects decreased 

plastic rotation capacity for beams with hinging 

occurring over a shorter length. This modifier is based 

on the plastic rotation capacities corresponding to the 

FEMA 350 L/d limits of 5 and 8.

The beam flange and web slenderness modifier is 

based on the same modifications to beam acceptance 

criteria contained in Tables 5-6 and 5-7. While not an 

aspect of the connection itself, beam flange and web 

slenderness affects the behavior of the connection 

assembly.

Type FR connections designed to promote yielding of 

the beam in the span, remote from the column face, are 

discussed in FEMA 350.

C5.5.2.5 Rehabilitation Measures

The following measures, which are presented in 

greater detail in FEMA 351, may be effective in 

rehabilitating FR moment frames:

1. Add steel braces to one or more bays of each story 

to form concentric or eccentric braced frames to 

increase the stiffness of the frames. The attributes 

and design criteria for braced frames shall be as 

specified in Section 5.6. The location of added 

braces should be selected so as to not increase 

horizontal torsion in the system.

2. Add ductile concrete or masonry shear walls or 

infill walls to one or more bays of each story to 

increase the stiffness and strength of the structure. 

The attributes and design requirements of concrete 

and masonry shear walls shall be as specified in 

Sections 6.8 and 7.4, respectively. The attributes 

and design requirements of concrete and masonry 

infills shall be as specified in Sections 6.7 and 7.5, 

respectively. The location of added walls should be 

selected so as not to increase horizontal torsion in 

the system.

3. Attach new steel frames to the exterior of the 

building. The rehabilitated structure should be 

checked for the effects of the change in the 

distribution of stiffness, the seismic load path, and 

the connections between the new and existing 

frames. The rehabilitation scheme of attaching new 

steel frames to the exterior of the building has been 

used in the past and has been shown to be very 

effective under certain conditions. This 

rehabilitation approach may be structurally 

efficient, but it changes the architectural appearance 

of the building. The advantage is that the 

rehabilitation may take place without disrupting the 

use of the building.

4. Reinforce moment-resisting connections to force 

plastic hinge locations in the beam material away 

from the joint region to reduce the stresses in the 

welded connection, thereby reducing the possibility 

of brittle fractures. This scheme should not be used 

if the full-pen connection of the existing structure 

did not use weld material of sufficient toughness to 

avoid fracture at stresses lower than yield or when 

strain hardening at the new hinge location produces 

larger stresses than existing at the weld. The 

rehabilitation measures to reinforce selected 

moment-resisting connections shall consist of 

providing horizontal cover plates, vertical 

stiffeners, or haunches. Removal of beam material 

to force plastic hinge in the beam and away from 

the joint region shall also be permitted subject to 

the above restrictions. Guidance on the design of 

these modifications of FR moment connections is 

discussed in FEMA 351.

5. Add energy dissipation devices as specified in 

Chapter 9.

6. Increase the strength and stiffness of existing 

frames by welding steel plates or shapes to selected 

members.
5-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.5.3 Partially Restrained Moment Frames

5.5.3.1 General

Partially restrained (PR) moment frames shall be 

defined as those moment frames with connections 

identified as PR in Table 5-4. Moment frames with 

connections not included in Table 5-4 shall be defined 

as PR if the deformations of the beam-to-column joints 

contribute greater than 10% to the total lateral 

deflection of the frame or where the strength of the 

connections is less than the strength of the weaker of the 

two members being joined. For a PR connection with 

two or more failure modes, the weakest failure 

mechanism shall be considered to govern the behavior 

of the joint. Design provisions for PR frames specified 

in AISC (1997) Seismic Provisions or ASCE 7 shall 

apply unless superseded by the provisions in this 

standard. Equations for calculating nominal design 

strength shall be used for determining the expected 

strength, except φ = 1, and either the expected strength 

or lower-bound strength shall be used in place of Fy, as 

further indicated in this standard.

5.5.3.2 Stiffness

5.5.3.2.1 Linear Static and Dynamic Procedures

1. Beams, columns, and panel zones: Axial area, shear 

area, moment of inertia, and panel zone stiffness shall 

be determined as specified in Section 5.5.2.2 for FR 

frames.

2. Connections: The rotational stiffness Kθ of each PR 

connection for use in PR frame analysis shall be 

determined by the procedure of this section, by 

experiment, or by an approved rational analysis. The 

deformation of the connection shall be included when 

calculating frame displacements.

The rotational spring stiffness, Kθ, shall be calculated in 

accordance with Equation (5-15):

(5-15)

where: 

MCE =Expected moment strength of connection for the 

following PR connections:

1. PR connections encased in concrete, where the 

nominal resistance, MCE, determined for the 

connection shall include the composite action 

provided by the concrete encasement.

2. PR connections encased in masonry, where 

composite action shall not be included in the 

determination of connection resistance, MCE.

3. Bare steel PR connections.

For PR connections not listed above, the rotational 

spring stiffness shall be calculated in accordance with 

Equation (5-16):

(5-16)

As a simplified alternative, modeling the frame as for 

FR joints but with the beam stiffness, EIb, adjusted to 

account for the flexibility of the joints in accordance 

with Equation (5-17) shall be permitted:

(5-17)

C5.5.3.1 General

Table 5-4 includes simple shear or pinned connections 

classified as PR connections. Although the gravity load 

carrying beams and columns are typically neglected in 

the lateral analysis of steel moment frame structures, 

SAC research contained in FEMA 355D indicates that 

these connections are capable of contributing nonnegligible stiffness through very large drift demands. 

Including gravity load carrying elements (subject to the 

modeling procedures and acceptance criteria in this 

section) in the mathematical model could be used by 

the design engineer to reduce the demands on the 

moment frame elements.

Kθ

MCE

0.005 = -------------

Kθ

MCE

0.003 = -------------

EIb adjusted 1

6h

Lb

2

Kθ

------------ 1

EIb

+ --------

= ----------------------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-23

where: 

When Equation (5-17) is used, the adjusted beam 

stiffness shall be used in standard rigid-connection 

frame analysis and the rotation of the connection shall 

be taken as the rotation of the beam at the joint.

5.5.3.2.2 Nonlinear Static Procedure

If the Nonlinear Static Procedure of Chapter 3 is used, 

the following criteria shall apply:

1. The elastic component properties shall be modeled 

as specified in Section 5.5.3.2.1.

2. The nonlinear moment-curvature or loaddeformation behavior for beams, beam-columns, 

and panel zones shall be modeled as specified in 

Section 5.5.2.2 for FR frames.

3. In lieu of relationships derived from experiment or 

analysis, the generalized load-deformation curve 

shown in Figure 5-1 with its parameters a, b, c as 

defined in Tables 5-6 and 5-7, shall be used to 

represent moment-rotation behavior for PR 

connections in accordance with Section 5.5.2.2.2. 

The value for θy shall be 0.005 for connections, for 

which Equation (5-15) in Section 5.5.3.2.1 applies, 

or 0.003 for all other connections.

5.5.3.2.3 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be modeled as verified by experiment.

5.5.3.3 Strength

5.5.3.3.1 General

Component strengths shall be computed in accordance 

with the general requirements of Section 5.4.2 and the 

specific requirements of this section.

5.5.3.3.2 Linear Static and Dynamic Procedures

The strength of steel beams and columns in PR Frames 

being analyzed using linear procedures shall be 

computed in accordance with Section 5.5.2.3.2 for FR 

Frames.

The expected strength, QCE, for PR connections shall 

be based on procedures specified in AISC (1993) LRFD 

Specifications, based on experiment, or based on the 

procedures listed in the subsequent sections.

1. Top and Bottom Clip Angle Connection: The moment 

strength, MCE, of the riveted or bolted clip angle 

connection, as shown in Figure 5-3, shall be the 

smallest value of MCE computed for the following four 

limits states:

1.1 Limit State 1: If the shear connectors between the 

beam flange and the flange angle control the capacity of 

the connection, QCE shall be computed in accordance 

with Equation (5-18): 

(5-18)

Kθ = Equivalent rotational spring stiffness of 

connection per Equation (5-15) or (5-16)

MCE = Expected moment strength

Ib = Moment of inertia of the beam

E = Modulus of elasticity

h = Average story height of the columns

Lb = Centerline span of the beam

C5.5.3.2.1 Linear Static and Dynamic Procedures

The design professional is directed to FEMA 274 for 

information concerning stiffness properties and 

modeling guidelines for PR connections.

C5.5.3.2.2 Nonlinear Static Procedure

The design professional is directed to FEMA 355D for 

information concerning nonlinear behavior of various 

tested connection configurations.

C5.5.3.2.3 Nonlinear Dynamic Procedure

The design professional is directed to FEMA 355D for 

information concerning nonlinear behavior of various 

tested connection configurations.

QCE MCE db FveAbNb = = ( )
5-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

where: 

1.2 Limit State 2: If the tensile capacity of the 

horizontal leg of the connection controls the capacity, 

PCE shall be taken as the smaller of that computed by 

Equation (5-19) or (5-20):

(5-19)

(5-20)

and QCE shall be calculated in accordance with 

Equation (5-21):

(5-21)

where:

1.3 Limit State 3: If the tensile capacity of the rivets or 

bolts attaching the vertical outstanding leg to the 

column flange controls the capacity of the connection, 

QCE shall be computed in accordance with Equation 

(5-22):

(5-22)

where: 

1.4 Limit State 4: If the flexural yielding of the flange 

angles controls the capacity of the connection, QCE

shall be given by Equation (5-23):

(5-23)

where: 

2. Double Split Tee Connection: The moment strength, 

MCE, of the double split tee (T-stub) connection, as 

shown in Figure 5-4, shall be the smallest value of MCE

computed for the following four limit states: 

Figure 5-3 Top and Bottom Clip Angle Connection

Ab = Gross area of rivet or bolt

db = Overall beam depth

Fve = Unfactored nominal shear strength of the bolts 

or rivets given in AISC (1993) LRFD 

Specifications

Nb = Least number of bolts or rivets connecting the 

top or bottom angle to the beam flange

PCE FyeAg ≤

PCE FteAe ≤

QCE MCE PCE db t

a = ≤ ( ) +

Fye = Expected yield strength of the angle

Fte = Expected tensile strength of the angle

Ae = Effective net area of the horizontal leg

Ag = Gross area of the horizontal leg

ta = Thickness of angle

Ab = Gross area of rivet or bolt

ba = Dimension in Figure 5-3 

Fte = Expected tensile strength of the bolts or rivets

Nb = Least number of bolts or rivets connecting top or

bottom angle to column flange

ba = Dimension shown in Figure 5-3

w = Length of the flange angle

QCE MCE db ba ( ) + FteAbNb = = ( )

QCE MCE

wta

2

Fye

4 ba

t

a

2 – ---

------------------------ db ba = = ( ) +
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-25

2.1 Limit State 1: If the shear connectors between the 

beam flange and the web of the split tee control the 

capacity of the connection, QCE shall be calculated 

using Equation (5-18).

2.2 Limit State 2: If the tension capacity of the bolts or

rivets connecting the flange of the split tee to the column flange control the capacity of the connection, QCE

shall be calculated using Equation (5-24):

(5-24)

where: 

2.3 Limit State 3: If tension in the stem of the split tee 

controls the capacity of the connection, Equations 

(5-21) and (5-22) shall be used to determine QCE, with 

Ag and Ae being the gross and net areas of the split tee 

stem and replacing ta with ts.

2.4 Limit State 4: If flexural yielding of the flanges of 

the split tee controls the capacity of the connection, QCE

shall be determined in accordance with Equation (5-25): 

(5-25)

where: 

3. Bolted Flange Plate Connections: [For bolted flange 

plate connections, as shown in Figure 5-5, the flange 

plate shall be welded to the column and welded or 

bolted to the beam flange. This connection shall be 

considered fully restrained if its strength equals or 

exceeds the strength of the connected beam. The 

expected strength of the connection shall be calculated 

in accordance with Equation (5-26):

(5-26)

Figure 5-4 Double Split Tee Connection

db = Overall beam depth

bt = Distance between one row of fasteners in the 

split tee flange and the centerline of the stem as 

shown in Figure 5-4

ts = Thickness of the split tee stem

Fte = Expected tensile strength of the bolts or rivets

QCE MCE db 2bt t

s ( ) + + FteAbNb = = ( )

Ab = Gross area of rivet or bolt

Nb = Number of fasteners in tension connecting the 

flanges of one split tee to the column flange

k1 = Distance from the center of the split tee stem to 

the edge of the split tee flange fillet

bt = Distance between one row of fasteners in the 

split tee flange and the centerline of the stem as 

shown in Figure 5-4

w = Length of split tee

tf = Thickness of split tee flange

QCE MCE

db t

s ( ) + wtf

2

Fye

2 bt k1 ( ) – = = ---------------------------------------

QCE MCE PCE db t

p = = ( ) +
5-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

where: 

4. Bolted End Plate Connections: Bolted end plate 

connections, as shown in Figure 5-6, shall be 

considered FR if their expected and lower-bound 

strengths equal or exceed the expected strength of the 

connecting beam. The lower-bound strength, 

QCL=MCL, shall be the value determined for the limit 

state of the bolts under combined shear and tension and 

the expected strength, QCE = MCE, shall be determined 

for the limit state of bending in the end plate calculated 

in accordance with the procedures of the AISC (1993) 

LRFD Specifications or by another approved procedure 

5. Composite Partially Restrained Connections: Strength 

and deformation acceptance criteria of composite 

partially restrained connections shall be based on 

approved rational analysis procedures and experimental 

evidence.

5.5.3.3.3 Nonlinear Static Procedure

The complete load-deformation relationship of each 

component as depicted by Figure 5-1 shall be 

determined in accordance with Section 5.5.2.2.2. The 

values for expected strength, QCE, of PR connections 

shall be the same as those used for linear procedures as 

specified in Section 5.5.3.3.2.

5.5.3.3.4 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be determined experimentally.

PCE = Expected strength of the flange plate 

connection as governed by the net section of 

the flange plate, the shear capacity of the bolts, 

or the strength of the welds to the column 

flange

tp = Thickness of flange plate

db = Overall beam depth

Figure 5-5 Bolted Flange Plate Connection 

Figure 5-6 Bolted End Plate Connection 

C5.5.3.3.4 Nonlinear Dynamic Procedure

The design professional is directed to FEMA 355D for 

information concerning nonlinear behavior of various 

tested connection configurations.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-27

5.5.3.4 Acceptance Criteria

5.5.3.4.1 General

Component acceptance criteria shall be computed in 

accordance with the general requirements of 

Section 5.4.2 and the specific requirements of this 

section.

5.5.3.4.2 Linear Static and Dynamic Procedures

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2. m-factors for steel 

components and connections of PR frames shall be 

selected from Table 5-5. Limit states for which no mfactors are provided in Table 5-5 shall be considered 

force-controlled.

Acceptance criteria for steel beams and columns in PR 

frames shall be computed in accordance with 

Section 5.5.2.4.2.

5.5.3.4.3 Nonlinear Static and Dynamic Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3. Maximum permissible 

inelastic deformations shall be taken from Tables 5-6 

and 5-7.

5.5.3.5 Rehabilitation Measures 

PR moment frames that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard. 

5.6 Steel Braced Frames

5.6.1 General

Steel braced frames shall be defined as those frames 

that develop seismic resistance primarily through axial 

forces in the components.

Modeling procedures and rehabilitation measures for 

concentric braced frames and eccentric braced frames 

shall be as specified in Sections 5.6.2 and 5.6.3, 

respectively. Components of concentric and eccentric 

braced frames shall include columns, beams, braces, 

and connections. Eccentric braced frames shall also 

include link beam components. 

C5.5.3.4.1 General

The strength and behavior of partially restrained steel 

moment-resisting frames is typically governed by the 

connections. The design professional is urged to 

consider the acceptance criteria for the mechanism that 

controls the system.

C5.5.3.5 Rehabilitation Measures

The rehabilitation measures for FR moment frames 

described in C5.5.2.5 may be effective for PR moment 

frames as well. PR moment frames are often too 

flexible to provide adequate seismic performance. 

Adding concentric or eccentric bracing, or reinforced 

concrete or masonry infills, may be a cost-effective 

rehabilitation measure.

Connections in PR moment frames are usually 

components that are weak, flexible, or both. 

Connections may be rehabilitated by replacing rivets 

with high-strength bolts, adding weldment to 

supplement rivets or bolts, or welding stiffeners to 

connection pieces or combinations of these measures. 

Refer to FEMA 351 for additional information 

concerning the rehabilitation of PR moment frames.

C5.6.1 General

Steel braced frames act as vertical trusses where the 

columns are the chords and the beams and braces are 

the web members.

Components can be either bare steel, steel with a 

nonstructural coating for fire protection, or steel with 

concrete or masonry encasement.
5-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.6.2 Concentric Braced Frames (CBF)

5.6.2.1 General

Concentric braced frames (CBF) shall be defined as 

braced frame systems where component worklines 

intersect at a single point in a joint, or at multiple points 

such that the distance between points of intersection, or 

eccentricity, e, is less than or equal to the width of the 

smallest member connected at the joint. Bending due to 

such eccentricities shall be considered in the design of 

the components.

5.6.2.2 Stiffness 

5.6.2.2.1 Linear Static and Dynamic Procedures

Axial area, shear area, and moment of inertia shall be 

calculated as specified for FR frames in 

Section 5.5.2.2.1.

FR connections shall be modeled as specified in 

Section 5.5.2.2.1. PR connections shall be modeled as 

specified in Section 5.5.3.2.1.

Braces shall be modeled as columns as specified in 

Section 5.5.2.2.1.

5.6.2.2.2 Nonlinear Static Procedure

If the Nonlinear Static Procedure of Chapter 3 is used, 

the following criteria shall apply:

1. The elastic component properties shall be modeled 

as specified in Section 5.6.2.2.1.

2. The nonlinear moment-curvature or loaddeformation behavior to represent yielding and 

buckling shall be as specified in Section 5.5.2.2.2 for 

beams and columns and Section 5.5.3.2.2 for PR 

connections.

In lieu of relationships derived from experiment or 

analysis, the nonlinear load-deformation behavior of 

braces shall be modeled as shown in Figure 5-1 with 

parameters as defined in Tables 5-6 and 5-7. For braces 

loaded in compression, the parameter ∆ in Figure 5-1 

shall represent plastic axial deformation. The parameter 

∆c shall represent the axial deformation at the expected 

buckling load. The reduction in strength of a brace after 

buckling shall be included in the model. Modeling of 

the compression brace behavior using elasto-plastic 

behavior shall be permitted if the yield force is assumed 

as the residual strength after buckling, as defined by 

parameter c in Figure 5-1 and Tables 5-6 and 5-7. 

Implications of forces higher than this lower-bound 

force shall be evaluated relative to other components to 

which the brace is connected. For braces in tension, the 

parameter ∆T shall be the axial deformation at 

development of the expected tensile yield load in the 

brace.

5.6.2.2.3 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be based on experiment or other approved method.

5.6.2.3 Strength

5.6.2.3.1 General

Component strengths shall be computed in accordance 

with the general requirements of Section 5.4.2 and the 

specific requirements of this section.

5.6.2.3.2 Linear Static and Dynamic Procedures

The expected strength, QCE, of steel braces under axial 

compression shall be the lowest value obtained for the 

limit states of buckling or local buckling. The effective 

design strength, PCE, shall be calculated in accordance 

with AISC (1993) LRFD Specifications, taking φ=1.0 

and using the expected yield strength, Fye, for yield 

strength.

C5.6.2.2.2 Nonlinear Static Procedure

The design professional is directed to FEMA 274 for 

information regarding nonlinear load-deformation 

behavior of braces.

C5.6.2.2.3 Nonlinear Dynamic Procedure

The design professional is directed to FEMA 274 for 

information concerning hysteretic behavior of bracedframe components.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-29

For common cross bracing configurations where both 

braces cross at their midpoints and are attached to a 

common gusset plate, the effective length of each brace 

shall be taken as 0.5 times the total length of the brace 

including gusset plates for both axes of buckling. For 

other bracing configurations (chevron, V, single brace), 

the length shall be taken as the total length of the brace 

including gusset plates, and the effective length shall be 

taken as 0.8 times the total length for in-plane buckling 

and 1.0 times the total length for out-of-plane buckling.

The expected strength, QCE, of steel braces in tension 

shall be calculated as for columns, in accordance with 

Section 5.5.2.3.2.

Expected, QCE, and lower bound, QCL, strengths of 

beams and columns shall be calculated as for FR beams 

and columns in Section 5.5.2.3. Strength of beams with 

non-negligible axial load shall be as calculated for FR 

columns.

The lower-bound strength of brace connections shall be 

calculated in accordance with the AISC (1993) LFRD 

Specifications, taking φ=1.0 and using the lower-bound 

yield strength, FyLB, for yield strength.

5.6.2.3.3 Nonlinear Static Procedure

In lieu of relationships derived by experiment or 

analysis, the complete load-deformation behavior of 

each component as depicted by Figure 5-1 shall be 

determined in accordance with Section 5.5.2.2.2. The 

values for expected strength, QCE, shall as specified in 

Section 5.6.2.3.2 for linear procedures.

5.6.2.3.4 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be determined experimentally.

5.6.2.4 Acceptance Criteria

5.6.2.4.1 General

Component acceptance criteria shall be computed in 

accordance with the general requirements of 

Section 5.4.2 and the specific requirements of this 

section.

Axial tension and compression in braces shall be 

considered deformation-controlled. Actions on beams 

and columns with non-negligible axial load shall be 

considered force- or deformation-controlled as 

determined for FR frame columns in Section 5.5.2.4. 

Compression, tension, shear, and bending actions on 

brace connections including gusset plates, bolts, welds, 

and other connectors shall be considered forcecontrolled.

5.6.2.4.2 Linear Static and Dynamic Procedures

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2. m-factors for steel 

components shall be selected from Table 5-5.

Stitch plates for built-up members shall be spaced such 

that the largest slenderness ratio of the components of 

the brace does not exceed 0.4 times the governing 

slenderness ratio of the brace as a whole. The stitches 

for compression members shall be able to transfer the 

maximum force in one element to adjacent elements. If 

not, stitch plates shall be added, or the m-factors in 

Table 5-4 shall be reduced by 50%, but need not be 

taken less than 1.0.

5.6.2.4.3 Nonlinear Static and Dynamic Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3. Deformations limits shall 

be taken from Tables 5-6 and 5-7.

5.6.2.5 Rehabilitation Measures

Concentric braced frame components that do meet not 

the acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 5.4.3 

and other provisions of this standard.

C5.6.2.3.4 Nonlinear Dynamic Procedure 

The design professional is directed to FEMA 274 for 

information concerning hysteretic behavior of braced 

frame components.

C5.6.2.5 Rehabilitation Measures

The rehabilitation measures for FR moment frames 

described in Section C5.5.2.5 may be effective for 

braced frames. Other modifications which may be 

effective include replacement or modification of 

connections that are insufficient in strength and/or 

ductility, and encasement of columns in concrete to 

improve their performance.
5-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.6.3 Eccentric Braced Frames (EBF)

5.6.3.1 General

Eccentric braced frames (EBF) shall be defined as 

braced frames where component worklines do not 

intersect at a single point and the distance between 

points of intersection, or eccentricity, e, exceeds the 

width of the smallest member connected at the joint. 

The component segment between these points is 

defined as the link component with a span equal to the 

eccentricity.

5.6.3.2 Stiffness

5.6.3.2.1 Linear Static and Dynamic Procedures

The elastic stiffness of beams, columns, braces, and 

connections shall be the same as those specified for FR 

and PR moment frames and concentric braced frames. 

The load-deformation model for a link beam shall 

include shear deformation and flexural deformation.

The elastic stiffness of the link beam, Ke, shall be 

computed in accordance with Equation (5-27):

(5-27)

where:

(5-28)

(5-29)

5.6.3.2.2 Nonlinear Static Procedure

In lieu of relationships derived from experiment or 

analysis, the nonlinear load-deformation behavior of 

member of EBFs shall be modeled as shown in Figure 

5-1 and in accordance with Section 5.5.2.2.2.

Nonlinear models for beams, columns, and connections 

for FR and PR moment frames, and for the braces for a 

CBF, shall be permitted.

The link rotation at yield shall be calculated in 

accordance with Equation (5-30): 

(5-30)

5.6.3.2.3 Nonlinear Dynamic Procedure

If the Nonlinear Dynamic Procedure is used, the 

complete hysteretic behavior of each component shall 

be modeled and shall be based on experiment or an 

approved rational analysis procedure.

5.6.3.3 Strength

5.6.3.3.1 General

Component strengths shall be computed in accordance 

with the general requirements of Section 5.4.2 and the 

specific requirements of this section.

5.6.3.3.2 Linear Static and Dynamic Procedures

Lower-bound compressive strength, PCL, of braces in 

eccentric braced frames shall be calculated as for 

columns in accordance with Section 5.5.2.3.2 except 

that lower-bound yield strength, FyLB, shall be used for 

yield strength.

Expected, QCE, and lower bound, QCL, strengths of 

beams and columns shall be calculated as for FR beams 

and columns in Section 5.5.2.3. Strength of beams with 

non-negligible axial load shall be as calculated for FR 

columns.

Aw = (db – 2tf

) tw

e = Length of link beam

G = Shear modulus

Ke = Stiffness of the link beam

Kb = Flexural stiffness

Ks = Shear stiffness

db = Beam depth

tf = Thickness of flange

tw = Thickness of web

Ke

KsKb

Ks Kb + = ------------------

Ks

GAw

e = -----------

Kb

12EIb

e

3 = --------------

C5.6.3.2.3 Nonlinear Dynamic Procedure

The design professional is directed to FEMA 274 for 

guidelines on modeling the link beams and information 

regarding the hysteretic behavior of EBF components.

θy

QCE

Kee = ----------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-31

The lower-bound strength of brace connections shall be 

calculated in accordance with AISC (1993) LRFD 

Specifications, taking φ=1.0 and using the lower-bound 

yield strength, FyLB, for yield strength.

The strength of the link beam shall be governed by 

shear, flexure, or the combination of shear and flexure. 

MCE shall be taken as the expected moment capacity 

and VCE shall be taken as 0.6 FyeAw.

If , Equation (5-31) shall be used to compute 

the expected strength of the link beam:

(5-31)

If , Equation (5-32) shall be used to compute 

the expected strength of the link beam:

(5-32)

Linear interpolation between Equations (5-31) and 

(5-32) shall be used for intermediate values of e.

5.6.3.3.3 Nonlinear Static Procedure

Strengths for EBFs shall be the same as those specified 

in Section 5.6.2.3.3 for CBFs. In lieu of relationships 

derived from experiment or analysis, the loaddeformation behavior of each component, as depicted 

by Figure 5-1, shall be determined in accordance with 

Section 5.6.3.2.2.

5.6.3.3.4 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be determined experimentally.

5.6.3.4 Acceptance Criteria

5.6.3.4.1 General

Component acceptance criteria shall be computed in 

accordance with the general requirements of 

Section 5.4.2 and the specific requirements of this 

section.

Shear and flexure in link beams shall be considered 

deformation-controlled actions. All other actions, and 

actions on other EBF components, shall be considered 

force-controlled. Compression, tension, shear, and 

bending actions on brace connections including gusset 

plates, bolts, welds, and other connectors shall be 

considered force-controlled.

5.6.3.4.2 Linear Static and Dynamic Procedures

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2. m-factors for steel 

components shall be selected from Table 5-5.

Link beams shall conform to the requirements of the 

AISC (1997) Seismic Provisions with regard to 

detailing. The brace connecting to a link beam shall be 

designed for 1.25 times the link strength to ensure link 

yielding without brace or column buckling. Where the 

link beam is attached to the column flange with full-pen 

welds, the provisions for these connections shall be the 

same as for FR frame full-pen connections. m-factors 

for flexure and shear in link beams shall be taken from 

Table 5-5. 

5.6.3.4.3 Nonlinear Static and Dynamic Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3. Deformations limits shall 

be taken from Tables 5-6 and 5-7.

e 1.6MCE

VCE

≤ ------------------

QCE VCE 0.6FyeAw = =

e 2.6MCE

VCE

> -------------------

QCE 2

MCE

e = -----------

C5.6.3.4.2 Linear Static and Dynamic Procedures

The acceptance criteria for full-penetration welded 

beam-to-column connections is based on testing of 

typical moment frame proportioning and span ratios.
5-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.6.3.5 Rehabilitation Measures

Eccentric braced frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 5.4.3 

and other provisions of this standard. 

5.7 Steel Plate Shear Walls

5.7.1 General

A steel plate shear wall, with or without perforations, 

shall be provided with boundary members on all four 

sides and shall be welded to these boundary elements. 

The steel plate walls shall be designed to resist seismic 

loads acting alone or in conjunction with other existing 

lateral load resisting elements. The boundary elements 

shall be evaluated as beams and/or columns. 

5.7.2 Stiffness

5.7.2.1 Linear Static and Dynamic 

Procedures

Use of a plane stress finite element with beams and columns as boundary elements to analyze a steel plate 

shear wall shall be permitted. The global stiffness of the 

wall, Kw, shall be calculated in accordance with Equation (5-33) unless another method based on principles 

of mechanics is used.

(5-33)

where:

5.7.2.2 Nonlinear Static Procedure

The elastic stiffness of the load-deformation 

relationship for the wall shall be as specified in 

Section 5.7.2.1. The complete nonlinear loaddeformation relationship shall be based on experiment 

or approved rational analysis. Alternatively, use of the 

generalized load-deformation relationship shown in 

Figure 5-1, as specified in Section 5.5.2.2.2, shall be 

permitted.

5.7.2.3 Nonlinear Dynamic Procedure

The complete hysteretic behavior of each component 

shall be modeled by a rational procedure verified by 

experiment.

5.7.3 Strength

5.7.3.1 General

Component strengths shall be computed in accordance 

with the general requirements of Section 5.4.2 and the 

specific requirements of this section.

C5.6.3.5 Rehabilitation Measures

The rehabilitation measures described in C5.4.2.4 for 

FR moment frames and in C5.5.2.4 for CBFs may be 

effective for many of the beams, columns, and braces. 

Cover plates and/or stiffeners may be effective in 

rehabilitating these components. The strength of the 

link may be increased by adding cover plates to the 

beam flange(s), adding doubler plates or stiffeners to 

the web, or changing the brace configuration.

C5.7.1 General

A steel plate wall develops its seismic resistance 

through shear stress in the plate wall.

Although steel plate walls are not common, they have 

been used to rehabilitate a few essential structures 

where Immediate Occupancy and operation of a 

facility is mandatory after a large earthquake. Due to 

their stiffness, the steel plate walls attract much of the 

seismic shear. It is essential that the new load paths be 

carefully established.

The provisions for steel plate walls in this standard 

assume that the plates are sufficiently stiffened to 

prevent buckling. The design professional is referred to 

Timler (2000) for additional information regarding the 

behavior and design of steel plate shear walls.

G = Shear modulus of steel

a = Clear width of wall between columns

h = Clear height of wall between beams

tw = Thickness of plate wall

C5.7.2.3 Nonlinear Dynamic Procedure

This procedure is not recommended in most cases.

Kw

Ga t

w

h = --------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-33

5.7.3.2 Linear Static and Dynamic 

Procedures

The expected strength of the steel wall, QCE, shall be 

determined using the applicable equations in Part 6 of 

AISC (1993) LRFD Specifications, with φ=1.0 and the 

expected yield strength, Fye, substituted for Fy. The wall 

shall be permitted to be modeled as the web of a plate 

girder. If stiffeners are provided to prevent buckling, 

they shall be spaced such that buckling of the wall does 

not occur and the expected strength of the wall shall be 

determined by Equation (5-34):

(5-34)

where: 

5.7.3.3 Nonlinear Static and Dynamic 

Procedures

The generalized load-deformation curve shown in 

Figure 5-1, as specified in Section 5.5.2.2.2, shall be 

used to represent the complete load-deformation 

behavior of the steel shear wall to failure unless another 

load-deformation relationship based on experiment or 

approved rational analysis verified by experiment is 

used. The expected strength, QCE, shall be calculated in 

accordance with Equation (5-34).The yield deformation 

shall be calculated in accordance with Equation (5-35):

(5-35)

5.7.4 Acceptance Criteria

5.7.4.1 Linear Static and Dynamic 

Procedures

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2. m-factors for steel 

components shall be selected from Table 5-5.

Shear behavior in steel plate shear walls shall be 

considered a deformation-controlled action, with 

acceptance criteria as provided in Table 5-5. Design 

restrictions for plate girder webs given in AISC (1993) 

LRFD Specifications, including those related to 

stiffener spacing, shall be followed.

In lieu of providing stiffeners, the steel wall shall be 

permitted to be encased in concrete. If buckling is not 

prevented by the use of stiffeners, equations for VCE

given in AISC (1993) LRFD Specifications for plate 

girders shall be used to calculate the expected strength 

of the wall.

5.7.4.2 Nonlinear Static and Dynamic 

Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3. Deformation limits shall 

be taken from Tables 5-6 and 5-7.

5.7.5 Rehabilitation Measures

Steel plate walls that do not meet the acceptance criteria 

for the selected Rehabilitation Objective shall be 

rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard. 

a = clear width of the wall between columns.

CE CE ye w Q = V = 0.6F at

∆y

QCE

Kw

= ----------

C5.7.5 Rehabilitation Measures

Rehabilitation measures may include the addition of 

stiffeners, encasement in concrete, or the addition of 

concrete or steel plate shear walls.
5-34 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.8 Steel Frames with Infills

Steel frames with partial or complete infills of 

reinforced concrete or reinforced or unreinforced 

masonry shall be evaluated considering the combined 

stiffness of the steel frame and infill material.

The engineering properties and acceptance criteria for 

the infill walls shall comply with the requirements in 

Chapter 6 for concrete and Chapter 7 for masonry. Infill 

walls and frames shall be considered to carry the 

seismic force in composite action, considering the 

relative stiffness of each element, until complete failure 

of the walls has occurred. The interaction between the 

steel frame and infill shall be considered using 

procedures specified in Chapter 6 for concrete frames 

with infill. The analysis of each component shall be 

done in stages, considering the effects of interaction 

between the elements and carried through each 

performance level. At the point where the infill has 

been deemed to fail, as determined by the acceptance 

criteria specified in Chapter 6 or Chapter 7, the wall 

shall be removed from the analytical model. The 

analysis shall be resumed on the bare steel frame taking 

into consideration any vertical discontinuity created by 

the degraded wall. At this point, the engineering 

properties and acceptance criteria for the frame, as 

specified in Section 5.5, shall apply.

C5.8 Steel Frames with Infills

Seismic evaluation of infill walls is required because, in 

many cases, these walls are unreinforced or lightly 

reinforced, and their strength and ductility may be 

inadequate. Before the loss of the wall, the steel frame 

adds confining pressure to the wall and enhances its 

resistance. The actual effective forces on the steel frame 

components, however, are probably minimal. As the 

frame components attempt to develop force they 

deform and the stiffer concrete or masonry components 

on the far side of the member pick up load. However, 

beam end connections, column splices, and steel frame 

connections at the foundation should be investigated for 

forces due to interaction with the infill similar to 

procedures specified for concrete frames in Chapter 6.

The stiffness and resistance provided by concrete 

and/or masonry infills may be much larger than the 

stiffness of the steel frame acting alone with or without 

composite actions. Gaps or incomplete contact between 

the steel frame and the infill may negate some or all of 

this stiffness. These gaps may be between the wall and 

columns of the frame or between the wall and the top 

beam enclosing the frame. Different strength and 

stiffness conditions must be expected with different 

discontinuity types and locations. Therefore, the 

presence of any gaps or discontinuities between the 

infill walls and the frame must be determined and 

considered in the design and rehabilitation process. The 

resistance provided by infill walls may also be included 

if proper evaluation of the connection and interaction 

between the wall and the frame is made and if the 

strength, ductility, and properties of the wall are 

properly included.

The stiffness provided by infill masonry walls is 

excluded from the design and rehabilitation process 

unless integral action between the steel frame and the 

wall is verified. If complete or partial interaction 

between the wall and frame is verified, the stiffness is 

increased accordingly. The seismic performance of 

unconfined masonry walls is far inferior to that of 

confined masonry walls; therefore, the resistance of the 

attached wall can be used only if strong evidence as to 

its strength, ductility, and interaction with the steel 

frame is provided.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-35

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components

m-factors for Linear Procedures1

IO

Primary Secondary

Component/Action LS CP LS CP

Beams – flexure

 a. 

and 2 6 8 10 12

 b. 

or 

1.25 2 3 3 4

c. Other

Linear interpolation between the values on lines a and b for both flange slenderness 

(first term) and web slenderness (second term) shall be performed, and the lowest 

resulting value shall be used

Columns – flexure 12, 13

For P/PCL < 0.20

a. 

and 2 6 8 10 12

b. 

or 

1.25 1.25 2 2 3

c. Other

Linear interpolation between the values on lines a and b for both flange slenderness 

(first term) and web slenderness (second term) shall be performed, and the lowest 

resulting value shall be used

bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 418

Fye

≤ ------------

bf

2t

f

------ 65

Fye

≥ ------------

h

t

w

---- 640

Fye

≥ ------------

bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 300

Fye

≤ ------------

bf

2t

f

------ 65

Fye

≥ ------------

h

t

w

---- 460

Fye

≥ ------------
5-36 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

 For 0.2 < P/PCL < 0.50

a. 

and 1.25 —2 —3 —4 —5

b. 

or 

1.25 1.25 1.5 2 2

c. Other

Linear interpolation between the values on lines a and b for both flange slenderness 

(first term) and web slenderness (second term) shall be performed, and the lowest 

resulting value shall be used

Column Panel Zones – Shear 1.5 8 11 12 12

Fully Restrained Moment Connections15

WUF14 1.0 4.3-0.083d 3.9-0.043d 4.3-0.048d 5.5-0.064d

Bottom haunch in WUF with slab 1.6 2.7 3.4 3.8 4.7

Bottom haunch in WUF without slab 1.3 2.1 2.5 2.8 3.3

Welded cover plate in WUF14 2.4-0.030d 4.3-0.067d 5.4-0.090d 5.4-0.090d 6.9-0.118d

Improved WUF-bolted web14 1.4-0.008d 2.3-0.021d 3.1-0.032d 4.9-0.048d 6.2-0.065d

Improved WUF-welded web 2.0 4.2 5.3 5.3 6.7

Free flange14 2.7-0.032d 6.3-0.098d 8.1-0.129d 8.4-0.129d 11.0-0.172d

Reduced beam section14 2.2-0.008d 4.9-0.025d 6.2-0.032d 6.5-0.025d 8.4-0.032d

Welded flange plates

a. Flange plate net section 1.7 3.3 4.1 5.7 7.3

b. Other limit states force-controlled

Welded bottom haunch 1.6 3.1 3.8 4.6 5.9

Welded top and bottom haunches 1.6 3.1 3.9 4.7 6.0

Welded cover-plated flanges 1.7 2.8 3.4 3.4 4.2

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components (continued)

m-factors for Linear Procedures1

IO

Primary Secondary

Component/Action LS CP LS CP

 bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 260

Fye

≤ ------------

bf

2t

f

------ 65

Fye

≥ ------------

h

t

w

---- 400

Fye

≥ ------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-37

Partially Restrained Moment Connections

Top and bottom clip angle8

a. Shear failure of rivet or bolt (Limit 

State 1)9

1.5 4 6 6 8

b. Tension failure of horizontal leg 

of angle (Limit State 2)

1.25 1.5 2 1.5 2

c. Tension failure of rivet or bolt 

(Limit State 3)9

1.25 1.5 2.5 4 4

d. Flexural failure of angle (Limit 

State 4)

2 5 7 7 14

Double split tee8

a. Shear failure of rivet or bolt (Limit 

State 1)9

1.5 4 6 6 8

b. Tension failure of rivet or bolt 

(Limit State 2)9

1.25 1.5 2.5 4 4

c. Tension failure of split tee stem 

(Limit State 3)

1.25 1.5 2 1.5 2

d. Flexural failure of split tee (Limit 

State 4)

2 5 7 7 14

Bolted flange plate8

a. Failure in net section of flange 

plate or shear failure of bolts or 

rivets9

1.5 4 5 4 5

b. Weld failure or tension failure on 

gross section of plate

1.25 1.5 2 1.5 2

Bolted end plate

a. Yield of end plate 2 5.5 7 7 7

b. Yield of bolts 1.5 2 3 4 4

c. Failure of weld 1.25 1.5 2 3 3

Composite top and clip angle bottom 8

a. Failure of deck reinforcement 1.25 2 3 4 6

b. Local flange yielding and web 

crippling of column

1.5 4 6 5 7

c. Yield of bottom flange angle 1.5 4 6 6 7

d. Tensile yield of rivets or bolts at 

column flange

1.25 1.5 2.5 2.5 3.5

e. Shear yield of beam flange 

connections

1.25 2.5 3.5 3.5 4.5

Shear connection with slab14 1.6-0.005dbg -- -- 13.0-0.290dbg 17.0-0.387dbg

Shear connection without slab14 4.9-0.097dbg -- -- 13.0-0.290dbg 17.0-0.387dbg

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components (continued)

m-factors for Linear Procedures1

IO

Primary Secondary

Component/Action LS CP LS CP
5-38 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

EBF Link Beam7, 10

a. 1.5 9 13 13 15

b. Same as for beams.

c. Linear interpolation shall be used.

Braces in Compression (except EBF braces)

a. Double angles buckling 

in-plane

1.25 6 8 7 9

b. Double angles buckling 

out-of-plane

1.25 5 7 6 8

c. W or I shape 1.25 6 8 6 8

d. Double channels buckling 

in-plane

1.25 6 8 7 9

e. Double channels buckling 

out-of-plane

1.25 5 7 6 8

f. Concrete-filled tubes 1.25 5 7 5 7

g. Rectangular cold-formed tubes

1. 1.25 5 7 5 7

2. 1.25 2 3 2 3

3. Linear interpolation shall be used.

h. Circular hollow tubes

1. 1.25 5 7 5 7

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components (continued)

m-factors for Linear Procedures1

IO

Primary Secondary

Component/Action LS CP LS CP

e 1.6 MCE

VCE

≤ -------------------

e 2.6 MCE

VCE

≥ -------------------

1.6 MCE

VCE

------------------- e 2.6 MCE

VCE

< < -------------------

Fy t

d 90

≤

Fy t

d 190

≥

Fy t

d

Fy

90 190

≤ ≤

y t F

d 1500

≤
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-39

2. 1.25 2 3 2 3

3. Linear interpolation shall be used.

Braces in Tension (except EBF 

braces)16

1.25 6 8 8 10

Beams, Columns in Tension 

(except EBF beams, columns)

1.25 3 5 6 7

Steel Plate Shear Walls11 1.5 8 12 12 14

Diaphragm Components

Diaphragm shear yielding or panel or 

plate buckling

1.25 2 3 2 3

Diaphragm chords and collectors—

full lateral support

1.25 6 8 6 8

Diaphragm chords and collectors—

limited lateral support

1.25 2 3 2 3

1. For built-up members where the lacing plates do not meet the requirements of Section 5.6.2.4.2, divide m-factors by 2.0, but values need not be less than 

1.0.

2. m=9(1-1.7 P/PCL).

3. m=12(1-1.7 P/PCL).

4. m=15(1-1.7 P/PCL).

5. m=18(1-1.7 P/PCL).

6. Not used.

7. Values are for link beams with three or more web stiffeners. If no stiffeners, divide values by 2.0, but values need not be less than 1.25. Linear 

interpolation shall be used for one or two stiffeners.

8. Web plate or stiffened seat shall be considered to carry shear. Without shear connection, action shall not be classified as secondary. If db > 18 inches, 

multiply m-factors by 18/db, but values need not be less than 1.0.

9. For high-strength bolts, divide values by 2.0, but values need not be less than 1.25.

10. Assumes ductile detailing for flexural link, in accordance with AISC (1995) LRFD Specifications.

11. Applicable if stiffeners, or concrete backing, is provided to prevent buckling.

12. Columns in moment or braced frames shall be permitted to be designed for the maximum force delivered by connecting members. For rectangular or 

square columns, replace bt /2tf

 with b/t, replace 52 with 110, and replace 65 with 190.

13. Columns with P/PCL > 0.5 shall be considered force-controlled.

14. d is the beam depth; dbg is the depth of the bolt group.

15. Tabulated values shall be modified as indicated in Section 5.5.2.4.2, item 4.

16. For tension-only bracing, m-factors shall be divided by 2.0.

Table 5-5 Acceptance Criteria for Linear Procedures—Structural Steel Components (continued)

m-factors for Linear Procedures1

IO

Primary Secondary

Component/Action LS CP LS CP

y t F

d 6000

≥

y t F

d

y F

1500 6000

≤ ≤
5-40 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Table 5-6 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Structural Steel 

Components

Component/Action

Modeling Parameters Acceptance Criteria

Plastic Rotation

Angle,

Radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, Radians

IO

Primary Secondary

a b c LS CP LS CP

Beams—flexure

 a. 

and 

9θy 11θy 0.6 1θy 6θy 8θy 9θy 11θy

 b. 

or 

4θy 6θy 0.2 0.25θy 2θy 3θy 3θy 4θy

c. Other

Linear interpolation between the values on lines a and b for both flange slenderness (first term) and 

web slenderness (second term) shall be performed, and the lowest resulting value shall be used

Columns—flexure 2, 7

For P/PCL < 0.20

a. 

and 

9θy 11θy 0.6 1θy 6θy 8θy 9θy 11θy

b. 

or 

4θy 6θy 0.2 0.25θy 2θy 3θy 3θy 4θy

 c. Other Linear interpolation between the values on lines a and b for both flange slenderness (first term) and 

web slenderness (second term) shall be performed, and the lowest resulting value shall be used

bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 418

Fye

≤ ------------

bf

2t

f

------ 65

Fye

≥ ------------

h

t

w

---- 640

Fye

≥ ------------

bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 300

Fye

≤ ------------

bf

2t

f

------ 65

Fye

d ≥ ------------

h

t

w

---- 460

Fye

≥ ------------
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-41

For 0.2 < P/PCL < 0.50

a. 

and — 3 — 4 0.2 0.25θy — 5 — 3 — 6 — 4

b. 

or 

1θy 1.5θy 0.2 0.25θy 0.5θy 0.8θy 1.2θy 1.2θy

c. Other

Linear interpolation between the values on lines a and b for both flange slenderness (first term) and 

web slenderness (second term) shall be performed, and the lowest resulting value shall be used

Column Panel Zones 12θy 12θy 1.0 1θy 8θy 11θy 12θy 12θy

Fully Restrained Moment Connections13

WUF12 0.051-0.0013d 0.043-0.0006d 0.2 0.0128-

0.0003d

0.0337-

0.0009d

0.0284-

0.0004d

0.0323-

0.0005d

0.043-0.0006d

Bottom haunch in WUF with 

slab

0.026 0.036 0.2 0.0065 0.0172 0.0238 0.0270 0.036

Bottom haunch in WUF 

without slab

0.018 0.023 0.2 0.0045 0.0119 0.0152 0.0180 0.023

Welded cover plate in 

WUF12

0.056-0.0011d 0.056-0.0011d 0.2 0.0140-

0.0003d

0.0319-

0.0006d

0.0426-

0.0008d

0.0420-

0.0008d

0.056-0.0011d

Improved WUF-bolted 

web12

0.021-0.0003d 0.050-0.0006d 0.2 0.0053-

0.0001d

0.0139-

0.0002d

0.0210-

0.0003d

0.0375-

0.0005d

0.050-0.0006d

Improved WUF-welded web 0.041 0.054 0.2 0.0103 0.0312 0.0410 0.0410 0.054

Free flange12 0.067-0.0012d 0.094-0.0016d 0.2 0.0168-

0.0003d

0.0509-

0.0009d

0.0670-

0.0012d

0.0705-

0.0012d

0.094-0.0016d

Reduced beam section12 0.050-0.0003d 0.070-0.0003d 0.2 0.0125-

0.0001d

0.0380-

0.0002d

0.0500-

0.0003d

0.0525-

0.0002d

0.07-0.0003d

Welded flange plates

a. Flange plate 

 net section

0.03 0.06 0.2 0.0075 0.0228 0.0300 0.0450 0.06

b. Other limit states force-controlled

Welded bottom haunch 0.027 0.047 0.2 0.0068 0.0205 0.0270 0.0353 0.047

Welded top and bottom 

haunches

0.028 0.048 0.2 0.0070 0.0213 0.0280 0.0360 0.048

Welded cover-plated 

flanges

0.031 0.031 0.2 0.0078 0.0177 0.0236 0.0233 0.031

Table 5-6 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Structural Steel 

Components (continued)

Component/Action

Modeling Parameters Acceptance Criteria

Plastic Rotation

Angle,

Radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, Radians

IO

Primary Secondary

a b c LS CP LS CP

 bf

2t

f

------ 52

Fye

≤ ------------

h

t

w

---- 260

Fye

≤ ------------

bf

2t

f

------ 65

Fye

≥ ------------

h

t

w

---- 400

Fye

≥ ------------
5-42 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Partially Restrained Moment Connections

Top and bottom clip angle9

a. Shear failure of rivet 

or bolt 

(Limit State 1)8

0.036 0.048 0.200 0.008 0.020 0.030 0.030 0.040

b. Tension failure of 

horizontal leg of 

angle (Limit State 2)

0.012 0.018 0.800 0.003 0.008 0.010 0.010 0.015

c. Tension failure of 

rivet or bolt 

(Limit State 3)8

0.016 0.025 1.000 0.005 0.008 0.013 0.020 0.020

d. Flexural failure of 

angle (Limit State 4)

0.042 0.084 0.200 0.010 0.025 0.035 0.035 0.070

Double split tee9

a. Shear failure of rivet 

or bolt 

(Limit State 1)8

0.036 0.048 0.200 0.008 0.020 0.030 0.030 0.040

b. Tension failure of 

rivet or bolt 

(Limit State 2)8

0.016 0.024 0.800 0.005 0.008 0.013 0.020 0.020

c. Tension failure of 

split tee stem 

(Limit State 3)

0.012 0.018 0.800 0.003 0.008 0.010 0.010 0.015

d. Flexural failure of 

split tee 

(Limit State 4)

0.042 0.084 0.200 0.010 0.025 0.035 0.035 0.070

Bolted flange plate9

a. Failure in net 

section of flange 

plate or shear failure 

of bolts or rivets8

0.030 0.030 0.800 0.008 0.020 0.025 0.020 0.025

b. Weld failure or 

tension failure on 

gross section of 

plate

0.012 0.018 0.800 0.003 0.008 0.010 0.010 0.015

Bolted end plate

a. Yield of end plate 0.042 0.042 0.800 0.010 0.028 0.035 0.035 0.035

b. Yield of bolts 0.018 0.024 0.800 0.008 0.010 0.015 0.020 0.020

c. Failure of weld 0.012 0.018 0.800 0.003 0.008 0.010 0.015 0.015

Composite top clip angle bottom 9

a. Failure of deck 

reinforcement

0.018 0.035 0.800 0.005 0.010 0.015 0.020 0.030

b. Local flange yielding 

and web crippling of 

column

0.036 0.042 0.400 0.008 0.020 0.030 0.025 0.035

Table 5-6 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Structural Steel 

Components (continued)

Component/Action

Modeling Parameters Acceptance Criteria

Plastic Rotation

Angle,

Radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, Radians

IO

Primary Secondary

a b c LS CP LS CP
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-43

c. Yield of bottom 

flange angle

0.036 0.042 0.200 0.008 0.020 0.030 0.025 0.035

d. Tensile yield of 

rivets or bolts at 

column flange

0.015 0.022 0.800 0.005 0.008 0.013 0.013 0.018

e. Shear yield of beam 

flange connection

0.022 0.027 0.200 0.005 0.013 0.018 0.018 0.023

Shear connection with 

slab12

0.029-

0.0002dbg

0.15-0.0036dbg 0.400 0.0073-

0.0001dbg

-- -- 0.1125-

0.0027dbg

0.15-

0.0036dbg

Shear connection without 

slab12

0.15-0.0036dbg 0.15-0.0036dbg 0.400 0.0375-

0.0009dbg

-- -- 0.1125-

0.0027dbg

0.15-

0.0036dbg

EBF Link Beam10, 11

a. 0.15 0.17 0.8 0.005 0.11 0.14 0.14 0.16

b. Same as for beams.

c. Linear interpolation shall be used.

Steel Plate Shear Walls 1 14θy 16θy 0.7 0.5θy 10θy 13θy 13θy 15θy

1. Values are for shear walls with stiffeners to prevent shear buckling.

2. Columns in moment or braced frames shall be permitted to be designed for the maximum force delivered by connecting members. For rectangular or square 

columns, replace bt /2tf with b/t, replace 52 with 110, and replace 65 with 190.

3. Plastic rotation = 11 (1-1.7 P/PCL) θy.

4. Plastic rotation = 17 (1-1.7 P/PCL) θy.

5. Plastic rotation = 8 (1-1.7 P/PCL) θy.

6. Plastic rotation = 14 (1-1.7 P/PCL) θy.

7. Columns with P/PCL > 0.5 shall be considered force-controlled.

8. For high-strength bolts, divide values by 2.0.

9. Web plate or stiffened seat shall be considered to carry shear. Without shear connection, action shall not be classified as secondary. If beam depth, db > 18 

inches, multiply m-factors by 18/db.

10. Deformation is the rotation angle between link and beam outside link or column.

11. Values are for link beams with three or more web stiffeners. If no stiffeners, divide values by 2.0. Linear interpolation shall be used for one or two stiffeners.

12. d is the beam depth; dbg is the depth of the bolt group.

13. Tabulated values shall be modified as indicated in Section 5.5.2.4.2, item 4.

Table 5-6 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Structural Steel 

Components (continued)

Component/Action

Modeling Parameters Acceptance Criteria

Plastic Rotation

Angle,

Radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, Radians

IO

Primary Secondary

a b c LS CP LS CP

e 1.6 MCE

VCE

≤ -------------------

e 2.6 MCE

VCE

≥ -------------------

.6 MCE

VCE

------------------- e 2.6 MCE

VCE

< < -------------------
5-44 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Table 5-7 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Structural Steel 

Components

Modeling Parameters Acceptance Criteria

Component/Action

Plastic Deformation

Residual 

Strength 

Ratio

Plastic Deformation

IO

Primary Secondary

a b c LS CP LS CP

Braces in Compression (except EBF braces)1

a. Double angles 

buckling in-plane

0.5∆c 9∆c 0.2 0.25∆c 5∆c 7∆c 7∆c 8∆c

b. Double angles 

buckling out-of-plane

0.5∆c 8∆c 0.2 0.25∆c 4∆c 6∆c 6∆c 7∆c

c. W or I shape 0.5∆c 8∆c 0.2 0.25∆c 5∆c 7∆c 7∆c 8∆c

d. Double channels 

buckling in-plane

0.5∆c 9∆c 0.2 0.25∆c 5∆c 7∆c 7∆c 8∆c

e. Double channels 

buckling out-of-plane

0.5∆c 8∆c 0.2 0.25∆c 4∆c 6∆c 6∆c 7∆c

f. Concrete-filled tubes 0.5∆c 7∆c 0.2 0.25∆c 4∆c 6∆c 6∆c 7∆c

g. Rectangular cold-formed tubes

1. 0.5∆c 7∆c 0.4 0.25∆c 4∆c 6∆c 6∆c 7∆c

2. 0.5∆c 3∆c 0.2 0.25∆c 1∆c 2∆c 2∆c 3∆c

3. Linear interpolation shall be used.

h. Circular hollow tubes

1. 0.5∆c 9∆c 0.4 0.25∆c 4∆c 6∆c 5∆c 8∆c

2. 0.5∆c 3∆c 0.2 0.25∆c 1∆c 2∆c 2∆c 3∆c

3. Linear interpolation shall be used.

Braces in Tension

(except EBF braces)2 11∆T 14∆T 0.8 0.25∆T 7∆T 9∆T 11∆T 13∆T

Beams, Columns in 

Tension (except 

EBF beams, columns)2

5∆T 7∆T 1.0 0.25∆T 3∆T 5∆T 6∆T 7∆T

1. ∆c is the axial deformation at expected buckling load.

2. ∆T is the axial deformation at expected tensile yielding load.

Fy t

d 90 ≤

Fy t

d 190

≥

Fy t

d

Fy

90 190

≤ ≤

Fy t

d 1500

≤

F y t

d 6000

≥

y t F

d

y F

1500 6000

≤ ≤
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-45

5.9 Diaphragms

5.9.1 Bare Metal Deck Diaphragms

5.9.1.1 General

Metal deck diaphragms shall be composed of metal 

plate or gage thickness steel sheets formed in a 

repeating pattern with ridges and valleys. Decking units 

shall be attached to each other and to the structural steel 

supports by welds or by mechanical fasteners. Bare 

metal deck diaphragms shall be permitted to resist 

seismic loads acting alone or in conjunction with 

supplementary diagonal bracing complying with the 

requirements of Section 5.9.4. Steel frame elements, to 

which bare metal deck diaphragms are attached at their 

boundaries, shall be considered to be the chord and 

collector elements.

Criteria shall apply to existing diaphragms as well as to 

stiffened, strengthened, or otherwise rehabilitated 

diaphragms. Interaction of new and existing elements of 

rehabilitated diaphragms shall be evaluated to ensure 

stiffness compatibility. Load transfer mechanisms 

between new and existing diaphragm elements shall be 

evaluated.

5.9.1.2 Stiffness

5.9.1.2.1 Linear Procedures

Metal deck diaphragms shall be classified as flexible, 

stiff, or rigid in accordance with Section 3.2.4. 

Flexibility factors for use in the analysis shall be 

calculated by an approved rational method.

5.9.1.2.2 Nonlinear Static Procedure

Inelastic properties of diaphragms shall not be included 

in inelastic seismic analyses if the weak link of the 

diaphragm is connection failure. Procedures for 

developing models for inelastic response of wood 

diaphragms in unreinforced masonry (URM) buildings 

shall be permitted for use as the basis of an inelastic 

model of a flexible metal diaphragm. A strainhardening modulus of 3% shall be used in the postelastic region.

5.9.1.3 Strength

The strength of bare metal deck diaphragms shall be 

determined in accordance with Section 5.4.2 and the 

specific requirements of the general requirements of 

this section.

Expected strength, QCE, for bare metal deck 

diaphragms shall be taken as two times allowable 

values specified in approved codes and standards, 

unless a larger value is justified by test data.

Lower-bound strengths, QCL, of welded connectors 

shall be as specified in the Welding Code for Sheet 

Steel, AWS D1.3, or other approved standard. 

C5.9.1.1 General

Bare metal deck diaphragms are usually used for roofs 

of buildings where there are very light gravity loads 

other than support of roofing materials. Load transfer 

to frame elements that act as chords or collectors in 

modern frames is through shear connectors, puddle 

welds, screws, or shot pins.

C5.9.1.2.1 Linear Procedures

Flexibility factors for various types of metal decks are 

available from manufacturers’ catalogs. In systems for 

which values are not available, values can be 

established by interpolating between the most 

representative systems for which values are available. 

Flexibility factors for use in the analysis can also be 

calculated using the SDI, Steel Deck Institute 

Diaphragm Design Manual.

C5.9.1.3 Strength

Capacities of steel deck diaphragms are given in 

International Conference of Building Officials (ICBO) 

reports, in manufacturers’ literature, or in the 

publications of the Steel Deck Institute (SDI). Where 

allowable stresses are given, these may be multiplied 

by 2.0 in lieu of information provided by the 

manufacturer or other knowledgeable sources.

Connections between metal decks and steel framing 

commonly use puddle welds. Connection capacities 

are provided in ICBO reports, manufacturers’ data, the 

SDI Manual, or AWS D1.3. Other attachment systems, 

such as clips, are sometimes used.
5-46 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.9.1.4 Acceptance Criteria

Connections of bare metal deck diaphragms shall be 

considered force-controlled. Connection capacity shall 

be checked for the ability to transfer the total diaphragm 

reaction into the steel framing. Diaphragms that are 

governed by the capacity of the connections shall also 

be considered force-controlled. Bare metal deck 

diaphragms not governed by the capacity of the 

connections shall be considered deformationcontrolled. m-factors for shear yielding or plate 

buckling shall taken from Table 5-5.

For the Life Safety Structural Performance Level, a loss 

of bearing support or anchorage of the deck shall not be 

permitted. For higher performance levels, the amount of 

damage to the connections shall not impair the load 

transfer between the diaphragm and the steel frame. 

Deformations shall not exceed the threshold of 

deflections that cause unacceptable damage to other 

elements (either structural or nonstructural) at specified 

performance levels.

5.9.1.5 Rehabilitation Measures

Bare metal diaphragms that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard. 

5.9.2 Metal Deck Diaphragms with 

Structural Concrete Topping

5.9.2.1 General

Metal deck diaphragms with structural concrete 

topping, consisting of either a composite deck with 

indentations, or a noncomposite form deck and the 

concrete topping slab with reinforcement acting 

together, shall be permitted to resist diaphragm loads. 

The concrete fill shall be either normal or lightweight 

structural concrete, with reinforcing composed of wire 

mesh or reinforcing steel. Decking units shall be 

attached to each other and to structural steel supports by 

welds or by mechanical fasteners. The steel frame 

elements to which the topped metal deck diaphragm 

boundaries are attached shall be considered the chord 

and collector elements.

Criteria shall apply to existing diaphragms as well as 

new and rehabilitated diaphragms. Interaction of new 

and existing elements of rehabilitated diaphragms shall 

be evaluated for stiffness compatibility. Load transfer 

mechanisms between new and existing diaphragm 

components shall be considered in determining the 

flexibility of the diaphragm.

C5.9.1.4 Acceptance Criteria

If bare deck capacity is controlled by connections to 

frame members or panel buckling, then inelastic action 

and ductility are limited and the deck should be 

considered to be a force-controlled member.

C5.9.1.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating bare metal diaphragms:

1. Adding shear connectors for transfer of stress to 

chord or collector elements.

2. Strengthening existing chords or collectors by the 

addition of new steel plates to existing frame 

components.

3. Adding puddle welds or other shear connectors at 

panel perimeters.

4. Adding diagonal steel bracing to form a horizontal 

truss to supplement diaphragm strength.

5. Replacing nonstructural fill with structural 

concrete.

6. Adding connections between deck and supporting 

members.

C5.9.2.1 General

Metal deck diaphragms with structural concrete 

topping are frequently used on floors and roofs of 

buildings where there are typical floor gravity loads. 

Concrete has structural properties that significantly add 

to diaphragm stiffness and strength. Concrete 

reinforcing ranges from light mesh reinforcement to a 

regular grid of small reinforcing bars (#3 or #4). Metal 

decking is typically composed of corrugated sheet steel 

from 22 ga. down to 14 ga. Rib depths vary from 1-1/2 

to 3 inches in most cases. Attachment of the metal deck 

to the steel frame is usually accomplished using puddle 

welds at one to two feet on center. For composite 

behavior, shear studs are welded to the frame before 

the concrete is cast.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-47

5.9.2.2 Stiffness

5.9.2.2.1 Linear Procedures

For existing topped metal deck diaphragms, a rigid 

diaphragm assumption shall be permitted if the span-todepth ratio is not greater than five-to-one. For greater 

span-to-depth ratios, and in cases with plan 

irregularities, diaphragm flexibility shall be explicitly 

included in the analysis in accordance with 

Section 3.2.4. Diaphragm stiffness shall be calculated 

using an approved method with a representative 

concrete thickness.

5.9.2.2.2 Nonlinear Procedures

Inelastic properties of diaphragms shall not be included 

in inelastic seismic analyses if the weak link in the 

diaphragm is connection failure. Procedures for 

developing models for inelastic response of wood 

diaphragms in unreinforced masonry (URM) buildings 

shall be permitted for use as the basis of an inelastic 

model of a flexible metal deck diaphragm with 

structural to concrete topping.

5.9.2.3 Strength

Capacities of metal deck diaphragms with structural 

concrete topping shall be established by an approved 

procedure

Alternatively, the expected strength, QCE, of topped 

metal deck diaphragms shall be taken as two times 

allowable values specified in approved codes and 

standards unless a larger value is justified by test data. 

Lower-bound strengths, QCL, of welded connectors 

shall be as specified in AWS D1.3 or other approved 

standards. Lower-bound strengths, QCL, for headed stud 

connectors shall be as specified in AISC (1993) LRFD 

Specifications, with φ=1.0.

5.9.2.4 Acceptance Criteria

Connections of metal deck diaphragms with structural 

concrete topping shall be considered force-controlled. 

Connection capacity shall be checked for the ability to 

transfer the total diaphragm reaction into the steel 

framing. Diaphragms that are governed by the capacity 

of the connections shall also be considered forcecontrolled. Topped metal deck diaphragms not 

governed by the capacity of the connections shall be 

considered deformation-controlled. m-factors for shear 

yielding shall be taken from Table 5-5.

For the Life Safety Structural Performance Level, a loss 

of bearing support or anchorage shall not be permitted. 

For higher performance levels, the amount of damage to 

the connections or cracking in concrete-filled slabs shall 

not impair the load transfer between the diaphragm and 

the steel frame. Deformations shall be limited to be 

below the threshold of deflections that cause damage to 

other elements (either structural or nonstructural) at 

specified performance levels. Acceptance criteria for 

collectors shall be as specified in Section 5.9.6.4.

Load transfer to frame elements that act as chords or 

collectors in modern frames is usually through puddle 

welds or headed studs. In older construction where the 

frame is encased for fire protection, load transfer is 

made through bond.

C5.9.2.2.1 Linear Procedures

Flexibility factors for topped metal decks are available 

from manufacturers’ catalogs. For combinations in 

which values are not available, values can be 

established by interpolating between the most 

representative systems for which values are available. 

Flexibility factors for use in the analysis can also be 

calculated using the SDI Manual.

C5.9.2.3 Strength

Member capacities of steel deck diaphragms with 

structural concrete are given in manufacturers’

catalogs, ICBO reports, or the SDI Manual. If 

composite deck capacity is controlled by shear 

connectors, inelastic action and ductility are limited. It 

would be expected that there would be little or no 

inelastic action in steel deck/concrete diaphragms, 

except in long span conditions; however, perimeter 

transfer mechanisms and collector forces must be 

considered to be sure this is the case. SDI calculation 

procedures or ICBO values with a multiplier of 2.0 

should be used to bring allowable values to a strength 

level. Connector capacities may also be found in ICBO 

reports, manufacturers’ data, or the SDI Manual.
5-48 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Shear connectors for steel beams designed to act 

compositely with the slab shall have the capacity to 

transfer both diaphragm shears and composite beam 

shears. Where the beams are encased in concrete, use of 

bond between the steel and the concrete shall be 

permitted to transfer loads.

5.9.2.5 Rehabilitation Measures

Metal deck diaphragms with structural concrete topping 

that do not meet the acceptance criteria for the selected 

Rehabilitation Objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 5.4.3 and other provisions of this standard.

5.9.3 Metal Deck Diaphragms with 

Nonstructural Concrete Topping

5.9.3.1 General

Metal deck diaphragms with nonstructural concrete 

topping shall be evaluated as bare metal deck 

diaphragms, unless the strength and stiffness of the nonstructural topping is substantiated through approved test 

data. 

5.9.3.2 Stiffness

5.9.3.2.1 Linear Procedures

The potential for composite action and modification of 

load distribution shall be considered. Interaction of new 

and existing elements of strengthened diaphragms shall 

be evaluated by maintaining stiffness compatibility 

between the two, and the load transfer mechanisms 

between the new and existing diaphragm elements shall 

be considered in determining the flexibility of the 

diaphragm. Similarly, the interaction of new 

diaphragms with existing frames shall be evaluated, as 

well as the load transfer mechanisms between them. 

C5.9.2.4 Acceptance Criteria

Shear failure of topped metal deck diaphragms requires 

cracking of the concrete or tearing of the metal deck, 

so m-factors have been set at conservative levels.

C5.9.2.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating metal deck diaphragms with structural 

concrete topping:

1. Adding shear connectors to transfer forces to chord 

or collector elements.

2. Strengthening existing chords or collectors by the 

addition of new steel plates to existing frame 

components, or attaching new plates directly to the 

slab by embedded bolts or epoxy.

3. Adding diagonal steel bracing to supplement 

diaphragm strength.

C5.9.3.1 General

Metal deck diaphragms with nonstructural concrete fill 

are typically used on roofs of buildings where there are 

very small gravity loads. The concrete fill, such as very 

lightweight insulating concrete (e.g., vermiculite), 

usually does not have usable structural properties and 

is most often unreinforced. Consideration of any 

composite action must be done with caution after 

extensive investigation of field conditions. Material 

properties, force transfer mechanisms, and other 

similar factors must be verified in order to include such 

composite action. Typically, the decks are composed 

of corrugated sheet steel from 22 gage down to 14 

gage, and the rib depths vary from 9/16 to 3 inches in 

most cases.

C5.9.3.2.1 Linear Procedures

Flexibility of the diaphragm will depend on the 

strength and thickness of the topping. It may be 

necessary to bound the solution in some cases using 

both rigid and flexible diaphragm assumptions.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-49

5.9.3.2.2 Nonlinear Procedures

Inelastic properties of diaphragms shall not be included 

in inelastic seismic analyses if the weak link in the 

diaphragm is connection failure. Procedures for 

developing models for inelastic response of wood 

diaphragms in unreinforced masonry (URM) buildings 

shall be permitted as the basis of an inelastic model of a 

flexible bare metal deck diaphragm with nonstructural 

concrete topping.

5.9.3.3 Strength

Capacities of metal deck diaphragms with nonstructural 

topping shall be taken as specified for bare metal deck 

in Section 5.9.1. Capacities for welded and headed stud 

connectors shall be taken as specified in 

Section 5.9.2.3.

5.9.3.4 Acceptance Criteria

Connections of metal deck diaphragms with 

nonstructural concrete topping shall be considered 

force-controlled. Connection capacity shall be checked 

for the ability to transfer the total diaphragm reaction 

into the steel framing. Diaphragms that are governed by 

the capacity of the connections shall also be considered 

force-controlled. Topped metal deck diaphragms not 

governed by the capacity of the connections shall be 

considered deformation-controlled. m-factors for shear 

yielding or plate buckling shall taken from Table 5-5.

For the Life Safety Structural Performance Level, a loss 

of bearing support or anchorage shall not be permitted. 

For higher performance levels, the amount of damage to 

the connections or cracking in concrete filled slabs shall 

not impair the load transfer mechanism between the 

diaphragm and the steel frame. Deformations shall be 

limited to be below the threshold of deflections that 

cause damage to other elements (either structural or 

nonstructural) at specified performance levels.

5.9.3.5 Rehabilitation Measures

Metal deck diaphragms with nonstructural concrete 

topping that do not meet the acceptance criteria for the 

selected Rehabilitation Objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 5.4.3 and other provisions of this standard. 

5.9.4 Horizontal Steel Bracing (Steel Truss 

Diaphragms)

5.9.4.1 General

Horizontal steel bracing (steel truss diaphragms) shall 

be permitted to act as diaphragms independently or in 

conjunction with bare metal deck roofs. Where 

structural concrete fill is provided over the metal 

decking, relative rigidities between the steel truss and 

concrete systems shall be considered in the analysis.

Criteria shall apply to existing truss diaphragms, 

strengthened truss diaphragms, and new diaphragms.

Where steel truss diaphragms are added as part of a 

rehabilitation plan, interaction of new and existing 

elements of strengthened diaphragm systems (stiffness 

compatibility) shall be evaluated and the load transfer 

mechanisms between new and existing diaphragm 

elements shall be considered in determining the 

flexibility of the strengthened diaphragm.

C5.9.3.4 Acceptance Criteria

Generally, there should be little or no inelastic action 

in the diaphragms, provided the connections to the 

framing members are adequate. SDI calculation 

procedures should be used for strengths, or ICBO 

values with a multiplier of 2 should be used to bring 

allowable values to strength levels.

C5.9.3.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating metal deck diaphragms with 

nonstructural concrete topping:

1. Adding shear connectors to transfer forces to chord 

or collector elements.

2. Strengthening existing chords or collectors by the 

addition of new steel plates to existing frame 

components, or attaching new plates directly to the 

slab by embedded bolts or epoxy.

3. Adding puddle welds at panel perimeters of 

diaphragms.

4. Adding diagonal steel bracing to supplement 

diaphragm strength.

5. Replacing nonstructural fill with structural 

concrete.
5-50 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

Load transfer mechanisms between new diaphragm 

elements and existing frames shall be considered in 

determining the flexibility of the diaphragm/frame 

system.

5.9.4.2 Stiffness

5.9.4.2.1 Linear Procedures

Truss diaphragm systems shall be modeled as 

horizontal truss elements (similar to braced steel 

frames) where axial stiffness controls deflections. Joints 

shall be permitted to be modeled as pinned except when 

joints provide moment resistance or where 

eccentricities exist at the connections. In such cases, 

joint rigidities shall be modeled. Flexibility of truss 

diaphragms shall be explicitly considered in distribution 

of lateral loads to vertical elements.

5.9.4.2.2 Nonlinear Procedures

Elastic properties of truss diaphragms shall be permitted 

in the model for inelastic seismic analyses. Inelastic 

models similar to those of braced steel frames shall be 

permitted.

5.9.4.3 Strength

Capacities of truss diaphragm members shall be 

calculated as specified for steel braced frame members 

in Section 5.6. Lateral support of truss diaphragm 

members provided by metal deck, with or without 

concrete fill, shall be considered in evaluation of truss 

diaphragm capacities. Gravity force effects shall be 

included in the calculations for those members that 

support gravity loads.

5.9.4.4 Acceptance Criteria

Force transfer mechanisms between various members 

of the truss at the connections, and between trusses and 

frame elements, shall be evaluated to verify the 

completion of the load path. 

For the Life Safety Structural Performance Level, a loss 

of bearing support or anchorage shall not be permitted. 

For higher performance levels the amount of damage to 

the connections or bracing elements shall not result in 

the loss of the load transfer between the diaphragm and 

the steel frame. Deformations shall be limited to be 

below the threshold of deflections that cause damage to 

other elements (either structural or nonstructural) at 

specified performance levels.

5.9.4.4.1 Linear Procedures

Linear acceptance criteria for horizontal steel truss 

diaphragm components shall be as specified for 

concentric braced frames in Section 5.6.2.4 except that 

beam and column criteria need not be used. Use of 

m-factors specified for diagonal brace components, in 

lieu of those for beam and column components of 

braced frames, shall be permitted for strut and chord 

members in the truss.

5.9.4.4.2 Nonlinear Procedures

Nonlinear acceptance criteria for horizontal steel truss 

diaphragm components shall be as specified for 

concentric braced frames in Section 5.6.2.4 except that 

beam and column criteria need not be used. Use of 

plastic deformations specified for diagonal brace 

components, in lieu of those specified for beam and 

column components of braced frames, shall be 

permitted for strut and chord members in the truss.

C5.9.4.1 General

Steel truss diaphragm elements are typically found in 

conjunction with vertical framing systems that are of 

structural steel framing. Steel trusses are more 

common in long span situations, such as special roof 

structures for arenas, exposition halls, auditoriums, and 

industrial buildings. Diaphragms with a large span-todepth ratios may often be stiffened by the addition of 

steel trusses. The addition of steel trusses for 

diaphragms identified to be deficient may provide a 

proper method of enhancement.

Horizontal steel bracing (steel truss diaphragms) may 

be made up of any of the various structural shapes. 

Often, the truss chord elements consist of wide flange 

shapes that also function as floor beams to support the 

gravity loads of the floor. For lightly loaded 

conditions, such as industrial metal deck roofs without 

concrete fill, the diagonal members may consist of 

threaded rod elements, which are assumed to act only 

in tension. For steel truss diaphragms with large loads, 

diagonal elements may consist of wide flange 

members, tubes, or other structural elements that will 

act in both tension and compression. Truss element 

connections are generally concentric, to provide the 

maximum lateral stiffness and ensure that the truss 

members act under pure axial load. These connections 

are generally similar to those of gravity-load-resisting 

trusses.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-51

5.9.4.5 Rehabilitation Measures

Steel truss diaphragms that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard. 

5.9.5 Archaic Diaphragms

5.9.5.1 General

Archaic diaphragms in steel buildings are those 

consisting of shallow brick arches that span between 

steel floor beams, with the arches packed tightly 

between the beams to provide the necessary resistance 

to thrust forces.

5.9.5.2 Stiffness

5.9.5.2.1 Linear Procedures

Existing archaic diaphragm systems shall be modeled as 

a horizontal diaphragm with equivalent thickness of 

brick arches and concrete fill. Modeling of the archaic 

diaphragm as a truss with steel beams as tension 

elements and arches as compression elements shall be 

permitted. The flexibility of flexible archaic 

diaphragms shall be considered in calculating the 

distribution of lateral loads to vertical elements. 

Analysis results shall be evaluated to verify that 

diaphragm response remains elastic as assumed.

Interaction of new and existing elements of 

strengthened diaphragms shall be evaluated by 

checking the stiffness compatibility of the two in cases 

where steel trusses are added as part of a seismic 

upgrade. Load transfer mechanisms between new and 

existing diaphragm elements shall be considered in 

determining the flexibility of the strengthened 

diaphragm.

5.9.5.2.2 Nonlinear Procedures

Archaic diaphragms shall be required to remain in the 

elastic range unless otherwise approved.

5.9.5.3 Strength

Member capacities of archaic diaphragm components 

shall be permitted to be calculated, assuming no tension 

capacity exists for all components except steel beam 

members. Gravity force effects shall be included for 

components of these diaphragms. Force transfer 

mechanisms between various members and between 

frame elements shall be evaluated to verify the 

completion of the load path.

C5.9.4.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating steel truss diaphragms:

1. Diagonal components may be added to form 

additional horizontal trusses as a method of 

strengthening a weak existing diaphragm.

2. Existing chords components strengthened by the 

addition of shear connectors to enhance composite 

action.

3. Existing steel truss components strengthened by 

methods specified for braced steel frame members.

4. Truss connections strengthened by the addition of 

welds, new or enhanced plates, and bolts.

5. Structural concrete fill added to act in combination 

with steel truss diaphragms after verifying the 

effects of the added weight of concrete fill.

C5.9.5.1 General

Archaic steel diaphragm elements are almost always 

found in older steel buildings in conjunction with 

vertical systems of structural steel framing. The brick 

arches were typically covered with a very low-strength 

concrete fill, usually unreinforced. In many instances, 

various archaic diaphragm systems were patented by 

contractors.

C5.9.5.2.2 Nonlinear Procedures

Inelastic properties of archaic diaphragms should be 

chosen with caution for seismic analyses. For the case 

of archaic diaphragms, inelastic models similar to those 

of archaic timber diaphragms in unreinforced masonry 

buildings may be appropriate. Inelastic deformation 

limits of archaic diaphragms should be lower than those 

prescribed for a concrete-filled diaphragm.
5-52 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.9.5.4 Acceptance Criteria

Archaic diaphragms shall be considered forcecontrolled. For the Life Safety Structural Performance 

Level, diaphragm deformations and displacements shall 

not lead to a loss of bearing support for the elements of 

the arches. For higher performance levels, the 

deformation due to diagonal tension shall not result in 

the loss of the load transfer mechanism. Deformations 

shall be limited below the threshold of deflections that 

cause damage to other elements (either structural or 

nonstructural) at specified performance levels. These 

values shall be established in conjunction with those for 

steel frames.

5.9.5.5 Rehabilitation Measures

Archaic diaphragms that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard.

5.9.6 Chord and Collector Elements

5.9.6.1 General

Steel framing that supports the diaphragm shall be 

permitted as diaphragm chord and collector elements. 

When structural concrete is present, additional slab 

reinforcing shall be permitted to act as the chord or 

collector for tensile loads, while the slab carries chord 

or collector compression. When the steel framing acts 

as a chord or collector, it shall be attached to the deck 

with spot welds or by mechanical fasteners.

5.9.6.2 Stiffness

Modeling assumptions specified for equivalent steel 

frame members in this chapter shall be used for chord 

and collector elements.

5.9.6.3 Strength

Capacities of structural steel chords and collectors shall 

be as specified for FR beams and columns in 

Section 5.5.2.3.2. Capacities for reinforcing steel 

embedded in concrete slabs and acting as chords or 

collectors shall be determined in accordance with the 

provisions of Chapter 6.

5.9.6.4 Acceptance Criteria

Inelastic action in chords and collectors shall be 

permitted if it is permitted in the diaphragm. Where 

such actions are permissible, chords and collectors shall 

be considered deformation-controlled. m-factors shall 

be taken from Table 5-5 and inelastic acceptance 

criteria shall be taken from FR beam and column 

components in Section 5.5. Where inelastic action is not 

permitted, chords and collectors shall be considered 

force-controlled components. Where chord and 

collector elements are force-controlled, QUD need not 

exceed the total force that can be delivered to the 

component by the expected strength of the diaphragm 

or the vertical elements of the lateral-force-resisting 

system. For the Life Safety Structural Performance 

Level, the deformations and displacements of chord and 

collector components shall not result in the loss of 

vertical support. For higher performance levels chords 

and collectors shall not impair the load path.

C5.9.5.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating archaic diaphragms:

1. Adding diagonal members to form a horizontal 

truss as a method of strengthening a weak archaic 

diaphragm.

2. Strengthening existing steel members by adding 

shear connectors to enhance composite action.

3. Removing weak concrete fill and replacing it with a 

structural concrete topping slab after verifying the 

effects of the added weight of concrete fill.

C5.9.6.1 General

When reinforcing acts as the chord or collector, load 

transfer occurs through bond between the reinforcing 

bars and the concrete.
 Chapter 5: Steel

FEMA 356 Seismic Rehabilitation Prestandard 5-53

Welds and connectors joining the diaphragms to the 

chords and collectors shall be considered forcecontrolled. If all connections meet the acceptance 

criteria, the diaphragm shall be considered to prevent 

buckling of the chord member within the plane of the 

diaphragm. Where chords or collectors carry gravity 

loads in combination with seismic loads, they shall be 

checked as members with combined axial load and 

bending in accordance with Section 5.5.2.4.2.

5.9.6.5 Rehabilitation Measures

Chord and collector elements that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 5.4.3 

and other provisions of this standard. 

5.10 Steel Pile Foundations

5.10.1 General

A pile shall provide strength and stiffness to the 

foundation either by bearing directly on soil or rock, by 

friction along the pile length in contact with the soil, or 

by a combination of these mechanisms. Foundations 

shall be evaluated as specified in Chapter 4. Concrete 

components of foundations shall conform with 

Chapter 6. The design of the steel piles shall comply 

with the requirements of this section.

5.10.2 Stiffness

If the pile cap is below grade, the foundation stiffness 

from the pile cap bearing against the soil shall be 

permitted to be represented by equivalent soil springs 

derived as specified in Chapter 4. Additional stiffness 

of the piles shall be permitted to be derived through 

bending and bearing against the soil. For piles in a 

group, the reduction in each pile’s contribution to the 

total foundation stiffness and strength shall be made to 

account for group effects. Additional requirements for 

calculating the stiffness shall be as specified in 

Chapter 4.

5.10.3 Strength

Except in sites subject to liquefaction of soils, it shall be 

permitted to neglect buckling of portions of piles 

embedded in the ground. Flexural demands in piles 

shall be calculated either by nonlinear methods or by 

elastic methods for which the pile is treated as a 

cantilever column above a calculated point of fixity.

5.10.4 Acceptance Criteria

The acceptance criteria for the axial force and 

maximum bending moments for the pile strength shall 

be as specified for a steel column in Section 5.5.2.4.2 

for linear methods and in Section 5.5.2.4.3 for nonlinear 

methods, where the lower-bound axial compression, 

expected axial tension and flexural strengths shall be 

computed for an unbraced length equal to zero for those 

portions of piles that are embedded in non-liquefiable 

soils.

Connections between steel piles and pile caps shall be 

considered force-controlled. 

C5.9.6.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating chord and collector elements:

1. Strengthen the connection between diaphragms and 

chords or collectors.

2. Strengthen steel chords or collectors with steel 

plates attached directly to the slab with embedded 

bolts or epoxy, and strengthen slab chord or 

collectors with added reinforcing bars.

3. Add chord members.

C5.10.1 General

Steel piles of wide flange shape (H-piles) or structural 

tubes, with and without concrete infills, shall be 

permitted to be used to support foundation loads. Piles 

driven in groups should have a reinforced concrete pile 

cap to transfer loads from the superstructure to the 

piles.

C5.10.4 Acceptance Criteria

Nonlinear methods require the use of a computer 

program. The design professional is referred to FEMA 

274 for additional information.
5-54 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 5: Steel

5.10.5 Rehabilitation Measures

Steel pile foundations that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 5.4.3 and other provisions of 

this standard. 

5.11 Cast and Wrought Iron

5.11.1 General

Existing components of cast and wrought iron shall be 

permitted to participate in resisting seismic forces in 

combination with concrete or masonry walls. Cast iron 

frames, in which beams and columns are integrally cast, 

shall not be permitted to resist seismic forces as primary 

elements of the lateral-force-resisting system. The 

ability of cast iron elements to resist the design 

displacements at the selected earthquake hazard level 

shall be evaluated.

5.11.2 Stiffness 

The axial and flexural stiffness of cast iron shall be 

calculated using elastic section properties and a 

modulus of elasticity, E, of 25,000 kips per square inch.

5.11.3 Strength and Acceptance Criteria

Axial and flexural loads on cast iron components shall 

be considered to be force-controlled behaviors. Lower 

bound material properties for cast iron shall be based on 

Table 5-1.

The lower-bound strength of a cast iron column shall be 

calculated as:

(5-36)

where:

Ag = Gross area of column

 for 

 for 

Cast iron columns shall only be permitted to carry axial 

compression.

C5.10.5 Rehabilitation Measures

Rehabilitation of the concrete pile cap is specified in 

Chapter 6. Criteria for the rehabilitation of the 

foundation element are specified in Chapter 4. The 

following measure may be effective in rehabilitating 

steel pile foundations: driving additional piles near 

existing groups and then adding a new pile cap to 

increase stiffness and strength of the pile foundation. 

Monolithic behavior gained by connecting the new and 

old pile caps with epoxied dowels may also be 

effective. In most cases, it is not possible to rehabilitate 

the existing piles.

QCL PCL AgFcr = =

Fcr = 12ksi l

c ⁄ r ≤ 108

Fcr

1.40 5×10

l

c ( ) ⁄ r 2 = ----------------------ksi l

c ⁄ r > 108
FEMA 356 Seismic Rehabilitation Prestandard 6-1

6. Concrete

6.1 Scope

This chapter sets forth requirements for the Systematic 

Rehabilitation of concrete lateral-force-resisting 

elements within a building. The requirements of this 

chapter shall apply to existing concrete components of a 

building system, rehabilitated concrete components of a 

building system, and new concrete components that are 

added to an existing building system.

Sections 6.2 and 6.3 specify data collection procedures 

for obtaining material properties and performing 

condition assessments. Section 6.4 specifies general 

analysis and design requirements for concrete 

components. Sections 6.5, 6.6, 6.7, 6.8, 6.9, and 6.10 

provide modeling procedures, component strengths, 

acceptance criteria, and rehabilitation measures for 

concrete and precast concrete moment frames, braced 

frames, and shear walls. Sections 6.11, 6.12, and 6.13 

provide modeling procedures, strengths, acceptance 

criteria, and rehabilitation measures for concrete 

diaphragm systems. 

6.2 Material Properties Based on 

Historical Information

Available construction documents and as-built 

information shall be obtained as specified in 

Section 2.2. Use of material properties based on 

historical information as default values shall be as 

specified in Section 6.3.2.5.

C6.1 Scope

Techniques for repair of earthquake-damaged concrete 

components are not included in this standard. The 

design professional is referred to FEMA 306, 

FEMA 307, and FEMA 308 for information on 

evaluation and repair of damaged concrete wall 

components.

C6.2 Material Properties Based on 

Historical Information

The form, function, concrete strength, concrete quality, 

reinforcing steel strength, quality and detailing, forming techniques and concrete placement techniques have 

constantly evolved and have had a significant impact 

on the seismic resistance of a concrete building. Innovations such as prestressed and precast concrete, post 

tensioning, and lift slab construction have created a 

multivariant inventory of existing concrete structures.

It is important to investigate the local practices relative 

to seismic design when trying to analyze a concrete 

building. Specific benchmark years can be determined 

for the implementation of earthquake-resistant design 

in most locations, but caution should be exercised in 

assuming optimistic characteristics for any specific 

building.

Particularly with concrete materials, the date of original building construction significantly influences seismic performance. In the absence of deleterious 

conditions or materials, concrete gains compressive 

strength from the time it is originally cast and in-place. 

Strengths typically exceed specified design values (28-

day or similar). Early uses of concrete did not specify 

any design strength, and low-strength concrete was not 

uncommon. Also, early use of concrete in buildings 

often employed reinforcing steel with relatively low 

strength and ductility, limited continuity, and reduced 

bond development. Continuity between specific existing components and elements (e.g., beams and columns, diaphragms and shear walls) is also particularly 

difficult to assess, given the presence of concrete cover 

and other barriers to inspection.

Properties of welded wire fabric for various periods of 

construction can be obtained from the Wire 

Reinforcement Institute.
6-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Table 6-1 Default Lower-Bound Tensile and Yield Properties of Reinforcing Bars for Various Periods1

Grade

Structural2 Intermediate21 Hard21

33 40 50 60 70 75

Year3 Minimum Yield2 (psi) 33,000 40,000 50,000 60,000 70,000 75,000

Minimum Tensile2 (psi) 55,000 70,000 80,000 90,000 95,000 100,000

1911-1959 x xx

1959-1966 x x xx x

1966-1972 x xx

1972-1974 x xx

1974-1987 x xxx

1987-present x xxx x

Notes:

1. An entry of “x” indicates the grade was available in those years.

2. The terms structural, intermediate, and hard became obsolete in 1968.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-3

Table 6-2 Default Lower-Bound Tensile and Yield Properties of Reinforcing Bars for Various ASTM 

Specifications and Periods1

Structural2 Intermediate2 Hard2

ASTM 

Grade 33 40 50 60 70 75

Minimum 

Yield2

(psi)

33,000 40,000 50,000 60,000 70,000 75,000

ASTM 

Designation5

Steel

Type

Year

Range

3

Minimum 

Tensile2

(psi)

55,000 70,000 80,000 90,000 95,000 100,000

A15 Billet 1911-

1966

x xx

A16 Rail3 1913-

1966

x

A61 Rail3 1963-

1966

x

A160 Axle 1936-

1964

x xx

A160 Axle 1965-

1966

x x xx

A408 Billet 1957-

1966

x xx

A431 Billet 1959-

1966

x

A432 Billet 1959-

1966

x

A615 Billet 1968-

1972

x xx

A615 Billet 1974-

1986

x x

A615 Billet 1987-

1997

x xx

A6164 Rail3 1968-

1997

x x

A617 Axle 1968-

1997

x x

A706 LowAlloy51974-

1997

x

A955 Stainless1996-

1997

x xx

Notes:

1. An entry of “x” indicates the grade was available in those years.

2. The terms structural, intermediate, and hard became obsolete in 1968.

3. Rail bars are marked with the letter “R.”

4. Bars marked “s!” (ASTM 616) have supplementary requirements for bend tests.

5. ASTM steel is marked with the letter “W.”
6-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.3 Material Properties and 

Condition Assessment

6.3.1 General

Mechanical properties for concrete materials and 

components shall be based on available construction 

documents and as-built conditions for the particular 

structure. Where such information fails to provide 

adequate information to quantify material properties or 

document the condition of the structure, such 

information shall be supplemented by materials tests 

and assessments of existing conditions as required in 

Section 2.2.6.

Material properties of existing concrete components 

shall be determined in accordance with Section 6.3.2. A 

condition assessment shall be conducted in accordance 

with Section 6.3.3. The extent of materials testing and 

condition assessment performed shall be used to 

determine the knowledge factor as specified in 

Section 6.3.4.

Use of default material properties shall be permitted in 

accordance with Section 6.3.2.5.

6.3.2 Properties of In-Place Materials and 

Components

6.3.2.1 Material Properties

6.3.2.1.1 General

The following component and connection material 

properties shall be obtained for the as-built structure:

1. Concrete compressive strength.

2. Yield and ultimate strength of conventional and 

prestressing reinforcing steel and metal connection 

hardware.

When materials testing is required by Section 2.2.6, the 

test methods to quantify material properties shall 

comply with the requirements of Section 6.3.2.3. The 

frequency of sampling, including the minimum number 

of tests for property determination shall comply with 

the requirements of Section 6.3.2.4.

Table 6-3 Default Lower-Bound Compressive Strength of Structural Concrete (psi)1

Time Frame Footings Beams Slabs Columns Walls

1900–1919 1000–2500 2000–3000 1500–3000 1500–3000 1000–2500

1920–1949 1500–3000 2000–3000 2000–3000 2000–4000 2000–3000

1950–1969 2500–3000 3000–4000 3000–4000 3000–6000 2500–4000

1970–Present 3000–4000 3000–5000 3000–5000 3000–100002 3000–5000

Table 6-4 Factors to Translate Lower Bound 

Material Properties to Expected 

Strength Material Properties

Material Property Factor

Concrete Compressive Strength 1.50

Reinforcing Steel Tensile & Yield 

Strength

1.25

Connector Steel Yield Strength 1.50

C6.3.1 General

This section identifies properties requiring 

consideration and provides guidelines for determining 

the properties of buildings. Also described is the need 

for a thorough condition assessment and utilization of 

knowledge gained in analyzing component and system 

behavior. Personnel involved in material property 

quantification and condition assessment shall be 

experienced in the proper implementation of testing 

practices and the interpretation of results.

Documentation of properties and grades of material 

used in component/connection construction is 

invaluable and may be effectively used to reduce the 

amount of in-place testing required. The design 

professional is encouraged to research and acquire all 

available records from original construction.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-5

6.3.2.1.2 Nominal or Specified Properties

Nominal material properties, or properties specified in 

construction documents, shall be taken as lower bound 

material properties. Corresponding expected material 

properties shall be calculated by multiplying lowerbound values by a factor taken from Table 6-4 to 

translate from lower bound to expected values. 

Alternative factors shall be permitted where justified by 

test data.

6.3.2.2 Component Properties

The following component properties and as-built 

conditions shall be established:

1. Cross-sectional dimensions of individual 

components and overall configuration of the 

structure.

2. Configuration of component connections, size of 

anchor bolts, thickness of connector material, 

anchorage and interconnection of embedments and 

the presence of bracing or stiffening components.

3. Modifications to components or overall 

configuration of the structure.

4. Current physical condition of components and 

connections, and the extent of any deterioration 

present.

5. Presence of conditions that influence building 

performance. 

6.3.2.3 Test Methods to Quantify Material 

Properties

6.3.2.3.1 General

Destructive and non-destructive test methods used to 

obtain in-place mechanical properties of materials 

identified in Section 6.3.2.1 and component properties 

identified in Section 6.3.2.2 shall comply with the 

requirements of this section. Samples of concrete and 

reinforcing and connector steel shall be examined for 

physical condition as specified in Section 6.3.3.2.

C6.3.2.1.1 General

Other material properties that may be of interest for 

concrete elements and components include:

1. Tensile strength and modulus of elasticity, which 

can be derived from the compressive strength, do 

not warrant the damage associated with the extra 

coring required.

2. Ductility, toughness, and fatigue properties of 

concrete.

3. Carbon equivalent present in the reinforcing steel.

4. Presence of any degradation such as corrosion, 

bond with concrete, and chemical composition.

The effort required to determine these properties 

depends on the availability of accurate updated 

construction documents and drawings, quality and type 

of construction (absence of degradation), accessibility, 

and condition of materials. The method of analysis 

selected (e.g., Linear Static Procedure, Nonlinear 

Static Procedure) may also influence the scope of the 

testing. 

The size of the samples and removal practices to be 

followed are referenced in FEMA 274. Generally, 

mechanical properties for both concrete and 

reinforcing steel can be established from combined 

core and specimen sampling at similar locations, 

followed by laboratory testing. Core drilling should 

minimize damaging the existing reinforcing steel as 

much as practicable.

C6.3.2.2 Component Properties

Component properties may be needed to characterize 

building performance properly in the seismic analysis. 

The starting point for assessing component properties 

and condition should be retrieval of available 

construction documents. Preliminary review of these 

documents shall be performed to identify primary 

vertical- (gravity-) and lateral load-carrying elements, 

systems, and their critical components and 

connections. In the absence of a complete set of 

building drawings, the design professional must 

perform a thorough inspection of the building to 

identify these elements, systems and components as 

indicated in Section 6.3.3.
6-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

If the determination of material properties is 

accomplished through removal and testing of samples 

for laboratory analysis, sampling shall take place in 

primary gravity- and lateral-force-resisting components 

in regions with the least stress.

Expected material properties shall be based on mean 

test values. Lower bound material properties shall be 

based on mean test values minus one standard 

deviation.

6.3.2.3.2 Sampling

For concrete, the sampling program shall consist of the 

removal of standard cores. Core drilling shall be 

preceded by nondestructive location of the reinforcing 

steel. Core holes shall be filled with comparablestrength concrete or grout. If conventional reinforcing 

and bonded prestressing steel is tested, sampling shall 

consist of the removal of local bar segments and 

installation of replacement spliced material to maintain 

continuity of the rebar for transfer of bar force.

Core strength shall be converted to in situ concrete 

compressive strength (ƒc) by an approved procedure.

If a sample population greater than the minimum 

specified in Section 6.3.2.4 is used in the testing 

program and the coefficient of variation in test results is 

less than 14%, the mean strength derived shall be 

permitted to be used as the expected strength in the 

analysis. The expected concrete strength shall not 

exceed the mean less one standard deviation in 

situations where the coefficient of variation is greater 

than 14%.

Removal of core samples and performance of 

laboratory destructive testing shall be permitted as a 

method of determining existing concrete strength 

properties. Removal of core samples shall employ the 

procedures contained in ASTM C42/C42M-99. Testing 

shall follow the procedures contained in ASTM 

C42/C42M-99, ASTM C39/C39M-99, and ASTM

C496-96. The measured strength from testing shall be 

correlated to in-place concrete compressive strength. 

Removal of bar or tendon length samples and 

performance of laboratory destructive testing shall be 

permitted as a method of determining existing 

reinforcing steel strength properties. The tensile yield 

strength and ultimate strength for reinforcing and 

prestressing steels shall be obtained using the 

procedures contained in ASTM A370-97a. Prestressing 

materials also shall meet the supplemental requirements 

in ASTM A416/A416M-99, ASTM A421/A421M-98a, or 

ASTM A722/A722M-98, depending on material type. 

Properties of connector steels shall be permitted to be 

determined by wet and dry chemical composition tests, 

and direct tensile and compressive strength tests as 

specified by ASTM A370-97a. Where strengths of 

embedded connectors are required, in situ testing shall 

satisfy the provisions of ASTM E488-96. 

6.3.2.4 Minimum Number of Tests

Materials testing is not required if material properties 

are available from original construction documents that 

include material test records or material test reports.

The minimum number of tests necessary to quantify 

properties by in-place testing for comprehensive data 

collection shall be as specified in Sections 6.3.2.4.1 

through 6.3.2.4.4. The minimum number of tests for 

usual data collection shall be as specified in 

Section 6.3.2.4.5. If the existing vertical or lateralforce-resisting system is being replaced in the 

rehabilitation process, material testing shall be required 

C6.3.2.3 Test Methods to Quantify Material 

Properties

ACI 318 and FEMA 274 provide further guidance on 

correlating core strength to in-place strength and 

provides references for various test methods that may 

be used to estimate material properties.

The chemical composition may also be determined 

from the retrieved samples. 

FEMA 274 provides references for these tests.

Usually, the reinforcing steel system used in the 

construction of a specific building is of a common 

grade and strength. Occasionally one grade of 

reinforcement is used for small-diameter bars (e.g., 

those used for stirrups and hoops) and another grade 

for large-diameter bars (e.g., those used for 

longitudinal reinforcement). Furthermore, it is possible 

that a number of different concrete design strengths (or 

“classes”) have been employed. Historical research 

and industry documents also contain insight on 

material mechanical properties used in different 

construction eras.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-7

only to qualify properties of existing materials at new 

connection points. 

6.3.2.4.1 Comprehensive Testing

Unless specified otherwise, a minimum of three tests 

shall be conducted to determine any property. If the 

coefficient of variation exceeds 14%, additional tests 

shall be performed until the coefficient of variation is 

equal to or less than 14%.

6.3.2.4.2 Concrete Materials

For each concrete element type (such as a shear wall), a 

minimum of three core samples shall be taken and 

subjected to compression tests. A minimum of six total 

tests shall be performed on a building for concrete 

strength determination, subject to the limitations of this 

section. If varying concrete classes/grades were 

employed in the construction of the building, a 

minimum of three samples and tests shall be performed 

for each class. The modulus of elasticity shall be 

permitted to be estimated from the data of strength 

testing. Samples shall be taken from randomly selected 

components critical to structural behavior of the 

building. Tests also shall be performed on samples from 

components that are damaged or degraded, if such 

damage or degradation is identified to quantify their 

condition. Test results shall be compared with strength 

values specified in the construction documents. If test 

values less than the specified strength in the 

construction documents are found, further strength 

testing shall be performed to determine the cause or 

identify the extent of the condition.

The minimum number of tests to determine 

compressive and tensile strength shall conform to the 

following criteria.

1. For concrete elements for which the specified design 

strength is known and test results are not available, a 

minimum of three cores/tests shall be conducted for 

each floor level, 400 cubic yards of concrete, or 

10,000 square feet of surface area, whichever 

requires the most frequent testing.

2. For concrete elements for which the design strength 

is unknown and test results are not available, a 

minimum of six cores/tests shall be conducted for 

each floor level, 400 cubic yards of concrete, or 

10,000 square feet of surface area, whichever 

requires the most frequent testing. Where the results 

indicate that different classes of concrete were 

employed, the degree of testing shall be increased to 

confirm class use. 

Quantification of concrete strength via ultrasonics or 

other nondestructive test methods shall not be 

substituted for core sampling and laboratory testing.

6.3.2.4.3 Conventional Reinforcing and Connector 

Steels

The minimum number of tests required to determine 

reinforcing and connector steel strength properties shall 

be as follows. Connector steel shall be defined as 

additional structural steel or miscellaneous metal used 

to secure precast and other concrete shapes to the 

building structure. Tests shall determine both yield and 

ultimate strengths of reinforcing and connector steel. A 

minimum of three tensile tests shall be conducted on 

conventional reinforcing steel samples from a building 

C6.3.2.4 Minimum Number of Tests

In order to quantify in-place properties accurately, it is 

important that a minimum number of tests be 

conducted on primary components in the lateral-forceresisting system. The minimum number of tests is 

dictated by available data from original construction, 

the type of structural system employed, desired 

accuracy, and the quality and condition of in-place 

materials. The accessibility of the structural system 

may also influence the testing program scope. The 

focus of this testing shall be on primary lateral-forceresisting components and on specific properties needed 

for analysis. The test quantities provided in this section 

are minimum numbers; the design professional should 

determine whether further testing is needed to evaluate 

as-built conditions. 

Testing is generally not required on components other 

than those of the lateral-force-resisting system. 

The design professional (and subcontracted testing 

agency) should carefully examine test results to verify 

that suitable sampling and testing procedures were 

followed and that appropriate values for the analysis 

were selected from the data.

C6.3.2.4.2 Concrete Materials

Ultrasonics and nondestructive test methods should not 

be substituted for core sampling and laboratory testing 

since they do not yield accurate strength values 

directly.
6-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

for strength determination, subject to the following 

supplemental conditions.

1. If original construction documents defining 

properties exist, at least three strength coupons shall 

be randomly removed from each element or 

component type and tested.

2. If original construction documents defining 

properties do not exist, but the approximate date of 

construction is known and a common material grade 

is confirmed, at least three strength coupons shall be 

randomly removed from each element or component 

type for every three floors of the building. If the date 

of construction is unknown, at least six such 

samples/tests, for every three floors, shall be 

performed.

All sampled steel shall be replaced with new fully 

spliced and connected material unless an analysis 

confirms that replacement of original components is not 

required. 

6.3.2.4.4 Prestressing Steels

The sampling of prestressing steel tendons for 

laboratory testing shall be required only for those 

prestressed components that are a part of the lateralforce-resisting system. Prestressed components in 

diaphragms shall be permitted to be excluded from 

testing.

Tendon or prestress removal shall be avoided if possible 

by sampling of either the tendon grip or extension 

beyond the anchorage.

All sampled prestressed steel shall be replaced with new 

fully connected and stressed material and anchorage 

hardware unless an analysis confirms that replacement 

of original components is not required.

6.3.2.4.5 Usual Testing

The minimum number of tests to determine concrete 

and reinforcing steel material properties for usual data 

collection shall be based on the following criteria:

1. If the specified design strength of the concrete is 

known, at least one core shall be taken from samples 

of each different concrete strength used in the 

construction of the building, with a minimum of 

three cores taken for the entire building.

2. If the specified design strength of the concrete is not 

known, at least one core shall be taken from each 

type of component, with a minimum of six cores 

taken for the entire building.

3. If the specified design strength of the reinforcing 

steel is known, use of nominal or specified material 

properties shall be permitted without additional 

testing.

4. If the specified design strength of the reinforcing 

steel is not known, at least two strength coupons of 

reinforcing steel shall be removed from a building 

for testing. 

6.3.2.5 Default Properties

Use of default material properties to determine 

component strengths shall be permitted in conjunction 

with the linear analysis procedures of Chapter 3.

Default lower-bound concrete compressive strengths 

shall be taken from Table 6-3. Default expected strength 

concrete compressive strengths shall be determined by 

multiplying lower-bound values by an appropriate 

factor selected from Table 6-4 unless another factor is 

justified by test data. The appropriate default 

compressive strength—lower bound or expected 

strength as specified in Section 2.4.4—shall be used to 

establish other strength and performance characteristics 

for the concrete as needed in the structural analysis.

Default lower-bound values for reinforcing steel shall 

be taken from Table 6-1 or 6-2. Default expected 

strength values for reinforcing steel shall be determined 

by multiplying lower-bound values by an appropriate 

factor selected from Table 6-4 unless another factor is 

justified by test data. For Rehabilitation Objectives in 

which default values are assumed for existing 

reinforcing steel, welding or mechanical coupling of 

C6.3.2.4.5 Usual Testing

For other material properties, such as hardness and 

ductility, no minimum number of tests is prescribed. 

Similarly, standard test procedures may not exist. The 

design professional should examine the particular need 

for this type of testing and establish an adequate 

protocol.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-9

new reinforcement to the existing reinforcing steel shall 

not be used.

The default lower-bound yield strength for steel 

connector material shall be taken as 27,000 psi. The 

default expected yield strength for steel connector 

material shall be determined by multiplying lowerbound values by an appropriate factor selected from 

Table 6-4 unless another value is justified by test data.

Default values for prestressing steel in prestressed 

concrete construction shall not be used.

6.3.3 Condition Assessment

6.3.3.1 General

A condition assessment of the existing building and site 

conditions shall be performed as specified in this 

section.

The condition assessment shall include the following:

1. The physical condition of primary and secondary 

components shall be examined and the presence of 

any degradation shall be noted.

2. The presence and configuration of components and 

their connections, and the continuity of load paths 

between components, elements, and systems shall be 

verified or established.

3. Other conditions including neighboring party walls 

and buildings, presence of nonstructural 

components, prior remodeling, and limitations for 

rehabilitation that may influence building 

performance shall be reviewed and documented.

4. A basis for selecting a knowledge factor in 

accordance with Section 6.3.4 shall be formulated.

5. Component orientation, plumbness, and physical 

dimensions shall be confirmed.

6.3.3.2 Scope and Procedures

The scope of the condition assessment shall include all 

accessible structural elements and components involved 

in lateral load resistance.

6.3.3.2.1 Visual Condition Assessment

Direct visual inspection of accessible and representative 

primary components and connections shall be 

performed to identify any configurational issues, 

determine whether degradation is present, establish 

continuity of load paths, establish the need for other test 

methods to quantify the presence and degree of 

degradation, and measure dimensions of existing 

construction to compare with available design 

information and reveal any permanent deformations.

Visual inspection of the building shall include visible 

portions of foundations, lateral-force-resisting 

members, diaphragms (slabs), and connections. As a 

minimum, a representative sampling of at least 20% of 

the elements, components, and connections shall be 

visually inspected at each floor level. If significant 

damage or degradation is found, the assessment sample 

of all critical components of similar type in the building 

shall be increased to 40%.

If coverings or other obstructions exist, indirect visual 

inspection through the obstruction, using drilled holes 

and a fiberscope, shall be permitted.

C6.3.2.5 Default Properties

Default values provided in this standard are generally 

conservative. While strength of reinforcing steel may 

be fairly consistent throughout a building, the strength 

of concrete in a building could be highly variable, 

given variability in concrete mix designs and 

sensitivity to water-cement ratio and curing practices. 

Until about 1920, a variety of proprietary reinforcing 

steels was used. Yield strengths are likely to be in the 

range of 33,000 to 55,000 psi, but higher values are 

possible and actual yield and tensile strengths may 

exceed minimum values. Once commonly used to 

designate reinforcing steel grade, the terms structural, 

intermediate and hard became obsolete in 1968. Plain 

and twisted square bars were sometimes used between 

1900 and 1949. 

Factors to convert default reinforcing steel strength to 

expected strength include consideration of material 

overstrength and strain hardening.

C6.3.3.2 Scope and Procedures

The degree to which the condition assessment is 

performed will affect the knowledge (κ) factor as 

specified in Section 6.3.4.
6-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.3.3.2.2 Comprehensive Condition Assessment

Exposure is defined as local minimized removal of 

cover concrete and other materials to allow inspection 

of reinforcing system details. All damaged concrete 

cover shall be replaced after inspection. The following 

criteria shall be used for assessing primary connections 

in the building for comprehensive data collection:

1. If detailed design drawings exist, exposure of at least 

three different primary connections shall occur, with 

the connection sample including different types of 

connections. If no deviations from the drawings 

exist, it shall be permitted to consider the sample as 

being representative of installed conditions. If 

deviations are noted, then at least 25% of the 

specific connection type shall be inspected to 

identify the extent of deviation.

2. In the absence of detailed design drawings, at least 

three connections of each primary connection type 

shall be exposed for inspection. If common detailing 

among the three connections is observed, it shall be 

permitted to consider this condition as representative 

of installed conditions. If variations are observed 

among like connections, additional connections shall 

be inspected until an accurate understanding of 

building construction is gained.

6.3.3.2.3 Additional Testing

If additional destructive and nondestructive testing is 

required to determine the degree of damage or presence 

of deterioration or to understand the internal condition 

and quality of concrete, approved test methods shall be 

used. 

6.3.3.3 Basis for the Mathematical Building 

Model

The results of the condition assessment shall be used to 

quantify the following items needed to create the 

mathematical building model:

1. Component section properties and dimensions.

2. Component configuration and the presence of any 

eccentricities or permanent deformation.

3. Connection configuration and the presence of any 

eccentricities.

C6.3.3.2.3 Additional Testing

The physical condition of components and connectors 

will affect their performance. The need to accurately 

identify the physical condition may also dictate the 

need for certain additional destructive and 

nondestructive test methods. Such methods may be 

used to determine the degree of damage or presence of 

deterioration, and to improve understanding of the 

internal condition and quality of the concrete. Further 

guidelines and procedures for destructive and 

nondestructive tests that may be used in the condition 

assessment are provided in FEMA 274 and FEMA 306. 

The following paragraphs identify those 

nondestructive examination (NDE) methods having the 

greatest use and applicability to condition assessment. 

• Surface NDE methods include infrared 

thermography, delamination sounding, surface 

hardness measurement, and crack mapping. These 

methods may be used to find surface degradation in 

components such as service-induced cracks, 

corrosion, and construction defects.

• Volumetric NDE methods, including radiography 

and ultrasonics, may be used to identify the 

presence of internal discontinuities, as well as to 

identify loss of section. Impact-echo ultrasonics is 

particularly useful because of ease of 

implementation and proven capability in concrete.

• Structural condition and performance may be 

assessed through on-line monitoring using acoustic 

emissions and strain gauges, and in-place static or 

dynamic load tests. Monitoring is used to determine 

if active degradation or deformations are occurring, 

while nondestructive load testing provides direct 

insight on load-carrying capacity.

• Locating, sizing, and initial assessment of the 

reinforcing steel may be completed using 

electromagnetic methods (such as a pacometer) or 

radiography. Further assessment of suspected 

corrosion activity should use electrical half-cell 

potential and resistivity measurements.

• Where it is absolutely essential, the level of 

prestress remaining in an unbonded prestressed 

system may be measured using lift-off testing 

(assuming original design and installation data are 

available), or another nondestructive method such 

as “coring stress relief” specified in ASCE 11.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-11

4. Presence and effect of alterations to the structural 

system since original construction.

5. Interaction of nonstructural components and their 

involvement in lateral load resistance.

All deviations between available construction records 

and as-built conditions obtained from visual inspection 

shall be accounted for in the structural analysis.

Unless concrete cracking, reinforcing corrosion, or 

other mechanisms are observed in the condition 

assessment to be causing damage or reduced capacity, 

the cross-sectional area and other sectional properties 

shall be taken as those from the design drawings. If 

some sectional material loss has occurred, the loss shall 

be quantified by direct measurement and sectional 

properties shall be reduced accordingly, using principles 

of structural mechanics.

6.3.4 Knowledge Factor

A knowledge factor (κ) for computation of concrete 

component capacities and permissible deformations 

shall be selected in accordance with Section 2.2.6.4 

with the following additional requirements specific to 

concrete components.

A knowledge factor, κ, equal to 0.75 shall be used if 

any of the following criteria are met:

1. Components are found damaged or deteriorated 

during assessment, and further testing is not 

performed to quantify their condition or justify the 

use of κ=1.0.

2. Component mechanical properties have a coefficient 

of variation exceeding 25%.

3. Components contain archaic or proprietary material 

and the condition is uncertain.

6.4 General Assumptions and 

Requirements

6.4.1 Modeling and Design

6.4.1.1 General Approach 

Seismic rehabilitation of concrete structural elements of 

existing buildings shall comply with the requirements 

of ACI 318, except as otherwise indicated in this 

standard. Seismic evaluation shall identify brittle or 

low-ductility failure modes of force-controlled actions 

as defined in Section 2.4.4.

Evaluation of demands and capacities of reinforced 

concrete components shall include consideration of 

locations along the length where lateral and gravity 

loads produce maximum effects, where changes in 

cross-section or reinforcement result in reduced 

strength, and where abrupt changes in cross section or 

reinforcement, including splices, may produce stress 

concentrations, resulting in premature failure. 

6.4.1.2 Stiffness

Component stiffnesses shall be calculated considering 

shear, flexure, axial behavior and reinforcement slip 

deformations. Consideration shall be given to the state 

of stress on the component due to volumetric changes 

from temperature and shrinkage, and to deformation 

levels to which the component will be subjected under 

gravity and earthquake loading. 

6.4.1.2.1 Linear Procedures

Where design actions are determined using the linear 

procedures of Chapter 3, component effective 

stiffnesses shall correspond to the secant value to the 

yield point of the component. The use of higher 

stiffnesses shall be permitted where it is demonstrated 

by analysis to be appropriate for the design loading. 

C6.4.1.1 General Approach

Brittle or low-ductility failure modes typically include 

behavior in direct or nearly-direct compression, shear in 

slender components and in component connections, 

torsion in slender components, and reinforcement 

development, splicing, and anchorage. It is 

recommended that the stresses, forces, and moments 

acting to cause these failure modes be determined from 

a limit-state analysis considering probable resistances 

at locations of nonlinear action.
6-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Alternatively, the use of effective stiffness values in 

Table 6-5 shall be permitted.

6.4.1.2.2 Nonlinear Procedures

Where design actions are determined using the 

nonlinear procedures of Chapter 3, component loaddeformation response shall be represented by nonlinear 

load-deformation relations. Linear relations shall be 

permitted where nonlinear response will not occur in 

the component. The nonlinear load-deformation 

relation shall be based on experimental evidence or 

taken from quantities specified in Sections 6.5 through 

6.13. For the Nonlinear Static Procedure (NSP), use of 

the generalized load-deformation relation shown in 

Figure 6-1 or other curves defining behavior under 

monotonically increasing deformation shall be 

permitted. For the Nonlinear Dynamic Procedure 

(NDP), load-deformation relations shall define behavior 

under monotonically increasing lateral deformation and 

under multiple reversed deformation cycles as specified 

in Section 6.4.2.1.

The generalized load-deformation relation shown in 

Figure 6-1 shall be described by linear response from A 

(unloaded component) to an effective yield B, then a 

linear response at reduced stiffness from point B to C, 

then sudden reduction in lateral load resistance to point 

D, then response at reduced resistance to E, and final 

loss of resistance thereafter. The slope from point A to 

B shall be determined according to Section 6.4.1.2.1. 

The slope from point B to C, ignoring effects of gravity 

loads acting through lateral displacements, shall be 

taken between zero and 10% of the initial slope unless 

an alternate slope is justified by experiment or analysis. 

Point C shall have an ordinate equal to the strength of 

the component and an abscissa equal to the deformation 

at which significant strength degradation begins. 

Representation of the load-deformation relation by 

points A, B, and C only (rather than all points A–E), 

shall be permitted if the calculated response does not 

exceed point C. Numerical values for the points 

identified in Figure 6-1 shall be as specified in 

Sections 6.5 through 6.13. Other load-deformation 

relations shall be permitted if justified by experimental 

evidence or analysis. 

Table 6-5 Effective Stiffness Values

Component Flexural Rigidity Shear Rigidity Axial Rigidity

Beams—nonprestressed 0.5EcIg 0.4EcAw —

Beams—prestressed EcIg 0.4EcAw —

Columns with compression due to design 

gravity loads > 0.5 Agf’

c

0.7EcIg 0.4EcAw EcAg

Columns with compression due to design 

gravity loads < 0.3 Agf’

c or with tension

0.5EcIg 0.4EcAw EsAs

Walls—uncracked (on inspection) 0.8EcIg 0.4EcAw EcAg

Walls—cracked 0.5EcIg 0.4EcAw EcAg

Flat Slabs—nonprestressed See Section 6.5.4.2 0.4EcAg —

Flat Slabs—prestressed See Section 6.5.4.2 0.4EcAg —

Note: It shall be permitted to take Ig for T-beams as twice the value of Ig of the web alone. Otherwise, Ig shall be based on the effective width as defined in 

Section 6.4.1.3. For columns with axial compression falling between the limits provided, linear interpolation shall be permitted. Alternatively, the more 

conservative effective stiffnesses shall be used.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-13

 

C6.4.1.2.2 Nonlinear Procedures

Typically, the responses shown in Figure 6-1 are 

associated with flexural response or tension response. 

In this case, the resistance at Q/Qy = 1.0 is the yield 

value, and subsequent strain hardening accommodates 

strain hardening in the load-deformation relation as the 

member is deformed toward the expected strength. 

When the response shown in Figure 6-1 is associated 

with compression, the resistance at Q/Qy = 1.0 

typically is the value at which concrete begins to spall, 

and strain hardening in well-confined sections may be 

associated with strain hardening of the longitudinal 

reinforcement and the confined concrete. When the 

response shown in Figure 6-1 is associated with shear, 

the resistance at Q/Qy = 1.0 typically is the value at 

which the design shear strength is reached, and no 

strain hardening follows.

The deformations used for the load-deformation 

relation of Figure 6-1 shall be defined in one of two 

ways, as follows:

(a) Deformation, or Type I. In this curve, deformations 

are expressed directly using terms such as strain, 

curvature, rotation, or elongation. The parameters a

and b shall refer to those portions of the deformation 

that occur after yield; that is, the plastic deformation. 

The parameter c is the reduced resistance after the 

sudden reduction from C to D. Parameters a, b, and c

are defined numerically in various tables in this 

chapter. Alternatively, it shall be permitted to 

determine the parameters a, b, and c directly by 

analytical procedures justified by experimental 

evidence.

(b) Deformation Ratio, or Type II. In this curve, 

deformations are expressed in terms such as shear 

angle and tangential drift ratio. The parameters d and e

refer to total deformations measured from the origin. 

Parameters c, d, and e are defined numerically in 

various tables in this chapter. Alternatively, it shall be 

permitted to determine the parameters c, d, and e

directly by analytical procedures justified by 

experimental evidence.

Figure 6-1 Generalized Force-Deformation 

Relations for Concrete Elements or 

Components
6-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.4.1.3 Flanged Construction

In beams consisting of a web and flange that act 

integrally, the combined stiffness and strength for 

flexural and axial loading shall be calculated 

considering a width of effective flange on each side of 

the web equal to the smaller of: (1) the provided flange 

width, (2) eight times the flange thickness, (3) half the 

distance to the next web, or (4) one-fifth of the span for 

beams. When the flange is in compression, both the 

concrete and reinforcement within the effective width 

shall be considered effective in resisting flexure and 

axial load. When the flange is in tension, longitudinal 

reinforcement within the effective width and that is 

developed beyond the critical section shall be 

considered fully effective for resisting flexural and axial 

loads. The portion of the flange extending beyond the 

width of the web shall be assumed ineffective in 

resisting shear.

In walls, effective flange width shall be in accordance 

with Chapter 21 of ACI 318.

6.4.2 Strength and Deformability

6.4.2.1 General

Actions in a structure shall be classified as being either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. Design strengths for deformationcontrolled and force-controlled actions shall be 

calculated in accordance with Sections 6.4.2.2 and 

6.4.2.3, respectively.

Components shall be classified as having low, 

moderate, or high ductility demands according to 

Section 6.4.2.4.

Where strength and deformation capacities are derived 

from test data, the tests shall be representative of 

proportions, details, and stress levels for the component 

and comply with requirements specified in 

Section 2.8.1.

The strength and deformation capacities of concrete 

members shall correspond to values resulting from 

earthquake loadings involving three fully reversed 

cycles to the design deformation level unless a larger or 

smaller number of deformation cycles is determined 

considering earthquake duration and the dynamic 

properties of the structure.

6.4.2.2 Deformation-Controlled Actions

Strengths used for deformation-controlled actions shall 

be taken as equal to expected strengths, QCE, obtained 

experimentally, or calculated using accepted principles 

of mechanics. Expected strength is defined as the mean 

maximum resistance expected over the range of 

deformations to which the concrete component is likely 

to be subjected. When calculations are used to define 

expected strength, expected material properties shall be 

used. Unless other procedures are specified in this 

standard, procedures specified in ACI 318 to calculate 

design strengths shall be permitted except that the 

strength reduction factor, φ, shall be taken equal to 

unity. Deformation capacities for acceptance of 

deformation-controlled actions calculated by nonlinear 

procedures shall be as specified in Sections 6.5 to 

Section 6.13. For components constructed of 

lightweight concrete, QCE shall be modified in 

accordance with ACI 318 procedures for lightweight 

concrete.

C6.4.2.1 General

Strengths and deformation capacities given in this 

chapter are for earthquake loadings involving three 

fully reversed deformation cycles to the design 

deformation levels, in addition to similar cycles to 

lesser deformation levels. In some cases—including 

some short-period buildings and buildings subjected to 

a long-duration design earthquake—a building may be 

expected to be subjected to additional cycles to the 

design deformation levels. The increased number of 

cycles may lead to reductions in resistance and 

deformation capacity. The effects on strength and 

deformation capacity of additional deformation cycles 

should be considered in design. Large earthquakes will 

cause additional cycles.

C6.4.2.2 Deformation-Controlled Actions

Expected yield strength of reinforcing steel, as 

specified in this standard, includes consideration of 

material overstrength and strain hardening.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-15

6.4.2.3 Force-Controlled Actions

Strengths used for force-controlled actions shall be 

taken as lower-bound strengths, QCL, obtained 

experimentally, or calculated using established 

principles of mechanics. Lower-bound strength is 

defined as the mean minus one standard deviation of 

resistance expected over the range of deformations and 

loading cycles to which the concrete component is 

likely to be subjected. When calculations are used to 

define lower-bound strengths, lower bound estimates of 

material properties shall be used. Unless other 

procedures are specified in this standard, procedures 

specified in ACI 318 to calculate design strengths shall 

be permitted, except that the strength reduction factor, 

φ, shall be taken equal to unity. For components 

constructed of lightweight concrete, QCL shall be 

modified in accordance with ACI 318 procedures for 

lightweight concrete.

6.4.2.4 Component Ductility Demand 

Classification

Where procedures in this chapter require classification 

of component ductility demand, components shall be 

classified as having low, moderate, or high ductility 

demands, based on the maximum value of the demand 

capacity ratio (DCR) defined in Section 2.4.1 for linear 

procedures, or the calculated displacement ductility for 

nonlinear procedures in accordance with Table 6-6. 

6.4.3 Flexure and Axial Loads

Flexural strength and deformation capacity of members 

with and without axial loads shall be calculated 

according to the procedures of ACI 318 or by other 

approved methods. Strengths and deformation 

capacities of components with monolithic flanges shall 

be calculated considering concrete and developed 

longitudinal reinforcement within the effective flange 

width as defined in Section 6.4.1.3.

Strength and deformation capacities shall be determined 

considering available development of longitudinal 

reinforcement. Where longitudinal reinforcement has 

embedment or development length that is insufficient 

for development of reinforcement strength, flexural 

strength shall be calculated based on limiting stress 

capacity of the embedded bar as defined in 

Section 6.4.5.

Where flexural deformation capacities are calculated 

from basic principles of mechanics, reductions in 

deformation capacity due to applied shear shall be taken 

into consideration. When using analytical models for 

flexural deformability that do not directly consider 

effect of shear, and where design shear equals or 

exceeds Aw, where f ′

c is in psi and Aw is gross 

area of web in square inches, the design value shall not 

exceed eighty percent of the value calculated using the 

analytical model.

For concrete columns under combined axial load and 

biaxial bending, the combined strength shall be 

evaluated considering biaxial bending. When using 

linear procedures, the design axial load, PUF, shall be 

calculated as a force-controlled action in accordance 

with Section 3.4. The design moments, MUD, shall be 

calculated about each principal axis in accordance with 

Section 3.4. Acceptance shall be based on the following 

equation:

(6-1)

Table 6-6 Component Ductility Demand 

Classification

Maximum value of DCR or 

displacement ductility Descriptor

< 2 Low Ductility Demand

2 to 4 Moderate Ductility Demand

> 4 High Ductility Demand

6 f

c′

MUDx

mxκMCEx

------------------------

      2 MUDy

myκMCEy

------------------------

      +

2

≤ 1
6-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

where:

Alternative approaches based on principles of 

mechanics shall be permitted.

6.4.3.1 Usable Strain Limits

Without confining transverse reinforcement, the 

maximum usable strain at the extreme concrete 

compression fiber shall not exceed 0.002 for 

components in nearly pure compression and 0.005 for 

other components unless larger strains are substantiated 

by experimental evidence and approved. Maximum 

usable compressive strains for confined concrete shall 

be based on experimental evidence and shall consider 

limitations posed by fracture of transverse 

reinforcement, buckling of longitudinal reinforcement, 

and degradation of component resistance at large 

deformation levels. Maximum compressive strains in 

longitudinal reinforcement shall not exceed 0.02, and 

maximum tensile strains in longitudinal reinforcement 

shall not exceed 0.05.

6.4.4 Shear and Torsion

Strengths in shear and torsion shall be calculated 

according to ACI 318 except as modified in this 

standard.

Within yielding regions of components with moderate 

or high ductility demands, shear and torsional strength 

shall be calculated according to procedures for ductile 

components, such as the provisions in Chapter 21 of 

ACI 318. Within yielding regions of components with 

low ductility demands and outside yielding regions for 

all ductility demands, calculation of design shear 

strength using procedures for effective elastic response 

such as the provisions in Chapter 11 of ACI 318 shall be 

permitted.

Where the longitudinal spacing of transverse 

reinforcement exceeds half the component effective 

depth measured in the direction of shear, transverse 

reinforcement shall be assumed not more than 50% 

effective in resisting shear or torsion. Where the 

longitudinal spacing of transverse reinforcement 

exceeds the component effective depth measured in the 

direction of shear, transverse reinforcement shall be 

assumed ineffective in resisting shear or torsion. For 

beams and columns in which perimeter hoops are either 

lap-spliced or have hooks that are not adequately 

anchored in the concrete core, transverse reinforcement 

shall be assumed not more than 50% effective in 

regions of moderate ductility demand and shall be 

assumed ineffective in regions of high ductility demand.

Shear friction strength shall be calculated according to 

ACI 318, taking into consideration the expected axial 

load due to gravity and earthquake effects. Where 

rehabilitation involves the addition of concrete 

requiring overhead work with dry-pack, the shear 

friction coefficient μ shall be taken as equal to 70% of 

the value specified by ACI 318.

MUDx = design bending moment about x axis for 

axial load PUF, kip-in.

MUDy = design bending moment about y axis for 

axial load PUF, kip-in.

MCEx = expected bending moment strength about x 

axis, kip-in.

MCEy = expected bending moment strength about y 

axis, kip-in.

mx = m-factor for column for bending about x 

axis

my = m-factor for column for bending about y 

axis

C6.4.3 Flexure and Axial Loads

Laboratory tests indicate that flexural deformability 

may be reduced as co-existing shear forces increase. 

As flexural ductility demands increase, shear capacity 

decreases, which may result in a shear failure before 

theoretical flexural deformation capacities are reached. 

Caution should be exercised when flexural 

deformation capacities are determined by calculation.

FEMA 306 is a resource for guidance regarding the 

interaction between shear and flexure. 
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-17

6.4.5 Development and Splices of 

Reinforcement

Development of straight bars, hooked bars, and lapspliced bars shall be calculated according to the 

provisions of ACI 318, with the following 

modifications:

1. Within yielding regions of components with 

moderate or high ductility demands as classified in 

Section 6.4.2.4, deformed straight bars, hooked bars, 

and lap-spliced bars shall meet the development 

requirements of Chapter 21 of ACI 318. Within 

yielding regions of components with low ductility 

demands, and outside yielding regions for all 

ductility demands, bars shall meet the development 

requirements of Chapter 12 of ACI 318, except 

requirements for lap splices shall be the same as 

those for straight development of bars in tension 

without consideration of lap splice classifications.

2. Where existing deformed straight bars, hooked bars, 

and lap-spliced bars do not meet the development 

requirements of (1) above, the capacity of existing 

reinforcement shall be calculated using 

Equation (6-2):

(6-2)

where fs = maximum stress that can be developed in 

the bar for the straight development, hook, or lap 

splice length lb provided; fy = yield strength of 

reinforcement; and ld = length required by Chapter 

12 or Chapter 21 (as appropriate) of ACI 318 for 

straight development, hook development, or lap 

splice length, except required splice lengths may be 

taken as straight bar development lengths in tension. 

Where transverse reinforcement is distributed along 

the development length with spacing not exceeding 

one-third of the effective depth of the component, it 

shall be permitted to assume the reinforcement 

retains the calculated maximum stress to high 

ductility demands. For larger spacings of transverse 

reinforcement, the developed stress shall be assumed 

to degrade from fs to 0.2fs at a ductility demand or 

DCR equal to 2.0.

3. Strength of deformed straight, discontinuous bars 

embedded in concrete sections or beam-column 

joints, with clear cover over the embedded bar not 

less than 3db, shall be calculated according to 

Equation (6-3):

(6-3)

where fs = maximum stress (in psi) that can be 

developed in an embedded bar having embedment 

length le (in inches), db = diameter of embedded bar 

(in inches), and fy = bar yield stress (in psi). When fs

is less than fy, and the calculated stress in the bar due 

to design loads equals or exceeds fs, the maximum 

developed stress shall be assumed to degrade from fs

to 0.2fs at a ductility demand or DCR equal to 2.0. In 

beams with short bottom bar embedments into 

beam-column joints, flexural strength shall be 

calculated considering the stress limitation of 

Equation (6-3).

4. For plain straight bars, hooked bars, and lap-spliced 

bars, development and splice lengths shall be taken 

as twice the values determined in accordance with 

ACI 318 unless other lengths are justified by 

approved tests or calculations considering only the 

chemical bond between the bar and the concrete.

5. Doweled bars added in seismic rehabilitation shall 

be assumed to develop yield stress when all the 

following conditions are satisfied:

5.1. Drilled holes for dowel bars are cleaned with a 

stiff brush that extends the length of the hole.

5.2. Embedment length le is not less than 10db

5.3. Minimum spacing of dowel bars is not less 

than 4le and minimum edge distance is not less 

than 2le. Design values for dowel bars not 

satisfying these conditions shall be verified by 

test data. Field samples shall be obtained to 

ensure design strengths are developed in 

accordance with Section 6.4.6.3.

f

s

l

b

l

d

---f

y =

f

s

2500

db

-----------l

e fy = ≤
6-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.4.5.1 Square Reinforcing Bars

Square reinforcing bars in a building shall be classified 

as either twisted or straight. The developed strength of 

twisted square bars shall be as specified for deformed 

bars in Section 6.4.5, using an effective diameter 

calculated based on the gross area of the square bar. 

Straight square bars shall be considered as plain bars, 

and the developed strength shall be as specified for 

plain bars in Section 6.4.5.

6.4.6 Connections to Existing Concrete

Connections used to connect two or more components 

shall be classified according to their anchoring systems 

as cast-in-place or as post-installed.

6.4.6.1 Cast-In-Place Systems

Component actions on cast-in-place connection 

systems, including shear forces, tension forces, bending 

moments, and prying actions, shall be considered forcecontrolled. Lower-bound strength of connections shall 

be ultimate values as specified in an approved building 

code with .

The capacity of anchors placed in areas where cracking 

is expected shall be reduced by a factor of 0.5.

6.4.6.2 Post-Installed Systems

Component actions on post-installed connection 

systems shall be considered force-controlled. The 

lower-bound capacity of post-installed anchors shall be 

mean minus one standard deviation of ultimate values 

published in approved test reports.

6.4.6.3 Quality Assurance

Connections between existing concrete components and 

new components added to rehabilitate the structure shall 

be subject to the quality assurance provisions specified 

in Section 2.7. The design professional shall specify the 

required inspection and testing of cast-in-place and 

post-installed anchors as part of the Quality Assurance 

Plan.

6.4.7 Rehabilitation—General 

Requirements

Upon determining that concrete elements in an existing 

building are deficient for the selected Rehabilitation 

Objective, these elements shall be rehabilitated or 

replaced or the structure shall be otherwise rehabilitated 

so that the element is no longer deficient for the selected 

rehabilitation objective. If replacement of the element is 

selected, the new element shall be designed in 

accordance with an approved building code.

Rehabilitation measures shall be evaluated in 

accordance with the principles and requirements of this 

standard, to assure that the completed rehabilitation 

achieves the selected Rehabilitation Objective. The 

effects of rehabilitation on stiffness, strength, and 

deformability shall be taken into account in an 

analytical model of the rehabilitated structure. The 

compatibility of new and existing components shall be 

checked at displacements consistent with the selected 

performance level.

Connections required between existing and new 

elements shall satisfy the requirements of Section 6.4.6 

and other requirements of this standard.

C6.4.5 Development and Splices of 

Reinforcement

Chapter 21 requirements for development of 

reinforcement in ACI 318 are intended for use in 

yielding components of reinforced concrete moment 

frame elements, and not shear wall components. When 

checking development of bars in shear wall 

components, Chapter 12 requirements should be used.

For buildings constructed prior to 1950, the bond 

strength developed between reinforcing steel and 

concrete may be less than present-day strength. 

Current equations for development and splices of 

reinforcement account for mechanical bond due to 

deformations present in deformed bars in addition to 

chemical bond. The length required to develop plain 

bars will be much greater than that required for 

deformed bars, and will be more sensitive to cracking 

in the concrete. Procedures for testing and assessment 

of tensile lap splices and development length of plain 

reinforcing steel may be found in CRSI.

φ =1.0
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-19

6.5 Concrete Moment Frames

6.5.1 Types of Concrete Moment Frames

Concrete moment frames shall be defined as elements 

composed primarily of horizontal framing components 

(beams and/or slabs), vertical framing components 

(columns) and joints connecting horizontal and vertical 

framing components. These elements resist lateral loads 

acting alone, or in conjunction with shear walls, braced 

frames, or other elements in a dual system.

Frames that are cast monolithically, including 

monolithic concrete frames created by the addition of 

new material, shall meet the provisions of this section. 

Frames covered under this section include reinforced 

concrete beam-column moment frames, prestressed 

concrete beam-column moment frames, and slabcolumn moment frames. Precast concrete frames, 

concrete frames with infills, and concrete braced frames 

shall meet the provisions of Sections 6.6, 6.7, and 6.10, 

respectively.

6.5.1.1 Reinforced Concrete Beam-Column 

Moment Frames

Reinforced concrete beam-column moment frames shall 

satisfy the following conditions:

1. Framing components shall be beams (with or 

without slabs), columns, and their connections. 

2. Beams and columns shall be of monolithic 

construction that provides for moment transfer 

between beams and columns. 

3. Primary reinforcement in components contributing 

to lateral load resistance shall be nonprestressed. 

Special Moment Frames, Intermediate Moment Frames, 

and Ordinary Moment Frames as defined in ASCE 7, 

shall be deemed to satisfy the above conditions. This 

classification shall include existing construction, new 

construction, and existing construction that has been 

rehabilitated.

6.5.1.2 Post-Tensioned Concrete BeamColumn Moment Frames

Post-tensioned concrete beam-column moment frames 

shall satisfy the following conditions:

1. Framing components shall be beams (with or 

without slabs), columns, and their connections.

2. Frames shall be of monolithic construction that 

provides for moment transfer between beams and 

columns.

3. Primary reinforcement in beams contributing to 

lateral load resistance shall include post-tensioned 

reinforcement with or without mild reinforcement.

This classification shall include existing construction, 

new construction, and existing construction that has 

been rehabilitated.

6.5.1.3 Slab-Column Moment Frames

Slab-column moment frames shall satisfy the following 

conditions:

1. Framing components shall be slabs (with or without 

beams in the transverse direction), columns, and 

their connections.

2. Frames shall be of monolithic construction that 

provides for moment transfer between slabs and 

columns. 

3. Primary reinforcement in slabs contributing to 

lateral load resistance shall include nonprestressed 

reinforcement, prestressed reinforcement, or both.

This classification shall include frames intended as part 

of the lateral-force-resisting system and frames not 

intended as part of the lateral-force-resisting system in 

the original design, including existing construction, new 

construction, and existing construction that has been 

rehabilitated.
6-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.5.2 Reinforced Concrete Beam-Column 

Moment Frames

6.5.2.1 General Considerations

The analytical model for a beam-column frame element 

shall represent strength, stiffness, and deformation 

capacity of beams, columns, beam-column joints, and 

other components of the frame, including connections 

with other elements. Potential failure in flexure, shear, 

and reinforcement development at any section along the 

component length shall be considered. Interaction with 

other elements, including nonstructural elements and 

components, shall be included.

Analytical models representing a beam- column frame 

using line elements with properties concentrated at 

component centerlines shall be permitted. Where beam 

and column centerlines do not intersect, the effects of 

the eccentricity between centerlines on framing shall be 

taken into account. Where the centerline of the 

narrower component falls within the middle third of the 

adjacent framing component measured transverse to the 

framing direction, however, this eccentricity need not 

be considered. Where larger eccentricities occur, the 

effect shall be represented either by reductions in 

effective stiffness, strength, and deformation capacity, 

or by direct modeling of the eccentricity.

The beam-column joint in monolithic construction shall 

be represented as a stiff or rigid zone having horizontal 

dimensions equal to the column cross-sectional 

dimensions and vertical dimension equal to the beam 

depth, except that a wider joint shall be permitted where 

the beam is wider than the column and where justified 

by experimental evidence. The model of the connection 

between the columns and foundation shall be selected 

based on the details of the column-foundation 

connection and rigidity of the foundation-soil system.

Action of the slab as a diaphragm interconnecting 

vertical elements shall be represented. Action of the 

slab as a composite beam flange shall be considered in 

developing stiffness, strength, and deformation 

capacities of the beam component model, according to 

Section 6.4.1.3.

Inelastic action shall be restricted to those components 

and actions listed in Tables 6-7 through 6-9, except 

where it is demonstrated by experimental evidence and 

analysis that other inelastic action is acceptable for the 

selected performance level. Acceptance criteria shall be 

as specified in Section 6.5.2.4.

6.5.2.2 Stiffness for Analysis

6.5.2.2.1 Linear Static and Dynamic Procedures

Beams shall be modeled considering flexural and shear 

stiffnesses, including the effect of the slab acting as a 

flange in monolithic construction. Columns shall be 

modeled considering flexural, shear, and axial 

stiffnesses. Joints shall be modeled as either stiff or 

rigid components. Effective stiffnesses shall be 

according to Section 6.4.1.2.

6.5.2.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations shall follow the 

requirements of Section 6.4.1.2.

Beams and columns shall be modeled using 

concentrated plastic hinge models or distributed plastic 

hinge models. Other models whose behavior has been 

demonstrated to represent the behavior of reinforced 

concrete beam and column components subjected to 

lateral loading shall be permitted. The beam and 

column model shall be capable of representing inelastic 

response along the component length, except where it is 

shown by equilibrium that yielding is restricted to the 

component ends. Where nonlinear response is expected 

in a mode other than flexure, the model shall be 

established to represent these effects.

Monotonic load-deformation relations shall be 

according to the generalized load-deformation relation 

shown in Figure 6-1, except that different relations shall 

be permitted where verified by experiments. The 

overall load-deformation relation shall be established so 

that the maximum resistance is consistent with the 

design strength specifications of Sections 6.4.2 and 

6.5.2.3.

For beams and columns, the generalized deformation in 

Figure 6-1 shall be either the chord rotation or the 

plastic hinge rotation. For beam-column joints, the 

generalized deformation shall be shear strain. Values of 

the generalized deformation at points B, C, and D shall 

be derived from experiments or rational analyses, and 

shall take into account the interactions between flexure, 

axial load, and shear. 
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-21

Table 6-7 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Reinforced Concrete Beams

Conditions

Modeling Parameters3 Acceptance Criteria3

Plastic Rotation 

Angle, radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, radians

Performance Level

IO

Component Type

Primary Secondary

a b c LS CP LS CP

i. Beams controlled by flexure1

Trans. 

Reinf.2

≤ 0.0 C ≤ 3 0.025 0.05 0.2 0.010 0.02 0.025 0.02 0.05

≤ 0.0 C ≥ 6 0.02 0.04 0.2 0.005 0.01 0.02 0.02 0.04

≥ 0.5 C ≤ 3 0.02 0.03 0.2 0.005 0.01 0.02 0.02 0.03

≥ 0.5 C ≥ 6 0.015 0.02 0.2 0.005 0.005 0.015 0.015 0.02

≤ 0.0 NC ≤ 3 0.02 0.03 0.2 0.005 0.01 0.02 0.02 0.03

≤ 0.0 NC ≥ 6 0.01 0.015 0.2 0.0015 0.005 0.01 0.01 0.015

≥ 0.5 NC ≤ 3 0.01 0.015 0.2 0.005 0.01 0.01 0.01 0.015

≥ 0.5 NC ≥ 6 0.005 0.01 0.2 0.0015 0.005 0.005 0.005 0.01

ii. Beams controlled by shear1

Stirrup spacing ≤ d/2 0.0030 0.02 0.2 0.0015 0.0020 0.0030 0.01 0.02

Stirrup spacing > d/2 0.0030 0.01 0.2 0.0015 0.0020 0.0030 0.005 0.01

iii. Beams controlled by inadequate development or splicing along the span1

Stirrup spacing ≤ d/2 0.0030 0.02 0.0 0.0015 0.0020 0.0030 0.01 0.02

Stirrup spacing > d/2 0.0030 0.01 0.0 0.0015 0.0020 0.0030 0.005 0.01

iv. Beams controlled by inadequate embedment into beam-column joint1

0.015 0.03 0.2 0.01 0.01 0.015 0.02 0.03

1. When more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcement. A component is conforming if, within the flexural plastic 

hinge region, hoops are spaced at ≤ d/3, and if, for components of moderate and high ductility demand, the strength provided by the hoops (Vs) is at least 

three-fourths of the design shear. Otherwise, the component is considered nonconforming.

3. Linear interpolation between values listed in the table shall be permitted.

ρ ρ′ –

ρbal

-------------- V

bwd fc

′ -------------------
6-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Table 6-8 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Reinforced Concrete Columns

Conditions

Modeling Parameters4 Acceptance Criteria4

Plastic Rotation 

Angle, radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, radians

Performance Level

IO

Component Type

Primary Secondary

a b c LS CP LS CP

i. Columns controlled by flexure1

Trans. 

Reinf.2

≤ 0.1 C ≤ 3 0.02 0.03 0.2 0.005 0.015 0.02 0.02 0.03

≤ 0.1 C ≥ 6 0.016 0.024 0.2 0.005 0.012 0.016 0.016 0.024

≥ 0.4 C ≤ 3 0.015 0.025 0.2 0.003 0.012 0.015 0.018 0.025

≥ 0.4 C ≥ 6 0.012 0.02 0.2 0.003 0.01 0.012 0.013 0.02

≤ 0.1 NC ≤ 3 0.006 0.015 0.2 0.005 0.005 0.006 0.01 0.015

≤ 0.1 NC ≥ 6 0.005 0.012 0.2 0.005 0.004 0.005 0.008 0.012

≥ 0.4 NC ≤ 3 0.003 0.01 0.2 0.002 0.002 0.003 0.006 0.01

≥ 0.4 NC ≥ 6 0.002 0.008 0.2 0.002 0.002 0.002 0.005 0.008

ii. Columns controlled by shear1, 3

All cases 5 — — — ——— .0030 .0040

iii. Columns controlled by inadequate development or splicing along the clear height1,3

Hoop spacing ≤ d/2 0.01 0.02 0.4 0.005 0.005 0.01 0.01 0.02

Hoop spacing > d/2 0.0 0.01 0.2 0.0 0.0 0.0 0.005 0.01

iv. Columns with axial loads exceeding 0.70Po

1, 3

Conforming hoops over the entire 

length

0.015 0.025 0.02 0.0 0.005 0.01 0.01 0.02

All other cases 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

1. When more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcement. A component is conforming if, within the flexural plastic 

hinge region, hoops are spaced at ≤ d/3, and if, for components of moderate and high ductility demand, the strength provided by the hoops (Vs) is at least 

three-fourths of the design shear. Otherwise, the component is considered nonconforming. 

3. To qualify, columns must have transverse reinforcement consisting of hoops. Otherwise, actions shall be treated as force-controlled.

4. Linear interpolation between values listed in the table shall be permitted.

5. For columns controlled by shear, see Section 6.5.2.4.2 for acceptance criteria.

P

Agf

c

′ ------------ V

bwd fc

′ -------------------
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-23

Table 6-9 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Reinforced Concrete Beam-Column Joints

Conditions

Modeling Parameters4 Acceptance Criteria4

Plastic Shear 

Angle, radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, radians

Performance Level

IO

Component Type

Primary Secondary

a b c LS CP LS CP

i. Interior joints2, 3

 Trans. 

Reinf. 3

≤ 0.1 C ≤ 1.2 0.015 0.03 0.2 0.0 0.0 0.0 0.02 0.03

≤ 0.1 C ≥ 1.5 0.015 0.03 0.2 0.0 0.0 0.0 0.015 0.02

≥ 0.4 C ≤ 1.2 0.015 0.025 0.2 0.0 0.0 0.0 0.015 0.025

≥ 0.4 C ≥ 1.5 0.015 0.02 0.2 0.0 0.0 0.0 0.015 0.02

≤ 0.1 NC ≤ 1.2 0.005 0.02 0.2 0.0 0.0 0.0 0.015 0.02

≤ 0.1 NC ≥ 1.5 0.005 0.015 0.2 0.0 0.0 0.0 0.01 0.015

≥ 0.4 NC ≤ 1.2 0.005 0.015 0.2 0.0 0.0 0.0 0.01 0.015

≥ 0.4 NC ≥ 1.5 0.005 0.015 0.2 0.0 0.0 0.0 0.01 0.015

ii. Other joints2, 3

Trans. 

Reinf.1

≤ 0.1 C ≤ 1.2 0.01 0.02 0.2 0.0 0.0 0.0 0.015 0.02

≤ 0.1 C ≥ 1.5 0.01 0.015 0.2 0.0 0.0 0.0 0.01 0.015

≥ 0.4 C ≤ 1.2 0.01 0.02 0.2 0.0 0.0 0.0 0.015 0.02

≥ 0.4 C ≥ 1.5 0.01 0.015 0.2 0.0 0.0 0.0 0.01 0.015

≤ 0.1 NC ≤ 1.2 0.005 0.01 0.2 0.0 0.0 0.0 0.0075 0.01

≤ 0.1 NC ≥ 1.5 0.005 0.01 0.2 0.0 0.0 0.0 0.0075 0.01

≥ 0.4 NC ≤ 1.2 0.0 0.0 – 0.0 0.0 0.0 0.005 0.0075

≥ 0.4 NC ≥ 1.5 0.0 0.0 – 0.0 0.0 0.0 0.005 0.0075

1. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcement. A joint is conforming if hoops are spaced at ≤ hc/3 within 

the joint. Otherwise, the component is considered nonconforming.

2. P is the design axial force on the column above the joint and Ag is the gross cross-sectional area of the joint.

3. V is the design shear force and Vn is the shear strength for the joint. The design shear force and shear strength shall be calculated according to 

Section 6.5.2.3. 

4. Linear interpolation between values listed in the table shall be permitted.

P

Ag f c

′ ------------- VVn

-----

P

Ag f c

′ ------------- V

Vn

-----
6-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.5.2.2.3 Nonlinear Dynamic Procedure

For the NDP, the complete hysteretic behavior of each 

component shall be modeled using properties verified 

by experimental evidence. The use of the generalized 

load-deformation relation described by Figure 6-1 to 

represent the envelope relation for the analysis shall be 

permitted. Unloading and reloading properties shall 

represent significant stiffness and strength degradation 

characteristics.

6.5.2.3 Strength

Component strengths shall be computed according to 

the general requirements of Sections 6.4.2 as modified 

in this section.

The maximum component strength shall be determined 

considering potential failure in flexure, axial load, 

shear, torsion, development, and other actions at all 

points along the length of the component under the 

actions of design gravity and earthquake load 

combinations.

6.5.2.3.1 Columns

For columns, the contribution of concrete to shear 

strength, Vc, calculated according to Equation (6-4) 

shall be permitted.

(6-4)

in which k = 1.0 in regions of low ductility demand, 0.7 

in regions of high ductility demand, and varies linearly 

between these extremes in regions of moderate ductility 

demand; λ = 0.75 for lightweight aggregate concrete 

and 1.0 for normal weight aggregate concrete; Nu = 

axial compression force in pounds (= 0 for tension 

force); M/V is the largest ratio of moment to shear under 

design loadings for the column but shall not be taken 

greater than 3 or less than 2; d is the effective depth; and 

Ag is the gross cross-sectional area of the column. It 

shall be permitted to assume d=0.8h, where h is the 

dimension of the column in the direction of shear. 

Where axial force is calculated from the linear 

procedures of Chapter 3, the maximum compressive 

axial load for use in Equation (6-4) shall be taken as 

equal to the value calculated using Equation (3-4) 

considering design gravity load only, and the minimum 

compression axial load shall be calculated according to 

Equation (3-18). Alternatively, limit analysis as 

specified in Section 3.4.2.1.2 shall be permitted to be 

used to determine design axial loads for use with the 

linear analysis procedures of Chapter 3. Alternative 

formulations for column strength that consider effects 

of reversed cyclic, inelastic deformations and that are 

verified by experimental evidence shall be permitted.

For columns satisfying the detailing and proportioning 

requirements of Chapter 21 of ACI 318, the shear 

strength equations of ACI 318 shall be permitted to be 

used.

Table 6-10 Values of γ for Joint Strength Calculation

ρ"

Value of γ

Interior joint with 

transverse 

beams

Interior joint 

without 

transverse 

beams

Exterior joint 

with transverse 

beams

Exterior joint 

without 

transverse 

beams Knee joint

<0.003 12 10 8 6 4

≥0.003 20 15 15 12 8

ρ" = volumetric ratio of horizontal confinement reinforcement in the joint; knee joint = self-descriptive (with transverse beams or not).

Vc λk

6 f ′

c

M Vd ⁄ --------------- 1

Nu

6 f’

cAg

+ -------------------

      0.8bw = ( ) h
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-25

For beam-column joints, the nominal cross-sectional 

area, Aj

, shall be defined by a joint depth equal to the 

column dimension in the direction of framing and a 

joint width equal to the smallest of (1) the column 

width, (2) the beam width plus the joint depth, and 

(3) twice the smaller perpendicular distance from the 

longitudinal axis of the beam to the column side. 

Design forces shall be calculated based on development 

of flexural plastic hinges in adjacent framing members, 

including effective slab width, but need not exceed 

values calculated from design gravity and 

earthquake-load combinations. Nominal joint shear 

strength Vn shall be calculated according to the general 

procedures of ACI 318, as modified by Equation (6-5): 

(6-5)

in which λ = 0.75 for lightweight aggregate concrete 

and 1.0 for normal weight aggregate concrete, Aj

 is the 

effective horizontal joint area with dimensions as 

defined above, and γ is as defined in Table 6-10.

6.5.2.4 Acceptance Criteria

6.5.2.4.1 Linear Static and Dynamic Procedures

All actions shall be classified as being either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. In primary components, deformationcontrolled actions shall be restricted to flexure in beams 

(with or without slab) and columns. In secondary 

components, deformation-controlled actions shall be 

restricted to flexure in beams (with or without slab), 

plus restricted actions in shear and reinforcement 

development, as identified in Tables 6-11 through 6-13. 

All other actions shall be defined as being forcecontrolled actions.

Design actions on components shall be determined as 

prescribed in Chapter 3. Where the calculated DCR 

values exceed unity, the following design actions shall 

be determined using limit analysis principles as 

prescribed in Chapter 3: (1) moments, shears, torsions, 

and development and splice actions corresponding to 

development of component strength in beams and 

columns; (2) joint shears corresponding to development 

of strength in adjacent beams and columns; and (3) 

axial load in columns and joints, considering likely 

plastic action in components above the level in 

question.

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2.2. m-factors shall be 

selected from Tables 6-11 through 6-13. Those 

components that satisfy Equations (3-20) and (3-21) 

shall satisfy the performance criteria.

Where the average DCR of columns at a level exceeds 

the average value of beams at the same level, and 

exceeds the greater of 1.0 and m/2 for all columns, the 

level shall be defined as a weak column element. For 

weak column elements, one of the following shall be 

satisfied. 

1. The check of average DCR values at the level shall 

be repeated, considering all primary and secondary 

components at the level with a weak column 

element. If the average of the DCR values for 

vertical components exceeds the average value for 

horizontal components at the level, and exceeds 2.0, 

the structure shall be reanalyzed using a nonlinear 

procedure, or the structure shall be rehabilitated to 

remove this deficiency.

2. The structure shall be reanalyzed using either the 

NSP or the NDP of Chapter 3.

3. The structure shall be rehabilitated to remove the 

weak story.

6.5.2.4.2 Nonlinear Static and Dynamic Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.3.2. Where the generalized 

deformation is taken as rotation in the flexural plastic 

hinge zone in beams and columns, the plastic hinge 

rotation capacities shall be as defined by Tables 6-7 and 

6-8. Where the generalized deformation is shear 

distortion of the beam-column joint, shear angle 

capacities shall be as defined by Table 6-9. For columns 

designated as primary components and for which 

calculated design shears exceed design shear strength as 

defined by Equation (6-4), the permissible deformation 

for the Collapse Prevention Performance Level shall not 

exceed the deformation at which shear strength is 

calculated to be reached; the permissible deformation 

for the Life Safety Performance Level shall not exceed 

three quarters of that value. Where inelastic action is 

indicated for a component or action not listed in these 

tables, the performance shall be deemed unacceptable. 

Alternative approaches or values shall be permitted 

where justified by experimental evidence and analysis.

QCL Vn λγ f

c

′ Aj = = , psi
6-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

 

Table 6-11 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete Beams

Conditions

m-factors3

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Beams controlled by flexure1

Trans. 

Reinf.2

≤ 0.0 C ≤ 3 3 6 7 6 10

≤ 0.0 C ≥ 62 3 4 3 5

≥ 0.5 C ≤ 32 3 4 3 5

≥ 0.5 C ≥ 62 2 3 2 4

≤ 0.0 NC ≤ 32 3 4 3 5

≤ 0.0 NC ≥ 6 1.25 2 3 2 4

≥ 0.5 NC ≤ 32 3 3 3 4

≥ 0.5 NC ≥ 6 1.25 2 2 2 3

ii. Beams controlled by shear1

Stirrup spacing ≤ d/2 1.25 1.5 1.75 3 4

Stirrup spacing > d/2 1.25 1.5 1.75 2 3

iii. Beams controlled by inadequate development or splicing along the span1

Stirrup spacing ≤ d/2 1.25 1.5 1.75 3 4

Stirrup spacing > d/2 1.25 1.5 1.75 2 3

iv. Beams controlled by inadequate embedment into beam-column joint1

22334

1. When more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcement. A component is conforming if, within the flexural plastic 

hinge region, hoops are spaced at ≤ d/3, and if, for components of moderate and high ductility demand, the strength provided by the hoops (Vs) is at least 

three-fourths of the design shear. Otherwise, the component is considered nonconforming.

3. Linear interpolation between values listed in the table shall be permitted.

ρ ρ′ –

ρbal

-------------- V

bwd fc

′ -------------------
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-27

Table 6-12 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete Columns

Conditions

m-factors4

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Columns controlled by flexure1

Trans. 

Reinf.2

≤ 0.1 C ≤ 32 3 4 4 5

≤ 0.1 C ≥ 6 2 2.4 3.2 3.2 4

≥ 0.4 C ≤ 3 1.25 2 3 3 4

≥ 0.4 C ≥ 6 1.25 1.6 2.4 2.4 3.2

≤ 0.1 NC ≤ 32 2 3 2 3

≤ 0.1 NC ≥ 6 2 1.6 2.4 1.6 2.4

≥ 0.4 NC ≤ 3 1.25 1.5 2 1.5 2

≥ 0.4 NC ≥ 6 1.25 1.5 1.75 1 1.6

ii. Columns controlled by shear1,3

Hoop spacing ≤ d/2, 

or ≤ 0.1

––– 2 3

Other cases ––– 1.5 2

iii. Columns controlled by inadequate development or splicing along the clear height1,3

Hoop spacing ≤ d/2 1.25 1.5 1.75 3 4

Hoop spacing > d/2 ––– 2 3

iv. Columns with axial loads exceeding 0.70Po

1,3

Conforming hoops over the entire length 1 1 2 2 2

All other cases ––– 1 1

1. When more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcement. A component is conforming if, within the flexural plastic 

hinge region, hoops are spaced at ≤ d/3, and if, for components of moderate and high ductility demand, the strength provided by the hoops (Vs) is at least 

three-fourths of the design shear. Otherwise, the component is considered nonconforming. 

3. To qualify, columns must have transverse reinforcement consisting of hoops. Otherwise, actions shall be treated as force-controlled.

4. Linear interpolation between values listed in the table shall be permitted.

P

Agf

c

′ ------------ V

bwd fc

′ -------------------

P

Ag f c

′ ------------
6-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Table 6-13 Numerical Acceptance Criteria for Linear Procedures—

Reinforced Concrete Beam-Column Joints

Conditions

m-factors4

Performance Level

IO

Component Type

Primary5 Secondary

LS CP LS CP

i. Interior joints2, 3

Trans. Reinf.

≤ 0.1 C ≤ 1.2 ––– 3 4

≤ 0.1 C ≥ 1.5 ––– 2 3

≥ 0.4 C ≤ 1.2 ––– 3 4

≥ 0.4 C ≥ 1.5 ––– 2 3

≤ 0.1 NC ≤ 1.2 ––– 2 3

≤ 0.1 NC ≥ 1.5 ––– 2 3

≥ 0.4 NC ≤ 1.2 ––– 2 3

≥ 0.4 NC ≥ 1.5 ––– 2 3

ii. Other joints2, 3

Trans. Reinf.

≤ 0.1 C ≤ 1.2 ––– 3 4

≤ 0.1 C ≥ 1.5 ––– 2 3

≥ 0.4 C ≤ 1.2 ––– 3 4

≥ 0.4 C ≥ 1.5 ––– 2 3

≤ 0.1 NC ≤ 1.2 ––– 2 3

≤ 0.1 NC ≥ 1.5 ––– 2 3

≥ 0.4 NC ≤ 1.2 ––– 1.5 2.0

≥ 0.4 NC ≥ 1.5 ––– 1.5 2.0

1. “C” and “NC” are abbreviations for conforming and nonconforming transverse reinforcements. A joint is conforming if hoops are spaced at ≤ hc/3 within 

the joint. Otherwise, the component is considered nonconforming.

2. P is the ratio of the design axial force on the column above the joint and Ag is the gross cross-sectional area of the joint.

3. V is the design shear force and Vn is the shear strength for the joint. The design shear force and shear strength shall be calculated according to 

Section 6.5.2.3. 

4. Linear interpolation between values listed in the table shall be permitted.

5. For linear procedures, all primary joints shall be force-controlled; m-factors shall not apply.

P

Ag f c

′ ------------ V

Vn

-----

P

Ag f c

′ ------------ V

Vn

-----
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-29

6.5.2.5 Rehabilitation Measures

Concrete beam-column moment frame components that 

do not meet the acceptance criteria for the selected 

rehabilitation objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 6.4.7 and other provisions of this standard. 

6.5.3 Post-Tensioned Concrete 

Beam-Column Moment Frames

6.5.3.1 General Considerations

The analytical model for a post-tensioned concrete 

beam-column frame element shall be established 

following the criteria specified in Section 6.5.2.1 for 

reinforced concrete beam-column moment frames. In 

addition to potential failure modes described in 

Section 6.5.2.1, the analysis model shall consider 

potential failure of tendon anchorages.

The analysis procedures described in Chapter 3 shall 

apply to frames with post-tensioned beams satisfying 

the following conditions: 

1. The average prestress, fpc, calculated for an area 

equal to the product of the shortest cross-sectional 

dimension and the perpendicular cross-sectional 

dimension of the beam, does not exceed the greater 

of 750 psi or f’c /12 at locations of nonlinear action.

C6.5.2.5 Rehabilitation Measures

The following rehabilitation measures may be 

effective in rehabilitating reinforced concrete beamcolumn moment frames:

1. Jacketing existing beams, columns, or joints 

with new reinforced concrete, steel, or fiber 

wrap overlays. The new materials should be 

designed and constructed to act compositely with 

the existing concrete. Where reinforced concrete 

jackets are used, the design should provide 

detailing to enhance ductility. Component strength 

should be taken to not exceed any limiting strength 

of connections with adjacent components. Jackets 

should be designed to provide increased 

connection strength and improved continuity 

between adjacent components.

2. Post-tensioning existing beams, columns, or 

joints using external post-tensioned 

reinforcement. Post-tensioned reinforcement 

should be unbonded within a distance equal to 

twice the effective depth from sections where 

inelastic action is expected. Anchorages should be 

located away from regions where inelastic action is 

anticipated, and should be designed considering 

possible force variations due to earthquake 

loading.

3. Modification of the element by selective 

material removal from the existing element. 

Examples include: (1) where nonstructural 

elements or components interfere with the frame, 

removing or separating the nonstructural elements 

or components to eliminate the interference; (2) 

weakening, due to removal of concrete or severing 

of longitudinal reinforcement, to change response 

mode from a nonductile mode to a more ductile 

mode (e.g., weakening of beams to promote 

formation of a strong-column, weak-beam 

system); and (3) segmenting walls to change 

stiffness and strength.

4. Improvement of deficient existing 

reinforcement details. Removal of cover concrete 

for modification of existing reinforcement details 

should avoid damage to core concrete and the bond 

between existing reinforcement and core concrete. 

New cover concrete should be designed and 

constructed to achieve fully composite action with 

the existing materials.

5. Changing the building system to reduce the 

demands on the existing element. Examples 

include addition of supplementary lateral-forceresisting elements such as walls or buttresses, 

seismic isolation, and mass reduction.

6. Changing the frame element to a shear wall, 

infilled frame, or braced frame element by 

addition of new material. Connections between 

new and existing materials should be designed to 

transfer the forces anticipated for the design load 

combinations. Where the existing concrete frame 

columns and beams act as boundary elements and 

collectors for the new shear wall or braced frame, 

these should be checked for adequacy, considering 

strength, reinforcement development, and 

deformability. Diaphragms, including drag struts 

and collectors, should be evaluated and, if 

necessary, rehabilitated to ensure a complete load 

path to the new shear wall or braced frame 

element.
6-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

2. Prestressing tendons do not provide more than onequarter of the strength for both positive moments 

and negative moments at the joint face.

3. Anchorages for tendons are demonstrated to have 

performed satisfactorily for seismic loadings in 

compliance with the requirements of ACI 318. These 

anchorages occur outside hinging areas or joints, 

except in existing components where experimental 

evidence demonstrates that the connection will meet 

the performance objectives under design loadings.

Alternative procedures shall be provided where these 

conditions are not satisfied.

6.5.3.2 Stiffness

6.5.3.2.1 Linear Static and Dynamic Procedures

Beams shall be modeled considering flexural and shear 

stiffnesses, including the effect of the slab acting as a 

flange in monolithic and composite construction. 

Columns shall be modeled considering flexural, shear, 

and axial stiffnesses. Joints shall be modeled as either 

stiff or rigid components. Effective stiffnesses shall be 

according to Section 6.4.1.2.

6.5.3.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations shall comply with 

the requirements of Section 6.4.1.2 and the reinforced 

concrete frame requirements of Section 6.5.2.2.2.

Values of the generalized deformation at points B, C, 

and D in Figure 6-1 shall be either derived from 

experiments or approved rational analyses, and shall 

take into account the interactions between flexure, axial 

load, and shear. Alternatively, where the generalized 

deformation is taken as rotation in the flexural plastic 

hinge zone, and where the three conditions of 

Section 6.5.3.1 are satisfied, beam plastic hinge rotation 

capacities shall be as defined by Table 6-7. Columns 

and joints shall be modeled as described in 

Section 6.5.2.2.

6.5.3.2.3 Nonlinear Dynamic Procedure

For the NDP, the complete hysteretic behavior of each 

component shall be modeled using properties verified 

by experimental evidence. The relation of Figure 6-1 

shall be taken to represent the envelope relation for the 

analysis. Unloading and reloading properties shall 

represent significant stiffness and strength degradation 

characteristics as influenced by prestressing.

6.5.3.3 Strength

Component strengths shall be computed according to 

the general requirements of Sections 6.4.2 and the 

additional requirements of Section 6.5.2.3. Effects of 

prestressing on strength shall be considered.

For deformation-controlled actions, prestress shall be 

assumed to be effective for the purpose of determining 

the maximum actions that may be developed associated 

with nonlinear response of the frame. For forcecontrolled actions, the effects on strength of prestress 

loss shall also be considered as a design condition, 

where these losses are possible under design load 

combinations including inelastic deformation reversals.

6.5.3.4 Acceptance Criteria

Acceptance criteria for post-tensioned concrete beamcolumn moment frames shall follow the criteria for 

reinforced concrete beam-column frames specified in 

Section 6.5.2.4.

Modeling parameters and acceptance criteria shall be 

based on Tables 6-7 through 6-9 and 6-11 through 6-13.

6.5.3.5 Rehabilitation Measures

Post-tensioned concrete beam-column moment frame 

components that do not meet the acceptance criteria for 

the selected Rehabilitation Objective shall be 

rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 6.4.7 and other provisions of 

this standard. 

6.5.4 Slab-Column Moment Frames

6.5.4.1 General Considerations

The analytical model for a slab-column frame element 

shall represent strength, stiffness, and deformation 

capacity of slabs, columns, slab-column connections, 

and other components of the frame. Potential failure in 

flexure, shear, shear-moment transfer, and 

reinforcement development at any section along the 

component length shall be considered. Interaction with 

other elements, including nonstructural elements and 

components, shall be included.

C6.5.3.5 Rehabilitation Measures

The rehabilitation measures described in C6.5.2.5 for 

reinforced concrete beam-column moment frames 

may also be effective in rehabilitating post-tensioned 

concrete beam-column moment frames.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-31

The analytical model that represents the slab-column 

frame, using either line elements with properties 

concentrated at component centerlines or a combination 

of line elements (to represent columns) and platebending elements (to represent the slab), based on any 

of the following approaches, shall be permitted.

1. An effective beam width model, in which the 

columns and slabs are represented by line elements 

that are rigidly interconnected at the slab-column 

joint.

2. An equivalent frame model in which the columns 

and slabs are represented by line elements that are 

interconnected by connection springs.

3. A finite element model in which the columns are 

represented by line elements and the slab is 

represented by plate-bending elements.

In any model, the effects of changes in cross section, 

including slab openings, shall be considered.

The connection between the columns and foundation 

shall be modeled based on the details of the columnfoundation connection and rigidity of the foundationsoil system.

Action of the slab as a diaphragm interconnecting 

vertical elements shall be represented.

In the design model, inelastic deformations in primary 

components shall be restricted to flexure in slabs and 

columns, plus nonlinear response in slab-column 

connections. Other inelastic deformations shall be 

permitted as part of the design in secondary 

components. Acceptance criteria shall be as specified in 

Section 6.5.4.4.

6.5.4.2 Stiffness

6.5.4.2.1 Linear Static and Dynamic Procedures

Slabs shall be modeled considering flexural, shear, and 

torsional (in the slab adjacent to the column) stiffnesses. 

Columns shall be modeled considering flexural, shear, 

and axial stiffnesses. Joints shall be modeled as either 

stiff or rigid components. The effective stiffnesses of 

components shall be determined according to the 

general principles of Section 6.4.1.2, but adjustments 

on the basis of experimental evidence shall be 

permitted.

6.5.4.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations shall comply with 

the requirements of Section 6.4.1.2.

Slabs and columns shall be modeled using concentrated 

plastic hinge models, distributed plastic hinge models, 

or other models whose behavior has been demonstrated 

to adequately represent behavior of reinforced concrete 

slab and column components subjected to lateral 

loading. The model shall be capable of representing 

inelastic response along the component length, except 

where it is shown by equilibrium that yielding is 

restricted to the component ends. Slab- column 

connections shall be modeled separately from the slab 

and column components in order to identify potential 

failure in shear and moment transfer; alternatively, the 

potential for connection failure shall be otherwise 

checked as part of the analysis. Where nonlinear 

response is expected in a mode other than flexure, the 

model shall be established to represent these effects.

Monotonic load-deformation relations shall be 

according to the generalized relation shown in Figure 

6-1, with definitions according to Section 6.5.2.2.2. The 

overall load-deformation relation shall be established so 

that the maximum resistance is consistent with the 

design strength specifications of Sections 6.4.2 and 

6.5.4.3. Where the generalized deformation shown in 

Figure 6-1 is taken as the flexural plastic hinge rotation 

for the column, the plastic hinge rotation capacities 

shall be as defined by Table 6-8. Where the generalized 

deformation shown in Figure 6-1 is taken as the rotation 

of the slab-column connection, the plastic rotation 

capacities shall be as defined by Table 6-14.

6.5.4.2.3 Nonlinear Dynamic Procedure

The requirements of Sections 6.4.2 6.5.2.2.3 for 

reinforced concrete beam-column moment frames shall 

apply to slab-column moment frames.

6.5.4.3 Strength

Component strengths shall be computed according to 

the general requirements of Sections 6.4.2, as modified 

in this section.
6-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

The maximum component strength shall be determined 

considering potential failure in flexure, axial load, 

shear, torsion, development, and other actions at all 

points along the length of the component under the 

actions of design gravity and earthquake load 

combinations. The strength of slab-column connections 

also shall be determined and incorporated in the 

analytical model.

The flexural strength of a slab to resist moment due to 

lateral deformations shall be calculated as MnCS –

MgCS, where MnCS is the design flexural strength of the 

column strip and MgCS is the column strip moment due 

to gravity loads. MgCS shall be calculated according to 

the procedures of ACI 318 for the design gravity load 

specified in Chapter 3. 

For columns, the evaluation of shear strength according 

to Section 6.5.2.3 shall be permitted.

Shear and moment transfer strength of the slab-column 

connection shall be calculated considering the 

combined action of flexure, shear, and torsion acting in 

the slab at the connection with the column. The 

procedures described below shall be permitted to satisfy 

this requirement. 

For interior connections without transverse beams, and 

for exterior connections with moment about an axis 

perpendicular to the slab edge, the shear and moment 

transfer strength calculated as the minimum of the 

following strengths shall be permitted: 

1. The strength calculated considering eccentricity of 

shear on a slab critical section due to combined 

shear and moment, as prescribed in ACI 318. 

2. The moment transfer strength equal to ΣMn/γf

, 

where ΣMn = the sum of positive and negative 

flexural strengths of a section of slab between lines 

that are two and one-half slab or drop panel 

thicknesses (2.5h) outside opposite faces of the 

column or capital; γf

 = the fraction of the moment 

resisted by flexure per ACI 318; and h = slab 

thickness.

For moment about an axis parallel to the slab edge at 

exterior connections without transverse beams, where 

the shear on the slab critical section due to gravity loads 

does not exceed 0.75Vc, or the shear at a corner support 

does not exceed 0.5 Vc, the moment transfer strength 

shall be permitted to be taken as equal to the flexural 

strength of a section of slab between lines that are a 

distance, c1, outside opposite faces of the column or 

capital. Vc is the direct punching shear strength defined 

by ACI 318.

6.5.4.4 Acceptance Criteria

6.5.4.4.1 Linear Static and Dynamic Procedures

All component actions shall be classified as being either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. In primary components, deformationcontrolled actions shall be restricted to flexure in slabs 

and columns, and shear and moment transfer in slabcolumn connections. In secondary components, 

deformation-controlled actions shall also be permitted 

in shear and reinforcement development, as identified 

in Table 6-15. All other actions shall be defined as 

being force-controlled actions.

Design actions on components shall be determined as 

prescribed in Chapter 3. Where the calculated DCR 

values exceed unity, the following design actions shall 

be determined using limit analysis principles as 

prescribed in Chapter 3: (1) moments, shears, torsions, 

and development and splice actions corresponding to 

development of component strength in slabs and 

columns; and (2) axial load in columns, considering 

likely plastic action in components above the level in 

question.

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2.2, Tables 6-12 and 

6-15. Those components that satisfy Equations (3-20) 

and (3-21) shall satisfy the performance criteria. 

Components that reach their design strengths shall be 

further evaluated according to this section to determine 

performance acceptability.

Where the average of the DCRs of columns at a level 

exceeds the average value of slabs at the same level, 

and exceeds the greater of 1.0 and m/2, the element 

shall be defined as a weak story element and shall be 

evaluated by the procedure for weak story elements 

described in Section 6.5.2.4.1.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-33

6.5.4.4.2 Nonlinear Static and Dynamic Procedures

In the design model, inelastic response shall be 

restricted to those components and actions listed in 

Tables 6-8 and 6-14, except where it is demonstrated by 

experimental evidence and analysis that other inelastic 

action is acceptable for the selected performance levels.

Calculated component actions shall satisfy the 

requirements of Chapter 3. Maximum permissible 

inelastic deformations shall be as listed in Tables 6-8 

and 6-14. Where inelastic action is indicated for a 

component or action not listed in these tables, the 

performance shall be deemed unacceptable. Alternative 

approaches or values shall be permitted where justified 

by experimental evidence and analysis.

6.5.4.5 Rehabilitation Measures

Reinforced concrete slab-column, beam-column 

moment frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard. 

C6.5.4.5 Rehabilitation Measures

The rehabilitation measures described in C6.5.2.5 for 

reinforced concrete beam-column moment frames 

may also be effective in rehabilitating reinforced 

concrete slab-column moment frames.

Table 6-14 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Two-way Slabs and Slab-Column Connections

Conditions

Modeling Parameters4 Acceptance Criteria4

Plastic Rotation 

Angle, radians

Residual 

Strength 

Ratio

Plastic Rotation Angle, radians

Performance Level

IO

Component Type

Primary Secondary

a b c LS CP LS CP

i. Slabs controlled by flexure, and slab-column connections1

2

Continuity 

Reinforcement3

≤ 0.2 Yes 0.02 0.05 0.2 0.01 0.015 0.02 0.03 0.05

≥ 0.4 Yes 0.0 0.04 0.2 0.0 0.0 0.0 0.03 0.04

≤ 0.2 No 0.02 0.02 – 0.01 0.015 0.02 0.015 0.02

≥ 0.4 No 0.0 0.0 – 0.0 0.0 0.0 0.0 0.0

ii. Slabs controlled by inadequate development or splicing along the span1

0.0 0.02 0.0 0.0 0.0 0.0 0.01 0.02

iii. Slabs controlled by inadequate embedment into slab-column joint1

0.015 0.03 0.2 0.01 0.01 0.015 0.02 0.03

1. When more than one of the conditions i, ii, and iii occurs for a given component, use the minimum appropriate numerical value from the table.

2. Vg = the gravity shear acting on the slab critical section as defined by ACI 318; Vo = the direct punching shear strength as defined by ACI 318.

3. Under the heading “Continuity Reinforcement,” use “Yes” where at least one of the main bottom bars in each direction is effectively continuous through 

the column cage. Where the slab is post-tensioned, use “Yes” where at least one of the post-tensioning tendons in each direction passes through the 

column cage. Otherwise, use “No.”

4. Linear interpolation between values shown in the table shall be permitted.

Vg

Vo

-----
6-34 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.6 Precast Concrete Frames

6.6.1 Types of Precast Concrete Frames 

Precast concrete frames shall be defined as those 

elements that are constructed from individually made 

beams and columns that are assembled to create 

gravity-load-carrying systems. These systems shall 

include those that are considered in design to resist 

design lateral loads, and those that are considered in 

design as secondary elements that do not resist design 

lateral loads but must resist the effects of deformations 

resulting from design lateral loads.

The provisions of this section shall apply to precast 

concrete frames that emulate cast-in-place moment 

frames defined in Section 6.6.1.1, precast concrete 

beam-column moment frames constructed with dry 

joints defined in Section 6.6.1.2, and precast concrete 

frames not expected to directly resist lateral loads 

defined in Section 6.6.1.3.

Table 6-15 Numerical Acceptance Criteria for Linear Procedures—

Two-way Slabs and Slab-Column Connections

Conditions

m-factors

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Slabs controlled by flexure, and slab-column connections1

2 Continuity Reinforcement3

≤ 0.2 Yes 2 2 3 3 4

≥ 0.4 Yes 1 1 1 2 3

≤ 0.2 No 2 2 3 2 3

≥ 0.4 No 1 1 1 1 1

ii. Slabs controlled by inadequate development or splicing along the span1

––– 3 4

iii. Slabs controlled by inadequate embedment into slab-column joint1

22334

1. When more than one of the conditions i, ii, and iii occurs for a given component, use the minimum appropriate numerical value from the table.

2. Vg = the gravity shear acting on the slab critical section as defined by ACI 318; Vo = the direct punching shear strength as defined by ACI 318.

3. Under the heading “Continuity Reinforcement,” use “Yes” where at least one of the main bottom bars in each direction is effectively continuous through 

the column cage. Where the slab is post-tensioned, use “Yes” where at least one of the post-tensioning tendons in each direction passes through the column 

cage. Otherwise, use “No.”

Vg

Vo

-----
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-35

6.6.1.1 Precast Concrete Frames that 

Emulate Cast-in-Place Moment 

Frames

Precast concrete frames that emulate cast-in-place 

moment frames shall be defined as those precast beamcolumn systems that are interconnected using 

reinforcement and wet concrete to create a system that 

resists lateral loads in a manner similar to cast-in-place 

concrete systems.

6.6.1.2 Precast Concrete Moment Frames 

Constructed with Dry Joints

Frames of this classification shall be assembled using 

dry joints (connections are made by bolting, welding, 

post-tensioning, or other similar means) in a way that 

results in significant lateral force resistance in the 

framing element. Frames of this classification resist 

lateral loads either acting alone, or acting in conjunction 

with shear walls, braced frames, or other lateral load 

resisting elements in a dual system.

6.6.1.3 Precast Concrete Frames Not 

Expected to Resist Lateral Load 

Directly

Frames of this classification shall be assembled using 

dry joints in a way that does not result in significant 

lateral force resistance in the framing element. Shear 

walls, braced frames, or moment frames provide the 

entire lateral load resistance, with the precast concrete 

frame system deforming in a manner that is compatible 

with the structure as a whole.

6.6.2 Precast Concrete Frames that Emulate 

Cast-in-Place Moment Frames

6.6.2.1 General Considerations

The analytical model for a frame element of this 

classification shall represent strength, stiffness, and 

deformation capacity of beams, columns, beam-column 

joints, and other components of the frame. Potential 

failure in flexure, shear, and reinforcement development 

at any section along the component length shall be 

considered. Interaction with other elements, including 

nonstructural elements and components, shall be 

included. All other considerations of Section 6.5.2.1 

shall be taken into account. In addition, the effects of 

shortening due to creep, and other effects of 

prestressing and post-tensioning on member behavior, 

shall be evaluated.

6.6.2.2 Stiffness

Stiffness for analysis shall be as defined in 

Section 6.5.2.2. The effects of prestressing shall be 

considered when computing the effective stiffness 

values using Table 6-5.

6.6.2.3 Strength

Component strength shall be computed according to the 

requirements of Section 6.5.2.3, with the additional 

requirement that the following effects be included in the 

analysis: 

1. Effects of prestressing that are present, including, 

but not limited to, reduction in rotation capacity, 

secondary stresses induced, and amount of effective 

prestress force remaining;

2. Effects of construction sequence, including the 

possibility of construction of the moment 

connections occurring after portions of the structure 

are subjected to dead loads;

3. Effects of restraint due to interaction with 

interconnected wall or brace components.

6.6.2.4 Acceptance Criteria

Acceptance criteria for precast concrete frames that 

emulate cast-in-place moment frames shall be as 

specified in Section 6.5.2.4, except that the factors 

defined in Section 6.5.2.3 shall also be considered.

C6.6.1.1 Precast Concrete Frames that 

Emulate Cast-in-Place Moment 

Frames

These systems are recognized and accepted by 

FEMA 222A, and are based on ACI 318, which 

requires safety and serviceability levels expected from 

monolithic construction. There is insufficient research 

and testing data at this time to qualify systems 

assembled using dry joints as emulated moment 

frames.

C6.6.1.2 Precast Concrete Moment Frames 

Constructed with Dry Joints

The appendix to Chapter 6 of FEMA 222A contains a 

trial version of code provisions for new construction of 

this classification.
6-36 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.6.2.5 Rehabilitation Measures

Precast concrete frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard.

6.6.3 Precast Concrete Moment Frames 

Constructed with Dry Joints

6.6.3.1 General Considerations

The analysis model for precast concrete moment frames 

constructed with dry joints shall be as specified in 

Section 6.5.2.1 for reinforced concrete beam-column 

moment frames, with additional consideration of the 

special nature of the dry joints used in assembling the 

precast system. Where connections yield under design 

lateral loads, the analysis model shall take this into 

account.

6.6.3.2 Stiffness

Stiffness for analysis shall be as defined in 

Section 6.6.2.2. Flexibilities associated with 

connections shall be included in the analytical model.

6.6.3.3 Strength

Component strength shall be computed according to the 

requirements of Section 6.6.2.3, with the additional 

requirement that connection strength shall comply with 

the requirements of Section 6.4.6.

6.6.3.4 Acceptance Criteria

Acceptance criteria for precast concrete moment frames 

constructed with dry joints shall be as specified in 

Section 6.6.2.4, with the additional requirement that the 

connections comply with the requirements of 

Section 6.4.6.

6.6.3.5 Rehabilitation Measures

Precast concrete moment frame components that do not 

meet the acceptance criteria for the selected 

Rehabilitation Objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 6.4.7 and other provisions of this standard. 

C6.6.2.5 Rehabilitation Measures

The rehabilitation measures described in C6.5.2.5 for 

reinforced concrete beam-column moment frames 

may also be effective in rehabilitating precast 

concrete frames that emulate cast-in-place moment 

frames. When installing new elements, components, 

or materials to the existing system, existing 

prestressing strands should be protected.

C6.6.3.1 General Considerations

The requirements given in the appendix to Chapter 6 of 

FEMA 222A for this type of structural system should 

be adhered to where possible, and the philosophy and 

approach should be employed when designing new 

connections for existing components.

C6.6.3.3 Strength

In addition to complying with the provisions of 

Section 6.6.3.3, the connections should comply with 

the requirements given in the appendix to Chapter 6 of 

FEMA 222A.

C6.6.3.4 Acceptance Criteria

In addition to complying with the provisions of 

Section 6.6.3.4, the acceptance criteria should comply 

with the requirements given in Section 6A.4 of the 

appendix to Chapter 6 of FEMA 222A.

C6.6.3.5 Rehabilitation Measures

The rehabilitation measures described in C6.5.2.5 for 

reinforced concrete beam-column moment frames 

may also be effective in rehabilitating precast 

concrete frames constructed with dry joints. When 

installing new elements, components, or materials to 

the existing system, existing prestressing strands 

should be protected.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-37

6.6.4 Precast Concrete Frames Not 

Expected to Resist Lateral Loads 

Directly

6.6.4.1 General Considerations

The analytical model for precast concrete frames that 

are not expected to resist lateral loads directly shall 

comply with the requirements of Section 6.6.3.1 and 

shall include the effects of deformations that are 

calculated to occur under the design earthquake 

loadings.

6.6.4.2 Stiffness

The analytical model shall either include realistic lateral 

stiffness of these frames to evaluate the effects of 

deformations under lateral loads or, if the lateral 

stiffness is ignored in the analytical model, the effects 

of calculated building drift on these frames shall be 

evaluated separately. The analytical model shall 

consider the negative effects of connection stiffness on 

component response where that stiffness results in 

actions that may cause component failure.

6.6.4.3 Strength

Component strength shall be computed according to the 

requirements of Section 6.6.3.3. All components shall 

have sufficient strength and ductility to transmit 

induced forces from one member to another and to the 

designated lateral-force-resisting system.

6.6.4.4 Acceptance Criteria

Acceptance criteria for components in precast concrete 

frames not expected to directly resist lateral loads shall 

be as specified in Section 6.6.3.4. All moments, shear 

forces, and axial loads induced through the deformation 

of the structural system shall be checked for 

acceptability by appropriate criteria in the referenced 

section.

6.6.4.5 Rehabilitation Measures

Precast concrete frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard. 

6.7 Concrete Frames with Infills

6.7.1 Types of Concrete Frames with Infills

Concrete frames with infills are elements with complete 

gravity-load-carrying concrete frames infilled with 

masonry or concrete, constructed in such a way that the 

infill and the concrete frame interact when subjected to 

vertical and lateral loads. 

Isolated infills are infills isolated from the surrounding 

frame complying with the minimum gap requirements 

specified in Section 7.5.1. If all infills in a frame are 

isolated infills, the frame shall be analyzed as an 

isolated frame according to provisions given elsewhere 

in this chapter, and the isolated infill panels shall be 

analyzed according to the requirements of Chapter 7.

The provisions of Section 6.7 shall apply to concrete 

frames with existing infills, frames that are rehabilitated 

by addition or removal of material, and concrete frames 

that are rehabilitated by the addition of new infills.

C6.6.4.2 Stiffness

The stiffness used in the analysis should consider 

possible resistance that may develop under lateral 

deformation. In some cases it may be appropriate to 

assume zero lateral stiffness. However, the Northridge 

earthquake graphically demonstrated that there are few 

instances where the precast column can be considered 

to be completely pinned top and bottom, and as a 

consequence, not resist any shear from building drift. 

Several parking structures collapsed as a result of this 

defect. Conservative assumptions should be made.

C6.6.4.5 Rehabilitation Measures

The rehabilitation measures described in C6.5.2.5 for 

reinforced concrete beam-column moment frames 

may also be effective in rehabilitating precast 

concrete frames not expected to resist lateral loads 

directly. When installing new elements, components, 

or materials to the existing system, existing 

prestressing strands should be protected.
6-38 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.7.1.1 Types of Frames

The provisions of Section 6.7 shall apply to concrete 

frames as defined in Sections 6.5, 6.6, and 6.10, where 

those frames interact with infills.

6.7.1.2 Masonry Infills

The provisions of Section 6.7 shall apply to masonry 

infills as defined in Chapter 7, where those infills 

interact with concrete frames.

6.7.1.3 Concrete Infills

The provisions of Section 6.7 shall apply to concrete 

infills that interact with concrete frames, where the 

infills were constructed to fill the space within the bay 

of a complete gravity frame without special provision 

for continuity from story to story. The concrete of the 

infill shall be evaluated separately from the concrete of 

the frame.

6.7.2 Concrete Frames with Masonry Infills

6.7.2.1 General Considerations

The analytical model for a concrete frame with masonry 

infills shall represent strength, stiffness, and 

deformation capacity of beams, slabs, columns, beamcolumn joints, masonry infills, and all connections and 

components of the element. Potential failure in flexure, 

shear, anchorage, reinforcement development, or 

crushing at any section shall be considered. Interaction 

with other nonstructural elements and components shall 

be included.

For a concrete frame with masonry infill resisting 

lateral forces within its plane, modeling of the response 

using a linear elastic model shall be permitted provided 

that the infill will not crack when subjected to design 

lateral forces. If the infill will not crack when subjected 

to design lateral forces, modeling the assemblage of 

frame and infill as a homogeneous medium shall be 

permitted.

For a concrete frame with masonry infills that will crack 

when subjected to design lateral forces, modeling of the 

response using a diagonally braced frame model, in 

which the columns act as vertical chords, the beams act 

as horizontal ties, and the infill acts as an equivalent 

compression strut, shall be permitted. Requirements for 

the equivalent compression strut analogy shall be as 

specified in Chapter 7.

Frame components shall be evaluated for forces 

imparted to them through interaction of the frame with 

the infill, as specified in Chapter 7. In frames with fullheight masonry infills, the evaluation shall include the 

effect of strut compression forces applied to the column 

and beam, eccentric from the beam-column joint. In 

frames with partial-height masonry infills, the 

evaluation shall include the reduced effective length of 

the columns above the infilled portion of the bay.

6.7.2.2 Stiffness

6.7.2.2.1 Linear Static and Dynamic Procedures

In frames having infills in some bays and no infill in 

other bays, the restraint of the infill shall be represented 

as described in Section 6.7.2.1, and the noninfilled bays 

shall be modeled as frames as specified in appropriate 

portions of Sections 6.5, 6.6, and 6.10. Where infills 

create a discontinuous wall, the effects of the 

discontinuity on overall building performance shall be 

evaluated. Effective stiffnesses shall be in accordance 

with Section 6.4.1.2.

6.7.2.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Static Procedure (NSP) shall follow the 

requirements of Section 6.4.1.2.2.

C6.7.1.3 Concrete Infills

The construction of concrete-infilled frames is very 

similar to that of masonry-infilled frames, except that 

the infill is of concrete instead of masonry units. In 

older existing buildings, the concrete infill commonly 

contains nominal reinforcement, which is unlikely to 

extend into the surrounding frame. The concrete is 

likely to be of lower quality than that used in the frame, 

and should be investigated separately from 

investigations of the frame concrete.

C6.7.2.1 General Considerations

The design professional is referred to FEMA 274 and 

FEMA 306 for additional information regarding the 

behavior of masonry infills.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-39

Modeling beams and columns using nonlinear truss 

elements shall be permitted in infilled portions of the 

frame. Beams and columns in noninfilled portions of 

the frame shall be modeled using the relevant 

specifications of Sections 6.5, 6.6, and 6.10. The model 

shall be capable of representing inelastic response along 

the component lengths.

Monotonic load-deformation relations shall be 

according to the generalized relation shown in Figure 

6-1, except different relations shall be permitted where 

verified by tests. Numerical quantities in Figure 6-1 

shall be derived from tests or by analyses procedures as 

specified in Chapter 2, and shall take into account the 

interactions between frame and infill components. 

Alternatively, the following procedure shall be 

permitted for monolithic reinforced concrete frames.

1. For beams and columns in noninfilled portions of 

frames, where the generalized deformation is taken 

as rotation in the flexural plastic hinge zone, the 

plastic hinge rotation capacities shall be as defined 

by Table 6-18. 

2. For masonry infills, the generalized deformations 

and control points shall be as defined in Chapter 7. 

3. For beams and columns in infilled portions of 

frames, where the generalized deformation is taken 

as elongation or compression displacement of the 

beams or columns, the tension and compression 

strain capacities shall be as specified in Table 6-16.

6.7.2.2.3 Nonlinear Dynamic Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Dynamic Procedure (NDP) shall model 

the complete hysteretic behavior of each component 

using properties verified by tests. Unloading and 

reloading properties shall represent stiffness and 

strength degradation characteristics.

6.7.2.3 Strength

Strengths of reinforced concrete components shall be 

calculated according to the general requirements of 

Sections 6.4.2, as modified by other specifications of 

this chapter. Strengths of masonry infills shall be 

calculated according to the requirements of Chapter 7. 

Strength calculations shall consider:

1. Limitations imposed by beams, columns, and joints 

in nonfilled portions of frames.

2. Tensile and compressive capacity of columns acting 

as boundary elements of infilled frames.

3. Local forces applied from the infill to the frame.

4. Strength of the infill.

5. Connections with adjacent elements. 

6.7.2.4 Acceptance Criteria

6.7.2.4.1 Linear Static and Dynamic Procedures

All component actions shall be classified as either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. In primary components, deformationcontrolled actions shall be restricted to flexure and axial 

actions in beams, slabs, and columns, and lateral 

deformations in masonry infill panels. In secondary 

components, deformation-controlled actions shall be 

restricted to those actions identified for the isolated 

frame in Sections 6.5, 6.6, and 6.10, as appropriate, and 

for the masonry infill in Section 7.5.

Design actions shall be determined as prescribed in 

Chapter 3. Where calculated DCR values exceed unity, 

the following design actions shall be determined using 

limit analysis principles as prescribed in Chapter 3: 

(1) moments, shears, torsions, and development and 

splice actions corresponding to development of 

component strength in beams, columns, or masonry 

infills; and (2) column axial load corresponding to 

development of the flexural capacity of the infilled 

frame acting as a cantilever wall.

Design actions shall be compared with design strengths 

in accordance with Section 3.4.2.2.

Values of m-factors shall be as specified in 

Section 7.5.2.3 for masonry infills; applicable portions 

of Sections 6.5, 6.6, and 6.10 for concrete frames; and 

Table 6-17 for columns modeled as tension and 

compression chords. Those components that have 

design actions less than design strengths shall be 

assumed to satisfy the performance criteria for those 

components. 

6.7.2.4.2 Nonlinear Static and Dynamic Procedures

In the design model, inelastic response shall be 

restricted to those components and actions that are 

permitted for isolated frames as specified in 

Sections 6.5, 6.6, and 6.10, as well as for masonry 

infills as specified in Section 7.5.
6-40 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Calculated component actions shall satisfy the 

requirements of Section 3.4.3.2, and shall not exceed 

the numerical values listed in Table 6-16, the relevant 

tables for isolated frames given in Sections 6.5, 6.6, and 

6.10, and the relevant tables for masonry infills given in 

Chapter 7. Component actions not listed in Tables 6-7 

through 6-9 shall be treated as force-controlled. 

Alternative approaches or values shall be permitted 

where justified by experimental evidence and analysis.

6.7.2.5 Rehabilitation Measures

Concrete frames with masonry infill that do not meet 

the acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard.

Table 6-16 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Reinforced Concrete Infilled Frames

Conditions

Modeling Parameters4 Acceptance Criteria

Total Strain

Residual 

Strength 

Ratio

Total Strain

Performance Level

IO

Component Type

Primary Secondary

d e c LS CP LS CP

i. Columns modeled as compression chords3

Columns confined along entire 

length2

0.02 0.04 0.4 0.003 0.015 0.020 0.03 0.04

All other cases 0.003 0.01 0.2 0.002 0.002 0.003 0.01 0.01

ii. Columns modeled as tension chords3

Columns with well-confined 

splices, or no splices

0.05 0.05 0.0 0.01 0.03 0.04 0.04 0.05

All other cases See 

note 1

0.03 0.2 See note 1 0.02 0.03

1. Potential for splice failure shall be evaluated directly to determine the modeling and acceptability criteria. For these cases, refer to the generalized 

procedure of Sections 6.4.2. For primary actions, Collapse Prevention Performance Level shall be defined as the deformation at which strength 

degradation begins. Life Safety Performance Level shall be taken as three-quarters of that value.

2 A column shall be permitted to be considered to be confined along its entire length when the quantity of hoops along the entire story height including the 

joint is equal to three-quarters of that required by ACI 318 for boundary elements of concrete shear walls. The maximum longitudinal spacing of sets of 

hoops shall not exceed either h/3 or 8db. 

3. If load reversals will result in both conditions i and ii applying to a single column, both conditions shall be checked.

4. Interpolation shall not be permitted.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-41

6.7.3 Concrete Frames with Concrete Infills

6.7.3.1 General Considerations

The analytical model for a concrete frame with concrete 

infills shall represent the strength, stiffness, and 

deformation capacity of beams, slabs, columns, beamcolumn joints, concrete infills, and all connections and 

components of the elements. Potential failure in flexure, 

shear, anchorage, reinforcement development, or 

crushing at any section shall be considered. Interaction 

Table 6-17 Numerical Acceptance Criteria for Linear Procedures—Reinforced Concrete Infilled Frames

Conditions

m-factors3

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Columns modeled as compression chords2

Columns confined along entire length1 13445

All other cases 1 1 1 1 1

ii. Columns modeled as tension chords2

Columns with well-confined splices, or no 

splices

34556

All other cases 1 2 2 3 4

1. A column may be considered to be confined along its entire length when the quantity of hoops along the entire story height including the joint is equal to 

three-quarters of that required by ACI 318 for boundary elements of concrete shear walls. The maximum longitudinal spacing of sets of hoops shall not 

exceed either h/3 or 8db. 

2. If load reversals will result in both conditions i and ii applying to a single column, both conditions shall be checked.

3. Interpolation shall not be permitted.

C6.7.2.5 Rehabilitation Measures

The rehabilitation measures described in relevant 

commentary of Sections 6.5, 6.6, and 6.10 for isolated 

frames, and rehabilitation measures described in 

relevant commentary or Section 7.5 for masonry 

infills, may also be effective in rehabilitating concrete 

frames with masonry infills. The design professional 

is referred to FEMA 308 for further information in this 

regard. In addition, the following rehabilitation 

measures may be effective in rehabilitating concrete 

frames with infills:

1. Post-tensioning existing beams, columns, or 

joints using external post-tensioned 

reinforcement. Vertical post-tensioning may be 

effective in increasing tensile capacity of columns 

acting as boundary zones. Anchorages should be 

located away from regions where inelastic action is 

anticipated, and should be designed considering 

possible force variations due to earthquake 

loading.

2. Modification of the element by selective 

material removal from the existing element.

Either the infill should be completely removed 

from the frame, or gaps should be provided 

between the frame and the infill. In the latter case, 

the gap requirements of Chapter 7 should be 

satisfied.

3. Changing the building system to reduce the 

demands on the existing element. Examples 

include the addition of supplementary lateralforce-resisting elements such as walls, steel braces, 

or buttresses; seismic isolation; and mass 

reduction.
6-42 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

with other nonstructural elements and components shall 

be included.

The analytical model shall be established considering 

the relative stiffness and strength of the frame and the 

infill, as well as the level of deformations and 

associated damage. For low deformation levels, and for 

cases where the frame is relatively flexible, the infilled 

frame shall be permitted to be modeled as a shear wall, 

with openings modeled where they occur. In other 

cases, the frame-infill system shall be permitted to be 

modeled using a braced-frame analogy such as that 

described for concrete frames with masonry infills in 

Section 6.7.2.

Frame components shall be evaluated for forces 

imparted to them through interaction of the frame with 

the infill as specified in Chapter 7. In frames with fullheight infills, the evaluation shall include the effect of 

strut compression forces applied to the column and 

beam eccentric from the beam-column joint. In frames 

with partial-height infills, the evaluation shall include 

the reduced effective length of the columns above the 

infilled portion of the bay.

In frames having infills in some bays and no infills in 

other bays, the restraint of the infill shall be represented 

as described in this section, and the noninfilled bays 

shall be modeled as frames as specified in appropriate 

portions of Sections 6.5, 6.6, and 6.10. Where infills 

create a discontinuous wall, the effects of the 

discontinuity on overall building performance shall be 

evaluated.

6.7.3.2 Stiffness

6.7.3.2.1 Linear Static and Dynamic Procedures

Effective stiffnesses shall be calculated according to the 

principles of Section 6.4.1.2 and the procedure of 

Section 6.7.2.2.1.

6.7.3.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Static Procedure (NSP) shall follow the 

requirements of Section 6.4.1.2.2.

Monotonic load-deformation relations shall be 

according to the generalized relation shown in Figure 

6-1, except different relations shall be permitted where 

verified by tests. Numerical quantities in Figure 6-1 

shall be derived from tests or by analysis procedures 

specified in Section 2.8, and shall take into account the 

interactions between frame and infill components. 

Alternatively, the procedure of Section 6.7.2.2.2 shall 

be permitted for the development of nonlinear modeling 

parameters for concrete frames with concrete infills.

6.7.3.2.3 Nonlinear Dynamic Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Dynamic Procedure (NDP) shall model 

the complete hysteretic behavior of each component 

using properties verified by tests. Unloading and 

reloading properties shall represent stiffness and 

strength degradation characteristics.

6.7.3.3 Strength

Strengths of reinforced concrete components shall be 

calculated according to the general requirements of 

Sections 6.4.2, as modified by other specifications of 

this chapter. Strength calculations shall consider:

1. Limitations imposed by beams, columns, and joints 

in unfilled portions of frames.

2. Tensile and compressive capacity of columns acting 

as boundary elements of infilled frames.

3. Local forces applied from the infill to the frame.

4. Strength of the infill.

5. Connections with adjacent elements.

Strengths of existing concrete infills shall be 

determined considering shear strength of the infill 

panel. For this calculation, procedures specified in 

Section 6.8.2.3 shall be used for calculation of the shear 

strength of a wall segment.

Where the frame and concrete infill are assumed to act 

as a monolithic wall, flexural strength shall be based on 

continuity of vertical reinforcement in both (1) the 

columns acting as boundary elements, and (2) the infill 

wall, including anchorage of the infill reinforcement in 

the boundary frame.

6.7.3.4 Acceptance Criteria

The acceptance criteria for concrete frames with 

concrete infills shall comply with relevant acceptance 

criteria of Sections 6.7.2.4, 6.8, and 6.9.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-43

6.7.3.5 Rehabilitation Measures

Concrete frames with concrete infills that do not meet 

the acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard. 

6.8 Concrete Shear Walls

6.8.1 Types of Concrete Shear Walls and 

Associated Components

The provisions of Section 6.8 shall apply to all shear 

walls in all types of structural systems that incorporate 

shear walls. This includes isolated shear walls, shear 

walls used in dual (wall-frame) systems, coupled shear 

walls, and discontinuous shear walls. Shear walls shall 

be permitted to be considered as solid walls if they have 

openings that do not significantly influence the strength 

or inelastic behavior of the wall. Perforated shear walls 

shall be defined as walls having a regular pattern of 

openings in both horizontal and vertical directions that 

creates a series of pier and deep beam elements referred 

to as wall segments.

Coupling beams, and columns that support 

discontinuous shear walls, shall comply with provisions 

of Section 6.8.2. These special frame components 

associated with shear walls shall be exempted from the 

provisions for beams and columns of frame elements 

covered in Section 6.5.

C6.7.3.5 Rehabilitation Measures

Rehabilitation measures described in C6.7.2.5 for 

concrete frames with masonry infills may also be 

effective in rehabilitating concrete frames with 

concrete infills. In addition, application of shotcrete to 

the face of an existing wall to increase the thickness 

and shear strength may be effective. For this purpose, 

the face of the existing wall should be roughened, a 

mat of reinforcing steel should be doweled into the 

existing structure, and shotcrete should be applied to 

the desired thickness. The design professional is 

referred to FEMA 308 for further information 

regarding rehabilitation of concrete frames with 

concrete infill.

C6.8.1 Types of Concrete Shear Walls and 

Associated Components

Concrete shear walls are planar vertical elements or 

combinations of interconnected planar elements that 

serve as lateral-load-resisting elements in concrete 

structures. Shear walls (or wall segments) shall be 

considered slender if their aspect ratio (height/length) 

is >3.0, and shall be considered short or squat if their 

aspect ration is <1.5. Slender shear walls are normally 

controlled by flexural behavior; short walls are 

normally controlled by shear behavior. The response of 

walls with intermediate aspect ratios is influenced by 

both flexure and shear. 

Identification of component types in concrete shear 

wall elements depends, to some degree, on the relative 

strengths of the wall segments. Vertical segments are 

often termed piers, while horizontal segments may be 

called coupling beams or spandrels. The design 

professional is referred to FEMA 306 for additional 

information regarding the behavior of concrete wall 

components. Selected information from FEMA 306 has 

been reproduced in the commentary of this standard, in 

Table C6-1 and Figure C6-1 to clarify wall component 

identification.
6-44 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Figure C6-1 Identification of Component Types in Concrete Shear Wall Elements (from FEMA 306)
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-45

6.8.1.1 Monolithic Reinforced Concrete 

Shear Walls and Wall Segments

Monolithic reinforced concrete shear walls shall consist 

of vertical cast-in-place elements, either uncoupled or 

coupled, in open or closed shapes. These walls shall 

have relatively continuous cross sections and 

reinforcement and shall provide both vertical and lateral 

force resistance, in contrast with infilled walls defined 

in Section 6.7.1.3.

Shear walls or wall segments with axial loads greater 

than 0.35 Po shall not be considered effective in 

resisting seismic forces. The maximum spacing of 

horizontal and vertical reinforcement shall not exceed 

18 inches. Walls with horizontal and vertical 

reinforcement ratios less than 0.0025, but with 

reinforcement spacings less than 18 inches, shall be 

permitted where the shear force demand does not 

exceed the reduced nominal shear strength of the wall 

calculated in accordance with Section 6.8.2.3.

Table C6-1 Reinforced Concrete Shear Wall Component Types (from FEMA 306)

Component Type

per FEMA 306 Description FEMA 356 Designation

RC1 Isolated Wall or 

Stronger Wall Pier

Stronger than beam or spandrel elements that may frame into it 

so that nonlinear behavior (and damage) is generally 

concentrated at the base, with a flexural plastic hinge, shear 

failure, etc. Includes isolated (cantilever) walls. If the 

component has a major setback or cutoff of reinforcement 

above the base, this section should be also checked for 

nonlinear behavior

Monolithic reinforced 

concrete wall or vertical wall 

segment

RC2 Weaker Wall Pier Weaker than the spandrels to which it connects; characterized 

by flexural hinging top and bottom, or shear failure, etc.

RC3 Weaker Spandrel or 

Coupling Beam

Weaker than the wall piers to which it connects; characterized 

by hinging at each end, shear failure, sliding shear failure, etc.

Horizontal wall segment or 

coupling beam

RC4 Stronger Spandrel Should not suffer damage because it is stronger than attached 

piers. If this component is damaged, it should probably be reclassified as RC3.

RC5 Pier-Spandrel Panel 

Zone

Typically not a critical area in RC walls Wall segment

C6.8.1.1 Monolithic Reinforced Concrete 

Shear Walls and Wall Segments

The wall reinforcement is normally continuous in both 

the horizontal and vertical directions, and bars are 

typically lap-spliced for tension continuity. The 

reinforcement mesh may also contain horizontal ties 

around vertical bars that are concentrated either near 

the vertical edges of a wall with constant thickness, or 

in boundary members formed at the wall edges. The 

amount and spacing of these ties is important for 

determining how well the concrete at the wall edge is 

confined, and thus for determining the lateral 

deformation capacity of the wall.
6-46 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.8.1.2 Reinforced Concrete Columns 

Supporting Discontinuous Shear 

Walls

Reinforced concrete columns supporting discontinuous 

shear walls shall be evaluated and rehabilitated to 

comply with the requirements of Section 6.8.2.

6.8.1.3 Reinforced Concrete Coupling Beams

Reinforced concrete coupling beams used to link two 

shear walls together shall be evaluated and rehabilitated 

to comply with the requirements of Section 6.8.2.

6.8.2 Reinforced Concrete Shear Walls, 

Wall Segments, Coupling Beams, and 

RC Columns Supporting 

Discontinuous Shear Walls

6.8.2.1 General Considerations

The analytical model for a shear wall element shall 

represent the stiffness, strength, and deformation 

capacity of the shear wall. Potential failure in flexure, 

shear, and reinforcement development at any point in 

the shear wall shall be considered. Interaction with 

other structural and nonstructural elements shall be 

included.

In general, slender reinforced concrete shear walls will 

be governed by flexure and will tend to form a plastic 

flexural hinge near the base of the wall under severe 

lateral loading. The ductility of the wall will be a 

function of the percentage of longitudinal 

reinforcement concentrated near the boundaries of the 

wall, the level of axial load, the amount of lateral shear 

required to cause flexural yielding, and the thickness 

and reinforcement used in the web portion of the shear 

wall. In general, higher axial load stresses and higher 

shear stresses will reduce the flexural ductility and 

energy absorbing capability of the shear wall. Short or 

squat shear walls will normally be governed by shear. 

These walls will normally have a limited ability to 

deform beyond the elastic range and continue to carry 

lateral loads. Thus, these walls are typically designed 

either as displacement-controlled components with low 

ductility capacities or as force-controlled components.

C6.8.1.2 Reinforced Concrete Columns 

Supporting Discontinuous Shear 

Walls

In shear wall buildings it is not uncommon to find that 

some walls are terminated either to create commercial 

space in the first story or to create parking spaces in the 

basement. In such cases, the walls are commonly 

supported by columns. Such designs are not 

recommended in seismic zones because very large 

demands may be placed on these columns during 

earthquake loading. In older buildings such columns 

will often have “standard” longitudinal and transverse 

reinforcement; the behavior of such columns during 

past earthquakes indicates that tightly spaced closed 

ties with well-anchored 135-degree hooks will be 

required for the building to survive severe earthquake 

loading.

C6.8.1.3 Reinforced Concrete Coupling 

Beams

The coupled walls are generally much stiffer and 

stronger than they would be if they acted 

independently. Coupling beams typically have a small 

span-to-depth ratio, and their inelastic behavior is 

normally affected by the high shear forces acting in 

these components. Coupling beams in most older 

reinforced concrete buildings will commonly have 

“conventional” reinforcement that consists of 

longitudinal flexural steel and transverse steel for 

shear. In some, more modern buildings, or in buildings 

where coupled shear walls are used for seismic 

rehabilitation, the coupling beams may use diagonal 

reinforcement as the primary reinforcement for both 

flexure and shear. The inelastic behavior of coupling 

beams that use diagonal reinforcement has been shown 

experimentally to be much better with respect to 

retention of strength, stiffness, and energy dissipation 

capacity than the observed behavior of coupling beams 

with conventional reinforcement.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-47

Slender shear walls and wall segments shall be 

permitted to be modeled as equivalent beam-column 

elements that include both flexural and shear 

deformations. The flexural strength of beam-column 

elements shall include the interaction of axial load and 

bending. The rigid-connection zone at beam 

connections to this equivalent beam-column element 

shall represent the distance from the wall centroid to the 

edge of the wall. Unsymmetrical wall sections shall 

model the different bending capacities for the two 

loading directions.

A beam element that incorporates both bending and 

shear deformations shall be used to model coupling 

beams. The element inelastic response shall account for 

the loss of shear strength and stiffness during reversed 

cyclic loading to large deformations. For coupling 

beams that have diagonal reinforcement satisfying ACI 

318, a beam element representing flexure only shall be 

permitted.

For columns supporting discontinuous shear walls, the 

model shall account for axial compression, axial 

tension, flexure, and shear response including rapid loss 

of resistance where this behavior is likely under design 

loadings. The diaphragm action of concrete slabs that 

interconnect shear walls and frame columns shall be 

represented in the model.

6.8.2.2 Stiffness

The effective stiffness of all the elements discussed in 

Section 6.8 shall be defined based on the material 

properties, component dimensions, reinforcement 

quantities, boundary conditions, and current state of the 

member with respect to cracking and stress levels. 

Alternatively, use of values for effective stiffness given 

in Table 6-5 shall be permitted. To obtain a proper 

distribution of lateral forces in bearing wall buildings, 

all of the walls shall be assumed to be either cracked or 

uncracked. In buildings where lateral load resistance is 

provided by either structural walls only, or a 

combination of walls and frame members, all shear 

walls and wall segments discussed in this section shall 

be considered to be cracked.

For coupling beams, the effective stiffness values given 

in Table 6-5 for nonprestressed beams shall be used 

unless alternative stiffnesses are determined by more 

detailed analysis. The effective stiffness of columns 

supporting discontinuous shear walls shall change 

between the values given for columns in tension and 

compression, depending on the direction of the lateral 

load being resisted by the shear wall.

6.8.2.2.1 Linear Static and Dynamic Procedures

Shear walls and associated components shall be 

modeled considering axial, flexural, and shear stiffness. 

For closed and open wall shapes, such as box, T, L, I, 

and C sections, the effective tension or compression 

flange widths shall be as specified in Section 6.4.1.3. 

The calculated stiffnesses to be used in analysis shall be 

in accordance with the requirements of Section 6.4.1.2.

Joints between shear walls and frame elements shall be 

modeled as stiff components or rigid components, as 

appropriate.

6.8.2.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations for use in analysis 

by nonlinear static and dynamic procedures shall 

comply with the requirements of Section 6.4.1.2.

Monotonic load-deformation relationships for 

analytical models that represent shear walls, wall 

elements, coupling beams, and columns that support 

discontinuous shear walls shall be in accordance with 

the generalized relation shown in Figure 6-1.

C6.8.2.1 General Considerations

For rectangular shear walls and wall segments with 

, and flanged wall sections with 

, either a modified beam-column analogy 

or a multiple-node, multiple-spring approach should be 

used. Because shear walls usually respond in single 

curvature over a story height, the use of one multiplespring element per story should be permitted for 

modeling shear walls. Wall segments should be 

modeled with either the beam-column element or with 

a multiple-spring model with two elements over the 

length of the wall segment.

Coupling beams that have diagonal reinforcement 

satisfying FEMA 222A will commonly have a stable 

hysteretic response under large load reversals. 

Therefore, these members could adequately be 

modeled with beam elements used for typical frame 

analyses.

hw l

w ⁄ ≤ 2.5

hw l

w ⁄ ≤ 3.5
6-48 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

For shear walls and wall segments having inelastic 

behavior under lateral loading that is governed by 

flexure, as well as columns supporting discontinuous 

shear walls, the following approach shall be permitted. 

The load-deformation relationship in Figure 6-1 shall be 

used with the x-axis of Figure 6-1 taken as the rotation 

over the plastic hinging region at the end of the member 

shown in Figure 6-2. The hinge rotation at point B in 

Figure 6-1 corresponds to the yield point, θy, and shall 

be calculated in accordance with 

Equation (6-6):

(6-6)

where:

For analytical models of shear walls and wall segments, 

the value of lp shall be set equal to 0.5 times the flexural 

depth of the element, but less than one story height for 

shear walls and less than 50% of the element length for 

wall segments. For columns supporting discontinuous 

shear walls, lp shall be set equal to 0.5 times the flexural 

depth of the component.

Values for the variables a, b, and c required to define the 

location of points C, D, and E in Figure 6-1(a), shall be 

as specified in Table 6-18. 

For shear walls and wall segments whose inelastic 

response is controlled by shear, the following approach 

shall be permitted. The load-deformation relationship in 

Figure 6-1(b) shall be used, with the x-axis of Figure 

6-1(b) taken as lateral drift. For shear walls, this drift 

shall be the story drift as shown in Figure 6-3. For wall 

segments, Figure 6-3 shall represent the member drift.

For coupling beams, the following approach shall be 

permitted. The load-deformation relationship in Figure 

6-1(b) shall be used, with the x-axis of Figure 6-1(b) 

taken as the chord rotation as defined in Figure 6-4.

My = Yield moment capacity of the shear wall or 

wall segment

Ec = Concrete modulus

I = Member moment of inertia

lp = Assumed plastic hinge length

Figure 6-2 Plastic Hinge Rotation in Shear Wall 

where Flexure Dominates Inelastic 

Response

θy

My

EcI -------

     l

p =

Figure 6-3 Story Drift in Shear Wall where Shear 

Dominates Inelastic Response

Figure 6-4 Chord Rotation for Shear Wall Coupling 

Beams
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-49

Values for the variables d, e, and c required to find the 

points C, D, and E in Figure 6-1(b), shall be as specified 

in Table 6-19 for the appropriate members. Linear 

interpolation between tabulated values shall be used if 

the member under analysis has conditions that are 

between the limits given in the tables.

6.8.2.2.3 Nonlinear Dynamic Procedure

For the NDP, the complete hysteretic behavior of each 

component shall be modeled using properties verified 

by experimental evidence. Use of the generalized loaddeformation relation shown in Figure 6-1 to represent 

the envelope relation for the analysis shall be permitted. 

The unloading and reloading stiffnesses and strengths, 

and any pinching of the load-versus-rotation hysteresis 

loops, shall reflect the behavior experimentally 

observed for wall elements similar to the one under 

investigation.

6.8.2.3 Strength

Component strengths shall be computed according to 

the general requirements of Sections 6.4.2, with the 

additional requirements of this section. Strength shall be 

determined considering the potential for failure in 

flexure, shear, or development under combined gravity 

and lateral load.

Nominal flexural strength of shear walls or wall 

segments, Mn, shall be determined using the 

fundamental principles given in Chapter 10 of ACI 318. 

For calculation of nominal flexural strength, the 

effective compression and tension flange widths 

defined in Section 6.8.2.2 shall be used, except that the 

first limit shall be changed to one-tenth of the wall 

height. When determining the flexural yield strength of 

a shear wall, as represented by point B in Figure 6-1(a), 

only the longitudinal steel in the boundary of the wall 

shall be included. If the wall does not have a boundary 

member, then only the longitudinal steel in the outer 

25% of the wall section shall be included in the 

calculation of the yield strength. When calculating the 

nominal flexural strength of the wall, as represented by 

point C in Figure 6-1(a), all longitudinal steel 

(including web reinforcement) shall be included in the 

calculation. For all moment strength calculations, the 

strength of the longitudinal reinforcement shall be taken 

as the expected yield strength to account for material 

overstrength and strain hardening, and the axial load 

acting on the wall shall include gravity loads as defined 

in Chapter 3.

The nominal shear strength of a shear wall or wall 

segment, Vn, shall be determined based on the 

principles and equations given in Chapter 21 of 

ACI 318. The nominal shear strength of columns 

supporting discontinuous shear walls shall be 

determined based on the principles and equations given 

in Chapter 21 of ACI 318. For all shear strength 

calculations, 1.0 times the specified reinforcement yield 

strength shall be used. There shall be no difference 

between the yield and nominal shear strengths, as 

represented by points B and C in Figure 6-1.

When a shear wall or wall segment has a transverse 

reinforcement percentage, ρn, less than the minimum 

value of 0.0025 but greater than 0.0015, the shear 

strength of the wall shall be analyzed using the ACI 318

equations noted above. For transverse reinforcement 

percentages less than 0.0015, the contribution from the 

wall reinforcement to the shear strength of the wall shall 

be held constant at the value obtained using 

ρn = 0.0015.

Splice lengths for primary longitudinal reinforcement 

shall be evaluated using the procedures given in 

Section 6.4.5. Reduced flexural strengths shall be 

evaluated at locations where splices govern the usable 

stress in the reinforcement. The need for confinement 

reinforcement in shear wall boundary members shall be 

evaluated by the procedure in ACI 318 or other 

approved procedure.

The nominal flexural and shear strengths of coupling 

beams shall be evaluated using the principles and 

equations contained in Chapter 21 of ACI 318. The 

expected strength of longitudinal or diagonal 

reinforcement shall be used.

The nominal shear and flexural strengths of columns 

supporting discontinuous shear walls shall be evaluated 

as defined in Section 6.5.2.3.

C6.8.2.3 Strength

Data presented by Wood (1990) indicate that wall 

strength is insensitive to the quantity of transverse 

reinforcement when it drops below a steel ratio of 

0.0015.
6-50 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.8.2.4 Acceptance Criteria

6.8.2.4.1 Linear Static and Dynamic Procedures

Shear walls, wall segments, coupling beams, and 

columns supporting discontinuous shear walls shall be 

classified as either deformation- or force-controlled, as 

defined in Section 2.4.4. For columns supporting 

discontinuous shear walls, deformation-controlled 

actions shall be restricted to flexure. In other 

components, deformation-controlled actions shall be 

restricted to flexure or shear. All other actions shall be 

defined as being force-controlled actions.

The nominal flexural strength of a shear wall or wall 

segment shall be used to determine the maximum shear 

force in shear walls, wall segments, and columns 

supporting discontinuous shear walls. For cantilever 

shear walls and columns supporting discontinuous shear 

walls, the design shear force shall be equal to the 

magnitude of the lateral force required to develop the 

nominal flexural strength at the base of the wall, 

assuming the lateral force is distributed uniformly over 

the height of the wall. For wall segments, the design 

force shall be equal to the shear corresponding to the 

development of the positive and negative nominal 

moment strengths at opposite ends of the wall 

segment.

Design actions (flexure, shear, or force transfer at rebar 

anchorages and splices) on components shall be 

determined as prescribed in Chapter 3. When 

determining the appropriate value for the design 

actions, proper consideration shall be given to gravity 

loads and to the maximum forces that can be 

transmitted considering nonlinear action in adjacent 

components. Design actions shall be compared with 

design strengths in accordance with Section 3.4.2.2. 

Table 6-20 and 6-21 specify m values for use in 

Equation (3-20). Alternate m values shall be permitted 

where justified by experimental evidence and analysis.

6.8.2.4.2 Nonlinear Static and Dynamic Procedures

In the design model, inelastic response shall be 

restricted to those elements and actions listed in 

Tables 6-18 and 6-19, except where it is demonstrated 

that other inelastic actions are justified for the selected 

performance levels. For members experiencing inelastic 

behavior, the magnitude of other actions (forces, 

moments, or torque) in the member shall correspond to 

the magnitude of the action causing inelastic behavior. 

The magnitude of these other actions shall be shown to 

be below their nominal capacities.

Components experiencing inelastic response shall 

satisfy the requirements of Section 3.4.3.2, and the 

maximum plastic hinge rotations, drifts, or chord 

rotation angles shall not exceed the values given in 

Tables 6-18 and 6-19, for the selected performance 

level. Linear interpolation between tabulated values 

shall be used if the member under analysis has 

conditions that are between the limits given in the 

tables. 

The need for confinement reinforcement in shear wall 

boundary members may be evaluated by the method 

recommended by Wallace (1994 and 1995) for 

determining maximum lateral deformations in the wall 

and the resulting maximum compression strains in the 

wall boundary.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-51

Table 6-18 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Members Controlled by Flexure

Conditions

Plastic Hinge 

Rotation

(radians)

Residual

Strength

Ratio

Acceptable Plastic Hinge Rotation

(radians)

Performance Level

IO

Component Type

Primary Secondary4

a b c LS CP LS CP

i. Shear walls and wall segments

Confined 

Boundary1

≤ 0.1 ≤3 Yes 0.015 0.020 0.75 0.005 0.010 0.015 0.015 0.020

≤ 0.1 ≥ 6 Yes 0.010 0.015 0.40 0.004 0.008 0.010 0.010 0.015

≥ 0.25 ≤ 3 Yes 0.009 0.012 0.60 0.003 0.006 0.009 0.009 0.012

≥ 0.25 ≥ 6 Yes 0.005 0.010 0.30 0.0015 0.003 0.005 0.005 0.010

≤ 0.1 ≤ 3 No 0.008 0.015 0.60 0.002 0.004 0.008 0.008 0.015

≤ 0.1 ≥ 6 No 0.006 0.010 0.30 0.002 0.004 0.006 0.006 0.010

≥ 0.25 ≤ 3 No 0.003 0.005 0.25 0.001 0.002 0.003 0.003 0.005

≥ 0.25 ≥ 6 No 0.002 0.004 0.20 0.001 0.001 0.002 0.002 0.004

ii. Columns supporting discontinuous shear walls

Transverse reinforcement2

Conforming 0.010 0.015 0.20 0.003 0.007 0.010 n.a. n.a.

Nonconforming 0.0 0.0 0.0 0.0 0.0 0.0 n.a. n.a.

iii. Shear wall coupling beams

Longitudinal reinforcement and 

transverse reinforcement3

Conventional longitudinal 

reinforcement with conforming 

transverse reinforcement

≤ 3 0.025 0.050 0.75 0.010 0.02 0.025 0.025 0.050

≥ 6 0.02 0.040 0.50 0.005 0.010 0.020 0.020 0.040

Conventional longitudinal 

reinforcement with nonconforming 

transverse reinforcement

≤ 3 0.020 0.035 0.50 0.006 0.012 0.020 0.020 0.035

≥ 6 0.010 0.025 0.25 0.005 0.008 0.010 0.010 0.025

Diagonal reinforcement n.a. 0.030 0.050 0.80 0.006 0.018 0.030 0.030 0.050

1. Requirements for a confined boundary are the same as those given in ACI 318.

2. Requirements for conforming transverse reinforcement in columns are: (a) hoops over the entire length of the column at a spacing ≤ d/2, and (b) strength 

of hoops Vs ≥ required shear strength of column.

3. Conventional longitudinal reinforcement consists of top and bottom steel parallel to the longitudinal axis of the coupling beam. Conforming transverse 

reinforcement consists of: (a) closed stirrups over the entire length of the coupling beam at a spacing ≤ d/3, and (b) strength of closed stirrups Vs ≥ 3/4 of 

required shear strength of the coupling beam.

4. For secondary coupling beams spanning <8’-0”, with bottom reinforcement continuous into the supporting walls, secondary values shall be permitted to 

be doubled.

As As ( ) – ′ f

y + P

t

wlwfc

′ ----------------------------------- Shear

t

wlw fc′ --------------------

Shear

t

wlw fc′ --------------------
6-52 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Table 6-19 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Members Controlled by Shear

Conditions

Total Drift Ratio 

(%), or Chord 

Rotation 

(radians)1

Residual 

Strength 

Ratio

Acceptable Total Drift (%) or Chord 

Rotation (radians)1

Performance Level

IO

Component Type

Primary Secondary

d e c LS CP LS CP

i. Shear walls and wall segments

All shear walls and wall segments2 0.75 2.0 0.40 0.40 0.60 0.75 0.75 1.5

ii. Shear wall coupling beams4

Longitudinal reinforcement and 

transverse reinforcement3

Conventional longitudinal 

reinforcement with conforming 

transverse reinforcement

≤ 3 0.002 0.030 0.60

0.006 0.015 0.020 0.020 0.030

≥ 6 0.016 0.024 0.30

0.005 0.012 0.016 0.016 0.024

Conventional longitudinal 

reinforcement with 

nonconforming transverse 

reinforcement

≤ 3 0.012 0.025 0.40

0.006 0.008 0.010 0.010 0.020

≥ 6 0.008 0.014 0.20

0.004 0.006 0.007 0.007 0.012

1. For shear walls and wall segments, use drift; for coupling beams, use chord rotation; refer to Figures 6-3 and 6-4.

2. For shear walls and wall segments where inelastic behavior is governed by shear, the axial load on the member must be ≤ 0.15 Ag fc

’; otherwise, the 

member must be treated as a force-controlled component.

3. Conventional longitudinal reinforcement consists of top and bottom steel parallel to the longitudinal axis of the coupling beam. Conforming 

transverse reinforcement consists of: (a) closed stirrups over the entire length of the coupling beam at a spacing ≤ d/3, and (b) strength of closed 

stirrups Vs ≥ 3/4 of required shear strength of the coupling beam. 

4. For secondary coupling beams spanning <8’-0”, with bottom reinforcement continuous into the supporting walls, secondary values shall be permitted to 

be doubled.

Shear

t

wlw fc′ --------------------
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-53

Table 6-20 Numerical Acceptance Criteria for Linear Procedures—Members Controlled by Flexure

Conditions

m-factors

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Shear walls and wall segments

5

Confined 

Boundary1

≤ 0.1 ≤ 3 Yes 2 4 6 6 8

≤ 0.1 ≥ 6 Yes 2 3 4 4 6

≥ 0.25 ≤ 3 Yes 1.5 3 4 4 6

≥ 0.25 ≥ 6 Yes 1.25 2 2.5 2.5 4

≤ 0.1 ≤ 3 No 2 2.5 4 4 6

≤ 0.1 ≥ 6 No 1.5 2 2.5 2.5 4

≥ 0.25 ≤ 3 No 1.25 1.5 2 2 3

≥ 0.25 ≥ 6 No 1.25 1.5 1.75 1.75 2

ii. Columns supporting discontinuous shear walls

Transverse reinforcement2

Conforming 1 1.5 2 n.a. n.a.

Nonconforming 1 1 1 n.a. n.a.

iii. Shear wall coupling beams4

Longitudinal reinforcement and transverse 

reinforcement3 5

Conventional longitudinal reinforcement with 

conforming transverse reinforcement

≤ 3 24669

≥ 6 1.5 3 4 4 7

Conventional longitudinal reinforcement with 

nonconforming transverse reinforcement

≤ 3 1.5 3.5 5 5 8

≥ 6 1.2 1.8 2.5 2.5 4

Diagonal reinforcement n.a. 2 5 7 7 10

1. Requirements for a confined boundary are the same as those given in ACI 318.

2. Requirements for conforming transverse reinforcement in columns are: (a) hoops over the entire length of the column at a spacing ≤ d/2, and (b) 

strength of hoops Vs ≥ required shear strength of column.

3. Conventional longitudinal reinforcement consists of top and bottom steel parallel to the longitudinal axis of the coupling beam. Conforming 

transverse reinforcement consists of: (a) closed stirrups over the entire length of the coupling beam at a spacing ≤ d/3, and (b) strength of closed 

stirrups Vs ≥ 3/4 of required shear strength of the coupling beam.

4. For secondary coupling beams spanning <8’-0”, with bottom reinforcement continuous into the supporting walls, secondary values shall be permitted to 

be doubled.

5. Design shear shall be calculated using limit-state analysis procedures.

As As ( ) – ′ f

y + P

t

wlwfc

′ ----------------------------------- Shear

t

wlw fc′ --------------------

Shear

t

wlw fc′ --------------------
6-54 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Table 6-21 Numerical Acceptance Criteria for Linear Procedures—Members Controlled by Shear

Conditions

m-factors

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

i. Shear walls and wall segments

All shear walls and wall segments1 22323

ii. Shear wall coupling beams3

Longitudinal reinforcement and transverse reinforcement2

Conventional longitudinal reinforcement with conforming 

transverse reinforcement

≤ 3 1.5 3 4 4 6

≥ 6 1.2 2 2.5 2.5 3.5

Conventional longitudinal reinforcement with 

nonconforming transverse reinforcement

≤ 3 1.5 2.5 3 3 4

≥ 6 1.25 1.2 1.5 1.5 2.5

1. For shear walls and wall segments where inelastic behavior is governed by shear, the axial load on the member must be ≤ 0.15 Ag f ′

c, the longitudinal 

reinforcement must be symmetrical, and the maximum shear demand must be ≤ 6 ; otherwise, the shear shall be considered to be a force-controlled 

action.

2. Conventional longitudinal reinforcement consists of top and bottom steel parallel to the longitudinal axis of the coupling beam. Conforming transverse 

reinforcement consists of: (a) closed stirrups over the entire length of the coupling beam at a spacing ≤ d/3, and (b) strength of closed stirrups Vs ≥ 3/4 of 

required shear strength of the coupling beam.

3. For secondary coupling beams spanning <8’-0”, with bottom reinforcement continuous into the supporting walls, secondary values shall be permitted to 

be doubled.

Shear

t

wlw fc′ --------------------

f

c′
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-55

6.8.2.5 Rehabilitation Measures

Reinforced shear walls, wall segments, coupling beams, 

and columns supporting discontinuous shear walls that 

do not meet the acceptance criteria for the selected 

Rehabilitation Objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 6.4.7 and other provisions of this standard. 

C6.8.2.5 Rehabilitation Measures

The following measures may be effective in 

rehabilitating reinforced shear walls, wall segments, 

coupling beams, and reinforced concrete columns 

supporting discontinuous shear walls:

1. Addition of wall boundary members. Addition 

of boundary members may be an effective measure 

in strengthening shear walls or wall segments that 

have insufficient flexural strength. These members 

may be either cast-in-place reinforced concrete 

elements or steel sections. In both cases, proper 

connections should be made between the existing 

wall and the added members. The shear capacity of 

the rehabilitated wall should be re-evaluated.

2. Addition of confinement jackets at wall 

boundaries. Increasing the confinement at the 

wall boundaries by the addition of a steel or 

reinforced concrete jacket may be an effective 

measure in improving the flexural deformation 

capacity of a shear wall. For both types of jackets, 

the longitudinal should not be continuous from 

story to story unless the jacket is also being used to 

increase the flexural capacity. The minimum 

thickness for a concrete jacket should be three 

inches. Carbon fiber wrap should be permitted for 

improving the confinement of concrete in 

compression.

3. Reduction of flexural strength. Reduction in the 

flexural capacity of a shear wall to change the 

governing failure mode from shear to flexure may 

be an effective rehabilitation measure. It may be 

accomplished by saw-cutting a specified number 

of longitudinal bars near the edges of the shear 

wall.

4. Increased shear strength of wall. Increasing the 

shear strength of the web of a shear wall by casting 

additional reinforced concrete adjacent to the wall 

web may be an effective rehabilitation measure. 

The new concrete should be at least four inches 

thick and should contain horizontal and vertical 

reinforcement. The new concrete should be 

properly bonded to the existing web of the shear 

wall. The use of carbon fiber sheets, epoxied to the 

concrete surface, should also be permitted to 

increase the shear capacity of a shear wall.

5. Confinement jackets to improve deformation 

capacity of coupling beams and columns 

supporting discontinuous shear walls. The use 

of confinement jackets specified above as a 

rehabilitation measure for wall boundaries, and in 

Section 6.5 for frame elements, may also be 

effective in increasing both the shear capacity and 

the deformation capacity of coupling beams and 

columns supporting discontinuous shear walls.

6. Infilling between columns supporting 

discontinuous shear walls. Where a 

discontinuous shear wall is supported on columns 

that lack either sufficient strength or deformation 

capacity to satisfy design criteria, making the wall 

continuous by infilling the opening between these 

columns may be an effective rehabilitation 

measure. The infill and existing columns should be 

designed to satisfy all the requirements for new 

wall construction, including any strengthening of 

the existing columns required by adding a concrete 

or steel jacket for strength and increased 

confinement. The opening below a discontinuous 

shear wall should also be permitted to be “infilled”

with steel bracing. The bracing members should be 

sized to satisfy all design requirements and the 

columns should be strengthened with a steel or a 

reinforced concrete jacket.

All of the above rehabilitation measures require an 

evaluation of the wall foundation, diaphragms, and 

connections between existing structural elements and 

any elements added for rehabilitation purposes.
6-56 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.9 Precast Concrete Shear Walls

6.9.1 Types of Precast Shear Walls 

Precast concrete shear walls shall consist of story-high 

or half-story-high precast wall segments that are made 

continuous through the use of either mechanical 

connectors or reinforcement splicing techniques with or 

without a cast-in-place connection strip. Connections 

between precast segments shall be permitted along both 

the horizontal and vertical edges of a wall segment.

The design of the following types of precast shear walls 

shall meet the requirements of Section 6.9:

1. Construction that emulates cast-in-place shear wall 

defined as that construction in which the 

reinforcement connections are made to be stronger 

than the adjacent precast panels so that the lateral 

load response of the precast wall system will be 

comparable to that for monolithic shear walls.

2. Jointed construction defined as construction in 

which inelastic action is permitted to occur at the 

connections between precast panels.

3. Tilt-up construction defined as a special technique 

for precast wall construction where there are vertical 

joints between adjacent panels and horizontal joints 

at the foundation level, and where the roof or floor 

diaphragm connects with the tilt-up panel.

6.9.1.1 Construction that Emulates 

Cast-In-Place Shear Wall

For this type of precast wall, the connections between 

precast wall elements shall be designed and detailed to 

be stronger than the panels they connect. The shear 

walls and wall segments of precast walls that emulate 

cast-in-place construction shall be evaluated by the 

criteria defined in Section 6.8.

6.9.1.2 Jointed Construction

Shear walls and wall segments of jointed construction 

type of precast walls shall be evaluated by the criteria 

defined in Section 6.9.2.

C6.9.1.1 Construction that Emulates 

Cast-In-Place Shear Wall

When the precast shear wall is subjected to lateral 

loading, any yielding and inelastic behavior should 

take place in the panel elements away from the 

connections. If the reinforcement detailing in the panel 

is similar to that for cast-in-place shear walls, then the 

inelastic response of a precast shear wall should be 

very similar to that for a cast-in-place wall.

Modern building codes permit the use of precast shear 

wall construction in high seismic zones if it satisfies 

the criteria for construction that emulates a cast-inplace shear wall.

C6.9.1.2 Jointed Construction

For most older structures that contain precast shear 

walls, and for some modern construction, inelastic 

activity can be expected in the connections between 

precast wall panels during severe lateral loading. 

Because joints between precast shear walls in older 

buildings have often exhibited brittle behavior during 

inelastic load reversals, jointed construction had not 

been permitted in high seismic zones. Therefore, when 

evaluating older buildings that contain precast shear 

walls that are likely to respond as jointed construction, 

the permissible ductilities and rotation capacities given 

in Section 6.8 should be reduced.

For some modern structures, precast shear walls have 

been constructed with special connectors that are 

detailed to exhibit ductile response and energy 

absorption characteristics. Many of these connectors 

are proprietary and only limited experimental evidence 

concerning their inelastic behavior is available. 

Although this type of construction is clearly safer than 

jointed construction in older buildings, the 

experimental evidence is not sufficient to permit the 

use of the same ductility and rotation capacities given 

for cast-in-place construction. Thus, the permissible 

values given in Section 6.8 should be reduced.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-57

6.9.1.3 Tilt-up Construction

Shear walls and wall segments of tilt-up type of precast 

walls shall be evaluated by the criteria defined in 

Section 6.9.2.

6.9.2 Precast Concrete Shear Walls and 

Wall Segments

6.9.2.1 General Considerations

The analytical model for a precast concrete shear wall 

or wall segment shall represent the stiffness, strength, 

and deformation capacity of the overall member, as well 

as the connections and joints between any precast panel 

components that compose the wall. Potential failure in 

flexure, shear, and reinforcement development at any 

point in the shear wall panels or connections shall be 

considered. Interaction with other structural and 

nonstructural elements shall be included.

Modeling of precast concrete shear walls and wall 

segments within the precast panels as equivalent beamcolumns that include both flexural and shear 

deformations shall be permitted. The rigid-connection 

zone at beam connections to these equivalent beamcolumns shall represent the distance from the wall 

centroid to the edge of the wall or wall segment. The 

different bending capacities for the two loading 

directions of unsymmetrical precast wall sections shall 

be modeled.

For precast shear walls and wall segments where shear 

deformations have a more significant effect on behavior 

than flextural deformation, a multiple spring model 

shall be used.

The diaphragm action of concrete slabs interconnecting 

precast shear walls and frame columns shall be 

represented in the model.

6.9.2.2 Stiffness

The modeling assumptions defined in Section 6.8.2.2 

for monolithic concrete shear walls and wall segments 

shall also be used for precast concrete walls. In 

addition, the analytical model shall model the axial, 

shear, and rotational deformations of the connections 

between the precast components that compose the wall 

by either softening the model used to represent the 

precast panels or by adding spring elements between 

panels.

6.9.2.2.1 Linear Static and Dynamic Procedures

The modeling procedures given in Section 6.8.2.2.1, 

combined with a procedure for including connection 

deformations as noted above, shall be used.

6.9.2.2.2 Nonlinear Static Procedure

Nonlinear load-deformation relations shall comply with 

the requirements of Section 6.4.1.2. The monotonic 

load-deformation relationships for analytical models 

that represent precast shear walls and wall elements 

within precast panels shall be in accordance with the 

generalized relation shown in Figure 6-1, except that 

alternative approaches shall be permitted where verified 

by experiments. Where the relations are according to 

the Figure 6-1, the following approach shall be 

permitted.

Values for plastic hinge rotations or drifts at points B, C, 

and E for the two general shapes shall be as defined 

below. The strength levels at points B and C shall 

correspond to the yield strength and nominal strength, 

as defined in Section 6.8.2.3. The residual strength for 

the line segment D–E shall be as defined below.

For precast shear walls and wall segments whose 

inelastic behavior under lateral loading is governed by 

flexure, the general load-deformation relationship shall 

be defined as in Figure 6-1(a). For these members, the 

x-axis of Figure 6-1(a) shall be taken as the rotation 

over the plastic hinging region at the end of the member 

as shown in Figure 6-2. If the requirements for 

construction that emulates cast-in- place shear wall are 

satisfied, the value of the hinge rotation at point B shall 

correspond to the yield rotation, θy, and shall be 

calculated by Equation (6-6). The same expression shall 

also be used for wall segments within a precast panel if 

flexure controls the inelastic response of the segment. If 

the precast wall is of jointed construction and flexure 

governs the inelastic response of the member, then the 

value of θy shall be increased to account for rotation in 

C6.9.1.3 Tilt-up Construction

Tilt-up construction should be considered to be a 

special case of jointed construction. The walls for most 

buildings constructed by the tilt-up method are longer 

than their height. Shear would usually govern their inplane design. The major concern for most tilt-up 

construction is the connection between the tilt-up wall 

and the roof diaphragm. That connection should be 

carefully analyzed to be sure the diaphragm forces can 

be safely transmitted to the precast wall system.
6-58 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

the joints between panels or between the panel and the 

foundation.

For precast shear walls and wall segments whose 

inelastic behavior under lateral loading is governed by 

shear, the general load-deformation relationship shall be 

defined as in Figure 6-1(b). For these members, the xaxis of Figure 6-1(b) shall be taken as the story drift for 

shear walls, and as the element drift for wall segments 

as shown in Figure 6-3.

For construction that emulates cast-in-place shear walls, 

the values for the variables a, b, and c required to define 

the location of points C, D, and E in Figure 6-1(a), shall 

be as specified in Table 6-18. For construction 

classified as jointed construction, the values of a, b, and 

c specified in Table 6-18 shall be reduced to 50% of the 

given values, unless experimental evidence available to 

justify higher values is approved. In no case, however, 

shall values larger than those specified in Table 6-18 be 

used.

For construction that emulates cast-in-place shear walls, 

values for the variables d, e, and c required to find the 

points C, D, and E in Figure 6-1(b), shall be as specified 

in Table 6-19 for the appropriate member conditions. 

For construction classified as jointed construction, the 

values of d, e, and c specified in Table 6-19 shall be 

reduced to 50% of the specified values unless 

experimental evidence available to justify higher values 

is approved. In no case, however, shall values larger 

than those specified in Table 6-19 be used.

For Tables 6-18 and 6-19, linear interpolation between 

tabulated values shall be permitted if the member under 

analysis has conditions that are between the limits given 

in the tables.

6.9.2.2.3 Nonlinear Dynamic Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Dynamic Procedure (NDP) shall model 

the complete hysteretic behavior of each component 

using properties verified by experimental evidence. The 

generalized relation shown in Figure 6-1 shall be taken 

to represent the envelope for the analysis. The 

unloading and reloading stiffnesses and strengths, and 

any pinching of the load versus rotation hysteresis 

loops, shall reflect the behavior experimentally 

observed for wall elements similar to the one under 

investigation.

6.9.2.3 Strength

The strength of precast concrete shear walls and wall 

segments within the panels shall be computed according 

to the general requirement of Sections 6.4.2, except as 

modified here. For construction emulating cast-in-place 

shear wall, the strength calculation procedures given in 

Section 6.8.2.3 shall be followed.

For jointed construction, calculations of axial, shear, 

and flexural strength of the connections between panels 

shall be based on fundamental principles of structural 

mechanics. Expected yield strength for steel 

reinforcement of connection hardware used in the 

connections shall be used when calculating the axial 

and flexural strength of the connection region. The 

unmodified specified yield strength of the 

reinforcement and connection hardware shall be used 

when calculating the shear strength of the connection 

region.

For all precast concrete shear walls of jointed 

construction, no difference shall be taken between the 

computed yield and nominal strengths in flexure and 

shear. The values for strength represented by the points 

B and C in Figure 6-1 shall be computed following the 

procedures given in Section 6.8.2.3.

6.9.2.4 Acceptance Criteria

6.9.2.4.1 Linear Static and Dynamic Procedures

For precast shear wall construction that emulates castin-place construction and for wall segments within a 

precast panel, the acceptance criteria defined in 

Section 6.8.2.4.1 shall be followed. For precast shear 

wall construction defined as jointed construction, the 

acceptance criteria procedure given in Section 6.8.2.4.1 

shall be followed; however, the m values specified in 

Tables 6-20 and 6-21 shall be reduced by 50%, unless 

experimental evidence justifies the use of a larger value. 

In no case shall an m value be taken as less than 1.0.

C6.9.2.3 Strength

In older construction, particular attention must be 

given to the technique used for splicing reinforcement 

extending from adjacent panels into the connection. 

These connections may be insufficient and can often 

govern the strength of the precast shear wall system.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-59

6.9.2.4.2 Nonlinear Static and Dynamic Procedures

Inelastic response shall be restricted to those shear walls 

(and wall segments) and actions listed in Tables 6-18 

and 6-19, except where it is demonstrated by 

experimental evidence and analysis that other inelastic 

action is acceptable for the selected performance levels. 

For components experiencing inelastic behavior, the 

magnitude of the other actions (forces, moments, or 

torques) in the component shall correspond to the 

magnitude of the action causing the inelastic behavior. 

The magnitude of these other actions shall be shown to 

be below their nominal capacities.

For precast shear walls that emulate cast-in-place 

construction and wall segments within a precast panel, 

the maximum plastic hinge rotation angles or drifts 

during inelastic response shall not exceed the values 

specified in Tables 6-18 and 6-19. For precast shear 

walls of jointed construction, the maximum plastic 

hinge rotation angles or drifts during inelastic response 

shall not exceed one-half of the values specified in 

Tables 6-18 and 6-19 unless experimental evidence 

justifies a higher value. However, in no case shall 

deformation values larger than those specified in these 

tables be used for jointed type construction.

If the maximum deformation value exceeds the 

corresponding tabular value, the element shall be 

considered to be deficient, and either the element or 

structure shall be rehabilitated.

Alternative approaches or values shall be permitted 

where justified by experimental evidence and analysis.

6.9.2.5 Rehabilitation Measures

Precast concrete shear walls or wall segments that do 

not meet the acceptance criteria for the selected 

Rehabilitation Objective shall be rehabilitated. 

Rehabilitation measures shall meet the requirements of 

Section 6.4.7 and other provisions of this standard.

C6.9.2.5 Rehabilitation Measures

Precast concrete shear wall systems may suffer from 

some of the same deficiencies as cast-in-place walls. 

These may include inadequate flexural capacity, 

inadequate shear capacity with respect to flexural 

capacity, lack of confinement at wall boundaries, and 

inadequate splice lengths for longitudinal 

reinforcement in wall boundaries. A few deficiencies 

unique to precast wall construction are inadequate 

connections between panels, to the foundation, and to 

floor or roof diaphragms.

The rehabilitation measures described in 

Section 6.8.2.5 may also be effective in rehabilitating 

precast concrete shear walls. In addition, the following 

rehabilitation measures may be effective:

1. Enhancement of connections between adjacent 

or intersecting precast wall panels. Mechanical 

connectors such as steel shapes and various types of 

drilled-in-anchors, or cast-in-place strengthening 

methods, or a combination of the two, may be 

effective in strengthening connections between 

precast panels. Cast-in-place strengthening methods 

may include exposing the reinforcing steel at the 

edges of adjacent panels, adding vertical and 

transverse (tie) reinforcement, and placing new 

concrete.

2. Enhancement of connections between precast 

wall panels and foundations. Increasing the shear 

capacity of the wall panel-to-foundation connection 

by using supplemental mechanical connectors or by 

using a cast-in-place overlay with new dowels into 

the foundation may be an effective rehabilitation 

measure. Increasing the overturning moment 

capacity of the panel-to-foundation connection by 

using drilled-in dowels within a new cast-in-place 

connection at the edges of the panel may also be an 

effective rehabilitation measure. Adding 

connections to adjacent panels may also be an 

effective rehabilitation measure in eliminating 

some of the forces transmitted through the panel-tofoundation connection.
6-60 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

6.10 Concrete-Braced Frames

6.10.1 Types of Concrete-Braced Frames

Reinforced concrete-braced frames shall be defined as 

those frames with monolithic, non-prestressed, 

reinforced concrete beams, columns, and diagonal 

braces that are coincident at beam-column joints and 

that resist lateral loads primarily through truss action.

Where masonry infills are present in concrete-braced 

frames, requirements for masonry infilled frames as 

specified in Section 6.7 shall also apply.

The provisions of Section 6.10 shall apply to existing 

reinforced concrete-braced frames and existing 

reinforced concrete-braced frames rehabilitated by 

addition or removal of material.

6.10.2 General Considerations

The analytical model for a reinforced concrete-braced 

frame shall represent the strength, stiffness, and 

deformation capacity of beams, columns, braces, and all 

connections and components of the element. Potential 

failure in tension, compression (including instability), 

flexure, shear, anchorage, and reinforcement 

development at any section along the component length 

shall be considered. Interaction with other structural 

and nonstructural elements and components shall be 

included.

The analytical model that represents the framing, using 

line elements with properties concentrated at 

component centerlines, shall be permitted. The 

analytical model also shall comply with the 

requirements specified in Section 6.5.2.1.

In frames having braces in some bays and no braces in 

other bays, the restraint of the brace shall be represented 

in the analytical model as specified above, and the 

nonbraced bays shall be modeled as frames in 

compliance with the applicable provisions in other 

sections of this chapter. Where braces create a vertically 

discontinuous frame, the effects of the discontinuity on 

overall building performance shall be considered.

Inelastic deformations in primary components shall be 

restricted to flexure and axial load in beams, columns, 

and braces. Other inelastic deformations shall be 

permitted in secondary components. Acceptance 

criteria for design actions shall be as specified in 

Section 6.10.5.

6.10.3 Stiffness

6.10.3.1 Linear Static and Dynamic 

Procedures

Modeling of beams, columns, and braces in braced 

portions of the frame considering only axial tension and 

compression flexibilities shall be permitted. Nonbraced 

portions of frames shall be modeled according to 

procedures described elsewhere for frames. Effective 

stiffnesses shall be according to Section 6.4.1.2.

6.10.3.2 Nonlinear Static Procedure

Nonlinear load-deformation relations shall comply with 

the requirements of Section 6.4.1.2.

Beams, columns, and braces in braced portions shall be 

modeled using nonlinear truss components or other 

models whose behavior has been demonstrated to 

adequately represent behavior of concrete components 

dominated by axial tension and compression loading. 

Models for beams and columns in nonbraced portions 

shall comply with requirements for frames specified in 

Section 6.5.2.2.2. The model shall be capable of 

representing inelastic response along the component 

lengths, as well as within connections.

Monotonic load-deformation relations shall be 

according to the generalized load-deformation relation 

shown in Figure 6-1, except that different relations are 

permitted where verified by experiments. The overall 

load-deformation relation shall be established so that 

the maximum resistance is consistent with the design 

strength specifications of Sections 6.4.2 and 6.5.2.3. 

Numerical quantities in Figure 6-1 shall be derived 

from tests, rational analyses, or criteria of 

3. Enhancement of connections between precast 

wall panels and floor or roof diaphragms.

Strengthening these connections by using either 

supplemental mechanical devices or cast-in-place 

connectors may be an effective rehabilitation 

measure. Both in-plane shear and out-of-plane 

forces should be considered when strengthening 

these connections.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-61

Section 6.7.2.2.2, with braces modeled as columns in 

accordance with Table 6-16.

6.10.3.3 Nonlinear Dynamic Procedure

Nonlinear load-deformation relations for use in analysis 

by Nonlinear Dynamic Procedure (NDP) shall model 

the complete hysteretic behavior of each component 

using properties verified by experimental evidence. 

Unloading and reloading properties shall represent 

stiffness and strength degradation characteristics.

6.10.4 Strength

Component strengths shall be computed according to 

the general requirements of Sections 6.4.2 and the 

additional requirements of Section 6.5.2.3. The 

possibility of instability of braces in compression shall 

be considered.

6.10.5 Acceptance Criteria

6.10.5.1 Linear Static and Dynamic 

Procedures

All actions shall be classified as being either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. In primary components, deformationcontrolled actions shall be restricted to flexure and axial 

actions in beams and columns, and axial actions in 

braces. In secondary components, deformationcontrolled actions shall be restricted to those actions 

identified for the braced or isolated frame in this 

chapter.

Calculated component actions shall satisfy the 

requirements of Section 3.4.2.2. The m-factors for 

concrete frames shall be as specified in other applicable 

sections of this chapter, and m-factors for beams, 

columns, and braces modeled as tension and 

compression components shall be as specified for 

columns in Table 6-17. The m-factors shall be reduced 

to half the values in that table, but need not be less than 

1.0, where component buckling is a consideration. 

Alternate approaches or values shall be permitted where 

justified by experimental evidence and analysis.

6.10.5.2 Nonlinear Static and Dynamic 

Procedures

Calculated component actions shall satisfy the 

requirements of Section 3.4.2.2 and shall not exceed the 

numerical values listed in Table 6-16 or the relevant 

tables for isolated frames specified in other sections of 

this chapter. Where inelastic action is indicated for a 

component or action not listed in these tables, the 

performance shall be deemed unacceptable. Alternate 

approaches or values shall be permitted where justified 

by experimental evidence and analysis.

6.10.6 Rehabilitation Measures

Concrete-braced frame components that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard.

6.11 Cast-in-Place Concrete 

Diaphragms

6.11.1 Components of Concrete Diaphragms

Cast-in-place concrete diaphragms transmit inertial 

forces within a structure to vertical lateral-forceresisting elements.

Concrete diaphragms shall be made up of slabs, struts, 

collectors, and chords. Alternatively, diaphragm action 

may be provided by a structural truss in the horizontal 

plane. Diaphragms consisting of structural concrete 

topping on metal deck shall comply with the 

requirements of Section 5.9.2.

6.11.1.1 Slabs

Slabs shall consist of cast-in-place concrete systems 

that, in addition to supporting gravity loads, transmit 

inertial loads developed within structure from one 

vertical lateral-force-resisting element to another, and 

provide out-of-plane bracing to other portions of the 

building.

6.11.1.2 Struts and Collectors

Collectors are components that serve to transmit the 

inertial forces within the diaphragm to elements of the 

lateral-force-resisting system. Struts are components of 

a structural diaphragm used to provide continuity 

C6.10.6 Rehabilitation Measures

Rehabilitation measures that may be effective in 

rehabilitating concrete-braced frames include the 

general approaches listed for other concrete elements 

in this chapter, plus other approaches based on 

rational principles.
6-62 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

around an opening in the diaphragm. Struts and 

collectors shall be monolithic with the slab, occurring 

either within the slab thickness or being thicker than the 

slab.

6.11.1.3 Diaphragm Chords

Diaphragm chords are components along diaphragm 

edges with increased longitudinal and transverse 

reinforcement, acting primarily to resist tension and 

compression forces generated by bending in the 

diaphragm. Exterior walls shall be permitted to serve as 

chords provided there is adequate strength to transfer 

shear between the slab and wall.

6.11.2 Analysis, Modeling, and Acceptance 

Criteria

6.11.2.1 General Considerations

The analytical model for a diaphragm shall represent 

the strength, stiffness, and deformation capacity of each 

component and the diaphragm as a whole. Potential 

failure in flexure, shear, buckling, and reinforcement 

development shall be considered.

Modeling of the diaphragm as a continuous or simple 

span horizontal beam supported by elements of varying 

stiffness shall be permitted. The beam shall be modeled 

as rigid, stiff, or flexible considering the deformation 

characteristics of the actual system.

6.11.2.2 Stiffness

Diaphragm stiffness shall be modeled according to 

Section 6.11.2.1 and shall be determined using a linear 

elastic model and gross section properties. The modulus 

of elasticity used shall be that of the concrete as 

specified in ACI 318. When the length-to-width ratio of 

the diaphragm exceeds 2.0 (where the length is the 

distance between vertical elements), the effects of 

diaphragm flexibility shall be considered when 

assigning lateral forces to the resisting vertical 

elements.

6.11.2.3 Strength

Strength of cast-in-place concrete diaphragm 

components shall comply with the requirements of 

Sections 6.4.2 as modified in this section.

The maximum component strength shall be determined 

considering potential failure in flexure, axial load, 

shear, torsion, development, and other actions at all 

points in the component under the actions of design 

gravity and lateral load combinations. The shear 

strength shall be as specified in Chapter 21 of ACI 318. 

Strut, collector, and chord strengths shall be as 

determined for frame components in Section 6.5.2.3.

6.11.2.4 Acceptance Criteria

Diaphragm shear and flexure shall be considered 

deformation-controlled. Acceptance criteria for slab 

component actions shall be as specified for shear walls 

in Section 6.8.2.4, with m values taken according to 

similar components in Tables 6-20 and 6-21 for use in 

Equation (3-20). Acceptance criteria for struts, chords, 

and collectors shall be as specified for frame 

components in Section 6.5.2.4. Connections shall be 

considered force-controlled.

C6.11.1.3 Diaphragm Chords

When evaluating an existing building, special care 

should be taken to evaluate the condition of the lap 

splices. Where the splices are not confined by closely 

spaced transverse reinforcement, splice failure is 

possible if stress levels reach critical values. In 

rehabilitation construction, new laps should be 

confined by closely spaced transverse reinforcement.

C6.11.2.1 General Considerations

Some computer models assume a rigid diaphragm. 

Few cast-in-place diaphragms would be considered 

flexible; however, a thin concrete slab on a metal deck 

might be stiff depending on the length-to-width ratio of 

the diaphragm.

C6.11.2.2 Stiffness

The concern is for relatively flexible vertical members 

that may be displaced by the diaphragm, and for 

relatively stiff vertical members that may be 

overloaded by the same diaphragm displacement.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-63

6.11.3 Rehabilitation Measures

Concrete diaphragms that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 6.4.7 and other provisions of 

this standard. 

6.12 Precast Concrete Diaphragms

6.12.1 Components of Precast Concrete 

Diaphragms

Precast concrete diaphragms are elements composed 

primarily of precast components with or without 

topping, that transmit shear forces from within a 

structure to vertical lateral-force-resisting elements.

Precast concrete diaphragms shall be classified as 

topped or untopped. A topped diaphragm shall be 

defined as one that includes a reinforced structural 

concrete topping slab poured over the completed 

precast horizontal system. An untopped diaphragm 

shall be defined as one constructed of precast 

components without a structural cast-in-place topping.

6.12.2 Analysis, Modeling, and Acceptance 

Criteria

Analysis and modeling of precast concrete diaphragms 

shall conform to Section 6.11.2.2, with the added 

requirement that the analysis and modeling shall 

account for the segmental nature of the individual 

components.

Component strengths shall be determined in accordance 

with Section 6.11.2.3. Welded connection strength shall 

be based on rational procedures, and connections shall 

be assumed to have little ductility capacity unless test 

data verify higher ductility values. Precast concrete 

diaphragms with reinforced concrete topping slabs shall 

be considered deformation-controlled in shear and 

flexure. m-factors shall be taken as 1.0, 1.25, and 1.5 for 

IO, LS, and CP performance levels, respectively.

C6.11.3 Rehabilitation Measures

Cast-in-place concrete diaphragms can have a wide 

variety of deficiencies; see Chapter 10 and FEMA 310.

Two general alternatives may be effective in correcting 

deficiencies: either improve the strength and ductility, 

or reduce the demand in accordance with FEMA 172. 

Providing additional reinforcement and encasement 

may be an effective measure to strengthen or improve 

individual components. Increasing the diaphragm 

thickness may also be effective, but the added weight 

may overload the footings and increase the seismic 

loads. Lowering seismic demand by providing 

additional lateral-force-resisting elements, introducing 

additional damping, or base isolating the structure may 

also be effective rehabilitation measures.

C6.12.1 Components of Precast Concrete 

Diaphragms

Section 6.11 provided a general overview of concrete 

diaphragms. Components of precast concrete 

diaphragms are similar in nature and function to those 

of cast-in-place diaphragms with a few critical 

differences. One is that precast diaphragms do not 

possess the inherent unity of cast-in-place monolithic 

construction. Additionally, precast components may be 

highly stressed due to prestressed forces. These forces 

cause long-term shrinkage and creep, which shorten 

the component over time. This shortening tends to 

fracture connections that restrain the component.

Most floor systems have a topping system, but some 

hollow core floor systems do not. The topping slab 

generally bonds to the top of the precast elements, but 

may have an inadequate thickness at the center of the 

span, or may be inadequately reinforced. Also, 

extensive cracking of joints may be present along the 

panel joints. Shear transfer at the edges of precast 

concrete diaphragms is especially critical.

Some precast roof systems are constructed as untopped 

systems. Untopped precast concrete diaphragms have 

been limited to lower seismic zones by recent versions 

of the Uniform Building Code. This limitation has 

been imposed because of the brittleness of connections 

and lack of test data concerning the various precast 

systems. Special consideration shall be given to 

diaphragm chords in precast construction.
6-64 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

Untopped precast concrete diaphragms shall be 

considered force-controlled.

6.12.3 Rehabilitation Measures

Precast concrete diaphragms that do not meet the 

acceptance criteria for the selected Rehabilitation 

Objective shall be rehabilitated. Rehabilitation 

measures shall meet the requirements of Section 6.4.7 

and other provisions of this standard. 

6.13 Concrete Foundation Elements

6.13.1 Types of Concrete Foundations

Foundations shall be defined as those elements that 

serve to transmit loads from the vertical structural 

subsystems (columns and walls) of a building to the 

supporting soil or rock. Concrete foundations for 

buildings shall be classified as either shallow or deep 

foundations as defined in Chapter 4. Requirements of 

Section 6.13 shall apply to shallow foundations that 

include spread or isolated footing, strip or line footing, 

combination footing, and concrete mat footing; and to 

deep foundations that include pile foundations and castin-place piers. Concrete-grade beams shall be permitted 

in both shallow and deep foundation systems and shall 

comply with the requirements of Section 6.13.

The provisions of Section 6.13 shall apply to existing 

foundation elements and to new materials or elements 

that are required to rehabilitate an existing building.

6.13.1.1 Shallow Foundations

Existing spread footings, strip footings, and 

combination footings are reinforced or unreinforced. 

Vertical loads are transmitted by these footings to the 

soil by direct bearing; and lateral loads are transmitted 

by a combination of friction between the bottom of the 

footing and the soil, and passive pressure of the soil on 

the vertical face of the footing.

Concrete mat footings shall be reinforced to resist the 

flexural and shear stresses resulting from the 

superimposed concentrated and line structural loads and 

the distributed resisting soil pressure under the footing. 

Lateral loads shall be resisted by friction between the 

soil and the bottom of the footing, and by passive 

pressure developed against foundation walls that are 

part of the system.

6.13.1.2 Deep Foundations

6.13.1.2.1 Driven Pile Foundations

Concrete pile foundations shall be composed of a 

reinforced concrete pile cap supported on driven piles. 

The piles shall be concrete (with or without 

prestressing), steel shapes, steel pipes, or composite 

(concrete in a driven steel shell). Vertical loads shall be 

transmitted to the piling by the pile cap, and are resisted 

by direct bearing of the pile tip in the soil or by skin 

friction or cohesion of the soil on the surface area of the 

pile. Lateral loads are resisted by passive pressure of the 

soil on the vertical face of the pile cap, in combination 

with interaction of the piles in bending and passive soil 

pressure on the pile surface.

6.13.1.2.2 Cast-in-Place Pile Foundations

Cast-in-place concrete pile foundations shall consist of 

reinforced concrete placed in a drilled or excavated 

shaft. Cast-in-place pile or pier foundations shall resist 

vertical and lateral loads in the same manner as that of 

driven pile foundations specified in Section 6.13.1.2.1.

C6.12.2 Analysis, Modeling, and Acceptance 

Criteria

Welded connection strength can be determined using 

the latest version of the Precast Concrete Institute 

(PCI) Handbook.

C6.12.3 Rehabilitation Measures

Section 6.11.3 provides guidance for rehabilitation 

measures for concrete diaphragms in general. Special 

care should be taken to overcome the segmental 

nature of precast concrete diaphragms, and to avoid 

damaging prestressing strands when adding 

connections.

C6.13.1.2 Deep Foundations

C6.13.1.2.1 Driven Pile Foundations

In poor soils, or soils subject to liquefaction, bending 

of the piles may be the only dependable resistance to 

lateral loads.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-65

6.13.2 Analysis of Existing Foundations

For concrete buildings with columns or walls cast 

monolithically with the foundation, the vertical 

structural elements shall be considered fixed against 

rotation at the top of the foundation if the foundations 

and supporting soil are shown to be capable of resisting 

the induced moments. When columns are not 

monolithic with their foundations, or are designed to 

not resist flexural moments, they shall be modeled with 

pinned ends. In such cases, the column base shall be 

evaluated for the resulting axial and shear forces as well 

as the ability to accommodate the necessary end 

rotation of the columns. The effects of base fixity of 

columns shall be taken into account at the point of 

maximum displacement of the superstructure.

If a more rigorous analysis procedure is used, 

appropriate vertical, lateral, and rotational soil springs 

shall be incorporated in the analytical model as 

described in Section 4.4.2. The spring characteristics 

shall be as specified in Chapter 4. Rigorous analysis of 

structures with deep foundations in soft soils shall be 

based on special soil/pile interaction studies to 

determine the probable location of the point of fixity in 

the foundation and the resulting distribution of forces 

and displacements in the superstructure. In these 

analyses, the appropriate representation of the 

connection of the pile to the pile cap shall be included in 

the model. Piles with less than six inches of embedment 

without any dowels into the pile cap shall be modeled as 

being “pinned” to the cap. Unless the pile and pile cap 

connection detail is identified as otherwise from the 

available construction documents, the “pinned”

connection shall be used in the analytical model.

When the foundations are included in the analytical 

model, the responses of the foundation components 

shall be considered. The reactions of structural elements 

attached at the foundation (axial loads, shears, and 

moments) shall be used to evaluate the individual 

components of the foundation system.

6.13.3 Evaluation of Existing Condition

Allowable soil capacities (subgrade modulus, bearing 

pressure, passive pressure) and foundation 

displacements for the selected performance level shall 

be as prescribed in Chapter 4 or as established with 

project-specific data. All components of existing 

foundation elements and all new material, components, 

or elements required for rehabilitation shall be 

considered to be force-controlled based on the 

mechanical and analytical properties in Section 6.3.3. 

However, the capacity of the foundation components 

need not exceed 1.25 times the capacity of the 

supported vertical structural component or element 

(column or wall).

6.13.4 Rehabilitation Measures

Existing foundations that do not meet the acceptance 

criteria for the selected Rehabilitation Objective shall 

be rehabilitated. Rehabilitation measures shall meet the 

requirements of Section 6.4.7 and other provisions of 

this standard. 

C6.13.1.2.2 Cast-in-Place Pile Foundations

Segmented steel cylindrical liners are available to form 

the shaft in weak soils and allow the liner to be 

removed as the concrete is placed. Various slurry 

mixes are often used to protect the drilled shaft from 

caving soils. The slurry is then displaced as the 

concrete is placed by the tremie method. C6.13.2 Analysis of Existing Foundations

Overturning moments and economics may dictate the 

use of more rigorous analysis procedures.

C6.13.4 Rehabilitation Measures

Rehabilitation measures described in 

Section C6.13.4.1 for shallow foundations and in 

Section C6.13.4.2 for deep foundations may be 

effective in rehabilitating existing foundations.
6-66 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete

C6.13.4.1 Rehabilitation Measures for Shallow 

Foundations

1. Enlarging the existing footing by lateral 

additions. Enlarging the existing footing may be an 

effective rehabilitation measure. The enlarged 

footing may be considered to resist subsequent 

actions produced by the design loads, provided that 

adequate shear and moment transfer capacity are 

provided across the joint between the existing 

footing and the additions.

2. Underpinning the footing. Underpinning an 

existing footing involves the removal of unsuitable 

soil underneath, coupled with replacement using 

concrete, soil cement, suitable soil, or other 

material. Underpinning should be staged in small 

increments to prevent endangering the stability of 

the structure. This technique may be used to enlarge 

an existing footing or to extend it to a more 

competent soil stratum.

3. Providing tension hold-downs. Tension ties (soil 

and rock anchors—prestressed and unstressed) may 

be drilled and grouted into competent soils and 

anchored in the existing footing to resist uplift. 

Increased soil bearing pressures produced by the 

ties should be checked against the acceptance 

criteria for the selected Performance Level 

specified in Chapter 4. Piles or drilled piers may 

also be effective in providing tension hold-downs 

of existing footings. 

4. Increasing effective depth of footing. This method 

involves pouring new concrete to increase shear 

and moment capacity of the existing footing. The 

new concrete must be adequately doweled or 

otherwise connected so that it is integral with the 

existing footing. New horizontal reinforcement 

should be provided, if required, to resist increased 

moments.

5. Increasing the effective depth of a concrete mat 

foundation with a reinforced concrete overlay. 

This method involves pouring an integral topping 

slab over the existing mat to increase shear and 

moment capacity.

6. Providing pile supports for concrete footings or 

mat foundations. Adding new piles may be 

effective in providing support for existing concrete 

footing or mat foundations, provided the pile 

locations and spacing are designed to avoid 

overstressing the existing foundations.

7. Changing the building structure to reduce the 

demand on the existing elements. This method 

involves removing mass or height of the building or 

adding other materials or components (such as 

energy dissipation devices) to reduce the load 

transfer at the base level. New shear walls or braces 

may be provided to reduce the demand on existing 

foundations.

8. Adding new grade beams. This approach involves 

the addition of grade beams to tie existing footings 

together when poor soil exists, to provide fixity to 

column bases, and to distribute lateral loads 

between individual footings, pile caps, or 

foundation walls.

9. Improving existing soil. This approach involves 

grouting techniques to improve existing soil.

C6.13.4.2 Rehabilitation Measures for Deep 

Foundations

1. Providing additional piles or piers. Providing 

additional piles or piers may be effective, provided 

extension and additional reinforcement of existing 

pile caps comply with the requirements for 

extending existing footings in Section C6.13.4.1.

2. Increasing the effective depth of the pile cap. 

New concrete and reinforcement to the top of the 

pile cap may be effective in increasing its shear and 

moment capacity, provided the interface is designed 

to transfer actions between the existing and new 

materials.

3. Improving soil adjacent to existing pile cap. Soil 

improvement adjacent to existing pile caps may be 

effective if undertaken in accordance with guidance 

provided in Section 4.3. 

4. Increasing passive pressure bearing area of pile 

cap. Addition of new reinforced concrete 

extensions to the existing pile cap may be effective 

in increasing the vertical foundation bearing area 

and load resistance.
 Chapter 6: Concrete

FEMA 356 Seismic Rehabilitation Prestandard 6-67

5. Changing the building system to reduce the 

demands on the existing elements. New lateralload-resisting elements may be effective in 

reducing demand.

6. Adding batter piles or piers. Adding batter piles 

or piers to existing pile or pier foundation may be 

effective in resisting lateral loads. It should be 

noted that batter piles have performed poorly in 

recent earthquakes when liquefiable soils were 

present. This is especially important to consider 

around wharf structures and in areas having a high 

water table. Addition of batter pile to foundations in 

areas of such seismic hazards should be in 

accordance with requirements in [Sections 4.3.2 

and 4.4.2.2B].

7. Increasing tension tie capacity from pile or pier 

to superstructure. Added reinforcement should 

satisfy the requirements of Section 6.4.
6-68 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 6: Concrete
FEMA 356 Seismic Rehabilitation Prestandard 7-1

7. Masonry

7.1 Scope

This chapter sets forth requirements for the Systematic 

Rehabilitation of concrete- or clay-unit masonry lateralforce-resisting elements within a building. The 

requirements of this chapter shall apply to existing 

masonry components of a building system, rehabilitated 

masonry components of a building system, and new 

masonry components that are added to an existing 

building system.

Sections 7.2 and 7.3 specify data collection procedures 

for obtaining material properties and performing 

condition assessments. Sections 7.4 and 7.5 provide 

modeling procedures, component strengths, acceptance 

criteria, and rehabilitation measures for masonry walls 

and masonry infills. Section 7.6 specifies requirements 

for anchorage to masonry walls. Section 7.7 specifies 

requirements for masonry foundation elements. 

7.2 Historical Information

Available construction documents and as-built 

information shall be obtained as specified in 

Section 2.2. Use of material properties based on 

historical information as default values shall be as 

specified in Section 7.3.2.10. Other values of material 

properties shall be permitted if rationally justified, 

based on available historical information for a particular 

type of masonry construction, prevailing codes, and 

assessment of existing conditions.

7.3 Material Properties and 

Condition Assessment

7.3.1 General

Mechanical properties for masonry materials and 

components shall be based on available construction 

documents and as-built conditions for the particular 

structure. Where such information fails to provide 

adequate information to quantify material properties or 

document the condition of the structure, such 

information shall be supplemented by materials tests 

and assessments of existing conditions as required in 

Section 2.2.6.

C7.1 Scope

The provisions of this chapter should be applied to solid 

or hollow clay-unit masonry, solid or hollow concreteunit masonry, and hollow clay tile. Stone or glass block 

masonry is not covered in this chapter.

Portions of masonry buildings that are not subject to 

systematic rehabilitation provisions include parapets, 

cladding, and partition walls.

If the Simplified Rehabilitation Method of Chapter 10 

is followed, unreinforced masonry buildings with 

flexible floor diaphragms may be evaluated using the 

procedures given in FEMA 310.

Techniques for repair of earthquake-damaged masonry 

components are not included in this standard. The 

design professional is referred to FEMA 306, 

FEMA 307, and FEMA 308 for information on 

evaluation and repair of masonry wall components.

C7.2 Historical Information 

Construction of existing masonry buildings in the 

United States dates back to the 1500s in the 

southeastern and southwestern regions, to the 1770s in 

the central and eastern regions, and to the 1850s in the 

western half of the nation. The stock of existing 

masonry buildings in the United States is composed 

largely of structures constructed in the last 150 years. 

Since the types of units, mortars, and construction 

methods changed during this time, knowing the age of a 

masonry building may be useful in identifying the 

characteristics of its construction. Although structural 

properties cannot be inferred solely from age, some 

background on typical materials and methods for a 

given period can help to improve engineering judgment 

and provide some direction in the assessment of an 

existing building. The design professional should be 

aware that values given in some existing documents are 

working stress values rather than expected or lowerbound strengths used in this standard.

As indicated in Chapter 1, great care should be 

exercised in selecting the appropriate rehabilitation 

approaches and techniques for application to historic 

buildings to preserve their unique characteristics.
7-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

Material properties of existing masonry components 

shall be determined in accordance with Section 7.3.2. A 

condition assessment shall be conducted in accordance 

with Section 7.3.3. The extent of materials testing and 

condition assessment performed shall be used to 

determine the knowledge factor as specified in 

Section 7.3.4.

Use of default material properties shall be permitted in 

accordance with Section 7.3.2.10.

Procedures for defining masonry structural systems and 

assessing masonry condition shall be conducted in 

accordance with the provisions stated in Section 7.3.3.

7.3.2 Properties of In-Place Materials

7.3.2.1 General

The following component and connection material 

properties shall be obtained for the as-built structure in 

accordance with Sections 7.3.2.1 through 7.3.2.10:

1. Masonry compressive strength.

2. Masonry tensile strength.

3. Masonry shear strength.

4. Masonry elastic modulus.

5. Masonry shear modulus.

6. Strength and modulus of elasticity of reinforcing 

steel.

When materials testing is required by Section 2.2.6, test 

methods to quantify material properties shall comply 

with Sections 7.3.2.2 through 7.3.2.8. The minimum 

number of tests shall comply with the requirements of 

Section 7.3.2.9.

Expected material properties shall be based on mean 

values from test data. Lower bound material properties 

shall be based on mean values from test data minus one 

standard deviation.

The condition of existing masonry shall be classified as 

good, fair, or poor as defined in this standard, or based 

on other approved procedures that consider the nature 

and extent of damage or deterioration present. 

7.3.2.2 Nominal or Specified Properties

Nominal material properties, or properties specified in 

construction documents, shall be taken as lower-bound 

material properties. Corresponding expected material 

properties shall be calculated by multiplying lowerbound values by a factor as specified in Table 7-2 to 

translate from lower-bound to expected values.

7.3.2.3 Masonry Compressive Strength

Expected masonry compressive strength, fme, shall be 

measured using one of the following three methods.

1. Test prisms shall be extracted from an existing wall 

and tested in accordance with Section 1.4.B.3 of ACI 

530.1/ASCE 6/TMS 602 Specifications for Masonry 

Structures.

2. Prisms shall be fabricated from actual extracted 

masonry units, and a surrogate mortar designed on 

the basis of a chemical analysis of actual mortar 

samples. The test prisms shall be tested in 

C7.3.2.1 General

The design professional is referred to FEMA 306, 

FEMA 307, and FEMA 308 for additional information 

regarding the condition of masonry. The classification 

of the condition of masonry requires consideration of 

the type of component, the anticipated mode of 

inelastic behavior, and the nature and extent of damage 

or deterioration. These documents also contain 

extensive information regarding the effects of damage 

on strength, stiffness, and displacement limits for 

masonry components. Included are damage 

classification guides with visual representations of 

typical earthquake-related damage of masonry 

components, which may be useful in classifying the 

condition of masonry for this standard. The severity of 

damage described in FEMA 306, FEMA 307, and 

FEMA 308 is categorized as Insignificant, Slight, 

Moderate, Heavy, and Extreme. Masonry in good 

condition shall have severity of damage not exceeding 

Insignificant or Slight, as defined by FEMA 306. 

Masonry in fair condition shall have severity of 

damage not exceeding Moderate. Masonry with Heavy 

or Extreme damage shall be classified as Poor.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-3

accordance with Section 1.4.B.3 of ACI 530.1/

ASCE 6/TMS 602.

3. For solid unreinforced masonry, the strength of the 

masonry can be estimated using a flatjack test in 

accordance with ASTM C1196-92.

For each of the three methods enumerated in this 

section, the expected compressive strength shall be 

based on the net mortared area.

If the masonry unit strength and the mortar type are 

known, fme values shall be taken from Tables 1 and 2 of 

ACI 530.1/ASCE 6/TMS 602 for clay or concrete 

masonry constructed after 1960. The fme value shall be 

obtained by multiplying the table values by a factor as 

specified in Table 7-2 to translate lower-bound masonry 

compressive strength to expected strength.

7.3.2.4 Masonry Elastic Modulus in 

Compression

Expected values of elastic modulus for masonry in 

compression, Eme, shall be measured using one of the 

following two methods:

1. Test prisms shall be extracted from an existing wall 

and tested in compression. Stresses and 

deformations shall be measured to determine 

modulus values. 

2. For solid unreinforced masonry, the modulus can be 

measured using a flatjack test in accordance with 

ASTM C1197-92.

7.3.2.5 Masonry Flexural Tensile Strength

Expected flexural tensile strength, fte, for out-of-plane 

bending shall be measured using one of the following 

three methods:

1. Test samples shall be extracted from an existing wall 

and subjected to minor-axis bending using the bondwrench method of ASTM C1072-99.

2. Test samples shall be tested in situ using the bondwrench method.

3. Sample wall panels shall be extracted and subjected 

to minor-axis bending in accordance with ASTM 

E518-00.

Flexural tensile strength for unreinforced masonry 

(URM) walls subjected to in-plane lateral forces shall 

be assumed to be equal to that for out-of-plane bending, 

unless testing is done to define the expected tensile 

strength for in-plane bending.

C7.3.2.3 Masonry Compressive Strength

The three test methods are further described in 

Section C7.3.2.1 of FEMA 274. As an alternative to the 

test methods given in this section of the standard, the 

expected masonry compressive strength may be 

deduced from a nominal value prescribed in 

ACI 530.1/ASCE 6/TMS 602.

Default values of compressive strength are set at very 

low stresses to reflect an absolute lower bound. 

Masonry in poor condition is given a strength equal to 

one-third of that for masonry in good condition, to 

reflect the influence of mortar deterioration and unit 

cracking on compressive strength.

C7.3.2.4 Masonry Elastic Modulus in 

Compression

Both methods measure vertical strain between two gage 

points to infer strain, and thus elastic modulus. They are 

further described in FEMA 274 Section C7.3.2.2. The 

coefficient of 550 for default values in Table 7-1 is set 

lower than values given in IBC (2000) to compensate 

for larger values of expected strength.

C7.3.2.5 Masonry Flexural Tensile Strength

The flexural tensile strength of older brick masonry 

walls constructed with lime mortars may often be 

neglected. The tensile strength of newer concrete- and 

clay-unit masonry walls can result in appreciable 

flexural strengths.
7-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

7.3.2.6 Masonry Shear Strength

For URM components, expected masonry shear 

strength, vme, shall be measured using an approved inplace shear test. Expected shear strength shall be 

determined in accordance with Equation (7-1):

(7-1)

where:

Values for the mortar shear strength, vte , shall not 

exceed 100 psi for the determination of vme in Equation 

(7-1). The 0.75 factor on vte shall not be applied for 

single wythe masonry walls.

Individual bed joint shear strength test values, vto, shall 

be determined in accordance with Equation (7-2):

(7-2)

where: 

The in-place shear test shall not be used to estimate 

shear strength of reinforced masonry components. The 

expected shear strength of reinforced masonry 

components shall be determined in accordance with 

Section 7.4.4.2.

7.3.2.7 Masonry Shear Modulus

The expected shear modulus of masonry (unreinforced 

or reinforced), Gme, shall be permitted to be taken as 0.4 

times the elastic modulus in compression.

7.3.2.8 Strength and Modulus of Reinforcing 

Steel

The expected yield strength of reinforcing bars, fye, 

shall be based on mill test data, or tension tests of actual 

reinforcing bars taken from the subject building. 

Tension tests shall be performed in accordance with 

ASTM A615/A615M-00.

The modulus of elasticity of steel reinforcement, Ese, 

shall be assumed to be 29,000,000 psi.

The three test methods for out-of-plane bending are 

further described in Section C7.3.2.3 of FEMA 274. For 

in-plane bending, flexural stress gradients across the 

section width are much lower than for out-of-plane 

bending. Thus, data from tests described in this section 

will be very conservative and should be used only in 

lieu of data on in-plane tensile strength. Default values 

for flexural tensile strength are set low even for 

masonry in good condition because of its dependence 

on the unit-mortar bonding, which can be highly 

variable due to the variability of the condition of the 

mortar.

PCE = Expected gravity compressive force applied to 

a wall or pier component considering load 

combinations given in Equations (3-18) and 

(3-19)

An = Area of net mortared/grouted section of a wall 

or pier

vte = Average bed-joint shear strength, vto, given in 

Equation (7-2)

vme

0.75 0.75vte

PCE

An

+ ----------

     

1.5 = --------------------------------------------------

vto

Vtest

Ab

----------- PD L + = –

Vtest = Test load at first movement of a masonry unit

Ab = Sum of net mortared area of bed joints above 

and below the test unit

PD+L = Stress due to gravity loads at the test location

C7.3.2.6 Masonry Shear Strength

The available standard for masonry shear strength test 

is UBC 21-6. Section C7.3.2.4 of FEMA 274 further 

describes this test and also an alternate procedure. 

Comparison of default values with values that may be 

obtained from Equation (7-1) shows that if in-place 

shear tests are done, a significant increase in strength 

over default values is possible.

C7.3.2.7 Masonry Shear Modulus

Shear stiffness of post-cracked masonry should be 

taken as a fraction of the initial uncracked masonry 

shear stiffness value. The design professional is 

referred to FEMA 274 Section C7.3.2.5 for additional 

information regarding masonry shear modulus.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-5

7.3.2.9 Minimum Number of Tests

Materials testing is not required if material properties 

are available from original construction documents that 

include material test records or material test reports.

7.3.2.9.1 Usual Testing

The minimum number of tests to determine masonry 

and reinforcing steel material properties for usual data 

collection shall be based on the following criteria:

1. If the specified design strength of the masonry is 

known, and the masonry is in good or fair condition, 

at least one test shall be performed on samples of 

each different masonry strength used in the 

construction of the building, with a minimum of 

three tests performed for the entire building. If the 

masonry is in poor condition, additional tests shall 

be performed to determine the extent of the reduced 

material properties.

2. If the specified design strength of the masonry is not 

known, at least one test shall be performed on each 

type of component, with a minimum of six tests 

performed on the entire building.

3. If the specified design strength of the reinforcing 

steel is known, use of nominal or specified material 

properties shall be permitted without additional 

testing.

4. If the specified design strength of the reinforcing 

steel is not known, at least two strength coupons of 

reinforcing steel shall be removed from a building 

for testing.

7.3.2.9.2 Comprehensive Testing

The minimum number of tests necessary to quantify 

properties by in-place testing for comprehensive data 

collection shall be based on the following criteria:

1. For masonry in good or fair condition as defined in 

this standard, a minimum of three tests shall be 

performed for each masonry type, and for each three 

floors of construction or 3,000 square feet of wall 

surface, if original construction records are available 

that specify material properties; six tests shall be 

performed if original construction records are not 

available. At least two tests shall be performed for 

each wall or line of wall elements providing a 

common resistance to lateral forces. A minimum of 

eight tests shall be performed for each building.

2. For masonry in poor condition as defined in this 

standard, additional tests shall be done to estimate 

material strengths in regions where properties differ, 

or nondestructive condition assessment tests in 

accordance with Section 7.3.3.2 shall be used to 

quantify variations in material strengths.

Samples for tests shall be taken at locations 

representative of the material conditions throughout the 

entire building, taking into account variations in 

workmanship at different story levels, variations in 

weathering of the exterior surfaces, and variations in the 

condition of the interior surfaces due to deterioration 

caused by leaks and condensation of water and/or the 

deleterious effects of other substances contained within 

the building.

An increased sample size shall be permitted to improve 

the confidence level. The relation between sample size 

and confidence shall be as defined in ASTM E139-00.

If the coefficient of variation in test measurements 

exceeds 25%, the number of tests performed shall be 

doubled.

If mean values from in situ material tests are less than 

the default values prescribed in Section 7.3.2.10, the 

number of tests performed shall be doubled.

C7.3.2.9 Minimum Number of Tests

The number and location of material tests should be 

selected to provide sufficient information to adequately 

define the existing condition of materials in the 

building. Test locations should be identified in those 

masonry components that are determined to be critical 

to the primary path of lateral-force resistance.
7-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

7.3.2.10 Default Properties

Use of default material properties to determine 

component strengths shall be permitted with the linear 

analysis procedures in Chapter 3.

Default lower-bound values for masonry compressive 

strength, elastic modulus in compression, flexural 

tensile strength, and masonry shear strength shall be 

based on Table 7-1. Default expected strength values for 

masonry compressive strength, elastic modulus in 

compression, flexural tensile strength, and masonry 

shear strength shall be determined by multiplying 

lower-bound values by an appropriate factor taken from 

Table 7-2.

Default lower-bound and expected strength yield stress 

values for reinforcing bars shall be determined in 

accordance with Section 6.3.2.5.

 

Table 7-1 Default Lower-Bound Masonry Properties

Masonry Condition1

Property Good Fair Poor

Compressive Strength (f’m) 900 psi 600 psi 300 psi

Elastic Modulus in Compression 550f’m 550f’m 550f’m

Flexural Tensile Strength2 20 psi 10 psi 0

Shear Strength3

Masonry with a running bond lay-up 27 psi 20 psi 13 psi

Fully grouted masonry with a lay-up other than running bond 27 psi 20 psi 13 psi

Partially grouted or ungrouted masonry with a lay-up other 

than running bond

11 psi 8 psi 5 psi

1. Masonry condition shall be classified as good, fair, or poor as defined in this standard.

Table 7-2 Factors to Translate Lower-Bound 

Masonry Properties to Expected 

Strength Masonry Properties1

Property Factor

Compressive Strength (fme) 1.3

Elastic Modulus in Compression2 –

Flexural Tensile Strength 1.3

Shear Strength 1.3

1. See Chapter 6 for properties of reinforcing steel.

2. The expected elastic modulus in compression shall be taken as 550fme, 

where fme is the expected masonry compressive strength.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-7

7.3.3 Condition Assessment

A condition assessment of the existing building and site 

conditions shall be performed as specified in 

Sections 7.3.3.1 through 7.3.3.3.

A condition assessment shall include the following:

1. The physical condition of primary and secondary 

components shall be examined and the presence of 

any degradation shall be noted.

2. The presence and configuration of components and 

their connections, and the continuity of load paths 

between components, elements, and systems shall be 

verified or established.

3. Other conditions, including the presence and 

attachment of veneer, neighboring party walls and 

buildings, presence of nonstructural components, 

prior remodeling, and limitations for rehabilitation 

that may influence building performance, shall be 

identified and documented.

The condition of the masonry shall be classified as 

good, fair, or poor as defined in this standard, based on 

the results of visual examination conducted in 

accordance with Section 7.3.3.1.

7.3.3.1 Visual Condition Assessment

The size and location of all masonry shear and bearing 

walls shall be determined by visual examination. The 

orientation and placement of the walls shall be noted. 

Overall dimensions of masonry components shall be 

measured or determined from plans, including wall 

heights, lengths, and thicknesses. Locations and sizes of 

window and door openings shall be measured or 

determined from plans. The distribution of gravity loads 

to bearing walls shall be estimated.

Walls shall be classified as reinforced or unreinforced, 

composite or noncomposite, and grouted, partially 

grouted, or ungrouted. For reinforced masonry (RM) 

construction, the size and spacing of horizontal and 

C7.3.3 Condition Assessment

Buildings are often constructed with veneer as an 

architectural finish, which may make the wall appear 

thicker than the actual structural thickness. In many 

areas of the country, the veneer wythe is separated from 

the structural wall by an air space to provide ventilation 

and moisture control. This is called cavity wall 

construction. In this case, the veneer may be anchored, 

but does not add any strength to the assembly.

In areas of the southwest United States and along the 

California coast (as well as other regions), the veneer is 

placed directly against the building wall. It will be in a 

running bond pattern without a header course. Other 

patterns are also seen. If the veneer is not anchored, or 

has a layer of building paper between it and the inner 

wythe, it cannot be considered as part of the structural 

wall.

Veneer on modern buildings may be adhered or 

anchored. In either case, the veneer is a weight to be 

considered, but does not contribute to a wall’s strength. 

In all cases, the veneer must be anchored to prevent its 

detaching during an earthquake. Requirements for 

veneer are specified in Chapter 11.

Face brick bonded to the inner wythes with a regular 

pattern of header courses is not veneer. In this case, the 

outer wythes are part of the structural wall, and can be 

used in evaluating the height-to-thickness ratio of the 

wall. 

See Section C7.3.2.1 regarding the use of FEMA 306, 

FEMA 307, and FEMA 308 for additional information 

in classifying the condition of masonry.
7-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

vertical reinforcement shall be estimated. For multiwythe construction, the number of wythes shall be 

noted, as well as the distance between wythes, and the 

placement of inter-wythe ties. The condition and 

attachment of veneer wythes shall be noted. For grouted 

construction, the quality of grout placement shall be 

assessed. For partially grouted walls, the locations of 

grout placement shall be identified.

The type and condition of the mortar and mortar joints 

shall be determined. Mortar shall be examined for 

weathering, erosion, and hardness, and to identify the 

condition of any repointing, including cracks, internal 

voids, weak components, and/or deteriorated or eroded 

mortar. Horizontal cracks in bed joints, vertical cracks 

in head joints and masonry units, and diagonal cracks 

near openings shall be noted.

Vertical components that are not straight shall be 

identified. Bulging or undulations in walls shall be 

observed, as well as separation of exterior wythes, outof-plumb walls, and leaning parapets or chimneys.

Connections between masonry walls and floors or roofs 

shall be examined to identify details and condition. If 

construction drawings are available, a minimum of 

three connections shall be inspected for each connection 

type. If no deviations from the drawings are found, the 

sample shall be considered representative. If drawings 

are unavailable, or if deviations are noted between the 

drawings and constructed work, then a random sample 

of connections shall be inspected until a representative 

pattern of connections is identified.

7.3.3.2 Comprehensive Condition 

Assessment

The following nondestructive tests shall be permitted to 

quantify and confirm the uniformity of construction 

quality and the presence and degree of deterioration for 

comprehensive data collection:

1. Ultrasonic or mechanical pulse velocity to detect 

variations in the density and modulus of masonry 

materials and to detect the presence of cracks and 

discontinuities.

2. Impact echo test to confirm whether reinforced walls 

are grouted.

3. Radiography to confirm location of reinforcing steel.

The location and number of nondestructive tests shall 

be determined in accordance with the requirements of 

Section 7.3.2.9.2.

C7.3.3.2 Comprehensive Condition 

Assessment

Nondestructive tests may be used to supplement the 

visual observations required by Section 7.3.3.1.

C7.3.3.2.1 Ultrasonic Pulse Velocity

Measurement of the velocity of ultrasonic pulses 

through a wall can detect variations in the density and 

modulus of masonry materials as well as the presence 

of cracks and discontinuities. Transmission times for 

pulses traveling through a wall (direct method) or 

between two points on the same side of a wall (indirect 

method) are measured and used to infer wave velocity.

Test equipment with wave frequencies in the range of 

50 kHz has been shown to be appropriate for masonry 

walls. Use of equipment with higher frequency waves 

is not recommended because the short wave length and 

high attenuation are not consistent with typical 

dimensions of masonry units. Test locations should be 

sufficiently close to identify zones with different 

properties. Contour maps of direct transmission wave 

velocities can be constructed to assess the overall 

homogeneity of a wall elevation. For indirect test data, 

vertical or horizontal distance can be plotted versus 

travel time to identify changes in wave velocity (slope 

of the curve). Abrupt changes in slope will identify 

locations of cracks or flaws.

Ultrasonic methods are not applicable for masonry of 

poor quality or low modulus, or with many flaws and 

cracks. The method is sensitive to surface condition, 

the coupling material used between the transducer or 

receiver and the brick, and the pressure applied to the 

transducer.

The use of ultrasonic pulse velocity methods with 

masonry walls has been researched extensively by 

Calvi (1988); Epperson and Abrams (1989); Kingsley 

et al. (1987). A standard for the use of ultrasonic 

methods for masonry is currently under development 

in Europe with RILEM Committee 76LUM.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-9

7.3.3.3 Supplemental Tests

Supplemental tests shall be permitted to enhance the 

level of confidence in masonry material properties, or 

the assessment of masonry condition for justifying the 

use of a higher knowledge factor, as specified in 

Section 7.3.4. 

C7.3.3.2.2 Mechanical Pulse Velocity

The mechanical pulse velocity test consists of 

impacting a wall with a hammer blow and measuring 

the travel time of a sonic wave across a specified gage 

distance. An impact hammer is equipped with a load 

cell or accelerometer to detect the time of impact. A 

distant accelerometer is fixed to a wall to detect the 

arrival time of the pulse. Wave velocity is determined 

by dividing the gage length by the travel time. The 

form and duration of the generated wave can be varied 

by changing the material on the hammer cap.

The generated pulse has a lower frequency and higher 

energy content than an ultrasonic pulse, resulting in 

longer travel distances and less sensitivity to small 

variations in masonry properties and minor cracking. 

The mechanical pulse method should be used in lieu of 

the ultrasonic pulse method when overall mean 

properties of a large portion of masonry are of interest.

The use of mechanical pulse velocity measurements 

for masonry condition assessments has been confirmed 

through research by Epperson and Abrams (1989) and 

Kingsley et al. (1987). Although no standard exists for 

mechanical pulse velocity tests with masonry, a 

standard for concrete materials (ASTM C597-97) does 

exist.

C7.3.3.2.3 Impact Echo

The impact-echo technique can be useful for 

nondestructive determination of the location of void 

areas within grouted reinforced walls - Sansalone and 

Carino (1988). Commercial devices are available or 

systems can be assembled using available electronic 

components. Since this technique cannot distinguish 

between a shrinkage crack at the grout-unit interface 

and a complete void in the grout, drilling of small holes 

in the bed joint or examination using an optical 

borescope should be performed to verify the exact 

condition.

C7.3.3.2.4 Radiography

A number of commercial radiographic (x-ray) devices 

exist that can be used to identify the location of 

reinforcing steel in masonry walls. They are also useful 

for locating bed-joint reinforcing steel, masonry ties 

and anchors, and conduits and pipes. The better 

devices can locate a No. 6 bar at depths up to 

approximately six inches; however, this means that for 

a 12-inch-thick concrete masonry wall, a bar located 

off-center cannot be found when access is limited to 

only one side of the wall. These devices are not able to 

locate or determine the length of reinforcing bar splices 

in walls in most cases. They work best for identifying 

the location of single isolated bars and become less 

useful when the congestion of reinforcing bars 

increases.

C7.3.3.3 Supplemental Tests

Ancillary tests are recommended, but not required, to 

enhance the level of confidence in masonry material 

properties, or to assess condition. Possible 

supplemental tests are described below.

C7.3.3.3.1 Surface Hardness

The surface hardness of exterior-wythe masonry can be 

evaluated using the Schmidt rebound hammer. 

Research has shown that the technique is sensitive to 

differences in masonry strength, but cannot by itself be 

used to determine absolute strength. A Type N hammer 

(5000 lb.) is recommended for normal-strength 

masonry, while a Type L hammer (1600 lb.) is 

recommended for lower-strength masonry. Impacts at 

the same test location should be continued until 

consistent readings are obtained, because surface 

roughness can affect initial readings.

The method is limited to tests of only the surface 

wythe. Tuckpointing may influence readings and the 

method is not sensitive to cracks.

Measurement of surface hardness for masonry walls 

has been studied by Noland et al. (1987).
7-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

C7.3.3.3.2 Vertical Compressive Stress

In situ vertical compressive stress resisted by the 

masonry can be measured using a thin hydraulic flat 

jack that is inserted into a removed mortar bed joint. 

Pressure in the flat jack is increased until distortions in 

the brickwork are reduced to the pre-cut condition. 

Existing vertical compressive stress is inferred from 

the jack hydraulic pressure, using correction factors for 

the shape and stiffness of the flat jack.

The method is useful for measurement of gravity load 

distribution, flexural stresses in out-of-plane walls, and 

stresses in masonry veneer walls that are compressed 

by a surrounding concrete frame. The test is limited to 

only the face wythe of masonry.

Not less than three tests should be done for each 

section of the building for which it is desired to 

measure in situ vertical stress. The number and 

location of tests should be determined based on the 

building configuration and the likelihood of overstress 

conditions.

C7.3.3.3.3 Diagonal Compression Test

A square panel of masonry is subjected to a 

compressive force applied at two opposite corners 

along a diagonal until the panel cracks. Shear strength 

is inferred from the measured diagonal compressive 

force based on a theoretical distribution of shear and 

normal stress for a homogeneous and elastic 

continuum. Using the same theory, shear modulus is 

inferred from measured diagonal compressive stress 

and strain.

Extrapolation of the test data to actual masonry walls is 

difficult because the ratio of shear to normal stress is 

fixed at a constant ratio of 1.0 for the test specimens. 

Also, the distribution of shear and normal stresses 

across a bed joint may not be as uniform for a test 

specimen as for an actual wall. Lastly, any 

redistribution of stresses after the first cracking will not 

be represented with the theoretical stress distributions. 

Thus, the test data cannot be useful to predict nonlinear 

behavior.

If the size of the masonry units relative to the panel 

dimension is large, masonry properties will be not 

continuous, but discrete. Test panels should be a 

minimum of four feet square. The high cost and 

disruption of extracting a number of panels this size 

may be impractical. The standard test method specified 

in ASTM E519-81 may be used.

C7.3.3.3.4 Large-Scale Load Tests

[Large-scale destructive tests may be done on portions 

of a masonry component or element to (1) increase the 

confidence level on overall structural properties, (2) 

obtain performance data on archaic building materials 

and construction materials, (3) quantify effects of 

complex edge and boundary conditions around 

openings and two-way spanning, and (4) verify or 

calibrate analytical models. Large-scale load tests do 

not necessarily have to be run to the ultimate limit 

state. They may have value for simply demonstrating 

structural integrity up to some specific Performance 

Level.

Out-of-plane strength and behavior of masonry walls 

can be determined with air-bag tests. Behavior of test 

panels incorporating connections and edge details can 

be determined from such a test, in addition to flexural 

and arching properties of a solid or perforated wall. 

Strength and deformation capacity under in-plane 

lateral forces can be determined by loading an 

individual portion of wall that is cut free of the 

surrounding masonry. Loading actuators are reacted 

against adjacent and stronger portions of masonry. 

Such testing is particularly useful when the wall is 

composed of different materials that cannot be 

evaluated by testing an individual unit of an individual 

wythe.

Visual and nondestructive surveys should be used to 

identify locations for test samples.

Standards for laboratory test methods are published by 

ASTM. Procedures for removal and transportation of 

masonry samples are given in NBS 62.

Large-scale tests are expensive and limited to a single 

or few samples. They may result in considerable local 

damage and may require substantial reconstruction 

near the sample location. Test data must be 

extrapolated to the remainder of the system, based on a 

low confidence level.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-11

7.3.4 Knowledge Factor 

A knowledge factor for computation of masonry 

component capacities and permissible deformations 

shall be selected in accordance with Section 2.2.6.4.

7.4 Engineering Properties of 

Masonry Walls

The procedures set forth in this section for 

determination of stiffness, strength, and deformation of 

masonry walls shall be applied to building systems 

comprising any combination of existing masonry walls, 

masonry walls enhanced for seismic rehabilitation, and 

new walls added to an existing building for seismic 

rehabilitation.

Actions in a structure shall be classified as being either 

deformation-controlled or force-controlled as defined in 

Section 2.4.4.3. Design strengths for deformationcontrolled and force-controlled actions shall be 

calculated in accordance with this section.

Strengths used for deformation-controlled actions are 

denoted QCE and shall be taken as equal to expected 

strengths obtained experimentally, calculated using 

accepted mechanics principles, or based on default 

values listed in Section 7.3.2.10. Expected strength is 

defined as the mean maximum resistance expected over 

the range of deformations to which the component is 

likely to be subjected. When calculations are used to 

define expected strength, expected material properties 

shall be used. Unless otherwise specified in this 

standard, use of procedures specified in IBC (2000) to 

calculate design strengths shall be permitted except that 

the strength reduction factor, φ, shall be taken equal to 

unity.

Force-controlled actions shall be as defined in 

Section 2.4.4. Strengths used in design for forcecontrolled actions are denoted QCL and shall be taken as 

equal to lower bound strengths obtained experimentally, 

calculated using established mechanics principles, or 

based on default values listed in Section 7.3.2.10. 

Lower bound strength is defined as the mean minus one 

standard deviation of resistance over the range of 

deformations and loading cycles to which the 

component is subjected. When calculations are used to 

define lower bound strengths, lower bound material 

properties shall be used. Unless otherwise specified in 

this standard, use of procedures specified in IBC (2000) 

to calculate design strengths shall be permitted except 

that the strength reduction factor, φ, shall be taken equal 

to unity. Where alternative definitions of design 

strength are used, they shall be justified by 

experimental evidence.

Where design actions are determined using the 

nonlinear procedures of Chapter 3, component forcedeformation response shall be represented by nonlinear 

force-deformation relations. Force-deformation 

relations shall be based on experimental evidence or the 

generalized force-deformation relation shown in Figure 

7-1, with parameters c, d, and e as defined in Tables 7-4 

and 7-7. 

Figure 7-1 Generalized Force-Deformation Relation 

for Masonry Elements or Components

C7.4 Engineering Properties of 

Masonry Walls

Expected yield strength of reinforcing steel, as 

specified in this standard, includes consideration of 

material overstrength and strain hardening.

Component drift ratios are the ratio of differential 

displacement, , between each end of the 

component over the effective height, heff, of the 

component. Depending on the geometry of the wall or 

pier configuration, the elevations at which these 

parameters are determined may vary within the same 

wall element, as shown in Figure C7-1.

∆eff
7-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

7.4.1 Types of Masonry Walls

Masonry walls shall be categorized as unreinforced or 

reinforced; ungrouted, partially grouted, or fully 

grouted; and composite or noncomposite. Masonry 

walls shall be capable of resisting forces applied 

parallel to their plane and normal to their plane, as 

described in Sections 7.4.2 through 7.4.5.

7.4.1.1 Existing Masonry Walls

Existing masonry walls shall include all structural walls 

of a building system that are in place prior to seismic 

rehabilitation.

Existing masonry walls shall be assumed to behave in 

the same manner as new masonry walls, provided that 

the masonry is in fair or good condition as defined in 

this standard.

7.4.1.2 New Masonry Walls

New masonry walls shall include all new wall elements 

added to an existing lateral force-resisting system. 

Design of new walls shall follow the requirements set 

forth in an approved building code.

7.4.1.3 Enhanced Masonry Walls

Enhanced masonry walls shall include existing walls 

that are rehabilitated by an approved method. 

Figure C7-1 Effective Height and Differential 

Displacement of Wall Components

C7.4.1 Types of Masonry Walls

Any of these categories of masonry elements can be 

used in combination with existing, rehabilitated, or new 

lateral-force-resisting elements of other materials such 

as steel, concrete, or timber.

C7.4.1.2 New Masonry Walls

Codes for new buildings include the International 

Building Code (IBC), National Building Code (NBC), 

Standard Building Code (SBC), and the Uniform 

Building Code (UBC). Guidelines for seismic design of 

new buildings are found in FEMA 302.

C7.4.1.3 Enhanced Masonry Walls

Methods of enhancing masonry walls are intended to 

improve performance of masonry walls subjected to 

both in-plane and out-of-plane lateral forces.

Possible rehabilitation methods are described in 

Sections C7.4.1.3.1 through C7.4.1.3.10.

C7.4.1.3.1 Infilled Openings

An infilled opening may be considered to act 

compositely with the surrounding masonry if new and 

old masonry units are interlaced at the boundary with 

full toothing, or attached with anchorage that provides 

compatible shear strength at the interface of new and 

old units.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-13

Stiffness assumptions, strength criteria, and acceptable 

deformations for masonry walls with infilled openings 

should be the same as given for non-rehabilitated solid 

masonry walls; differences in elastic moduli and 

strengths for the new and old masonry walls should be 

considered for the composite section.

C7.4.1.3.2 Enlarged Openings

Openings in URM shear walls may be enlarged by 

removing portions of masonry above or below windows 

or doors.

Openings are enlarged to increase the height-to-length 

aspect ratio of piers so that the limit state may be 

altered from shear to flexure. This method is only 

applicable to URM walls.

Stiffness assumptions, strength criteria, and acceptable 

deformations for URM walls with enlarged openings 

shall be reassessed to reflect the final condition of the 

wall.

C7.4.1.3.3 Shotcrete

An existing masonry wall with an application of 

shotcrete may be considered to behave as a composite 

section if anchorage is provided at the shotcretemasonry interface to transfer the shear forces calculated 

in accordance with Chapter 3. Stresses in the masonry 

and shotcrete should be determined considering the 

difference in elastic moduli for each material, or the 

existing masonry wall should be neglected and the new 

shotcrete layer should be designed to resist all of the 

force.

Stiffness assumptions, strength criteria, and acceptable 

deformations for masonry components with shotcrete 

should be the same as that for new reinforced concrete 

components. Variations in boundary conditions should 

be considered.

C7.4.1.3.4 Coatings for Unreinforced Masonry Walls

A coated masonry wall may be considered a composite 

section as long as anchorage is provided at the interface 

between the coating and the masonry wall to transfer 

shear forces. Stresses in the masonry and coating 

should be determined considering the difference in 

elastic moduli for each material. If stresses exceed 

expected strengths of the coating material, then the 

coating should be considered ineffective.

Stiffness assumptions, strength criteria, and acceptable 

deformations for coated masonry walls should be the 

same as that for existing URM walls.

C7.4.1.3.5 Reinforced Cores for Unreinforced 

Masonry Walls

A reinforced-cored masonry wall should be considered 

to behave as a reinforced masonry wall, provided that 

the bond between the new reinforcement and the grout 

and between the grout and the cored surface are capable 

of transferring seismic forces computed in accordance 

with Chapter 3. Vertical reinforcement should be 

anchored at the base of the wall to resist the full tensile 

strength of the wall.

Grout in new reinforced cores should consist of 

cementitious materials whose hardened properties are 

compatible with those of the surrounding masonry.

Adequate shear strength must exist, or should be 

provided, so that the strength of the new vertical 

reinforcement can be developed.

Stiffness assumptions, strength criteria, and acceptable 

deformations for URM walls with reinforced cores 

should be the same as that for existing reinforced walls.

C7.4.1.3.6 Prestressed Cores for Unreinforced 

Masonry Walls

A prestressed-cored masonry wall with unbonded 

tendons should be considered to behave as a URM wall 

with increased vertical compressive stress.

Losses in prestressing force due to creep and shrinkage 

of the masonry should be accounted for in analyses 

conducted in accordance with Chapter 3.

Stiffness assumptions, strength criteria, and acceptable 

deformations for URM walls with unbonded 

prestressing tendons should be the same as for existing 

unreinforced masonry walls subjected to vertical 

compressive stress.

C7.4.1.3.7 Grout Injections

Grout used for filling voids and cracks should have 

strength, modulus, and thermal properties compatible 

with the existing masonry.

Inspections should be conducted in accordance with 

Chapter 2 during the grouting process to ensure that 

voids are completely filled with grout.
7-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

7.4.2 Unreinforced Masonry Walls and 

Piers In-Plane 

Engineering properties of unreinforced masonry (URM) 

walls subjected to lateral forces applied parallel to their 

plane shall be determined in accordance with this 

section. Requirements of this section shall apply to 

cantilevered shear walls that are fixed against rotation at 

their base, and piers between window or door openings 

that are fixed against rotation top and bottom.

Stiffness and strength criteria presented in this section 

shall apply to both the Linear Static and Nonlinear 

Static Procedures prescribed in Chapter 3.

7.4.2.1 Stiffness

The lateral stiffness of masonry walls subjected to 

lateral in-plane forces shall be determined considering 

both flexural and shear deformations.

The masonry assemblage of units, mortar, and grout 

shall be considered to be a homogeneous medium for 

stiffness computations with an expected elastic modulus 

in compression, Eme, as specified in Section 7.3.2.4.

For linear procedures, the stiffness of a URM wall or 

pier resisting lateral forces parallel to its plane shall be 

considered to be linear and proportional with the 

geometrical properties of the uncracked section 

excluding veneer wythes.

Story shears in perforated shear walls shall be 

distributed to piers in proportion to the relative lateral 

uncracked stiffness of each pier.

Stiffnesses for existing and enhanced walls shall be 

determined using principles of mechanics used for new 

walls. 

Stiffness assumptions, strength criteria, and acceptable 

deformations for masonry walls with grout injections 

should be the same as that for existing unreinforced or 

reinforced walls.

C7.4.1.3.8 Repointing

Bond strength of new mortar should be equal to or 

greater than that of the original mortar. Compressive 

strength of new mortar should be equal to or less than 

that of the original mortar.

Stiffness assumptions, strength criteria, and acceptable 

deformations for repointed masonry walls should be the 

same as that for existing masonry walls.

C7.4.1.3.9 Braced Masonry Walls

Masonry walls with height-to-thickness ratios in excess 

of those permitted by Table 7-5, or out-of-plane 

bending stresses in excess of those permitted by 

Section 7.4.3.2, may be braced with external structural 

elements. Adequate strength should be provided in the 

bracing element and connections to resist the transfer of 

forces from the masonry wall to the bracing element. 

Out-of-plane deflections of braced walls resulting from 

the transfer of vertical floor or roof loadings should be 

considered.

Stiffness assumptions, strength criteria, and acceptable 

deformations for braced masonry walls should be the 

same as that for existing masonry walls. The reduced 

span of the masonry wall should be considered.

C7.4.1.3.10 Stiffening Elements

Masonry walls with inadequate out-of-plane stiffness or 

strength may be stiffened with external structural 

members. The stiffening members should be 

proportioned to resist a tributary portion of lateral load 

applied normal to the plane of a masonry wall. 

Connections at the ends of the stiffening element 

should be provided to transfer the reaction force. 

Flexibility of the stiffening element should be 

considered when estimating lateral drift of a masonry 

wall panel.

Stiffness assumptions, strength criteria, and acceptable 

deformations for stiffened masonry walls should be the 

same as that for existing masonry walls. The stiffening 

action that the new element provides shall be 

considered.

C7.4.1.3.11 Veneer Attachment

Veneer not bonded to the structural core of a masonry 

wall may be rehabilitated by the use of pins inserted 

through the joints and into the brick substrate. Spacing 

of pins should match current code requirements given 

the seismicity of the region.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-15

7.4.2.2 Strength

7.4.2.2.1 Expected Lateral Strength of 

Unreinforced Masonry Walls and Piers

Expected lateral strength, QCE , of existing and 

enhanced URM walls or pier components shall be the 

lesser of the lateral strength based on expected bed-joint 

sliding shear strength or expected rocking strength, 

calculated in accordance with Equations (7-3) and 

(7-4), respectively: 

(7-3)

(7-4)

where:

7.4.2.2.2 Lower Bound Lateral Strength of 

Unreinforced Masonry Walls and Piers

Lower bound lateral strength, QCL, of existing and 

enhanced URM walls or pier components shall be taken 

as the lesser of the lateral strength values based on 

diagonal tension stress or toe compressive stress 

calculated in accordance with Equations (7-5) and 

(7-6), respectively. L / heff shall not be taken less than 

0.67 for use in Equation (7-6).

(7-5)

(7-6)

C7.4.2.1 Stiffness

Laboratory tests of solid shear walls have shown that 

behavior can be depicted at low force levels using 

conventional principles of mechanics for homogeneous 

materials. In such cases, the lateral in-plane stiffness of 

a solid cantilevered shear wall, k, can be calculated 

using Equation (C7-1):

(C7-1)

where:

heff = Wall height

A

v = Shear area

Ig = Moment of inertia for the gross section 

representing uncracked behavior

E

m = Masonry elastic modulus

G

m = Masonry shear modulus

Correspondingly, the lateral in-plane stiffness of a pier 

between openings with full restraint against rotation at 

its top and bottom can be calculated using Equation 

(C7-2):

(C7-2)

The design professional should be aware that a 

completely fixed condition is often not present in 

actual buildings.

k 1

heff

3

3EmIg

--------------- heff

AvGm

+ --------------

= ------------------------------------

k 1

heff

3

12EmIg

------------------ heff

AvGm

+ --------------

= ---------------------------------------

An = Area of net mortared/grouted section

heff = Height to resultant of lateral force

L = Length of wall or pier

PE = Expected axial compressive force due to 

gravity loads specified in Equation (3-3)

vme = Expected bed-joint sliding shear strength in 

accordance with Section 7.3.2.6

Vbjs = Expected shear strength of wall or pier based 

on bed-joint sliding shear strength

Vr = Strength of wall or pier based on rocking

α = Factor equal to 0.5 for fixed-free cantilever 

wall, or equal to 1.0 for fixed-fixed pier

QCE Vbjs vmeAn = =

QCE Vr 0.9αPE

L

heff

--------     = =

QCL Vdt f ′

dt An

L

heff

--------     1 f

a

f ′

dt

= = + -------

QCL Vtc αPL

L

heff

--------     1

f

a

0.7f ′

m

– --------------

      = =
7-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

where An, heff, L, and α are the same as given for 

Equations (7-3) and (7-4), and:

Substitution of the bed-joint shear strength, vme, for the 

diagonal tension strength, , in Equation (7-5) shall 

be permitted.

The lower bound masonry compressive strength, , 

shall be taken as the expected strength, fme , determined 

in accordance with Section 7.3.2.3, divided by 1.6.

7.4.2.2.3 Lower Bound Vertical Compressive 

Strength of Unreinforced Masonry Walls 

and Piers

Lower bound vertical compressive strength of existing 

URM walls or pier components shall be limited by 

lower bound masonry compressive stress in accordance 

with Equation (7-7):

(7-7)

where is equal to the lower bound compressive 

strength determined in accordance with Section 7.3.2.3.

7.4.2.3 Acceptance Criteria

Unreinforced masonry walls and piers shall be 

considered deformation-controlled components if their 

expected lateral strength limited by bed-joint sliding 

shear stress or rocking, as specified in Section 7.4.2.2.1, 

is less than the lower bound lateral strength limited by 

diagonal tension or toe compressive stress, as specified 

in Section 7.4.2.2.2. Unreinforced masonry walls not 

meeting the criteria for deformation-controlled 

components shall be considered force-controlled 

components. Axial compression on URM wall 

components shall be considered force-controlled.

7.4.2.3.1 Linear Procedures

For the linear procedures in Sections 3.3.1 and 3.3.2, 

component actions shall be compared with capacities in 

accordance with Section 3.4.2.2. The expected strength, 

QCE, for use in Equation (3-20) for components 

classified as deformation-controlled, shall be the lower 

of the two expected strengths as determined from 

Equations (7-3) and (7-4). The m-factors for use with 

corresponding expected strength shall be obtained from 

Table 7-3. 

fa = Axial compressive stress due to gravity loads 

specified in Equation (3-3)

f ′

dt = Lower bound masonry diagonal tension 

strength

f ′m = Lower bound masonry compressive strength

PL = Lower bound axial compressive force due to 

gravity loads specified in Equation (3-4)

Vdt = Lower bound shear strength based on diagonal 

tension stress for wall or pier

Vtc = Lower bound shear strength based on toe 

compressive stress for wall or pier

f ′

dt

f ′

m

QCL PCL 0.80 0.85f ′

m An = = ( )

f ′

m

Table 7-3 Linear Static Procedure—m-factors for URM In-Plane Walls and Piers

m-factors

Performance Level

Limiting 

Behavioral Mode

IO

Primary Secondary

LS CP LS CP

Bed-Joint Sliding 1 3 4 6 8

Rocking 1.5heff/L

(not less than 1)

3heff/L

(not less than 1.5)

4heff/L

(not less than 2)

6heff/L

(not less than 3)

8heff/L

(not less than 4)

Interpolation shall be used between table values.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-17

For determination of m-factors from Table 7-3, the 

vertical compressive stress, fae, shall be based on an 

expected value of gravity compressive force given by 

the load combination in Equation (3-3).

7.4.2.3.2 Nonlinear Procedures

For the Nonlinear Static Procedure given in 

Section 3.3.3, wall and pier components shall meet the 

requirements of Section 3.4.3.2. For deformationcontrolled components, nonlinear deformations shall 

not exceed the values given in Table 7-4. Variables d

and e, representing nonlinear deformation capacities for 

primary and secondary components, shall be expressed 

in terms of drift ratio percentages as defined in Figure 

7-1. The limiting behavior mode in Table 7-4 shall be 

identified from the lower of the two expected strengths 

as determined from Equations (7-3) and (7-4). .

For the Nonlinear Dynamic Procedure given in 

Section 3.3.4, wall and pier components shall meet the 

requirements of Section 3.4.3.2. Nonlinear forcedeflection relations for deformation-controlled wall and 

pier components shall be established based on the 

information given in Table 7-4, or an approved 

procedure based on a comprehensive evaluation of the 

hysteretic characteristics of those components.

7.4.3 Unreinforced Masonry Walls 

Out-of-Plane

As required by Section 2.6.7, URM walls shall be 

evaluated for out-of-plane inertial forces as isolated 

components spanning between floor levels, and/or 

spanning horizontally between columns or pilasters. 

URM walls shall not be analyzed out-of-plane with the 

Linear or Nonlinear Static Procedures prescribed in 

Chapter 3.

7.4.3.1 Stiffness

The out-of-plane stiffness of walls shall be neglected in 

analytical models of the global structural system in the 

orthogonal direction.

7.4.3.2 Strength

Unless arching action is considered, flexural cracking 

shall be limited by the expected tensile stress values 

given in Section 7.3.2.5.

Arching action shall be considered only if surrounding 

floor, roof, column, or pilaster elements have sufficient 

stiffness and strength to resist thrusts from arching of a 

wall panel, and a condition assessment has been 

performed to ensure that there are no gaps between a 

wall panel and the adjacent structure.

The condition of the collar joint shall be considered 

when estimating the effective thickness of a wall for 

out-of-plane behavior. The effective void ratio shall be 

taken as the ratio of the collar joint area without mortar 

to the total area of the collar joint. Wythes separated by 

collar joints that are not bonded, or have an effective 

Table 7-4 Nonlinear Static Procedure—Simplified Force-Deflection Relations for URM In-Plane Walls 

and Piers

Acceptance Criteria

Limiting Behavioral 

Mode

Performance Level

IO

%

Primary Secondary

c

%

d

%

e

%

LS

%

CP

%

LS

%

CP

%

Bed-Joint Sliding 0.6 0.4 0.8 0.1 0.3 0.4 0.6 0.8

Rocking 0.6 0.4heff /L 0.8heff /L 0.1 0.3heff /L 0.4heff /L 0.6heff /L 0.8heff /L

Interpolation shall be used between table values. 
7-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

void ratio greater than 50% shall not be considered part 

of the effective thickness of the wall.

7.4.3.3 Acceptance Criteria

For the Immediate Occupancy Structural Performance 

Level, flexural cracking in URM walls due to out-ofplane inertial loading shall not be permitted as limited 

by the tensile stress requirements of Section 7.4.3.2. For 

the Life Safety and Collapse Prevention Structural 

Performance Levels, flexural cracking in URM walls 

due to out-of-plane inertial loading shall be permitted 

provided that cracked wall segments will remain stable 

during dynamic excitation. Stability shall be checked 

using analytical time-step integration models 

considering acceleration time histories at the top and 

base of a wall panel. For the Life Safety and Collapse 

Prevention Structural Performance Levels, stability 

need not be checked for walls spanning vertically with a 

height-to-thickness (h/t) ratio less than that given in 

Table 7-5.

7.4.4 Reinforced Masonry Walls and Piers 

In-Plane

7.4.4.1 Stiffness 

The stiffness of a reinforced masonry wall or pier 

component in-plane shall be determined as follows:

1. The shear stiffness of RM wall components shall be 

based on uncracked section properties.

2. The flexural stiffness of RM wall components shall 

be based on cracked section properties. Use of a 

cracked moment of inertia equal to 50 percent of Ig

shall be permitted.

In either case, veneer wythes shall not be considered in 

the calculation of wall component properties. 

Stiffnesses for existing and new walls shall be assumed 

to be the same.

7.4.4.2 Strength

The strength of RM wall or pier components in flexure, 

shear, and axial compression shall be determined in 

accordance with the requirements of this section. The 

assumptions, procedures, and requirements of this 

section shall apply to both existing and new RM wall or 

pier components.

7.4.4.2.1 Flexural Strength of Walls and Piers

Expected flexural strength of an RM wall or pier shall 

be determined based on the following assumptions:

1. Stress in reinforcement below the expected yield 

strength, fye, shall be taken as the expected modulus 

of elasticity, Ese, times the steel strain. For 

reinforcement strains larger than those 

corresponding to the expected yield strength, the 

stress in the reinforcement shall be considered 

independent of strain and equal to the expected yield 

strength, fye.

2. Tensile strength of masonry shall be neglected when 

calculating the flexural strength of a reinforced 

masonry cross-section.

3. Flexural compressive stress in masonry shall be 

assumed to be distributed across an equivalent 

rectangular stress block. Masonry stress of 0.85 

times the expected compressive strength, fme, shall 

be distributed uniformly over an equivalent 

C7.4.3.2 Strength

This section applies to treatment of veneer for out-ofplane behavior of walls only. For in-plane resistance, 

effective thickness is the sum of all wythes without 

consideration of the condition of the collar joints.

C7.4.3.3 Acceptance Criteria

For further information on evaluating the stability of 

unreinforced masonry walls out-of-plane, refer to ABK

(1984).

Table 7-5 Permissible h/t Ratios for URM 

Out-of-Plane Walls

Wall Types

SX1

≤0.24g

0.24g<SX1

≤0.37g

SX1

>0.37g

Walls of one-story 

buildings

20 16 13

First-story wall of 

multistory building

20 18 15

Walls in top story of 

multistory building

14 14 9

All other walls 20 16 13
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-19

compression zone bounded by the edge of the 

cross-section and a depth equal to 85% of the depth 

from the neutral axis to the extreme fiber of the 

cross-section.

4. Strains in the reinforcement and masonry shall be 

considered linear through the cross-section. For 

purposes of determining forces in reinforcing bars 

distributed across the section, the maximum 

compressive strain in the masonry shall be assumed 

to be equal to 0.003.

7.4.4.2.2 Shear Strength of Walls and Piers

The lower-bound shear strength of RM wall or pier 

components, VCL, shall be determined using Equation 

(7-8):

(7-8)

where:

The lower bound shear strength of an RM wall or pier, 

VCL, shall not exceed the value computed in accordance 

with Equations (7-9) and (7-10). For intermediate 

values of M/Vdv, interpolation shall be used.

For M/Vdv less than 0.25:

(7-9)

For M/Vdv greater than or equal to 1.00:

(7-10)

where:

The lower-bound shear strength, VmL, provided by the 

masonry shall be determined using Equation (7-11):

(7-11)

where M/Vdv shall be limited to 1.0, and PL is the 

lower-bound vertical compressive force in pounds due 

to gravity loads, specified in Equation (3-4).

The lower-bound shear strength, VsL, resisted by the 

reinforcement shall be determined using Equation 

(7-12):

(7-12)

where:

For RM walls or piers in which shear is considered a 

deformation-controlled action, expected shear strength, 

VCE, shall be calculated using Equations (7-8) through 

(7-12) substituting expected material properties in lieu 

of lower-bound.

7.4.4.2.3 Strength Considerations for Flanged 

Walls

Wall intersections shall be considered effective in 

transferring shear when either condition (1) or (2) and 

condition (3) are met:

1. The face shells of hollow masonry units are removed 

and the intersection is fully grouted.

2. Solid units are laid in running bond, and 50% of the 

masonry units at the intersection are interlocked.

3. Reinforcement from one intersecting wall continues 

past the intersection a distance not less than 40 bar 

diameters or 24 inches.

The width of flange considered effective in 

compression on each side of the web shall be taken as 

the lesser of six times the thickness of the web, half the 

VmL = Lower bound shear strength provided by 

masonry

VsL = Lower bound shear strength provided by 

reinforcement

An = Area of net mortared/grouted section

f ′m = Lower bound compressive strength of 

masonry

M = Moment on the masonry section

V = Shear on the masonry section

dv = Wall length in direction of shear force

QCL VCL VmL VsL = = +

VCL 6 f ′

m An ≤

VCL 4 f ′

m An ≤

Av = Area of shear reinforcement

s = Spacing of shear reinforcement

fy = Lower bound yield strength of shear 

reinforcement

VmL 4.0 1.75 M

Vdv

---------     – An f ′

m 0.25PL = +

VsL 0.5

Av

s

-----    f

ydv =
7-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

distance to the next web, or the actual flange on either 

side of the web wall.

The width of flange considered effective in tension on 

each side of the web shall be taken as the lesser of 3/4 of 

the wall height, half the distance to an adjacent web, or 

the actual flange on either side of the web wall.

7.4.4.2.4 Vertical Compressive Strength of Walls 

and Piers

Lower bound vertical compressive strength of existing 

RM wall or pier components shall be determined using 

Equation (7-13):

(7-13)

where: 

7.4.4.3 Acceptance Criteria

The shear required to develop the expected strength of 

reinforced masonry walls and piers in flexure shall be 

compared to the lower bound shear strength defined in 

Section 7.4.4.2.2. For reinforced masonry wall 

components governed by flexure, flexural actions shall 

be considered deformation-controlled. For reinforced 

masonry components governed by shear, shear actions 

shall be considered deformation-controlled. Axial 

compression on reinforced masonry wall or pier 

components shall be considered force-controlled. 

Expected strength in flexure shall be determined in 

accordance with Section 7.4.4.2.1, and lower bound 

strength in axial compression shall be determined in 

accordance with Section 7.4.4.2.4.

7.4.4.3.1 Linear Procedures

For the linear procedures of Section 3.3.2, component 

actions shall be compared with capacities in accordance 

with Section 3.4.2.2. The m-factor for use in Equation 

(3-20) for those components classified as deformationcontrolled shall be as specified in Table 7-6. 

For determination of m-factors from Table 7-6, the ratio 

of vertical compressive stress to expected compressive 

strength, fae / fme, shall be based on gravity compressive 

force determined in accordance with the load 

combinations given in Equations (3-3) and (3-4). 

7.4.4.3.2 Nonlinear Procedures

For the Nonlinear Static Procedure of Section 3.3.3, 

wall and pier components shall meet the requirements 

of Section 3.4.3.2. Nonlinear deformations on 

deformation-controlled components shall not exceed 

the values given in Table 7-7. Variables d and e, 

representing nonlinear deformation capacities for 

primary and secondary components, shall be expressed 

in terms of story drift ratio percentages as defined in 

Figure 7-1.

For determination of the c, d, and e values and the 

acceptable drift levels using Table 7-7, the vertical 

compressive stress, fae, shall be based on gravity 

compressive force determined in accordance with the 

load combinations given in Equations (3-3) and (3-4).

For the Nonlinear Dynamic Procedure of Section 3.3.4, 

wall and pier components shall meet the requirements 

of Section 3.4.3.2. Nonlinear force-deflection relations 

for deformation-controlled wall and pier components 

shall be established based on the information given in 

Table 7-7, or an approved procedure based on 

comprehensive evaluation of the hysteretic 

characteristics of those components.

Acceptable deformations for existing and new walls 

shall be assumed to be the same. 

= Lower bound masonry compressive strength 

determined in accordance with 

Section 7.3.2.3

fy = Lower bound reinforcement yield strength 

determined in accordance with 

Section 7.3.2.8

QCL PCL 0.8 0.85f ′

m An As ( ) – As fy = = [ ] +

f ′

m

C7.4.4.3.2 Nonlinear Procedures

For primary components, collapse is considered at 

lateral drift percentages exceeding values of d in Table 

7-7, and the Life Safety Structural Performance Level is 

considered at approximately 75% of d. For secondary 

components, collapse is considered at lateral drift 

percentages exceeding the values of e in the table, and 

the Life Safety Structural Performance Level is 

considered at approximately 75% of e. Story drift ratio 

percentages based on these criteria are given in Table 

7-7.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-21

Table 7-6 Acceptance Criteria for Linear Procedures—Reinforced Masonry In-Plane Walls 

fae /fme L/heff ρgfye/fme

m-factors1

Performance Level

IO

Component Type

Primary Secondary

LS CP LS CP

Wall Components Controlled by Flexure

0.00 ≤ 0.5 0.01 4.0 7.0 8.0 8.0 10.0

0.05 2.5 5.0 6.5 8.0 10.0

0.20 1.5 2.0 2.5 4.0 5.0

1.0 0.01 4.0 7.0 8.0 8.0 10.0

0.05 3.5 6.5 7.5 8.0 10.0

0.20 1.5 3.0 4.0 6.0 8.0

≥ 2.0 0.01 4.0 7.0 8.0 8.0 10.0

0.05 3.5 6.5 7.5 8.0 10.0

0.20 2.0 3.5 4.5 7.0 9.0

0.038 ≤ 0.5 0.01 3.0 6.0 7.5 8.0 10.0

0.05 2.0 3.5 4.5 7.0 9.0

0.20 1.5 2.0 2.5 4.0 5.0

1.0 0.01 4.0 7.0 8.0 8.0 10.0

0.05 2.5 5.0 6.5 8.0 10.0

0.20 1.5 2.5 3.5 5.0 7.0

≥ 2.0 0.01 4.0 7.0 8.0 8.0 10.0

0.05 3.5 6.5 7.5 8.0 10.0

0.20 1.5 3.0 4.0 6.0 8.0

0.075 ≤ 0.5 0.01 2.0 3.5 4.5 7.0 9.0

0.05 1.5 3.0 4.0 6.0 8.0

0.20 1.0 2.0 2.5 4.0 5.0

1.0 0.01 2.5 5.0 6.5 8.0 10.0

0.05 2.0 3.5 4.5 7.0 9.0

0.20 1.5 2.5 3.5 5.0 7.0

≥ 2.0 0.01 4.0 7.0 8.0 8.0 10.0

0.05 2.5 5.0 6.5 8.0 10.0

0.20 1.5 3.0 4.0 4.0 8.0

Wall Components Controlled by Shear

All cases2 All cases2 All cases2 2.0 2.0 3.0 2.0 3.0

1. Interpolation shall be used between table values.

2. For wall components governed by shear, the axial load on the member must be less than or equal to 0.15 Agf′m, otherwise the component shall be treated 

as force-controlled.
7-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

Table 7-7 Modeling Parameters and Acceptance Criteria for Nonlinear Procedures—Reinforced 

Masonry In-plane Walls

fae / fme L / heff ρgfye / fme c

d

%

e

%

Acceptable Drift Ratio (%)1

Performance Level

IO

%

Component Type

Primary Secondary

LS

%

CP

%

LS

%

CP

%

Wall Components Controlled by Flexure

0.00 ≤ 0.5 0.01 0.5 2.6 5.3 1.0 2.0 2.6 3.9 5.3

0.05 0.6 1.1 2.2 0.4 0.8 1.1 1.6 2.2

0.20 0.7 0.5 1.0 0.2 0.4 0.5 0.7 1.0

1.0 0.01 0.5 2.1 4.1 0.8 1.6 2.1 3.1 4.1

0.05 0.6 0.8 1.6 0.3 0.6 0.8 1.2 1.6

0.20 0.7 0.3 0.6 0.1 0.2 0.3 0.5 0.6

≥ 2.0 0.01 0.5 1.6 3.3 0.6 1.2 1.6 2.5 3.3

0.05 0.6 0.6 1.3 0.2 0.5 0.6 0.9 1.3

0.20 0.7 0.2 0.4 0.1 0.2 0.2 0.3 0.4

0.038 ≤ 0.5 0.01 0.4 1.0 2.0 0.4 0.8 1.0 1.5 2.0

0.05 0.5 0.7 1.4 0.3 0.5 0.7 1.0 1.4

0.20 0.6 0.4 0.9 0.2 0.3 0.4 0.7 0.9

1.0 0.01 0.4 0.8 1.5 0.3 0.6 0.8 1.1 1.5

0.05 0.5 0.5 1.0 0.2 0.4 0.5 0.7 1.0

0.20 0.6 0.3 0.6 0.1 0.2 0.3 0.4 0.6

≥ 2.0 0.01 0.4 0.6 1.2 0.2 0.4 0.6 0.9 1.2

0.05 0.5 0.4 0.7 0.1 0.3 0.4 0.5 0.7

0.20 0.6 0.2 0.4 0.1 0.1 0.2 0.3 0.4

0.075 ≤ 0.5 0.01 0.3 0.6 1.2 0.2 0.5 0.6 0.9 1.2

0.05 0.4 0.5 1.0 0.2 0.4 0.5 0.8 1.0

0.20 0.5 0.4 0.8 0.1 0.3 0.4 0.6 0.8

1.0 0.01 0.3 0.4 0.9 0.2 0.3 0.4 0.7 0.9

0.05 0.4 0.4 0.7 0.1 0.3 0.4 0.5 0.7

0.20 0.5 0.2 0.5 0.1 0.2 0.2 0.4 0.5

≥ 2.0 0.01 0.3 0.3 0.7 0.1 0.2 0.3 0.5 0.7

0.05 0.4 0.3 0.5 0.1 0.2 0.3 0.4 0.5

0.20 0.5 0.2 0.3 0.1 0.1 0.2 0.2 0.3

Wall Components Controlled by Shear

All cases2 All cases2 All cases2 0.4 0.75 2.0 0.4 0.6 0.75 0.75 1.5

1. Interpolation shall be used between table values.

2. For wall components governed by shear, the axial load on the member must be less than or equal to 0.15 Agf′m, otherwise the component shall be treated as force-controlled.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-23

7.4.5 Reinforced Masonry Walls 

Out-of-Plane

Reinforced masonry (RM) walls shall be capable of 

resisting out-of-plane inertial forces as isolated 

components spanning between floor levels, and/or 

spanning horizontally between columns or pilasters. 

Walls shall not be analyzed out-of-plane with the Linear 

or Nonlinear Static Procedures prescribed in Chapter 3, 

but shall be capable of resisting out-of-plane inertial 

forces as given in Section 2.6.7, or be capable of 

responding to earthquake motions as determined using 

the Nonlinear Dynamic Procedure, while satisfying the 

deflection criteria given in Section 7.4.5.3.

7.4.5.1 Stiffness

RM walls shall be considered local elements spanning 

out-of-plane between individual story levels.

The out-of-plane stiffness of walls shall be neglected in 

analytical models of the global structural system.

Stiffness shall be based on the net mortared/grouted 

area of the uncracked section, provided that net flexural 

tensile stress does not exceed the expected tensile 

strength, fte, in accordance with Section 7.3.2.5. 

Stiffness shall be based on the cracked section for a wall 

when the net flexural tensile stress exceeds the expected 

tensile strength.

Stiffnesses for existing and new reinforced out-of-plane 

walls shall be assumed to be the same.

7.4.5.2 Strength

Expected flexural strength shall be based on 

Section 7.4.4.2.1. For walls with an h/t ratio exceeding 

20, second-order moment effects due to out-of-plane 

deflections shall be considered.

The strength of new and existing walls shall be assumed 

to be the same.

7.4.5.3 Acceptance Criteria

Out-of plane forces on reinforced masonry walls shall 

be considered force-controlled actions. Out-of-plane 

RM walls shall be sufficiently strong in flexure to resist 

the out-of-plane loads prescribed in Section 2.6.7.

If the Nonlinear Dynamic Procedure is used, the 

following performance criteria shall be based on the 

maximum out-of-plane deflection normal to the plane 

of a wall.

1. For the Immediate Occupancy Structural 

Performance Level, the out-of-plane story drift ratio 

shall be equal to or less than 2%.

2. For the Life Safety Structural Performance Level, 

the out-of-plane story drift ratio shall be equal to or 

less than 3%.

3. For the Collapse Prevention Structural Performance 

Level, the out-of-plane story drift ratio shall be equal 

to or less than 5%.

Acceptable deformations for existing and new walls 

shall be assumed to be the same.

7.5 Engineering Properties of 

Masonry Infills

The requirements of this section shall apply to masonry 

infill panels comprised of any combination of existing 

panels, panels enhanced for seismic rehabilitation, and 

new panels added to an existing building for seismic 

rehabilitation. The procedures for determination of 

stiffness, strength, and deformation of masonry infills 

shall be based on this section and used with the 

analytical methods and acceptance criteria prescribed in 

Chapter 3, unless noted otherwise.

Masonry infill panels shall be considered as primary 

elements of a lateral force-resisting system. If the 

analysis shows that the surrounding frame remains 

stable following the loss of an infill panel, infill panels 

shall not be subject to limits set by the Collapse 

Prevention Structural Performance Level.

C7.4.5.3 Deformation Acceptance Criteria

The limit states specified in this section are based on 

the masonry units having significant cracking for IO, 

masonry units at a point of being dislodged and falling 

out of the wall for LS, and masonry units on the verge 

of collapse for CP.

C7.5 Engineering Properties of 

Masonry Infills

The design professional is referred to FEMA 306, 

FEMA 307, and FEMA 308 for additional information 

regarding the engineering properties of masonry infills.
7-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

7.5.1 Types of Masonry Infills

Infills shall include panels built partially or fully within 

the plane of steel or concrete frames, and bounded by 

beams and columns.

Infill panel types considered in this standard include 

unreinforced clay-unit masonry, concrete masonry, and 

hollow-clay tile masonry. Infills made of stone or glass 

block are not addressed in this standard.

Infill panels considered isolated from the surrounding 

frame shall have gaps at top and sides to accommodate 

maximum expected lateral frame deflections. Isolated 

panels shall be restrained in the transverse direction to 

ensure stability under normal forces. Panels in full 

contact with the frame elements on all four sides are 

termed “shear infill panels”.

Frame members and connections surrounding infill 

panels shall be evaluated for frame-infill interaction 

effects. These effects shall include forces transferred 

from an infill panel to beams, columns, and 

connections, and bracing of frame members across a 

partial length.

7.5.1.1 Existing Masonry Infills

Existing masonry infills considered in this section shall 

include all structural infills of a building system that are 

in place prior to seismic rehabilitation. Infill types 

included in this section consist of unreinforced and 

ungrouted panels, and composite or noncomposite 

panels. Existing infill panels subjected to lateral forces 

applied parallel with their plane shall be considered 

separately from infills subjected to forces normal to 

their plane, as described in Sections 7.5.2 and 7.5.3.

Existing masonry infills shall be assumed to behave the 

same as new masonry infills, provided that the masonry 

is in good or fair condition as defined in this standard.

7.5.1.2 New Masonry Infills

New masonry infills shall include all new panels added 

to an existing lateral-force-resisting system for 

structural rehabilitation. Infill types shall include 

unreinforced or reinforced, grouted, ungrouted, or 

partially grouted, and composite or noncomposite.

7.5.1.3 Enhanced Masonry Infills

Enhanced masonry infill panels shall include existing 

infills that are rehabilitated by an approved method. 

C7.5.1.3 Enhanced Masonry Infills

Masonry infills may be rehabilitated using the methods 

described in this section. Masonry infills enhanced in 

accordance with this section should be analyzed using 

the same procedures and performance criteria used for 

new infills.

Unless stated otherwise, methods are applicable to 

unreinforced infills, and are intended to improve 

performance of masonry infills subjected to both inplane and out-of-plane lateral forces.

Guidelines from the following sections pertaining to 

enhancement methods for reinforced masonry walls 

listed in Section C7.4.1.3, may also apply to 

unreinforced masonry infill panels: (1) “Infilled 

Openings,” (2) “Shotcrete,” (3) “Coatings for URM 

Walls,” (4) “Grout Injections,” (5) “Repointing,” and 

(6) “Stiffening Elements.” In addition, the following 

two enhancement methods may apply to masonry infill 

panels.

C7.5.1.3.1 Boundary Restraints for Infill Panels 

Infill panels not in tight contact with perimeter frame 

members should be restrained for out-of-plane 

forces.This may be accomplished by installing steel 

angles or plates on each side of the infills, and welding 

or bolting the angles or plates to the perimeter frame 

members.

C7.5.1.3.2 Joints Around Infill Panels

Gaps between an infill panel and the surrounding frame 

may be filled if integral infill-frame action is assumed 

for in-plane response.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-25

7.5.2 Masonry Infills In-Plane

The calculation of masonry infill in-plane stiffness and 

strength based on nonlinear finite element analysis of a 

composite frame substructure with infill panels that 

account for the presence of openings and post-yield 

cracking of masonry shall be permitted. Alternatively, 

the methods of Sections 7.5.2.1 and 7.5.2.2 shall be 

used.

7.5.2.1 Stiffness

The elastic in-plane stiffness of a solid unreinforced 

masonry infill panel prior to cracking shall be 

represented with an equivalent diagonal compression 

strut of width, a, given by Equation (7-14). The 

equivalent strut shall have the same thickness and 

modulus of elasticity as the infill panel it represents.

(7-14)

where:

and

For noncomposite infill panels, only the wythes in full 

contact with the frame elements shall be considered 

when computing in-plane stiffness unless positive 

anchorage capable of transmitting in-plane forces from 

frame members to all masonry wythes is provided on all 

sides of the walls.

Stiffness of cracked unreinforced masonry infill panels 

shall be represented with equivalent struts; the strut 

properties shall be determined from analyses that 

consider the nonlinear behavior of the infilled frame 

system after the masonry is cracked.

The equivalent compression strut analogy shall be used 

to represent the elastic stiffness of a perforated 

unreinforced masonry infill panel; the equivalent strut 

properties shall be determined from stress analyses of 

infill walls with representative opening patterns.

Stiffnesses for existing and new infills shall be assumed 

to be the same. 

C7.5.2 Masonry Infills In-Plane

Finite element programs such as FEM 1 may be useful 

in analyzing masonry infills with openings.

hcol = Column height between centerlines of 

beams, in.

hinf = Height of infill panel, in.

Efe = Expected modulus of elasticity of frame 

material, ksi

Eme = Expected modulus of elasticity of infill 

material, ksi

Icol = Moment of inertia of column, in 4.

Linf = Length of infill panel, in.

rinf = Diagonal length of infill panel, in.

tinf = Thickness of infill panel and equivalent strut, 

in.

a 0.175 λ1hcol ( )–0.4

rinf =

λ1

Emet

infsin2θ

4EfeIcolhinf

--------------------------------

1

4

--

=

= Angle whose tangent is the infill height-tolength aspect ratio, radians

= Coefficient used to determine equivalent 

width of infill strut

C7.5.2.1 Stiffness

In-plane lateral stiffness of an infilled frame system is 

not the same as the sum of the frame and infill 

stiffnesses because of the interaction of the infill with 

the surrounding frame. Experiments have shown that 

under lateral forces, the frame tends to separate from 

the infill near windward lower and leeward upper 

corners of the infill panels, causing compressive contact 

stresses to develop between the frame and the infill at 

the other diagonally opposite corners. Recognizing this 

behavior, the stiffness contribution of the infill is 

represented with an equivalent compression strut 

connecting windward upper and leeward lower corners 

of the infilled frame. In such an analytical model, if the 

thickness and modulus of elasticity of the strut are 

assumed to be the same as those of the infill, the 

problem is reduced to determining the effective width 

of the compression strut. Solidly infilled frames may be 

modeled with a single compression strut in this fashion.

θ

λ1
7-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

For global building analysis purposes, the compression 

struts representing infill stiffness of solid infill panels 

may be placed concentrically across the diagonals of 

the frame, effectively forming a concentrically braced 

frame system (Figure C7-2). In this configuration, 

however, the forces imposed on columns (and beams) 

of the frame by the infill are not represented. To 

account for these effects, compression struts may be 

placed eccentrically within the frames as shown in 

Figure C7-3. If the analytical models incorporate 

eccentrically located compression struts, the results 

should yield infill effects on columns directly.

Figure C7-2 Compression Strut Analogy–Concentric 

Struts

Figure C7-3 Compression Strut Analogy–Eccentric 

Struts

Figure C7-4 Compression Strut Analogy–Perforated 

Infills
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-27

7.5.2.2 Strength

The transfer of story shear across a masonry infill panel 

confined within a concrete or steel frame shall be 

considered a deformation-controlled action. Expected 

in-plane panel shear strength shall be determined in 

accordance with the requirements of this section.

Expected infill shear strength, Vine, shall be calculated 

in accordance with Equation (7-15):

(7-15)

where:

Expected shear strength of existing infills, fvie, shall not 

exceed the expected masonry bed-joint shear strength,

vme, as determined in accordance with Section 7.3.2.6.

Shear strength of new infill panels, fvie, shall not exceed 

values specified in an approved building code for zero 

vertical compressive stress.

For noncomposite infill panels, only the wythes in full 

contact with the frame elements shall be considered 

when computing in-plane strength, unless positive 

anchorage capable of transmitting in-plane forces from 

frame members to all masonry wythes is provided on all 

sides of the walls.

7.5.2.3 Acceptance Criteria

7.5.2.3.1 Required Strength of Column Members 

Adjacent to Infill Panels

The expected flexural and shear strengths of column 

members adjacent to an infill panel shall exceed the 

forces resulting from one of the following conditions:

1. The application of the horizontal component of the 

expected infill strut force at a distance lceff from the 

top or bottom of the infill panel, where lceff shall be 

as defined by Equation (7-16):

(7-16)

where shall be as defined by Equation (7-17):

(7-17)

2. The shear force resulting from development of 

expected column flexural strengths at the top and 

bottom of a column with a reduced height equal to 

lceff .

The reduced column length, lceff, in Equation (7-16) 

shall be equal to the clear height of opening for a 

captive column braced laterally with a partial height 

infill.

The requirements of this section shall be waived if the 

expected masonry shear strength, vme, as measured in 

accordance with test procedures of Section 7.3.2.6, is 

less than 20 psi.

7.5.2.3.2 Required Strength of Beam Members 

Adjacent to Infill Panels

The expected flexural and shear strengths of beam 

members adjacent to an infill panel shall exceed forces 

resulting from one of the following conditions:

Alternatively, global analyses may be performed using 

concentric braced frame models, and the infill effects 

on columns (or beams) may be evaluated at a local level 

by applying the strut loads onto the columns (or 

beams).

Diagonally concentric equivalent struts may also be 

used to incorporate infill panel stiffnesses into 

analytical models for perforated infill panels (e.g., 

infills with window openings), provided that the 

equivalent stiffness of the infill is determined using 

appropriate analysis methods (e.g., finite element 

analysis) in a consistent fashion with the global 

analytical model. Analysis of local effects, however, 

must consider various possible stress fields that can 

potentially develop within the infill. A possible 

representation of these stress fields with multiple 

compression struts, as shown in Figure C7-4, have been 

proposed by Hamburger (1993). Theoretical work and 

experimental data for determining multiple strut 

placement and strut properties, however, are not 

sufficient to establish reliable guidelines; the use of this 

approach requires judgment on a case-by-case basis.

Ani = Area of net mortared/grouted section across 

infill panel

fvie = Expected shear strength of masonry infill

QCE Vine Ani f

vie = =

l

ceff

a

θc cos = --------------

θc tan

θc tan

hinf

a

θc cos – --------------

Linf

= -----------------------------
7-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

1. The application of the vertical component of the 

expected infill strut force at a distance, lbeff, from the 

top or bottom of the infill panel, where lbeff shall be 

as defined by Equation (7-18):

(7-18)

where shall be as defined by Equation (7-19):

(7-19)

2. The shear force resulting from development of 

expected beam flexural strengths at the ends of a 

beam member with a reduced length equal to lbeff.

The requirements of this section shall be waived if the 

expected masonry shear strength, vme, as measured 

using the test procedures of Section 7.3.2.6, is less than 

50 psi.

7.5.2.3.3 Linear Procedures

Actions on masonry infills shall be considered 

deformation-controlled. For the linear procedures of 

Section 3.3.1, component actions shall be compared 

with capacities in accordance with Section 3.4.2.2. mfactors for use in Equation (3-20) shall be as specified 

in Table 7-8. For an infill panel, QE shall be the 

horizontal component of the unreduced axial force in 

the equivalent strut member.

For determination of m-factors in accordance with 

Table 7-8, the ratio of frame to infill strengths, β, shall 

be determined considering the expected lateral strength 

of each component.

7.5.2.3.4 Nonlinear Procedures

For the Nonlinear Static Procedure given in 

Section 3.3.3, infill panels shall meet the requirements 

of Section 3.4.3.2. Nonlinear lateral drifts shall not 

exceed the values given in Table 7-9. The variable d, 

representing nonlinear deformation capacities, shall be 

expressed in terms of story drift ratio in percent as 

defined in Figure 7-1.

For determination of acceptable drift levels using Table 

7-9, the ratio of frame to infill strengths, β, shall be 

determined considering the expected lateral strength of 

each component. 

If the surrounding frame can remain stable following 

the loss of an infill panel, infill panels shall not be 

subject to limits set by the Collapse Prevention 

Structural Performance Level.

For the Nonlinear Dynamic Procedure given in 

Section 3.3.4, infill panels shall meet the requirements 

of Section 3.4.3.2. Nonlinear force-deflection relations 

for infill panels shall be established based on the 

information given in Table 7-9 or an approved 

procedure based on a comprehensive evaluation of the 

hysteretic characteristics of those components.

Acceptable deformations for existing and new infills 

shall be assumed to be the same. 

l

beff

a

θb sin = -------------

θb tan

θb tan

hinf

Linf

a

θb sin – -------------

= ----------------------------

Table 7-8 Linear Static Procedure—m-factors 

for Masonry Infill Panels

m-factors

IO LS CP

0.5 1.0 4.0 n.a.

1.0 1.0 3.5 n.a.

2.0 1.0 3.0 n.a.

0.5 1.5 6.0 n.a.

1.0 1.2 5.2 n.a.

2.0 1.0 4.5 n.a.

0.5 1.5 8.0 n.a.

1.0 1.2 7.0 n.a.

2.0 1.0 6.0 n.a.

Interpolation shall be used between table values. 

C7.5.2.3.4 Nonlinear Procedures

The Immediate Occupancy Structural Performance 

Level is assumed to be reached when significant visual 

cracking of an unreinforced masonry infill occurs. The 

Life Safety Structural Performance Level is assumed to 

be reached when substantial cracking of the masonry 

infill occurs and the potential is high for the panel, or 

some portion of it, to drop out of the frame.

β

Vfre

Vine

= ---------- Linf

hinf

--------

β < 0.7

0.7 ≤ β < 1.3

β ≥ 1.3
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-29

7.5.3 Masonry Infills Out-of-Plane

Unreinforced infill panels with hinf /tinf ratios less than 

those given in Table 7-10, and meeting the requirements 

for arching action given in the following section, need 

not be analyzed for out-of-plane seismic forces.

7.5.3.1 Stiffness

Infill panels shall be considered local elements 

spanning out-of-plane vertically between floor levels or 

horizontally across bays of frames.

The out-of-plane stiffness of infill panels shall be 

neglected in analytical models of the global structural 

system in the orthogonal direction.

Flexural stiffness for uncracked masonry infills 

subjected to transverse forces shall be based on the 

minimum net sections of mortared and grouted 

masonry. Flexural stiffness for unreinforced, cracked 

infills subjected to transverse forces shall be assumed to 

be equal to zero unless arching action is considered.

Arching action shall be considered only if all of the 

following conditions exist. 

1. The panel is in full contact with the surrounding 

frame components.

2. The product of the elastic modulus, Efe, times the 

moment of inertia, If

, of the most flexible frame 

component exceeds a value of 3.6 x 109 lb-in.2

3. The frame components have sufficient strength to 

resist thrusts from arching of an infill panel.

4. The hinf /tinf ratio is less than or equal to 25.

If arching action is considered, mid-height deflection 

normal to the plane of an infill panel, ∆inf, divided by 

the infill height, hinf, shall be determined in accordance 

with Equation (7-20):

Table 7-9 Nonlinear Static Procedure—Simplified Force-Deflection Relations for Masonry Infill Panels

c

d

%

e

%

Acceptance Criteria

LS

%

CP

%

0.5 n.a. 0.5 n.a. 0.4 n.a.

1.0 n.a. 0.4 n.a. 0.3 n.a.

2.0 n.a. 0.3 n.a. 0.2 n.a.

0.5 n.a. 1.0 n.a. 0.8 n.a.

1.0 n.a. 0.8 n.a. 0.6 n.a.

2.0 n.a. 0.6 n.a. 0.4 n.a.

0.5 n.a. 1.5 n.a. 1.1 n.a.

1.0 n.a. 1.2 n.a. 0.9 n.a.

2.0 n.a. 0.9 n.a. 0.7 n.a.

Note: Interpolation shall be used between table values.

β

Vfre

Vine

= ---------- Linf

hinf

--------

β < 0.7

0.7 ≤ β < 1.3

β ≥ 1.3

Table 7-10 Maximum hinf /tinf Ratios1

Low 

Seismic 

Zone

Moderate 

Seismic 

Zone

High 

Seismic 

Zone

IO 14 13 8

LS 15 14 9

CP 16 15 10

1. Out-of-plane analysis shall not be required for infills with hinf / t

inf ratios less than the values listed herein.
7-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry

(7-20)

For infill panels not meeting the requirements for 

arching action, deflections shall be determined in 

accordance with the procedures given in Sections 7.4.3 

or 7.4.5.

Stiffnesses for existing and new infills shall be assumed 

to be the same.

7.5.3.2 Strength

When arching action is not considered, the lower bound 

strength of a URM infill panels shall be limited by the 

lower bound masonry flexural tension strength, f’t

, 

which shall be taken as 0.7 times the expected tensile 

strength, fte, as determined in accordance with 

Section 7.3.2.5.

If arching action is considered, the lower bound out-ofplane strength of an infill panel in pounds per square 

foot, qin, shall be determined using Equation (7-21):

(7-21)

where: 

7.5.3.3 Acceptance Criteria

Infill panels loaded out-of-plane shall not be analyzed 

with the Linear or Nonlinear Static Procedures 

prescribed in Chapter 3.

The lower bound transverse strength of URM infill 

panels shall exceed normal pressures as prescribed in 

Section 2.6.7. 

If the Nonlinear Dynamic Procedure is used, the 

following performance criteria shall be based on the 

maximum out-of-plane deflection normal to the plane 

of the wall.

1. For the Immediate Occupancy Structural 

Performance Level, the out-of-plane story drift ratio 

of a panel shall be equal to or less than 2%.

2. For the Life Safety Structural Performance Level, 

the out-of-plane story drift ratio of a panel shall be 

equal to or less than 3%.

3. For the Collapse Prevention Structural Performance 

Level, the out-of-plane story drift ratio of a panel 

shall be equal to or less than 5%.

If the surrounding frame is shown to remain stable 

following the loss of an infill panel, infill panels shall 

not be subject to limits for the Collapse Prevention 

Structural Performance Level.

Acceptable deformations of existing and new walls 

shall be assumed to be the same.

7.6 Anchorage to Masonry Walls

7.6.1 Types of Anchors

Anchors considered in Section 7.6.2 shall include plate 

anchors, headed anchor bolts, and bent bar anchor bolts 

= Lower bound of masonry compressive 

strength determined in accordance with 

Section 7.3.2.3

λ2 = Slenderness parameter as defined in Table 

7-11

Table 7-11 Values of λ2 for Use in Equation 

(7-21)

hinf / tinf 5 10 15 25

λ2 0.129 0.060 0.034 0.013

Interpolation shall be used.

∆inf

hinf

---------

0.002

hinf

t

inf

--------

     

1 1 0.002

hinf

t

inf

--------

      2

+ –

= -----------------------------------------------------

QCL qin

0.7f ′

m λ2

hinf

t

inf

--------

     

= = --------------------- × 144

f ′

m

C7.5.3.3 Acceptance Criteria

The Immediate Occupancy Structural Performance 

level is assumed to be reached when significant visual 

cracking of an unreinforced masonry infill occurs. The 

Life Safety Structural Performance Level is assumed to 

be reached when substantial damage of the 

unreinforced masonry infill occurs and the potential is 

high for the panel, or some portion of it, to drop out of 

the frame.
 Chapter 7: Masonry

FEMA 356 Seismic Rehabilitation Prestandard 7-31

embedded into clay-unit and concrete masonry. 

Anchors in hollow-unit masonry shall be embedded in 

grout.

Pullout and shear strength of expansion anchors shall be 

verified by approved test procedures.

7.6.2 Analysis of Anchors

Anchors embedded into existing or new masonry walls 

shall be considered force-controlled components. 

Lower bound values for strengths of embedded anchors 

with respect to pullout, shear, and combinations of 

pullout and shear, shall be as specified in an approved 

building code.

The minimum effective embedment length for 

considerations of pullout strength of embedded anchors 

shall be as specified in the building code. When the 

embedment length is less than four bolt diameters or 

two inches, the pullout strength shall be taken as zero.

The minimum edge distance for considerations of full 

shear strength shall be 12 diameters. Shear strength of 

anchors with edge distances equal to or less than one 

inch shall be taken as zero. Linear interpolation of shear 

strength for edge distances between these two bounds 

shall be permitted.

7.7 Masonry Foundation Elements

7.7.1 Types of Masonry Foundations

Masonry foundations shall be rehabilitated in 

accordance with this section.

7.7.2 Analysis of Existing Foundations

The deformability of the masonry footings and the 

flexibility of the soil under them shall be considered in 

the lateral force analysis of the building system. The 

strength and stiffness of the soil shall be determined in 

accordance with the requirements of Section 4.4.

Masonry footings shall be considered force-controlled 

components. Masonry footings shall be modeled as 

elastic components with no inelastic deformation 

capacity, unless verification tests are done in 

accordance with Section 2.8 to prove otherwise.

Masonry retaining walls shall be evaluated to resist 

active and passive soil pressures in accordance with 

Section 4.5. Stiffness, strength, and acceptability 

criteria for masonry retaining walls shall be the same as 

that for other masonry walls subjected to out-of-plane 

loadings, as specified in Sections 7.4.3 and 7.4.5.

7.7.3 Rehabilitation Measures

Masonry foundation elements shall be rehabilitated in 

accordance with Section 6.13.4 or by another approved 

method.

C7.6.2 Analysis of Anchors

Anchors in masonry may be analyzed in accordance 

with FEMA 302.

C7.7.1 Types of Masonry Foundations

Masonry foundations are common in older buildings 

and are still used for some modern construction. Such 

foundations may include footings and foundation walls 

constructed of stone, clay brick, or concrete block. 

Generally, masonry footings are unreinforced; 

foundation walls may or may not be reinforced.

Spread footings transmit vertical column and wall loads 

to the soil by direct bearing. Lateral forces are 

transferred through friction between the soil and the 

masonry, as well as by passive pressure of the soil 

acting on the vertical face of the footing.

C7.7.3 Rehabilitation Measures

Possible rehabilitation methods include:

1. Injection grouting of stone foundations.

2. Reinforcing of URM foundations.

3. Prestressing of masonry foundations.

4. Enlargement of footings by placement of reinforced 

shotcrete.

5. Enlargement of footings with additional reinforced 

concrete sections.

Procedures for rehabilitation should follow provisions 

for enhancement of masonry walls where applicable, 

according to Section 7.4.1.3.
7-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 7: Masonry
FEMA 356 Seismic Rehabilitation Prestandard 8-1

8. Wood and Light Metal Framing

8.1 Scope

This chapter sets forth requirements for the Systematic 

Rehabilitation of wood and light metal frame buildings 

or wood and light metal framed lateral-force-resisting 

elements within a building. The requirements of this 

chapter shall apply to existing wood and light metal 

frame components of a building system, rehabilitated 

wood and light metal frame components of a building 

system, and new wood and light metal frame 

components that are added to an existing building 

system.

Sections 8.2 and 8.3 specify data collection procedures 

for obtaining material properties and performing 

condition assessments. Section 8.4 specifies general 

assumptions and requirements. Sections 8.5 and 8.6 

provide modeling procedures, component strengths, 

acceptance criteria, and rehabilitation measures for 

wood and light frame shear walls and wood 

diaphragms. Section 8.7 specifies requirements for 

wood foundations. Section 8.8 specifies requirements 

for other wood components including, but not limited 

to, knee-braced frames, rod-braced frames, braced 

horizontal diaphragms, and components supporting 

discontinuous shear walls. 

8.2 Historical Information

Available construction documents and as-built 

information shall be obtained as specified in 

Section 2.2. Use of material properties based on 

historical information for use as default values shall be 

as specified in Section 8.3.2.5. Other approved values 

of material properties shall be permitted if based on 

available historical information for a particular type of 

wood frame construction, prevailing codes, and 

assessment of existing condition. 

C8.1 Scope

The Linear Static Procedure (LSP) presented in 

Chapter 3 is most often used for the systematic analysis 

of wood frame buildings; however, properties of the 

idealized inelastic performance of various elements and 

connections are included so that nonlinear procedures 

can be used if desired.

A general history of the development of wood framing 

methods is presented in Section 8.2, along with the 

features likely to be found in buildings of different 

ages. The evaluation and assessment of various 

structural elements of wood frame buildings is found in 

Section 8.3. For a description and discussion of 

connections between the various components and 

elements, see Section 8.3.2.2.2. Properties of shear 

walls are described in Section 8.5, along with various 

rehabilitation or strengthening methods. Horizontal 

floor and roof diaphragms are discussed in Section 8.6, 

which also covers engineering properties and methods 

of upgrading or strengthening the elements. Wood 

foundations and pole structures are addressed in 

Section 8.7. For additional information regarding 

foundations, see Chapter 4.

C8.2 Historical Information

Wood frame construction has evolved over the years; 

wood is the primary building material of most 

residential and small commercial structures in the 

United States. It has often been used for the framing of 

roofs and floors, and in combination with other 

materials.

Establishing the age and recognizing the location of a 

building can be helpful in determining what types of 

lateral-force-resisting systems may be present.

As indicated in Chapter 1, great care should be 

exercised in selecting the appropriate rehabilitation 

approaches and techniques for application to historic 

buildings in order to preserve their unique 

characteristics.
8-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.3 Material Properties and 

Condition Assessment

8.3.1 General

Mechanical properties for wood and light metal framing 

materials, components, and assemblies shall be based 

on available construction documents and as-built 

conditions for the particular structure. When such 

information fails to provide adequate information to 

quantify material properties, capacities of assemblies, 

or condition of the structure, such information shall be 

supplemented by materials tests, mock-up tests of 

assemblies, and assessments of existing conditions as 

required in Section 2.2.6.

Based on the approximate age of a building, various 

assumptions can be made about the design and features 

of construction. Older wood frame structures that 

predate building codes and standards usually do not 

have the types of elements considered essential for 

predictable seismic performance. These elements will 

generally have to be added, or the existing elements 

upgraded by the addition of lateral-load-resisting 

components to the existing structure in order to obtain 

predictable performance.

If the age of a building is known, the code in effect at 

the time of construction and the general quality of the 

construction usual for the time can be helpful in 

evaluating an existing building. The level of 

maintenance of a building may be a useful guide in 

determining the structure’s capacity to resist loads.

The earliest wood frame buildings in the U.S. were 

built with post and beam or frame construction adopted 

from Europe and the British Isles. This was followed by 

the development of balloon framing in about 1830 in 

the Midwest, which spread to the East Coast by the 

1860s. This, in turn, was followed by the development 

of western or platform framing shortly after the turn of 

the century. Platform framing is the system currently in 

use for multistory construction.

Drywall or wallboard was first introduced in about 

1920; however, its use was not widespread until after 

World War II, when gypsum lath (button board) also 

came into extensive use as a replacement for wood lath.

With the exception of public schools in high seismic 

areas, modern wood frame structures detailed to resist 

seismic loads were generally not built prior to 1934. For 

most wood frame structures, either general seismic 

provisions were not provided—or the codes that 

included them were not enforced—until the mid-1950s 

or later, even in the most active seismic areas. This time 

frame varies somewhat depending on local conditions 

and practice.

Buildings constructed after 1970 in high seismic areas 

usually included a well-defined lateral-force-resisting 

system as a part of the design. However, site 

inspections and code enforcement varied greatly. Thus, 

the inclusion of various features and details on the plans 

does not necessarily mean that they are in place or fully 

effective. Verification is needed to ensure that good 

construction practices were followed.

Until about 1950, wood residential buildings were 

frequently constructed on raised foundations and in 

some cases included a short stud wall, called a “cripple 

wall,” between the foundation and the first floor 

framing. This occurs on both balloon-framed and 

platform-framed buildings. There may be an extra 

demand on these cripple walls because most interior 

partition walls do not continue to the foundation. 

Special attention is required in these situations. 

Adequate bracing must be provided for cripple walls as 

well as the attachment of the sill plate to the foundation.

In more recent times, light gage metal studs and joists 

have been used in lieu of wood framing for some 

structures. Lateral-load resistance is either provided by 

metal straps attached to the studs and top and bottom 

tracks, or by structural panels attached with sheet metal 

screws to the studs and the top and bottom track in a 

manner similar to that of wood construction. The metal 

studs and joists vary in size, gage, and configuration, 

depending on the manufacturer and the loading 

conditions.

For systems using structural panels for bracing, see 

Section 8.5 for analysis and acceptance criteria. For the 

all-metal systems using steel strap braces, see Chapter 5 

for guidance.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-3

Material properties of existing wood and light metal 

framing components and assemblies shall be 

determined in accordance with Section 8.3.2. A 

condition assessment shall be conducted in accordance 

with Section 8.3.3. The extent of materials testing and 

condition assessment performed shall be used to 

determine the knowledge factor, κ , as specified in 

Section 8.3.4.

8.3.2 Properties of In-Place Materials and 

Components

8.3.2.1 Material Properties

8.3.2.1.1 General

The species and grade of wood shall be established by 

one of the following methods:

1. Construction documents shall be reviewed.

2. An inspection shall be conducted.

3. Samples shall be tested in a laboratory.

When materials testing is required by Section 2.2.6, 

grading shall be performed using the ASTM D245-00

grading methodology or an approved grading handbook 

for the assumed wood species and application. Samples 

shall be taken from regions of reduced stress and tested 

in accordance with Section 8.3.2.3. The properties of 

adhesives used in the fabrication of laminated products 

other than plywood shall be evaluated.

Use of default properties for wood and light metal 

frame shear walls, wood diaphragms, components, and 

connectors shall be permitted in accordance with 

Section 8.3.2.5. For materials comprising individual 

components, the use of default properties shall be 

permitted where the species and grade of wood have 

been determined. Use of default properties for 

connectors shall be permitted where the species of the 

connected members has been determined.

C8.3.1 General

Various grades and species of wood have been used in a 

cut dimension form, combined with other structural 

materials (e.g., steel/wood elements), or in multiple 

layers of construction (e.g., glue-laminated wood 

components). Wood materials have also been 

manufactured into hardboard, plywood, and 

particleboard products, which may have structural or 

nonstructural functions in construction. The condition 

of the in-place wood materials will greatly influence the 

future behavior of wood components in the building 

system.

Quantification of in-place material properties and 

verification of existing system configuration and 

condition are necessary to properly analyze the 

building. The focus of this effort shall be given to the 

primary vertical- and lateral-load-resisting elements 

and components thereof. These primary components 

may be identified through initial analysis and 

application of loads to the building model.

The extent of in-place materials testing and condition 

assessment that must be accomplished is related to 

availability and accuracy of construction documents 

and as-built records, the quality of materials used and 

construction performed, and physical condition. A 

specific problem with wood construction is that 

structural wood components are often covered with 

other components, materials, or finishes; in addition, 

their behavior is influenced by past loading history. 

Knowledge of the properties and grades of material 

used in original component/connection fabrication is 

invaluable, and may be effectively used to reduce the 

amount of in-place testing required. The design 

professional is encouraged to research and acquire all 

available records from original construction, including 

design calculations.

Connection configuration also has a very important 

influence on response to applied loads and motions. A 

large number of connector types exist, the most 

prevalent being nails and through bolts. However, more 

recent construction has included metal straps and 

hangers, clip angles, and truss plates. An understanding 

of connector configuration and mechanical properties 

must be gained to properly analyze the anticipated 

performance of the building.
8-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.3.2.1.2 Nominal or Specified Properties

Use of nominal material properties or properties 

specified in construction documents to compute 

expected and lower bound material properties shall be 

permitted in accordance with Section 8.3.2.5. 

8.3.2.2 Component Properties

8.3.2.2.1 Elements

The following component properties shall be 

determined in accordance with Section 8.3.3:

1. Cross-sectional shape and physical dimensions of 

the primary components and overall configuration of 

the structure.

2. Configuration of connections, size and thickness of 

connected materials, and continuity of load path.

3. Modifications to individual components or overall 

configuration of the structure.

4. Location and dimension of braced frames and shear 

walls; type, grade, nail size, and spacing of holddowns and drag/strut members.

5. Current physical condition of components and 

extent of any deterioration present. 

8.3.2.2.2 Connections

Details of the following connections shall be 

determined or verified in accordance with 

Section 8.3.3:

1. Connections between horizontal diaphragms and 

shear walls and braced frames.

2. Size and character of all drag ties and struts, 

including splice connections.

3. Connections at splices in chord members of 

horizontal diaphragms.

C8.3.2.1.2 Nominal or Specified Properties

Actions associated with wood and light metal framing 

components generally are deformation-controlled; thus, 

expected strength material properties will be used most 

often. Lower-bound values will be used with 

components supporting discontinuous shear walls, 

bodies of connections, and axial compression of 

individual timber frame components, which are forcecontrolled. Material properties listed in this chapter are 

expected strength values. If lower-bound material 

properties are needed, they should be taken as mean 

minus one standard deviation values, or adjusted from 

expected strength values in accordance with Section 

8.3.2.5.

C8.3.2.2.1 Elements

Structural elements of the lateral-force-resisting system 

comprise primary and secondary components, which 

collectively define element strength and resistance to 

deformation. Behavior of the components—including 

shear walls, beams, diaphragms, columns, and braces—

is dictated by physical properties such as area; material 

grade; thickness, depth, and slenderness ratios; lateral 

torsional buckling resistance; and connection details.

The actual physical dimensions should be measured; 

e.g., 2" x 4" stud dimensions are generally 1.5" x 3.5". 

Connected members include plywood, bracing, 

stiffeners, chords, sills, struts, and hold-down posts. 

Modifications to members include notching, holes, 

splits, and cracks. The presence of decay or 

deformation should be noted.

These primary component properties are needed to 

properly characterize building performance in the 

seismic analysis. The starting point for establishing 

component properties should be the available 

construction documents. Preliminary review of these 

documents shall be performed to identify primary 

vertical- (gravity-) and lateral-load-carrying elements 

and systems, and their critical components and 

connections. Site inspections should be conducted to 

verify conditions and to assure that remodeling has not 

changed the original design concept. In the absence of a 

complete set of building drawings, the design 

professional must thoroughly inspect the building to 

identify these elements, systems, and components as 

indicated in Section 8.3.3. Where reliable record 

drawings do not exist, an as-built set of plans for the 

building must be created.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-5

4. Connections of horizontal diaphragms to exterior or 

interior concrete or masonry walls for both in-plane 

and out-of-plane loads.

5. Connections of cross tie members for concrete or 

masonry buildings.

6. Connections of shear walls to foundations for 

transfer of shear and overturning forces.

7. Method of through-floor transfer of wall shear and 

overturning forces in multistory buildings. 

8.3.2.3 Test Methods to Quantify Material 

Properties

The stiffness and strength of wood and light metal 

framing components and assemblies shall be 

established through in situ testing or observation, or 

mock-up testing of assemblies in accordance with 

Section 2.8, unless default values are used in 

accordance with Section 8.3.2.5. The number of tests 

required shall be based on Section 8.3.2.4. Expected 

material properties shall be based on mean values of 

tests. Lower bound material properties shall be based on 

mean values of tests minus one standard deviation.

8.3.2.4 Minimum Number of Tests

8.3.2.4.1 Usual Testing

The minimum number of tests to quantify expected 

strength material properties for usual data collection 

shall be based on the following criteria:

1. If design drawings containing material property 

information are available, at least one location for 

each story shall be randomly verified by observing 

grade stamps or by compliance with grading rules.

2. If design drawings are incomplete or not available, 

at least two locations for each story shall be 

randomly verified by observing grade stamps or by 

compliance with grading rules.

C8.3.2.2.2 Connections

The method of connecting the various elements of the 

structural system is critical to its performance. The type 

and character of the connections must be determined by 

a review of the plans and a field verification of the 

conditions.

C8.3.2.3 Test Methods to Quantify Material 

Properties

To obtain the desired in-place mechanical properties of 

materials and components, including expected strength, 

it is often necessary to use proven destructive and 

nondestructive testing methods.

Of greatest interest to wood building system 

performance are the expected orthotropic strengths of 

the installed materials for anticipated actions (e.g., 

flexure). Past research and accumulation of data by 

industry groups have led to published mechanical 

properties for most wood types and sizes (e.g., 

dimensional solid-sawn lumber, and glue-laminated or 

“glulam” beams). Section 8.3.2.5 addresses these 

established default strengths and distortion properties. 

This information may be used, together with tests from 

recovered samples or observation, to establish the 

expected properties for use in component strength and 

deformation analyses. Where possible, the load history 

for the building shall be assessed for possible influence 

on component strength and deformation properties.

To quantify material properties and analyze the 

performance of archaic wood construction, shear walls, 

and diaphragm action, more extensive sampling and 

testing may be necessary. This testing should include 

further evaluation of load history and moisture effects 

on properties, and an examination of wall and 

diaphragm continuity and the suitability of in-place 

connectors.

Where it is desired to use an existing assembly and little 

or no information about its performance is available, a 

cyclic load test of a mock-up of the existing structural 

elements can be used to determine the performance of 

various assemblies, connections, and load transfer 

conditions. See Section 2.8 for an explanation of the 

backbone curve and the establishment of alternative 

modeling parameters.
8-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.3.2.4.2 Comprehensive Testing

The minimum number of tests necessary to quantify 

expected strength properties for comprehensive data 

collection shall be defined in accordance with the 

following requirements:

1. If original construction documents exist that define 

the grade of wood and mechanical properties, at 

least one location for each story shall be randomly 

verified by observing grade stamps, or by 

compliance with grading rules for each component 

type identified as having a different material grade. 

2. If original construction documents defining 

properties are not complete or do not exist but the 

date of construction is known and single material 

use is confirmed, at least three locations shall be 

randomly verified—by sampling and testing or by 

observing grade stamps and conditions—for each 

component type, for every two floors in the building.

3. If no knowledge of the structural system and 

materials used exists, at least six locations shall be 

randomly verified—by sampling and testing or by 

observing grade stamps and conditions—for each 

element and component type, for every two floors of 

construction. If it is determined from testing or 

observation that more than one material grade exists, 

additional observations and testing shall be 

conducted until the extent of use for each grade in 

component fabrication has been established.

4. In the absence of construction records defining 

connector features present, at least three connectors 

of each connector type shall be observed for every 

floor of the building. 

5. A full-scale mock-up test shall be conducted for 

archaic assemblies; at least two cyclic tests of each 

assembly shall be conducted. A third test shall be 

conducted if the results of the two tests vary by more 

than 20%.

8.3.2.5 Default Properties

Use of default properties to determine component 

strengths shall be permitted in conjunction with the 

linear analysis procedures of Chapter 3.

Default expected strength and stiffness values for wood 

and light metal frame shear wall assemblies shall be 

taken from Table 8-1. Default expected strength and 

stiffness values for wood diaphragm assemblies shall be 

taken from Table 8-2.

C8.3.2.4 Minimum Number of Tests

In order to quantify expected strength and other inplace properties accurately, a minimum number of tests 

must be conducted on representative components. The 

minimum number of tests is dictated by available data 

from original construction, the type of structural system 

employed, desired accuracy, and quality/condition of 

in-place materials. Visual access to the structural 

system also influences testing program definition. As 

an alternative, the design professional may elect to use 

the default strength properties in accordance with 

Section 8.3.2.5. However, using default values without 

testing is only permitted with the linear analysis 

procedures. It is strongly encouraged that the expected 

strengths be derived through testing of assemblies in 

order to model behavior accurately.

Removal of coverings, including stucco, fireproofing, 

and partition materials, is generally required to 

facilitate sampling and observations.

Component types include solid-sawn lumber, glulam 

beam, and plywood diaphragm. Element types include 

primary gravity- and lateral-load-resisting components. 

The observations shall consist of each connector type 

present in the building (e.g., nails, bolts, straps), such 

that the composite strength of the connection can be 

estimated.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-7

Table 8-1 Default Expected Strength Values for Wood and Light Frame Shear Walls

Property

Shear Wall Type1

Shear Stiffness—Gd

(lb/in)

Yield Capacity (QCE)

(plf)

Single Layer Horizontal Lumber Sheathing or Siding 2000 80

Single Layer Diagonal Lumber Sheathing 8000 700

Double Layer Diagonal Lumber Sheathing 18000 1300

Vertical Wood Siding 1000 70

Wood Siding over Horizontal Sheathing 4000 500

Wood Siding over Diagonal Sheathing 11000 1100

Wood Structural Panel Sheathing2 -- --

Stucco on Studs, Sheathing, or Fiberboard 14000 350

Gypsum Plaster on Wood Lath 8000 400

Gypsum Plaster on Gypsum Lath 10000 80

Gypsum Wallboard 8000 100

Gypsum Sheathing 8000 100

Plaster on Metal Lath 12000 150

Horizontal Lumber Sheathing with Cut-in Braces or Diagonal 

Blocking

2000 80

Fiberboard or Particleboard Sheathing 6000 100

1. As defined in Section 8.5.

2. See Section 8.5.9 for shear stiffness and yield capacity of wood structural panel shear walls.
8-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

Default expected strength values for wood materials 

comprising individual components shall be based on 

design resistance values associated with the AF&PA/

ASCE 16 Standard for Load and Resistance Factor 

Design (LRFD) for Engineered Wood Construction

(ASCE 16) as determined in accordance with 

ASTM D5457-93. All adjustment factors, including the 

time-effect factor, that are applicable in accordance 

with ASCE 16 shall be considered. The resistance 

factor, φ, shall be taken as unity. If components are 

damaged, reductions in capacity and stiffness shall be 

applied, considering the position and size of the 

ineffective cross-section.

Default expected strength values for connectors shall be 

based on design resistance values associated with 

ASCE 16 as determined in accordance with 

ASTM D5457-93. All adjustment factors, including the 

time-effect factor, that are applicable in accordance 

with ASCE 16 shall be considered. The resistance 

factor, φ, shall be taken as unity.

Alternatively, expected strength values shall be 

permitted to be directly computed from allowable stress 

values listed in an approved code using the method 

contained in ASTM D5457-93.

Table 8-2 Default Expected Strength Values for Wood Diaphragms

Property

Diaphragm Type1

Shear Stiffness—Gd

(lb/in)

Yield Capacity (QCE)

(plf)

Single Straight Sheathing5 2,000 120

Double Straight Sheathing Chorded 15,000 600

Unchorded 7,000 400

Single Diagonally Sheathing Chorded 8,000 600

Unchorded 4,000 420

Diagonal Sheathing with Straight 

Sheathing or Flooring Above

Chorded 18,000 900

Unchorded 9,000 625

Double Diagonal Sheathing Chorded 18,000 900

Unchorded 9,000 625

Wood Structural Panel Sheathing2 Unblocked, 

Chorded

8,000 -

Unblocked, 

Unchorded

4,000 -

Wood Structural Panel Overlays on:

a. Straight or Diagonal Sheathing3

or

b. Existing Wood Structural 

Panel Sheathing4

Unblocked, 

Chorded

9,000 450

Unblocked, 

Unchorded

5,000 300

Blocked, Chorded 18,000 -

Blocked, Unchorded 7,000 -

1. As defined in Section 8.6.

2. See Section 8.6.8 for shear stiffness and yield capacity of wood structural panel diaphragms.

3. See Section 8.6.9 for yield capacity of wood structural panel overlays on straight or diagonal sheathing.

4. See Section 8.6.10 for yield capacity of wood structural panel overlays on existing wood structural panel sheathing.

5. For single straight sheathing, yield capacity shall be multiplied by 1.5 when built-up roofing is present. The value for stiffness shall not be 

changed.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-9

Default deformations at yield of connectors shall be 

taken as:

1. 0.02 inches for wood-to-wood and wood-to-metal 

nailed connections.

2. 0.05 inches for wood screws.

3. 0.10 inches for lag bolts.

4. 0.2 inches for wood-to-wood bolted connections.

5. 1.05 inches for wood-to-steel bolted connections.

The estimated deformation of any hardware including 

allowance for poor fit or oversized holes, shall be 

summed to obtain the total deformation of the 

connection.

Default expected strength values for connection 

hardware shall be taken as the average ultimate test 

values from published reports.

Default lower-bound strength values, when required in 

this chapter, shall be taken as expected strength values 

multiplied by 0.85.

C8.3.2.5 Default Properties

The results of any material testing performed should be 

compared to the default values for the particular era of 

building construction. If significantly reduced 

properties from testing are discovered, further 

evaluation should be undertaken.

Tables 8-1 and 8-2 contain default values for strength 

and stiffness of shear wall and diaphragm assemblies. 

The shear stiffness, Gd, for the assemblies should not 

be confused with the modulus of rigidity, G, for wood 

structural panels.

The LRFD methodology of ASCE 16 is based on the 

concepts of limit state design, similar to the provisions 

for strength design in steel or concrete. The reference 

resistance values for wood elements and connections 

associated with this standard are contained in the LRFD 

Manual for Engineered Wood Construction, including 

supplements and guidelines, (AF&PA LRFD). The 

resistance values in these documents were developed 

using ASTM D5457-93, which provides methodologies 

for calculation directly from data or by format 

conversion from approved allowable stress values. Use 

of a format conversion (i.e., the LRFD equivalent of 

allowable stresses) for computing expected strengths of 

wood materials comprising individual wood 

components and for wood connectors (nails, screws, 

lags, bolts, split rings, etc.) is permitted. This 

methodology is not applicable for wood shear wall and 

diaphragm assemblies covered in Tables 8-1 and 8-2. 

For use with this chapter, capacities for shear wall and 

diaphragm assemblies are to be taken directly from the 

tables or as indicated by the table footnotes.

The LRFD reference resistance is computed as the 

allowable stress value multiplied by a format 

conversion factor. The format conversion factor is 

defined as KE = 2.16/φ, where φ is the specified LRFD 

resistance factor: 0.90 for compression, 0.85 for 

flexure, 0.80 for tension, 0.75 for shear/torsion, and 

0.65 for connections. The allowable stress value shall 

include all applicable adjustment factors, except for the 

load duration factor. If allowable values already include 

consideration of duration effects, the load duration 

adjustment factor must be divided out prior to format 

conversion. Note that the time-effect factor specified 

for LRFD is 1.0 for load combinations that include 

earthquake loads.
8-10 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.3.3 Condition Assessment

8.3.3.1 General

A condition assessment of the existing building and site 

shall be performed as specified in this section.

A condition assessment shall include the following:

1. The physical condition of primary and secondary 

components shall be examined and the presence of 

degradation shall be noted.

2. The presence and configuration of components and 

their connections, and the continuity of load paths 

between components, elements, and systems shall be 

verified or established.

3. Other conditions, including neighboring party walls 

and buildings, presence of nonstructural 

components, prior remodeling, and limitations for 

rehabilitation that may influence building 

performance, shall be reviewed and documented. 

The NEHRP Recommended Provisions (BSSC, 2000) 

contain strength-based resistance values for wood 

structural panel shear walls and diaphragms. Allowable 

stress values for wood components and connections can 

be found in the National Design Specification for Wood 

Construction (NDS, 1997) and the ASD Manual for 

Engineered Wood Construction, including supplements 

and guidelines (AF&PA ASD).

AF&PA LRFD contains a guideline for calculating 

resistance values for connection hardware for which 

published report values are in allowable stress format. 

When computing the expected strength of connections, 

all limit states, including that of the connection 

hardware, must be considered (e.g., in addition to the 

published strength of a hold-down device, consider the 

limit states for the stud bolts, the anchor bolts in the 

foundation, etc.).

Actions associated with wood and light metal framing 

components generally are deformation-controlled, and 

expected strength material properties will be used most 

often. Lower bound values are needed for actions that 

are force-controlled. The 0.85 factor included in this 

standard to convert expected strength to lower bound 

values is based on the results of shear wall testing. If 

more precise lower bound material properties are 

desired, they should be taken as mean minus one 

standard deviation from test data for the components in 

question.

C8.3.3.1 General

The physical condition of existing components and 

elements and their connections must be examined for 

degradation. Degradation may include environmental 

effects (e.g., decay; splitting; fire damage; biological, 

termite, and chemical attack) or past/current loading 

effects (e.g., overload, damage from past earthquakes, 

crushing, and twisting). Natural wood also has inherent 

discontinuities such as knots, checks, and splits that 

must be noted. Configuration problems observed in 

recent earthquakes, including effects of discontinuous 

components, improper nailing or bolting, poor fit-up, 

and connection problems at the foundation level, should 

also be evaluated. Often, unfinished areas such as attic 

spaces, basements, and crawl spaces provide suitable 

access to wood components and can give a general 

indication of the condition of the rest of the structure. 

Invasive inspection of critical components and 

connections is typically required. Neighboring party 

walls and buildings, the presence of nonstructural 

components, prior remodeling, and limitations for 

rehabilitation should also be noted.

Connections require special consideration and 

evaluation. The load path for the system must be 

determined, and each connection in the load path(s) 

must be evaluated. This includes diaphragm-tocomponent and component-to-component connections. 

The strength and deformation capacity of connections 

must be checked where the connection is attached to 

one or more components that are expected to 

experience significant inelastic response. Anchorage of 

exterior walls to roof and floors in concrete and 

masonry buildings, for which wood diaphragms are 

used for out-of-plane loading, requires detailed 

inspection. Bolt holes in relatively narrow straps 

sometimes preclude the ductile behavior of the steel 

strap. Twists and kinks in the strap can also have a 

serious impact on its anticipated behavior. Cross ties, 

which are part of the wall anchorage system, need to be 

inspected to confirm their presence, along with the 

connection of each piece, to ensure that a positive load 

path exists to tie the building walls together.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-11

8.3.3.2 Scope and Procedures

All primary structural elements and components 

involved in gravity- and lateral-load resistance shall be 

included in the condition assessment.

8.3.3.2.1 Visual Condition Assessment

The dimensions and features of all accessible 

components shall be measured and compared to 

available design information. Similarly, the 

configuration and condition of all accessible 

connections shall be visually verified, with any 

deformations or anomalies noted.

8.3.3.2.2 Comprehensive Condition Assessment

If coverings or other obstructions exist, indirect visual 

inspection through the use of drilled holes and a 

fiberscope shall be used, or covering materials shall be 

removed locally based on the following requirements:

1. If detailed design drawings exist, at least three 

different primary connections shall be exposed for 

each connection type. If no capacity reducing 

deviations from the drawings exist, the sample shall 

be considered representative. If deviations are noted, 

then all coverings from primary connections of that 

type shall be removed unless the connection strength 

is ignored in the seismic evaluation.

2. In the absence of accurate drawings, at least 50% of 

all primary connection types shall be exposed and 

inspected or inspected fiberscopically. If common 

detailing is observed, this sample shall be considered 

representative. If any details or conditions are 

observed that result in a discontinuous load path, all 

primary connections shall be exposed. 

The condition assessment also affords an opportunity to 

review other conditions that may influence wood 

elements and systems and overall building 

performance. Of particular importance is the 

identification of other elements and components that 

may contribute to or impair the performance of the 

wood system in question, including infills, neighboring 

buildings, and equipment attachments. Limitations 

posed by existing coverings, wall and ceiling space 

insulation, and other material shall also be defined such 

that prudent rehabilitation measures can be planned.

C8.3.3.2 Scope and Procedures

Accessibility constraints may necessitate the use of 

instruments such as a fiberscope or video probe to 

reduce the amount of damage to covering materials and 

fabrics. The knowledge and insight gained from the 

condition assessment is invaluable to understanding 

load paths and the ability of components to resist and 

transfer loads. The degree of assessment performed also 

affects the knowledge factor discussed in Section 8.3.4.

Direct visual inspection provides the most valuable 

information, as it can be used to identify any 

configuration issues, allows measurement of 

component dimensions, and identifies the presence of 

degradation. The continuity of load paths may be 

established by viewing components and connection 

condition. From visual inspection, the need for other 

test methods to quantify the presence and degree of 

degradation may be established.

The scope of the removal effort is dictated by the 

component and element design. For example, in a 

braced frame, exposure of several key connections may 

suffice if the physical condition is acceptable and the 

configuration matches the design drawings. However, 

for shear walls and diaphragms, it may be necessary to 

expose more connection points because of varying 

designs and the critical nature of the connections. For 

encased walls and frames for which no drawings exist, 

it is necessary to indirectly view or expose all primary 

end connections for verification.

Physical condition of components and connectors may 

also support the need to use certain destructive and 

nondestructive test methods. Devices normally used for 

the detection of reinforcing steel in concrete or masonry 

may be used to verify the metal straps and hardware 

located beneath finish surfaces.
8-12 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.3.3.3 Basis for the Mathematical Building 

Model

The results of the condition assessment shall be used to 

quantify the following items needed to create the 

mathematical building model:

1. Component section properties and dimensions.

2. Component configuration and eccentricities.

3. Interaction of nonstructural components and their 

involvement in lateral-load resistance.

4. Presence and effects of alterations to the structural 

system.

All deviations noted between available construction 

records and as-built conditions shall be accounted for in 

the structural analysis.

8.3.4 Knowledge Factor

A knowledge factor, κ, for computation of wood and 

light metal framing component capacities and 

permissible deformations shall be selected in 

accordance with Section 2.2.6.4, with the following 

additional requirements specific to wood components 

and assemblies.

If a comprehensive condition assessment is performed 

in accordance with Section 8.3.3.2.2, a knowledge 

factor κ = 1.0 shall be permitted in conjunction with 

default properties of Section 8.3.2.5, and testing in 

accordance with Section 8.3.2.4 is not required.

8.4 General Assumptions and 

Requirements

8.4.1 Stiffness

Component stiffnesses shall be calculated in accordance 

with Sections 8.5 through 8.8.

Where design actions are determined using the linear 

procedures of Chapter 3, stiffnesses for wood materials 

comprising individual components shall be based on 

material properties determined in accordance with 

Section 8.3.2.

Where design actions are determined using the 

nonlinear procedures of Chapter 3, component forcedeformation response shall be represented by nonlinear 

force-deformation relations. Linear relations shall be 

permitted where nonlinear response will not occur in 

the component. The nonlinear force-deformation 

relation shall be either based on experimental evidence 

or the generalized force-deformation relation shown in 

Figure 8-1, with parameters c, d, and e as defined in 

Table 8-4 for wood components and assemblies. 

Distance d is considered the maximum deflection at the 

point of first loss of strength. Distance e is the 

maximum deflection at a strength or capacity equal to 

value c. Where the yield strength is not determined by 

testing in accordance with Section 2.8, the strength at 

point C shall be taken as 1.5 times the yield strength.

C8.3.3.3 Basis for the Mathematical Building 

Model

The acceptance criteria for existing components depend 

on the design professional’s knowledge of the condition 

of the structural system and material properties, as 

previously noted. Certain damage—such as water 

staining, evidence of prior leakage, splitting, cracking, 

checking, warping, and twisting—may be acceptable. 

The design professional must establish a case-by-case 

acceptance for such damage on the basis of capacity 

loss or deformation constraints. Degradation at 

connection points should be carefully examined; 

significant capacity reductions may be involved, as well 

as a loss of ductility.

Figure 8-1 Generalized Force-Deformation Relation 

for Wood Elements or Components
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-13

8.4.2 Strength and Acceptance Criteria

8.4.2.1 General

Actions in a structure shall be classified as being either 

deformation-controlled or force-controlled, as defined 

in Section 2.4.4. Design strengths for deformationcontrolled and force-controlled actions shall be 

calculated in accordance with Sections 8.4.2.2 and 

Sections 8.4.2.3, respectively.

8.4.2.2 Deformation-Controlled Actions

Expected strengths for deformation-controlled actions, 

QCE, shall be taken as yield strengths obtained 

experimentally or calculated using accepted principles 

of mechanics. Unless other procedures are specified in 

this chapter, the expected strengths shall be permitted to 

be based on the LRFD procedures contained in 

ASCE 16, except that the resistance factor, φ, shall be 

taken as unity. Material properties shall be determined 

in accordance with Section 8.3.2. Acceptance criteria 

for deformation-controlled actions shall be as specified 

in Sections 8.5 through 8.8.

8.4.2.3 Force-Controlled Actions

Where obtained by testing, lower-bound strengths for 

force-controlled actions, QCL, shall be taken as the 

mean minus one standard deviation of yield strengths. 

Where calculated using established principles of 

mechanics or based on LRFD procedures contained in 

ASCE 16, lower-bound strength values shall be 

determined using the default lower bound material 

properties defined in Section 8.3.2.5.

Where the force-controlled design actions, QUF, 

calculated in accordance with Section 3.4.2.1.2 are 

based on a limit-state analysis, the expected strength of 

the components delivering load to the component under 

consideration shall be taken as 1.5 times the yield 

strength.

8.4.3 Connection Requirements

Unless otherwise specified in this standard, connections 

between wood components in a lateral-force-resisting 

system shall be considered in accordance with this 

section. Demands on connectors, including nails, 

screws, lags, bolts, split rings, and shear plates used to 

link wood components to other wood or metal 

components, shall be considered deformationcontrolled actions. Demands on bodies of connections, 

and bodies of connection hardware, shall be considered 

force-controlled actions.

C8.4.2.2 Deformation-Controlled Actions

The relative magnitude of the m-factors alone should 

not be interpreted as a direct indicator of performance. 

The stiffness of a component and its expected strength, 

QCE, must be considered when evaluating expected 

performance, For example, while the m-factors for 

gypsum plaster are higher than those for wood 

structural panels, the stiffness assigned to gypsum 

plaster is relatively high and the expected strength 

values are much lower than those for wood structural 

panels. As a result, worse performance for a given 

displacement is predicted.

C8.4.2.3 Force-Controlled Actions

The maximum forces developed in yielding shear walls 

and diaphragms are consistently 1.5 to 2 times the yield 

force. Other wood components and connectors exhibit 

similar overstrength.

C8.4.3 Connection Requirements

In considering connections between wood components 

in this standard, connectors are distinguished from 

bodies of connections. Connectors, which consist of the 

nails, screws, lags, bolts, split rings, and shear plates 

used to link pieces of a connection assembly together, 

are considered to have the ability to deform in a ductile 

manner, provided the bodies of the connections do not 

prematurely fracture. Much of the ductility in a wood 

shear wall or diaphragm assembly comes from bending 

in the nails prior to point where nails pull through the 

sheathing material. In bolted connections, bolt bending 

or crushing of the wood around the bolt hole are ductile 

sources of deformation in an assembly, as long as net 

section fracture or splitting do not occur. For this 

reason, connectors are considered deformationcontrolled and bodies of connections are considered 

force-controlled. When determining the demand on 

force-controlled portions of the connection assembly, 

use of a limit-state analysis to determine the maximum 

force that can be delivered to the connection is 

recommended.
8-14 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.4.4 Rehabilitation Measures

If portions of a wood building structure are deficient for 

the selected Rehabilitation Objective, the structure shall 

be rehabilitated, reinforced, or replaced. If replacement 

of the element is selected, the new element shall be 

designed in accordance with an approved building code. 

If reinforcement of the existing framing system is 

selected, the following factors shall be considered:

1. Degree of degradation in the component from such 

mechanisms as biological attack, creep, high static 

or dynamic loading, moisture, or other effects.

2. Level of steady state stress in the components to be 

reinforced and the potential to temporarily remove 

this stress if appropriate.

3. Elastic and inelastic properties of existing 

components; strain compatibility with any new 

reinforcement materials shall be preserved.

4. Ductility, durability, and suitability of existing 

connectors between components, and access for 

reinforcement or modification.

5. Efforts necessary to achieve appropriate fit-up for 

reinforcing components and connections.

6. Load path and deformation of the components at end 

connections.

7. Presence of components manufactured with archaic 

materials, which may contain material 

discontinuities and shall be examined during the 

rehabilitation design to ensure that the selected 

reinforcement is feasible.

8.5 Wood and Light Frame Shear 

Walls

8.5.1 General

Wood and light frame shear walls shall be categorized 

as primary or secondary elements. Walls that are 

considered part of the lateral-force-resisting system 

shall be considered primary elements. Walls that are not 

considered part of the lateral-force-resisting system, but 

must remain stable to support the gravity loads during 

seismic excitation, shall be considered secondary 

elements.

Dissimilar wall sheathing materials on opposite sides of 

a wall shall not be combined when calculating the 

capacity of the wall. Different walls sheathed with 

dissimilar materials along the same line of lateral-force 

resistance shall be analyzed based on only the wall 

sheathing with the greatest capacity. The walls shall be 

analyzed based on the relative rigidity and capacity of 

the materials to determine if performance of the 

secondary elements is acceptable.

For overturning calculations on shear wall elements, 

stability shall be evaluated in accordance with 

Section 3.2.10. Net tension due to overturning shall be 

resisted by uplift connections.

When computing the strength of connections, all 

potential limit states should be considered, including 

those associated with the bodies of connection 

hardware or connectors with which the assembly may 

be composed. For example, in addition to the strength 

of a hold-down device itself, limit states for the stud 

bolts, foundation bolts, and net section of the end post 

should be considered. The controlling condition will 

determine the expected or lower-bound strength of the 

connection.

C8.4.4 Rehabilitation Measures

Special attention is required where connections such as 

bolts and nails are encountered.

Wood structural panels are used to provide lateral 

strength and stiffness to most modern wood frame 

buildings and are generally recommended for the 

rehabilitation of horizontal diaphragms and shear walls 

of existing buildings. The system relies on the in-plane 

strength and stiffness of the panels and their connection 

to the framing. Panels are connected together by nailing 

into the same structural member to create, in effect, one 

continuous panel. The various panels are described in 

Sections 8.5 and 8.6. The performance of the structural 

panels is dependent to a great degree on the nailing or 

attachment to the framing. The nail spacing and 

effectiveness of the attachment should be investigated 

if the existing panels are expected to withstand 

significant loads. If nails are to be added to existing 

panels, they should be the same size as the existing 

nails.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-15

The effects of openings in wood shear walls shall be 

considered. Where required, reinforcement consisting 

of chords and collectors shall be added to provide 

sufficient load capacity around openings to meet the 

requirements for shear walls.

Connections between shear walls and other components 

including drag struts, collectors, diaphragms, posts, and 

foundations shall be considered in accordance with 

Section 8.4.3, and designed for forces calculated in 

accordance with Chapter 3. Components supporting 

discontinuous shear walls shall be considered in 

accordance with Section 8.8.2.

The expected strength, QCE, of wood and light frame 

shear walls shall be taken as the yield capacity of the 

shear wall assembly determined in accordance with 

Sections 8.5.4 through 8.5.18.

8.5.2 Types of Wood Frame Shear Walls

8.5.2.1 Existing Wood Frame Shear Walls

8.5.2.1.1 Single Layer Horizontal Lumber 

Sheathing or Siding

Single layer horizontal lumber sheathing or siding shall 

include horizontal sheathing or siding applied directly 

to studs or horizontal boards nailed to studs 2 inches or 

greater in width.

C8.5.1 General

The behavior of wood and light frame shear walls is 

complex and influenced by many factors, the primary 

factor being the wall sheathing. Wall sheathings can be 

divided into many categories (e.g., brittle, elastic, 

strong, weak, good at dissipating energy, poor at 

dissipating energy). In many existing buildings, the 

walls were not expected to act as shear walls (e.g., a 

wall sheathed with wood lath and plaster). Most shear 

walls are designed based on values from monotonic 

load tests and historically accepted values. The 

allowable shear per unit length used for design was 

assumed to be the same for long walls, narrow walls, 

walls with stiff tie-downs, and walls with flexible tiedowns. Only recently have shear wall assemblies—

framing, covering, anchorage—been tested using cyclic 

loading.

Another major factor influencing the behavior of shear 

walls is the aspect ratio of the wall. The NEHRP 

Recommended Provisions (BSSC, 2000) limit the 

aspect ratio (height-to-width) for structural panel shear 

walls to 2:1 for full design shear capacity and permit 

reduced design shear capacities for walls with aspect 

ratios up to 3.5:1. The interaction of the floor and roof 

with the wall, the end conditions of the wall, and the 

redundancy or number of walls along any wall line 

would affect the wall behavior for walls with the same 

aspect ratio. In addition, the rigidity of the tie-downs at 

the wall ends has an important effect in the behavior of 

narrow walls.

The presence of any but small openings in wood shear 

walls will cause a reduction in the stiffness and yield 

capacity due to a reduced length of wall available to 

resist lateral forces. Special analysis techniques and 

detailing are required at the openings. The presence or 

addition of chord members around the openings will 

reduce the loss in overall stiffness and limit damage in 

the area of openings. See BSSC (2000) for 

reinforcement requirements around openings in wood 

shear walls.

For wood and light frame shear walls, the important 

limit states are sheathing failure, connection failure, tiedown failure, and excessive deflection. Limit states 

define the point of life safety and, often, of structural 

stability. To reduce damage or retain usability 

immediately after an earthquake, deflection must be 

limited (see Section 2.5). The ultimate capacity is the 

maximum capacity of the assembly, regardless of the 

deflection.

C8.5.2.1.1 Single Layer Horizontal Lumber 

Sheathing or Siding

Typically, 1"x horizontal sheathing or siding is applied 

directly to studs. Forces are resisted by nail couples. 

Horizontal boards, from 1" x 4" to 1" x 12", typically 

are nailed to 2"x or greater width studs with two or 

more nails (typically 8d or 10d) per stud.
8-16 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.2.1.2 Diagonal Lumber Sheathing

Diagonal lumber sheathing shall include sheathing 

applied at a 45-degree angle to the studs in a single or 

double layer with three or more nails per stud, sill and 

top plates. 

8.5.2.1.3 Vertical Wood Siding Only

Vertical wood siding shall include vertical boards nailed 

directly to studs and blocking 2 inches or greater in 

width.

8.5.2.1.4 Wood Siding over Horizontal Sheathing

Wood siding over horizontal sheathing shall include 

siding connected to horizontal sheathing with nails that 

go through the sheathing to the studs.

8.5.2.1.5 Wood Siding over Diagonal Sheathing

Wood siding over diagonal sheathing shall include 

siding connected to diagonal sheathing with nails that 

go through the sheathing to the studs.

8.5.2.1.6 Wood Structural Panel Sheathing or 

Siding

Wood structural panel sheathing or siding shall include 

wood structural panels, as defined in this standard, 

oriented vertically or horizontally and nailed to studs 2 

inches or greater in width.

8.5.2.1.7 Stucco on Studs

Stucco on studs (over sheathing or wire-backed 

building paper) shall include portland cement plaster 

applied to wire lath or expanded metal lath. Wire lath or 

expanded metal lath shall be nailed to the studs.

8.5.2.1.8 Gypsum Plaster on Wood Lath

Gypsum plaster on wood lath shall include gypsum 

plaster keyed onto spaced wood lath that is nailed to the 

studs. 

C8.5.2.1.2 Diagonal Lumber Sheathing

Typically, 1" x 6" or 1" x 8" diagonal sheathing, applied 

directly to the studs, resists lateral forces primarily by 

triangulation (i.e., direct tension and compression). 

Sheathing boards are installed at a 45-degree angle to 

studs, with three or more nails (typically 8d or 10d) per 

stud, and to sill and top plates. A second layer of 

diagonal sheathing is sometimes added on top of the 

first layer, at 90 degrees to the first layer (called Double 

Diagonal Sheathing), for increased load capacity and 

stiffness.

C8.5.2.1.3 Vertical Wood Siding Only

Typically, 1" x 8", 1" x 10", or 1" x 12" vertical boards 

are nailed directly to 2"x or greater width studs and 

blocking with 8d or 10d galvanized nails. The lateral 

forces are resisted by nail couples, similarly to 

horizontal siding.

C8.5.2.1.4 Wood Siding over Horizontal Sheathing

Typically, siding is nailed with 8d or 10d galvanized 

nails through the sheathing to the studs. Lateral forces 

are resisted by nail couples for both layers.

C8.5.2.1.5 Wood Siding over Diagonal Sheathing

Typically, siding is nailed with 8d or 10d galvanized 

nails to and through the sheathing into the studs. 

Diagonal sheathing provides most of the lateral 

resistance by triangulation (see Section 8.5.2.1.2).

C8.5.2.1.6 Wood Structural Panel Sheathing or 

Siding

Typically, 4′ x 8′ panels are applied vertically or 

horizontally to 2"x or greater studs and nailed with 6d 

to 10d nails. These panels resist lateral forces by panel 

diaphragm action.

C8.5.2.1.7 Stucco on Studs

Typically, 7/8-inch portland cement plaster is applied to 

wire lath or expanded metal lath. Wire lath or expanded 

metal lath is nailed to the studs with 11 gage nails or 16 

gage staples at 6 inches on center. This assembly resists 

lateral forces by panel diaphragm action.

C8.5.2.1.8 Gypsum Plaster on Wood Lath

Typically, 1-inch gypsum plaster is keyed onto spaced 

1-1/4-inch wood lath that is nailed to studs with 13 gage 

nails. Gypsum plaster on wood lath resists lateral forces 

by panel diaphragm-shear action.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-17

8.5.2.1.9 Gypsum Plaster on Gypsum Lath

Gypsum plaster on gypsum lath shall include plaster 

that is glued or keyed to gypsum lath nailed to studs.

8.5.2.1.10 Gypsum Wallboard or Drywall

Gypsum wallboard or drywall shall include 

manufactured panels with a paper facing and gypsum 

core that are oriented horizontally or vertically and 

nailed to studs or blocking in a single layer or multiple 

layers.

8.5.2.1.11 Gypsum Sheathing

Gypsum sheathing shall include manufactured gypsum 

panels that are oriented horizontally or vertically and 

nailed to studs or blocking.

8.5.2.1.12 Plaster on Metal Lath

Plaster on metal lath shall include gypsum plaster 

applied to expanded wire lath that is nailed to the studs.

8.5.2.1.13 Horizontal Lumber Sheathing with Cut-In 

Braces or Diagonal Blocking

Horizontal lumber sheathing with cut-in braces or 

diagonal blocking shall include 1"x horizontal 

sheathing or siding applied directly to studs or 1" x 4" to 

1" x 12" horizontal boards nailed to studs 2 inches or 

greater in width. The wall shall be braced with diagonal 

cut-in braces or blocking extending from corner to 

corner.

8.5.2.1.14 Fiberboard or Particleboard Sheathing

Fiberboard or particleboard sheathing walls shall 

include fiberboard or particleboard panels that are 

applied directly to the studs with nails.

8.5.2.2 Enhanced Wood Frame Shear Walls

Enhanced wood frame shear walls shall include existing 

shear walls rehabilitated in accordance with an 

approved method. Enhanced wood shear walls shall be 

evaluated in accordance with Section 8.5.9.

C8.5.2.1.9 Gypsum Plaster on Gypsum Lath

Typically, 1/2-inch plaster is glued or keyed to 16" x 

48" gypsum lath, which is nailed to studs with 13 gage 

nails. Gypsum plaster on gypsum lath resists lateral 

loads by panel diaphragm action.

C8.5.2.1.10 Gypsum Wallboard or Drywall

Typically, 4′x 8′ to 4′ x 12′ panels are laid-up 

horizontally or vertically and nailed to studs or 

blocking with 5d to 8d cooler nails at 4 to 7 inches on 

center. Multiple layers are used in some situations. The 

assembly resists lateral forces by panel diaphragm 

action.

C8.5.2.1.11 Gypsum Sheathing

Typically, 4′ x 8′ to 4′ x 12′ panels are laid-up 

horizontally or vertically and nailed to studs or 

blocking with galvanized 11 gage 7/16-inch diameter 

head nails at 4 to 7 inches on center. Gypsum sheathing 

is usually installed on the exterior of structures with 

siding over it in order to improve fire resistance. Lateral 

forces are resisted by panel diaphragm action.

C8.5.2.1.12 Plaster on Metal Lath

Typically, 1-inch gypsum plaster is applied on 

expanded wire lath that is nailed to the studs. Lateral 

forces are resisted by panel diaphragm action.

C8.5.2.1.13 Horizontal Lumber Sheathing with Cut-In 

Braces or Diagonal Blocking

Horizontal sheathing with cut-in braces or diagonal 

blocking is installed in the same manner as horizontal 

sheathing, except the wall is braced with cut-in (or letin) braces or blocking. The bracing is usually installed 

at a 45-degree angle and nailed with 8d or 10d nails at 

each stud, and at the top and bottom plates. Bracing 

provides only nominal increase in resistance.

C8.5.2.1.14 Fiberboard or Particleboard Sheathing

Typically, 4′ x 8′ panels are applied directly to the studs 

with nails. Fiberboard requires nails (typically 8d) with 

large heads such as roofing nails. Lateral loads are 

resisted by panel diaphragm action.

C8.5.2.2 Enhanced Wood Frame Shear Walls

Possible rehabilitation methods for wood shear walls 

are described in Sections C8.5.2.2.1 through 

C8.5.2.2.5.

C8.5.2.2.1 Wood Structural Panel Sheathing Added 

to Unfinished Stud Walls

Wood structural panel sheathing may be added to one 

side of unfinished stud walls to increase the wall shear 

capacity and stiffness.
8-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

Examples of unfinished stud walls are cripple walls and 

attic end walls.

C8.5.2.2.2 Wood Structural Panel Sheathing Overlay 

of Existing Shear Walls

The following types of existing shear walls may be 

overlaid with wood structural panel sheathing:

1. Single layer horizontal lumber sheathing or siding.

2. Single layer diagonal lumber sheathing.

3. Vertical wood siding only.

4. Gypsum plaster or wallboard on studs (also on 

gypsum lath and gypsum wallboard).

5. Gypsum sheathing.

6. Horizontal lumber sheathing with cut-in braces or 

diagonal blocking.

7. Fiberboard or particleboard sheathing.

The original sheathing should not be included in the 

evaluation conducted in accordance with Section 8.5.9 

and the yield capacity of the overlay material should be 

reduced by 20%.

This method results in a moderate increase in shear 

capacity and stiffness and can be applied in most places 

in most structures. For example, plywood sheathing can 

be applied over an interior wall finish. For exterior 

applications, the wood structural panel can be nailed 

directly through the exterior finish to the studs.

When existing shear walls are overlaid with wood 

structural panels, the connections of the overlay to the 

existing framing must be considered. Splitting can 

occur in both the wood sheathing and the framing. The 

length of nails needed to achieve full capacity 

attachment in the existing framing must be determined. 

This length will vary with the thickness of the existing 

wall covering. Sometimes staples are used instead of 

nails to prevent splitting. The overlay is stapled to the 

wood sheathing instead of the framing. Nails are 

recommended for overlay attachment to the underlying 

framing. In some cases, new blocking at wood 

structural panel joints may also be needed.

C8.5.2.2.3 Wood Structural Panel Sheathing Added 

under Existing Wall Covering

The existing wall covering may be removed; wood 

structural panel sheathing, connections, and tie-downs 

may be added; and the wall covering may be replaced.

This method will result in a significant increase in shear 

capacity. In some cases, where earthquake loads are 

large, this may be the best method of rehabilitation. 

This rehabilitation procedure can be used on any of the 

existing shear wall assemblies. Additional framing 

members can be added if necessary, and the wood 

structural panels can be cut to fit existing stud spacings.

C8.5.2.2.4 Increased Attachment

Additional nailing, collector straps, splice straps, tiedowns or other collectors may be added to existing 

wood structural panel-sheathed walls to increase their 

rigidity and capacity.

For existing structural panel-sheathed walls, additional 

nailing will result in higher capacity and increased 

stiffness. Other connectors—collector straps, splice 

straps, or tie-downs—are often necessary to increase 

the rigidity and capacity of existing structural panel 

shear walls. Increased ductility will not necessarily 

result from the additional nailing. Access to these shear 

walls will often require the removal and replacement of 

existing finishes.

C8.5.2.2.5 Connections

Where absent, new connections between shear walls 

and diaphragms and foundations may be added. Where 

needed, blocking between floor and roof joists at shear 

walls may be added. Blocking should be connected to 

the shear wall and the diaphragm to provide a load path 

for lateral loads. Wood for framing members or 

blocking should be kiln-dried or well-seasoned to 

prevent it from shrinking away from the existing 

framing, or splitting.

Most shear wall rehabilitation procedures require a 

check of all existing connections, especially to 

diaphragms and foundations. Sheet metal framing clips 

can be used to provide a verifiable connection between 

the wall framing, the blocking, and the diaphragm. 

Framing clips are also often used for connecting 

blocking or rim joists to sill plates.

Frequently, bolting between sill plates and foundations 

must be added.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-19

8.5.2.3 New Wood Frame Shear Walls

New wood frame shear walls shall include all new 

wood structural panel shear walls added to an existing 

lateral-force-resisting system. Design of new walls shall 

be in accordance with the requirements of an approved 

building code.

8.5.3 Types of Light Gage Metal Frame 

Shear Walls

8.5.3.1 Existing Light Gage Metal Frame 

Shear Walls

8.5.3.1.1 Plaster on Metal Lath

Plaster on metal lath shall include gypsum plaster 

applied to metal lath or expanded metal lath that is 

connected to the metal framing with wire ties.

8.5.3.1.2 Gypsum Wallboard

Gypsum wallboard shear walls shall include gypsum 

wallboard panels that are attached to the studs.

8.5.3.1.3 Wood Structural Panel Sheathing or 

Siding

Wood structural panel shear walls shall include 

structural panels that are attached to the studs and 

tracks.

8.5.3.2 Enhanced Light Gage Metal Frame 

Shear Walls

Enhanced light gage metal frame shear walls shall 

include existing shear walls rehabilitated in accordance 

with an approved method.

The framing in existing buildings is usually very dry, 

hard, and easily split. Care must be taken not to split the 

existing framing when adding connectors. Predrilling 

holes for nails will reduce splitting, and framing clips 

that use small nails are less likely to split the existing 

framing.

C8.5.2.3 New Wood Frame Shear Walls

New shear walls using the existing framing or new 

framing generally are sheathed with wood structural 

panels (i.e., plywood or oriented strand board). 

According to the NEHRP Recommended Provisions 

(BSSC, 2000), only wood structural panel sheathing is 

permitted for use in wood frame shear walls in 

engineered construction. The thickness and grade of 

these panels can vary. In most cases, the panels are 

placed vertically and fastened directly to the studs and 

plates. This reduces the need for blocking at the joints. 

All edges of panels must be blocked to obtain full 

capacity. The thickness, size, and number of fasteners, 

and aspect ratio and connections will determine the 

capacity of the new walls. Additional information on 

the various panels available and their application for 

shear walls can be found in documents from the 

American Plywood Association (APA) such as APA 

(1995 and 1997) and Tissell (1993).

C8.5.3.1.1 Plaster on Metal Lath

Typically, 1 inch of gypsum plaster is applied to metal 

lath or expanded metal that is connected to the metal 

framing with wire ties.

C8.5.3.1.2 Gypsum Wallboard

Typically, 4′ x 8′ to 4′ x 12′ panels are laid-up 

horizontally and screwed with No. 6 x 1-inch-long selftapping screws to studs at 4 to 7 inches on center.

C8.5.3.1.3 Wood Structural Panel Sheathing or 

Siding

Typically, the wood structural panels are applied 

vertically and screwed to the studs and tracks with No. 

8 to No. 12 self-tapping screws.

C8.5.3.2 Enhanced Light Gage Metal Frame 

Shear Walls

Possible rehabilitation methods for light gage metal 

frame shear walls are described in Sections C8.5.3.2.1 

and C8.5.3.2.2. See Section 8.5.2.2 for additional 

information concerning enhancement of existing shear 

walls.

C8.5.3.2.1 Wood Structural Panel Sheathing Added 

to Existing Metal Stud Walls

Any existing covering other than wood structural 

panels shall be removed and replaced with wood 

structural panels. Connections to the diaphragm(s) and 

the foundation shall be checked and strengthened when 

not adequate to resist enhanced wall capacity.

C8.5.3.2.2 Increased Attachment

Screws and connections shall be added to connect 

existing wood structural panels to framing.
8-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.3.3 New Light Gage Metal Frame Shear 

Walls

New light gage metal frame shear walls shall include all 

new wood structural panel elements added to an 

existing lateral-force-resisting system. Design of new 

walls shall be in accordance with the requirements of an 

approved building code.

8.5.4 Single Layer Horizontal Lumber 

Sheathing or Siding Shear Walls

8.5.4.1 Stiffness

The deflection of single layer horizontal lumber 

sheathing or siding shear walls shall be calculated in 

accordance with Equation (8-1):

∆y = vy h/Gd + (h/b)da (8-1)

where:

Properties used to compute shear wall deflection and 

stiffness shall be based on Section 8.3.2. 

8.5.4.2 Strength

The yield capacity of horizontal sheathing or siding 

shall be determined in accordance with Section 8.3.2. 

8.5.4.3 Acceptance Criteria

For linear procedures, m-factors for use with deformation-controlled actions shall be taken from Table 8-3. 

For nonlinear procedures, the coordinates of the generalized force-deformation relations, described by Figure 

8-1, and deformation acceptance criteria for primary 

and secondary components shall be taken from Table 

8-4.

8.5.4.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

b = Shear wall width

h = Shear wall height

vy = Shear at yield in the direction under 

consideration

Gd = Shear stiffness from Table 8-1

∆y = Calculated deflection of shear wall at yield

da = Elongation of anchorage at end of wall 

determined by anchorage details and load 

magnitude

C8.5.4.1 Stiffness

Horizontal lumber sheathed shear walls are weak and 

very flexible and have long periods of vibration. The 

strength and stiffness degrade with cyclic loading. 

These shear walls are suitable only where earthquake 

shear loads are low and deflection control is not 

required.

C8.5.4.2 Strength 

This capacity is dependent on the width of the boards, 

spacing of the studs, and the size, number, and spacing 

of the nails. Allowable capacities are listed for various 

configurations, together with a description of the nail 

couple method, in the WWPA (1996). See also ATC-7

for a discussion of the nail couple method.

C8.5.4.3 Acceptance Criteria

Deformation acceptance criteria are determined by the 

capacity of lateral- and gravity-load-resisting components and elements to deform with limited damage or 

without failure. Excessive deflection could result in 

major damage to the structure and/or its contents.

C8.5.4.4 Connections

The capacity and ductility of these connections will 

often determine the failure mode0well as the capacity 

of the assembly. Ductile connections with sufficient 

capacity will give acceptable and expected performance 

(see Section 8.3.2.2.2).
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-21

Table 8-3 Numerical Acceptance Factors for Linear Procedures—Wood Components

m-factors

IO

Primary Secondary

LS CP LS CP

Wood and Light Frame Shear Walls1, 3 Height/Width

Ratio (h/b)

Horizontal 1" x 6" Sheathing h/b ≤ 1.0 1.8 4.2 5.0 5.0 5.5

Horizontal 1" x 8" or 1" x 10" Sheathing h/b ≤ 1.0 1.6 3.4 4.0 4.0 5.0

Horizontal Wood Siding Over Horizontal 1" x 6" Sheathing h/b ≤ 1.0 1.4 2.6 3.0 3.1 4.0

Horizontal Wood Siding Over Horizontal 1" x 8" or 1" x 10" Sheathing h/b ≤ 1.5 1.3 2.3 2.6 2.8 3.0

Diagonal 1" x 6" Sheathing h/b ≤ 1.5 1.5 2.9 3.3 3.4 3.8

Diagonal 1" x 8" Sheathing h/b ≤ 1.5 1.4 2.7 3.1 3.1 3.6

Horizontal Wood Siding Over Diagonal 1" x 6" Sheathing h/b ≤ 2.0 1.3 2.2 2.5 2.5 3.0

Horizontal Wood Siding Over Diagonal 1" x 8" Sheathing h/b ≤ 2.0 1.3 2.0 2.3 2.5 2.8

Double Diagonal 1" x 6" Sheathing h/b ≤ 2.0 1.2 1.8 2.0 2.3 2.5

Double Diagonal 1" x 8" Sheathing h/b ≤ 2.0 1.2 1.7 1.9 2.0 2.5

Vertical 1" x 10" Sheathing h/b ≤ 1.0 1.5 3.1 3.6 3.6 4.1

Wood Structural Panel Sheathing or Siding2 h/b < 1.0 1.7 3.8 4.5 4.5 5.5

2.0 ≤ h/b ≤ 3.5 1.4 2.6 3.0 6.0 7.0

Stucco on Studs2 h/b ≤1.0 1.5 3.1 3.6 3.6 4.0

h/b = 2.0 1.3 2.2 2.5 5.0 6.0

Stucco over 1"-x Horizontal Sheathing h/b ≤ 2.0 1.5 3.0 3.5 3.5 4.0

Gypsum Plaster on Wood Lath h/b ≤ 2.0 1.7 3.9 4.6 4.6 5.1

Gypsum Plaster on Gypsum Lath h/b ≤ 2.0 1.8 4.2 5.0 4.2 5.5

Gypsum Plaster on Metal Lath h/b ≤ 2.0 1.7 3.7 4.4 3.7 5.0

Gypsum Sheathing h/b ≤ 2.0 1.9 4.7 5.7 4.7 6.0

Gypsum Wallboard2 h/b ≤ 1.0 1.9 4.7 5.7 4.7 6.0

h/b = 2.0 1.6 3.4 4.0 3.8 4.5

Horizontal 1" x 6" Sheathing with Cut-In Braces or Diagonal Blocking h/b ≤ 1.0 1.7 3.7 4.4 4.2 4.8

Fiberboard or Particleboard Sheathing h/b ≤ 1.5 1.6 3.2 3.8 3.8 5.0

1. Shear walls shall be permitted to be classified as secondary components or nonstructural components, subject to the limitations of Section 3.2.2.3. 

Acceptance criteria need not be considered for walls classified as secondary or nonstructural.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

5. For diaphragm components with aspect ratios between maximum listed values and 4.0, m-factors shall be decreased by linear interpolation between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.
8-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

Diaphragms5 Length/Width

Ratio (L/b)

Single Straight Sheathing, Chorded L/b ≤ 3.0 1 2.0 2.5 2.4 3.1

Single Straight Sheathing, Unchorded L/b ≤ 3.0 1 1.5 2.0 1.8 2.5

Double Straight Sheathing, Chorded L/b ≤ 3.0 1.25 2.0 2.5 2.3 2.8

Double Straight Sheathing, Unchorded L/b ≤ 3.0 1 1.5 2.0 1.8 2.3

Single Diagonal Sheathing, Chorded L/b ≤ 3.0 1.25 2.0 2.5 2.3 2.9

Single Diagonal Sheathing, Unchorded L/b ≤ 3.0 1 1.5 2.0 1.8 2.5

Straight Sheathing Over Diagonal Sheathing, Chorded L/b ≤ 3.0 1.5 2.5 3.0 2.8 3.5

Straight Sheathing Over Diagonal Sheathing, Unchorded L/b ≤ 3.0 1.25 2.0 2.5 2.3 3.0

Double Diagonal Sheathing, Chorded L/b ≤ 3.5 1.5 2.5 3.0 2.9 3.5

Double Diagonal Sheathing, Unchorded L/b ≤ 3.5 125 2.0 2.5 2.4 3.1

Wood Structural Panel, Blocked, Chorded2 L/b ≤ 3.0 1.5 3.0 4.0 3.0 4.5

L/b = 4 1.5 2.5 3.0 2.8 3.5

Wood Structural Panel, Unblocked, Chorded2 L/b ≤ 3 1.5 2.5 3.0 2.9 4.0

L/b = 4 1.5 2.0 2.5 2.6 3.2

Wood Structural Panel, Blocked, Unchorded2 L/b ≤ 2.5 1.25 2.5 3.0 2.9 4.0

L/b = 3.5 1.25 2.0 2.5 2.6 3.2

Wood Structural Panel, Unblocked, Unchorded2 L/b ≤ 2.5 1.25 2.0 2.5 2.4 3.0

L/b = 3.5 1.0 1.5 2.0 2.0 2.6

Wood Structural Panel Overlay on Sheathing, Chorded2 L/b ≤ 3 1.5 2.5 3.0 2.9 4.0

L/b = 4 1.5 2.0 2.5 2.6 3.2

Wood Structural Panel Overlay on Sheathing, Unchorded2 L/b ≤ 2.5 1.25 2.0 2.5 2.4 3.0

L/b = 3.5 1.0 1.5 2.0 1.9 2.6

Table 8-3 Numerical Acceptance Factors for Linear Procedures—Wood Components (continued)

m-factors

IO

Primary Secondary

LS CP LS CP

1. Shear walls shall be permitted to be classified as secondary components or nonstructural components, subject to the limitations of Section 3.2.2.3. 

Acceptance criteria need not be considered for walls classified as secondary or nonstructural.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

5. For diaphragm components with aspect ratios between maximum listed values and 4.0, m-factors shall be decreased by linear interpolation between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-23

Components/Elements

Frame components subject to axial tension and/or bending 1.0 2.5 3.0 2.5 4.0

Frame components subject to axial compression force-controlled

Wood piles, bending and axial 1.2 2.5 3.0 — —

Cantilever pole structures, bending and axial 1.2 3.0 3.5 — —

Pole structures with diagonal bracing 1.0 2.5 3.0 — —

Connectors4

Nails—8d and larger—Wood to Wood 2.0 6.0 8.0 8.0 9.0

Nails—8d and larger—Metal to Wood 2.0 4.0 6.0 5.0 7.0

Screws—Wood to Wood 1.2 2.0 2.2 2.0 2.5

Screws—Metal to Wood 1.1 1.8 2.0 1.8 2.3

Lag Bolts—Wood to Wood 1.4 2.5 3.0 2.5 3.3

Lag Bolts—Metal to Wood 1.3 2.3 2.5 2.4 3.0

Machine Bolts—Wood to Wood 1.3 3.0 3.5 3.3 3.9

Machine Bolts—Metal to Wood 1.4 2.8 3.3 3.1 3.7

Split Rings and Shear Plates 1.3 2.2 2.5 2.3 2.7

Bolts—Wood to Concrete or Masonry 1.4 2.7 3.0 2.8 3.5

Table 8-3 Numerical Acceptance Factors for Linear Procedures—Wood Components (continued)

m-factors

IO

Primary Secondary

LS CP LS CP

1. Shear walls shall be permitted to be classified as secondary components or nonstructural components, subject to the limitations of Section 3.2.2.3. 

Acceptance criteria need not be considered for walls classified as secondary or nonstructural.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

5. For diaphragm components with aspect ratios between maximum listed values and 4.0, m-factors shall be decreased by linear interpolation between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.
8-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

Table 8-4 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Wood Components

Modeling Parameters Acceptance Criteria

Residual 

Strength 

Ratio

Acceptable Deformation Ratio ∆ / ∆y

Performance Level

IO

Component Type

Primary Secondary

d e c LS CP LS CP

Wood and Light Frame 

Shear Walls1

Height/Width

Ratio (h/b)

Horizontal 1" x 6" Sheathing h/b ≤ 1.0 5.0 6.0 0.3 2.0 4.0 5.0 5.0 6.0

Horizontal 1" x 8" or 1" x 10"

Sheathing h/b ≤ 1.0 4.0 5.0 0.3 1.8 3.3 4.0 4.0 5.0

Horizontal Wood Siding Over 

Horizontal 1" x 6" Sheathing h/b ≤ 1.5 3.0 4.0 0.2 1.5 2.5 3.0 3.0 4.0

Horizontal Wood Siding Over 

Horizontal 1" x 8" or 1" x 10"

Sheathing

h/b ≤ 1.5 2.6 3.6 0.2 1.4 2.2 2.6 2.6 3.6

Diagonal 1" x 6" Sheathing h/b ≤ 1.5 3.3 4.0 0.2 1.6 2.7 3.3 3.3 4.0

Diagonal 1" x 8" Sheathing h/b ≤ 1.5 3.1 4.0 0.2 1.5 2.6 3.1 3.1 4.0

Horizontal Wood Siding Over 

Diagonal 1" x 6" Sheathing h/b ≤ 2.0 2.5 3.0 0.2 1.4 2.1 2.5 2.5 3.0

Horizontal Wood Siding Over 

Diagonal 1" x 8" Sheathing h/b ≤ 2.0 2.3 3.0 0.2 1.3 2.0 2.3 2.3 3.0

Double Diagonal 1" x 6"

Sheathing h/b ≤ 2.0 2.0 2.5 0.2 1.3 1.8 2.0 2.0 2.5

Double Diagonal 1" x 8"

Sheathing h/b ≤ 2.0 2.0 2.5 0.2 1.3 1.8 2.0 2.0 2.5

Vertical 1" x 10" Sheathing h/b ≤ 1.0 3.6 4.0 0.3 1.7 3.0 3.6 3.6 4.0

Wood Structural Panel 

Sheathing or Siding2 h/b ≤ 1.0 4.5 5.5 0.3 1.9 3.6 4.5 4.5 5.5

2.0 ≤ h/b ≤ 3.5 3.0 4.0 0.2 1.5 2.5 3.0 3.0 4.0

Stucco on Studs2 h/b ≤ 1.0 3.6 4.0 0.2 1.7 3.0 3.6 3.6 4.0

h/b = 2.0 2.5 3.0 0.2 1.4 2.1 2.5 2.5 3.0

Stucco Over 1"x Horizontal 

Sheathing h/b ≤ 2.0 3.5 4.0 0.2 1.6 2.9 3.5 3.5 4.0

Gypsum Plaster on Wood Lath h/b ≤ 2.0 4.6 5.0 0.2 1.9 3.7 4.6 4.6 5.0

Gypsum Plaster on Gypsum Lath h/b ≤ 2.0 5.0 6.0 0.2 2.0 4.0 5.0 5.0 6.0

1. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. For diaphragm components with aspect ratios between maximum listed values and 4.0, deformation ratios shall be decreased by linear interpolation 

between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

∆

∆y

------
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-25

Gypsum Plaster on Metal Lath h/b ≤ 2.0 4.4 5.0 0.2 1.9 3.6 4.4 4.4 5.0

Gypsum Sheathing h/b ≤ 2.0 5.7 6.3 0.2 2.2 4.5 5.7 5.7 6.3

Gypsum Wallboard2 h/b ≤ 1.0 5.7 6.3 0.2 2.2 4.5 5.7 5.7 6.3

h/b = 2.0 4.0 5.0 0.2 1.8 3.3 4.0 4.0 5.0

Horizontal 1" x 6" Sheathing with 

Cut-In Braces or Diagonal 

Blocking

h/b ≤ 1.0 4.4 5.0 0.2 1.9 3.6 4.4 4.4 5.0

Fiberboard or Particleboard 

Sheathing h/b ≤ 1.5 3.8 4.0 0.2 1.7 3.1 3.8 3.8 4.0

 Diaphragms3

Length/Width

Ratio (L/b)

Single Straight Sheathing, 

Chorded L/b ≤ 2.0 2.5 3.5 0.2 1.4 2.1 2.5 2.5 3.5

Single Straight Sheathing, 

Unchorded L/b ≤ 2.0 2.0 3.0 0.3 1.3 1.8 2.0 2.0 3.0

Double Straight Sheathing, 

Chorded L/b ≤ 2.0 2.5 3.5 0.2 1.4 2.1 2.5 2.5 3.5

Double Straight Sheathing, 

Unchorded L/b ≤ 2.0 2.0 3.0 0.3 1.3 1.8 2.0 2.0 3.0

Single Diagonal Sheathing, 

Chorded L/b ≤ 2.0 2.5 3.5 0.2 1.4 2.1 2.5 2.5 3.5

Single Diagonal Sheathing, 

Unchorded L/b ≤ 2.0 2.0 3.0 0.3 1.3 1.8 2.0 2.0 3.0

Straight Sheathing Over 

Diagonal Sheathing, Chorded L/b ≤ 2.0 3.0 4.0 0.2 1.5 2.5 3.0 3.0 4.0

Straight Sheathing Over 

Diagonal Sheathing, Unchorded L/b ≤ 2.0 2.5 3.5 0.3 1.4 2.1 2.5 2.5 3.5

Double Diagonal Sheathing, 

Chorded L/b ≤ 2.0 3.0 4.0 0.2 1.5 2.5 3.0 3.0 4.0

Double Diagonal Sheathing, 

Unchorded L/b ≤ 2.0 2.5 3.5 0.2 1.4 2.1 2.5 2.5 3.5

Table 8-4 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Wood Components (continued)

Modeling Parameters Acceptance Criteria

Residual 

Strength 

Ratio

Acceptable Deformation Ratio ∆ / ∆y

Performance Level

IO

Component Type

Primary Secondary

d e c LS CP LS CP

1. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. For diaphragm components with aspect ratios between maximum listed values and 4.0, deformation ratios shall be decreased by linear interpolation 

between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

∆

∆y

------
8-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

Wood Structural Panel, Blocked, 

Chorded2 L/b ≤ 3 4.0 5.0 0.3 1.8 3.3 4.0 4.0 5.0

L/b = 4 3.0 4.0 0.3 1.5 2.5 3.0 3.0 4.0

Wood Structural Panel, 

Unblocked, Chorded2 L/b ≤ 3 3.0 4.0 0.3 1.5 2.5 3.0 3.0 4.0

L/b = 4 2.5 3.5 0.3 1.4 2.1 2.5 2.5 3.5

Wood Structural Panel, Blocked, 

Unchorded2 L/b ≤ 2.5 3.0 4.0 0.3 1.5 2.5 3.0 3.0 4.0

L/b = 3.5 2.5 3.5 0.3 1.4 2.1 2.5 2.5 3.5

Wood Structural Panel, 

Unblocked, Unchorded2 L/b ≤ 2.5 2.5 3.5 0.4 1.4 2.1 2.5 2.5 3.5

L/b = 3.5 2.0 3.0 0.4 1.3 1.8 2.0 2.0 3.0

Wood Structural Panel Overlay 

On Sheathing, Chorded2 L/b ≤ 3 3.0 4.0 0.3 1.5 2.5 3.0 3.0 4.0

L/b = 4 2.5 3.5 0.3 1.4 2.1 2.5 2.5 3.5

Wood Structural Panel Overlay 

On Sheathing, Unchorded2 L/b ≤ 2.5 2.5 3.5 0.4 1.4 2.1 2.5 2.5 3.5

L/b = 3.5 2.0 3.0 0.4 1.3 1.8 2.0 2.0 3.0

Connections4

Nails—Wood to Wood 7.0 8.0 0.2 2.5 5.5 7.0 7.0 8.0

Nails—Metal to Wood 5.5 7.0 0.2 2.1 4.4 5.5 5.5 7.0

Screws—Wood to Wood 2.5 3.0 0.2 1.4 2.1 2.5 2.5 3.0

Screws—Wood to Metal 2.3 2.8 0.2 1.3 2.0 2.3 2.3 2.8

Lag Bolts—Wood to Wood 2.8 3.2 0.2 1.5 2.4 2.8 2.8 3.2

Lag Bolts—Metal to Wood 2.5 3.0 0.2 1.4 2.1 2.5 2.5 3.0

Bolts—Wood to Wood 3.0 3.5 0.2 1.5 2.5 3.0 3.0 3.5

Bolts—Metal to Wood 2.8 3.3 0.2 1.5 2.4 2.8 2.8 3.3

Table 8-4 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures—

Wood Components (continued)

Modeling Parameters Acceptance Criteria

Residual 

Strength 

Ratio

Acceptable Deformation Ratio ∆ / ∆y

Performance Level

IO

Component Type

Primary Secondary

d e c LS CP LS CP

1. Shear wall components with aspect ratios exceeding maximum listed values shall not be considered effective in resisting lateral loads.

2. Linear interpolation shall be permitted for intermediate values of aspect ratio.

3. For diaphragm components with aspect ratios between maximum listed values and 4.0, deformation ratios shall be decreased by linear interpolation 

between the listed values and 1.0. Diaphragm components with aspect ratios exceeding 4.0 shall not be considered effective in resisting lateral loads.

4. Actions on connectors not listed in this table shall be considered force-controlled.

∆

∆y

------
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-27

8.5.5 Diagonal Lumber Sheathing Shear 

Walls

8.5.5.1 Stiffness

The deflection of diagonal lumber sheathed shear walls 

shall be determined using Equation (8-1). Properties 

used to compute shear wall deflection and stiffness shall 

be based on Section 8.3.2. 

8.5.5.2 Strength

The yield capacity of diagonal sheathing shall be 

determined in accordance with Section 8.3.2. 

8.5.5.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.5.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1. 

8.5.6 Vertical Wood Siding Shear Walls

8.5.6.1 Stiffness

The deflection of vertical wood siding shear walls shall 

be determined using Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2. 

8.5.6.2 Strength

The yield capacity of vertical wood siding shear walls 

shall be determined in accordance with Section 8.3.2. 

8.5.6.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

C8.5.5.1 Stiffness

Diagonal lumber sheathed shear walls are stiffer and 

stronger than horizontal sheathed shear walls. They also 

provide greater stiffness for deflection control, and 

thereby greater damage control.

C8.5.5.2 Strength

The yield capacity of diagonal sheathing is dependent 

on the width of the boards, the spacing of the studs, the 

size of nails, the number of nails per board, and the 

boundary conditions. Allowable capacities are listed for 

various configurations in WWPA (1996).

C8.5.6.1 Stiffness

Vertical wood siding has a very low lateral-forceresistance capacity and is very flexible. The strength 

and stiffness degrade with cyclic loading. These shear 

walls are suitable only where earthquake shear loads 

are very low and deflection control is not needed.

C8.5.6.2 Strength

The yield capacity of vertical wood siding is dependent 

on the width of the boards, the spacing of the studs, the 

spacing of blocking, and the size, number, and spacing 

of the nails. The nail couple method WWPA (1996) can 

be used to calculate the capacity of vertical wood siding 

in a manner similar to the method used for horizontal 

siding.
8-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.6.4 Connections

The presence of connections between parts of the 

vertical wood siding shear wall assembly and other 

elements of the lateral-force-resisting system shall be 

verified. If connections are present, they need not be 

considered in the analysis conducted in accordance with 

Chapter 3. In the absence of connections, connections 

shall be provided in accordance with Section 8.5.1. 

8.5.7 Wood Siding over Horizontal 

Sheathing Shear Walls

8.5.7.1 Stiffness

The deflection of wood siding over horizontal sheathing 

shear walls shall be determined using Equation (8-1). 

Properties used to compute shear wall deflection and 

stiffness shall be based on Section 8.3.2. 

8.5.7.2 Strength

The yield capacity of wood siding over horizontal 

sheathing shall be determined in accordance with 

Section 8.3.2. 

8.5.7.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.7.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.8 Wood Siding over Diagonal Sheathing

8.5.8.1 Stiffness

The deflection of these shear walls shall be calculated in 

accordance with Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2. 

8.5.8.2 Strength

The yield capacity of wood siding over diagonal 

sheathing shall be determined in accordance with 

Section 8.3.2. 

C8.5.6.4 Connections

The load capacity of the vertical siding is low, which 

makes the capacity of connections between the shear 

wall and the other elements of less concern (see 

Section 8.3.2.2.2).

C8.5.7.1 Stiffness

Double-layer horizontal sheathed shear walls are stiffer 

and stronger than single-layer horizontal sheathed shear 

walls. These shear walls are often suitable for resisting 

earthquake shear loads that are low to moderate in 

magnitude. They also provide greater stiffness for 

deflection control and, thereby, greater damage control.

C8.5.7.2 Strength

This capacity is dependent on the width of the boards, 

the spacing of the studs, the size, number, and spacing 

of the nails, and the location of joints.

C8.5.8.1 Stiffness

Horizontal wood siding over diagonal sheathing will 

provide stiff, strong shear walls. These shear walls are 

often suitable for resisting earthquake shear loads that 

are moderate in magnitude. They also provide good 

stiffness for deflection control and damage control.

C8.5.8.2 Strength

The capacity of wood siding over diagonal sheathing is 

dependent on the width of the boards, the spacing of the 

studs, the size, number, and spacing of the nails, the 

location of joints, and the boundary conditions.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-29

8.5.8.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.8.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.9 Wood Structural Panel Sheathing

8.5.9.1 Stiffness

The deflection of wood structural shear walls at yield 

shall be determined using Equation (8-2):

∆y = 8 vy h3

/(E A b) + vy h/(G t) 

+ 0.75h en + (h/b)da (8-2)

where: 

Properties used to compute shear wall deflection and 

stiffness shall be based on Section 8.3.2. 

8.5.9.2 Strength

Where the strength of wood structural panel shear walls 

is derived from testing or based on principles of 

mechanics, the requirements in Section 8.4.2.2 shall 

apply. Where the strength is calculated using LRFDbased values in an approved code, the expected strength 

shall be taken as the nominal strength (φ = 1) times 0.8 

for plywood, or 0.65 for wood structural panels other 

than plywood. 

Conversion from tabulated allowable stress values in 

accordance with Section 8.3.2.5 shall not be permitted 

for wood structural panel shear walls, but approved 

allowable stress values for fasteners shall be permitted 

to be converted in accordance with Section 8.3.2.5 

where the strength of a shear wall is computed using 

principles of mechanics.

vy = Shear at yield in the direction under 

consideration in lb/ft.

h = Shear wall height, ft.

E = Modulus of elasticity of boundary 

member, psi

A = Area of boundary member cross section, 

in.2

b = Shear wall width, ft.

G = Modulus of rigidity of wood structural 

panel, psi

 t = Effective thickness of wood structural 

panel, in.

da = Deflection at yield of tie-down anchorage 

or deflection at load level to anchorage at 

end of wall, determined by anchorage 

details and dead load, in.

 en = Nail deformation at yield load per nail, 

in. Values listed are for Structural I 

panels; multiply by 1.2 for all other panel 

grades.

For 6d nails at yield, en = 0.13

For 8d nails at yield, en = 0.08

For 10d nails at yield, en = 0.08

C8.5.9.1 Stiffness

The response of wood structural panel shear walls is 

dependent on the thickness of the wood structural 

panels, the height-to-width (h/b) ratio, the nailing 

pattern, and other factors. Values for modulus of 

rigidity, G, and effective thickness, t, for various 

sheathing materials are contained in APA (1995 and 

1997).

C8.5.9.2 Strength

Shear capacities of wood structural panel shear walls 

are primarily dependent on the nailing at the plywood 

panel edges, and the thickness and grade of the 

plywood.
8-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.9.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described in 

Equation (8-1), and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.9.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.10 Stucco on Studs, Sheathing, or 

Fiberboard

8.5.10.1 Stiffness

The deflection of stucco on studs, sheathing, or 

fiberboard shear walls shall be determined using 

Equation (8-1). Properties used to compute shear wall 

deflection and stiffness shall be based on Section 8.3.2. 

8.5.10.2 Strength

The yield capacity of stucco on studs, sheathing, or 

fiberboard shall be determined in accordance with 

Section 8.3.2. 

8.5.10.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

The ratio between yield strength and nominal design 

strength is based on preliminary results of cyclic testing 

performed at the University of California at Irvine in 

the year 2000. This testing has shown that the ratio 

between yield strength and design strength is lower for 

sheathing materials other than plywood (e.g., oriented 

strand board).

LRFD-based design values for various configurations 

are listed in AF&PA LRFD and BSSC (2000). A method 

for calulating the capacity of wood structural shear 

walls based on accepted nail values is provided in 

Tissell (1993). For this method, use LRFD-based 

fastener strengths. Due to the differences in load 

duration / time-effect factors between the allowable 

stress and LRFD formats, direct conversion of shear 

wall tables using the method outlined in Section 8.3.2.5 

is not permitted. However, the tabulated LRFD design 

values, with φ = 1, are intended to be 2.0 times the 

associated allowable stress design values.

C8.5.10.1 Stiffness

Stucco is brittle, and the lateral-force-resisting capacity 

of stucco shear walls is low. The walls are stiff until 

cracking occurs, but he strength and stiffness degrade 

under cyclic loading. These shear walls are suitable 

only where earthquake shear loads are low.

C8.5.10.2 Strength

This capacity is dependent on the attachment of the 

stucco netting to the studs and the embedment of the 

netting in the stucco.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-31

8.5.10.4 Connections

The connection between the stucco netting and the 

framing shall be investigated. The connections between 

the shear wall and foundation, and between the shear 

wall and other elements of the lateral-force-resisting 

system, shall be considered in accordance with 

Section 8.5.1. 

8.5.11 Gypsum Plaster on Wood Lath

8.5.11.1 Stiffness

The deflection of gypsum plaster on wood lath shear 

walls shall be determined using Equation (8-1). 

Properties used to compute shear wall deflection and 

stiffness shall be based on Section 8.3.2. 

8.5.11.2 Strength

The yield capacity of gypsum plaster shall be 

determined in accordance with Section 8.3.2.

8.5.11.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates 

of the generalized force-deformation relation by 

Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.11.4 Connections

The presence of connections between parts of the shear 

wall assembly and other elements of the lateral-forceresisting system shall be verified. If connections are 

present, they need not be considered in the analysis 

conducted in accordance with Chapter 3. If connections 

are absent, they shall be provided in accordance with 

Section 8.5.1. 

8.5.12 Gypsum Plaster on Gypsum Lath

8.5.12.1 Stiffness

The deflection of gypsum plaster on gypsum lath shear 

walls shall be determined using Equation (8-1). 

Properties used to compute shear wall deflection and 

stiffness shall be based on Section 8.3.2. 

8.5.12.2 Strength

The yield capacity of gypsum plaster on gypsum lath 

shear walls shall be determined in accordance with 

Section 8.3.2.

8.5.12.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

C8.5.10.4 Connections

Of less concern is the connection of the stucco to the 

netting. Unlike plywood, the tensile capacity of the 

stucco material (portland cement) rather than the 

connections, will often govern failure. See 

Section 8.3.2.2.2.

C8.5.11.1 Stiffness

Gypsum plaster shear walls are similar to stucco, except 

their strength is lower. As is the case for stucco, the 

walls are stiff until failure, but the strength and stiffness 

degrade under cyclic loading. These shear walls are 

suitable only where earthquake shear loads are very 

low.

C8.5.11.4 Connections

The tensile and bearing capacity of the plaster, rather 

than the connections, will often govern failure. The 

relatively low strength of this material makes 

connections between parts of the shear wall assembly 

and the other elements of the lateral-force-resisting 

system of less concern.

C8.5.12.1 Stiffness

Gypsum plaster on gypsum lath is similar to gypsum 

wallboard (see Section 8.5.13).
8-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.12.4 Connections

The presence of connections between parts of the shear 

wall assembly and other elements of the lateral-forceresisting system shall be verified. If connections are 

present, they need not be considered in the analysis 

conducted in accordance with Chapter 3. If connections 

are absent, they shall be provided in accordance with 

Section 8.5.1.

8.5.13 Gypsum Wallboard

8.5.13.1 Stiffness

The deflection of gypsum wallboard shear walls shall 

be determined using Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2. 

8.5.13.2 Strength

The yield capacity of gypsum wallboard shear walls 

shall be determined in accordance with Section 8.3.2. 

8.5.13.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.13.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.14 Gypsum Sheathing

8.5.14.1 Stiffness

The deflection of gypsum sheathed shear walls shall be 

determined using Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2. 

8.5.14.2 Strength

The yield capacity of gypsum wallboard shear walls 

shall be determined in accordance with Section 8.3.2. 

8.5.14.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

C8.5.12.4 Connections

The tensile and bearing capacity of the plaster, rather 

than the connections, will often govern failure. The 

relatively low strength of this material makes 

connections between parts of the shear wall assembly 

and the other elements of the lateral-force-resisting 

system of less concern.

C8.5.13.1 Stiffness

Gypsum wallboard has a very low lateral-forceresisting capacity, but is relatively stiff until cracking 

occurs. The strength and stiffness degrade under cyclic 

loading. These shear walls are suitable only where 

earthquake shear loads are very low.

C8.5.13.2 Strength

The default capacity listed in Section Table 8-1 is for 

typical 7-inch nail spacing of 1/2-inch or 5/8-inch-thick 

panels with 4d or 5d nails. Higher capacities can be 

used if closer nail spacing, multilayers of gypsum 

board, and/or the presence of blocking at all panel 

edges is verified.

C8.5.14.1 Stiffness

Gypsum sheathing is similar to gypsum wallboard (see 

Section 8.5.13.1).

C8.5.14.2 Strength

The default capacity listed in Table 8-1 is based on 

typical 7-inch nail spacing of 1/2-inch or 5/8-inch-thick 

panels with 4d or 5d nails. Higher capacities can be 

used if closer nail spacing, multilayers of gypsum 

board, and/or the presence of blocking at all panel 

edges is verified.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-33

8.5.14.4 Connections

The connections between parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.15 Plaster on Metal Lath

8.5.15.1 Stiffness

The deflection of plaster on metal lath shear walls shall 

be determined using Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2.

8.5.15.2 Strength

The yield capacity of plaster on metal lath shear walls 

shall be determined in accordance with Section 8.3.2.

8.5.15.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.15.4 Connections

The presence of connections between parts of the shear 

wall assembly and other elements of the lateral-forceresisting system shall be verified. If connections are 

present, they need not be considered in the analysis 

conducted in accordance with Chapter 3. If connections 

are absent, they shall be provided in accordance with 

Section 8.5.1.

8.5.16 Horizontal Lumber Sheathing with 

Cut-In Braces or Diagonal Blocking

8.5.16.1 Stiffness

The deflection of horizontal lumber sheathing with cutin braces or diagonal blocking shear walls shall be 

calculated using Equation (8-1). Properties used to 

compute shear wall deflection and stiffness shall be 

based on Section 8.3.2. 

8.5.16.2 Strength

The yield capacity of horizontal sheathing or siding 

shall be determined in accordance with Section 8.3.2.

8.5.16.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

C8.5.15.1 Stiffness

Plaster on metal lath is similar to plaster on wood lath, 

and the lateral-force-resisting capacity of these shear 

walls is low. The walls are stiff until cracking occurs, 

but the strength and stiffness degrade under cyclic 

loading. These shear walls are suitable only where 

earthquake shear loads are low.

C8.5.15.4 Connections

The tensile and bearing capacity of the plaster, rather 

than the connections, will often govern failure. The 

relatively low strength of this material makes 

connections between parts of the shear wall assembly 

and the other elements of the lateral-force-resisting 

system of less concern.

C8.5.16.1 Stiffness

This assembly is similar to horizontal sheathing without 

braces, except that the cut-in braces or diagonal 

blocking provide higher stiffness at initial loads. After 

the braces or blocking fail (at low loads), the behavior 

of the wall is the same as with horizontal sheathing 

without braces. The strength and stiffness degrade 

under cyclic loading.
8-34 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.5.16.4 Connections

The connections between the parts of the shear wall 

assembly and other elements of the lateral-forceresisting system shall be considered in accordance with 

Section 8.5.1.

8.5.17 Fiberboard or Particleboard 

Sheathing

8.5.17.1 Stiffness

For structural particleboard sheathing, see 

Section 8.5.9. The deflection of shear walls sheathed in 

nonstructural particleboard shall be determined using 

Equation (8-1). Properties used to compute shear wall 

deflection and stiffness shall be based on Section 8.3.2. 

Fiberboard sheathing shall not be used to resist lateral 

loads. 

8.5.17.2 Strength

The strength of structural particleboard shall be based 

on Section 8.5.9. The strength of nonstructural 

fiberboard or particleboard sheathed walls shall be 

determined in accordance with Section 8.3.2. 

8.5.17.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria for 

primary and secondary components shall be taken from 

Table 8-4.

8.5.17.4 Connections

The connections between parts of structural 

particleboard shear wall assemblies and other elements 

of the lateral-force-resisting system shall be considered 

in accordance with Section 8.5.1.

The presence of connections between parts of 

nonstructural particleboard shear wall assemblies and 

other elements of the lateral-force-resisting system shall 

be verified. If connections are present, they need not be 

considered in the analysis conducted in accordance with 

Chapter 3. If connections are absent, they shall be 

provided in accordance with Section 8.5.1. 

8.5.18 Light Gage Metal Frame Shear Walls

8.5.18.1 Plaster on Metal Lath

The criteria for plaster on metal lath shall be based on 

Section 8.5.15.

8.5.18.2 Gypsum Wallboard

The criteria for gypsum wallboard shall be based on 

Section 8.5.13.

C8.5.16.4 Connections

The capacity and ductility of these connections will 

often determine the failure mode as well as the capacity 

of the assembly. Ductile connections with sufficient 

capacity will give acceptable performance (see 

Section 8.3.2.2.2).

C8.5.17.1 Stiffness

Fiberboard sheathing is very weak, lacks stiffness, and 

is unable to resist lateral loads. Particleboard comes in 

two varieties: one is similar to structural panels, the 

other (nonstructural) is slightly stronger than gypsum 

board but more brittle. Nonstructural particleboard 

should only be used where earthquake loads are very 

low.

C8.5.17.2 Strength

Fiberboard has very low strength.

C8.5.17.4 Connections

The capacity and ductility of the connections in 

structural particleboard shear walls will often determine 

the failure mode as well as the capacity of the assembly. 

Ductile connections with sufficient capacity will give 

acceptable performance. The tensile and bearing 

capacity of the nonstructural particleboard, rather than 

the connections, will often govern failure. The 

relatively low strength of this material makes 

connections between parts of the shear wall assembly 

and the other elements of the lateral-force-resisting 

system of less concern.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-35

8.5.18.3 Wood Structural Panels

The criteria wood structural panels shall be based on 

Section 8.5.9. The expected strength values of fasteners 

shall be calculated in accordance with Section 8.3.2.5, 

based on approved data.

8.6 Wood Diaphragms

8.6.1 General

The expected strength of wood diaphragms, QCE, shall 

be taken as the yield capacity of the diaphragm 

assembly determined in accordance with Sections 8.6.3 

through 8.6.10. The expected strength, QCE, of braced 

horizontal diaphragm systems shall be determined in 

accordance with Section 8.8.1.

The effects of openings in wood diaphragms shall be 

considered. Chords and collectors shall be added to 

provide sufficient load capacity around openings to 

meet the requirements for diaphragms.

Connections between diaphragms and other 

components including shear walls, drag struts, 

collectors, cross ties, and out-of-plane anchors shall be 

considered in accordance with Section 8.4.3, and 

designed for forces calculated in accordance with 

Chapter 3.

8.6.2 Types of Wood Diaphragms

8.6.2.1 Existing Wood Diaphragms

8.6.2.1.1 Single Straight Sheathing

Single straight-sheathed diaphragms shall include 

diaphragms with sheathing laid perpendicular to the 

framing members. 

C8.6.1 General

The behavior of horizontal wood diaphragms is 

influenced by the type of sheathing, size and amount of 

fasteners, existence of perimeter chord or flange 

members, and the ratio of span length to width of the 

diaphragm.

The presence of any but small openings in wood 

diaphragms will cause a reduction in the stiffness and 

yield capacity of the diaphragm due to a reduced length 

of diaphragm available to resist lateral forces. Special 

analysis techniques and detailing are required at the 

openings. The presence or addition of chord members 

around the openings will reduce the loss in stiffness of 

the diaphragm and limit damage in the area of the 

openings. See ATC-7 and Tissell and Elliott (1997) for a 

discussion of the effects of openings in wood 

diaphragms.

The presence of chords at the perimeter of a diaphragm 

will significantly reduce the diaphragm deflection due 

to bending, and increase the stiffness of the diaphragm 

over that of an unchorded diaphragm. However, the 

increase in stiffness due to chords in a single straightsheathed diaphragm is minimal due to the flexible 

nature of these diaphragms.

C8.6.2.1.1 Single Straight Sheathing

Typically, single straight-sheathed diaphragms consist 

of 1"x sheathing laid perpendicular to the framing 

members; 2"x or 3"x sheathing may also be present. 

The sheathing serves the dual purpose of supporting 

gravity loads and resisting shear forces in the 

diaphragm. Most often, 1"x sheathing is nailed with 8d 

or 10d nails, with two or more nails per sheathing board 

at each support. Shear forces perpendicular to the 

direction of the sheathing are resisted by the nail 

couple. Shear forces parallel to the direction of the 

sheathing are transferred through the nails in the 

supporting joists or framing members below the 

sheathing joints.
8-36 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.6.2.1.2 Double Straight Sheathing

Double straight-sheathed diaphragms shall include 

diaphragms with one layer of sheathing laid 

perpendicular to the framing members and a second 

layer of sheathing laid either perpendicular or parallel to 

the first layer. 

8.6.2.1.3 Single Diagonal Sheathing

Single diagonally sheathed diaphragms shall include 

diaphragms with sheathing laid at a 45-degree angle to 

the framing members. 

8.6.2.1.4 Diagonal Sheathing with Straight 

Sheathing or Flooring Above 

Diagonal sheathing with straight sheathing or flooring 

above shall include diaphragms with sheathing laid at a 

45-degree angle to the framing members, with a second 

layer of straight sheathing or wood flooring laid on top 

of the diagonal sheathing at a 90-degree angle to the 

framing members. 

8.6.2.1.5 Double Diagonal Sheathing

Double diagonally sheathed diaphragms shall include 

diaphragms with one layer of sheathing laid at a 45-

degree angle to the framing members and a second layer 

of sheathing laid at a 90-degree angle to the first layer. 

C8.6.2.1.2 Double Straight Sheathing

Construction of double straight-sheathed diaphragms is 

the same as that for single straight-sheathed 

diaphragms, except that an upper layer of straight 

sheathing is laid over the lower layer of sheathing. The 

upper sheathing can be placed either perpendicular or 

parallel to the lower layer of sheathing. If the upper 

layer of sheathing is parallel to the lower layer, the 

board joints are usually offset sufficiently that nails at 

joints in the upper layer of sheathing are driven into a 

common sheathing board below, with sufficient edge 

distance. The upper layer of sheathing is nailed to the 

framing members through the lower layer of sheathing.

C8.6.2.1.3 Single Diagonal Sheathing

Typically, 1"x sheathing is laid at an approximate 45-

degree angle to the framing members. In some cases 

2"x sheathing may also be used. The sheathing supports 

gravity loads and resists shear forces in the diaphragm. 

Commonly, 1"x sheathing is nailed with 8d nails, with 

two or more nails per board at each support. The 

recommended nailing for diagonally sheathed 

diaphragms is published in WWPA (1996) and BSSC

(2000). The shear capacity of the diaphragm is 

dependent on the size and quantity of the nails at each 

sheathing board.

C8.6.2.1.4 Diagonal Sheathing with Straight 

Sheathing or Flooring Above

Typically, these consist of a lower layer of 1"x diagonal 

sheathing laid at a 45-degree angle to the framing 

members, with a second layer of straight sheathing or 

wood flooring laid on top of the diagonal sheathing at a 

90-degree angle to the framing members. Both layers of 

sheathing support gravity loads, and resist shear forces 

in the diaphragm. Sheathing boards are commonly 

connected with two or more 8d nails per board at each 

support.

C8.6.2.1.5 Double Diagonal Sheathing

Typically, double diagonally sheathed diaphragms 

consist of a lower layer of 1"x diagonal sheathing with 

a second layer of 1"x diagonal sheathing laid at a 90-

degree angle to the lower layer. The sheathing supports 

gravity loads and resists shear forces in the diaphragm. 

The sheathing is commonly nailed with 8d nails, with 

two or more nails per board at each support. The 

recommended nailing for double diagonally sheathed 

diaphragms is published in WWPA (1996).
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-37

8.6.2.1.6 Wood Structural Panel Sheathing

Wood structural panel-sheathed diaphragms shall 

include diaphragms with plywood, or other wood 

structural panels as defined in this standard, fastened to 

the framing members. 

8.6.2.1.7 Braced Horizontal Diaphragms

Braced horizontal diaphragms shall include diaphragms 

with a horizontal truss system at the floor or roof level 

of the building. 

8.6.2.2 Enhanced Wood Diaphragms

Enhanced wood diaphragms shall include existing 

diaphragms rehabilitated by an approved method.

C8.6.2.1.6 Wood Structural Panel Sheathing

Typically, these consist of wood structural panels, such 

as plywood or oriented strand board, placed on framing 

members and nailed in place. Different grades and 

thicknesses of wood structural panels are commonly 

used, depending on requirements for gravity load 

support and shear capacity. Edges at the ends of the 

wood structural panels are usually supported by the 

framing members. Edges at the sides of the panels can 

be blocked or unblocked. In some cases, tongue and 

groove wood structural panels are used. Nailing 

patterns and nail size can vary greatly. Nail spacing is 

commonly in the range of 3 to 6 inches on center at the 

supported and blocked edges of the panels, and 10 to 12 

inches on center at the panel infield. Staples are 

sometimes used to attach the wood structural panels.

C8.6.2.1.7 Braced Horizontal Diaphragms

Typically, these consist of “X” rod bracing and wood 

struts forming a horizontal truss system at the floor or 

roof levels of the building. The “X” bracing usually 

consists of steel rods drawn taut by turnbuckles or nuts. 

The struts usually consist of wood members, which 

may or may not be part of the gravity-load-bearing 

system of the floor or roof. The steel rods function as 

tension members in the horizontal truss, while the struts 

function as compression members. Truss chords 

(similar to diaphragm chords) are needed to resist 

bending in the horizontal truss system.

C8.6.2.2 Enhanced Wood Diaphragms

Possible rehabilitation methods for wood diaphragms 

are described in Sections C8.6.2.2.1 through 

C8.6.2.2.3.

C8.6.2.2.1 Wood Structural Panel Overlays on 

Straight or Diagonal Sheathing 

Existing sheathed diaphragms may be overlaid with 

new wood structural panels. Nails or staples may be 

used to connect the new structural panels to the existing 

diaphragms. Nails should be of sufficient length to 

provide the required embedment into framing members 

below the sheathing.

These diaphragms typically consist of new wood 

structural panels placed over existing straight or 

diagonal sheathing and nailed or stapled to the existing 

framing members through the existing sheathing. If the 

new overlay is nailed to the existing framing members 

only—without nailing at the panel edges perpendicular 

to the framing—the response of the new overlay will be 

similar to that of an unblocked wood structural panel 

diaphragm.

If a stronger and stiffer diaphragm is desired, the joints 

of the new wood structural panel overlay should be 

placed parallel to the joints of the existing sheathing, 

with the overlay nailed or stapled to the existing 

sheathing. The edges of the new wood structural panels 

should be offset from the joints in the existing 

sheathing below by a sufficient distance that the new 

nails may be driven into the existing sheathing without 

splitting the sheathing. If the new panels are nailed at 

all edges as described above, the response of the new 

overlay will be similar to that of a blocked wood 

structural panel diaphragm. As an alternative, new 

blocking may be installed below all panel joints 

perpendicular to the existing framing members.
8-38 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.6.2.3 New Wood Diaphragms

8.6.2.3.1 New Wood Structural Panel Sheathing

New wood structural panel sheathed diaphragms shall 

include new wood structural panels connected to new 

framing members, or connected to existing framing 

members after existing sheathing has been removed.

8.6.2.3.2 New Single Diagonal Sheathing

New single diagonally sheathed wood diaphragms shall 

include new sheathing laid at a 45-degree angle and 

connected to the existing framing members.

Because the joints of the overlay and the joints of the 

existing sheathing may not be offset consistently 

without cutting the panels, it may be advantageous to 

place the wood structural panel overlay at a 45-degree 

angle to the existing sheathing. If the existing 

diaphragm is straight-sheathed, the new overlay should 

be placed at a 45-degree angle to the existing sheathing 

and joists. If the existing diaphragm is diagonally 

sheathed, the new wood structural panel overlay should 

be placed perpendicular to the existing joists at a 45-

degree angle to the diagonal sheathing. Nails should be 

driven into the existing sheathing with sufficient edge 

distance to prevent splitting of the existing sheathing. 

At boundaries, nails should be of sufficient length to 

penetrate the sheathing into the framing below. New 

structural panel overlays shall be connected to shear 

walls or vertical bracing elements to ensure the 

effectiveness of the added panel.

Care should be exercised when placing new wood 

structural panel overlays on existing diaphragms. The 

changes in stiffness and dynamic characteristics of the 

diaphragm may have negative effects by causing 

increased forces in other components or elements. The 

increased stiffness and the associated increase in 

dynamic forces may not be desirable in some 

diaphragms for certain performance levels.

C8.6.2.2.2 Wood Structural Panel Overlays on 

Existing Wood Structural Panels

Existing wood structural panel diaphragms may be 

overlaid with new wood structural panels. Panel joints 

should be offset, or the overlay should be placed at a 

45-degree angle to the existing wood structural panels.

The placement of a new overlay over an existing 

diaphragm should follow the same construction 

methods and procedures as those used for straightsheathed and diagonally sheathed diaphragms (see 

Section C8.6.2.2.1).

C8.6.2.2.3 Increased Attachment

The nailing or attachment of the existing sheathing to 

the supporting framing may be increased. Nailing or 

attachment to the supporting framing should be 

increased and blocking for the diaphragm at the 

plywood joints should be added.

For straight-sheathed diaphragms, the increase in shear 

capacity will be minimal. Double straight-sheathed 

diaphragms with minimal nailing in the upper or both 

layers of sheathing may be enhanced significantly by 

adding new nails or staples to the existing diaphragm. 

The same is true for diaphragms that are single 

diagonally sheathed, double diagonally sheathed, or 

single diagonally sheathed with straight sheathing or 

flooring.

In some cases, increased nailing at the plywood panel 

infield may also be required. If the required shear 

capacity or stiffness is greater than that which can be 

provided by increased attachment, a new overlay on the 

existing diaphragm may be required to provide the 

desired enhancement.

C8.6.2.3.1 New Wood Structural Panel Sheathing

Typically, these consist of wood structural panels—

such as plywood or oriented strand board—nailed or 

stapled to existing framing members after existing 

sheathing has been removed. Different grades and 

thicknesses of wood structural panels can be used, 

depending on the requirements for gravity load support 

and diaphragm shear capacity. In most cases, the panels 

are placed with the long dimension perpendicular to the 

framing members, and panel edges at the ends of the 

panels are supported by, and nailed to, the framing 

members. Edges at the sides of the panels can be 

blocked or unblocked, depending on the shear capacity 

and stiffness required in the new diaphragm. Wood 

structural panels can be placed in various patterns as 

shown in AF&PA LRFD and BSSC (2000).
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-39

8.6.2.3.3 New Double Diagonal Sheathing

New double diagonally sheathed wood diaphragms 

shall include diaphragms with new sheathing laid at a 

45-degree angle to the existing framing members with a 

second layer of sheathing laid at a 90-degree angle to 

the first layer.

8.6.2.3.4 New Braced Horizontal Diaphragms

New braced horizontal diaphragms shall include a new 

horizontal truss system attached to the existing framing 

at the floor or roof level of the building. 

8.6.3 Single Straight Sheathing

8.6.3.1 Stiffness

The deflection of straight-sheathed diaphragms shall be 

calculated using Equation (8-3):

∆y = vy L / (2Gd) (8-3)

where:

Properties used to compute diaphragm deflection and 

stiffness shall be based on Section 8.3.2.

8.6.3.2 Strength

The yield capacity of straight-sheathed diaphragms 

shall be determined in accordance with Section 8.3.2. 

8.6.3.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4. 

C8.6.2.3.4 New Braced Horizontal Diaphragms

Because new horizontal truss systems will induce new 

forces on existing framing members, it may be more 

economical to design floor or roof sheathing as a 

diaphragm. This eliminates the potential need to 

strengthen wood members at the compression struts. 

Braced horizontal diaphragms are more feasible where 

sheathing cannot provide sufficient shear capacity, or 

where diaphragm openings reduce the shear capacity of 

the diaphragm and additional shear capacity is needed.

Gd = Diaphragm shear stiffness from Table 8-2

L = Diaphragm span, distance between shear walls 

or collectors

vy = Shear at yield in the direction under 

consideration

∆y = Calculated diaphragm deflection at yield

C8.6.3.1 Stiffness

Straight sheathed diaphragms are characterized by high 

flexibility with a long period of vibration. These 

diaphragms are suitable for low shear conditions where 

control of diaphragm deflections is not needed to attain 

the desired performance levels.

C8.6.3.2 Strength

The yield capacity of straight-sheathed diaphragms is 

dependent on the size, number, and spacing between the 

nails at each sheathing board, and the spacing of the 

supporting framing members. The shear capacity of 

straight-sheathed diaphragms can be calculated using 

the nail-couple method. See ATC-7 for a discussion of 

calculating the shear capacity of straight-sheathed 

diaphragms.

C8.6.3.3 Acceptance Criteria

Deformation acceptance criteria will largely depend on 

the allowable deformations for other structural and 

nonstructural components and elements that are 

laterally supported by the diaphragm. Allowable 

deformations must also be consistent with the 

permissible damage state of the diaphragm.
8-40 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.6.3.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1. 

8.6.4 Double Straight Sheathing

8.6.4.1 Stiffness

The deflection of double straight-sheathed diaphragms 

shall be calculated using Equation (8-3). Properties 

used to compute diaphragm deflection and stiffness 

shall be based on Section 8.3.2. 

8.6.4.2 Strength

The yield capacity of double straight-sheathed 

diaphragms shall be determined in accordance with 

Section 8.3.2. 

8.6.4.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.4.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.5 Single Diagonal Sheathing

8.6.5.1 Stiffness

The deflection of single diagonally sheathed 

diaphragms shall be calculated using Equation (8-3). 

Properties used to compute diaphragm deflection and 

stiffness shall be based on Section 8.3.2. 

8.6.5.2 Strength

The yield capacity for diagonally sheathed wood 

diaphragms with chords shall be determined in 

accordance with Section 8.3.2. 

C8.6.3.4 Connections

The load capacity of connections between diaphragms 

and shear walls or other vertical elements, as well as 

diaphragm chords and shear collectors, is critical.

C8.6.4.1 Stiffness

The double-sheathed system will provide a significant 

increase in stiffness over a single straight-sheathed 

diaphragm, but very little test data is available on the 

stiffness and strength of these diaphragms. Both layers 

of straight sheathing must have sufficient nailing, and 

the joints of the top layer must be either offset or 

perpendicular to the bottom layer.

C8.6.4.2 Strength

The strength and stiffness of double straight-sheathed 

diaphragms is highly dependent on the nailing of the 

upper layer of sheathing. If the upper layer has minimal 

nailing, the increase in strength and stiffness over a 

single straight-sheathed diaphragm may be slight. If the 

upper layer of sheathing has nailing similar to that of 

the lower layer of sheathing, the increase in strength 

and stiffness will be significant.

C8.6.5.1 Stiffness

Single diagonally sheathed diaphragms are 

significantly stiffer than straight-sheathed diaphragms, 

but are still quite flexible.

C8.6.5.2 Strength

Diagonally sheathed diaphragms are usually capable of 

resisting moderate shear loads.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-41

8.6.5.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.5.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.6 Diagonal Sheathing with Straight 

Sheathing or Flooring Above

8.6.6.1 Stiffness

The deflection of diagonally sheathed diaphragms with 

straight sheathing or flooring above shall be calculated 

using Equation (8-3). Properties used to compute 

diaphragm deflection and stiffness shall be based on 

Section 8.3.2.

8.6.6.2 Strength

The yield capacity of diagonally sheathed diaphragms 

with straight sheathing or flooring above shall be 

determined in accordance with Section 8.3.2. 

8.6.6.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.6.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.7 Double Diagonal Sheathing

8.6.7.1 Stiffness

The deflection of double diagonally sheathed 

diaphragms shall be calculated using Equation (8-3). 

Properties used to compute diaphragm deflection and 

stiffness shall be based on Section 8.3.2.

Because the diagonal sheathing boards function in 

tension and compression to resist shear forces in the 

diaphragm, and the boards are placed at a 45-degree 

angle to the chords at the ends of the diaphragm, the 

component of the force in the sheathing boards that is 

perpendicular to the axis of the end chords will create a 

bending force in the end chords. If the shear in 

diagonally sheathed diaphragms is limited to 

approximately 300 pounds per foot or less, bending 

forces in the end chords are usually neglected. If shear 

forces exceed 300 pounds per foot, the end chords 

should be designed or reinforced to resist bending 

forces from the sheathing. See ATC-7 for methods of 

calculating the shear capacity of diagonally sheathed 

diaphragms.

C8.6.6.1 Stiffness

Straight sheathing or flooring over diagonal sheathing 

provides a significant increase in stiffness over singlesheathed diaphragms. The increased stiffness of these 

diaphragms may make them suitable where Life Safety 

or Immediate Occupancy Structural Performance 

Levels are desired.

C8.6.6.2 Strength

Shear capacity is dependent on the nailing of the 

diaphragm. The strength and stiffness of diagonally 

sheathed diaphragms with straight sheathing above is 

highly dependent on the nailing of both layers of 

sheathing. Both layers of sheathing should have at least 

two 8d common nails per board at each support.

C8.6.7.1 Stiffness

Double diagonally sheathed diaphragms have greater 

stiffness than diaphragms with single diagonal 

sheathing. The response of these diaphragms is similar 

to the response of diagonally sheathed diaphragms with 

straight sheathing overlays.

The increased stiffness of these diaphragms may make 

them suitable where Life Safety or Immediate 

Occupancy Structural Performance Levels are desired.
8-42 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.6.7.2 Strength 

The yield capacity of double diagonally sheathed wood 

diaphragms shall be determined in accordance with 

Section 8.3.2. 

8.6.7.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation, described by Figure 

8-1, and deformation acceptance criteria shall be taken 

from Table 8-4.

8.6.7.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.8 Wood Structural Panel Sheathing

8.6.8.1 Stiffness

The deflection of blocked and chorded wood structural 

panel diaphragms with constant nailing across the 

diaphragm length shall be determined using Equation 

(8-4):

∆y= 5 vy L3 / (8EAb) + vy L / (4Gt) 

+ 0.188 L en + Σ(∆cX) / (2b) (8-4)

where:

The deflection of blocked and chorded wood structural 

panel diaphragms with variable nailing across the 

diaphragm length shall be determined using Equation 

(8-5):

∆y = 5 vy L3 / (8EAb) + vy L / (4Gt) + 

0.376 L en + Σ(∆cX) / (2b) (8-5)

C8.6.7.2 Strength

Shear capacity is dependent on the nailing of the 

diaphragm, but these diaphragms are usually suitable 

for moderate to high shear loads.

Yield shear capacities are similar to those of diagonally 

sheathed diaphragms with straight sheathing overlays. 

The sheathing boards in both layers of sheathing should 

be nailed with at least two 8d common nails at each 

support. The presence of a double layer of diagonal 

sheathing will eliminate the bending forces that single 

diagonally sheathed diaphragms impose on the chords 

at the ends of the diaphragm. As a result, the bending 

capacity of the end chords does not have an effect on 

the shear capacity and stiffness of the diaphragm.

A = Area of diaphragm chords

cross-section, in.2

b = Diaphragm width, ft.

E = Modulus of elasticity of diaphragm 

chords, psi

en = Nail deformation at yield load per nail, 

in. Values listed are for Structural I 

panels; multiply by 1.2 for all other 

panel grades.

For 6d nails at yield, en = 0.13

For 8d nails at yield, en = 0.08

For 10d nails at yield, en = 0.08

G = Modulus of rigidity of wood structural 

panels, psi.

L = Diaphragm span, distance between 

shear walls or collectors, ft.

t = Effective thickness of wood structural 

panel for shear, in.

vy = Shear at yield in the direction under 

consideration, lb/ft.

∆y = Calculated deflection of diaphragm at 

yield, in.

Σ (∆ cX) = Sum of individual chord-splice slip 

values on both sides of the diaphragm, 

each multiplied by its distance to the 

nearest support
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-43

The deflection of unblocked diaphragms shall be 

calculated using Equation (8-3). Properties used to 

compute diaphragm deflection and stiffness shall be 

based on Section 8.3.2. 

8.6.8.2 Strength

The strength of wood structural panel diaphragms shall 

be determined in accordance with Section 8.4.2.2.

Conversion for tabulated allowable stress values in 

accordance with Section 8.3.2.5 shall not be permitted 

for wood structural panel diaphragms, but approved 

allowable stress values for fasteners shall be permitted 

to be converted in accordance with Section 8.3.2.5 

where the strength of a shear wall is computed using 

principles of mechanics.

The yield shear capacity of unchorded diaphragms shall 

be calculated by multiplying the values given for 

chorded diaphragms by 0.70. 

8.6.8.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.8.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.9 Wood Structural Panel Overlays on 

Straight or Diagonal Sheathing

8.6.9.1 Stiffness

Placement of the new wood structural panel overlay 

shall be consistent with Section 8.6.2.2.

The deflection of wood structural panel overlays on 

straight or diagonally sheathed diaphragms shall be 

calculated using Equation (8-3). Properties used to 

compute diaphragm deflection and stiffness shall be 

based on Section 8.3.2. 

C8.6.8.1 Stiffness

The response of wood structural panel diaphragms is 

dependent on the thickness of the wood structural 

panels, the length-to-width (L/b) ratio, nailing pattern, 

and presence of chords in the diaphragm, as well as 

other factors. Values for modulus rigidity, G, and 

effective thickness, t, for various sheathing materials 

are contained in APA (1995 and 1997).

In most cases the area of the diaphragm chord equals 

the area of the continuous wood (or steel) member to 

which the sheathing is attached. For buildings with 

wood diaphragms and concrete or masonry walls, 

however, the area of the diaphragm chord is more 

difficult to identify and engineering judgment is 

required. The tension area of the diaphragm chord on 

both edges of the diaphragm should be used for 

deflection calculations. Generally, this is conservative 

as it results in a larger calculated deflection. Use of the 

tension area of the diaphragm chord may not yield 

conservative results, however, when calculating the 

period of the building using Equation (3-8).

C8.6.8.2 Strength

Shear capacities of wood structural panel diaphragms 

are primarily dependent on the nailing at the plywood 

panel edges, and the thickness and grade of the 

plywood in the diaphragm.

LRFD-based design values for various configurations 

are listed in AF&PA LRFD and BSSC (2000). A method 

for calculating the capacity of wood structural panel 

diaphragms based on accepted nail values and panel 

shear strength is provided in Tissell and Elliott (1997). 

For this method, use LRFD-based fastener strengths. 

Due to the differences in load duration/time effect 

factors between the allowable stress and LRFD formats, 

direct conversion of diaphragm tables using the method 

outlined in Section 8.3.2.5 is not permitted. However, 

the tabulated LRFD design values, with φ = 1, are 

intended to be 2.0 times the associated allowable stress 

design values.

C8.6.9.1 Stiffness

The stiffness of existing straight-sheathed diaphragms 

can be increased significantly by placing a new 

plywood overlay over the existing diaphragm. The 

stiffness of existing diagonally sheathed diaphragms 

and plywood diaphragms will be increased, but not in 

proportion to the stiffness increase for straight-sheathed 

diaphragms.
8-44 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.6.9.2 Strength

Strength of wood structural panel overlays shall be 

determined in accordance with Section 8.4.2.2. It shall 

be permitted to take the yield capacity as the value for 

the corresponding wood structural panel diaphragm 

without the existing sheathing below, computed in 

accordance with Section 8.6.8.2.

8.6.9.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.9.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.10 Wood Structural Panel Overlays on 

Existing Wood Structural Panel 

Sheathing

8.6.10.1 Stiffness

Diaphragm deflection shall be calculated in accordance 

with Equation (8-3) or using accepted principles of 

mechanics. Nails in the upper layer of plywood shall 

have sufficient embedment in the framing to meet the 

requirements of ASCE 16. 

8.6.10.2 Strength

Yield capacity shall be calculated based on the 

combined two layers of plywood. The yield shear 

capacity of the overlay shall be limited to 75% of the 

values calculated in accordance with Section 8.6.8.2.

8.6.10.3 Acceptance Criteria

For linear procedures, m-factors for use with 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, the coordinates of 

the generalized force-deformation relation, described 

by Figure 8-1, and deformation acceptance criteria shall 

be taken from Table 8-4.

8.6.10.4 Connections

Connections between diaphragms and shear walls and 

other vertical elements shall be considered in 

accordance with Section 8.6.1.

8.6.11 Braced Horizontal Diaphragms

Braced horizontal diaphragms shall be considered in 

accordance with Section 8.8.1.

Connections between members of the horizontal 

bracing system and shear walls or other vertical 

elements shall be considered in accordance with 

Section 8.6.1.

8.7 Wood Foundations

8.7.1 Types of Wood Foundations

Types of wood foundations include wood piling, wood 

footings, and pole structures. Wood piling shall include 

friction or end-bearing piles that resist only vertical 

loads. 

Depending on the nailing of the new overlay, the 

response of the diaphragm may be similar to that of a 

blocked or an unblocked diaphragm.

The increased stiffness of these diaphragms may make 

them suitable where Life Safety or Immediate 

Occupancy Structural Performance Levels are desired.

C8.6.10.1 Stiffness

According to Tissell and Elliott (1997), Equation (8-4) 

is not applicable to two-layer diaphragms, presumably 

due to the difficulty in estimating the combined nail 

slip. Diaphragm deflection may be estimated using 

principles of mechanics that include consideration of 

nail slip, blocking, and the embedment of nails into the 

framing.

C8.7.1 Types of Wood Foundations

1. Wood Piling. Wood piles are generally used with a 

concrete pile cap and are usually keyed into the base of 

the concrete cap. The piles are usually treated with 

preservatives.
 Chapter 8: Wood and Light Metal Framing

FEMA 356 Seismic Rehabilitation Prestandard 8-45

8.7.2 Analysis, Strength, and Acceptance 

Criteria of Wood Foundations

The expected strength of wood piles shall be computed 

in accordance with Section 8.4.2.2. Deflection of piles 

under seismic loads shall be calculated based on an 

assumed point of fixity. Unless rigidly connected to the 

pile cap, wood piles shall be taken as pinned at the top.

Flexure and axial loads in wood piles shall be 

considered deformation-controlled. m-factors shall be 

taken from Table 8-3.

Wood footings shall be thoroughly investigated for the 

presence of deterioration. Acceptability of soils below 

wood footings shall be determined in accordance with 

Chapter 4.

Component and connection strength of pole structures 

shall be based on Section 8.3. Pole structures shall be 

modeled as cantilever elements and analyzed in 

accordance with Chapter 3.

Flexure and axial loads in pole structures shall be 

considered deformation controlled. m-factors shall be 

taken from Table 8-3. Where concentrically braced 

diagonals are added to enhance the capacity of the pole 

structure, reduced m-factors taken from Table 8-3 shall 

be used.

8.7.3 Rehabilitation Measures

Wood foundations not meeting the acceptance criteria 

for the selected Rehabilitation Objective shall be 

rehabilitated by approved methods. Wood foundations 

exhibiting signs of deterioration shall be rehabilitated or 

replaced. 

Piles are either friction- or end-bearing piles resisting 

only vertical loads. Piles are generally not able to resist 

uplift loads because of the manner in which they are 

attached to the pile cap. The piles may be subjected to 

lateral loads from seismic loading, which are resisted 

by bending of the piles. The analysis of pile bending is 

generally based on a pinned connection at the top of the 

pile, and fixity of the pile at some depth established by 

the geotechnical engineer. However, it should be 

evaluated with consideration for the approximate nature 

of the original assumption of the depth to point of fixity. 

Where battered piles are present, the lateral loads can 

be resisted by the horizontal component of the axial 

load.

2. Wood Footings. Wood grillage footings, sleepers, 

skids, and pressure-treated all-wood foundations can be 

encountered in existing structures. These foundations 

are highly susceptible to deterioration. The seismic 

resistance of wood footings is generally very low; they 

are essentially dependent on friction between the wood 

and soil for their performance.

3. Pole Structures. Pole structures resist lateral loads 

by acting as cantilevers fixed in the ground, with the 

lateral load considered to be applied perpendicular to 

the pole axis. It is possible to design pole structures to 

have moment-resisting capacity at floor and roof levels 

by the use of knee braces or trusses. Pole structures are 

frequently found on sloping sites. The varying unbraced 

lengths of the poles generally affect the stiffness and 

performance of the structure, and can result in 

unbalanced loads to the various poles along with 

significant torsional distortion, which must be 

investigated and evaluated. Additional horizontal and 

diagonal braces can be used to reduce the flexibility of 

tall poles or reduce the torsional eccentricity of the 

structure.

C8.7.2 Analysis, Strength, and Acceptance 

Criteria of Wood Foundations

The strength of the components, elements, and 

connections of a pole structure are the same as for a 

conventional structure.

C8.7.3 Rehabilitation Measures

Wood footings showing signs of deterioration may be 

replaced with reinforced concrete footings. Wood pole 

structures can be rehabilitated with the installation of 

diagonal braces or other supplemental lateral-forceresisting elements. Wood piles may be rehabilitated by 

the installation of additional piles.
8-46 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 8: Wood and Light Metal Framing

8.8 Other Wood Elements and 

Components

8.8.1 General

Wood elements and components, other than shear walls, 

diaphragms, and foundations, shall be considered in 

accordance with this section. Where an assembly 

includes wood components and steel rods, the rods shall 

be considered in accordance with applicable provisions 

of Chapter 5. 

8.8.1.1 Stiffness

The stiffness and deflection of wood elements shall be 

determined based on a mathematical model of the 

assembly considering the configuration, stiffness, and 

interconnection of the individual components.

8.8.1.2 Strength

The capacities of individual components, including 

connections, shall be determined in accordance with 

Section 8.4.2. 

8.8.1.3 Acceptance Criteria

Design actions shall be compared with design capacities 

in accordance with Section 3.4.2.2. Connections shall 

be considered in accordance with Section 8.4.3. Axial 

tension, axial tension with bending shall be considered 

deformation-controlled. Axial compression, and 

connections between steel rods and wood components 

shall be considered force-controlled. m-factors for 

deformation-controlled actions shall be taken from 

Table 8-3. For nonlinear procedures, coordinates of the 

generalized force-deformation relation described by 

Figure 8-1, and deformation acceptance criteria shall be 

taken from Table 8-4. 

8.8.2 Components Supporting 

Discontinuous Shear Walls

Axial compression on wood posts and flexure and shear 

on wood beams that support discontinuous shear walls 

shall be considered force-controlled actions. Lowerbound strengths shall be determined in accordance with 

Section 8.4.2.3.

C8.8.1 General

Other wood elements include knee-braced frames, rodbraced frames, and braced horizontal diaphragms, 

among other systems.

Knee-braced frames produce moment-resisting joints 

by the addition of diagonal members between columns 

and beams. The resulting “semi-rigid” frame resists lateral loads. The moment-resisting capacity of kneebraced frames varies widely. The controlling part of the 

assembly is usually the connection; however, bending 

of members can be the controlling feature of some 

frames. Once the capacity of the connection is determined, members can be checked and the capacity of the 

frame can be determined by statics. Particular attention 

should be given to the beam/column connection. Additional tensile forces may be developed in this connection due to knee-brace action under vertical loads.

Similarly to knee-braced frames, the connections of 

rods to timber framing will usually govern the capacity 

of the rod-braced frame. Typically, the rods act only in 

tension. Once the capacity of the connection is 

determined, the capacity of the frame can be 

determined by statics.

Braced horizontal diaphragms are described in 

Section 8.6.2.1.7.

C8.8.1.2 Strength

The strength of wood elements is dependent on the 

strength of the individual components that comprise the 

assembly. In many cases the capacity of the connections 

between components will be the limiting factor in the 

strength of the assembly.

C8.8.1.3 Acceptance Criteria

Deformation acceptance criteria will largely depend on 

the allowable deformations for other structural and 

nonstructural components and elements that are 

supported by the element. Allowable deformations 

must also be consistent with the desired performance 

level. Actions on connection types that do not appear in 

Table 8-3 (e.g., truss plates) are force-controlled.
FEMA 356 Seismic Rehabilitation Prestandard 9-1

9. Seismic Isolation and Energy Dissipation

9.1 Scope 

This chapter sets forth requirements for the Systematic 

Rehabilitation of buildings using seismic isolation and 

energy dissipation systems. Section 9.2 provides 

analysis and design criteria for seismic isolation 

systems. Section 9.3 provides analysis and design 

criteria for passive energy dissipation systems. 

Components and elements in buildings with seismic 

isolation and energy dissipation systems shall also 

comply with the requirements of Chapters 1 through 8 

and 11 of this standard, unless modified by the 

requirements of this chapter.

C9.1 Scope 

The basic form and formulation of requirements for 

seismic isolation and energy dissipation systems have 

been established and coordinated with the 

Rehabilitation Objectives, target Building Performance 

Levels, and seismic ground shaking hazard criteria of 

Chapter 1 and the linear and nonlinear procedures of 

Chapter 3.

Criteria for modeling the stiffness, strength, and 

deformation capacities of conventional structural 

components of buildings with seismic isolation or 

energy dissipation systems are given in Chapters 5 

through 8 and Chapter 10. 

Limited guidance for other special seismic systems, 

including active control systems, hybrid active and 

passive systems, and tuned mass and liquid dampers, is 

provided in this chapter.

Special seismic protective systems should be evaluated 

as possible rehabilitation strategies based on the 

Rehabilitation Objectives established for the building. 

Seismic isolation and energy dissipation systems are 

viable design strategies that have already been used for 

seismic rehabilitation of a number of buildings. Other 

special seismic protective systems—including active 

control, hybrid combinations of active and passive 

energy devices, and tuned mass and liquid dampers—

may also provide practical solutions in the near future. 

These systems are similar in that they enhance 

performance during an earthquake by modifying the 

building’s response characteristics.

Seismic isolation and energy dissipation systems will 

not be appropriate design strategies for most buildings, 

particularly buildings that have only Limited 

Rehabilitation Objectives. In general, these systems 

will be most applicable to the rehabilitation of 

buildings whose owners desire superior earthquake 

performance and can afford the special costs associated 

with the design, fabrication, and installation of seismic 

isolators and/or energy dissipation devices. These costs 

are typically offset by the reduced need for stiffening 

and strengthening measures that would otherwise be 

required to meet Rehabilitation Objectives.

Seismic isolation and energy dissipation systems are 

relatively new and sophisticated concepts that require 

more extensive design and detailed analysis than do 

most conventional rehabilitation schemes. Similarly, 

design (peer) review is required for all rehabilitation 

schemes that use either seismic isolation or energy 

dissipation systems.

Seismic isolation and energy dissipation systems 

include a wide variety of concepts and devices. In most 

cases, these systems and devices will be implemented 

with some additional conventional strengthening of the 

structure; in all cases they will require evaluation of 

existing building elements. As such, this chapter 

supplements the requirements of other chapters of this 

document with additional criteria and methods of 

analysis that are appropriate for buildings rehabilitated 

with seismic isolators and/or energy dissipation 

devices.
9-2 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

Seismic isolation is increasingly being considered for 

historic buildings that are free-standing and have a 

basement or bottom space of no particular historic 

significance. In selecting such a solution, special 

consideration should be given to the possibility that 

historic or archaeological resources may be present at 

the site. If historic or archaeological resources are 

present at the site, the guidance of the State Historic 

Preservation Officer should be obtained in a timely 

manner. Isolation is also often considered for essential 

facilities, to protect valuable contents, and on buildings 

with a complete but insufficiently strong lateral-forceresisting system.

Conceptually, isolation reduces response of the 

superstructure by “decoupling” the building from the 

ground. Typical isolation systems reduce forces 

transmitted to the superstructure by lengthening the 

period of the building and adding some amount of 

damping. Added damping is an inherent property of 

most isolators, but may also be provided by 

supplemental energy dissipation devices installed 

across the isolation interface. Under favorable 

conditions, the isolation system reduces drift in the 

superstructure by a factor of at least two—and 

sometimes by as much as factor of five—from that 

which would occur if the building were not isolated. 

Accelerations are also reduced in the structure, 

although the amount of reduction depends on the forcedeflection characteristics of the isolators and may not 

be as significant as the reduction of drift. Reduction of 

drift in the superstructure protects structural 

components and elements, as well as nonstructural 

components sensitive to drift-induced damage. 

Reduction of acceleration protects nonstructural 

components that are sensitive to acceleration-induced 

damage.

Passive energy dissipation devices add damping (and 

sometimes stiffness) to the building. A wide variety of 

passive energy dissipation devices are available, 

including fluid viscous dampers, viscoelastic materials, 

and hysteretic devices. Ideally, energy dissipation 

devices dampen earthquake excitation of the structure 

that would otherwise cause higher levels of response 

and damage to components of the building. Under 

favorable conditions, energy dissipation devices reduce 

drift of the structure by a factor of about two to three 

(if no stiffness is added) and by larger factors if the 

devices also add stiffness to the structure. Energy 

dissipation devices will also reduce force in the 

structure—provided the structure is responding 

elastically—but would not be expected to reduce force 

in structures that are responding beyond yield.

Active control systems sense and resist building 

motion, either by applying external force or by 

modifying structural properties of active elements 

(e.g., so-called “smart” braces). Tuned mass or liquid 

dampers modify properties and add damping to key 

building modes of vibration.

Special seismic systems, such as isolation or energy 

dissipation systems, should be considered early in the 

design process and be based on the Rehabilitation 

Objectives established for the building (Chapter 2). 

Whether a special seismic system is found to be the 

“correct” design strategy for building rehabilitation 

will depend primarily on the performance required at 

the specified level of earthquake demand. In general, 

special seismic systems will be found to be more 

attractive as a rehabilitation strategy for buildings that 

have more stringent Rehabilitation Objectives (i.e., 

higher levels of performance and more severe levels of 

earthquake demand). Table C9-1 provides some simple 

guidance on the performance levels for which isolation 

and energy dissipation systems should be considered as 

possible design strategies for building rehabilitation. 
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-3

9.2 Seismic Isolation Systems

9.2.1 General Requirements

Seismic isolation systems using seismic isolators, 

classified as either elastomeric or sliding, as defined in 

Section 9.2.2, shall comply with the requirements of 

Section 9.2. Properties of seismic isolation systems 

shall be based on Section 9.2.2. Seismic isolation 

systems shall be designed and analyzed in accordance 

with Section 9.2.3. Linear and nonlinear analyses shall 

be performed, as required by Section 9.2.3, in 

accordance with Sections 9.2.4 and 9.2.5, respectively. 

Nonstructural components shall be rehabilitated in 

accordance with Section 9.2.6. Additional requirements 

for seismic isolation systems as defined in Section 9.2.7 

shall be met. Seismic isolation systems shall be 

reviewed and tested in accordance with Sections 9.2.8 

and 9.2.9, respectively. 

The seismic isolation system shall include windrestraint and tie-down systems, if such systems are 

required by this standard. The isolation system also 

shall include supplemental energy dissipation devices, 

if such devices are used to transmit force between the 

structure above the isolation system and the structure 

below the isolation system.

For seismically isolated structures, the coefficients C0, 

C1, C2, C3, and J defined in Chapter 3, shall be taken as 

1.0 

Table C9-1 suggests that isolation systems should be 

considered for achieving the Immediate Occupancy 

Structural Performance Level and the Operational 

Nonstructural Performance Level. Conversely, 

isolation will likely not be an appropriate design 

strategy for achieving the Collapse Prevention 

Structural Performance Level. In general, isolation 

systems provide significant protection to the building 

structure, nonstructural components, and contents, but 

at a cost that precludes practical application when the 

budget and Rehabilitation Objectives are modest.

Energy dissipation systems should be considered in a 

somewhat broader context than isolation systems. For 

the taller buildings (where isolation systems may not 

be feasible), energy dissipation systems should be 

considered as a design strategy when performance 

goals include the Damage Control Performance Range. 

Conversely, certain energy dissipation devices are 

quite economical and might be practical for 

performance goals that address only Limited Safety. In 

general, however, energy dissipation systems are more 

likely to be an appropriate design strategy when the 

desired Structural Performance Level is Life Safety, or 

perhaps Immediate Occupancy. Other objectives may 

also influence the decision to use energy dissipation 

devices, since these devices can also be useful for 

control of building response due to small earthquakes, 

wind, or mechanical loads.

Table C9-1 Applicability of Isolation and Energy 

Dissipation Systems

Performance

Level

Performance

Range Isolation

Energy

Dissipation

Operational Damage 

Control

Very 

Likely

Limited

Immediate

Occupancy

Likely Likely

Life

Safety

Limited 

Safety

Limited Likely

Collapse

Prevention

Not

Practical 

Limited

C9.2.1 General Requirements

Analysis methods and design criteria for seismic 

isolation systems are based on criteria for the 

Rehabilitation Objectives of Chapter 1. 

The methods described in this section augment the 

analysis requirements of Chapter 3. The analysis 

methods and other criteria of this section are based 

largely on FEMA 302, 1997 NEHRP Provisions. 
9-4 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

9.2.2 Mechanical Properties and Modeling 

of Seismic Isolation Systems

9.2.2.1 General

Seismic isolators shall be classified as either 

elastomeric or sliding. Elastomeric isolators shall 

include any one of the following: high-damping rubber 

bearings (HDR), low-damping rubber bearings (RB) or 

low-damping rubber bearings with a lead core (LRB). 

Sliding isolators shall include flat assemblies or have a 

curved surface, such as the friction-pendulum system 

(FPS). Rolling systems shall be characterized as a 

subset of sliding systems. Rolling isolators shall be flat 

assemblies or have a curved or conical surface, such as 

the ball and cone system (BNC). Isolators that cannot 

be classified as either elastomeric or sliding are not 

addressed in this standard. 

9.2.2.2 Mechanical Properties of Seismic 

Isolators

9.2.2.2.1 Elastomeric Isolators

Force-deformation response properties shall be 

established for elastomeric isolators taking into 

consideration axial-shear interaction, bilateral 

deformation, load history including the effects of 

scragging of virgin elastomeric isolators, temperature, 

and other environmental loads and aging effects over 

the design life of the isolator. 

For mathematical modeling of isolators, mechanical 

characteristics based on analysis or available material 

test properties shall be permitted. For design, 

mechanical characteristics shall be based on tests of 

isolator prototypes in accordance with Section 9.2.9.

Seismic isolation has typically been used as a 

rehabilitation strategy that enhances the performance of 

the building above that afforded by conventional 

stiffening and strengthening schemes. Seismic isolation 

rehabilitation projects have targeted performance at 

least equal to, and commonly exceeding, the Basic 

Safety Objective of this standard, effectively achieving 

a target Building Performance Level of Immediate 

Occupancy or better.

A number of buildings rehabilitated with seismic 

isolators have been historic. For these projects, seismic 

isolation reduced the extent and intrusion of seismic 

modifications on the historical fabric of the building 

that would otherwise be required to meet desired 

performance levels. 

C9.2.2.1 General

A seismic isolation system is the collection of all 

individual seismic isolators (and separate wind restraint 

and tie-down devices, if such devices are used to meet 

the requirements of this standard). Seismic isolation 

systems may be composed entirely of one type of 

seismic isolator, a combination of different types of 

seismic isolators, or a combination of seismic isolators 

acting in parallel with energy dissipation devices (i.e., a 

hybrid system).

Elastomeric isolators are typically made of layers of 

rubber separated by steel shims.

C9.2.2.2.1 Elastomeric Isolators

Elastomeric bearings represent a common means for 

introducing flexibility into an isolated structure. They 

consist of thin layers of natural rubber that are 

vulcanized and bonded to steel plates. Natural rubber 

exhibits a complex mechanical behavior, which can be 

described simply as a combination of viscoelastic and 

hysteretic behavior. Low-damping natural rubber 

bearings exhibit essentially linearly elastic and linearly 

viscous behavior at large shear strains. The effective 

damping is typically less than or equal to 0.07 for shear 

strains in the range of 0 to 2.0.

Lead-rubber bearings are generally constructed of 

low-damping natural rubber with a preformed central 

hole into which a lead core is press-fitted. Under lateral 

deformation, the lead core deforms in almost pure 

shear, yields at low levels of stress (approximately 8 to 

10 MPa in shear at normal temperature), and produces 

hysteretic behavior that is stable over many cycles. 

Unlike mild steel, lead recrystallizes at normal 

temperature (about 20°C), so that repeated yielding 

does not cause fatigue failure. Lead-rubber bearings 

generally exhibit characteristic strength that ensures 

rigidity under service loads. Figure C9-1 shows an 

idealized force-displacement relation of a lead-rubber 

bearing. The characteristic strength, Q, is related to the 

lead plug area, , and the shear yield stress of lead, 

:

 (C9-1)

Ap

σYL

Q ApσYL =
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-5

Figure C9-1 Idealized Hysteretic Force-Displacement 

Relation of a Lead-Rubber Bearing

The post-yield stiffness, , is typically higher than the 

shear stiffness of the bearing without the lead core:

 (C9-2)

where is the bonded rubber area, is the total 

rubber thickness, G is the shear modulus of rubber 

(typically computed at shear strain of 0.5), and is a 

factor larger than unity. Typically, is 1.15, and the 

elastic stiffness ranges between 6.5 to 10 times the postyield stiffness. 

kp

kp

ArGfL

Σt = ---------------

Ar Σt

f

L

f

L

The behavior of lead-rubber bearings may be 

represented by a bilinear hysteretic model. Computer 

programs 3D-BASIS (Nagarajaiah et al.; Reinhorn et al. 

(1994); Tsopelas et al. (1994b), and ETABS, Version 6

have the capability of modeling hysteretic behavior for 

isolators. These models typically require definition of 

three parameters, namely, the post-yield stiffness , 

the yield force Fy, and the yield displacement Dy . For 

lead-rubber bearings in which the elastic stiffness is 

approximately equal to 6.5 , the yield displacement 

can be estimated as:

 (C9-3)

The yield force is then given by: 

 (C9-4)

High-damping rubber bearings are made of specially 

compounded rubber that exhibits effective damping 

between 0.10 and 0.20 of critical. The increase in 

effective damping of high-damping rubber is achieved 

by the addition of chemical compounds that may also 

affect other mechanical properties of rubber. Figure 

C9-2 shows representative force-displacement loops of 

a high-damping rubber bearing under scragged 

conditions.

Scragging is the process of subjecting an elastomeric 

bearing to one or more cycles of large amplitude 

displacement. The scragging process modifies the 

molecular structure of the elastomer and results in more 

stable hysteresis at strain levels lower than that to 

which the elastomer was scragged. Although it is 

usually assumed that the scragged properties of an 

elastomer remain unchanged with time, recent studies 

by Cho and Retamal (1993) and Murota et al. (1994) 

suggest that partial recovery of unscragged properties is 

likely. The extent of this recovery is dependent on the 

elastomer compound.

kp

kp

Dy

Q

5.5kp

= ------------

Fy Q kpDy = +
9-6 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

Figure C9-2 Force-Displacement Loops of a 

High-Damping Rubber Bearing

Mathematical models capable of describing the 

transition between virgin and scragged properties of 

high-damping rubber bearings are not yet available. It is 

appropriate in this case to perform multiple analyses 

with stable hysteretic models and obtain bounds on the 

dynamic response. A smooth bilinear hysteretic model 

that is capable of modeling the behavior depicted in 

Figure C9-1 is appropriate for such analyses, as long as 

the peak shear strain is below the stiffening limit of 

approximately 1.5 to 2.0, depending on the rubber 

compound. Beyond this strain limit many elastomers 

exhibit stiffening behavior, with tangent stiffness 

approximately equal to twice the tangent stiffness prior 

to initiation of stiffening. For additional information, 

refer to Tsopelas et al. (1994a).

To illustrate the calculations of parameters from 

prototype bearings test data, Figure C9-3 shows 

experimentally determined properties of the highdamping rubber bearings, for which loops are shown in 

Figure C9-2. The properties identified are the tangent 

shear modulus, G, and the effective damping ratio, 

(described by Equation (C9-18), which is now defined 

for a single bearing rather than the entire isolation 

system), under scragged conditions. With reference to 

Figure C9-1, G is related to the post-yielding stiffness 

. 

 (C9-5)

where A is the bonded rubber area. The results of Figure 

C9-3 demonstrate that the tangent shear modulus and 

equivalent damping ratio are only marginally affected 

by the frequency of loading and the bearing pressure, 

within the indicated range for the tested elastomer. 

Different conclusions may be drawn from the testing of 

other high-damping rubber compounds.

The parameters of the bilinear hysteretic model may be 

determined by use of the mechanical properties G and 

at a specific shear strain, such as the strain 

corresponding to the design displacement D. The postyield stiffness is determined from Equation (C9-5), 

whereas the characteristic strength, Q, can be 

determined as:

βeff

kp

kp

GA

Σt = -------

βeff

kp
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-7

Figure C9-3 Tangent Shear Modulus and Effective 

Damping Ratio of High-Damping Rubber 

Bearing

 (C9-6)

where Dy is the yield displacement. The yield 

displacement is generally not known a priori. However, 

experimental data suggest that Dy is approximately 

equal to 0.05 to 0.1 times the total rubber thickness, . 

With the yield displacement approximately determined, 

the model can be completely defined by determining 

the yield force (Equation (C9-4)). It should be noted 

that the characteristic strength may be alternatively 

determined from the effective stiffness, (Equation 

(C9-17)), of the bearing, as follows:

 (C9-7)

Q

πβeffkpD2

2 πβeff ( ) – D 2Dy – = ----------------------------------------------

Σt

keff

Q πβeffkeffD2

2 D Dy ( ) – = ----------------------------

The effective stiffness is a more readily determined 

property than the post-yielding stiffness. The effective 

stiffness is commonly used to obtain the effective shear 

modulus, , defined as: 

 (C9-8)

The behavior of the bearing for which the forcedisplacement loops are shown in Figure C9-2 is now 

analytically constructed using the mechanical 

properties at a shear strain of 1.0 and a bearing pressure 

of 7.0 MPa. These properties are Geff = 0.50 MPa and 

= 0.16. With the bonded area and total thickness of 

rubber known, and assuming , a bilinear 

hysteretic model was defined and implemented in the 

program 3D-BASIS. The simulated loops are shown in 

Figure C9-4, where it may be observed that the 

calculated hysteresis loop at shear strain of 1.0 agrees 

well with the corresponding experimental hysteresis 

loop. However, at lower peak shear strain the analytical 

loops have a constant characteristic strength, whereas 

the experimental loops have a characteristic strength 

dependent on the shear strain amplitude. Nevertheless, 

the analytical model will likely produce acceptable 

results when the design parameters are based on the 

mechanical properties at a strain corresponding to the 

design displacement.

Geff

Geff

keffΣt

A = -------------

βeff

Dy = 0.1Σt
9-8 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

9.2.2.2.2 Sliding Isolators

Force-deformation response properties shall be 

established for sliding isolators, taking into 

consideration contact pressure, rate of loading or 

velocity, bilateral deformation, temperature, 

contamination, and other environmental loads and 

aging effects over the design life of the isolator.

Mechanical characteristics for use in mathematical 

models shall be based on analysis and available material 

test properties. Verification of isolator properties used 

Figure C9-4 Analytical Force-Displacement Loops of 

High-Damping Rubber Bearing

Elastomeric bearings have finite vertical stiffness that 

affects the vertical response of the isolated structure. 

The vertical stiffness of an elastomeric bearing may be 

obtained from

 (C9-9)

where is the compression modulus. Although a 

number of approximate empirical relations have been 

proposed for the calculation of the compression 

modulus, the correct expression for circular bearings is 

 (C9-10)

(Kelly, 1993) where K is the bulk modulus (typically 

assumed to have a value of 2000 MPa) and S is the 

shape factor, which is defined as the ratio of the loaded 

area to the bonded perimeter of a single rubber layer. 

For a circular bearing of bonded diameter φ and rubber 

layer thickness t, the shape factor is given by

kv

EcA

Σt = ---------

Ec

Ec

1

6GeffS

2 ------------------- 4

3K

+ ------

      –1

=

 (C9-11)

Seismic elastomeric bearings are generally designed 

with a large shape factor, typically 12 to 20. 

Considering an elastomeric bearing design with S = 15, 

 = 1 MPa, and K = 2000 MPa, the ratio of vertical 

stiffness (Equation (C9-9)) to effective horizontal 

stiffness (Equation (C9-8)) is approximately equal to 

700. Thus, the vertical period of vibration of a structure 

on elastomeric isolation bearings will be about 26 times 

(i.e., ) less than the horizontal period, on the order 

of 0.1 second. This value of vertical period provides 

potential for amplification of the vertical ground 

acceleration by the isolation system. The primary effect 

of this amplification is to change the vertical load on 

the bearings, which may need to be considered for 

certain design applications.

Another consideration in the design of seismically 

isolated structures with elastomeric bearings is 

reduction in height of a bearing with increasing lateral 

deformation (Kelly, 1993). While this reduction of 

height is typically small, it may be important when 

elastomeric bearings are combined with other isolation 

elements that are vertically rigid (such as sliding 

bearings). In addition, incompatibilities in vertical 

displacements may lead to a redistribution of loads.

S φ

4t = ----

Geff

700
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-9

for design shall be based on tests of isolator prototypes 

in accordance with Section 9.2.9.

C9.2.2.2.2 Sliding Isolators

Sliding bearings will tend to limit the transmission of 

force to an isolated structure to a predetermined level. 

While this is desirable, the lack of significant restoring 

force can result in significant variations in the peak 

displacement response, and can result in permanent 

offset displacements. To avoid these undesirable 

features, sliding bearings are typically used in 

combination with a restoring force mechanism.

The lateral force developed in a sliding bearing can be 

defined as:

 (C9-12)

where

F N

R

---U + μsN sgn U

· = ( )

U = Displacement

= Sliding velocity

R = Radius of curvature of sliding surface

= Coefficient of sliding friction

N = Normal load on bearing

U

·

μs

The normal load consists of the gravity load, W, the 

effect of vertical ground acceleration, , and the 

additional seismic load due to overturning moment, :

 (C9-13)

The first term in Equation (C9-13) denotes the restoring 

force component, and the second term describes the 

friction force. For flat sliding bearings, the radius of 

curvature is infinite, so the restoring force term in 

Equation (C9-13) vanishes. For a spherical sliding 

surface (Zayas et al., 1987), the radius of curvature is 

constant, so the bearing exhibits a linear restoring force; 

that is, under constant gravity load the stiffness is equal 

to , where is the radius of the spherical 

sliding surface. When the sliding surface takes a conical 

shape, the restoring force is constant. Figure C9-5 

shows idealized force-displacement loops of sliding 

bearings with flat, spherical, and conical surfaces.

U

··

v

Ps

N W 1

U

··

v

g

------ Ps

W

+ + -----     =

W Ro ⁄ Ro
9-10 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

Figure C9-5 Idealized Force Displacement Loops of Sliding Bearings

Sliding bearings with either a flat or single curvature 

spherical sliding surface are typically made of PTFE or 

PTFE-based composites in contact with polished 

stainless steel. The shape of the sliding surface allows 

large contact areas that, depending on the materials 

used, are loaded to average bearing pressures in the 

range of 7 to 70 MPa. For interfaces with shapes other 

than flat or spherical, the load needs to be transferred 

through a bearing as illustrated in Figure C9-5 for the 

conical sliding surface. Such an arrangement typically 

results in a very low coefficient of friction.

For bearings with large contact area, and in the absence 

of liquid lubricants, the coefficient of friction depends 

on a number of parameters, of which the three most 

important are the composition of the sliding interface, 

bearing pressure, and velocity of sliding. For interfaces 

composed of polished stainless steel in contact with 

PTFE or PTFE-based composites, the coefficient of 

sliding friction may be described by 

μ (C9-14) s f

max - fmax fmin ( ) – exp a– U

· = ( )

where parameters and describe the 

coefficient of friction at small and large velocities of 

sliding and under constant pressure, respectively, all as 

depicted in Figure C9-6. Parameters , , and a

depend on the bearing pressure, although only the 

dependency of fmax on pressure is of practical 

significance. A good approximation to the experimental 

data (Constantinou et al., 1993b) is

(C9-15)

where the physical significance of parameters 

and is as illustrated in Figure C9-6. The term p is 

the instantaneous bearing pressure, which is equal to 

the normal load N computed by Equation (C9-13), 

divided by the contact area; and ε is a parameter that 

controls the variation of with pressure.

f

min fmax

f

max fmin

f

max fmaxo fmaxo fmaxp = – ( )ε – tanh p

f

maxo

f

maxp

f

max
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-11

9.2.2.3 Modeling of Isolators

9.2.2.3.1 General

If the mechanical characteristics of a seismic isolator 

are dependent on axial load (due to gravity, earthquake 

overturning effects, and vertical earthquake shaking), 

rate of loading (velocity), bilateral deformation, 

temperature, or aging, then upper- and lower-bound 

values of stiffness and damping shall be used in 

multiple analyses of the model to determine the range 

and sensitivity of response to design parameters.

9.2.2.3.2 Linear Models

The restoring force, F, of an isolator shall be calculated 

as the product of effective stiffness, keff, and response 

displacement, D: 

 (9-1)

The effective stiffness, keff, of an isolator shall be 

calculated from test data using Equation (9-12). The 

area enclosed by the force-displacement hysteresis loop 

shall be used to calculate the effective damping, βeff, of 

an isolator using Equation (9-13). Effective stiffness 

and effective damping shall be evaluated at all response 

displacements of design interest.

Figure C9-6 illustrates another feature of sliding 

bearings. On initiation of motion, the coefficient of 

friction exhibits a static or breakaway value, , which 

is typically higher than the minimum value . To 

demonstrate frictional properties, Figure C9-6 shows 

the relation between bearing pressure and the friction 

coefficients , , and of a PTFE-based 

composite material in contact with polished stainless 

steel at normal temperature. These data were compiled 

from testing of bearings in four different testing 

programs (Soong and Constantinou, 1994).

Figure C9-6 Coefficient of Friction of PTFE-based 

Composite in Contact with Polished 

Stainless Steel at Normal Temperature

Combined elastomeric-sliding isolation systems have 

been used in buildings in the United States. Japanese 

engineers have also used elastomeric bearings in 

combination with mild steel elements that are designed 

to yield in strong earthquakes and enhance the energy 

dissipation capability of the isolation system (Kelly, 

1988). These mild steel elements exhibit either elastoplastic behavior or bilinear hysteretic behavior with low 

post-yielding stiffness. Moreover, fluid viscous energy 

dissipation devices have been used in combination with 

elastomeric bearings. The behavior of fluid viscous 

devices is described in Section 9.3.3.2.3.

μB

f

min

f

max μB fmin

Hybrid seismic isolation systems composed of 

elastomeric and sliding bearings should be modeled 

taking into account the likely significant differences in 

the relationships between vertical displacement as a 

function of horizontal displacement. The use of 

elastomeric and sliding isolators in close proximity to 

one another under vertically stiff structural framing 

elements (e.g., reinforced concrete shear walls) may be 

problematic and could result in significant 

redistributions of gravity loads.

C9.2.2.3.2 Linear Models

Linear procedures use effective stiffness, keff, and 

effective damping, βeff, to characterize nonlinear 

properties of isolators.

For linear procedures (see FEMA 274 Section C9.2.3), 

the seismic isolation system can be represented by an 

equivalent linearly elastic model. The force in a seismic 

isolation device is calculated as:

 (C9-16)

F keff = D

F keff = D
9-12 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

where all terms are as defined in Section 9.2.2.3.2 of 

this standard. The effective stiffness of the seismic 

isolation device may be calculated from test data as 

follows:

 (C9-17)

Figure C9-7 illustrates the physical significance of the 

effective stiffness.

Analysis by a linear method requires that either each 

seismic isolator or groups of seismic isolators be 

represented by linear springs of either stiffness keff or 

the combined effective stiffness of each group. The 

energy dissipation capability of an isolation system is 

generally represented by effective damping. Effective 

damping is amplitude-dependent and calculated at 

design displacement, D, as follows:

 (C9-18)

where is the sum of the areas of the hysteresis 

loops of all isolators, and is the sum of the 

effective stiffnesses of all seismic isolation devices. 

Both the area of the hysteresis loops and the effective 

stiffness are determined at the design displacement, D.

keff

F+ F– +

∆+ ∆– + = -------------------------

βeff

1

2π

------ ΣED

KeffD2 = ----------------

ΣED

Keff

Figure C9-7 Definition of Effective Stiffness of 

Seismic Isolation Devices

The application of Equations (C9-16) through (C9-18) 

to the design of isolation systems is complicated if the 

effective stiffness and loop area depend on axial load. 

Multiple analyses are then required to establish bounds 

on the properties and response of the isolators. For 

example, sliding isolation systems exhibit such 

dependencies as described in Section C9.2.2.2.2. To 

account for these effects, the following procedure is 

proposed.
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-13

9.2.2.3.3 Nonlinear Models

The nonlinear force-deflection properties of isolators 

shall be explicitly modeled if nonlinear procedures are 

used.

The inelastic (hysteretic) response of the isolators shall 

represent damping. Additional viscous damping shall 

not be included in the model unless supported by ratedependent tests of isolators.

In sliding isolation systems, the relation between 

horizontal force and vertical load is substantially linear 

(see Equation (C9-16)). Accordingly, the net effect of 

overturning moment on the mechanical behavior of a 

group of bearings is small and can be neglected. 

Al-Hussaini et al. (1994) provided experimental results 

that demonstrate this behavior up to the point of 

imminent bearing uplift. Similar results are likely for 

elastomeric bearings.

1. The effect of vertical ground acceleration is to 

modify the load on the isolators. If it is assumed that 

the building is rigid in the vertical direction, and 

axial forces due to overturning moments are absent, 

the axial loads can vary between and 

, where is the peak vertical ground 

acceleration. However, recognizing that horizontal 

and vertical ground motion components are likely 

not correlated unless in the near field, it is 

appropriate to use a combination rule that uses only 

a fraction of the peak vertical ground acceleration. 

Based on the use of 50% of the peak vertical ground 

acceleration, maximum and minimum axial loads on 

a given isolator may be defined as:

 (C9-19)

where the plus sign gives the maximum value and the 

minus sign gives the minimum value. Equation (C9-19) 

is based on the assumption that the short-period spectral 

response parameter, SDS, is 2.5 times the peak value of 

the vertical ground acceleration. For analysis for the 

Maximum Considered Earthquake, the axial load 

should be determined from

 (C9-20)

Equations (C9-19) and (C9-20) should be used with 

caution if the building is located in the near field of a 

major active fault. In this instance, expert advice should 

be sought regarding correlation of horizontal and 

vertical ground motion components.

W 1 U

·· ( ) – ⁄ g

W 1 U

·· ( ) + ⁄ g U··

Nc W 1 0.20 ± SDS = ( )

Nc W 1 0.20 ± SMS = ( )

Load represents a constant load on isolators, which 

can be used for determining the effective stiffness and 

area of the hysteresis loop. To obtain these properties, 

the characteristic strength Q (see Figure C9-7) is 

needed. For sliding isolators, Q can be taken as equal to 

, where is determined at the bearing 

pressure corresponding to load . For example, for a 

sliding bearing with spherical sliding surface of radius 

 (see Figure C9-5), the effective stiffness and area of 

the loop at the design displacement D are:

 (C9-21)

 (C9-22)

C9.2.2.3.3 Nonlinear Models

For dynamic nonlinear time history analysis, the 

seismic isolation elements should be explicitly 

modeled. FEMA 274 Sections C9.2.2.2 through 

C9.2.2.4 present relevant information. When 

uncertainties exist, and when aspects of behavior 

cannot be modeled, multiple analyses should be 

performed in order to establish bounds on the dynamic 

response.

Nc

f

maxNc fmax

Nc

Ro

keff

1

Ro

----- f

max

D

+ ----------

     Nc =

Loop Area 4f

maxNc = D
9-14 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

9.2.2.4 Isolation System and Superstructure 

Modeling

9.2.2.4.1 General

Mathematical models of the isolated building, including 

the isolation system, the lateral-force-resisting system 

of the superstructure, other structural components and 

elements, and connections between the isolation system 

and the structure, shall meet the requirements of 

Chapters 2 and 3 and Sections 9.2.2.4.2 and 9.2.2.4.3.

9.2.2.4.2 Isolation System Model

The isolation system shall be modeled using 

deformation characteristics developed and verified by 

test in accordance with the requirements of 

Section 9.2.9.

The isolation system shall be modeled with sufficient 

detail to:

1. Account for the spatial distribution of isolator units.

2. Calculate translation, in both horizontal directions, 

and torsion of the structure above the isolation 

interface, considering the most disadvantageous 

location of mass eccentricity.

3. Assess overturning/uplift forces on individual 

isolators.

4. Account for the effects of vertical load, bilateral 

load, and/or the rate of loading, if the force 

deflection properties of the isolation system are 

dependent on one or more of these factors.

5. Assess forces due to P-∆ moments.

6. Account for nonlinear components. Isolation 

systems with nonlinear components include systems 

that do not meet the criteria of Section 9.2.3.3.1, 

Item 2.

9.2.2.4.3 Superstructure Model

The maximum displacement of each floor, the total 

design displacement, and the total maximum 

displacement across the isolation system shall be 

calculated using a model of the isolated building that 

incorporates the force-deformation characteristics of 

nonlinear components.

Calculation of design forces and displacements in 

primary components of the lateral-force-resisting 

system using linearly elastic models of the isolated 

structure shall be permitted if both of the following 

criteria are met:

1. Pseudo-elastic properties assumed for nonlinear 

isolation system components are based on the 

maximum effective stiffness of the isolation system.

2. The lateral-force-resisting system remains linearly 

elastic for the earthquake demand level of interest.

A lateral-force-resisting system that meets both of the 

following criteria may be classified as linearly elastic:

1. For all deformation-controlled actions, Equation 

(3-20) is satisfied using an m-factor equal to 1.0.

For simplified nonlinear analysis, each seismic 

isolation element can be modeled by an appropriate 

rate-independent hysteretic model. Elastomeric 

bearings may be modeled as bilinear hysteretic 

elements as described in FEMA 274 Section C9.2.2.2. 

Sliding bearings may also be modeled as bilinear 

hysteretic elements with characteristic strength (see 

Figure C9-5) given by

 (C9-23)

where is determined by either Equation (C9-19) or 

Equation (C9-20), and is the coefficient of sliding 

friction at the appropriate sliding velocity. The postyield stiffness can then be determined as:

 (C9-24)

where R is as defined in FEMA 274 Section C9.2.2.2.B. 

The yield displacement Dy in a bilinear hysteretic 

model of a sliding bearing should be very small, 

perhaps on the order of 2 mm. Alternatively, a bilinear 

hysteretic model for sliding bearings may be defined to 

have an elastic stiffness that is at least 100 times larger 

than the post-yield stiffness .

Isolation devices that exhibit viscoelastic behavior as 

shown in Figure C9-7 should be modeled as linearly 

elastic elements with effective stiffness as 

determined by Equation (C9-21).

Q fmaxNc =

Nc

f

max

kp

Nc

R = -----

kp

keff
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-15

2. For all force-controlled actions, Equation (3-21) is 

satisfied.

9.2.3 General Criteria for Seismic Isolation 

Design

9.2.3.1 General

The design, analysis, and testing of the isolation system 

shall be based on the requirements of this section.

9.2.3.1.1 Stability of the Isolation System

The stability of the vertical load-carrying components 

of the isolation system shall be verified by analysis and 

test, as required by Section 9.2.9, for a lateral 

displacement equal to the total maximum displacement 

computed in accordance with Section 9.2.4.3.5 or 

Section 9.2.5.1.2, or for the maximum displacement 

allowed by displacement-restraint devices, if such 

devices are part of the isolation system.

9.2.3.1.2 Configuration Requirements

The isolated building shall be classified as regular or 

irregular, as defined in Section 2.4.1.1, based on the 

structural configuration of the structure above the 

isolation system.

9.2.3.2 Ground Shaking Criteria

Ground shaking criteria for the Design Earthquake and 

the Maximum Considered Earthquake shall be 

established in accordance with Section 1.6 as modified 

by this section. The design Earthquake Hazard Level 

shall be user-specified and shall be permitted to be 

chosen equal to the BSE-1 Earthquake Hazard Level. 

The Maximum Considered Earthquake shall be taken 

equal to the BSE-2 Earthquake Hazard Level.

9.2.3.2.1 User-Specified Design Earthquake

For the Design Earthquake, the following ground 

shaking criteria shall be established:

1. Short period spectral response acceleration 

parameter, SXS and spectral response acceleration 

parameter at 1.0 second, SX1, in accordance with 

Section 1.6.1.4.

2. Five-percent-damped response spectrum of the 

design earthquake (when a response spectrum is 

required for linear procedures by Section 9.2.3.3.2, 

or to define acceleration time histories).

3. At least three acceleration time histories compatible 

with the design earthquake spectrum (when 

acceleration time histories are required for nonlinear 

procedures by Section 9.2.3.3.3).

9.2.3.2.2 Maximum Considered Earthquake

For the BSE-2, the following ground shaking criteria 

shall be established: 

1. Short period spectral response acceleration 

parameter, SXS and spectral response acceleration 

parameter at 1.0 second, SX1, in accordance with 

Section 1.6.1.4.

2. Five-percent-damped site-specific response 

spectrum of the BSE-2 (when a response spectrum is 

required for linear procedures by Section 9.2.3.3.2, 

or to define acceleration time histories).

3. At least three acceleration time histories compatible 

with the BSE-2 spectrum (when acceleration time 

histories are required for nonlinear procedures by 

Section 9.2.3.3.3).

9.2.3.3 Selection of Analysis Procedure

9.2.3.3.1 Linear Procedures

Linear procedures shall be permitted for design of 

seismically isolated buildings, provided the following 

criteria are met.

1. The building is located on Soil Profile Type A, B, C, 

or D; or E if for BSE-2.

2. The isolation system meets all of the following 

criteria:

2.1. The effective stiffness of the isolation system 

at the design displacement is greater than 

one-third of the effective stiffness at 20% of 

the design displacement.

C9.2.3.1 General

Criteria for the seismic isolation of buildings are 

divided into two sections:

1. Rehabilitation of the building.

2. Design, analysis, and testing of the isolation 

system.

S1 ≥ 0.6
9-16 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

2.2. The isolation system is capable of producing a 

restoring force as specified in 

Section 9.2.7.2.4.

2.3. The isolation system has force-deflection 

properties that are independent of the rate of 

loading.

2.4. The isolation system has force-deflection 

properties that are independent of vertical load 

and bilateral load.

2.5. When considering analysis procedures, for the 

BSE-2, the isolation system does not limit 

BSE-2 displacement to less than the ratio of 

the design spectral response acceleration at one 

second (SX1) for the BSE-2 to that for the 

Design Earthquake times the total design 

displacement.

3. The structure above the isolation system exhibits 

global elastic behavior for the earthquake motions 

under consideration.

9.2.3.3.2 Response Spectrum Analysis

Response spectrum analysis shall be used for design of 

seismically isolated buildings that meet any of the 

following criteria.

1. The building is over 65 feet (19.8 meters) in height.

2. The effective period of the structure, TM, is greater 

than three seconds. 

3. The effective period of the isolated structure, TD, is 

less than or equal to three times the elastic, fixedbase period of the structure above the isolation 

system.

4. The structure above the isolation system is irregular 

in configuration.

9.2.3.3.3 Nonlinear Procedures

Nonlinear procedures shall be used for design of 

seismic-isolated buildings for which any of the 

following conditions apply:

1. The structure above the isolation system is nonlinear 

for the earthquake motions under consideration.

2. The isolation system does not meet all of the criteria 

of Section 9.2.3.3.1.

Nonlinear acceleration time history analysis shall be 

performed for the design of seismically isolated 

buildings for which conditions (1) and (2) apply.

C9.2.3.3 Selection of Analysis Procedure

Linear procedures include prescriptive formulas and 

Response Spectrum Analysis. Linear procedures based 

on formulas (similar to the seismic-coefficient equation 

required for design of fixed-base buildings) prescribe 

peak lateral displacement of the isolation system, and 

define “minimum” design criteria that may be used for 

design of a very limited class of isolated structures 

(without confirmatory dynamic analyses). These simple 

formulas are useful for preliminary design and provide 

a means of expeditious review of more complex 

calculations.

Response Spectrum Analysis is recommended for 

design of isolated structures that have either (1) a tall or 

otherwise flexible superstructure, or (2) an irregular 

superstructure. For most buildings, Response Spectrum 

Analysis will not predict significantly different 

displacements of the isolation system than those 

calculated by prescriptive formulas, provided both 

calculations are based on the same effective stiffness 

and damping properties of the isolation system. The 

real benefit of Response Spectrum Analysis is not in the 

prediction of isolation system response, but rather in the 

calculation and distribution of forces in the 

superstructure. Response Spectrum Analysis permits 

the use of more detailed models of the superstructure 

that better estimate forces and deformations of 

components and elements considering flexibility and 

irregularity of the structural system.

Nonlinear procedures include the Nonlinear Static 

Procedure (NSP) and the Nonlinear Dynamic 

Procedure (NDP). The NSP is a static pushover 

procedure, and the NDP is based on nonlinear Time 

History Analysis. The NSP or the NDP is required for 

isolated structures that do not have essentially linearly 

elastic superstructures (during BSE-2 demand). In this 

case, the superstructure would be modeled with 

nonlinear elements and components.
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-17

9.2.4 Linear Procedures

9.2.4.1 General

Seismically isolated buildings for which linear analysis 

procedures are selected based on the criteria of 

Section 9.2.3.3 shall be designed and constructed to 

resist the earthquake displacements and forces specified 

in this section, at a minimum.

9.2.4.2 Deformation Characteristics of the 

Isolation System

The deformation characteristics of the isolation system 

shall be based on tests performed in accordance with 

Section 9.2.9.

The deformation characteristics of the isolation system 

shall explicitly include the effects of the wind-restraint 

and tie-down systems, and supplemental energydissipation devices, if such systems and devices are 

used to meet the design requirements of this standard.

9.2.4.3 Minimum Lateral Displacements

9.2.4.3.1 Design Displacement

The isolation system shall be designed and constructed 

to withstand, as a minimum, lateral earthquake 

displacements that act in the direction of each of the 

main horizontal axes of the structure in accordance with 

Equation (9-2):

 (9-2)

where: 

SX1 is evaluated for the Design Earthquake.

9.2.4.3.2 Effective Period at the Design 

Displacement

The effective period, TD, of the isolated building at the 

design displacement shall be determined using the 

deformation characteristics of the isolation system in 

accordance with Equation (9-3):

 (9-3)

9.2.4.3.3 Maximum Displacement

The maximum displacement of the isolation system, 

DM, in the most critical direction of horizontal response 

shall be calculated in accordance with Equation (9-4):

(9-4)

where: 

Time History Analysis is required for isolated 

structures on very soft soil (i.e., Soil Profile Type E 

when shaking is strong, or Soil Profile Type F) that 

could shake the building with a large number of cycles 

of long-period motion, and for buildings with isolation 

systems that are best characterized by nonlinear 

models. Such isolation systems include:

1. Systems with more than about 30% effective 

damping (because high levels of damping can 

significantly affect higher-mode response of the 

superstructure).

2. Systems that lack significant restoring force 

(because these systems may not stay centered during 

earthquake shaking).

3. Systems that are expected to exceed the sway-space 

clearance with adjacent structures (because impact 

with adjacent structures could impose large 

demands on the superstructure).

4. Systems that are rate- or load-dependent (because 

their properties will vary during earthquake 

shaking).

For the types of isolation systems described above, 

appropriate nonlinear properties must be used to model 

isolators. Linear properties could be used to model the 

superstructure, provided the superstructure’s response 

is essentially linearly elastic for BSE-2 demand.

The restrictions placed on the use of linear procedures 

effectively suggest that nonlinear procedures be used 

for virtually all isolated buildings. However, lowerbound limits on isolation system design displacement 

and force are specified by this standard as a percentage 

of the demand prescribed by the linear formulas, even 

when dynamic analysis is used as the basis for design. 

These lower-bound limits on key design attributes 

ensure consistency in the design of isolated structures 

and serve as a “safety net” against gross underdesign.

DD

g

4π

2 -------- SX1TD

BD1

= ----------------

TD 2π

W

KDming = ------------------

DM

g

4π

2 -------- SX1TM

BM1

= ----------------
9-18 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

SX1 is evaluated for the BSE-2.

9.2.4.3.4 Effective Period at the Maximum 

Displacement

The effective period, TM, of the isolated building at the 

maximum displacement shall be determined using the 

deformation characteristics of the isolation system in 

accordance with Equation (9-5):

 (9-5)

9.2.4.3.5 Total Displacement

The total design displacement, DTD, and the total 

maximum displacement, DTM, of components of the 

isolation system shall include additional displacement 

due to actual and accidental torsion calculated 

considering the spatial distribution of the effective 

stiffness of the isolation system at the design 

displacement and the most disadvantageous location of 

mass eccentricity.

The total design displacement, DTD, and the total 

maximum displacement, DTM, of components of an 

isolation system with a uniform spatial distribution of 

effective stiffness at the design displacement shall be 

taken as not less than that prescribed by Equations (9-6) 

and (9-7):

(9-6)

 (9-7)

A value for the total maximum displacement, DTM, less 

than the value prescribed by Equation (9-7), but not less 

than 1.1 times DM, shall be permitted, provided the 

isolation system is shown by calculation to be 

configured to resist torsion.

9.2.4.4 Minimum Lateral Forces

9.2.4.4.1 Isolation System and Structural 

Components and Elements at or below 

the Isolation System

The isolation system, the foundation, and all other 

structural components and elements below the isolation 

system shall be designed and constructed to withstand a 

minimum lateral seismic force, Vb, prescribed by 

Equation (9-8):

 (9-8)

9.2.4.4.2 Structural Components and Elements 

above the Isolation System

The components and elements above the isolation 

system shall be designed and constructed to resist a 

minimum lateral seismic force, Vs , equal to the value of 

Vb, prescribed by Equation (9-8).

9.2.4.4.3 Limits on Vs

The value of Vs shall be taken as not less than the 

following:

1. The base shear corresponding to the design wind 

load.

2. The lateral seismic force required to fully activate 

the isolation system factored by 1.5.

9.2.4.4.4 Vertical Distribution of Force

The total force, Vs, shall be distributed over the height 

of the structure above the isolation interface in 

accordance with Equation (9-9):

 (9-9)

At each level designated as x, the force Fx shall be 

applied over the area of the building in accordance with 

the weight, wx, distribution at that level, hx. Response of 

structural components and elements shall be calculated 

as the effect of the force Fx applied at the appropriate 

levels above the base.

TM 2π

W

KMming = ------------------

DTD DD 1 y

12e

b

2 d2

+

= + -----------------

DTM DM 1 y

12e

b

2 d2

+

= + -----------------

C9.2.4.4.3 Limits on Vs

Examples of lateral seismic forces required to fully 

activate the isolation system include the yield level of a 

softening system, the ultimate capacity of a sacrificial 

wind-restraint system, or the break-away friction level 

of a sliding system.

Vb KDmaxDD =

Fx

Vswxhx

wihi

n

∑

= --------------------
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-19

9.2.4.5 Response Spectrum Analysis

9.2.4.5.1 Earthquake Input

The Design Earthquake spectrum shall be used to 

calculate the total design displacement of the isolation 

system and the lateral forces and displacements of the 

isolated building. The BSE-2 spectrum shall be used to 

calculate the total maximum displacement of the 

isolation system.

9.2.4.5.2 Modal Damping

Response spectrum analysis shall be performed, using a 

damping value for isolated modes equal to the effective 

damping of the isolation system, or 30% of critical, 

whichever is less. The damping value assigned to 

higher modes of response shall be consistent with the 

material type and stress level of the superstructure.

9.2.4.5.3 Combination of Earthquake Directions

Response spectrum analysis used to determine the total 

design displacement and total maximum displacement 

shall include simultaneous excitation of the model by 

100% of the most critical direction of ground motion, 

and not less than 30% of the ground motion in the 

orthogonal axis. The maximum displacement of the 

isolation system shall be calculated as the vector sum of 

the two orthogonal displacements.

9.2.4.5.4 Scaling of Results

If the total design displacement determined by response 

spectrum analysis is found to be less than the value of 

DTD prescribed by Equation (9-6), or if the total 

maximum displacement determined by response 

spectrum analysis is found to be less than the value of 

DTM prescribed by Equation (9-7), then all response 

parameters, including component actions and 

deformations, shall be adjusted upward proportionally 

to the DTD value, or the DTM value, whichever is 

greater, and used for design. 

9.2.4.6 Design Forces and Deformations

Components and elements of the building shall be 

designed for forces and displacements estimated by 

linear procedures using the acceptance criteria of 

Section 3.4.2.2, except that deformation-controlled 

components and elements shall be designed using 

component m-factors equal to or less than 1.5.

9.2.5 Nonlinear Procedures

Seismically isolated buildings evaluated using 

nonlinear procedures shall be represented by threedimensional models that incorporate the nonlinear 

characteristics of both the isolation system and the 

structure above the isolation system.

9.2.5.1 Nonlinear Static Procedure

9.2.5.1.1 General

The Nonlinear Static Procedure (NSP) for seismically 

isolated buildings shall be based on the criteria of 

Section 3.3.3, except that the target displacement and 

pattern of applied lateral load shall be based on the 

criteria given in Sections 9.2.5.1.2 and 9.2.5.1.3, 

respectively.

9.2.5.1.2 Target Displacement

In each principal direction, the building model shall be 

pushed to the Design Earthquake target displacement, 

, and to the BSE-2 target displacement, , as 

defined by Equations (9-10) and (9-11):

(9-10)

(9-11)

where Te is the effective period of the structure above 

the isolation interface on a fixed base as prescribed by 

Equation (3-14). The target displacements, and , 

shall be evaluated at a control node that is located at the 

center of mass of the first floor above the isolation 

interface. 

9.2.5.1.3 Lateral Load Pattern

The pattern of applied lateral load shall be proportional 

to the distribution of the product of building mass and 

the deflected shape of the isolated mode of response at 

the target displacement. 

9.2.5.2 Nonlinear Dynamic Procedure

9.2.5.2.1 General

The Nonlinear Dynamic Procedure (NDP) for 

seismically isolated buildings shall be based on the 

nonlinear procedure requirements of Section 3.3.4, 

D′

D D′M

D′

D

DD

1

Te

TD

------

      2

+

= ----------------------------

D′

M

DM

1

Te

TM

-------

      2

+

= -----------------------------

D′

D D′M
9-20 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

except that results shall be scaled for design based on 

the criteria given in the following section.

9.2.5.2.2 Scaling of Results

If the design displacement determined by time-history 

analysis is less than the value of prescribed by 

Equation (9-10), or if the maximum displacement 

determined by response spectrum analysis is found to 

be less than the value of prescribed by Equation 

(9-11), then all response parameters, including 

component actions and deformations, shall be adjusted 

upward proportionally to the value or the 

value, whichever is greater, and used for design.

9.2.5.3 Design Forces and Deformations 

Components and elements of the building shall be 

designed for the forces and deformations estimated by 

nonlinear procedures using the acceptance criteria of 

Section 3.4.3.2.

9.2.6 Nonstructural Components 

9.2.6.1 General

Permanent nonstructural components and the 

attachments to them shall be designed to resist seismic 

forces and displacements as given in this section and the 

applicable requirements of Chapter 11.

9.2.6.2 Forces and Displacements

9.2.6.2.1 Components and Elements at or above 

the Isolation Interface

Nonstructural components, or portions thereof, that are 

at or above the isolation interface, shall be designed to 

resist a total lateral seismic force equal to the maximum 

dynamic response of the element or component under 

consideration.

EXCEPTION: Design of elements of seismically 

isolated structures and nonstructural components, or 

portions thereof, to resist the total lateral seismic force 

as required for conventional fixed-base buildings by 

Chapter 11, shall be permitted.

9.2.6.2.2 Components and Elements that Cross the 

Isolation Interface

Nonstructural components, or portions thereof, that 

cross the isolation interface shall be designed to 

withstand the total maximum (horizontal) displacement 

and maximum vertical displacement of the isolation 

system at the total maximum (horizontal) displacement. 

Components and elements that cross the isolation 

interface shall not restrict displacement of the isolated 

building or otherwise compromise the Rehabilitation 

Objectives of the building.

9.2.6.2.3 Components and Elements below the 

Isolation Interface

Nonstructural components, or portions thereof, that are 

below the isolation interface shall be designed and 

constructed in accordance with the requirements of 

Chapter 11.

9.2.7 Detailed System Requirements

9.2.7.1 General

The isolation system and the structural system shall 

comply with the detailed system requirements specified 

in Section 9.2.7.2 and 9.2.7.3, respectively.

9.2.7.2 Isolation System

9.2.7.2.1 Environmental Conditions

In addition to the requirements for vertical and lateral 

loads induced by wind and earthquake, the isolation 

system shall be designed with consideration given to 

other environmental conditions, including aging effects, 

creep, fatigue, operating temperature, and exposure to 

moisture or damaging substances.

9.2.7.2.2 Wind Forces

Isolated buildings shall resist design wind loads at all 

levels above the isolation interface in accordance with 

the applicable wind design provisions. At the isolation 

interface, a wind-restraint system shall be provided to 

limit lateral displacement in the isolation system to a 

value equal to that required between floors of the 

structure above the isolation interface.

9.2.7.2.3 Fire Resistance

Fire resistance rating for the isolation system shall be 

consistent with the requirements of columns, walls, or 

other such elements of the building.

9.2.7.2.4 Lateral Restoring Force

The isolation system shall be configured to produce 

either a restoring force such that the lateral force at the 

total design displacement is at least 0.025W greater than 

the lateral force at 50% of the total design displacement, 

or a restoring force of not less than 0.05W at all 

displacements greater than 50% of the total design 

displacement.

D′

D

D′

M

D′

D D′M
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-21

EXCEPTION: The isolation system need not be 

configured to produce a restoring force, as required 

above, provided the isolation system is capable of 

remaining stable under full vertical load and 

accommodating a total maximum displacement equal to 

the greater of either 3.0 times the total design 

displacement or 36 SX1 inches, where SX1 is calculated 

for the BSE-2.

9.2.7.2.5 Displacement Restraint

Configuration of the isolation system to include a 

displacement restraint that limits lateral displacement 

due to the BSE-2 to less than the ratio of the design 

spectral response acceleration parameter at one second 

(SX1) for the BSE-2 to that for the Design Earthquake 

times the total design displacement shall be permitted, 

provided that the seismically isolated building is 

designed in accordance with the following criteria when 

more stringent than the requirements of Section 9.2.3.

1. BSE-2 response is calculated in accordance with the 

dynamic analysis requirements of Section 9.2.5, 

explicitly considering the nonlinear characteristics 

of the isolation system and the structure above the 

isolation system.

2. The ultimate capacity of the isolation system, and 

structural components and elements below the 

isolation system, shall exceed the force and 

displacement demands of the BSE-2.

3. The structure above the isolation system is checked 

for stability and ductility demand of the BSE-2.

4. The displacement restraint does not become 

effective at a displacement less than 0.75 times the 

total design displacement, unless it is demonstrated 

by analysis that earlier engagement does not result in 

unsatisfactory performance.

9.2.7.2.6 Vertical Load Stability

Each component of the isolation system shall be 

designed to be stable under the full maximum vertical 

load, 1.2QD + QL + |QE|, and the minimum vertical 

load, 0.8QD - |QE|, at a horizontal displacement equal to 

the total maximum displacement. The earthquake 

vertical load on an individual isolator unit, QE, shall be 

based on peak building response due to the BSE-2.

9.2.7.2.7 Overturning

The factor of safety against global structural 

overturning at the isolation interface shall be not less 

than 1.0 for required load combinations. All gravity and 

seismic loading conditions shall be investigated. 

Seismic forces for overturning calculations shall be 

based on the BSE-2, and the vertical restoring force 

shall be based on the building’s weight, W, above the 

isolation interface.

Local uplift of individual components and elements 

shall be permitted, provided the resulting deflections do 

not cause overstress or instability of the isolator units or 

other building components and elements. A tie-down 

system to limit local uplift of individual components 

and elements shall be permitted, provided that the 

seismically isolated building is designed in accordance 

with the following criteria when more stringent than the 

requirements of Section 9.2.3.

1. BSE-2 response is calculated in accordance with the 

dynamic analysis requirements of Section 9.2.5, 

explicitly considering the nonlinear characteristics 

of the isolation system and the structure above the 

isolation system.

2. The ultimate capacity of the tie-down system 

exceeds the force and displacement demands of the 

BSE-2.

3. The isolation system is designed and shown by test 

to be stable (Section 9.2.9.2.4) for BSE-2 loads that 

include additional vertical load due to the tie-down 

system.

9.2.7.2.8 Inspection and Replacement

Access for inspection and replacement of all 

components and elements of the isolation system shall 

be provided.

9.2.7.2.9 Manufacturing Quality Control

A manufacturing quality control testing program for 

isolator units shall be established by the engineer 

responsible for the structural design.

9.2.7.3 Structural System

9.2.7.3.1 Horizontal Distribution of Force

A horizontal diaphragm or other structural components 

and elements shall provide continuity above the 

isolation interface. The diaphragm or other structural 

components and elements shall have adequate strength 
9-22 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

and ductility to transmit forces (due to non-uniform 

ground motion) calculated in accordance with this 

section from one part of the building to another, and 

have sufficient stiffness to effect rigid diaphragm 

response above the isolation interface. 

9.2.7.3.2 Building Separations

Separations between the isolated building and 

surrounding retaining walls or other fixed obstructions 

shall be not less than the total design displacement.

9.2.8 Design Review

9.2.8.1 General

A review of the design of the isolation system and 

related test programs shall be performed by an 

independent engineering team, including persons 

experienced in seismic analysis methods and the theory 

and application of seismic isolation.

9.2.8.2 Isolation System

Isolation system design review shall include the 

following:

1. Site-specific seismic criteria, including site-specific 

spectra and ground motion time history, and all other 

design criteria developed specifically for the project.

2. Preliminary design, including the determination of 

the total design and total maximum displacement of 

the isolation system, and the lateral force design 

level.

3. Isolation system prototype testing in accordance 

with Section 9.2.9.

4. Final design of the isolated building and supporting 

analyses. 

5. Isolation system quality control testing in 

accordance with Section 9.2.7.2.9.

9.2.9 Isolation System Testing and Design 

Properties

9.2.9.1 General

The deformation characteristics and damping values of 

the isolation system used in the design and analysis of 

seismically isolated structures shall be based on the 

following tests of a selected sample of the components 

prior to construction.

The isolation system components to be tested shall 

include isolators and components of the wind restraint 

system and supplemental energy dissipation devices if 

such components and devices are used in the design.

The tests specified in this section establish design 

properties of the isolation system, and shall not be 

considered as satisfying the manufacturing quality 

control testing requirements of Section 9.2.7.2.9.

9.2.9.2 Prototype Tests

9.2.9.2.1 General

Prototype tests shall be performed separately on two 

full-size specimens of each type and size of isolator of 

the isolation system. The test specimens shall include 

components of the wind restraint system, as well as 

individual isolators, if such components are used in the 

design. Supplementary energy dissipation devices shall 

be tested in accordance with Section 9.3.8. Specimens 

tested shall not be used for construction unless 

approved by the engineer responsible for the structural 

design.

9.2.9.2.2 Record

For each cycle of tests, the force-deflection and 

hysteretic behavior of the test specimen shall be 

recorded.

9.2.9.2.3 Sequence and Cycles

The following sequence of tests shall be performed for 

the prescribed number of cycles at a vertical load equal 

to the average QD + 0.5QL on all isolators of a common 

type and size:

1. Twenty fully reversed cycles of loading at a lateral 

force corresponding to the wind design force.

2. Three fully reversed cycles of loading at each of the 

following displacements: 0.25DD, 0.50DD, 1.0DD, 

and 1.0DM.

3. Three fully reversed cycles at the total maximum 

displacement, 1.0DTM.

4. 30SX1 / SXSBD1, but not less than 10, fully reversed 

cycles of loading at the design displacement, 1.0DD. 

SX1 and SXS shall be evaluated for the Design 

Earthquake.
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-23

9.2.9.2.4 Vertical Load-Carrying Isolators

If an isolator is also a vertical-load-carrying element, 

then Item 2 of the sequence of cyclic tests specified in 

Section 9.2.9.2.3 shall be performed for two additional 

vertical load cases:

1. 1.2QD + 0.5QL + |QE|

2. 0.8QD - |QE|

where D, L, and E refer to dead, live, and earthquake 

loads. QD and QL are as defined in Section 3.2.8. The 

vertical test load on an individual isolator unit shall 

include the load increment QE due to earthquake 

overturning, and shall be equal to or greater than the 

peak earthquake vertical force response corresponding 

to the test displacement being evaluated. In these tests, 

the combined vertical load shall be taken as the typical 

or average downward force on all isolators of a 

common type and size.

9.2.9.2.5 Isolators Dependent on Loading Rates

If the force-deflection properties of the isolators are 

dependent on the rate of loading, then each set of tests 

specified in Sections 9.2.9.2.3 and 9.2.9.2.4 shall be 

performed dynamically at a frequency equal to the 

inverse of the effective period, TD, of the isolated 

structure.

EXCEPTION: If reduced-scale prototype specimens 

are used to quantify rate-dependent properties of 

isolators, the reduced-scale prototype specimens shall 

be of the same type and material and be manufactured 

with the same processes and quality as full-scale 

prototypes, and shall be tested at a frequency that 

represents full-scale prototype loading rates.

The force-deflection properties of an isolator shall be 

considered to be dependent on the rate of loading if 

there is greater than a plus or minus 10% difference in 

the effective stiffness at the design displacement 

(1) when tested at a frequency equal to the inverse of 

the effective period of the isolated structure and 

(2) when tested at any frequency in the range of 0.1 to 

2.0 times the inverse of the effective period of the 

isolated structure.

9.2.9.2.6 Isolators Dependent on Bilateral Load

If the force-deflection properties of the isolators are 

dependent on bilateral load, then the tests specified in 

Sections 9.2.9.2.3 and 9.2.9.2.5 shall be augmented to 

include bilateral load at the following increments of the 

total design displacement: 0.25 and 1.0; 0.50 and 1.0; 

0.75 and 1.0; and 1.0 and 1.0.

EXCEPTION: If reduced-scale prototype specimens 

are used to quantify bilateral-load-dependent properties, 

then such scaled specimens shall be of the same type 

and material, and manufactured with the same 

processes and quality as full-scale prototypes.

The force-deflection properties of an isolator shall be 

considered to be dependent on bilateral load, if the 

bilateral and unilateral force-deflection properties have 

greater than a plus or minus 15% difference in effective 

stiffness at the design displacement.

9.2.9.2.7 Maximum and Minimum Vertical Load

Isolators that carry vertical load shall be statically tested 

for the maximum and minimum vertical load, at the 

total maximum displacement. In these tests, the 

combined vertical loads of 1.2QD + 1.0QL + |QE| shall 

be taken as the maximum vertical force, and the 

combined vertical load of 0. 8QD - |QE| shall be taken as 

the minimum vertical force, on any one isolator of a 

common type and size. The earthquake vertical load on 

an individual isolator, QE, shall be based on peak 

building response due to the BSE-2.

9.2.9.2.8 Sacrificial Wind-Restraint Systems

If a sacrificial wind-restraint system is part of the 

isolation system, then the ultimate capacity shall be 

established by testing in accordance with this section.

9.2.9.2.9 Testing Similar Units

Prototype tests need not be performed if an isolator unit, 

when compared to another tested unit, complies with 

the following criteria:

1. Is of similar dimensional characteristics.

2. Is of the same type and materials.

3. Is fabricated using identical manufacturing and 

quality control procedures.

The testing exemption shall be approved by the review 

team specified in Section 9.2.8.
9-24 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

9.2.9.3 Determination of Force-Deflection 

Characteristics

The force-deflection characteristics of the isolation 

system shall be based on the cyclic load testing of 

isolator prototypes specified in Section 9.2.9.2.3.

As required, the effective stiffness of an isolator unit, 

keff, shall be calculated for each cycle of deformation by 

Equation (9-12): 

(9-12)

where and are the positive and negative forces at 

positive and negative test displacements, ∆+ and ∆–, 

respectively.

As required, the effective damping of an isolator unit, 

βeff, shall be calculated for each cycle of deformation by 

Equation (9-13):

(9-13)

where the energy dissipated per cycle of loading, ELoop, 

and the effective stiffness, keff, are based on test 

displacements, ∆+ and ∆–

.

9.2.9.4 System Adequacy

The performance of the test specimens shall be assessed 

as adequate if the following conditions are satisfied.

1. The force-deflection plots of all tests specified in 

Section 9.2.9.2 have a nonnegative incremental 

force-carrying capacity.

2. For each increment of test displacement specified in 

Section 9.2.9.2.3, Item 2, and for each vertical load 

case specified in Section 9.2.9.2.3, the following 

criteria are met:

2.1. There is no greater than a plus or minus 15% 

difference between the effective stiffness at 

each of the three cycles of test and the average 

value of effective stiffness for each test 

specimen.

2.2. There is no greater than a 15% difference in the 

average value of effective stiffness of the two 

test specimens of a common type and size of 

the isolator unit over the required three cycles 

of test.

3. For each specimen there is no greater than a plus 

or minus 20% change in the initial effective stiffness 

of each test specimen over the 30SX1/ SXSBD1, but 

not less than 10, cycles of the test specified in 

Section 9.2.9.2.3, Item 3. SX1 and SXS shall be 

evaluated for the Design Earthquake. 

4. For each specimen there is no greater than a 20% 

decrease in the initial effective damping over the 

30SX1/ SXSBD1, but not less than 10, cycles of the 

test specified in Section 9.2.9.2.3, Item 4. SX1 and 

SXS shall be evaluated for the Design Earthquake.

5. All specimens of vertical-load-carrying elements of 

the isolation system remain stable at the total 

maximum displacement for static load as prescribed 

in Section 9.2.9.2.6.

6. The effective stiffness and effective damping of test 

specimens fall within the limits specified by the 

engineer responsible for structural design.

9.2.9.5 Design Properties of the Isolation 

System

9.2.9.5.1 Maximum and Minimum Effective 

Stiffness

At the design displacement, the maximum and 

minimum effective stiffness of the isolation system, 

KDmax and KDmin, shall be based on the cyclic tests of 

Section 9.2.9.2 and calculated by Equations (9-14) and 

(9-15):

(9-14)

 (9-15)

At the maximum displacement, the maximum and 

minimum effective stiffness of the isolation system 

shall be based on cyclic tests of Section 9.2.9.2 and 

calculated by Equations (9-16) and (9-17): 

keff

F+ F– +

∆+ ∆– +

= ------------------------

F+ F–

βeff

2

π

-- ELoop

keff ∆+ ∆– ( ) +

2 = -----------------------------------------

KDmax

FD

+

max FD

–

∑ max ∑ +

2DD

= ---------------------------------------------------------

KDmin

FD

+

min FD

–

∑ min ∑ +

2DD

= -------------------------------------------------------
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-25

(9-16)

 (9-17)

9.2.9.5.2 Effective Damping

At the design displacement, the effective damping of 

the isolation system, βD, shall be based on the cyclic 

tests of Section 9.2.9.2 and calculated by Equation 

(9-18):

 (9-18)

In Equation (9-18), the total energy dissipated in the 

isolation system per displacement cycle, ΣED, shall be 

taken as the sum of the energy dissipated per cycle in all 

isolators measured at test displacements, ∆+ and ∆–, 

that are equal in magnitude to the design displacement, 

DD.

At the maximum displacement, the effective damping 

of the isolation system, βM, shall be based on the cyclic 

tests of Section 9.2.9.2 and calculated by Equation 

(9-19):

 (9-19)

In Equation (9-19), the total energy dissipated in the 

isolation system per displacement cycle, ΣEM, shall be 

taken as the sum of the energy dissipated per cycle in all 

isolators measured at test displacements, ∆+ and ∆–, 

that are equal in magnitude to the maximum 

displacement, DM.

9.3 Passive Energy Dissipation 

Systems

9.3.1 General Requirements

Passive energy dissipation systems classified as either 

displacement-dependent, velocity-dependent, or other, 

as defined in Section 9.3.3, shall comply with the 

requirements of Section 9.3. Linear and nonlinear 

analyses shall be performed, as required, in accordance 

with Section 9.3.4 and 9.3.5, respectively. Additional 

requirements for passive energy dissipation systems, as 

defined in Section 9.3.6, shall be met. Passive energy 

dissipation systems shall be reviewed and tested in 

accordance with Sections 9.3.7 and 9.3.8, respectively.

The energy dissipation devices shall be designed with 

consideration given to environmental conditions 

including wind, aging effects, creep, fatigue, ambient 

temperature, operating temperature, and exposure to 

moisture or damaging substances.

The mathematical model of the rehabilitated building 

shall include the plan and vertical distribution of the 

energy dissipation devices. Analyses shall account for 

the dependence of the devices on excitation frequency, 

ambient and operating temperature, velocity, sustained 

loads, and bilateral loads. Multiple analyses of the 

building shall be conducted to bound the effects of each 

varying mechanical characteristic of the devices.

Energy dissipation devices shall be capable of 

sustaining larger displacements for displacementdependent devices and larger velocities for velocitydependent devices than the maximum calculated for the 

BSE-2 in accordance with the following criteria: 

1. If four or more energy dissipation devices are 

provided in a given story of a building in one 

principal direction of the building, with a minimum 

of two devices located on each side of the center of 

stiffness of the story in the direction under 

consideration, all energy dissipation devices shall be 

capable of sustaining displacements equal to 130% 

of the maximum calculated displacement in the 

device in the BSE-2. A velocity-dependent device as 

described in Section 9.3.3 shall be capable of 

sustaining the force associated with a velocity equal 

to 130% of the maximum calculated velocity for that 

device in the BSE-2.

KMmax

FM

+

max FM

–

∑ max ∑ +

2DM

= ----------------------------------------------------------

KMmin

FM

+

min FM

–

∑ min ∑ +

2DM

= --------------------------------------------------------

βD

1

2π

------ E ∑ D

KDmaxDD

2 = ------------------------

βM

1

2π

------ E ∑ M

KMmaxDM

2 = -------------------------
9-26 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

2. If fewer than four energy dissipation devices are 

provided in a given story of a building in one 

principal direction of the building, or fewer than two 

devices are located on each side of the center of 

stiffness of the story in the direction under 

consideration, all energy dissipation devices shall be 

capable of sustaining displacements equal to 200% 

of the maximum calculated displacement in the 

device in the BSE-2. A velocity-dependent device 

shall be capable of sustaining the force associated 

with a velocity equal to 200% of the maximum 

calculated velocity for that device in the BSE-2.

The components and connections transferring forces 

between the energy dissipation devices shall be 

designed to remain linearly elastic for the forces 

described in items 1 or 2 above.

9.3.2 Implementation of Energy Dissipation 

Devices

Energy dissipation devices shall be implemented in 

accordance with requirements specified in Chapters 1 

through 3 but as modified in the subsequent sections of 

this chapter.

9.3.3 Modeling of Energy Dissipation 

Devices

Displacement-dependent devices shall include devices 

that exhibit either rigid-plastic (friction devices), 

bilinear (metallic yielding devices), or trilinear 

hysteresis. The response of displacement-dependent 

devices shall be independent of velocity and frequency 

of excitation. Velocity-dependent devices shall include 

solid and fluid viscoelastic devices, and fluid viscous 

devices. Devices not classified as displacement- or 

velocity-dependent shall be classified as “other.”

Models of the energy dissipation system shall include 

the stiffness of structural components that are part of the 

load path between energy dissipation devices and the 

ground and whose flexibility affects the performance of 

C9.3.1 General Requirements

The increase in displacement (and velocity) capacity is 

dependent on the level of redundancy in the 

supplemental damping system. 

Passive energy dissipation is an emerging technology 

that enhances the performance of the building by 

adding damping (and in some cases, stiffness) to the 

building. The primary use of energy dissipation devices 

is to reduce earthquake displacement of the structure. 

Energy dissipation devices will also reduce force in the 

structure—provided the structure is responding 

elastically—but would not be expected to reduce force 

in structures that are responding beyond yield.

For most applications, energy dissipation provides an 

alternative approach to conventional stiffening and 

strengthening schemes, and would be expected to 

achieve comparable performance levels. In general, 

these devices would be expected to be good candidates 

for projects that have a target Building Performance 

Level of Life Safety or perhaps Immediate Occupancy, 

but would be expected to have only limited 

applicability to projects with a target Building 

Performance Level of Collapse Prevention.

Other objectives may also influence the decision to use 

energy dissipation devices since these devices can also 

be useful for control of building response due to small 

earthquakes, wind, or mechanical loads. The analysis 

procedures set forth in this standard are approximate. 

Roof displacements calculated using the linear and 

nonlinear procedures are likely to be more accurate 

than the corresponding estimates of interstory drift and 

relative velocity between adjacent stories. Accordingly, 

this standard requires that energy dissipation devices be 

capable of sustaining larger displacements (and 

velocities for velocity-dependent devices) than the 

maxima calculated by analysis in the BSE-2. 

Recognizing that the response of a building frame 

incorporating four or more devices in each principal 

direction in each story will be more reliable than a 

frame with fewer devices in each principal direction, 

the increase in displacement (and velocity) capacity is 

dependent on the level of redundancy in the 

supplemental damping system. The increased force 

shall be used to design the framing that supports the 

energy dissipation devices–reflecting the objective of 

keeping the device support framing elastic in the 

BSE-2. The increases in force and displacement 

capacity listed in this standard are based on the 

judgment of the authors.
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-27

the energy dissipation system, including components of 

the foundation, braces that work in series with the 

energy dissipation devices, and connections between 

braces and the energy dissipation devices.

Energy dissipation devices shall be modeled as 

described in the following subsections, unless approved 

methods are used.

9.3.3.1 Displacement-Dependent Devices

A displacement-dependent device shall have a forcedisplacement relationship that is a function of the 

relative displacement between each end of the device. 

The response of a displacement-dependent device shall 

be independent of the relative velocity between each 

end of the device and frequency of excitation.

Displacement-dependent devices shall be modeled in 

sufficient detail to capture their force- displacement 

response, and their dependence, if any, on axial-shearflexure interaction, or bilateral deformation response.

For evaluating the response of a displacementdependent device from testing data, the force in a 

displacement-dependent device shall be calculated in 

accordance with Equation (9-20):

(9-20)

where the effective stiffness, keff, of the device is 

calculated in accordance with Equation (9-21):

 (9-21)

The forces in the device, F+ and F –, shall be evaluated 

at displacements D+ and D–, respectively.

9.3.3.2 Velocity-Dependent Devices

9.3.3.2.1 Solid Viscoelastic Devices

Solid viscoelastic devices shall be modeled using a 

spring and dashpot in parallel (Kelvin model). The 

spring and dashpot constants selected shall capture the 

frequency and temperature dependence of the device 

consistent with fundamental frequency of the 

rehabilitated building (f1), and the operating 

temperature range. If the cyclic response of a 

viscoelastic solid device cannot be captured by single 

estimates of the spring and dashpot constants, the 

response of the rehabilitated building shall be estimated 

by multiple analyses of the building frame, using 

limiting upper- and lower-bound values for the spring 

and dashpot constants.

The force in a viscoelastic device shall be determined in 

accordance with Equation (9-22):

(9-22)

where C is the damping coefficient for the viscoelastic 

device, D is the relative displacement between each end 

of the device, is the relative velocity between each 

end of the device, and keff is the effective stiffness of the 

device calculated in accordance with Equation (9-23):

(9-23)

where is the storage stiffness.

The damping coefficient for the device shall be 

calculated in accordance with Equation (9-24):

(9-24)

where is the loss stiffness, the angular frequency ω1

is equal to 2πf1, Dave is the average of the absolute 

values of displacements D+ and D–, and WD is the area 

C9.3.3 Modeling of Energy Dissipation 

Devices

Examples of “other” devices include shape- memory 

alloys (superelastic effect), friction-spring assemblies 

with recentering capability, and fluid restoring forcedamping devices.

F keff = D

keff

F+ F– +

D+ D– +

= --------------------------

F keffD CD· = +

D

·

keff

F+ F– +

D+ D– +

= = -------------------------- K′

K′

C

WD

πω1Dave

2 ---------------------- K′′

ω1

= = ------

K′′
9-28 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

enclosed by one complete cycle of the forcedisplacement response of the device.

9.3.3.2.2 Fluid Viscoelastic Devices

Fluid viscoelastic devices shall be modeled using a 

spring and dashpot in series (Maxwell model). The 

spring and dashpot constants selected shall capture the 

frequency and temperature dependence of the device 

consistent with fundamental frequency of the 

rehabilitated building (f1), and the operating 

temperature range. If the cyclic response of a 

viscoelastic fluid device cannot be captured by single 

estimates of the spring and dashpot constants, the 

response of the rehabilitated building shall be estimated 

by multiple analyses of the building frame, using 

limiting upper- and lower-bound values for the spring 

and dashpot constants.

9.3.3.2.3 Fluid Viscous Devices

Linear fluid viscous dampers exhibiting stiffness in the 

frequency range 0.5 f1 to 2.0 f1 shall be modeled as a 

fluid viscoelastic device.

In the absence of stiffness in the frequency range 0.5 f1

to 2.0 f1, the force in the fluid viscous device shall be 

computed in accordance with Equation (9-25):

(9-25)

where C0 is the damping coefficient for the device, α is 

the velocity exponent for the device, is the relative 

velocity between each end of the device, and sgn is the 

signum function that, in this case, defines the sign of the 

relative velocity term.

9.3.3.3 Other Types of Devices

Energy dissipation devices not classified as either 

displacement-dependent or velocity-dependent shall be 

modeled using approved methods. Such models shall 

accurately describe the force-velocity-displacement 

response of the device under all sources of loading 

including gravity, seismic, and thermal.

9.3.4 Linear Procedures

Linear procedures shall be permitted only if the 

following criteria are met:

1. The framing system exclusive of the energy 

dissipation devices remains linearly elastic for the 

selected Earthquake Hazard Level after the effects of 

added damping are considered. 

2. The effective damping afforded by the energy 

dissipation does not exceed 30% of critical in the 

fundamental mode. 

3. The secant stiffness of each energy dissipation 

device, calculated at the maximum displacement in 

the device, is included in the mathematical model of 

the rehabilitated building.

C9.3.3.2.1 Solid Viscoelastic Devices

The cyclic response of viscoelastic solids is generally 

dependent on the frequency and amplitude of the 

motion and the operating temperature (including 

temperature rise due to excitation).

C9.3.3.2.2 Fluid Viscoelastic Devices

The cyclic response of viscoelastic fluid devices is 

generally dependent on the frequency and amplitude of 

the motion and the operating temperature (including 

temperature rise due to excitation).

F C0 D

· α

 sgn D

· = ( )

D

·

C9.3.3.3 Other Types of Devices

Other energy dissipating devices, such as those having 

hysteresis of the type shown in Figure C9-8, require 

modeling techniques different from those described 

above. Tsopelas and Constantinou (1994a), Nims et al. 

(1993), and Pekcan et al. (1995) describe analytical 

models for some of these devices.

Figure C9-8 Idealized Force-Displacement Loops of 

Energy Dissipation Devices with 

Recentering Capability
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-29

4. When evaluating the regularity of a building, the 

energy dissipation devices are included in the 

mathematical model.

9.3.4.1 Linear Static Procedure

9.3.4.1.1 Displacement-Dependent Devices

Use of The Linear Static Procedure (LSP) shall be 

permitted to analyze displacement-dependent energy 

dissipation devices, provided that in addition to the 

requirements of Section 9.3.4, the following 

requirements are satisfied:

1. The ratio of the maximum resistance in each story, in 

the direction under consideration, to the story shear 

demand calculated using Equations (3-11) and 

(3-12), shall range between 80% and 120% of the 

average value of the ratio for all stories. The 

maximum story resistance shall include the 

contributions from all components, elements, and 

energy dissipation devices.

2. The maximum resistance of all energy dissipation 

devices in a story, in the direction under 

consideration, shall not exceed 50% of the resistance 

of the remainder of the framing where said 

resistance is calculated at the displacements 

anticipated in the BSE-2. Aging and environmental 

effects shall be considered in calculating the 

maximum resistance of the energy dissipation 

devices.

The pseudolateral load of Equation (3-10) shall be 

reduced by the damping modification factors of 

Table 1-6 to account for the energy dissipation 

(damping) afforded by the energy dissipation 

devices. The damping effect shall be calculated in 

accordance with Equation (9-26):

(9-26)

where β is the damping in the framing system and 

shall be set equal to 0.05 unless modified in 

Section 1.6.1.4, Wj

 shall be taken as the work done 

by device j in one complete cycle corresponding to 

floor displacements δi

, the summation extends over 

all devices j, and Wk is the maximum strain energy in 

the frame, determined using Equation (9-27):

(9-27)

where Fi

 shall be taken as the inertia force at floor 

level i and the summation extends over all floor 

levels.

9.3.4.1.2 Velocity-Dependent Devices

Use of the LSP shall be permitted to analyze velocitydependent energy dissipation devices, provided that in 

addition to the requirements of Section 9.3.4, the 

following requirements are satisfied:

1. The maximum resistance of all energy dissipation 

devices in a story in the direction under 

consideration shall not exceed 50% of the resistance 

of the remainder of the framing where said 

resistance is calculated at the displacements 

anticipated in the BSE-2. Aging and environmental 

effects shall be considered in calculating the 

maximum resistance of the energy dissipation 

devices.

2. The pseudolateral load of Equation (3-10) shall be 

reduced by the damping modification factors of 

Table 1-6 to account for the energy dissipation 

(damping) afforded by the energy dissipation 

devices. The damping effect shall be calculated in 

accordance with Equation (9-28):

(9-28)

where β is the damping in the structural frame and shall 

be set equal to 0.05 unless modified in 

Section 1.6.1.5.3, Wj shall be taken as the work done by 

device j in one complete cycle corresponding to floor 

displacements δi

, the summation extends over all 

devices j, and Wk is the maximum strain energy in the 

frame, determined using Equation (9-27).

The work done by linear viscous device j in one 

complete cycle of loading shall be calculated in 

accordance with Equation (9-29):

(9-29)

βeff β

Wj

j

∑

4πWk

= + --------------

Wk

1

2

-- Fi

δi

i

= ∑

βeff β

Wj

j

∑

4πWk

= + --------------

Wj

2π

2

T

--------Cj

δrj

2 =
9-30 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

where T is the fundamental period of the rehabilitated 

building including the stiffness of the velocitydependent devices, Cj

 is the damping constant for 

device j, and δrj is the relative displacement between the 

ends of device j along the axis of device j. 

Calculation of effective damping in accordance with 

Equation (9-30) rather than Equation (9-28) shall be 

permitted for linear viscous devices:

(9-30)

where is the angle of inclination of device j to the 

horizontal, is the first mode relative displacement 

between the ends of device j in the horizontal direction, 

wi

 is the reactive weight of floor level i, is the first 

mode displacement at floor level i, and other terms are 

as defined above.

9.3.4.1.3 Design Actions

The design actions for components of the rehabilitated 

building shall be calculated in three distinct stages of 

deformation as follows. The maximum action shall be 

used for design.

1. At the stage of maximum drift. The lateral forces 

at each level of the building shall be calculated using 

Equation (3-11), where V is the modified equivalent 

base shear.

2. At the stage of maximum velocity and zero drift.

The viscous component of force in each energy 

dissipation device shall be calculated by Equations 

(9-22) or (9-25), where the relative velocity is 

given by 2π f1 D, where D is the relative 

displacement between the ends of the device 

calculated at the stage of maximum drift. The 

calculated viscous forces shall be applied to the 

mathematical model of the building at the points of 

attachment of the devices and in directions 

consistent with the deformed shape of the building at 

maximum drift. The horizontal inertia forces at each 

floor level of the building shall be applied 

concurrently with the viscous forces so that the 

horizontal displacement of each floor level is zero. 

3. At the stage of maximum floor acceleration.

Design actions in components of the rehabilitated 

building shall be determined as the sum of actions 

determined at the stage of maximum drift times CF1,

and actions determined at the stage of maximum 

velocity times CF2, where

(9-31)

(9-32)

in which βeff is defined by either Equation (9-28) or 

Equation (9-30).

9.3.4.2 Linear Dynamic Procedure

If the Linear Dynamic Procedure (LDP) is selected 

based on the requirements of Section 9.2.3.3 and 

Section 2.4, the LDP of Section 3.3.2.2 shall be 

followed unless explicitly modified by this section.

Use of the response spectrum method of the LDP shall 

be permitted when the effective damping in the 

fundamental mode of the rehabilitated building, in each 

principal direction, does not exceed 30% of critical.

9.3.4.2.1 Displacement-Dependent Devices

Application of the LDP for the analysis of rehabilitated 

buildings incorporating displacement-dependent 

devices shall comply with the restrictions set forth in 

Section 9.3.4.1.1.

For analysis by the Response Spectrum Method, 

modification of the 5%-damped response spectrum 

shall be permitted to account for the damping afforded 

by the displacement-dependent energy dissipation 

devices. The 5%-damped acceleration spectrum shall be 

reduced by the modal-dependent damping modification 

factor, B, either Bs or B1, for periods in the vicinity of 

the mode under consideration; the value of B will be 

different for each mode of vibration. The damping 

modification factor in each significant mode shall be 

determined using Table 1-6 and the calculated effective 

damping in that mode. The effective damping shall be 

determined using a procedure similar to that described 

in Section 9.3.4.1.1.

βeff β

T Cj

 cos

2

θj φrj

2

j

∑

4π

wi

g

-----     φi

2

i

∑

= + ------------------------------------------

θj

φrj

φi

D

·

CF1 tan–1 2βeff = cos[ ] ( )

CF2 tan–1 2βeff = sin[ ] ( )
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-31

If the maximum base shear force calculated by dynamic 

analysis is less than 80% of the modified equivalent 

base shear of Section 9.3.4.1, component and element 

actions and deformations shall be proportionally 

increased to correspond to 80% of the modified 

equivalent base shear.

9.3.4.2.2 Velocity-Dependent Devices

For analysis by the Response Spectrum Method, 

modification of the 5%-damped response spectrum 

shall be permitted to account for the damping afforded 

by the velocity-dependent energy dissipation devices. 

The 5%-damped acceleration spectrum shall be reduced 

by the modal-dependent damping modification factor, 

B, either Bs or B1, for periods in the vicinity of the mode 

under consideration; note that the value of B will be 

different for each mode of vibration. The damping 

modification factor in each significant mode shall be 

determined using Table 1-6 and the calculated effective 

damping in that mode.

The effective damping in the m-th mode of vibration 

 shall be calculated in accordance with 

Equation (9-33):

(9-33)

where βm is the m-th mode damping in the building 

frame, Wmj is work done by device j in one complete 

cycle corresponding to modal floor displacements δmi, 

and Wmk is the maximum strain energy in the frame in 

the m-th mode, determined using Equation (9-34):

(9-34)

where Fmi is the m-th mode horizontal inertia force at 

floor level i and δmi is the m-th mode horizontal 

displacement at floor level i. The work done by linear 

viscous device j in one complete cycle of loading in the 

m-th mode may be calculated in accordance with 

Equation (9-35):

(9-35)

where Tm is the m-th mode period of the rehabilitated 

building including the stiffness of the velocitydependent devices, Cj

 is the damping constant for 

device j, and δmrj is the m-th mode relative 

displacement between the ends of device j along the 

axis of device j.

In addition to direct application of the Response 

Spectrum Method in accordance with this section to 

obtain member actions at maximum drift, member 

actions at maximum velocity and maximum 

acceleration in each significant mode shall be 

determined using the procedure described in 

Sections 9.3.4.1.2. The combination factors CF1 and 

CF2 shall be determined based on Equations (9-31) and 

(9-32) using βeff –m for the m-th mode.

If the maximum base shear force calculated by dynamic 

analysis is less than 80% of the modified equivalent 

base shear of Section 9.3.4.1, component and element 

actions and deformations shall be proportionally 

increased to correspond to 80% of the modified 

equivalent base shear.

9.3.5 Nonlinear Procedures

9.3.5.1 Nonlinear Static Procedure

If the Nonlinear Static Procedure (NSP) is selected 

based on the requirements of Section 9.2.3.3 and 

Section 2.4, the NSP of Section 3.3.3 shall be followed 

unless explicitly modified by this section.

The nonlinear mathematical model of the rehabilitated 

building shall include the nonlinear force-velocitydisplacement characteristics of the energy dissipation 

devices explicitly, and the mechanical characteristics of 

the components supporting the devices. Stiffness 

characteristics shall be consistent with the deformations 

corresponding to the target displacement and a 

frequency equal to the inverse of period Te, as defined in 

Section 3.3.3.2.

The nonlinear mathematical model of the rehabilitated 

building shall include the nonlinear force-velocitydisplacement characteristics of the energy dissipation 

devices, and the mechanical characteristics of the 

components supporting the devices. Energy dissipation 

devices with stiffness and damping characteristics that 

are dependent on excitation frequency and/or 

temperature shall be modeled with characteristics 

consistent with (1) the deformations expected at the 

βeff m– ( )

βeff m– βm

Wmj

j

∑

4πWmk

= + -----------------

Wmk

1

2

-- Fmiδmi

i

= ∑

Wmj

2π

2

Tm

--------Cj

δmrj

2 =
9-32 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

target displacement, and (2) a frequency equal to the 

inverse of the effective period.

Equation (3-15) shall be used to calculate the target 

displacement.

9.3.5.1.1 Displacement-Dependent Devices

The stiffness characteristics of the energy dissipation 

devices shall be included in the mathematical model.

9.3.5.1.2 Velocity-Dependent Devices

The target displacement and the spectral acceleration in 

Equation (3-15) shall be reduced to account for the 

damping added by the velocity-dependent energy 

dissipation devices. The calculation of the damping 

effect shall be calculated in accordance with Equation 

(9-36):

(9-36)

where β is the damping in the structural frame and shall 

be set equal to 0.05 unless modified in Section 1.6.1.5, 

Wj

 shall be taken as the work done by device j in one 

complete cycle corresponding to floor displacements 

δi

, the summation extends over all devices j, and Wk is 

the maximum strain energy in the frame, determined 

using Equation (9-27).

The work done by device j in one complete cycle of 

loading shall be calculated based on Equation (9-37):

(9-37)

where Tss is the secant fundamental period of the 

rehabilitated building including the stiffness of the 

velocity-dependent devices (if any), calculated using 

Equation (3-14) but replacing the effective stiffness 

(Ke) with the secant stiffness (Ks) at the target 

displacement as shown in Figure 9-1; Cj

 is the damping 

constant for device j; and δrj is the relative displacement 

between the ends of device j along the axis of device j at 

a roof displacement corresponding to the target 

displacement. 

The acceptance criteria of Section 3.4.3 shall apply to 

buildings incorporating energy dissipation devices. 

Checking for displacement-controlled actions shall use 

deformations corresponding to the target displacement. 

Checking for force-controlled actions shall use 

component actions calculated for three limit states: 

maximum drift, maximum velocity, and maximum 

C9.3.5.1 Nonlinear Static Procedure

Benefits of Adding Energy Dissipation Devices

The benefit of adding displacement-dependent energy 

dissipation devices is recognized in this standard by the 

increase in building stiffness afforded by such devices, 

and the reduction in target displacement associated with 

the reduction in Te . The alternative NSP uses a different 

strategy to calculate the target displacement and 

explicitly recognizes the added damping provided by 

the energy dissipation devices.

The benefits of adding velocity-dependent energy 

dissipation devices are recognized by the increase in 

stiffness and equivalent viscous damping in the 

building frame. For most velocity-dependent devices, 

the primary benefit will result from the added viscous 

damping. Higher-mode damping forces in the energy 

dissipation devices must be evaluated regardless of the 

NSP used.

βeff β

Wj

j

∑

4πWk

= + -------------

Figure 9-1 Calculation of Secant Stiffness, Ks

Wj

2π

2

Tss

--------Cj

δrj

2 =
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-33

acceleration. Maximum actions shall be used for design. 

Higher-mode effects shall be explicitly evaluated.

9.3.5.2 Nonlinear Dynamic Procedure

If the Nonlinear Dynamic Procedure (NDP) is selected 

based on the requirements of Section 9.2.3.3 and 

Section 2.4, a nonlinear time history analysis shall be 

performed as required by Section 3.3.4.2, except as 

modified by this section. The mathematical model shall 

account for both the plan and vertical spatial 

distribution of the energy dissipation devices in the 

rehabilitated building. If the energy dissipation devices 

are dependent on excitation frequency, operating 

temperature (including temperature rise due to 

excitation), deformation (or strain), velocity, sustained 

loads, and bilateral loads, such dependence shall be 

accounted for in the analysis by assuming upper- and 

lower-bound properties to bound the solution.

The viscous forces in velocity-dependent energy 

dissipation devices shall be included in the calculation 

of design actions and deformations. Substitution of 

viscous effects in energy dissipation devices by global 

structural damping for nonlinear time-history analysis 

shall not be permitted.

9.3.6 Detailed Systems Requirements

9.3.6.1 General

The energy dissipation system and the remainder of the 

lateral-force-resisting system shall comply with the 

detailed systems requirements specified in this section.

9.3.6.2 Operating Temperature

The analysis of a rehabilitated building shall account for 

variations in the force-displacement response of the 

energy dissipation devices due to variation in the 

ambient temperature and temperature rise due to 

earthquake cyclic excitation. Multiple analysis shall be 

performed to bound the seismic response of the building 

during the Design Earthquake, and develop limits for 

defining the acceptable response of the prototype 

devices and production devices.

9.3.6.3 Environmental Conditions

In addition to the requirements for vertical and lateral 

loads induced by wind and earthquake actions, the 

energy dissipation devices shall be designed with 

consideration given to other environmental conditions, 

including aging effects, creep, fatigue, ambient 

temperature, and exposure to moisture and damaging 

substances.

C9.3.5.1.2 Velocity-Dependent Devices

The use of Equation (9-36) will generally capture the 

maximum displacement of the building.

C9.3.5.2 Nonlinear Dynamic Procedure

If energy dissipation devices are dependent on loading 

frequency, operating temperature (including 

temperature rise due to excitation), deformation (or 

strain), velocity, sustained loads, and bilateral loads, 

such dependence should be accounted for in the 

nonlinear time history analysis. One way to account for 

variations in the force-deformation response of energy 

dissipation devices is to perform multiple analyses of 

the rehabilitated building using the likely bounding 

response characteristics of the energy dissipation 

devices. The design of the rehabilitated building, 

including the energy dissipation devices, should be 

based on the maximum responses computed from the 

multiple analyses.

The viscous forces (if any) developed in the seismic 

framing system should be accounted for in the analysis 

and design of the seismic framing system. Evaluation of 

member action histories should be based on nodal 

displacements (operating on member stiffness matrices) 

and nodal velocities (operating on member damping 

matrices).

Key to the acceptable response of a rehabilitated 

building incorporating energy dissipation devices is the 

stable response of the energy dissipation devices. The 

forces and deformations in the energy dissipation 

devices that develop during the Design Earthquake 

should be demonstrated to be adequate by prototype 

testing in accordance with Section 9.3.8.

C9.3.6.2 Operating Temperature

The force-displacement response of an energy 

dissipation device will generally be dependent on 

ambient temperature and temperature rise due to cyclic 

or earthquake excitation.
9-34 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

9.3.6.4 Wind Forces

The fatigue life of energy dissipation devices, or 

components thereof, including seals in a fluid viscous 

device, shall be investigated and shown to be adequate 

for the design life of the devices. Devices subject to 

failure by low-cycle fatigue shall resist wind forces in 

the linearly elastic range.

9.3.6.5 Inspection and Replacement

Access for inspection and replacement of the energy 

dissipation devices shall be provided.

9.3.6.6 Manufacturing Quality Control

A manufacturing quality control plan for production of 

energy dissipation devices shall be established by the 

engineer of record. This plan shall include descriptions 

of the manufacturing processes, inspection procedures, 

and testing necessary to ensure quality control of 

production devices.

9.3.6.7 Maintenance

The engineer of record shall establish a maintenance 

and testing schedule for energy dissipation devices to 

ensure reliable response of the devices over the design 

life of the devices. The degree of maintenance and 

testing shall reflect the established in-service history of 

the devices.

9.3.7 Design Review

9.3.7.1 General

Design review of all rehabilitated buildings 

incorporating energy dissipation devices shall be 

performed in accordance with the requirements of 

Section 2.7, unless modified by the requirements of this 

section. Design review of the energy dissipation system 

and related test programs shall be performed by an 

independent engineering review panel that includes 

persons experienced in seismic analysis and the theory 

and application of energy dissipation methods.

The following items shall be included in the design 

review:

1. Preliminary design including sizing of the devices.

2. Prototype testing conducted in accordance with 

Section 9.3.8.2.

3. Final design of the rehabilitated building and 

supporting analyses.

4. Manufacturing quality control program for the 

energy dissipation devices.

9.3.8 Required Tests of Energy Dissipation 

Devices

9.3.8.1 General

The force-displacement relations and damping values 

assumed in the design of the energy dissipation system 

shall be confirmed by the tests conducted in accordance 

with this section prior to production of devices for 

construction. If tests conducted in accordance with this 

section precede the design phase of a project, the results 

of the testing program shall be used for the design.

The tests specified in this section shall be conducted to: 

(1) confirm the force-displacement properties of the 

energy dissipation devices assumed for design, and 

(2) demonstrate the robustness of individual devices to 

extreme seismic excitation. These tests shall not be 

considered as satisfying the manufacturing quality 

control (production) plan of Section 9.3.6.6.

The engineer of record shall provide explicit acceptance 

criteria for the effective stiffness and damping values 

established by the prototype tests. These criteria shall 

reflect the values assumed in design, account for likely 

variations in material properties, and provide limiting 

response values outside of which devices will be 

rejected.

The engineer of record shall provide explicit acceptance 

criteria for the effective stiffness and damping values 

established by the production tests of Section 9.3.6.6. 

The results of the prototype tests shall form the basis of 

the acceptance criteria for the production tests unless an 

alternate basis is established by the engineer of record 

in the specification. Such acceptance criteria shall 

recognize the influence of loading history on the 

response of individual devices by requiring production 

testing of devices prior to prototype testing.

The fabrication and quality control procedures used for 

all prototype and production devices shall be identical. 

These procedures shall be approved by the engineer of 

record prior to the fabrication of prototype devices.
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-35

9.3.8.2 Prototype Tests

9.3.8.2.1 General

The following prototype tests shall be performed 

separately on two full-size devices of each type and size 

used in the design. If approved by the engineer of 

record, selection of representative sizes of each type of 

device shall be permitted for prototype testing, rather 

than each type and size, provided that the fabrication 

and quality control procedures are identical for each 

type and size of devices used in the rehabilitated 

building.

Test specimens shall not be used for construction unless 

approved in writing by the engineer of record.

9.3.8.2.2 Data Recording

The force-deflection relationship for each cycle of each 

test shall be recorded electronically.

9.3.8.2.3 Sequence and Cycles of Testing

For the following minimum test sequence, each energy 

dissipation device shall be loaded to simulate the 

gravity loads on the device as installed in the building 

and the extreme ambient temperatures anticipated.

1. Each device shall be loaded with the number of 

cycles expected in the design wind storm, but not 

less than 2000 fully-reversed cycles of load 

(displacement-dependent and viscoelastic devices) 

or displacement (viscous devices) at amplitudes 

expected in the design wind storm, at a frequency 

equal to the inverse of the fundamental period of the 

rehabilitated building.

EXCEPTION: Devices not subject to wind-induced 

forces or displacements need not be subjected to 

these tests.

2. Each device shall be loaded with 20 fully reversed 

cycles at the displacement in the energy dissipation 

device corresponding to the BSE-2, at a frequency 

equal to the inverse of the fundamental period of the 

rehabilitated building.

EXCEPTION: Testing methods for energy 

dissipation devices other than those noted above 

shall be permitted, provided that: (1) equivalency 

between the proposed method and cyclic testing can 

be demonstrated; (2) the proposed method captures 

the dependence of the energy dissipation device 

response to ambient temperature, frequency of 

loading, and temperature rise during testing; and (3) 

the proposed method is approved by the engineer of 

record.

9.3.8.2.4 Devices Dependent on Velocity and/or 

Frequency of Excitation

If the force-deformation properties of the energy 

dissipation devices at any displacement less than or 

equal to the total design displacement change by more 

than 15% for changes in testing frequency from 0.5 f1 to 

2.0 f1, the preceding tests shall be performed at 

frequencies equal to 0.5 f1, f1, and 2.0 f1.

EXCEPTION: If reduced-scale prototypes are used to 

quantify the rate-dependent properties of energy 

dissipation devices, the reduced-scale prototypes shall 

be of the same type and materials—and manufactured 

with the same processes and quality control 

procedures—as full-scale prototypes, and tested at a 

similitude-scaled frequency that represents the fullscale loading rates.

9.3.8.2.5 Devices Dependent on Bilateral 

Displacement

If the energy dissipation devices are subjected to 

bilateral deformation, the preceding tests shall be made 

at both zero bilateral displacement, and peak lateral 

displacement in the BSE-2.

EXCEPTION: If reduced-scale prototypes are used to 

quantify the bilateral displacement properties of the 

energy dissipation devices, the reduced-scale prototypes 

shall be of the same type and materials, and 

manufactured with the same processes and quality 

control procedures as full-scale prototypes, and tested at 

similitude-scaled displacements that represent the fullscale displacements.

9.3.8.2.6 Testing Similar Devices

Energy dissipation devices that are (1) of similar size, 

identical materials, internal construction, and static and 

dynamic internal pressures (if any), and (2) fabricated 

with identical internal processes and manufacturing 

quality control procedures, and that have been 

previously tested by an independent laboratory in the 

C9.3.8.2.3 Sequence and Cycles of Testing

Energy dissipation devices should not form part of the 

gravity-load-resisting system, but may be required to 

support some gravity load.
9-36 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation

manner described above need not be tested, provided 

that:

1. All pertinent testing data are made available to, and 

are approved by, the engineer of record.

2. The manufacturer can substantiate the similarity of 

the previously tested devices to the satisfaction of 

the engineer of record.

3. The submission of data from a previous testing 

program is approved in writing by the engineer of 

record.

9.3.8.3 Determination of Force-Displacement 

Characteristics

The force-displacement characteristics of an energy 

dissipation device shall be based on the cyclic load and 

displacement tests of prototype devices specified in 

Section 9.3.8.2.

As required, the effective stiffness (keff) of an energy 

dissipation device with stiffness shall be calculated for 

each cycle of deformation in accordance with Equation 

(9-38):

(9-38)

where forces F+ and F– shall be calculated at 

displacements ∆+ and ∆–, respectively. The effective 

stiffness of an energy dissipation device shall be 

established at the test displacements given in 

Section 9.3.8.2.3.

The equivalent viscous damping of an energy 

dissipation device (βeff) exhibiting stiffness shall be 

calculated for each cycle of deformation based on 

Equation (9-39):

(9-39)

where keff shall be calculated in accordance with 

Equation (9-38), and WD shall be taken as the area 

enclosed by one complete cycle of the forcedisplacement response for a single energy dissipation 

device at a prototype test displacement (∆ave) equal to 

the average of the absolute values of displacements ∆+ 

and ∆–.

9.3.8.4 System Adequacy

The performance of a prototype device shall be 

considered adequate if all of the following conditions 

are satisfied:

1. The force-displacement curves for the tests in 

Section 9.3.8.2.3 have nonnegative incremental 

force-carrying capacities.

EXCEPTION: Energy dissipation devices that 

exhibit velocity-dependent behavior need not 

comply with this requirement.

2. Within each test of Section 9.3.8.2.3, the effective 

stiffness (keff) of a prototype energy dissipation 

device for any one cycle does not differ by more 

than plus or minus 15% from the average effective 

stiffness as calculated from all cycles in that test.

EXCEPTIONS: (1) The 15% limit may be 

increased by the engineer of record in the 

specification, provided that the increased limit has 

been demonstrated by analysis to not have a 

deleterious effect on the response of the rehabilitated 

building. (2) Fluid viscous energy dissipation 

devices, and other devices that do not have effective 

stiffness, need not comply with this requirement.

3. Within each test of Section 9.3.8.2.3, the maximum 

force and minimum force at zero displacement for a 

prototype device for any one cycle does not differ by 

more than plus or minus 15% from the average 

maximum and minimum forces as calculated from 

all cycles in that test.

EXCEPTION: The 15% limit may be increased by 

the engineer of record in the specification, provided 

that the increased limit has been demonstrated by 

analysis to not have a deleterious effect on the 

response of the rehabilitated building.

4. Within each test of Section 9.3.8.2.3, the area of the 

hysteresis loop (WD) of a prototype energy 

dissipation device for any one cycle does not differ 

by more than plus or minus 15% from the average 

keff

F– F++

∆– ∆++

= ------------------------

βeff

1

2π

------ WD

keff∆ave

2 = -------------------
Chapter 9: Seismic Isolation and 

Energy Dissipation

FEMA 356 Seismic Rehabilitation Prestandard 9-37

area of the hysteresis curve as calculated from all 

cycles in that test.

EXCEPTION: The 15% limit may be increased by 

the engineer of record in the specification, provided 

that the increased limit has been demonstrated by 

analysis to not have a deleterious effect on the 

response of the rehabilitated building.

5. For displacement-dependent devices, the average 

effective stiffness, average maximum and minimum 

force at zero displacement, and average area of the 

hysteresis loop (WD), calculated for each test in the 

sequence described in Section 9.3.8.2.3, shall fall 

within the limits set by the engineer of record in the 

specification. The area of the hysteresis loop at the 

end of cyclic testing shall not differ by more than 

plus or minus 15% from the average area of the 20 

test cycles.

6. For velocity-dependent devices, the average 

maximum and minimum force at zero displacement, 

effective stiffness (for viscoelastic devices only), 

and average area of the hysteresis loop (WD), 

calculated for each test in the sequence described in 

Section 9.3.8.2.3, shall fall within the limits set by 

the engineer of record in the specification.

9.4 Other Response Control Systems

The analysis and design of other response control 

systems shall be reviewed by an independent 

engineering review panel in accordance with the 

requirements of Section 9.3.7. This review panel shall 

be selected by the owner prior to the development of the 

preliminary design.

C9.4 Other Response Control Systems

Response control strategies other than base isolation 

(Section 9.2) and passive energy dissipation 

(Section 9.3) systems have been proposed. Dynamic 

vibration absorption and active control systems are two 

such response control strategies. Although both 

dynamic vibration absorption and active control 

systems have been implemented to control the windinduced vibration of buildings, the technology is not 

sufficiently mature and the necessary hardware is not 

sufficiently robust to warrant the preparation of general 

guidelines for the implementation of other response 

control systems.
9-38 Seismic Rehabilitation Prestandard FEMA 356

Chapter 9: Seismic Isolation and 

Energy Dissipation
FEMA 356 Seismic Rehabilitation Prestandard 10-1

10. Simplified Rehabilitation

10.1 Scope

This chapter sets forth requirements for the 

rehabilitation of buildings using the Simplified 

Rehabilitation Method. Section 10.2 outlines the 

procedure of the Simplified Rehabilitation Method. 

Section 10.3 specifies actions for correction of 

deficiencies using the Simplified Rehabilitation 

Method. 

10.2 Procedure

Use of Simplified Rehabilitation shall be permitted in 

accordance with the limitations of Section 2.3.1. The 

Simplified Rehabilitation Method shall be implemented 

by completing each of the following steps:

1. The building shall be classified as one of the Model 

Building Types listed in Table 10-1 and defined in 

Table 10-2. 

2. A Tier 1 and a Tier 2 Seismic Evaluation of the 

building in its existing state shall be performed for 

C10.1 Scope

The Simplified Rehabilitation Method is intended 

primarily for use on a select group of simple buildings.

The Simplified Rehabilitation Method only applies to 

buildings that fit into one of the Model Building Types 

and conform to the limitations of Table 10-1, which 

sets the standard for simple, regularly configured 

buildings defined in Table 10-2. Building regularity is 

an important consideration in the application of the 

method. Regularity is determined by checklist 

statements addressing building configuration issues. 

The Simplified Rehabilitation Method may be used if 

an evaluation shows no deficiencies with regard to 

regularity. Buildings that have configuration 

irregularities (as determined by an FEMA 310 Tier 1 or 

Tier 2 Evaluation) may use this Simplified 

Rehabilitation Method to achieve the Life Safety 

Building Performance Level only if the resulting 

rehabilitation work eliminates all significant vertical 

and horizontal irregularities and results in a building 

with a complete seismic lateral-force-resisting load 

path.

The technique described in this chapter is one of the 

two rehabilitation methods defined in Section 2.3. It is 

to be used only by a design professional, and only in a 

manner consistent with this standard. Consideration 

must be given to all aspects of the rehabilitation 

process, including the development of appropriate asbuilt information, proper design of rehabilitation 

techniques, and specification of appropriate levels of 

quality assurance.

“Simplified Rehabilitation” reflects a level of analysis 

and design that (1) is appropriate for small, regular 

buildings and buildings that do not require advanced 

analytical procedures; and (2) achieves the Life Safety 

Performance Level for the BSE-1 Earthquake Hazard 

Level as defined in Chapter 1, but does not necessarily 

achieve the Basic Safety Objective (BSO).

FEMA 178, the NEHRP Handbook for the Seismic 

Evaluation of Existing Buildings, a nationally 

applicable method for seismic evaluation of buildings, 

was the basis for the Simplified Rehabilitation Method 

in FEMA 273. FEMA 178 is based on the historic 

behavior of buildings in past earthquakes and the 

success of current code provisions in achieving the 

Life Safety Building Performance Level. It is 

organized around a set of common construction styles 

called model buildings.

Since the preliminary version of FEMA 178 was 

completed in the late 1980s, new information has 

become available and has been incorporated into 

FEMA 310, which is an updated version of FEMA 178. 

This information includes additional Model Building 

Types, eight new evaluation statements for potential 

deficiencies, a reorganization of the procedure to 

clearly state the intended three-tier approach, and new 

analysis techniques that parallel those of FEMA 273. 

FEMA 310 is the basis of the Simplified Rehabilitation 

Method in this standard.

The Simplified Rehabilitation Method may yield a 

more conservative result than the Systematic Method 

because of a variety of simplifying assumptions.
10-2 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

the Life Safety Building Performance Level in 

accordance with FEMA 310. In the event of 

differences between this standard and the FEMA 310

procedures, the FEMA 310 procedures shall govern.

3. The deficiencies identified by the FEMA 310

Evaluation conducted in Step 2 shall be ranked from 

highest to lowest priority. 

4. Rehabilitation measures shall be developed in 

accordance with Section 10.3 to mitigate the 

deficiencies identified by the FEMA 310 Evaluation. 

5. The proposed rehabilitation scheme shall be 

designed such that all deficiencies identified by the 

FEMA 310 Evaluation of Step 2 are eliminated. 

6. A complete Tier 1 and Tier 2 Evaluation of the 

building in its proposed rehabilitated state shall be 

performed in accordance with FEMA 310. In the 

event of differences between this standard and the 

FEMA 310 procedures, the FEMA 310 procedures 

shall govern.

7. Rehabilitation measures for architectural, 

mechanical, and electrical components shall be 

developed in accordance with Chapter 11 for the 

Life Safety Nonstructural Performance Level at the 

BSE-1 Earthquake Hazard Level. 

8. Construction documents, including drawings and 

specifications and a quality assurance program, shall 

be developed as defined in Chapter 2.

C10.2 Procedure

The basis of the Simplified Rehabilitation Method is 

the FEMA 310 procedure. There are intentional 

differences between the provisions of this standard and 

FEMA 310 with regard to site class amplification 

factors, seismicity, and design earthquake, among 

other issues.

For simple buildings with specific deficiencies, it is 

possible and advisable to prioritize the rehabilitation 

measures. This is often done when the construction has 

limited funding or must take place while the building is 

occupied. In both cases, it is preferable to correct the 

worst deficiency first.

Potential deficiencies are ranked in Tables C10-1 

through C10-19; items in these tables are ordered 

roughly from highest priority at the top to lowest at the 

bottom, although this can vary widely in individual 

cases.

FEMA 310 lists specific deficiencies both by Model 

Building Type and by association with each building 

system. Tables C10-1 through C10-19 of this standard 

further group deficiencies by general characteristics. 

For example, the deficiency listing “Diaphragm 

Stiffness/Strength,” includes deficiencies related to the 

type of sheathing used, diaphragm span, and lack of 

blocking. Table C10-20 provides a complete crossreference for sections in this standard, in FEMA 310, 

and in FEMA 178.

Within the table for each Model Building Type, each 

deficiency group is ranked from most critical at the top 

to least critical at the bottom. For example, in Table 

C10-12, in a precast/tilt-up concrete shear wall with 

flexible diaphragm (PC1) building, the lack of positive 

gravity frame connections (e.g., of girders to posts by 

sheet metal hardware or bolts) has a greater potential to 

lower the building’s performance (a partial collapse of 

the roof structure supported by the beam), than a 

deficiency in lateral forces on foundations (e.g., poor 

reinforcing in the footings).

The ranking was based on the following characteristics 

of each deficiency group:

1. Most critical

1.1. Building systems: those with a discontinuous 

load path and little redundancy.

1.2. Building elements: those with low strength 

and low ductility.

2. Intermediate

2.1. Building systems: those with a discontinuous 

load path but substantial redundancy.

2.2. Building elements: those with substantial 

strength but low ductility.
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-3

3. Least critical

a. Building systems: those with a substantial load 

path but little redundancy.

b. Building elements: those with low strength but 

substantial ductility.

The intent of Tables C10-1 to C10-19 is to guide the 

design professional in accomplishing a Partial 

Rehabilitation Objective. For example, if the 

foundation is strengthened in a PC1 building but a poor 

girder/wall connection is left alone, relatively little has 

been done to improve the expected performance of the 

building. Considerable professional judgment must be 

used when evaluating a structure’s unique behavior and 

determining which deficiencies should be strengthened 

and in what order.

As a rule, the resulting rehabilitated building must be 

one of the Model Building Types. For example, adding 

concrete shear walls to concrete shear wall buildings or 

adding a complete system of concrete shear walls to a 

concrete frame building meets this requirement. Steel 

bracing may be used to strengthen wood or URM 

construction. For large buildings, it is advisable to 

explore several rehabilitation strategies and compare 

alternative ways of eliminating deficiencies.

For a Limited Rehabilitation Objective, the 

deficiencies identified by the FEMA 310 Evaluation of 

Step 2 should be mitigated in order of priority based on 

the ranking performed in Step 3.

A complete evaluation of the building should confirm 

that the strengthening of any one element or system has 

not merely shifted the deficiency to another.

Specific application of the Systematic Rehabilitation 

Method is needed to achieve the BSO. The total 

strength of the building should be sufficient, and the 

ability of the building to experience the predicted 

maximum displacement without partial or complete 

collapse must be established.

If only a Partial Rehabilitation or Limited 

Rehabilitation Objective is intended, deficiencies 

should be corrected in priority order and in a way that 

will facilitate fulfillment of the requirements of a 

higher objective at a later date. Care must be taken to 

ensure that a Partial Rehabilitation effort does not 

make the building’s overall performance worse by 

unintentionally channeling failure to a more critical 

element.
10-4 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Table 10-1 Limitations on Use of the Simplified Rehabilitation Method

Model Building Type2

Maximum Building Height in Stories by 

Seismic Zone1 for Use of the Simplified 

Rehabilitation Method

Low Moderate High

Wood Frame

Light (W1) 3 3 2

Multistory Multi-Unit Residential (W1A) 3 3 2

Commercial and Industrial (W2) 3 3 2

Steel Moment Frame

Stiff Diaphragm (S1) 6 4 3

Flexible Diaphragm (S1A) 4 4 3

Steel Braced Frame

Stiff Diaphragm (S2) 6 4 3

Flexible Diaphragm (S2A) 3 3 3

Steel Light Frame (S3) 22 2

Steel Frame with Concrete Shear Walls (S4) 64 3

Steel Frame with Infill Masonry Shear Walls

Stiff Diaphragm (S5) 3 3 n.p.

Flexible Diaphragm (S5A) 3 3 n.p.

Concrete Moment Frame (C1) 3 n.p. n.p.

Concrete Shear Walls

Stiff Diaphragm (C2) 6 4 3

Flexible Diaphragm (C2A) 3 3 3

Concrete Frame with Infill Masonry Shear Walls

Stiff Diaphragm (C3) 3 n.p. n.p.

Flexible Diaphragm (C3A) 3 n.p. n.p.

Precast/Tilt-up Concrete Shear Walls

Flexible Diaphragm (PC1) 3 2 2

Stiff Diaphragm (PC1A) 3 2 2

Precast Concrete Frame

With Shear Walls (PC2) 3 2 n.p.

Without Shear Walls (PC2A) n.p. n.p. n.p.

Reinforced Masonry Bearing Walls

Flexible Diaphragm (RM1) 3 3 3

Stiff Diaphragm (RM2) 6 4 3

 = Use of Simplified Rehabilitation Method shall not be permitted.

1. Seismic Zones shall be as defined in Section 1.6.3.

2. Buildings with different types of flexible diaphragms shall be permitted to be considered as having flexible diaphragms.

Multistory buildings having stiff diaphragms at all levels except the roof shall be permitted to be considered as having stiff diaphragms.

Buildings having both flexible and stiff diaphragms, or having diaphragm systems that are neither flexible nor stiff, in accordance with this chapter, shall

be rehabilitated using the Systematic Method.

n.p.
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-5

Unreinforced Masonry Bearing Walls

Flexible Diaphragm (URM) 3 3 2

Stiff Diaphragm (URMA) 3 3 2

Table 10-1 Limitations on Use of the Simplified Rehabilitation Method (continued)

Model Building Type2

Maximum Building Height in Stories by 

Seismic Zone1 for Use of the Simplified 

Rehabilitation Method

Low Moderate High

 = Use of Simplified Rehabilitation Method shall not be permitted.

1. Seismic Zones shall be as defined in Section 1.6.3.

2. Buildings with different types of flexible diaphragms shall be permitted to be considered as having flexible diaphragms.

Multistory buildings having stiff diaphragms at all levels except the roof shall be permitted to be considered as having stiff diaphragms.

Buildings having both flexible and stiff diaphragms, or having diaphragm systems that are neither flexible nor stiff, in accordance with this chapter, shall

be rehabilitated using the Systematic Method.

n.p.
10-6 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Table 10-2 Description of Model Building Types

Building Type 1—Wood Light Frame 

W1: These buildings are single or multiple family dwellings of one or more stories in height. Building loads are light and the 

framing spans are short. Floor and roof framing consists of wood joists or rafters on wood studs spaced no more than 

24 inches apart. The first floor framing is supported directly on the foundation, or is raised up on cripple studs and post 

and beam supports. The foundation consists of spread footings constructed on concrete, concrete masonry block, or 

brick masonry in older construction. Chimneys, when present, consist of solid brick masonry, masonry veneer, or wood 

frame with internal metal flues. Lateral forces are resisted by wood frame diaphragms and shear walls. Floor and roof 

diaphragms consist of straight or diagonal lumber sheathing, tongue and groove planks, oriented strand board, or 

plywood. Shear walls consist of straight or lumber sheathing, plank siding, oriented strand board, plywood, stucco, 

gypsum board, particle board, or fiberboard. Interior partitions are sheathed with plaster or gypsum board.

W1A: These buildings are multi-story, similar in construction to W1 buildings, but have openings in the exterior walls framed 

with post-and-beam construction in the lowest level.

Building Type 2—Wood Frames, Commercial and Industrial 

W2: These buildings are commercial or industrial buildings with a floor area of 5,000 square feet or more. There are few, if 

any, interior walls. The floor and roof framing consists of wood or steel trusses, glulam or steel beams, and wood posts 

or steel columns. Lateral forces are resisted by wood diaphragms and exterior stud walls sheathed with plywood, 

oriented strand board, stucco, plaster, straight or diagonal wood sheathing, or braced with rod bracing. Wall openings 

for storefronts and garages, when present, are framed by post-and-beam framing. 

Building Type 3—Steel Moment Frames 

S1: These buildings consist of a frame assembly of steel beams and steel columns. Floor and roof framing consists of castin-place concrete slabs or metal deck with concrete fill supported on steel beams, open web joists, or steel trusses. 

Lateral forces are resisted by steel moment frames that develop their stiffness through rigid or semi-rigid beam-column 

connections. When all connections are moment-resisting connections, the entire frame participates in lateral force 

resistance. When only selected connections are moment-resisting connections, resistance is provided along discrete 

frame lines. Columns may be oriented so that each principal direction of the building has columns resisting forces in 

strong axis bending. Diaphragms consist of concrete or metal deck with concrete fill and are stiff relative to the frames. 

When the exterior of the structure is concealed, walls consist of metal panel curtain walls, glazing, brick masonry, or 

precast concrete panels. When the interior of the structure is finished, frames are concealed by ceilings, partition walls, 

and architectural column furring. Foundations consist of concrete-spread footings or deep pile foundations.

S1A: These buildings are similar to S1 buildings, except that diaphragms consist of wood framing or untopped metal deck, 

and are flexible relative to the frames. 

Building Type 4—Steel Braced Frames 

S2: These buildings have a frame of steel columns, beams, and braces. Braced frames develop resistance to lateral forces 

by the bracing action of the diagonal members. The braces induce forces in the associated beams and columns such 

that all elements work together in a manner similar to a truss, with all element stresses being primarily axial. When the 

braces do not completely triangulate the panel, some of the members are subjected to shear and flexural stresses; 

eccentrically braced frames are one such case. Diaphragms transfer lateral loads to braced frames. The diaphragms 

consist of concrete or metal deck with concrete fill and are stiff relative to the frames.

S2A: These buildings are similar to S2 buildings, except that diaphragms consist of wood framing or untopped metal deck, 

and are flexible relative to the frames. 

Building Type 5—Steel Light Frames 

S3: These buildings are pre-engineered and prefabricated with transverse rigid steel frames. They are one story in height. 

The roof and walls consist of lightweight metal, fiberglass or cementitious panels. The frames are designed for 

maximum efficiency and the beams and columns consist of tapered, built-up sections with thin plates. The frames are 

built in segments and assembled in the field with bolted or welded joints. Lateral forces in the transverse direction are 

resisted by the rigid frames. Lateral forces in the longitudinal direction are resisted by wall panel shear elements or rod 

bracing. Diaphragm forces are resisted by untopped metal deck, roof panel shear elements, or a system of tensiononly rod bracing.
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-7

Building Type 6—Steel Frames with Concrete Shear Walls 

S4: These buildings consist of a frame assembly of steel beams and steel columns. The floors and roof consist of cast-inplace concrete slabs or metal deck with or without concrete fill. Framing consists of steel beams, open web joists or 

steel trusses. Lateral forces are resisted by cast-in-place concrete shear walls. These walls are bearing walls when 

the steel frame does not provide a complete vertical support system. In older construction, the steel frame is designed 

for vertical loads only. In modern dual systems, the steel moment frames are designed to work together with the 

concrete shear walls in proportion to their relative rigidity. In the case of a dual system, the walls shall be evaluated 

under this building type and the frames shall be evaluated under S1 or S1A, Steel Moment Frames. Diaphragms 

consist of concrete or metal deck with or without concrete fill. The steel frame may provide a secondary lateral-forceresisting system depending on the stiffness of the frame and the moment capacity of the beam-column connections.

Building Type 7—Steel Frame with Infill Masonry Shear Walls 

S5: This is an older type of building construction that consists of a frame assembly of steel beams and steel columns. The 

floors and roof consist of cast-in-place concrete slabs or metal deck with concrete fill. Framing consists of steel beams, 

open web joists or steel trusses. Walls consist of infill panels constructed of solid clay brick, concrete block, or hollow 

clay tile masonry. Infill walls may completely encase the frame members, and present a smooth masonry exterior with 

no indication of the frame. The seismic performance of this type of construction depends on the interaction between 

the frame and infill panels. The combined behavior is more like a shear wall structure than a frame structure. Solidly 

infilled masonry panels form diagonal compression struts between the intersections of the frame members. If the walls 

are offset from the frame and do not fully engage the frame members, the diagonal compression struts will not develop. 

The strength of the infill panel is limited by the shear capacity of the masonry bed joint or the compression capacity of 

the strut. The post-cracking strength is determined by an analysis of a moment frame that is partially restrained by the 

cracked infill. The diaphragms consist of concrete floors and are stiff relative to the walls.

S5A: These buildings are similar to S5 buildings, except that diaphragms consist of wood sheathing or untopped metal deck, 

or have large aspect ratios and are flexible relative to the walls.

Building Type 8—Concrete Moment Frames 

C1: These buildings consist of a frame assembly of cast-in-place concrete beams and columns. Floor and roof framing 

consists of cast-in-place concrete slabs, concrete beams, one-way joists, two-way waffle joists, or flat slabs. Lateral 

forces are resisted by concrete moment frames that develop their stiffness through monolithic beam-column 

connections. In older construction, or in regions of low seismicity, the moment frames may consist of the column strips 

of two-way flat slab systems. Modern frames in regions of high seismicity have joint reinforcing, closely spaced ties, 

and special detailing to provide ductile performance. This detailing is not present in older construction. Foundations 

consist of concrete-spread footings or deep pile foundations.

Building Type 9—Concrete Shear Wall Buildings 

C2: These buildings have floor and roof framing that consists of cast-in-place concrete slabs, concrete beams, one-way 

joists, two-way waffle joists, or flat slabs. Floors are supported on concrete columns or bearing walls. Lateral forces 

are resisted by cast-in-place concrete shear walls. In older construction, shear walls are lightly reinforced, but often 

extend throughout the building. In more recent construction, shear walls occur in isolated locations and are more 

heavily reinforced with concrete slabs and are stiff relative to the walls. Foundations consist of concrete-spread 

footings or deep pile foundations.

C2A: These buildings are similar to C2 buildings, except that diaphragms consist of wood sheathing, or have large aspect 

ratios, and are flexible relative to the walls.

Building Type 10—Concrete Frame with Infill Masonry Shear Walls 

C3: This is an older type of building construction that consists of a frame assembly of cast-in-place concrete beams and 

columns. The floors and roof consist of cast-in-place concrete slabs. Walls consist of infill panels constructed of solid 

clay brick, concrete block, or hollow clay tile masonry. The seismic performance of this type of construction depends on 

the interaction between the frame and the infill panels. The combined behavior is more like a shear wall structure than 

a frame structure. Solidly infilled masonry panels form diagonal compression struts between the intersections of the 

frame members. If the walls are offset from the frame and do not fully engage the frame members, the diagonal 

compression struts will not develop. The strength of the infill panel is limited by the shear capacity of the masonry bed 

joint or the compression capacity of the strut. The post-cracking strength is determined by an analysis of a moment 

frame that is partially restrained by the cracked infill. The shear strength of the concrete columns, after racking of the 

infill, may limit the semiductile behavior of the system. The diaphragms consist of concrete floors and are stiff relative 

to the walls.

C3A: These buildings are similar to C3 buildings, except that diaphragms consists of wood sheathing or untopped metal 

deck, or have large aspect ratios and are flexible relative to the walls.

Table 10-2 Description of Model Building Types (continued)
10-8 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Building Type 11—Precast/Tilt-up Concrete Shear Wall Buildings 

PC1: These buildings are one or more stories in height and have precast concrete perimeter wall panels that are cast on site 

and tilted into place. Floor and roof framing consists of wood joists, glulam beams, steel beams or open web joists. 

Framing is supported on interior steel columns and perimeter concrete bearing walls. The floors and roof consist of 

wood sheathing or untapped metal deck. Lateral forces are resisted by the precast concrete perimeter wall panels. Wall 

panels may be solid, or have large window and door openings which cause the panels to behave more as frames than 

as shear walls. In older construction, wood framing is attached to the walls with wood ledgers. Foundations consist of 

concrete-spread footings or deep pile foundations.

PC1A: These buildings are similar to PC1 buildings, except that diaphragms consist of precast elements, cast-in-place 

concrete, or metal deck with concrete fill, and are stiff relative to the walls.

Building Type 12—Precast Concrete Frames 

PC2: These buildings consist of a frame assembly of precast concrete girders and columns with the presence of shear walls. 

Floor and roof framing consists of precast concrete planks, tees or double-tees supported on precast concrete girders 

and columns. Lateral forces are resisted by precast or cast-in-place concrete shear walls. Diaphragms consist of 

precast elements interconnected with welded inserts, cast-in-place closure strips, or reinforced concrete topping slabs.

PC2A: These buildings are similar to PC2 buildings, except that concrete shear walls are not present. Lateral forces are 

resisted by precast concrete moment frames that develop their stiffness through beam-column joints rigidly connected 

by welded inserts or cast-in-place concrete closures. Diaphragms consist of precast elements interconnected with 

welded inserts, cast-in-place closure strips, or reinforced concrete topping slabs.

Building Type 13—Reinforced Masonry Bearing Wall Buildings with Flexible Diaphragms 

RM1: These buildings have bearing walls that consist of reinforced brick or concrete block masonry. Wood floor and roof 

framing consists of steel beams or open web joists, steel girders and steel columns. Lateral forces are resisted by the 

reinforced brick or concrete block masonry shear walls. Diaphragms consist of straight or diagonal wood sheathing, 

plywood, or untopped metal deck, and are flexible relative to the walls. Foundations consist of brick or concrete-spread 

footings.

Building Type 14—Reinforced Masonry Bearing Wall Buildings with Stiff Diaphragms 

RM2: These building are similar to RM1 buildings, except that the diaphragms consist of metal deck with concrete fill, precast 

concrete planks, tees, or double-tees, with or without a cast-in-place concrete topping slab, and are stiff relative to the 

walls. The floor and roof framing is supported on interior steel or concrete frames or interior reinforced masonry walls.

Building Type 15—Unreinforced Masonry Bearing Wall Buildings

URM: These buildings have perimeter bearing walls that consist of unreinforced clay brick masonry. Interior bearing walls, 

when present, also consist of unreinforced clay brick masonry. In older construction, floor and roof framing consists of 

straight or diagonal lumber sheathing supported by wood joists, which are supported on posts and timbers. In more 

recent construction, floors consist of structural panel or plywood sheathing rather than lumber sheathing. The 

diaphragms are flexible relative to the walls. When they exist, ties between the walls and diaphragms consist of bent 

steel plates or government anchors embedded in the mortar joints and attached to framing. Foundations consist of 

brick or concrete-spread footings.

URMA:These buildings are similar to URM buildings, except that the diaphragms are stiff relative to the unreinforced masonry 

walls and interior framing. In older construction or large, multistory buildings, diaphragms consist of cast-in-place 

concrete. In regions of low seismicity, more recent construction consists of metal deck and concrete fill supported on 

steel framing.

Table 10-2 Description of Model Building Types (continued)
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-9

10.3 Correction of Deficiencies

For Simplified Rehabilitation, deficiencies identified by 

an FEMA 310 Evaluation shall be mitigated by 

implementing approved rehabilitation measures. The 

resulting building, including strengthening measures, 

shall comply with the requirements of FEMA 310 and 

shall conform to one of the Model Building Types 

contained in Table 10-1, except that steel bracing in 

wood or unreinforced masonry buildings shall be 

permitted.

The Simplified Rehabilitation Method shall only be 

used to achieve Limited Rehabilitation Objectives. To 

achieve the Life Safety Building Performance Level 

(3-C) at the BSE-1 Earthquake Hazard Level, all 

deficiencies identified by an FEMA 310 Evaluation 

shall be corrected to meet the FEMA 310 criteria. To 

achieve a Partial Rehabilitation Objective, only selected 

deficiencies need be corrected.

To achieve the Basic Safety Objective, the Simplified 

Rehabilitation Method is not permitted, and 

deficiencies shall be corrected in accordance with the 

Systematic Rehabilitation Method of Section 2.3. 

C10.3 Correction of Deficiencies

Implementing a rehabilitation scheme that mitigates all 

of a building’s FEMA 310 deficiencies using the 

Simplified Rehabilitation Method does not, in and of 

itself, achieve the Basic Safety Objective or any 

Enhanced Rehabilitation Objective as defined in 

Chapter 2 since the rehabilitated building may not 

meet the Collapse Prevention Structural Performance 

Level for the BSE-2 Earthquake Hazard Level. If the 

goal is to attain the Basic Safety Objective as described 

in Chapter 2 or other Enhanced Rehabilitation 

Objectives, this can be accomplished using the 

Systematic Rehabilitation Method defined in 

Chapter 2. 

Suggested rehabilitation measures are listed by 

deficiency in the following sections.

C10.3.1 Building Systems

C10.3.1.1 Load Path

Load path discontinuities can be mitigated by adding 

elements to complete the load path. This may require 

adding new well-founded shear walls or frames to fill 

gaps in existing shear walls or frames that are not 

carried continuously to the foundation. Alternatively, it 

may require the addition of elements throughout the 

building to pick up loads from diaphragms that have no 

path into existing vertical elements (FEMA 310, 

Section 4.3.1).

C10.3.1.2 Redundancy

The most prudent rehabilitation strategy for a building 

without redundancy is to add new lateral-forceresisting elements in locations where the failure of a 

single element will cause an instability in the building. 

The added lateral-force-resisting elements should be of 

the same stiffness as the elements they are 

supplementing. It is not generally satisfactory just to 

strengthen a non-redundant element (such as by adding 

cover plates to a slender brace), because its failure 

would still result in an instability (FEMA 310, Sections 

4.4.1.1.1, 4.4.2.1.1, 4.4.3.1.1, 4.4.4.1.1).

C10.3.1.3 Vertical Irregularities

New vertical lateral-force-resisting elements can be 

provided to eliminate the vertical irregularity. For 

weak stories, soft stories, and vertical discontinuities, 

new elements of the same type can be added as needed. 

Mass and geometric discontinuities must be evaluated 

and strengthened based on the Systematic 

Rehabilitation Method, if required by Chapter 2 

(FEMA 310, Sections 4.3.2.4–4.3.2.5).

C10.3.1.4 Plan Irregularities

The effects of plan irregularities that create torsion can 

be eliminated with the addition of lateral-forceresisting bracing elements that will support all major 

diaphragm segments in a balanced manner. While it is 

possible in some cases to allow the irregularity to 

remain and instead strengthen those structural elements 

that are overstressed by its existence, this does not 

directly address the problem and will require the use of 

the Systematic Rehabilitation Method (FEMA 310, 

Section 4.3.2.6).
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C10.3.1.5 Adjacent Buildings

Stiffening elements (typically braced frames or shear 

walls) can be added to one or both buildings to reduce 

the expected drifts to acceptable levels. With separate 

structures in a single building complex, it may be 

possible to tie them together structurally to force them 

to respond as a single structure. The relative stiffnesses 

of each and the resulting force interactions must be 

determined to ensure that additional deficiencies are 

not created. Pounding can also be eliminated by 

demolishing a portion of one building to increase the 

separation (FEMA 310, Section 4.3.1.2).

C10.3.1.6 Lateral Load Path at Pile Caps

Typically, deficiencies in the load path at the pile caps 

are not a life safety concern. However, if the design 

professional has determined that there is a strong 

possibility of a life safety hazard due to this deficiency, 

piles and pile caps may be modified, supplemented, 

repaired, or in the most severe condition, replaced in 

their entirety. Alternatively, the building system may 

be rehabilitated such that the pile caps are protected 

(FEMA 310, Section 4.6.3.10).

C10.3.1.7 Deflection Compatibility

Vertical lateral-force-resisting elements can be added 

to decrease the drift demands on the columns, or the 

ductility of the columns can be increased. Jacketing the 

columns with steel or concrete is one approach to 

increase their ductility (FEMA 310, Section 4.4.1.6.2).

C10.3.2 Moment Frames

C10.3.2.1 Steel Moment Frames

C10.3.2.1.1 Drift

The most direct mitigation approach is to add properly 

placed and distributed stiffening elements—new 

moment frames, braced frames, or shear walls—that 

can reduce the inter-story drifts to acceptable levels. 

Alternatively, the addition of energy dissipation 

devices to the system may reduce the drift, though 

these are outside the scope of the Simplified 

Rehabilitation Method (FEMA 310, Section 4.4.1.3.1).

C10.3.2.1.2 Frames

Noncompact members can be eliminated by adding 

appropriate steel plates. Eliminating or properly 

reinforcing large member penetrations will develop the 

demanded strength and deformations. Lateral bracing 

in the form of new steel elements can be added to 

reduce member unbraced lengths to within the limits 

prescribed. Stiffening elements (e.g., braced frames, 

shear walls, or additional moment frames) can be 

added throughout the building to reduce the expected 

frame demands (FEMA 310, Sections 4.4.1.3.7, 

4.4.1.3.8, and 4.4.1.3.10).

C10.3.2.1.3 Strong Column-Weak Beam

Steel plates can be added to increase the strength of the 

steel columns to beyond that of the beams to eliminate 

this issue. Stiffening elements (e.g., braced frames, 

shear walls, or additional moment frames) can be 

added throughout the building to reduce the expected 

frame demands (FEMA 310, Section 4.4.1.3.6).

C10.3.2.1.4 Connections

Adding a stiffer lateral-force-resisting system (e.g., 

braced frames or shear walls) can reduce the expected 

rotation demands. Connections can be modified by 

adding flange cover plates, vertical ribs, haunches, or 

brackets, or removing beam flange material to initiate 

yielding away from the connection location (e.g., via a 

pattern of drilled holes or the cutting out of flange 

material). Partial penetration splices, which may 

become more vulnerable for conditions where the 

beam-column connections are modified to be more 

ductile, can be modified by adding plates and/or welds. 

Adding continuity plates alone is not likely to enhance 

the connection performance significantly (FEMA 310, 

Sections 4.4.1.3.3 – 4.4.1.3.5, and 4.4.1.3.9).

Moment-resisting connection capacity can be 

increased by adding cover plates or haunches, or using 

other techniques as stipulated in FEMA 351.

C10.3.2.2 Concrete Moment Frames

C10.3.2.2.1 Frame and Nonductile Detail Concerns

Adding properly placed and distributed stiffening 

elements such as shear walls will fully supplement the 

moment frame system with a new lateral forceresisting system. For eccentric joints, columns and/or 

beams may be jacketed to reduce the effective 

eccentricity. Jackets may also be provided for shearcritical columns.
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It must be verified that this new system sufficiently 

reduces the frame shears and inter-story drifts to 

acceptable levels (FEMA 310, Section 4.4.1.4).

C10.3.2.2.2 Precast Moment Frames

Precast concrete frames without shear walls may not be 

addressed under the Simplified Rehabilitation Method 

(see Table 10-1). Where shear walls are present, the 

precast connections must be strengthened sufficiently 

to meet the FEMA 310 requirements.

The development of a competent load path is 

extremely critical in these buildings. If the connections 

have sufficient strength so that yielding will first occur 

in the members rather than in the connections, the 

building should be evaluated as a shear wall system 

Type C2 (FEMA 310, Section 4.4.1.5).

C10.3.2.3 Frames Not Part of the 

Lateral-Force-Resisting System

C10.3.2.3.1 Complete Frames

Complete frames of steel or concrete form a complete 

vertical load-carrying system.

Incomplete frames are essentially bearing wall 

systems. The wall must be strengthened to resist the 

combined gravity/seismic loads or new columns added 

to complete the gravity load path (FEMA 310, Section 

4.4.1.6.1).

C10.3.2.3.2 Short Captive Columns

Columns may be jacketed with steel or concrete such 

that they can resist the expected forces and drifts. 

Alternatively, the expected story drifts can be reduced 

throughout the building by infilling openings or adding 

shear walls (FEMA 310, Section 4.4.1.4.5).

C10.3.3 Shear Walls

C10.3.3.1 Cast-in-Place Concrete Shear Walls

C10.3.3.1.1 Shearing Stress

New shear walls can be provided and/or the existing 

walls can be strengthened to satisfy seismic demand 

criteria. New and strengthened walls must form a 

complete, balanced, and properly detailed lateralforce-resisting system for the building. Special care is 

needed to ensure that the connection of the new walls 

to the existing diaphragm is appropriate and of 

sufficient strength such that yielding will first occur in 

the wall. All shear walls must have sufficient shear and 

overturning resistance to meet the FEMA 310 load 

criteria (FEMA 310, Section 4.4.2.2.1).

C10.3.3.1.2 Overturning

Lengthening or adding shear walls can reduce 

overturning demands; increasing the length of footings 

will capture additional building dead load (FEMA 310, 

Section 4.4.2.2.4).

C10.3.3.1.3 Coupling Beams

To eliminate the need to rely on the coupling beam, the 

walls may be strengthened as required. The beam 

should be jacketed only as a means of controlling 

debris. If possible, the opening that defines the 

coupling beam should be infilled (FEMA 310, Section 

4.4.2.2.3).

C10.3.3.1.4 Boundary Component Detailing

Splices may be improved by welding bars together 

after exposing them. The shear transfer mechanism can 

be improved by adding steel studs and jacketing the 

boundary components. (FEMA 310, Sections 4.4.2.2.5, 

4.4.2.2.8, and 4.4.2.2.9).

C10.3.3.1.5 Wall Reinforcement

Shear walls can be strengthened by infilling openings, 

or by thickening the walls (see FEMA 172, Section 

3.2.1.2) (FEMA 310, Sections 4.4.2.2.2 and 4.4.2.2.6).

C10.3.3.2 Precast Concrete Shear Walls

C10.3.3.2.1 Panel-to-Panel Connections

Appropriate Simplified Rehabilitation solutions are 

outlined in FEMA 172, Section 3.2.2.3 (FEMA 310, 

Section 4.4.2.3.5).
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Inter-panel connections with inadequate capacity can 

be strengthened by adding steel plates across the joint, 

or by providing a continuous wall by exposing the 

reinforcing steel in the adjacent units and providing 

ties between the panels and patching with concrete. 

Providing steel plates across the joint is typically the 

most cost-effective approach, although care must be 

taken to ensure adequate anchor bolt capacity by 

providing adequate edge distances (see FEMA 172, 

Section 3.2.2).

C10.3.3.2.2 Wall Openings

Infilling openings or adding shear walls in the plane of 

the open bays can reduce demand on the connections 

and eliminate frame action (FEMA 310, Section 

4.4.2.3.3).

C10.3.3.2.3 Collectors

Upgrading the concrete section and/or the connections 

(e.g., exposing the existing connection, adding 

confinement ties, increasing embedment) can increase 

strength and/or ductility. Alternative load paths for 

lateral forces can be provided, and shear walls can be 

added to reduce demand on the existing collectors 

(FEMA 310, Section 4.4.2.3.4).

C10.3.3.3 Masonry Shear Walls

C10.3.3.3.1 Reinforcing in Masonry Walls

Nondestructive methods should be used to locate 

reinforcement, and selective demolition used if 

necessary to determine the size and spacing of the 

reinforcing. If it cannot be verified that the wall is 

reinforced in accordance with the minimum 

requirements, then the wall should be assumed to be 

unreinforced, and therefore must be supplemented with 

new walls, or the procedures for unreinforced masonry 

should be followed (FEMA 310, Section 4.4.2.4.2).

C10.3.3.3.2 Shearing Stress

To meet the lateral force requirements of FEMA 310, 

new walls can be provided or the existing walls can be 

strengthened as needed. New and strengthened walls 

must form a complete, balanced, and properly detailed 

lateral-force-resisting system for the building. Special 

care is needed to ensure that the connection of the new 

walls to the existing diaphragm is appropriate and of 

sufficient strength to deliver the actual lateral loads or 

force yielding in the wall. All shear walls must have 

sufficient shear and overturning resistance 

(FEMA 310, Section 4.4.2.4.1).

C10.3.3.3.3 Reinforcing at Openings

The presence and location of reinforcing steel at 

openings may be established using nondestructive or 

destructive methods at selected locations to verify the 

size and location of the reinforcing, or using both 

methods. Reinforcing must be provided at all openings 

as required to meet the FEMA 310 criteria. Steel plates 

may be bolted to the surface of the section as long as 

the bolts are sufficient to yield the steel plate 

(FEMA 310, Section 4.4.2.4.3).

C10.3.3.3.4 Unreinforced Masonry Shear Walls

Openings in the lateral-force-resisting walls should be 

infilled as needed to meet the FEMA 310 stress check. 

If supplemental strengthening is required, it should be 

designed using the Systematic Rehabilitation Method 

as defined in Chapter 2. Walls that do not meet the 

masonry lay-up requirements should not be considered 

as lateral force-resisting elements and shall be 

specially supported for out-of-plane loads (FEMA 310, 

Sections 4.4.2.5.1 and 4.4.2.5.3).

C10.3.3.3.5 Proportions of Solid Walls

Walls with insufficient thickness should be 

strengthened either by increasing the thickness of the 

wall or by adding a well-detailed strong back system. 

The thickened wall must be detailed in a manner that 

fully interconnects the wall over its full height. The 

strong back system must be designed for strength, 

connected to the structure in a manner that: (1) 

develops the full yield strength of the strong back, and 

(2) connects to the diaphragm in a manner that 

distributes the load into the diaphragm and has 

sufficient stiffness to ensure that the elements will 

perform in a compatible and acceptable manner. The 

stiffness of the bracing should limit the out-of-plane 

deflections to acceptable levels such as L/600 to L/900 

(FEMA 310, Sections 4.4.2.4.4 and 4.4.2.5.2).

C10.3.3.3.6 Infill Walls

The partial infill wall should be isolated from the 

boundary columns to avoid a “short column” effect, 

except when it can be shown that the column is 

adequate. In sizing the gap between the wall and the 

columns, the anticipated inter-story drift must be 

considered. The wall must be positively restrained 

against out-of-plane failure by either bracing the top of 

the wall or installing vertical girts. These bracing 

elements must not violate the isolation of the frame 

from the infill (FEMA 310, Section 4.4.2.6).
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C10.3.3.4 Shear Walls in Wood Frame 

Buildings

C10.3.3.4.1 Shear Stress

Walls may be added or existing openings filled. 

Alternatively, the existing walls and connections can 

be strengthened. The walls should be distributed across 

the building in a balanced manner to reduce the shear 

stress for each wall. Replacing heavy materials such as 

tile roofing with lighter materials will also reduce shear 

stress. (FEMA 310, Section 4.4.2.7.1).

C10.3.3.4.2 Openings

Local shear transfer stresses can be reduced by 

distributing the forces from the diaphragm. Chords 

and/or collector members can be provided to collect 

and distribute shear from the diaphragm to the shear 

wall or bracing (see FEMA 172, Figure 3.7.1.3). 

Alternatively, the opening can be closed off by adding 

a new wall with plywood sheathing. (FEMA 310, 

Section 4.4.2.7.8).

C10.3.3.4.3 Wall Detailing

If the walls are not bolted to the foundation or if the 

bolting is inadequate, bolts can be installed through the 

sill plates at regular intervals (see FEMA 172, 

Figure 3.8.1.2a). If the crawl space is not deep enough 

for vertical holes to be drilled through the sill plate, the 

installation of connection plates or angles may be a 

practical alternative (see FEMA 172, Figure 3.8.1.2b). 

Sheathing and additional nailing can be added where 

walls lack proper nailing or connections. Where the 

existing connections are inadequate, adding clips or 

straps will deliver lateral loads to the walls and to the 

foundation sill plate (FEMA 310, Section 4.4.2.7.9).

C10.3.3.4.4 Cripple Walls

Where bracing is inadequate, new plywood sheathing 

can be added to the cripple wall studs. The top edge of 

the plywood is nailed to the floor framing and the 

bottom edge is nailed into the sill plate (see 

FEMA 172, Figure 3.8.1.3). Verify that the cripple wall 

does not change height along its length (stepped top of 

foundation). If it does, the shorter portion of the cripple 

wall will carry the majority of the shear and significant 

torsion will occur in the foundation. Added plywood 

sheathing must have adequate strength and stiffness to 

reduce torsion to an acceptable level. Also, it should be 

verified that the sill plate is properly anchored to the 

foundation. If anchor bolts are lacking or insufficient, 

additional anchor bolts should be installed. Blocking 

and/or framing clips may be needed to connect the 

cripple wall bracing to the floor diaphragm or the sill 

plate. (FEMA 310, Section 4.4.2.7.7).

C10.3.3.4.5 Narrow Wood Shear Walls

Where narrow shear walls lack capacity, they should 

be replaced with shear walls with a height-to-width 

aspect ratio of two-to-one or less. These replacement 

walls must have sufficient strength, including being 

adequately connected to the diaphragm and sufficiently 

anchored to the foundation for shear and overturning 

forces (FEMA 310, Section 4.4.2.7.4).

C10.3.3.4.6 Stucco Shear Walls

For strengthening or repair, the stucco should be 

removed, a plywood shear wall added, and new stucco 

applied. The plywood should be the manufacturer’s 

recommended thickness for the installation of stucco. 

The new stucco should be installed in accordance with 

building code requirements for waterproofing. Walls 

should be sufficiently anchored to the diaphragm and 

foundation (FEMA 310, Section 4.4.2.7.2).

C10.3.3.4.7 Gypsum Wallboard or Plaster Shear 

Walls

Plaster and gypsum wallboard can be removed and 

replaced with structural panel shear wall as required, 

and the new shear walls covered with gypsum 

wallboard (FEMA 310, Section 4.4.2.7.3).
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C10.3.4 Steel Braced Frames

C10.3.4.1 System Concerns

If the strength of the braced frames is inadequate, more 

braced bays or shear wall panels can be added. The 

resulting lateral-force-resisting system must form a 

well-balanced system of braced frames that do not fail 

at their joints, are properly connected to the floor 

diaphragms, and whose failure mode is yielding of 

braces rather than overturning (FEMA 310, Sections 

4.4.3.1.1 and 4.4.3.1.2).

C10.3.4.2 Stiffness of Diagonals

Diagonals with inadequate stiffness should be 

strengthened using supplemental steel plates, or 

replaced with a larger and/or different type of section. 

Global stiffness can be increased by the addition of 

braced bays or shear wall panels (FEMA 310, Sections 

4.4.3.1.3 and 4.4.3.2.2).

C10.3.4.3 Chevron or K-Bracing

Columns or horizontal girts can be added as needed to 

support the tension brace when the compression brace 

buckles, or the bracing can be revised to another 

system throughout the building. The beam elements 

can be strengthened with cover plates to provide them 

with the capacity to fully develop the unbalanced 

forces created by tension brace yielding (FEMA 310, 

Sections 4.4.3.2.1 and 4.4.3.2.3).

C10.3.4.4 Braced Frame Connections

Column splices or other braced frame connections can 

be strengthened by adding plates and welds to ensure 

that they are strong enough to develop the connected 

members. Connection eccentricities that reduce 

member capacities can be eliminated, or the members 

can be strengthened to the required level by the 

addition of properly placed plates. Demands on the 

existing elements can be reduced by adding braced 

bays or shear wall panels (FEMA 310, Sections 

4.4.3.1.4 and 4.4.3.1.5).

C10.3.5 Diaphragms

C10.3.5.1 Re-entrant Corners

New chords with sufficient strength to resist the 

required force can be added at the re-entrant corner. If 

a vertical lateral-force-resisting element exists at the 

re-entrant corner, a new collector element should be 

installed in the diaphragm to reduce tensile and 

compressive forces at the re-entrant corner. The same 

basic materials used in the diaphragm should be used 

for the chord (FEMA 310, Section 4.5.1.7).

C10.3.5.2 Cross Ties

New cross ties and wall connections can be added to 

resist the required out-of-plane wall forces and 

distribute these forces through the diaphragm. New 

strap plates and/or rod connections can be used to 

connect existing framing members together so they 

function as a crosstie in the diaphragm (FEMA 310, 

Section 4.5.1.2).

C10.3.5.3 Diaphragm Openings

New drag struts or diaphragm chords can be added 

around the perimeter of existing openings to distribute 

tension and compression forces along the diaphragm. 

The existing sheathing should be nailed to the new 

drag struts or diaphragm chords. In some cases it may 

also be necessary to: (1) increase the shear capacity of 

the diaphragm adjacent to the opening by overlaying 

the existing diaphragm with a wood structural panel, or 

(2) decrease the demand on the diaphragm by adding 

new vertical elements near the opening (FEMA 310, 

Sections 4.5.1.4 through 4.5.1.6 and 4.5.1.8).

C10.3.5.4 Diaphragm Stiffness/Strength

C10.3.5.4.1 Board Sheathing

When the diaphragm does not have at least two nails 

through each board into each of the supporting 

members, and the lateral drift and/or shear demands on 

the diaphragm are not excessive, the shear capacity and 

stiffness of the diaphragm can be increased by adding 

nails at the sheathing boards. This method of upgrade 

is most often suitable in areas of low seismicity. In 

other cases, a new wood structural panel should be 

placed over the existing straight sheathing, and the 

joints of the wood structural panels placed so they are 

near the center of the sheathing boards or at a 45-

degree angle to the joints between sheathing boards 

(see FEMA 172, Section 3.5.1.2; ATC-7, and 

FEMA 310, Section 4.5.2.1).
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C10.3.5.4.2 Unblocked Diaphragm

The shear capacity of unblocked diaphragms can be 

improved by adding new wood blocking and nailing at 

the unsupported panel edges. Placing a new wood 

structural panel over the existing diaphragm will 

increase the shear capacity. Both of these methods will 

require the partial or total removal of existing flooring 

or roofing to place and nail the new overlay or nail the 

existing panels to the new blocking. Strengthening of 

the diaphragm is usually not necessary at the central 

area of the diaphragm where shear is low. In certain 

cases when the design loads are low, it may be possible 

to increase the shear capacity of unblocked diaphragms 

with sheet metal plates stapled on the underside of the 

existing wood panels. These plates and staples must be 

designed for all related shear and torsion caused by the 

details related to their installation (FEMA 310, Section 

4.5.2.3).

C10.3.5.4.3 Spans

New vertical elements can be added to reduce the 

diaphragm span. The reduction of the diaphragm span 

will also reduce the lateral deflection and shear 

demand in the diaphragm. However, adding new 

vertical elements will result in a different distribution 

of shear demands. Additional blocking, nailing, or 

other rehabilitation measures may need to be provided 

at these areas (FEMA 172, Section 3.4 and FEMA 310, 

Section 4.5.2.2).

C10.3.5.4.4 Span-to-Depth Ratio

New vertical elements can be added to reduce the 

diaphragm span-to-depth ratio. The reduction of the 

diaphragm span-to-depth ratio will also reduce the 

lateral deflection and shear demand in the diaphragm. 

Typical construction details and methods are discussed 

in FEMA 172, Section 3.4.

C10.3.5.4.5 Diaphragm Continuity

The diaphragm discontinuity should in all cases be 

eliminated by adding new vertical elements at the 

diaphragm offset or the expansion joint (see 

FEMA 172, Section 3.4). In some cases, special details 

may be used to transfer shear across an expansion 

joint—while still allowing the expansion joint to 

function—thus eliminating a diaphragm discontinuity 

(FEMA 310, Section 4.5.1.1).

C10.3.5.4.6 Chord Continuity

If members such as edge joists, blocking, or wall top 

plates have the capacity to function as chords but lack 

connection, adding nailed or bolted continuity splices 

will provide a continuous diaphragm chord. New 

continuous steel or wood chord members can be added 

to the existing diaphragm where existing members lack 

sufficient capacity or no chord exists. New chord 

members can be placed at either the underside or 

topside of the diaphragm. In some cases, new vertical 

elements can be added to reduce the diaphragm span 

and stresses on any existing chord members (see 

FEMA 172, Section 3.5.1.3, and ATC-7). New chord 

connections should not be detailed such that they are 

the weakest element in the chord (FEMA 310, Section 

4.5.1.3).

C10.3.6 Connections

C10.3.6.1 Diaphragm/Wall Shear Transfer

Collector members, splice plates, and shear transfer 

devices can be added as required to deliver collector 

forces to the shear wall. Adding shear connectors from 

the diaphragm to the wall and/or to the collectors will 

transfer shear. See FEMA 172, Section 3.7 for Wood 

Diaphragms, 3.7.2 for concrete diaphragms, 3.7.3 for 

poured gypsum, and 3.7.4 for metal deck diaphragms 

(FEMA 310, Sections 4.6.2.1 and 4.6.2.3).

C10.3.6.2 Diaphragm/Frame Shear Transfer

Adding collectors and connecting the framing will 

transfer loads to the collectors. Connections can be 

provided along the collector length and at the collectorto-frame connection to withstand the calculated forces. 

See FEMA 172, Sections 3.7.5 and 3.7.6 (FEMA 310, 

Sections 4.6.2.2 and 4.6.2.3).

C10.3.6.3 Anchorage for Normal Forces

To account for inadequacies identified by FEMA 310, 

wall anchors can be added. Complications that may 

result from inadequate anchorage include cross-grain 

tension in wood ledgers or failure of the diaphragm-towall connection due to: (1) insufficient strength, 

number, or stability of anchors; (2) inadequate 

embedment of anchors; (3) inadequate development of 

anchors and straps into the diaphragm; and (4) 

deformation of anchors and their fasteners that permit 

diaphragm boundary connection pullout, or cross-grain 

tension in wood ledgers.
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Existing anchors should be tested to determine load 

capacity and deformation potential, including fastener 

slip, according to the requirements in FEMA 310. 

Special attention should be given to the testing 

procedure to maintain a high level of quality control. 

Additional anchors should be provided as needed to 

supplement those that fail the test, as well as those 

needed to meet the FEMA 310 criteria. The quality of 

the rehabilitation depends greatly on the quality of the 

performed tests (FEMA 310, Sections 4.6.1.1 through 

4.6.1.5).

C10.3.6.4 Girder-Wall Connections

The existing reinforcing must be exposed, and the 

connection modified as necessary. For out-of-plane 

loads, the number of column ties can be increased by 

jacketing the pilaster or, alternatively, by developing a 

second load path for the out-of-plane forces. Bearing 

length conditions can be addressed by adding bearing 

extensions. Frame action in welded connections can be 

mitigated by adding shear walls (FEMA 310, Section 

4.6.4.1).

C10.3.6.5 Precast Connections

The connections of chords, ties, and collectors can be 

upgraded to increase strength and/or ductility, 

providing alternative load paths for lateral forces. 

Upgrading can be achieved by such methods as adding 

confinement ties or increasing embedment. Shear walls 

can be added to reduce the demand on connections 

(FEMA 310, Section 4.4.1.5.3).

C10.3.6.6 Wall Panels and Cladding

It may be possible to improve the connection between 

the panels and the framing. If architectural or 

occupancy conditions warrant, the cladding can be 

replaced with a new system. The building can be 

stiffened with the addition of shear walls or braced 

frames to reduce the drifts in the cladding elements 

(FEMA 310, Section 4.8.4.6).

C10.3.6.7 Light Gage Metal, Plastic, or 

Cementitious Roof Panels

It may be possible to improve the connection between 

the roof and the framing. If architectural or occupancy 

conditions warrant, the roof diaphragm can be replaced 

with a new one. Alternatively, a new diaphragm may 

be added using rod braces or plywood above or below 

the existing roof, which remains in place (FEMA 310, 

Section 4.6.5.1).

C10.3.6.8 Mezzanine Connections

Diagonal braces, moment frames, or shear walls can be 

added at or near the perimeter of the mezzanine where 

bracing elements are missing, so that a complete and 

balanced lateral-force-resisting system is provided that 

meets the requirements of FEMA 310 (FEMA 310, 

Section 4.3.1.3).

C10.3.7 Foundations and Geologic Hazards

C10.3.7.1 Anchorage to Foundations

For wood walls, expansion anchors or epoxy anchors 

can be installed by drilling through the wood sill to the 

concrete foundation at an appropriate spacing of four 

to six feet on center. Similarly, steel columns and wood 

posts can be anchored to concrete slabs or footings, 

using expansion anchors and clip angles. If the 

concrete or masonry walls and columns lack dowels, a 

concrete curb can be installed adjacent to the wall or 

column by drilling dowels and installing anchors into 

the wall that lap with dowels installed in the slab or 

footing. However, this curb can cause significant 

architectural problems. Alternatively, steel angles may 

be used with drilled anchors. The anchorage of shear 

wall boundary components can be challenging due to 

very high concentrated forces (FEMA 310, Sections 

4.6.3.2 through 4.6.3.9).

C10.3.7.2 Condition of Foundations

All deteriorated and otherwise damaged foundations 

should be strengthened and repaired using the same 

materials and style of construction. Some conditions of 

material deterioration can be mitigated in the field, 

including patching of spalled concrete. Pest infestation 

or dry rot of wood piles can be very difficult to correct, 

and often require full replacement. The deterioration of 

these elements may have implications that extend 

beyond seismic safety and must be considered in the 

rehabilitation (FEMA 310, Sections 4.7.2.1 and 

4.7.2.2).
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-17

C10.3.7.3 Overturning

Existing foundations can be strengthened as needed to 

resist overturning forces. Spread footings may be 

enlarged, or additional piles, rock anchors, or piers 

may be added to deep foundations. It may also be 

possible to use grade beams or new wall elements to 

spread out overturning loads over a greater distance. 

Adding new lateral-load-resisting elements will reduce 

overturning effects of existing elements (FEMA 310, 

Section 4.7.3.2).

C10.3.7.4 Lateral Loads

As with overturning effects, the correction of lateral 

load deficiencies in the foundations of existing 

buildings is expensive and may not be justified by 

more realistic analysis procedures. For this reason, the 

Systematic Rehabilitation Method is recommended for 

these cases. (FEMA 310, Sections 4.7.3.1, 4.7.3.3 

through 4.7.3.5).

C10.3.7.5 Geologic Site Hazards

Site hazards other than ground shaking should be 

considered. Rehabilitation of structures subject to life 

safety hazards from ground failures is impractical 

unless site hazards can be mitigated to the point where 

acceptable performance can be achieved. Not all 

ground failures need necessarily be considered as life 

safety hazards. For example, in many cases 

liquefaction beneath a building does not pose a life 

safety hazard; however, related lateral spreading can 

result in collapse of buildings with inadequate 

foundation strength. For this reason, the liquefaction 

potential and the related consequences should be 

thoroughly investigated for sites that do not satisfy the 

FEMA 310 requirements. Further information on the 

evaluation of site hazards is provided in Chapter 4 of 

this standard (FEMA 310, Sections 4.7.1.1 through 

4.7.1.3).

C10.3.8 Evaluation of Materials and 

Conditions

C10.3.8.1 General

Proper evaluation of the existing conditions and 

configuration of the existing building structure is an 

important aspect of the Simplified Rehabilitation 

Method. As Simplified Rehabilitation is often 

concerned with specific deficiencies in a particular 

structural system, the evaluation may either be focused 

on affected structural elements and components, or be 

comprehensive and include the complete structure. If 

the degree of existing damage or deficiencies in a 

structure has not been established, the evaluation shall 

consist of a comprehensive inspection of gravity- and 

lateral-load-resisting systems that includes the 

following steps.

1. Verify existing data (e.g., accuracy of drawings).

2. Develop other needed data (e.g., measure and 

sketch building if necessary).

3. Verify the vertical and lateral systems.

4. Check the condition of the building.

5. Look for special conditions and anomalies.

6. Address the evaluation statements and goals during 

the inspection.

7. Perform material tests that are justified through a 

weighing of the cost of destructive testing and the 

cost of corrective work.
10-18 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

C10.3.8.2 Condition of Wood

An inspection should be conducted to grade the 

existing wood and verify physical condition, using 

techniques from Section C10.3.8.1. Any damage or 

deterioration and its source must be identified. Wood 

that is significantly damaged due to splitting, decay, 

aging, or other phenomena must be removed and 

replaced. Localized problems can be eliminated by 

adding new appropriately sized reinforcing 

components extending beyond the damaged area and 

connecting to undamaged portions. Additional 

connectors between components should be provided to 

correct any discontinuous load paths. It is necessary to 

verify that any new reinforcing components or 

connectors will not be exposed to similar deterioration 

or damage (FEMA 310, Section 4.3.3.1).

C10.3.8.3 Overdriven Fasteners

Where visual inspection determines that extensive 

overdriving of fasteners exists in greater than 20% of 

the installed connectors, the fasteners and shear panels 

can generally be repaired through addition of a new 

same-sized fastener for every two overdriven fasteners. 

To avoid splitting because of closely spaced nails, it 

may be necessary to predrill to 90% of the nail shank 

diameter for installation of new nails. For other 

conditions, such as cases where the addition of new 

connectors is not possible or where component damage 

is suspected, further investigation shall be conducted 

using the guidance of Section C10.3.8.1 (FEMA 310, 

Section 4.3.3.2).

C10.3.8.4 Condition of Steel

Should visual inspection or testing conducted in 

accordance with Section C10.3.8.1 reveal the presence 

of steel component or connection deterioration, further 

evaluation is needed. The source of the damage shall 

be identified and mitigated to preserve the remaining 

structure. In areas of significant deterioration, 

restoration of the material cross-section can be 

performed by the addition of plates or other reinforcing 

techniques. When sizing reinforcements, the design 

professional shall consider the effects of existing 

stresses in the original structure, load transfer, and 

strain compatibility. The demands on the deteriorated 

steel elements and components may also be reduced 

through careful addition of bracing or shear wall panels 

(FEMA 310, Section 4.3.3.3).

C10.3.8.5 Condition of Concrete

Should visual inspections or testing conducted in 

accordance with Section C10.3.8.1 reveal the presence 

of concrete component or reinforcing steel 

deterioration, further evaluation is needed. The source 

of the damage shall be identified and mitigated to 

preserve the remaining structure. Existing deteriorated 

material, including reinforcing steel, shall be removed 

to the limits defined by testing; reinforcing steel in 

good condition shall be cleaned and left in place for 

splicing purposes as appropriate. Cracks in otherwise 

sound material shall be evaluated to determine cause, 

and repaired as necessary using techniques appropriate 

to the source and activity level (FEMA 310, Section 

4.3.3.4).

C10.3.8.6 Post-Tensioning Anchors

Prestressed concrete systems may be adversely 

affected by cyclic deformations produced by 

earthquake motion. One rehabilitation process that 

may be considered is to add stiffness to the system. 

Another concern for these systems is the adverse 

effects of tendon corrosion. A thorough visual 

inspection of prestressed systems shall be performed to 

verify absence of concrete cracking or spalling, 

staining from embedded tendon corrosion, or other 

signs of damage along the tendon spans and at 

anchorage zones. If degradation is observed or 

suspected, more detailed evaluations will be required 

as indicated in Chapter 6. Rehabilitation of these 

systems, except for local anchorage repair, should be in 

accordance with the Systematic Rehabilitation 

provisions in this standard. Professionals with special 

prestressed concrete construction expertise should also 

be consulted for further interpretation of damage 

(FEMA 310, Section 4.3.3.5).
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-19

C10.3.8.7 Quality of Masonry

Should visual inspections or testing conducted in 

accordance with Section C10.3.8.1 reveal the presence 

of masonry components or construction deterioration, 

further evaluation is needed. Certain damage such as 

degraded mortar joints or simple cracking may be 

rehabilitated through repointing or rebuilding. If the 

wall is repointed, care should be taken to ensure that 

the new mortar is compatible with the existing 

masonry units and mortar, and that suitable wetting is 

performed. The strength of the new mortar is critical to 

load-carrying capacity and seismic performance. 

Significant degradation should be treated as specified 

in Chapter 7 of this standard (FEMA 310, Sections 

4.3.3.7, 4.3.3.8, 4.3.3.10, 4.3.3.11, and 4.3.3.12).

Table C10-1 W1: Wood Light Frame

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Shear Walls in Wood Frame Buildings

Shear Stress

Openings

Wall Detailing

Cripple Walls

Narrow Wood Shear Walls

Stucco Shear Walls

Gypsum Wallboard or Plaster Shear Walls

Diaphragm Openings

Diaphragm Stiffness/Strength

Spans

Diaphragm Continuity

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Condition of Wood

Table C10-2 W1A: Multistory, Multi-Unit, Wood 

Frame Construction

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Shear Walls in Wood Frame Buildings

Shear Stress

Openings

Wall Detailing

Cripple Walls

Narrow Wood Shear Walls

Stucco Shear Walls

Gypsum Wallboard or Plaster Shear Walls

Diaphragm Openings

Diaphragm Stiffness/Strength

Spans

Diaphragm Continuity

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Condition of Wood

Table C10-3 W2: Wood, Commercial, and 

Industrial

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Shear Walls in Wood Frame Buildings

Shear Stress

Openings

Wall Detailing

Cripple Walls

Narrow Wood Shear Walls

Stucco Shear Walls

Gypsum Wallboard or Plaster Shear Walls

Diaphragm Openings

Diaphragm Stiffness/Strength

Sheathing

Unblocked Diaphragms

Spans

Span-to-Depth Ratio

Diaphragm Continuity

Chord Continuity

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Condition of Wood 
10-20 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

 

 

 

Table C10-4 S1 and S1A: Steel Moment Frames 

with Stiff or Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Adjacent Buildings

Lateral Load Path at Pile Caps

Steel Moment Frames

Drift Check

Frame Concerns

Strong Column-Weak Beam

Connections

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Frame Shear Transfer

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Steel

Table C10-5 S2 and S2A: Steel Braced Frames 

with Stiff or Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Stress Level

Stiffness of Diagonals

Chevron or K-Bracing

Braced Frame Connections

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Frame Shear Transfer

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Steel

Table C10-6 S3: Steel Light Frames

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Steel Moment Frames

Frame Concerns

Masonry Shear Walls

Infill Walls

Steel Braced Frames

Stress Level

Braced Frame Connections

Re-entrant Corners

Diaphragm Openings

Diaphragm/Frame Shear Transfer

Wall Panels and Cladding

Light Gage Metal, Plastic, or Cementitious Roof Panels

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Condition of Steel

Table C10-7 S4: Steel Frames with Concrete 

Shear Walls

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Cast-in-Place Concrete Shear Walls

Shear Stress

Overturning

Coupling Beams

Boundary Component Detailing

Wall Reinforcement

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Wall Shear Transfer

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Steel

Condition of Concrete
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-21

Table C10-8 S5, S5A: Steel Frames with Infill 

Masonry Shear Walls and Stiff or 

Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Frames Not Part of the Lateral Force Resisting System

Complete Frames

Masonry Shear Walls

Reinforcing in Masonry Walls

Shear Stress

Reinforcing at Openings

Unreinforced Masonry Shear Walls

Proportions, Solid Walls

Infill Walls

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Span/Depth Ratio

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Steel

Quality of Masonry

Table C10-9 C1: Concrete Moment Frames

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Adjacent Buildings

Lateral Load Path at Pile Caps

Deflection Compatibility

Concrete Moment Frames

Quick Checks, Frame and Nonductile Detail Concerns

Precast Moment Frame Concerns

Frames Not Part of the Lateral Force Resisting System

Short “Captive” Columns

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Frame Shear Transfer

Precast Connections

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete
10-22 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Table C10-10 C2, C2A: Concrete Shear Walls 

with Stiff or Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Deflection Compatibility

Frames Not Part of the Lateral Force Resisting System

Short "Captive" Columns

Cast-in-Place Concrete Shear Walls

Shear Stress

Overturning

Coupling Beams

Boundary Component Detailing

Wall Reinforcement

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Sheathing

Diaphragm/Wall Shear Transfer

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete

Table C10-11 C3, C3A: Concrete Frames with 

Infill Masonry Shear Walls and Stiff 

or Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Deflection Compatibility

Frames Not Part of the Lateral Force Resisting System

Complete Frames

Masonry Shear Walls

Reinforcing in Masonry Walls

Shear Stress

Reinforcing at Openings

Unreinforced Masonry Shear Walls

Proportions, Solid Walls

Infill Walls

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Span/Depth Ratio

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete

Quality of Masonry
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-23

Table C10-12 PC1: Precast/Tilt-up Concrete 

Shear Walls with Flexible 

Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Deflection Compatibility

Precast Concrete Shear Walls

Panel-to-Panel Connections

Wall Openings

Collectors

Re-entrant Corners

Cross Ties

Diaphragm Openings

Diaphragm Stiffness/Strength

Sheathing

Unblocked Diaphragms

Span/Depth Ratio

Chord Continuity

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Girder/Wall Connections

Stiffness of Wall Anchors

Anchorage to Foundations

Condition of Foundation

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete

Table C10-13 PC1A: Precast/Tilt-up Concrete 

Shear Walls with Stiff Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Precast Concrete Shear Walls

Panel-to-Panel Connections

Wall Openings

Collectors

Re-entrant Corners

Diaphragm Openings 

Diaphragm Stiffness/Strength

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Girder/Wall Connections

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete
10-24 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Table C10-14 PC2: Precast Concrete Frames 

with Shear Walls

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Lateral Load Path at Pile Caps

Deflection Compatibility

Concrete Moment Frames

Precast Moment Frame Concerns

Cast-in-Place Concrete Shear Walls

Shear Stress

Overturning

Coupling Beams

Boundary Component Detailing

Wall Reinforcement

Re-entrant Corners

Cross Ties

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Girder/Wall Connections

Precast Connections

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete

Table C10-15 PC2A: Precast Concrete Frames 

Without Shear Walls

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Adjacent Buildings

Lateral Load Path at Pile Caps

Deflection Compatibility

Concrete Moment Frames

Precast Moment Frame Concerns

Frames Not Part of the Lateral-Force-Resisting System

Short Captive Columns

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Frame Shear Transfer

Precast Connections

Anchorage to Foundations

Condition of Foundations

Overturning

Lateral Loads

Geologic Site Hazards

Condition of Concrete
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-25

Table C10-16 RM1: Reinforced Masonry Bearing 

Wall Buildings with Flexible 

Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Masonry Shear Walls

Reinforcing in Masonry Walls

Shear Stress

Reinforcing at Openings

Re-entrant Corners

Cross Ties

Diaphragm Openings

Diaphragm Stiffness/Strength

Sheathing

Unblocked Diaphragms

Span/Depth Ratio

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Stiffness of Wall Anchors

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Quality of Masonry

Table C10-17 RM2: Reinforced Masonry Bearing 

Wall Buildings with Stiff 

Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Masonry Shear Walls

Reinforcing in Masonry Walls

Shear Stress

Reinforcing at Openings

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Quality of Masonry

Table C10-18 URM: Unreinforced Masonry 

Bearing Wall Buildings with 

Flexible Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Adjacent Buildings

Masonry Shear Walls

Unreinforced Masonry Shear Walls

Properties, Solid Walls

Re-entrant Corners

Cross Ties

Diaphragm Openings

Diaphragm Stiffness/Strength

Sheathing

Unblocked Diaphragms

Span/Depth Ratio

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Stiffness of Wall Anchors

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Quality of Masonry

Table C10-19 URMA: Unreinforced Masonry 

Bearing Walls Buildings with Stiff 

Diaphragms

Typical Deficiencies 

Load Path

Redundancy

Vertical Irregularities

Plan Irregularities

Adjacent Buildings

Masonry Shear Walls

Unreinforced Masonry Shear Walls

Properties, Solid Walls

Re-entrant Corners

Diaphragm Openings

Diaphragm Stiffness/Strength

Diaphragm/Wall Shear Transfer

Anchorage for Normal Forces

Anchorage to Foundations

Condition of Foundations

Geologic Site Hazards

Quality of Masonry
10-26 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers

FEMA 310 FEMA 178 FEMA 356 Standard

Section Section Heading Section Section Section Heading

4.3.1.1 Load Path 3.1 C10.3.1.1 Load Path

4.3.1.2 Adjacent Buildings 3.4 C10.3.1.5 Adjacent Buildings

4.3.1.3 Mezzanines — C10.3.6.8 Mezzanine Connections

4.3.2 Configuration 3.3 C10.3.1 Building Systems

4.3.2.1 Weak Story 3.3.1 C10.3.1.3 Vertical Irregularities

4.3.2.2 Soft Story 3.3.2 C10.3.1.3 Vertical Irregularities

4.3.2.3 Geometry 3.3.3 C10.3.1.3 Vertical Irregularities

4.3.2.4 Vertical Discontinuities 3.3.5 C10.3.1.3 Vertical Irregularities

4.3.2.5 Mass 3.3.4 C10.3.1.3 Vertical Irregularities

4.3.2.6 Torsion 3.3.6 C10.3.1.4 Plan Irregularities

4.3.3 Condition of Materials 3.5 C10.3.8 Evaluation of Materials and Conditions

4.3.3.1 Deterioration of Wood 3.5.1 C10.3.8.2 Condition of Wood

4.3.3.2 Wood Structural Panel Shear Wall 

Fasteners

3.5.2 C10.3.8.3 Overdriven Fasteners

4.3.3.3 Deterioration of Steel 3.5.3 C10.3.8.4 Condition of Steel

4.3.3.4 Deterioration of Concrete 3.5.4 C10.3.8.5 Condition of Concrete

4.3.3.5 Post-Tensioning Anchors 3.5.5 C10.3.8.6 Post-Tensioning Anchors

4.3.3.6 Precast Concrete Walls 3.5.8 C10.3.8.5 Condition of Concrete

4.3.3.7 Masonry Units 3.5.10 C10.3.8.7 Quality of Masonry

4.3.3.8 Masonry Joints 3.5.9 C10.3.8.7 Quality of Masonry

4.3.3.9 Concrete Wall Cracks 3.5.6 C10.3.8.5 Condition of Concrete

4.3.3.10 Reinforced Masonry Wall Cracks — C10.3.8.7 Quality of Masonry

4.3.3.11 Unreinforced Masonry Wall Cracks — C10.3.8.7 Quality of Masonry

4.3.3.12 Cracks in Infill Walls 3.5.11 C10.3.8.7 Quality of Masonry

4.3.3.13 Cracks in Boundary Columns 3.5.7 C10.3.8.5 Condition of Concrete

4.4.1.1.1 Redundancy 3.2 C10.3.1.2 Redundancy

4.4.1.2 Frames with Infill Walls 4.1 C10.3.3 Shear Walls

4.4.1.2.1 Interfering Walls 4.1.4 C10.3.3.3.6 Infill Walls

4.4.1.3 Steel Moment Frames 4.2 C10.3.2.1 Steel Moment Frames

4.4.1.3.1 Drift Check 4.2.1 C10.3.2.1.1 Drift

4.4.1.3.2 Axial Stress Check — C10.3.2.1.2 Frames

4.4.1.3.3 Moment-Resisting Connections 4.2.4 C10.3.2.1.4 Connections

4.4.1.3.4 Panel Zones 4.2.6 C10.3.2.1.4 Connections

4.4.1.3.5 Column Splices 4.2.5 C10.3.2.1.2 Frames

4.4.1.3.6 Strong Column-Weak Beam 4.2.8 C10.3.2.1.3 Strong Column-Weak Beam

4.4.1.3.7 Compact Members 4.2.2 C10.3.2.1.2 Frames

4.4.1.3.8 Beam Penetration 4.2.3 C10.3.2.1.2 Frames
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-27

4.4.1.3.9 Girder Flange Continuity 4.2.7 C10.3.2.1.4 Connections

4.4.1.3.10 Out-of-Plane Bracing 4.2.9 C10.3.2.1.2 Frames

4.4.1.3.11 Bottom Flange Bracing — C10.3.2.1.2 Frames

4.4.1.4 Concrete Moment Frames 4.3 C10.3.2.2 Concrete Moment Frames

4.4.1.4.1 Shear Stress Check 4.3.1 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.2 Axial Stress Check — C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.3 Flat Slab Frames 4.3.15 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.4 Prestressed Frame Elements 4.3.3 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.5 Short Captive Columns — C10.3.2.3.2 Short Captive Columns

4.4.1.4.6 No Shear Failures 4.3.5 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.7 Strong Column-Weak Beam 4.3.6 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.8 Beam Bars 4.3.10 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.9 Column-Bar Splices 4.3.9 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.10 Beam-Bar Splices 4.3.11 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.11 Column-Tie Spacing 4.3.8 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.12 Stirrup Spacing 4.3.12 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.13 Joint Reinforcing 4.3.14 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.14 Joint Eccentricity 4.3.4 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.4.15 Stirrup and Tie Hooks 4.3.7 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.3.2 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.3.13 C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.1.5 Precast Moment Frames 4.4 C10.3.2.2.2 Precast Moment Frames

4.4.1.5.1 Precast Connection Check — C10.3.2.2.2 Precast Moment Frames

4.4.1.5.2 Precast Frames 4.4.1 C10.3.2.2.2 Precast Moment Frames

4.4.1.5.3 Precast Connections 4.4.2 C10.3.6.5 Precast Connections

4.4.1.6 Frames Not Part of the 

Lateral-Force-Resisting System

4.5 C10.3.2.3 Frames Not Part of the Lateral-ForceResisting System

4.4.1.6.1 Complete Frames 4.5.1 C10.3.2.3.1 Complete Frames

4.4.1.6.2 Deflection Compatibility — C10.3.1.7 Deflection Compatibility

4.4.1.6.3 Flat Slabs — C10.3.2.2.1 Frame and Nonductile Detail Concerns

4.4.2.2 Concrete Shear Walls 5.1 C10.3.3 Shear Walls

4.4.2.1.1 Redundancy 3.2 C10.3.1.2 Redundancy

4.4.2.2.1 Shear Stress Check 5.1.1 C10.3.3.1.1 Shearing Stress

4.4.2.2.2 Reinforcing Steel 5.1.7 C10.3.3.1.5 Wall Reinforcement

4.4.2.2.3 Coupling Beams 5.1.3 C10.3.3.1.3 Coupling Beams

4.4.2.2.4 Overturning 5.1.2 C10.3.3.1.2 Overturning

4.4.2.2.5 Confinement Reinforcing 5.1.6 C10.3.3.1.4 Boundary Component Detailing

4.4.2.2.6 Reinforcing at Openings 5.1.8 C10.3.3.1.5 Wall Reinforcement

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers (continued)

FEMA 310 FEMA 178 FEMA 356 Standard
10-28 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

4.4.2.2.7 Wall Thickness — C10.3.3.1.1 Shearing Stress

4.4.2.2.8 Wall Connections 5.1.5 C10.3.3.1.4 Boundary Component Detailing

4.4.2.2.9 Column Splices 5.1.4 C10.3.3.1.4 Boundary Component Detailing

4.4.2.3 Precast Concrete Shear Walls 5.2 C10.3.3.2 Precast Concrete Shear Walls

4.4.2.3.1 Shear Stress Check — C10.3.3.1.1 Shearing Stress

4.4.2.3.2 Reinforcing Steel — C10.3.3.1.5 Wall Reinforcement

4.4.2.3.3 Wall Openings 5.2.2 C10.3.3.2.2 Wall Openings

4.4.2.3.4 Corner Openings 5.2.3 C10.3.3.2.3 Collectors

4.4.2.3.5 Panel-to-Panel Connections 5.2.1 C10.3.3.2.1 Panel-to-Panel Connections

4.4.2.3.6 Wall Thickness — C10.3.3.1.1 Shearing Stress

4.4.2.4 Reinforced Masonry Shear Walls 5.3 C10.3.3.3 Masonry Shear Walls

4.4.2.4.1 Shear Stress Check 5.3.1 C10.3.3.3.2 Shearing Stress

4.4.2.4.2 Reinforcing Steel 5.3.2 C10.3.3.3.1 Reinforcing in Masonry Walls

4.4.2.4.3 Reinforcing at Openings 5.3.3 C10.3.3.3.3 Reinforcing at Openings

4.4.2.4.4 Proportions — C10.3.3.3.5 Proportions of Solid Walls

4.4.2.5 Unreinforced Masonry Shear Walls 5.4 C10.3.3.3.4 Unreinforced Masonry Shear Walls

4.4.2.5.1 Shear Stress Check 5.4.1 C10.3.3.3.4 Unreinforced Masonry Shear Walls

4.4.2.5.2 Proportions — C10.3.3.3.5 Proportions of Solid Walls

4.4.2.5.3 Masonry Lay-up 5.4.2 C10.3.3.3.4 Unreinforced Masonry Shear Walls

4.4.2.6 Infill Walls in Frames 5.5 C10.3.3.3.6 Infill Walls

4.4.2.6.1 Wall Connections 5.5.4 C10.3.3.3.6 Infill Walls

4.4.2.6.2 Proportions 5.5.1 C10.3.3.3.5 Proportions of Solid Walls

4.4.2.6.3 Solid Walls 5.5.2 C10.3.3.3.5 Proportions of Solid Walls

4.4.2.6.4 Infill Walls 5.5.3 C10.3.3.3.6 Infill Walls

4.4.2.7 Walls in Wood Frame Buildings 5.6 C10.3.3.4 Shear Walls in Wood Frame Buildings

4.4.2.7.1 Shear Stress Check 5.6.1 C10.3.3.4.1 Shear Stress

4.4.2.7.2 Stucco (Exterior Plaster) Shear Walls — C10.3.3.4.6 Stucco Shear Walls

4.4.2.7.3 Gypsum Wallboard or Plaster Shear 

Walls

— C10.3.3.4.7 Gypsum Wallboard or Plaster Shear 

Walls

4.4.2.7.4 Narrow Wood Shear Walls — C10.3.3.4.5 Narrow Wood Shear Walls

4.4.2.7.5 Walls Connected Through Floors — C10.3.3.4.3 Wall Detailing

4.4.2.7.6 Hillside Site — C10.3.3.4.4 Cripple Walls

4.4.2.7.7 Cripple Walls 5.6.4 C10.3.3.4.4 Cripple Walls

4.4.2.7.8 Openings 5.6.2 C10.3.3.4.2 Openings

4.4.2.7.9 Hold-Down Anchors 5.6.3 C10.3.3.4.3 Wall Detailing

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers (continued)

FEMA 310 FEMA 178 FEMA 356 Standard
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-29

4.4.3.1 Braced Frames 6.1 C10.3.4 Steel Braced Frames

4.4.3.1.1 Redundancy 3.2 C10.3.1.2 Redundancy

4.4.3.1.2 Axial Stress Check 6.1.1 C10.3.4.1 System Concerns

4.4.3.1.3 Slenderness of Diagonals 6.1.2 C10.3.4.2 Stiffness of Diagonals

4.4.3.1.4 Connection Strength 6.1.6 C10.3.4.4 Braced Frame Connections

4.4.3.1.5 Column Splices 6.1.7 C10.3.4.4 Braced Frame Connections

4.4.3.1.6 Out-of-Plane Bracing — C10.3.4.1 System Concerns

4.4.3.2 Concentrically Braced Frames — C10.3.4 Steel Braced Frames

4.4.3.2.1 K-Bracing — C10.3.4.3 Chevron or K-Bracing

4.4.3.2.2 Tension-Only Braces 6.1.3 C10.3.4.2 Stiffness of Diagonals

4.4.3.2.3 Chevron Bracing 6.1.4 C10.3.4.3 Chevron or K-Bracing

4.4.3.2.4 Concentric Joints 6.1.5 C10.3.4.4 Braced Frame Connections

4.4.3.3 Eccentrically Braced Frames — C10.3.4.1 System Concerns

4.5 Diaphragms 7.1 C10.3.5 Diaphragms

4.5.1.1 Diaphragm Continuity 7.2.5 C10.3.5.4.5 Diaphragm Continuity

4.5.1.2 Cross Ties 7.1.2 C10.3.5.2 Cross Ties

4.5.1.3 Roof Chord Continuity 7.2.6 C10.3.5.4.6 Chord Continuity

4.5.1.4 Openings at Shear Walls 7.1.4 C10.3.5.3 Diaphragm Openings

4.5.1.5 Openings at Braced Frames 7.1.5 C10.3.5.3 Diaphragm Openings

4.5.1.6 Openings at Exterior Masonry Shear 

Walls

7.1.6 C10.3.5.3

4.5.1.7 Plan Irregularities 7.1.1 C10.3.5.1 Re-entrant Corners

4.5.1.8 Reinforcing at Openings 7.1.3 C10.3.5.3 Diaphragm Openings

4.5.2 Wood Diaphragms 7.2 C10.3.5 Diaphragms

4.5.2.1 Straight Sheathing 7.2.1 C10.3.5.4.1 Board Sheathing

4.5.2.2 Spans 7.2.2 C10.3.5.4.3 Spans

4.5.2.3 Unblocked Diaphragms 7.2.3 C10.3.5.4.2 Unblocked Diaphragms

7.2.4 C10.3.5.4.4 Span-to-Depth Ratio

4.5.3 Metal Deck Diaphragms — C10.3.5 Diaphragms

4.5.3.1 Non-Concrete Diaphragms — C10.3.5 Diaphragms

4.5.4 Concrete Diaphragms — C10.3.5 Diaphragms

4.5.5 Precast Concrete Diaphragms — C10.3.5 Diaphragms

4.5.5.1 Topping Slab — C10.3.5 Diaphragms

4.5.6 Horizontal Bracing — C10.3.5 Diaphragms

4.5.7.1 Other Diaphragms — C10.3.5 Diaphragms

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers (continued)

FEMA 310 FEMA 178 FEMA 356 Standard
10-30 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation

4.6.1 Anchorage for Normal Forces 8.2 C10.3.6.3 Anchorage for Normal Forces

4.6.1.1 Wall Anchorage 8.2.2 C10.3.6.3 Anchorage for Normal Forces

4.6.1.2 Wood Ledgers 8.2.1 C10.3.6.3 Anchorage for Normal Forces

4.6.1.3 Anchor Spacing 8.2.4 C10.3.6.3 Anchorage for Normal Forces

4.6.1.4 Precast Panel Connections 8.2.5 C10.3.6.3 Anchorage for Normal Forces

4.6.1.5 Stiffness of Wall Anchors 8.2.3 C10.3.6.3 Anchorage for Normal Forces

4.6.2 Shear Transfer 8.3 C10.3.6 Connections

4.6.2.1 Transfer to Shear Walls 8.3.1 C10.3.6.1 Diaphragm/Wall Shear Transfer

4.6.2.2 Transfer to Steel Frames 8.3.2 C10.3.6.2 Diaphragm/Frame Shear Transfer

4.6.2.3 Topping Slab to Walls and Frames 8.3.3 C10.3.6.1 Diaphragm/Wall Shear Transfer

4.6.3 Vertical Components 8.4 C10.3.7.1 Anchorage to Foundations

4.6.3.1 Steel Columns 8.4.1 C10.3.7.1 Anchorage to Foundations

4.6.3.2 Concrete Columns 8.4.2 C10.3.7.1 Anchorage to Foundations

4.6.3.3 Wood Posts 8.4.3 C10.3.7.1 Anchorage to Foundations

4.6.3.4 Wood Sills 8.4.7 C10.3.7.1 Anchorage to Foundations

4.6.3.5 Foundation Dowels 8.4.4 C10.3.7.1 Anchorage to Foundations

4.6.3.6 Shear-Wall-Boundary Columns 8.4.5 C10.3.7.1 Anchorage to Foundations

4.6.3.7 Precast Wall Panels — C10.3.7.1 Anchorage to Foundations

4.6.3.8 Wall Panels 8.4.6 C10.3.7.1 Anchorage to Foundations

4.6.3.9 Wood Sill Bolts 8.4.7 C10.3.7.1 Anchorage to Foundations

4.6.3.10 Lateral Load Path at Pile Caps — C10.3.7.4 Lateral Loads

4.6.4 Interconnection of Elements 8.5 C10.3.6 Connections

4.6.4.1 Girder/Column Connection C10.3.6.4 Girder-Wall Connections

4.6.4.2 Girders 8.5.1 C10.3.6.4 Girder-Wall Connections

4.6.4.3 Corbel Bearing 8.5.2 C10.3.6.4 Girder-Wall Connections

4.6.4.4 Corbel Connections 8.5.3 C10.3.6.4 Girder-Wall Connections

4.6.5 Panel Connections — C10.3.6 Connections

4.6.5.1 Roof Panels 8.6.1 C10.3.6.7 Light Gage Metal, Plastic, or 

Cementitious Roof Panels

4.6.5.2 Wall Panels 8.6.2 C10.3.6.6 Wall Panels and Cladding

4.6.5.3 Roof Panel Connections — C10.3.6.7 Light Gage Metal, Plastic, or 

Cementitious Roof Panels

4.7.1 Geologic Site Hazards 9.3 C10.3.7 Foundations and Geologic Hazards

4.7.1.1 Liquefaction 9.3.1 C10.3.7.5 Geologic Site Hazards

4.7.1.2 Slope Failure 9.3.2 C10.3.7.5 Geologic Site Hazards

4.7.1.3 Surface Fault Rupture 9.3.3 C10.3.7.5 Geologic Site Hazards

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers (continued)

FEMA 310 FEMA 178 FEMA 356 Standard
 Chapter 10: Simplified Rehabilitation

FEMA 356 Seismic Rehabilitation Prestandard 10-31

4.7.2 Condition of Foundations 9.1 C10.3.7.2 Condition of Foundations

4.7.2.1 Foundation Performance 9.1.1 C10.3.7.2 Condition of Foundations

4.7.2.2 Deterioration 9.1.2 C10.3.7.2 Condition of Foundations

4.7.3 Capacity of Foundations 9.2 C10.3.7 Foundations and Geologic Hazards

4.7.3.1 Pole Foundations 9.2.4 C10.3.7.4 Lateral Loads

4.7.3.2 Overturning 9.2.1 C10.3.7.3 Overturning 

4.7.3.3 Ties Between Foundation Elements 9.2.2 C10.3.7.4 Lateral Loads

4.7.3.4 Deep Foundations 9.2.3 C10.3.7.4 Lateral Loads

4.7.3.5 Sloping Sites 9.2.5 C10.3.7.4 Lateral Loads

Table C10-20 Cross-Reference Between this Standard, FEMA 310 and FEMA 178 

Deficiency Reference Numbers (continued)

FEMA 310 FEMA 178 FEMA 356 Standard
10-32 Seismic Rehabilitation Prestandard FEMA 356

 Chapter 10: Simplified Rehabilitation
FEMA 356 Seismic Rehabilitation Prestandard 11-1

11. Architectural, Mechanical, and Electrical Components

11.1 Scope

This chapter sets forth requirements for the seismic 

rehabilitation of existing architectural, mechanical, and 

electrical components and systems that are permanently 

installed in, or are an integral part of, a building system. 

Procedures of this chapter are applicable to both the 

Simplified and Systematic Rehabilitation Methods. 

Requirements are provided for nonstructural 

components that are rehabilitated to the Immediate 

Occupancy, Life Safety, and Hazards Reduced 

Nonstructural Performance Levels. Requirements for 

Operational Performance are outside the scope of this 

standard.

Sections 11.2, 11.3, 11.4, and 11.5 provide requirements 

for condition assessment, component evaluation, 

Rehabilitation Objectives, and structural-nonstructural 

interaction. Section 11.6 defines acceleration and 

deformation sensitive components. Section 11.7 

specifies procedures for determining design forces and 

deformations on nonstructural components. 

Section 11.8 identifies rehabilitation methods. 

Sections 11.9, 11.10, and 11.11 specify evaluation and 

acceptance criteria for architectural components; 

mechanical, electrical, and plumbing (MEP) systems; 

and other equipment.

New nonstructural components installed in existing 

buildings shall conform to the requirements for similar 

components in new buildings.

C11.1 Scope

The assessment process necessary to make a final 

determination of which nonstructural components are 

to be rehabilitated is not part of this standard, but the 

subject is discussed briefly in Section 11.3.

The core of this chapter is contained in Table 11-1, 

which provides:

1. A list of nonstructural components subject to the 

Hazards Reduced, Life Safety and Immediate 

Occupancy requirements of this standard.

2. Rehabilitation requirements related to the zone of 

seismicity and Hazards Reduced, Life Safety, and 

Immediate Occupancy Performance Levels. 

Requirements for Operational Performance are not 

included in this standard. Requirements for Hazards 

Reduced Performance will generally be based on 

the requirements for Life Safety Performance, so 

separate evaluation procedures and acceptance 

criteria have not been provided.

3. Identification of the required evaluation procedure 

(analytical or prescriptive).

Section 11.4 provides general requirements and 

discussion of Rehabilitation Objectives, Performance 

Levels, and Performance Ranges as they pertain to 

nonstructural components. Criteria for means of egress 

are not specifically included in this standard.

Section 11.5 briefly discusses structural-nonstructural 

interaction, and Section 11.6 provides general 

requirements for acceptance criteria for accelerationsensitive and deformation-sensitive components, and 

those sensitive to both kinds of response.

Section 11.7 provides sets of equations for a simple 

“default” force analysis, as well as an extended 

analysis method that considers a number of additional 

factors. This section defines the Analytical Procedure 

for determining drift ratios and relative displacement, 

and outlines general requirements for the Prescriptive 

Procedure.

Section 11.8 notes the general ways in which 

nonstructural rehabilitation is carried out.

Sections 11.9, 11.10, and 11.11 provide the 

rehabilitation criteria for each component category 

identified in Table 11-1. For each component the 

following information is given.

1. Definition and scope.

2. Component behavior and rehabilitation concepts.

3. Acceptance criteria.

4. Evaluation requirements.
11-2 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.2 Procedure

Nonstructural components shall be rehabilitated by 

completing the following steps.

1. The rehabilitation objectives shall be established in 

accordance with Section 11.4, which includes 

selection of a Nonstructural Performance Level and 

earthquake hazard level. The zone of seismicity shall 

be determined in accordance with Section 1.6.3. A 

target Building Performance Level that includes 

Nonstructural Performance Not Considered need not 

comply with the provisions of this chapter.

2. A walk-through and condition assessment shall be 

performed in accordance with Sections 11.2.1 and 

11.2.2.

3. Analysis and rehabilitation requirements for the 

selected Nonstructural Performance Level and 

appropriate zone of seismicity shall be determined 

for nonstructural components using Table 11-1. 

“Yes” indicates that rehabilitation shall be required 

if the component does not meet applicable 

acceptance criteria specified in Section 11.3.2.

4. Interaction between structural and nonstructural 

components shall be considered in accordance with 

Section 11.5.

5. The classification of each type of nonstructural 

component shall be determined in accordance with 

Section 11.6.

6. Evaluation shall be conducted in accordance with 

Section 11.7 using the procedure specified in Table 

11-1. The acceptability of bracing elements and 

connections between nonstructural components and 

the structure shall be determined in accordance with 

Section 11.3.2.

7. Nonstructural components not meeting the 

requirements of the selected Nonstructural 

Performance Level shall be rehabilitated in 

accordance with Section 11.8. 

11.2.1 Condition Assessment

A condition assessment of nonstructural components 

shall be performed as part of the nonstructural 

rehabilitation process. As a minimum, this assessment 

shall determine the following:

1. The presence and configuration of each type of 

nonstructural component and its attachment to the 

structure.

2. The physical condition of each type of nonstructural 

component and whether or not degradation is 

present.

3. The presence of nonstructural components that 

potentially influence overall building performance.

11.2.2 Sample Size

Direct visual inspection shall be performed on each type 

of nonstructural component in the building as follows:

1. If detailed drawings are available, at least one 

sample of each type of nonstructural component 

shall be observed. If no deviations from the 

drawings exist, the sample shall be considered 

representative of installed conditions. If deviations 

are observed, then at least 10% of all occurrences of 

the component shall be observed.

2. If detailed drawings are not available, at least three 

samples of each type of nonstructural component 

shall be observed. If no deviations among the three 

components are observed, the sample shall be 

considered representative of installed conditions. If 

deviations are observed, at least 20% of all 

occurrences of the component shall be observed. 

C11.2 Procedure

When Hazards Reduced Performance is used, the 

engineer should consider the location of nonstructural 

components relative to areas of public occupancy. The 

owner and building official should be consulted to 

establish the areas of the building for which 

nonstructural hazards will be considered. Other 

nonstructural components, such as those designated by 

the owner also should be included in those that are 

evaluated.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-3

Table 11-1 Nonstructural Components: Applicability of Hazards Reduced, Life Safety and Immediate 

Occupancy Requirements and Methods of Analysis

COMPONENT

Performance Level

Evaluation 

IO Procedure

Seismicity

High & Moderate 

Seismicity

Low

Seismicity

LS HR LS HR

ARCHITECTURAL (Section 11.9)

1. Exterior Wall Elements

Adhered Veneer Yes Yes Yes15 No No F/D

Anchored Veneer Yes Yes Yes15 No No F/D

Glass Blocks Yes Yes Yes15 No No F/D

Prefabricated Panels Yes Yes Yes15 Yes Yes15 F/D

Glazed Exterior Wall Systems Yes Yes Yes15 Yes Yes15 F/D/PR

2. Partitions 

Heavy Yes Yes Yes15 No No F/D

Light Yes No No No No F/D

Glazed Yes Yes Yes15 Yes Yes15 F/D/PR

3. Interior Veneers 

Stone, Including Marble Yes Yes18 Yes15 No No F/D

4. Ceilings 

Directly Applied to Structure Yes No13 No15 No No F

Dropped Furred Gypsum Board Yes No No No No F

Suspended Lath and Plaster Yes Yes Yes15 No No F

Suspended Integrated Ceiling Yes No11 No No11 No PR

5. Parapets and Appendages Yes Yes Yes15 Yes Yes F1

6. Canopies and Marquees Yes Yes Yes15 Yes Yes F

7. Chimneys and Stacks Yes Yes Yes15 No No F2

8. Stairs Yes Yes No Yes No *

MECHANICAL EQUIPMENT (Section 11.10)

1. Mechanical Equipment 

Boilers, Furnaces, Pumps, and Chillers Yes Yes No Yes No F

General Mfg. and Process Machinery Yes No3 No No No F

HVAC Equipment, Vibration-Isolated Yes No3 No No No F

HVAC Equipment, Non-Vibration-Isolated Yes No3 No No No F

HVAC Equipment, Mounted In-Line with 

Ductwork

Yes No3 No No No PR

2. Storage Vessels and Water Heaters 

Structurally Supported Vessels (Category 1) Yes No3 No No No Note4

Flat Bottom Vessels (Category 2) Yes No3 No No No Note5

3. Pressure Piping Yes Yes No No No Note5

4. Fire Suppression Piping Yes Yes No No No PR
11-4 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

5. Fluid Piping, not Fire Suppression 

Hazardous Materials Yes Yes Yes12 Yes Yes12 PR/F/D

Nonhazardous Materials Yes14 No No No No PR/F/D

6. Ductwork Yes No6 No No No PR

ELECTRICAL AND COMMUNICATIONS (Section 11.11)

1. Electrical and Communications 

Equipment 

Yes No7 No No No F

2. Electrical and Communications 

Distribution Equipment 

Yes No8 No No No PR

3. Light Fixtures 

Recessed No No No No No PR17

Surface Mounted No No No No No PR17

Integrated Ceiling Yes Yes Yes15 No No PR

Pendant Yes No9 No No No F/PR

FURNISHINGS AND INTERIOR EQUIPMENT (Section 11.11)

1. Storage Racks Yes Yes10 Yes16 No No F

2. Bookcases Yes Yes No No No F

3. Computer Access Floors Yes No No No No PR/FD

4. Hazardous Materials Storage Yes Yes No12 No12 No12 PR

5. Computer and Communication Racks Yes No No No No PR/F/D

6. Elevators Yes Yes No No No F/D/PR

7. Conveyors Yes No No No No F/D/PR

1. Rehabilitation of unreinforced masonry parapets not over 4 ft. in height by the Prescriptive Design Concept shall be permitted.

2. Rehabilitation of residential masonry chimneys by the Prescriptive Design Concept shall be permitted.

3. Equipment type A or B that is 6 ft. or more in height, equipment type C, equipment forming part of an emergency power system, and gas-fired equipment 

in occupied or unoccupied space shall be rehabilitated to the Life Safety Nonstructual Performance Level in areas of High Seismicity. In areas of Moderate 

Seismicity, this equipment need not be considered.

4. Rehabilitation of residential water heaters with capacity less than 100 gal. by the Prescriptive Procedure shall be permitted. Other vessels shall meet the 

force provisions of Sections 11.7.3 or 11.7.4.

5. Rehabilitation of vessels or piping systems according to Prescriptive Standards shall be permitted. Storage vessels shall meet the force provisions of 

Sections 11.7.3 or 11.7.4. Piping shall meet drift provisions of Section 11.7.5 and the force provisions of Sections 11.7.3 or 11.7.4.

6. Ductwork that conveys hazardous materials, exceeds 6 sq. ft. in cross-sectional area, or is suspended more than 12 in. from top of duct to supporting 

structure at any support point shall meet the requirements of the selected Rehabilitation Objective.

7. Equipment that is 6 ft. or more in height, weighs over 20 lbs., or forms part of an emergency power and/or communication system shall meet the Life 

Safety Nonstructural Performance Level.

8. Equipment that forms part of an emergency lighting, power, and/or communication system shall meet the Life Safety Nonstructural Performance Level.

9. Fixtures that exceed 20 lbs. per support shall meet the Life Safety Nonstructural Performance Level.

(continued)

Table 11-1 Nonstructural Components: Applicability of Hazards Reduced, Life Safety and Immediate 

Occupancy Requirements and Methods of Analysis (continued)

COMPONENT

Performance Level

Evaluation 

IO Procedure

Seismicity

High & Moderate 

Seismicity

Low

Seismicity

LS HR LS HR
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-5

10. Rehabilitation shall not be required for storage racks in unoccupied spaces.

11. Panels that exceed 2 lbs./sq. ft., or for which Enhanced Rehabilitation Objectives have been selected, shall meet the Life Safety Nonstructural Performance 

Level.

12. Where material is in close proximity to occupancy such that leakage could cause an immediate life safety threat, the requirements of the selected 

Rehabilitation Objective shall be met.

13. Plaster ceilings on metal or wood lath over 10 sq. ft. in area shall meet the Life Safety Nonstructural Performance Level.

14. Unbraced pressure pipes with a 2-inch or larger diameter and suspended more than 12 inches from the top of the pipe to the supporting structure at any 

support point shall meet the requirements of the selected Rehabilitation Objective.

15. Where heavy nonstructural components are located in areas of public occupancy or egress, the components shall meet the Life Safety Nonstructural 

Performance Level.

16. Storage racks in areas of public assembly shall meet the requirements of the selected Rehabilitation Objective.

17. Evaluation for the presence of an adequate attachment shall be checked as described in Section 11.10.9.3.

18. In areas of Moderate Seismicity, interior veneers of ceramic tile need not be considered.

Key:

HR Hazards Reduced Nonstructural Performance Level

LS Life Safety Nonstructural Performance Level 

IO Immediate Occupancy Nonstructural Performance Level

PR Use of the Prescriptive Procedure of Section 11.7.2 shall be permitted.

F The Analytical Procedure of Section 11.7.1 shall be implemented and a force analysis shall be performed in accordance with Sections 11.7.3 or 11.7.4.

F/D The Analytical Procedure of Section 11.7.1 shall be implemented and a force and deformation analysis shall be performed in accordance with 

Sections 11.7.4 and 11.7.5, respectively.

* Individual components shall be rehabilitated as required.

Table 11-1 Nonstructural Components: Applicability of Hazards Reduced, Life Safety and Immediate 

Occupancy Requirements and Methods of Analysis (continued)

COMPONENT

Performance Level

Evaluation 

IO Procedure

Seismicity

High & Moderate 

Seismicity

Low

Seismicity

LS HR LS HR
11-6 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.3 Historical and Component 

Evaluation Considerations

11.3.1 Historical Information

Available construction documents, equipment 

specification and data, and as-built information shall be 

obtained as specified in Section 2.2. Data on 

nonstructural components and equipment shall be 

collected to ascertain the year of manufacture or 

installation of nonstructural components to justify 

selection of rehabilitation approaches and techniques 

based on available historical information, prevailing 

codes, and assessment of existing condition.

C11.3.1 Historical Information

The architectural, mechanical, and electrical 

components and systems of a historic building may be 

historically significant, especially if they are original to 

the building, very old, or innovative. Historic buildings 

may also contain hazardous materials, such as lead 

pipes and asbestos, that may or may not pose a hazard 

depending on their location, condition, use or 

abandonment, containment, and/or disturbance during 

the rehabilitation.

C11.3.1.1 Background

Prior to the 1961 Uniform Building Code and the 1964 

Alaska earthquake, architectural components and 

mechanical and electrical systems for buildings had 

typically been designed with little, if any, regard to 

stability when subjected to seismic forces. By the time 

of the 1971 San Fernando earthquake, it became clear 

that damage to nonstructural elements could result in 

serious casualties, severe building functional 

impairment, and major economic losses, even when 

structural damage was not significant (Lagorio, 1990). 

This historical perspective presents the background for 

the development of building code provisions, together 

with a historical review of professional and 

construction practices related to the seismic design and 

construction of nonstructural components.

Since the 1964 Alaska earthquake, the poor 

performance of nonstructural elements has been 

identified in earthquake reconnaissance reports. 

Subsequent editions of the Uniform Building Code

(ICBO, 1994), as well as California and Federal codes 

and laws have increased both the scope and strictness 

of nonstructural seismic provisions in an attempt to 

achieve better performance. Table C11-1 and Table 

C11-2 provide a comprehensive list of nonstructural 

hazards that have been observed in these earthquakes.

The following quote, taken from statements made after 

the Alaska earthquake, characterizes the hazard 

nonstructural components pose to building occupants:

“If, during an earthquake, [building occupants] 

must exit through a shower of falling light fixtures 

and ceilings, maneuver through shifting and 

toppling furniture and equipment, stumble down 

dark corridors and debris-laden stairs, and then be 

met at the street by falling glass, veneers, or facade 

elements, then the building cannot be described as a 

safe structure.”

(Ayres and Sun, 1973a)

In reviewing the design and construction of 

architectural nonstructural components in this century, 

four general phases can be distinguished.

A. Phase 1: 1900 to 1920s

Buildings featured monumental classical architecture, 

generally with a steel frame structure using stone 

facing with a backing of unreinforced masonry and 

concrete. Interior partitions were of unreinforced 

hollow clay tile or brick unit masonry, or wood 

partitions with wood lath and plaster. These buildings 

had natural ventilation systems with hot water radiators 

(later, forced-air), and surface- or pendant-mounted 

incandescent light fixtures.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-7

B. Phase 2: 1930s to 1950s

Buildings were characterized by poured-in-place 

reinforced concrete or steel frame structures, 

employing columns and (in California) limited exterior 

and interior shear walls. Windows were large and 

horizontal. Interior partitions of unreinforced hollow 

clay tile or concrete block unit masonry, or light wood 

frame partitions with plaster, were gradually replaced 

by gypsum. Suspended ceilings and fluorescent lights 

arrived, generally surface- or pendant-mounted. Air 

conditioning (cooling) was introduced and HVAC 

systems became more complex, with increased 

demands for duct space.

C. Phase 3: 1950s to 1960s

This phase saw the advent of simple rectangular metal 

or reinforced concrete frame structures (“International 

Style”), and metal and glass curtain walls with a 

variety of opaque claddings (porcelain enamel, 

ceramic tile, concrete, cement plaster). Interior 

partitions became primarily metal studs and gypsum 

board. Proprietary suspended ceilings were developed 

using wire-hung metal grids with infill of acoustic 

panels, lighting fixtures, and air diffusion units. HVAC 

systems increased in size, requiring large mechanical 

rooms and increased above-ceiling space for ducts. 

Sprinklers and more advanced electrical control 

systems were introduced, and more HVAC equipment 

was spring-mounted to prevent transmission of motor 

vibration.

D. Phase 4: 1960s to Date

This period saw the advent of exterior precast concrete 

and, in the 1980s, glass fibre reinforced concrete 

(GFRC) cladding. Interior partition systems of metal 

studs and gypsum board, demountable partitions, and 

suspended ceiling systems become catalog proprietary 

items. The evolution of the late 1970s architectural 

style (“Post-Modern”) resulted in less regular forms 

and much more interior and exterior decoration, much 

of it accomplished by nonstructural components: 

assemblies of glass, metal panel, GFRC, and natural 

stone cladding for the exteriors, and use of gypsum 

board for exaggerated structural concealment and 

form-making in interiors. Suspended ceilings and 

HVAC systems changed little, but the advent of office 

landscaping often reduced floor-to-ceiling partitions to 

almost nothing in general office space. Starting in the 

1980s, the advent of the “smart” office greatly 

increased electrical and communications needs and the 

use of raised floors, and increased the need for the 

mechanical and electrical systems to remain functional 

after earthquakes.

C11.3.1.2 Background to Mechanical and 

Electrical Considerations

Prior to the 1964 Alaska earthquake, mechanical and 

electrical systems for buildings had been designed with 

little, if any, regard to stability when subjected to 

seismic forces. The change in design from the heavily 

structured and densely partitioned structures of the prewar era, with their simple mechanical, electrical and 

lighting systems, to the light frame and curtain wall, 

gypsum board and integrated ceiling buildings of the 

1950s and onward, had been little reflected in the 

seismic building codes. The critical yet fragile nature 

of the new nonstructural systems was not fully 

realized, except for nuclear power plant design and 

other special-purpose, high-risk structures. Equipment 

supports were generally designed for gravity loads 

only, and attachments to the structure itself were often 

deliberately designed to be flexible to allow for 

vibration isolation or thermal expansion.
11-8 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

Few building codes, even in regions with a history of 

seismic activity, have contained provisions governing 

the behavior of mechanical and electrical systems until 

relatively recently. One of the earliest references to 

seismic bracing can be found in NFPA-13, Standard for 

the Installation of Sprinkler Systems. This pamphlet 

has been updated periodically since 1896, and seismic 

bracing requirements have been included since 1947. 

Piping systems for building sprinklers are static and do 

not require vibration isolation. They do, however, 

require flexibility where the service piping enters the 

building. The issue of protecting flexibly mounted 

piping was not studied until after the 1964 Alaska 

earthquake.

The designers of building mechanical systems must 

also address the seismic restraints required for 

emergency generators, fire protection pumps, and 

plumbing systems that are vital parts of an effective 

fire suppression system.

Studies published following the 1971 San Fernando 

earthquake all indicated that buildings that sustained 

only minor structural damage became uninhabitable 

and hazardous to life due to failures of mechanical and 

electrical systems.

C11.3.1.3 HVAC Systems

A study by Ayres and Sun (1973b) clearly identified 

the need to anchor tanks and equipment that did not 

require vibration isolation, and to provide lateral 

restraints on equipment vibration isolation devices. 

Some of these suggested corrective measures are now 

incorporated into manufactured products. The HVAC 

system designers had to become aware of the 

earthquake-induced forces on the system’s components 

and the need for seismic restraints to limit damage; 

they also had to understand the requirements for the 

suspension and bracing of ceilings and light fixtures 

because of their adjacency to and interaction with the 

HVAC system components.

To provide technical guidance to HVAC system 

designers and installers, the Sheet Metal Industry Fund 

of Los Angeles published its first manual, Guidelines 

for Seismic Restraint of Mechanical Systems (Sheet 

Metal Industry Fund, 1976). This manual was updated 

in 1982 with assistance from the Plumbing and Piping 

Industry Council (PPIC). The most recent manual, 

Seismic Restraint Guidelines for Mechanical 

Equipment (SMACNA, 1991), is designed for use in 

California as well as other locations with lower seismic 

hazard levels.

Secondary effects of earthquakes (fires, explosions, 

and hazardous materials releases resulting from 

damaged mechanical and electrical equipment) have 

only recently being considered. In addition, the 

potential danger of secondary damage from falling 

architectural and structural components, which could 

inflict major damage to adjacent equipment and render 

it unusable, needs to be carefully assessed.

These secondary effects can represent a considerable 

hazard to the building, its occupants, and its contents. 

Steam and hot water boilers and other pressure vessels 

can release fluids at hazardous temperatures. 

Mechanical systems often include piping systems filled 

with flammable, toxic, or noxious substances, such as 

ammonia or other refrigerants. Some of the nontoxic 

halogen refrigerants used in air-conditioning apparatus 

can be converted to a poisonous gas (phosgene) upon 

contact with open flame. Hot parts of disintegrating 

boilers, such as portions of the burner and firebrick, are 

at high enough temperatures to ignite combustible 

materials with which they might come in contact.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-9

Table C11-1 Nonstructural Architectural 

Component Seismic Hazards

Component Principal Concerns

Suspended ceilings Dropped acoustical tiles, 

perimeter damage, 

separation of runners and 

cross runners

Plaster ceilings Collapse, local spalling

Cladding Falling from building, 

damaged panels and 

connections, broken glass

Ornamentation Damage leading to a falling 

hazard

Plaster and gypsum board 

walls

Cracking

Demountable partitions Collapse

Raised access floors Collapse, separation 

between modules

Recessed light fixtures and 

HVAC diffusers

Dropping out of suspended 

ceilings

Unreinforced masonry walls 

and partitions

Parapet and wall collapse 

and spalling, partitions 

debris and falling hazard

Table C11-2 Mechanical And Electrical 

Equipment Seismic Hazards

Equipment/Component Principal Concerns

Boilers Sliding, broken gas/fuel and 

exhaust lines, broken/bent 

steam and relief lines

Chillers Sliding, overturning, loss of 

function, leaking refrigerant

Emergency generators Failed vibration isolation 

mounts; broken fuel, signal, 

and power lines, loss of 

function, broken exhaust 

lines

Fire pumps Anchorage failure, 

misalignment between 

pump and motor, broken 

piping

On-site water storage Tank or vessel rupture, pipe 

break

Communications 

equipment

Sliding, overturning, or 

toppling leading to loss of 

function

Main transformers Sliding, oil leakage, bushing 

failure, loss of function

Main electrical panels Sliding or overturning, 

broken or damaged conduit 

or electrical bus

Elevators (traction) Counterweights out of 

guide rails, cables out of 

sheaves, dislodged 

equipment

Other fixed equipment Sliding or overturning, loss 

of function or damage to 

adjacent equipment

Ducts Collapse, separation, 

leaking, fumes

Piping Breaks, leaks
11-10 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.3.2 Component Evaluation

Nonstructural components shall be evaluated to achieve 

the Rehabilitation Objective selected in accordance 

with Section 1.4. Analysis and rehabilitation 

requirements for the Hazards Reduced, Life Safety, and 

Immediate Occupancy Nonstructural Performance 

Levels for the appropriate zone of seismicity shall be as 

specified in Table 11-1. Design forces shall be 

calculated in accordance with Section 11.7.3 or 11.7.4, 

and design deformations shall be calculated in 

accordance with Section 11.7.5. Analysis and 

rehabilitation requirements for the Hazards Reduced 

Nonstructural Performance Level shall follow the 

requirements for the Life Safety Nonstructural 

Performance Level. Analysis and rehabilitation 

requirements for the Operational Nonstructural 

Performance Level shall be based on approved codes.

Acceptance criteria for nonstructural components being 

evaluated to the Life Safety and Immediate Occupancy 

Nonstructural Performance Levels shall be based on 

criteria listed in Sections 11.9 through 11.11. Forces on 

bracing and connections for nonstructural components 

calculated in accordance with Section 11.7 shall be 

compared to capacities using strength design 

procedures. Acceptance criteria for the Life Safety 

Nonstructural Performance Level shall be used for 

nonstructural components being evaluated to the 

Hazards Reduced Nonstructural Performance Level. 

For nonstructural components being evaluated to the 

Operational Nonstructural Performance Level, 

approved acceptance criteria shall be used.

C11.3.2 Component Evaluation

The Hazards Reduced Nonstructural Performance 

Level applies only to high hazard components as 

specified in Section 1.5.2.4 and Table 11-1. Life Safety 

Nonstructural Performance Level criteria—or other 

approved criteria—should be used for the Hazards 

Reduced Nonstructural Performance Level. Criteria for 

the Operational Nonstructural Performance Level has 

not been developed to date. Evaluation, rehabilitation, 

and acceptance criteria for the Immediate Occupancy 

Nonstructural Performance Level may be used for the 

Operational Nonstructural Performance Level if more 

appropriate data are not available.

Forces on nonstructural components calculated in 

accordance with Section 11.7 are at a strength design 

level. Where allowable stress values are available for 

proprietary products used as bracing for nonstructural 

components, these values shall be factored up to 

strength design levels. In the absence of 

manufacturer’s data on strength values, allowable 

stress values can be increased by a factor of 1.4 to 

obtain strength design values.

When nonstructural components are evaluated using 

Hazards Reduced Nonstructural Performance Level, 

the force level associated with Life Safety 

Nonstructural Performance in Section 11.7 should be 

used. In many instances, if bracing of the nonstructural 

component exists, or if it is rehabilitated, there would 

not be a substantial justification for evaluating or 

rehabilitating the component using a force level or 

acceptance criteria less stringent than Life Safety. 

However, in cases where it is not considered critical or 

feasible, the engineer may, with appropriate approval, 

evaluate or rehabilitate the nonstructural component 

using a criteria that is less stringent than Life Safety.

In cases where the Basic Safety Objective is not 

required—such as when the Limited Safety 

Performance Range applies—there may be more 

latitude in the selection of components or criteria for 

nonstructural rehabilitation.

A suggested general procedure for developing a 

mitigation plan for the rehabilitation of nonstructural 

components is as follows:

1. It is assumed that the building has been evaluated in 

a feasibility phase, using a procedure such as that 

described in FEMA 310. For nonstructural 

components, use of this procedure will have 

provided a broad list of deficiencies that are 

generally, but not specifically, related to a 

Rehabilitation Objective. Issues related to other 

objectives and possible nonstructural components 

not discussed in FEMA 310, as well as issues raised 

by nonstructural rehabilitation unaccompanied by 

structural rehabilitation (e.g., planning, costbenefit) are outlined in this commentary, and 

references are provided for more detailed 

investigation.

2. The decision is made to rehabilitate the building, 

either structurally, nonstructurally, or both.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-11

11.4 Rehabilitation Objectives and 

Performance Levels

Rehabilitation objectives that include performance 

levels for nonstructural components shall be established 

in accordance with Section 1.4. The zone of seismicity 

shall be determined in accordance with Section 1.6.3.

3. From Chapter 2 of this standard, the designer 

reviews Rehabilitation Objectives and, in concert 

with the owner, determines the objective. 

Alternatively, the objective may have been already 

defined in an ordinance or other policy.

4. Following a decision on the Rehabilitation 

Objective, which includes the Nonstructural 

Performance Level or Range as well as ground 

motion criteria, the designer consults Chapter 11 of 

this standard.

5. Using Chapter 11, the designer prepares a definitive 

list of nonstructural components that are within the 

scope of the rehabilitation, based on the selected 

Nonstructural Performance Level and an 

assessment of component condition. For the Life 

Safety Nonstructural Performance Level and, to 

some extent, the Immediate Occupancy 

Nonstructural Performance Level, Chapters 2 and 

11 of this standard specify requirements. However, 

for other levels and ranges, there is a need to 

evaluate and prioritize. From the list of 

nonstructural components within the project scope, 

a design assessment is made to determine if the 

component requires rehabilitation and, from Table 

11-1, the rehabilitation Analysis Method 

(Analytical or Prescriptive) for each component or 

component group is determined.

6. For those components that do not meet the criteria, 

an appropriate analysis and design procedure is 

undertaken, with the aim of bringing the component 

into compliance with the criteria appropriate to the 

Nonstructural Performance Level or Range and the 

ground motion criteria.

7. Nonstructural rehabilitation design documents are 

prepared.

C11.4 Rehabilitation Objectives and 

Performance Levels

The nonstructural Rehabilitation Objective may be the 

same as the Structural Rehabilitation Objective, or it 

may differ. For the BSO, structural and nonstructural 

requirements specified in this standard must be met.

This standard is also intended to be applicable to the 

situation where nonstructural—but not structural—

components are to be rehabilitated. Rehabilitation that 

is restricted to the nonstructural components will 

typically fall within the Limited Safety Nonstructural 

Performance Range unless the structure is already 

determined to meet a specified Rehabilitation 

Objective. To qualify for any Rehabilitation Objective 

higher than Limited Safety, consideration of structural 

behavior is necessary to properly take into account 

loads on nonstructural components generated by 

inertial forces or deformations imposed by the 

structure.

C11.4.1 Regional Seismicity and 

Nonstructural Components

Requirements for the rehabilitation of nonstructural 

components relating to the three Seismic Zones—

High, Moderate, and Low—are shown in Table 11-1 

and noted in each section, where applicable. In general, 

in regions of low seismicity, certain nonstructural 

components have no rehabilitation requirements with 

respect to the Life Safety Nonstructural Performance 

Level. Rehabilitation of these components, particularly 

where rehabilitation is simple, may nevertheless be 

desirable for damage control and property loss 

reduction.

C11.4.2 Means of Egress: Escape and Rescue

Preservation of egress is accomplished primarily by 

ensuring that the most hazardous nonstructural 

elements are replaced or rehabilitated. The items listed 

in Table 11-1 for achieving the Life Safety 

Nonstructural Performance Level show that typical 

requirements for maintaining egress will, in effect, be 

accomplished if the egress-related components are 

addressed. These would include the following items 

listed in FEMA 310.

1. Walls around stairs, elevator enclosures, and 

corridors are not hollow clay tile or unreinforced 

masonry.
11-12 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.5 Structural-Nonstructural 

Interaction

11.5.1 Response Modification

Nonstructural components shall be included in the 

mathematical model of the building in accordance with 

the requirements of Section 3.2.2.3. Nonstructural 

components included in the mathematical model of the 

building shall be evaluated for forces and deformations 

imposed by the structure, computed in accordance with 

Chapter 3.

11.5.2 Base Isolation

In a base-isolated structure, nonstructural components 

located at or above the isolation interface shall comply 

with the requirements in Section 9.2.6.2.1. 

Nonstructural components that cross the isolation 

interface shall comply with the requirements of 

Section 9.2.6.2.2. Nonstructural components located 

below the isolation interface shall comply with the 

requirements of this chapter.

11.6 Classification of AccelerationSensitive and DeformationSensitive Components

Nonstructural components shall be classified based on 

their response sensitivity as follows:

1. Nonstructural components that are sensitive to and 

subject to damage from inertial loading shall be 

classified as acceleration-sensitive components.

2. Nonstructural components that are sensitive to 

deformation imposed by drift or deformation of the 

structure shall be classified as deformation-sensitive 

components. Nonstructural components that are 

sensitive to both the inertial loading and deformation 

of the structure shall also be classified as 

deformation-sensitive components.

2. Stair enclosures do not contain any piping or 

equipment except as required for life safety.

3. Veneers, cornices, and other ornamentation above 

building exits are well anchored to the structural 

system.

4. Parapets and canopies are anchored and braced to 

prevent collapse and blockage of building exits.

Beyond this, the following list describes some 

conditions that might be commonly recognized as 

representing major obstruction; the building should be 

inspected to see whether these, or any similar 

hazardous conditions exist. If so, their replacement or 

rehabilitation should be included in the rehabilitation 

plan.

1. Partitions taller than six feet and weighing more 

than five pounds per square foot, if collapse of the 

entire partition—rather than cracking—is the 

expected mode of failure, and if egress would be 

impeded.

2. Ceilings, soffits, or any ceiling or decorative ceiling 

component weighing more than two pounds per 

square foot, if it is expected that large areas (pieces 

measuring ten square feet or larger) would fall.

3. Potential for falling ceiling-located light fixtures or 

piping; diffusers and ductwork, speakers and 

alarms, and other objects located higher than 42 

inches off the floor.

4. Potential for falling debris weighing more than 100 

pounds that, if it fell in an earthquake, would 

obstruct a required exit door or other component, 

such as a rescue window or fire escape.

5. Potential for jammed doors or windows required as 

part of an exit path—including doors to individual 

offices, rest rooms, and other occupied spaces.

Of these, the first four are also taken care of in the Life 

Safety Nonstructural Performance Level requirement. 

The last condition is very difficult to remove with any 

assurance, except for low levels of shaking in which 

structural drift and deformation will be minimal, and 

the need for escape and rescue correspondingly slight.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-13

C11.6 Classification of AccelerationSensitive and DeformationSensitive Components

Classification of acceleration-sensitive or deformationsensitive components are discussed, where necessary, 

in each component section (Sections 11.9, 11.10, and 

11.11). Table C11-3 summarizes the sensitivity of 

nonstructural components listed in Table 11-1, and 

identifies which are of primary or secondary concern. 

The guiding principle for deciding whether a 

component requires a force analysis, as defined in 

Section 11.7, is that analysis of inertial loads generated 

within the component is necessary to properly consider 

the component’s seismic behavior. The guiding 

principle for deciding whether a component requires a 

drift analysis, as defined in Section 11.7, is that 

analysis of drift is necessary to properly consider the 

component’s seismic behavior.

Glazing or other components that can hazardously fail 

at a drift ratio less than 0.01 (depending on installation 

details) or components that can undergo greater 

distortion without hazardous failure resulting—for 

example, typical gypsum board partitions—should be 

considered.

Use of Drift Ratio Values as Acceptance Criteria.

The data on drift ratio values related to damage states 

are limited, and the use of single median drift ratio 

values as acceptance criteria must cover a broad range 

of actual conditions. It is therefore suggested that the 

limiting drift values shown in this chapter be used as a 

guide for evaluating the probability of a given damage 

state for a subject building, but not be used as absolute 

acceptance criteria. At higher Nonstructural 

Performance Levels, it is likely that the criteria for 

nonstructural deformation- sensitive components may 

control the structural rehabilitation design. These 

criteria should be regarded as a flag for the careful 

evaluation of structural/nonstructural interaction and 

consequent damage states, rather than the required 

imposition of absolute acceptance criteria that might 

require costly redesign of the structural rehabilitation.

Table C11-3 Nonstructural Components: 

Response Sensitivity

COMPONENT

Sensitivity

Acc. Def.

ARCHITECTURAL (Section 11.9)

1. Exterior Skin 

Adhered Veneer S P

Anchored Veneer S P

Glass Blocks S P

Prefabricated Panels S P

Glazing Systems S P

2. Partitions 

Heavy S P

Light S P

3. Interior Veneers S P

Stone, Including Marble S P

Ceramic Tile S P

4. Ceilings 

Directly Applied to Structure P

Dropped Furred Gypsum Board P

Suspended Lath and Plaster S P

Suspended Integrated Ceiling S P

5. Parapets and Appendages P

6. Canopies and Marquees P

7. Chimneys and Stacks P

8. Stairs P S

MECHANICAL EQUIPMENT (Section 11.10)

1. Mechanical Equipment 

Boilers and Furnaces P

General Mfg. and Process 

Machinery

P

HVAC Equipment, VibrationIsolatedP

HVAC Equipment, Non-VibrationIsolatedP

HVAC Equipment, Mounted 

In-Line with Ductwork

P
11-14 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.7 Evaluation Procedures

One of the following evaluation procedures for 

nonstructural components shall be selected based on the 

requirements of Table 11-1:

1. Analytical Procedure.

2. Prescriptive Procedure.

11.7.1 Analytical Procedure

When the Prescriptive Procedure is not permitted based 

on Table 11-1, forces and deformations on nonstructural 

components shall be calculated as follows:

1. If a force analysis only is permitted by Table 11-1 

and either the Hazards Reduced or Life Safety 

Nonstructural Performance Level is selected, then 

use of the default equations given in Section 11.7.3 

shall be permitted to calculate seismic design forces 

on nonstructural components.

2. If a force analysis only is permitted by Table 11-1 

and a Nonstructural Performance Level higher than 

Life Safety is selected, then the default equations of 

Section 11.7.3 do not apply, and seismic design 

forces shall be calculated in accordance with 

Section 11.7.4. 

3. If both force and deformation analysis are required 

by Table 11-1, then seismic design forces shall be 

calculated in accordance with Section 11.7.4 and 

drift ratios or relative displacements shall be 

calculated in accordance with Section 11.7.5. The 

deformation and associated drift ratio of the 

structural component(s) to which the deformationsensitive nonstructural component is attached shall 

be determined in accordance with Chapter 3. 

4. Alternatively, the calculation of seismic design 

forces and deformations in accordance with 

Section 11.7.6 shall be permitted.

11.7.2 Prescriptive Procedure

Where the Prescriptive Procedure is permitted in Table 

11-1, the characteristics of the nonstructural component 

shall be compared with characteristics as specified in 

approved codes.

2. Storage Vessels and Water 

Heaters 

Structurally Supported Vessels 

(Category 1)

P

Flat Bottom Vessels (Category 2) P

3. Pressure Piping P S

4. Fire Suppression Piping P S

5. Fluid Piping, not Fire 

Suppression 

Hazardous Materials P S

Nonhazardous Materials P S

6. Ductwork P S

Acc. = Acceleration-Sensitive P = Primary Response

Def. = Deformation-Sensitive S = Secondary Response

Table C11-3 Nonstructural Components: 

Response Sensitivity (continued)

COMPONENT

Sensitivity

Acc. Def.

C11.7.1 Analytical Procedure

For nonstructural components, the Analytical 

Procedure, which consists of the default equation and 

general equation approaches, is applicable to any case. 

The Prescriptive Procedure is limited by Table 11-1 to 

specified combinations of seismicity and component 

type for compliance with the Life Safety Nonstructural 

Performance Level.

C11.7.2 Prescriptive Procedure

A Prescriptive Procedure consists of published 

standards and references that describe the design 

concepts and construction features that must be present 

for a given nonstructural component to be seismically 

protected. No engineering calculations are required in 

a Prescriptive Procedure, although in some cases an 

engineering review of the design and installation is 

required.

Suggested references for prescriptive requirements are 

listed in the commentary of the “Component Behavior 

and Rehabilitation Concepts” subsection of 

Sections 11.9 through 11.11 for each component type.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-15

11.7.3 Force Analysis: Default Equations

Calculation of seismic design forces on nonstructural 

components using default Equations (11-1) and (11-2) 

shall be permitted in accordance with Section 11.7.1.

Fp = 1.6 SXSIpWp (11-1)

Fpv = 2/3Fp (11-2)

where: 

11.7.4 Force Analysis: General Equations

11.7.4.1 Horizontal Seismic Forces

When default equations of Section 11.7.3 do not apply, 

horizontal seismic design forces on nonstructural 

components shall be determined in accordance with 

Equation (11-3).

 (11-3)

Fp calculated in accordance with Equation (11-3) is 

based on the stiffness of the component and ductility of 

its anchorage, but it need not exceed the default value of 

Fp calculated in accordance with Equation (11-1) and 

shall not be less than Fp computed in accordance with 

Equation (11-4).

Fp (minimum) = 0.3 SXS Ip Wp (11-4)

where:

11.7.4.2 Vertical Seismic Forces

When the default equations of Section 11.7.3 do not 

apply, vertical seismic design forces on nonstructural 

components shall be determined in accordance with 

Equation (11-5).

(11-5)

Fp calculated in accordance with Equation (11-5) need 

not exceed Fp calculated in accordance with Equation 

(11-2) and shall not be less than Fpv computed in 

accordance with Equation (11-6).

Fpv(minimum) = 0.2 SXSIpWp (11-6)

where:

Fp = Component seismic design force applied 

horizontally at the center of gravity of the 

component or distributed according to the 

mass distribution of the component

Fpv = Component seismic design force applied 

vertically at the center of gravity of the 

component or distributed according to the 

mass distribution of the component

SXS = Spectral response acceleration parameter at 

short periods for any Earthquake Hazard 

Level and any damping determined in 

accordance with Section 1.6.1.4 or 1.6.2.1

Ip = Component performance factor; 1.0 shall be 

used for the Life Safety Nonstructural 

Performance Level and 1.5 shall be used for 

the Immediate Occupancy Nonstructural 

Performance Level

Wp = Component operating weight

Fp

0.4apSXSIpW

p

1 2x

h + -----    

Rp

= ---------------------------------------------------------

ap = Component amplification factor from Table 

11-2

Fp = Component seismic design force applied 

horizontally at the center of gravity of the 

component and distributed according to the 

mass distribution of the component

SXS = Spectral response acceleration parameter at 

short periods for any Earthquake Hazard 

Level and any damping determined in 

accordance with Section 1.6.1.4 or 1.6.2.1

h = Average roof elevation of structure, relative 

to grade elevation

Ip = Component performance factor; 1.0 shall be 

used for the Life Safety Nonstructural 

Performance Level and 1.5 shall be used for 

the Immediate Occupancy Nonstructural 

Performance Level

Rp = Component response modification factor 

from Table 11-2

x = Elevation in structure of component relative 

to grade elevation

Fpv = Component seismic design force applied 

vertically at the center of gravity of the 

component or distributed according to the 

mass distribution of the component

Fpv

0.27apSXS I

pWp

Rp

= --------------------------------------
11-16 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

All other terms in Equations (11-5) and (11-6) shall be 

as defined in Section 11.7.4.1.

11.7.5 Deformation Analysis

When nonstructural components are anchored by 

connection points at different levels x and y on the same 

building or structural system, drift ratios (Dr) shall be 

calculated in accordance with Equation (11-7).

Dr = (δxA - δyA) / (X – Y) (11-7)

When nonstructural components are anchored by 

connection points on separate buildings or structural 

systems at the same level x, relative displacements (Dp) 

shall be calculated in accordance with Equation (11-8). 

Dp = | δxA | + | δxB | (11-8)

where:

The effects of seismic displacements shall be 

considered in combination with displacements caused 

by other loads that are present.

11.7.6 Other Procedures

Other approved procedures shall be permitted to 

determine the maximum acceleration of the building at 

each component support and the maximum drift ratios 

or relative displacements between two supports of an 

individual component.

Dp = Relative seismic displacement

Dr = Drift ratio

X = Height of upper support attachment at level x

as measured from grade

Y = Height of lower support attachment at level y

as measured from grade

δxA = Deflection at building level x of Building A, 

determined by analysis as defined in 

Chapter 3

δyA = Deflection at building level y of Building A, 

determined by analysis as defined in 

Chapter 3

δxB = Deflection at building level x of Building B, 

determined by analysis as defined in 

Chapter 3 or equal to 0.03 times the height X 

of level x above grade or as determined using 

other approved approximate procedures

C11.7.6 Other Procedures

Linear and nonlinear procedures may be used to 

calculate the maximum acceleration of each 

component support and the interstory drifts of the 

building, taking into account the location of the 

component in the building. Consideration of the 

flexibility of the component, and the possible 

amplification of the building roof and floor 

accelerations and displacements in the component, 

would require the development of roof and floor 

response spectra or acceleration time histories at the 

nonstructural support locations, derived from the 

dynamic response of the structure. If the resulting floor 

spectra are less than demands calculated in accordance 

with Sections 11.7.3 and 11.7.4, it may be 

advantageous to use this procedure.

Relative displacements between component supports 

are difficult to calculate, even with the use of 

acceleration time histories, because the maximum 

displacement of each component support at different 

levels in the building might not occur at the same time 

during the building response.

Guidelines for these dynamic analyses for 

nonstructural components are given in Chapter 6 of 

Seismic Design Guidelines for Essential Buildings, a 

supplement to TM5-809-10.1.

These other analytical procedures are considered too 

complex for the rehabilitation of nonessential building 

nonstructural components for Immediate Occupancy 

and Life Safety Nonstructural Performance Levels.

Recent research (Drake and Bachman) has shown that 

the analytical procedures in Sections 11.7.3 and 11.7.4, 

which are based on FEMA 302 analytical procedures, 

provide an upper bound for the seismic forces on 

nonstructural components.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-17

Table 11-2 Nonstructural Component Amplification and Response Modification Factors

COMPONENT ap

1 Rp2

ARCHITECTURAL (Section 11.9)

1. Exterior Wall Elements

Adhered Veneer 1 4

Anchored Veneer 1 33

Glass Block 1 2

Prefabricated Panels 1 33

Glazed Exterior Wall Systems 1 2

2. Partitions

Heavy 1 1.5

Light 1 3

Glazed 1 2

3. Interior Veneers

Stone, Including Marble 1 1.5

Ceramic Tile 1 1.5

4. Ceilings

Directly Applied to Structure 1 1.5

Dropped Furred Gypsum Board 1 1.5

Suspended Lath and Plaster 1 1.5

Suspended Integrated Ceiling 1 1.5

5. Parapets and Appendages 2.5 1.25

6. Canopies and Marquees 2.5 1.5

7. Chimneys and Stacks 2.5 1.25

8. Stairs 1 3

MECHANICAL EQUIPMENT (Section 11.10)

1. Mechanical Equipment

Boilers, Furnaces, Pumps, and Chillers 1 3

General Mfg. and Process Machinery 1 3

HVAC Equipment, Vibration-Isolated 2.5 3

HVAC Equipment, Non-Vibration-Isolated 1 3

HVAC Equipment, Mounted In-Line with Ductwork 1 3

2. Storage Vessels and Water Heaters

Vessels on Legs (Category 1) 2.5 1.5

Flat Bottom Vessels (Category 2) 2.5 3

3. High-Pressure Piping 2.5 4

4. Fire Suppression Piping 2.5 4

5. Fluid Piping, not Fire Suppression

Hazardous Materials 2.5 1

Nonhazardous Materials 2.5 4
11-18 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

6. Ductwork 1 3

ELECTRICAL AND COMMUNICATIONS EQUIPMENT (Section 11.11)

1. Electrical and Communications Equipment 13

2. Electrical and Communications Distribution Equipment 2.5 5

3. Light Fixtures

Recessed 1 1.5

Surface Mounted 1 1.5

Integrated Ceiling 1 1.5

Pendant 1 1.5

FURNISHINGS AND INTERIOR EQUIPMENT (Section 11.11)

1. Storage Racks4 2.5 4

2. Bookcases 1 3

3. Computer Access Floors 1 3

4. Hazardous Materials Storage 2.5 1

5. Computer and Communications Racks 2.5 6

6. Elevators 1 3

7. Conveyors 2.5 3

1. A lower value for ap shall be permitted if justified by detailed dynamic analysis. The value for ap shall be not less than 1. Where flexible diaphragms 

provide lateral support for walls and partitions, the value of ap shall be increased to 2.0 for the center one-half of the span.

The value of ap = 1 is for equipment generally regarded as rigid and rigidly attached. The value of ap = 2.5 is for equipment generally regarded as flexible 

and flexibly attached. See the definitions (Section 11.12) for explanations of “Component, rigid” and “Component, flexible.”

2. For anchorage design where component anchorage is provided by expansion anchor bolts, shallow chemical anchors, or shallow 

(nonductile) cast-in-place anchors, or where the component is constructed of nonductile materials, Rp shall be taken as 1.5. 

Shallow anchors are those with an embedment length-to-bolt diameter ratio of less than 8.

3. Values shall apply when attachment is of ductile material and design, otherwise 1.5.

4. Storage racks over six feet in height shall be designed in accordance with the provisions of Section 11.11.1.

Table 11-2 Nonstructural Component Amplification and Response Modification Factors (continued)

COMPONENT ap

1 Rp2
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-19

11.8 Rehabilitation Methods

Nonstructural rehabilitation shall be accomplished 

through replacement, strengthening, repair, bracing, 

attachment, or other approved methods.

C11.8 Rehabilitation Methods

A general set of alternative methods is available for the 

rehabilitation of nonstructural components. These are 

briefly outlined in this section with examples to clarify 

the intent. However, the choice of rehabilitation 

technique and its design is the responsibility of the 

design professional, and the use of alternative methods 

to those noted below or otherwise customarily in use is 

acceptable, provided it can be shown to the satisfaction 

of the building official that the acceptance criteria can 

be met.

C11.8.1 Replacement

Replacement involves the complete removal of the 

component and its connections, and its replacement by 

new components; for example, the removal of exterior 

cladding panels, the installation of new connections, 

and installation of new panels. As with structural 

components, the installation of new nonstructural 

components as part of a seismic rehabilitation project 

should be the same as for new construction.

C11.8.2 Strengthening

Strengthening involves additions to the component to 

improve its strength to meet the required force levels; 

for example, additional members might be welded to a 

support to prevent buckling.

C11.8.3 Repair

Repair involves the repair of any damaged parts or 

members of the component to enable the component to 

meet its acceptance criteria; for example, some 

corroded attachments for a precast concrete cladding 

system might be repaired and replaced without 

removing or replacing the entire panel system.

C11.8.4 Bracing

Bracing involves the addition of members and 

attachments that brace the component internally or to 

the building structure. A suspended ceiling system 

might be rehabilitated by the addition of diagonal wire 

bracing and vertical compression struts.

C11.8.5 Attachment

Attachment refers to methods that are primarily 

mechanical, such as bolting, by which nonstructural 

components are attached to the structure or other 

supporting components. Typical attachments are the 

bolting of items of mechanical equipment to a 

reinforced concrete floor or base. Supports and 

attachments for mechanical and electrical equipment 

should be designed according to good engineering 

principles. The following guidelines are recommended.

1. Attachments and supports transferring seismic 

loads should be constructed of materials suitable for 

the application, and designed and constructed in 

accordance with a nationally recognized standard.

2. Attachments embedded in concrete should be 

suitable for cyclic loads.

3. Rod hangers may be considered seismic supports if 

the length of the hanger from the supporting 

structure is 12 inches or less. Rod hangers should 

not be constructed in a manner that would subject 

the rod to bending moments.

4. Seismic supports should be constructed so that 

support engagement is maintained.

5. Friction clips should not be used for anchorage 

attachment.

6. Expansion anchors should not be used for 

mechanical equipment rated over 10 hp, unless 

undercut expansion anchors are used.

7. Drilled and grouted-in-place anchors for tensile 

load applications should use either expansive 

cement or expansive epoxy grout. 

8. Supports should be specifically evaluated if weakaxis bending of cold-formed support steel is relied 

on for the seismic load path.

9. Components mounted on vibration isolation 

systems should have a bumper restraint or snubber 

in each horizontal direction. The design force 

should be taken as 2Fp.

10.Oversized washers should be used at bolted 

connections through the base sheet metal if the base 

is not reinforced with stiffeners.
11-20 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.9 Architectural Components: 

Definition, Behavior, and 

Acceptance Criteria

11.9.1 Exterior Wall Elements

11.9.1.1 Adhered Veneer

11.9.1.1.1 Definition and Scope

Adhered veneer shall include the following types of 

exterior finish materials secured to a backing material, 

which shall be masonry, concrete, cement plaster, or to 

a structural framework material by adhesives: 

1. Tile, masonry, stone, terra cotta, or other similar 

materials not over one inch thick.

2. Glass mosaic units not over 2" x 2" x 3/8" thick.

3. Ceramic tile.

4. Exterior plaster (stucco).

11.9.1.1.2 Component Behavior and Rehabilitation 

Methods

Adhered veneer shall be considered deformationsensitive.

Adhered veneer not conforming to the acceptance 

criteria of Section 11.9.1.1.3 shall be rehabilitated in 

accordance with Section 11.8.

11.9.1.1.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

1. Life Safety Nonstructural Performance Level. Backing 

shall be adequately anchored to resist seismic forces 

computed in accordance with Section 11.7.3 or 

11.7.4. The drift ratio calculated in accordance with 

Section 11.7.5 shall be limited to 0.02.

2. Immediate Occupancy Nonstructural Performance 

Level. Backing shall be adequately attached to resist 

seismic design forces computed in accordance with 

Section 11.7.4. The drift ratio computed in 

accordance with Section 11.7.5 shall be limited to 

0.01.

11.9.1.1.4 Evaluation Requirements

Adhered veneer shall be evaluated by visual 

observation and tapping to discern looseness or 

cracking.

11.9.1.2 Anchored Veneer

11.9.1.2.1 Definition and Scope

Anchored veneer shall include the following types of 

masonry or stone units that are attached to the 

supporting structure by mechanical means:

1. Masonry and stone units not over five inches 

nominal thickness.

2. Stone units from five inches to ten inches nominal 

thickness.

3. Stone slab units not over two inches nominal 

thickness.

The provisions of this section shall apply to units that 

are more than 48 inches above the ground or adjacent 

exterior area.

11.9.1.2.2 Component Behavior and Rehabilitation 

Methods

Anchored veneer shall be considered both accelerationsensitive and deformation-sensitive.

Lighting fixtures resting in a suspended ceiling grid 

may be rehabilitated by adding wires that directly 

attach the fixtures to the floor above, or to the roof 

structure to prevent their falling.

C11.9.1.1.2 Component Behavior and Rehabilitation 

Methods

Adhered veneers are predominantly deformationsensitive. Deformation of the substrate leads to 

cracking or separation of the veneer from its backing. 

Poorly adhered veneers may be dislodged by direct 

acceleration.

Nonconformance requires limiting drift, special 

detailing to isolate substrate from structure to permit 

drift, or replacement with drift-tolerant material. 

Poorly adhered veneers should be replaced.

C11.9.1.1.4 Evaluation Requirements

Tapping may indicate either defective bonding to the 

substrate or excessive flexibility of the supporting 

structure.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-21

Anchored veneer and connections not conforming to the 

acceptance criteria of Section 11.9.1.2.3 shall be 

rehabilitated in accordance with Section 11.8.

11.9.1.2.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

1. Life Safety Nonstructural Performance Level. Backing 

shall be adequately anchored to resist seismic forces 

computed in accordance with Section 11.7.3 or 

11.7.4. The drift ratio calculated in accordance with 

Section 11.7.5 shall be limited to 0.02.

2. Immediate Occupancy Nonstructural Performance 

Level. Backing shall be adequately attached to resist 

seismic design forces computed in accordance with 

Section 11.7.4. The drift ratio computed in 

accordance with Section 11.7.5 shall be limited to 

0.01.

11.9.1.2.4 Evaluation Requirements

Stone units shall have adequate stability, joint detailing, 

and maintenance to prevent moisture penetration from 

weather that could destroy the anchors. The anchors 

shall be visually inspected and tested to determine 

capacity if any signs of deterioration are visible.

11.9.1.3 Glass Block Units and Other 

Nonstructural Masonry

11.9.1.3.1 Definition and Scope

Glass block and other units that are self-supporting for 

static vertical loads, held together by mortar and 

structurally detached from the surrounding structure, 

shall be rehabilitated in accordance with this section.

11.9.1.3.2 Component Behavior and Rehabilitation 

Methods

Glass block units and other nonstructural masonry shall 

be considered both acceleration- and deformationsensitive.

Rehabilitation of individual walls less than 144 square 

feet or 15 feet in any dimension using Prescriptive 

Procedures based on Section 2110 of IBC (2000) shall 

be permitted. For walls larger than 144 square feet or 15 

feet in any dimension, the analytical procedure shall be 

used.

Glass block units and other nonstructural masonry not 

conforming with the requirements of Section 11.9.1.3.3 

shall be rehabilitated in accordance with Section 11.8.

11.9.1.3.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

1. Life Safety Nonstructural Performance Level. Glass 

block and other nonstructural masonry walls and 

their enclosing framing, shall be capable of resisting 

both in-plane and out-of-plane forces computed in 

accordance with Section 11.7.3 or 11.7.4, or shall 

meet the requirements of the Prescriptive Procedure 

if permitted. The drift ratio calculated in accordance 

with Section 11.7.5 shall be limited to 0.02.

C11.9.1.2.2 Component Behavior and Rehabilitation 

Methods

Anchored veneer is both acceleration- and 

deformation-sensitive. Heavy units may be dislodged 

by direct acceleration, which distorts or fractures the 

mechanical connections. Deformation of the 

supporting structure, particularly if it is a frame, may 

similarly affect the connections, and the units may be 

displaced or dislodged by racking.

Drift analysis is necessary to establish conformance 

with drift acceptance criteria related to performance 

level. Nonconformance requires limiting structural 

drift, or special detailing to isolate substrate from 

structure to permit drift. Defective connections must be 

replaced.

C11.9.1.3.2 Component Behavior and Rehabilitation 

Methods

Failure in-plane generally occurs by deformation in the 

surrounding structure that results in unit cracking and 

displacement along the cracks. Failure out-of-plane 

takes the form of dislodgment or collapse caused by 

direct acceleration.

Nonconformance with deformation criteria requires 

limiting structural drift, or special detailing to isolate 

the glass block wall from the surrounding structure to 

permit drift. Sufficient reinforcing must be provided to 

deal with out-of-plane forces. Large walls may need to 

be subdivided by additional structural supports into 

smaller areas that can meet the drift or force 

acceptance criteria.
11-22 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

2. Immediate Occupancy Nonstructural Performance 

Level. Glass block and other nonstructural masonry 

walls and their enclosing framing shall be capable of 

resisting both in-plane and out-of-plane forces 

computed in accordance with Section 11.7.4. The 

drift ratio calculated in accordance with 

Section 11.7.5 shall be limited to 0.01.

11.9.1.3.4 Evaluation Requirements

Glass block units and other nonstructural masonry shall 

be evaluated based on the criteria of Section 2110 of 

IBC (2000).

11.9.1.4 Prefabricated Panels

11.9.1.4.1 Definition and Scope

The following types of prefabricated panels designed to 

resist wind, seismic, and other applied forces shall be 

rehabilitated in accordance with this section:

1. Precast concrete, and concrete panels with facing 

(generally stone) laminated or mechanically 

attached.

2. Laminated metal-faced insulated panels.

3. Steel strong-back panels with insulated, waterresistant facing, or mechanically attached metal or 

stone facing.

11.9.1.4.2 Component Behavior and Rehabilitation 

Methods

Prefabricated panels shall be considered both 

acceleration- and deformation-sensitive.

Prefabricated panels not conforming to the acceptance 

criteria of Section 11.9.1.4.3 shall be rehabilitated in 

accordance with Section 11.8.

11.9.1.4.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

1. Life Safety Nonstructural Performance Level. 

Prefabricated panels and connections shall be 

capable of resisting in-plane and out-of-plane forces 

computed in accordance with Section 11.7.3 or 

11.7.4. The drift ratio computed in accordance with 

Section 11.7.5 shall be limited to 0.02.

2. Immediate Occupancy Nonstructural Performance 

Level. Prefabricated panels and connections shall be 

capable of resisting in-plane and out-of-plane forces 

computed in accordance with Section 11.7.4. The 

drift ratio computed in accordance with 

Section 11.7.5 shall be limited to 0.01.

11.9.1.4.4 Evaluation Requirements

Connections shall be visually inspected and tested to 

determine capacity if any signs of deterioration or 

displacement are visible.

11.9.1.5 Glazed Exterior Wall Systems

11.9.1.5.1 Definition and Scope

Glazed exterior wall systems shall include the following 

types of assemblies:

1. Glazed curtain wall systems that extend beyond the 

edges of structural floor slabs, and are assembled 

from prefabricated units (e.g., “unitized” curtain 

C11.9.1.4.1 Definition and Scope

Prefabricated panels are generally attached around 

their perimeters to the primary structural system.

C11.9.1.4.2 Component Behavior and Rehabilitation 

Methods

Lightweight units may be damaged by racking; heavy 

units may be dislodged by direct acceleration, which 

distorts or fractures the mechanical connections. 

Excessive deformation of the supporting structure—

most likely if it is a frame—may result in the units 

imposing external racking forces on one another and 

distorting or fracturing their connections, with 

consequent displacement or dislodgment.

Drift analysis is necessary to establish conformance 

with drift acceptance criteria related to the 

Nonstructural Performance Level.

Nonconformance requires limiting structural drift, or 

special detailing to isolate panels from structure to 

permit drift; this generally requires panel removal. 

Defective connections must be replaced.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-23

wall systems) or assembled on site (e.g., “stick”

curtain wall systems).

2. Glazed storefront systems that are installed between 

structural floor slabs and are prefabricated or 

assembled on site.

3. Structural silicone glazing in which silicone sealant 

is used for the structural transfer of loads from the 

glass to its perimeter support system and for the 

retention of the glass in the opening.

11.9.1.5.2 Component Behavior and Rehabilitation 

Methods

Glazed exterior wall systems shall be considered both 

deformation-sensitive and acceleration-sensitive.

Glazed exterior wall systems not conforming to the 

acceptance criteria of Section 11.9.1.5.3 shall be 

rehabilitated in accordance with Section 11.8.

11.9.1.5.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

1. Life Safety Nonstructural Performance Level. Glazed 

exterior wall systems and their supporting structure 

shall be capable of resisting seismic design forces 

C11.9.1.5.1 Definition and Scope

The following types of glass are used within each of 

the glazed exterior wall systems:

1. Annealed glass.

2. Heat-strengthened glass.

3. Fully tempered glass.

4. Laminated glass.

5. Sealed insulating glass units.

The use of some of these glass types is regulated in 

building codes.

There are two glazing methods for installing glass in 

glazed curtain wall and glazed storefront systems:

1. Wet glazing, which can utilize three types of 

materials:

1.1. Pre-formed tape.

1.2. Gunable elastomeric sealants.

a. Non-curing.

b. Curing.

1.3. Putty and glazing compounds.

2. Dry glazing, which utilizes extruded rubber gaskets 

as one or both of the glazing seals.

C11.9.1.5.2 Component Behavior and Rehabilitation 

Methods

Glazed exterior wall systems are predominantly 

deformation-sensitive but may also become displaced 

or detached by large acceleration forces. Glass 

components within glazed exterior wall systems are 

deformation-sensitive. Glass performance during 

earthquakes, which is a function of the wall system 

type, glazing type, and glass type, falls into one of four 

categories:

1. Glass remains unbroken in its frame or anchorage.

2. Glass shatters but remains in its frame or anchorage 

while continuing to provide a weather barrier, and 

remains otherwise serviceable.

3. Glass shatters and remains in its frame or anchorage 

in a precarious condition, liable to fall out at any 

time.

4. Glass falls out of its frame or anchorage, either in 

fragments, shards, or whole panels.

Drift analysis and testing or compliance with 

prescriptive procedures are necessary to establish 

conformance with drift acceptance criteria related to 

performance level. Nonconformance requires limiting 

structural drift, or special detailing to isolate the 

glazing system from the structure to accommodate 

drift, or selection of a glass type that will shatter safely 

or remain in the frame when shattered. This would 

require removal of the glass or glazed wall system and 

replacement with an alternative design.
11-24 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

computed in accordance with Section 11.7.3 or 

11.7.4. Glass components meeting any of the 

following criteria need not be rehabilitated for the 

Hazards Reduced or Life Safety Nonstructural 

Performance Level:

1.1. Any glass component with sufficient clearance 

from the frame such that physical contact 

between the glass and the frame will not occur 

at the relative seismic displacement that the 

component must be designed to accommodate, 

as demonstrated by Equation (11-9).

 (11-9)

1.2. Fully tempered monolithic glass that is located 

no more than 10 ft. above a walking surface.

1.3. Annealed or heat-strengthened laminated glass 

in single thickness with interlayer no less than 

0.03 in. that is captured mechanically in a wall 

system glazing pocket, and whose perimeter is 

secured to the wall system frame by a 

wet-glazed perimeter bead of 1/2 in. minimum 

glass contact width, or other approved 

anchorage system.

1.4. Any glass component that meets the relative 

displacement requirement of Equation (11-10).

(11-10)

or 0.5 inch, whichever is greater,

where:

2. Immediate Occupancy Nonstructural Performance 

Level. Glazed exterior wall systems and their 

supporting structure shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.4. Glass components meeting any of 

the following criteria need not be rehabilitated for 

performance levels higher than the Life Safety 

Nonstructural Performance Level:

2.1. Any glass component with sufficient clearance 

from the frame such that physical contact 

between the glass and the frame will not occur 

at the relative seismic displacement that the 

component must be designed to accommodate, 

as demonstrated by Equation (11-9).

2.2. Annealed or heat-strengthened laminated glass 

in single thickness with interlayer no less than 

0.03 in. that is captured mechanically in a wall 

system glazing pocket, and whose perimeter is 

secured to the wall system frame by a 

wet-glazed perimeter bead of 1/2 in. minimum 

glass contact width, or other approved 

anchorage system.

2.3. Any glass component that meets the relative 

displacement requirement of Equation (11-11).

(11-11)

or 0.5 inch, whichever is greater.

where:

Dclear =

hp = height of rectangular glass

bp = width of rectangular glass

c1 = clearance (gap) between vertical glass 

edges and the frame

c2 = clearance (gap) between horizontal glass 

edges and the frame

Dp = relative seismic displacement that the 

component must be designed to 

accommodate. Dp shall be determined by 

Equation (11-8) over the height of the glass 

component under consideration.

Dclear 1.25Dp ≥

2c1 1

hpc2

bpc1

+ ----------

     

∆fallout 1.25Dp ≥

Dp = relative seismic displacement that the 

component must be designed to 

accommodate

∆fallout = relative seismic displacement (drift) 

causing glass fallout from the curtain wall, 

storefront, or partition, as determined in 

accordance with an approved engineering 

analysis method

C11.9.1.5.3 Acceptance Criteria

One method of determining ∆fallout, which is used in 

Equation (11-10), is to use AAMA 501.4.

∆fallout 1.5 1.25 × Dp ≥
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-25

11.9.1.5.4 Evaluation Requirements

To establish compliance with criteria 1.1, 1.2, 1.3, 2.1, 

or 2.2 in 11.9.1.5.3, glazed exterior wall systems shall 

be evaluated visually to determine glass type, support 

details, mullion configuration, sealant type, and 

anchors. To establish compliance with criteria 1.4 or 

2.3, an approved analysis shall be used.

11.9.2 Partitions

11.9.2.1 Definition and Scope

Partitions shall include vertical non-load-bearing 

interior elements that provide space division.

Heavy partitions shall include partitions constructed of 

masonry materials or assemblies.

Light partitions shall include partitions constructed of 

metal or wood studs surfaced with lath and plaster, 

gypsum board, wood, or other facing materials.

11.9.2.1.1 Evaluation Requirements

Glazed partitions that span from floor to ceiling or to 

the underside of floor or roof above shall be 

rehabilitated in accordance with Section 11.9.1.5.

11.9.2.2 Component Behavior and 

Rehabilitation Methods

Partitions shall be considered both acceleration- and 

deformation-sensitive.

Partitions not meeting the acceptance criteria of 

Section 11.9.2.3 shall be rehabilitated in accordance 

with Section 11.8.

Dclear in Equation (11-9) is derived from a similar 

equation in Bouwkamp and Meehan (1960) that 

permits calculation of the interstory drift required to 

cause glass-to-frame contact in a given rectangular 

window frame. Both equations are based on the 

principle that a rectangular window frame (specifically 

one that is anchored mechanically to adjacent stories of 

the primary structural system of the building) becomes 

a parallelogram as a result of interstory drift, and that 

glass-to-frame contact occurs when the length of the 

shorter diagonal of the parallelogram is equal to the 

diagonal of the glass panel itself.

The 1.25 factor in Equations (11-10) and (11-11) 

reflect uncertainties associated with calculated 

inelastic seismic displacements in building structures. 

Wright (1989) stated that “post-elastic deformations 

calculated using the structural analysis process may 

well underestimate the actual building deformation by 

up to 30%. It would therefore be reasonable to require 

the curtain wall glazing system to withstand 1.25 times 

the computed maximum interstory displacement to 

verify adequate performance.” Wright’s comments 

form the basis for using the 1.25 factor.

C11.9.1.5.4 Evaluation Requirements

Alternatively, to establish compliance with criteria 1.4 

or 2.3, glazed exterior wall systems may be tested in 

accordance with AAMA 501.4.

C11.9.2.1 Definition and Scope

Heavy partitions include hollow clay tile or concrete 

block. Only non-load bearing partitions are considered 

in this section. Structural partitions including heavy 

masonry partitions shall be rehabilitated in accordance 

with Chapter 7.

Partitions may span laterally from floor to underside of 

floor or roof above, with connections at the top that 

may or may not allow for isolation from in-plane drift. 

Other partitions extend only up to a hung ceiling, and 

may or may not have lateral bracing above that level to 

structural support, or may be freestanding.

Modular office furnishings that include movable 

partitions are considered as contents rather than 

partitions, and as such are not within the scope of this 

standard.

C11.9.2.2 Component Behavior and 

Rehabilitation Methods

Partitions attached to the structural floors both above 

and below, and loaded in-plane, can experience shear 

cracking, distortion and fracture of the partition 

framing, and detachment of the surface finish because 

of structural deformations. Similar partitions loaded 

out-of-plane can experience flexural cracking, failure 

of connections to structure, and collapse. The high 

incidence of unsupported block partitions in low and 

moderate seismic zones represents a significant 

collapse threat.
11-26 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.9.2.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.2.3.1 Life Safety Nonstructural Performance Level

1. Heavy Partitions. Nonstructural heavy partitions 

shall be capable of resisting out-of-plane forces 

computed in accordance with Section 11.7.3 or 

11.7.4. The drift ratio computed in accordance with 

Section 11.7.5 shall be limted to 0.01.

2. Light Partitions. Nonstructural light partitions need 

not be rehabilitated for the Life Safety Nonstructural 

Performance Level.

11.9.2.3.2 Immediate Occupancy Nonstructural 

Performance Level

1. Heavy Partitions. Nonstructural heavy partitions 

shall be capable of resisting out-of-plane forces 

computed in accordance with Section 11.7.4. The 

drift ratio computed in accordance with 

Section 11.7.5 shall be limted to 0.005.

2. Light Partitions. Nonstructural light partitions shall 

be capable of resisting the out-of-plane forces 

computed in accordance with Section 11.7.4. The 

drift ratio computed in accordance with 

Section 11.7.5 shall be limted to 0.01.

11.9.2.4 Evaluation Requirements

Partitions shall be evaluated to ascertain the type of 

material.

11.9.3 Interior Veneers

11.9.3.1 Definition and Scope

Interior veneers shall include decorative-finish 

materials applied to interior walls and partitions. These 

provisions of this section shall apply to veneers 

mounted four feet or more above the floor.

11.9.3.2 Component Behavior and 

Rehabilitation Methods

Interior veneers shall be considered deformationsensitive.

Interior veneers not conforming to the acceptance 

criteria of Section 11.9.3.3 shall be rehabilitated in 

accordance with Section 11.8.

11.9.3.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.3.3.1 Life Safety Nonstructural Performance 

Level

Backing shall be adequately attached to resist seismic 

design forces computed in accordance with 

Section 11.7.3 or 11.7.4. The drift ratio computed in 

accordance with Section 11.7.5 shall be limited to 0.02.

Partitions subject to deformations from the structure 

can be protected by providing a continuous gap 

between the partition and the surrounding structure, 

combined with attachment that provides for in-plane 

movement but out-of-plane restraint. Lightweight 

partitions that are not part of a fire-resistive system are 

regarded as replaceable.

C11.9.2.4 Evaluation Requirements

For concrete block partitions, presence of reinforcing 

and connection conditions at edges are important. For 

light partitions, bracing or anchoring of the top of the 

partitions is important.

C11.9.3.2 Component Behavior and 

Rehabilitation Methods

Interior veneers typically experience in-plane cracking 

and detachment, but may also be displaced or detached 

out-of-plane by direct acceleration. Interior partitions 

loaded out-of-plane and supported on flexible backup 

support systems can experience cracking and 

detachment.

Drift analysis is necessary to establish conformance 

with drift acceptance criteria related to the 

Nonstructural Performance Level. Nonconformance 

requires limiting structural drift, or special detailing to 

isolate the veneer support system from the structure to 

permit drift; this generally requires disassembly of the 

support system and veneer replacement. Inadequately 

adhered veneer must be replaced.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-27

11.9.3.3.2 Immediate Occupancy Nonstructural 

Performance Level

Backing shall be adequately attached to resist seismic 

design forces computed in accordance with 

Section 11.7.4. The drift ratio computed in accordance 

with Section 11.7.5 shall be limited to is 0.01.

11.9.3.4 Evaluation Requirements

Backup walls or other supports and the attachments to 

that support shall be evaluated, as well as the condition 

of the veneer itself.

11.9.4 Ceilings

11.9.4.1 Definition and Scope

Ceilings shall include horizontal and sloping assemblies 

as well as soffits, which are ceilings in an exterior 

location that are attached to or suspended from the 

building structure, and assemblies that are separately 

supported.

Ceilings shall be categorized as one of the following 

types:

1. Category a. Surface-applied or furred with 

materials that are applied directly to wood joists, 

concrete slabs, or steel decking with mechanical 

fasteners or adhesives.

2. Category b. Short-dropped gypsum board sections 

attached to wood or metal furring supported by 

carrier members.

3. Category c. Suspended metal lath and plaster.

4. Category d. Suspended acoustical board inserted 

within T-bars, together with lighting fixtures and 

mechanical items, to form an integrated ceiling 

system.

11.9.4.2 Component Behavior and 

Rehabilitation Methods

Ceiling systems shall be considered both accelerationand deformation-sensitive.

Ceiling systems not conforming to the acceptance 

criteria of Section 11.9.4.3 shall be rehabilitated in 

accordance with Section 11.8.

11.9.4.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.4.3.1 Life Safety Nonstructural Performance 

Level

Ceilings in category a, b, or d need not be rehabilitated 

for the Life Safety Nonstructural Performance Level 

except as noted in the footnotes to Table 11-1. Where 

rehabilitation is required for ceilings in category a or b, 

they shall be strengthened to resist seismic design 

forces computed in accordance with Section 11.7.3 or 

11.7.4. Ceilings in Category c shall be capable of 

accommodating the relative displacement computed in 

accordance with Section 11.7.5. Where rehabilitation is 

required for ceilings in category d, they shall be 

rehabilitated by the Prescriptive Procedure of 

Section 11.7.2.

C11.9.4.1 Definition and Scope

Furring materials include wood or metal furring 

acoustical tile, gypsum board, plaster, or metal panel 

ceiling materials.

Some older buildings have heavy decorative ceilings of 

molded plaster, which may be directly attached to the 

structure or suspended; these are typically Category a 

or Category c ceilings.

C11.9.4.2 Component Behavior and 

Rehabilitation Methods

Surface-applied or furred ceilings are primarily 

influenced by the performance of their supports. 

Rehabilitation of the ceiling takes the form of ensuring 

good attachment and adhesion. Metal lath and plaster 

ceilings depend on their attachment and bracing for 

large ceiling areas. Analysis is necessary to establish 

the acceleration forces and deformations that must be 

accommodated. Suspended integrated ceilings are 

highly susceptible to damage if not braced, causing 

distortion of grid and loss of panels; however, this is 

not regarded as a life safety threat with lightweight 

panels (less than two pounds per square foot).

Rehabilitation takes the form of bracing, attachment, 

and edge details designed to prescriptive design 

standards such as CISCA 1991 for seismic zones 0-2 

and in CISCA 1990 for seismic zones 3 and 4.
11-28 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.9.4.3.2 Immediate Occupancy Nonstructural 

Performance Level

Ceilings in category a or b shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.4. Ceilings in category c shall be capable 

of accommodating the relative displacement computed 

in accordance with Section 11.7.5. Ceilings in 

category d shall be rehabilitated by the Prescriptive 

Procedure of Section 11.7.2.

11.9.4.4 Evaluation Requirements

The condition of the ceiling finish material, its 

attachment to the ceiling support system, the attachment 

and bracing of the ceiling support system to the 

structure, and the potential seismic impacts of other 

nonstructural systems on the ceiling system shall be 

evaluated.

11.9.5 Parapets and Appendages

11.9.5.1 Definition and Scope

Parapets and appendages shall include exterior 

nonstructural features that project above or away from 

the building. They shall include sculpture and ornament 

in addition to concrete, masonry, or terra cotta parapets. 

The following parapets and appendages shall be 

rehabilitated in accordance with this section:

1. Unreinforced masonry parapets with an aspect ratio 

greater than 1.5.

2. Reinforced masonry parapets with an aspect ratio 

greater than 3.0.

3. Cornices or ledges constructed of stone, terra cotta, 

or brick, unless supported by a steel or reinforced 

concrete structure.

11.9.5.2 Component Behavior and 

Rehabilitation Methods

Parapets and appendages shall be considered 

acceleration-sensitive in the out-of-plane direction.

Parapets and appendages not conforming to the 

requirements of Section 11.9.5.3 shall be rehabilitated 

in accordance with Section 11.8.

11.9.5.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.5.3.1 Life Safety Nonstructural Performance 

Level

Parapets and appendages shall meet prescriptive 

requirements of Section 11.7.2 or shall be capable of 

resisting seismic forces computed in accordance with 

Section 11.7.3 or 11.7.4.

11.9.5.3.2 Immediate Occupancy Nonstructural 

Performance Level

Parapets and appendages shall meet prescriptive 

requirements of Section 11.7.2 or shall be capable of 

resisting seismic forces computed in accordance with 

Section 11.7.4.

11.9.5.4 Evaluation Requirements

The condition of mortar and masonry, connection to 

supports, type and stability of the supporting structure, 

and horizontal continuity of the parapet coping, shall be 

considered in the evaluation.

C11.9.5.1 Definition and Scope

Other appendages, such as flagpoles and signs that are 

similar to the above in size, weight, or potential 

consequence of failure, may be rehabilitated in 

accordance with this section.

C11.9.5.2 Component Behavior and 

Rehabilitation Methods

Materials or components that are not properly braced 

may become disengaged and topple; the results are 

among the most seismically serious consequences of 

any nonstructural components.

Prescriptive design strategies for masonry parapets not 

exceeding four feet in height consist of bracing in 

accordance with the concepts shown in FEMA 74 and 

FEMA 172, with detailing to conform to accepted 

engineering practice. Braces for parapets should be 

spaced at a maximum of eight feet on center and, when 

the parapet construction is discontinuous, a continuous 

backing element should be provided. Where there is no 

adequate connection, roof construction should be tied 

to parapet walls at the roof level. Other parapets and 

appendages should be analyzed for acceleration forces, 

and braced and connected according to accepted 

engineering principles.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-29

11.9.6 Canopies and Marquees

11.9.6.1 Definition and Scope

Canopies shall include projections from an exterior wall 

that are extensions of the horizontal building structure 

or independent structures that are tied to the building. 

Marquees shall include free-standing structures. Canvas 

or other fabric projections need not be rehabilitated in 

accordance with this section.

11.9.6.2 Component Behavior and 

Rehabilitation Methods

Canopies and marquees shall be considered 

acceleration-sensitive.

Canopies and marquees not conforming to the 

acceptance criteria of Section 11.9.6.3 shall be 

rehabilitated in accordance with Section 11.8.

11.9.6.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.6.3.1 Life Safety Nonstructural Performance 

Level

Canopies and marquees shall be capable of resisting 

both horizontal and vertical seismic design forces 

computed in accordance with Section 11.7.3 or 11.7.4.

11.9.6.3.2 Immediate Occupancy Nonstructural 

Performance Level

Canopies and marquees shall be capable of resisting 

both horizontal and vertical seismic design forces 

computed in accordance with Section 11.7.4.

11.9.6.4 Evaluation Requirements

Buckling in bracing, connection to supports, and type 

and stability of the supporting structure shall be 

considered in the evaluation.

11.9.7 Chimneys and Stacks

11.9.7.1 Definition and Scope

Chimneys and stacks that are cantilevered above 

building roofs shall be rehabilitated in accordance with 

this section. Light metal residential chimneys need not 

comply with the provisions of this document.

11.9.7.2 Component Behavior and 

Rehabilitation Methods

Chimneys and stacks shall be considered accelerationsensitive.

Chimneys and stacks not conforming to the acceptance 

criteria of Section 11.9.7.3 shall be rehabilitated in 

accordance with Section 11.8.

11.9.7.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.7.3.1 Life Safety Nonstructural Performance 

Level

Chimneys and stacks shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.3 or 11.7.4. Residential chimneys shall be 

permitted to meet the prescriptive requirements of 

Section 11.7.2.

C11.9.6.1 Definition and Scope

Canopies and marquees are generally used to provide 

weather protection.

Marquees are often constructed of metal or glass.

C11.9.6.2 Component Behavior and 

Rehabilitation Methods

The variety of design of canopies and marquees is so 

great that they must be independently analyzed and 

evaluated for their ability to withstand seismic forces. 

Rehabilitation may take the form of improving 

attachment to the building structure, strengthening, 

bracing, or a combination of measures.

C11.9.7.2 Component Behavior and 

Rehabilitation Methods

Chimneys and stacks may fail through flexure, shear, 

or overturning. They may also disengage from 

adjoining floor or roof structures and damage them, 

and their collapse or overturning may also damage 

adjoining structures. Rehabilitation may take the form 

of strengthening and/or bracing and material repair. 

Residential chimneys may be braced in accordance 

with the concepts shown in FEMA 74.
11-30 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.9.7.3.2 Immediate Occupancy Nonstructural 

Performance Level

Chimneys and stacks shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.4. Residential chimneys shall be permitted 

to meet the prescriptive requirements of Section 11.7.2.

11.9.7.4 Evaluation Requirements

The condition of the mortar and masonry, connection to 

adjacent structure, and type and stability of foundations 

shall be considered in the evaluation.

Concrete shall be evaluated for spalling and exposed 

reinforcement. Steel shall be evaluated for corrosion.

11.9.8 Stairs and Stair Enclosures

11.9.8.1 Definition and Scope

Stairs shall include the treads, risers, and landings that 

make up passageways between floors, as well as the 

surrounding shafts, doors, windows, and fire-resistant 

assemblies that constitute the stair enclosure.

11.9.8.2 Component Behavior and 

Rehabilitation Methods

Each of the separate components of the stairs shall be 

defined as either acceleration- or deformation-sensitive.

Stairs not conforming to the acceptance criteria of 

Section 11.9.8.3 shall be rehabilitated in accordance 

with Section 11.8.

11.9.8.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.9.8.3.1 Life Safety Nonstructural Performance 

Level

Stairs shall be capable of resisting the seismic design 

forces computed in accordance with Section 11.7.3 or 

11.7.4 and shall be capable of accommodating the 

expected relative displacement computed in accordance 

with Section 11.7.5.

11.9.8.3.2 Immediate Occupancy Nonstructural 

Performance Level

Stairs shall be capable of resisting the seismic design 

forces computed in accordance with Section 11.7.4 and 

shall be capable of accommodating the expected 

relative displacement computed in accordance with 

Section 11.7.5.

11.9.8.4 Evaluation Requirements

The materials and condition of stair members and their 

connections to supports, and the types and stability of 

supporting and adjacent walls, windows, and other 

portions of the stair shaft system shall be considered in 

the evaluation.

11.10 Mechanical, Electrical, and 

Plumbing Components: 

Definition, Behavior, and 

Acceptance Criteria

11.10.1 Mechanical Equipment

11.10.1.1 Definition and Scope

Equipment used for the operation of the building, and 

that meets one or more of the following criteria shall be 

rehabilitated in accordance with this section.

C11.9.8.2 Component Behavior and 

Rehabilitation Methods

The stairs themselves may be independent of the 

structure, or integral with the structure. If integral, they 

should form part of the overall structural evaluation 

and analysis, with particular attention paid to the 

possibility of response modification due to localized 

stiffness. If independent, the stairs must be evaluated 

for normal stair loads and their ability to withstand 

direct acceleration or loads transmitted from the 

structure through connections.

Stair enclosure materials may fall and render the stairs 

unusable due to debris.

Rehabilitation of integral or independent stairs may 

take the form of necessary structural strengthening or 

bracing, or the introduction of connection details to 

eliminate or reduce interaction between stairs and the 

building structure.

Rehabilitation of enclosing walls or glazing should 

follow the requirements of the relevant sections of this 

document.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-31

1. All equipment weighing over 400 pounds.

2. Unanchored equipment weighing over 100 pounds 

that does not have a factor of safety against 

overturning of 1.5 or greater when design loads, 

calculated in accordance with Section 11.7.3 or 

11.7.4, are applied.

3. Equipment weighing over 20 pounds that is attached 

to ceiling, wall, or other support more than four feet 

above the floor.

4. Building operation equipment including

4.1. Boilers and furnaces.

4.2. Conveyors (nonpersonnel).

4.3. HVAC system equipment, vibration-isolated.

4.4. HVAC system equipment, 

non-vibration-isolated.

4.5. HVAC system equipment mounted in-line with 

ductwork. 

11.10.1.2 Component Behavior and 

Rehabilitation Methods

Mechanical equipment shall be considered accelerationsensitive.

Mechanical equipment not conforming to the 

acceptance criteria of Section 11.10.1.3 shall be 

rehabilitated in accordance with Section 11.8.

11.10.1.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.1.3.1 Life Safety Nonstructural Performance 

Level

Equipment anchorage shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.3 or 11.7.4.

11.10.1.3.2 Immediate Occupancy Nonstructural 

Performance Level

Equipment anchorage shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.4.

C11.10.1.1 Definition and Scope

Equipment such as manufacturing or processing 

equipment related to the occupant’s business should be 

evaluated separately for the effects that failure due to a 

seismic event could have on the operation of the 

building.

C11.10.1.2 Component Behavior and 

Rehabilitation Methods

Failure of these components consists of sliding, tilting, 

or overturning of floor- or roof-mounted equipment off 

its base, and possible loss of attachment (with 

consequent falling) for equipment attached to a vertical 

structure or suspended, and failure of piping or 

electrical wiring connected to the equipment.

Construction of mechanical equipment to nationally 

recognized codes and standards, such as those 

approved by the American National Standards 

Institute, provides adequate strength to accommodate 

all normal and upset operating loads.

Basic rehabilitation consists of securely anchoring 

floor-mounted equipment by bolting, with detailing 

appropriate to the base construction of the equipment.

Seismic forces can be established by analysis using the 

default Equations (11-1) and (11-2). Equipment 

weighing over 400 pounds and located on the third 

floor or above (or on a roof of equivalent height) 

should be analyzed using Equations (11-3) and (11-4).

Existing attachments for attached or suspended 

equipment must be evaluated for seismic load capacity, 

and strengthened or braced as necessary. Attachments 

that provide secure anchoring eliminate or reduce the 

likelihood of piping or electrical distribution failure.
11-32 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.10.1.4 Evaluation Requirements

Equipment shall be analyzed to establish accelerationinduced forces, and supports, hold-downs, and bracing 

shall be visually evaluated.

11.10.2 Storage Vessels and Water Heaters

11.10.2.1 Definition and Scope

Storage vessels and water heaters shall include all 

vessels that contain fluids used for building operation.

Vessels shall be classified into one of the following two 

categories:

1. Category 1. Vessels with structural support of 

contents, in which the shell is supported by legs or a 

skirt.

2. Category 2. Flat-bottom vessels in which the weight 

of the contents is supported by the floor, roof, or a 

structural platform.

11.10.2.2 Component Behavior and 

Rehabilitation Methods

Tanks and vessels shall be considered accelerationsensitive.

Tanks and vessels not conforming to the acceptance 

criteria of Section 11.10.2.3 shall be rehabilitated in 

accordance with Section 11.8.

11.10.2.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.2.3.1 Life Safety Nonstructural Performance 

Level

1. Category 1 Equipment. If the analytical procedure 

is selected based on Table 11-1, Category 1 

equipment and supports shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.3 or 11.7.4. If the prescriptive 

procedure is selected based on Table 11-1, Category 

1 equipment shall meet prescriptive requirements in 

accordance with Section 11.7.2.

2. Category 2 Equipment. If the analytical procedure 

is selected based on Table 11-1, Category 2 

equipment and supports shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.3 or 11.7.4. If the prescriptive 

procedure is selected based on Table 11-1, Category 

2 equipment shall meet prescriptive requirements in 

accordance with Section 11.7.2.

C11.10.1.4 Evaluation Requirements

Existing concrete anchors may have to be tested by 

applying torque to the nuts to confirm that adequate 

strength is present.

C11.10.2.1 Definition and Scope

The vessel may be fabricated of materials such as steel 

or other metals, or fiberglass, or it may be a glass-lined 

tank. These requirements may also be applied, with 

judgment, to vessels that contain solids that act as a 

fluid, and vessels containing fluids not involved in the 

operation of the building.

C11.10.2.2 Component Behavior and 

Rehabilitation Methods

Category 1 vessels fail by stretching of anchor bolts, 

buckling and disconnection of supports, and 

consequent tilting or overturning of the vessel. A 

Category 2 vessel may be displaced from its 

foundation, or its shell may fail by yielding near the 

bottom, creating a visible bulge or possible leakage. 

Displacement of both types of vessel may cause 

rupturing of connecting piping and leakage.

Category 1 residential water heaters with a capacity no 

greater than 100 gallons may be rehabilitated by 

prescriptive design methods, such as concepts 

described in FEMA 74 or FEMA 172. Category 1 

vessels with a capacity less than 1000 gallons should 

be designed to meet the force provisions of 

Section 11.7.3 or 11.7.4, and bracing strengthened or 

added as necessary. Other Category 1 and Category 2 

vessels should be evaluated against a recognized 

standard, such as API 650 for vessels containing 

petroleum products or other chemicals, or AWWA 

D100-96 for water vessels.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-33

11.10.2.3.2 Immediate Occupancy Nonstructural 

Performance Level

1. Category 1 Equipment. If the analytical procedure 

is selected based on Table 11-1, Category 1 

equipment and supports shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.4. If the prescriptive procedure is 

selected based on Table 11-1, Category 1 equipment 

shall meet prescriptive requirements in accordance 

with Section 11.7.2.

2. Category 2 Equipment. If the analytical procedure 

is selected based on Table 11-1, Category 2 

equipment and supports shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.4. If the prescriptive procedure is 

selected based on Table 11-1, Category 2 equipment 

shall meet prescriptive requirements in accordance 

with Section 11.7.2.

11.10.2.4 Evaluation Requirements

All equipment shall be visually evaluated to determine 

the existence of hold-downs, supports, and bracing.

11.10.3 Pressure Piping

11.10.3.1 Definition and Scope

The requirements of this section shall apply to all piping 

(except fire suppression piping) that carries fluids 

which, in their vapor stage, exhibit a pressure of 15 psi, 

gauge, or higher.

11.10.3.2 Component Behavior and 

Rehabilitation Methods

Piping shall be considered acceleration-sensitive. 

Piping that runs between floors or across seismic joints 

shall be considered both acceleration- and deformationsensitive.

Piping not conforming to the acceptance criteria of 

Section 11.10.3.3 shall be rehabilitated in accordance 

with Section 11.8.

11.10.3.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.3.3.1 Life Safety Nonstructural Performance 

Level

If the Prescriptive Procedure is selected based on Table 

11-1, piping shall meet the prescriptive requirements of 

Section 11.7.2. If the Analytical Procedure is selected 

based on Table 11-1, piping shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.3 or 11.7.4. Piping that runs between floors 

or across seismic joints shall be capable of 

accommodating relative displacements computed in 

accordance with Section 11.7.5.

11.10.3.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, piping shall meet the prescriptive requirements of 

Section 11.7.2. If the Analytical Procedure is selected 

based on Table 11-1, piping shall be capable of resisting 

seismic forces computed in accordance with 

Section 11.7.4. Piping that runs between floors or 

across seismic joints shall be capable of 

accommodating relative displacements computed in 

accordance with Section 11.7.5.

C11.10.2.4 Evaluation Requirements

Existing concrete anchors may have to be tested by 

applying torque to the nuts to confirm that adequate 

strength is present.

C11.10.3.2 Component Behavior and 

Rehabilitation Methods

The most common failure of piping is joint failure, 

caused by inadequate support or bracing.

Rehabilitation is accomplished by prescriptive design 

approaches to support and bracing. Piping systems 

should be evaluated for compliance with consensus 

standards such as ASME B31, B31.1, B31.3, B31.4, 

B31.5, B31.8, B31.9, and B31.11 and ASHRAE where 

applicable. For large critical piping systems, the 

building official or responsible engineer must establish 

forces and evaluate supports.
11-34 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.10.3.4 Evaluation Requirements

High-pressure piping shall be tested by an approved 

method. Lines shall be hydrostatically tested to 150% of 

the maximum anticipated pressure of the system.

11.10.4 Fire Suppression Piping

11.10.4.1 Definition and Scope

Fire suppression piping shall include fire sprinkler 

piping consisting of main risers and laterals weighing, 

loaded, in the range of 30 to 100 pounds per lineal foot, 

with branches of decreasing size to two pounds per foot.

11.10.4.2 Component Behavior and 

Rehabilitation Methods

Fire suppression piping shall be considered 

acceleration-sensitive. Fire suppression piping that runs 

between floors or across seismic joints shall be 

considered both acceleration- and deformationsensitive.

Fire suppression piping not conforming to the 

acceptance criteria of Section 11.9.4.3 shall be 

rehabilitated in accordance with Section 11.8.

11.10.4.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.4.3.1 Life Safety Nonstructural Performance 

Level

If the Prescriptive Procedure is selected based on Table 

11-1, fire suppression piping shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

Procedure is selected based on Table 11-1, fire 

suppression piping shall be capable of resisting seismic 

design forces computed in accordance with 

Section 11.7.3 or 11.7.4. Fire suppression piping that 

runs between floors or across seismic joints shall be 

capable of accommodating relative displacements 

computed in accordance with Section 11.7.5.

11.10.4.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, fire suppression piping shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

Procedure is selected based on Table 11-1, fire 

suppression piping shall be capable of resisting seismic 

design forces computed in accordance with 

Section 11.7.4. Fire suppression piping that runs 

between floors or across seismic joints shall be capable 

of accommodating relative displacements computed in 

accordance with Section 11.7.5. 

11.10.4.4 Evaluation Requirements

The support, flexibility, protection at seismic movement 

joints, and freedom from impact from adjoining 

materials at the sprinkler heads shall be evaluated.

11.10.5 Fluid Piping other than Fire 

Suppression

11.10.5.1 Definition and Scope

Piping, other than pressure piping or fire suppression 

lines, that transfers fluids under pressure by gravity, or 

that are open to the atmosphere—including drainage 

and ventilation piping, hot, cold, and chilled water 

piping; and piping carrying liquids, as well as fuel gas 

lines—shall meet the requirements of this section.

Fluid piping other than fire suppression piping shall be 

classified into one of the following two categories:

1. Category 1. Hazardous materials and flammable 

liquids that would pose an immediate life safety 

danger if exposed, because of inherent properties of 

the contained material.

C11.10.3.4 Evaluation Requirements

High-pressure piping may be tested in accordance with 

ASME B31.9.

C11.10.4.2 Component Behavior and 

Rehabilitation Methods

The most common failure of fire suppression piping is 

joint failure, caused by inadequate support or bracing, 

or by sprinkler heads impacting adjoining materials.

Rehabilitation is accomplished by prescriptive design 

approaches to support and bracing. The prescriptive 

requirements of NFPA-13 should be used.

C11.10.4.4 Evaluation Requirements

The support and bracing of bends of the main risers 

and laterals, as well as maintenance of adequate 

flexibility to prevent buckling, are especially 

important.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-35

2. Category 2. Materials that, in case of line rupture, 

would cause property damage, but pose no 

immediate life safety danger.

11.10.5.2 Component Behavior and 

Rehabilitation Methods

Fluid piping other than fire suppression piping shall be 

considered acceleration-sensitive. Piping that runs 

between floors or across seismic joints shall be 

considered both acceleration- and deformationsensitive.

Fluid piping not conforming to the acceptance criteria 

of Section 11.10.5.3 shall be rehabilitated in accordance 

with Section 11.8.

11.10.5.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.5.3.1 Life Safety Nonstructural Performance 

Level

1. Category 1 piping systems. If the Prescriptive 

Procedure is selected based on Table 11-1, fluid 

piping supports and bracing shall meet the 

prescriptive requirements of Section 11.7.2. If the 

Analytical Procedure is selected based on Table 

11-1, fluid piping shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.3 or 11.7.4. Piping that runs between 

floors and across seismic joints shall be capable of 

accommodating relative displacements computed in 

accordance with Section 11.7.5.

2. Category 2 piping systems. If the Prescriptive 

Procedure is selected based on Table 11-1, fluid 

piping supports and bracing shall meet the 

prescriptive requirements of Section 11.7.2. If the 

Analytical Procedure is selected based on Table 

11-1, fluid piping shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.3 or 11.7.4. Piping that runs between 

floors and across seismic joints shall be capable of 

accommodating relative displacements computed in 

accordance with Section 11.7.5.

11.10.5.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, fluid piping supports and bracing shall meet the 

prescriptive requirements of Section 11.7.2 for essential 

facilities. If the Analytical Procedure is selected based 

on Table 11-1, fluid piping shall be capable of resisting 

seismic design forces computed in accordance with 

Section 11.7.4. Piping that runs between floors and 

across seismic joints shall be capable of 

accommodating relative displacements computed in 

accordance with Section 11.7.5.

11.10.5.4 Evaluation Requirements

The support, flexibility, and protection at seismic joints 

of fluid piping other than fire suppression piping shall 

be evaluated.

C11.10.5.1 Definition and Scope

Hazardous materials and flammable liquids that would 

pose an immediate life safety danger if exposed are 

defined in NFPA 325-94, 49-94, 491M-91, and 704-90.

C11.10.5.2 Component Behavior and 

Rehabilitation Methods

The most common failure is joint failure, caused by 

inadequate support or bracing.

Category 1 piping rehabilitation is accomplished by 

strengthening support and bracing, using the 

prescriptive methods of SP-58. The piping systems 

themselves should be designed to meet the force 

provisions of Section 11.7.3 or 11.7.4 and relative 

displacement provisions of Section 11.7.5. The effects 

of temperature differences, dynamic fluid forces, and 

piping contents should be taken into account.

Category 2 piping rehabilitation is accomplished by 

strengthening support and bracing using the 

prescriptive methods of SP-58 as long as the piping 

falls within the size limitations of those guidelines. 

Piping that exceeds the limitations of those guidelines 

shall be designed to meet the force provisions of 

Section 11.7.3 or 11.7.4 and relative displacement 

provisions of Section 11.7.5.
11-36 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

Piping shall be insulated from detrimental heat effects.

11.10.6 Ductwork

11.10.6.1 Definition and Scope

Ductwork shall include HVAC and exhaust ductwork 

systems. Seismic restraints shall not be required for 

ductwork that is not conveying hazardous materials, 

and that meets either of the following conditions:

1. HVAC ducts are suspended from hangers 12 inches 

or less in length from the top of the duct to the 

supporting structure. Hangers shall be installed 

without eccentricities that induce moments in the 

hangers.

2. HVAC ducts have a cross-sectional area of less than 

six square feet.

11.10.6.2 Component Behavior and 

Rehabilitation Methods

Ducts shall be considered acceleration-sensitive. 

Ductwork that runs between floors or across seismic 

joints shall be considered both acceleration- and 

deformation-sensitive.

Ductwork not conforming to the acceptance criteria of 

Section 11.10.6.3 shall be rehabilitated in accordance 

with Section 11.8.

11.10.6.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.6.3.1 Life Safety Nonstructural Performance 

Level

Ductwork shall meet the requirements of prescriptive 

standards in accordance with Section 11.7.2.

11.10.6.3.2 Immediate Occupancy Nonstructural 

Performance Level

Ductwork shall meet the requirements of prescriptive 

standards in accordance with Section 11.7.2.

11.10.6.4 Evaluation Requirements

Ductwork shall be evaluated visually to determine its 

length, connection type, and cross-sectional area.

11.10.7 Electrical and Communications 

Equipment

11.10.7.1 Definition and Scope

All electrical and communication equipment, including 

panel boards, battery racks, motor control centers, 

switch gear, and other fixed components located in 

electrical rooms or elsewhere in the building that meet 

any of the following criteria shall comply with the 

requirements of this section:

1. All equipment weighing over 400 pounds.

2. Unanchored equipment weighing over 100 pounds 

that does not have a factor of safety against 

overturning of 1.5 or greater when design loads 

computed in accordance with Section 11.7.3 or 

11.7.4 are applied.

3. Equipment weighing over 20 pounds that is attached 

to ceiling, wall, or other support more than four feet 

above the floor.

4. Building operation equipment.

11.10.7.2 Component Behavior and 

Rehabilitation Methods

Electrical equipment shall be considered accelerationsensitive.

C11.10.5.4 Evaluation Requirements

The support and bracing of bends in the main risers 

and laterals, as well as maintenance of adequate 

flexibility to prevent buckling, are especially 

important.

C11.10.6.2 Component Behavior and 

Rehabilitation Methods

Damage to ductwork is caused by failure of supports or 

lack of bracing that causes deformation or rupture of 

the ducts at joints, leading to leakage from the system.

Rehabilitation consists of strengthening supports and 

strengthening or adding bracing. Prescriptive design 

methods may be used in accordance with SMACNA 

1980 and 1985.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-37

Electrical equipment not conforming to the acceptance 

criteria of Section 11.10.7.3 shall be rehabilitated in 

accordance with Section 11.8.

11.10.7.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.7.3.1 Life Safety Nonstructural Performance 

Level

If the Prescriptive Procedure is selected based on Table 

11-1, electrical equipment shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

Procedure is selected based on Table 11-1, electrical 

equipment shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.3 or 

11.7.4.

11.10.7.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, electrical equipment shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

Procedure is selected based on Table 11-1, electrical 

equipment shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.4.

11.10.7.4 Evaluation Requirements

Equipment shall be visually evaluated to determine its 

category and the existence of the hold-downs, supports, 

and braces.

11.10.8 Electrical and Communications 

Distribution Components

11.10.8.1 Definition and Scope

All electrical and communications transmission lines, 

conduit, and cables, and their supports, shall comply 

with the requirements of this section.

11.10.8.2 Component Behavior and 

Rehabilitation Methods

Electrical distribution equipment shall be considered 

acceleration-sensitive. Wiring or conduit that runs 

between floors or across expansion or seismic joints 

shall be considered both acceleration- and deformationsensitive.

Electrical and communications distribution components 

not conforming to the acceptance criteria of 

Section 11.10.8.3 shall be rehabilitated in accordance 

with Section 11.8.

11.10.8.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

C11.10.7.2 Component Behavior and 

Rehabilitation Methods

Failure of these components consists of sliding, tilting, 

or overturning of floor- or roof-mounted equipment off 

its base, and possible loss of attachment (with 

consequent falling) for equipment attached to a vertical 

structure or suspended, and failure of electrical wiring 

connected to the equipment.

Construction of electrical equipment to nationally 

recognized codes and standards, such as those 

approved by the American National Standards Institute 

(ANSI), provides adequate strength to accommodate 

all normal and upset operating loads.

Basic rehabilitation consists of securely anchoring 

floor-mounted equipment by bolting, with detailing 

appropriate to the base construction of the equipment.

C11.10.7.4 Evaluation Requirements

Larger equipment requiring the Analytical Procedure 

must be analyzed to determine forces, and visually 

evaluated. Concrete anchors may have to be tested by 

applying torque to the nuts to confirm that adequate 

strength is present.

C11.10.8.2 Component Behavior and 

Rehabilitation Methods

Failure occurs most commonly by inadequate support 

or bracing, deformation of the attached structure, or 

impact from adjoining materials.

Rehabilitation may be accomplished by strengthening 

support and bracing using the prescriptive methods 

contained in SMACNA 1980 and 1985.
11-38 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.10.8.3.1 Life Safety Nonstructural Performance 

Level

Electrical and communications distribution components 

shall meet the requirements of prescriptive standards in 

accordance with Section 11.7.2.

11.10.8.3.2 Immediate Occupancy Nonstructural 

Performance Level

Electrical and communications distribution components 

shall meet the requirements of prescriptive standards for 

essential facilities in accordance with Section 11.7.2.

11.10.8.4 Evaluation Requirements

Components shall be visually evaluated to determine 

the existence of supports and bracing.

11.10.9 Light Fixtures

11.10.9.1 Definition and Scope

Lighting fixtures shall be classified into one of the 

following categories:

Category 1. Lighting recessed in ceilings.

Category 2. Lighting surface-mounted to ceilings or 

walls.

Category 3. Lighting supported within a suspended 

ceiling system (integrated ceiling).

Category 4. Lighting suspended from ceilings or 

structure by a pendant or chain.

11.10.9.2 Component Behavior and 

Rehabilitation Methods

Light fixtures not conforming to the acceptance criteria 

of Section 11.10.9.3 shall be rehabilitated in accordance 

with Section 11.8.

11.10.9.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.10.9.3.1 Life Safety Nonstructural Performance 

Level

1. Categories 1 and 2. The connection to ceiling or 

wall shall be present with no visible signs of distress.

2. Category 3. Systems bracing and support shall meet 

prescriptive requirements in accordance with 

Section 11.7.2. 

3. Category 4. Fixtures weighing over 20 pounds shall 

be adequately articulated or connections to the 

building shall be ductile and the fixture shall be free 

to swing without impacting adjoining materials.

11.10.9.3.2 Immediate Occupancy Nonstructural 

Performance Level

1. Categories 1 and 2. The connection to ceiling or 

wall shall be present with no visible signs of distress. 

2. Category 3. Systems bracing and support shall meet 

prescriptive requirements for essential facilities. 

C11.10.9.2 Component Behavior and 

Rehabilitation Methods

Failure of Category 1 and 2 components occurs 

through failure of attachment of the light fixture and/or 

failure of the supporting ceiling or wall. Failure of 

Category 3 components occurs through loss of support 

from the T-bar system, and by distortion caused by 

deformation of the supporting structure or deformation 

of the ceiling grid system, allowing the fixture to fall. 

Failure of Category 4 components is caused by 

excessive swinging that results in the pendant or chain 

support breaking on impact with adjacent materials, or 

the support being pulled out of the ceiling.

Rehabilitation of Category 1 and 2 components 

involves attachment repair or fixture replacement in 

association with necessary rehabilitation of the 

supporting ceiling or wall. Rehabilitation of Category 

3 components involves the addition of independent 

support for the fixture from the structure or 

substructure in accordance with FEMA 74 design 

concepts. Rehabilitation of Category 4 components 

involves strengthening of attachment and ensuring 

freedom to swing without impacting adjoining 

materials.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-39

3. Category 4. Fixtures weighing over 20 pounds shall 

be articulated or connections to the building shall be 

ductile and the fixture shall be free to swing without 

impacting adjoining materials.

11.10.9.4 Evaluation Requirements

Light fixture supports shall be visually evaluated to 

determine the connection type and adequacy.

11.11 Furnishings and Interior 

Equipment: Definition, Behavior, 

and Acceptance Criteria

11.11.1 Storage Racks

11.11.1.1 Definition and Scope

Storage racks shall include systems for holding 

materials either permanently or temporarily.

11.11.1.2 Component Behavior and 

Rehabilitation Methods

Storage racks shall be considered acceleration-sensitive.

Storage racks not conforming to the acceptance criteria 

of Section 11.11.1.3 shall be rehabilitated in accordance 

with Section 11.8.

11.11.1.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.1.3.1 Life Safety Nonstructural Performance 

Level

Storage racks shall be capable of resisting seismic 

design forces computed in accordance with 

Section 11.7.3 or 11.7.4.

11.11.1.3.2 Immediate Occupancy Nonstructural 

Performance Level

Storage racks shall be capable of resisting seismic 

design forces computed in accordance with 

Section 11.7.4.

11.11.1.4 Evaluation Requirements

Buckling or racking failure of storage rack elements, 

connection to support structures, and type and stability 

of supporting structure shall be considered in the 

evaluation.

11.11.2 Bookcases

11.11.2.1 Definition and Scope

Bookcases constructed of wood or metal, in excess of 

four feet high, shall meet the requirements of this 

section.

11.11.2.2 Component Behavior and 

Rehabilitation Methods

Bookcases shall be considered acceleration-sensitive.

Bookcases not conforming to the acceptance criteria of 

Section 11.11.2.3 shall be rehabilitated in accordance 

with Section 11.8.

C11.11.1.1 Definition and Scope

Storage racks are usually constructed of metal. Storage 

racks are generally purchased as proprietary systems 

installed by a tenant and are often not under the direct 

control of the building owner. Thus, they are usually 

not part of the construction contract, and often have no 

foundation or foundation attachment. However, they 

are often permanently installed, and their size and 

loaded weight make them an important hazard to either 

life, property, or the surrounding structure. Storage 

racks in excess of four feet in height located in 

occupied locations shall be considered when the Life 

Safety Nonstructural Performance Level is selected.

C11.11.1.2 Component Behavior and 

Rehabilitation Methods

Storage racks may fail internally—through inadequate 

bracing or moment-resisting capacity—or externally, 

by overturning caused by absence or failure of 

foundation attachments.

Rehabilitation is usually accomplished by the addition 

of bracing to the rear and side panels of racks and/or by 

improving the connection of the rack columns to the 

supporting slab. In rare instances, foundation 

improvements may be required to remedy insufficient 

bearing or uplift load capacity.

Seismic forces can be established by analysis in 

accordance with Section 11.7.3 or 11.7.4. However, 

special attention should be paid to the evaluation and 

analysis of large, heavily loaded rack systems because 

of their heavy loading and lightweight structural 

members.
11-40 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.11.2.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.2.3.1 Life Safety Nonstructural Performance 

Level

Bookcases shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.3 or 

11.7.4.

11.11.2.3.2 Immediate Occupancy Nonstructural 

Performance Level

Bookcases shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.4.

11.11.2.4 Evaluation Requirements

The loading, type, and condition of bookcases, their 

connection to support structures, and type and stability 

of supporting structure shall be considered in the 

evaluation.

11.11.3 Computer Access Floors

11.11.3.1 Definition and Scope

Computer access floors shall include panelized, 

elevated floor systems designed to facilitate access to 

wiring, fiber optics, and other services associated with 

computers and other electronic components.

11.11.3.2 Component Behavior and 

Rehabilitation Methods

Computer access floors shall be considered both 

acceleration- and deformation-sensitive.

Computer access floors not conforming to the 

acceptance criteria of Section 11.11.3.3 shall be 

rehabilitated in accordance with Section 11.8.

11.11.3.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.3.3.1 Life Safety Nonstructural Performance 

Level

Computer access floors need not be rehabilitated for the 

Life Safety Nonstructural Performance Level.

11.11.3.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, prescriptive requirements of Section 11.7.2 shall 

be met. If the Analytical Procedure is selected based on 

Table 11-1, computer access floors shall be capable of 

resisting seismic design forces computed in accordance 

with Section 11.7.4.

C11.11.2.2 Component Behavior and 

Rehabilitation Methods

Bookcases may deform or overturn due to inadequate 

bracing or attachment to floors or adjacent walls, 

columns, or other structural members. Rehabilitation is 

usually accomplished by the addition of metal cross 

bracing to the rear of the bookcase to improve its 

internal resistance to racking forces, and by bracing the 

bookcase both in- and out-of-plane to the adjacent 

structure or walls to prevent overturning and racking.

C11.11.3.1 Definition and Scope

Access floors vary in height but generally are less than 

three feet above the supporting structural floor. The 

systems include structural legs, horizontal panel 

supports, and panels.

C11.11.3.2 Component Behavior and 

Rehabilitation Methods

Computer access floors may displace laterally or 

buckle vertically under seismic loads. Rehabilitation of 

access floors usually includes a combination of 

improved attachment of computer and communication 

racks through the access floor panels to the supporting 

steel structure or to the underlying floor system, while 

improving the lateral-load-carrying capacity of the 

steel stanchion system by installing braces or 

improving the connection of the stanchion base to the 

supporting floor, or both.

Rehabilitation should be designed in accordance with 

concepts described in FEMA 74. The weight of the 

floor system, as well as supported equipment, should 

be included in the analysis.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-41

11.11.3.4 Evaluation Requirements

Buckling and racking of access floor supports, 

connection to the support structure, and the effects of 

mounted equipment shall be considered in the 

evaluation.

11.11.4 Hazardous Materials Storage

11.11.4.1 Definition and Scope

Hazardous materials storage shall include permanently 

installed containers—freestanding, on supports, or 

stored on countertops or shelves—that hold materials 

defined to be hazardous by the National Institute for 

Occupational Safety and Health, including the 

following types:

1. Propane gas tanks.

2. Compressed gas vessels.

3. Dry or liquid chemical storage containers.

Large nonbuilding structures, such as large tanks found 

in heavy industry or power plants, floating-roof oil 

storage tanks, and large (greater than ten feet long) 

propane tanks at propane manufacturing or distribution 

plants need not meet the requirements of this section.

11.11.4.2 Component Behavior and 

Rehabilitation Methods

Hazardous materials storage shall be considered 

acceleration-sensitive.

Hazardous materials storage not conforming to the 

acceptance criteria of Section 11.11.4.3 shall be 

rehabilitated in accordance with Section 11.8.

11.11.4.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.4.3.1 Life Safety Nonstructural Performance 

Level

Hazardous materials storage shall meet prescriptive 

requirements in accordance with Section 11.7.2.

11.11.4.3.2 Immediate Occupancy Nonstructural 

Performance Level

Hazardous materials storage shall meet prescriptive 

requirements for essential facilities in accordance with 

Section 11.7.2.

11.11.4.4 Evaluation Requirements

The location and types of hazardous materials, 

container materials, manner of bracing, internal lateral 

resistance, and the effect of hazardous material spills 

shall be considered in the evaluation.

11.11.5 Computer and Communication Racks

11.11.5.1 Definition and Scope

Computer and communication racks shall include freestanding rack systems in excess of four feet in height 

designed to support computer and other electronic 

equipment. Equipment stored on computer and 

communication racks need not meet the requirements of 

this section.

C11.11.3.4 Evaluation Requirements

Possible future equipment should also be considered in 

the evaluation.

C11.11.4.2 Component Behavior and 

Rehabilitation Methods

Upset of the storage container may release the 

hazardous material. Failure occurs because of buckling 

and overturning of supports and/or inadequate bracing. 

Rehabilitation consists of strengthening and increasing 

supports or adding bracing designed according to 

concepts described in FEMA 74 and FEMA 172.

C11.11.5.1 Definition and Scope

Racks may be supported on either structural or access 

floors and may or may not be attached directly to these 

supports.
11-42 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components

11.11.5.2 Component Behavior and 

Rehabilitation Methods

Computer and communication racks shall be considered 

acceleration-sensitive.

Computer communication racks not conforming to the 

acceptance criteria of Section 11.11.5.3 shall be 

rehabilitated in accordance with Section 11.8.

11.11.5.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.5.3.1 Life Safety Nonstructural Performance 

Level

Computer and communication racks need not be 

rehabilitated for the Life Safety Nonstructural 

Performance Level.

11.11.5.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, computer and communication racks shall meet the 

prescriptive requirements of Section 11.7.2. If the 

Analytical Procedure is selected based on Table 11-1, 

computer and communication racks shall be capable of 

resisting seismic design forces computed in accordance 

with Section 11.7.4.

11.11.5.4 Evaluation Requirements

Buckling or racking failure of rack elements, their 

connection to support structures, and type and stability 

of the supporting structure shall be considered in the 

evaluation. The effect of rack failure on equipment shall 

also be considered.

11.11.6 Elevators

11.11.6.1 Definition and Scope

Elevators shall include cabs and shafts, as well as all 

equipment and equipment rooms associated with 

elevator operation, such as hoists, counterweights, 

cables, and controllers.

11.11.6.2 Component Behavior and 

Rehabilitation Methods

Elements of elevators shall be considered accelerationsensitive. Shafts and hoistway rails, which rise through 

multiple floors, shall be considered both accelerationand deformation-sensitive.

Elevator components not conforming to the acceptance 

criteria of Section 11.11.6.2 shall be rehabilitated in 

accordance with Section 11.8.

11.11.6.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.6.3.1 Life Safety Nonstructural Performance 

Level

If the Prescriptive Procedure is selected based on Table 

11-1, elevator components shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

C11.11.5.2 Component Behavior and 

Rehabilitation Methods

Computer and communication racks may fail 

internally—through inadequate bracing or momentresisting capacity—or externally, by overturning 

caused by absence or failure of floor attachments.

Rehabilitation is usually accomplished by the addition 

of bracing to the rear and side panels of the racks, and/

or by improving the connection of the rack to the 

supporting floor using concepts shown in FEMA 74 or 

FEMA 172.

C11.11.6.2 Component Behavior and 

Rehabilitation Methods

Elements of elevators may become dislodged or 

derailed. Shaft walls and the construction of machinery 

room walls are often not engineered and must be 

considered in a way similar to that for other partitions. 

Shaft walls that are of unreinforced masonry or hollow 

tile must be considered with special care, since failure 

of these elements violates Life Safety Nonstructural 

Performance Level criteria.

Elevator machinery may be subject to the same 

damage as other heavy floor-mounted equipment. 

Electrical power loss renders elevators inoperable.

Rehabilitation measures include a variety of techniques 

taken from specific component sections for partitions, 

controllers, and machinery. Rehabilitation specific to 

elevator operation can include seismic shutoffs, cable 

restrainers, and counterweight retainers; such measures 

should be in accordance with ASME A17.1.
Chapter 11: Architectural, Mechanical, and 

Electrical Components

FEMA 356 Seismic Rehabilitation Prestandard 11-43

Procedure is selected based on Table 11-1, elevator 

components shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.3 or 

11.7.4.

11.11.6.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Prescriptive Procedure is selected based on Table 

11-1, elevator components shall meet the prescriptive 

requirements of Section 11.7.2. If the Analytical 

Procedure is selected based on Table 11-1, elevator 

components shall be capable of resisting seismic design 

forces computed in accordance with Section 11.7.4.

11.11.6.4 Evaluation Requirements

The construction of elevator shafts shall be considered 

in the evaluation.

11.11.7 Conveyors

11.11.7.1 Definition and Scope

Conveyors shall include material conveyors, including 

all machinery and controllers necessary to operation.

11.11.7.2 Component Behavior and 

Rehabilitation Methods

Conveyors shall be considered both acceleration- and 

deformation-sensitive.

Conveyors not conforming to the acceptance criteria of 

Section 11.11.7.3 shall be rehabilitated in accordance 

with Section 11.8.

11.11.7.3 Acceptance Criteria

Acceptance criteria shall be applied in accordance with 

Section 11.3.2.

11.11.7.3.1 Life Safety Nonstructural Performance 

Level

Conveyors need not be rehabilitated for the Life Safety 

Nonstructural Performance Level.

11.11.7.3.2 Immediate Occupancy Nonstructural 

Performance Level

If the Analytical Procedure is selected based on Table 

11-1, conveyors shall be capable of resisting seismic 

design forces computed in accordance with 

Section 11.7.4. If the Prescriptive Procedure is selected 

based on Table 11-1, conveyors shall meet prescriptive 

standards in accordance with Section 11.7.2.

11.11.7.4 Evaluation Requirements

The stability of machinery shall be considered in the 

evaluation.

C11.11.6.4 Evaluation Requirements

The possibility of displacement or derailment of 

hoistway counterweights and cables should be 

considered, as should the anchorage of elevator 

machinery.

C11.11.7.2 Component Behavior and 

Rehabilitation Methods

Conveyor machinery may be subject to the same 

damage as other heavy floor-mounted equipment. In 

addition, deformation of adjoining building materials 

may render the conveyor inoperable. Electrical power 

loss renders the conveyor inoperable.

Rehabilitation of the conveyor involves prescriptive 

procedures using special skills provided by the 

conveyor manufacturer.
11-44 Seismic Rehabilitation Prestandard FEMA 356

Chapter 11: Architectural, Mechanical, and 

Electrical Components
FEMA 356 Seismic Rehabilitation Prestandard A-1

A. Use of this Standard for Local or 

Directed Risk Mitigation Programs

A.1 General

This ASCE Standard for Seismic Rehabilitation of 

Buildings is written in mandatory language suitable for 

adoption and enforcement by code officials in local risk 

mitigation programs, by organizations or governmental 

agencies in directed mitigation programs covering 

many buildings, or for reference by building owners 

voluntarily undertaking rehabilitation of buildings. This 

appendix provides guidance on the use of this standard 

for local or directed risk mitigation programs.

Local or directed risk mitigation programs may target 

certain building types for rehabilitation or require 

complete rehabilitation coupled with other remodeling 

work. The incorporation of variable Rehabilitation 

Objectives and the use of Model Building Types in this 

standard allows creation of subsets of rehabilitation 

requirements to suit local conditions of seismicity, 

building inventory, social and economic considerations, 

and other factors. Provisions appropriate for local 

situations can be extracted, put into regulatory 

language, and adopted into appropriate codes, 

standards, or local ordinances.

A.2 Initial Considerations for 

Mitigation Programs

Local or directed programs can either target high-risk 

building types or set overall priorities. These decisions 

should be made with full consideration of physical, 

social, historic, and economic characteristics of the 

building inventory. Although financial incentives can 

induce voluntary risk mitigation, carefully planned 

mandatory or directed programs, developed in 

cooperation with those whose interests are affected, are 

generally more effective. Potential benefits of such 

programs include reduction of direct earthquake 

losses—casualties, costs to repair damage, and loss of 

use of buildings—as well as more rapid overall 

recovery. Rehabilitated buildings may also increase in 

value and be assigned lower insurance rates. Additional 

issues that should be considered for positive or negative 

effects include the interaction of rehabilitation with 

overall planning goals, historic preservation, and the 

local economy. These issues are discussed in FEMA 

275.

A.2.1 Potential Costs of Local or Directed 

Programs

The primary costs of seismic rehabilitation—the 

construction work itself, including design, inspection, 

and administration—are normally paid by the owner. 

Additional costs that should be weighed when creating 

seismic risk reduction programs are those associated 

with developing and administering the program, such as 

the costs of identifying high-risk buildings, 

environmental or socioeconomic impact reports, 

training programs, plan checking and construction 

inspection.

The construction costs include not only the cost of the 

pure structural rehabilitation, but also the costs 

associated with new or replaced finishes that may be 

required. In some cases, seismic rehabilitation work 

will trigger other local jurisdictional requirements, such 

as hazardous material removal or partial or full 

compliance with the Americans with Disabilities Act. 

The costs of seismic or functional improvements to 

nonstructural systems should also be considered. There 

may also be costs to the owner associated with 

temporary disruption or loss of use of the building 

during construction. To offset these costs, there may be 

low interest earthquake rehabilitation loans available 

from state or local government, or building tax credits.

If seismic rehabilitation is the primary purpose of 

construction, the costs of various nonseismic work that 

may be required should be included as direct 

consequences. On the other hand, if the seismic work is 

an added feature of a major remodel, the nonseismic 

improvements probably would have been required 

anyway, and therefore should not be attributed to 

seismic rehabilitation.

A discussion of these issues, as well as guidance on the 

range of costs of seismic rehabilitation, is included in 

FEMA 156 and 157, and in FEMA 276. Since the data 

for these documents were developed prior to this 

standard, the information is not based on buildings 

rehabilitated specifically in accordance with the current 

document. However, performance levels defined in this 

standard are not intended to be significantly different 

than parallel levels used previously, and costs should 

still be reasonably representative.
A-2 Seismic Rehabilitation Prestandard FEMA 356

Appendix A: Use of this Standard for Local 

or Directed Risk Mitigation Programs

A.2.2 Timetables and Effectiveness

Presuming that new buildings are being constructed 

with adequate seismic protection and that older 

buildings are occasionally demolished or replaced, the 

inventory of seismically hazardous buildings in any 

community will be gradually reduced. This attrition rate 

is normally small, since the structures of many 

buildings have useful lives of 100 years or more and 

very few buildings are actually demolished. If buildings 

or districts become historically significant, they may 

not be subject to attrition at all. In many cases, then, 

doing nothing (or waiting for an outside influence to 

force action) may present a large cumulative risk to the 

inventory.

It has often been pointed out that exposure time is a 

significant element of risk. The time aspect of risk 

reduction is so compelling that it often appears as part 

of book and workshop titles; for example, Between Two 

Earthquakes: Cultural Property in Seismic Zones

(Feilden, 1987); Competing Against Time (California 

Governor’s Board of Inquiry, 1990); and “In Wait for 

the Next One” (EERI, 1995). Therefore, an important 

consideration in the development of programs is the 

time allotted to reach a certain risk reduction goal. It is 

generally assumed that longer programs create less 

hardship than short ones by allowing more flexibility in 

planning for the cost and possible disruption of 

rehabilitation, as well as by allowing natural or 

accelerated attrition to reduce undesirable impacts. On 

the other hand, the net reduction of risk is smaller due to 

the increased exposure time of the seismically deficient 

building stock.

Given a high perceived danger and certain 

advantageous characteristics of ownership, size, and 

occupancy of the target buildings, mandatory programs 

have been completed in as little as five to ten years. 

More extensive programs—involving complex 

buildings such as hospitals, or with significant funding 

limitations—may have completion goals of 30 to 50 

years. Deadlines for individual buildings are also often 

determined by the risk presented by building type, 

occupancy, location, soil type, funding availability, or 

other factors.

A.2.3 Historic Preservation

Seismic rehabilitation of buildings can affect historic 

preservation in two ways. First, the introduction of new 

elements that will be associated with the rehabilitation 

may in some way impact the historic fabric of the 

building. Second, the seismic rehabilitation work can 

serve to better protect the building from possibly 

unrepairable future earthquake damage. The effects of 

any seismic risk reduction program on historic 

buildings or preservation districts should be carefully 

considered during program development, and 

subsequent work should be carefully monitored to 

assure compliance with national preservation guidelines 

discussed in Section A.6.

A.3 Use in Passive Programs

Programs that only require seismic rehabilitation in 

association with other activity on the building are often 

classified as “passive.” “Active” programs, on the other 

hand, are those that mandate seismic rehabilitation for 

targeted buildings in a certain time frame, regardless of 

other activity associated with the building (see 

Section 1.6.3). Activities in a building that may 

passively generate a requirement to seismically 

rehabilitate—such as an increase in occupancy, 

structural modification, or a major remodeling that 

would significantly extend the life of the building—are 

called “triggers.” The concept of certain activities 

triggering compliance with current standards is well 

established in building codes. However, the details of 

the requirements have varied widely. These issues have 

been documented with respect to seismic rehabilitation 

in California (Hoover, 1992). Passive programs reduce 

risk more slowly than active programs.

A.3.1 Selection of Seismic Rehabilitation 

Triggers

This standard does not cover triggers for seismic 

rehabilitation. The extent and detail of seismic triggers 

will greatly affect the speed, effectiveness, and impacts 

of seismic risk reduction, and the selection of triggers is 

a policy decision expected to be done locally by the 

person, agency, or jurisdiction responsible for the 

inventory. Triggers that have been used or considered in 

the past include revision of specified proportions of the 

structure, remodeling of specified percentages of the 

building area, work on the building that costs over a 

specified percentage of the building value, change in 

use that increases the occupancy or importance of the 

building, and changes of ownership.
Appendix A: Use of this Standard for Local or 

Directed Risk Mitigation Programs

FEMA 356 Seismic Rehabilitation Prestandard A-3

A.3.2 Selection of Passive Seismic 

Rehabilitation Standards

This standard purposely affords a wide variety of 

options that can be adopted for seismic rehabilitation to 

facilitate risk reduction. Standards can be selected with 

varying degrees of risk reduction and varying costs by 

designating different Rehabilitation Objectives. As 

described previously, a Rehabilitation Objective is 

created by specifying a desired target Building 

Performance Level for specified earthquake ground 

motion criteria. A jurisdiction can thus specify 

appropriate standards by extracting applicable 

requirements and incorporating them into its own code 

or standard, or by reference.

A single Rehabilitation Objective could be selected 

under all triggering situations (the BSO, for example), 

or more stringent objectives can be used for important 

changes to the building, less stringent objectives for 

minor changes. For example, it is sometimes necessary 

for design professionals, owners, and building officials 

to negotiate the extent of seismic improvements done in 

association with building alterations. Complete 

rehabilitation is often required by local regulation for 

complete remodels or major structural alterations. It is 

the intent of the standard to provide a common 

framework for all of these various uses.

A.4 Use in Active or Mandated 

Programs

Active programs are most often targeted at high-risk 

building types or occupancies. Active seismic risk 

reduction programs are those that require owners to 

rehabilitate their buildings to specified Rehabilitation 

Objectives in a certain time frame or, in the case of 

government agencies or other owners of large 

inventories, to set self-imposed deadlines for 

completion.

A.4.1 Selection of Buildings to be Included

Programs would logically target only the highest-risk 

buildings or at least create priorities based on risk. Risk 

can be based on the likelihood of building failure, the 

occupancy or importance of buildings, soil types, or 

other factors. This standard is primarily written to be 

used in the process of rehabilitation and does not 

directly address the comparative risk level of various 

building types or other risk factors. Certain building 

types, such as unreinforced masonry bearing wall 

buildings and older improperly detailed reinforced 

concrete frame buildings, have historically presented a 

high risk, depending on local seismicity and building 

practice. Therefore, these building types have 

sometimes been targeted in active programs.

A more pragmatic consideration is the ease of locating 

targeted buildings. If certain building types cannot be 

easily identified, either by the local jurisdiction or by 

the owners and their engineers, enforcement could 

become difficult and costly. In the extreme, every 

building designed prior to a given acceptable code cycle 

would require a seismic evaluation to determine 

whether targeted characteristics or other risk factors are 

present, the cost of which may be significant. An 

alternate procedure might be to select easily identifiable 

building characteristics to set timelines, even if more 

accurate building-by-building priorities are somewhat 

compromised.

A.4.2 Selection of Active Seismic 

Rehabilitation Standards

As discussed for passive programs in Section A.3.2, the 

standard is written to facilitate a wide variation in risk 

reduction. Factors used to determine an appropriate 

Rehabilitation Objective include local seismicity, the 

costs of rehabilitation, and local socioeconomic 

conditions.

It may be desirable to use Simplified Rehabilitation 

Methods for active or mandated programs. Only 

Limited Performance Objectives are included in this 

standard for this method. However, if a program has 

identified a local building type with few variations in 

material and configuration, a study of a sample of 

typical buildings using Systematic Methods may 

establish that compliance with the requirements of 

Simplified Rehabilitation meets the BSO, or better, for 

this building type in this location. Such risk and 

performance decisions can only be made at the local 

level.

A.5 Social, Economic, and Political 

Considerations

The scope of this standard is limited to the engineering 

basis for seismically rehabilitating a building, but the 

user should also be aware of significant nonengineering 

issues and social and economic impacts presented in 

this section. These problems and opportunities, which 

vary with each situation, are discussed in FEMA 275.
A-4 Seismic Rehabilitation Prestandard FEMA 356

Appendix A: Use of this Standard for Local 

or Directed Risk Mitigation Programs

A.5.1 Construction Cost 

If seismic rehabilitation were always inexpensive, the 

social and political costs and controversies would 

largely disappear. Unfortunately, seismic rehabilitation 

often requires removal of architectural materials to 

access the vulnerable portions of the structure. 

Nonseismic upgrading (e.g., electrical, handicapped 

access, historic restoration) is frequently “triggered” by 

a building code’s remodeling permit requirements and 

is desirable to undertake at the same time.

A.5.2 Housing 

While seismic rehabilitation ultimately improves the 

housing stock, units can be temporarily lost during the 

construction phase, which may be very lengthy, and can 

require relocation of tenants.

A.5.3 Impacts on Lower-Income Groups

Lower-income residents and commercial tenants can be 

displaced by seismic rehabilitation and nonseismic 

upgrading, which can raise rents and real estate prices 

because of the need to recover the costs of the work. 

Possible hardships on these groups need to be given 

heavy consideration because they may affect the very 

societal fabric of a community.

A.5.4 Regulations

As with efforts to impose safety regulations in other 

fields, mandating seismic rehabilitation is often 

controversial. This standard is written as mandatory 

code provisions for possible application and adaptation 

for that use. In such cases political controversy should 

be expected, and nonengineering issues of all kinds 

should be carefully considered.

A.5.5 Architecture 

Even if a building is not historic, there are often 

significant architectural impacts. The exterior and 

interior appearance may change, and the division of 

spaces and arrangement of circulation routes may be 

altered.

A.5.6 Community Revitalization

Seismic rehabilitation not only poses issues and implies 

costs, it also confers benefits. In addition to enhanced 

public safety and economic protection from earthquake 

loss, seismic rehabilitation can play a leading role in the 

revitalization of older commercial and industrial areas 

as well as residential neighborhoods. Potential 

synergies between these two programs in a community 

should be carefully explored by local planners, officials, 

and design professionals.

A.6 Considerations for Historic 

Buildings

It must be determined early in the process whether a 

building is “historic.” A building is historic if it is at 

least 50 years old, and is listed in or potentially eligible 

for the National Register of Historic Places and/or a 

state or local register as an individual structure, or as a 

contributing structure in a district. Structures less than 

50 years old may also be historic if they possess 

exceptional significance. For historic buildings, users 

should develop and evaluate alternative solutions with 

regard to their effect on the loss of historic character 

and fabric. This section provides guidance for 

developing such alternative solutions. 

A.6.1 Secretary of Interior’s Standards

For historic buildings, users should develop alternative 

solutions using the Standards for Rehabilitation

(Secretary of the Interior, 1990).

In addition to rehabilitation, the Secretary of the Interior 

also has standards for preservation, restoration, and 

reconstruction (Secretary of the Interior, 1992). A 

seismic rehabilitation project may include work that 

falls under the Rehabilitation Standards, the Treatment 

Standards, or both.

For historic buildings as well as for other structures of 

architectural interest, it is important to note that the 

Secretary of the Interior’s Standards define 

rehabilitation as “the process of returning a property to 

a state of utility, through repair or alteration, which 

makes possible an efficient contemporary use while 

preserving those portions and features of the property 

which are significant to its historic, architectural and 

cultural values.” Further guidance on the treatment of 

historic properties is contained in publications listed in 

the Catalog of Historic Preservation Publications

(NPS, 1995).

A.6.2 Application of Building Codes and 

Standards

It should be noted that many codes covering historic 

buildings allow some amount of flexibility in required 
Appendix A: Use of this Standard for Local or 

Directed Risk Mitigation Programs

FEMA 356 Seismic Rehabilitation Prestandard A-5

performance, depending on the effect of rehabilitation 

on important historic features.

If a building contains items of unusual architectural 

interest, consideration should be given to the value of 

these items. It may be desirable to rehabilitate the 

building to the Damage Control Structural Performance 

Range as specified in this standard to ensure that the 

architectural fabric survives certain earthquakes.

A.6.3 Rehabilitation Strategies

In development of initial risk mitigation strategies, 

consideration must be given to the architectural and 

historic value of the building and its fabric. 

Development of a Historic Structure Report identifying 

the primary historic fabric may be essential in the 

preliminary planning stages for certain buildings. Some 

structurally adequate solutions may nevertheless be 

unacceptable because they involve destruction of 

historic fabric or character. Alternate rehabilitation 

methods that lessen the impact on the historic fabric 

should be developed for consideration. Partial 

demolition may be inappropriate for historic structures. 

Elements that create irregularities may be essential to 

the historic character of the structure. The advice of 

historic preservation experts may be necessary early on 

in the rehabilitation process. 

Structural rehabilitation of historic buildings may be 

accomplished by hiding the new structural members or 

by exposing them as admittedly new elements in the 

building’s history. Often, the exposure of new structural 

members is preferred because alterations of this kind 

are “reversible”; that is, they could conceivably be 

undone at a future time with no loss of historic fabric to 

the building. The decision to hide or expose structural 

members is a complex one and is best made by a 

preservation professional.

A.6.4 Rehabilitation Objectives

If seismic rehabilitation is required by the governing 

building jurisdiction, the minimum seismic 

requirements should be matched with a Rehabilitation 

Objective defined in this standard.
A-6 Seismic Rehabilitation Prestandard FEMA 356

Appendix A: Use of this Standard for Local 

or Directed Risk Mitigation Programs
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-1

Symbols

A Cross-sectional area of a pile, Equation 

(4-9)

Cross-sectional area of shear wall 

boundary members or diaphragm chords 

in.2

, Equations (8-2), (8-4), (8-5)

Ab Gross area of bolt or rivet, Equations 

(5-18), (5-22), (5-24)

Sum of net mortared area of bed joints 

above and below the test unit, Equation 

(7-2)

Ac Area of column, Equation (5-8)

Ae Effective net area of the horizontal leg, 

Equation (5-20)

Ag Gross area of the horizontal leg, Equation 

(5-19)

Gross area of cast iron column, Equation 

(5-36)

Gross area of column, in.2, Equation (6-4)

Aj Effective cross-sectional area of a beamcolumn joint, in.2, in a plane parallel to 

plane of reinforcement generating shear in 

the joint calculated as specified in 

Section 6.5.2.3.1, Equation (6-5)

An Area of net mortared/grouted section, 

Equations (7-1), (7-3), (7-5), (7-7), (7-9), 

(7-10), (7-11), (7-13)

Ani Area of net mortared/grouted section of 

masonry infill, Equation (7-15)

As Area of nonprestressed tension reinforcement, in.2

, Tables 6-18, 6-20

Area of reinforcement, Equation (7-13)

A′s Area of compression reinforcement, in.2

, 

Tables 6-18, 6-20

Aw Area of shear reinforcement, Equation 

(7-12)

Nominal area of the web, Equation (5-7)

Area of link stiffener web, Equation 

(5-28), (5-31)

Area of the web cross section, = bwd, 

Chapter 6

Ax Accidental torsion amplification factor, 

Equation (3-1) 

B Width of footing, Equations (4-6), (4-7), 

(4-8)

B1 Damping coefficient used to adjust onesecond period spectral response for the 

effect of viscous damping, , Equations 

(1-10), (1-11)

BD1 Numerical damping coefficient taken 

equal to the value of B1, as set forth in 

Table 1-6, at effective damping β equal to 

the value of βD, Equation (9-2)

BM1 Numerical damping coefficient taken 

equal to the value of B1, as set forth in 

Table 1-6, at effective damping β equal to 

the value of βM, Equation (9-4)

BS Coefficient used to adjust short-period 

spectral response for the effect of viscous 

damping, Equations (1-8), (1-9), (1-11)

C (or Cj

 ) Damping coefficient for viscoelastic 

device (or device j), Equations (9-22), 

(9-24), (9-29), (9-30), (9-35), (9-37)

C0 Modification factor to relate spectral 

displacement of an equivalent SDOF system to the roof displacement of the building MDOF system, Equation (3-15)

Damping coefficient for fluid-viscous 

device, Equation (9-25)

C1 Modification factor to relate expected 

maximum inelastic displacements to displacements calculated for linear elastic 

response, Equations (3-5), (3-6), (3-10), 

(3-15), (3-19)
Symbols-2 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

C2 Modification factor to represent the effects 

of pinched hysteresis shape, stiffness degradation and strength deterioration on the 

maximum displacement response, 

Equations (3-5), (3-6), (3-10), (3-15), 

(3-19)

C3 Modification factor to represent increased 

displacements due to p-∆ effects, Equations (3-5), (3-6), (3-10), (3-15), (3-17), 

(3-19)

Cb Coefficient to account for effect of nonuniform moment given in AISC (1993) LRFD 

Specifications, Equation (5-9)

CFi Stage combination factors for use with 

velocity-dependent energy dissipation 

devices as calculated by Equations (9-31) 

or (9-32) 

Cm Effective mass factor from Table 3-1, 

Equations (3-10), (3-16)

Ct Numerical value for adjustment of period 

T, Equation (3-7)

Cvx Vertical distribution factor for the pseudo 

lateral load, Equations (3-11), (3-12)

D Generalized deformation, unitless

Relative displacement between two ends 

of an energy dissipation unit, Equations 

(9-1), (9-20), (9-22)

D– Maximum negative displacement of an 

energy dissipation unit, Equations (9-21), 

(9-23)

D+ Maximum positive displacement of an 

energy dissipation unit, Equations (9-21), 

(9-23)

•

D Relative velocity between two ends of an 

energy dissipation unit, Equations (9-22), 

(9-25)

Dave Average displacement of an energy dissipation unit, equal to (|D+| + |D–

|)/2, 

Equation (9-24)

Dclear Required clearance between a glass 

component and the frame, Equation (11-9)

DCR Demand-capacity ratio, computed in 

accordance with Equation (2-1) or required 

in Equation (2-2) 

____

DCR Average demand-capacity ratio for a story, 

computed in accordance with Equation 

(2-2)

DD Design displacement, in. (mm) at the center of rigidity of the isolation system in the 

direction under consideration, Equations 

(9-2), (9-6), (9-8), (9-10), (9-14), (9-15), 

(9-18), (9-22) 

D′D Design Earthquake target displacement, in. 

(mm) at a control node located at the center of mass of the first floor above the 

isolation system in the direction under consideration, as prescribed by Equation 

(9-10) 

DM Maximum displacement, in. (mm) at the 

center of rigidity of the isolation system in 

the direction under consideration, 

Equations (9-4), (9-7), (9-11), (9-16), 

(9-17), (9-19)

D′M BSE-2 target displacement, in. (mm) at a 

control node located at the center of mass 

of the first floor above the isolation system 

in the direction under consideration, as 

prescribed by Equation (9-11) 

Dp Relative seismic displacement that the 

component must be designed to accommodate, Equations (11-8), (11-9), (11-10), 

(11-11)

Dr Drift ratio for nonstructural components, 

Equation (11-7)

DTD Total design displacement, in. (mm) of an 

element of the isolation system, including 

both translational displacement at the 

center of rigidity and the component of 

torsional displacement in the direction 

under consideration, as specified by 

Equation (9-6) 
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-3

DTM Total maximum displacement, in. (mm) of 

an element of the isolation system, 

including both translational displacement 

at the center of rigidity and the component 

of torsional displacement in the direction 

under consideration, as specified by 

Equation (9-7) 

E Young’s modulus of elasticity, Equations 

(4-9), (5-1), (5-2), (5-17), (8-2), (8-4), 

(8-5)

Ec Modulus of elasticity of concrete, psi, 

Equation (6-6)

Efe Expected elastic modulus of frame 

material, ksi, Equation (7-14)

ELoop Energy dissipated, in kip-inches (kN-mm), 

in an isolator unit during a full cycle of 

reversible load over a test displacement 

range from ∆+ to ∆-

, as measured by the 

area enclosed by the loop of the 

force-deflection curve, Equation (9-13)

Eme Expected elastic modulus of masonry in 

compression as determined per 

Section 7.3.2.4, Equation (7-14)

Es Modulus of elasticity of reinforcement, 

psi, Chapter 6

Ese Expected elastic modulus of reinforcing 

steel per Section 7.3.2.8 

F Force in an energy dissipation unit, 

Equations (9-1), (9-20), (9-22), (9-25)

F– Negative force, in k, in an isolator or 

energy dissipation unit during a single 

cycle of prototype testing at a displacement amplitude of ∆−, Equations (9-12), 

(9-21), (9-23), (9-38)

F+ Positive force, in k, in an isolator or energy 

dissipation unit during a single cycle of 

prototype testing at a displacement 

amplitude of ∆+, Equations (9-12), (9-21), 

(9-23), (9-38)

Fa Factor to adjust spectral acceleration in the 

short-period range for site class, 

Equation (1-7)

Fcr Allowable axial buckling stress, see

Equation (5-36)

FEXX Classification strength of weld metal, 

Chapter 5

Fi Inertia force at floor level i, Equation 

(9-27)

Lateral load applied at floor level i, 

Equation (3-13)

Fmi m-th mode horizontal inertia force at floor 

level i, Equation (9-34)

Fp Horizontal seismic force for design of a 

structural or nonstructural component and 

its connection to the structure, Equations 

(2-3), (2-4), (2-5), (2-6), (2-7)

Component seismic design force applied 

horizontally at the center of gravity of the 

component or distributed according to the 

mass distribution of the component, 

Equations (11-1), (11-2), (11-3), (11-4)

Fpv Component seismic design force applied 

vertically at the center of gravity of the 

component or distributed according to the 

mass distribution of the component, 

Equations (11-2), (11-5), (11-6)

Fpx Diaphragm lateral force at floor level x, 

Equation (3-13)

Fte Expected tensile strength, Equations 

(5-20), (5-22), (5-24)

Fv Factor to adjust spectral acceleration at one 

second for site class, Equation (1-8)

Design shear strength of bolts or rivets, 

Chapter 5

Fve Unfactored nominal shear strength of bolts 

or rivets given in AISC(1993) LRFD 

Specifications, Equation (5-18)

Fx Lateral load applied at floor level x, 

Equation (3-11)

Fy Specified minimum yield stress for the 

type of steel being used, Equation (5-7)

Fyb Fy of a beam, Chapter 5

Fyc Fy of a column, Chapter 5
Symbols-4 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

Fye Expected yield strength, Equations (5-1) to 

(5-8), (5-19), (5-23), (5-25), (5-31), (5-34)

Fyf Fy of a flange, Chapter 5

FyLB Lower-bound yield strength, Chapter 5

G Soil Shear modulus, Equation (4-6)

Shear modulus of steel, Equations (5-28), 

(5-33)

Modulus of rigidity of wood structural 

panels, psi, Equations (8-2), (8-4), (8-5)

Gd Shear stiffness of shear wall or diaphragm 

assembly, Equations (8-1), (8-3)

Gme Shear modulus of masonry as determined 

per Section 7.3.2.7 

Go Initial or maximum shear modulus, 

Equations (4-4), (4-5)

H Thickness of a soil layer in feet, 

Chapter 11

Horizontal load on footing, Chapter 4

Hrw Height of the retaining wall, Equation 

(4-11)

I Moment of inertia, Equation (6-6)

Ib Moment of inertia of a beam, Equations 

(5-1), (5-17)

Ic Moment of inertia of a column, Equation 

(5-2)

Icol Moment of inertia of column section, 

Equation (7-14)

If Moment of inertia of most flexible frame 

member confining infill panel, Chapter 7

Ig Moment of inertia of gross concrete section about centroidal axis, neglecting 

reinforcement, Chapter 6

Ip Component performance factor; 1.0 shall 

be used for the Life Safety Nonstructural 

Performance Level and 1.5 shall be used 

for the Immediate Occupancy Nonstructural Performance Level, Equations (11-1), 

(11-3), (11-4), (11-5), (11-6)

J A coefficient used in linear procedures to 

estimate the actual forces delivered to 

force-controlled components by other 

(yielding) components, Equations (3-5), 

(3-19)

K Length factor for brace; defined in AISC 

(1993) LRFD Specifications, Chapter 5

K’ Storage stiffness as prescribed by Equation 

(9-23)

K" Loss stiffness as prescribed by Equation 

(9-24)

Kθ Rotational stiffness of a partially restrained 

connection, Equations (5-15), (5-16), 

(5-17)

Kb Flexural stiffness, Equations (5-27), (5-29)

KDmax Maximum effective stiffness, in k/in., of 

the isolation system at the design displacement in the horizontal direction under 

consideration, as prescribed by Equation 

(9-14)

KDmin Minimum effective stiffness, in k/in. (kN/

mm), of the isolation system at the design 

displacement in the horizontal direction 

under consideration, as prescribed by 

Equation (9-15)

Ke Effective stiffness of the building in the 

direction under consideration, for use with 

the NSP, Equation (3-14) 

Elastic stiffness of a link beam, 

Equations (5-27), (5-30)

Ki Elastic stiffness of the building in the 

direction under consideration, for use with 

the NSP, Equation (3-14)

KMmax Maximum effective stiffness, in k/in., of 

the isolation system at the maximum 

displacement in the horizontal direction 

under consideration, as prescribed by 

Equation (9-16)

KMmin Minimum effective stiffness, in k/in., of 

the isolation system at the maximum 

displacement in the horizontal direction 

under consideration, as prescribed by 

Equation (9-17)
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-5

Ks Shear stiffness, Equations (5-27), (5-28)

L Length of footing in plan dimension, 

Equations (4-7), (4-8)

Length of pile in vertical dimension, 

Equation (4-9)

Length of member along which deformations are assumed to occur, Chapter 6

Length of wall or pier, Equations (7-4), 

(7-5)

Diaphragm span, distance between shear 

walls or collectors, Equations (8-3), (8-4), 

(8-5)

Lb Length or span of beam, Equations (5-6), 

(5-17)

Distance between points braced against 

lateral displacement of the compression 

flange or between points braced to prevent 

twist of the cross-sections; given in AISC 

(1993) LRFD Specifications, Equation 

(5-9)

Linf Length of infill panel, Equations (7-17), 

(7-19)

Lp The limiting unbraced length between 

points of lateral restraint for the full plastic 

moment capacity to be effective; given in 

AISC (1993) LRFD Specifications, 

Equations (5-6), (5-9)

Lr The limiting unbraced length between 

points of lateral support beyond which 

elastic lateral torsional buckling of the 

beam is the failure mode; given in AISC 

(1993) LRFD Specifications, Equation 

(5-9)

M Design moment at a section, Equation 

(6-4)

Moment on masonry section, Equation 

(7-11)

Mc Ultimate moment capacity of footing, 

Equation (4-8)

MCE Expected flexural strength of a member or 

joint, Equation (5-3), (5-4), (5-6), 

(5-15), (5-16), (5-18), (5-22), (5-24), 

(5-25), (5-26), (5-32)

MCEx Expected bending strength of a member 

about the x-axis, Equations (5-10), 

(5-11), (5-13), (6-1)

MCEy Expected bending strength of a member 

about y-axis, Equations (5-10), (5-11), 

(5-13), (6-1)

MCLx Lower-bound flexural strength of the 

member about the x-axis, Equation (5-12)

MCLy Lower-bound flexural strength of the 

member about the y-axis, Equation (5-12)

MgCS Moment acting on the slab column strip, 

Chapter 6

Mn Nominal moment strength at section, 

Chapter 6

MnCS Nominal moment strength of the slab 

column strip, Chapter 6

MOT Total overturning moment induced on the 

element by seismic forces applied at and 

above the level under consideration, 

Equations (3-5), (3-6)

MPCE Expected plastic moment capacity, 

Equation (5-6)

MST Stabilizing moment produced by dead 

loads acting on the element, Equations 

(3-5), (3-6)

MUD Design moment, Chapter 6

MUDx Design bending moment about x axis for 

axial load PUF, kip-in., Equation (6-1)

MUDy Design bending moment about y axis for 

axial load PUF, kip-in., Equation (6-1)

MUFx Bending moment in the member about the 

x-axis, calculated in accordance with

Section 3.4.2.1.2, Equation (5-12)

MUFy Bending moment in the member about the 

y-axis, calculated in accordance with 

Section 3.4.2.1.2, Equation (5-12)

Mx Bending moment in a member for the 

x-axis, Equations (5-10), (5-11), (5-13)
Symbols-6 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

My Bending moment in a member for the 

y-axis, Equations (5-10), (5-11), (5-13)

Yield moment strength at section, 

Equation (6-6)

N Number of piles in a pile group, Equation 

(4-9)

—N Average SPT blow count in soil within the 

upper 100 feet of soil, calculated in 

accordance with Equation (2-8) 

(N1)60 Standard Penetration Test blow count 

normalized for an effective stress of 1 ton 

per square foot and corrected to an 

equivalent hammer energy efficiency of 

60%, Equation (4-5)

Nb Number of bolts or rivets, Equations 

(5-18), (5-22), (5-24)

Nu Factored axial load normal to cross-section 

occurring simultaneously with Vu. To be 

taken as positive for compression, negative 

for tension, and to include effects of 

tension due to creep and shrinkage, 

Equation (6-4)

P Vertical load on footing, Equation (4-8)

Axial force in a member, Equations (5-2), 

(5-4)

Pc Lower bound of vertical compressive 

strength for wall or pier, Equations (7-7), 

(7-13)

PCE Expected axial strength of a member or 

joint, Equations (5-19), (5-20), (5-21), 

(5-26)

Expected gravity compressive force, 

Equations (7-1), (7-4)

PCL Lower-bound axial strength of column, 

Equations (5-10), (5-11), (5-12), (5-36)

Lower bound axial compressive force due 

to gravity loads specified in Equation (3-4)

PEY Probability of exceedance in Y years, 

expressed as a decimal, Equation (1-2)

PI Plasticity Index for soil, determined as the 

difference in water content of soil at the 

liquid limit and plastic limit, 

Section 1.6.1.4.1

Pi Portion of the total weight of the structure 

including dead, permanent live, and 25% 

of transient live loads acting on the 

columns and bearing walls within story 

level i, Equation (3-2)

Po Nominal axial load strength at zero 

eccentricity, Chapter 6

PR Mean return period, Equation (1-2)

PUF Design axial force in a member, Equations 

(5-10), (5-11), (5-12)

Pye Expected yield axial strength of a member, 

Equations (5-2), (5-4)

Q Generalized force in a component, 

Figures 2-3, 2-5, 5-1, 6-1, 7-1, 8-1

Qallow Allowable bearing load specified for the 

design of deep foundations for gravity 

loads (dead plus live loads) in the available 

design documents, Equation (4-2)

Qc Expected bearing capacity of deep or 

shallow foundation, Equations (4-2), (4-3), 

(4-7)

QCE Expected strength of a component or element at the deformation level under consideration, Equations (2-1), (3-20), (5-3) to 

(5-8), (5-18), (5-22), (5-24), (5-25), (5-26), 

(5-30), (5-31), (5-32), (5-34), (5-35), (7-3), 

(7-4), (7-15) 

QCEb Expected bending strength of the beam, 

Equation (5-14)

QCL Lower-bound estimate of the strength of a 

component or element at the deformation 

level under consideration, Equations 

(3-21), (5-36), (6-5), (7-5) to (7-8), (7-13), 

(7-21)

QCLc Lower-bound strength of the connection, 

Equation (5-14)

QD Design action due to dead load, Equations 

(3-3), (3-4)

QE Design action due to design earthequake 

loads, Equations (3-18), (3-19)
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-7

QG Design action due to gravity loads, 

Equation (3-3), (3-4), (3-18), (3-19)

QL Design action due to live load, Equations 

(3-3), (3-4)

QS Design action due to snow load, Equations 

(3-3), (3-4)

QUD Deformation-controlled design action due 

to gravity and earthquake loads, 

Equations (2-1), (3-18), (3-20)

QUF Force-controlled design action due to gravity and earthquake loads, Equations (3-19), 

(3-21))

Qy Yield strength of a component, 

Figures 2-3, 2-5

Q′

y Substitute yield strength, Figure 2-5

R Ratio of the elastic-strength demand to the 

yield-strength coefficient, Equations 

(3-15), (3-16), (3-17)

ROT Response modification factor for overturning moment MOT, Equation (3-6)

Rp Component response modification factor 

from Table 11-2, Equation (11-3))

S1 Spectral response acceleration parameter 

at a one-second period, obtained from 

response acceleration maps, Equations 

(1-1), (1-3), (1-5)

Sa Spectral response acceleration, g, 

Equations (1-8), (1-9), (1-10), (3-10), 

(3-15), (3-16)

Sn Distance between nth pile and axis of rotation of a pile group, Equation (4-10)

SS Spectral response acceleration parameter 

at short periods, obtained from response 

acceleration maps, Equations (1-1), 

(1-3), (1-7)

SX1 Spectral response acceleration parameter 

at a one-second period for any earthquake 

hazard level and any damping, adjusted for 

site class, Equations (1-5), (1-10), (1-11), 

(1-13), (1-14), (1-15), (1-16)

SXS Spectral response acceleration parameter 

at short periods for the selected Earthquake 

Hazard Level and damping, adjusted for 

site class, and determined in accordance 

with Section 1.6.1.4 or 1.6.2.1, 

Equation (1-4), (1-8), (1-9), (1-11), (1-13), 

(1-14), (1-15), (1-16), (4-11), (11-1), 

(11-3), (11-4), (11-5), (11-6) 

T Fundamental period of the building in the 

direction under consideration, seconds, 

Equations (1-8), (1-10), (3-7), (3-8), 

(3-9), (3-10), (9-29)

Tensile load in column, Equation (5-13)

T0 Period at which the constant acceleration 

region of the design response spectrum 

begins at a value = 0.2TS, Equations (1-8), 

(1-12)

TCE Expected tensile strength of column computed in accordance with Equation (5-8)

TD Effective period, in seconds, of the 

seismic-isolated structure at the design 

displacement in the direction under 

consideration, as prescribed by Equation 

(9-3)

Te Effective fundamental period of the 

building in the direction under consideration, for use with the NSP, Equations 

(3-14), (3-15), (3-17)

Effective fundamental period, in seconds, 

of the building structure above the 

isolation interface on a fixed base in the 

direction under consideration, Equations 

(9-10), (9-11)

Ti Elastic fundamental period of the building 

in the direction under consideration, for 

use with the NSP, Equation (3-14)

TM Effective period, in seconds, of the seismic-isolated structure at the maximum displacement in the direction under 

consideration, as prescribed by Equation 

(9-5)

Tm m-th mode period of the rehabilitated 

building including the stiffness of the 

velocity-dependent devices, Equation 

(9-35)
Symbols-8 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

TS Period at which the constant acceleration 

region of the design response spectrum 

transitions to the constant velocity region, 

Equations (1-8), (1-9), (1-10), (1-11), 

(1-12), (1-13), (3-10), (3-15)

Tss Secant fundamental period of a rehabilitated building calculated using Equation 

(3-14) but replacing the effective stiffness 

(Ke) with the secant stiffness (Ks) at the 

target displacement, Equation (9-37)

V Pseudo lateral load, Equations (3-10), 

(3-11)

Design shear force at section, Equation 

(6-4)

Shear on masonry section, Equation (7-11)

V* Modified equivalent base shear, Chapter 9

Vb The total lateral seismic design force or 

shear on elements of the isolation system 

or elements below the isolation system, as 

prescribed by Equation (9-8) 

Vbjs Expected shear strength of wall or pier 

based on bed-joint sliding shear stress, see

Equation (7-3)

Vc Nominal shear strength provided by 

concrete, Equation (6-4)

VCE Expected shear strength of a member, 

Equations (5-11), (5-31), (5-32), 

(5-34)

VCL Lower bound shear strength, Equations 

(7-8), (7-9), (7-10)

Vdt Lower bound shear strength based on 

diagonal tension stress for wall or pier, 

Chapter 7

Vfre Expected story shear strength of the bare 

steel frame taken as the shear cpacity of 

the column, Chapter 7

Vg Shear acting on slab critical section due to 

gravity loads, Chapter 6

Vi The total calculated lateral shear force in 

the direction under consideration in an 

element or at story i due to earthquake 

response to the selected ground shaking 

level, as indicated by the selected linear 

analysis procedure, Equations (2-2), (3-2)

Vine Expected shear strength of infill panel, 

Equation (7-15)

VmL Lower bound shear strength provided by 

masonry, Equations (7-8), (7-11)

Vn Nominal shear strength at section, 

Equation (6-5)

Vo Shear strength of slab at critical section, 

Chapter 6

Vpz Panel zone shear, Chapter 5

Vr Expected shear strength of wall or pier 

based on rocking shear, Equation (7-4)

Vs Nominal shear strength provided by shear 

reinforcement, Chapter 6

The total lateral seismic design force or 

shear on elements above the isolation 

system, as prescribed by Section 9.2.4.4.2, 

Equation (9-9)

VsL Lower bound shear strength provided by 

shear reinforcement, Equations (7-8), 

(7-12)

Vt Base shear in the building at the target 

displacement, Chapter 3

Vtc Lower bound shear strength based on toe 

compressive stress for wall or pier, 

Chapter 7

Vtest Test load at first movement of a masonry 

unit, Equation (7-2)

Vu Factored shear force at section, Chapter 6

Vy Yield strength of the building in the direction under consideration, for use with the 

NSP, Equation (3-16)

Vya Nominal shear strength of a member modified by the axial load magnitude, Chapter 5
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-9

W Weight of a component, calculated as 

specified in this standard, Chapter 2.

Effective seismic weight of a building 

including total dead load and applicable 

portions of other gravity loads listed in 

Section 3.3.1.3.1, Equations (3-10), (3-16)

The total seismic dead load in kips (kN). 

For design of the isolation system, W is the 

total seismic dead-load weight of the 

structure above the isolation interface, 

Equations (9-3), (9-5)

WD Energy dissipated in a building or element 

thereof or energy dissipation device during 

a full cycle of displacement, Equations 

(9-24), (9-39)

Wj Work done by an energy dissipating 

device, j, in one complete cycle corresponding to floor displacement, Equations 

(9-26), (9-28), (9-29), (9-36), (9-37)

Wk Maximum strain energy in a frame as calculated by Equation (9-27)

Wmj Work done by device j in one complete 

cycle corresponding to modal floor 

displacements δmi Equation (9-33)

Wmk Maximum strain energy in the frame in the 

m-th mode determined using Equation 

(9-34)

Wp Component operating weight, 

Equations (11-1), (11-3), (11-4), (11-5), 

(11-6)

X Height of upper support attachment at 

level x as measured from grade, see

Equation (11-7)

Y Time period in years corresponding to a 

mean return period and probability of 

exceedance, Equation (1-2)

Height of lower support attachment at 

level y as measured from grade, see

Equation (11-7)

Z Plastic section modulus, Equations (5-1), 

(5-2), (5-3), (5-4), (5-6)

Z’ Adjusted resistance for mechanical 

fastener, Chapter 8

a Parameter used to measure deformation 

capacity in component load-deformation 

curves, Figures 2-3, 5-1, 6-1

Clear width of wall between columns, 

Equations (5-33), (5-34)

Equivalent width of infill strut, 

Equations (7-14), (7-16), (7-17), (7-18), 

(7-19)

a′ Parameter used to measure deformation 

capacity in component load-deformation 

curve, Figure 2-5

ap Component amplification factor from 

Table 11-2, Equation (11-3)

b Parameter used to measure deformation 

capacity in component load-deformation 

curves, Figures 2-3, 5-1, 6-1

Shear wall length or width, Equations 

(8-1), (8-2)

Diaphragm width, Equations (8-4), (8-5)

The shortest plan dimension of the rehabilitated building, in ft. (mm), measured 

perpendicular to d, Equations (9-6), (9-7)

ba Connection dimension, Equations (5-22), 

(5-23)

bbf Beam flange width in Equations for BeamColumn Connections in Sections 5.5.2.4.2 

and 5.5.2.4.3

bcf Column flange width in Equations for 

Beam-Column Connections in 

Sections 5.5.2.4.2 and 5.5.2.4.3

bf Flange width, Tables 5-5, 5-6, 5-7

bp Width of rectangular glass, Equation 

(11-9)

bt Connection dimension, Equations (5-24), 

(5-25)

bw Web width, in., Equation (6-4)

c Parameter used to measure residual 

strength, Figures 2-3, 5-1, 6-1, 7-1, 8-1
Symbols-10 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

c1 Size of rectangular or equivalent rectangular column, capital, or bracket measured in 

the direction of the span for which 

moments are being determined, in, 

Section 6.5.4.3

Clearance (gap) between vertical glass 

edges and the frame, Equation (11-9)

c2 Clearance (gap) between horizontal glass 

edges and the frame, Equation (11-9)

d Depth of soil sample for calculation of 

effective vertical stress, Equation (4-5)

Parameter used to measure deformation 

capacity, Figures 2-3, 5-1, 6-1, 7-1, 8-1

Distance from extreme compression fiber 

to centroid of tension reinforcement, in., 

Equation (6-4)

The longest plan dimension of the rehabilitated building, in ft. (mm), Equations 

(9-6), (9-7)

da Elongation of anchorage at end of wall 

determined by anchorage details and load 

magnitude, Equation (8-1)

Deflection at yield of tie-down anchorage 

or deflection at load level to anchorage at 

end of wall determined by anchorage 

details and dead load, in., Equation (8-2)

db Overall beam depth, Equations (5-7), 

(5-8), (5-21), (5-22), (5-23), (5-24), (5-25), 

(5-26), (5-29)

Nominal diameter of bar, in., Equation 

(6-3)

dbg Depth of the bolt group, Table 5-5

dc Column depth, Equation (5-5)

di Depth, in feet, of a layer of soils having 

similar properties, and located within 100 

feet of the surface, Equations (1-6), (1-7)

dv Length of component in the direction of 

shear force, Equations (7-11), (7-12)

dw Depth to ground-water level, Equation 

(4-5)

dz Overall panel zone depth between continuity plates, Chapter 5

e Length of EBF link beam, Equations 

(5-28), (5-29), (5-30), (5-32)

Parameter used to measure deformation 

capacity, Figures 2-3, 5-1, 6-1, 7-1, 8-1

Actual eccentricity, ft. (mm), measured in 

plan between the center of mass of the 

structure above the isolation interface and 

the center of rigidity of the isolation 

system, plus accidental eccentricity, ft. 

(mm), taken as 5% of the maximum building dimension perpendicular to the direction of force under consideration, 

Equations (9-6), (9-7)

en Nail deformation at yield load per nail for 

wood structural panel sheathing, 

Equations (8-2), (8-4), (8-5)

f1 Fundamental frequency of the building, 

Equation (9-24)

fa Axial compressive stress due to gravity 

loads specified in Equations (3-3), (7-5), 

(7-6)

fae Expected vertical compressive stress, 

Chapter 7

fc Compressive strength of concrete, psi, 

Equations (6-4), (6-5)

f ′

dt Lower bound masonry diagonal tension 

strength, Equation (7-5)

f ′

m Lower bound masonry compressive 

strength, Equations (7-6), (7-7), (7-9), 

(7-10), (7-11), (7-13), (7-21)

fme Expected compressive strength of masonry 

as determined in Section 7.3.2.3 

fpc Average compressive stress in concrete 

due to effective prestress force only (after 

allowance for all prestress losses), 

Chapter 6

fs Stress in reinforcement, psi, Equations 

(6-2), (6-3)

f ′

t Lower bound masonry tensile strength, 

Chapter 7

fte Expected masonry flexural tensile strength 

as determined in Section 7.3.2.5 
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-11

fvie Expected shear strength of masonry infill, 

Equation (7-15)

fy Yield strength of tension reinforcement, 

Equations (6-2), (6-3)

Lower bound of yield strength of reinforcing steel, Equations (7-12), (7-13)

fye Expected yield strength of reinforcing steel 

as determined in Section 7.3.2.8

g Acceleration of gravity (386.1 in./sec.2

, or 

9,807 mm/sec2

 for SI units), Equations 

(3-15), (9-2), (9-3), (9-4), (9-5), (9-30)

h Average story height above and below a 

beam-column joint, Equation (5-17)

Clear height of wall between beams, 

Equations (5-33), (5-35)

Distance from inside of compression 

flange to inside of tension flange, Equation 

(5-7)

Height of member along which deformations are measured, Chapter 6

Overall thickness of member, in, 

Equation (6-4)

Height of a column, pilaster, or wall, 

Chapter 7

Shear wall height, Equations (8-1), (8-2)

Average roof elevation of structure, 

relative to grade elevation, Equation (11-3)

hc Assumed web depth for stability, 

Chapter 5

Gross cross-sectional dimension of column 

core measured in the direction of joint 

shear, in, Chapter 6

hcol Height of column between beam centerlines, Equation (7-14)

heff Effective height of wall or pier components under consideration, Equations (7-4), 

(7-5), (7-6)

hi

 Height from the base of a building to floor 

level i, Equations (3-12), (9-9)

Height of story i between two floors at 

common points of reference, Equation 

(3-2)

hinf Height of infill panel, Equations (7-14), 

(7-17), (7-19), (7-20), (7-21)

hn Height to roof level, ft, Equation (3-7)

hp Height of rectangular glass, Equation 

(11-9)

hx Height from base to floor level x, ft, 

Equations (3-12), (9-9)

k Exponent used for determining the vertical 

distribution of lateral forces, Equation 

(3-12)

Coefficient used for calculation of column 

shear strength, Chapter 6

k1 Distance from the center of the split tee 

stem to the edge of the split tee flange fillet, Equation (5-25)

keff Effective stiffness of an isolator unit, as 

prescribed by Equation (9-12), or an 

energy dissipation unit, as prescribed by 

Equations (9-23) or (9-38)

kh Horizontal seismic coefficient in soil acting on retaining wall, Equation (4-11)

ksr Winkler spring stiffness in overturning 

(rotation) for pile group, expressed as 

moment/unit rotation, Equation (4-10)

ksv Winkler spring stiffness in vertical direction, expressed as force/unit displacement/

unit area, Equation (4-6) 

Pile group axial spring stiffness expressed 

as force/unit displacement, Equation (4-9)

kv Shear buckling coefficient, Chapter 5

kvn Axial stiffness of nth pile in a pile group, 

Equation (4-10)

lb Length of beam, Equation (5-1)

Provided length of straight development, 

lap splice, or standard hook, in., Equation 

(6-2)

lbeff Assumed distance to infill strut reaction 

point for beams, Equation (7-18)

lc Length of column, Equations (5-2), (5-36)

lceff Assumed distance to infill strut reaction 

point for columns, Equation (7-16)
Symbols-12 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

ld Required length of development for a 

straight bar, in., Equation (6-2)

le Length of embedment of reinforcement, 

in., Equation (6-3)

lp Length of plastic hinge used for calculation of inelastic deformation capacity, in., 

Equation (6-6)

lw Length of entire wall or a segment of wall 

considered in the direction of shear force, 

in., Chapter 6

m Modification factor used in the acceptance 

criteria of deformation-controlled components or elements, indicating the available 

ductility of a component action, Equations 

(3-20), (5-9)

me Effective m-factor, Equation (5-9)

mt Value of m-factor for the column in tension, Equation (5-13)

mx Value of m for bending about x-axis of a 

member, Equations (5-10), (5-11), 

(5-13), (6-1)

my Value of m for bending about y-axis of a 

member, Equations (5-10), (5-11), 

(5-13), (6-1)

n Total number of stories in a vertical seismic framing, Equations (3-12), (3-13)

pD+L Expected gravity stress at test location, 

Equation (7-2)

q Vertical bearing pressure, Equation (4-8)

qallow Allowable bearing pressure specified in 

the available design documents for the 

design of shallow foundations for gravity 

loads (dead plus live loads), Equation (4-1)

qc Expected bearing capacity of shallow 

foundation expressed in load per unit area, 

Equations (4-1), (4-3), (4-7), (4-8)

qin Expected transverse strength of an infill 

panel, Equation (7-21)

r Governing radius of gyration, Equation 

(5-36)

rinf Diagonal length of infill panel, Equation 

(7-14)

s Spacing of shear reinforcement, Equation 

(7-12)

si Minimum separation distance between 

adjacent buildings at level i, Equation 

(2-8)

su Undrained shear strength of soil, pounds/

ft.2

, Chapter 1

—su Average value of the undrained soil shear 

strength in the upper 100 feet of soil, calculated in accordance with Equation (1-6), 

pounds/ft.2

t Effective thickness of wood structural 

panel or plywood for shear, in., Equations 

(8-2), (8-4), (8-5)

ta Thickness of angle, Equations (5-21), 

(5-23)

tbf Thickness of beam flange, Chapter 5

tbw Thickness of beam web, Chapter 5

tcf Thickness of column flange, Chapter 5

tcw Thickness of column web, Chapter 5

tf Thickness of flange, Equations (5-25), 

(5-29)

tinf Thickness of infill panel, Equations (7-14), 

(7-20), (7-21)

tp Thickness of panel zone including doubler 

plates, Equation (5-5)

Thickness of flange plate, Equation (5-26)

ts Thickness of split tee stem, Equations 

(5-24), (5-25)

tw Thickness of web, Equations (5-7), (5-29)

Thickness of plate wall, Equation (5-33)

Thickness of wall web, in., Chapter 6

tz Thickness of panel zone (doubler plates 

not necessarily included), Chapter 5

v Maximum shear in the direction under 

consideration, Equation (8-5)
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-13

vme Expected masonry shear strength, 

Equation (7-1)

Expected masonry bed-joint sliding shear 

strength, Equation (7-3)

vte Average bed-joint shear strength, Equation 

(7-1)

vto Bed-joint shear stress from single test, 

Equation (7-2)

vy Shear at yield in the direction under 

consideration in lb./ft., Equations (8-1), 

(8-2), (8-3), (8-4), (8-5)

w Water content of soil, calculated as the 

ratio of the weight of water in a unit 

volume of soil to the weight of soil in the 

unit volume, expressed as a percentage, 

Section 1.6.1.4.1

Length of connection member, see

Equations (5-23), (5-25)

wi

 Portion of the effective seismic weight 

corresponding to floor level i, Equations 

(3-12), (3-13), (9-9)

wx Portion of the effective seismic weight 

corresponding to floor level x, Equations 

(3-12), (3-13), (9-9)

wz Width of panel zone between column 

flanges, Chapter 5

x Elevation in structure of component 

relative to grade elevation, Equation (11-3)

y The distance, in ft. (mm), between the 

center of rigidity of the isolation system 

rigidity and the element of interest, 

measured perpendicular to the direction of 

seismic loading under consideration, 

Equations (9-6), (9-7)

∆ Generalized deformation, Figures 2-3, 2-5, 

5-1, 6-1, 8-1

Total elastic and plastic displacement, 

Chapter 5

Calculated deflection of diaphragm, wall, 

or bracing element, in.

∆− Negative displacement amplitude, in. 

(mm), of an isolator or energy dissipation 

unit during a cycle of prototype testing, 

Equations (9-12), (9-13), (9-38)

∆+ Positive displacement amplitude, in. (mm), 

of an isolator or energy dissipation unit 

during a cycle of prototype testing,

Equations (9-12), (9-13), (9-38)

∆ave Average displacement of an energy dissipation unit during a cycle of prototype 

testing, equal to (|∆+| + |∆−|)/2, Equation 

(9-39)

∆d Diaphragm deformation, Equations (3-8), 

(3-9)

∆eff Differentiated displacement between the 

top and bottom of the wall or pier components under consideration over a height, 

heff, Figure 7-1

∆fallout Relative seismic displacement (drift) 

causing glass fallout from the curtain wall, 

storefront, or partition, as determined in 

accordance with an approved engineering 

analysis method, Equations (11-10), 

(11-11)

∆i Inter-story displacement (drift) of story i

divided by the story height, Chapter 5

∆i1 Estimated lateral deflection of building 1 

relative to the ground at level i, 

Equation (2-8)

∆i2 Estimated lateral deflection of building 2 

relative to the ground at level i, 

Equation (2-8)

∆inf Deflection of infill panel at mid-length 

when subjected to transverse loads, 

Equation (7-20)

∆p Additional earth pressure on retaining wall 

due to earthquake shaking, Equation 

(4-11)

∆w Average in-plane wall displacement, 

Equation (3-8)
Symbols-14 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

∆y Generalized yield deformation, unitless, 

Figure 5-1

Calculated deflection of diaphragm, shear 

wall, or bracing element at yield, see

Equations (8-1), (8-2), (8-3), (8-4), (8-5)

Σ(∆ cX) Sum of individual chord-splice slip values 

on both sides of the diaphragm, each 

multiplied by its distance to the nearest 

support, Equations (8-4), (8-5)

ΣED Total energy dissipated, in in-kips, in the 

isolation system during a full cycle of 

response at the design displacement, DD, 

Equation (9-18)

ΣEM Total energy dissipated, in in-kips, in the 

isolation system during a full cycle of 

response at the maximum displacement, 

DM, Equation (9-19)

Σ|F+

D|max Sum, for all isolator units, of the maximum 

absolute value of force, in kips (kN), at a 

positive displacement equal to DD, 

Equation (9-14)

Σ|F+

D|min Sum, for all isolator units, of the minimum 

absolute value of force, in kips (kN), at a 

positive displacement equal to DD,

Equation (9-15)

Σ|F+

M|max Sum, for all isolator units, of the maximum 

absolute value of force, in kips (kN), at a 

positive displacement equal to DM, 

Equation (9-16)

Σ|F+

M|min Sum, for all isolator units, of the minimum 

absolute value of force, in kips (kN), at a 

positive displacement equal to DM, 

Equation (9-17)

Σ|F -

D|max Sum, for all isolator units, of the maximum 

absolute value of force, in kips (kN), at a 

negative displacement equal to DD, 

Equation (9-14)

Σ|F -

D|min Sum, for all isolator units, of the minimum 

absolute value of force, in kips (kN), at a 

negative displacement equal to DD, 

Equation (9-15)

Σ|F -

M|max Sum, for all isolator units, of the maximum 

absolute value of force, in kips (kN), at a 

negative displacement equal to DM, 

Equation (9-16)

Σ|F -

M|min Sum, for all isolator units, of the minimum 

absolute value of force, in kips (kN), at a 

negative displacement equal to DM, 

Equation (9-17)

α Ratio of post-yield stiffness to effective 

stiffness, Equation (3-17)

Factor equal to 0.5 for fixed-free cantilevered shear wall, or 1.0 for fixed-fixed 

pier, Equation (7-4)

Velocity exponent for a fluid viscous 

device in Equation (9-25)

β Modal damping ratio, Table 1-6

Factor to adjust fundamental period of the 

building, Equation (3-7)

Ratio of expected frame strength, vfre, to 

expected infill strength, vine, Chapter 7

Damping inherent in the building frame 

(typically equal to 0.05), Equations (9-26), 

(9-28), (9-30)

βb Equivalent viscous damping of a bilinear 

system, Chapter 9

βD Effective damping of the isolation system 

at the design displacement, as prescribed 

by Equation (9-18)) 

βeff Effective damping of isolator unit, as 

prescribed by Equation (9-13), or an 

energy dissipation unit, as prescribed by 

Equation (9-39); also used for the effective 

damping of the building, as prescribed by 

Equations (9-26), (9-28), (9-30), (9-31), 

(9-32), (9-36)

βeff-m Effective damping in m-th mode 

prescribed by Equation (9-33)

βM Effective damping of the isolation system 

at the maximum displacement, as 

prescribed by Equation (9-19)) 

βm m-th mode damping in the building frame, 

Equation (9-33)
 Symbols

FEMA 356 Seismic Rehabilitation Prestandard Symbols-15

γ Unit weight, weight/unit volume (pounds/

ft3

 or N/m3), Equation (4-4)

Coefficient for calculation of joint shear 

strength, Equation (6-5)

γf Fraction of unbalanced moment transferred by flexure at slab-column 

connections, Chapter 6

γt Total unit weight of soil, Equations (4-5), 

(4-11)

γw Unit weight of water, Equation (4-5)

δi Lateral drift in story i, in the direction 

under consideration, at its center of 

rigidity, using the same units as for measuring hi

, Equation (3-2)

Displacement at floor i, Equations (9-26), 

(9-27)

δmi m-th mode horizontal displacement at floor 

i, Equation (9-34)

δmrj m-th relative displacement between the 

ends of device j along its axis, 

Equation (9-35)

δrj Relative displacement between the ends of 

energy dissipating device j along the axis 

of the device, Equations (9-29), (9-37)

δt Target displacement, Figure 3-1

δxA Deflection at level x of Building A, 

determined by an elastic analysis as 

defined in Chapter 3, Equations (11-7), 

(11-8)

δxB Deflection at level x of Building B, determined by an elastic analysis as defined in 

Chapter 3, Equation (11-8)

δyA Deflection at level y of Building A, determined by an elastic analysis as defined in 

Chapter 3, Equation (11-7)

η Displacement multiplier, greater than 1.0, 

to account for the effects of torsion, 

Equation (3-1)

θ Generalized deformation, radians, 

Figures 5-1, 6-1

Angle between infill diagonal and horizontal axis, tanθ = hinf/Linf, radians, see

Equation (7-14)

θb Angle between lower edge of compressive 

strut and beam, radians, Equations (7-18), 

(7-19)

θc Angle between lower edge of compressive 

strut and column, radians, Equations 

(7-16), (7-17)

θi Stability coefficient indicative of the 

stability of a structure under gravity loads 

and earthquake-induced deflection,

Equation (3-2)

Inter-story drift ratio, radians, Chapter 5

θj Angle of inclination of energy dissipation 

device, Equation (9-30)

θy Generalized yield deformation, radians, 

Figure 5-1

Yield rotation, radians, Equations (5-1), 

(5-2), (5-30), (5-35), (6-6)

κ A knowledge factor used to reduce 

component strength based on the level of 

knowledge obtained for individual components during data collection, Equations 

(3-20), (3-21), (6-1)

λ Correction factor related to unit weight of 

concrete, Equation (6-5)

λ1 Coefficient used to determine equivalent 

width of infill strut, Equation (7-14)

λ2 Infill slenderness factor, Equation (7-21)

λp Limiting slenderness parameter for 

compact element, Chapter 5

λr Limiting slenderness parameter for 

noncompact element, Chapter 5

μ Coefficient of shear friction, Chapter 6

ν Poisson’s ratio of soil, Equation (4-4)
Symbols-16 Seismic Rehabilitation Prestandard FEMA 356

 Symbols

νs Shear wave velocity in soil, in feet/sec., 

Section 1.6.1.4.1

Shear wave velocity at low strains, 

Equation (4-4)

__

vs Average value of the soil shear wave 

velocity in the upper 100 feet of soil, 

calculated in accordance with Equation 

(1-6), feet/sec.

ρ Ratio of non-prestressed tension reinforcement, Chapter 6

ρbal Reinforcement ratio producing balanced 

strain conditions, Chapter 6

ρg Ratio of area of total wall or pier vertical 

plus horizontal reinforcement to area of 

wall or pier cross-section, Chapter 7

ρlp Yield deformation of a link beam, 

Chapter 5

ρn Ratio of distributed shear reinforcement in 

a plane perpendicular to the direction of 

the applied shear, Chapter 6

ρ′ Ratio of non-prestressed compression 

reinforcement, Chapter 6

ρ′′ Reinforcement ratio for transverse joint 

reinforcement, Chapter 6

σ Standard deviation of the variation of the 

material strengths, Chapter 2

σ′o Effective vertical stress, Equation (4-5)

φ Strength reduction factor 

φi Modal displacement of floor i, see

Equation (9-30)

φrj Relative modal displacement in horizontal 

direction of energy dissipation device j, 

Equation (9-30)

χ A factor to calculate horizontal seismic 

force, Fp, Equations (2-6), (2-7)

ω1 Fundamental angular frequency equal to 

2πf1, Equation (9-24)
 Acronyms

FEMA 356 Seismic Rehabilitation Prestandard Acronyms-1

Acronyms

AAMA American Architectural Manufacturers 

Association

ABK Agbabian, Barnes and Kariotis joint venture

ACI American Concrete Institute

AISC American Institute of Steel Construction

AISI American Iron and Steel Institute

ANSI American National Standards Institute

APA American Plywood Association

API American Petroleum Institute

ASCE American Society of Civil Engineers

ASHRAE American Society of Heating, Refrigeration and Air Conditioning Engineers

ASME American Society of Mechanical Engineers

ASTM American Society for Testing and Materials

ATC Applied Technology Council

AWS American Welding Society

AWWA American Water Works Association

BNC Ball and cone system, a rolling seismic 

isolator

BOCA Building Officials and Code Administrators

BRANZ Building Research Association of New 

Zealand

BSE-1 Basic Safety Earthquake-1

BSE-2 Basic Safety Earthquake-2

BSO Basic Safety Objective

BSSC Building Seismic Safety Council

CBF Concentric Braced Frame

CISCA Ceilings and Interior Systems Construction Association

CP Collapse Prevention

CQC Complete Quadratic Combination

CRSI Concrete Reinforcing Steel Institute 

CUREE California Universities for Research in 

Earthquake Engineering

CUSEC Central United States Earthquake Consortium

DCR Demand Capacity Ratio

DDS Double Diagonal Sheathing

EBF Eccentric Braced Frame

EDD Energy Dissipation Device

EDS Energy Dissipation System

EERC Earthquake Engineering Research Center

EERI Earthquake Engineering Research Institute

FEMA Federal Emergency Management Agency

FPS Friction-pendulum system, a sliding seismic isolator

FR Fully Restrained

GFRC Glass Fiber Reinforced Concrete

HDR High-damping rubber bearings, an elastomeric seismic isolator

HR Hazards Reduced

HVAC Heating, ventilation, and air conditioning

IBC International Building Code

ICBO International Conference of Building Officials

IO Immediate Occupancy

LDP Linear Dynamic Procedure

LRB Low-damping rubber bearings with a lead 

core, an elastomeric seismic isolator

LRFD Load and Resistance Factor Design

LS Life Safety
Acronyms-2 Seismic Rehabilitation Prestandard FEMA 356

 Acronyms

LSP Linear Static Procedure

MCE Maximum Considered Earthquake

MDOF Multi-degree of Freedom System

MEP Mechanical, electrical, and plumbing

MSJC Masonry Standards Joint Committee

NAVFAC Publication of the U.S. Department of the 

Navy

NBS National Bureau of Standards

NCEER National Center for Earthquake Engineering Research

NDE Nondestructive Examination 

NDP Nonlinear Dynamic Procedure

NDS National Design Specification

NEHRP National Earthquake Hazard Reduction 

Program

NFPA National Fire Protection Association

NIST National Institute of Standards and Technology (formerly NBS)

NSP Nonlinear Static Procedure

OMF Ordinary Moment Frame

PCI Precast Concrete Institute

PR Partially Restrained 

PS-# Product Standard-#

QAP Quality Assurance Plan

RB Low-damping rubber bearings, an elastomeric seismic isolator

RM Reinforced Masonry

SAC SEAOC, ATC and CUREe joint ventures

SBC Southern Building Code

SBCCI Southern Building Code Congress, International

SDI Steel Deck Institute

SDOF Single-degree of Freedom

SEAOC Structural Engineers Association of California

SJI Steel Joist Institute

SMACNA Sheet Metal and Air Conditioning Contractors National Association

SMF Special Moment Frame

SPT Standard Penetration Test

SSI Soil-structure interaction

TMS The Masonry Society

UBC Uniform Building Code

UCBC Uniform Code for Building Conservation

URM Unreinforced Masonry

USGS United States Geological Survey

WWPA Western Wood Products Association
 Definitions

FEMA 356 Seismic Rehabilitation Prestandard Definitions-1

Definitions

A

Acceleration-sensitive nonstructural component: A nonstructural component that is sensitive to,

and subject to, damage from inertial loading. 

Acceptance criteria: Limiting values of properties

such as drift, strength demand, and inelastic deformation

used to determine the acceptability of a component at a

given performance level. 

Action: An internal moment, shear, torque, axial load,

deformation, displacement, or rotation corresponding to

a displacement due to a structural degree of freedom;

designated as force- or deformation-controlled. 

Active Fault: A fault for which there is an average historic slip rate of 1 mm per year or more, and evidence of

seismic activity within Holocene times (past 11,000

years). 

Adjusted Resistance: The reference resistance

adjusted to include the effects of applicable adjustment

factors resulting from end use and other modifying factors excluding time-effect adjustments, which are considered separately and not included.

Aspect ratio: Ratio of height to width for shear walls

and span to width for horizontal diaphragms. 

Assembly: Two or more interconnected components. 

B

Balloon framing: Continuous stud framing from sill

to roof, with intervening floor joists nailed to studs and

supported by a let-in ribbon. 

Base: The level at which earthquake effects are

imparted to the building. 

Beam: A structural member whose primary function is

to carry loads transverse to its longitudinal axis. 

Bearing wall: A wall that supports gravity loads of at

least 200 pounds per lineal foot from floors and/or roofs. 

Bed joint: The horizontal layer of mortar on which a

masonry unit is laid. 

Boundary component (boundary member): A

member at the perimeter (edge or opening) of a shear

wall or horizontal diaphragm that provides tensile and/or

compressive strength. 

Braced frame: A vertical lateral-force-resisting element consisting of vertical, horizontal, and diagonal

components joined by concentric or eccentric connections. 

BSE-1: Basic Safety Earthquake-1, taken as the lesser

of the ground shaking for a 10%/50 year earthquake or

two-thirds of the BSE-2 at a site. 

BSE-2: Basic Safety Earthquake-2, taken as the ground

shaking based on the MCE at a site. 

BSO: Basic Safety Objective is a Rehabilitation Objective that achieves the dual rehabilitation goals of the Life

Safety Building Performance Level for the BSE-1 Earthquake Hazard Level and the Collapse Prevention Building Performance Level for the BSE-2 Earthquake

Hazard Level. 

Building Occupancy: The purpose for which a building, or part thereof, is used, or intended to be used, designated in accordance with the applicable building code. 

Building Performance Level: A limiting damage

state for a building, considering structural and nonstructural components, used in the definition of Rehabilitation Objectives. 

C

Cast Iron: A hard, brittle nonmalleable iron-carbon

alloy containing 2.0 to 4.5 percent carbon. Shapes are

obtained by reducing iron ore in a blast furnace, forming

it into bars (or pigs), and remelting and casting it into its

final form. 

Cavity wall: A masonry wall with an air space between

wythes. 

Chord: See diaphragm chord. 

Clay tile masonry: Masonry constructed with hollow

units made of clay tile. 
Definitions-2 Seismic Rehabilitation Prestandard FEMA 356

 Definitions

Clay-unit masonry: Masonry constructed with solid,

cored, or hollow units made of clay; can be ungrouted or

grouted. 

Closed stirrups or ties: Transverse reinforcement

defined in Chapter 7 of ACI 318 consisting of standard

stirrups or ties with 90-degree hooks and lap splices in a

pattern that encloses longitudinal reinforcement. 

Code Official: The organization, political subdivision,

office, or individual legally charged with responsibility

for administering and enforcing the provisions of this

standard. 

Coefficient of variation: For a sample of data, the

ratio of the standard deviation for the sample to the mean

value for the sample. 

Collar joint: Vertical longitudinal joint between

wythes of masonry or between masonry wythe and backup construction; can be filled with mortar or grout. 

Collector: See drag strut. 

Column (or beam) jacketing: A rehabilitation method in

which a concrete column or beam is encased in a steel or

concrete “jacket” to strengthen and/or repair the member

by confining the concrete. 

Component, flexible: A component, including

attachments, having a fundamental period greater than

0.06 seconds. 

Component, rigid: A component, including attachments, having a fundamental period less than or equal to

0.06 seconds. 

Components: The basic structural members that constitute a building, including beams, columns, slabs,

braces, walls, piers, coupling beams, and connections;

designated as primary or secondary. 

Composite masonry wall: Multi-wythe masonry

wall acting with composite action. 

Composite panel: A structural panel comprising thin

wood strands or wafers bonded together with exterior

adhesive. 

Concentric Braced Frame: Braced frame element in

which component worklines intersect at a single point or

at multiple points such that the distance between intersecting components, or eccentricity, is less than or equal

to the width of the smallest member connected at the

joint. 

Concrete masonry: Masonry constructed with solid

or hollow units made of concrete; can be ungrouted or

grouted. 

Condition of service: The environment to which the

structure will be subjected.

Connection: A link that transmits actions from one

component or element to another component or element,

categorized by type of action (moment, shear, or axial).

Connection hardware: Proprietary or custom fabricated body of a component that is used to link wood

components. 

Connectors: Nails, screws, lags, bolts, split rings, and

shear plates used to link wood components to other

wood or metal components. 

Contents: Movable items within the building introduced by the owner or occupants, weighing 400 pounds

or more. 

Continuity plates: Column stiffeners at the top and

bottom of a panel zone. 

Control node: A node located at the center of mass at

the roof of a building used in the NSP to measure the

effects of earthquake shaking on a building. 

Corrective measure: Any modification of a component or element, or the structure as a whole, implemented to improve building performance. 

Coupling beam: A component that ties or couples

adjacent shear walls acting in the same plane. 

Cripple studs: Short studs between a header and top

plate at openings in wall framing, or studs between the

base and sill of an opening. 

Cripple wall: Short wall between the foundation and

first floor framing. 

Critical action: The component action that reaches its

elastic limit at the lowest level of lateral deflection or

loading of the structure. 

Cross tie: A component that spans the width of the diaphragm and delivers out-of-plane wall forces over the

full depth of the diaphragm. 
 Definitions

FEMA 356 Seismic Rehabilitation Prestandard Definitions-3

D

Decay: Decomposition of wood caused by action of

wood-destroying fungi. The term “dry rot” is used interchangeably with decay. 

Decking: Solid sawn lumber or glue-laminated decking, nominally two to four inches thick and four inches

and wider. Decking shall be tongue-and-groove or connected at longitudinal joints with nails or metal clips. 

Deep foundation: Driven piles made of steel, concrete, or wood, or cast-in-place concrete piers or drilled

shafts of concrete. 

Deformation-sensitive nonstructural component: A nonstructural component that is sensitive to

deformation imposed by the drift or deformation of the

structure, including deflection or deformation of diaphragms. 

Demand: The amount of force or deformation imposed

on an element or component. 

Design displacement: The design earthquake displacement of an isolation or energy dissipation system,

or elements thereof, excluding additional displacement

due to actual and accidental torsion. 

Design earthquake: A user-specified earthquake for

the design of an isolated building having ground shaking

criteria described in Chapter 2. 

Design resistance (force or moment as appropriate): Resistance provided by member or connection;

the product of adjusted resistance, the resistance factor,

and time effect factor. 

Diagonal bracing: Inclined components designed to

carry axial load, enabling a structural frame to act as a

truss to resist lateral forces. 

Diaphragm: A horizontal (or nearly horizontal) structural element used to distribute inertial lateral forces to

vertical elements of the lateral-force-resisting system. 

Diaphragm chord: A component provided to resist

tension or compression at the edges of a diaphragm. 

Diaphragm collector: A component provided to

transfer lateral forces in the diaphragm to vertical elements of the lateral-force-resisting system or to other

portions of the diaphragm. 

Diaphragm ratio: See aspect ratio. 

Diaphragm strut: See drag strut. 

Differential compaction: An earthquake- induced

process in which soils become more compact and settle

in a nonuniform manner across a site. 

Dimensioned lumber: Lumber from nominal two

through four inches thick and nominal two or more

inches wide. 

Displacement-dependent energy dissipation

devices: Devices having mechanical properties such

that the force in the device is related to the relative displacement in the device. 

Displacement restraint system: Collection of

structural components and elements that limit lateral displacement of seismically-isolated buildings during the

BSE-2. 

Dowel-bearing strength: The maximum compression strength of wood or wood-based products when

subjected to bearing by a steel dowel or bolt of specific

diameter. 

Dowel type fasteners: Bolts, lag screws, wood

screws, nails, and spikes. 

Drag strut: A component parallel to the applied load

that collects and transfers diaphragm shear forces to the

vertical lateral-force-resisting elements, or other portions of the diaphragm. Also called collector, diaphragm

strut, or tie. 

Dressed size: The dimensions of lumber after surfacing with a planing machine. 

Dry rot: See Decay. 

Dry service: Structures wherein the maximum equilibrium moisture content does not exceed 19%. 

Dual system: A structural system with the following

features: 

1. A space frame included to support gravity loads with

or without capability of resisting lateral loads. 

2. Lateral-load-resisting system included to resist at least

25% of the lateral loads provided by one or more of the

following: concrete or steel shear walls, steel eccentrically braced frames (EBF), concentrically braced frames

(CBF), and moment-resisting frames (Special Moment

Frames, or Ordinary Moment Frames). 

3. Each system designed to resist the total lateral load in

proportion to relative rigidity. 
Definitions-4 Seismic Rehabilitation Prestandard FEMA 356

 Definitions

E

Earthquake Hazard Level: Ground shaking

demands of specified severity, developed on either a

probabilistic or deterministic basis. 

Eccentric Braced Frame: Braced frame element in

which component worklines do not intersect at a single

point and the distance between the intersecting components, or eccentricity, exceeds the width of the smallest

member connecting at the joint. 

Edge distance: The distance from the edge of the

member to the center of the nearest fastener. 

Effective damping: The value of equivalent viscous

damping corresponding to the energy dissipated by the

building, or element thereof, during a cycle of response. 

Effective stiffness: The value of the lateral force in

the building, or an element thereof, divided by the corresponding lateral displacement. 

Effective Void Ratio: Ratio of collar joint area without mortar to the total area of the collar joint.

Element: An assembly of structural components that

act together in resisting forces, including gravity frames,

moment-resisting frames, braced frames, shear walls,

and diaphragms. 

Energy dissipation device: Non-gravity-load-supporting element designed to dissipate energy in a stable

manner during repeated cycles of earthquake demand. 

Energy dissipation system: Complete collection of

all energy dissipation devices, their supporting framing,

and connections. 

Expected Strength: The mean value of resistance of

a component at the deformation level anticipated for a

population of similar components, including consideration of the variability in yield strength as well as strain

hardening and plastic section development. 

F

Fair Condition: Masonry found during condition

assessment to have mortar and units intact but with

minor cracking. 

Fault: Plane or zone along which earth materials on

opposite sides have moved differentially in response to

tectonic forces. 

Flexible connection: A link between components

that permits rotational and/or translational movement

without degradation of performance, including universal

joints, bellows expansion joints, and flexible metal hose. 

Flexible diaphragm: A diaphragm with horizontal

deformation along its length more than twice the average

interstory drift. 

Foundation system: An assembly of structural components, located at the soil-structure interface, that transfer loads from the superstructure into the supporting soil. 

Fundamental period: The highest natural period of

the building in the direction under consideration. 

G

Gauge or row spacing: The center-to-center distance between fastener rows or gauge lines. 

Glulam beam: Shortened term for glue-laminated

beam, which is a wood-based component made up of

layers of wood bonded with adhesive.

Good Condition: Masonry found during condition

assessment to have mortar and units intact and no visible

cracking. 

Grade: The classification of lumber with regard to

strength and utility, in accordance with the grading rules

of an approved agency. 

Grading rules: Systematic and standardized criteria

for rating the quality of wood products. 

Gypsum wallboard or drywall: An interior wall surface sheathing material; can sometimes be considered

for resisting lateral forces. 

H

Head joint: Vertical mortar joint placed between

masonry units in the same wythe. 

Hold-down: Hardware used to anchor vertical chord

forces in a shear wall to the foundation or framing of the

structure in order to resist the effects of overturning. 
 Definitions

FEMA 356 Seismic Rehabilitation Prestandard Definitions-5

Hollow masonry unit: A masonry unit with net crosssectional area in every plane parallel to the bearing surface less than 75% of the gross cross-sectional area in

the same plane. 

Hoops: Transverse reinforcement defined in Chapter

21 of ACI 318 consisting of closed ties with 135-degree

hooks embedded into the core and no lap splices. 

I

Infill: A panel of masonry placed within a steel or concrete frame. Panels separated from the surrounding

frame by a gap are termed “isolated infills.” Panels that

are in full contact with a frame around its full perimeter

are termed “shear infills.”

In-plane wall: See shear wall. 

Inter-story drift: The relative horizontal displacement

of two adjacent floors in a building; can also be

expressed as a percentage of the story height separating

the two adjacent floors. 

Isolation interface: The boundary between the upper

portion of the structure (superstructure), which is isolated, and the lower portion of the structure, which

moves rigidly with the ground. 

Isolation system: The collection of structural elements that includes all individual isolator units, all structural elements that transfer force between elements of

the isolation system, and all connections to other structural elements. The isolation system also includes the

wind-restraint system, if such a system is used to meet

the design requirements of this section. 

Isolator unit: A horizontally flexible and vertically

stiff structural element of the isolation system that permits large lateral deformations under seismic load. An

isolator unit shall be used either as part of or in addition

to the weight-supporting system of the building. 

J

Joint: An area where ends, surfaces, or edges of two or

more components are attached; categorized by type of

fastener or weld used and method of force transfer. 

K

King stud: Full height studs adjacent to openings that

provide out-of-plane stability to cripple studs at openings. 

Knee Joint: A joint that in the direction of framing has

one column and one beam. 

L

Landslide: A down-slope mass movement of earth

resulting from any cause. 

Lateral support member: A member designed to

inhibit lateral buckling or lateral-torsional buckling of a

component. 

Lateral-force-resisting system: Those elements of

the structure that provide its basic lateral strength and

stiffness. 

Light framing: Repetitive framing with small, uniformly spaced members. 

Lightweight concrete: Structural concrete that has

an air-dry unit weight not exceeding 115 pcf. 

Link beam: A component between points of eccentrically connected members in an eccentric braced frame

element.

Link intermediate web stiffeners: Vertical web

stiffeners placed within a link. 

Link rotation angle: Angle of plastic rotation

between the link and the beam outside of the link,

derived using the specified base shear, V.

Liquefaction: An earthquake-induced process in

which saturated, loose, granular soils lose shear strength

and liquefy as a result of increase in pore-water pressure

during earthquake shaking. 

Load and Resistance Factor Design: A method of

proportioning structural components (members, connectors, connecting elements, and assemblages) using load

factors and strength reduction factors such that no applicable limit state is exceeded when the structure is subjected to all design load combinations. 

Load duration: The period of continuous application

of a given load, or the cumulative period of intermittent

applications of load. See time effect factor. 
Definitions-6 Seismic Rehabilitation Prestandard FEMA 356

 Definitions

Load path: A path through which seismic forces are

delivered from the point at which inertial forces are generated in the structure to the foundation and, ultimately,

the supporting soil.

Load sharing: The load redistribution mechanism

among parallel components constrained to deflect

together. 

Load/slip constant: The ratio of the applied load to a

connection and the resulting lateral deformation of the

connection in the direction of the applied load. 

Lumber: The product of the sawmill and planing mill,

usually not further manufactured other than by sawing,

resawing, passing lengthwise through a standard planing

machine, crosscutting to length, and matching. 

M

Masonry: The assemblage of masonry units, mortar,

and possibly grout and/or reinforcement; classified with

respect to the type of masonry unit, including clay-unit

masonry, concrete masonry, or hollow-clay tile

masonry. 

Mat-formed panel: A structural panel manufactured

in a mat-formed process including oriented strand board

and waferboard. 

Maximum Considered Earthquake (MCE): An

extreme earthquake hazard level defined by MCE maps

which are a combination of mean 2%/50 year probabilistic spectra and 150% of median deterministic spectra at

a given site. 

Maximum displacement: The maximum earthquake

displacement of an isolation or energy dissipation system, or elements thereof, excluding additional displacement due to actual or accidental torsion. 

Mean Return Period: The average period of time, in

years, between the expected occurrences of an earthquake of specified severity. 

Model Building Type: One of the common building

types listed and described in Table 10-2. 

Moisture content: The weight of the water in wood

expressed as a percentage of the weight of the ovendried wood. 

Moment frame: A building frame system in which

seismic shear forces are resisted by shear and flexure in

members and joints of the frame. 

N

Narrow wood shear wall: Wood shear walls with an

aspect ratio (height-to-width) greater than two-to-one. 

Nominal size: The approximate rough-sawn commercial size by which lumber products are known and sold

in the market. Actual rough-sawn sizes vary from nominal. Reference to standards or grade rules is required to

determine nominal to actual finished size relationships,

which have changed over time. 

Nominal strength: The capacity of a structure or

component to resist the effects of loads, as determined

by (1) computations using specified material strengths

and dimensions, and formulas derived from accepted

principles of structural mechanics; or (2) field tests or

laboratory tests of scaled models, allowing for modeling

effects and differences between laboratory and field conditions. 

Nonbearing wall: A wall that supports gravity loads

less than 200 pounds per lineal foot. 

Noncompact member: A steel section that has

width-to-thickness ratios exceeding the limiting values

for compactness specified in AISC (1993) LRFD Specifications. 

Noncomposite masonry wall: Multi-wythe

masonry wall acting without composite action. 

Nonstructural component: Architectural, mechanical or electrical components of a building that are permanently installed in, or are an integral part of, a building

system. 

Nonstructural Performance Level: A limiting

damage state for nonstructural building components

used to define Rehabilitation Objectives. 

O

Ordinary Moment Frame: A moment frame system

that meets the requirements for Ordinary Moment

Frames as defined in seismic provisions for new construction in AISC (1997) Seismic Provisions, Chapter 5. 
 Definitions

FEMA 356 Seismic Rehabilitation Prestandard Definitions-7

Oriented strand board: A structural panel composed

of thin elongated wood strands with surface layers

arranged in the long panel direction and core layers

arranged in the cross panel direction. 

Out-of-plane wall: A wall that resists lateral forces

applied normal to its plane. 

Overturning: Action resulting when the moment produced at the base of vertical lateral-force-resisting elements is larger than the resistance provided by the

building weight and foundation resistance to uplift. 

P

Panel: A sheet-type wood product. 

Panel rigidity or stiffness: The in-plane shear rigidity of a panel; the product of panel thickness and modulus of rigidity. 

Panel shear: Shear stress acting through the panel

thickness. 

Panel zone: Area of a column at a beam-to-column

connection delineated by beam and column flanges. 

Parapet: Portions of a wall extending above the roof

diaphragm. 

Partially grouted masonry wall: A masonry wall

containing grout in some of the cells. 

Particleboard: A panel manufactured from small

pieces of wood, hemp, and flax, bonded with synthetic

or organic binders, and pressed into flat sheets. 

Perforated wall or infill panel: A wall or panel not

meeting the requirements for a solid wall or infill panel. 

Pier: Vertical portion of a wall between two horizontally adjacent openings. Piers resist axial stresses from

gravity forces and bending moments from combined

gravity and lateral forces. 

Pitch or spacing: The longitudinal center-to-center

distance between any two consecutive holes or fasteners

in a row. 

Plan irregularity: Horizontal irregularity in the layout

of vertical lateral-force-resisting elements, producing a

misalignment between the center of mass and center of

rigidity. 

Platform framing: Construction method in which stud

walls are constructed one floor at a time, with a floor or

roof joist bearing on top of the wall framing at each

level. 

Ply: A single sheet of veneer, or several strips laid with

adjoining edges that form one veneer lamina in a glued

plywood panel. 

Plywood: A structural panel composed of plies of

wood veneer arranged in cross-aligned layers bonded

with adhesive cured upon application of heat and pressure. 

Pole: A round timber of any size or length, usually used

with the larger end in the ground. 

Pole structure: A structure framed with generally

round continuous poles that provide the primary vertical

frame and lateral-load-resisting system. 

Poor condition: Masonry found during condition

assessment to have degraded mortar, degraded masonry

units and significant cracking. 

Pounding: The action of two adjacent buildings coming into contact with each other during earthquake excitation as a result of their close proximity and differences

in dynamic response characteristics.

Preservative: A chemical that, when suitably applied

to wood, makes the wood resistant to attack by fungi,

insects, marine borers, or weather conditions. 

Pressure-preservative treated wood: Wood products pressure-treated by an approved process and preservative. 

Primary elements or components: Those elements

or components that are essential to the ability of the

structure to resist collapse under earthquake-induced

forces and deformations. Primary elements or components resist lateral forces at full capacity, prior to the

onset of strength degradation.

Primary (strong) panel axis: The direction that

coincides with the length of the panel. 

Probability of Exceedance: The chance, expressed

as a percentage (%), that a more severe event will occur

within a specified mean return period expressed in number of years. 

Punched metal plate: A light steel plate fastener with

punched teeth of various shapes and configurations that

are pressed into wood members to effect force transfer. 
Definitions-8 Seismic Rehabilitation Prestandard FEMA 356

 Definitions

P-∆ effect: The secondary effect of column axial loads

and lateral deflection on the shears and moments in various components of a structure. 

R

Redundancy: The quality of having alternative paths

in the structure by which the lateral forces can be transferred, which allows the structure to remain stable following the failure of any single element. 

Re-entrant corner: Plan irregularity in a diaphragm,

such as an extending wing, plan inset, or E-, T-, X-, or

L-shaped configuration, where large tensile and compressive forces can develop. 

Rehabilitation Measures: Modifications to existing

components, or installation of new components, that

correct deficiencies identified in a seismic evaluation as

part of a scheme to rehabilitate a building to achieve a

selected Rehabilitation Objective. 

Rehabilitation Method: For the purpose of this standard, a rehabilitation method is one or more procedures

and strategies for improving the seismic performance of

existing buildings. 

Rehabilitation Objective: A Rehabilitation Objective consists of one or more rehabilitation goals, each

goal consisting of the selection of a target Building Performance Level and an Earthquake Hazard Level. 

Rehabilitation Strategy: A technical approach for

developing rehabilitation measures for a building to

improve seismic performance. 

Reinforced masonry wall: A masonry wall with the

following minimum amounts of vertical and horizontal

reinforcement: vertical reinforcement of at least 0.20 in2

in cross section at each corner or end, at each side of

each opening, and at a maximum spacing of at least 4

feet throughout. Horizontal reinforcement of at least

0.20 in2

 in cross section at the top of the wall, at the top

and bottom of wall openings, at structurally connected

roof and floor openings, and at a maximum spacing of 10

feet.

Repointing: A method of repairing cracked or deteriorating mortar joints in which the damaged or deteriorated mortar is removed and the joints are refilled with

new mortar. 

Required member resistance (or required

strength): Load effect acting on an element or connection, determined by structural analysis, resulting from

the factored loads and the critical load combinations. 

Resistance: The capacity of a structure, component,

or connection to resist the effects of loads. 

Resistance factor: A reduction factor applied to

member resistance that accounts for unavoidable deviations of the actual strength from the nominal value, and

the manner and consequences of failure. 

Rigid diaphragm: A diaphragm with horizontal

deformation along its length less than half the average

interstory drift as specified in Section 3.2.4. 

Rough lumber: Lumber as it comes from the saw prior

to any dressing operation. 

Row of fasteners: Two or more fasteners aligned

with the direction of load. 

Running bond: A pattern of masonry where the head

joints are staggered between adjacent courses by more

than a third of the length of a masonry unit. Also refers

to the placement of masonry units such that head joints

in successive courses are horizontally offset at least onequarter the unit length. 

S

Scragging: The process of subjecting an elastomeric

bearing to one or more cycles of large amplitude displacement. 

Seasoned lumber: Lumber that has been dried either

by open air drying within the limits of moisture contents

attainable by this method, or by controlled air drying. 

Secondary elements or components: Those elements or components not designated as primary but

affect the lateral stiffness of the structure, the distribution of the stresses in the building, or are loaded as a

result of lateral deformation of the building. In nonlinear

analyses, secondary elements or components can resist

lateral forces at residual strength levels. 

Seismic demand: Seismic hazard expressed in the

form of a ground shaking response spectrum or accelogram with or without an estimate of permanent ground

deformation. 
 Definitions

FEMA 356 Seismic Rehabilitation Prestandard Definitions-9

Seismic evaluation: An approved process or methodology of evaluating deficiencies in a building which prevent the building from achieving a selected

Rehabilitation Objective. 

Shallow foundation: Isolated or continuous spread

footings or mats. 

Shear wall: A wall that resists lateral forces applied

parallel with its plane. Also known as an in-plane wall. 

Sheathing: Lumber or panel products that are attached

to parallel framing members, typically forming wall,

floor, ceiling, or roof surfaces. 

Short captive column: Columns with height-todepth ratios less than 75% of the nominal height-todepth ratios of the typical columns at that level. 

Shrinkage: Reduction in the dimensions of wood due

to a decrease of moisture content. 

Simplified NSP Analysis: A nonlinear static analysis

in which only primary lateral-force-resisting elements

are modeled, and component degradation is not explicitly modeled. 

Simplified Rehabilitation Method: An approach

applicable to certain types of buildings and Rehabilitation Objectives in which an analysis of the response of

the entire building to earthquake hazards is not required. 

Slip-critical joint: A bolted joint in which slip resistance of the connection is required. 

Solid masonry unit: A masonry unit with net crosssectional area in every plane parallel to the bearing surface equal to 75% or more of the gross cross-sectional

area in the same plane. 

Solid wall or solid infill panel: A wall or infill panel

with openings not exceeding 5% of the wall surface area.

The maximum length or height of an opening in a solid

wall must not exceed 10% of the wall width or story

height. Openings in a solid wall or infill panel must be

located within the middle 50% of a wall length and story

height, and must not be contiguous with adjacent openings. 

Special Moment Frame (SMF): A moment frame

system that meets the special requirements for frames as

defined in seismic provisions for new construction. 

Stack bond: A placement of masonry units such that

the head joints in successive courses are aligned vertically. 

Stiff diaphragm: A diaphragm that is neither flexible

nor rigid. 

Storage racks: Industrial pallet racks, movable shelf

racks, and stacker racks made of cold-formed or hotrolled structural members. Does not include other types

of racks such as drive-in and drive-through racks, cantilever wall-hung racks, portable racks, or racks made of

materials other than steel. 

Strength: The maximum axial force, shear force, or

moment that can be resisted by a component. 

Stress resultant: The net axial force, shear, or bending moment imposed on a cross section of a structural

component. 

Strong back system: A secondary system, such as a

frame, commonly used to provide out-of-plane support

for an unreinforced or under-reinforced masonry wall. 

Strong column-weak beam: A connection required

to localize damage and control drift; the capacity of the

column in any moment frame joint must be greater than

that of the beams, to ensure inelastic action in the beams. 

Structural components: Components of a building

that provide gravity and lateral load resistance as part of

a continuous load path to the foundation. 

Structural Performance Level: A limiting structural damage state; used in the definition of Rehabilitation Objectives. 

Structural Performance Range: A range of structural damage states; used in the definition of Rehabilitation Objectives. 

Structural system: An assemblage of load-carrying

components that are joined together to provide regular

interaction or interdependence. 

Stud: Vertical framing member in interior or exterior

walls of a building. 

Subassembly: A portion of an assembly. 

Sub-diaphragm: A portion of a larger diaphragm used

to distribute loads between members. 

Systematic Rehabilitation Method: An approach

to rehabilitation in which complete analysis of the

response of the building to earthquake hazards is performed. 
Definitions-10 Seismic Rehabilitation Prestandard FEMA 356

 Definitions

T

Target displacement: An estimate of the maximum

expected displacement of the roof of a building calculated for the design earthquake. 

Tie: See drag strut. 

Tie-down: Hardware used to anchor the vertical chord

forces to the foundation or framing of the structure in

order to resist overturning of the wall. 

Tie-down system: The collection of structural connections, components, and elements that provide

restraint against uplift of the structure above the isolation system. 

Timbers: Lumber of nominal five or more inches in

cross-section dimension. 

Time effect factor: A factor applied to adjusted resistance to account for effects of duration of load. (See

load duration.) 

Total design displacement: The BSE-1 displacement of an isolation or energy dissipation system, or elements thereof, including additional displacement due to

actual and accidental torsion. 

Total maximum displacement: The maximum

earthquake displacement of an isolation or energy dissipation system, or elements thereof, including additional

displacement due to actual and accidental torsion. 

Transverse wall: A wall that is oriented transverse to

in-plane shear walls, and resists lateral forces applied

normal to its plane. Also known as an out-of-plane wall. 

U

Unreinforced masonry (URM) wall: A masonry

wall containing less than the minimum amounts of reinforcement as defined for masonry (RM) walls. An unreinforced wall is assumed to resist gravity and lateral

loads solely through resistance of the masonry materials. 

V

V-braced frame: A concentric braced frame (CBF) in

which a pair of diagonal braces located either above or

below a beam is connected to a single point within the

clear beam span. 

Velocity-dependent energy dissipation

devices: Devices having mechanical characteristics

such that the force in the device is dependent on the relative velocity in the device. 

Veneer: A masonry wythe that provides the exterior

finish of a wall system and transfers out-of-plane load

directly to a backing, but is not considered to add loadresisting capacity to the wall system. 

Vertical irregularity: A discontinuity of strength,

stiffness, geometry, or mass in one story with respect to

adjacent stories. 

W

Waferboard: A non-veneered structural panel manufactured from two- to three-inch flakes or wafers bonded

together with a phenolic resin and pressed into sheet

panels.] 

Wind-restraint system: The collection of structural

elements that provides restraint of the seismic-isolated

structure for wind loads. The wind-restraint system may

be either an integral part of isolator units or a separate

device. 

Wood structural panel: A wood-based panel product

bonded with an exterior adhesive, meeting the requirements of PS 1-95 or PS 2-92, including plywood, oriented strand board, waferboard, and composite panels. 

Wrought Iron: An easily welded or forged iron containing little or no carbon. Initially malleable, it hardens

quickly when rapidly cooled. 

Wythe: A continuous vertical section of a wall, one

masonry unit in thickness. 

X

X-braced frame: A concentric braced frame (CBF) in

which a pair of diagonal braces crosses near the midlength of the braces. K

Y

Y-braced frame: An eccentric braced frame (EBF) in

which the stem of the Y is the link of the EBF system. 
 References

FEMA 356 Seismic Rehabilitation Prestandard References-1

References

ACI 318, 1999, Building Code Requirements for 

Reinforced Concrete, American Concrete Institute, 

Detroit, Michigan. 

ACI 530/ASCE 5/TMS 402, 1999, Masonry Standards 

Joint Committee (MSJC), Building Code Requirements 

for Masonry Structures, American Concrete Institute, 

Detroit, Michigan; American Society of Civil 

Engineers, Reston, Virginia; and The Masonry Society, 

Boulder, Colorado. 

ACI 530.1/ASCE 6/TMS 602, 1999, Masonry 

Standards Joint Committee (MSJC), Specification for 

Masonry Structures, American Concrete Institute, 

Detroit, Michigan; American Society of Civil 

Engineers, Reston, Virginia; and The Masonry Society, 

Boulder, Colorado. 

AISC, 1993, Load and Resistance Factor Design 

Specification for Structural Steel Buildings (LRFD), 

American Institute of Steel Construction, Chicago, 

Illinois. 

AISC, 1997, Seismic Provisions for Structural Steel 

Buildings, with Supplement No. 1 dated 1999, 

American Institute of Steel Construction, Chicago, 

Illinois. 

ASCE 7, 1998, Minimum Design Loads for Buildings 

and Other Structures, American Society of Civil 

Engineers, Reston, VA. 

ASCE 8, 1990, Specification for the Design of ColdFormed Steel Stainless Steel Structural Members, 

American Society of Civil Engineers, Reston, Virginia. 

ASCE 16, 1996, Standard for Load and Resistance 

Factor Design (LRFD) for Engineered Wood 

Construction, AF&PA/ASCE Standard No. 16-95, 

American Society of Civil Engineers, New York, New 

York.

ASTM A36/A36M-00, 2000, Standard Specification for 

Carbon Structural Steel, American Society for Testing 

and Materials, West Conshohocken, Pennsylvania. 

ASTM A242/A242M-00, 2000, Standard Specification 

for High-Strength Low-Alloy Structural Steel, American 

Society for Testing and Materials, West Conshohocken, 

Pennsylvania. 

ASTM A307-00, 2000, Standard Specification for 

Carbon Steel Bolts and Studs, 60,000 PSI Tensile 

Strength, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania.

ASTM A370 -97a, 1997, Standard Test Methods and 

Definitions for Mechanical Testing of Steel Products, 

American Society for Testing and Materials, West 

Conshohocken, Pennsylvania. 

ASTM A416/A416M-99, 1999, Standard Specification 

for Steel Strand, Uncoated Seven-Wire for Prestressed 

Concrete, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania. 

ASTM A421/A421M-98a, 1998, Standard 

Specification for Uncoated Stress-Relieved Steel Wire 

for Prestressed Concrete, American Society for Testing 

and Materials, West Conshohocken, Pennsylvania. 

ASTM A572/A572M-89, 1989 (formerly A441/ 

A441M), Standard Specification for High-Strength 

Low-Alloy Columbium-Vanadium Structural Steel, 

American Society for Testing and Materials, West 

Conshohocken, Pennsylvania.

ASTM A615/A615M-00, 2000, Standard Specification 

for Deformed and Plain Billet-Steel Bars for Concrete 

Reinforcement, American Society for Testing and 

Materials, West Conshohocken, Pennsylvania. 

ASTM A722/A722M-98, 1998, Standard Specification 

for Uncoated High-Strength Steel Bar for Prestressing 

Concrete, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania. 

ASTM A913/A913M-00, 2000, Standard Specification 

for High-Strength Low-Alloy Steel Shapes of Structural 

Quality, Produced by Quenching and Self-Tempering 

Process (QST), American Society for Testing and 

Materials, West Conshohocken, Pennsylvania.

ASTM A972/A972M-00, 2000, Standard Specification 

for Fusion-Bonded Epoxy-Coated Pipe Piles, American 
References-2 Seismic Rehabilitation Prestandard FEMA 356

 References

Society for Testing and Materials, West Conshohocken, 

Pennsylvania.

ASTM C39/C39M-99, 1999, Standard Test Method for 

Compressive Strength of Cylindrical Concrete 

Specimens, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania. 

ASTM C42/C42M-99, 1999, Standard Test Method for 

Obtaining and Testing Drilled Cores and Sawed Beams 

of Concrete, American Society for Testing and 

Materials, West Conshohocken, Pennsylvania. 

ASTM C597-97, 2000, Standard Test Method for Pulse 

Velocity through Concrete, American Society for 

Testing and Materials, West Conshohocken, 

Pennsylvania.

ASTM C1072-99, 1999, Standard Test Method for 

Measurement of Masonry Flexural Bond Strength, 

American Society for Testing and Materials, West 

Conshohocken, Pennsylvania. 

ASTM C1196-92, 1997, Standard Test Method for In 

Situ Compressive Stress Within Solid Unit Masonry 

Estimated Using Flatjack Measurements, American 

Society for Testing and Materials, West Conshohocken, 

Pennsylvania. 

ASTM C1197-92, 1997, Standard Test Method for In 

Situ Measurement of Masonry Deformability Properties 

Using Flatjack Method, American Society for Testing 

and Materials, West Conshohocken, Pennsylvania. 

ASTM C496-96, 1996, Standard Test Method for 

Splitting Tensile Strength of Cylindrical Concrete 

Specimens, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania. 

ASTM D245-00, 1992, Standard Methods for 

Establishing Structural Grades and Related Allowable 

Properties for Visually Graded Lumber, American 

Society for Testing and Materials, West Conshohocken, 

Pennsylvania. 

ASTM D1586-99, 1999, Standard Test Method for 

Penetration Test and Split-Barrel Sampling of Soils, 

American Society for Testing and Materials, West 

Conshohocken, Pennsylvania. 

ASTM D5457-93, 1998, Standard Specification for 

Computing the Reference Resistance of Wood-Based 

Materials and Structural Connections for Load and 

Resistance Factor Design, American Society of Testing 

and Materials, West Conshohocken, Pennsylvania.

ASTM E139-00, 2000, Standard Test Methods for 

Conducting Creep, Creep-Rupture, and Stress-Rupture 

Tests of Metallic Materials, American Society for 

Testing and Materials, West Conshohocken, 

Pennsylvania. 

ASTM E488-96, 1996, Standard Test Methods for 

Strength of Anchors in Concrete and Masonry 

Elements, American Society for Testing and Materials, 

West Conshohocken, Pennsylvania. 

ASTM E518-00, 2000, Standard Test Measures for 

Flexural Bond Strength of Masonry, American Society 

for Testing and Materials, West Conshohocken, 

Pennsylvania. 

ASTM E519-81,1999, Standard Test Method for 

Diagonal Tension (Shear) in Masonry Assemblages, 

American Society for Testing and Materials, West 

Conshohocken, Pennsylvania. 

ATC, 1997, Guidelines for the Seismic Rehabilitation of 

Buildings: Example Applications, prepared by the 

Applied Technology Council, for the Building Seismic 

Safety Council and the Federal Emergency 

Management Agency (FEMA Publication No. 276), 

Washington, D.C. 

AWS D1.1, 2000, Structural Welding Code–Steel, 

American Welding Society, Miami, Florida. 

AWS D1.3, 1998, Structural Welding Code–Sheet Steel, 

American Welding Society, Miami, Florida. 

AWWA D100, 1996, Welded Steel Tanks for Water 

Storage, American Water Works Association, Denver, 

Colorado. 

FEMA 310, 1998, Handbook for the Seismic 

Evaluation of Buildings—A Prestandard, prepared by 

the American Society of Civil Engineers for the Federal 

Emergency Management Agency, Washington, D.C. 

(FEMA Publication No. 310). 

IBC, 2000, International Building Code, International 

Code Council, Falls Church, Virginia. 
 References

FEMA 356 Seismic Rehabilitation Prestandard References-3

NBC, 1999, National Building Code, Building Officials 

and Code Administrators International, Country Club 

Hills, Illinois. 

PS 1, 1995, U.S. Product Standard PS 1-95,

Construction & Industrial Plywood with Typical APA 

Trademarks, National Institute of Standards and 

Technology, Washington, D.C. 

PS 2, 1992, U.S. Product Standard PS 2-92, 

Performance Standard for Wood-Based Structural Use 

Panels, National Institute of Standards and Technology, 

Washington, D.C. 

SBC, 1999, Standard Building Code, Southern Building 

Code Congress International, Birmingham, Alabama. 

SJI, 1990, Standard Specification, Load Tables and 

Weight Tables for Steel Joists and Joist Girders, Steel 

Joist Institute, Myrtle Beach, South Carolina. 

UBC, 1997, Uniform Building Code, International 

Conference of Building Officials, Whittier, California. 
References-4 Seismic Rehabilitation Prestandard FEMA 356

 References

Commentary References

AAMA 501.4, 2000, Recommended Static Test Method 

for Evaluating Curtain Wall and Storefront Systems 

Subjected to Seismic and Wind Induced Interstory 

Drift, American Architectural Manufacturers 

Association, Schaumberg, Illinois. 

ABK, 1984, Methodology for Mitigation of Seismic 

Hazards in Existing Unreinforced Masonry Buildings, 

(Topical Report 08), ABK joint venture, El Segundo, 

California.

ABK, 1991, Methodology for Mitigation of Seismic 

Hazards in Existing Unreinforced Masonry Buildings: 

Wall Testing, Out-of-Plane, (Topical Report 04). 

ACI 437R-91, 1991, Strength Evaluation of Existing 

Concrete Buildings, American Concrete Institute, 

Detroit, Michigan. 

AF&PA ASD, 1997, ASD Manual for Engineered 

Wood Construction, including supplements and 

guidelines, American Forest & Paper Association, 

Washington, D.C.

AF&PA LRFD, 1996, LRFD Manual for Engineered 

Wood Construction, including supplements and 

guidelines, American Forest & Paper Association, 

Washington, D.C.

Al-Hussaini, T., Zayas, V., and Constantinou, M. C., 

1994, Seismic Isolation of Multi-Story Frame 

Structures using Spherical Sliding Isolation Systems, 

Report No. NCEER-94-0007, National Center for 

Earthquake Engineering Research, State University of 

New York at Buffalo, New York. 

APA, 1995, Design Capacities of APA Performance 

Rated Structural-Use Panels, Technical Note N375B, 

American Plywood Association, Tacoma, WA.

APA, 1997, Plywood Design Specification, American 

Plywood Association, Tacoma, Washington. 

API 650, 1998, 10th Edition, Welded Steel Tanks for 

Oil Storage, American Petroleum Institute, 

Washington, D.C. 

ASCE 4, 1986, Seismic Analysis of Safety-related 

Nuclear Structures, American Society of Civil 

Engineers, Reston, VA. 

ASCE 11, 1990, Standard Guideline for Structural 

Condition Assessment of Existing Buildings, American 

Society of Civil Engineers, New York, New York. 

ASHRAE, 1995, Applications Manual Chapter 50, 

American Society of Heating, Refrigeration, and Air 

Conditioning Engineers, Atlanta, Georgia. 

ASME B31, 2000, Code for Pressure Piping, 

American Society of Mechanical Engineers, New 

York, New York. 

ASME B31.1, 2000, Power Piping, American Society 

of Mechanical Engineers, New York, New York. 

ASME B31.4, 2000, Liquid Transportation Systems for 

Hydrocarbons, Liquid Petroleum Gas, Anhydrous 

Ammonia, and Alcohols, American Society of 

Mechanical Engineers, New York, New York. 

ASME B31.5, 2000, Refrigeration Plant, American 

Society of Mechanical Engineers, New York, New 

York. 

ASME B31.8, 2000, Gas Transmission and 

Distribution Piping Systems, American Society of 

Mechanical Engineers, New York, New York. 

ASME B31.9, 2000, Building Services Piping, 

American Society of Mechanical Engineers, New 

York, New York. 

ASME B31.11, 2000, Slurry Transportation Systems, 

American Society of Mechanical Engineers, New 

York, New York. 

ASME B31.37, 2000, Chemical Plant and Refinery 

Piping, American Society of Mechanical Engineers, 

New York, New York. 

ATC-7, 1981, Guidelines for the Design of Horizontal 

Wood Diaphragms, Applied Technology Council, 

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ATC-40, 1996, Seismic Evaluation and Retrofit of 

Concrete Buildings, prepared by the Applied 

Technology Council (Report No. ATC-40), Redwood 

City, California for the California Seismic Safety 

Commission (Report No. SSC 96-01). 

ATC-282, 1993, Proceedings of the Workshop to 

Resolve Seismic Rehabilitation Subissues—July 29 and 

30, 1993; Development of Guidelines for Seismic 

Rehabilitation of Buildings, Phase I: Issues 

Identification and Resolution, Applied Technology 

Council, Redwood City, California. (Report No. ATC28-2). 
 References

FEMA 356 Seismic Rehabilitation Prestandard References-5

AWWA D100, 1996, Welded Steel Tanks for Water 

Storage, American Water Works Association, Denver, 

Colorado. 

Ayres, J. M., and Sun, T. Y., 1973a, “Nonstructural 

Damage to Buildings, The Great Alaska Earthquake of 

1964,” Engineering, National Academy of Sciences, 

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Ayres, J. M., and Sun, T. Y., 1973b, “Nonstructural 

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Atmospheric Administration, Washington, D.C. 

Bartlett, S. F., and Youd, T. L., 1992, “Empirical 

Prediction of Lateral Spread Displacement,” edited by 

Hamada, M., and O’Rourke, T. D., Proceedings of the 

Fourth Japan-U.S. Workshop on Earthquake Resistant 

Design of Lifeline Facilities and Countermeasures for 

Soil Liquefaction, Report No. NCEER-92-0019, 

National Center for Earthquake Engineering Research, 

Buffalo, New York, Vol. I, pp. 351–365. 

Baziar, M. H., Dobry, R., and Elgamal, A-W.M., 1992, 

Engineering Evaluation of Permanent Ground 

Deformations Due to Seismically-Induced 

Liquefaction, Report No. NCEER-92-0007, National 

Center for Earthquake Engineering Research, Buffalo, 

New York. 

Bouwkamp, J. G., and Meehan, J. F. (1960). “Drift 

Limitations Imposed by Glass,” Proceedings of the 

Second World Conference on Earthquake Engineering, 

Tokyo, Japan, pp. 1763-1778. 

Bowles, J.E., 1988, Foundation Analysis and Design,

Fourth Edition, McGraw-Hill, New York, NY. 

Bracci, J. M., Kunnath, S. K., and Reinhorn, A. M., 

1995, “Simplified Seismic Performance and Retrofit 

Evaluation,” submitted to the Journal of the Structural 

Division, American Society of Civil Engineers, New 

York, New York. 

BSSC, 2000, NEHRP Recommended Provisions for 

Seismic Regulations for New Buildings and Other 

Structures, 2000 Edition, prepared by the Building 

Seismic Safety Council for the Federal Emergency 

Management Agency, Washington, D.C.

California Governor’s Board of Inquiry on the 1989 

Loma Prieta Earthquake, 1990, Competing Against 

Time, report to Governor George Deukmejian, State of 

California, Office of Planning and Research, 

Sacramento, California. 

Calvi, G. M., 1988, “Correlation between Ultrasonic 

and Load Tests on Old Masonry Specimens,”

Proceedings of Eighth International Brick/Block 

Masonry Conference, Elsevier Applied Science, Essex, 

England, pp. 1665–1672. 

Cho, D. M., and Retamal, E., 1993, “The Los Angeles 

County Emergency Operations Center on HighDamping Rubber Bearings to Withstand an Earthquake 

Bigger than the Big One,” Proceedings of Seminar on 

Seismic Isolation, Passive Energy Dissipation, and 

Active Control, Applied Technology Council Report 

No. ATC-17-1, Redwood City, California, pp. 209–

220. 

CISCA, 1990, Recommendations for Direct-Hung 

Acoustical and Lay-in Panel Ceilings, Seismic 

Zones 3-4, Ceilings and Interior Systems Construction 

Association, Deerfield, Illinois. 

CISCA, 1991, Recommendations for Direct-Hung 

Acoustical and Lay-in Panel Ceilings, Seismic 

Zones 0-2, Ceilings and Interior Systems Construction 

Association, Deerfield, Illinois. 

CRSI, 1981, Evaluation of Reinforcing Steel Systems in 

Old Reinforced Concrete Structures, Concrete 

Reinforcing Steel Institute, Chicago, Illinois. 

CSI, 1994, ETABS (Version 6.0): Linear and Nonlinear, 

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Drake, R. M., and Bachman, R. E., 1995, 

“Interpretation of Instrumental Building Seismic Data 

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SEAOC Annual Convention, Structural Engineering 

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Eberhard, M. O., and Sozen, M. A., 1993, “BehaviorBased Method to Determine Design Shear in 

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EERI, 1995, “In Wait for the Next One,” Proceedings 

of the Fourth Japan/U.S. Workshop on Urban 

Earthquake Hazard Reduction, Earthquake 

Engineering Research Institute and Japan Institute of 

Social Safety Science, sponsors, Osaka, Japan. 
References-6 Seismic Rehabilitation Prestandard FEMA 356

 References

Epperson, G. S., and Abrams, D. P., 1989, 

“Nondestructive Evaluation of Masonry Buildings, 

Advanced Construction Technology Center,” Report 

No. 89-26-03, College of Engineering, University of 

Illinois at Urbana, Illinois. 

Fajfar, P., and Fischinger, M., 1988, “N2—A Method 

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Feilden, Bernard M., 1987, Between Two Earthquakes: 

Cultural Property in Seismic Zones, Getty 

Conservation Institute, Marina del Rey, California. 

FEMA 74, 1994, Reducing the Risks of Nonstructural 

Earthquake Damage, A Practical Guide, Federal 

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(FEMA Publication No. 74) .

FEMA 154, 1988, Rapid Visual Screening of Buildings 

for Potential Seismic Hazards: A Handbook, prepared 

by the Applied Technology Council (Report No. ATC21, 1988) for the Federal Emergency Management 

Agency, Washington, D.C. (FEMA Publication No. 

154). 

FEMA 156, Typical Costs for Seismic Rehabilitation of 

Buildings, Second Edition, Volume 1: Summary, 

prepared by the Hart Consultant Group for the Federal 

Emergency Management Agency, Washington, D.C. 

(FEMA Publication No. 156). 

FEMA 157, Typical Costs for Seismic Rehabilitation of 

Buildings, Second Edition, Volume II: Supporting 

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Group for the Federal Emergency Management 

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157) 

FEMA 172, 1992, NEHRP Handbook of Techniques 

for the Seismic Rehabilitation of Existing Buildings, 

prepared by the Building Seismic Safety Council for 

the Federal Emergency Management Agency, 

Washington, D.C. (FEMA Publication No. 172). 

FEMA 178, 1992, NEHRP Handbook for the Seismic 

Evaluation of Existing Buildings, prepared by the 

Building Seismic Safety Council for the Federal 

Emergency Management Agency, Washington, D.C. 

(FEMA Publication No. 178). 

FEMA 222A, 1995, NEHRP Recommended Provisions 

for Seismic Regulations for New Buildings, 1994 

Edition, Part 1: Provisions and Part 2: Commentary, 

prepared by the Building Seismic Safety Council for 

the Federal Emergency Management Agency, 

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223A). 

FEMA 237, 1992, Development of Guidelines for 

Seismic Rehabilitation of Buildings, Phase I: Issues 

Identification and Resolution, prepared by the Applied 

Technology Council for the Federal Emergency 

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FEMA 273, 1997, NEHRP Guidelines for the Seismic 

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FEMA 274, 1997, NEHRP Commentary on the 

Guidelines for Seismic Rehabilitation of Buildings,

prepared by the Building Seismic Safety Council for 

the Federal Emergency Management Agency, 

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FEMA 275, Planning for Seismic Rehabilitation: 

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Building Seismic Safety Council and Federal 

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FEMA 276, 1997, Guidelines for the Seismic 

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prepared by the Applied Technology Council for the 

Building Seismic Safety Council and the Federal 

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(FEMA Publication No. 276). 

FEMA 302, 1997, NEHRP Recommended Provisions 

for Seismic Regulations for New Buildings and Other 

Structures, 1997 Edition, Part 1: Provisions and Part 

2: Commentary, prepared by the Building Seismic 

Safety Council for the Federal Emergency 

Management Agency, Washington, D.C. (FEMA 

Publication Nos. FEMA 302 and 303). 

FEMA 306, 1998, Evaluation of Earthquake-Damaged 

Concrete and Masonry Wall Buildings—Basic 

Procedures Manual, prepared by the Applied 

Technology Council (ATC-43 Project), for the Federal 

Emergency Management Agency, Washington, D.C. 

(FEMA Publication No. 306). 
 References

FEMA 356 Seismic Rehabilitation Prestandard References-7

FEMA 307, 1998, Evaluation of Earthquake-Damaged 

Concrete and Masonry Wall Buildings—Technical 

Resources, prepared by the Applied Technology 

Council (ATC-43 Project), for the Federal Emergency 

Management Agency, Washington, D.C. (FEMA 

Publication No. 307). 

FEMA 308, 1998, Repair of Earthquake Damaged 

Concrete and Masonry Wall Buildings, prepared by the 

Applied Technology Council (ATC-43 Project), for the 

Federal Emergency Management Agency, Washington, 

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FEMA 310, 1998, Handbook for the Seismic 

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the American Society of Civil Engineers for the 

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FEMA 350, 2000, Recommended Seismic Design 

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prepared by the SEAOC, ATC, and CUREE Joint 

Venture for the Federal Emergency Management 

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350). 

FEMA 351, 2000, Recommended Seismic Evaluation 

and Upgrade Criteria for Existing Welded Moment 

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ATC, and CUREE Joint Venture for the Federal 

Emergency Management Agency, Washington, D.C. 

(FEMA Publication No. 351). 

FEMA 355D, 2000, State of Art Report on Connection 

Performance, prepared by the SEAOC, ATC, and 

CUREE Joint Venture for the Federal Emergency 

Management Agency, Washington, D.C. (FEMA 

Publication No. 355D)] 

FEMA 355F, 2000, State of Art Report on Performance 

Prediction and Evaluation, prepared by the SEAOC, 

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References-8 Seismic Rehabilitation Prestandard FEMA 356

 References

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NFPA, 704-90, 1990, Standard System for the 

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National Fire Protection Association, Quincy, 

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 References

FEMA 356 Seismic Rehabilitation Prestandard References-9

Nims, D. F., Richter, P. J., and Bachman, R. E., 1993, 

“The Use of the Energy Dissipation Restraint for 

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Chung, R. M., 1985, “Influence of SPT Procedures in 

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Addendum, Sheet Metal and Air Conditioning 

Contractors National Association, Chantilly, Virginia. 
References-10 Seismic Rehabilitation Prestandard FEMA 356

 References

SP-58, 1993, Pipe Hangers and Supports: Materials, 

Design and Manufacture, Manufacturers 

Standardization Society of the Valve and Fitting 

Industry, Vienna, Virginia. 

Stark, T. D., and Mesri, G., 1992, “Undrained Shear 

Strength of Liquefied Sands for Stability Analysis,”

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Columbia, Canada, pp. 197-208. 

Tissell, John R., 1993, Wood Structural Panel Shear 

Walls, Research Report #154, American Plywood 

Association, Tacoma, Washington.

Tissell, John R., and Elliott, James R., 1997, Plywood 

Diaphragms, Research Report #138, American 

Plywood Association, Tacoma, Washington.

TM5-809-10.1, 1986, Department of the Army, Navy, 

and Air Force, Seismic Design of Buildings,

(Publication Nos. Air Force AFM 88-3, Army TM5-

809-10.1, Navy NAVFAC P-355.1, Chapter 13.1), 

Department of the Army, Navy, and Air Force, 

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Tokimatsu, A. M., and Seed, H. B., 1987, “Evaluation 

of Settlements in Sands Due to Earthquake Shaking,”

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National Center for Earthquake Engineering Research, 

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Experimental and Analytical Study of Systems 

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Wood, S. L., 1990, “Shear Strength of Low-Rise 

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WWPA, 1983, Western Woods Use Book, Western 

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Report, Report No. UCB/EERC-87/01, Earthquake 

Engineering Research Center, University of California, 

Berkeley, California. 
 Index

FEMA 356 Seismic Rehabilitation Prestandard Index-1

Index

A

acceleration time histories 1-35

acceleration-sensitive nonstructural components 11-12

acceptance criteria 2-12

for alternative modeling parameters 2-27

for component capacities 2-16

for expected and lower bound strengths 2-16

for general requirements 2-12, 3-25

for linear procedures 3-25

for material properties 2-16

for nonlinear procedures 3-27

for primary and secondary elements and 

components 2-12

for strength and deformation

of concrete 6-14

of foundation 4-27

of masonry 7-16, 7-18, 7-20, 7-23, 7-27, 7-30

of steel 5-9

of wood and light metal framing 8-13

See also strength acceptance criteria

actions

deformation and force-controlled 2-14

See also forces and deformations; deformation-controlled

actions; force-controlled actions

active control systems 9-37

adhered veneer exterior wall elements 11-20

adjacent buildings 2-23

corrective measures for deficiencies in 10-10

hazards from 2-3

alternative modeling parameters and acceptance criteria 2-27

backbone curve for experimental data 2-29

data reduction and reporting 2-27

design parameters and acceptance criteria for 2-28

experimental setup 2-27

Analysis Procedures 3-1

Alternative Rational Analysis 2-12

for nonstructural components 11-14

Linear Dynamic Procedure (LDP) 2-8, 3-16

Linear Procedures 2-9

Linear Static Procedure (LSP) 3-10

Nonlinear Dynamic Procedure (NDP) 3-24

Nonlinear Procedures 2-11

Nonlinear Static Procedure (NSP) 3-18

See also general design requirements; stiffness for 

analysis; general analysis requirement

anchorage to masonry walls 7-23

anchored veneer exterior wall elements 11-20

archaic diaphragms 5-52

architectural components 11-20

canopies and marquees 11-29

ceilings 11-27

chimneys and stacks 11-29

exterior wall elements 11-20

interior veneers 11-26

Nonstructural Performance Levels and damage to 1-20

parapets and appendages 11-28

partitions 11-25

stairs and stair enclosures 11-30

architectural, mechanical, and electrical components and 

systems 11-1

acceleration-sensitive components 11-12

architectural components 11-20

deformation-sensitive components 11-12

furnishings and interior equipment 11-39

mechanical, electrical, and plumbing components 11-30

nonstructural components

assessment of 11-6

procedures for rehabilitation 11-2

rehabilitation concepts 11-19

Rehabilitation Objectives 11-11

structural-nonstructural interaction 11-12

as-built information 2-1

for adjacent buildings 2-3

for building configurations 2-2

for component properties 2-2

for data collection requirements 2-4

for primary and secondary elements and components 2-4

for site characterization and geotechnical information 2-2

B

backbone curve 2-29

base isolation. See seismic isolation

base shear. See pseudo lateral load

bookcases 11-39

braced frames 5-27, 6-60

braced horizontal steel diaphragms 5-50

braced horizontal wood diaphragms 8-37, 8-39, 8-44

building

as-built information 2-2

configuration 2-2

historical use

of concrete in 6-1

of masonry in 7-1

of steel in 5-1
Index-2 Seismic Rehabilitation Prestandard FEMA 356

 Index

of wood and light metal framing 8-1

irregularities 2-9

Model Building Types for Simplified Rehabilitation 10-6

simplified corrective measures for deficiencies in 10-17

Building Performance Levels 1-10, 1-23

Collapse Prevention Level 1-25

Immediate Occupancy Level 1-24

Life Safety Level 1-24

Operational Level 1-24

building pounding 2-3

building separation 2-23

for seismic isolation systems 9-22

C

canopies and marquees 11-29

cast iron 5-54

cast-in-place concrete diaphragms 6-61

cast-in-place pile foundations 6-64

ceilings 11-27

chimneys and stacks 11-29

chords

and steel diaphragms 5-52

and wood diaphragms 8-35

Collapse Prevention Building Performance Level 1-25

as Structural Performance Level 1-14

compressive strength of structural concrete 6-4

computer access floors 11-40

concrete 6-1

condition assessment

for concrete 6-9

for masonry 7-7

for nonstructural components 11-2

for steel 5-8

for wood and light metal framing 8-10, 8-11

continuity 2-20

control node 3-18

conveyors 11-43

D

Damage Control Structural Performance Range 1-12

damping

calculating effective

for energy dissipation devices 9-36

coefficients for modifying design response spectra 1-34

effective

for isolation systems 9-25

energy dissipation devices and 9-25

DCRs (demand-capacity ratios) 2-9

default material properties

for concrete 6-1

for masonry 7-6

for steel 5-5

for wood 8-6

deficiencies

for Simplified Rehabilitation Method 10-19

deformation-controlled actions 2-13

using linear procedures 3-26

using nonlinear procedures 3-27

deformations. See forces and deformations

deformation-sensitive nonstructural components 11-12

demand-capacity ratios (DCRs) 2-9

design and construction review

for seismic isolation systems 9-22

design review

for passive energy dissipation 9-34

foundation loads 4-2

diagonal lumber sheathing shear walls 8-27

diaphragms 2-21, 3-4

chords 2-21

classification 3-5

collectors 2-21

concrete 6-61

forces and deformations 3-15, 3-24, 3-25

modeling 3-5

precast concrete 6-63

steel 5-45

ties 2-21

wood 8-35

differential compaction 4-7

directional effects. See multidirectional seismic effects

drift ratios and relative displacements 11-16

drilled shafts 4-27

ductwork 11-36

dynamic vibration absorption control systems 9-37

E

earthquake ground shaking hazard 1-27

eccentric braced frames (EBF) 5-30

eigenvalue (dynamic) analysis 3-11

elastomeric isolators 9-4

electrical components

electrical and communications distribution 

components 11-37

electrical and communications equipment 11-36

Nonstructural Performance Levels and damage to 1-21

elements and components

primary and secondary 3-4

elevators 11-42

energy dissipation devices

determining force-displacement characteristics of 9-36

displacement-dependent devices
 Index

FEMA 356 Seismic Rehabilitation Prestandard Index-3

Linear Dynamic Procedure for 9-30

Linear Static Procedure for 9-29

modeling 9-27

general information about 9-33

linear procedures 9-28

modeling of 9-26, 9-27

Nonlinear Static Procedure for 9-31, 9-32

other types 9-28

prototype tests for 9-35

system adequacy and 9-36

energy dissipation systems. See passive energy 

dissipation systems

Enhanced Rehabilitation Objectives 1-9

expected strength

criteria for use of 2-17

exterior wall elements

adhered veneer 11-20

anchored veneer 11-20

glass block units 11-21

glazing systems 11-22

prefabricated panels 11-22

F

fault rupture

as seismic hazard 4-2

fiberboard shear walls 8-30

fiberboard sheathing 8-34

fire suppression piping 11-34

flexible diaphragm 3-5

flooding

as seismic hazard 4-8

fluid piping 11-34

fluid viscoelastic damping devices 9-28

fluid viscous damping devices 9-28

footings

masonry 7-31

rigid 4-20, 4-26

spread 4-30

wood 8-44

force deformation curve, alternative 2-29

force-controlled actions 2-13

using linear procedures 3-25

using nonlinear procedures 3-28

forces and deformations

determining with Linear Dynamic Procedure 3-17

determining with Linear Static Procedure 3-13

determining with Nonlinear Dynamic Procedure 3-25

determining with Nonlinear Static Procedure 3-20

foundation acceptability criteria 4-27

foundation loads 4-2

design 4-2

foundation soil information 4-1

foundation strength and stiffness 4-10

foundation acceptability criteria 4-27

foundation ultimate bearing pressures 4-11

load-deformation characteristics for foundations 4-15

foundation ultimate bearing pressure 4-11

foundations

foundation soil information 4-1

load-deformation characteristics for 4-15

masonry 7-31

mathematical modeling 3-4

retaining walls 4-28

shallow bearing 4-20, 4-26

soil foundation rehabilitation 4-29

stiffness of 4-10

ultimate bearing pressures for 4-11

See also geotechnical site hazards; pile foundations

furnishings and interior equipment 11-39

bookcases 11-39

computer access floors 11-40

computer and communication racks 11-41

conveyors 11-43

elevators 11-42

hazardous materials storage 11-41

storage racks 11-39

G

general analysis requirements 3-1

analysis procedure selection 3-1

component gravity loads for load combinations 3-8

configuration 3-4

diaphragms 3-4

horizontal torsion 3-2

mathematical modeling 3-2

multidirectional seismic effects 3-7

overturning 3-9

P-D effects 3-5

soil-structure interaction 3-6

verification of design assumptions 3-8

general component behavior curves

illustrated 2-13

general design requirements 2-20

building separation 2-23

continuity 2-20

diaphragms 2-21

horizontal torsion 2-20

multidirectional seismic effects 2-20

nonstructural components 2-23

overturning 2-20

P-∆ effects 2-20

structures sharing common elements 2-23
Index-4 Seismic Rehabilitation Prestandard FEMA 356

 Index

walls 2-22

See also analysis procedures; stiffness for analysis

Geologic Site Hazards 4-1

See also Seismic Geologic Site Hazards

glass block units 11-21

glazing systems 11-22

global structural stiffening 2-18

global structural strengthening 2-19

ground motion characterization 3-16, 3-24

ground shaking hazards. See seismic hazard

ground water conditions

differential compaction 4-7

liquefaction and 4-3

gypsum plaster shear walls 8-31

gypsum wallboard 8-32

H

hazardous materials storage 11-41

hazards. See Geologic Site Hazards; Seismic 

Geologic Site Hazards

Hazards-Reduced Nonstructural Performance Level 1-21

high-pressure piping 11-33

historic status 1-6

historical perspective

nonstructural components 11-6

historical use

of concrete 6-1

of masonry 7-1

of steel 5-1

of wood 8-1

horizontal lumber sheathing with cut-in braces 

or diagonal blocking shear walls 8-33

I

Immediate Occupancy Building Performance Level 1-23

as Nonstructural Performance Level 1-18

as Structural Performance Level 1-11

Immediate Occupancy Level

as Building Performance Level 1-24

infill masonry shear wall

model buildings

description 10-7

infill panels

m factors for masonry

infill panels 7-28

simplified force deflection relations masonry infill 

panels simplified force deflection relations 7-29

infills. See concrete; masonry

in-place materials and components 6-4

concrete 6-60

masonry 7-2

steel 5-2

wood and light metal framing 8-5

in-plane discontinuity irregularity 2-10

in-plane masonry infills 7-25

inspection

for construction quality 2-25

for passive energy dissipation devices 9-34

for seismic isolation systems 9-21

interior veneers 11-26

inundation. See flooding

isolation systems. See seismic isolation

isolators

elastomeric 9-4

modeling of 9-11

sliding 9-8, 9-9

K

knowledge (κ) factor

for concrete 6-11

for masonry 7-11

for steel 5-9

for wood and light metal framing 8-12

L

landslides

as seismic hazard 4-7

lateral load distribution 3-19

Life Safety Building Performance Level 1-25

as Nonstructural Performance Level 1-18

as Structural Performance Level 1-12

light fixtures 11-38

light gage metal frame shear walls 8-19

limitations

of Simplified Rehabilitation Method 10-4

on use of linear procedures 2-9

Limited Rehabilitation Objectives 1-10

Limited Safety Structural Performance Range 1-12

linear analysis procedures. See Linear Dynamic 

Procedure; Linear Static Procedure

Linear Dynamic Procedure (LDP) 3-16

basis of 3-16

determination of forces and deformations 3-17

modeling and analysis considerations for 3-16

linear procedures 2-9

for overturning 3-9

Linear Static Procedure (LSP) 2-11, 3-10

basis of 3-10

determination of forces and deformations 3-13

period determination 3-11
 Index

FEMA 356 Seismic Rehabilitation Prestandard Index-5

liquefaction

as seismic hazard 4-3

mitigation of 4-9

susceptibility to 4-4, 4-14, 4-15

load capacity for pile foundations 4-25

load path discontinuities

corrective measures for deficiencies in 10-9

loads

determining load combinations 3-8

local risk mitigation programs A-1

lower-bound strength 2-16

LSP. See Linear Static Procedure

M

manufacturing quality control

for energy dissipation devices 9-34

mapped response spectrum acceleration parameters. 

See response spectrum acceleration parameters

masonry 7-1

masonry, reinforced

Model Building Types

typical deficiencies 10-25

masonry, unreinforced

Model Building Types

typical deficiencies 10-25

mass reduction 2-19

material properties and condition assessment

for concrete 6-4

for masonry 7-1

for steel 5-1

for wood and light metal framing 8-2

mathematical modeling. See modeling

mechanical systems

mechanical equipment 11-30

Nonstructural Performance Levels and damage to 1-21

mechanical, electrical, and plumbing components 11-30

mitigation

of Seismic Geologic Site Hazards 4-8

See also local risk mitigation programs

Model Building Types

description 10-6

typical deficiencies 10-19

modeling

for Linear Dynamic Procedure (LDP) 3-16

for Nonlinear Static Procedure (NSP) 3-18

of energy dissipation devices 9-26, 9-27

displacement-dependent devices 9-27

other types of devices 9-28

velocity-dependent devices 9-27

of isolation system and superstructure 9-14

of soil-structure interaction 4-15

moment frames 5-10, 6-19

multidirectional seismic effects 2-20, 3-7

N

NDP. See Nonlinear Dynamic Procedure

nondestructive examination (NDE) methods

for concrete 6-10

nonlinear analysis procedures. See Nonlinear Dynamic 

Procedure; Nonlinear Static Procedure

Nonlinear Dynamic Procedure (NDP) 2-12, 3-24

basis of 3-24

determination of forces and deformations 3-25

modeling and analysis considerations for 3-24

Nonlinear Static Procedure (NSP) 2-11, 3-18

basis of 3-18

determination of forces and deformations for 3-20

modeling and analysis considerations for 3-18

nonstructural components 2-23, 9-3, 11-1

Nonstructural Performance Levels 1-17, 11-11

NSP. See Nonlinear Static Procedure

O

operating temperature

for passive energy dissipation devices 9-33

Operational Building Performance Level 1-24

as Nonstructural Performance Level 1-18

Operational Level

as Building Performance Level 1-24

out-of-plane wall forces 2-22

overdriven nails

corrective measures for deficiencies in 10-18

overturning 3-9

for seismic isolation systems 9-21

P

parapets and appendages 11-28

Partial Rehabilitation 1-10

partially restrained steel moment frames 5-22

particleboard sheathing shear walls 8-34

partitions 11-25

passive energy dissipation systems 9-25

criteria selection for 9-26

design and construction review 9-34

detailed system requirements for 9-33

general requirements for 9-25

linear procedures 9-28

modeling of energy dissipation devices 9-26, 9-27

nonlinear procedures 9-31

required tests of energy dissipation devices 9-34
Index-6 Seismic Rehabilitation Prestandard FEMA 356

 Index

passive programs for mitigation A-2

selecting standards for A-3

triggers for A-2

P-∆ effects 3-5

Performance Levels 1-10

See also Building Performance Levels

Performance Ranges

Damage Control 1-12

Limited Safety 1-12

period determination 3-11, 3-20

piers and piles 4-11

piers, masonry 7-14

pile caps

lateral load path

corrective measures for deficiencies in 10-10

pile foundations 4-25

concrete 6-64

steel 5-53

vertical load capacity for 4-25

wood 8-44

piping

fire suppression 11-34

fluid 11-34

high-pressure 11-33

plan irregularities

corrective measures for deficiencies in 10-9

plans for quality assurance 2-25

plastic hinge rotation

in concrete shear walls 6-51

plate steel shear walls 5-32

plumbing systems and components

ductwork 11-36

fire suppression piping 11-34

fluid piping 11-34

high-pressure piping 11-33

Nonstructural Performance Levels and damage to 1-21

storage vessels and water heaters 11-32

pole structures 8-45

political considerations of rehabilitation A-3

post-tensioning anchors

corrective measures for deficiencies in 10-18

precast/tilt-up concrete walls

Model Building Types

typical deficiencies 10-23

prefabricated panels 11-22

Prescriptive Procedure

for rehabilitation 11-14

prestressing steels 6-8

primary elements and components 3-4

pseudo lateral load 3-13

Q

quality assurance 2-24

construction requirements for 2-25

plans for 2-24

quality control

for seismic isolation systems 9-21

R

racks

computer and communication 11-41

storage 11-39

Reduced Rehabilitation Objective 1-10

rehabilitation measures 6-29

for concrete 6-18

for masonry foundation elements 7-31

for steel 5-9

rehabilitation methods. See Simplified Rehabilitation 

Method; Systematic Rehabilitation Method

Rehabilitation Objectives 1-8

rehabilitation process 1-4

rehabilitation requirements 1-1

rehabilitation strategies 2-17

global structural stiffening 2-18

global structural strengthening 2-19

local modification of components in 2-17

mass reduction 2-19

removal or lessening of existing irregularities 2-18

seismic isolation 2-19

social, economic, and political considerations A-3

supplementary energy dissipation 2-20

reinforced masonry bearing walls

Model Building Types

typical deficiencies 10-25

Model Building Types for 10-8

reporting and compliance procedures

for construction quality assurance requirements 2-26

response spectrum acceleration parameters

adjusting for variations of viscous damping 1-34

adjusting mapped 1-29

for BSE-1 1-29

for BSE-2 1-28

general response spectrum for 1-34

values as a function of site class and mapped short period

spectral response acceleration 1-33

S

safety regulations A-4

secondary elements and components 3-4

Seismic Geologic Site Hazards 1-27, 4-2
 Index

FEMA 356 Seismic Rehabilitation Prestandard Index-7

differential compaction 4-7

fault ruptures 4-2

flooding 4-8

landsliding 4-7

liquefaction 4-3

mitigation of 4-8

seismic hazards 1-26

general procedure 1-27

seismicity zones 1-35

site-specific procedures 1-34

See also geologic site hazards; Seismic 

Geologic Site Hazards

seismic isolation 9-1

seismic isolation systems 9-3

seismic rehabilitation process. See rehabilitation process

seismicity zones 1-35

shallow bearing foundations 4-18

capacity parameters for 4-20, 4-26

shared structural elements

collecting data for 2-3

design requirements for 2-23

shear walls 5-32, 6-43, 8-14

shear wave velocity 4-14, 4-18

simplified nonlinear static analysis procedure 3-18, 3-27

Simplified Rehabilitation Method 2-6, 10-1

single straight sheathed diaphragms 8-35, 8-39

site characterization 4-1

site classes 1-31

site soil foundation conditions 4-1

site-specific ground shaking hazards. See site-seismic hazards

slab-column concrete moment frames 6-30

sliding isolators 9-8, 9-9

social considerations of rehabilitation A-3

soil

foundation rehabilitation 4-29

foundation soil information 4-1

load-deformation behavior for 4-12, 4-13, 4-19, 4-23

material improvements 4-29

presumptive ultimate foundation pressures 4-11

susceptibility to liquefaction 4-4, 4-14, 4-15

soil-structure interaction (SSI) 3-6

solid viscoelastic devices 9-27, 9-28

spread footings and mats 4-30

stairs and stair enclosures 11-30

steel 5-1

steel diaphragms 5-45

steel plate shear walls 5-32

steel truss diaphragms 5-49

stiffness

diaphragms 3-4

effective lateral 3-20

elastic lateral 3-20

of foundations 4-10

See also foundation strength and stiffness; 

stiffness for analysis

stiffness for analysis 3-4

See also analysis and design requirements; 

analysis procedures

storage racks 11-39

storage vessels and water heaters 11-32

story drift

concrete shear wall 6-48

strength acceptance criteria

expected and lower bound strength 2-16

Structural Performance Levels and Ranges 1-12

structural-nonstructural interaction 11-12

supplemental damping devices. See passive energy 

dissipation systems

system requirements

for passive energy dissipation systems 9-33, 9-36

for seismic isolation systems 9-3

See also rehabilitation requirements

Systematic Rehabilitation Method 2-7

T

target displacement 3-21

testing

for concrete materials and components 6-5

for construction quality assurance requirements 2-25

for masonry materials and components 7-5

for steel materials and components 5-3

for wood and light metal framing 8-5

prototypes for energy dissipation devices 9-35

required for energy dissipation devices 9-34

torsion

accidental 3-3

actual 3-3

horizontal 3-2

mathematical modeling of 3-2

triggers for local risk mitigation programs A-2

U

URM bearing walls 10-25

URM in-plane walls and piers

m factors for 7-16

V

velocity-dependent damping devices 9-27

veneer

adhered 11-20

anchored 11-20
Index-8 Seismic Rehabilitation Prestandard FEMA 356

 Index

vertical irregularities

See also irregularities and discontinuities

vertical load stability

for seismic isolation system 9-21

viscoelastic damping devices 9-28

viscous damping devices 1-34, 9-28

visual inspections. See inspections

W

walls

calculating out-of-plane wall forces 2-22

concrete 6-43, 6-56

general design requirements for 2-22

masonry 7-12, 7-14, 7-17, 7-23

retaining 4-28

steel 5-32

URM bearing 10-25

wood and light frame 8-14

wood and light metal framing 8-1

Y

yield strength of component 2-16