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PUBLICATIONS

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ICSSC RP-1

SEISMIC DESIGN GUIDELINES FOR FEDERAL

BUILDINGS

February 1987

Prepared by:

Interagency Committee on Seismic

Safety in Construction

Sponsored by:

Federal Emergency Management Agency

Washington, DC 20472

National Bureau of Standards

Gaithersburg, MD 20899

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87-3524

1987

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NBSIR 87-3624 ICSSC RP-1

SEISMIC DESIGN GUIDELINES FOR FEDERAL

BUILDINGS

February 1987

Prepared by:

Interagency Committee on Seismic

Safety in Construction

Sponsored by:

Federal Emergency Management Agency

Washington, DC 20472

and

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE. Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

PREFACE

This report, Seismic Design Guidelines for Federal Buildings)

(referred t.o as the Seismic Guidelines), was prepared by the

Interagency Committee on Seismic Safety in Construction as one

part of the National Earthquake Hazards Reduction Program, the

President's plan to implement the Earthquake Hazards Reduction

Act of 1977 (Public Law 95-124) . They are intended for consideration

and use, as appropriate, by Federal agencies for the planning,

design, and construction of buildings, both within and outside

the United States.

The Seismic Guidelines are intended primarily for use in designing

new buildings. They are not intended for the design of special

structures such as dams, piers, drydocks, and nuclear facilities.

Structures designed in accord with these Seismic Guidelines are

expected to provide the minimum level of life safety that is

considered reasonable. A moderate earthquake would be expected

to produce only minor damage; a large earthquake might produce

serious damage but. would be unlikely to cause the structure to

collapse. Structures which must remain functional after an

earthquake may warrant a higher level of resistance, and a few

structures may warrant a lower level of resistance.

The Seismic Guidelines were prepared as a coordinated adaptation

of appropriate portions of existing voluntary standards, model

building codes, Federal regulations, and research reports.

However, they are most closely related to the 1985 Uniform

Building Code (UBC) , published by the International Conference of

Building Officials, Whittier, CA. Because several source

documents were used, considerable care was exercised to ensure

that the resulting guidelines were consistent throughout the

report. Effort was also made to ensure that the Seismic Guidelines

were flexible enough to allow use without modification or to

allow inclusion of special agency requirements.

Comments on this report are welcome and solicited. Since certain

sections of these guidelines may have not been thoroughly tested

or used, they should be incorporated with engineering judgement.

Federal agencies using these criteria are requested to document

their experience using them. Such information will be used in the

per iodic r ev i ew an d up d at. e of the Guidelines.

Commen t s sh ou 1 d be f or wa r d ed t o

s

Sec retar i at

I n t er agen c y Comm i 1 1 ee on Se i smi c Safety in

Construct i on

Room B260, Building 226

Nation a 1 Bu r ea u of St a n d ar d

s

Ga i t h er s b ur g , Maryland 20899

:L i i
OVERVIEW

Bui Idi ng®

pr ovi si ons for

This report, Seismic Design Guidelines for Federal

(also referred to as Seismic Guidelines), contains

the reduction of earthquake hazards in Federal buildings. The

Seismic Guideline® are intended primarily for use in designing

new buildings. They are not intended for the design of special

structures such as dams, piers, drydocks, and nuclear facilities.

The report also contains a commentary on the provisions.

The Guidelines were prepared by a subcommittee of the Interagency

Committee for Seismic Safety in Construction (ICSSC) after a review of existing voluntary standards, model building codes, Federal

regulations, and research reports. The seismic regulations of

the Veterans Admi ni strat i on , Army, Navy, Air Force, General

Services Administration, and Department of Housing and Urban

Development were all considered in the development of these

gui del i nes

.

It is worth emphasizing that this report was originally prepared

in response to the requirement in the Implementation Plan of the

Earthquake Hazards Reduction Act to develop a uniform set of

earthquake design guidelines suitable for uniform use by all

agencies. The ICSSC subcommittee charged with this responsibility

developed several criteria for preparing these guidelines,

(l)they should be as close to current practice in both the public

and private sectors as possible and (2)since several Federal

agency have extensive seismic programs underway, they should be

flexible enough to allow incorporation of special agency requirements.

The subcommittee determined that the Uniform Building Code (UBC)

met criteria (1) most closely. However, there are three model

codes referenced for use in the United States. Thus a determination

was made that the guidelines should reference national standards

rather than the UBC standards used in the UBC. It also became

apparent that there are seismic requirements spread throughout

the UBC and not just in the seismic design chapter. Thus it

became necessary to reorganize the material somewhat in order to

have all of the material required in one document.. The report is

a self-contained set of seismic guidelines that references

national standards, closely resembles the UBC in requirements,

and allows inclusion of special agency requirements.
The -foliow i n g d oc um en t s r ec e i ve d sp ec i a 1 speci al reference:

at t en t i on a n d

NEHRP Recommended Provisions for the Development of

Seismic Regulations for New Buildings, Earthquake

Hazards Reduction Series 17 and IS, Federal Emergency

Management Agency, Washington, DC, 1986. 1

Recommended Design Loads for Buildings and other

Structures, ANSI A 58=1, American Natdional Standards

Institute, New York, New York, 1982

Recommended Lateral Force Requirements and Commentary,

Structural Engineers Association of California, San Francisco,

California, 1978. 32

Uniform Building Code, I nt er nat i onal Conference of Building

Officials, Whittier, CA, 1985.

Since portions of each document were used in this report,

considerable care was exercised to ensure that the resulting

guidelines were consistent throughout. Because the seismic

provisions of the UBC are the most widely used and because they

served as the starting point for these guidelines, particular

care is taken to relate these provisions to those of the UBC.

Although there are differences with the UBC, owing to different

contexts, policies, and styles, the basic technical approach to

The original draft of this report used the Applied

Technology Report, Tentative Provisions for the

Development of Seismic Regulations for Buildings, NBS

SP 510, published by the National Bureau of Standards,

1978 as the resource document. That has undergone

considerable review and evaluation since publication

and served as the basis of the NEHRP document. The

NEHRP document is referenced here since it is a more

recent publication and will be updated on appr ox i matel y a three year cycle.

The Uniform Building Code is based on this report

which is also referred to as the SEAOC Requirements in

this document. The report , published in 1975 was

extremely valuable in interpreting some portions of the

intent of the UBC. The SEAOC Requirements have recently

undergone a major revision which has been proposed as a. code change to the UBC. Since the revision is so

different from the current UBC and since the proposal

has not yet been incorporated in the LJBC, it has not

been used in these guidelines.

v
the analysis of seismic loads and the design of buildings to

resist such loads is the same. The Commentary of this report

contains a discussion of the differences between these Guidelines

and the UBC . Where other sources are used, they are identified.

As with the voluntary standards and codes upon which these

guidelines are based, the requirements

"are intended to provide criteria to fulfill life

safety concepts. It is emphasized that the recommended

design levels are not directly comparable to recorded

or estimated peak ground accelerations from earthquakes.

They are however, related to the effective peak

accel erat i ons to be expected in seismic events. More

specifically with regard to earthquakes, structures

designed in conformance with the provisions and

principles set forth therein should, in general , be

able to:

1. Resist minor earthquakes without damage?

2. Resist moderate earthquakes without structural

damage, but with some nonstr uctur al damage;

3. Resist major earthquakes, of the intensity of

severity of the strongest experienced in

California, without collapse, but with some

structural as well as nonstr uctural damage.

In most structures it is expected that structural

damage, even in a major earthquake, could be limited to

repairable damage. This, however, depends upon a number of factors, including the type of construction

selected for the structure. 1,3

Recommended Lateral Force Requirements and

Commentary, Structural Engineers Association

of California, 1978.

vi
One of the objectives of the commentary is to explain the

differences between the provisions of these guidelines and those

of their sources. Because the seismic provisions of the UBC are

the most widely used and because they served as the starting

point for these guidelines, particular care is taken to relate

these provisions to those of the UBC. Although there are many

differences with the UBC, owing to different contexts, policies,

and styles, the basic technical approach to the analysis of

seismic loads and the design of buildings to resist such loads is

the same.

The commentary also addresses specific issues to assist the user

of the guidelines, but it is not a complete commentary on

seismic-resistant design. Both the SEAOC and NEHRP provisions ' are accompanied by extensive commentaries that are recommended

reading for users of these guidelines. In addition, the Army,

Navy, and Air Force manual Seismic Design for Buildings referred

to as the Tri -Services Manual) contains guidelines for procedures

and details that facilitate implementation of provisions for seismic

resistance of buildings.

vi 1
ACKNOWLEDGEMENTS

This report was originally developed by the members of the

Interagency Committee on Seismic Safety in Construction (ICSSC)

Subcommittee 2 - Building Standards and published in '1981. In a reorganization of the ICSSC this became Subcommittee 1 - Standards

•for New and Existing Buildings with a new membership. Subsequently

Subcommittee 1 reviewed the original report and, with some

modifications reported it to the ICSSC for ballot. The membership

of the two subcommittees (denoted in parentheses) consisted of

(affiliation at time of participation is shown):

Vartan M. Bedjanian (2)

Earl R. Bell (1)

Lincoln Chang (2)

Donald M. Evick (1)

Edward Ference (2)

Peter E. Gurvin (1,2)

James R. Harris (2)

James R. Hill ( 1

)

Boyd H. Lefevre (1)

Edgar V. Leyendecker (1,2)*

Allen Li m (2)

George Lippert (1)

Raymond W. Little (1)

George M. Matsumura (1,2)

Flichard D. McConnell (1,2)

John Mehnert (1)

Janina Z. Mirski (1)

Howard D. Nickerson (2)

William D. Rust, Jr. (1,2)

John B. Seals i (1,2)

Constantine Spyropoulos (1,2)

Joseph Tyrrell (1)

Marco F. Venturino (1,2)

Spencer Wu ( 1

)

Michael Vachnis (1,2)

Naval Facilities Engineering

Command, Western Division

Department of Agriculture

Department of Housing and

Urban Development

Postal Service

Naval Facilities Engineering

Command

Department of State

National Bureau of Standards

Department of Energy

Department of Transportation

National Bureau of Standards

Department of Air Force

Department of Agriculture

Department of Health &

Human Services

Army Corps of Engineers

Veterans Administration

Department of Housing and

Urban Development

Veterans Administration

Naval Facilities Engineering

Command

General Services

Administration

National Science Foundation

Department of Housing and

Urban Development

Naval Facilities Engineering

Command

Naval Facilities Engineering

Command, Western Division

National Bureau of Standards

Naval Faci 1 i t i es Eng i neer i ng

Command

vi i i

* denotes Chairman
The original report has received numerous comments since its

original publication in 1981. Some of these were comments from

interested individuals or organizations while others accompanied

the ICSSC ballots. This document has incorporated as many of

these comments as possible.

The work of the committee members, many of whom contributed

considerable effort, and the reviewers is appreciated.

ix
SI Conversion Units

The following list of conversion factors for the most frequently used quantities

in building design and construction may be used.

QUANTITY

LENGTH

AREA

VOLUME

CAPACITY

ACCELERATION

MASS

DENSITY

FORCE

MOMENT OF FORCE.

Y 6ft 0ufe

PRESSURE. STRESS

WORK. ENERGY. OUAwtlTV OP HEAT

POWER. HEAT FLOW

U.S. CUSTOMARY UNIT

IS!

foot Inch

INTERNATIONAL (SI) UNIT

meter (m) mTTTTmeter (mm)

square meter (m*)

square millimeter (itm8

)

cubic meter (m*)

cubic millimeter (ran 8

) liter (L) milliliter (ml)

meter per second (m/s) kilometer per hour (km/h)

meter per second squared (m/s*)

metric ton (t) (1000 kg) kilogram (kg) gram (g)

metric ton per cubic maber (t/m‘) ton per cubic yard (ton /yd 1

) ’) pound per cubic foot (lb/ft*)

square yard (yd* square foot (ft' square Inch (In*

cubic yard (yd® cubic foot (ft 8 cubic Inch (in 8

gallon (gal) fluid ounce (fl ox)

foot per second (ft/s or f.p.s.)

srile par hour (mlle/h or m.p.h.)

foot per second squared (ft/s*)

short ton [2000 lb) pound (lb) ounce (oz)

kilogram per cubic meter (kg/m8

)

kllonewton (kN)

newton (N)

kllonewton meter (kN*m) newton meter (N*m)

megapascal (MPa)

kllopascal (kPa)

megajoule (H3) kilojoule (kJ) Joule (j)

kilowatt (kW) watt [W)

COEFFICIENT OF HEAT watt per square meter kelvln transfer [u-vaTuei (u/P-it) I-Vm-'C)!

THERMAL CONDUC- watt per TIVITY [k-value]ter kelvln (W/**K) T-(HVt)i

ten-force (tonf) kip [1000 lbf) pound-force (lbf)

ton-force foot (tonf* ft) pound-force Inch (lbf* In)

ton-force per square Inch (tonf/ln*) ton-force per square foot (tonf/ft'l

pound-force per square inch (lbf/1n*) pound- force per square foot (lbf/ft')

kllowatthour (kWh) British thermal unit (Btu) foot pound-force (ft*1bf)

horsepower (hp) British thermal unit per hour (Btu/h)

Btu per square foot hour degree

Fahrenheit (Btu/ft'*h*'F)

Btu per square foot degree Fehrenhelt 1 W/m*K

(Btu/ft**®F)

APPROXIMATE CONVERSION

1 B - 3.2608 ft

1 0.0394 In

1 a* - 1.1960 yd*

1 m® - 10.764 ft*

1 - 1.55 x 10*» In*

1 m

8 » 1.3080 yd8

1 B

s - 35.315 ft 8

1 nen* - 61.024 x 10**1n'

1 L - 0.2642 gal

1 it » 0.0338 fl oz

1 a/s - 3.2808 ft/s

1 km/h - 0.6214 mlle/h

1 m/s* 3.2808 ft/s'

1 t • 1.1023 ton

1 kS - 2.2046 1b

1 9

- 0.0353 oz

1 t/m8 - 0.8428 ton/yd*

1 kg/m* • 0.0624 1b/ ft 8

1 kN * 0.1124 tonf

1 kN - 0.2248 kip

1 N - 0.2248 lbf

1 kN*« - 0.3638 tonf* ft

1 N*m • 8.8508 lbf*1n

1 K>a 0.0725 tonf/ln*

1 Wa 10.443 tonf/ft*

1 kPa • 0.1450 lbf/ In*

1 kPa - 20.885 lbf/ft*

1 MJ - 0.2778 kWh

1 kJ - 0.9478 Btu

1 J » 0.7376 ft* lbf

1 kW *> 1.3410 hp

1 W a 3.4121 Btu/h

1 w ® 0.7376 ft*1bf/s

1 *W/«®*K - 0.1761 Btu/ft*»h*®F

1 W/m*K - 0.5778 Btu/ft**®F

base unit.)

LC 1978, Revised November 1977;

NOTES: (1) The above conversion factor* are shown to three or four places of dadaals.

REFERENCES: NBS Guidelines for the Use of the Metric System, LC1056, Revised August 1977;

The Metric System of Measurement. Federal Rsglstsr Motlca of Octobar 26, 1977, NBS Special Publication 330, "TYie International System of Units (SI) ," 1977 Edition;

NBS Technical Note 938, "Recoanendad Practice for the Use of Metric (SI) Units In Building Design and Construction," Revised edition June 1977; ASTM Standard E621-78, "Standard Practice for the Use of Metric (SI) Unite In Building Design and Construction,” (based on NBS TN 938), March 1978; ANSI Z210. 1-1976, "American National Standard for Metric Practice."

ASTM E380-79e

, "Standard for Metric Practice."

IEEE Std. 268-1979, "Standard for Metric Practice.

X
SEISMIC DESIGN GUIDELINES FOR

FEDERAL BUILDINGS

ABSTRACT

This document has been prepared as a coordinated adaptation of

existing voluntary standards, model building codes, Federal

regulations, and research reports tor use by Federal agencies.

The technical content is similar to the seismic requirements of

the 1985 Uniform Building Code (UBC) . However, there are instances

of substantive difference from the UBC. Several important

provisions have been incorporated from other sources considered

in this adaptation. For example, the seismic zone map is the one

in current use in ANSI A58. 1-1982 Minimum Design Load® for

Buildings and Other Structures. A number of provisions have been

added to these guidelines that are based on the current practices

and policies of various Federal agencies. Furthermore, in the

spirit of improvement, this document is organized considerably

differently from the UBC and many provisions are phrased differently.
TABLE OF CONTENTS

Page

PREFACE iii

OVERVIEW . iv

ACKNOWLEDGEMENTS vi i i SI CONVERSION UNITS. x ABSTRACT x i

1.

REGULATION 1

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

1 . 2 De-f i ni t i ons ........................................ 1

1 . 3 Not at i on 4

1.4 Hazard Classifications ............................. 6

1.4.1 Seismic Ground Shaking Hazard ............... 6

1.4.2 Occupancy Hazard ............................ 7

1.5 ftl ternati ve Provisions ............................. 7

GENERAL REQUIREMENTS ......... 11

2.

1 General Performance Requirement 11

2.2 Site Planning for New Buildings .................... 11

2.2.1 Site Evaluation Study..... 11

2.2.2 Site Limitations ............................ 11

2.3 Design of New Buildings 11

2.3.1 Application of the Provisions ............... 11

2.3.2 Documentation 12

2. 4 Construct i on ....................................... 12

2.5 Existing Buildings ................................. 12

2.5.1 Alterations and Repairs 12

2.5.2 Changes of Use or Locations 12

3.

STRUCTURAL DESIGN CRITERIA 13

3.1

Seismic Force-Resisting Systems 13

3.1.1 Integrity 13

3.1.2 System Response Cl assi f i cat i on 13

3.1.3 Strength 14

3.1.4 Stiffness and Building Separations 15

x i i
TABLE OF CONTENTS (CONTINUED)

Page

3.1.5 Overturning Stability

3.1.6 Height ...............

3.2 Other Structural Elements

2. 1 Strength and Anchorage

2.2 Compatibility .........

F oundati on

5

3.3.1 Soil and Foundation Capacity

3.3.2 Structural Ducti 1 i ty ........

STRUCTURAL ANALYSIS PROCEDURES

4. 1 A Required Method tor Seismic-Resisting System?

Elastic Static Lbad Analysis ................

4.2. 1 Base uhear ..................... 4.2.2 Period of Vibration ............ 4.2.3 Site Coefficient

4.2.4 Vertical Distribution of Farces

4.3 Elastic Dynamic Load Analysis , 4.3.1 Mode Shapes and Periods

4.3.2 Modal Base Shear

4.3.3 Design Values ..........

4.4

Elastic Load Effect Analysis

4.4.1 Shear 23

4.4.2 Horizontal Torsion 23

4.4.3 Diaphragm Forces 24

4.4.4 Over turn i ng 24

4.4.5 Orthogonal Effect 25

4.4.6 Vertical Motion Effect 25

4.4.7 Displacements ............................... 25

4.5 Analysis of Other Structural Elements 26

x 1

U

KlM

m.

m.

<i

CD

sj

si

sj

si

O'

O'

O'

rjl

CJ1

01

01

Ol
TABLE OF CONTENTS (CONTINUED)

Page

5. DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL

MATERIALS 29

5. 1 Steel 29

5.

2

Concrete 30

5. 3 Wood 30

5. 4 Masonry 31

5.5 Aluminum 31

5 . 6 Gypsum 32

6. STRUCTURAL DESIGN DETAILS 33

6.1

Moment-Resisting Frames 33

6.1.1 Ductile Moment-Resi sti ng Space Frames ....... 33

6. 1.2 Concrete Frames 33

6.2 Steel Ductile Moment-Resisting Space Frames 34

6.3 Rein-forced Concrete Ductile Moment-Resisting Space

Frames 34

6.3.1 Flexural Members 34

6.3.2 Columns 35

6.4

Braced Frames

6.4.1 Required Capacity.. 35

6.4.2 Steel Braced Frames 35

6.4.3 Rein-forced Concrete Braced Frames. ........... 36

6.5 Rein-forced Concrete Shear Walls..................... 36

6.6 Reinforced Masonry Walls... 36

6.7 Di aphragms. 36

6.7.1 Ti es Between Chor ds . ......................... 36

6.7.2 Anchorages to Wood Diaphragms....... 36

6.8 Openings in Shear Walls and Diaphragms. . . . . . „

.

. . . . . . 37

6.9 Concrete and Masonry Elements. ...................... 37

6.9. 1 Reinforcement, 37

6.9.2 Anchorage of Walls... 37

6. 10 Foundations. ........................................ 37

6. 10. 1 Ties Between Foundation Units. .............. 37

6.10.2 Pile Cap Connections........................ 38

6. 10.3 Concrete Piles. ............................. 38

x i v
TABLE OF CONTENTS (CONTINUED)

Page

7. NONSTRUCTURAL DESIGN REQUIREMENTS 40

7 * 1 Anchorage for Inertial Forces. 40

7.2 Distortion Compatibility -: or Exterior Panels........ 40

7.

3

Protection Against Secondary Hazards. ............... 41

7.4 Functionality of Essential Elements......... 41

7.

7

Reinforcement of Concrete and Masonry. .............. 42

8. CONSTRUCTION QUALITY CONTROL..... 45

8.1

Special Inspector. 45

8.1.1 Qualifications.................... 45

8.1.2 Inspection Reports. 45

8.1.3 Final Reports ...............................

.

45

B.2 Required Special Inspection.............. 45

8.2.1 Piling, Drilled Piers and Caissons........... 46

8.2.2 Excavation and Filling.... 46

8. 2.

3

Concrete. 46

8.2.4 Reinforcing Steel and Prestressing Steel..... 46

8.2.5 Ductile Moment-Resisting Concrete Frame. . . . . . 47

8.2.6 Welding......... 47

8.2.7 High-Strength Bolting........................ 48

8. 2.

8

Structural Masonry. .......................... 49

8.2.9 Reinforced Gypsum Concrete Used as a

Di aphragm. 49

8.2.10 Insulating Concrete Used as a Diaphragm. 49

8.2.11 Special Cases.................... 50

xv
LIST OF TABLES

Table 1.1 - Zone -for Sites with Approved Site

Evaluation 8

Table 1.2 ~ Values for Occupancy Importance Factor 8

Table 4.1 - Zone Coefficient Z .27

Table 4.2 - K for Bu i 1 d i ngs 27

Table 4.3 - K for Other Structures 27

Table 4.4 - Site Coefficient 28

Table 4.5 - Horizontal Force Factor C^ for Elements

of Structures 28

Table 6.1 ~ Minimum Reinforced and Maximum Spacing

for Reinforced Masonry Walls ....39

Table 7.1 - Horizontal Force Factors C^ for

Nonstructural Elements of Buildings 43

LIST OF FIGURES

Fi gure 1.1 -• Sei smi c Zone Map 9
SEISMIC DESIGN GUIDELINES FOR FEDERAL BUILDINGS

- PROVISIONS -

1. REGULATION

1 . 1 SCOPE

These guidelines are -for use in the planning, design, and

construction of new buildings and their appurtenances and in the

alteration, repair, or change of use of existing buildings. The

guidelines are intended to provide appropr i atel y varying degrees

of safety of buildings against the effects of seismic ground shaking.

1.2 DEFINITIONS

The following definitions apply to the terms used in this

document

.

APPROVED, as t o materials and types of construct i on , refers to

approval by the designated authority as the result of investigation

and tests conducted by him, or by reason of accepted principles

or tests by national authorities, technical or scientific

organizations.

BASE OF STRUCTURE is the level at which the earthquake motions

are assumed to be imparted to the structure or the level at which

the structure as a dynamic vibrator is supported. This level

does not necessarily coincide with the ground level.

BEARING WALL is any wall meeting either of the following classifi cat i ons;

(1) Any metal or wood stud wall which supports more than

100 pounds per lineal foot of superimposed load.

(2) Any masonry or concrete wall which supports more than

200 pounds per lineal foot of superimposed load, or any

such wall supporting its own weight for more than one

story

.

BOX SYSTEM is a system in which a significant fraction of the

gravity load is supported on bearing walls. Also see Sections

3.1.2 and 3.1.3.

BRACED FRAME is a truss system or its equivalent which is

provided to resist lateral seismic forces in the frame system and

1
in which the members are subjected primarily to axial stresses by

the seismic forces.

BUILDING is any structure used or intended for supporting or

sheltering any human use or occupancy.

DEAD LOAD is the vertical load due to the weight of all permanent

structural and nonstructural components of a building, such as

walls, floors, roofs, and fixed service equipment.

DESIGNATED AUTHORITY is the official representative of the

government who is charged with the administration and enforcement

of these guidelines, or his duly authorized representative.

DIAPHRAGM is a horizontal, or nearly horizontal, component or

system, including bracing systems, that is designed to transmit

lateral seismic forces to the vertical elements of the seismic

force-resi st: i ng system.

DUAL SYSTEM is a system in which essentially all the total

gravity load is supported on framing without the use of bearing

walls and in which the designated seismic f orce—real st i ng system

in the direction under consideration is composed of a combination

of reinforced concrete or structural steel ductile

moment-resisting space frames with shear walls or braced frames.

Also see Sections 3.1.2 and 3.1.3.

DUCTILE MOMENT-RESISTING SPACE FRAME is a moment-resisting space

frame with special ductility provisions to permit repeated

inelastic straining.

DUCTILE MOMENT-RESISTING SPACE FRAME SYSTEM is a system in which

essentially all the gravity load is supported on framing without

the use of bearing walls and in which the designated seismic

force-resisting system in the direction under consideration is

composed entirely of reinforced concrete or structural steel

ductile moment-resisting space frames (unbraced frames) . Also

see Sections 3.1.2 and 3.1.3.

ESSENTIAL FACILITIES are those buildings or their appurtenances

which must be safe and usable for emergency purposes after a

major earthquake in order to preserve the health and

safety of the general public. Also see Section 1.4.2 and Table

1.2. Such f aci 1 i t i es sha 1 1 include but not be limited to:

(

1

) Hospitals and other medical facilities having surgery

or emergency treatment areas

(2) Fire and police stations
(3) Government disaster operation and communi cati on centers

deemed to be vital in emergencies

(4) Power stations anti other utilities required as

emergency f sl i 1 i ii i es

EXTERIOR WALL is any wall or element of a wall, or any member or

group of members, which defines the exterior boundaries or courts

of a building and which has a slope of 60 degrees or greater with

the horizontal plane.

HEIGHT is the vertical distance from the base to uppermost level

in the structure unless otherwise indicated.

HIGH RISK FACILITIES are those buildings where the primary

occupancy is for assembly use for more than 300 persons, or where

the occupants ' mobility is restricted or impaired, or where the

contents of the building are hazardous. Also see Section 1.4.2

and Table 4=1.

LIVE LOAD is the load superimposed by the use and occupancy of

the building not including the wind load, earthquake load, or

Q 8c*.d 1 oad . MOMENT—RESISTING SPACE FRAME for lateral forces is an unbraced

vertical load-carrying space frame in which members are

restrained at the joints and arranged so that they are subjected

p* r x mar 1 x y to t 1 ex ural str esses

.

PARAPET WALL is that part of any wall entirely above the roof

I ine.

SEISMIC FORCE-RESISTING SYSTEM is that part of the structural

system assigned to resist seismic forces.

SHEAR WALL is a wall designed to resist lateral forces parallel

to the wall.

SPACE FRAME is a three-di mensi onal structural system without

bearing walls, composed of interconnected members laterally

supported so as to function as a complete self-contained unit

with or without the aid of a horizontal diaphragms or

~ oor o racing syst ems

.

MOMENT-RESISTING SPACE FRAME for lateral forces is an unbraced vertical load-carrying space frame in which members

are restrained at the joints and arranged so that they are

subjected primarily to flexural stresses. (This definition

x rrr !' op cfci Ltru i i et e t L- 1 a. r 1 1 y . )
DUCTILE MOMENT-RESISTING SPACE FRAME is a moment—real st i ng space -frame with special ductility

provisions to permit repeated inelastic straining^

(This definition is repeated here for clarity.)

STRUCTURE is that which is built or constructed, an edifice or

building of any kind, or any piece of work artificially built up

or composed of parts joined together in some definite manner.

1.3 NOTATION

The1 following notations are used in these guidelines.

C - Numerical coefficient for the vibratory response of a

structure to seismic motions, as specified in Section

4.2.1.

Value of C used in calculating a lower limit for the

base shear, a-s: specified in Section 4

Value of C for the specific mode of vibration, as

specified in Section 4.3.2.

Numerical coefficient for the vibratory response of a

part of a structure to seismic motions, as specfied

i n Sect i on 4=5.

D = The dimension of the structure, in feet, in a

! I r e«_ •_ 1 uH mallei to the applied forces,

F i , F,-, , F

>

Lateral seismic force applied to level i, n, or k,

respect! vel y

.

Lateral seismic forces on a part of the structure and

in the direction under consideration.

r *: That portion of V considered concentrated at the top

of the structure in addition to Fn as specified in

Sect! on 4.2. 4.

Lateral seismic force applied to level k when

considering the m

fc ^ mode of vibration.

Distributed portion c-f total lateral force at level i for use in determining the period of vibration, T, in

Equation 4.5.

4
y = Acceleration due to gravity

hi ; h n ^ hx = Height in feet above the base to level i, n, or x,

respect i vel y .

I = Numerical coefficient for occupancy hazard, as

specified in Section 1.4.2 and Table 1.4.

K = Numerical coefficient for structural system response

to seismic motions, as specified in Sections 3.1.2

and O' . 1 . o*

.

Level i = Level of the structure referred to by the subscript

i ; i = 1 designates the first level above the base.

Level n = That level which is uppermost in the main portion of

the structure.

Level x = That level which is under design consideration; x = 1 designates the first level above the base.

M„ m = Overturning moment at level x when considering the

mth mode of vibration.

N = The total number of stories above the base to

level n.

S

T*

i

= Numerical coefficient for site-structure resonance in

response to seismic motions, as specified in Section

4.2.3.

= Fundamental elastic period of vibration of the

building or structure in seconds in the direction

under consideration.

T = Value of T used in calculating a lower limit for the

base shear.

Tm = Period of vibration for the m

tt"* mode, in seconds.

T. = Characteristic site period.

V

v

= The total lateral seismic force or shear at the base.

= A lower limit of V when using modal analysis.

i

* *v m = The value of V when considering the m**’ mode of

vi brat i on

.

when considering the made of
= The total lateral seismic: force or shear at the base

determined by means of modal analysis.

The total lateral seismic force at level x when

considering the mth mode of vibration.

W = The total dead load including the partition loading

where applicable; see Section 4.2.1.

Wm - The portion of W effective for the mtM mode of

vibration.

Wi ,w„ = That portion of W which is located at or is assigned

to level i or x, respect i vel y

.

W. The weight of a portion of a structure or

nonstructural component.

Z = Numerical coefficient for the seismic hazard zone, as

specified in Section 4.2.1 and determined by Figures

1.1

and 1.2. For locations in Zone No. 1, Z = 3/16.

For locations in Zone No. 2, Z = 3/8. For locations

in Zone No. 3, Z = 3/4. For locations in Zone No. 4,

Z = 1.

= Deflection at level i relative to the base, due to

applied lateral seismic forces, f t used in determining

the period of vibration, T.

01m) 0«m The displacement amplitude at level i, or x,

building for the fixed-based condition when

in its mth mode.

of the

vi brat i ng

1.4 HAZARD CLASSIFICATIONS

1.4.1 Seismic Ground Shaking Hazard

The zone representing the level of seismic ground shaking hazard

shall be established for each building site according to the maps

shown in Figure 1.1. For locations not included in Figure 1.1,

the zone? shall be established from approved documents or from a site evaluation as indicated in the following paragraph.

For those building sites that have had a design ground acceleration

established by means of an approved site evaluation (refer to

Section 2.2.1), the zone shall be determined according to Table

1.1 for use in these guidelines where a zone is required.

6
1.4.2 Occupancy Hazard

The occupancy of the building shall be classified and the

occupancy importance factor I shall be established for each

building according to Table 1.2, unless otherwise specified by

the designated authority.

1 . 5 ALTERNAT I VE PROV I S I ONS

Alternate materials, methods of construction, structural

concepts, and analytical procedures to those prescribed in this

standard may be used subject to the approval of the designated

authority. Substant i at i ng evidence demonstrating that the

proposed alternate, for the purpose intended, will be at least

equal in strength, durability, seismic resistance, validity, and

safety shall be submitted.
TABLE 1.1 - ZONE FOR SITES WITH APPROVED SITE EVALUATION

Desi gn ground acceleration, a Zone

a < 0. 05g 0

0 . 05g < a < 0. lOg 1

0. 1 0g < a < 0 . 20g n

0 . 2Gg ^ 3. 0 » 40q rr

0 . 40g < a 4

TABLE 1.2 - VALUES FOR OCCUPANCY IMPORTANCE FACTOR

I W— of Q>_cupani_y

Essential Facilitites. Essential facilities are

those buildings or their appurtenances which must

be safe and usable for emergency purposes after a major earthquake in order to preserve the health and

safety of the general public. Such facilities

shall include but not be limited to:

1. Hospitals and other medical facilities having

surgery or emergency treatment areas

2. Fire and police stations

3. Government disaster operation and communication centers deemed to be vital in emergencies

4. Power stations and other utilities required as

emergency facilities

I

1.5

High Risk Facility. Any building where the primary 1.25

occupancy is for assembly use for more than 300

persons, or where the occupants' mobility is

restricted or impaired, or where the contents of

the building are hazardous

All Other. 1.0

S
9

FIGURE

1.1

SEISMIC

ZONE

MAP
^“Q V

HAWAII

FIGURE 1.2 SEISMIC ZONE MAP

ALASKA

10
GENERAL REQUIREMENTS

2.1 GENERAL PERFORMANCE REQUIREMENT

Every building and the appurtenances and parts thereof shall be

designed and constructed to resist the forces produced by seismic

ground shaking as provided in these guidelines except as may be

specified by the designated authority. Buildings located in zone

0 are exempt from the requi rements in these guidelines.

2.2 SITE PLANNING FOR NEW BUILDINGS

2.2.1 Site Evaluation Study

A site evaluation study shall be conducted for all hospitals in

zones 3 or 4 and other buildings specified by the designated

authority. The study shall establish the design ground motion

for the site and shall evaluate the likelihood and effect of the

following phenomena;

(1) surface rupture due to active fault displacement

(2) liquefaction

(3) landslide or slope stability failure

(4) subsidence

2.2.2 Site Limitations

This section applies only to those buildings for which a site

evaluation study is required. Essential Facilities shall not be

sited such that surface rupture due to fault displacement would

pass through the building. For sites that have a potential for

liquefaction, landslide, or subsidence, the building, foundation,

and/or subsoil shall be engineered to mitigate the hazard or the

effects of the phenomena.

2.3 DESIGN OF NEW BUILDINGS

2.3.1 Application of the Provisions

The structural portion of the building shall be designed to

satisfy the requirments of Chapter 3, STRUCTURAL DESIGN

CRITERIA. For all buildings in Zones 3 or 4 and buildings with

an Importance Factor 1 greater than 1.0 in Zone 2, the

nonstructural portion of the building shall be designed to

satisfy the requirements of Chapter .7, NONSTRUCTURAL DESIGN

REQU I REMENTS

.
2.3.2 Documentation

Drawings, spec i f i cat i ons , basis of design, calculations, reports,

certifications, and other substantiation necessary to verify

compliance with the design provisions shall be submitted to the

designated authority.

2.4 CONSTRUCTION

The construction quality of all buildings in Zones 3 or 4 and

buildings with an Importance Factor I greater than 1.0 in Zone 2

shall be assured by satisfying the requirements of Chapter 8,

CONSTRUCTION QUALITY CONTROL.

2.5 EXISTING BUILDINGS

2.5.1 Alterations and Repairs

When specified by the designated authority any Federal building

for which the cost of renovations or repairs, exclusive of

seismic strengthening, exceeds 50 percent of the replacement cost

of the improved building, it must be corrected to resist the

appropriate level of earthquake forces.

Minor structural alterations may be made in existing buildings

and other structures, but the resistance to lateral seismic

forces shall be not less than that before such alterations were

made, unless the building as altered meets the requirements of

these guidelines.

2.5.2 Changes of Use or Location

Changes of use that increase the occupancy importance factor I,

or of location that increase the seismic hazard zone shall be

permitted only if the building is made to satisfy the requirements

of this standard.
3. STRUCTURAL DESIGN CRITERIA

3.1 SEISMIC FORCE-RESISTING SYSTEMS

3.1.1 Integrity

The seismic force-resisting system shall include a continuous

load path, or paths, to transfer all seismic forces to the final

point of resistance. Connections and elements shall be provided

to transfer the seismic forces from other parts of the building

to the seismic force—resisting system, using the forces specified

in Section 4.5 and Section 7.1, where applicable.

3.1.2 System Response Classification

Each building shall be assigned to one of the following

categories based on the type of elements used to support gravity

loads and on the type and ductility of elements designated to be

the seismic force-resisting system;

DUCTILE MOMENT-RESISTING SPACE FRAME SYSTEM (K = 0.67)

A system in which essentially all the gravity load is

supported on framing without the use of bearing walls and in

which the designated seismic f orce—resi st i ng system in the

direction under consideration is composed entirely of

reinforced concrete or structural steel ductile

moment-resisting space frames (unbraced f rames)

.

DUAL SYSTEM (K = 0.B0)

A system in which essentially all the total gravity load is

supported on framing without the use of bearing walls and in

which the designated seismic force—resisting system in the

direction under consideration is composed of a. combination

of reinforced concrete or structural steel ductile

moment—resi sti ng space frames with shear walls or braced

f rames

.

BOX SYSTEM <K = 1.33)

A system in which a significant fraction of the gravity load

is supported on bearing walls.

BUILDING FRAME SYSTEM <K = 1.0)

Any other structural system
Rigid elements that are not designated as part of the seismic

force-resisting system may be incorporated into buildings

provided that their e-f-fect on the action o-F the seismic

force-resisting system is considered and provided for in the

design. In particular, moment-resisting space frames and ductile

moment-resisting space frames may be enclosed by or adjoined by

other rigid elements if it can be shown that the action or

failure of the other rigid elements will not impair the vertical

and lateral 1 oad resisting ability of the space frame.

Structural steel ductile moment-resisting space frames shall

satisfy the ductility provisions of Section 6.2, and reinforced

concrete ductile moment—res i st i ng space frames shall satisfy the

ductility provisions of Section 6.3.

3.1.3 Strength

Members and connections shall resist the effect of combined

gravity and seismic forces. The resistance shall be determined

according to Chapter 5, DESIGN AND CONSTRUCTION STANDARDS FOR

STRUCTURAL MATERIALS. In computing the effect of seismic force

in combination with vertical loads, gravity load stresses induced

in members by dead load plus design live load and snow load,

except roof live load, shall be considered. Consideration shall

also be given to minimum gravity loads acting in combination with

seismic forces.

In addition, the following special requirements apply to the

ductile moment-resisting space frame system and the dual system:

DUCTILE MOMENT-RESISTING SPACE FRAME SYSTEM (K = 0.67)

The ductile moment-resisting space frames shall have the

capacity to resist the total required lateral seismic force

by themsel ves.

DUAL SYSTEMS <K = 0.80)

(a) The frames and shear walls or braced frames shall

resist the total lateral force in accordance with their

relative rigidities considering the interaction of the

shear walls and frames.

<b) The shear walls or braced frames acting independently

of the ductile moment-resisting portions of the space

frame shall resist the total required seismic forces.

14
<c) The ductile moment—resi st i ng space frame shall have the

capacity to resist not less than 25 percent of the

total required lateral seismic force.

3.1.4 Stiffness and Building Separations

Lateral deflections or drift of each story relative to its

adjacent stories due to seismic forces as determined in Section

4.4.7 shall not exceed 0.015 times the story height , unless it

can be demonstrated that greater drift can be tolerated.

Diaph ragm deformations shall be considered in the design of the

supported wa! Is.

ftl 1 portions of structures shall be designed and constructed to

act as an integral unit in resisting horizontal forces unless

separated structurally to avoid contact under deflection from

seismic action.

3.1.5 Overturning Stability

Every building shall be designed to resist the overturning

effects caused by the seismic forces specified in this standard.

3.1.6 Hei ght

All buildings in zones 3 or 4 and buildings with an importance

factor I greater than 1.0 in zone 2 that 'are more than 160 feet

in height shall have ductile moment-resisting space frames

capable of resisting not less than 25 percent of the required

seismic: forces for the structure as a whole.

3.2 OTHER STRUCTURAL ELEMENTS

3.2.1 Strength and Anchorage

Structural elements and their anchorages shall resist the seismic

forces induced by their own mass and by connected elemencSj as

determined in Section 4,6.1. Resistance shall be determined in

accordance with chapter 5, DESIGN AND CONSTRUCTION STANDARDS FOR

STRUCTURAL MATERIALS.

3.2.2 Compatibility

Fur all buildings in Zones 3 or 4 and buildings with an

importance factor I greater than 1.0 in Zone 2, all framing

elements not required by design to be part of the seismic

f arcs—resi st i ng system shall be investigated and shown to be
adequate -for vertical load-carrying capacity and induced moment

due to the -force effects of the distortions calculated according

to Section 4.4.7. The rigidity of other elements shall be

considered in accordance with Section 4.4.1.

3.3 FOUNDATIONS

3.3.1 Soil and Foundation Capacity

In the -determi nati on of the foundation design criteria,

recognition shall be given to the dynamic nature of the forces,

the expected ground motions, and the design basis for strength

and ductility of the structure.

3.3.2 Structural Ductility

For all buildings in Zones 3 or 4 and buildings with an

Importance Factor I greater than 1.0 in Zone 2 that have a dual

system or a ductile moment-resisting space frame system, the

special ductility requirements for structural steel or reinforced

concrete specified in Sections 6.2 and 6.3 shall apply to all

structural elements below the base which are required to transmit

forces to the foundation resulting from the application of the

design lateral seismic forces to the building.

16
4. STRUCTURAL ANALYSIS PROCEDURES

Stresses shall be calculated as the

horizontally at each floor and roof

force shall be assumed to come from

buildings shall be analyzed for the

effect of a force applied

level above the base. The

any horizontal direction;

force on each principal axis.

4. 1 REQUIRED METHOD FOR SEISMIC-RESISTING SYSTEMS

The seismic loads for all buildings shall be analyzed according

to Section 4.2, as a minimum, except for the following buildings,

which shall be analyzed according to Section 4.3 as a minimum:

<1) buildings specified by the designated authority

(2) hospitals in Zones 3 or 4 that have shapes or framing

systems irregular in a vertical sense

(3) buildings over 4 stories in Zone 4 that have shapes or

framing systems irregular in a vertical sense.

For buildings with irregular shapes or framing systems in a

horizontal sense, special attention should be given to the

distribution of forces; the designated authority may require the

use of a more sophisticated analysis for such buildings.

The designated authority may require or approve the use of a

soi 1 -structure interaction analysis that will modify the seismic

forces and displacements determined in this chapter. The seismic

load effects shall be analyzed according to Section 4.4.

4.2 ELASTIC STATIC LOAD ANALYSIS

4.2.1 Base Shear

The total lateral seismic force assumed to act at the base of the

structure shall be determined as follows for each main axis:

V = ZIKCSW <Eq. 4.1)

where the terms are as follows:

Z - Shall be determined from Table 4.1 for buildings that

do not have an approved site evaluation. For buildings

that have a design ground acceleration established

according to an approved site evaluation study, Z = 2.5

times the design ground acceleration (see Section

2.2.1) expressed as a fraction of the acceleration of

gravi ty

.

17
I

•- As spec i f i ed in Sect ion 1.4. 2

C - Shall be determined by Equation 4.2 as

1 C = (Eq. 4.2)

15 /T

The value of C need not exceed 0.12. The value of T is

specified in Section 4.2.2.

S -- Shall be determined in accordance with Section 4.2.3,

except that the product CS need not exceed 0. 14.

K - Shall be determined from Table 4.2 for buildings. For

other structures and appurtenances associated with

buildings K shall be determined from Table 4.3.

For elevated tanks, the minimum value of KC shall be

0.12 and the maximum value of KCS need not exceed

0.30. Elevated tanks which are supported by buildings

or are not. sup) p or ted on four or more cross-braced legs

as described above shall be designed in accordance with

Sec t i on 4.5, us i n g Cp = 0.3.

W -• Shall be equal to the total dead load. For storage and

warehouse occupancies, 25 percent of the floor live

load shall be included in W. Where the design snow

load is 30 psf or less, no part need be included in the

value of W. Where the snow load is greater than 30

psf, the snow load shall be included; however, the snow

load may be reduced by up to 75 percent, where the snow

load duration warrants and the designated authority

approves the reduction.

4.2.2 Period of Vibration

The period T shall be established using the structural properties

and def ormati onal character i st i cs of the resisting elements in a properly substantiated analysis, which could make use of an

equation such as:

n T = 2 tt/( Y, Wifit 2 ) i = 1

n <g£ fifii)

i =1

( Eq . 4 . 5

)

where the values of f 4 represent any lateral force distributed

appr ox i matel y in accordance with the principles of Section 4.2.4

18
or any other rational distribution. The elastic deflections, 1 shall be calculated using the applied lateral -forces, f 4 . The

value of T so determined shall not exceed the value calculated by

the appropriate choice Equation 4.3 or 4.4 below by more than 20

percent

.

In the absence of a determination as indicated above, the value

of T for buildings may be determined ass

0. 05hn

T = - - — (Eq. 4.3)

/D

or in buildings in which the lateral f or ce-resi st i ng system

consists of ductile moment-resisting space frames capable of

resisting 100 percent of the required lateral forces and such

system is not enclosed by or adjoined by more rigid elements

tending to prevent the frame from resisting lateral forces:

T = 0 . 1 ON (Eq .4.4)

where N is the total number of stories above the base.

4.2.3 Site Coefficient

The value of S shall be determined by one of the following two

methods

.

Method A

The value of S shall be determined by the following equations,

but shall not be less than 1.0:

For T/T„ < 1.0

S = 1.0 + (T/T„) - 0.5 (T/Tm)'-2 (Eq. 4. 6)

For T/Tm

S =

> than 1.0

1.2 + 0.6 (T/T.) - 0.3 (T/T.) 22 (Eq. 4.7)

The period T in Equations 4.6 and 4.7 shall be as determined in

Section 4.2.2 but T shall not be less than 0.3 second.

19
The range o-f values of TOT may be established from properly

substant i ated geotechnical data, except that Ts shall not be

taken as less than 0=5 second nor more than 2-5 seconds- T„

shall be that value within the range of site periods, as

determined above, that is nearest to T.

When T s is not properly established, the value of S shall be 1.5-

Exception ; Where T has been established by a properly substantiated

analysis and exceeds 2.5 seconds, the value of S may be

determined by assuming a value of 2-5 seconds for Tm -

Method B

The effects of site conditions on building response shall be

established based on soil profile types defined as follows:

( 1 ) Soil Profile Type 1 is a profile withs

(a) rock of any characteristic , either shale—like or

crystalline in nature. Such material may be

characterized by a shear wave velocity greater than

2,500 feet per seconds or,

(b) stiff soil conditions where the soil depth is less

than 200 feet and the soil types overlying rock are

stable deposits of sands, gravels, or stiff clays.

(2) Soil Profile Type 2 is a profile with deep cohesion less

or stiff clay conditions, including sites where the

soil depth exceeds 200 feet and the soil types

overlying rock are stable deposits of sands, gravels,

or stiff clays.

(3) Soil Profile Type 3 is a profile with soft to

medium—stiff clays and sands, character i zed by 30 feet

or more of soft to medium-stiff clays with or without

intervening layers of sand or other cohesion! ess

soi 1 s.

In locations where the soil properties are not known in

sufficient detail to determine the soil profile type or where the

profile does not fit any of the three types. Soil Profile Type 3

shall be used. The coefficient S for the effects of site

conditions on building response is given in Table 4.4.

20
CL

4.2.4 Vertical Distribution of Forces

(A) Structures having irregular shapes or framing systems

The distribution of the seismic lateral forces in structures

which have highly irregular shapes, large differences in lateral

resistance or stiffness between adjacent stories, or other

unusual structural features, shall be determined considering the

dynamic characteristics of the structure.

Buildings having setbacks wherein the plan dimension of the tower

in each direction is at least 75 percent of the correspond! ng

Ian d i mensi on of the lower part may be considered as uniform

uildings without setbacks for the purpose of this section,

provided other irregularities do not exist.

(B> Structure having regular shapes or framing systems

The total lateral force V shall be distributed over the height of

the structure as follows:

n V = Ft + F t (Eg. 4.S)

i = 1 The concentrated force at the top shall be determined ass

Ft = 0.07TV <Eq . 4.9)

Ft need not exceed 0.25V and may be considered as zero where T is

0.7 second or less. The remaining portion of the total base

shear V shall be distributed over the height of the structure,

including level n , as follows:

<V - Ft> w~h M F* (Eg. 4. 10)

n Wi h

i = 1

4.3 ELASTIC DYNAMIC LOAD ANALYSIS

The lateral seismic forces shall be determined

this section using all modes of vibration with

than 0.04 second, but in no case less than the

in either principal direction.

in accordance with

a period greater

first three modes

21
4 1 Mode Shapes and Periods

The mode shape, ga im , and the modal period, T m shall be determined

for each mode in accordance with the principles of mechanics.

4.3.2 Modal Base Shear

The total lateral seismic force for a mode shall be determined as

I r 1 1 r-i' -cz *

£ U i i Ufv brVm - ZIKCmSWm <Eq. 4.12)

where

Z, I, K and S are as defined in Section 4=2

Cm shall be determined for each mode ass

1 Cm <Eq. 4. 13)

15trZ

The value of Cm need not exceed 0.12 and the product of CmS need

not exceed 0=14. T m is the period of vibration for the mth mode,

in seconds. Subject to the approval of the designated authority,

a site specific spectral shape may be used in lieu of Eq . 13.

UJ m shall be determined for each mode ass

n

< £ "***«.> 38 i=l

Wm = (Eq. 4= 14) n

1=1

4.3.3 Design Values

The following quantities shall be determined for each mode

according to the principles of mechanics:

£1) Fx m ~ the equivalent lateral seismic force applied to

each level
/ n\ a, / 0x m - the lateral displacement at each level

(3) x m — the lateral seismic shear force at each level

(4) M1 x m - the overturning moment at each level

(5) the story drift at each level

total

shear

Vdl U

i i Vt

te f or

shal 1 each of the above quantities and the totalnot be less than that obtained as the square

root of the sum of the squares of the quantity for each mode. Vt

shall be compared with the quantity V, where

V is determined from Equation 4.1 by substituting C for C

C is determined from Equation 4.2 by substituting T for T

T is determined as 1.4 times the value determined for T in

Equation 4.3 or 4.4, as appropriate.

Where V*. is less than V, the design value for each quantity shall

be the product of the total value and the following factor. As

A = V/Vt <Eq. 4.15)

Vt need not exceed V determined from Equation 4.1,

The value of base shear shall not be less than 90 per cent of

that computed by Equation 4.1.

4.4 ELASTIC LOAD EFFECT ANALYSIS

4.4.1 Shear

Total shear in any horizontal plane shall be distributed to the

various elements of the seismic force—resi sti ng system in

proportion to their rigidities considering the total rigidity of

the horizontal bracing system or diaphragm.

4.4.2 Horizontal Torsion

At each level designated as x, the force FM shall be applied over

the area of the building in accordance with the mass distribution

on that level.

Provisions shall be made for the increase in shear resulting from

the horizontal torsion due to an eccentricity between the center

of mass and the center of rigidity. Negative torsional shears

shall be neglected. Where the vertical resisting elements depend
on diaphragm action for shear distribution at. any level, the

shear-resi st i ng elements shall be capable of resisting a

torsional moment assumed to be equivalent to the story shear

acting with an eccentricity of not less than 5 percent o-f the

maximum building dimension at that level.

4.4.3 Diaphragm Forces

Floor and roof diaphragms shall be designed to resist the effects

of forces determined as follows;

.E F*

Fp,„ = CEq . 4.16)

nEi = 1 where

Fi = the lateral force applied to level i

Wi ~ the portion of W at level i

wpx — the weight of the diaphragm and the elements

tributary thereto at level x, including 25 percent of

the floor live load in storage and warehouse

oc c up an c i es

,

The force F,-,* determined from Equation 4.16 need not exceed

0. 30 ( ZIwp « ) = When the diaphragm is required to transfer lateral forces from

the vertical resisting elements above the diaphragm to other

vertical resisting elements below the diaphragm due to offsets in

the placement of the elements or to changes in stiffness in the

vertical elements, these forces shall be added to those

determined from Equation 4.16.

However, in no case shall lateral force on the diaphragm be less

t h an 0 „ 1 4 ( Z I w^ « ) . 4.4.4 Overturning

At any level the incremental changes of the design overturning

moment in the story under consideration shall be distributed to

the various resisting elements in the same proportion as the

distribution of shears in the resist ing system.

24
Where other vertical members are provided which are capable of

partially resisting the overturning moments, a redistribution may

be made to these members if framing members of sufficient

strength and stiffness to transmit the required loads are

provi ded

.

Where a vertical resisting element is discontinuous, the

overturning moment carried by the lowest story of that element

shall be carried down as loads to the foundation.

4.4.5

Orthogonal Effect

For all buildings in Zones 1 or 2, the design seismic load

effects may be determined assuming separate application of the

seismic loads on each of the main axes of the structure. For all

buildings in Zones 3 or 4, the seismic load effect shall be

determined from the most critical direction of application of the

seismic loads, which may be assumed to be satisfied if the

following combination is taken; 100 percent of the force effect

for one direction of motion plus 30 percent of the force effect

for the perpendicular direction of motion. The combination

requiring the maximum element strength shall be used.

Except! on

;

Diaphragms, and components of the seismic f orce-resi st i ng

system utilised in only one of the two orthogonal directions

need not be designed for the combined effects,

4.4.6 Vertical Motion Effect

For horizontal cantilever components and prestressed members, a

vertical acceleratioin equal to one-half of the horizontal

accerleratioin must be considered in design.

4.4.7 Displacements

The displacement calculated from the application of the required

lateral forces shall be multiplied fay (3.0/K) to obtain the

design displacement (and drift). The ratio (3.0/K) shall not be

less than 3.U.
4.5 ANALYSIS OF OTHER STRUCTURAL ELEMENTS

Parts or portions of structures, nonstructural components and

their anchorage to the main structural system shall resist the

following lateral seismic forces;

Fp = ZICpW^ (Eq . 4.17)

wher e

Z and I are the coefficients used for the building (see

Section 4.2.1 and Section 1.4.2)

Is the weight of the part or portion

is set forth in Table 4.5.

Interconnection forces between two parts of the structure shall

not be less than 0.133ZI times the weight of the smaller portion.

26
TABLE 4. 1 - ZONE COEFFICIENT

jLUS it;

4

1

z

1 3/4

3/S

3/16

r J o

TABLE 4.2 - K FOR BUILDINGS

System Response Cl assi f i cat i on (see 3.1=2) K

Ductile Moment-Resi st i ng Space Frame 0.67

Dual System 0.G0

Box System 1 . 33

Bui 1 di ng Frame System 1 .

0

TABLE 4.3 - K FOR OTHER STRUCTURES

Type of Structure K

Elevated tanks plus full contents, on 2.5

four or more cross-braced legs and not

supported by a building

Structures other than buildings and 2.00

other than those set forth in 4=6=1

vJ « DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS

This chapter specifies the commonly accepted standards for

materials, design, and construct i on that are presumed as a basis

for this standard. The designated authority may require or

approve the use of a different edition or standard than specified

here. In overseas construction, where local materials of grades

other than those herein are used, the working stresses, grades,

and other requirements of this standard shall be modified as

applicable in accordance with good engineering practice.

5. 1 STEEL

The quality and testing of steel materials and the design and

construction of steel components which resist seismic forces

shall conform to the following references, except as modified by

other provisions of this standard.

Cl) Specification for the Design, Fabrication and Erection

of Structural Steel for Buildings, American Institute

of Steel Construction (AISC), I960.

C2) Structural Welding Code (AWS D1 . 1-84) , American Welding

Society (AWS), 19S4.

(3) Specification for Structural Joints Using ASTM A325 or

A490 Bolts, AISC, 1980.

(4) Specification for the Design of Cold—formed Steel

Structural Members, American Iron and Steel Institute

( A I S I ) , 19S0 Edition.

(5) Standard Specifications, Load Tables, and Weight Tables

for Steel Joint Girders, the Steel Joist Institute

CSJI), 1984.

<£> Criteria for Structural Applications for Steel Cables

far Buildings, AISI, 1973 Edition.

(7) Steel Deck Institute Diaphragm Design Manual , Steel

Deck Institute, St. Louis, Missouri, 1981.
5.2 CONCRETE

The quality and testing of concrete and steel materials and the

design and construction of reinforced concrete components which

resist seismic forces shall conform to the following references

except as modified by other provisions of this standards

( 1

)

Building Code Requirements for Reinforced Concrete,

(ACI 318-83), American Concrete Institute (ACI), 1983.

(2) Specifications for Structural Concrete for Buildings

(ACI 301-84), ACI, 1984.

5.3 WOOD

The quality, design, and construction of members and their

fastenings in wood systems which resist seismic forces shall

conform to the following references except as modified by other

provisions of this standard:

< 1 ) National Design Speci f i cat i on for Wood Construction,

1982, and Design Values for Wood Constrution, 1982,

National Forest Products Association, 1982.

(2) American Softwood Lumber Standard, Voluntary Product

Standard , PS 20-70, Lh S. Department of Commerce, 1970.

(3) Plywood Design Speci f i cat i on , American Plywood

Association, 1983.

(4) Construction and Industrial Plywood, Voluntary Product

Standard , PS 1-83, U.S. Department of Commerce, 1983.

(5) Standard Specifications for Structural Glued Laminated

Timber of Softwood Species, AITC 117-84, American

Institute of Timber Construction, 1984.

(6) Structural Gi ued-Lami nated Timber, ANSI/AITC

A 190. 1-1983.

(7) Chapter 25: Wood, in Uniform Building Code,

International Conference of Building Officials, 1985.

(8) Part III of the One- and Two-Family Dwelling Code, 198

editions, published by International Conference of

Building Of f i ci al s , Bui 1 di ng Officials and Code

Administrators, and Southern Building Code Congress.

30
( 9 ) Section 4713: "Shear-resisting Construction with Wood

Frame," Uni-form Building Code, International Conference

of Building Officials, 1965.

5.4 MASONRY

The quality and testing of masonry and steel materials and the

design and construction of masonry and reinforced masonry

components that resist seismic farces shall conform to one or

more of the following references, except as modified by other

provisions of this standards

(!) Chapter 24s Masonry, in the Uniform Building Code,

International Conference of Buiding Officials, 1985.

<2' Section 4; Reinforced Masonry, in Seismic Design for

Buildings, TM 5—809—10, Departments of the Army, Navy

and Air Force, 1982.

(3)

Building Code Requirements for Concrete Masonry

Structures, ACI 531-79, American Concrete institute,

(4) American Standard Building Code Requirements for

Masonry, A41. 1-1953, National Bureau of Standards

Mi seel 1 an ecus F’ubl ication , 1954

.

(5) Building Code Requirements for Reinforced Masonry,

A41. 2-1960 (R 1970), American National Standards

Institute,

<6> Specification for the Design and Construction of Load

Bearing Concrete Masonry, National Concrete Masonry

Association, 1970.

(7) Building Code Requirements for Engineered Brick

Masonry, Brick Institute of America, 1969.

(8) Part III of the One- and Two—Family Dwelling Code, 1982

edition, published by International Conference of

Building Officials, Building Officials and Code

Administrators, and Southern Building Code Congress.

5.5 ALUMINUM

The quality, testing, design, and construction of aluminum

members which resist seismic forces shall conform to the

following reference, except as modified by other provisions of

this standard:

31
(1)

Speci f i cati ons -for Aluminum Structures, 4th

Edition, The Aluminum Association, 1982.

5.6 GYPSUM

The quality, testing, design, and construction of gypsum

components which resist seismic forces shall conform to the

following references, except as modified by other provisions of

t h i s s t an Card

:

<1> Section 2627: Reinforced Gypsum Concrete, in Uniform

Building Code, Internet i onal Conference of Building

Officials, 19S5.

(2) Section 4711: Gypsum Wall board, in Uniform Building

Code, International Conference of Building Officials,

1 985

.

(3) Section 5-05; Gypsum Diaphragms, Cast-i n-Pl ace , in

Seismic Design for Buildings, TM 5—809—10, Department

of the Army, Navy, and Air Force, 1982.

(4) Standard Spec i f i cat 1 on for Gypsum Concrete, ASTM

C317-81, 1981.

(5) Standard Spec i f i cat i on for Lightweight Aggregate for

Insulating Concrete, ASTM C332-83, 1983.

(6) Recommended Specifications for the Application and

Finishing of Gypsum Board, The Gypsum Association,

1 982

.

(7) Using Gypsum Board for Walls and Ceilings, The Gypsum

Association, 1980.
6. STRUCTURAL DESIGN DETAILS

Where a single building includes framing systems that have

different values of the coefficient for structural system

response, K, each component common to systems having different K

values shall satisfy the more stringent detailing requirements.

Portions of the following documents are frequently cited in the

provisions of this chapter by a reference number enclosed in

square hr ackets.

Cll Uniform Building Code, Internati onal Conference of

L23 Recommended Lateral Force Requirements and Commentary,

Structural Engineers Association of California, 1980.

C33 Seismic Design for Buildings, Departments of the Army,

Navy and Air Force (TM 5—809—10), 1982.

LAI Specification for the Design, Fabrication, and Erection

of Structural Steel for Buildings, American Institute

of Steel Construction, 1980.

C51 Building Code Requirements for Reinforced Concrete,

American Concrete Institute, 1983 <ACI 318-83).

6.1 MOMENT-RESISTING FRAMES

6.1.1 Ductile Moment-Resisting Space Frames

Ductile moment-resisting space frames shall be structural steel

complying with Section 6.2 or reinforced concrete complying with

Section 6.3.

6.1.2 Concrete Frames

In Zones 2, 3 and 4, all concrete space frames required by design

to be part of the lateral force-resisting system and all concrete

frames located in the perimeter line of vertical support shall be

ductile moment-resisting space frames.

Building Officials, 1985

EXCEPTION

Frame

h='-: 1 in the perimeter line of the vertical support ofgs designed with shear walls taking 100 percent of

ign lateral forces need only conform with Section
6.2 STEEL DUCTILE MOMENT-RESISTING SPACE FRAMES

The design and construction of moment-resistant joints for steel

ductile moment-resi sti ng space frames shall comply with all

applicable requirements for "Type 1 Construction" as defined in

reference C43, unless it can be shown that adequate ductility can

be obtained by deformations of the connection materials and that

the added drift, is accounted for.

In addition, steel ductile moment-resisting space frames for all

buildings in Zones 3 and 4 and buildings with an Importance

Factor I greater than 1.0 in Zone 2 shall comply with the

r equi rements of Section 2722s "Steel Ductile Moment—Resi sti ng

Space Frames" of reference E

1

1 , or Section 4 "Steel Ductile

Moment-Resisting Space Frames" of reference E23, with the following cl ar i f i cat i on s the requirements for "plastic design sections" are the minimum thickness and lateral bracing requirements

(Sections 2.7 and 2.9) of Part II of reference £41.

6.3 REINFORCED CONCRETE DUCTILE MOMENT-RESISTING SPACE FRAMES

The design and construction of concrete ductile moment-resisting

space frames for all buildings in Zone 3 or 4 and buildings with

an importance factor I greater than 1.0 in Zone 2 shall comply

with the requirements of one of the followings

(1) Section 2625s "Reinforced Concrete Structures Resisting Forces Induced by Earthquake Motions" of Reference

Ell.

(2) Section 2s "Concrete Ductile Moment-Resisting Space

Frames" of reference E23.

(3) Paragraph 7-04: "Concrete Ductile Moment-Resisting

Space Frames" of reference E33.

Concrete ductile moment-resisting space frames in other buildings

shall comply with either the previous requirements or the

requirements of reference E51 , plus the following requirements of

this section. The terms "web reinforcement, " "tie," and "spiral"

and the symbol "d" in the following shall be used as defined in

reference E51.

6.3.1 Flexural Members

Web reinforcement shall be required throughout the length of the

member. It shall be designed according to Chapter 11 of

reference E51, except that such web reinforcement shall be not

less than 0.5 percent of the area computed as the product of the

34
width of the web and the spacing

1 ongi tud i nal ax i s of the member . located *1 inches from the col unin

shall be spaced not over d/4.

Positive moment reinforcement at

subject to reversal of moments s! mechanical anchors in or through

t h e y i eld strength of the b ar

.

of web rei nf orcement along the

The first stirrup shall be

f ace . The next six sti r r ups

all supports of flexural members

all be anchored by bond or

the supporting member to develop

Lapped

sha.l 1 splices located in a region of tension ore cunt x red by at 1 ease two c 1 osed 1 1 es at

reversing stress

each splice.

6.3.2 Columns

The spacing of ties at the ends of tied columns shall not exceed

4 inches for a distance equal to the maximum column dimension but

not less than one—sixth of the clear height of the column from

the face of the joint. The first tie shall be located 2 inches

from the face of the Joint. Joints of exterior and corner

columns shall be confined by lateral rei nf orcement through the

joint. Such lateral rei nf orcement shall consist of spirals or

ties as required at the ends of columns.

6.4 BRACED FRAMES

In zones 3 and 4 and for buildings having an occupancy importance

factor , I , greater than 1.0 located in zone 2 , braced frames

shall satisfy the following requirements.

6.4.1 Required Capacity

All members in braced frames shall be designed for 1.25 times the

force determined in accordance with Chapter 4 T STRUCTURAL

ANALYSIS PROCEDURES. Connections shall be designed to develop

the full capacity of the members or shall be based on the above

forces without the one-third increase usually permitted far

stresses resulting from earthquake forces.

6.4.2 Steel Braced Frames

Braced frames shall be composed of axially loaded bracing members

of ASTM A36 , A441 5 A500 T A501 , A572 (Grades 42 and 50)

or A5B8

structural steel. A500 steel shall not be welded.

TC
6.4.3 Reinforced Concrete Braced Frame®

Reinforced concrete members of braced frames subjected primarily

to axial stresses shall have special transverse reinforcing as

specified for axially loaded frame members in the requirements

cited by reference in Section 6.3 throughout the full length of

the member. Tension members additionally shall meet the requirements

for compression members.

6.5

REINFORCED CONCRETE SHEAR WALLS

Reinforced concrete shear walls for all buildings in Zones 3 or 4

and buildings with an importance factor I greater than 1.0 in

Zone 2 shall comply with the applicable requirements of one of

the foil owi ng

:

(1) Section 2625: "Reinforced Concrete Structures Resisting Forces Induced by Earthquake Motions" of reference

C 1 In

(2) Section 3s "Concrete Shear Walls and Braced Frames" of

reference C23.

6.6 REINFORCED MASONRY WALLS

Masonry walls required to be reinforced masonry by Sections 6.9

or 7.5 shall comply with the minimum amount and maximum spacing

of reinforcement specified in Table 6.1.

Splices may be made only at such points and in such manner that

the structural strength of the member will not be reduced.

Lapped splices shall provide sufficient lap to transfer the

working stress of the reinforcement by bond and shear , but in no

case shall the lap be less than 30 bar diameters. Welded or

mechanical connections shall develop the strength of the reinforcement . 6.7 DIAPHRAGMS

6.7.1 Ties Between Chords

Diaphragms providing lateral support to concrete or masonry walls

by means of anchor bolts or similar connections shall have ties

to distribute the anchorage forces into the diaphragm.

6.7.2 Anchorage® to Wood Diaphragm®

In Zones 2, 3 or 4 where? wood diaphragms are used to laterally

support concrete or masonry walls, the anchorage shall not be

accomplished by use of toenails or nails subjected to withdrawal;

nor shall wood framing be used in cross-grain bending or cross-grain

tension

.

36
6.8

OPENINGS IN SHEAR WALLS AND DIAPHRAGMS

Where steps in the edges or openings occur in shear walls or

diaphragms or other plate-like elements, chords shall be provided

at the edges o-f the discontinuity to resist the local stresses

created by the presence o-f the discontinuity. These chords shall

extend into the body o-f the wall or diaphragm a distance sufficient

to develop and distribute the stress of the chord member.

6.9

CONCRETE AND MASONRY ELEMENTS

6.9.1 Reinforcement

All elements within structures located in Zones 2, 3, or 4 which

are of masonry or concrete shall be reinforced so as to qualify

as reinforced masonry or concrete under the provisions of

Sectiion 6.6 for masonry and reference 1153 for concrete.

6.9.2 Anchorage of Walls

Concrete or masonry walls shall be anchored to all floors and

roofs which provide lateral support for the wall. Such anchorage

shall provide a positive direct connection capable of resisting

the horizontal forces specified in this standard or a minimum for

of 200 pounds per linear foot, of wall, whichever is greater.

Walls shall be designed to resist bending between anchors where

the anchor spacing exceed 4 feet. Required anchors in masonry

walls of hollow units or cavity walls shall be embedded in a reinforced grouted structural element of the wall.

6.10

FOUNDATIONS

6.10.1 Ties Between Foundation Units

Unless it can be demonstrated that equivalent restraint can be

provided by other approved methods, ties at approx i mat el y right

angles shall be provided between foundation units as follows?

(1) in Zones 2, 3, or 4, between individual pile caps and

caissons in all buildings

(2) in Zones 3 or 4, between isolated spread footings in

buildings over three stories tall or in buildings

constructed over crawl spaces.

The ties shall resist the induced lateral seismic forces, but not

less than a minimum horizontal force of 0.10(ZI) times the vertical

1 oad on the pile cap, caisson, or footing.

37
6.10.2 Pile Cap Connection®

In Zones 2, 3, or 4, all piles shall be connected to the pile cap

to resist an uplift force of not less than 0.15(ZI) times the

vertical load on the pil e„

6.10.3 Concrete Piles

In Zones 2, 3, or 4, all concrete piles shall be provided with

longitudinal reinforcement sufficient to resist the uplift force

specified in Section 6.10.2 throughout the entire length of the

pile, except that the reinforcement only need be provided in the

upper one-third of the pile in Zone 2.

Furthermore, in Zones 2, 3, or 4, all concrete piles shall be

provided with transverse ties spaced no further apart than 4

inches over the top 4 feet of the pile.

Properly bonded metal casing, such as steel pipe, may be used to

satisfy these reinforcement requirements.
Tabl e 6.1

Mini mum Reinforcement and Maximum Spacing for Reinforced Masonry

Wal 1 s

Type of

Wal 1

! StrucItural

! ( i . e . ,

! bear inq

lor shear)

Total Area 1 of Rein- ! ! for cement as a Percent ! Maximum Spacing of Bars22

! of Gross Area of Wall 1 ( i nches )

! (nominal dimensions) 1 Vertical ! Horizontal 1 Seismic Zones 1 Seismic Zone ! Seismic Zone!

4S/.3 4&3

0 . 20 0. 20 0. IS 72 1

1 Nonstruc— 1 ! ! 1 111 111

Itural 1 0.15 1 0.15 ! 0.15! 48 ! 60! 72 ! 84 ! 84 ! 96!

The total minimum reinforcement is the sum of the vertical

and horizontal reinforcement; not less than 1/3 of the prescribed

total minimum reinforcement shall be used in each direction.

Principal reinforcement in masonry shall be spaced 2 ft

maximum on centers, in buildings using a moment-resisting space

f rame

.
7 NONSTRUCTURAL DESIGN REQUIREMENTS

The requirements of this section apply to all buildings in zones

3 or 4 and to buildings with an importance factor I greater than

1.0 in zone 2.

7.1 ANCHORAGE FOR INERTIAL FORCES

Nonstructural components and their anchorage to the main structural

system shall resist the following lateral seismic forces;

Fp> = ZIC^W^ (Eq. 7.1)

where

Z is specified in Section 4.2.1

I is specified in flection 1.4.2 EXCEPT;

1. For connectors of precast or pref abr i cati on

panels, the value of I shall be as

given in Section 7.2.

2. For the anchorage of machinery and equipment

required for life safety systems, the value of

I shall be 1.5.

is given in table 7.1.

is the weight, of the component, EXCEPT;

1. For storage racks, shall be the weight of

the rack plus contents.

2. For ceilings, Wp shall include all light

fixtures and other equipment which is laterally

supported by the ceiling, and shall be taken

as not. less than 4 pounds per square foot.

The distribution of these forces shall be according to the

gravity loads pertaining thereto.

In lieu of this section, steel storage racks may be designed

in accordance with ANSI Standard MH 16.1--1974, or where a number

of storage rack units are interconnected so that there are a

minimum of four vertical elements in each direction on each

column line designed to resist horizontal forces, the racks may

be designed as a structure in accordance with 4.2.1 with the

design coefficients CS ~ 0.2 and W equal to the total dead load

p 1 us 50 p er c en t of t h e rac k -rated cap ac i t y

.

7.2 DISTORTION COMPATIBILITY FOR EXTERIOR PANELS

Precast, or pref abr i cated nonbearing, nonshear wall panels or

similar elements which are attached to or enclose the exterior

40
shall be designed to resist -forces determined -from Eq. 7„ 1 and

shall accommodate movements o-f the structure resulting -from

lateral forces. The concrete panels or other similar elements

shall be supported by means of cast-in-place concrete or mechanical

connections and fasteners in accordance with the following provisions

Connections and panel joints shall allow for a relative movement

between stories of not less than the drift calculated in Section

4.4.7 or 1/2 inch, whichever is greater. Connections to permit

movement in the plane of the panel for story drift shall be

properly designed sliding connections using slotted or oversized

holes or may be connections which permit movement by bending of

steel or other connections providing equivalent sliding and duct .i 1 .i. t y c ap ac i t y

.

Bodies of connectors shall have sufficient ductility and rotation

capacity so as to preclude fracture of the concrete or brittle

failures at or near welds.

The body of the connector shall be designed for one and one-third

times the -force determined by Eq. 7.1. Fasteners attaching the

connector to the panel or the structure such as bolts, inserts,

welds, dowels, etc:., shall be designed to ensure ductile behavior

of the connector or shall be designed for four times the load

determined from Eq. 7.1.

Fasteners embedded in concrete shall be attached to or hooked

around reinforcing steel or otherwise terminated so as to

effectively transfer forces to the reinforcing steel.

The value of the coefficient I shall be 1.0 for the entire

connector assembly in E.’q. 7.1.

7.3 PROTECTION AGAINST SECONDARY HAZARDS

Hazardous contents and services shall not. present undue hazard to

life in the event of seismic ground shaking. As a minimum, for

Essential Facilities and High Risk occupancies (I = 1.5 and 1.25,

respectively) in zones 3 and 4, the utility and service interface

of all gas, hi gh~t.emperat.ure energy, and electrical supply shall

be provided with shutoff devices or special protection.

7.4 FUNCTIONALITY OF ESSENTIAL ELEMENTS

The design and detailing of equipment which must remain in place

and be functional following a major earthquake shall be based

upon the requirements of Section 7.1. In addition, their design

and detailing shall consider effects induced by the structural

drift calculated in Section 4,.4.7. Special consideration shall

also be given to relative movement at separation joints.

41
7.5 REINFORCEMENT OF CONCRETE AND MASONRY

All nonstructural elements within structures located in zones 3

or 4 which are of masonry or concrete shall be reinforced so as

to qualify as reinforced masonry or concrete as defined in

chapter 5, DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL

MATERIALS and chapter 6, STRUCTURAL DESIGN DETAILS. Principal

reinforcement in masonry shall be spaced 2 feet maximum on center

in buildings using a moment-resisting space frame.
Table 7.

1

% Horizontal Force Factors C^ for Nonstructural

Elements of Buildings

Component

Direction of Value of

Horizontal Forces of

Exterior and interior walls S< Normal to flat

partitions surface

Masonry or concrete fences

over 6 feet high

Cantilever elements:

a. Parapets Normal to flat

surf ace

0 . 2

0 . 8

b. Chimneys or stacks Any direction 0.8

Exterior and interior ornamentations S< appendages Any direction 0.8

When connected to, part of,

or housed within a build—

i ng

:

a. Penthouses, anchorage for*'

chimneys and stacks and

tanks, including contents

b. Storage racks with upper

storage level at more

than 8 feet in height, I Any direction

plus contents \

c. All equipment or

mach i nery

d. Large ducts, large pipes,

and critical or hazardous

pipes

J

Suspended ceiling framing

systems Any direction

r>

0 ,

43
Table 7.1 (continued)

1. Cp for element® laterally sel f -supported only at the ground

level may be two-thirds of value shown.

2. For flexible and flexibly mounted equipment and machinery,

the appropriate values of Cp shall be determined with consideration given to both the dynamic proportion of the equipment

and machinery and to the building or structure in which it is

placed but shall be not less than the listed values. The design

of the equipment and machinery and their anchorage is an integral

part of the design and spac i f i cat i on of such equipment and

mach i nery.

3. The value of Cp for racks over two storage support levels in

height shall be 0.24 for the levels below the top two levels.

44
8 » CONSTRUCTION QUALITY CONTROL

In accordance with agency quality assurance procedures, all

buildings in zones 3 or 4 and buildings with an importance factor

I greater than 1.0 zone 2 shall be subject to inspection by the

designated authority, and certain types of construction shall

have special inspection to assure the quality and performance of

the seismic resisting systems, as specified in this section. The

requirements in the section supplement existing agency programs,

but do not replace them.

8.1 SPECIAL INSPECTOR

A special inspector shall be employed by the designated authority

during construction to observe the work specified in 8.2 to be

certain it conforms to the design drawings and speci f i cat i ons.

The designated authority may waive the requirement for a special

inspector if he finds that the construction is of minor nature.

8.1.1 Qual i f i cat i ons

The special inspector shall be a qualified person who shall

demonstrate his competence, to the satisfaction of the designated

authority, for inspection of the particular type of construction

or operation requiring special inspection.

8.1.2 Inspection Reports

The special inspector shall furnish inspection reports to the

designated authority, the engineer or architect of record , and

other designated persons. All d i scr epanc i es shall be brought to

the immediate attention of the contractor and the engineer or

architect of record for correction, then, if uncorrected, to the

designated authority.

8.1.3 Final Report

The special inspector shall submit a final signed report stating

whether the work requiring special inspection was, to the best of

his knowledge, in conformance with the approved plans and

spec i f i cat i ons and the applicable workmanship provisions of these

codes

.

8.2 REQUIRED SPECIAL INSPECTION

The following objects and operations shall be subject to continuous

inspection by a special inspector. Some inspections

45
may be made on a periodic basis and satisfy the requirements of

continuous inspection, provided this periodic scheduled

inspection is performed as outlined in the project plans and

specifications and approved by the designated authority. Special

inspections required by this standard shall not be required where

the work is done on the premises of a fabricator approved by the

designated authority to perform such work without special

i nspect i on

.

8.2.1 Piling, Drilled Piers and Caissons

During driving and testing of piles and construction of

cast-in-place drilled piles or caissons. See Sections 8.2.3 and

8.2.4 for concrete and reinforcing steel inspection.

8.2.2 Excavation and Filling

During earthwork excavations, grading, and filling operations

inspection to satisfy the requirements of the plans and

speci f i cations.

8.2.3

Concrete

During the taking of test specimens and placing of all reinforced

concrete and pneumatically placed concrete.

EXCEPTIONS;

(1) For foundation concrete when the structural design is

based on f no greater than 2000 psi .

(2) Nonstructural slabs on grade, including prestressed

slabs on grade when effective prestress in concrete is

less than 150 pounds per square inch, unless the slab

is used as a tie to satisfy Section 6.10.1.

(3) Site work concrete f ul 1 —supported on earth and concrete

where no special hazard exists.

8.2.4

Reinforcing Steel and Prestressing Steel

During all stressing and grouting of prestressed concrete, and

during placing of reinforcing steel, placing of tendons and

prestressing steel for all concrete required to have special

inspection by Section 8.2.3.

46
EXCEPTION:

The special

reinforcing

provided he

plans prior

concrete to

inspector need not be present during entire

steel and prestressing steel -pi aci no operations,

has inspected for conformance with the approved

to the closing of forms or the delivery of

the job site.

8.2.5 Ductile Moment-Resisting Concrete Frame

Continuous inspection by a specially qualified inspector under

the supervision of the person responsible for the structural

design during the placement of r ei nf or cement and concrete.

8.2.6 Welding

(1) All structural welding, including welding of reinforcing

steel

.

EXCEPTIONS:

When welding is done in an approved fabricator's shop; or

when approved by the designated authority, single-pass

fillet welds when stressed to less than 50 percent of the

allowable stresses and floor and roof deck welding and

welded studs when used for structural diaphragm or composite

systems may have periodic inspections. For periodic

inspection, the inspector shall check qualifications of

welders at start of work and then make final inspection of

all welds for compliance prior to completion of welding.

( r>

)

Ductile moment -resi sti ng steel frames shall receive the

following nondestructive testing:

Welded connections between the primary members of ductile

moment-resisting space frames shall be tested by

nondestructive methods, either ultrasonic testing or

radiography, for compliance with the AWS

Structural Welding Code (D1 . 1 -84) and job specifications. A

program for this testing shall be established by the

engineer responsible for structural design and as shown on

plans and specifications. As a minimum, this program shall

include the following:

<a) All complete penetration groove welds contained in

joints and splices shall be tested, 1007. either by

ultrasonic testing or radiography.

47
EXCEPTION

When approved, the non-destructive testing rate tor an

individual welder or welding operator may be reduced to

25 percent, provided the reject rate is demonstrated to

be five percent or less of the welds tested for the

welder or welding operator. A sampling of at least 40

completed welds for a job shall be made for such

reduction evaluation. Reject rate is defined as the

sample number of welds that do not pass the tests

divided by the sample number of welds inspected. For

evaluating the reject rate of continuous welds over 3

feet in length where the effective size is 1 inch or

less, each 12— inch increment or fraction thereof shall

be considered as one weld. For evaluating the reject

rate on continuous welds over 3 feet in length where

the effective size is greater than 1 inch, each 6

inches of length or fraction thereof shall be

c ons i der ed one we 1 d

,

When approved by the designated authority and outlined

in the project plans and specifications, this

nondestructive testing may be performed in the shop of

an approved f a.hr i cat or ut i 1 i z i no qua! i f i ed test

techniques in the employment of the fabricator.

(b> All partial penetration groove welds when used in

column splices shall be tested when required by the

plans and specifications.

<c> Base metal thicker than l-i/2 inches, when subjected to

through-thickness weld shrinkage strains, shall be

Inspected by ultrasonic testing or radiography for

discontinuities directly behind such welds after joint

completion. Any material discontinuities shall be

accepted or rejected on the basis of the defect rating

in accordance with the criteria of the AWS

Structural Welding Code (D1 . 1-84)

.

8=2.7 High-Strength Bolting

During all bolt installations and tightening operations.

EXCEPTIONS;

(1) The special inspector need not be present during

the entire installation and tightening

operation , provided he;

48
(a) inspects the surfaces and bolt type, including

diameter and length, -for conformance to plans and

specifications prior to start of bolting, and

(b) will verify the minimum specified bolt tension for

10 percent of the bolts for each "type" of

connection, for a representative number of total

connections established by the plans and

specif i cat i ons.

(2) In bearing—type connections when threads are not

required by design to be excluded from the shear plane,

inspection prior to or during installation will not be

r squired

.

B.2.8 Structural Masonry

During preparation of masonry wall prisms, sampling and placing

of all masonry units, placement of reinforcement, inspection of

grout space, immediately prior to closing of cleanouts, and

during all grouting operations. Where the f is less than 2600

psi and special inspection stresses are used, test specimens mayconsist of either one prism test for each 5000 square feet of

wall area or a series of tests based on both grout and mortar for

the first 3 consecutive days and each third day thereafter.

EXCEPTION? Special inspection will not be required for

structures designed in accordance with the values in appropriate

tables for noncont i nuous inspection.

8.2.9 Reinforced Gypsum Concrete Used as a Diaphragm

When cast— in-place Class "B" <1000 psi minimum compressive

strength) gypsum concrete is being mixed and placed.

8.2.10 Insulating Concrete Used as a Diaphragm

During the application of insulating concrete.

EXCEPTION;

The special inspection may be limited to an initial

inspection to check the deck surface and placement of

reinforcing. The special inspector shall supervise the

preparation of compression test specimens during this

Initial inspection.

49
8.2.11 Special Cases

Any other work which, in the opinion o-f the designated

requires special inspection.

authority
!

if" L ITA l'T<V

* . J i v a a ¥ IIubw a ‘Hi! a # 'is a, §

i

i

i

.
TABLE OF CONTENTS

REGULATION

Fags

C6

Cl - 1 SCQPS .1 C 1 , 2 De-f i n i t i on 5 . . . . . , . . = , C 1 » 3 Notat ion * . .

.

. . . . . . . * , Cl „ 4 Hazard Cl assi-f i cation;

C6

C7

C9

CIO

Cl. 4.1 Seismic Ground Shaking Hazard .... Cl .4.2 Occupancy Hazard .................

Cl 1 C12

Cl Alternative Provisions ..... GENERAL REQUIREMENTS ........

C 1

2

Cl 4

C2. 1. General Performance Requirement

Lk. 2 site Pi anni nq t or New Bui 1 ox nos

C 1 4

ro *t> 1 c -; +- r-. cr. 4- •; tr 4- , iri,,

•_J -C_ a -Z. 3 1 JL L :~ 3 V a J. '.•.a U A Ul! —! U. l_! y

'“I r-1 J~! Bite Limitation;

C 1

4

Cl 4

Desi gn o-f New Bui 1 dings ......... construct i on ....................

CIS

r-1 ET u i J

CIS

L, ’Z. .

u_< 2L = -_J

A ] 4— j—i u— ni u —T ( Li GHa cr.k Hi Li rVcfpfil f

.i! Lr h- <=*. n q ?=* of Use *_j f~ lcls.1i i ons » Ci^j

C16

STRUCTURAL DESIGN CRITERIA . Seismic Force—Resi sti nq Systems

C 1

7

C17

C3. 1 . 1 Integr i ty ....................... C3.1.2 System Response Classification ..

L-j* . 1 . btr enqth ........................

C3.1.4 Sti-f-fness and Building Separation;

C3.1.5 Overturning Stability ...........

C3. 1 . 6 Hei ght ..........................

CIS

CIS

C 1

9

C20

C20

C21
TABLE OF CONTENTS (CONTINUED)

C3.2 Other Structural Elements * 03,2=1 Strength and Anchorage ...... C3.2.2 Compatibility

C3.3 Foundations

Page

C21

C21

C21

C21

C3.3.1 Soil and Foundation Capacity ......... C21

C3. 3. 2 Structural Duct l lity ................. C22

C4. STRUCTURAL ANALYSES PROCEDURES C23

C4 , 1 C4 2

Required Method -for Seismic—Resisting

Elastic Static Lb ad Analysis

systems i C23

C23

C4 ,2.1

C4, 2.

2

C4 .2.3

C4.2.

4

Base Shear .................... Period of Vibration

Site Coefficient .............. Vertical Distribution of Force;

C23

C24

C24

C24

i_4 . j El ast 1 Dynami Load Anal yai s C4.3.3 Design Values

.4 El ast Load Effect Analysis ,

i

C4 .4.1 Shear ................. C4.4.2 Horizontal Torsion .... C4.4.4 Overturning .......... C4.4.5 Orthogonal Effect ..... C4.4.6 Vertical Motion Effect

C4.4.7 Displacements ........ C4.5 Analysis of Other Structural Elements

C2'

C2E

C2!

C26

C26

C26

C27

C27

C27

C5. DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL

MATER I ALS .......................................

5. 1 Steel

5.2 Concrete . 5. 3 Wood ..... 5.4 Masonry .. 5.5 Aluminum . 5.6 Gypsum ...

C2S

C28

C29

C3
TABLE OF CONTENTS (CONTINUED)

6) m STRUCTURAL DESIGN DETAILS

6. i Moment-Resisting Frames

6.1.1 Ductile Moment-Resisting Space Frames

6. 1.2 Concrete Frames ......................

6.2 Steel Ductile Moment-Resisting Space Frames , 6.3 Rein-forced Concrete Ductile Moment-Resisting

Space Fr ames

cj . . i FI ex ur <ri 1 Members .......... ..........i

6.3.2 Col umns ..............................

O c i— * ' Li ! f Si. ! i ! ^— —, ..............................01

6.4.

1

Required Capacity. ............... .... s 6. 4.

2

Steel Braced Frames. .................. 6.4=3 Reinforced Rein -c ore Concrete Braced Frames....,

£ u 5 Rei n -forced Cone

6 . £ Reinforced Maso

6j d / Di aphragms

.

EBBS

6 . S

Q „ V

6.7. 1 Ties Between Chords. ............ 0.7.^ Anuhof aijaa to Wood Dx cspiif egnvn. . . Openings in Shear Walls and Diaphragms.

Concrete »nd

Rei nf or cement

.

6.10 Foundation s

,

6 . 10.

1

Between Foundation Units.

Pile Cap Connections.

6. 10. 3 Con of ete Pi ls=. .......

7. NONSTRUCTURAL DESIGN REQUIREMENTS...

7.1 Anchorage tor Inertial Forces.

C4

Page

C30

C30

C30

C30

C31

C32

C32

C32

ryt -~ C32

r^T,

C33

C33

C33

C34

C34
TABLE OF CONTENTS (CONTINUED)

Page

Distortion Compat i bi I i ty for Exterior Panels... C34

Protection Against Secondary Hazards. .......... C34

Functionality of Essential Elements. ........... C34

Reinforcement of Concrete and Masonry. ......... C34

CONSTRUCTION QUALITY CONTROL. C35

Special Inspector.

5 . 1 . 1 Qual i f i cat i ons ..........................

8.1.2 Inspection Reports......................

8.1.3 Final Reports...........................

Required Special Inspection. ................... C35

8 . 2 . 1 8 . 2.2

8.2.3

3.2.4

8.2. 5

8 . 2.6

8.2.7

8 . 2.8

8. 2. 9

8 . 2. 10

8 . 2.11

Pi ling ^ Drilled Piers and Caissons......

Exuavati on and Fixiing. . . . . . . . . . . . . . . . . .

—i cd ( i •_ r lj t ................................ Reinforcing Steel and Prestressing

_j t 1 —

1 e j. ...................................

Ductile Moment—Rest st i ng Concrete

r r* 3fH & 33EB3ait3B 'iII30A3SSBaa3CBXaaa3SI3BSa:

Welding.................................

High-Strength Bolting. .................. Structural Masonry. ..................... Reinforced Gypsum Concrete Used as a

D x rf p h r a .{ m ..... .............. ....... . . . . . Insulating Concrete Used as a Diaphragm.

Special Cases.

C5
SEISMIC DESIGN GUIDELINES FOR FEDERAL BUILDINGS

- COMMENTARY -

Cl. REGULATION

Cl . 1 SCOPE

These guidelines are primarily intended -for new buildings.

Structures that are not associated with buildings are outside the

scope because their particular -functional requirements and the

nature of hazard they present have not been considered in

developing the requirements of these guidelines and because the

idealization of seismic loadings presented in these guidelines

may not be an appropriate model for predicting their physical

response to seismic ground shaking. Another exception is that

buildings and structures associated with nuclear power plants are

subjected to the more rigorous requirements of the Nuclear

Regu 1 a t or y Commission.

The coverage of existing buildings in these guidelines is briefs

future reports planned for issue by the Interagency Committee on

Seismic Safety in Construction (ICS'SC) are expected to provide

more specific criteria for those occasions when the requirements

of these guidelines indicate the need for their application. The

application of these guidelines to Federally leased buildings and

to Federal grant and regulatory programs is also expected to be

c over ed i n f utur e I C3SC reports

.

The reference to varying degrees of safety is, in part, a

recognition that different levels of reliability are desired for

buildings that present different risks. Just as in the Uniform

Building Code (UBC) , these guidelines accomplish this purpose bymeans of a numerical coefficient (the Importance Factor, I) for

occupancy hazard, which is specified in Section 1.4.2. The

statement is also a recognition that some provisions are based on

approximations and may result in different levels of safety for

di f f erent si tuati ons

.

These guidelines are limited to consideration of the effects of

seismic ground shaking. Other seismic effects, such as tsunami,

and other environmental loads, such as wind, are not within the

scope. Existing codes and -standards commonly contain clauses

pertaining to wind forces in

and overturning resistance.

man y p r ov i si ons , such as stiffness

No such clause is in these

guidelines, because criteria for resistance to the two forces are

too different. The response to seismic ground shaking will

ordinarily require inelastic straining of the seismic

fores—resisting system, thus the many ductility and detailing

06
requi rtoisnts in these guidelines must be satisfied even far

buildings in which wind force exceeds the nominal design seismic

-farce. For buildings i n which the nominal design seismic force

exceeds the nominal design wind force, it is likely that wind

requirements may yet control the design of various components

because the local pressure and suction coefficients may create

higher force resultants or because the drift criterion is

different for wind than for seismic loadings, and so on. Thus,

no comparisons of the two loadings are stated or implied in the

provisions of the guidelines. Similarly, design for seismic does

not exclude the need to evaluate other non—seismic sources of

1 oad i n q such as wind.

Cl.

2

DEFINITIONS

The bulk of the definitions are taken from, or based upon the

Uniform Building Code. In all the definitions an emphasis has

been placed on lateral seismic forces when compared to the

definitions in the UBC, although are sources are used. The

reference is shown below for each definition. Unless otherwise

noted, the source definition is used word for word.

approved - UBC Section 402 (except the term "designated

a.atnur xty. wn i Lh is definec in these guideline^, i ^ substituted for the term "building official")

.tructure UBC Section 2312(b)

bearing wall — UBC Section 424

box system — Modified from UBC 2312(b) whi

system is a structural system without

ver 1 1 c a 1 1 oad carrying space frame.

rsqui red lateral forces are resisted

braced f r <=* m s as her Bi. Hdl defined,

thought to be simpler and clearer but

to change the meaning. Al=>o see the

ch reads "Box

a complete

In this system the

by shear walls or

" The change was

was not intended

d i scussi on i

n

Chapter 3 of this commentary

.

ad frame - UBC Section 2312(b), except "lateral forces"

is changed to " lateral seismic forces" and "by the

seismic forces" is added after axial stresses. The

rewording was done to clarify that the source of the

lateral forces is due to an earthquake and not some

other source such as wind.

C7
building - UBC Section 403

dead load - UBC Section 2302

designated authority - The definition is original, and in

the center t of the UBC it can be thought to replace the

term building official (which uses similar wording in

its definition) which was not appropriate for use in

these guidelines since the government representative

may not be a building official

=

diaphragm — A definition was not available in the UBC. The

definition is based upon that used in Chapter 2 of the

NEHRP Provisions and is similar to ANSI A5B.1.

dual system - Not explicitly defined in the UBC. The

definition can be inferred from UBC Table 23—1 from the

description of a system using a K factor of 0.80.

Since the phrase is widely used, a formal definition

was desirable. Also see discussion in Chapter 3 of

this commentary

.

ductile moment—resi sti ng space frame - Based on UBC Section

2312(b) which uses “Ductile moment-resisting space

frame is a. moment-resisting space frame complying with

the requirements for a ductile moment—resi sti ng space

frame as given in Section 2312(j)." The requirements

given in that section are intended to provide the

capability to undergo inelastic straining. Similar

requirements are in these guidelines.

ductile moment—resisting space frame system - A si mi liar

phrase is not used in the UBC but is used in the NEHRP

Provisions. Its use simplifies discussion of seismic

resisting resisting systems. Also see discussion in

the Chapter 3 of this commentar y . essential facilities - UBC Section 2312 (k)

ex ter

i

or wall — UBC Section 424

!—l ,—. — i—c

!—. 4*

1 iCA ql L - The d5t IHl tl UH I b U?’ 1 y 1 n d I j but is consistent with

4- he use of the terms in the UBC. UBC uses the phrase

ii hei ght of building" defined in Sect! on 409.

high risk facility - The phrase is not explicitly used in

the UBC; however, the phrase was developed for use with

the UBC description of the building used for the type

cf uccupancey requiring an importance factor of 1.25 in

C8
LU

hUBC Table 2-5—K« The definition used here and the

description in the UBC are identical.

live load - UBC Section 2302

moment-resisting space frame - Based on UBC Section 2312(b)

which reads " Moment-resisting space frame is a vertical load-carrying space frame in which trhe

members and joints are capable of resisting farces

primarily by flexure." The phrases are added for

clarity and emphasis and are not intended to change the

definition.

parapet wall - UBC Section 424

seismic force-resisting system — The phrase is not used

explicitly in the UBC. The definition is based on a

modification of that used in Chapter 2 of the NEHRP

Provi si ons.

shear wall - UBC Section 2312(b)

- pe l_ e fr ame UBC ejection Bo• 1 2 ( b ) . The definitions which

are repeated here are for the purpose of clarifying the

V*aF i OUb t yp S Ot 'IpdLy I r structure - UBC Section 420

Cl.

3

NOTATION

ach of the symbols used in section 2312(c) of the UBC is used

or the same meaning in these guidelines. The verbal expression

defining a few of the symbols is changed from the UBC in an

attempt to make the collected notation more complete; however

,

the use in the various equations has not changed. Addi tionly,

the section and equation in which the symbol is used is

frequently provided in the definition. In addition, several new

symbols are added for modal analysis equations that appear in

these guidelines that are not found in the UBC since the UBC does

does not cover dynamic analysis. Only modified or new symbols are

discussed below.

Mod i f i ed Symbols

C - Adds the phrase "for the vibratory response of a structure to to seismic motions" to clarify use of

the symbol.
Cp - Adds the phrase "-for the vibratory response of a part of a structure to seismic motions" to clarify

use of the symbol

.

Ft, Fn , Fx - Changes the phrase "lateral force" to

"lateral seismic force” to clarify the source of

the loading.

Fp, - Changes the phrase "lateral" to "lateral seismic

force to clarify the source of the loading.

I - Adds the phrase "numerical coefficient for

occupancy hazard" to clarify the use of the

symbol

.

K - Adds the phrase "numerical coeffieient for

structural system response to seismic motions" to

clarify the use of the symbol.

- Adds the phrase "in response to seismic motions"

to clarify the use of the symbol.

- Changes the phrase "lateral force" to "lateral

seismic force" to clarify the source of the

1 oad i ny

«

Adds the phrase "for the seismic hazard zone" to

clarify the use of the symbol.

- Adds the phras

'i br at i on "

•— J. C3 !

-;d in determine the period of

y the use of the symbol.

Syi"! : fa Li i. rs T Ur U fcr With iTI Od S X ai idl ysl S

II I J II I j m ? ^ < V m j ^ x m 5 01 m ? 0xi

Cl.

4

HAZARD CLASSIFICATIONS

Bui 1 ding

as they

I i kei i ho

oc c up an c structu.r

af t? Ubtd

s are c 1 assi f i ed on two

are in the UBC. One sc

od of ssisrn i c a c t i v i t y , e importance factor, re

al failure due to an ea

throughout the g u x d e 1

i

scales in these guidelines, much

ale, the zone, related to the

and the other scale, the

i at es to che consequences of

rthquake. These classifications

n es to determine tne appl i ca&i

1

1 ly

of specific requi cements. Tab

I

Lns use of these hazard classx

f

should be noted that there are

e Cl summarizes, very generally,

i cations for this purpose. It

several differences with the UBC.

C 1

0
Cl. 4.1 Seismic Ground Shaking Hazard

The map in this document has been derived -from the "Effective

Peak Vel oc i ty—Eel ated Acceleration" map contained in the NEHRP

Commentary. It has the following char ac ter i st i cs necessary for

consistent use with the basic provisions of the guidelines:

(1) It is a zone map, not a contour map, with Zones, 0, 1, 2, 3,

and 4.

(2) The boundaries are smooth lines that do not necessarily

accomplish mi crozonat i on

.

(3) The relative design acceleration for the five zones 4

through 0 is in the proportion 1 s 3/4 : 3/8 : 3/16 : 0,

respecti vel y

.

There are other maps with these characteristics. The Subcommittee

on Standards for Buildings preferred this particular map over the

current UBC map because it was developed on a basis of consistent,

risk across all zones and over the NEHRP "Effective Peak Acceleration

map because it accounts for the effect of large, distant earthquake

on tall buildings. The map is the same as that used in ANSI

A58. 1 and similar to the one proposed by SEAOC for a UBC Code change.

It is expected that improvements will be made in the map as

knowledge is accumulated in the extensive research programs

ongoing in seismic hazard assessment. It should be expected that

individual site evaluations will vary with regard to this map,

because it is not possible to microzone with such a microzone

with such a map. These variations may be particularly significant

in the zones of highest seismicity. Various catalogs are

available that correlate the seismic hazards in cities of

interest around the world with the seismic hazard zones used for

design in the United States.

Some buildings will be located on sites for which a comprehensi ve

site evaluation will have been performed, and thus a site-specific

value for design ground acceleration will occasionally be

available. It is not possible to microzone on the map included

in these guidelines and thus, in many instances, such site

specific accelerations may not be equivalent to the ground

acceleration implied by the map. The relation to obtain a zone from a value of site-specific ground acceleration is

provided for such buildings. Such a relation is necessary for

the proper application of detailing requirements that depend on

the zone even though the seismic forces on such buildings will

normally be calculated directly from the si te-spec i f i c ground

Cl 1
acceleration. The relation for the conversion is based on the

assumption that the design ground motion would have, roughly, a

0.002 chance of being exceeded in one year. For approved site

evaluations based on a different probability of earthquake

occurence, the values in the table should be adjusted

accordingly. The assumption corresponds to the basis for the map

in this document.

Cl. 4. 2 Occupancy Hazard

The categories of occupancies in this section are the same as in

section 2312 (k) and Table 23—K of the UBC with these exceptions:

power stations and other emergency utilities are added to the

essential category, and buildings in which the occupant's

mobility is restricted or impaired or in which the contents are

hazardous are added to the high risk category. The term "high

risk facility" is new in this document but its definition 'see

definition commentary) is the same as the description of the use

in UBC

.

Occupancy Importance can be a relative matter. For example,

small police stations might be of less concern than a headquarters building. Similarly, all hospitals may not be of

equal importance. The single hospital that provides the only

service in a large isolated area is a critical resource. But a

hospital that is one of many may, if necessary, transfer its

services to others. In some instances, a small nursing home may

become i. itica.l. General guidance on these matters is outside

the scope of these guidelines. Local emergency plans may be the

most appropriate means of attackinlg such matters.

Cl. 5 ALTERNATIVE PROVISIONS

This provision is very general and is intended to allow new

and/or innovative systems and means of analysis not covered in

the guidelines to be used if they satisfy the designated

authority as to their level of safety. Similar provisions are

found in Section 2312(a) of UBC for materials and Section 2312(i)

of UBC for analytical methods.

Cl 2
TABLE Cl APPLICABILITY OF REQUIREMENTS

Zone Occupancy Importance Factor

1 1 , 25 1 D J

0 (a) (a) (a)

1 (b) <b > (b)

n (b) (c) (c)

:r (c) < c ) C c ) + ( d

)

4 Ce) ( 0 ) (e) + (d)

KEY:

( a ) no requirements apply

<b? basic structural resistance required

(c) provisions consistent with current practice in California

required, including upgraded ductility, nonstructural

component resistance, and improved quality control

(d) special site evaluations required for some buildings

(e) modal analysis required for some buildings

C 1

3
C2. GENERAL REQUIREMENTS

This document is intended to be self contained with regard to

seismic design requi r entente. Thus this chapter contains general

provisions that might apply to all areas of design and not just

seismic. Accordingly they would be found in the general

requirements of a building code and not specifically in a chapter

on seismic: design.

C2.1 GENERAL PERFORMANCE REQUIREMENT

This very general requirement is essentially the same as the

first sentence of the seismic provisions in UBC Section 2312(a),

The exemption for Zone 0 merely gives formal recognition to

present practice, although designers would be well advised to

satisfy the intent of Section 3.1.1 of these guidelines even in

Zone 0, particularly for important structures.

C2.2 SITE PLANNING FOR NEW BUILDINGS

C2.2.1 Site Evaluation Study

This section is quite similar to the present practice of the

Army, Navy, Air Force, and the Veterans Administration. The

requirement is not arbitrarily applied to all essential

facilities in high risk zones for reason of economics. The cost

of the site evaluation could exceed the cost of the building for

very small important structures such as some fire stations, which

might not be the most efficient way of providing the additional

reliability desired. Nor should the requirement for all

hospitals be arbitrarily extended to all medical buildings;

clinics and other small medical facilities may be provided with

additional safety without resorting to full site evaluations.

Thus, the designated authority is called upon to judge each case

on its own merits. Procedures for carrying out site evaluation

studies and guidelines for the approval of site evaluation

studie are described in TR—2, "Evaluation of Potential Surface

Faulting and other Tectonic Deformation; " TR-3, “Evaluation of

Earthquake— Induced Ground Failure;" TR—6, "An Introduction to

Technical Issues in the Evaluation of Seismic Hazards for

Earthquake—resistant Design;" and TR-8, "Tsunamis; Hazard

Definition and Effects on Facilities" all published by the Inter—

a g enc y

r ommi ttee on Se i sm i c Saf et y in Construc t i on

.

C2.2.2 Site Limitations

Note that the requirement for siting essential facilities to

C 1

4
avoid sir-face rupture due to -fault di spl acsment does not apply to

those essential facilities for which no site evaluation study is

performed. Various engineering solutions for liquefaction,

landslide, and subsidence problems exist, but ro criteria are

provided in these guidelines. The ICSSC manual s previously

ef e*- -C8 j i rlI ud*.: some 1 n f or mat i on on these subjects.

C2.3 DESIGN OF NEW BUILDINGS

The bull- of these guidelines deals with design. This section

merely establishes the appi icabi 1 i ty of the design requirements

and requires a standard amount of documentation to confirm

amp 1 1 a n c: e with the r equi remen t s

.

C2.4 CONSTRUCTION

The importance of quality assurance cannot be overstated.

FL'uc't -t: agencies ha’^e qeneral quality* assurance programs; this

provision supplements, but does not replace, those agency

provisions in the higher seismic zones for issues of special

c on c er n i n se i

s

m i c safet y

.

C2.5 EXISTING BUILDINGS

C2.5.1 Alterations and Repairs

These guidelines contain limited criteria for existing

buildings. Future reports by the ICSSC will include more detail

on the subject. The UBC requirement in Section 104(b) for

existing buildings is rather different and is quoted below;

Additions, alterations or repairs may be made to any

building or structure without requiring the existing

building or structure to comply with all the

requirements of this code, provided the addition,

alteration or repair conforms to that required for a new building or structure. Additions or alterations

shall not be made to an existing building or structure

which will cause the existing building or structure to

he in violation of any of the provisions of this code

nor shall such additions or alterations cause the

existing building or structure to become unsafe. An

unsafe condition shall be deemed to have been created

if an addition or alteration will cause the existing

building or structure to become structurally unsafe or

overloaded; will not provide adequate egress in

compliance with the provi onons of this code or will
obstruct existing exits; will create a -fire hazard; will

reduce required fire resistance or will otherwise create

conditions dangerous to human life. Any building so

al ered, which involves a change in use or occupancy, shall

not exceed the heighty , number of stories and area permitted

for new buildings. Any building plus new additions shall

not exceed the height, number of stories and area specified

for new buildings. Additions or alterations shall not be

made to an existing building or structure when such existing

building or structure is not in full compliance with the

pravi cions of this code except when such addition or

alteration will result in the existing building or structure

being no more hazardous based on life safety, fire safety

and sanitation, than before such additions or alterations

a r e undertaken

,

The second paragraph of 2.5.1 is taken from 23 1 2 < j ) 2

A

of the

UBC . Note that over-strengthening one portion of a building could

cause higher loads in other portions of the building and thus

bho j

; j u b v i u ed . C2.5.2 Changes of Use or Location

Ties section is similar to intent and wording of UBC Section

104(e) which says "Buildings or structures moved into or within

the jurisdiction shall comply with the provisions of this code

•for new buildings or structures" except that change of use is

added to the requirement.

C 1

6
CLTJ

LI

C3 STRUCTURAL DESIGN CRITERIA

Chapter 3 includes the governing criteria for the structural

rtians of a building. Reference is made to Chapter 4 for the

etermi nati on of the force effects of seismic ground shaking, to

hap ter 5 for the basic standards for proportioning structural

components, and to Chapter 6 for special details important to

assure the assumed behavior of the seismic -force-resisting system

in an earthquake.

C3. 1 SEISMIC FORCE-RESISTING SYSTEMS

The ground motions observed in past large earthquakes are greater

than those corresponding to the forces prescribed in this

document (or in any other current standards for ordinary

structures) . In spite of discrepancy between real and implied

ground motions, many buildings designed according to the UBC and

similar standards have performed well in past earthquakes. The

seismic force-resisting systems described in some detail in this

section are based on UBC Section 23 1 2 ( j) and UBC Table 23—1.

There is no intended conflict between these guidelines and the

UBC. However, it is intended that the organization of the

material will clarify the systems and selection of K—factors.

There are several factors that contribute to this successful

performance, but ductility, the ability of a structure to be

strained beyond its elastic limit, is probably the most important

factor. Large earthquakes will ordinarily subject some portions

of a building to repeated cycles of inelastic strain. Thus, it

is important for a designer to define a seismic force-resisting

system. The seismic force-resisting system must be designed and

constructed with special attention so that it will maintain its

resistance while undergoing the repeated cycles of inelastic

straining caused by strong ground shaking.

The seismic force-resisting system will frequently be a subset of

the overall structural system. For example, in a building with

many frame bents in each direction, a few in each direction might

-

- d e ^ i g n

n

l et* a seismic t uue r tbi bti ng and designed c* s ductile

moment-resisting space frames or as braced frames. Although it

would not be a common occurrence, it is possible for a designer

to use a two-level approach in this. In such an approach,

components more rigid yet less ductile than the designated

seismic force—resist ing system are considered effective in

moderate earthquakes. Such components may not be used to satisfy

the strength criteria of 3.1.3, but may be used to satisfy the

stiffness criteria of 3,1.4.

Cl 7
C3. 1 . 1 Integrity

This requi rement , taken from the NEHRF1 provisions, is very

elementary, so much so that its consideration is recommended even

in Zone 0 where seismic design consi derati on is not required.

Movement of the ground beneath a building generates inertial

forces due to each mass within the building, because the building

responds as an integral unit in the motion. This provision

simulates the effect of these inertial forces by specifying

equivalent seismic farces to be applied at each story. This

requirement reminds the designer that the simulation is complete

only when the specified seismic forces are carried back into the

ground, which is the "final point of resistance. " Conspicuous

failures of building components in past earthquakes can be

attributed to the lack of a complete and continuous path of

structural resistance for seismic loads.

C3.1.2 System Response Classification

Seismic force-resisting systems possess different degrees of

ductility, damping, redundancy, etc. These important

characteristics affect the level of inertial force generated by a

given ground motion and level of safety for a given level of

force. Therefore, different seismic force coefficients and

detailing rules are specified for various types of seismic

force-resisting systems. The four classes defined in this

50c t i on ~e taken from the UBC. The exact description of the

systems is slightly different than in the UBC, but the changes

are only an attempt to clarify the classification. The SEAOC

Commentary provided the basis for discerning the intent of the

original classification.

Several features of the cl assi f i cat i on deserve comment. The

first decision in classifying a building concerns bearing walls.

This decision often requires experienced judgment. Buildings in

which "a significant fraction of the gravity load is supported on

bearing walls" must be classed as a "Box System" in each

principal direction. The presence of minor load bearing walls

(for example, around a stairwell within one bay of the frame)

does not mean that a building must be categorized as a "Box

System" if the overall response of the building is not

significantly influenced by the walls. The seismic

force-resisting system of "Box Systems," will normally include

the bearing walls functioning as shear walls plus any other

designated components. Buildings that are not classed as "Box

Systems" may be classed separately about their two principal

3. :< Bb .

Cl 8
If

The second important decision regards the use of ductile

moment-resisting space -frames in the designated seismic

f orce-'-ssi sti ng system. Because rigid elements may exist in

build' ngs without being a part of the designated seismic

f orce- resist ing system, it is possible for a building with both

ductile moment—resi sti ng space frames and shear walls (or braced

frames! to be in any of the three remaining classes, as follows:

1) where the designated seismic force-resisting system

includes only the ductile moment-resisting space frame,

K 0.67 is correct:

2) where the designated seismic force—resisting system

includes both types of components and where the

relative strengths of the two types of components

satisfy the requirements of Section 3.1.3, K = 0.80 is

correct

:

3) otherwise, K = 1.00 is correct.

The classification of such buildings becomes quite complex when

the two level approach mentioned in the commentary on seismic

f orce—resisting systems is adopted.

qreai variety of seismic force-resisting systems is included in

he "Building Frame System" class, such as shear walls, braced

frames, arches, moment—resisting frames that do not meet the

special ductility requirements of chapter 6, etc.

Section 3,1.6 places restrictions on the class of seismic-force

resisting systems allowed for tall buildings in zones 2, 3, and

4. This is also done in UBC Section 2312(j),

03.1.3 Strength

This provision is consistent with the UBC, Table 23—1 is the

source. The intent is to continue present UBC practice

unchanged, which generally means increasing the allowable stress

by 1/3 when considering the effects of seismic forces. Increases

in allowable stresses and factors for the combinations of loads

are specified in the material design standards referenced in

Chapter 5.

C19
C3.1.4 Stiffness and Building Separations

Although the number looks quite different, these requirements are

essentially the same as Section 2312(h) of the UBC. Drift limits

are imposed on the basis of experience and judgment. The

principal reasons are to ensure that the stiffness is large

enough to prevent stability failures and to control life hazards

resulting from the failure of brittle nonstructural elements such

as windows. In both cases the protection provided by the

specified drift limit is only approximate. An added, but not

primary, reason for the drift limit is to reduce damage and

repair costs following moderate earthquakes. The designer should

recognize that the actual deflections and drifts will be larger

than those calculated on an elastic basis, due to the inelastic

straining of the seismic force—resi sting system. The SEAQC

Commentary states that the real deflections will exceed the

calculated elastic deflections by a factor of 3/K. Thus, the UBC

limit of 0.005 times the story height is simply a nominal value

applied to the elastic deflections. The SEAOC Commentary further

advises that the anticipated real deflections rather than the

elastic; deflections be used in determining the distance necessary

for structural separation joints. In order to avoid confusion

and reduce the number of computations, all deflections and drifts

are multiplied by 3.0/K, but with 3.0/K not less than 3.0 (in

4.4.7) and the drift limit in Section 3.1.4 is correspondingly

changed by a factor of 3.0 from 0.005 to 0.015.

C3.1.5 Overturning Stability

This requirement is the same as that in section 2312(f) of the

UBC, except that wind is not mentioned, for the reasons stated in

CI.l. Overturning stability has rarely been a problem in real

buildings subject to earthquakes. The calculated overturning

moment is likely to be conservative because these provisions do

not account for the rocking of a building on its foundation, the

lengthening of the period of vibration due to inelastic effects

below the base and in the soil, the contributions of the higher

modes of vibration (except in Section 4.4.4 for tall buildings)

and other similar factors which tend to reduce the real

overturning in the building. Therefore, no margin of safety is

called for between the overturning and resisting moments.

5
C3 ,1.6 Hei ght

The requirement is essentially the same as Section 2312 (j) IB of

the UBC, Its impact is that buildings over 160 feet high in the

specified zones will have structural systems that qualify for a K

value lj O a 6 / t

1

; O D Su«

C3.2 OTHER STRUCTURAL ELEMENTS

Seismic ground shaking affects the entire structural system , not

just the designated seismic f orce-resi st i ng system. These

effects are primarily of two types, the inertial farces due to

the mass of the structural element and the distortions the

structural element experiences as the seismic f orce-resi st i ng

systems responds to the ground shaking.

C3,2 Other Structural Elements

C3.2.1 Strength and Anchorage

This requirement is based on Section 2312(g) of the UBC. It

applies in Zone 1, just as the basic requirements for the seismic

force-resisting system in Section 3.1. The increase in allowable

stresses by 1/3 normally permitted in reference standards for

seismic forces is applicable when satisfying this requirement.

C3.2.2 Compatibility

This rsqui rement is taken from Section 2312 (j) ID of the UBC. The

distortion specified in Section 4.4.7 (which includes the

amplification by the factor 3/K) is intended to include both the

ductility of the seismic f orce-resi sti ng system and the F’-delta

effect, as indicated in the SEOAC Commentary.

C3.3 FOUNDATIONS

C3.3.1 Soil and Foundation Capacity

This requirement is very performance oriented, by necessity. It

is not possible to develop specific provisions at this time

because soil and foundation conditions for buildings exhibit such

a wide variety. The warding used is quite similar to the NEHRF'

provisions. The intent is to cause the geotechnical engineer and

C21
the -foundation engineer to be cognizant of the differing effects

of ground shaking on the properties of various soil types when

establishing the allowable bearing pressures and other design

criteria for load combinations involving earthquake. The

performance objectives are to avoid bearing capacity failures and

to avoid settlements so severe as to cause failure of the

structural system of the building. The requirement should not be

interpreted to imply that soi 1 —structure interaction analyses are

necessary; such analyses may be useful for special types of

structures with specific soil and foundation conditions, but that

is ai i issue to be decided on a case oy case basis.

C3.3.2 Structural Ductility

As this provision indirectly indicates, the base and the

foundation of a structure need not be the same entity. For a

building with one or more levels below grade in which the levels

below grade are considerably more stiff than the levels above

grade and the soil around the basement levels is not

exceptionally soft, the base can be considered to be at grade,

because the most accurate simple model is to consider that the

rigid substructure moves with the surrounding ground in imparting

the motions to the superstructure. On the other hand, buildings

in which the soil around the basement levels is except i anal 1

y

soft are more accurately modeled by considering the base to be at

the foundation level. For those buildings in which the base is

above the foundation, it is only reasonable that the ductility

the seismic force—rest st i ng system be continued to the

f oundat i on

.

of
C4. STRUCTURAL ANALYSIS PROCEDURES

This chapter provides for the calculation of seismic loads and

their effects., The SEAOC Commentary is a valuable resource for

better understanding of the provisions in this chapter. The

reader is referred to that resource.

C4.1 REQUIRED METHOD FOR SEISMIC-RESISTING SYSTEMS

The minimum level of analysis, contained in Section 4.2, is the

same as UBC except as noted and is thought appropriate for most

buildings. The modal analysis, contained in Section 4.3, is

somewhat similar to the NEHRP provisions and is appropriate for

multistory buildings that are not uniform throughout their

height. This provision of analytical procedures for irregular

buildings should not be inferred to encourage such buildings.

Indeed, because such buildings have been shown to be more

vulnerable in past earthquakes and because their response is

considerably more difficult to predict, irregular buildings are

ui scout c?. g ed .

It should be noted that soi 1 —structure interaction analyses will

generally have the effect of reducing the forces and increasing

the deflections in the structure. In some instances, secondary'

geometrical effects resulting from the increased deflections will

have the effect of a. net increase on the forces,

C4.2 ELASTIC STATIC LOAD ANALYSIS

Section 4.2 is based on Sections 2312(d) and (e) Gf the UBC.

Unless otherwise noted herein or elsewhere in this document, the

same equations, meanings, and limits are used in both these

guidelines and the UBC.

C4.2.1 Base Shear

Th is sect i un combines Sections 2312 (d) and (e) uf the UBC. An

additional provision for determining Z is provided for those

buildings on sites with an approved site evaluation. This is

simply a means of calibrating the spectrum for base shear to the

site acceleration. If the site acceleration is greater than 40

percent of gravity, the resulting Z will be greater than 1.0.

This Z value is required for determining ductility requi rements.

Permanent loads that are fixed to the structure, such as some

types of computer installations, should be included in W. When

dealing with liquids, W should be the weight of the effective

C23
C4.2.2 Period of Vibration

The equations for calculating the period are the same as given in

the UBC Section 2312 (d). Equations 4.3 and 4.4 are appro;-; i mate

and are based on the periods found in actual buildings. The use

of a proper analysis for the period is encouraged, but a limit is

placed on the result in order to prevent the use of periods

si gni f i cant 1 y larger than observed in real buildings. Use of

unrealistically large values for the period results in low and

unsafe values for the base shear. UBC does not contain such

limits. The limit used in these guidelines is the same as that

used in ANSI ASS. i which uses the same set of formulas for

deter m i n i ng the per i od

.

C4.2.3 Site Coefficient

Two alternative methods are presented. Both methods are

specified in the 1985 UBC Section 2312(e). Method A has been

used for several years in the highly seismic areas of the

country. It requires the determination of a value for the site

period, for which SEAOC Standard No. 1, "Determination of the

Characteristic Site Period, Ts" is recommended (also published as

UBC Standard No. 23-1).

Method B was incorporated in UBC in 1985 after appearing in an

earlier draft of these guidelines. In this method. Soil Profile

Type 3 is specified for sites at which the soil properties are

not known in detail. This may be conservative since the designer

would possibly be aware of the soil properties at sites actually

fitting Soil Profile Type 3 because of the likely need for deep

or special foundations. The NEHRP Provisions specifies Soil

Profile Type 2 for this case while ANSI ASS. 1 specifies that the

soil profile resulting the larger value of the product CS be

C4.2.4 Vertical Distribution of Forces

The provision for irregular shapes or frames is based on the

combination of UBC Sections 2312 (e) 2 and 3. The provision for

regular shapes and framing systems is based on UBC Section

2312(e) 1. The provisions are the same.

The specified distribution is based on buildings in which the

stiffness, mass , and strength are relatively consistent from one

level to the next. The proceduress of 4.3 will account for the

lack of such consistency in stiffness and mass, but more

sophisticated analyses are required for substantial differences

in strength.

C2
C4 ELASTIC DYNAMIC LOAD ANALYSIS

This analysis is only applicable to multistory buildings. The

UBC has no provisions for dynamic analysis. Accordingly, the

provisions are based on the NEHRP procedures for modal analysis,

although they are not as detailed. The intent is to establish

the basic limits for such analyses rather than to completely

specify a method. The design spectrum is not from the NEHRP, but

is simply consistent with the spectrum used in Section 4.2.1.

Although the combination of modes by means of the common square

root of the sum of the squares method is specified, more precise

combinations may be necessary for buildings with closely coupled

iii LJ d . C4.3.3 Design Values

The limits placed on the base shear are intended to prevent

misuse of advanced analyses. The reason to use the advanced

analysis is primarily to determine the distribution of seismic

fences more accurately, not to reduce the overall force. The 90

percent limit is an arbitrary limit which is also used in ANSI

A53. 1

C4.4 ELASTIC LOAD EFFECT ANALYSIS

Except where noted, the provisions of 4.4 are taken from Sections

2312 <e) and (f ) of the UBC.

C4 .4.1 Shear

It is frequently useful to idealize the relative rigidity of

n or x z on t a I to vertical b r ac i n g systems as 11 f 1 ex i b a e

1 or "rigid.

For "flexible" diaphragms (or bracing systems), the shear is

distributed from the diaphragm to the vertical elements by

modeling it as a beam on unyielding supports. The amount of

shear in a particular wall or frame would depend on the shear in

the diaphragm spans that are tributary to it. There would be no

effect of continuity in the diaphragm, since the shear strain

normally dominates the flexural strain in the diaphragm. For the

"rigid" diaphragm, the shear is distributed by modeling the

diaphragm as a rigid beam on yielding supports. The amount of

shear in a particular wall would depend on its rigidity in

relation to all other walls. Buildings with plywood deck

ci ^ hi* csgins c5. • ! d masof ?r y *_ ? o• * s* itr s n c? ai* I is ar tr normally

C25
considered to have "flexible" diaphragms, while buildings with

concrete slabs of normal proportions without large openings are

normally considered to have "rigid" diaphragms. Where the

horizontal and vertical bracing systems have equivalent

rigidities, a more complex analysis is required. For such cases,

it is normally acceptable to conduct two simple analyses, one for

each of the previously described extremes, and use the more

conservative values for design.

C4.4.2 Horizontal Torsion

In consideration of the commentary on 4.4.1, the phrase, "Where

the vertical resisting elements depend on diaphragm action for

shear distribution at any level," can be interpreted as "where

the horizontal bracing systems cannot be character i zed as

'flexible' .

C4.4.4 Overturning

Th e sec t i on is t a k en

ap p r oaches I ave been

A58. 1

.

C4.4.5 Orthogonal Effect

This provision is similar to the NEHRP provisions and is

currently used by the Veterans Administration. Vertical elements

at or near the corners of buildings are a typical example of a component that is utilized in both directions and would be

affected by this provision. For conventional rectangular

buildings with horizontal and vertical framing, the beams,

girders, diagonals of individual braced frames, and shear walls

not continuous with orthogonal walls are examples Gf components

that <pre utilized in only one direction for seismic resistance.

It is not the intent of this section to require a great amount of

ex t r a c a I cu 1 at i on . Although the direction of force is critical for some types of

structures, such as four legged towers, independent analysis on

the two principal axes is sufficient for buildings, given the

special provision in this section for combining orthognal load

ef f ect s

.

from the UBC Section 2312(f). Other

proposed such as that in the NEHRP and ANSI

C26
C4.4.6 Vertical Motion Effect

No provision for vertical motion is in the UBC. Similarly, no

analysis is provided -for the vertical motions of ground shaking

in these guidelines, except for the approximation introduced in

this section for cantilever members and prestressed members.

This approx i mat i on provides some degree of conservatism for

members that might be particularly sensitive to the effects of

vertical motion and is one that is being currently used by the

Veter ans Ad mi ni strat i on

.

More sophisticated provisions are contained in the NEHRF'

Pravi si ans.

C4.4.7 Displacements

The amplification of the displacements by 3.0/K is different than

in the UBC, which specifies 1 . Q/K. The SEAOC Commentary states

that the real displacements are likely to be about 3.0/K, and the

UBC uses this factor in some provisions. As explained in Section

C3 .1.4, the amplification by 3.0/K is used throughout in these

guidelines, but 3.0/K shall not be less than 3.0.

C4.5 ANALYSIS OF OTHER STRUCTURAL ELEMENTS

This section is taken from 2312(g) of the UBC except for the

minimum interconnection force, which is taken from the NEHRF*

.
C5. DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS

These guidelines make reference to widely accepted national

standards -for design and construct i on provisions for specific

structural materials. This is in keeping with both the current

practice of Federal agencies and Federal policy as set forth in

Circula- A— 13.9 of the Office of Management and Budget. In many

instances the materials' provisions in the UBC are derived from

these same national standards. Thus , the application of this

chapter should produce results similar to present practices and

to the UBC,

The provisions of these guidelines frequently modify or take

exception to the referenced standards, in which cases these

guidelines shall control (for example, most of the provisions of

chapter 6) . UJi th the exception of the standards for masonry, the

references are listed such that the designer or contractor will

make use of each standard as it is applicable. As discussed in

C5. 4, these guidelines allow some choice between different

standar i s f or ma. son r y

,

The set of standards referenced does not form a complete set of

standards for construction or for structural design. Only those

standards which would fulfill some need in carrying out the

previsions of these guidelines are referenced. In some instances

the standards referenced here may conflict with other standards

r af ev - ced b y Fe er

a

1 ag

a

n c i es . Far issues concerned with

seism: : safes y , priority should be given to these guidelines and

the if references. The editions listed for each standard are the

latest available at the time of development of these guidelines.

Revisions to these editions should be examined by designers and

designated authorities on a timely basis.

C5.

1

STEEL

The "Design Manual for Floor Decks and Roof Decks" published by

the Steel Deck Institute does not provide allowable diaphragm

shear values for steel deck diaphragms. It is expected that the

Steel Deck Institute will soon adopt a standard design manual for

diaphragm construction that would include such values? however,

until such a document becomes an accepted standard, the

Tri—Services Manual is an available source of design values for

steel deck diaphragms.

C28
C5.4 MASONRY

There is more regional diversity in the design and construction

practices tor masonry than -for other construct i on materials.

Therefore, the standards referenced for masonry tend to overlap

more than the standards referenced for other materials. The UBC

is widely used in the West but rarely used in the East, where the

standards of ANSI, ACI, NCMA, and BIA are more widely used.

Although uniformity has some positive aspects, uniformity in

masonry practices will not be accomplished by thesegui del i nes

alone. It is expected that current regional practices will

continue under this standard, although a general preference for

the UBC is expressed for use in the higher zones, regardless of

the geographic region.

C29
C6. STRUCTURAL DESIGN DETAILS

The details at proport i oni ng , reinforcing, and connecting

structural members are of extreme importance in achieving

successful performance in earthquakes. This is because the

details have an enormous effect on the capability of the seismic

f orce—resisting system to dissipate energy through ductility and

damping. Five widely accepted standards for structural detailing

for seismic performance are referenced at several points in this

chapter. The referencing is consistent with the philosophy

expressed in C5 and it has the added benefit of brevity in

thesegui del i nes. The designer need not have all five references

on hand. Because they are required by Chapter 5, he would

already have the standards of AC I and A ISC on hand. The UBC,

SEAOC, and Tri -Services Manual are always used as alternates, so

no more than one is absolutely necessary. UBC is referenced here

because of its familiarity to those experienced in seismic design

and because of the convenience of its self-contained nature.

SEAOC is referenced because it is the original source of much

seismic provisions of the UBC and because it is accompanied by a

valuable commentary. The Tri—Services Manual is referenced

because of its unique treatment of several levels of performance

for ductile moment-r esi st i ng frames of reinforced concrete.

C6. 1 MOMENT-RESISTING FRAMES

This section is taken from Section 2312(j)l of the UBC.

C6.1.2 Concrete Frames

Unless the actual drift is substant i al 1 y less than the maximum

allowable drift, the repeated distortions imposed on a concrete

frame, whether it is a part of the seismic force-resisting system

or not, are likely to cause substantial cracking and spalling of

the concrete. Thus, any concrete frame used in the seismic

farce-resisting system needs the rei nf orcement required for

ductile moment-resisting frames in order to maintain its

integrity. Likewise, any concrete frame on the exterior of a

building needs the same rei nf orcement to prevent spalling

hazardous large chunks of concrete unless that building has a very stiff seismic f orce—resi sti ng system.

C6.2 STEEL DUCTILE MOMENT-RESISTING SPACE FRAMES

This section is based on 2312 (j) IF of the UBC. The following

C30
table summarizes the appropriate K -factor, and thus the category

o-f the seismic force—resi sting system, for the two common types

of steel frames used as seismic f or ce—resi st i ng systems:

Zone

1 2(1=1) 2 ( I > 1 ) 3&4

Steel frame in compliance

with section 2722 of the UBC 0.67 0.67 0.67 0.67

Ordinary steel frame with

joints meeting A

I

SC Type I 0.67 0.67 1.0 1.0

C6.3 REINFORCED CONCRETE DUCTILE MOMENT-RESISTING SPACE FRAMES

This section is based on 23121 j) IF and 2625(e) and (f) of the

UBC. The following table summarizes the appropriate K factor for

three types of reinforced concrete frames:

Zone

1(1 = 1) 1 ( I >1 ) 2(1 = 1) 2 < I > 1 ) 3?v4

Highly ductile frame meeting

section 2626 of the UBC

Moderately ductile frame meeting 6.3. 1 and 6.3.2

Ordinary frame meeting AC I 318

without Appendix A

* system not permitted

** the UBC specifies a different

1 . 0 .

0 . 67 . 67 0.67 0.67 0 . 67

0 . 67 . 67 0.67 * *

1 . 0 * * * *

K factor for this system, K =

C31
C6. 4 BRACED FRAMES

These requirements are taken -from 2312 (j)lG and 2627(b) o-f the

UBC; the only difference is in the application o-f the

requi cements in zones 1 and 2= Higher member and connection

capacity is called -for braced -frames to assure the necessary

ductility and to reduce the possibility o-f non-ductile connection

fail ures.

It is possible to construct braced frames with diagonal members

that are ineffective in resisting compression due to their

extreme slenderness. Repeated inelastic straining of such frames

leads to very large deflections because each cycle causes a net

increase in the length of the diagonals; the phenomenon is often

called "slap-back." Depending on the type of structure, this

behavior may be very undesirable. The NEHRP provisions effectively prohibit such bracing systems for buildings over two

stories in the highest seismic zones by requiring that the compressive strength of members in braced frames be at least 50

percent of the required tensile strength.

C6.4.1 Required Capacity

The term "full capacity" means the true failure load for the

member. Thus strain hardening should be taken into account.

C6.5 REINFORCED CONCRETE SHEAR WALLS

This section is taken from 2312(j)lH of the UBC', except that it

is not applied to the lower seismic zones.

C6.6 REINFORCED MASONRY WALLS

The table of minimum reinforcement in masonry walls is taken from

the Tri -Service Manual and the seismic regulations of the

Veterans Administration. It is not identical to the UBC.

C6.7 DIAPHRAGMS

This section is based on 2312 <j) 2D and 3A of the UBC, with

significant simplification that is in accord with current

practice. The need for these requirements was demonstrated by

al Tdi I ures in the 1971 dai * ret- nando ea thqudke.
C6.8 OPENINGS IN SHEAR WALLS AND DIAPHRAGMS

This requirement is roughly based on a. similar requirement in the

ATC provisions. The importance o+ providing continuity in the

chords of plate-like elements is often overlooked.

C6.9 CONCRETE AND MASONRY ELEMENTS

This section is taken from 2312 (j)2B and 2310 of the UBC.

C6. 10 FOUNDATIONS

C6. 10. 1 Ties Between Foundation Units

The provision for pile caps is taken from 2312(j)3B of the UBC;

the provision for spread footings is original. In both cases the

concerns are to assure that the foundation transmits the ground

motion uniformly to the structure and to allow adjacent

foundation uni ts to par t i ci pate in sharing 1 ateral force

over 1 oads

.

C6.10.2 Pile Cap Connections

The NEHRP provisions require the connection between the pile ca

and the pile to be reinforced. One reason for a minimum tensi

1

capacity, separate from consideration of overturning resistance,

is vertical ground motions. The requirement given in this

section is roughly equivalent to the NEHRP requirements, but it

is stated in a performance-oriented fashion rather than in a series of prescriptive requirements for various types of piles.

C6.10.3 Concrete Piles

In addition to the need for tensile capacity implied by the

preceding section, piles also need a minimum level of ductility,

particularly near the top. Once again, these provisions are

similar to the NEHRP provisions, although they are less

detailed. Note that some types of metal casing might substitute

for one type of reinforcement, but not the other. Some

corrugated casings might fulfill the function of the transverse

reinforcement without fulfilling the function of the longitudinal

reinforc emen t

.

C33

a

ai
C7 NONSTRUCTURAL DESIGN REQUIREMENTS

07. 1 ANCHORAGE FOR INERTIAL FORCES

This section is based an 2312(g) o-f the UBC. One difference is

that consi derati on of nonstructural components has been separated

from structural components in this document. The ATC provisions

give some guidance on ducts and piping that are small enough so

that special seismic restraints need not be designed. The

Tri—Services Manual and the General Services Administration 's

Design Guidelines for Earthquake Resistance of Buildings both

gives specific recommendat i ons for the anchorage and protection

of nonstructural components.

C7.2 DISTORTION COMPATIBILITY FOR EXTERIOR PANELS

This section is the same as 2312(j)3C of the UBC. In discussing

a similar provision, the SEAOC Commentary notes that the force

specified for fasteners attaching the connector to the panel or

the structure shall be taken in any direction, not just

horizontal, and that it need not be combined with other forces.

C7.3 PROTECTION AGAINST SECONDARY HAZARDS

This provision is based on a similar provision in the ATC.

C7.4 FUNCTIONALITY OF ESSENTIAL ELEMENTS

This provision is also based on a similar provision in the ATC.

Full consi derati on of design for functional capability

immediately following a major earthquake is beyond the scope of

this standard.

C7.5 REINFORCEMENT OF CONCRETE AND MASONRY

This section is the same as 2312 (j)3C of the UBC. It requires

the same minimum reinf orcement in zones 3 and 4 for nonstructural

components as 6.9.1 does in zones 2, 3 and 4 for structural

components.

C34
C8 CONSTRUCTION DUALITY CONTROL

This chapter is loosely based on section 306 of the UBC. The

intent is to cover those items whose successful performance in an

earthquake is strongly dependent on sound quality control. It is

not the basis for a complete quality control program, but should

eupp i emen t existing agency programs*

C8.2 REQUIRED SPECIAL INSPECTION

In identifying the needed special insp

follows the UBC particularly closely,

universal agreement on the subject of

is no intent to create new problems wi

should be noted that continuous specie

synonymous with full-time inspection.

ection, the standard

Although there is no

special inspection, there

th this standard. It

1 inspection is not

C35
NBS-II4A (REV. 2-80) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 87-3524 February 1987

4. TITLE AND SUBTITLE

Seismic Design Guidelines for Federal Buildings

5. AUTHOR(S)

Edgar V. Leyendecker, Editor, U.S. Geological Survey, Denver, CO

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS ______

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Federal Emergency Management Agency

Washington, DC 20472

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) This document has been prepared as a coordinated adaptation of existing voluntary

standards, model building codes, Federal regulations, and research reports for use

by Federal agencies. The technical content is similar to the seismic requirements

of the 1985 Uniform Building Code (UBC) . However, there are instances of substantive

difference from the UBC. Several important provisions have been incorporated from

other sources considered in this adaptation. For example, the seismic zone map

is the one in current use in ANSI A58. 1-1982 Minimum Design Loads for Buildings

and Other Structures. A number of provisions have been added to these guidelines

that are based on the current practices and policies of various Federal Agencies.

Furthermore, in the spirit of improvement, this document is organized considerably

differently from the UBC and many provisions are phrased differently.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Building codes; minimum design loads; seismic; voluntary standards.

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

QX] Unl imited

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] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

102

15. Price

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USCOMM-DC 6043-P80


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