IMBSIR 81-2195

Draft Seismic Standard for

Federal Buildings

J. R. Harris

E. V. Leyendecker

Center for Building Technology

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

Lincoln Chang

Andrei Gerich

Peter E. Gurvin

Allen Lim

George M. Matsumura

Richard D. McConnell

Howard D. Nickerson

William D. Rust, Jr. Constantine Spyropoulos

Macro F. Venturino

Michael Yachnis

Department of Housing and Urban Development

Department of Housing and Urban Development

Department of State

Department of Air Force

Army Corps of Engineers

Veterans Administration

Naval Facilities Engineering Command

General Services Administration

Department of Housing and Urban Development

Naval Facilities Engineering Command,

Western Division

Naval Facilities Engineering Command

January 1981

Prepared for use by:

Interagency Committee on Seismic Safety in Construction

Sponsored by:

Federal Emergency Management Agency

Washington, DC 20742

...

tional Bureau of

shington, DC 2

Standards

20234

National Bureau of Standards

Library, E-01 Admin. Bldg.

NBSIR 81-2195 !Db-L cite - C> sc DRAFT SEISMIC STANDARD FOR

FEDERAL BUILDINGS

J. R. Harris

E. V. Leyendecker

Center for Building Technology

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

CIO,

/tfZi

Lincoln Chang

Andrei Gerich

Peter E. Gurvin

Allen Lim

George M. Matsumura

Richard D. McConnell

Howard D. Nickerson

William D. Rust, Jr. Constantine Spyropoulos

Macro F. Venturino

Michael Yachnis

Department of Housing and Urban Development

Department of Housing and Urban Development

Department of State

Department of Air Force

Army Corps of Engineers

Veterans Administration

Naval Facilities Engineering Command

General Services Administration

Department of Housing and Urban Development

Naval Facilities Engineering Command,

Western Division

Naval Facilities Engineering Command

January 1981

Prepared for use by:

Interagency Committee on Seismic Safety in Construction

Sponsored by:

Federal Emergency Management Agency

Washington, DC 20742

and

National Bureau of Standards

Washington, DC 20234

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

PREFACE

This draft standard was developed within the Subcommittee on Building

Standards of the Interagency Committee on Seismic Safety in Construction

(ICSSC). The membership of the Subcommittee is:

Vartan M. Bedjanian

Lincoln Chang

Edward Ference

Earl L. Flanagan

Andrei Gerich

Peter E. Gurvin

James R. Harris

James Lefter

Edgar V. Leyendecker*

Allen Lim

George M. Matsumura

Richard D. McConnell

Howard D. Nickerson

Edward 0. Pfrang

William D. Rust, Jr.

John B. Scalzi

Constantine Spyropoulos

Marco F. Venturino

Michael Yachnis

* denotes Chairman

Naval Facilities Engineering Command,

Western Division

Department of Housing and Urban Development

Naval Facilities Engineering Command

Department of Housing and Urban Development

Department of Housing and Urban Development

Department of State

National Bureau of Standards

Veteran Administration

National Bureau of Standards

Department of Air Force

Army Corps of Engineers

Veteran Adminstration

Naval Facilities Engineering Command

National Bureau of Standards

General Services Administration

National Science Foundation

Department of Housing and Urban Development

Naval Facilities Engineering Command,

Western Division

Naval Facilities Engineering Command

The able editorial and secretarial assistance of Ms. Sandra Berry of

the National Bureau of Standards deserves recognition.

The Subcommittee has recommended that this draft be submitted to all

concerned agencies with the request that they test its implementation through

use in design, contract administration, and quality control, either on a trial or real basis during 1981. Following the trial implementation, the

Subcommittee plans to review the draft, revise as necessary, and then recommend its adoption by the Interagency Committee as a standard for Federal

Buildings. Comment on this draft standard is welcomed. Comment should be

forward to:

Dr. E. V. Leyendecker

Chairman, ICCSSC Subcommittee #2

Room B168, Building 226

National Bureau of Standards

Washington, D.C. 20234

iii
ABSTRACT

This standard has been prepared for uniform use by all Federal agencies

as an adaptation of existing voluntary standards, model building codes, Federal

regulations, and research reports. It is closely based on the seismic requirements of the Uniform Building Code (which, in turn, are based on the Recommended Lateral Force Requirements and Commentary published by the Structural

Engineers Assocation of California). However, there are many instances of

substantive differences from the UBC. Several important provisions, including the seismic zoning map, have been adapted from the Tentative Provisions

for the Development of Seismic Regulations for Buildings developed by the

Applied Technology Council. A number of provisions have been added to this

standard that are based on the current practices and policies of various

Federal agencies. Furthermore, in the spirit of improvement, this standard

is organized considerably differently from the UBC and many provisions are

phrased differently.

iv
SI Conversion Units

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

in building design and construction may be used.

QUANTITY INTERNATIONAL (SI) UNIT U.S. CUSTOMARY UNIT APPROXIMATE CONVERSION

LENGTH meter (m) millimeter (mm)

AREA SQuare meter (m*)

square millimeter (mm*)

VOLUME cubic meter (m*

)

cubic millimeter (mm*) CAPACITY liter (L) milliliter (mL)

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

ACCELERATION meter per second squared (m/s*)

MASS metric ton (t) [1000 kg]

kiloqram (kg) gram (g)

DENSITY metric ton per cubic mrter (t/m*) kiloqram per cubic meter (kg/m1

)

FORCE kilonewton (kN)

newton (N)

MOMENT OF FORCE, TORQUE kilonewton meter (kN*m) newton meter (N*m)

PRESSURE, STRESS megapascal (MPa)

kilopascal (kPa)

WORK. ENERGY, 0UANTITY OF HEAT megajoule (MJ) kilojoule (kJ) joule (J)

POWER, HEAT FLOW

RATE kilowatt (kW) watt (W)

COEFFICIENT OF HEAT watt per square meter kelvin TRANSFER [U-value] (W/m**K) [= (W/m'* 6 C)]

THERMAL C0NDUC- watt per meter kelvin (W/m*K) TIVITY [k-value] t= (W/m-^C) ]

foot (ft Inch (In

square yard (yd*) square foot (ft*) square Inch (in*)

cubic yard (yd*) cubic foot (ft*) cubic inch (in*) gallon (gal) fluid ounce (fl oz)

foot per second (ft/s or f.p.s.) mile per hour (mile/h or m.p.h.)

foot per second squared (ft/s*)

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

ton per cubic yard (ton/yd*)

pound per cubic foot (lb/ft*)

ton -force (tonf) kip [1000 lbf] pound-force (lbf)

ton-force foot (tonf* ft) pound-force inch ( lbf* in)

ton-force per square inch (tonf/in*) ton-force per square foot (tonf/ft*)

kilowatthour (kWh) British thermal unit (Btu) foot pound- force (ft* lbf)

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 Fahrenheit

(Btu/ft**°F)

1 m - 3.2808 ft

1 ran - 0.0394 In

1 m* = 1.1960 yd*

1 m* = 10.764 ft*

1 mm* = 1.55 x 10* 3 In*

1 m’ = 1.3080 yd’

1 m* = 35.315 ft*

1 ntn’ = 61.024 x 10

-6

in*

1 L = 0.2642 gal

1 mL = 0.0338 fl oz

1 m/s = 3.2808 ft/s

1 km/h = 0.6214 mile/h

1 m/s* = 3.2808 ft/s*

1 t = 1.1023 ton

1 kg = 2.2046 lb

1 g = 0.0353 oz

1 t/m* = 0.8428 ton/yd*

1 kg/m’ = 0.0624 lb/ft*

1 kN = 0.1124 tonf

1 kN = 0.2248 kip

1 N = 0.2248 lbf

1 kN*m = 0.3688 tonf* ft

1 N*m = 8.8508 1 bf• i n

1 MPa = 0.0725 tonf/in*

1 MPa = 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 = 3.4121 Btu/h

1 W = 0.7376 ft*lbf/s

1 W/m* *K = 0.1761 Btu/ft**h*°F

1 W/m*K = 0.5778 Btu/ft**°F

NOTES: (1) The above conversion factors are shown to three or four places of decimals.

(2) Unprefixed SI units are underlined. (The kilogram, although prefixed, is an SI base unit.)

REFERENCES: NBS Guidelines for the Use of the Metric System, LC1056, Revised August 1977; The Metric System of Measurement, Federal Register Notice of October 26, 1977, LC 1378, Revised November 1977; NBS Special Publication 330, "The International System of Units (SI)," 1977 Edition; NBS Technical Note 938, "Recommended 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) Units in Building Design and Construction," (based on NBS TN 938), March 1978; ANSI Z210. 1-1976, "American National Standard for Metric Practice." ASTM E380-79 e

, "Standard for Metric Practice."

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

V
Table of Contents

Page

PREFACE iii

ABSTRACT iv

SI CONVERSION UNITS v FOREWORD 1

1. REGULATION 2 1.1 Scope 2 1.2 Definitions 2 1.3 Notation 5

1.4 Hazard Classifications 7 1.4.1 Seismic Ground Shaking Hazard 7 Table 1 - Zone for Sites with Approved Site Evaluation ........ 7 Figure 1 - Seismic Zone Map 8

1.4.2 Occupancy Hazard 10

Table 2 - Values for Occupancy Importance Factor 10

1.5 Alternative Provisions 10

2. GENERAL REQUIREMENTS 12

2.1 General Performance Requirement 12

2.2 Site Planning for New Buildings 12

2.2.1 Site Evaluation Study 12

2.2.2 Site Limitations 12

2.3 Design of New Buildings 13

2.3.1 Application of the Provisions 13

2.3.2 Documentation 13

2.4 Construction 13

2.5 Existing Buildings 13

2.5.1 Alterations and Repairs 13

2.5.2 Changes of Use or Locations 14

3. STRUCTURAL DESIGN CRITERIA 15

3.1 Seismic Force-Resisting Systems 15

3.1.1 Integrity 15

3.1.2 System Response Classification 15

3.1.3 Strength ...'. 16

3.1.4 Stiffness and Building Separations 17

3.1.5 Overturning Stability 17

3.1.6 Height 17

3.2 Other Structural Elements 18

3.2.1 Strength and Anchorage 18

3.2.2 Compatibility 18

3.3 Foundations 18

3.3.1 Soil and Foundation Capacity 18

3.3.2 Structural Ductility 18

vi
Table of Contents (Continued)

Page

4. STRUCTURAL ANALYSIS PROCEDURES 19

4.1 Required Method for Seismic-Resisting Systems 19

4.2 Elastic Static Load Analysis 20

4.2.1 Base Shear 20

Table 3 - Zone Coefficient Z 20

Table 4 - K for Buildings 21

Table 5 - K for Other Structures 21

4.2.2 Period of Vibration 22

4.2.3 Site Coefficient 23

Table 6 - Site Coefficient 24

4.2.4 Vertical Distribution of Forces 25

4.2.5 Overturning Moment 26

4.3 Elastic Dynamic Load Analysis 26

4.3.1 Mode Shapes and Periods 26

4.3.2 Modal Base Shear 27

4.3.3 Design Values 27

4.4 Elastic Load Effect Analysis 28

4.4.1 Shear 28

4.4.2 Horizontal Torsion 28

4.4.3 Diaphragm Forces 29

4.4.4 Overturning 30

4.4.5 Orthogonal Effect 30

4.4.6 Vertical Motion Effect 31

4.4.7 Displacements 32

4.5 Inelastic Analysis 32

4.6 Analysis of Other Structural Elements 32

Table 7 - Horizontal Force Factor Cp for Elements of

Structures 33

5. DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS 34

5.1 Steel 34

5.2 Concrete 35

5.3 Wood 35

5.4 Masonry 36

5.5 Aluminum 36

5.6 Gypsum 37

6. STRUCTURAL DESIGN DETAILS 38

6.1 Moment-Resisting Frames 38

6.1.1 Ductile Moment-Resisting Space Frames 38

6.1.2 Concrete Frames 38

6.2 Steel Ductile Moment-Resisting Space Frames 39

6.3 Reinforced Concrete Ductile Moment-Resisting Space Frames 39

6.3.1 Flexural Members 40

6.3.2 Columns 40

vii
Table of Contents (Continued)

Page

6.

A Braced Frames 40

6.4.1 Required Capacity 41

6.4.2 Steel Braced Frames 41

6.4.3 Reinforced Concrete Braced Frames 41

6.5 Reinforced Concrete Shear Walls 41

6.6 Reinforced Masonry Walls 42

Table 8 - Minimum Reinforced and Maximum Spacing for

Reinforced Masonry Walls 42

6.7 Diaphragms 43

6.7.1 Ties Between Chords 43

6.7.2 Anchorages to Wood Diaphragms 43

6.8 Openings in Shear Walls and Diaphragms 43

6.9 Concrete and Masonry Elements 43

6.9.1 Reinforcement 43

6.9.2 Anchorage of Walls 43

6.10 Foundations 44

6.10.1 Ties Between Foundation Units 44

6.10.2 Pile Cap Connections 44

6.10.3 Concrete Piles 45

7. NONSTRUCTURAL DESIGN REQUIREMENTS 46

7.1 Anchorage for Inertial Forces 46

Table 9 - Horizontal Force Factors Cp for Nonstructural

Elements of Buildings 47

7.2 Distortion Compatibility for Exterior Panels 48

7.3 Protection Against Secondary Hazards 49

7.4 Functionality of Essential Elements 49

7.5 Reinforcement of Concrete and Masonry 50

8. CONSTRUCTION QUALITY CONTROL 51

8.1 Special Inspector 51

8.1.1 Qualifications 51

8.1.2 Inspection Reports 51

8.1.3 Final Report 51

8.2 Required Special Inspection 52

8.2.1 Piling, Drilled Piers and Caissons 52

8.2.2 Excavation and Filling 52

8.2.3 Concrete 52

8.2.4 Reinforcing Steel and Prestressing Steel 53

8.2.5 Ductile Moment-Resisting Concrete Frame 53

8.2.6 Welding 53

8.2.7 High-Strength Bolting 55

8.2.8 Structural Masonry 56

8.2.9 Reinforced Gypsum Concrete Used as a Diaphragm 56

8.2.10 Insulating Concrete Used as a Diaphragm 56

8.2.11 Special Cases 56

COMMENTARY 57

viii
FOREWORD

This standard has been 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). The standard contains provisions for

the reduction of earthquake hazards in Federal buildings. It is intended to

be uniformly applied by all Federal agencies for the planning, design, and

construction of buildings, both within and outside the United States. The

Public Law also encourages agencies to define comprehensive screening and

evaluation programs for existing buildings and establish priorities and

programs for corrective actions. Guidelines for such programs for existing

buildings are included in another document,* also prepared by the Interagency

Committee.

The standard has been prepared for uniform use by all Federal agencies

and is an adaptation of existing voluntary standards, model building codes,

Federal regulations, and research reports. The standard is most closely

related to the Uniform Building Code , published by the International Conference of Building Officials, Whittier, CA, 1979, which, in turn, is based on

the Recommended Lateral Force Requirements and Commentary , published by the

Structural Engineers Association of California, San Francisco, CA, 1975. The

use made of the following document also deserves special note: Tentative

Provisions for the Development of Seismic Regulations for Buildings , prepared

by the Applied Technology Council and published by the National Bureau of

Standards, Washington, DC, 1978.

* In preparation by Subcommittee 3.

1
1. REGULATION

1.1 SCOPE. This standard shall be used in the planning, design, and

construction of new buildings and their appurtenances and in the alteration,

repair, or change of use of existing buildings. This standard also establishes

criteria for the evaluation of the seismic safety of existing buildings and

for the performance of corrective actions. This standard is intended to provide varying degrees of safety in buildings against the effects of seismic

ground shaking.

1.2 DEFINITIONS. The following definitions provide the meaning of the terms

used in this standard.

approved , as to materials and types of construction, 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 is the level at which the earthquake motions are considered to be

imparted to the structure.

bearing wall is any wall meeting either of the following classifications:

(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 see 3.1.2.

2
braced frame is a truss system or its equivalent which is provided to

resist lateral seismic forces in the frame system and 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 this standard, 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 resisting system.

dual system see 3.1.2.

ductile moment-resisting space frame is a moment-resisting (unbraced)

space frame with special ductility provisions to permit repeated inelastic

straining.

ductile moment-resisting space frame system see 3.1.2.

essential facilities see 1.4.2.

3
exte rior wal l 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.

l ive load is the load superimposed by the use and occupancy of the

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

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.

parapet wall is that part of any wall entirely above the roof line.

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-dimensional structural system without bearing

walls, laterally supported so as to function as a complete self-contained

unit. It may or may not included horizontal diaphragms or floor-bracing

systems.

structure is 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.

4
1.3 NOTATION. The following notations are used in this standard.

c

= Numerical coefficient for the vibratory response of a structure

to seismic motions

c

» Value of C used in calculating a lower limit for the base shear

Cm

*

t" Vi Value of C for the m

L specific mode of vibration

s

- Numerical coefficient for the vibratory response of a part of a structure to seismic motions

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

to the applied forces

Si - Deflection at level i relative to the base, due to arbitrary lateral

forces, Ef-j_ for use in determining the period of vibration, T

^i>^n>^x Lateral seismic force applied to level i, n, or x, respectively

XI n Lateral seismic forces on a part of the structure

il

•U Pm That portion of V considered concentrated at the top of the

structure in addition to Fn

^xm

t" Lateral seismic force applied to level x when considering the ra

1 mode of vibration

*i " Distributed portion of an arbitrary lateral force at level i for

use in determining the period of vibration, T

8

= Acceleration due to gravity

^i > ^n * ^x Height in feet above the base to level i, n, or x, respectively

I = Numerical coefficient for occupancy hazard

K = Numerical coefficient for structural system response to seismic

motions

lD

= the effect of dead load

lE

= the effect of lateral seismic load

= the effect of live load

LS " the effect of snow load

5
Level i, n, x:

1 Level of the structure referred to by the subscript i

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

x = That level which is under design consideration

^xm

i or x = 1 designates the first level above the base

y. Overturning moment at level x when considering the m

Ln mode of

vibration

N = The total number of stories above the base to level n

S = Numerical coefficient for site-structure resonance in response to

seismic motions

T = 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

T_ = m

A.1. Period of vibration for the m

tn mode, in seconds

ii H cn Characteristic site period

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

V = A lower limit of V when using modal analysis

II s

>

i.1. The value of V when considering the m

1

^ mode of vibration

Vt - The total lateral seismic force or shear at the base determined

by means of modal analysis

sr

'^xm The total lateral seismic force at level x when considering the

mode of vibration

W = The total dead load including the partition loading where

applicable; see 4.2.1

Wm = m

i.1. The portion of W effective for the m

tn mode of vibration

w = w

p The weight of a portion of a structure or nonstructural component

wi» wx

= That portion of W which is located at or is assigned to level 1 or x, respectively

Z = Numerical coefficient for the seismic hazard zone

6
^im^xm = T^e displacement amplitude at level i, or x, of the building

for the fixed-based condition when vibrating in its mfc ^ mode.

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. For locations not included in

figure 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 2.2.1), the

zone shall be determined according to table 1:

Table 1

Zone for Sites with Approved Site Evaluation

Design ground acceleration, a Zone

a < 0. 05g 0

0.05g < a < 0.10g 1

0.10g < a < 0. 20g 2

0. 20g < a < 0. 40g 3

0.40g < a 4

7
8 .
0

1

ALASKA

Figure 1. SEISMIC ZONE MAP

9
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 2, unless otherwise specified by the designated

authority:

Table 2

Values for Occupancy Importance Factor

Type of Occupancy I

Essential Facilitites. Essential facilities are 1.5

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

High Risk. Any building where the primary occu- 1.25

pancy 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

1.5 ALTERNATIVE PROVISIONS. 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.

10
Substantiating 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.

11
2. 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 this standard, except as

may be specified by the designated authority. Buildings located in zone 0

are exempt from the requirements in this standard.

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.

12
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 A and buildings

with an importance factor I 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 REQUIREMENTS.

2.3.2 Documentation. Drawings, specifications, 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 25 percent of the replacement

cost of the improved building must be corrected to resist the appropriate

level of earthquake forces, as recommended by the provisions of *

, also prepared by the Interagency Committee.

* In Preparation by Subcommittee 3.

13
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 this standard.

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.

14
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 4.6 and 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:

(1) 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 force-resisting system

in the direction under consideration is composed entirely of reinforced concrete or structural steel ductile moment-resisting space frames (unbraced

frames).

(2) Dual System (K = 0.80) - 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-resisting space frames with shear walls or braced frames.

15
(3) Box System (K « 1 . 33) - a system in which a significant fraction of

the gravity load is supported on bearing walls.

(4) Building Frame System (K = 1.0) - any other structural system.

Rigid elements that are not designated as part of the seismic forceresisting system may be incorporated into buildings provided that their

effect on the action of 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 load resisting ability

of the space frame.

Structural steel ductile moment -resisting space frames shall satisfy the

ductility provisions of 6.2, and reinforced concrete ductile moment-resisting

space frames shall satisfy the ductility provisions of 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:

16
(1) Ductile Moment-Resisting Space Frame Systems (K = 0.67): The

ductile moment-resisting space frames shall have the capacity to resist the

total required lateral seismic force by themselves.

(2) Dual Systems (K = 0.80): (i) The frames and shear walls shall

resist the total lateral force in accordance with their relative rigidities

considering the interaction of the shear walls and frames. (ii) The shear

walls acting independently of the ductile moment-resisting portions of the

space frame shall resist the total required seismic forces. (iii) The ductile

moment-resisting 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 4.4.7 shall not exceed 0.015 times the story height, unless it can be

demonstrated that greater drift can be tolerated. Diaphragm deformations

shall be considered in the design of the supported walls.

All 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 Height. 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.

17
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

elements, as determined in 4.6.1. Resistance shall be determined in accordance

with chapter 5, DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS.

3.2.2 Compatibility. For 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 force-resisting 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 4.4.7. The rigidity of other elements shall be considered in accordance

with 4.4.1.

3. 3 FOUNDATIONS

3.3.1 Soil and Foundation Capacity. In the determination 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 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.
4. STRUCTURAL ANALYSIS PROCEDURES

Stresses shall be calculated as the effect of a force applied horizontally

at each floor and roof level above the base. The force shall be assumed to

come from any horizontal direction; buildings shall be analyzed for the

force on each principal axis.

4.1 REQUIRED METHOD FOR SEISMIC-RESISTING SYSTEMS. The seismic loads for

all buildings shall be analyzed according to 4.2, as a minimum, except for

the following buildings, which shall be analyzed according to 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 soil-structure

interaction analysis that will modify the seismic forces and displacements

determined in this chapter. The seismic load effects shall be analyzed according to 4.4. The seismic loads and effects may be analyzed by other methods

according to the limitations given in 4.5.

19
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

where the terms are as follows:

(Eq. 1)

Z shall be determined from table 3 for buildings that do not have an

approved site evaluation:

Table 3

Zone Coefficient Z

Zone Z

4 1

3 3/4

2 3/8

1 3/16

0 0

For buildings that have a design ground acceleration established

according to an improved site evaluation study, Z = 2.5 times the

design ground acceleration (see 2.2.1) expressed as a fraction of the

acceleration of gravity.

I is specified in 1.4.2

K shall be determined from table 4 for buildings:

20
Table 4

* K for Buildings

System Response Classification (see 3.1.2) K

Ductile Moment-Resisting Space Frame 0.67

Dual System 0.80

Box System 1.33

Building Frame System 1.0

For other structures and appurtenances associated with buildings K

shall be determined from table 5:

Table 5

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

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 supported on four or more crossbraced legs as described above shall be designed in accordance with

4.6, using Cp = 0.3.

C shall be determined as:

C = 1 (Eq. 2)

15/r

21
The value of C need not exceed 0.12. The value of T is specified in

4.2.2.

S shall be determined in accordance with 4.2.3, except that the product

CS need not exceed 0.14.

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 value of T for buildings shall be

determined as:

0.05h

T = n (Eq. 3)

/D

except for buildings in which the lateral force-resisting system consists of

ducile 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, in

which case T shall be determined as:

T = 0. 10N (Eq. 4)

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

The period T may be established using the structural properties and

def ormational characteristics of the resisting elements in a properly

substantiated analysis, which could make use of an equation such as:

22
2ir ./( I w^S (Eq. 5)

2

) * (g Z f^)

y i-1 i-1

where the values of f£ represent any lateral force distributed approximately

in accordance with the principles of 4.2.4 or any other rational distribution.

The elastic deflections, 5^, shall be calculated using the applied lateral

forces, f^. However, the value of T so determined shall not exceed the value

calculated by the appropriate equation 3 or 4 by more than 20 percent.

4.2.3 Site Coefficient. The value of S shall be determined by one of

the following two methods.

Method I

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 with:

(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 second; 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 cohesionless 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.

23
(3) Soil Profile Type 3 is a profile with soft- to medium-stiff clays

and sands, characterized by 30 feet or more of soft- to medium-stiff clays

with or without intervening layers of sand or other cohesionless soils.

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 2 shall be used.

S is a coefficient for the effects of site conditions on building

response given in table 6:

Table 6

Site Coefficient

Soil Profile Type S

1 1.0

2 1.2

3 1.5

In zones 3 and 4, the product CS for Soil Profile Type 3 need not exceed

0 . 11 .

Method II

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

not be less than 1.0:

For T/T

g = 1.0 or less

S = 1.0 + (X ) - 0 .5 (JL ) 2

< E(1* 6 > Ts Ts

For T/T

g greater than 1.0 S=12+06— - 0 3 (— )

2 (Eq.

24
where

T in equations 6 and 7 shall be as determined in A. 2. 2 but T shall

not be less than 0.3 second.

Tg The range of values of Ts may be established from properly

substantiated geotechnical data, except that Ts shall not be taken

as less than 0.5 second nor more than 2.5 seconds. T g shall be

that value within the range of site periods, as determined above,

that is nearest to T.

When Ts 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 T s

.

4.2.4 Vertical Distribution of Forces. 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 corresponding plan dimension of the lower part may be considered as uniform

buildings without setbacks for the purpose of this section, provided other

irregularities do not exist.

For uniform buildings, the distribution of the lateral seismic forces

shall be as follows:

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

structure as follows:

25
(Eq. 8) n V 3 F t + E Fj

i=l

The concentrated force at the top shall be determined as:

F t = 0.07TV (Eq. 9)

F t 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:

p = (V - F t

) wx

hx

(Eq. 10)

x —

Z w^h^

i=l

4.2.5 Overturning Moment. The overturning moment at each story shall

be calculated as follows:

n Mx

= F t (hn

- hx) + Z Fi (hi - hx) (Eq. 11)

i=x

For structures in which the seismic resisting system acts essentially as

an isolated cantilever, the overturning moment shall be modified to account

for the dynamic characteristics of the structure.

4.3 ELASTIC DYNAMIC LOAD ANALYSIS. The lateral seismic forces shall be

determined in accordance with this section using all modes of vibration with

a period greater than 0.4 second, but in no case less than the first three

modes in either principal direction.

4.3.1 Mode Shapes and Periods. The mode shape, <J>i m , and the modal

period, Tm shall be determined for each mode in accordance with the principles

of mechanics.

26
4.3.2 Modal Base Shear. The total lateral seismic force for a mode

shall be determined as follows:

Vm

- ZIKCjjjSWjjj

where

Z, I, K and S are as defined in 4.2

Cm

shall be determined for each mode as:

(Eq. 12)

(Eq. 13)

The value of C^j need not exceed 0.12 and the product of CmS need

not exceed 0.14. Tm

is the period of vibration for the m

1"*1 mode, in

seconds. Subject to the approval of the designated authority, a site

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

Wm shall be determined for each mode as:

W

m

n

( 2 w

i

<p i ) i=l

2

n

£ w^<j>

i=l

2

im

(Eq. 14)

4.3.3 Design Values. The following quantities shall be determined for

each mode according to the principles of mechanics:

(1) Fxm - the equivalent lateral seismic force applied to each level

(2) <f>xm - the lateral displacement at each level

(3) Vxuj - the lateral seismic shear force at each level

(4) - the overturning moment at each level

(5) the story drift at each level

27
The total value for each of the above quantities and the total base shear

V t shall not 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 1 by substituting C for C

C is determined from equation 2 by substituting T for T

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

3 or 4, as appropriate

Where Vt is less than V, the design value for each quantity shall be the

product of the total value and the following factor, A:

A = V/Vt (Eq. 15)

V t need not exceed V determined from equation 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-resisting system in proportion

to their rigidities considering the rigidity of the horizontal bracing

system or diaphragm.

4.4.2 Horizontal Torsion. At each level designated as x, the force

F

x 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

28
the vertical resisting elements depend on diaphragm action for shear

distribution at any level, the shear-resisting 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 of 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:

n

. Z Fi

F = i~x w px n px

E w^

i=x

where

(Eq. 16)

F^ = 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 occupancies.

The force FpX determined from equation 16 need not exceed 0.30ZIWpX .

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 16.

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

0.14ziWpX .

29
4.4.4 Overturning. The increment of overturning moment at each story

shall be distributed to the resisting elements in the same proportion as the

distribution of the horizontal shears. For tall buildings analyzed according

to 4.2, the overturning moment effect in any element may be multiplied by the

factor k depending on the location of the element as follows:

(1) k = 1.0 for the top 10 stories

(2) k = 0.8 for the 20th story from the top and below

(3) k = a value between 1.0 and 0.8 determined by a straight line

interpolation for stories between the 10th and 20th stories below the top.

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 provided.

Where a vertical resisting element is discontinuous, provision shall

be made to carry the overturning moment carried by the lowest story of that

element to the foundation.

At the soil-foundation interface, the design overturning moment may

be modified as follows:

(1) for buildings analyzed according to 4.2, 75 percent of the value

determined in 4.2.5 may be used.

(2) for buildings analyzed according to 4.3, 90 percent of the value

determined in 4.3.3 may be used.

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

30
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. Exception: diaphragms, and

components of the seismic force-resisting system utilized in only one of the

two orthogonal directions need not be designed for the combined effects.

4.4.6 Vertical Motion Effect. When combining gravity and seismic load

effects for buildings in zones 3 or 4, vertical seismic loads shall be

accounted for by increasing or decreasing the dead load as given in this

section:

additive load combination = 1.2 Lj) + Ll + Lg + Lg (Eq. 17)

counteracting load combination = 0.8 Lp + Lg (Eq. 18)

where

Lq = dead load effect

Ll

= live load effect

Lg = snow load effect

Lg = lateral seismic load effect

The combination requiring the larger resistance shall be used. For brittle

elements, such as welded steel column splices, etc., or for horizontal prestressed components, the coefficient 0.8 in equation 18 shall be changed to

0.5. For horizontal cantilever components, the coefficient 0.8 in equation

18, shall be changed to -0.2.

31
4.4.7 Displacements. The displacement calculated from the application

of the required lateral forces shall be multiplied by (3.0/K) to obtain the

design displacement (and drift).

4.5 INELASTIC ANALYSIS. Any analytical procedure based on the principles

of mechanics may be used subject to the approval of the designated authority.

In no case shall the force effects for which the building is designed be

less than that determined using 4.3.3.

4.6 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:

F

p = ZICpWp (Eq. 19)

where

Z and I are the coefficients used for the building (see 4.2.1 and 1.4.2)

Wp is the weight of the part or portion

Cp is set forth in table 7.

Interconnection forces between two parts of the structure shall not be

less than 0.133ZI times the weight of the smaller portion.

32
Table 7

Horizontal Force Factor Cp for Elements of Structures

Direction of Value

Part or Portion of Buidings Horizontal

Forces

of C

p

Exterior bearing and nonbearing

walls, interior bearing walls

and partitions, interior non- bearing walls and partitions.

Masonry or concrete fences

over 6 feet high.

Normal to

flat surface

0.3

Cantilever elements, chimneys

or stacks

Any direction 0.8

Connections for prefabricated

structural elements other than

walls, with force applied at

center of gravity of assembly.

Any direction 0.3

33
5. DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS

This chapter specifies the commonly accepted standards for materials,

design, and construction 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.

(1) Specification for the Design, Fabrication and Erection of Structural

Steel for Buildings, American Institute of Steel Construction

(AISC), 1978.

(2) Structural Welding Code (AWS Dl.1-80), American Welding Society

(AWS ) , 1980.

(3) Specification for Structural Joints Using ASTM A325 or A490 Bolts,

AISC, 1976.

(4) Specification for the Design of Cold-formed Steel Structural

Members, American Iron and Steel Institute (AISI), 1980 Edition,

(5) Standard Specification for Open Web Steel Joists, J- and H-Series,

adopted by the Steel Joist Institute (SJI) and AISC on October 1,

1974.

(6) Standard Specification for Longspan Steel Joists LJ- and LH-Series

and Deep Longspan Steel Joists, DLJ- and DLH-Series, adopted by

SJI and AISC on October 1, 1974.

(7) Criteria for Structural Applications for Steel Cables for Buildings,

AISI, 1973 Edition.

34
(8) Design Manual for Floor Decks and Roof Decks (SDI #23), Steel Deck

Institute.

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 standard:

(1) Building Code Requirements for Reinforced Concrete, (ACI 318-77,

excluding Appendix A), American Concrete Institute (ACI), 1977.

(2) Specifications for Structural Concrete for Buildings (ACI 301-72),

ACI, revised 1975.

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 Specification for Stress Grade Lumber and Its

Fastenings, National Forest Products Association, 1977, with

1980 Supplement.

(2) American Softwood Lumber Standard, Voluntary Product Standard,

PS 20-70, U.S. Department of Commerce, 1970.

(3) Plywood Design Specification, American Plywood Association, 1977.

(4) Plywood Diaphragm Construction, American Plywood Association, 1977

(5) Construction and Industrial Plywood, Voluntary Product Standard,

PS 1-74, U.S. Department of Commerce, 1974.

(6) Standards for the Design of Structural Timber Framing, AITC 102-76

American Institute of Timber Construction, 1976.

(7) Standard Specifications for Structural Glued Laminated Timber of

Douglas Fir, Western Larch, Southern Pine, and California Redwood,

AITC 117-76, American Institute of Timber Construction, 1976.

(8) Structural Glued-Laminated Timber, Voluntary Product Standard,

PS 56-73, U.S. Department of Commerce, 1973.

35
(9) Part III of the One- and Two-Family Dwelling Code, 1979 editions,

published by International Conference of Building Officials,

Building Officials and Code Administrators, and Southern Building

Code Congress.

(10) Section 4713: "Shear-resisting Construction with Wood Frame,"

Uniform Building Code, International Conference of Building

Officials, 1979.

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 forces shall conform to one or more of the following references,

except as modified by other provisions of this standard:

(1) Chapter 24: Masonry, in the Uniform Building Code, International

Conference of Buiding Officials, 1979.

(2) Section 4: Reinforced Masonry, in Seismic Design for Buildings,

TM 5-809-10, Departments of the Army, Navy and Air Force, 1973.

(3) Building Code Requirements for Concrete Masonry Structures, ACI

531-79, American Concrete Institute, 1979.

(4) American Standard Building Code Requirements for Masonry, A41. 1-1953,

National Bureau of Standards Miscellaneous Publication, 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, 1979 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:

36
Specifications for Aluminum Structures, 3rd Edition, The Aluminum

Association, 1976.

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 this standard:

(1) Section 2407: Reinforced Gypsum Concrete, in Uniform Building Code,

International Conference of Building Officials, 1979.

(2) Section 4711: Gypsum Wallboard, in Uniform Building Code,

International Conference of Building Officials, 1979.

(3) Section 5-05: Gypsum Diaphragms, Cast-in-Place, in Seismic Design

for Buildings, TM 5-809-10, Departments of the Army, Navy, and Air

Force, 1973.

(4) Standard Specification for Gypsum Concrete, ASTM C317-76.

(5) Standard Specification for Lightweight Aggregate for Insulating

Concrete, ASTM C332-77a.

(6) USA Standard Specification for Reinforced Gypsum Concrete, The

Gypsum Association, 1968.

(7) Recommended Specifications for the Application and Finishing of

Gypsum Board, The Gypsum Association, 1979.

(8) Using Gypsum Board for Walls and Ceilings, The Gypsum Association,

1977.

37
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 brackets:

[1] Uniform Building Code, International Conference of Building

Officials, 1979.

[2] Recommended Lateral Force Requirements and Commentary, Structural

Engineers Association of California, 1978.

[3] Seismic Design for Buildings, Departments of the Army, Navy and

Air Force (TM 5-809-10), 1973.

[4] Specification for the Design, Fabrication, and Erection of Structural

Steel for Buildings, American Institute of Steel Construction, 1979.

[5] Building Code Requirements for Reinforced Concrete, American Concrete

Institute, 1977 (ACI 318-77).

6.1

MOMENT-RESISTING FRAMES

6.1.1 Ductile Moment-Resisting Space Frames. Ductile moment-resisting

space frames shall be structural steel complying with 6.2 or reinforced

concrete complying with 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. EXCEPTION: Frames in the perimeter

line of the vertical support of buildings designed with shear walls taking

100 percent of the design lateral forces need only conform with 3.2.2.

38
6.2 STEEL DUCTILE MOMENT-RESISTING SPACE FRAMES. The design and construction

of moment-resistant joints for steel ductile moment-resisting space frames

shall comply with all applicable requirements for "Type 1 Construction" as

defined in reference [4], 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 requirements of Section 2722: "Steel Ductile

Moment-Resisting Space Frames" of reference [1], or Section 4 "Steel Ductile

Moment-Resisting Space Frames" of reference [2], with the following clarification: 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 [4],

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 following:

(1) Section 2626: "Ductile Moment-Resisting Space Frames - Seismic

Zones Nos. 3 and 4" of reference [1].

(2) Section 2: "Concrete Ductile Moment-Resisting Space Frames" of

reference [2],

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

of reference [3].

Concrete ductile moment-resisting space frames in other buildings shall

comply with either the previous requirements or the requirements of reference

[5], excluding Appendix A, plus the following requirements of this section.

39
The terms "web reinforcement," "tie," and "spiral" and the symbol "d" in the

following shall be used as defined in reference [5].

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 [5], except that such web reinforcement shall be not less than 0.15

percent of the area computed as the product of the width of the web and the

spacing of web reinforcement along the longitudinal axis of the member. The

first stirrup shall be located 2 inches from the column face. The next six

stirrups shall be spaced not over d/4.

Positive moment reinforcement at all supports of flexural members subject

to reversal of moments shall be anchored by bond or mechanical anchors in or

through the supporting member to develop the yield strength of the bar.

Lapped splices located in a region of tension or reversing stress shall

be confined by at least two closed ties at 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 reinforcement

through the joint. Such lateral reinforcement 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.

40
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, 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 for stresses resulting from earthquake

forces.

6.4.2 Steel Braced Frames. Braced frames shall be composed of axially

loaded bracing members of ASTM A36, A440, A441, A500, A501, A572 (except

Grades 60 and 65) or A588 structural steel. A500 steel shall not be welded.

6.4.3 Reinforced Concrete Braced Frames. 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 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 following:

(1) Section 2627: ’’Earthquake Resisting Concrete Shear Walls and

Braced Frames" of reference [1].

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

[ 2 ].

41
6.6 REINFORCED MASONRY WALLS. Masonry walls required to be reinforced

masonry by 6.9 or 7.5 shall comply with the minimum amount and maximum spacing

of reinforcement specified in table 8.

Table 8

Minimum Reinforcement and Maximum Spacing for Reinforced Masonry Walls

Type of Wall

I Total Area1 of ReinIforcement as a Percent

I of Gross Area of Wall

I (nominal dimensions)

1

Maximum Spacing of Bars (inches)

Vertical Bars

1 Horizontal Bars

Seismic Zones

1 Seismic Zone

1 Seismic Zone

I 4&3 1 2 1 1 4&3 | 2 1 1 4&3 1 2 I 1

Structural

1

1

1

1

1

1

1

1

1 1

1 1

1

1 T1 (i. e. , bearing 1 1 1 1 1 1 1 1 or shear) | 0.20

1

1

1 0.20 | 0.15

1

24 1

1 36 1 60 |

1 1 48 11 60 1 721

Nonstructural

1

I 0.15

1

1

1

1

1 0.15 | 0.15

1

48

1

1

1 60

1 1

1 72 |

1 1 84

1

1

1 84

1

1 96

1

(1) 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.

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.

42
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 Anchorages to Wood Diaphragms. 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.

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 of the discontinuity to resist the local

stresses created by the presence of the discontinuity. These chords shall

extend into the body of 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 6.6 for

masonry and reference [5] for concrete. Principal reinforcement in masonry

shall be spaced 2 feet maximum on center in buildings using a moment-resisting

space frame.

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

43
anchorage shall provide a positive direct connection capable of resisting the

horizontal forces specified in this standard or a minimum force of 200 pounds

per linear foot of wall, whichever is greater. Walls shall be designed to

resist bending between anchors where the anchor spacing exceeds 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

approximately 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 0.10ZI times the vertical load on the pile,

cap, caisson, or footing.

6.10.2 Pile Cap Connections. In zones 2, 3, or 4, all piles shall be

connected to the pile cap to resist an uplift force of not less than 0.15ZI

times the vertical load on the pile.

44
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 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.

45
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:

F

p = ZICpW

p

(Eq. 19)

where

Z is specified in 4.2.1

I is specified in 1.4.2 EXCEPT:

1. For connectors of precast or prefabrication panels,

the value of I shall be as given in 7.2.

2. For the anchorage of machinery and equipment required for

life safety systems, the value of I shall be 1.5.

Cp is given in table 9.

Wp is the weight of the component, EXCEPT:

1. For storage racks, Wp 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.

46
Table 9

Horizontal Force Factors Cp for Nonstructural Elements of Buildings

Component

Direction of

Horizontal Forces

Value

of C^

Exterior and interior walls and partitions

Masonry or concrete fences over 6 feet high

Normal to flat

surface

0.3

Cantilever elements:

a. Parapets Normal to flat

surface

0.8

b. Chimneys or stacks Any direction 0.8

Exterior and interior ornamentations and

appendages

Any direction 0.8

When connected to, part of, or housed

within a building:

a. Penthouses, anchorage and supports for \

chimneys and stacks and tanks, including

contents

b. Storage racks with upper storage level

at more than 8 feet in height, plus

contents

c. All equipment or machinery

d. Large ducts, large pipes, and critical

or hazardous pipes

^Any direction 0.3 2 > 3

Suspended ceiling framing systems Any direction 0.3

1. Cp for elements laterally self-supported only

two-thirds of value shown.

at the ground level may be

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 specification of such equipment

and machinery.

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.

47
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 plus 50 percent of

the rack-rated capacity.

7.2 DISTORTION COMPATIBILITY FOR EXTERIOR PANELS. Precast or prefabricated

nonbearing, nonshear wall panels or similar elements which are attached to

or enclose the exterior shall be designed to resist forces determined from

Eq. 19 and shall accommodate movements of 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 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 ductility

capacity.

48
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. 19. 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. 19.

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 Eq. 19.

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, high-temperature 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 7.1. In addition, their

design and detailing shall consider effects induced by the structural drift

calculated in 4.4.7. Special consideration shall also be given to relative

movement at separation joints.

49
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.

50
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 greatter than 1.0 in

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.

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 specifications. The

designated authority may waive the requirement for a special inspector if he

finds that the construction is of minor nature.

8.1.1 Qualifications. 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 discrepancies shall be brought to the immediate

attention of the contractor for correction, then, if uncorrected, to the

engineer or architect of record and 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

specifications and the applicable workmanship provisions of these codes.

51
8.2

REQUIRED SPECIAL INSPECTION. The following objects and operations shall

be subject to continuous inspection by a special inspector. Some inspections

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 inspection.

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

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 specifications.

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

£'c 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 6.10.1.

(3) Site work concrete full-supported on earth and concrete where no

special hazard exists.

52
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 8.2.3. EXCEPTION: The special inspector need

not be present during entire reinforcing steel and prestressing steel-placing

operations, provided he has inspected for conformance with the approved plans

prior to the closing of forms or the delivery of concrete to 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 reinforcement

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.

(2) Ductile moment-resisting steel frames shall receive the following

nondestructive testing:

53
Welded connections between the primary members of ductile

moment-resisting space frames shall be tested by nondestructive

methods for compliance with the AWS Structural Welding Code

(Dl.1-80) and job specifications. A program for this testing

shall be established by the person 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. EXCEPTION: When approved, the nondestructive testing rate for 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 number of

welds completed. 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 considered one weld.

54
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 fabricator utilizing

qualified 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 1-1/2 inches, when subjected to

through-thickness weld shrinkage strains, shall be inspected

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 (Dl.1-80).

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:

(a) inspects the surfaces and bolt type 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

specifications.

(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 required.

55
8.2.8 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 may consist 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

noncontinuous 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.

8.2.11 Special Cases. Any other work which, in the opinion of the

designated authority requires special inspection.

56
COMMENTARY

This standard contains provisions for the reduction of earthquake hazards

in Federal buildings. One purpose is to provide a uniform standard for use

by all Federal agencies for the planning, design, and construction of buildings,

both within and outside the United States. As with the voluntary standards

and codes upon which this standard is 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 accelerations 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 nonstructural 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 nonstructural 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.

The standard has been prepared for the purposes of Federal agencies as

an adaptation of existing voluntary standards, model building codes, Federal

regulations, and research reports. The standard is most closely related to

the Uniform Building Code , 1979 edition (published by the International

Conference of Building Officials and subsequently referred to as the UBC)

The seismic provisions of the UBC are based on the Recommended Lateral Force

Requirements and Commentary , 1975 edition (published by the Structural

Engineers Association of California and subsequently referred to as the SEAOC

1 From the SEAOC Commentary

57
requirements). Substantial use is also made of the Tentative Provisions for

the Development of Seismic Regulations for Buildings (prepared by the Applied

Technology Council and published by the National Bureau of Standards and subsequently referred to as the ATC provisions). The seismic regulations of the

Veterans Administration, Army, Navy, Air Force, General Services Administration, and Department of Housing and Urban Development were all considered in

the development of this standard.

One of the objectives of this commentary is to explain the differences

between the provisions of this standard and those of its sources. Because

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

served as the starting point for this standard, 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.

This commentary also addresses specific issues to assist the user of

the standard, but it is not a complete commentary on seismic-resistant design.

Both the SEAOC and ATC provisions are accompanied by extensive commentaries

that are recommended reading for users of this standard. 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.

Cl.l SCOPE. This standard is primarily intended for new buildings.

Structures that are not associated with buildings are outside the scope

58
because their particular functional requirements and the nature of hazard

they present have not been considered in developing the requirements of this

standard and because the idealization of seismic loadings presented in* this

standard 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 standards of the Nuclear Regulatory Commission.

The coverage of existing buildings in this standard is brief; a related

document (also to be issued by the Interagency Committee on Seismic Safety

in Construction) will provide more specific criteria for those occasions

when the requirements of this standard indicate the need for their application. The application of this standard to Federally leased buildings and to

Federal grant and regulatory programs is covered in another document, which

will be issued by the Interagency Committee on Seismic Safety in Construction.

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 UBC, this standard accomplishes this purpose

by means of a numerical coefficient for occupancy hazard, which is specified

in 1.4.2. The statement is also a recognition that many provisions are based

on crude approximations and may result in different levels of safety for

different situations.

This standard is 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 many provisions, such

as stiffness and overturning resistance. No such clause is in this standard,

59
because criteria for resistance to the two forces are too different. Because

the response to seismic ground shaking will ordinarily require inelastic straining of the seismic force-resisting system, the many ductility and detailed

requirements in this standard must be satisfied even for buildings in which

wind force exceeds the nominal design seismic force. For buildings in 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 standard.

Cl. 2 DEFINITIONS. The bulk of the definitions are taken from, or based upon,

the following sections of the UBC: Chapter 4 for general terms, section 2302

for structural terms, and 2312(b) for seismic terms. The definition for

height is original, but is consistent with the use of the terms in the UBC.

Designated authority is original, and in the context of the UBC it can be

thought to replace the term building official . The definition for diaphragm

is taken from the ATC. In all the definitions an emphasis has been placed

on lateral seismic forces when compared to the definitions in the UBC. The

definitions of the classes of building systems are contained in 3.1.2, and

the discussion of those definitions is in that section of commentary. The

definitions for space frame , moment-resisting space frame, and ductile

moment-resisting space frame are reworded in an attempt to improve their

clarity.

60
Cl. 3 NOTATION. Each of the symbols used in section 2312 of the UBC are used

for the same meaning in this standard. In addition, several symbols for

modal analysis and for load combination equations appear in this standard

that are not found in the UBC. The verbal expression defining many of the

symbols is changed from the UBC in an attempt to make the collected notation

more useful.

Cl. 4 HAZARD CLASSIFICATIONS. Buildings are classified on two scales in this

standard, much as they are in the UBC. One scale, the zone, relates to the

likelihood of seismic activity, and the other scale, the occupancy importance

factor, relates to the consequences of structural failure due to an earthquake. These classifications are used throughout the standard to determine

the applicability of specific requirements. Table Cl summarizes, very generally, the use of these hazard classifications for this purpose. It should

be noted that there are several differences with the UBC.

Cl. 4.1 Seismic Ground Shaking Hazard. The map in this draft has been

derived from the "Effective Peak Velocity-Related Acceleration" map contained

in the ATC Commentary. It has the following characteristics necessary for

consistent use with the basic provisions of the standard:

(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

microzonation.

61
Table Cl.

Applicability of Requirements

Zone Occupancy Importance Factor

1 1 1 1.25 1 1.5

0

1

1

1 (a)

1

1

I (a)

1

1jfl (a)

1

1

1

i (b)

I

1

I (b)

1

1 (b)

2

1

1

1 (b)

l

1

I (c)

1

1

I (c)

3

1

1

1 (c)

l

1

| (c)

1

1

1 (c)+(d)

4

1

1 (e)

1

1 (e)

1

1 (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

62
(3) The relative design acceleration for the five zones 4 through 0 is

in the proportion 1 : 3/4 : 3/8 : 3/16 : 0.

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 ATC

"Effective Peak Acceleration" map because it accounts for the effect of large,

distant earthquakes on tall buildings. The Subcommittee on Evaluation of Site

Hazards also tentatively agreed to recommend this map.

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

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 comprehensive 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 this standard, 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 zone from a value of sitespecific ground acceleration is provided for such buildings. Such a relation

is necessary for the proper application of various requirements that depend

on the zone even though the seismic forces on such buildings will normally

63
be calculated directly from the site-specific ground 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

occurance, the values in the table should be adjusted accordingly. The

assumption corresponds to the basis for the map in this standard.

Cl. 4. 2 Occupancy Hazard. The categories of occupancies in this section

are the same as in section 2312(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.

Cl. 5 ALTERNATIVE PROVISIONS. This provision is very general. Similar

provisions are found in sections 2312(a) and (i) of the UBC.

C2. GENERAL REQUIREMENTS

Because this standard is not a chapter of a larger document dealing with

all aspects of buildings, as are the seismic provisions in the UBC, and

because this standard incorporates several provisions not found in the UBC,

the organization of this standard is quite different from that of the seismic

provisions of the UBC. This chapter sets the framework for the use of all

the remaining chapters of this standard.

C2.1 GENERAL PERFORMANCE REQUIREMENT. This very general requirement is

essentially the same as the first sentence of the UBC seismic provisions.

The exemption for zone 0 merely gives formal recognition to present practice,

64
although designers would be well advised to satisfy the Intent of 3.1.1 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 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 studies are included in the manual of

Standard Practice for the Evaluation of Site Hazards published by the

Interagency Committee on Seismic Safety in Construction.

C2.2.2 Site Limitations. Note that the requirement for siting essential

facilities to avoid surface rupture due to fault displacement 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 no criteria are provided in this standard. The Interagency Committee manual on site hazard evaluations previously referenced

includes some information on this subject.

65
C2.3 DESIGN OF NEW BUILDINGS. The bulk of this standard deals with design.

This section merely establishes the applicability of the design requirements

and requires a standard amount of documentation to confirm compliance with

the requirements.

C2.4 CONSTRUCTION. The importance of quality assurance cannot be overstated.

Federal agencies have general quality assurance programs; this provision

supplements those agency provisions in the higher seismic zones for issues

of special concern in seismic safety.

C2.5 EXISTING BUILDINGS. This standard does not contain much in the way of

detailed criteria for existing buildings. Another document published by the

Interagency Committee on Seismic Safety in Construction includes much more

detail on the subject [in preparation by Subcommittee 3, Existing Buidings].

In particular, that document contains the methodology and mitigation techniques

for corrective actions and it defines the appropriate level of strengthening

called for in 2.5.2.

The second paragraph of 2.5.2 is taken from 2312(j)2A of the UBC. Note

that overstrengthening one portion of a building could cause higher loads in

other portions of the building and thus should be avoided.

C3. STRUCTURAL DESIGN CRITERIA

Chapter 3 includes the governing criteria for the structural portions of

a building. Reference is made to chapter 4 for the determination of the

force effects of seismic ground shaking, to chapter 5 for the basic standards

for proportioning structural components, and to chapter 6 for special details

66
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 standard (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. 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 be designated as seismic

force-resisting and designed as 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-resisting system are considered effective in moderate earthquakes.

67
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.

*

C3.1.1 Integrity. This requirement, taken from the ATC provisions,

is very elementary. 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 design standard simulates

the effect of these inertial forces by specifying equivalent seismic forces

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 section are 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 classification deserve comment. The first

decision in classing a building concerns bearing walls. Unfortunately,

68
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 axes.

The second important decision regards the use of ductile moment-resisting

space frames in the designated seismic force-resisting system. Because rigid

elements may exist in buildings without being a part of the designated seismic

force-resisting system, it is possible for a building with both ductile momentresisting space frames and shear walls (or braced frames) to be in any of the

three remaining classes, as follows: 1) where the designated seismic forceresisting 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 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 force-resisting systems is adopted.

A great variety of seismic force-resisting systems is included in the

"Building Frame System" class, such as shear walls, braced frames, arches,

69
moment-resisting frames that do not meet the special ductility requirements

of chapter 6, etc.

3.1.6 places restrictions on the class of seismic-force resisting systems

allowed for tall buildings in zones 2, 3, and 4.

C3.1.3 Strength. This provision is consistent with the UBC. The intent

is to continue present 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.

C3.1.4 Stiffness. 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-resisting system. The

SEAOC 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

70
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 (in 4.4.7) and the drift limit is changed 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 Cl.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 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.

C3.1.6 Height. The requirement is essentially the same as section

2312(j)lB 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

of 0.67 or 0.80.

C3.2 OTHER STRUCTURAL ELEMENTS. Seismic ground shaking affects the entire

structural system, not just the designated seismic force-resisting system.

These effects are primarily of two types, the inertial forces due to the

mass of the structural element and the distortions the structural element

71
experiences as the seismic force-resisting systems responds to the ground

shaking.

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 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 requirement is taken from section 231 2 ( j ) ID

of the UBC. The distortion specified in 4.4.7 (which includes the amplification by the factor 3/K) is intended to include both the ductility of the

seismic force-resisting system and the P-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 wording used is quite similar to the ATC

provisions. The intent is to cause the geotechnical engineer and 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

72
that soil-structure interaction analyses are necessary; such analyses may

be useful for special types of structures with specific soil and foundation

conditions, but that is an issue to be decided on a case by 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 exceptionally 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 of the seismic force-resisting system be continued to the

foundation.

C4. STRUCTURAL ANALYSIS PROCEDURES

This chapter provides for the calculation of seismic loads and their

effects. No analysis is provided for the vertical motions of ground shaking,

except for the approximation introduced by varying the load factor for dead

load as specified in 4.4.6. 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 for combining load effects in 4.4.5.

73
C4.1 REQUIRED METHOD FOR SEISMIC-RESISTING SYSTEMS. The minimum level of

analysis, contained in 4.2, is quite similar to the UBC and is thought

appropriate for most buildings. The modal analysis, contained in 4.3, is

somewhat similar to the ATC provisions and is appropriate for multistory

buildings that are not uniform throughout their height. The use of more

sophisticated analyses is discussed in C4.5. The 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 discouraged.

It should be noted that soil-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. The Interagency Committee's Manual on site evaluation methods referred to previously, discusses both the technique and

appropriateness of soil-structure interaction analyses.

C4.2 ELASTIC STATIC LOAD ANALYSIS. Except where noted, 4.2 is based on

sections 2312(d) and (e) of the UBC.

C4.2.1 Base Shear. The SEAOC Commentary is a valuable resource for

understanding these provisions. The provision for calculating Z for those

buildings on sites with an approved site evaluation 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. Permanent loads that are fixed to the structure,

74
such as some types of computer installations, should be included in W. When

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

C4.2.2 Period of Vibration. Although the equations for calculating the

period are the same as given in the UBC, the philosophy of their use is more

like that given in the ATC provisions. Equations 3 and 4 are very approximate 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 significantly larger than

observed in real buildings. Use of unrealistically large values for the

period results in low and unsafe values for the base shear.

C4.2.3 Site Coefficient. Two alternative methods are presented.

Method I is taken from the ATC, and method II is taken from the UBC.

Method II 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,

T s

" is recommended (also published as UBC Standard No. 23-1).

In method I, Soil Profile Type 2 is specified for sites at which the

soil properties are not known in detail. It is anticipated that the designer

would always be aware of the soil properties at sites actually fitting Soil

Profile Type 3 because of the likely need for deep or special foundations.

C4.2.4 Vertical Distribution. 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

75
of such consistency in stiffness and mass, but more sophisticated analyses

are required for substantial differences in strength.

C4.3 ELASTIC DYNAMIC LOAD ANALYSIS. This analysis is only applicable to

multistory buildings. The provisions are based on the ATC 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 ATC, but is simply consistent

with the spectrum used in 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

modes

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 to determine the distribution of seismic forces more accurately, not

to reduce the overall force.

C4.4 ELASTIC LOAD EFFECT ANALYSIS. Except where noted, the provisions of

4.4 are takken from sections 2312(e) and (f) of the UBC.

C4.4.1 Shear. It is frequently useful to idealize the relative rigidity

of horizontal to vertical bracing systems as "flexible" 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

76
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 diaphragms and masonry or concrete shear walls are normally 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 characterized as 'flexible’."

C4.4.4 Overturning. The reduction allowed for tall buildings is taken

from the ATC. It is allowed because the story forces defined in 4.2.4 overestimate the overturning moment in such structures. Those story forces are

designed to produce story shear forces that are consistent with the envelope

of maximum story shear forces found in modal analysis for such structures

over a wide range of periods. Similar story forces could be specified to

produce overturning moments found in such modal analyses, but the forces

would not be identical. It is simpler to adjust the overturning moments to

remove the discrepancy. The reduction is unrelated to live load reduction

77
for area, to load combination factors, or to rocking of a building foundation.

When applying this reduction, designers should be particularly alert to

situations where uplift from overturning is combined with minimum likely

dead load.

The additional reduction allowed at the soil-foundation interface accounts

for the rocking on a foundation in a very approximate way. It is also taken

from the ATC. Both reductions are allowed in this standard in an attempt to

partially account for the discrepancy between the lack of overturning failures

of buildings and the fact that design force levels are below the real force

levels in a strong earthquake.

C4.4.5 Orthogonal Effect. This provision is similar to the ATC

provisions. 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 of components that are utilized in only one direction for seismic

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

of extra calculation.

C4.4.6 Vertical Motion Effect. This provision is also taken from the

ATC. It accounts for vertical accelerations in an approximate way. The

+ 20 percent does not reflect the maximum vertical response likely, however,

since it was considered unlikely for the maximum horizontal and vertical

responses to occur simultaneously. Changing the coefficient on dead load

78
for horizontal cantilevers accounts for a dynamic response of an upward

acceleration of 120 percent of gravity.

C4.4.7 Displacements. The amplification of the displacements by 3.0/K

is different than in the UBC, which specifies 1.0/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 C3.1.4, the

amplification by 3.0/K is used throughout in this standard.

C4.5 INELASTIC ANALYSIS. The specified methods of analysis are the minimum

levels deemed appropriate. More sophisticated analyses are frequently necessary for adequate prediction of the structural response to ground shaking.

It is important to realize that dynamic analysis should be used primarily to

determine a more accurate distribution of forces and deformations among the

various parts of a structure, and not to bring about a significant reduction

in the overall base shear. The philosophy behind the lower limit on base

shear is similar to that in the ATC.

C4.6 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 ATC.

C5 DESIGN AND CONSTRUCTION STANDARDS FOR STRUCTURAL MATERIALS

This standard makes reference to widely accepted national standards for

design and construction provisions for specific structural materials. This

is in keeping with both the current practice of Federal agencies and Federal

policy as set forth in Circular A-119 of the Office of Management and Budget.

79
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 this standard frequently modify or take exception to

the referenced standards, in which cases this standard shall control (for

example, most of the provisions of chapter 6). With 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, this standard allows some choice between different standards for

masonry.

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 provisions of this standard are referenced. In some instances the standards referenced here may conflict with

other standards referenced by Federal agencies. For issues concerned with

seismic safety, priority should be given to this standard and its references.

The editions listed for each standard are the latest available at the time

of development of this standard. 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

80
standard, the Tri-Services Manual is an available source of design values

for steel deck diaphragms.

C5.2 MASONRY. There is more regional diversity in the design and

construction practices for masonry than for other construction 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 this standard

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.

C6 STRUCTURAL DESIGN DETAILS

The details of proportioning, 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 force-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 this standard. The designer

need not have all five references on hand. Because they are required by

Chapter 5, he would already have the standards of ACI and AISC 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

81
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-resisting frames of reinforced concrete.

C6.1 MOMENT-RESISTING FRAMES. This section is taken from 2312(j)C and F

of the UBC.

C6.1.2 Concrete Frames. Unless the actual drift is substantially 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 force-resisting system needs

the reinforcement 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 reinforcement to prevent spalling hazardous large

chunks of concrete unless that building has a very stiff seismic forceresisting system.

C6.2 STEEL DUCTILE MOMENT-RESISTING SPACE FRAMES. This section is based

on 2312(j)F of the UBC. The following table summarizes the appropriate K

factor, and thus the category of the seismic force-resisting system, for the

two common types of steel frames used as seismic force-resisting systems:

82
1 Zone

1

1 1 2(1-1) 2(I>1

)

3&4

1 Steel frame in compliance

with section 2722 of the UBC

| 0.67 0.67 0.67 0.67

1 Ordinary steel frame with

joints meeting AISC Type I I 0.67 0.67 1.0 1.0

C6.3 REINFORCED CONCRETE DUCTILE MOMENT-RESISTING SPACE FRAMES. This

section is based on 2312(j)lF and 2625(b) and (c) of the UBC . The following

table summarizes the appropriate K factor for three types of reinforced

concrete frames:

Zone

1 2(1=1) 2(I>1) 3&4

Highly ductile frame meeting

section 2626 of the UBC I 0.67 0.67 0.67 0.67

Moderately ductile frame meeting 6.3.1 and 6.3.2 ** | 0.67 0.67 * *

Ordinary frame meeting ACI 318

without Appendix A | 1.0 * * *

* system not permitted

** the UBC specifies a different K factor for this system, K = 1.0.

C6.4 BRACED FRAMES. These requirements are taken from 2312(j)lG and 2627(b)

of the UBC; the only difference is in the application of the requirements

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 of

non-ductile connection failures.

83
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 ATC 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 an accord with current practice. The need

for these requirements was demonstrated by several failures in the 1971 San

Fernando earthquake.

84
C6.8 OPENINGS IN SHEAR WALLS AND DIAPHRAGMS. This requirement is roughly

based on a similar requirement in the ATC provisions. The importance of

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

units to participate in sharing lateral force overloads.

C6.10.2 Pile Cap Connections. The ATC provisions require the connection

between the pile cap and the pile to be reinforced. One reason for a minimum

tensile capacity, separate from consideration of overturning resistance, is

vertical ground motions. The requirement given in this section is roughly

equivalent to the ATC requirements, but it is stated in a performanceoriented 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 ATC 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

85
transverse reinforcement without fulfilling the function of the longitudinal

reinforcement.

C7 NON STRUCT ION DESIGN REQUIREMENTS

C7.1 ANCHORAGE FOR INERTIAL FORCES. This section is based on 2312(g) of the

UBC. One difference is that consideration 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 recommendations for the anchorage

and protection of nonstructural components.

C7.2 DISTORTION COMPATIBILITY FOR EXTERIOR PANELS. This section is the

same as 23 1 2 ( 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 consideration of design for functional

capability immediately following a major earthquake is beyond the scope of

this standard.

86
C7.5 REINFORCEMENT OF CONCRETE AND MASONRY. This section is the same as

2312(j)3C of the UBC. It requires the same minimum reinforcement in zones

3 and 4 for nonstructural components as 6.9.1 does in zones 2, 3 and 4 for

structural components.

C8 CONSTRUCTION QUALITY 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 supplement existing agency programs.

C8.2 REQUIRED SPECIAL INSPECTION. In identifying the needed special

inspection, the standard follows the UBC particularly closely. Although there

is not universal agreement on the subject of special inspection, there is no

intent to create new problems with this standard. It should be noted that

continuous special inspection is not synonymous with full-time inspection.

87
NBS-114A (REV. 8-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 81-21952l'Oovrt ’Accession Nelli

4. TITLE AND SUBTITLE

Draft Seismic Standard for Federal Buildings

5. Publication Date January 1981

ganlzatton Code — ' —

7. AUTHOR(S)

James Robert Harris and Edgar V. Leyendecker

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, city, state, zip)

Federal Emergency Management Agency, Washington, D.C. 20472

and National Bureau of Standards, Washington, D.C. 20234

13. Type of Report & Period Covered

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or lesa factual summary of moat aighificant information. If document includes a significant bibliography or

literature survey, mention it here,) This standard has been prepared for uniform use by all Federal agencies as an adaptation of existing voluntary standards, model building codes. Federal regulations,

and research reports. It is closely based on the seismic requirements of the

Uniform Building Code (which, in turn, are based on the Recommended Lateral Force

Requirements and Commentary published by the Structural Engineers Association of

California). However, there are many instances of substantive differences from the

UBC. Several important provisions, including the seismic zoning map, have been

adapted from the Tentative Provisions for the Development of Seismic Regulations for

Buildings developed by the Applied Technology Council. A number of provisions have

been added to this standard that are based on the current practices and policies of

various Federal agencies. Furthermore, this standard is organized considerably

differently from the UBC and many provisions are phrased differently.

17, KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Building; building design; earthquakes; engineering; Federal government; seismic

safety; standards; structural engineering.

18. AVAILABILITY [xl Unlimited

I | For Official Distribution. Do Not Release to NTIS

] Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

| | Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

95

22. Price

USCOMM-DC

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