Department of Civil and Environmental Engineering Stanford University

A COMPARISON OF EARTHQUAKE BUILDING CODE REGULATIONS

by

John T. Egbert III

Report No. 42 April 1979

The John A. Blume Earthquake Engineering Center was established to promote research and education in earthquake engineering. Through its activities our understanding of earthquakes and their effects on mankind’s facilities and structures is improving. The Center conducts research, provides instruction, publishes reports and articles, conducts seminar and conferences, and provides financial support for students. The Center is named for Dr. John A. Blume, a well-known consulting engineer and Stanford alumnus. Address: The John A. Blume Earthquake Engineering Center Department of Civil and Environmental Engineering Stanford University Stanford CA 94305-4020 (650) 723-4150 (650) 725-9755 (fax) earthquake @ce. stanford.edu http://blume.stanford.edu

©1979 The John A. Blume Earthquake Engineering Center

ACKNOWLEDG»IENTS

The help of each of the many contributors to this project is grate-

fu~ly acknowledged.

The Seismology Committee of the Structural Engineers Association

of Northern California was responsible for providing the subject matter

Special help was received from Chris Poland, Ed Zackerof this project.

Bill Holmes and Eric Elsesser.

Funding for computer analysis was not available at Stanford Univer-

However, the firms GKT Consulting Engineers and URS/John A. Blumeatty.

and Associates both offered the use of their computers for this project.

The help of Ben Kacyra t Onder Kustu andThe GKT computer was used.

A very special acknowledgement to HratchPatrick Lau is appreciated.

Kouyoumdjian and Ed Haverlah for their effort spent checking the design

procedures, calculations and computer data.

The assistance with the calculations from Professor Helmut Krawinkler

is appreciated

The generosity of Professors Haresh C. Shah and Theodore C. Zsutty

for their helpful suggestions and encouragement is most gratefully ap-

Professor Shah and Zsutty's time was supported by thepreciated.

This support is gratefully acknowledgedNSF Grant No. ENV-77-17834.

Very much appreciated were the efforts of Laura Selby in typing

this dissertation.

The support that the United States Coast Guard has given is

gratefully acknowledged.

111

PREFACE

It is important to constantly review the building codes that are

currently being used in order to determine what improvements might be

For example, the formulae for obtaining base shear, lateral forcemade.

distribution and building period are continually being evaluated. Each

year design force levels increase in order to meet regulations which re-

Buildingsduce the likelihood of failure in the event of an earthquake.

must be constructed stronger and this may result in more structural re-

When a change to a code isdundancies, some of which may be unnecessary.

proposed~ the effect of this change on the variety of structural shapes

For example, a code change could affectand systems must be considered.

a two or thfee story concrete shear wall building much differently than

Rather than randomly increasinga twenty story steel frame high rise.

design levels or altering code requirements a code change should first

Thisbe examined for effects on a representative set of structures.

examination procedure is the subject of this work where the set of struc-

tures has been designed by current building codes and can be used for

comparative pruposes in evaluating the overall usefulness of a proposed

change and its value to certain structural systems

The Seismology Committee of the Structural Engineers Association of

Northern California (SEAONC) has studied a method which will standardize

and simplify the procedure for examining the effect of proposed building

The findings strongly indicate the need for the study ofcode changes.

a typical or standard set of buildings which would include not only the

general specifications for design of each building, but also several sets

of completed designs done by use of the most widely used building codes

This proposal offers a simple procedure that can be utilizedof today.

iv

to compare the impact of a code change against a code with a known per-

formance

v

TABLE OF CONTENTS

111Acknowledgements

IvPreface

viTable of Contents

ixList of Tables

List of Illustrations x

Chapter 1 SEISMOLOGY COHMITrEE PROJECT

14BUILDING DESIGN METHODSChapter 2

16Chapter 3 THE ATC 3 METHOD.

16172024262626272.727282830

3.13.23.33.43.53.63.73.83.93.103.113.123.133.14

31313232

Symbols and Notation. . . . . . . . . . . . . . .

Seismic Performance. . .. . . . . . . . . . . . .

Classification and Use of Framing Systems. . . .

Si te Effects. . . . . . . . . . . . . . . . . . .

Building Configurations. . . . . . . . . . . . .

Regular and Irregular Structures. . . . . . . . .

Load Combinations. . . . . . . . . . . . . . . .

Orthogonal Effects. . . . . . . . . . . . . . . .

Inverted Pendulum-~e Structures. . . . . . . .

Deflection and Drift Limits. . . . . . . . . . .

Base Shear. . . . . . . . . . . . . . . . . . . .

The Seismic Coefficient. . . . . . . . . . . . .

Building Period. . . . . . . . . . . . . . . . .

Distribution of Lateral Forces Along theHeight of the Structure.. . . . . . . . . . . . . .

Horizontal Shear Distribution and Torsion. . . .

Story Drift Determination. . . . . . . . . . . .

P-Delta Effects. . . . . . . . . . .. . . . . . .3.153.163.17

34THE STANFORD METHODChapter 4

343535373739394444

4.14.24.34.44.54.64.74.84.94.10

Symbols and Notation. . ~ . . . . . . . . . . . .

Base Shear. . . . . . . . . . . . . . . . . . . .

Zone Acceleration Value. . . . . . . . . . . . .

Mean Dynamic Amplification Factor. . . . . . . .

Building Period. . . . . . . . . . . . . . . . .

Structural Behavior Factor . ~ . . . . . . . . . .

Quality Factor. . . . . . . . . . . . . . . . . .

Structural Weight. . . . . . . . . . . . . . . .

Load Combinations. . . . . . . . . . . . . . . .

Distribution of L~~eral Forces Along theHeight of the Structure. . . . . . . . . . . . . 44

vi

TABLE OF CONTENTS (Continued)

4'454646

4.114.124.134.14

Building Setbacks and Irregular Shapes. . . . . .

Horizontal Shear Distribution and Torsion. . . .

Drift and Building Separations. . . . . . . . . .

Structural Systems. . . . . . . . . . . . . . . .

48Chapter 5 THE 1976 UNIFORM BUILDING CODE. . . . . . . . . .

48484953

5.15.25.35.45.5

Earthquake Regulations. . .. .. . , . . , . . , .. ..

Symbols and Notations. . .. , .. . . , .. . .. . , ..

Base Shear.. .. .. .. .. . . . . .. . . .. . .. . . .. .. ..

Building Period.. .. . . . . .. .. . . . . . .. .. .. ..

Distribution of Lateral Forces Along theHeight of the Structure. . .. , . .. . . .. . . .. .

Setbacks and Irregular Structures. .. . . .. . .. ,

Distribution of Horizontal Shear. . . . . .. . .. ..

Horizontal Torsional Moments. . . , .. .. . .. .. . ..

Building Drift and Separations. . .. .. . .. .. , .. ..

Structural Systems.. .. .. . . .. . .. .. . . .. . .. . .

Load Combinations.. .. . .. . . .. .. . . .. . .. .. . .

Essential Facilities.. . .. .. . .. .. .. .. . . .. .. .. ..

5454545555555656

5.65.75.85.95.105.115.12

57Chapter 6 THE 1973 UNIFORM BUn.DING CODE. . . . . . . . . .

5757

6.16.26.3

Symbols and Notation. . . . . . . . . . . . . . .

Base Shear. . . . . . . . . . . . . . . . . . . .

Distribution of Lateral Forces Along theHeight of the Structure. . . . . . . . . . .. . .

Distribution of Horizontal Shear. . . . . . . . .

Horizontal Torsional Moments. . . . . . . . . . .

Setbacks. . . . . . . . . . . . . . . . . . . . .

Structural Systems. . . . . . . . . . . . . . . .

Drift and Building Separations. . . . . . . . . .

S96060606161

6.46.56.66.76.8

62Chapter 7 THE BUILDING DESIGN

626464656565

7.17.27.37.47.57.6

Introduction. . . . . . . . . . . . . . . . . . .

Seismicity of the Area. . . . . . . . . . . . . .

Base Shear. . . . . . . . . . . . . . . . . . . .

Dead and Live Load. . . . . . . . . . . . . . . .

Fixed End Moments. . . . . . . . . . . . . . . .

Portal Frame and Me1'1ber Sizing. . . . . . . . . .

68Chapter 8 CODE COMPARISON

6868

8.18.28.3

70

Introduction. . . . . . . . . . . .. . . . L . . .

Base Shear. . . . . . . . , . . . .. . . . , . . .

Distribution of Lateral Forces Along theHeight of the Structure. . . . . . . . . . . . .

vii

TABLE OF COl~TENTS (Continued)

707577

8.48.58.6

Building Period. . . . . . . . . . . . . . . . .Load Combinations. . . . . . . . . . . . . . . .The Common Base for Comparison. . . . . . . . . .

89References. . . . . . . . . . . . . . . . . . . . . . . . . . .

viii

LIST OF TABLES

1-1 8Story Masses. . . . . . . . . . . . . . . . . . . . . . .Coefficients A , A , and Seismicity Indexa v 19

21Seismic Performance Category. . . . . . . . . . . . . . .

Structural Systems and Related Coefficients 22

25Soil Profile Coefficient. . . . . . . . . . . . . . . . .

Allowable Story Drift, A 29a

36Zone Acceleration Values. . . . . . . . . . . . . . . . .

Structural Types and Behavior Factor. B 40

Penalty Values, P . . . . . . . . . . . . . . . . . . . .q

Horizontal Force Factor, K . . . . . . . . . . . . . . . .

43

51

Occupancy Importance Factor, I . . . . . . . . . . . . . . 52

58Horizontal Force Factor, K . . . . . . . . . . . . . . . .

66Accidental Torsion. . . . . . . . . . . . . . , . . . .

69Comparison of Base Shears

71Lateral Load Distribution Formulae. . . . . . . . . . . .

8-.3 Distribution of Lateral Forces Along the Height ofthe Structure. . . . . . . . . . . . . . . . . . . . . . 72

74Proportion of the Lateral Force Distribution. . . . . . .

76Effects on Base Shear Due ~o Increased Period

78Acceptable Design Level

8-7 81Girder Member Sizes

8-8 84Total Girder Weight

8-9 85Section Modulus Comparisor . . . . . . . . . . . . . . . .

87Section Modulus Comparison. . . . . . . . , . . . . . . .

88Code Comparison Table

ix

LIST OF ILUJSTRATlONS

3SEAONC Standard Building Set. . . . . . . . . . . . . . .

1Basic Geometry for the Standard Buildings

38Mean Dynamic Amplification Factor

50Seismic Zone Map . . . . . . . . . . . . . . . . .

Plan and Elevation View of the Fifteen Story Building 637-1

73Distribution of Lateral Forces Along the Height ofthe Structure. . . . . . . . . . . . . . . . . . . . . .

x

Chapter 1

SEISMOLOGY COMMITTEE PROJECT

The Seismology Committee of the Structural Engineers Association

of Northern California has proposed a set of "Standard Buildings" which

The standardwill aid in evaluating the impact of building code changes.

buildings represent the basic structural systems that are encountered in

Simplicity has been incorporated into the composition of a stan-practice.

Each typicaldard building type in order to make its utilization appealing.

building has been specified only by plan and elevation dimensions, typical

openings, and story masses.

In this dissertation, all standard buildings will be designed by

(1) The ATC 3-06 Tentative Provisions for the Developmentfour methods:

of Seismic Regulations for Buildings (Ref. 1); (2) The Recommended Seismic

Resistant Design Provisions for Guatemala and Algeria (Refs. 2 and 3);

4); and (4) The 1973 Uniform(3) The 1976 Uniform Building Code (Ref.

Building Code (Ref. 5)

A standard building can be designed by any newly proposed building

code and the results of this design can easily be compared to the results

This manner ofof design obtained from the four methods just named.

examining a proposed code becomes a useful tool for evaluating the impact

of the change

A standard building is classified by its structural system (correspon-

ding to the K values from the 1976 Uniform Building Code), building material,

The standard buildings are ninety by ninety feet inand building height.

plan with four frames that are thirty feet on center in both principal

The standardThe story height is twelve feet six inches.directions.

building set includes one, two, six and fifteen story buildings with

1

structural systems of ductile moment resisting frames, dual systems, braced

Also included in the set are box systemsframes. and shear wall systems.

consisting of concrete shear walls, a one hundred by two hundred feet

glu-laminated tilt up, and rectangular "motel style" timber and masonry

The standard building set and the typical geometry are shownbuildings.

The typical story masses that were used for this

*:in Figures 1-1 and 1-2.

project are listed in Table 1-1.

As more experience is gained in working with these standard buildings

any deficiencies that become apparent can be eliminated by adding more

Such additions might include build-sophisticated buildings to the set.

ings with setbacks, small irregularities in plan, or an offset center of

The SEAONC project will thus become a standard base againstrigidity.

which to compare code changes and future building codes.

*Received from the Seismology Committee of SEAONC.

2

Figure 1-1

SEAONC STANDARD BUILDING SETPlan Views.

Ductile Moment Resisting Space FrameK = 0.67

ConcreteSteel

Tube SystemTube System

! I

1'.SN\Dnber of Stories:1SNumber of Stories:

Moment Resisting FrameMoment Resisting Frame

2,6,15Number of Stories:2,6, 15Number of Stories:

*Each plan view corresponds to one building for each building height

(in stories) listed.

3

Figure 1-1 (Continued)

K - 0.80 Dual System

Steel Frame/Concrete Core

Y IJ

Number of Stories: 6,15

4

(Continued)Figure 1-1

K - 1.0 Braced Frame and Shear Wall System

ConcreteSteel

Exterior Shear WallBraced Frame

I

2,6, 15Number of Stories:2,6, 15Number of Stories:

Shear Wall Core

ft"-rI

6Number of Stories:

5

K - 1.33 Box System

*MasonryConcrete

Exterior Shear Wall

2.6.15Number of Stories:Number of Stories: 2,6, 15

Corner Shear Wall

Timber**

Number of Stories: 2,62Number of Stories:

20' Tilt up with Glu-laminated Beams and Paneled Roof

100" X 200t

*The masonry."Motel Style" structure has a double bearing corridor,tr~Dsverse bearing walls, and concrete plank floors.. '**The "Timber Style" structure has a double bearing corridor and trans-

verse bearing walls.6

Figure 1-2

Basic Geometry for All Standard Buildings(Except tile-up, masonry, and timber)

-R

-2

-1

-G

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4 X 6' Openings Equally Spaced

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Chapter 2

BUILDING DESIGN METHODS

Four methods of seismic resistant design will be examined in this

These are applied to the design of a standard building anddissertation.

the results are tabulated for comparison.

The ATC 3-06 "Tentative Provisions for the Development of Seismic

Regulations for Buildings" and "The Recommended Seismic Resistant Design

Provisions for Guatemala and Algeria" will be referred to in this disser-

"Stanford Method, II respectively.tation as the "ATC 3 Method" and the

the Uniform Building Codes will be referred to as the "1976 UBC" and

"1976 UBC."

The ATC 3 Method is meant to establish design and construction cri-

teria for the buildings that are subject to earthquake motions in order to

minimize the hazard to life and improve the capability of essential facil1-

ties to function during and after an earthquake.

The design earthquake motions that are specified for this method have

been selected so that there is a low probability of their being exceeded

during the normal life expectancy of the building- Buildings which are

designed to resist these motions in conformance with the specified require-

ments may suffer damage, but should have a very low probability of collapse

due to seismic-induced ground shaking.

The Stanford Method was developed for the countries of Guatemala and

Algeria in order to fulfill those countries' special needs for seismic

design regulations for buildings. Special attention is given to the struc-

tural qualities of redundancey, plan symmetry, regularity, and construction

inspection which sets this method apart from other design methods or codes.

Having good structural qualities in a building will result in the design

14

force levels being near those of the 1913 UBC, whereas poor structural

qualities will cause the design force levels to be near. or even larger,

than those of the 1976 UBC.

The 1976 UBC was derived by expanding upon the 1973 UBC such that a

more stringent code with much higher design levels has resulted.

15

Chapter 3

THE ATC 3 METHOD

3.1 Symbols and Notation

The symbols and notation that are used in the ATC 3 Method are listed

below:

= The seismic coefficient representing the Effective Peak

Acceleration.Aa

= The seismic coefficient representing the Effective Peak

Velocity.Av

- The incremental factor related to P-delta effects.ad

= The deflection amplification factor as given in Table 3-3.Cd

c - The seismic design coefficient.s

The vertical distribution factor.

= The portion of the seismic base shear, V, induced at level

i, n, or x, respectively.F i ,F ,Fn x

= The acceleration due to gravityg

= The height above the base to level i, n, or x, respectively.hi,hn,h x

.i . 1- The building level referred to by the subscript i.designates the first level above the base.

1

k - The distribution coefficient.

= The overall length of the building (in feet) at the base

in the direction being analyzed.L

= The torsional moment resulting from the location of thebuilding masses.Mt

- The accidental torsional momentt:a

= Designates the level which is uppermost in the main por-

tion of the building.n

= The effect of dead load~= The effect of seismic (earthquake-induced) forces.

QB= The effect of live load

'L- The effect of snow load.

Qs

16

R - The seismic response modification coefficient as given

in Table 3-3.

s = The seismic coefficient for the soil profile character-

istics of the site, as given in Table 3-4.

51.52.53. The Soil Profile Types.

T = The fundamental period of the building.

T = The approximate fundamental period of the building.a

v - The seismic shear force at any levelx

w - The total gravity load of the building.

w..w.w = The portion of W which is located at or assigned to levelJ. n x

i, n, or x. respectively.

- The level under consideration.

level above the base.

x x = 1 designates the first

4 = The design story drift

A - The allowable story drift.a

~ z The deflection at level x.x

a = The deflection at level x, determined by an elastic analysisxe

e . The stability coefficient for P-delta effects

Seismic Performance

Seismic performance is a measure of the amount of protection provided

to the public against potential hazards resulting from the effects of

building response to earthquake ground motions

A Seismicity Index and a Seismic Hazard Exposure Group are used in

assigning buildings to the proper Seismic Performance Category. The

Seismicity Indices range from 4 down to 1, where 4 is associated with the

most severe ground shaking. The Seismic Hazard Exposure Group classifi-

cation is from III down to I, where group III is associated with uses

requiring the greatest level of protection. The Seismic Performance

Categories range from D down to A, where category D is assigned to pro-

the highest level of design criteria.

1.7

The Seismicity Index is obtained from the design ground motion which

is defined in terms of Effective Peak Acceleration or Effective Peak

These parameters are represented by the two coefficients AVelocity. a

The geographical area of concern in this disserta-and A , respectively.vFrom the maps included with the ATC 3is the San Francisco Bay area.

* it is found that San Francisco county as well as most of the sur-Method

and A coefficientsrounding counties are map area 7 for both the Aa v

From Table 3-1 the coefficients are obtained:

-0.4Aa

- 0.4Av

Seismicity Index = 4

All buildings are assigned to one of the three Seismic Hazard Per-

formance Groups.

Seismdc Hazard Exposure Group III is for buildings1. Group Ill.

which contain essential facilities necessary for post-earthquake recovery.

These buildings and essential facilities which include mechanical equip-

and related systems must have the capability to function during and

immediately after an earthquake.

Fire stations. PoliceExamples of possible Group III facilities:

facilities, structures housing medical facilities capable of surgery and

emergency treatment, emergency preparedness centers, and power stations

or other emergency back-up facilities.

Seismic Hazard Exposure Group II contains buildings2. Group II.

that have a large number of occupants or buildings in which the occupants'

movements are restricted or their mobility is impaired.

*Due to their large size. it is impractical to reproduce these maps;

however. they are contained in Reference 1.

18

Table 3-1

Seismicity IndexCoefficient ACoefficient AMap Area va

0.40 40.407

40.30O!JO6

40.200.205

30.150.154

20.103 0.10

20.050.052

0.050.051

*Table I-B of Reference 1.

19

Examples of possible Group II facilities: Public assembly for 100

persons or more~ open air stands for 2000 persons or more~ day care cen-

ters, schools, shopping centers with covered malls and over 30,000 square

feet, offices over four stories in height or more than 10,000 square feet

per floor, hotels over four stories in height, hospital facilities other

than those of Group III, and factories over four stories in height.

3. Group I. Seismic Hazard Exposure Group I is composed of all

buildings that are not in Group II or III

4. Protected Access. Buildings that are sssigned to Seismic Hazard

Exposure Group III must be accessible both during and after an earthquake.

Where access 1s through another structure, that structure must conform

to the requirements of Group III. Where access is within ten feet of

side property lines, protection against potential falling hazards from

the adjacent property must be provided.

5. Multiple Use. Buildings having multiple uses must be assigned

the classification of the highest Seismic Hazard Exposure Group which

occupies fifteen percent or more of the total building area

The Seismic Performance Category is obtained from Table 3-2 and is

determined using both the Seismicity Index and the Seismic Hazard Exposure

The Seismic Performance Category determines the requirements forGroup.

design as discussed in Sections 3.3 and 3.6

3.3 Classification and Use of Framing Systems

Each building or portion of a building is classified as one of the

four types of framing systems which are: Bearing Wall, Building Frame

Each structural system is de-Moment Resisting Frame, and Dual System.

scribed in Table 3-3. Also from this table the Seismic Response Modifica-

tion Coefficient, R, and the Deflection Amplification Factor, Cd' are

obtained

20

Table 3-2

SEISMIC PERFORMANCE CATEGORY.

Seismic Hazard Exposure GroupSeismicity

IndexIII II I

c4 D c

B3 c c

2 BB B

1 A A A

'itTable I-A of Reference I.

21

Table 3-3

STRUCTURAL SYSTFJfS AND RELATED COEFFICIENTS.

VertlCl1 Sels~fc CoefflcfentsTvoe of Str'UCtur.1 Snte8 Resfstl~ Sn*..L ...f4-

BEARING WALL SYSTEM: A structura1 syst88 with Light framed wa11sbearing wa11s providing support for 111. or with shHr ~ne1s fiAt 4-.jor portions of. the vertlCl1 10.ds.

Sels.ic force resistance Is provided Shear wl11sby shear wa11s or braced fr~s. Reinforced concrete 4~ 4

Reinforced masonry]a. J

Brac~fr_es 4 ~ -

Unreinforced andpartfl11y reinforcedNSonry shear w.11s 1~ 1~

Lfght framed w.11swfth ShHr pane1s 7 '.

Shear wa11sReinforced concrete St 5Reinforced NSOnry 4It 4

Braced frames 5 4It

Urrefnforced andplrtia11y reinforced

-~- - Masonry sh~r wl11s 1~ 1..

Specf.1 ~nt f~sStee1 B litReinforced concr.te 7 I

r.~tnlry _nt f~sStee1 4ItReinforced concr.te 2 -Shear wl11sReinforced concrete 8 91Reinforced masonry 6~ SIt

J: Wood sheathed shear

Plne1s,j Brlced fra~s

BUILDING fRAHE SYSTEM: A structural sYSte8with .n essenti.lly c~lete Space fr-providing support for vertical loads.

Sei~ic force resistance is provided byshe.r walls or braced frames.

4".

--- -- -

MOMENT RESISTING FRAME SYSTEM: A structuralsys~ with in essentti11y ~lete SpiceFr- providt"9 support for ftrttcal 10ads.

Set~ic force resistance ts provided byOrdinary or Specii1 IbIIent Frl.s Cipableof resisting the toti1 prescribed fOrces. 4

2

5

,

OOAl SYSTEI4: A structur.l systen with .nessenti.lly ~Iete S~ce Fr.. providingsupport for vertical lo.ds.

A Speci.1 Moment FraMe shall be provide<which s~ll be cipable of resisting it least25 pe~ent of tile prescribed sef_ic forces.The totil seis.fc fo~e resis~nce is providedby the combination of the Special ItINnt FraN.nd shHr walls or bricld fr_s in proport i onto their relative rigidities. INVERTED PEHDULUH STRUCTURES. Structures

where the fr.fng resisting the totil prescribedsei_ic forces .cts essenti.lly.s isolitedc.ntflevers and provides support for vertic.lload.

Specfa1 ~nt Fr_sStructurl1 s tee 1 2.. ZItReinforced concrete 2\ ~

Ordf nary ftlment Fr..sStructura1 stee1 1~ 1\

*Table 3-8 of Reference 1

22

Where combinations of framing systems are incorporated into the same

building the R value in any direction and at any level does not exceed

the lowest R value obtained from Table 3-3 for the lateral force resistin8

system, in the direction considered

Any type of framing system may be used for buildings assigned to

Seismic Performance Categories A and B. Those buildings of Seismic Per-

formance Category C must conform to the requirements of Category B in

addition to the following requirements:

Seismic Resisting systems in buildings over one hundred sixty feet

in height must be designed with one of the framing systems listed below:

Special moment resisting frames which are defined as onea.

hundred percent moment resisting.

b. Dual fraIlling system

c. A system with structural steel or cast in place concrete

braced frames or shear walls which are so arranged that the

braced frames or shear walls in any plane resist no more than

~hirty three percent of the seismic design force including

torsional effects. This is limited to buildings not over two

hundred and forty feet in height

Moment resisting space frames which are adjoined by more rigid

elements not considered to be p"art of the seismic resisting system must

be designed such that the action or failure of the nonstructural elements

will not impair either the vertical or lateral load carrying capability

of the space frame

All structural elements that are not part of the lateral force

resisting system must be adequate for vertical load carrying capability

and the induced moments which result from the design story drift.

23

A special moment resisting frame that is used but is not re-

quired by these provisions may be discontinued and supported by a more

rigid system with a lower R value. However, the potential adverse effects

of adjacent stories with different strengths must be considered.

When a special moment resisting frame is required in these

provisions it must go all the way to the ground

Buildings of Seismic Performance Category D conform to the require-

ments of Category C except that the height limitations of Category Care

reduced from one hundred sixty feet to one hundred feet and from two

hundred forty feet to one hundred sixty feet

3.4 Site Eft~cts

The effects of site conditions on building response is established

based on soil profile types that are defined as follows:

Soil Profile Type 81 is given to rock of any characteristic with a

shear wave velocity greater than 2500 feet per second or where stable

deposits less than 200 feet thick of sand, gravel, or stiff clay are

overlying rock.

Soil Profile Type 52 is a profile with deep cohesion1ess or stiff

clay conditions including stable deposits of sand, gravel, or stiff clay

more than 200 feet thick overlying rock.

Soil Profile Type S3 is a profile with soft to medium stiff clays

and sands 30 or more feet thick with or without intervening layers of

sand or other cohesionless soils.

Site locations where soil properties are not known or do not fit

into any of the three categories use Soil Profile Type S2.

The Soil Profile Coefficient S is obtained from the appropriate

Soil Profile Typ~ in Table 3-4.

24

Table 3-4

SOIL PROFILE COEFFICIENT*

Soil Profile Type

51 82 53

s 1.0 1.2 1.5

*Tabel 3-A of Reference 1

25

B~ilding Configurations

For the purposes of seismic design, buildings are classified as either

regular or irregular structures, depending upon both the plan and vertical

When the geometry is nearly symmetrical and when the cen-configuration.

ter of mass and center of rigidity are nearly coincident, the building

is considered regular

A building is considered irregular when:

The building does not have an approximately symmetrical geo-(1)

metric shape, has re-entrant corners with significant dimensions in plan,

or has horizontal offsets with substantial dimensions in elevation.

(2) If the diaphragm at any level has significant changes in

strength or stiffness.

If the mass stiffness ratio between adjacent stories varies(3)

significantly.

Regular and Irregular Structures

Buildings of Seismic Performance Category At whether regular or ir-

regular, need not be analyzed for seismic loading. Regular structures

classified in Category B, C, or D must, as a minimum, be designed in

accordance with the procedures of the ATC 3 Method.

Irregular structures of Seismic Performance Categroy B are designed

However, those irregular structures ofthe same as regular struct~res.

Cetegories C and D must be analyzed with special consideration for the

dynamic characteristics of the building.

3.7 Load Combinations

Gravity and seismic loads are combined in accordance with formula

3-1 or as applicable 3-2 or 3-3.

(3-1)Combination of Load Effects - l.2~ + 1.OQL + 1.OQS t 1.OQE

26

Combination of Load Effects. O.8QD t 1.OQE (3-2)

When there are partial penetration welded steel column splices or un-

reinforced masonry and other brittle materials9 systems 9 and connections:

Combination of Load Effects. O.5QD:t 1.OQE (3-3)

where: QD = The effect of dead load.

QL = The effect of live load.

QE - The effect of seismic (earthquake-induced) forces.

Qs - The effect of snow load.

3.8 Orthogonal Effects

Each building must be designed to resist one hundred percent of the

seismic forces in one direction» plus thirty percent of these forces in

the orthogonal direction. The combination requiring the maximum component

strength must be used

3.9 Inverted Pendulum-Type ~tructures

Traditionally~ an inverted pendulum-type system has meant a single

degree of freedom system that is hinged at the base. However, as used

in the ATC 3 Method, such a system is fixed at the base and models a

structure having a seismic resisting system that acts essentially as an

isolated cantilever. The supporting columns or piers of the inverted

pendulum-type structure must be designed for the bending moment calcu-

lated at the base, which is determined by the procedures set forth in

this chapter.

3.10 Deflection and Drift Limits

All portions of the building must be designed and constructed to

act as an integral unit in resisting seismic forces unless separated

27

structurally by a distance sufficient to avoid damaging contact under

deflection. The allowable story drift is obtained from Table 3-5.

3.11 Base Shear

Buildings, considered to be fixed at the base, must be designed to

resist the seismic base shear V in the direction being analyzed as deter-

mined by the formula:

v = c ws (3-4)

where: c = Seismic Design Coefficient.sW = the total gravity load of the building.

The weight W shall be taken equal to the total weight of the structure

and applicable portions of the other components including but not limited

to:

(1) Partitions and permanent equipment including operating contents.

(2) For storage and warehouse structures, a minimum of twenty per-

of the floor live load.

(3) The effective snow load

3.12 The Seismic Coefficient

The seismic coefficient for a structure can be calculated either

based on the period of the structure or calculated independent of period

When the seismic coefficient is dependent upon period the equation

used is:

I.2A Sv

-;;"273c (3-5)=

s

where: A - Effective Peak Velocity from Table 3-1.vS = Coefficient for the soil profile characteristics

of the site, as given in Table 3-4.

R - The Response Modification Factor, as given in

Table 3-3.28

Table 3-5

*ALLOWABLE STORY DRIFT, l:J.a

*Table 3-C of Reference 1.

29

T - The fundamental period of the building as deter-

mined in Section 3.13

When the period of the building is not calculated, the value of Cs

is determined by:

A(3-6)cs

= The seismic coefficient representing the EffectiveAwhere: a

Peak Acceleration, from Table 3-1.

is less than or equal to 0.30 and the soil profile typeHowever, when Aa

18S3' the following formula is used to calculate Cs:

~

(3-7)A

C. - 2.0 -f

obtained from Equation 3-5 need not exceed the value ofThe value of Cs

as determined by either Equations 3-6 or 3-7cs

Period Determination--3.13

The fundamental period of a building, T, may be determined based on

the properties of the seismic resisting system using methods of mechanics

This calculatedand assuming that the base of the building is fixed.

period need not exceed 1.2 times the approximate building period, T .a

The approximate period is dependent upon the type of structural

For moment-resisting structures where the frames are not adjoinedsystem.

by more rigid elements or otherwise prevented from deflecting when sub-

is:jected to seismic forces the equation for Ta

= C h 3/4Tn (3-8)Ta

where: Cr - 0.035 for steel frames

~. 0:025 for concrete frames.

= The height in feet above the base to the highesthnlevel of the building.

30

Fpr all other buildings:

O.OShn

"~2

~

(3-9)T .a

where: L = Overall length in feet of the building at the base

in the direction under consideration.

3.14 Di$tribution of Lateral Forces Alon t of the Structure

The induced lateral seismic shear force, Fx' at any level is deter-

aiDed by the following equation:

(3-10)F C- vvxx

where:

(3-11)c .c!lrc\.I;!'vx nL w h k

i-I i i

Wi' Wx z The weight of level i or x

hit h = The height above the base to level i or xxk = The period related exponent

In Equation 3-11, the exponent k is related to buildLng period. Building$

having a period of 0.5 seconds or les$ have a corresponding k value of t

When the period of a building is 2.5 seconds or more the k va:J.ue is 2

Interpolation is used in order to obta!n the k value when bu!lding period

is between 0.5 and 2.5 seconds

Horizontal Shear Distribution and Torsion3~ 15

Th~ seismic shear force at any level V is expressed as:x

nV - L F

ix i-I (3-12)

31

and associated torsional forces must be distributedThe shear force Vx

to the various vertical components of the seismic resisting system in the

story below level x in accordance with the relative stiffness of the

The design must provide for thevertical components and the diaphragm.

torsional moment Mt' which results when the center of mass and the center

of rigidity do not coincide, plus the accidental torsional moment, M .ta

Accidental torsion is assumed to be the story shear acting at an eccentri-

city of five percent of the base dimension in a direction perpendicular

to the applied forces.

StOry Drift Determination

The story drift, 6, is computed as the difference of the deflections,

The deflection0 , at the top and bottom of the story under consideration.x

0 is evaluated by the equationx

(3-13)0 - C 0x. d xe

Cd = The deflection amplification factor from Table 3-3.where:

= The deflection determined by an elastic analysisqxeusing the prescribed seismic design forces from

Section 3.14 and considering the building fixed

at the base

P-Delta Effect

P-Delta effects on story shears and moments, the resulting member

forces and moments, and the story drifts induced by these effects are not

considered when the stability coefficient e is less than or equal to 0.10

P 6xe - v h Cdx sx

(3-14)

32

6 = Design story drift.where:

= Seismic shear force acting between level x and x-I.vx

= Story height below level x.

n= r wi' which is the total gravity load at and above

i-x

bsx

px

level x

When e is greater than 0.10, the P-Delta Amplification factor ad is

computed:

(3-15)ead - (1 - e)

The coefficient ad takes into account the multiplier effect due to the

initial story drift leading to another increment of drift which leads to

2still another increment, etc. The resulting factor is 1 + e + e + ...

which is 1/(1 - 6) or (1 + ad) and is multiplied by the design story

The story sheardrift to give the drift including the P-Delta effect.

is multiplied by the factor (1 + ad) for that story to obtain thevx

new shears

33

Chapter 4

THE STANFORD METHOD

4.1 Symbols and Notation

The units used throughout the Stanford Method are kilograms, meters

The symbols and notations used in the codeor centimeters, and seconds.

are listed below:

= Zone Acceleration Value.A

- Structural Behavior factor from Table 4-2B

- Mean dynamic amplification factor from Figure 4-fD

- The dimension of the effective width of the lateral forceresisting system in a direction parallel to the applied

forces.

Ds

a1= Deflection at level i. relative to the base. due to applied

lateral forces, rfi"

= Lateral force applied to level i, n, or x, respectively"Fi ,F ,Fn x- Lateral forces on a part of the structure and in the

direction under consideration.Fp

- Lateral force on a diaphragm at level x.Fpx

- That portion of V considered concentrated at the top ofthe structure in addition to F .n

- Distributed portion of total distributed lateral forceat level i.

Ft

£1

- Acceleration due to gravity.g

- Height above the base to level i, x, or n, respectively.hi ,h ,h

x n

Level i - Level of the structure referred to by the subscript i.i-I designates the first level above the base.

= That level which is uppermost in the main portion of

the structure.Level n

That level which is under design consideration.designates the first level above the base.

x = 1Level x -

- The total number of stories above the base to level nN

- Quality factor from Table 4-3Q

34

T = Fundamental elastic period of vibration of the structureI

in seconds in the direction under consideration.

. The total lateral force or shear at the basev

w = The total dead load and applicable portions of o-ther

loads.

e That portion of W which is located at or is assigned to

level i or x, respectively.

w., W1 X

4-.2 Base Shear

Every structure must be designed and constructed to resist the mini-

mum total lateral force that may occur in the direction of each main

axis of the structure but assumed to act nonconcurrently. The equation

for the minimum total lateral force is:

(4-1)V=ADBQW

4.3 Zone Acceleration Value

The Zone Acceleration Value A is obtained from Table 4-1 and is

determined by the Use Group Classification and the seismic zone in which

the structure is located. The three Use Group Classifications are:

Use Group 1: Essential facilities necessary for life care and safety.

Use Group 2: Ordinary coumercial, residential, public assembly, and

industrial buildings that have not been included in

Use Groups 1 or 3

Use Group 3: Facilities which are relatively nonessential for public

safety.

The seismic zones which are given with this method as it was published

However, the seismic zones I, II, and IIIare not for this country.

divide an area into zones of different seismicity. Seismic Zone III is the

area where the expected effects of seismic activity would be the greatest

and Seismic Zone I is for areas where such effects would be the slightest.

35

Table 4-1

ZONE ACCELERATION VALUES.(Decimal Fraction of Gravity)

*Table C-l of Reference 2. Thesevalues are for the country ofGuatemala; however, they can beapplied to the San FranciscoBay Area, as explained in Section4.3.

36

4.4 Mean Dynamic Amplifica~!onF!ct2!

value of the Mean Dynamic Amplification Factor. D. is a function

of period and is obtained from Figure 4-1. The value D depends upon the

soil type for a site. The soil type is determined from the average value

of shear wave velocity by the equations:

-.{fv (4-2)8

and

(4-3)EG. 2(1 + v)

where: v = shear wave velocity (meters/second)s

2G = shear modulus (kg/cm )

p = soil density (kg/sec2/cm' l,..

v - Poisson's ratio

2E - Young's Modulus (kg/cm )

Firm soil requires Vs

aeters/second, whereas soft soil has a shear wave velocity between one

to be greater than or equal to six hundred

hundred fifty and six hundred meters/second. When V is less than ones

hundred fifty meters/second or when the structure is of Use Group 1, a

geotechnical investigation must be performed to determine the seismic

site response characteristics.

4.5 Building P!!:iod

The building period T can be determined from the structural proper-

ties and deformational characteristics of the resisting elements in a

properly substantiated analysis such as by the equation:

(4-4)

37

fi

where: = Any lateral force distributed approximately in

accordance with the lateral distribution of forceequations of the code

0i = The elastic deflection due to ft.

In the absence of a period determination such as the one above, T

may be determined by the equation:

O.O9hn

~

T~ (4-5)

where: h and D..[D:

are expressed in meters.sn

Buildings which have moment resisting space frames that are capable of

resisting one hundred percent of the required lateral forces and which are

not prevented from doing so by more..~igid adjoining elements may use the

following equation in evaluating the period:

T = 0.10 N (4-6)

S_tructural Behavior Factor

The Structural Behavior Factor B depends on the type of lateral

The structure type number, definitions and cor-force resisting system.

responding B values are given in Table 4-2

Quality Factor

The quality factorQ for the lateral force resisting system of a

given building is a function of the system redundancy, plan symmetry,

elevation regularity, and construction quality control. The value of Q

is determined by the equation:

5r

q-l(4-7)o~ +

Pq

where: Pq is the penalty increment which depends upon whetheror not the structure meets a given quality criterion q

39

Table 4-2

STRUCTURAL TYPES AND BEHAVIOR FACTOR B*

Type or Arrangement of Lateral ForceResisting Elements

Valueof B

TypeNumber

16

1. Buildings with a ductile moment resisting space framedesigned with the capacity to resist the total re-quired lateral force. This frame must be capable ofcarrying all the weight of the structure togetherwith the entire design lateral load after it has beensubjected to deformations well beyond the yield pointdefQrmations of the structural members.

Buildings with a dual bracing system consisting of aductile moment resisting space frame and ductile shearwalls or braced frames designed in accordance with thefollowing criteria:

15

2.

a. The frame and shear walls or braced frames shallresist the total lateral force in accordance withtheir relative rigidities considering the interactionof the shear walls and frames.b. The shear walls or braced frames shall resist thetotal required lateral force.c. The ductile moment resisting space frame shallhave the capacity to resist not less than 25 percentof the required lateral force and carry the weight ofthe structure after the primary lateral bracing isdeformed well beyond its yield point deformation.

Buildings not greater than 5 stories in height with astructural steel moment resisting space frame thatdoes not necessarily satisfy the compact section re-quirement for a ductile moment resisting steel frame(type 1). The frame must, however, satisfy all otherrequirements for the type 1 system.

1'4

3.

1"4

4. Buildings not greater than 10 stories in height with aspace frame that is laterally supported by shear wallsor braced frames designed with the capacity to resistthe total required lateral force.EXCEPTION: If failure of the shear wall or bracedframe lateral force resisting system could result inthe loss of the vertical load carrying stability ofthe- space frame, the building will be classified asa type 5 Box System. The vertical supporting membersmust have the capacity to carry the weight of thestructure at deformations well beyond the yield pointdeformation of the lateral bracing system.

(Continued)

*Table C-2 of References 2 and 3.

40

Table 4-2 (Continued)

TypeNumber

Type or Arrangement of Lateral ForceResisting Elements

Valueof B

5. 13

Buildings less than 10 stories in height with a BoxSystem (i.e.. a structural system without a completevertical load carrying space frame) laterally supportedby shear walls or braced frames. The lateral bracingsystem is such that collapse may occur if the bracingsystem fails.

6. 1Z

Other Concrete Structural Systems for Buildings. All ,I

concrete sections must carry the lateral forces and theweight of the structure with concrete strain values lessthan 0.003. All elements supporting vertical load suchthat their failure would result in collapse shall have

1)

2)

3)

Shear strength capacity necessary to support ver-tical loads and develop flexural yield capacity attheir ends.Beam-column joint shear strength capacity to supportflexural yield capacity of framing members underlateral load conditions.Confining reinforcement necessary to develop con-crete strain of at least 0.01.

7. Buildings not more than three stories in height with aBox System as described for Type 5, but with standard-ized brick masonry panels in confining frames of rein-forced concrete.

2""3"

41

The criteria and corresponding P values are given in Table 4-3. Theq

definitions of the criteria which establish P at a value of zero areq

listed below:

1 Frame Redundancy Line. The individual frame and/or wall line

in the direction of the applied lateral load must have the following

measures of redundancy in all stories:

At least three bays having a relative width ratioFrame System.a.

of not more than 1.5. The frame bays may contain shear walls.

At least one wall pier with a story height to widthb. Wall System.

ratio less than or equal to 0.67, or at least two piers with a

story height to width ratio less than or equal to 1.0. The piers

must extend over the full story height and cannot contain openings

of any kind that can significantly reduce the stiffness or strength

2. Plan Redundancy. The plan of each story must have at least

four lines of frames or walls in the direction of the applied lateral

load. These lines of bracing elements must be spaced with reasonable

symmetry where the ratio of maximum to minimum spacing does not exceed

1.5

3,. The eccentricity between the center of massPlan Sytmnetry.

supported by any story and its center of rigidity cannot exceed fifteen

percent of the effective building width measured normal to the direction

of the applied lateral load.

In any story, the translational stiffness4. Elevation Regularity.

in line with the applied lateral load and the total rotational stiffness

against plan torsion cannot change by more than fifteen percent from the

stiffness values for the adjacent upper and lower stories. The stiffness

values must remain nearly constant or gradually decrease with height.

42

Table 4-3

PENALTY VALUES, P *q

Pq Value

Criterionq MeetsCriterion

Does not meetCriterion

1 Frame line redundancy 0 0.1

2 0 0.1Plan Redundancy

3 0 0.1Plan Symmetry

4 Elevation Regularity 0 0.1

s 0 0.2Construction Quality Contro~

*Table C-3 of References 2 and 3.

43

5. Construction Quality Control. There must be a provision within

the contract for the performance of inspection at the important stages

Theduring construction. inspection must be done under the direct super-

vision of a responsible design engineer. Material testing must be

in cases where dependable levels of quality are necessary for structural

performance.

4.8 Structural Weight

The structural weight W is the total dead load and applicable por-

tions of the other loads such as: Partitions, permanent equipment, and

for warehouses and storage areas a minimum of twenty five percent of the

live load must be included.

4.9 Load Combinations

The seismic forces and specified vertical load combinations as given

in Equations 4-8,4-9, and 4-10 must be resisted by member capacities

based on ultimate strength design for concrete and the equivalent of

ultimate strength design for steel, wood, and masonry.

U-D+L+E

U = a.8CD 't E)

U - 1.7(D + L) (4-10)

where: U = Elements strength requirement

D - Dead load effect on the element

L - Live load effect on the element

E = Seismic effect evaluated by using formula 4-1.

4.10 Distribution of Lateral Forces Along the Height of the Structure

The total lateral force or base shear V is distributed over the

height of buildings classified as regular structures or as having regular

systems in the following manner

44

nV=F+E Ft 1-1 i (~1.l.)

The concentrated force at the top, Ft' is found by;

Ft=O.O7TV (4-12)

However, Ft need not exceed O.25V and may be considered zero when T is

less than or equal to 0.7 seconds. The remaining portion of the base

shear is distributed over the height of the structure including the top

level as follows:

F (4-13)x nr w hi-I i i

4.11 Building Setba,c!.! and Irregu!a~ ~b!pes

Buildings having setbacks where the plan dimension of the tower is

at least seventy five percent of the corresponding plan dimension of the

lower part may be considered as uniform buildings without setbacks, pro-

viding that no other irregularities exist

The distribution of lateral force, in structures having irregular

shapes, large differences in lateral resistance or stiffnesses between

stories, or other unusual structural features must be determined using

or considering the dynamic characteristics of the structure.

4.12 Horizontal Shear Distribution and Torsion

The total shear in any horizontal plane shall be distributed to the

various elements of the lateral force resisting system in proportion to

their rigidities. Rigid elements that are assumed Qot to be part of the

lateral force resisting system may be inco~orated into the building

theirprovided that effect is considered in the destgn.

45

Horizontal torsional moments due to an eccentricity between the center

of mass and the center of rigidity result in additional shear forces that

must be accounted for in the design. Negative torsional shears are neg-

lected. In the case where the vertical resisting elements depend upon

diaphragm action to transfer the shear forces, the vertical elements must

be capable of resisting the total story shear force acting at a minimum

eccentricity of five percent of the maximum building dimension at that

level.

Drift and Building Separations

Lateral deflection, or drift ~f a story relative to its adjacent

stories is not to exceed 0.01 times the story height unless it is shown

The displacement calculated from thethat greater drift can be tolerated.

application of the required lateral forces must be multiplied by (1.O/2B)

This ratio shall not be less than 1..0..to obtain the drift.

All portions of a structure must be designed and constructed to act

as an integral unit in resisting the horizontal forces unless separated

structurally by a distance that is sufficient to avoid contact due to

deflection from seiSmic action or wind forces.

Structural Systems

Buildings designed with a structural behavior factor of B - 1/6

1/5 must have ductile moment resisting space frames. In zones of

high seismicity buildings more than ten stories tall must have ductile

moment resisting space frames capable of resisting at least twenty five

percent of the seismic force for the whole structure. All concrete space

frames required to be part of the lateral force resisting system and all

concrete frames located in the perimeter line of the vertical support must

be ductile moment resisting space frames.

46

All framing elements that are not part of the lateral force resisting

system must be adequate to withstand the vertical load and the induced

moment due to (I.O/B) times the distortion that results from the applica-

tion of the required lateral forces.

Moment resisting space frames may be adjoined by more rigid elements

that prevent the space frame from resisting the lateral load provided

that the failure of the rigid elements do not impair the resisting ability

of the space frame either laterally or vertically.

47

Chapter 5

THE 1976 UNIFORM BUILDING CODE

5.1 Earthquake Regulations

Every building or structure and every portion thereof must be designed

and constructed to resist stresses produced by lateral forces as discussed

The lateral forces are assumed to come from any direc-in this section.

tion and are applied at each floor or roof level above the base.

When wind loading produces higher stress levels, these shall be

Wind and earthquake loads need not beused instead of earthquake loads.

assumed to act simultaneously.

All allowable stresses and soil bearing values specified for working

stress design may be increased by one third when wind or earthquake forces

are either acting alone or when combined with vertical loads.

5.2 Symbols and Notations

The following symbols and notations are used in this code

- The dimension of the structure in feet in 8 directionparallel to the applied forces.

D

- Deflections at levels i and n, respectively, relativeto the base, due to applied lateral forces.Si,Sn

- Lateral force applied to levels i, n, or x, respectively.Fi ,F ,Fn x

= Lateral forces on a part of the structure and in the

direction under consideration.F

p

= That portion of V considered concentrated at the top ofthe structure in addition to F .Ft

n

- Acceleration due to gravity.g

h i ,h ,hn x= Height in feet above the base to levels i, n, or x,

respectively.

= Occupancy Importance Factor

= Numerical Coefficient from Table 5-1K

48

i = 1 designates the firstLevel i . The level of the structure.

level above the base.

. That level which is uppermost in the main portion of

the structure.

Leve 1 n

- That level which is under design consideration.Level x

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

s - Numerical coefficient for site-structure resonance.

- The fundamental elastic period of vibration of the buildingor structure in seconds in the direction under consideration

T

= The total lateral force or shear at the basev

- The total dead load of the structure, including the par-

tition loading where applicable.w

- That portion of W which is located at or is assigned to

levels i or x, respectively.Wi'wx

- Numerical coefficient dependent upon the zone as deter-mined from Figure 5-1.

z

S.3 Base Shear

Every structure must be designed and constructed to resist minimum

total lateral seismic forces which are assumed to act nonconcurrently,

The totalin the direction of each of the main axes of the structure.

lateral seismic force or base shear V is expressed as:

(5-1)V= ZKICSW

Z = The seismic zone coefficient from Figure 5-1.where:

K = Horizontal Force Factor from Table 5-1

S = The site-structure resonance coefficient and is

determined from the building period T and the site

characteristic period T .s

49

Figure 5-1

SEISMIC ZONE M.APS*

*Figures 1, 2, and 3 of Reference 4

50

Table 5-1

HORIZONTAL FORCE FAC'l'OR, K*

*Table 23-1 of Reference 4

51

Table 5-2

OCCUPANCY DofiJORTANCE FACTOR, r*

*Table 23-K of Reference 4.

52

TFot 1.0 or less

T s

T , T 12S - 1.0 + r - 0.5 Fs s

TFor ~ greater than 1.0s

s .

more than 2.5 seconds. When T is not properly established, the values

of S is taken as 1.5. The value of the product CS need not exceed 0.14.

5.4 Building Per!od

The building period T can be established from the structural pro-

perties and the deformational characteristics of the resisting elements.

One properly substantiated formula for this is:

I ( n n-1 '

JT = 2~1V\i:1 wiSi' ~ 8 i:1 FiSi + (Ft + Fn)Sn

In the absence of the period as determined above, T may be taken as:

O.OShn

.JD

~

T . (5-6)

Or in buildings where the lateral force resisting system consists of

ductile moment resisting space frames capable of carrying one hundred

percent of the lateral load and such a system is not prevented from

resisting the lateral forces by more rigid elements in the building. T

may be used as:

T - O.lON

53

Dtstribution of Lateral Forces Along the Height of the Structure

Buildings with regular shapes or framing systems have the total

lateral force distributed over the height of the structure as follows:

nV - Ft + 1: Fi

i-I(5-8)

The concentrated force at the top, Ft' is:

(5-9)Ft - O.O7TV

Ft does not exceed 0.25V and may be considered zero when T is 0.7 seconds

The remaining portion of the base shear is distributed to eachor less.

floor level as:

(V - Ft )w hx x (5-10)F .10. ,.'~ ,- .x n

r w h1-1 1 x

Setbacks and Irregular Structures

Buildings having setbacks of Which the plan dimension of the tower

in each direction is at least seventy five"percent of the corresponding

dimension of the lower part of the building can be considered to

be regular structures with no setbacks.

Structures which have highly irregular shapes, large differences in

lateral resistance or stiffness between adjacent stories or other unusual

structural features must be analyzed utilizing the dynamic characteristics

of the structure in order to determine the distribution of lateral forces.

Distribution of Horizontal Shear

Total shear in any horizontal plane is distributed to the various

elements of the lateral force resisting system in proportion to their

Rigid elements that are not considered to be part of therigidities.

54

lateral force resisting system may be incorporated into buildings provided

their effect on the action of the system is considered and provided

for in the design.

~o~1zontal Torsional Moments

Provisions must be made for the shear forces that result from tor-

sional moments due to an eccentricity between the center of mass and the

center of rigidity. Negative torsional shears are neglected. When ver-

tical resisting elements depend on diaphragm action t.o di8tribute the

shear at any level, the shear resisting elements must be capable of re-

sisting a torsional moment which is assumed to be the story shear acting

at an eccentricity of not less than five percent of the maximum building

dimension at that level

Building Drift an~ SeE!!:ations

Drift of a story relative to adjacent stories cannot exceed 0.005

times the story height unless it can be demonstrated that greater drift

can be tolerated. Displacements calculated from the application of the

required lateral forces is multiplied by (l.O/K) to obtain the drift

The ratio (1.0/K) shall not be less than 1.0

All portions of a structure must be designed to act as one unit in

resisting horizontal forces unless separated structurally by a distance

sufficient to avoid contact under deflection from earthquake or wind

forces.

Structural Systems

All buildings designed with a K factor of 0.67 or 0.80 must have

ductile moment resisting space frames. Buildings more than one hundred

sixty feet in height must have ductile moment resisting space frames

capable of resisting not less than twenty five percent of the required

55

seismic force for the structure as a whole. However, in seismic zone 1,

buildings more than one hundred sixty feet high may have concrete shear

walls in lieu of a ductile moment resisting space frame system, provided

that the K factor assigned is 1.00 or 1.33. In seismic 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 the vertical support are required to be ductile moment resisting

space frames. The framing elements that are not required to be part of

the lateral force resisting system of buildings in seismic zones 2, 3

and 4 must be adequate for vertical load carrying capacity and the induced

moment due to (3/K) times the distortions resulting from the required

lateral forces.

5.11 Load Combinations

In computing the effect of seismic force in combination with ver-

tical loads, gravity load stresses which are induced by dead load plus

design live load, except roof live load, must be considered. Minimum

gravity loads must also be considered acting in combination with lateral

forces.

5.12 Essential Facilities

Essential facilities are those structures or buildings which must be

safe and operational for emergency purposes after an earthquake in order

to preserve the health and safety of the general public. Examples of

essential facilities are listed below:

1. Hospitals and other medical facilities having surgery or emer-

gency treatment areas.

2. Fire and police stations.

3. Municipal government disaster operation and communications centers.

56

Chapter 6

THE 1973 UNIFORM BUILDING CODE

6.1 Symbols and Notation

c = Numerical coefficient for base shear.

D = The dimension of the building in feet in the direction

parallel to the applied forces.

= Plan dimension of the vertical lateral force resisting

system in feet.Ds

Fi .F .Fn x- Lateral forces applied to a level i, n, or x, respectively.

= That portion of V considered concentrated at the top of

the structure at level n.Ft

- Horizontal force factor from Table 6-1K

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

- That level which is uppermost in the main portion of

the structure.Level n

Level x - That level which is under design consideration.

- Total number of stories above grade to level D.N

- The fundamental period of vibration of the structure inseconds in the direction considered.

T

- The total dead load including partitions.w

= That portion of W which is located at or is assigned to

the level designated i or x, respectively.Wi'wx

6.2 Base Shear

Base shear is expressed as:

(6-1)V= KCW

The factor C in Equation 6-1 is determined by:

0.05

;IT(6-2)c =

57

Table 6-

HORIZONTAL FORCE FACTOR, K*

Value of KType or Arangement of Resisting Elements

All building framing systems except as hereinafterclassifiedl 1.00

1.33Buildings with a box system

0.80

Buildings with a dual bracing system consisting of aductile moment-resisting space frame and shear wallsor vertical bracing frames designed in accordance withthe following criteria:

1. The frame and shear walls or vertical bracingframes shall resist the total lateral force inaccordance with their relative regidities con-sidering the interaction of the shear walls.or vertical bracing frames. and frame.

2. The shear walls or vertical bracing frames act-ing independently of the ductile moment-resistingspace frame shall resist the total requiredlateral force.

3. The ductile moment-resisting space frame shallhave the capacity to resist not less than 25%of the required lateral force.

Buildings with a ductile moment-resisting space framedesigned in accordance with the following criteria:The ductile moment-resisting space frame shall havethe capacity to resist the total required lateralforce.

0.67

Elevated tanks plus full contents on four or morecross-braced columns and not supported by a building 2 3.00

Structures other than buildings and other than thoseset forth in Chapter 23 of Reference 5. 2.00

*Table 23-H of Reference 5.1A Horizontal Force Factor K - 1.0 shall be used only for buildings where

failure of shear walls would not endanger the vertical load carryingcapacity of the structure. For other shear wall buildings, K - 1.33shall apply.

2The minimum value of KC ahall be 0.12 and the maximum value of KC neednot exceed 0.25.

58

For all one and two story structures the value of C cannot be less

than 0.10. All other structures must have a C value not exceeding 0.10.

Structures with a highly irregular shape, or large differences in lateral

resistance or stiffness between different stories or other unusual struc-

tural features must be designed considering the dynamic properties of

the structure.

The fundamental period of a building, T, is expressed as:

O.O5hnT. (6-3)

..Jii'

Lateral force resisting systems consisting of one hundred percent moment

resisting frames that are not prevented from resisting the lateral load

by more rigid elements which adjoin the frame result in a building's

period being determined by:

T - 0.10 N (6-4)

6.3 Diatr:1bution of Lateral Forces Along the Height of the Structure

The total base shear is distributed over the height of a building

by the formula:

(6-5)

. 0.004 V[~ 2(6-6)Ft

The value of Ft need not exceed O.15V and it may be assumed that Ft - 0

when (~/Ds) is 3 or less.

The above application is valid except for one and two story structures

which shall have a uniform distribution of lateral forces over the height.

59

Distribution of Horizontal Shear-- -

The total shear in any horitontal plane is distributed to the elements

of the lateral force resisting system in proportion to their rigidities

at the same time considering the rigidity of the diaphragm. Rigid elements

are not part of the lateral force resisting system may be utilized

provided that their effect on the action of the system is considered and

provided for in the design.

Horizontal Torsional Moments

Provisions must be made for the increase in shear which results from

the horizontal torsion due to an eccentrictiy between the center of mass

Negative torsional shears are neglected.and the center of rigidity.

When 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 equivalent to the story shear acting with

an eccentricity of not less than five percent of the maximum building.d~en8ion at that level.

Setbacks

Buildings having setbacks in which the plan dimension in each direc-

tion at the setback is at least seventy five percent of the corresponding

dimension of the lower part of the structure may be considered

regular structures with no setbacks.

Buildings with irregularities that are classified as setbacks must

be designed differently. The portion that is set back or the tower as

it is referred to, is designed as a separate building. The resulting

total shear from the tower is applied to the top of the lower part of

the building which is then considered separately for its own height,

60

Structural Systems

All of the frames that are required to be part of the lateral force

resisting system must be ductile moment resisting frames. Buildings which

are greater than 160 feet in height must have a ductile moment resisting

space frame system that is capable of resisting at least twenty five

percent of the required lateral load for the structure as a whole. If

the building is more than three hundred twenty feet ti\ll, the frame must

consist of structural steel

All framing elements that are not required by design to be part of

the lateral force resisting system must be adequate for vertical load

carrying capacity when deflected a total of four times that which results

from the application of the required lateral forces

Moment resisting frames may be adjoined by more rigid elements that

tend to prevent the frame from resisting the lateral load where it can be

shown that failure of the more rigid element will not impair the vertical

or lateral load resisting ability of the frame

Drift and Building. Separatione

Lateral deflections, or drift of a story relative to adjacent stories

shall be considered in accordance with accepted engineering practice.

All portions of a structure must be designed and constructed to act

as a single unit in resisting the horizontal forces unless structurally

separated by a distance sufficient to avoid contact under deflection due

to seismic action or wind forces.

61

Chapter 7

THE BUILDING DESIGN

7.1 Introduction

The building chosen to be designed for this dissertstion was the

fifteen story ductile moment resisting steel frame from the Seismology

Committee's set of standard buildings. The building is symmetric in plan

with four frames in each major axis direction at intervals of thirty

feet. The overall base dimensions are ninety by ninety feet and the story

height is twelve feet six inches. Two beams within each bay transfer the

floor load to the girders. The floor beams, which are simply supported,

run only in the North-South direction and therefore rest on the girders

of the East-West frames. Box sections were chosen for the columns in

order to make the structure perfectly symmetric. All girder to column

Figure 7-1 pre-connections are one hundred percent moment resisting.

sents a typical plan and elevation view of the building.

The structure is assumed to be an office building located in the

San Francisco Bay Area. There are no structural interferences from any

parts such as elevators, stair towers, interior or exterior walls.

The San Francisco firm, GKT Consulting Engineers, donated computer

time and the computer program BATS, a modified version of the more well

known TABS, with which a static load analysis on the building was performed.

Computer output results were used to confirm that proper member sizes

had been chosen.

The building was designed using the procedures of the ATC 3 Method

which are discussed in the following sections. This ATC 3 design was

used as a standard and then Chapter 8 compares the results of this design

with the results of designs obtained from the other methods.

62

Seismicity of the Area2

The fifteen story office building is located in the San Francisco

and AThis location determines the two coefficients A asBay Area. va

well as the Seismicity Index.

- 0.4Aa

- 0.4Av

with a resulting Seismicity Index = 4

7.3 Base Shear

The ATC 3 Method gives the option of calculating the base shear

either based on building period or independent of building period. When

computed based on period:

5%(W)

and independent of period:

v - 12.5%(W)

Obviously there is a substantial difference between the two methods.

Calculations have been carried out using both values of base shear for

However, upon choosing girder member sizes itcomparative purposes.

becomes quite evident that 12.5%(W) is too large a value for base shear

and would not normally be used in practice for structures above three

The resulting values for the two base shears are:stories.

5% (W) = 640 K12.5%(W) = 1600 K

From this point on only the base shear of 5%(W) is considered..

The dis-

tribution of the base shear over the height of the building is shown for

comparison with the other design methods in Table 8-3 and Figure 8-1.

64

It was assumed that the interior frames resisted twice as much of

the lateral load as the exterior frames. However, the additional load

caused by accidental torsion was carried entirely by the exterior frames.

The accidental torsion was calculated to be O.lV. The resulting dis-

tribution of base shear to the individual frames is thirty three percent

to each interior frame and twenty seven percent to each exterior frame.

This is shown in Table 7-1.

7.4 Dead and Live Load

From the story masses listed in Table 1-1, an average dead load was

The buildingcalculated to be one hundred and five pounds per square foot.

contains offices which are assumed to have a live load of fifty pounds

per square foot and corridors which are generally designed for one hun-

As a conservative measure, a uniform livedred pounds per square foot.

load of seventy five pounds per square foot was used for the total floor

These results were compared to calculations that were based on a

*

area.

and at the point of choosinglive load of fifty pounds per suqare foot,

girder member sizes little or no difference was noticed.

7.S Fixed End Moments

The ends of each girder were assumed to be fixed. Moments were

calculated based on tributary area of the member and for the East-West

girders, the point loads due to the simply supported floor beams.

7.6 Portal Frame Analysis and Member Sizing

The portal method of frame analysis was used to compute column and

girder moments due to the lateral load. Assumptions of this method are

that the interior columns take twice as much shear as the exterior columns

and that the interior columns have no axial load.

*These calculations were done by Hratch H. Kouyoumdj ian of GKTConsulting Engineers.

65

Table 7-1

ACCIDENTAL TORS ION

~ - Torsional Moment

Hr is taken by the outer frame45 feet from the center

~ = ~ = O.IV at the outerframe

-L O.IV

45'

Typical Plan

USEV

!roT

0.17 V

VT

7Frames

0.21 VA and 1

0.33 V0.33 V0Band 2

0.33 V0.33 V0C and 3

0.27 V0.27 V+0.1 V

~Q1"6 v - O.l7V

2"6 v = O.33V

2"6 v z O.33V

1"6 v = O.l7VD and 4

66

Girder member sizes were selected based on these fixed end moments

in combination with vertical load moments as follows:

~ + 1.O~ + 1.O~ = ~

The ATC 3 Method allows a stress increase of 1.7 times the allowable

stress. Thus the quantity MTOT is divided by 1.7 to produce an allowable

moment MA. However, with guidance from the Seismology Committee it was

realized that, due to the combination of its height, structural system,

and configuration, this building would be governed by drift control re-

quirements. In order to control the inter-story drift the MA was increased

by one-third to bring it from the allowable to what is termed as an accept-

able design moment MACCEPT. From MACCEPT the girder member sizes were

chosen from the Allowable Stress Design Selection Table of the AISC Steel

In all cases the most economical section was selected.Construction Manual.

The column sizes were determined using the largest column moment

values which. indidently. occurred at the second story level. These

column moments received contributions from the lateral load and an assumed

twenty percent of the fixed end moments from girder dead and live loads

In addition to this design moment acting on the column, the ATC 3 Method

requires that thirty percent of this moment be applied simultaneously in

the orthogonal direction, along with the direct axial load effects.

Using the combined inter-action stress relationships in Section 1.6.1

of the AISC Specifications, it was determined that the column size should

be an eighteen by eighteen inch box-section made up of two and one half

inch thick plates

67

Chapter 8

CODE COMPARISON

Introduction

Having the building design, as completed by the ATC 3 Method as a

standard, the results were compared to designs of the same building done

according the the Stanford Method, the 1976 UBC and the 1973 UBC. The

procedures utilized in these other methods are similar to those of ATC 3

However, appropriate steps will beand will not be discussed in detail.

compared throughout the design process.

Base Shear

The different base shear equations and their values are shown for

Each equation is broken down in order to showcomparison in Table 8-1.

which variables are taken into account.

The equation used in the Stanford Method considers more factors

concerning the building qualities than do the other methods; thus, it is

able to deal with a wider variety of specific structures on a more accurate

One portion of the Stanford Method equation may pose a potentialbasis.

A component of the Quality Factor, Q, must judge the qualityproblem.

However, since this controlcontrol that will be performed on a job.

will occur after the design is completed, the designer must be able to

insure that the proper level of quality control will be available.

The Importance Factor of the ATC 3 Method is not directly included

However, this factor, termed the Seismicin the equation for base shear.

Hazard Exposure Group Classification, becomes incorporated into the design

when using the ATC 3 Method in determining the allowable story drift.

68

Table 8-1

COMPARISON or BASE SHEARS

'*628 K4.9%(W)ATC 3

692 K5.4%(W)Stanford Method

701 K5.5%(W)76 UBC

378 K3.0%(W)73 UBC

Factors

~~+'~

8

>-+'~.-IIU~

no

~4-J(/)>-

C/)

.4-J(J~1-44-J~

.~:3=

QJ,...:I~CJ:I,...~r"

I 00i , ~

gCo>

r

~~

I .-1-S-

OJ~0

N

CJ-rofSU)

-rofOJ

(/)

Formula GIt)

~~~

!

Code

~0

kQI

~

r"4~0

fI)

1.U Sv

-;;273wRATC 3 v s w A s T

v

wQ A B QSTANFORD, VzADBQW D DA

1 K ws c76 UBC v- ZICKSW z

K \'lcV=KCW73 UBC

*In the actual ATC 3 calculations the value of V = 4.9%(W) wasrounded off to V - 5%(W) or V - 640K.

69

Distribution of Lateral Forces Along the Height of the StTUcture

The manner in which the base shear is distributed over the height

of the building is shown for each method in Tables 8-2 and 8-3. All of

the methods distribute the lateral load as a function of the story mass

Since the top (roof) story is much lighter than the others,and height.

the special shape of the ATC 3 lateral force distribution is shown in

Figure 8-1, where the lateral load at the top is relatively small. However,

it should be noted that the distributions for the Stanford Method, the

1976 UBC» and the 1973 UBC all have an additional top story force which

Note that for the particularaffects the shape of their distributions.

building under consideration the distributions of the Stanford Method

The particular distribution ofand the 1976 UBC are nearly the same.

lateral forces by the ATC 3 Method varies exponentially with height where-

Except for theas the distributions by the other methods vary linearly.

top story, the 1973 UBC lateral force distribution is directly proportional

to the lateral force distribution of both the 1976 UBC and Stanford Method.

These differ by a factor of forty one percent as shown in Table 8-4.

Building Period

The building for this dissertation was designed with a structural

The buildingsystem made up of one hundred moment resisting steel frames.

period as calculated by the different methods is:

ATC 3 Method

3/4 T - O. 10 NT - 0.035 hn

T. 1.5 secondsT - 1.77 seconds

It is interesting to note that the method of calculating the building

period would have been the same for all four methods considered in this

70

Table 8-2

LATERAL LOAD DISTRIBUTION FORMULAE

w h kx xpoATC 3 Method ."'~,c'~'x n

I:i=1

L k

(V - Ft )w hx x po - O.O7TVtStanford Method and

1976 UBCP' .c"'"C~Cx n

t1-1

(v - Ft )w hx xFtF1973 UBC . .

x nt

1-1

71

Table 8-3

DISTRIBUTION OF LATERAL FORCES ALONG THE HEIGHTOF THE STRUCTURE

StanfordMethod

F

ATC 3Method

F

1976UBC

1973UBCLevel

xx

62 + 73* 63 + 74* 37 + 7*84R

74 4495 7315

69 41688414

3864637.513

3559586412

32545311 55

48 29484610

264343399

38 2231 378

193332247

27 1618 276

132222135

16 108 164

7111143

36512

*Ft

72

Figure 8-1

DISTRIBUTION OF LATERAL FORCES ALONG THE HEIGHT OF THE STRUCTURE

Lateral Force (kips)

75 50 25' 0100125ISO

~

>-~0~tn

~~~~~~~

13

Table 8-4

PROPORTION OF THE LATERAL FORCE DISTRIBUTION

(378K - 7K)(701K - 74K) 0.59.-;;~

(v:"Ft176

1 - 0.59 - 0.41

In percent. the 1973 UBC lateral force dis-tribution is forty one percent less thanthose of the 1976 UBC and the Stanford Method

74

dissertation provided that the structural system would have been other

than a one hundred percent moment resisting frame. It must be remembered

however, that metric units (meters) must be used in the equation from the

Stanford Method; however, the same results are obtained. The equations

are

Stanford Method

O.OShn

"\/D

O.O9hn

{D

~~

T -.

In order to compare the effects of period on base shear the equations

have been rewritten with T isolated in the denominator. The base shear

for each method is compared to base shear calculated with a ten percent

increase in period, as shown in Table 8-5.

The ATC 3 Method is the most sensitive to change in period with the

Stanford Method being nearly as sensitive. The 1973 UBC is the least

sensitive to period change.

8.5 Load Combinations .

The manner in which the gravity and seismic laods are combined, along

with any stress increases that are permitted for combinations with earth-

quake loads, will determine the required size of the members. The load

combinations that were used from each of the four methods are listed

below:

ATC 3 Method 1.2D + L + E

Stanford Method D+L

19'76 UBC D+L

1973 UBC D+L+E

(Note that E is different for each method)

75

Table 8-5

EFFECTS ON BASE SHEAR DUE TO INCREASED PERIOD

l:.:!:. ~ s w

!v = 2/3T

2/3 - 1.46

TATC 3 Method

*v = 2V0:3 ABQW

~Stanford Method

"T+ lO%T

...[i...JT + lO%T

76 UBC-v- -VT

O.O5KW

~~

-iJT + IOn

- 1.1473 UBC v-- 1.18

*For firm soil and 0.3 ~ T ~ 2.0 seconds.

**The values actually calculated were as shown: 628K and 4.9%W. However,the 4.9%W was rounded off to 5%W or 640K, which was used in the calculation

76

A stress increases beyond allowable is permitted by each method when

This isconsidering earthquake forces combined with vertical loads.

in order to take advantage of the reserve strength that members have

between the elastic design level and the plastic or ultimate strength

The permitted increases are listed below:design level.

1976 and 1973 UBCATC 3 and Stanford Methods

t.31.7

The CotJDnon Base for Comparison

live. and earthquake load moments as computed by theThe dead t

3 Method and as combined according to lo2MD + lo0~ + 1.0~ repre-

the plastic or ultimate strength design resisting moment requirements.

These moments were divided by the permitted stress increase value of 1.7

Throughto reduce them to equivalent allowable stress design moments.

engineering judgment based on the particular building height and the

rather fle:xible structural system, the allowable design level was then

This one thirdincreased by one third to allow for control of drift.

increase required to provide the extra member section and stiffness for

It would have been overlooked incontrol is an important factor.

a purely academic study, and yet it is a very real constraint for which

Only practical design experience (from theprovisions must be made.

The new design level which resultsSEAONC/GKT advisor) made this evident.

from this additional factor is referred to as the "Acceptable Design

Design levels from other methods were brought to this AcceptableLevel."

Design Level for comparative purposes; the calculations for this are shown

in Table 8-6.

77

Table 8-6

ACCEPTABLE DES IGN LEVEL

UltimateStress Increase

- AllowableLoad Combination - Ultimate

Allowable X 1.3 - Acceptable Design Level

ATC 3 Method

ULT1.3

(l.lD + ~ + E) X 1.3 = Acceptable -

1.7

Stanford Method- -

ULTCD + L + E) X 1.3 - Acceptable - 1:31.7 (Equivalent to ATC 3 Method)

1976 and 1973 UBC

(Equivalent to ATC 3 Method)(D + L + E) X 1.3 = Acceptable = ULT1.3

78

Member sizes were chosen using the Acceptable Design Moment as cal-

culated by each method. These moments for the buildings designed by

the ATC 3 and Stanford Methods were so close that the same member sizes

were selected. Therefore the resulting designs are identical. From this

point on, the 1976 and 1973 UBC buildings will be compared to the one

building that corresponds to both the ATC 3 and the Stanford Methods.

Table 8-7 lists the member sizes by story for comparison.

The buildings were compared in a more quantitative way by computing

the weight of the girders chosen by each method. Girder ~eights alone

were used in this comparison as they produce an acceptable, simple com-

parison without complicating the matter by introducing weight due to

columns or "in-bay" framing. The weights are shown at the bottom of each

page of Table 8-7 and are tabulated in Table 8-8. The total weight of

the girders in the building as designed by the ATC 3 and Stanford Methods

falls in between the value of the total weights of the girders found for

the 1976 and 1973 UBC buildings. This is an important factor from a cost

standpoint since the weight of steel is directly proportional to the cost

of a structural system

In addition to the weight, it is also important to compare the rela-

tive strength of the structures. The method developed in this disserta-

tion, though not unique, was deemed to be the best way to reduce the

strength of a building to a single number for comparative purposes. The

section moduli of the girders were averaged over every three stories,

except for the roof, for each frame. This was done in order to calculate

an average section modulus value for the structure. The results are

presented and compared in Tables 8-9 and 8-10.

In Table 8-11 the relative differences among the methods are reduced

to single numbers. The 1976 UBC building is thirteen percent heavier

79

and twenty one percent stronger than the building from the ATC 3 and

Stanford Methods. The 1973 UBC building is twenty nine percent lighter

and thirty percent weaker than the ATC 3 and Stanford Method building-

Averaging the percentage differences of weight and strength, it can be

in general that the design level of the 1976 UBC building is seven-

teen percent above that of the ATC'3 and Stanford Methods, and in general

the 1973 UBC building design level is thirty percent below the ATC 3 and

Stanford Methods.

In summary, the results of this study of one building system have

shown where the principal differences occur due to various design methods.

the study was limited to the framing system and its important details;

other factors such as the foundation design were not considered. The main

The equations for calculatingdifferences in the methods considered were:

the base shear; the way in which the lateral forces were distributed

the height of the structure; and the manner in which the loads were

The general results of this comparisoncombined for member size selection.

of design methods are considered valid for the fifteen story ductile moment

resisting steel frame building and can apply reasonably well to buildings

having similar heights, structural systems, and configurations

80

Table 8-7

GIRDER MEMBER SIZES

976 UBC

(Picked on the Basis of the Most Economical Section)

Fr. B & C Fr. A & DFr. 2 & 3 Fr. 1 & 4Level

W 18 x 35 W 14 x 26 W 24 x 61 W 16 x 40R

W 21 x 44 W 27 x 9415 W 24 x 55 W 24 x 61

W 24 x 68 W 30 x 9914 W 18 x 55 W 24 x 68

W 24 x 76 W 24 x 61 W 30 x 10813 W 24 x 76

W 24 x 84 W 30 x 116W 21 x 6812 W 24 x 84

W 24 x 94 W 24 x 68 W 30 x 116 W 27 x 8411

W 27 x 94 W 33 x 118W 24 x 76 W 27 x 9410

W 30 x 99 W 24 x 84 fIT 33 x 118 W 27 x 949

W 30 x 99 W 24 x 84 W 33 x 130 W 30 x 998

W 30 x 99 W 27 x 84 W 33 x 130 W 30 x 997

W 30 x 108 W 27 x 84 W 33 x 130 W 30 x 996

W 27 x 84 W 33 x 130 W 30 x 99W 30 x 1085

W 27 :c 84 W 33 x 130 W 30 x 994 W 30 x 108

W 27 x 84 W 30 x 99W 33 x 130W 30 x 1083

W 27 x 84 W 33x130 W 30 x 99W 30 x 1082

I wt/ft(lb/ft)

1070 1740 12941343

X 168'Fr. wt.(kips)'

180 292 211226

Total Weight - 915 kips

81

Table 8-7 (Continued)

GIRDER MEMBER SIZES

ATC 3 Method (V E 5%W)

Stanford Method

(Picked on the Basis of the Most Economical Section)

Fr. A & DFr. B & CFr. 1 & 4Fr. 2 & 3Level

W 12 x 22 W 21 x 55W 16 x 31 W 18 x 35R

W 18 x 35W 21 x 49 W 24 x 8415 W 21 x 55

W 21 x 44W 24 x 55 W 27 x 84 W 24 x 6114

W 21 x 49W 21 x 68 W 27 x 94 W 21 x 6813

W 21 x 55W 24 x 68 W 30 x 99 W 24 x 6812

W 24 x 61W 24 x 76 W 30 x 99 W 24 x 7611

W 24 x 61 W 30 x 108W 24 x 84 W 24 x 8410

W 21 x 68 W 30 x 108 W 24 x 84W 24 x 849

W 24 JC 68 W 30 x 108 W 24 x 84W 27 x 848

W 24 x 68 W 30 x 116 W 27 x 84W 27 x 847

W 24 x 76 W 30 x 116 W 27 x 84W 24 x 946

'W 24 x 76 W 30 x 116 W 27 x 84W 24 x945

W 24 x 76 W 30xl16 W 27 x 84W 24 x 944

W 24 x 76 W 30 x 116W 24 x 94 W 27 x 843

W 30 x 116 W 27 x 84W 24 x 76W 24 x 942

I wt/ft(lb/ft)

1535 11199111153

X 168'Fr. wt.(kips)"

188258194 153

r Frame Weights - Total Weight

Total Weight - 793 kips

82

Table 8-7 (Continued)

GIRDER MEMBER SIZES

1973 UBC

(Picked on the Basis of the Most Economical Section)

Fr. A & DFr. 1 & 4 Fr. B & CFr. 2 & 3Level

W 16 ~ 31WI" x 19 W 18 x 50W 14 x 26R

tJ 21 x 44W 14 x 34 W 24 x 6815 W 18 x 40

W 18 x 35 W 21 x 49W 21 x 44 W 24 x 7614

W 16 x 40 W 24 x 76 W 18 x 55W 18 x 5013

W 21 x 44 W 21 x 5SW 18 x 55 W 24 x 8412

W 21 x 44 W 24 x 84 W 24 x 55W 21 x 5511

W 18 x 50 W 24 x 61W 27 x 84W 24 x 5510

W 18 x 50 W 24 x 61W 24 x 61 W 27 x 849

W 21 x 49 W 21 x 68W 24 x 61 W 27 x 848

W 21 x 68W 21 x 68 W 24 x 94W 18 x 557

W 21 x 68W 21 x 68 1-124 x 94W 21 x 556

W 24 x 68 W 27 x 94 W 24 x 68W 21 x 555

W 24 x 68W 24 x 68 W 27 x 94W 21 x 554

W 24 x 68W 24 x 68 W 27 x 94W 21 x 553

W 24 x 68W 27 x 94W 24 x 68 W 21 x 552

I wt/ft(lb/ft)

887670855 1254

x )-68'Fr. wt.(k_~p~) .

149211 113144

Total Weight - 616 kips

83

Table 8-8

TOTAL GIRDER WEIGHT

1976 UBC 915 K 13% above

Reference level793 KATC 3 MethodStanford Method

29% below1973 UBC 616 K

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Table 8-10

SECTION MODUWS COMPARISON

AverageSection Modulus

Method

1976 UBC 21% above

Reference LevelATC 3 Method

Stanford Method

1973 UBC 30% below

87

Table 8-11

CODE COMPARISON TABLE.

LevelMethod

1976 UBC 17% above

Reference levelATC 3 Method

Stanford Method

1973 UBC 30% above

*This table is valid only for thebuilding discussed in this dis-

sertation.

88

REFERENCES

1.

Zsutty, T.C. and Haresh C. Shah, Recommended Seismic Resistant DesignProvisions for Guatemala. Technical Report for The John A. BlumeEarthquake Engineering Center, Stanford University, Department ofCivil Engineering, Stanford, California, May 1978.

2.

Zsutty, T.C. and Haresh C. Shah, Recommended Seismic Resistant DesignProvisions for Algeria. Technical Report for The John A. Blume Earth-quake Engineering Center, Stanford University, Department of CivilEngineering, Stanford, California, June, 1978.

3.

International Conference of Building Officials. 1976, ~niform BuildingCode.

4.

International Conference of Building Officials, 1973, Uniform BuildingCode.

5.

RQ