is !eview and Refinement of

ATC 3-06 Tentative Seismic Provisions

Joint Committee on Review and Refinement

r

1 Coordinating Committee T 1

Technical Committee

Committee 1: Seismic Risk Maps

Committee 3: Foundations

Committee 4: Concrete

Committee 5: Masonry

Committee 6: Steel

Committee 7: Wood

Committee 8: Architectural, Mechanical and

Electrical

Committee 9: Regulatory Use

Report of Technical Committee 2:^^

Structural Design

This report documents the deliberations of a group of professionals jointly

selected by the Building Seismic Safety Council and the National Bureau

of Standards and is for use in modifying the Tentative Provisions for trial designs.

> 111-2

U.S. Department of Commerce

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, D.C. 20234

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NBSIR 80-2111-2

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REVIEW AND REFINEMENT OF ATC 3-06 TENTATIVE SEISMIC PROVISIONS m

REPORT OF TECHNICAL COMMITTEE 2: STRUCTURAL DESIGN

Hal Iyengar, Chairman, American Society of Civil Engineers

James Robert Harris, Secretary, National Bureau of Standards

Timothy Reinhold, Assistant Secretary, National Bureau of Standards

Howard Simpson, American National Standards Institute

Richard McConnell, Interagency Committee on Seismic Safety in Construction

Nicholas Forell, Structural Engineers Association of California

Robert Englekirk, Technical Committee 1: Seismic Risk

Joseph V. Tyrrell, Technical Committee 3: Foundations

Mark Fintel, Technical Committee 4: Concrete

Alan Yorkdale, Technical Committee 5: Masonry

William A. Sontag, Technical Committee 6: Steel

Edwin G. Zacher, Technical Committee 7: Wood

Roland L. Sharpe, Applied Technology Council

Henry L. Degenkolb, Applied Technology Council

Ajit S. Virdee, Building Seismic Safety Council

William J. LeMessurier, Building Seismic Safety Council

Prepared for use by:

BUILDING SEISMIC SAFETY COUNCIL

Sponsored by:

FEDERAL EMERGENCY MANAGEMENT AGENCY

Center for Building Technology

National Bureau of Standards

Washington, D.C. 20234

October 1980

U.S. DEPARTMENT OF COMMERCE, Phillip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity,

Technology and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
> « *.**»

»
ABSTRACT

The Tentative Provisions for the Development of Seismic Regulations for

Bui ldings were developed by the Applied Technology Council to present,

in one comprehensive document, current state-of-knowledge pertaining to

seismic engineering of buildings. The Tentative Provisions are in the

process of being assessed by the building community. This report is one of a series of reports that documents the deliberations of a group

of professionals jointly selected by the Building Seismic Safety Council

and the National Bureau of Standards and charged with reviewing the

Tentative Provisions prior to the conduct of trial designs. The report

contains the recommendations and records of the committee charged with

review of the general structural design and analysis provisions. The

committee made 27 recommendations for revisions to the Tentative

Provisions and five additional recommendations concerning subsequent

activities, such as the conduct of trial designs. These recommendations

were made to the parent group, the Joint Committee on Review and Refinement, and their action on these recommendations is documented in a companion report.

Keywords: building; building codes; building design; earthquakes;

engineering; standards; structural engineering.
TABLE OF CONTENTS

Page

1.0 Introduction 1

1.1 General 1 1.2 Committee Summary * 1 1.3 Chairman's Statement 3

2.0 Committee Actions 5

2.1 Recommendations for Change.... 5 2.2 Recommendations for Commentary 21

2.3 Recommendations for Trial Design 22

2.4 Other Recommendations.... 22

3.0 Committee Records 23

3.1 Minutes of Meetings 23

3.2 Roster 58

3.3 Selected Committee Correspondence and Applied

Technology Council Comments 61

iv
1.0 INTRODUCTION

1.1 General

The Tentative Provisions for the Development of Seismic Regulations were developed by the Applied Technology Council (ATC) in an effort that included

a wide range of experts in the actual drafting of the provisions. Two

external review drafts were circulated to a large portion of the interested

and informed community of eventual users. However, because the Tentative

Provisions were innovative, doubts about them existed. Consequently, an attempt was made to investigate these doubts and to improve the Tentative

Provisions where possible before an expensive assessment of the Tentative

Provisions was undertaken by conducting trial designs.

This review and refinement project was planned and conducted by the National

Bureau of Standards with the advice and approval of the Building Seismic

Safety Council, a private sector organization formed in 1979 with the

purpose of enhancing public safety by providing a national forum to foster

improved seismic safety provisions for use by the building community.

The review of the Tentative Provisions was performed using the committee

structure shown in figure 1. Nine Technical Committees were formed with

interests that collectively cover the Tentative Provisions . The Joint

Committee on Review and Refinement consists of all voting members of the

Technical Committees. The chairman of the Technical Committees form a Coordinating Committee.

Membership of each Technical Committee is made up of representatives of

organizations that have particular interest in the Tentative Provisions ; the participants are listed in the committee membership section of this

report.

In addition to the voting members, each Technical Committee includes a non-voting member from each of the following organizations: The Applied

Technology Council (ATC), the Building Seismic Safety Council (BSSC)

and the National Bureau of Standards (NBS). The ATC representative was

a technical resource to the committee since he was closely involved with

the development of the provisions of interest to the committee. The NBS

representative was the technical support throughout the effort. The

BSSC representative provided a link with the Building Seismic Safety

Council, which will be involved in trial designs and evaluations.

1.2 Committee Summary

Technical Committee Number 2 on Structural Design was charged with

determining the adequacy, for purposes of trial design, of the following

portions of the ATC 3-06 Tentative Provisions for the Development of

Seismic Regulations for Buildings : Chapter 3, Structural Design

Requirements, Chapter 4 , Equivalent Lateral Force Procedure, and

Chapter 5, Modal Analysis Procedure, and the appropriate portions of

Chapter 1, Administration, and Chapter 2, Definitions and Symbols.

1
JOINT COMMITTEE ON

REVIEW AND REFINEMENT

COORDINATING

COMMITTEE

tech:*1 CAL COMMITTEES

Co~ittce 1

Seismic Risk Maps

Cocnittee 2: Structural Design

Corccittee 3: Foundat iens

Cc~.it tee 4: Concrete

Corrrittee 5 : Masonry

Co remittee 6: Steel

Conmittee 7: Wood

Committee 8:

Mechanical,

Architectural

,

and Electrical

Coremittee 9: Regulatory Use

Figure 1: Committee Structure
The committee proposed 23 revisions to the provisions of ATC 3-06 (see

Section 3.1). In most instances these proposals carried the committee

by a unanimous ballot. Some of these proposals involve a change in the

commentary as well as the provision. The committee also proposed four

changes to the commentary that are relatively independent of the changes

proposed for the provisions (see section 2.2). The committee also made

five recommendations concerning the execution of the upcoming trial

designs and the development of seismic provisions in general (see

sections 2.3 and 2.4).

The committee carried out its work through a combination of correspondence

and working meetings. Three meetings were held:

December 11, 1979, National Bureau of Standards, Gaithersburg, MD

February 27-28, 1980, Quality Inn/Desert Sky, Phoenix, Arizona

April 2-3, 1980, O'Hare American Inn, Des Plaines, Illinois

The minutes of these meetings are in section 3.2, and the correspondence

is summarized in section 3.3. Section 3.2 contains the complete committee

roster.

Nearly everyone connected with the committee felt that, on the whole, the

committee carried out its charge in a responsible and professional manner,

particularly considering the nature of the task of preparing for trial designs

and the short time available. The committee wishes to emphasize that the

provisions must be reconsidered carefully following the trial designs.

1.3 Chairman's Statement

Committee Number 2 is a well balanced committee with respect to geographical locations and professional and industrial representation. The

Committee adopted the view that mid-course corrections will be made if

found necessary within the original intent and philosophy of the document.

The Committee assumed that trial designs are necessary for the evaluation

of many critical items. It was also recognized that trial design should

not be realistically relied upon to verify all items. Therefore, the

Committee made corrections and revisions which were needed for which

trial design results were not completely essential. The Committee also

attempted to state specific recommendations for trial design and other

studies when needed.

I feel the following items have a significant impact on the eventual use- fulness and relevancy of ATC 3-06 and be attended to in the trial design

phase and by the BSSC.

1. The relationship of seismicity index to map area (Table 1-B). The

impact of imposing seismic design and detailing requirements where

currently no such current application is needed should be carefully

evaluated. Please refer to the Minority Report and my Closure

Statement (Exhibit E and F, respectively in Section 3.3).

2. Response modification coefficients (Table 3-B). This table plays a key role in seismic design according to ATC 3-06. The Committee

through one of its task groups, attempted to evaluate this table.

3
Because of the lack of time, data and trial design solutions, a thorough evaluation of the table was not feasible. Trial designs

should focus heavily on this table not only regarding the R,

factors, but also with respect to definitions of systems that fit

different categories.

3. There was significant discussion of coupled shear walls (which are claimed to be the best concrete system when designed with ductile

linkage) and eccentric braced frames. Although some data was

available, the Committee felt that additional studies are needed.

A special recommendation to BSSC to formulate such a study group

was stated by the Committee. Also, in this regard, a general

statement on the non-linear analysis approach was included in the

Commentary

4
2.0 Committee Actions

2.1 Recommended Changes

The following pages contain the changes to the Tentative Provisions

recommended by the committee, along with the final ballot tally for each

recommendation and a comment on the proposal. For convenience, these 23

changes are listed below:

Item Section of

ATC 3-06

Short Description

1-7 2.1 Snow loads less than 30 psf

1-8 2.2 Definition of live load effect

1-9 2.2 Definition of snow load effect

1-10 3.1 Allowance for alternative analysis procedures

1-11 3.2.1 Classification of rock

1-12 3.2.3 Use of soil-structure interaction analysis

1-13 3.3.1 Name of inverted pendulum structures

1-14 3.3.2(A) Value of R for mixed systems

1-16 3.3.4(C) Deformational compatibility of structural

components

1-17 3.7.2 Orthogonal load combinations

1-18 3.6.2(A)

& 3.7.3

Consideration of strength discontinuities

1-19 3.7.4 Consideration of redundancy

1-20 3.7.5 Interconnection of building parts

1-21 3.7.9 Name of the symbol Vx

1-23 4.2 Use of simple equation C s 1-24 4.5 Restriction on overturning moment resultant

1-25 2.2 & 4.6.2 Definition of Px , the vertial load

2-1 2.1 Definition of shear panels

2-2 3.3.4(A) Height limits for torsionally stiff systems

2-3 3.5 Use and limitation for alternate analyses

2-4 3.8 Exception to drift limit for certain buildings

2-5 Table 3-C Magnitude of drift limits

2-6 4.6.2 Calculation of P-delta effect

5
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-7

ATC-3-06 SECTION REFERENCE: 2.1

Add the following sentence immediately following the definition of SNOW LOAD.

EXCEPTION: Where snow load is less than 30 pounds per square foot, no part

of the load need be included in seismic loading.

FINAL BALLOT: 5 YES

2 NO

1 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The change introduces consistency with the model building code and simplifies

computations for those locations in which only a small snow load would be

considered simultaneously with seismic loads. The minority view was that the

current ATC provision (use of from 20% to 70% of the full snow load, depending

on the judgement of the building official) was an adequate allowance for the

small probability of simultaneous occurrence of snow load and seismic load.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-8

ATC-3-06 SECTION REFERENCE: 2.2

Change the definition to read as follows:

Ql = The effect of live load, reduced as permitted in section 2.1

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The added phrase clarifies the use of live load reduction based on tributary

area when combining the effects of live load and seismic load.

6
KEVIEW and refinement of tentative seismic provisions

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-9

ATC-3-06 SECTION REFERENCE: 2^2

Change the definition of Qg to read as follows:

Qg = The effect of snow load, reduced as permitted in section 2.1 .

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The added phrase clarifies the use of the reduction from the full design snow

load when combining the effects of snow load and seismic load.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2 , STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-10

ATC-3-06 SECTION REFERENCE: 3.1

Change the second and third sentences to read as follows:

The design forces, and their distribution over the height of the building,

shall be established in accordance with the procedures in Chapter 4 or Chapter 5; the corresponding internal forces in the members of the building

shall be determined using a lineariy elastic model. An approved alternate

procedure may be used to establish the seismic forces and their distribution ; the corresponding internal forces and deformations in the members shall be

determined using a model consistent with the procedure adopted . Individual

members shall be sized . . .

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revisions permits the use of method incorporating inelastic models of

material behavior, subject to explicit approval of the authority.

7
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-11

ATC-3-06 SECTION REFERENCE: 3.2.1

Change the first paragraph under soil profile type 1 to read as follows:

1. Rock of any characteristic, either shale-like or crystalline in nature.

Such material may be characterized by a shear wave velocity greater than

2500 feet per second or by other appropriate means of classification , or

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The added phrase removes the implication that shear wave velocity tests are necessary in order to class a subsoil material as rock.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-12

ATC-3-06 SECTION REFERENCE: 3.2.3

Change to read as follows:

The base shear, story shears, overturning moments, and deflections determined

in Chapter 4 or Chapter 5 may be modified in accordance with procedures set

forth in Chapter 6 to account for the effects of soil-structure interaction.

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

Two issues are involved in this item. First, the committee decided to retain

the provision allowing soil-structure interaction analysis because it felt

that Chapter 6, Soil-Structure Interaction, was a worthwhile component of the

overall seismic design provisions. Second, the revision to the provision was made in recognition of the possible increase in force effects due to the

increased P-delta effect resulting from rotation of the base of a building.

8
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: # 2 , STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-13

ATC-3-06 SECTION REFERENCE: 3.3,1

Delete the word "Special” from the third sentence of the first paragraph.

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

Since a "special" inverted pendulum in nowhere distinguished from any other

type of inverted pendulum, the removal of the word prevents possible confusion.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-14

ATC-3-06 SECTION REFERENCE: 3.3.2(A)

Change the first paragraph to read as follows:

R VALUE. The value of R in the direction under consideration at any level shall

not exceed the lowest value of R obtained from Table 3-B for the seismic resisting

system in the same direction considered above that level.

FINAL BALLOT : 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revisions clarify the original intent of the provision.

9
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

I

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-16

ATC-3-06 SECTION REFERENCE: 3.3.4(C)

Change to read as follows:

DEFORMATIONAL COMPATIBILITY. Every structural component not included In the

seismic force resisting system In the direction under consideration shall be

investigated and shown to be adequate for the vertical load-carrying capacity

and the induced moments resulting from the design story drift, as determined

in accordance with Sec. 4.6.

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision has the effect of requiring a check on the ability of the seismic

resisting system to maintain vertical load carrying capacity when subject to

the lateral displacement of the seismic resisting system in the orthogonal

direction. (For example, consider the ability of a bearing and shear wall

to support vertical load when the wall is laterally supported by an unbraced

frame). The provision already required such a check for structural components

that were not part of the seismic resisting system.

10
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-17

ATC-3-06 SECTION REFERENCE: 3.7.2

Change to read as follows:

ORTHOGONAL EFFECTS . In buildings assigned to Category B, the design seismic

forces may be applied separately in each of two orthogonal directions .

In buildings assigned to Category C and D, the critical load effect due to

direction of application of seismic forces on the building may be assumed

to be satisfied if components and their foundations are designed for the

following combination of prescribed loads: 100 percent of the forces for one direction plus 30 percent of the forces for the perpendicular direction.

The combination requiring the maximum component strength shall be used.

EXCEPTION: Diaphragms, and components of the seismic resisting sys tem

util ized in only one of two orthogonal directions need not be designed

for the combined effects .

FINAL BALLOT: 7 YES

1 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The objective in revising the provision is to reduce the amount of unnecessary

computation required. The committee believes that more improvement toward

this objective may be possible and looks for the trial designs to provide

such information.

11
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-18

ATC-3-06 SECTION REFERENCE: 3.6.2(A) and 3.7.3

Change the second line of 3.6.2(A) to read as follows: . . .shall conform to

the requirements of Sec. 2.7 (except Sec. 3.7.3 and Sec. 3.7.12). . .

Change 3.7.3 to read as follows:

For Buildings assigned to Seismic Performance Categories C or D the design of

the building shall consider. . .

FINAL BALLOT: 8 YES

0

NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision removes the potential inconsistency of requiring formal consideration

of strength discontinuities for buildings in which formal consideration of stiffness discontinuities is not required. Consideration of discontinuities in stiffness need not be formally considered for buildings in Seismic Performance Category

B (to wit: Modal Analysis is not required for buildings in Category B with

vertical irregularities).

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-19

ATC 3-06 SECTION REFERENCE: 3.7.4

Change to read as follows:

The design of a building shall consider the potentially adverse effect that the

failure of a single member, connection, or component of the seismic resisting

system would have on the stability of the building.

FINAL BALLOT: 7 YES

1 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

No guidance is given on just how- redundancy is to be checked. The revision

reduces, slightly, the magnitude of this problem.

12
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-20

ATC-3-06 SECTION REFERENCE: 3.7.5

Change the first line to read:

All parts of the building between separation joints shall be interconnected

and the connections shall be. . .

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision clarifies the orignial intent of the provisions.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-21

ATC-3-06 SECTION REFERENCE: 3.7.9

Change the second line of the third paragraph to read:

. . .elements of the building attached thereto plus the portion of the seismic

shear force at that level , Vx , required to be transferred. . .

FINAL BALLOT : 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision clarified the original intent of the provision.

13
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2 , STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-23

ATC-3-06 SECTION REFERENCE: 4.2

Change the last paragraph to read as follows:

The value of C

g may be determined in accordance with Formula 4-2, 4-3, or 4-3a , as appropriate . Formula 4-2 requires calculation of the fundamental period of

the building as specified in Sec. 4.2.2. For low buildings, or in other

instances when it is not desired to calculate the period of the buildings , C

g shall be determined using Formula 4-3, 4-3a, as appropriate.

FINAL BALLOT : 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision encourages the use of the simple equations for those situations

in which the calculation of building period has no impact on the design force

level.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-24

ATC-3-06 SECTION REFERENCE: 4.5

Delete the last sentence of the last paragraph.

FINAL BALLOT : 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The deleted sentence had potential for creating serious design problems for

those buildings using piles or piers as holddown anchors, yet no convincing

argument has been forwarded for retaining the deleted sentence.

14
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 1-25

ATC-3-06 SECTION REFERENCE: 2.2 and 4.6.2

Change the definition of Px

to read as follows:

Px

= the total unfactored vertical design load at and above level x.

FINAL BALLOT: 8 YES

0 NO

0 ABSTAIN

2 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The original deifinitions for Px

in sections 2.2 and 4.6.2 were not identical.

The revised definition specifies the pertinent load for the investigation of

instability.

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-1

ATC-3-06 SECTION REFERENCE: 2.1

Delete the word "wood" from the definition of SHEAR PANEL.

FINAL BALLOT : 7 YES

0 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

It is possible to design and rely on shear panels constructed from materials

other than wood, for example studs with gypsum board.

15
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: //2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-2

ATC-3-06 SECTION REFERENCE: 3.3.4(A)

Revise paragraph 3 to read as follows:

3. A system with structural steel or cast-in-place concrete braced frames or shear walls in which there are braced frames or shear walls so arranged

that braced frames or shear walls in one plane resist no more than the

following proportion of the seismic design force in each direction , including torsional effects.

a. Sixty (60) percent when the braced frames or shear walls are arranged only on the perimeter .

b. Forty (40) percent when some of the braced frames or shear

walls are arranged on the perimeter .

c. Thirty (30) percent for other arrangements.

FINAL BALLOT: 7 YES

0 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision explicitly recognizes the improved torsional performance of

buildings with the principal seismic resisting elements located on the

perimeter by relaxing the requirement for four independent lines of

resistance for such buildings.

16
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-3

ATC-3-06 SECTION REFERENCE: 3.5

Revise to read as follows:

This section prescribes the minimum analysis procedure to be followed.

An alternate generally accepted procedure, including the use of an approved site specific spectrum , if desired, may be used in lieu of

the minimum applicable procedure. The limitations upon the base shear

stated in section 5.8 apply to any such analysis .

FINAL BALLOT: 7 YES

0 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision removes any implication that the provisions of chapter 5 constitute

the only acceptable procedure for modal analysis and specifically allows the use

of site specific design spectra, which is the current state of practice for

important buildings in highly seismic areas. The precise limit on base shear

given in section 5.8 is easier to understand and apply than the limit on building period given in present wording of section 3.5.

17
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-4

ATC 3-06 SECTION REFERENCE: 3.8

Revise by adding the following sentence to the end of the last paragraph of

the section:

Single story buildings in Seismic Hazard Exposure Group I that are constructed

with non-brittle finishes and whose seismic resisting system is not attached

to equipment or processes need not meet the drift requirement in table 3-C .

FINAL BALLOT : 7 YES

0 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

This revision is coupled with the revision proposed for table 3-6, (item 2-5

from Committee #2) in which the footnote allowing a higher limit for certain

buildings is deleted. The types of buildings described in the revised provision

have performed well from a drift standpoint in past earthquakes.

18
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-5

ATC 3-06 SECTION REFERENCE: Table 3-C

Remove the footnot from the table and revise the table to read:

Table 3-C

ALLOWABLE STORY DRIFT A a

Seismic Hazard Exposure Group

III II I

Aa 0.015hsx 0.025h sx 0.025h sx

FINAL BALLOT : 6 YES

1 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The drift limitations of Sec. 3.8 of ATC 3-06 are, for many structures,

considerably more restrictive than the UBC and usual current design

practice. Becuase of the lack of a close relationship between story

drift and either the amount of inelastic strain or the magnitude of the

P-delta problems, and because damage control unrelated to safety is not

a code objective, the drift limits have been increased.

The revised values were chosen to minimize the possibility of imposing

drift constraints more severe than those reflected in current design

practice. In specific instances, however, such as for controlling the

magnitude of relative movements at joints, the designer may find it

necessary or desirable to impose more restrictive limits.

19
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #2, STRUCTURAL DESIGN COMMITTEE ITEM NUMBER: 2-6

ATC 3-06 SECTION REFERENCE: 4.6.2

Revise the second sentence of the last paragraph to read as follows:

The design story drift determined in Section 4.6.1 shall be multiplied by

the factor (SLi.2.. > 1.0) to obtain the story drift including P-delta effects.

1-0 =

FINAL BALLOT: 7 YES

0 NO

0 ABSTAIN

3 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The revision explicitly defines for design use the increase in story drift

due to P-delta, and by means of introducing the approximation (0.9 « 1.0),

it avoids a troublesome discontinuity that would occur when 0 = 0.10.

20
2.2 Recommendations for Commentary

The committee recommends four specific changes to the commentary of the

Tentative Provisions , as follows:

C-l, for section C3.5, Analysis Procedure

It is possible with presently available computer programs to perform two dimensional inelastic analyses of reasonably symmetric structures. The intent

of such analyses could be to estimate the sequence in which components become

inelastic and to indicate those components requiring strength adjustments

so as to remain within the required dectility limits. It should be emphasized that with the present state-of-the-art in inelastic analysis there is on one method that can be applied to all types of buildings, and further

the reliability of the analytical results are sensitive to:

1. the number of and appropriateness of the time-histories

of input motion

2. the practical limitations of mathematical modelling

including interacting effects of nonstructural

elements

3. the non-linear algorithms

4. the assumed hysteretic behavior

Because of these sensitivities and limitation the maximum base shear

produced in the inelastic analysis should be not less than that required

by Chapter 5 (Modal Analysis).

C-2, for section C3.3.1, Classification of Framing Systems

A large table of framing systems is to be inserted in the commentary with

an indication of where each system would fall in Table 3-B.

C-3, for section C4.6, Drift Determination and P-delta Effects

The last paragraph on page 368 should be considered as a part of the

acceptable P-delta analysis referred to on page 367.

C-4, for section C5.5, Modal Base Shear

A plot should be inserted in the commentary to illustrate the pattern

of spectral coefficients for R and Av

.

21
2.3 Recommendations for Trial Design

The committee made the following recommendations for the planning and

conduct of the trial designs that will be used to assess the impact of

the Tentative Provisions :

R-3 The descriptions of the building systems in Table 3-B and the R

factors in that table are adequate for the trial designs. They

should be reexamined following the trial designs. To aid in

this, the designers should be asked to make an intelligent

assessment of just what the impact on cost of differing R values

would be.

R-4 1) Trial designs should include examination of drift control

needs for different types of building systems.

2) Trial designs should include calibration with existing

standards around the country.

3) Trial designs should include examination of the impact of

drift limits on life safety for different occupancies.

R-5 The trial designs and subsequent studies should examine carefully

the impact of and the validity of the P-delta procedure.

2.4 Other Recommendations

The committee made two other recommendations concerning the Tentative

Provisions and the improvement of seismic safety provisions in general:

R-l The committee recommends to BSSC that technical groups be established

to develop standard provisions for new types of seismic resisting

systems that depend on the concentration of inelastic straining in

special members for good performance in earthquakes, in particular,

coupled shear walls and eccentric braced frames. For coupled shear

walls, the provisions should delineate the details and the stiffness

and strength ratios between the shear walls and the coupling beams

to assure that the inelasticity is concentrated primarily in and

accounted for in the coupling beams. For eccentric brace frames,

the provisions should delineate the connection details and the

relative member proportions to assure that the inelasticity occurs

in the flexural or shear links and does not occur in members that

primarily are loaded axially.

R-2 Following the approval of any recommended changes to the ATC 3-06

provisions, the Commentary and the Guide to Use of ATC 3-06 should

be carefully reviewed for any needed revision.

22
3.0 Committee Records

3.1 Minutes of Meetings

Three meetings were held:

December 11, 1979, in Gaithersburg, Maryland

February 27-28, 1980, in Phoeniz, Arizona

April 2-3, 1980, in Des Plaines, Illinois

The minutes for these meetings follow this page, except that none of the

attachments mentioned in those minutes are included in this section. One

important attachment to the minutes of the second meeting, the response of

the ATC representative to the proposed changes is included in section 3.3.

23
Minutes of First Meeting

Technical Committee 2 - Structural Design

Review and Refinement of Tentative Seismic

Provisions (ATC-3-06)

at

National Bureau of Standards

December 11, 1979

The meeting was convened at 12:00 noon in the Green Auditorium of the . National Bureau of Standards by James Harris of NBS, the committee

secretariat, with the following members present: r

. *

_ &

Richard McConnell, representing the Interagency Committee on Seismic

Safety in Construction.

Nicholas Forell, representing the Structural Engineers Association

of California.

Rene Luft, the alternate representative for the American National

Standards Institute.

William Ayer, temporarily representing the American Society of

Civil Engineers.

Roland Sharpe of the Applied Technology Council.

James Harris of the National Bureau of Standards.

Tim Reinhold, also of NBS

Members not present or organizations not represented were:

Aj it S. Virdee of the Building Seismic Safety Council

Mr. Ayer stated that the ASCE representative for the committee would be

Mr. Hal Iyengar of Skidmore, Owings and Merrill of Chicago, Illinois.

Procedures for conduct of the project were discussed. The requirement for

a 2/3 majority of the joint committee to pass a proposal as a recommended

change was criticized by some, the feeling being that the provisions are too

tentative to require such a backing for a change, that the issues are too

technical for such wide agreement, and that the technical committees would

be wasting time working on proposals that would not pass the final ballot.

Others felt that the 2/3 majority rule is appropriate. General agreement

24
was not reached on the 2/3 majority rule, but it was agreed that unsuccessful

proposals should be retained in the eventual report to the Building Seismic

Safety Council. It was also agreed that recommendations for the conduct

of test and trial designs would be appropriate output from the committee,

in addition to the primary output, namely, recommended changes to the

ATC-03-06 seismic provisions.

The committee recessed at 1:00 p.m. and reconvened by Harris at 1:30 p.m.

in the NBS cafeteria with the following additional members in attendance:

Joseph Tyrrell, representing Committee 3: Foundations

Mark Fintel, representing Committee 4: Concrete

Alan Yorkdale, representing Committee 5: Masonry

William Sontag, representing Committee 6: Steel

Edwin Zacher, representing Committee 7: Wood.

Robert Englekirk, representing Committee 1: Seismic Risk Maps^

Edward Pfrang of NBS, observer.

The first item of business was the election of a chairman. As the nominations

were opened, discussion ensued concerning the desirable qualifications

for a chairman. Zacher, seconded by Sontag, then nominated Simpson for

chairman and Iyengar for vice-chairman, both subject to their acceptance.

McConnell, seconded by Yorkdale, nominated Forell for chairman. After

the nominations were closed, Forell withdrew. No additional nominations

were forthcoming, and_the committee approved Simpson and Iyngar, subject

to their acceptence. —

After comparing the scheduled meeting dates for the other committees, it

was decided to hold the next meeting on the days immediately preceding

the BSSC Executive Board meeting, which is in Phoenix on February 29.

Luft was then designated acting chairman for the duration of the meeting.

The committee recessed at 2:00 and reconvened at 2:30 in the Green Auditorium

with the same members as were present at the 12:00 noon session.

Harris introducted a list of areas in which the committee might receive

proposals for change, based on his reading of the external review comments

received by ATC in 1976 and 1977:

The factor R for modification of the elastic response:

Both changes and additions are possible.

The formulas for approximate period of vibration.

— Englekirk was a visitor at this meeting. The BSSC subsequently approved

the representation of Committee 1 on Committee 2, and Englekirk is now a member of Committee.

2 / Both gentlemen were contacted by phone later in the day. Simpson

declined the offer, and Iyengar accepted the offer, thus succeeding to

the chairmanship of the committee.

25
- The load combinations, especially the 0.5 factor for dead load

for brittle components.

- The orthogonal load combination.

- The design spectrum for buildings with very short periods and

high values of R.

- The design spectrum for modal analysis in the low frequency range.

- The lower limits on base shear and the upper limits on calculated

periods

.

The height limits for various building types.

- The seismic performance categories

- The calculation of the value 0 for use in determining the need for

P-delta analysis.

A simpler method of analysis

The provisions requiring modal analysis for certain buildings.

The reduction in the overturning moment at the base of a structure.

Sharpe then added the following:

- The factor for amplification of elastic deflections.

The drift limits.

McConnell added that the section for an intermediate level of ductility

for reinforced concrete needs simplification and editing.

Forell then contributed several points of concern (only the additional

ones are listed)

Load factor design

Lack of provision for horizontal irregularity

- Restraints on certain combinations of seismic resisting systems

(are lacking in ATC)

The provision for disconinuity in a vertical sense

The formula for the distribution of base shear to story forces

- The applicability of the torsion provision to wood diaphragms

- The provisions implying that plastic analysis be used for unbraced

steel frames.

2 b
- The use of single degree of freedom per node modal analysis

instead of a three degree of freedom method.

- R values for large flexible diaphragms

- Resolution of forces in the foundations, particularly for systems

with low values for R.

The committee was joined during the session by William Sontag, the

representative of Committee 6 and by William LeMessurier, the BSSC liaison

for Committee 1. LeMessurier indicated an intent to participate in the

meetings of this committee,,

Sontag stated a concern with the requirements for the use of rolled steel

sections qualified for plastic design in all "special moment frames," which

effectively prohibit the single story rigid frame "metal building" in

the highest seismic zones.

Luft questioned the use of light gage cold rolled sections for earthquake

resistance.

Considering the wide range of possible proposals, the committee decided to

allow two days for the next meeting. The next meeting will be on February

27 and 28 in Phoenix, Arizona , exact time and place to be announced.

~ ” ’ "ted.

(James Robert Harris

Secretary

27
Minutes of Second Meeting

Technical Committee 2 - Structural Design

Review and Refinement of Tentative Seismic

Provisions (ATC-3-06)

at

Quality Inn/Desert Sky, Phoenix, AZ

February 27-28, 1979

The meeting was convened at 9:00 am, February 27th in the Summit Room of the

Quality Inn/Desert Sky by Hal Iyengar, the committee chairman. The following

voting members were present:

Mark Fintel - representing Committee 4: Concrete

Nicholas Fore 11 - representing SEAOC

Hal Iyengar - representing ASCE

Richard McConnell - representing the Interagency Committee on Seismic

Safety in Construction

Howard Simpson - representative for ANSI

William Sontag - representing Committee 6: Steel

Joseph Tyrrell - representing Committee 3: Foundations

Alan Yorkdale - representing Committee 5: Masonry

Edwin Zacher - representing Committee 7: Wood

Robert Englekirk - representing Committee 1: Sesimic Risk Maps, arrived

at noon on the 27th.

The following nonvoting members were present:

Representing ATC: Roland Sharpe

Henry Degenkolb

Representing the BSSC Overview Committee:

Aiit Virdee

William LeMessurier

NBS Secretariat: James Harris

Timothy Re inhold

Several observers were also present:

William Ayer - with ASCE

Mario Catani - with PCA, attended only on the 27th.

Harry Mejdell - with WSCSEA (Western States Conference of Structural

Engineers Associations ) Avi Singhal - with Arizona State University, attended only on the 27th

Jesse Wyatt - with PCA - Phoenix

28
Mr. Iyengar opened the meeting with a discussion of the agenda. He proposed

that lengthy discussions be postponed to the second day.

The minutes of the first meeting held December 11, 1979 at NBS were reviewed.

McConnell noted that a correction should be made to page 3 of the minutes to

indicate that he had stated that the section on ductility for reinforced con- crete needed much simplification and editing. He pointed out that he had not

suggested a need for an intermediate level of ductility for reinforced concrete.

A motion to approve the minutes of the December 11th meeting, as corrected by

McConnell, was made, seconded, and passed. The remainder of these minutes are arranged by topic rather than by strict chronology.

Table 1-A and 1-B. With regard to the changes to table 1-A proposed by the

masonry committee, Yorkdale noted that the transcript contained an error. The masonry committee was not suggesting that the seismic performance category

for exposure group I and seismicity index 2 be changed to A but rather that

it remain B. The effect of their proposal was only to change the performance

category from A to B for seismicity index 1 and exposure group III. This

proposal would in effect require some specific design considerations for all

buildings in exposure group III. The proposed change was considered by some

of the members to be contingent upon approval of changes in table 1-B which

would reduce the seismicity index for several map areas.

Sharpe responded by noting that originally ATC was under pressure to eliminate

design requirements wherever possible. ATC felt that the requirement that

building components be tied together, as required for category A, was adequate.

At this point the discussion shifted to consider of proposed changes in

Table 1-B. Sharpe prepared a table on the chalkboard to indicate the proposed changes to table 1-B and to illustrate the effects of the changes on the performance categories. The table is reproduced below.

Seismicity Indices Performance Categories

Current

Map # ATC Masonry Fintel CRSI III II I

7 0.40 4 4 4 4 D C C

6 0.30 4 4 4 4 D C C

5 0.20 4 3 3 3 D(C) C C(B)

4 0.15 3 2 2 2 C(B) C(B) B

3 0.10 2 1 1 2 B(A or B) B(A) B(A)

2 0.05 2 1 1 1 B(A or B) B(A) B(A)

1 0.05 (0.00) 1 0 1 1 A( ? ) A( ? ) A(?)

Sharpe further noted that changes in table 1-B impacts all the other chapters

and that provisions are interwoven in the various chapters. Harris reported

Ted Algermissen, the chairman of Committee #1, suggested that it might be more appropriate to change the actual requirements that depend on the

seismicity indices, than to change the indices.

29
Fintel stated that seismicity indices are used to correlate ground accelerations to detailing requirements and that the real question concerns the level

of ductility required for intermediate levels of acceleration. He suggested

that for acceleration levels of 0.05g, to perhaps levels as high as 0.10g,

buildings can be expected to respond elastically. For accelerations of 0.10g

to 0.20g a better understanding is needed of the ductility requirements. He

felt the provisions should not call for greater ductility than is provided in

current design.

A lengthy discussion followed on the pros and cons regarding the level of

detailing required with various members relating personal observations of

buildings that had experienced earthquakes of different levels to back up

their arguments. Iyengar summarized the committee's dilemma by noting that

there were strong opinions supporting changes in table 1-B, strong opinions

against making changes and strong opinions that a wider study is needed in

order to define ductility requirements.

Yorkdale suggested that the committee recommend the trial designs be con- ducted using both the current and proposed seismicity indices. Simpson noted

that trial designs are very expensive and care must be taken to minimize the

number of cases to be studied. Sharpe suggested that it might be possible to

recommend consideration of alternative values of the seismicity index for

certain buildings or specific types of buildings rather than considering the

alternative values for all cases in the trial designs.

Simpson suggested that changes in the seismicity indices should not be made

unless there was a strong reason for the change and that the people wanting

the change must bear the burden of providing the strong documentation.

It was decided to place the proposed changes on the letter ballot as individual items for each map area. Also, it was decided to place the suggested

change in Table 1-A on the ballot. Sontag and Yorkdale indicated that the

proposed change in table 1-A should be contingent on changing the seismicity

indices in table 1-B as proposed, at least for accelerations of 0.1 and

be low

Section 1.6 Quality Assurance :

Three proposed changes to this section were considered briefly. Harris and

Iyengar suggested that the proposals be considered by the appropriate

material committees, particularly since Committee #9 did not plan to discuss

those particular items. A motion was made, seconded and passed that the

proposed changes to the quality assurance provisions be returned to the

material committees.

Section 2.1 Definitions :

Sontag 's proposal to change the definition of snow loads to effectively

eliminate consideration of snow loads when computing seismic effects for areas where the snow load is less than 30 psf was considered. Sontag noted

that UBC and other codes contained that exemption. He felt that it would

30
account for the small probability of maximum earthquake and maximum snow

load oc curing simultaneously.

1 Zacher responded by noting that the ATC provisions are adequate since they

do allow a reduction from the maximum snow load. Furthermore he indicated

that the new version of ANSI may propose dropping the exception from 30 psf.

Tyrrell noted that the real question of whether snow loads and earthquakes

loads occur simultaneously requires knowledge of the duration of snow loads

and not on the maximum value.

Forell moved that the proposal by Sontag be included on the ballot since he

felt that members needed more time to think about the issue. The motion

was second and passed.

(Secretariat's note: Inadvertently, the proposal by Sontag concerning the

definition of a Shear Panel was not discussed. It will be considered at the

next meeting.)

Chapter 3

Section 3.1 Design Basis :

Forell' s proposed change to the first paragraph which would make it possible

to obtain exceptions to the drift limitations in table 3-C was considered.

Zacher suggested that the intent of the proposal could be better achieved

by adding a second footnote to table 3-C. Forell agreed. The proposal was changed to read:

O In accordance with section 1.5, the Regulatory Authority may approve

deformation limits exceeding these where it can be demonstrated in an acceptable manner that the deformation limits used provide equivalent

performance, strength and safety.

Committee members appeared to be in general agreement concerning this footnote. Forell noted that it might be possible to avoid the footnote by

changing section 1.5 to be closer to UBC provisions. Zacher and Sharpe

agreed and noted that section 1.5 needed to be changed. (Secretariats

note: no explicit change for section 1.5 was considered at the meeting.)

Fintel's proposal to change the first paragraph to allow for alternative

approved methods of design was considered. Fintel felt that there should

be a mechanism for allowing alternative design procedures and especially to

allow inelastic methods which could be used to reduce internal forces.

Simpson and Iyengar agreed. Forell and Sharpe noted that elastic methods

are inherent in all the ATC provisions and that a separate sentence was needed to insure that consistent procedures were used in the analysis and

in sizing individual members. Zacher, Sharpe and Fintel volunteered to

write out alternative wording for the second and third sentence of 3.1 over

lunch.

31
When the topic was taken up again after lunch, the alternative wording was further modified, resulting in:

The design seismic forces, and their distribution over the height of the

building, shall be established in accordance with the procedures in

Chapter 4 or Chapter 5; the corresponding internal forces in the members

of the building shall be determined using a linearly elastic model. An

approved alternative procedure may be used to establish the seismic

forces and their distribution; the corresponding internal forces and

deformations in the members shall be determined using a model consistent

with the procedure adopted. Individual members shall be sized...

A motion was made, seconded, and passed, to add the above change to the

ballot

.

Section 3.2.1 Soil Profie Type :

McConnell's proposal for removing part of the definition of rock was considered.

McConnell felt that inclusion of the reference characterizing rock by a shear wave velocity greater than 2500 feet per second would effectively legislate

that soil consultants would have to make shear wave velocity tests. He pointed

out that there are other ways to determine whether a site can be classified

as rock.

After a brief discussion, Iyengar suggested that the sentence under Soil Profile Type S^, No. 1 be changed to read:

. . . Such material may be characterized by a shear wave velocity greater

than 2500 feet per second or by other means of classification, or

Zacher moved that the above clause be added to the ballot as a possible revision rather than McConnell's original suggestion. The motion was second and

passed.

Section 3.2.3 Soil Structure Interaction :

Zsutty's proposal that section 3.2.3 and Chapter 6 be deleted was considered.

Tyrell supported the proposal by noting that Committee 3, Foundations wanted

to delete Chapter 6 also. Sharpe replied that use of the chapter is voluntary

and is a step forward because it recognizes soil structure interaction effects.

Degenkolb stated that he had originally opposed inclusion of Chapter 6 because

he felt is was striving for accuracy that in fact was not possible, but no longer opposes it.

Iyengar asked whether the chapter reflected the state of the art in soil

structure interaction and whether inclusion of Chapter 6 was a step forward

for the profession. McConnell noted that any model of the soil behavior can change in 2 years or so especially if a new building is built nearby. He felt

that it was conservative not to use soil structure interaction. Singhal

mentioned that he had worked through the method and liked it but that use of

the method could lead to increased forces for some structures.

32
As the discussion proceeded it was suggested that the problem really centered

on section 3.2.3 where it is stated that the base shear, story shears and

overturning moments may be reduced. The feeling was that owners would require

use of Chapter 6 because of the implied reduction. Forell and Zacher proposed

that the problem be handled by changing the wording to read:

The base shear, story shears, overturning moments and deflections determined in Chapter 4 or Chapter 5 may be modified in accordance with ...

It was moved, seconded and passed that the above proposed revision appear on the

ballot

Section 3.3.1 Classification of Framing Systems :

In response to McConnell's question concerning what is meant by a special

inverted pendulum-type structure it was decided to include on the ballot a proposal that the word "special" before inverted pendulum-type structure be

deleted.

Section 3.3.3 Combination of Framing Systems :

a) McConnel requested a sample defintion of a supported structure. Considerable discussion followed with a variety of definitions, including piping,

mechanical systems, machinery, non-structural systems, mezzanines, structure

within a structure, penthouses, etc.

It was noted that the commentary provided some help in defining the meaning

of a structure within a structure. No specific change was suggested.

b) Forell' s suggested change to include provisions for combinations of

framing systems at the same level was considered. Forell cited the use of

moment frames and shear wall or bearing walls in orthogonal horizontal directions as an example. He felt that stiffness compatibility was desirable

between the systems especially where they joined together at corners. Zacher

suggested that the problem could be considered in section 3.3.4 (c) and

volunteered to develop a specific provision with Forell.

The discussion did bring out the fact that several members were confused by

the language in section 3.3.2(A). Harris suggested changing the words "any

direction" to "the direction under consideration" and changing "in the direction considered above the level" to "in the same direction considered above

that level". It was moved, seconded and passed that the suggestion be added

to the ballot as a possible revision.

The committee meeting was recessed for lunch at 12:30 pm and reconvened at

1:30 pm.

33
3.3.4(A) Seismic Resisting Systems [Height Limits for Performance Category C ]

:

Three comments were received on this section and quite a long discussion

resulted, at the end of which no specific proposal for change appeared to

be acceptable to the committee. It was decided to set up a task committee

to study the issues and prepare specific language for changing the section.

Degenkolb, and Fintel and Zacher where appointed to the committee, with

Degenkolb acting as chairman.

The next few paragraphs document some of the major points raised in the discussion. Forell requested clarification of what was intended by the requirement that braced frames or walls in any plane resist no more than 33% of the

seismic design force including torsional effects. Iyengar and Englekirk

expressed concern that the language used might eliminate certain shape buildings.

Zacher responded that the requirement does not prohibit unconventional shapes,

it only requires redundancy. Several numbers agreed with that concept, but

felt that the provision was arbitrary.

Degenkolb commented that he wanted the provision to make it possible to lose an element and still have the structure remain standing. He felt that, with

real world practice in mind, there was a need to apply restrictions.

The comments by Sheppard and Fintel concerned removing the 240 foot height

limitation for buildings described in paragraph (A) 3 and defining coupled

shear walls as a new system. Professor Bertero's response to these proposals

is attached to these minutes.

Fintel suggested that height limits should be maintained for buildings using

regular shear walls but should not be applied to coupled shear wall buildings,

since the inelastic response is concentrated in the horizontal members rather

than the vertical load carrying members. Harris noted that adding a new

system would require changes in other chapters, for example, for items such

as coupling beams.

Zacher advocated arbitrary limits to keep from extending designs beyonds our knowledge. Forell and Degenkolb echoed this idea by noting that design of

buildings that exceed certain limits requires special analysis which is

beyond the capabilities of many average engineers. They felt that the provisions should protect the public and the profession from buildings with

less than special analysis in such situations.

Iyengar responded by asking whether it would be possible to soften the

requirements to allow cases where sophisticated analysis and design are conducted. Sharpe suggested that would require a review committee, because

most building officials would not have the time, resources or capabilities

to review special methods of analysis and design.

34
McConnell remarked that what Sharpe was suggesting sounded like a variance

committee. Iyengar and Yorkdale responded that a variance committee would

not suffice and that what would be needed is a strong technical review

committee. Simpson added that establishing a review committee would not be

simple and would necessitate providing specific requirements for the review

committee.

Section 3.3.4(B) Interaction Effects :

McConnell requested clarification of this section. The discussion was postponed until a specific change was suggested by Zacher and McConnell.

The following alternate wording for the first sentence appears on the

ballot:

Moment resisting space frames which are enclosed by or, adjoined by,

more rigid elements, whose proportionate stiffnesses preclude their

consideration as part of the seismic resisting system, shall be designed

so that the action or failure of those elements will not impair the

vertical load and seismic force resisting capability of the space frame.

Section 3.3.4(C) Deformation Compatibility :

Forell's concern for insuring compatibility in the response of two dissimilar

seismic systems in the horizontal plane, raised during the discussion of

section 3.3.2, was accounted for in this section. After some discussion,

Simpson suggested the following wording which was approved for inclusion in

the ballot.

DEFORMATION COMPATIBILITY. Every structural component, whether or not

it is part of the lateral force resisting system for the direction under

consideration, shall be investigated and shown to be adequate for the

vertical load-carrying capacity and induced moments resulting from the

design story drift. A, as determined in accordance with section 4.6.

Zsutty's comment was noted but no specific proposal for a change could be

developed.

Section 3.3.5 Seismic Performance Category D

Suggestions to delete the height limitations were referred to the task com- mittee created to study height limits specified in section 3.3.4(A).

Section 3.4 Building Configuration

Forell's request that words such as "nearly" and "approximately" be replaced

by more specific definitions was not acted upon because no one could provide

specific definitions.

35
Section 3.4.2 Vertical Configuration

McConnell’s request for a more specific definition than "significant" was withdrawn because no specific language could be suggested.

Sections 3.5 Analysis Procedures and 3.6 Design and Detailing Requirements

Proposed changes to these sections were received from Committee 5: Masonry.

However, the proposals were considered to fit better in Chapter 12 on Masonry

rather than in Chapter 3. The committee decided to refer the proposals back

to the masonry committee for their consideration and their determination of

whether to include the changes in Chapter 12.

Section 3.5.1 Seismic Performance Category A (Analysis Procedure)

McConnell questioned the philosophy behind not requiring analysis for the

seismic forces for the building as a whole. He pointed out that most other

codes include wind effects, which controls the design in low seismicity areas. Wind is not included in the ATC provisions, and therefore some level of

seismic analysis might be necessary for category A. Zacher responded that

while analysis is not required in ATC, certain details and ties are required

that will provide the necessary strength. The comment was withdrawn.

Section 3.5.3 Seismic Performance Categories C and D (Analysis Procedures)

McConnell's requested clarification of the implications of this section with

regard to modal analysis. Sharpe noted that the second sentence in the sec- tion requires special analysis which considers the dynamic characteristics

of all irregular buildings. Thus, modal analysis or some other technique

is required. However, the last sentence notes that the procedures in

Chapter 5 are only adequate for vertical irregularities. McConnell's comment

was withdrawn.

Zsutty's comment was considered. Zacher noted that the second sentence covers

the case described by Zsutty in general terms and recommended that the com- mentary to the section be extended to include Zsutty's comment.

Section 3.7.1 Combination of Load Effects

See the written comment by Forell to the effect that the load factor approach

is undesirable and the response by ATC. Iyengar pointed out that many groups

are moving ahead in the area of load factor design and that discrepancies must

exist for now. No specific proposal for a ballot item came out of this

discussion.

McConnell had a question about the definition of Q and recommended that

symbols and special terms be defined where they are first used. Sharpe

responded by noting that the symbols are defined in section 2.2.

Sontag's proposal to change equation 3.1 was also considered. However, it was suggested that the loads used in the equation were intended to be reduced

36
loads so that the k factor proposed was already included. The committee con- cluded that the proper place to clearify the issue was in the definitions in

section 2.2. Consequently it was moved, seconded, and passed that the definitions of Ql and Qg in section 2.2, page 42 be changed by adding the phrase,

"reduced as permitted in 2.1," after each of the definitions.

3.7.2 Orthogonal Effects

Several comments and proposals for alternate wording were received for this

section. The major concern with the section was that it required a tremendous amount of busy work on the part of designers, yet many special configurations make it difficult to write a general provision. A subcommittee composed

of Zacher, Simpson and LeMessurier recommended the following alternative

wording on the morning of the 28th:

3.7.2

ORTHOGONAL EFFECTS

In buildings assigned to category B, the design seismic forces may

be applied separately in each of two orthogonal directions.

In buildings assigned to category C and D, the critical load effect

due to direction of application of seismic forces on the building may be

assumed to be satisfied if components and their foundations are designed

for the following combination of prescribed loads: 100 percent of the

forces for one direction plus 30 percent of the forces for the perpendicular direction. The combination requiring the maximum component

strength shall be used.

EXCEPTION: Diaphrams, and components of the seismic resisting

system utilized in only one of two orthogonal directions need not

be designed for the combination effects.

A motion was made, seconded and passed that the above alternative wording

for section 3.7.2 be added to the letter ballot.

3.7.3 Discontinuities in Strength of Vertical Resisting System

McConnell felt that the problem was a question of relative stiffness between

stories rather than strength. The ATC response indicated that the section

was primarily designed to flag the potential adverse effects that could occur

during inelastic response. Forell requested that the section be more than

a flag and actually prohibit discontinuities in strength.

Iyengar responded that the problem can't be controlled easily by a general

statement. He pointed out that the commentary contains guidance on how to

consider the problem. Degenkolb stated that the commentary is enforced along

with the code in some areas.

LeMessurier raised a concern about requiring consideration of strength discontinuities in ares where there are no current requirements for consideraing discontinuities in stiffness. He pointed out that requiring these

37
considerations for buildings in category B would add considerable work for

buildings designed in a large portion of the U.S. A number of members

indicated a belief that the section was not originally supposed to apply to

category B structures.

It was agreed to place an item on the ballot which would change section 3.7.3

to indicate that it only applied for categories C and D. While many members

felt that a stronger statement should be included to warn against discontinuities in strength, it was felt that the committee could not produce the

wording at the meeting.

Presentation of Inelastic Analysis Method by Mark Fintel

Consideration of specific proposals ended at 5:00 pm and a presentation on

the advantages of introducing an inelastic method was given by Fintel. Many

of the points raised in his presentation are briefly outlined in his written

proposal to add a section describing an alternative inelastic procedure.

The meeting adjourned for the day at 5:30 pm.

The meeting was reconvened by Chairman Iygenar at 8:00 am, February 28th.

Again the meeting took place in the summit room of the Quality Inn/Desert

Sky. All committee members were present. Only two observers, as noted

earlier, did not return for the second day.

The first item of business was consideration of the alternate wording

for section 3.7.2: Orthogonal Effects. This has been included with the

notes from the 27th on section 3.7.2.

Section 3.7.4 Nonredundant Systems

McConnell felt that this section needed rewriting or removal. Fintel agreed

stating that in its present form the section gives the design engineer

responsibilities he can't handle. Sharp responded that the intent of the

section is to provide redundancy. Degenkolb added that experience shows

that damage will occur in a severe earthquake and the section reflects the

desire to prevent collapse. After deciding that the redundancy was only

necessary for the seismic resisting system, the following alternate wording

was placed on the ballot.

The design of a building shall consider the potentially adverse effect

that the failure of a single member, connection or component of the

seismic resisting system would have on the stability of the building.

Section 3.7.5 Ties and Continuity

McConnell suggested that the definition of all parts of the building be

expanded to note "or units between expansion joints" as is indicated in the

commentary, page 350. The proposed wording that came out of the discussion

is:

38
All parts of the building between expansion joints shall be interconnected and . .

.

Section 3.7»6 Concrete and Masonry Wall Anchorage

McConnell's request for a reference for the provision with relation to

bending was withdrawn after it was pointed out that the provision is

identical to one in the UBC.

Section 3.7.8 Collector Elements

McConnell's suggestion to add the words "where analysis requires," after

the word "provided” was dropped. There was confusion concerning the definition of a collector element. No agreement could be reached on any specific

modification and the problem seems to be an editorial one.

Section 3.7.9 Diaphrams

McConnell requested a parenthetic reference for Vx

to define it. Zacher

suggested the following wording for the 3rd paragraph:

A minimum force equal to 0.5 Ay times the weight of the diaphram and

other elements of the building attached thereto plus the portion of the

seismic shear force at that level, Vx , required to ...

The proposed alternate wording was approved for inclusion on the ballot.

Section 3.7.11 Inverted Pendulum - Type Structure

McConnell's suggestion to waive this provision if analysis has considered

the effect of the rotational inertia of the mass was withdrawn following a short discussion. ATC felt the provision should remain as is and that the

commentary on page 351 makes the situation clear.

Section 3.8 Deflection and Drift Limits

Zsutty's comment indicated that he considered the drift limits to be too

restrictive and about twice as stringent as UBC. A number of committee

members agreed, suggesting that the drift limits might be from 2 to 4

times more restrictive than other codes. ATC stated that it was recognized

that the drift limits needed to be further evaluated and that the effects

of varying the limits should be studied in the trial and test designs.

Several questioned why drift limits were included in ATC-3-06. Sharpe noted

that the SEAOC originally did not include drift limits, but that they do now. Zacher added that after every major earthquake there has been considerable

public reaction to the extensive damage that has occurred and there has been

a growing demand for damage control.

Simpson noted that while it may be economically feasible and politically

desirable to have damage control in areas where earthquakes occur frequently,

39
the concern in areas with a low probability of an earthquake occurrence is for

life safety, because there is no economic basis for requiring damage control.

Simpson and LeMessurier asked for an indication of what level of drift corres- ponded to requirements of life safety, which could not be answered. Tryell

noted that response of mechanical systems and nonstructural elements can impact

life safety.

Iyengar suggested that findings of the trial designs may lead to establishing

exceptions to the drift limits, where special precautions are taken. Zacher

noted that an exception was originally considered but it does not appear in the

ATC-3-06. Forell commented that the problem arises because a dual spectrum

approach is not used.

Iyengar suggested that the committee's feelings on the question of drift

limits should be combined to produce recommendations for the trial designs.

Some concern was raised that a few design cases can't cover the possibilities

well. There also was some feeling that too much was being left to the trial

designs. Sharpe responded that the trial designs are the only way to evaluate

the values of R and C^. Englekirk felt that recommendations for the trial

designs should include questions for the engineer performing the design such

as (1) does the drift limit improve the design? (2) what is the impact of the

drift provisions?

A summary of the recommendations is:

1) Trial designs should include examination of drift control needs for different types of building systems

2) Trial designs should include calibration with existing standards around

the country

3) Trial designs should include examination of impact of drift limits on

life safety for different occupancies.

It was decided that each member should come to the next meeting with more information based on individual studies. A task group consisting of

LeMessurier, Sontag, Zacher and Englekirk was also set up to study the problem and bring recommendations for the trial designs to the next meeting.

Englekirk was appointed chairman of the task group.

New Section 3.9 Alternative Inelastic Design Procedure

Fintel recommended that a new section be added which would allow an alternative inelastic design procedure. He felt that the means are now available

to do economical inelastic design and that such design would provide a method

for reducing internal forces and insuring that hinges form in beams rather

than in columns.

Zacher and Sharpe responded that description of such a procedure might be

included in the commentary. They strongly objected to the section being

40
added to the provisions. They pointed out that section 3.1 does not preclude use of an alternative method. McConnell felt that if the inelastic

procedure is included in the commentary that a strong statement should be

added to point out the severe limitations of nonlinear analysis.

Sontag felt that a specific alternative design procedure should not be

included in the commentary since other procedures should be considered as well.

A task group consisting of Fintel, McConnell and Sharpe was established to

study the feasibility of adding the alternative inelastic design procedure

to the commentary. Fintel was appointed chairman of the task group.

Table 3 -A Soil Profile Coefficient

Virdee requested an explanation of why profile S

2 is used in section 3.2.1

to describe soil of unknown character rather than type S

3

. In response it

was pointed out that S

2 actually provides the largest forces for small

buildings because of the difference between equations (4-3) and (4-3a) and

that soils so soft as to be S

3 would be easily indentif iable.

Table 3-B Response Modification Coefficients

The comments on table 3-B related to the definitions of the varius categories and to actual values of R and C^ that were chosen.

Several questions were raised concerning where a specific structural system

would fit within the table and a concensus appeared to form that some clarification was needed. It was suggested that the clarification might best fit

within the commentary. A suggestion was made that a long list of systems

might be given in the commentary together with a guide on where each system

fell within table 3-B.

Sharpe and Degenkolb indicated that such a table had been created several

years ago and agreed to reproduce it and distribute it to the committee

members. Sharpe also indicated that he would send a matrix of the proposed

trial designs to the committee. (These items are attached to the minutes).

Considerable discussion took place concerning the values given in table 3-B.

It was generally suggested that the values are arbitrary and need study.

Fintel requested on explanation of how the values were determined.

Degenkolb gave a brief review of the sequence and history of the committee

work to develop the R factors. Work began with a list of framing systems.

Test data and information gained from experience was combined with available information on damping values and ductility. People on the committee

and on the steering committee had input and the actual table of values went

through at least four cycles. In the end there was surprising agreement

among the committee members. Sharpe added that lots of different values were suggested at the outset of the process but that as discussions proceeded the

results converged.

41
Iyengar asked whether there was much research into procedures for determining

R and values. Sharpe responded by noting that there is little specific

work, what is required is full scale tests. He added that there is the

possibility of using some Japanese work and some shaking table work but that

research has not been specifically aimed at determining R values.

Iyengar suggested that a procedure is needed for establishing R values.

Degenkolb responded that a procedure may be possible for clean concrete or steel structures but probably not for wood or composite materials. Sharpe

indicated that ATC hopes that it will be possible to upgrade values as knowledge is gained in the future but that he feels that the values given are an improvement over the K values given in UBC. He noted that the trial

designs will be one step in improving the values.

It was suggested that BSSC is responsible for periodic improvement to the

ATC document, but that a method for change has not yet been set up. Zacher

moved that the committee recommend to BSSC that a method be established for

updating the ATC document as new information becomes available. Iyengar

added that the motion suggest that R values be verified by the trial designs

and that a consistent criterion be developed for establishing reasonable R

values. No specific wording was worked out for the motion.

Englekirk and Fintel suggested that the inelastic time history analysis be

used in the trial designs. The feeling was that comparing against existing

codes was not sufficient and that the R values should be compared with the

results of nonlinear time history analysis in order to establish bench marks.

No action was taken on the various proposals for changing table 3-B. A task

committee consisting of Simpson, Forell and Le Messurier with Simpson as chairman was established to delineate the problem, collect all the comments

on the R factors into an intelligent unit, and to consider what recommendation should be made to BSSC concerning the trial designs and establishing a method for updating the ATC document.

Fintel wanted the committee to consider a method for coming up with rational

R values. He expresed willingness to do work on reinforced concrete and

wanted someone to look at steel systems. It was decided that any specific

work would be done on an individual basis and would constitute a second step

beyond the immediate charge of the task group.

Table 3-C Allowable Story Drift Aa

The proposal by Sontag to change the footnote to exempt one story metal

buildings was not considered at any length. It is expected that the task

group on drift limits, see minutes for Section 3.8, will make some recom- mendation concerning this proposal.

42
Section 4.2 Seismic Base Shear

Forell's request that a statement be added to section 4.2.1 to note that

Formula 4-3 will generally apply for short buildings was handled by proposing a change to the last paragraph in section 4.2. Zacher suggested the

following wording:

The value of C

g may be determined in accordance with Formula 4-2, 4-3, or 4-3a, as appropriate. Formula 4-2 requires calculation of the fundamental period of the building as specified in section 4.2.2. For low

buildings, or in other instances when it is not desired to calculate

the period of the building, C

g shall be determined using Formula 4-3 or 4-3a, as appropriate.

A motion was made seconded and passed that this revision be included on the

ballot

Section 4.2.2 Period Determination

McConnells proposal that an exception be allowed to the limit of T = 1.2 T

g was dropped after some discussion, although he felt that an exception should

be provided for well analyzed special structures with long periods. Forell

noted that SEAOC feels that the limit is very necessary.

The CRSI proposal to revise equation 4.4 was dropped. The committee saw no point in using a less sophisticated equation that didn't account for story

height.

Section 4.3 Vertical Distribution of Seismic Forces

McConnell and Forell both had comments on the exponent k, which were withdrawn after a short discussion, see the ATC response and commentary on page 364.

Section 4.4 Horizontal Shear Distribution and Torsion

The proposals by Forell and Zacher were discussed together. Several committee

members including Simpson and Degenkolb were concerned about the difficulties

in coming up with specific numbers for the rigidity of the horizontal and

vertical sytems. After some discussion the proposals were withdrawn and no ballot items were suggested.

Inadvertently, the Masonry task group's proposal was not considered. It will

be taken up at the Chicago meeting.

Section 4.5 Overturning

Comments by Forell and Zacher were considered. Forell and Zacher noted that

the formula suggested higher overturning than actually exists. Englekirk

pointed out that the real problem for design lies in the last sentence where

the resultant of the seismic forces and vertical loads is not allowed to fall

I

43
outside of the middle 1/2 of the base. Zacher felt that the provisions were inadequate but could not suggest a better wording.

It was decided to add an item to the ballot which would drop the last sen- tence from the provision.

Section 4.6.2 P-Delta Effects

This section was originally taken up in the morning of the 28th to allow

LeMessurier to present a proposal. It was also brought up again in the

afternoon and a question was raised that the committee decided it wanted

LeMessurier to consider.

LeMessurier 's proposal would change the last paragraph as follows:

When 0 is greater than 0.10 for any story, the story shear for that

story shall be multiplied by the amplification factor a^, where

a^ shall not be less than 1. The overturning moments, deflections,

and drifts shall be redetermined corresponding to the amplified story

shears

LeMessurier 's proposal was accepted for inclusion on the ballot.

A question was also raised concerning the definition of W^ used in the

equation for Px

. It was agreed that Px should be redefined as the total

unfactored vertical design load at and above level X. This item was also

accepted for inclusion on the ballot.

McConnell requested instructions indicating that the computations were not

needed for short buildings. Englekirk wanted similar instructions for

short and medium period buildings. It was noted that such instructions

would require determination of a cutoff level, which would vary according

to the zone, for use of the provision. McConnell agreed to look at the

possibility of setting such a cutoff. No action was taken at the meeting.

Degenkolb raised the question of whether C^ should appear in the denominator of equation 4-10. It was decided that Sharpe and Degenkolb would study

this question and that it would be referred to LeMessurier for comment.

Section 5.2 Modeling

After some discussion of semantics, McConnell's comment was withdrawn. See

the ATC response.

44
Section 5.3 Modes

The answer to McConnell's question question is that modal analysis can be

helpful for irregular structures. The comment was withdrawn.

Section 5.4 Periods

McConnell asked whether soil modeling was completely ruled out. The answer given was that it was not ruled out. The analysis procedure does require

starting with a fixed base but the last sentence in section 5.5 allows con- sideration of soil-structure interaction.

Section 5.5 Model Base Shear

McConnell recommended that a plot be included in the commentary to ilustrate

the pattern of spectral coefficients for R and A^. Sharpe responded that

such a plot could be added.

It was moved seconded and passed that a recommendation be made requesting

such a plot be added to the commentary.

Next Meeting

The next meeting was set for April 2 and 3 in the Chicago area.

45
Minutes of Third Meeting

Technical Committee 2 - Structural Design

Review and Refinement of Tentative Seismic

Provisions (ATC 3-06)

at

O'Hare American Inn, Des Plaines, Illinois

April 2-3, 1980

The meeting was convened at 9:10 a.m., April 2nd by chairman Hal Iyengar. The

following voting members were present:

Mark Fintel, representing Committee 4: Concrete

William Holmes, alternate for Nicholas Forell, representing SEAOC

Hal Iyengar, representing ASCE

Richard McConnell, representing the Interagency Committee

Howard Simpson, representing ANSI Committee A38

William Sontag, representing Committee 6: Steel

Joseph Tyrrell, representing Committee 3: Foundations

Edwin Zacher, representing Committee 7: Wood

Robert Englekirk - representing Committee 1: Seismic Risk Maps, attended

on April 3.

Alan Yorkdale, the representative of Committee 5: Masonry, did not attend.

The following nonvoting members were present:

Representing ATC: Roland Sharpe, on April 2 only

Henry Degenbolb

Representing the BSSC Overview Committee:

Ajit Virdee

William LeMessurier

NBS Secretariat: Jim Harris

The following guests attended at various times:

A.K. Gosh, from the Portland Cement Association

Jerry Neville, also from Portland Cement Association

Mr. Iyengar open the meeting with a discussion of the agenda, noting that

the nature of the meeting would be different than the previous one; extented

discussion would focus on the problems assigned to the four task groups.

The minutes of the second meeting were reviewed and approved subject to several

corrections in spelling and grammar and the following changes of substance:

46
page 5, last line of first paragraph under Section 3.2.3: extend

the sentence thus: ”. . . , but he no longer opposes it."

page 6, third line of paragraph b) under Section 3.3.3: change

"opposite" to "orthogonal.

page 7, second line of fifth paragraph: change "a plane" to

"an element."

Mr. Reinhold was praised for the accuracy and completeness of his minutes.

The following items were distributed to those present:

1. Letter from Neil Hawkins, representing the Post Tensioning

Institute, dated February 26, 1980.

2. Letter from Nicholas Forell, dated March 31, 1980.

3. Letter from William Sontag, dated April 1, 1980

4. Suggested wording for section 3.7.2 from Ed Zacher.

5. Suggested wording for section 4.6.2 from Ed Zacher.

6. Deflection limitation calculations by Ed Zacher.

7. Letter to the task group on drift limits from Hal Iyengar,

dated March 25, 1980.

8. Letter from Henry Degenbolb, dated March 26, 1980, with five

attachments, including a letter from Mark Fintel, dated

March 19, 1980, and a letter from Henry Degenbolb, dated

March 10, 1980.

9. Suggested wording for section 3.7.2 from Bill Holmes (handwritten).

Ballot n

The ballots of the eight voting members present on the first day were collected

and tabulated, and the reservations and negative ballots were discussed with

the following results (nonvoting members also balloted for purposes of discussion during the meeting, but their votes are not in the tabulation; they

were generally in agreement):

(

47
Ballot Item Initial Tally*

yes no Final Tally*

yes no Remarks

Following

1 . S. Perf. Category 5 3 0 8 a

2. S. Index, Area 5 3 5 2 6 a

3. S. Index, Area 4 2 6 2 6 a

4. S. Index, Area 3 2 6 2 6 a

5. S. Index, Area 2 4 4 2 6 a

6. S. Index, Area 1 2 5 0 7 a

7. Snow Load 5 2 5 2

8. Qj definition 8 0 8 0

9. Qg definition 8 0 8 0

10. Alt. Analysis 8 0 8 0

11. Rock Classification 8 0 8 0 b

12. Soil-struct. Int. 8 0 8 0

13. Inverted Pendulum 8 0 8 0 c

14. Combined R Value 8 0 8 0

15. Frame Interaction 6 2 3 5 d

16. Drift Compatibility 8 0 8 0 e

17. Orthogonal 7 1 7 1 f

18. Vert, discontinuity 7 0 8 0

19. Redundancy 7 1 7 1 g

20. Expansion joints 8 0 8 0 h

21. Name for Vv 8 0 8 0

22. Drift Exception 5 3 0 8 i

23. C e Calculation 8 0 8 0 j

24. Overturning 7 0 8 0 k

25. P„ definition 8 0 8 0

26. P-delta 7 0 0 8 1

* Note: "yes with reservation" is counted as "yes" and is addressed in the

following remarks.

48
Notes on the ballot items:

a. Harris pointed out that further consideration of the discussion

in Phoenix convinced him that item 1 should have been contingent

on item 6 alone. The committee agreed. None of the changes

proposed for the seismicity index carried on the initial tally,

and the sentiment of the committee shifted somewhat towards

recommending no change for the purpose of trial design. Iyengar

felt that item 5, changing the seismicity index for map area 2

from a 2 to a 1 was quite important; he felt that many locations

in that map area would unilaterally decide to ignore seismic

provisions such as those included for seismicity index 2.

b. Zacher had a reservation about the suggested wording for item

11. His proposed change was dropped in favor of changing the

phrase "... other means of classification. . . " to " . . . other

appropriate means of classification. . ."

c. McConnell had a reservation about the lack of a reference to

a definition for inverted pendulums, but the committee decided

no reference was necessary. Discussion indicated a range of

opinion as to just what the propoer definition was. The ATC

intent is indicated in the commentary.

d. The term "proportionate stiffness" was attacked as the wrong term

for description of the situation section 3.3.4(B) is addressing.

The committee could not agree to better wording than is in the

ATC-3 document, and thus decided to defeat the ballot item

(number 15).

e. Holmes and Zacher proposed that the change be reworded to exclude

consideration of the seismic resisting system in the direction

under consideration. The committee agreed, and section 3.3.4 (C)

is now to read as follows:

DEFORMATIONAL COMPATIBILITY. Each structural component

not included in the design as a part of the seismic force

resisting system in the direction under consideration

shall be investigated and shown to be adequate for ..."

f. Zacher and Holmes both suggested alternate wording for the

orthogonal combination provision (see handouts 4 and 9). Their

intent was to reduce the amount of calculation, but the committee

doubted that their suggestions accomplished the purpose. The

proposed change stands as balloted, but the committee expects

that it may be reworded following the trial designs.

g. Virdee questioned how redundancy might be checked. No answer

was forthcoming.
h. It was decided to change the word "expansion" to "separation"

for ballot item 20.

i. The drift question was deferred until Thursday, at which

time the task group on drift reported. That discussion

resulted in the replacement of item 22 with a new ballot

item for ballot #2.

j. Holmes thought the term "low buildings" was meaningless.

k. Sharpe felt that some limit on overturning is necessary, but

could not offer a specific suggestion. Many others agreed,

but no change in the ballot item was made.

l. Zacher withdrew his proposed text (handout 5). LeMessurier

stated that the minutes of the previous meeting did not

contain his recommendation for coordination with the ACI

code. He felt that ACI is more conservative and that the

conflict created between section 4.6.2 and chapter 11'

reference to the ACI code should be resolved. He noted

that chapter 10 (Steel) manages to avoid a similar conflict

with the AISC design specification. The problem will be

referred to committees 4 and 6. Degenbolb, Sharpe, and

Harris questioned the use of C^ in section 4.5.2. The

issue was taken up again on Thursday and resulted in a new

ballot item to replace ballot item 26. (See subsequent

item in these minutes).'

Height Limits

The task group on height limits (section 3.3.4) held a breakfast meeting

on April 2. Their report to the committee recommended:

1. the height limit be retained

2. the provisions for a minimum number of planes for shear

walls or braced frames be revised so that paragraph

3.3.4(A)3 reads as follows:

"3. A system with structural steel or cast-in-place

concrete braced frames or shear walls in which there

are braced frames or shear walls so arranged that braced

frames or shear walls in one plane resist no more than

the following proportion of the seismic design force in

each direction, including torsional effects:

a. Sixty (60) percent when the braced frames

or shear walls are arranged only on the

perimeter

50
b. Forty (40) percent when some of the braced frames

or sheer walls are arranged on the perimeter

c. Thirty (30) percent for other arrangements

This system is limited to buildings not over 240 feet in height.

3. A recommendation be forwarded to BSSC that provisions be defined

for coupled shear walls.

The committee agreed to ballot the recommended revision to paragraph

3.3.4(A)3. Fintel desired to see a paragraph addressing coupled shear

walls for inclusion in the commentary. McConnell held that the commentary

is not tutorial, but that the purpose is to explain the provisions.

Iyengar thought that the recommendation to BSSC would be more effective

then a commentary. Holmes, McConnell, and Zacher agreed and suggested that

excentric braced frames be included in this recommendation. Sontag cautioned

that the committee should not imply that such systems are unfit for present

use. Fintel was charged with writing his recommendation, and he and Harris

presented the following wording to the committee on the morning of April 3:

"The committee recommends to BSSC that technical groups be

established to develop standard provisions for new types of

seismic resisting systems that depend on the concentration

of inelastic straining in special members for good performance

in earthquakes, in particular, coupled shear walls and eccentric

braced frames. For coupled shear walls, the provisions should

delineate the details and the stiffness and strength ratios

between the shear walls and the coupling beams to assure that

the inelasticity is concentrated primarily in and accounted

for in the coupling beams. For eccentric braced frames, the

provisions should delineate the connection details and the

relative member proportions to assure that the inelasticity

occurs in the flexural or shear links and does not occur in

members that primarily are loaded axially.

The committee approved the recommendation.

Inelastic Analysis Procedures

The task group on inelastic analysis held a luncheon meeting on Wednesday

and reported to the committee on Wednesday afternoon. Task group chairman

Fintel proposed to add material to the commentary on section 3.5, Analysis

Procedures. Task group members McConnell and Sharpe did not agree with

the proposal, however, and following discussion among the entire committee,

the task group was charged with drafting a compromise proposal. That

proposal was presented on Thursday. Following discussion, the committee

decided to adopt the proposal that the following paragraph be inserted

in the commentary following the fourth paragraph on page 342:

51
"It is possible with presently available computer programs to

perform two dimensional inelastic analyses of reasonably

symmetric structures. The intent of such analyses could be

to estimate the sequence in which components become inelastic

and to indicate those components requiring strength adjustments

so as to remain within the required dectility limits. It

should be emphasized that with the present state-of-the-art in

inelastic analysis there is no one method that can be applied

to all types of buildings, and further the reliability of the

analytical results are sensitive to:

1 . the number and appropriateness of the timehistories of input motion

2. the practical limitations of mathematical modelling

including interacting effects of nonstructural

elements

3 . the nonlinear algorithms

4. the assumed hysteretic behavior

Because of these sensitivities and limitations the maximum base

shear produced in the inelastic analysis should be not less

than that required by chapter 5 (Model Analysis)."

R Factors

The task group on the R factors and building system description held a luncheon meeting on Wednesday and reported to the committee on Wednesday

afternoon. Their findings were:

1 . The descriptions in table 3-B are adequate for the trial

designs, although they should then be re-examined. The

trial designs would be aided by the incorporation of an amplified table in the commentary.

2. The discussion of the method for establishing values for

R contained in the commentary is as good as can be done,

thus, for now no explicit procedure for establishing

R values can be recommended.

3. No changes to the present R values can be recommended.

With respect to varying the R values during the trial

designs to estimate marginal costs, the task group felt

that it would be too expensive to do so, but that the

designers should be asked to make an intelligent

assessment of just what the impact on cost of differing

R values would be.

52
The committee agreed with each of the recommendations. Chairman Iyengar

charged Sharpe with preparation of the amplified table of building systems

based on the 12/10/76 draft of table 2C distributed with the minutes

of the previous meeting. Committee members are to send suggestions for

that table to Sharpe as soon as possible.

Drift

The task group on drift held a breakfast meeting on Thursday and reported

to the committee on Thursday afternoon. Task group chairman Englekirk

reported that:

1. Drift limits control the design of many structures over

the strength limit, thus are quite important.

2. The drift limits seem to be 30% to 60% more severe than

the UBC

Two options exist: adjust the limit or delete the

requirment. The task group favors adjusting the limit

for Seismic Hazard Exposure Groups I and II upward

to 0.025 hgx in areas where A

y

= 0.4g and to 0.040 hgx

in areas where Av

= 0.05g.

Iyengar reviewed the data offered as a comparison:

1. Englekirk's data showed a 30% to 40% increase in stiffness

for two buildings (about 17 stories).

2. Skidmore-Owings-Merrill' s San Francisco office found a 15% to 60% increase would be required for five recently

designed buildings ranging from 5 to 50 stories.

3. Sontag's data showed a 5% to 40% increase for single

story buildings.

4. Zacher's data showed a 33% to 67% increase for various

story heights of a 20 story steel frame.

There was significant sentiment in the committee to drop the limit entirely

because of its obvious relation to damage control. However, most present

felt that this was a major change of intent, not a mid-course correction.

Therefore, the option of adjusting the limit was selected. The option of

making the limit vary inversely with Av was suggested as a means to provide

more damage control in those locations where damaging earthquakes of less

than the design amplitude are likely to occur. In the end, a simpler

change was adopted by the committee as a new ballot item, it being to

change table 3-C to:

I

53
Seismic Hazard - Exposure Group

III II I

Aa 0.015hsx 0.025 hsx 0.025 hsx Among the items discussed were the questions of whether the calculated

drift. A, was very close to actual drift in an earthquake, with Englekirk

feeling that A overestimated the real drift and Degenbolb feeling that

it was about right (and thus that the values were about right). The

problems of separation joints functioning at the higher drift levels were also discussed, with most feeling that some joints would be so expensive

or difficult as to economically justify a more stringent drift limit

for certain buildings. It was decided that a special commentary was needed for the revised drift limits, and Simpson was charged with drafting

it. The commentary agreed to is:

"The drift limitations of Sec. 3.8 of ATC 3-06 are, for many

structures, considerably more restrictive than the UBC and

usual current design practice. Because of the lack of a close relationship between story drift and either the amount

of inelastic strain or the magnitude of the P-delta problems,

and because damage control unrelated to safety is not a code

objective, the drift limits have been increased.

"The revised values were chosen to minimize the possibility

of imposing drift constraints more severe than those reflected

in current design practice.' In specific instances, however,

such as for controlling the magnitude of relative movements

at joints, the designer may find it necessary or desirable

to impose more restrictive limits."

Following the decision to revise the drift limits, the committee decided

to withdraw the previous ballot item 22. Sontag suggested a revised

exception to the drift limits, and the following ballot item was agreed to:

Delete footnote number 1 from table 3-C and revise section 3.8

by adding the following sentence to the end of the second paragraph:

" Single story buildings in Seismic Hazard Exposure Group I that are constructed with non-brittle finishes and whose seismic

resisting system is not attached to equipment or processes need

not meet the drift requirement in table 3-C. "

Other Proposals for Change

Section 2.1 , definition of "Shear Panel:" It was decided to delete the word

"wood" from the definition. Discussion centered on the distinction of shear

panel from shear wall , but no recommendation for clarification or change

could be formulated.

54
Section 3.5 , Analysis Procedures: As a result of the discussion about

inelastic analysis procedures and about the implications that chapter 5

constitutes the only acceptable procedure for model analysis, it was decided to modify the section to read as follows:

"This section prescribes the minimum analysis procedure to

be followed. An alternate generally accepted procedure,

including the use of an approved site specific spectrum, if

desired , may be used in lieu of the minimum applicable

procedure. The limitations upon the base shear stated in

section 5.8 apply to any such analysis. "

It was felt that the precise limit on the base shear given in section 5.8 was easier to understand and apply than the limit on building period

given in the present section 3.5.

Section 3.7.12 , Vertical Seismic Motions: The proposed modification submitted

by Professor Hawkins through committee 4 was considered. Harris questioned

whether the proposed really stated what Hawkins really meant. Holmes

speculated that the intent was to apply an upward seismic force of 0.2Qp,

not an upward net force of 0.2Qjj. Iyengar pointed out that the stated

reason did not correspond to the recommended change. The proposal was tabled and Fintel was charged with contacing Hawkins prior to the Thursday

session. Fintel was unable to contact Hawkins, and the proposal received

no further consideration.

Section 4.2.2 , Period Determination: The proposed modification for flat slab

structures submitted by Professor Hawkins through committee 4 was considered.

Zacher pointed out that the intent of ATC-3 was to provide an appropriate

formula for building period that predicted periods of about 70%, on the

average, of the actual periods measured in strong ground shaking, and that

is why the coefficient 0.025 was used for concrete frame structures rather

than 0.035. The committee decided to turn down Hawkins' proposal for this

section. At this time, the committee discussed the remainder of Hawkins'

proposals for concrete flat slab structures in Seismic Performance Category

B. Degenbolb stated that ATC's intent was that flat slab structures could

be used as frames in Category B. He further stated that Hawkins' proposed

changes to section 11.6.1 (items A, B, C, and D on page 10 of Hawkins'

proposal) appeared to be acceptable if^ some continuous reinforcement is

provided top and bottom and if the shear and movement transfer problem

at the column head is adequately considered. He cited the PCA report by

Hanson and Hanson (cited by Hawkins as reference 1 on page 9 of his

proposal) as an excellent discussion of the problem at the column head.

The committee decided that Hawkins' proposals for flat slabs should be

considered by committee 4, and they generally agreed with Degenbolb 's comments. The letter from Jacob Grossman concerning flat slab structures

(dated November 19, 1979, and distributed on January 17, 1980) was also

considered at this time. Iyengar pointed out that the issue was as much

a problem of zoning (seismicity index and seismic performance categories)

as it was a problem of detailing.

55
Section 4.4 , Torsion: The porposal of the masonry task group to make

the assumed torsion a minimum value rather than an additive value was

considered. (This proposal was inadvertently skipped at the previous

meeting.) The committee decided against the proposal.

Section 4.6.2 , P-Delta Effects: Considerable discussion took place without

arriving at a true resolution of opinion. LeMessurier maintained that

the elastic model for the amplification factor 0 is a very adequate prediction for the ultimate strength, and cited studies by Professor Yura

as evidence. Harris argued that the inelastic multiplier should be

considered when calculating the P-delta moment. LeMessurier felt that

doing so would require tremendous increases in the stiffness of ordinary

buildings. Degenbolb stated that the commentary on page 367-368, if read

very carefully, seemed to indicate that the factor 0 should be calculated

on an elastic basis and that the inelastic amplification should be included

when calculating other effects. Three points of agreement were reached.

First, ballot item 26 would be discarded and replaced by the following

change: the second sentence of the last paragraph of section 4.6.2

shall be modified to read as follows:

"The design story drift determined in Sec. 4.6.1 shall be

multiplied by the factor >.1*0 to obtain the

1-0 “

story drift including P-delta effects."

Second, the committee recommended a change in the commentary for section

4.6.2 to state: "The last paragraph on page 368 should be considered

as a part of the acceptable P-delta analysis referred to on page 367."

Third, the committee recommends that the trial designs and subsequent

studies should examine carefully the impact of and the validity of

the P-delta procedure.

Other Discussion

Several other topics were discussed during the meeting and are briefly

summarized here.

Sharpe mentioned that some of the other committees seemed to be taking

different approaches to this review and refinement task, citing the

steel and concrete conjmittees as two extremes. Iyengar and Harris

agreed and stated that committee 2 seemed to be progressing well within

the original guidelines.

Sharpe pointed out that it must be made clear that we are not pushing

for adoption now and that this review is for the purpose of trial

designs. He cited a letter from the chairman of the steel committee

to the members of that committee which reflects the notion that ATC

and NBS are pushing for adoption now. Sharpe recommended that any

such notions be dispelled.

56
Holmes and Iyengar suggested that the "Guide to Use" and the "Commentary"

of ATC-3-06 be thoroughly reviewed for consistency following the incorporation of any changes resulting from this project. The committee agreed

to the recommendation.

Iyengar raised the issue of looking for some mechanism to pull together

the work of the committee. Harris is to compile all proposed changes

together with a commentary for each one and all the committee recommendations for circulation to the committee. Following written comment,

this package will be submitted to the coordinating committee at their

next meeting. It was confirmed at this time that other committees were making recommendations for the conduct of the trial designs.

It was decided that no meetings of committee 2 appeared necessary until

the joint committee meeting, which is tentatively set for July. The

meeting was adjourned at approximately 1:30 p.m. , Thursday, April 3.

57
3.2 Roster

American National Standards Institute

Dr. Howard Simpson Alter: Dr. Rene W. Luft

Simpson Gumpertz & Heger Inc. (send mail c/o Howard Simpson)

1696 Massachusetts Ave.

Cambridge, MA 02138

Phone: 617-491-8300

American Society of Civil Engineers

Mr. hal Iyengar (Chairman of the Committee)

Skidmore, Owings & Merrill

30 West Monroe St.

Chicago, Illnoise 60603

Phone: 312-246-6161

Interagency Committee on Seismic Safety in Construction

Dr. Richard D. McConnell

Veterans Administration (085A)

810 Vermont Avenue, N.W.

Washington, D.C. 20420 '

Phone: 202-389-3103 or 2394

Structural Engineers Association of California

Mr. Nicholas Forell

Forell/Elsesser Engrs.

631 Clay St.

Third Floor

San Francisco, CA 94111

Phone: 415-397-2768

Representative from Committee 1 (Seismic Risk)

Dr. Robert Englekirk

3242 West 8th Street

Los Angeles, CA 90005

Phone: 213-385-9487

58
Committee 2 (continued)

Representative from Committee 3 (Foundations)

Mr. Joseph V. Tyrrell

Director, Civil/Struc. Div.

Naval Facilities Engineering Comnd.

200 Stoval Street

Alexandria, VA 22332

Phone: 703-325-0064

Representative from Committee 4 (Concrete

Mr. Mark Fintel

Portland Cement Association

Engineering Development Department

5420 Old Orchard Road

Skokie, ILL 60077

Representative from Committee 5 (Masonry)

Mr. Alan Yorkdale

Brick Institute of America

1750 Old Meadow Lane

McLean, VA 22101

Phone: 703-893-4010

Representative from Committee 6 (Steel)

Mr. William A. Sontag

Pascoe Steel Corporation

P. 0. Box 2628

Pomona, CA 91766

Phone: 714-623-1411

Representative from Committee 7 (Wood)

Mr. Edwin G. Zacher

H. J. Brunier Associates

55 New Montgomery

Suite 608

San Francisco, CA 94105

Phone: 415-781-0370

59
Committee 2 (continued)

Applied Technology Council

Mr. Roland L. Sharoe

Executive Director

Applied Technology Council

480 California Ave., #205

Palo Alto, CA 94306

Phone: 415-326-4029

Building Seismic Safety Council

Mr. Ajit S. Virdee

Associate Professor

Dept, of Civil Engineering

Californiz State University

Sacramento, CA 95819

Phone: 916-446-6128

National Bureau of Standards

Dr. James Harris

Secretariat

Committee 2, Structural Design

National Bureau of Standards

Rm. B-168, Bldg. 226

Washington, D.C. 20234

Phone: 301-921-2170

Mr. Henry J. Degenkolb

H. J. Degenkolb & Associates

350 Sansome St.

San Francisco, CA 94104

Phone: 415-392-6952

Mr. William J. LeMessurier

Sippican Consultants International

1033 Massachusetts Ave.

Chambridge, MA 02138

Phone: 617-868-1200

Dr. Tim Reinhold

Secretariat

Committee 2, Structural Design

National Bureau of Standards

Rm. B-168, Bldg. 226

Washington, D.C. 20234

Phone: 301-921-2186

60
3.3 Selected Committee Correspondence and Applied Technology Council Comments

Following is a complete list of all correspondence concerning technical issues.

Some of the items are reproduced in this report, as noted in the list. All of

the items are on file with the secretary of the committee.

I. Initial Proposals for Change:

Date* Author

1/15/80

1/17

1/22

1/25

1/31

2/8

Sontag#

SEAOC: Forell,

Zsutty, Zacher

Sheppard (PCI)

Fintel

Grossman

Comm. #5 (Masonry)

Fintel

McConnell

CRSI

Remarks

transmitted directly by author

via Comm. #4 (Concrete)

via AC I 318

transmitted directly by author

via Comm. #4 (Concrete)

* date transmitted from NBS, unless sent directly by author

# the secretariat wishes to note that one of Sontag' s proposals, concerning

the inspection of welding in the shop of an approved fabricator, was inadvertently not considered by any of the technical committees. It

should be considered following the trial designs.

II. Handouts and Attachments to Minutes at Second Meeting:

Summary list of comments by section of the provisions (NBS)

ATC response to the proposals for change — included in this

report as Exhibit A

Report of the MUTO Institute

Changes by Englekirk

Response by Bertero to proposals concerning coupled shear walls

Early ATC drafts of tables for the R value (Degenkolb)

Proposed matrix of trial designs (Sharpe)

III. First letter ballot (26 items) — included in this report as Exhibit B

The results of the ballot are included in the minutes of the third

meeting (see section 3.1 of this report).

IV. Correspondence among the four task groups operating between the second and

third meetings (the task groups were on the Height Limits, Nonlinear Analysis,

the Drfit Limits, and the R Value):

Date Author and Group

3/3 Chairman Iyengar to each group on their charge (four letters)

3/12 Degenkolb to Height Limit group

3/19 Fintel to Height Limit group

3/19 Fintel to Nonlinear Analysis group

? Englekirk to Drift Limit group

61
3/25

3/26

Iyengar to Drift Limit group

Degenkolb to Height Limit group

V. Handouts at the Third Meeting:

Hawkin' s proposals concerning design of flat plate/slabs and vertical

motions

Forell's letter commenting on the R value, drift limits, etc.

Sontag's letter commenting on drift limits

Zacher's proposals for the orthogonal effect and P-delta provisions

Zacher's comparisons concerning drift limits

Iyengar's letter of 3/25 to the Drift Limit Task Group

Degenkolb 's letter of 3/26 to the Height Limit Task Group

Holmes' proposal for the orthogonal effect provision

VI. Second letter ballot (six items) — included in this report as Exhibit C

Each item on this ballot passed, and the vote talley is included for each

recommendation in section 2 of this report.

VII. Dissenting Views of Committee Actions with Closure by Chairman Iyengar

Date Author and Subject

5/29

5/29

Fintel on the R value - included in the report as Exhibit D* Fintel and Yorkdale on the Seismicity Index - included in

this report as Exhibit E

Iyengar on the Seismicity Index - included in this report

as Exhibit F

6/12

* see the Chairman's Statement, section 1.3 of the report, for

closure on Fintel 's comment regarding the R value.

62
Exhibit A

COMMITTEE 2 STRUCTURAL DESIGN

ATC RESPONSE TO COMMENTS

The coiments submitted on ATC-3-06 are far-reaching and varied. It is

apparent that considerable effort and care have been expended in

developing them. Many are quite helpful, all require serious

consideration, and some need to be addressed as to whether they fall

within the scope of the present program.

It is our understanding that the scope and intent of the NBS effort is to

review the provisions for inconsistencies, errors and ambiguities, and to

develop "mid-course adjustments" such that the provisions will be

appropriate for use in making comparative test designs. It is on this

basis that the following responses are being made. The responses are made by chapter and section and include chapters which have significant

impact on the design.

Chapter 1 Administration

Table 1-A Seismic Performance Category

A task group of Committee 5 recommended:

"1. For Seismicity Index 2, SHE Group I, change Category B to A.

2. For SI 1, SHE Group III, change Category A to B. For 1, it is felt that based on performance history SHE Group I buildings in SI 2 need not be required to be reinforced masonry.

For 2, it is felt that SHE Group III buildings should be

investigated and analyzed, even for SI 1."

Item 1, SI 2 includes areas with Aa and Av values ranging from 0.05 g to

greater than 0.1 g; the ATC's Committee's opinion, based on its review of

available data (research and historical), was that some reinforcing

should be provided for structures subjected to Aa or Av in the 0.1 g range.

63
Exhibit A

Item 2, the ATC Committee considered this type of requirement, but felt

that the requirement for building components to be tied together was adequate.

Table 1-B Coefficients Aa and Av and Seismicity Index

Aa Map Area Av Seismic Index

0.40 7 0.40 4

0.30 6 0.30 4

0.20 5 0.20 4 3

0.15 4 0.15 3 2

0.10 3 0.10 l 1 (2) CRSI

0.05 2 0.05 l 1 0.05 1 0.05 1

PCA (Fintel) also recommended the above changes in S.I. values. CRSI had

similar comments except for Aa and Av of 0.10." The ATC Committee notes

in the commentary "a minimum value of Aa and Av of 0.05 was used

throughout and designated as Map Area 1. Where the seismic risk

procedure produces values of 0.05 the map area value is changed to 2 and

the SI becomes 2. The response to what the listed values of Aa and Av

mean is the province of Committee 1, however, it should be noted that the

ATC Structural Design Committee after lengthy consideration recommended

the SI values of 4 for Aa and Av values of 0.20 or larger, and the

corresponding values for lower Aa and Av values. The structural design,

analysis, detailing, and materials requirements are all carefully

interwoven with the Seismic Performance Categories. The categories as listed represent appropriate requirements. As additional data becomes

available and further studies are made these listings may be modified.

Chapter 3 Structural Design Requirements

Comments on this chapter were made by Forell (SEAOC), Fintel (PCA),

Sheppard (PCI), CRSI, McConnell (ICSSC), and Committee 5 Task Group. The

responses to comments on each section are grouped together.

64
Exhibit A

Section 3.1 Design Basis

(Fore'll ) "Proposes increased deformation if it can be demonstrated the

resulting design provides equivalent performance, strength and safety."

There is the difficulty of the code official being able to determine the

equivalency. Also see Section 1.5 Alternate Materials and Methods of

Construction.

Section 3.2.1 Soil Profile Types

(McConnell) "Delete shear wave velocity." The shear wave velocity

provides a quantitative definition, it is not a mandatory requirement.

There is considerable variation in meaning given to the term "rock",

hence the definition was provided.

Section 3.2.3 Soil -Structure Interaction

(Zsutty) "Delete this section."

This section is optional; deleting would not permit the designer to

consider SSI.

Section 3.3.1 Classification of Framing Systems

(McConnell) "Need inverted pendulum definition." Sec. 3.7.11 defines

inverted pendulum- type structures.

Section 3.3.2 Combinations of Framing Systems

(McConnell) "Need definition of supporting systems." A definition would

be helpful.

(Forell) "Enlarge section to include dissimilar systems in horizontal

plane. Add "In buildings where moment resisting frames are used in

65
ExIrubiX. A

combination with bearing wall systems in different horizontal axes or planes, the lowest value of "R" and the corresponding value of "C

d

"

shall be used in the design of all resisting elements and components."

This addition has merit and should be discussed by Committee 2.

Section 3.3.4 (A) 3 Seismic Resisting Systems

(Forell) "In last line before semicolon insert: "resisting elements

shall be arranged in no less than four different planes". The added

words are an improvement.

Section 3.3.4 (B) Interaction Efforts

(McConnell) "What if rigid elements "not considered" become, in reality,

the primary lateral resisting system?" The provision is intended to

cover this situation, but perhaps clarifying wording could be added.

Section 3.3.4 (A) 3 Seismic Resisting Systems

(PCA) (PCI) "Delete height limitation of 240 feet. The ATC committee

discussed the height limitation at length and there was disagreement;

however, the height limitations were agreed upon. It was also agreed

further studies were needed.

(PCI) "Add new type (A) "Coupled shear wall systems with primary

inelastic action along these vertical coupling elements providing energy

dissipation." This should be discussed by Committee 2; see Bertero and

Degenkolb comments.

Section 3.3.4 (C) Deformational Compatibility

(Zsutty) "Need additional commentary (as per SEAOC Blue Book) to show how

to verify the stability of the non-seismic system."

Additional commentary would be helpful.

66
Exhibit A

Section 3.3.5 Seismic Performance Category D

(PCI) (CRSI) "delete height limitation."

See 3.3.4 (A) 3 above and Degenkolb comments.

Section 3.4 Building Configuration

(Forell) "Definitions need to be improved. Adjectives such as "approximately" and "nearly" do not clarify but will lead to controversy."

These or similar adjectives are needed to allow flexibility in design;

deleting them would make the provision extremely restrictive.

Section 3.4.2 Vertical Configuration

(McConnell) "Word "significant" is too ambiguous. Specific information

should be given."

See 3.4 above.

Section 3.5.1 Seismic Performance Category A

(McConnell) "This is opposite to philosophy of other codes."

What part is in conflict with other codes?

Section 3.5.3 Seismic Performance Categories C and D

(McConnell) "Is this saying "modal analysis," in general, is inadequate

for horizontal irregul ari ties."

The intent - Chapter 5 modal analysis procedures are only adequate for

vertical irregul arities (they are not 3-D).

67
tx.ru,dxa. a

(Zsutty) "Consideration or "evaluation" of the dynamic characteristics

(mode shapes and periods) may be difficult for short (two- or three-story) irregular plan (and elevation) shear wall structures. In

these complex but common cases, the use of separation joints, or a conservative static force torsional analysis, may be the only practical

means of evaluating the element stresses and deformations."

Good comment. Clarifying language would be helpful.

Section 3.7.1 Combination of Load Effects

(Forell) "The concept of a load factored design based on yield strength

is, at this time, undesirable."

The ATC committees adopted the concept of load factored design because

they felt this concept will be adopted in future codes. There was not

universal agreement on this approach as many engineers do not agree with

the load factor design approach.

(McConnell) Define "Q".

See definitions on page 42.

Section 3.7.2 Orthogonal Effects

(McConnell) "Is the total force-vector requirement commensurate here with

the map acceleration levels of Chapter 1?"

The intent was to be consistent with Tables 1-A and 1-B. This provision

needs further work, see below.

(Forell) "This provision implies a lot of busy work. The concern is with

corner columns and other load carrying elements."

See response to Zacher below, improvement is needed.

68
ExinibiX A

Section 3.7.2 Contd.

(Zsutty) "Eliminate this section and replace it with either:

1. An additional load combination in 3.7.1 for vertical members

(columns and their foundations) with a load factor of 1.2 for

Q

e

. 2. Use a <J) = 0.5 for concrete columns if we do not want to punish

steel design."

The 1.2 does not fully satisfy the intent of 3.7.2.

(Zacher) Replace wording:

"Seismic effects can be imposed on a building from any direction. These

effects will be considered to be satisfied when the building is designed

for the prescribed forces assumed to act non-concurrently in the

direction of two axes of the building perpendicular to each other.

Exception: Vertical components of the lateral force resisting system

having horizontal flexural components of the lateral force resisting

system framing to them from two or more directions shall be designed to

resist the seismic force from the direction requiring the greatest

strength. This may be satisfied by combining the effects on the members

of 100 percent of the forces acting along one axis with 30 percent of the

forces acting along the other axis. The combination requiring the

greater component strength shall be used."

The proposed wording seems to be an improvement and should be given

careful consideration.

Section 3.7.3 Discontinuities in Strength of Vertical Resisting System

(McConnell) "I find this ambiguous. The problem in the initial elastic

response is one of variations in stiffness . Only in the inelastic range

will variations of strength -and/or ductility also be of concern."

69
Exhibit A

The provision says the potential adverse effects shall be

considered. See Commentary page 349.

(Forell) "This paragraph needs to be strengthened. It attempts to deal

with problems such as Olive View and Imperial Valley failures but does

not do so adequately. The best solution would be to not permit the kind

of discontinuity described."

There was extensive work on this subject of discontinuities of strength,

but no solution acceptable as a regulatory requirement could be

developed. The "soft story" concept is one part of the problem, see Commentary.

Section 3.7.4 Nonredundant Systems

(McConnell) "How does one make a transfer girder fail-safe? This needs

rewriting or removal."

The intent of the provision is to call attention to the need for

considering redundancy. See Commentary.

Section 3.7.5 Ties and Continuity

(McConnell) "Include here the commentary on "units" within joints."

It is not clear what is intended by this comment.

Section 3.7.6 Concrete or Masonry Wall Anchorage

(McConnell) "Give reference for requirements in regard to "bending"."

UBC 76 page 130, Sec. 2310 and SEAOC Blue Book.

Section 3.7.8 Collector Elements

(McConnell) "Add after "provided", the words "where analysis requires"."

70
Exhibit A

The collector element would be sized based on the analysis.

Section 3.7.9 Diaphragms

(McConnell) "Provide parenthetic references for V » This could be

A

added as part of format. Definitions are given in Chapter 2.

Section 3.7.11 Inverted Pendulum-Type Structures

(McConnell) "This should only be required if analysis has not considered

the contribution of rotational inertial mass."

The ATC committee felt, for code purposes, this requirement should be

stated, see Commentary page 351.

Section 3.8 Deflection and Drift Limits

(Zsutty) "For a K = 100, R = 5.5 system, the base shear used to compute

ATC-3 drift is about 7 times the base shear value of UBC for drift

calculation. However, the allowable ATC drift (0.015 h

gx ) is only 3

times the UBC allowable drive of 0.005 h sx

. Therefore, ATC calls for a structure to be about 7/3 more rigid than UBC. I believe that this can very much affect design comparisons between these provisions and is in error . The values given in Table 3-C should be doubled, since they

represent drift in the structure due to the major earthquake

(PGA = 0.4 g) event. Or, if we want to keep the Table 3-C values, then

the corresponding calculated drift should be for Cy2 in order to

represent the moderate (or damage control) earthquake having PGA = 0.2 g.

It was recognized that the drift limits need to be evaluated further.

The effects of varying the limits should be studied in the trial test

desi gns.

New Section 3.9 Alternative 'Inelastic Design Procedure

(PCA) An alternative inelastic design procedure is proposed.

71
ExkibxX A

The state of the art does not justify inclusion of an inelastic procedure

such as that proposed. See Bertero comments to Committee 4 and Degenkolb

comments.

Table 3-B Response Modification Coefficients

(CRSI) "Revise Table 3-B:

Type of Structural System

Bearing Wall System

Building Frame System

Moment Resisting Frame System

Dual System

Inverted Pendulum Structures

The response modification factors, R, are out of necessity arbitrary.

These numbers will have significantly greater impact on the construction

industry than the current K values because of the more detailed breakdown

of systems and materials. It is obvious these values must be determined

by a rational means and not arbitrarily selected. Until such time as this can be done it is suggested that the R coefficients for the type of

structural system be selected similar to the method used for the current

K values rather than R values for individual systems and materials."

Simplifying the R values as proposed would be a step backward because

there is a lot more data available (including observation of earthquake

damage) upon which to make judgments than there was when the K values were developed. See Bertero comments and Degenkolb letter.

(PCA) "A procedure is proposed to develop rational R values."

See Bertero comments and Degenkolb letter.

(Forell) "Although much concern has been expressed about the magnitude of

the "R" and "Cd" values, a re-evaluation should be postponed until the

Coefficients

-JL- -£d_

4 4

6 4

8 6

7 5

2 - 1/2 2

- 1/2

72
Exhibit A

completion of trial designs. Further editorial work is needed to clarify

the systems described. This could be accompanied in the Commentary with

the aid of illustrations. . As this section reads now, the use

of an insignificant shear wall or bracing element will permit use of a higher R value."

Recommend acceptance of the above suggestion.

Chapter 4 Equivalent Lateral Force Procedures

Section 4.2.1 Calculation of Seismic Coefficient

(Forell) "A statement "for low buildings with short fundamental periods

of vibration. Formula (4-3) will generally apply" would be helpful."

Recommend acceptance.

Section 4.2.2 Period Determination

(McConnell) "Exceptions should be permitted where adequately analyzed and

justified."

The provision does allow calculation of the period other than the

empirical formulas given.

(CRSI) "Revise equation (4-4) as follows:

Ta = 0. ION

Recommended for two reasons: simplicity and Cy affects base shear out

of proportion to its significance. For example, the period for a 15

story frame affects the base shear twice as much as the response

modification factor. This great of an impact on the base shear is not

warranted.

The formula (4-4) was developed based on the analysis of numerous

records, see Commentary. T = 0.1N has been shown to be erroneous for

73
xhsLbAX A

many buildings. Recommend leave (4-4) as is until further data is

developed.

Section 4.3 Vertical Distribution of Seismic Forces

(Forell) "The introduction of an exponent into this procedure creates

undue design effort on all but very tall structures. Consideration

should be given to the traditional method of vertical distribution for

buildings under an agreed upon height, or the cut off point for k = 1 should be raised to 1 second or higher."

The vertical distribution resulting from formulas (4-6) and (4-6a) is

considered to be more accurate than the distribution represented by a concentrated force at the top plus the summation of lateral forces at

each level, see Commentary page 364.

(McConnell) "'k' seems unnecessary except for tall buildings, which would

probably have a modal analysis anyway."

See response above.

Section 4.4 Horizontal Shear Distribution and Torsion

(Forell) "Add statement to last sentence excluding structure using

flexible diaphragms where lateral forces are distributed to resisting

elements by tributary area method."

See Zacher comments below.

Section 4.4 contd.

(Zacher) "Introduce new Section 4.3 ahead of "Vertical Distribution of

Seismic Force". Renumber following sections and eliminate from present

Section 4.4 the "and Torsion'1 from the title and the last paragraph."

74
Exhibit A

"Section 4.3 Torsion. The design shall provide for the effects of

torsion whenever the rigidity of the horizontal lateral force resisting

system is equ3l to or greater than the rigidity of the vertical lateral

force resisting system. The effects may be satisfied by using a design

torsional moment equal to that resulting from the location of the

building masses, M

t> plus the torsional moment, M

ta> caused by

assumed displacement of the mass each way from its actual location by a distance equal to five percent of the dimension of the building

perpendicular to the direction of the applied forces.

When the rigidity of the horizontal force resisting system is equal to 50

percent, or less, of that of the vertical lateral force resisting system,

no torsional effects need be considered. For intermediate conditions,

reduced torsional moments may be used."

New wording should be studied carefully. The new text answers many of

the questions raised, but the 50 percent limitation should be evaluated

together with the reduction for -intermediate conditions. The new section

might better fit as a new Section 4.4 and then renumber.

Section 4.5 Overturning

(Forell) "Additional work is desperately needed. Definitions of "k" make

no sense."

(Zacher) "The seismic where torsional forces are present , the

force, V When torsional forces need not be considered,

A

the force, V shall be distributed to the various vertical components

A

of the seismic resisting system below level x on a tributary basis."

Editorial work is needed— any suggestions? Zacher comment is not clear.

Section 4.6.2 P-Delta Effects

(McConnell) "This appears to be unjustified except for tall buildings.

Simplify instructions as to when to use to avoid unnecessary

computations. 75
Exhibit. A

Low buildings if flexible could be subject to P-delta effects. Any

suggestions on simplifying the instructions?

Chapter 5 Modal Analysis Procedure

(Forell) "Time did not permit a review of this section; however, the

general consensus appears to be that this section requires a complete and

careful restudy and rewrite."

Who is the general consensus? The ATC committees started out with a very

detailed modal analysis procedure, but backed off considerably because of

the many regulatory-enforcement type questions raised.

(Zsutty) "Dynamic analysis needs to be completely redone."

See above comments. It is difficult to modify a section based on general

criticisms as above.

Section 5.2 Modeling

(McConnell) "One degree of freedom is technically incorrect. There will

probably be few times when rotary inertial mass is included but the

rotational displacement degree of freedom is vital."

The analysis procedure presented is 2-D.

Section 5.3 Modes

(McConnell) "Why do modal for less than three stories?"

If the structure is quite irregular vertically a modal analysis would be

helpful

.

Section 5.4 Periods

(McConnell) "Have you completely ruled out soil modeling?"

76
ExIvibAX 8

ATC Review and Refinement

Committee //2: Structural Design

Proposals for change to be balloted

March 1980

1. Table 1-A: change the Seismic Performance Category for Seismic

Hazard Exposure III buildings located in areas with a Seismicity

Index of 1 from A to B.

2. Table 1-B: change the Seismicity Index for Map Area 5 from 4 to 3.

3. Table 1-B: change the Seismicity Index for Map Area 4 from 3 to 2.

4. Table 1-B: change the Seismicity Index for Map Area 3 from 2 to 1 .

5. Table 1-B: change the Seismicity Index for Map Area 2 from 2 to 1 .

6. Table 1-B: change the Seismicity Index for Map Area 1 from 1 to 0 .

7. Section 2.1 : Add the following sentence immediately following the

definition of SNOW LOAD.

EXCEPTION: Where snow load is less than 30 pounds per square

foot, no part of the load need be included in seismic loading.

8. Section 2.2: change the definition to read as follows:

Qt = The effect of live load, reduced as permitted in section 2.1.

Li

9. Section 2.2: change the definition of Qg to read as follows:

Qg

= The effect of snow load, reduced as permitted in section 2.1 .

10. Section 3.1: change the second and third sentences to read as follows:

The design seismic forces, and their distribution over the height

of the building, shall be established in accordance with the procedures

in Chapter 4 or Chapter 5; the corresponding internal forces in the

members of the building shall be determined using a linearly elastic

model. An approved alternate procedure may be used to establish the

seismic forces and their distribution; the corresponding internal

forces and deformations in the members shall be determined using a model consistent with the procedure adopted . Individual members

shall be sized. . .

11. Section 3.2.1: change the first subparagraph under soil profile

type 1 to read as follows:

1. Rock of any characteristic, either shale-like or crystalline in

nature. Such material may be characterized by a shear wave velocity

greater than 2500 feet per second or by other means of classification , or

12. Section 3.2.3: change to read as follows:

The base shear, story shears, overturning moments, and deflections

determined in Chapter 4 or Chapter 5 may be modified in accordance

with procedures set forth in Chapter 6 to account for the effects of

soil-structure interaction.

77
ExhLbAJt B

13. Section 3.3.1: delete the word "Special" from the third sentence

of the first paragraph.

14. Section 3.3.2(A): change the first paragraph to read as follows:

R VALUE. The value of R in the direction under consideration at

any level shall not exceed the lowest value of R obtained from

Table 3-B for the seismic resisting system in the same direction

considered above that level.

15. Section 3.3.4(B): change the first sentence to read as follows:

Moment resisting space frames which are enclosed by, or adjoined

by, more rigid elements, whose stiffnesses preclude their consideration as part of the seismic resisting system , shall be designed so that the action or failure of those elements will not impair the

vertical load and seismic force resisting capability of the space

frame.

16. Section 3.3.4(C): change to read as follows:

DEFORMATIONAL COMPATIBILITY. Every structural component , whether

or not it is part of the lateral force resisting system for the

direction under consideration , shall be investigated and shown to

be adequate for the vertical load-carrying capacity and the induced

moments resulting from the design story drift, as determined in

accordance with Sec. 4.6.

17. Section 3.7.2: change to read as follows:

ORTHOGONAL EFFECTS . In buildings assigned to Category B, the design

seismic forces may be applied separately in each of two orthogonal

directions .

In buildings assigned to Category C and D , the critical load effect

due to direction of application of seismic forces on the building

may be assumed to be satisfied if components and their foundations

are designed for the following combination of prescribed loads:

100 percent of the forces for one direction plus 30 percent of the

forces for the perpendicular direction. The combination requiring

the maximum component strength shall be used.

EXCEPTION: Diaphragms, and components of the seismic

resisting system utilized in only one of two orthogonal

directions need not be designed for the combined effects .

18. Section 3.7.3: change to read as follows:

For buildings assigned to Seismic Performance Categories C or D

the design of the building shall consider. . .

Note: Section 3.6.2(A) would be changed editorially to be consistent

with this.

78
Exhibit A

19. Section 3.7.4: change to read as follows:

The design of a building shall consider the potentially adverse

effect that the failure of a single member, connection, or component

of the seismic resisting system would have on the stability of the

building.

20. Section 3.7.5: change the first line to read:

All parts of the building between expansion joints shall be

interconnected and the connections shall be. . .

21. Section 3.7.9: change the second line of the third paragraph to read:

. . .elements of the building attached thereto plus the portion

of the seismic shear force at that level , V , required to be

transferred. . .

22. Table 3-C: add a footnote to the entire table, as follows:

2

In accordance with Section 1.5, the Regulatory Authority may

approve deformation limits exceeding these where it can be

demonstrated by an acceptable manner that the deformation

limits used provide equivalent performance, strength, and

safety.

23. Section 4.2: change the last paragraph to read as follows:

The value of C may be determined in accordance with Formula

4-2, 4-3, or 4-3a, as appropriate . Formula 4-2 requires

calculation of the fundamental period of the building as specified in Sec. 4.2.2. For low buildings, or in other

instances when it is not desired to calculate the period of

the buildings , C shall be determined using Formula 4-3 or 4-3a,

as appropriate.

24. Section 4.5: Delete the last sentence of the last paragraph.

25. Section 4.6.2: Change the definition of Px

to read as follows:

P = the total unfactored vertical design load at and above

level x.

Note: the corresponding definition in Section 2.2 would be changed

to agree with this.

26. Section 4.6.2: change the last paragraph to read as follows:

When 0 is greater than 0.10 for any story, the story shear for

that story shall be multiplied by the amplification factor for

P-delta effects, a^, where

0.9

a

d 1-0

a^ shall not be less than 1. The overturning moments, deflections

and drifts shall be redetejmined corresponding to the amplified

story shears .

Note: this would also change the word "incremental" to "amplification" in

the definition for a, in Section 2.2.

79
Exhibit C

ATC Review and Refinement

Committee #2: Structural Design

Proposals for change to be balloted (Ballot #2) April 1980

1. Section 2.1: Delete the word "wood" from the definition of

SHEAR PANEL.

2. Section 3.3.4(A): Revise paragraph 3 to read as follows:

A system with structural steel or cast-in-place concrete braced

frames or shear walls in which there are braced frames or shear

walls so arranged that braced frames or shear walls in one plane

resist no more than the following proportion of the seismic design

force in each direction , including torsional effects:

a. Sixty (60) percent when the braced frames or shear walls are arranged only on the perimeter

b . Forty (40) percent when some of the braced frames or shear

walls are arranged on the perimeter

c. Thirty (30) percent for other arrangements

This system is limited to 240 feet in height.

3. Section 3.5: Revise to read as follows:

This section prescribes the minimum analysis procedure to be

followed. An alternate generally accepted procedure, including

the use of an approved site specific spectrum, if desired , may be

used in lieu of the minimum applicable procedure. The limitations

upon the base shear stated in section 5.8 apply to any such analysis .

4. Section 3.8: Revise by adding the following sentence to the

end of the last paragraph of the section:

Single story buildings in Seismic Hazard Exposure Group I that are constructed with non-brittle finishes and whose

seismic resisting system is not attached to equipment or processes need not meet the drift requirement in table 3-C .

5. Table 3-C: Remove the footnote from the table and revise the table

to read:

TABLE 3-C

ALLOWABLE STORY DRIFT A

a

Seismic Hazard Exposure Group

III II I

A

a

0. 015h

sx

0. 025h

sx

0. 025h

80
Exhibit C

6. Section 4.6.2: Revise the second sentence of the last paragraph

to read as follows:

The design story drift determined in Sec. 4.6.1 shall be multiplied

by the factor / 0.9 > . » \ to obtain the story drift including P-delta

effects. k 1.6 =

* U /

81
Exhibit V

PORTLAND CEMENT ASSOCIATION

5420 Old Orchard Road, Skokie, Illinois 60077 Area Code (312) %b-6200

May 29, 1980

Mr. H. Iyengar

Skidmore, Owings and Merrill

30 W. Monroe

Chicago, II. 60603

Dear Hal

I feel the subject of Response Modification Coefficients, R, deserves more consideration than it has received during our committee meetings on February

27-28 in Phoenix and on April 2 and 3 in Chicago. Response Modification

Factors, R, as introduced in ATC 3-06, present a significant conceptual

change in the overall design approach and a drastic departure from the previous K-values. This change will have a serious impact on the seismic re- sistance of structures and on the construction industry. The concept of

response modification factors, R, ranging from lk to 8, to account for energy

dissipation due to inelasticity and damping of the various structural systems

and materials has been explained in only a cursory manner in the Commentary;

the R-factors have not been clearly defined in either the body of ATC 3-06 or its Commentary.

The method using R-factors seems generally simple and easy to apply and represents a significant improvement over the presently used K-factors. However,

the apparently arbitrary selection of R-factors in Table 3B, without a background study of the energy dissipation implications and of the effects on member ductilities, makes utilization of the concept questionable at this time.

Since the overall underlying approach is aimed at attaining a balance between

strength and ductility, a lack of correlation between R-factors and actual

member ductilities makes these values as fnadequate as the previously used

K-values. A major uncertainty regarding the arbitrarily selected R-factors is

the question whether the member ductilities actually available always meet the

ductility demands generated during an earthquake. Viable "R" values which answer

this question can only be derived by means of inelastic response studies.

The suggestion made at the Committee meetings in Phoenix and Chicago that the

upcoming comparative test designs would validate the chosen R-factors of Table

3B does not seem to hold much promise. Considering all the changes in the design

process incorporated into ATC 3-06, the possibility seems remote that the com- parative test designs would provide the answers to all the questions.

To evaluate the suggested Response Modification Coefficients, R, of

various structural systems and materials by comparing them with the previous

"K" values seems pointless and an exercise in syllogism, since the earlier

values were also adopted arbitrarily 40 years ago, without substantiating evidence.

82
ExbibaX V

PORTLAND CEMENT ASSOCIATION

Mr. H. Iyengar

page 2

May 29, 1980

The objective of comparative studies should be not only to assure that the

new approach does not deviate too much from the present one, but also to

establish a baseline founded on rationality, to be able to check the technical

viability of the new approach.

The behavior of some structures in the earthquakes in San Fernando (1971) and

El Centro (1979) have not verified the validity of the present philosophy based on K-factors. On the contrary, they have opened up very serious questions as to the actual implementation of the energy dissipation approach. The drastic

increases in the base shear during the 1970s which followed observations in

recent earthquakes, is an "inflationary policy" which has resulted primarily

in an increase in internal response forces and has not improved the energy

dissipation process upon which we have been relying for the safety of our

structures. The degree to which the overall seismic safety of our buildings

has been improved by the increase in base shears is an open question.

Studies to determine R and C. values rationally must be carried out for the

various structural systems listed in Table 3B. The value of R can be derived

from response history analyses as the ratio of base shear for the undamped elastic

system to the base shear for the damped inelastic system, with both systems

representing the same structure and being subjected to a properly selected ground

motion. The inelastic response history analysis of the damped inelastic system

(designed by the R-factor approach) would yield the required member ductilities

corresponding to the assumed R-factor. If these required ductilities are attainable with the specified detailing, then the R-factor is realistic; otherwise,

it needs revision.

The total effort required to determine realistic numbers for R is extensive.

However, it must be undertaken and systematically carried out, if the proposed

ATC 3-06 design provisions are to be based on a firm foundation. The effort

could begin with establishing a definition for R. and developing a methodology

to determine the response modification factors, and then carrying out the inelastic response studies for the various structural systems and materials. The

profession has the necessary tools to carry out such studies.

Sincerely

Mark Fintel

Director

Advanced Engineering Services

cc : Jim Harris, NBS

83
ExIvibjJ: E

PORTLAND CEMENT ASSOCIATION

5420 Old Orchard Road, Skokie, Illinois 60077 Area Code (312) 966-6200

May 29, 1980

To: Coordinating Committee

From

Mark Fintel, Member Committee 4 (Portland Cement Association)

Alan Yorkdale, Member Committee 5 (Brick Institute of America)

Re: MINORITY REPORT - Revision of Table 1-B of ATC 3-06

The following suggested changes to the Seismicity Index of Table 1-B were defeated 6 to 2 at the Committee 2 (Design) meeting on April 3, 1980:

TABLE 1-B

Coefficients A, and A. and Seismicity Index

a v Coeff. A

a Figure 1

Map Area

Number

a v Coeff. A

y

Figure 2

Seismicity

Index

0.40 7 0.40 4

0.30 6 0.30 4

0.20 5 0.20 # 3

0.15 4 0.15 3 2 0.10 3 0.10 l 1 0.05 2 0.05 2 1 0.05 1 0.05 1

Table 1-B as incorporated in ATC 3-06 will require *additional detailing

beams, columns and connections in vast areas of the United States where

details have not previously been required. In cities like New York and

Chicago, such requirements for additional seismic details based largely on judgment would increase construction costs and should not be introduced without adequate background evidence that such changes are needed.

The seismicity indices were introduced as a device to relate the seven map

areas (acceleration intensities) with the various levels of detailing requirements, as classified in the four seismic performance categories (A, B, C and D)

.

The indices and the performance categories have been apparently arbitrarily

interrelated with the seismic hazard exposure groups (Table 1-A).

84
PORTLAND CEMENT ASSOCIATION

To: Coordinating Committee

page 2

May 29, 1980

MINORITY REPORT - Revision of Table 1-B of ATC 3-06

There is little question about the extent of detailing requirements for

the highest seismicity index (4), as required in California, and for the

lowest seismicity index (1), for Texas, Florida, Wisconsin, etc. However,

detailing requirements for seismicity index levels of 2 and 3 remain

questionable without adequate background information. It is not acceptable

to arbitrarily require the same level of ductility detailing for acceleration

levels of .40 (map area 7) as for acceleration levels of 0.15 (map area 4).

Buildings located in map areas 1 and 2, subjected to acceleration levels of

0 . 05 , will undoubtedly respond within the elastic range, requiring no additional ductility details. The acceleration level of 0.10 (map area 2) will,

in all probability, create an elastic response in buildings designed in con- formity with modern reinforced concrete and steel codes.

For buildings located in map areas 4 and 5, with acceleration levels of 0.15

and 0.20, the major question is which structural members will be yielding and

how much ductility should be required in them. It should also be considered

that designs using current codes (i.e., ACI 318) basically result in ductile

members, as provisions over the last 20 years have been devised to eliminate

brittleness. To suddenly require additional detailing (also adding 30% of

forces in perpendicular direction) in cities like New York and Chicago seems questionable, particularly since the requirement is based largely on judgment

and is not supported by adequate background studies. Added ductility requirements should be imposed only if seismicity vs ductility correlation studies

for map areas with acceleration levels of 0.10, 0.15 and 0.20 indicate levels

of ductility demands requiring such detailing.

In view of the interest expressed by other committees on this subject, it is

requested that this item be included in the Coordinating Committee ballot, and

in test designs.
ExklbAX F

Skidmore, Owings & Merrill

June 12, 1980

Coordinating Committee

H. Iyengar

Chairman, Committee No. 2^ ^

Closure Statement regarding Minority Report on Table I-B,

ATC 3-06, filed by Messrs. M. Fintel and A. Yorkdale

To:

From:

Re:

Each of the changes in the seismicity indices included in the Minority

Report was debated in the two meetings of Committee No. 2 (Phoenix and

Chicago). Each map area was separately balloted with the end result

that all the proposed changes were defeated by a vote of 6 to 2, with

the exception of the last line relating to map area 1, which was defeated by a vote of 7 to 0. These are part of the Minutes of the Corn- mi tee. All the points of view expressed in the Minority Report were

aired and briefly discussed. The nature of the discussion cannot be

construed as thorough or exhaustive simply because of the lack of time

available and the lack of specific data to evaluate the impact of a certain provision. It is my feeling that the Committee Members relied

on their experiences and judgments in reaching conclusions rather than

on any substantive data.

Since this issue has a significant impact on a large portion of the

country that does not currently use any type of earthquake design, it

would be ideal if this issue can be addressed by a broader group. I believe other committees have recommendations on this table as well.

All things considered, I would support the idea of the entire group

balloting and, therefore, support the idea of this being included in

the Coordinating Committee Ballot.

/rep

cc : J. Harris
NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2111-22. Gov’t. Accession No. 3. Recipient's Accession No.

7:.:...':..v. —

4. TITLE AND SUBTITLE

REVIEW AND REFINEMENT OF ATC 3-06 TENTATIVE SEISMIC

PROVISIONS Report of Technical Committee 2: Structural

Design

5. Publication Date October 1980

6. Performing Organization Code

7. AUTHOR(S)

James Robert Harris

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

U. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP)

Federal Emergency Management Agency

Washington, D.C. 20472

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

1 1 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-^ord or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) The TENTATIVE PROVISIONS FOR THE DEVELOPMENT OF SEISMIC REGULATIONS FOR BUILDINGS

were developed by the Applied Technology Council to present, in one comprehensive

document, current state-of-knowledge pertaining to seismic engineering of buildings.

The TENTATIVE PROVISIONS are in the process of being assessed by the building com- munity. This report is one of a series of reports that documents the deliberations

of a group of professionals jointly selected by the Building Seismic Safety Council

and the National Bureau of Standards and charged with reviewing the TENTATIVE

PROVISIONS prior to the conduct of trial designs. The report contains the recom- mendations and records of the committee charged with reivew of the general structural

design and analysis provisions. The committee made 27 recommendations for revisions

to the TENTATIVE PROVISIONS and five additional recommendations concerning subsequent

activities, such as the conduct of trial designs. These recommendations were made

to the parent group, the Joint Committee on Review and Refinement, and their action on these recommendations is documented in a companion report.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the lirat letter of the first key word unless a proper name;

separated by semicolons)

Building; building codes; building design; earthquakes; engineering; standards;

structural engineering.

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