um

NAT *. INST. OF STAND & TECH R.I.C

rovision

nement

NBS

Publications

ee

: Risk Maps

ral Design

tions

Architectural, Mechanical and

Electrical

): Regulatory Use

of Technical Committee 4:

Concrete

:uments the deliberations of a group of professionals jointly

f the Building Seismic Safety Council and the National Bureau

i and is for use in modifying the Tentative Provisions for triai designs.

imerce

October 1980

NBSIR 2111-4

NATIONAL BOBJtAO

07 STANDARD*

LIBRARY NOV i 6 1981

• USh

REVIEW AND REFINEMENT OF ATC 3-06 TENTATIVE SEISMIC PROVISIONS

REPORT OF TECHNICAL COMMITTEE #4: CONCRETE

Edward Cohen, Chairman,. American Concrete Institute

Richard Marshall, Secretary,. National Bureau of Standards

Kyle Woodward, Secretary, National Bureau of Standards

Eugene Holland, American Society of Civil Engineers

Joseph Manning, Concrete Reinforcing Steel Institute

James Prendergast, Interagency Committee on Seismic Safety in Construction

Mark Fintel, Portland Cement Association

Neil Hawkins, Post-Tensioning Institute

David Sheppard, Prestressed Concrete Institute

Loring Wyllie, Jr. , Structural Engineers Association of California

James Lefter, Building Seismic Safety Council

Prepared for use by the:

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
<i' 8-3

- - ,

f'< ' !J*

r . v;:
Abstract

The TENTATIVE PROVISIONS FOR THE DEVELOPMENT OF SEISMIC REGULATIONS FOR BUILDING

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 beign 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 recomr- mendations and records of the committee, charged with review of the reinforced concrete

design provisions. The committee made 19 recommendations for revisions to the

TENTATIVE PROVISIONS. These recommendations were made toi the parent group, the

Joint Committee on Review and Refinement, and their action on these recommendations

is documented in a companion report.

Key Words: Building; building codes; building design; earthquakes; engineering;

reinforced concrete; standards; structural engineering.

iii
TABLE OF CONTENTS

Page

1.0 INTRODUCTION 1

1.1 General 1

1.2 Committee Summary 3

1.3 Chairman's Statement. - 5

2.0 COMMITTEE ACTIONS 17

2.1 Recommendations for Change.. 18

2.2 Recommendations for Trial Designs (none). —

2.3 Recommendation for Commentary 29

2.4 Other Recommendations (none) —

3.0 COMMITTEE RECORDS 41

3.1 Minutes of Meeting... 42

3.2 Committee Roster 122

3.3 Selected Committee Correspondence and Applied

Technology Council Comments 125

3.4 Reference Documents 195

4.0 MINORITY REPORTS (none) —

5.0 CLOSURE (none)

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 for the

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

improved seismic safety- provisions for use by the building community.

The assessment 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 chairmen 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 served

as 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 secretary throughout the effort. The

BSSC representative provided a link with the Building Seismic Safety

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

REVIEW AND REFINEMENT

COORDINATING

COMMITTEE

TECHNICAL. COMMITTEES

Committee 1:

Committ ee 2 :

Committee 3

:

Committee 4:

Committee 5

Committee 6:

Committee 7

:

Committ ee 3

Mechanical,

Seismic Risk Maps

Structural Design

Foundations

Concrete

Masonry

Steel

Wood

Archit ectural

,

and Electrical

Committee 9: Regulatory Use

Figure 1: Committee Structure

2
1.2 Committee Summary

Technical Committee A had as its principal responsibility the- review and

refinement of the provisions in Chapter 11, Reinforced Concrete, of the

Tentative Provisions for the Development of'; Seismic Regulations for

Buildings (ATC3-06). The committee membership was- drawn from industry,

professional organizations, and standards development organizations.

The committee conducted four meetings. Two meetings, the first and

fourth, were held in Gaithersburg, Maryland. The second meeting was held in San Francisco, California and the third meeting was conducted in

Skokie, Illinois* Following is a, brief summary of the committee actions

during each meeting- and a summary of the overall direction of the

committee.-

The first meeting was a half day meeting held on December 11, 1979, in

Gaithersburg, Maryland* The committee chairman, Mr. Cohen, was elected

and Mr* Fintel. was elected to serve as the committee's representative on

Technical. Committee 2 - Structural Design. The committee expressed its

intent to concentrate on the provisions of Chapter 11 and to also consider

changes to provisions in other chapters. Prepared comments from Mr. Sheppard

representing the Prestressed Concrete Institute and Mr. Fintel representing

the Portland Cement Association were received and reviewed by the committee.

The comments by Mr. Sheppard generally addressed the omission of specific

mention and requirements for precast and/or prestressed concrete in the

ATC3-06 provisions. The restriction against the use of precast-prestressed

piles in Seismic Performance Category D buildings was also discussed by

Mr. Sheppard. The thrust of Mr. Fintel' s comments was a basic objection

to the manner in which the seismic response modification coefficient (R)

and the deflection amplification factor (C^) were determined. The meeting

adjourned without finishing the discussion of the prepared comments.

The second meeting was held in San Francisco, California on February 21,

1980. The meeting lasted for a full day and evening. The meeting was

announced in several national professional publications and the announcement

called attention tor the fact that the meeting was open to any interested

party. A major issue addressed in the meeting was a proposal to adopt the

19 March 1980 draft version of ACT 318 Appendix A in lieu of the ATC3-06

Chapter 11. After considerable discussion the committee agreed to ask

for guidance from the Coordinating Committee before taking action on the

proposal. The committee was unsure that such a major change was within

the scope of the committee's task* The committee adopted the position

that it would continue to revise ATC3-06 Chapter 11 while waiting for

guidance from the Coordinating Committee. The committee then discussed

the proposed changes to ATC3-06 submitted by Mr. Sheppard, Mr. Fintel,

Mr. Manning, and Mr. Forrell. The committee decided by voice vote which

changes would appear on a committee letter ballot. The committee adjourned

the meeting with some proposed changes requiring further discussion, but

decided before adjournment to issue a letter ballot containing the agreed

upon recommendations.

A letter ballot (dated March 27, 1980) containing six proposed changes to

ATC3-06 Chapter 11 and nine proposed changes to other chapters was distributed to the committee between the second and third meetings. Some

committee members failed to return their ballot in time for the results
to be discussed at the third meeting- As a result, the resolution of

"no” and "yes with reservations" votes could not be completed at the

third meeting.

The third meeting- of Committee 4 was held for a full day in Skokie, Illinois

on April 14, 1980. The first issue that was discussed was the proposed

adoption of the 19 March 1980 draft version of ACI 318 Appendix A in lieu

of ATC3-06 Chapter 11- In response to concerns about the compatibility

between the remainder of ATC3-06 and Appendix A, and at the request of the

committee, Mr- Neville, ACI Committee 318 secretary, prepared a new Chapter

11 (hereinafter called Revised Chapter 11) to serve as a transition chapter

between ATC3-06 and Appendix A. The Revised Chapter 11 used ACI 318-77

"Building Code Requirements for Reinforced Concrete” and the 19 March 1980

draft version of Appendix A "Requirements for Reinforced Concrete Building

Structures Resisting Forces Induced by Earthquake Motions” as cited references. Considerable discussion by the committee resulted in a compromise

between making changes to the ATC3-06 Chapter 11 and replacing ATC3-06

Chapter 11 with the Revised Chapter 11- The compromise was to cite the

19 March 1980 draft: Appendix A in the reference- of the ATC3-06 Chapter 11

and make the recommended changes to ATC3-06 Chapter 11. The compromise

was placed on a letter ballot (the second letter ballot, dated May 5, 1980).

The committee then continued discussion of the proposed changes remaining

from the second meeting and discussed proposed changes concerning flat

slab systems submitted by Mr. Hawkins- The committee decided by voice

vote which proposed changes would appear on a letter ballot.

The second letter ballot (dated May 5, 1980) was prepared and distributed

to the committee after the third meeting and prior to the fourth meeting

which was called at the request of the voting members to discuss the

issue of the Revised Chapter 11 once again.

The fourth and final meeting was held in Gaithersburg, Maryland on

June 4, 1980. The meeting lasted a full day and evening. The committee

took up the resolution of "no” and "yes with reservation" votes on the

two letter ballots as the first order of business. The process was tabled to consider the adoption of the Revised Chapter 11 in lieu of the

original Chapter 11 in ATC3-06 . After vigorous discussion on the appropriateness of making such a change, the committee voted by a show of

hands to adopt the Revised Chapter 11. The committee then completed

action on the letter ballot items. The committee reviewed specific

objections to the Revised Chapter 11 and the 19 March 1980 draft Appendix

A in an attempt to resolve the objections. As a final action, the committee prepared letter ballot items for issues raised in the meeting

and conducted the ballot.

Technical Committee 4 began its work by considering changes to the existing

ATC3-06 provisions, both in Chapters 11 and others. The direction changed

such that the final committee position was to recommend a completely new Chapter 11 which cited the 19 March 1980 draft version of ACI 318 Appendix A

as the reference for the principal technical provisions. It was clear that

the committee was firmly resolved to incorporate the latest version of

Appendix A in Chapter 11 because it represented the state-of-the-art in

reinforced concrete seismic provisions. Other major issues endorsed by

4
Committee 4 were provisions for the design of flat slab systems in Seismic

Performance Category B buildings, the inclusion of a clause to permit any

system which could be analytically and experimentally demonstrated to have

characteristics similar to a comparable monolithic cast-in-place reinforced

concrete system, and the use of precast— prestressed piles in Seismic Performance Categories C and D buildings.

Those members of Committee 4 present in Gaithersburg, Maryland for the

Joint Committee Meeting (July 16—17, 1980) met on the afternoon of July 16.. The meeting- was informal and impromptu. The discussion in the meetingcentered on the Joint Committee's reaction to the revised Chapter 11.

It was generally agreed that the presentation of the all inclusive ballot

item was not as desirable as a detailed breakdown* The committee members

present agreed that if the inclusive ballot item were to fail. Committee 4

should request that the Building Seismic Safety Council permit a restructuring of the ballot item and its submission to the Building Seismic

Safety Council for balloting as part of its own letter ballot.

1.3 Chairman's Statement

As set forth in the work plan for review and refinement of ATC3-06, Technical

Committee 4's primary responsibility was Chapter 11 - Reinforced Concrete*

The committe made an in-depth review of the chapter, particularly with

respect to impending action within American Concrete Institute's (ACI's)

Building Code Committee 318. The Committee action was to include the latest

ACI seismic provisions in the ATC document. The Committee attempted to

compare the design- provisions of Chapter 11 with the more recently developed ACI provisions and realized that numerous changes would be necessary to

upgrade existing Chapter 11 to the latest ACI criteria. Thus, Committee 4

determined to recommend adoption of the new ACI provisions for earthquake

resistance into ATC, considering this to be the most efficient approach.

(Two notable examples of more recent developments contained in the ACI

criteria are (1) anchorage length for reinforcement provisions in ACI are

upgraded, based on new experimental data and reevaluation of all previous

data, and (2) design of joints of frames is upgraded to reflect the latest

report of the ACI-ASCE Joint Committee 352).

Therefore, with respect to Chapter 11, Committee 4 is recommending that the

nationally accepted design standard ACI 318-77 "Building Code Requirements

for Reinforced Concrete", including proposed revision - Appendix A "Requirements for Reinforced Concrete Building Structures Resisting Forces Induced

by Earthquake Motions", dated 19 March 1980, be adopted by reference into

ATC3-06 for proportioning and detailing concrete structures. (Revised

Appendix A, dated 19 March 1980, is to supercede Appendix A of ACI 318-77).

Revised Appendix A is now before the full ACI Building Code Committee 318.

Final Committee action and full ACI consensus balloting is forthcoming.

Considering that the primary mission in development of ATC3-06 is to provide

the most current state-of-knowledge for seismic design, Committee 4 considers it prudent to use the latest seismic proportioning provisions for the

trial design phase of the ATC review process. Should further revision occur

in the ACI seismic design provisions between now and final ACI adoption of

new Appendix A, appropriate cross reference correction can be made in

Chapter 11 of ATC. It is however, the intent of Committee 4 that new

Appendix A, dated 19 March 1980, be used in the trial design phase.
Committee 4 also adopted unanimously the following resolution:

"Regardless of subsequent actions. It is the firm intent of

Committee 4 that the final version of ACI 318 Appendix A,

with appropriate modifications, be incorporated into

ATC3-06 after trial design."

Justification for the above recommendation is outlined as follows for

consideration by the Joint Committee:

1. Adoption of the total ACI 318 Standard is considered appropriate because

seismic resistance is considered in the overall development of the 318

Standard, including Appendix A on special provisions for earthquake

resistance.

2. Existing ATC 3 Chapter 11 originated from an early draft of a proposal

by an ACI 318 Seismic Subcommittee to update the ACI 318 seismic design

provisions. The basis of existing Chapter 11 was work developed under

the guidance of Dr. Mete Sozen who served on the original ATC Concrete

Task Group. Dr. Sozen is current Chairman of the ACI 318 Seismic Subcommittee which has the prime responsibility for the new proposed

Appendix A of ACI 318. The ACI 318 Seismic Subcommittee worked towards

producing a document that would be acceptable to the two professional

communities involved—ACI and SEAOC. Two members of SEAOC, Clarkson

Pinkham and Loring Wyllie serve on the 318 Seismic Subcommittee to

provide SEAOC and ATC technical perspectives to ACI 318.

3. The ACI 318 Standard is prepared and continuously updated in accordance

with a rigorous consensus procedure approved by the American National

Standards Institute and designated as ANSI/ACI 318-77 (A89.1). The ACI

318 Standard is unique among material design specifications in this

regard. Because of the extensive review and adoption procedure, ACI 318

represents the state-of-knowledge for reinforced concrete and is widely

adopted by model building code groups to regulate concrete design and

construction.

4. Membership of the ACI Building Code Committee has a wide geographical

representation, with input from design professionals (including prominent

engineers from earthquake-prone areas), educators, researchers, material

and construction industries, government agencies, and building officials.

The consensus procedure under which the document is prepared draws from

the best documented data available.

Adoption of the ACI 318 Standard, including new Appendix A, into ATC3-06

necessitated a complete revision of Chapter 11. The following new Chapter 11 has been formulated to correlate appropriate ACI 318 design provisions with

the four ATC seismic performance categories by reference only, without the

need for duplicating in the ATC document the wording already contained in

the ACI document. New Chapter 11 specifies where the design provisions of

ACI 318 apply for seismic resistance within the framework of the established

ATC seismic analysis and performance criteria. Further, new Chapter 11 includes special provisions for flat plate framing systems for buildings

assigned to Category B and special consideration of precast/prestressed

framing systems. These two items are discussed in the following attachment.

6
In summary, existing ATC Chapter 11 is "technically" updated to the new

Appendix provisions of the ACI 318 Standard.

Under these circumstances, and since the ACI 318 Standard is a fully

approved consensus document , to avoid overlapping and conflicting efforts

and criteria, and to assure that Chapter 11 represents the highest practical

state-of-knowledge r Committee 4- strongly recommends that, in the national

interest, full adoption of ACI 318 Standard, by reference, is approved.

The Committee wishes to thank Messrs. V. V. Bertero and James Lefter for

their dedication and many technical contributions to the work of the

Committee over the past months, and in addition, special thanks to

Committee Secretaries R. Marshall and K. Woodward for their support

of the Committee work.
ATTACHMENT

In addition to adoption of ACI 318-77, and the revised Appendix A,

Committee A is recommending twa exceptions in Chapter 11:

1. SPECIAL PROVISIONS FOR FLAT PLATE FRAMING SYSTEMS FOR BUILDINGS

ASSIGNEE TO CATEGORY B T and

2. SPECIAL CONSIDERATION OF PRECAST/PRESTRESSED FRAMING SYSTEMS.

Both items are- included irr Chapter 11 as EXCEPTIONS. The. flat plate framing

exception is under Sec. 11. A. 1. The EXCEPTION applies only for flat plate

framing systems assigned to. Category B. Explanation of the special provisions

is giver in Sec. 11. A. on page 3 of new Commentary to Chapter 11. The precast/

prestressed exception is in Sec. 11. A. 2 for Category B and Sec. 11.5.2 for

Categories C and D. The exception refers to systems that are shown to meet

the performance requirements (strength, toughness, ductility, etc.) of monolithic cast-in-place reinforced concrete structures or, alternatively, are proportioned for acceptable higher lateral forces to remain elastic under earthquake

loadings. The Commentary emphasizes that precast and/or prestressed concrete

elements and assemblages may be used to meet either of the- above requirements,

which is similar to the situation under which precast and/or prestressed concrete

structures are currently designed and built under the Uniform Building Code.

Documentation for the flat plate exception follows:

SPECIAL PROVISIONS FOR FLAT PLATE FRAMING SYSTEMS FOR BUILDINGS ASSIGNED TO

CATEGORY B.

1 . Implication of ATC 3-06 if unamended for flat plate construction in

seismic performance Category B . The intention of ATC 3 with respect to restrictions on the use of flat plate

framing to resist lateral forces for Category C and D structures is clear.

Such use is highly undesirable. However, for buildings in seismic hazard ex- posure Category B, ATC 3-06 also effectively prohibits flat plate construction. Category B includes all facilities in New York, Boston, Buffalo, and

the New England states, much of North and South Carolina and Tennessee, large

areas of Oklahoma, Arkansas, Illinois, and Missouri, and much of New Mexico,

Montana, Idaho, Utah, Washington and Wyoming. The potential economic impact

8
Attachment - 2

of that prohibition is staggering. For the post-tensioning industry alone,

that prohibition could mean about a 25£ drop in its- work volume. Posttensioning is used in about 30 million square feet of suspended- slabs constructed each year in the U.S.A. and much- of that construction is flat plate.

In his letter of November 19, 1979, to ATC > Jacob Srossman of Robert Rosenwasser

and Associates of New York,, details his experience with respect to the economics

of flat plate construction and its seismic response when properly detailed. He

states "I cannot even begin to describe the construction havoc the exclusion of

flat-slab Structures can introduce in strong union-high construction cost areas."

He points out that enough research and knowledge are available to incorporate

flat-slabs and allow them as "ordinary" frames without shear reinforcing.

It is not clear that it was intended that ATC 3-06 prohibit flat-slab construction for "ordinary" frames. Contrary to- the situation for Category C and D

exposures, neither the provisions nore the Commentary explicitly state such a prohibition. However,- they require in flexural members of ordinary frames for

Category B exposure, web reinforcement perpendicular to the longitudinal reinforcement throughout the length of the member. The minimum reinforcement is

two leg No. 9 stirrups at a spacing of d/2. Inclusion of such reinforcement in

flat slabs would create economic as well as logistic problems.

It is suggested that:

(a) the provisions state clearly whether flat plate, flat slab, or waffle

slab construction is feasible for ordinary frames for Category B;

(b) if flat plate,, flat slab, or waffle slab construction is feasible, the

provisions specify any special restrictions for that construction.

2. Behavior of flat plate construction under cyclic loading

2.1 Laboratory results

There have been seven major laboratory investigations of flat plate connections subjected to cyclic loading (1-8). The results of extensive

University of Washington investigations are summarized in the attached

articles.

The lateral load response is strongly influenced by:

(a) the amount and distribution of the flexural reinforcement in the slab,

(b) the amount, type and extent of any shear reinforcement, and

(c) the level of shear stress transferred to the column simultaneous

with the moment.
Attachment - 3

Even when there has been a low flexural reinforcement ratio and a connection well over-designed for shear, there has still been little

ductility under reversed cyclic loading. For specimens with high

reinforcement ratios within lines one and. one-half times the slab

thickness either side of the column,, there has been a considerable

increase in the lateral Toad stiffness. However, there has been as

much as a 1015 reduction in the moment transfer capacity as compared

to that for monotonic loading and a punching failure has occurred

shortly after the reinforcement passing through- the column has

yielded. Since there is little improvement in the ductility

with the use of low reinforcement ratios and a considerable reduction in stiffness, concentration of column strip reinforcement

is desirable.

The only proven ways of maintaining capacity through large rotations has been to add properly detailed shear reinforcement consisting of either integral beam stirrups or thin steel H sections

or studs anchored above and below* the flexural reinforcement passing

through the column. Shear reinforcement in the form of shearheads

or bent bars increases the capacity but does not increase ductility.

The shear reinforcement must hold the top and bottom flexural mats

together and prevent the development of a splitting crack between

those mats. The shear reinforcement should have a spacing not exceeding d/2 and need not extend further than about 5 slab thicknesses out

from each col umrr face. Rules for proper detailing of such shear reinforcement are described in Reference 7. Slab-column connections are so flexible that flat plate structures are unlikely to meet ATC 3-06'

stiffness requirements for ductile moment resistant frames. Thus,

shear reinforcement in flat plates is probably unnecessary unless the

flat plate structure is the only line of defense or unless the flat

plate structure is to provide a required secondary line of defense.

The level of shear stress transferred simul taneously with the moment

markedly affects the energy dissipation and ductility characteristics

of slab-column connections. To obtain desirable characteristics, the

flexural reinforcement within lines one and one-half times the slab

thicknesses, either side of the column should be limited to one percent

and the shear stress due to shear transfer on the critical section d/2

from the column perimeter to 3/FJ. At that latter stress, shear cracks

have not developed in the slab prior to the application of lateral load

ing.

10
Attachment - 4

After a punching, failure has occurred, bottom bar flexural reinforcement

continuous through the column is essential to the connection being able

to maintain its gravity load carrying capacity. Such reinforcement can

carry a shear force equal to its shearing yield capacity. Alternatively,

prestressi ng reinforcement passing through a column or over a lift slab

collar is alsa a very effective means of tying- a slab-column- connection

together after a punching failure- With prestressing reinforcement,

a residual capacity can be obtained equal to 90 percent of the prepunching shear capacity.

Shear or torsional cracking develops at the discontinuous edge of a slab adjacent to an exterior column, when the shear stress at that

location evaluated according to ACI 318-77 provisions, exceeds 3/fT.

If that stress is exceeded, stirrups having a size not less than No..

3, a spacing equal to or less than d/2, and extending up to four times

the slab, thickness from the torsional faces of the column should be

provided to prevent opening of those cracks. While the best ductility

and energy dissipation characteristics are obtained with integral beam

stirrups, hairpin stirrups inserted perpendicular to the edge and extending a distance equal to the column projection into the slab plus

or twice the slab thickness plus 2- d

, whichever is less, into the slab

will also provide adequate control to the opening of those cracks.

Tests have shown- that the above results are also applicable to waffle

slab-interior column connections (4) and that when there is moment

transfer about both axes of a column- (8), the effect of the minor

moment on the shear capacity can be neglected if that moment does not

exceed 30£ of the major moment and there is adequate reinforcement

within lines one and one-half times the slab thickness either side of

the column to transfer that minor moment.

The recent tests on flat plate frames at the University of Washington

(3) have shown that in a frame, a punching failure will occur at a connection without stirrups at a displacement and at a capacity consistent with subassemblage results. However, that punching failure

did not lead to an immediate loss in capacity of the overall frame

since the adjacent connection with shear reinforcement was able to

supply the required additional moment transfer capacity. Displacements much greater than those for punching at the connection without

shear reinforcement had to be applied before the capacity of the overall frame deteriorated . During that period the connection without

1 ^
Attachment -

5~

shear reinforcement continued to carry its share of the gravity load.

Further, after lateral loading was completed, it. was found that at

the punched connection- the slab could be readily jacked back up to

its original elevation and the connection repaired.

Z.Z Field results

Reports (8) have beer issued orr the behavior of several flat plate

structures in the San- Fernanda earthquake; the Holiday Inrr, Orion

Avenue,, the Holiday Inn,. Marengo, and the Muir Medical Center. The

Holiday Inn, Orion Avenue, was a seven-story reinforced concrete flat

plate structure with typical plan dimensions 6Z by 160 ft. The building was supported on piles centered under the columns which were spaced

at approximately 20 ft. centers. Spandrel beams approximately 16 x22%

in. surrounded the perimeter of the structure. The flat plate floor was

10 in. thick at th& second floor, 8 in. thick at. the roof, and in.

thick for all other floors. The spandrel beams were figured as creating

exterior frames roughly twice as stiff as the interior flat plates so that in the short and long directions of the building, 36% and 67%,

respectively, of the stiffness was provided by the exterior frames.

Peak accelerations at the* first floor level were Q.25g and 0.13g in

the short and Tong directions, respectively . Roof accelerations were

0.41 and Q.33g, respectively. Repairs cost 11% of the initial construction cost and were nearly all nonstructural . Some structural distress

occurred at the corner column beam connections and in the construction

joints at the soffit of the exterior column-beam connections. The re- sponse was most marked in the short direction with a lengthening of the

period part way through the record indicating that the structure began

responding inelastically . The analysis indicated that beams and slabs

yielded, that columns generally remained elastic, and that interstory

drifts as large as 0.13 ft. occurred. The elastic limit displacement

was roughly 2% times the design code displacement.

The Holiday Inn, Marengo Street, had dimensions and member sizes almost

exactly the same as the Orion Avenue building. Peak accelerations at

the first floor level were 0.15g and 0.14g in the short and long directions, respectively . Roof accelerations were 0.43g and 0.25g, respectively. Repairs cost 7% of the initial construction cost and were

nearly all non-structural . Structural distress was similar to that for

the Orion Avenue building. The dynamic response was also similar to

the Orion Avenue building. The analysis indicated that heams and slabs

12
Attachment - 6

yielded at their connections with the columns but that the columns generally remained elastic. Interstory drifts were as. large as 0.14 ft.

In this structure, as in the Orion Avenue structure, it was apparent

that the stiffness of the frame was sufficiently low- that the nonstructural elements such as partitions, played an appreciable role in

the character- of the structural response to seismic forces.

The Muir Medical Center was an 11-story office tower with an 18% in.

deep waffTe slab at the ground leveT and perimeter basement walls.

For the second floor and above, the 9-in. thick flat slab had 15 in.

deep tapered column capitals with deep spandrel beams around the pe^

rimeter. The deep spandrel beams framing provided 70S of the lateral

load stiffness and the interior flat-slab-tapered drop panel framing

the other 30&. Peak accelerations were Q.10g at the basement level

» and O.Zg at the roof TeveT^ Some of the structural members were predicted to- yield during the earthquake and the maximum story drift was

computed'to be 0.64 in. The general performance of the structure was

linear-elastic with only minor lengthening of the building period during

the earthquake. Damage was all non-structural and estimated at less than

$2 , 000 .

2.3 Period of Vibration

Fundamental periods for those structures for man-induced excitations

prior to the earthquake, at the beginning of the earthquake, mid-way

through the earthquake, and for man-induced excitations after the

earthquake are listed in Table L. It is apparent that the period of

the predominantly flat plate structures, the Holiday Inns, increased

noticeably during the earthquakes with the increase being larger for

the more heavily shaken Orion Avenue building.

TABLE 1

Periods of Vibration for Flat Slab Structures

Stories Direction

Peri ods

Before

Quake

Start

of Quake

Mi dway

Thru Quake

After

Quake

Holiday Inn short 0.48 0.79 1.6 0.68

Orion Ave. 7 long 0.53 0.88 1.24 0.72

Holiday Inn long 0.53 0.38 1.0 0.64

Marengo 7 short 0.49 0.79 1.2 0.63

Muir long 0.90 1.43 1.4 1.02

Medical 11 short 1.03 1.60 1.5 1.14
‘ i

Attachment - 7

If the values of the periods at the start of the earthquake are compared with the general data on Fig. C4-2, page 373 of ATC 3-06, then

it is apparent that the periods for these structures are better char3/4

acterized by the relationship, T„ * Q.035H ' than the relationship

I

R

. = 0.025h

n

3'*.

2.4 Stiffness

The ATC 2-06 provisions limit the allowable story drift for Seismic

Hazards Exposure Groups I and II to 0.015 radians. When there are

no brittle-type finishes in buildings three stories or less in height,

. those values can be increased to 0.02 radians. *If it is accepted that

for a reinforced concrete structure, a load factor of 1.4 is required

on earthquake forces and. a capacity reduction factor of 0.9 for flexure,

then connection rotations at 65% of the ultimate capacity should not

exceed the story drift specified above divided by C^. Maximum- measured

values of for a story drift of say 0.015 radians for a given column

proportion and spacing can be evaluated directly from the subassemblage

specimens

.

Table 2 lists values calculated according to that concept for several

different investigations. Values range from a low of 2.4 for the flat

plate frame test (8) with a low p value through to a high of 4.3 for the

waffle slab specimen (4).' There is a marked increase in values with increasing slab depth and a lesser increase with increasing -col umn size.

Not apparent from that table is the wide variation in results obtained

for supposedly identical specimens. C

d

values varied by as much as 50%

for similar specimens and averaged about 20%. higher for specimens with

shear reinforcement than those without.

Based on these subassemblage results and experience from the San Fernando

earthquake, it is apparent that a conservative value of for flat plate

structures is 2. Although higher values can be obtained by careful detailing, even for waffle slabs, it is unrealistic to expect that the

value of 6 required for a ductile moment resistant frame can be obtained.

Thus, flat plate framing should only be recognized as an acceptable

lateral load resisting system when classified as an ordinary frame. The

only possible exception might be for a waffle slab structure without

brittle finishes and less than three stories high. Even in that case,

experience from the San Fernando earthquake with the Olive View Hospital

14
'Attachment - 8

Ambulance Port was undesirable. However, the 14 x 18 in. columns were

smaller than desirable and failure occurred irr the columns and not in

the slab-column* connection.

2. 5 Cone! usions:

Based on this summary' of* fieTd and laboratory experience* it is concluded

that:

(1) ft at plate structures of normal proportions and without

shear reinforcement will have little difficulty in meeting the

strength* stiffness, ductility* etc., requirements for ordinary

frames* especially if certain detailing requirements specified

later* are satisfied.

(2) with flat pTate structures of normal proportions it would

be extremely difficult, if not impossible, to meet the stiffness

requirements for utilizing such frames as special moment frames

Category C and 0 buildings.

(3) with flat plates of normal proportions punching failures

will not occur until interstory drifts: greater than the limiting

values specified in Table 3-C, page 53, of ATC 3-06.

(4) with flat plate structures used as the gravity load carrying

system in Category C and D buildings, it is not necessary to consider punching failures as unacceptable provided the detailing

requirements, specified later, are satisfied.

(5) wittr fTat plate structures yielding should be defined as either:

(a) the development of the negative moment yield capacity

of the slab on a line extending across the width of the slab

at the column face, or

(b) the development of the moment transfer capacity at the

slab-column connection for yielding of the reinforcement at

that connection. That capacity can be taken as the flexural

capacity of the reinforcement top and bottom within lines one

and one-half times the slab thickness either side of the column.

(6) the period of structures with 35% or more of the lateral load

stiffness provided by flat plate framing can be estimated from the

3/4 relationship T0 - O.Q35h '

. "

-
. Attachment - 9

TABLE. 2

VALUES OF C

d MEASURED lit SUB-ASSEMBLAGE: TESTS

Full Scale Properties

—

Reference Scale

Slab

Thickness

in.

Column

Spaci ng ft.

Column

Size

in. x In.

Story

Height

ft. C

d Specimen

TypeT 3/8 3 ia 16 x 16 13 2.5 Flat Plate

2 Full 7.5 19 18 x 18 11 2.5 Flat Plate

3 0.4- Iff 2ff 20 x 20 10 3.5 Flat Plate

4 1/4 14 20 20 x 20 11 4.3 Waffle Slab

7 3/4- a 16 21 x 21 11 2.3 Flat Plate

3 1/2 9 2* •19H x 3 9 2.4 Flat Plate

Frame-1 own

References

(1) Hanson, N. and Hanson, J. r "Shear and Moment Transfer Between Concrete Slabs

and Columns," Journal of the PCA Research and Development Laboratories,

January 1968. = 2.5

(2) Carpenter, J.E., Kaar, P.H., and Corley, W.G., "Design of Ductile Flat Plate

Structures, to Resist Earthquakes," Proc . 5th World Conf. Earthquake Eng.,

Rome, Italy, 1973.

(3) Kanoh, Y. and Yashinzaki, S., "Experiments orr Slab-to~Col umn and Slabto-Wall Connections," Japan Concrete Journal , VoT. 13, No. 6, June 1975

C

d

- 3.5

(4) Rodriguez, M'.R., "Diseno Sismico De Conexiones Entre Losas Planas Reticulares

y Columnas," M.E. Thesis, University of Mexico, July 1-979. C^ = 4.3

(5) Islam, S. and Park, R., "Tests on Slab-Column Connections with Shear and

Unbalanced Flexure," Journal of the Structural Division, ASCE, Vol . 102,

No. ST3, March 1976, pp. 549-568.

(5) Zaghlool, E.E.R., "Strength and Behavior of Corner and Edge Column-Slab

Connections in Reinforced Concrete Flat Plates," Ph.D. Thesis, University

of Calgary, Alberta,, Canada, 1971.

(7) Hawkins, N.M., Mitchell, D. and Symonds, D.W., "Hysteretic Behavior of

Concrete Slab to Column Connections," Proc. 6th World Conf. Earthquake

Engrg., New Delhi, India, 1977.

(3) Hawkins, N.M., "Seismic Response of Concrete Flat Plate Structures," Proc.

Seventh World Conference on- Earthquake Engineering, Istanbul, 1980.

(9) San Fernando, California, Earthquake of February 9, 1971, U.S. Department of

Commerce, National Oceanic and Atmospheric Administration, 1973'.

16
2. 0 COMMITTEE ACTIONS

2*1 Recoronendations for Change

2.2 Recommendations for Trial Designs (none)

2. 3 Recommendations for Commentary

2.4 Other Recommendations (none)
2.1 Recommendations for Change

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: H, Concrete COMMITTEE ITEM NUMBER: M2

ATC-3-06 SECTION REFERENCE: I .6.3(A)

Alter the sentence under EXCEPTION to read as fol lows:

Certified mill tests may be accepted for ASTM A706 and, where no welding is required, for ASTM A6I5 reinforcing steel.

"INAL 3ALL0T: 3 YES

__0 NO

0. ABSTAIN

0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

AC I 318, Appendix A permits ASTM A6I5 Grades 40 and 60 rei nforcement. Mill

tests specify actual yield and tensile strengths.

18
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COWITTEE: U. Concrete COMMITTEE ITEM NUMBER-: Bli

ATC-3-06 SECTION REFERENCE: -Chapter I r Table l-B

Assign a Seismicity Index of I to Map Area Number 2 and careful I y- review Map

Area Number 3 to determine whether or not" certain areas such as New York City

should more appropriately be designated as Map Area Number 2 for concrete

construction.

FINAL BALLOT: 3 YES

0 NO

0 A3STAIN

0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The seismicity indices were introduced as a device to relate the seven map areas

(acceleration intensities) with the various levels of detailing requ i rements,

as classified in the four seismic performance categori es - (A, 3, C, and D). The

indices and the performance categories have been apparently arbitrarily interrelated with the seismic hazard exposure groups (Table I -A).

While there is little question about detailing requirements for the highest

seismicity (4), and for the lowest seismicity (I), detailing requirements for

seismicity index levels of 2 and 3 remain a gray area without adequate background

i nformat ion.

OVER
COMMENT ON PROPOSED CHANGE (continued):

Buildings located in the map areas I and 2, subjected to acceleration levels of

0.05, will undoubtedly always remain in the elastic range, requiring no additional

ductility details* The acceleration level of 0*10 (map area 3) wiN, in all

probab i I ity,. create an elastic response in bui I dings designed in conformity

with modern reinforced concrete and steel codes. It should also be considered

that current codes (i.e., ACI 318) basically result in ducti I e members, as provisions over the last 20 years have been devised to eliminate brittleness.

To suddenly- requi re additional detailing (also adding 30l of forces in perpendicular direction) irr cities like New York and Chicago, based largely on judgment, not necessarily supported by adequate background studies, seems questionable. Seismic code writers bear the responsibility to substantiate

the need for any restrictive changes made to codes which have been developed

in a consensus process over the last several decades* It is not for industries

to prove that such changes are unnecessary and will increase the cost of

buildings without adding to their safety.
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVIS I ONS

PROPOSED CHANGE

TECHN I CA L COMM I TTEE : #4, Concrete

ATC-3-06 SECTION REFERENCE: 3.7.12

Delete the third sentence.

COMMITTEE ITEM NUMBER: M8

FINAL BALLOT: 3 YES

0 NO

0 ABSTA I N

0 DID NOT VOTE

sp I ices or

and connections."

COMMENT ON PROPOSED CHANGE:

Formula 3-2a is "for partial penetration welded steel columnfor reinforced masonry and other brittle materials, systems.

The implication that prestressed members can have a brittle failure is consistent with the possible behavior of some long span extruded precast prestressed

products instal led without integral topping. However, where topping, properly

reinforced and bonded, is used on such units or the component is a pretensioned

or post-tensioned unit including supplementary bonded rei nforcement equal to

the AC I Code 313-77 specified minimums, such brittle failures do not occur

and seismic provisions can be consistent with those for reinforced concrete

units.
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

_ TECHN I CAL COMM ITTEET_ #4. Concrete "COMMITTEE ~ITEM NUMBER;! B6C T)

ATC-3-06 SECTION REFERENCE: 7 - 4 - 4

At The- end of- the first sentence, second paragraph, add the following sentence

The pile cap connection may be made by the use of field-placed

dowe I s-- anchored in the concrete pile^

FINAL 9ALLQT: Jj YES

_0 NO

_0 ABSTAIN

_0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

This is the presently accepted practice in UBC-79 and CAL-TRANS specifications
REV I EW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4. Concrete COMMITTEE ITEM NUMBER:

ATC-3.-06 SECTION REFERENCE: 7.4.4(E)

Add the fol lowing sentence aT the end. of paragraph:

The piJe cap connection for Category B structures may also be

made by developing exposed strands

PINAL BALLOT: 8 YES.

0 NO

0 ABSTA I

N

0 DID NOT VOTE

B6(2)

COMMENT ON PROPOSED CHANGE:

This is the presently accepted practice in UBC-79 and CAL-TRANS SDeci fi cat ions.
REV I EW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMlTTEEr #4. Concrete COMMITTEE ITEjM NUMBER:

ATC-3-06 SECTION REFERENCE: 7.5 and 7.6

Make The following changes:

(a) Delete Section 7.6.

(b) Alter the title of Section 7.5 to read as fol lows:

SEISMIC PERFORMANCE CATEGORIES C AND D.

(c) Alter the first sentence in Section 7.5 to read as follows:

Bui I dings, classified as. Category C or D shal I conform to a I I of the- requirements for Category B construction except as modified in this Section..

FINAL 3ALL0T: 6_ YES

2_ NO

2__ ABSTAIN

0_ DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

The use of prestressed concrete piling should not be precluded in seismic

categories C and D. Performance requirements should be given for their

design. See Committee Item Number MIO.

24
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE 'ITEM NUMBER: MIO

ATC-3-06 SECTION REFERENCE: 7.5.5

Insert the following in Section 7.5.3:-

(E) PRECAST-PRESTRESSED PILES

(I) For the body of fully embedded foundation piling subjected to

vertical loads only, or where the design bending moment does not

exceed 0.20 Mnb (where Mn b is the un factored ultimate moment capacity

at baianced strain conditions as defined in Reference II. I, Section 10.3.2),

spiral reinforcing shall be provided such that ps > 0.006 (0.2$)-.

(2) For free standing piling and holloa core' or marine piling subject

to severe installation and operational forces, spiral reinforcing shall

be provided such that p s £ 0.022 (0.7$), or a spacing satisfying the

following rel ationsh ip, if it results in- a percentage of spiral greater

than that given above:

S

sp

*y Asp

(C + 7 d

b

) f p

FINAL BALLOT: 7_ YES

l_ NO

0__ ABSTA I N

0 0 1 0 NOT VOTE

OVER

COMMENT ON PROPOSED CHANGE:

The use of prestressed concrete piling should not be precluded in seismic

categories C and D; performance requirements should be given for their design.

References

1. Gerwick & Brauner — Design of Hich-Per^ormance Prestressed Concrete

Piles for Dynamic Loading (ASTM STP 570, 1979).

2. Margason - Pile Bending During Earthquakes, lecture series at U.C.

Berkeley on Effects of Ground Shaking and Movement on P i I es

,

March 6, 1975.

OVER
ATC-3-06 SECTION REFERENCE: 7 . 5,5 (continued)

where S

S p

fY

- spacing of spiral reinforcing

= yield strength of spiral reinforcing = area of spiral reinforcing = cover over ther spiral reinforcing = diameter of spiral reinforcing = modulus of rupture of concrete

= ratio of volume of spiral reinforcing to total

volume of core (out-to-out of spirals) and not

less than that given in Section I 1.7.2 (C).

(3) Any piling installed in layered soils imposing severe curvatures

during earthquake shal I have the same amount of spiral reinforcing

indicated in item (2) above, accompanied by additional amounts of

flexural reinforcing indicated by moment-curvature relatiorrshi ps

developed for the pile and soil profile present.

(4) The top and bottom portion of hollow core piling and rigid

frame piling where high values of shear and moment occur simultaneously

should contain spiral reinforcing with p s >0.031 (1.0/6) fora distance

of 2 pile diameter, or 2 times the width of the pile.

COMMENT ON PROPOSED CHANGE (continued):

3. Bertero, Lin, Seed, Gerwick, Brauner, and Foti.nos - A Seismic Oes iqn

of Prestressed Concrete Piling, FIP Congress NYC, May 25, 1974.

4. Margason - Earthquake Effects on Embedded Pile Foundations, paper

presented at Pile talk Seminar, San Francisco, March, 1977.

5. Test data from dynamic cyclic prestressed piling tests conducted

under the sponsorship of the Prestressed Concrete Manufacturers

Association of California.

5. Test data from Tests conducted by H. Makita of the Tokyu Concrete

Pile Company.
REV I EW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4. Concrete COMMITTEE ITEM NUMBER: _QJ_

ATC-3-06 SECTION REFERENCE: 8.2.2

Add the following, sentence immediately after the definition of P and just

prior to EXCEPTIONS:

The force, F , shall be applied independently vertically,

longitudinally and laterally in combination with the static

load of the element.

FINAL BALLOT: _8 yes

_0 NO

_0 ABSTA I N

_0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

UBC-79: The effect of vertical acceleration should be included in the design

of nonstructura I components and systems.
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4. Concrete COMMITTEE ITEM NUMBER: 88

ATC-3-06 SECTION REFERENCE:- Chapter 8, Table 8-B

Immediately following "Wall Attachments'"' and indented therefrom, msert

"Connector Fasteners" with a correspond! ng: Cc Factor of 6.0.

FINAL BALLOT: 7 YES

J NO

Q ABSTA I

N

0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

Current practice as outlined in UBC-79.
oo

2 .3 Recommendations, for Commentary

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED ADDITION TO COMMENTARY

TECHN I CA L COMM I TTEE : M, Concrete COMMITTEE ITEM NUMBER: M6

ATC-3-06 SECTION REFERENCE: J.6.3

Alter eighth paragraph,. starting, with the eighth sentence so as to read:

The loading is cyclical, so static ultimate load capacities may

not be- reached* If the combi nation* with the values given in

Table 3-B.

connections

satisfy the

In the example of the flaT plate warehouse, the

can still carry the design gravity loadings if they

requirements of Section I 1 .4. 1

FINAL BALLOT: YES

_0 NO

_0 A3STA I

N

_0 DID NGT VOTE

COMMENT ON PROPOSED CHANGE:

I arifi cation of wording is required to make it consistent with the revised

hapter I I

.
REV I EW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED ADDITION TO COMMENTARY

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE ITEM NUMBER:

ATC-3-06 SECTION REFERENCE: ~5J.Z

Add the following sentence- to the second paragraph:

For two-way slabs orthogonal effects at* s lab-to-co! umn connections

can be* neglected provided the moment transferred in the minor

direction does no*t exceed 30 percent ot that transferred in the

orthogonal direction and there is adequate reinforcement within

lines one and one-half times the slab thickness either side of

the column to transfer a I I the minor direction moment.

FINAL BALLOT: 8 Y£S

Q NO

0_ ABSTA I

N

0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

Considerable simplification that is predictable using beam-analogy

concepts (1,2) and has been proven by testing (2).

1. Hawkins, N.M., Mithcel I D. and Symonds, D.W.,. "Hysteretic Behavior of

Concrete Slab to Column Connections,” Proc. 6th World Conf. Earthquake

Engrg., New Delhi, India, 1977.

2. Hawkins, N.M., "Seismic Response of Concrete Flat Plate Structures,”

Proc. Seventh World Conference on Earthquake Engrg., Instanbul, 1980.

30
REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE ITEM NUMBER:

ATC-3-06 SECTION REFERENCE: Chapter I I and COMMENTARY

Revise Chapter II and Commentary Chapter II of ATC 3-06 to read as per

28 May 1980 proposal „ as modified in meeting of 4 June 1 980 ^ and changes

necessary to incorporate those revisions into the remainder of ATC 3-06.

FINAL BALLOT: l YES

J NO

0 ABSTAIN

0 DID NOT VOTE

COMMENT ON PROPOSED CHANGE:

Chapter II is revised to reference the nationally recognized design standard,

ANSI./AC I 318-77 ’’Building Code Requirements for Reinforced Concrete” for

proportion i ng and detailing concrete structures. Seismic resistance is

considered in the overall development of the AC I 318 Standard, including

Appendix A on special- provisions for earthquake resistance.

Existing Chapter II originated from an early drafT of a proposal by an AC I 318 Seismic Subcommittee to update the AC I 318 seismic design provisions.

The current draft of Appendix A (19 March 1980) now before the Main Committee 318

has undergone numerous revisions. Final Committee action and full ACI consensus

balloting is in process.

The revised Chapter II is formulated to correlate appropriate ACI 313 design

provisions with the four ATC seismic performance categories by reference only

without the need for ATC to duplicate the wording already contained in the

ACI document.
JOINT BALLOT NUMBER: '+/'1-3

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: Concrete COMMITTEE BALLOT NUMBER: _A1

ATC-3—06 SECTION REFERENCE: 11.1 __

Alter Section 11.1 such that the reference reads as follows:

"Reference 11.1 Building Code Requirements for Reinforced Concrete,

American Concrete Institute (ACI 31&—77) excluding Appendix A and

replacing Section 9.2.3 with. Section 3.7.1 of this document.

Final Ballot: 1 Yes

0 No

1 Abstain

3 Did Not Vote

COMMENTS:

This ballot item updates the reference to include the latest version of the

ACI Building Code for Concrete (ACI 318-77). The replacement of Section 9.2.3

in Che ACI Code by ATC 3-06 Section 3.7.1 reminds the designer that the combination of load effects used in ATC 3-06 is different than that in ACI 318-77.

This ballot item appeared on the first of the two committee letter ballots.

The final wording was modified so as to read exactly as revised and approved

by the ATC representative. The abstentions were the result of the ballot

item being superseded by the committee ballot item Y1 ( Joint Ballot Number

4/12)

.

The committee was in full agreement that the reference should be

updated, but the issue of adopting Appendix A overshadowed that intent.
JOINT BALLOT NUMBER: 4/14

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE. BALLOT NUMBER: _A2

ATC- 3- 06 SECTION REFERENCE: 11.2

Altar' Section LI. 2, first paragraph, second, sentence by inserting "Precast and/or

prestressed" in place of "Precast."

Final Ballot: 5 Yes

0 No

0 Abstain.

3 Did Not Vote

COMMENTS:

The intent of the ballot item is to expressly include prestressed concrete as

a permissible building material.. Initially, the ATC representative was opposed

to mention of prestressed construction without any accompanying criteria for

its proper design. However, with the introduction of the material contained

in committee ballot item M9 (Joint Ballot Number 4 /15 ), the ATC representative

approved this change to the existing ATC 3-06 Chapter 11.
JOINT BALLOT NUMBER: 4/15

REVIEW AND REFINEMENT OF TENTATIVE. SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMBER: M9

ATC—3-06 SECTION REFERENCE: New Section 11.9

Add the following as a new Section: in Chapter 11 immediately following

Section 11.8:

Section 11.9 STRUCTURES COMPRISED OF PRECAST

AND/OR PRESTRESSED CONCRETE

SUBASSEMBLAGES

The provisions of this Section apply- to buildings constructed with precast

and/or prestressed concrete elements nor conforming to the detailing provisions

given elsewhere in this Chapter for cast-in-place concrete.

; ,11.9.1 LINEAR ELASTIC DESIGN

Structures with assemblages of precast and/or prestressed concrete components

furnishing lateral resistance, against, seismic forces shall be designed to

elastically resist equivalent lateral forces equal to those specified in this

document with an R value of 1.0.

COMMENTS

OVER

The intent of this change to the existing ATC 3-06 Chapter 11 is to provide a clear mechanism by which a designer can use a precast and/or prestressed con—

struction within the framework, of the. ATC 3-Q6 provisions. Section 11.9.1

presents a method by which a structure can be designed to resist elastically

earthquake forces and which is likely to be an economically viable solution

for low-rise construction only (<. 3 stories). Section 11.2 presents a method

which follows the more conventional approach of permitting inelastic action

providing the system offers the same behavioral characteristics (e.g. strength,

stiffness, damping, etc.) as comparable monolithic cast-in-place ordinarily

reinforced concrete construction.

The ATC representative reviewed and approved of the proposed ballot item. There

were two reservations, of a technical nature expressed by members of the committee.

The first concerned the use of an R value of 1.0 in the Linear Elastic Design

section. The committee member felt that to be overly conservative and suggested

a value of R = 1.5. The other reservation accompanied the "No" vote and was

an objection to the lack of a provision limiting the height and/or the number

of stories.

34
11.9.2 "DUCTILE" CONSTRUCTION

Energy dissipating lateral load resisting systems comprised of precast

and/or prestressed concrete components shall be permitted provided satisfactory evidence can be shown- in. the form of experiments, testing, and

analysis based upon- established engineering principles that the resulting

construction complies with the requirements of Sections 3.6 and 3.7 and

this Chapter,, and that- they offer the same strength, stiffness, stability,

durability, damping^ eneryv absorption, and energy dissipation capabilities

(ductility) as monolithic- cast—in-place ordinarily reinforced concrete

construction*

Final Ballot: 7 Yes

1 No

0 Abstain

0 Did Not Vote
JOINT BALLOT NUMBER: 4/16

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMBER: ML

AIC-3-06 SECTION REFERENCE: 11 . 5.1

Alter Section 11.5.1, third paragraph such that it reads as follows:

"Reinforcement resisting earthquake—induced flexural and axial

forces in frame elements and in wall boundary members shall comply

with ASTM A706. ASTM A615 Grades 40 and 60 reinforcement may be

used in these elements if (a) the actual yield stress based on mill tests does not exceed the specified' yield stress by more

than 18,000 psi (retests shall not exceed this value by more

than an additional 4,000 psi) and (b) the ratio of the actual

ultimate tensile stress to the actual tensile yield stress is

not less than 1.25."

Final Ballot: 8_ Yes

0 No

0 Abstain

0 Did Not Vote

COMMENTS:

This change replaces the current wording in ATC 3-06 Chapter 11 with the

wording included in the latest draft version of the ACI Committee 318

Appendix A (Requirements for Reinforced Concrete Building Structures

Resisting Forces Induced by Earthquake Motions) . The committee was in

complete agreement that the Appendix A wording was more desirable than

the existing wording. The ATC representative objected to this change

because it did not sufficiently emphasize that if ASTM A615 Grade 60 steel

is used careful attention must be given to the metallurgy of the steel

and the welding practice.
JOINT BALLOT NUMBER: 4/17

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED: change:

TECHNICAL COMMITTEE: H- Concrete COMMITTEE BALLOT NUMBER: M3

ATC- 3-06 SECTION REFERENCE: 11.8-2

Alter Section. 11.8.2 by deleting in its entirety the third paragraph and replace

it with the following:.

"A cast-in-place topping on a precast floor system, may serve as the

diaphragm provided the cast-in-place topping is proportioned and

detailed to resist, the design shear forces under the effects of any

loading combination (wfaicir could induce tensile or compressive

stresses simultaneously to the shear forces) - For buildings in

performance Categories C and D, alternate techniques based on the

use of untopped precast and/or prestressed components of concrete

floor systems may be used only- if it can be shown by experiments

. and analysis based on established engineering principles that they

will offer the same shear strength, stiffness, stability, durability,

and sufficient energy dissipation capacity, as a monolithic castin-place ordinarily reinforced concrete diaphragm."

Final Ballot: 8 Yes 0 Abstain

0 No Q Did Not Vote

COMMENTS

The ballot item modifies the existing complete restriction against the use of

untopped precast and/or prestressed components of floor systems as diaphragms.

Instead, the change would permit such systems to- be considered as diaphragms if

it can be shown that the untopped system provides behavior comparable to that

of a monolithic cast-in-place ordinarily reinforced concrete diaphragm.

The ballot item was reviewed by the ATC representative who supported its

adoption. One committee member, however, expressed reservations about the

practicality of verification and the lack of a commentary section giving a clear explanation of the provision’s intent.

1

i
JOINT BALLOT NUMBER: 4/18

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE:

TECHNICAL- COMMITTEE: »4, Concrete COMMITTEE BALLOT NUMBER: M4

ATC-3-06 SECTION REFERENCE: 11.6.1

Four part item

a) Alter Section 11.6.1, second paragraph, second sentence so as to read:

"At least two No. 5 or larger bars shall be provided continuously both

top and bottom except in slabs-. ,r

b) Alter Section 11.6.1, sixth paragraph, first sentence so as to read:

"Web reinforcement perpendicular- to the longitudinal reinforcement

shall be provided throughout the length of all members, except slabs."

c) Alter Section 11.6.1, seventh paragraph, first sentence so as to read:

"Within a distance equal to- twice the effective depth from the end of

all members except slabs, the amount. .. from the end of the member."

OVER

COMMENTS:

The ballot icem introduces design provisions for flat slab construction. Such

provisions are not present in the existing ATC 3-06 Chapter 11 and it was felt

by the committee that such an omission would not be representative of the current

building practice in many areas of the nation.

The ATC representative reviewed and approved of the provisions included in this

ballot item.

While approving this item, committee members expressed concern about the use of

unfactored gravity loads in the proposed equation 11-2. The use of unfactored

loads is inconsistent with all other sections of Chapter 11 where factored loads

are used.

38
Four part item (continued)

d) Alter Section 11.6.1 by adding the following paragraph after the seventh

paragraph:

"Slabs without beams and supported on columns- may be used for ordinary

moment frames provided those slabs satisfy the requirements of Chapter 13

of Reference 11.1 and this Section- Bottom bar reinforcement, Ag, shall.

be provided continuous through or anchored within a column and not less

than that given by the following formula:

» 2 CV-Vp)

s 0.35fy ( 11- 2)

where V is the shear force transferred to column due to unfactored gravity

loads and Vp is the sum of the vertical components of the forces in any

prestressing tendons passing through or anchored within the column. At

least two No. 4 or larger bars shall be provided continuous through or

anchored within the column in both directions- and both top and bottomIn slabs without beams, column strip negative moment reinforcement shall

be distributed so that at least 60 percent of the required reinforcement

is concentrated within lines one and one—half times the slab thickness

either side, of the column- The shear stress, v, on a critical section

located half the effective depth of the slab from the column perimeter,

and caused by the shear force V shall not exceed 2/f^. If there is no spandrel beam at the discontinuous edge of a slab, reinforcement within

four slab thicknesses either side of a column face and adjacent to the

edge shall be detailed so that it can act effectively as torsion reinforcement considering the possibility of full reversals of the sense

of the torsional moments. If the torsional strength of the spandrel

beam framing into a column exceeds the flexural strength -of the slab

at its connection with the beam for the adjacent half panel width, all

shear shall be assumed transferred to the column via the beam."

Final Ballot: 8 Yes

Q No

0 Abstain

0 Did Not Vote
JOINT BALLOT NUMBER: 4/19

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

-

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMBER: M5

ATC-3-06 SECTION REFERENCE: Commentary C 11. 5.1

Alter Commentary Section 11.5.1, fifth, paragraph by including the following

sentence at the end of the paragraph:

"The flat plates of flat plate frames of normal proportions and

detailed as specified in. Section 11. b will not undergo any

significant yield until story drifts greater than those allowable

(Table 3-C)

Final Ballot: 8 Yes

0 No

0 Abstain

0 Did Not Vote

COMMENTS:

This change to the Commentary emphasizes that flat plate frames are considerably

more flexible than other framing, systems

The ATC representative reviewed and approved the proposed ballot item which

incorporates his suggested revisions. There was one reservation expressed by

a committee member. He felt that while what was stated in the ballot item was true for most "normal proportions" there were exceptions and suggested

that the word "will" be replaced by "should."
3.0

COMMITTEE RECORDS

5.1 Minutes of Meetings

3.2 Committee Roster3.3- Selected Committee Correspondence and

Applied Technology Council Comments

3.4 Reference Documents
3.1 Minutes of Meetings

Minutes, of First Meeting

Technical Committee. 1: Concrete

Review and. Refinement, of Tentative

Seismic Provisions. (AIC 3-06)

Meeting: Held, at National 3ureau of Standards

Gaithersburg, Maryland

December 11,. 1979

The first meeting of Technical Committee 1 was called to order at 12:10 p.m.

by Acting Chairman Richard D- Marshall. The following members were present:

Name Representative of

Edward Cohen American Concrete- Institute

Mark Fintel

Neil M. Hawkins

Joseph Manning

James Prendergast

David A. Sheppard

W. Gene Corley (alternate)

Vitelmo V. Bertero

James Lefter

Richard Marshall

Fortland Cement Association

Post-Tensioning Institute

Concrete Reinforcing Steel Institute

Interagency Committee on Seismic

Safety in Construction

Prestressed Concrete Institute

Portland Cement Association

Applied Technology Council

Building Seismic Safety Council

National Bureau of Standards

The first order of business was the selection of a permanent committee

chairman. Edward Cohen was nominated and unanimously elected. Mr. Cohen

chaired the subsequent committee deliberations..

The next item of business was the selection of an individual to serve Technical Committee- 2 — Structural Design, 'lark Fintel was nominated

elected.

on

and

42
Time and. place of the second meeting- (public work, session) was the

nest item of business* This meeting is to be- announced in selected

publications having national circulation- After considerable discussion, it was decided that the meeting would be held on February 21 (and

22, if necessary) r 1980 at the Airport Hilton Hotel,. San Francisco,. California- It was agreed that the Committee Secretary,, R- D- Marshall,

would make arrangements for a conference roomThe committee broke for lunch ar 1:00 p.m- and reconvened at 2:0Q p-mThe afternoon session opened with general discussion as to what sections

of AIC. 3-06 were to. be reviewed by Committee 1 and what procedures were

to be. followed in developing and submitting proposed changes- In addition to the provisions of Chapter 11 — Reinforced Concrete,, concern, was

expressed regarding certain provisions of Chapters 3, 4, 5, 7 and 8.

Edward Cohen inquired as to the status of refinements to the provisions

related to reinforced concrete which are now being carried out by the

Interagency Committee on Seismic Safety in Construction- James Lefter,

representative of the BSSC Overview Committee, stated that he would provide the secretary with the latest draft for distribution to members of

Technical Committee 4-

With regard to- proposed changes, it was determined that individual

members may submit proposed changes directly to the appropriate technical

committees with copies to the membership of Committee 4. Also, it was

agreed that proposals may be developed jointly by the membership of

Committee 4, for consideration by other technical committees.

The chairman, next asked for specific: comments on the current provisions

of ATC 3-06. Prepared comments by the Prestressed Concrete Institute were

distributed to the membership (see Attachment A) by David Sheppard and

were discussed at length. Regarding the provisions of Chapter 7, it was

pointed out by the chairman that foundation design criteria should be

the responsibility of Technical Committee 3, but that material-specific

design provisions should be presented in Chapters 10 and 11 (steel and

reinforced concrete)

.

Mark Fintel also referred to prepared comments (see Attachment 3) in

addressing the relevant provisions of ATC 3-06. The issue of Response

Modification Coefficients, R, was discussed at some length. Fintel pointed

out that while he feels the general approach is a significant step forward,

the R values (Table 3-B) axe based primarily on the judgment of a group

of individuals rather than on rational analysis. To rectify this situation, Fintel proposed that studies of dynamic, inelastic response history

be carried out for various structural systems identified in Table 3-B.

V. Bertero stated that while the studies proposed by Fintel would be very

useful, they would, in. his opinion,, require considerable effort and would

quite likely require, more than one year to complete. Joseph Manning

suggested that additional insight regarding the response modification coefficients could be obtained during the trial design process by subjecting

43
a building- Co both elastic and inelastic analysis. T. Bertero stated

that additional information considered by the Applied Technology Council,,

but not contained in Table 3-B, could be made available to the members

of Committee 4.

Neil Hawkins, pointed out; that, the current provisions- allow the substitution of grade 60 for ASTM A-615 grade 40 reinforcement which, could, in

certain cases,, be detrimental.

3ecause_of tight travel schedules,- the committee adjourned at 4:00 p.nu

_without completing discussion of comments by individual members.

Respectfully submitted^

Richard 0. Marshall

44
' ATTACHMENT A

snucnji.

,

AtcwrtcnjtAi

PRESTRESSED CONCRETE INSTITUTE•

reelt to:

1 3 SO OfiL RIO COURT

CONCORD. CALIFORNIA *4510

20 NORTH-. PACKER ORIVE / CHICAOO, ILLINOIS SOSOS

TELEPHONE 312 / 346-4071 TELEPHONE: At t / t*7-132r

November 5, 1979-

William W. Moore-, Chairman

Board of Direction

Building- Seismic Safety Council

Dames and Moore

500 Sansome Street

San Francisco, CA 94111

Rer Constructive comments on ATC 3-06- regarding the design

of precast and prestressed concrete under seismic

conditions^

Dear Mr. Moore:

The Prestressed Concrete Institute is an organization devoted

to the development and advancement of knowledge and use of

plant cast precast and prestressed concrete. To that end,

we are appreciative of this opportunity to work with our

peers on the Building Seismic Safety Council in the critique

and review of ATC 3-06 as it pertains to precast and prestressed concrete. Of major concern to our industry is the

fact that this widely used material, is not recognized per se

in the document. As a general recommendation we feel that

creation of a separate subsection for precast and prestressed

concrete is fully warranted, considering the unique uses of

the design aspects of seismic design associated with this

material, and in light of the extensive use of the material

in seismic zones. A separate subsection under Chapter II

(Reinforced Concrete) should be established. This subsection

should address the use of lateral load resisting systems and

components, as well as proper design of non lateral load

resisting components to assure their ability to accommodate

movements and distortions of the structure under seismic

loading without suffering structural distress or contributing

inadvertantly to the stiffness of the lateral force resisting

system of the building. The effects of vertical acceleration,

as well as lateral forces, on precast and prestressed concrete

should be covered. This subsection should be further divided

into the following categories:

Plant cast prestressed concrete

Post tensioned concrete

Plant cast precast concrete

Site cast precast concrete

PQR THE ADVANCEMENT OF THg_QESIg£L^AA&n£Arxuflg^ttfl,^gc,a^SS i
-2-

This would enable us to group in one section requirements for

precast, and prestressed concrete that are at present scattered

about the entire document; also some essential seismic design

aspects, such as the ductile design of precast concrete

cladding connectors, are omitted entirely- This treatment is

analogous to the distinct treatment currently afforded precast

and prestressed concrete in UBC-79 and ACI 318—77. An

additional proviso should be added in this subsection similar

to those apprearing in UBC-79 and ACX-77, to witr

"All provisions of this document shall

apply to precast and prestressed concrete

except as specifically modified herein."

There are also several items in the body of ATC 3-06 that we

feel should be modified- These are discussed briefly below t

1. Section 11.2 - Connections of Precast Components - Assigning an arbitrary low value of capacity reduction factor

to connections does not adequately assure proper performance

under seismic conditions. The connections of precast elements

should be able to achieve ductility and at the same time

maintain their anchorage integrity within the concrete. This

requirement should be modified with a statement that ensures

proper performance of .the connector to accommodate maximum

induced drift movements of the structure.

2. Section 11.2 - Axial Compression The arbitrary

assignment of a low capacity reduction factor for a "pin-ended1 column is not warranted when the top and bottom connections

are designed to accommodate maxiumum drift movements and

increased bending movements induced, by the P-A. effect.

3- Sections 3.3.4 and 3.3.5 - Height Limitation . Once

again, we have an arbitrarily assigned value for height which

is inconsistent with the evidence of performance of shear wall

and braced frame buildings in recent earthquakes (Managua,

Romania) . Proper building design and location of stiffening

elements should be the controlling factor, as is alluded to

correctly in Section 3.4.1.

4. Section 11.8.2 - Diaphragm Details and Limitations

No provision is made for "untopped" diaphragms consisting of

grouted castellated shear keys and boundary closure pours, or

untopped precast elements tied together with shear friction

reinforcement as described in Section 2611 (p). of the Uniform

Building Code. Recent test information is available substantiating the effectiveness of untopped floor diaphragms in

transmitting lateral forces

46
—3—

5. Section II. 8. 4 - Boundary Members . Some of these

provisions are not warranted in light, of current practice

and research in the area, of large panel precast concrete

systems building.* Tests by Bertero show that boundary

elements assure continued flexural behavior under extreme

• seismic loading* Becker and Mueller have achieved ductile

behavior with coupled walls without boundary elements. Once

again, it is the design of the structure that is critical;

this cannot be assumed by arbitrarily assigned restrictions

such as we see here*

6 . Section 7.4.4 - Special Pile Requirements . Concerning the anchorage of piles to pile cap, the use of field

• placed anchor dowels grouted into sleeves cast in the pile top

should also be allowed* as outlined in CAL-TRANS Standards and

Specifications, Section 49-1.09.

T'i Section T. 5.3fc) and T. 6.1 - Special Pile Requirements and Limitations . The use of prestressed concrete piling

should not be precluded in seismic categories C & D; performance

requirements should be given for their design. A proposed

revision to this section is furnished to the Council under

• separate, cover.

8. Section 8.2.2 - Lateral Design Forces on Nonload

Bearing Cladding Panel Elements . The forces^ assigned are in

some cases in excess of current code requirements as outlined

in UBC-79 - Table 23-J. At the same time, the connector

fastener should be designed for forces well in .excess of the

values assigned. This section should also emphasize the

necessity of the connector body yielding to achieve ductility

in lieu of approaching forces which would cause fracture of

welds or brittle failure of concrete at the connector embedment location.

Many of these items were first discussed in a letter to the

National Bureau of Standards dated 2 June 1978. We have not

had a response to this communication. I have included a copy

of that letter with these comments. Included with the letter

is an extensive bibliography of papers concerning precast and

prestressed concrete design and construction, which contain a

wealth of substantiating evidence for some of the comments we

have made here.

Thank you for your consideration.

^i^ecy truly yours,

^ x^Dayid A. Sheppard

Prestressed Concrete Institute
sepp firnkas engineering, inc. 251 newbury st:.. boston, mass. tel. CST77 2S7r-S'715

(v June 2> 1978

United States Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

Attention: Mr. Charles CuTver, Disaster Research Coordinator*.

Center for Building Technology

Reference: Review of "Tentative Provisions for the developmant of Seismic

regulations for buildings"-

Dear Mr. Culver,

On behalf of the Prestressed Concrete Institute,.! have reviewed the "Tentative

Provisions" and would like to comment on the attached sheets.

I have tried to be specific and positive wherever possible and due to the time

restraints l have commented only on subjects directly or indirectly related to

precast and or prestressed concrete elements or assemblies of these elements.

As a member of the PCI Seismic Committee and the MIT Seismic Research Review

Board I have had the opportunity to keep abreast of the most recent design and

research developments in this particular field, and as a practicing design

engineer had occasions to apply Seismic codes to actual design and experience

the intracacies of interpretations of codes.

May I state in behalf of PCI that we are extremely interested to contribute

to the further development and refinement of the "Tentative Provisions".

Yours truly.

It is in this spirit that the comments*shoul d be taken.

sepp firnkas engineering, inc.

4i

f

Se,.

SF/ezk

enc.

cc: Mr. Daniel Jenny, Prestressed Concrete Institute

sapp firnkas ulrich baehlke lawrenca ogdar

48

chan I i n
bp firnkas- engineering, Inc.

!June 2nd, 1978

Review and Comments orr "Tentative Provisions for the Development of Seismic

Regulations for Buildings'*-

I. General

r Precast concrete is referred to once in Chapter 11: "Reinforced Concrete'*'

indicating a capacity reduction factor of d * 0.5 for connections of

precast components, and then in the commentary where it states:

"The experience, both in the field and in the laboratory, which has led to

the special proportioning and detailing requi rements • documented in this

Chapter for Categories C and 0 has been predominantly with monolithic castin-place reinforced concrete construction. Therefore,' these requirements

must be projected with great caution to types of construction which differ

in concept or fabrication. Precast reinforced concrete elements may be

used as part of the seismic resisting system provided their strengths,

proportions, and details can be demonstrated to comply with the requirements

stated for Categories C and D construction."

' Ch^ 7 "Foundation Design requi rements" mentions briefly the tie and longii tudinal steel requirements in the upDer part of PRECAST pile sections and

\ further .in sections 7.4.4 (D.) 4 ( E), 7.5.3 (C) and in 7.6.1 which eliminates

j precast1 prestressed concrete piles from resisting flexure caused by earthquake motions for buildings of performance category D. The commentary to

Section 7.6 amplifies this with: "At the present time, there is little or

no information available on the ductility capacity of precast-prestressed

piles; in fact, the type of reinforcing orovided is counter to present

concepts of concrete ductility development. Hence, until further data are

available, they should not be used in situations where pile bending may be

\ induced by earthquake motions.

A short review of the Bibliography of Cfr. 7 and 11 indicates not a single

reference to precast and/or prestressed concrete elements, connections or

assemblies. Considering the above a review of the "Tentative Provisions"

specifically as far as precast and/or prestressed concrete and its numerous

applications are concerned is handicapped and can therefore only be general.

I will, however, try to introduce as many specific subjects as time will

permit.

!

l

I

I

I

I

n Page 1 of 4
sepp firnkas engineering, inc.

2. Chapter 3. "Structural Design Requirements". Section 3.3L : 4 types of general framing systems are mentioned - table 3-8 lists 5.

This should be clarified.

Sections 3.7.4 & 3.3.5: The height limitations imposed on pure shear walT

or braced frame systems seem arbitrary and should seriously be reviewed in

view of the performance of such buildings in recent earthquakes * Managua.

for example - Ref. (135) and. research references (185,. 187, 2, 5, 7, 8,. 165,

166, 167 and 189).

Section 3.4-. : A regularity in pTan configuration should be required for

Categories C. & D. This is a discipline the engineering - ultimately

responsible for Safety in E.Q's - should impose on architectural whims.

1. - Re-entrant corners of significant dimensions should be separated by

adequate separation joints from the main part of the building to

create independently stable buildings. • 2. - Torsional moments should be minimized bjf controlled layout.

3. - Controlled layout can provide significant diaphragm strength.

Section 3.4.2.: Same coiranents as above apply*.

The Architects' preference for an open ground floor or a building on stilts

should seriously be discouraged for Categories C & D. Locations of expansion

joints should be directed by symmetry.. The Earthquakes of Caracas 1967 and

Alaska 1964- - Ref. (183, 184) demonstrated clearly the importance of a controlled regular, plan and verical layout.

A7

3.- Chapter 7. "Foundation Design Requirements".

Section 7.4.4. (D) & (E): It is not obvious at this point why a distinction

between precast and precast & prestressed piles should be made. The longitudinal reinforcing is mostly determined by handling and driving stresses.

The minimum tie spacing should be equal for both types and specified considering thatmost of the time the upper portion of the pile is cut off i.e.:

the minimum tie spacing after cut off should extend 2' below the bottom of

the pile cap.

Section 7.5.3 (A) & (C): It is difficult to see in this connection the

difference bewtween a cast-in-place and a precast concrete pile.

Section 7.6.1 : The commentary to this section states the lack of information

on ductility of prestressed concrete piles as a reason to eliminate them in

Category D to resist flexure caused by earthquake motion. This is obviously

an "easy way out" instead of assemblying and evaluating available research

and performance data.

Prestressed concrete piles can be compared to prestressed columns which have

been researched and used for a long time - Ref. (56, 53, 188 and others) and

performed for many years in offshore and marine structures and for bridge

foundations in the open sea subject to continuous wave and live load actions.

Extensive literature and research has been published in the PCI Journal by

FIP and can be obtained from "Raymond International" (the former Raymond

Concrete Pile Co.); "Brown & Root Inc.", "The Bayshore Concrete Corp." and

European Sources.

50

Page- 2 of 4
i epp firnkas engineering, ino.

Upon studying these data it can be concluded that prestressed concrete

piles do have superior flexural qualities in the elastic stage and seem

ideal for energy dissipation and damping and it appears that they are

preferable to just plain concrete piles, thin steelshell concrete filled

piles or piers.

Since the "Provisions" cover extensively all structural systems, the

omission of prestressed (posttensioned) concrete mat foundations may suggest

to the average reader a negative aspect. The increased use of posttensioned

mats especially in difficult soil conditions (expansive clay, fine sands,

silts, subsidence areas, etc.) and its ability to bridge areas of weakness

has also great advantages in case of ground motions that may disturb the

regularity of supporting strength of the subsoil.

Theoretical and practical backup data could be obtained from a similar'

structural system i.e. from prestressed flat plates. and the Posttensioning Institute

4-. Chapter 11.

'

It is stated in this chapter that precast reinforced concrete components

may be used if the resulting construction complies with the requirements

of Section 3.6 and this chapter. The comments elaborate further that:

", these requirements must be protected with great caution to types of

construction which differ in concept or fabrication. Precast reinforced

elements may be used provided their strength, proportions and details

can be demonstrated to comply with the requirements stated for categories

C & D construction"'. This is fair but sounds like a negative acceptance

of precast reinforced concrete. It is accepted that the burden of proof lies

with the newcomer, but it should be the obligation of the investigator to

avail himself, study and evaluate all published research and experience

data on the subject. Further should be recognized that precast reinforced

concrete elements may have similarities with cast-in-place concrete, however

the force reansfer details of precast concrete elements do not have a counterpart in cast-in-place concrete joints.

The attached references of type 1 - marked with a * are concerned with

behavior of precast and/or prestressed elements subject to seismic motions,

while the references of type 2 - marked with ** investigate the performance

of various types of connections and joints.

Section 11.2

To assign a single even if low 4 factor to connections does not insure

ductility. In practically all connections is steel and concrete involved - two materials with quite different characteristics. Concrete is brittle

compared to steel. To achieve ductility of the connection a yield of steel

elements at or near the concrete interface must be obtained while the concrete

stresses should at this stage remain below rupture.

Recent PCI Special Committee and research work contained in "Mannual for

Design of Archi tectural Precast Concrete" Chapter 2 - Connections resolved

the problem by using equal strength design for steel and concrete and separata

t factors of 6S * 0.-90 and 4c * 0-65 respectively to assure ductility. This

method allows a fairly uniform design for ductility for complex connection

details where sometimes 6 force transfers are involved.
app firnkas engineering. \nc~

Since precast-pres tressed concrete is an established construction method

and industry - and will be more so in the future, the "Provisions” should

include realistic evaluations of behavior and performance of connections

and not dismiss it in general terms.

Section 11.8.2.

The last paragraph about topping is vague and may Tead to misinterpretations.

It has been proven experimentally and can be substantiated analytically that

the shear key connections between individual floor elements (shear-friction:

concept) can transfer diaphragm forces usually in excess of the design forces.

The effectiveness of a thin topping slab on floor elements seems questionable

if the floor slabs are tied together by longitudinal, transverse and

peripheral ties according to current design standards - Ref. (.155). There

are several full scale test results available demonstrating the satisfactory

behavior of grouted untopped floor elements subject to "in plane” forces.

Section 11.8.4.

This section should be reviewed in its entirety as to its applicability to

precast concrete systems construction. The most recent research conducted

at MIT - Ref. (3, 4,5, 6,7 etc.) and the various Japanese, Russian and

Yugoslavian test results should be used to develop guidelines for precast

concrete systems.

Boundary members for diaphragms - See Ref. (155).

Table 11-A.

The shear and tension values for bolts given in this table should be

checked. Since seismic forces cause most of the time shear and tension

an interaction diagram should be given instead of separate val ues for

shear & tension. See Ref. (106).

52 Page 4 of 4
ATTACHMENT B

Response of the Concrete Industry ta ATC 3-OC

Presented to

Building- Seismic Safety Council

San Francisco* CA

November 3* 1979

by

Marie Firrtel, director, Advanced Engineering Services

Portland Cement Association* Skokie, Tllinois

INTRODUCTIONI appreciate this opportunity to. present the reponse of the Concrete

Industry ta ATC-3- First of all* we would like to express our compliments

to the Applied Technology Council for preparing a document which, in many

respects, advances seismic design concepts a long step forward- New

approaches ta seismic zoning, ta sail -structure interaction, and ta period

determination, are specific examples of improvements utilizing knowledge

gained during recent decades, which will affect the daily practice of

earthquake engineeringOn the other hand, many shortcomings contained in present practice,

especially as related ta special moment frames for reinforced concrete,

are continued within ATC-3* These provisions make it practically impossible to construct highrise concrete structures in areas of high

seismicity*

Looking bade at the history of earthquake codes related ta reinforced

concrete multistory structures in the United States, we find that in 1959

the SEAOC recommendations restricted the height of concrete buildings to

13 stories or 16a ftAs a direct response, the concrete- industry produced, in 1961, the

book entitled “Response of Multistory Reinforced Concrete Buildings to

Earthquake Motions'* by Blume, Mewmark and Coming, which firmly established

the fundamentals for earthquake resistance of reinforced concrete multistory structures-
At that time the specified requirement was- that concrete structures

must show* the same ductility as structures constructed of A7 steel; also,

the prevalent moment-resi sting frame Ted SEAOC and the concrete industry

ta develop the QuctiTe-Moment-flesisting-Spaca-Frame (DMRSr) _

In* 1366, the 13-story height limitation was removed and provisions

requiring the 04RSF system- for concrete buildings above 13 stories were

introduced- Since that time,. onTy about half-a-dozen DMRSF structures of

reinforced concrete, talTer than- 160 ft, have been built in California.

It is only in retrospect that we can see our mistake in not pursuing

the development of ductility in shear walls in the S0‘s. At that time we

did not clearly foresee that legislating concrete into structural forms

suitable and desirable for steel may not work. In concrete we cannot emulate steel; we need to utilize the inherent rigidity and strength of concrete walls for lateral resistance of buildings. Reinforced concrete

walls have been penalized by Codes because of their supposed lack of

ductility; however, recent experimental and analytical research has

clearly shown that walls can be made ductile when properly proportioned

and reinforced.

The reason that highrise concrete buildings are not built in California

under existing codes is not that reinforced concrete is a material unsuitable for seismic resistance. Rather, it is that we require ductility where

it is not needed, thus creating expensive, even unbuildable, structures.

This is a direct result of the use of elastic analysis under Code-specified

static loads, which- cannot give us a proper assessment of ductility

requirements. We have not yet adopted the more realistic inelastic analysis techniques for structural response which have been developed in recent

years. ATC-3 needs to consider these.

54
AU Indications ar* that ATC-3, in its present form, .ITT not improve

the buildabllity of highrls* concrete buildings in seismic areas.

to more clearly assess the effects ATC-3 provisions may have on

concrete holdings, let us examine, separately, the three basic components

vhieh comprise the design process, and which directly affect safety and

economy.

These area

® loading;

<r overall concept (including analysis and design), and

o proportioning.

SEISMIC LOAD IMS

The na» seismic maps Incorporated into ATC-3 which consider historical

records of earthquake occurrences, and also distance from earthquake

sources, have created a much more realistic basis for assessment of earthquake forces. Also, such apparent inconsistencies as requiring the same

1^1 of seismic forces for 3oston as for Sar Francisco have been elimi-

"a:8d - r"6 ne* ”aps affar * «ner gradation of earthquake Intensity

across the United States, and. wiTl make it possible to more effectively

rational approaches to aseismic design of buildings, thereby reducexpensive overdesign.

3mk CONCEPT - Analysis and

9 a laird s-eye view of the state-of-the-art* we see that the

uction of earthquake response spectra, more than three decades aga ***** * ,<na^or staP forward: In seismic engineering. Also, the introoff of the ductility concept brought a perspective of realism to the

of buildings.

* recant years* the academic profession has developed powerfu-l ccra- grams which permit inexpensive inelastic response history analyses
of buildings subjected ta ground motions. ATso, the experimental i sts have

accumulated an extensive body of knowledge about the strength, stiffness

and ductility of the individual structural elements and their assemblies

when subjected to cyclic reversing loads. However, when we Took at the

implementation of this vast store of recent knowledge into the practical

design of our baildings, we find a wide gap. ATC-3 is continuing to use

the same static elastic method of analysis to determine seismic forces and

deformations that we used 30 years ago. This is not appropriate for

structures which respond i ne lasti cal ly.

The present overalT philosophy for seismic design of yielding structures continued in ATC-3. is based on a balance between strength and ductility. While the basic concept is undoubtedly valid, its implementation

as currently practiced has shortcomings with respect to strength, and particularly with respect to ductility. The concept is implemented in present

codes primarily through K-factors, and also through load and understrength

factors, and through detailing requirements for ductility.

Strength. Elastic static analysis cannot adequately determine forces

and deformations in inelastic structures. Designing on the basis of elastic analysis may lead to inadvertent' shear failures, such as observed in

the 3ancc de America building in the 1973 Managua earthquake. Unfortunately, this analysis is still in the forefront of the ATC-3 approach.

Ductility .* ATCs implementation of the concept of ductility within

the design process, which is in accordance with current practice, causes

•major construction difficulties and unnecessarily increases cost, without

* We are continuing to use the term "ductil i ty" with hesitation, since no other term has been advocated. Whatever term is used, we are talking

about energy dissipation associated with damping and yielding in the

structure.

-16
improving safety or performance* Originally, the concept- was

- developed on

the basis of" studies of si ngle-degree-of-freedom systems, and system displacement ductilities of 4- to 5 were utilized for a I34Q. El -Centro type

earthquake* However* in designing a structure* we deal w-ith- the ductilities of individual members* and not wittr overall system* ductility* The

relationship between the two may be different for each- member in a structure* and changes of structural configuration will result in changes in

the individual member ductilities* Therefore, while we are talking about

system ductilities of 4- to 5* we. may be faced with member rotational ductilities several times larger, depending on the structural configuration,

and strength and stiffness relationships. No systematic studies have been

carried out to determine the distribution and magnitude of member ductilities within a structure. Consequently, in the present implementation of

the concept to assure safety against brittle failures, we must, of necessity, provide maximum ductility in alT columns, beams, and their connections, whether needed or not. Trr reality, from experience in earthquakes,

and from inelastic analyses* it is knowrr that ductility is not required in

alT members of a frame* Unfortunately, this important1 economic consideration is not included in ATC-3.

Elastic analysis. The major drawback of elastic analysis when applied

to inelastic structures is that it does not allow us to determine the

amount and distribution of ductiTity throughout the structure. We hope

that the details specified in ATC-3 and other seismic codes will assure

the required ductiTity in alT members which:. may become inelastic. We

hope—we do not know* for sure.

Other shortcomings resulting fronr the use of elastic analysis for an

inelastic structure are the possibility of inadvertent yielding of columns
during very severe earthquakes with- its consequent effects on overall

structural stability* and alsa the lade of an active control over the

sequence of yielding during seismic response.

Just a few years age we could not have commented about the unsuitability of elastic analysis, because we had no- practical alternative.

Today, with the avail ab-ility of inexpensive- inelastic dynamic response

history analyses and inelastic static analyses, we da have a practical

alternative. Significant progress towards the development of a practical

inelastic analysis and design procedure, including design examples, has

been accomplished in recent years at PCA. This procedure can be used to

design structures which warrant dynamic analysis. More importantly, we

can use this procedure to verify the present: and other suggested design

approaches, ta weed out the inadvertent deficiencies which may. result from

the use of elastic analysis.

Modal Superposition Analysis. The dynamic analysis suggested in ATC-3,

using the modal superposition method, is reasonably accurate for elastic

structures such as nuclear power plants. However, for structures intended

to yield in their earthquake response, it has the same drawbacks as the

empirical method, since it relies on elastic static analysis for memberforces and deformati ons . The amount and distribution of ductility cannot

be determined, and therefore, we must indiscriminately provide ductility

in all members.

Response Modification Factors . The concept of response modification

factors introduced in ATC-3 to account for the inelasticity and. damping of

the various structural systems and materials is conceptually clear, simple

and easy to apply. It has the potential to update, refine and improve the

58 ~
previous K-factors, provided the R-factors can be established with at

least a reasonable degree of confidence. However, the way the R-f actors

have been- compiled in Table 35, makes the implementation of the concept

very questionable at this time.. Usings the judgment of a smaTT group of

individuals, however knowledgeable, to- arbitrarily select the R-factors,

without the resource of any published background material, and without

appraisal by the profession* and by the concrete and steel industries,

raises more questions than car be answered.

Determination of a reliable table of R-values and its correlation with

the required and available member ductilities must not be done on an arbitrary basis- ductility of members is greatly dependent upon geometry of

the structure, and upon streigth- and stiffness interrelationships; each

.change in the internal makeup of a. structure causes changes in the amounts

and distribution of member ductilitiesTo evaluate the suggested arbitrary Response Modification Factors, R,

of various individual systems and materials by comparing them with the

previous "K* values adopted arbitrarily 40. years ago is like the blind

% leading: the blind- Acceptable "R* values can be derived only with the

help of inelastic response studiesAs long as ATC-1 continues to specify elastic analysis in conjunction

with the suggested arbitrary R-factors ranging from 1—1/4- to 3, any further

sophistication- of the seismic loads is of questionable meritNo criticisnr is constructive unless accompanied by suggestions far

improvement, so we would like to make the following specific proposal for

the determination of R-values:

I The studies to determine R and values must be carried out for the

various structural systems and materials of Table 38- For each system
type, structures with varying periods within the practical range must be

considered. In the analysis of each structure, one must use a set of several ground acceleration time histories corresponding to the target

response spectra* In- these analyses, the strength levels in the structures

should be adjusted so that the ratio of the base shear calculated from an

inelastic response history analysis to the base shear from the undamped

elastic response history analysis under the same ground motion will equal

1/R. The inelastic response history analyses would yield required member

ductilities corresponding to the prescribed R factors* If these required

ductilities are attainable with the specified detailing, then the prescribed R-factors. are realistic; otherwise, they need revision*

We recognize that the total effort required is very extensive*

However, it must be undertaken and systematically carried out, if the

' proposed design provisions are to be based on a solid foundation.

It is hoped that the dynamic inelastic response history studies proposed above for both concrete and steel structures will also lead to a

relaxation of the ATC-3 requirement that ductility be provided throughout

an entire structure, while it may actually be needed only in certain specific locations. For instance, in shear wall-frame structures, it is

unlikely that ductility provided in most columns can ever be utilized. A

recognition of this fact would make concrete structures much more practicable in seismic regions.

Height Limitations . The height limitations for the various framing

systems, as given in Section 3.3 seem questionable. The best performer in

reinforced concrete, the shear wall -frame interactive system, has justifiably been assigned a high R-f actor. The shear wall -frame, however, is

limited to 240 ft, while the special moment frame, which in reality becomes
unbuildable at about IS stories, Is the only concrete system allowed above

240 ft- We da not believe that the reasons and circumstances which- prevailed in the early sixties and Ted ta such height limitations (primarily

a lade of knowledge) are stiTT valid today

PROPORTION INS

While most provisions of Chapter II, Reinforced Concrete* are based on

the present state-of-the art* there are a number of specific details inconsistent with available research results and current building- code requirements* For examp Ter

ASTM designation A615 Grade 50 reinforcement is not permitted* even

though it is currently in wide use* Rather, onTy A706 reinforcement is

permitted, a steeT that is not readiTy available and one for which a premium price has ta be paid. This economic penalty is not justified* Also,

despite the requirement of. A70S reinforcement. Toad factors on joint

details and shear walls are based on tests using A615 Grade 60 bars.

Similarly, all- lightweight aggregate concrete is penalized by unrealistic restrictions on design strengths* Research data do not justify this

1 imitation.

Qne of the mast restrictive suggestions in Chapter II is Equation 11-5.

The enclosed graph shows the proposed ATC-3. design requirement compared

j with results of tests on short walls* On the ordinate, shear strength is

plotted, and on the abscissa, the amount of horizontal reinforcement* The

|

top line indicates measured strength, the line marked (ACT) is strength

I permitted by ACT 313-77, the line marked v^ is the observed cracking

I I

i strength and the bottom line is the strength proposed by ATC-3. As can be

seen, at ultimate load the walls would have a load factor of 1.5 or more

against cracking. The Toad factor on strength could be as high as 14.
CONCLUSIONS

There can be twa reasons for code changes: either the old provision has

been- shown- in- the field ta be unsafe or too conservative^ or a new* provision is known ta produce better structures* In the case of the R-factors,

neither of these is clearly the case* It would seenr prudent ta continue

with- the present iC-values untiT we are ready ta use a rare rational

approach ta structural response with an accuracy which is not only implied,

but is actual*

ATC-2 has continued to impose on multistory concrete buildings requirements which unnecessari Ty increase their cost* Ta provide ductility in

places where it can never be utilized makes our buildings more expensive,

without adding an iota ta their safety. We need to incorporate inelastic

behavior into our design process sa that we can incorporate ductility

details only where they can- be utilized* This item- merits urgent consideration by the Applied Technology Council.

62
SHEAR STRENGTH

O' L0 0.2 0.4 0.6
Minutes of Technical Committee 4

Review and Refinement of AIC 3-06

February 21,. 1980

San Francisco, CA.

9:00 AM PST Meeting is called to order: by Chairman Edward Cohen., Those

present are:

Name Representative Of

Edward Cohen (chairman) American Concrete Institute

James ?r endergast Interagency Committee on Seismic

. Safety in Construction

Joseph Manning Concrete Reinforcing Steel Institute

James Lefter Building Seismic Safety Council

Vitelmo V., Bertero Applied Technology Council

Neil M. Hawkins Post-Tensioning Institute

Mark Fintel Portland Cement Association

David A. Sheppard Prestressed Concrete Institute

Richard Marshall National Bureau of Standards

Kyle Woodward National Bureau of Standards

Robert Park. Guest

Discussion began with consideration of the recommendation made by Mr. Cohen

(see letter dated 2/11/80) to adopt the draft revision of ACT 318—’'Building

Code Requirements for Reinforced Concrete,” including: Appendix A, as the reference

in Sec. 11.1. The draft version of Appendix A is expected to go before the

full ACI 318 Committee at the ACI Spring- Convention, March 3-8, 1980.

Mr. FIntel suggested that trial designs could be based on the draft provisions

of Appendix A because few substantive changes to the Appendix A provisions

are anticipated prior to its final adoption.

Mr. Lefter suggested that the committee must make a decision on the use of

Appendix A before proceeding with future committee work.

64
Mr. Bertero raised, strong objections to the use of the draft Appendix A

provisions. He suggested, that it would, be improper to adopt them because

they have not been officially adopted, by ACT 318. Mr. Bertero also suggested,

that certain incompatibilities exist between the ATC 3-06 document and the

Appendix A provisions* especially with regard, to the way in which loads are

defined. He recommended that the present provisions in Chapter 11 of ATC 3-06

be improved rather than, adopt the draft Appendix A provisions*

Mr. Sheppard pointed out that there is at present no mechanism for regularly

updating the ATC provisions. By adopting Appendix A, any changes resulting

from the ACT review process would automatically be incorporated into the ATC

provision. In addition* since ACT in a consensus code and has national

representation* the provisions would be more widely accepted.

Mr. Pint el suggested that since ATC 3-06 is not a legal document as yet,

there would be no problem in using the draft Appendix A.

Mr. Bertero expressed doubts that the Joint Committee on Review and Refinement

would accept the legality of using the draft Appendix A*

Mr. Marshall explained that the committee r s purpose is to develop a Chapter 11

which can be used in conducting trial designs. The provisions of Chapter 11

will very likely be revised on the basis of trial design results. The legality

of the draft is not at issue* Only the technical aspects of the design

recommendations need to be considered.

Mr. Fintel suggested that a section in Chapter 11 be included to serve as the

necessary link between the Appendix A provisions and the remainder of the ATC

provisions. Any incompatibilities could be resolved in this section.

A general discussion relating to the adoption of the draft Appendix A

provisions led to the following recommendations:

a) The committee recommended that the Coordinating Committee be asked to

consider the proposal ta adopt the draft Appendix A.

b) The committee recommended that the proposed use of the draft Appendix

A provisions be discussed with ACI Committee 318 at the ACI Spring Convention.

c) Mr. Lefter will suggest to ACX 318 subcommittee 10 (Appendix A) that

reference be made in Appendix A to the ATC zones for earthquake loading.

d) Mr. Neville, ACI 318 Secretary, will be asked to write the transition

section in Chapter 11.

e) The committee recommended that the draft Appendix A provisions* with

the necessary interface* be adopted as Chapter 11.

Mr. Hawkins suggested, and it was generally agreed, that Appendix A be modified

to recognize precast and prastressed construction. He suggested that for

category B buildings the current Appendix A provisions are too restrictive.

Break
The committee began discussing Mr. Bertero 's comments on the proposed

revisions submitted by Mr. Sheppard, Mr. Forell (SEAONC representative to

Technical Committee 2) , Mr. Fintel* and Mr. Manning.

Mr. Sheppard's proposals were discussed first. (Mr. Sheppard's proposals are

contained in the letter dated 12/21/79^. Mr. Bertero'a replys are in the letter

dated 1/31/80 with the cover letter from Mr. Marshall dated 2/7/80.)

1.1 Section 11.2'

Mr. Sheppard and Mr. Hawkins both suggest: that specific mention be made of

precast and/or prestressed concrete construction. Mr. Hawkins stated that the

current ACT 318 Building Code deals only with site cast monolithic reinforced

concrete construction.

Mr. Bertero suggested that a completely new section or chapter be developed

to cover precast and/or prestressed construction rather than adding something

in Chapter 11.

It was agreed that the committee should recommend to ACT 318 that provisions

for precast and/or prestressed construction be developed, including seismic

considerations.

Mr. 3ertero noted that the required detailing provisions would vary for each

of the different types of precast and/or prestressed construction.

Mr. Hawkins suggested that detailing provisions for certain specific types of

construction could be developed. immediately. Mr. Hawkins and Mr. Sheppard

agreed to draft a section describing the construction type and detailing

provisions. The draft is to be submitted to the committee within one month.

A paragraph in section 1.3.1 will be added to refer the reader to the appropriate

section in Chapter 11.

The wording of section 11.2 is to be changed to include the phrase "precast

and/or prestressed" instead of "precast."

1.2 Section 11.2

Mr. Bertero 's comment that the proposed revision should not be accepted was adopted for the reasons stated by Mr. Bertero.

Adjourned for Lunch

1.3

Section 11.8

Mr. Sheppard agreed to Mr. Bertero 's modification.

Mr. Fintel questioned the use of only the topping as the load resisting

mechanism. He considered it to be overly conservative and restrictive.

66
Mr. Hawkins suggested that Mr* Bertero T s modification, be altered by deleting

"...like those expected for seismic performance categories C and D„" and

inserting "For buildings in. performance categories C and D" at the beginning

of the last sentence.

Mr. Bertero f s modification with Mr. Hawkin’ s change was. adopted by the

committee.

1.4 Section 11.3

Mr. Bertero ’ s rejection of the proposed revision was accepted by the committee

for the reasons given by- Mr. Bertero.

1.5 Section 11.9 to 11.12

Not discussed again because the idea of separate provisions for precast and/or

prestressed construction had already been discussed.

1.6 Section 11.2

Mr. Bertero r s rejection of the proposed revision was accepted by the committee

because it was generally agreed that providing confining steel is good design

practice.

1.7 Section 3.3.4

1.8 Section 3.3.4

There was:.a general discussion of the meaning of the height limitations and for

what types of systems they applied.

Mr. Cohen suggested that paragraph 3 on page 339 (commentary) limited dual

systems to heights less than 240 feet.

Mr. Fintel suggested that this was not what was actually intended. He stated

that the 240 foot limitation applied to single wall systems only.

Both Mr. Bertero and Mir. Manning suggested that the committee recommend a

change in wording of the relevant sections to establish coupled

shear wall systems, as a separate definition. The committee agreed that the

section needed clarification anti recommended that Committee 2 study- it.

1.9 Section 3 .3 .5

Mr. Bertero stated that the limitations were to emphasize the need for not only

survivability,, but functionality after an earthquake, for performance Category D

buildings.

1.10 Sections 7.4.4,. 7.5.3, and 7.6.1

Mr. Bertero agreed with the general concept of using prestressed piles, but

pointed out that there are a number of variables still undefined in soilstructure interaction.
Mr. Sheppard repeated that his proposed revision was based, on published results

and methods. Mr. Sheppard presented the information to Mr. Marshall to be

copied and distributed to the members of the committee.

Mr. Fintel proposed that: Mr. Sheppard go before the Foundation Committee (3)

to present the views of Committee 4-

Mr. Bertero suggested that prestressed piles should not be excluded because

their performance demonstrated adequate deformational capacity if properly

detailed.

Mr. Cohen proposed that Committee 4 present the data on prestressed pile

performance to Committee 3 and recommend that the restriction against using

prestressed piles in Category D (Section 7.6.1) be deleted. Mr. Cohen proposed

that Committee 4 develop provisions to be included in Chapter 7 that would

specify the necessary detailing requirements for prestressed piles used in

performance Category D. Mr. Sheppard agreed to prepare draft provisions for . the detailing requirements and submit them to the committee within one month.

The committee agreed with Mr. Cohen's proposals.

Mr. Cohen suggested that the provisions of section 7.4.4 be moved to the

appropriate materials-specific chapters.

Mr. Hawkins objected because certain pile types have no corresponding materialsspecific chapters.

Committee 4 agreed to suggest: to Committee 3 that the wording in section 7.4.4

be altered to allow dowels embedded in pile caps as well as dowels embedded

in the pile.

1.11 Sections 8.Z.2 and 8.2.3

Committee 4 suggests to Committee 8 that Mr. Sheppard's proposed revisions be

reviewed.

Mr. Forell’s proposed revisions were discussed.

2.1 Sections 11.8.1, 11.8.2, and 11.8.4

Mr. Bertero' s suggested modifications were discussed and adopted.

Mr. Fintel raised questions as to how designers could compute the axial stresses

in the diaphragms to know whether or not the provisions of Section 11.8.2

proposed by Mr. Bertero apply. The question was unresolved.

2.2 Section 11.8.4

The committee was unclear as to what clarification was required. Mr. Fintel

agreed to request more specific information from Mr. Forell.

Break

Mr. Fintel 's proposed revisions were discussed.
3.1

Table 1-B

Mr. Bertero suggested that Tables: 1-A and. 1-B may unduly penalize reinforced

concrete*

Mr. Cohen proposed, that in Chapter 11 the level of required detailing could be

related to the performance category and seismic area*

Mr. Hawkins- expressed concern that the transitions between zones on the seismic

map created problems which need- additional study.

Mr. Bertero emphasized that the provisions must be directed to the average

professional engineer. This requires that detailing provisions account for

badly configured systems in seismic, areas

The committee proposes a modified Table 1-B on the basis of Mr. Fintel’s

revision. The following seismicity indices were suggested:

3.2 Section 3.3.4

The discussion of height limitations was presented in previous comments.

3.3 Section 3.9

Mr. Bertero expressed concern about emphasizing the use of a unique structural

system.

The committee agreed that some specific mention of alternate procedures is

desirable* The committee- recommends to Committee 2 that the phrase

"or on approved alternate procedures." be added to the sentence beginning

’’The internal forces..." in section 3.1. The commentary should include a

reference to the paper by Mr. Fintel (to be written by him) outlining the method

developed at the Portland. Cement Association.

3.4 Table 3-B

Mr. Bertero suggested that the response analyses of the trial designs could

provide valuable information to develop better estimates of R values.

Adjourned for Dinner

Map Area Number Seismicity Index

7

6

5

A

3

2

1

4

4

3

2

2

1

1
The proposed revisions of Mr. Manning were discussed (refer to letter dated

1/31/80 from Mr. Manning to Technical Committee 1 and Mr. Bertero 's comments

dated 2/11/80).

4.1 Section 11.1

The committee agreed to adopt Mr.. Bertera's modification.

4.2 Section 11.2

The committee agreed to adopt Mr. Manning's proposed revision.

4.3 Section 11.5.1

Mr. Bertero pointed out that experience shows that welding Grade 60 reinforcing

steel creates problems and. requires greater care.

Mr. Manning stated that ASTM A—706 reinforcing steel is difficult to obtain and

is gradually being phased out of the marketMr. Cohen proposed that the committee eliminate references to ASTM A-706 steel

and call for ASTM A-615 steel with the proviso that special welding techniques

must, be used.

The resulting discussion led to the following proposed change in section 1.6. 3.

Add the sentences:

"ASTM A-615 reinforcing steel may be used in place of ASTM A—706 reinforcing

steel where no welding of the reinforcing steel is required. ASTM A-615 reinforcing steel may be used in place of ASTM A—706 reinforcing steel and welded

only if the provisions of Ref. 11.1, section 3.5 are satisfied."

4.4 Section 11.8.1

The proposed revision was rejected for the reasons given by Mr. Bertero.

Mr. Manning agreed with the comments of Mr. Bertero.

Discussion continued on the other proposed revisions submitted by Mr. Manning

which were not commented on by Mr. Bertero.

Table 1-B, Seismicity Index

Discussion had already taken place during the review of Mr. Fintel's proposed

revisions. The table proposed by Mr. Manning was adopted by the committee and

the committee recommends it to committee 2.

Section 3.3.5 Height Limitations

Previously discussed.
Section. 4.2.2 Period Determination

Mr. Bertero stated that equations for period reflected the observed trends

that r/c structures were generally stiffer than steel structures.

Mr. Manning felt that the current formula for period determination unduly

penalized r/c construction. He suggested that the formula be modified on the

basis- of results from response analyses of the trial designs.

Mr. Bertero felt that the simple formula was adequate and complicated formulas

were not justified on the basis of available data.

The committee asked Mr. Manning to review: the data on which the period determination formula was based to ascertain its validity.

Committee ended technical discussion.

Next meeting of Technical Committee 4 was discussed- April 14 at the Portland

Cement Association was tentatively agreed to.

Meeting adjourned.

Respectfully submitted by

Kyle Woodward

Richard D. Marshall
Minutes' of Technical. Committee 4

Review and Refinement of AIC 3-06

Meeting- at. Portland Cement Association

Skokie,. Illinois.

April 14„ 1980

9:00 AM CST Meeting called to; order by Chairman Edward Co hen The

following individuals were present:

Name Representative Of

Edward Cohen (Chairman) American Concrete Institute

Mark. Pint el Portland Cement Association

Joseph Manning Concrete Reinforcing Steel Institute

Neil Hawkins Post-Tensioning Institute

David A. Sheppard Prestressed Concrete Institute

Loring A. Wyllie, Jr. Structural Engineers Association of

California

James Prendergast

(delayed by weather)

Non-voting Members

Interagency Committee on Seismic

Safety in Construction

Vitelmo V_ Bertero Applied Technology Council

James Lefter Building Seismic Safety Council

Richard Marshall National Bureau of Standards

Kyle Woodward National Bureau of Standards

Alternates, Guests and Observers

Gerald R. Neville Portland Cement Association

S. K~ Ghosh Portland Cement Association

Daniel Jenny Prestressed Concrete Institute (Alternate)

Edward 0. Pfrang National Bureau of Standards

72
The first order of business was the issue of adopting ACT 318—"Building

Code Requirements for Reinforced Concrete,"' including the draft revision of

Appendix A, as the reference cited in Sec. 11.1* Mr* Cohen asked Mr. Neville

for a status report on the development of Appendix A and changes to Chapter 11,

ATC 3-06,. that would be required: if the provisions of Appendix A were to be

adopted as the basis for trial designs* Z

Mr* Neville referred tn the ACT 318-Appendix A draft dated March 19v 1980 and

to a revised Chapter 11 (with commentary) which he had prepared and distributed to Technical Committee 4- on March 28. Mr. Neville summarized the changes

reflected in his version of Chapter 11 (hereinafter referred to as the "Neville

draft") and- pointed out that while changes to Appendix A could be expected

prior to its adoption by ACT Committee 318, the March 19 draft (hereinafter

referred to as "Appendix A") was being, proposed as the basis for trial designs.

Mr. Cohen asked the members of Technical Committee 4 for comments.

Mr* Hawkins stated that his review of the Neville draft and Appendix A identified some 15 items that must be revised to ensure consistency with ATC 3-06*

Mr* Bert ero stated that in his opinion,. ATC 3-06- has certain weaknesses in the

areas of loads, the treatment of Category B structures, and the treatment of

shear* And while he feels that the wording of Appendix A in certain cases

represents some improvement over ATC 3-06, Appendix A does not represent any

improvement in technical content* Specifically, it does not represent any

improvement in the areas just identified.

In response to a question. from Mr. Bertero, Mr. Cohen stated that the reasons

for considering Appendix A are that a mechanism would be available for its

future updating and that ACI Committee 318 is an ongoing activity with wide

industry input. He also stated that the intent of Technical Committee 4

regarding Appendix A had been made clear to Subcommittee 10 of ACI 318 and

that he was not aware of. any reluctance on the part of Subcommittee 10 to see

it referenced in ATC 3-06.

Mr. Pfrang noted that the possibility of Technical Committee 4 recommending

the adoption of Appendix A was made clear to Committee 318 at the ACI convention

in Las Vegas, Nevada. No formal approval for such action was granted by

Committee 318 because such approval was not specifically requested. However,

he stated his belief that there would be no objection on the part of Committee

318 to such an action*

General discussion followed on what might be done with the work already

accomplished by Technical Committee 4 in improving Chapter 11. Mr. Neville

stated that these revisions could be channeled to Committee 318 in the form of

recommendations for the improvement of Appendix A.

Mr. Hawkins inquired about, the treatment of precast concrete in Appendix A.

Mr. Neville offered that precast concrete was covered in the Neville draft

and Appendix A. Mr. Hawkins and Mr. Sheppard noted that this coverage was

not to the same degree that Technical Committee 4 had in mind when it set out

to improve and refine the provisions of Chapter 11.
Discussion followed concerning the possibility of assessing the impact of

various options (improved Chapter 1L or the Neville draft and Appendix A)

during the trial designs. Mr. Pfrang stated that it would probably be too

expensive to pursue various optional provisions- during the trial designs.

Mr. Fintel concurred in this and offered the- opinion that the trial designs

will probably be more directly affected by the overall design philosophy

presented in Chapters 3, 4 and 5 of ATC 3-06. -

In the discussion that followed, Mr- Hawkins pointed out that the bond provisions contained in Chapter 11 and Appendix A are significantly different,

and that the provisions recommended by ACX Committee 408 (Bond and Development

of Reinforcement) were not developed with cyclic loading in mind. Mr. Hawkins

suggested that member dimensions would be affected by the- differences in bond

provisions, contained in ATC 3-06 and in Appendix A. Mr. Wyllie noted that

Subcommittee 10 was still waiting for Subcommittee 3 to solve the hook problem.

Mr. Sheppard inquired as to the mechanism that would be used to update ATC

3-06. Mr. Pfrang stated that ATC 3-06 was viewed by the BSSC as a resource

document, not a code or standard, and that if codes do reference the document

in the future, updating should be carried, out by a consensus process.

Mr. Bertero stated his opinion that the Committee should move ahead with the

refined Chapter 11 and update this chapter after Appendix A has been formally

adopted by Committee 318.

The motion was made by Mr. Manning to alter Ref. 11.1 in Sec. 11.1 of Chapter

11 to read as follows:

Ref. 11.1 Building Code Requirements for Reinforced Concrete,

American Concrete Institute. (ANSI/ACI 318-77,

including draft Appendix A dated March 19, 1980 —

Requirements for Reinforced Concrete Building Structures

Resisting Forces Induced by Earthquake Motions)

The motion was seconded and Mr. Cohen called for discussion. Mr. Neville

stated his belief that what is really needed is a vote on his draft of

Chapter 11. Mr. Bertero reiterated his objections to adopting Appendix A in

lieu of the provisions of the current Chapter 11 with revisions. Mr. Hawkins

summarized his list of items that would have to be addressed if the Neville

draft of Chapter 11 and Appendix A were to replace the current Chapter 11.

Mr. Neville stated that he would be available to make any changes required

to mesh the provisions of Appendix A with ATC 3-06. Mr. Bertero stated that

he would not have the time to conduct a critical review of Appendix A as he

had done to date in the case of proposed revisions to Chapter 11.

Mr. Fintel offered an amendment to Mr. Manning’s motion, the amendment being

as follows:

To adopt the draft version of Chapter 11 prepared by Mr.

Neville and distributed to the Committee as an attachment

to letter to Mr. Marshall dated March 28, 1980.

The motion to amend was seconded and Mr. Cohen called for discussion.

74

i

U
Mr. Sheppard asked for a recess prior to. voting on Mr. Fiat el's motion.

After a brief recess, the Committee voted by secret ballot. The motion to

amend was defeated with one vote "yes", four votes "no" and one abstention.

Note: Mr. Prendergast did not artend the morning; session* having been delayed

by bad weather.

Mr. Cohen then asked if there were any questions concerning Mr. ‘Manning ' s motion.

Mr. Wyllie asked that the original motion be read back for clarification.

The motion was read back by the Secretary and was voted on by secret ballot.

The motion carried five votes "yes" to one vote "no".

The next item of business was review of the minutes for the previous meeting

of Technical Committee 4 held at San Francisco, California on February 21*

1980.

Mr. Cohen pointed- out that most of the issues raised by Mr. Bert ero with

regard to the minutes (See Mr. Bertero's letter to Mr. Marshall dated

March 21* 1980) were now moot in view of the vote on Mr. Manning's motion.

Mr. Bertero agreed* but pointed out that the third paragraph under Item 1.8

(page 4 of the minutes) should read as follows: "Mr. Bertero suggested

that this was...."

Mr. Sheppard stated that the third paragraph under Item 1.1 (page 3 of the

minutes) should read as follows: "...prestressed construction be developed

for incorporation into Appendix A." (See Item 1 of Mr. Sheppard's letter to

Mr. Marshall dated March 18, 1980)'

Discussion followed concerning the development of appropriate R and values

for precast/prestressed construction. Mr. Cohen stated that it would be the

policy of Technical Committee 4 to pass- along all improvements and developments

to Subcommittee 10 of ACI Committee 318. Mr. Bertero suggested that a

subcommittee could be established to look into R and C^ values appropriate for

precast/ prestressed construction, but that such a task could not be undertaken

by Technical Committee 4 with its limited membership and tight schedule.

Mr. Pfrang suggested that Technical Committee 4 could decide to remain active

during the trial design period and add members or designate individuals to

work through the Committee in developing recommendations for precast /prestressed

construction. Mr. Cohen suggested that an ACI-PCA-PCI task force could be

organized to develop recommendations for consideration by Technical Committee 4.

Mr . Manning pointed out a misstatement in the minutes, page 7, second paragraph under the heading 4.3 Section 11.5.1. The phrase "and is gradually...

the market" was stricken from the minutes.

The conclusion of the discussion regarding the minutes was to accept

Mr. Bertero' s correction, Mr. Manning's correction, and Item 1 of Mr. Sheppard’s

letter of March 13, 1980. With these corrections, the minutes were approved.

Adjourned for Lunch
Mr. Cohen reconvened the meeting and asked that the ballot of March 27 be

handed in. Those members who had not. completed the ballot, were requested

to return it to the Secretary by April 18..

Mr. Fintel reported on the actions taken by Technical Committee 2 at their

meeting of April. 2 St 3. 1980, Des- Plaines* Illinois. In summary* Technical

Committee 2 — rejected by a. vote of 6 to 2 all recommendations for changes in

seismicity indices in Table 1-B. — did not vote on recommendation to alter Section 3.3.4 so as to

define the coupled shear wall system as a separate category to

emphasize that it is a dual system, but did recommend that the

BSSC establish a task group to address coupled shear walls.

- approved the addition of wording in Section 3.1 to allow

alternate methods of analysis. - added a. section in the commentary describing possibilities and

limitations of inelastic analyses.

Attention next turned to the refinements and improvements of Chapter 11

remaining to be addressed by Technical Committee 4. Mr. Hawkins pointed out

that Sec. A.2.5.1 of Appendix A should replace the last paragraph of Section

11.5.1. Mr. Manning proposed as. new ballot items: (1) that the last paragraph

of Section 11.5.1 be replaced by Sec. A.2.5.1 of Appendix A, and (2) that the

proposed wording, of Item B. 2 of tha.March 27 ballot be replaced by the

following

"Certified mill tests may be accepted for ASTM A-706 and,

where no welding is required, for ASTM A-615 reinforcing steel."

.Mr. Manning’s proposal was put in the form of a motion which carried.

The Technical Committee next considered the issue of seismic provisions for

flat plate, flat slab and waffle slab structures as presented in Mr. Hawkins’

letter of February 26, 1980. After considerable discussion on the intentions

of the ATC 3-06 provisions relating to flat plate construction, Mr. Wyllie

offered a motion to consider as a ballot item the changes to Sec. 11.6.1

proposed by Mr. Hawkins and identified as Items 5.1 A-D in Mr. Bertero’s

evaluation dated April 7, 1980, with Item 5.1 D modified as indicated on page

2 of Mr. Bertero's evaluation. The motion was seconded and adopted.

The following proposals by Mr. Hawkins and identified in Mr. Bertero's

evaluation of April 7, 1980 were put in the form of motions and adopted by

the Technical Committee as ballot items.

Item 5.2 - As proposed by Mr. Hawkins with modification proposed

by Mr. Bertero.

Item 5.3 - As proposed by Mr. Hawkins.

Item 5.5 - As proposed by Mr. Hawkins.
Item. 5.6. — Modify current Section. 3.7.12 by deleting, last sentence.

Mr. Fintel proposed a change lit Item A.6 of the March 27 ballot; that the

phrase "ductility and stable hysteretic behavior** be replaced by "sufficient

energy dissipation capacity ." The proposed change was put in. the form of a

motion,, was seconded, and carried. The revised ballot item A. 6 will be presented as a new ballot item on. the next committee ballot.

The Technical Committee next considered requirements for prestressed concrete

piling. Mr. Lefter questioned whether the data on prestressed concrete pile

performance referred to by Mr. Sheppard at the meeting of February 21 (San

Francisco) was based on cyclic loading. Mr. Hawkins agreed with Mr. Sheppard

that cyclic loads were used. Additional information on this issue is to be

provided by Mr. Sheppard.

Mr. Sheppard offered a motion that a new Section 7.5.3(E) be placed on the

ballot. Wording of Section 7.5.3(E) is to be as indicated in Mr. Sheppard r s letter to the Technical Committee (dated March 25, 1980) with the following

changes

Page 1 :

o Title to read*. PSECAST-PRESTRESSED PILES

o Formula for s.^: change 7 d to 7 d^

Page 2 :

o Change d to d, * diameter of longitudinal reinforcing or strands.

Sp D

o Add the phrase "and not less than that given in Section 11.7.2(C)."

to the definition of p in the new Section 7.5.3(E).

s

The motion was seconded and adopted.

Mr. Sheppard proposed the current Section 7.6.1 be replaced by the wording

proposed in his letter to the Technical Committee dated December 21, 1979.

Mr. Cohen expressed reservations about requiring a dynamic analysis for steel

H piles, but proposed that this issue be placed on the ballot with the understanding that Mr. Sheppard prepare a justification for elimination of the

Category D restriction. Mr. Bertero suggested that the major objection to

precast piles is the connection to the pile cap. Mr. Wyllie offered to look

into the basis for the exclusion of precast-prestressed piles in Section 7.6.1.

Mr. Sheppard made a motion that, as a ballot item. Section 7.6 be deleted and

that Section 7.5 be revised to include seismic performance Categories C and D.

The motion was seconded and approved.
Mr. Sheppard next, proposed as a ballot item the: addition of a new section

in Chapter 11 to be designated as Section 11.9.2 and as presented on page 2

of his letter to the Technical Committee dated April 8, 1980. After considerable

discussion, the following wording, was proposed:

11.9.2 "DUCTILE" CONSTRUCTION

Energy dissipating lateral load resisting systems comprised of precast

and/or prestressed concrete components shall be permitted provided satisfactory

evidence can. be shown in the form of experiments, testing, and analysis based

upon established engineering principles that the resulting construction complies

with the requirements of Sections 3.6 and 3.7 and this Chapter, and that they

offer the same strength, stiffness, stability, durability, damping, energy

absorption, and energy dissipation capabilities (ductility) as monolithic cast—

in-place ordinarily reinforced concrete construction.

The proposal was put in the form of a motion which was seconded and carried.

Mr. Sheppard nexr proposed for ballot items the new sections 11.9 and 11.9.1

as presented in his letter of April 8.

The following wording was agreed upon after much discussion and was presented

as a motion, was seconded and carried.

11.9 STRUCTURES COMPRISED OF PRECAST AND/OR PRESTRESSED CONCRETE

SUBASSEMBLAGES

The provisions of this section apply to buildings constructed with

precast and/or prestressed concrete elements not conforming to the detailing

provisions given elsewhere in this chapter for cast-in-place concrete.

11.9.1 LINEAR ELASTIC DESIGN

Structures with assemblages of precast and/or prestressed concrete

components furnishing lateral resistance against seismic forces shall be designed

to elastically resist equivalent lateral forces equal to those specified in this

document with an R value of 1.0.

Mr. Cohen requested that Mr. Sheppard prepare appropriate material for the

commentary on Sections 11.9.1 and 11.9.2, and that this material be included

on the next ballot. This was put in the form of a motion, was seconded and

carried.

Mr. Cohen asked if there were any additional items to be considered.

Mr. Fintel expressed his view that additional work is needed to develop adequate

provisions for coupled shear walls. Mr. Bertero agreed and suggested that

Technical Committee 4 could recommend to ACI that a committee be appointed to

study the issues relating to coupled shear walls. Mr. Cohen suggested that this

and other items could be identified and that the Technical Committee could make

recommendations to both ACI Committee 318 and BSSC for further study.

78
Mr. Hawkins noted points of confusion in the commentary on coupled shear walls

(page 339, and Figures 3C on page 356)* In the interest of improving the

commentary on coupled shear walls, a motion was made and seconded that Mr* Fintel

develop a new commentary on coupled shear walls, this new commentary to be

included as an item on the next: ballot.

There being no additional business,, the meeting adjourned at 4:10 put.

Respectfully submitted by

R. D. Marshall

Kyle Woodward
UNITED STATES DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, O.C. 20234

Minutes of Technical Committee 4

Review and Refinement of ATC 3-06

Meeting at National Bureau, of Standards

June 4, 1980

9:00 AM EDT Meeting called to order

following individuals were present:

Name

Edward Cohen (Chairman)

Mark Fintel

Neil Hawkins

Eugene Holland

James Prendergast

Loring A. Wyllie, Jr.

Danniel Jenny (Alternate for

David Sheppard)

William Wagner, Jr. (Designated

representative for

Joseph Manning)

Nonvoting Members

James Lefter

Richard Marshall

Kyle Woodward

Guests and Observers

Gerald Neville

by Chairman Edward Cohen. The

Representative of

American Concrete Institute

Portland Cement Association

Post-Tensioning Institute

American Society of Civil Engineers

Interagency Committee on Seismic

Safety in Construction

Structural Engineers Association

of California

Prestressed Concrete Institute

Concrete Reinforcing Steel Institute

Building Seismic Safety Council

National Bureau of Standards

National Bureau of Standards

Portland Cement Association

The first order of business was the adoption of an agenda for the Fourth

Meeting. This being the last meeting of Technical Committee 4, the

Chairman set out the following ground rules prior to consideration of

the agenda:

• All business of the committee must be completed before

adjournment. There will be no pending actions after

adjournment.

80
- 2 -

» Actions requiring letter ballot: approval will be done by signed

written vote during the meeting- The votes will be recorded in

the minutes for approval by the committee.

* The resolution of" reservations from the letter ballots of

March 27, 1980 and May 5, 1980 will be completed before the

introduction of new business.

It was moved and seconded that the agenda (.see Attachment A) be adopted.

The motion carried by unanimous vote.

The next item of business was review: of the minutes of the Third Meeting of

Technical Committee 4 held at Skokie, Illinois on April 14, 1980. Mo corrections were offered and the minutes were approved as distributed to the

committee on April 30,. 1980.

The committee next considered the letter ballot of March 27, 1980. Mr. Woodward

presented a brief, summary of the balloting; and noted that of eight voting

members ,. three did not return their ballot. Ee also pointed out that ballot

items Al, A6 and B2 had been, superceded by the letter ballot of May 5, 1980.

Prior to discussion and final action by the committee , each ballot item was

summarized along with the vote tabulation and the reservations and/or

reasons for negative votes. In the following notes, results of the March 27

ballot are summarized in parentheses for each ballot item (Y =*• yes, YWR =* yes with reservations* N =*- no and A * abstain)

Al. This item was superceded by the letter ballot of May 5, 1980.

A2 (Y * 3, YWR * 1, N * 1) . Discussion centered on the intent of the

proposed change. It was agreed that the proposed change would not

circumvent ATC 3-06 requirements for R and values and that ductility

requirements would still apply for resistance to lateral loads produced

by seismic events. Reservations and objections were withdrawn and the

ballot item was unanimously adopted.

A3 (Y * 3 , YWR = 2) . The reservations concerned the lack of ties at

midheight of columns that would result from the proposed change and the

corresponding changes in & factors for column design. Following discussion of the issue, the committee voted to adopt the change. Mr. Wyllie

requested that the record show his reservation with regard to the proposed

change.

A4 (Y * 3, YWR * 1, M * 1) . The need for boundary members in the case

of tensile axial forces was questioned* as was the basis for the change

when originally proposed. The committee decided there was no basis for

the change as stated and unanimously voted to reject it.
- 3 -

A5 (Y * 3, YWR * 1*. N » 1) . After a brief discussion the committee

unanimously rejected the proposed change for the same reasons stated

under Item. A4.

A6 . This itenr was superceded by the letter ballot of May 5» 1980.

Category B items on the May 5 ballot were next considered. It was explained that these items required action by other committees and,

depending on final action taken by Technical Committee 4, would be taken

up by the Coordinating Committee at its- meeting on June 5-6.

B1 (Y * 2, YWR 3 2, A = 1) . Mr. Fintel was asked to review the comments

and response of Technical Committee 2 to proposed changes in the seismicity

indices of Table 1-B. .After discussing the potential impact of Table 1-B on concrete construction in various map areas, there, was a consensus of

the committee that some changes to Table 1-B were needed. It was agreed

that changes in the original indices for map area 4 through 7 would not

be appropriate. After a lengthy discussion of map areas 2 and 3, the

committee unanimously approved the following motion:

"Recommend that Committee 2 alter the Seismicity Indices in

Table 1-B, Chapter 1 to read as listed below and that Committee 2

carefully review map area 3 to determine whether or not certain

areas such as New York City should more appropriately be assigned

to a map area of 2 for concrete construction.

Map Area Number Seismicity Index

7

6

5

4

3

2

1

4

4

4

3

2

1

1

B2 . This item was superceded by the letter ballot of May 5, 1980.

B3 (Y = 1, YWR =2, N = 1, A = 1) . Mr. Fintel explained that Technical

Committee 2 has already taken action that is responsive to the intent

of this proposed change and, therefore. Item B3 is moot. Based on this,

the committee unanimously agreed to withdraw the proposed change.

82
- 4 -

B4 (Y *3, YWR = 1, A = 1) . Mr* Fintel reported that Technical Committee 2

has recommended a change which responds to Item B4 and the issue is now

moot. Thus, the committee agreed to withdraw the proposed change.

B5 (Y * 3, N » 1,. A: *

1) - Mr. Fintel reviewed Che action taken by

Technical Committee 2 in recommending to the BSSC that a committee be

established to study coupled shear walls and eccentrically placed frames.

Technical Committee 4 unanimously agreed to withdraw the proposed change.

B6 (Y * lr YWR =* 3, A * 1).. Mr. Salomone, Secretary of Technical Committee 3,

reviewed the response of that committee to the proposed changes to Section

7.4.4 submitted by David Sheppard in his letter of December 21, 1979, to

Technical Committee 4. Technical Committee 4 decided that the issues of

dowels and exposed 3trand should be treated separately and took the following actions

1. Unanimously recommended that the following be added to the

second paragraph of Section 7.4.4.

"The pile cap connection may be made by the use of fieldplaced dowels anchored in the concrete pile."

2. Unanimously recommended that the following sentence be

added to Section 7.4.4(E).

"The pile cap connection for Category B structures

may also be by means of developing exposed strand.""

B7 (Y = 2, YWR =1, N = 1, A = 1) . The committee concluded that the

proposed change was not clear as stated and unanimously recommended

that the following wording be added to Section 8.2.2 just prior to

"EXCEPTIONS."

"The force , Fp* shall be applied independently vertically,

longitudinally and laterally in combination with the static

load, of the element."

B8; (Y = 3, N * 1* A * 1) . Discussion centered on what UBC requires for

exterior wall attachments and whether it was appropriate to double the

elastic forces rather than to modify the performance factor. The committee

decided that the proposed change should be withdrawn and that Table 8-B

should be modified by inserting the words "Connector Fasteners" indented

and immediately under "Wall Attachments" with a corresponding C c factor

of 6.Q. Mr. Fintel opposed the change.

B9 (Y *

4, A s 1) . Mr. Fintel reported that Technical Committee 2 has

taken this proposal under consideration and it was unanimously agreed

to withdraw the original resolution.
- 5 -

At this point, Mr. Leyendecker outlined for the committee the schedule

for completing the review and refinement of ATC 3-06.

It was moved by Mr. Holland and seconded by Mr. Jenny that Item 4 of

the agenda be tabled in view of the need to consider the March 19, 1980

draft of Appendix A (ACT Standard 318—77) and the May 28 version of

Chapter 11 prepared by Mr. Neville of the Portland Cement Association.

In the discussion which followed, it was pointed out that certain items

on the letter ballot of May 5, 1980, involved provisions of ATC 3-06

outside of Chapter 11 and would, therefore, have to be considered by

the committee, regardless of what action was taken on Chapter 11. The

original motion was then amended to table ballot items Ml, M3, M4, M5,

M9 and M12. The motion, as amended, passed unanimously and the committee

then addressed the remaining issues on the May 5 letter ballot.

M2 (Y *- 7, YWR * 1) . Reservations regarding this proposed change were

withdrawn and the- proposed: change was approved by unanimous vote.

M6 (Y * 7, N * 1) . Discussion centered on the ability of flat plate

construction (waffle slabs in particular) to share in resisting lateral

loads when properly detailed. The committee unanimously agreed to

delete the last sentence of the proposed change to the eighth paragraph

of Section 3.6.3 which is then to read as follows:

"The loading is cyclical, so static ultimate load capabilities

may not be reached. If the combination—with the values given

in Table 3-B. In the example of the flat plate warehouse, the

connections can still carry the design gravity loadings if they

satisfy the requirements of Section 11. 6. 1."

M7 (Y - 7, N * 1) . In discussing the proposed change,. it was pointed out

that there is no reason to check shear stresses if the procedure for

design of slab-to-column connections is properly carried out. Mr. Wyllie

stated that he would withdraw his negative vote, but that his reservation

regarding the proposed change was to stand.

M8 (Y =* 7, N * 1) . The discussion centered on simply supported prestressed

beams developing a hinge at midspan due to vertical accelerations and the

fact that 0.5 Qq would be an excessive requirement. Mr. Wyllie agreed to

change his vote from "no" to "yes with comment," the comment being as stated on his May 5 ballot.

The committee adjourned for lunch.

84
6

1:35 PM EDT Meeting reconvened by Chairman Cohen.

It was moved by Mr. Holland and seconded by Mr. Fintel that the May 28

version of Chapter H and Commentary submitted by Mr. Fintel (see

Attachment B) be adopted to replace Che current Chapter 11 and Commentary

of ATC 3-06. Mr. Fintel^ who deferred to Mr. Seville, was asked to give

a summary of the May 28 version, the reason' for the proposed change, and

how the May 28 version and referenced March 19 draft of Appendix A

(ACI 318-1977) would affect previous ballot items and actions taken by

the committee to date. Mr. Neville stated that the items contained in

the letter ballots of March 27 and May 5 had been incorporated. Mr. Cohen

noted that additional items contained in Mr. Bertero r s memorandum to

E. Cohen and E. Pfrang and distributed to members of the committee during

the morning session would have to be considered by the committee if the

May 28 version of Chapter 11 were adopted. Mr. Wyllie questioned the

wisdom of adopting for trial designs a new set of provisions that are

incomplete and have not been, thoroughly reviewed. A lengthy discussion

ensued concerning the evolution of Appendix A, the advantages and disadvantages in replacing the current Chapter U with the May 28 version,,

and reasons supporting the proposed change. The motion was put to a

vote and carried 6 votes "yes" and 1 vote "no."

It was moved and seconded that the following resolution, be adopted by

Technical Committee 4.

"Regardless of subsequent actions, it is the firm intent of this

committee that the final version of Appendix A, with appropriate

modifications, be incorporated in ATC 3-06 after completion of

trial designs."

The committee adopted the resolution by unanimous vote. The Chairman

then requested a motion for the following statement of appreciation.

"This committee wishes to thank Professor Bertero for his

dedicated work and many technical contributions over the

past months."

The motion was seconded and unanimously approved.

The committee next considered the provisions of the May 28 version of

Chapter 11 in light of action already taken on letter ballot items.

The following changes to Chapter 11 and Commentary were moved, seconded

and unanimously approved.

Section 11.4.1, paragraph (D) under "EXCEPTION:" Delete 3/f<T b

Qd and
- 7 -

Add new Section 11.4.2 — FRAMING SYSTEMS. Wording to be identical to

Section 11.5.2 except as follows:

First paragraph under "EXCEPTION:

Second line — delete ,rACI 318 , Appendix A"' and add "Section. 11.4.1"

Fourth line - delete "and toughness" and add "stiffness, stability,

durability,, and energy dissipation capacity"

Last line — delete "Appendix A" and add "Section 11.4.1."

Second paragraph under "EXCEPTION :

Last line — delete 1.0 and add 1.5.

Section 11.5.2

First paragraph under "EXCEPTION:"

Fourth line — delete "and toughness" and add "stiffness, stability,

durability, and energy dissipation capacity"

Second paragraph under "EXCEPTION:"

Last line — delete 1.0 and add 1.5.

Section 11.5.3

Delete "WALLS AND" from section heading.

Delete first and second paragraphs.

Commentary — Section 11.4

Fourth paragraph — move to end of Section 11.5.4 of Commentary

(Note: 11.5.3 should be 11.5.4).

Mr. Holland and Mr. Wagner left the meeting because of flight schedules

and assigned their proxy to the Chairman.

The committee next considered the changes to the May 28 version of Chapter 11

recommended by Mr. Bertero in his undated memorandum to E. Cohen and

E. Pfrang. This memorandum was distributed to the commi ttee during the

morning session and is included in these minutes as Attachment C. In the

following, the page and item, numbers are identical to those in the Bertero

memorandum.

86
t

— 8 —

I. CHANGES NEEDED IN CHAPTER 11

Pag& L. The committee adopted the following for reference documents.

Reference 11. 1-ANSI/ACT 318-17 "Building Code Requirements

for Reinforced Concrete," including proposed revision of

Appendix A — "Requirements for Reinforced Concrete Building

Structures Resisting Forces Induced by Earthquake Motions,"

dated 19 March 1980 v American. Concrete Institute.

Reference 11.2-AWS Dl.4-79 "Structural Welding Code - Reinforcing

Steel," American Welding Society.

Page 2. Section 11.4.1.. The committee adopted the following change.

! First paragraph,, first line:

Replace "Where Moment Resisting Frame Systems are..." with "Where

Ordinary Moment Frames are...”

Page 3 .

• Section 11.4.1(E) . The committee adopted the following change.

; Last line - delete "as torsion reinforcement." and add "to resist

torsion at discontinuous edges."

Page 3 . Section 11.5.2. The committee recommended that the following

be added to the definition of BRACED FRAME, Chapter 2, page 37.

"In Chapter 11, reinforced concrete braced frames may be

referred to as structural trusses."

Page 3. Section 11.5.3. This paragraph has been deleted.

Page 4. Section 11.5.3. This paragraph has been deleted.

Page 4 . Section 11.5.4. The committee adopted the following wording

for this section.

"All frame components assumed to be not part of the seismic

resisting system shall have demonstrated capabilities satisfying Section 3.3.4(C) and shall conform to the requirements of

ACI 318, Appendix A. 8; except, the lateral deformation requirements of A. 8.1 shall not apply. If nonlinear behavior...”

With regard to the following items in Mr. Bertero's memorandum (identified

under I. CHANGES NEEDED IN CHAPTER. 11) , the committee determined that

they should be sent forward to ACI Committee 318-Sub 10 for consideration.

Page 3. A. 4. 3.

Section 11.5.1

Section 11.5.2
- 9-

The committee agreed to the addition of a new Section 11.5.5 to Chapter 11

which reads as follows:

11.5.5 - RELATIVE FLEXURAL STRENGTH OF COLUMNS-

"In lieu of ACL Appendix A.4.2, the following: shall apply for relative

strength of columns.”

Insert 11.7.2(A) of ATC 3-06 with, the following- changes.

First line after "joint” - insert "where framing columns resist a

factored axial compressive force larger than Agfc

/IQ and in the

plane. . .”

Third line from bottom - delete "Section 11.7.2(C)" and add "ACI

Appendix A. 4. 4"

On page 3 of the Commentary,, the committee agreed to add a paragraph and

figure prepared by Mr. Hawkins which address reinforcement details at a

discontinuous edge. The paragraph and figure are to be inserted after

the third paragraph of Section 11.4.

The committee next considered those items listed under II. CHANGES NEEDED

IN THE NEW APPENDIX A TO MAKE IT CONSISTENT WITH THE ATC 3-06 PROVISIONS

in Mr. Bertero's memorandum. The following items were accepted by the

committee as requiring a change in ACI Appendix A or as already accomplished

through changes to the May 28 version of Chapter 11.

Page 1. A.O

Page 2. A.l

Page 4. A.2.1.4

Page 8. A.4.2.

Page 9. A.4.3.2

Page 9. A. 4. 4.1

Page 11. A. 5. 3.1

Page 14. A. 7. 1.3

The committee agreed that all other Appendix A items identified in

Mr. Bertero’s memorandum should be sent forward to ACI Committee 318-

Sub 10 for consideration.

The committee next took up unresolved items on the letter ballot of

May 5, 1980.

M1Q (Y = 6 , YWR =* 1, N * 1) . Discussion centered on the documentation

supporting the proposed additions to Section 7.5.3. Specifically, the

nature of the cyclic load tests was called into question. After extensive

discussion it was moved and seconded that the proposed change as stated

under Item M10 on the letter ballot of May 5 be withdrawn. The vote was

Y = 1, N = 2, A = 2. Therefore, the change will be sent forward as originally stated.
- 10 -

Mil (Y » 7, IT * 1) The committee discussed this, issue at length*

considering the possible reasons for the limitation in Section 7.6.1,

documented damage to precast-prestressed piles subjected to seismic

loads and the basis for removal of the limitation* It was moved and

seconded to send the proposed change forward as stated under Item Mil

on the letter ballot of May 5* The vote was Y * 3, M * 2- Therefore,

the change will be sent forward as. stated under Item Mil*

Ml

> Because of actions taken, by the committee up to this point in the

meeting , this- item was deemed to be moot.

To complete its action on the adoption of the May 28 version of Chapter 11

and references indicated therein, the committee conducted a letter

ballot. The ballot item, designated as Yl, was stated as follows:

Yl. ’’Revise Chapter 11 and Commentary Chapter 11 of AIC 3-06 to read

as per May 28, 1980 proposal, as modified in meeting of June 4, 1980,

and changes necessary to incorporate those revisions into the remainder

of AIC 3-06.

The results of the ballot were as follows:

Mr. Cohen "yes" Mr. Prendergast "yes"

Mr. Fintel ”yesM Mr. Wyllie "no"

Mr. Hawkins "yes" Mr. Jenny "yes"

Mr. Holland "yes" Mr. Wagner "yes"

The committee next conducted a letter ballot regarding its intent to

see ACT Appendix A incorporated in AIC 3-06. The ballot item designated

as Rl, was stated as follows:

Rl . "Regardless of subsequent actions, it is the firm intent of this

committee that the final version of Appendix A, with appropriate modifications, be incorporated in AIC 3-06 after completion of trial designs."

The results of the ballot were as follows:

Mr. Cohen "yes" Mr. Prendergast "yes"

Mr. Fintel "yes" Mr. Wyllie "yes"

Mr. Hawkins "yes" Mr. Jenny "yes"

Mr. Holland "yes" Mr. Wagner "yes"

There being no further business, the meeting was adjourned at 9:20 PM EDT.

Respectfully submitted.

R. D. Marshall Kyle Woodward
ATTACHMENT A

AGENDAMeeting of Technical Committee 4- - Concrete

National Bureau of Standards

Gaithersburg* Maryland

June 4-, 1980

T. Purpose of meeting and ground; rales.

2. ' Approval of minutes of previous meeting.

3. Resolution- of negative votes and reservations on letter ballot of March 27* 1980.

4. Resolution of negative votes and reservations on

1 etter bal 1 ot of May 5* 1 980.

5. New- items for consideration.

6. Approval of final committee recommendations.

90
ATTACHMENT R

Msy 28, 198(1

CHAPTER U

REINFORCED CONCRETE

Sect 'll*! - REFERENCE

- DOCUMENTS' V

‘ : V ^

The quality and testing of concrete and steel materials and the design and

construction- of reinforced concrete components that resist seismic forces

shall conform to the requirements of the references listed- in this Section,,

except as modified by* the provisions of this Chapter.

Ref. II. 1 ANSI/ACI 318-77 "Building Code Requirements for Reinforced

Concrete* including Appendix A* - Requirements for Reinforced

Concrete BuiTding Structures Resisting Forces induced by

Earthquake Motions, American Concrete Institute.

; Sec. 11.2 - REQUIRED STRENGTH

Required strength to resist seismic forces determined by analysis procedures

of Chapter 4 or 5 shall be in- accordance with Sec. 3.7.1 in lieu of ACI 313

Section 9.2.3.

Sec. 11.2 - SEISMIC PERFORMANCE CATEGORY A

Buildings assigned to Category A may be of any construction permitted by ACI

318, and shall conform to the minimum requirements of ACI 318, excluding

Appendix A.

Anchor bolts at tops of columns and similar locations shall be closely

enclosed within not less than two #4 or three #3 ties located within

4 inches from top of columns. Allowable loads on anchor bolts shall not

exceed those given in Table 11-A.

Sec. 11.4 - SEISMIC PERFORMANCE CATEGORY B

8ui!dings assigned to Category 3 shall conform to all the requirements for

Category A and to the additional requirements of this Section.

* "Appendix A-Reauirements for Reinforced Concrete 3uilding Structures

Resisting Forces induced by Earthquake Motions," 19 March, 1980;

copy attached..

CHAPTER 11 - Pages 101-110

" v '

REVISE CHAPTER II TO READ AS FOLLOWS:
-2-

11.4.1 - ORDINARY MOMENT FRAMES

Where Moment Resisting. Frame Systems are used for the seismic resisting

system, frame components (beams and columns) shaTT be proportioned to

satisfy the additional provisions, of ACT 318*. Appendix A. 3. 2, A.3-3*. A. 4.3,

and A.8.2- (See ACI 318 Appendix A. 2.1.3)*

EXCEPTION?

Where slab, systems without beams between supports and supported on

columns are used for the seismic resisting system, the following

provisions shall appTy to slab components in lieu of ACI 318,

Appendix A. 2. 2 and A .3. 3-

(A) Area of bottom slat rei nforcement not less than 1.3 V

u /

shaTT be provided continuous through or anchored within

column supports, where V is factored shear force transferred

U- to supporting columns due to gravity loading only. Shear force

may be reduced by vertical component of effective prestress

force for slab systems with prestressing tendons continuous

through or anchored w-ithin supporting columns-

(3) In each direction, at least 2 bars shall be provided in both

top and bottom of slab and made continuous through or anchored

within supporting columns.

(C) At least 60 percent of column strip negative moment reinforcement shall be concentrated between lines that are one and

one-half slab thickness (1.5h) outside opposite faces of columns.

(D) Shear strength of slab at slab-column connections shall not

be taken greater than 3

1/rf^b

Q

d when subject to shear force Vu , where b

Q

is perimeter of a critical section perpendicular to

plane of slab and located so- that its perimeter is a minimum,

but need not approach closer than d/2 to- perimeter of supporting

column.

92
V -3-

(E) At discontinuous, edges of slabs without an edge beam, reinforcement within a: distance 4h on either side of a supporting

column shall be detailed as torsion reinforcement.

Sec. 11.5 - SEISMIC PERFORMANCE CATEGORY C ANC D

Buildings assigned to Categories C and Q shall conform ta all the

requirements for Category 8 and ta the additional requirements of this

Section.

11.5.1 - MATERIAL REQUIREMENTS

Materials used in the components of the seismic resisting system snail

conform to ACI 318* Appendix A. 2.4 and A.2.E.

11.4.2 - FRAMING SYSTEMS

All components of the seismic resisting system (moment frames, structural

walls, braced frames, and diaphragms! . shall be proportioned in accordance

with provision of ACI 318, Appendix A. 2. I.

EXCEPTION::

Seismic resisting framing systems not satisfying the requirements of Sec. 11 .4.1 , maY be used

_if i tTs^detnohstrated

by experimental evidence and analysis that a proposed system

will have strength and toughness equal to or exceeding that

provided by a comparable monolithic cast-in-place framing

system satisfying Sec. 11.4.1.

Alternatively, seismic resisting framing systems that do not

contain required special details or energy dissipating mechanisms may be used if designed for forces determined by the

analysis procedures of Chapters 4 or 5 with an R value of 1.5.

11.5.3 - STRUCTURAL WALLS AND DIAPHRAGMS

Structural walls shall have vertical boundary members at wall edges as required by ACI 313, Appendix A. 5. 3.1. Vertical boundary members shall also

be provided at any level of a structural wall where tensile axial forces can

be developed.
-4-

Structural diaphragms shall have special transverse reinforcement as required

by ACI 318, Appendix A. 5. 2. 3. Special transverse reinforcement shall also be

provided whenever tensile axial forces can be developed across the entire

diaphragm section.

Cast -in-place topping on precast floor systems may serve as structural

diaphragms to transmit inertia forces to seismic resisting elements provided

the cast-in-place topping is proportioned and detailed to resist the shear

forces under the effects of any loading combination (which could induce

tensile or compressive stresses simultaneously to the shear forces). Alternate techniques based on the use of untopped precast and/or prestressed

components of concrete floor systems may be used only if shown by test and

analysis based on established engineering principles that the floor systems

will provide the same strength, stiffness, stability, durability and sufficient energy dissipation capacity as a monolithic cast-in-place ordinary

reinforced concrete diaphragm.

11. 5.4 - FRAME COMPONENTS NOT PART OF SEISMIC RESISTING SYSTEM

All frame components assumed to be not part of the seismic resisting system

shall conform to the requirements of ACI 318, Appendix A. 3; except that frame

elements assumed not to be part of the lateral force resisting system shall

have demonstrated capabilities satisfying Sec. 3.3.4(c). If nonlinear

behavior is required in such components to comply with Sec. 3.3.4(c), the

critical portions shall be provided with special transverse reinforcement in

accordance with ACI 318, Appendix A. 3. 3 or A. 4. 4.
TABLE II-fit

ALLOWABLE SHEAR ANU TENSION ON BOLTS*

i DIAMETER

MINIMUM 7

EMBEDMENT

1 SHEAR' TENSION

(inches) (inches) (lbs) (lbs.)

1/4 2% 50Q 360

3/E

' - 3 1100 900

1/E 4 1900 1700

5/3 5 3000 2700

• 3/4- 5% 4300 4050

7/S 6 5900 5750

I T 7700 7500

^Values showrr are for minimum- concrete compressive strength

of 3000 psi at ZS days.

Values are for natural stone aggregate concrete and bolts

of at least A-307 quality. Bolts shall have a standard

bolt head or equal deformity irr the embedded portion.

Values, are based upon a bolt spacing of 12 diameters with

a minimum edge distance of 6 diameters. Such spacing and

edge distance may be reduced 50 percent with an equal

reduction in value. Use linear interpolation for intermediate spacings and edge margins.

2

A minimum embedment of 9 bolt diameters shall be provided

for anchor bolts located in the top of columns for buildings located in Seismicity Index Areas 3 and 4.
COMMENTARY CHAPTER 11 - Pages 449-459

REVISE COMMENTARY CHAPTER 11 TO READ AS FOLLOWS:

COMMENTARY

CHAPTER 11: REINFORCED CONCRETE

For the proper detailing of reinforced concrete construction for earthquake resistance, design standard ANSI/ACI 318-77 "Building Code Requirements for Reinforced Concrete" is referenced. Seismic resistance is

considered in the overall development of the ACI 313 Standard, including an Appendix A on Special Provisions for Reinforced Concrete Building Structures

to Resist Forces Induced by Earthquake Motions.

Chapter 11 is formulated to reference appropriate ACI 318 design provisions

within the four ATC seismic performance categories (A through D). ACI 313

Appendix A refers to zones of different seismicity (Zones 0 through 4) for

application of the special provisions for seismic design. For application

of Appendix A within the ATC Seismic performance categories, buildings

assigned to ATC Category A are interpreted as located in Zone 0 or 1 (regions of no or minor seismic risk), requiring no special provisions for

seismic design. Buildings assigned to ATC Category 3 are interpreted as located in Zone 2 (regions of moderate seismic risk) per Appendix A. 2. 1.3.

Buildings assigned to ATC Category C and D are interpreted as located in

Zones 3 and 4 (regions of high seismic risk), per Appendix A. 2. 1.4. The

prcporti oning and detailing requirements for frames and walls resisting

seismic forces are summarized as follows:

For buildings in seismic performance category A, no special provisions are reouired; the general requirements of ACI 318-77 apply for prcporti oning and

detailing concrete structures.

7ne code sections cited in ACI 313, Appendix A. 2. 1.3 for ordinary moment

frames (beam-column framing systems) in seismic performance Category 3

Wall

rrame

Category A Category B ACI 318-77 Appendix A. 2. 1.3

ACI 313-77 ACI 313-77

Categories C & D Appendix A

Appendix A

96
govern reinforcement details, of the beam and column components as follows

For slab systems without beams between calumrr supports, the slab components

of the frame are detailed' irr accordance with- the special EXCEPTION provisions

of Sec. II.4-. 1.

There are no special requirements for other structural or nonstructural

components of buildings in Category B.

In regions of high seismic risk (Categories C and 0), the entire building*

including the foundation and nonstructural elements, must satisfy ACT 31E

Appendix A.

It should be noted that a structural system in a higher category (D being

higher than A) must satisfy the requirements specified for the lower categories: A structural frame which forms part of the seismic resisting system

of a Category C building must satisfy all of the frame requirements of ACI

318 Appendix A, including Appendix A.2.1.3.

Sec. 11.2 - REQUIRED STRENGTH

Calculations to determine the strength of structural components and members

are to be based on Ref. II. 1; except, the factored loads and load combinations to resist seismic forces must be in accordance with Sec. 3.7.1 in lieu

of ACI 318 Section 9.2.3. This exception is necessary so that the required

strength for seismic resistance. Sec. 3.7.1, is compatible with the design

forces specified in Chapter 3.

Sec. 11.3. - SEISMIC PERFORMANCE CATEGORY A

Construction qualifying under Category A- as identified in Table 1-A (Chapter

I) may be built with no special detail requirements for earthquake resistance

except for ties around anchor bolts as indicated in Sec. 11.3. "Closely

enclosed*' is intended to mean that the ties should be located within 3 to A

bolt diameters of the bolts.

Longi tudi nal rei nforcement

Transverse reinforcement

Seams

A.3.

A.3.2

Columns

A.A.3

A.8.2
-3-

Sec. 11.4 - SEISMIC PERFORMANCE CATEGORY B A frame used as part of the lateral force resisting system in Category 3

as identified in Table 3-8 is required to have certain details which are intended to help sustain integrity of the frame when subjected to deformation reversals into the nonlinear range of response.

For beam and column framing systems, the reinf orcement details of ACI 318

Appendix A. 3.2 and A. 3. 3 apply for beam components and A. 4.3 and A. 3. 2 apply

for column components.

For slab and column framing systems, the slab component must satisfy the

special EXCEPTION provisigns of Sec. 11.4.1, in lieu of A.3.Z and A. 3. 3.

Columns must satisfy the provisions of A. 4. 3 and A. 3. 2. For slab-column

connections, paragraph (A) provides slab reinforcement through a column to

support the slab gravity load in the unexpected event that a punching

failure occurs. Paragraph(B) specifies a minimum amount for that reinforcement. Concentration of negative moment reinforcement at the column as provided by paragraph (C), is required to create a situation whereby the

total negative moment reinforcement across the entire slab width will yield

simultaneously. Without the heavier concentration of reinf orcement, the

slab region at the column will yield considerably before the outer regions

of the slab, with markedly decreased lateral load stiffness. Paragraph (D)

in effect limits the shear stress caused by gravity loads to a sufficiently

low value so that the slab-column connection will have a ductility ratio of

at least 2. Paragraph (E) ensures that if shear or torsional cracks develop

at the slab edges, properly detailed reinf orcement is present to control

crack i ng.

Slab systems without beams between supports (flat plates) of normal proportions and detailed as specified in Sec. 11.4.1 (EXCEPTION) will not

undergo any significant yield until story drifts greater than these

allowable. (Table 3-C)

Structural (shear) walls of buildings in Category 3' are to be built in

accordance with the general requirements of ACI 318-77.

98
Sec. II .

S

- SEISMIC PERFORMANCE CATEGORY C AND D

In regions of high- seismic risk, the entire building* including the foundation and nonstructural elements* must satisfy aTT of the requirements of

ACI 318 Appendix A»

Appendix & contains special proportioning and reinforcement detailing

requirements which* are currently considered ta be the minimum for producing

a monolithic reinforced concrete structure with adequate proportions and

details ta make it possible for the structure to undergo a series of

oscillations into the inelastic range of response without critical decay* in

strength. The demand for integrity of the structure in the inelastic range

of response is consistent with the rationalization of design forces specified

in Chapter 3*

Field and laboratory experience which has led to the special proportioning

and detailing requirements in ACI 318 Appendix A has been predominantly with

monolithic reinforced concrete building structures. Therefore, the projection of these requirements to other types of reinforced concrete structures,

which may differ in concept or fabrication from monolithic construction,

must be tempered by* relevant physical evidence and analysis. Precast and/or

prestressed elements may be used for* earthquake resistance provided it is

shown that the resulting structure will satisfy the safety and serviceability

(during and after the earthquake) levels provided by monolithic construction.

A detailed explanation of the specific provisions of ACI 318 Appendix A is

contained in the ACI Code Conmentary ta Appendix A.

11.5.2 - FRAMING SYSTEMS

The "toughness 1 * requirement for framing systems not satisfying the requirements. of ACI 318 Appendix A refers to the concern for the- integrity of the

entire lateral-force structure at lateral displacements anticipated for

ground motions corresponding to design intensity. Depending on the energydissipation characteristics of the structural system used, such displacements may have to be more than those for a monolithic reinforced concrete

structure.
-5-

For systems that remain elastic or that have limited special details for

energy dissipation, such as assemblages of precast and/or prestressed

concrete, appropriate R-factors should be used to reflect damping characteristics and energy dissipation. For example, R ^ l3? can be used for

systems responding primarily elastically to account for damping, and R ^ up

to ZH. may be used for walls with properly distributed web reinforcement that

will assure good distribution of cracks and thus provide a degree of energy

dissipation.

11. S. 3 - FRAME COMPONENTS NOT PART OF SEISMIC RESISTING SYSTEM

In the event of a strong earthquake, it is assumed that the structure will

undergo reversals of large lateral displacements. It is essential that all

structural components be able to accommodate these displacements without

critical loss of strength. Even if a particular frame has been designed to

support only gravity loads and is not intended to be part of the structural

system resisting seismic forces, it must sustain the gravity loads after

having been subjected to approximately the same displacements as the seismic resisting system. Therefore, all frame components (which are not

designed to resist seismic forces) in Categories C and D buildings are required to have, as a minimum, the details specified in ACI 318 Appendix

A. 8. Furthermore, if calculations show that frame components (which are not

part of the structural system resisting seismic forces) will have to yield

in order to accommodate the calculated displacements of the seismic resisting system, those components must have special transverse reinforcement as specified for Special Moment Frames.

100
OTHER REVISIONS TO INCORPORATE NEW CHAPTER II - (REINFORCED CONCRETE)

INTO ATC 3-OS •

1. SEC. 1.5.3(E) - PACE ZZ

Changer reference "ACL 313-71"' to "ACI 3IE-77 ,r

2. SEC. 2.1 DEFINITIONS - PAGE 37

Revise the following defi ni tf one:

CROSS-TIE is a continuous bar» No. 3 or larger in size, having a 135-degree hook with a ten-diameter extension at one end and a

90-degree hook with a six-diameter extension at the other end. The

hooks shall engage hoop bars and be secured to longitudinal bars.

HOG? is a closed tie or continuously wound tfe Cnotr smaller than

No. 3 in size) the ends of which have 135-degree hooks with tendiameter extensions,. that encloses the longitudinal reinforcement.

JOINT,, LATERALLY CONFINED is a joint where members frame into

all four sides of the joint and- where each member width is at

least three-fourths the column width.

In definition of ORDINARY MOMENT FRAME change reference "Sec. 11.6"

to "Sec. LI .4. 1"1 .

In definition of SPECIAL MOMENT FRAME change reference "Sec. 11.7"

to "Sec. LL.S."

Add the following definitions:

BOUNDARY ELEMENTS are portions along the edges of walls and diaphragms strengthened by longitudinal and transverse rei nf orcement

Boundary elements da not necessarily require an increase in the

thickness of the wall or diaphragm. Edges of openings within walls

and diaphragms, may also have to be provided with boundary elements.

COLLECTOR ELEMENTS are elements which serve to transmit the inertia

forces within the diaphragms to elements of the 1 ateral -force resisting systems
3. ScC. 2.2 SYMBOuS - PAGE 40

Delate symbols A ch , A

sh>

fyh> h ;

, P

p

, s„

Add the following new symbols and definitions:

b Q * perimeter of critical section for slabs, Sec. 11.4.1

d = distance from extreme compression fiber to centroid of

tension reinforcement. Sec. 11.4.1

f^ = specified compressive strength of concrete, psi

fy = specified yield strength of r ei n f ore emen t , psi

h = overall thickness of member, Sec.- 11.4.1

V = factored shear force due to gravity loading, Sec. 11.4.1.

4. TABLE 3-8 - PAGE 52

Revise footnote (4) to read as follows:

i

'As defined in Sec. 11.5

5 . SEC . 7.5.3(C) - PAGE 75

Change reference "Sec. 11.6.2" to "Ref. 11.1, ACI 313 Appendix

A . 3 . 2

5. SEC. 12.5.1(D) - PAGE 114

Change paragraph (1) to read as follows:

"1. Ref. 11.1, ACI 313 Appendix A. 5. 3 when of reinforced

concrete or Chapter 10 when of structural steel."

102
REASON:: Chapter 11 is revised to reference the nationally recognized desigrr

standard, ANSI/ACI 318-77 “Building Code Requirements for Reinforced

Concrete" for proportioning and detailing concrete structures. Seismic

resistance is considered in the overall development of the ACI 318 Standards

including Appendix A on special provisions for earthquake resistance.

Existing Chapter II originated from an early draft of a proposal by an ACI 318 Seismic Subcommittee to update the ACI 318 seismic design provisions. The current draft of Appendix A (19- March 1980) nov* before the

main Committee 318 has undergone numerous revisions. FinaT Comnittee actionand full ACI consensus balloting is in process.

The revised Chapter 11 is formulated to correlate appropriate ACI 318

design provisions with the four ATC seismic performance categories by

reference only without the need for ATC to duplicate the wording already

contained irr the ACI documents

103
ATTACHMENT C

MEMO TO:

FROM:

RE:

According Co the request formulated by you through Mr. Fintel's letter

of May 29, 1980, I met with Mr. Fintel and Mr. Neville, ACI Committee 318

Secretary, on Friday, May 3°! 1980, at 5 p.m. in 750 Davis Hall, University

of California, Berkeley, to discuss the above technical implications. As

requested in the same letter, the following are my written comments. It

should be noted that these comments are of a preliminary nature as I did not

have time to go through the document as thoroughly as I would like since it was only delivered to me on the evening of Wednesday, May 28, 1980. For

example, the provisions regarding joints of frames (Section A. 6 of the new Appendix A) differs considerably from the ATC provisions on joints’

(Section 11.7.3). To comment properly on the implications of this change

would require the technical background material (data) on which the changes

have been based and the time to study it. I did not have either.

I. CHANGES NEEDED IN CHAPTER 11 . Page 1. Sec. 11.1 should read: Refs. 11.1:

[1] ANSI/ACI 318-77 "Building Code Requirements For Reinforced Concrete"

but excluding Appendix A ; and

[2] New proposed Appendix A - Requirements for Reinforced Concrete Building

Structures Resisting Forces induced by Earthquake Motions, 19 March,

1980.

Page 2. Sec. 11.4.1 should read "Where Ordinary Moment-Resisting Frame

Systems are used for the seismic-resisting system, frame components

(beams, columns, and their joints ) shall be proportioned to satisfy,

in addition to the requirements of Chapters 1 through 17 of Ref. [l]

(ANSI/ACI 318-77), the provisions A. 3. 2, A. 3. 3, A. 4. 3 and A. 8. 2 of

Ref. [2]. [NEW APPENDIX A] with the following additions and exceptions:

1. A. 3. 2.1 Last sentence should read "At least two No. 5 or larger

bars shall be provided continuously both top and bottom."

2. A new section, A. 3. 2. 5, should be added in the new Appendix A. This section A. 3.2.5 should contain the provisions required in ATC

Sec. 11.6.1, paragraphs 4 and 5, i.e., "A flexural member framing

. . . yield stress." "Longitudinal reinforcement . . . for the

reinforcement.

3. A. 4.3.2 The first sentence should read "Lap splices are permitted

only within the center half of the soan and shall be proportioned as tension splices . Welded ..."

E. Cohen, Chairman of Technical Committee 4: Concrete Review

and Refinement of ATC 3-06, and

E. Pfrang, Chief of Structures and Material Division, NEL

V. Bertero, Representative of ATC

Technical Implications of Incorporating ACI 318-77 and New

Appendix A by Reference into ATC 3-06
Page 3. Sec* 11.4.1 (E) . Add ,r

. . . considering the probability of full

reversals of the sense of the torsional moments (torsional resistance

combined with flexural under reversal moments deteriorate significantly

when conventional web reinforcement, is used.) ."

Page 3. Sec. 11.5 . 1. Add at the end of this section . . A. 2.5, except

that ASTM. 613 Grade 60 reinforcement should not be used when welding,

of this reinforcement is used.’” (See my comments of Feb. 11,. 1980.)

Page 3. Sec. 11.5.2. First paragraph, last line should be changed as follows:

" . provisions of Ref. [2], i.e. , new proposed Appendix A. ,r' Second paragraph, second line , same change as above. (The same change

should be made throughout the whole proposed draft.)

Ih; the first paragraph it is necessary to clarify that ATC refers to

"braced frames" while A. 5 refers to trusses. This inconsistency should

be removed. I recommend that, rather than incorporating the

exceptions here, a new Section 11.6.1 be added on page 4. as it was

recommended be done on the May 5,. 1980, ballot, 1. e. , a new Section

11.9 of the ATC document.

Page 3. Sec. IX. 5.1* Should read "Structural walls; shall have vertical

boundary members which shall be proportioned ta satisfy the provision

A. 5.

3

of the New Appendix. Vertical boundary . . . can be developed.

If lap splices are needed ar these levels, they shall be proportioned

as tension splices. "

Page 4. Sec. 11.5.3 . First paragraph (top of page) should be changed to

read "Structural diaphragms shall be provided with boundary or edge

elements at any section where tensile axial,forces can be developed

across the entire diaphragm section. These boundary elements shall

be designed as required by A. 5. 3. If lap splices are needed at these

sections, they shall be proportioned as tension splices.'*

Page 4. Sec. 11.5.4. This section should read as follows : "STRUCTURAL

COMPONENTS NOT PART OF THE SEISMIC-RESISTING SYSTEM.

All structural components assumed to be not part of the seismic—

resisting system shall comply with Sec. 3.3.4(C) and shall conform

with the provisions of Sec. A. 8 of the new Appendix A except for

Sec. A. 5.1. This Sec. A. 8.1 does not apply to the investigation of the

deformation compatibility of these components; Sec. 3.3.4(C) is the one

that should be used. The design of such components shall satisfy the mini mum reinforcement

requirements specified in Chapters 7, 10 and 11 of ACI 313 and

Secs. A. 3. 2.1 and A. 5. 2.1. If nonlinear behavior is required in such

components to comply with Sec. 3.3.4(C), the critical portions shall

ber provided with, special transverse reinforcement in accordance with

provisions. A.3. 3 and/or A. 4. 4. of the new Appendix. A.

II. CHANGES NEEDED IN THE NEW APPENDIX A TO MAKE IT CONSISTENT WITH THE

ATC 3-06 PROVISIONS

Page 1, A.O Notation

h — should read h"

Note that some notations are different from those of ATC. For example,

h." is hc in ATC, S is in ATC, and Pj is P^ in ATC.^ Therefore it is
3

recommended the notations be reviewed thoroughly for Appendix A and

ATC to assure their consistency.

Page 2. A.Definitions

There are discrepancies in some of the definitions used by ATC and

Appendix A. For example, the definitions of cross-tie do not agree;

also Structural Wall vs. Shear Wall, Structural Diaphragms vs. Diaphragm,

Structural Trusses vs. Braced Frames, etc. Therefore it is recommended

that the definitions in the two documents be thoroughly reviewed and

the discrepancies removed.

Page 3. Definition of Anchorage Length for a Bar with a Standard Hook . This definition does not agree with results of laboratory experiments

and field inspection of damages. The effective length of anchorage

cannot be counted from the critical section (where the strength of the

bar which is located at the faces of the joint is to be developed) . The

concrete of the joint that is not confined (which has the shape of a cone) is not effective in supplying anchorage. This definition should

be changed to consider the cone of unconfined concrete.

Page 3. Sec. A. 2. 1.1 This provision should be clarified. Limitations on

the amount of energy dissipation that can be used, or would be acceptable or tolerable, should be specified. Can these provisions be used when

the nonlinear response of the structure would demand " displacement

ductility " of the order of 10, 20, 30, 40, 50, 60 . . . ? As is it

written now, it is too vague and could lead to misuse of the provisions.

Page 4. Sec. A. 2.1.

3

.- Are the requirements for Zone 2 as defined by the

UBC 1979 (I assume that it is the 1979 edition of the UBC to which

this Appendix A refers) compatible with the requirements for good seismic

performance of buildings assigned to Category 3? This should be

discussed and clarified.

Page 4. Sec. A. 2.1.4 . Are the requirements of the UBC 1979 for regions

following Zones 3 and 4 sufficient to guarantee good seismic

performance for buildings assigned to Categories C and D? This should

be discussed and clarified.

Page 5. Sec. A.2.3.2 . Does <J> * 0.5 apply only to the computation of the

strength of the element under concentric axial force, or does it apply

also to the combined axial force and bending moment, i.e., to the whole

N-M Interaction diagram for N > A fl/10 (as it was established in ATC)?

g

Page 5. Sec. A. 2.5.1 . A flag regarding the weldability of ASTM A615

Grade 60 should be inserted. Furthermore, it should be noted that,

while ATC required that in tests the actual yield stress not exceed

the specified yield stress by more than 21,000 psi (18,000 + 3,000),

the new Appendix A allows 22,000 psi (18,000 + 4,000). I do not have

the background material that has been used to justify this change.

Note that the higher the value that is accepted, the less meaningful

become the computations based on specified yielding (quality control

of material is a must if we want to improve seismic-resistant design

and construction)

106
Page 5. Sec. A.3.2.1 . The last sentence should read "At least two No. 5

or larger bars shall - .

Page 8. Sec. A. 4,2.

, This section should be modified to read as follows:

"At any joint . . . the suit of the flexural strengths of the columns

calculated considering the critical combination with the possiblecritical axial forces (whole range of possible axial forces acting in

combination with the moments should be considered) shall exceed the sum

of the moments at the columns obtained from the equilibrium at the joint

when it is considered that the beams framing into that joint in the plane

of the frame under consideration reached their flexural strength. The

flexural strenghs shall be *

•'*

Page 8., Sec. A. 4. 2. 2. This section should, be deleted or completely modified.

Reasons : It allows the design of weak column-strong beam frames that

can lead to soft story. Since the time this philosophy was proposed, I

have opposed it because it leads to an unsound seismic-resistant system.

It is. not that the columns, cannot be made ductile, but rather chat the

formation of a soft story leads to such large demands of energy dissipation capacity (ductility displacement demands) from the columns that

these demands cannot be supplied. Therefore, it should be made clear

that, except for frames of more than 2 stories , attempts should be made

to prevent the development of soft stories. Any provision that will

allow the formation of such soft stories should be deleted. Following

this basic seismic-resistant guideline, if this section is not deleted

it should be modified as follows: "A. 4. 2. 2 — At any story level of

a frame, a certain number of col:mmis could be allowed to not satisfy

Sec. A. 4. 2.1 provided, that the remaining columns in that story of the

frame complying with the requirements of Sec. A. 4.2.1 are capable of

elastically resisting, the. entire stqry shear at that level, accounting

for the altered rigidities and tors^n resulting from the omission of

elastic action of the nonconforming columns. In addition, the nonconforming columns shall be provided with transverse reinforcement as specified in. Sec. A. 4. 4- over their full height if the factored axial

force in. those columns exceeds: (A^fJ/lO).'*

Page 9. Sec. A. 4. 3.2. At the end of the first sentence should be added

". . . span, and shall be proportioned as tension splices . Welded . . ."

Page 9. Sec. A. 4.4. 1. In the list of notations, the following corrections

should be made: Replace h with h", also in the definition of As . If this notation is used, the notation, in AIC, pp. 40-43, should " be modified also.

Page 10. Sec. A.4.4. 1 Item (4) . This item should be deleted as it can

lead to unsound seismic-resistant practice by allowing columns without

- ductility since no confinement is required. Confinement of the concrete

core is not only required for developing extra strength in the

confined concrete required to compensate for the loss of the cover, but

also- to increase the deformation capacity (ductility) . It is well

documented through experiments and field inspection of earthquake

damages that the cover of the columns at the joints will . pull out and

spall, reducing the effective area of concrete available to resist the

internal forces to an effective- cross-sectional area even smaller than
5

that of the confined core. Application of the requirements of this

Appendix does not guarantee that the column will remain elastic,

because of the effects of strain hardening of beam reinforcement and

the effects of higher modes of vibration. It is for these same reasons

that I strongly support the recommendation in the present UBC (1979)

that requires that shear strength of columns be computed based on the

column core area. The application of the provision of this section together with Sec. A. 4.2, can lead to disaster. Therefore, I strongly recommend the deletion of

these two sections or their modification.

PagelQ.' Sec. A. 4. 4.

. At the end of this provision should be added "Tor

members for which the calculated point of contraflexure is not

within the middle half of their span, the special transverse reinforcement specified above should be provided over the full height of the

members." (See ATC 11. 7.2(B) 5 (p. 106).

Page 11. Sec. A. 5. 2.

3

. What is understood by "elements of structural

diaphragms" should be clarified. Are these Collector Elements and/or • Boundary Elements ? This should be specified. I also consider it

necessary to add after the fifth line of this provision the following

requirement: ". . . 0.13 f£, provided that no tensile forces or significant shear forces are developed simultaneously in these elements.

If these elements could be subjected to significant shear forces

(e.g., vu

* 3/f^T) and to tensile forces , they shall have special trans- verse reinforcement as specified in Sec. A. 4.4 over the total length of

the element.

Page 11. Sec. A. 5. 3.1. The requirement should be added for the case where

tensile axial forces can be developed (see 11.5.3).

Page 13. Sec. A. 6. 3.1 . This whole provision needs clarification.

(1) It is suggested that the definition of Aj be given in the notation.

Sec. A.0, or directly in this section rather than giving it in

Sec. A. 6. 3. 2. Furthermore, the definition given i3 not clear. What

does "the design shear commentary force" mean? Should this read

"shear generating force"? Should Aj be the total area, the effective

area bd, or the confined core area?

(2) In lines 2 and 5 the symbol ^ is missing; they should read

"coefficient

Personally, I question the soundness of some of these provisions (see

my general comments about weaknesses in the ATC and Appendix A

provisions)

Page 13. Sec. A. 6.4 . This section needs clarification . The value of $

is not given in this section. The reader has to go to the Commentary

to find that 1 has been defined in Sec. A. 2. 3. 3. No indication is

given of the location of the critical section for computing the

development lengths Z ah and 2 as . I personally would like to see explicitly in the equation for the estimation of the anchorage length

the 1.25 fy. This is a new section which appears able to give quite

different results than those obtained according to the recommendations

108
of Committee- 352 (ACL Journal/July 1976) , depending on where Che

critical section for anchorage is taken. I did not have the background

material at hand to study this new section, but it appears to me these

provisions do not properly consider the effects of deformation

reversals to which the anchored bar can be subjected. The reasons

follow.

(1) The commentary refers ta data presented by ACI Committee 408 which,

does not include the effect of deformation, reversals. Apparently the

only attempt to account for this effect has been to specify a

reduction factor of $ * 0.65 rather than the 4> * 0.80 recommended by

Committee 408. This is again a misuse of the original intent of the

reduction factor <£. (2) No indication is given where the critical section for anchorage

should be located. The research I have conducted clearly shows that

there is a core of unconfined concrete ^yhose depth depends on cover

(shell concrete) and spacing of reinforcement in the joint

core] which is ineffective in developing the reinforcement. Thus it

appears to me that, if designers assume that the critical section is

at the face of the joint, the application of this provision A. 6.4

can lead to unconservative anchorage, particularly in the case of

narrow columns . Therefore at present I cannot support or recomment the inclusion of

this provision.

Page 14. Sec. A. 7. 1.2. Although this-, section is similar to that in ATC

11.7.2(C), p. 106, I believe it is incorrect. The nominal moment

strengths should be calculated for the critical axial force in the

possible range of axial forces. In the selection of this critical

axial force, proper N vs. M interaction diagram and the variation of

the shear strength with N should be considered.

Page 14. Sec. A. 7.1.3 . This section cannot be used in conjunction with the

ATC document. The design shear force shall be obtained from the

factored loads and combinations of Sec. 3.7 of the ATC document, and

not from Sec. 9.2 of ACI 318.

Page 15. Sec. A. 7. 3.1. The application of equation (A-5) to barbell and

flanged wall cross sections is not clear because, according to the

definitions of Ac and p a, only the areas of concrete and steel bounded

by web thickness and height of section should be considered. It appears

to me that all the steel located in the edge member of the barbell

shape should be considered. Similarly, all the steel located in the

flange effective width of the flanged cross section should be considered.

Page 17. Sec. A. 9. 2. 2. Equation (A-6) does not agree with equation 11-6

of ATC. Note that in (A-6) the reduction factor <p is missing. This

appears, contrary to the main philosophy of the whole ACI 318—77

document in which Required Strength < <f> [Nominal Strength]. Furthermore

,

notation for the factored compressive force at the construction joint,

i.e. , Pj

,

in ATC is* PQ

. Therefore, a change should be made either in

Sec. 2.2 Symbols of ATC or in A.O and A. 9.2 of the new Appendix A.

Note the inconsistency in A. 9. 2 regarding the notation of this force.

In equation (A-6) this force is designated as Pj but three lines

below this equation (A-6) it is defined as Pu

.
f

110
Summary of Committee 4- Action:

on

July 16-17, 1980

Those members who* were present are as follower

Name

Neil Hawkins (Acting Chairman)

Daniel Jenny

Loring A- Wyllie, JrJames Prendergast

S. K- Ghosh (alternate)

James Lefter

Richard Marshall (Secretary)

Kyle Woodward (Secretary)

Representing

Post.—Tensioning Institute

Prestressed Concrete Institute

Structural Engineers Association

of California

Interagency Committee on Seismic Safey

in Construction.

Portland Cement Association

Building Seismic Safety Council

National Bureau of Standards

National Bureau of Standards

At the request of Mr. Cohen, Committee Chairman who could not be present,

Mr. Hawkins served as Acting Chairman of Committee 4 and served as the

Committee Spokesman during the Joint Committee meeting.

The changes to ATC3-06 recommended by Committee 4- were presented to the

Joint Committee by the Acting Chairman July 16* There was considerable

reaction by the Joint Committee to several of the proposed changes especially

those pertaining to the issue of a revised AIC3-06 Chapter 11 referencing

the draft version of ACI 318 Appendix A.

A meeting of those committee members present (5 out of 8 voting members)

was called in the afternoon of July 16 to discuss the implications of

the Joint Committee's reaction to- the revised Chapter 11. The committee

agreed that the single ballot item including so many proposed changes was

a handicap to the adoption of particular revisions unanimously endorsed by

the committee. It was agreed by the committee that if the ballot item on

the all inclusive revised Chapter 11 was defeated by the Joint Committee,

then Committee 4- would request that the Building Seismic Safety Council

(BSSC) permit a restructuring of the ballot item and resubmission on the

BSSC ballot in the Fall of this year. The restructuring would involve

the separation of each individual proposed revision included in the

overall ballot item as an individual ballot Item.

i
The actions of the Joint Committee on the following day (July 17), however,

permitted Committee 4 to submit additional items to the Joint Committee

for inclusion on the Joint Committee's letter ballot. The instructions

to the committee were such that the additional items had to have been

directly discussed and balloted by Committee 4 in its previous meetings.

The acting chairman, upon discussion with the chairman, directed the

secretaries to prepare the additional ballot items. The ballot items

addressed the particular issues included in the overall ballot item

covering the adoption of the revised Chapter 11. It was felt that the

votes on each of the separable issues (e.g. flat slabs) would be helpful

to the BSSC members in ascertaining the level of support for the proposed

revisions. Such information would not be present from the vote total on

the single overall ballot item.

The additional ballot items were prepared and submitted to the Acting

Chairman and Mr. Sharpe of ATC for comments. After review by each, the

items were sent to the Joint Committee for balloting. See the attachments

for the additional letter ballot items submitted to the Joint Committee.

112
JOINT BALLOT NUMBER: W3

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSES CHANGE

I TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMB-.?. : _AI

ATC—3—06 SECTION REFERENCE: II. I

Alter Section. 11.1 such that, the reference reads as follows:

"Reference 11.1 Building Code Requirements for Reinforced Concrete,

American Concrete Institute (ACI 318—77) excluding Appendix A and

replacing Section. 9.2*3 with Section 3.7.1 of this document."

Final Ballot: 1_ Yes

0 No

4 Abstain

3 Did Not Vote

COMMENTS:

This ballot item updates the reference to include the latest version of the

ACI Building Code for Concrete (ACT 318—77). The replacement of Section 9.2.3

in the ACI Code by ATC 3-06 Section 3.7.1 reminds the designer that the combination of load effects used in ATC 3-06 is different than that in ACI 318-77.

This ballot item appeared on the first of the two committee letter ballots.

The final wording was modified so as to read exactly as revised and approved

by the ATC representative. The abstentions were the result of the ballot

item being superseded by the committee ballot item Y1 ( Joint Ballot Number

4/12). The committee was in full agreement that the reference should be

updated, but the issue of adopting Appendix A overshadowed that intent.

i
JOINT BALLOT NUMBER: 4/14

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: i/4. Concrete COMMITTEE 3ALL0T NUMBER: A2

ATC-3-06 SECTION REFERENCE: 11.2

Alter Section 11.2, first paragraph, second sentence by inserting "Precast and/or

prestressed" in place of "Precast."

Final Ballot: _5_

_0

_0

3

Yes

No

Abstain

Did Not Vote

COMMENTS:

The intent of the ballot item is to expressly include prestressed concrete as

a permissible building material. Initially, the ATC representative was opposed

to mention of prestressed construction without any accompanying criteria for

its proper design. However, with the introduction of the material contained

in committee ballot item M9 (Joint Ballot Number 4/15), Che ATC representative

approved this change to the existing ATC 3-06 Chapter 11.

114
JOINT BALLOT NUMBER: 4/15

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: H, Concrete COMMITTEE BALLOT NUMBER:

ATC-3-06 SECTION, REFERENCE: New Section 11.9

Add Che following: as a. new SecciotL in Chapter 11 immediately following

Section 11.8:

Section 11.9- STRUCTURES COMPRISED OF PRECAST

AND/OR PRESTRESSED CONCRETE

SUBASSEMBLAGES

The provisions of this Section- apply* to- buildings constructed with precast

and/or prestressed concrete elements not conforming to the detailing provisions

given elsewhere in this Chapter for cast-in-place concrete.

,11.9.1 LINEAR ELASTIC DESIGNStructures with assemblages of precast and/or prestressed concrete components

furnishing lateral resistance- against seismic forces shall be designed to

elastically resist equivalent lateral forces equal to those specified in this

document with an R value of 1.0-

COMMENTS:

OVER

The intent of this change to the existing ATC 3-06 Chapter 11 is to provide a clear mechanism- by which a designer can use a precast and/or prestressed construction within the framework of the ATC 3-06 provisions. Section 11.9.1

presents a method by which a structure can be designed to resist elastically

earthquake forces and which is likely to be an economically viable solution

I for low-rise construction only (< 3 stories) . Section 11.2 presents a method

which follows the more conventional approach of permitting inelastic action

providing the system offers the same behavioral characteristics (e.g. strength,

stiffness, damping, etc.) as comparable monolithic cast-in-place ordinarily

reinforced concrete construction.

The ATC representative reviewed and approved of the proposed ballot item. There

were two reservations of a technical nature expressed by members of the committee.

The first concerned the use of an R value of 1.0 in the Linear Elastic Design

section. The committee member felt that to be overly conservative and suggested

[ a value of R * 1.5. The other reservation accompanied the "No" vote and was

an objection to the lack of a provision limiting the height and/or the number

of stories.

|

‘

|

i
11.9.2 "DUCTILE" CONSTRUCTION

Energy dissipating lateral load resisting systems comprised of precast

and/or prestressed concrete components shall be permitted provided satisfactory evidence can be shown in the form of experiments, testing, and

analysis based upon established engineering principles that the resulting

construction complies with the requirements of Sections 3.6 and 3.7 and

this Chapter, and that they offer the same strength, stiffness, stability,

durability, cu. aping- energy absorption, and energy dissipation capabilities

(ductility) as monolithic cast-in-place ordinarily reinforced concrete

construction.

Final Ballo-t: 7 Yes

1 No

0 Abstain

0 Did Not Vote

116
JOINT BALLOT NUMBER: 4/16

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4 * Concrete COMMITTEE BALLOT NUMBER: _M1

ATC-3-06 SECTION REFERENCE: U-5.

Alter Section 11*5.1, third paragraph such that it reads as follows:

’’Reinforcement resisting earthquake-induced flexural and axial

forces in frame elements and in wall boundary members shall comply

with ASTM A706.- ASTM A615 Grades- 40 and 60 reinforcement may be

used in these elements if (a) the actual yield 3tres« based on

mill tests does not exceed the specified yield stress by more

than 18 r 000 psf (retests shall not exceed this value by more

than an additional 4,000 psi) and (b) the ratio of the actual

ultimate tensile stress to the actual tensile yield stress isnot less than 1.25.”"

Final Ballot: 3_ Yes

o No

0 Abstain

0 Did Not Vote

COMMENTS:

This change replaces the current wording in ATC 3-06 Chapter 11 with the

wording included in the latest draft version of the ACT Committee 318

Appendix A (Requirements for Reinforced Concrete Building Structures

Resisting Forces Induced by Earthquake Motions) . The committee was in

complete agreement that the Appendix A wording was more desirable than

the existing wording* The ATC representative objected to this change

because it did not sufficiently emphasize that if ASTM A615 Grade 60 steel

is used careful attention must be given to the metallurgy of the steel

and the welding practice.
JOINT BALLOT NUMBER: -ill

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: Concrete COMMITTEE BALLOT NUMBER: M3

AT C- 3-06 SECTION REFERENCE: ^--3.2

Alter Section 11. S. 2 by delating in its entirety the third paragraph and reolace

it with the following:

"A cast-in-place topping on a precast floor system may serve as the

diaphragm provided the cast-in-placa topping is proportioned and

detailed to resist the design shear forces under the effects of any

loading combination (which could induce tensile or compressive

stresses simultaneously to the shear forces) . For buildings in

performance Categories C and D, alternate techniques based on the use of untoppec precast and/or prestressed components of concrete

floor systems may be used only if it can be shown by experiments

and analysis based on established engineering principles that they

will offer the same shear strength, stiffness, stability, durability,

and sufficient energy dissipation capacity, as a monolithic castin-place ordinarily reinforced concrete diaphragm."

Final Ballot: 3 Yes 0 Abstain

0 No 0 Did Not Vote

COMMENTS

The ballot item modifies the existing complete restriction against the use of

untopped precast and/or prestressed components of floor systems as diaphragms.

Instead, the change would permit such systems to be considered as diaphragms if

it can be shown that the untopped system provides behavior comparable to that

of a monolithic cast-in-place ordinarily reinforced concrete diaphragm.

The ballot item was reviewed by the ATC representative who supported its

adoption. One committee member, however, expressed reservations about the

practicality of verification and the lack of a commentary section giving a clear explanation of the provision's intent.
JOINT BALLOT NUMBER: 4/18

REVIEW AND REFINEMENT OF TENTATIVE. SEISMIC PROVISIONS

PROPOSED CHANGE

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMBER: M4

ATC-3-06 SECTION REFERENCE: 11.6.1

Four part item

a) Alter Section 11.6.1, second paragraph, second sentence so as to read:

"At. least two No. 5 or larger bars shall be provided continuously both

top and bottom, except in slabs.,'r

b) Alter Section 11.6.1, sixth: paragraph, first sentence so as to read:

"Web reinforcement perpendicular to the longitudinal reinforcement

shall be provided throughout the- length of all members- except slabs ."

c) Alter Section 11.6.1, seventh paragraph , first sentence so as to read:

"Within a distance equal ta twice the effective depth from the end of

all members except slabs,, the amount. .. from the end of the member."

OVER

COMMENTS:

The ballot item introduces design provisions for flat slab construction. Such

provisions are not present in the existing ATC 3-06 Chapter 11 and it was felt

by the committee that such an omission would not be representative of the current

building practice in many areas of the nation.

The ATC representative reviewed and approved of the provisions included in this

ballot item.

While approving this item, committee members expressed concern about the use of

unfactored gravity loads in the proposed equation 11-2. The use of unfactorad

loads is inconsistent with all other sections of Chapter 11 where factored loads

are used.
Four part item (continued)

d) Alter Section 11.6.1 by adding the following paragraph after the seventh

paragraph

"Slabs without beams and supported on columns may be used for ordinary

moment frames provided those slabs satisfy the requirements of Chapter 13

of Preference 11.1 and this Section. Bottom bar reinforcement, Ag , shall

be provided continuous through or anchored within, a column and not less

than that given by the following formula:

Al

2. (V-Vp)

0.35fy ( 11- 2 )

where V is the shear force transferred to column due to unfactored gravity

loads and Vp is the sum of the vertical components of the forces in any

prestressing tendons passing through or anchored within the column. At

least two No. 4 or larger bars shall be provided continuous through or anchored within the column in both directions and both top and bottom.

In slabs without beams, column strip negative moment reinforcement shall

be distributed so that at least 60 percent of the required reinforcement

is concentrated within lines one and one-half times the slab thickness

either side of the column. The shear stress, v, on a critical section

located half the effective depth of the slab from t he column perimeter,

and caused by the shear force V shall not exceed 2vfl. If there is no spandrel beam at the discontinuous edge of a slab, reinforcement within

four slab thicknesses either side of a column face and adjacent to the

edge shall be detailed so that it can act effectively as torsion reinforcement considering the possibility of full reversals of the sense

of the torsional moments. If the torsional strength of the spandrel

beam framing into a column exceeds the flexural strength of the slab

at its connection with the beam for the adjacent half panel width, all

shear shall be assumed transferred to the column via the beam."

r ana- 3auUot

3_ Yes

0_ No

0 Abstain

0 Did Not Vote

120
JOINT BALLOT NUMBER

4/19

REVIEW AND REFINEMENT OF TENTATIVE SEISMIC PROVISIONS

PROPOSED CHANGE

r?

TECHNICAL COMMITTEE: #4, Concrete COMMITTEE BALLOT NUMBER >15

ATC—3-06 SECTION REFERENCE: Commentary Cll.5.1

Alter Commentary Section 11-5.1,. fifth, paragraph by including the following

sentence at the end of the paragraph:

"The flat plates of flat plate frames of normal proportions and

detailed as specified in. Section 11.6 will not undergo any

significant yield until story drifts greater than those allowable

(Table 3-C)

Final Ballot: 8_ Yes

Q No

Q Abstain

0 Did Not Vote

COMMENTS

This change to the Commentary emphasizes that flat plate frames are considerably

more flexible than other framing systems.

The ATC representative reviewed and approved the proposed ballot item which

incorporates his suggested, revisions. There was one reservation expressed by

a committee member. Ee felt that while what was stated in the ballot Item

was true for most "normal proportions" there were exceptions and suggested

that the word "will" be replaced by "should."
3.2 Committee Roster

American Concrete Institute

Edward Cohen (Chairman)

Ammann & Whitney, Consulting Engineers

Two World Trade Center

New York., New York 10048

Phone: 212-938-8267

American Society of Civil Engineers

Eugene P. Holland

President

Coder-Tavlor Assocs., Inc.' 500 Greenbay Road

Kenilworth, Illinois 60043

Phone: 312-441-4200

Concrete Reinforcing Steel Institute

Joseph G. Manning

Regional Director

Concrete Reinforcing Steel Institute

Western Region

1499 Bayshore Highway

Suite 113

Burlingame, California 94010

Phone: 415-697-1437

Interagency Committee on Seismic Safety in Construction

James D. Prendergast

U.S. Army - ?.0. Bex 4005

Construction Engineering Research Laboratory

Champaign, Illinois 61820

Phone: 217-352-6511 Ext. 242

Portland Cement Association

Mark Pint el

Portland Cement Association

5420 Old Orchard Road

Skokie, Illinois 60077

Phone: 312-966-6200

Alternate: Gene Corley

(same address as Fintel)

(representative on Committee 2: Structural Design) - Fintel

122
Post-Tensioning Institute

Neil Hawkins<

Professor and Chairman;

Department of Civil Engineering.

University of Washington

201 More Hall FX-10

Seattle, Washington 98195

Phone:' 206-543-2575

Prestressed Concrete Institute

David A. Sheppard Alternate: Daniel P. Jenny

California Marketing Director

Prestressed Concrete Institute

1350 Del Rio Court

Concord, California 94518

Phone: 415-957-1327

Technical Director

Prestressed Concrete Institute

20 North Wacker Drive

Chicago, Illinois 60606

Phone: 312-346-4071

Structural Engineers Association of California

Loring A. Wyllie, Jr.

H. J. Degenkolb Associates

350 Sansome Street

San Francisco, California 94104

Phone: 415-392-6952

Applied Technology Council

V. V. Bertero

Professor of Civil Engineering

Department of Civil Engineering

783 Davis Hall

University of California

Berkeley, California 94720

Phone: 415-642-3655

3uilding Seismic Safety Council

James Lefter

Director, Civil Engineering Service (085)

Lafayette Building, Room 507

811 Vermont Avenue, NW

Washington, D.C. 20420

Phone: 202-389-2864

123
National Bureau of Standards

Richard D. Marshall and Kyle Woodward

Secretariat

Committee 4, Concrete

National Bureau of Standards

Room B168 , Building 226

Washington, D.C. 20234

Phone: 301-921-3471 (Marshall)

301-921-2885 (Woodward)
3.3 Selected Committee Correspondence and Applied Technology Council Comments

I. Letter from Mr. Sheppard to Committee 4* December 21 * 1979 - 4 pages

2- Letter from Mr. Firrtel to Sec. Committee 4* January 8* 1980 - 13 pages

3. Letter from Mr. Fore! I to Sec. Committee 2* January 1 1 * 1980 - 2 pages4. Latter from. Mr. Bertero- to Sec. Committee 4> January 31,. 1980 - 9 pages

5. Letter from Mr. Manning to Committee 4* January 31* 1980 - 5 pages

6. Mr. Bertero’ s comments on- revisions proposed by Mr. Manning*

February 1

1 * 1980 - 2 pages

7. Letter from Mr. Cohere to Sec. Committee 4* February 1 I* 1980 — I page

8. Letter from Mr. Hawkins to Sec. Committee 4, February 26, 1980 - 16 pages

9. Letter from Mr. Sheppard to Committee 4* March 25* 1980 - 2 pages

10. Mr. Bertero f s comments ore revisions proposed by Mr. Hawkins*

April 7* 1980 —4 pages

II. Letter from Mr. Sheppard to Committee 4-* April 2* 1980 - 4 pages

.12. Memorandum from Mr. 8ertero to Committee 4, June 2, 1980 - 2 pages

Memorandum from Mr. Bertero to Mr. Cohen and Mr. Pfrang (undateddistributed to Cormiittee 4 on June 4, 1980) - 7 pages

13 .
REPLY TO:

1350 OEL RIO COURT

CONCORO. CALIFORNIA 94 5 1 5 TELEPHONE: 4 1 5 / 957- 1 327

F>

r-P

AMCH/rfCTUMAi Lr r

smucTu*Ai /

i — u prestressed concrete institute•

20 NORTH WACKER 0RIV6 / CHICAGO. ILLINOIS SOSOS

TELEPHONE 312 / 346-4071

December 21 , 1979

TO: Dan Jenny

Edward Cohen

Eugene D. Holland ' Joe Manning

Jim Prendergast Li

MarkFintel

Gene Corley co Neil Hawkins o

Vitelmo Bertero

Jim Lefter

Richard Marshall

RE: Proposed Revisions to ATC 3-06

Gentlemen

In accordance with instructions given by Committee Chairman

Ed Cohen, I have submitted for your consideration proposed

revisions to the document written in code language, with

appropriate reasons for each. Please note that these proposed

revisions must be reviewed by the Technical Activities Committee

of the Prestressed Concrete Institute before they become our

official industry position; however, I am not aware of any

conflicts in philosophy at this time.

SEC . 11.2 Revise the second sentence in Section 11.2 to read

as follows: "Precast and/or prestressed concrete

components may be used if the resulting construction

complies with the requirements of Sec. 3.6 and this

chapter, except as specifically modified in Sections

11.9, 11.10, 11.11 and 11.12."

BASIS: Present provisions of ATC 3-06 exclude the

use of prestressed concrete (by omission);

specific subsections should be established

for the unique and separate design

characteristics of precast and prestressed

concrete

NON-PROFIT ORGANIZATION for rue ADVANCEMENT OF THE OESlGN MANUFACTURE ANO USE OF PR ESTRESSEO CONCRETE ANO PRECAST CO' 126
- 2-

SEC. 11.2 Revise- capacity reduction factore for connections, of

precast components ta read as fallows;

Connection capacity as governed by concrete; 0*0.65

Connection capacity as governed by steel; 0»Q.9D

BASIS; Conservative industry guidelines recommend

a 5/ A factor to be used in connection design

far concrete shear. This results in a value

of Q.75 x Q.85 = 0.65. Chapter 10 indicates

a value of ft = 0.9 for steel

SEC 11.

Revise the last sentence of paragraph 11.8.2 to read

as follows; "Diaphragms for precast concrete floor

systems may be developed with cast-in-place concrete

topping, shear friction boundary reinforcing r or

properly designed; component connectors* either welded

or grouted."'

BASIS; Current provisions exclude the use of untapped

precast or prestressed concrete floor systems.

SEC. 11.8 Revise the first sentence of Section 11.8.4 to read as

follows: "Boundary members shall be provided as

required by Section 11.8.1 and 11.8.2, except for

large panel precast concrete systems building construction with energy dissipating mechanisms formed in

coupling links, as indicated in Section 11.11."

BASIS: Research and testing conducted at MIT and by

Yugoslavs, Japanese and Russians.

SEC. 11.9-

to 11.12 Add the following new sections to Chapter 11:

11.9 Plant Cast Prestressed Concrete

11.10 Post-Tensioned Concrete

11.11 Plant Cast Precast Concrete

11.12 Site Cast Precast Concrete

BASIS: Provisions for precast and prestressed concrete

are currently scattered throughout the document.

1 Requirements in design sections should be

. performance oriented, applicable to all materials

specifics for prestressed or precast concrete

should be covered in the above sections. See

also my letter to William W. Moore presented at

the 1st Annual Building Seismic Safety Council

Meeting on November 8, 1979.
-3-

SEC . 11.2 Add at the end of the sentence reading "Axial compression or axial. . . . for the full height of the

component.": "Non lateral load resisting compression

members designed in accordance with Sections 11.11 or 11.12 shall have capacity reduction factors as given

in AC I 318-77.

BASIS: The arbitrary assignment of a low capacity

reduction factor for "pin-ended" compression

members is not warranted, when top and bottom

connections are designed to accommodate

maximum drift movements and increased bending

moments induced by the P-^effect.

SEC . 3.3.4 In Section (A) ^ . - Delete the last sentence reading

"This system is limited to buildings not over 24ofeet

in height."

BASIS: Assignment of height limitations on these

structures is arbitrary and inconsistent

with actual performance of these structures.

Proper building design and location of

stiffening elements should govern as is

alluded to in Section 3.4.1. The design

requirements should be performance oriented,

and not consist of arbitrary requirements.

S EC . 3.3.4 Add new type (A) ^ : "Coupled shear wall systems with

primary inelastic action along these vertical coupling

elements providing energy dissipation."

BASIS: The work of Becker at MIT.

SEC . 3.3.3 Delete the second sentence in this section in its

entirety

BASIS: Arbitrary height limitation; see above.

SEC. 7.4.4 Revise Section 7.4.4(E) to read as follows: "The

upper 2 feet .... or equivalent spirals. The

pile cap connection may be made by developing exposed

strand or by the use of field placed anchor dowels

grouted into sleeves cast in the pile top as outlined

in Section 11.9.

BASIS: Present accepted practice in U8C-79 and CALTRANS specifications.

128
-4—.

SEC. 7.5.3~ Revise- the- last sentence of Section 7.5.3(c) ta read,

as follows: "Precast concrete and. prestressed,

concrete piling; shall be designed, to withstand

maximum imposed curveatures resulting from e dynamic

analysis of the sail profile present,, with detailing

as specified in' Section 11. 9^"“

BASIS: See my letter and accompanying documentation

from Gerwick, et al presented at the BSSC

meeting on November 8 r 1979".

SEC. 7.6.1 Revise this section to read as follows: "All piling

types in Category 0 shall be designed to withstand

maximum imposed- curveatures resulting from a dynamic

response analysis of the soil profile present."

BASISt Same as 7.5.3 a-bove. Foundation requirements

should be performance oriented, and not

arbitrarily penalize certain materials

(prestressed concrete) because of local bias,

in spite of recent tests and successful design

applications developing large curveatures

resulting from layered sail movements in

maximum credible seismic conditions.

SEC. 8.7.3 Add the following sentence at the end of this section:

"Connector fasteners, shall develop elastic farces

resulting from- twice the loads determined from

Section 8.2. 2 above.'*

BASIS: Current practice as outlined in UBC-79.

SEC . 8.2.2 Add the following sentence at the end of this section:

"The force Fp shall be applied in the vertical direction, as well as longitudinally and laterally, in

combination with the static load of the element."

BASIS: UBC-79; The effect of vertical acceleration

should be included in design of non -structural components and systems.

Detailed provisions for Sections 11.9, 11.11, and 11.12 will be

developed later. I am assuming PTI will develop material' for

Section 11.10.

^^-V-e^ry trury yours,

A. Shepp^

ilifornia Marketing Director

DAS : rd
PORTLAND CEMENT ASSOCIATION

3420 Old Orcnard Road. Skokie. Illinois *>0077 Vea Coae ; 332! -^6-6200

January 3, 1980

Mr. Richard Marshall, SecretaryTechnical Committe 4, Concrete

Tentative Seismic Provision Project

3163, Slag. 226

National Bureau of Standards

Washington, D.C. 20234

Dear Mr . Marshall :

Enclosed are four proposed changes of provisions in ATC3-06 relating

to concrete buildings.

Would you kindly transmit the proposed changes that also relate to other

committees to the relevant groups.

Yours

’lark Fintel

Director Advanced Engineering

MF:gh

cc: Mr. Edward Cohen - American Concrete Institue

Mr. Eugene D. Holland - American Society of Civil Engineers

Mr. Joseph Manning - Concrete Reinforcing Steel Institute

Mr. James D. Prendergast - Interagency Committee on Seismic Safety

in Construction

Professor Neil Hawkins - Post Tensioning Institute

Mr. David A. Sheppard - Prestressed Concrete Institute

Mr. Victor Bertero - Applied Technology Council

Mr. James Lefter - Building Seismic Safety Council

130
Submitted: by

Portland Cement Association

Mark FinteT

January 1980.

TABLE 1-5 - Page 35

REVISE THE “SEISMICITY" INDEX* COLUMN- OF TABLE 1-8 TO READ A

S' SHOWN* BELOW:

TABLE I-S

Coefficients A^ and A

v and Seismicity Index

Coeff. A.

Ftqure I*

Map Area

Number

Caeff. A

Fiqure 2

Seismicity

Index

0.4a 7 0.40 4

0*3(1 5 0.30 4

0.20 5 0.20 4 3

a.is 4 0.15 J z

0.10- Z 0.10 l 1

0.05 Z 0.05 Z 1

0.05 L 0.05 1

REASON:. The seismicity indices were introduces 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 (Ar 8, C, and D). The indices and the performance categories

have been apparently arbitrarily interrelated with the seismic hazard

exposure groups (Table L-A)„

While there is little question about detailing requirements for the

highest seismicity (4-), and for the lowest seismicity (1), detailing

requirements for seismicity index levels of 2 and 3 remain a gray area

without adequate background information*
It is not acceptable to require arbitrarily the same level of ductility

detailing for acceleration levels of .40 (map area 7) as for acceleration

level 0.15 (map area 4)

Buildings located in the map areas 1 and 2, subjected to acceleration

levels of 0.05, will undoubtedly always remain in the elastic range,

requiring no additional ductility details. The acceleration level of 0.10

(map area 3) will, in all probability, create an elastic response in

buildings designed in conformity with modern reinforced concrete and steel

codes.

Regarding the acceleration levels of 0.15 and 0.20, (map areas 4 and 5),

the major question is which structural members will be yielding and how much

ductility will be required in them. It should also be considered that

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, based largely on

judgment, net necessarily supported by adequate background studies, seems

questionable. Seismic code 'writers bear the responsibility to substantiate

the need for any restrictive changes made to codes which have been developed

in a consensus process over the last several decades. It is not for

industries to prove that such changes are unnecessary and will increase the

cost of buildings without adding to their safety. Added ductility recuirements should be ’mposed only if seismicity vs ductility correlation studies

*or maD areas with acceleration levels of 0.10, 0.35 and 0.20 indicate

levels of ductility demands requiring such detailing.

132
Submitted by

Portland Cement Association*

Marie Fintel

January 1980

SECTION- 3.5.4- - Page 45

DELETE SECTION T.3:.4(A)5

REASON: The height limitations are arbitrary, unjustified by today's TeveT

of knowledge of structural response and element strength and ductility, and

should be removed. The best performer in reinforced concrete, the shear

wall-frame interactive system, is limited. to a height of 240 ft. In

comparison, the special moment frame, which in reality becomes unbuildable

at about 15 - 15 stories, is the only concrete system allowed above 240 ft.

We do not believe that the reasons and circumstances which prevailed in the

early sixties and led to similar height limitations (primarily a lade of

knowledge) are still valid today.

To assure safety o-f multistory buildings above a height of 240 ft they

may be analyzed and designed by the more realistic inelastic procedures, to

make certain that ductility demands are within available limits. The only

limiting factors to determine the height of buildings should be merter

capacity for strength* and ductility and the overall response of the

structure. Also, the rigidity of the structure should be considered in

limiting the interstory distortions, thus assuring realistic damage control

of nonstructural elements. Tn structures so designed aTT the earthquake

forces and deformations are resisted by the elements of the structure in

accordance with- their relative strength and rigidities. To assure stability

of inelastic structures, the inelastic procedure permits control of

inelasticity so it may be confined to horizontal elements only, while

assuring elastic behavior of columns or walls at all times if the designer

so chooses.
As Corrected on 1/24/80

Submitted by

Portland Cement Association

Mark Fintel

January 1980

Section 3.9 - Page 51

ADD A NEW SECTION 3.9 TO READ AS FOLLOWS:

Sec. 3.9 - ALTERNATE INELASTIC DESIGN PROCEDURE

3.9.1 - INELASTIC RESPONSE HISTORY ANALYSIS

Structural systems may be analyzed by multi -degree-of-freedon inelastic

response history analyses using appropriate earthquake records (adjusted in

intensity to local seismicity). Resulting base shear shall not be less than

90% of that required by Eq. (4-1) of Chapter 4.

Such systems shall have members (beams, columns and/or structural walls)

designed for resulting forces and deformations, as required by the inelastic

analysis.

Interstory distortions (story drift) as computed by the inelastic

response history analysis shall not exceed the allowable story drift a

a

obtained from Table 3-C for any story.

3.9.2 - STRENGTH AND DUCTILITY

In proportioning of members, elastic strength or inelastic strength and

ductility, as required by the analysis, shall be used.

Members of the structural system shown by the analysis to remain elastic

during the response shall be proportioned as required by Sec. 11.6.

Members of the structural system shown by the analysis to undergo

inelastic deformations during the response shall be proportioned as required

by Sec. 11.7 for structural frames, and Sec. 11.3 for structural walls.

134
Max imunr rotational ductility required by analysis of members

proportioned according to Sec. 11.7* and 11.8 shall not exceed:

S in beams with a span-to-depth ratio larger than $

1Z for beams with diagonal reinforcement having span-to-depth ratio of

less than Zh

2 in shear walls with a hei ght-tu-depth ratio of more than 2 and having

vertical boundary elements

2 for columns

REASONr Elastic static analysis cannot adequately determine forces and

deformations in inelastic structures- Designing on the basis of elastic

analysis may lead to insufficient ductility in some members, and to

building in the 1973 Managua earthquake.

The concept of ductility within the design process, which is in

accordance with current practice, was developed on the basis of studies of

single-degree-of-freedom systems. System displacement ductilities of 4 to 6

I were utilized for a 1940 El -Centre type earthquake. However, in designing a

structure,, we deal with the ductilities of individual members, and not with

overall system ductility. The relationship between the two may be different

for each member in a structure, and changes in structural configuration will

result in changes in the individual member ductilities. Therefore, while we

are talking about system ductilities of 4 to we may be faced with member

rotational ductilities considerably larger, depending on the structural

configuration, and strength and stiffness relationships. No systematic

studies have been carried out to determine the distribution and magnitude of

inadvertent shear failures, such as observed in the Banco- de America
implementation of the overall concept to assure safety against brittle

failures, we must, of necessity, provide maximum ductility in all columns,

beams, and their connections, whether needed or not. In reality, from

experience in earthquakes, and from inelastic analyses, it is known that

ductility is not required in all members of a frame. Unfortunately, this

important economic consideration is not included in ATC-3.

The major drawback of elastic analysis when applied to inelastic

structures is that it does not allow us to determine the amount and

distribution of ductility throughout the structure. We hope that the

details specified in ATC-3 and other seismic codes will assure availability

of the required ductility in all members which may become inelastic. We

hope — we do not know for sure.

Other shortcomings resulting from the use of elastic analysis for an

inelastic structure are the possibility of inadvertent yielding of columns

during very severe earthquakes, with its consequent effects on overall

structural stability, and also the lack of an active control over the

sequence of yielding during seismic response.

A procedure based on inelastic analysis needs to be introduced as an

alternate approach for multistory buildings. Such a procedure became

practicable with the development in recent years of highly efficient

two-dimensional response history analysis computer programs. A good example

of such a program is DRAIN-20, developed at the University of California,

Berkeley. The dynamic response is determined in the program by using a

stap-by-step integration of equations of motion. Inelastic characteristics

of structural elements of both concrete and steel have been incorporated by

the University of California, Berkeley (concrete) and by the University of

Michigan (steel), respectively.

136
The explicit inelastic dynamic analysis design procedure entails the

following steps

I. Preliminary layout and design of the structural system based on

gravity Toad* requi rements* code wind loading and code earthquake

loading.

Z. Modelling the structure for dynamic analysis in each of the two

orthogonal directions. Frames and shear walls are to be lumped

into the least number of vertical lines; the masses are

concentrated at floor levels.

J. Selection*- on the basis of local seismicity and of structural and

soil characteristics* of design accel erograms with a potential to

critically excite the structure.

4. Determination of forces and deformations in the members under the

design earthquake, using inelastic response history analysis. A

number of runs are required to choose the optimal combination

between strength and ductility.

5. Proporti oni ng of members for strength and deformab i 1 i ty in the

elastic and post-elastic ranges, based on resistances and ductility

capacities known fronr tests.

6. Checking that the structure has enough ductility to survive,

without collapse, the maximum credible earthquake possible at the

site.

This alternate inelastic approach gives the design engineer a valuable

tool for designing multistory structures, in which the amount and distribution of inelasticity during the response can be controlled by the choice of

strength relationships; consequently, ductility details can be included

where they can be best utilized. Other advantages include the ability to:
o Design into the yielding members of the structure a desirable

balance between strength and ductility.

o Predetermine a sequence of p last if i cation so that energy can be

dissipated without endangering stability. An early onset of

yielding in beams limits buildup of axial loads in columns, of

column moments and of shears in beam-column joints.

o Select perfromance criteria for the design earthquake (i.e., to

have yielding beams and elastic columns), thus providing better

damage control.

o Devise innovative and more effective structural configurations to

dissipate seismic energy— systems we have not yet been able to

devise because we have lacked the means to analyze them.

A number of design examples, carried out for shear wall-frame

interactive systems, and for coupled wall systems, show the feasibility and

technical superiority of the solutions, as well as the economic advantages

of the inelastic approach. The procedure is applicable to both reinforced

concrete and structural steel highrise structures.

The procedure is limited to fairly symmetrical structures for which a

two dimensional model can be used with a degree of confidence.

Conclusion

While the present code provisions are of necessity overly conservative

with respect to distribution of ductility, new procedures have recently

become- avai 1 able which result in more rational and more economical

structures

Explicit inelastic response history analysis permits an alternate

approach (based on energy dissipation considerations) that is applicable to

multistory building structures of reasonably regular layout, for which

inelastic dynamic analysis appears to be warranted. This inelastic response

138

1
history analysis makes it possible to analyze a structure and to proportion

its members for an optimum1 balance between strength and ductility, and- to.

provide ductility details in alt parts of the structure which are designed

to undergo inelastic deformations. Obviously, information on available

ductility of the members in question is a prerequisite.

The objective of the procedure is to establish a sequence of energy

dissipating- mechanisms and: thereby impose on the structure a desired

response, permitting- no alternate types of behavior. A structure so

designed is then detailed for ductility only in the predetermi ned hinging

regions^ this results in a more economical and technically superior

structure.
Submitted by

Portland Cement Association

Mark Fintel

January 1980

TABLE 3-B - Page 52

PROPOSED PROCEDURE TO DEVELOP RATIONAL VALUES FOR RESPONSE MODIFICATION

COEFFICIENTS, R.

Response modification factors, R, introduced in ATC-3-06, are a

significant departure from the previous !<-values, and may have a serious

impact on the construction industry. The concept of response modification

factors, R, ranging from lh to 3 to account for energy dissipation due to

inelasticity and damping of the various structural systems and materials is

conceptually clear, simple, and easy to apply, and represents a significant

improvement over the present use of K-f actors. However, the apparently

arbitrary selection of R-f actors in Table 3B, without studying their effect

on member ductilities, makes the practical application of the concept very

questionable. Since the overall underlying concept is a balance between

strength and ductility, if the R-values lack a correlation with member

ductilities, they are not much superior to the previously used K-values. A

major uncertainty of the arbitrarily chosen R-values is the question whether

the member ductilities actually available 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.

To evaluate the suggested arbitrary Response Modification Factors, R, of

various individual systems and materials by comparing them with the previous

"K" values (also unsubstantiated and adopted arbitrarily AO years ago) is

like the blind leading the blind.

140
Studies to determine realistic R and values must be carried out for

the various structural systems and materials listed in- TabTe 38. The vajue

of R to be derived from response history analyses is the ratio of base shear

for the undamped- elastic systenr to the base shear for the damped inelastic

system,, both systems representing: the same, structure* and both being

subjected to a properly selected ground motion. The inelastic response

history analysis of the damped inelastic systenr (designed by the R-factor

approach) would yield 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 following is a suggested procedure to derive R-vaTues for a given

structural system:

1. Prepare a preliminary* design based on gravity loads and the

traditionally Code-specified earthquake forces.

2. Prepare a 2-dimensional mathematical model of the structure, with

masses concentrated at fToor levels; use lumping to minimize the

number of vertical lines.

3. Determine the fundamental period of the elastic structure, and

assume a certain period change due to inelasticity during response.

4. Select from the library of accelerograms one, or several, records

having a broad-band velocity response spectra potentially damaging

to the given structure* considering the initial and lengthened

periods. Normalize the records to a given intensity.

5. Run a response history analysis for the undamped elastic response.

Determine the base shear, V
5. Divide the base shear, V -j, by the assumed "R" (as given in Table

38 for the given system) and distribute the resulting base shear,

V, over the height of the structure. Using a static elastic

analysis, determine forces and proportion the members.

7. Run an inelastic response history analysis for the model in (2),

using strength of members as determined in (6), customary damping

values, and proper hysteretic models (for steel or concrete). Use

the same imput motion record as in (5). Determine base shear, V„.

8. If the base shear is not the same as V in (6), adjust the

strength of the members in proportion of V/V , and repeat step 7.

9. Determine the rotational ductility demands of all members. If

these required ductilities are attainable with the specified

detailing, then the prescribed R-factors are realistic; otherwise,

they need revision.

The total effort required to determine practical 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 solid

foundati on.

142
FORELL / ELSESSER ENGINEERS, INC.

For®1 1 • Eisesser • Chan Structural Engineers.

N»c*io; 3’< : c . Sfe £fic Eisesse' Sc

F C Ch# SE

January IT, 198C

James Harris, Secretary

Technical Committee No. Z

\ Tentative Seismic Provisions Project 8168

Building 226

National Bureau of Standards

Washington, D.C. 20234-

Gentlemen:

The enclosed lists- of comments and recommendations are intended to improve

on the Tentative Provisions to be used in the trial design test program.

The list prepared by me had assistance fronrmembers of the Structural Engineers Association of Northern California and was briefly discussed in a meeting of the Steering Committee of the Seismology Committee of SEAONC.

The list prepared by T. Zsutty, Chairman of the State Seismology Committee,

and Ed Zacker, past President of SEAONC, are transmitted as received.

I wish to restate my expressed concern at the December 11th meeting at the

National Bureau of Standards. The importance of the Tentative Provisions

is too great to limit the time for the preparation of comments and recommendations as severely as the schedule demands. The result of placing

such a severe time restraint on this process will be a lingering doubt

in the minds of the participants and their sponsoring organizations that

they have not been given a fair opportunity to have their voices heard.

I sincerely hope the door will not be closed for future well reasoned

and sincere comments.

/ cs end.

cc: Steve Johnston

631 Clay Street San Francisco. California 9 4 i 1 1 Teieononei4i5) 397-2768
Section 11.8.1., 2. and 4. Meed clarification that edge members or

chords are required whenever tension stress exists in walls and

diaphragms. These members must have ductile ties when computed gross

section stress exceeds 0.2f' , and only this requirement for ductile

ties is discontinued when stress falls below 0.15 f

1

; but the edge

c member may be required for tension resistance beyond this level.

Section 11.8.4. Boundary Members: Clarify last Daragraph.

Chapter 5. Dynamic Analysis needs to be completely redone.

( 1 ) It is an omission in the "Provision" that no

made to the use of seismic separation joints

eliminate irregularities in building shapes.

F. Fore! 1

)

reference is

as a device to

(Comment by N.

144
UNIVERSITY OF CALIFORNIA, BERKELEY

BEHXELEY • DAVIS • IRVINE • LOS ANGELES • RIVERSIDE • SAN DISCO • SAN FRANCISCO SANTA BARBARA • SANTA CHCZ.

COLLEGE Or ENGINEERING

department of civil engineering

DIVISION OF STRUCTURAL ENGINEERING

AND STRUCTURAL MECHANICS

BERKELEY, CALIFORNIA 94730

January 31, 198&

CO

Mr. Richard. Marshall, Secretary

Technical Committee 4, Concrete

Tentative Seismic Provision Project

B168, Bldg. 226

National Bureau of Standards

Washington, D.C. 20234

RE: Review and Comments- on the Proposed Revision of Chapter 11 of the

AIC 3-06

Dear Mr. Marshall:

Enclosed you will find my review and comments on the revisions

proposed by Dave Sheppard on behalf of the Prestressed Concrete Institute;

Nicholas Farell,the SEAONC representative; and Mark Fintel, the PCA

representative. In some cases it has been difficult to make comments

because there were no specific proposed revisions and/or there was a lack

of supporting evidence and reasoning. However, I think I have reviewed

and commented on. all the revisions that I have received so we have some

basis for discussing the suggested changes more thoroughly at our February 21

meeting.

WB/ al-m

Enel.

Sincerely yours.

V.. V. Bertero

Professor of Civil Engineering
PROPOSED REVISIONS TO ATC 3-06

REVISIONS PROPOSED BY:

I. David A. Sheppard, Representative of the Prestressed Concrete

Institute

1.1 SEC. 11.2 Revise the second sentence in Section 11.2 to read

“""1—————— as f 0 2_]_ 0WS; "Precast and/or prestressed concrete

components may be used if the resulting construction

complies with the requirements of Sec. 3.6 and this

chanter#! except as specifically modified in Sections

111.9, 11.10, il.ll and 11.12."

4— J

COMMENT : This revision as proposed cannot be introduced until the

proposed

- new sections. 11.1 tnrougn 11.12, are developed and further

studies regarding adequate values of R and C^ for these precast and

prestressed concrete systems are conducted. A modified revision is

proposed.

This will:

be needed

it will be part of thi chapter.

REASONS : The requirements established in Chapter 11 cannot be considered independently, as they are the consequence of Che structural

design requirements (Chapter 3) which include the accepted analysis

procedures (Chapters 4 and 5). In developing the requirements of

Chapter 11, attempts were made to assure that the basic design equation,

i.e. ,

DEMAND

of

f Strength < Strength > Stiffness Stiffness

Stability

< SUPPLY , of

Stability

Energy Absorption Energy Absorption f and and

Energy Dissipation Energy Dissipation

Capacities (Ductility)^ ^ Capacities (Ductility/

is satisfied. Because of the substantial uncertainties involved in the

current methods of estimating the DEMANDS , it is a good policy in seismicresistant design to be generous in the SUPPLY, a philosophy which has

been adopted in developing the requirements of Chapter 11. The estimation of the DEMAND is based, among other factors, on the use of the

response modification factor, R. In the selection of the R values for

R/ C systems, besides the examination of Che research data available

regarding the seismic behavior of the systems, special consideration was given [as explained in the commentary of Section 3.3 (pp. 336-338)] to the observed general performance of these systems during past earthquakes:

the general toughness (ability to absorb energy without serious degradation under reversals of deformations i.e., stable hysteretic behavior

that guarantees good dissipation of energy); and the general amount of

damping present in the system when undergoing inelastic deformation.

146
z

With thi« in mind, it. should be noted that the R values given, in

Table 3B for R/C systems (7 for special moment frames., 5 1/2 for shear

walls, 8 for dual systems, etc.) have been selected on the basis of

the observed seismic performance and field and laboratory experimental

date available on structural concrete systems designed and constructed

on the basis of the present techniques far MONOLITHIC CAST—IN-PLACE

ORDINARILY REINFORCED CONCRETE CONSTRUCTION. Because at present

there is a lack, of reliable information and experience regarding the

seismic behavior of bulldings with structural concrete systems based

on the use of precast and/or prestressed components [see Proceedings

of a Workshop on Earthquake-Resistant Reinforced Concrete Building

Construction, July 1977, Berkeley, CA, and Bertero, V. 77, ’’Seismic

Behavior of Structural Concrete Linear Elements (Beams, Columns) and

their Connections,” CEB Bulletin No. 131, AICAP-CEB Symposium, Rome,

May 1979, pp. 123-313], it is recommended that the R and C^ values

given in Table 3B not be used for these systems.

Recognizing the great, potential offered by the proper use of

precast and/or prestressed (particularly partially prestressed)

components, and taking, advantage of Sec. 1.3, it is proposed to modify

Sec. 11.1 as* follows.

MODIFICATION OF SEC. 11.1 Revise the second sentence to read: "Precast

and/or prestressed reinforced concrete components may be used only if

it can be shown by experiments and analysis based on established engineering principles that the resulting construction complies with the

requirements of Secs. 3.6 and 3.7 and this chapter, and that they offer

the same strength, stiffness, stability, durability, damping, and

energy absorption and energy dissipation capacities (ductility) as required from the monolithic cast-in-place ordinarily reinforced concrete

construction that they replace if the R and values given in Table 3B

are used. ,r

1.2^ SEC. 11.2 Revise capacity reduction factors for connections of

precas t components to read as follows

Connection capacity as governed by concrete: $=0.65

Connection capacity as governed by steel: $=0.90

COMMENT : Thi3 proposed revision should not be Introduced .

REASONS

The values suggested do not appear to be supported by reliable

experimental data. The value of $ * 0.5 has been derived from the observed

performance of connections of precast components during earthquakes and

from analysis of data available from laboratory tests up to 1977. The

observed earthquake performance of these connections either governed by

concrete or by steel has been poor. Although it is recognized that,

since 1977, new laboratory data have become available [Aswad, Spencer,

Pall, Jurukovski (Yugoslavia) and others], these data are not sufficient

to justify the proposed increase, particularly for the connection capacity

as governed by steel, i.e., $ = 0.90. The argument given that Chapter 10
3

indicates a value of $ = 0.9 for steel does not seem to be valid.

Field inspections indicate that the quality control and workmanship

used in the construction of joints in precast component connections

are not the same as those of steel member connections. The uncertainties in design and construction in precast component connections seem considerably larger. Therefore, the <p cannot be the same.

1.3 SEC. 11.8 Revise the last sentence of paragraph 11.8.2 to read

as follows: "Diaphragms for precast concrete floor

systems may be developed with cast-in-place concrete

topping, shear friction boundary reinforcing, or properly designed component connectors, either welded

or grouted."

COMMENT: A modified revision is suggested.

REASONS : The proposed revision is not clear. It is not simply a question of constructing a diaphragm, but of developing sufficient

resistance (strength), stiffness, stability, durability and ductility to

guarantee the transmission of forces (inertia acting together with those

due to gravity field and to other changes in environment conditions) to

the seismic resisting system. Continuity should be assured in order to have stable resistance and stiffness under the combined stresses that can act in these diaphragms. A good technique to assure the satisfaction of these requirements appears to be the use of a cast-in-place

topping. Recognizing that other techniques could be used in certain

cases which could satisfy the above requirements, the following modified

language could be developed (it should be noted that these are requirements for Categories C and D)

MODIFICATION OF SEC. 11.8.2 Revise the last paragraph of Sec. 11.8.2

to read as follows: "A cast-in-place topping on a precast floor system

may serve as the diaphragm provided the cast-in-place topping is

proportioned and detailed to resist the design shear forces under the

effects of any loading combination (which could induce tensile or compressive stresses simultaneously to the shear forces). Alternate

techniques based on the use of untopped precast and/or prestressed

components of concrete floor systems may be used only if it can be

shown by experiments and analysis based on established engineering

principles that they will offer the same shear strength, stiffness,

stability, durability and ductility and stable hvsteretic behavior as the

monolithic cast-in-place ordinarily reinforced concrete diaphragm, when

subjected to cyclic loading conditions like those expected for seismic

performance Categories C and D."

1.4 SEC. 11.8 Revise the first sentence of Section 11.3.4 to read as follows: "Boundary members shall be provided as required by Section 11.3.1 and 11.8.2, except for large

panel precast concrete systems building construction

with energy dissipating mechanisms formed in coupling

links, as indicated in Section 11.11."

143
A

COMMENT: The proposed revision: cannot be recommended.

REASONS ; Lack of reliable experimental data regarding the behavior of

large panel precast, concrete systems building; construction with energy

dissipating mechanisms formed in coupling, links when subjected to

severe earthquake ground shakings. The basis given for the proposed

revision, . i.e. , reaseach at MIT and by Yugoslavs, Japanese and RussIansr to the best of this writer's knowledge is far from, adequate to justify

the revision. The research, conducted at MIT by Becker and Mueller is

completely analytical, and they have pointed out clearly that, although

the concept of coupling links seems quite promising, unfortunately there

is very limited experimental data. Therefore, further development of

such a- concept requires additional analytical and experimental studies.

Although the writer is familiar with some experimental work conducted

by the Yugoslavs and Japanese on panel precast concrete systems

buildings , the data available does not seem to justify the proposed

change. It should be kept: in mind that the requirement on the use of

these boundary members is for the case of shear walls and diaphragms

of seismic performance categories C and Dv i. e. , buildings which may be

subjected to severe seismic motions and which therefore must be

provided with large energy dissipation capacities. Note that the R

values for these walls are 8 for tall buildings (dual system) and 5 1/2

for short buildings. Analysis of the experiments cnnducted by the

PGA,, in Berkeley and Japan, on R/C walls shows that, to obtain the

ductility Implied in these R values, it is necessary to have these

boundary members. Again, the present AIC 3-06 does not prohibit the

proposed use of coupling links- (see Sec. 1.5 ) r but substantiating

evidence demonstrating that, the proposed new system will have at least

a seismic performance equal to the system recommended should be

submitted.

1.5 SEC. 11.9 to 11.2 Add the following new sections to Chapter 11:

11.9 Plant Cast Prestressed Concrete

11.10 Post-Tensioned Concrete

11.11 Plant Cast Precast Concrete

11.12 Site Cast Precast Concrete

COMMENT : The writer supports the idea of the development of provisions

for precast and prestressed concretes . These provisions should be

grouped under a new subsection of Chapter 11. Precedents for doing so already exist.- The recently proposed '’Code of practice for the design

of concrete structures" of New Zealand has a completely separate

chapter of provisions for the design of prestressed and partially pre—

stressed concrete members of fully ductile moment-resis ting frames and

joints between members. It should be pointed out, however, that in the

development of these provisions it will be necessary to study the

possibility of not only developing provisions peculiar to members with

prestressing with the objective of developing the same strength, stiffness, stability, durability, and energy absorption and energy dissipation capacities (ductility) as the non-prestressed member, i.e., using
5

Che same R and values, buC also the possibility of assigning new

values to R and for precast and prestressed structures. At present

perhaps all that can be done is to introduce the modification of

Section 11.2 as proposed above in 1.1, noting that, in the case of

prestressed members for seismic performance categories C and D,

the prestressed members shall conform to the requirements of Sec. 3.7.12.

1.6

SEC. 11.2 Add at the end of the sentence reading "Axial compression or axial. . . . for the full height of the com- ponent.": "Non-lateral load resisting compression

members designed in accordance with Sections 11.11 or 11.12 shall have capacity reduction factors as given in

ACI 318-77."

COMMENT : The proposed revision cannot be recommended until provisions

11.11 and 11.12 have been developed.

REASONS : It should be noted that it will not usually be convenient to use a "pin-ended" compression member as a part of the lateral

seismic force resisting system. If, in spite of this, such a pinended element is used as part of the seismic resisting system, because

of the detrimental consequences of the interacting effects of the

so-called nonstructural elements usually attached to the structural

elements , it is believed a good policy to recommend the use of a reduced value of <f> to discourage the use of elements without proper

lateral reinforcement. A recent illustration of the need for special

lateral reinforcement along the full height of the component is the

failure of the ground-story columns of the Imperial County Services

3uilding in El Centro.

3

1.7

SEC. 3.3.4 In Section (A) . - Delete the last sentence reading

"This system is limited to buildings not over 240

feet in height."

COMMENT : This revision should be reviewed by Committee 2: Structural

Design . It should be noted that, if this section is changed, Sec. 3.3.5

should also be changed.

4

1 .

8

SEC. 3.3.4 Add new type (A) : "Coupled shear wall systems with

primary inelastic action along these vertical

coupling elements providing energy dissipation."

COMMENT : This change should be discussed bv Committee 2: Structural Design . The proposed system is not a new type, but the

writer agrees with the basic idea put forward in the proposed revisions. As discussed and illustrated in several of his publications.

150
the writer believes that the use of a structural system based on. ductile walls coupled with girders having- large energy dissipation,

capacity (large ductility and stable hysteretic behavior) leads to the

best strong column-weak girder system , which is the basic requirement

for the design, of special (ductile) moment-resisting frames. Thus, the

use of this system should be encouraged. Perhaps the best way ta do sa

is la the commentary of Sec. 3.3.4.

1.9 SEC. 3.3.5 Delete the second sentence ixr this section in its

entirety.

COMMENT : This is a subject for discussion and comments bv Committee 2 : Structural Design . Note that this height limi tation is only for Category D and only for cantilever wall or braced frame systems. It does not

apply to dual systems.

1. 10 SECS. 7.4.4, 7.5.3 and 7.6.1

COMMENT; These proposed revisions should be reviewed by Committee 3 : Foundations

The writer agrees with some of the statements made by

Mr. Sheppard in his Basis* such as ’’Foundation requirements should be

performance oriented” and in theory with the proposed revision to

Sec. 7.5.3 and 7.6.1. However, it should be noted that the revision

as stated is not complete. It will be necessary to specify a reliable

method of analysis for the dynamic response of the soil-pile system.

Furthermore, the proposed revision for these two sections cannot be

accepted or even discussed until Section 11.9 is developed and accepted1.11

SECS. 8.2.2 and 8.2.3

COMMENT: These proposed revisions should be reviewed by Committee 8:

Architectural, Mechanical and Electrical.

IT. Nicholas Forell, SEAONC Representative

2.1 SEC . 11.8.1, 2 and 4 Need clarification that edge members or chords

are required whenever tension stress exists in

walls and diaphragms. These members must

have ductile ties when computed gross section

stress exceeds 0.2 fj, and only this requirement for ductile ties is discontinued when

stress falls below 0.15 f^; but the edge

member may be required for tension resistance

beyond this level.

COMMENT: To introduce the requested clarification, the following changes

are suggested:
7

Sec. 11.8.1 Add the following sentence at the end of the fifth

paragraph of this section (top of page 108): "These shear walls

shall have vertical boundary members along the edges as described in

Sec. 11.8.4 at any level where tensile axial forces can be developed

in the walls."

Sec. 11.8.2 Add the following sentence at the end of the second

paragraph of this section: "Diaphragms shall have boundary members

along their edges as described in Sec. 11.8.4 whenever tensile axial

forces can be developed in these diaphragms."

2.2

SEC. 11.8.4 Boundary Members: Clarify last paragraph.

COMMENT: It is not clear what needs to be clarified.

III. Mark Fintel, PCA Representative

3.1 TABLE 1-B

COMMENT : These suggested changes should be reviewed by Committee 1:

Seismic Risk Maps, and Committee 2: Structural Design.

3

3.2

SEC. 3.3.4 - page 46 Delete Section 3.3.4(A)

COMMENT : This proposed revision should be reviewed by Committee 2 : Structural Design . Although the writer favors the deletion of the

limitation of 240 feet in height, he does not agree with the deletion

of the rest of the other requirements recommended in 3.3.4(A) 3

.

3.3

SEC. 3.9 - page 51 Add a new section 3.9.

COMMENT : This proposed addition should be reviewed by Committee 2 : Structural Design . Although the writer favors the design of most of

buildings using inelastic design procedures, and would like to be able

to recommend a specific code method , based on inelastic design, which

could be applied to all types of buildings, present knowledge does not

permit this. Only in the case of very particular types of buildings

to be built at certain sites in regions where sufficient seismic

records exist is it possible to carry out rational inelascic design.

One of the main problems is the sensitivity of the earthquake response

of the building to (1) the dynamic characteristics of the ground

motion, and (2) the modeling of the building (soil-foundacion structural

and nons true tural elements system) which should include the interacting effects of the construe tural elements. Further study of these

problems is required before a specific code inelascic design procedure

1 2 1
a

can be recommended-. At present the lack, of reliable three-dimen—

sional computer programs to analyze real buildings hampers advances

in this field.

The main problems in the proposed "alternate inelastic design

procedure" are, first* what constitutes "appropriate earthquake

records" and, second, how is the ^maximum rotational ductility

required" defined and computed? The writer supports the idea of

perhaps taking: advantage of the following statement made in Sec. 3-1,

"... with the procedures in Chapter 4 or Chapter 5 or an approved

alternate procedure" to add, between parentheses, "The development

and application of inelastic design procedures such as the one described

in general terms in the commentary of this section is encouraged." If

this suggestion is accepted, it is recommended that a special committee

be appointed to study the method proposed by Mark Fintel.

3.4 TABLE 3—S — page 52 "Proposed Procedure to Develop- Rational

Values for Response Modification

Coefficients, R"

COMMENT: The suggested procedure should be reviewed by Committee 2:

Structural Design and other committees, since any change in this

coefficient may affect other provisions.

The writer agrees with the need to review the R values. This need

was expressed at the time the tentative provisions were formulated

(see page 4 of the tentative provisions). Therefore, it is suggested

that some effort be devoted to studying the reliability of the present

recommended values of R. A committee should be appointed to conduct

the required studies. The procedure suggested by Fintel might be

considered as one possible procedure. In doing so, the comments made

previously (3.3) should be kept in mind.
CONCRETE REINFORCING STEEL INSTITUTE

1499 BAYSHORE HIGHWAY SUITE 113 BURLINGAME CA 94010 TELEPHONE 41 5/697-1437

JOSEPH G MANNING. Regional Director — CRSI Western Region

January 31,1980

Members of Techncial Committee 4:

Concrete

Review of ATC 3-06

Victor Bertero

Edward Cohen

Mark Fintel

Neil Hawkins

Eugene Holland

Gentlemen

James Lefter

Richard Marshall

James Prendergast

David Sheppard

;-0

The following proposed revisions to ATC 3-06 are submitted for

your consideration. These are written in code language, with

appropriate reasons for each per instructions by the Committee

Chairman

.

Section 1.6.3(A) Special Testing

Revise exception under paragraph one as follows

Exception

Certified mill test certificates may be accepted for ASTM

A-706 and A-615 reinforcing steel.

Reason: Section 11.5.1, as suggested to be revised, would permit

ASTM A615 grade 40 or 60 reinforcement. Mill tests specify actual

yield and tensile strengths.

Table 1-B Seismicity Index

Revise the "Seismicity Index" of table 1-3 to read as follows:

Hf AOOUAH rPW. Ill NORTH l A'.AIIF ‘ TREFT 5* ( HlOvG. - ILLINOIS60f.nl TELEPHONE J I ? 37? -5059
January 31,1980

Members of Technical. Committee 4

ATC 3-06

page 2

Map Area.

Number

7

6. 5

4

3

2

1

Seismicity

Index

4

4

/r 3

1 2

2

2 1

1

Reason: The seismicity index relates to various levels of detailing requirements through, the seismic performance category. Under

ATC 3-06, in some areas suclr as Phoenix, AZ. , detailing requirements

would be increased to the same level as that for say San Francisco.

This obviously should not. be required. It is therefore recommended

to maintain current levels of detailing that have been determined

by the local engineering profession.

Section 3.3.5 Seismic Performance Category D

Delete second paragraph modifying height limitations of Sec. 3. 3.4

Reason: These limitations are considered overly restrictive and

arbitrary. Height alone is no critera for the performance of a

structure under seismic loading.. The limitations in Section 3.3.4

would appear to provide adequate performance.

Table 3-B Response Modification Coefficients

Revise table 3-B as follows:

Coefficients

Type of. Structural System R C^

Bearing Wall System: ... 4 4

Building Frame System: ... 6 4

Moment Resisting Frame System:... 3 6

Dual System: ... 75

Inverted Pendulum Structures: ... 2^ 2^
January 31,1980

Members of Technical Committee 4 ATC 3-06

page 3

Reason: The Response Modification Factors ,R, are out of necessity

arbitary. These numbers will have a 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 that 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

Section 4.2.2 Period Determination

Revise equation (4-4) as follows:

T*«

= 0.10 N

where N = The total number of stories above the base to the

highest level of the building.

Reason: This is recommended for two reasons. First, for simplicity.

Second, the coefficient Ct affects the 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 great of an impact on the base shear is not

warrented

Section 7.5.3(C) Precast Concrete Piles

Revise second sentence to read as follows:

Precast concrete and prestressed precast concrete piling

shall be designed to withstand maximum imposed curvatures

resulting from the maximum soil deformations that would

occur during an earthquake.

Reason: Prestressed precast concrete piling can withstand considerable curvature and through proper detailing confinement and ductility

can be provided.

Section 7.6.1 Special Pile Limitations

Delete this section.

Reason: See comments on Section 7.5.3 .

L56
January 31,1980

Members of Technical committee 4

ATC 3—06

page 4

Section 11.1 Reference Documents.

Revise reference 11. L as. follower

Ref. 11.1 Building Code Requirements for Reinforced Concrete,.

American Concrete Institute. (ACX 318-77 but excluding

Appendix A)

Reason: Reference should be to the most recent edition of ACI

standard. References to sections throughout document must be

revised as appropriate if this change is approved.

Section 11.2 Strength of Members and Connections

Revise third paragraph as follows r Axial compression or axial compression combined with bending

on any member where axial stress due to all loads exceeds

0.10f c and the axial stress due to seismic forces exceeds

O.OSf'c and special lateral reinforcement as specified in

section 11.7.2 (C)

Reason: The statement for the full height of the component is

misleading. Further, the extent of special lateral reinforcement

is specified in Section 11.7.2 (C)

Section 11,5.1 Material Requirements

Revise third paragraph, second sentence as follows:

ASTM A-615, grade 40 or 60 reinforcement may be used in

these elements if ... .

Reason: ASTM A615 grade 60 will meet the physical requirements

desired and it has performed satidfactorily in its current use.

Further A706, which is also a grade 60 reinforcement is not readily

available at the present, time.

Section 11.8.1 Shear Wall Details and' Limitations

Delete third paragraph reuiring two curtains of steel.
January 31,1980

Members of Technical committee 4

ATC 3-06

page 5

Reason: This provision seems overly restrictive. Many tilt-up

buildings with a single curtain of steel have performed satisfact

orily under earthquake loads. Further, any shear wall in a major

structure and one carrying high shear is likely to be 10 inches

or more in thickness. Section 14.2(g) of ACI 318-71 requires 2 curtains of reinforcement in such walls.

Time for review does not permic a more detailed study of this

document. Therefore additional comments may be forthcoming later

in the review process.

Sincerely

,

.{ \\

•WJ IT I \ V I

I ' i \ ] ^ ' Joseph G. Manning

Regional Director

JGM : jm

cc: Dr. Gene Corley

Paul Rice
February 11, 1980

COMMENTS ON PROPOSED REVISIONS TO ATC 3-06

V. T. Bertero, Representative of ATC

REVISIONS PROPOSED' BYr

IY. Joseph, (5. Manning, Representative of the Concrete Reinforcing Steel

Institute

4.1 SEC, 11.

Building Code Requirements for Reinforced Concrete,

American Concrete Institute (ACI 318-77 but excluding

Appendix A)

COMMENT ? This revision: should be introduced but modified as- follows:

"Ref. 11.1 Building Code Requirements for Reinforced Concrete, American.

Concrete Institute (ACI 318—775 excluding Appendix A and replacing Section

9.2.3 by Section 3.7.1 of this document," or the following alternative:

. . provisions of this. ATC whole document . Ref. 11.1 Building Code

Requirements for Reinforced Concrete, American Concrete Institute (ACI

318-77) excluding Appendix A."

REASONS: The purpose of excluding Section 9.2.3 is- to remind the designer

that the combination of- load effects adopted- by ATC 3-06 differs from, that

required by ACI 318—77. For this reason I prefer the first alternative

revision. I had already proposed this correction together with these related

revisions.

SEC. 11.2 3rd paragraph should read: "The capacity reduction factor in

Ref. 11.1, Sec. 9.

3

shall be modified as follows:"

SEC. 11.7.1 5th paragraph, second line should read: ". . . splicing

conforming to Ref. 11.1, Sec. 12.15.3 may be used."

SEC. 11.7.2(B) 1st line at top of page 106 should read: "Welded splices

and approved . mechanical connections conforming to Ref. 11.1,

Sec. 12.5.3 may be used . . ."

Appropriate revisions should be made also in the Commentary of Chapter 11,

i.e., pages 449, 450, 451, and 453.

4.2 SEC. 11.2 Revise third paragraph as follows: "Axial compression or

a-g-tal compression combined with bending on any member where

axial stress due to all loads exceeds 0.10 f£ and the axial

stress due to seismic forces exceeds 0.05 f£ and special

. lateral reinforcement as specified in Section 11.7.2(C)."

COMMENT : The proposed revision should be introduced .
4.3 SEC. 11.5.1 Revise third paragraph, second sentence, as follows:

ASTM A-615, grade 40 or 60 reinforcement may be used

in these elements if . . .

COMMENT : This revision could be introduced if, at the end of the paragraph , the following addition is made : "... and (3) the welding, when it is

required, can be shown to offer the same strength and toughness as the

ASTM A-706 under cyclic loading including strain reversals."

4.4 SEC. 11.8.1 Delete third paragraph requiring two curtains of steel.

COMMENT : This revision should not be introduced . Walls are subjected to

bending about their weak axis due to inertia forces perpendicular to the

plane of the wall. There are cases, particularly when barbell cross-section

walls are used, when the thickness of the wall panel could be less than

10 inches.

160
Partners EOWARO COHEM EOWARO LAINC ALLEN CUSTEH

JACOB ELOAR

SEORBE CROSS

AMMANN &. WHITNEY

CONSULTING ENGINEERS

TWO WORLD TRADE CENTER, NEW YORK. N. Y. 10048

(212) 938-8200

CABLE: AMMWMIT N.Y. iXse^jr

TELEX: 12-797*

Dr. Richard D. Marshall r Secretary February 11,

Technical Committee 4: Concrete

Review and Refinement of ATC 306

U.S. Department of Commerce

National Bureau of Standards

Washington, D.C. 20254-

Dear Dick:

CommmltamtM WERNER AMMANN MYO c. anoersom

MILTON BRUMER

LEOPOLD H. JUST

PmctptU Aiaocimtm

C CORSE RCCHT

Controller ANTHONY T. RUSSO

1980

With respect to Chapter 11 - Reinforced Concrete, it appears that*

this is based on an early draft of the pending revision of ACI 318, ' __ Appendix A. This draft has been substantially revised since it was used

to develop Chapter IK I have been assured that a revised , nearly V ^

final, draft will be available for our Committee meeting on February 21 ^ jo

and that the final draft will be available for the Trial Design phase ofV

^

ATC-306. r

This draft is scheduled to go to the full Committee 318 on March 1 at its meeting in Las Vegas and can be balloted by Coiranittee 318

immediately thereafter.

It would then be available for publication and membership ballot in

January 1981. Future revisions of Appendix A could be readily

coordinated with the appropriate committees of ATC, which have

overlapping membership with ACI 318, and published concurrently with

future ATC 306 revisions.

Under these circumstances and since ACI 318 including Appendix A is

a fully approved concensus document, to avoid overlapping and

conflicting efforts and criteria, and to assure that Chapter 11 represents the highest practical state of the art, I strongly recommend

that , in the national interest , Reference 11.1 read as follows

"Building Code Requirements for Reinforced Concrete, American

Concrete Institute. (ACI 318 Current Edition)."

I apologize for the delay in forwarding this recommendation but

trust that you will be able to distribute it to all members of Committee

4 and other appropriate groups.

EC:mrm Edward Cohen

MEW YORK BOSTON

JAKARTA

MILWAUKEE NEW ORLEANS

AMMAN DACCA MANILA TEHRAN
UNIVERSITY OF WASHINGTON

SEATTLE, WASHINGTON 98195

Department of Civil Engineering,

February 26, 1980

Dr. R. D. Marshall

Secretary, Technical Comnittee 4

ATC 3-06 Review

U. S. Department of Commerce

National Bureau of Standards

Washington D. C. 202S4

Dear Dick:

As promised February 21, 1980, I enclose my suggested revisions to

ATC 3-06 for the tasks assigned to me at our December 11 meeting in

Washington D. C. These comments assume that the committee is already

proposing to amend ATC 3-06 as agreed at our San Francisco meeting. My

suggested revisions therefore address only two substantive issues:

(1) Section 3.7.12. Vertical Seismic Motions for Buildings

Assigned to Categories C and D, and

(2) Seismic Provisions for Flat Plate, Flat Slab, and Waffle

Slab Structures.

My input for the latter issue consists of three parts:

(1) A discussion of the apparent implications of ATC 3-06 if

unamended for flat plate construction.

(2) A review of the state of knowledge on the behavior of flat

plate construction under reversed' cyclic loading.

(3) A suggested set of revisions to the provisions and the commentary, and a set of reason statements for the revisions.

My discussion uses the term flat plate to cover flat slab and waffle

slab structures as well as flat plate structures in both reinforced and

prestressed concrete.

Neil M. Hawkins

Professor and Chairman

PTI Representative

ST

cc: Members AT 3-06, Technical Review Committee 4 . . , .

^ W. G. Corley, M. A. Sozen, J. Grossman, C. L. Freyermuth 'wl enc

162
[I

'[/

)

Section 3. T, 12

I

Vertical Seismic Motions for Buildings

Assigned to Categories C and D

The vertical component of earthquake motion shall be considered in the

design of horizontal cantilever and horizontal prestressed components. For

horizontal cantilever components,. these effects may be satisfied by designing

for & net upward force of Q.2QD

„ For horizontal prestressed components, these

effects may be satisfied by designing for a net upward force of 0. 2CL if the

prestressed component is not part of the seismic resisting system aha bonded

reinforcement not less than tne minimums required by these provisions is

provided where maximum moments may occur for both horizontal and vertical

components of the earthquake motion! For other horizontal prestressed

components, these effects may be satisfied by Formula 3- 2a.

REASON

Formula 3- 2a is "for partial penetration welded steel column splices or

for reinforced masonry and other brittle materials , systems , and connections .

The implication, that prestressed members can have a brittle failure is consistent with, the possible behavior of some long span extruded precast prestressed

products installed without integral topping. However, where topping, properly

reinforced and bonded, is used on such units or the component is a pretensioned

or post- tensioned unit including supplementary bonded reinforcement equal to

the ACI Code 318-77 specified minimums, such brittles failures do not occur

and seismic provisions can be consistent with those for reinforced concrete

units.
(2) FLAT PLATE CONSTRUCTION

1. General

1.1 Exposure Group B

For buildings of seismic hazard exposure group B, ATC 3-06 effectively

prohibits flat plate construction. Group B includes all facilities in New

York, Boston, Buffalo, and the New England states, much of North and South

Carolina and Tennessee, large areas of Oklahoma, Arkansas, Illinois, and

Missouri, and much of New Mexico, Montana, Idaho, Utah, Washington and

Wyoming. The potential economic impact of that prohibition is staggering.

For the post- tensioning industry alone, that prohibition could mean about a 25% drop in its work volume. Post- tensioning is used in about 30 million

square feet of suspended slabs constructed each year in the U.S.A. and much

of that construction is flat plate.

In his letter of November 19, 1979, to ATC, Jacob Grossman of Robert

Rosenwasser and Associates of New York, details his experience with respect

to the economics of flat plate construction and its seismic response when

properly detailed. He states "I cannot even begin to describe the construction havoc the exclusion of flat -slab structures can introduce in strong

union-high construction cost areas." He points out that enough research

and knowledge are available to incorporate flat -slabs and allow them as "ordinary" frames without shear reinforcing.

It is not clear that it was intended that ATC 3-06 prohibit flat-slab

construction for "ordinary" frames. Contrary to the situation for group

C and D exposures, neither the provisions nor the coimentary explicitly

state such a prohibition. However, they require in flexural members of

ordinary frames for group B exposure, web reinforcement perpendicular to

the longitudinal reinforcement throughout the length of the member. The

minimum reinforcement is two leg No. 3 stirrups at a spacing of d/2.

Inclusion of such reinforcement in flat slabs would create economic as well as logistic problems.

It is suggested that:

(1) the provisions state clearly whether flat plate, flat slab, or waffle slab construction is feasible for ordinary frames for Category

B.

(2) If flat plate, flat slab, or waffle slab construction is feasible, the provisions specify any special restrictions for that

construction.

1.2 Exposure Groups C and D

The intention of ATC 3 with respect to restrictions on the use of

flat plate framing to resist lateral forces for category C and D structures is clear. Such use is highly undesirable. However, the intention

for category C and D structures where seismic forces are resisted by a parallel structural system, is not clear. In the Commentary to Chapter 11 on page 450 dealing with Material Requirements for Seismic Categories C

and D it is stated:

1 f\L
"Even if* a particular frame has been designed to support only gravity

loads and is not intended to be part of the structural system resisting

seismic forces, it must sustain, the gravity loads after having been

subjected to approximately the same displacements as the seismic resis*

ting system."*

That statement is logical and non-controversial . However , the statement continues

,

"Therefore, all frame components (which are not designed to resist

seismic forces) in Categories C and D buildings , are required to have

as a mininum, the details specified in Sec. 11.6.”

That section gives requirements for ordinary moment frames assigned

to Category S.

"Furthermore,, if calculations show that frame components which are not

part of the structural system resisting seismic forces, will have to

yield in order to accommodate the calculated displacements of the

seismic resistance, those components must have special transverse

reinforcement as specified for Special Moment Frames."

Effectively, those statements prohibit the use of any flat plate

frame, slab, or waffle slab in Category C and D structures. They require

special transverse reinforcement of a type illogical for. flat plates,

especially if yielding- is predicted. How to define yielding in a flat

plate is also unclear.

The Coimentary for Section 3.6.3 on Seismic Performance Category C

is more explicit on page 346. It states:

"In many buildings, the seismic resisting system does not include all

of the components that support the gravity loads. A common example

would be a flat slab concrete warehouse of several stories in height

where the lateral seismic loads are resisted by exterior shear walls

or exterior ductile moment resistant frames.

"Subsec. (c) , (apparently refers to Section 3.3.4(c)), requires that

the vertical load carrying capacity be reviewed at the actual deformations

resulting from the earthquake. In the example of the flat slab warehouse,

there will be bending moments in the columns and slabs and an uneven shear

distribution at the column capitals. At the calculated deflections and

the resulting imposed moments and shears, it must be demonstrated that the

members and connections will not. fail under the design gravity loadings."

That statement is. logical and non-controversial . However, the

statement continues

"The loading is cyclical so static ultimate load capacities are not

acceptable. If the combination of those loads and deformations result

in stresses below yield, it can be assumed that the system is capable of

supporting the gravity loads. If the stresses are above yield, then

sufficient ductility under cyclic loading must be provided. If the

gravity load bearing system- is to provide any calculated resistance to
- 3

-

seismic resistance (no matter how small), then the detailing for ductility

must be consistent with the values given in Table 3-B,"

What yielding is for a slab-column connection is not defined and for

the example discussed what ultimate load capacity would be acceptable for

cyclic loading is not defined in ATC 3-06 or ACI 318-77.

Finally, the Commentary on Section 11,7.1 Flexural Members in Special

Moment Frames on page 453 states:

'The geometric constraints given for flexural members are based primarily

on past practice. The maximum width limitation explicitly and intentionally eliminates the use of a flat plate or flat slab working as a frame

unless special details are incorporated in the structure. It should be

pointed out that even if it may be possible to provide the necessary

flexural strength in that portion of the slab permitted to be designated

as a beam, it is likely that the drift criteria will govern the design

for Categories C and D. Furthermore, if a flat plate oh a flat slab is

used as a frame working parallel with a structural wall, the actual

relative stiffnesses of these two systems in the non-linear range of

response should be evaluated elastically considering the effect of

cracking and reinforcement slip, rather than on the basis of gross

section,"

That statement is correct and consistent with test data.

Behavior of Flat Plate Construction under Cyclic Loading

2.1 Laboratory Results

There have been seven major laboratory investigations of flat plate

connections subjected to cyclic loading (1-8). The results of the extensive University of Washington investigations are sunmarized in the attached

articles

.

The lateral load response is strongly influenced by:

(1) the amount and distribution of the flexural reinforcement in the

slab,

(2) by the amount, type, and extent of any shear reinforcement, and

(3) by the level of shear stress transferred to the column simultaneous with the moment.

Even when there has been a low flexural reinforcement ratio and a connection well over-designed for shear, there has still been little

ductility under reversed cyclic loading. For specimens with high reinforcement ratios within lines one and one-half times the slab thickness either

side of the column, there has been a considerable increase in the lateral

load stiffness. However, there has been as much as a 10*» reduction in the

moment transfer capacity as compared to that for monotonic loading and a punching failure has occurred shortly after the reinforcement passing

through the column has yielded. Since there is little improvement in the

ductility with the use of low reinforcement ratios and a considerable

reudction in stiffness, concentration of column strip reinforcement is

desirable.

166
The only* proven: ways, of maintaining capacity through large rotations

has been to add properly detailed shear reinforcement consisting of either

integral bean stirrups or thin steel H sections or studs anchored above

and below the flexural reinforcement passing through the column. . Shear

reinforcement in the form of shearheads or bent bars increases the capacity

but does not increase ductility. The shear reinforcement must hold the top

and bottom flexural mats together and prevent the development of a splitting

crack between those mats. The shear reinforcement should have a spacing not

exceeding d/2 and need not extend further than about 5 slab thicknesses out

from each column face. Rules for proper detailing of such shear reinforcement are described in Reference 7. Slab-column connections are so flexible

that flat plate structures are unlikely to meet ATC 3-06 ' s stiffness requirements for ductile moment resistant frames. Thus, shear reinforcement in

flat plates is probably unnecessary unless the flat plate structure is the

only line of defense or unless the flat-plate structure is to provide a

required secondary line of defense.

The level of shear stress transferred simultaneously with the moment'

markedly affects the energy dissipation and ductility characteristics of

slab-column connections. To obtain desirable characteristics, the flexural

reinforcement within lines one and one-half times the slab thicknesses

,

either side of the column should be limited to one percent and the shear

stress due to shear transfer on the critical section d/2 from the column

perimeter to 2 At that latter stress, shear cracks have not developed

in the slab prior to .the application, of lateral loading.

After a punching failure has occurred, bottom bar flexural reinforcement continuous through the column is essential to the connection being

able to maintain its gravity load carrying capacity. Such reinforcement

can carry a shear force equal to its shearing yield capacity. Alternatively,

prestressing, reinforcement passing through a column or over a lift slab

collar is also a very effective means of tying a slab-column connection

together after a punching failure. With prestressing reinforcement, a residual capacity can be obtained equal to 90 percent of the pre-punching

shear capacity.

Shear or torsional cracking develops at the discontinuous edge of a

slab adjacent to an exterior column, when the shear stress at that location

evaluated according to ACI 318-77 provisions, exceeds 2/TT. If that stress

is exceeded, stirrups having a size not less than No. 3, a spacing equal to

or less than d/2, and extending up to four times the slab thickness from

the torsional faces of the column should be provided to prevent opening of

those cracks. While the best ductility and energy dissipation characteristics are obtained with integral beam stirrups , hairpin stirrups inserted

perpendicular to the edge and extending a distance equal to the column

projection into the slab plus or twice the slab thickness plus i,,

whichever is less, into the slao will also provide adequate control to the

opening of those cracks.
-5-

Tests have shown that the above results are also applicable to waffle

slab- interior column connections (4) and that when there is moment transfer

about both axes of a column (8), the effect of the minor moment on the

shear capacity can be neglected if that moment does not exceed 30% of the

major moment and there is adequate reinforcement within lines one and one- half times the slab thickness either side of the column to transfer that

minor moment.

The recent tests on flat plate frames at the University of Washington

(8), have shown that in a frame, a punching failure will occur at a connection without stirrups at a displacement and at a capacity consistent with

subassemblage results. However, that punching failure did not lead to an

iranediate loss in capacity of the overall frame since the adjacent connection with shear reinforcement was able to supply the required additional

moment transfer capacity. Displacements much greater than those for punching at the connection without shear reinforcement had to be applied before

the capacity of the overall frame deteriorated. During that period the

connection without shear reinforcement continued to carry its share of the

gravity load. Further, after lateral loading was completed, it was found

that at the punched connection the slab could be readily jacked back up to

its original elevation and the connection repaired,

2.2 Field Results

Reports (9) have been issued on the behavior of several flat plate

structures in the San Fernando earthquake; the Holiday Inn, Orion Avenue,

the Holiday Inn, Marengo, and the Muir Medical Center. The Holiday Inn,

Orion Avenue, was a seven- story reinforced concrete flat plate structure

with typical plan dimensions 62 by 160 ft. The building was supported on piles centered under the columns which were spaced at approximately 20 ft.

centers. Spandrel, beams approximately 16 x 22-1/2 in. surrounded the

perimeter of the structure. The flat plate floor was 10 in. thick at the

second floor, 8 in. thick at the roof, and 8-1/2 in. thick for all other

floors. The spandrel beams were figured as creating exterior frames

roughly twice as stiff as the interior flat plates so that in the short

and long directions of the building, 36% and 67%, respectively, of the

stiffness was provided by the exterior frames. Peak accelerations at the

first floor level were 0.2Sg and 0.13g in the short and long directions,

respectively. Roof accelerations were 0.41 and 0.33g, respectively.

Repairs cost 11% of the initial construction cost and were nearly all non- structural. Some structural distress occurred at the comer column beam

connections and in the construction joints at the soffit of the exterior

column- beam connections. The response was most marked in the short direction with a lengthening of the period part way through the

record indicating that the structure began responding inelasticallv . The

analysis indicated that beams and slabs yielded, that columns generally

remained elastic, and that interstory drifts as large as 0.13 ft. occurred.

The elastic limit displacement was roughly 2-1/2 times the design code

displacement
Hie Holiday Inn, Marengo Streetr had dimensions and member sizes

almost exactly the- same as the Orion Avenue building. Peak accelerations

at the first floor level were O.lSg and 0.14g in the short and long

directions,. respectively. Roof accelerations were 0.43g and 0.25g,

respectively. Repairs cost. 7% of the initial construction cost and were

nearly all non-structural _ Structural distress was similar to- that for

tiie Orion Avenue building. The dynamic response was also similar to the

Orion Avenue buildings The analysis indicated that beams and slabs yielded

at their connections with the columns but that the columns generally remained

elastic. Interstory drifts were as large as 0.14 ft. In this structure,

as in the Orion Avenue structure, it was apparent that the stiffness of the

frame was sufficiently low that the non- structural elements such as partitions, played an appreciable role in the character of the structural

response to seismic forces*

The Muir Medical Center was an. 11-story office tower with an 18-1/1 in.

deep waffle slab at the ground level and perimeter basement walls , For

the second floor and above,, the 9-in* thick flat slab had 15 in. deep

tapered column capitals with deep spandrel beams around the perimeter.

The deep spandrel beams framing provided 70% of the lateral load stiffness

and the interior flat-slab- tapered drop panel framing the other 30%. Peak

accelerations were 0.10g at the basement level and 0.2g at the roof level.

Some of the structural members were predicted to yield during the earthquake

and the maximum story drift was computed to be 0.64 in. The general performance of the structure was linear-elastic with only minor lengthening

of the building period during the earthquake. Damage was all non- structural

and estimated at less than $2,000.

2.3 Period of Vibration

Fundamental periods for those structures for man- induced excitations

prior to the earthquake, at the beginning of the earthquake, mid-way through

the earthquake, and for man- induced excitations after the earthquake are

listed in Table 1. It is apparent that the period of the predominantly

flat plate structures, the Holiday Inns , increased noticeably during the

earthquakes with the increase being larger for the more heavily shaken

Orion Avenue building.

TABLE 1

Periods of Vibration for Flat Slab Structures

Stories Direction

Periods : aetore

Quake

start or

Quake

Mid- way

Through Record

Alter

Quake

Holiday Inn T Short 0.48 0.79 1.6 0,68

Orion Avenue Long 0.53 0.88 1.24 0,72

Holiday Inn T

Long 0.53 0.88 1,0 0,64

Marengo / Short 0.4* 0.79 1.2 0,63

Niiir Medical IX Long 0.90 1.43 1,4 1,02

Short 1.03 1.60 1,6 1.14
-7-

If the values of the periods at the start of the earthquake are compared

with the general data on Fig. C4-2, page 373 of ATC 3-06, then it is

apparent that the periods for these structures are better characterized by

the relationship, T

R

= 0.035 h

fl

J ' 4 than the relationship TR

= 0.025 h

n .

2.4 Stiffness

The ATC 3-06 provisions limit the allowable story drift for Seismic

Hazards Exposure Groups I and II to 0.015 radians. When there are no brittle- type finishes in buildings three stories or less in height, those

values can be increased to 0.02 radians. If it is accepted that for a reinforced concrete structure, a load factor of 1.4 is required on earthquake forces and a capacity reduction factor of 0,9 for flexure, then

connection rotations at 65% of the ultimate capacity should not exceed the

story drift specified above divided by C^. Maximum measured values of

for a story drift of say 0.015 radians for a given column proportion and

a spacing can be evaluated directly from the subassemblage specimens.'

Table 2 lists values calculated according to that concept for

several different investigations. Values range from a low of 2.4 for the

flat plate frame test (8) with a low p value through to a high of 4.3 for

the waffle slab specimen (4). There is a marked increase in values with

increasing slab depth and a lesser increase with increasing column size.

Not apparent from that table is the wide variation in results obtained for

supposedly identical specimens. values varied by as much as 50% for

similar specimens and averaged about 20% higher for specimens with shear

reinforcement than those without.

Based on these subassemblage results and experience from the San

Fernando earthquake, it is apparent that a conservative value of C, for

flat plate structures is 2. Although higher values can be obtained by

careful detailing, even for waffle slabs, it is unrealistic to expect that

the value of 6 required for a ductile moment resistant frame can be

obtained. Thus, flat plate framing should only be recognized as an acceptable lateral load resisting system when classified as an ordinary frame.

The only possible exception might be for a waffle slab structure without

brittle finishes and less than three stories high. Even in that case,

experience from the San Fernando earthquake with the Olive View Hospital

Ambulance Port was undesirable. However, the 14 x 18 in, columns were

smaller than desirable and failure occurred in the columns and not in the

slab-column connection,

. 2.5 Conclusions

Based on this summary of field and laboratory experience, it is

concluded that:

(1) flat-plate structures of normal proportions and without shear

reinforcement will have little difficulty in meeting the strength,

stiffness, ductility, etc., requirements for ordinary frames, especially

if certain detailing requirements specified later, are satisfied.

170
VALUES

OFCH

MEASURED

IN

SUp-ASSEMBLAGE

TESTS I

xt

Ob OL 01 (O 01 oi a.

4*- 4* 4-* 4-> -4* ^ <3- <o <o to- 19 <a ofBB

01 CL. CL. a. 0b CL. a. i E a* *» 0b ' OL 4*- 4* 44 «4> 44- *41 E O >> (TJ <9 •4- <9 <9 <9

<v t— fH» f9»- <9 L. CL u_ LL. lL Ll. LL LL

in

1X9- UT to CO CO

*o •- » •- 9 u CM. CM. CO- *** CM CM

££ . O 0144 rr o ov

-4-1

—<4— CO O) • *— =

fZ 3 t» ca o o p» CO

tn E 4

| CM CM CM

01 3 N

X

X

X

X

XXX 44 O to Jf* u o c to ao o o f—

Ov

a

«f"B- CM CM CM

ClO

L. a.

o> c- a»

<o E c ay or o O VO o 3 •*- CM CM CM

CO <—

U 4-»

O

C_5 CL. to 3

B»

</T tn to

(V •* o -0 3*

JC c ^ U *—

to -4-

CO r*«» co os

t—

at CO CM 3 • (O en U_ o cn u

to

01u • 3

01V.01

<4-

CM- CO rr - ao

01 cc
(2) With flat plate structures of normal proportions it would be

extremely difficult, if not impossible, to meet the stiffness

requirements for utilizing such frames as special moment frames for

Category C and D buildings.

(3) With flat plates of normal proportions punching failures will

not occur until interstory drifts greater than the limiting values

specified in Table 3-C, page 53, of ATC 3-06.

(4) With flat plate structures used as the gravity load carrying

system in Category C and D buildings, it is not necessary to consider

punching failures as unacceptable provided the detailing requirements,

specified later, are satisfied.

(5) With flat plate structures yielding should be defined as either:

(a) the development of the negative moment yield capacity of the

slab on a line extending across the width of the slab at the

column face, or

(b) the development of the moment transfer capacity at the slabcolumn connection for yielding of the reinforcement at that

connection. That capacity can be taken as the flexural capacity

of the reinforcement top and bottom within lines one and one -half

times the slab thickness either side of the column.

(6) The period of structures with 35% or more of the lateral load

stiffness provided by flat plate framing can be estimated from the

relationship T

R

= 0.035 h 3/4
-9-

2.6 REFERENCES

2.

Hanson, N. and Hanson, J„, "Shear and Moment Transfer Between Concrete

Slabs and CoIumns, ,r Journal o£ the PCA. Research and Development Laboratories,

January 1968. C^® 2.5

2. Carpenter, J.B. , Kaar, P.H. and Corley, W.G., "Design of Ductile Flat Plate

Structures to Resist Earthquakes,” Proc. 5th World Conf, Earthquake Eng.

,

i Rome, Italy, 1975.

3. Kanoh, Y. and Yoshizaki, S. , "Experiments on Slab-to-Column and Slab- to

Wall Connections,” Japan Concrete Journal , Vol. 13, No. 6, June 1975

Cd

- 3.5

4. Rodriguez, M.R., "Diseno Sismico De Conexiones Entre Losas Planas Reticulares

y Columnas,” M. E. Thesis, University of Mexico, July 1979. C^ * 4.3

5. Islam, S. and Park, R., ’Tests on Slab-Column Connections with Shear and

Unbalanced Flexure,” Journal of the Structural Division, ASCE, Vol. 102,

No. ST3, March 1976, pp. 549-568.

6. Zaghlool, E.E.R. , "Strength and Behavior of Comer and Edge Column-Slab

Connections, in Reinforced Concrete Flat Plates,” Ph.D. Thesis, University

of Calgary, Alberta, Canada, 1971.

7. Hawkins, N.M. , Mithcell D. and Symonds, D.W. , "Hysteretic Behavior of

Concrete Slab to Column Connections , " Proc. 6th World Conf. Earthquake Engrg,,

New Delhi, India, 1977.

8. Hawkins, N.M. , "Seismic Response of Concrete Flat Plate Structures,” Proc,

Seventh World Conference on Earthquake Engrg. , Istanbul, 1980.

9. San Fernando, California, Earthquake of February 9, 1971, U.S. Department

of Connerce. National Oceanic and Atmospheric Administration, 1973.
- 10 -

3. Suggested Revisions

3.1 Page 105, 11.6.1, Flexural Members

A. Alter sentence 2 of paragraph 2 as follows:

"At least two No. 5 or larger bars shall be provided continuously

both top and bottom except in slabs.

B. Alter sentence 1 of paragraph 6 as follows:

"Web reinforcement perpendicular to the longitudinal reinforcement

shall be provided throughout the length of all members except slabs ."

C. Alter sentence 1 of paragraph 7 as follows:

"Within a distance equal to twice the effective depth from the

end of all members except slabs, ...."

D. Add paragraph 8 as follows:

"Slabs without beams and supported on columns may be used for

ordinary moment frames provided those slabs satisfy the requirements

of Chapter 13 of Ref. 11.1 and this Section. Bottom bar reinforcement, A' shall be provided continuous through or anchored within a column and not less than that given by the following formula:

AA'

s 2(V-Vn) ony

( 11 - 2 )

where V Is the shear force transferred to column due to unfactored

gravity loads and Vp is the sum of the vertical components of the

forces in any prestressing tendons passing through or anchored

within the column. At least two No. 4 or larger bars shall be

provided continuous through or anchored within the column in both

directions and both top and bottom. In slabs without beams column

strip negative moment reinforcement shall be distributed so that

at least 60 percent of the required reinforcement is concentrated

within lines one and one-half times the slab thickness either side

of the column. The shear stress, v, on a critical section located

half the effective depth of the slab from the column Derimeter,

and caused by the shear force V shall not exceed 2 /fit If there

is no spandrel beam at the discontinuous edge of a slab, reinforcement within four slab thicknesses either side of a column face and

adjacent to the edge shall be detailed so that it can act as torsion

reinforcement. If the torsional strength of the spandrel beam

framing into a column exceeds the flexural strength of the slab at its connection with the beam for the adjacent half panel width, all

shear shall be assumed transferred to the column via the beam.

174
-11-

i Reasons

j Section 11.6.1 is altered so that is dear that flat plate, flat slab,,

or waffle slab construction is acceptable for ordinary frames. Revision D‘ spells out special restrictions for that framing.

i A* B, and C, Elimination of requirements for slabs is viable when

Revision 0 is added.

D. Sentence 1 requires that slabs be defined according to the two-way

systems envisaged in Chapter 13 of ACI 318-77.

j Sentence 2 requires sufficient reinforcement through a column to be

able to support the gravity load of a slab in the unexpected event that a

punching failure occurs.

Sentence 3 specifies a minimum amount for that reinforcement.

Sentence 4 creates a situation where the steel passing through the

column head area will yield shortly before or simultaneously with yielding

on a maximum negative moment line extending across the width of the slab.

If that condition is not satisfied and only the requirements of Chapter 13

of ACI 318-77 satisfied the negative moment reinforcement passing through

the column can be yielding under gravity loads. The lateral load stiffness

of the flat plate framing would be decreased markedly.

Sentence 5 requires that the shear stress caused by the gravity loads

will be sufficiently low that the connection will have a ductility ratio

I of at least 2.

Sentences 6 and 7 add requirements identified in the Suggested Revisions to ACI Code 318-77 by AC1-ASCE Committee 426 and the previous

discussion. Sentence 6 ensures that if shear or torsional cracks develop

| at the edges of slabs, there is reinforcement that can control the opening

of those cracks. Sentence 7 specifies how to distribute shears when there

is a spandrel beam and no flexural beam.

3.2 E. Page 451 in Commentary

Revision

Add ta end of paragraph for 11.5.1 finishing, on that page:

"Flat plate frames of normal proportions and detailed as specified in

Sec. 11.6 will not yield until story drifts greater than 0.03 h

sx

."

Reason

Clarifies that flat plate frames are very flexible relative to other

framing systems and corrects deficiency noted in discussion.
- 12 -

3.

3

F Page 347 of Commentary

Revision

Alter starting at the top of page 347 as follows:

’’Loading is cyclical, so static ultimate load capacities may not be

reached. If . .

. (to end of paragraph) . In the exa:tple of the flat

plate warehouse, the connections can still carry the design gravity

loadings if they satisfy the requirements of Sec. 11.6.1. If,

however, they are to provide any calculated seismic resistance,

they must be detailed for ductility consistent with that required

for the parallel exterior shear wall or ductile moment resisting

frames."

Reason

Clarification of wording to make it consistent with the revised

Sec. 11.6.1.

3.4

G Section 4.2.2 Page 56

Revision

Alter Eq. (4-4) as follows:

"where Cp = 0.035 for steel frames or concrete frames where flat

plate framing provides 351 or more of the lateral load stiffness.”

Reason

Flat plate framing is considerably more flexible that beam and column

framing, slab sections are lightly reinforced, and cracked at the column

face under gravity loadings. The three structures shown on Fig. C4-2

Page 373 satisfying the 35% requirement had initial periods at the start

of the earthquake on or above the broken line in that figure and their

periods increased with the duration of shaking. Part of the greater initial

stiffness was attributed in the San Fernando reports to the stiffening

effects of non- structural elements. Closer attention to architectural

requirements, as specified in Chapter 8, would increase the conservancy

of calculating Cp values as recommended above.

3.

5

H Page 348 of Commentary

Revision

Add to last paragraph of Page 348:

"For two-way slabs orthogonal effects at slab -to -column connections

can be neglected provided the moment transferred in the minor direction does not exceed 30 percent of that transferred in the orthogonal

direction and there is adequate reinforcement within lines one and

one-half times the slab thickness either side of the column to transfer

all the minor direction moment."

176
-13-

Reason

Considerable simplification that is predictable using beam-analogy

concepts C? » 8) and has been proven by testing (8).
ARCHITECTURAL

REPLY TO : 1350 OEL RIO COURT

CONCORD. CALIFORNIA 94518

TELEPHONE: 4 1 5 / 9 5 7 - 1 3 2 7

STRUCTURAL

r PRESTRESSED CONCRETE INSTITUTE5

20 NORTH WACKER ORlVS / CHICAGO. ILLINOIS S0606

TELEPHONE 312 / 346-4071 March 25 , 19 80

TO: Members of Technical Committee 4: Concrete

Edward Cohen

Eugene Holland . ^

Joe Manning \ /

Jim Prendergast - ^ Mark Fintel

Neil Hawkins “0

Vitelmo Bertero —

;

Jim Lefter __ Di ck Marsh all ao

RE : ATC 3-06 Review

Gentlemen :

As discussed and committed in our 21 Feb 80 meeting, I have developed recommended detailing requirements for

prestressed concrete piling, to be inserted into Chapter 7.

Add new Section 7.5.3 (E)

(1) For the body of fully embedded foundation piling

subjected to vertical loads only, or where the design

bending moment does not exceed 0.2 0 Mfvj q , spiral reinforcing

shall be provided such that ^^.0.006 ( 0 . 2?o

)

(2) For free standing piling and hollow core or marine

piling subject to severe installation and operational forces,

spiral reinforcing shall be provided such that^s - 0.022 ( 0 . 7 % ) , or a spacing satisfying the following relationship, if it

results in a percentage of spiral greater than that given

above :

w here

SsD _ ,-LL-A_

s P

p

( c -h 7 ds p ) fr

Ssp = spacing of spiral reinforcing

fy = yield strength of spiral reinforcing

Asp = Area of spiral reinforcing

c = cover over the spiral reinforcing

,3or;s.- ORGANIZATION cO« TH 6 ADVANCEMENT OF TW£ DESIGN MANUFACTURE AND USE OF PRESTRESSED CONCRETE ANO PRECAST EONC 178
dsp = diameter of spiral reinforcing

fr =• modulus of rupture of concrete

is = ratia of volume of spiral reinforcing to

* total volume of core (out to out of spirals)

(3) Any piling installed, in layered soils Imposing severe

curveatures during earthquake shall have the same amount of

spiral reinforcing indicated in item ( Z) above, accompanied

by additional amounts of flexural reinforcing indicated, by

moment - curveature relationships developed for the pile and

soil profile present.

(4) The top and bottom portion of hollov* core piling and

rigid frame piling where high values* of shear and moment

occur simultaneously should contain spiral reinforcing with

p* £.0.031 (1.0ft) far a distance of Z pile diameter r or Z

times* the width of the' pile.

References :

1. Gerwick 1 Brauner - Design of High-Performance Pre - stressed Concrete Piles for Dynamic Loading

( ASTM STP 670, 1979)

Z. Margason - Pile Bending During Earthquakes , lecture

series at U.C. Berkeley on Effects of Ground Shaking

and Movement on Piles. March 6, 1975.

3. Bertero, Lin, Seed, Gerwick, Brauner, and Fotinos -

A Seismic Design of Prestressed Concrete Piling , FIP Congress NYC, May Z5 , 1974.

4. Margason - earthquake Effects on Embedded Pile Foundations , paper presented at Pile talk Seminar,

San Francisco, March 1977.

5.

' Test data from dynamic cyclic prestressed piling tests

conducted under, the sponsorship of the Prestressed

Concrete Manufacturers Association of California.

6. Test data from tests conducted by H. Makita of the

Tokyu. Concrete Pile Co.

California Marketing Director

cc: California Steering Committee

Dan Jenny , PCI

Ben C . Gerwick. Jr.
PROPOSED REVISIONS TO ATC 3-06

A PC* Af”l $

’ April 7, 1980

V. V. Bertero - Representative of ATC

REVISIONS PROPOSED BY :

V. Neil M. Hawkins, PTI Representative

5.1 SEC. 11.6.1 Flexural Members, page 103

A. Alter sentence 2 of paragraph 2 as follows:

"At least two No. 5 or larger bars shall be provided continuously

both top and. bottom except in slabs.

B. Alter sentence 1 of paragraph 6 as follows:

"Web reinforcement perpendicular to the longitudinal reinforcement

shall be provided throughout the length of all members except slabs ."

C. Alter sentence 1 of paragraph 7 as follows:

''Within a distance equal to twice the effective depth from the

end of ail members except slabs, ..."

D. Add paragraph 8 as follows:

"Slabs without beams and supported on columns may be used for

ordinary moment frames provided those slabs satisfy the requirements

of Chapter 13 of Ref. 11.1 and this Section. Bottom bar reinforcement, Ag, shall be provided continuous through or anchored within a column and not less than that given by the following formula:

2 (V-V ) - orl7 (u' 2)

where V is the shear force transferred to column due to unfactored

gravity loads and Vp is the sum of the vertical components of the

forces in any prestressing tendons passing through or anchored

within the column. At least two No. 4 or larger bars shall be

provided continuous through or anchored within the column in both

directions and both top and bottom. In slabs without beams column

strip negative moment reinforcement shall be distributed so that

at least 60 percent of the required reinforcement is concentrated

within lines one and one-half times the slab thickness either side

of the column. The shear stress, v, on a critical section located

half the effective depth of the slab from the column Derimeter,

and caused by the shear force V shall not exceed 2 /f£. If there

is no spandrel beam at the discontinuous edge of a slab, reinforcement within four slab thicknesses either side of a column face and

L80
2

adjacent to the edge shall be detailed so that It can. act as torsion

reinforcement- If the torsional strength of the spandrel beam

framing into a column exceeds the flexural strength of the slab at

its connection with, the beam for the adjacent half panel width , all

shear shall be assumed, transferred to the column via the beamCOMMENT:

Revision A should be introduced

Revision 3T should be introduced.

Revision C should be introduced.

Revision S should be introduced but with the following correction and

addition . The end of sentence 6 of this suggested new paragraph 8 should

read as follows: ". . . it can act effectively as torsion reinforcement

considering the possibility of full reversals of the sense of the

torsional moments ."-

Furthermore, it is suggested that in the commentary to this Section11- 6.1 some guidelines regarding the proper detailing of such torsion

reinforcement be given5.2 COMMENTARY ON SEC. 11.5.1 on page 451.

Add to end of paragraph for 11.5.1 finishing on that page: "Flat

plate frames of normal proportions and detailed as specified in

Sec. 11.6 will not yield until story drifts greater than 0.03 h ."

92

COMMENT: This proposed revision should be introduced modified as follows : "The flat plates of flat plate frames of normal proportions and

detailed as specified in Sec- 11.6 will not undergo any significant

yield until story drifts greater than those allowable (Table 3~C)

5.3 COMMENTARY ON SEC. 3.6.3 on page 347.

Alter starting at the top of page 347 as follows:

"Loading is cyclical, so static ultimate load capacities may not be

reached- If - . . (to end of paragraph). In the example of the flat

plate warehouse, the connections can still carry the- design gravity

loadings if they satisfy the requirements of Sec. 11.6.1. If,

however, they are to provide any calculated seismic resistance, they

must be detailed for ductility consistent with that required for the

parallel exterior shear wall or ductile moment resisting frames."

COMMENT: This proposed revision should be introduced . However, it should

be noted that there appears to be an inconsistency between this

proposed revision and the previous one where it was stated that the
3

flat place frames will not yield until story drifts greater than

0.03 h sx which is larger than the maximum allowable story drift of

0.02 hSv . Thus it appears there is no way that detail for ductility

larger than 1 can be developed for the allowable story drift.

5 . 4 SEC. 4.2.2, page 56 .

Alter Eq. (4-4) as follows:

"where C<j = 0.035 for steel frames or concrete frames where flat

plate framing provides 35% or more of the lateral load stiffness."

COMMENT

:

Thi* g proposed revision should not be introduced

REASONS : Although bare flat plate frames are very flexible, and their

periods are larger than the values given by Ta = 0.035 Gj h^/4

when they are used in buildings the initial periods of these

buildings usually decrease considerably due to the effects of the

nonstructural components, even to values below those given by

Eq. 4-4 using C-j = 0.035. The ATC policy in specifying values for

the period to be used in estimating the seismic forces has been to

specify lower values than the real ones, particularly in the case

of flexible buildings , with the main objective of forcing the design

of stronger and sciffer structures to avoid the large nonstructural

damages that have been observed in these buildings during even moderate ground shaking. Furthermore, if it is considered that ATC

allows the use of T = 1.2 Ta (see Sec. 4.2.4) and even T = 1.4 Ta (see Sec. 5.3) when T is computed according to established methods

of mechanics, the acceptance of C^ = 0.035 will permit the use of

T values larger than those that have been measured in the field.

This is not desirable.

5 . 5 COMMENTARY ON SEC. 3.7.2 on page 348 .

Add to last paragraph of page 348:

"For two-way slabs orthogonal effects at slab-to-column connections

can be neglected provided the moment transferred in the minor

direction does not exceed 30 percent of that transferred in the

orthogonal direction and there is adequate reinforcement within lines one and one-half times the slab thickness either side of the column

to transfer all the minor direction moment."

COMMENT: This revision should be introduced.

182
4

5.6r SEC. 3.7.12 . Vertical Seismic Motions for Buildings Assigned to

Categories C and D.

The vertical component of earthquake motion shall be considered in

the design of horizontal cantilever and horizontal prestressed components.

For horizontal cantilever components* these effects may be satisfied by

designing: for a net upward force of Q.2Qq. For horizontal prestressed

components,, these effects may be satisfied by designing for a net upward

force of Q.2Qp if the prestressed component is not part of the seismic

resisting systear and bonded reinforcement not less than the minimums

required by these provisions is: provided where maximum moments may

occur for both horizontal and vertical components of the earthquake

mo cion. For other horizontal prestressed components* these effects may

be satisfied by Formula 3—2a.

COMMENT^ This proposed revision should be reviewed by Committee 2: Structural

Design. In view of the little data available on the behavior of

prestressed tjpes of construction, and of the possibility that the

vertical ground, motions can excite inertial forces on the order of

the writer suggests that design examples be carried out with.

Equation 3..2a as well as the G.2Qq net upward force suggested by Professor

Hawkins.-
APR n. Letter to: Ed Cohen

Gene Holland

Joe Manning

Jim Prendergast

Mark Fintel

Neil Hawkins

Vitelmo Bertero

Jim Lefter

Dick Marshall

RE: ATC 3-06 Review - Concrete Provisions

Gentlemen :

As indicated and committed in the minutes of our last meeting

on 21 Feb 80 in. San Francisco, enclosed are the draft provisions

for precast concrete to be reviewed for inclusion in the ATC 3

document :

Add New Paragraph to Section 1.3.1

"Structures comprised of precast and/or prestressed

concrete sub assemb lages shall be designed in accordance

with the requirements of Section 11.9."

Add New Section 11.9

11.9 Structures comprised of precast and/or prestressed

concrete s ub ass emb 1 age

s

The provisions of this section apply to buildings constructed with precast concrete elements not conforming to

the detailing provisions given elsewhere in this section

for c as t - i n -p 1 ace concrete.

11.9.1 "Non Ductile" Construction

Structures with assemblages of precast concrete components

furnishing lateral resistance against seismic forces and which

do not possess energy absorption mechanisms shall be designed

to resist equivalent lateral forces equal to four times the

value of V

e =CsW determined from the procedure given in Section

A. 2 , but not to exceed V e =1.5AvW. 184
Lateral load resisting: walls formed by interconnecting

precast elements together shall have a ratio of wall height

(h) tar total coupled wall length* ( d) - h/d of not greater

than four.Walls with h/d greater tharr four* or where the

design- compressive stress exceeds Q-2f r c shall containvertical boundary- members irr accordance with- Section 11.8,4 r and will not be designed under this section^

X bracing systems used to furnish lateral support for

vertical load carrying frames comprised of precast and/or

prestressed concrete components shall be designed to resist

equivalent lateral forces equal to four times the value of

V e =CsVf determined fromr the procedure given in Section 1.2,

but not to exceed V e s2.0AvVfIn developing the above forces, prestress strands,

reinforcing, and concrete shall remain in the elastic range

at the threshold of the yield point, or proportional limit

state of the material11-9.2 "Ductile" Construction

Energy absorbing lateral load resisting systems comprised

of precast and/or prestressed concrete components shall be

permitted provided satisfactory evidence can be shown in the

form of experiments, testing, and analysis based upon established engineering principles that the resulting construction

complies- with the requirements of Sections J.6 and J.7 and this

chapter, and that they offer the same strength, stiffness,

stability, durability, damping, energy absorption, and energy

dissipation capacities (ductility) as required from the monolithic cast-in-place ordinarily reinforced concrete construc185
tion that they replace if the R and values given in

Table 38 are used.

Included with these draft recommendations is a graph of

equivalent lateral force values versus period, showing also the

force levels generated by the 1940 El Centro earthquake, long

recognized as the standard maximum credible earthquake in seismic

zone 4.

Very truly yours,

David A. Sheppard

California Marketing Director

cc : Dan Jenny

California Steering Committee

PCI Seismic Committee

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UNIVERSITY OF CALIFORNIA, BERKELEY

BERKELEY • DAVIS • IRVINE • LOS ANCELZS • RIVERSIDE • SAN DIEGO • SAN FRANCISCO

COLLECE OF ENCINEERINC BERKELEY, CALIFORNIA. 94720

DEPARTMENT OF CIVIL ENCINEERINC

DIVISION OF STRUCTURAL ENCINEERINC

AND STRUCTURAL MECHANICS

June 2, 1 980

MEMO TO: • Members of the Technical Committee 4 Concerning the Review

and Refinement of ATC3-06

FROM: V. V. Bertero

REGARDING: Comnents Regarding the Technical Implications of Incorporating

New Appendix A into ATC3-06

I must apologize to you for the way I presented my comments on the

rough draft but I have been working since Friday May 30 at 5:00 p.m. practically

until 8:00 a.m. today, Monday June 2, and I do not have any more time to

finish my comments or polish them. Attached I have given my conclusions

and recommendations and the reasons for them.

I regret to inform you that I have presented my resignation as a representative of ATC to this conmittee. I have enjoyed very much working

with you in the technical matters. However, lately I have not enjoyed being

involved in what appears to be a struggle for power over who is to write codes

regarding seismic resistant design of structures. I don't like to conduct

my review under pressure. I do not agree with the way that the activities of

this committee have been conducted lately.

In my memo to the secretary of the committee, dated Ma r? 21 , 1980, I not only requested but pleaded that the committee let me know at that time

whether I should try to improve Chapter 11 or try to improve the final draft

of the new Appendix A. I thought that this issue was resolved at the meeting

on April 14. However, I learned that the industries disallowed the vote of

their representatives. I consider this unacceptable of the committee. It was not until last week that I learned that I have been requested to review

the new draft of Chapter 11 that was proposed to be used to incorporate the new Appendix A into ATC and that there will be an emergency meeting of the committee on June 4. My previous committment does not allow me to attend such a meeting.

I don't have the time to do a review as I would like to do. For example, I could

not review the commentaries of the new Appendix A and therefore I had difficulty

in going through the proposed integration of the present Chapter 11 of ATC and

the draft of the new proposed Appendix A. But according to the experience gained

in these last two days of working, I feel that it will be a disservice to the

designers that have to do trial design runs to request that they use all these

conflicting documents (ATC, ACI 318-77, the interface between Chapter 11 and

Appendix A and the new Appendix A).

VVB/ed

cc: R. Sharpe

E. Leyendecker

136
REVIEW’ OF AM UPDATED CHAPTER. IX (Hay 28,. 1980) SUBMITTED BY FTNTEX.

AMD. QF THE APPENDIX A, DATED MARCH 1980

CONCLUSIONS AMD RECOMMENDATIONS:

by Vitalmo V- Bertero, Representative of ATC

CONCLUSIONSr Although, e complete review could not be done because of lack:

of time; the attached comments and observations, clearly lead to* thefollowing; conclusions

THE UPDATED DRAFT OF CHAPTER 11 SUBMITTED BY FINTEL ON MAY 29, 1980, AS

SUGGESTED BY THE INDUSTRIES, CANNOT BE ACCEPTED FOR INCORPORATION

TOGETHER WITH A NEW APPENDIX A INTO THE ATC 3-06.

Even if new drafts of this chapter and Appendix A* Including, all the

corrections, additions and clarifications suggested in the attached comments^

are prepared, I strongly believe it would be a mistake to introduce it in

the ATC 3-06 for the TRIAL DESIGN PHASE OF ATC 3-06. The main reason is

that the designers will, have to consider two new and very confusing cross

references (Chapter 11 and the new Appendix A) which would increase the

probability of misinterpreting the provisions. Considering that, even if

the designers were able to interpret correctly the interfacing provisions

of the new Chapter 11 and Appendix A, no significant technical, improvement

in the design will be obtained,, the writer believes:-it is not wise at this

time to introduce the new chapter and appendix.

RECOMMENDATIONS : The writer agrees that Chapter II of ATC 3-06 needs to be

updated and integrated with the new Appendix A. Therefore it is recommended

that.

A TECHNICAL SUBCOMMITTEE, WITH: MEMBERS FROM COMMITTEE 4 AND THE ACT

COMMITTEE THAT HAS PREPARED THE NEW APPENDIX A, BE FORMED AND CHARGED WITH

THE MISSION OF IMPROVING AND INTEGRATING THE NEW APPENDIX A INTO CHAPTER 11

OF ATC 3-06-

cc: Roland Sharpe

E- Leyendecker
MEMO TO: E. Cohen, Chairman of Technical Committee 4: Concrete Review

and Refinement of ATC 3-06, and

E. Pfrang, Chief of Structures and Material Division, NEL

FROM: V. Bertero, Representative of ATC

RE: Technical Implications of Incorporating ACI 318—77 and New

Appendix A by Reference into ATC 3-06

According to the request formulated by you through Mr. Fintel's letter

of May 29, 1980, I met with Mr. Fintel and Mr. Neville, ACI Committee 313

Secretary, on Friday, May 3^-» 1980, at 5 p.m. in 750 Davis Hall, University

of California, Berkeley, to discuss the above technical implications. As

requested in the same letter, the following are my written comments. It

should be noted that these comments are of a preliminary nature as I did not

have time to go through the document as thoroughly as I would like since it was only delivered to me on the evening of Wednesday, May 28, 1980. For

example, the provisions regarding joints of frames (Section A. 6 of the new Appendix A) differs considerably from the ATC provisions on joints’

(Section 11.7.3). To comment properly on the implications of this change

would require the technical background material (data) on which the changes

have been based and the time to study it. I did not have either.

I. CHANGES NEEDED IN CHAPTER 11 . Page 1. Sec. 11.1 should read: Refs. 11.1:

[1] ANSI/ACI 318-77 "Building Code Requirements For Reinforced Concrete"

but excluding Appendix A ; and

[2] New proposed Appendix A - Requirements for Reinforced Concrete Building

Structures Resisting Forces induced by Earthquake Motions, 19 March,

1980.

Page 2. Sec. 11.4.1 should read "Where Ordinary Moment-Resisting Frame

Systems are used for the seismic-resisting system, frame components

(beams, columns, and their joints ) shall be proportioned to satisfy,

in addition to the requirements of Chapters 1 through 17 of Ref. [l]

(ANSI/ACI 318-77), the provisions A. 3. 2, A. 3. 3, A. 4.3 and A. 8. 2 of

Ref. [2]. [NEW APPENDIX a] with the following additions and exceptions:

1. A. 3.2.1 Last sentence should read "At least two No. 5 or larger

bars shall be provided continuously both top and bottom."

2. A new section, A. 3. 2.5, should be added in the new Appendix A.

This section A. 3.2.5 should contain the provisions required in ATC

Sec. 11.6.1, paragraphs 4 and 5, i.e., "A flexural member framing

. . . yield stress." "Longitudinal reinforcement . . . for the

reinforcement."

3. A. 4.3.2 The first sentence should read "Lap splices are permitted

only within the center half of the snan and shall be proportioned as tension splices . Welded ..."

188
i z

Page 3. Sec. 11.4.1 (E) . Add " . . . considering- the probability of full

reversals of the sense of the torsional moments, (torsional resistance

combined with flexural under reversal moments deteriorate significantly

when conventional web reinforcement: is used) "*

Page 3. Sec. 11,5,1.. Add: at the end of this section ". . . A. 2. 5, excep

t

that ASTM 615 Grade 6G reinforcement should not be used when welding

of this reinforcement is used.” (See my comments of Feb. 11, 198Q.)

Page 3. Sec. 11.5.2. First paragraph, last line should be changed as

follows: ", . . provisions of Ref. [2],. i.e.* new proposed Appendix A.”

Second paragraph, second line , same change as above. (The same change

should be made throughout the whole proposed draft.)

In the first paragraph it is necessary to clarify that ATC refers to

"braced frames" while A. 5 refers to trusses. This inconsistency should

be removed. I recommend that* rather than incorporating the

exceptions here, a new Section 11.6.1 be added on page 4. as it was

recommended be done on the May 5, 1980, ballot,, i.e. * a new Section

11.9- of the AXC documents

Page 3. Sec. 11. 5. J. Should read "Structural walls shall have vertical

boundary members which, shall be proportioned to satisfy the provision

A. 5.

3

of the New Appendix. Vertical boundary ... can be developed.

If lap splices are needed at these levels, they shall be proportioned

as tension splices. "

Page 4. Sec. 11.5.3 . First paragraph (top of page) should be changed to

read "Structural diaphragms shall be provided with boundary or edge

elements at any section where tensile axial forces can be developed

across the entire diaphragm section. These boundary elements shall

be designed as required by A. 5.3. If lap splices are needed at these

sections, they shall be proportioned as tension splices."

Page 4. Sec. 11.5.4. This section should read as follows: "STRUCTURAL

COMPONENTS NOT PART OF THE. SEISMIC-RESISTING SYSTEM.

All structural components assumed to be not part of the seismicresisting system shall comply with Sec. 3.3.4(C) and shall conform

with the provisions of Sec. A. 8 of the new Appendix A except for

Sec. A. 8.1. This Sec. A. 8.1 does not apply to the investigation of the

deformation compatibility of these components; Sec. 3.3.4(C) is the one

that should be used. The design of such components shall satisfy the minimum reinforcement

requirements specified in Chapters 7, 10 and 11 of ACI 318 and

Secs. A.3.2.1 and A.5.2. 1. If nonlinear behavior is required in such

components to comply with Sec. 3.3.4(C), the critical portions shall

be provided with special transverse reinforcement in accordance with

provisions A.3.3 and/or A. 4.1 of the new Appendix A.

II. CHANGES NEEDED IN THE NEW APPENDIX A TO MAKE IT CONSISTENT WITH THE

ATC 3-06 PROVISIONS

Page 1. A.

Notation

h - should read h"

Note that some notations are different from those of ATC. For example,

h" is in ATC, S is S^ in ATC, and Pj is P&

in ATC-^ Therefore it is
3

recommended Che notations be reviewed thoroughly for Appendix A. and

ATC to assure their consistency.

Page 2. A.

1

Definitions

There are discrepancies in some of the definitions used by ATC and

Appendix A. For example, the definitions of cross-tie do not agree;

also Structural Wall vs. Shear Wall, Structural Diaphragms vs. Diaphragm,

Structural Trusses vs. Braced Frames, etc. Therefore it is recommended

that, the definitions in the two documents be thoroughly reviewed and

the discrepancies removed.

Page 3. Definition of Anchorage Length for a Bar with a Standard Hook . This definition does not agree with results of laboratory experiments

and field inspection of damages. The effective length of anchorage

cannot be counted from the critical section (where the strength of the

bar which is located at the faces of the joint is to be developed) . The

concrete of the joint that is not confined (which has the shape of a

cone) is not effective in supplying anchorage. This definition should

be changed to consider the cone of unconfined concrete.

Page 3. Sec. A. 2.1.1 This provision should be clarified. Limitations on

the amount of energy dissipation that can be used, or would be acceptable or tolerable, should be specified. Can these provisions be used when

the nonlinear response of the structure would demand " displacement

ductility" of the order of 10, 20, 30, 40, 50, 60 . . . ? As is it

written now, it is too vague and could lead to misuse of the provisions.

Page 4. Sec. A. 2. 1.3 . Are the requirements for Zone 2 as defined by the

UBC 1979 (I assume that it is the 1979 edition of the UBC to which

this Appendix A refers) compatible with the requirements for good seismic

performance of buildings assigned to Category B? This should be

discussed and clarified.

Page 4. Sec. A.2.1.4 . Are the requirements of the UBC 1979 for regions

following Zones 3 and 4 sufficient to guarantee good seismic

performance for buildings assigned to Categories C and D? This should

be discussed and clarified.

Page 5. Sec. A. 2. 3.

2

. Does <p « 0.5 apply only to the computation of the

strength of the element under concentric axial force, or does it apply

also to the combined axial force and bending moment, i.e., to the whole

N-M interaction diagram for N > A fl/10 (as it was established in ATC)?

S

Page 5. Sec. A. 2. 5.1 . A flag regarding the weldability of A5TM A615

Grade 60 should be inserted. Furthermore, it should be noted that,

while ATC required that in tests the actual yield stress not exceed

the specified yield stress by more than 21,000 psi (18,000 + 3,000),

the new Appendix A allows 22,000 psi (18,000 + 4,000). I do not have

the background material that has been used to justify this change.

Note that the higher the value that is accepted, the less meaningful

become the computations based on specified yielding (quality control

of material is a must if we want to improve seismic-resistant design

and construction)

.

190
4

Page 5. Sec. A. 3. 2.1 . The last sentence should read "At least two No. 5

or larger bars shall . .

Page 8. Sec. A. 4. 2.1. This section should be modified to read as follows:

"At any joint . . the sum of the flexural strengths of the columns

calculated considering, the critical combination with the possible

critical axial forces (whole range of possible axial forces acting in

combination with the moments should be considered) shall exceed the sum

of the moments at the columns obtained from the equilibrium at the joint

when it is considered that the beams framing into that joint in the plane

of the frame under consideration reached their flexural strength. The

flexural strengfas shall be . .

Page 8'. Sec. A. 4. 2.

. This section should be deleted or completely modified.

Reasons : It allows the design of weak column-strong beam frames that

can lead to soft story. Since the time this philosophy was proposed, I

have opposed it because it leads to an unsound seismic-resistant system.

It is not that the columns cannot be made ductile, but rather that the

formation of a soft story leads to such large demands of energy dissipation capacity (ductility displacement demands) from the columns that

these demands cannot be supplied. Therefore, it should be made clear

that, except for frames of more than 2 stories, attempts should be made

to prevent the development of soft stories. Any provision that will

allow the formation of such soft stories should be deleted. Following

this basic seismic-resistant guideline, if this section is not deleted

it should be modified as follows: "A. 4.2.2 — At any story level of

a frame, a certain number of columns could be allowed to not satisfy

Sec. A. 4. 2.1 provided that the remaining columns in that storv of the

frame complying with the requirements of Sec. A. 4.2.1 are capable of

elastically resisting the entire stgry shear at that level, accounting

for the altered rigidities and torson resulting from the omission of

elastic action of the nonconforming columns. In addition, the nonconforming columns shall be provided with transverse reinforcement as specified in Sec. A. 4.4* over their full height if the factored axial

force in those- columns exceeds* (Agf £/10) ."

Page 9. Sec. A. 4.3. 2. At the end. of the first sentence should be added

"... span and shall be proportioned as tension splices. Welded ..."

Page 9. Sec. A. 4. 4.1. In the list of notations, the following corrections

should be made: Replace h with h", also in the definition of As . If this notation is used, the notation in AXC, pp. 40-43, should ^ be modified also.

Page 10. Sec. A. 4.4.1 Item (4). This item should be deleted as it can

lead to unsound seismic-resistant practice by allowing columns without

ductility since no confinement is required. Confinement of the concrete

core is not only required for developing extra strength in the

confined concrete required to compensate for the loss, of the cover, but

also to increase the deformation capacity (ductility) . It is well

documented through experiments and field inspection of earthquake

damages that the cover of the columns at the joints will. pull out and

spall, reducing the effective area of concrete available to resist the

internal forces to an effective cross-sectional area even smaller than
5

that of the confined core. Application of the requirements of this

Appendix does not guarantee that the column will remain elastic,

because of the effects of strain hardening of beam reinforcement and

the effects of higher modes of vibration. It is for these same reasons that 1 strongly support the recommendation in the present UBC (1979)

that requires that shear strength of columns be computed based on the

column core area. The application of the provision of this section together with Sec. A. 4.2. ran lead to disaster. Therefore, I strongly recommend the deletion of

these two sections or their modification.

PagelQ. Sec. A. 4.4.4 . At the end of this provision should be added "For

members for which the calculated point of contraflexure is not

within the middle half of their span, the special transverse reinforcement specified above should be provided over the full height of the

members. " (See ATC 11.7.2(B)5 (p. 106).

Page 11. Sec. A. 5.2.3 . What is understood by "elements of structural

diaphragms" should be clarified. Are these Collector Elements and/or

Boundary Elements ? This should be specified. I also consider it

necessary to add after the fifth line of this provision the following

requirement: ". . . 0.15 f£» provided that no tensile forces or significant shear forces are developed simultaneously in these elements.

If these elements could be subjected to significant shear forces

(e.g., v

u

= 3i/f^) and to tensile forces, they shall have special transverse reinforcement as specified in Sec. A. 4. 4 over the total length of the element.

Page 11. Sec. A. 5. 3.1. The requirement should be added for the case where

tensile axial forces can be developed (see 11.5.3).

Page 13. Sec. A. 6. 3.1 . This whole provision needs clarification.

(1) It is suggested that the definition of A- be given in the notation,

Sec. A.0, or directly in this section rather than giving it in

Sec. A.6.3.2. Furthermore, the definition given is not clear. What

does "the design shear commentary force" mean? Should this read

"shear generating force"? Should Aj be the total area, the effective area bd, or the confined core area?

(2) In lines 2 and 5 the symbol ^ is missing; they should read

"coefficient £".

Personally, I question the soundness of some of these provisions (see

my general comments about weaknesses in the ATC and Appendix A

provisions)

.

Page 13. Sec. A. 6.

4

. This section needs clarification . The value of <p is not given in this section. The reader has to go to the Commentary

to find that 1 has been defined in Sec. A. 2. 3. 3. No indication is

given of the location of the critical section for computing the

development lengths and I personally would like to see explicitly in the equation for the estimation of the anchorage length

the 1.25 fy. This is a new section which appears able to give quite

different results than those obtained according to the recommendations

192
e

of Committee 352 (ACI Journal/July 1976), depending, on where the

critical section for anchorage is taken. I did. nor have the background

material at hand to study this new section,, but it appears to me these

provisions do not properly consider the effects of deformation

reversals to which the anchored bar can be subjected.. The reasons

follow:.

(1) The commentary refers, to data presented by ACI Committee 403 which

does not include the effect of deformation reversals. Apparently the

only attempt to account for this effect has been to specify a. reduction factor of » 0.65 rather than the <£ * 0.80 recommended by

Committee 408. This is again a misuse of the original intent of the

reduction factor

(2) No indication is given where the critical section for anchorage

should be located. The research I have conducted clearly shows that

there is a core of unconfined concrete hose depth depends on cover

(shell concrete) and spacing of reinforcement in the joint

Corel which is ineffective in developing the reinforcement. Thus it

appears tame that, if designers assume that the critical section is

at the face of the joint, the application of this provision A. 6.4

can. lead to unconservative anchorage,, particularly in the case of

narrow columns.

Therefore at present I cannot support or recomment the inclusion of

this, provision.

Page 14. Sec. A. 7. 1.2. Although this section is similar to that in ATC

11.7.2(C), p. 106, I believe it is incorrect. The nominal moment

strengths should be calculated for the critical axial force in the

possible range of axial, forces. In the selection of this critical

axial force, proper N vs. M interaction diagram and the variation of

the shear strength with N should be considered.

Page 14. Sec. A. 7.1.3. This section cannot be used in conjunction with the

AIC document. The design shear force shall be obtained from the

factored loads and combinations of Sec. 3.7 of" the ATC document, and

not front Sec. 9.2 of ACI 318.

Page 15. Sec. A. 7.3.1. The application of equation (A-5) to barbell and

flanged wall cross sections is not clear because, according to the

definitions of Ac and pa, only the areas of concrete and steel bounded

by web thickness and height: of section should be considered. It appears

to me that all the steel located in the edge member of the barbell

shape should be considered. Similarly, all the steel located in the

flange effective width of the flanged cross section should be considered.

Page 17. Sec. A. 9.2.2. Equation (A-6) does not agree with equation 11-6

of ATC. Note that in (A-6) the reduction factor <p is missing. This

appears contrary to the main philosophy of the whole ACI 318-77

document in which Required Strength < <p [Nominal Strength]. Furthermore,

notation for the factored compressive force at the construction joint,

i.e. , Pj, in ATC is Pn

. Therefore, a change should be made either in

Sec. 2.2 Symbols of ATC or in A.O and A. 9.2 of the new Appendix A.

Note the inconsistency in A. 9.2 regarding the notation of this force.

In equation (A-6) this force is designated as Pj but three lines

below this equation (A-6) it is defined as Pn

.
REVIEW OF AN UPDATED CHAPTER. 11 (May 28, 1980) SUBMITTED BY FINTEL

AND OF THE APPENDIX A, DATED MARCH 1980

CONCLUSIONS AND RECOMMENDATIONS

by Vitelmo V. Bertero, Representative of ATC

CONCLUSIONS : Although a complete review could not be done because of lack

of time, the attached comments and observations clearly lead to thefollowing conclusion:

THE UPDATED DRAFT OF CHAPTER 11 SUBMITTED BY FINTEL ON MAY 29, 1980, AS

SUGGESTED BY THE INDUSTRIES, CANNOT BE ACCEPTED FOR INCORPORATION

TOGETHER WITH A NEW APPENDIX A INTO THE ATC 3-06.

Even if new drafts of this chapter and Appendix A, including all the

corrections, additions and clarifications suggested in the attached comments, are prepared, I strongly believe it would be a mistake to introduce it in

the ATC 3-06 for the TRIAL DESIGN PHASE 07 ATC 3-06 . The main reason is

that the designers will have to consider two new and very confusing cross references (.Chapter 11 and the new Appendix A) which would increase the

probability of misinterpreting the provisions. Considering that, even if

the designers were able to Interpret correctly the interfacing provisions

of the new Chapter 11 and Appendix A, no significant technical improvement

in the design will be obtained, the writer believes it is not wise at this

time to introduce the new chapter and appendix.

RECOMMENDATIONS : The writer agrees that Chapter 11 of ATC 3-06 needs to be

updated and integrated with the new Appendix A. Therefore it is recommended

that

A TECHNICAL SUBCOMMITTEE, WITH MEMBERS FROM COMMITTEE 4 AND THE ACI

COMMITTEE THAT HAS PREPARED THE NEW APPENDIX A, BE FORMED AND CHARGED WITH

THE MISSION OF IMPROVING AND INTEGRATING THE NEW APPENDIX A INTO CHAPTER 11

OF ATC 3-06.

cc: Roland Sharpe

E. Leyendecker
3.4 Reference Documents

Revised Chapter I I — Reinforced Concrete (June 4, 1980)

Commentary Chapter II - Reinforced Concrete (June 4, 1980) • Revisions to Incorporate Revised Chapter II Into ATC 3-06 (June 4, 1980)

•* Proposed Revision of AC I 31 8, Appendix A - ’’Requirements for

Reinforced Concrete* Bui I ding Structures Resisting Forces

Induced by Earthquake- Motions'*1 (March- 19, 1980)
June 4, 1980

CHAPTER 11 - Pages 101-110

REVISE CHAPTER 11 TO READ AS FOLLOWS:

CHAPTER 11

REINFORCED CONCRETE

Sec. 11.1 - REFERENCE DOCUMENTS

The quality and testing of concrete and steel materials and the design and

construction of reinforced concrete components that resist seismic forces

shall conform to the requirements of the references listed in this Section,

except as modified by the provisions of this Chapter.

Ref. 11.1 ANSI/ACI 318-77 "Building Code Requirements for Reinforced

Concrete1 ' including proposed revision Appendix A* - “Requirements

for Reinforced Concrete Building Structures Resisting Forces induced by Earthquake Motions" dated 19 March 1980, American

Concrete Institute.

; Ref. 11.2 AWS Dl.4-79 "Structural Welding Code - Reinforcing Steel" American

Welding Society.

Sec. 11.2 - REQUIRED STRENGTH

Required strength to resist seismic forces determined by analysis procedures

of Chapter 4 or 5 shall be in accordance with Sec. 3.7.1 in lieu of ACI 318

Section 9.2.3.

Sec. 11.3 - SEISMIC PERFORMANCE CATEGORY A

Buildings assigned to Category A may be of any construction permitted by ACI

318, and shall conform to the minimum requirements of ACI 318, excluding

Appendix A.

All welding of reinforcement shall conform to Ref. 11.2.

* "Appendix A-Requirements for Reinforced Concrete Building Structures

Resisting Forces induced by Earthquake Motions," 19 March, 1980;

copy attached.

196 .
Anchor bolts at tops of columns and similar locations shall be closely

enclosed withirr not less than- two #4 or three #2 ties located within

4 inches fronr top of columns.. Allowable Toads on anchor bolts shalT not

exceed those given- in- Table 1L-A.

Sec. 11.4 - SEISMIC PERFORMANCE CATEGORY- g

Buildings assigned to Category & shalT conform- to all the requirements for

Category A and to the additional requirements of this Section.

11.4.1 - ORDINARY MOMENT FRAMES:

Where ordinary moment frames are used for the seismic resisting system,

frame components (beams and columns) shall be proportioned- to satisfy the

additional provisions of ACT 318* Appendix A.3.Z, A .2. 2* A.4.2 y and A.8.Z.

(See ACT 318 Appendix: A.Z.1.2).

EXCEPTION

Where slab systems without beams between supports and supported on columns are used for the seismic resisting system, the following

provisions shall apply ta slab components in lieu of ACI 318,

Appendix A.2.Z and A. 2.3.

(A) Area of bottom slab reinforcement not less than 1.3 V^/ $f

shall be provided continuous through or anchored within

column supports* where is factored shear force transferred

to supporting- columns due to gravity loading only. Shear force

may be reduced by vertical component of effective prestress

force for slab systems with prestressing tendons continuous

through or anchored within supporting columns.

(B) In each direction,., at least Z bars shall be provided in both

top and bottom of slab and made continuous through or anchored

within supporting columns.

(C) At least 60 percent of column strip negative moment reinforcement shall be concentrated between lines that are one and

one-half slab thickness (1.5h) outside opposite faces of columns.
(D) Shear strength of slab at slab-column connections shall not

be taken greater than (1 +> 4/S

c )/Fibo

d when subject to shear

force V

u

, where b

Q

is perimeter of a critical section perpendicular to plane of slab and located so that its perimeter is a minimum, but need not approach closer than d/2 to perimeter of

supporting column.

(E) At discontinuous edges of slabs without an edge beam, reinforcement within a distance 4h on either side of a supporting

column shall be detailed to resist torsion at discontinuous

edges.

11.4.2 - FRAMING SYSTEMS

All components of the seismic resisting system (moment frames,

structural walls, braced frames, and diaphragms) shall be

proportioned in accordance with provisions of ACT 313, Appendix

A. 2.1.

EXCEPTION:

Seismic resisting framing systems not satisfying the requirements

of Sec. 11.4.1 may be used if it is demonstrated by experimental

evidence and analysis that a proposed system will have strength,

stiffness, stability, durability, and energy dissipation

capacity equal to or exceeding that provided by a comparable

monolithic cast-in-place framing system satisfying Sec. 11.4.1.

Alternatively, seismic resisting framing systems that do not

contain required special details or energy dissipating

mechanisms may be used if designed for forces determined by the

analysis procedures of Chapters 4 or 5 with an R value of 1.5.

Sec. 11.5 - SEISMIC PERFORMANCE CATEGORY C AND D 3u i 1 dings assigned to Categories C and 0 shall conform to all the

requirements for Category 3 and to the additional requirements of this

Section.
11.5*1 - MATERIAL REQUIREMENTS

Materials used irr the components of the seismic resisting system shall

conform to ACI 318, Appendix A.Z.4 and A. 2 .5*

11.5.2 - FRAMING SYSTEMS

ATT components of the seisnric resisting- system (moment frames, structural

walls, braced: frames, and diaphragms) shaTT be proportioned in accordance

with- provisions of ACI 318V Appendix. A*

. EXCEPTION r. Seismic resi sting- framing systems not satisfying the requirements of ACT 318, Appendix A, may be used if it is demonstrated

by experimental' evidence and analysis that a proposed system

will have strength*, stiffness,. stability, durability, and

energy dissipation- capacity equal to or exceeding that provided

by a comparable monolithic cast-in-place framing system

satisfying Appendix A,

Alternatively, seismic resisting framing systems that do not

contain required special details or energy dissipating mechanisms may be used if designed for forces determined by the

analysis procedures of Chapters 4 or 5 with an R value of 1.5.

11.5.3 - STRUCTURAL DIAPHRAGMS

Cast-in-place topping on precast floor systems may serve as structural

diaphragms to transmit inertia- forces to seismic resisting elements provided

the cast-in-place topping is proportioned and detailed to resist the shear

forces under the effects of any loading combination (which could induce

tensile or compressive stresses simultaneously to the shear forces). Alternate techniques based on the use of untopped precast and/or prestressed

components of concrete floor systems may be used only if shown by test and

analysis based, or established- engineering principles that the floor systems

wilT provide the same strength, stiffness, stability, durability and sufficient energy dissipation- capacity as a monolithic cast-in-place ordinary

reinforced concrete diaphragm.

i
11.5.4 - FRAME COMPONENTS NOT PART OF SEISMIC RESISTING SYSTEM

All frame components assumed to be not part of the seismic resisting system

shall have demonstrated capabilities satisfying Sec. 3.3.4(c) and shall

conform to the requirements of ACI 318, Appendix A. 3; except, the lateral

deformation requirement of A. 3.1 shall not apply. If nonlinear behavior is

required in such components to comply with Sec. 3.3.4(c), the critical

portions shall be provided with special transverse reinforcement in

accordance with ACI 318, Appendix A. 3. 3 or A. 4. 4.

11.5.5 - RELATIVE FLEXURAL STRENGTH OF COLUMNS

In lieu of ACI 318, Appendix A. 4. 2, the following shall apply for relative

strength of columns.

At any joint where the framing columns resist a factored axial compressive

force larger than (A f^/10), the moment in the plane of the frame' con- sidered and about the center of the joint corresponding to the flexural

strengths of the columns or column shall exceed that corresponding to the

flexural strengths of the beams framing into the joint. If this requirement

is not satisfied for certain beam-column connections, the remaining columns

in the building frame and connected flexural members shall comply and shall

be capable of resisting the entire shear at that level accounting for the

altered relative rigidities and torsion resulting from the omission of

elastic action of the nonconforming beam-column connections. In addition,

the columns framing into the affected joint shall be provided with special

lateral reinforcement as specified in ACI 318, Appendix A. 4. 4 throughout

their entire story height. Column flexural strengths shall be calculated for

the most critical axial design force consistent with the direction of the

seismic forces considered.

200
TABLE 11-A

ALLOWABLE SHEAR ANO TENSION ON BOLTS1

'DIAMETER

MINIMUM 7

EMBEDMENT^ SHEAR TENSION

( inches) (inches) TW TlbsTT

1/4- 2% 500 360

3/8- 3 noo 900

l/Z 4 1900 • 1700

5/8 5 3000 2700

3/4 5h 4300 4050

7/8 6 5900 5750

1 7 • 7700 ' 7500

^Values shown are for minimum concrete compressive strength

of 3000 psi at 28 days*

Values are for natural stone aggregate concrete and bolts

of at least A-307 quality. Bolts shall have a standard

bolt head or equal deformity in the embedded portion.

Values are based upon a bolt spacing of 12 diameters with

a minimum edge distance of 6 diameters^ Such spacing and

edge distance may be reduced 50 percent with an equal

reduction in value. Use linear interpolation for intermediate spacings and edge margins..

7

A minimum embedment of 9 bolt diameters shall be provided

for anchor bolts located in the top of columns for buildings located in Seismicity Index Areas 3 and A.
COMMENTARY CHAPTER 11 - Pages 449-459

REVISE COMMENTARY CHAPTER 11 TO READ AS FOLLOWS:

COMMENTARY

CHAPTER 11: REINFORCED CONCRETE

For the proper detailing of reinforced concrete construction for earthquake resistance, design standard ANSI/ACI 318-77 "Building Code Requirements for Reinforced Concrete" is referenced. Seismic resistance is

considered in the overall development of the ACI 318 Standard, including an Appendix A on Special Provisions for Reinforced Concrete Building Structures

to Resist Forces Induced by Earthquake Motions.

Chapter 11 is formulated to reference appropriate ACI 318 design provisions

within the four ATC seismic performance categories (A through D). ACI 318

Appendix A refers to zones of different seismicity (Zones 0 through 4) for

application of the special provisions for seismic design. For application

of Appendix A within the ATC Seismic performance categories, buildings

assigned to ATC Category A are interpreted as located in Zone 0 or 1 (regions of no or minor seismic risk), requiring no special provisions for

seismic design. Buildings assigned to ATC Category B are interpreted as located in Zone 2 (regions of moderate seismic risk) per Appendix A. 2. 1.3.

Buildings assigned to ATC Category C and D are interpreted as located in

Zones 3 and 4 (regions of high seismic risk), per Appendix A. 2. 1.4. The

proportioning and detailing requirements for frames and walls resisting

seismic forces are summarized as follows:

For buildings in seismic performance category A, no special provisions are required; the general requirements of ACI 318-77 apply for proportioning and

detailing concrete structures.

Frame

Wall

Category A Category B ACI 318-77 Appendix A. 2. 1.3

ACI 318-77 ACI 318-77

Categories C & D Appendix A

Appendix A

The code sections cited in ACI 318, Appendix A. 2. 1.3 for ordinary moment

frames (beam-column framing systems) in seismic performance Category 8
govern reinforcement details of the beanr and. column components as follows:

Beams Columns

Longitudinal reinforcement A. 3.

A. 4.

3

Transverse rei nforcement A.3.3 A.8.2

For slat systems without beams between column supports, the slab components

of the frame are detahTed in accordance witlr the special EXCEPTION provisions

of Sec- 11. 4.1-

There are no special requirements for other structural or nonstructural

components of buildings in Category 8.

In regions of higfr seismic risk (Categories C and 0), the entire building,

including- the foundation and nonstructural elements, must satisfy ACI 313

Appendix A.

Tt should be noted that a structural system in a higher category (D being

higher than A) must satisfy the requirements specified for the lower categories: A structural frame which forms part of the seismic resisting system

of a Category C building must satisfy all of the frame requirements of ACI

313 Appendix A, including Appendix A. 2.1.3.

Sec. 11.2 - REQUIRED STRENGTH

Calculations to determine- the strength of structural components and members

are to be based on Ref- 11. 1; except, the factored loads and load combinations to resist seismic forces must be in accordance with Sec. 3.7.1 in lieu

of ACI 318 Section 9.2.3. This exception is necessary so that the required

strength for seismic resistance. Sec- 3.7.1, is compatible with the design

forces specified in Chapter 3.

Sec. 11.3 - SEISMIC PERFORMANCE CATEGORY A

Construction qualifying under Category A as identified in Table i-A (Chapter

1) may be built with no special detail requirements for earthquake resistance

except for ties around anchor bolts as indicated in Sec. 11.3. “Closely

enclosed" is intended to mean that the ties should be located within 3 to 4

bolt diameters of the bolts.
Sec. 11.4 - SEISMIC PERFORMANCE CATEGORY B A frame used as part of the lateral force resisting system in Category B

as identified in Table 3-B is required to have certain details which are intended to help sustain integrity of the frame when subjected to deformation reversals into the nonlinear range of response.

For beam and column framing systems, the reinforcement details of ACI 318

Appendix A.

3

.

Z

and A. 3. 3 apply for beam components and A. 4. 3 and A. 8. 2 apply

for column components.

For slab and column framing systems, the slab component must satisfy the

special EXCEPTION provisions of Sec. 11.4.1, in lieu of A. 3. 2 and A. 3. 3.

Columns must satisfy the provisions of A. 4. 3 and A. 8. 2. For slab-column

connections, paragraph (A) provides slab reinforcement through a column to

support the slab gravity load in the unexpected event that a punching

failure occurs. Paragraph B) specifies a minimum amount for that reinforcement. Concentration of negative moment reinforcement at the column as provided by paragraph (C), is required to create a situation whereby the

total negative moment reinforcement across the entire slab width will yield

simultaneously. Without the heavier concentration of reinforcement, the

slab region at the column will yield considerably before the outer regions

of the slab, with markedly decreased lateral load stiffness. Paragraph (D)

in effect limits the shear stress caused by gravity loads to a sufficiently

low value so that the slab-column connection will have a ductility ratio of

at least 2. Paragraph (E) ensures that if shear or torsional cracks develop

at the slab edges, properly detailed reinforcement is present to control

cracking.

As shown in Fig. A there should be top and bottom bars in the slab

paralleling and as close to the discontinuous edge as possible, continuous

through the column and enclosed within transverse reinforcement having a spacing not greater than 0.5d. The transverse reinforcement can be closed

hoops, hairpin stirrups projecting l beyond the face of the column as shown in Fig. A or slab bars bent to satisfy the requirements for hairpin.
Fig-. A - Reinforcement Details

Satisfying Section 11.4.1 (E)

Structural (shear) walls of buildings in Category B are to be built in

accordance with the general requirements of ACT 318-77.

Sec. 11.5 - SEISMIC PERFORMANCE CATEGORY C AND D

In regions of high seismic risk, the entire building, including the foundation and nonstructural elements,, must satisfy all of the requirements of

ACI 31B Appendix A.

Appendix A contains special proportioning and reinforcement detailing

requirements which are currently considered to be the minimum for producing

a monolithic reinforced concrete structure with adequate proportions and

details to make it possible for the structure to undergo a series of

oscillations into the inelastic range of response, without critical decay in

strength1 . The demand for integrity of the structure in the inelastic range

of response is consistent with the rationalization of design forces specified

in Chapter 3.
Field and laboratory experience which has led to the special proportioning

and detailing requirements in ACI 318 Appendix A has been predominantly with

monolithic reinforced concrete building structures. Therefore, the projection of these requirements to other types of reinforced concrete structures,

which may differ in concept or fabrication from monolithic construction,

must be tempered by relevant physical evidence and analysis. Precast and/or

prestressed elements may be used for earthquake resistance provided it is

shown that the resulting structure will satisfy the safety and serviceability

(during and after the earthquake) levels provided by monolithic construction.

A detailed explanation of the specific provisions of ACI 318 Appendix A is

contained in the ACI Code Commentary to Appendix A.

11. 5. Z - FRAMING SYSTEMS

The strength and "toughness 1 * requirements for framing systems not satisfying

the requirements of ACI 318 Appendix A refer to the concern for the

integrity of the entire lateral-force structure at lateral displacements

anticipated for ground motions corresponding to design intensity. Depending

on the energy-dissipation characteristics of the structural system used,

such displacements may have to be more than those for a monolithic

reinforced concrete structure.

For systems that remain elastic or that have limited special details for

energy dissipation, such as assemblages of precast and/or prestressed

concrete, appropriate R- factors should be used to reflect damping characteristics and energy dissipation. For example, R * lh can be used for

systems responding primarily elastically to account for damping, and R ^ up

to 2h may be used for walls with properly distributed web reinforcement that

will assure good distribution of cracks and thus provide a degree of energy

dissipation.
11.5.4' - FRAME COMPONENTS NOT PART OF SEISMIC RESISTING SYSTEM

In the event of a strong earthquake* it is assumed that the structure will

undergo reversals of large lateral displacements. It is essential that all

structural components be able to accommodate these displacements without

critical loss of strengths Even- if a particular frame has been designed to

support on-ly gravity loads and is not intended to be part of the structural

system resisting- seismic forces* it must sustain the gravity loads after

having been- subjected: to approximately the same displacements as the seismic resisting system. Therefore* alT frame components (which are not

designed to resist seismic forces) in Categories C and D buildings are

required to have, as a minimum* the details specified in ACT 318 Appendix

A. 8. Furthermore, if calculations show that frame components (which are not

part of the structural system- resisting seismic forces) will have to yield

in order to accommodate the calculated displacements of the seismic resisting system* those components must have special transverse reinforcement as specified for Special Moment Frames.

: Slab systems without beams between supports (flat plates) of normal proportions and detailed as specified in Sec. 11.4.1 (EXCEPTION) will not

undergo any significant yield until story drifts greater than those

allowable. (Table 3-C).
OTHER REVISIONS TO INCORPORATE NEW CHAPTER 11 - (REINFORCED CONCRETE)

INTO ATC 3-06

1. SEC. 1.6.3(B) - PAGE 32

Change reference "ACT 318-71" to "AC I 318-77"

2. SEC. 2.1 DEFINITIONS - PAGE 37

Revise the following definitions:

CROSS-TIE is a continuous bar. No. 3 or larger in size, having a 135-degree hook with a ten-diameter extension at one end and a 90-degree

hook with a six-diameter extension at the other end. The hooks shall

engage hoop bars and be secured to longitudinal bars.

HOOP is a closed tie or continuously wound tie (not smaller than No^ 3

in size) the ends of which have 135-degree hooks with ten-diameter

extensions, that encloses the longitudinal reinforcement

.

JOINT, LATERALLY CONFINED is a joint where members frame into all four

sides of the joint and where each member width is at least three-fourths

the column width.

In definition of BRACED FRAME, add the following sentence at the end:

"In Chapter 11, reinforced concrete braced frames may be referred to as structural trusses."

In definition of ORDINARY MOMENT FRAME change reference "Sec. 11.6" to

"Sec. 11.4.1."

In definition of SPECIAL MOMENT FRAME change reference "Sec. 11.7" to

Sec. 11.5."

Add the following definitions:
BOUNDARY ELEMENTS are- portions along the edges of walls and diaphragms

strengthened by longitudinal and transverse reinforcement. Boundary

elements do not necessarily require arr increase in- the thickness of the

wall or diaphragm-. Edges of openings within walls and diaphragms may

alsa have ta be provided with boundary elements.

COLLECTOR ELEMENTS are elements which serve to transmit the inertial

forces within the diaphragms to elements of the lateraT-farce resisting

systems,.

3. SEC. 2.2 SYMBOLS - PAGE 40

Delete symbols A

ch>

A

s(t, f^, lrc

* ?

n

, s„

Add the following new symbols and definitions:

b

Q - perimeter of critical sectiorr for slabs* Sec. 11.4.

d * distance from extreme compression fiber to centroid of tension

reinforcement* Sec. 11.4.1

f '* specified compressive strength of concrete, psi wf * specified yield strength of reinforcement, psi

h * overall thickness of member. Sec. 11.4.1

V * factored shear force due to gravity loading. Sec. 11.4.1.

4. TABLE 3-8 - PAGE 52

Revise footnote (4) ta read as follows:

4

As defined in Sec. 11.5.

5. SEC. 7.5.3(C) - PAGE 75

Change reference "Sec. 11.5.2" to "Ref. 11.1, ACI 318 Appendix

A. 8. 2"

5. SEC. 12.5.1(D) - PAGE 114

Change paragraph (1) to read as follows:

“1. Ref. 11.1, ACT 318 Appendix A. 5.3 when of reinforced concrete or Chapter 10 when of structural steel."
PROPOSED REVISION TO Ad STANDARD 318-77 19 March 1980

APPENDIX A - REQUIREMENTS FOR REINFORCED CONCRETE BUILDING STRUCTURES

RESISTING FORCES INDUCED BY EARTHQUAKE MOTIONS

A. 0 -Not ation

Ac

* net area of concrete section resisting shear, bounded by web

thickness and. section height,, sq.in.

A

c^ - cross-sectional area of a structural element measured out-to-out

of transverse reinforcement, sq.in.

A

Cp = area of concrete section resisting shear of an individual pier,

sq.in.

Ag - gross area of section, sq.in.

A

^

* total cross-sectional area of transverse reinforcement (including cross-ties) within spacing "s" and perpendicular to dimension "h"

A

v * total cross-sectionaT area of shear reinforcement within

spacing "s'* and perpendicul ar to longitudinal axis of structural

element, sq.in.

A

v

^r 3 total cross-sectional area of reinforcement perpendicular to a construction joint, sq.in.

b - effective compressive flange width of a structural element, in.

f'c

3 specified compressive strength of concrete, psi

fy s specified yield stress of reinforcement, psi

f^ 3 specified yield stress of transverse reinforcement, psi

h" 3 cross-sectional dimension of column core measured c-to-c of

confining re inf orcement

3 anchorage length for a bar with a standard hook as defined

in Section A.l

2> as 3 anchorage length for a straight bar

3 minimum length, measured from joint face along axis of

structural element, over which transverse reinforcement must be

provided, in.

Pj 3 minimum factored compressive force at a construction joint

(positive for compression), lb.

s 3 spacing of transverse reinforcement measured along the longitudinal axis of the structural element, in.

s0

3 maximum spacing of transverse reinf orcement, in.
V. * nominal shear force at a construction joint r lb.

Y

* dimensionless factor reflecting the influence of confinement

of a. joint by structural elements, framing inta joint

p . * reinforcement ratio,, rati a of non prestressed tension reinforcement

* area, at a section- ta the product "bd*

P

a * A' sa/A

c

; where A$a is the projection on A- of total area of reinforcement crossing the plane of A

c

Pjj » reinforcement ratio on a plane perpendicular to A

p

$ * ratio of volume of spiral rei nforcement to the core volume

confined by the spiral reinforcement (measured out-to-out)

<J> * strength reduction factor

A.l-Oefinitions

Cross-Tie - A continuous bar* No. I or larger in size, having a

135-degree hook with a ten-diameter extension at one end and a

SO-degree hook with a six-diameter extension at the other end. The

hooks shall engage hoop bars and be secured to longitudinal bars.

Hoop - A closed tie or continuously wound tie (not smaller than No. 3

in size) the ends of which have 135-degree hooks with ten-diameter

extensions* that encloses the longitudinal reinforcement.

Structural Walls - Walls proportioned to resist combinations of shears,

moments, and axial forces induced by earthquake motions.

Structural Diaphragms - Structural elements, such as floor and roof

slabs* which transmit the inertial forces to the lateral -force

resisting elements.

Structural Trusses - Assemblages of reinforced concrete elements subjected primarily to axial forces.

Lateral -Force Resisting System- - That portion of the structure composed

of elements proportioned to resist forces related to earthquake effects.
3ase of Structure - The level at which the earthquake motions are

assumed to be imparted to the building.

Boundary Elements - Portions along the edges of walls and diaphragms

strengthened by longitudinal and transverse reinforcement. Boundary

elements do not necessarily require an increase in the thickness of the

wall or diaphragm. Edges of openings within walls and diaphragms may

also have to be provided with boundary elements.

Collector Elements - Elements which serve to transmit the inertial

, 1 forces within the diaphragms to elements of the 1 ateral -force resisting

systems

.

Anchorage Length for a Bar with a Standard Hook - The shortest distance

between the critical section (where the strength of the bar is to be

developed) and a tangent, perpend i cu 1 ar to the axis of the bar

anchored, to the outer edge of the hook.

Lightweight Concrete - Concrete in which any part or all of the

aggregates has been replaced by lightweight material.

Shell Concrete - Concrete outside the transverse reinforcement confining the concrete.

A. 2-General Requirements

A. 2.1-Scope

A. 2. 1.1-Appendix A contains special requirements for design and

construction of reinforced concrete elements of a structure for which

the design forces, related to earthquake motions, have been determined

on the basis of energy dissipation in the nonlinear range of response.

A.2.1.2-The provisions of Chapters 1 through 17 shall apply except as modified by the provisions of Appendix A.

212
A.2.1~3-In regions of moderate seismic risk**, reinforced concrete

frames resisting farces induced by earthquake motions shall be proportioned to satisfy, in addition- to the requirements of Chapters L

through 17, only Sections A. 2*2, A .3. 3V A-.4*3, and A. 3. 2 of Appendix A.

A.2*I.4-rn regions of high seismic risk***, all components of reinforced

concrete structures. shalT satisfy aTT requirements of Appendix AA.2..1.5-A reinforced concrete structure! system- not satisfying the

requirements of Appendix A may be used if it is demonstrated by

experimental evidence and analysis that the proposed system will have

strength and toughness equal to or exceeding those provided by a comparable monolithic reinforced concrete structure satisfying Appendix A»

A.2.Z-Analysis and proportioning of structural elements

A.2.2.I-The interaction of all structural and nonstructural elements

which materially affect the linear and nonlinear response of the

structure to earthquake motions shall be considered in the analysis.

A.2.Z.2-fligid elements assumed not to be a part of the lateral force

resisting system may- be used provided their effect on the response of

the system is considered and accommodated in the structural design*.

Consequences of failure of structural and nonstructural elements which

are not a part of the lateral -force resisting system shall also be

consi dered..

A.2.2.3-Structural elements below the base of structure required to

transmit forces resulting from lateral loads to the foundation shall

also comply with the requirements of Appendix A.

A. 2. 2.4-All structural elements assumed not tc be part of the lateral

force resisting system shall conform to Section A. 3.

Regions falling in Zone Z as defined by the Uniform Building Code

**flegions falling in Zones 3 and A as defined by the Uniform Building Code
A.2.2.5-Except as required otherwise in Appendix A, structural elements

and connections shall be proportioned to resist the load effects with

adequate strength in accordance with the provisions of this code using

the load factors and strength reduction factors specified in Chapter 9.

A. 2. 3- Strength reduction factors

Strength reduction factors shall be as given in Chapter 3 except for

the following:

A.2.3.1-The strength reduction factor shall be 0.5 for any structural

element if its nominal shear strength is less than the shear .corresponding to its nominal flexural strength for the design loading

conditions,

A.2.3.2-The strength reduction factor for axial compressive force shall

be 0.5 for all frame elements with factored axial compressive forces

exceeding (A f’/10) if the transverse reinforcement does not conform

g c

to Section A. 4.

A. 2. 3. 3-Strength reduction factor for anchorage length of reinforcement shall be 0.65.

A. 2. 4-Concrete in elements resisting earthquake- induced forces

The specified 28-day compressive strength, f' of the concrete shall

be not less than 3,000 psi. The specified 23-day compressive strength,

f', shall not exceed 4,000 psi for lightweight concrete.

A. 2. 5- Reinforcement in elements resisting earthquake-induced forces

A. 2. 5 .1-Reinforcement resisting earthquake- induced flexural and axial

forces in frame elements and in wall boundary members shall comply with

ASTM A706. ASTM A615 Grades 40 and 50 reinforcement may be used in

these elements if (a) the actual yield stress based on mill tests does

not exceed the specified yield stress by more than 18,000 psi (retests

shall not exceed this value by more than an additional 4,000 psi) and

(b) the ratio of the actual ultimate tensile stress to the actual

tensile yield stress is not less than 1.25.

214
A.2.5.2'-Spli ces irr the rei nforcement effected through* welding or mechan

icaT connections shalT confornr to Sections 12.15. 3. L through 12.15.3.4.

A.3 •Flexural elements of frames

A.Z.L-Scope

The requirements of this section* appiy tc frame elements (a) resisting

earthquake-induced: forces (b) proportioned primarily tar resist flexure,

and (c) satisfying the fallowing conditions:

A.S.I.l-factored axial compressive force on the element shall not

exceed (A^fl/IQ)

A.2.I.2-C1 ear spar for the element shall not be less than* four times

its effective depth.

A.3.1.3-The width-to-depth ratio shalT not be less than 0.3.

A.3.1.4-The width shall not be less than* 10 in. or more than the width

of the supporting element (measured on a plane perpendicular to the

longitudinal axis of the flexural element) plus distances on each side

of the supporting element not exceeding three-fourths of the depth of

the flexuraT element.

A.3. 2-Longitudinal rei nforcement

A.J.2.I-At any section of a member subjected to bending, the reinforcement ratio, p, for the top and for the bottom reinforcement, shall not

be less than (200/f^) and shall not exceed 0.025 at any section. At

least two bars shall be provided continuously both top and bottom.

A.3.2.Z-The positive-moment strength at the face of the joint shall be

not less than one-half of the negative-moment strength provided at that

face of the joint. The negative- and the positive -moment strengths at

any section along the length of the element shall not be less than

one-fourth the maximum moment strength provided at the face of either

joint.
A. 3. 2.3-Lap splicing of flexural reinforcement is permitted only if

hoop or spiral reinforcement is provided over the lap length. Maximum

spacing of the transverse reinforcement over the lap length shall not

exceed d/A or A in. Lap splices shall not be used (a) within the

joints, (b) within a distance of twice the member depth and the face of

the joint, and (c) at locations where analysis indicates flexural

yielding in connectin with inelastic lateral displacements of the frame.

A.3.2.A-Welded splices and mechanical connections conforming to Sections

12. 15. 3. L through 12. 15. 3. A may be used for splicing provided not more

than alternate bars in each layer of longitudinal reinforcement are spliced at a section and the distance between splices of adjacent bars

is 2A in. or more,, measured along the longitudinal axis of the frame

el ement.

A. 3. 3 -Transverse reinforcement

A. 3. 3. 1-Hoops shall be provided in the following regions of frame

elements

:

(1) Over a length equal to twice the member depth measured from the

face of the supporting member toward midspan, at both ends of the

flexural member.

(2) Over lengths equal to twice the member depth on both sides of a section where flexural yielding may occur in connection with inelastic

lateral displacements of the frame.

(3) Wherever compression reinforcement is required by analysis.

A. 3. 3. 2 -The first hoop shall be located nor more than. 2 in. from the

face of a supporting member. Maximum spacing of the hoops shall not

exceed (a) d/A, (b) eight times the diameter of the smallest longitudinal bars, (c) 2A times the diameter of the hoop bars, and (d) 12 in.

A.3.3.3-Where hoops are required, longitudinal bars shall have lateral

support conforming to Section 7.10.5.3.

216
I

A.3.2.4-Where hoops are not required* stirrups shall be spaced at no more than d/2 throughout the length of the member*

A. 2. 3.5-Hoops in- flexural elements may be made up of two pieces of

reinforcement: a stirrup having 135-degree hooks with ten-di ameter

extensions anchored irr the confined core and a cross-tie to make a

closed hoop~ Consecutive cross-ties shall have their 90-degree hooks

at opposite sides of the flexural element.

A.4-Frame elements subjected to. bending and axial load

A. 4. 1-Scope

The requirements of this section- apply to frame elements (a) resisting earthquake-induced forces (h) having a factored axial compressive

force exceeding (A^L/IG) and (c) satisfying the following conditions:

A.4.t.l-The shortest cross-secti onal dimension, measured on a straight

line passing through the geometric centroid, shall not be less than

12 in.

A.4.1.2-The ratio of the shortest cross-sectional dimension to the

perpendicular dimension shall hot be less than 0.4.

A.4.2-Helative Strength of Columns

A.4.2.1-At any joint where the framing columns resist a: factored axial

compressive force larger than (A^fj/IG), the sum of the flexural

strengths of the columns calculated for the maximum design axial force

shall exceed the sum of the flexural strengths of the beams framing

into that joint in the same vertical plane. The flexural strengths

shall be sumned such that the column moments oppose the beam moments,

and the check shall be made in both directions.

A.4.2.2-If Section A. 4. 2.1 is not satisfied at a joint, columns

supporting reactions from that joint shall be provided with transverse

reinforcement as specified in Section A. 4. 4 over their full- height if
the factored axial force in those columns,- related to earthquake

effect, exceeds (A f'/10).

g c

A.4.3-longitudi nal reinf orcement

A.4.3,.l-The re i nforcement ratio, P , shall not be less than 0.01 and

shall not exceed 0.061

A. 4. 3. 2-Lap splices are: permitted only within the center half of the

member span. Welded splices and mechanical connections conforming to

Sections 12.15.3.1 through 12.15.3.4 may be used for splicing the

reinforcement at any section provided not more than alternate longitudinal bars are spliced at a section and the distance between splices

is 24 in. or more, along the longitudinal axis of the reinforcement.

A.4.4-Transverse reinforcement

A.4.4.1-Transverse re i nforcement as specified below shall be provided

unless a larger amount is required to resist shear by Section A. 7.

(1)

The volumetric ratio of spiral or circular hoop reinforcement, P

s

, shall not be less than that indicated by Eq. (A-l).

p

s * o.i2 ryr (A-l)

and shall not be less than that required by Eq. (10-5).

(2)

The total cross-sectional area of rectangular hoop reinforcement

shall not be less than that given by Eq. (A-2) and (A-3).

sh

- °- 3 ' sh ” f

yv QW - 1

]

(A-2)

sh - °- 12 < sh,,fyv (A-3)

(3)

Transverse reinforcement may be provided by single or overlapping

hoops. Cross-ties of the same size and spacing as the hoops may be

used. Each end of the cross-tie shall engage a peripheral longitudinal

218
reinforcing bar. Consecutive cross-ties shall be alternated end -for - end along the longitudinal rei nforcement.

(4) If the core of the member is sufficient to resist the forces

resulting fronr the specified combination- of dead load,, live Toad* =and

earthquake effects* compliance with Eg. (A-2) and (IQ-5) is not

requi red,

A. 4.4. Z-Transverse reinforcement shall be spaced at distances not

exceeding (a) one-quarter of the mi nimunr member dimension- and

(b) 4 in,

A.4. 4. 3 -Cross-ties or legs of overlapping hoops shall not be spaced

more tharr 14 in-, oit center in the direction perpendicular to the

longitudinal axis of the structural element,

A. 4. 4 . 4-Transverse reinforcement in amount specified in Section A. 4. 4.1

through A.4.4.3 shall be provided over a length from- each joint face

and on both sides of any section where flexural yielding may occur in

connection with .inelastic lateral displacements of the frame. The

length shall not be less than (a) the depth of the member at the joint

face or at the section where flexural yielding may occur, (b) one-sixth

of the clear span of the member, and (c) 13 in.

A.4. 4. 5-Columns supporting reactions from discontinued stiff elements,

such as walls or trusses, shall be provided with transverse reinforcement as specified above over their full height beneath the level at

which the discontinuity occurs if the factored axial compressive force

in these members, related to earthquake effect, exceeds (A f^/10).

A.5-Structural Walls,, diaphragms, and trusses

A.5. 1-Scope

The requirements of this section apply to structural walls and trusses

serving as parts of the earthquake-force resisting systems as well as
to diaphragms, struts, ties, chords and collector elements which

transmit axial forces induced by earthquake. Frame elements, resisting

earthquake forces, not complying with Section A. 3 or A. 4, shall comply

with this section.

A . 5 . 2-Rei nforcement

A.5.2.L-The reinforcement ratio, p, for structural walls shall not be

less tharr 0.0025 along the longitudinal and transverse axes. Reinforcement spacing each way shall not exceed 13 in. The re i nforcement

required by analysis for shear strength shall be distributed uniformly.

A.5.2.2-At least two curtains of reinforcement shall be used in a wall if

the in-plane factored shear force assigned to the wall exceeds 2A

A.5.2.3-StructuraT-truss elements and elements of structural diaphragms

having compressive stresses exceeding 0.2 f', shall have special transw verse reinforcement, as specified in Section A. 4. 4, over the total length

of the element. The special transverse reinforcement may be discontinued

at a section where the calculated compressive stress is less than 0.15

Stresses shall be calculated for the factored forces using a linearly

elastic model of the element considered.

A. 5. 2. 4-All continuous reinforcement in structural walls, diaphragms,

trusses, struts, ties, chords, and collector elements shall be anchored

or spliced in accordance with the provisions for reinforcement in

tension as specified in Section A. 6. 4.

A. 5. 3-Vertical boundary members for structural walls

A.5.3.1-8oundary members shall be provided at edges of structural walls

for which the maximum extreme-fiber stress, corresponding to factored

forces including earthquake effect, exceeds 0.2 f' unless the entire

c wall element is reinforced to satisfy Section A. 4. 4. The boundary

member may be discontinued at a level where the calculated compressive

stress is less than 0.15 f'.

c

220
A.5.3.2-8oundary members: shall have transverse reinforcement. as specified

in Section A. 4.4 along- their full" length.

A.5.3.3-3oundary members and similar elements: shalT be designed to carry

all gravity loads on- the wall, including tributary loads and self-weighty

as well as the vertical force required to resist the overturn' ng moment

caused by earthquake.

A.5.3.4—Transverse reinforcement in the walls shalT be anchored within

the confined core of the boundary member ta develop the yield stress in

tension of the transverse reinforcement.

S-Joints of frames

A.S.l-General requirements

A.5.t.I-Forces in longitudinal beam reinforcement at the joint face shall

be determined by assuming that the stress in the flexural tensile reinforcement is 1.25. f .

A. 5. 1.2-Strength of joint shall be governed by the appropriate strength

reduction factors specified in Section 9.3. Section A. 2. 3.1 shall not

apply to joints.

A.o.l.3-3eam longitudinal reinforcement terminated in a column shall be

extended to the far face of the confined column core and anchored in

tension according to Section A. 5. 4 and in compression according to

Chapter 12.

A.5.2-Transverse reinforcement

A.S.Z.l-Transverse hoop reinforcementr as specified: in Section A.4.4

shall be provided within the joint,, unless the joint is confined by

structural elements as specified in Section A.S.2.2.
A.6.2.2-Within the depth of the shallowest framing member, transverse

reinforcement equal to at least one-half the amount required by Section

A .4.4 shall be provided where members frame into all four sides of the

joint and were each member width is at least three-fourths the column

wi dth

.

\ A. S. 2. 3 -Trans verse reinforcement as required by Section A .4.4 shall be

provided through the joint to provide confinement for longitudinal

reinforcement outside the column core if such confinement is not p' by a beam framing into the joint,

A. S. 3-Shear stress

A.S.3.1-The design shear strength of the joint shall not exceed yA

for normalweight concrete. The coefficient Y shall not exceed 16 i members frame into all vertical faces of the joint and if each frai

member covers at least three-quarters of the width and three-quart

the depth of each joint face. Otherwise, the coefficientY shall n

exceed 12.

A.S.3.2-For lightweight concrete, the joint shear stress shall not exceed

three-quarters of the limits given in Section A. 6. 3.1, where Aj is the

minimum sectional area of the joint irr a plane parallel to the axis of

the reinforcement generating the design shear commentary* force.

A. 6. 4-Anchorage length for reinforcement in tension

A.6.4.1-The anchorage length, 2,^, for a bar with a standard 90-degree

hook in normalweight concrete shall not be less than 3d^, 6 in., and

the length required by Eq. (A-4).

for bar sizes No. 3 through No. 11.

For lightweight concrete, the anchorage length for a bar with a standard

hook shall not be less than 10d,

Q

,7.5 in., and 1.25 required by Eq. (A-4).

I (A-4)

222
A.6.4.2-The 90-degree hook shall be located within the confined core of a

column or of a boundary member.

A.6.4-.3-For bar sizes No. 2 through* No- 11, the anchorage length , .1 , for a straight bar shalT not be less than (a) twice the length required

by Section 4.3.4.L if the depth of the concrete cast in one lift beneath

the bar does not exceed 12 in. and: (b) 2.3 times the length required by

Section £.6-4-. L if the depth of the concrete cast in one Tift beneath the

bar exceeds 12 in.

A.6.4.4-For bar sizes No. 14 and. No. 18, the anchorage length for a

straight bar shall not be Tess than l.S times that required by Section

A. 6.4.3.

A.6.4.S-Straight bars terminated at a joint shalT pass through the

confined core of a column or of a boundary msnber.

A. 7 Shear- strength requirements

A.7.I-0esign forces’

A.7.1.1-For frame elements subjected primarily to bending, the design

shear force shall be determined from* consideration of the statical forces

on the portion of the element between faces of the joints. It shall be

assumed that moments of opposite sign, corresponding to probable strength,

act at the joint faces and that the member is loaded with the factored

tributary gravity load along its span. The moments corresponding to

probable strength shall be calculated using the properties of the member

at the joint faces without strength reduction factors and assuming that

the stress in the tensile reinforcement is equal to at least 1.25 f .

A.7.1.2-For frame elements subjected to combined bending and axial load,

the design shear shall be determined from consideration of the forces on the member, with the nominal moment strengths calculated for the maximum

factored axial compressive design force on the column, acting at the

faces of the joints.
A.7 .1.3-For structural walls, diaphragms and trusses, the design shear

force shall be obtained from the lateral load analysis in accordance with

the factored loads and combinations specified in Section 9.2.

A.7.2-Transverse reinforcement in frame elements

A.7.2.1-For determining the required transverse reinforcement in frame

elements in which the earthquake- induced shear force determined in

accordance with Section A. 7.1. I represents one-half or more of total

design shear, the quantity V shall be assumed to be zero if the

factored axial compressive force, related to earthquake effects, is less

than (A f'/20).

g c

A. 7. 2. 2-Stirrups or ties required to resist shear shall be hoops over

lengths of members as specified in Sections A .3.3, A. 4*. 4, and A. 6. 2.

A. 7. 3-Shear strength of structural walls and diaphragms

A.7.3.1-The nominal shear strength, V

n> of structural walls and

diaphragms shall not exceed that given by Eq. (A-5).

V

n (A-5)

A

c

- net area of concrete section resisting shear bounded by web thick- ness and height of section.

? 3 reinforcement ratio A /A., where A__ is the projection on A_

a 5a C 5a C

of total area of reinforcement crossing the plane of A

0

f'c

3 compressive strength of the concrete in- psi.

f 3 yield strength of reinforcement perpendicular to the area A . J ^

A. 7. 3. 2-Reinforcement ratio indicating the amount of reinforcement

perpend icu lar to the direction of reinforcement correspond ing to o.,

d

shall be equal to or exceed p . d

224
A.T.S'.J-The nominal shear strength of all -wall piers sharing a commorr lateral force shall not exceed 8A_ [f\ where k is the total crosses c c

sectional area, and the nominal shear strength of. any one of the individual walT piers shalT not exceed 10 ^cp/^c w^er8: A

cp

rePr€Sents the

secti onal area of the pi er consi dered.

AvT.3.4-The nominal shear strength of horizontal wall elements shall not

exceed 10 A where A represents the secti onal area of a hori zontal wal T

elementA. 3-Frame elements not proportioned to resist forces induced by earthquake

moti ons.

A.3.I-A1T frame elements assumed not ta be part of the lateral force

resisting systenr shalT be investigated and shown ta be adequate for

vertical load carrying capacity with the structure assumed ta have

deformed laterally four times that calculated for the specified lateral

• forces- Such elements shalT satisfy the minimum rei nforcement requirements specified in Sections A.0.2.1 and A. 5. 2.1 as well as those

specified in Chapters T* 10* and 11-

A. 3. 2-All frame elements with factored axial compressive forces exceeding

(Agf^lO) shall satisfy the following special requirements unless they

comply with Section A.4.AA. 3. 2. 1-Ties shall have 135-degree hooks with extensions not less than

six tie diameters or 1 in- Cross-ties, as defined, in this Appendix, may

be used.

A.3.2.2-The maximum tie spacing shall be s Q

over a length Z

Q

measured

from the joint face. The spacing s Q

shall be not more than (a) eight

diameters of the smallest longitudinal bar enclosed, (b) 24 tie diameters,

and (3) one-half the least cross-sectional dimension of the column. The

length shall not be less than (a) one-sixth of the clear height of

the column, (b) the maximum cross-sectional dimension of the column, and

(c) 13 in.
A.3.2.3-The first tie shall be within a distance equal to 0.5 s Q

from

the face of the joint.

A.8.2.4—The tie spacing shall not exceed 2 s Q

in any part of the column.

A. 9-Construction joints

A. 9.1-Construction joints in structural walls, diaphragms, and other

members resisting lateral forces induced by earthquake shall be designed

to resist the design forces at the joint.

A.9.2-Where shear is resisted at a construction joint solely by friction

between two roughened concrete surfaces and dowel action, the factored

shear force across the joint shall not exceed Vj determined from

Eq. ( A-6 )

.

V

j * \ff

y

+ °- 75 ?

j

( A*6 >

where A represents the total amount of reinforcement (including

flexural reinforcement) normal to the construction joint acting as shear-friction reinforcement and Pj is the algebraic sum of the

gravity and earthquake forces on the joint surface acting simultaneously with the shear. For lightweight' concrete, the shear strength

V. calculated from Eq. (A-6) shalT be multiplied by 0.75.

A.9.3-The surfaces of all construction joints in elements resisting

lateral forces shall be thoroughly roughened.

226
COMMENTARY

APPENDIX A - REQUIREMENTS FOR REINFORCED CONCRETE BUILDING STRUCTURES

RESISTING FORCES INDUCED BY EARTHQUAKE MOTIONS

A. 2-General requirements

.A.Z.I-Scope

This chapter contains a set of specifications which are currently

considered: to be the minimunr requirements for producing a monolithic

reinforced concrete structure w-ith adequate proportions and details to

make it possible for the structure to undergo: a series of oscillations

into the inelastic range of response without critical decay irr strengths

The demand for integrity of the structure irr the inelastic range of

response is created by the rationalization- of design forces specified:

by documents such as the 1974 report of the Seismology Committee of the

A 1

~ Structural Engineers Association of California. *

The lateral design forces specified in Reference A.l are considerably

less than those corresponding to linear response for the anticipated

A 2 AS A 4- earthquake intensity. * * * As a properly detailed reinforced

concrete structure responds to strong ground motion, its effective

stiffness decreases and its capability to dissipate energy increases.

These developments tend to reduce the response accelerations or lateral

inertia forces with respect to those, forces calculated for a linearly

A 5 elastic model of the uncracked and moderately damped structure.

*

Thus, the use of design forces representing earthquake effects such as those in Reference A.l requires that the structure be able to respond

in the inelastic range without critical failures. The extent of

required nonlinear response- is not explicitly established. It is a function of the type and strength of the structure as well as the

nature- of the ground motion. It is generally assumed that, with the

currently used design forces and anticipated earthquake motions, the

rotations at connections of reinforced concrete frames are likely to

exceed six times the yield rotation. A structural wall similarly
proportioned, would be likely to develop relatively less inelastic

response. In either case it is essential to have a lateral -force

resisting system which- will sustain a substantial portion of its

strength as it is subjected to successive reversals of displacements

into the inelastic range.

The perennial question of a trade-off between strength and special

detail requirements has been considered at length. Given a design

earthquake intensity or a design response spectrum indexed by an effective peak acceleration, it appears plausible to soften or

relinquish some of the detail requirements if the design strength is

increased with respect to the minimum code requirement. However,

available knowledge on ground motion and structural response to such

motion does not make precise estimates of inelastic displacement

possible for all structures at large. Furthermore, it is not currently

possible to devise explicit quantitative relationships between the

required extent and number of inelastic displacements and required

reinforcing details. The choice is between (1) a system with sufficient strength to respond to the ground motion within the linear or nearly linear range of reponse and (2) a system with special details

to permit nonlinear response without critical loss of strength. The

requirements in this appendix have been developed in relation to the

second option, on the assumption that the design forces are based on Reference A.l or a comparable document having a similar approach to the

determination of design forces.

The code sections cited in Section A. 2. 1.3 (which refers to zones of

moderate seismic risk) govern reinforcement details of the structuralframe components as follows:

Requirements of Section A. 3. 2, which have been developed for columns

not resisting earthquake effects in high seismic risk zones, apply to

columns designed for earthquake effects in moderate seismic risk zones.

Longitudinal Reinforcement

Transverse Reinforcement

Girders Columns

A. 3. 2 A. 4.

3

A. 3. 3 A. 3.

2

223
There, are no special requirements- for other structural or nonstructural

components: of buildings: in zones of moderate seismic risk*

Tn regions of high seismic risJc„ the entire building, including the

foundation and nonstructural elements, must- satisfy Appendix A

(Section A. 2.1*4)

Field and laboratory experience which has led to the special proportioning and detailing requirements in Appendix A has been predominantly with* monolithic reinforced concrete building structures*

Therefore, the projection of these requirements to other types of

reinforced concrete structures,. which may differ in concept or fabrication from monolithic constructi on, must be tempered by relevant

physical evidence and analysis* Precast and/or prestressed elements

may be used for earthquake resistance provided it is shown that the

resulting structure will satisfy the safety and serviceability (during

and after the earthquake) levels provided by monolithic construction.

The "toughness ,r requirement in Section A. 2.1.5 refers to the concern

for the integrity of the entire lateral -force structure at lateral

displacements anticipated for gound motions corresponding to design

intensity. Depending on the energy-dissipation characteristics of the

structural system used, such displacements may have to be more than

those for a monolithic reinforced concrete structure*

A.2.2-Analysis and proportioning of structural elements

It is assumed that the distribution of strength to the various

components of a lateral-force resisting system will be guided by the

analysis of a linearly elastic model of the system acted on by the

factored forces*

Because the design basis is assumed to admit nonlinear response, it is

necessary to investigate the stability of the lateral load resisting

system and its interactin' with other structural and nonstructural

elements at displacements larger than those resulting from linear
analysis. To handle this problem without having to resort to nonlinear

response analysis^ one option- is to increase by a factor of four the

displacements from linear analysis for the specified: lateral forces,

providing an approximate measure of displacement in the event of a

design- earthquake,, unless the governing code specifies the factors to

be used: as in References A. 5 and: A. 7V

The main concern of Appendix A; is the safety of the structure* The

intent of Sections A.2.2.L and: A.2. 2. 2 is to draw* attention to the

influence of nonstructural elements on structural response and to: hazards from falling objects*

Section A. 2.2.2 is included because the base of the structure as defined in analysis may not correspond to the foundation level*

A.2.3-Strength reduction factors.

Section A.2.3.I refers to brittle elements carrying earthquake induced

forces such as low-rise walls or portions of walls between openings of

which proportions are such that it becomes impractical to reinforce

them to have their nominal shear strength in excess of the shear

corresponding to nominal flexural strength for the pertinent loading

conditions. This requirement does not apply to the design of connecti ons.

i

Section A. 2. 3. 2 is included to discourage the use of tied columns to

resist earthquake induced forces.

The strength reduction factor of 0.65 is to be used in Eq. (A-4) in

determining anchorage length of reinforcing bars with standard hooks.

It applies only to anchorage of reinforcement essential to the integrity of the lateral -force resisting structure..

A. 2. 4-Concrete in elements resisting earthquake-induced forces

The requirements of this section refer to the concrete quality in

frames, trusses, or walls proportioned to resist earthquake-induced
forces- The maximum- design compressive strength- of lightweightaggregate concrete is limited ta 4,000 psi primarily because of paucity

of experimental and field data on the behavior of elements, made with

lightweight concrete,. subjected ta displacement reversals in the

nonlinear rangeA-Z-5-Reinforcement in elements resisting earthquake-induced forces

The use of longitudinal reinforcement with substantially higher

strength than assumed in design may lead to primary shear or bond

failures which are to be avoided even if such failures may occur at

higher loads than those anticipated in design- Therefore, an upper

limit is placed on the strength of the steel

To insure adequate inelastic rotation in frame elements it is essential to use a reinforcement with an ultimate stress well in excess of

the yield stress- For the same reason, any splice must be able to

develop a stress equaT to L.25 times the. nominal yield stress of the

reinforcementA.S-FTexural elements of frames

A-1. 1-Scope

This section refers to horizontal elements of girders of frames resisting lateral loads induced by earthquake motions- If any horizontal

element is subjected to an axial design compressice force exceeding

(Agf

c</10), in addition to the flexure at any section, it is to be

treated as a column as described in Section A. 4.

Experimental evidence * indicates that under reversals of displacement into the nonlinear range,, behavior of continuous elements having

length-to -depth ratios of less than four is significantly different

from- the behavior of relatively slender elements. Oesign rules derived

fronr experience with relatively slender elements do not apply directly

to elements with length -to-depth ratios less than four, especially with

respect to shear strength-
The geometric constrai nts indicated in Sections A. 3.1.3 and A. 3. 1.4-

derive from practice with reinforced concrete frames resisting

A L

earthquake induced forces.

A.3.2-LongitudinaJ reinforcement

Section- IQ.3.3 limits the tensile reinforcement rati a irr a: fTexuraT

member as a fraction^ of the amount which- would produce balanced strainconditions. For a section subjected to bending only and loaded mono—

tonically ta yielding-* this approach is feasible because the likelihood

of compressive failure can be estimated reliably with the behavioral

model assumed for determining the reinforcement ratio corresponding to

"balanced" failure. The same behavioral model (because of incorrect

assumptions such as linear strain distribution* well-defined yield

paint for the steeT* limiting compressive strain in the concrete of

Q.003* and compressive stresses in the shell concrete) fails ta

describe the conditions in e flexural member subjected ta reversals,

of displacements welT inta the inelastic range. Thus, there is little

rationale for continuing to- refer to "balanced conditions" in earthquake resistant design of reinforced concrete structures.

The limit of Q.025 is based primarily on considerations of steel

congestion and, indirectly* on limiting shear stresses in girders of

typical proportions. The minimum requirement: of two No. 5 bars* top

and bottom* refers again ta construction rather than behavioral

requirements.

Up splices of reinforcement (Section A.3.2.3) are prohibited at

regions where flexural yielding is anticipated because such splices

are not considered reliable under conditions of cyclic loading into

the inelastic range. Transverse reinforcement for lap splices at

any location are mandatory because of the likelihood of loss of shell

concrete.

A.3.3-Transverse reinforcement
Special transverse reinforcement is required primarily for confining

the concrete and maintaining lateral support for the reinforcing bars

in regions where yielding is expected* Examples of hoops suitable for

flexural elements of frames are shown in Figs. A-L and A-2.

x. Shall Not Excaod 14 inches

Fig. A-L

In the case of elements with varying strength along the span or elements

for which the permanent load represents a large proportion of the total

design Toad, concentrations of inelastic rotation may occur within the

span, rf such a condition is anticipated, transverse reinforcement

must be provided throughut. the region where yielding is expected.

•• i * 7* * V &w • t

V*

r-

•*

V; V.

i. al a:= c is

Fig. A-2
This, section* applies: ta elements carrying axial loads or columns of

frames proportioned: to resist, earthquake farces. The geometric constraints required: by Sections A.4-.I.I* and A.4J..Z fallow^ from- previous

LL 1 practice vfitir columns.

A.4.Z-ReTative strength- of columns

;

The intent of Section A.4.Z.L is to limit fTexural yielding to the

horizontal elements of the frame. If this requirement cannot be

satisfied at a joint as, for example, irr the case of heavy transfer

girders, additional transverse reinforcement is required in the columns

affected by forces at the joint.

A.4.3-LongitudinaT reinforcement

The lower bound to the rei nforcement ratio in elements carrying axial

forces as weTT as flexure refers to the traditional concenr for the

effects of time-dependent deformations of the concrete as well as desire to avoid a sizeable difference between the cracking and yielding moments. The upper bound reflects concern, for steel congestion,

load transfer in Tow-rise construction, and the development of large

shear stresses in columns of ordinary proportions.

Spalling of the shelT concrete, which is likely to occur near the ends

of the column in frames of typical configuration, makes lap splices in

those locations quite vulnerable. If lap splices are to be used at

all, they must be located near the mid-height where stress reversal is

likeTy ta be limited ta a smaller stress range than at locations near

the joints.

Welding and mechanical splices may occur at any level but not more than

half the bars may be spliced at any one section.

A .4-Frame elements subjected ta bending and axial load

A. 4. 1-Scope

234
A.4-.4-Transverse rei nforcement

The main reason for the requirements in this section is concern for

confining the concrete and providing lateral support ta the reinforcements

For axial Ty compressed elements subjected ta steadily increasing load,,

the effect of helical (spiral) reinforcement on the strength- of the

confined concrete has teen welT established- * Eg* (IQ-3) follows

from* the arbitrary design concept that* under axial loading* the maximum- capacity of the column before lass- of shell be equal to that at

large compressive strains with the spiral rei nforcement stressed to its

useful limit* The toughness o-f the axially loaded "spiral* column is

not directly relevant to its role in the earthquake-resistant frame

vrfrere toughness or ductility is related to its performance under

reversals of moment as well as axial load* For the earthquake problem*

there is no reason to modify Eg* (10-5) other than adding the varying

lower bound given by Eg* (A-L) which governs for larger columns with

gross cross-sectional area* A^* less than approximately 1.26 times

the core area* A_*

c

A conservative evaluation of” the available dataA *^* orT the

effect of rectilinear transverse reinforcement on the behavior of

reinforced concrete would suggest that such reinforcement has little

influence on strength but improves ductility although not as effectively as spiral reinforcement* Consequently, there is no explicit

basis for relating the required amount of rectilinear transverse to

spiral transverse reinforcement. However, it is evident that

rectilinear transverse rei nforcement is less efficient and if it is

used there should be more of it to have an effect comparable to that of

spiral reinforcement* Thus,. Eg* ( A—1) and (A-3) compare to Eqs. (10-5)

and (A-2)* respectively, but Eg. (A-L) and (A-3) require more reinforcement per unit length of column.

The requirement of Eq. (A-2) which governs for large sections is

ignored if the design stresses on the gross section are low.
The transverse reinforcement required by 5q* (10.5), (A-l), (A-Z), and

(A-3) is distributed over regions where inelastic action is considered

to. be likely (Section A.A.d.4)

.

Fig** A-L shows arr exanpTe of transverse reinforcement provided by two

hoops and a cross-tie*

Dynamic response analyses and field observations indicate that columns

supporting discontinued: stiff elements such as walls or trusses* tend

to develop: considerable inelastic response* Therefore, it is required

that these columns have special transverse reinforcement throughout

their length* This rule covers alT columns beneath the level at which

' the stiff element has been discontinued.

A*5-StructuraT waTTs* diaphragms* and trusses

A. 5*1-Scope

This section contains requirements for the dimensions and details of

relatively stiff structural systems including parts of roof and floor

systems, transmitting inertia forces as well as walls and trusses*

Stubby frame elements, which constitute parts of the lateral force

resisting, system, must also satisfy the requirements of this section.

A. 5.2-Reinforcement

Reinforcement minima (Sections A.5.2.1 and A. 5. 2.5) follow fronr

preceding codes. The uniform-distribution requirement of the shear

reinforcement results, from the intent to control the width of inclined

cracks* The requirement, for two layers of reinforcement in walls

carrying substantial design shears is based on the observation that,

under ordinary construction conditions, the probability of maintaining

the location of a single layer of reinforcement near the middle of the

wall plane is quite low* Compressive stress calculated for the

factored forces acting on a linearly elastic model of the structural
element is used as an index value to determine whether confining reinforcement is required- A calculated compressive stress of 0.2 f 1 on an element is assumed to indicate that integrity of the entire structure

is dependent on the ability of that element to resist substantial

conpressive force under severe cyclic loading. Therefore,, transverse

reinforcement* as specified, in Section A-4.4, is required' in such*

elements ta provide confinement for the concrete and the compressed

reinforcement (Section A.5-2-4)- If this requirement should govern in

a solid fToor slab* it may be satisfied by a boundary member, as

defined in Section A.5.1, rather than providing confinement for the

entire slabBecause, the actual stresses in longitudinal reinforcing bars of stiff

elements may exceed the calculated stresses, it is required (Section

A.5.2.5) that alT continuous rei nforcement be developed fullyA. 5.5-Vertical boundary members for structural walls

A simplified diagram- showing the forces on the critical section A-A of

a structural wall acted on by permanent loads, W, and the maximum shear

and moment induced by earthquake in a given direction are shewn in Fig.

A-3- Under the given conditions, the conpressed flange is required to

resist the acting gravity load plus the total tensile force generated

in the vertical reinforcement (or the compressive force associated with

the bending moment at section A-A). Recognizing that this loading

condition may be repeated many times during the strong motion, it

becomes essential to confine the concrete in all wall flanges where the

compressive forces are likely to be large as indicated by the design

compressive stress exceeding 0.2 f' (Sections A. 5.3.1 and A. 5. 3. 2).

The stress is to be calculated for the factored forces on the section

assuming linear response of the gross concrete section. The compressive

stress of 0.2 f* is used as air index value and does not describe the

c

conditions which- may arise at the critical section under the influence

of the actual inertia forces for the anticipated earthquake intensity.
Ffg- A-3

The requirement in Section A .5.3.1 is based on the assumption that the

boundary- element may have tor carry ell compressive forces, at the

critical section at the time when maximum* lateral forces are acting on

the structural wall. The design requirements involve only the section

properties! The cross section of the boundary element must have

adequate strength (calculated as an axially loaded column) to resist

the factored axial oppressive force at the critical section.

Because the horizontal reinforcement in walls requiring boundary menfcers

is likely to act as wed- reinforcement, it should be fully anchored in

the boundary members which act as flanges (Section A. 5. 3. 4). To achieve

this anchorage, is made difficult by stress reversals, by and the possibility of large transverse cracks in the boundary members. Wherever

feasible standard hooks or mechanical anchorage schemes should be

considered.

A. 5-Joints of frames

238

A. 5. 1-General requirements
Development of inelastic rotations at the faces of joints of

reinforced concrete frames is associated with stresses in the flexural

reinforcement well in excess of the yield stress* Consequently* joint

shear stresses generated by the flexural reinforcement are calculated

for 1.2S f irr the reinforcement (Section A. 5.1.1). An explanation

of the reasons for the high; stresses in girder tensile reinforcement is

provided: in Reference A.12*

Because the design requirements for joints were developed recognizing

that the strength" of a joint is typ.ica.liy governed by a brittle mode of

failure*. Section A.2.Z.I does not apply to joints* The appropriate

strength-reduction factor is (T.85 for shear strength*

A. 8.2-Transverse reinforcement

However lout the calculated shear stresses in a joint of a frame

resisting earthquake-i nduced forces* confining reinforcement (Section

A.4-. 4) must be provided through the joint around the column reinforcement (Section A.8.Z.1). Confining reinforcement may be reduced if

horizontal menfcers frame Into all four sides of the joint as described

in Section A. 8. 2.2*

At joints where the girder is wider than the column, girder reinforcement not passing through the confined core of the column is to be

provided with lateral support is* provided by framing into the joint.

A. 8.2-Shear stress

The requirements for the proportioning of joints in Appendix A are

based on Reference A.12 in that behavioral phenomena within the joint

are interpreted in terms of a nominal shear stress* Because tests of

A Id A 2Q joints * and deep beams indicated that shear strength was not

as sensitive to joint or web: reinforcement as implied by the expression

developed by ACI Committee 32S^*^~ for beams and adopted to apply to

joints by ACI Comnittee 352*. it was decided to permit a constant shear

stress (derived from the data in Reference A. 19) in a joint core having

a minimum amount of transverse reinforcement as specified in Section

A. 8.2.
The designer should note that the joint problem is better solved irr proportioning- the girders, and that tensile stresses may exist irr a continuous beam bar through arr interior joint at both faces of the

joint because of limited anchorage length.

Anchorage length of bars irr tension

Eg- (A-4) provides a. routine far determining the minimum anchorage

length of deformed reinforcing bars: with standard: hooks embedded in

confined concrete made with normalweight aggregate. It is based on

cl 22

' recomnendati cn s of ACI Conmittee 408*. Because the hook is

specified to be Tocatad' in confined concrete, special multipliers for

confinement conditions proposed, by ACI Conmittee 408 have been eliminated to simplify calculations.

The- anchorage length in tension for a. reinforcing bar with a standard

hook: is defined, as the distance,, parallel ta the bar, from the critiIcaT section (where the bar is ta be developed) to a tangent drawn- to

the outside edge of the hook. The tangent is to be drawn perpendicular

ta the axis of the bar as shown in Fig. A-4. -

Not* \ Hcote Must 3*

Within Contin«d Cor*.

Fig. A-4

240
For lightweight concrete* the Tength required by Eq* (A-4) is: increased

by 25 percent*

Eq*. (A-4) is not intended: for use with* No* 14 and No* IE bars having

standard: hooks*

The strength* reduction* factor to be used: irr Eg* (A-4) is (1.65

(Section* A.Z..J*!) * It has been* reduced, fronr 0.E proposed by Ad

Connrfttee 408“ because of the effects of Toad reversals*

Section A.5.4.I specifies the minimum anchorage length for straight

bars as a multiple of the length indicated by Section A. 6. 4.1. Case

(b) of Section A. 5*4.1 refers to "top* bars*

Even though* Eg* (A-4) does not apply to hooked Nov 14 and No* IS bars*

it is to be used to determine anchorage lengths for strai qht No* 14 and

No* IS bars* Straight bars are to pass through the confined core in

all cases even if the entire anchorage length cannot be accomnodated

within the confined core*

A*7-Shear-strength requirements

A*7*l -Oesi gn forces

In determining the equivalent lateral forces representing earthquake

effects for the type of frames considered it is assumed that frame

elements wiTT dissipate energy in the nonlinear range of response.

Unless a frame element possesses a strength that is a multiple, on the

order of three to four, of the design forces, it must be assumed that

it will yield in the event of the design earthquake* The design shear

force must be a good approximation of the maximum shear that may

develop in an element* Therefore the design shear for frame elements

is related to the flexural strength of the designed element,, rather

than to the shear indicated by lateral -load analysis. The conditions

described by Sections A. 7.1.1 and A. 7. 1.2. reflect this requirement.

Because girders are assumed to develop extensive nonlinear response,

design shears, in the girders are* determi ned using stresses in the longi-
tudirraT rei nforcement (1*2? fj which* reflect* the effects: of strain*

117 J

hardening** *

- Column design shears (Section A. 711.2) are determined

on the basis of limiting- moments calculated from- interaction diagrams*

In both cases strength-reduction factors are assumed to be unity*

Cosiqir

Not*; Sort* Sad Moiwii n STtoutd 3*

id 3etl* Qirtcrtow* Coear»«3«* zug

Ffg. A-?

Oesign shears for structural walls., trusses, and diaphragms are

obtained from- the lateral-load analysis with the appropriate load

factors* (However, the designer should consider the possibility of

yielding in conponents of such structures, as in the portion of a wall

between two window openings, in which case the actual shear may be well

in excess of the shear indicated by lateral-load analysis based on

factored design forcas.

)

The ternr "probable strength" in Section A. 7.1 refers to moment strength

calculated with A* 1.0 and f * 7 25 f

S —

* y*
A.7.2-Transverse reinforcement irr frame elements

Experimental studies at various laboratories of reinforced concrete

elements subjected to cyclic loading- have demonstrated that more web

reinforcement is required to insure a flexural failure if the element

is subjected to alternating1 nonlinear displacements than if the element

is loaded in one direction onTy„ the necessary increase of web reinforcement being higher in the case of nc axiaT load. This observation

is reflected in the specifications (Section A,7. 2.1) by eliminating- the

term- representing the contribution of concrete to shear resistance.

However, this stratagem^ chosen for its relative sinplicity, should not

be interpreted to mean- that nc concrete is required to resist shear.

On the contrary, it may be argued that the concrete core resists all

the shear with the web reinforcement confining and thus strengthening

the concrete. The confined concrete core plays an important role in

the behavior of the beam and should not be reduced to a minimum just

because the design expression dees not recognize it explicitly.

Because spalling of the concrete shelT is anticipated during strong

motion, especiaTTy at and near regions of flexural yielding, all web

reinforcement must be provided in the form of closed hoops as defined

in Section A. 7. 2. 2.

A. 7.2-Reinforcement in structural walls and diaphragms

Eq. (A-5) has been selected for general use primarily because it

provides a simple and familiar vehicle for the determination of the

required amount of transverse reinforcement. To differentiate between

stubby and slender walls was considered to be unwarranted considering

the increased calculation effort the differentiation requires would be

likely to offset any economy in material it might effect.

The requirement for the distribution of calculated shear stress in

walls working in parallel reflects the need to avoid overloading one of

the piers while the others are barely loaded.
"Horizontal waTT element'*

5 in Section A* 7.3 *4- refers ta wall sections

between- two vertically aligned openings (Fig-. A-d ) .

•

Fig* A-d

A. 3-frame elements not proporti aned to resist forces induced by earthquake

motions*

The intent of Section A,3.I is to insure that the parts of the structural system, designed for gravity loading only, will continue to be

functional at lateral displacemerts for which the lateral-force resisting system has been designed* Consequently, the gravity-load system

need only accommodate the specified lateral displacements without

reduction in gravity-Toad carrying capacity* Reduction in flexural

stiffness of reinforced, concrete elements qf the gravity-load system

may be recognized in cal eolations* It is not necessary to reinforce

the gravity-load system for moments related to lateral forces.
A. 9-Constructi orr joi nts

Construction- joints require explicit attention during the design as

well as the construction of a building* Eq* (A-6) reflects the

influence on shear strength of the estimated net force normal to the

construction joint* It should be noted: that the normal force related

ter the lateral motion will reduce the compressive force due to

gravity* A positive value for P^ refers to compression on the joint*

References

A.l "Recomnended Lateral Force Requirements and Conmentary, " Structural

Engineers Association of California* San Francisco, 1974, 21 pp*

A.Z Blume*, J* A**. Nevanark* It* ML and Coming* L* H., "Design of Multistory

Reinforced Concrete Buildings for Earthquake Motions*" Portland Cement

Association* Skokie* 1961*. 313 ppv

A *3 Clough* "Dynamic Effects of Earthquakes," Journal of the Structural

Division* ASCE* V* 86* No* ST4* April 1960* pp* 49-66.

A. 4 Housner, G* W., "Limit Design of Structures to Resist Earthquakes,"

Proceedings* Wbrld Conference on Earthquake Engineering* EERI,

Berkeley* Calif.* 1956* pp* 5-L ta 6-16*

A. 5 Gulkan, P. and Sozen, M. A.* "Inelastic Response of Reinforced Concrete

i Structures to Earthquake Motions*" ACI Journal, V. 71, No* 12, Dec*

1974, pp* 601-609*

A. 6 "Tentative Provisions for the Development of Seismic Regulations for

Buildings"1 Applied Technology Council, San Francisco, Calif., 1973

(Printed by ILS* Govt* Printing Office*. Washington, D.C*, 1973).

A. 7 "Earthquake-Resistant Design Requirements for VA Hospital Facilities,"

Office of Construction, Veterans Administration, March 1975, Washington,

D.C*
A. 3 Committee on R7C Columns, Building Research Institute of Japan,

"Experimental ReseardT on Improving- Ductility of Reinforced Concrete

Columns- under Cyclic Lateral Loads (in Japanese) Concrete Journal,

W II, Nov 1„ Jan* 1975, pp.. 2-13*

A.? Ri chart, F. E., Brandtzaeg, A*, and Drown, B* L*, "The Failure of

PTairr and Spirally Reinforced Concrete in Compression,"' University of

ITTinaris Engineering Experiment Station Bulletin Nov ISO, Urbane,

AprtT 1929*, 74 pp*

A *10 Roy, Hv E* H*, and Sozen, M* A'*, "Ductility of Concrete, ,r Proc* of the

Int* Symposiunr on Flexural Mechanics of Concrete-, Miami, ACI Special

Publication No-* 12, No* '/- 1964, pp* 21I-23E*

A.ll Burdette, E. £*, and HiTsdorf, tt* £*, "Behavior of Laterally

Reinforced Concrete Columns,* JoumeT af the Structural Division,

ASCE, Y* 97, No* STZ, Feb* 1971, pp* 587-302.

A.12 ACI-ASCE Committee 352, "Recommendations for Design of Beam-Column

Joints in Monolithic Reinforced Concrete Structures,* ACI Journal,

Proc* V* 71, No* 7, July 1976*, pp* 375-391*

A. 13 Ikeda, A., "Load-Oeformati on Characteristics of Reinforced Concrete

Columns Subjected to Alternative Loading" (in Japanese), Report of the

training Inst* for Eng. Teachers, Yokohama National University, March

1963, 9 pp*

A. 14 Popov, E* PL, Bertero, V* V., and Krawinkler, H., "Cyclic Behavior of

Three R/C Flexural Members with High Shear," Report EERC 72-5, University of California, Berkeley, Oct* 1972*

A. IS Wight, J* <*, and Sozen, Mu A*, "Shear Strength Decay in Reinforced

Concrete Columns Subjected to Large Deflection Reversals," Journal of

the Structural Oivision, ASCE, V* 101, No. STS, May 197S, pp.

1053-106S*
A. 15 Barda, R., Hanson, J. ML, and Corley, W. S-. , "Shear Strength of

Low-Rise WalTs with Boundary Elements, " ACI Special Publication,

Reinforced Concrete Structures in Seismic Zones , Detroit* 1975.

A. 17 Cardenas* Alex E., and Magura, D. 5.* "Strength of High-Rise Shear

WaTls of Rectangular Cross Sections,"1 ACI Special Publication SP-36,

1973, pp. H9-15H.

A.1S Mattock, A. Hv, Chen*, 1C* C., and: Soongswang, K., "The Strength of

Reinforced Concrete CbrbeTs,'*' Report SM 76-3, Dept* of Civ. Eng.,

University- of Washington, Seattle, 34- pp.

A. 19 Meinheit, 0* F., and Jirsa, J* 0., "The Shear Stregth of Reinforced

Concrete Seam-Column Joints,* CESRL Report Ho. 77.1, Univ. of Texas,

Austin, Jan. 1977.

A.20 Hirosawa, M., "Strength and Ductility of Reinforced Concrete Members

(in Japanese),* Report of the Biulding Research Institute Ho. 75,

Ministry of Construction, March 1977. (Data summarized in Report

Ho. 452, Structural Research Series, Dept, of Civil Engineering,

University of Illinois, Urbana, Illinois, 1973).

A.2I ACI-ASCE Committee 326, "Shear and Oi agonal Tensin," ACI Journal,

Proc. V59, Ho. 1, Jan. 1962, pp. 1-30; Ho. 2, Feb. 1962, pp. 277-334;-

Ho. 3, March 1962, pp. 352-396.

A.22 International Conference of Building Officials, "Uniform Building

Code," Whittier, California.

A.23 ACI Committee 403, "Suggested Development, Splice, and Standard Hook

Provisions for Deformed Bars in Tension, Concrete International, July

1979 , pp. 44-46.
4.0 MINORITY REPORTS (none)

5.0 CLOSURE (none)

248
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1. PUBLI CATION- OFt

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2. Perform infcQrgan.. Report No. . 3. Publication Date

NBSTR 80-2111-4- October 1980

4* TITLE AND SUBTITLE

REVIEW AND. REFINEMENT OF AIC 2-06 TENTATIVE SEISMIC PROVISIONS Report of

Technical. Committee 4r Concrete’

5. AlkTHQR(S)

Richard EL Marshall and Kyle: Woodward

ff. PERF0RMING.QRGANIZAT10Ni(/f j aincar other dram N 8S-. see instructions):

MATON-AL. BUREAUS (IF STANDARQSL

UEFA RTMElfcT OF COMMERCE

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7. Contract/Grant Mo.

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Federal Emergency Management Agency

Washington^ D.C~ 2Q47Z

10L SUPPLEMENTARY NOTES'

| | Document describes* computer program: SF-1 85, FIPS Software Summary, is attached.

II. ABSTRACT (A 200-word or less factual summary of most significant: information. If document includes a significant

bi bliography or literature: survey, mentiorrit here

}

The TENTATIVE PROVISIONS FOR THE DEVELOPMENT OF SEISMIC REGULATIONS FOR BUILDING

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 reinforced concrete

design provisions. The committee made 19 recommendations for revisions to the

TENTATIVE PROVISIONS. 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.

12. KEY WORDS (Six to twelver entries;, alphabetical order,, capitalize only proper names; and separate key words by semicolons)

Building; • building codes r building design; earthquakes; engineering; reinforced

concrete; standards;, structural engineering

13. AVAILABILITY

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