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Meeting 6 of the BSSC PUC Issue Team on Shear Walls KPFF Consulting Engineers

1601 Fifth Avenue, Suite 1600, Seattle, WA 98101

August 15 (8.30a – 6.00p) and August 16 (8.00a – 12.30p), 2017

Minutes

Attendance: Day 1: Dick Bennett, Jeff Berman, Jason Collins, Larry Fahnestock, Joe Ferzli, David Fields, S.K. Ghosh, Dawn Lehman, Rafael Sabelli, Andy Taylor, Tom Xia Leigh Arber (remote), Gino Kurama (remote), Siamak Sattar (remote), Christopher Segura (remote) Day 2: Dick Bennett, Jason Collins, David Fields, S.K. Ghosh, Dawn Lehman, Rafael Sabelli, Andy Taylor, Tom Xia Attachments:

1) Item 7: Presentation by Fields on definition of ductile coupled concrete walls 2) Item 8: Presentation by Ferzli on practical range of coupling beam aspect ratios 3) Item 9: Presentation by Fahnestock on “Large-Scale Testing and Numerical Simulations

of Coupled Steel Shear Walls” 4) Item 9: Paper by Fahnestock on coupled steel shear walls 5) Item 10: Presentation by Bennett on “Masonry Shear Walls: Partially Grouted Shear

Walls” 6) Item 11: Presentation by Lehman on “Impact of Stiffness Irregularities on Collapse

Potential of Walled Buildings” 7) Item 17: Draft IT4 report outline

1. Call to order Ghosh called the meeting to order at 8:45 AM 2. Self-introductions Attendees introduced themselves 3. Opening remarks Ghosh noted that there may be some confusion about the agendas for this meeting as some were titled “Meeting 5” and others were titled “Meeting 6”. This is Meeting 6.

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Ghosh discussed what the committee hopes to produce by the end of 2018.

Modifications to Part 1 of the NEHRP Provisions. Also, any modifications to Part 1 will require commentary for Part 2. Specifically, create modifications to ASCE 7-16 Table 12.2-1

o Ductile coupled concrete shear walls o Possibly other systems

Write resource papers for Part 3 of the NEHRP Provisions. Ghosh drew attention to an item from the last meeting notes: Item 11 - research papers for Part 3 of the Provisions. We initially need introductory papers on basic behavior of shear walls of all types. Ghosh and Cobeen consulted after the last meeting on a summary for wood shear walls. Ghosh noted that concrete and masonry shear walls are designed similarly, but that a design summary should also include differences between the two types of walls. Steel and wood shear walls are designed fundamentally differently. Ghosh would like to see written material that gives practitioners an idea of how to design shear walls of all types. This would be Chapter 1, followed by more detailed technical papers. Ghosh asked for discussion: is this a good approach? It was generally agreed that this would be a good approach Ghosh discussed possible changes to Part 1 of the NEHRP Provisions.

Definition of concrete coupled walls

Fahnestock asked: what about coupled composite shear walls? Ghosh said that a grant has been made on a P-695 study for coupled concrete shear walls. He said a similar study would be needed for coupled composite shear walls. Fahnestock said that there is a study underway on coupled composite shear walls co-funded by AISC and the Pankow Foundation

Ghosh thought that there would likely not be new material for NEHRP Part 1 for wood and masonry shear walls.

Collins: Are we proposing modifications to design of wood shears walls?

Ghosh: No, we are just explaining the basics of design of wood shear walls.

Sabelli: There are some inherent discrepancies between design philosophies for different wall

types. There are also some false analogies made between wall types.

Ferzli: What would these papers look like?

Ghosh: These would be just the basic philosophy for each type of wall.

Fields: Is there a blueprint for this type of paper?

Ghosh: I proposes to write the summary for concrete walls, and this could serve as a template

for other wall types.

Ferzli: There are advantages to including all wall types in one paper.

Ghosh: I anticipates a 12- to 15- page document for the entire Chapter 1.

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Arber: Steel shear walls are described in an AISC guide currently. The steel option may not fit in

very well with descriptions of other wall types.

Ghosh: Some description of steel plate shear walls should be included. The content of that

section would be up to the author. Short summaries for various shear wall types are

hard to find.

Collins: Perhaps include an illustration of typical shear wall height ranges

Ghosh: This might be construed as promoting certain wall types for certain applications

Bennett: Some engineers are just encountering seismic design of shear walls for the first time,

with recent changes in Seismic Design Category in many areas of the country.

4. Summary of web meeting of June 29, 2017 Review of notes from phone call of June 29. Ghosh asked for comments or corrections. There were none. 5. Review of agenda – possible revisions/additions Ghosh asked for any revisions. There were none. 6. Update on a P-695 study to justify a proper R-value for a ductile coupled reinforced

concrete shear wall system

Ghosh: We want ductile concrete coupled shear walls to be recognized as a separate system in

ASCE 7 Table 12.2-1. Work is underway on a definition for this system in ACI 318

Subcommittee H. Also, there is a proposal for a FEMA P-695 study by John Wallace. The

proposal has been funded by the Pankow Foundation and it is hoped that the ACI

Foundation will also contribute to the research. Ghosh read from an e-mail from John

Wallace regarding the status of the study. It is required for a P-695 study that an

advisory group be formed, and that the work be performed with input from the advisory

group. The proposed review group is S.K. Ghosh, Jim Harris, Ron Klemencic or David

Fields, Andy Taylor and Laura Lowes. A kickoff meeting around September 1st is

proposed. The project team is John Wallace of UCLA and K. Kolozvari of Cal State

Fullerton. Ghosh will continue to coordinate with Wallace.

Ferzli: Why is the aspect ratio for coupling beams of 2.4 commonly used in research?

Fields: A few years ago Wallace and Fields discussed typical actual aspect ratios for office and

residential applications. 2.4 was used for offices and 3.3 for residential. These numbers

have tended to be perpetuated in subsequent research programs.

Ferzli: Wondered why more research has not been performed in the range of aspect ratios

between 2 and 4. Suggested more research be performed on aspect ratios of 2.0 and

2.5.

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Ghosh: The ratios commonly used in research consider available test data.

7. Definition of a ductile coupled reinforced concrete shear wall system – Taylor/Fields Ghosh: A definition of coupled shear walls is contained in the Canadian concrete standard, but

there is none in ACI 318. This definition was discussed in ACI 318 Sub-H, but it was not

balloted. Klemencic proposed that a parametric study should be performed to explore a

definition for a coupled shear wall system based on energy dissipation. This research

was performed at MKA, and the resulting definition was balloted in ACI 318 Sub-H.

Fields has responded to every comment submitted by Sub-H members. He also slightly

modified the definition in response to comments and has updated the supporting

background materials. The definition is currently under further consideration by Sub-H

a. Definition balloted by ACI 318H Taylor: I will re-contact members of Sub-H to get their reactions to the proposed responses to

comments.

Ghosh: Wyllie made a comment that many existing coupling beams have low length to depth

ratios. What about these coupling beams? In response, Sub-H has proposed “ductile”

coupling beams as those with an aspect ratio in the range of 2 to 5.

b. ACI 318H comments and proposed responses Fields reviewed the comments on the ACI 318H ballot and his proposed responses to the

comments. Fields’ presentation is attached to these minutes. His study covered buildings in

the range of 5 to 50 stories. Several variables were studied and varied over the ranges of

“high”, “medium” and “low”. This resulted in many analysis runs. Coupling beam aspect ratios

varied from 1 to 8. Analyses revealed the balance of energy dissipation between the walls and

the coupling beams. Aggregated results indicate that the coupling beams dissipate most of the

energy when the aspect ratios are generally in the range of 2 to 5. Fields also examined degree

of coupling. The analyses indicate that degree of coupling, using elastic analysis, is not a very

consistent indicator of the type of ductile behavior of the coupling beams. For example, with a

coupling beam aspect ratio of 1, the walls are highly coupled, but inelastic action occurs mainly

in the walls rather than the beams.

Fahnestock asked if degree of coupling has been explored on a plastic basis. Fields said that the

analyses performed so far have not considered this.

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c. Revised definition to be balloted by ACI 318H Fields: The revised definition proposed to Sub-H is for an average aspect ratio in the range of 2

to 5.

Ghosh asked for discussion on the part of the definition that specifies that the “average” aspect

ratio of the coupling beams must be between 2 and 5. There was a significant objection to the

use of “average” ratios in the responses from Sub-H.

Ferzli suggested that coupling beams are designed as a group, not individually. There are

always one or two outliers, for example at the lobby level. So, we need to discuss whether

having one or two outliers is acceptable.

Lehman: Is it acceptable for one beam to have an aspect ratio of 1, and the rest to have aspect

ratios in the range of 2 to 5, so that the average is in the range of 2 to 5? This would

meet the current definition, but the beam with aspect ratio of 1 would be badly

damaged.

Fields: If a coupling beams has too low an aspect ratio, it is always possible to make the beam

more shallow, raising the aspect ratio.

Collins: Are we trying to create a simple definition, followed by more specific provisions to

avoid misinterpretation, or are we trying to create a definition that covers all

possibilities within the definition itself?

Ghosh is in favor of a definition that does not require a lot of explanation or exceptions.

Ghosh recommends deleting the word “average” from the definition.

Others agreed that “average” should be deleted. Commentary should be added.

Taylor will contact Sub-H voters to get their reactions to Fields’ responses.

8. Input to Taylor/Fields by Joe Ferzli and others (See also discussion from Item 7 above). Ferzli: What if a core has a coupled wall on one side, but is not coupled on another side? He

has found that shear in the non-coupled wall is higher than in the coupled walls.

Ferzli showed and discussed information on practical ranges of coupling beam span-to-depth

ratios actually used in design. This information is attached to these minutes. He raised the

question of what R values to use if there are coupled walls in one direction of the core, but solid

walls in the other direction. He showed several examples of core wall systems with various

potentials for R values.

Fahnestock: What will be the target R value from the P-695 study?

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Ghosh: There may not be a target value; the P-695 study should reveal what the appropriate

value of R ought to be.

Ghosh: Regarding the ductile coupled wall definition, so far we have a definition in terms of

coupling beam span-to-depth ratio. Wallace has brought up the point that wall axial

loads may be higher than designers are currently considering. The upper bound of this

axial load is when all of the coupling beams yield simultaneously, but this has never

been suggested as a design value because it is considered unrealistically high. Paulay

considered only 40 percent of the total axial load resulting from all beams yielding.

Should a definition of design axial load in the walls be part of the definition of a ductile

coupled wall?

Fields and Ferzli noted that axial tension can control the quantity of steel in coupled walls.

Fields: It is not clear why the old UBC axial load limit of 0.30f’c has disappeared from the code.

Lehman noted that adding more tension reinforcement can result in escalating axial forces,

requiring further addition of tension reinforcement.

Sabelli: Adding axial reinforcement also increases moment capacity, resulting in increased shear

demands in walls.

Ghosh: What is the conclusion?

Fields: The question has been raised about wall axial forces. We are proposing amplifying shear

by omega, and amplifying axial load considering coupling beam overstrength; this

effectively results in capacity-based design.

Lehman: How would one quantify the axial load effect, to make a practical recommendation to

designers?

Ghosh: Axial load in coupled walls has not been one of our considerations up to this point.

Should we bring this into our discussions of a definition of ductile coupled walls?

Lehman is more concerned about shorter buildings with isolated L-shaped or planar walls than

about tall buildings with core walls.

Ferzli’s analytical study was on a 41-story building. He found that as long as axial compression

is accommodated in the design, axial tension capacity will not be a concern.

Ghosh proposed proceeding with the current definition of a coupled wall. In addition we

should study axial load effects to determine if we need to make other recommendations.

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Berman: Should the axial load ratio be a parameter that is considered in the development of

the P-695 archetype studies?

Ghosh: Taylor, Lowes, and Ghosh will be part of the P-695 advisory panel. Any input from this

group (IT) will be transmitted to the P-695 investigators.

Ghosh suggested that Ferzli write commentary related to the core wall cross sections that he

displayed at the meeting, and send this commentary around for feedback from the committee.

It is important for all committee members to record their thoughts and recommendations in

writing. This is how the committee begins to develop the content of our work products.

9. Steel shear walls – Fahnestock/Berman Fahnestock made a presentation titled “Large-Scale Testing and Numerical Simulations of

Coupled Steel Shear Walls.” A copy of this presentation is attached.

Focus is on potential code changes for design of steel coupled shear walls. He discussed mainly analyses that have been recently completed. M. Wang performed most of the analyses. Fahnestock covered large-scale testing; numerical simulations; and design recommendations. There are a few examples of coupled steel shear walls in existence. There are two distinct shear-resisting mechanisms: shear in the steel plates, and frame action. These walls can be considered as acting like a dual system. Fahnestock summarized large-scale tests at Illinois. A 3-story coupled wall was tested, representing the lower 3 stories of a 6-story structure. Loading was a cyclic load protocol with increasing amplitude. Stable, symmetric hysteretic behavior was observed. Final failure was a tension fracture of a column at the base of the wall. Maximum drift was 4 percent. Tests were followed by development of detailed numerical models. The numerical model was calibrated using the test data. Additional numerical simulations were then performed. Optimal degree of coupling seems was found to be in the neighborhood of 0.5. Simulations were on 6-story models. Copies of Fahnestock’s papers are attached to these minutes. Ghosh asked if the development of understanding of steel shear walls is mature enough that

provisions can be formulated.

Fahnestock responded that his research papers, and papers by others, describe design rules.

Design guidance is required so that designers do not make unwise choices about performance

and economy of steel shear walls.

Berman: With steel plate shear walls, capacity design is required; as a result, brittle failure

modes are largely avoided. For this reason he anticipates an R-factor of around 8.

Ferzli pointed out that 2016 provisions (AISC 341 2016 seismic provisions) for steel plate shear

walls result in a very inefficient (uneconomical) design. The optimal design, on the other hand,

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might reduce steel weight by 40 to 50 percent. The optimal design is based on sharing shear

capacity between the steel plate elements and the steel frame.

Sabelli brought up the possibility of steel plate shear walls with outriggers. This would be a very

practical configuration for core shear wall layouts. Fahnestock said that this would be a useful

topic for further study.

Ghosh: Have composite coupled steel plate shear walls (composite walls with steel coupling

beams) been studied?

Berman said some limited testing was done in Korea, but these tests were not very informative.

Ghosh asked if the behavior of composite walls themselves is well understood. Lehman said

some tests have been run, but that they are difficult walls to test because of the force levels

required. Michel Bruneau and Amit Varma have limited funding to perform tests on composite

shear walls. The plan is to conduct a FEMA P-695 evaluation. Ghosh asked, if these composite

walls have been used in practice and if they have been tested. Berman and Fields said that

components of the composite walls have been tested, but not entire cores.

There was a follow-up discussion about AISC 341-16 and coupled steel shear walls. It appears that the current AISC 341 provisions do not sufficiently address coupled walls. Design rules for coupled walls are needed. Ghosh asked if there is a new AISC 341 committee in place. Sabelli said there is, and the committee is working on 2022 provisions. Ghosh said that it would be very useful to write a NERHP Provisions Part 3 paper to provide guidance to the AISC committee on steel plate shear walls, particularly coupled shear walls. It would also be useful to summarize the state of knowledge about composite shear walls. Fahnestock asked if this would be a stand-alone paper, or part of one resource paper representing the work of this committee. Ghosh said it could be either one, but that it is important to publish a summary of the current state of knowledge, as well as cautions to designers. Sabelli said that this summary could include information on steel plate shear walls with outriggers.

Ghosh followed up on discussion from this morning. This IT will propose in Part 1 of the NEHRP

Provisions a modification to ASCE 7-16 Table 12.2-1 to add ductile concrete shear walls.

Whether we would like to do the same thing with coupled steel shear walls or coupled

composite walls is not clear at this time. There is a stumbling block, because neither of these

systems has been defined. Ghosh suggested a resource paper for Part 3, which would cover the

basics of shear wall design for all of the most common materials.

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Lehman suggested that proposals related to walls in ACI 318 Sub H should be coordinated.

Currently they are not – individual proposals are developed independently. Lehman wondered

if this coordination might take place through IT4. Subjects like wall detailing could be

coordinated.

Ghosh commented that there has been a long history of development of seismic design of

concrete shear walls in regions of high seismicity. The ACI design procedure in place until the

early part of the 90s was not very good. Since then, the situation has improved. In 1999, ACI

introduced the New Zealand concept of basing design on neutral axis depth. But, at the same

time the concept of limiting axial compressive forces in concrete shear walls was abandoned.

Also, minimum shear wall thicknesses were not mandated. ACI 318-14 made special reinforced

concrete shear wall detailing much more stringent than before. Currently there are 6 or 8

proposed changes to shear wall detailing, and all of these make detailing requirements more

stringent. He is concerned that the ACI code is returning to shear wall design so stringent that

the use of special reinforced concrete shear walls in buildings would be avoided.

Lehman agreed about the complexity of overlapping provisions that are being proposed. If our

goal really is collapse prevention, we should note that much of the damage observed comes

from asymmetries.

Ferzli said that CKC has performed a study internally to assess the overall effect of recent

changes to ACI 318-14 for detailing special reinforced concrete shear walls.

There was a discussion of overlapping requirements for detailing of reinforced concrete seimic force-resisting systems in ACI 318. The total effect of some of these provisions is to create infeasible and uneconomical construction that may or may not be justified from a technical point of view. There is no mechanism for coordinating overlapping provisions in ACI 318. There is also a tendency within ACI 318 to “err on the side of safety” so that multiple layers of conservatism are applied to detailing requirements. Ghosh commented that this IT should examine the detailing provisions for concrete walls that have been approved, and provisions that are in the pipeline. Ferzli suggested that these effects should be studied in a practical sense. 10. Masonry shear walls – Bennett Bennett gave a presentation titled “Masonry Shear Walls: Partially Grouted Shear Walls”. A copy of the presentation is attached to these notes.

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Bennett gave a brief history of TMS 402 provisions. The majority of masonry design in the U.S. is still conducted using allowable stress design. Revised partially grouted shear wall provisions were adopted in 2013. Bennett reviewed recent research on partially grouted shear walls. More research is needed on ductility of partially grouted shear walls. Bennett described a shake table test of a partially grouted building. Future research should focus on ductility and detailing. Many masonry structures are very over-designed with respect to shear due to architectural considerations. Bennett also discussed coupled masonry shear walls. Two types are slab-coupled shear walls and beam-coupled shear walls. A third suggested type is perforated shear walls. Bennett described a shake table test by Stavridis. Bennett recommended that the coupling provisions should be moved from ASCE 7 to TMS 402. Ghosh suggested that the ASCE 7 provisions address beam-coupling, which is uncommon in masonry building, and could therefore possibly be just dispensed with. Bennett suggested that TMS 402 commentary should be added, alerting designers that coupling can occur even when not designed for. Increased awareness of TMS 402 Appendix C (Limit State Design) is needed, which results in more economical designs and better energy dissipation capacity. 11. Solid walls, coupled walls and walls with openings – Lehman Lehman made a presentation titled “Impact of Stiffness Irregularities on Collapse Potential of Walled Buildings”. A copy of the presentation is attached to these notes. System irregularities were considered through collapse simulation. For example, an opening at the base of a wall. She used continuum modeling with Atena, which explicitly models reinforcement, including confinement. Lehman also described analytical modeling of a planar shear wall building. Lehman presented a sensitivity study, which evaluated the impact of the constitutive model on the collapse margin ratio of solid and coupled walls. There was a follow-up discussion of punched opening in walls, and the transition from solid wall, to a wall with punched openings, to a coupled wall, to a moment frame. There was also a discussion of openings (doors, corridors) at the base of tall shear walls. Fields noted that most common in shear walls are mechanical openings and window and door openings. Fields also noted that ACI 318-14 Section 18.10.8.2 requires additional horizontal reinforcement above and below wall piers. Ghosh noted that the transition between a wall with punched openings and a moment frame is partially prescribed by the ACI 318 definition of a column. 12. Classification of reinforced concrete shear walls Ghosh read from the May 2017 web meeting (Meeting 4) notes, Item 7 “Classification of reinforced concrete shear walls”. Ghosh wants to carry on from that discussion.

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Ghosh: One distinction that needs to be established is that between a shear-controlled and a

flexure-controlled wall.

Lehman: Certainly “squat” walls should not be classified as flexure-controlled walls.

Ghosh: Consider the quantity Vu/(Phi x Vn) where Vu is the expected shear demand, including

amplification effects (possibly an Omega-sub-zero multiplier). Phi is 0.6. Vn is expected

strength, including overstrength. If Omega x Vu < Phi x Vn then the wall is flexure-

controlled; if Omega x Vu > Phi x Vn, the wall is shear-controlled.

A squat wall, defined by Hw/Lw < 1, is always shear-controlled. This is true irrespective of

whether there are wall flanges or not.

A slender wall, defined by Hw/Lw > 2, Will be flexure-controlled if Amplification Factor x Vu < Phi x Vn May be shear-controlled if Amplification Factor x Vu > Phi x Vn (the Amplification Factor may eventually turn out to be equal to Omega-sub-zero) 1 < Hw/Lw < 2 represents a transition range. In this range the wall may be flexure-controlled or shear-controlled. Ghosh asked Lehman what effect wall flanges might have on this definition. She said that the flanges will resist some of the shear, so the overall shear capacity would be greater. In addition, the behavior is no longer that of an elastic system with plane sections remaining plane. Ghosh also asked about the effects of asymmetric flange widths on the behavior of slender walls. Lehman said that flanges will affect flexural capacity, and the capacity will be controlled by the smaller flange in compression. For example, a T-shaped wall could be shear-controlled for loading in one direction and flexure-controlled for loading in the opposite direction. For the purposes of our classification, if an asymmetric wall is shear-controlled in one direction, then it is considered as a shear-controlled wall in general. Lehman noted that there is currently no minimum flexural reinforcement ratio for walls, other than the minimum vertical reinforcement ratio of 0.0025. The Amplification Factor is due to two influences. The first is higher mode effects. The second is flexural overstrength. The higher mode effects are larger than the flexural overstrength effects. The flexural overstrength component is between 1.25 and 1.5. Ghosh raised the topic of deformation capacity. Taylor noted that Wallace currently has a proposal before 318 Sub-H related to deformation capacity. The discussion did not result in any conclusions.

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Lehman showed fragility curves for walls with symmetric and asymmetric flanges, and with a range of axial loads. Walls with symmetric flanges have more robust fragility curves (lower probabilities of failure) than walls with asymmetric flanges. Shape of cross section can affect deformability (for example a circular column is more deformable than a rectangular column), so it is not surprising that asymmetric and symmetric flanged walls exhibit different levels of deformability. Lehman suggested some sort of a provision to promote symmetry of reinforcement in walls. (Chair Ghosh recessed the meeting at 6:05 PM) (Chair Ghosh reconvened the meeting at 8:15 AM on August 16) (The previous discussion was resumed on August 16) There was further discussion on ductile wall definitions. Lehman said that the degree of ductility achieved in walls will never approach the degree of ductility exhibited by ductile columns. The purpose of wall detailing is to provide for post-peak strength. The detailing prevents compression failure, and preserves stability, of the compression boundary element. Ghosh said that the current set of detailing requirements for special walls is onerous. The purpose of these requirements is to prevent brittle behavior of walls. Ghosh noted that there are shear-controlled and flexure-controlled walls. The shear-controlled walls fail non-ductilely. The flexure-controlled walls may fail ductilely or non-ductilely. Ghosh asked, if we are to define a ductile shear wall would we first specify that the wall is detailed according to ACI 318, and second would we limit the axial load acting on the wall? Lehman said that in tests by Elwood there was a reduction in drift capacity with an increase in axial load capacity. In the realm of flexural-controlled slender walls, would we ever want to permit a nonductile failure mode? Ghosh thought that there are common examples of walls in this class with high axial loads, which would tend to fail in a nonductile manner. Fields wondered why a designer would choose to amplify shear by a factor of three, but still accept a mode of failure that is not ductile. Ghosh asked how we should approach coupled walls. Fields noted that the inelastic action occurs mainly in the coupling beams, but may also occur in the walls under certain conditions. Collins asked if there were any lessons learned about walls from the 2011 Tohoku earthquake. Ghosh said that the damage to buildings was actually relatively minor in the Tohoku earthquake. The damage that was observed in concrete shears walls occurred for obvious reasons. 13. Report from Gino Kurama on Loading Rates on Shear Walls Kurama summarized tests from Japan: monotonic high-speed shear loading of wall segments. Papers related to these tests will be provided by Kurama for the committee’s library of papers.

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There was an increase in shear strength of 30 percent at a loading rate of 0.1 m/sec, and an increase of 50 percent at a loading rate of 1.0 m/sec. The increase in shear strength correlated with the observed increase in compressive strength of concrete, investigated in separate tests. He also summarized tests from China, which were conducted at a much lower rate of 0.01 m/sec. Even at this slower rate of loading there appeared to be an increase in strength related to load rate (when compared with quasi-static loading). The increase or Dynamic Impact Factor (DIF) appeared to be about 14 percent. Ghosh suggested that Kurama summarize his findings in writing. Then the committee can review the summary and write a statement about what further research is needed. Kurama said he will also contact John Wallace to find out if he has heard of any other rate-related tests of shear walls. Ghosh asked Kurama for his opinion about the best dates for meetings after October 1st of 2017. Kurama thought that early October might be a good time. He will check his calendar. He suggested that a summer meeting should be early in the summer, rather than late. 14. Changes in special shear wall detailing being processed by ACI 318H - Taylor Taylor reported on items that have either passed or are currently under consideration by ACI 318 Subcommittee H. There was a discussion of cross ties in special walls and columns. There was a concern about constructability when cross ties with 135 degree hooks at both ends are required to be used. There was a discussion of lap splices at the base of special walls. Currently there is disagreement within the research community on the advisability of locating lap splices at the base of walls. Kurama will send a copy of a report that describes variability in performance of ASTM A706 reinforcement. Ghosh asked if this committee wants to take a position on any detailing issues related to special concrete walls. We will revisit this issue when we have discussed detailing issues further. Taylor said that he will pass along any recommendations of IT4 to ACI 318 Sub-H. 15. Identification of problems in the shear design of shear walls ACI determination of required shear strength – There was no discussion of this item. Φ-factor used in shear design of shear walls – There was no discussion of this item.

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Flexural overstrength – This was discussed at previous meetings. There was no further discussion on this topic. Dynamic amplification – This was discussed at previous meetings. There was no further discussion on this topic. Shear strength of concrete under high compression and high rate of loading – see the report on the presentation by Kurama in Item 13. ACI 318H Proposal CH19-009, any update? - Taylor said this proposal is related to definition of flexure-dominated shear walls. It has been considered by Sub-H but not passed. Shear migration to compression pier and shear-compression interaction in a coupled shear wall system - Lehman feels this topic is important. Other aspects? Lehman noted that the basis of ACI 318 design of walls is strength based design in combination with ductile detailing. There is no consideration of deformation demands. The code does not address deformations directly. Lehman and Lowes worked on ATC 114 project on modeling. They developed an approach to estimating drift at the onset of strength loss. Low-cycle fatigue fracture of flexural bars in walls was discussed. Kurama noted that tests he performed resulted in fracture of bars at wall bases that occurred at low bar elongations. 16. Wood shear walls – remote report by Cobeen or Line There was no report on this item. Cobeen and Line are working on defining the scope and focus of their report. 17. Assignments – See the attached report outline for writing assignments. 18. Other business There was no other business. 19. Next meeting Ghosh asked if there were particularly good or bad times for meetings. October will probably be too soon. November is a more likely month. Ghosh will probably try to schedule a conference call between now and the next face-to-face meeting. 20. Adjournment Chair Ghosh adjourned the meeting at 1:00 PM

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