Re: Proposed AC for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies, Subject AC R3

Transcription

1 AMERICAN FOREST & PAPER ASSOCIATION American Wood Council Engineered and Traditional Wood Products Kurt Stochlia, P.E. Vice President, External Operations ICC Evaluation Service, Inc. January 23, 2007 Re: Proposed AC for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies, Subject AC R3 Dear Kurt: Please consider the following comments and modifications: AC R3 25 1) Section 7.2. Revise section to more closely align with building code reference provisions for height limits and seismic design category limits for low R systems: 7.2 Since tthis criteria will allow the use of the assemblies within height limits and in all seismic design categories (IBC) permitted for the equivalent R system listed in ASCE 7 Table , wwhen the assemblies are installed in jurisdictions governed by the IBC, periodic inspections in Seismic Category C, D, E, or F shall be provided for fastening and anchoring the assembly within the seismic-force-resisting system, including connections of the assemblies to drag struts and holddowns, in accordance with Section of the IBC, unless exempted by Exception 3 of Section of the IBC. Reason: This revision intends to more closely align height and seismic design category limits for proprietary systems with comparable systems specified in the applicable building code. Such an approach was contemplated in development of ASCE 7-02 (Section ) for alternative systems. In ASCE 7-02 Table , low R systems are generally not permitted in high seismic design categories and are subject to height limitations. This trend continues into the 2006 IBC and ASCE The current draft of AC322 recognizes low R factor systems (R=2) yet does not stipulate use of building code specified seismic design category and height limits. To better agree with basic requirements of the IBC, limitations for low R systems in the IBC should extend to the low R systems in AC322 unless the relaxation in limitations is substantiated through criteria contained in AC322. Thanks again for the opportunity to comment. Please let me know if I can provide any further clarification of comments above. Sincerely, Philip Line, P.E. Senior Manager, Engineering Research 1111 Nineteenth Street, NW, Suite Washington, DC Fax: America s Forest & Paper People - Improving Tomorrow s Environment Today

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4 From: Avik Ghosh Sent: Thursday, January 25, :08 AM To: Kurt Stochlia; Peter Bahlo; Brian Gerber Cc: George Richards P.E.; Masoud Bokaie; Jeremy Andreasen Subject: Our Comments for the Hearing Importance: High Dear Kurt, Based on meetings with Dr. Reynaud Serrette and discussions with others, attached is a pdf file of a powerpoint presentation containing our comments regarding AC 322. Is it still acceptable to submit our comments? We would really like an opportunity to present this information and lead a discussion on it. We only have one modification and a follow up recommendation in case our one recommendation does not take effect. In summary, we are requesting the following: 1.) Allow a more thorough hysteresis analysis to assign R-values based on directly comparing to the hyesteresis data of Code-approved systems. Any further restrictions on R- values will be based on those limits imposed by governing building Code. If one does not perform such an analysis, then he/she can revert back to Table 1 of the current proposed criteria (which Dr. Serrette has proposed and allows R=6.5 max). How to analyze a hysteresis will be explained by us at the hearing and is illustrated in the attached pdf file. 2.) If item 1 above is NOT implemented in AC 322, then immediately begin work on a new acceptance criteria by committee. This committed should include consulting engineers, academics experts, 2 or more manufacturers, and ICC representatives. This new acceptance criteria should be completed before November 2007 because we would like to have all pre-manufactured systems tested and approved by January 2008 for the new CBC. This AC would be generic to lateral force resisting elements of ANY building material. It would include a thorough hysteresis analysis and allow R values as high as the future Code will permit. This AC may also take into account the findings of ATC-63 if the committee agrees on the details. The philosophy behind this proposal can be discussed at the meeting, but I would like to get a feel for what the parties attending the upcoming hearing think about this. Dr. Serrette and I both agree that this new criteria would help put CFS and Wood on an even playing field. We strongly feel that the opinions of a consulting engineer, such as BORM, should at least be expressed and heard at this hearing since we will ultimately be impacted heavily by AC 322. Thank you. Avik Ghosh, M.S., P.E. Research Manager BORM 555 Anton Blvd. Suite 850 Costa Mesa, CA P: , ext 1824 D: F: avikg@borm.com AC R3 25

5 Engineers Comments and Proposed Modifications to AC322 Comments and Proposed Modifications to AC 322 Avik Ghosh, M.S., P.E. Research Manager Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson

6 Engineers Comments and Proposed Modifications to AC322 Topics BORM s Statement of Purpose for ICC-ES How Are We Progressing? Review/Summary of Seismic Coefficients Rational Methods for Evaluating Structural Systems Proposed Modification to AC322 Hysteresis Analysis Moving Forward Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 1

7 Engineers Comments and Proposed Modifications to AC322 BORM s Statement Of Purpose for ICC-ES We encourage and promote solutions that center around safety, practicality, feasibility, and are progressive in nature. We believe this principle should be placed above all other political and business incentives. Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 2

8 Engineers Comments and Proposed Modifications to AC322 How Are We Progressing? Goal Close To Real Answer? We Are Here ERROR Future Step? Future Step? ATC-63? Next AC? AC 322 AC 130 ESTIMATED KNOWELDGE OF PERFORMANCE OF LATERAL SYSTEMS Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 3

9 Engineers Comments and Proposed Modifications to AC322 Review and Summary of Seismic Coefficients R Value (1999 SEAOC Blue Book): Where, R = R o R d R o = Total System Response Resistance Factor Overstrength (System and Component) Redundancy Load Redistribution R d = Dynamic Response Factor Inelastic Softening Furthermore, Ω o = 1.1R o Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 4

10 Engineers Comments and Proposed Modifications to AC322 Rational Methods for Evaluating Structural Systems 1. Element Hysteresis Analysis and Comparison 2. System Static Pushover Analysis 3. System Incremental Dynamic Analysis (IDA) (i.e., dynamic pushover) Proposed Modification To AC322 ATC-63 Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 5

11 Engineers Comments and Proposed Modifications to AC322 Summary of Evaluation Methods Hysteresis Analysis Perform Full Scale Test Of Element Compare ductility, hysteresis, and failure mode to a predetermined Code approved system. Static Pushover Analysis (See FEMA 273, ATC 40) Perform Full Scale Test of Element to obtain inelastic response. Using test results, perform nonlinear pushover analysis on entire structure. Incremental Dynamic Analysis (similar to ATC-63?) Perform Full Scale Test of Element to obtain inelastic response. Using test results, perform nonlinear dynamic analysis on entire structure. Assign same response coeffiicients as a pre-approved system but limit the use of the new system such that it is equal to or better in overstrength, redundancy, building type, and overall use to that of the preapproved system. Base response coefficients on averages and standard deviations from a suite of structures. Limit the use of the element to the type(s) of building(s) analyzed. Base response coefficients on averages and standard deviations from a suite of structures and ground motions. Limit the use of the element to the type(s) of building(s) analyzed. Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 6

12 Engineers Comments and Proposed Modifications to AC322 Summary of Evaluation Methods Hysteresis Analysis Static Pushover Analysis Incremental Dynamic Analysis (IDA) Relatively simple More accurate Most accurate Advantages Can be used widely if a wide spectrum of buildings is analyzed Can be used widely if a wide spectrum of buildings is analyzed Superior energy dissipation characteristics can be achieved Disadvantages Proposed system is limited in use to that of the pre-approved system it is compared to. Analytically more intensive Limited to the types of buildings analyzed Analytically intensive and time consuming Limited to the types of buildings analyzed Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 7

13 Engineers Comments and Proposed Modifications to AC322 Proposed Modifications to AC322 Allow more extensive evaluation of R, C d, and Ω o by comparing Hysteresis data to that of a code-specified system. Otherwise refer to Table 1 of AC 322 as currently written. The use of the proposed system shall be limited to that of the Code approved system upon which it is compared. Purpose is to allow the option for implementing a well performing, superior energy dissipating, element, given that other system affects are accounted for. As a result, seismic coefficients, R, C d, and Ω 0, beyond those within the limitations of a wood equivalent shearwall system can be used in certain cases. Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 8

14 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4. Compare inelastic energy dissipation 5. Compare failure mode and post failure condition Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 9

15 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4. Compare inelastic energy dissipation 5. Compare failure mode and post failure condition µ = u y y u Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 10

16 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4. Compare inelastic energy dissipation 5. Compare failure mode and post failure condition Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 11

17 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: First Cycle 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4.Compare inelastic energy dissipation 5. Compare failure mode and post failure condition Strength Loss Stiffness Loss Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 12

18 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4. Compare inelastic energy dissipation 5. Compare failure mode and post failure condition E elastic E inelastic Seismic Performance ~ E inelastic E elastic y u Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 13

19 Engineers Comments and Proposed Modifications to AC322 Hysteresis Analysis Based on a lateral element/system that is already approved in the Code with established seismic coefficients, compare its hysteresis to that of the proposed new element/system with respect to the following characteristics: 1. Compare ductility 2. Compare number cycles at ultimate load 3. Compare degredation (Strength, Stiffness, Energy) 4. Compare inelastic energy dissipation 5. Compare failure mode and post failure condition Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 14

20 Engineers Comments and Proposed Modifications to AC322 Moving Forward 1. Provisions for more detailed hysteresis analysis should be implemented in AC 322 to allow direct comparison of Code approved lateral systems to new systems in obtaining seismic coefficients (R, C d, Ω 0 ) beyond those within the limitations of a wood shearwall equivalent system (R>6.5). 2. If item 1 above is not implemented in AC 322, then a new Acceptance Criteria must be in the works immediately developing the criteria for hysteresis analysis which can be extended to lateral elements of any building material. Thus, the new criteria will be generic to any type of system. This new criteria should be developed before November If item 2 above takes effect, then the new acceptance criteria should be developed by Committee including: ICC-ES representative(s) Consulting Engineer(s) Academic representative(s) 2 or more Manufacturers 4. Findings of ATC-63 should be considered and investigated in the new acceptance criteria for possible option of calculation of new seismic coefficients for certain types of structures in the future. Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 15

21 Engineers Comments and Proposed Modifications to AC322 Thank you Discussion? Structural, Civil, Mechanical, Electrical, Plumbing, Land Development, Surveying, Construction Administration, Design Build Costa Mesa Las Vegas Phoenix Roseville Pleasanton Denver Tucson Page 16

22 AC R3 25 Response to Request for Comments ICC-ES Staff Letter Date January 3, 2007 on Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral- Force Resisting Vertical Assemblies Subject AC R3 (KS/BG) ICC-ES February 8, 2007 Hearing The following comments are based on discussions between Ray Yu and Gary Hardy (Hardy Frames, Inc.), Reynaud Serrette (CLFSR, Santa Clara University) and practicing engineers in the San Francisco Bay Area. 1. The International Residential Code (IRC) is a prescriptive document, and the proposed criteria relies heavily on an engineered approach. In order to include the IRC in an evaluation report, complete engineered design (including a load path analysis) in accordance with Section R should be furnished and noted as a requirement in the evaluation report. As an alternative, additional information could be developed that would allow the assemblies to be recognized as alternatives to the bracing methods specified in Section R of the 2006 IRC. This approach is much more involved. It appears, for now, that the first approach should be used. Comment: Acceptance criteria, consistent with the performance expected of structures designed prescriptively under the IRC, should be developed to allow any qualifying prefabricated vertical lateral-force resisting assembly, regardless of the specific material used to construct that assembly, to be recognized as an alternative/replacement for the bracing methods permitted in Section R of the IRC. To this end, it is important that performance parameters, in particular resistance, stiffness and deflection, be clearly defined in the criteria. Proper identification of these performance requirements requires additional work that would further delay a resolution on AC322. In the interim, if it is desired to include the IRC in an evaluation report, complete engineered design (including a load path analysis) in accordance with IRC Section R should be furnished and noted as a requirement in the evaluation report. 2. If the alternative approach noted in comment 1 is used, another item needs to be resolved involving the design of the anchorage. The question is, should the anchorage for the lateral-force resisting (L-FR) element be designed for the full capacity of the L-RF, or just for the prescriptive tie-down capacity noted in Section R (Table R ) of the IRC? Staff believes the anchorage should be designed for the full capacity of the L-FR. Comment: Anchorage should not be required to be designed for the full capacity of the L-FR element. Instead, anchorage should be designed for Ω o times the prescriptive tie-down capacity or the maximum resistance the replaced wall element is capable of developing, whichever is less. 1

23 If the underlying concern in this comment stems from the notion that L-FR element will attract more load due to a higher stiffness, compared to the wall element being replaced, it should be emphasized that the overall stiffness of any L-FR element is dependent on all the components in the L-FR element load path. Further, if the prescriptive requirements in the IRC are based on the assumption that diaphragms are flexible, replacement of a wall element with a stiffer L-FR element does not change this assumption and, as a result, the intended distribution of force. If the prescriptive method is based on a rigid diaphragm assumption, then stiffer replacement elements, after consideration of the entire load path associated with that element, may result in a greater stiffness and the attraction of more load. Assuming the second condition to be true, provision of anchorage in accordance with the engineered element requirements (i.e. use the anchorage specified by the manufacturer for engineered design) would address all design issues. The following recommendation, taken from ASCE 7-05, sheds some light on the diaphragm issue Flexible Diaphragm Condition. Diaphragms constructed of untopped steel decking or wood structural panels are permitted to be idealized as flexible in structures in which the vertical elements are steel or composite steel and concrete braced frames, or concrete, masonry, steel, or composite shear walls. Diaphragms of wood structural panels or untopped steel decks in one-and two-family residential buildings of light-frame construction shall also be permitted to be idealized as flexible. Thus, in accordance with the ASCE 7 provisions and the intent of the IRC, anchorage should be designed for Ω o times the prescriptive tie-down capacity or the maximum resistance the replaced wall element is capable of developing, whichever is less. Using this approach, anchorage capacity shall be evaluated at the nominal strength level. 3. The issue of shear friction (at a base plate) in the design of the anchorage to concrete has not been completely resolved. It appears that if shear friction is to be considered, at least one issue that needs to be resolved is verification that the concrete cover in the direction of the loading is adequate to prevent concrete breakout. Comment: For L-FR elements with a flat base, shear friction undoubtedly provides some shear resistance. Resistance provided by shear friction potentially depends on a number of factors including concrete cover, rod/bolt pretension force, and condition of concrete surface (clean, flat, higher water content). Concrete cover and rod/bolt pretension force can be prescribed. It may not be possible to uniformly control the condition of the concrete surface in the field. To what degree can the condition of the concrete surface effect the expected friction coefficient? How would lateral response be affected in terms of wall slip? The reliability and predictability of shear friction warrants further investigation. Shear friction as a mechanism of resistance should not be considered at this time. 4.(a) A new approach to establishing seismic coefficients and factors, including an R value, has been proposed and is noted in Section 5. A value of 0.65P peak is noted in Section 5.2. Additional information is requested justifying this value, since the more traditional value has been 0.80P peak. Comment: The 0.8P peak load level has been traditionally used in the development of equivalent energy elastic-plastic (EEE-P) curves for elements with robust to relatively robust (may exhibit some strength and stiffness degradation) hysteresis, as illustrated in Figure (a). 2

24 P Outline of Robust Hyst. P Δ Δ Simple Yielding (Robust) Figure (a) Robust hysteresis Relatively Robust Strength Degradation For elements that exhibit strength and stiffness degradation in combination with pinching, the use of the 0.8P peak value as a yield load limit becomes questionable due to the significant difference between the robust hysteresis envelope and that of the pinched element, as illustrated in Figure (b). Outline of Robust Hyst. P Δ Pinched Figure (b) Robust hysteresis envelope versus pinched hysteresis behavior It appears that a more rational approach for estimation of the yield point in the pinched element, using the equivalent energy elastic-plastic curve, would involve a consideration the area bounded by the entire hysteresis envelope. For example, referring to Figure (c), if the area enclosed by the pinched hysteresis envelope is defined as A P, then to develop an equivalent energy robust elastic-plastic envelope (with similar elastic stiffness) with enclosed area A EF = A P, the derived yield strength of the equivalent robust envelope (A EF ) will be different from 0.8P peak. In the example shown, the derived yield strength is approximately 0.5P peak. If the behavior of a L-FR element is such that there is no energy dissipation in the upper left and lower right quadrants (severely pinched) and the envelope response in the other quadrants is elastic-perfectly plastic, then A P /A EF will be exactly 0.5. The CUREE-Caltech Woodframe Project (Publication No. W-30b, Section M.7.2) notes the difficulty in defining the yield strength for wood frame shear walls, yet this value is an important parameter in estimating the elastic-plastic model for the shear wall. Recognizing the potential range in values for P yield, Krawinkler et al. in the CUREE-Caltech Woodframe Project on Seismic Demands for Single- and Multi-Story Wood Buildings considered P yield values of 0.6P peak, 0.7P peak and 0.8P peak in their analyses. The 0.65P peak value in the current version of AC322 is based on a simple average of 0.5P peak and 0.8P peak values, where the 0.5 value represents an approximate lower bound on the derived yield (no energy dissipation in two quadrants) and 0.8 the upper bound for relatively robust systems. 3

25 A F : Area bounded by full (robust) hysteresis envelope P peak A F : Area bounded by full (robust) hysteresis envelope P peak A EF : Area bounded by an equivalent full (robust) hysteresis envelope ~ 0.5P peak A EF : Area bounded by an equivalent full (robust) hysteresis envelope ~ 0.5P peak A P : Area bounded by pinched hysteresis envelope Applied load A P : Area bounded by pinched hysteresis envelope A EF = A P A EF = A P Lateral displacement Figure (c) Comparative hysteresis energy envelopes 4.(b) Also, additional information is requested concerning the relationship between the ratio noted in Section a and the C d factor noted in Table 1. These appear to be incompatible. Comment: The criteria in Section 5.2.1(a) is not required to be compatible with the C d factor noted in Table 1. Determination of design values in AC322 is a two-step process: first, the behavior of an element is evaluated to determine applicable seismic response modification factors and second, design values are determined using the Code provisions. The goal of Table 1 is to associate a type of element performance/behavior with established seismic modification factors. Element ductility μ, as defined in Section 5.2.1, depends on a defined yield load (P yield ), yield displacement (Δ y ) and ultimate displacement (Δ u ). The C d (deflection amplification) factor is used to estimate the maximum inelastic displacement (δ x ) of an element based on the elastic displacement at the LRFD strength level displacement (δ xe ), as illustrated in the Figure (d). Δ u is not tied to Code inelastic drifts and P yield is not tied dependent on P LRFD. V V E V m V s V e R/0.7 R Ω o Elastic Response Inelastic Response C d I E Unreduced design spectrum Reduced design spectrum δ xa δ xe δ x δ E δ Figure (d) An interpretation of C d 4

26 5. During our review of proposed Sections 4.1 and it was noted that a situation could occur where 72 cycles would not be enough to establish the nonlinear curve. This could be a problem, especially if the FME is underestimated. ASTM E 2126 allows for more cycles to establish a curve. Comments are requested as to whether ASTM E 2126 should be added to the criteria. Comment: Testing should permit the number of cycles necessary to develop the response curve sought. If the test protocol is based on an estimation of the FME and testing must be limited to 72 cycles, then the FME estimate could not be correct (i.e. the value used was not the FME). It is recommended that the number of cycles be permitted to exceed 72 and the sequence of load steps after the 72 nd cycle should follow the protocol used in the preceding cycles. 6. Revisiting the issue of redundancy, it appears that the portal type of L-FR elements should not be allowed in higher seismic risk areas, unless there is an additional L-FR element in the same wall line. Comments are requested. Comment: The concerned raised here is warranted from the point of view that the portal-type L-FR assembly involves field connection of structural members that influence the performance of assembly. As an alternative to requiring an additional L-FR element, staff may want to consider a higher safety factor for portal-type L-FR assemblies. 5

27 ICC EVALUATION SERVICE, INC. Evaluate P Inform P Protect January 3, 2007 TO: PARTIES INTERTESTED IN EVALUATION REPORTS ON PREFABRICATED, COLD-FORMED, STEEL LATERAL-FORCE- RESISTING VERTICAL ASSEMBLIES SUBJECT: Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateralforce-resisting Vertical Assemblies, Subject AC R3 (KS/BG) Dear Madam or Sir: Hearing Information: Thursday, February 8, :00 a.m. The Westin Los Angeles Airport 5400 West Century Boulevard Los Angeles, California (310) The enclosed proposed acceptance criteria is on the agenda for consideration at the Evaluation Committee hearing noted above. The subject proposed criteria was previously on the February and June 2006 Evaluation Committee agendas. The criteria was held for further study to allow staff time to work with industry to resolve outstanding issues. Several issues have been resolved, but a few remain. The enclosed draft has been revised to be as consistent as possible with the written comments received and with the verbal comments made at the February and June hearings. The following comments concern the few remaining issues: 1. The International Residential Code (IRC) is a prescriptive document, and the proposed criteria relies heavily on an engineered approach. In order to include the IRC in an evaluation report, complete engineered design (including a load path analysis) in accordance with Section R should be furnished and noted as a requirement in the evaluation report. As an alternative, additional information could be developed that would allow the assemblies to be recognized as alternatives to the bracing methods specified in Section R of the 2006 IRC. This approach is much more involved. It appears, for now, that the first approach should be used. Business/Regional Office P 5360 Workman Mill Road, Whittier, California P (562) Regional Office P 900 Montclair Road, Suite A, Birmingham, Alabama P (205) Regional Office P 4051 West Flossmoor Road, Country Club Hills, Illinois P (708)

28 AC R If the alternative approach noted in comment 1 is used, another item needs to be resolved involving the design of the anchorage. The question is, should the anchorage for the lateral-force resisting (LFR) element be designed for the full capacity of the LRF, or just for the prescriptive tie-down capacity noted in Section R (Table R ) of the IRC? Staff believes the anchorage should be designed for the full capacity of the LFR. 3. The issue of shear friction (at a base plate) in the design of the anchorage to concrete has not been completely resolved. It appears that if shear friction is to be considered, at least one issue that needs to be resolved is verification that the concrete cover in the direction of the loading is adequate to prevent concrete breakout. 4. A new approach to establishing seismic coefficients and factors, including an R value, has been proposed and is noted in Section 5. A value of 0.65 P peak is noted in Section 5.2. Additional information is requested justifying this value, since the more traditional value has been 0.80 P peak. Also, additional information is requested concerning the relationship between the ratio noted in Section a and the C d factor noted in Table 1. These appear to be incompatible. 5. During our review of proposed Sections 4.1 and it was noted that a situation could occur where 72 cycles would not be enough to establish the nonlinear curve. This could be a problem, especially if the FME is underestimated. ASTM E 2126 allows for more cycles to establish a curve. Comments are requested as to whether ASTM E 2126 should be added to the criteria. 6. Revisiting the issue of redundancy, it appears that the portal type of LFR elements should not be allowed in higher seismic risk areas, unless there is an additional LFR element in the same wall line. Comments are requested. You are cordially invited to submit written comments, or to attend the Evaluation Committee hearing and present verbal comments. Written comments will be forwarded to the committee, prior to the hearing, if received by January 23, If the deadline is missed, you must provide 35 copies of the submittal material, collated, stapled and threehole punched, to the Los Angeles business/regional office before the committee meeting. Your consideration in providing written responses by the deadline would be greatly appreciated. Consideration of written comments and presentations of a significant nature received the week of the hearing or at the hearing may be delayed until a future meeting as the committee and staff may not have adequate time for review. NEW FOR THE FEBRUARY 2007 MEETING! On a trial basis, starting with the February 2007 Evaluation Committee meeting, comments from interested parties that are submitted in response to proposed acceptance criteria will be posted on the ICC-ES web site prior to the meeting. Postings will occur shortly after the comment deadline (January 23, 2007). Staff memos responding to some of the comments, and comments received after the January 23 deadline, will be posted on February 1, 2007.

29 AC R3 3 The purpose for posting the comments prior to the meeting is to help interested parties be better prepared to discuss the issues at the meeting. Any written material submitted for committee consideration will be available for public distribution as set forth in Section 2.7 of the Rules of Procedure for the Evaluation Committee (copy enclosed). Visual aids (including, but not limited to, charts, overhead transparencies, slides, videos, or presentation software) for viewing at meetings will be permitted only if the presenter provides to ICC-ES, before the presentation, a copy of the visual aid(s) in a medium that can be retained by ICC-ES with its record of the meeting, and that can also be provided to interested parties. Your cooperation is requested in forwarding to the Los Angeles business/regional office all material directed to the Evaluation Committee. Parties interested in the deliberations of the committee should refrain from communicating, whether in writing or verbally, with committee members regarding agenda items. The committee reserves the right to refuse communications that do not comply with this request. Newly approved acceptance criteria may involve test methods or test protocols that are not currently included in the scope of testing services offered by accredited testing laboratories. As noted in the ICC-ES Rules of Procedure for Evaluation Reports, the scope of the laboratory s accreditation must include the type of testing that is to be reported to ICC-ES. We encourage accredited laboratories to expand their scopes of accreditation to include testing under newly approved acceptance criteria. Please note that testing laboratories must be accredited by the International Accreditation Service (IAS) or by another accreditation body that is a signatory to the International Laboratory Accreditation Cooperation Mutual Recognition Arrangement. For further information, please contact IAS at (562) , extension 3309, or send an to pmccullen@iasonline.org. If you have any questions, please contact the undersigned at (800) , extension 3733, or Brian Gerber, S.E., principal structural engineer at extension You may also reach us by at es@icc-es.org. Yours very truly, KS/ll Enclosures Kurt Stochlia Vice- President, External Operations cc: Evaluation Committee

30 ICC EVALUATION SERVICE, INC. Evaluate P Inform P Protect ICC EVALUATION SERVICE, INC., RULES OF PROCEDURE FOR THE EVALUATION COMMITTEE 1.0 PURPOSE The purpose of the Evaluation Committee is to monitor the work of ICC-ES, in issuing evaluation reports; to evaluate and approve acceptance criteria on which evaluation reports may be based; and to sponsor related changes in the applicable codes. 2.0 MEETINGS 2.1 The Evaluation Committee shall schedule meetings that are open to the public in discharging its duties under Section 1, subject to Section All scheduled meetings shall be publicly announced. 2.3 Two-thirds ( 2 / 3 ) of the voting Evaluation Committee members shall constitute a quorum. A majority vote of members present is required on any action. 2.4 In the absence of the nonvoting chairman-moderator, Evaluation Committee members present shall elect an alternate chairman from the committee for that meeting. The alternate chairman shall be counted as a voting committee member for purposes of maintaining a committee quorum and to cast a tie-breaking vote of the committee. 2.5 Minutes of the meetings shall be kept. 2.6 An electronic audio record of meetings shall be made by ICC-ES; no other audio, video, electronic or stenographic recordings of the meetings will be permitted. Visual aids (including, but not limited to, charts, overhead transparencies, slides, videos, or presentation software) viewed at meetings shall be permitted only if the presenter provides ICC-ES before presentation with a copy of the visual aid in a medium which can be retained by ICC-ES with its record of the meeting and which can also be provided to interested parties requesting a copy. A copy of the ICC-ES recording of the meeting and such visual aids, if any, will be available to interested parties upon written request made to ICC-ES together with a payment as required by ICC-ES to cover costs of preparation and duplication of the copy. These materials will be available beginning five days after the conclusion of the meeting but will no longer be available after 30 days have elapsed from the conclusion of the meeting. 2.7 Parties interested in the deliberations of the committee should refrain from communicating, whether in writing or verbally, with committee members regarding agenda items. All written communications and submissions regarding agenda items should be delivered to ICC-ES. All such written communications and submissions shall be considered nonconfidential and available for discussion in open session of an Evaluation Committee meeting, and shall be delivered at least ten days before the scheduled Evaluation Committee meeting if they are to be forwarded to the committee. Correspondence received by ICC-ES will not be released to any party, except to the Evaluation Committee, prior to the meeting without permission of the author. The committee reserves the right to refuse recognition of communications which do not comply with the provisions of this section. All such communications and submissions will be available from ICC-ES upon written request and payment of costs associated with duplication. The materials will be available beginning five days after the conclusion of the meeting but will no longer be available after 30 days have elapsed from the conclusion of the meeting. 3.0 CLOSED SESSIONS Evaluation Committee meetings shall be open except that the chairman may call for a closed session to seek advice of counsel. 4.0 ACCEPTANCE CRITERIA 4.1 Acceptance criteria are established by the committee to provide a basis for issuing ICC-ES evaluation reports on products and systems under codes referenced in Section 2.0 of the Rules of Procedure for Evaluation Reports. They also clarify conditions of acceptance for products and systems specifically regulated by the codes. Acceptance criteria may involve a product, material, method of construction, or service. Consideration of any acceptance criteria must be in conjunction with a current and valid application for an ICC-ES evaluation report, an existing ICC-ES evaluation report, or as otherwise determined by the Evaluation Committee. 4.2 Procedure: Proposed acceptance criteria shall be developed by the ICC-ES staff and discussed in open session with the Evaluation Committee during a scheduled meeting, except as permitted in Section 5.0 of these rules Proposed acceptance criteria shall be available to interested parties at least 30 days before discussion at the committee meeting The committee shall be informed of all pertinent written communications received by ICC-ES Attendees at Evaluation Committee meetings shall have the opportunity to speak on acceptance criteria listed on the meeting agenda, to provide information to committee members. 4.3 Approval of acceptance criteria shall be as specified in Section 2.3 of these rules. 4.4 The action of the Evaluation Committee may be appealed in accordance with the ICC-ES Rules of Procedure for Appeal of Acceptance Criteria. Business/Regional Office P 5360 Workman Mill Road, Whittier, California P (562) Regional Office P 900 Montclair Road, Suite A, Birmingham, Alabama P (205) Regional Office P 4051 West Flossmoor Road, Country Club Hills, Illinois P (708)

31 ICC EVALUATION SERVICE, INC., RULES OF PROCEDURE FOR THE EVALUATION COMMITTEE 5.0 COMMITTEE BALLOTING FOR ACCEPTANCE CRITERIA 5.1 Acceptance criteria may be issued without a public hearing following a 45-day public comment period and a majority vote for approval by the Evaluation Committee when, in the opinion of ICC-ES staff, one or more of the following conditions have been met: 1. The subject is nonstructural, does not involve life safety, and is addressed in nationally recognized standards or generally accepted industry standards. 2. The subject is a revision to an existing acceptance criteria that requires a formal action by the Evaluation Committee, and public comments raised were resolved by staff with commenters fully informed. 3. Other acceptance criteria and/or the code provide precedence for the revised criteria. 5.2 Negative votes must be based upon one or more of the following, for the ballots to be considered valid and require resolution: a. Lack of clarity: There is insufficient explanation of the scope of the acceptance criteria or insufficient description of the intended use of the product or system; or the acceptance criteria is so unclear as to be unacceptable. (The areas where greater clarity is required must be specifically identified.) b. Insufficiency: The criteria is insufficient for proper evaluation of the product or system. (The provisions of the criteria that are in question must be specifically identified.) c. The subject of the acceptance criteria is not within the scope of the applicable codes: A report issued by ICC- ES is intended to provide a basis for approval under the codes. If the subject of the acceptance criteria is not regulated by the codes, there is no basis for issuing a report, or a criteria. (Specifics must be provided concerning the inapplicability of the code.) d. The subject of the acceptance criteria needs to be discussed in a public hearings. The committee member requests additional input from other committee members, staff or industry. 5.3 An Evaluation Committee member, in voting on an acceptance criteria, may only cast the following ballots: Approved Approved with Comments Negative: Do Not Proceed 6.0 COMMITTEE COMMUNICATION Direct communication between committee members, and between committee members and an applicant or concerned party, with regard to the processing of a particular acceptance criteria or evaluation report shall take place only in a public hearing of the Evaluation Committee. Accordingly: 6.1 Committee members receiving an electronic ballot should respond only to the sender (staff). Committee members who wish to discuss a particular matter with other committee members, before reaching a decision, should ballot accordingly and bring the matter to the attention of ICC-ES staff, so the issue can be placed on the agenda of a future committee meeting. 6.2 Committee members who are contacted by an applicant or concerned party on a particular matter that will be brought to the committee will refrain from private communication and will encourage the applicant or concerned party to forward their concerns through the ICC- ES staff in writing, and/or make their concerns known by addressing the committee at a public hearing, so that their concerns can receive the attention of all committee members.# Effective November 6,

32 ICC EVALUATION SERVICE, INC. Evaluate P Inform P Protect PROPOSED ACCEPTANCE CRITERIA FOR PREFABRICATED, COLD-FORMED, STEEL LATERAL-FORCE-RESISTING VERTICAL ASSEMBLIES AC322 Proposed January 2007 PREFACE Evaluation reports issued by ICC Evaluation Service, Inc. (ICC-ES), are based upon performance features of the International family of codes and other widely adopted code families, including the Uniform Codes, the BOCA National Codes, and the SBCCI Standard Codes. Section of the International Building Code reads as follows: The provisions of this code are not intended to prevent the installation of any materials or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. Similar provisions are contained in the Uniform Codes, the National Codes, and the Standard Codes. ICC-ES may consider alternate criteria, provided the report applicant submits valid data demonstrating that the alternate criteria are at least equivalent to the criteria proposed in this document, and otherwise meet the applicable performance requirements of the codes. Notwithstanding that a product, material, or type or method of construction meets the requirements of the criteria proposed in this document, or that it can be demonstrated that valid alternate criteria are equivalent to the criteria in this document and otherwise meet the applicable performance requirements of the codes, ICC-ES retains the right to refuse to issue or renew an evaluation report, if the product, material, or type or method of construction is such that either unusual care with its installation or use must be exercised for satisfactory performance, or malfunctioning is apt to cause unreasonable property damage or personal injury or sickness relative to the benefits to be achieved by the use of the product, material, or type or method of construction. Business/Regional Office P 5360 Workman Mill Road, Whittier, California P (562) Regional Office P 900 Montclair Road, Suite A, Birmingham, Alabama P (205) Regional Office P 4051 West Flossmoor Road, Country Club Hills, Illinois P (708)

33 PROPOSED ACCEPTANCE CRITERIA FOR PREFABRICATED, COLD-FORMED, STEEL LATERAL-FORCE-RESISTING VERTICAL ASSEMBLIES AC R3 Page 2 January % % 17 % INTRODUCTION 1.1 Purpose: The purpose of this acceptance criteria is to establish requirements for lateral (seismic and wind) racking loads and deflections on prefabricated, cold-formed, steel lateral-force-resisting (LFR) assemblies, including vertical elements, to be recognized in an ICC Evaluation Service, Inc. (ICC-ES), evaluation report under the 2006 International Building Code (IBC), the 2006 International Residential Code (IRC) and the 1997 Uniform Building Code (UBC). The bases of recognition are IBC Section , IRC Section R and UBC Section The reason for the development of the criteria is to provide guidelines for testing and assignment of design loads and deflections, where the codes do not provide the necessary requirements for the products covered in this criteria. The criteria also provides a means to assign seismic design coefficients and factors for alternative basic seismic force-resisting systems. 1.2 Scope: This criteria applies to prefabricated, cold-formed, steel shearresisting bearing wall assemblies used in conjunction with wood and cold-formed steel wall framing light-frame construction to resist lateral and (when included in the testing and analysis) vertical and transverse loads. 1.3 Codes and Referenced Standards:

34 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 3 January International Building Code (IBC), International Code 21 Council International Residential Code (IRC), International Code 23 Council Uniform Building Code (UBC) AISI (2001) North American Specification for the Design of Coldformed Steel Structural Members (AISI NASPEC), with Appendix A and 2004 Supplement, American Iron and Steel Institute AISI (1996) Specification for the Design of Cold-formed Steel Structural Members, American Iron and Steel Institute ASCE 7-05, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers Standard Test Method of Cyclic (Reversed) Test for Shear Resistance of Framed Walls for Buildings, by the Structural Engineers Association of Southern California (SEAOSC), dated August 1, 1996 (revised January 20, 1997). 1.4 Definitions: Prefabricated Shear Resisting Assembly (PSRA): An assembly consisting of a single structural unit, the integral parts of which are constructed or assembled prior to incorporation in the building. The assembly is field-connected such that the LFR (lateral-force resisting) performance only depends on the prefabricated assembly.

35 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 4 January % Composite Shear Resisting Assembly (CSRA): An assembly consisting of a prefabricated shear resisting assembly, with a field connection to a structural member, such as a header, such that the LFR performance depends on the prefabricated assembly and the attached structural member Structural System Type Definition: The assembly shall be defined as one of the following: Moment Frame: A structural assembly in which one or more members and joints resist lateral forces by flexure, as well as along the axis of the members. In addition to these lateral forces, axial forces and overturning forces in the plane of the wall and lateral forces perpendicular to the wall, are also resisted by elements of the moment frame. As defined in Section 11.2 of ASCE Braced Frame: A vertical truss assembly that resists the effects of lateral forces. Axial forces and overturning forces in the plane of the wall and lateral forces perpendicular to the wall may or may not be resisted by independent framing members attached to the braces Shear Wall: A nonperforated structural assembly that resists lateral forces, in the plane of the wall, using the in-plane shear resistance of an attached structural plate. Axial forces and overturning forces in the plane of the wall and lateral forces perpendicular to the wall are primarily resisted by independent framing members attached to the structural plate. 2.0 BASIC INFORMATION

36 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 5 January % 67 % 68 % Testing Laboratories: Testing laboratories shall comply with Section 2.0 of the ICC-ES Acceptance Criteria for Test Reports (AC85) and Section 4.2 of the ICC- ES Rules of Procedure for Evaluation Reports. 2.2 Test Reports: Test reports shall comply with AC Product Sampling: The test prefabricated LFR assemblies shall be sampled in accordance with Section 3.1 of AC85. The testing laboratory shall verify the construction of the test assemblies. Verification shall also be provided that the components of the test assemblies comply with the quality control manual addressed in Section 5.0 of this criteria. 3.0 ASSEMBLY INFORMATION 3.1 General: The description shall include the following information: Dimensions: The width, height and length for each assembly type Assembly: A complete description of the prefabricated assembly elements and material specifications. 3.2 Connections: Connections shall be detailed or adequately described. Mechanical fasteners and welds shall be properly specified, including fastener type, size, length and location. Assemblies shall be constructed with fasteners having approved values. 3.3 Miscellaneous Assembly Information: Field Modification of Assemblies: Field modification of the assemblies for openings in the sheathing or framing elements is not permitted beyond what was specifically tested.

37 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 6 January % 99 % 100 % Structural Field Connections: Structural connections between the prefabricated assembly and the structure, necessary for installation of the assembly, made in the field at the time of installation, shall be consistent with the tests conducted in accordance with this criteria. 4.0 TEST AND PERFORMANCE REQUIREMENTS 4.1 Purpose: To be evaluated under this criteria, all assemblies shall be tested and analyzed as described in this section. Assemblies shall be limited to the sizes and materials used in the tests. Cyclic shear tests shall be performed in accordance with one of the following procedures: The Standard Method of Cyclic (Reversed) Test for Shear Resistance of Framed Walls for Buildings, by the Structural Engineers Association of Southern California (SEAOSC), dated August 1, 1996 (revised January 20, 1997), as noted in Section 5.1, Items 1 through 4, of the Acceptance Criteria for Prefabricated Wood Shear Panels (AC130) The SEAOSC method as modified by Section 5.1, Items 1 through 4, of the Acceptance Criteria for Prefabricated Wood Shear Panels (AC130) As an acceptable alternative to Sections 7.3 and 7.4 of the SEAOSC method, assemblies may be tested as noted in Section 5.1, Item 5, of AC General: Additional test information applicable to both test protocols Reports of Tests: Reports shall comply with Section 2.0 of this criteria. No substitution of materials is allowed unless permitted by ICC-ES.

38 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 7 January Test Setup: For compliance with this criteria, cyclic shear tests in accordance with Section 4.1 of this criteria shall be conducted using boundary conditions reflective of the intended use, as noted in this section Foundation-on-grade: Assemblies intended to be installed on a foundation-on-grade condition shall be tested on a rigid base First-floor Raised Floor: Assemblies intended to be installed on the first floor of a structure with a crawl space foundation shall be tested by placing the walls over a representative floor system constructed on a rigid base Second Floor: Assemblies intended to be installed in the second floor of a structure (or higher) shall be tested by placing the assemblies on a representative floor system constructed over a representative wall system, all of which is supported by a rigid base. The representative wall system supporting the assembly need not be a full-height wall Representative Systems: A floor or wall system shall be considered representative if it is constructed in such a way that the stiffness and strength are similar to that which is expected to be encountered in typical usage. The use of less than full-height stud systems under the second floor platforms, and the use of floors constructed with reduced length members, is acceptable. Qualifying the prefabricated assembly performance for all floor framing alternatives is not necessarily required. Secondary connections required to transfer shear and overturning through the floor system shall also be constructed with materials and methods typical for the end

39 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 8 January % 130 % 131 % use. The representative floor/wall systems, as well as the materials and methods for shear and overturning continuity, shall be fully detailed in the test report. The ICC-ES evaluation report shall specify these details or other equivalent details Initial Pretension of Overturning Restraint: Initial pretension shall be based on the prefabricated component or element manufacturer s installation requirements. If wood perpendicular-to-grain stress is involved in transferring overturning forces produced by the wall to the foundation (such as sitting on top of a sill plate, or wood floor), then the overturning restraint device (including anchor bolts) pretension shall not exceed 500 pounds (2,225 N). If the initial pretension is not monitored during the test, anchor bolt nuts shall be installed finger tight plus one half turn System Effects: If the prefabricated assembly is defined as a CSRA, then tests of systems including attached structural members representative of in-service conditions shall be performed. Tests used to qualify allowable loads shall be based on the minimum assembly stiffness that will be approved for application Load Beam: To the extent practical, the load beam shall be minimized with regard to its mass, length and stiffness. Under no circumstance shall the selected load beam contribute to the strength and stiffness of the assembly being tested Shear Walls: When testing is conducted on shear walls or other assemblies that rely on a structural plate for lateral resistance, the plate shall not bear on the top or bottom fixtures of the test frame.

40 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 9 January % % Anchor Bolts: The strength and stiffness of the anchor bolts shall be representative of the anchor bolts used in the actual field construction UBC Design Capacities: The following provisions apply to the basic design parameters listed in Section 5.1 of this criteria Allowable Stress Design (ASD): The assigned ASD load for the test sample shall be the lesser of the allowable loads based on a drift limit, ultimate load limit, or calculation limit determined as follows: Drift Limit (Seismic): The ASD load which satisfies the drift limit requirements of UBC Section shall be computed as follows: Maximum inelastic response displacement, ) m, shall be defined as the lesser of the calculated inelastic drift limit defined in UBC Section , or the mean displacement at the Strength Limit State of the tested prefabricated assemblies, ) SLS Using ) m determined above and the R factor listed in Section 5.1 Table 1 of this criteria, the Strength Design (LRFD) level response displacement, ) S, shall be equal to ) m /(0.7R) (UBC equation 30-17) From the first-cycle backbone curve of the cyclic-load testing, the force corresponding to ) S shall be determined In accordance with Section of the UBC, this Strength-level factored resistance shall then be divided by a factor of 1.4 to determine the equivalent ASD load.

41 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 10 January % % 182 % 183 % The drift corresponding to the ASD load derived in Section of this criteria, shall be derived from the first-cycle backbone curve and included in the evaluation report Drift Limit (Wind): The ASD load shall be equal to the load derived from the first-cycle backbone curve at a deflection of H / 180, where H = the height of the tested assembly Ultimate Load Limit (Wind and Seismic): For assemblies classified as wood structural panel compatible or limited ductile in accordance with Section 5.2 of this criteria, The ASD load shall be derived by dividing the ultimate test load, as determined by Section 4.1 of this acceptance criteria, by a factor of safety of for seismic and for wind. For assemblies defined as a CSRA, the minimum safety factor shall be for seismic and for wind For assemblies classified as nonductile in accordance with Section 5.2 of this criteria, the ASD load shall be derived by dividing the ultimate test load, as determined by Section 4.1 of this criteria, by a factor of safety of 2.5. For assemblies defined as a CSRA, the minimum safety factor shall be The drift corresponding to the ASD load derived from Section or shall be derived from the first-cycle backbone curve and shall be included in the evaluation report Calculation Limit (Wind and Seismic): The ASD load shall be calculated in accordance with the document cited in Section of this criteria.

42 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 11 January % Load and Resistance Factor Design (LRFD): LRFD factored resistance values for the prefabricated assembly shall be established through calculations in accordance with Section , using the LRFD provisions; and by increasing the resistance determined in Section , or by a factor of 1.4. The lowest value shall govern Additional CSRA Design Information: Where a prefabricated assembly is defined as a CSRA based upon Section of this criteria, information necessary for design shall be provided defining the level and nature of the demand imposed on the attached structural elements (such as a header) due to lateral loading of the prefabricated assembly. The minimum stiffness of these elements shall also be defined to correspond with the tested configurations IBC Design Capacities: The following provisions apply to the basic design parameters listed in Section 5.1 of this criteria Allowable Stress Design (ASD): The assigned ASD load for the test sample shall be the lesser of the allowable loads based on a drift limit, ultimate load limit, or calculation limit determined as follows: Drift Limit (Seismic): The ASD load which satisfies the drift limit requirements of ASCE 7-05 Section shall be computed as follows: Maximum inelastic response displacement, * x, shall be the lesser of the calculated inelastic drift limit defined in ASCE 7-05 Table , or the mean displacement at the Strength Limit State of the tested wall assemblies, ) SLS.

43 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 12 January % Using * x determined in accordance with Section and the C d factor listed in Table 1, the Strength Design (LRFD) level response displacement, * xe, shall be equal to * x /C d (ASCE 7-05 Equation ), assuming importance factor is equal to 1.0. For other importance factors * xe shall be adjusted accordingly From the first-cycle backbone curve of the cyclic-load testing, the force corresponding to * xe, shall be determined. This corresponds to a Strength-level (LRFD) factored resistance In accordance with Section of the IBC, this Strength-level factored resistance shall then be divided by a factor of 1.4 to determine the appropriate ASD load for use with the alternate basic load combinations of that section The drift, corresponding to the ASD load derived in Section of this criteria, shall be derived from the first-cycle backbone curve and included in the evaluation report Drift Limit (Wind): The ASD load shall be equal to the load derived from the first-cycle backbone curve at a deflection of H / , where H = the height of the wall Ultimate Load Limit (Wind and Seismic): For assemblies classified as wood structural panel compatible or limited ductile in accordance with Section 5.2 of this criteria, The

44 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 13 January % 239 % 240 % ASD load shall be derived by dividing the ultimate test load, as determined by Section 4.1 of this acceptance criteria, by a factor of safety of for seismic and for wind. For assemblies defined as a CSRA, the minimum safety factor shall be for seismic and for wind For assemblies classified as nonductile in accordance with Section 5.2 in this criteria, the ASD load shall be derived by dividing the ultimate test load, as determined by Section 4.1 of this criteria, by a factor of safety of 2.5. For assemblies defined as CSRA, the minimum safety factor is The drift corresponding to this allowable load capacity shall be derived from the first-cycle backbone curve and included in the evaluation report Calculation Limit (Wind and Seismic): The ASD load as determined from calculations in accordance with the document cited in Section of this criteria (AISI NASPEC) Load and Resistance Factor Design (LRFD): LRFD factored resistance values for the prefabricated assembly shall be established through calculations in accordance with Section of this criteria, using the LRFD provisions; and by increasing the resistance determined in Section , or of this criteria by a factor of 1.4. The lowest value shall govern Additional CSRA Design Information: Where a prefabricated assembly is defined as a CSRA, information necessary for design shall be provided

45 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 14 January % 271 % % defining the level and nature of the demand imposed on the attached structural elements (such as a header) due to lateral loading of the prefabricated assembly. The minimum stiffness of these elements shall also be defined to correspond with the tested configurations Ultimate Strength: The average ultimate strength as derived from the first-cycle backbone curve shall be reported. 4.5 Axial Loading: As detailed in Section 4.1 of this criteria, all testing used to establish lateral design loads shall be conducted without an applied axial load. The ability of PSRA and CSRA systems to support gravity loads, both alone and in combination with lateral load, shall be evaluated in accordance with the document referenced in Section of this criteria (AISI NASPEC). In addition to this calculation, when a component of the PSRA or CSRA that carries both axial and lateral load during the ASTM E 2126 cyclic test buckles, supplemental testing shall be provided to show verify that the system can support a combination of lateral and axial load without significant degradation of performance. The details of this testing shall be submitted to ICC-ES in advance for review before the testing is conducted. At a minimum, the testing shall include the following: Lateral load testing in accordance with Section 4.1, except simultaneous axial load shall be applied The applied axial compressive load shall be maintained throughout the test with a constant magnitude of 1.5 times equal to the maximum axial service

46 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 15 January % % (unfactored) load that will be approved to act in combination with the approved lateral design load The axial load shall be applied in a manner that moves with the CSRA or PSRA to simulate the P-Delta effects of gravity loading. The assembly shall not be tested beneath a stationary axial load. 5.0 CONDITIONS OF USE 5.1 Establishment of Seismic Design Capacities Coefficients: For use with the PSRA and CSRA systems qualified under this criteria, seismic design coefficients and factors shall be assigned in accordance with Table Braced Frame: Where the brace is designed to act in tension only, the requirements of UBC Section 2219 and IBC Section 2210 shall apply For all braced frames, boundary elements and their connections shall have the design strength (NR n ) to resist the combined effects of the maximum capacity of the brace in either tension or compression and gravity loads Regardless of the PSRA or CSRA type or performance classification, if the primary yield mechanism in tested performance or design is anchor bolt yielding, the basic system values for braced frames with tension-only braces in Table 1 shall apply A moment frame may be classified as being limited ductile if it both meets the criteria defined in Section of this criteria, and buckling does not render the cross section ineffective in resisting axial loads.

47 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 16 January Seismic Performance Classifications: For the purposes of determining whether a component or element is wood structural panel compatible, has limited ductility, or is nonductile under this criteria, the following criteria shall be used: Nonductile Component/Element: A nonductile assembly is one that meets the following criteria when tested in accordance with Section 4.1. ) m $ 1.1) yield (UBC) or * x $ 1.1) yield (IBC) where: ) m is defined in Section of this criteria * x is defined in Section of this criteria ) yield is defined in ASTM E 2126 Section Baseline Performance: Systems that exhibit a performance that falls between that defined in Section for a nonductile and Section for a limited ductile system Limited Ductility Component/Element: a. ) m $ 2) yield (UBC) or * x $ 2) yield (IBC) b. at ) = 3) yield, P $ 0.4P peak where: ) m is defined in Section of this criteria * x is defined in Section of this criteria ) and P are defined per Figure 2 of ASTM E 2126 ) yield and P peak are defined in ASTM E 2126 Section 3.2.

48 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 17 January Wood Structural Panel Compatible: In addition to meeting the conditions for a limited ductility component/element in Section 5.2.3, a component or element that is wood structural panel compatible shall also meet the following conditions: a. ) u $ H Δ Δ u b. $ 4.0 yield % 335 % where: ) u, ) yield, are defined in ASTM E 2126 Section 3.2. H is the height of the PSRA or CSRA. 5.2 For the purposes of classifying the seismic performance of an assembly, in accordance with the assembly type designations noted in table 1, the following criteria shall be used: Type 1 Shear Resisting Assembly: A Type 1 assembly is one that meets both of the following criteria when tested in accordance with Section 4.1: 336 % Δ u a. 1.0 # < 1.5 Δ yield 337 % Ppeak b. $ 2.5 P LRFD

49 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 18 January % where: 339 % 340 % 341 % 342 % 343 % 344 % 345 % 346 % 347 % 348 % 349 % 350 % P peak is the maximum lateral resistance of the assembly. ) yield is the displacement at 0.65 P peak in the positive stiffness region of the response curve for an elastic stiffness defined by a line from the origin to the point on the response curve corresponding to P peak (50% of 0.65 P peak ). ) u is the envelope displacement at 0.65 P peak in the post-peak region of the response envelope. If a line corresponding to 0.65 P peak does not intersect the response curve in the post-peak region, ) u shall be taken as the displacement corresponding to P peak. P LRFD is established as noted in Sections and of this criteria Type 2 Shear Resisting Assembly: A Type 2 assembly is one that meets both of the following criteria when tested in accordance with Section 4.1: 351 % Δ u Δ yield a. 1.5 # < % Ppeak b. $ 2.5 P LRFD 353 % 354 % 355 % 356 % where: P peak, ) yield, ) u and P LRFD are defined in Section of this criteria Type 3 Shear Resisting Assembly: A Type 3 assembly is one that meets both of the following criteria when tested in accordance with Section 4.1:

50 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 19 January % Δ u Δ yield a. $ % Ppeak b. $ 2.5 P LRFD 359 % where: 360 % P peak, ) yield, ) u and P LRFD are defined in Section of this criteria. 6.0 QUALITY CONTROL The product shall be manufactured under an approved quality control program with inspections by an inspection agency accredited by the International Accreditation Service (IAS) or otherwise acceptable to ICC-ES. A quality documentation system complying with the ICC-ES Acceptance Criteria for Quality Documentation (AC10) shall be submitted. 7.0 EVALUATION REPORT RECOGNITION 7.1 The assembly identification label shall include the manufacturer s name and address, the evaluation report number, the inspection agency s name and other information deemed necessary by ICC-ES. The label shall be visible after the wall is installed. 7.2 Since this criteria will allow the use of the assemblies in all seismic categories (IBC), when the assemblies are installed in jurisdictions governed by the IBC, periodic inspections in Seismic Category C, D, E, or F shall be provided for fastening and anchoring the assembly within the seismic-force-resisting system, including connections of the assemblies to drag struts and hold-downs, in accordance

51 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 20 January with Section of the IBC, unless exempted by Exception 3 of Section of the IBC. 7.3 In addition to the requirements noted in this criteria, anchorage to concrete details (engineered design and details), in accordance with Section 1913 of the IBC, shall be submitted. The engineered details will be included in the evaluation report. 7.4 The allowable load tables in the evaluation report will not include a 1.33 increase, multiple transient loading. For tables that establish the design loads for the UBC, there will be a footnote that indicates that the designer must determine if a 1.33 increase in the allowable load is appropriate when using the Alternate Load Combinations outlined in Section of the UBC. 7.5 Assemblies evaluated under this criteria are permitted for use in lightframe wood and steel construction. When the seismic coefficients for the tested assembly assigned using this criteria differ from other lateral-force-resisting assemblies in the structure, Section of the UBC and Section of the IBC shall be employed during the design of the structure to promote compatibility. 7.6 If the assembly is defined as a CSRA based upon Section of this criteria, and a connection is made to a solid sawn lumber header (not an engineered wood product), documentation shall be provided to the building official verifying that the moisture content of the sawn lumber header is less than 12 percent at the time of installation.# KS/ll

52 Proposed Acceptance Criteria for Prefabricated, Cold-formed, Steel Lateral-force-resisting Vertical Assemblies AC R3 Page 21 January 2007 TABLE 1 ASSIGNMENT OF SEISMIC DESIGN COEFFICIENTS AND FACTORS STRUCTURAL SYSTEM TYPE 16 Braced frame (braces used in tension only) Braced frame (braces used in tension only) Moment frame Shear wall defined in Section PERFORMANCE UBC IBC CLASSIFICATION 2 R S o R S o C d Baseline Limited ductile Baseline Baseline Limited ductile Wood structural panel compatible Structural system types as defined in Section Performance classifications as defined in Section Any structural system that is tested or designed with anchor bolt yielding as the primary yield mechanism. 4 When calculating design capacities for the UBC in accordance with Section , the factor 0.7R shall be assumed equal to If the system is found to be nonductile per Section 5.2, then the W o shall be increased to The systems may only be qualified as limited-ductile if buckling under lateral load does not render the cross section ineffective in resisting axial loads. If it does, then the system shall be categorized as baseline regardless of its Section 5.2 classification. See Section 4.5 for additional details. % TABLE 1 ASSIGNMENT OF SEISMIC DESIGN COEFFICIENTS AND FACTORS SHEAR RESISTING ASSEMBLY : P PEAK TARGET TARGET R SRA UBC IBC DESIGNATION P LRD ASSEMBLY VALUE R d R o % R d VALUE R S o R S o C d % Type % Type % Type

53 AC R3 25 SIMPSON STRONG-TIE COMPANY, INC. The World s No Equal Structural Connector Company 5956 W. Las Positas Blvd. Pleasanton, California Phone: 800/ Fax: 925/ Kurt Stochlia January 23, 2007 Vice President ICC Evaluation Services, Inc Workman Mill Rd. Whittier, CA VIA RE: Comments on AC322, Proposed Acceptance Criteria for Prefabricated, Cold-Formed, Steel Lateral-Force Resisting Vertical Assemblies, Subject AC R3 (KS/BG) Dear Kurt: We appreciate the efforts by staff to continue working on AC322 as reflected in the revision being considered. The revisions proposed in this draft, however, do not ensure that basic, fundamental seismic design principles, both at the element (wall) level and at the complete structure level, are safeguarded for light-frame structures. As written, the provisions of section 5 in the proposed criteria do not require that the walls developed under this acceptance criteria merit the basic seismic design coefficients and parameters awarded them. Concerning the specific issues delineated in the staffs cover letter we offer the following comments: 1. We agree with staff s intent to provide for compatibility with the IRC, but we have some significant differences of opinion as to what the IRC is really requiring. R , Engineered Design, requires that elements be designed in accordance with accepted engineering practice. While this statement is rather broad, the code clarifies it with the following: The extent of such design need only demonstrate compliance of nonconventional elements (i.e., the steel walls for which approval is sought) with other applicable provisions and shall be compatible with the performance of the conventional framed system. In our opinion, this does not mean a complete load path analysis. In fact, lack of a complete, identifiable load path in conventionally built structures is something engineers and code writers struggle with. Perhaps our understanding of staffs intent is incomplete and will be clarified through further discussion. 2. The design of anchorage for walls to be deemed compatible with the IRC is a difficult subject. On one hand, full anchorage design, allowing the full strength and ductility of the wall to be realized, is a worthy design objective and one that Simpson would favor being enforced in all of the IRC wall bracing methods. On the other hand, the requirement of R is for the wall to be compatible with the performance of the conventional framed system. When one looks at the performance of the various wall bracing methods allowed in the IRC two things are very clear: wall bracing can be very brittle and overturning restraint is not required to develop the full strength and ductility of the braced wall panel. We are in favor of changes to the building codes to correct this, but that is a process that takes time and may never come to fruition because of the many opposing views. In recent code cycles new - 1 -