August 1, 2018 PARTIES INTERESTED IN NONPRESTRESSED DEFORMED HIGH- STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT

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1 August 1, 2018 TO: PARTIES INTERESTED IN NONPRESTRESSED DEFORMED HIGH- STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT SUBJECT: Proposed Revisions to the Acceptance Criteria for Nonprestressed Deformed High-Strength Steel Bars For Concrete Reinforcement, Subject AC R1 (WG/WU) Dear Colleague: Enclosed is a proposal. dated June 14, 2018, from Wiss, Janney, Elstner Associates, Inc. on behalf of report holder Dywidag Systems International U.S.A, Inc. (DSI, ESR- 3367) with proposed revisions to AC237. The proposal seeks to increase the upper limit on recognized concrete strengths from 12,000 psi to 18,000 psi, and make associated changes and additions to the criteria. This change would satisfy demands of the reinforced concrete high-rise building industry where high-strength reinforcing steel bars are being used with higher strength concrete in columns and walls for high-rise buildings. The rationale for the WJE proposal notes that ACI Section imposes no general upper limit on concrete design compressive strength, f c, and further cites ACI ITG 4.3R-07 and ACI research by Ozbakkalalogu and Saatcioglu (2004) as the basis for the revisions and additions to the criteria. We are seeking your comments on the proposed revisions to the subject acceptance criteria, as presented in the enclosed draft. The revisions, which are being posted on the ICC-ES web site for 30 days of public comment. If approved, updating current evaluation report holders will be at the option of the report holder. While the Evaluation Committee will be voting on the revised criteria during the 30- day comment period, we will consider all comments from the public and will pull the criteria back for reconsideration if public comments raise major issues. In that case, we would seek a new committee vote; further revise the draft and post it for a new round of public comments; or put the revised criteria on the agenda for a future Evaluation Committee hearing. If they are of interest, please review the proposed revisions and send us your comments at the earliest opportunity. At the end of the 30-day comment period, we

2 AC R1 2 will post on our web site the correspondence we have received and, in memo form, the responses of our technical staff. To submit your comments, please use the form on the web site and attach any letters or other materials. If you would like an explanation of the alternate criteria process, under which we are soliciting comments, this too is available on the ICC-ES web site. Please do not try to communicate directly with any Evaluation Committee member about a criteria under consideration, as committee members cannot accept such communications. Thank you for your interest and your contributions. If you have any questions, please contact me at (800) , extension 3205, or Will Utsey, Senior Staff Engineer, at extension You may also reach us by at es@icc-es.org. Yours very truly, WG/raf Encl. cc: Evaluation Committee William Gould, P.E. Vice President

3 Wiss, Janney, Elstner Associates, Inc. 225 South Lake Avenue, Suite 500 Pasadena, California tel Via June 14, 2018 Mr. David Zhao Principal Structural Engineer ICC Evaluation Service, LLC 3060 Saturn Street, Suite 100 Brea, California Re: Proposed Modification to ICC-ES AC237 WJE No Dear Mr. Zhao: On behalf of Dywidag Systems International U.S.A., Inc. (DSI), Wiss, Janney, Elstner Associates, Inc. (WJE) has prepared proposed modifications to AC237, Acceptance Criteria for Nonprestressed Deformed High-Strength Steel Bars for Concrete Reinforcement, approved February DSI holds a current evaluation report, ESR-3367, for Dywidag Grade 100 Threadbars and Couplers, which have been evaluated in accordance with AC237. This letter replaces our prior letter on this matter dated April 20, We propose these modifications in anticipation that, after review by ICC-ES staff, the proposed modifications will be heard at the ICC Evaluation Service (ICC-ES) Evaluation Committee hearing scheduled for October Background on AC237 Since its inception, the scope of AC237 has narrowly limited the use of the high-strength reinforcement that is addressed by the criteria. The following are the more notable use limitations listed in Sections 1.2.1, and of AC237: The reinforcement is generally limited to use in structural components that are not part of special seismic systems. The reinforcement shall not be used in beams or slabs. The bars are limited to use in structures assigned to Seismic Design Categories A or B; the use in structures assigned to Seismic Design Categories C through F is outside the scope of AC237. As a result of these limitations, high-strength reinforcement recognized under AC237 is generally used in structural members that are dominated by gravity axial loads, such as columns and structural walls, and that are also in non-seismic applications where ductility-related demands at ultimate strength are relatively low. Section of AC237 limits the recognition of the product being evaluated to applications with specified concrete compressive strengths in the range of 6,000 psi to 12,000 psi. This limitation was included in the first edition of AC237 (approved October 2003) and has remained unchanged since that time. It is our understanding that these concrete strength values were established by the proponent of the first edition of Headquarters & Laboratories Northbrook, Illinois Atlanta Austin Boston Chicago Cleveland Dallas Denver Detroit Honolulu Houston Indianapolis Los Angeles Minneapolis New Haven New York Philadelphia Pittsburgh Portland Princeton Raleigh San Antonio San Francisco Seattle South Florida Washington, DC

4 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 2 AC237, based on what they believed was the range of concrete strengths anticipated for use with their reinforcement product at the time that the first edition of AC237 was developed 1. The same values of concrete compressive strength appear in Table 4 and Table A1 as required concrete strengths for bond test specimens; these required concrete strengths for bond testing remain unchanged from the first edition of AC237. It is our understanding that bond tests were included in the first edition of AC237 because the thread-like deformations on the first proponent s reinforcing bars were perceived to be unlike the deformations on conventional ASTM A615 and ASTM A706 reinforcing bars 1. It is our further understanding that, at that time, the in-concrete bond testing was also intended to provide some level of assurance that the thread-like deformations were able to reasonably develop structural interaction between the reinforcement and the concrete to the minimum degree that is normally presumed to occur in reinforced concrete members. Annex B of AC237, which first appeared as Annex A in the February 2015 edition of AC237, also references the same values of concrete compressive strengths for use in parametric analytical analyses of reinforced concrete sectional strength. The application of Annex B is limited to those products where yield strength in tension is determined by the 0.2 percent offset method; Annex B is not applied to products where yield strength is determined by the 0.35 percent extension under load method. Current Use of High Strength Reinforcement It is reported to us by DSI that, based on applications in certain urban jurisdictions on the East Coast of the United States, the economics of construction generally limit the use of high-strength reinforcement recognized under AC237 to columns and walls in the lowest stories of high-rise structures where the timedependent effects of creep and shrinkage can be relied upon by the engineer of record to rationalize the use of the full specified yield strength as the available design strength in compression for the high-strength reinforcement. As a result, the high-strength reinforcement recognized under AC237 is reportedly not used in the upper levels of high-rise structures or at any level in low-rise structures because the economics of construction are not favorable to its use, and also because the time-dependent effects of creep and shrinkage are not present to the degree necessary to rationalize the use of the full specified yield strength in compression. Additionally, the high-strength reinforcement recognized by AC237 is reportedly not used in horizontal members such as slabs and beams, not only because it is not recognized for these applications by AC237, but also because the time-dependent effects of creep and shrinkage are perceived to be not present to the degree necessary to rationalize the use of the full specified yield strength in compression. As reported by DSI, concrete compressive strengths of up to 14,000 psi have been already used along with high-strength bars covered by AC237 in high-rise construction in New York City, strengths as high as 16,000 psi are being proposed for new designs, and concrete mixes are proposed to be developed for strengths of 18,000 psi. It is further reported that the use in actual construction beyond the present limit of 1 S. K. Ghosh Associates, Inc., letter dated October 10, 2016, addressed to ICC-ES, Subject: ASTM A1035 Grade 100 Bars and 16-ksi Concrete. In the last paragraph on Page 1 of the letter, it is stated that Because the threading [that is, thread-like deformation pattern] of high-strength bars within the scope of AC237 is different from that of ASTM A615 or A706 bars, bond testing is required by AC237. The bond testing that was carried out as a result at North Carolina State University did not extend beyond a compressive strength of 12,000 psi. The only reason for the upper and lower limits was that it was felt at the time that the threaded high-strength bars were highly unlikely to be used in conjunction with higher- or lower-strength concretes. S. K. Ghosh Associates prepared the first edition of AC237 as a representative to the proponent.

5 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 3 12,000 psi is based on the judgement of the engineer of record. It is also reported that, in New York City, designs of this nature are typically put forth by the engineer of record under the self-certification process of the jurisdiction having authority, the jurisdiction having authority does not necessarily individually review or approve of these kinds designs on a project-by-project basis, and many of the designs are subject to the structural peer review process. Proposed Modification It is proposed to increase the upper limit on recognized concrete strengths in Section of AC237 to 18,000 psi. Specific modifications to various sections of AC237 in support of this proposed change are given at the end of this letter, beginning on Page 9. Our rationale for the proposed changes is given in the next section of this letter. For reasons also given in the next section of this letter, we do not propose any changes to the required concrete compressive strengths listed in Table 4 and Table A1 of AC237. Rationale Section The main intent for proposing the revised upper limit of 18,000 psi on recognized concrete compressive strength in Section is to satisfy demands of the reinforced concrete high-rise building industry, where the general trend is to use higher-strength concrete in columns and walls for high-rise buildings, particularly where high strength concrete is paired with high-strength reinforcing steel. In support of the revised upper limit on concrete compressive strength, it is noted that ACI , Section imposes no general upper limit on concrete design compressive strength f c. Modified Section and New Annex C With concrete compressive strengths of 10,000 psi and greater, ACI ITG 4.3R-07 2 along with Ozbakkaloglu and Saatcioglu (2004) 3 suggest that the ACI 318 approach to calculation of concentric axial compressive strength and combined flexural and axial strength may become unconservative under certain conditions. Additionally, these references suggest that the degree of unconservatism may become more severe with increasing concrete compressive strength. The concern expressed by these references may be summarized as follows: The concern for high-strength concrete columns under concentric axial compression is that spalling of the concrete cover occurs before the development of strains associated with concrete crushing, which in turn means that the column may not develop the concentric axial compression strength, P 0, predicted by ACI 318. When combined with visual observations of cover spalling during laboratory tests, these observations suggest that concrete cover in high-strength concrete columns suffers instability failure rather than crushing failure. However, for reasons described below, concrete cover instability is not likely to occur in columns under combined bending and axial compression. 2 ACI Innovation Task Group 4, Report on Structural Design and Detailing for High-Strength Concrete in Moderate to High Seismic Applications (ITG 4.3R-07), American Concrete Institute, Farmington Hills, Mich., 66 pp. 3 Ozbakkaloglu, T., and Saatcioglu, M., 2004, Rectangular Stress Block for High-Strength Concrete, ACI Structural Journal, V. 101, No. 4, July-Aug., pp

6 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 4 Ozbakkaloglu and Saatcioglu (2004) provide a detailed review and analysis of the concerns related to premature concrete cover spalling in high strength concrete columns. As summarized above, it appears that the prematurely-spalling concrete cover in high-strength concrete columns is an instability failure rather than a concrete crushing failure. The strength loss associated with cover spalling is a function of the area of unconfined cover concrete. For this reason, the strength loss effect can be quantified in terms of the ratio of core area to gross area (A c /A g ) of the column. As this ratio decreases (that is, as cover thickness increases), the strength loss becomes more severe. For columns under combined bending and axial compression, Ozbakkaloglu and Saatcioglu (2004) describe that the deflected shape of the column is such that the maximum compression in the concrete cover is always on the concave side of the column, whether single or double curvature in bending. Although the cover with maximum compression is the cover that is most susceptible to instability, because this cover is also on the concave side of the column under combined bending and axial load, this cover has a tendency to buckle toward the core concrete. Therefore, the cover concrete in compression on the concave side of the column is constrained against buckling and remains available to resist compressive forces. The authors concluded that cover instability is not likely to occur in columns subjected to bending combined with axial compression. These observations suggests that, when implementing 18,000 psi as the recognized upper limit on concrete compressive strength, a somewhat sophisticated approach to column and wall sectional strength should be considered. Therefore, new Section and new Annex C are proposed. New Section permits calculation of column and wall sectional strength in accordance with current provisions of ACI 318, which determines P 0 using the constant value χ 1 = 0.85 (the notation χ 1 is defined below), where particular conditions are satisfied: Condition (a) is simply an extension of practice under the current AC237, which recognizes that designs using concrete compressive strengths of up to 12,000 psi can be made using the sectional strength provisions of ACI 318 without modification and without restriction on the ratio A c A g of the section under consideration. Data from Ozbakkaloglu and Saatcioglu (2004) providing substantiation of this condition are presented in Figure 1 on Page 8 of this letter, where it can be seen that χ 1 = k 3 k over the domain 6,000 psi f c 11,000 psi for the entire range of A c A g reflected in the test data. Condition (b) is based on a detailed review of data presented graphically in Ozbakkaloglu and Saatcioglu (2004) over the domain 12,000 psi < f c 18,000 psi. Our review finds that where A c A g 0.8 for a section under consideration, the factor χ 1 = k 3 k over the domain 12,000 psi < f c 18,000 psi. Data from Ozbakkaloglu and Saatcioglu (2004) that provide substantiation of this condition are presented in Figure 2 on Page 8 of this letter. In the above-described conditions: χ 1 =k 3 k 4 = factor relating mean concrete compressive stress at axial load failure of concentrically loaded columns to specified compressive strength of concrete; A c = area of core concrete within perimeter tie (center-to-center of tie); and A g = gross area of column concrete section. For the data summarized in Figure 1 and Figure 2, Ozbakkaloglu and Saatcioglu (2004) included only those columns that did not have confinement sufficient to otherwise offset the lost-strength effects of cover

7 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 5 instability. Thus, the effects of cover instability on the concentric compression strength of ordinarilyconfined concrete columns (non-seismically detailed, gravity load and wind load columns) are represented as a function of the ratio A c A g in Figure 1 and Figure 2. Where neither condition (a) or (b) of proposed new Section is satisfied, sectional capacity calculations are stipulated to proceed utilizing the modified stress block provisions given in proposed Annex C. The modified provisions of Annex C are based upon the recommendations of Ozbakkaloglu and Saatcioglu (2004). During our review of readily-available references, we found that the scope of ACI ITG 4.3R-07, which also proposes alternative axial and flexural stress block factors, is for high-strength concrete in moderate- to high-seismic applications (SDC Categories C, D and E). However, the recommendations of ITG 4.3R-07 for high-seismic design may potentially be unnecessarily conservative for the non-seismic and low-seismic applications (SDC A and B) recognized under AC237. Therefore, because the scope of AC237 does not extend to moderate- and high-seismic applications, our recommendations rely upon Ozbakkaloglu and Saatcioglu (2004) instead of ACI ITG 4.3R-07. Proposed New Section As described in the Current Use section of this letter, it is our understanding that designers utilizing AC237 reinforcement typically limit its use only to columns and walls in the lowest stories of high-rise structures, where the time-dependent effects of creep and shrinkage can be relied upon by the designer to rationalize the use of the full specified yield strength as the available design strength in compression for the highstrength reinforcement. This application limitation, however, is not expressed in AC237. Therefore, a new Section is proposed. Table 4 While we propose to revise the upper limit on concrete strength in Section 1.2.6, we do not see a need for making a change to the maximum concrete strength for testing of bond to concrete as specified in Table 4. This is because ACI imposes the following limitation: The values of f c used to calculate development length shall not exceed 100 psi. The Commentary to ACI explains the purpose of this limitation: R Darwin et al. (1996) shows that the force developed in a bar in development and lap splice tests increases at a lesser rate than f c with increasing compressive strength. Using f c, however, is sufficiently accurate for values of f c up to 100 psi, and because of the long-standing use of the f c in design, ACI Committee 318 has chosen not to change the exponent applied to the compressive strength used to calculate development and lap splice lengths, but rather to set an upper limit of 100 psi on f c.

8 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 6 A review of the data presented in Darwin et al (1996) 4, along with data presented in successor documents such as Zuo and Darwin (2000) 5 and committee report ACI 408R-03 6, finds that concrete compressive strengths of up to 16,000 psi evidently were considered by ACI Committee 318 when the explanation given in Commentary R for the limitation f c 100 psi on calculations related to development length was prepared. As an example, Darwin et al (1996) include15 data points (out of 299 data points total) in the range of 10,000 psi to 16,100 psi. These data are presumed to be the basis of the Committee 318 statement given in Commentary R The limitation f c 100 psi means that the calculated development length of reinforcement in concrete for applications where f c > 10,000 psi will be the same length as calculated for the case of where f c = 10,000 psi. Thus, the value of f s,pred used in the condition of acceptance in Equation 3-1 of AC237 (February 2018) will be calculated using f c = 10,000 psi for any concrete compressive strength value greater than 10,000 psi, regardless of whether the compressive strength of the concrete in the test beam is 12,000 psi or 18,000 psi. On this basis, it is found that actual strengths exceeding 10,000 psi for the concrete in the test beam are moot for determination of f s,pred. With respect to f s,test in Equation 3-1 of AC237, it is commonly accepted that, for a given bonded length of bar in the test beam, f s,test will increase with increasing concrete strength, albeit at a lesser rate than f c with increasing compressive strength, as indicated by ACI 318 Commentary R Therefore, with all other test parameters held constant, bond testing with f c = 12,000 psi will result in a lesser value for f s,test than testing with f c = 16,000 psi or 18,000 psi, leading to a more conservative assessment of the ability of the high-strength bar to appropriately bond with the concrete. As a result of the above-described considerations, we conclude that bond testing with f c = 12,000 psi remains appropriate and that there is no need to change this value in Table 4 of AC237. Table A1 The intent of Annex A is for assessment of already-existing bond data that was developed during laboratory test programs carried out under prior editions of AC237. Given that testing must have been completed by the sunset date of February 28, 2018 for assessment under the provisions of Annex A, it is not possible for new testing to be performed under Annex A provisions. Consequently, it is a moot point to change the maximum concrete strength for testing of bond to concrete in Table A1 of Annex A of AC237 (February 2018). Sections B3.2 and B7.2 We propose changing the maximum concrete strength limits listed in Annex B of AC237, Sections B3.2 and B7.2, to the value of 18,000 psi, to match the proposed upper limit on concrete strength of Section Previously some concern had been expressed that it might be necessary to make related changes to the conditions of acceptance of Section B9.0, or to the methodology for assessing these particular conditions of acceptance, if the upper limit on recognized concrete strength were to be increased. However, given that 4 Darwin, D.; Zuo, J.; Tholen, M. L.; and Idun, E. K., 1996, Development Length Criteria for Conventional and High Relative Rib Area Reinforcing Bars, ACI Structural Journal, V. 93, No. 3, May-June, pp Zuo, J., and Darwin, D., 2000, Splice Strength of Conventional and High Relative Rib Area Bars in Normal and High-Strength Concrete, ACI Structural Journal, V. 97, No. 4, July-Aug., pp ACI Committee 408, Bond and Development of Straight Reinforcing Bars in Tension, ACI 408R-03, American Concrete Institute, 2003, 49 pp.

9 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 7 the equivalent concrete stress block parameters are also proposed to be modified under certain conditions (refer to proposed Section and proposed Annex C), we do not propose at the present time to make any change to Section B9.0. Closing We look forward to working with ICC-ES on finalizing the proposed change and its rationale, for presentation before the ICC-ES Evaluation Committee at the October 2018 hearing. Sincerely, WISS, JANNEY, ELSTNER ASSOCIATES, INC. Scott Graham Senior Associate Conrad Paulson, CA PE C64119 Principal and Project Manager

10 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 8 k3k f c = 6-11 ksi f' c = MPa A c /A g Figure 1. Excerpt from Figure 5 of Ozbakkaloglu and Saatcioglu (2004), annotated to show domain of A c /A g ratios of interest (red box) for concrete compressive strengths in the range of 6 to 11 ksi. k3k f c = ksi f' c = MPa A c /A g k3k f c = ksi f' c = MPa A c /A g k3k f c = ksi f' c = MPa A c /A g Figure 2. Series of excerpts from Figure 5 of Ozbakkaloglu and Saatcioglu (2004), annotated to show domains of A c /A g ratios of interest (red boxes) for concrete compressive strengths in the overall range of 12 to 20 ksi.

11 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 9 Proposed Modifications to February 2018 edition of AC237 Modify Section 1.2.6: The specified concrete compressive strength shall range from 6,000 psi (41.3 MPa) to 12,000 psi (82.7 MPa) 18,000 psi (124.1 MPa). Modify Section 1.2.7, as follows: This criteria is applicable to reinforcement under provisions of ACI 318 described in Table 2 of this criteria, as referenced in Section of the IBC., where either (a) or (b) is satisfied: (a) 6,000 psi f c 12,000 psi without limitation on A c A g (b) 12,000 psi < f c 18,000 psi where A c A g 0.8 Where A c = area of core concrete within perimeter tie (center-to-center of ties) A g = gross area of column concrete section If neither (a) or (b) is satisfied, sectional strength shall be calculated in accordance with the provisions of ACI (ACI and -08) as modified by Annex C. Introduce a new Section 1.2.9: Where it can be substantiated that the effects of creep in a reinforced concrete column or wall under sustained, in-situ, unfactored axial compression forces result in sufficient transfer of axial compressive stresses from concrete to longitudinal highstrength reinforcement at the section under consideration, it is permitted to use the specified yield strength for f y in compression in calculations for flexural and axial compression sectional strength; specified yield strength in compression used in calculations shall be in accordance with Section Otherwise, if sufficient internal stress transfer effects cannot be substantiated, f y in compression used for high-strength reinforcing bars shall not exceed 80,000 psi (551 MPa) in the calculation of flexural and axial compression sectional strength. Renumber existing Sections and to become Sections and , respectively. Modify Sections B3.2 and B7.2: B3.2 Include a variation of concrete compressive strengths: 6,000 psi and 12,000 psi 18,000 psi; B7.2 Include a variation of concrete compressive strengths: 6,000 psi and 12,000 psi 18,000 psi;

12 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 10 Add a new Annex C. NOTE: The proposed, new Annex C for AC237 is presented below in a clean format where strike-out and underline represent only required modifications to ACI 318. The entirety of what is presented below as Annex C will be new to AC237. C1.0 Modifications to ACI Annex C: Mandatory Modifications to ACI 318 C1.1 Definitions: Modify Section 2.2 of ACI to add the following notation (notation for β 1 and A g from ACI 318 included without change for the convenience of the user of AC237): α 1 = factor relating magnitude of uniform stress in the equivalent rectangular compressive stress block to specified compressive strength of concrete. β 1 = factor relating depth of equivalent rectangular compressive stress block to neutral axis depth. χ 1 = factor relating mean concrete compressive stress at axial load failure of concentrically loaded columns to specified compressive strength of concrete. A cc = area of core concrete within perimeter tie (center-to-center of tie) A g = gross area of concrete section C1.2 Equivalent Rectangular Concrete Stress Distribution: Modify ACI Section : The equivalent rectangular concrete stress distribution in accordance with through satisfies Concrete stress of 0.85f c α 1 f c shall be assumed uniformly distributed over an equivalent compression zone bounded by edges of the cross section and a line parallel to the neutral axis located a distance a from the fiber of maximum compressive strain, as calculated by: a = β 1 c ( ) Distance from the fiber of maximum compressive strain to the neutral axis, c, shall be measured perpendicular to the neutral axis Values of α 1 shall be in accordance with Table a and values of β 1 shall be in accordance with Table b.

13 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 11 Table a Values of α1 for equivalent rectangular concrete stress distribution fc, psi α f c (a) 4000 < f c < 17, ( f c 4000) 1000 (b) f c 17, (c) Table b Values of β1 for equivalent rectangular concrete stress distribution fc, psi β f c (a) 4000 < f c < , ( fc 4000) ( fc 4000) (b) f c , (c) C1.3 Maximum axial compressive strength: Modify ACI Section : For nonprestressed members and composite steel and concrete members, P o shall be calculated by: P o = 0.85f c χ 1 f c (A g A st ) + f y A st ( a) Where: A st = total area of nonprestressed longitudinal reinforcement χ 1 = 0.9[γ + (1 γ)(a cc A g )] 0.85 and 0.65 ( b) and γ = 1.1 f c 0.8 where f 20,000 c is in psi ( c)

14 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page 12 C2.0 Modifications to ACI and-08 C2.1 Definitions: Modify Section 2.1 of ACI and -08 to add the following notation (notation for β 1 and A g included without change for the convenience of the user of AC237): α 1 = factor relating magnitude of uniform stress in the equivalent rectangular compressive stress block to specified compressive strength of concrete. β 1 = factor relating depth of equivalent rectangular compressive stress block to neutral axis depth. χ 1 = factor relating mean concrete compressive stress at axial load failure of concentrically loaded columns to specified compressive strength of concrete. A cc = area of core concrete within perimeter tie (center-to-center of tie) A g = gross area of concrete section C2.2 Equivalent Rectangular Concrete Stress Distribution: Modify ACI and-08 Section : Requirements of are satisfied by an equivalent rectangular concrete stress distribution defined by the following: Concrete stress of 0.85f c α 1 f c shall be assumed uniformly distributed over an equivalent compression zone bounded by edges of the cross section and a straight line located parallel to the neutral axis at a distance a = β 1 c from the fiber of maximum compressive strain Distance from the fiber of maximum strain to the neutral axis, c, shall be measured in a direction perpendicular to the neutral axis For f c between 2500 and 4000 psi, β 1 shall be taken as For f c above 4000 psi, β 1 shall be reduced linearly at a rate of for each 1000 psi of strength in excess of 4000 psi, but β 1 shall not be taken less than For f c between 2500 and 4000 psi, 1 shall be taken as For f c above 4000 psi, 1 shall be reduced linearly at a rate of for each 1000 psi of strength in excess of 4000 psi, but 1 shall not be taken less than C2.3 Maximum axial compressive strength: Modify ACI and -08 Section : Design axial strength φp n of compression members shall not be taken greater than φp n,max, computed by Eq. (10-1) or (10-2).

15 David Zhao ICC Evaluation Service, LLC June 14, 2018 Page For nonprestressed members with spiral reinforcement conforming to or composite members conforming to 10.13: where φp n,max = 0.85φ [0.85f c χ 1 f c (A g A st ) + f y A st ] (10-1) χ 1 = 0.9[γ + (1 γ)(a cc A g )] 0.85 and 0.65 (10-1a) and γ = 1.1 f c 20, where f c is in psi (10-1b) For nonprestressed members with tie reinforcement conforming to : φp n,max = 0.80φ [0.85f c χ 1 f c (A g A st ) + f y A st ] (10-2) where χ 1 is computed by Eq. (10-1a) and Eq. (10-1b) For prestressed members, design axial strength, φp n, shall not be taken greater than 0.85 (for members with spiral reinforcement) or 0.80 (for members with tie reinforcement) of the design axial strength at zero eccentricity, φp o, assuming concrete stress of χ 1 f c uniformly distributed across the entire depth of the concrete section.

16 (800) (562) A Subsidiary of the International Code Council PROPOSED REVISIONS TO THE ACCEPTANCE CRITERIA FOR NONPRESTRESSED DEFORMED HIGH-STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT AC237 Proposed August 2018 Previously approved February 2018, February 2017, October 2016, February 2015, June 2009, October 2006, October 2003 (Previously editorially revised February 2014) PREFACE Evaluation reports issued by ICC Evaluation Service, LLC (ICC-ES), are based upon performance features of the International family of codes. (Some reports may also reference older code families such as the BOCA National Codes, the Standard Codes, and the Uniform 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. ICC-ES may consider alternate criteria for report approval, provided the report applicant submits data demonstrating that the alternate criteria are at least equivalent to the criteria set forth in this document, and otherwise demonstrate compliance with the performance features of the codes. ICC-ES retains the right to refuse to issue or renew any evaluation report, if the applicable product, material, or method of construction is such that either unusual care with its installation or use must be exercised for satisfactory performance, or if malfunctioning is apt to cause injury or unreasonable damage. Acceptance criteria are developed for use solely by ICC-ES for purposes of issuing ICC-ES evaluation reports. Copyright 2018 ICC Evaluation Service, LLC. All rights reserved.

17 PROPOSED REVISIONS TO THE ACCEPTANCE CRITERIA FOR NONPRESTRESSED DEFORMED HIGH-STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT (AC237) 1.0 INTRODUCTION 1.1 Purpose: The purpose of this criteria is to establish procedures for nonprestressed deformed highstrength steel bars to be recognized in an ICC Evaluation Service, LLC (ICC-ES), evaluation report under the 2015, 2012, and 2009 International Building Code (IBC). The basis of recognition is IBC Section Scope: This acceptance criteria applies to nonprestressed deformed high-strength steel bars, as defined in Section 1.4, subject to the following restrictions (the restrictions in Sections 1.2.1, 1.2.9, and have been simplified in Table 5): The high-strength steel bars are limited for use as (a) longitudinal reinforcement for resisting flexure, axial force, and for shrinkage and temperature, in reinforced concrete structures that are not special seismic systems; (b) lateral support of longitudinal bars or for concrete confinement, in reinforced concrete structures that are not special seismic systems; (c) shear reinforcement including shear friction, in reinforced concrete structures that are not special seismic systems; and (d) torsional reinforcement including longitudinal and transverse reinforcement The high-strength bars shall not be used in beams or slabs The high-strength bars are for use in structures assigned to Seismic Design Category A or B. Use of the high-strength bars in structures assigned to Seismic Design Category C, D, E, or F is outside the scope of this criteria The high-strength bars shall not be welded The high-strength bars shall not be bent, if the nominal bar size exceeds No. 14 (43 mm) diameter The specified concrete compressive strength shall range from 6,000 psi (41.3 MPa) to 12, 000 psi (82.7 MPa) 18,000 psi (124.1 MPa) This criteria is applicable to reinforcement under provisions of ACI 318 described in Table 2 of this criteria, as referenced in Section of the IBC, where either (a) or (b) is satisfied: (a) 6,000 psi < f c < 12,000 psi without limitation on Acc/Ag, (b) 12,000 psi < f c < 18,000 psi where Acc/Ag > 0.8 Where: Acc = cross-sectional area of concrete column or wall center-to-center of transverse reinforcement, Ag = gross area of column or wall concrete section. If neither (a) or (b) is satisfied, sectional strength shall be calculated in accordance with the provisions of ACI (ACI and -08) as modified by Annex C This criteria is limited to uncoated reinforcement installed in normal-weight concrete Where it can be substantiated that the effects of creep in a reinforced concrete column or wall under sustained, in-situ, unfactored axial compression forces Page 2 of 17 result in sufficient transfer of axial compressive stresses from concrete to longitudinal high-strength reinforcement at the section under consideration, it is permitted to use the specified yield strength for fy in compression in calculations for flexural and axial compression sectional strength; specified yield strength in compression used in calculations shall be in accordance with Section Otherwise, if sufficient internal stress transfer effects cannot be substantiated, fy in compression used for highstrength reinforcing bars shall not exceed 80,000 psi (551 MPa) in the calculation of flexural and axial compression sectional strength For the purpose of providing lateral support of longitudinal steel reinforcing bars and for providing concrete confinement, fy and fyt of high-strength steel bars used for design calculations shall not exceed 100,000 psi (689 MPa) for spirals and 80, 000 psi (551 MPa) for non-spiral reinforcing bars (or lateral ties) in accordance with Section and Table a of ACI (Section 9.4 of ACI and -08) For the purpose of providing shear and torsional resistance, fy and fyt of high-strength steel bars used for design calculations shall not exceed 60,000 psi (413 MPa) in accordance with Section and Table a of ACI (Sections , and of ACI and -08) The modulus of elasticity of highstrength steel bars used for design calculations shall be 29,000,000 psi, in accordance with Section of ACI (Section of ACI and -08). 1.3 Codes and Referenced Standards: Table 1 provides the editions of the referenced standards applicable to each edition of the IBC. These standards shall be applied consistently with the IBC edition upon which compliance is based , 2012 and 2009 International Building Code (IBC), International Code Council ACI 318, Building Code Requirements for Structural Concrete, American Concrete Institute ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM International ASTM A615, Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, ASTM International ACI 408R-03 (Reapproved 2012), Bond and Development of Straight Reinforcing Bars in Tension, American Concrete Institute. 1.4 Definition: Nonprestressed Deformed High-strength Steel Bars: Steel bars that: are not prestressed; have deformations or transverse protrusions (including threaded protrusions) for bonding to concrete; and have specified yield strengths between 80,000 psi (551 MPa) and 100,000 psi (689 MPa). Connections between bars are made with lap or mechanical splices.

18 PROPOSED REVISIONS TO THE ACCEPTANCE CRITERIA FOR NONPRESTRESSED DEFORMED HIGH-STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT (AC237) Specified Yield Strength: For the purpose of this acceptance criteria, specified yield strength shall mean the minimum yield strength of high-strength steel bars, in tension or in compression, as applicable, which is specified in the manufacturer s product specification fy and fyt: fy and fyt are as defined in ACI BASIC INFORMATION 2.1 General: The following information shall be submitted: Product Description: Description of the bars, mechanical splice systems, and anchorages shall be reported, including general specifications, dimensions, tolerances, threading requirements if applicable, deformation requirements and mechanical properties Installation Instructions: Complete installation instructions for the placement of bars, mechanical splice systems, and anchorages shall be provided. The instructions shall include provisions to mark bars for proper mechanical splice system installation Identification: Steel Bars: Bundled bars shall have an attached tag identifying the production mill, heat number and roll number. An additional tag shall bear the ICC-ES evaluation report number. Individual bars shall be identified by a distinguishing set of marks, rolled into the surface of one side of the bar, denoting point of origin, size designation and specified yield strength designation Mecanical Splice Systems: Mechanical splice systems shall be identified in accordance with the ICC-ES Acceptance Criteria for Mechanical Splice Systems for Steel Reinforcing Bars (AC133). 2.2 Testing Laboratories: Testing laboratories shall comply with the ICC-ES Acceptance Criteria for Test Reports (AC85), and Section 4.2 of the ICC-ES Rules of Procedure for Evaluation Reports. 2.3 Test Reports: Test reports shall comply with AC85. In addition, the test reports shall include sampling procedures, test specimen preparation, test procedures, and results of all tests. Where indicated, photographs shall be included in the report. 2.4 Product Sampling: Sampling of the steel bars for tests under this criteria shall comply with Sections 3.2, 3.3 and 3.4 of AC85. Sampling of mechanical splice systems shall comply with AC Qualification Test Plan: A qualification test plan shall be submitted to and approved by ICC-ES staff prior to any testing being conducted. 3.0 TEST AND PERFORMANCE REQUIREMENTS 3.1 Bond: General: High-strength steel bars shall comply with provisions for bond testing and conditions of acceptance prescribed in Sections and Exception: For tests conducted prior to February 28, 2018, it is permitted to use the alternative test procedures and conditions of acceptance given in Annex A Procedure: Testing for steel bar bond to concrete shall be in accordance with Section Conditions of Acceptance: The result of every test shall satisfy the requirement in equation (3-1): where: ff ss,tttttttt ff ss,tttttttt ff ss,pppppppp (3-1) = maximum tensile stress experienced in a reinforcing bar of a beam-splice specimen during the bond testing (psi or MPa) ff ss,pppppppp = predicted tensile stress in a reinforcing bar of a beam-splice specimen (psi or MPa) The maximum tensile stress experienced in a reinforcing bar of a beam-splice specimen during the bond testing, ff ss,tttttttt, shall be determined from engineering analysis based on a moment-curvature method using the following parameters: the measured test loads at bond failure, and the measured (as-built) dimensions and properties of the test beam and its materials, including the actual stress-strain relationship of the longitudinal reinforcement used to fabricate the test beam, except that bar diameter and bar cross-sectional area shall be the nominal dimensions specified in the manufacturer s product specification. Where the maximum moment determined from test loads exceeds the maximum moment derived from the moment-curvature method, ff ss,tttttttt shall be determined from engineering analysis based on an ultimate strength method. Appropriate moment-curvature method and ultimate strength method are referenced in Sections 5.1 and 6.5 of ACI 408R-03. Measured strains (refer to Section 4.1) shall be used to corroborate the bar tensile stress determined from engineering analysis based on the applicable method (i.e., the moment-curvature method or the ultimate strength method). Significant differences between analytical and measured strains shall be investigated and assessed, and findings of the assessment shall be described in the test report. The predicted tensile stress in a reinforcing bar of a beam-splice specimen, ff ss,pppppppp, shall be based on ACI Equation a (Equation 12-1 in ACI and - 08), and shall be derived as follows: where ff ss,pppppppp is substituted for ff yy, the measured (as-built) lap length is substituted for ll dd, bar diameter and bar cross-sectional area shall be the nominal dimensions specified in the manufacturer s product specification, the remaining parameters in the equation are based on measured (as-built) properties of the test beam and its materials; and the equation shall then be solved for ff ss,pppppppp. 3.2 Steel Bar Mechanical Properties: Procedure: Testing for mechanical properties of steel bars shall be in accordance with ASTM A370 for a Page 3 of 17

19 PROPOSED REVISIONS TO THE ACCEPTANCE CRITERIA FOR NONPRESTRESSED DEFORMED HIGH-STRENGTH STEEL BARS FOR CONCRETE REINFORCEMENT (AC237) minimum of one sample of each bar size of each grade for which recognition is sought Specified Yield Strengths of High-strength Steel Bars: Since steel reinforcement may be subjected to tension and compression over the service life of the structure, the specified yield strength of reinforcement in both tension and compression shall be determined. The specified yield strength of reinforcement in tension shall be determined in accordance with one of the following two options: Option 1: The yield strength of reinforcement in tension shall be taken as the stress corresponding to a strain of 0.35 percent (known as Extension Under Load Method in ASTM A370). Option 2: The yield strength of reinforcement in tension shall be determined by the offset method, using an offset of 0.2 percent in accordance ASTM A370, provided that an analytical assessment described in Annex B of this criteria is properly completed to substantiate the use of the 0.2 percent offset method to determine yield strength of the particular type of steel reinforcing bars to be recognized. Regardless of whether Option 1 or Option 2 is used to determine the specified yield strength of reinforcement in tension, the specified yield strength of reinforcement in compression shall be taken as the stress corresponding to a strain of 0.35 percent (known as Extension Under Load Method in ASTM A370) from load-deformation relationship of the reinforcing bar tested in accordance with Section of this criteria. Conditions of Acceptance: Each sample tested shall satisfy the conditions of acceptance listed in Table 3. Additionally, when yield strength of a reinforcing bar in tension is determined according to the 0.2 percent offset method, described as Option 2 in Section of this criteria, an analytical assessment described in Annex B of this criteria shall comply with the condition of acceptance prescribed in Item 9 of the Annex B. 3.3 Steel Bar Dimensions: For each bar size of each grade for which recognition is sought, dimensions shall be determined on a single sample of bar and reported by the testing laboratory. The following dimensions shall comply with the manufacturer s product specifications/drawings: weight, plf (kg/m); diameter, in. (mm); cross-sectional area, in 2 (mm 2 ); perimeter, in. (mm); and deformations (gap, height, and spacing), in. (mm). Deformations shall be determined based on procedures in Section 8 of ASTM A Steel Bar Bending Requirements: For each bar size of each grade for which recognition is sought, a single sample of bar shall be bend-tested. Test procedures and conditions of acceptance for each steel bar size up to No. 14 shall be in accordance with ASTM A for Grade 80 bars. Steel bar size exceeding No. 14 shall not be bent. 3.5 Splices: Splices may consist of lap splices or mechanical splices Mechanical splices shall be in conformance with Section of ACI (Section of ACI and -08) and shall be Type 1 in compliance with AC133. Verification of compliance, in the form of test results, in accordance with Section 4.2, shall be provided to ICC-ES Lap splices shall comply with ACI Chapter 25 (ACI and -8 Chapter 12) based on compliance with Section 3.1 of this criteria The clearance between a splice and an adjacent reinforcing bar, or clearance between splices, shall not be less than the maximum size of coarse aggregates. In the event of making a splice after arrangement of reinforcing bars, clearances allowing insertion of equipment for construction of splices shall be provided The cover for a splice shall satisfy the requirements of Section 20.6 of ACI (Section 7.7 of ACI and -08) Splices of reinforcing bars of different diameters shall be in accordance with the following: In case the degree of concentration of splices is 1 /2 or under, the ratio of cross-sectional areas of reinforcing bars having different diameters shall be not less than 1 /2. The degree of concentration of splices is to be determined by the ratio of the sum of cross-sectional areas of reinforcing bars to be spliced and the total sum of cross-sectional areas of all reinforcing bars at the cross section under consideration In case the degree of concentration of splices exceeds 1 /2, the ratio of cross-sectional areas of reinforcing bars having different diameters shall be not less than 3 / Anchorage: Anchorage shall be provided by development length in accordance with Chapter 25 of ACI (Chapter 12 of ACI and -08) based on compliance with Section 3.1 of this criteria. Mechanical anchorages are permitted to be used in addition, but shall not be utilized to decrease the embedment length needed to transfer stresses by bond alone. 4.0 TEST METHODS 4.1 Required Bond Tests: Bond tests shall be carried out on beam-splice test specimens, as required by Table 4, for each grade of reinforcement for which recognition is sought. The beam-splice test specimens shall be configured as shown in Figure 1, with additional requirements specified in Table 4. One tie consisting of No. 3 (8 mm diameter) Grade 60 reinforcing bar at each end of the splice shall be provided for No. 20 (63.5 mm) bars. For testing of beam-splice test specimens, the longitudinal bars shall be instrumented so that the strains developed are monitored. Equal load increments shall be applied at the two ends of a beam. The load at each end shall be applied in increments of 0.5 to 2 kips (2.22 to 8.89 kn), depending on the estimated strength of the beam specimens. Displacement control shall be used for specimens with ties, following yielding of the longitudinal bars. Load and displacement increments shall continue until a specimen fails. 4.2 Required Mechanical Splice System Tests: Mechanical splice systems shall be tested with all Page 4 of 17