aci_318b_cb09b-01_ballot_summary_w_responses090319

Issued: February 2, 2009 Canvass Date: March 10, 2009 ACI 318-B Ballot CB09B-01 Summary (March 11, 2009) Name CB004 CB008 CB001 Anderson Browning Cagley Cook Darwin Fiorato French Gustafson Jirsa Kopczynski Lobo Lutz Meinheit Mize Paulson Tolles Wyllie Y/C Y Y/C Y Y Y Y Y Y Y/C Y Y Y Y Y Y/C N N Y/C Y N Y Y Y N Y N Y Y Y Y Y Y Y Y/C N Y Y N Y Y Y Y N Y/C Y Y N Y N N Total Y 12 13 Total Y/C Total N Total A or 0 Also received comments by Ghali on CB013 o o o o o o o o o CB013 CB016 CB100 CB106 CB116 N Y Y Y N N N N Y Y/C A N Y/C Y Y Y/C N Y Y Y Y Y N Y/C Y Y/C Y Y Y/C Y Y Y/C Y Y 12 N Y Y N N N Y/C Y/C N N A N Y/C Y N A N 3 N A Y N Y N N A Y Y Y Y N Y Y/C Y/C N N Y Y Y Y Y/C Y Y Y Y Y Y/C N Y Y/C Y N 11 3 CB001 – Change bar size factor,  s, for No bars (Darwin)1 CB004 – Revise 3.5.3.1, 3.5.3.2, R.3.5.3.1 and R.3.5.3.2 (Gustafson) CB008 – Lightweight concrete factor for bond (Browning) CB013 – Clarification of existing provisions related to headed reinforcement (Paulson) CB016 – Add zinc and epoxy dual-coated reinforcing bars to the code (Gustafson) CB100 – Design requirements for adhesive anchors (Silva, Eligehausen, Cook) CB106 – Bi-directional shear and shear-tension interaction (Lutz) CB116 – Remove reference to “prism” in Appendix D (French) Informational item – (Lutz) Name in parentheses indicates author of code proposal ACI 318-B Ballot CB09B-01 Summary (March 11, 2009) o Last Name Submittal # Page # Line # Vote: Y Y/C N1 A Y Comments Clearly the s = 1.0 for No bars is needed to remove the unconservative calculation of ld Meinheit CB001 Cook CB001 Fiorato CB001 Jirsa CB001 Anderson CB001 27 Y/C For the second column heading, we indicate deformed wires Is this for all deformed wires? If so, please add the word “all” to before deformed wires Alternately, we know the #5 bar is a W31 and a #6 bar is a W44 wire size Do we need to indicate a similar wire distinction because we are changing the bar size limits from a #6 to a #5? Anderson CB001 Y/C See above comment Anderson CB001 11 Y/C See above comment French CB001 22 Y/C Lines 22-29 Consider changing reason statement in commentary It was my understanding that bars smaller than No also indicated that the small-bar factor was not appropriate, but the rationale for not changing the requirement was because the smaller size bars were typically used in situations like slabs or walls where the bar spacing Y/C I assume that the check has also been made on #3’s, #4’s, and #5’s using the revised database If not, this should be done before we make the change Y/C Given that the “break point” is now the No bar size, should we consider going to 1.0 for all bars and eliminate the bar factor completely? How significant would this be relative to use of No bars and smaller? N It is impossible to determine if the “new” data available for #6 bars has changed the distribution significantly I assume that is the case However, maybe if we had more data for # bars, we would recommending a change there as well This change seems to be tinkering with the code without any indication that #6 bars are a special problem Since we not have a sliding function, the break has to be made somewhere and I am not persuaded that the change is needed Responses (to be provided by individual code proposal authors) would reduce the likelihood of a splitting failure Anderson CB001 22 Wyllie CB004 LUTZ CB004 20 Paulson CB004 21 Y/C See above comment C Is this true? A615 is no longer the most widely used? Y/C Inasmuch as the extension-under-load method has been removed and the former provisions of 3.5.3.2 have been removed, it is desirable to educate the typical user by adding to R.3.5.3.1— N The commentary statement is not relevant Such a statement should reside, for example, in Committee 439's report on properties and availability of steel reinforcement Agree Add a new fifth paragraph to R3.5.3; on Page 2, Line 21, insert: “Inasmuch as these ASTM specifications now employ the offset method to determine yield strength, requiring yield strength to be taken as the stress at a strain of 0.35 percent for bars with fy exceeding 60,000 psi is no longer required.” Inasmuch as these ASTM specifications now employ the offset method to determine yield strength, requiring yield strength to be taken as the stress at a strain of 0.35 percent for bars with fy exceeding 60,000 psi is no longer required Use of the offset Lines 21-22 and 26-28 See response below to Wyllie method provides a procedure to use a constant limiting plastic strain (0.2 %) to define the yield strength, which is valid and consistent at any strength level The commentary clause contains a factual error: the specified absolute minimum tensile strength for ASTM A706 Substitution initiative is withdrawn GR60 is 80,000 psi and also 1.25 times actual yield, which is less than the 90,000 psi required for A615 GR60 for actual yield strengths up to 72,000 psi This is not “more restrictive” Statistical analysis of a database of mill test data (The University of Kansas, Structural Engineering and Engineering Materials, SL Report 04-1, December 2004) finds that some 14% of A706 GR60 bars not satisfy the 90,000 psi requirement of A615 GR60 When the substitution is performed, what is the consequence of having a decreased specified tensile strength in some instances? This needs to be brought out and discussed in the ballot statement, even if all that happens is that we state that there is no consequence Furthermore, while I have no major objection to the basic concept of substitution under 3.5.3.2, the background statement does not explain why we are making this particular change Is there a demand from designers for this? An explanation is needed Wyllie CB004 21 N Why we need this in the Code? Should be a routine project RFI Agree On Page 2, delete lines 21-22 and 26-28 And on Page 1, Line 42, delete "3.5.3.2 and" Paulson CB004 22 N Lines 22-24 and 31-32 See above response to Lutz While the bar producers have moved to the 0.2% offset method, the Code included the 0.35 percent strain requirement for structural engineering purposes, not bar production purposes We need to explain in the background statement why we no longer have structural engineering concerns about higher strength bars that not exhibit elastic-plastic stress strain curves The producers of steel reinforcing bars did not initiate the revision to adopt the offset method in the ASTM standards Rather, the revision was championed by a seasoned metallurgical engineer who is employed by a firm that produces vanadium and is a supplier of vanadium alloys A metallurgical engineer with the Illinois DOT also played a role in the revision process The intent of the revision was not for bar production purposes Fiorato CB004 26 N I am not sure I understand the proposed changes to Sections Agree to deletions as noted in above response to 3.5.3.2 and R3.5.3.2 relative to use of A706 steel Wyllie Why does 3.5.3.2 need to be changed to state that A706 Grade 60 can be substituted for A615 Grade 60? Isn’t it already permitted in Section 3.5.3.2 of ACI 318-08 which states that “Deformed reinforcing bars shall conform to one of the ASTM specifications listed in 3.5.3.1, except that for bars with fy exceeding 60,000 psi, the yield strength shall be taken as the stress corresponding to a strain of 0.35 percent See 9.4” The Code does not restrict use of A706 Grade 60 vs A615 Grade 60 It only gives a method for determining the yield strength when fy exceeds 60,000psi Given the changes to the ASTM standards as noted in the rationale for CB004, can 3.5.3.2 be deleted? (This would also require deleting the proposed “3.5.3.2 and” on p Line 42 of CB004 and renumbering the remainder of the sections.) Even if the Subcommittee chooses to keep the reference to substituting A706, is the proposed wording in R3.5.3.2 needed? What is meant by indicating “the requirements for mechanical properties and chemical composition” are more “restrictive”? If the mechanical and chemical requirements need to be more restrictive we should mandate use of A706 only Don’t we mean that either the requirements for ASTM A706 Grade 60 or the requirements for ASTM 615 Grade 60 are satisfactory unless specifically noted? Presumably we would not permit the substitution if they were not at least equivalent for purposes of design by the Code Therefore, suggest deletion of the entire commentary in section R3.5.3.2 whether or not the statement on substitution of A706 is retained Wyllie CB004 French CB008 Anderson CB008 Meinheit CB008 N No test data or other reported failures were given as evidence to justify this change If evidence exists, they the change may be justified Jirsa CB008 N Has a problem with these cases been identified? Fiorato CB008 N The rationale for this change in effect states that the lightweight factor must be applied to deformed bars in compression for “consistency” in the Code What test data say about whether the factor is needed for compression lap splices in lightweight concrete and, if needed, what value should be used? Have there been field problems with the current provisions? 34 N I believe we need a Commentary sentence or two why this prehistoric 0.35 strain requirement has been removed N I think that it is good information to have out on the table for discussion by ACI318B, and prior to making further changes for consistency regarding the use of the lightweight factor for concrete, the committee should revisit the appropriateness of the lightweight factor for the compressive development length and seek input from ACI 408 Y/C Is there any research to back up this change? Or is this just a bookkeeping / editorial change to stay consistent in the Code? 19 Assuming the data indicate the factor for compression is needed, the wording of 12.16.1 could be clearer Suggest something like: 12.16.1 — Minimum compression lap splice length shall be the largest of (a) through (d): Agree See above response to Lutz (a) (0.02fy /λ f’)d , with λ as given in 12.2.4(d) (b) 0.0005fydb, for fy ≤ 60,000 psi (c) (0.0009fy -24)db for fy > 60,000 psi (d) 12 in For f'c less than 3000 psi, the length of lap shall be increased by one-third Wyllie CB008 Paulson CB008 LUTZ CB008 N No objection to the proposed change, but by the same logic we should apply the same lambda reduction for development of prestressing strand in 12.9 Y/C Shouldn’t there be a set of parenthesis around “lambda-rootfc-prime” to prevent a possible misinterpretation? Someone could divide by lambda and then multiply by root-fc-prime Same thing would apply to this same expression as found in 12.3.2 N Lines 8-9 Remove the change Insertion of the compression development length is inconsistent with the splice lengths given which are significantly larger To be cautious one could introduce the λ into the current splice expressions If this were done then λ should also be added to the 0.0003d bfy expression in 12.3 LUTZ CB008 Tolles CB008 Y/C Also note that there is an extra ‘the’ in the 3rd to last line of R12.16.1 N Lines 8-9 I ran some numbers with fc 2500 – 8000 psi and rebar fy 60 or 75 ksi and it doesn’t appear that the added equation based on compression development length to include λ would ever govern over the existing equations Include λ in existing equations: 12.16 — Splices of deformed bars in compression 12.16.1 — Compression lap splice length shall be 0.0005fydb/ λ, for fy of 60,000 psi or less, or (0.0009fy -24)db/ λ for fy greater than 60,000 psi, but not less than 12 in and with λ as given in 12.2.4(d) For f'c less than 3000 psi, length of lap shall be increased by one-third French CB013 N Lobo CB013 A Paulson CB013 Y Mize Browning CB013 Y CB013 Y Tolles CB013 Jirsa CB013 Y Cook CAGLEY CB013 Y CB013 Y Darwin CB013 N The key goal of the proposed change is to allow the net bearing area of the head Abrg to be based on the gross area of the head minus that area of the bar unless an obstruction exceeds the limits in newly proposed section 3.5.9(d) The proposed changes in 3.5.9 include specific restrictions that are not in 318-08, but the meaning of proposed 3.5.9(c) is not clear in light of the restriction that is retained in 3.5.9(d) The proposal does not include a technical justification for changing the definition of Abrg Such a justification is needed before approving this proposal Under any circumstances, a less complex modification would be advantageous Fiorato CB013 N I have questions regarding the rationale for the proposed changes and the means to implement the changes It is my understanding that this requirement would exclude one of the systems upon which the code provisions for headed bars is based We should further consider the implications of this change Y/C Hopefully these detailed requirements for head design can be transferred to ASTM A970 in the future and removed from 318 The assumption that the shapes shown between Lines 10 and 11 on p of CB013 may not provide the same anchorage as the shapes used in the tests that served as the basis for the provisions in ACI 318-08 (between Lines 14 and 15 on p.1) seems logical However, from the figures it is not clear that the “non-conforming” products would in fact meet the requirements of ACI 318-08 Section 3.5.9 Are they being used in practice and they meet the current requirements of 3.5.9? Assuming data support the rationale and the changes are needed, should some of the proposed revisions to 3.5.9 really reside in ASTM A970? The ASTM A970 standard is supposed to cover headed steel bars for concrete reinforcement, including deformed bars Currently Section 4.1.6 of ASTM A970-07 states the purchaser must specify: “Head geometry, including thickness, height, width, and cross-sectional area.” However, the standard can (and should) be updated to include the geometric limitations related to obstructions Actually, ASTM A970 should also include the requirement that the net bearing area of the head Abrg shall not be less than 4Ab This is because there is a clause in Section 5.3 of ASTM A970 that permits alternate head designs by the manufacturer if agreed to in advance by the purchaser Thus, the manufacturer is permitted to propose an alternative design that does not meet ACI 318 requirement on head bearing area (if the purchaser agrees) The purchaser is usually the contractor or subcontractor, not the designer If the contractor or subcontractor is not aware of the provision in ACI 318, this could result in “non-conforming” products inadvertently being used I realize this may be considered to be an ASTM committee issue, but if ASTM A970 is not referenced in ACI 318 it is less likely it will be used Therefore, I would expect ASTM Subcommittee A01.05 to be receptive to recommendations from ACI 318 Subcommittee B Darwin CB013 N To be accurate, line five should read “…are based in part on testing reported in the following references…” Darwin CB013 N Lines 6-10 This is not an accurate statement, in that “nonconforming” heads of the type shown were available at the time of the tests reported in the cited references It’s not clear that this statement is needed It would be satisfactory to indicate that they exist and that the provisions of 12.6.1 and 12.6.2 where written to preclude their use Darwin CB013 12 N Lines 12-14 This statement is not totally accurate It’s not participation of the bar adjacent to the bearing face that is the key concern; what is of concern is the potential of an obstruction to lower the anchorage capacity of the head by lowering the load at which a splitting failure will occur in the concrete Darwin CB013 22 N Lines 22-23 The statement that ”the definition of obstructions given in 3.5.9 appears to be too restrictive” is off base because the proposed definition of an obstruction in newly proposed section 3.5.9(d) includes, without change, the language that has been removed from the current 3.5.9 Darwin CB013 N Lines 1-2 It is not clear that the proposed changes fully reflect the heads used to establish 12.6.1 and 12.6.2 If obstructions such as addressed in proposed 3.5.9(d) were used, they were used in very few tests Gustafson CB013 Darwin CB013 36 36 N According to ASTM A970/A970M, the headed bar, shown in Illustration i and Photograph i on Page 1, would be classified as Class A Such headed bars were used in the tests upon which the existing Code provisions are based What then is the logic for excluding such Class A headed bars from the Code? This negative vote will be withdrawn if the exception on Page 3, Line 36, i.e., "Class B", is deleted N Lines 36-38 I think that we’ll have a problem specifying only Class B heads because a majority of the tests on which the current provisions are based were made on (would now qualify as) Class A heads In addition, the requirement that heads “satisfy all of the following additional requirements” is confusing because the paragraph after section (d) indicates that section (d) is not mandatory Kopczynski CB013 40 Y/C Lines 40-45 (a) and (c) deal with the bearing face; (b) deals with obstructions on the bar Reverse (b) and (c) to make the flow of information more logical Ghali CB013 40 N Lines 40-41 Ghali (recommends N) 3.5.9 Permits only headed bars that satisfy: “(a) The bearing face shall consist of a surface, nominally flat surface that lies in a plane perpendicular to the longitudinal axis of the bar.” The wording should be changed to clearly permit tapered heads with the configuration in Fig R3.5.5 of ACI 318-08 This type of head should be permitted because: It has been used extensively in testsa,b,c,d and in practice It does not need to be approved by a building official (as required in 12.6.4) Forged heads are permitted; they commonly have the configuration in Fig R3.5.5 To enable the forming of a head, of the required size, by the forging of a straight bar, it is necessary that the forging displaces a minimum volume of material Thus, the thickness of the head is designed to provide the required strength with minimum variable thickness (tapered as in Fig R3.5.5) Without minimizing the volume of the material of the head, an excessive length of the bar has to be deformed to the shape of the head; this long length is vulnerable to buckling under the forging force, rather than forging to the desired configuration At the intersection of a straight bar with a plane bearing face, there is a re-internet corner at which the bearing stress on the concrete is extremely high (theoretically infinite) This high stress concentration is avoided by the fillets connecting the stem to the head in Fig R3.5.5 Entrapment of air bubbles below the head during casting is less likely to occur with the configuration in Fig R3.5.5, compared to a head satisfying 3.5.9(a) of CB013 The entrapment of air weakens the concrete in a critical location "strength"? Meinheit CB116 N The word prism was a substitute for the previous description for the breakout surface, that is, cone Regardless of the angle of the concrete breakout, the breakout failure still looks like a cone If cone were substituted for prism, the description would not be inappropriate I prefer to use cone to describe the failure surface A generic “breakout” that has no geometrical significance Although the physical concrete breakout surface may be conical, the word “prism” attempted to describe the truncated pyramid used to determine the rectilinear projection of the idealized breakout failure on the concrete surface Cone implies a conical breakout and may confuse reader in the determination of the idealized surface projection Should discuss where the following terms should be used: “cone” to describe actual chunk of concrete “breakout failure” “idealized breakout failure” “idealized concrete breakout failure” “projected area” or “surface area” or “projected surface area” Use of “full” or “complete” etc etc Wyllie CB116 - - LUTZ CB116 16 N Can we discuss this? While prism may not be perfectly correct, I find it much clearer than the proposed language I believe we went to prism to emphasize the rectilinear nature of the prism vs the old circular cones We could go to pyramid and pyramid with truncated apex for groups but I don’t think so Y/C Lines 16&19 These two wordings should be the same—I prefer “breakout failure with an angle…” In any case the line 16 should be modified Line 16 could alternately be ”breakout surface angle” or “breakout failure angle” Anderson CB116 18 Y/C The CCD model is an idealized, mathematical model with the angle set as 35 degrees I feel we need to better emphasize this fact throughout the commentary When giving the Appendix D seminars, designers believe this represents true breakout behavior, and rigidly interpret the Discuss Also see response to Meinheit Accept Changed to “idealized concrete breakout failure with an angle of approximately 35o…” Accept See response to Lutz physical breakout in this fashion To that end: Change “ assuming a concrete breakout failure “ to “ assuming an idealized concrete breakout failure “ Anderson CB116 27 Y/C Lines 27-28 Accept Change “ based on individual, breakout failures “ to “ based on individual, idealized breakout failures “ Fiorato Paulson Anderson CB116 CB116 CB116 1 36 36 42 Y/C Should the phrase “breakout cone angle” be replaced by “breakout failure angle” to be consistent with the revised Fig RD4.2.2(b)? Accept Y/C Since we are eliminating the word “cone” from figure captions, change “breakout cone” in this sentence to “breakout failure” Accept with slight modification Y/C Change “ the full breakout failure for “ to “ the full, idealized breakout failure for “ Accept Choose between: And change figure title slightly “They assume an idealized concrete breakout failure cone with an angle of approximately 35 degrees…” “AVco is the maximum projected area for a single anchor that approximates the surface area of the full idealized breakout failure prism or cone for an anchor unaffected by edge distance, spacing,…” “AVco is the maximum projected surface area for a single anchor that approximates the surface area of the full breakout failure prism or cone for an single anchor unaffected by edge distance, spacing,…” Paulson CB116 Y/C Since we are eliminating the word “cone” from figure captions, change “breakout cone” in this sentence to “breakout failure” Accept with slight modification Delete “full” Choose between: “AVc approximates the full surface area of the idealized breakout cone failure for the particular arrangement of anchors.” “AVc approximates the full projected surface area of the associated with the idealized concrete breakout failure cone…” Paulson CB116 Paulson CB116 Anderson CB116 Anderson CB116 Anderson CB116 12 Y/C Not shown in this CB is the next paragraph of RD.6.2.1, which includes “failure cone” Since we are eliminating the word “cone” from figure captions, change this additional occurrence of “failure cone” to “breakout failure” Accept Y/C Not shown in this CB is RD.6.2.9, which includes “breakout cone” Since we are eliminating the word “cone” from figure captions, change this additional occurrence of “breakout cone” to “breakout failure” Consider leaving as “cone” because want reinforcement to intersect failure Do we need to change figure? “enclosing the edge reinforcement embedded in the breakout cone and placed…” N I have always referred to a tension breakout as a “breakout cone,” as have others I suggest the wording “Idealized breakout failure cone for tension” for the figure Y/C Add “Idealized” to before breakout in the figure caption N Change caption to read “Section through idealized breakout failure cone.” “the front edge begins to form a breakout failure cone” Accept with slight modification (i.e., not add “cone”) “Idealized breakout failure for tension” and “Idealized breakout failure breakout for shear” Accept Accept with slight modification (i.e., not add “cone”) Section through idealized breakout failure surface LUTZ CB116 Y/C Use of ‘surface’ is incorrect; better to replace with ‘surface’ Anderson Informational Item I believe Don Meinheit and I need to discuss this item further with Mr Lutz before further action can be taken Our research for PCI showed that corner influences are much bigger than what the CCD method implies Paulson Informational Item Y/C Agree with the general suggestion that something should be done to coordinate 318 Appendix D with the PCI approach With some of the graphs showing that Appendix D approach is 50% to maybe even 100% greater than the PCI approach, this suggests that either Appendix D is too liberal or the PCI approach is rather conservative As a minimum, this subcommittee member would like to see a graphical and statistical comparison of Appendix D approach with the data behind the PCI approach Perhaps this has been already performed as part of the development of the PCI approach? This could help settle the difference I suspect that some of our other subcommittee members can enlighten us on the source of the apparent differences Jirsa Informational Item We would make life easier for the designer if we settled on a single procedure ?? Not sure what is meant here…” Cook Informational Item N This needs a comparison of the App D and PCI methods to a data base with both the PCI stud tests and stud tests from other data bases I believe that Meinheit and Anderson are doing this as part of their work on their public comment on ACI 318-05 CAGLEY Informational Item N We have a basis for what we have in 318 I don’t see reason for changing just for PCI Let them adjust to us CB004—March 18, 2009 Conversion of A615/A615M and A706/A706M Yield Strength Determination from Extension under Load (EUL) Method to Offset Method Background and Rationale Section 9.2.2 of A615/A615M allowed the use of extension under load (EUL) at a prescribed strain for determining “yield strength” The amount of prescribed strain was defined as follows: “The strain shall be 0.5% of gage length for Grade 40 [280] and Grade 60 [420] and shall be 0.35% of gage length for Grade 75 [520].” Section 9.1.1.1 of A706/A706M also allowed the use of EUL for determining yield strength The extension under load (prescribed strain) was defined as: “However, the extension under load shall be 0.0035 in./in [0.0035 mm/mm] (0.35%).” Since A706/A706M is Grade 60 [420] only, it is obvious that if an extension under load method of determining yield strength is used, a different reading point on the loadelongation curve was necessary if tested as A706/A706 rather than A615/A615M Taken literally, this means that to certify a given product to both specifications (dual certification), and an extension under load type of yield strength was determined, it was required to report two different values of yield strength, 0.35% and 0.50% extension under load Practically, two values were seldom reported In addition, A615/A615M had the unusual requirement, as defined above, of using a smaller total strain extension (0.35%) for Grade 75 [520] than for the lower strength Grades 40 [280] and 60 [420] (0.5%) This use of a lower specified strain extension for a higher strength grade for an extension under load yield determination is in complete disagreement of accepted methods of mechanical testing As stated in Note 10, Section 13.2.2 of A370, “The appropriate magnitude of the extension under load will obviously vary with the strength range of the particular steel under test In general, the value of extension under load applicable to steel at any strength level may be determined from the sum of the proportional strain and the plastic strain expected at the specified yield strength.” In other words, as the strength of the steel increases, the appropriate strain value for determining extension under load stress values should increase, not decrease As stated in Note 6, Section 13.1.3 of A370, “For steel with a yield point specified not over 80,000 psi (550 MPa), an appropriate value is 0.005 in./in of gauge length For values above 80,000 psi, this method is not valid unless the limiting total extension is increased.” Similar language exists in ASTM E8-04 In summary, the prescribed strain for EUL load yield strength determination should have been consistent for all reinforcing bar specifications, and should have been increasing with higher strengths rather than decreasing As a better alternative, consideration was given to using the offset method for yield strength determination as defined in Section 13.2.1 of A370, and used in the specification A1035/A1035M (issued in 2004) The use of the offset method provides a procedure to use a constant limiting plastic strain (0.2%) to define the yield strength, which is valid and consistent at any strength level After deliberation, ASTM Sub A01.05 voted to change both A615/A615M and A706/A706M, replacing the EUL method with the 0.2% offset method to determine yield strength in deformed and plain bars for concrete reinforcement Yield points may also be determined by the “drop of the beam or halt in the gage” methods which were not changed With this change, yield strength determination of reinforcing bars is consistent with most other ASTM structural steel grades, and consistent with other specifications for reinforcing bars used around the world CB004—Revise 3.5.3.1, 3.5.3.2, R3.5.3.1 and R3.5.3.2 Reason: Update Code and Commentary to reflect changes adopted in the ASTM specifications for reinforcing bars for determining yield strength— the offset method has replaced the extension under load (EUL) method, and revise 3.5.3.2 to permit substitution of low-alloy steel bars (A706) for Grade 60 carbon-steel bars (A615) Background: In CB004, Sub B was asked to evaluate Commentary Section R3.5.3.2, and in particular, the third paragraph of the section in response to the question: The last sentence of R3.5.3.2 seems to indicate that the actual stress at ultimate is less than the specified yield strength Clarification is needed Is this because the specified yield strength is that corresponding to strain of 0.35% and section may not reach 0.0035 at ultimate strength? At a 318B meeting during the last Code cycle, it was suggested that the question about the third paragraph of R3.5.3.2 could possibly be addressed via wordsmithing However, much has transpired, since an editorial "fix" was suggested As an example, low-carbon, chromium steel reinforcing bars (ASTM A1035/A1035M) were introduced into the 2008 Code for which the ASTM standard includes provisions for determining the yield strength by the offset method (0.2 % offset) Also, ASTM specifications A615/A615M and A706/A706M were revised to include provisions for determining the yield strength by the offset method In January 2009, ASTM Sub A01.05 on Steel Reinforcement plans to ballot proposed revisions of Specifications A955/A955M and A996/A006M, which will implement the offset method for determining yield strength With the ASTM specifications introduction of the offset method for determining yield strength, the second and third paragraphs of R3.5.3.2 are moot Code Section 3.5.3.2 and Commentary Section R3.5.3.2 are impacted by the revised ASTM specifications This Change Submittal also includes a minor proposed revision of Code Section 3.5.3.1, proposed editorial revisions of Commentary Section R3.5.3.1, and a proposed revision of Code Section 3.5.3.2 to permit substitution of low-alloy steel bars (A706) for Grade 60 carbon-steel bars (A615) When Committee 318 updates the referenced ASTM standards in Section 3.8.1, ACI 318B will propose adoption of the latest editions of Specifications A615/A615M, A706/A706M, A955/A955M and A996/A996M—the editions which include the offset method for yield strength determination Proposed Revisions: 3.5.3 — Deformed reinforcement 3.5.3.1 — Deformed reinforcing bars shall conform to the requirements for deformed bars in one of the following specifications, except as permitted by 3.5.3.2 and 3.5.3.3: (a) Carbon steel: ASTM A615; (b) Low-alloy steel: ASTM A706; (c) Stainless steel: ASTM A955; (d) Rail steel and axle steel: ASTM A996 Bars from rail steel shall be Type R R3.5.3 — Deformed reinforcement R3.5.3.1 — ASTM A615 covers deformed carbon-steel reinforcing bars that are currently the most widely used type of steel bar in reinforced concrete construction in the United States The specification requires that the bars be marked with the letter S for type of steel ASTM A706 covers Grade 60 low-alloy steel deformed bars intended for applications where controlled tensile properties, restrictions on chemical composition to enhance weldability, or both, are required The specification requires that the bars be marked with the letter W for type of steel Grade 60 Ddeformed bars produced to meet both ASTM A615 and A706 are required to be marked with the letters S and W for type of steel Stainless steel bars are used in applications where high corrosion resistance or controlled magnetic permeability are required The physical and mechanical property requirements for stainless steel bars under ASTM A955 are the same as those for carbon-steel bars under ASTM A615 Rail steel reinforcing bars used with this Code are required to conform to ASTM A996 including the provisions for Type R bars, and marked with the letter R for type of steel Type R bars are required to meet more restrictive provisions for bend tests Inasmuch as these ASTM specifications now employ the offset method to determine yield strength, requiring yield strength to be taken as the stress at a strain of 0.35 percent for bars with fy exceeding 60,000 psi is no longer required Use of the offset method provides a procedure to use a constant limiting plastic strain (0.2 %) to define the yield strength, which is valid and consistent at any strength level 3.5.3.2 —It shall be permitted to substitute a Grade 60 bar conforming to ASTM A706 for the same size Grade 60 bar conforming to ASTM A615 Deformed reinforcing bars shall conform to one of the ASTM specifications listed in 3.5.3.1, except that for bars with fy exceeding 60,000 psi, the yield strength shall be taken as the stress corresponding to a strain of 0.35 percent See 9.4 R3.5.3.2 —For Grade 60 bars, the requirements for mechanical properties and chemical composition under ASTM A706 are more restrictive than those under ASTM A615 Thus, 3.5.3.2 permits substitution of a bar conforming to ASTM A706 for the same size Grade 60 bar conforming to ASTM A615 includes provisions for Grade 75 bars in sizes No through 18 The 0.35 percent strain limit is necessary to ensure that the assumption of an elasto-plastic stress-strain curve in 10.2.4 will not lead to unconservative values of the member strength The 0.35 strain requirement is not applied to reinforcing bars having specified yield strengths of 60,000 psi or less For steels having specified yield strengths of 40,000 psi, as were once used extensively, the assumption of an elastoplastic stress-strain curve is well justified by extensive test data For steels with specified yield strengths, up to 60,000 psi, the stress-strain curve may or may not be elasto-plastic as assumed in 10.2.4, depending on the properties of the steel and the manufacturing process However, when the stress-strain curve is not elasto-plastic, there is limited experimental evidence to suggest that the actual steel stress at ultimate strength may not be enough less than the specified yield strength to warrant the additional effort of testing to the more restrictive criterion applicable to steels having specified yield strengths greater than 60,000 psi In such cases, the φfactor can be expected to account for the strength deficiency CB016—Add Zinc and Epoxy Dual-Coated Reinforcing Bars to the Code Reason: Add another type of corrosion-resistant reinforcing bar to the Code Background: ASTM A1055/A1055M, which was issued in 2008, prescribes the requirements for "dual-coated" reinforcing bars A zinc-alloy layer is applied to the bars by the thermal spray method (metallizing) and then followed by an epoxy coating applied by the electrostatic spray method The aim or benefit of the dual coating is if the outer epoxy coating sustains damage, the inner layer of zinc coating will provide corrosion resistance Because the outer coating is epoxy, the bond strength of the dual-coated bars would be similar to that of epoxy-coated bars (ASTM A775/A775M and A934/A934M) Revise Code Section 3.5.3.8: 3.5.3.8 —Zinc-coated (Ggalvanized) reinforcing bars shall conform to ASTM A767 Epoxy-coated reinforcing bars shall conform to comply with ASTM A775 or to with ASTM A934 Zinc and epoxy dual-coated reinforcing bars shall conform to ASTM A1055 Bars to be zinc-coated (galvanized), or epoxy-coated, or zinc and epoxy dual-coated shall conform to one of the specifications listed in 3.5.3.1 Revise Commentary Section R3.5.3.8: R3.5.3.8 —Zinc-coated (Ggalvanized) reinforcing bars (ASTM A767), and epoxy-coated reinforcing bars (ASTM A775 and A934), and zinc and epoxy dual-coated reinforcing bars (ASTM A1055) are used in applications were added to the 1983 Code, and epoxycoated prefabricated reinforcing bars (ASTM A934) were added to the 1995 Code recognizing their usage, especially for conditions where corrosion resistance of reinforcement is of particular concern They have typically been used in parking structures, decks, bridge structures, and other highly corrosive environments Add to Code Section 3.8.1: A1055/A1055M-08a Standard Specification for Zinc and Epoxy Dual-Coated Steel Reinforcing Bars Revise Code Section 12.2.4(b): (b) For epoxy­coated bars, zinc and epoxy dual­coated bars, or epoxy­coated wires with cover less than 3db, or clear spacing less than 6db, ψe = 1.5. For all other epoxy­coated bars, zinc and epoxy dual­coated bars, or epoxy­coated wires, ψe = 1.2. For uncoated and zinc­coated  (galvanized) reinforcement, ψe = 1.0 Revise fourth paragraph of Commentary Section R12.2.4: Because the bond of epoxy-coated bars or zinc and epoxy dual-coated bars is already reduced due to the loss of adhesion between the bar and the concrete, an upper limit of 1.7 is established for the product of the factors for top reinforcement and epoxy-coated reinforcement or zinc and epoxy dual-coated reinforcement factors CB116 – Remove reference to “prism” in Appendix D