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6 Table 1. Uncoated reinforcing steel permitted by 2004 AASHTO LRFD Bridge Construction Specifications. Tested Designation Title Note in This Study?* AASHTO M31 Deformed and Plain Carbon- standard reinforcing steel unless yes ASTM A615 Steel otherwise specified AASHTO M322 Rail-Steel and Axle-Steel Plain no ASTM A996 Bars ASTM A706 Low-Alloy Steel Deformed and "weldable" reinforcing steel yes Plain Bars AASHTO M225 Deformed Steel Wire "cold-rolled" deformations on yes ASTM A496 A82 plain wire AASHTO M55 Welded Plain Wire Fabric welded A82 wire no ASTM A185 AASHTO M32 Plain Steel Wire yes ASTM A82 AASHTO M221 Deformed Steel Welded Wire welded wire fabric having wires no ASTM A497 Reinforcement conforming to A496 ASTM A955 Deformed and Plain Stainless different types (allowable Steel Bars chemistries) of stainless steel yes are permitted within A955 * See Appendix A. grades are more resistant to corrosion and therefore very ment into the LRFD specifications. As described in Chapter 2, attractive in reinforced-concrete applications. For instance, this program included parametric, experimental, and analytic the A1035 reinforcing steel used in this study is reported to studies in addition to a number of "proof tests" intended to be between 2 to 10 times more resistant to corrosion than validate existing LRFD provisions when applied to higher conventional A615 "black" reinforcing steel. In some appli- strength reinforcing steel. cations, A1035 reinforcing steel has replaced A615 steel on a Thus, a crucial objective of the present work is to identify one-to-one basis on the premise that it is more resistant to an appropriate steel strength and/or behavior model to ade- corrosion but not as costly as stainless steel grades. Clearly, quately capture the behavior of high-strength reinforcing if the enhanced strength of A1035 steel could be used in steel while respecting the tenets of design and the needs of the design calculations, less steel would be required, and this designer. As will be described throughout this report, a value would result in a more efficient and economical structural of yield strength, fy, not exceeding 100 ksi was found to be system. permissible without requiring significant changes to the LRFD specifications or, more critically, to the design philosophy 1.2 Objectives of NCHRP Project 12-77 and methodology prescribed therein. Some limitations to this increase in permissible yield strength were identified and also The objective of the study presented in this report is to are discussed. evaluate existing AASHTO LRFD Bridge Design Specifications relevant to the use of high-strength reinforcing steel and other grades of reinforcing steel having no discernable yield 1.3 Literature Review plateau. The focus of the experimental phase of this study is 1.3.1 Mechanical Properties of A1035 the use of ASTM A1035 (2009) reinforcing steel since it cap- Reinforcing Steel tures both behavioral aspects of interest (i.e., it has a very high strength and has no discernable yield plateau). The analytical A number of mechanical properties for reinforcing steel program of this study supplements the experimental data and have been reported in the literature, although by far the most evaluates design issues related to other grades of reinforcing important are the tensile yield (fy) and ultimate strengths (fu); steel with no distinct yield plateau. these parameters are discussed at length below. El-Hacha and The project identified aspects of reinforced-concrete design Rizkalla (2002) report other mechanical properties of A1035 and of the AASHTO LRFD Bridge Design Specifications that to be consistent with the higher tensile yield strength. Based may be affected by the use of high-strength reinforcing steel. on tests of #4, #6, and #8 bars, they report the following: Design issues were prioritized and an integrated experimen- tal and analytical program was designed to develop the data Compressive yield strength is the same as tensile yield, fy; required to permit the integration of high-strength reinforce- Poisson Ratio, = 0.26;