Behavior of standard hook anchorage with corrosion resistant reinforcement : final report, June 2008.
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2008-06-01
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Edition:Final report.
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Abstract:The objective of this study was to evaluate the behavior of standard books that are made using corrosion resistant reinforcement, which typically have higher yield and ultimate strengths than that of ASTM A615 Grade 60 reinforcement. Two steel types were evaluated in this research. The stainless steel was 316LN, which is a low-carbon austenitic stainless steel that has been nitrogen strengthened. The mechanical properties conformed to ASTM A955. The corrosion resistant bar was a low-carbon steel bar with chromium added and conformed to ASTM A1035. The impetus is that the current ACI/AASHTO equations for the development length of standard hooks do not directly address the use of high-strength steel bars that do not have a well-defined yield point or a relatively flat post-yield slope. Hooked reinforcement is typically used to develop reinforcement in a relatively short distance and is usually associated with a nodal region of a strut and tie system. A test setup was devised that uses the strut and tie behavior of hooked anchorage to impose forces similar to those occurring in the structure. The specimen configuration and test setup were arranged to promote a splitting tension failure of the concrete in the plane of the hook, which is the typical behavior of hooked anchorage without ties. Single no. 5 and no. 7 bars were tested with either 90- or 180- deg standard hooks. Grade 60-reinforcement was first tested to ensure that the desired failure mode was achieved and that the ACI and AASHTO development length equations for hooks did indeed ensure that the reinforcement reached yield before the concrete failed. Stainless steel reinforcement with a yield strength over 100 ksi and corrosion resistant reinforcement with a yield strength over 120 ksi were also tested. Anchorage capacity ratios (ultimate load/specified yield load) were calculated for each of the specimens to determine the effectiveness of the development lengths. In addition, strain ductility ratios (strain at ultimate capacity/yield strain from bare bar to tension test) were determined for each specimen to provide a basis for comparison. Finally, recommendations for adjusting the equation for hook development length were developed.
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