Experimental and code analyses for shear design of AASHTO prestressedconcrete girders

摘要

A 40-year-old girder was removed from the Interstate 244 highway bridge crossing the Arkansas River in Tulsa, Okla., and was tested and analyzed to determine whether the experimental results exceeded estimated shear capacities. The results of this experiment provided direct evidence regarding the performance of girders designed according to the quarter-point rule being overloaded in shear. In addition, nominal shear capacity of American Association of State Highway and Transportation Officials (AASHTO) prestressed concrete model girders was analyzed to determine the relationship between past and more-recent codes. Comparisons of nominal shear capacities showed the progression of analysis but were only relevant to their corresponding shear demands. In light of this limitation, the shear demands were calculated so that a comparison of the margins of safety could be made. Margin of safety is defined in this study as the ratio of shear strength to shear demand, considering all load and strength reduction factors from the respective codes. Strut-and-tie models were also used to analyze nominal strength considering provisions from both ACI 318-08 and AASHTO LRFD Bridge Design Specifications. Overall, code-to-code and code-to-experiment comparisons provided better guidelines and validation for evaluating the safety of AASHTO bridge girders designed according to the quarter-point rule.