Behavior of curved steel trapezoidal box girders during construction
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Due to advances in fabrication technology, the use of steel trapezoidal box girders for curved interchange structures has become popular. The rapid erection, long span capability, economics, and aesthetics of these girders make them more favorable than other structural systems. Composite box girders with live loading, and quasi-closed box girders during construction, have to be evaluated during the design of these bridges. Considering both cases, the design for construction loading is the least understood and is the most important. Stresses due to construction loading can reach up to 60-70 percent of the total design stress for a given cross section. A three-phase study has been undertaken to investigate the behavior of curved trapezoidal box girders during construction. In the first phase, laboratory tests have been performed to investigate the shear transfer between the concrete deck and steel girder at early concrete ages. In the second phase, an easy-to-use finite element program has been developed for the analysis of these systems under construction loads. The program has the capability of modeling the effects of semi-cured concrete. The third phase focused on the monitoring of two curved trapezoidal box bridges during construction. The measured forces and stresses in the field were compared with the analyses using the developed software. Findings from laboratory and field tests revealed that composite action develops at very early concrete ages. The developed software provides good correlation between measured field data and computed results.