Seismic response of bent caps in as-built and retrofitted reinforced concrete box-girder bridges

Bridges are key components of infrastructure that are vulnerable to earthquakes and many are undergoing retrofit or complete replacement. Rigorous seismic design of new bridges and informed retrofit decisions are indispensable. A specific design issue that is concerned with the structural response of bent cap beams in as-built and retrofitted box-girder bridges under gravity and seismic loads is tackled in this paper. A combined experimental and computational research was undertaken in this study to investigate the bent cap capacity and effective slab width in reinforced concrete box-girder bridges for enhanced seismic capacity design approach. Two large-scale as-built and retrofitted column-bent cap-box-girder subassemblies were developed and tested using bidirectional quasi-static cyclic loading and hybrid simulation approach, respectively. In addition, detailed finite element models were calibrated and further used to complement the experimental programs. The study revisited the effective slab width code values for bent caps and concluded that the slab reinforcement within an effective width, especially in tension, should be included for accurate bent cap capacity estimation. Accordingly, recommendations are suggested for the relevant bridge seismic design codes.