Seismic Performance of Rocking Column–Supported Continuous Rigid-Frame Bridge: Phenomenological Damage State Definitions, Computations, and Fragility Assessment

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Post-tensioned (PT) rocking systems have been developed aimed at mitigating structural seismic damage, with extensive experiments and numerical studies demonstrating advantages of PT rocking columns against earthquake. However, these studies are mostly limited to the element level (i.e., columns), whereas the seismic performance of a system-level bridge structure supported by PT rocking columns is yet to be well-documented. To fill in this gap, this study applied probabilistic methods to develop the first-of-its-kind seismic fragility models of a typical continuous rigid-frame bridge with post-tensioned concrete-filled steel tube (PCST) versus relatively traditional post-tensioned reinforced concrete (PRC) columns, both rocking columns. To facilitate the fragility analyses, phenomenological minor, moderate, and severe damage states were defined based on a series of cyclic loading tests on PCST and PRC columns, followed by three-dimensional finite-element (FE) modeling of the PCST and PRC columns that was validated to well predict not only seismic demands, but also the three damage states (i.e., capacity). Accordingly, a typical three-span rigid-frame bridge was modeled to evaluate the component- and system-level fragility of the bridge that is characterized by vulnerable components including rocking column, bearing at abutment, and abutment itself. The system-level fragility results demonstrate the outperformance of the PCST bridge over the PRC counterpart regardless of against longitudinal or transverse excitations, mainly owing to the significant reduction of column fragility in the PCST bridge. The use of PCST leads to the shift of the most vulnerable component from the column to the easier-to-repair bearing, implying a more resilient seismic isolation strategy for rigid-frame bridges.