Displacement-based seismic design of bridge bents retrofitted with various bracing devices and their seismic fragility assessment under near-fault and far-field ground motions

Implementing energy dissipation braces can be an effective option for mitigating the seismic damage of double- or multi-column bridge bents. This study compares the relative effectiveness of different braces in seismically retrofitting a reinforced concrete (RC) double-column bent. The considered braces include buckling-restrained braces (BRBs), viscous damper braces (VDBs) and piston-based self-centering braces (PBSCs). First, a direct displacement-based design method (DBD) is utilized to design the braces for satisfying the same performance criterion under design earthquakes. Based on that, fragility analysis is conducted to evaluate the seismic vulnerability of the retrofitted bents subjected to near-fault and far-field ground motions. The self-centering performance of the retrofitted bents is also compared by using the post-earthquake residual displacement as a performance indicator. Results indicate that the PBSCs are more effective than BRBs and VDs in reducing the vulnerability of the bent at different damage states under either near-fault or far-field ground motions. In addition, the PBSCs are superior to the other braces in terms of self-centering performance by recovering more bent drift from an earthquake.