Seismic performance of RC bridges with double-column medium height bents retrofitted with SCEBs under near-field ground motions

RC double-column medium height bents (DCMBs) are widely applied in the mountain areas as the substructure of highway bridges, and the two columns are normally connected by RC link beams to enhance the lateral stability. However, serious damage and/or large residual displacement were repeatedly observed in the DCMBs after many major earthquakes, which may make the bridges lose functionality and have to be demolished and rebuilt. In order to improve the seismic performance of the bridges, a novel self-centering variable friction dissipation brace (SCVFB) using SMA plates is developed to replace the traditional RC link beams in the DCMBs in this study. The mechanical properties of the shape memory alloy (SMA) plate were investigated experimentally. Then, the analytical model of the DCMBs with inverted-V SCVFBs (DCMB-SVFB) is built, and the corresponding design philosophies of the SCVFB in the DCMB are proposed based on the concept of structural fuse. Subsequently, the hysteretic behaviors of the DCMB-SCVFB in the transverse direction are analyzed, and the dynamic responses of the whole bridge under near-field ground motions are also investigated. For comparison, the seismic behaviors of the bridges with original bents (the bridges with and without link beams) and the bridges retrofitted with buckling restrained braces (BRBs) are also presented. The results show that the SCVFB has stable energy dissipation capability and excellent self-centering ability, even without the need of prestressing. Compared with the original bridge, the bridges with SCVFBs and BRBs are featured by higher strength, larger stiffness, better energy dissipation capacity, and less damage. In particular, the SCVFB can effectively reduce the residual displacement of the bridge and quickly restore the traffic capacity.