Seismic performance of prefabricated square hollow section piers strengthened by jacketing using UHPC and high-strength steel

Pier damages have become a primary contributing factor to bridge seismic damage, because they may cause serious loss of integrity and even the collapse of the whole bridge structure. Therefore, developing and improving methods for the seismic strengthening of existing bridge piers can play a significant role in preventing bridge failures. In this study, ultra-high-performance concrete (UHPC) and HTRB600E high-strength steel bars were used to strengthen prefabricated square hollow section piers that had undergone severe flexural damage due to seismic demands. By conducting quasi-static tests on the prefabricated piers before and after strengthening, seismic performance indices, such as the hysteresis curve, skeleton curve, energy dissipation, stiffness degradation, residual displacement, and curvature, were compared and analysed. Under cyclic loading, the deformation of the strengthened pier shaft section was small, and no evident plastic failure was observed. The unreinforced pier shaft exhibited a clear bending shear failure mode, with a plastic hinge first developing at the top of the strengthened shaft section. Based on the quasi-static test results, a refined finite element model of the pier was implemented and verified. By varying the thickness and height of the UHPC reinforcing layer and the strength of the steel bars, their influence on the seismic capacity of the pier was explored. The experimental results indicate that the jacketing using UHPC and high-strength steel bars significantly improved the flexural capacity, energy dissipation, and initial stiffness of the retrofitted specimens and effectively restored and enhanced their seismic performance.