Experimental investigation and fragility analysis on seismic performance of precast UHPC hollow piers under varying axial load

Precast bridge piers are attractive in the context of rapid construction, quality control, and reduced traffic disturbances. Nevertheless, conventional precast piers are featured by solid sections. If designed with hollow sections, it would not only reduce self-weight, facilitating transportation and lifting, but also lower costs. Meanwhile, ultra-high-performance concrete (UHPC) can be considered for the thin-walled pier shaft material to enhance bearing capacity without compromising its structural performance and safety. Although some studies have been carried out on the pier columns retrofitted with UHPC jacket or using UHPC connections, there has been limited research on precast UHPC hollow piers, particularly concerning their structural response to varying axial loads. In this study, the hysteretic behavior of three UHPC hollow bridge piers under varying axial load was investigated by quasi-static tests, along with one normal concrete (NC) hollow pier and one NC solid pier for comparison. The interested indicators include failure mode, energy dissipation, stiffness degradation, residual displacement, pinching effect, and curvature distribution. Then, a refined finite element (FE) model was established in OpenSees, incorporating the effects of bond-slip and the cyclic behavior of the joint interface. Finally, fragility analyses on five tested piers were conducted with both near-fault and far-fault ground motions. The results demonstrated that increased axial load resulted in a higher peak load but reduced ductility, ultimate displacement, and residual displacement, along with a more significant pinching effect. The fragility analysis results indicated that UHPC hollow piers exhibited lower damage probability compared to NC solid/hollow piers. However, as the axial load on the UHPC piers increased, the damage probability also increased.