Seismic behaviors of precast sidewall-bottom slab joints of U-bar connections with UHPC permanent formwork in precast subway station structures

To further optimize the construction process of composite monolithic precast concrete (MPC) subway station structures, a novel sidewall-bottom slab joint of U-bar overlapping connections with UHPC permanent formwork was proposed. To investigate the seismic behavior of the proposed joint, the experimental study was conducted on two half-scale precast sidewall-bottom slab joint specimens (PSJ-300 and PSJ-250) with different overlap length and a half-scale monolithic sidewall-bottom slab joint specimen (MSJ) under cyclic reversal loadings. The experimental results showed that the proposed joint could effectively mitigate concrete cracking and failure by installing UHPC formwork. Additionally, the loading capacity and stiffness degradation capacity of PSJ-300 and PSJ-250 were comparable to those of MSJ under the positive loadings. However, the loading capacity, ductility and energy dissipation capacity of Specimen PSJ-300 were better than those of Specimen MSJ. The U-bar overlap length affected the seismic performance of the proposed joint, which demonstrated that the hysteretic performance, energy dissipation capacity and ductility of the precast specimens increased with the overlap length of the U-bars. The finite element model based on ABAQUS was established for the joints, and the parametric analysis was conducted. A flexure-based bearing capacity prediction model for precast joint was then established correspondingly and showed sufficient accuracy with the test results. • A novel precast sidewall-bottom slab joint that can be constructed efficiently was proposed. • The proposed joint showed asymmetric hysteretic characteristics. • The proposed joint with excellent seismic performance has potential for application.