Finite Element Analysis of Seismic Performance of Post-Cast UHPC Beam–Column Assembled Joints

Prefabricated post-pouring UHPC (ultra-high performance concrete) beam–column joints have the advantages of strong integrity, excellent seismic performance and good durability, but there are also problems of easy cracking of old and new concrete interfaces and concrete near the interface. Therefore, a new type of post-cast UHPC joint is designed in this paper. The joint is connected by post-cast UHPC at the beam and column sections far from the core area, and the keyway is set in the connection section to solve the defect that the old and new interfaces easily crack. The refined finite element model of the joint was established by using the finite element software ABAQUS (2023). Through the simulation of 10 working conditions, the typical failure modes and seismic performance of the joint were discussed in depth, and the influence of key parameters such as the lap length of steel bars, the strength of steel bars and the strength of post-pouring UHPC was analyzed. The results show that the joint cracks first appear at the junction of the beam–column core area and develop along the cut-off interface between ordinary concrete and UHPC. No macroscopic cracks were observed in the post-pouring UHPC connection section, and the structure was finally destroyed due to the crushing of ordinary concrete. Increasing the lap length of the steel bar can improve the peak bearing capacity and stiffness of the joint, but it will accelerate the stiffness degradation. Increasing the strength grade of steel bars can significantly improve the bearing capacity and stiffness of the joints, but the energy dissipation capacity is slightly reduced. In addition, the improvement effect of UHPC strength is closely related to the strength of steel bars: when an HRB500 steel bar is used, high-strength UHPC can show better bearing capacity, stiffness and energy dissipation performance, while the improvement effect is not significant when an HRB400 steel bar is used. The research results can effectively inhibit the development of interface cracks and provide a theoretical reference for the subsequent full-scale test and the seismic design of precast joints with post-cast UHPC connections.