Seismic performance and flexural bearing capacity of UHPC prefabricated reinforcement cage formwork concrete column-RC ring beam joints

Existing research on ring beam joints is mostly limited to the concrete-filled steel tube (CFST) column system, which has inherent deficiencies in fire resistance and durability. To address this issue, the present study proposes a novel structural configuration that applies ultra-high-performance concrete (UHPC) to the reinforced concrete (RC) ring beam joints connected to UHPC prefabricated reinforcement cage formwork concrete columns. A finite element (FE) model was established using ABAQUS, and its reliability was first verified against RC ring beam T-joints. Subsequently, eleven specimens of the UHPC prefabricated reinforcement cage formwork concrete column-RC ring beam joint were designed, with ring beam dimensions, stirrup spacing, shear key size, and axial compression ratio as variable parameters. The influence of these parameters on the hysteresis curves, skeleton curves, mechanical performance at characteristic points, stiffness degradation, and energy dissipation capacity of the joints was systematically analyzed. Based on the ultimate equilibrium analysis method for isolated bodies, a formula for calculating the flexural bearing capacity of the ring beam joints was derived, and its accuracy was verified through a comparison of calculated and simulated values. The results show that: (1) The modeling method adopted in this study can accurately reflect the failure mechanism and mechanical response of the joints; (2) The bearing capacity, ductility, and energy dissipation performance of the ring beam joint can be significantly improved by increasing the ring beam height, reducing the stirrup spacing, and adopting a lower axial compression ratio. Meanwhile, the ring beam width has an optimal range, and a value between 200 mm and 225 mm is suggested for design, while the shear key size has a minor effect on the mechanical performance of the joints; (3) For the derived bearing capacity formula, the average ratio of calculated to simulated values is 0.92, with a maximum deviation of 15%. The calculated results prove conservative, demonstrate high accuracy, and meet the requirements for engineering design.