Seismic performance of X-shaped stud steel reinforced concrete columns under composite torsion

To investigate the seismic performance of X-shaped steel-reinforced concrete (SSRC) columns subjected to combined torsion, eleven specimens were designed with varying parameters including torsion-to-bending ratio, axial load ratio, steel ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and stud spacing. Quasistatic loading tests were conducted to observe the failure process and failure modes. The results indicate that the SSRC column ultimate failure mode is predominantly determined by the stirrup reinforcement ratio, leading to either flexural-torsional failure or torsional failure. The torque-torsion angle hysteresis loops exhibit a pinched, inverted "S" shape, while the moment-displacement hysteresis loops display a more pronounced, spindle-like shape. The axial load ratio and torsion-to-bending ratio exert the most significant influence on the seismic performance of the specimens. As the steel ratio, longitudinal reinforcement ratio, and stirrup reinforcement ratio increase, the ductility, energy dissipation capacity, and other seismic performance indicators of the components improve to varying degrees. Among these parameters, the steel ratio has the most pronounced impact on energy dissipation capacity. When the steel ratio increases from 2.39 % to 2.90 %, the energy dissipation capacity of the component improves by 36.8 %. Reducing the stud spacing appropriately enhances the seismic performance of the component, but excessively sparse or dense stud spacing can have detrimental effects. Based on the experimental results and existing research, a formula for calculating the torsional capacity of X-shaped SSRC columns subjected to combined torsion was developed using the superposition principle. The calculated results align well with the experimental results, with an average error within 5 %.