Simulation and seismic performance of the novel CTSRC column-steel beam joint

This study proposes a numerical model for an improved type of circular tubed steel-reinforced concrete (CTSRC) joint and evaluates its seismic performance and fragility in high-rise buildings. Based on the diagonal compression strut mechanism, a method for establishing the shear force-shear strain relation for CTSRC joints was proposed and the parameters of the hysteretic rules were optimized using genetic algorithms. To assess the seismic performance of CTSRC joints within the structural system, nonlinear time-history and seismic fragility analyses were conducted on five representative frame structures, with various building heights, seismic intensities, and joint tube thicknesses. The effect of joint panel was also discussed in detail by comparing the frame behaviors with various joint modeling methods. The study results indicate that the CTSRC joints designed according to the current code exhibit excellent seismic performance and satisfy the desirable design principle of “strong joint and weak member”, with the collapse margin ratio (CMR) exceeding 7.9. Compared to the model regarding the joints as common nodes, the frames considering the joint effect shows a 30.4 % lower collapse probability under severe earthquakes and a 3.7 % higher CMR, due to the consideration of joint stiffness and less-severe stiffness degradation. Increasing the joint tube thickness can effectively reduce the maximum shear strain and delay the joint damage, but its effect on improving the collapse resistance is limited. Finally, the analysis results are further discussed and the simulation and seismic design suggestions are proposed for the improved CTSRC joints.