Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes ("RC beam" for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.