Experimental and analytical study on CFST column-steel beam joints with stiffening ring and stirrups under high axial compression ratio

Super high-rise structures frequently employ concrete-filled steel tubular (CFST) column-steel beam joints with stiffening ring because of its superior performance. This study examined the structural behavior of high axial compression ratio stiffening ring joints with stirrups in the column. Three 1/2-scaled joints with different stirrup arrangements and axial compression ratios were designed and tested. Apart from analyzing the hysteresis behavior, skeleton curve, stiffness degradation, energy dissipation, and steel strain of each specimen, an investigation was conducted into the failure mechanisms of the specimens under low cycle reciprocating load on the beam end. Furthermore, a three-dimensional nonlinear solid finite element (FE) model was developed for the joint. The results of the FE analysis and the experimental data agreed well regarding failure modes, hysteresis curves, and steel strain. Furthermore, the energy dissipation allocation mechanism of joints with various parameters was revealed. The results show that the seismic performance of the stiffening ring joint with stirrups was excellent, and stirrup confinement effectively improved the seismic performance of stiffening ring joints. Under a high axial compression ratio of 0.8, the joint with stirrup exhibited bending failure at the beam end, avoiding the phenomenon of column end bending failure in traditional specimens. In addition, the stiffening ring joint underwent a transition from beam energy dissipation to column energy dissipation when the beam-column flexural capacity ratio reached 1.39. The study's findings can serve as a guide for engineers using stirrups in square CFST column-steel beam joints with stiffening rings.