Experimental and analytical investigation on post-tensioned beam-to-CFST column connection using wedge-shaped devices

A post-tensioned (PT) beam-to-column connection using wedge-shaped devices (WSDs) and concrete-filled square steel tubular (CFST) column is proposed in this study. The WSD is designed to eliminate the gap between the nut on the energy-dissipating (ED) bar acting as “fuse” and the end plate of the beam when the ED bars yield during an earthquake. Cyclic tests were carried out on four 2/3 scaled specimens to investigate the mechanical behaviour and seismic behaviour of the connection considering the effect of the initial PT force, the area of ED bars and the use of WSDs. Findings demonstrate that the connections using WSDs exhibited desired flag-shaped hystereses before the bottom of the U-shaped surface on the wedge contacted with the ED bar. All the specimens were able to recentre while the structural elements behaved elastically after each cyclic loading and the “fuses” were replaced after each test. Besides, the self-centring behaviour was insensitive to the initial PT force and the size of ED bars. Smaller amount of energy dissipation and initial rotational stiffness were observed after the bottom of the U-shaped surface contacted with the ED bar. Moreover, simplified equations were developed to predict the mechanical behaviour of the PT connection and showed good correlation compared with the experimental results, which can be used in a non-linear structural analysis program.