Pseudo-dynamic response and analytical evaluation of blind bolted CFT frames with BRBs

This paper presents the experimental and analytical studies on the blind bolted end plate concrete-filled steel tube (CFT) composite frames with buckling-restrained braces (BRBs). A series of pseudo-dynamic tests (PDTs) on two 2/3-scaled two-story, one-bay blind bolted end plate CFT (BECFT) composite frames with BRBs showed that the novel dual system exhibited good hysteretic behavior and high ductility. The moment capacity, initial rotational stiffness, rotation capacity and the mathematical moment-rotation model of a BECFT composite joint were systematically analyzed and modified to some extent. Meanwhile, the shear force-deformation relation of a CFT panel zone was suggested and checked for its applicability. Furthermore, the macroscopic finite element (FE) model incorporating semi-rigid characteristic of the joint and shear response of the panel zone was developed by OpenSees program. The numerical analytical results would match better with experimental data when the FE model took the gusset plate stiffness into account in comparison with other models neglecting this case. Both experimental and FE analytical results indicated that the BRBs were in elastic state to provide great lateral stiffness and resistance under small earthquakes, and they yield first to stably dissipate energy under severe earthquakes. The combination of BECFT composite frames with BRBs will extend the feasibility of the novel dual system in high- or even super high-rise buildings.