Seismic behavior of exterior-diaphragm CFSST connections with or without PBL

Abstract

The exterior-diaphragm connection to concrete-filled square steel tubular columns with perfobond ribs (i.e., exterior-diaphragm CFSST connection with PBL) is an innovative connection formed by arranging PBL in steel tube of the small-sized-exterior-diaphragm CFSST connection. To explore the seismic behavior of this type of connection, cyclic tests of exterior-diaphragm connections with or without PBL were carried out. The failure modes, P-Δ hysteretic curves, stiffness degradation, energy dissipation capacity, shear deformation of joint region, strain distribution in diaphragm and panel zone of different specimens were compared and analyzed. On this basis, the tensile force transfer paths in different connections were compared by FE numerical simulation quantitatively. It is found that PBL carry a considerable portion of the tensile forces from steel beam flanges and transmit them to core concrete in joint regions, and enable the core concrete to participate in tensile load transferring and then in horizontal shear resisting of the novel connections, which greatly alleviates the stress concentrating at corners of steel tubes and exterior-diaphragm, and decreases the shear deformation and strain in joint regions. So, the stiffness, ductility, load carrying and energy dissipating capacity of exterior-diaphragm connections with PBL are improved a lot. Higher axial load level reduces the shear stiffness and strength of concrete dowels, and then deteriorates the stiffness degradation, energy dissipation capacity and shear deformation of panel zone. Even if the dimension of exterior-diaphragm is much smaller than that specified in codes, the innovative connections under common and high axial load level have good seismic behavior and fail as the yielding of steel beam flanges without obvious damage in exterior-diaphragm and steel tubes.