Behavior Research And Aseismic Design Criterion On New Type Connections Of Concrete-filled Square Tubular Column And Steel Beam

Concrete-filled square steel tubular (CFST) structures have been widely used in building construction because of their excellent mechanical behavior, constructional suitability and economy in comparison to their circular counterparts. A series of new type connection details were brought forward: Through high-strength bolts-end plates (THB), Single through interior diaphragm (STI), T-shaped anchorage (A), studs on the non-welded side (S), non-welded on the fourth side of the interior diaphragm (COM). A total of 24 quasi-static experimental specimens were tested to investigate the hysteretic behavior, the strength and stiffness degradation, the energy dissipation capacity and the failure modes of the connections. The horizontal load was applied on the top of the columns. The force transfer mechanism and failure modes of A, S and COM connections were studied briefly.The experimental results showed that the THB and STI connections had excellent hysteretic behavior and ductility, and the plastic hinges formed in the beams. The punching shear cones were observed in the panel zones for the A type connections, and the energy dissipation coefficients of A type connections were between the RC joints and SRC joints. The pre-failure of the welds of studs greatly decreased the energy dissipation capacity, strength and stiffness in the case of the S type connection details. The coefficients of equivalent viscous damping of most S type connections were similar to the SRC connections at the peak load. The improved connection details were put forward for A and STI type connections.Comprehensive three-dimensional finite element models were presented for the STI test specimens, the THB test specimens and SSTI joints using the ANSYS 10.0 nonlinear finite element program. The geometric large deformation, material nonlinearity and contact nonlinearity were involved. The force transfer mechanism and hysteretic behavior of these joints were investigated. The results obtained from the finite element analysis were compared to the experimental data, and good agreements between calculated results and experimental results were found.The influences of the axial ratio, the concrete strength, the pre-tensioning force of through high strength bolts, the thickness of end plates and the stiffening plates of the end plates on the hysteretic behavior of the THB joints were systematically studied based on geometric, material and contact nonlinearities using the ANSYS finite element program. The influences of the concrete strength and the axial ratio on the SSTI joints were investigated.Based on the review of previous studies and the accurate finite element analysis of force transfer mechanism for SSTI and THB joints, the load carrying capacity models and the ultimate shear capacity formulas of the diagonal compression concrete strut were presented. Comparison between the proposed formulas and previous experimental data demonstrated that they can accurately predict the ultimate shear load carrying capacity of the panel zones. The proposed ultimate shear load carrying capacity models had specific mechanical concept and force transfer mechanism.Experimental and analytical results can guide the design and research. The proposed formulas of ultimate shear load carrying capacity of panel zones can be used for design based on further experimental verifications.