Experimental Research On Seismic Behavior Of Interior Joints In The Composite Frame Consisting Of CFST Special-Shaped Section Columns And Steel Beams

Based on the seismic performance theory and calculation method of round and rectangular section steel tube concrete beam-column joints,4one half scaled models of the weak joint and the strong joint were designed and manufactured, and the destruction test on the model was carried out under vertical stable loads and lateral cyclic loads, by taking interior joints in the composite frame consisting of concrete-filled steel tubular(CFST) crisscross section columns and steel beams as the research object. The stress process and failure form of each jiont model were observed under different axial compression ratio, the hysteretic performance, strength and stiffness degradation, ductility and energy dissipation capacity, strain distribution and panel zone deformation were analysed, stress mechanism was discussed.Test results are described as follows:(1) All the joint model hysteresis curve show basically the full spindle shape, and the knead shrink is not obvious, stiffness degradation is slow, this joint style has good plastic deformation and energy-dissipation of the performance. All specimens possessed better ductility, the displacement ductility coefficient between layers μ reach3.99to5.65, equivalent viscous damping coefficient ht reach0.603to0.631, reasonable design of CFST crisscross section columns and steel beams joints meet the structure seismic design requirements.(2) The failure mode of the weak joint is the shear failure in the panel zone, weld and concrete in the panel zone crack, the maximum shear angle is83%～95%of limit intersection angle, the main structure deformation is shear deformation in the panel zone; The failure mode of the strong joint is the bending failure at the beam end, yield occured at the beam flange, then plastic hinge occurred, the maximum shear angle is48%of limit intersection angle only, shear deformation in the panel zone is not the main factor in structure deformation.(3) Axial compression ratio affects the shear bearing capacity and ductility performance of the joints to some extent, when the axial compression ratio increase, the shear bearing capacity of the joint will increase, but its ductility performance will reduce.The ductility coefficient and energy dissipation capacity of MJ-4is better than that of the other three specimens. It means bending failure mode has better seismic performance.(4) The failure mode of the weak joints occurred at the webs weld in the panel zone, but weld should avoid setting in the main stress position in construction process;The corner of the column and stiffening ring appeared buckling or weld, stiffening rib should be set in the corner to avoid appearing buckling.The study on the special-shaped section CFST column-steel beam joints still in initial stage, this topic provided reference for theory of special-shaped section CFST structure system, and put forward some engineering proposals also.