Seismic Performance Of Concrete-encased Concrete-filled Steel Tubular Column To Steel Beam Joints

Concrete-encased concrete-filled steel tubular(CFST)columns are being widely used in high-rise buildings.Research on concrete-encased concrete-filled steel tubular column to steel beam joints is rarely reported,and analytical study is required for the composite joints.Through experimental and analytical methods,this paper investigated seismic performance of concrete-encased concrete-filled steel tubular column to steel beam joints under both planar and spatial loading.The main achievements are summarized as follows:1.Experiments of concrete-encased concrete-filled steel tubular column to steel beam joints with slab were conducted under cyclic loading.The parameters consisted of the type of the joint(planar or spatial),the axial load ratio of column and strength ratio of beam to column.Seismic performance of the joints was investigated with different parameters.The failure modes of the joints were analyzed.The results were compared between the planar and spatial joints.It was found that compared to planar joints,the spatial joints owned lower capacity and ductility.The damage of concrete in panel zone of the spatial joints was more severe.2.Finite element analysis(FEA)model was established for concrete-encased CFST column to steel beam joints.The concrete cross section was divided into several parts according to different confinement and different material models were applied.Cumulative damage of concrete under cyclic loading and interaction between steel and concrete were considered in the FEA model.The proposed FEA model can reproduce the experimental results with good accuracy.3.The failure modes and distribution of stress and damage were investigated by the proposed FEA model.The internal forces and deformation were analyzed during the full-range loading.The shear-force transfer and the shear-resisting mechanism were described.Comparisons were made between planar and spatial joints on failure modes,ultimate strength and shear stiffness,as well as their different shear-resisting mechanism.The influence of thickness of slab on shear-force transfer and influence of loading methods on strength and stiffness of the spatial joints were analyzed.The parametric analysis was conducted to investigate influences of key parameters on the seismic performance of the joints.The paremeters included: properties of slab,stiffness ratio of beam to column,strength ratio of beam to column,the axial load ratio of panel zone,properties of panel zone and initial loading of column during construction.4.Based on the parametric analysis results,theoretical formula of shear capacity was developed for panel zone of concrete-encased CFST column to steel beam joints.A simplified shear versus shear deformation hysteretic model was proposed,which was verified by both the experimental and the FEA results.The thickness and width of the external diaphragm connecting the tube and beam flange were suggested.