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

Concrete-encased concrete-filled steel tubular(CFST)columns have been applied in building and bridge engineerings.However,limited study is available on the design methodology,the constructional details and the seismic performance of the concrete-encased CFST column to RC beam joints.This paper presents an investigation on seismic performance of concrete-encased CFST column to RC beam joints.The simplified hysteretic model was proposed as well as the fibre-based joint model.The main research work and results are summarized as follows:1.The hysteretic tests were conducted on thirteen concrete-encased CFST column to RC beam joints.The test parameters include axial force ratio(0.2-0.6),beam to column bending strength ratio(0.2-1.2),beam to column linear stiffness ratio(0.12-5.1),joint type and connections.The joint types involved rectangular column exterior joint,rectangular column interior joint,square column interior joint,double beam joint,staggered joint and unsymmetrical joint.The connection configuration involved the ring plate connection,the sleeve connection,the wing plate connection and the anchorage connection.The seismic performance of the joints was examined through experiments,in terms of the strength and stiffness,degradation and ductility,deformation capacity and energy dissipation capacity.2.A detailed high-fidelity finite element analysis(FEA)model was established to simulate the concrete-encased CFST column to RC beam joint under cyclic loading.The material nonlinearity and geometric nonlinearity,the cracking behaviour of concrete and the interaction between concrete and steel were considered in the FEA model.The FEA model was verified by the test results,which indicated that the FEA model was able to reflect the cyclic behaviour of the concrete-encased CFST column to RC beam joint.3.Based on the experimental and analytical results,the concrete-encased CFST column to RC beam joint was analyzed thoroughly.The failure modes and ultimate state were analyzed firstly.Then the internal force,deformation distribution and stress development were studied based on the FEA model.A parameter analysis was conducted on the joint,including the dimensional parameters(steel ratio,the ratio of the steel tube diameter to sectional width,column volume stirrup ratio,column longitudinal rebar ratio,beam volume stirrup ratio,beam longitudinal rebar ratio,beam shear span,beam effective height to width ratio,slab rebar ratio,width of slab,thickness of slab,ring plate width,ring plate thickness to longitudinal rebars diameter ratio,panel zone volume stirrup ratio,panel zone effective height to width ratio),material parameters(outer concrete strength,core concrete strength,yield strength of column stirrup,yield strength of column longitudinal rebar,yield strength of steel tube,yield strength of beam stirrup,yield strength of beam longitudinal rebar,yield strength of ring plate)and column axial load level.Key parameters affecting the failure modes were identified.4.Based on the results of parameter analysis,the joint design methodology of the concrete-encased CFST column to RC beam joint was proposed,including the bearing capacity and constructional details.The simplified hysteretic model was also proposed.Furthermore,a fibre-based joint model was proposed and applied in the structural analysis.