Seismic Behavior Of Prefabricated Joint Between CFDST Column And Steel Beam

Studies has demonstrated the superior seismic performance of the concrete-filled doubleskin steel tubular(CFDST)columns,it has been used as load-bearing members of buildings and bridges.There were few studies on the prefabricated CFDST column-beam joints,which limited the application of the CFDST columns in prefabricated structures.Therefore,a prefabricated joint between the CFDST column and the steel beam was proposed in this paper.Tests,finite element simulations and theoretical analyses were carried out with the seismic performance and analytical model of the joint as the research objectives.The main research contents and results are as follows.1.A prefabricated joint between the CFDST column and the steel beam was proposed.The joint allows for modular production and assembled construction,and it mainly includes the CFDST column module with reserved bolt holes and the steel beam module with endplate,and fully bolted constructions are required on-site.Quasi-static tests were performed on twelve joints.The parameters included the endplate type,the endplate thickness,the axial compression ratio of the column,the bolt diameter,the filling degree of concrete,and the cross-sectional shape of the inner tube.Damage characteristics of the joints contained bending of endplates,local buckling of steel beam flanges,cracking of welds,and warpage fracture of bolts.The loaddisplacement hysteretic curves were plump.The displacement ductility coefficients were great.The stiffness degradation coefficients were steady.The stiffness was great,and the accumulated energy dissipation values were high.The above results indicate that the joint has good seismic behavior.Then,the effects of each parameter on the seismic indexes were analyzed such as the bearing capacity,ductility,energy dissipation capacity and so on.2.Thorough and accurate finite element analysis(FEA)models of the joint were created with reference to the tests.Cumulative damage of concrete under cyclic loading,the interaction between steel components,and the interaction between steel tubes and concrete were considered in the FEA model.Compared with test results,the failure modes and loaddisplacement relationships obtained from the FEA were less inaccurate,which verified the accuracy of the FEA model.Based on the FEA results,the stress variation of each component of the joint throughout the loading was analyzed,and parametric analysis was performed in terms of both geometric parameters and material properties.The optimization measures for the extended endplate joint and flush endplate joint were proposed,respectively.3.Based on the energy dissipation principle and load-displacement skeleton curve,a structural damage assessment model was established.Based on the experimental phenomena,the damage evolution law of the prefabricated joints between the CFDST column and steel beams was analyzed by the model.Damage assessment criteria for two kinds of endplate joints were proposed,respectively.Based on the experimental results and FEA parameter analysis,the effects of each parameter on the damage evolution of the joint were analyzed.4.A theoretical model for the moment-rotation relationship of the joints was established,which included the initial rotational stiffness,the ultimate moment,and the shape parameter.Based on the component method,the analytical model for the initial rotational stiffness of the joint was established.Depending on the forces and constraints,the components were simplified as the corresponding mechanical models.Considering the possible failure modes,a calculation method for determining the ultimate moment of the joint was proposed.Based on the superposition principle,the shear bearing capacity model of the core area of the joint was established.Then,the calculation methods of the shear bearing capacity of the outer steel tube,the sandwich concrete,the inner steel tube,and the core concrete were proposed,respectively.Finally,the strength design method and the constructional measures of the joint were proposed.The proposed prefabricated joint in this paper can realize the prefabricated construction of the CFDST structure.It also has reliable seismic performance.Besides,the proposed FEA models and the theoretical models have high accuracy and computational efficiency,which can be used in the structural design of practical engineering.The research results provide a reference for the application of this type of system.