Study On Mechanical Behaviour Of Concrete Filled Steel Tubular Column With Inner Core Column To Steel Beam External Stiffened Ring Connections

In recent years,FRP material has attracted attention because of its advantages of light weight,high tensile strength,good performance in corrosion resistance and fatigue resistance.After FRP is installed in the concrete-filled steel tubular column,it can solve the problem of insufficient restraint of the diagonal concrete of square steel tube,give full play to the performance of the material,greatly improve the bearing capacity of the column,and the combination form of the inner circle and the outer circle is convenient for the connection of beams and columns.The research on this kind of cross-section combination mainly focuses on the axial compression members,and there is little research on the joints,and the beam column joints are the key parts of the frame structure,so it is necessary to study the mechanical properties of this kind of joints.In this paper,the mechanical properties of this kind of joint under the reciprocating load are studied and analyzed through the experimental research and finite element simulation.The main contents are as follows:(1)This paper analyzes the constitutive relationship of concrete,steel,FRP,UHPC and other materials,sets up the contact and connection,mesh division,boundary conditions of the joint model,uses ABAQUS software to establish the finite element model,and verifies the correctness and rationality of the joint model.(2)The finite element method is used to analyze the influence of the change of the parameters on the failure mode of the joint when the constraint changes the diameter of the core and the constraint strength.The results show that the failure of the joint specimen is mainly manifested in the local yield deformation failure of the stiffened ring plate near the beam end of the joint area,the flange of the steel beam and the web.The performance of the core column is to give full play to the economic factors.Under the condition of meeting the vertical bearing capacity demand of the steel column,the straight diameter of the core column and the thickness of the FRP pipe should be used as small as possible.The quasi-static test of 4 CFST column steel beam external strengthened ring joints with internal core columns is designed based on FRP pipe thickness,core column diameter and axial compression ratio.(3)In this paper,the seismic behavior of concrete-filled steel tubular column steel beam joints with core columns is analyzed.The hysteretic curves of the joints are relatively full,the displacement ductility and energy consumption capacity of the joints are good.The influence of parameters such as steel ratio of column section,thickness and width of ring plate,axial compression ratio,thickness of FRP pipe and diameter of core column on the joint skeleton curve is analyzed.(4)According to the results of the analysis,the shear capacity of the beam end web and flange is analyzed,and the shear capacity of the joint at the yield failure of the beam end is deduced;then the stress of the steel tube,sandwich concrete,outer ring plate and FRP confined UHPC core column outside the core area of the joint is analyzed,and the shear capacity formula of the core area of this type of joint is established by superposition of each part.The upper and lower limit values of the shear capacity of the joint are obtained.The results of the formula are in good agreement with those of the finite element simulation.