Study On The Pseudo-static Performance Of The Inner Tube Ribbed Square Sleeve Hollow Sandwich Steel Tube Column-steel Beam Joint

Recycled concrete-filled hollow sandwich steel tubular column steel beam joint inherits the advantages of hollow sandwich concrete-filled steel tubular members,such as light weight,good bending capacity and so on.Although the connection structure of hollow sandwich concrete-filled steel tubular joints can learn from solid concrete-filled steel tubular joints,there are obvious differences between them.Compared with the solid concrete-filled steel tubular joint,the difference of hollow sandwich concrete-filled steel tubular joint is mainly the size of inner tube（which can be reflected in the hollow ratio of column section）and the transmission mode of internal force.If the inner pipe is connected with the beam,the integrity of the joint is good,but the construction is particularly complex and may cause large welding residual stress.If there is no connection between the inner tube and the beam,the test shows that the local deformation of the inner tube in the joint area is large,which will affect the load shared by the inner tube in the joint.In this paper,the inner tube stiffened circular hollow sandwich concrete-filled steel tubular column steel beam joint is proposed to strengthen the connection between the inner tube and the concrete by adding ribs to the inner tube in the joint area,so as to ensure the coordination of the inner and outer steel tubes and the sandwich concrete and facilitate the construction.Based on experimental study and finite element simulation,this paper discusses the influence of the parameters of the joints on the hysteretic curve,strength degradation,stiffness degradation,ductility and energy consumption of the specimens.The main contents of this paper are as follows:（1）In this paper,the quasi-static tests of 12 concrete-filled square hollow sandwich steel tubular column steel beam joints are carried out with four parameters of concrete type,rib length,axial compression ratio and void ratio.The seismic indexes of the joints,such as strength degradation,stiffness degradation,ductility and energy dissipation capacity,are analyzed.（2）In this paper,ABAQUS finite element software is used to establish the finite element analysis model of recycled concrete-filled steel tubular steel beam joint with inner tube stiffened circular hollow sandwich.According to the mechanical characteristics of the material,the appropriate constitutive relationship model of steel and concrete is selected,and the reasonable boundary conditions are set according to the experimental loading mode.The finite element simulation results are compared with the experimental results,and the results show that the failure of the specimen is obvious The shape,hysteretic curve and bearing capacity are similar to the test results.The rationality and accuracy of the finite element modeling are verified.（3）Based on the verification of the rationality and accuracy of the established finite element model,the load displacement curve,moment rotation curve and shear shear strain curve of the joint under the change of rib length,rib width,void ratio,axial compression ratio,beam column bending capacity ratio,recycled concrete strength and other parameters are analyzed systematically by using ABAQUS finite element software,The parameters affecting the seismic performance of the joints are determined.（4）Through a large number of finite element model analysis,the failure mode of recycled concrete filled steel tubular column steel beam joint with inner tube stiffened square sleeve hollow sandwich is related to the ratio of beam to column bending capacity.When k_m≦0.97,the steel beam of this type of joint is twisted;when 0.97m≦1.21,the shear failure of this type of joint occurs;when k_m>1.21,the recycled concrete-filled square hollow sandwich steel tubular column is bent.（5）The stress state of the external steel tube,core concrete and inner circular steel tube is analyzed when the internal tube reinforced square sleeve circular hollow sandwich steel tube recycled concrete column steel beam joint is under the peak load under the low cycle reciprocating load.The analysis shows that the stress concentration of the inner pipe,outer pipe and core concrete in the joint area is relieved by the stiffener.