Study On Mechanical Behavior Of Square CFRP-Steel Composite Tubed Steel-reinforced Concrete Columns

There are few studies on square CFRP-steel composite tubed SRC columns,and the studies on the influence of different steel section forms on the mechanical properties of the structure are even less.Therefore,based on the previous research,this paper proposes a square CFRP-steel composite tubed steel reinforced concrete column with a new steel section form,in order to explore the feasibility of increasing the confining effect by increasing the confining range of section steel.The influences of steel tube thickness,CFRP layer,section area,section form and stress state of steel tube on the mechanical properties of the specimens were discussed.In this paper,experimental research,theoretical analysis and numerical simulation of the axial compression performance of square CFRP-steel composite tubed SRC columns are carried out.The specific research works are as follows:（1）Conduct the axial compression test of 17 square CFRP-steel composite tubed SRC columns and 2 square SRC filled steel tube columns.The macroscopic stress condition of the specimen is presented by showing the failure mode of the specimen.The curves of the relationship between axial load and axial displacement,the relationship between various parameters and the increase in bearing capacity,and the relationship between various parameters and ductility are drawn,providing reliable test data for subsequent research.The test results show that increasing the section area and the thickness of the steel tube can effectively improve the bearing capacity and deformation capacity of the specimen.Increasing the thickness of CFRP can effectively increase the constraint on the lateral expansion of core concrete,the bearing capacity and change the mechanical properties of the specimen after the first peak value.However,the ductility of the specimen will decrease with the increase of the thickness of CFRP.If the steel tube is not directly subjected to axial force,the buckling of steel tube under axial force at the beginning of loading will weaken effectively,thus improving the deformation ability and mechanical properties of the specimens.The steel section forms have an obvious influence on the bearing capacity and deformation capacity of the specimen,and Lshaped steel is better than B-shaped steel and N-shaped steel.（2）The curves of the axial and lateral strain and the comparison of the axial strain of the specimen and the lateral strain at different positions were obtained by numerical analysis,and the influences of various parameters on the above relations were analyzed in detail.At the same time,according to the stress peeling analysis,the load-steel tube stress curve is obtained.The radial interaction between steel tube,CFRP and core concrete was determined by force equilibrium condition was deeply analyzed.（3）By using the finite element analysis software（ABAQUS）,the finite element model of square CFRP-steel composite tubed SRC columns under axial compression is established by selecting the befitting element,grid,contact model and constitutive model of material.The validity of the finite element model is verified by comparison with test specimens.Then,based on the model,the effect seven parameters such as section steel area,section steel flange width,section steel flange thickness,concrete strength,steel strength,steel tube thickness and the thickness of CFRP are analyzed.The results show that each parameter has different influence on the mechanical properties,and the flange width and thickness of the section steel have mutual influence with the other parameters.（4）The advantages and disadvantages of the existing axial bearing capacity model are analyzed.Based on this,the coefficient of concrete strength,yield strength of steel,thickness of steel tube,thickness of CFRP,section area of steel and form of steel are proposed by using121 finite element simulation specimens.Through regression analysis,a new formula for calculating the axial bearing capacity is obtained.The validity analysis of the existing formula and the proposed formula showing that the proposed formula has better validity and applicability,which provides theoretical guidance for the in-depth study and practical engineering application of square CFRP-steel composite tubed SRC columns.