Experimental Study On Static Behavior Of New Type Side Joint Of Concrete-encased CFST Columns To RC Beam

Concrete-encased concrete-filled steel tubular(CFST)columns are widely used in high-rise buildings because of their high bearing capacity,good earthquake resistance,convenient construction and low cost of anti-rust,anti-corrosion and fire protection.Concrete-encased CFST columns to reinforced concrete(RC)beam is a structural form which is widely used at present.According to the existing joint configurations of concrete-encased CFST columns to RC beam joint,the application of concrete-encased CFST columns are restricted because of their complex structure(longitudinal reinforcement going through the steel tube or adding welded member)and large welding workload.In this paper,a new type of connection joint of concrete-encased CFST columns to RC beam is proposed,which is reliable in force transmission,clear in mechanical performance and simple in construction.The ring reinforcement sets in the concrete-encased CFST column is used to balance the tensile force of longitudinal reinforcement of concrete frame beam..The longitudinal reinforcement of the beam is anchored with the ring reinforcement in column in the form of buckle((?) type),bending(L type and (?) type).In order to study the mechanical behavior of the joint,this paper adopted the form of the joint structure,made the side joint specimens to carry out the monotonic load test,and then carried on the analysis through the finite element simulation software ABAQUS.The main works and research results are as follows:1)A new type of concrete-encased CFST columns to RC beam buckle-anchor joint was presented,and 6 specimens were designed to carry out the monotonic load test at the beam end.Variable parameters included three joint forms,beam longitudinal reinforcement strength grade,span height ratio of RC beam,and welded short steel bar length in type.The results showed that the bending failure of beam roots occurred in all specimens,and the longitudinal reinforcement and the ring reinforcement in column could be anchored reliably from the beginning of loading to final failure.The three concrete beam joint forms were not only simple in structure,convenient in construction,but also had good anchorage mechanism.2)The load displacement curve,rotation angle,displacement ductility coefficient and key reinforcement strain of 6 specimens under different parameters were analyzed to study the force transfer mechanism and mechanical performance of the buckle-anchor joint structure,which further proves the feasibility of the buckle-anchor structure proposed in this paper.3)Using the finite element simulation software ABAQUS to establish concrete-encased CFST columns to RC beam joint model,the monotonic loading numerical simulation analysis was carried out on the specimen,and compared with the test results analysis.The results showed that the finite element simulation result tallied with the test results and the established finite element model could reasonably and effectively simulate the stress process of the joint.4)Based on the above finite element model,the parametric analysis of the joints was carried out to study the influence of axial compression ratio,the steel ratio of columns,span height ratio,beam reinforcement ratio,the ratio of inside concrete strength to outer concrete strength,joint area stirrup ratio,and whether there is floor on the bearing capacity of the joints,which provided technical and theoretical support for the subsequent experimental research.