Study On Unidirectional Eccentric Compression Behavior Of Square High Strength Concrete Filled Steel Tubular Columns With Built-in Reinforcement Cage

In order to improve the ultimate bearing capacity and ductility of the structure,reduce the size of members and reduce the self weight of the structure to get a better service space,scholars at home and abroad have conducted in-depth research on the mechanical properties of concrete filled steel tubular and gradually put it into engineering application.In order to further improve the performance of members,scholars at home and abroad use high-strength steel tube and high-strength concrete as the basic materials of composite structures to improve the performance of members.However,because the use of high-strength materials will lead to worse ductility of the members,and there is a weak Constraint Zone in the concrete-filled square steel tubular,some improvement measures can be taken to improve the mechanical properties of the members.However,at present,the research is less and mainly focused on the axial compression properties of the specimens.In this paper,the reinforced cage concrete-filled steel tubular composite column is proposed by placing the specimen in the reinforced cage.The mechanical properties of the square high-strength concrete-filled steel tubular column with the reinforced cage in the steel tube under axial compression and unidirectional eccentric compression are studied.The main research contents are as follows:(1)18 concrete filled steel tubular columns were tested.The main parameters of the specimen are: slenderness ratio,section width thickness ratio,loading eccentricity and the form of internal reinforcement cage.After the loading test,the failure mode,load axial displacement curve,load column lateral deflection curve,specimen lateral deflection deformation curve,and load strain curve of steel pipe and longitudinal reinforcement are obtained.The ultimate bearing capacity,stiffness,ductility and failure mode of concrete filled steel tubular columns are analyzed.(2)After selecting the appropriate material constitutive model and reasonable contact relationship,the finite element simulation analysis of the specimen is carried out,and the rationality of the finite element model is verified by comparing the test results.The stress analysis of concrete,steel pipe,tie bar and other components is carried out to deeply explore the stress change and cooperative working mode of each component during the whole loading process of the specimen.(3)Select the verified finite element model,expand the parameters of the specimen,draw the relationship curve through the analysis results,and further explore the factors affecting the mechanical properties of the specimen.The results show that the restraint effect between steel tube and core concrete of specimens without reinforcement cage is mainly concentrated in the corner area,while the reinforcement cage and steel tube restrain the core concrete together during the loading process of specimens with built-in reinforcement cage.The built-in reinforcement cage in the specimen can significantly improve the mechanical properties of the specimen,and changing the section form of the reinforcement cage has little effect on the mechanical properties of the specimen.The ultimate bearing capacity of square high-strength concrete-filled steel tubular columns with built-in reinforcement cage decreases with the increase of eccentricity,slenderness ratio and width thickness ratio.Changing the width thickness ratio and slenderness ratio of the specimen has little effect on the ductility of the specimen,but the greater the eccentricity,the better the ductility of the specimen.The initial stiffness decreases with the increase of eccentricity,slenderness ratio and width thickness ratio.