Experimental Study On Axially Compressive Behavior Of Rectangular Concrete-filled Thin-walled Steel Tube Short Column

Because of its excellent mechanical properties,CFST composite specimens are widely used in engineering.In recent years,the research and application of the rectangular section have also made great progress.In this paper,the failure mechanism and mechanical performance of rectangular concrete-filled steel tube(CFST)are analyzed from the aspects of combined stress,cooperative work,size effect and local buckling of the steel tube wrapped around.Combined with the test,the failure process,stress mechanism and performance of the thin-walled CFST short columns under axial compression are studied and analyzed by numerical simulation,and the collaborative work of steel tube and core concrete is discussed.Based on the mechanism and influencing factors,this paper analyzes and discusses the restraining effect of rectangular concrete-filled thin-walled steel tube(RCTST)short columns on the core concrete and the analysis method of its bearing capacity,and derives the calculation formula of the bearing capacity under axial compression.(1)The tests of thirty-two RCTST short columns under the axially compression are carried out by using the section width ratio,the concrete strength,and the wall thickness of steel tube as experimental parameters.The behaviors of specimen,such as the failure process,failure mode,ultimate bearing capacity,deformation behavior are analyzed.The experimental research shows that the local buckling of broad face of steel tube occurs firstly under axially load.The final failure mode and bearing capacity of the specimen are related to the buckling of broad face of steel tube.The confinement effect of RCTS short columns are less than square CFST short columns and circular CFST short columns,due to the local buckling of broad face of rectangular steel tube occurring easily.The confinement effect is greatly affected by the section width ratio and the wall thickness of steel tube.The ultimate bearing capacity and deformation behavior of RCTST short column are related not only to the section width ratio and the wall thickness of steel tube,but also to the compressive strength ratio of steel tube to core concrete.(2)In this paper,the finite element method is used to simulate the process and performance of the axial compression of RCTST short columns.The numerical simulation analysis shows that the core concrete with rectangular section is in the state of non-uniform lateral compressive stress,and there is a weak restraint zone.The lateral restraint provided by the thin-walled rectangular steel tube to the core concrete is relatively small,and the restraint strength and deformation capacity of the core concrete can not be fully distributed,thus affecting the axial bearing capacity,deformation performance and ductility of the thinwalled rectangular steel tube concrete.From the division of section stress and the buckling deformation diagram of the thin-walled steel tube,it can be seen that the stress distribution and size of the core concrete have a strong correlation with the buckling deformation of the steel tube.The buckling of the thin-walled steel tube significantly affects the stress distribution and size of the core concrete,and ultimately affects the bearing capacity and deformation of the component.The simulation results are in good agreement with the experimental phenomena,failure modes,load deformation curves and the load-strain relationship of steel pipes.(3)Based on the experiment and numerical simulation,the confined zone model of core concrete and the failure criterion of thin-walled steel tube are established,and the calculation formula of bearing capacity of RCTST short columns under axial compression is established.The calculated results are in good agreement with the experimental and numerical simulation results.Based on the formula of bearing capacity,the performance of RCTST compression specimens is analyzed.The research and analysis show that the general calculation theory of CFST composite structure can not be directly applied to the r RCTST composite specimens.(4)In order to improve the performance of RCTST short columns,the performance of reinforced RCTST stiffening ribs are simulated.The simulation analysis parameters are the section width ratio,the height and arrangement of stiffeners,etc.The mechanism and degree of improving performance of stiffeners are studied and analyzed.The results show that the stiffener can significantly improve the mechanical properties of the composite members.The research results have important reference value for analyzing and improving the performance of steel tube-concrete composite shear wall.