Study On Equivalent Stress-Strain Relationship Of Steel Tube Of Square Concrete-Filled Steel Tube

With the continuous development of composite structures,the square concrete-filled steel tube possess the advantages of high capacity,good ductility and good energy dissipation capacity,it had become an increasing emphasis on the engineering sector,and also used more and more widely in the high-level structure.However,the theoretical and experimental studies are focused on circular concrete-filled steel tube columns,there is less theoretical analysis on the squre concrete-filled steel tube column,and design and calculation methods are not yet ripe,therefore,there is a need for square concrete-filled tubular column finite element model and further research.Based on the previous study of the square concrete-filled steel tube,finite element analysis method and fiber model is establish to study the mechanism.The work focused on the analysis of the equivalent uniaxial constitutive relation curve of steel and the seismic performance of the square concrete-filled steel tube.This provide a theoretical basis for engineering application. Main work as follow:(1)A three-dimensional nonlinear finite element model is developed in this article. The steel tube is modeled using plasticity model which is isotropic elasticity and plasticity model with a Von Mises yield surface.In the model,the effect of the bond between steel tube and concrete is considered.The core concrete is modeled using concrete damaged plasticity model with a Drucker-Prager surface to describe the concrete brittle damage in the low pressure and plastic flow in high confining pressure.The role of the bond-slip of the two material,hard contact in the normal direction and Coulomb friction model in tangential direction is considered,it also assumed that the initial geometry defects of the pipe is half-wave distribution.(2) According to the basic theory of finite element,mechanical properties of square concrete-filled steel tube are studied.The effects of different parameters such as strength of concrete and steel,width-wall thickness ratio (aspect ratio) to the stress-strain relationship curves are considered.Mechanics concept specific and form simpleness calculational model is proposed,equivalent axial stress-strain relationship of steel tube for fiber-based model numerical analysis is put forward.(3) A fiber beam-Column model is establish by DRAIN-2DX to analysis the square concrete-filled steel tube under horizontal load - horizontal displacement,P-â–³curve is obtained by using equivalent constitutive relation of materials from the finite element.