Bending Behavior Of Square Concrete-filled Steel Tubular Columns

Concrete Filled Steel Tubular (CFST) is made up by the special way. Because it has a series of superior mechanizes performance, has got more and more extensive application at domestic and abroad. With CFST increasing in actual projects, it is necessary to make further study to mechanical behaviors of CFST.Based on the previous study of the square CFST, the finite element software ABAQUS was used to establish finite element model of concrete filled square CFST under axial load, then the work focused on the analysis of the equivalent uniaxial constitutive relation curve of steel. The level bending moment-curvature curve under bending load were studied by nonlinear dynamic response analysis procedure DRAIN-2DX.Details are listed bellows:(1) A three-dimensional nonlinear finite element model is developed in the paper. The steel tube is modeled using plasticity modeled which is isotropic elasticity and plasticity model with a Von Misses yield surface. 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.(2) The longitudinal stress-strain curves of square CFST under monotonic loading was studied. The effects of different parameters such as strength of concrete and steel, width-wall thickness ratio to the stress-strain relationship curves were considered. Mechanics concept specific and form simplified calculation model was proposed, equivalent axial stress-strain relationship of steel tube for fiber-based model numerical analysis was put forward.(3) A fiber beam-column model was established by the nonlinear dynamic analysis program DRAIN-2DX to analysis the square CFST under monotonic loading. The steel tube is modeled using equivalent stress-strain of CFST under axial pressure. The concrete is modeled using simplified equivalent stress - strain relation. In the model, the 15 units (fiber beam-column units) was selected, a P-Δeffect was considered.(4) The influence to moment-curvature curve of the yield strength of concrete, axial compression ratio and yield strength of steel was analysis. Based on theoretical analysis of the moment - curvature curves simplified calculation model and hysteretic rules was put forward.