Study On Mechanical Behavior Of Concrete Filled Steel Tubular Columns Subjected To Bending,Shearing And Torsion

To investigate the mechanical properties and failure mechanism of Concrete Filled Steel Tubular(CFST)columns under compound forces,following work has been done in this paper:1)An experimental study of 10 CFST short column specimens under reversed cyclic and monotonic bending moment,shearing force and torsion moment has been conducted.The load-displacement curve and the strain distribution law of the CFST short columns under reversed cyclic and monotonic loading are obtained.Test results show that CFST columns perform fine load carrying capacity and plastic properties and failure modes depends on the bending-torsion ratio and shear-span ratio.When specimens subjected to bending moments,the axial cross section deformation meets the “plane section assumption”.Under pure torsion cyclic loading,the skeleton curve and the monotonic loading curve almost coincide.2)Fine finite element modeling and calculation of CFST columns are carried out by using ABAQUS.While modeling,the constitutive model of the material is the essential factor to consider.To confirm the accuracy of the finite element model,it is necessary to compare the calculated results and the experimental results.Finite element method is also used in the next number of parameter analysis.3)In this paper,several factors: steel yield strength,concrete strength and cross section dimension are considered.Through the analysis of large number of finite element calculation,the influence of these factors on the pure twist,pure bending and pure shear capacity of CFST columns is studied;the load-displacement curve and the stress-strain distribution law are obtained.The simplified calculation formulas for pure twist,pure bend and pure shear of CFST columns are recommended.Based on the finite element calculation,the initial stiffness and the using stage stiffness of the CFST columns under pure twist,pure bending and pure shear are obtained by the load-displacement curve.The stiffness of the CFST columns is calculated by regression analysis method.The influence of length-diametier ration is considered when calculating the torsional bearing capacity of CFST columns.4)In this paper,the interaction relation between the bearing capacity of CFST columns under the bending-shear-torsional composite force is studied by using a large number of finite element calculations.The interaction relation equation of CFST columns under bending,shearing and torsion is obtained.