Study On Axial Compression Performance Of Cold-formed Thin-walled Square Steel Tube Lightweight Concrete Column

Cold-formed thin-walled square steel tube lightweight concrete column(CSST-LCC)is a new type of lightweight component composed of cold-formed thin-walled steel and lightweight concrete.Compared with the steel column in the traditional light steel house,the component has higher bearing capacity and stability.At the same time,the infill of lightweight concrete can effectively suppress the local buckling of the outer steel tube,and its self-weight is not much different from that of the steel tube.It can be used in various low-rise and multi-story light steel houses to form a ’light steel concrete frame structure’.The structural steel members are relatively few,simple to install and low in steel consumption,and still have lightweight characteristics.In order to promote the application of CSST-LCC members in practical engineering,it is necessary to have systematic theoretical support.Therefore,by combining ABAQUS finite element numerical simulation with theoretical research,the axial compression performance of CSST-LCC is systematically studied.The following research results are obtained:(1)Three finite element numerical models of cold-formed thin-walled square steel tube lightweight concrete short column(CSST-LCSC),cold-formed thin-walled square steel tube lightweight concrete long column(CSST-LCLC)and cold-formed thin-walled square steel tube lightweight concrete pure bending member(CSST-LCPBM)were established.The three finite element models were compared and verified according to the existing test results.The results show that the peak load comparison results of the specimens are within the allowable range of error,and the simulation and test failure modes are basically the same.The load-displacement curve is in good agreement,which determines the reliability of the model.(2)The mechanical properties of short columns,long columns and pure bending members are analyzed,and the failure mode,load-displacement relationship,the whole process of stress and the stress distribution at the characteristic points are obtained.At the same time,the failure mode,bending moment-deflection relationship,bending moment-curvature relationship,the whole process of stress and the stress distribution at the characteristic points are obtained.It is found that the 0.5mm and 1mm short columns with thin steel tube wall thickness are prone to shear failure,and the 1.5mm and 2mm short columns with thin steel tube wall thickness are prone to buckling failure.The elastic working stage of the short column can continue to about80%～85% of the peak load,which is higher than that of ordinary concrete filled steel tube.The overall instability failure occurs in the long columns,and the elastic working stage of the specimens can last to about 83% of the peak load.The pure bending member is a typical bending failure.Through the maximum plastic strain of concrete,it is judged that the tensile zone of concrete will first produce cracks,and the cracks will extend to the compressive zone when the specimen is destroyed.According to the theoretical calculation,the bending moment-curvature curve of the typical specimen is calculated,and the value of the bending stiffness of the component is determined.(3)Based on the orthogonal test method,three factors and four levels of orthogonal test(including 16 CSST-LCSC models,16 CSST-LCLC and CSST-LCPBM models)were designed by selecting different steel tube wall thickness,lightweight concrete strength and section size.The influence of steel tube wall thickness,lightweight concrete strength and section size on the mechanical properties of the three components was studied by range and variance analysis.It is found that the significance of the influence of three factors on the axial compression performance of CSST-LCSC is: section size>lightweight concrete strength>steel tube wall thickness;the significance of the influence on the axial compression performance of CSST-LCLC is: section size>lightweight concrete strength>steel tube wall thickness;the significance of the influence on the flexural performance of CSST-LCPBM is: steel tube wall thickness>section size>lightweight concrete strength.(4)The finite element results are compared with the calculation formula of axial compression bearing capacity and bending stiffness of concrete filled steel tube in ’specification’.The calculation formula of axial compression bearing capacity of short column in Japanese ’AIJ’specification is selected.Considering the influence of various material parameters,the concrete strength coefficient kc in the formula is modified.According to the regression analysis of finite element analysis results,the bearing capacity calculation formula of CSST-LCSC is obtained.Similarly,the bending stiffness calculation formula of concrete filled steel tube in Japanese’AIJ’ specification is selected,and the bending stiffness reduction coefficient 0.2 of concrete in the formula is modified.According to the regression analysis of finite element analysis results,the bending stiffness calculation formula of CSST-LCPBM is obtained.Finally,combined with the Perry-Robertson formula considering the defect of the rod,the formula for calculating the stability bearing capacity of CSST-LCLC is derived,and the accuracy of the formula is verified by comparing with the finite element results.