Mechanical Behavior And Design Of Elliptical Concrete-filled Steel Tube Members Under Combined Forces

Elliptical concrete-filled steel tube(ECFST)is a composite member with new section shape,obtained by filling in steel tube with core concrete.The circular and square concrete-filled steel tubes tend to have high bearing capacity,low weight and strong plasticity.These advantages result from the confinement effect of concrete-filled steel tubes,so that its material properties can be fully exhibited.Its unique streamlined appearance further meets the demand of architectural aesthetics.In addition,the corresponding lateral stiffness in the long axis and short axis directions provides strong axis and weak axis favorable to the structure,and effectively reduces the impact of water flow on the component.Therefore,the new ECFST has recently been adopted in many areas including airport terminals,bridge piers,railway stations,etc.However,the academic study on ECFST is still limited.Among the existing work,most of them only focus on the single stress state of axial compression,pure bending or pure torsion,which impedes the potential application and development of ECFST in engineering projects.In our paper,we fully consider the material’s section characteristics.Specifically,we propose an equivalent constitutive model of ECFST.Based on the new model,we adopted the ABAQUS numerical analysis and comprehensively tested the effect of a group of variables on the performance of ECFST under the composite stress.The specific work is as following:(1)Based on the equivalent constitutive model of ECFST,this paper establishes the numerical analysis model of the component under the combined stress of compression and torsion.The stress mechanism and failure mode of the component under the same condition is discussed.This paper also analyzes the effect of steel strength,concrete strength,diameter thickness ratio,long short axis ratio and section size on the combined stress performance of ECFST,and proposes the formula of the bearing capacity of ECFST under combined compression and torsion.(2)Based on the equivalent constitutive model of ECFST,this paper establishes the numerical analysis model of the component under the combined stress of bending and torsion.The stress mechanism and failure mode of the component under the same condition is discussed.This paper also analyzes theeffect of steel strength,concrete strength,diameter thickness ratio,long short axis ratio and section size on the combined stress performance of ECFST,and proposes the formula of the bearing capacity of ECFST under combined bending and torsion.(3)Based on the equivalent constitutive model of ECFST,this paper establishes the numerical analysis model of the component under the combined stress of compression and bending.The stress mechanism and failure mode of the component under the same condition is discussed.This paper also analyzes the effect of steel strength,concrete strength,diameter thickness ratio,long short axis ratio and section size on the combined stress performance of ECFST,and proposes the formula of the bearing capacity of ECFST under combined compression and bending.(4)Based on the equivalent constitutive model of ECFST,this paper establishes the numerical analysis model of the component under the combined stress of compression,bending and torsion.The stress mechanism and failure mode of the component under the same condition is discussed.This paper also analyzes the effect of steel strength,concrete strength,diameter thickness ratio,long short axis ratio and section size on the combined stress performance of ECFST,and proposes the formula of the bearing capacity of ECFST under combined compression,bending and torsion.(5)Based on the equivalent constitutive model of ECFST,this paper analyzes the effects of four different loading paths on the ultimate bearing capacity of ECFST under compression,bending and torsion,and determines the effect of the order of exerted forces on calculation.