Research On Eccentric Compressive Behavior Of Round-ended Concrete-filled Steel Tubular Members

With good mechanical properties and excellent architectural shape,round-ended concrete filled steel tubular members have been widely used in bridge engineering.However,studies on the eccentric compression performance of these members are limited.Combined with eccentric compression test,numerical calculation and theoretical analysis,the eccentric compression behavior and bearing capacity of round-ended concrete filled steel tubular members are researched in depth in this paper.On the basis of previous studies,the theory of confined zoning of core concrete and the equivalent uniaxial constitutive relationship model are proposed,the eccentric compression test of concrete members is carried out,the numerical analysis model of eccentric compression of concrete members is established,and the eccentric compressive properties of concrete filled steel tubes with different cross-section types are compared.Based on the test results and theoretical analysis,a formula for the eccentric bearing capacity suitable for engineering practice is proposed.The specific research contents,methods and conclusions are shown as below:(1)The mechanical mechanism of concrete filled round-ended steel tubular members subjected to axial compression is analyzed.Based on the constitutive relationship of confined concrete,a numerical analysis model of equivalent uniaxial constitutive relationship of concrete filled circular steel tubular members is proposed.The fiber model is used to calculate the bearing capacity of members under axial compression.The calculation result is reasonable and the application is convenient.It can be used as a reference for engineering practice.(2)The eccentric compression test of round-ended concrete filled steel tubular members is carried out.The effects of cross-section height-width ratio,slenderness ratio and load eccentricity on the eccentric compression performance and bearing capacity of the members are studied.The eccentric compression deformation characteristics and failure modes of the members are analyzed.The test results show that the failure modes of eccentric compression specimens of round-ended concrete filled steel tube are mainly the integral flexural deformation of the members,partial buckling of the flat section steel tube of some specimens and concrete failure.(3)Through the finite element software ABAQUS,the eccentric compression calculation model of round-ended concrete filled steel tubular members is established,and the whole process of eccentric loading is calculated and analyzed.Based on the test results to verify the reliability of the model,the eccentric compression mechanism and parameter analysis of round-ended concrete filled steel tubular members are carried out.The results show that the confinement of steel tube to core concrete is mainly concentrated in arc section,while the confinement of steel tube to concrete in straight section is relatively small;the eccentric bearing capacity increases with the increase of steel tube strength,concrete strength and section steel content,and decreases with the increase of eccentricity and slenderness ratio.(4)The eccentric compression behavior of circular,round-ended and rectangular CFST members is analyzed by finite element method.The eccentric compression behavior of circular,round-ended and rectangular CFST members is compared and analyzed from the aspects of failure mode,stress analysis,interaction between steel tube and concrete,and stress distribution of section.It is found that the buckling failure modes of concrete filled steel tubular members with different cross-sections are different,and the different confinement and bending capacity of the sections make the calculation of eccentric compression bearing capacity different.(5)The foreign and domestic existing regulations and research results of concrete filled steel tubular(CFST)at are summarized,and the test results are compared with the calculation results.Based on the existing research,an innovative method for calculating the eccentric bearing capacity of members suitable for engineering practice is proposed.