Abstract:

In this paper,first,a uniaxial stress-strain relation of the core concrete is proposed for the finite element( FE) analysis of the square concrete-filled steel tubular ( CFST) stub columns with binding bars.Then,based onthe ABAQUS FE platform,a USDFLD subroutine is presented by considering the Poisson ratio changes and the nonlinearconstitutive relation of many materials in the loading process,and a FE model is then established to simulatethe square CFST stub columns.Finally，the mechanical behavior of the square CFST stub columns is discussed interms of the stress-strain relation and the confined effect among the steel tube,the core concrete and the bindingbars,as well as of the longitudinal stress distribution of the core concrete.The results show that ( 1) the computationresults obtained through the proposed FE model accord well with the test results; ( 2) the binding bars can delaythe local buckling of the steel tube and thus make the steel tube yield before the ultimate strength of the specimenoccurs,and they can also improve the concrete confinement of the corner and central regions and thus increasethe longitudinal stress of the core concrete,so that the bearing capacity and ductility of the specimen can be improved;and ( 3) the concrete confinement of the corner and the central regions increases with the decrease of thespacing between the binding bars

Key words: binding bar, square concrete-filled steel tubular, uniaxial stress-strain relation of core concrete, Poissonratio, confined effec