Behavior of concrete-filled steel tube reinforced concrete columns subjected to axial compression

Based on rational constitutive models of steel and concrete,load-deformation relationship curves of concrete-filled steel tube(CFST) reinforced concrete columns subjected to axial compression were calculated by the fiber model method and finite element method to investigate the behavior of composite column subjected to axial compression.The results of theoretical analysis are in good agreement with the experimental ones.Based on the research conclusion mentioned above,behavior analysis of concrete-filled steel tube reinforced concrete columns subjected to axial compression including failure mode,axial load distribution,and the interaction between outer concrete,steel tube and core concrete were carried out.Practical simplified formulae of bearing capacity were proposed,and results calculated using the formulae agreed well with test results.At last,it is suggested that in order to ensure the collaborating between outer concrete and inner concrete filled steel tube,the ratio of stirrup constraint index in outer concrete to constraint effect coefficient in inner concrete filled steel tube should not be less than 0.188.