Buckling bearing capacity of square steel tube filled with concrete

To analyze the behavior of hollow steel tube filled with concrete, the influences of initial deformation, the residual stress and the post-buckling behavior on the behavior of steel tube in composite columns are studied. The finite element method is used to analyze the behavior of square steel tube filled with concrete. The accuracy of theoretical results is validated by comparing them with corresponding experimental results. It is showed that when the relative width-to-thickness ratio is less than 50, the local buckling has no evident influence on the bearing capacity; when the relative width-to-thickness ratio is over 50, the local buckling will result in the decrease of bearing capacity of steel tube in square composite columns. For the steel tube with high width-to-thickness ratio, the initial deformation and the residual stress result in the decrease of bearing capacity, and the post-buckling behavior provides higher bearing capacity. At last, the simplified formula to calculate the bearing capacity of steel tube with higher width-to-thickness ratio is given and can be used in the design.