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摘要
A set of tests are conducted for evaluating the behaviors of cross-shaped concrete-filled steel tubular stub columns subjected to axial compression, including eleven specimens with binding bars and five specimens without binding bars. The parameters are the spacing and diameter of binding bars, the thickness and strength of steel plates, and section size. The axial compression behaviors of the specimens are discussed, such as the characteristics of failure, the bearing capacity and ductility, and the development characteristics of the strain of binding bars and steel tube. The results indicate that by setting binding bars the buckling modes of the steel plates are changed, the appearance of local buckling is postponed, the outward deformation around the concave corners of tube is restrained, and the strain distribution of steel tube is more uniformly. Then the longitudinal bearing capacity of the tube can be guaranteed, the confinement effects of steel tube on the core concrete are increased, and the bearing capacity and ductility are enhanced. The confinement effects of binding bars to the outward deformation of steel tube are increased with the decrease of distance of bars, as well as the increase of thickness of plates or the increase of diameter of bars. The methods in current standards for calculating the ultimate strength of rectangle or square CFST stub columns are used to evaluate the maximum strengths of the specimens. The results indicate that only when the width-thickness ratio is less than 22, the maximum strengths of specimens without bars can be evaluated by the Code EC4 in which the strength superposition method is adopted. When the distance of bars is small or the thickness of steel tube is large, the Codes GJB 4142-2000 and DBJ 13-51-2003 can be used to evaluate the maximum strengths of specimens with bars, otherwise the strength superposition method is also appropriate. Finally, considering the confinement effects of steel tube and binding bars, and the loss of longitudinal capacity of steel tube in the specimens without bars, a method is proposed for the columns with and without binding bars, and the calculated results are in a good agreement with the experimental data.
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