圆钢管约束加强的方钢管混凝土短柱轴压性能研究

To repair or strengthen the existing square concrete-filled steel tube (SCFST), it was proposed to improve the confinement in the form of the outer circular steel tube and grout. To make clear the difference of the deformation characteristics and overall failure mode of SCFSTs after strengthening, six strengthened and three unstrengthened SCFSTs were designed and tested under axial compression loading. The influence of diameter of circular steel tube on the mechanical performance was discussed in detail. The development of the strain and the stress of inner square and outer circular steel tubes were analyzed. The test results show that due to the effective concrete confinement by the outer circular steel pipe, not only the bearing capacity of the inner SCFST is improved but also the brittle shear failure is prevented in the outer tube strengthened zone. Based on the experiment results, a finite element model of strengthened SCFST with a modified stress-strain relationship of core concrete was established and validated. The failure mode, the distribution of longitudinal stress of core concrete, and the dual confinement mechanisms of the inner and outer steel tubes were analyzed. Due to the outer steel tube, the constraint to core concrete and the peak load of SCFST can be improved effectively. Meanwhile, the stress state of core concrete is much decent owing to the multiple confinements offered by the inner and outer tubes, but the concrete is confined more effectively near the inner steel tube corner.