钢-混凝土组合方形截面柱内置螺旋筋约束增强机理及承载力计算

为揭示钢-混凝土组合方形截面柱(简称“方柱”)内置螺旋筋的约束增强机理，明确螺旋筋间距、螺旋筋直径以及螺旋筋径宽比等设计参数对组合柱的约束增强效果的影响规律，设计并完成了30个螺旋筋约束增强钢-混凝土组合方柱(15个角钢试件、15个钢管试件)的轴心受压试验，观察了方柱的破坏过程，揭示了其约束增强机理，对比分析了各变化参数对方柱轴压性能指标的影响规律，提出了具有统一形式的组合柱轴压承载力计算公式。试验结果表明：内置螺旋筋可有效改善方形角钢骨架或钢管对核心混凝土存在的约束“拱效应”,提升组合柱的承载力和变形性能，但对轴压刚度无明显增益效果；增大螺旋筋的体积配筋率可进一步提高组合柱的轴压延性，且增大螺旋筋径宽比时单位体积用钢量获得的承载力性能提升效果最为显著，其次是减小螺旋筋间距，再次是增大螺旋筋直径；组合柱承载力的提高程度随着螺旋筋用量的增大有所减缓，且内置螺旋筋对角钢混凝土柱承载力的提高效果显著优于钢管混凝土柱；结合所提的约束模型和Mander约束混凝土理论建立的轴压承载力计算式可较精确地计算螺旋筋约束增强钢-混凝土组合方柱的轴压承载力。

Restraint mechanism and bearing capacity calculation of steel- concrete composite square columns with internal spiral bars

In order to reveal the restraint mechanism of steel-concrete composite columns with spiral bars, and clarify the influence of design parameters such as the spacing of spiral bars, the diameter of spiral bars and the ratio of diameter to width of spiral bars on the restraint strengthening effect of composite columns, 30 specimens of steel-concrete composite square columns confined with spiral bars, including 15 angle steel specimens and 15 steel tube specimens, were tested under axial compression. The failure process of specimens was observed, the mechanism of constraint strengthening was revealed, the influence of various parameters on axial compression behavior of the specimens was analyzed, and the unified formulas for calculating the axial compression bearing capacity of composite columns were proposed. The test results show that the built-in spiral bars can effectively improve the restraint arch effect of square angle steel skeleton or steel tube on the core concrete, and improve the bearing capacity and deformation performance of composite columns, but has no obvious effect on stiffness. The ductility of composite columns can be further improved by increasing the volume reinforcement ratio of spiral bars, and the bearing capacity of composite columns can be improved most significantly by increasing the diameter width ratio of spiral bars, followed by reducing the spacing of spiral bars and increasing the diameter of spiral bars. The improvement degree of the bearing capacity slows down with the increase of the amounts of spiral bars, and the improvement effect of the built-in spiral bars on the bearing capacity of angle steel reinforced concrete columns is significantly better than that of concrete-filled steel tube columns. Combined with the constraint model and Mander’s theory of confined concrete, the formulas established in this paper can accurately calculate the axial bearing capacity of steel-concrete composite square columns confined with spiral bars.