钢管约束的钢管混凝土短柱轴压性能试验研究

为增强核心混凝土约束作用并改善其力学性能，在钢管混凝土外部增设圆钢管形成钢管约束的钢管混凝土组合柱，以构件类型、内层和外层钢管含钢率及核心混凝土强度等级为参数，设计并完成了14个钢管约束的钢管混凝土短柱和14个钢管混凝土短柱的轴压试验；观察试验现象和不同试件的破坏模式，研究各关键参数对试件轴压力学性能的影响，分析内层和外层钢管应力和应变发展规律，对比分析钢管混凝土和钢管约束的钢管混凝土的承载力和变形性能。研究结果表明:当钢管约束的钢管混凝土套箍系数不小于0.87,可使钢管混凝土柱的剪切脆性破坏转为截面压溃破坏，外观表现为腰鼓形破坏；达到承载力时，外层钢管横向应力可以达到钢材屈服强度，对核心混凝土的约束作用较强；钢管约束的钢管混凝土短柱轴压承载力较含钢率相近的常规钢管混凝土承载力可以提高20%左右，较内部钢管混凝土承载力可提高约70%。基于叠加法和GB 50936—2014《钢管混凝土结构技术规范》，提出两种钢管约束的钢管混凝土轴压承载力计算方法，预测结果与试验结果吻合良好。

Experimental study on behavior of steel-tube-confined CFST short columns under axial compression

To improve the confinement and mechanical properties of the concrete core, this paper newly proposes steel-tube-confined concrete-filled steel tubes (TCFST) by adding circular steel tubes at the outside of traditional concrete-filled steel tubes (CFST). 14 TCFST and 14 CFST short columns were designed and constructed to determine the influence of the column type, the steel ratio of the inner and the outer steel tube, and the in-filled concrete strength. The performance and failure modes were observed during the test, and the influence of critical parameters on the mechanical properties was determined. The strain and stress development of the inner and outer steel tubes were studied. Then the ultimate capacity and deformation capacity of TCFST and CFST under axial compression were compared. The results show that the suggested new type columns, with the confining index no less than 0.87, can prevent the inner CFST from shear failure; the transverse stress of the outer steel tube can reach its yield strength and provide effective confinement to the core concrete. Moreover, the new type of column can also achieve a bearing capacity of 20% higher than the corresponding CFST with the same steel ratio and about 70% higher than the inner CFST. Based on the superposition method and GB 50936—2014 ‘Technical code for concrete filled steel tubular structures’, two calculation methods were proposed to predict the ultimate bearing capacity of TCFST; the predicted results are in good agreement with the experimental results.