This paper describes the experimental and numerical study on the axial compressive behaviour of circular-in-circular concrete-filled double-skin steel tube (CFDST) stub columns with large void ratio. Nine specimens with various void ratio (R_v), diameter-to-thickness ratio of outer tube (D_o/t_o) and compressive strength of concrete (f_cu) were tested under axial compression. The failure patterns, load versus displacement (strain) relationship, ultimate capacity and elastic composite stiffness of the specimens were investigated. The experimental results show that all specimens have good structural performance. The typical failure patterns of this new type of columns include local buckling of outer or inner tubes and crushing of concrete infill at the primary buckling locations of both tubes. It is observed from the tests that, there are three key stages in the load versus displacement (strain) relationship, namely: approximative elastic, elastoplastic and nonlinear post-peak, and with the augment of R_v and D_o/t_o and the reduce of f_cu, the ultimate capacity and elastic composite stiffness of the specimens decrease. Apart from tests, a finite element (FE) model was developed to further study the axial compressive behaviour of circular-in-circular CFDST stub columns with large void ratio, and the model was validated against the experimental results. Finally, a simplified analytical model to predict the ultimate capacity of circular-in-circular CFDST stub columns with large void ratio was developed, and the accuracy of the model was verified by the available experimental results. It can be used by the practising engineers in the future design of this type of columns.

本文描述了具有大孔隙比的圆形内圆双皮钢管 (CFDST) 短柱的轴向压缩行为的试验和数值研究。九个不同孔隙比（R _v）、外管径厚比（D _o / t _o）和混凝土抗压强度（f _{cu ）的试件}) 在轴向压缩下进行测试。研究了试样的失效模式、载荷与位移（应变）关系、极限承载力和弹性复合材料刚度。实验结果表明，所有试件均具有良好的结构性能。这种新型柱的典型破坏模式包括外管或内管的局部屈曲以及两个管的主要屈曲位置处的混凝土填充物的压碎。从试验中可以看出，载荷与位移（应变）关系存在三个关键阶段，即：近似弹性、弹塑性和非线性峰值后，随着R _v和D _o / t _{o 的增加}和减少f_cu，_试件的极限承载力和弹性复合刚度减小。除了测试之外，还开发了一个有限元 (FE) 模型，以进一步研究具有大孔隙比的圆内圆 CFDST 短柱的轴向压缩行为，并根据实验结果对该模型进行了验证。最后，开发了一个简化的分析模型来预测具有大孔隙比的圆内圆 CFDST 短柱的极限容量，并通过可用的实验结果验证了模型的准确性。可供实践工程师在今后设计此类柱子时使用。