The composite action in circular concrete-filled steel tube (CFST) columns under axial compression is one of the most fundamental problems in the research area of steel-concrete composite structures. However, it cannot be easily investigated through experiments as the load components of the steel tube and concrete infill cannot be measured in a conventional axial loading test. In this study, an innovative testing method was devised to directly measure the load components of circular CFST columns under axial compression. Six innovative specimens with varying concrete strength and diameter-to-thickness (D/t) ratio and their conventional counterparts were tested. Although some difference existed between the load-deformation responses of the innovative and corresponding conventional specimens, it was essentially insignificant. The development of hoop stresses in the steel tube tends to reduce the corresponding axial stresses, but this effect can be offset by the strain hardening of the steel tube. Strain hardening of the steel tube should be considered when evaluating the confinement effect at the ultimate load, especially for columns with low concrete strength and small D/t ratio. The average values of the coefficients related to the axial and hoop stresses of the steel tube at the ultimate load, computed using available tests results, are 0.92 and −0.14, respectively. The proposed axial load capacity formula with these two values can reasonably predict the ultimate loads of circular CFST columns under axial compression.

圆形钢管混凝土柱在轴压作用下的复合作用是钢-混凝土复合结构研究领域中最基本的问题之一。但是，由于无法通过常规的轴向载荷测试来测量钢管和混凝土填充物的载荷分量，因此无法通过实验轻松地对其进行研究。在这项研究中，设计了一种创新的测试方法来直接测量圆形CFST圆柱在轴向压缩下的载荷分量。六个具有不同混凝土强度和厚度对厚度的创新标本（D / t）比率和它们的常规对应物进行了测试。尽管在创新型和相应的常规试件的载荷-变形响应之间存在一些差异，但本质上是无关紧要的。钢管中环向应力的发展趋向于减小相应的轴向应力，但是钢管的应变硬化可以抵消这种影响。在评估极限载荷下的约束效果时，应考虑钢管的应变硬化，特别是对于混凝土强度低且D / t小的柱子比率。使用现有测试结果计算得出的与钢管在极限载荷下的轴向应力和环向应力相关的系数的平均值分别为0.92和-0.14。提出的具有这两个值的轴向载荷能力公式可以合理地预测圆形CFST圆柱在轴向压缩下的极限载荷。