This study experimentally explored the torsional behaviour of 33 specimens, which comprises of 18 concrete filled steel tube (CFST), 9 steel tube (ST) and 6 concrete (C) specimens. The length to diameter (L/D) ratio was 7.14 while the ratios of diameter to thickness (D/t) were 60.9, 46.7 and 40.0. The compressive strength of the infill concrete was 24.2 MPa (normal) and 33.3 MPa (relatively high). All specimens were tested to failure and the obtained data was analysed. The results indicated that buckling failure of CFST specimens was prevented due to the presence of concrete infill. Diagonal cracks of concrete infill observed on CFST specimens after cutting steel tubes are the evidence for the collaboration between steel tube and concrete. This evidence also reveals that the concrete infill contributes to increase the torsional moment capacity of CFST and helps steel tubes to work effectively. The superposition method fails to apply for CFST members under torsion because it does not take into account the mutually beneficial collaboration and interaction between steel tubes and concrete infill which resulted in the improvement on the failure mode, mechanical properties and behaviour of CFST specimens under torsion. Details of the test results and above-mentioned findings are reported in this paper.

这项研究通过实验探索了33个试样的扭转行为，其中包括18根钢管混凝土（CFST），9根钢管（ST）和6根混凝土（C）试样。长度与直径之比（D / t ）为7.14，而直径与厚度之比（D / t）分别为60.9、46.7和40.0。填充混凝土的抗压强度分别为24.2 MPa（正常）和33.3 MPa（相对较高）。测试所有样本的破坏性，并对获得的数据进行分析。结果表明，由于存在混凝土填充物，可防止CFST试件屈曲失败。切割钢管后，在CFST试件上观察到的混凝土填充物的对角裂纹是钢管与混凝土之间协同作用的证据。该证据还表明，混凝土填充物有助于提高CFST的扭转力矩能力，并有助于钢管有效地工作。由于没有考虑钢管与混凝土填充物之间的互利协作和相互作用，因此叠加方法不适用于受扭的CFST构件，从而导致CFST试样在受扭状态下的破坏模式，力学性能和性能得到改善。测试结果的详细信息和上述发现报告在本文中。