The concrete-filled fiber-reinforced polymer tube (CFFT) is a unique structural element that is well suited for reinforced concrete applications in harsh environments due to the corrosion-resistant reinforcement. It also benefits from the stay-in-place formwork capabilities of the reinforcement and the beneficial concrete confinement offered primarily in cases of axial compression. The strength and response of the CFFT system have been studied under axial, flexural, and combined loading conditions; however, its torsional behavior has not been evaluated. Some of the challenges have been the ability to provide successful gripping of the circular cross-section as well as avoiding the undesired second-order effects when pure torsion is investigated. This paper presents a novel apparatus developed to test circular members, including CFFTs, to failure under a variety of loading conditions including pure torsion, and combined torsion, bending, and axial compression. The apparatus can accommodate a complex set of geometric nonlinearity effects associated with the deformations arising from multiple degrees of freedom. The functionality of the testing system under a state of pure torsion and combined loading was verified. The results showed that the testing apparatus effectively simulated the intended loading condition. The samples experience relatively large and complex displacements that justified the details incorporated in the design of various components of the testing configuration.

填充混凝土的纤维增强聚合物管（CFFT）是一种独特的结构元素，由于具有抗腐蚀的增强作用，因此非常适合苛刻环境中的钢筋混凝土应用。它还得益于钢筋的原位模板功能和主要在轴向压缩情况下提供的有益的混凝土约束。已经研究了在轴向，弯曲和组合载荷条件下CFFT系统的强度和响应。但是，其扭转性能尚未得到评估。其中的一些挑战是，在研究纯扭力时，能否成功握住圆形横截面以及避免产生不希望的二阶效应。本文介绍了一种新颖的设备，用于测试圆形构件，包括CFFT，在包括纯扭力，扭力，弯曲和轴向压缩组合在内的各种载荷条件下均会失效。该设备可以容纳与由多个自由度引起的变形相关的一组复杂的几何非线性效应。验证了测试系统在纯扭力和组合载荷状态下的功能。结果表明，该测试设备有效地模拟了预期的加载条件。样本经历了相对较大和复杂的位移，这证明了在测试配置的各个组件的设计中包含的细节是合理的。该设备可以容纳与由多个自由度引起的变形相关的一组复杂的几何非线性效应。验证了测试系统在纯扭力和组合载荷状态下的功能。结果表明，该测试设备有效地模拟了预期的加载条件。样本经历了相对较大和复杂的位移，这证明了在测试配置的各个组件的设计中包含的细节是合理的。该设备可以容纳与由多个自由度引起的变形相关的一组复杂的几何非线性效应。验证了测试系统在纯扭力和组合载荷状态下的功能。结果表明，该测试设备有效地模拟了预期的加载条件。样本经历了相对较大和复杂的位移，这证明了在测试配置的各个组件的设计中包含的细节是合理的。