A hybrid double-skin tubular column (DSTC) is a modern composite column with concrete sandwiched between outer fibre-reinforced polymer (FRP) and inner steel tube. Recently, a new variation form of DSTC, called stiffened DSTC, has evolved with longitudinal stiffeners provided on the outer surface of the inner steel tube. The stiffened DSTCs have better composite action between the DSTC components and mitigate the negative effects of inward local buckling of the inner steel tube. Scant research or design guidelines from standard specifications are presently available on the compressive behavior of this variation form of DSTC. This paper proposes the first ever design-oriented compressive strength model for confined concrete in circular stiffened DSTCs. The proposed axial stress model is based on the experimental results of the present study and a similar test dataset available from the literature. The experimental test results consisted of both normal FRP and large-rupture-strain FRP outer tubes used in circular DSTCs. In total, twelve circular DSTC specimens were tested in this study, and stiffener characteristics including the quantity, configuration, dimensions (i.e., width and thickness), and shape of the stiffeners, were studied. The test results showed that stiffened DSTCs had an enhanced compressive strength of confined concrete (up to about 29% increase in this study), resulting in higher axial load capacity and more ductile behavior compared to DSTCs without stiffeners. The proposed design model for compressive stress performed reasonably well and depicted close agreement with the experimental results for circular DSTCs, using both normal and large-rupture-strain FRP-based outer tubes.

混合式双层皮管柱（DSTC）是一种现代复合柱，混凝土夹在外纤维增强聚合物（FRP）和内钢管之间。近来，已经开发出一种新的变型形式的DSTC，称为加强型DSTC，其在内部钢管的外表面设有纵向加劲肋。加强的DSTC在DSTC组件之间具有更好的复合作用，并减轻了内钢管向内局部屈曲的负面影响。目前，对于这种DSTC变形形式的压缩行为，目前尚缺乏标准规范的研究或设计指南。本文提出了有史以来第一个面向设计的圆形加筋DSTC中承压混凝土的抗压强度模型。所提出的轴向应力模型基于本研究的实验结果和可从文献中获得的相似测试数据集。实验测试结果包括用于圆形DSTC的正常FRP和大断裂应变FRP外管。在这项研究中，总共测试了十二个圆形DSTC试样，并研究了加劲肋的特性，包括加劲肋的数量，外形，尺寸（即宽度和厚度）和形状。测试结果表明，与不加筋的DSTC相比，加筋的DSTC具有更高的承压混凝土抗压强度（在本研究中提高了约29％），从而具有更高的轴向承载能力和更大的延性。