Flexural behaviour of concrete-filled double-skin corrugated steel tubes

Concrete-filled double-skin thin-walled corrugated steel tube (CFDCST) is a novel composite member proposed to improve the corrosion resistance and ductility of conventional hollow reinforced concrete (HRC) structures, which is suitable for applications such as piers, towers, and offshore platforms with durability requirements. Given that the existence of the hollow region and double-layer CSTs endows CFDCST members with distinctive flexural characteristics, it is necessary to specially evaluate their flexural performance for rational design guidelines. Therefore, in this study, eight large-scale specimens, including seven CFDCSTs and one HRC, were tested under pure bending. Experimental variables included specimen types, hollow ratios, outer CST thicknesses, and longitudinal reinforcement ratios. Failure modes, flexural performance, and strain distributions were analyzed, and the definition of flexural capacity was proposed. Experimental results indicated that the CFDCST specimens exhibited ductile failure modes and high structural efficiency, with effectively improved flexural capacity and ductility compared with the HRC specimen with the same reinforcement configuration. Subsequently, detailed finite element (FE) models were developed and validated, and a comprehensive parametric analysis was conducted. The working mechanisms of CFDCST members under pure bending were revealed. Finally, the prediction models for both flexural capacity and flexural stiffness were proposed.