CFDST stub columns having outer circular and inner square sections under compression

Concrete filled double skin steel tubular (CFDST) members, having a hollow section consisting of two concentric steel tubes and filled concrete between the two walls of the tubes, are lighter than the ordinary concrete filled steel tubular (CFT) members, which have solid cross-sections. Therefore, the CFDST members can work effectively as seismic resistant structures such as bridges high piers during earthquake. The present study aims to investigate experimentally centric loading characteristics of the CFDST stub column consisting of an outer circular steel tube and an inner square steel tube with in-filled concrete between the double walls, which are abbreviated as CS-CFDST. The two selected testing parameters are the outer tube's diameter-to-thickness ratio and inner width to outer diameter ratio. From the results, observed failure modes were divided into two groups: local buckling associated with shear failure of in-filled concrete and local buckling of the double tubes. These failure modes were affected by inner width to outer diameter ratio. Axial load capacities were also determined by the above described failure modes. Additionally, elasto-plastic biaxial stress behavior of both tubes under plane stress condition is also mentioned. Methods to predict the axial load capacities of CS-CFDST stub columns are also provided. •Behavior of a concrete filled double skin tubular stub column under compression is described.•Methods to predict axial loading capacity of CS-CFDST are discussed.•Effect of inner-to-outer width ratio on the axial load capacity is provided.•Biaxial stress behavior of steel tubes induced by the in-filled concrete is mentioned.