Behaviour of concrete-filled double-skin steel tubular columns with outer galvanized corrugated steel tubes under monotonic and cyclic axial compression

Concrete-filled double-skin steel tubular (CFDST) column with an outer galvanized corrugated steel tube (CST) is a novel composite member, which has the advantages of hollow-section components and competitive anti-corrosion performance. Existing investigations on such composite members are limited. This study, therefore, investigates the basic axial compressive behaviour of CFDST columns with outer CSTs under monotonic and cyclic loads. A total of 14 specimens have been tested, with the main test variables of the hollow ratios, inner and outer tube thicknesses, specimen types, and loading modes. Results demonstrate that the confining stresses provided by the outer CST and inner steel tube enhance the strength and ductility of sandwiched concrete significantly. The average hoop stress level of outer CSTs can reach 0.7–0.9 times of yield strengths, and the inner flat steel tube primarily maintains the integrity and improves the post-peak mechanical behaviour of sandwiched concrete. The failure modes, working mechanisms, axial stress-strain responses, plastic strains, and stress degradations have been discussed meticulously, with the analysis of the effects of key parameters. Existing monotonic and cyclic axial stress-strain models, as well as existing methods for axial bearing capacity, were evaluated. Finally, the design method for axial compressive bearing capacity was proposed.