Experimental behavior of concrete-filled double-skin tubular columns with outer galvanized corrugated steel tubes under axial compression

Twelve lightweight and corrosion-resistant concrete-filled double-skin tubular (CFDST) columns with outer galvanized corrugated steel tubes (CSTs) and inner flat carbon steel tubes were subjected to monotonic axial compression tests. Compared to a traditional CFDST column, a CFDST column with a CST as the outer tube can reduce the longitudinal stress transmitted by the steel and better provide hoop confinement for the sandwiched concrete. The key parameters were the hollow ratio (chi) and inner tube thickness (ti). The failure mode, axial load capacity, strain and ductility of specimens with different parameters were analysed. There was noticeable slip -page at the lock seam of the CST under axial loading, which releases the CST and results in the relatively low strength and ductility of the specimens. Keeping other parameters constant, an increase in chi and a decrease in ti led to a reduction in the peak load (Nu), strength index (SI) and ultimate strain (epsilon cc). On the other hand, the ductility index (DI) increased as chi and ti increased. The strain development of the outer CST in one corrugation period was nonuniform. The hoop strain (epsilon ho) dominated at the crest of the CST, while the vertical strain (epsilon vo) dominated at the trough. epsilon vo gradually decreased from the trough to the crest, whereas epsilon ho increased from the trough to the crest. The applicability of the current standard design code formulae and axial load capacity equations for circular CFDST columns was evaluated using a newly expanded database, and a satisfactory axial load capacity model for circular CFDST columns with outer CSTs was proposed.