Experimental behavior of concrete-filled thin-walled corrugated steel tubes with large helical angles under monotonic and cyclic axial compression

Concrete-filled thin-walled galvanized corrugated steel tube (CFCST) is an attractive composite member consisting of an external corrugated steel tube (CST) multi-functionally used as a confining tube, an anti-corrosive shell, and a permanent template. In practice, the CSTs with large helical angles may be employed in some projects; their working mechanism may be different from that of CSTs with small helical angles. Therefore, 26 short columns, including 17 CFCSTs with large helical angles, are tested under monotonic and cyclic axial compression. The main experimental variables are the diameter-to-thickness ratios of external CST, loading patterns, and volumetric steel ratios of transverse stirrups. The failure modes, axial load-displacement responses, plastic strains, and stress deteriorations have been discussed carefully. The test results showed that the slippage of lock-seam weakens the combined effect between the CST and core concrete, leading to a relatively lower strength and ductility. The strain and stress properties of CST having a large helical angle are analyzed, and the work mechanism of CFCST has also been examined. Based on the test results and the comparison with existing models, design suggestions are proposed eventually.