Experimental and numerical studies of circular sandwiched concrete axially loaded CFDST short columns

This paper aims to experimentally and numerically investigate the compressive behavior of circular concrete filled double-skin steel tubular (CFDST) short columns, in which only the sandwiched concrete is under axial compression. In total, 28 CFDST columns were loaded axially, and their axial load-shortening curves, ultimate strength and failure modes were briefly discussed. Results suggest that the wall thickness and yield stress of outer steel tube have a significant effect on the failure modes, while the concrete strength shows an insignificant effect. The tested columns exhibited good ductility concerned by seismic resistant design. The ultimate strength of the columns using STK490 outer steel tubes was about 20-26% than that of ones with STK400 outer steel tubes. With an increase in the concrete strength and wall thickness of outer steel tube, the ultimate strength of the columns was improved by 32% and 43%, respectively. Moreover, finite element (FE) models were established and verified by comparing with the test results, and then an extensive parametric analysis was carried out to ascertain the effects of key variables on the compressive behaviour of the studied CFDST short columns. Finally, based on the numerical and test results, a novel formula was proposed to estimate the ultimate strength of CFDST columns, and high prediction performance was found in the proposed formula. The proposed formula is not only applicable for the strength prediction of CFDST columns, but also for that of steel tube confined concrete (STCC) columns.