Stub concrete-filled double-skin circular tubes in compression

When short concrete-filled double skin tubular (CFDST) columns are subjected to an axial compressive load, the sandwiched concrete pushes outward on the outer steel tube and inward on the inner steel tube. In the process, the steel tubes resist the expansion of the sandwiched concrete. This results in an increase in the strength of the concrete and a reduction in the strength of the steel tube. A total of 24 stub columns were tested to failure to understand the behaviour of these columns. The diameter-to-thickness ratio of the outer tubes ranged from 47 to 54, and two concrete grades (normal-to-moderate strength concrete) of self-compacting concrete were employed. Failure modes, axial deformations and ductility of the specimens are all investigated, and the results of the experimental investigation revealed that there is some confinement of the concrete core in CFDST columns, and the columns showed significant ductility. The predicted strengths showed great correlation with the experimental strengths.