Nonlinear concrete model for double-skinned composite tubular columns

The use of concrete filled steel tube (CFT) columns is growing because of their superior performance. However, in some applications, CFT columns might be uneconomical or massive because they should be fully filled with concrete. To overcome these disadvantages, double-skinned composite tubular (DSCT) columns were suggested and have been studied by many researchers. In this study, a nonlinear concrete model was suggested for the analysis of DSCT columns. The model was developed by modifying Mander et al.’s unified concrete model. The stress–strain model of the concrete in a DSCT column was defined by identifying the possible failure modes of the column and deriving the equations for the confining pressure for each failure mode from equilibriums. By using derived equations, a computer program was coded and parametric studies were performed for some examples. The analysis results were verified by comparisons with the experimental results from other researchers. The proposed nonlinear concrete model explains why a DSCT column has enhanced strength beyond the sum of the strengths of its component parts which are an inner tube, an outer tube, and unconfined concrete.