Numerical investigation of the axial compressive capacity of reinforced concrete-filled doubleskin steel tubular short columns

This study presents a numerical investigation into the axial compressive behavior of reinforced concrete-filled double-skin steel tubular (R-CFDST) columns. A finite element model (FEM) for R-CFDST columns was developed based on validated FE models of both reinforced concrete-filled steel tubular (R-CFST) columns and circular concrete-filled double-skin steel tubular (CFDST) columns. Using the proposed FE model, a comprehensive parametric study was conducted to evaluate the effects of longitudinal reinforcement ratio, geometric dimensions, and material properties on the ultimate axial strength of R-CFDST columns. The results show that increasing the longitudinal reinforcement ratio from 0% to 2.93% enhances the column’s ultimate capacity by up to 17.91%, underscoring the critical role of rebar in enhancing column performance. Furthermore, existing design equations for predicting the ultimate strength of R-CFST and CFDST columns were reviewed and adapted for application to R-CFDST columns. The accuracy of these modified equations was validated against the FE results, and the most accurate formulation was recommended for the compressive design of R-CFDST columns under uniaxial loading.