Experimental and numerical investigation of square concrete-filled double-skin steel stiffened tubular stub columns with CHS inner tubes under axial compression

•Experimental tests of CFDSST columns is presented in detail in this paper.•Using ABAQUS, 3D finite element CFFSST column models under axial compression are developed.•The fundamental behaviour of the CFDSST columns is discussed in detail.•The feasibility of current design codes to design the CFDSST columns is evaluated.•The proposed design model is shown to predict well the strengths of CFDSST columns. This paper explores the performance of concrete-filled double-skin (square stiffened hollow sections (SHS) outer and circular hollow sections (CHS) inner) steel tubular (CFDSST) stub columns under axial compression through experimental research and finite element analysis. The static axial compression experiments of six concrete-filled stiffened steel tubular (CFST) stub columns and fifteen CFDSST stub columns were conducted. The test method, process, phenomena and results are introduced in detail. The results indicated that compared with conventional CFST stub columns, CFDSST stub columns with reasonable hollow ratio can maintain load-carrying capacity, increase ductility and reduce self-weight. Increasing the strength of concrete is the most effective way to increase the load-carrying capacities of specimens when other variables remain constant. Finite element (FE) software was then utilised to generate the models of current specimens. The simulation results showed reasonableness and accuracy compared to the experimental results. Based on the validated models, parameter analysis was performed to reveal the influence of concrete strength, width-to-thickness ratio of the outer steel tube, stiffener depth, hollow ratio and yield strength of the outer steel tube on the ultimate strengths of the specimens. In addition, compared with test and FE strengths, the ultimate strengths predicted by available international codes were found to be quite conservative. Consequently, a formula was proposed to predict the load-carrying capacity of CFDSST stub columns considering the effective cross-sectional areas of the outer steel tubes and the strength of the confined concrete. The formula has been shown to provide the best prediction with acceptable reliability.