Experimental and numerical investigation on the behaviour of square concrete-filled cold-formed double-skin steel stiffened tubular short columns

This paper presents an investigation into a new cold-formed concrete-filled double-skin steel stiffened tubular (CFDSST) column. It consists of concrete filled between two concentrically-located square hollow steel tubes where the outer steel tube is made with four lipped angles of cold-formed plates and lips which can be regarded as longitudinal stiffeners. This new composite column has fewer welds compared to traditional concrete-filled double-skin steel tubular columns with stiffeners. To investigate the axial compression mechanical properties of the column, fifteen short columns were designed and fabricated, including thirteen CFDSST short columns and two concrete-filled stiffened steel tubular (CFSST) columns, for comparison. The specimens were examined under axial compression, and a finite element (FE) model was then developed and validated using the test results. Next, a parametric analysis was carried out to explore the behaviour of the CFDSST columns with different properties. The results show that the ultimate strength of CFDSST columns is significantly affected by the strength of concrete. Finally, different international design methods were assessed to evaluate their applicability and accuracy for these members. In light of the results, a new design formula was proposed for CFDSST columns which accounts for the lateral confining pressure as well as the size effect.