Modeling of octagonal concrete-filled double-skin steel tube stub columns under axial compression

Octagonal concrete-filled double-skin steel tube (OCFDST) columns have drawn the attention of academia and building industries since they combined the advances of higher confinement of circular CFDST columns and the better constructability options of square CFDST columns. Therefore, this paper investigates numerically the behavior of axially compressed OCFDST stub columns by the means of finite element analysis employing ABAQUS software. The accuracy of the developed finite element (FE) models was validated against the experimental results in terms of axial load-axial shortening curves and the ultimate strength of the test specimens. Then, subsequent parametric studies considering a wide range of outer parameters were performed by the verified FE model on the effects of various parameters including the thickness of outer steel tube (t_o), the thickness of inner steel tube (t_i), the diameter of inner steel tube (D_i) and type and arrangement of stiffening schemes. The numerically generated data were then used to evaluate the applicability of the design guidelines provided by existing European, North American, and Chinese provisions for composite columns. Based on the results, it was found that EC4 and modified EC4 formulas can safely be adopted to predict the design ultimate strength of OCFDST stub columns. AISC360 can also give a reasonable for non-stiffened specimens while, DBJ provides un-conservative predictions of ultimate strength when applied to non-stiffened OCFDST stub columns, while it can accurately calculate the ultimate strength of the OCFDST axial members with different stiffening schemes.