Steel and Composite Structures   Volume 20, Number 3, February29 2016, pages 571-597 DOI: http://dx.doi.org/10.12989/scs.2016.20.3.571 Nonlinear analysis and design of concrete-filled dual steel tubular columns under axial loading Cheng-Yong Wan and Xiao-Xiong Zha Abstract     [Full Text] A new unified design formula for calculating the composite compressive strength of the axially loaded circular concrete filled double steel tubular (CFDST) short and slender columns is presented in this paper. The formula is obtained from the analytic solution by using the limit equilibrium theory, the cylinder theory and the &\$34;Unified theory" under axial compression. Furthermore, the stability factor of CFDST slender columns is derived on the basis of the Perry-Robertson formula. This paper also reports the results of experiments and finite element analysis carried out on concrete filled double steel tubular columns, where the tested specimens include short and slender columns with different steel ratio and yield strength of inner tube; a new constitutive model for the concrete confined by both the outer and inner steel tube is proposed and incorporated in the finite element model developed. The comparisons among the finite element results, experimental results, and theoretical predictions show a good agreement in predicting the behavior and strength of the concrete filled steel tubular (CFST) columns with or without inner steel tubes. An important characteristic of the new formulas is that they provide a unified formulation for both the plain CFST and CFDST columns relating to the compressive strength or the stability bearing capacity and a set of design parameters. Key Words concrete filled double steel tube (CFDST); bearing capacity; unified formula; axial compression experiment; finite element analysis (FEA) Address Department of Civil and Environmental Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, People's Republic of China.

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