The objective of this study is to investigate the mechanical properties and the composite action of circular concrete-filled steel tube (CFST) columns subjected to compression-torsion load using finite element model analysis. Load-strain (T-γ) curves, normal stress, shear stress, and the composite action between the steel tubes and the interior concrete were analyzed based on the verified 3D finite element models. The results indicate that with the increase of axial force, the maximum shear stress at the core concrete increased significantly, and the maximum shear stress of the steel tubes gradually decreased. Meanwhile, the torsional bearing capacity of the column increased at first and then decreased. The torque share in the columns changed from the tube-sharing domain to the concrete-sharing domain, while the axial force of the steel tube remained unchanged. Practical design equations for the torsional capacity of axially loaded circular CFST columns were proposed based on the parametric analysis. The accuracy and validity of the proposed equations were verified against the collected experimental results.
Keywords: composite action; compression-torsion; concrete-filled steel tubes; confinement effect; finite element; ultimate strength.