Meso-scale modeling of size effect on pure torsional failure of concrete-filled steel tubular columns

The mechanical properties of concrete-filled steel tubular (CFST) columns with different sizes under torsional load were studied, aiming to further explore the pure torsional failure mechanism and size effect behavior of CFST columns. First, a 3D meso-scale numerical model of CFST is established and compared with the existing experimental data. Second, the torsional failure mechanism of CFST column under different section sizes, constraints (confinement coefficient), and cross-sectional shapes is considered. Results show that: (1) the nominal torsional strength of CFST columns presents a size effect, and the columns with square cross-section present stronger size effect than the ones with circular shape; (2) with the increase of the confinement coefficient, the size effect of the nominal torsion strength is weakened. Finally, considering the quantitative influence of the size effect, a formula for calculating the pure torsional capacity of CFST columns was developed.