Size effect of circular concrete-filled steel tubular short columns subjected to axial compression

In this paper, thirty-six short columns with different diameters (150 mm ≤ d ≤ 460 mm) and steel ratios (4.0% ≤ α ≤ 10.0%) were tested to failure to investigate the size effect of circular concrete-filled steel tubular short columns subjected to axial compression. Size effects on the peak axial stress, peak axial strain, composite elastic modulus, and ductility coefficient were studied. The experimental results showed that the peak axial stress, peak axial strain and ductility coefficient of the specimens tended to decrease with the increase in the column diameter. The values of the composite elastic modulus remained almost constant when the diameter of the specimens increased, indicating that size effect on the composite elastic modulus was not obvious. Meanwhile, size effect on the peak axial stress was influenced by the steel ratio in the range of 4-10%. Furthermore, the size effect tended to decrease as the steel ratio increased. By comparing with the current codes, a reduction coefficient was introduced to consider the size effect of concrete core. Based on the reduction coefficient, the size effect of the concrete core inside the steel tube is found to be weaker compared with that of the unconfined concrete columns because of the confinement effect.