Experimental study on size effect of circular concrete-filled steel tubular columns subjected to axial compression

Eighteen short columns with different diameters and steel ratios were tested to failure to investigate the size effect behavior of concrete-filled steel tubular columns subjected to axial compression. Size effect on composite elastic modulus and peak axial stress were studied. The experimental results show that the value of the composite modulus remains almost constant when the diameter of the specimens is increased; the peak axial stress of the specimens tends to decrease with the increase of the column diameter, and it is related to steel ratio. For the specimens with the steel ratio of 4.5%, the peak axial stress is decreased from 71.4 MPa to 68.9 MPa when the column diameter is increased from 182 mm to 346 mm, showing a 3.5% decrease in compressive strength. In addition, the size-dependent bearing capacity of concrete filled steel tubular columns was proposed on the basis of concrete's size effect and component analysis. The comparison between predicted and test results indicates that the proposed formula can provide satisfactory estimation. Finally, the influences of steel ratio, yield stress of steel, and compressive strength of concrete on size effect were analyzed based on the proposed formula.