Experimental study on square concrete-filled double skin steel tubular short columns

Concrete-filled double skin steel tubular (CFDST) columns have been increasingly applied in the fields of bridge and building construction due to their superior structural performance. This paper experimentally studied the compressive behavior of square CFDST short columns with double internal steel tubes (2 x SHS or 2 x CHS). The influence of concrete strength, eccentricity ratio, and section hollow ratio on the strength, deformation, and ductility of specimens was systematically investigated. Experimental research showed that the concrete strength had the most remarkable impacts on the ultimate strength of the column, followed by the section hollow ratio. However, the effect of eccentricity ratio on the ultimate strength of the column could be nearly neglected. The ductility of the column was positively correlated with the section hollow ratio, which was completely contrary to the effect of concrete strength. Nevertheless, the eccentricity ratio negligibly affected the ductility of the column. Furthermore, comparisons of the experimental ultimate strength of CFDST columns were made with three different design methods (AISC-360, Eurocode 4, and Han's formulae). The design formulae suggested by Han et al. (2009) could better predict the ultimate strength of CFDST short columns with double internal square steel tubes, but the prediction result was unconservative to some extent. Finally, the simplified formulae were proposed to estimate the ultimate strength of CFDST short columns, which could authentically reflect the combined impacts of the eccentricity ratio and section hollow ratio.