Behaviors of improved multi-cell T-shaped concrete-filled steel tubular columns under eccentric loads

The improved multi-cell T-shaped CFST section is composed of four square or rectangular cavities infilled with concrete, in which the steel plates added in the section are developed as stiffeners to avoid or delay local buckling of the tube wall. In practical engineering, columns are generally subjected to eccentric load. A total of eleven multi-cell T-shaped concrete-filled steel tubular (CFST) columns were tested under eccentric loads in the symmetric axis. Effects of the web height, the slenderness ratio, the load eccentricity, and the eccentric direction of load on the mechanical behaviors of the specimens were investigated. The experimental results showed two failure modes of the specimens: before the peak load, local buckling was observed in the specimen ET-11 owing to the relatively large width-to-thickness ratio of steel plates in the web; before the peak load, slight local buckling occurred at the mid-span of the other specimens but was not observed during the test, and after the peak load, the local buckling gradually increased, which resulted from the large bending deformation. The improved multi-cell T-shaped CFST columns exhibited a better restraint effect of steel tubes on core concrete and the local buckling of steel plates was delayed or restrained. The ultimate bearing capacity of the specimen under eccentric load located on the flange (y-) was relatively larger. Furthermore, finite element (FE) models were developed to simulate the mechanical behaviors of multi-cell T-shaped CFST columns under eccentric loads and verified with the experimental results. The stress and strain analyses of core concrete at the ultimate state were conducted by using the FE models. Based on both experimental and finite element methods, the simplified calculation formulae for predicting the ultimate bearing capacity of multi-cell T-shaped CFST columns subjected to axial and eccentric compression were put forward. The calculated results agree well with the results of the test and the FE models.