Improved Composite Effect of Square Concrete-Filled Steel Tubes with Diagonal Binding Ribs

This paper proposes a scheme to improve the structural behavior of square concrete-filled steel tubular (CFST) columns, in which diagonal binding ribs are welded at all the four pairs of adjacent sides of the square tube. Thus, both the confinement from the stiffened square steel tube to the infilled concrete and local buckling behavior of the tube can be enhanced. The diagonal binding ribs made of perforated thin-walled steel plates can facilitate concreting and enhance the integrity of the columns. This kind of composite columns is called diagonal rib-stiffened square CFST columns in this paper. Nineteen specimens with the tube width:thickness ratios between 50 and 150 were tested under axial compression to investigate the effect of thicknesses, opening dimensions and opening shapes of the stiffeners. In addition, square CFST specimens without stiffeners and octagonal CFST specimens and square CFST specimens with longitudinal stiffeners on each tube face were also tested for comparison. Test results showed that the diagonal binding ribs can improve the composite effect effectively by cocarrying the axial compression force and confining both the steel tube and concrete. The diagonal binding ribs can increase load-carrying capacity by 10%-20% and ductility by 30% or more compared with the CFST specimens without stiffeners. The diagonal rib-stiffened square CFST columns also behaved better than the octagonal CFST specimens and square CFST specimens with longitudinal stiffeners. Finally, two calculating methods which well predict the axial load-carrying capacities of diagonal ribs stiffened square CFST columns are recommended.