RESERCH ON ULTIMATE LOAD-CARRYING CAPACITY OF CONCRETE FILLED STEEL TUBULAR DUMBBELL SHAPED LONG COLUMNS UNDER ECCENTRIC LOAD

Total of 16 CFST dumbbell shaped columns subjected to eccentric loads were tested with variation of slenderness ratio and eccentricity ratio. The test procedure and the failure modes of specimens are introduced, and the load-deflection curves, ultimate load-carrying capacity are obtained. Test results indicate that the specimens fail in global buckling, and their ultimate load-carrying capacities and the tangential stiffness in elastic-plastic phase decrease with the increase of the slenderness ratio and the eccentricity ratio. Furthermore, finite element models are established to analyze the behavior of CFST dumbbell shaped long columns under eccentric loads, showing that the effect of slenderness ratio to load-carrying capacity and that of eccentricity ratio are independent, so their total effect can be accounted by a multiplication of individual effect. The calculation of stability coefficient is identical to that of long axial columns. The eccentric reduction coefficient can be predicted by the proposed formula from regression analysis of both experimental and computational results.