RESEARCH ON LOAD-CARRYING CAPACITY OF CONCRETE-FILLED-STEEL TUBULAR DUMBBELL-SHAPED LONG COLUMNS UNDER AXIAL LOADS

Experiments of 10 concrete-filled-steel tubular (CFST) dumbbell-shaped Long columns with various slenderness ratio subjected to axial load were carried out, in which 5 specimen were failed in the strong-stress-axis direction; another 5 were failed in the weak-stress-axis direction. It is proved by the test that the failure of dumbbell shaped specimen in strong-stress-axis direction can be realized by welding corrugated steel webs in its weak-stress-axis direction to increase flexible rigidity in this direction. Similar with the long columns of single tube section, the load-carrying capacity and the elastic-plastic tangential stiffness of CFST dumbbell-shaped long columns decrease with the increasing of slenderness ratio. But elastic-plastic instability occurred on dumbbell-shaped long columns instead of the elastic instability in one of single tube section with same slenderness ratio. A nonlinear finite element method is provided for dumbbell-shaped long column, and the influence of slenderness ratio on its load-carrying capacity is analyzed by parametric studies. It is shown that the stability coefficient of dumbbell-shaped long CFST columns is different from that of long CFST columns of single tube section. However, the rules of load-carrying capacity in the weak-stress-axis and strong-stress-axis directions for dumbbell-shaped long CFST column, varying with the slenderness ratio, are similar. A simplified formula to calculate the stability coefficient is presented by unifying the rule in two directions.