Strength Deterioration Behavior of Concrete-Filled Steel Tubular Beam-Columns

Cantilever bcam-columns of steel square hollow section with or without filled-concrete were tested under constant axial load and alternately repeated horizontal load to investigate. the strength deterioration phenomena due to local buckling, with varying values of the experimental parameters ; axial load ratio, width-thickness ratio and displacement amplitude in the repeated loasing. The effects of filled-concrete and the experimental parameters on the deterioration of strength and energy dissipation capacity with the load repetition are discussed, in view of the results of analysis based on the degrading type of stress-strain ralation of the steel representing the effect of local buckling. In the case that the displacement amplitude in the repeated loading was set equal to the displacement at which the local buckling occurred, the peak strength in each cycle of loading and the energy dissipation capacity of the concrete-filled steel tubular beam-columns tended to converge, because of the restraint of concrete against the progress of the buckling deformation, whercas some of the beam-columns without filled-concrete showed continuous deterioration of the strength and the energy dissipation capacity. When the displacement amplitude was set greater than the local buckling displacement, the strength deterioration was drastic even in the case of the concrete-filled beam-columns