FATIGUE PROPERTIES OF SLENDER CONCRETE-FILLED SQUARE STEEL TUBE BEAM-COLUMNS

This paper investigates fatigue properties of the slender concrete-filled square steel tube (CFT) beam-columns to assess their cumulative fatigue damage in the plastic region. Limit state for fatigue damage is defined by the state in which the shear force is reduced to 95% of maximum load. This investigation is based on a database including parameters such as axial compression ratio, width-thickness ratio of steel tube, concrete strength and ratio of buckling length to depth of cross section from previous test results. The limit state for fatigue damage is affected by the deformation ratio, which is the ratio of design rotation angle to deformation capacity under monotonic loading. Predictions from multiple regression formulas, which involve the deformation ratio as a main factor, almost agree with test results for fatigue damage in the plastic region.