Post-local buckling failure of slender and over-design circular CFT columns with high-strength materials

This paper investigates the ultimate behavior and post-local buckling failures of circular concrete-filled steel tubular (CFT) beam-columns under cyclic loading with constant axial force. The test specimens are fabricated by thin-walled steel tubes with 2 mm in thickness to clarify the main failure modes, and to evaluate the ultimate flexural behavior of slender and over-design circular CFT columns. Test results indicated that the column specimens with a large D/t ratio together with a thin-walled steel tube tend to trigger highly concentrated local buckling at column bottom where sequentially experienced low cycle fatigue fracture and the fragmentation of concrete infill. From the orthogonal analysis on the test results, it is found that the D/t ratio and concrete-to-steel strength ratio respectively play the most significant influences on the ultimate flexural strength and the critical axial load ratio. Finally, the fiber element model incorporating strength and stiffness degradation can accurately predict hysteresis behavior. This study provides fundamental supports for the design and analysis of thin-walled steel tubes to circular CFT columns with slender cross-section.