Eccentric compressive performance of CFST columns reinforced with annular stiffeners

A concrete-filled steel tube (CFST) column reinforced with annular stiffeners is a novel composite member that exhibits enhanced axial compressive and flexural performance owing to improved confinement. The annular stiffeners consist of curved steel connected by circular plates. This study investigates the eccentric compressive performance of such composite columns. Eccentric compression tests were first conducted, followed by the development of a refined finite element model to explore the underlying mechanical mechanisms. A comprehensive parametric analysis was then performed to examine the effects of design parameters. The applicability of existing design codes or theoretical models was also assessed through comparative evaluation. Based on the experimental and analytical findings, design formulas for the normalized load–bending moment ( N / N u – M / M u ) interaction curve were developed to predict the ultimate eccentric bearing capacity of this composite member. The results reveal that the annular stiffeners provide strong confinement to the core concrete under eccentric compression, resulting in higher stress levels in the core concrete than in the extreme compression-fiber concrete at the ultimate state. An increase in concrete strength elevates the balanced failure point of the interaction curve, causing it to approach that of reinforced concrete columns. In contrast, increasing the strength and thickness of the outer steel tube, as well as the strength, thickness, and distribution angle of the curved steel, or increasing the slenderness ratio, reduces the balanced failure point and shifts the interaction curve toward that of steel members. Comparisons with experimental results confirm the high predictive accuracy of the proposed design formulas.