Eccentric loading behavior of CFDEST short columns: Testing, modeling and design

Elliptical steel tube (EST) has gained increasing adoption in structural engineering due to their favorable mechanical performance and architectural appeal. This study investigates the behavior of eccentrically-loaded concrete-filled double-skin elliptical steel tube (CFDEST) short columns through experimental and numerical analyses. The effects of key parameters, including load eccentricity, hollow ratio, diameter-to-thickness ratio, and aspect ratio, on failure modes, strength, and ductility are systematically examined. Furthermore, the distribution mechanisms of interfacial contact stress and longitudinal stress in concrete and EST are revealed. Based on experimental and analytical results, simplified design formulas are proposed to predict the eccentric compression strength of CFDEST columns, incorporating the influences of load eccentricity, hollow ratio, and cross-sectional characteristics. The results show that failure is characterized by semi-circumferential bulging of the outer EST, local inward buckling of the inner EST, and concrete crushing. The eccentric compressive strength decreases with increasing load eccentricity, hollow ratio, and diameter-to-thickness ratio. To optimize steel strength utilization, the strength of the inner EST should be designed lower than that of the outer EST. The findings provide a scientific basis for the design and implementation of CFDEST structures in practice.