Influence of Concrete Fill on the Buckling Characteristics of Slender Circular Steel Tubes

Abstract

AbstractThe strength, stiffness and buckling characteristics of hollow structural steel tubes can be significantly enhanced by filling it with concrete. AISC 360-16 classifies circular concrete-filled steel tubes (CFSTs) as compact, non-compact and slender based on the section slenderness ratio λ = D/t (outer diameter/thickness of the steel tube). The steel in compact and non-compact sections yield before buckling, and slender sections are assumed to buckle elastically. However, a comparison of the design provisions suggested by AISC 360-16 with the existing experimental results shows that the predicted strength is highly conservative for slender sections. To investigate the influence of concrete core on the buckling characteristics of slender circular CFSTs, a finite element (FE) analysis is performed using ABAQUS. A parametric study is conducted to study the influence of the input parameters of the concrete damage plasticity model. The post-peak branch of the stress-strain relation of unconfined concrete is also modified to account for the increase in the peak-axial strain of confined concrete. The results from the FE analysis of a slender CFST short column is in good agreement with the experimental observations. The analysis shows that the steel tube did not elastically buckle, and crushing of concrete led to the failure of the specimen. This is contrary to AISC 360-16 provisions, which assumes that slender CFSTs fail by elastic local buckling. This could probably be the reason for the overly conservative prediction of the ultimate load capacity of slender CFSTs by AISC 360-16, and needs further investigation.KeywordsConcrete-filled steel tubeFinite element modellingSteel tubeBucklingSlender