Shear strength of stiffened square thin-walled concrete-filled steel tubular columns

Abstract

In comparison to extensive researches on compressive or flexural behavior of stiffened square concrete-filled steel tubular (CFST) columns, few were conducted on shear behavior. The cyclic-shear behavior between stiffened and unstiffened square thin-walled CFST columns was different, and the cyclic-shear behavior of CFST columns stiffened by the diagonal ribs, which were welded on the adjacent sides of a square tube, was significantly improved, as demonstrated by recent experimental results. This work uses detailed finite element (FE) analysis and parametric analysis to explore the shear mechanism and shear contribution of each component in the stiffened CFST column. The refined FE model was developed using ABAQUS and verified by the test results of both stiffened and unstiffened CFST columns subjected to cyclic and monotonic shear loading. Based on the analysis of test results, a method based on the degree of the cross-sectional plasticity was proposed to distinguish shear failure from bending failure, as typical bending failure phenomena (concrete crushing and tube buckling) were also observed at the ends of column specimens with shear failure. Analytical results showed that the steel tube and diagonal ribs resisted the shear through shear stress, and the concrete resisted the shear through the developed compression strut confined by the horizontal stress of steel. A shear model considering the interaction between concrete and steel was then established. The mechanics-equations and regression-equations were proposed and compared with the shear test results reported in the existing literature and FE analysis. Both types of equations were found to well predict the shear strength of both stiffened and unstiffened square CFST columns.