Behavior of concrete-filled steel tubular cold-formed built-up slender square columns under eccentric compression

Nowadays, the uses of concrete-filled steel tubular (CFST) columns have been significantly increased in civil engineering infrastructures due to their inherent ductility, high load-bearing capability and excellent energy absorption capacity. This paper presents both experimental and numerical investigations on the structural responses of built-up slender square concrete-filled steel tubular (SCFST) columns under uniaxial eccentric compression. In this study, a total of eleven welded built-up slender SCFST columns were tested with nominal concrete cylinder strengths of 27 MPa, 35 MPa and 44 MPa, respectively. The effects of different parameters including the concrete strength, column overall slenderness ratio, plate slenderness ratio and variation of eccentricities on the buckling modes, ultimate axial strength and post-peak ductility of the specimens were investigated. The test results indicated that the ultimate strength of the columns varied inversely with the load eccentricity ratio. The concrete grades have significant influence on the load-bearing capacity and ductility of the columns. Moreover, the ultimate strength as well as ductility of the tested specimens moderately decreased with the increase of column overall slenderness ratio and plate slenderness ratio, respectively. Thereafter, ABAQUS software was used to develop the finite element (FE) models of the tested specimens. The developed FE models of built-up slender SCFST columns were validated by comparing the simulated results with test results. It was found that the proposed FE models are capable to predict the structural behavior of built-up slender SCFST columns with high accuracy. Finally, the test results were compared with the corresponding failure loads and ultimate bending moments predicted by the EN 1994-1-1 provisions, which appear slightly insecure.