Cross-sectional behavior of cold-formed steel semi-oval hollow sections

This paper presents an investigation on the material properties, residual stress distributions and cross-sectional behavior of cold-formed steel semi-oval hollow sections. Four cross-section series were included in the test program. The test specimens were cold-formed from hot-extruded seamless steel circular sections. Tensile coupon tests were conducted on coupon specimens extracted from three critical locations, namely the flat, curved and corner portions, of each cross-section as well as half of the cross-section of a representative section. Membrane and bending residual stresses distributions on the representative section were measured in both longitudinal and transverse directions. In addition, initial geometric imperfections were measured for each cross-section series and stub column tests were conducted to determine the average stress-strain relationship over the complete cross-section in the cold-worked state and to examine the cross-sectional behavior of cold-formed steel semi-oval hollow sections. Furthermore, a finite element model was developed and validated against the test results. With the verified finite element model, an extensive parametric study over a wide range of cross-section geometries was performed. The load-carrying capacities of stub columns obtained from experimental and numerical investigation were compared with the design strengths predicted by the Direct Strength Method using the design equations originally developed for open sections and the Continuous Strength Method with the design curves originally developed for traditional tubular sections. The comparison results show that the existing design methods provide conservative design strength predictions. In this study, modification on the Continuous Strength Method is proposed, which is shown to improve the accuracy of the design strength predictions in a reliable manner.