Beam-Column Tests of Cold-Formed Steel Built-Up Closed Sections

Abstract

This study aimed to investigate the buckling behavior of cold-formed steel built-up closed section members subjected to combined minor axis bending and compression. The channels were fabricated from zinc-coated steel sheets of grades G500 and G550 to compose built-up closed sections. A total of 30 beam-column specimens with nominal member lengths of 300, 900, and 1,500 mm as well as nominal plate thicknesses of 0.75 and 1.2 mm were eccentrically loaded under pin-ended boundary condition. The initial loading eccentricity was varied for the specimens in each test series to obtain the data evenly distributed in the axial load-moment interaction diagram. Experimental results including failure modes, loading capacities, and full-history responses of the test specimens were obtained. In addition, the experimental loading capacities were compared with nominal strengths to evaluate the suitability of the provisions as stipulated in the North American specification, Australian/New Zealand standard, European code, and American specification for the built-up section beam-columns. It is shown that the aforementioned design codes are overall unreliable and unconservative for strength predictions of the cold-formed steel built-up closed section members under combined minor axis bending and compression.