Tests of cold-formed steel built-up open section beam-columns subjected to unequal end moments

A test program is presented in this paper to investigate the behaviour of cold-formed steel built-up open section members under combined compression and non-uniform minor axis bending. The longitudinally stiffened channels were press-braked from zinc-coated steel sheets that had the nominal 0.2% proof stresses of 500 and 550 MPa. The built-up open section test specimens were fabricated through assembling two identical channels back-to-back with self-tapping screws. A total of 17 specimens were categorized into four test series. The end moment ratio varied for the specimens of each test series to examine the influence of non-uniform bending on beam-column members. All the specimens were eccentrically loaded under pinned supports to obtain loading capacities, failure modes and full-history responses. Moreover, the comparison of experimental loading capacities with nominal strengths was performed to assess the applicability of the current design rules for the thin-walled section beam-columns under moment gradients.