Experimental and Numerical Investigation on Flexural Behavior of Novel Unsymmetrical Cold-Formed Steel Built-Up Stiffened Box Sections

AbstractThe use of cold-formed steel (CFS) built-up sections for portal frames is gaining popularity due to their ability to provide sustainable solutions and more optimized section design opportunities. This paper presents an experimental and numerical investigation conducted on a novel unsymmetrical CFS built-up stiffened box beam. The sections are manufactured with a complex arrangement of stiffeners and have an overall web depth of up to 550 mm. In the literature, to our best knowledge, no large-scale bending testing has been conducted on CFS beams of such dimensions. A total of 12 full-scale four-point bending tests are reported. Nonlinear elasto-plastic finite element (FE) models were developed and validated against the experimental test results. A comprehensive parametric study involving 200 FE models was conducted to investigate the effects of key design parameters on the flexural capacity performance. The parameters included section thickness, screw spacing, and unrestrained beam length. It was found that, for the sections investigated, lateral-torsional buckling was not observed when the unrestrained length was less than 4 m. The results were then compared against the design flexural capacities determined by the American Iron and Steel Institute (AISI S100) and Australian and New Zealand Standards (AS/NZS 4600). The current design flexural capacities were conservative by 7% on average compared with the experimental and FE results. Finally, new design equations were proposed, and a reliability analysis was conducted to assess the feasibility of the proposed equations.