Flexural behaviour of cold-formed steel built-up section members

This paper presents experimental and numerical investigations on cold-formed steel built-up section beams. The channels with longitudinal stiffeners were brake-pressed from steel sheets with nominal thicknesses of 0.75 and 1.2 mm. First of all, minor axis bending tests were undertaken to explore buckling behaviour of the newly designed built-up open and closed sections. The test setup, experimental procedure, ultimate moments and failure modes were reported. Then, finite element models were developed and validated against the test results. The parametric study incorporating 107 built-up open and closed section flexural members was performed to generate further numerical data over a wide range of sectional configurations and geometric parameters. After that, the comparisons of ultimate moments obtained from experiments and finite element analyses with nominal strengths calculated on the basis of direct strength method (DSM) that provided in the North American Specification and Australian/New Zealand Standard were carried out to evaluate the appropriateness of current design rules for cold-formed steel built-up section beams. It is shown that the codified DSM equations are generally conservative for flexural strength predictions of the built-up open sections, while provide unconservative predictions for the built-up closed sections under minor axis bending.