Design of cold-formed steel built-up open section members under combined compression and bending

The numerical investigation on cold-formed steel built-up open section members under combined compression and minor axis bending is described in this paper. Through validating against experimental results in the literature, a rational finite element model of built-up section beam–column members was developed. The verified numerical model was employed for a comprehensive parametric study to obtain the results of 280 eccentrically loaded built-up section members. Furthermore, the applicability of the design formulae provided in the AISI Specification, AISC Specification, AS/NZS Standard and European Code was examined by comparing nominal strengths with loading capacities of the 280 numerical data produced in this study and 33 existing test data. Overall, the strength predictions determined by the codified interaction formulae based on the nominal compressive and flexural resistances calculated by the current direct strength method (DSM) were found to be highly scattered and underestimated by average of 17% – 27% for the built-up open section components experiencing combined loading. Hence, the modified DSM was recommended to determine the nominal resistances of the members under isolated compression or bending for more accurate endpoints of the load–moment interaction curve. In addition, a bi-linear interaction expression was proposed in this study for the design of the cold-formed steel built-up section beam–columns, which offered better strength predictions in accuracy and consistency compared to the codified interaction formulae.