Web crippling behavior of CFS built-up beams under end two-flange loading

Compared to a single cold-formed steel (CFS) channel beam, a built-up I-beam comprising of two such channels possesses a higher bending capacity and greatly increased stability. However, since CFS webs are typically slender elements, they are susceptible to web crippling under concentrated loading. Most of the previous research in this area has focused on single sections, with very limited data being available for built-up sections. The web crippling response of a single CFS channel may differ from that of an I-section, due to the presence of contact and connectors in the latter. Hence, the web crippling design rules in the current North American Specifications (AISI S100) and the Eurocode (EN1993-1-3) for single sections may not be adequate for built-up beams and need further exploration across a wide range of parameters. A finite element (FE) model was developed in ABAQUS of two plain channel sections, fastened through the web at discrete points cross-sectionally and longitudinally, and calibrated against relevant test data reported in the literature. The verified FE model was then used to conduct an extensive parametric study by varying critical parameters such as the web slenderness, the bearing length, and the corner radius-to-thickness ratio, under end two-flange loading. The accuracy of the North American and European design standards was also assessed by comparing their web crippling strength predictions against the FE results. It was concluded that both design codes made inconsistent predictions, overestimating the web crippling strengths in some cases, while significantly underestimating them in others.