DSM design of fixed-ended slender built-up back-to-back cold-formed steel compression members

Abstract

Built-up back-to-back cold-formed steel channel (BC) sections have gained increased application as compression members in building structures. Although many researchers have studied the behaviour and design of BC compression members, the design equations in the current standards are still inadequate for them, while the new design equations proposed in recent studies are inconsistent and lead to predictions with varying accuracy. This study focuses on slender BC members with fixed ends, which are sensitive to local-global interaction or global buckling. Many tests of fixed-ended slender channel and BC compression members, which failed mostly by local-global interaction buckling, were conducted first, followed by developing validated finite element models. The models were then used in a parametric study of BC compression members with varying sections, screw arrangements and lengths, to investigate their failures by local-global interaction and global buckling. The outcomes from tests and finite element analyses provided improved understanding of the behaviour of BC members, and were used to compare their compression capacities against twice the individual member capacities, and show the limitations of the current design equations available in the standards and research publications. Finally, reliable design guidelines were proposed using the Direct Strength Method (DSM).