Built-up back-to-back cold-formed steel compression members failing by local and distortional buckling

The current design methods for built-up back-to-back cold-formed steel (CFS) channel compression members are considered inadequate despite several research studies in recent times. These research studies have proposed improved DSM based design equations, however, they have in general led to predictions of varying accuracy. Further, there were some contradicting observations regarding the effects of screw connections on their compression behaviour and capacities. Therefore, this research focused on the compression behaviour and capacity of built-up back-to-back CFS channel sections subject to local and/or distortional buckling. It included compression tests of short single and back-to-back channel members failing by local-distortional interaction buckling, development and validation of finite element models and finally a parametric study to examine the effects of screw fastener characteristics and arrangements on the compression behaviour and capacities of back-to-back channel members failing in local and/or distortional buckling. Using the results, the accuracy of currently available design equations in the CFS design standards and recently published research papers was investigated and a simple DSM based design method is recommended. This paper presents the details of this research and the results including its findings.