Analysis and testing of cold-formed steel beams

Laterally braced cold-formed steel beams generally fail due to local or distortional buckling. For many cold-formed steel studs, joists, purlins, or girts, distortional buckling occurs before local buckling, unless the compression flange is partially restrained by attachment to sheathing or paneling, The effectiveness of the attachments ranges from complete restriction of distortional buckling to, little or no restriction. Two series of 4 point bending tests on laterally braced C and Z members have recently been completed to examine the bounds of the capacity for laterally braced beams. The first series uses a corrugated panel with special fastener details, experimentally and numerically determined, to insure distortional buckling is restricted. The focus of this paper is a second series, of nominally identical specimens, in which the corrugated panel is removed in the constant moment region and distortional buckling failures are allowed to occur. With reliable test data for local and distortional buckling now available, new design methods for the two failure modes can be developed and evaluated. Further, the experimental results can be used to provide insight on the design of members with partially restrained flanges.