Distortional Buckling of Cold-Formed Steel Members in Bending
Schafer, Benjamin W.
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Laterally braced cold-formed steel beams generally fail due to local and/or distortional buckling in combination with yielding. For many cold-formed steel (CFS) studs, joists, purlins, or girts, distortional buckling may be the predominant buckling mode. However, distortional buckling of CFS beams remains a largely unaddressed problem in the current North American Specification for the Design of Cold-Formed Steel Structural Members (NAS). Further, adequate experimental data on unrestricted distortional buckling in bending is unavailable. Therefore, two series of bending tests on industry standard CFS C and Z-sections were performed and presented in this dissertation. The testing setup was carefully designed in the first series of tests (Phase 1) to allow local buckling failure to form while restricting distortional and lateral-torsional buckling. The second series of tests (Phase 2) used nominally identical specimens to Phase 1 tests, and a similar testing setup. However, the corrugated panel attached to the compression flange was removed in the constant moment region so that distortional buckling could occur. The experimental data was used to examine current specifications and new design methods. Finite element modeling in ABAQUS was developed and verified by the two series of bending tests and then applied to analyze more CFS beams.