Strength Design Curves for Thin-Walled Sections Undergoing Distortional Buckling

Certain types of cold-formed sections, notably those composed of high-strength steel, some decking sections and racking sections may undergo a mode of buckling called distortional in which edge and intermediate stiffeners are inadequate to prevent lateral movement of the flanges which they support. The existing design methods in current standards and specifications are often not adequate to account for distortional buckling. This paper describes proposed strength design curves for thin-walled sections undergoing distortional buckling. The design curves are based on testing and the test data base is included in the paper. The influence of local buckling on distortional buckling is also discussed. A A¢ b be Fy M~ M y Z Z~ O'de O'di N O T A T I O N Gross sect ion area Effective par t of gross section area Pla te width Effective par t of plate width Yield stress used in design Ul t ima te m o m e n t capaci ty M o m e n t at first yield Gross section modu lus Effective sect ion modu lus Elastic d is tor t iona l buckl ing stress Inelast ic d is tor t iona l buckl ing stress