Extending the Direct Strength Method for Cold-Formed Steel Design to Through-Fastened Simple Span Girts and Purlins with Laterally Unbraced Compression Flanges

Abstract

AbstractA direct-strength method (DSM) prediction approach is introduced and validated for metal building wall and roof systems that are constructed with steel panels through-fastened with screws to girts or purlins. The focus is capacity prediction for simple spans under wind uplift or suction; however, the DSM framework is generally formulated to accommodate gravity loads, continuous spans, standing-seam roofs, and insulated roof and wall systems in the future. System flexural capacity is calculated with the usual DSM approach; global buckling, local-global buckling interaction, and distortional buckling strengths are determined with a finite-strip Eigen-buckling analysis, including a rotational spring that simulates restraint provided by the through-fastened steel panel. The DSM flexural capacity is then reduced with a code-friendly equation consistent with existing standard provisions to account for the additional stress at the intersection of the web and free flange that occurs as the girt or purlin ...