Local buckling tests on cold-formed steel beams

C and Z sections are two of the most common cold-formed steel shapes in use today. Accurate prediction of the bending performance of these sections is important for reliable and efficient cold-formed steel structures. Recent analytical work has highlighted discontinuities and inconsistencies in the American Iron and Steel Institute (AISI) and Canadian Standards Association (S136) design provisions for stiffened elements under a stress gradient (i.e., the web of C or Z sections). New methods have been proposed for design, and an interim method has been adopted in the North American Specification (NAS). However, existing tests on C and Z sections do not provide a definitive evaluation of the design expressions, due primarily to incomplete restriction of the distortional buckling mode. Described in this paper is a series of flexural tests with details selected specifically to insure that local buckling is free to form, but distortional buckling and lateral-torsional buckling are restricted. The members selected for the tests provide systematic variation in the web slenderness (h/t) while varying other relevant nondimensional parameters (i.e., h/b, b/t, d/t, d/b). Initial analysis of the completed testing indicates that overall test-to-predicted ratios for AISI, S136, NAS, and the direct strength method are all adequate, but systematic differences are observed.