This chapter addresses the derivation of Generalized Beam Theory (GBT)-based analytical distortional buckling formulae for cold-formed steel rack-section columns and beams. Such formulae provide bifurcation stress estimates for members with arbitrarily inclined intermediate stiffeners and pinned/free-to-warp or fixed/warping-free end sections. The accuracy and validity of the GBT-based analytical estimates are assessed by means of a comparison with exact FEM results concerning several rack-section member geometries and, for some pinned/free-to warp columns only, also with the values yielded by the formulae developed by Lau & Hancock. The various concepts and steps involved in deriving GBT-based (approximate) analytical formulae to estimate distortional buckling stresses in thin-walled rack-section columns and beams are presented in the chapter. Such formulae automatically incorporate folded-plate theory concepts—an important feature which is responsible for the fact that they directly account for cross-section distortion and (partially) flexural deformation effects. The derived formulae, which require the preliminary (numerical) solution of an auxiliary standard matrix eigen value problem and can be readily programmed even in a hand calculator, provide distortional critical lengths and bifurcation stress resultant estimates for rack-section columns and beams with arbitrarily inclined intermediate stiffeners and pinned/free-to-warp or fixed/warping-free end sections. The chapter presents a detailed analysis of a set of four identical columns/beams with pinned/free-to-warp or fixed/warping-free end sections, in order to illustrate the application of the proposed formulae.
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