Design Provisions for Sections Containing Unstiffened Elements with Stress Gradient

This paper presents a general design procedure for calculating the moment capacity of sections containing unstiffened elements with stress gradient. The method uses design equations for effective widths of unstiffened elements with stress gradients based on plate test results. Current international design provisions allow the capacity of sections that contain stiffened elements with stress gradients to be calculated on the basis of inelastic reserve capacity, whereas sections that contain unstiffened elements must be designed on the basis of initiation of yielding in the section. This paper presents methods for the calculation of the capacity where inelastic reserve capacity may be taken into account, for sections containing fully effective unstiffened elements with stress gradient. The methods are shown to be in good agreement with experimental data of I-sections and plain channels in minor axis bending. Particular attention is given to the effect of both the elastic buckling coefficient used in the effective width method, and the use of inelastic considerations, on the bending capacity. Specific design proposals are presented in the form of amendments to the current American and Australian standards for cold-formed steel structures, for elements (effective width equations) and sections in bending (inelastic reserve capacity equations).