The material stress–strain behaviour of structural carbon steel may be suitably accurately reflected for design purposes by an idealised elastic, perfectly-plastic material model; such material behaviour lends itself to the concept of section classification. There are, however, a number of structural materials, such as aluminium, stainless steel and some high strength, cold-worked steels, where this idealised model becomes inaccurate due to non-linearity of the stress–strain response below the yield point and considerable strain hardening beyond the yield point. Resulting design methods, developed on the basis of the idealised material behaviour, are necessarily overly conservative. A new method has been developed that utilises a more accurate material model and a continuous measure of cross-section deformation capacity (rather than the discretised system of section classification) to provide more rational and efficient designs. This paper describes the basis for the proposed design method and presents a comparison with results obtained from laboratory testing and those predicted by the current Eurocode approach. The proposed design method offers average increases in member resistances of around 20% over the current Eurocode approach, and a reduction in scatter of the prediction.