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.

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Appropriate assessment of the fire resistance of structures depends largely on the ability to accurately predict the material response at elevated temperature. The material characteristics of stainless steel differ from those of carbon steel due to the high alloy content. These differences have been explored in some detail at room temperature, whilst those at elevated temperatures have been less closely scrutinised. This paper presents an overview and reappraisal of previous pertinent research, together with an evaluation of existing elevated temperature stainless steel stress-strain test data and previously proposed material models. On the basis of examination of all available test data, much of which have been recently generated, revised strength and stiffness reduction factors at elevated temperatures for a range of grades of stainless steel have been proposed, including four grades not previously covered by existing structural fire design guidance. A total of eight sets of strength reduction factors are currently provided for different grades of stainless steel in EN 1993-1-2 and the Euro Inox/ SCI Design Manual for Structural Stainless Steel, compared to a single set for carbon steel. A number of sets of reduction factors is appropriate for stainless steel since the elevated temperature properties can vary markedly between different grades, but this has to be justified with sufficient test data and balanced against ease of design -it has been proposed herein that the eight sets of reduction factors be rationalised on the basis of Gardner, L., Insausti, A., Ng, K. T. and Ashraf, M. (2010) . Elevated temperature material properties of stainless steel alloys. Journal of Constructional Steel Research. 66(5), 634-647.

Stainless steel's characteristic nonlinear, rounded stress-strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more