Design of structural stainless steel members by second order inelastic analysis with CSM strain limits

Abstract System-level advanced analysis is now a viable tool for widespread use in structural design. By directly capturing frame and member level instability effects, plasticity, initial geometric imperfections and residual stresses in the analysis, the need for subsequent individual member checks can be eliminated. The analysis of structural members and frames is typically carried out using beam elements, which are unable to capture the effects of local buckling. However, local buckling dictates the strength and ductility of cross-sections and the extent to which plastic redistribution of forces and moments can be exploited; it cannot therefore be disregarded. A proposal is made herein, in which strain limits, defined by the continuous strength method, are applied to simulate local buckling in beam element models, thereby controlling the degree to which spread of plasticity, force and moment redistribution and strain hardening can be utilised in the design of structural elements and systems. Strains are averaged over a defined distance along the member length to reflect the fact that local buckling requires a finite length over which to develop and to allow for local moment gradient effects. Design is based directly on the application of strain limits to all cross-sections in the structure. The accuracy of the proposed method for the design of stainless steel members is assessed through comparisons with benchmark shell finite element results; both I-section and hollow section members are considered. Comparisons against current design methods confirm the significant benefits of applying the proposed approach in terms of both the accuracy and the consistency of the resistance predictions. The reliability of the design approach is demonstrated through statistical analyses performed in accordance with EN 1990. Application of the proposed method is particularly appropriate for stainless steel structures due to the high material value and the complexities presented by the nonlinear material stress–strain response for traditional design treatments. The proposed method is due to be included in the two major international stainless steel design standards EN 1993-1-4 and AISC 370.