Optimal design of steel frames with non-uniform members

Material savings for structural steel frames on the background of reliable design procedure are of high relevance for competitive steel design. Optimisation with respect to material however will require more refined analysis and design procedures for such frames. Traditional methods are found to be not suitable for this purpose. For frames with non-uniform members a procedure for practical application was developed using stochastically optimisation to find a cross section distribution for optimal weight design. Compared to traditional design methods weight savings of up to 15 % were achieved. Design requirements are based on in-plane stability specifications in the national German Code DIN 18800 [2] and the EC 3 [1]. Load carrying capacity from lateral torsional buckling may be determined by application of buckling curves from codes using reduction factors depending on the buckling slenderness or by flexural-torsional theory of second order analysis. The procedure developed in this study combines effectively an optimised in-plane-design with subsequent checking of local buckling and lateral buckling, thus leading to a highly economic and also safe design of structural steel frames.