The paper considers the problem of optimization of the box section of the main girder of the double beam bridge crane for the case of placing the rail above the web plate. Reduction of the girder mass is set as the objective function. Research on the mutual dependence of geometric parameters of cross section, and their ratio, using the method of Lagrange multiplier as characteristic criteria is done. Also, the paper shows an algorithm for selection of the optimal criteria and determining the optimal geometric parameters of cross section. The criteria of lateral stability and local stability of plates were applied as the constraint functions. The obtained results of optimization of geometrical parameters were verified on numerical examples.

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