One of most effective and traditional ways for the economic design of steel plate girders is to vary their cross-sectional dimensions along their length, in accordance to their bending moment diagram. The design guideline was published in 2000. However, in spite of the existence of practical design rules to determine the number of cross-sections and the cross-section variation points, the final decision still relies on the experience and good sense of the bridge designer. In this paper, we show the outlines of determination system that, by applying genetic algorithms, not only determines the most economic resistance moment and their respective transition points, but also gives an evaluation of the bending moment diagram, without having to perform the conventional structural analysis.
