A numerical study is carried out on the effect of stiffeners and the corresponding design method of hybrid steel plate girders. A hybrid steel plate girder is a steel girder whose flange plates are composed of high strength steel, and the web plate of low strength steel in order to decrease the material cost. In such a hybrid steel girder, just before the ultimate state, the top and bottom parts of the web plate have been yielded although the flange plates are still remain in the elastic region. Therefore, usual design method cannot be used for the hybrid steel girders. In this paper, numerical analysis is conducted on the strength and behaviour of hybrid steel girders, with especially highlighting the effect of longitudinal stiffeners and the load bearing stiffeners. According to the analysis, it is shown, for example, that the longitudinal stiffeners located lower than the usual position is slightly effective.
