The evolutionary structural optimization (ESO) is one of the shape optimization methods of a structure, in which the low stressed part of a structure is removed from the structure step-by-step until an optimal design is obtained. In the shape optimization of box girder using the ESO method, section of box girder cannot be successfully obtained when both the transeverse and longitudinal behavior is considered on the starting step. Previous studies improved that problem but did not solve totally. The rejected elements before the longitudinal behavior is considered may have possibility that the longitudinal behavior may need them actually.
This study deals with the two models which describe transverse behavior and longitudinal behavior and superposed after the rejecting process of elements in each model. And the size of elements shrink gradually for the smooth shape. The optimal design by that method is compared to a real blueprint.