Various assumptions and/or suppositions have been established in order to simplify calculations in the structural design of a bridge. Particularly, with regard to connections between perpendicularly crossing members such as main girders and cross beams or cross beams and stringers, simple supports or pin connections are often specified, and deflections and stresses obtained from design calculations differ considerably from those in actual structures, especially in the vicinities of connections. These design calculations are usually on the conservative side when determining the cross-sectional dimensions of members, but fatigue is often caused by unexpected stresses due to restraint moments at the connections, for example.