Orthotropic steel deck (OSD) is widely applied to long span bridges and urban
viaducts in Japan because its light weight contributes to reduce their dead load. In the early
decades of application of OSDs, valve plates were used for longitudinal ribs, then trough
ribs had been increasing through 1970’s, and it became common in 1980’s. Trough ribs
have some advantages that they can be fabricated by one side welding and bring more
longitudinal rigidity so that spacing of transverse ribs can be widened. During 1990’s,
fatigue cracks observed in OSDs had been a few types, however many types of cracks are
observed in recent years as depicted in Figure 1. They are1);