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);
1. Fillet weld between deck plate and trough rib
1-1. Crack propagates into deck Plate
1-2. Crack propagates into bead
2. Fillet weld between transverse rib and trough rib
3. Butt weld connection of trough rib
4. Fillet weld between vertical stiffener and deck plate
If Crack 1-1 penetrates a deck plate, it threatens not only to cause damage on
pavement but also to deteriorate serviceability and safety to the traffic. What is worse is
that Crack1-1 is invisible until it causes visible damage on the pavement. Therefore PWRI
has given priority to investigate this type of fatigue crack. Crack1-2 is also problematic
because the number of this type of crack is increasing, it is fast growing, and it tends to
1 Team Leader, the Structures Research Group, Public Works Research Institute
(1-6 Minamihara, Tsukuba City, 305-8516)
2 Senior Researcher, Bridge Structure Team, Public Works Research Institute
3 Chief Research Engineer, Research Laboratory Technical Div. Yokogawa Bridge Corp.