propagate into deck plate and/or trough rib webs eventually. The cause of these types of
crack is guessed that local bending of deck plate induces high stress concentration at root
of trough rib weld as shown in right bottom of Figure 1. Since the damaged cases are
increasing, research on the cause of cracks and developments of repair/reinforcement
methods are strongly needed. It is the same for crack 3 and 4.