Orthotropic steel deck bridges are increasing because of them light weight in longer span bridges. But fatigue damages due to increasing of through traffic load are often reported on the slit with the connections between open section type longitudinal rib and floor rib in recent years. To study the prevention method of fatigue damages, both F.E.M,analysis and large scale model fatigue testing were carried out. To prevent the fatigue damages, the best is the none of slit. If it can not applied for any reason, both none of scallop and narrower width of upper slitare conformable. Key Words : Floor Rib, Fatigue, Fabrication, Orthotropic Steel Deck