Fatigue life in orthotropic steel bridge deck using a newly developed steel plate, which specially improved crack propagation rate da/dN in the low ΔK range, was examined by the structural model fatigue tests. A fatigue crack initiated at the weld root of the trough rib and deck plate was simulated. The stiffness changes during cyclic loading and the fracture surfaces suggested the fatigue life improvement in the specimen whose deck plate was replaced to the newly developed steel plate. The mechanism in which the fatigue crack resistance improvement of the deck plate reflected on the fatigue life of the structural model specimens was discussed from viewpoint of ΔK change along the fatigue crack path.
