In this study, we investigated the fatigue strength of butt weld joints with 10% or more misalignment of the plate thickness, through fatigue tests of 3 girder specimens that have aligned butt weld joint, 18% and 36% misaligned butt weld joints against the 11mm-thick plate in the bottom flange. And we also verified the effect of the taper grinding and toe grinding against the misaligned butt weld joints. As a result, it was confirmed the fatigue strength of 18% or less misaligned butt joints was satisfied JRA Class D and that of 36% misaligned butt joint may not be satisfied JRA Class D. By taper grinding and toe grinding, the fatigue strength of 36% misaligned butt weld joint was improved about 1 rank.
