The effects of cyclic plastic strains on the fracture toughness of structural steels and also the effects of strain aging on the fracture toughness of structural steels subjected to cyclic plastic strains are investigated by Charpy V-notch impact tests. The Charpy V-notch absorbed energy decreases with the increase of cycles of plastic strains. Especially, it drops greatly at the early cycles. The decrease of the absorbed energy is larger with the increase of the magnitude of plastic strains. The influence of the strain aging is small on the absorbed energy for the specimens under no loads and monotonic loading, but it is large under cyclic loading. The Charpy V-notch impact toughness is examined on the top and bottom flanges of a girder of a highway bridge hit by the 1995 Hyogoken-Nanbu Earthquake, Japan. The girder is shown to have not been subjected to cyclic plastic strains during the earthquake.
