Earthquakes sometimes give damages to steel structures. The structures which have not been seriously damaged are still used after an earthquake. The fatigue strength of these structures, however, might have been decreased due to the cyclic loads during an earthquake. In order to clarify the effect of seismic loading on the fatigue strength of the welded joint of a steel structure, varying loading fatigue test of welded joint after large straining was performed. However, few researches have been done on the residual fatigue strength after large strain cycling which enters into gross plasticity. The objective of this study is to clarify the integrity evaluation method of steel structures which experienced seismic loading. The varying loading fatigue test of a welded joint which had been subjected to a large cyclic strain as a simulation of a seismic loading was conducted and the residual fatigue strength was investigated.
