A structural analysis is developed in order to evaluate the long term mechanical performance of steel structures by taking into account the effects of the histories of corrosion loss of material and repair. This analysis is characterized by the point that the volume change in material due to corrosion or repair is adopted as a new controlling parameter along with the conventional parameters such as load and displacement. With the proposed analysis method, it is examined how the seismic behaviors of the repaired bridges are influenced by the difference of the repair methods in comparison with that of the corresponding virgin bridge.