Many existing bridges in Japan are suffering from damage due to the deterioration of materials, heavy traffics and aging. In the future, it is evident that serious social problems will arise as the number of damaged bridges increases. Considering the present social and economic situation of Japan, it is urgent and important to establish an optimal maintenance strategy for such existing bridges so as to ensure their safety in satisfactory levels. Life-Cycle Cost (LCC) has been paid attention as a possible and promising method to archive a rational maintenance program. Generally, LCC consists of initial cost, maintenance cost, and renewal cost. However, when considering Life-Cycle Cost in the region that frequent earthquakes occur, it is important to take into account the social and economical effects due to the collapse of structures as well as the minimization of maintenance cost. The loss by the collapse of structures due to the earthquakes can be defined in terms of an expected cost and introduced into the calculation of LCC. In this study, a stochastic model of structural response is proposed, which accounts for the variation due to the uncertain characteristics of earthquakes, and the probability of failure is calculated based on the reliability theory. Then, the expected cost can be obtained by multiplying the failure probability with the loss.
