SummaryThe total cost minimization is the optimal criterion of decision making for design and maintenance of structures.In this study, a sequential cost minimization method and its consistent formulation are presented for the inspection planning problem of deteriorating structures. The method aims to find an optimal inspection strategy so that the total expected cost in the period between the present inspection and the next be minimum. The optimization variables are the inspection methods at the present inspection and the interval to the next inspection for the structure. The optimization is repeatedly carried out at every inspection.The optimal inspection methods are selected from the following five methods : 1) no inspection, 2) visual inspection, 3) mechanical inspection, 4) visual and conditional mechanical inspection, and 5) sampling mechanical inspection. The cost evaluation equation is developed for each inspection method, where the following cost items are included : inspection cost, repair cost, risk of member failure, risk of catastrophic failure and loss due to service suspension caused by scheduled and accidental system downs. The selection of suitable inspection interval for the structure is to be achieved by comparison of total expected costs evaluated for possible interval plans.The applicability of the proposed method is demonstrated through the numerical calculations by assuming a structural member set and a structure. Fatigue failure is considered as the deterioration damage of the members. Further, discussion is made on the value of the sequential cost minimization method, comparing with the optimal inspection strategy throughout the life time.
