Risk acceptance and maintenance optimization of aging civil engineering infrastructures

The renewal model for cost-benefit optimization including maintenance is presented. Three types of maintenance strategies are proposed, i.e. age-dependent maintenance, block maintenance and maintenance by inspection and (perfect) repair. Then, new concepts for risk acceptability based on the life quality index philosophy are introduced. It is demonstrated that in limiting the failure rate three concepts can be used, the first addressing the maximum failure rate, a second using a time-average and the third an asymptotic value which may be proposed for practical use. All concepts, however, require computation of the exact failure rate (renewal intensity) or, at least, the asymptotic failure rate. A suitable asymptotic failure rate related to all corrective renewals after failure is given. A numerical example is given showing that the inspection/repair maintenance strategy is more cost-effective than the age-dependent strategy.