Maintenance planning for deteriorating concrete bridges

In an effort to prioritize the repair, rehabilitation, and replacement of existing bridges, bridge management programs have been developed. In recent years, reliability-based optimum-maintenance planning strategies applicable to bridges have been proposed. Optimum inspection and repair times can be identified using these strategies. In this study, the effect of repair on time-variant failure probability is illustrated for several repair/replacement strategies. Time-variant reliability computations are performed using a combined technique of adaptive importance sampling and numerical integration. Several repair strategies are investigated for a typical bridge in Colorado. For this bridge, it is shown that for a single repair performed about halfway through the design life, the postrepair strength must be at least 80% of the original strength for the repair to have a significant influence on the system failure probability of the bridge during its remaining service life. Also, for maintenance using shotcrete, multiple repairs appear to have little influence on the lifetime system failure probability. Also presented are optimal maintenance strategies in which optimal inspection/repair times are identified based on minimum expected cost within prescribed reliability constraints. It is shown that the optimum repair time is dependent on the failure cost of the bridge and that the discount rate influences the optimum repair time and life-cycle cost. As the discount rate increases, the optimum repair time increases until it reaches an upper bound that is dependent on the system failure probability constraint. The results can be applied to the prediction of optimal lifetime maintenance planning strategies for concrete bridges under corrosion.