Risk-based Optimization and Reliability Levels of Coastal Structures

Identification of optimum reliability levels for coastal structures is considered. A class of breakwaters is considered where no human injuries can be expected in cases of failure. The optimum reliability level is identified by minimizing the total costs over the service life of the structure, including building costs, maintenance and repair costs, downtime costs and decommission costs. Different formulations are considered. Stochastic models are presented for the main failure modes for rubble mound breakwaters without superstructures, typically used for outer protection of basins. The influence on the minimumcost reliability levels is investigated for different values of the real rate of interest, the service lifetime, the downtime costs due to malfunction and the decommission costs.