摘要: |
Breakwaters are of vital importance, especially to ports on exposed location. Moreover, the costs of breakwaters is quite often very large. The costs depends of course on the type of breakwater, on the water depth and the wave climate, but also on the safety level applied for the design. The safer the design, the larger the expected cost of repair during structure service lifetime will be smaller. Damage to a breakwater can cause down-time for port operation. This is certainly the case if berths for vessels are located along the inner side of a breakwater. However a breach in a breakwater might cause wave disturbance enough to affect operation for example of a container berth. The optimum safety level of a breakwater should be the one that gives minimum total costs during the structure service lifetime. The total costs is the sum of initial (construction) costs, repair costs, and down-time costs. The relation between damage cost and safety level is different for each breakwater type, so the optimum is also different for each breakwater type. The design specifications given in national standards and recommendations are not based on cost optimization analyses but simply reflects common practice. There is a need for a more stringent investigation of the optimum safety levels for breakwaters reflecting the circumstance for the individual breakwaters. Typical cases should be selected for analyses of optimum safety levels as a basis for more thorough standards. In doing so, the more difficult steps will be to asses down-time costs and to define structure service lifetime. The MARCOM session will discuss the problems involved in these assessments. |