There is a need for more stringent investigation of the optimum safety levels for breakwaters reflecting the circumstance for the individual breakwaters. RnThe design specifications given in national standards and recommendations are not based on cost optimisation analyses but simply reflect common practice. A second point is that there is also damage to third parties, which is not included in the budgeting plan of the port owner. Also the financial resources are usually different. For a port authority financing regularly the repair of small damage may be much easier than financing a large repair work. RnApart from the overall financial aspects, there is also the cash-flow problem related to repairs, the amount of which depends on structure safety. RnIt is expected that the cost curves, showing the optimum design, have different shapes for the various types of breakwaters (rubble mound, caisson, berm breakwater). Indirect costs (downtime costs) have seldom been included. In the past the optimisation studies have been performed for rubble mound breakwaters, taking into account initial costs and direct maintenance 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 total costs are the sum of initial (construction) costs, repair costs, and downtime costs. RnThe optimum safety level of a breakwater should be the one that gives minimum total costs during the structure service lifetime. But also a breach in a breakwater might cause wave disturbance enough to affect operation, for example of a container berth. This is certainly the case if berths for vessels are located along the inner side of a breakwater. Damage to a breakwater can cause downtime for port operation. When the design is safer, the expected cost of repair during structure service lifetime will be smaller. The costs depend not only on the type of breakwater, the water depth and the wave climate, but also on the safety level applied for the design. Moreover, the costs of breakwaters are quite often very large. RnBreakwaters are of vital importance, especially to ports on exposed locations. The length and layout of a breakwater for a specific harbour is a separate subject outside the scope of this report. RnThe report addresses the design of the cross section of breakwaters. It is not intended to provide details of how a designer can perform such analysis for alternative designs and safety levels for a particular project and location. RnThis report is intended to be used by designers to obtain guidance when selecting the type of breakwater and related safety levels appropriate to a particular project, taking into consideration the performance requirements of the project, the location and the type of breakwater selected. Therefore, a major task of WG 47 was to advise on the choice of safety levels. However, no advice on choice of safety level is included in the reports. RnIn the reports of WGs 12 and 28, safety coefficients related to the most important failure mode design equations corresponding to a range of safety levels are presented. Following the PIANC PTC II Working Group 12 on ?Analyses of Rubble Mound Breakwaters? and the MarCom Working Group 28 on ?Breakwaters with Vertical and Inclined Concrete Walls? and Working Group 40 on ?Guidelines for the Design and Construction of Berm Breakwaters?, MarCom decided to set up a Working Group 47 with the scope of providing guidance to designers on the choice of type of breakwater and related safety levels.
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