This paper analyses experimental results from 2d and 3d model tests. The purpose was to derive a criterion to predict breaking wave height in presence of simple and composite vertical breakwaters. A new empirical formula is discussed and its validity is examined by the laboratory experiments. Subsequently a description is given of a model developed for the prediction of the percentage of waves impacting on this structure in a sea state.
Forces on vertical breakwaters may be very severe, particularly when the incoming waves break against the wall causing impact loads. Through a recent case-history of the collapse of vertical breakwaters it has been possible to point out the destructive potential of these loads (Oumeraci, 1994) and recent research by Takahashi et al. (1994 a, b) Oumeraci et al. (1995) has confirmed that in a sea state a large number of impact loads can be generated of such severity as to cause cumulative sliding and eventually bring about the failure of the breakwater-foundation system. Historically, wave loads on vertical breakwaters and related structures have been derived as quasi-static forces using the empirical method by Goda (1985). Goda's method calculates wave loads equivalent to the effective sliding force inducted by standing and slightly breaking waves (not impulsive), but was never intended to estimate impact loads. This gave rise to studies, most of them experimental, aimed at better understanding of their generation and at improving the reliability of the design procedures of vertical breakwaters. However, the research carried out cannot be considered exhaustive and further work is in progress under the Research Project "PROVERBS" ("Probabilistic design tools for vertical breakwaters"), included in the Programme "Marine Advanced Science and Technology" (MAST III) financed by the European Community.
