A dynamic analysis method, based on the equilibrium of a two-degree of freedom visco-elastic model was used to simulate the behaviour of a vertical breakwater under breaking wave impact loads. Numerical analysis were carried out with reference to a large scale physical model and then extended to an actual structure. The results made it possible to individuate the range load parameters for which the dynamic analysis should be the only reliable tool for design predictions.
Hydrodynamic wave loads on vertical breakwaters induce a dynamic motion of the structure in conditions which lead to impulsive breaking wave pressures. Previous observations (Oumeraci, 1994: Takahashi et al. 1994: Oumeraci et al., 1995) have indicated that the impact loads of breaking waves can strongly affect the stability of the vertical wall. triggering even the failure of the breakwater-foundation system. In presence of impulse loads, the motion of the monolithic caisson not only depends on the attributes of the dynamic excitation, but also on the geometry and inertia of the foundation and superstructure, as well as on the nature and deformability of the supporting ground. Therefore, a reliable design prediction requires an analysis of the dynamic response of the breakwater-foundation system. In most up-to-date dynamic analysis methods, the breakwater-foundation system is idealised assuming the caisson as a rigid block. while the soil-caisson contact is usually, supposed purely elastic (e.g. Goda. 1994), visco-elastic (e.g. Oumeraci and Kortenhaus, 1994) or rigid-plastic (e.g. Oumeraci et al., 1995). In this paper, the fundamentals of a two-degree-of-freedom visco-elastic model (Benassai et al., 1997) will be resumed. The caisson motion is expressed by the horizontal translation, x, mad the rocking rotation, φ The soil-caisson interaction parameters are introduced into the model following the suggestions by Oumeraci and Kortenhaus (1994), and the indications on the dynamic behaviour of a rigid foundation on elastic layer or half-space, given by Gazetas (1991).