Hydrodynamic loads on buildings caused by overtopping waves

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Abstract

There is a chance that storm surges occurring in coastal areas cause overtopping over wide crested dikes. The overtopping water results in a hydrodynamic load on the structures built on top of the crest. This is for example the case at the Belgian coast where houses and hotels are constructed on top of the dike crest. In this study, physical model tests were executed on a schematized model scaled 1/30. The aim was to come up with a relationship describing the force on a vertical plane exerted by the overtopping water as a function of wave parameters and geometrical characteristics. Due to time constraints the number of tests had to be restricted so only a limited number of parameters could be varied. Despite these restrictions, the experiments revealed the most important mechanism of the impact process under the two dike configurations included: the dike side case with dike crest width of 0 m and the inland case with dike crest of width 0.5 m in model scale. The overtopping wave force could directly be related to the overtopping wave momentum flux, resulting in a simple formulation for the prediction of the wave force. Thus, the overtopping wave force is proportional to the overtopping wave momentum flux, obtained by integrating the maximum water depth in front of the vertical plane for the inland case and the dike side case. The coefficients of these two cases are almost the same, namely around 0.33. When building the relationship between the overtopping wave force and the incident wave and dike geometrical characteristics, three other approaches were also applied. Firstly, the concept of overtopping wave tongue thickness was introduced into the relationship between the overtopping wave force and incident wave characteristics; secondly, overtopping flow velocity and water layer thickness at the beginning crest of the sea dike were also added into the analysis of overtopping wave force and finally, a new dimensionless overtopping wave force was developed. This dimensionless overtopping wave force is also proportional to the dimensionless freeboard: the least scatter for this parameter gave a rather good potential suitability for force prediction, especially with the conditions of large incident wave height impacts on the relatively low freeboard. The coefficient related to the two dimensionless parameters could also be dimensionless with a form of crest width divided by wave length, however due to the limited configurations, this dimensionless coefficient still needs to be explored further in future study. The reduction effect for crest width of 0.5 m is about 65%. Due to the fact that only two widths crest were tested in the present study, the relationship between the width and overtopping wave force could not be presented. Therefore, in future study, variation of the width of the crest should be increased, and the effect of the crest width could be further researched.

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