Abstract

NEVES, Maria da Graça; VILCHEZ, Montse; CLAVERO, Maria  and  LOSADA, Miguel A.. Forces on vertical and composite breakwaters. RGCI [online]. 2012, vol.12, n.2, pp.159-174. ISSN 1646-8872.

An important issue for a maritime structure design is the determination of the resultant of the wave forces acting at the structure and the stability conditions in each part of the structure. Verification of failure modes that can affect vertical and composite breakwaters is essencially related with sliding and overturning and failure related with geothecnical causes are usually not taken into account. In order to analyse the safety agains sliding and overturning and calculate the loads at the structure, the static equilibrium of the system is considered, assuming that the load are constant. Types of total horizontal wave loadings on the vertical-front structures are a function of structure geometry and wave characteristics. Once the horizontal and vertical resultant of the forces are calculated, safety factors agains sliding and overturning are established, relating the resistance force to the applied force in the horizontal and vertical direction and the stability is verified. Empirical and semi-empirical formula and physical modeling are the most frequent used tools to calculate loads in vertical and composite breakwaters. At present, empirical or semi-empirical formulas are the most widely used tools for predicting loads, which have the great advantage of being very easy to apply. Direct application of these formulas is limited to particular structural configurations, water levels and wave conditions. Besides that, the formulas have assumptions that might not be correct in specific cases. This paper presents the most used formulas to calculate the pressure diagrams, and based on that, the loads acting at vertical and composite breakwaters, together with their main caracteristics and application domain. A more accurate method for determining loads is based on physical model tests since they allow the reprodution of the physical phenomena involved in wave-structure interaction without the simplified assumptions that are presented in the formulas and at analitycal and numerical modelling. However, they are more expensive and more time consuming than the use of formulas and could be affected by scale effects. The paper presents a summary of the different methods to measure the pressures and forces in physical models and the main errors that could affect the measurements of loads at vertical structures. Prototype data are rather rare but extremely important since it allows the verification of the formulae accuracy in calculating the loads. The field measurements made between January and March 2010 at the North Breakwater of the Port of Gijón (Spain), allowed the analisys of the accuracy of the loads calculation made by the formulas and define some main incorrections on the formulas assumptions. Based on these measurements, some recommendations are presented to increase the accuracy of the loads predicted by the formulas at vertical and composite breakwaters.

Keywords : Wave forces; dynamic pressure; vertical breakwaters; composite breakwaters; semi-empirical formulae; physical models; prototype measurements.

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