· · · Repository Hydraulic Engineering Reports

In most developed coastal areas, seawalls protect towns, road, rail and rural infrastructure against wave overtopping. Similar structures protect port installations worldwide, and may be used for cliff protection. When a large tidal excursion and severe environmental conditions concur to expose seawalls and vertical face breakwaters to wave impact loading, impulsive loads from breaking waves can be very large. Despite their magnitude, wave impact loads are seldom included in structural analysis of coastal structures and dynamic analysis is rare, leading to designers ignoring short-duration wave loads, perhaps contributing to damage to a range of breakwaters, seawalls and suspended decks. Over the last 10 years, improved awareness of wave-impact induced failures of breakwaters in Europe and Japan has focussed attention on the need to include wave impact loads in the loading assessment, and to conduct dynamic analysis when designing coastal structures. Recent experimental work has focused more strongly on recording and analyzing violent wave impacts. These new data are however only useful if methodologies are available to evaluate dynamic responses of maritime structures to short-duration loads. Improvements in these predictions require the development of more complete wave load models, based on new measurements and experiments. Moving from a brief review of documented structural failures of caisson breakwaters and existing design methods for wave impact loads, this paper reports advances in knowledge of impulsive wave loads on vertical and steeply battered walls, based on physical model tests in the large wave flume at Barcelona under the VOWS project (Violent Overtopping of Waves at Seawalls). These data are used to support a revised simple prediction formula for wave impact forces on vertical walls. The paper also discusses dynamic characteristics of linear single degree of freedom systems to non-stationary excitation. Responses are derived to pulse excitation similar to those induced by wave impacts. Response to short pulses is shown to be dominated by the ratio of impact rise time tr to the natural period of the structure Tn. A functional relation between impact maxima and rise-times is given for non-exceedance joint probability levels. The relation is integrated in a simplified method for the evaluation of the static-equivalent design load and the potential cumulative sliding distance of caisson breakwaters.

Description of the original tests of Bagnold on wave impacts.

This paper deals with shock pressure phenomena due to breaking waves acting on sloping faces of sea dykes and other dike revetments. The full-scale investigations were carried out in the new research facility LARGE WAVE CHANNEL in Hannover. Germany. Maximum shock pressure estimations are given for practical slopes 1:4 and 1:6. An extension of the results to steeper and flatter slopes is proposed. For the slope 1:6 the spatial shock pressure distribution and the shock pressure transfer to the subsoil are treated additionally.

Classic article on wave pressures on vertical walls.

Research on rubble mound breakwaters when confronted with waves. The rapport covers the flow characteristics and mound stability under regular waves and under oblique wave attack. The authors find a formula for rough, permeable slopes, flow characteristics under the action of a regular wave train by a function of the type. Furthermore they conclude that the distribution of flow characteristics in sea state can be obtained on the basis of interaction curves and joint probability density function of wave heights and periods. The conclusions on the mound stability of breakwaters are: -Stability conditions of an undefined, rough, permeable slope are governed by the stability function. -The stability function depends only on Iribarren's number. -Randomness can be accounted for by using confidence bands for the stability function. -For each type of armour unit, an optimum slope of maximum stability exists. The greater the interlocking among armour units the steeper the optimum slope and the more peaked the stability maximum. -Given a rubble mound breakwater a minimum sea state exists which produces a significant failure probability. If a sea state is presented which is the same or higher than this minimum, failure of the structure is only a question of the duration of the sea state. Conclusions on the characteristics and stability of rubble mound breakwaters under oblique wave attack: -There is a dangerous lack of experimental data on the subject. -Run-up and run-down under small oblique incidence of waves (angle lower than 45 degrees) are function of Ir.cos(theta). For higher incidence angles the hypothesis is unreliable. -The stability of steep slopes under oblique wave attack is not worse than under perpendicular wave incidence. For milder slopes the opposite may be true. -The failure of probability of a rubble mound breakwater under a sea state with oblique incidence, can be calculated by taking into account the breaking limit, the interaction curve and a joint distribution of wave heights and periods.