Evaluation of wave impact loads on caisson breakwaters based on joint probability of impact maxima and rise times

When waves break against seawalls, vertical breakwaters, piers or jetties, they abruptly transfer their momentum into the structure. This energy transfer is always spectacular and perpetually unrepeatable but can also be very violent and affect the stability and the integrity of coastal structures. Over the last 15 years, increasing awareness of wave-impact induced structural failures of maritime structures has emphasised the need for a more complete approach to dynamic responses, including effects of impulsive loads. At the same time, movement of design standards toward probabilistic approaches requires new statistical tools able to account for uncertainties in the variability of wave loading processes. This paper presents a new approach to the definition of loads for use in performance design of vertical coastal structures subject to breaking wave impacts. Based on conservation of momentum and joint probability of non-dimensional wave impact maxima and rise times from large-scale test measurements, a new set of equations have been derived to characterise design impact loads at different non-exceedance probability levels and guidance is given for the estimation of the static-equivalent design loads to be used in early-stage feasibility studies. Predictions of static equivalent design loads and corresponding safety factor against sliding using the proposed methodology are found to be in very good agreement with both predictions by most established deterministic methods and field observations reported in literature