Structural Deflections from Wave Forces

Coastal design guidance is available to estimate structural forces caused by waves breaking against vertical surfaces. Studies have been made to evaluate forces created by these significant hydrodynamic transient forces. Studies on both rigid wall and scale-model wood structures from wave impacts have shown that there is a time delay between the initial wave contact and the peak deflection recorded. This delay is generally consistent for individual systems and structures, regardless of wave size or orientation. The purpose of this study is to review existing literature and to evaluate possible explanations for this phenomenon observed in wave tank studies at OSU (Oregon State University). It is proposed that structural response to wave impact loads is analogous to that created by seismic events. Following theories are proposed based on literature review and analyses. These are required to be confirmed through additional research. 1. Structures respond to coastal wave impacts similar to forces created by seismic events. Buildings or walls respond to wave forces based on natural or fundamental frequencies of structural systems impacted. 2. Building uplift forces and horizontal deflection vary based on wave characteristics, but the time to the peak response does not. Waves generate negative acceleration upon initial impact. The presence of water around the structure after impact appears to dampen the deceleration phase. 3. Normalized equations are developed that predict deflections and time to peak. The fundamental deflection equation appears to be primarily a function of a peak k_g value, gravity coefficient, and time. The harmonic portion of the equation is a cubic parabola function of the natural frequency of the impacted structural system. 4. A peak k_g function determines magnitude of deflection and appears to be predominantly a sigmoidal curve distribution function of the structures inertia and wave heights. Oscillation frequencies create minor transients as structures and waves interact. These findings if expanded and validated by further research can simplify wave force analysis for onshore coastal structures. It can also potentially reduce damages to structures and resulting financial losses due to storm surge.