Wave and Surge Vulnerability of Coastal Residences

Coastal communities are vulnerable to damage from hurricane or tsunami-generated water level rises, current velocities, and wave forces. Engineers must employ methods to mitigate damage caused by these events. A critical first step in damage prevention is the ability to relate environmental conditions at a location to the expected damage to or load on a structure. This thesis combines case studies of damage from previous hurricanes and large scale experiments of tsunami propagation through idealized urban arrays to better understand the relationship between waves and structural vulnerability.

After Hurricane Ike affected the Bolivar Peninsula, Texas in 2008, a post-storm survey characterized 1922 homes as 'surviving,' 'destroyed,' or 'wave damaged.' The combined ADCIRC+SWAN wave circulation model simulated the storm-generated environmental conditions at each house’s location. Results were used to derive second order fragility functions that predicted a home's likelihood of collapse based on a combination of environmental conditions and structural attributes. Freeboard and significant wave height were identified as critical variables influencing survival.

A similar reconnaissance survey of 380 New Jersey residences affected by Hurricane Sandy in 2012 resulted in the development of a standardized damage scale that can be used to objectively classify damage into seven categories. Results were used to derive vulnerability models that extended the model developed after Hurricane Ike to predict the probability of a house experiencing a specific damage state as defined by the standardized scale. This model identified water velocity and a home's relative shielding as important in effecting a specific damage state and indicated that numerical models must include wave-structure interaction in storm simulations.

To better understand the effects of urban elements on wave propagation, large scale experiments were conducted in a hybrid tsunami flume to measure water surface elevation, water velocity, and pressure on and around idealized structural elements and arrays of structures. Wave conditions in which waves broke on or just before a specimen caused maximum impulsive pressures. When arrays of obstacles were added to simulate urban macro-roughness, shielded structures exposed to breaking waves experienced pressure reductions of 40-70% compared with unobstructed measurements.