Physical modeling of progressive damage and failure of wood-frame coastal residential structures due to surge and wave forces

Abstract

A physical model study was performed to examine the forces and response of 1:6 scale wood-frame coastal residential structures subjected to storm surge and waves. An on-grade and an elevated specimen were tested and exposed to regular waves with varying water depths and wave heights to simulate typical wave/surge conditions resulting from landfall hurricanes on low-lying barrier islands such as Hurricane Sandy that impacted the US East Coast in 2012 and Hurricane Ike that affected the US Gulf Coast in 2008. Results show that through careful design, wood-frame model specimens can be constructed to have similar strength and stiffness compared to full-scale structures. The two specimens were subjected to increasing surge and wave conditions, and the progressive damage was monitored using LiDAR. The on-grade specimen failed at a lower water level than the elevated specimen as expected. Both specimens showed failure modes consistent with the observed damage of residential structures in Ortley Beach, NJ, after Hurricane Sandy and on the Bolivar Peninsula, TX, after Hurricane Ike. The pressure distribution on the underside of the elevated structure and the resulting vertical forces on the on-grade structure were also examined in this study. The pressure distribution and the resulting vertical forces were significantly affected by water depth, wave height, and air gap. The results indicate that maximum vertical forces are positively correlated to wave height and water depth and negatively correlated to the air gap. The breaking type also affects vertical forces. Nonbreaking waves correlated to relatively small vertical forces, and waves breaking directly on the specimen correlated to peak vertical forces. Accelerometer data showed that the specimen decreased in stiffness during the tests due to progressive damage. An uplift pressure distribution equation was developed for an elevated residential structure as a function of wave height and air gap. The equation is generally conservative when compared to other data sets. The results and data presented in this study increase the current knowledge of the interaction between waves and residential structures, which may be useful to increase the resiliency of coastal communities.