Methodology for Wind-Driven Rainwater Intrusion Fragilities for Light-Frame Wood Roof Systems

Light-frame wood buildings represent most of residential structures throughout the United States. Approximately half of the U.S. population lives within 50 miles of the coast with many of those dwellings in the Gulf Coast region or along the eastern seaboard, both of which can be negatively impacted by hurricanes. The majority of damage during a hurricane is the result of wind-driven rainwater entering a building through openings caused by strong wind. To date, wind fragility approaches to examine the probability of damage to a light-frame wood building have focused only on component or subassembly strength, thereby providing information up to the point of first failure of the building envelope. These previous analyses, while valuable, will not allow hurricane engineering research to progress to fully mechanistic loss modeling, which is needed to mitigate losses caused by these events. In this paper a methodology to develop fragility curves and fragility surfaces for the volume of rainwater intrusion is summarized and demonstrated on an example structure. To do this, nonlinear structural analysis, computational fluid dynamics, and reliability theory are combined with particle dynamics for rainwater trajectory modeling, essentially providing the first fragilities of their kind and going beyond first failure of the building envelope. It should be emphasized that it is the methodology that is the focus and some level of calibration is still necessary.