Of all the environmental loads on buildings and structures, wind is perhaps the most damaging. Almost three-fourths of all catastrophe claims paid by insurance carriers in the last 20 years have been for hurricane and tornado damage. Scientists classify wind intensity and damage potential differently for hurricanes, tornados, and general wind storms. Hurricanes are ranked by the Saffir-Simpson Hurricane Scale, which ranges from Category 1 (sustained wind speeds 74 to 95 mph, storm surge of 4 to 5 feet) to Category 5 (sustained wind speed greater than 156 mph, storm surge greater than 18 feet). Tornados are ranked by the recently adopted Enhanced Fujita Scale, which ranges from Category EF0 (65 to 85 mph gust wind) to Category EF5 (200 top 234 mph gust). In addition, the Beaufort Scale, which was originally used by sailors to describe sea conditions, has now been extended to relate observed damage to wind speed. The Beaufort scale ranges from Beaufort Number 0 (calm) to Number 12 (Category 1 hurricane winds).
When wind is obstructed by a building or structure, it must change direction, resulting in a force being applied to the obstacle. The nature and magnitude of wind forces on structures are complex functions of shielding, stagnation, vortex shedding, and other phenomena. Building codes provide approximate relationships between wind speed and wind pressure on building and structure components that are intended to be used for design. More precise mapping of actual wind pressures requires wind-tunnel testing, or in some circumstances, computer modeling of the wind flow. However, experience shows that wind pressures are typically highest at architectural discontinuities high on the structure, such as roof eaves, dormers, or parapet corners, and wind damage often starts at these locations.
Exponent provides holistic wind engineering solutions to help our clients understand the wind hazard, the mechanisms and contributing cause(s) of wind damage, and the best measures to mitigate risk of future damage. We have helped owners of facilities in areas of high wind hazard quantify and mitigate their risks, and we have helped insurance carriers investigate the cause(s) and differentiate damage mechanisms after storms (including hundreds of structures after Hurricane Katrina).
Our services include:
- Probabilistic risk assessment for properties located in hurricane-prone areas
- Investigation of wind damage, including triage (to help insurers manage the high volume of claims), determining the nature and extent of damage, and identifying appropriate repairs
- Advanced structural analysis, often incorporating wind-tunnel testing and advanced computer simulation (computational fluid dynamics, or CFD)
- Investigation of envelope performance as it is affected by wind-driven rain