There have been many instances of aircraft hangars' roof systems being damaged during high winds, yet other buildings' roof systems at an airport and in nearby communities were not damaged. Obviously, the wind did not target the hangars' roof systems, so why did damage occur? The answer lies with the unique characteristics of aircraft hangars, which many roof system designers do not recognize. Following is some information about these unique characteristics and how they contribute to wind-related roof system damage, as well as design solutions that can be implemented to avoid or minimize damage.
A distinguishing characteristic of hangars is location. Because an airport's surrounding terrain typically is flat, vegetation is low and there are few nearby buildings, virtually all hangars are in Exposure C as defined in ASCE 7, "Minimum Design Loads for Buildings and Other Structures."
ASCE 7 defines three common exposure classifications: B (urban, suburban and wooded areas); C (open terrain with scattered obstructions and shorelines in hurricane-prone areas); and D (shorelines exposed to wind flowing over open water for a distance of at least 1 mile [1.6 km]). A building's exposure classification strongly influences its wind load. For example, for an enclosed building (a building whose exterior envelope is relatively air-impermeable), the uplift loads on roof systems in Exposure C are 40 percent greater than those in Exposure B, and the loads in Exposure D are 66 percent greater than those in Exposure B. Because of a terrain's influence on wind loads, a windstorm delivers about 40 percent higher uplift loads to roof systems on most airport buildings versus loads delivered to buildings in nearby urban or suburban areas.