|National Institute of Standards and Technology, www.nist.gov|
Last May, a thunderstorm outside Irving, Tex., leveled the fabric-covered, steel-frame practice facility owned by the NFL’s Dallas Cowboys, injuring 12. NIST researchers studied the building’s design documents, the wreckage, and the actual weather conditions at the time of the accident to determine what went wrong. They concluded that assumptions and approaches used to design the building — a series of identical, riblike steel frames supporting a tensioned fabric covering — were incomplete and overestimated its strength. For example, NIST technicians factored in internal wind pressures from vents and several doors when they calculated wind loads, saying the building was “partially enclosed.” The design documents, however, classified the structure as “fully enclosed.”
The NIST team also concluded that the building’s fabric outer covering did not laterally brace the frames, despite what documents said. They determined the winds that brought down the building were blowing perpendicular to the long side of the structure and between 55 and 65 mph, well below the national standard of 90 mph.
Following its investigation, NIST recommended that fabric-covered steel-frame structures be checked to ensure they can survive wind loads for which they were designed. They warn that if one frame member in such a structure fails, it can propagate, leading to partial or total collapse of the building.