Windswept_ The Story of Wind and Weather - Marq de Villiers [54]
VII
As meteorologists, and then mechanical engineers and the aircraft industry, understood more and more about the turbulent and occasionally violent nature of air and wind, and as they came more and more to see the importance of vortexes, a focus of these new wind engineers became the physics of boundary layers, defined as the distance from a surface at which a velocity of wind reaches 99 percent of the unobstructed "free stream." This might all seem too esoteric for real-world applications, but boundary layer studies, combined with studies of turbulent flow, have generated a much greater understanding of how buildings and structures like bridges withstand the force of wind. It was the belated realization that wind's "energy content," in the scientific jargon, was affected by turbulence at the boundary layers that finally pushed wind engineering from something theoretical to something that would have a real impact on how buildings were designed.
The pioneers in this endeavor were Jack Cermak, a professor emeritus at Colorado State University in Fort Collins, Colorado, and Alan Davenport, who founded the Boundary Layer laboratory and wind tunnel at the University of Western Ontario, in London. Others include, most notably, Richard Kind, at Carleton University in Ottawa, whose research includes snow and sand movement in wind, wind-damage control mechanisms for roofers, and wind studies of retractable stadium roofs. But Cermak and Davenport are by far the best known. Cermak had built a massive wind tunnel in Colorado in the 1960s, big enough to model full-scale atmospheric boundary layers. In 1964 Davenport and his associate Les Robertson showed up at Cermak's lab to see if they could borrow his wind tunnel to check out designs for a new building project in Manhattan. They needed the best models they could get, because the project was difficult and expensive. They wanted to test everything— wind loads, pressures, and potential flexibility, everything they could. This new building would call for innovative structural concepts, and would be an incredible 1,368 feet tall. It was to be called the World Trade Center.42
The British-born Davenport has done the critical wind studies for many of the world's most complex engineering projects, among them the world's longest bridges and tallest buildings—not just the World Trade Center but also the Sears Tower in Chicago, the CN Tower in Toronto, the proposed 1,900-yard span crossing the Messina Straits in Italy, the Normandy bridge in France, the Storebaelt bridge in Denmark, and the Tsing Ma Bridge in Hong Kong. The lab has re-created a miniature city and simulated wind conditions for Hong Kong, where turbulent typhoon winds put every building, including the Hong Kong Bank and the Bank of China, to the test. Davenport's resume seems endless; he helped write the Caribbean Uniform Building Code, implemented in the 1980s, which is intended to render low-rise buildings more resistant to hurricanes. He is a founder of the insurance-industry-funded Institute for Catastrophic Loss Reduction, and the chairman of the steering committee of Project Storm Shelter, a facility sponsored by the International Association of Wind Engineering to improve the wind resistance of housing. And he is developing a series of high performance, low cost, prefabricated housing for use in postdisaster situations and other applications.43
It was a study of the proposed CN Tower in Toronto that cemented Davenport's reputation beyond his professional colleagues. The tower, a needle like structure that dominates Toronto's skyline, was for years the world's tallest free-standing structure, a banal boast pretty much calculated