Wind Wizard by Roberts Siobhan

Author:Roberts, Siobhan
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2013-04-10T04:00:00+00:00

In fact, Rothman long had his eye on the Whitestone, walking its steel and climbing its cables, conducting spot checks for worrisome wear and tear, since the mid-1950s. In 1954, tests were conducted by F. Bert Farquharson at the University of Washington, also the site of tests on the Tacoma Narrows replacement bridge. As far as the Whitestone went, Farquharson advised it could be in grave danger in winds as low as 45 miles per hour. Every time a high wind came up, Rothman received a call from the Triborough Bridge Authority asking him to make an emergency checkup. Purportedly, during each visit he lost his glasses to the wind. Everyone’s dissatisfaction grew. The old retrofits drew greater criticism as ever more sophisticated analyses produced increasingly worrisome results. Encouragingly, however, the vertical and torsional mode frequencies remained constant from storm to storm, regardless of wind speed or direction. And the vertical mode amplitude peaked in milder winds, paradoxically dropping as the wind increased. But the torsional mode ampli tude never seemed to climax, continually escalating with the wind. “This is typical of a bridge made torsionally unstable by negative aerodynamic damping,” Rothman noted at an American Society of Civil Engineers congress. “Significant damage in feasible very strong winds could not be ruled out,” he said, adding in conclusion: “Still to be determined was the speed at which it would become unstable. Further study was needed.”

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