lec20_viv1 - 13.42 Lecture Vortex Induced Vibrations Prof A...

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Unformatted text preview: 13.42 Lecture: Vortex Induced Vibrations Prof. A. H. Techet 21 April 2005 Offshore Platform Courtesy of U.S. DOE. Fixed Rigs Tension Leg Platforms Figures removed for copyright reasons. Spar Platforms Figures removed for copyright reasons. Genesis Spar Platform Photos of Genesis Spar Oil Platform removed for copyright reasons. Please See: http://www.offshore-technology.com/projects/genesis/. VIV Catastrophe If neglected in design, vortex induced vibrations can prove catastrophic to structures, as they did in the case of the Tacoma Narrows Bridge in 1940. Image removed for copyright reasons. John Hancock Building “I n another city, the John Hancock tower wouldn't be anything special -- just another reflective glass box in the crowd. But because of the way Boston and the rest of New England has grown up architecturally, this "70's modern" building stands out from the rest. Instead of being colonial, it breaks new ground. Instead of being quaint, it soars and imposes itself on the skyline. And Instead of being white like so many buildings in the region, this one defies the local conventional wisdom and goes for black. For these reasons and more the people of Boston have fallen in love with the 790-foot monster looming as the tallest building in New England at the time of its completion. In the mid-1990's, The Boston Globe polled local architects who rated it the city's third best architectural structure. Much like Boston's well-loved baseball team, the building has had a rough past, but still perseveres, coming back stronger to win the hearts of its fans. The trouble began early on. During construction of the foundation the sides of the pit collapsed, nearly sucking Trinity Church into the hole. Then in late January, 1973 construction was still underway when a winter storm rolled into town and a 500-pound window leapt from the tower and smashed itself to bits on the ground below. Another followed. Then another. Within a few weeks, more than 65 of the building's 10,344 panes of glass committed suicide, their crystalline essence piling up in a roped-off area surrounding the building. The people of Bean Town have always been willing to kick a brother when he's down, and started calling the tower the Plywood Palace because of the black-painted pieces of wood covering more than an acre of its façade. Some people thought the building was swaying too much in the wind, and causing the windows to pop out. Some thought the foundation had shifted and it was putting stress of the structural geometry. It turns out the culprit was nothing more than the lead of the structural geometry....
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lec20_viv1 - 13.42 Lecture Vortex Induced Vibrations Prof A...

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