Skyscraper
Picture in your mind the skyline of downtown Toronto. There's the CN Tower1, of course, and the 72-floor First Canadian Place, the city's tallest skyscraper (Figure 1). Cascading from there are the assorted banks and hotels and insurance towers. Now, use your imagination to construct some new buildings, these ones reaching three, four and five times higher than the others. Top it all off with a skyscraper one mile high (three times as high as the CN Tower). Sound fanciful? It did 30 years ago when Frank Lloyd Wright2 proposed the first mile-high building. But not today. The World is now said to be entering the age of the superskyscraper, with tall buildings poised to take a giant new leap into the sky. Skyscrapers approaching the mile mark may still be awhile off, but there are proposals now for megastructures soaring 900 m -- twice as high as the United States' tallest building, the 110-story Sears Tower in Chicago. Suppose that you were asked to erect such a building. How would you do it? What are the obstacles you'd face? What materials would you use? And where would you put it? Well, the first information you would need to know is the kind of land to put this skyscraper on.
Tall buildings also encounter the problem of vortex shedding. This is a phenomenon that occurs as the wind swirls around the front corners of the building, forming a series of eddies or vortices. At certain wind speeds, these vortices vibrate the building, threatening to shake it apart. In New York City's Citicorp Center, engineers have tackled vortex shedding with a 400-tonne concrete block that slides around in a special room on one of the upper stories. Connected to a large spring and a shock absorber, and riding on a thin slick of oil, the big block responds to oscillations of the building by moving in the opposite direction. This meant that it was nearing its maximum strength limit even without any wind blowing on it. The suction of the low pressure area on the leeward side of the building caused the wall to billow out and pop windows like buttons. The mechanical engineers, realizing that the negative air pressure was too much for the wall, decided to fight that negative pressure with negative air pressure of their own.
Some common words found in the essay are:
Trade Center, John Hancock, Victoria Figure, Center2 Figure, Chicago Suppose, Bernoulli's Principle, Wind Factors, Bay Boston, Fire Protection, Citicorp Center, tall buildings, air pressure, sand silt, john hancock, stack effect, vortex shedding, wind tall buildings, tension curtain, loose sand, individual grains, loose sand silt, curtain wall, negative air pressure, world trade center, tension curtain wall,
Approximate Word count = 2097
Approximate Pages = 8 (250 words per page double spaced)
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