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Online Ethics Center: The Discovery of the Change from Welds to BoltsGo back to Part 2Back to LeMessurier Main Pagehttp://onlineethics.org/moral/lemessurier/3.html (2 of 2) [10/13/2004 1:44:45 PM]
Online Ethics Center: Exploring the Effects of Quartering WindsTexto en EspañolPart 4 Exploring the Effects of Quartering WindsIn June 1978, a month after LeMessurier was told of the switch from welds to bolts in the Citicorpbuilding, he received a telephone call from a student. This student's professor had been studyingLeMessurier's Citicorp design and had concluded that LeMessurier had put the building's nine-storysupports in the wrong place. The supports belonged on the tower's corners, according to this professor,not at the tower's midpoints.The professor had not understood the design problem that had been faced, so LeMessurier explained hisentire line of reasoning for putting the tower's supports at the building's midpoints. He added that hisunique design, including the supports and the diagonal-brace system, made the building particularlyresistant to quartering, or diagonal, winds -- that is, winds coming on the diagonal and so hitting twosides of the building simultaneously. Pictured is a diagram of why perpendicular winds cause sway in abuilding.Shortly thereafter, LeMessurier decided that the subject of the Citicorptower and quartering winds would make an interesting topic for thestructural engineering class he taught at Harvard. Since at the time therequirements of the New York building code, like all other buildingcodes, had covered only perpendicular winds, LeMessurier did not knowhow his design would fare in quartering winds.Interested to see if the building's diagonal braces would be as strong inquartering winds as they had been calculated to be in perpendicularwinds, LeMessurier did some computations. He found that for a given quartering wind, stresses in half ofa certain number of structural members increased by 40 percent.Then he became concerned about the substitution of bolts for welds. Had the New York contractors takenquartering winds into account when they replaced the welds with bolts? Had they used the right numberof bolts? The second question was particularly important -- a 40 percent increase in stress on certainstructural members resulted in a 160 percent increase of stress on the building's joints, so it was vital thatthe correct number of bolts be used to ensure that each joint was the proper strength.What he found out was disturbing. The New York firm had disregarded quartering winds when theysubstituted bolted joints for welded ones. Furthermore, the contractors had interpreted the New Yorkbuilding code in such a way as to exempt many of the tower's diagonal braces from loadbearingcalculations, so they had used far too few bolts.http://onlineethics.org/moral/lemessurier/4.html (1 of 2) [10/13/2004 1:44:47 PM]
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