TedEd: How one design flaw almost toppled a skyscraper

A TedEd by Alex Gendler

In 1978, Diane Hartley was writing her architectural thesis when she discovered something shocking. The Citicorp Center had a fatal flaw in its building plans that could cause it to tumble into a densely populated area. The flaw stemmed from the building's unique structure. The building site was partially occupied by a church, so it was supported by 4 columns. Because the church was at the corner of the block, those columns were also in the middle of each side of the building, rather than the corners. This worried many people, but the architect William LeMessurier used both a 400-ton mass damper and a V-shaped chevron exoskeleton to ensure the building met safety standards. However, the builders assumed that the building would be getting the most wind from the sides. What Hartley found was that because of the positioning of the base, the most stress would actually be on the corners of the building. LeMessurier had built the skyscraper with this in mind, but when he looked at the building plans again, he found that there had been a fatal change he hadn't been informed of. The joints of the exoskeleton were bolted rather than welded, decreasing structural integrity so much that a strong storm could bring it down. A secret plan was launched with the city to weld the joints at night. Construction was completed without the press knowing because it was completed in the midst of a strike. Only years later did magazines and Diane Hartley find out just how close the building had been to falling.