Friday, March 4, 2016

The Citycorp Building and the disaster that didn't happen



Above, from an old postcard.  I googled the Citicorp Building, and was astounded by what I discovered.

The 59-storey Citicorp Building was completed in 1977 at a cost of $195 million. Because the skyscraper had to be built around St. Peter's Church, it had to be supported on 114-foot stilts at the building's centre, rather than at its corners.  To compensate for this structural sacrifice, the project's chief engineer, William LeMessurier, brilliant designed V-shaped supports running through the building to act as its skeleton.  To address the sway that would result, a 400-ton concrete ball was installed at the top of the structure, acting as one of the world's first tuned mass damper.  One year following the completion of the building, an undergraduate in architecture phoned LeMessurier to ask for clarification, since one of her program's professors had questioned the strength of the design. LeMessurier was incensed, but decided to check over the building just to satisfy himself.  He discovered that the joints connecting the chevrons had been made with bolts, rather than welds as required by his original specification.  As a result, he was faced with the conclusion that the building would not be strong enough to withstand the kind of storm that buffets New York City every 16 years, and that might take out the electric power necessary for the mass damper to perform its function.  The building would collapse and set off a domino effect in the other Manhattan skyscrapers.  In 1978, in total secrecy, the repairs were carried out, along with the development of an emergency evacuation plan.  Half-way through the process, Hurricane Ella came barreling towards the city, but fortunately veered off.  The story of this near disaster didn't break until 1995.

To read the full account, go to the Daily Mail.

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