Check out this cool story on the Veritasium channel about a critical flaw discovered in the Citicorp skyscraper after the building was finished.
The incident occurred 46 years ago, in 1978, just a year after its inauguration, when structural engineer Bill LeMessur discovered a critical error in the design of one of New York’s most ambitious skyscrapers — Citicorp. The 59-story building was constructed on stilts that were positioned at the center of each side rather than at the corners, as is typical, to preserve an old church that stood at one corner. This unusual decision required a unique system of diagonal braces (chevrons) that redistributed the loads. However, it was later revealed that due to the substitution of welded joints with bolted ones, under diagonal wind — initially not accounted for in the calculations — the building could completely collapse from a hurricane with just 110 km/h winds, creating a real threat to the city with a shocking probability of 1/16. Had it fallen, the surrounding skyscrapers would have toppled like a house of cards.
Recognizing the scale of the threat, LeMessur clandestinely began overnight repair operations named Project Serene, literally sealing every vulnerable joint in the structure with metal ‘patches’ while office workers went about their day undisturbed. Neither the employees nor the citizens were aware of the danger in order to avoid panic. A covert evacuation plan for ten city blocks was even developed. Despite the patches, everything depended on a tuned mass damper — a massive 400-ton concrete slab installed on the roof of the building, which oscillated out of phase to dampen swaying movements. It was so critical that if the power went out, the system would stop working, and the building could almost certainly collapse in strong winds. The patches did help.
For a long time, it was believed that a Princeton student named Diana Hartley brought attention to the building’s problem. However, in 2011, architect Lee DeCarolus, who was a freshman architecture student at the New Jersey Institute of Technology at the time, claimed that he was the one who called William LeMessur in the spring of 1978. His interest in the building’s unique design and a remark from his professor, who doubted the project’s reliability, prompted his call. But, there still are doubts about who the real hero was. Well, it’s clear as mud.
Hi, I'm Rauf Aliev. 