3.2K 
In the course of our daily reporting, we often uncover unusual projects, places, or connections that don't make the final cut. Instead of keeping it to ourselves, we're pleased to share our weekly architrivia.
The Citigroup Center's unique geometric features make it a standout skyscraper on the New York City skyline. Its 45-degree roofline and innovative stilt-style base are the 59-storey building's most notable architectural elements. Yet the tower's distinctive design was also nearly its downfall.
During the design stages, structural engineer William LeMessurier only calculated potential wind load on the building from due north, south, east and west. Focusing only on wind blowing directly against the building's flat faces, he neglected the effect that quartering winds — from the northwest, northeast, southwest and southeast — would have against any of the building's four corners. The question of wind loads was raised by a civil engineering student at Princeton University in 1978, which prompted swift recalculations that included quartering winds. The resulting examinations presented a scary situation.
Instead of the welded joints specified under the city-approved plans, builders used weaker bolted-joint chevron load braces to save money. When tested, it was determined that a 110-kilometre-per-hour hurricane force quartering wind would be of sufficient strength to collapse the building. In further tests, it was revealed that wind speeds strong enough to knock down the tower — even with itstuned mass damper— occurred once every 55 years. In the event of a power failure, the damper would shut down. Without an operational damper, a strong wind speed occurring every 16 years on average would collapse the Citigroup Center.
As the hurricane season approached, LeMessurier moved quickly to solve the problem. To avoid public scrutiny, construction crews worked overnight for three months installing welded two-inch steel plates to each of the building's 200 bolted joints. Halfway into the fix, the approaching Hurricane Ella threatened to cause a potentially catastrophic situation, but it thankfully turned eastward and avoided Manhattan. The public was unaware of the impending disaster until an article was published nearly 20 years later in a 1995 edition of The New Yorker.
Do you have city or building trivia to share? Join the conversation in the Architrivia Tipline thread in our Forum.
