The story of the Citigroup Center building is engineering history. Citibank wanted the property, but on the corner of the building site was a church. The church agreed to sell to Citibank, but on the condition it would have a new independent building on the same corner. To do this, the bank tower would be supported by four columns. However, the church objected to a design that would plant one of the columns into the church, so the columns were placed on the side of the building and not at the corners.
When the building was complete, Joel Weinstein, the design engineer was giving a presentation at Cooper Union about the the building. One of the students quizzed Weinstein about whether the building would stand up to hurricane winds, and Weinstein assured the student that everything was fine. Afterwards Weinstein wasn’t so sure, and he and William LeMessurier, the original structural engineer recalculated the wind load of the building.
They suddenly realized it was sufficient if the wind loads came straight on, but if the wind load came at a 45° angle, the loads on the joint would increase by over 150%. LeMessurier approached Citibank about the issue, but did not tell the city. Since hurricane season approached, they worked day and night repairing the structure. When it was revealed what took place, LeMessurier was accused of putting the city in danger and attempting to protect his reputation by not telling anyone, but Citibank was given credit for immediately handling the issue.
There’s a 400 ton tuned mass damper in the very top of the building. It sits on a thin film of oil and is connected by two very large springs that sit at right angles to each other. When the building sways, the damper actually sways the other direction dampening the swaying of the building.