NYC - Citicorp Center
The Citigroup Center, formerly Citicorp Center, located at 601 Lexington Avenue between 53rd Street and 54th Street is a 59-floor, 915-foot skyscraper and one of the most distinctive and imposing in New York's skyline, with a 45° angled top and a unique stilt-style base. Designed by Hugh Stubbins Jr. and completed in 1977, it contains 1.3 million square feet of office space.
To help stabilize the building, a tuned mass damper was placed in the mechanical space at its top. This substantial piece of stabilizing equipment weighs 400 tons (350 metric tons) and has a volume of 255 cubic feet (7 m³). Designed to counterbalance the effects of wind by making the building sway, it is a concrete block that slides on a thick layer of oil and converts the kinetic energy of the building into friction. This mass reduces the building's movement from wind deflection by 50%. Citigroup Center was the first skyscraper in the United States to feature a tuned mass damper. The building features double-deck elevators, which are separated to serve only odd or even floors.
In 2007, Citicorp Center was ranked #125 on the AIA 150 America's Favorite Architecture list.