The Citigroup Center (First called Citicorp Center) is in New York City. There´s also another Citigroup Center in Chicago, but I´m going to speak about the skyscraper of New York. It is 278.9m (915 foot) tall, with 59 floors. It is easily distinguised in the skyline of NY because of his 45º angled top base, which was thought to have luxury apartments on it and then, solar panels, but finally they didn´t do anything.
The skyscraper, completed in 1977, was designed by the american architect Hugh Stubbins Jr. for Citibank. The engineers were William LeMessurier and Associates.
This building was pioneer in using a shock absorber, technically called tuned mass damper (TMD). They were used in bridges but not in buildings. Nowadays the tuned mass dampers are used in skyscraper architecture to reduce movements of the building in windy days or when earthquakes happen. The Citigroup Centers TMD is a 400 tonne concrete block moved by a hydraulic system.
In these 2 videos we can learn how engineers resolved structural problems before the design and once the skyscraper was built.
Citigroup Center´s secrets 1/2
Citigroup Center´s secrets 2/2
From: wikipedia, PBS, tuned mass damper, youtube