99% Invisible-110- Structural Integrity by Roman Mars published on 2014/04/15 19:30:43 +0000 When it was built in1977, Citicorp Center (later renamed Citigroup Center, now called 601 Lexington) was, at 59 stories, the seventh-tallest building in the world. You can pick it out of the New York City skyline by its 45-degree angled top. But it's the base of the building that really makes the tower so unique. The bottom nine of its 59 stories are stilts. This thing does not look sturdy. But it has to be sturdy. Otherwise they wouldn't have built it this way. Right? The architect of Citicorp Center was Hugh Stubbins, but most of the credit for this building is given to its chief structural engineer, William LeMessurier. According to LeMessurier, in 1978 he got a phone call from an undergraduate architecture student making a bold claim about LeMessurier's building. He told LeMessurier that Citicorp Center could blow over in the wind.