Description

In July 1978, a possible structural flaw was discovered in Citicorp Center, a skyscraper that had recently been completed in New York City. Workers surreptitiously made repairs over the next few months. The building, now known as Citigroup Center, occupied an entire block and was to be the headquarters of Citibank. Its structure, designed by William LeMessurier, had several unusual design features, including a raised base supported by four offset stilts and a column in the center, diagonal bracing which absorbed wind loads from upper stories, and a tuned mass damper with a 400-ton concrete weight floating on oil to counteract oscillation movements. It was the first building that used active mechanical elements for stabilization. Concerned about "quartering winds" directed diagonally toward the corners of the building, Princeton University undergraduate student Diane Hartley investigated the structural integrity of the building and found it wanting. However, it is not clear whether her study ever came to the attention of LeMessurier, the chief structural engineer of the building.