BUILDING BIG: Databank: Citicorp Center

From the very beginning, the Citicorp Center (today, the Citigroup Center) in New York City was an engineering challenge. When planning for the skyscraper began in the early 1970s, the northwest corner of the proposed building site was occupied by St. Peter's Lutheran Church. The church allowed Citicorp to build the skyscraper under one condition: a new church would have to be built on the same corner, with no connection to the Citicorp building and no columns passing through it.

How did the engineers do it? They set the 59-story tower on four massive columns, positioned at the center of each side, rather than at the corners. This design allowed the northwest corner of the building to cantilever 72 feet over the new church.

In 1978, the skyscraper's chief structural engineer, William LeMessurier, discovered a potentially fatal flaw in the building's design: the skyscraper's bolted joints were too weak to withstand 70-mile-per-hour wind gusts. With hurricane season fast approaching, LeMessurier took no chances. He convinced Citicorp officers to hire a crew of welders to repair the fragile building. For the next three months, a construction crew welded two-inch-thick steel plates over each of the skyscraper's 200 bolted joints, permanently correcting the problem.

Fast Facts:

The Citicorp crisis of 1978 was hidden from the public for almost 20 years.
The 30-page document outlining the structural mistakes in the Citicorp building was called "Project SERENE." The acronym stands for "Special Engineering Review of Events Nobody Envisioned."
Six weeks into Citicorp's repair, a major storm, Hurricane Ella, was off Cape Hatteras and heading for New York. With only half the repairs finished, New York City was hours away from emergency evacuation. Luckily, Ella turned eastward and veered out to sea.
Citicorp Center was the first skyscraper in the United States to contain a tuned mass damper, a pendulum-like device that reduces the sway in tall buildings caused by the wind.