Engineers Uncover Flaw in Iconic NYC Skyscraper, Potential Disaster Averted

New York, NY — Citicorp Center, the tallest skyscraper built in New York City since the 1930s, faced a near-catastrophic design flaw that could have endangered thousands of lives after its opening in 1977. The 915-foot tower, known for its distinctive sloped roof, was not as stable as its designers believed.

The engineering miscalculation was discovered by structural engineer William LeMessurier just a year after the building was completed. He realized the tower was highly vulnerable to wind, particularly during hurricane season. Without power to its stabilizing devices, a strong gust could cause the building to collapse. According to LeMessurier’s calculations, winds strong enough to topple it could occur every 16 years.

“You have this one man who’s put in the impossible position of discovering a terrible structural flaw,” said Michael M. Greenburg, author of the book detailing the crisis, “The Great Miscalculation: The Race to Save New York City’s Citicorp Tower.”

The structure’s unique design, featuring a cantilevered base, faced complications from the site on which it was built. Citicorp had to negotiate with St. Peter’s Lutheran Church, the sole holdout on the lot. The church’s pastor insisted that any deal include the construction of a new church.

Architect Hugh Stubbins and LeMessurier devised a plan that allowed the tower to rise while also incorporating the church. However, to support the weight of the 59-story skyscraper, they placed the main support columns in the center of the tower’s four faces, creating a structural instability.

To stabilize the building, LeMessurier designed a unique bracing system and a tuned mass damper to minimize swaying during high winds. This innovative design initially led to acclaim but later prompted serious concerns after the engineering flaw was uncovered.

Ultimately, it was two college students—one of whom was Diane Hartley at Princeton University—who would help to reveal the structural vulnerability. Studying the tower for her thesis, Hartley noticed discrepancies in the reported wind stress calculations.

“It never occurred to me that I had discovered something unusual,” she recalled. “I was trying to figure out why I was wrong.”

As LeMessurier worked in haste to correct the flaw, welders performed nighttime repairs to the structure. A newspaper strike at the time helped keep the incident largely under wraps until the mid-1990s.

Today, Citicorp Center, now known as 601 Lexington, still stands but is a reminder of the engineering challenges and the human stories behind its construction and subsequent crisis management.