In 1978, engineers discovered a design flaw in New York's Citigroup Center that could have caused the skyscraper to collapse during a storm.

The Citigroup Center, now known as 601 Lexington Avenue, stands 915 feet tall and was designed by architect Hugh Stubbins and structural engineer William LeMessurier. To accommodate St. Peter's Lutheran Church, the tower was elevated on four 114-foot-tall stilts. Unlike traditional designs, these stilts were positioned at the center of each face, making the building's corners cantilevered and potentially unstable under specific conditions.In 1978, Diane Hartley, an undergraduate engineering student at Princeton University, questioned the building's stability. Her inquiry prompted LeMessurier to recalculate the effects of 'quartering winds,' which strike the building's corners at a 45-degree angle. He discovered that these winds increased the stress on the building's joints by 40 percent compared to perpendicular winds. This was particularly dangerous because the joints had been bolted rather than welded during construction to save costs.LeMessurier realized that a once-in-16-year storm could exceed the structural capacity of the bolts, leading to a total collapse. To rectify this, a secret emergency repair project was launched in August 1978. For three months, welders worked through the night to reinforce 200 joints with two-inch-thick steel plates. This work was kept hidden from the public to prevent a mass evacuation of Midtown Manhattan.The urgency peaked when Hurricane Ella began moving toward New York in September 1978. Fortunately, the storm turned out to sea, and the repairs were successfully completed in October. The story remained a secret until 1995, when it was finally published in an article by Joe Morgenstern in The New Yorker. This event is now a landmark case study in engineering ethics and structural safety.