Answer by Joel Lewenstein:
One of my favorite stories is of a structural engineer William J. LeMessurier who discovered that his crowning achievement, the Citicorp Center in New York City, was in danger of collapsing in a strong wind.
As a structural consultant to the architect Hugh Stubbins Jr., [William J. LeMessurier] had designed the twenty-five-thousand-ton steel skeleton beneath the tower's sleek aluminum skin. And, in a field where architects usually get all the credit, the engineer, then fifty-two, had won his own share of praise for the tower's technical elegance and singular grace; indeed, earlier that year he had been elected to the National Academy of Engineering, the highest honor his profession bestows.
LeMessurier and Stubbins designed the unique building to stand on 9-story-high columns, allowing it to fit into the tight space allotted in Manhattan and stand hover above a historic church. To protect against swaying in heavy wind, LeMessurier designed a novel series of wind braces:
The tower's unusual system of wind braces, which LeMessurier had first sketched out, in a burst of almost ecstatic invention, on a napkin in a Greek restaurant in Cambridge: forty-eight braces, in six tiers of eight, arrayed like giant chevrons behind the building's curtain of aluminum and glass.
Through a remarkable series of events (beginning with a random call from an architecture student) LeMessurier discovered both some miscalculations in the building's sensitivity to quartering winds, and a previously unknown decision to bolt the braces together, a weaker bond than the planned welding. Together, these changed decisions made for a much more precarious building than originally designed:
The weakest joint, he discovered, was at the building's thirtieth floor; if that one gave way, catastrophic failure of the whole structure would follow. Next, he took New York City weather records provided by Alan Davenport and calculated the probability of a storm severe enough to tear that joint apart. His figures told him that such an event had a statistical probability of occurring as often as once every sixteen years–what meteorologists call a sixteen-year storm.
The building was in full use at the time of this discovery. Aware of the situation, LeMessurier considered his options:
Silence was one of them; only Davenport knew the full implications of what he had found, and he would not disclose them on his own. Suicide was another, if LeMessurier drove along the Maine Turnpike at a hundred miles an hour and steered into a bridge abutment, that would be that. But keeping silent required betting other people's lives against the odds, while suicide struck him as a coward's way out … What seized him an instant later was entirely convincing, because it was so unexpected almost giddy sense of power. "I had information that nobody else in the world had," LeMessurier recalls. "I had power in my hands to effect extraordinary events that only I could initiate. I mean, sixteen years to failure–that was very simple, very clear-cut. I almost said, thank you, dear Lord, for making this problem so sharply defined that there's no choice to make.' '
LeMussurier ultimately chose the route of intellectual honesty, alerting key people of the situation. He worked with other architects, the president of Citicorp, and the city of New York to fortify the building over the course of a several months and at a cost of a few million dollars. These repairs went on somewhat secretly and spanned an impending storm that almost forced a full building evacuation and PR nightmare. Finally, the repairs were completed:
The crisis at Citicorp Center was noteworthy in another respect. It produced heroes, but no villains; everyone connected with the repairs behaved in exemplary fashion, from Walter Wriston and his Citicorp management team to the officials at the city's Department of Buildings. The most striking example, of course, was set by LeMessurier, who emerged with his reputation not merely unscathed but enhanced. When Robertson speaks of him, he says, "I have a lot of admiration for Bill, because he was very forthcoming. While we say that all engineers would behave as he did, I carry in my mind some skepticism about that."
All quotes are from a really extraordinary New Yorker article with a lot more detail and nuance on the engineering and personalities involved: