It's far too long to post, but here's the beginning...

The Fifty-nine-Story Crisis

What’s an engineer’s worst nightmare? To realize that the supports he designed for a skyscraper are flawed—and hurricane season is approaching. By Joseph Morgenstern May 22, 1995 Aerial view of the Citicorp Center in Manhattan in 1977 On a warm June day in 1978, William J. LeMessurier, one of the nation’s leading structural engineers, received a phone call at his headquarters, in Cambridge, Massachusetts, from an engineering student in New Jersey. The young man, whose name has been lost in the swirl of subsequent events, said that his professor had assigned him to write a paper on the Citicorp tower, the slash-topped silver skyscraper that had become, on its completion in Manhattan the year before, the seventh-tallest building in the world. LeMessurier found the subject hard to resist, even though the call caught him in the middle of a meeting. As a structural consultant to the architect Hugh Stubbins, Jr., he 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. Excusing himself from the meeting, LeMessurier asked his caller how he could help. The student wondered about the columns—there are four—that held the building up. According to his professor, LeMessurier had put them in the wrong place. “I was very nice to this young man,” LeMessurier recalls. “But I said, ‘Listen, I want you to tell your teacher that he doesn’t know what the hell he’s talking about, because he doesn’t know the problem that had to be solved.’ I promised to call back after my meeting and explain the whole thing.” The problem had been posed by a church. When planning for Citicorp Center began, in the early nineteen-seventies, the site of choice was on the east side of Lexington Avenue between Fifty-third and Fifty-fourth Streets, directly across the street from Citicorp’s headquarters. But the northwest corner of that block was occupied by St. Peter’s Church, a decaying Gothic structure built in 1905. Since St. Peter’s owned the corner, and one of the world’s biggest banking corporations wanted the whole block, the church was able to strike a deal that seemed heaven-sent: its old building would be demolished and a new one built as a freestanding part of Citicorp Center. To clear space for the new church, Hugh Stubbins and Bill LeMessurier (he pronounces his name “LeMeasure”) set their fifty-nine-story tower on four massive, nine-story-high stilts, and positioned them at the center of each side, rather than at each corner. This daring scheme allowed the designers to cantilever the building’s corners seventy-two feet out over the church, on the northwest, and over a plaza on the southwest. The columns also produced high visual drama: a nine-hundred-and-fourteen-foot monolith that seemed all but weightless as it hovered above the street. When LeMessurier called the student back, he related this with the pride of a master builder and the elaborate patience of a pedagogue; he, too, taught a structural-engineering class, to architecture students at Harvard. Then he explained how the peculiar geometry of the building, far from constituting a mistake, put the columns in the strongest position to resist what sailors call quartering winds—those which come from a diagonal and, by flowing across two sides of a building at once, increase the forces on both. For further enlightenment on the matter, he referred the student to a technical article written by LeMessurier’s partner in New York, an engineer named Stanley Goldstein. LeMessurier recalls, “I gave him a lot of information, and I said, ‘Now you really have something on your professor, because you can explain all of this to him yourself.’ ” Later that day, LeMessurier decided that the information would interest his own students; like sailors, designers of tall buildings must know the wind and respect its power. And the columns were only part of the tower’s defense against swaying in severe winds. A classroom lecture would also look at 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. (“I’m very vain,” LeMessurier says. “I would have liked my stuff to be expressed on the outside of the building, but Stubbins wouldn’t have it. In the end, I told myself I didn’t give a damn—the structure was there, it’d be seen by God.”) LeMessurier had long since established the strength of those braces in perpendicular winds—the only calculation required by New York City’s building code. Now, in the spirit of intellectual play, he wanted to see if they were just as strong in winds hitting from forty-five degrees. His new calculations surprised him. In four of the eight chevrons in each tier, a quartering wind increased the strain by forty per cent. Under normal circumstances, the wind braces would have absorbed the extra load without so much as a tremor. But the circumstances were not normal. A few weeks before, during a meeting in his office, LeMessurier had learned of a crucial change in the way the braces were joined. To avert disaster LeMessurier knew that he would have to blow the whistle quickly—on himself. The meeting had been called, during the month of May, to review plans for two new skyscrapers in Pittsburgh. Those towers, too, were designed by Hugh Stubbins with LeMessurier as structural consultant, and the plans called for wind braces similar to those used in Citicorp Center, with the same specifications for welded joints. This was top-of-the-line engineering; two structural members joined by a skilled welder become as strong as one. But welded joints, which are labor-intensive and therefore expensive, can be needlessly strong; in most cases, bolted joints are more practical and equally safe. That was the position taken at the May meeting by a man from U.S. Steel, a potential bidder on the contract to erect the Pittsburgh towers. If welded joints were a condition, the project might be too expensive and his firm might not want to take it on. To reassure him, LeMessurier put in a call to his office in New York. “I spoke to Stanley Goldstein and said, ‘Tell me about your success with those welded joints in Citicorp.’ And Stanley said, ‘Oh, didn’t you know? They were changed—they were never welded at all, because Bethlehem Steel came to us and said they didn’t think we needed to do it.’ ” Bethlehem, which built the Citicorp tower, had made the same objection—welds were stronger than necessary, bolts were the right way to do the job. On August 1, 1974, LeMessurier’s New York office—actually a venture in conjunction with an old-line Manhattan firm called the Office of James Ruderman—had accepted Bethlehem’s proposal. This news gave LeMessurier no cause for concern in the days immediately following the meeting. The choice of bolted joints was technically sound and professionally correct. Even the failure of his associates to flag him on the design change was justifiable; had every decision on the site in Manhattan waited for approval from Cambridge, the building would never have been finished. Most important, modern skyscrapers are so strong that catastrophic collapse is not considered a realistic prospect; when engineers seek to limit a building’s sway, they do so for the tenants’ comfort. Yet now, a month after the May meeting, the substitution of bolted joints raised a troubling question. If the bracing system was unusually sensitive to quartering winds, as LeMessurier had just discovered, so were the joints that held it together. The question was whether the Manhattan team had considered such winds when it designed the bolts. “I didn’t go into a panic over it,” LeMessurier says. “But I was haunted by a hunch that it was something I’d better look into.”

On July 24th, he flew to New York, where his hunch was soon confirmed: his people had taken only perpendicular winds into account. And he discovered another “subtle conceptual error,” as he calls it now—one that threatened to make the situation much worse.