Within this seemingly simple computation, however, lurks a powerful multiplier. At any given level of the building, the compression figure remains constant; the wind may blow harder, but the structure doesn’t get any heavier. Thus, immense leverage can result from higher wind forces. In the Citicorp tower, the forty-per-cent increase in tension produced by a quartering wind became a hundred-and-sixty-per-cent increase on the building’s bolts.
Precisely because of that leverage, a margin of safety is built into the standard formulas for calculating how strong a joint must be; these formulas are contained in an American Institute of Steel Construction specification that deals with joints in structural columns. What LeMessurier found in New York, however, was that the people on his team had disregarded the standard. They had chosen to define the diagonal wind braces not as columns but as trusses, which are exempt from the safety factor. As a result, the bolts holding the joints together were perilously few. “By then,” LeMessurier says, “I was getting pretty shaky.”
He later detailed these mistakes in a thirty-page document called “Project serene”; the acronym, both rueful and apt, stands for “Special Engineering Review of Events Nobody Envisioned.” What emerges from this document, which has been confidential until now, and from interviews with LeMessurier and other principals in the events, is not malfeasance, or even negligence, but a series of miscalculations that flowed from a specific mind-set. In the case of the Citicorp tower, the first event that nobody envisioned had taken place when LeMessurier sketched, on a restaurant napkin, a bracing system with an inherent sensitivity to quartering winds. None of his associates identified this as a problem, let alone understood that they were compounding it with their fuzzy semantics. In the stiff, angular language of “Project serene,” “consideration of wind from non-perpendicular directions on ordinary rectangular buildings is generally not discussed in the literature or in the classroom.”
LeMessurier tried to take comfort from another element of Citicorp’s advanced design: the building’s tuned mass damper. This machine, built at his behest and perched where the bells would have been if the Citicorp tower had been a cathedral, was essentially a four-hundred-and-ten-ton block of concrete, attached to huge springs and floating on a film of oil. When the building swayed, the block’s inertia worked to damp the movement and calm tenants’ queasy stomachs. Reducing sway was of special importance, because the Citicorp tower was an unusually lightweight building; the twenty-five thousand tons of steel in its skeleton contrasted with the Empire State Building’s sixty-thousand-ton superstructure. Yet the damper, the first of its kind in a large building, was never meant to be a safety device. At best, the machine might reduce the danger, not dispel it.
Before making a final judgment on how dangerous the bolted joints were, LeMessurier turned to a Canadian engineer named Alan Davenport, the director of the Boundary Layer Wind Tunnel Laboratory, at the University of Western Ontario, and a world authority on the behavior of buildings in high winds. During the Citicorp tower’s design, Davenport had run extensive tests on scale models of the structure. Now LeMessurier asked him and his deputy to retrieve the relevant files and magnetic tapes. “If we were going to think about such things as the possibility of failure,” LeMessurier says—the word “failure” being a euphemism for the Citicorp tower’s falling down—“we would think about it in terms of the best knowledge that the state of the art can produce, which is what these guys could provide for me.”
On July 26th, he flew to London, Ontario, and met with Davenport. Presenting his new calculations, LeMessurier asked the Canadians to evaluate them in the light of the original data. “And you have to tell me the truth,” he added. “Don’t go easy if it doesn’t come out the right way.”
It didn’t, and they didn’t. The tale told by the wind-tunnel experts was more alarming than LeMessurier had expected. His assumption of a forty-per-cent increase in stress from diagonal winds was theoretically correct, but it could go higher in the real world, when storms lashed at the building and set it vibrating like a tuning fork. “Oh, my God,” he thought, “now we’ve got that on top of an error from the bolts being underdesigned.” Refining their data further, the Canadians teased out wind-tunnel forces for each structural member in the building, with and without the tuned mass damper in operation; it remained for LeMessurier to interpret the numbers’ meaning.
First, he went to Cambridge, where he talked to a trusted associate, and then he called his wife at their summerhouse in Maine. “Dorothy knew what I was up to,” he says. “I told her, ‘I think we’ve got a problem here, and I’m going to sit down and try to think about it.’ ” On July 28th, he drove to the northern shore of Sebago Lake, took an outboard motorboat a quarter of a mile across the water to his house on a twelve-acre private island, and worked through the wind-tunnel numbers, joint by joint and floor by floor.
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.
“That was very low, awesomely low,” LeMessurier said, his voice hushed as if the horror of discovery were still fresh. “To put it another way, there was one chance in sixteen in any year, including that one.” When the steadying influence of the tuned mass damper was factored in, the probability dwindled to one in fifty-five—a fifty-five-year storm. But the machine required electric current, which might fail as soon as a major storm hit.
As an experienced engineer, LeMessurier liked to think he could solve most structural problems, and the Citicorp tower was no exception. The bolted joints were readily accessible, thanks to Hugh Stubbins’ insistence on putting the chevrons inside the building’s skin rather than displaying them outside. With money and materials, the joints could be reinforced by welding heavy steel plates over them, like giant Band-Aids. But time was short; this was the end of July, and the height of the hurricane season was approaching. To avert disaster, LeMessurier would have to blow the whistle quickly—on himself. That meant facing the pain of possible protracted litigation, probable bankruptcy, and professional disgrace. It also meant shock and dismay for Citicorp’s officers and shareholders when they learned that the bank’s proud new corporate symbol, built at a cost of a hundred and seventy-five million dollars, was threatened with collapse.
On the island, 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 and—although he was passionate about nineteenth-century classical music—unconvincingly melodramatic. What seized him an instant later was entirely convincing, because it was so unexpected—an 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.’ ”
At his office in Cambridge on the morning of Monday, July 31st, LeMessurier tried to reach Hugh Stubbins, whose firm was upstairs in the same building, but Stubbins was in California and unavailable by phone. Then he called Stubbins’ lawyer, Carl Sapers, and outlined the emergency over lunch. Sapers advised him against telling Citicorp until he had consulted with his own company’s liability insurers, the Northbrook Insurance Company, in Northbrook, Illinois. When LeMessurier called Northbrook, which represented the Office of James Ruderman as well, someone there referred him to the company’s attorneys in New York and warned him not to discuss the matter with anyone else.
At 9 a.m. on Tuesday, in New York, LeMessurier faced a battery of lawyers who, he says, “wanted to meet me to find out if I was nutty.” Being lawyers, not engineers, they were hard put to reconcile his dispassionate tone with the apocalyptic thrust of his prophecy. They also bridled at his carefully qualified answers to seemingly simple questions. When they asked how big a storm it would take to blow the building down, LeMessurier confined himself to statistical probabilities—a storm that might occur once in sixteen years.
When they pressed him for specific wind velocities—would the wind have to be at eighty miles per hour, or ninety, or ninety-five?—he insisted that such figures were not significant in themselves, since every structure was uniquely sensitive to certain winds; an eighty-five-mile-per-hour wind that blew for sixteen minutes from the northwest might pose less of a threat to a particular building than an eighty-mile-per-hour wind that blew for fourteen minutes from the southwest.
But the lawyers certainly understood that they had a crisis on their hands, so they sent for an expert adviser they trusted: Leslie Robertson, an engineer who had been a structural consultant for the World Trade Center. “I got a phone call out of the blue from some lawyer summoning me to a meeting,” Robertson says. “ ‘What’s it about?’ ‘You’ll find out when you get there.’ ‘Sorry, I have other things to do—I don’t attend meetings on that basis.’ A few minutes later, I got another call, from another lawyer, who said there’d been a problem with Citicorp Center. I went to the meeting that morning, and I didn’t know anybody there but Bill. He stood up and explained what he perceived were the difficulties with the building, and everyone, of course, was very concerned. Then they turned to me and said, ‘Well?’ I said, ‘Look, if this is in fact the case, you have a very serious problem.’ ”