Citicorp Center engineering crisis
In July 1978, a possible structural flaw was discovered in Citicorp Center, a skyscraper that had recently been completed in New York City.
Its structure, designed by William LeMessurier, had several unusual design features, including a raised base supported by four offset stilts and a column in the center, diagonal bracing which absorbed wind loads from upper stories, and a tuned mass damper with a 400-ton concrete weight floating on oil[1] to counteract oscillation movements.
At around the same time as Hartley was studying the question, an architecture student at New Jersey Institute of Technology (NJIT) named Lee DeCarolis chose the building as the topic for a report assignment in his freshman class on the basic concepts of structural engineering.
Estimates at the time suggested that if the mass damper was disabled by a power failure, the building could be toppled by a 70-mile-per-hour (110 km/h) quartering wind, with possibly many people killed as a result.
A NIST reassessment using modern technology later determined that the quartering wind loads were not the threat that LeMessurier and Hartley had thought.
[18]) To allow this design to work, Bill LeMessurier specified that load-bearing braces in the form of inverted chevrons be stacked above the stilts inside each face of the building.
To save money, Bethlehem Steel proposed changing the construction plans to use bolted joints, a design modification accepted by LeMessurier's office but unknown to the engineer himself until later.
In June 1978, Princeton University engineering student Diane Hartley was writing her senior thesis about Citicorp Center's design at the suggestion of her professor, David Billington.
Only Weinstein was indicated as signing off on the copies of the calculations he provided to her, although she expected to see them initialed by a second person to confirm them, as was the usual practice in the industry.
Weinstein assured her that the building could handle the necessary forces, and she did not further pursue the issue beyond writing about it in her thesis, which recorded her concerns and the response she received.
[21] In June 1978, LeMessurier was answering questions via phone with a young architectural student,[1] self-identified more than 40 years later as Lee DeCarolis.
[21][26] With the tuned mass damper active, LeMessurier estimated that a wind capable of toppling the building had a one in fifty-five chance of happening any year.
[27][21] But if the tuned mass damper could not function due to a power outage, a wind strong enough to cause the building's collapse had one chance in sixteen of happening any year.
If the issues were made known to the public, he risked ruining his professional reputation and causing panic in the immediate area surrounding the building and the occupants.
[31] Very few people were made aware of the issue, besides Citicorp leadership, mayor Ed Koch, acting buildings commissioner Irving E. Minkin, and the head of the welder's union.
Officials made no public mention of any possible structural issues, and the city's three major newspapers had gone on strike.
[34] As precautions, emergency generators were installed for the mass damper, strain gauges were placed on critical beams and weather forecasters were engaged.
The reinforcement was only half-finished, with New York City hours away from emergency evacuation, but at that point the backup generators were in place and the mass damper was being continually monitored by special staff, and enough of the bracing had been completed that the tower was estimated to be able to survive a 200-year storm.
[32][37] The 1995 story in The New Yorker described the student as a "young man, whose name has been lost in the swirl of subsequent events" who called LeMessurier saying "that his professor had assigned him to write a paper on the Citicorp tower".
[24] He said he learned in 2011 how he played a part in the Citicorp Building history from reading Einstein's Refrigerator, a 2001 book by the high school teacher and podcaster Steve Silverman.
