Crisis Averted: Architect Student ‘Saves’ Citigroup Skyscraper from Collapsing

Screenshot 2014-04-21 at 10.03.42 AMWith its distinctive 45-degree diagonal crown the Citigroup Center is one of Manhattan’s most prominent skyscrapers.

But nearly 40 years ago, as a hurricane threatened the Eastern Seaboard, New York’s Office of Emergency Management was hurriedly planning a mass evacuation of Midtown in case the tower collapsed – decimating 18 blocks of Midtown like dominoes all the way to Central Park.

Thankfully, that plan was never put into action, and the story of how just one phone call from an architecture undergraduate set off the chain of events that saved New York City from certain disaster went untold for almost 20-years.

When it was topped-out in 1977, the 59-story, $195 million skyscraper on Lexington Avenue was the seventh-tallest building in the world.

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In fact, the most distinctive part of its construction are its four massive, 114-foot-tall stilts that are located in the center of the building, rather than its corners.

They exist because the skyscraper had to be built around the remodeled St. Peter’s Church which originally existed on the corner of 53rd Street.

But these stilts caused a potentially catastrophic structural design flaw which went unnoticed from drawing board to completion.

Had the weakness not been discovered and fixed under cover of night, the Citigroup Center could have come down during any of the major storms which hit New York City in summertime.

While the architect of the building was Hugh Stubbins, the real genius behind its unusual design belongs to its chief engineer, William LeMessurier.

Designing the building around the church called for the stilts so as to allow the building to start more than one hundred feet above the ground.

Because the stilts were not on the corner of the building, where they would obviously traditionally be, LeMessurier came up with a brilliant chevron structure – literally eight rows of steel V’s running vertically through the building, acting as its skeleton.

Indeed, LeMessurier was aware that this chevron structure would make the building very light for a skyscraper, meaning it would sway in strong winds.

To account for that, one of the first ever tuned mass dampers – a 400-ton concrete ball at the top of the building – that would compensate like a stabilizing force for the movement in wind, was added.

However, one year after the building had opened, full of office workers and tens of thousands of oblivious New York commuters below, LeMessurier got a phone call.

An undergraduate named Diane Hartley phoned him to ask for his considerable expertise on the design, which had begun to confuse her.

She explained that her professor had expressed his own doubts about the 25,000 ton skyscraper because the stilts were not on the corners.

‘Listen, I want you to tell your teacher that he doesn’t know what the hell he’s talking about,’ LeMessurier told Hartley according to ‘because he doesn’t know the problem that had to be solved.’

The esteemed engineer, then 51, explained to Hartley that the tuned mass damper was in perfect alignment with the stilts and chevrons, leaving it able to withstand huge winds, especially from a diagonal angle – the most powerful.

After putting the phone down, LeMessurier decided to double check because he had been so forceful in his rebuttal of Hartley’s questions.

He became especially fixated on a minor engineering change that took place during the construction phase.

Le Messurier discovered that the joints on the chevrons were bolts, not welds, because the actual builders of the skyscraper had not been aware that the Citigroup Center was vulnerable to diagonal or quartering winds.

This set huge alarm bells off.

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