Source: http://www.dailymail.co.uk, April 21, 2014
By: James Nye

• New York City authorities and 2,500 Red Cross members prepared for the Citigroup Center to come crashing down on Manhattan in the summer of 1978

• A catastrophic design flaw was uncovered when an architecture student phoned the building’s chief engineer

• He discovered that the building could not withstand high winds

• Hurricane Ella began to form off the East Coast in August 1978 – launching authorities into action

• Disaster planners believed that 18 blocks of Midtown would be destroyed if the building came down

• Contingency plans were made in secret and the story was not made public for nearly 20-years

With 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.

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 DamnInteresting.com ‘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 according to 99 Percent Invisible.com

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.

Usually, all buildings are strongest at the corners and winds that face full on, or perpendicular winds are the most troublesome.

However, because of the unique design of the Citigroup Center, LeMessurier discovered that Hartley and her professor had made a frighteningly correct observation.

LeMessurier came to the terrifying conclusion that without the damper, a storm powerful enough to bring down the skyscraper hits New York every 16-years.

But, that only works on the proviso that the high-tech tuned mass damper, which is powered by electricity, is operational.

What if the storm caused a power-cut?

So, in the spring of 1978, with hurricane season fast approaching, LeMessurier took his findings to his friend, Alan Davenport, who confirmed his worst fears.

Devastated, LeMessurier retreated to Sebago Lake, in Maine to work out what to do. His reputation might be ruined, he would possibly face bankruptcy.

He contemplated suicide.

However, he knew that if he didn’t act, tens of thousands of people would, in all probability die.

He rushed to meet with Citigroup executives and using a book, which they slammed shut, dramatically demonstrated to the bank’s executive vice-president, John S. Reed, what would happen.

Getting to work in secret in June of 1978, Citigroup, the NYPD and the Office of Emergency Management began work on repairs and an evacuation plan that spanned a 10 block radius.

The public had no idea the danger they faced and a fortuitous newspaper strike helped authorities keep a lid on the crisis.

More than 2,500 Red Cross volunteers were on standby along with three different weather services constantly watching the weather.

Welders worked through the night, after staff had left the building.

But then in August, with repairs only half-way completed Hurricane Ella formed off Bermuda and seemed on a collision course with Manhattan.

The evacuation plan to empty most of the eastern side of Midtown Manhattan was readied.

Luckily Ella did not make landfall and the repairs were completed in September, revealing the skyscraper to now be one of the sturdiest in the world.

The story remained secret until reporter Joe Morgenstern overheard it being told at a party and published the piece in the New Yorker magazine in 1995.

Diane Hartley did not even know she was responsible for saving thousands of lives until she saw a BBC documentary in the early 2000s.

Up until then, the undergraduate was anecdotally referred to as a man.
LeMessurier’s swift action despite his reputation being on the line caused him to became a symbol of ethics in architecture.

Indeed, executives at Citigroup were allegedly so relived he came to them that they covered $6 million of the $8 million costs of the repairs – asking LeMessurier to pay the $2 million maximum his insurance allowed.