Terrible moment when a gust of wind almost knocked over the seventh tallest building in the world

In 1978, a student at Princeton University called an architectural firm and helped prevent the collapse of one of the world’s tallest buildings in New York

Strong winds almost toppled the world’s seventh tallest building due to a major structural failure – but luckily a student saved the day.

The Citicorp Center in New York was built in 1977 and was the seventh tallest building in the world at the time.

But without the intervention of Princeton University student Diane Hartley, the skyscraper could have toppled at 70 miles per hour.

The building housed Citibank’s Manhattan headquarters and was built in three years at a cost of $175 million.

Despite the high price, the building had a major defect that threatened to collapse it.

Seasoned architects didn’t notice this flaw, and in fact it only came to light when Diane called her.

Potential wind loads on the building were miscalculated in the original design – it was estimated that the building could topple over in winds of 110 km/h.

Solutions were tried to fix the problem, but more and more problems kept popping up.

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The problem was that the entire structure was vulnerable to being knocked over by a strong enough storm, since the first nine stories of the building were on stilts.

Below the Citi Building is a church, St. Peter’s Lutheran Church, which refused to move and caused the architects a headache.

They decided the best solution was to continue the building and place Citi above the church.

The church approved the renovation and the plan went ahead.

However, the stilts were placed in the middle of the building to avoid making the church unstable.

Structural engineer William LeMessurier and a team proposed a solution to the problem.

They thought of adding V-shaped chevrons to the building frame, which transfer the floor loads to the center.

But eight-story chevrons only created more problems, since Citi’s structure was extremely light compared to other skyscrapers.

Strong winds could even shake the building.

So another solution was proposed: a tuned mass damper that weighs 400 tons and vibrates to reduce sway.

When building skyscrapers, architects must consider two types of wind that can affect the building.

Vertical winds hit the structure face-on, while crossing winds hit the corners of a building.

Although skyscrapers are usually strongest at their corners, Citi was not prone to strong winds.

LeMessurier had modeled the building for vertical winds, but not for quartering winds, which actually posed Citi’s greatest danger.

One day, in 1978, Diana, then a student at Princeton, called LeMessurier’s office.

She examined the building for a thesis, pointed out the problem of the crossing wind and her analysis was correct.

Using the information, LeMessurier’s team found that a storm with winds strong enough to topple the tower occurs every 55 years.

To do this, however, the 400-ton damper would have to function properly.

If a storm disrupts power, it could take a much weaker storm to topple Citi.

Suddenly, the team realized that about every 16 years, a storm can occur with winds strong enough to seriously damage the tower.

The situation was a potential disaster and required an urgent solution.

Things got even worse when a category four hurricane began to form on the east coast in August 1978.

If it hit New York and Citi fell, thousands of people were at risk of being killed.

The solution was to weld steel plates over the tower’s bolted joints, at a cost of $8million with insurance only covering £2million.

LeMessurier urged Citi to act quickly and help was found.

MIT-trained engineer John S. Reed was Citi’s EVP and together they convinced the company’s board of directors to take action.

A plan was drawn up to covertly carry out the welding process, and two and a half thousand police officers and Red Cross volunteers were placed on standby for a possible evacuation.

The work was carried out over several weeks in the evenings and early mornings.

Worker strikes at a number of newspapers of the time, such as the New York Times, kept word of what was happening at Citi in check.

Luckily, the hurricane that threatened to topple the tower never made it to New York, but one of the world’s tallest buildings came perilously close to becoming the scene of a major disaster.

The story was unknown for years, until a New Yorker writer heard it at a party and interviewed LeMessurier.

Today, the Citi building is named 601 Lexington Avenue and its 45-degree roof is an iconic part of Manhattan’s skyline.