This thing is in real trouble. LeMessurier faced a stark choice. He could stay silent and hope for the best, or he could try to fix it and risk professional ruin and mass panic.
If they were to maximize the floor area, they would have to notch out one corner of the tower for the church. LeMessurier agreed that could work, but why not notch two, three, or even all four corners, essentially constructing the skyscraper on stilts. So it's probably the first time in history that an engineer has come to an architect and said, "Let's make our job harder for us."
There are many different types of TMDs, like pendulums, liquid columns, and a large mass on springs. LeMessurier used this last one in Citicorp. What you see is a mass of concrete, which is 29 feet square and about eight feet thick and weighs 400 tons.
Citicorp's oscillations are damped through those energy losses as the block oscillates out of phase to the building's motion. LeMessurier expected the damper to reduce the amplitude of swaying by roughly 50%, and he saved around $4 million by not needing an additional 2,800 tons of structural steel. With both the chevron bracing to channel forces to the stilts and the tuned mass damper to reduce sway, LeMessurier was convinced
The first hint of trouble came in May, 1978. LeMessurier was talking with another client about welding similar chevron braces. The architect and the steel fabricator said, "Tell me, how did those welded braces work out?" Seems like overkill, they thought.
And even then, it wasn't a lot of tension. LeMessurier trusted that his team did the right calculations, and the substitution was fine, logical, even. But around a month later, LeMessurier got a phone call from a student who wanted to ask some questions about the Citicorp Center.
But that wasn't the case anymore. LeMessurier remembered his earlier phone call. The welds holding the chevrons together were swapped for bolts.
I didn't panic right away, but I decided to go down to New York to my office. LeMessurier requested the building diagrams and poured over all of the connections. He looked at how his firm calculated the number of bolts.
But then it turned out they had done something else. LeMessurier's firm considered the braces to be minor structural elements. They didn't use the right factor of safety to calculate the number of bolts.
To LeMessurier's horror, the wind tunnel analysis showed that the stresses could increase up to 60% more than originally anticipated. LeMessurier squirreled himself away in Maine and worked through the data from the wind tunnel again, joint by joint on every floor. The weakest joints were at the building's 30th floor.
But what were the chances that a storm strong enough to topple the building would pass through New York City? LeMessurier dug through the historical weather reports. On average, a storm strong enough to tear the building apart occurred every 67 years.
it could fall down the summer of 1978. LeMessurier needed to decide and decide fast. But revealing this mistake could mean lawsuits, bankruptcy and professional ruin.
The TMD was originally designed to stabilize any swaying for comfort, but now it became the crutch that the tower leaned on. LeMessurier pinned all his hopes on it. He called the confidential repair plan Project Pandora, but that sounded ominous, so he came up with the Special Engineering Review
If he didn't respond, they would know something was up. LeMessurier described that next morning in New York as the most beautiful day that the world's ever seen.
Exactly. So it created an engineering problem. As LeMessurier considered the problem, he suddenly had a flash of inspiration. He grabbed a napkin and sketched out an idea.
The architect and the steel fabricator said, "Tell me, how did those welded braces work out?" Seems like overkill, they thought. And LeMessurier says, "Yeah, they were fine. Let me call my guys in New York and I'll check." So he put the call into his office in New York
We bolted those connections." The contractor had suggested saving a quarter of a million dollars by using bolts to attach the braces instead of welds. And LeMessurier's firm had agreed. There is nothing that says a bolt is inherently worse or better than a weld.
But the wind tunnel gave LeMessurier a dynamic analysis, how the forces change when the building is moving around. To LeMessurier's horror, the wind tunnel analysis showed that the stresses could increase up to 60% more than originally anticipated. LeMessurier squirreled himself away in Maine and worked through the data from the wind tunnel again, joint by joint on every floor.
After, they'd replaced the wall and clean everything up before the office workers came back the next morning, They needed to weld over 200 joints and LeMessurier ranked them by importance, starting with the ones on the 30th floor. But the repairs wouldn't be completed before hurricane season.
Several newspapers reported on it, but they didn't have the details. Then LeMessurier got a message. The New York Times was trying to reach him.
If he didn't respond, they would know something was up. Like LeMessurier said, we were sweating blood.
If he didn't respond, they would know something was up. that LeMessurier was basically tipped off by his New York engineers.
The way they could solve this was just let's add more structural steel and make it a lot stiffer. But the solution that LeMessurier came up with was far more elegant. He adopted something that had been regularly used in bridges, power lines and ships, but never before in a building: a tuned mass damper or TMD.
Since the force on each side was F over the square root of two, these beams get double that. Compared to LeMessurier calculations for the perpendicular wind load, the forces here were 40% higher. So 1.4 by itself is not enough to wreck havoc.
I mean, should probably take this. But even though LeMessurier tried to keep Project Serene under wraps, people started asking questions. On August 8th, Citicorp released a statement about the repairs.
If he didn't respond, they would know something was up. She never spoke to LeMessurier personally.
If he didn't respond, they would know something was up. with what LeMessurier himself said.
If he didn't respond, they would know something was up. As for LeMessurier, the engineering field still regards his actions as upstanding.
So it's much bigger than what's going on on the 60th floor. So these chevrons were key to LeMessurier's design, but the braces were massive, almost 40 meters long end to end. So even if you could fabricate a steel brace that long, there would be no way to get it through Manhattan.
This is called static conditions. But the wind tunnel gave LeMessurier a dynamic analysis, how the forces change when the building is moving around. To LeMessurier's horror, the wind tunnel analysis showed that the stresses could increase up to 60% more than originally anticipated.
If he didn't respond, they would know something was up. because I didn't speak to LeMessurier.
If he didn't respond, they would know something was up. She never claimed to speak to LeMessurier personally.
If he didn't respond, they would know something was up. The assumption was that either LeMessurier was mistaken and that it was Diane Hartley who made the call, it was a female, or more likely
If he didn't respond, they would know something was up. We reached out to a LeMessurier Associates and they refused to respond to our request.
fog's background he's the inventor of hundreds of patents he started 30 plus companies he's got the lemelson MIT prize for invention and Innovation um he has got the he's in the National inventor Hall of Fame and he's got the national medical sorry the national medal of technology and Innovation that
They should put 'em in the corners. That's silly." And I told the student, I said, "Well, you're a professor's full of it. He doesn't understand the problem we had to solve." LeMessurier went through the calculations with the student to reassure him the stilts were in the right place. But the interesting thing is, is in that moment, he's thinking about wind loads from all directions.
Just one year before Citicorp was completed, wind gusts of 110 kilometers per hour roared through New York City as Hurricane Belle passed through. What do you think this moment was like for LeMessurier, when he ran these calculations, like- Oh, it must have been devastating. I mean, it just must have been, I can't imagine the fear.
If he didn't respond, they would know something was up. Far from being vilified, LeMessurier was praised for owning up to his mistake and fixing the issue as soon as possible.
If he didn't respond, they would know something was up. an engineering student from New Jersey reaching out to LeMessurier.
If he didn't respond, they would know something was up. Sadly, LeMessurier passed away in 2007 before he could confirm the student's identity.
If he didn't respond, they would know something was up. And so if you think about the emotional pressure that Bill LeMessurier was under and then needing to come back and do something about it
vocabulary speech recognition May's rent many many honors he is the recipient of the $500,000 MIT lemelson prize the world's largest for innovation in 1999 he received the national medal of Technology the nation's highest honor in
And again, most importantly, two thirds of the space above the church had to be free and clear, had to be open. Citicorp then hired architect Hugh Stubbins to design the tower and the church and Bill LeMessurier as the structural engineer, Stubbins explained the constraints they faced. The church needed to be in the exact same spot and they needed to build the tower around it.
LeMessurier trusted that his team did the right calculations, and the substitution was fine, logical, even. But around a month later, LeMessurier got a phone call from a student who wanted to ask some questions about the Citicorp Center. And his teacher said to him, "That engineer didn't know what he's doing and nobody should put the columns in the middle.
So that was all they used. But when he added quartering winds, LeMessurier's calculations showed there were some braces that needed far more bolts. At this particular part of the building, which I can show you on my calculations is right about here, and Bill LeMessurier talked about the 30th floor,
After speaking to a few lawyers and other engineering experts, LeMessurier told the architect, Stubbins, and together they informed Citicorp's chairman, Walter Wriston. Within hours of that meeting, LeMessurier acquired emergency generators for the tuned mass damper. The TMD was originally designed to stabilize any swaying for comfort, but now it became the crutch that the tower leaned on.
If he didn't respond, they would know something was up. Now the building, according to LeMessurier, can withstand a one in 1000 storm.
Yeah, well, this particular system was entirely unique, driven by the placement of the columns, driven by the conditions of the building. As satisfied the chevrons could transfer the gravity load, LeMessurier turned his attention to the second problem, the wind. When wind hits the left side of a normal building with corner columns, the entire frame deforms like this.
I thought this thing is in real trouble. Imagine, you know, what Bill LeMessurier was thinking at that moment. You see that number and you're like, "Oh my God, this is serious. It's really serious." LeMessurier was starting to panic.
He didn't wanna rush to conclusions, so he flew to Canada to check his calculations with Alan Davenport at the Boundary Layer Wind Tunnel. After running more tests, they found that it was even worse than LeMessurier thought. The estimated 40% increase in stress was technically correct, but LeMessurier made his calculations assuming the building wasn't moving.