99% Invisible #110 (rerun 14 Oct 2015): Structural Integrity
Citigroup Center (formerly Citicorp Center, AKA 601 Lexington, wikipedia page but I’m not consulting it for this) is a NY skyscraper that seems like it’s floating above you. It’s supported on stilts, and the stilts are in the middles of the sides, not the corners like you’d normally expect. The reason for this is that when the developers bought the land, they did so on condition that they’d rebuild a church where it already was, which was a corner.
The structural engineer did some neat trick with chevron-shaped supports to make this work, and then the architect didn’t want to see them and covered them up. The supports turned out to also be pretty light, so they added a mass dampener to the top of the building to reduce wind sway. It was neat.
Then one day the engineer got a call from some (arcitecture?) student, he doesn’t know who or what school they’re from, asking how he’d dealt with cornering winds, i.e. winds blowing on to the corner of the building rather than the side. He thought for a bit and was like, oh dear. He hadn’t done the calculations for those because normally the corners are the strongest, but with the stilts at the side that’s no longer the case. Looking at historical winds, he figured a storm that would knock the building down came along every 55 years. Except, the mass dampener needed power, and storms sometimes take out power, and without power a storm that would knock the building down came along every 16 years. And if the building (900ish feet tall?) went down it would topple and take over a lot of other stuff.
It would have been fine, but during construction some welds were swapped out for bolts. Sounds like that was done without consulting him? It would normally be fine but this is an unusual building.
Anyway, he contacted the relevant people and everyone teamed up to get it fixed, by replacing those bolts with welds. It didn’t cost much compared to the building itself. Teams worked through the night for (months?) and packed up before the office workers started to arrive. The public didn’t know this was happening. Normally you’d think this kind of work is hard to hide, but the NYT was on strike at the time so no reporters sniffing around wondering what’s up with all the blowtorches.
And it’s kind of sketchy that they didn’t tell the public. At one point a storm large enough that they’d have triggered an evac of the area was within hours of hitting, but it diverted. The story got out later, when a reporter overheard the story being told at a party.
Twist! Turns out it wasn’t a student who talked to the engineer. What seems to have happened is that a student got assigned to do a thesis on this building, and tried to recreate the calculations. She wasn’t sure what was going on with cornering winds, assumed the engineer had done it right, but called his company to try to get details. The person she spoke to is likely the person who spoke to the engineer, but that person doesn’t actually remember.
The student only found out about all this when she saw it on TV. It mentioned an unknown student and she was like “oh, I guess some other student was looking into this at the same time”. But someone who knows everyone relevant says no one else was. The student doesn’t think she’s a hero or anything, she just asked some questions without pushing very hard.
99% Invisible #110 (rerun 14 Oct 2015): Structural Integrity
Citigroup Center (formerly Citicorp Center, AKA 601 Lexington, wikipedia page but I’m not consulting it for this) is a NY skyscraper that seems like it’s floating above you. It’s supported on stilts, and the stilts are in the middles of the sides, not the corners like you’d normally expect. The reason for this is that when the developers bought the land, they did so on condition that they’d rebuild a church where it already was, which was a corner.
The structural engineer did some neat trick with chevron-shaped supports to make this work, and then the architect didn’t want to see them and covered them up. The supports turned out to also be pretty light, so they added a mass dampener to the top of the building to reduce wind sway. It was neat.
Then one day the engineer got a call from some (arcitecture?) student, he doesn’t know who or what school they’re from, asking how he’d dealt with cornering winds, i.e. winds blowing on to the corner of the building rather than the side. He thought for a bit and was like, oh dear. He hadn’t done the calculations for those because normally the corners are the strongest, but with the stilts at the side that’s no longer the case. Looking at historical winds, he figured a storm that would knock the building down came along every 55 years. Except, the mass dampener needed power, and storms sometimes take out power, and without power a storm that would knock the building down came along every 16 years. And if the building (900ish feet tall?) went down it would topple and take over a lot of other stuff.
It would have been fine, but during construction some welds were swapped out for bolts. Sounds like that was done without consulting him? It would normally be fine but this is an unusual building.
Anyway, he contacted the relevant people and everyone teamed up to get it fixed, by replacing those bolts with welds. It didn’t cost much compared to the building itself. Teams worked through the night for (months?) and packed up before the office workers started to arrive. The public didn’t know this was happening. Normally you’d think this kind of work is hard to hide, but the NYT was on strike at the time so no reporters sniffing around wondering what’s up with all the blowtorches.
And it’s kind of sketchy that they didn’t tell the public. At one point a storm large enough that they’d have triggered an evac of the area was within hours of hitting, but it diverted. The story got out later, when a reporter overheard the story being told at a party.
Twist! Turns out it wasn’t a student who talked to the engineer. What seems to have happened is that a student got assigned to do a thesis on this building, and tried to recreate the calculations. She wasn’t sure what was going on with cornering winds, assumed the engineer had done it right, but called his company to try to get details. The person she spoke to is likely the person who spoke to the engineer, but that person doesn’t actually remember.
The student only found out about all this when she saw it on TV. It mentioned an unknown student and she was like “oh, I guess some other student was looking into this at the same time”. But someone who knows everyone relevant says no one else was. The student doesn’t think she’s a hero or anything, she just asked some questions without pushing very hard.