I don't know the physics involved nor do I have any knowledge of architecture or building construction but when I look at tall buildings it's really hard for me to imagine how they remain standing.
The bottom floor of a 100 story building is holding up 99 floors of weight. The base of a 100 story building it really thin relative to it's height. If I built anything out of legos to the same dimensions it would not be structurally sound. Well, the legos at the bottom would easily hold the weight). Yea I know reinforced steel and concrete is not legos. Other examples though, every piece of furinture I own has some degree of wobbliness. It's easy to see how the pyramids hold up. It's not so easy to see how the Vancouver House Building stays up (https://en.wikipedia.org/wiki/Vancouver_House). The one in the article as well just looks, at the bottom, like it has to tip over eventually. (not saying it will, only that it looks like it)
I'm not in any way denying science. I'm only in awe that more builings don't fall down. Bridges too. I'm surprised to some degree an 93 year old steel bridge being sprayed with salt water for the entire time hasn't had its cables snap.
Maybe a need a physics simulation game like 3d world of goo that lets me see how such structures hold togehter.
If you're not familiar with it, steel is actually surprisingly strong for its size. Look up "ultimate tensile strength" and "compressive yield strength". They are many tens of thousands of pounds per square inch for structural steel. Even the tensile strength of small fasteners like bolts is very high in "human" terms:
I think a lot of the answer here is in the foundation. a 100 story building isn't sitting on top of the ground. it has several stories of foundation below the ground, and likely has concrete piles that go hundreds of feet further down.
This. It is like roots of a tree for instance. The trunk by itself is actually much smaller than the branches — like the opposite of a pyramid.
I guess most of the stress is distributed throughout the building frame going into the foundation - like they drive those pylons into the ground before building a large building.
But still, it could snap from all that stress, like a tree that’s been felled by the wind…
That is why the other part is that skyscrapers are designed to sway in the wind and have the entire structure above the ground absorb the kinetic energy and sorta cancel it out before it reaches the base.
Some buildings use tuned mass dampers (like the giant pendulum in Taipei 101) to counteract swaying by moving in opposition to the wind-induced motion.
In fact, a lot of the time the majority of the building’s outer shell (glass etc) can be blown out by the wind, if it is too strong, and the steel structure will then have a lot of holes in it for the wind to pass through.
They test these structures for how the wind and water will flow around them. Look at the base of the Burj Al Arab, and how they built it to withstand the 100-year storm.
Don't worry, engineers can imagine (or, more accurately, analyze) how these buildings will remain standing. A good chunk of it is understanding how to distribute forces throughout a structure. The other chunk of it is understanding the properties of materials. While I didn't read the article in question, I did see the Veritasium video a while back. They have a decent overview of how it works, and how they figured out that there was a problem before the building collapsed. (Specifically, how the change from the original concept to the constructed building posed a problem.)
By the way, trust engineers and never trust physicist with these things. Physicists do have the theoretical tools to handle such problems, but they rarely have the practical knowledge to successfully implement them. :)
OK, but at the bottom floor, the support structure is carrying the weight of the 99 higher floors. It's not the ceiling, but it's still a subset of the cross section of that floor.
The support structure that is carrying the weight of the building is not a floor.
It's bedrock, a/o concrete pylons. Force doesn't ever take a 90-degree turn. Floors are only structural to carpet, furniture, and meatbags (tensioning members aren't part of the floor, even though they run parallel to them).
Fine, call it the "vertical supports" instead of the "support structure".
The vertical supports that carry the weight of a floor run vertically through that floor. They also carry the weight of all the higher floors. So there are vertical structures that pass through the bottom floor that support the weight of the bottom floor, plus the weight of every floor above it.
I know virtually nothing about architecture or structural engineering, but I imagine all the weight isn’t necessarily going down from floor to floor, but a lot of the weight is attached to support columns, and the floors are built out from that.
All the weight is still on those support columns though, and I also have a hard time wrapping my head around how something like that is possible. Engineering is amazing.
I'm somewhat familiar with the engineering but I still marvel that this kind of building is possible. I think we are damn lucky to have a material such as steel to build with - all the engineering in the world wouldn't help without it.
The irony that this was printed just 6 years before 9/11. The lesson is it's hard to anticipate all the possible risks. The two WTC towers were engineered to withstand a jet plane impact (a 707, which was a common passenger jet at the time in the late 60s), just not not a modern airplane packed with fuel at max speed.
As far as weights go, the 707 and the 767-200s that hit the towers were fairly close in size, weight and fuel capacity and that is demonstrated by both towers surviving their impacts. The problem was the fire and specifically the inability to fight the scale of the fire effectively.
And insufficient modelling for the heat of jet fuel mixed with office supplies which severely weakened the structure allowing it to pancake in a cascading fashion from the first support columns to buckle.
The designers also assumed that the airplane would be moving pretty slowly if it was so close to the ground, either departing from or landing at a nearby airport, not coming in at near top speed.
First of all, the WTC towers did withstand the impacts but collapsed due to the ensuing fires which weakened the remaining core columns (notably not due to collapsing floors, which did not in fact occur, according to Thornton-Tomasetti who have modeled the impacts and ensuing collapses as part of their forensic investigation commissioned for the insurance claim litigation).
Leslie Robertson, who lead the WTC structural engineering team along with John Skilling, is on tape making the 707 claim, but no surviving documentation has been uncovered to reveal the specific scenario that was modeled or the calculations used.
An important reason why the towers survived the impacts at all was the presence of the two hat trusses, which allowed the increasingly unsupported loads to be redistributed to the surviving exterior columns. Najib N. Abboud of Thornton-Thomasetti has given a detailed account of the findings of the forensic investigation that's available on Youtube[1].
> On Tuesday morning, August 8th, the public-affairs department of Citibank, Citicorp's chief subsidiary, put out the long-delayed press release. In language as bland as a loan officer's wardrobe, the three-paragraph document said unnamed "engineers who designed the building" had recommended that "certain of the connections in Citicorp Center's wind bracing system be strengthened through additional welding." The engineers, the press release added, "have assured us that there is no danger." When DeFord expanded on the handout in interviews, he portrayed the bank as a corporate citizen of exemplary caution -- "We wear both belts and suspenders here," he told a reporter for the News -- that had decided on the welds as soon as it learned of new data based on dynamic-wind tests conducted at the University of Western Ontario.
> There was some truth in all this. [...] At the time, LeMessurier viewed this piece of information as one more nail in the coffin of his career, but later, recognizing it as a blessing in disguise, he passed it on to Citicorp as the possible basis of a cover story for the press and for tenants in the building.
Seems questionable to lie to conceal that kind of catastrophic risk.
Knowing that the skyscraper would fail in some kinds of winds is information that could be used by rational people to help protect themselves and their businesses.
> Shortly before dawn on Friday, September 1st, weather services carried the news that everyone had been dreading—a major storm, Hurricane Ella, was off Cape Hatteras and heading for New York. At 6:30 a.m., an emergency-planning group convened at the command center in Robertson's office. "Nobody said, ‘We're probably going to press the panic button,' " LeMessurier recalls. "Nobody dared say that. But everybody was sweating blood."
> As the storm bore down on the city, the bank's representatives, DeFord and Dexter, asked LeMessurier for a report on the status of repairs. He told them that the most critical joints had already been fixed and that the building, with its tuned mass damper operating, could now withstand a two-hundred-year storm. It didn't have to, however. A few hours later, Hurricane Ella veered from its northwesterly course and began moving out to sea.
I see gambling people.
Presumably, some were gambling to avoid temporary public disorder in the city, or temporary disruption to general commerce there.
But it sounds like others of them wanted cover up a scandal in which they and the company were now implicated. And they were willing to gamble with other people's lives and businesses to do so.
You seem awfully quick to indict them. While honesty is definitely a virtue, too much can hurt. They wanted to avoid causing a panic, and they monitored risk carefully. Presumably they had time to issue evacuation orders in the event the storm turned towards the city. In the end they completed the repairs and no one had to panic.
Compare that with the evacuation of Fukushima after the incident at the nuclear plant, which released a very minor amount of radiation. Many people suffered severe psychological stress at not being able to return home and not knowing when or if they'd be allowed to go home. Some to the point of suicide. In that case the issue was more about unnecessary evacuation as opposed to messaging, but the point stands the unnecessary panic can cause real harm.
I'd much rather see someone who did the right thing get celebrated. There are so many possible other routes he could have taken that all involve less integrity (or extremely harmful integrity, like suicide, which he admits to having briefly considered), and some measure of public harm.
It's also such a nuanced issue, with bolts vs welds and arguably no one having done anything wrong individually, that I can't imagine a way to explain this to the public that people could understand and be like "yea that makes sense" and proceed to act rationally. Add to that the fact that there's so much probability involved in the potential path and strength of any storm and I'm not sure a member of the general public could reach a rational conclusion.
Of course we'll never know, but the point is that the man did the right thing, and of course we should celebrate that.
Agreed, I have mixed and nuanced feelings about this. The article seemed a little too generous at points, though.
Maybe the writer was trying to celebrate, and to head off some kneejerk criticisms, but still with the idea that people would be looking over this reporting, and that there'd be a place for constructive criticism?
Many good lessons from this, including the importance of speaking up, one person making a difference, and the importance of drilling down into sources. The Wikipedia article used to state "This was in spite of the fact that up to 200,000 people could have been killed in a potential collapse." using an article in the magazine 'Cross Currents' as the source. If you follow that through the layers of citations, it turns out the 200,000 figure came from an unnamed source at the American Red Cross, which really isn't a reasonable source of such an estimate. I felt a bit chagrined to have used that number when explaining the situation to my nieces about how important it can be for one person speak up and not default to assuming those in authority always have a full understanding of a situation.
There's actually a recording of a talk that LeMessurier gave on this incident on YouTube. It's a very interesting listen, though he clearly is a bit... defensive... about the whole thing.
Just walked past this building in person the other day. I had to a triple take when I saw the base. It seems very unintuitive that it could stand safely.
I don't know the physics involved nor do I have any knowledge of architecture or building construction but when I look at tall buildings it's really hard for me to imagine how they remain standing.
The bottom floor of a 100 story building is holding up 99 floors of weight. The base of a 100 story building it really thin relative to it's height. If I built anything out of legos to the same dimensions it would not be structurally sound. Well, the legos at the bottom would easily hold the weight). Yea I know reinforced steel and concrete is not legos. Other examples though, every piece of furinture I own has some degree of wobbliness. It's easy to see how the pyramids hold up. It's not so easy to see how the Vancouver House Building stays up (https://en.wikipedia.org/wiki/Vancouver_House). The one in the article as well just looks, at the bottom, like it has to tip over eventually. (not saying it will, only that it looks like it)
I'm not in any way denying science. I'm only in awe that more builings don't fall down. Bridges too. I'm surprised to some degree an 93 year old steel bridge being sprayed with salt water for the entire time hasn't had its cables snap.
Maybe a need a physics simulation game like 3d world of goo that lets me see how such structures hold togehter.
If you're not familiar with it, steel is actually surprisingly strong for its size. Look up "ultimate tensile strength" and "compressive yield strength". They are many tens of thousands of pounds per square inch for structural steel. Even the tensile strength of small fasteners like bolts is very high in "human" terms:
https://www.engineeringtoolbox.com/us-bolts-tensile-proof-lo...
The bottom floor of a 100 story building is holding up 99 floors of weight.
That's not how it works. All the load of the floors above is held by the columns, which go into the foundation.
Kind of like a stand of bamboo, and we're just critters weaving little platforms at different heights.
I think a lot of the answer here is in the foundation. a 100 story building isn't sitting on top of the ground. it has several stories of foundation below the ground, and likely has concrete piles that go hundreds of feet further down.
Unless you try to cheap out, then you end up costing yourself more in the long run, lol: https://en.wikipedia.org/wiki/161_Maiden_Lane
This. It is like roots of a tree for instance. The trunk by itself is actually much smaller than the branches — like the opposite of a pyramid.
I guess most of the stress is distributed throughout the building frame going into the foundation - like they drive those pylons into the ground before building a large building.
But still, it could snap from all that stress, like a tree that’s been felled by the wind…
That is why the other part is that skyscrapers are designed to sway in the wind and have the entire structure above the ground absorb the kinetic energy and sorta cancel it out before it reaches the base.
Some buildings use tuned mass dampers (like the giant pendulum in Taipei 101) to counteract swaying by moving in opposition to the wind-induced motion.
In fact, a lot of the time the majority of the building’s outer shell (glass etc) can be blown out by the wind, if it is too strong, and the steel structure will then have a lot of holes in it for the wind to pass through.
They test these structures for how the wind and water will flow around them. Look at the base of the Burj Al Arab, and how they built it to withstand the 100-year storm.
https://theskydeck.com/do-skyscrapers-sway/
>Maybe a need a physics simulation game like 3d world of goo that lets me see how such structures hold together.
Bridge Designer, formerly West Point Bridge Designer is a physics simulation that does almost that, though is more a learning tool than a game.
https://bridgedesigner.org/
Don't worry, engineers can imagine (or, more accurately, analyze) how these buildings will remain standing. A good chunk of it is understanding how to distribute forces throughout a structure. The other chunk of it is understanding the properties of materials. While I didn't read the article in question, I did see the Veritasium video a while back. They have a decent overview of how it works, and how they figured out that there was a problem before the building collapsed. (Specifically, how the change from the original concept to the constructed building posed a problem.)
By the way, trust engineers and never trust physicist with these things. Physicists do have the theoretical tools to handle such problems, but they rarely have the practical knowledge to successfully implement them. :)
What you think of as a “floor” is more accurately described as hanging off the support structure.
OK, but at the bottom floor, the support structure is carrying the weight of the 99 higher floors. It's not the ceiling, but it's still a subset of the cross section of that floor.
No.
The support structure that is carrying the weight of the building is not a floor.
It's bedrock, a/o concrete pylons. Force doesn't ever take a 90-degree turn. Floors are only structural to carpet, furniture, and meatbags (tensioning members aren't part of the floor, even though they run parallel to them).
Fine, call it the "vertical supports" instead of the "support structure".
The vertical supports that carry the weight of a floor run vertically through that floor. They also carry the weight of all the higher floors. So there are vertical structures that pass through the bottom floor that support the weight of the bottom floor, plus the weight of every floor above it.
I know virtually nothing about architecture or structural engineering, but I imagine all the weight isn’t necessarily going down from floor to floor, but a lot of the weight is attached to support columns, and the floors are built out from that.
All the weight is still on those support columns though, and I also have a hard time wrapping my head around how something like that is possible. Engineering is amazing.
I think what they meant was not literally the bottom floor, but the columns at the bottom floor.
I'm somewhat familiar with the engineering but I still marvel that this kind of building is possible. I think we are damn lucky to have a material such as steel to build with - all the engineering in the world wouldn't help without it.
That podcast shines it all
https://99percentinvisible.org/episode/structural-integrity/
Veritasium did a whole video on this building last month
https://youtu.be/Q56PMJbCFXQ?feature=shared
Veritasium covered this recently and did some debunking about the original student.
https://youtu.be/Q56PMJbCFXQ?si=pjfmTrrA7JGuTZxd
The irony that this was printed just 6 years before 9/11. The lesson is it's hard to anticipate all the possible risks. The two WTC towers were engineered to withstand a jet plane impact (a 707, which was a common passenger jet at the time in the late 60s), just not not a modern airplane packed with fuel at max speed.
As far as weights go, the 707 and the 767-200s that hit the towers were fairly close in size, weight and fuel capacity and that is demonstrated by both towers surviving their impacts. The problem was the fire and specifically the inability to fight the scale of the fire effectively.
And insufficient modelling for the heat of jet fuel mixed with office supplies which severely weakened the structure allowing it to pancake in a cascading fashion from the first support columns to buckle.
The designers also assumed that the airplane would be moving pretty slowly if it was so close to the ground, either departing from or landing at a nearby airport, not coming in at near top speed.
First of all, the WTC towers did withstand the impacts but collapsed due to the ensuing fires which weakened the remaining core columns (notably not due to collapsing floors, which did not in fact occur, according to Thornton-Tomasetti who have modeled the impacts and ensuing collapses as part of their forensic investigation commissioned for the insurance claim litigation).
Leslie Robertson, who lead the WTC structural engineering team along with John Skilling, is on tape making the 707 claim, but no surviving documentation has been uncovered to reveal the specific scenario that was modeled or the calculations used.
An important reason why the towers survived the impacts at all was the presence of the two hat trusses, which allowed the increasingly unsupported loads to be redistributed to the surviving exterior columns. Najib N. Abboud of Thornton-Thomasetti has given a detailed account of the findings of the forensic investigation that's available on Youtube[1].
[1] https://youtu.be/b2wimsBPmYI?feature=shared
https://archive.is/3Ed3T
> On Tuesday morning, August 8th, the public-affairs department of Citibank, Citicorp's chief subsidiary, put out the long-delayed press release. In language as bland as a loan officer's wardrobe, the three-paragraph document said unnamed "engineers who designed the building" had recommended that "certain of the connections in Citicorp Center's wind bracing system be strengthened through additional welding." The engineers, the press release added, "have assured us that there is no danger." When DeFord expanded on the handout in interviews, he portrayed the bank as a corporate citizen of exemplary caution -- "We wear both belts and suspenders here," he told a reporter for the News -- that had decided on the welds as soon as it learned of new data based on dynamic-wind tests conducted at the University of Western Ontario.
> There was some truth in all this. [...] At the time, LeMessurier viewed this piece of information as one more nail in the coffin of his career, but later, recognizing it as a blessing in disguise, he passed it on to Citicorp as the possible basis of a cover story for the press and for tenants in the building.
Seems questionable to lie to conceal that kind of catastrophic risk.
Knowing that the skyscraper would fail in some kinds of winds is information that could be used by rational people to help protect themselves and their businesses.
> Shortly before dawn on Friday, September 1st, weather services carried the news that everyone had been dreading—a major storm, Hurricane Ella, was off Cape Hatteras and heading for New York. At 6:30 a.m., an emergency-planning group convened at the command center in Robertson's office. "Nobody said, ‘We're probably going to press the panic button,' " LeMessurier recalls. "Nobody dared say that. But everybody was sweating blood."
> As the storm bore down on the city, the bank's representatives, DeFord and Dexter, asked LeMessurier for a report on the status of repairs. He told them that the most critical joints had already been fixed and that the building, with its tuned mass damper operating, could now withstand a two-hundred-year storm. It didn't have to, however. A few hours later, Hurricane Ella veered from its northwesterly course and began moving out to sea.
I see gambling people.
Presumably, some were gambling to avoid temporary public disorder in the city, or temporary disruption to general commerce there.
But it sounds like others of them wanted cover up a scandal in which they and the company were now implicated. And they were willing to gamble with other people's lives and businesses to do so.
You seem awfully quick to indict them. While honesty is definitely a virtue, too much can hurt. They wanted to avoid causing a panic, and they monitored risk carefully. Presumably they had time to issue evacuation orders in the event the storm turned towards the city. In the end they completed the repairs and no one had to panic.
Compare that with the evacuation of Fukushima after the incident at the nuclear plant, which released a very minor amount of radiation. Many people suffered severe psychological stress at not being able to return home and not knowing when or if they'd be allowed to go home. Some to the point of suicide. In that case the issue was more about unnecessary evacuation as opposed to messaging, but the point stands the unnecessary panic can cause real harm.
I acknowledged that's a factor for some people.
Throughout the article, from the beginning, the writer keeps going out of their way to exonerate the main character.
But elsewhere they do acknowledge the risks to the company's stock price, individual reputations, etc.
So it does seem that was a factor for some, and a potential conflict of interest.
I'd much rather see someone who did the right thing get celebrated. There are so many possible other routes he could have taken that all involve less integrity (or extremely harmful integrity, like suicide, which he admits to having briefly considered), and some measure of public harm.
It's also such a nuanced issue, with bolts vs welds and arguably no one having done anything wrong individually, that I can't imagine a way to explain this to the public that people could understand and be like "yea that makes sense" and proceed to act rationally. Add to that the fact that there's so much probability involved in the potential path and strength of any storm and I'm not sure a member of the general public could reach a rational conclusion.
Of course we'll never know, but the point is that the man did the right thing, and of course we should celebrate that.
Agreed, I have mixed and nuanced feelings about this. The article seemed a little too generous at points, though.
Maybe the writer was trying to celebrate, and to head off some kneejerk criticisms, but still with the idea that people would be looking over this reporting, and that there'd be a place for constructive criticism?
2 years ago: https://news.ycombinator.com/item?id=37684604
Thanks! Macroexpanded:
A skyscraper that could have toppled over in the wind (1995) - https://news.ycombinator.com/item?id=37684604 - Sept 2023 (21 comments)
Many good lessons from this, including the importance of speaking up, one person making a difference, and the importance of drilling down into sources. The Wikipedia article used to state "This was in spite of the fact that up to 200,000 people could have been killed in a potential collapse." using an article in the magazine 'Cross Currents' as the source. If you follow that through the layers of citations, it turns out the 200,000 figure came from an unnamed source at the American Red Cross, which really isn't a reasonable source of such an estimate. I felt a bit chagrined to have used that number when explaining the situation to my nieces about how important it can be for one person speak up and not default to assuming those in authority always have a full understanding of a situation.
This is one case in which our layperson's naive intuition would've been the right answer (for the wrong reasons):
https://en.wikipedia.org/wiki/File:53rd_St_Lex_Av_td_08_-_Ci...
There's actually a recording of a talk that LeMessurier gave on this incident on YouTube. It's a very interesting listen, though he clearly is a bit... defensive... about the whole thing.
https://www.youtube.com/watch?v=um-7IlAdAtg
There’s a great keynote by Nickolas Means [1] about this building and the story around it.
[1]: https://youtu.be/NLXys9vgWiY
I saw the title and thought it was about Boston's John Hancock Tower, which also had to be reinforced before it (theoretically) fell down.
Just walked past this building in person the other day. I had to a triple take when I saw the base. It seems very unintuitive that it could stand safely.
What a great story: remarkable how the New Yorker of 1995 has the same efficient but easy-going clarity as 2025.
Seriously - I find myself coming back to read this once every few years because of how riveting the piece is (oh no -just realized the pun)
Also I’ve heard wonderful things about The Great Miscalculation[0], a recently released book about the Citicorp Tower incident
[0]: https://search.worldcat.org/en/title/1458613829
[dead]