Would the WTC Twin Towers have collapsed from fire alone, without plane impact?

[Henkka]

Then this will surprise you:

Any child setting off a domino chain reaction is not incredulous about it, why were you?

Two things:

1) The dominoes decelerate as they impact the bigger domino, something the top block of WTC 1 did not do.

2) I've shown you many videos of building collapses that arrest halfway. It's therefore not some rule that building collapses, once initiated, will inevitably result in total collapse like a row of dominoes being knocked over.

No, @econ41 simply hasn't posted since then.

I meant before that. I tried asking what would happen if for example someone just hauled up barrels of fuel, doused the impacted floors of WTC 1, and then set them on fire. So exactly the same fires, but no plane impact. It seemed to me he was saying a similar collapse would happen, but he didn't like that I was presenting such a cartoonish hypothetical... That was my interpretation, at least. Maybe he can clarify.

 

[Thomas B]

Then this will surprise you

Can we not agree that it would be very surprising if skyscrapers were built to be vulnerable in this way?

Note that even a very weak connection between the dominos -- sufficient to transfer the force of the first (very small) one toppling -- would be enough to prevent this effect.

Why would anyone build anything like this? [Edit: i.e., why would anyone build anything without such a transfer mechanism?]

What the truthers essentially argue is that a robust connection between each domino, sufficient to transfer the impact (from any possible toppled domino at any point further up the line) down to a much heavier, more inertial domino, was part of the design. These connections, they claim, were severed with demolition charges before the first domino fell. And that -- plus "physics" -- explains what we saw on 9/11.

 

[deirdre]

Can we not agree that it would be very surprising if skyscrapers were built to be vulnerable in this way?

they werent that vulnerable, they stood up for a long time. ("long" as far as giving people time to escape an extreme, unfathomable event)

are we surprised they built the buildings in a way that didn't allow the people on the top floors a way to escape? because apparently they did.

 

[Gamolon]

So exactly the same fires, but no plane impact. It seemed to me he was saying a similar collapse would happen, but he didn't like that I was presenting such a cartoonish hypothetical... That was my interpretation, at least. Maybe he can clarify.

How in the world are you getting your above interpretation from econ41's quotes below?!?!

So I will present my outline argument that without the plane impacts both WTC Twin Towers would probably have survived any likely fire that could have occurred.

My contention is that the 9/11 Twin Towers collapses resulted from a combination of the consequences of aircraft impact and unfought fires.

All four of those were consequences of aircraft impact. Without aircraft impact the fires of the scale of 9/11 could not have been initiated.

Yes. That is my position. The aircraft impacts were essential to the 9/11 collapses. Not as a direct result of structural damage but by causing the four factors I outlined previously. Probably assisted by the structural damage caused by the initial impact.

And the nail in the coffin? When econ41 answered your question, "Is it your position that the WTC towers could have collapsed from fire alone, without plane impact?" with:

No!

 

[Henkka]

How in the world are you getting your above interpretation from econ41's quotes below?!?!

Because of this statement...

Of course, a fire could cause collapse provided it was big enough to overwhelm the resources available to resist it.

So I took that to mean that yes, a large enough fire would cause the building to collapse, even if it hadn't been rammed by a plane first. He just thinks that the only way to set fires of that scale was to ram a plane into the building, as you quoted:

Without aircraft impact the fires of the scale of 9/11 could not have been initiated.

Which led to me asking about hypothetical scenarios where someone would haul up hundreds of barrels of fuel up the elevators and dump them on the floors, set the fire that way. He dismissed this as logistically impossible, but in my opinion logistics don't really matter in hypotheticals.

 

[benthamitemetric]

Because of this statement...


So I took that to mean that yes, a large enough fire would cause the building to collapse, even if it hadn't been rammed by a plane first. He just thinks that the only way to set fires of that scale was to ram a plane into the building, as you quoted:


Which led to me asking about hypothetical scenarios where someone would haul up hundreds of barrels of fuel up the elevators and dump them on the floors, set the fire that way. He dismissed this as logistically impossible, but in my opinion logistics don't really matter in hypotheticals.

Do you believe that, no matter how much fuel was added to the building, no resulting fire could have caused a collapse?

 

[benthamitemetric]

Can we not agree that it would be very surprising if skyscrapers were built to be vulnerable in this way?

Note that even a very weak connection between the dominos -- sufficient to transfer the force of the first (very small) one toppling -- would be enough to prevent this effect.

Why would anyone build anything like this? [Edit: i.e., why would anyone build anything without such a transfer mechanism?]

What the truthers essentially argue is that a robust connection between each domino, sufficient to transfer the impact (from any possible toppled domino at any point further up the line) down to a much heavier, more inertial domino, was part of the design. These connections, they claim, were severed with demolition charges before the first domino fell. And that -- plus "physics" -- explains what we saw on 9/11.

Were the WTC towers built to withstand the collapse of a block the size of 6 or more of its floors? If so, please cite exactly who did the design work for such a scenario and how they designed for it.

 

[Oystein]

Going to extremes sometimes is illuminating. So here is a claim, which I genuinely consider to be true:

A sufficiently severe hydrocarbon fire can bring down entirely the Great Pyramid of Giza (Khufu's one).

Think about that for a while.

 

[Thomas B]

Were the WTC towers built to withstand the collapse of a block the size of 6 or more of its floors? If so, please cite exactly who planned for such a scenario and how they designed for it.

They were built to redistribute loads (in all directions, from wind, quake, etc.) continuously throughout the whole structure. There were no spaces between the structural elements as in the domino example.

I'm just saying that domino example is a terrible analogy. I'm happy to hear how some other simple model captures the dynamics that happened on 9/11.

 

[Thomas B]

A sufficiently severe hydrocarbon fire can bring down entirely the Great Pyramid of Giza (Khufu's one).

What would be the volume of the fuel required? Even the most efficient fuel we can imagine. Would it be greater than the volume of the pyramid?

 

[Oystein]

Can we not agree that it would be very surprising if skyscrapers were built to be vulnerable in this way?
...

This comes across as an extremely dishonest way to describe how engineers design things.

Skyscrapers are not "built to be vulnerable". They simply are vulnerable. It is extremely difficult to build a tall building such that it doesn't collapse already during construction, or from the slightest of disturbances. It's why you and I would never be entrusted with designing a skyscraper. In fact, most civil engineers would never be entrusted with designing a skyscraper, because most designs of most engineers would be so damned likely to turn out to be highly vulnerable failures.
Nobody designs for vulnerabilities; the best you can do is design against the vulnerabilities that are fundamentally, conceptually there, always, unavoidably. It is fundamentally impossible to make a skyscraper invulnerable.

 

[Oystein]

What would be the volume of the fuel required? Even the most efficient fuel we can imagine. Would it be greater than the volume of the pyramid?

I have no idea.
And it doesn't matter.
I am pointing out a truism: The most stable, enduring building in world history is fundamentally vulnerable to attack, even to attack with conventional incendiaries.
I went to extremes to plant i side your head that you cannot possibly design a skyscraper to invulnerable to fire, nor to progressive collapse. Because not even Khufu's pyramid is.
(Can you tell us the main reason why the Great Pyramid is so much more enduring, stable than the Twin Towers?)

 

[Thomas B]

This comes across as an extremely dishonest way to describe how engineers design things.

I'm sorry you find me dishonest. (I don't think you are.) I totally agree with your point and no part of my mine depends on the idea that buildings are literally designed to be vulnerable. I'm happy to rephrase it as follows: it would be surprising if buildings were vulnerable in this way.

 

[Henkka]

Do you believe that, no matter how much fuel was added to the building, no resulting fire could have caused a collapse?

Um, "no matter how much fuel" includes very farfetched scenarios... Like millions of gallons of fuel being constantly poured on the building as it burned. I don't know what would happen in such a scenario, but I suppose it could collapse.

But in what actually happened, most of the fuel from the plane exploded instantly in the fireball... And the remaining fuel burned up over the next 10-20 minutes, if I recall correctly. After that, you just had office combustibles which had been ignited by the fuel. In cases like One Meridian, the fire just burned until it had exhausted all that fuel.

edit: Here is the quote from Sunder to back this up:

Dr. Shyam Sunder, Lead Investigator: "The jet fuel probably burned out in less than 10 minutes. And what did burn over the next hour, or hour and a half, was much of the contents of the buildings."

https://www.firehouse.com/home/news/10525910/a-look-inside-a-radical-new-theory-of-the-wtc-collapse

 

[benthamitemetric]

They were built to redistribute loads (in all directions, from wind, quake, etc.) continuously throughout the whole structure. There were no spaces between the structural elements as in the domino example.

I'm just saying that domino example is a terrible analogy. I'm happy to hear how some other simple model captures the dynamics that happened on 9/11.

So I'll take that as a "no"--you are not aware of anyone specifically designing the towers to withstand collapse in a scenario where 6 or more floors worth of its construction fell upon the rest of it. And we all know, of course, that no such designing was ever undertaken. So it should not surprise you, nor any of the imaginary "truthers you talk to" (though I thought you only talk to them about non-engineering topics, so it's odd to see you summarizing their views on an engineering topic...), that the buildings would behave in a way that is not in any way outside of what they were designed for. And the reason why the buildings were not designed that way is so glaringly obvious that it pains me to have to point it out to you after 4 threads on similar topics that always converge back to these same points: It's not economical to design a building to withstand all manner of black swan events.

And the Domino collapse is only a bad analogy because it over-illustrated the point: in the case of the towers, the impacting dominos, not the standing dominos, effectively became larger over time as the mass of fall floors accreted and accelerated, while the floors in the towers were all capable of withstanding the same fixed amount.

 

[Thomas B]

I have no idea.
And it doesn't matter.
I am pointing out a truism: The most stable, enduring building in world history is fundamentally vulnerable to attack, even to attack with conventional incendiaries.
I went to extremes to plant i side your head that you cannot possibly design a skyscraper to invulnerable to fire, nor to progressive collapse. Because not even Khufu's pyramid is.
(Can you tell us the main reason why the Great Pyramid is so much more enduring, stable than the Twin Towers?)

I just find this weird. If there was a fire in the burial chamber of the Khufu pyramid and, about an hour into fighting it, the whole pyramid collapsed, it would be pretty clear that the "hydrocarbon fire" didn't do it, right? We'd be looking for bombs.

The reason is that there couldn't possibly be enough hydrocarbon in the pyramid to bring it down.

 

[benthamitemetric]

Um, "no matter how much fuel" includes very farfetched scenarios... Like millions of gallons of fuel being constantly poured on the building as it burned. I don't know what would happen in such a scenario, but I suppose it could collapse.

But in what actually happened, most of the fuel from the plane exploded instantly in the fireball... And the remaining fuel burned up over the next 10-20 minutes, if I recall correctly. After that, you just had office combustibles which had been ignited by the fuel. In cases like One Meridian, the fire just burned until it had exhausted all that fuel.

Well, I'll let econ speak for himself, but it seems obvious to me that his only reservation about whether fire would cause the collapse was because of far fetched scenarios.

And whatever you think you are "recalling" about the fuel in the towers has nothing to do with reality. Why don't you take 10 min and double check the NIST reports? For the towers, they even built scale models of the floors and did extensive real world testing to inform their models of how the fires burned. There is no need to guess something ridiculous that you just pulled out of thin air.

 

[Mendel]

They were built to redistribute loads (in all directions, from wind, quake, etc.) continuously throughout the whole structure. There were no spaces between the structural elements as in the domino example.

That's not true at all, and we have talked about this.

 

[Mendel]

most of the fuel from the plane exploded instantly in the fireball...

Are you sure of this?

 

[Landru]

Um, "no matter how much fuel" includes very farfetched scenarios... Like millions of gallons of fuel being constantly poured on the building as it burned. I don't know what would happen in such a scenario, but I suppose it could collapse.

But in what actually happened, most of the fuel from the plane exploded instantly in the fireball... And the remaining fuel burned up over the next 10-20 minutes, if I recall correctly. After that, you just had office combustibles which had been ignited by the fuel. In cases like One Meridian, the fire just burned until it had exhausted all that fuel.

Source please.

 

[Henkka]

Are you sure of this?

Actually, no. This is something I remember reading somewhere, but I'm not sure what the actual numbers are on what percentage of the jet fuel exploded instantly, and how long the remainder lasted. If anyone has the hard facts on this, that would be great

 

[Oystein]

I'm sorry you find me dishonest. (I don't think you are.) I totally agree with your point and no part of my mine depends on the idea that buildings are literally designed to be vulnerable. I'm happy to rephrase it as follows: it would be surprising if buildings were vulnerable in this way.

But it actually isn't.
Controlled demolitions are possible and frequently done only because tall buildings are generally vulnerable to total gravitational collapse. What CD generally does is get a collapse going, then let gravity do the rest of the work (see e.g. Danny Jowenko in the 2006 interview often quote-mined by Truthers, but they never show the parts where Jowenko is totally unsurprised the twins would collapse completely, that in his opinion explosive demolition of the twins was impossible, and that, in the end, he could not explain how Building 7 could have been CDed)

 

[Thomas B]

So I'll take that as a "no"--you are not aware of anyone specifically designing the towers to withstand collapse in a scenario where 6 or more floors worth of its construction fell upon the rest of it.

As I understand it, the Towers were designed to absorb a suddenly applied gust of wind capable of moving the top (and all the mass that this implies) one foot outside of its footprint (and probably more). I don't know how those forces compare. But I'm always happy to see some math to put it in perspective.

 

[Oystein]

I just find this weird. If there was a fire in the burial chamber of the Khufu pyramid and, about an hour into fighting it, the whole pyramid collapsed, it would be pretty clear that the "hydrocarbon fire" didn't do it, right? We'd be looking for bombs.

I agree about the "an hour into fighting it" - but wonder why you even say "fighting it" - no one was fighting any fire in the WTC towers.
Why bombs?
Are you aware that at least one ancient Egyption pyramid DID collapse, during construction or shortly after? Do you suspect bombs?

The reason is that there couldn't possibly be enough hydrocarbon in the pyramid to bring it down.

No. Fuel is not the bottleneck, and also not the key factor deciding vulnerability to collapse.

 

[benthamitemetric]

As I understand it, the Towers were designed to absorb a suddenly applied gust of wind capable of moving the top (and all the mass that this implies) one foot outside of its footprint (and probably more). I don't know how those forces compare. But I'm always happy to see some math to put it in perspective.

If you think the force of a sudden gust of wind is comparable to 6+ floors of the building dropping ~10 ft, then please, by all means, go ahead and do the math or whatever else you think you need to do to support that and show your work here.

 

[Thomas B]

Controlled demolitions are possible and frequently done only because tall buildings are generally vulnerable to total gravitational collapse.

Before 9/11, I'm sure I thought that controlled demolition was a matter of making buildings vulnerable to a total gravitional collapse they had been designed to resist. That is, much of the structure is pre-weakened and then, when everything is ready, the remaining critical columns are blown out with explosives.

That is, buildings are not "generally vulnerable to total gravitional collapse". They are just subject to gravity in general. Until the demolition crews do their very specific work, they're solidly standing.

 

[Thomas B]

If you think the force of a sudden gust of wind is comparable to 6+ floors of the building dropping ~10 ft, then please, by all means, go ahead and do the math or whatever else you think you need to do to support that and show your work here.

This is the impasse. None of us can do the math. (And the people who can, don't participate in these discussions.)

 

[benthamitemetric]

This is the impasse. None of us can do the math.

But some of us can still recognize it is a ridiculous comparison.

 

[Thomas B]

Are you aware that at least one ancient Egyption pyramid DID collapse, during construction or shortly after?

Interesting. Source?

 

[Thomas B]

But some of us can still recognize it is a ridiculous comparison.

There are things I thought were ridiculous until someone showed me the math. Maybe it's different for you.

 

[Henkka]

Actually, no. This is something I remember reading somewhere, but I'm not sure what the actual numbers are on what percentage of the jet fuel exploded instantly, and how long the remainder lasted. If anyone has the hard facts on this, that would be great

Okay, I may have found where this idea came from, at least possibly... The "Why Indeed Did the WTC Buildings Completely Collapse?" article by Steven Jones contains this bit:

It is highly unlikely that jet fuel was present to generate such explosions especially on lower floors, and long after the planes hit the buildings. Dr. Shyam Sunder, Lead Investigator for NIST stated: "The jet fuel probably burned out in less than 10 minutes.” (Field, 2005)

http://www.journalof911studies.com/...rldTradeCenterBuildingsCompletelyCollapse.pdf

However, the source leads to a dead page. But when I googled the quote, I found this article: https://www.firehouse.com/home/news/10525910/a-look-inside-a-radical-new-theory-of-the-wtc-collapse

This seems to be the source of the quote, although it is mistakenly cited as being from 2005 in the text by Jones.

 

[benthamitemetric]

There are things I thought were ridiculous until someone showed me the math. Maybe it's different for you.

In this case, it is.

 

[Oystein]

As I understand it, the Towers were designed to absorb a suddenly applied gust of wind capable of moving the top (and all the mass that this implies) one foot outside of its footprint (and probably more).

You understand incorrectly.
The design wind load is not measured in feet of lateral replacement, and it being "suddenly aplied" does not enter into it.
The design load was merely a sustained wind speed (something in the "hurricane" spectrum), resulting in a particular lateral force on the perimeter as a whole, like a sail.
The specific danger of such a wind load, the way the tower would most likely fail if that load got exceeded, would have been an overloading of the perimeter on the side away from the wind (leeward) pretty low above ground.

I don't know how those forces compare. But I'm always happy to see some math to put it in perspective.

Upthread, @benthamitemetric reproduced an excerpt from "City in the Sky" by James Glantz, which has the story of how come some engineers figured out that the towers would survive a plane hit: the calculated that a 707 at 600 mph would exert a lateral force that is maybe 30% higher than the maximum wind load the towers were indeed designed for - and that exceeding that by only 30% would probably be within the margin of safety. That's the result of the math done with slide rulers in the early 1960s, when it was utterly impossible the calculate the effect of multi-floor fires started by a plane crash and fanned by wind blowing through large gashes in the walls.

The other calculation they did was what would happen when you cut out perimeter columns along the width of the wings of a 707, and they found that there would be enough capacity for load redistribution around such a failure.

(I don't recall what the assumptions were wrt to where that hypothetical 707 would hit a tower, or what its mass would be, with fuel, cargo and passengers; a 707 is roughly the same size - wingspan and live mass - as a 767).

Both predictions proved to be correct.

 

[Oystein]

Before 9/11, I'm sure I thought that controlled demolition was a matter of making buildings vulnerable to a total gravitional collapse they had been designed to resist. That is, much of the structure is pre-weakened and then, when everything is ready, the remaining critical columns are blown out with explosives.

This is generally not true.
If you imagine that buildings undergoing controlled demolition are "pre-weakened" to a point of almost imminent collapse, you are severely mistaken - that would put the lives of the demolition workers haphazardly at risk.

That is, buildings are not "generally vulnerable to total gravitional collapse". They are just subject to gravity in general. Until the demolition crews do their very specific work, they're solidly standing.

It is barely believable and deeply frustrating that after all this time, you still pretend that you don't know the HUGE difference between static and dynamic load.

 

[Thomas B]

You understand incorrectly.

I'm pretty sure that the top of the building could easily sway by about a foot. I'm just saying that the rest of the building was able to manage the motion of all that mass. That may or may not be trivial compared to a one foot fall of the same mass. Again, I'm always open to thoughts from someone who claims to be able to do the math.

 

[benthamitemetric]

I'm pretty sure that the top of the building could easily sway by about a foot. I'm just saying that the rest of the building was able to manage the motion of all that mass. That may or may not be trivial compared to a one foot fall of the same mass. Again, I'm always open to thoughts from someone who claims to be able to do the math.

Why don't you describe how the top floor's ability to sway by about a foot (14 inches, to be precise) in high wind loads would help a lower section of the building arrest the collapse of 6+ floors, something which you already understand that no section of the building was designed to achieve? If you can't explain it, then let's end this pointless thread hijack right here.

 

[Oystein]

Interesting. Source?

https://en.wikipedia.org/wiki/Meidum

 

[Thomas B]

This is generally not true.
If you imagine that buildings undergoing controlled demolition are "pre-weakened" to a point of almost imminent collapse, you are severely mistaken - that would put the lives of the demolition workers haphazardly at risk.

I'm pretty sure that it is delicate work. And a bit dangerous. It takes a lot of expertise to know which columns can be (safely) weakened (by how much) and which ones must be left for the final charges.

The building that comes down is much weaker than the one that was originally built.

It is barely believable and deeply frustrating that after all this time, you still pretend that you don't know the HUGE difference between static and dynamic load.

I certainly don't see how it's relevant here. If you're up to it, you can enlighten me.

 

[Mendel]

NIST said no.

Article:

Source: https://www.nist.gov/publications/reconstruction-fires-world-trade-center-towers-federal-building-and-fire-safety-0

See NIST NCSTAR 1-5, section 6.15.

 

[Oystein]

I'm pretty sure that the top of the building could easily sway by about a foot. I'm just saying that the rest of the building was able to manage the motion of all that mass. That may or may not be trivial compared to a one foot fall of the same mass. Again, I'm always open to thoughts from someone who claims to be able to do the math.

Oh it surely DID swing more than that - and that has practically nothing to do with how the structure would handle a 1-foot fall. I cannot fathom the brain processes that even attempt to compare the two.