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

[benthamitemetric]

How is my example of a brick wrong, though? A brick weighs about 2kg, and the same brick chopped up into pieces will weigh the same. Yet it's obvious which one you would rather have dropped on your head.

I think Bazant understood this problem, which is why he insisted the upper block stayed intact during the "crush-down" phase, and then got crushed itself during the "crush-up" phase... Like a car crash where one car becomes deformed first, and then the other one, haha.

Your example is wrong because it goes to an extreme: it assumes the falling floors were reduced very small pieces, which we know isn't the case based on both common sense and, more importantly, the debris field. But, even if the floors were powderized, it's not a foregone conclusion that the collapse would not ensue, it just gets much more complicated to calculate the forces at each stage. After all, if you drop 300 lbs of sand on yourself from 20 ft, it could kill you just as a 300 lbs piano could, and we all know the devastation that water can do in a tsunami or flood. The truth of the tower floor collapses is somewhere in between: fully rigid floors were broken to an extent, but its hard to imagine the mass of those concrete slabs and steel trusses acting more like sand than like rigid structures when compacted together with other failed floors in the debris wave. Remember we know the floors were sheered from the perimeter at the truss connections because that was observed and documented in the debris (see, e.g., NIST NCSTAR 1-3C).

 

[Mendel]

I don't know if a "runaway" collapse makes sense to me in general, if by that you mean a collapse that would have continued all the way to the ground no matter how many floors were below. I think it would decelerate and stop eventually... But that made think of another interesting hypothetical:

WTC 1 had 12 floors in the "upper block", and was overall 110 floors. Those 12 floors falling on the rest caused a runaway collapse that destroyed the entire building. But what would have happened if the upper block was the same 12 floors, but the tower itself was much taller? Let's say it was twice as tall, at 220 floors. If you dropped 12 floors on 208 floors, would that have destroyed this "Super WTC" tower in its entirety? Or would the collapse have decelerated and stopped eventually? In other words, we know that the upper block of 12 floors could destroy 98 floors below, but is there an upper limit? Or are you saying the 12 floors could theoretically destroy an infinite number of floors, since it was a "runaway" collapse?

How many dominoes can you chain up? Is there a limit?

 

[Mendel]

Loose debris is not going to deliver the same kind of impact as an intact block... It's like, would you rather have an intact brick dropped on your head, or an identical brick that has been ground up into tiny pieces first?

Not enough weight, try a ton of bricks vs. a ton of gravel. Remember, we know the weight alone was enough to break the floor, the impact is all bonus.

 

[benthamitemetric]

Remember, we know the weight alone was enough to break the floor, the impact is all bonus.

Very good point that I did not emphasize in my responses. But this is a big part of why NIST's calculations were so conservative.

 

[econ41]

Well as I said, I don't know if a "runaway" collapse makes much sense to me, but I know that in verinage demolitions they usually start the collapse in the middle. So if you dropped the top 55 floors on the bottom 55 floors, they would maybe destroy each other simultaneously. But in verinage demolitions, the initial drop is deliberately engineered to give the top block significant momentum, and then it comes crashing down. If all you had was fires slowly weakening the steel on floors 54-56, I don't know why the top block would come crashing straight down, rather than maybe tipping over or such.

Utter nonsense. The mechanism has been explained for both you and @Thomas B in multiple posts which you ignore.

1) The mechanism of the "initiation stage" ensured that the top block columns as they started to descend missed their lower parts. << That has been explained. The columns did not drop to impact as per the false hypothetical you posted with the giant crane.

2) The Top Block did NOT "topple" because the rate of falling was faster than the rotation of toppling << That step has not been explained in these recent discussions but is bleeding obvious from any number of video clips.

3) The start of floor overloading leading to ROOSD runaway progression was triggered by the impact both downwards and (relatively) upwards of the Top Block perimeters impacting on floors inside the line of the perimeter as per this example which I have posted several times.


4) A period of "mutual destruction" ensued when the "Top Block" and the upper levels of the lower tower were concurrently dismantled. (Yes Bazant and Verdure's "Crush Down/Crush up" is wrong.) I don't have a "pretty picture" of that process.

5) "ROOSD" progression followed. This is the section originally identified as "ROOSD" (Actually the diagram was posted Nov 2007 - the appellation "ROOSD" was introduced into mainstream online debate in early 2009.)


The failure of the core is analogous - as evidenced by the "spires".

So feel free to continue ignoring my explanations.

Better still agree with them and stop pretending ignorance.

OR prove me wrong. And best of luck if you take that path.

 

[econ41]

How is my example of a brick wrong, though? A brick weighs about 2kg, and the same brick chopped up into pieces will weigh the same. Yet it's obvious which one you would rather have dropped on your head.

It could be a good analogy if you targeted it correctly on the actual collapse mechanism. Hence the advice offered many times to understand the actual collapse mechanism:

(a) The solid brick impact is analogous to the stage of "transition" where the still intact (AKA == "solid brick") Top Block impacted the upper floors of the lower tower and the "still solid" aspect ensured the linear concentrated impact load which started ROOSD. The "solid brick" of the still intact "Top Block" guaranteed that necessary form of impact. AS PER THIS DIAGRAM:



THEN
(b) The "chopped into pieces" situation is analogous to the later stage of established progression. Where the original
"Solid Brick" has been broken up PLUS augmented by a lot more accumulated broke parts debris. AS PER THIS DIAGRAM:



You will find it easier to construct analogies if you understand the actual mechanism. AND it will make it easier to assess if the analogy is relevant and accurate.

I think Bazant understood this problem, which is why he insisted the upper block stayed intact during the "crush-down" phase, and then got crushed itself during the "crush-up" phase...

Possibly, but if you read the history of the issue, Bazant was engaged in a multi-year target of developing a generic model of explanation for high-rise progressive collapses. His approach was based on energy considerations plus a foundation of 1D approximation. His energy calculations are included in the B&V paper. And his claimed basis for CD followed by CU is on the energy advantage that downwards destructive movement has over upwards destruction. That is the published reason for him preferring of CD/CU. I won't present fuller explanation because it goes too far off-topic. But there are several fatal issues. Including that it is based on all columns being crush buckled - as per your "Giant Crane" example. AND the false assumptions that column buckling was the main feature of WTC Twin Towers progression. It wasn't. "1D Approximation" is diametrically opposite to ROOSD failure of Tube-in-Tube designs. Don't assume that Bazant or NIST are always correct.

Like a car crash where one car becomes deformed first, and then the other one, haha.

Agreed. Ridicule is appropriate.

 

[Thomas B]

Thanks for the link, but doesn't answer much of the question at hand. The paper doesn't say whether this pre-weakening is
- done always, often, sometimes or rarely
- necessary (always, often, sometimes, rarely, or not at all) to facilitate a total collapse (or merely to save resources, or to control collapse sequence and where debris falls)
- done to facilitate collapse initiation, or collapse progression (we are here interested in that only), or both

My guess is that it's quite normal. All things considered, it's safer to use less explosives. It makes sense that you'd try to weaken the buildings mechanically as much as possible.

Basically, as I understand it, demolition involves much more than just causing some portion of a building to fall freely onto the rest. (CD is not just an intentional ROOSD.) In CD a great deal of thought and work goes in to destroying a structure that was originally designed to stand very firm.

I haven't looked at it in very much detail. But how much of our argument hinges on it? I mean, if it turned out that buildings are normally significantly weakened before collapse is initiated, and that, in many cases, they wouldn't collapse if this wasn't done, would that change your view of the issues I raise?

Maybe these issues would make a good thread? Maybe truthers exaggerate the practical difference between controlled demolition and fire-induced runaway progressive collapse?

 

[Mendel]

Maybe truthers exaggerate the practical difference between controlled demolition and fire-induced runaway progressive collapse?

Article:

A simple structure like a chimney can be prepared for a controlled demolition in less than a week but larger, more complex or multiple structures can take up to six months of preparation to remove internal walls, drilling holes for placing of explosives, wrapping columns with fabric and fencing before firing the explosives.

Source: https://www.hughesandsalvidge.co.uk/news/controlled-demolitions-work-use/

 

[econ41]

Maybe these issues would make a good thread?

It would be great if everyone tried to stay with the discipline of one topic per thread. Recognising that what may initially look like one complete topic could actually be a part of a broader issue that should not be broken into parts which are then discussed in isolation.

Maybe truthers exaggerate the practical difference between controlled demolition and fire-induced runaway progressive collapse?

Truthers are not the only sinners.

Many from both sides persist in discussing details that are not related to any understanding of the real collapse mechanisms. It is a hobby horse of mine as you may have noticed. But the fundamental issue is that the collapses we saw were the collapses that happened. Whether or not they were triggered by a bit of CD "help". No argument - a truther claim for CD or debunker opposing CD - is valid if the argument does not align with the collapse mechanism which actually happened.

So read most of these threads and there should be no wonder if they make me cry.

Then on your comment of " Maybe truthers exaggerate the practical difference between controlled demolition and......."

The most common issue with truther claims is that they assume CD can perform magic. It cannot. It is rigorously governed by the same laws of physics as any "No CD needed" counterclaim. Any valid claim for CD must be backed by (or at least be capable of being backed by) reasoned argument. The same standard should apply to debunker assertions in rebuttal.

And far too many debunker "rebuttals" are not backed by argument - they are arguments from third-party "authority". "NIST said!" or "Bazant said" or "Arup said" et simile. IF you are going to quote some authority be prepared to back your support of that authority. You are the one posting claims here. Not NIST, Bazant, Arup et al.

Which is a large part of the reason I never rely on NIST. But an equally important issue is that understanding of the WTC collapses has advanced a long way since NIST reported. NIST may be wrong - tho I've never found a serious significant error in NIST's claims. BUT they are dated and mostly do not address the current state of understanding. Why persist in going back to 2005 2007 documents?

But even worse they are redundant. A recent post claims something like: "we know the falling material was enough to shear the joist connections because NIST said so!" The statement is NOT true because NIST said so, It is true because it is correct and bleedingly obvious even to a layman that it is correct. The fact that NIST "got it right" does not change reality.

So, back on my hobby horse, The WTC collapses happened. The collapse mechnaisms we saw whoud be understod by and agreed as understood by "both sides". The debate about "CD o no cD" can start at thatpoint. No truther claim can possibly be true if it does not fit with - match - the actual collapse mechanism. BUT no debunker attempted rebuttal is valid unless it also matches reality. And debunkers claim to be the "good guys" so they have zero excuse for not giving correct explanations....

[/End Rant]

 

[econ41]

Article:

A simple structure like a chimney can be prepared for a controlled demolition in less than a week but larger, more complex or multiple structures can take up to six months of preparation to remove internal walls, drilling holes for placing of explosives, wrapping columns with fabric and fencing before firing the explosives.

Source: https://www.hughesandsalvidge.co.uk/news/controlled-demolitions-work-use/

Remember also that truther goals for "demolition" did not need "controlled demolition". I've seen debunker rebuttals based on the fact that a lot of debris flew great distances so it wasn't "controlled". That argument contains its own strawman. "demolition" on 9/11 for whatever purposes did not need to be "controlled" as in minimising collateral damage.

 

[Henkka]

Your example is wrong because it goes to an extreme: it assumes the falling floors were reduced very small pieces, which we know isn't the case based on both common sense and, more importantly, the debris field. But, even if the floors were powderized, it's not a foregone conclusion that the collapse would not ensue, it just gets much more complicated to calculate the forces at each stage. After all, if you drop 300 lbs of sand on yourself from 20 ft, it could kill you just as a 300 lbs piano could, and we all know the devastation that water can do in a tsunami or flood. The truth of the tower floor collapses is somewhere in between: fully rigid floors were broken to an extent, but its hard to imagine the mass of those concrete slabs and steel trusses acting more like sand than like rigid structures when compacted together with other failed floors in the debris wave. Remember we know the floors were sheered from the perimeter at the truss connections because that was observed and documented in the debris (see, e.g., NIST NCSTAR 1-3C).

Well, however small the pieces were, they would have less destructive potential than an intact block. Like if you cut the brick into 4 pieces weighing 0.5kg each, that's still going to hurt less than the intact 2kg brick. Also, the concrete floors literally were powderized, along with much of the office contents and people trapped in the towers. As for 300 lbs of sand or a piano, the difference is I couldn't hold up a 300 lbs piano even if it were stationary, let alone dropped from 20 feet up. The WTC towers were obviously designed to hold up the weight of the upper floors, and then some. This is kind of macabre, but it's kind of like how my body is "designed" (by evolution) to hold up the weight of my head. So if my head were to be detached and dropped, it's hard to imagine it crushing my body... It would roll off.

How many dominoes can you chain up? Is there a limit?

I don't really agree it's comparable to a row of dominoes... But I commend you guys on biting the bullet on the "infinite number of floors" thing, I wasn't sure if you would. So not only did 12 floors destroy 98 floors below, they could have just as well destroyed 980, or 9800. Imo, that's a pretty absurd conclusion.

 

[Mendel]

Remember also that truther goals for "demolition" did not need "controlled demolition". I've seen debunker rebuttals based on the fact that a lot of debris flew great distances so it wasn't "controlled". That argument contains its own strawman. "demolition" on 9/11 for whatever purposes did not need to be "controlled" as in minimising collateral damage.

Yes but then why the constant comparisons to CD ("verinage")? How to topple the top block at the (essentially random) aircraft strike level? how to effect collapse from it that "would surely arrest by itself", unless you can control demolition all the way down, without sight of the building, leaving the outer walls intact, and the core columns standing for about half their length?

Like muttering "aliens" at anything that's hard to understand in a UAP sighting, muttering "controlled demolition" at the WTC collapses shuts down the path to understanding—that's its job.

 

[Mendel]

Like if you cut the brick into 4 pieces weighing 0.5kg each, that's still going to hurt less than the intact 2kg brick.

Why does a jackhammer work the way it does?

The WTC towers were obviously designed to hold up the weight of the upper floors, and then some

The columns carried the weight of the upper floors, the floors did not. This is offtopic here, please see my bookshelf question in the other thread.
https://www.metabunk.org/threads/ho...ill-caused-a-total-collapse.12423/post-274554

I don't really agree it's comparable to a row of dominoes...

Why is it not comparable?

It takes the same force to topple the 10th domino as it takes the 100th. It takes the same force to destroy the 10th floor as it takes the 70th. Because the floors are not designed to bear any gravity loads except their own.

(See the Hyatt Regency walkway collapse for an example of a structure failing at carrying more than its own weight, which it wasn't designed to do.)

 

[econ41]

But I commend you guys on biting the bullet on the "infinite number of floors" thing, I wasn't sure if you would.

Whilst "infinite" is hyperbole that diverts from the reality that the actual logic of the process is very simple. The actual 9/11 WTC Twin Towers progression would either arrest or continue.
(a) IF the energy was not sufficient for the actual mechanism progression would arrest.
(b) if there was more than sufficient energy for the actual mechanism progression it would continue - plausibly ad infinitum but demonstrably as "80or90floorsium". << And THAT is what happend no matter how hard you try to not understand. And excuse my "pig latin".

So not only did 12 floors destroy 98 floors below, they could have just as well destroyed 980, or 9800. Imo, that's a pretty absurd conclusion.

It is only absurd to you because you refuse to understand the simple mechanism. And the mechanism of Twin Towers progression - often called "ROOSD" - is the simplest explanation of any of the stages of WTC collapses. Twin Towers "initiation" is a couple of grades more complex. As is the WTC7 collapse..tho for different reasons. But once again I suggest that you make your mind up to learn. Because progression for Twin Towers is easy and it has been explained in outline for you numerous times.

 

[Henkka]

It is only absurd to you because you refuse to understand the simple mechanism. And the mechanism of Twin Towers progression - often called "ROOSD" - is the simplest explanation of any of the stages of WTC collapses. Twin Towers "initiation" is a couple of grades more complex. As is the WTC7 collapse..tho for different reasons. But once again I suggest that you make your mind up to learn. Because progression for Twin Towers is easy and it has been explained in outline
for you numerous times.

Well, I'm going to compare it to verinage demolitions again... In those, the collapse is started near the middle, so the top 50% is used to destroy the lower 50%. But if you're seriously saying the collapse mechanism in the WTC towers was such that 12 floors could destroy 9800 floors below, that would be 0.12% of the building used to destroy 99.88% below. Why aren't verinage demolitions done by just dropping the top floor, then? Can you induce ROOSD in other buildings besides WTC?

 

[econ41]

Well, I'm going to compare it to verinage demolitions again...

Why?

In those, the collapse is started near the middle, so the top 50% is used to destroy the lower 50%.

Yes. And the physics of the resulting collapse is understandable. So what? Why do you persist in false analogies when the actual physics of the 9/11 WTC Twin Towers collapses is so easy to understand?

Here is the first "pretty picture"*** I'm aware of being posted online - Nov 2007 - to explain the outer end of the simple mechanism. What about it do you not understand?

The falling mass of debris gets bigger as every successive floor is added.
And the floors were the same strength all the way to the ground EXCEPT the mechanical ones which were a bit stronger but still not strong enough to resist the falling debris.
So what rational argument can you propose for the collapse arresting?

*** And I"ll admit the picture is not "pretty".

But if you're seriously saying the collapse mechanism in the WTC towers was such that 12 floors could destroy 9800 floors below, that would be 0.12% of the building used to destroy 99.88% below.

Hogwash. It was "much more than six floors of debris" destroying one floor at a time. Please stop pretending you don't understand.

Why aren't verinage demolitions done by just dropping the top floor, then? Can you induce ROOSD in other buildings besides WTC?

Probably could if you want to destroy a "tube-in-tube" designed building. Again "So bleeding what!!!???" Why persist with irrelevancies?

 

[Mendel]

Well, I'm going to compare it to verinage demolitions again...

but why? those buildings weren't even steel framed

In those, the collapse is started near the middle, so the top 50% is used to destroy the lower 50%. But if you're seriously saying the collapse mechanism in the WTC towers was such that 12 floors could destroy 9800 floors below, that would be 0.12% of the building used to destroy 99.88% below.

you deliberately maintain your incredulity by refusing to acknowledge the main structural features of the WTC. You want to make statements about it without actually furthering your understanding. Is this your actual aim?

the collapse mechanism in the WTC towers was such that 12 floors could destroy 9800 floors below

5 mm domino topples 1m domino, ratio 1:200 (1:8,000,000 by volume)
do you disbelieve this as well?

Source: https://m.youtube.com/watch?v=y97rBdSYbkg

Why aren't verinage demolitions done by just dropping the top floor, then? Can you induce ROOSD in other buildings besides WTC?

Which type of building feature does the "OOS" in ROOSD explicity designate?

What are the disadvantages of a top-down collapse in a controlled demolition?

 

[Henkka]

Why is it not comparable?

It takes the same force to topple the 10th domino as it takes the 100th. It takes the same force to destroy the 10th floor as it takes the 70th. Because the floors are not designed to bear any gravity loads except their own.

Well, I've already shown you videos of building collapses that arrest halfway... Like failed demolitions. So we know that building collapses are not like dominoes being knocked over in all instances. You would need to present some reasoning for why the WTC towers, some of the strongest buildings ever made, behaved like a row of dominoes and other buildings didn't.

Probably could if you want to destroy a "tube-in-tube" designed building. Again "So bleeding what!!!???" Why persist with irrelevancies?

Are WTC 1 and WTC 2 the only examples of ROOSD in all of history? Can you build a scale model that demonstrates ROOSD?

 

[Mendel]

Well, I've already shown you videos of building collapses that arrest halfway... Like failed demolitions. So we know that building collapses are not like dominoes being knocked over in all instances. You would need to present some reasoning for why the WTC towers, some of the strongest buildings ever made, behaved like a row of dominoes and other buildings didn't.

I did. Repeatedly. Referencing NIST FAQ #18.

That's why I wrote that "you deliberately maintain your incredulity by refusing to acknowledge the main structural features of the WTC."

Are WTC 1 and WTC 2 the only examples of ROOSD in all of history? Can you build a scale model that demonstrates ROOSD?

They're the only examples of skyscrapers brought down by airliners, too.

Stack a dozen empty pizza boxes (tape them together at the "walls"). Load the corners of the stack with bricks until they start to buckle. Alternately, place a wooden board (hat truss) across the top and load that.

Duplicate the stack, drop the same weight in the center this time.

(probably works best if you soften the lids and bottoms of the boxes with water first, for both experiments)

 

[econ41]

Well, I've already shown you videos of building collapses that arrest halfway...

Yes. And we have videos of buildings that did NOT arrest halfway. The WTC Towers on 9/11 did not arrest.

Again I ask so bleeding what? What are you trying to say? The WTC Towers fell exactly like the WTC Towers. "Other buildings" - believe it or not - fall like "other buildings".

Like failed demolitions. So we know that building collapses are not like dominoes being knocked over in all instances.

Wow. Such inspiring brilliance.

Here! Let me explain some of the relative aspects. "Domino toppling" is a base level cascading failure. The simplest form of cascading failure. Each step is binary - yes the next one topples or no the next one doesn't topple. A more complex level of cascading failure is an electricity grid failure. Where "load redistribution" triggers the failure of sub-nets in a sequence. The overload of each sub-net is analogue BUT the decision to trip is binary - over the threshold and it fails. Now the WTC Twin Towers failures offer two examples (two for each tower that is) of cascading failures. The "initiation stage" of each collapse was a complex failure of columns in axial load carrying capacity. Successive columns failed in sequence. Similar to toppling dominoes. BUT every single column failure was an analogue complexity of strength, heat weakening and progressively applied loads which were redistributed from other failing columns. Personally, i can process the "domino" analogy but I doubt that it helps persons who may not be able to visualise multi-layered analog failures. In contrast the ROOSD progression was essentially simple binary. But I again doubt that the analogy is helpful to those people who cannot process the simplicity of the actual model without the "help" of the analogy.

You would need to present some reasoning for why the WTC towers, some of the strongest buildings ever made,

Hogwash. Why the strawman lie about "some of the strongest". They were buildings of adequate stregth which pushed the linits of structural design for their era.

behaved like a row of dominoes and other buildings didn't.

If you don't appreciate analogies just ignore them. But don't make a fool of yourself by trying to use them "in reverse".;

Are WTC 1 and WTC 2 the only examples of ROOSD in all of history?

Obviously. Despite the circular logic. "ROOSD" is the term used to describe how the WTC Twin Towers collapsed. So - again setting aside your apparent incredulity - the WTC Towers fell exactly like the WTC Towers fell. Hardly a serious adult observation.

Can you build a scale model that demonstrates ROOSD?

Yes. Several have been built. Why do you need one? Don't you understand the easiest part of WTC collapses?

 

[Henkka]

I did. Repeatedly. Referencing NIST FAQ #18.

And I've shown you multiple instances where NIST admits they did not do any calculations on why the collapse was not arrested after initiation, like John Gross saying it was "clear from the videos", so they didn't bother. NIST also responded to a request for correction with the following:

“NIST carried its analysis to the point where the buildings reached global instability. At this point, because of the magnitude of deflections and the number of failures occurring, the computer models are not able to converge on a solution…. [W]e are unable to provide a full explanation of the total collapse.” — p. 3-4, NIST Response to Request for Correction

https://www.ae911truth.org/evidence/near-free-fall-acceleration

So NIST FAQ #18 seems to be talking about the initiation of the collapse, although it does include this language:

Since the number of floors above the level where the collapse initiated exceeded six for both towers (12 for WTC 1 and 29 for WTC 2), neither tower could have arrested the progression of collapse once collapse initiated.

But that seems to contradict John Gross saying they did not calculate this. Here is that video again just in case (I don't want to clog up the thread with a video I've posted before, remove the space if you want to watch it): https://www.youtube.com/watch?v= ZAuA19IPCso

Obviously. Despite the circular logic. "ROOSD" is the term used to describe how the WTC Twin Towers collapsed. So - again setting aside your apparent incredulity - the WTC Towers fell exactly like the WTC Towers fell.

This is called "begging the question". You can't just assume the truth of the thing you're trying to show to be true. When we're talking about the WTC collapses in the context of conspiracies, the dispute is over whether the buildings collapsed the way they did simply because the top block fell on the bottom, or because there were some sort of demolition charges going off in the building. Now, truthers can point to thousands of examples of buildings collapsing very rapidly due to demolition charges. But you can seemingly only point to two examples of "ROOSD" ever taking place, and those two are the collapses that are under dispute! It's totally circular.

 

[Mendel]

But I again doubt that the analogy is helpful to those people who cannot process the simplicity of the actual model without the "help" of the analogy.

I wanted to reset the intuition that a very long cascade from a small initial impulse is possible.

Source: https://m.youtube.com/watch?v=4_qDAhVa7yc

There's no reason to be incredulous about it.

 

[benthamitemetric]

Well, however small the pieces were, they would have less destructive potential than an intact block. Like if you cut the brick into 4 pieces weighing 0.5kg each, that's still going to hurt less than the intact 2kg brick. Also, the concrete floors literally were powderized, along with much of the office contents and people trapped in the towers. As for 300 lbs of sand or a piano, the difference is I couldn't hold up a 300 lbs piano even if it were stationary, let alone dropped from 20 feet up. The WTC towers were obviously designed to hold up the weight of the upper floors, and then some. This is kind of macabre, but it's kind of like how my body is "designed" (by evolution) to hold up the weight of my head. So if my head were to be detached and dropped, it's hard to imagine it crushing my body... It would roll off.

I don't really agree it's comparable to a row of dominoes... But I commend you guys on biting the bullet on the "infinite number of floors" thing, I wasn't sure if you would. So not only did 12 floors destroy 98 floors below, they could have just as well destroyed 980, or 9800. Imo, that's a pretty absurd conclusion.

This is just more incredulity without any actual reasoning as to why these particular floors, as built with known parameters, would not continue to overload all the way down. As Mendel pointed out, even if the concrete and all of the steel elements of each floor were reduced to powder (and we know they were not), collapse would still ensue per NIST's very conservative calculation, which only factors in the weight of the debris and not the force it imparted upon impact from the momentum generated by its fall. It's "absurd" to believe that the the floors would magically support greater loads than their elements, as designed and built, could bear. When you express surprise that 12 of something could destroy 9800 of something, you are missing that it is not 12 destroying 9800 at once; it is 12 destroying 1, then 13 destroying 1, then 14 destroying 1, then 15 destroying 1, etc.

 

[econ41]

I wanted to reset the intuition that a very long cascade from a small initial impulse is possible.

Understood. And the concept is very simple. A child can understand it. Without demanding unnecessary "sums".

There's no reason to be incredulous about it.

None whatsoever if understanding is the goal. Trolling has different expectations.

 

[Mendel]

So NIST FAQ #18 seems to be talking about the initiation of the collapse, although it does include this language:
But that seems to contradict John Gross saying they did not calculate this.

There is no contradiction.
a) the FAQ was written later
b) the FAQ #18 does not "calculate"/simulate the actual collapse, it makes a simplified argument why progressive collapse ensued and could not be arrested.

There is no reason for you to ignore it, except that its truth is inconvenient to you.

 

[Mendel]

Now, truthers can point to thousands of examples of buildings collapsing very rapidly due to demolition charges.

But only 2 tall buildings destroyed by aircraft.

There is a reason for that. Think!

 

[Henkka]

I wanted to reset the intuition that a very long cascade from a small initial impulse is possible

There's no reason to be incredulous about it.

Yes, I understand that... The question is whether something like this can happen top-down to skyscrapers. You can cite two examples of it happening in all of history, but those are the two collapses under dispute. The dispute being that some people claim there were demolition charges going off in the building. To convince these people that there didn't have to be demolition charges in the building, you would need to show another tall building experiencing a total, top-down, accelerating collapse. This is where verinage demolitions are such a useful reference point, since everyone can agree there are no demolition charges being used in those, and they are top-down. But unfortunately, they decelerate, and there are no examples of verinage demolitions where the top 10% of a tall building is used to destroy the lower 90%. So you're left with claiming this can happen, with your examples being either the disputed collapses themselves (circular reasoning), or entirely different physical phenomena like dominoes.

 

[econ41]

This is called "begging the question". You can't just assume the truth of the thing you're trying to show to be true.

Stop your childish attempts at patronising. YOU introduced the ridiculous "argument" I simply pointed it out.

When we're talking about the WTC collapses in the context of conspiracies, the dispute is over whether the buildings collapsed the way they did simply because the top block fell on the bottom, or because there were some sort of demolition charges going off in the building.

And that must be a deliberate lie. You CANNOT be unaware of what really happened so your "false dichotomy" is inexcusable. They did not SIMPLY "top block fell on the bottom" AND how they did fall is well understood. AND - the key point - you have been informed of how they fell and you are pretending ignorance. YOU have essentially conceded that you are wrong and that you cannot support your position.

Now, truthers can point to thousands of examples of buildings collapsing very rapidly due to demolition charges.

Again the divert to irrelevancy. We are not discussing the thousands of collapses resulting from explosive demolition. We are discussing the WTC Towers which did not collapse from explosive demolition.

But you can seemingly only point to two examples of "ROOSD" ever taking place,

Because ROOSD is a term that means "The progressive collapse stage of the WTC Twin Towers collapses" And there have only been two WTC Twin Towers collapses. If there is ever a "tube-in-tube" designed tower that collapses by the analogous mechanism we will be able to agree that it was a ROOSD-like mechanism.

and those two are the collapses that are under dispute! It's totally circular.

The response is NOT circular - your argument is. Stop projecting your own failings onto those of us who are still trying to help you overcome your apparent lack of understanding of some simple physics.

 

[Henkka]

We are not discussing the thousands of collapses resulting from explosive demolition. We are discussing the WTC Towers which did not collapse from explosive demolition.

Again, you can't just assert that when that's the whole dispute... Like a prosecutor telling the judge the defendant is guilty because he's a murderer.

Because ROOSD is a term that means "The progressive collapse stage of the WTC Twin Towers collapses" And there have only been two WTC Twin Towers collapses. If there is ever a "tube-in-tube" designed tower that collapses by the analogous mechanism we will be able to agree that it was a ROOSD-like mechanism.

So do you think traditional skyscrapers with evenly spaced columns can't undergo ROOSD? Only "tube-in-tube" structures?

 

[Mendel]

The dispute being that some people claim there were demolition charges going off in the building. To convince these people that there didn't have to be demolition charges in the building, you would need to show another tall building experiencing a total top-down, accelerating collapse.

I'm not trying to convince other people, I'm trying to convince you.
If you say you hate maths and suck at physics, you'll never know; but at least then you know why there is a limit to your understanding.

Nobody demolishes buildings top-down, because it is much more dangerous than the alternative; your demand won't be met, and even if it could, we wouldn't be able to "prove" the absence of explosives. You've retreated to an unfalsifiable position that is not supported by any evidence, and dismiss all other evidence. Have fun in your rabbit hole.

 

[Mendel]

So do you think traditional skyscrapers with evenly spaced columns can't undergo ROOSD? Only "tube-in-tube" structures?

OOS means open office space, so obviously, a traditional skyscraper (e.g. the Empire State Building) lacking a column-less open office space can not undergo ROOSD.

There are probably other structures that could undergo similar failures.

 

[Mendel]

This is where verinage demolitions are such a useful reference point, since everyone can agree there are no demolition charges being used in those, and they are top-down.

a) they are not bombings
b) didn't you say the charge is placed only halfway up?

 

[Henkka]

Nobody demolishes buildings top-down, because it is much more dangerous than the alternative; your demand won't be met, and even if it could, we wouldn't be able to "prove" the absence of explosives. You've retreated to an unfalsifiable position that is not supported by any evidence. Have fun there.

I don't want someone to demolish a building top-down... I want someone to drop the upper floors on the lower floors, have it not decelerate, and collapse the structure all the way to the ground. The first step of that is done in verinage demolitions, but they decelerate. People will always say the building is too different to the WTC to draw a comparison, but if you insist someone should build an near-exact replica of the WTC and fly a plane into it for the comparison to be valid, it's you who has an unfalsifiable position.

OOS means open office space, so obviously, a traditional skyscraper (e.g. the Empire State Building) lacking a column-less open office space can not undergo ROOSD.

There are probably other structures that could undergo similar failures.

Wasn't the core of the building basically a traditional skyscraper? So the Empire State Building as it is today can not undergo ROOSD, but if you put it inside a massive steel perimeter tube, it could?

 

[Mendel]

Wasn't the core of the building basically a traditional skyscraper?

No. It required bracing from the surrounding structure to be stable.

The core was not involved in the ROOSD, as the spire proves. (I wonder why you don't recall me telling you about this.)

 

[Mendel]

I don't want someone to demolish a building top-down... I want someone to drop the upper floors on the lower floors, have it not decelerate, and collapse the structure all the way to the ground.

you just described demolishing a building top-down

 

[benthamitemetric]

I want someone to drop the upper floors on the lower floors, have it not decelerate, and collapse the structure all the way to the ground.

So just focus for a minute.

• The weight of 6 floors of the building dynamically applied will destroy any floor in the building (and, again, this is based off of NIST's very conservative calculation that ignores the momentum those floors gain from accelerating over the course of any initial fall).
• A section of the building weighing far more than 6 floors does, in fact, fall into and easily destroy the first floor below it.
• The mass of that section of the building + the mass of the first floor it destroyed then falls to impact the next floor down.

Why do you think the next floor down can arrest the collapse?

 

[Henkka]

you just described demolishing a building top-down

Oh, I thought you meant like with explosives. If you think verinage demolitions count as top-down demolitions, why did you say "Nobody demolishes buildings top-down"?

No. It required bracing from the surrounding structure to be stable.

The core was not involved in the ROOSD, as the spire proves. (I wonder why you don't recall me telling you about this.)

I guess I understand how ROOSD could strip the floors off of the core, but I'm unclear on why the core itself would collapse so rapidly. Was there a spire left after the South Tower collapsed? Don't think I've seen such a video or picture of it.

• A section of the building weighing far more than 6 floors does, in fact, fall into and easily destroy the first floor below it.

Destruction requires energy. Where does the energy come from that destroys this floor?

 

[Thomas B]

Why do you think the next floor down can arrest the collapse?

I think this is a great and challenging question. My best theory is that the collapses could have been slowed and eventually arrested because much of the load would not just impact the floor connections but the columns, especially in the core.

Now, it turns out that the columns were also overloaded by this process (especially after having lost lateral support from local floors detaching). And some of the perimeter of course just peeled off.

According to the truthers, the cores and perimeter walls wouldn't have behaved that way if they hadn't been either preweakened by thermite or blown out by timed charges or both. They would have stayed in tact and resisted the falling section as a unit.

That is, the alternative view is that, even if the collapse had initiated spontaneously (although the truthers of course think the initiation was also "controlled"), then the top section would just have been sort of "impaled" on the structure below with maybe six floors of the top section tangled up into six floors of the bottom section until the downward motion was arrested in a mess of metal and glass and concrete.

This is easy to imagine with small-scale physical models of wire-mesh cages and gypsum. And that's roughly what truthers think should have happened.

The only way I can get ROOSD to make sense is if the structural elements were much more loosely connected, especially laterally, so that each column and floor connection basically had to fend for itself and couldn't transfer any loads to its neigbors. Sort of like @Mendel's dominoes, I guess.

 

[benthamitemetric]

Destruction requires energy. Where does the energy come from that destroys this floor?

Gravity accelerates the mass downwards, converting the potential energy of the mass into kinetic energy. If you do not understand basic kinematics, then your time would be much better spent taking a quick physics course over at Khan Academy and coming back here in a week to see if you can answer the question then. Without an understanding of basic kinematics, you cannot understand any part of this conversation at even a rudimentary level, which may be why these arguments don't make sense to you. The kinematic equations are something that most people learn in a high school physics class, but not everyone takes such a class (and that's ok). You can still learn them in a relatively quickly with some effort and a guided study plan, like the one provided by Khan Academy (which is free).

My best theory is that the collapses could have been slowed and eventually arrested because much of the load would not just impact the floor connections but the columns, especially in the core.

How could the columns catch the bulk of the falling mass? Please describe in detail how you think the force of the falling debris would be transferred to the columns in way that is not accounted for in NIST's very conservative calculation of the strength of the floors (which strength was based on the floors' connection to the columns).

 

[Henkka]

Gravity accelerates the mass downwards, converting the potential energy of the mass into kinetic energy.

Exactly, and now take it one step further. It's the kinetic energy that is used to destroy the floor below. Energy is neither created or destroyed, so the energy to destroy the floor is subtracted from that kinetic energy, and the equation for kinetic energy is 1/2 mv^2. If the mass isn't decreasing, what has to decrease for the kinetic energy to destroy the floor below?