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

[Oystein]

Well, I just mean replicating the minimum required lethal damage you believe the buildings suffered, but with targeted explosives. If a plane impact and fires can destroy the South Tower in a mere 56 minutes, it should be trivial to replicate the damage with demolition charges. That's because in a fire, a lot of the energy is wasted on heating up things that weren't necessary for the building to collapse. With explosives, you can focus all the energy to do the bare minimum required to trigger the collapse. You can't say that it would take tons and tons of large explosives, if you believe the same thing was accomplished by a fire.

At peril of falling victim to another distraction:

One theory holds that fires made the floor trusses sag, so they pulled walls inward by catenary action, and collapse ensued.

One way to make the floor trusses sag would be to cut their bottom chords, which are steel rods no more than 1 inch thick, if memory serves. The top trusses would sag and pull in, having lost the trusses' internal stability. Do this on all trusses on one side of the tower over 3 floors or so, and I think you might initiate a collapse in a similar fashion as the fires did. I'd guess, wildly, that half a pound of explosives per chord would be plenty. We are talking about perhaps 150 trusses? So 75 pounds of explosives. You could even fire them without time coordination, or at random times, or triggered by the heat of fires, just cut onf after another until you have cut enough for collapse to initiate.

Now what? What do you do with that theory?

 

[econ41]

Now what? What do you do with that theory?

Great minds think alike. That was the scenario I proposed in those long ago days when I helped a couple of truthers formulate hypotheses. I forget when - the posts should still be on ISF (ex R Dawkins Net Forum).

 

[Henkka]

Yes, And, surprisingly, that is the key issue that few people have looked at or considered seriously.

Agreed... Like if you look at the NIST FAQ on the towers, the word 'core' is found only 8 times. And as far as I can tell, this is the only sentence in the FAQ that directly discusses what happened to the core:

Thus, yielding and buckling of the steel members (floor trusses, beams, and both core and exterior columns) with missing fireproofing were expected under the fire intensity and duration determined by NIST for the WTC towers.

The focus is always on the floor trusses and the perimeter columns. But when the antenna starts moving down, the core under it must have already failed. Now I don't want to get too conspiratorial, but it almost feels as if they don't want you to think about it too hard.

Do this on all trusses on one side of the tower over 3 floors or so, and I think you might initiate a collapse in a similar fashion as the fires did. I'd guess, wildly, that half a pound of explosives per chord would be plenty. We are talking about perhaps 150 trusses? So 75 pounds of explosives. You could even fire them without time coordination, or at random times, or triggered by the heat of fires, just cut onf after another until you have cut enough for collapse to initiate.

Now what? What do you do with that theory?

The only point here is whether or not it makes sense to you that the WTC towers could have been utterly destroyed by explosives weighing about as much as a 10-year old child.

 

[econ41]

Agreed... Like if you look at the NIST FAQ on the towers, the word 'core' is found only 8 times. And as far as I can tell, this is the only sentence in the FAQ that directly discusses what happened to the core:

The focus is always on the floor trusses and the perimeter columns. But when the antenna starts moving down, the core under it must have already failed. Now I don't want to get too conspiratorial, but it almost feels as if they don't want you to think about it too hard.

Which is part of the reasoning why I decided to never rely on NIST's arguments.

 

[Abdullah]

What are you trying to say or ask? And is it on the OP topic or relevant to recent discussions.

The OO. And I honestly don't understand why we are discussing the topic of progression here.

 

[Oystein]

The only point here is whether or not it makes sense to you that the WTC towers could have been utterly destroyed by explosives weighing about as much as a 10-year old child.

That's a silly, utterly unscientific, irrational way of "thinking".

75 pounds of explosives are (probably - I am not an expert, substitute better number if you have, but I am at least not underestimating by a magnitude of order) enough to cut 150 truss chords.
Cutting a bottom truss chord is probably enough to make the truss fail its truss action, such that it will sag.
150 trusses sagging on one side of the tower over 3 floors exert a great pull-in force on the walls.
Remember the walls depend on the trusses providing lateral support in order for the walls to remain plumb.
When the trusses FAIL to provide that lateral support over 3 floors, so unbraced length is multiplied by 4, he walls are 16 times as likely to buckle - whithout any additional lateral force.
But with the trusses actively pulling inwards, YES, I can see easily that this WILL pull the columns out of plumb.
Once you have an entire wall caving in, YES, I can see easily that the tower becomes instable and may creep close to collapse.

That is for cold steel.
Now if you heat up some of the steel, creep (that's a technical term in engineering - look it up if you are unfamiliar) becomes even more of an issue.

So absolutely YES, it absolutely DOES make sense to me that 75 pounds of explosives, smartly placed, suffice to make such a tower collapse.

---

I presented an ARGUMENT.
Where is yours? All you bring is incredulity and failure of imagination based on a silly, irrelevant comparison.
Perhaps it works better for you when you consider that 75 pounds is about the same mass as 35,000,000,000 termites (workers, that is)?
ETA: oops, 35,000,000 termites only ,

 

[Mendel]

I can't believe that the WTC was built that way, i.e., to be held together exclusively by the floor connections.

So investigate the engineering and convince yourself.

Yes, falling off to the sides or down through the empty spaces (shafts) of the cores.

How big are these shafts, and how were their openings?

I think it's important to emphasize that I understand all of these things. That is, I understand that this is the theory NIST has proposed and how that mechanism is supposed to have worked. What I don't understand is why a building would be made this way. It seems like arranging dominoes in that video @Mendel has been emphasising, where small causes can have enormous consequences. Or, indeed, like building a bookcase (let alone a skyscraper) in that rickety way Mick did.

The "small cause" was an airliner crashing into it, and then extensive fires burning. This has only happened to 0.005% of highrises in the world.

I think Thomas B is saying that he can see debris piling up and failing the first floor, but the debris pile lessens due to portions of it falling off as it progresses downward until there is not enough debris to fail the remaining floors.

it looks like Thomas imagines the debris to behave like water instead of like debris

I think the middle ground here is that I think it should have been a bit more of a scandal that they collapsed. If it had been presented as the result of a serious design flaw right from the beginning, I'd be more comfortable with it.

The building survived the impact of a loaded 737, that's a design success

we've repeatedly mentioned (even to you) that building codes changed as a result of 9/11, both with respect to evacuations and progressive collapse modes.

 

[Abdullah]

Cutting a bottom truss chord is probably enough to make the truss fail its truss action, such that it will sag.

That's quite an understatement of the significance of cutting an entire chord

 

[Mendel]

So you could do a controlled demolition of the tower just by attacking these flimsy little things with explosives?



That doesn't look like it would take a powerful explosive to take out the connection. Cut the trusses on a couple floors to get the unstoppable cascade going, columns lose lateral support, and it's RIP World Trade Center. Doable?

You'd have to do it to the core-side connections, too.

So it's doable if you
- can access hundreds of locations in the walls of the building (more than 1000 if you do several floors)
- without anyone noticing (not even in retrospect)
- wire them to explode

but you would leave hundreds of pieces of evidence as steel deforms a certain way when exploded. NTSB investigators look for this in crashed aircraft debris, for example. But no such evidence was found in the WTC debris.

No terrorist has ever bombed any building that way, the risk of the preparations being discovered is simply too great. They do car/truck bombs, which are quick to place and detonate; flying the aircraft into the towers is simply an advanced version of this method.

 

[Thomas B]

The "small cause" was an airliner crashing into it, and then extensive fires burning. This has only happened to 0.005% of highrises in the world.

The tricky thing is that this is all relative. You're not going to get a much less rare event if you posit the "small cause" as Cessna 172 crashing into it, but such a plane would obviously still be a small cause. It's hard to know exactly where to draw the line where "small cause" becomes ridiculous. (I assume you're trying to ridicule that description.) Where would you draw the line between a plane that it would be scandalous for a building not to survive and one that it's ridiculous to think it should survive?

If a Nor'easter knocked over a skyscraper in New York City we wouldn't shrug and show a film of progressively larger dominoes knocking each other over. If someone said, "That seems like a bad model, because it's a structure where a small cause will have enormous consequences and no one would build something like that," we wouldn't say, "Dude, the 'small cause' you're talking about was an extratropical cyclone!"

 

[Henkka]

So absolutely YES, it absolutely DOES make sense to me that 75 pounds of explosives, smartly placed, suffice to make such a tower collapse.

13,227 pounds of explosives were used to demolish the Mina Plaza in UAE:


Source: https://www.youtube.com/watch?v=5ceXT5PYTGI

144 floors were demolished using 13,227 pounds (6,000 kg) of explosives — all safely carried out, explained the Gulf News.

https://interestingengineering.com/...zas-demolished-in-abu-dhabi-within-10-seconds

And of course, they were also "smartly placed" by demolition professionals. But for this:



Eh, 75 pounds should suffice.

 

[Abdullah]

@Henkka that's ridiculous; these people needed to do it safely - they needed to make sure that, for instance, they would not have to take mortal risk to rig half a building

 

[benthamitemetric]

13,227 pounds of explosives were used to demolish the Mina Plaza in UAE:

[video omitted]

And of course, they were also "smartly placed" by demolition professionals. But for this:

[image omitted]

Eh, 75 pounds should suffice.

Well, congratulations--you finally did it: you demonstrated that an expressly speculative and highly unlikely limit case proposal for the bare minimum way that a certain steel framed building could be demolished is not the way that professional demolition teams, subject to no such limitations, would choose to demolish four completely different structures. Before you made this brilliant observation, I really expected that professional demolition teams would be attempting to apply the bare minimum amount of explosives in order to maximize the chances that their attempted demolition would fail, leaving them with the very expensive problem of a damaged and very dangerous building that would be difficult to re-rig. But, bravo! Now we know! I guess we can call it a day, boys!

 

[Henkka]

@Henkka that's ridiculous; these people needed to do it safely - they needed to make sure that, for instance, they would not have to take mortal risk to rig half a building

I'm not sure I understand, are you saying the 13,000 pounds was overkill, to make absolutely sure the building came all the way to the ground? That way, they wouldn't have to take a risk to demolish what was left. I suppose that's partly true, but going way overboard would be a waste of money. If the Mina Plaza could be demolished with 100 pounds of smartly placed explosives, they're not just going to tack on an extra 12,900 pounds just to make sure.

 

[Jeffrey Orling]

At peril of falling victim to another distraction:

One theory holds that fires made the floor trusses sag, so they pulled walls inward by catenary action, and collapse ensued.

One way to make the floor trusses sag would be to cut their bottom chords, which are steel rods no more than 1 inch thick, if memory serves. The top trusses would sag and pull in, having lost the trusses' internal stability. Do this on all trusses on one side of the tower over 3 floors or so, and I think you might initiate a collapse in a similar fashion as the fires did. I'd guess, wildly, that half a pound of explosives per chord would be plenty. We are talking about perhaps 150 trusses? So 75 pounds of explosives. You could even fire them without time coordination, or at random times, or triggered by the heat of fires, just cut onf after another until you have cut enough for collapse to initiate.

Now what? What do you do with that theory?

bottom cords were double angles with the web bars welded in between

 

[Henkka]

Well, congratulations--you finally did it: you demonstrated that an expressly speculative and highly unlikely limit case proposal for the bare minimum way that a certain steel framed building could be demolished is not the way that professional demolition teams, subject to no such limitations, would choose to demolish four completely different structures. Before you made this brilliant observation, I really expected that professional demolition teams would be attempting to apply the bare minimum amount of explosives in order to maximize the chances that their attempted demolition would fail, leaving them with the very expensive problem of a damaged and very dangerous building that would be difficult to re-rig. But, bravo! Now we know! I guess we can call it a day, boys!

Ah you know what, you're right... Of course a professional demolition team would not place a "bare minimum" of explosives, how foolish of me. They would place at least double just to make sure, which would be a whopping 150 pounds. So not the weight of a 10-year old by any means, but the weight of an entire, if thin, adult. Totally different situation, makes way more sense now.

 

[Abdullah]

I'm not sure I understand, are you saying the 13,000 pounds was overkill, to make absolutely sure the building came all the way to the ground?

Remember the core remnant? Imagine what a headache it would have been if that thing hadn't collapsed. The same is true for large sections of the walls stripped of their burden.

 

[benthamitemetric]

Ah you know what, you're right... Of course a professional demolition team would not place a "bare minimum" of explosives, how foolish of me. They would place at least double just to make sure, which would be a whopping 150 pounds. So not the weight of a 10-year old by any means, but the weight of an entire, if thin, adult. Totally different situation, makes way more sense now.

If you have an actual view, let alone an informed one, as to what it would take to demolish the buildings, we've yet to see it. And this whole trip down incredulity lane is a gigantic waste of time that has nothing to do with this thread. So maybe put your brilliant theory in a new OP so we can be wowed anew by how well you understand the tower structures.

 

[Henkka]

If you have an actual view, let alone an informed one, as to what it would take to demolish the buildings, we've yet to see it. And this whole trip down incredulity lane is a gigantic waste of time that has nothing to do with this thread. So maybe put your brilliant theory in a new OP so we can be wowed anew by how well you understand the tower structures.

I'm not the one proposing what exactly it would take to demolish the buildings, that was Oystein. All I argued was that the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives. I'm not going to put an exact number on how much explosives it would take, I don't really know. But so far I've received nothing but agreement that yes, this could theoretically be done, and it would not take that much explosives. You wouldn't need large amounts of extremely heavy explosives to cut the core columns for example, because that supposedly did not happen on 9/11. All you need is the bare minimum sufficient damage the impact and fires caused, which has now been estimated by one person could be done with a whopping 75 pounds of explosives.

Now you can say I'm just being incredulous, and sure, I agree that I am incredulous of the totally absurd claims being made... That although appearing strong, the WTC towers were actually susceptible to being demolished by explosives weighing about as much as a child. I've no engineering or physics background to actually calculate the maths of why this isn't possible, but I also can't calculate for you why humans can't jump to the moon or whatever.

 

[Thomas B]

I've had the same thought. Imagine using the steel to make a single round, hollow mast with 2-foot thick walls and a 32-foot radius. That's just scaling up the text-book example I referred to in a post on another thread, in a way that approximates the WTC proportions. (The cores were 87 feet on the narrow side and the columns at the base were almost solid steel blocks 22"x52".)

Source: https://ocw.mit.edu/courses/2-080j-structural-mechanics-fall-2013/resources/mit2_080jf13_lecture10/

Note the walls in the example are a tenth of an inch, so more than 200 hundred times thinner than the walls in the one-column core we're imagining. I'll get to work on the math later today, but if anyone beats me to it, that's just a good thing.

A quick update on this. One way to try to understand what @benthamitemetric calls @Henkka's and my (and truthers') "incredulity" is to imagine this two-foot thick, 64-foot wide pipe, surrounded by another one, one-foot thick and, say, 200 feet wide. Imagine them bolted directly to bedrock and standing 1000 feet high and then put in 100 evenly spaced round floors on trusses connecting the outer pipe to the inner pipe.

[Edit: feel free to have the thickness of the pipe tapering appropriately as you go up if you think that's better.]

Now, imagine it going through ROOSD. Of course, that structure isn't exactly like the WTC (and it is in many ways impossible to build), but the WTC (as I imagine it) was at least as strong.

 

[Abdullah]

I wonder what would happen if you cut the channel girders that support thrme trusses

 

[Jeffrey Orling]

I'm not the one proposing what exactly it would take to demolish the buildings, that was Oystein. All I argued was that the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives. I'm not going to put an exact number on how much explosives it would take, I don't really know. But so far I've received nothing but agreement that yes, this could theoretically be done, and it would not take that much explosives. You wouldn't need large amounts of extremely heavy explosives to cut the core columns for example, because that supposedly did not happen on 9/11. All you need is the bare minimum sufficient damage the impact and fires caused, which has now been estimated by one person could be done with a whopping 75 pounds of explosives.

Now you can say I'm just being incredulous, and sure, I agree that I am incredulous of the totally absurd claims being made... That although appearing strong, the WTC towers were actually susceptible to being demolished by explosives weighing about as much as a child. I've no engineering or physics background to actually calculate the maths of why this isn't possible, but I also can't calculate for you why humans can't jump to the moon or whatever.

Having seen the runaway floor collapse (ROOSD)... it seems that if explosive were placed at perhaps 50%+ of the floor truss seat connection... on 5 or 6 floors on consecutive high floors (80-86 for example) one might be able to initiated a ROOSD. This would leave perhaps an intact standing core and an intact and unbraced hollow tube facade. The facade would likely be too unstable to stand and it would collapse (from bucking?.... wind loads?) And intact core might be able to stand without the outside the core floors and facade.

 

[benthamitemetric]

I'm not the one proposing what exactly it would take to demolish the buildings, that was Oystein. All I argued was that the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives. I'm not going to put an exact number on how much explosives it would take, I don't really know. But so far I've received nothing but agreement that yes, this could theoretically be done, and it would not take that much explosives. You wouldn't need large amounts of extremely heavy explosives to cut the core columns for example, because that supposedly did not happen on 9/11. All you need is the bare minimum sufficient damage the impact and fires caused, which has now been estimated by one person could be done with a whopping 75 pounds of explosives.

Now you can say I'm just being incredulous, and sure, I agree that I am incredulous of the totally absurd claims being made... That although appearing strong, the WTC towers were actually susceptible to being demolished by explosives weighing about as much as a child. I've no engineering or physics background to actually calculate the maths of why this isn't possible, but I also can't calculate for you why humans can't jump to the moon or whatever.

You haven't argued that "the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives," you've just asserted it. Arguing it would involve taking the time to understand why the plane crashes + fires caused the buildings to collapse and how explosive demolitions work and then actually takng the time to propose the "easy" demolition system that would mimic entirely that collapse mode. Of course if you actually understood that collapse mode, wherein the heated trusses slowly pulled the columns inwards as those trusses failed, which helped induce the column buckling, you would understand that such a collapse mode is inherently difficult for *explosives* to replicate, but expecting you to pay attention to such details at this point is a lost cause. So all you are left saying is that "because we accept that planes + fires or a even very severe, artificially constructed fire could bring down the building, then we should also accept that there is a way to bring down the building with explosives." And exactly zero people disagree with that banal observation.

 

[benthamitemetric]

A quick update on this. One way to try to understand what @benthamitemetric calls @Henkka's and my (and truthers') "incredulity" is to imagine this two-foot thick, 64-foot wide pipe, surrounded by another one, one-foot thick and, say, 200 feet wide. Imagine them bolted directly to bedrock and standing 1000 feet high and then put in 100 evenly spaced round floors on trusses connecting the outer pipe to the inner pipe.

[Edit: feel free to have the thickness of the pipe tapering appropriately as you go up if you think that's better.]

Now, imagine it going through ROOSD. Of course, that structure isn't exactly like the WTC (and it is in many ways impossible to build), but the WTC (as I imagine it) was at least as strong.

Why do you think a building built of a porous mesh of interconnected columns and girders would be *at least as strong* as unitary pipe of the same outward dimensions?

 

[Thomas B]

Why do you think a building built of a porous mesh of interconnected columns and girders would be *at least as strong* as unitary pipe of the same outward dimensions?

I believe that's how they're built. If you were to cut the outer pipe [vertically] into, say, four sections and bend each of them into smaller pipes, and then join them with spandrels, there is a way of doing this that would produce a structure of equal strength but greater utility. You can then imagine doing it with 240 sections. An engineer would be able to explain why this would give you the windows you need while maintaining the strength of a single column. It's how I've understood all popular accounts of why the tube-in-tube structure was such a brilliant design.

But let me hear you on this point: Do you agree that the structure I've describe would not be vulnerable to ROOSD, i.e., that it is VERY strong?

 

[benthamitemetric]

I believe that's how they're built. If you were to cut the outer pipe into, say, four sections and bend each of them into smaller pipes, and then join them with spandrels, there is a way of doing this that would produce a structure of equal strength but greater utility. You can then imagine doing it with 240 sections. An engineer would be able to explain why this would give you the windows you need while maintaining the strength of a single column. It's how I've understood all popular accounts of why the tube-in-tube structure was such a brilliant design.

But let me hear you on this point: Do you agree that the structure I've describe would not be vulnerable to ROOSD, i.e., that it is VERY strong?

You've chosen arbitrary parameters, but I do not think it is possible to build a realistic open span floor system like the towers that is invulnerable to ROOSD. The floors will still have a failure point and the columns will still have a failure point. Those points may be higher than the failure points in the towers, but that'd just be a function of your arbitrary parameters. If you want to build a completely unrealistic system, such as a completely solid core or extremely thick-walled unitary core, then I suppose such a system could by itself of course survive ROOSD (though the floors would still be shearable). But that's not the system that was in the towers.

 

[Gamolon]

A quick update on this. One way to try to understand what @benthamitemetric calls @Henkka's and my (and truthers') "incredulity" is to imagine this two-foot thick, 64-foot wide pipe, surrounded by another one, one-foot thick and, say, 200 feet wide. Imagine them bolted directly to bedrock and standing 1000 feet high and then put in 100 evenly spaced round floors on trusses connecting the outer pipe to the inner pipe.

What the heck?

That's not even close to the tower's structure! How does this help anyone understand what happened?

 

[Thomas B]

That's not even close to the tower's structure! How does this help anyone understand what happened?

It's closer than you think. I'll try to find Starossek's textbook where tube-in-tube design is described basically like this.

 

[Thomas B]

You've chosen arbitrary parameters, but I do not think it is possible to build an open span floor system like the towers that is invulnerable to ROOSD. The floors will still have a failure point and the walls will still have a failure point. Those points may be higher than the failure points in the towers, but that'd just be a function of your arbitrary parameters.

I'm didn't quite get the answer to the question. Leaving aside whether my two-single-pipes structure is "like the towers", is it vulnerable to ROOSD?

 

[benthamitemetric]

I'm didn't quite get the answer to the question. Leaving aside whether my two-single-pipes structure is "like the towers", is it vulnerable to ROOSD?

Again, it's a function of arbitrary parameters that you have not specified and likely not even thought about, but I very clearly said that such a structure could be vulnerable to ROOSD.

 

[Jeffrey Orling]

You haven't argued that "the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives," you've just asserted it. Arguing it would involve taking the time to understand why the plane crashes + fires caused the buildings to collapse and how explosive demolitions work and then actually takng the time to propose the "easy" demolition system that would mimic entirely that collapse mode. Of course if you actually understood that collapse mode, wherein the heated trusses slowly pulled the columns inwards as those trusses failed, which help induced the column buckling, you would understand that such a collapse mode is inherently difficult for *explosives* to replicate, but expecting you to pay attention to such details at this point is a lost cause. So all you are left saying is that "because we accept that planes + fires or a even very severe, artificially constructed fire could bring down the building, then there should also be a way to bring down the buiding with explosives." And exactly zero people disagree with that banal observation.

I am not convinced that the heated sagging trusses pulled in sufficient number of facade columns to induce its buckling. It would seem this would require fires throughout most of the foot print.... and the short spans would sag and pull less... What would happen to the corners?

 

[benthamitemetric]

I am not convinced that the heated sagging trusses pulled in sufficient number of facade columns to induce its buckling. It would seem this would require fires throughout most of the foot print.... and the short spans would sag and pull less... What would happen to the corners?

I don't think it was the trusses alone, but I think NIST demonstrated that they materially contributed to the buckling of the columns. The damage they caused to the columns, in combination with the other damage to the structure from the impact and the columns that lost insulation and were highly heated eventually brought about the total collapse--first slowly then all at once, as the saying goes.

 

[Mendel]

I'm not sure I understand, are you saying the 13,000 pounds was overkill, to make absolutely sure the building came all the way to the ground? That way, they wouldn't have to take a risk to demolish what was left. I suppose that's partly true, but going way overboard would be a waste of money. If the Mina Plaza could be demolished with 100 pounds of smartly placed explosives, they're not just going to tack on an extra 12,900 pounds just to make sure.

well the facade falling on the WTC damaged many buildings and we know about WTC7

so you could collapse a WTC tower with 100 pounds only if you didn't mind the collateral damage

note also that this was explicitly only for collapsing the floors

 

[Jeffrey Orling]

I don't think it was the trusses alone, but I think NIST demonstrated that they contributed to the buckling of the columns. That, in combination with the other damage to the structure and the columns that lost insulation and were highly heated eventually brought about the total collapse--first slowly then all at once, as the saying goes.

I suppose we'll never know.... My hunch is that the core had a heat driven failure.... elongated lateral steel displacing columns leading to buckling which engulfed the core... the top block dropped with the hat truss holding it together...
There may have been some isolated perimeter buckling (opposite core's corners) but facade's may mode of destruction was "peeling" when the floors went "ROOSD"
Seems a stretch to think the entire footprint was burning. More likely a "path" related to the planes "path" through the structure. The impact of heat was principally on LATERAL steel (core).

 

[Henkka]

You haven't argued that "the damage you believe the plane impact and fires caused, which was sufficient to destroy the entire building, could be easily and far more efficiently done with targeted explosives," you've just asserted it.

I thought you agreed:

So you could do a controlled demolition of the tower just by attacking these flimsy little things with explosives?

Why not? Of course, as with the real collapses, it wouldn't be meaningfully "controlled"; but it would all collapse if you got a sufficiently larger top block moving by destroying lateral support of the columns below it sufficiently to allow those columns to buckle. Of course, the truss connections breaking is not why collapse *initiated* in the case of the towers (it's why the collapse progressed), so you seem to be conflating things somewhat in attempt to play the incredulity card here again, but there is an infinite number of ways to destroy a building and that's one of them.

(I added the bolding)

Of course if you actually understood that collapse mode, wherein the heated trusses slowly pulled the columns inwards as those trusses failed, which helped induce the column buckling, you would understand that such a collapse mode is inherently difficult for *explosives* to replicate, but expecting you to pay attention to such details at this point is a lost cause.

Whatever damage the heated trusses pulling on the columns does, could obviously also be done with explosives.

 

[benthamitemetric]

I thought you agreed:



(I added the bolding)


Whatever damage the heated trusses pulling on the columns does, could obviously also be done with explosives.

And why do you think such an explosive scheme would be "easy"? That's the strawman that is at the heart of this waste of time. For example, when you later came back to clarify how many truss seats you would have to fail to induce a collapse, what did I say? I think it's clear that I disagree that you would likely be able to destroy the towers by failing the trusses on a single floor. I think you would need to fail them across several floors at least. But that's a totally different failure mode than the fire induced one, anyway. And so, SO WHAT? What's the minimum amount of explosives you think would be necessary to induce a collapse and why should we care?

 

[Thomas B]

it's a function of arbitrary parameters that you have not specified

Not specified?

One way to try to understand what @benthamitemetric calls @Henkka's and my (and truthers') "incredulity" is to imagine this two-foot thick, 64-foot wide pipe, surrounded by another one, one-foot thick and, say, 200 feet wide. Imagine them bolted directly to bedrock and standing 1000 feet high and then put in 100 evenly spaced round floors on trusses connecting the outer pipe to the inner pipe.

Scale it down so it's inches rather than feet. Or go all out and make it centimeters. It's now a 10m pipe-in-pipe. Could you get it to ROOSD? The answer now is "of course not!" because of the scaling problem that we're familiar with.

I'm asking whether the full-scale version (of something we all know wouldn't be susceptible to ROOSD) might be susceptible to ROOSD.

And, please remember that I'm only saying this to formalize my "incredulity" as something you can (literally) poke holes in. Why is it you think the mesh is so much weaker than the single pipe?

 

[benthamitemetric]

Not specified?

Scale it down so it's inches rather than feet. Or go all out and make it centimeters. It's not a 10m pipe. Could you get it to ROOSD? The answer now is "of course not!" because of the scaling problem that we're familiar with.

I'm asking whether the full-scale version (of something we all know wouldn't be susceptible to ROOSD) might be susceptible to ROOSD.

And, please remember that I'm only saying this to formalize my "incredulity" as something you can (literally) poke holes in. Why is it you think the mesh is so much weaker than the single pipe?

You didn't even say what the pipe was made of. You didn't specify the strength of the floor connections or the weight of the floor systems. Etc. Like I said, you could build an arbitrarily strong imaginary building that would not be subject to ROOSD. But you could also build an imaginary pipe building like you describe that would be subject to ROOSD. All of these thought experiments are a waste of time because we know exactly how the towers were built and thus do not need to analyze them by analogy to whatever half-baked pipe dream you come up with (which imaginary buildings you are not actually analyzing with any precision, anyway).

 

[Abdullah]

I am not convinced that the heated sagging trusses pulled in sufficient number of facade columns to induce its buckling. It would seem this would require fires throughout most of the foot print.... and the short spans would sag and pull less... What would happen to the corners

You have s false impression of the tower being pulled in from all sides. In reality, only one wall was pulled in. Refer to NCSTAR 1-6D Executive Summary

 

[Jeffrey Orling]

You have s false impression of the tower being pulled in from all sides. In reality, only one wall was pulled in. Refer to NCSTAR 1-6D Executive Summary

I don't have a false impression. Partial pull in from one side would not lead to buckling of the entire perimeter.
Best guess is the collapse was core led caused by expanded lateral steel from fires in the core region (path of plane/fuel) There is visual evidence of one perhaps 20' long facade buckling... south facade east side.

Can you point to images of more extensive facade buckling pre collapse?