Kostack Studios WTC2 (South Tower) Collapse Simulation

Wow! My biggest initial takeaway is how much less the tower "fell straight down, into it's own footprint" than I imagined.

I mean, I always believed that people were exaggerating on that claim...but this tells a very, very different story.

It looks like this simulation supports the conclusion from the final report by NIST (NCSTAR 1) in depicting floors sagging and collapsing due to weakening floor trusses, in turn triggering the structural collapse of each tower.

By contrast, Thornton Tomasetti (then Weidlinger Associates), who modeled the impact, fires, and collapse of each tower as part of their forensic investigation commissioned for subsequent insurance claim litigation, drew a slightly different conclusion, namely that the collapses were core-driven, from columns severed at impact and the subsequent weakening of the remaining core columns from the ensuing fires. ...

We need to consider that Kostack did not do very much do model the initiating event and I think makes no claim that his simulation is intended to pinpoint the initiation. In particular, no fires are simulated. From the video description:

The collapse trigger is a localized weakening of elements around the impact region, implemented as a spatially decaying gradient that reduces element strength and stiffness with distance from the centre of impact. In addition, a small number of core columns that engineering judgment indicated had suffered total failure after the impact were removed from the model; these removals are few and, taken alone, would not have produced global collapse. Trusses and façade elements in the affected area were also weakened. After this prepared initial state no further manual removals, scripted impulses or ad-hoc forces were applied: the sequence unfolds under gravity, inertia, contact and material response.

That is not how the fires played out. The assumption that "center of impact" is equal to the region with hottest fires (or fasted heat-up) is almost certainly wrong. Inertia durong the crash event would have pushed flammables (jet fuel as well as office contents) towards the periphery of the impact area.
Thus, he has the initiating event quite probably on the wrong side of the tower, and consequently, the macro events do not play out in the same places. Example: In reality, a big wall section peeled towards the south to reach over to and impact 130 Liberty St (aka Bankers Trust or Deutsche Bank building), but this siulation has a big chunk peeling towards the East, a chunk that even includes the entire top (including an almost intact roof plus ca. 10 floors worth of perimeter) falling smack onto WTC4. A tall wall section there is pushed way across Church St and would have impacted 1 Liberty Plaza the way that, in reality, WFC2+3 and 130 Liberty were impacted and damaged. This did not happen in reality.

So do not expect Kostack to create a facsimile of the historical collapses. That was probably not the intention, nor could it have been without an assessment of true fire temperatures developing dynamically.

I take this video as Mick put it: as showing "the various aspects of the collapse" such as:

• The banana peeling
• The pancaking
• How the collapse fromt was very much staggered and uneven
• How perimeter wall sections from the falling top passing on inside of the walls of the standing bottomm (and vice versa) cut off floor trusses, like blades.
• And even: Crush Down before Crush Up!

This is a very detailed physical simulation that shows (without the smoke and dust) the various aspects of the collapse that have puzzled people like AE911Truth. It's shown from various angles, with some cutaways.

I've never been a great believer in "a simulation". They've had to put an enormous number of parameters into that, and there's uncertainty in every single one of them. (So "precision" is actually not what you want at all, the more precision you bake in, the most assumptions you are making.) How many thousands of simulations with perturbations to each parameter did they run? The modelled outcome(s) should then be the largest macrostates (sets of outcomes that are mostly similar). Of course, they'll want to focus on just one run for show, but that should be a typical one in the largest macrostate - is that what they did?

I've never been a great believer in "a simulation". They've had to put an enormous number of parameters into that, and there's uncertainty in every single one of them. (So "precision" is actually not what you want at all, the more precision you bake in, the most assumptions you are making.) How many thousands of simulations with perturbations to each parameter did they run? The modelled outcome(s) should then be the largest macrostates (sets of outcomes that are mostly similar). Of course, they'll want to focus on just one run for show, but that should be a typical one in the largest macrostate - is that what they did?

Indeed. And also, the "simulation" is only based on a Blender add-on. This add only simulates the connections of rigid bodies. So the whole sim does not consider bending elements.. Serious restriction in the model, so not very scientifically interesting.

This feels more like an illustration of the collapses than a simulation. It doesn't do anything to overcome my intuition that the buildings couldn't have been this weak. (They're falling apart like houses of cards or towers of wooden blocks.) My inititial reaction is simply that the connections between each of the elements aren't strong enough. I want to know how much stronger they had to be to resist the collapses (I assume the value was discovered by experimentation.) And what real-world design parameter this would translate into (a few more or slightly stronger bolts?)

Also, in the simulation, the inititating floor failures are not caused by the weight of 10+ floors falling on one floor but by individual floors spontaneously detaching and falling on the floor below. As understand it, even if the initial floor-connection failures in this simulation had happened, the floor connections on the intact floors below should have resisted a progression.

Finally, although i'm not sure this is possible in Blender, it would be interesting to subject a pristine model, i.e., prior to the introduction of the aircraft damage (which was introduced by removing elements), to a lateral impact event equivalent to a 767 travelling at 440 mph. This would be a way to begin to satisfy me that the connections were adequate, i.e., that they represented the building in good working order.

Perhaps human intuition regarding very tall buildings isn't going to be great.

Yes, this is the issue. My hope for simulations like this is that they fill the gap between our intuitions about 10' steel cages and 1000' tall buildings ...

or perhaps just the difference between an 18" model and an 18' one!

This would actually be somewhat interesting: how does the simulation run if we simply convert all the lengths from feet to inches? I assume that if the gravity function is the same, we'd be able to see exactly what "gravity doesn't scale well" means for the performance of these models.

how does the simulation run if we simply convert all the lengths from feet to inches?

1) putting 36 inches instead of 3 feet won't change anything (and iirc Kostack is European and would use metric)

2) you've had explained to you that lengths, cross-sections, volumes, weight, and buckling strengths do not scale proportionally. Unfortunately, you seem to have never understood that explanation.

This feels more like an illustration of the collapses than a simulation.

Agreed. And the distinction can be important in debate.

It doesn't do anything to overcome my intuition that the buildings couldn't have been this weak. (They're falling apart like houses of cards or towers of wooden blocks.) My inititial reaction is simply that the connections between each of the elements aren't strong enough. I want to know how much stronger they had to be to resist the collapses (I assume the value was discovered by experimentation.) And what real-world design parameter this would translate into (a few more or slightly stronger bolts?)

IMNSHO not likely. Keep in mind the two critical stages. (Out of four.)
The failure of the initiation stage was by cascading sequenced failure of columns in axial overload. Bolts (or fastenings) not critical.

Whilst the key structural failure of the progression stage was the bolted connection arrangement OOS floor joists to columns. The impact of the falling mass of debris was orders of magnitude overwhelming - stronger bolts/angle brackets/welds would not have changed anything. Certainly not to cause arrest. (And the beam to column connections in the core - tho much more sturdy - were also overwhelmed. Remember the "spires" were stripped clean of horizontal members.) Also the progression stage was at 2/3rsds "G". And the "lost" 1/3rg G is accounted for to the order of capable accuracy by momentum accumulation as debris is added floor by floor. THEREFORE the effect of structural resistance - failure of beam or joist connections to columns - was second order. Minimal in the face of overwhelming impact forces.

Also, in the simulation, the inititating floor failures are not caused by the weight of 10+ floors falling on one floor but by individual floors spontaneously detaching and falling on the floor below. As understand it, even if the initial floor-connection failures in this simulation had happened, the floor connections on the intact floors below should have resisted a progression.

I'll pass on this section.

Finally, although i'm not sure this is possible in Blender, it would be interesting to subject a pristine model, i.e., prior to the introduction of the aircraft damage (which was introduced by removing elements), to a lateral impact event equivalent to a 767 travelling at 440 mph. This would be a way to begin to satisfy me that the connections were adequate, i.e., that they represented the building in good working order.

Ditto.

Finally, although i'm not sure this is possible in Blender, it would be interesting to subject a pristine model, i.e., prior to the introduction of the aircraft damage (which was introduced by removing elements), to a lateral impact event equivalent to a 767 travelling at 440 mph.

this has been done, and the study was discussed on metabunk

I don't know how Blender works, but I'm guessing that the connections have some value indicating their strength and that this value could just be turned up until the model doesn't collapse (i.e., behaves as the conspiracy theorists say it would have without demolition). My question is just how much would the values have to be turned up. That is, what's the difference between the official and truther models of the strength of the buildings? To me, exploring that difference quantitatively would be a good way to get people out the rabbit hole.

(If I'm understanding it correctly, there was no parameter for failure by bending of the elements? So it's really just a matter of the forces overwhelming some strength parameter at the points where the elements are connected. (If I understand the commentary, the connections do get stronger down the length of the building, but the materials don't really get stronger since their failure isn't being modelled at all. I could be very wrong about this.)

I don't know how Blender works,

We are seeing the umpteenth recycling of a feature of discussion we have had on multiple previous occasions.

What are we (i.e. the modeller) trying to achieve? Something that looks like the collapses, or something that replicates the physics of the collapses. As I understand it Blender is a graphics animation tool - a "looks like" model producer - with some capability to include elements of physics reality. But it is not a structural physics modelling tool.

And as I have said in previous discussions, we need to be clear on the objective - neither conflating the two nor disregarding the distinction.

but I'm guessing that the connections have some value indicating their strength and that this value could just be turned up until the model doesn't collapse (i.e., behaves as the conspiracy theorists say it would have without demolition). My question is just how much would the values have to be turned up.

For what objective? Making it "look like" whatever you are seeking OR legitimately demonstrating applied physics relevant to the actual collapses?

That is, what's the difference between the official and truther models of the strength of the buildings? To me, exploring that difference quantitatively would be a good way to get people out the rabbit hole.

There is no "truther model". And not much in the form of any "official model" that clearly explains the four stage reality.
And how to "get people out of the rabbit hole" using EITHER visual animation OR physics simulation modelling won't be resolved if we keep recycling the same process confusing two types of simulation.

(If I'm understanding it correctly, there was no parameter for failure by bending of the elements? So it's really just a matter of the forces overwhelming some strength parameter at the points where the elements are connected.

What failure by "bending". The critical failures were axial overloading of columns in the initiation stage and shearing of floor<>column connections in the progression stage.
So, whether you want a "looks like" animation or a structural model, those are the features needing attention. NOT "bending" unless you can falsify my claim that those two are the dominant factors.

(If I understand the commentary, the connections do get stronger down the length of the building, but the materials don't really get stronger since their failure isn't being modelled at all. I could be very wrong about this.)

"Getting stronger" is not an issue because all the critical points of failure involved inexorable progress of load redistribution (initiation stage) OR overwhelming impact loads (progression stage). Correct it is not modelled. I'm not persuaded it needs modelling >>> again "What is the objective"? If the object is to "Get someone out of a rabbit hole" what part does any model play in the de-holeing?

Kai Kostack's bullet constraints builder is open source, available at https://github.com/KaiKostack/bullet-constraints-builder . The readme claims it uses the discrete element method (DEM) of simulation, which allows it to track the interactions of the falling parts of the building. Ansys can do DEM nowadays, too.

Chapter 9 of the user manual starts out with these contents:

The computationally less demanding finite element method would mostly employ compressive and tensile strengths, and the other types of breakage would be simulated by modelling the structure inside a material, if needed (i.e. model a beam from several elements).
Bullet Constraints Builder models bending, shearing and plastic deformation.

BCB is still nominally a university project, so there may be papers.

There is no "truther model".

I disagree with you on this. I think it's important to understand the truthers' position as a model of tall buildings that is more resistant to progressive collapse than they are in reality. The trick to leading people out of the rabbit hole is to get them to understand how skyscrapers can be both very strong under "normal" (including extreme weather) conditions but yet vulnerable to precisely this sort of very rare event. That means showing them that their mental model of "why buildings stand up" (cf. Salvadori 1980) exaggerates their structural resilience. Truthers don't deny that the buildings collapsed, only that they could do so without additional damage to the structure (beyond the impacts and the fires). They're pretty clear about this in their presentations.

Truthers don't deny that the buildings collapsed

it boggles the mind that you felt the need to say this

The trick to leading people out of the rabbit hole is to get them to understand how skyscrapers can be both very strong under "normal" (including extreme weather) conditions but yet vulnerable to precisely this sort of very rare event.

Normal people don't require a trick. They understand that when an airliner crashed into a building that then burned for quite some time, it is substantially weakened and can collapse. That's why firefighters do not go into burning buildings unless lives are at stake.

People who have difficulty coming to terms with 9/11 as a fundamentally uncontrollable event seek comfort in a narrative where some secret control exists. Your "trick" does not work because it does not address the underlying problem.

"Getting stronger" is not an issue because all the critical points of failure involved inexorable progress of load redistribution (initiation stage) OR overwhelming impact loads (progression stage).

I just noticed this in the Salvadori book I linked to before (p. 49):

This is the sort of thing that suggests the truthers' "model" of the strength of the towers. Because of the wind loads they have been built to deal with, they are fifty times stronger than 200-foot buildings. To see them fail under their own weight is the mindblowing part for many people, even ones that don't become avid truthers. I don't think people should be ridiculed for finding it hard to understand. Their model should be acknowledged, respected, and corrected.

Because of the wind loads they have been built to deal with, they are fifty times stronger than 200-foot buildings. To see them fail under their own weight is the mindblowing part for many people, even ones that don't become avid truthers.

And yet, you had seemed to understand previously that the wind loads are met structurally by the tube-in-tube design of the WTC, while the collapse was driven by the progressive failure of the floors that provided rigidity to the tubes.

I think it's important to understand the truthers' position as a model of tall buildings that is more resistant to progressive collapse than they are in reality.

That's just a belief arrived at from incredulity. There's no model.

... Because of the wind loads they have been built to deal with, they are fifty times stronger than 200-foot buildings. To see them fail under their own weight is the mindblowing part ...

It may blow the minds of people who do not understand that wind loads (lateral forces; bend the whole structure, tend to increase loads low on the downwind side) and gravity loads are two different things, structurally dealt with in different ways.

Perhaps a "Truther" can be disabused of this particular blown mind when they finally understand, after a whole generation has grown up since it first appeared in NIST's FAQ and has been taught patiently to them, that the gravity load bearing capacity of the floor systems was the same at all levels and thus totally independet of height, and also essentially independent of wind considerations.

Another angle, I hope against hope, to get someone to understand the issue is to consider that buildings, particular such high-profil one-off buildings such as the WTC twins (the tallest building in human history up to that point) are carefull designed for well-defined loads and stresses:

• Lateral wind loads as caused by a hurricance wind of up to X mph windspeed
• Vertical (gravity) load including the weight of the structure itself plus the weight of any contents that may ever be put inside them up to reasonable maxima
• Fire loads representing some plausible worst case
• Others maybe

All of these design objectives have some maximum load or stress in mind. You exceed that maximum? Then all bets and guarantees are off!!!
Say you design a New York Skyscraper for at most a Category 4 hurricane, but then a category 5 strikes. Collapse ensues - can you wrap your mind around that?
Say you design the tower for a maximum total mass of 400,000 tons, but then D. Trump buys it and loots Fort Knox to have every column clad with 1-inch plates of gold, and weight increases to 500,000 tons. Collapse ensues - can you wrap your mind around that?
Say you design the tower for a fire that engulfs one floor, after a while a second, after a while a third, while sprinklers sprinkle and fire-resistant spray-on fibers slow the transfer of heat to the trusses, with a view to prevent collapse for at least 2 or 3 hours. But then someone starts fires on six floors by dumping and igniting 10,000 gallons of liquid fuel, removes a lot of fire-protectiv fibers, cuts water to the sprinklers, cuts large gaps into the walls for increased oxygen flow to fan the fires, and also to lower structural capacity to begin with. A total cluster-fuck of exceeding design objectives in several ways simultaneously. Collapse ensues after one hour - can you wrap your mind around that?

after a whole generation has grown up since it first appeared in NIST's FAQ and has been taught patiently to them

This, seriously, is a history that I am unaware of. Can you provide, say, ten key moments in this "teaching". I mean what, and how, was a generation "patiently taught" about the collapse of those buildings? Where did this teaching happen? What books were written? What documentaries were made?

What books were written? What documentaries were made?

that sounds very entitled

I just noticed this in the Salvadori book I linked to before (p. 49):
View attachment 84595
This is the sort of thing that suggests the truthers' "model" of the strength of the towers. Because of the wind loads they have been built to deal with, they are fifty times stronger than 200-foot buildings. To see them fail under their own weight is the mindblowing part for many people, even ones that don't become avid truthers. I don't think people should be ridiculed for finding it hard to understand. Their model should be acknowledged, respected, and corrected.

Some pedantry - the square law exists for buildings that maintain the same maximum width up their entire height, and corresponds to the force felt at the base of the building. It's from a simple integration of the torque (~width*height) over height, hence ends up being ~height^2. Does not apply to pyramids or shards or burj khalifas. Fortunately the WTCs were cuboids, so it does apply, but do not absorb this rule as a rule of thumb without understanding where it does and doesn't apply.

Please don't miss the significance of the two points I made.

I just noticed this in the Salvadori book I linked to before (p. 49):
View attachment 84595

Yes, but.... That is Engineering physics 001 - should not be in contention.

This is the sort of thing that suggests the truthers' "model" of the strength of the towers. Because of the wind loads they have been built to deal with, they are fifty times stronger than 200-foot buildings. To see them fail under their own weight is the mindblowing part for many people,

YES. "Mind blowing" incredulity was maybe 2/3rds of what was becoming the truther side audience when I first entered debate - 2006-7. Genuine, non conspiracy theorist people who did not comprehend the applied physics reality. Including quite a few engineers. In fact engineers who were out of their depth have caused me more challenges with explanations than any truther. The genuine truthers in those earlier times say 2006 thru about 2010 would split into the conspiracy theory never want to learn types and some genuine want to learn. The core of four "truthers" who contributed to my debates on JREF and The911Forum were all willing to learn.

...even ones that don't become avid truthers.

Yes. See my preceding comments.

I don't think people should be ridiculed for finding it hard to understand.

Yes.

Their model should be acknowledged, respected, and corrected.

If they have one. Not having a "model", not even having a concept of "overall scenario" affects many including engineers from both sides of the divide. It is a limitation for those debunker engineers I referred to previously. I have had one-on-one discussions with several leading truthers. eg Tony Szamboti and Wayne Coste. Both have difficulty putting an element of detail into a legitimate, fuller context.

All of these design objectives have some maximum load or stress in mind. You exceed that maximum? Then all bets and guarantees are off!!!
Say you design a New York Skyscraper for at most a Category 4 hurricane, but then a category 5 strikes. Collapse ensues - can you wrap your mind around that?

At risk of going further off the main track.

The issue of resistance to progressive collapse. Europe and Rest of World were ahead of USA designing for "soft fail". The WTC Towers were not designed for, were not required by regulation to be designed for, resistance to progressive collapses.

There is another complicating factor. The integration of fire resistance design with structural strength design. They were separately managed - not integrated - when the WTC Towers were designed.

So, yes, for the WTC Towers "You exceed that maximum? Then all bets and guarantees are off!!!" That correct but infamous comment by NIST. Words to the effect of: "From that point global collapse was inevitable".

Their model should be acknowledged, respected, and corrected.

A good example, which we've talked about here many times, is that some truthers think of the structure of the outer walls of the WTC as "hollow tubes" (cf. Salvadori, pp. 120-122), a model of which might be a piece of ordinary printer paper folded and taped into a square tube. It would stand up without any floors in place and could easily support 4x its own weight (four more pieces of paper) set on top. The truthers' "incredulity" stems from the fact that there is no way (they know of) to make this paper model strong enough to resist a piercing impact from the side and yet weak enough to be crushed by, say, 1/5 of it's own weight.

Now, obviously, this is not something people here would to take to be an adequate model of the WTC towers. But when you read Salvadori or watch videos about the ingenious (and infamous)* structural building designs you have to forgive people for thinking in these terms. After all, folding a piece of paper is, indeed, a pretty standard way of explaining the bracing function of a shear wall: set a piece of paper on its edge and it buckles in two dimensions. Fold it, and it stands up in three.

So my approach is just to respect this initial model and then try to find a way to correct it, i.e., complicate it up to the point where something they can get their minds around does actually collapse under its own weight. As I unfortunately always have to admit, I still haven't found a way to do this. And people here aren't very helpful because they simply don't take that second step of respecting where the truthers are coming from.

Some, to be sure, simply deny that any truthers are actually coming to the discussion with this sort of model in mind. That is, they don't even take the first step of acknowledging it. I obviously can't learn anything from them either. I'm fine with that, by the way. We all have our own little corners of the problem to work on.

-----
*I hope I'm following the linking policy to videos correctly when I now offer the example of Veritasium's really interesting episode about the 1978 Citicorp refit. It's not something I propose we discuss here, just an example of the sort of video that leads to thinking about building structures in ways that make the behavior the WTC towers puzzling. Note the part starting around 21:45 about the 10-block evacuation plan, which was made because of the risk that the building would topple over, something we've come tell truthers is a misunderstanding of how skyscrapers collapse. Let's not debate that here; I'm just saying that truthers can be forgiven for not applying popular engineering about other buildings precisely to the towers. By "forgiven," I of course simply mean "respected and corrected".

Take care Thomas B - we are drifting too far off the topic.

A good example, which we've talked about here many times,

I'm aware of multiple previous discussions. BUT this thread is about the latest Kostack Studios model.

It is a reasonably good picture. As good as I have seen.
But my primary reservations include:
What benefit does this simulation offer to understanding the Twin Towers collapses? AND
My often expressed concern - where is the line between "visual representation AKA 'Looks like" " and rigorous structural modelling. Because I have seen multiple previous discussions gloss over the distinction.

is that some truthers think of the structure of the outer walls of the WTC as "hollow tubes" (cf. Salvadori, pp. 120-122), a model of which might be a piece of ordinary printer paper folded and taped into a square tube. It would stand up without any floors in place and could easily support 4x its own weight (four more pieces of paper) set on top. The truthers' "incredulity" stems from the fact that there is no way (they know of) to make this paper model strong enough to resist a piercing impact from the side and yet weak enough to be crushed by, say, 1/5 of it's own weight.

How does discussion about 'paper modelling' assist assessment of the value of the Kostack alleged simulation?

Now, obviously, this is not something people here would to take to be an adequate model of the WTC towers. But when you read Salvadori or watch videos about the ingenious (and infamous)* structural building designs you have to forgive people for thinking in these terms. After all, folding a piece of paper is, indeed, a pretty standard way of explaining the bracing function of a shear wall: set a piece of paper on its edge and it buckles in two dimensions. Fold it, and it stands up in three.

So my approach is just to respect this initial model and then try to find a way to correct it, i.e., complicate it up to the point where something they can get their minds around does actually collapse under its own weight. As I unfortunately always have to admit, I still haven't found a way to do this. And people here aren't very helpful because they simply don't take that second step of respecting where the truthers are coming from.

Some, to be sure, simply deny that any truthers are actually coming to the discussion with this sort of model in mind. That is, they don't even take the first step of acknowledging it. I obviously can't learn anything from them either. I'm fine with that, by the way. We all have our own little corners of the problem to work on.

If understanding the collapse mechanism is the goal - it is relatively easy to explain for any person who is seriously interested.
And anyone who cannot comprehend a competent explanaton of what happened will NOT be able to relate the analogy of a model.
Does the Kostack model help our explanations?

Unsubtle HINT .. we are drifting way off topic AND back into circling debates we have had on many previous occsions.

Have you actually researched the evacuation plan before you made it part of your argument,

I haven't made an argument. I only offered the video as an example of a popular engineering presentation that might provide some context in which to empathize a little with how the truthers understand tall buildings.

or did you just assume it would support your point without checking? (Even the video contains clues why it might not.)

If the video itself can be used to correct this misunderstanding that would be excellent. (For my part, I've tried, without success so far, to draw load-path diagrams like the ones in the video that could help me understand the sorts of explanations that @econ41 has offered me, unfortunately also thus far without much success -- if by "success" we mean my getting it. After all, those diagrams do help me understand the dangerous situation that the Citicorp building was in and LeMessurier's predicament.)

I haven't made an argument.

Your argument was:

the 10-block evacuation plan [...] was made because of the risk that the building would topple over, something we've come tell truthers is a misunderstanding of how skyscrapers collapse.

You imply that the evacuation plan somehow proves that the claim "skyscrapers don't topple over like broomsticks" (or similar) is false.
I contend that it does not prove that.

In fact, the Kostack simulation is another illustration of this.

(Don't just draw load paths, play with them! Play a bridge building game, and you'll learn)

This, seriously, is a history that I am unaware of. Can you provide, say, ten key moments in this "teaching". I mean what, and how, was a generation "patiently taught" about the collapse of those buildings? Where did this teaching happen? What books were written? What documentaries were made?

Strangely, in your partial quote of my reply, you cut off a paragraph in mid-sentence, without also quoting WHAT it is that has been taught to "Truthers" (and I have next to no doubt that this includes you) - that follows immediately after your cut in the original:

"that the gravity load bearing capacity of the floor systems was the same at all levels and thus totally independet of height, and also essentially independent of wind considerations."
(Emphasis added)

Do you understand that "floor systems" is that part of the tower design between the columns - floor slabs, floor trusses, truss seats etc.?
You know, or don't you, that NIST's FAQ #18, created in September 2011, explains exactly what the limit of the vertical load bearing capacity of the floor systems was? I quote:

External Quote:

The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case).
[...]
...with a total vertical load capacity for the connections on a typical floor of 29,000,000 pounds...

Has no one ever explained, here or elsewhere that you are reading along, that if one floor system fails because more than (half of) 29,000,000 pounds fell on it, then all the floor systems below would likewise fall, because they all have a very similar capacity - it does not increase the further down you go in the tower.
You see, "Truthers" often point out that the columns got thicker the further down you go, because they carry an ever greater vertical load and thus needed an ever greater capacity.
But the floor systems did not.
However, the columns were mosty bypassed in the collapse. A high percentage of the falling material loaded floor systems dynamically, with an ever increasing mass.

That's why, once pancaking had started and not arrested after one or two floors, total collapse was inevitable.

You sure this has never been explained to a "Truther" while you were reading along?

I brought this up in the context of you talking about the towers needing to be "fifty times stronger" because of windload increasing disproportionally faster than building height and using that fact as an excuse for incredulity with respect to "To see them fail under their own weight". The "under their own weight" aspect is independent of the building hight when we are dealing with merely the vertical capacity of individual floor systems, which have the same capacity irrespective of the hight of the building or the heigt of the floor. And neither has much of anything to do with wind loads.

Kostack's simulation shows this (the progression "under their own weight" through the floor systems) "perhaps best in this version, where the wall nearest to the POV is made invisible so we can see that the floor systems are doing:
Source: https://www.youtube.com/watch?v=WpHXj62Ylw0&t=250s

Just follow the bulk of the debris that squeezes itself down between core and perimeter on both sides of the core.

In the video they say explicitly that the evacuation plan was made because there was a risk of toppling and, indeed, that this could be progressive, like dominoes:

how far would it need to topple to produce that domino effect?

and how far did we say that skyscrapers topple?

Strangely, in your partial quote of my reply, you cut off a paragraph in mid-sentence, without also quoting WHAT it is that has been taught

Sorry about that. Yes, you did mention one thing that has been said quite often these past 20 years or so. I thought you were implying a somewhat richer curriculum and a broader public. But I see what you mean now. Thanks for clarifying.

how far would it need to topple to produce that domino effect?

and how far did we say that skyscrapers topple?

Yes, I think these are good questions to answer for the people I have in mind.