# AE911 New Collapse Hypothesis

#### arsyn

##### New Member
(This is my first "real" post, so please go easy on me )

The AE911 folks are promoting another kind of numerical calculation of the collapse that centers around what they call the "crush-down" equation, which is a one-dimensional ordinary differential equation (ODE) that models a progressive floor collapse. They come in different varieties, of which the one by Ansgar Schneider [1a, 1b] is the one I have been looking more closely at (because a 9/11-truther at another forum was touting it, claiming it was proof of...something).

The model is, as far as I can see, not validated against any real empirical evidence, but is more like a numerical fitting of the ODE solution to the first few seconds of collapse of the North Tower, after which some extrapolation is done. Then, when the model predictions fail to replicate the empirical data (roofline measurements collected from videos of the collapsing building) after approx 4 seconds, an extra force term is inserted into the equation to adapt the model to the data. Schneider calls this "re-computation of the structural resistance of the building once the downward movement of the building has been quantified". In any case, the model is one-dimensional, it assumes a progressive collapse of one floor at a time. With the one-dimensional approach, he attempts to calculate the energy dissipation of the collapse, and argues that the extra inserted "resistance" force should be sufficient to arrest the collapse. In a recorded video presentation of the paper [2], Schneider presents his conclusion that "The building's structural resistance was reduced by some «unknown phenomenon»!" This conclusion is not in the paper, only in the presentation.

There are several things one can criticize about this approach, for example that it assumes a homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one. After seeing posts #119 and #120 in another thread [3], it occured to me that the basic assumptions Schneider - and also Bažant et al. (see references 2,3,4 in ref. [1]) - have made with the crushing front are false, as the collapse obviously did not happen as assumed in these naïve models. Thus, their approach is invalid.

My truther "opponent" over at the other forum initially acknowledged my criticism of Schneider's approach, but after a few more posts being thrown back and forth, he was back at insisting Schneider "proved" foul play. Now he's ghosting me. *Sob*

[1a] Ansgar Schneider: The Structural Dynamics of the World Trace Center Catastrophe, arXiv:1910.10801v2 [physics.class-ph].
[1b] Presentation of Schneider's paper at ae911truth.org
[2] Presentation of the paper at International Association for Bridge and Structural Engineering (IABSE) on September 5, 2019, available on YouTube.
[3] Debunked: The WTC 9/11 Angle Cut Column. [Not Thermite, Cut Later]

Edit: inserted ref 1b.

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I'm impressed they finally used a differential equation. I've long said that if something this dynamic is mathematically modeled without them, it's obviously BS.

This assumption of perfectly level, symmetrical pancaking is so bizarre. It's like looking at a shotgun wound and saying, "The shot pellets would have only created a bunch of little tunnels"... There must be an unknown phenomenon involved! Otherwise the observations are unexplained!

Welcome to the Forum @arsyn. And my congratulations for spotting the "elephant in the room" which has derailed, confused and generally caused a lot of misunderstanding of the central issues about the WTC Twin Towers collapse mechanisms over many years. This point:

There are several things one can criticize about this approach, for example that it assumes a homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one. After seeing posts #119 and #120 in another thread [3], it occured to me that the basic assumptions Schneider - and also Bažant et al. (see references 2,3,4 in ref. [1]) - have made with the crushing front are false, as the collapse obviously did not happen as assumed in these naïve models. Thus, their approach is invalid.
Exactly and well spotted. Excuse my enthusiasm but that simple observation has either been missed, misunderstood or vigorously denied over many years.

The principal error is that a lot of early attempts at explaining Twin Towers collapses followed the lead set by Bazant & Zhou in their 2001/2 papers. They did a quick "back of an envelope" assessment based on a 1D approximation. They used it as the basis of a "limit case". The logic of the "limit case" was accurate BUT a large number of persons did not understand it and assumed it was what literally happened. Those who made their mistake of "taking it literally" included many "debunkers" although the situation pre-dates the now established "two sides polarisation of debate" and the polarising terminology of "truthers" and "debunkers". It was the same error that also derailed Truther Engineer Tony Szamboti in his paper "Missing Jolt". Likewise the similar error by truther D Chandler and similar errors by J Cole. All of them failing to understand the actual collapse mechanism.

The central issue is that the key feature of WTC Twin Towers collapses - the rapid progression stage of collapse at about 2/3rds "G" - occurred because the falling debris missed the columns and landed on the floors. The columns were essentially missed - resulting in very little of resistance to falling. Hence the big error. "1D approximation" assumes that columns and floors are all taking part in what you correctly describe as an "homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one". That simply did not happen but most explanations prior to about 2009 presumed columns resisting and being buckled in the process.

The big irony which very few debunkers are prepared to acknowledge or even discuss >> Bazant fell for the same error in his 2007 paper with Verdure. That paper introduced the "Crush Down/Crush Up" hypothesis ["CD/CU"]. I assert that CD/CU is false as an explanation for Twin Towers collapse. From memory, there are four sources of error and three of them independently fatal to the CD/CU hypothesis applied to WTC Twin Towers.

That much should summarise where I agree with you and where I am "coming from". The central point "Bazant was wrong" is not acceptable to many.... Do you want to explore other aspects?

From memory - I will need to re-read the full paper - but the paper by Ansgar Schneider was essentially an 18 or so years regression to repeat the errors that many attributed to the Bazant & Zhou papers. B&Z did not fall for the trap. I assert that Bazant & Verdure did. We will probably need to review the details depending on where you want to take the discussion.

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Then, when the model predictions fail to replicate the empirical data (roofline measurements collected from videos of the collapsing building) after approx 4 seconds, an extra force term is inserted into the equation to adapt the model to the data. [...] With the one-dimensional approach, he attempts to calculate the energy dissipation of the collapse, and argues that the extra inserted "resistance" force should be sufficient to arrest the collapse.
So basically, he makes a model, which doesn't fit reality, then tries to make it fit by adding extra bits, and when it still doesn't work, he blames reality because obviously his approach is correct and hence reality must be wrong? Seems legit.

So basically, he makes a model, which doesn't fit reality,
Yes. Actually the model was an old one that he "borrowed" and tried to fix by add-ons without recognising the error in the foundation premise. He should have gone back to zero base or at least before the assumption of the false premise. It's a long complicated story but this is the key technical point:

The falling material missed the columns and landed on the floor. That crude graphic, as far as I am aware, was the first time the issue was explicitly identified in on-line posting. That was Nov 2007.

Most of the papers from "both sides" have assumed - many still assume - that the falling material landed on and "crushed" the columns. @arsyn is one of very few I have seen identify and critique the central issue. Hence my enthusiasm.

(This is my first "real" post, so please go easy on me )

The AE911 folks are promoting another kind of numerical calculation of the collapse that centers around what they call the "crush-down" equation, which is a one-dimensional ordinary differential equation (ODE) that models a progressive floor collapse. They come in different varieties, of which the one by Ansgar Schneider [1a, 1b] is the one I have been looking more closely at (because a 9/11-truther at another forum was touting it, claiming it was proof of...something).

The model is, as far as I can see, not validated against any real empirical evidence, but is more like a numerical fitting of the ODE solution to the first few seconds of collapse of the North Tower, after which some extrapolation is done. Then, when the model predictions fail to replicate the empirical data (roofline measurements collected from videos of the collapsing building) after approx 4 seconds, an extra force term is inserted into the equation to adapt the model to the data. Schneider calls this "re-computation of the structural resistance of the building once the downward movement of the building has been quantified". In any case, the model is one-dimensional, it assumes a progressive collapse of one floor at a time. With the one-dimensional approach, he attempts to calculate the energy dissipation of the collapse, and argues that the extra inserted "resistance" force should be sufficient to arrest the collapse. In a recorded video presentation of the paper [2], Schneider presents his conclusion that "The building's structural resistance was reduced by some «unknown phenomenon»!" This conclusion is not in the paper, only in the presentation.

There are several things one can criticize about this approach, for example that it assumes a homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one. After seeing posts #119 and #120 in another thread [3], it occured to me that the basic assumptions Schneider - and also Bažant et al. (see references 2,3,4 in ref. [1]) - have made with the crushing front are false, as the collapse obviously did not happen as assumed in these naïve models. Thus, their approach is invalid.

My truther "opponent" over at the other forum initially acknowledged my criticism of Schneider's approach, but after a few more posts being thrown back and forth, he was back at insisting Schneider "proved" foul play. Now he's ghosting me. *Sob*

[1a] Ansgar Schneider: The Structural Dynamics of the World Trace Center Catastrophe, arXiv:1910.10801v2 [physics.class-ph].
[1b] Presentation of Schneider's paper at ae911truth.org
[2] Presentation of the paper at International Association for Bridge and Structural Engineering (IABSE) on September 5, 2019, available on YouTube.
[3] Debunked: The WTC 9/11 Angle Cut Column. [Not Thermite, Cut Later]

Edit: inserted ref 1b.
All truther arguments about the collapse of the twin towers are a classic straw man fallacy. They misrepresent the "official theory" about the collapse of the towers, prove that their distorted version of events is not physically possible and then argue that government scientists who supposedly promote it must be either incompetent or lying. The paper by Ansgar Schneider is a prime example of this. Schneider provides volumes of scientific theory and calculations to show that the collapse of the twin towers should have slowed and been arrested after crushing only a few floors. But his initial assumptions are fatally flawed. The primary failure mode after collapse initiation was not crushing of the columns on each floor. It was progressive failure of the connections between the floors and the columns that allowed the floors to progressively collapse into the basement ("ROOSD"). Here is a picture of a sheet of 50 or 60 stories worth of exterior columns laid out on the ground, still mostly bolted together, that had peeled away from the North Tower after the floors had fallen away:

Pictures like this are NEVER presented on the AE911Truth website, in their literature or at their presentations and I am amazed that Ansgar Schneider did not consider this evidence before publishing his misleading paper.

@Marc Powell There is a long and, to me, amusing history of ironies associated with this current topic. Best suited to reminiscences over post-conference drinks. Two of the issues you identify in this paragraph actually have resulted in a collection of about six or seven overlaid ironies:

The paper by Ansgar Schneider is a prime example of this. Schneider provides volumes of scientific theory and calculations to show that the collapse of the twin towers should have slowed and been arrested after crushing only a few floors. But his initial assumptions are fatally flawed. The primary failure mode after collapse initiation was not crushing of the columns on each floor. It was progressive failure of the connections between the floors and the columns that allowed the floors to progressively collapse into the basement ("ROOSD").
The two issues:
(a) Schneider claims that in the 1D approximation progression would have been arrested. Bazant & Zhou claimed it wouldn't arrest. Yes - back in 2001 Bazant and Zhou didn't claim that the 1D approximation was what really happened. That mistake came later with Bazant & Verdure 2007. Yes Schneider was wrong in 2018?? to use 1D approx as if it really happened. BUT he may not have been wrong on the "would arrest". Another truther paper - by Szuladzinski, Szamboti and Johns came to the same conclusion. They claim B&Z's quantification of energy was wrong - overestimated. And AFAIK neither has been rigorously falsified.

(b) "ROOSD" - both the descriptive acronym and the explanation of the underlying mechanism was put into the mainstream discussion by researchers from the truther side. And ran into a wall of denial on the basis of "no truther can ever be right". And most of those doing the debunker side denying were accepting 1D approximation as per B&Z as being the real mechanism.

So two of the multiple ironies. First: NIST's finding "from that point global collapse was inevitable" appeared to be based on Bazant's limit case. If Bazant was wrong then NIST's presumption was flawed. BUT "ROOSD" proves that NIST was right.. So for a few years, NIST may have been "right for the wrong reasons" And second: NIST was proven right by truther research which debunkers disagreed with. It's best not to assume that all truthers are always wrong.

After that little side journey I'll return listeners to the scheduled broadcast ... err -- "topic"

The falling material missed the columns and landed on the floor. [..]

Most of the papers from "both sides" have assumed - many still assume - that the falling material landed on and "crushed" the columns.
Schneider does this in section 2.5. It results in an increasing resistance as the collapse progresses downward, because the cross-section of the beams increases:
External Quote:

In reality, with "pancaking" or ROOSD, the force should be essentially constant, simply the force required to break a floor loose; this explains why in reality the collapse didn't stop before the building hit the ground.

Proof that the columns didn't need to be crushed is a) the peeled-off facade columns, b) the "spire" of core columns. Maybe Schneider's approach can be used to justify the spire?

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So basically, he makes a model, which doesn't fit reality, then tries to make it fit by adding extra bits, and when it still doesn't work, he blames reality because obviously his approach is correct and hence reality must be wrong? Seems legit.
Afterthought: I believe this is where the rabbit hole opens for many people: because their thoughts and convictions don't match reality, they conclude that reality is not what it appears to be.

Schneider does this in section 2.5. It results in an increasing resistance as the collapse progresses downward, because the cross-section of the beams increases:
Yes. Hence some of the ironies I alluded to in a previous post. The 1D approximation does not match what really happened. It was a legitimate approach to defining a "limit case" as was Bazant & Zhou's intention with their 2001/2 paper. But two truther side papers - both I think legitimately peer-reviewed and published - claim that B&Z's quantification of energy was wrong.

With "pancaking" or ROOSD, the force should be essentially constant, simply the force required to break a floor loose.
Yes. Actually three main "resistance" forces are readily identified. In order of magnitude:
(a) The force associated with changes of momentum as debris is accumulated with the successive shearing off of each floor;
(b) The force to shear off the floor joist to column connections (see the response to next paragraph); AND
(c) Some friction forces resulting from the debris "rubbing down" the faces of the columns.

The momentum forces alone account for much of the 1/3rd "G" "lost" as the progression fell at approximately 2/3rds "G". Ironically a lot of early researchers quantified the momentum and several studies agreed that it was the dominant force causing the reduction from free-fall acceleration to the measured ~2/3rds "G" And many also identified debris landing on floors. But it wasn't until 2007 that any explanation explicitly identified what became known as ROOSD (Runaway Open Office Space Destruction.) But It was 2009 onwards before the mainstream debate started to add the bits together. And it was contentious because the key element - "ROOSD" and the errors derived from Bazant associated errors - were put into debate by truther side researchers. And it disagreed with the prevailing debunker side "wisdom".. ' And we all know that truthers can never be right...
Proof that the columns didn't need to be crushed is a) the peeled-off facade columns, b) the "spire" of core columns. Maybe the approach can be used to justify the spire?
Yes. In hindsight is should have been bleeding obvious. BUT most research up till those events in 2007 and 2009 had focussed on gross motions and macro scale measurements plus 1D approximations.

The spires are easily explained if you slightly extend the ROOSD concept. ROOSD as defined by researcher "Majot_Tom" strictly only referred to the shearing of the floors in the office space outer tube. Major_Tom sometimes includes the toppling fall away of the perimeter column sheets within the scope of ROOSD. Then I extended the definition to "three sub-mechanisms" viz (a) ROOSD stripping the OOS floors; (b) Perimeter columns peel off and fall away; and (c) Core Strip Down shearing the beams of the core area off the columns. So the "full explanation" of the concept that ROOSD - debris falling on floors - would and probably did operate analogously in the core area. i.e. causing the core beams to fail in the same manner that the OOS floor joists failed. Hence the core area "spires" were stripped clean of horizontal beams. And happened that some of them remained standing for a few seconds.

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Let me try a summary:

The AE911 presentation of the A Schneider paper claims this key assumption:

Schneider’s approach is to assume that Bažant’s mathematical model of a progressive collapse is valid.

This assumption is wrong: Bažant’s mathematical model of a progressive collapse, at least as Schneider applies it, is NOT valid.

Schneider's paper is not very explicit on what that "model of a progressive collapse" actually is, as he separates the two main elements (doesn't mention them in the same sentence or even paragraph in the introduction).

Here is the first element - on page 2:

#### 2.2. Progressive Floor Collapse​

In a series of papers Bažant et al. [2,3,4] have proposed the model of a progressive floor collapse: After the failure of one storey the falling top segment of the building impacts the structure below, then floor by floor the building structure is destroyed (cp. Figure 1).

I.e. a claim that the destruction is "floor by floor", and thus repeats at every single one of 110 (or 95 or whatever) floors.

And here is the second element - on page 3:

#### 2.3. The Crush-Down Equation​

[...]
So momentum conservation yields an ordinary differential equation [...] wherein [...] F(z) is the upward directed resistance force of the crushing columns (that is the quantity in which we are interested); [...] The origin [...] of the term involving F(z) is obvious.

I.e. a claim that columns provide an upward resistance as they are being crushed. This second element of Schneider's assumption is hidden well and not made explicit, let alone justified, in the previous segment, which purported to present the (elements of the) "Progressive Floor Collapse"

Together then, Schneider's assumption is that columns (all columns - an implicit additional assumption!) are being crushed on all floors. Nothing could be further from the truth, as the most cursory inspection of the columns post-collapse immediately and very obviously reveals: Very nearly no column was "crushed" (nor was any column manipulated in any way to not be able to resist design loads by any other mechanism: almost all columns were still whole and straight).
And anyway, there is direct visual evidence that many columns were not in the collapse path: The core "spires" - part of the core standing as tall as 70 floors still standing for several seconds after the "crush front" and the "roofline" that Schneider tries to model have gone by; and the images of large segments of perimeter column having toppled over to the sides.

I find it mildly amusing that he would make that odd remark "The origin [...] of the term involving F(z) is obvious" - it is a matter of many science jokes that whenever a scientist says "xyz is obvious", that's a euphemism for "I cannot explain or prove it, I hope you will just believe me because I say so".

With the central assumption so wrong, any conclusion Schneider draws about the actual collapses must be considered invalid,
(His conclusions about any previous work that share the same false assumptions may or may not be correct and valuable)

Afterthought: I believe this is where the rabbit hole opens for many people: because their thoughts and convictions don't match reality, they conclude that reality is not what it appears to be.
Agreed though I've also explained it more cynically. The shorthand version says: "It is too complicated for me to understand. It cannot be limitations of my knowledge or reasoning skills. So it must be someone else's problem. Who to blame >> government or authority of "the Man" are easy targets." And a lifetime of blaming "them" creates a conditioned reflex - "Anything I don't understand is not my fault - "they" are to blame. "They" must be lying".

I have a far more rigorous explanation - but it is better suited to a psychology forum than one dominated by engineers and other technocrats. And as an engineer, I wouldn't expect an easy time on a forum of professional psychology/psychiatry persons. It's hard enough being an iconoclast engineer disagreeing with practising structural engineers and similar scientist types.

I have always accept the ROOSD explanation for what was happening in the "destruction" of the lower blocks in both towers.

If the top blocks lost axial support the mass would be what was required for ROOSD. The issue may be was the floor failures in the lower block failures of truss connections to the perimeter and the core's belt girder?.... Or was it a more overall footprint shattering of the floor slabs... inside and outside the core? If the floor collapse was an overall shattering of the floor slabs one would also expected to see failure of the truss connections to the frame.

Seems to me the idea of pancakes is quite absurd. However if the collapse front was "uniform" over the footprint... each floor would fail at "once" breaking up under the force of the ROOSD mass. The floors collapsed at about 1 floor for each 1/10 of a second. I suspect that sounded like a continuous thundering.

The top blocks seem to have maintained integrity (at least the shells) and appear to move as blocks... self destructing on impact with the lower blocks.

Thank you everyone for interesting replies. You all have interesting arguments worth pursuing. In any case:
That much should summarise where I agree with you and where I am "coming from". The central point "Bazant was wrong" is not acceptable to many.... Do you want to explore other aspects?

In section 4, Schneider concludes that
It seems to be crucial to point out that the sometimes expressed belief that the building structure was a priori too weak to arrest the collapse after it had begun is false (even after the top segment of the building had gained a significant amount of momentum).

As I see it, we have three options here:
1. The collapse was indeed (temporarily) arrested, which is what we see in the images below, with the remains of the core from the South Tower and a remaining wedge-like pointy structure (from the viewpoint of the photographer) from the North Tower (images from this posting). But that presents Schneider with the problem that the rest of his paper and his conclusions are nonsense.
2. The collapse did not happen as modeled, which is a problem for the entire paper and his model.
3. All of the above.

So what is Schneider trying to say with the above quote? Is it a camouflaged reference to controlled demolition? In any case, he is wrong whichever way you look at it.

The following quote from Richard Feynman is as relevant as ever:
It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong.

Most of the papers from "both sides" have assumed - many still assume - that the falling material landed on and "crushed" the columns. @arsyn is one of very few I have seen identify and critique the central issue. Hence my enthusiasm.

I have only recently started to take an interest into the actual mechanisms of the collapses and the truther claims. The truther with the Schneider paper I speak of in the op was what caught my attention(*). Although the floor-by-floor column buckling assumption sounded ludicrous to me, I couldn't quite formulate exactly why. So I initially criticized some other more technical points about the model and the calculations, like the total absence of consideration of lateral forces on the columns/beams and snapping of joints once the collapse started, and the actual geometry of the "crush-down front" (how realistic was a homogenous and flat front – couldn't it just as well be wedge-shaped(**)?). But it was only after seeing the images of the structure parts still standing that it occured to me that the basic assumption of the progressive floor-by-floor collapse was erroneous.

(*) He initially tried to use flattery to try to lure me down the rabbit hole (he failed, I'm by nature immediately skeptical about the motives once flattery is directed at me for trivial observations or for no reason), but once he realized he was unsuccessful and was not able to dictate the direction of the discussion and the topics, he turned 180 degrees and started belittling me and started acting like a fundamental religious zealot.

(**) If we look at how the collapse started (see video below, at approx. 1:40), the collapse starts roughly in the middle, so the "crushing front" is obviously not flat and homogenous.

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The major point Schneider intends to make with the paper linked in the OP, and with its predecessor, is that he has empirical data that would imply that the resisting forces during the collapse did not increase steadily - they started low, then increased by an order of magnitude over the height of about 10 stories, and then went down again.

Let me explain:
He lists 5 data points - pairs of time in s and roof line height in m, and plots them in Figure 3.
Here are the data points (numbers as per the paper):

 Data point​ height​ time​ avg. velocity​ #​ m​ s​ m/s​ (5)​ 408​ 1,64​ ​ (6)​ 383​ 3,2​ -16,03​ (7)​ 349​ 4,57​ -24,82​ (12)​ 312​ 7,71​ -11,78​ (13)​ 285​ 9,25​ -17,53​

The last column is mine - I simply calculate delta-height divided by delta-time.

The simple take-away is that velocity increases from (5-6) to (6-7), then decreases to (7-12) and increases again to (12-13). This means acceleration is negative, then positive, then negative, and the curve for resisting force will have a similar shape (just multiplied by a steadily increasing mass involved).

So even if the "Crush-Down Equation" that Schneider uses incorrectly assumes that the resisting force is proportional to column thickness, that's not really the issue here. He tries to fit that function to the five data points, and finds it's not possible because neither force nor velocity nor acceleration are steadily increasing or decreasing. The thing is: Any sensible - and thus "correct" - function describing the collapse dynamics would assume that the building is pretty uniformly designed from top to bottom, with every important parameter either being constant throughout (i.e. mass of floor slab) or increasing steadily (i.e. accumulating mass, mass and strength of columns, ...), and hence any such function would yield steady curves for all important variables.

I am attaching here Fig 3(B) from the paper. The five pairs of black lines represent the five data points, The red curve is a solution for his "Crush Down Equation" with an initial average resisting force chosen to best fit the first three points. The other two curves introduce an additional force term that's active between 363 and 318 meters of roof height.

The unsteadiness of velocity according to his five data points would be difficult to explain no matter what collapse mechanism you propose and model, it's not (just) a result of him assuming column crush.

---

But the data points are problematic: They are derived from three different source videos (Sauret, CBS, History Channel), and measure the height of four different things (some point on roofline, some point on antenna, two different puffs of dust) to approximare a different fifth thinng (the height of the crush front), while making the invalid and false assumption, that at any time there is one defined height of the crush front.
To translate roofline to crush front, he applies two further assumptions, both of which are burdened with some degree of uncertainty: a) That the structure above the crush zone stays neatly on top of the compacted debris layer and does not itself collapse any bit, ever; b) That the debris layer grows in thickness, at its bottom, by 15% of a floor height per every floor crushed.

In previous papers, Schneider has gone to great lengths and troubles to synchronize and calibrate the source videos and justify his measurements, and that's way too much for me to check out in all glorious detail, so I don't know yet if and how he perhaps has already addressed my points of caution.

---

The interpretation that all this is supposed to suggest, is this:
That this interval between 363 and 318 meters represents the "real" resisting forced you'd expect from a gravity collapse (velocity goes down! collapse arrests eventually!), while before and after, it was helped by blasting to smithereens 90% of the columns.

The thing is: Any sensible - and thus "correct" - function describing the collapse dynamics would assume that the building is pretty uniformly designed from top to bottom, with every important parameter either being constant throughout (i.e. mass of floor slab) or increasing steadily (i.e. accumulating mass, mass and strength of columns, ...), and hence any such function would yield steady curves for all important variables.

If I'm pouring cornflakes out of the bag, they appear uniform, but don't come out evenly, and on a small opening, can even get stuck ("arrested"). Because the collapse was initiated asymmetrically (top block tilting), it's foolish to assume it progressed symetrically, so some chaotic interactions are to be expected.

If the best source of data is pixel counting in a dust cloud, we have inaccuracy on top of irregularity.

Why would hypothetical conspirators want to accelerate a collapse that, by the same theory, was meant to look "natural"? I can only see drawbacks to that strategy, no benefit.

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If I'm pouring cornflakes out of the bag, they appear uniform, but don't come out evenly, and on a small opening, can even get stuck ("arrested"). Because the collapse was initiated asymmetrically (top block tilting), it's foolish to assume it progressed symetrically, so some chaotic interactions are to be expected.

If the best source of data is pixel counting in a dust cloud, we have inaccuracy on top of irregularity.

Why would hypothetical conspirators want to accelerate a collapse that, by the same theory, was meant to look "natural"? I can only see drawbacks to that strategy, no benefit.
There is no such bottleneck as the cereal box opening in the WTC towers.
Schneider is correct that his data, if it fairly represents how the bulk of mass moves (ideally: The center of gravity of the accumulating top and debris part) implies that resisting forces went up by roughly an order of magnitude after 8 floors or so, then went down again. That would be such a huge change, I'd want to have a better explanation than "well, how about cornflakes".

I am convinced the problem lies with the data, not with unidentified mechanisms that we yet fail to account for.

For example, the last data point responds to the very last puff of dust that Schneider could identify as being caused by the collapse front, before everything is shrouded by a cover of falling dust and debris. It therefore is also the lowest such puff, the most advanced, and thus more likely an outlier than representative. Perhaps it is with the other way around with the second-to-last data point: that Schneider picked the highest dust ejection he could find.
Furthermore: I am quite certain that, at least early on (first 2, 3, 5 floors), the roofline accelerates downward faster than the budding collapse front, on account of loose colums easily punching through floor slabs.
Correcting for any of these alleged systematic errors would make Schneider's curve steadier.

As I see it, we have three options here:
1. The collapse was indeed (temporarily) arrested, which is what we see in the images below, with the remains of the core from the South Tower and a remaining wedge-like pointy structure (from the viewpoint of the photographer) from the North Tower (images from this posting). But that presents Schneider with the problem that the rest of his paper and his conclusions are nonsense.
2. The collapse did not happen as modeled, which is a problem for the entire paper and his model.
3. All of the above.
Take care. There are TWO fundamental options which are:
1) Analyse and discuss the actual mechanism of the real collapse which DID NOT have columns "in-line" offering resistance and being overcome by "crushing" OR

2) Analyse, discuss and possibly attempt to identify and correct errors in assumed models which do not adopt the actual mechanisms of 9/11.

No amount of fog, obscurity or mental gymnastics will correct a fundamentally wrong model to make it a valid model of what really happened. (And I recognise the risk I take in resorting to global claims hyperbole.) Schneider has columns "in-line" You @arsyn and I explicitly identify that was not the situation with the real event. I have no problem with persons who want to discuss Schneider's, Bazant's, Szamboti's or any other persons abstract model of what never happened. Provided they don't slip into the trap of arguing as if it was the real event.

So:
1: ....But that presents Schneider with the problem that the rest of his paper and his conclusions are nonsense.
True. He is wrong for two very distinct types of errors viz:
(a) He has the wrong model - he has columns in line - so he is not discussing the real event << And that is fatal before we adress the errors of maths and other details.
(b) His numbers for his imagined scenario seem to be wrong. << If anyone wants to correct his maths or details of physics - go for it but don't assume it has any relation to the actual event UNLESS you present argument showing why you consider it to be relevant.

2. The [ACTUAL] collapse did not happen as modeled [by Schneider], which is a problem for the entire paper and his model.
True if anyone conflates abstract modelling with the real event. The exact problem which confounded debate of the issue for many years. You CANNOT "mix and match" (say) arguments from an abstract model with measurements from a different real event. (That was one of the errors made by T Szamboti in his own "Missing Jolt" paper which makes similar errors to Schneider's.)

3. All of the above.
Even that option risks conflating actual event with wrong abstract model. The two difference models are mutually exclusive.

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Take care. There are TWO fundamental options which are:
1) Analyse and discuss the actual mechanism of the real collapse which DID NOT have columns "in-line" offering resistance and being overcome by "crushing" OR

2) Analyse, discuss and possibly attempt to identify and correct errors in assumerd models which do not adopt the actual mechanisms of 9/11.

You are of course correct here, and I think we speak of different aspects of the same thing. However, I am open to me being guilty of sloppy formulation and not making my assumptions clear enough. Let me see if I can formulate it more properly.

1. If we (for the sake of argument) assume Schneider's model is correct, the images show that the collapse was indeed (temporarily) arrested for at least parts of the structure, with the remains of the core from the South Tower and a remaining wedge-like pointy structure (from the viewpoint of the photographer) from the North Tower still standing after the main collapse. This means that Schneider's assumption of total floor-by-floor collapse all the way down, the discussion and conclusions are wrong.
2. The wedge-like shape of the still stading structure after the main collapse combined with (what seems to me) no visible signs of column buckling strongly suggests that the collapse did not happen as modeled by Schneider. This means that Schneider's modelling does not reflect the actual physics of the collapse. It is therefore wrong, and the entire paper is nonsense.

Giving as much benefit of doubt as possible to Schneider, we could hypothetically have a Schneider-like collapse down to the parts still standing, where a new collapse mode (again hypothetically) started. This, however, sounds extremely unlikely to me, as the Schneider-mode with column buckling would likely require much more energy per height unit than ROOSD (provided I have understood it correctly). In other words, to have the collapse start with a high energy dissipation mode that switches to a lower energy dissipation mode as momentum builds up sounds unlikely. But considering this scenario is purely academic nitpicking. Further, empirical evidence from the post-collapse site does not (as far as I understand it) support it, with there not being found any evidence of large-scale column buckling in the upper part of the debris pile. This scenario therefore seems highly unlikely.

In any case, Schneider's model - and by extension Bažant et al. - lack, as far as I know, empirical verification against similar physical structures, either through detailed physics-based modelling, experiments, scale models or other building collapses. This alone makes me dubious whether these 1D-models have any predictive (or even explanatory) power at all.

In short, even if Schneiders model is plausible, his paper make wrong assumptions, he applies a model not reflecting the actual physics involved, and thus asks the wrong questions and give the wrong answers.

(b) His numbers for his imagined scenario seem to be wrong. << If anyone wants to correct his maths or details of physics - go for it but don't assume it has any relation to the actul event UNLESS you present argument showing why you consider it to be relevant.

Being a physicist by training, I think discussing models, different approaches to attack a problem and what if-scenarios can be an interesting academic exercise in and of itself. But, ultimately, empirical data is king.

Edit: Some minor modifications.

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That would be such a huge change, I'd want to have a better explanation than "well, how about cornflakes".
well, how about one of the mechanical floors

there's irregularity in how far down core columns were destroyed
I think there's irregularity in different amounts of energy getting lost by different materials being ejected
heck, maybe some companies used extra sturdy furniture

and on top of that the data isn't great
so maybe it's a bit of both

You are of course correct here, and I think we speak of different aspects of the same thing. However, I am open to me being guilty of sloppy formulation and not making my assumptions clear enough. Let me see if I can formulate it more properly.
We are playing the same tune. We are not quite agreed on the rhythm or dynamics... YET. If I drop the musical metaphor we are agreeing on the principles, not quite using the same words to describe things. YET!!

1. If we assume Schneider's model is correct, the images show that the collapse was indeed (temporarily) arrested for at least parts of the structure, with the remains of the core from the South Tower and a remaining wedge-like pointy structure (from the viewpoint of the photographer) from the North Tower still standing after the main collapse. This means that Schneider's assumption of total floor-by-floor collapse all the way down, the discussion and conclusions are wrong.
2. The wedge-like shape of the structure combined with (what seems to me) no visible signs of column buckling strongly suggests that the collapse did not happen as modeled by Schneider. This means that Schneider's modelling does not reflect the actual physics of the collapse. It is therefore wrong, and the entire paper is nonsense.
The last two sentences are most important. They outrank the other considerations. The two facts that: "It is therefore wrong, and the entire paper is nonsense." are FATAL to any attempt to directly use Schneider's paper to explain the "real event". What "really happened". Then:
"If we assume Schneider's model is correct..." puts us into discussion of an abstract scenario. A "moot" discussion. And all your comments which follow are legitimate topics for moot discussion. But never forget that they are not "real event".

I would reverse the order of paras "1" and "2" - put "2" first - it puts them in better relationship.

In any case, Schneider's model - and by extension Bažant et al. - lack, as far as I know, empirical verification against similar physical structures, either through detailed physics-based modelling, experiments, scale models or other building collapses. This alone makes me dubious whether these 1D-models have any predictive (or even explanatory) power at all.
There is a whole PhD dissertation project in that concept. Around 2013 I attempted to discuss with a couple of otherwise switched on engineering debunkers how we could make Bazant's "CD/CU" hypothesis work. It required modifying one of the energy factors in his equation to allow for "column spread" >> the extent to which open office space wide column spacings make 1D approximations less valid as the column spacing increases. Clearly if a building was all column - no spaces - it would be legitimately "homogeneous". If columns spacings are small - little space between columns - the scenario still approximates homogeneous 1D. The wider the spacing the less homogeneous the less valid the 1D approximation. So let's see if we can create a formula with fakes homogeneity... The idea simple enough. But my two colleagues bailed out as soon as they realised I was saying "Bazant was wrong". Apparently that amounts to "lèse-majesté". AKA High Treason.

In short, even if Schneiders model is plausible, his paper make wrong assumptions, he applies a model not reflecting the actual physics involved, and thus asks the wrong questions and give the wrong answers.
Yes. That should be bleeding obvious. Sadly for many years it wasn't obvious to many people.
Being a physicist by training, I think discussing models, different approaches to attack a problem and what if-scenarios can be an interesting academic exercise in and of itself. But, ultimately, empirical data is king.
I'm retired engineer with both civil and military qualifications and experience. So I'm a practical applied physicist. And biased by both my careers to making timely operational decisions. When your part of the world is running in real time you have to make the decisions that have to be made. You cannot wait for all the committees to agree or better research completed.

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I have only recently started to take an interest into the actual mechanisms of the collapses and the truther claims. The truther with the Schneider paper I speak of in the op was what caught my attention(*). Although the floor-by-floor column buckling assumption sounded ludicrous to me, I couldn't quite formulate exactly why.
My own introduction to WTC Collapse physics was very different. I saw the "plane strikes >> tower collapses" as breaking news on the day. I was on holiday in UK. My initial reactions called on my civilian brain - initially didn't realise it was real, then horror. Then after about 10 seconds my callous military-trained brain took over and I stored the technique away for future reference. "How to use planes to demolish a highrise tower!" I forgot about it until 2007 when, as the City Engineer of my former city of residence, I was approached by the son-in-law of a former Mayor. He was a conspiracy theorist and asked for my comments about the "CD of the Twin Towers". I laughed before I realised that he was serious. Having regard to my professional credibility in small-town politics I realised that I needed to give him a serious professional opinion. That led to me discovering online forums and I set about understanding the Twin Towers collapse physics.... In Nov 2007 I joined a high-grade forum that was not mainstream for 9/11 debate. (The former Richard Dawkins Forum - strongly into biological science.) And I was the only engineer sceptic posting on the WTC Threads.

I know, in hindsight, that most of the early 9/11 debate was lost down false trails... as per my hinted comments in several recent posts. The details can wait. But I made a couple of naive choices within a few days of starting to post on the forum. The first was my recognition that claims for CD at WTC were trivial - the real issues were in the politics. So I thought my goal was to "clear up this CD nonsense so we can discuss the real issues in politics". Naive as I said. The second became a big advantage. Since I was wanting to teach laypersons I couldn't be sidelined into reading all the academic material which was written in complicated language and "confuse the laypersons" styles. So I simply explained what really happened with this crude graphic:

.. And not being on a mainstream 9/11 forum I wasn't trapped into following the several false trails that dominated debate pre about 2007-8-9 I never realised for years that explaining the real event was NOT the prevailing wisdom. So, tho' I've never pushed the claim about "first to publish", I was probably the first to explicitly identify that "real mechanism". Major_Tom - a truther side researcher - published exactly the same thing labelled "ROOSD" in 2009. Several years of denial and mental gymnastics followed - it is a long and complex story that is not relevant now. BUT you will still encounter reservations and outright denials of both the process and the label "ROOSD" on the spurious ground that it was invented by a truther and truthers can never be right. You may notice that I disagree.

But it was only after seeing the images of the structure parts still standing that it occured to me that the basic assumption of the progressive floor-by-floor collapse was erroneous.
I cannot recall my own "Eureka" point. To me it was bleeding obvious once I started looking for understanding BUT - remember - I was not mixing with mainstream 9/11 debaters. I may have been trapped into going with the crowd if I had joined with the mainstream before I understood what I was seeing.

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So, tho' I've never pushed the claim about "first to publish", I was probably the first to explicitly identify that "real mechanism".
Well, NIST can't have been far behind, there's a "FAQ Supplement" of December 14th, 2007:

1. Was there enough gravitational energy present in the World Trade Center Towers to cause the collapse of the intact floors below the impact floors? Why was the collapse of WTC 1 and 2 not arrested by the intact structure below the floors where columns first began to buckle?
Yes, there was more than enough gravitational load to cause the collapse of the floors below the level of collapse initiation in both WTC Towers. 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). Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC Tower (12 and 29 floors, respectively), the floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings. Details of this finding are provided below:

NIST NCSTAR 1-6D only says "global collapse ensued".

The last two sentences are most important. They outrank the other considerations. The two facts that: "It is therefore wrong, and the entire paper is nonsense." are FATAL to any attempt to directly use Schneider's paper to explain the "real event". What "really happened". Then:
"If we assume Schneider's model is correct..." puts us into discussion of an abstract scenario. A "moot" discussion. And all your comments which follow are legitimate topics for moot discussion. But never forget that they are not "real event".

To use another metaphor, I think we are at different chapters in the same book. It seems to me you are reading the "This is what happened" chapter, using your experience and insight into civil engineering as a basis for understanding it, while I'm in the "This is what not happened, and why" chapter, using my background in physics and experience in R&D.

Since my introduction to looking at the collapse mechanics was to argue with a conspiracy-minded truther and to criticize the simple model he takes as gospel, I am still in a debunk-the-bunk mode. So I am taking the more academic approach of showing that Schneider got it wrong in this paper, regardless of whether his model reflect actual physics or not, by looking at the central assumptions he makes. Then, by pointing to empirical observations that contradict his assumptions, conclude that his equation and method is irrelevant, as he is arguing against something that didn't happen. In other words, he is beating away at a straw man. Or, if you prefer, flogging a dead horse.

Even though the model is a pile of matter expelled from the rear end of an animal in the bovine family, I still find it mildly interesting to explore the model to find out what it gets wrong and why, and to use this as ammunition against the arguments coming from the conspiracy-minded truther camp. This approach allows me to explain why they are wrong, not just making contrary assertions. That's the idea, at least. "My" truther has by now clammed up regarding the Schneider model, realizing he's getting nowhere. When I discuss this and other bunk on online forums, my main goal is not necessarily to convert the belivers, but to demonstrate to the silent readers/bystanders that the claims made by the deniers (of whatever flavour) do not stand up against critical investigation. If that can prevent others from going down whatever rabbit hole is nearby, it is time well spent.

I would reverse the order of paras "1" and "2" - put "2" first - it puts them in better relationship.

The order of the two paragraphs is not important to me, so I will gladly reverse the order.

Well, NIST can't have been far behind, there's a "FAQ Supplement" of December 14th, 2007:
NIST almost certainly understood the situation. The problem was that in general debate the discussion diverged mostly down two paths.
1) Those who took Bazant's "limit case" - B&Z 2001/2 - literally; OR
2) Didn't realise the significance of "columns not in-line"...

and a lot of the participants in the debate got themselves lost between three conflicting bits of explanation. (1) The falling material landed on and sheared off the floors. (NIST says that) (2) Most of the papers claimed floors were crushed - i.e. implicitly accepting an homogeneous 1D approximation which in turn subsumes the false presumption of "columns in-line and resisting; WHILST (3) Most of the online debate was attempting analysis by macro motions and energies - specifically NOT considering the actual mechanisms. And that also implicitly subsumes 1D approximation.

Bottom lines:
(a) - yes NIST seemed to understand but it was not explicitly clear in the reports and most people missed it. Which is why I said "explicitly".
I was probably the first to explicitly identify that "real mechanism"
AND
(b) Most debate was focussed on macro approximations - few if any attempting to explain the actually observed collapse mechanisms.

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To use another metaphor, I think we are at different chapters in the same book. It seems to me you are reading the "This is what happened" chapter, using your experience and insight into civil engineering as a basis for understanding it, while I'm in the "This is what not happened, and why" chapter, using my background in physics and experience in R&D.
EXACTLY!!! You correctly identify the different approaches. My motivation and goal has always been "explain what did happen" rather than "debunk the errors". Which by the way causes me frustration with this forum. It is arguably the best currently active forum but my goal is explaining NOT "debunking". "Debunking" too often locks you within the limiting scope and constraints of the "bunk" argument.

Since my introduction to looking at the collapse mechanics was to argue with a conspiracy-minded truther and to criticize the simple model he takes as gospel, I am still in a debunk-the-bunk mode. So I am taking the more academic approach of showing that Schneider got it wrong in this paper, regardless of whether his model reflect actual physics or not, by looking at the central assumptions he makes. Then, by pointing to empirical observations that contradict his assumptions, conclude that his equation and method is irrelevant, as he is arguing against something that didn't happen. In other words, he is beating away at a straw man. Or, if you prefer, flogging a dead horse.
Agreed. And even your choice of metaphoric language aligns well with my own preferences
Even though the model is a pile of matter expelled from the rear end of an animal in the bovine family,
I often use similar constructs e.g. "The probability is less than the likelihood of aeronautical exploits by members of the family Suidae"
I still find it mildly interesting to explore the model to find out what it gets wrong and why, and to use this as ammunition against the arguments coming from the conspiracy-minded truther camp.
Whilst I prefer to work from the scenario of what actually happened.
This approach allows me to explain why they are wrong, not just making contrary assertions. That's the idea, at least.
Sure. I also can explain what is wrong if it is the best approach in a given discussion. My broader goal is that "they" understand what really happened so "they" can see for themselves why "they" are wrong. BUT it is at least 8 years since I met an old-style, honest, who wants to learn truther. The demography of trutherdom has shifted a long way. Sadly downhill.
"My" truther has by now clammed up regarding the Schneider model, realizing he's getting nowhere. When I discuss this and other bunk on online forums, my main goal is not necessarily to convert the belivers, but to demonstrate to the silent readers/bystanders that the claims made by the deniers (of whatever flavour) do not stand up against critical investigation. If that can prevent others from going down whatever rabbit hole is nearby, it is time well spent.
Understood. In my 14-15 years of experience the goal of "preaching for the lurkers" has, sadly, become a lot less effective than it possibly was in the heyday of debate - the "both sides learning" era of 2006-7-8-9-10. Most currently active truthers are resorting to trolling because all the legit truther technical questions have been asked and answered many times.
The order of the two paragraphs is not important to me, so I will gladly reverse the order.
I tend to be pedantic about "issue taxonomy". The logical ranking of importance of the parts of an argument. The whole system is "higher" than the sub-systems. And if the system is fatally flawed the sub-systems are irrelevant.

(a) - yes NIST seemed to understand but it was not explicitly clear in the reports and most people missed it. Which is why I said "explicitly".
I understand that. Which is why I gave the quotes that showed the 12/2007 FAQ was explicit, but the 2005 report wasn't (as far as I could see). They kind of say in the report that there was floor damage and the floors lost their seating, but that feels more like it's still initiation and not quite progression yet. I suspect the authors of the report expected the floors getting overloaded to be a kind of no-brainer consequence.

This image! Which images has this composite been made from, and/or where can I find the source images?

Which part of a floor in the WTC towers fails when overloaded past ~29,000,000 pounds is Not understood by AE911T, as they "beg" for more money. I stopped looking up their 990 tax returns for nonprofits after they bilked millions from people. I suspected tax fraud could be in play, some contributed substantial amounts.

Bazant's work is theoretical, academic work... those who start their fantasy attacking Bazant's papers, is a sign nonsense is coming, in this case the collapse would have been arrested. AE911 truth can't change the fact the floors fail, even when the core and shell become stronger and thicker.

The floor collapse is trivial engineering. All materials... assemblies... have strength characteristics... the floors can only suppose X pounds per square foot. When this limit is exceeded... the assembly (floor) will fail.

This image! Which images has this composite been made from, and/or where can I find the source images?
I got it from a reddit post that got them from a blog post that has no image credits (and claims small nukes were used); maybe a reverse image search helps?

One of the source images is this:

I understand that. Which is why I gave the quotes that showed the 12/2007 FAQ was explicit, but the 2005 report wasn't (as far as I could see).
Many people understand the issue now - 2021. Most of them have done so since around 2010. My purpose was to explain the history of misunderstanding.

They kind of say in the report that there was floor damage and the floors lost their seating, but that feels more like it's still initiation and not quite progression yet.
Most explanations - from "both sides" fail to explicitly define the stages. The distinction between "initiation" and "progression" is vital to clear understanding. The mechanisms were very different yet conflating those two stages was a significant factor adding to confusion and unclear reasoning. And it still occurs. FRom "both sides" and it started before "two sides polarisation" was entrenched PLUS, once the principal need to identify stages is recognised it can help to define two more "stages viz the transition from "initiation" to "progression". It was chaotic but that stage ensured that the reality of "column ends not aligned" - which was set-up by ignition >> then continued into "progression". Hence "ROOSD".

Then it can also add to the clarity of understanding if "progression" is seen as two substages. THe "early progression" stage where the Top Block and the upper levels of lower towers both broke up in a process of mutual self destruction. << And, as far as I am aware, that reality has not been explicitly recognised by many researchers. Then the "established progression" AKA "ROOSD".

I suspect the authors of the report expected the floors getting overloaded to be a kind of no-brainer consequence.
Probably true. I took it as self evident from my earliest look at the evidence. But I was not aware of the commitment of most main-stream debate down the potentially misleading paths of gross macro measurements and implied 1D approximations.

Overloaded floors, debris missing the columns is the key to understanding the "progression stage" whether we label it ROOSD or not.

And I suggest that understanding cascading sequenced failure of columns in axial loading is the key to "initiation stage".

Both should be easily seen in hindsight even tho much of the early debate was confused.

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Having a few hours spare time this evening, I asked duckduckgo to give me the results for the search terms "roosd wtc explanation", whereupon I found this old thread from 2013 at another forum. I gather the user "ozeco41" is you, @econ41? In any case, following a link from that thread led me to this thread, where someone discussed the applicability of the Bažant model. And lo and behold, what did I find? This quote from Bažant and Verdure (2007) (emphasis is mine):
External Quote:
The parameters are the compaction ratio of a crushed story, the fracture of mass ejected outside the tower perimeter, and the energy dissipation per unit height. The last is the most important, yet the hardest to predict theoretically. It is argued that, using inverse analysis, one could identify these parameters from a precise record of the motion of floors of a collapsing building. Due to a shroud of dust and smoke, the videos of the World Trade Center are only of limited use. It is proposed to obtain such records by monitoring with millisecond accuracy the precise time history of displacements in different modes of building demolitions.
Which is along the lines of what I stated in the OP:
[the Schneider] model is, as far as I can see, not validated against any real empirical evidence, but is more like a numerical fitting of the ODE solution to the first few seconds of collapse of the North Tower

I haven't had time to read the Bažant papers yet (I know I should, but given the limited time I can allocate to this activity, I think I'll pursue understanding ROOSD better first), but the Bažant and Verdure quote seemingly flies in the face of Schneider's paper.

I've stated it before, and I'll do it again: empirical data is king for this kind of calculations. If your model does not agree with reality, it's the model that is wrong, not reality. Sure, you can extract some interesting qualitative information from even naïve models, but once you aim for quantitative solutions and want to make sweeping conclusions, you'd better make damn sure your model and your empirical input is on firm ground first. Maybe Schneider should consider heeding the advice of the papers he cites before making those sweeping conclusions based on incomplete and inaccurate data?

If possible, my regard for Schneider's work dropped even further.

Having a few hours spare time this evening, I asked duckduckgo to give me the results for the search terms "roosd wtc explanation", whereupon I found this old thread from 2013 at another forum. I gather the user "ozeco41" is you, @econ41?
Yes. "econ41" from Eric Conley - and if you are good at maths you can work out how old I am. (June 29 1941) Then, for reasons no longer important, I adopted the alternate user name "ozeco41" "oz" for "Aussie".

More importantly the couple of threads you identified go to the heart of these topics we are now discussing 8 or 10 years later. Major_Tom was one of a small group of 9/11 WTC collapse researchers who started from the truther side perspective. I fully supported a number of his claims where he identified correct fundamental factors which were rejected as false on the basis that MT was a truther and "no truther can ever be right". Utter barefaced bigotry. When confronted by debunker side insults and bigotry he deliberately chose to give as good as he copped. He also has a very arrogant "style" which didn't help. A long, complex and interesting story. Probably of little interest but it does illustrate the growth of animosity between the "two sides" as they became more polarised.
In any case, following a link from that thread led me to this thread, where someone discussed the applicability of the Bažant model.
For years I deliberately ignored both NIST and Bazant's papers. They don't help layperson understanding IMNSHO. And my goal was to explain to laypersons. Plus far too many accept both NIST and Bazant as "papally infallible". (Since they speak "ex-cathedra" ) They aren't. Bazant has made errors. I've not found any serious ones in NIST's work but a couple of NIST FAQ answers are IMO misleading. Bottom line. Read the posts following that one. OPed by "pgimeno" who asked me to explain Major-Tom's concern about the limitations of Bazant's work. Note the acknowledgement at the end of pgimeno's OP:
(Thanks to ozeco41 for raising the point that led to writing this text.)
Where ozeco41 == econ41 == Me!

Given this forum's "no-clicks rule if we want to discuss the material we will need to import the relevant bits to this forum. And there is far too much of it. And I suspect the same barriers we faced on JREF will also be relevant here - possible not as strongly emphasised.

I haven't had time to read the Bažant papers yet (I know I should, but given the limited time I can allocate to this activity, I think I'll pursue understanding ROOSD better first), but the Bažant and Verdure quote seemingly flies in the face of Schneider's paper.
I recommend understanding the collapse mechanisms FIRST. Then read Bazant and see if his work helps or hinders. A lot of debunkers simply are not up to the challenge of assessing whether NIST, Bazant or other "authorities" are correct. So they necessarily put NIST and Bazant as the "peak" of understanding. I consider that a limiting glass ceiling.

I've stated it before, and I'll do it again: empirical data is king for this kind of calculations. If your model does not agree with reality, it's the model that is wrong, not reality. Sure, you can extract some interesting qualitative information from even naïve models, but once you aim for quantitative solutions and want to make sweeping conclusions, you'd better make damn sure your model and your empirical input is on firm ground first. Maybe Schneider should consider heeding the advice of the papers he cites before making those sweeping conclusions based on incomplete and inaccurate data?
You are playing my song. And the central theme we have been discussing. If the abstract model gives wrong answers - trust the real world. But far more important - if the abstract model gives the right answers >> be very wary. "Right answers for wrong reasons" can have very pervasive bad effects.
If possible, my regard for Schneider's work dropped even further.
He is no further "off the spectrum" than many others.

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For years I deliberately ignored both NIST and Bazant's papers. They don't help layperson understanding IMNSHO.

The Schneider paper is easy enough to understand and - with the right qualifications - to see right through. I would expect a bright graduate student in physics or applied mathematics to see through the fluff and dissicate Schneider's paper (actually, I suspect the biggest obstacle would not be the math and the numerics, but to muster the courage to criticize someone with a ph.d. in mathematics - because they are infallible, right? ). I have only barely glanced at the Bažant paper I linked to, but on the surface, it seems more thorough. I don't expect the mathematics to be the biggest obstacle, but rather the engineering aspects of it - to understand the technical terms and not make bloopers based on incomplete understanding of engineering practices.

Note the acknowledgement at the end of pgimeno's OP:

Where ozeco41 == econ41 == Me!

Yes, I noticed that.

I recommend understanding the collapse mechanisms FIRST. Then read Bazant and see if his work helps or hinders. A lot of debunkers simply are not up to the challenge of assessing whether NIST, Bazant or other "authorities" are correct. So they necessarily put NIST and Bazant as the "peak" of understanding. I consider that a limiting glass ceiling.

I'd like to understand plausible mechanisms. I regard Bažant-like 1D models as macroparameter explorations potentially useful for phenomenological studies.

You are playing my song. And the central theme we have been discussing. If the abstract model gives wrong answers - trust the real world. But far more important - if the abstract model gives the right answers >> be very wary. "Right answers for wrong reasons" can have very pervasive bad effects.

He is no further "off the spectrum" than many others.

As I've stated before, abstract and simplified models can be very useful, but you'd have to be well aware of their limitations. They can be useful for suggesting theoretical mechanisms behind certain observable effects, for qualitatively making theoretical predictions later to be verified experimentally, or for using as a baseline for further research. But if you want to use its quantitative results for more than, say, exploring the relative impact of your parameters, you'd better be prepared to upgrade the model to better reflect reality once more data is in. I see that all the time professionally - at work we use a whole set of physics-based numerical and theoretical tools spanning several fields. Even professional and commercial state of the art simulation models and software packages have their limitations once you start applying the results to the real world. The results might look good on the computer screen, but then reality comes along and slaps you in your face, by being more complex and unpredictable than even the best models.

And that's the problem with big and complex systems such as the WTC buildings and other big structures - they are way too complex to fit into a 1D equation if you want to make any kind of predictions and map them quantitatively. I think I'll dare make the suggestion that Schneider has no limited experience in applying the math he's learned while studying for his ph.d. to the real world, so he makes rookie mistakes.

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I would expect a bright graduate student in physics or applied mathematics to see through the fluff and dissicate Schneider's paper
I'm pretty sure any student with first-year knowledge can do that. After all, I've done it above.
You don't need to be able to re-do all of the analysis to understand the nature of the fallacy: to understand that the mathematical model in the paper doesn't match what actually happened.
Schneider has limited experience in applying the math he's learned while studying for his ph.d. to the real world, so he makes rookie mistakes.
It's not a rookie mistake, it's an "ivory tower" mistake: he's devised his own theoretical model and uses it without having ascertained that it works in practice.
Finite Element Analysis is so powerful because we know where it works, and what its limitations are - something that can't be said for Schneider's method. Schneider is a 42-year-old research mathematician and not an engineer, and that's the reason.

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The "initiation" phase... is likely quite complex as it leads to a critical loss of axial capacity... then movement and drop of the top ensues. In both towers columns were severed by the plane impact and both likely had columns which were dented, bent and so forth. The plane's fuel entered the building, ignited and the heat acted on the steel frame. The loss of axial capacity from the plane strikes was not enough to drive capacity below service loads so both tops remained in place. The initiation phase began as the fires / heat began to damage the remaining beams, trusses and columns.

We don't know how the "weakening" of the frame proceeded. We can only guess at where the fires were... and how long they burned and or how they fires may have spread. NIST makes the claim that the trusses were the elements which kicked off the collapse of the top sections. They point to visible damage along the south facade of 1WTC. It certainly seems odd that this was the only visible evidence... one location of maybe 50' of a 800' perimeter... and I don't recall any inward or outward bowing of the perimeter of 2WTC. I don't think NIST's sagging truss thesis is supported by evidence. If so... I have not seen it.

That leads me to look to core or core and perimeter loss of capacity/failure as a more sensible explanation. So if heat drove the loss of capacity... one needs to model how heat worked in the tower in the period from plane impact to release of the tops. What can be concluded from the observation of the top block of 2WTC falling to the south east? Perhaps that was the weaker side... columns lost and like fire concentrated in the SE quadrant???

One thing to look at... discussed here tangentially... was the notion of load redistribution when columns lose capacity. It hardly makes sense that the load redistribution was a "slow" process... that is one column fails and hands off loads to 2, 3 or 4 others adjacent to the failed columns... Or perhaps one row failing leading to the adjacent row failing. m And then that row failing leading to the next row failing. This seems to linear and organized.

More likely the fire had spread around the footprint. Heat was weakening floor truss, steel bracing inside the core and steel core columns simultaneously. There is no reason to assume the loss of capacity was "uniform" throughout the footprint as the intensity of fire was likely not uniform throughout the footprint. It is reasonable to assume that all steel on the floors of the plane impact burning was losing capacity... some more than others. It is reasonable to assume that multiple columns and braces and trusses failed in the same time frame and that led to multiple other failures in short order and that repeated and grew and essentially once the axial failures began they progressed in a "runaway" fashion and quickly axial capacity was eroded below service capacity.

In 7WTC the process was not dissimilar. Once the structure around columns 79 failed... it rapidly progressed throughout the footprint leading to the entire interior to lose axial capacity... the floors came crashing down... the facade was undermined and then it came down almost as a hollow trapezoidal solid.

In the twin towers... if / when the core lost capacity below service loads... it would leave the perimeter columns supporting all the floor loads. The perimeter would buckle... the floors in the top block would separate from the perimeter as the top block perimeter buckled and slid past the lower block and the ROOSD mass came crashing down through the lower block. Heat would do this... drive capacity of most columns (core) so low that the perimeter would then fail. MAYBE

You don't need to do intricate calculations. If capacity dropped by perhaps about 50% from heat the core would likely fail to do its thing. The top black lost the support they needed and dropped.

As we know one the collapse began the columns did nothing to slow the collapse and were not "involved". The perimeter columns peeled away... the core columns were striped of floors...The growing floor mass plunged down with little resistance taking out one floor at a time adding to the descending mass.

The movement of the top blocks indicates the region where the axial loss was first and greatest.

I would expect a bright graduate student in physics or applied mathematics to see through the fluff and dissicate Schneider's paper
I'm pretty sure any student with first-year knowledge can do that. After all, I've done it above.
Let me offer a word of caution.... Temper your optimism as to what other people "see" or don't "see" when it is bleeding obvious to you. It wont be for many. In fact @arsyn - I haven't tested it but if you search those 8 or 10 year old threads you have seen with some of my comments and use "bleeding (or "bleedingly..) obvious" as the search term. You may find a number of situations where I was frustrated by what other members did not "see".

(There were many of them - the only doubt is whether you can easily locate them by searching. Two examples of the type of "cannot see" are:

(a) Issues at a detail level which should be bleeding obvious. e.g. "Since the Top Block was moving downwards ("falling") ALL columns must have failed" << I've seen that type of assertion denied many times by otherwise competent persons. AND
(b) Failure to comprehend issues of higher taxonomy - i.e. "bigger picture" or "more strategic". A lot of left-brained technical persons who engage in these discussions simply cannot break their habit of focussing on details and losing the "plot". They do not recognise the taxonomy of "overall or part", "system versus sub-system" et simile. That problem is possibly best described by the "trees or forests" aphorism. Or the version that I wrote many years ago at a time of some frustration: '"How many leaves on the seventh branch of the fourth tree?" is meaningless when you are in the wrong forest.') At least we three should be in the same forest - as shown by this examples from @Mendel's recent post:
You don't need to be able to re-do all of the analysis to understand the nature of the fallacy: to understand that the mathematical model in the paper doesn't match what actually happened.
My caution and advice -- Failing to recognise the difference between an abstract model and the real event has been one of the biggest causes of confusion over the years of WTC 9/11 collapse discussion. It is safer to NOT assume that the difference is "bleeding obvious". It may not be. It probably isn't.

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@Jeffrey Orling. Your recent post restates a number of accepted truths explaining the WTC collapses and also repeats several of your own speculations as to alternate explanations which differ from the accepted hypotheses. I refer to this post - which I have shortened for brevity:
The "initiation" phase... is likely quite complex as it leads to a critical loss of axial capacity... then movement and drop of the top ensues. In both towers columns were severed by the plane impact and both likely had columns which were dented, bent and so forth. The plane's fuel entered the building, ignited and the heat acted on the steel frame. The loss of axial capacity from the plane strikes was not enough to drive capacity below service loads so both tops remained in place. The initiation phase began as the fires / heat began to damage the remaining beams, trusses and columns.
....[EDITED].....

The movement of the top blocks indicates the region where the axial loss was first and greatest.
It would be an off-topic distraction if I responded here in this thread.

Why don't you make your own OP with the same post? Then I can give you a comprehensive, on-topic response to both the parts which are accepted hypotheses and reasoned critiques of your speculations as to alternate mechanisms?

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