Claim: Jim Hoffman's "9/11 progressive collapse challenge" can't be met

[Mick West]

If you just describe the model, we know how it's going to respond.

That's ridiculous. I built the model, after extensive experimentation and discussion, and until I pushed the top 1/4 off its supports I did not know how it was going to respond.

It's bizarre that you claim to have total understanding of what a verbally described model will do, but no understanding of what the WTC did (despite having a detailed explanation of the construction of the building, and video of the event). Once again, you come across as trolling.

Build a model that you know will replicate my model. Video the first test. Email me when you have the video, and we can resume the discussion at that point.

 

[deirdre]

Next drill

as someone whose done some crafts in my day.. hint: you should drill all the holes first

 

[Mick West]

I've removed Thomas B from posting in this thread so he can focus on his model. He told me he will not be returning.

 

[Oystein]

...
We imagine a WTC tower on a windless sunny day before 9/11. My thought experiment proceeds in stages. First, we magically remove all floors except the "mechanical floors". We will leave the core in place. This will, of course, remove the lateral bracing the floors provided (I don't deny that they did provide such bracing) but it will also remove their gravity load. While the effective length of the columns (for purposes of doing a Euler buckling calculation) will be longer, they are also under considerably less strain.

My gut tells me that the combination of the (effective) lengthening of the columns and reduction of gravity loads puts the tower in an overall stronger position, not a weaker one. In this configuration it would be better able to handle a hurricane or an earthquake. The structure is doing much less work than it was designed to.
...

I don't think anyone responded to post #251, which contains a number of errors of imagination, but here is the most important:

Thomas failed to understand that, while removing consecutive floors reduces the load proportional to the number of floors removed, it reduces column capacity proportional to the square of number of floors removed.

And thus, his gut gets it on its head: The ability of the tube to resist buckling goes down faster than the load as you remove floor after floor.

 

[Jeffrey Orling]

I don't think anyone responded to post #251, which contains a number of errors of imagination, but here is the most important:

Thomas failed to understand that, while removing consecutive floors reduces the load proportional to the number of floors removed, it reduces column capacity proportional to the square of number of floors removed.

And thus, his gut gets it on its head: The ability of the tube to resist buckling goes down faster than the load as you remove floor after floor.

Please explain why floor removal reduces capacity to the square of the number of floors removed?

So... the process was top down... and if one looks at say 2 column lengths of loss of floors... 6 floors as the columns were 36' tall...
the floor mass of those 6 floors is no longer being applied as loads to the sides of the columns of the tube at the top. But those columns would then only be supporting themselves... so they would be 72' tall with no lateral bracing. Admittedly weaker than if the bracing were in place. but would a 6 story column of that cross sectional area... self buckle? Up at that level the wall thickness were the thinnest... being 1/4" at the top and as thick as 1/2" at floor 92-99... the box columns were 13 1/2" x 14". I think that that column 6 stories tall would not self buckle with the bracing removed. Just a hunch.

 

[FatPhil]

Please explain why floor removal reduces capacity to the square of the number of floors removed?

Susceptibility to Euler buckling. Stable load ~ 1/L^2, where L is length of the unbraced column (with fudge factors depending on degrees of freedom that will be constant for each of the elements in a large tower, so don't change the proportionality relation).

This is kinda what I was trying to communicate in my wire example. I was hoping that was something tangible that anyone could get a real feel for, but that seems to have been taken in the wrong context, and misunderstood. My bad. (I now have the thought experiment of comparing the difficulty of bending short wires between each consecutive finger with the ease of bending a single wire of 3 times the length between little and index finger, but perhaps this analogy is a dead duck and I should give up on it.)

Of course, this only makes a difference one slender columns are the weakest link, it may never make a difference in some structures, as it never gets a chance to be relevant. And this is one of the problems with scaling - the failure modes change in annoying ways, and anything that is set up to replicate behaviour from one perspective may well be completely unable to reproduce another component of the full-scale behaviour, or dominated by a behaviour that the full scale model wouldn't be affected by.

 

[Jeffrey Orling]

I am just about the get into a real world project related to stiffness. I have to put a new teak trim on the hull of my boat. The length of the trim is about 35' long. The profile of the teak is 1 1/2" wide x 2 1/2" tall and 12'-5" long. The lumber is quite stiff.

I intend to make 2 - 14" long lap joints glued and epoxied and create one piece the full 35' length. I intend to attach it at the bow end which is reasonably straight and screw it working to the stern at about 6" oc. I think I can use the long lever and the power of the screw to pull the teak to the curve of the hull. Each "increment" will be a rather small "bend"... a fraction of an inch. Leverage will make it possible to bend the wood.

 

[econ41]

I don't think anyone responded to post #251, which contains a number of errors of imagination, but here is the most important:
.....
And thus, his gut gets it on its head:

That is one specific example of what was his persistent generic problem. Trying to analyse a situation by starting from a model which was only distantly related to the real issue THEN trying to work back to the actual situation BUT repeatedly getting distracted by side tracks.

Somewhat analogous to the endemic problem affecting many engineers and left brained technocrats...

... "How many leaves on the seventh branch of the fourth tree?" is meaningless when you are in the wrong forest. He so many times had the debate onto remote analogies of bits of paper when it would have been a lot easier to simply explain/understand the original issue.

 

[Jeffrey Orling]

The 5 Hoffman challenges:

1 and 2 - are trivial and simple to model
3 - my proposed model may meet the challenge
4 - forget the 100 mph wind - can't scale wind pressure
5 - same reason as 4 - not happinin'

Mick's model demonstrated top down progressive collapse
To achieve the facade falling away cannot be done with a single homogeneous sheet... it has to be made from "panels"or separate columns... The model I described might show this depending on the strength or weakness of the glue between columns.

Out on a limb!

 

[Oystein]

Please explain why floor removal reduces capacity to the square of the number of floors removed?

Well, you got me there.
It's proportional to the (number of floors removed +1) squared.

 

[Jeffrey Orling]

Does anyone think a model will "convert" truthers to the fact that the collapses on 9/11 were not CDs?

 

[Mick West]

Does anyone think a model will "convert" truthers to the fact that the collapses on 9/11 were not CDs?

It will help some people understand the collapses more accurately, which is a helpful step in their overall journey.

 

[Jeffrey Orling]

For sure if the model has all the key elements of the structures and they behave in a similar manner a model with slo mo videos would help people see what happened in the collapse phase. But the real world videos were all researchers needed to understand the collapse phase/process (dubbed ROOSD)... what can't be seen in real world and a collapse model won't help... is how the static building began to collapse top down.... the creation (freeing up from the structure) of the driving mass (for ROOSD).

Can the "initiation" be modeled?

 

[NoParty]

You see, I don't actually believe that. With your past threads, you have established a history on these forums of misrepresenting your experience with and views on these topics and so I believe you are more likely trying to use this thread to demonstrate that you believe Hoffman was correct. The way you dismiss, ignore or nitpick at legitimate criticisms to your approach here, which isn't consistent with a "trying to learn and get it right" mindset, reinforces that. As such, I am just pointing out the flaws in your methodologies along the way so that the ultimate conclusion you are working towards remains in proper context.

Thank you for saying that. I almost wrote something similar
(though mine would've focused on the many, many attempted false equivalences of "debunker and truther" positions) about 5 times, but wasn't sure I could say it within the politeness policy...

 

[NorCal Dave]

Does anyone think a model will "convert" truthers to the fact that the collapses on 9/11 were not CDs?

When I first started to read this thread I was excited that, as a not overly bright Contractor, I could make a meaningful contribution to the forum. I was going to head out to my shop and make a model along the lines that you spelled out Jeffery Orling....But, to what end? It's time I can use elsewhere right now. It seems most of the truthers I've interacted with are all about the conspiracy. The "evidence", like the failure of non-truthers to complete the model challenge, is just one of many floating goal posts. As Mick said above, it may help a few on their journey, but most would reject any model, no matter how accurate.
Still, if I get some spare time on my hands. And I would not drop something on it, I'd light off one of the floors with diesel fuel and see what happens.

 

[econ41]

Does anyone think a model will "convert" truthers to the fact that the collapses on 9/11 were not CDs?

Probably not for a single stand alone model. "Conversion" is not simply a matter of technical argument. It involves multiple aspects of the "truthers" psychology of belief. The two main ones probably are - first - the persons willingness to learn - to be "converted" which is itself complex. The second is somewhat more transparent. Understanding the collapses requires some cognitive ability to "visualise" what is being understood. Some people are better at visualising than others. And there is a small subset who cannot visualise without 3D models. Others can visualise 3D from 2D graphics. Still others can visualise without any graphic or visual aids. But only a small portion of the population actually "needs" - must have models and cannot comprehend without them.

Then I would suggest that the key aspect of ROOSD as shown in my graphic from 2007 and modeled in dynamic 3D by Mick is actually the easiet part of Twin Towers to both visualise and model. BUT that creates a big problem for the target group of those truthers who need 3D models. It is only 1/3rd of the progression stage. That stage is itself only one of three stages which involve very different mechanisms. AND stand alone whether my graphic or Mick's model still requires further visualising to "see" how it fits into the full progression stage mechanism. And the target group is people who by definition are not good at visualising. Catch 22.

As Mick said " It will help some people understand the collapses more accurately, which is a helpful step in their overall journey."
.. but the limitations are in "some", "helpful step" and "journey". Don't expect miracle cures and don't think that a technical explanation will change deeply embedded beliefs.

Can the "initiation" be modeled?

I doubt it can be modeled to serve any useful practical purpose in "converting truthers". Aside from the problems of cognitive psychology there are fundamental technical problems with models. Models fall broadly into three classes viz (a) Models which "look like" the real thing visually but will be of limited quantitative value - you cannot "measure" anything useful; (b) Models suited for quantified measurement of engineering data but which will usually be scale distorted therefore poor visual representations AND (the rare option) (c) Those which successfully combine "a" and "b".
And the predisposition of most truthers - if presented with a "look like" model they will question quantification data OR if presented with quantified valid modelling they will question "doesn't look like". Remember one of the key marketing tricks of the Hulsey farce - fudging the alleged simulations to make them "look like" becase the valid NIST simulations dont "look like".

Plus the "initiation stage" is inherently complex 4D (3D plus time). It is relatively trivial to model bits of it. I've done it in series of simple graphics. BUT the big issue remains - truthers esp those who cannot visualise - will by definition face difficulties "visualising" where the simplified elements fit into the overall scheme. Here - one diagram which can be used to clearly illustrate heat driven cascading failure of columns. THE "key" feature of initiation.

It is not hard to see why a "must have models" visual person would have difficulty putting that simplified element into an overal scheme. And - yes - the graphic could easily be translated into a physicsal model. With a suitably flexible "Top Beam", stress/strain gauges in columns C thru G and an Oxy torch turned on A and B

 

[Sauron]

@econ41 Do you believe there are many people left on the truther side who are there because they disbelieve the physics/mechanism? A good number of 911 truthers had reasons for wanting it be an inside job e.g. those who equate criticism of Islam with racism, dislike of Middle East intervention wars (I'm with them!), and used spurious physics arguments as a cover.

I suspect the number of people who sincerely disbelieve the collapse mechanism (particularly for towers 1 & 2) has been heading downwards ever since 2001, and is now very small. In my opinion 911Truth indirectly admit this when they focus their attention on WTC7 which is inherently more baffling, but annoyingly for them I'm sure, is not the natural centrality of 911 conspiracy.

Now, the genral public's understanding is I believe very poor, and that is where visual models can be helpful, since they can appeal to intuition. Apart from general education, it can prevent people falling down a rabbit hole. Has enough time passed now that people can stomach a dispassionate documentary on just the collapse, as I think nearly all concentrate understandably on the human element.

But models to genuinely 'convert' people? I'm not so sure.

 

[Jeffrey Orling]

@econ41 Do you believe there are many people left on the truther side who are there because they disbelieve the physics/mechanism? A good number of 911 truthers had reasons for wanting it be an inside job e.g. those who equate criticism of Islam with racism, dislike of Middle East intervention wars (I'm with them!), and used spurious physics arguments as a cover.

I suspect the number of people who sincerely disbelieve the collapse mechanism (particularly for towers 1 & 2) has been heading downwards ever since 2001, and is now very small. In my opinion 911Truth indirectly admit this when they focus their attention on WTC7 which is inherently more baffling, but annoyingly for them I'm sure, is not the natural centrality of 911 conspiracy.

Now, the genral public's understanding is I believe very poor, and that is where visual models can be helpful, since they can appeal to intuition. Apart from general education, it can prevent people falling down a rabbit hole. Has enough time passed now that people can stomach a dispassionate documentary on just the collapse, as I think nearly all concentrate understandably on the human element.

But models to genuinely 'convert' people? I'm not so sure.

The collapse of 7wtc is a matter of accepting that heat from fires left burning for hours can fatally impact a steel frame high rise. This is settle fire science and engineering. The "mystery" is simply that it is almost impossible to know precisely where the fire was acting. AE911T and Hulsey simply try to claim that NIST made mistakes... I mean... lied about what happened and the reason they posit it that it was a cover up for a CD. They make no serious/credible claims to support CD.

The twin towers came down from a top down over load condition also created by heat from fire failing the structure. Again basic engineering which is settled science.

7wtc failed low down and so the collapse form resembles a CD and makes it easier for AE911T to pull the wall over the eyes of naive people. If it looks like a duck is must be a duck... hardly sound reasoning.

Any model has to resemble the tower... so I believe it has to be 4D... and have heat as the cause of the collapse.

Will it change any minds? I doubt it.

 

[econ41]

@econ41 Do you believe there are many people left on the truther side who are there because they disbelieve the physics/mechanism? A good number of 911 truthers had reasons for wanting it be an inside job e.g. those who equate criticism of Islam with racism, dislike of Middle East intervention wars (I'm with them!), and used spurious physics arguments as a cover.

No. There are very few remaining whose primary reason for truther belief is not understanding collapse physics or the other technical issues.

I suspect the number of people who sincerely disbelieve the collapse mechanism (particularly for towers 1 & 2) has been heading downwards ever since 2001, and is now very small. In my opinion 911Truth indirectly admit this when they focus their attention on WTC7 which is inherently more baffling, but annoyingly for them I'm sure, is not the natural centrality of 911 conspiracy.

That is my perception also. Whether it was a deliberate strategic choice (and primarily led by AE911Truth) the switch to focus on WTC7 is easily explained. The TM had essentially lost the battle for CD over the Twin Towers BUT had created an ethos where "debunkers" readily accepted the "Burden of DISproof". It is harder to "DISprove" CD at WTC7 because the evidence is hidden. And Gage/AE911 had sufficient source of gullible supporters believing in CD at WTC >> stick with the same tactics "there was CD THEREFORE we demand a new investigation".

Yes the "natural centrality" of 9/11 concern - both genuine and CT caused - is in the political/behavioral domain. The immediate issue of "Why didn't the USA prevent it?" should have been the primary focus rather than the apparent technical issues which were quickly shown to be without sufficient foundation. And serious political debate should recognise the lead up issues including how western colonialism and hegemony led to the rise of Middle East "angst".

Now, the genral public's understanding is I believe very poor, and that is where visual models can be helpful, since they can appeal to intuition. Apart from general education, it can prevent people falling down a rabbit hole. Has enough time passed now that people can stomach a dispassionate documentary on just the collapse, as I think nearly all concentrate understandably on the human element.

That is an intersting topic BUT is too complex for this thread and goes too far "off-topic" IMO. Put simply the general public at large is no longer interested in 9/11 and most accept "terrorists did it". The minority hold different views and IMNHO the psychological reasons for obsessive CT belief are more important than the choice of technical topic whether 9/11 or JFK or Apollo landings (OR more contemporary - COVID and anti-vax)

But models to genuinely 'convert' people? I'm not so sure.

They could play a trigger role but for a small sector of demography. And much smaller than seems to be assumed in many of these discussions. And THAT is a topic for discussion in a different setting.

 

[Mendel]

On paper tubes

Office paper is engineered to be strong, because it needs to withstand mechanical processing in copiers and printers and retain its shape. Its fibres make it so.

I suggest constructing the tower from wallpaper or paper tablecloth, these are typically weaker, and can be bought in rolls large enough to construct a person-height tube from a single piece. My intuition tells me that there is no way to make a person-high tube of wallpaper stand up with no bracing, no matter what the diameter is. If it does stand up, you can spray water on it to weaken it and induce collapse.

Or use aluminum foil, or clingfilm. (Clingfilm is used to wrap objects stacked on pallets, giving the stack greater stability against lateral loads, but the clingfilm has no stability by itself.)

The scaling problem is one that if you scale a structure up by factor of 2, its mass increases in 3 dimensions, by a factor of 8. The stability of that structure rarely increases on the same scale, i.e. if it only increases quadratic (by a factor of 4), you'd soon find a size where the load from the weight of the mass has outstripped the stability. That is why we need to change something (maybe the material) when we make a smaller-scale model that is supposed to demonstrate the same effect.

However, doubters will use that change to reject the validity of the model.
I have done that on youtube, demonstrating that water will stick to a spinning ball if the ball is spun at a speed that generates the same centrifugal force that the globe does - change introduced because of scaling. I don't think many of the Flat Earthers who have viewed the video have understood this.

When you choose your materials willy-nilly, don't expect your conclusions to be meaningful.

 

[Mendel]

On the original challenge

Debunkers have not fared well with challenegs offered by conspiracy theorists; there is a long history of challenges in the Flat Earth domain, some of which have been decided in court, and the answers to the challenge have never managed to convince the challenge setter. They're not a means of learning, they're a means of propaganda. So, realistically, I don't expect that Jim Hofmann's challenge can be met in a manner that Jim Hoffmann would concede to.

Therefore, it makes sense to consider the challenge as a starting point to making a household model that would demonstrate some principles of the WTC collapse to laypeople, even if it wouldn't serve to convince any truthers.

My own approach to that would be to utilize the domino effect, where a small lateral impulse can set dozens or hundreds of dominoes toppling.
1) I'd make a square floor plate, cut it in half, then set it on dominoes such that we have a square floor, but I can push the plates apart a little, and they will then continue to move apart as the dominoes holding them up topple over.
2) Obviously, stack several floors of these.
3) Make a hole in the center of the square = a semicircular hole in each rectangle. Make a heavy conical weight (maybe from cement) slightly larger than the hole, so that it can be dropped down the shaft of that multi-storey domino floor building. The cone, if dropped, would push the plates of the top floor apart (losing some energy), gain some energy dropping to the next floor, lose energy pushing these plates apart, etc. The weight of the cone and the distances need to be adjusted to make this process unstoppable.
4) It helps to make the "seam" rotate 90° from one floor to the next.
5) Wrap the whole structure in a paper shell; tack the paper to the floor plates. (Or use cling film?) This provides 100mph wind stability. Burn the shell away as the first stage of demolition. Put the cone weight on a paper support that also burns away after the paper shell has burned.
6) Instead of dominoes, use toothpicks to support the floors. This is aided by conical depressions in the floor boards, and two "comb" type supports that can be put at 90° , leaving holes to support the tooth picks until the next floor plate is placed that fixes the tooth picks in place; the combs can then be pulled out sideways. The picks would need to be set at a slight inward slant to keep the construction stable when the paper shell burns away.
7) Instead of 2 rectangles, 4 approximately triangular sections per floor.

The model would demonstrate a two-stage top-down collapse that is energized by a falling weight and enabled by the loss of lateral rigidity, with mass being propelled outward by the collapse.

The floor plates and combs would need to be created once through manual labor, or by CNC, or possibly by 3D printing, though that would not work well with the idea of burning away the paper shell. If the floorplates are made from metal, the paper shell could be held on by magnets.

P.S.: it occurs to me that the cone weight does not need a special support; it would simply sit in the hole of the top floor until the burning of the outer shell allows the plates of this floor to move apart. The process should then be mostly self-sustaining if the weight is heavy enough.

 

[econ41]

Greetings @Mendel

There are two distinct themes in your post. I'm interested in discussing both. Let's take the "What is the topic and who is the target?" issues first... and defer your suggested and well thought through modelling at this stage.

You seem to be on similar paths to me with the "topic and target" aspects as raised in this part of your post:

On the original challenge

Debunkers have not fared well with challenegs offered by conspiracy theorists; there is a long history of challenges in the Flat Earth domain, some of which have been decided in court, and the answers to the challenge have never managed to convince the challenge setter. They're not a means of learning, they're a means of propaganda. So, realistically, I don't expect that Jim Hofmann's challenge can be met in a manner that Jim Hoffmann would concede to.

Therefore, it makes sense to consider the challenge as a starting point to making a household model that would demonstrate some principles of the WTC collapse to laypeople, even if it wouldn't serve to convince any truthers.

If you read this thread and the more specific modelling discussion thread I suggest it shows that I identify similar key points to those you identify:

1) The realistic goal is "... making a household model that would demonstrate some principles of the WTC collapse to laypeople..." WHILST,
2) Recognising that "...it wouldn't serve to convince any truthers". Although I would modify that to "Many truthers". My position differs slightly from Mick's - I recognise that some truthers are determined to never learn. Whilst some may be amenable to learning. And - my opinion - the number interested in learning NOW - 2021 - is far less than it was 2007-8-9-10>>

BUT the legitimate target I suggest should be "laypersons who want to learn or understand". I think we agree on that. I also suggest that that focus was not agreed or maintained in most of the discussions. There have been digressions into higher level professional explanations which are not suitable for the lay-person target audience and also into modelling for the fun of modelling rather than with the designated purpose of helping lay persons understand. Bottom line - no explicit agreement as to either scope of topic or the objective of the modelling.

So just a couple of preliminary comments which should serve to show where I am "coming from" without presenting detailed argument of the issues at this stage.

You say "Debunkers have not fared well with challenges offered by conspiracy theorists". In my opinion too many debunkers are not sufficiently "on top" of the implicit level of complexity of the topics they attempt to debate. Put simply IF the topic is of Grade #4 or #5 complexity. The truther presents a Grade #2 claim and argument. And the debunker responds at Grade #2 a "draw" or "tie" is near inevitable. A Grade #3 debunker response may "beat" the Grade $2 claim but could well fall short of the real answer which needs Grade #4 or #5.

Then - I agree your comment: "They're not a means of learning, they're a means of propaganda." and I agree your assessment that "I don't expect that Jim Hofmann's challenge can be met in a manner that Jim Hoffmann would concede to." Even tho the challenge is so loosely defined that beating it is trivial - I agree your assessment of Hoffman's likely denial.

I find your modelling proposal interesting but two suggestions:
(a) Would it not be better in the alternate thread? https://www.metabunk.org/threads/cr...e-world-trade-center-twin-towers.11685/page-2

(b) My own thoughts as to a model suitable for lay-persons would prefer a simpler single feature model. But that is a topic for debate. I can see the benefits of a "full features" model such as your proposal and we can discuss the choice - full featured OR single principle. Also the issue of how realistic we want to model WTC. That topic could also see benefits with either choice. Or both.

 

[Mendel]

I find your modelling proposal interesting but two suggestions:
(a) Would it not be better in the alternate thread? https://www.metabunk.org/threads/cr...e-world-trade-center-twin-towers.11685/page-2

Thank you for making me aware of that thread. Its aim is to model the initiation stage of the actual collapse, which my model would not do, as far as I understand it, except on very general principles: "fire weakens the structure,which then starts to collapse from the top" -- but obviously the WTC fire did not weaken the outer shell to the point where that initiated the collapse, which is what happens in my proposed model.
If you want to discuss it there, feel free to do so!

(b) My own thoughts as to a model suitable for lay-persons would prefer a simpler single feature model. But that is a topic for debate. I can see the benefits of a "full features" model such as your proposal and we can discuss the choice - full featured OR single principle. Also the issue of how realistic we want to model WTC. That topic could also see benefits with either choice. Or both.

I don't see any harm in having more than model, or even more than one goal. There's no need for a consensus here.

I chose to have "two features" because the small scale I envision (my model should fit on a table top) requires a setup that can be easily upset by a small amount of energy. People who set up large domino chains put stops in place that prevent the whole chain from toppling prematurely; if I wrap each stage after I set it up, that helps me not destroy my model as I keep stacking floors. (and hopefully, it would even allow for such a model to be pre-assembled and then be transported to a venue where its collapse is to be demonstrated.) That necessitates the "double feature" of first destroying the bracing, and then collapsing the structure itself. If the model was single-feature, it would either be harder to assemble, or the weight-driven destruction would require more energy.

 

[econ41]

@Mendel Let me respond in order of what I think is the importance of the points:

I don't see any harm in having more than model, or even more than one goal. There's no need for a consensus here.

Agreed - provided if we discuss several we maintain clarity of which one we are debating.... the discussions - both threads - so far have often changed models and/or goals without recognising or addressing the resulting confusions.

Thank you for making me aware of that thread.(a) Its aim is to model the initiation stage of the actual collapse, which my model would not do, as far as I understand it, except on very general principles: "fire weakens the structure,which then starts to collapse from the top" -- but obviously the WTC fire did not weaken the outer shell(b) to the point where that initiated the collapse,(c) which is what happens in my proposed model.
If you want to discuss it there, feel free to do so!(d)

(d) Here until we decide the two scope factors - viz how much we want to replicate the real event AND we are agreed as to which stages of collapse we are discussing.
(a) No problem - stay here for now - the Metabunk Rules about "on-topic" may limit us on the other "initiation only" thread.
(b) Actually fire did weaken the outer perimeter shell AND
(c) To the point where it probably initiated collapse. (NIST says it did - I'm personally open on the options but NIST is probably correct.)

I chose to have "two features" because the small scale I envision (my model should fit on a table top) requires a setup that can be easily upset by a small amount of energy.(e) People who set up large domino chains put stops in place that prevent the whole chain from toppling prematurely(f); if I wrap each stage after I set it up, that helps me not destroy my model as I keep stacking floors.(g) (and hopefully, it would even allow for such a model to be pre-assembled and then be transported to a venue where its collapse is to be demonstrated.)(h) That necessitates the "double feature" of first destroying the bracing,(i) and then collapsing the structure itself.(j) If the model was single-feature, it would either be harder to assemble, or the weight-driven destruction would require more energy.(k)

(e) Understood
(f) Two points
-----Understood BUT
----- The actual initiation for Twin Towers was by a "Cascading Sequenced Failure of Columns" which is a close analog to domino toppling (EXCEPT domino toppling is binary at each stage - the next domino either topples or it doesn't. Heat driven cascade failures are multi factor analogue... take that on board - we can defer explanation BUT it is the #1 defining characteristic of the actual WTC 9/11 TwinTowers collapse initiation.) (So we will need to incorporate it if we choose any significant level of repl;icating the actual 9/11 event.)
(g) Understood and a good principle whatever model we finally choose
(h) Yes. A desirable feature
(i) (j) Both specific to your model.
(k) Maybe. Let's reserve judgement. It is not true of the two initial concepts of single-feature models that Mick and I have been considering. And both those are "initiation stage".

 

[Mendel]

(b) Actually fire did weaken the outer perimeter shell AND
(c) To the point where it probably initiated collapse. (NIST says it did - I'm personally open on the options but NIST is probably correct.)

You're a lot better informed than I am on that matter; I may have been thinking of the progression stage, where the tower collapses inside the shell, and the empty facade then topples later.

My process works the opposite way: the shell goes first, then the floors topple, and they topple sideways, not downwards; but that would still meet Jim Hoffman's challenge (at least as I interpret it).

 

[Jeffrey Orling]

You're a lot better informed than I am on that matter; I may have been thinking of the progression stage, where the tower collapses inside the shell, and the empty facade then topples later.

My process works the opposite way: the shell goes first, then the floors topple, and they topple sideways, not downwards; but that would still meet Jim Hoffman's challenge (at least as I interpret it).

It's hard to know with certainty the sequence of failures and how this moved through the structure to become fatal.

I tend to think that the facade of the twin towers was less likely to suffer directly from the heat of the fires. It may have had some IB from heated sagging trusses.

My sense is that the heat was mostly acting on horizontal elements... slabs, trusses, beams, girders.. and less on columns.. heat rises! Heated beams and girders inside the damaged core were pushing columns and may have initiated local buckling leading to load re distribution and it may lowered axial capacity and buckling.

It appears to me that the facade failed from translation / misalignment caused buckling... that led to the upper facade dropping. The interior in the upper block may have disintegrated just prior to and causing the facade to move laterally. In 2wtc is looks like to upper block lost axial support on the SE and the NW buckled. In 1wtc it looks to me that the center (core) lost capacity, buckled and pulled-pushed the perimeter/facade to misalign, buckle and collapse...

Maybe

 

[econ41]

You're a lot better informed than I am on that matter; I may have been thinking of the progression stage, where the tower collapses inside the shell, and the empty facade then topples later.

I'm a retired engineer both civil and military qualified with an extensive background in training. My interest in 9/11 WTC collapse explanation grew out of a need to explain WTC Twin Towers collapses to a lay person colleague in 2007. Which meant that I needed to understand the collapse mechanism comprehensively and in detail sufficient to explain to a layman. So I never saw the authoritative reports as suitable. Either as a source or as material for a layperson to try to understand. So I never took either NIST or Bazant as authoritative preferring to define my own explanations and proofs. And that "explain to lay-persons focus" has remained as my preferred modus operandi. Tho' I can explain at graduate or post graduate levels if appropriate to the audience

The Twin Towers collapses took three very different stages each with distinctive mechanisms. (Plus another sub-stage which is not relevant at this time in our discussion.) THEREFORE my emphasis on the importance of how closely we want our "model" to replicate the real event. Yes your are correct - that is the progression stage that you are thinking about. My assessment for the scope of modelling the three stages is:

1)Initiation stage - what allowed the "Top Block" to start moving downwards - well nigh impossible to model in full details with detailed accuracy. The key feature is model-able but has a problem of ambiguity. There are two plauible "triggers" either of which may have started the process. And both did influence the mechanism independent of which made the bigger contribution. The key feature was a cascading failure of columns which progressively in sequence lost the abilty to support vetical loads. How they lost the load carrying capacity is of little relevance and the exact sequence of failures can never be known. BUT we can model "sequenced cascading failure". The problem is that there were two potential "trigger factors" and we cannot be sure of which one dominated. And we cannot model the two in one model to see which one wins. So it calls for two models of a principal of mechnaism. I"ll explain later BUT Mick and I have already identifed the two without explicitly saying so... see the other thread. Or better still let me summarise what the two are and why they are necessary... IF we want to replicate the WTC 9/11 real event >>>HENCE why that choice is important.

2) "Transition Stage" >> not capable of modelling - it was too chaotic BUT only ONE factor matters >> explanation later.

3) Progression stge >> "Why it collapsed so fast once it got started" AND "Why it wouldn't stop." Mick has already modelled the main and dominating feature. Probably as good a model as we should legitmately need for the goal of explain to a layperson. It does NOT fully explain the progression stage but the shortcomings are minor. It would be a worse explanation for laypersons if we tried to improve the model.

My process works the opposite way: the shell goes first, then the floors topple, and they topple sideways, not downwards; but that would still meet Jim Hoffman's challenge (at least as I interpret it).

Which again highlights the importance of deciding our goal. "meet Hoffman's challenge" OR "explain for a layman".. OR BOTH >> but separately and not getting lost as to which one we are pursuing.

And there are benefits in my preference to explain the principles of mechnaism. Also with your preference to make a visual representation. I doubt we can do both in one model. In fact I'm convinced that we cannot.

 

[Jeffrey Orling]

I'm a retired engineer both civil and military qualified with an extensive background in training. My interest in 9/11 WTC collapse explanation grew out of a need to explain WTC Twin Towers collapses to a lay person colleague in 2007. Which meant that I needed to understand the collapse mechanism comprehensively and in detail sufficient to explain to a layman. So I never saw the authoritative reports as suitable. Either as a source or as material for a layperson to try to understand. So I never took either NIST or Bazant as authoritative preferring to define my own explanations and proofs. And that "explain to lay-persons focus" has remained as my preferred modus operandi. Tho' I can explain at graduate or post graduate levels if appropriate to the audience

The Twin Towers collapses took three very different stages each with distinctive mechanisms. (Plus another sub-stage which is not relevant at this time in our discussion.) THEREFORE my emphasis on the importance of how closely we want our "model" to replicate the real event. Yes your are correct - that is the progression stage that you are thinking about. My assessment for the scope of modelling the three stages is:

1)Initiation stage - what allowed the "Top Block" to start moving downwards - well nigh impossible to model in full details with detailed accuracy. The key feature is model-able but has a problem of ambiguity. The key feature was a cascading failure of columns which progressively in sequence lost the abilty to support vetical loads. How they lost the load carrying capacity is of little relvance and the exact sequence of failures can never be known. BUT we can model "sequenced cascading failure". The problem is that there were two potential "trigger factors" and we cannot be sure of which one dominated. And we cannot model the two in one model to see which one wins. So it calls for two models of a principal of mechnaism. I"ll explain later BUT Mick and I have already identifed the two without expliclty sayng so... see the other thread. Or better still let me summarise what the two are and why they are necessary... IF we want to replicate the WTC 9/11 real event >>>HENCE why that choice is important.

2) "Transition Stage" >> not capable of modelling - it was too chaotic BUT only ONE factor matters >> explanation later.

3) Progression stge >> "Why it collapsed so fast once it got started" AND "Why it wouldn't stop." Mick has already modelled the main and dominating feature. Probably as good a model as we should legitmately need for the goal of explain to a layperson. It does NOT fully explain the progression stage but the shortcomings are minor. It would be a worse explanation for laypersons if we tried to improve the model.

The importance of deciding our goal. "meet Hoffman's challenge" OR "explain for a layman"

And there are benfits in my prefernce to explin the principles of mechnaism. And your preference to make a visual representation. I doubt we can do both in one model. In fact I'm convinced that we cannot.

Probably not a mechanism per se... but surely a very important concept int the collapse of the WTC buildings is the concept of progressive failure... rapid in some cases, but nevertheless one component / element fails leading to other elements failing and their failure leading to other elements failing. Structures falling means loss of capacity. But failures are not simply axial structures - columns. Failures occurred in welds, bolts, trusses, beam seats, slabs, beams, girders... all ultimately leading to falling. The ROOSD process was not about column failures ... but columns without the other elements did fall in the end as well... and they didn't fail from over load... not loads were added. Many columns failed because of instability related to their slenderness ratio - Euler forces/buckling. That concept is not intuitive or something that lay persons typically understand. And of course the effect of heat is not only weakening... but with steel lengthening (expansion joints are part of all large steel structures) and this lengthening can be a key feature of the progression of failures. Heat was not a driver in the ROOSD phase. But is for sure was in the initiation phase.

Probably the a difficult concept to understand is how heat worked on those structures. And this is hard to know because actual field data is not available... so researchers have to make educated guesses.

So a "column failure" model can use loss of axial capacity - weakening... But it also can use beam expansion -leading to displacement / translation / mis alignment of columns and column buckling / failure.

And as Econ mentions the process was rather chaotic

 

[psikeyhackr]

One answer might be simply to cite Mick's experiments. Though they're obviously not complete attempts to meet Hoffman's challenge, we might be able to extend them in various ways "towards" the "replicable physical model" they suggest -- i.e., something that can be built and destroyed repeatedly at a reasonable cost. (I'm not sure the challenge is entirely "fair", btw.

How much damage was inflicted on any of the components of Mick's model during the collapse? Could he just rebuild it with the same pieces? Is it just like a house of cards?

Wouldn't damage demand the use of energy even if the component was just paper? The only source would be the kinetic energy of the falling mass, slowing it down.

 

[econ41]

For sure if the model has all the key elements of the structures and they behave in a similar manner a model with slo mo videos would help people see what happened in the collapse phase. But the real world videos were all researchers needed to understand the collapse phase/process (dubbed ROOSD)... what can't be seen in real world and a collapse model won't help... is how the static building began to collapse top down.... the creation (freeing up from the structure) of the driving mass (for ROOSD).

Can the "initiation" be modeled?

No.

 

[econ41]

Probably the a difficult concept to understand is how heat worked on those structures. And this is hard to know because actual field data is not available... so researchers have to make educated guesses.

Anyone who MUST know specific details such as which column failed first will not be able to get very far thinking through the problem. Those who can process "the first column then the second columns...." WITHOUT needing to "hang up" on which column was "first" will get a lot further in understanding. Sadly we have just lost most "left brained" engineers. And it is NOT "guessing".

So a "column failure" model can use loss of axial capacity - weakening... But it also can use beam expansion -leading to displacement / translation / mis alignment of columns and column buckling / failure.

Loss of axial (vertical load) carrying capacity is probably the easiest path to reason along. It is one of several known "key facts":
1) The "Top Block" started to move downwards THEREFORE the columns had lost capacity to carry vertical download. Take THAT as FACT. Don't confuse yourself asking "Why?"

THEN loss of axial capacity is the relevant issue. Your second concern is about "Why?" And it is a derail we dont need to take. Especially as we cannot answer the questions. MORAL: Don't lock up your thinking by looking for paths into the unknown. If you don't need to go there is is irrelevant.

And as Econ mentions the process was rather chaotic

SOME parts were chaotic. Doesn't mean we cannot process other parts. And we have enough in those "other parts" to form relevant conclusions. For the four sub-stages of Twin Towers collapses we only NEED one or two facts to progress the logic from any sub-stage to the next sub-stage.

 

[Jeffrey Orling]

Econ.,.. collapse from "loss of capacity" is a trivial engineering concept. This is settled "science". However this is probably too general because the implication is that the columns at some location from top to bottom... presumably at the same elevation lost axial capacity. If the cause was heat... most would take that to mean that heated steel column with less axial capacity "failed" likely from "buckling". My sense related to this is that as many columns would be "doing this"in the same time frame. That steel would loose capacity gradually. And that makes me think perhaps they would "warp".., and deform.. not "snap" as they heat up. So if there are "going" from rigid, strong, to softer and weak I would expect to be able to observe some deformations.
Another aspect related to loosing capacity is what we were told about col 79. Essentially it lost capacity because it lost bracing.. its unbraced length increased essentially lowering its axial capacity and it "buckled" (Euler). I don't understand the time involved with respect to... bracing fails... and then how long does column buckle? Or how does it buckle... deform or snap? Presumably a deformed column has some capacity... let's say bent flanges for example... But for the axial force from above to move down... significantly... the deformation of the buckled column would have to be more than bent flanges... I am thinking... the horseshoe column... as an extreme example. Google search for images of buckled columns show others which much less deformity. and YES the elevation of the top of the column is decreased... The mass above would therefor "settle" or move down...
So now we need to go from warped, bulging, buckled columns to so much loss of capacity that essentially there is NOT ENOUGH SUPPORT and the mass above descends. Frankly I find this scenario no a good fit.
So... I think we should explore other ways the columns could fail... lost their ability to support axial loads. For my crude thinking this might be mis alignment. If somehow the upper columns are moved out of axial alignment... the load path is interrupted and the top drops. Conceptualizing this is as simple as looking at your phone sitting on the desk... it supported by the desk. Not slide it over the edge of the desk. The weight of the phone (it hasn't changed) is not "bearing" on a smaller area of the desk. So it can be supported and have some mis alignment so to speak. Move it more... more than 50% off the desk. What happens is the phone drops to the floor. In my thinking this is a MORE reasonable and likely scenario for loss of capacity and descent of the top.
Now how would that manifest? My best guess is that the horizontal elements of the structure... beams and girders... even slabs EXPANDED when heated. Expanded beams when attached to thew sides of columns as they were in the WTC and most steel high rises...exert lateral... horizontal force on the columns. If the column is restrained and can't move... the horizontal elements sag. So we know that bridges and other structures have "expansion joints" because the normal range of temps would lead to buckling... likely the horizontal elements. Look at the steel design details for connections where lateral expansion is present. These details permit the beams to expand and NOT cause the columns to loose axial alignment.
My guess is the WTC streel frames did not have such expansion joints because they did not expect the frame to be exposed to elevated temps for long periods. Concentrated heat from welding torch will not cause and entire beam to expand. But a long duration fire under the entire length of the beam will. THAT IS WHAT HAPPENED
So the very hot beams expanded and pushed at the steel columns. If the column's lateral motion was restrained... the beam would deform and sag... the columns would remained axially aligned and not fail. The floors might collapse... but not the columns.
When looking into this "scenario" it can only lead to mis aligned columns if there are laterally unrestrained columns. But when there is are beams in both X and Y axes the column is unable to move. Now... what happens when a beam fails? The column it supports/braces... will be unrestrained on THAT side. The consider the restraint "difference" between steel bar trusses around the core and large WF sections inside the core. Perhaps expanding core beams expanded and the floor trusses could not provide the necessary restraint... maybe the columns would move out toward to perimeter?
I can envision heated core beams pushing steel columns laterally and the column end to end connections were not strong enough to keep the axially aligned. So... the column ends moved out of axially alignment... resulting is diminished bearing area... destruction of load path... and this could lead (I am guessing) to a runaway buckling at the column ends and lateral movement and descent of the upper mass...when axial support dropped below capacity.
Now one column seeing this fate would not be fatal.,.. it's load could be handed off to adjacent columns. So it's conceivable that a local single column not not lead to a total collapse of the top block. I would imagine that the fires were over such a large area that MANY beams were pushing on multiple columns and there were no lateral expansion joint... or connections which could function with that much lateral movement of the beams.
How might we know if this happened? Look at the steel found in the pile after the collapse. Massive sudden overloading would show massive deformation of the column webs and flanges.. (buckling). You would see things like several horseshoe columns. You would lots of"intact" columns fallen but with not signs of buckling.... from the so called "collapse" elevation. So I think a careful survey of the columns from the collapse elevation... plane impact zones... might tell how the columns failed and the tops came down. My hunch is won't be from columns being softened and weakened from heat. I don't know what column ends which lost bearing area and failed would look like. I suppose this could be modeled experimentally.
Experiment:
Load a column up and heat the column until it fails. What does it look like?
Load a column and heat all the bracing until it fails. What does it look like?
Load a column and heat SOME of the bracing until it fails. What does it look like?

My guess the column failures lateral translation of the top block... was caused by overheated beams and that over heating of the columns was not a key factor.

MAYBE

 

[Mendel]

and YES the elevation of the top of the column is decreased... The mass above would therefor "settle" or move down...
So now we need to go from warped, bulging, buckled columns to so much loss of capacity that essentially there is NOT ENOUGH SUPPORT and the mass above descends. Frankly I find this scenario no a good fit.

I understand that in this scenario, the hat truss redistributed the load, until either some other columns are overloaded and fail, or the hat truss itself fails?

 

[Jeffrey Orling]

I understand that in this scenario, the hat truss redistributed the load, until either some other columns are overloaded and fail, or the hat truss itself fails?

So my conception of how the hat truss "worked" and why it was part of the design....was as follows. I may be and probably am wrong. Please feel free to correct my misunderstanding.

The cores of the twins were basically for elevators, elevator lobbies, bathrooms and "mechanicals" The office uses were outside the core (supported on truss joists. The core was designed with the 24 perimeter columns to support a cantilevered "belt girder" which surrounded it on all sides. The girder supported approximately 50% of the outside the core floor loads. There were no long spans and large loads on any floors but the mechanical floors. there were 8 mech floors in 4 groups of 2 floors each... above the 7 story lobby at the top below the roof and two locations dividing the tower into thirds. There was office use in the core area above "terminated" elevator shafts.
So... there was a 360' tall 360 ton antenna in the center of 1wtc, 2 wtc was designed for another antenna. The antenna had a footprint which was above the center of the core where there 3 of the "smallest" cross section columns. My hunch is the concentrated antenna load could not be supported by those 3 columns. The solution was to build a 3D space frame over the core.. to distribute the antenna load to all 47 core columns. The hat truss had outriggers which were bolted to the perimeter panel columns in 16 locations

The members are not to scale. There was no tenant space on those floors except radio equipment. This diagram suggests that the hat truss distributed the antenna loads to MOST of the columns. Those columns in addition to support mech floors supported and were PART OF the hat truss structure.

My guess is that the destruction the core columns in the plane crash zones removed axial support for the hat truss. The design was effectively able to redistribute all axial loads until it was not. What may have happened is the region (center of the core) failed... some from the plane crash... some from effect of heat... Perhaps the hat truss failed/collapsed in the center over the region of column destruction in the crash zone. That would be directly under the antenna. Perhaps the antenna support failed and the antenna began to drop.

The hat truss may have held the top block together as a 3 story "structure"... a much more rigid end "plate" than a roof deck. The truss made 3 mech floors act as a "composite"... and "drop" as a block... even move laterally as a block.

Maybe