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

Thomas B

Active Member
Many years ago, Jim Hoffman issued a "progressive collapse challenge" on his 9-11 Research website (see quote below). "If [the WTC's] mode of structural failure is so likely to happen," he asked, "why is it so difficult to reproduce?" At the time, his target was "pancake collapse", not the ROOSD model that I know some people here hold to, but the challenge itself still seems to make intuitive sense whatever explanation you prefer. If we know how the WTC structures failed, shouldn't we be able to build simpler/cheaper structures that fail in the same way? The WTC collapses were a "mechanism" that ran its course from a known initial state (through a well-understood process) to a known final state. Why can't we build such a mechanism to demonstrate how it works?

How do we answer this challenge? Why is the non-existence of simple physical models of the WTC collapse mechanism not important? Or how (in what sense) can/has the challenge be/en met?

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. For example, I don't think a garage or backyard model would need to stand up in a 100 mph wind. But I imagine some of the specifications are negotiable in the minds of truthers, as long as the model is plausible, or a plausible reason for its impossibility is provided.)

THE PROGRESSIVE COLLAPSE CHALLENGE

The challenge is in 5 parts, from the easiest to the most difficult.

All five require building a structure that will undergo top-down progressive total collapse -- i.e.: when disturbed near the top, it will collapse from the top down to the bottom, leaving no part standing. The disturbance can include mechanical force, such as projectile impacts, and fires, augmented with hydrocarbon fuels. Explosives and electromagnetic energy beams are not permitted.

Your structure can be made out of anything: straws, toothpicks, cards, dominoes, mud, vegetables, pancakes, etc.

The designers of the Twin Towers were able to meet all 5 challenges using steel and concrete.

CHALLENGE #1:

Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse.

CHALLENGE #2:

Build a structure with a square footprint and a vertical aspect ratio of at least 6.5 (6.5 times as high as it is wide), and induce it to undergo top-down total progressive collapse.

CHALLENGE #3:

Build a structure as required by CHALLENGE #2 which, in the process of collapsing, will throw pieces outward in all directions such that at least 80% of the mass of the materials ends up lying outside of the footprint, but their center of mass lies inside the footprint.

CHALLENGE #4:

Build a structure as required by CHALLENGE #2 which is capable of remaining intact in 100 MPH cross wind.

CHALLENGE #5:

Build a structure that meets the requirements of both CHALLENGES #3 and #4.

deirdre

Senior Member.
How do we answer this challenge?
you can't because forces cannot be scaled. It has something to do with something called "the square cube law".

I'm not sure exactly which thread inspired Mick to make the MB thread you link above, but the thread was about how it is impossible to do because of scale. So Mick though that maybe we could at least model individual aspects for general demonstration purposes.

edit add: a not engineery example of this i always liked (to help me understand it) is
Article:
Another example of "you can't scale nature" is contained in some [dark] humour from the coalfield. It relates to mammals when they accidentally fall down a mine shaft. Apparently mice walk away unharmed, dogs break their legs, men break all their bones, but horses splash. (F = mv2)

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econ41

Senior Member
OK - I'll open the debate (EDIT: Ooops - Deirdre beat me to post. ) which is of some interest to me given that I was one of the first to postulate the method of collapse often described as "ROOSD". And this will only be an opening explanation. Not a comprehensive hypothesis or even a full description of the challenge.

Many years ago, Jim Hoffman issued a "progressive collapse challenge" on his 9-11 Research website (see quote below). "If [the WTC's] mode of structural failure is so likely to happen," he asked, "why is it so difficult to reproduce?" At the time, his target was "pancake collapse", not the ROOSD model that I know some people here hold to, but the challenge itself still seems to make intuitive sense whatever explanation you prefer.
The opening statement already is unclear as to the purpose of the modelling. The implicit need is to validly replicate the collapse mechanism of the Twin Towers. So Hoffman's target of whatever he meant by "pancake collapse" is not the answer. It did not happen. Sure ROOSD was the start of a correct explanation - with or without the convenient acronym label. But it is only one of three sub-mechanisms of one of three major stages. Which are conveniently described as "initiation", "transition" and "progression. Yes "ROOSD" is the distinctive feature of the "progression stage" but it does not describe either "initiation" or the "transition" and without both those stages the conditions for valid modelling of the commencement of the "progression" stage do not arise. I suggest that the final criterion "whatever explanation you prefer" is too broad. It should be a process to model the actual collapse BUT I recognise that as posted here in quotation Hoffman's challenge does not appear to require modelling the WTC collapses. So we need to decide what our target is.

The next comments rely on the assumption that we "know how the WTC structures failed". I doubt that is true at the depth of understanding needed for successful modeling:

If we know how the WTC structures failed, shouldn't we be able to build simpler/cheaper structures that fail in the same way? The WTC collapses were a "mechanism" that ran its course from a known initial state (through a well-understood process) to a known final state. Why can't we build such a mechanism to demonstrate how it works?
Agreed that we know the "initial state" and the final state" but we have no generally accepted understanding of the three stages of collapse process in between. And the three stages are very different. Yes we have (should have??) agreement of the ROOSD distinctive feature of the progression stage but I doubt we are at this stage agreed the other two parts of progression.
How do we answer this challenge? Why is the non-existence of simple physical models of the WTC collapse mechanism not important? Or how (in what sense) can/has the challenge be/en met?
Without attempting to fully explain at this stage I would reverse the question. "Why is it important to have simple physical models?" That issue was raised numerous times by me in discussions at the time of Mick's modelling of ROOSD. Part of my contention was that modelling of ROOSD is redundant if the mechanism is understood - it is so simple as to not require demonstration by a physical model. We can re-explore that simplification if necessary.
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 don't want to rain on your parade BUT Mick's models are the easy bit and the bit we already understood. That is much of the reason that Mick was able to model them. I'll state the challenge briefly. I doubt that valid models of the other two stages can be built because we don't know the mechanisms in sufficient detail and never will know with the specific detail needed to build a model. And, yes, I fully recognise the challenge implicit in those assertions. Obviously more discussion and explanation will be needed.

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 doubt it for reasons already outlined.

(I'm not sure the challenge is entirely "fair", btw. For example, I don't think a garage or backyard model would need to stand up in a 100 mph wind. But I imagine some of the specifications are negotiable in the minds of truthers, ....
It would almost certainly be a small scale model therefore the wind would need to be appropriately scaled. (And that is "tip of the iceberg" -- there are many related issues about scaling.)

... as long as the model is plausible, or a plausible reason for its impossibility is provided.)
And plausibility will IMNSHO be the #1 issue for debate.

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econ41

Senior Member
You beat me to the post Deirdre - it took me some time to draft my comprehensive response.
you can't because forces cannot be scaled. It has something to do with something called "the square cube law".
That is one of several "big problems"

Thomas B

Active Member
I doubt that valid models of the other two stages can be built because we don't know the mechanisms in sufficient detail and never will know with the specific detail needed to build a model.
I don't think the point of the challenge is to model the actual collapses. It's just to build something that behaves "like" the twin towers both before and after the planes hit. That is, it's got to be quite strong when undamaged. But it also has be vulnerable to total collapse "when disturbed near the top".

And plausibility will IMNSHO be the #1 issue for debate.
Yes, once a model that does collapse completely has been presented, I'm sure there could be some (even a lot of) debate about whether it is sufficiently "like" the WTC towers to prove anything. As far as I know we haven't been in that situation yet, though.

deirdre

Senior Member.
nce a model that does collapse completely has been presented, I'm sure there could be some (even a lot of) debate about whether it is sufficiently "like" the WTC towers to prove anything. As far as I know we haven't been in that situation yet, though.
even i could build/buy something that is strong before i drop something on it. but why bother when you know AE911 will just argue it isnt sufficiently "like" the WTC to prove anything. Even the NIST computer models (hundreds and hundreds of hours) were apparently not sufficient enough to "prove anything".

Just like Husley's 7 wasnt sufficiently done to prove anything.

In my opinion, if someone offers a large reward "challenge" that alone is a red flag that they have built in criteria they know will cause everyone to fail. like the James Randi challenge. Psychic phenomenon simply doesnt work like "that". and scale models simply don't work like "that" either.
Again, thats my opinion.

Amber Robot

Active Member
I don't think the point of the challenge is to model the actual collapses. It's just to build something that behaves "like" the twin towers both before and after the planes hit. That is, it's got to be quite strong when undamaged. But it also has be vulnerable to total collapse "when disturbed near the top".
It is very likely may not be possible without building something almost the same size as the WTC.

Not all models are scalable. This is a very reasonable idea that many non-scientists may not fully appreciate.

I recall on a tour of one of the wind tunnels at NASA Ames being told that helicopters have to be tested at full scale because the range of forces in the blades at various parts of the blades can’t be scaled to get useful results.

Thomas B

Active Member
It is very likely may not be possible without building something almost the same size as the WTC.
It's possible that the progressive collapse depends on a certain height between floors, but I can't imagine that you'd need 110 of them (the process worked just fine on first few floors after all). Also, I don't think the structure would need to be as wide. I'm sure there are limits to how much you can simplify the WTC structure and still have it collapse working with steel and concrete.

But the challenge lets you use any materials you like. So, as Mick suggests, the next move would be to scale down the strength of the materials and the connections between them. At the end of the day, you just need something that undergoes top-down progressive collapse. It would be surprising if only structures as big as WTC can do that.

deirdre

Senior Member.
you just need something that undergoes top-down progressive collapse. It would be surprising if only structures as big as WTC can do that.
Verinage demolition does that all the time. MB has threads with lots of videos of such demolitions. search "verinage".

I cant rememebr the 911 truther arguments about those though. you'd have to find the threads and read them.

Thomas B

Active Member
Verinage demolition does that all the time.
Perhaps, but that's a real world example, not a model. I think what Hoffman is asking for is a demonstration that can be set up to show how progressive collapse works (and test various theories about it) without having to actually demolish a real building. It should be significantly easier and cheaper to arrange than the real thing.

PS (edit): I'll grant that I may just be projecting what I'm looking for into Hoffman's challenge. I really wish I could demonstrate how natural the WTC collapses were with some simple materials.

econ41

Senior Member
Perhaps, but that's a real world example, not a model. I think what Hoffman is asking for is a demonstration that can be set up to show how progressive collapse works (and test various theories about it) without having to actually demolish a real building. It should be significantly easier and cheaper to arrange than the real thing.
That points to the first challenge which is to define what your objective is.

As you say "...set up to show how progressive collapse works (and test various theories about it).." which implies a range of different progressive collapse mechanisms NOT the one or not just the one which occurred with the WTC Twin Towers. And, if you are after something which covers multiple mechanisms it is almost certain that it cannot be one generic model. Rather specific models for each type of identified mechanism.

I suggest start with WTC Twin Towers as a basis for discussion of practicality THEN if that succeeds - move on to consider different mechanisms.
PS (edit): I'll grant that I may just be projecting what I'm looking for into Hoffman's challenge. I really wish I could demonstrate how natural the WTC collapses were with some simple materials.
So your own preference is to "...demonstrate how natural the WTC collapses were..." which raises two issues:

First - how much - what part of the WTC collapses do you want to demonstrate? Mick's work is probably the best example of a demonstration of mechanism for the critical and defining sub-mechanism of WTC Twin Towers progression stage. It demonstrates the "ROOSD" sub mechanism with qualitative (descriptive) accuracy and sort of demonstrates the "peel and topple" sub mechanism for the perimeter. It does not visually demonstrate the third mechanism of "core strip down". And it does not in any way explain how the progression stage was started.

So is that as much as you want - the key elements of the dramatic fast falling "progression stage" or do you want more?

And are you satisfied with the WTC progression? THEN

Second - and the big question. Why do you need a model when the process can easily be explained by words and pictures. For example this is the crude graphic which as far as I am aware started the explanation back in Nov 2007.

So ask the question "What is the purpose of the model?" "Does Mick West's demonstration achieve that purpose?" "What audience needs the more kinaesthetic attraction of a physical model?

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deirdre

Senior Member.
Why do you need a model when the process can easily be explained by words and pictures.
or a cheap book case with plastic brackets. am i only one who ever owned a cheap bookcase and overloaded the top shelf? (disclosure: when the top shelf collapses the rest all come tumbling down).

Mick West

Staff member
or a cheap book case with plastic brackets. am i only one who ever owned a cheap bookcase and overloaded the top shelf? (disclosure: when the top shelf collapses the rest all come tumbling down).
That's a good visual. My model was essentially a set of shelves with no back, and proportionatly weak connections. Bookcases, even cheap ones, are (to scale) vastly stronger than the WTC towers.You would need to load each shelf with bricks - or something heavy that still allowed sufficient travel between impacts.

The big problem with my model was always getting reusable connections. Revisiting it now, I wonder something like 1/16" dowels might work.

I'm unlikely to try it again, unless someone wants to pay me to do it. It was a lot of work.

Oystein

Senior Member
Challenges #3 and #4 are odd, and I would like to know how Hoffman justified them:

#3 "... at least 80% of the mass of the materials ends up lying outside of the footprint ..."
-> Does Hoffman claim this happened with the twin towers? How did he determine this? Does anyone agree? My gut tells me this is wildly wrong - Truthers tend to vastly overestimate the mass of the dust ejections. Much of the mass that fell outside the footprint was the walls. That would account for no more than 30% of weight. Truthers tend to underappreciate the depth and volume of the basement levels extending beneath the footprint - the entire material volume of the 110 floors above ground could have fit entirely into the basement and inside the footprint, and there still would have been a pit.

#4 "... capable of remaining intact in 100 MPH cross wind ..."
-> It's odd he would prescribe an absolute value for wind load, when previously he only prescribed relative dimensions (height to width ratio). Surely you would have to scale wind speed (and, very likely, barometric pressure) in non-trivial ways - and I could not even say if fair wind speed for a 1:100 model would be higher or lower.

The entire challenge comes across as having been posed by someone who know not the first thing about modelling in engineering (like, for example, wind-tunneling).

No scale model can ever replicate all properties of the real thing. Hoffman clobbered together about four properties that he, for reasons unexplained, considers important.

At the end of the day, a talented engineer with vivid imagination could, no doubt, build a model that meets all of Hoffman's challenges - and it might be a bizarre contraption void of any similarities with the WTC towers. Say, use unexpected materials (rubber, glass, spaghetti, gels, 80% of the mass liquid), or distribute mass very unequally (say, 75% of the mass is lead cubes at the four corners of the "roof"). Challenge met - nothing learned.

JMartJr

Senior Member
I had a surprisingly difficult time tracking down what ROOSD stands for. For readers who, like me, are new to this topic and who might be similarly struggling, ROOSD means "Runaway OOS Destruction" -- where OOS stands for "Open Office Space" which, unless I am mistaken, refers to the flooring system in the towers. That should be enough to let anyone interested in learning more about the terms behind the acronyms to do so...

deirdre

Senior Member.
You would need to load each shelf with bricks - or something heavy that still allowed sufficient travel between impacts.
you dont have to use all the shelves.

edit add: or actually you could use all the shelves and just load the top one with bricks. it will still crash through the lower shelves without bricks... trust me.
Revisiting it now, I wonder something like 1/16" dowels might work.
didnt you use magnets at one point? that sounds like a pretty good idea. (but did they roll all over the garage because you didnt Krazy Glue them to the floors and columns? hhmmm...

I think Thomas B should do any work since he brought it up again!

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econ41

Senior Member
I had a surprisingly difficult time tracking down what ROOSD stands for. For readers who, like me, are new to this topic and who might be similarly struggling, ROOSD means "Runaway OOS Destruction" -- where OOS stands for "Open Office Space" which, unless I am mistaken, refers to the flooring system in the towers. That should be enough to let anyone interested in learning more about the terms behind the acronyms to do so...
My apology - Although "ROOSD" was quoted in the OP I responded and forgot that many may not be familiar with the acronym. The acronym is descriptive and once the meaning is familiar it is very useful "shorthand".

EXCEPT it had a contentious history. It was made up and put into mainstream debate by a couple of agnostic members who were regarded as "Truthers" in the context of the anti-truther animosity of JREF. The dreaded alleged "truthers" happened to be right on a few things which disagreed with the then prevailing wisdom of debunkerdom. It resulted in recycling of debates involving a lot of mental gymnastics over about 4 or 5 years. Still on record BUT of little consequence now. Provided we understand that the actual mechanism of WTC Twin Towers progression stage collapse was by the mechanism described as ROOSD. If anyone can think of a better acronym without the baggage - let me know.

SO --- for this current discussion all we need to know is that the acronym is (a) Convenient and descriptive shorthand for the actual real mechanism of collapse; AND (b) A lot of debunkers on other forums variously (i) don't like it or (ii) reject the acronym or even (iii) deny the mechanism because of its truther side origins. Shouldn't be a problem on MetaBunk and it is convenient.

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econ41

Senior Member
or actually you could use all the shelves and just load the top one with bricks. it will still crash through the lower shelves without bricks... trust me.
I do trust you. I've been there - done that or similar on too many occasions for an engineer to admit.

The real weakness of the original challenge is that it is far too loosely defined.

The OP claim - in the title - is: "Jim Hoffman's "9/11 progressive collapse challenge" can't be met"

FALSE. The challenge definition is so wide open it can easily be met. If anyone wants to take the discusion down that path I'll bet several members will join me in accepting the challenge to DESCRIBE how we would do it. I'm not going to build any models.

didnt you use magnets at one point? that sounds like a pretty good idea. (but did they roll all over the garage because you didnt Krazy Glue them to the floors and columns? hhmmm...
Yes on the magnets and I think your memory is correct on the other details.

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econ41

Senior Member
At the end of the day, a talented engineer with vivid imagination could, no doubt, build a model that meets all of Hoffman's challenges - and it might be a bizarre contraption void of any similarities with the WTC towers. ..........Challenge met - nothing learned.
I'm sure that a talented engineer could walk through the loosely defined "challenge".

Lets start a collection. My first entry - starting with the easy ones:
" CHALLENGE #1: Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse."

Make it 150mm square 450mm tall (yes - over spec) Use minimal small sections of balsa wood. Drop a house brick on the top from 300mm above.

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Mick West

Staff member
Article:
CHALLENGE #1:

Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse.

CHALLENGE #2:

Build a structure with a square footprint and a vertical aspect ratio of at least 6.5 (6.5 times as high as it is wide), and induce it to undergo top-down total progressive collapse.

CHALLENGE #3:

Build a structure as required by CHALLENGE #2 which, in the process of collapsing, will throw pieces outward in all directions such that at least 80% of the mass of the materials ends up lying outside of the footprint, but their center of mass lies inside the footprint.

CHALLENGE #4:

Build a structure as required by CHALLENGE #2 which is capable of remaining intact in 100 MPH cross wind.

CHALLENGE #5:

Build a structure that meets the requirements of both CHALLENGES #3 and #4.

Other than the rather vague "capable of remaining intact in 100 MPH cross wind." (i.e. is that to scale, or actually 100mph), the rest of these seem trivially easy, if time-consuming. My model was 4x as high as it was wide. Making it square and 6.5x is simply a matter of time. The scattering of debris would seem to be a natural consequence of making it taller

Thomas B

Active Member
Drop a house brick on the top from 300mm above.
I think the idea [is] that the mass/energy that destroys the structure has to be part of the structure in its initial state. So you could build a structure with a brick on top, but I don't think you'd be allowed to lift it and drop it. You would only be able to "disturb" the structure underneath it.

... the rather vague "capable of remaining intact in 100 MPH cross wind." (i.e. is that to scale, or actually 100mph) ...
I agree that this one is vague. It might be improved by challenging your model to remain standing after a lateral impact strong enough to sever one or more columns.

In fact, as Econ's suggestion (the brick) shows, there has to be a limitation on the "disturbance near the top". It has to be a short, sharp shock that doesn't add a lot of energy to the system, but merely changes the structure (somewhere in the top 20%), which could include setting it on fire (using the energy already in the materials).

What you're doing up there on the ladder is more like introducing explosives (or an energy beam!) than an airplane impact that the structure, initially, absorbs and survives. If you applied the same forces to the side of your structure (the force needed to lift and shift the top section as you do), I'm pretty sure you'd knock the whole thing over. Build it strong enough to withstand that, and I don't think the collapse would progress.

trivially easy, if time-consuming
Instructions for building the structures would be sufficient. In fact, that's the whole point of reproducibility. You don't just want to show it once. You want to let anyone demonstrate it for themselves (if they want to put in the time).

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Thomas B

Active Member
At the end of the day, a talented engineer with vivid imagination could, no doubt, build a model that meets all of Hoffman's challenges
I'm sure that a talented engineer could walk through the loosely defined "challenge".
I've been thinking about paying one to solve a more tightly defined problem. It might be possible to find someone on Upwork who could design a structure that would model both the strength and vulnerability of WTC towers in a meaningful way. This would let me put together a sort of "kit" that could be used for teaching/rhetorical purposes.

Ideally, nothing would need to actually break during the demonstration, just disconnect, but if it makes it cheaper/easier some parts could break as long as they're available in some standard issue and can be purchased in bulk (for repeated demonstrations). Obviously, I'd want the engineer to come up with the simplest (fewest parts) model using the cheapest materials, for greatest possible effect.

Part of the task would be to provide explanations of the scaling considerations. (E.g., why, say, balsa wood was used instead of metal because metal would be ridiculously strong on the smaller scale.)

But it would in any case meet Hoffman's challenge too. And it would have the authority of having been designed by an engineer. It looks like you can get one for between \$20 and \$200/hour. I wonder how many hours it would take.

EDIT: It occurs to me that this could be crowdfunded with contributions from people on both sides of the issue.

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deirdre

Senior Member.
It might be improved by challenging your model to remain standing after a lateral impact strong enough to sever one or more columns.
100 mph wind did not sever columns in the twins. at Micks scale thats the equivalent of like blowing a hair dryer on the top of the structure. which really has nothing to do with progressive collapse.

as far as mimicking the plane severing a column.. you could just shoot (with a bullet) anything you build with a meticulously pieced together webbing/lattice around the exterior, but this also has nothing to do with progressive collapse.
collapse initiation and progressive collapse are two very different things.

This would let me put together a sort of "kit" that could be used for teaching/rhetorical purposes.
you wanting a reusable model is a separate issue to the challenge as presented in the OP.

JMartJr

Senior Member
If anyone can think of a better acronym without the baggage - let me know.
I suppose "WAH" for "What Actually Happened" would come across as a bit "IYF" -- "In Yer Face!"

econ41

Senior Member
I suppose "WAH" for "What Actually Happened" would come across as a bit "IYF" -- "In Yer Face!"
I actually used that one and variants many times over the years of ongoing controversy. "What Actually Happened" OR "What Really Happened".
I preferred "Really" - because it was a bit more "in your face" for those who were stubbornly trying to justify false explanations. Didn't have a lot of success because I was agreeing with a perceived truther who was saying it loudest and "no truther can ever be right" dominated the debate. Supporting a "truther" who happens to be right is not going to win you many friends especially when you are telling those "friends" that they are fundamentally wrong.

The "Big Picture" problem was that most of the early attempts to explain the "speed" of progression took a false path dominated by misunderstanding of Bazant & Zhou's "limit case" explanation of 2001-2. Misled by assumptions that the progression collapse "crushed" the columns. That wasn't what actually happened. Just look at the pictures - the perimeter columns peeled off and broke away in "sheets" of various sizes and not a buckled example in sight.

econ41

Senior Member
I think the idea [is] that the mass/energy that destroys the structure has to be part of the structure in its initial state. So you could build a structure with a brick on top, but I don't think you'd be allowed to lift it and drop it. You would only be able to "disturb" the structure underneath it.
But you are redefining the problem which is why in my first response I raised the issue of "The opening statement already is unclear as to the purpose of the modelling. The implicit need is to validly replicate the collapse mechanism of the Twin Towers." You quoted the Hoffman Challenge and I followed by others identified that the Hoffman Challenge is poorly defined.

You are now starting to define your own challenge with this and similar comments:

I've been thinking about paying one to solve a more tightly defined problem. It might be possible to find someone on Upwork who could design a structure that would model both the strength and vulnerability of WTC towers in a meaningful way. This would let me put together a sort of "kit" that could be used for teaching/rhetorical purposes.
So I'll restate bluntly my previous comment: Why? What is your purpose? Your objective? Who is the target "audience" and what do you think the model can teach them?

I'm well aware that those are the issues that were raised in previous discussions. AND you won't be able to engage anyone to do the work until you are clear as to what you want.

So - before you try this path:
I've been thinking about paying one to solve a more tightly defined problem. It might be possible to find someone on Upwork who could design a structure that would model both the strength and vulnerability of WTC towers in a meaningful way. This would let me put together a sort of "kit" that could be used for teaching/rhetorical purposes.
I strongly recommend that you understand clearly why you are doing it.
But it would in any case meet Hoffman's challenge too. And it would have the authority of having been designed by an engineer. It looks like you can get one for between \$20 and \$200/hour. I wonder how many hours it would take.
Don't overlook that you already have one engineer and a couple of good applied scientists who have already shown that they can meet the Hoffman Challenge. Why not finalise your definition of what YOU want the challenge to be using the resource you have availble in this discussion? We wont insist on payment. Yet.

Thomas B

Active Member
you already have one engineer and a couple of good applied scientists who have already shown that they can meet the Hoffman Challenge.
I'm not clear about how this has been shown yet. But, if so, we should rename this thread "debunked", I guess. We just need clear instructions for how to build the five structures. (As we've discussed #4 may need to be softened a little, but it should withstand significant shear forces relative to its size and weight.)

Why not finalise your definition of what YOU want the challenge to be using the resource you have availble in this discussion?
Okay, let me give it a shot. If I were to formulate a challenge like this, I think I'd say something like this:

[1] Design a structure composed of 6 cube frames stacked on top of each other, with a heavy solid slab mounted in the upper face of each cube. (All the slabs must have the same weight and dimensions and must not support any load -- they are the load.) Other than the slab (top of each cube), the faces (i.e, the remaining sides and bottom) of each cube should be open. The edges (the cube frames) can be made of any material and the vertices can be joined however you like. The slabs can be joined to the frame however you like as well.

[2] The cubes do not have to be identical in strength or materials, but they must be the same size.

[3] The structure must remain standing if a second slab is placed on top of each of the six slabs. (Essentially, the load on each "floor" can be doubled without causing the structure to fail.) [EDIT: That is, the structure must be able to remain standing when loaded with 12 slabs.]

[4] The structure must remain standing under significant shear stress. By "significant" I mean relative to the total mass of the structure. I'm not sure exactly how to define it but I understand that wind loads dominate in tall building design and that's what I'm trying to capture here. Maybe something like: the structure should be able to survive shear forces applied to the top cube that double the load on the opposite side of the bottom cube. (Does that sound reasonable? Too easy?)

[5] In the absence of shear, the structure must remain standing if any one edge of any one cube is removed. (No column section or beam is allowed to be "critical".) The structure must be able to transfer loads around a single failed column section or beam.) Also, the structure must survive the slicing of any one column section by a fast-moving blade made of weaker material.

[6] Finally, if the top cube is detached and lifted the height of one cube and dropped, the whole structure must undergo total collapse. All the cubes must be destroyed. [EDIT: Each cube must fail either at the vertices or somewhere along the edges (columns or beams), or some combination, such that it can no longer support the weight of its slab. It is not sufficient that the connections between the slabs and frames fail.] Before being dropped the top cube may be rotated and tilted up to 10 degrees in any direction.

The cubes (and therefore the whole structure) may be any size, but, generally speaking, the "winning" design will be the smallest and cheapest to build that satisfies these conditions.

There may be something I've missed or explained badly. Let me know if there's something that doesn't make sense or seems like an unreasonable constraint.

We wont insist on payment. Yet.
How much do you think an engineer (hired through Upwork, for example) would want to design such a structure? How many hours would it take? What would you charge? I assume it's mainly a math problem.

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deirdre

Senior Member.
(All the slabs must have the same weight and dimensions and must not support any load -
each twin tower slab could support (dont quote me its been a long time) like 6 more slabs. so youd want your model to match the twins math as much as possible. and i would add some filing cabinet paper and furniture weight to mimic better.

Thomas B

Active Member
each twin tower slab could support (dont quote me its been a long time) like 6 more slabs. so youd want your model to match the twins math as much as possible. and i would add some filing cabinet paper and furniture weight to mimic better.
Yes, thanks. I've clarified at [3].

econ41

Senior Member
@Thomas B Thanks for your effort to define the challenge. I think it is progressing BUT let's see if we can get the various aspects into some sort of order. And I mean taxonomic order - the hierachy of importance of the various aspects in proper relationship.

I have asked you to clarify two things viz:
(a) Define what challenge you are pursuing AND
(b) be clear whether it is or is not intended to represent WTC Twin Towers collapses.

So in your lengthy post two factors go to defining the challenge. They are:
Okay, let me give it a shot. If I were to formulate a challenge like this, I think I'd say something like this:
[econ41 EDIT>>Much detail follows - defer till later]
So you explicitly state it is YOUR challenge. Which means we can discard the Hoffman Challenge - it has served it's purpose of starting the discussion; AND
Finally, if the top cube is detached and lifted the height of one cube and dropped, the whole structure must undergo total collapse. All the cubes must be destroyed. Before being dropped the top cube may be rotated and tilted up to 10 degrees in any direction.
Now that comment shouts out loud and clear that you have the WTC Twin Towers collapses in mind. Those comments reflect two of the main errors or misunderstandings about WTC Twins collapse viz: "the top cube is detached and lifted the height of one cube and dropped" and "the top cube may be rotated and tilted up to 10 degrees".

I have already in my first post identified some of the issues with the attempts to explain the actual WTC Twins collapses. The "Top cube lifted and dropped" DID NOT HAPPEN at WTC. It was - still is - impossible. It is possible for the model you propose but (i) pre-determimes the collapse mechnism that your challenge imposes on "competitors" AND (ii) has no relevance to collapse of any building of practical full scale. The reference to tilting also looks like you are adhering to another irrelvant side track of meaningless debate about the actual WTC Towers collapses. Many people have been confused by "tilting". It is irrelvant and I can provide full explanations if needed - BUT - be warned - it is a side track derail.

So lets keep clarifying where you are heading:
(1) You are now pursuing your own challewnge - not Hoffman's; AND
(2) Please confirm that you intend to constrain the debate and challenge to meet some WTC 9/11 derived features. If so you will need to say exactly how much of WTC youwant to mimic. I note all your details about "cube" boxes.

I'm not clear about how this has been shown yet. But, if so, we should rename this thread "debunked", I guess. We just need clear instructions for how to build the five structures. (As we've discussed #4 may need to be softened a little, but it should withstand significant shear forces relative to its size and weight.)
Appears to be superceded since youare now framing your own challenge and those comments refer to the Hoffman Challenge.

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Thomas B

Active Member
Which means we can discard the Hoffman Challenge
I want to insist that my specifications would meet the Hoffman Challenge, though. And also that no one (certainly not on this thread) has described a structure that meets the Hoffman Challenge. So the OP claim has not been directly debunked (though it would be by a structure that meets my challenge.)

Now that comment shouts out loud and clear that you have the WTC Twin Towers collapses in mind.
Yes.

Those comments reflect two of the main errors or misunderstandings about WTC Twins collapse viz: "the top cube is detached and lifted the height of one cube and dropped" and "the top cube may be rotated and tilted up to 10 degrees".
The idea is to make Hoffman's "disturbance near the top" less vague; all entries would need to fail after the same initiating event. (And, in fact, to rule out your idea of just dropping a brick on a balsa wood tower.) It tries to model the idea that the WTC was overwhelmed by a dynamic load it easily managed while it was static.

This initiating mechanism may not be realistic, but it is "conservative" for debunking purposes because it is much worse than what really happened. You wouldn't argue that the WTC towers would have survived if the top 20 floors had been severed, lifted 3 meters, rotated 10 degrees, and dropped, would you?

Note: I let it be tilted and rotated (but did not require it) in order not to require the column-on-column impact of Bazant's model, which, as you've mentioned, is not relevant.

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econ41

Senior Member
Great @Thomas B - we are progressing and getting closer to agreeing the challenge
Which means we can discard the Hoffman Challenge
I want to insist that my specifications would meet the Hoffman Challenge, though. And also that no one (certainly not on this thread) has described a structure that meets the Hoffman Challenge. So the OP claim has not been directly debunked (though it would be by a structure that meets my challenge.)
Understood. Tho I said "discard Hoffman" your approach recognises that Hoffman is a subset of your more comprehensively defined challenge. I think I can live with that. I will disagree with pedantic stubbornness your assertion that "no one... has described a structure that meets the Hoffman Challenge." My attempt certainly meets the wide open and loose Hoffman Challenge #1. And I could easily postulate responses to challenges #2 thru #4. I have ZERO interest in building any model so forget Hoffman #5.

So the status is: Yes my response to challenge #1 doesn't meet your more restrictive definition of YOUR challenge. But it certainly meets Hoffman. Take care that you are not generously reading Hoffman as saying what it doesn't say or as reading what you want it to say. The distinction may not matter but I leave it "on the table" as a reservation.

The idea is to make Hoffman's "disturbance near the top" less vague; all entries would need to fail after the same initiating event. (And, in fact, to rule out your idea of just dropping a brick on a balsa wood tower.) It tries to model the idea that the WTC was overwhelmed by a dynamic load it easily managed while it was static.
OK So recall my several cautions about understanding the real WTC Twin Towers collapse. What sort of "dynamic" load are you considering. Because I'm still suspecting you have "dropping top block" in mind a la Bazant's never intended to be real hypothesis (or Tony Szamboti, or D Chandler's misunderstandings). The Top Block NEVER "dropped with dynamic impact of the "Missing Jolt" variety OR the artificial pretend version of Bazant & Zhou.
This initiating mechanism may not be realistic, but it is "conservative" for debunking purposes because it is much worse than what really happened. You wouldn't argue that the WTC towers would have survived if the top 20 floors had been severed, lifted 3 meters, rotated 10 degrees, and dropped, would you?
What "initiating mechanism" are you referring to?

Sure I wouldn't argue "...would have survived if the top 20 floors had been severed," for two reasons (a) It didn't happen that way; BUT more to the point (b) It cannot be achieved - it could not be set up in a model - it is the same as my "drop a brick" suggestion which you have already rejected.

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Thomas B

Active Member
The Top Block NEVER "dropped with dynamic impact of the "Missing Jolt" variety OR the artificial pretend version of Bazant & Zhou.
I let it be tilted and rotated (but did not require it) in order not to require the column-on-column impact of Bazant's model, which, as you've mentioned, is not relevant.
You've given me a good idea. Let the "disturbance at the top" be any damage to the structure of the upper cube you like, including completely vaporizing it and re-orienting the (now free-falling slab) 10 degrees in any direction. I.e., you can do whatever you like to the frame or [of] the top cube. [Edit: but you must leave the lower 5 cubes in their initial state.]

What "initiating mechanism" are you referring to?
By "initiating mechanism" I mean what Hoffman is gesturing at with "disturbance at the top". The structure must be quite stable until you do something locally to the topmost block, which must have catastrophic consequences. Lifting it through the distance of its own height was the worst thing I could think of that could still be considered "local". But the new idea is better because it should avoid the confusion you rightly point out.

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deirdre

Senior Member.
the upper cube
the twin towers weren't cubes.

meaning, it wasnt built like a bunch of cardboard boxes stacked on each other. if that is what you are picturing.

Thomas B

Active Member
the twin towers weren't cubes
The main reason to set up the challenge this way is that makes the structure easy to understand.

Do you think this simplification makes it impossible to meet the challenge? Or do you think that it could be met but wouldn't prove anything? Does requiring cubes make the challenge too easy or too hard?

I think showing that a structure with the demonstrated strengths I've specified [3,4,5] could be completely destroyed by the initial failure of elements confined to its upper 1/6th would be a strong counter to the claim that the "official" WTC collapses were "physically impossible".

Sauron

Member
I used to have a few buddies who were pretty big into this stuff, building various models. One of them was a frequent visitor to 'Windows on the World' on his trips to NY. Not really a CT, but what I would describe as suspicions as how a building like that could fall so quickly from an 'office fire'. Anyway I remember they couldn't get the top to fully crush the bottom. This would have been over 15 years ago. Then like a lot of folk, life took over, particulary the financial crash in 08, and they moved on.

deirdre

Senior Member.
The main reason to set up the challenge this way is that makes the structure easy to understand.
i dont think you understand the structure.

Do you think this simplification makes it impossible to meet the challenge?
i could build a structure with lattice-like easily breakable " cube walls", that could break if i dropped another tilted cube with a sufficiently heavy base floor onto it. sure.

but that is not even remotely modeling the reality of the twin towers. If you want to pay someone to build such a thing, go ahead. But it isnt going to prove anything to anyone because that's not what happened.

Thomas B

Active Member
i could build a structure with lattice-like easily breakable " cube walls", that could break if i dropped another tilted cube with a sufficiently heavy base floor onto it. sure.
Are you even trying to meet any conditions of the challenge other than "a stack of cubes"?

deirdre

Senior Member.
Are you even trying to meet any conditions of the challenge other than "a stack of cubes"?
it would meet your criteria. But the twins werent cubes. so what would be the point?

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