What's the best popular account of the WTC collapses?

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Just wanted to point out why it's hard to learn anything definite from forums like this:
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Notice that these are two different accounts of what the tragic flaw of the buildings were: the open floor space vs. the welds. And neither of them has been acknowledged as the explanation for the total progressive collapse by anyone with the expertise and authority to make such judgments.
They are NOT "two different accounts" of anything and specifically not of what "THE [implied singular] tragic flaw of the buildings were" )

Jeffrey Orling's comment identifies - correctly - two of the features that dominated the overall collapse mechanism.

Mick West's comment identifies - also correctly - ONE of the key details of the collapse mechanism.

Both comments state partial truths which are complementary parts of the overall explanation The are NOT alternate total hypotheses. And neither member claimed they were total solutions.
 
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Please desist from insulting the people posting here.
That was not my intention and I apologize. I think I said quite clearly that it is difficult to evaluate the expertise of people in a forum like this. I have at no point suggested you or anyone else doesn't know their stuff. I have found some of your explanations difficult to follow and -- I thought we agreed on this -- they do remain incomplete in the sense of not offering a generalizable model with testable parts. I've been waiting to hear more from you on that.
 
We might say that this option doesn't "scale" well. So it explains why a lot of people still don't understand the collapses and are therefore open to the arguments for CD, at least long enough to begin down the "inside job" rabbit hole. Even if I don't technically need it, a good book would save me and a lot of other people (even you) a lot of time.
Focus. Focus. Focus.

The "First Principle of War" UK and AU version:
"Selection and Maintenance of the Aim - A single, unambiguous aim is the keystone of successful military operations."

If you prefer the US version it is:
"Objective – Direct every military operation toward a clearly defined, decisive and attainable objective."

I suggest that the AIM (or OBJECTIVE) is that YOU understand the WTC collapses. Not all the other things you continually "shift the goalposts" to. YOU decide what YOU want to achieve. Make your mind up what you want to achieve.
 
@ThomasB...
Note that NIST punts on explain the final phase and simply state.... global collapse ensued. They imply that the structures lost integrity and the only outcome was collapse. And this is true but they fail to explain on ANY level what mechanisms were in play in they call "global collapse".

My observation was that the independent online "researchers" (if that is the term you want to use) examined some of the MAIN claims that NIST made about the "initiation" period which led to their punt calling the next phase global collapse. NIST focused on what would happen to overheated floor trusses... and they even made scale models to test their proposition. I found some basic flaw in their approach.
1. The heat was not uniform over the entire footprint of the floors. They do not demonstrate this or how it would even be possible.
2. If the heat WAS uniform over the entire floor... there is no evidence, for example, that the entire perimeter was pulled inward at the floor where the heat was 100% engulfed in flames.
3. Wouldn't the NIST pull in force be different for the long span, short span and 2 way areas of the foot print?
4. As the pull in forces were almost certainly different at various locations.... would these forces be sufficient for example in the case of 1wtc where the drop of the top was pretty much straight down. That is... how would a local pull in lead to the uniform collapse?

It appears that NIST failed to look into core led collapse scenarios... despite the tell that the antenna was the first sign of actual "collapse" of the top "block" of 1wtc. And there is no visual evidence that the entire SE perimeter of 2wtc was the cause of its top block dropping and tilting SE.

Econ has correctly identified that the collapses has recognizable phases... and transitions from one phase to the next. The 911FreeForums was the first "appearance" of what is called ROOSD which is the best fit explanation for the "global collapse" or final phase. NB the columns DID survive the collapse of the floors and most lateral bracing. But they too failed without the bracing to keep them stable... from Euler buckling forces.... which explains the behavior slender of columns which have slenderness ratios exceeding 150.

So YES "researchers" have drilled down to the level of details of the failures within each phase. These details all conform to known engineering principles. For examples... all typical office use floor slabs were the same strength... and all mech floors were another... stronger specification. The failure from exceeding the superimposed load is known engineering... whether it is a static or (worse) a dynamic load. Floor failures were from the slabs being over loaded with debris which fell from above. Truss seats would experience similar failures if loading exceeded the design spec. Shatter slabs rendered to small chunks or concrete, aggregate and dust plus ripped and mangled trussed and truss seats are evidence of over loading. There was also evidence of weld failure and bolt pull out, shearing and so forth. These too are evidence that the collapse produced over spec conditions on the "detail" level.

There appears to be no consensus among the independent "researchers" on what were the mechanisms of the core led collapse. This took place unseen behind the facade.... with only the cumulative result visible... tops move downward and "then" ROOSD process destroys all floors. The main driver during the first "phase" was heat from fires... and the mechanical failures they caused. Progressive structural failure is also a known engineering concept. Yet the precise sequence may never be "knowable".
 

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Make your mind up what you want to achieve.
He already has. You can't force him to want to understand the collapses.

Think of this thread conversation as if the topic was "man made climate change". My understanding of what Thomas is trying to get across is that without an "expert" who is willing to write a full explanation of the science and mechanics behind AGW in a "AGW for Dummies" style book that could be easily understood by someone like me (ie. someone with no science education and almost no interest in learning the science) then AGW deniers will still exist.

Thomas isn't trying to learn. He is trying to teach YOU.

(although Thomas' responses in this thread is a perfect indication of why a forum is still needed in addition to the book. Mick's model isnt very hard to mentally expand, but if people dont understand or agree with that simple model - then the book is useless really.)
 
I feel more like this: I was pretty good at math and physics in high school, and I'm trying to build (at least) a (mental) model of WTC that shows how the the potential energy of the upper section was converted into the destruction of the lower section. My intuition tells me I should be able to do it with 4-8 columns and maybe 10 or 20 floors. (And that I should, in principle, be able to build it in Mick West's garage.) I'm told that this is impossible due to problems of "scaling". But I recall Newton was able to model the orbit of the moon with an imaginary cannonball and I've seen Brian Greene model a supernova for Stephen Colbert with five balls stacked on top of each other. That seems pretty well scaled down and was entirely illuminating. And I guess I feel like that's what such a resource might look like. But it just doesn't exist. Other than the WTC, I've never seen a structure crush itself like that.

You seem to have two issues that I can identify.

The first is the lack of a simple guide, history or explanation of 911. Despite being referred to numerous publications you don't regard these as simplistic enough. This is your issue, not the engineers. Some things in life are complex. In the absence of 911 For Dummies I guess you are just going to have to live with the detailed explanations.

I have emboldened a sentence in your post that seems to be an argument from incredulity. "I haven't seen it so it can't have happened". I haven't seen it personally either but the evidence for a collapse of that nature is overwhelming. The French technique of verinage, demolition without explosives, gives exactly the same results as we saw on 911. Catastrophic damage to a middling storey, collapse entirely within the footprint and "explosive" puffs from lower storeys.


Source: https://www.youtube.com/watch?v=NwFHEoiUZ7o&t=140s&ab_channel=Nexus

There are a dozen examples there, each of which would act as a scale model of the Twin Towers collapse.



(Edit: Apologies to @deirdre for appearing to plagiarise the Dummies reference. The posts crossed in the ether)
 
He already has. You can't force him to want to understand the collapses.

Think of this thread conversation as if the topic was "man made climate change". My understanding of what Thomas is trying to get across is that without an "expert" who is willing to write a full explanation of the science and mechanics behind AGW in a "AGW for Dummies" style book that could be easily understood by someone like me (ie. someone with no science education and almost no interest in learning the science) then AGW deniers will still exist.

Thomas isn't trying to learn. He is trying to teach YOU.

(although Thomas' responses in this thread is a perfect indication of why a forum is still needed in addition to the book. Mick's model isnt very hard to mentally expand, but if people dont understand or agree with that simple model - then the book is useless really.)
Unfortunately when you dumb down explanations which DEMAND technical understanding, training and knowledge... you can't properly explain complex phenomena. Dumbing down will not satisfy anyone!

So why would someone want to "write a book" dumbing down something that does not lend itself to being "dumbed down"?
 
Dumbing down will not satisfy anyone!
:) apparently it satisfies the newbie Truthers.

The truth is you guys on the internet that go back and forth, like to get into the nitty gritty and that is fine. But MOST 911 deniers are just random people who dont even understand what 911 Truth is saying... which is why the new advert tactic works.

ae911 says "this looks funny"
random person with no experience of cd, verinage or building collapses says "hhmmm. i does look funny, now that you mention it" (it doesnt look funny, but apparently some people think it does).

Either way Thomas is wrong. an engineer written book wont help. besides Husley is 'qualified' ..sort of. and he was wrong in all sorts of ways. so it doesn't matter who wrote this book, it would be dismissed by Truthers just like everything else is dismissed by Truthers.
 
Make your mind up what you want to achieve.
I'm sorry if I seem undecided on this and I'm not sure why you're getting that impression. As I said in a direct message to you back in August, "just so you don't spend too much time for nothing [explaining the collapses to me], keep in mind that my focus isn't on understanding the collapses themselves but on connecting them to the body of mainstream engineering knowledge."
 
The French technique of verinage, demolition without explosives, gives exactly the same results as we saw on 911.
Yes, this is in principle a very good model. The book I'm imagining might indeed basically teach the reader how and why verinage works and then apply that knowledge step-by-step to what happened to the WTC. I say "might" because I'm not sure it's the whole story, but I'm completely open to the idea.

By the way, I don't know where this idea that I want a book "for dummies" came from. (I hope I didn't encourage it.) I want a very smart popular science book for people who have a good grasp of physics and math but who are laypeople when it comes to structural engineering and tall buildings.
 
A lot of this comes down to a question of motivation.
What do you (or your hypothetical audience) want to achieve?

If it's a "complete" understanding of the collapse because you are interested in civil engineering, go study civil engineering. It's an interesting subject.

If it's to decide whether the conspiracy theorists are right, go look at the conspiracy theories with open eyes. That's been done, its conclusive.

Sometimes children will annoy their parents by not accepting any answer, asking "why" on the answer they're given, ad infinitum. You typically do that not from a constructive motivation such as the two outlined above, but because you want to defend an indefensible poisition. You are playing a game (for whatever reason) that you don't want to admit defeat to. It is impossible to shut this game down.

We need to acknowledge that a highly qualified group of engineers (NIST) has admitted partial defeat on finding these answers. The reason for this is that the WTC collapse is unprecedented. The existing body of research on large buildings hit by passenger jets is (happily) quite small, and even similar events are hard to come by, so the body of knowledge on these events is small and has many open questions that can't be answered conclusively. Spending more money on this has no benefit as most other skyscrapers are constructed differently.

But the most basic explanation is official: the aircraft collisions with the building were sufficient to initiate the building's total collapse; it is not necessary to look for other explanations.

So when you are asking for a more complete explanation that you found, you need to expend some introspection and ask yourself why you are doing it. If you want to learn more about civil engineering, choose better sources. If you want to debunk conspiracy theories, examine the claims made by them. If you want to question for questioning's sake, ask yourself what you're getting out of it -- why you are doing it. It's likely that getting no answer is what you want, and in that case, you can't get one that satisfies you.

We might say that this option doesn't "scale" well. So it explains why a lot of people still don't understand the collapses and are therefore open to the arguments for CD, at least long enough to begin down the "inside job" rabbit hole.
The thing to do is to look at the "arguments" for CD: how much explosive was needed, where was it needed, how would it have been installed, how would it have been ignoted, why would it have been ignited when it was, ...

You can't get people out of a cult just by looking at established religions.

These comparisons and thought experiments are really good and they are precisely the ones I hope to see an engineer or popularizer work through in detail.
What do you want to popularize, though? More simpified poplar accounts of the collapse exists; any popular simplified account can be questioned on the details, and we have no authoritative details on the collapse.

If you want to popularize civil engineering, choose collapses that are better understood to do this work. (I've said it before, there are fun computer games out there that simulate aspects of these.)

Again, it's the non-existence of even a thought experiment like this in the mainstream (popular media) conversation that disappoints me. Until someone (with authority) "builds" this model, the truthers will continue to be born out of sheer incomprehension (not a predisposed conspiracy mindset.)
I challenge this claim in its entirety.
I would love to see you support it.
 
By the way, I don't know where this idea that I want a book "for dummies" came from. (I hope I didn't encourage it.) I want a very smart popular science book for people who have a good grasp of physics and math but who are laypeople when it comes to structural engineering and tall buildings.




Even where conspiracy theories exist, there are usually several longform articles and books that ignore them altogether (or relegate them to a footnote) and just lay out the (often very interesting) story of how investigators solved the puzzle of how it happened. There's also usually a good documentary film or two.

(The narrative is usually: here's what puzzled scientists at first and here's how they finally solved it. Sometimes there's a subplot of scientists competing to be first with a solution.)

Since around 2005, when I first got interested in this question, I've been waiting for something definitive and detailed in this vein to be published. Something that requires ordinary intelligence and a grasp of highschool physics to follow
 
@Thomas B
I have been droning on for years that the 3 buildings were UNIQUE designs ie having unconventional innovative structural designs which DETERMINED the form of collapse... ie how / why structural failures could/would PROGRESS in a runway manner to complete destruction. In 7wtc the "faulty" DNA was the column free office space and the transfer structures needed to build over Con Ed. IN the twin it was the column free office spaces, the very thin non stone aggregate concrete supported on very lightweight bar trusses, the use of gyp board for shafts. The "genes"m manifest once there was uncontrolled fire which worked on the steel frame... expanding, contracting, displacing. etc.
These were unstoppable cascading failures.
THAT is something NIST did not want to leave with the public.
 
He already has. You can't force him to want to understand the collapses.

Think of this thread conversation as if the topic was "man made climate change". My understanding of what Thomas is trying to get across is that without an "expert" who is willing to write a full explanation of the science and mechanics behind AGW in a "AGW for Dummies" style book that could be easily understood by someone like me (ie. someone with no science education and almost no interest in learning the science) then AGW deniers will still exist.

Thomas isn't trying to learn. He is trying to teach YOU.

(although Thomas' responses in this thread is a perfect indication of why a forum is still needed in addition to the book. Mick's model isnt very hard to mentally expand, but if people dont understand or agree with that simple model - then the book is useless really.)
That is a good alternate summary Deirdre. The criticism of my "forcing" is valid as far as it goes.

BUT I'm not trying to force him to "want to understand" - he has already made that clear many times. I AM unashamedly pressing him to choose ONE goal out of several. To make it his priority. And to resolve it independently of his wish to pursue other goals OR impose other limiting criteria.

His understanding is an achievable goal. It is the only one of his goals that is within his own scope of control -- provided he can set aside his requirement that it must come from an authoritative published "book" or paper(s).

"I want to understand WTC collapses by learning from a published book that has wide professional acceptance" is NOT an achievable goal. And that goal only accommodates the two highest order issues out of the half dozen or so criteria he is seeking to combine.

I'm saying "take it one bit at a time" AND "understanding the mechanisms of collapse" is the most important because it lies at the foundation of the suite of other needs and criteria which Thomnas has expressed.
 
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I'm saying "take it one bit at a time" AND "understanding the mechanisms of collapse" is the most important because it lies at the foundation of the suite of other needs and criteria which Thomnas has expressed.

are you saying that if he learns what i have learned on Metabunk, then he would realize why no one has written such a book for 1)actual engineers in the building trades, or 2) lay people with above average intelligence for physics and math or 3) lay people with average intelligence and high school level physics. ?
 
I'm sorry if I seem undecided on this and I'm not sure why you're getting that impression. As I said in a direct message to you back in August, "just so you don't spend too much time for nothing [explaining the collapses to me], keep in mind that my focus isn't on understanding the collapses themselves but on connecting them to the body of mainstream engineering knowledge."
Then keep THAT as your prime focus. The Metabunk rules will help. So focus your discusion on your goal:
(a) avoid yourself pursuing other debates and
(b) ask others to keep to THAT topic.

And may I suggest it goes beyond the current thread topic of "what is the best [current] account...." because we all seem to be agreed there is no extant "book" that meets your standard.
 
are you saying that if he learns what i have learned on Metabunk, then he would realize why no one has written such a book for 1)actual engineers in the building trades, or 2) lay people with above average intelligence for physics and math or
Mmmm... I think that is close. I cannot comprehend exactly what you have "learned on Metabunk"

But I am confident of my version - what I have learned from all my experiences including over 40k posts on half a dozen forums and an uncounted lesser number on FaceBook. And my own primary reason for joining and continuing involvement in on-line debate was to improve my own understand so that I could assist others who are unsure about the applied physics of WTC collapses.

I fully agree the varying levels of target. They are all valid. My own focus mostly on "3) lay people with average intelligence and high school level physics." adding "who are prepared to join in serious honest debate".
 
You seem to have two issues that I can identify.

The first is the lack of a simple guide, history or explanation of 911. Despite being referred to numerous publications you don't regard these as simplistic enough. This is your issue, not the engineers. Some things in life are complex. In the absence of 911 For Dummies I guess you are just going to have to live with the detailed explanations.
..."or trust some of us who do understand and can explain."

Well said Sir. That is the core of the debate in a simple paragraph.
 
You are playing a game (for whatever reason) that you don't want to admit defeat to. It is impossible to shut this game down.
This is an unfortunate perception, but it's helpful that you state it. I do feel like many people here are playing some sort of game (maybe whatever game is normally played here). Hence the idea that there are "goalposts" to move, etc. I didn't start this thread to win anything, and so I wasn't expecting to lose. It's interesting that you see it this way. But it just isn't what I'm doing.

We need to acknowledge that a highly qualified group of engineers (NIST) has admitted partial defeat on finding these answers.
I'm not sure, but it's possible you're right about this. The book I'm imagining would get clear statements from the NIST investigators about where they had to give up and why. As in all other areas of scientific investigation, there are presumably engineers working on the questions that are still open. Again, an interesting story, and one that I would love to see covered in a work of popular science.

Spending more money on this has no benefit as most other skyscrapers are constructed differently.
Two things here. First, there are buildings that are in full use that use the same design principles. Aon Center in Chicago is one that I know of. These buildings are presumably vulnerable to collapse in the same way. (And I don't think the mainstream view is that the three buildings that collapsed on 9/11 were uniquely vulnerable. But, again, that would be in the book if it is the case.) Second, I'm not really proposing spending money on this, but, making money on it; it's a project for a publisher of books or magazines to take on -- out of self-interest, to satisfy market demand.

But the most basic explanation is official: the aircraft collisions with the building were sufficient to initiate the building's total collapse; it is not necessary to look for other explanations.
As I understand it, this isn't quite right. Certainly WTC7 would have come down by fire alone (as the NIST FAQ #22 explains). And it is usually said that the towers performed well against the aircraft impact but could not survive the fires. In any case, I'm not talking about what it was necessary to explain, but what it would be nice to be able understand.

So when you are asking for a more complete explanation that you found, you need to expend some introspection and ask yourself why you are doing it.
Out of curiosity. And (see below) because I think the strange "games" (see above) we play in these forums are dancing around the issue of unsatisfied curiosity.

What do you want to popularize, though? More simpified poplar accounts of the collapse exists; any popular simplified account can be questioned on the details, and we have no authoritative details on the collapse.
I want to popularize the science of the WTC collapses. (Just like one might popularize the research on the Titanic.) A lot of work has been done and some is ongoing (I look at the literature every now and then). A book like the one I'm imagining could be updated almost annually just because someone discovered something new and interesting.

I started this thread to find out what the best popular account is according to people who are obviously interested in the collapses too. You say "they exist" -- but what's your favorite one? Maybe it's one that I've missed. But I don't think it's exactly true that there are no authorities on the collapses. I'm sure that within the engineering community there are recognized experts on progressive collapse that have a well-formed opinion about what happened to the WTC towers. These authorities just haven't been given a clear voice in popular discourse -- at least not recently.

"Until someone (with authority) "builds" this model, the truthers will continue to be born out of sheer incomprehension (not a predisposed conspiracy mindset.)"

I challenge this claim in its entirety.
I would love to see you support it.
I regret the definite article in front of "truthers". I should have said, just "truthers", or maybe "some truthers" (though I think I mean -- very unscientifically -- "many truthers"). My theory is that 9/11 is for many people -- especially young people -- the first conspiracy theory they entertain. Some (many?) of them are predisposed to reject other conspiracy theories (about the moon landings, UFOs, JFK) but they find it difficult to dismiss the "controlled demolition" argument.

The reason is that they think, as I did back in 2005, that it must be a relatively simple matter of "looking up the science" and seeing that the "physically impossible" line that truthers take is just wrong. Back in 2005, before the NIST report had come out, it was still reasonable to say that the scientists were "working on it" and answers would be forthcoming soon. But 20 years after the collapses we really do expect there to be a solid, authoritative, scientific answer to the questions -- a straightforward structural model of progressive collapse applied in detail to the WTC towers.

So the mere fact that the only way to engage with these questions is through forums that are about conspiracy theories gives them credence that I don't think they deserve. It should be possible to go straight to the science and get satisfying answers to the questions that conspiracy theories say are unanswered. They should literally be wrong about that and it should be easy to show this.

Thus begins, I think, the journey down the rabbit hole for a significant number of people. I'm happy to grant that it's not the only trajectory for truthers (and probably not the ones you've engaged with here in the past), and that some do come to 9/11 "predisposed" to find something sinister there. But it's sad and unnecessary to let it be the first issue where young people lose their trust in (scientific and political) authorities. It should be possible to learn how the WTC collapsed without going down the rabbit hole.
 
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I'm not sure what such resources would look like.
With all due respect (and admiration) for Edward's comparison of WTC to a can of sodapop, consider Engineering Guy's explanation of how aluminum cans are literally made.

It breaks down a known process into clear and distinct operations that can be understood by a non-specialist. And it provides links at the end to even more detailed explanations and animations. The key here is that it's a known process and the presenter is obviously an enthusiastic admirer of that knowledge. There doesn't have to be any mystery at all about how aluminum cans work and how they are made. It's also easy to explain how they came to look as they do today (economic, environmental, safety issues are also touched on). There are nice juxtapositions of live action and animated models (to explain the leverage involved in the tab, for example).

Some people here have argued that the WTC collapses are actually not as well understood by engineers as the making of aluminum cans. But that's almost like saying we don't know how they remained standing up til their demise. The point is that we know exactly how tall buildings work (we don't just hope they'll remain standing) and we know how they fall down (often by demolition, sometimes by fire, sometimes partially, sometimes totally). We know what must have failed. We can explain this just as clearly and succinctly as Engineering Guy can talk about cans -- i.e., without embroiling ourselves in any controversy whatsoever.

Or that's at least what such resources would look like to me.

If the collapse of the WTC is not a "known process" in the sense I'm suggesting, then the truthers have a much stronger case (at least for more "investigations") than I think we generally give them credit for. My assumption remains that engineers, as a profession, are not still puzzled.
 
Perhaps this problem exists because buildings should not collapse "easily". And they don't. We also know that CD of tall building place charges on columns low in the structure and time the sequence of destruction to control where / how it falls... into a relatively compact pile of the property it is built on. Engineers design these destructions to conform to their objective of a "neat" collapse.

The impact of a large plane hitting a tower which is 95% air and less than 1% structural steel would destroy the plane and elements of structure where the plane impacted. There was not enough energy to "push" the tower over... and the tower was not stiff enough to act as a unit and break its connections at the base to allow it to tip over.

The plane strikes caused massive local structural damage which was not fatal with the fires which ensued. The towers survived the plane impacts... and one of the reasons is that they were mostly AIR.

If the entire mass of a twin tower were in one "column" standing as high as the towers were.... assuming that the column could self support and was not too slender.... and the plane hit it... what would happen? The plane would be sliced and the column likely would sway but remain standing. Engineer could calculate the forces needed to be applied at a dynamic point load at the equivalent height of the 92nd floor to break the column free at the foundation and cause it to topple over. This is a somewhat useless thought experiment.

The simplified explanation that is sought ... popular "every-man science"... would acknowledge that the collapse was a PROGRESSIVE process. And in a very real sense it was a runaway, ie unstoppable progression. Mick's models show a runaway progressive collapse in a highly simplified way.

Every-man wants to know how plane damage + fires lead to the building completely collapsing. And in the case of 7wtc... how fires alone can produce this result.

So Mick's model and the discussion of ROOSD is basic settled trivial engineering. A beam can support X pounds and then it fails... Once the sufficient threshold mass was dropping inside the tower... it would destroy each floor consecutively and uninterrupted. That accounts for the slabs. The columns and the facade fell for other basic structural reasons... and it is described in the Euler formulas for the limits of slender columns to self support. There is a limit of how tall a flag pole of X diameter can be. Try to extend it taller and it would buckle under its own weight... and topple over.

So....
Every-man needs to learn and understand what fire and heat do to building materials aside from combustion. The fires were fueled by available combustible materials... jet fuel at first and then office contents immediately thereafter.
Steel and concrete do not burn at the temps of the fires in the WTC.

"The behavior of concrete at high temperatures is influenced by several factors, including the rate of temperature rise and the aggregate type and stability. Abrupt temperature changes can cause cracking and spalling due to thermal shock, and aggregate expansion can also produce distress within the concrete.

High temperatures also affect the compressive strength of concrete. Above 212º F, the cement paste begins to dehydrate (loses chemically combined water of hydration), which gradually weakens the paste and paste-aggregate bond.

The temperature that concrete has reached often can be determined by observing color changes in the aggregate. For example, limestone aggregates turn pink when they reach about 570º F, which can result in substantial loss of compressive strength."

Spalling -
"There are two drivers for spalling of concrete: thermal strain caused by rapid heating and internal pressures due to the removal of water. Being able to predict the outcome of different heating rates on thermal stresses and internal pressure during water removal is particularly important to industry and other concrete structures.

Explosive spalling events of refractory concrete can result in serious problems. If an explosive spalling occurs, projectiles of reasonable mass (1–10 kg) can be thrust violently over many metres, which will have safety implications and render the refractory structure unfit for service. Repairs will then be required resulting in significant costs to industry.[2]"

Heat weakens and eventually destroys concrete.

Heat weakens steel
Heat causes steel to expand.

Excessive heat caused havoc in the WTC steel engulfed in flames. This included:
lateral beams / bracing
columns
bolted knife connections
splice plates
bar trusses
metal Q decking

All of the above are "settled engineering". What is NOT KNOWN is.... where the heat was causing the problems.... which beams and columns and so on were losing their ability to perform to design specification. We don't know the precise fuel load.... it can only be "guessed at" with some reasonable certainty. We can't know the precise sequence of failures without SEEING those failures which were taking place behind/inside the facade.

All that can be done are theoretical models of the sequence of failures which occurred to the compromised plane damaged structure. This is one "guess" of a possible "sequence of inside the core failures" for 1wtc.


Core Failure Cartoon_page1.jpg

It attempts to show the failure of core columns progressing southward.
It does not show what was happening to the bracing between those columns which was expanding and exerting lateral forces and perhaps causing the misalignment of columns, destroying bearing area and leading to buckling.
Loads do not disappear... so they are redistributed when a column "fails" and this causes other columns to assume increased loads which can lead to their being overloaded. THERE IS excess capacity in the design of the steel... beams and columns. But when the excess capacity is insufficient the steel member will fail and then the loads are redistributed and the these steel failures go "runaway".

When aggregate axial capacity is no longer sufficient to support what is above... "above" drops down.

All of this is settled engineering. There is nothing mysterious to discover about the WTC collapses... other than:

THE PROGRESSION OF FIRE/HEAT THROUGH THE STRUCTURE

THE PROGRESSION AND LOCATION OF STRUCTURAL STEEL AND CONCRETE FAILURES

This is unknowable without "being there". We can only make educated guesses based upon what WE CAN SEE... building movements, smoke, etc.

++++

So the discussion of interest may be.... can skyscrapers be designed to isolate and arrest structural failures to prevent them from going "runaway"?

Are some structural systems less PRONE to going runaway?

and the corollary...

Are some structural systems MORE prone to going runaway?

The above includes the construction DETAILS.

As building construction/design decisions are economically driven (as well as code and technology)... are designs less prone to going runaway more or less expensive or the same cost to build... including the time to erect the structure?

I leave it there for now.
 
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@Thomas B.
"If the collapse of the WTC is not a "known process" in the sense I'm suggesting, then the truthers have a much stronger case (at least for more "investigations") than I think we generally give them credit for. My assumption remains that engineers, as a profession, are not still puzzled."

Engineers are not puzzled.
EVERYONE is puzzled by what they can't see nor measure.
Engineers KNOW what fires and mechanical damages do to structures. THIS IS SETTLED ENGINEERING SCIENCE.

No one will make a declarative statement(s) about what PRECISELY happened leading to the collapse because there is NO DATA. There are only guesses.... estimates... and reasonable assumptions.

++++

Look at the "investigation" of the explosion of the space shuttle. The cause was solved by applying settled engineering to the design and some temperature data which indicated that the O-rings would fail at those temps.
NO ONE MEASURED THE TEMPS OF THE O RINGS.
The explanation was accepted because it aligned with the data they had and settled engineering.
 
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This is an unfortunate perception, but it's helpful that you state it. [..]But it just isn't what I'm doing.
This part of my statement wasn't aimed specifically at you, I was just listing possibilities (seeking knowledge on civil engineering, knowledge on the CT, or just asking for asking's sake). I didn't mean to presume your motivation.


Second, I'm not really proposing spending money on this, but, making money on it; it's a project for a publisher of books or magazines to take on -- out of self-interest, to satisfy market demand.
You'd need to spend money on research to produce the knowledge you want to put in the book -- far more money than this book could ever make.


As I understand it, this isn't quite right. Certainly WTC7 would have come down by fire alone (as the NIST FAQ #22 explains).
No. Read FAQ #4:
Article:
4. What caused the fires in WTC 7?

Debris from the collapse of WTC 1, which was 370 feet to the south, ignited fires on at least 10 floors in the building at its south and west faces. However, only the fires on some of the lower floors—7 through 9 and 11 through 13—burned out of control. These lower-floor fires—which spread and grew because the water supply to the automatic sprinkler system for these floors had failed—were similar to building fires experienced in other tall buildings. The primary and backup water supply to the sprinkler systems for the lower floors relied on the city's water supply, whose lines were damaged by the collapse of WTC 1 and WTC 2. These uncontrolled lower-floor fires eventually spread to the northeast part of WTC 7, where the building's collapse began.


And it is usually said that the towers performed well against the aircraft impact but could not survive the fires. In any case, I'm not talking about what it was necessary to explain, but what it would be nice to be able understand.
Yes, you are talking about that. You specifically claim that it is necessary to explain this to prevent more "truthers" being born.
If you're at "nice to be able to understand", then accept that you won't, because the data to base this understanding on just isn't there. You can understand the potential mechanisms, each of which would be sufficient to cause the collapse. But you won't be able to say with certainty what happened.

Out of curiosity. And (see below) because I think the strange "games" (see above) we play in these forums are dancing around the issue of unsatisfied curiosity.
If you perceive a "strange game" being played, the prudent move is not to play. Yet you do.

I want to popularize the science of the WTC collapses. (Just like one might popularize the research on the Titanic.) A lot of work has been done and some is ongoing (I look at the literature every now and then). A book like the one I'm imagining could be updated almost annually just because someone discovered something new and interesting.
Then why don't you write this book? Create a draft, then look for a co-author with civil engineering credentials (and pay them).

A Google search suggests "Structures: Or Why Things Don't Fall Down" and "Why Buildings Fall Down: Why Structures Fail" are good books on civil engineering principles if you're interested in the science of it.

The NTSB investigation into the Florida University pedestrian bridge collapse was an interesting read for me; that's how a thorough report looks like where the investigation had a strong set of data to work with. You're not going to see that level of understanding for the WTC collapse because much of what happened in the collapse sequence itself is not well documented -- most of what we have is footage of a dust cloud.

I'm sure that within the engineering community there are recognized experts on progressive collapse that have a well-formed opinion about what happened to the WTC towers. These authorities just haven't been given a clear voice in popular discourse -- at least not recently.
I doubt this claim. Can you support it?

Scientists work by communicating their findings and critiquing each other. A "recognized expert" that has kept quiet for years is an oxymoron.


I regret the definite article in front of "truthers". I should have said, just "truthers", or maybe "some truthers" (though I think I mean -- very unscientifically -- "many truthers"). My theory is that 9/11 is for many people -- especially young people -- the first conspiracy theory they entertain. Some (many?) of them are predisposed to reject other conspiracy theories (about the moon landings, UFOs, JFK) but they find it difficult to dismiss the "controlled demolition" argument.
To dismiss the CD argument, you need to look at the CD argument. That is not what you are asking.

What you need to come to grips with is that the CD theory stokes the fear of teams of government-supported terrorists installing tons of explosives in buildings all around the country that nobody has ever found. The people stoking unreasonable fears and keeping them going are profiting off that; people need to reflect on which media they consume to identify the sources of that and cut those out of their life. (My suggestion would be to stop watching Fox News and get off Facebook.)


The reason is that they think, as I did back in 2005, that it must be a relatively simple matter of "looking up the science" and seeing that the "physically impossible" line that truthers take is just wrong.
"physically possible" and "that's what definitely happened" are two different goal posts. The NIST report authoritatively establishes "physically possible".

But 20 years after the collapses we really do expect there to be a solid, authoritative, scientific answer to the questions -- a straightforward structural model of progressive collapse applied in detail to the WTC towers.
No, "we" don't; because the data isn't there that you could validate the model with. New answers require new evidence.

So the mere fact that the only way to engage with these questions is through forums that are about conspiracy theories gives them credence that I don't think they deserve. It should be possible to go straight to the science and get satisfying answers to the questions that conspiracy theories say are unanswered. They should literally be wrong about that and it should be easy to show this.
You are writing here that your motivation for answering these questions are the CTs, yet you ask that the forums who work on them should not engage the CTs?

I don't think that Metabunk "gives them credence"; Metabunk does not engage with questions, but rather with claims, and debunks them.

As I said before, you can play games with questions for eternity. That doesn't make the claims true. If you want to know about the CTs, look at the CTs. Anything else is detraction.

It should be possible to learn how the WTC collapsed without going down the rabbit hole.
It is. Read the Wikipedia article .

P.S.: The popular explanation of the slabs falling on other slabs to produce a runaway collapse was published in a popular German magazine back in September 2001. There was no reason to doubt it.
 
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NIST has spoken.
NIST has presented an outside the core truss failure cause for initiating the collapse. They modeled what happens to the trusses exposed to excessive heat. They showed that there would be lateral forces exerted by the over heated trusses at the facade which they assert would cause it to buckle. When the facade buckles it can't support the loads above and so the facade above and the floor slabs attached to it collapse downward.

Is there visual evidence to support this?

Color me unimpressed.

Why?

It would seem that (in the case of 1wtc) there would need to be a uniform floor truss failure of all trussed around the core at pretty much the same time.
This would imply uniform heating of all the trusses. Seems unlikely
This would mean that all trusses exert more or less the same lateral pull.
But there were short and long trusses and they would exert different pull in force.... less at the short span sides and more at the long span sides.
And likely little to no forces at the 4 corners where the heat expansion likely would pull at the 4 truss girders more than the facade (guess).
There is hardly inward bowing uniformly around the building just prior to the top's descent.

Lookie here:

Source: https://www.youtube.com/watch?v=WwXLIdMzmG8&ab_channel=mmmlink



Source: https://www.youtube.com/watch?v=iNS2Mld9v24&NR=1&ab_channel=achimspok


And if you want to read here is a website which has all research about the WTC collapses

http://www.sharpprintinginc.com/911/
 
Look at the "investigation" of the explosion of the space shuttle. The cause was solved by applying settled engineering to the design and some temperature data which indicated that the O-rings would fail at those temps.
NO ONE MEASURED THE TEMPS OF THE O RINGS.
The explanation was accepted because it aligned with the data they had and settled engineering.
There's a famous moment when Richard Feynman demonstrates the effect of temperature on the O-rings. The mechanism wasn't just supported by settled science and past temperature data. Once it had been proposed, it was also demonstrable. The effect could be modeled and reproduced in the lab. It could be tested without launching another shuttle.
 
There's a famous moment when Richard Feynman demonstrates the effect of temperature on the O-rings. The mechanism wasn't just supported by settled science and past temperature data. Once it had been proposed, it was also demonstrable. The effect could be modeled and reproduced in the lab. It could be tested without launching another shuttle.
Wrong... the behavior of the o ring related to temperature was settled science. The launch operators erred in authorizing the launch in out of (below) spec ambient temperatures.

But of course it was modeled and Feynman's thesis was proved correct.
 
Wrong... the behavior of the o ring related to temperature was settled science. The launch operators erred in authorizing the launch in out of (below) spec ambient temperatures.

But of course it was modeled and Feynman's thesis was proved correct.
What part are we disagreeing about?
 
There's a famous moment when Richard Feynman demonstrates the effect of temperature on the O-rings. The mechanism wasn't just supported by settled science and past temperature data. Once it had been proposed, it was also demonstrable. The effect could be modeled and reproduced in the lab. It could be tested without launching another shuttle.
Have you read the report? Or at least Feynman's account of his work on that commission? Do you know how much data they had on this?! A shuttle launch is a repeated event, NASA had data on the blowby effect on O-rings on past launches, paired with exact temperatures at the launch site (measured in various locations all around and up the shuttle), clear footage from multiple cameras, etc. The data they had for identifying the progression of the explosion of the shuttle, and the data used to validate the modeling that was done afterwards, is so much more than we have on the WTC collapse. The fact that the start of the progression of the disaster could be narrowed down to the O-ring blowby is due to this data being available in the first place.
 
Have you read the report? Or at least Feynman's account of his work on that commission? Do you know how much data they had on this?! A shuttle launch is a repeated event, NASA had data on the blowby effect on O-rings on past launches, paired with exact temperatures at the launch site (measured in various locations all around and up the shuttle), clear footage from multiple cameras, etc. The data they had for identifying the progression of the explosion of the shuttle, and the data used to validate the modeling that was done afterwards, is so much more than we have on the WTC collapse. The fact that the start of the progression of the disaster could be narrowed down to the O-ring blowby is due to this data being available in the first place.
Same question I asked Jeffrey: what are we disagreeing about? What did I say that you think is wrong?
 
The mechanism wasn't just supported by settled science and past temperature data.
Is it the "just" you're overlooking then? I agree with you that is was also supported by that. I was saying it wasn't just supported by it. I was adding the observation that the effect could be modeled in theory and demonstrated on a sample.
 
Is it the "just" you're overlooking then? I agree with you that is was also supported by that. I was saying it wasn't just supported by it. I was adding the observation that the effect could be modeled in theory and demonstrated on a sample.
I'm perceiving your argument to be that, because an aspect of the Challenger explosion could be demonstrated at a conference table, we can expect to see all aspects of the WTC collapse demonstrated in such a manner. (Some aspects have been demonstrated, e.g. the sideways ejection of boards in a collapsing model).

This expectation is misguided, because a) Feynman's demonstration encompassed only a small part, not the whole sequence of the explosion, and b) NASA has way more data on the launches than NIST has on the collapse.
 
I'm perceiving your argument to be that, because an aspect of the Challenger explosion could be demonstrated at a conference table, we can expect to see all aspects of the WTC collapse demonstrated in such a manner. (Some aspects have been demonstrated, e.g. the sideways ejection of boards in a collapsing model).

This expectation is misguided, because a) Feynman's demonstration encompassed only a small part, not the whole sequence of the explosion, and b) NASA has way more data on the launches than NIST has on the collapse.
No, I didn't have a big point like that in tow. I was responding to Jeffrey's remark about no one having measured the temperature of the actual O-rings on the ill-fated Challenger. (I assumed he meant that this was a bit like all the data we don't have on the WTC because it's obscured by dust.) And yet we can still identify the O-rings as a cause. Part of the reason, I suggested, is that once the "settled science" has suggested this as a possible cause, it can be modeled and tested.

Something similar goes for the WTC collapse mechanism. Since we know what the structure's initial state was, we can propose a variety of collapse mechanisms and model them. Some lead to total collapse, some don't. So we go with the ones that do -- since that's in fact what happened. That doesn't mean I expect everything to be modeled and demonstrated. It just means that the lack of data from the original event doesn't leave us clueless about what (probably) happened.
 
Most major (engineering as well as aviation) disasters have an often substantial "popular science" literature. Even where conspiracy theories exist, there are usually several longform articles and books that ignore them altogether (or relegate them to a footnote) and just lay out the (often very interesting) story of how investigators solved the puzzle of how it happened. There's also usually a good documentary film or two.
Can you give an example of a disaster and subsequent literature that gives an idea of how you'd like the WTC collapses to be covered/explained?
 
......

Something similar goes for the WTC collapse mechanism. Since we know what the structure's initial state was, we can propose a variety of collapse mechanisms and model them. Some lead to total collapse, some don't. So we go with the ones that do -- since that's in fact what happened. That doesn't mean I expect everything to be modeled and demonstrated. It just means that the lack of data from the original event doesn't leave us clueless about what (probably) happened.

Here's the deal as I see it.
There were no heat transducers in the towers. The temps of fires were INFERRED based upon what they assumed fuel which was burning at the time. Some temps at the surface could have been determined with infrared sensing from afar... I believe.
There is no way of knowing where the burning ACTUALLY was and how it spread. THESE are educated guess by "experts".
There is no way to know how the steel cooled when the fire "moved" or consumed the fuel. THESE are educated guess by "experts".

What is known:
The structural design - steel and concrete.... connection details
The performance of building materials at various temperatures
What was the damage to the the facade by the plane
What was the damage to the facade between plane strike and release of the top block (descent)
Movement of the parts of the building (time and displacement)
Smoke location, time and volume
movement of the top block... vertical, lateral, rotation etc.
movement of the antenna

What is approximated:
The amount of damage caused by the jet
The amount of jet fuel that entered and burned inside the tower and where that was
The amount of combustible material on the floors where the fire likely burned.
The impact on the sprinkler water before it was gone
The amount of fresh air / oxygen supply from inside and outside the tower for combustion
ERGO
the temperature of the fires
the duration of the fires

What can be modeled
the location of the fires
load redistribution based on assumed axial member failures
failure of joints/connections
lateral forces from expansion, sagging or contraction of a specific section
behavior of concrete subject to assumed heat

Any model has to produce what we observed in real world or the model is a failure.

All model needs to consider aspects / deformities etc. which might not be causal to the collapse, but artifacts of the process.
 
Can you give an example of a disaster and subsequent literature that gives an idea of how you'd like the WTC collapses to be covered/explained?
Titanic and Challenger are pretty good examples. In fact, I'm grateful to Jeffrey for reminding me of Feynman. I didn't know they had made a movie with Jeff "the Dude" Bridges William Hurt* in the lead role!

I'm watching it now. Great stuff so far. It shows precisely the sort of behind-the-scenes drama that we expect the scientific investigation to have. It also (by analogy) suggests some reasons to doubt the seriousness of the NIST report. Yes, I know, it's a dramatization and sort of a cliché of government bureaucracy (which Feynman hated, I'm told). But it's also a true story and Feynman really did sort of blow the whistle on what was turning out to be cover up / white wash. Interesting to think about.

In any case, it's that sort of narrative -- or rather, the basis of that sort of narrative (the political and science journalism that informs it) that I'm thinking of. Even if NIST did everything by the book, with no intrigues to speak of, the process of discovery can itself be a gripping story. It hasn't really been told.

*What a dumb mistake! My apologies to both great actors.
 
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Titanic and Challenger are pretty good examples. In fact, I'm grateful to Jeffrey for reminding me of Feynman. I didn't know they had made a movie with Jeff "the Dude" Bridges in the lead role!

I'm watching it now. Great stuff so far. It shows precisely the sort of behind-the-scenes drama that we expect the scientific investigation to have. It also (by analogy) suggests some reasons to doubt the seriousness of the NIST report. Yes, I know, it's a dramatization and sort of a cliché of government bureaucracy (which Feynman hated, I'm told). But it's also a true story and Feynman really did sort of blow the whistle on what was turning out to be cover up / white wash. Interesting to think about.

In any case, it's that sort of narrative -- or rather, the basis of that sort of narrative (the political and science journalism that informs it) that I'm thinking of. Even if NIST did everything by the book, with no intrigues to speak of, the process of discovery can itself be a gripping story. It hasn't really been told.
My suspicion.... with no evidence to support this.... is... NIST "needed" to produce a safe report which showed no liability or questioned the wisdom of decisions on any level for anyone associated with the development, design, maintenance, management or these buildings.

So....
It is my BELIEF that the A11 impact caused shorts... these caused explosions in MULTIPLE locations: sub basement, and in the substation itself. I would look into the fires damage from the sub station "fires" when switch gear exploded. This would impact the floors 5-7 which contained MECH equipment. Jennings and Hess experience damage from the sub station explosions and this MAY have been a cause of column failures at 79, 80 or 81. I don't believe that a scenario similar to this was explored.

Why were there so much fire on flrs 12/13 in the NE quadrant of 7WTC?
Not explained.

Why was the collapse of the top block of 1wtc virtually straight down? Wouldn't this indicate symmetry of failures in both north south and east west axes? Was the SE IB a non collapse causal artifact?
 
Titanic and Challenger are pretty good examples. In fact, I'm grateful to Jeffrey for reminding me of Feynman. I didn't know they had made a movie with Jeff "the Dude" Bridges in the lead role!

I'm watching it now. Great stuff so far. It shows precisely the sort of behind-the-scenes drama that we expect the scientific investigation to have. It also (by analogy) suggests some reasons to doubt the seriousness of the NIST report. Yes, I know, it's a dramatization and sort of a cliché of government bureaucracy (which Feynman hated, I'm told). But it's also a true story and Feynman really did sort of blow the whistle on what was turning out to be cover up / white wash. Interesting to think about.

In any case, it's that sort of narrative -- or rather, the basis of that sort of narrative (the political and science journalism that informs it) that I'm thinking of. Even if NIST did everything by the book, with no intrigues to speak of, the process of discovery can itself be a gripping story. It hasn't really been told.
Which specific substantial popular science literature or longform article/book for either the Titanic or Challenger disaster did you read that shows how you would like the WTC collapses explained in such a way that someone with ordinary intelligence and a grasp of highschool physics could follow?
 
Titanic and Challenger are pretty good examples. In fact, I'm grateful to Jeffrey for reminding me of Feynman. I didn't know they had made a movie with Jeff "the Dude" Bridges in the lead role!

I'm watching it now. Great stuff so far. It shows precisely the sort of behind-the-scenes drama that we expect the scientific investigation to have. It also (by analogy) suggests some reasons to doubt the seriousness of the NIST report. Yes, I know, it's a dramatization and sort of a cliché of government bureaucracy (which Feynman hated, I'm told). But it's also a true story and Feynman really did sort of blow the whistle on what was turning out to be cover up / white wash. Interesting to think about.

In any case, it's that sort of narrative -- or rather, the basis of that sort of narrative (the political and science journalism that informs it) that I'm thinking of. Even if NIST did everything by the book, with no intrigues to speak of, the process of discovery can itself be a gripping story. It hasn't really been told.
The WTC collapse after initial failure of the upper section is explained clearly by NIST, or anyone who wants to calculate what a floor in the WTC can hold. It is simple math adding up the connections of the floor attachments to the core and and shell. The WTC towers are a system of Shell, Core and Floors, the floors attached to the core and shell are a system. When the floors fail the core no longer has lateral support which was due to the Shell with connections to the floors. The collapse was due to floors being overloaded by mass above, that is simple, and it can't stop until the ground and structure below can support the mass moving. It is as simple as NIST explains.

12. Was there enough gravitational energy present in the WTC towers to cause the collapse of the intact floors below the impact floors? Why weren't the collapses of WTC 1 and WTC 2 arrested by the intact structure below the floors where columns first began to buckle?

Yes, there was more than enough gravitational load to cause the collapse of the floors below the level of collapse initiation in both WTC towers. The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case). Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC tower (12 floors in WTC 1 and 29 floors in WTC 2), the floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings.

Consider a typical floor immediately below the level of collapse initiation and conservatively assume that the floor is still supported on all columns (i.e., the columns below the intact floor did not buckle or peel off due to the failure of the columns above). Consider further the truss seat connections between the primary floor trusses and the exterior wall columns or core columns. The individual connection capacities ranged from 94,000 pounds to 395,000 pounds, with a total vertical load capacity for the connections on a typical floor of 29,000,000 pounds (see Section 5.2.4 of NIST NCSTAR 1-6C). The total floor area outside the core was approximately 31,000 square feet, and the average load on a floor under service conditions on Sept. 11, 2001, was 80 pounds per square foot. Thus, the total vertical load on a floor outside the core can be estimated by multiplying the floor area (31,000 square feet) by the gravitational load (80 pounds per square foot), which yields 2,500,000 pounds (this is a conservative load estimate since it ignores the weight contribution of the heavier mechanical floors at the top of each WTC tower). By dividing the total vertical connection capacity (29,000,000 pounds) of a floor by the total vertical load applied to the connections (2,500,000 pounds), the number of floors that can be supported by an intact floor is calculated to be a total of 12 floors or 11 additional floors.

This simplified and conservative analysis indicates that the floor connections could have carried only a maximum of about 11 additional floors if the load from these floors were applied statically. Even this number is (conservatively) high, since the load from above the collapsing floor is being applied suddenly. Since the dynamic amplification factor for a suddenly applied load is 2, an intact floor below the level of collapse initiation could not have supported more than six floors. Since the number of floors above the level where the collapse initiated exceeded six for both towers (12 for WTC 1 and 29 for WTC 2), neither tower could have arrested the progression of collapse once collapse initiated. In reality, the highest intact floor was about three (WTC 2) to six (WTC 1) floors below the level of collapse initiation. Thus, more than the 12 to 29 floors reported above actually loaded the intact floor suddenly. https://www.nist.gov/topics/disaster-failure-studies/faqs-nist-wtc-towers-investigation
And no one needs NIST to figure this out, it is not a NIST thing, it is a WTC tower Fact, the floors fail when overloaded as seen on 9/11. You can study the collapse, but why? The key to the collapse of each tower progression is based on the floor failure. The system of the Shell, Core and Floors are why the towers were so strong, the floors don't hold up other floors, the core and shell hold up each floor. The collapse progression is easy to understand, floors fail when the upper mass hits each floor - we can do this calculation if we wish to by adding up each connection, math, and calculate the mass above... and for extra credit to the physics to see the mass and velocity required to overload one lower floor. The fact is the upper mass was moving, not only was the upper mass more than the first lower floor could hold, the upper mass was moving.

The Titanic and Challenger were accidents, not crimes. One NIST goal was to confirm the Towers were built properly. Other studies confirmed if the shell had been thicker, the impacts of the aircraft may of been stopped at the shell. Study of the collapse progression is not needed since we know floors fail when overloaded and the collapse will progress as explained here, and other places. The WTC towers would have stopped the same aircraft is they were at Legal FAA speeds for the altitudes and approach speeds if the aircraft were lost in the fog/weather trying to land or make an approach...

NIST does not do crime, FBI does crime, the conspiracy theories surrounding WTC collapse are not based on evidence.

Collapse progression:
Floors in the WTC fail when overloaded, the mass falling above the lower floors caused each floor to fail, and the same mass and chaotic impacts ripped up the shell and core as seen on 9/11, the video of the collapse progression show how each tower collapse progression took place. The energy released by the towers gravity collapse was equal in energy to more than 130 tons of TNT, this energy is why the WTC complex looks like it did. The energy equal to 130 2,000 pound bombs, was stored in the towers due to E=mgh. Mass, Gravity, and Height destroyed the WTC after fires caused the initiation of the collapse.
 
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