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

[Thomas B]

I'm curious to know where members of this forum get their understanding of (the "official" version of) the WTC collapses from. 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.

(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. If something did come out, I missed it. (Note: I know Popular Mechanics did a debunking piece; but I haven't seen a "straight" popularization by them of the received engineering view.) I'd prefer a book on the subject, but a very good, long magazine article in a mainstream outlet would be a good start.

A related question: what's the best "textbook" account of the collapses? I.e., where can we read the explanation that engineering students are taught?

My follow-up question is: in the absence of such an account, how reasonable is it for someone to claim (after years of trying) that they don't understand (the "official" account of) how the collapses happened? (The conspiracy theories are, I would argue, easier to understand, if harder to believe.) Has the absence of a good popular science book about the WTC collapses given room for conspiracy theories to flourish?

 

[benthamitemetric]

The NIST reports remain the most comprehensive analysis of the collapses and related events.

There are also some additional engineering reports that were submitted to federal court in connection with a litigation over insurance payouts related to the collapses, as well as a major, award-winning engineering report by Weidlinger Associates that was prepared, but never submitted to court (due to how quickly the case was dismissed), in connection with the same litigation.

There are also quite a few books the related to the experiences of first responders and others on the ground on 9-11 and in its aftermath. The ones I've read can be seen below in a snippet from my google books library:

Popular Mechanics released a conspiracy theory debunking book that talked about the collapses at great length.

And there is the best selling book City in the Sky: The Rise and Fall of the World Trade Center, which I highly recommend for a very readable history of the towers with some high level explanations of their collapses (including commentary on the same from their designers).

I don't know how popular or widely read any of the foregoing are these days, but I guaranty that you'll understand the collapses better than 99.9999% of people if you find time to read 10% of them.

 

[Thomas B]

Thanks, Benthamitemetric. That's pretty much the state of the literature as I see it too. What is missing is some detailed, up-to-date science journalism focused on the physics of the collapses. (City in the Sky is pre-NIST, as I recall.) Today, we're left to our own devices -- cobbling together an understanding of the mechanics of the collapses from sources that often propose different mechanisms. (Some say floor failure, for example, while some say column failure.) It would be great if a science journalist were to look into it, talk to some leading engineers, and just provide a straight, coherent account for the science-literate reader. There must be a market for it.

PS: Who *are* the "leading engineers" in this area? Who is considered an authority on the WTC collapses? Who is credited with figuring out how the structures responded?

 

[benthamitemetric]

Thanks, Benthamitemetric. That's pretty much the state of the literature as I see it too. What is missing is some detailed, up-to-date science journalism focused on the physics of the collapses. (City in the Sky is pre-NIST, as I recall.) Today, we're left to our own devices -- cobbling together an understanding of the mechanics of the collapses from sources that often propose different mechanisms. (Some say floor failure, for example, while some say column failure.) It would be great if a science journalist were to look into it, talk to some leading engineers, and just provide a straight, coherent account for the science-literate reader. There must be a market for it.

PS: Who *are* the "leading engineers" in this area? Who is considered an authority on the WTC collapses? Who is credited with figuring out how the structures responded?

I think the principal NIST authors are generally considered the leading experts in this area, and most of them have gone on to publish many more peer reviewed papers on related topics (disproportionate collapse, fire modeling, etc.). Many of the experts from the Aegis litigation also continue to publish and speak on the WTC collapses and related topics. You could probably also consider the many thousands of high-rise specialized structural engineers around the world experts on this topic generally to some degree. There are hundreds and hundreds of articles on the related topics published every year. Just check ASCE, CTBUH or even just google scholar to get a sense of all of the tens of thousands of serious professionals who are actively working and publishing in these areas (none of whom are signatories to the AE 911Truth petition, by the way).

But I get your point and agree that, at least to my knowledge, none of those experts focuses significant attention on educating laypeople about the WTC collapses in particular. Based on my limited correspondence with some such experts, that makes perfect sense to me. There is no serious dispute among experts as to the broad strokes of what happened (i.e., damage from fires caused the buildings to collapse), which is sufficiently captured in the NIST reports. There are some differing theories and disputes about the exact details of the collapse mechanisms, but they turn on extremely complicated engineering that is entirely outside of the ken of laypeople. And, since there are not significant numbers of people who believe the collapses of the buildings were not caused by fires and laypeople generally do not seem to really care about these engineering issues in any event, there isn't much of a reason for these engineers, who are very busy professionals, to spend time on a popular summary that would necessarily avoid the most interesting engineering questions.

I'll also add that many of these experts, like most rational people, do not want to go out of their way to publish works for popular consumption that would invite harassment or worse from disgruntled conspiracy theorists. I don't blame them. I've had a few nutty conspiracy theorists threaten to go after me and my law firm just for my posts here and on International Skeptics. One only has so much time on this earth and not everyone is willing to spend any of it dealing with such nonsense.

 

[Thomas B]

... I get your point and agree that, at least to my knowledge, none of those experts focuses significant attention on educating laypeople about the WTC collapses in particular. Based on my limited correspondence with some such experts, that makes perfect sense to me. There is no serious dispute among experts ... who are very busy professionals ... [and] do not want to go out of their way to publish works for popular consumption that would invite harassment or worse from disgruntled conspiracy theorists.

What I'm looking for is not so much an engineer but a professional popularizer. When we tell conspiracy theorists that the collapses "are understood" or "have been explained" by science we are referring to a state of the discipline (of, say, structural engineering). A good science journalist should be able to write a gripping book about it, and, while I can see how it might get the backs of some conspiracy theorists up, that controversy itself might sell some books. (With the backing a good publisher, the harassment should be manageable.)

More importantly, I'm thinking of all the 15-year-old engineers-to-be who get interested in the collapses before even hearing about the conspiracy theories. They just want to know about the structures and the forces involved. I have to admit that I'm not confident I can explain the physics myself. But, like any physics problem, all the processes and mechanisms can be described and modeled with simple machines, illustrated with straightforward diagrams. And the story of how those explanations emerged would surely interest these kids. It's like wanting to know everything about the Titanic.

I guess what I'm saying is that maybe it's time to stop associating a serious interest in the mechanics of the collapse with the obsessions of conspiracy theorists and acknowledge that, tragedy aside, it's a really interesting disaster in its own right. Though it might annoy the conspiracy theorists, what is needed is a book that explains the collapses to a lay audience without even mentioning "demolition". Like I say, the absence of such a "cool" book all these years may have given the conspiracy theories room to thrive.

 

[Oystein]

... (The conspiracy theories are, I would argue, easier to understand, if harder to believe.) ...

Acknowledging that you put this in parentheses to mark it as a side issue, I am curious which "conspiracy theories" you know of that purport to explain any of the collapses such that they would be understood, if true?

I do not know of any such theory that goes beyond vaguely suggesting that a class of devices may have been employed somehow. The proto-theories that I come across all lack in the sort of detail that would make them testable, falsifiable. Even the Hulsey report deliberately stops short of providing a physical mechanism that causes the collapse of WTC7 - Hulsey merely conjures away willy-nilly ALL columns at once over at least 8 columns, makes them simply and literally disappear as if by magic.

I mean, has the CT side presented a model for the kind of popular, journalistic narrative that still manages to capture the technical details that purportedly caused the collapses (causes of collapse initiation as well as causes of collapse progression)? Do you know of such a work?

 

[Jeffrey Orling]

For sure the process was not simple with elements of chaos. In the case of the towers several of the mechanisms well describe aspects of the collapse of the twin towers. For sure there was a run away aspect to the event... one thing led to another to another and this was pretty rapid . It collapsed because axial load paths were "destroyed"... And this "negates" what a structure is... a construction to resist gravity (and other) forces allowing "loads"... people and objects to placed within the structure and conduct "activities".

We can see that the planes' strikes did not "knock" the towers down. But we can see and induce that they set off a series of structural failures which led to the complete collapse.

The term "pancake" collapse was used early on but it is rather misleading it turns out. There were apparently structural failures which initiated several high floors (above the plane strike zones) to collapse down onto floors which were not actually effected by the plane strike. However those floors were not designed to support the newly acquired loads from the collapse of the floors above... not as entire slabs... but as "floor debris". Essentially an unstoppable contained (with the exterior walls) avalanche took place. The axial structures... the columns were essentially bypassed by the collapsing floor debris. But they were may unstable by the floor's destruction. The columns needed the floors for lateral bracing. Without the bracing they were not stable enough to stand. The columns then succumbed to what is described as Euler buckling. Columns were multi part and their end to end connections were their weakest part... So when they failed the "broke first" at their connections.

All this has been discussed on this forum, and the 911 Free Forum exhaustively. NIST got much of it correct. But I think they got some of it wrong. They don't even discuss in any detail what the call the "global collapse". I don't think "sagging trusses caused by fires" was as significant as NIST seems to assert.

Many "sub mechanisms" have been described in detail. But it's hard to know the sequence, for example, and how large of role they played.

 

[deirdre]

Like I say, the absence of such a "cool" book all these years may have given the conspiracy theories room to thrive.

i saw a documentary years before i discovered Metabunk in 2013. no idea what it was called but they laid out how the building was made and why it collapsed. and I'm sure there are books on the subject.

Did you Google "why did the twin towers collapse" ? i see lots of 'popular' accounts.

 

[Keith Beachy]

The NIST final reports, thousands of pages are the answer. Here they are...
https://www.nist.gov/el/final-reports-nist-world-trade-center-disaster-investigation

One key to the collapse is the design of the WTC, and how WTC floors don't hold up upper floors, but only the floor. The shell and core hold each floor in place. When the collapse began, the next lower floor below the collapse cannot hold the upper failed floors and fails. This is explained by NIST. And summarized in their answer to questions and faqs.

https://www.nist.gov/topics/disaster-failure-studies/faqs-nist-wtc-towers-investigation

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. https://www.nist.gov/topics/disaster-failure-studies/faqs-nist-wtc-towers-investigation

The energy of the collapse, E=mgh was released as the collapse continued. Energy equal to more than 130 tons of TNT.

The best lay person reason for the collapse of the towers continuing, is what a WTC floor can hold. If the mass on a floor is greater than the floor can hold, the floor fails. Some people appear to believe the towers get stronger at lower floor. The core and the shell get thicker (stronger), but the key is the connection of each floor to the core and shell. Repeating, floors in the WTC do not hold up other floors, that is the function of the shell and the core.

The best and worse part of 9/11, we don't have to model the collapse, we see it as it happened, on video. No need to model it, we see exactly how the WTC tower collapses when fires not fought, with insulation dislodged by massive kinetic energy impacts, start a collapse.

It appears, most of the things needed are in the NIST reports. For the those inventing the conspiracy theories, all is needed is imagination, and ignore thousands of pages of the NIST reports, and many other studies which do not support the fantasy of conspiracy theories.

 

[Thomas B]

I do not know of any such theory that goes beyond vaguely suggesting that a class of devices may have been employed somehow.

You're right that I'm thinking of these vague theories about "devices" of some kind when I say "conspiracy theory". Someone who overestimates the strength of the towers and therefore can't understand how they collapsed "under their own weight" ("gravity driven") can easily understand how a sequence of "timed charges" would do the job. (However improbable it may be that such charges could be installed and detonated.) Ordinary controlled demolitions, after all, don't offend anyone's physical intuitions. On the CT view, the explanation for the structure not holding up is that it was explicitly destroyed *before* the buildings collapsed. If the destruction precedes the collapse, the collapse is easy to understand. If the collapse *causes* the destruction, a more detailed explanation may be necessary. Like I say, it becomes a more interesting physics problem, with a more interesting answer.

 

[Thomas B]

The NIST final reports, thousands of pages are the answer...

... we don't have to model the collapse, we see it as it happened, on video. No need to model it, we see exactly how the WTC tower collapses when fires not fought, with insulation dislodged by massive kinetic energy impacts, start a collapse.

It appears, most of the things needed are in the NIST reports. For the those inventing the conspiracy theories, all is needed is imagination, and ignore thousands of pages of the NIST reports, and many other studies which do not support the fantasy of conspiracy theories.

Some people like models. In fact, a good model disciplines the imagination. Such people will build a model of the towers in their imagination, an understanding of the buildings prior to the collapses, and then they'll imagine what its transformation under the weakening by fire. Some people get stuck even at the fires and need to be taught about how fires can seriously weaken steel. Others need to be taken through the floor-by-floor sequence floor and column in the chaos described by Jeffrey. The model will normally be a simplification but it will make the mechanism clear and prevent the flights of fancy you mention.

 

[Thomas B]

i saw a documentary years before i discovered Metabunk in 2013. no idea what it was called but they laid out how the building was made and why it collapsed. and I'm sure there are books on the subject.

Did you Google "why did the twin towers collapse" ? i see lots of 'popular' accounts.

I've seen a few documentaries. But they didn't provide the detail I'm looking for (if you remember the title of the one you're thinking of, let me know, and I can say what's missing). As for the google search -- I know they're personalized, but I'm not getting anything particularly good on the first few pages. Is there one you'd emphasize?

 

[Thomas B]

All this has been discussed on this forum, and the 911 Free Forum exhaustively. NIST got much of it correct. But I think they got some of it wrong. They don't even discuss in any detail what the call the "global collapse". I don't think "sagging trusses caused by fires" was as significant as NIST seems to assert.

Many "sub mechanisms" have been described in detail. But it's hard to know the sequence, for example, and how large of role they played.

Yes, this is a good way of putting the problem. Anyone who wades into this area ends up developing their own understanding of what must or might have happened. If someone is interested enough to look at the NIST report directly, they are disappointed by the lack of interest in the "global collapse" (especially if they were hoping to find an argument to use against their CT friend!)

You are right to raise the question of the space of reasonable disagreement among scientists (including taking issue with conclusions in the NIST report). My attempts to understand "what we know" ("we" = scientific consensus) have been frustrating in this regard. Not only isn't there a popular account, there doesn't seem to be a detailed textbook account (do let me know if you know of one). That is, I'm not even sure what a good engineering student would make of it. Also, it doesn't look like any of the major journals have commissioned a review article on the subject yet. I'm hoping there'll be one by 2021.

Every now and then, I run into a paper published in a mainstream engineering journal that suggests that there are "unresolved issues" (sometimes about the collapse times or the totality of the destruction), proposing a (non-conspiracist) mechanism to resolve it. (Most recently, Daigoro Isobe's work.) What is needed is a guide to all this research that properly weighs the core and peripheral insights. We need an accurate state of the science -- what is known, what is still being debated?

I did manage to get a hold of Uwe Starossek's Progressive Collapse of Structures, which (among other things) deals directly with the WTC. As far as I can tell, it doesn't propose floor-failure (as suggested by Keith / NIST) but the progressive buckling of the column sections between floors (as suggested by Bazant's early model, which I know many on this forum, including Mick, see as a straw man). I am not qualified to decide who is right, or even to fully understand these accounts. I can only register the confusion.

I don't bring this up to draw the science into question, only to suggest that some mainstream popular synthesis, based on input from named experts, would be a good idea. Most people who care about the issue at all seem to think of the WTC collapse as something only to "debunk". I think for many people (and especially young, science-interested people) it would be helpful to approach it afresh as something to explain.

 

[Jeffrey Orling]

My take about this matter has been that no one really is discussing the elephant in the room - the "2 structural designs of the 3 towers." Of course one reason... an easy escape path is the state that they stood for decades and so the designs were obviously adequate.

Yet I assert that is was precisely aspects of the engineering design decisions which one will find the keys to understanding why these buildings collapsed as they did.

This sort of examination also leads one to ask... Could a different structural design have fared better ie lasted longer or not even collapsed?

It has always struck me that these were not typical "garden variety" designs and they what appear to me to be key structural elements/features/details/aspects not seen in other high rises of similar size. For example:

How many other high rise buildings are erected over a major electric sub station requiring massive 3 story tall load transfer structures to support the 40 office tower structure above?

How many other high rise structures are built with column free open floors outside the core... relying on long span floor supports and moving as much as half the axial load paths to the facade of the structure? Note that in the case of 7wtc... there were 57 columns in the perimeter moment frame above floor 7 and only 26 below.... reason being that the sub station was "in the way of" the columns above going straight down to bedrock. I saw no discussion of the implication of this engineering feature.

How many high rises support a massive 360 ton antenna on top of them requiring a 2 story 36' tall hat truss to distribute concentrated antenna loads beyond the 4 columns directly below it? What would the implications be of a truss failure or loss of support for the antenna?

What is the implication of relying on the thin floor plates to transfer wind shear loads to the core? What is the implication of large sections on multiple consecutive floors collapsing (from plane impact? Was there a system to isolate local damage?

I believe, the above and other engineer details/design attribute played a key role in these buildings collapse. No they didn't cause it. But they did "facilitate" and "drive" how they progressed and perhaps were not able to arrest local damage.

We were led to believe that a single column failure could lead to the complete collapse of a building which has 81 columns. Is this something common to any high rise building?

If the collapse was not the result of a single column failure, what was the failure which triggered the global collapse? What role did the numerous load transfer play in the collapse? The building contained many examples/uses of load transfers.

+++++

So why was non (and more) not part of the discussion? No one knows. But I would guess that this would point to the wisdom of the engineering design and what drove those decisions... which we know is often economics... building needs to be cheaper and go up as fast as possible with as much rentable/usable space. How/why did the designers fail to provide adequate egress paths? What drove the design considerations of the egress options? While this may not be a cause of the collapses it does represent a type of design failure... protection of the inhabitants in emergencies.

We know that the buildings perform well until there was some sort of significant "trauma". Should "trauma" scenarios play more of a role in design of these structures?

What sort of code and building standards.practices were in place at the time they were designed and built... and were they followed, modified or avoided for any reason?

All the above and more have nothing to do with understanding the actual collapse mechanisms... the physics and engineering. But they DO seem to be the background which "framed" the collapses... informed them... and in a sense "allowed them" to unfold as they did.

 

[Thomas B]

We were led to believe that a single column failure could lead to the complete collapse of a building which has 81 columns. Is this something common to any high rise building?

I agree that many of the issues Jeffrey raises have been passed over in silence in the coverage of the collapses. It's to some extent understandable that the focus remained on the (obvious) terrorist attacks rather than the (possible) engineering failures of 9/11. But with the passage of time, these questions may gain more attention. Certainly, it's something a 200-300 page book on the subject would need to deal with.

I left WTC 7 on the side, but I agree that NIST's explanation is, at least at first pass, somewhat disconcerting. I would add that in its FAQ, NIST even downplayed the role of structural damage: "A separate analysis showed that even without the structural damage due to debris impact, WTC 7 would have collapsed in fires similar to those that occurred on Sept. 11, 2001" (Q21). The idea that modern skyscrapers are vulnerable to fires in this way is something I first learned by studying the WTC collapses, and I still don't quite understand why they're not just made strong enough to survive "burnout" at least in principle. (I get the general idea that the cost of doing so would be prohibitive; I don't understand what would make it so expensive.)

As a meta-reflection on the strange resilience of conspiracy theories, I would say that this apparent lack of interest in what was early on identified by CT-adjacent activists as "skyscraper safety" issues probably undermines the credibility of the "official" investigation to some. One way to think about this is: how vulnerable is a building like AON Center in Chicago to collapse by fire alone, or by a combination of local structural damage and fire? (I choose that building because it's basically a smaller version of WTC 1 & 2.) The WTC investigations seemed weirdly compartmentalized, detached from engineering science and practice in general.

Summing up Jeffrey's concerns, I would say they're about how the analysis of the WTC disaster "generalizes" as a critique of modern skyscraper design. Just as understanding the Tacoma Narrows bridge collapse generalized as a critique of its design principles and taught engineers how to build better bridges.

 

[deirdre]

and I can say what's missing

wtc7 was missing. probably because the general public doesnt care about wtc7 and it was a "popularized" documentary...meaning it was presented for laymen ie the general public.

As for the google search -- I know they're personalized, but I'm not getting anything particularly good on the first few pages. Is there one you'd emphasize?

based on your answers to Jeffry, i'm really not sure now what you are actually looking for. If you are looking for an engineering textbook, look for .edu url endings. or write to some engineering department heads and ask them. although im not sure why they would need a textbook when they have the NIST report and those other 2 popular reports i cant remember the authors anymore.

The idea that modern skyscrapers are vulnerable to fires in this way is something I first learned by studying the WTC collapses, and I still don't quite understand why they're not just made strong enough to survive "burnout" at least in principle.

that's why they studied the collapses.. to see how they can improve building design/materials/maintenance and fire protocols etc. That was the whole point.

wtc7 was a fairly unique situation in that there were no sprinklers- as the water lines had been damaged- and had no firefighter response. Still it survived plenty long enough for people to evacuate.

 

[Keith Beachy]

Some people like models. In fact, a good model disciplines the imagination. Such people will build a model of the towers in their imagination, an understanding of the buildings prior to the collapses, and then they'll imagine what its transformation under the weakening by fire. Some people get stuck even at the fires and need to be taught about how fires can seriously weaken steel. Others need to be taken through the floor-by-floor sequence floor and column in the chaos described by Jeffrey. The model will normally be a simplification but it will make the mechanism clear and prevent the flights of fancy you mention.

That's were the collapse of the WTC towers needs no model for the collapse, to show what it looks like. We can see what a collapse looks like from video. When we model things in engineering, many times the visual model does not look like the real world, but the engineering model is okay. People said the models by NIST don't look like the real world, and may not understand engineering models.

The other problem with simplified explanations for the WTC collapse, the people reading the explanation may not be familiar with the structure of the WTC. The more we know about the WTC structure, the more likely we might understand and accept a simplified explanation.

How to make a simplified explanation? Fire science, properties of steel, physics, energy E=mgh, the structure of the WTC, and more have to be explained. How can people understand the energy released in the WTC collapse due to the building itself. During the collapse the energy equal to 130 2,000 pound bombs wrecked havoc on the WTC as it collapsed and produced the damage seen over 19 acres around the WTC towers - how do you explain that? It will not stop conspiracy theories from being born in ignorance of physics with people who believe in fantasy evidence they can't produce to support the scenario they made up out of thin air.

Steel in fire, my favorite way to explain it is when structural wood holds up failed steel.

Knowing more about the WTC structure helps understand. I was looking at explanations about the collapse. The summary was correct saying the exterior shell was to support lateral loads on the tower, and the core was for gravity loads. However, the shell also supports gravity loads about 50 percent with the core.

Another study looked at how the aircraft broke the shell and offered engineering model to explain if the shell had been thicker steel, the aircraft would not have entered the WTC tower.

It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20 mm. https://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9399(2005)131:10(1066)?src=recsys

I have a copy of the paper, it was online in 2005, now it appears it is by subscription. Anyone need a copy I have it.

Do the aircraft impacts need to be explained at a simple level? Which study would help? What needs to be explained? http://web.mit.edu/civenv/wtc/PDFfiles/Chapter IV Aircraft Impact.pdf

 

[Thomas B]

It will not stop conspiracy theories from being born in ignorance of physics with people who believe in fantasy evidence they can't produce to support the scenario they made up out of thin air.

While fantasists do of course exist, I think a significant amount of truthers are born of genuine puzzlement about the collapses. These people are by no means ignorant of physics. In fact, it's precisely because they have a working understanding of mechanics that the (total progressive) collapses puzzle them. I think they find the "nothing to see" rhetoric (e.g., "no need for a model") frustrating, since surely these are interesting events in the history of structural engineering, worthy of detailed explanation (and modelling). Though it's a cliché, in the beginning they really do just "have questions".

These people are, curious about the collapses at first, then they feel disappointed by the state of the literature (a bit of a mess), and finally some of them begin to get suspicious that it's not all on the level. If the sort of account I'm looking for existed, they might be spared the whole trip down (and, fortunately, sometimes up) the rabbit hole.

As I've said before, I'm also interested in the curiosity of young people who are destined to be engineers. Every day some kid learns about the collapses for the first time. What are they given to read? What should they be given to read? The WTC offers a masterclass in progressive collapse. Why doesn't that masterclass exist? It's been almost twenty years. Though I understand the reticence of the experts, I don't actually blame people who suspect that the engineering profession is skirting the issue. It's time to get into it.

 

[deirdre]

The WTC offers a masterclass in progressive collapse. Why doesn't that masterclass exist?

if your structure cant hold up the building, (ie loads) it falls down. wouldn't that be the first thing they learn in structural engineering?

 

[Thomas B]

if your structure cant hold up the building, (ie loads) it falls down. wouldn't that be the first thing they learn in structural engineering?

I guess I'm saying it's more complicated and more interesting than that in the case of the WTC. What I'm looking for is the best 1000, 5000, 25,000 or even 125,000 words that explain how the WTC went from holding up against all kinds of weather to total collapse under its own weight. These explanations could be done really well by a competent writer working with qualified experts.

 

[Landru]

I guess I'm saying it's more complicated and more interesting than that in the case of the WTC. What I'm looking for is the best 1000, 5000, 25,000 or even 125,000 words that explain how the WTC went from holding up against all kinds of weather to total collapse under its own weight. These explanations could be done really well by a competent writer working with qualified experts.

First, tell us why the NIST report doesn't satisfy you.

 

[Thomas B]

First, tell us why the NIST report doesn't satisfy you.

Sure, a few reasons. First of all, it's huge. Even if we confine ourselves to main report.

It's a technical report and not really written for the layperson.

As Jeffrey pointed out above, it leaves the progression of the collapse almost entirely on the side. And it spends way too much time modelling the fires. I would invert that emphasis.

Also, it's quite old now. Researchers have continued to work on the problems. It would be nice to have current view of the state of knowledge.

It's not "puzzle" oriented. The reader doesn't get a clear sense of what needed to be explained, what could have happened differently.

Basically, while it's probably a perfectly good engineering report, and adequate within the scope of its mission, it's not a very good book about the collapses.

Caveat: it's been a while since I looked at it in detail. This is how I remember reacting when I read it.

 

[Landru]

Sure, a few reasons. First of all, it's huge. Even if we confine ourselves to main report.

It's a technical report and not really written for the layperson.

It's a technical problem.

As Jeffrey pointed out above, it leaves the progression of the collapse almost entirely on the side. And it spends way too much time modelling the fires. I would invert that emphasis.

Who besides conspiracy theorists care about progressive collapse? Once it failed gravity takes over.

Also, it's quite old now. Researchers have continued to work on the problems. It would be nice to have current view of the state of knowledge.

Irrelevant. It's old. So what? Has the information changed?

It's not "puzzle" oriented. The reader doesn't get a clear sense of what needed to be explained, what could have happened differently.

Irrelevant. The NIST study attempts to answer the question of why the towers came down. In my opinion it does.

 

[Keith Beachy]

...
As Jeffrey pointed out above, it leaves the progression of the collapse almost entirely on the side. And it spends way too much time modelling the fires. I would invert that emphasis. ...

Progression - once the upper floors fail, global collapse ensues... because

The collapse progression is the easiest part of the story. A floor in the WTC can only hold 29,000,000 pounds statically, and then it fails. NIST goes into some detail about why it is 29,000,000 pounds, with respect to the connections of each floor to the Shell and Core. When the collapse starts there is more mass than the lower floor can hold up, and the floor fails instantly (in a chaotic manner). Since the upper mass is moving, the lower floor does not need 29,000,000 pounds of mass for the floor to fail. NIST explains this.

Because of this simple fact, what a floor can hold, the collapse progression is explained. The collapse continues to the ground until it can't continue. We see the video of the collapse progression, and the core still standing for some 70 floors in one case. The core will fail, it was stripped of the floors which connected to the shell, the shell was the lateral support. No lateral support for the core, it will fail.

I don't know how to explain why the progression of the collapse past the fact the floor below can't hold the mass above after collapse begins. That is the progression. The floors below the initial collapse can't hold up the mass falling. Even if the floors above that collapsed were placed with zero velocity on the first floor below the initial collapse, the floor fails... then the next, and the next, essentially instant failures of floor. If modeled with a simple momentum mass equation for each floor impact, you come up with very close to the collapse times seen on the videos. WE could use excel spread sheet to do the timing based on mass, gravity, based on physics. A simple momentum model. I did one in excel all those years ago.

 

[Thomas B]

Who besides conspiracy theorists care about progressive collapse? Once it failed gravity takes over.

Isn't this forum about how to explain things to (i.e., debunk) conspiracy theorists? Telling someone who is genuinely curious/puzzled about how the buildings could completely destroy themselves that "no one cares" isn't very effective. Besides, engineers do care about progressive collapse and do see WTC as a prime example. For example, as I mentioned above, Uwe Starossek.

The NIST report may have completely satisfied you. But it obviously didn't close the question for everyone; and research, like I say, continues to this day. There's a government report on the 2008 financial crisis too; but that doesn't mean people aren't still writing books about it.

 

[Thomas B]

I don't know how to explain why the progression of the collapse past the fact the floor below can't hold the mass above after collapse begins.

Neither do I. That's why I'd like someone to write a good book about it. And that's why I have some sympathy for people who can't make sense of the collapses even after reading the NIST report.

I mentioned this above, but there seems to be some confusion about what exactly was destroyed at each step. You assume that the destructive energy goes into the floor connections (the points where the floors connect to the columns), right? But, as far as I can tell, Starossek has the forces going mainly into the columns, buckling them. On your account, it's the vertical load bearing capacity of the floor connections that was overwhelmed. But that still leaves the vertical and lateral support of the columns (in the shell and core) "standing" (in the sense of no energy going into their destruction in your model yet).

I can imagine that as the upper mass hits the floors there is some lateral inward tugging on the columns just before the connection fails. But remember that the walls were designed to resist pretty enormous shear forces (hurricanes). I don't think the floor connections could rip themselves loose both vertically and laterally with enough force to destroy even the single layer of columns of the shell. It's even harder to imagine the core being destroyed this way.

If I understand you correctly, you have the core collapsing freely after its lateral support (from the floors) has been removed. But doesn't the top section of the core come down along with everything else? By the time we see "the spire" collapse, the top section (including its core) has already passed through it. Again, as I understand it, when the top part of the core impacts the lower part of the core it doesn't just overwhelm the floor connections (there aren't any in the core). It must also be buckling the colums. Again, that's the story I've cobbled together, originally from reading Bazant*, but later in Starossek. It's the sort of thing I imagine could be explained really clearly in a book of a few hundred pages.

*As I mentioned above, I know Bazant isn't taken very seriously here. I've also talked to Mick about it. One of the things the book I'm imagining would do is settle the question of Bazant's status in the discussion. How seriously do engineers take his "simple analysis"? What role does it play in their understanding of the collapses?

 

[Landru]

Isn't this forum about how to explain things to (i.e., debunk) conspiracy theorists? Telling someone who is genuinely curious/puzzled about how the buildings could completely destroy themselves that "no one cares" isn't very effective. Besides, engineers do care about progressive collapse and do see WTC as a prime example. For example, as I mentioned above, Uwe Starossek.

The NIST report may have completely satisfied you. But it obviously didn't close the question for everyone; and research, like I say, continues to this day. There's a government report on the 2008 financial crisis too; but that doesn't mean people aren't still writing books about it.

Enough people care to write books about the 2008 financial crisis. Most people are satisfied with the WTC explanation.

 

[Keith Beachy]

Neither do I. That's why I'd like someone to write a good book about it. And that's why I have some sympathy for people who can't make sense of the collapses even after reading the NIST report. ...

... I mentioned above, I know Bazant isn't taken very seriously here. I've also talked to Mick about it. One of the things the book I'm imagining would do is settle the question of Bazant's status in the discussion. How seriously do engineers take his "simple analysis"? What role does it play in their understanding of the collapses?

I do understand the progression. A floor in the WTC tower can only hold up so much weight. On 9/11 went the upper floors failed at the impact zone, the lower floor can't hold up the mass and fails. This is the progression, this is why NIST said, "global collapse ensued". After the top section fails, the floor below will fail when the mass arrives - that is progression. When the floors fail the shell is exposed and destroyed by falling mass. The core can't stand without the floor connections to the shell, because the shell was the lateral support. The WTC was built from the bottom up. There is no reason to model the collapse progression in my opinion, I understand what a floor can hold up, and that floors in the WTC only held up themselves, not upper floors. The core and shell shared the gravity load. The physics of floor failure boil down to too much mass for a floor to hold, driven by gravity.

As for Bazant, from the first time I saw his work - I assumed he was wondering how it could happen so he modeled it based on assumptions to see if he could have a building fail based on his assumptions. As it turns out, the easiest model is checking the connections of the floors to the shell and core, and finding what weight overloads a floor. To find errors in Bazant's work we have to apply a lot math, and as an engineer I prefer not to revisit differential equations, or non-linear differential equations, or even remember the EoM for flight filling 8 giant chalk boards (oops) when earning a masters in engineering - it is a lot easier to figure out connections (even NIST can do that), and the total weight the floors in the WTC can hold, to understand the progression of the collapse.

How and why does the collapse of the WTC tower progress? Because WTC tower floors fail when overloaded. I understand progression of collapse, and damage to the WTC complex due to energy equal to more than 130 tons of TNT released (E=mgh) as the towers failed. Energy of collapse, a lot of joules, a lot of energy released.

Engineers may differ on how the collapse started. As for progression, the fact a floor fails at a specific weight/when overwhelming force is applied, solves the progression. There not much more to progression than the catastrophic failure of all the floor being overloaded in turn as the collapse front falls in gravity. A book on progression could be one paragraph. As for the shell being broken as the floors failed, someone could calculate the energy and force required to break the connections as sections peeled off and were broken up in various sized sections.

 

[Thomas B]

Enough people care to write books about the 2008 financial crisis. Most people are satisfied with the WTC explanation.

This sort of response doesn't make any sense to me. It sounds like your only answer to questions about the WTC collapse is "Read the NIST report." I don't see why anyone who is skeptical or merely curious should find that answer satisfactory.

Knowledge is always part of an ongoing conversation. This conversation didn't end fifteen years ago, neither in practice nor in principle. We should be looking for new ways of explaining familiar things. Sometimes this deepens, and even corrects, our understanding of them.

 

[Landru]

This sort of response doesn't make any sense to me. It sounds like your only answer to questions about the WTC collapse is "Read the NIST report." I don't see why anyone who is skeptical or merely curious should find that answer satisfactory.

Knowledge is always part of an ongoing conversation. This conversation didn't end fifteen years ago, neither in practice nor in principle. We should be looking for new ways of explaining familiar things. Sometimes this deepens, and even corrects, our understanding of them.

No one writes a book because not enough people see a need for it. You are glossing over the issue that the explanation of how the towers fell is irrelevant. The cause of the towers falling has been well established. People have written about other causes but those don't hold up to scrutiny.

 

[Thomas B]

The core can't stand without the floor connections to the shell, because the shell was the lateral support.

I'm not sure about this, but it does raise an interesting question that, again, a good book would answer. How many consecutive floors could have been removed between floors 70 and 90 before the whole building would come down in any case (without fire or other structural damage) for lack of lateral support on the core? According to NIST's calculation, each floor could carry the weight of about 11 floors. So suppose floors 71-80 were detached, lowered gently, and stacked on the 70th floor. Would the lack of lateral support on the core now cause it to fail? What is the maximum amount floors that could be detached in this way without initiating a global collapse?

Looking into all of this teaches people like me (who don't have the benefit of an engineering degree) many interesting things about structures. Like the way lateral support effectively shortens a column for the purpose of calculating buckling load. And the important difference between dynamic and static loads. Like I say, the WTC collapses would provide plenty of material for a masterclass in engineering. It's surprising that no one has made use of it yet. Even a good 45 minute presentation might inoculate quite a few people against conspiracy theories (without, like I say, even mentioning them). An ounce of education is worth a pound of debunking?

 

[benthamitemetric]

This sort of response doesn't make any sense to me. It sounds like your only answer to questions about the WTC collapse is "Read the NIST report." I don't see why anyone who is skeptical or merely curious should find that answer satisfactory.

Knowledge is always part of an ongoing conversation. This conversation didn't end fifteen years ago, neither in practice nor in principle. We should be looking for new ways of explaining familiar things. Sometimes this deepens, and even corrects, our understanding of them.

I responded to your original question in this thread in good faith and that answer stands, even if it might not be the one you wanted to hear. There has been plenty written about the collapses and the engineering community, outside of a few cranks and nutjobs who are not expert in any of the relevant specialties, is on the whole satisfied with that body of literature. The only context in which that literature really matters, in any case, is in the design of high rise structures, which is not a subject in which many laypeople dabble or even have a passing interest. Regardless, were a layperson sufficiently interested in the subject, all the material they need to understand it is out there for them.

If you think there needs to also be a new, layperson-specific tome on the topic, then perhaps you should write it. I strongly suspect that such a project in the hands of most people would be a colossal waste of time given the lack of demand for such a tome, but maybe you could lean into it Malcolm Gladwell-style and find some interesting angle with which to run.

Beyond that, it seems to me that this thread is devolving into a series of vague complaints by you. If you have some specific issue with any of the extant literature concerning the collapses, you should first see if that specific issue has been addressed on the forum before. If so, great--you can be edified or you can join the conversation in progress. If not, then you can start a thread stating the specific issue. That's how this forum works.

 

[Thomas B]

I responded to your original question in this thread in good faith...

Beyond that, it seems to me that this thread is devolving into a series of vague complaints by you.

I was grateful for your response, as I said at the time. I'm not sure where anyone's good faith has been drawn into question. (Unless you're drawing mine into question now?) Landru doesn't seem to see the point of this thread (and I think we've gotten as far as we can), but Keith and Jeffrey are helping me think through the details, and I'm grateful to them too.

As I said at the beginning, one "meta" question here is whether it is reasonable *not* to understand how the WTC collapsed -- even, let's say, after reading the NIST report. I think it is, and I think that can be the basis of a more constructive engagement with conspiracy theorists, precisely by treating the engineering issues as difficult problems that intelligent people can get wrong. I.e., as questions that not just conspiracy theorists are interested in.

I'm not complaining. And I'm sorry if I'm leaving that impression. I really appreciate everyone's thoughts on this.

 

[Landru]

This thread is starting to turn in circles. @Thomas B , do you have anything new to add?

 

[Thomas B]

I just added something a few minutes ago. Until I hear back from Jeffrey, Keith or Deirdre, or anyone else who is interested, I wasn't planning on saying anything more. Isn't it up to us to decide whether we're going circles? I feel like I'm getting to know a few you a little at the very least.

 

[deirdre]

But, as far as I can tell, Starossek has the forces going mainly into the columns, buckling them.

you are going to have to quote as per the Link Policy, so people can see what you are talking about. https://www.metabunk.org/threads/metabunks-link-policy.5158/

Isn't it up to us to decide whether we're going circles?

no

Until I hear back from Jeffrey, Keith or Deirdre, or anyone else who is interested,

i'm not. it sounds like you are saying that you want someone to comb through all the threads on Metabunk and perhaps ISF and condense them into a book..which no conspiracy theorist will believe anyway, because it would have to be too general to keep it short enough to keep people's laymen interests.

if you do actually read the MB threads (i've read maybe half) then you would have all the detailed information you seem to be asking in this thread.
I dont remember the name of the documentary i saw, and i don't buy amazon book son 9/11... so no, i do not know of a commercial book or a school textbook that discusses and analyzes everyone's various theories on the WTC collapses.

It is reasonable for lay people to not understand how the towers collapsed. Heck there are people who don't understand the setting sun or why contrails are formed. But i don't see how a short book is going to help these people. Keith just told you why in a short way but you don't believe him. This is why Metabunk exists, so you can discuss specific questions you don't fully understand or need more clarification on.
If you dont understand the progressive collapse, then read the threads on that topic. Its better than a book because with a book you you cant stop at every point and ask the author to clarify what you don't understand. Or take an engineering course on progressive collapse so the Professor can answer your questions when you get stuck.

 

[Thomas B]

Thanks for your time. I'll move along. Cheers, everyone.

 

[Jeffrey Orling]

if your structure cant hold up the building, (ie loads) it falls down. wouldn't that be the first thing they learn in structural engineering?

That statement is so basic it hardly explains anything about the design of structures.

In all the 3 buildings there were chain reactions of failures working at parts of the structure. The twins dud not loose axial support... column failure which is how a CD works... they blow out columns so they can't hold the building up.

7WTC supposedly lost one column on at one location - floor 12-13 which led to global collapse... by unexplained mechanisms.

There are some over arching themes which were not emphasized or even discussed... PROGRESSIVE failures of complex systems. This is not unknown... but what not, IMO sufficiently presented to explain the collapses.

 

[Jeffrey Orling]

First, tell us why the NIST report doesn't satisfy you.

It's not accurate/complete... and fails to explain "global collapse".

 

[Jeffrey Orling]

It's a technical problem.



Who besides conspiracy theorists care about progressive collapse? Once it failed gravity takes over.


Irrelevant. It's old. So what? Has the information changed?


Irrelevant. The NIST study attempts to answer the question of why the towers came down. In my opinion it does.

It failed? What sort of nonsense is that statement.... what is "it"? what as its failure?