Talk:Collapse of the World Trade Center/Archive 16

Design issues section
MONGO has reverted my suggestion to have a separate section on "Design issues" (perhaps "engineering issues" would be better). As I see it, the three sections aren't directly related to the collapse mechanism and might actually be better placed before the mechanics are explained. (E.g., the hat truss is mentioned in the collapse initiation section but is explained only afterwards. So my suggestion would be to take these three subsections ("structural design", "safety concerns", and "fireproofing"), give them their own main section, and move them to immediately before the mechanics section.--Thomas B (talk) 08:33, 1 February 2019 (UTC)
 * Sounds like conspiracy theory leanings to me, as it has been previously. The entire article is set to be rewritten so you can watch from afar.--MONGO (talk) 14:34, 1 February 2019 (UTC)
 * That sounds interesting. I've been watching it not being rewritten from afar for several years now. It certainly needs it. As you know, I'm not going to be giving you very much trouble, just some advice now and then when I think I've got something to contribute. Have fun with it.--Thomas B (talk) 18:07, 1 February 2019 (UTC)
 * From past experience ThomasB has a history of promoting conspiracy theories by stealth and his comments need careful reading. I look forward to an experienced, neutral, editor taking on the task of re-writing the article. David J Johnson (talk) 18:16, 1 February 2019 (UTC)
 * David, this is silly. For most of the decade I've been respecting a topic ban and no real progress has been made on the article. Obviously, my presence wasn't the problem. If Mongo is right that some sort of special team has been assembled to fix this article, that's great, and I can only support it. My view is that this article should present as clearly and informatively as possible the "official" explanation of why the buildings collapsed.--Thomas B (talk) 18:38, 1 February 2019 (UTC)
 * Why put official in quotation marks?--MONGO (talk) 22:27, 1 February 2019 (UTC)
 * Because it's a word conspiracy theorists use (without quotation marks). It's not part of the vocabulary of the article, nor, I would have thought, yours and David's. I was just acknowledging that.--Thomas B (talk) 07:18, 2 February 2019 (UTC)
 * PS. In the past, I thought that "conspiracy theories" (which I also put in scare quotes) provided a useful foil to explain the collapses against. They raised questions, I thought, whose answers were informative. I now acknowledge the consensus among editors on this article that these "outside critics" (Bazant et al. 2008, p. 1) should not be mentioned at all, and what I was saying in the above comment is simply that the explanation that has been "universally ... accepted by the communities of structural engineers" (ibid.) should be presented plainly, directly and completely enough that further questions simply don't arise. When confronted with a "conspiracy theory", an intelligent person will think, "Surely, this has been explained fully by science," and they should then find that explanation here at Wikipedia. The fact that such an article doesn't exist nurtures alternative accounts and forces sincere people to engage in all manner of independent research in an attempt to assuage their concerns. (After all, even Bazant and his colleagues acknowledge that the collapses were initially puzzling, even to engineers, so it's understandable that people get confused.) In fact, the main reason I ever got involved in this train wreck was that the article as I found it back in 2006 did not answer the questions I needed answers to and was, instead, mired in the very "conspiracy theory nonsense" that I had hoped it would have cut through like a hot knife through butter. It turns out that it's the article itself that is made of butter, and it simply doesn't tolerate any heating. Like I say, I hope the rewrite MONGO sees coming makes it more robust. I fully support that effort.--Thomas B (talk) 09:36, 2 February 2019 (UTC)

FEMA's failure mechanism is wrong
MONGO's preferred version of the mechanics of collapse section cites FEMA's "floor failure" explanation, which hasn't been current since the publication of the NIST report and always contradicted Bazant and Zhou's original (and currently received) column-failure model. My proposal solves this problem and should be considered the "last good version", whatever our other differences may be. I'm of course happy to discuss this in good faith on it its merits.--Thomas B (talk) 17:00, 4 February 2019 (UTC)
 * Sounds like the thin end of a wedge. Tom Harrison Talk 21:33, 4 February 2019 (UTC)
 * Interesting jargon (I've been away too long to know what a "wedge" is.) But you just need to defend the FEMA citation, Tom. Why are we using the completely outdated and totally wrong FEMA report to explain the collapses? And what's wrong with the fully NIST-Bazant account I've provided?--Thomas B (talk) 22:15, 4 February 2019 (UTC)
 * No, you're removing material supported by NIST. Your rationale makes no sense. From the NIST FAQ:
 * "'Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass. In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass.'"
 * The passage you keep removing is germane to either failure mode: "While the buildings were designed to support enormous static loads, they provided little resistance to the moving mass of the sections above the floors where the collapses initiated." is not contradicted by NIST or exclusive to FEMA. It's just a difference of what failed first, not what happened once the failure occurred. Static and dynamic loads are drastically different, and buildings aren't designed for dynamic loads of that kind.  Acroterion   (talk)   00:08, 5 February 2019 (UTC)
 * That passage about static and dynamic loads is in my version too. As I explained above, the problem is that "floor" is imprecise (and outright wrong in the way FEMA uses it, so we should not provide that source since it causes confusion.) The NIST FAQ rightly says "stories", not floors. My version explains that mechanism exactly.--Thomas B (talk) 07:33, 5 February 2019 (UTC)
 * You could say that you prefer "story" to "floor" instead of reverting. In broad American usage, "story" is a somewhat unusual or anachronistic usage nowadays, mainly used when referring to a building as a whole, as in a "20-story building," but one would say "my office is on the 11th floor." Where it confers better precision, it's fine. I don't see the use of "floor" in this context as implying that the floor failure scenario is being put forward, but a simple word substitution and citing NIST takes care of that.  Acroterion   (talk)   13:13, 5 February 2019 (UTC)
 * I originally tried to propose merely changing the word (from "floor failures" to "column failures"). The problem is that the reference is to the FEMA report, and in that report floor failure means something different (and wrong). What was needed was a rewrite of the section and that is what I've done. I think that NIST, in the FAQ you quoted, is right to use "story" in this context. I'm actually not sure what you're saying is wrong with my proposal.--Thomas B (talk) 13:59, 5 February 2019 (UTC)
 * Thomas, I am currently still rereading all pertinent materials on the collapses and have order some books but I am also very busy doing FEMA testing for CERT designation. My expertise is research mainly but Acroterion and Tom Harrison certainly have shown expertise that is not alien to this subject matter. I'd give their assessments due considerations.--MONGO (talk) 18:30, 5 February 2019 (UTC)
 * Yes, it's been disappointing not to see that expertise not being used all these years. I guess I keep coming back to it out of impatience to see this become a good article that explains how the buildings collapsed. The section we're discussing here is of course key. What books are you thinking of? For me, this has also been part of the problem: there isn't a good post-NIST report book on the collapses. Or not one that I'm aware of. Perhaps you've found one?--Thomas B (talk) 19:43, 5 February 2019 (UTC)
 * Well, working 60 hours a week and getting paid for expertise tends to make me want to do something else when I'm not working. I'm happy to help out, but I'm not prepared to undertake a major project for the foreseeable future, especially if it involves a detailed review of the technical literature. My participation on WP has declined considerably over the past few years due to outside obligations.  Acroterion   (talk)   04:35, 6 February 2019 (UTC)

I'm out for now. It sounds like you're all too busy in real life to do anything other than revert my changes. See you next time.--Thomas B (talk) 05:49, 6 February 2019 (UTC)
 * Looking a this over, numerous issues would arise at FAC and I am not sure the article in its current form would have any hope of being promoted to FA. A full rewrite is likely the best option, starting from scratch.--MONGO (talk) 19:17, 6 February 2019 (UTC)
 * FWIW, I agree with you. Has that ever been done on other articles? I guess the first step would be get consensus (you have my vote) to blank the article and replace it with something like a stub. Then very slowly and carefully build consensus about what sources to use and what facts to introduce. But is there anyone around who is willing to do that work? It seemed to me you were all too busy. And I'm pretty sure you're not going to let me do it.--Thomas B (talk) 21:55, 6 February 2019 (UTC)

Combining
Probably best to combine the sections on "Towers collapse" and the "Mechanics of the towers collapse" into one heading and have that in 4-5 subheadings total. Looking that over.--MONGO (talk) 16:49, 15 February 2019 (UTC)


 * Yes. In addition, we may not need a separate section on "Investigations." We might do better folding the relevant material from "Investigations" into the "Collapse" section. Tom Harrison Talk 16:59, 21 May 2019 (UTC)
 * My thoughts exactly. I'll work on that asap.--MONGO (talk) 07:10, 22 May 2019 (UTC)

Total progressive collapse section is outdated and wrong
Tom Harrison has restored FEMA's(2002) incorrect explanation of the total progressive collapse where I had put Bazant and Verdure's (2007) explanation, which I think is the generally accepted one. Note that I had preserved most of the (correct) descriptive portion of the now restored passage by moving it to the second paragraph of the intro of the mechanics section. (So in Tom's version the same sentences appear twice in the article.) This sentence is simply wrong:
 * "the mass of failing floors overwhelmed the floors below, causing a progressive series of floor failures which accelerated as the sequence progressed."

It was the falling upper section that overwhelmed the columns below, one story at a time, in two phases: crush-down then crush-up. I'm happy to hear how the restored version is "better", but I really don't see why we should be citing FEMA's report here. Whatever goes here should be a summary of a more recent source (like Bazant and Verdure 2007).--Thomas B (talk) 14:07, 2 June 2019 (UTC)
 * Isnt this the same conversation we had back in February?--MONGO (talk) 18:44, 2 June 2019 (UTC)
 * Yes, I got the impression that we agreed on the substance but you had a bigger rewrite planned that would fix it. That doesn't seem to have materialized, so I thought I'd try to fix this local issue again.--Thomas B (talk) 18:56, 2 June 2019 (UTC)
 * Please await MONGO's rewrite and not make questionable changes. Thank you, David J Johnson (talk) 11:38, 3 June 2019 (UTC)
 * I don't think that's how it works. Tell me what is wrong with the way I present Bazant's model, or tell me why it's wrong to use Bazant's model. Or tell me why FEMA is a more reliable source than Bazant (whose explanation is endorsed by NIST). Defend your revert. Otherwise the problem will persist into MONGO's rewrite too.--Thomas B (talk) 13:32, 3 June 2019 (UTC)

I'm quite happy with this version. Please consider it on its merits, and of course point out what can be improved.--Thomas B (talk) 21:26, 3 June 2019 (UTC)
 * A large-scale unilateral re-write is a bad idea. Tom Harrison Talk 10:09, 4 June 2019 (UTC)
 * In particular, the bit added about "crush-down" and "crush-up" is almost incoherent, and not a good summary of Bazant's paper (which paper seems to me to have a different purpose than explaining the collapse to laymen.) Tom Harrison Talk 10:16, 4 June 2019 (UTC)
 * It would be great to agree at least on what source to summarize. We're citing two Bazant papers in the first para of this section now. Why do you prefer the Hamburger et al. FEMA chapter for the second? (Note that it is describing a different failure mechanism, which was rejected by NIST.)--Thomas B (talk) 10:41, 4 June 2019 (UTC)
 * I'd appreciate a source for "it is describing a different failure mechanism" and "was rejected by NIST." Tom Harrison Talk 10:53, 4 June 2019 (UTC)
 * Here's how the Wikipedia article on The NIST World Trade Center Disaster Investigation puts it: "The NIST investigation's conclusions do not support the 'pancake theory' of collapse, in which there is a progressive failure of the floor system ," citing NIST's FAQ.. FEMA talks about "pancake-style collapse" on page 25. Here's the FEMA process:
 * "As the large mass of the collapsing floors above accelerated and impacted on the floors below, it caused an immediate progressive series of floor failures, punching each in turn onto the floor below, accelerating as the sequence progressed." (p. 27)
 * And here's Bazant and Zhou (2001, but which later work confirmed):
 * "For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally."
 * Does that clarify what I mean?--Thomas B (talk) 12:05, 4 June 2019 (UTC)
 * "assume", I was always taught never to assume anything unless there were reliable secondary sources backing up the statement. I agree with all Tom Harrison has written above.  How come ThomasB announced some time back that he was "leaving Wikipedia", only to start-up again? In haste, David J Johnson (talk) 15:01, 4 June 2019 (UTC)


 * Still reading some of Bazant's work yet, as well as reviewing the NIST docs. This material is extensive and I am not anything more than an armchair quarterback on these technical treatises. Its hard for me to know specifically what material is relevant and what isn't.--MONGO (talk) 16:53, 4 June 2019 (UTC)
 * I share your pain. It's difficult stuff. The question is what destroyed the load-bearing structure that wasn't hit by the planes. The two options are: (1) the brute force of the falling mass from above onto the columns and (2) the loss of lateral support, allowing the weight to pull the building down. Bazant, as I understand it, is arguing for option (1), FEMA proposed option (2), which was also the one NOVA went with in their documentary way back when. Then NIST endorsed Bazant. It's frustrating that there's no recent, detailed popularization of the science on these collapses. We need an expert engineer to walk us through these collapses floor by floor.--Thomas B (talk) 17:06, 4 June 2019 (UTC)

If there are two different and incompatible explanations, it seems like that would have been in the news. Anyway, if we can't understand and summarize the technical literature, we need to limit ourselves to news reports and sources accessible to laymen - like the Building Performance Study. Tom Harrison Talk 23:09, 4 June 2019 (UTC)
 * I don't think there's any controversy about this among engineers. Two explanations were considered but the column-failure model was ultimately accepted. I think when the NIST report was released it was mentioned, but the FEMA report's authors didn't object so that detail wouldn't have been particularly newsworthy. I'll do a quick search and see what I can find. I'm confident that the consensus is that FEMA's BPS has been totally superceded by the NIST report.--Thomas B (talk) 05:44, 5 June 2019 (UTC)
 * Probably not an issue with using all the references so long as they are placed in proper context. If indeed FEMA is totally invalidated by updated sources then we may only be able to use them as part of the historical perspective of how the investigations unfolded. I do not think it is invalidated though yet, though even the article states that more recently executed studies amended and or corrected FEMAs study and if that is not clear it may need to be made so. I too am not a fan of the Bazant lingo regarding "crush up" and "down" as that seems to go into a depth that is excessive for this more layman reader-friendly encyclopedic entry.--MONGO (talk) 01:23, 5 June 2019 (UTC)
 * I didn't even know the article The NIST World Trade Center Disaster Investigation existed until Basboll pointed it out above. Not sure why that was spun off or created when it seems to be closely aligned with the mission of this article. Unless it is simply about what NIST did in their research and investigations.--MONGO (talk) 01:30, 5 June 2019 (UTC)
 * I’m traveling and don’t have the means to properly compare, but I believe Bazant was addressing failure modes below and above the main plane of failure. I think we should be careful not to get too far down in the weeds with the crushing-upwards of the falling block, but it might be mentioned in somewhat less detail, as the column failure (it appears) worked both ways. The central point is that, once in motion, the inertial force was far in excess of the ability of structure above and below the failure point to resist.  Acroterion   (talk)   02:51, 5 June 2019 (UTC)
 * Yes, this section is about the failure of the sections above and below the impact zones. It's purpose is to explain the progress and totality of the collapses, not their initiation. We should imagine a reader who wants to know what happened during the 11 and 13 seconds after collapse initiated. This process has been explained by science and is part of our common knowledge. We just have to represent what is known.
 * At this point, unfortunately, our best basis is Bazant's various papers. While his equations are beyond me, I think I understand the basic model (and there are pictures!): the buildings were destroyed roughly one story at a time. There were probably some multi-story bucklings, when a floor did tear loose first, destroying the lateral support; basically the columns buckled immediately under crush front over the length of the unsupported columns (usually just the height of a story). What Bazant shows is that as long as the falling block kept causing sections of least one story to buckle, so that the block would then fall freely through that distance, it maintained enough momentum to crush the next floor. He also shows that the impact force will always crush the story below long before it buckles the column sections above the crush front. It's only when the top block impacts the immovable ground that these sections fail, again story by story. I'm happy to hear if anyone thinks I'm getting that wrong.--Thomas B (talk) 05:32, 5 June 2019 (UTC)

Version of progressive collapse section as of June 5
Here's my current suggestion. I've tried to make it more coherent, in recognition of Tom's issues. I'm sure even more can be done to make it clearer. Please note that the peeling off of the perimeter columns is still in the article, just up in the intro to the mechanics section. This section is only about how the load-bearing structure was overwhelmed. --Thomas B (talk) 16:43, 5 June 2019 (UTC)
 * Can we say "mediated by an accumulating layer of rubble," or possibly, "mediated by an accumulating layer of rubble, most significantly concrete from the floor slabs"? The lay misunderstanding here that I come across most often is, why didn't the collapse stop? People often argue that the columns toward the bottom were designed to be much stronger than those at the top, so the collapse "should have" slowed rather than accelerated — but this neglects the effect of the accumulating debris shield and its ever-increasing kinetic energy. I haven't checked Bazant but I'm pretty sure this is included in his calculations.  -Jord gette  [talk]  17:12, 5 June 2019 (UTC)
 * Good point. I've made the change. Feel free to improve on it if you like.--Thomas B (talk) 18:34, 5 June 2019 (UTC)

Descriptive or explanatory?
I've been waiting for MONGO to complete his rewrite of the article, and I'm in no rush, but I'd like to raise the question of whether this article should mainly be a description of the collapses or an explanation of them. My view is that readers come here to find out why they collapsed, not just how. There's a lot of (entirely correct) factual detail in this article that is presented without any clear sense of why the reader needs to know. The facts don't add up so much as pile up. If we instead presented the collapses as a puzzle that has been solved by engineering science, I think it would be a much better read.--Thomas B (talk) 18:41, 26 July 2019 (UTC)
 * Fair question and sorry for my delayed efforts. I have not reverted any of your alterations lately yet still see the article as being a bit away from Peer Review, partly due to your very question, as to whether the article should offer an explanation of why or how or both. The why is obviously due to the fact that hijacked planes were crashed into them at near full speed...the planes were nearly fully loaded with aviation fuel and the fuel caused fires weakening the supporting walls and structure to the point of failure. The How of course is what systems failed, and how they led to total collapse. I think we should discuss both but the actual mechanics of this is why I have been delayed as I lack the engineering expertise to streamline and parse some of the more technical data presented by various engineers.--MONGO (talk) 18:49, 26 July 2019 (UTC)
 * Also...as to the puzzle issue. I think the earliest commentary and evaluations made in the first few months after the collapses, before the evidence could be more thoroughly examined, should be greatly streamlined. The FEMA study should be offered only as a preliminary since they did not have the engineering corp and enlistment of outside voices to the degree the NIST reports did, so it needs to be very clear that FEMA wasn't so much "wrong" but more that as part of their compact they were obligated to offer some immediacy to the discussion as to what happened and how. FEMA is the emergency management entity and NIST is the agency better structured to offer a more nuanced and accurate engineering record.--MONGO (talk) 18:54, 26 July 2019 (UTC)
 * My suggestion is to model this article on the Sinking of the RMS Titanic. In that article we get a clear sense of how shocking the disaster was, not just on a human level, but as an engineering issue. The ship had been considered unsinkable. In the case of the WTC, there were many good reasons that first responders didn't hesitate to enter the buildings. As you point out, it's significant that the planes were going at full speed and were fully loaded with fuel. The buildings were designed with less severe aircraft impacts in mind. Also, FEMA originally thought one kind of failure mode was most likely; but NIST eventually settled on another as more plausible. I think the article should be organized around these engineering puzzles. This would make it more intellectually satisfying to read. It should satisfy the intelligent reader's curiosity about how this disaster could happen.--Thomas B (talk) 19:11, 26 July 2019 (UTC)
 * In practice it would look roughly like this:
 * 1. Background
 * 2. Impact and fires
 * 3. Collapse mechanism
 * 4. Investigations
 * 5. Aftermath
 * Most of the information we need is already in the article and just needs to be presented in a more useful way. Since so much of this is about mechanical processes, however, I thin it'd be great to find or make illustration and animations like those in the Titanic article. E.g., --Thomas B (talk) 21:10, 27 July 2019 (UTC)

Background section
I've gone ahead and created the background section, simply moving some of the info from the collapse section. It'll need some more work to focus it on the puzzle the collapses implied, but I thought I'd just get everyone's opinion on the basic idea.--Thomas B (talk) 14:39, 30 July 2019 (UTC)
 * No arguments. This looks good to me so far.--MONGO (talk) 18:13, 30 July 2019 (UTC)

Some thoughts on engineering sources
I just found a detailed model of the progressive collapse of the structures that introduces a twist on the collapse mechanism. Daigoro Isobe's work seems to suggest a "shock wave" that stressed some "inherent weaknesses" in the buildings (particularly the connections between column sections, as I understand it). He seems legit. Any thoughts on how to incorporate his perspective? In any case, it reminded me that there's very little secondary literature on the collapses. I'd really like to see a good popular book on the subject of the collapses themselves, written by someone with sufficient expertise to synthesize the consensus in the engineering literature.--Thomas B (talk) 14:44, 5 August 2019 (UTC)
 * Same author published a piece on the effect of the shock waves from when the planes struck that may have fractured some columns and caused fastening structures to have become disconnected, helping to facilitate the collapses. I'd say he is legit as well.--MONGO (talk) 17:13, 5 August 2019 (UTC)
 * Do we put it in "straight", as something that is known, or as a hypothesis that has been proposed? --Thomas B (talk) 17:16, 5 August 2019 (UTC)
 * Well, I don't know if it has been peer reviewed. Some of his work has been published but not positive it is accepted. It certainly seems like the alleged shock waves is a hypothesis but a plausible one, though one must take into consideration my limited knowledge of engineering specifics so I am armed with only my opinion on the studies.--MONGO (talk) 18:18, 5 August 2019 (UTC)
 * I'm hesitant about adding it because it seems to run somewhat against Bazant's confident assertion that no additional damage was needed to explain the collapses. Isobe presented his argument in a 2018 book, where he said, "The specific cause of such a high-speed collapse still remains unresolved." What he is suggesting (as far as I understand it, with the same caveats you make) is that the impacts seriously damaged the buildings, leaving them in a condition resembling toy blocks (that's a gross exaggeration of course), i.e., the column sections were now essentially stacked loosely on each other, rather than welded into one structure with all its initial strength. The work has definitely been peer-reviewed, but I haven't seen any comment from Bazant or anyone else.--Thomas B (talk) 18:44, 5 August 2019 (UTC)
 * PS. On page 66 of the book Isobe says that "the collapse speed in the analyses never reached a value as high as that of the free fall observed in the WTC collapse". (He must mean "near free fall" in the NIST sense.) The question is whether this means the collapse times constituted a legitimate engineering puzzle, and that one possible solution is to posit damage to the length of the structure, i.e., damage that was not confined to the impact areas. (Note that the article in its present form asserts as given that the upper and lower blocks were entirely undamaged.)--Thomas B (talk) 19:55, 5 August 2019 (UTC)
 * Common sense might seem to be that the towers speed of fall was increased or decreased from free fall speed depending on more factors than can be easily imagined. Obviously the south tower was hit at a lower elevation so my rudimentary mind would say that the weakened point had more mass above it than the area above the damaged section in the north tower. The offset way the south tower was hit may also explain the later crash but earlier failure. As the building collapsed it likely wasn't fluid... in split seconds there were surely stops and starts as the mass above slammed into the mass below. I think that yes, Bazant and NIST are correct that fires alone were all that was needed to bring the towers down but both also discussed the impacts of the aircraft and resultant damage. Isobe adds the argument of shockwaves snapping fastening points and fracturing columns but not positive this is reflected in the examined steel that was recovered, or if it was, that the remains could be distinguished between aircraft induced fracturing or collapse induced fracturing. I'd have to do more research.--MONGO (talk) 21:54, 5 August 2019 (UTC)
 * While it seems reasonable that the impact of a 767 moving near 500 knots might shear or weaken welds or connectors in distant locations, I'd like to see if it's been discussed more broadly in literature, since it's highly unlikely that there would be any kind of uniform pattern to the failure. Fastenings are subject to variations in material and technique, and some welds could fail differently simply because of a difference in welding technique or skill level, for instance. @MONGO, I think you mean that the speed of collapse would be increased or decreased relative to free-fall rather than from free-fall.  Acroterion   (talk)   00:30, 6 August 2019 (UTC)
 * Actually, I was just musing, pretending I have a clue about this at all!--MONGO (talk) 19:08, 7 August 2019 (UTC)
 * Hear hear! The Notorious MONGO is being coy. Indeed, relative to free-fall sounds correct, and I'm pretty confident that's what His Royal Apeness really meant. — JFG talk 00:41, 8 August 2019 (UTC)
 * All my relatives are in the deep woods...we occasionally make fleeting appearances at campsites and on unsuspecting hikers, offering brief glimpses of us, not enough to make a positive ID, but enough to to allow them to get a sketchy photograph or shaky camera footage.--MONGO (talk) 14:51, 8 August 2019 (UTC)

Bazant & Verdure vs. Isobe
For clarity, I just want to put the two passages that puzzle me alongside each other:
 * Bazant and Verdure: “The relative smallness of energy absorption capability compared to the kinetic energy also sufficed to explain, without any further calculations, why the collapse duration could not have been much longer (say, twice as long or more) than the duration of a free fall from the tower top. Therefore, no further analysis has been necessary to prove that the WTC towers had to fall the way they did, due to gravity alone.”
 * Isobe: “In general, the tower remained standing for a longer period of time due to the catenary action of the outrigger truss system only if the load paths in the tower were protected and if the member connections were strong enough. However, in these analyses, the collapse speed never reached a value as high as that of the free fall observed in the WTC collapse, which occurred while the splices between column sections still retained their tensile strength. From these results, it is evident that the high-speed collapse of the WTC towers might have been caused by an inherent weakness in their member connections in addition to the destruction directly caused by the aircraft impact.”

On the face of it, it looks like they disagree about the need for an explanation, i.e., the existence of a puzzle, in regard to the duration/speed of the collapses. (Isobe's "analyses" are computer simulations of simplified WTC-like structures.) I have ordered Uwe Starossek's Progressive Collapse of Structures to see if it might shed some light on it. I'll get back to this when it arrives.--Thomas B (talk) 17:03, 7 August 2019 (UTC)
 * Not seeing the need to do a detailed examination of the speed of the collapses. While the seismographs probably provide the best record of how long the collapses took delving deeply into this seems to be unnecessary. I would like to see more engineers opinions regarding Isobe's work on the matter before we post his studies as anything other than included addendums. His work would have to be qualified by saying something along the lines of "later engineering examinations by Isobe in (date) examined the aircraft impacts and he suggested the impacts may have sent shock waves throughout the structures, fracturing various connecting points and even the main steel work...however other engineers have yet to comment on this." I mean, the wording could be better, but until it is properly vetted not positive we can do more than that if we include his research.--MONGO (talk) 15:02, 8 August 2019 (UTC)
 * I think we have to leave Isobe out for now. We could have a section that reviews the entire engineering literature on the subject, but I think that's likely to become a synthesis. I'll see if I can find a review article we can summarise. (There ought to be a review article actually. Maybe a major engineering journal will commission one for 2021. That would be really useful.) We need someone who can weigh the arguments. Like I say, I'm hoping Starossek's book will help.--Thomas B (talk) 16:19, 8 August 2019 (UTC)

Aircraft impact studies (for background lead)
Here's MONGO's suggestion:
 * Though fire studies and even an analysis of the impacts of low speed jet aircraft impacts had been undertaken prior to their completion, the full scope of those studies no longer exists.

But if we're going to say that we can't know "the full scope" of the studies, and since we know (see note 1) that at least one account described them as fully loaded (23,000 gallons) and flying at cruising speed (600 mph), how can we describe them simply as "low speed jet aircraft impacts"? Shouldn't we (in the lead) just say "aircraft impacts had been considered in the design"? The relevant subsection provides all the details.--Thomas B (talk) 18:45, 22 October 2019 (UTC)

Two issues with the background section
I generally like what MONGO has done with it, but two points weaken it a little. The first is this sentence:
 * Though fire studies and even an analysis of the impacts of low speed jet aircraft impacts had been undertaken prior to their completion, no evaluations had considered the effects of fully fueled passenger jets flying at high speeds.

This of course serves to introduce the "Evaluations for aircraft impact" section. But it seems at odds with the last paragraph and note 1, which suggests that high speeds and lots of fuel were considered.

The second is this sentence:
 * Built with a novel design that maximized interior space, the towers were considered some of the strongest structures ever built relative to their weight, even though they lacked a traditional steel framed skeleton.

Do we need the "considered"? Has it since turned out that they weren't as strong as people thought? They didn't behave as expected, but surely they're still considered among the strongest structures (relative to their weight) ever built?

Also, I think readers are likely to understand the last part of the sentence as: the towers didn't have a steel skeleton. That is, they'll think "traditional" buildings do have such a skeleton, and the Towers didn't. It's of course true that the skeleton wasn't a traditional one: it was, as we put it, "novel". But it definitely had one. So I'd suggest just dropping everything after the comma, letting "novel" capture the non-traditional design.Thomas B (talk) 10:16, 20 October 2019 (UTC)
 * I reverted the changes you made. As my edit summary reveals it is important to keep the aircraft impact analysis of low speed impacts in this for it diverges from what ultimately took place. It's a false narrative otherwise.--MONGO (talk) 23:00, 20 October 2019 (UTC)
 * I have problems with "the towers were considered some of the strongest structures ever built relative to their weight." I had earlier changed "structures" to "skyscrapers," but even then it's not necessarily true, as there could be older concrete skyscrapers the same weight as a WTC tower, but stronger. What we really mean is more like density. Were they really that strong relative to their density, or were they just very lightweight for skyscrapers of that size? I don't recall that their factor of safety was particularly high. Also, "strongest" is weak and ambiguous, as strength can refer to different things (e.g. axial load-bearing strength vs. shear-resisting strength).


 * Maybe we can say, "...the towers were some of the most lightweight skyscrapers for their size, but they were considered very robust, even though their steel-framed skeleton was not a traditional design."  -Jord gette  [talk]  00:43, 21 October 2019 (UTC)


 * I think we should stay away from the whole strongest business. As Jordgette points out, they were notably light for their size. Fundamental strength and factors of safety are based on code minima, standardized calculation methodologies, and whatever extra makes the design engineer comfortable with the design. As for the "steel skeleton" terminology, I'm not keen on that, since they were clearly steel buildings - they just didn't use the framed-bay approach that had been standard up to that point, to avoid columns in the interior space. Framed-bay construction is still pretty much a standard construction technique, it's just been refined with composite deck construction. Steel strength has changed - the steel in the WTC varied from 36 to 100 ksi - nowadays we would use 50 ksi minimum, so we need to recognize that "ever built" might change.  Acroterion   (talk)   01:01, 21 October 2019 (UTC)


 * Reply to Acroterion: The point of this paragraph is basically to say, "The Twin Towers were very tall and very strong and engineers were surprised when they collapsed because airplanes flew into them." The two sections that follow provide the details of their design to flesh these claims out. I think we have to keep in mind that, though their design was novel at the time, the tube-in-tube structure is actually standard now. In a historical perspective (going back, say, 500 years) a building like Aon Center, built in 1974, according to the same principles as WTC, remains among "the strongest structures (relative to weight) ever built," or however we decide to capture this point. (Maybe they're the strongest buildings?) In other words, I don't think we should downplay the strength of the towers, since this would give a distorted image of skyscraper technology in general. I'm not sure about this, but I'd be surprised if today's skyscrapers are significantly stronger than the WTC, though the may be a little lighter, i.e., more efficient.--Thomas B (talk) 05:59, 21 October 2019 (UTC)
 * Actually, codes have changed since the early 70s, and by some measures structures of all kinds are provably more robust (I hesitate to say stronger) than they used to be. The collapses of the Hartford Civic Center and Kemper Arena brought revisions to make single-point failures less likely to result in progressive collapse (the same thing is a practice in current bridge design), and the Oklahoma City bombing caused more revisions to deal with progressive collapse. There are additional requirements that did not previously exist for second-order analysis (what happens when a structure that has already moved in response to a force is subjected to another force in the deflected condition), wind load response and updated seismic requirements. That has been abetted by automated methods of structural modeling and analysis, which would be time-prohibitive if carried out by hand.  Acroterion   (talk)   00:35, 22 October 2019 (UTC)
 * Interestingly, in checking the references for the Hartford Coliseum, I see that it may have been in part a victim of over-reliance on automated structural analysis. I've updated the content accordingly - there were several problems, and the editor who inserted the previous explanation strayed from the sourcing.  Acroterion   (talk)   02:32, 22 October 2019 (UTC)
 * Reply to MONGO: In note 1, we write about "an analysis of a Boeing 707 weighing 336,000 pounds (152 t) and carrying 23,000 US gallons (87 m3) of fuel striking the 80th floor of the buildings at 600 miles per hour (970 km/h)." As far as I can tell, that's a fully fueled Boeing 707 at cruising speed, which is the opposite of what our intro paragraph says.--Thomas B (talk) 05:30, 21 October 2019 (UTC)
 * I totally agree with Acroterion and MONGO's comments above. Why do I get the impression that Thomas B's "edits" are just a fog to get back to his previous conspiracy theories? David J Johnson (talk) 10:32, 21 October 2019 (UTC)
 * "Very strong" is sophistry. If you're going to cite the strength of the towers (which, again, is ambiguous and dodgy, like saying a TV personality is "popular"), at least cite a reliable source, preferably one that defines strength in this context.
 * "I don't think we should downplay the strength of the towers" Nobody's downplaying it, but you're trying to up-play it. The Towers were not built to be particularly "strong," whatever that means. They were built to be particularly lightweight, and fast to construct.  -Jord gette  [talk]  14:26, 21 October 2019 (UTC)
 * I don't want to put "very strong" in the article. I'm just saying that's the basic theme of the paragraph we're discussing. I do want to emphasize the strength of the Towers. It is a big part of the notability of the event. When a plane crashes into a barn, we don't need an explanation for why the barn collapsed. But when one of the strongest structures in the world collapses, we want a reason. By "one of the strongest structures/buildings in the world" I mean something like: able to support the greatest load, the strongest wind, and the most severe earthquakes (all at once!). It's the sort of strength that gets you on Popular Mechanics's "top ten toughest buildings" list.--Thomas B (talk) 16:19, 21 October 2019 (UTC)


 * A review of NIST updates in 2011 should help clarify that they could find no written documentation of any pre-build studies that involved the impacts that passenger jets might incur. see here. I'll work on making amendments to my wording as suggested by all above, as well as the post article note that discusses this matter in detail.--MONGO (talk) 17:48, 21 October 2019 (UTC)
 * I think I see the problem now. NIST did not say it was unable to verify the existence of such a study. It was just not able to verify its conclusion -- i.e., it couldn't check the math done in the study (because it couldn't find the study). (We're talking about point 7 in the FAQ, right?) The key (for me) is that engineers believed that this problem had been studied and the fully loaded 707 at 600 mph had been considered. NIST was "unable to verify the assertion" that this would only result in local damage. (Indeed, events proved that it could result in much greater damage.) The point is that pre-build studies appear to have underestimated the effect of aircraft impact (and perhaps the size of the aircraft by about 20%). But Skilling's remark in 1993 wasn't just a guess. It was based on the studies they had. Studies that, it appears, turned out to be wrong.--Thomas B (talk) 18:57, 21 October 2019 (UTC)
 * My reading of #7 in that link I provided, albeit as brief a summary as it is, is that back in the era when the planes were built they actually did not have the same capabilities to do the kind of analysis they could in the 21st century. The towers DID actually survive the impacts initially, but without having a comprehensive report as could be done today it is hard to impossible to know exactly what parameters were examined. Did they say yes, the Towers would remain standing...if so, what did that mean? Did it mean for an hour or long enough to get many people to safety? (and that was close to the case) Did it mean they buildings could be made fully habitable again? We and NIST and engineers cannot determine this since they don't have any written details to be able to determine what they analyzed back in the late 60s. More revisions are needed yet to get the point across that yes, the builders claim aircraft impacts were examined but that there are no written documentations remaining that can clarify the details of the examination.--MONGO (talk) 19:12, 21 October 2019 (UTC)
 * I guess that's one possible reading. But how do you interpret Skilling's remark? He seemed pretty convinced that there'd be a really big fire, but it would burn out leaving the building standing. And if that's what the engineers Bazant was talking about thought, it's no wonder they were surprised when the buildings came down.--Thomas B (talk) 19:20, 21 October 2019 (UTC)
 * Surprised in what way? I'm surprised they stood as long as they did after the impacts...In this piece where Leslie Robertson, the lead structural engineer of the towers states,"It appears that about 25,000 people safely exited the buildings, almost all of them from below the impact floors; almost everyone above the impact floors perished, either from the impact and fire or from the subsequent collapse. The structures of the buildings were heroic in some ways but less so in others. The buildings survived the impact of the Boeing 767 aircraft, an impact very much greater than had been contemplated in our design (a slow-flying Boeing 707 lost in the fog and seeking a landing field). Therefore, the robustness of the towers was exemplary. At the same time, the fires raging in the inner reaches of the buildings undermined their strength. In time, the unimaginable happened . . . wounded by the impact of the aircraft and bleeding from the fires, both of the towers of the World Trade Center collapsed." Regardless, without any written record to examine, its impossible to know what those reports said in detail.--MONGO (talk) 21:19, 21 October 2019 (UTC)
 * @Thomas: Structural performance under standard conditions is a different thing from performance while compromised by the thermal effects of fire, much less fire and impact. Those are not standard design or analysis conditions. Buildings are designed under a set of loading circumstances - live load, dead load, lateral forces of wind and seismic loads, and so on. Factors of safety to account for design errors, assembly errors and material inadequacies, and rounding at several stages add margins. Fire performance is a whole other issue - it is time-dependent, and uses a set of standard assumptions based on laboratory performance that are rarely analyzed to any significant degree. If fireproofing failed, then "strongest" won't mean much under fire conditions, as all of the safety factors erode under heat degradation and expansion stresses. I don't think it appropriate to emphasize in the article as some kind of contradiction. It's possible to have a strong structure that fails under unusual circumstances.  Acroterion   (talk)   02:25, 22 October 2019 (UTC)
 * I don't understand why MONGO has removed Bazant's assessment of the reaction in the engineering community. Bazant uses the words "big surprise" and says that "no experienced structural engineer" expected it. As far as I can tell, Acroterion is making exactly my point (and the point of the article), namely: these were really strong (tough) buildings, but the attacks nonetheless overwhelmed them. This sets up the whole theme of the article: explaining how that happened. I haven't said this is a contradiction. I have only noted a contradiction in the article: we say both that the effects of a fully loaded 707 at cruising speed were considered and that only a slow 707 that was low on fuel was studied. Robertson and Skilling recollected these studies differently, and NIST seems to have confirmed Skilling's memory. I'm sure we've talked about this before and even decided that Skilling probably was closer to the action on this point.--Thomas B (talk) 04:39, 22 October 2019 (UTC)
 * I'm not really making your point - there is no widespread consensus in sourcing that they were no more or less tough overall than any other building. They had some novel features which may have not served them well in 2001 - the reliance on the core was probably a bad thing, but the shell was strong, and the trussed floors performed poorly. Their design was driven by economic considerations for an open floor plan, which was coming into vogue, rather than smaller office spaces punctuated by columns, which led to the steel tube arrangement. Economics did not encourage a stronger-than-necessary design, and never does. The present WTC 1 is grossly overbuilt for reasons other than economics.
 * There is confusion in sources about the speed considered for airplane impact, so we shouldn't get into too many details on that. I personally doubt the high-speed scenario was actually considered, since no commercial airliner is designed or intended for high-speed flight near sea level, and the 9/11 planes were on the edge of structural failure or loss of control themselves. Our sources lack unanimity on this, so we just have to live with it and not be over-specific, or make broad statements like "strongest" in Wikipedia's voice.  Acroterion   (talk)   01:35, 23 October 2019 (UTC)
 * Thomas, why are you so interested in putting in the trivia about some engineers being surprised by the collapse? It's trivia. Who cares who was surprised; it collapsed.  -Jord gette  [talk]  18:07, 22 October 2019 (UTC)
 * I think you're unduly fixated on the word "surprise", which is just an ordinary language summary of the underlying fact: "no experienced structural engineer watching the attack expected the WTC towers to collapse." That reference to experience and expertise indicates the state of the science before 9/11. If an airliner were to fly into, say, the Aon Center tomorrow, not only would engineers not be surprised if it collapsed after an hour, they would more or less expect it to. That's simply important knowledge to have in this article. 9/11 changed the way engineers think about buildings like this, about how they perform under these conditions.--Thomas B (talk) 18:23, 22 October 2019 (UTC)
 * Engineers' expectations of the buildings' performance after the impacts and fires are irrelevant, and personally I think the post-crash, pre-collapse expectations (the sourcing of which remains dubious) should be removed from the article altogether. The buildings were novel in design but were built with sufficient factor of safety; planes crashed into them; fires raged; the buildings collapsed. Why is it relevant what engineers thought would happen in this totally new scenario, the combination of major structural damage and major fire in a design that had never experienced either?  -Jord gette  [talk]  20:42, 22 October 2019 (UTC)


 * Thomas Basboll...lets look at the diff here: and allow me to explain. Before I do, this does not mean either version is written in stone as this is a wiki afterall.
 * When they opened or upon completion?...not really important but they they were topped out the last few days of the year 1970, but ribbon cutting was not till 1973, which is when they opened. The Sears tower opened a year later, surpassing the WTC in height.
 * I'm sorry but I think we should link Kuala Lumpur, Malaysia as it is not as well known as Chicago in the English speaking world and this is en.wiki.
 * "earthquakes and hurricanes, and had already survived a bomb attack in 1993" is your latest change...all buildings get that study even back in 1960s. Adding that they survived the 1993 bombings does what? I think what that does is attempt to deliberately raise eyebrows...your effort seems to be that we want the event to be so "surprising" that something other than what happened, must have actually happened...the "engineers"...the most prominent engineers...no less...were "surprised".
 * Lastly, these were not "steel framed buildings in the traditional sense. Comparing the WTC Towers to the typical steel framed structure of that era is like comparing apples and oranges..they are both fruits, but they are actually very different.

If we're going to add the "surprised" notion, I want to see if 3-4 excellent level reliable sources to back that claim up.--MONGO (talk) 20:30, 22 October 2019 (UTC)


 * My replies:
 * It's just a style thing. "Upon" sounds too formal to me. Like you say, both are equally true.
 * To me it sounds unbalanced to identify the country (and link to the city) in one case and not the other. It's English Wikipedia, not American Wikipedia. I grew up in Canada and live in Denmark and it feels odd to be told what "Kuala Lumpur" means.
 * If you read that Leslie Robertson speech you linked to, you'll find he says that they "stood proud, strong, and tall. Indeed, with little effort, the towers shrugged off the efforts of terrorist bombers in 1993 to bring them down." I'm trying to describe their strength as engineers who cared about the buildings do. That's all.--Thomas B (talk) 09:17, 23 October 2019 (UTC)
 * They were "steel-framed buildings" in what is now essentially the standard sense. The WTC Towers behave as many buildings standing today presumably would under the same conditions. They were unique, but there are now many like them. Comparing them to the Aon Center (Chicago) is in any case apples to apples.


 * Anyway, I think I've made the best case I could this time around. I'll do a bit more reading/thinking and come back if I hit on something better. Cheers, Thomas B (talk) 10:35, 23 October 2019 (UTC)
 * The Aon Center was also new and novel at the same time. The entire storyline that this was the first time steel buildings were brought down by fire is overwrought. Firstly huge fires fueled by aviation fuel just dont happen often/ever in skyscrapers. Secondly, huge fires in large office buildings are incredibly rare to begin with. Thirdly, huge fires after perimeter and core support column damage from high speed wide body jets never happened before. Lastly, this doesn't mean it doesn't deserve mention but it sure shouldn't be much focus that there was surprise or that this was the first time because these were unique circumstances that were never evaluated by the original or even subsequent planners. As Acroterion stated above the successor building, the new One WTC, is over built as a reactionary response to the issues of the 2001 collapses.--MONGO (talk) 12:10, 23 October 2019 (UTC)
 * I've said this before, but the challenge I seem to be facing is persuading you that the collapses were an interesting puzzle for engineers to solve, not a no-brainer (planes went in, buildings came down, done). I think we should explain what the puzzle was and the interesting solution that emerged. But I can see I have my work cut out for me. Back to the drawing board! --Thomas B (talk) 13:33, 23 October 2019 (UTC)

Starossek
I've introduced some insights from Uwe Starossek's Progressive Collapse of Structures. The book is about progressive collapse in general, but uses WTC repeatedly as an example, and in some detail. You'll notice I'm mainly quoting, and I think if someone with more engineering knowledge than me could paraphrase the ideas it would improve the flow of the reading. Also, I'm working from the first edition (2009) of the book, which is the only one I've been able to find so far. If anyone has access to the second edition, maybe there's something better there.--Thomas B (talk) 17:47, 26 October 2019 (UTC)

Citation Style?
I'd like to clean up the references for this article. Does anyone have any objections? And do you have a preferred referencing style?--Thomas B (talk) 16:30, 31 October 2019 (UTC)
 * What's wrong with the current format?--MONGO (talk) 17:40, 31 October 2019 (UTC)
 * It's not one consistent style, as far as I can tell. Compare citations 71, 72, 73, for example.--Thomas B (talk) 17:55, 31 October 2019 (UTC)
 * I understand but this article is still being rewritten. Seems to be putting the cart before the horse.--MONGO (talk) 23:17, 31 October 2019 (UTC)
 * Checking the sources is part of the rewrite. For example, I'd like to cite the 9/11 Commission in the lead instead of the CBC (the first citation; in the current version, we don't cite the commission's report until the South Tower Collapse section). Some of the sources we cite no longer exist, or not at the links we provide (e.g., citation 23). As I make these improvements, I thought I'd also clean up the referencing format.--Thomas B (talk) 06:02, 1 November 2019 (UTC)

Any thoughts on this from others? I'm leaning towards named references with page numbers (WP:IBID) because I'd like a surveyable reference list. I'd also like to get rid of "further reading", which is mainly chapters from the FEMA report as far as I can tell. We can cite the report in the article (referencing it normally) and leave it at that.--Thomas B (talk) 17:55, 6 November 2019 (UTC)
 * We dont cite in the lead if the article us foing to be featured. For now I oppose anything other than standard cite templates as well as removal of the see also section. Let's not put the cart before the horse.--MONGO (talk) 05:43, 7 November 2019 (UTC)
 * That's sounds like a good solution. I'll remove the references in the lead and the further reading section. I will then go through all the other references and make them standard ref name (using citation templates) with pages numbers where appropriate. (My Starossek refs need to be fixed, for example.)--Thomas B (talk) 06:02, 7 November 2019 (UTC)
 * What about the bibliography? Should we move those items into the footnotes? Some of the references already appear in both places.--Thomas B (talk) 06:13, 7 November 2019 (UTC)
 * Can we slow down just a bit. Let's make sure that any ref=name citations aren't removed leaving later hanging refs with no initial citation. I'll check later today. We should avoid refs in the lead but we may be forced, due to the nature of this article, to keep a few. I just did not want to add anymore than we had unless it was truly needed.--MONGO (talk) 12:48, 7 November 2019 (UTC)
 * Okay, I'll step away for a few weeks.--Thomas B (talk) 19:10, 8 November 2019 (UTC)

Let's talk about aircraft impact evaluation
The article is looking pretty good, but I want to get the "Evaluations for aircraft impact" down to about 200 words (it's over 350 now) and seems weirdly undecided about what the buildings were designed to survive. I think if we put our minds to it we can agree on a statement that is clear and in line with the NIST report. I don't think we have to go into so much detail about the differences between Robertson and Skilling. And I don't think we need to say that the design considerations are basically unknowable. Once we've decided what to say in the subsection, in any case, we can adjust the language in the lead paragraph.--Thomas B (talk) 19:29, 2 December 2019 (UTC)
 * It looks fine to me, other than a bit of copy editing perhaps. It doesn't read long at all, so I don't know why it needs to be cut down. As for seeming to be undecided, the last sentence explains any ambiguity: analysis was limited in the 1960s.  -Jord gette  [talk]  22:23, 2 December 2019 (UTC)
 * If the article is going to discuss any planning for a potential aircraft impact then it needs to be clear what those studies supposedly found and what the limitations of those studies were.--MONGO (talk) 01:13, 3 December 2019 (UTC)
 * Yes, I'm suggesting we talk about what the studies found. Currently, in the subsection, we say two different things: (1) that the studies found that the buildings would survive the impacts of low-speed, low-fuel planes and fires weren't really considered, (2) that the studies found that they would survive high-speed, fully-loaded impacts and the subsequent fires. In the section lead we say mainly (1).
 * The ambiguity can be resolved by saying that aircraft impacts were considered in the design of the buildings and they were expected to survive such events. I agree with both of you that it should be mentioned that the ability to model such complex events in 1960s wasn't what it is today. Obviously, events proved that they were not strong enough to survive. But the question is what the designers -- and engineers in general -- believed before 9/11.--Thomas B (talk) 06:23, 3 December 2019 (UTC)
 * This really requires a modern article about the fact that the previous design specs were meant for 1960s aircraft tech, to put it into the proper perspective. &mdash;  The Hand That Feeds You :Bite 14:26, 3 December 2019 (UTC)
 * My suggestion is that we provide a summary of what it says on page 55 of the NIST report. As I read that paragraph, we can safely say that the impact of a 707 flying at 600 mph was considered and it was believed (or at least "asserted"), at the time, that such an event would cause only local damage (i.e., not total collapse). NIST, however, was unable to verify the basis of that claim. In other words, if you had asked an engineer in the 1990s (as people did after the bombing) what would happen if a modern airliner crashed into the buildings, they would have said, on the basis of their engineering knowledge, that the buildings would survive such an attack. They were proven wrong on 9/11. According to NIST, we can't know exactly why they believed the buildings would survive, but we can be sure that they did believe this. NIST must also have been aware of Robertson's "lost in fog" comments, but, presumably finding that he was wrong in his recollection of the study, decided not to include them in the report or in their FAQ. I think we should do the same, since it amounts to an internal contradiction in the section and makes it harder to understand the issue.--Thomas B (talk) 15:35, 3 December 2019 (UTC)
 * That's venturing way too much into WP:OR territory, especially the if you had asked an engineer in the 1990s bit. We need an article specifically about comparing the original design specs to what we now know, not drawing our own connections. Right now, you're drawing conclusions without actual sources to back them up. &mdash;  The Hand That Feeds You :Bite 17:23, 3 December 2019 (UTC)
 * I agree with User:HandThatFeeds views above, this is straying much too far into WP:OR territory. Also, whilst trying to assume WP:AGF, this contributor has strayed into conspiracy theories before - whilst trying to sound neutral. David J Johnson (talk) 17:46, 3 December 2019 (UTC)
 * My suggestion is to say only what is in the NIST report on this issue. In fact, my view is that the Robertson comment is OR. To be clear, I'm not suggesting that we say that "If you asked an engineer in 1990s..." I'm just saying that that's what they would have said. I think we all (and NIST) agree about that. As Bazant pointed out, engineers were surprised that the buildings collapsed. But once they did, they were able to explain it.--Thomas B (talk) 18:46, 3 December 2019 (UTC)
 * I'm just saying that that's what they would have said.
 * That's exactly what I mean by WP:OR! You're making assumptions about what people would have done in situations that never happened. We can't do that here. &mdash;  The Hand That Feeds You :Bite 20:42, 3 December 2019 (UTC)
 * Are you saying that the Skilling stuff in the article right now is OR?--Thomas B (talk) 20:48, 3 December 2019 (UTC)
 * While the NIST reports are the Bible study on the collapses it is not the only reference we have, nor should it be. Any building of such magnitudes would have had various risk assessments done before they were built, but since deliberate aircraft impacts into tall buildings was all but unheard of, of course the aircraft vs. building scenario that would have been looked at is surely the lost in the fog scenario. These risk assessments also surely looked at fire egress as well but as it turned out, lumping all those egress avenues into the central core ultimately proved to be a bad idea for the specific scenario...but again, there is zero evidence any study was done that analyzed what if wide body jets fully loaded with aviation fuel were flow at and even possibly over the speed these jets were ever intended to fly at low altitude and slammed directly into the buildings. I think this same conversation has happened on this page about a dozen times in the last dozen years and we always end up with no improvements.--MONGO (talk) 23:25, 3 December 2019 (UTC)
 * The existence of a casual analysis of a lost airliner impacting the towers similarly to the B-25 crash into the Empire State Building is well-known and documented. The content of that study and its ultimate extent and detailed assumptions do not survive, it just remains as an anecdote. It's worth including, but should not be treated as more than an anecdote. It really can't be taken as anything but an awareness that such an event was possible, and no conclusions can be drawn or implied, nor can we draw or imply any conclusions from the absence of mention in the NIST report.
 * I wouldn't assume that there was much done in the nature of risk assessments in the original design - there were no fire sprinklers, for instance, and stairs were code minimum, as the core was to be kept as small as possible. Building codes have always tended to be a five-years-later reaction to the last terrible thing that happened, and the whole specialty of fire protection engineering was embryonic in those days. The WTC towers were pretty much by-the-book designs insofar as their life safety systems were concerned, optimized for a large column-free interior.   Acroterion   (talk)   02:44, 4 December 2019 (UTC)
 * At present, the article presents the aircraft risk assessment using two anecdotes, which contradict each other. One of them says "lost in fog and flying at relatively low speeds", the other says "600 miles per hour". There is no need for this contradiction. The NIST report says, "the impact of a Boeing 707 flying at 600 mph was analyzed during the design stage" and does not mention the lost in fog scenario. If we said, "the impact of an airliner was considered in the design of the towers and it was believed that 'such collision would cause only local damage which could not cause collapse or substantial damage to the building'," then we're getting the gist of it, without the confusing tensions between Skilling's and Robertson's recollection of the study that was done. The study may have underestimated the force of the impacts or the intensity of the fires, or it may have overestimated the strength of the buildings. As you all point out, we don't know. But why insist on leaving the reader confused, when we're not?--Thomas B (talk) 06:08, 4 December 2019 (UTC)


 * If we said, "the impact of an airliner was considered in the design of the towers and it was believed that 'such collision would cause only local damage which could not cause collapse or substantial damage to the building'," then we're getting the gist of it...
 * No. That would be you drawing a conclusion from two anecdotes, which is pure WP:SYNTH. You keep claiming the readers will be "confused" while trying to reword the article to cast doubt on the ability of airliners to bring down the buildings. At this point, there is no consensus for what you're pushing. &mdash;  The Hand That Feeds You :Bite 12:33, 4 December 2019 (UTC)
 * I really am just trying to find a clear and concise way to say what the NIST report says. What about this: "Though their ability to model such events was limited at the time, the designers of the towers had taken possible aircraft impacts into account and believed the buildings would survive them." If we really want to keep both Robertson's and Skilling's accounts, I think we should address the tension between them directly. "Engineers have recalled these studies differently at different times. After the attacks, Robertson suggested they had studied only the possibility of impacts by planes flying at low speed and low on fuel, adding that they would not have been able to model the effects of the fires. Skilling, speaking after the 1993 bombing, said they determined that the fuel would cause a major fire but that the structure would survive. During their investigations, NIST found a document reporting a 1964 study of a hypothetical Boeing 707 hitting the buildings at 600 mph. While NIST was unable to verify the methods used in the study, it quoted its conclusion as follows: 'such collision would cause only local damage which could not cause collapse or substantial damage to the building'." This doesn't in any way cast doubt on the ability of planes to bring down the buildings. (It's clear that planes brought down the buildings.) It clarifies what engineers believed planes could do to the buildings before 9/11 showed them what really happens. It explains why Bazant says they were surprised.--Thomas B (talk) 16:59, 4 December 2019 (UTC)
 * That's actually more confusing. I say leave the section as is.  -Jord gette  [talk]  19:01, 4 December 2019 (UTC)
 * Well, that's all the time I have for it this time around. I'll see you sometime in the new year. I suggest you send it to GA review soon. You all seem satisfied that not much more needs to be done. Cheers.--Thomas B (talk) 19:35, 4 December 2019 (UTC)
 * That's a very flippant remark, and a misreading of the situation. That aside, I do hope you have a good holiday. &mdash;  The Hand That Feeds You :Bite 17:06, 5 December 2019 (UTC)

Buildings where debris fell
Do we wish to name the buildings where the debris fell (e.g. 90 West Street)? Just wondering, in case you or someone else wants to add the info later. Thanks. epicgenius (talk) 02:04, 6 March 2020 (UTC)
 * No reason not to so long as those are of prominence such as the one suggested.--MONGO (talk) 04:08, 6 March 2020 (UTC)

United 175 Crash Time
Hello Everyone, I was just posting this because I personally feel that the general consensus of the WTC2 Crash time is and should be 9:03 A.M. in comparison to 9:02 A.M. Even though the "Collapse of the World Trade Center" and "Timeline for the September 11 Attacks have it currently at 9:02 A.M. The reason for this consensus change, is because I personally believe that we should go by the consensus of authoritative websites from the current decade, such as the 9/11 Memorial Official timeline, the United Flight 93 Memorial Official Timeline, and History. com as well as past sources such as the FEMA Report, the 9/11 Commission Report, and most other timelines from the 2000s and 2010s state the crash time at 9:03 A.M. By Comparison only the NIST Report and the National Transportation Safety Beuaru show the crash time at 9:02 A.M. I personally believe that using the most authoritative source which in this case if the National 9/11 memorial and Museum page for the true time--Miked1992 (talk) 00:19, 23 March 2020 (UTC)Miked1992--Miked1992 (talk) 00:19, 23 March 2020 (UTC)
 * NIST was the chief investigative body of the attacks and they say 9:02.. Youve rehashed this stupid argument repeated over multiple articles using this and other sock accounts. Please stop.--MONGO (talk) 17:50, 23 March 2020 (UTC)
 * There is no consensus for these "changes" on Wikipedia. Please stop now and stop using sock accounts. Thank you, David J Johnson (talk) 17:57, 23 March 2020 (UTC)

I am aware that NIST was the primary investigative source. The source depending on who you look at is largely disputed it could very well be 9:02, but I am just going by the official united 93 and 9/11 memorial websites times which say 9:03. I am only using one account and here it is, no sock puppeting.Miked1992 (talk) 02:36, 24 March 2020 (UTC)Miked1992Miked1992 (talk) 02:36, 24 March 2020 (UTC)


 * The Lincoln Memorial has the wrong year for when Ohio entered the union! Memorials can be wrong and are not sacrosanct. It's time to stop this personal mission of yours.  -Jord gette  [talk]  19:19, 8 June 2020 (UTC)

First line is poorly written
The first line on this entry is confusing and leads the reader to believe there was only one tower. Current text as is: "The original World Trade Center in Lower Manhattan, New York City was destroyed during the terrorist attacks of September 11, 2001, after being struck by two hijacked commercial airliners."

Suggested edit: "The original World Trade Center towers (WTC1 and WTC2) were located in the borough of Lower Manhattan in New York City, United States. Both towers, WTC1 and WTC2, were destroyed as a result of the terrorist attacks of September 11, 2001. Two hijacked commercial airliners were flown, one after the other, into each of two towers, respectively. PortugeeStud82 (talk) 02:37, 12 September 2020 (UTC)
 * Before the 20th anniversary of the attacks, this article will be undergoing a full revision.--MONGO (talk) 05:07, 12 September 2020 (UTC)
 * I disagree on that edit. The entire World Trade Center was destroyed, and the first line doesn't say anything about a tower.  -Jord gette  [talk]  15:12, 12 September 2020 (UTC)

Semi-protected edit request on 23 February 2021
Suggestion is to add the following additional published research to the section "Other investigations."

Robert W. Rollings analyzed the collapse times and resistance of towers 1 and 2 based on the seismic record of their respective ground shocks, determining that 1 WTC (north tower) fell in 22.8 ± 1.3 s and 2 WTC (south tower) fell in 19.0 ± 1.0 s. Based on these collapse durations he furthermore determined that both towers 1 and 2 provided relative collapse resistances of 84% -97% of that needed to avoid total progressive collapse.

Citation Robert W. Rollings; Collapse Times and Resistance of the World Trade Center Towers Based on the Seismic Record of 11 September 2001. Seismological Research Letters 2015;; 86 (5): 1310–1317. doi: https://doi.org/10.1785/0220140161 Floyd2550 (talk) 17:10, 23 February 2021 (UTC)


 * Not done. Seismological Research Letters doesn't appear to be a peer-reviewed journal, the author of the paper appears to be non-notable, and no reliable secondary sources have reported on the paper as being significant.  -Jord gette  [talk]  17:21, 23 February 2021 (UTC)


 * Absolutely agree with Jordgette. This does not appear to be a notable or Reliable source WP:RS. David J Johnson (talk) 17:57, 23 February 2021 (UTC)


 * Marking request as answered, declined.   SITH   (talk)   21:15, 23 February 2021 (UTC)

Seismological Research Letters is a peer-reviewed scientific journal of the Seismological Society of America. The cited research was appropriately peer-reviewed and published in 2015. Since the cited source of this research does have proper scientific credentials, objection to this addition on the Wikipedia topic should primarily I believe be directed at the content, which I believe speaks convincingly for itself. — Preceding unsigned comment added by Floyd2550 (talk • contribs) 18:27, 25 February 2021 (UTC)


 * It doesn't appear to be a peer-reviewed journal. "The Seismological Research Letters (SRL) is a unique journal—the first to serve as a general forum for informal communication among seismologists, as well as between seismologists and those nonspecialists interested in seismology and related disciplines." Even if it were, it fails the other criteria.  -Jord gette  [talk]  22:34, 25 February 2021 (UTC)

Seismological Research Letters is indeed a well-established peer-reviewed journal. Here is the Seismological Society of America description of this specific journal: "Seismological Research Letters(SRL) is a peer-reviewed journal that seeks to publish informative articles for a broad scientific audience, highlighting recent seismic events and contemporary topics (e.g., induced seismicity, large-N deployments, nuclear tests). 'SRL' also features topics relevant to the seismology of central and eastern North America and intraplate tectonics. Periodic “Focus Sections” present a collection of papers on topics of special and timely interest to the community."

The Rollings research was published in 2015 in this (SRL) journal because it specifically employed seismological science, but for that reason it likely did not cross into the fields of interest to structural engineering. In any event, the major structural engineering analyses of the World Trade Center collapses were completed and published years before (primarily by the Northwestern University papers referenced as footnotes 6, 28, and 61), the last of which was published in 2008. The 2005 NIST report (reference 14) specifically looked at the factors leading up to collapses, but intentionally said little about the collapses themselves once commenced. To my knowledge no follow-up structural analyses of the WTC collapses has been published in recent years (where the Rollings findings would be appropriately cited). The Rollings research (even though published more than 5 years ago) provides a unique addition to the corpus of WTC studies: no other published research directly addresses the duration of the collapses. This turns out to be relevant because the structural collapse analyses (by the Northwestern authors, for example) adjusted their mathematical models to a presumption the towers 1 and 2 fell in 9-12s. The Rollings research determined this presumption was mistaken (and, as an aside, examined the source of this mistake as being ironically an early misinterpretation of the nearby seismic record). By establishing the correct collapse duration the Rollings research settles (at least objectively) some of the unfounded speculation (conspiracy theories) related to the plausibility or implausibility of a well-designed building purportedly falling with minimal resistance in a manner somewhat close to free-fall. A purported 9-12 s collapse duration would roughly comport with "minimal resistance." However, according to the Rollings research, towers 1 and 2 provided far more than "minimal resistance" during their collapses (by exhibiting 22.3 and 19.0 s collapse durations, which Rollings also confirmed using two independent analyses described in the published work). The Rollings research is already within the established peer-reviewed public scientific domain. It has been properly vetted. I believe its significance warrants a brief mention in the Wiki topic of concern here. — Preceding unsigned comment added by Floyd2550 (talk • contribs) 18:22, 26 February 2021 (UTC)


 * I would be suspicious of any journal that (1) doesn't disclose a process of blind expert refereeing and (2) charges for submissions, as Seismological Research Letters does. Regardless, that is irrelevant. We don't hand-pick scientific papers that have not been reported on as significant by reliable secondary sources (with the possible exception of papers by notable scientists publishing in a major journal such as JSE above, Nature, or Cell). Citing in this article an unknown scientist publishing an unnoticed paper in a minor journal severely violates WP:UNDUE. Sorry, it's not happening.  -Jord gette  [talk]  18:57, 26 February 2021 (UTC)

Merge from Vincent Dunn
It's unclear Vincent Dunn is notable other than being a consultant on the WTC collapse, and a large part of the bio is his opinions on fire fighting in this type of building, and the WTC investigation. Maybe those opinions should just be in the article? If not, that bio probably needs more material for balance. -- Beland (talk) 05:36, 25 March 2021 (UTC)

Footnote #21 typo
"Cabne" should be "Cable." Visiontele1 (talk) 13:28, 22 April 2021 (UTC)

South Tower Escapee Count Discrepancy
From South Tower Collapse:

"Only 14 people escaped from above the impact zone of the South Tower"

From Stanley Praimnath's wiki page detailing his experiences:

"They [Stanley and another person] were two of only eighteen survivors from at or above the impact zone in the South Tower."

14 vs 18 - which is right?

--138.38.168.250 (talk) 21:49, 8 May 2021 (UTC)
 * If read literally, those two statements don't rule out each other. It could have been 14 survivers from floors above the impact site plus four from the floors hit by the plane giving a total of 18. 80.62.29.143 (talk) 12:00, 11 September 2021 (UTC)

Mention of non-evacuation early on
There doesn't seem to be a mention of the facts that:
 * Many people in the North Tower continued to work as normal after the North Tower impact
 * Most people in the South Tower continued to work as normal after the North Tower impact
 * Many people in the North Tower continued to work as normal even after the impact and collapse of the South Tower

Thoughts? Facts707 (talk) 06:27, 25 June 2021 (UTC)
 * Source? --Hob Gadling (talk) 15:19, 11 September 2021 (UTC)

Error in section "Collapse" paragraph 3
>During each collapse, large portions of the perimeter columns and possibly the cores were left without any lateral support

Large portions of the core were observed standing without lateral support. Hence the word "possibly" should be removed 69.94.46.44 (talk) 09:28, 7 January 2022 (UTC)

New edits to collapse section
I've made a number of changes to the collapse section based on the new paper by Lalkovski and Starossek, which has convinced me that I've been wrong all these years about the column-failure model. It appears I misunderstood the Bazant and Zhou paper. I'm of course happy to hear what you all think of the changes. Cheers,--Thomas B (talk) 10:13, 8 January 2022 (UTC)

Inclusion of photographs of collapse related phenomena
I suggest including some of the many photographs that exist showing bowed walls and exposed cores. 69.94.46.44 (talk) 14:55, 8 January 2022 (UTC)

Recommendations for "collapse initiation"
The current section, while accurate, is quite vague and will lead to misunderstandings regarding

- the causes of the various processes (eg: the lack of damage above and below the impact floors has nothing to do with collapse initiation)

- their nature (eg: creep didnt merely unload the core by shortening the core columns, it also weakened them by slow motion buckling)

- their extent(eg: only one wall was pulled in and weakened)

- their timescale (eg: dramatic weakening and loss of support across the whole cross section occured over seconds as a result of the wall mentioned above suddenly buckling)

I strongly recommend rewriting this section with guidance from NIST NCSTAR 1-6D. The executive summary contains a concise, fairly easy to understand description of the processes mentioned in this section. 27.114.165.196 (talk) 05:35, 9 January 2022 (UTC)
 * Thanks for the suggestion. If you have time to make them a bit more concrete (suggest actual ways of rephrasing the section) and provide page numbers, that would be great. Please keep in mind that the section probably shouldn't be much longer.--Thomas B (talk) 09:08, 9 January 2022 (UTC)