Mendel
Senior Member.
Why? this goes directly to the heart of your "WTC=monolith" understanding!
The obvious conclusion is that your ignorance of the actual WTC structure is central to your beliefs.
Would the WTC Twin Towers have collapsed from fire alone, without plane impact?
- Thread starter econ41
- Start date
The obvious conclusion is that your ignorance of the actual WTC structure is central to your beliefs.
You don't seem to be using "braced tube" in the sense Fu does on p. 32.
Maybe, but you clearly don't have the knowledge I seek.
Mendel
Senior Member.
Could you quote that part?
You did quote, "the distance between the exterior and the core frames is spanned by beams or trusses". Am I wrong in assuming that the floors took on that role for the WTC towers?
See, I thought you had access to the book and we were literally on the same page. Do you see what I mean? I'm learning engineering from an engineering textbook and you're looking for an argument. This isn't a constructive way of doing it.
But here's the quote anyway:
WTC was clearly not a "braced tube" structure. It was a "framed tube":External Quote:
And that's where the whole "shear lag" problem comes in (to the opposite effect you suggested with "leverage"):External Quote:
Source: Fu, Feng. Advanced Modelling Techniques in Structural Design, John Wiley & Sons, Incorporated, 2015, pp. 31-2External Quote:
That is, the framed tubes ideally approximate the structural behavior of my "cartoon monolith", which "no one cares about" here, as @benthamitemetric puts it.
Like I say, I'm going to work on it and learn these things. But I'm not hopeful about learning them here.
Mendel
Senior Member.
Article: 4.3.3.3 Connection Between Exterior Tube and the Central Core
As shown in Fig. 4.15, the perimeter tube and central core was linked by composite trusses floor system. The floors consisted of 10 cm thick light-weight concrete slabs on a steel deck with shear connections for composite action. The slabs were supported with trusses [;] apart from resisting the gravity load, the floor system provides lateral stability to the exterior tube.
There you have it.
Last edited:
Mendel
Senior Member.
Yes. Because,
So Fu contradicts your conclusion, that "framed tubes ideally approximate the structural behavior of my 'cartoon monolith'". You quote Fu: "In designing this type of building, an engineer should limit the level of shear lag": the architect needs to explicitly design the building to not have shear lag, and the floors had that purpose in the WTC.External Quote:
If you remove the floors, you're left with a regular framed tube, which is susceptible to shear lag, and does not act as effectively as a cantilever. All according to Fu.
Gamolon
Active Member
Excerpt from the PDF document by Nikolay Lalkovski and Uwe Starossek I linked above in post #473:
We'll see. Maybe it all adds up to the shells crumpling in a light breeze. I doubt it. I think the floors just (obviously) add a bit of stability to the structure. The design concept, as far as I can tell at this point, is that the hollow tube can stand on its own.
It sounds like you're committed to the idea of a much weak perimeter structure than the truthers. So it's no wonder you can't persuade each other. Fortunately, it's a factual matter. I'm going to try to learn in my way.
benthamitemetric
Senior Member
The design concept was to make as much office space as possible with as little steel as possible. I have never seen, and you have never provided, any statement from any person involved in the design of the towers that says they saw it as a goal, or that it was even ever a fleeting consideration, that the perimeter would be able to stand by itself without the rest of the building. You are making that "design concept" up via the alchemy of motivated reasoning and ignorance.
Gamolon
Active Member
I'm sorry Thomas B, but this seems to be the only consistent factor in relation to your not understand the actual collapse mechanism or how the towers were actually designed to function structurally.
You're constant comparisons of the WTC towers to structures built in some fantasy setting or in some cases, existing structures that do not match their design (but you think they do), seem to be adding to your confusion.
It seems so far, "your way" hasn't gotten you any closer to understanding anything since this occurred back in 2001.
Gamolon
Active Member
Can you provide links to these experts along with their calculations (which you say you need to understand things)?
benthamitemetric
Senior Member
I, for one, would like to see their load path diagrams.
I've been providing them throughout. Search the thread for Fu and Nordenson and Robertson and Ali and Moon...
Plus the textbook example of the 213' mast made from 1/10" steel. Where the math is set out.
To me, at this point, it's enough that you (all) also see this as the crux. If the perimeters are as strong as I think they are (i.e., strong enough to stand alone -- hollow -- against wind and seismic loading) then you, too, I will presume, would find the collapses puzzling. Right?
So my goal in expression my "incredulity" in terms that are debatable has been reached. Now I just need to know if I'm right.
Gamolon
Active Member
Did you see the excerpt in post #487 from the paper by Uwe Starossek that gives an explanation of the collapse regarding the floors being overloaded and sheared from the columns?
Do you disagree with him?
Gamolon
Active Member
Calculations showing that the perimeter and core could stand on their own, independently?
Mendel
Senior Member.
No.
The outer tube was not designed to stand on its own.
I quoted Fu at you, explaining that the floors are needed to accomodate the deficiency of the framed tube design, in the WTC.
Here is another source:
External Quote:
I'm familiar with the sources saying the floors provided stability. That stablity was needed because with them in the buildings weighed about five times as much as they would without them. Removing the floors also removes the load they put on the columns. Without that load, I think, they could easily stand on their own.
Like I said in the next line there's this proof that a 1/10" hollow steel mast with a 4" diameter could stand over 200'.
https://ocw.mit.edu/courses/2-080j-structural-mechanics-fall-2013/resources/mit2_080jf13_lecture10/
benthamitemetric
Senior Member
Holy Dunning Krueger, Batman. How do you delude yourself into thinking this is telling you something useful about the structure of the perimeter walls of the towers, which were not prismatic and which cannot even be analyzed by this methodology because the columns that comprise them were bolted together and thus not uniform along their length (in addition to not being non-prismatic)? You don't even have to understand the subject very deeply to realize you are making a wildly inapt comparison given the assumptions expressly underlying the textbook calculation you cite; that would only require that you read and understand those assumptions, which are written in plain English. We are only left to conclude that you have absolutely no idea what you are talking about and don't care. What else is new?Like I said in the next line there's this proof that a 1/10" hollow steel mast with a 4" diameter could stand over 200'.
https://ocw.mit.edu/courses/2-080j-structural-mechanics-fall-2013/resources/mit2_080jf13_lecture10/
Last edited:
econ41
Senior Member
It's your own strawman. BUT, once again, you follow your SOP and shift the goalposts:
"We", and certainly I, do NOT think that your strawman shell collapsed completely from fire OR that - following your false implication, the WTC perimeter hollow shell "collapsed from fire". We understand how the WTC Perimeter shell did collapse.
A bare assertion that you cannot support. In the face of reasoned hypotheses explaining the actual WTC Twin Towers collapses. And in face of your persistent refusal to understand how the WTC Towers did fall.
That is one small step. Albeit an essential first step. You have a fair distance to travel.
Three points:
1) You first need to decide that you want to understand;
2) Then you need to stop playing evasive games by referencing false analogies and other buildings which offer nothing to help understanding of WTC collapses; AND
3) You need to find help or stop ignoring the expertise available for you here.
Why "tag" me when you have systematically ignored my attempts to help and have constructed an artificial barrier denying the expertise of persons who are not published academics?
Mendel
Senior Member.
1. Against which kinds of forces did the floors provide stability?
2. Where do these forces come from?
3. how does the weight of the interior of a building affect the forces it is subject to?
4. Which forces are not affected by the weight?
5. is it easier to tip an empty box or a full box?
6. Why is this relevant for wind shear?
This is a little amusing because debunkers happily suggest we imagine the WTC columns being crushed like pop cans, but anyway...
The point of the 1/10" steel mast example (think of it as a very tall, very strong, pop can if that helps) is that it must be much, much, and indeed "wildly", weaker than a WTC perimeter column. We can measure the aptness of my comparison very easily by calculating the critical length of the lower section of an isolated perimeter column (i.e., consider a column that is prismatic but using the heaviest column dimensions in the WTC perimeter).
What's your estimate of how that calculation comes out? (What I tried to say earlier is that I can't learn from someone who can't, or won't, at least estimate this height.) I'm not hundred percent sure of my calculation, but I think it's at least 400'.
Now, just ask yourself whether a structural system built out of either the masts or columns, which we now know the critical length for individually, would have a longer or shorter critical length than the individual masts or columns.
The textbook example just gives a (ridiculously) extreme lower bound on how tall the perimeters must have been able to stand on their own. That bound is over 200'. I simply believe the engineers designed the shells to stand 7 times taller than that ... under strong wind and seismic loading.
Last edited:
That's a totally understandable take on it. I guess I would just say, that in a way you don't have to "cover up" a crime you know every investigator will dismiss out of hand as absurd. It's only successfully covered up in the sense that people don't believe it. I mean, you can have a steel skyscraper fall straight down, with its roofline measured at 9.8 m/s^2, and even scientifically-minded skeptics will defend to the death the idea that the only valid interpretation of this event is that it fell because of office fires. It's like a husband can continually show up late, with lipstick on his cheeks, but his infidelity will be "covered up" as long as his wife believes he could not possibly be cheating on her.
I'm tempted to say it's actually your strawman. My current position is that the building you are explaining the collapse of (with ROOSD) is too weak to help me understand what must have really happened on 9/11. My self-standing perimeter is an attempt to "steel man" the building before tearing it down with fire alone. It's not surprising (or instructive) to me that your strawman burns down.
But I'm just trying to be clever now. I really think we've found the crux of our disagreement and have no easy way to settle it between us, i.e., to reach an agreement in this forum. So I'll just wish you the best in your endeavors. I've got my work cut out for me. But it is not my aim to persuade you that I'm right. Or even clever. Cheers.
Neat analogy. I'm very definitely trying to save my marriage to science, i.e., to maintain my trust in the engineering profession and the institutions of higher learning. But I agree her behavior is a bit troubling!
I think you may be misunderstanding a key point. The "box" of the perimeter columns is not "filled" by the floors. It is not just weighed down at the base. The floors are attached to the walls of the box.
The issue is not one of "tipping", i.e. lifting it off the floor on one side. We have to imagine it attached to the floor ("bedrock") with much stronger connections than the structure itself. (Tipping is the last thing that would happen.) The question is whether the leeward side will buckle on compression (or, though less likely, the windward side will rip from the tension).
Last edited:
LilWabbit
Senior Member
Maybe these two questions fit better in "Why Conspiracists Psychoanalyze" thread, but I'll shoot just as well. It's not out of topic here either.
Why do you and @Henkka assume that if an explanation doesn't fit your layman's logic of how a building should collapse, it can't be true and doesn't warrant an exertion of further intellectual energy?
It seems to me the discussion hits an impasse over and over again due to this basic assumption. So many scientific truths, especially in physics, challenge our simple and cursory intuitions, starting with the Copernican revolution.
You both seem like kind and well-meaning individuals. So it's hard for me to believe it's just sheer hubris.
Secondly, where does your deep distrust towards official reports and accounts originate from?
To ask this doesn't imply a naive acceptance of whatever is officially reported either. Just openness to review official reports properly before rendering a judgment and deeming it suspect.
Can you say a little about how you got the impression that we think this way? It's certainly not how I see things, and it doesn't match my sense of Henkka's approach either. Both of us are happy to expend a great deal of energy understanding the science.
The thing that intrigues me about 9/11 is that the same "logic", i.e., the same kind of inquiry, that prevents me from believing in ghosts, UFOs, telekinesis, and "we never landed on the moon", doesn't seem to work as easily on the demolition theory.
Anyway, thanks for the kind words.
Again, where do you get this impression? I have an ordinary, critical attitude about scientific results and official reports, both of which are known to be both fallible and "motivated". Engaging critically with a scientific paper or an engineering report will often uncover errors and contradictions that must be resolved before an understanding is possible.
It's not a "deep distrust". It's just healthy skepticism. It comes from being thoughtful.
LilWabbit
Senior Member
There are quite a few. But the latest is when you mentioned the debunkers expecting you to believe that the columns were crushed like pop cans. Not only is this statement incorrect in that it's not what the 'debunkers' actually claim. But sometimes in physics 'big and strong structures' in layman's logic do indeed behave in a manner that is counter-intuitive to the layman, owing to a complex of factors weakening them either suddenly or over a period of time, or both.
For an explanation to be complex doesn't mean it's over-reaching, suspect and trying to obfuscate a simpler and more sinister truth. Sometimes it's merely a reflection of a more complex reality that doesn't fit into easy and simple hypotheses. And when it doesn't, we must modify those hypotheses. That's what science is all about.
Last edited:
LilWabbit
Senior Member
Thanks for the above explanation. To me it confirms what I 'felt'. You seem to have a more moderate impression of yourself than how your 'skepticism' of the official accounts comes across. Healthy skepticism is also open to the possibility that maybe some government reports are really done honestly and objectively by commissioning experts seeking objective evidence even if that evidence may hurt the government. That a governmental report doesn't hurt the government is not a waterproof sign that it's biased.
In other words, when studying such reports with 'healthy skepticism' we should guard against both anti-bias and pro-bias, and pursue scientific openness to all testable hypotheses. From you and @Henkka I detect anti-bias and hence it explains (for me) why you're highly resistant (politely but quite firmly) to appreciating detailed explanations that are in line with official accounts. In addition to the fact that you seem resistant to agreeing with things that disagree with your layman intuitions on physics.
All this in no way precludes you being, on a conscious level, a truth-seeker and someone who values science.
Well, obviously I would disagree with characterising the issue this way. Nothing that I've said in any of these threads is really original, or something that hasn't been said by various experts in physics and engineering, such as David Chandler or Tony Szamboti. You can go down the list of various experts that have been interviewed by AE911 to see that this is not only "layman's logic". Now, I expect the counter to this to be that you can always find a tiny minority of experts who believe in kooky things in various fields. For example, you can find PhD biologists who don't believe in evolution. But these people are usually doing so for personal religious reasons, and they're compartmentalising their thinking so they can do their research while also believing it was all created by God. This strikes me as fundamentally different than the debates surrounding 9/11, and I struggle to think of another "kooky" belief that has comparable support from experts. For example, if there were a sizeable number of of professional geologists and astronomers making pretty compelling arguments for the flat earth, I would hear out what hey had to say. But such people don't exist, as far as I know.
I think I answered in the psychoanalysis thread that I got interested in this topic by doing a kind of deep dive into the arguments surrounding WTC 7 specifically. The only way to do so honestly is not to start out with a goal of debunking one side, but to hear out both to the extent that you can "steelman" their arguments, as opposed to strawman. Well, I feel like I did that, and as a result have a deep distrust of the official explanations of why that building fell, for various reasons that are off-topic here.
Mendel
Senior Member.
The shortest length across the cross-section is relevant.
This means if you have three separate identical columns that buckle, and you tie them together so that they buckle in parallel, it's clear that they can't support each other, and hence the critical length can't increase.
Think of the 10 legs as columns, and the knees as the places where they buckle. If linked, this arrangement is very stable against being pushed from the side, but if you have one helper each push each yellow person from the front, it doesn't matter whether they're linked or not.
Mendel
Senior Member.
I think you may have failed to actually consider my questions, or the provided diagram (from Fu).
another opportunity lost
Last edited:
Mendel
Senior Member.
If that's true, you're doing it wrong.
Asked what you have actually learned from these discussions, you've never been able to list much.
LilWabbit
Senior Member
Thank you for this honest and illuminating reply.
I think the bolded part is not the only way to do it honestly, and in fact already violates (while being well-meaning) the scientific approach.
It assumes at the get-go equivalence between two hypotheses as scientific despite (1) one being essentially testable and parsimonious and supported by extremely high degree of consensus amongst experts, other sources and even most lay observers, that are normally politically opposed to one another, and (1) the other being far more speculative and propounded by fringe groups while inviting a much broader burden of proof of a whole range of extra observables (unparsimonious). Your unwitting assumption of theoretical equivalence between the two hypotheses gives too much weight to something that is highly unscientific to start with and wouldn't be considered a plausible rival hypothesis as far as scientific hypotheses go. In the process you got lost in the details and credentials of the far more speculative theory (essentially a CT) which, by extension, started to convince you more and more that something fishy must have being going on.
Hence the distrust. And hence also the false impression that the layman reasoning offered by the experts on the CT side is in fact expert reasoning.
Last edited:
I was referring to this way @Mick West uses it:
https://www.metabunk.org/threads/ho...n-for-part-of-wtc7s-collapse.8270/post-204886
I'm using the 1/10" steel mast in the same way. Just "illustrating a general principle".
The point of my post #467 is that the opportunity is past.
I don't think directly pointing out what I take to be a false premise in one of your questions is "failing to consider" it.
Yes, again, the point of post #467 is that I've reached the same conclusion about debunkers on this forum. It's an impasse. We simply don't respect each other's basic understanding of the physics and engineering problem. We set up the problem differently, have widely divergent intuitions, and don't acknowledge each other's authorities. Not much of a way forward from there.
Thanks for your input. I'll join you on the psychoanalysis thread if I want to continue the session.
Similar threads
