AE911 New Collapse Hypothesis

I am of course aware of this part of the explanation. I think it is fascinating. I agree with you that it should be common knowledge; there should be a lot of popular science writing about it.

It amazes me that such large buildings were vulnerable to this kind of failure, and that it was part of the design of the buildings. Not that they were designed to fail like this, but that understanding their failure follows straightforwardly from understanding their design.

It raises a whole bunch of questions for me. But it doesn't sound like you're proposing to get into a discussion of them. I just wanted to say that, yes, I have heard about the 29,000,000 pounds. Thank you.
Well there's your answer right?

In order to prevent the collapse they should have designed floors to resist 29,000,000 pounds times whatever safety factor.
 
No building will / can survive the collapse of the top 12 (or more) stories. Once it drops.. a runaway collapse of all lower floors will ensue. Now tower will support the collapse of 12 floors falling on the uppermost intact floor.

So to survive... a design would have to prevent or arrest a top drop. Limited mechanical damage and fires which were suppressed.

Stronger columns could delay or maybe even prevent the tops from breaking free and dropping. Considerations would be how many columns were destroyed by a plane of some explosion. And how extensive and widespread were the fires.

The twin towers would not have their tops drop if the fire suppression and fire fighting were effective. Heat weakened the steel and led to there being too little axial capacity to support the top.

++++

It's not cost effective to add steel. Stronger slabs that are heavier and still subject to runaway collapse It is more cost effective to have more robust and redundant sprinklers and water to supply them.
 
I'm not sure I have much more to add at this point, but I did some searching of the engineering literature and found something that some of you might find interesting.

The Total Collapse of the Twin Towers: What It Would Have Taken to Prevent It Once Collapse Was Initiated Nikolay Lalkovski, Aff.M.ASCE; and Uwe Starossek, P.E., M.ASCE

Journal of Structural Engineering, Volume 148 Issue 2 - February 2022


External Quote:

Now, in any conventionally designed building, a given floor plate and its connections to the columns are only designed to carry this plate’s own dead and live loads with the corresponding safety factors; the columns supporting this floor plate, on the other hand, are designed for the loads from this and all above-lying floor plates, and can thus take a much greater load than the single floor plate. This obvious fact, combined with the realization that the IUS [intact upper section] can never land onto the ILS [intact lower section] with such precision that the columns of these two sections align perfectly and thus prevent activation of the topmost floor plate of the ILS (let alone the collapsing DIS mass, which will inevitably activate the topmost floor plate of the ILS), is all that is necessary to explain why the ILS in the WTC Twin Towers had no chance once the DIS and IUS were in motion: Any floor plate in the ILS was utterly unable to cope with the mere weight of the above-lying mass, not to mention the dynamic forces due to impact.

This realization makes it clear that the crush-down in the WTC Twin Towers was F-P-F-[floor-plate-failiure] driven, and that the ILS columns, much stronger than the governing floor plates, never had a say in the matter. Any possibly remaining doubt that this was the case is dispelled by the observations from available video footage of the collapses. Despite the dust cloud enshrouding the downward-traveling collapse front, it can be observed that “[a]s the floors collapsed, this left tall free-standing portions of the exterior wall and possibly central core columns” (FEMA 2002, p. 27). This is only possible in a F-P-F-driven crush-down [Fig. 2(b)]. If the crush-down had been C-F-[column-failure] driven [Fig. 2(a)], the ILS columns would have been crushed and would thus not have been left to stick above the downward-traveling collapse front.
I think this pretty much vindicates the view of the collapses that many of you are defending. But it does assume that "the explanation for the total collapse of the World Trade Center (WTC) Twin Towers proposed by Bažant and Zhou (2002) is correct, as currently widely accepted among engineering professionals." I'm going to have to read it a few times before I understand why their strong rejection of C-F in favor of F-P-F isn't a strong rejection of Bazant and Zhou. But I imagine it has something to do with C-F being a "limit case", as many of you emphasize here.

Anyway, it's published in a very reputable journal so I'm inclined to accept a statement like that about what is "widely accepted" in the engineering community.

And it includes some ideas about the how the WTC design could be modified to arrest a collapse once it has begun. Interesting stuff. Enjoy.
 
That would probably have been the outcome if there had been sufficient sprinklers and other fire fighting systems able to control the fires.

The "two thirds/one third staying erect" options were not plausible for the Twin Towers. Once progression started it was unstoppable.

The twin towers would not have their tops drop if the fire suppression and fire fighting were effective. Heat weakened the steel and led to there being too little axial capacity to support the top.

++++

It's not cost effective to add steel. Stronger slabs that are heavier and still subject to runaway collapse It is more cost effective to have more robust and redundant sprinklers and water to supply them.
We agree that global reality @Jeffrey Orling. No fire >> no collapse.
 
I'm not sure I have much more to add at this point, but I did some searching of the engineering literature and found something that some of you might find interesting.

The Total Collapse of the Twin Towers: What It Would Have Taken to Prevent It Once Collapse Was Initiated Nikolay Lalkovski, Aff.M.ASCE; and Uwe Starossek, P.E., M.ASCE

Journal of Structural Engineering, Volume 148 Issue 2 - February 2022

On the first scan through reading the paper is an interesting mixture of analyses that are correct and follow on reasoning that is far from correct.

Overall they, like Schnieder, come late to the debate. And fall for the same class of errors and confusions which misunderstood Bazant in the early era pre about 2009-10.

E&OE - these are what appear to be the main points - subject to more detailed consideration which should not be discussed in this thread which is already well off-topic.
1) They accept what we call "ROOSD" and they describe as floor-plate-failure-driven (F-P-F-driven), AND reject column-failure-driven (C-F-driven) >> CORRECT
2) They fail to comprehend Bazant & Verdures "Crush Down/CRush Up" hypothesis. Worse. They litter the paper with usages of both Crush Down and Crush Up terminology to describe a different collapse sequence to what B&V proposed. I will predict lots of confusion if the paper is discussed with the modest level of part understanding we typically see in these discussions,
3) They propose a "strong floor plate" >> a heavily reinforced full storey height strong barrier to halt any progression of collapse. EXCEPT -as far as I can see on first reading - they don't say where it is located in relation to where the failure initiates which, of course, would be critical to any success.

There are many more details - as I say I've only read the paper in a quick scan.
I think this pretty much vindicates the view of the collapses that many of you are defending.
Some bits are correct. Much of it is not. Proof later IF there is any serious interest.
But it does assume that "the explanation for the total collapse of the World Trade Center (WTC) Twin Towers proposed by Bažant and Zhou (2002) is correct, as currently widely accepted among engineering professionals."
The B&Z explanation as accepted by many professionals is wrong for reasons explained many times. B&Z's "Limit Case" reasoning is correct in logic. Their maths quantification has been subjected to claims that it overestimates >> if so their conclusion is wrong.
I'm going to have to read it a few times before I understand why their strong rejection of C-F in favor of F-P-F isn't a strong rejection of Bazant and Zhou. But I imagine it has something to do with C-F being a "limit case", as many of you emphasize here.
Yes. The challenge STARTS with understanding "limit case"
Anyway, it's published in a very reputable journal so I'm inclined to accept a statement like that about what is "widely accepted" in the engineering community.
More proof that "peer reviewed" is of little value in deciding if something is correct
And it includes some ideas about the how the WTC design could be modified to arrest a collapse once it has begun. Interesting stuff. Enjoy.
My initial reservations already identified.
 
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@Thomas B - a brief comment on the first "main point" I identified
E&OE - these are what appear to be the main points - subject to more detailed consideration which should not be discussed in this thread which is already well off-topic.
1) They accept what we call "ROOSD" and they describe as floor-plate-failure-driven (F-P-F-driven), AND reject column-failure-driven (C-F-driven) >> CORRECT
This is the relevant part of their rationale:
External Quote:

The reason is that there are two possible and mutually exclusive ways for this to occur; these are shown in Fig. 2. In what we here call a column-failure-driven (C-F-driven) downward collapse progression, the floor plates of the successively collapsing stories are stacked together due to the overloading and subsequent successive buckling of the columns in these stories [Fig. 2(a)]. This type of collapse progression is assumed by Bažant and Verdure (2007) (although those authors do not use the term C-F-driven) in developing their one-dimensional (1D) collapse model, an evolution of a simple model presented by Bažant and Zhou (2002). Bažant and Verdure (2007) employed the concept of the “mean crushing force”—a concept to which we will shortly return—to account for the force from the buckling columns acting at the collapse front and thereby slowing this collapse front down.

The second type of downward collapse progression, which we call floor-plate-failure-driven (F-P-F-driven), is shown in Fig. 2(b). Here, the floor plates of the successively collapsing stories are stacked together due to the shearing off of these floor plates at their connections to the columns; the columns themselves, resembling trees whose trunks are being disbranched, do not participate, a consequence being that the properties of these columns remain irrelevant with regard to the initiation and unfolding of the crush-down. The schematic representation in Fig. 2(b) focuses only on the F-P-F-driven crush-down, the topic at hand; in general, how ever, and for the same reasons explaining the F-P-F-driven crush-down, the IUS will be collapsing simultaneously in what may be called F-P-F-driven crush-up.

Now, in any conventionally designed building, a given floor plate and its connections to the columns are only designed to carry this plate’s own dead and live loads with the corresponding safety factors; the columns supporting this floor plate, on the other hand, are designed for the loads from this and all above-lying floor plates, and can thus take a much greater load than the single floor plate. This obvious fact, combined with the realization that the IUS can never land onto the ILS with such precision that the columns of these two sections align perfectly and thus prevent activation of the topmost floor plate of the ILS (let alone the collapsing DIS mass, which will inevitably activate the topmost floor plate of the ILS), is all that is necessary to explain why the ILS in the WTC Twin Towers had no chance once the DIS and IUS were in motion: Any floor plate in the ILS was utterly unable to cope with the mere weight of the above-lying mass, not to mention the dynamic forces due to impact.

This realization makes it clear that the crush-down in the WTC Twin Towers was F-P-F-driven, and that the ILS columns, much stronger than the governing floor plates, never had a say in the matter. Any possibly remaining doubt that this was the case is dispelled by the observations from available video footage of the collapses. Despite the dust cloud enshrouding the downward-traveling collapse front, it can be observed that “[a]s the floors collapsed, this left tall free-standing portions of the exterior wall and possibly central core columns” (FEMA 2002, p. 27). This is only possible in a F-P-F-driven crush-down [Fig. 2(b)]. If the crush-down had been C-F-driven [Fig. 2(a)], the ILS columns would have been crushed and would thus not have been left to stick above the downward traveling collapse front.

This raises the following question: if the ILS in the WTC Twin Towers had been topped by a floor plate strong enough to fully
mobilize the underlying columns,
Put simply whilst they use their own terminology they agree that progression was "F-P-F-driven" which is what I describe as ROOSD. i.e. the original Major_Tom and femr2 definition encompassing the "OOS" floor disconnection and subsequent perimeter peeling off plus the analogous extension into the core. Net result -- the falling debris landed on floor areas and missed -- "bypassed" -- the columns.
 
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@Thomas B - a brief comment on the first "main point" I identified

This is the relevant part of their rationale:
External Quote:

The reason is that there are two possible and mutually exclusive ways for this to occur; these are shown in Fig. 2. In what we here call a column-failure-driven (C-F-driven) downward collapse progression, the floor plates of the successively collapsing stories are stacked together due to the overloading and subsequent successive buckling of the columns in these stories [Fig. 2(a)]. This type of collapse progression is assumed by Bažant and Verdure (2007) (although those authors do not use the term C-F-driven) in developing their one-dimensional (1D) collapse model, an evolution of a simple model presented by Bažant and Zhou (2002). Bažant and Verdure (2007) employed the concept of the “mean crushing force”—a concept to which we will shortly return—to account for the force from the buckling columns acting at the collapse front and thereby slowing this collapse front down.

The second type of downward collapse progression, which we call floor-plate-failure-driven (F-P-F-driven), is shown in Fig. 2(b). Here, the floor plates of the successively collapsing stories are stacked together due to the shearing off of these floor plates at their connections to the columns; the columns themselves, resembling trees whose trunks are being disbranched, do not participate, a consequence being that the properties of these columns remain irrelevant with regard to the initiation and unfolding of the crush-down. The schematic representation in Fig. 2(b) focuses only on the F-P-F-driven crush-down, the topic at hand; in general, how ever, and for the same reasons explaining the F-P-F-driven crush-down, the IUS will be collapsing simultaneously in what may be called F-P-F-driven crush-up.

Now, in any conventionally designed building, a given floor plate and its connections to the columns are only designed to carry this plate’s own dead and live loads with the corresponding safety factors; the columns supporting this floor plate, on the other hand, are designed for the loads from this and all above-lying floor plates, and can thus take a much greater load than the single floor plate. This obvious fact, combined with the realization that the IUS can never land onto the ILS with such precision that the columns of these two sections align perfectly and thus prevent activation of the topmost floor plate of the ILS (let alone the collapsing DIS mass, which will inevitably activate the topmost floor plate of the ILS), is all that is necessary to explain why the ILS in the WTC Twin Towers had no chance once the DIS and IUS were in motion: Any floor plate in the ILS was utterly unable to cope with the mere weight of the above-lying mass, not to mention the dynamic forces due to impact.

This realization makes it clear that the crush-down in the WTC Twin Towers was F-P-F-driven, and that the ILS columns, much stronger than the governing floor plates, never had a say in the matter. Any possibly remaining doubt that this was the case is dispelled by the observations from available video footage of the collapses. Despite the dust cloud enshrouding the downward-traveling collapse front, it can be observed that “[a]s the floors collapsed, this left tall free-standing portions of the exterior wall and possibly central core columns” (FEMA 2002, p. 27). This is only possible in a F-P-F-driven crush-down [Fig. 2(b)]. If the crush-down had been C-F-driven [Fig. 2(a)], the ILS columns would have been crushed and would thus not have been left to stick above the downward traveling collapse front.

This raises the following question: if the ILS in the WTC Twin Towers had been topped by a floor plate strong enough to fully
mobilize the underlying columns,
Put simply whilst they use their own terminology they agree that progression was "F-P-F-driven" which is what I describe as ROOSD. i.e. the original Major_Tom and femr2 definition encompassing the "OOS" floor disconnection and subsequent perimeter peeling off plus the analogous extension into the core. Net result -- the falling debris landed on floor areas and missed -- "bypassed" -- the columns.
The main thing missing from the ROOSD acronym is that the runaway process is not limited to slabs outside the core. They were larger areas and more vulnerable. But runaway slab failure/collapse/destruction can and will occur within any structural "bay".
 
The main thing missing from the ROOSD acronym is that the runaway process is not limited to slabs outside the core. They were larger areas and more vulnerable. But runaway slab failure/collapse/destruction can and will occur within any structural "bay".
Correct. Hence the reason for my qualified comment "...perimeter peeling off plus the analogous extension into the core."

"ROOSD" as first presented by me without the acronym and later by Major_Tom with the acronym had ROOSD referring primarily to the "debris misses columns" aspect. M_T sometimes included "perimeter peel-off" as a subset of ROOSD. I maintained the distinction and subsequently incorporated the core because "core strip down" is analogous to "ROOSD". I then referred to the process either as "The Three Mechanisms of progression" OR the "Three Mechanisms of ROOSD" or similar.

So:
1) ROOSD shears off the floor joists in the "OOS"
2) Perimeter columns fall away - unbuckled WHILST
3) "Core strip down" has sheared the floor beams off the columns in the core area.
 
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I would still like to know what your definition of the towers surviving 9/11 is. What state would the towers have to have been in for you to say they survived?
The Lalkovski and Starossek paper that I posted above is a good example of the sort of analysis I'm looking for. It vindicates (if I may) my call for both a one-dimensional representation of ROOSD (though they supplement this with a 2D analysis) and a mathematical formulation of the problem. If I had found their paper earlier I would have approached this thread very differently. That may have spared us all some frustration. I apologise for that.

They talk explicitly about the meaning of "survival" here. I like their way of describing it. The damaged section will be "lost" in any case. Otherwise the problem of "suviving" doesn't really arise. That is, we can imagine the fires not weakening the columns on the impact floors sufficiently so that no collapse even begins. But, if the collapse does begin (if the top section begins to move downwards), we also have to "write it (i.e., the top section) off". The main question is whether the damage to the lower section could have been prevented.

I wasn't quite this precise in my thinking about "survival" until now. I'm glad I found this paper. Once again, sorry to have been a pain.

External Quote:
As shown in Fig. 1, three sections are distinguished in the considered building at collapse initiation. The following can be said regarding the survival chances of these sections. The damaged intermediate section (DIS) will inevitably be lost. This is a direct consequence of what we assume with regard to this section—namely, that all its columns lose their entire axial capacity thus initiating collapse. The intact upper section (IUS), which, like the DIS, finds itself in free fall, must be written off as well for the simple reason that we have no control over this section’s motion. In particular, we cannot prevent, but must rather expect, a rotation of the IUS during its free fall—a behavior that would result from a nonsimultaneous failure of the DIS columns across the building cross section and clearly observed in the case of the WTC Twin Towers. The intact lower section (ILS) is the only section whose saving we can begin to realistically consider.
https://ascelibrary.org/doi/10.1061/(ASCE)ST.1943-541X.0003244
 
The intact lower section (ILS) is the only section whose saving we can begin to realistically consider.
Because we can design it for a building crashing into it, and not just an airliner?

The way to prevent total collapse would have been to prevent the top from tilting as a block; but it did that by design to counter wind loads. A structure that allows for partial collapse can't be one-dimensional.
 
The main question is whether the damage to the lower section could have been prevented.
"Could have been prevented"?

This would have to have been thought out and designed into the tower's structure by the engineers prior to construction.

How in the world would you expect any engineer to do that? Let's use the towers as an example. You're asking an engineering to calculate loads for every possible collapse scenario where an upper block containing X amount of floors/levels descends upon the remaining lower block and then design a way to resist that load?

Think about that for a minute.

Would the load of the falling block be different if the failure started at floor 20 versus floor 98?

The next question is WHY are you wanting to know if damage to the lower section could have been prevented?
 
It's not cost effective to add steel. Stronger slabs that are heavier and still subject to runaway collapse It is more cost effective to have more robust and redundant sprinklers and water to supply them.

It's an analogue to only one particular property, but perhaps it might be useful if @Thomas B were to try using *only* A4 or equivalent sheets of paper to build a bridge between a 1.5m gap between two chairs. No tape, no glue, no chewing gum, *just* paper. I forget the actual gap where the problem manifests, if you find it too easy to do 1.5m, extend it by 30cm, and so on. Eventually there's a distance where the sagging looks like it's too much, and that the bridge needs "reinforcing" with another layer of paper. However, the additional layer does what your "add steel" does - it simply ramps up the jeopardy upon failure, rather than reducing the likelyhood of failure. (And the temptation is to reinforce the wrong part - I'll let people have a play and work that bit out themselves!)

(If you're ever given this challenge and you are permitted some small amount of tape, you will win if you simply build a "rope bridge" out of strips of paper with the two ends secured. Technically, if you can wrap the ends of your paper "rope" around something at the endpoints that will also work - winding works exponentially, you may only need to construct a few extra turns worth, depending on what you can wrap around.)
 
Would the load of the falling block be different if the failure started at floor 20 versus floor 98?
This is the issue I identified in my preliminary comments:
3) They propose a "strong floor plate" >> a heavily reinforced full storey height strong barrier to halt any progression of collapse. EXCEPT -as far as I can see on first reading - they don't say where it is located in relation to where the failure initiates which, of course, would be critical to any success.
... and, of course, the dynamic impact increases dramatically as both weight of debris and descent velocity increase. Greater distance to fall before impacting the "strong floor plate" would result in a much larger impulse force.
 
"Could have been prevented"?

This would have to have been thought out and designed into the tower's structure by the engineers prior to construction.

How in the world would you expect any engineer to do that? Let's use the towers as an example. You're asking an engineering to calculate loads for every possible collapse scenario where an upper block containing X amount of floors/levels descends upon the remaining lower block and then design a way to resist that load?

Think about that for a minute.

Would the load of the falling block be different if the failure started at floor 20 versus floor 98?

The next question is WHY are you wanting to know if damage to the lower section could have been prevented?
The issue of a "falling" top block is very much related to the strength of the columns at the level of the break. In the cases of the twin towers the columns were "thin enough" to be effected by the heat from fires. Lower floors' steel would take longer burning fires to weaken them. And that would mean more fuel.

Also higher up the columns were weaker and more vulnerable to the plane damage.

I suspect that to have the tops break free and collapse down it would have to be high up in the tower. Having said this if enough floors at any level were to break apart and begin a runaway collapse... a total collapse might occur from an initiation on a lower floor. In that case the facade columns without bracing might buckle and take the rest of the building with it... in a column free outside the core design. MAYBE
 
The next question is WHY are you wanting to know if damage to the lower section could have been prevented?
I'm sort of puzzled by your response. But I'll try to answer the question plainly.

Understanding counterfactuals is one way of understanding structures and processes. We know what did happen under the actual conditions, but in order to understand how it happened we have to understand what might have happened under slightly different conditions. We have to use our imaginations to get our minds around it.

We don't just have to understand the failure, we have to understand how a building like the WTC works. And a building "works" by absorbing and distributing loads. 9/11 (and, to give credit where it's due, the 9/11 truthers) got people like me really interested in that. I was sure there were good and interesting answers to questions like, Why did they collapse so soon, so quickly, and so completely? (These were all issues that truthers presented as smoking guns, but that I was sure would have straightforward and interesting scientific answers.) It took me a bit longer than I expected to find the answers. And I'm still working out some of the details.
 
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I'm sort of puzzled by your response. But I'll try to answer the question plainly.

Understanding counterfactuals is one way of understanding structures and processes. We know what did happen under the actual conditions, but in order to understand how it happened we have to understand what might have happened under slightly different conditions. We have to use our imaginations to get our minds around it.

We don't just have to undestand the failure, we have to understand how a building like the WTC works. And a building "works" by absorbing and distributing loads. 9/11 (and, to give credit where it's due, the 9/11 truthers) got people like me really interested in that. I was sure there were good and interesting answers to questions like, Why did they collapse so soon, so quickly, and so completely? (These were all issues that truthers presented as smoking guns, but that I was sure would have straightforward and interesting scientific answers.) It took a me bit longer than I expected to find them. And I'm still working out some of the details.
For the most part truthers don't understand the structural system of the twin towers... tube in tube designs... the implication of column free outside the core floors... and they don't care. They have a mickey mouse view that something smaller cannot destroy something larger and so the collapses were not possible. I guess they never understood the principal" the straw that broke the camel's back." This is not a simplification of what happened but it is a principle that a small failure in a large complex system can undo the entire system. Space Shuttle disaster is another example of a "runaway" failures in a complex system.
 
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For the most part truthers don't understand the structural system of the twin towers... tube in tube designs... the implication of column free outside the core floors... and they don't care. They have a mickey mouse view that something smaller cannot destroy something larger and so the collapses were not possible. I guess they never understood the principal" the straw that broke the camel's back."
It's not only truthers. Many debunkers have only a moderate level of understanding... it's easier for debunkers because they are on the "winning side" of the argument. Pity the truther who tries to argue for something that did not happen. CD was never needed.
This is not a simplification of what happened but it is a principle that a small failure in a large complex system can undo the entire system.
A small trigger can start a progression of failures. Toppling an array of dominoes is one often seen example. The "initiation" of Twin Towers collapses was a cascading sequence. Driven by load re-distribution. There were two plausible "triggers". Two possible "straws that broke the camel's back". Either inward bowing of perimeter columns (the indirect consequence of heat) OR direct heat weakening of core columns. Either could have been the trigger. It only needs a small force to trigger one first failure.
Space Shuttle disaster is another example of a "runaway" failures in a complex system.
Also a "cascading failure". The Electricity Grid failure of the "Northeast blackout of 2003" is another example of a cascading failure >> triggered by a "last straw" event >> spread by load re-distribution. In that case in the electrical power domain rather than structural collapse.

https://www.google.com/search?channel=fs&client=ubuntu&q=electricity+grid+failure+usa+canada
 
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Which is only part of the solution. If you strengthen the floors the columns become the "weak link".
Do you know if anyone has ever put together a procedural photographic "timeline" of the WTC collapses? Where they took photos showing "progression" at certain times during the collapse and then analyzed what was actually seen from a structural standpoint and maybe what was possibly going on?

Like the photo below for example. At what time during the collapse was this and what does it tell us? Some percentage of the core was still standing? The hat truss had come apart and fell to the ground? No floors were attached to the visible core?

WTCSpire.jpg


Then you progress to this photo below. What may have occurred between the first photo and the one below.
WTCSpire2.jpg
 
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Do you know if anyone has ever put together a procedural photographic "timeline" of the WTC collapses? Where they took photos showing "progression" at certain times during the collapse and then analyzed what was actually seen from a structural standpoint and maybe what was possibly going on?

I'm not aware of any such timeline of the actual collapse mechanism in photographic form. In fact, very few debunkers pay much attention to the timeline aspects whether in photographic form or written description. Yes, there has been a range of varying efforts to depict alternative false scenarios. Or the type of "confused conflation " which is causing @Thomas B so much difficulty in this thread as it did in previous threads. Trying to "mix and match" aspects of a false scenario onto the real event will always be problematic. Remember it was themain error with Tony Szamboti's "Missing Jolt" And David Chandler's equivalent process AND most of the video explanations from Jonathon Cole. (And a whole club of early debunkers pre about 2007-9 ;) )

Even among those debunkers who recognise the distinction between the two main stages of Twin Towers collapse viz "initiation" and "progression", many still get confused and overlap or conflate the two.

Personally, I have always distinguished three stages and in recent (2 or 3) years I have been recommending a four-stage understanding. In sequence those are:
1) "Initiation" - what happened from aircraft impact up to Top Block descending bodily. (And NOT "falling" >> that was the error most made wrongy following Bazant & Zhou.)
2) "Transition" >> complex and chaotic but we only need to comprehend two facts - viz it made sure that the falling column ends missed and it explains how ROOSD was started.
3a) "Early progression" >> The Top Block breaking up. Bazant & Verdure were wrong with CD/CU.
3b) "Established progression" > the pure ROOSD progression after the chaos of Top Block break up.
(The split of "progression" into two substages is the change I've made over recent years. It makes clearer the stage where the Top Block broke up. And puts me in direct opposition to Bazant and most debunkers who subordinate themselves to Bazant and/or NIST.)

Now if we get those clear - we have a valid frame for an explanation. The big problem is that the boundaries are hard to define in traditional "left-brained" style...doesn't matter but it is a barrier for those whose thinking cannot separate trees from forests.
Where they took photos showing "progression" at certain times during the collapse and then analyzed what was actually seen from a structural standpoint and maybe what was possibly going on?
I doubt that graphics help to separate the four legitimate stages OR the sub-stages of "progression". They may help to explain false models such as the Schneider paper which was the OP Topic of this thread AND the professional paper recently linked by @Thomas B BUT both those papers are not of the real event. And I don't see any benefit in using photos to support a false explanation.
Like the photo below for example. At what time during the collapse was this and what does it tell us?
Hard to say - I'm not sure what that picture shows BUT we can answer the questions which follow:
Some percentage of the core was still standing?
"..percentage...standing" I suggest will never help understanding - 36.7% is meaningless BUT we can assert how the core was taken apart - which parts in what sequence. During the "progression stages" esp "3b)" the falling debris stripped off the OOS floor joists and at the same time debris falling in the core stripped of the floor beams of the core -- setting the stage for leaving the "spires" standing as shown by the next photo. "Floors stripped first" THEN "Columns mostly followed" and "Some columns remained standing" are the factors of significance. Representing them as percentages does nothing to help.
The hat truss had come apart and fell to the ground?
Most of the Top Block broke up during the stage "3a) Early progression". Exactly how long that stage took cannot be defined but it was finite. The Hat Truss almost certainly mostly broke up but I have vague recollections over 10 years ago seeing photos suggesting that some portions of Hat Truss made it all the way down. So we may never know exactly where and what bits came apart. And we have no need to know - that is just one of the irrelevant side trails which get introduced in discussions of alternate models of the type that Thomas and others choose to pursue. Hence my preference to understand what actually happened BEFORE worrying about what didn't happen.
No floors were attached to the visible core?
At what "sub-stage"? They were all attached when progression started. They were all detached when it ended with global collapse. And we will never know where each and every single beam was disconnected. Nor do we need to.
Then you progress to this photo below. What may have occurred between the first photo and the one.
It is the last few seconds - progression essentially over. All floors sheared off in both the "Open Office Space" tube and in the core. Perimeter and most core columns have peeled off or toppled. And some core column "spires" remained standing for a few seconds. Which is substantial proof of my assertion that the core failure was analogous to ROOSD - falling debris sheared off the floor beams in the core.

And, back to the theme. "Could a photo timeline help the explanation?" I doubt it. BUT getting those four stages clear is essential to any clear and comprehensive understanding.

Please excuse the lengthy response - it is still a bit of a sketchy outline. If anything needs more explanation just ask.

And the brief bottom line answer to your question: 'No. And I don't think we need a photo timeline of EITHER the overall collapse OR the details of the "progression stage"'
 
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ROOSD was hidden behind a largely intact facade which peeled away and feel as the ROOSD mass "passed" leaving unbraced upper sections of the facade. Evidence of ROOSD is seen in the ejecta forced through and breaking windows just ahead of the ROOSD mass.

The tops' broken up mass undoubtedly did crush the top of the bottom block... that was what became the ROOSD mass and it was over the entire footprint... not simply outside the core floor areas.
 
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ROOSD was hidden behind a largely intact facade which peeled away and feel as the ROOSD mass "passed" leaving unbraced upper sections of the facade. Evidence of ROOSD is seen in the ejecta forced through and breaking windows just ahead of the ROOSD mass.

The tops' broken up mass undoubtedly did crush the top of the bottom block... that was what became the ROOSD mass and it was over the entire footprint... not simply outside the floor areas.
There was never any real doubt about the technical accuracy of ROOSD. The contention arose mostly because both the acronym and the concept were put into the mainstream debate by a member who was seen as a "truther". THEREFORE by bigotted definition, he MUST be wrong. Except he wasn't and a lot of debunkers couldn't accept that fact. There followed several years of mental gymnastics and re-writing of history. Despite the fact that the whole record was documented and online in full view for any honest person to see. It still is.
 
@Jeffrey Orling. There many amusing aspects about that introduction of "ROOSD". When I first became involved in the 9/11 online debate it was the consequence of a personal and professional need to explain why the Twin Towers collapsed to a non-engineer colleague. That was in mid-2007. I had seen the Twin Towers collapses (collapse actually - it was WTC1) on the day as breaking news. Once the civilian engineer side of my brain realised it was real and not "special effects" my military engineer brain simply recorded the techniques as an innovative method of demolishing a tall building >> hit it with a fast aircraft. I forgot about it until 2007. Started trying to explain the collapse and, as a real time operations biased engineer, simply looked at what really happened. Posted that graphic you have seen many times:
003c350.jpg


I never realised that is was contentious and not the "accepted wisdom" of on-line debate. Nor the core of confusion because most people misunderstood Bazant & Zhou. So when a year or so later Major_Tom put forward "ROOSD" on that other forum he walked straight into the anti-truther bigotry. Quite ironic because, together with femr2, M_T has probably rebutted more truther false claims than most debunkers. Ironic isn't it? So I spent 3-4-5 years defending M_T on the points he got right. Copped a bit of flack for daring to support a truther when I was supposed to know that truthers are always wrong. So I was not supporting the false "Party Line". Good job I'm neither US citizen nor right-wing politics - or I would be expected to support DT. ;)
 
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@Jeffrey Orling. There many amusing aspects about that introduction of "ROOSD". When I first became involved in the 9/11 online debate it was the consequence of a personal and professional need to explain why the Twin Towers collapsed to a non-engineer colleague. That was in mid-2007. I had seen the Twin Towers collapses (collapse actually - it was WTC1) on the day as breaking news. Once the civilian engineer side of my brain realised it was real and not "special effects" my military engineer brain simply recorded the techniques as an innovative method of demolishing a tall building >> hit it with a fast aircraft. I forgot about it until 2007. Started trying to explain the collapse and, as a real time operations biased engineer, simply looked at what really happened. Posted that graphic you have seen many times:
View attachment 48751

I never realised that is was contentious and not the "accepted wisdom" of on-line debate. Nor the core of confusion because most people misunderstood Bazant & Zhou. So when a year or so later Major_Tom put forward "ROOSD" on that other forum he walked straight into the anti-truther bigotry. Quite ironic because, together with femr2, M_T has probably rebutted more truther false claims than most debunkers. Ironic isn't it? So I spent 3-4-5 years defending M_T on the points he got right. Copped a bit of flack for daring to support a truther when I was supposed to know that truthers are always wrong. So I was not supporting the false "Party Line". Good job I'm neither US citizen nor right-wing politics - or I would be expected to support DT. ;)
This is going back more than a decade. Up until 2009 I was not sure about how the towers came down. I recall the pancake theory which was sketchy, not complete and seemed implausible. What would cause hundreds of slab connections to the core to fail at the same time? NIST punted and called the post "initiation" inevitable global collapse. Oh my! how descriptive. I looked and decided there was something akin to a vertical avalanche. Top block seemed to become disengaged from the structure (it also was internally breaking apart) and the material simply collapsed onto the top of the bottom setting off the avalanche. In my mind it was not a sequence of plate (slab) failures. It was more a sequence of chaotic plate destruction progressing top to bottom... and likely somewhat random in the location and timing of the interactions. We couldn't see inside but there was no reason to expect a entire footprint wide mass descending. So my conception was a vertical avalanche and then I found the discussion on 911FF which seemed to be driven by observations/movements of the buildings... and Tom had introduced the term ROOSD... which worked for me.
As I recall no one had tackled how things got going... the initiation. How was the ROOSD mass formed? NIST provided the sagging truss buckling the facade approach. This was unsatisfying, not because it was wasn't sound engineering... but it simply made no sense that there was fire over the entire floor plate heating all the trusses which were sagging together. Were this true there should have been visual evidence of the entire facade at one level buckling. NIST pointed to one location on the South side east end of 1WTC as their evidence. I then decided the collapse must have had a core driven explanation. I still think the collapse initiated in the core... and that created multiple "ROOSD-like" destructive masses which rained down on the lower block. I suspect the facade was not the recipient of more more loads (redistributed)... but the failure was more from a lateral displacement and disruption of load paths leading to buckling of core and displacement of facade columns. But once the destructive mass was freed from the structure it destroyed the floor plates which were the column bracing AND of course each plate it feel upon in a rapid unstoppable cascade of floor slab failures racing from top to bottom. My thinking had the main failure driver in the core more beam expansion and lateral displacement rather than loss of axial capacity from heat. But as Econ has shown load redistribution would drive column failures... and probably core collapse...with the core side of the OOS slabs losing supported and they too collapsing... and going runaway. So for me it was less an overloading of the truss connections to failure and more an overloading of the plates themselves... but it was both. The plates would have to maintain their integrity in order to cause their connections to the structure to failure and this would actually look like "falling plates". Hard for me to know which failed first... connections of slabs themselves. However I suspect the latter.
Once ROOSD was in progress, I suspect the "front" was not uniform over the OOS flooring which would be a tell that the plates were failing before the connections of the plates to the structure. Again it seems unlikely that the failure was uniform over the entire foot print. But the time differential was very compressed and probably impossible to detect. I suspect that all the truss seats from top to bottom would show failure from excessive vertical force. But that does not imply the slab failed as a unit.
 
This is going back more than a decade. Up until 2009 I was not sure about how the towers came down. I recall the pancake theory which was sketchy, not complete and seemed implausible.
"Up until 2009" the mainstream debate was mostly down a false trail - ignoring "what really happened" and focussing on Bazant & zhou style "1D approximations". Which MUST be wrong for an OOS "tube in tube" design. 1D approx is the diametric opposite of "tube in tube" with wide-open office spaces and no grid array of columns.

Then please note the advice I gave to @Gamolon - be very clear as to the four distinct stages of collapse. A couple of your comments are unclear because you conflate or overlap the stages.
What would cause hundreds of slab connections to the core to fail at the same time? NIST punted and called the post "initiation" inevitable global collapse. Oh my! how descriptive. I looked and decided there was something akin to a vertical avalanche. Top block seemed to become disengaged from the structure (it also was internally breaking apart) and the material simply collapsed onto the top of the bottom setting off the avalanche. In my mind it was not a sequence of plate (slab) failures. It was more a sequence of chaotic plate destruction progressing top to bottom... and likely somewhat random in the location and timing of the interactions. We couldn't see inside but there was no reason to expect a entire footprint wide mass descending. So my conception was a vertical avalanche and then I found the discussion on 911FF which seemed to be driven by observations/movements of the buildings... and Tom had introduced the term ROOSD... which worked for me.
As I recall no one had tackled how things got going... the initiation. How was the ROOSD mass formed?
There is little if any current interest in correct understanding of the actual physics of collapse. Yes "no one HAD tackled" EITHER "initiation" or "starting ROOSD. Past tense - like 10 years back. I've been posting explanations of "initiation" since at least as far back as 2012 and the explanation of how "ROOSD" got started for at least five years. This is what started "ROOSD" - just look where the yellow arrows of perimeter intersect the blue lines of floor slabs. It was that simple.
ArrowedROOSD.jpg

I cannot recall even a single agreement or counterclaim. Recall "leading horse to water". The explanation is out there. No-one interested. Debunkers have lost interest in the physics - most are content to keep recycling mediocre rebuttals which are just good enough to "beat the truther claim"


NIST provided the sagging truss buckling the facade approach. ....... I still think the collapse initiated in the core...
Both are plausible.
and that created multiple "ROOSD-like" destructive masses which rained down on the lower block. I suspect the facade was not the recipient of more more loads (redistributed)... but the failure was more from a lateral displacement and disruption of load paths leading to buckling of core and displacement of facade columns.
Take care - you are confusing the stages. (a) What started ROOSD >> transition stage. (b) load redistribution >> initiation stage. (c) initiation but the lateral effects were causal details. The key outcome was loss of vertical load-carrying capacity - observable fact independent of what contributed to it.
Once ROOSD was in progress, I suspect the "front" was not uniform over the OOS flooring which would be a tell that the plates were failing before the connections of the plates to the structure. Again it seems unlikely that the failure was uniform over the entire foot print. But the time differential was very compressed and probably impossible to detect. I suspect that all the truss seats from top to bottom would show failure from excessive vertical force. But that does not imply the slab failed as a unit.
True enough - pure "pancake" concurrent failure of all connections was not likely BUT the speed was so fast that for practical purposes it was co-incident. The difference between "simultaneous" and "nearly simultaneous" doesn't matter in the case of office floors pancaking. The available forces/energies were overwhelming. BUT the time sequence is vital in other situations. For the cascading failures of columns - both Twin Towers and WTC7 - the sequence with intervening time delays is critical to the load redistribution process. Truther - or Hulsey - claims for simultaneous column failures are near certainly wrong. There is not enough weight to fail a lot of columns simultaneously. Just one or a few at a time fail THEN the weight becomes available to fail more. But the sequence is essential.
 
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True enough - pure "pancake" concurrent failure of all connections was not likely BUT the speed was so fast that for practical purposes it was co-incident. The difference between "simultaneous" and "nearly simultaneous" doesn't matter in the case of office floors pancaking. The available forces/energies were overwhelming.
What many seem to miss is that the runaway floor collapse was UNLOADING the columns... removing loads from them (the floors) Conventional wisdom back then expected the forces "on" the columns to have been increasing... overloading them causing failures. But at the same time these unloaded columns were seeing their axial strength driven down because the floors (beams) were providing the bracing. A braced column has more strength and stability than an unbraced one. So the runaway floor collapse was what led to the columns failing.
The other mechanism working on the columns leading to the top's drop was the progressive failures of columns inside the core. A failed core column would lead to load redistribution to remaining intact columns. The core columns were in a high heat environment which was driving down their strength... and the too went into an unstoppable "runaway" mode of failures.
The notion of "arrest" and the notion of progressing failures in the core were also incompatible... especially given the individual design capacity of the core columns.
 
What many seem to miss is that the runaway floor collapse was UNLOADING the columns... removing loads from them (the floors) city of the core columns.
Those who "miss...that the runaway floor collapse was UNLOADING the columns" are at least trying to do some thinking. The commonest failing IMNSHO is even more worrying. So many people don't even try to think. They simply parrot the accepted wisdom. Whether it is truthers echoing the mantras laid down by TM "leaders" OR debunkers parroting some watered down inaccurate derivation from NIST or Bazant.

And even the higher level debunkers mostly accept that NIST and Bazant are infallible. How can you critique either NIST or Bazant if you a priori assume they are right???
 
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And even the higher level debunkers mostly accept that NIST and Bazant are infallible. How can you critique either NIST or Bazant if you a priori assume they are right???
The issue is not the infallibilty, or even correctness, of Bazant and NIST. It is that anything they are wrong about ought to have been acknowledged in the scientific literature long ago. If a debunker thinks that some previously accepted view among engineers is wrong, then they should be able to cite the source that demonstrates the error (and, preferrably, the source that states the now "received" view.)

One of the most convincing reasons* that the WTC collapses could not have been a demolition is that this would imply complicity among engineers in covering it up. They would know that it couldn't have happened the "official" way. If there are still important errors in the official explanation, then this suggests precisely what truthers assume: that the entire engineering community can be coerced into closing its eyes to facts that are right under its nose.

So I reject the idiosyncratic, NIST-critical version of "ROOSD" that @econ41 and @Jeffrey Orling are developing on the simple grounds that I trust the science to converge. At this point the Lalkovski & Starossek account settles things for me. I assume they've studied the problem as closely as anyone here, and I have no way to decide whether a critique of their work is valid.

Iconoclasm is of course fun to watch. But, with all due respect, it's as kooky as the truthers, guys!

_____
*Edit: I should qualify this. This is the most convincing reason to a moderately science-literate layman, like me and most of the interested public. Obviously, someone with independent engineering knowledge will have better reasons not to believe in controlled demolition.
 
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The issue is not the infallibilty, or even correctness, of Bazant and NIST. It is that anything they are wrong about ought to have been acknowledged in the scientific literature long ago. If a debunker thinks that some previously accepted view among engineers is wrong, then they should be able to cite the source that demonstrates the error (and, preferrably, the source that states the now "received" view.)

One of the most convincing reasons* that the WTC collapses could not have been a demolition is that this would imply complicity among engineers in covering it up. They would know that it couldn't have happened the "official" way. If there are still important errors in the official explanation, then this suggests precisely what truthers assume: that the entire engineering community can be coerced into closing its eyes to facts that are right under its nose.

So I reject the idiosyncratic, NIST-critical version of "ROOSD" that @econ41 and @Jeffrey Orling are developing on the simple grounds that I trust the science to converge. At this point the Lalkovski & Starossek account settles things for me. I assume they've studied the problem as closely as anyone here, and I have no way to decide whether a critique of their work is valid.

Iconoclasm is of course fun to watch. But, with all due respect, it's as kooky as the truthers, guys!

_____
*Edit: I should qualify this. This is the most convincing reason to a moderately science-literate layman, like me and most of the interested public. Obviously, someone with independent engineering knowledge will have better reasons not to believe in controlled demolition.
The flaw with Bazant and others like him... is not that his "physics" is incorrect... but that it does not describe or pertain to the collapse of the towers. It's like citing Newton as an explanation. YES gravity makes all things fall (that are not buoyant).
ROOSD as "science" or engineering... was not "discovered" online in the early 00s to explain the tower collapse. It is described in a paper about progressive floor plate collapse in high rise buildings... essentially a theoretical presentation.
The first explanations related to the collapse were mickey mouse cartoons and not BASED on the ACTUAL observations. ECON has noted that there were several phases with ROOSD being the destruction of the floors slabs of the lower block... which essentially is what was predicted by published paper in an academic journal.
Progressive floor collapse is not a "new" phenomena... it is basic settled engineering.... floor plates/slabs which are "overloaded" collapse and fail. Just like how a row of dominoes fail... all dominoes are of the same characteristics and will fall over with the force of another domino falling on it. A "key" to understanding is that the collapse was not "uniform" floor slabs... but excessive mass raining down over the entire footprint of each floor in a very short time interval. NIST didn't bother to describe "global collapse". Their focus was on a theory of what led to it. And practically speaking... if the initiation is understood and can be mitigated... hi rises can be more safely built.
Understanding the "toppling" of the spire... remaining core columns also is not a mystery. Engineers have understood why or what conditions lead to a column self buckling. This goes back to the work of Euler. Euler is too difficult for most people to understand.
So... what you see is people trying or wanting... "scale models" which reproduce the collapse of a tall building. The problem is that time and forces can be scaled down. So you see attempts with wax or spaghetti columns and so forth.
Most people do not understand engineering... and that makes technical explanations inaccessible to them. Ask the average person to explain how a plane flies. Same problem with lack of engineering/science understanding.

Understanding is informed by accurate observation and the technical expertise to understand them.
 
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Further to why Bazant is not real world. His "correct" theoretical model... imagine a top section of a building "magically" being "disconnected" from its axial support and then dropping. This is a fantasy can can never happen.

You could destroy all columns at one level simultaneously and then the top without load pathways through columns would simply drop. If it hadn't moved laterally the bottom of the upper columns would hit the top of the lower columns. Depending on the magnitude of drop impulse the drop might buckle the columns or it might be arrested. So conceptually a plane plowing through a building might sever its columns (all of them??? I doubt it... large place and small building) and lead to a Bazant situation. The colliding slabs would of course then do a crush down/crush up. Bazant's theory is not real world... it's fantasy.
 
You could destroy all columns at one level simultaneously and then the top without load pathways through columns would simply drop. If it hadn't moved laterally the bottom of the upper columns would hit the top of the lower columns. Depending on the magnitude of drop impulse the drop might buckle the columns or it might be arrested.
That is actually the central issue of the legitimate debate of the topic of this thread. Ignoring @Thomas B's SOP attempt to derail into his own favourite evasion trick - complaining that there isn't a layman's book explaining WTC collapses.

The Bazant & Zhou papers of 2001-2 presented a limit case. Based on "all columns failure" and the top block "dropping to impact". Bazant claimed that the "magnitude of drop impulse" would cause unstoppable progression. << THAT was the starting point for debate. It was NOT intended as "what really happened".

THEN most debate assumed Bazant meant "it really happened" >> and debate went off the rails for 8 or 9 years, Even those who understood Bazant did not mean it literally still assumed he got the sums right. A bit later Szuladzinski, Szamboti and Johns claimed Bazant got the sums wrong. And they have been ignored.

So - in this thread - the OP by @arsyn critiqued the paper by Schneider and discussion mostly between arsyn and me elaborated on the reasons why Schneider was wrong. Pur simply he made the same errors as those parsons who 14 years earlier took B&Z literally. The same error was made most prominent by truther engineer Tony Szamboti's paper "Missing Jolt".

Later in this thread, @Thomas B following his SOP preference for derailing debate introduced another paper which also made similar errors. A legitimate additional example of similar errors to those identified in the OP.

And the current status is that @Thomas B is resorting to further derail - one he has played on several previous threads. He moves the goalposts to his personal obsession with wanting a laypersons book written by academics. Whilst posting snide insults about those who like me can and have accurately explained the collapses. I have also in other threads comprehensively explained the reality which @Thomas B refuses to accept. All his related concerns as to why there is no "book".
 
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The issue is not the infallibilty, or even correctness, of Bazant and NIST. It is that anything they are wrong about ought to have been acknowledged in the scientific literature long ago. If a debunker thinks that some previously accepted view among engineers is wrong, then they should be able to cite the source that demonstrates the error (and, preferrably, the source that states the now "received" view.)
Hogwash. Once again you resort to derailing a thread to pursue your personal fantasy. There is no laypersons book and there is no point helping your derail of this thread by once again posting the reasons.
So I reject the idiosyncratic, NIST-critical version of "ROOSD" that @econ41 and @Jeffrey Orling are developing on the simple grounds that I trust the science to converge.
Your shallowly disguised personal attacks won't influence either me or @Jeffrey. The reality is that I and a couple of others have shown you the errors of your claims And you seem incapable of either accepting or legitimately rebutting our correct explanations.
Iconoclasm is of course fun to watch. But, with all due respect, it's as kooky as the truthers, guys!
The snide comments do not help your case. My obvious responses include: (a) "Prove it" or, more specifically, (b) prove ANY ONE of my explanations is wrong
_____
*Edit: I should qualify this. This is the most convincing reason to a moderately science-literate layman, like me and most of the interested public. Obviously, someone with independent engineering knowledge will have better reasons not to believe in controlled demolition.
Make your mind up with the dual standards. Because that "...someone with independent engineering knowledge..." is ME as my posting record shows. Your record shows that you persist in rejecting any sound, professional level, advice that is put to you.
 
None of the mechanism in play during the various stages/phases of the collapse are not "accepted engineering". ROOSD is a much more accurate description of a "pancake collapse" which every engineer will agree with. There is no dispute that heat led to the "tops' drop" but there are several ways "heat" could lead to the drop. As there were no data during the period of plane strike to top block... all "models"... based on engineering and fire science are "theories" or speculation. These can be debated but the root cause... heat "weakening" the axial structure can not be disputed. NIST's explanation of sagging trusses is theoretically plausible and the are SOME (few) visuals to support this. But unfortunately (for NIST) there are not enough visuals to support the number of perimeter columns buckling to induce the top drops we observed. And of course NIST punted on the collapse of the lower block by calling it "inevitable global collapse". That means nothing.
Does it matter? Only for those who truly want a sensible explanation and those who will be designing high rises in the future. Everyone seems to agree... more robust fire suppression and fire fighting is needed.
 
None of the mechanism in play during the various stages/phases of the collapse are not "accepted engineering". ROOSD is a much more accurate description of a "pancake collapse" which every engineer will agree with.
True tho I suggest "every engineer should agree with". (There will always be a few "stand outs".) (And anyone who is not an engineer should NOT disagree with. ;) )
There is no dispute that heat led to the "tops' drop" but there are several ways "heat" could lead to the drop. As there were no data during the period of plane strike to top block... all "models"... based on engineering and fire science are "theories" or speculation.
We have sufficient data to ensure we are correct on the three key characteristics viz the main process of "initiation" was.. can be seen to involve .. must have included... (a) Sequenced failure of columns; (b) driven by load re-distribution AND (c) causing loss of vertical load/axial column load bearing capacity, And we don't need more to understand the mechanism. We need additional quantification to "prove" CD was not needed.
These can be debated but the root cause... heat "weakening" the axial structure can not be disputed. NIST's explanation of sagging trusses is theoretically plausible and the are SOME (few) visuals to support this. But unfortunately (for NIST) there are not enough visuals to support the number of perimeter columns buckling to induce the top drops we observed.
Agreed with the exception of our long-standing different emphasis on "not enough visuals". IF perimeter column IB was the trigger THEN the amount of IB we observed was sufficient to be a "trigger". i.e. I'm saying we only need to understand what is needed to trigger the process.
And of course NIST punted on the collapse of the lower block by calling it "inevitable global collapse". That means nothing.
Actually, if you read NIST carefully and in detail, they understood "ROOSD" - the problem was they just didn't make it explicitly obvious in their report. (and BTW - a cynical observation" - most of those debunkers who denied or still deny "ROOSD" by claiming NIST already identified it are generously re-writing their own version of history. Ain't 20/20 hindsight great!!!).
Does it matter? Only for those who truly want a sensible explanation and those who will be designing high rises in the future.
Yes.
Everyone seems to agree... more robust fire suppression and fire fighting is needed.
Agreed. The main causes of deaths were the architectural specifications specifically the redundancy of escape paths and fire sprinkler systems.
 
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Your shallowly disguised personal attacks won't influence either me or @Jeffrey.
I apologise. I have been needlessly rude. This thread (and the new paper) has in fact shown me a few things that I've been wrong about. I'll just leave it humbly there for now since pretty much anything else I say seems to "derail" the discussion. Thanks, as always, for your time.

Bazant's theory is not real world... it's fantasy.
This is one of the things I'm beginning to understand may well be true. There is support for it in the Lalkovski and Starossek paper:
External Quote:
This strong dependence on unrealistic assumptions makes the model of Bažant et al. (2008) unfit for its intended purpose, at any rate when it comes to real buildings.
https://ascelibrary.org/doi/10.1061/(ASCE)ST.1943-541X.0003244
 
Bazant's theory is not real world... it's fantasy.
This is one of the things I'm beginning to understand may well be true.
As used in Bazant & Zhou 2001/2 it is a valid 1D limit case approximation. But remember that a lot of people misunderstood for a long time. So IF you - either of you - are unsure about what "limit case" means it is safer to treat it as fantasy. It certainly is NOT what actually happened and assuming it did - "literally" - happen has caused a lot of confusion.

THEN - as used in Bazant & Verdure 2007 and subsequent formal discussions in 2008 it is definitely wrong. And that is my opinion - very few debunkers dare to oppose Bazant. I can easily provide proof if you don't want to believe me. Lalkovski and Starossek agree with what I say. AKA they support "ROOSD"

There is support for it in the Lalkovski and Starossek paper:
External Quote:
This strong dependence on unrealistic assumptions makes the model of Bažant et al. (2008) unfit for its intended purpose, at any rate when it comes to real buildings.
https://ascelibrary.org/doi/10.1061/(ASCE)ST.1943-541X.0003244
Lalkovski and Starossek are correct to identify that the real event was what they call an "F-P-F-driven" failure and that Bazant & Verdure were wrong to identify it as a "C-F-driven" failure.
 
As used in Bazant & Zhou 2001/2 it is a valid 1D limit case approximation. But remember that a lot of people misunderstood for a long time. So IF you - either of you - are unsure about what "limit case" means it is safer to treat it as fantasy. It certainly is NOT what actually happened and assuming it did - "literally" - happen has caused a lot of confusion.
NIST used the term "an approximate lower bound" in NCSTAR 1-6, while pointing out all the ways that Bazant does not reflect reality.

https://www.metabunk.org/f/files/NCSTAR 1-6 UNLOCKED.pdf
External Quote:

The study performed by Northwestern University (Bazant 2002) was a simplified approximate analysis of the overall collapse of the WTC towers which addressed the question of why a total collapse occurred. The analysis addressed the results of prolonged heating which would have caused the columns of a single floor to lose their load carrying capacity and initiated the collapse of the building. The analysis assumed loss of thermal insulation during impact, uniform temperatures of 800 °C for a uniform column size and load across a single floor, and creep buckling and loss of load carrying capacity in over half of the columns. The analysis included evaluation of the dynamic amplification of the loads and the ability of the columns in the lower floors to dissipate the kinetic energy of the falling upper building mass through formation of plastic hinge mechanisms. The analysis found that the ratio of the kinetic energy of the upper building section dropping one floor to the deformation energy of plastic hinge rotation in the lower building columns was approximately a factor of eight.

The study by Northwestern [Bazant] did not address the details of impact damage, fire dynamics, or structural response of the towers. Rather, a generalized condition was assumed of heated columns, and the question of why there was total collapse was addressed. NIST agrees with the assessment of the tower’s required structural capacity to absorb the released energy of the upper building section as it began to fall as an approximate lower bound. The likelihood of the falling building section aligning vertically with the columns below was small, given the observed tilting, so that the required capacity would be greater if interaction with the floors was also considered, as pointed out in the study.
 
Thanks @Mick West.

There were many technical aspects and issues of obscure writing that contributed to that era of confusion. To me the fundamental issue of difference was always "column alignment". But the general online discussion in those early days focussed on gross motion analyses. Which pre-disposes to acceptance of 1D approximations. And 1D approximation is dubious at best >> it is diametrically opposed to "open office space" or "tube-in-tube" design. And Bazant's papers assume !D approx. Both B&Z 2001-2 and B&V 2007 are 1D.


There were two fundamental assumptions in the Bazant & Zhou 2001-2 hypothesis viz:
(1) The assumption that Top Block and lower Tower column ends remained aligned to provide maximum resistance; AND
(2) The assumption that the Top Block columns dropped to make an impact.

Both valid assumptions for Bazant's original purpose - a "limit case" assessment. But, even tho it was correct in principle, it was misunderstood by many and the B&Z paper caused much confusion. And a lot of debate went down a false trail assuming B&Z was "what really happend". So, circa 2007-8-9 "two polarised sides" were emerging and both sides were pursuing false explanations.

Throw in the NIST report and Tony Szamboti's "Missing Jolt" and intensive discussion led to a general recognition that Bazant's hypothesis was a "limit case" - not to be interpreted literally - and that column ends did not align. That mostly disposed of the first assumption as being realistic for Twin Towers collapses.

BUT the second assumption - that the "Top Block dropped to impact" is still mostly taken as accepted wisdom. NIST did not explicitly rebut it.

External Quote:
The analysis found that the ratio of the kinetic energy of the upper building section dropping one floor to the deformation energy of plastic hinge rotation in the lower building columns was approximately a factor of eight.
"dropping" one floor? It didn't happen. And anyone thinking "dropping" really should go back to the basics of how a column actually fails.

So one of those false assumptions continues to cause misunderstanding. Then the coup-de=grace" with Bazant & Verdure's Crush Down/Crush Up which is also wrong.... That is another topic - for a more suitable time, place and audience. However @Thomas B has linked and referenced the recent paper by Nikolay Lalkovski and Uwe Starossek which still includes some sources of confusion.

And those issues are of foundation premise importance to the discussion of the OP and related topics of this thread.
 
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Thanks @Mick West.

There were many technical aspects and issues of obscure writing that contributed to that era of confusion. To me the fundamental issue of difference was always "column alignment". But the general online discussion in those early days focussed on gross motion analyses. Which pre-disposes to acceptance of 1D approximations. And 1D approximation is dubious at best >> it is diametrically opposed to "open office space" or "tube-in-tube" design. And Bazant's papers assume !D approx. Both B&Z 2001-2 and B&V 2007 are 1D.


There were two fundamental assumptions in the Bazant & Zhou 2001-2 hypothesis viz:
(1) The assumption that Top Block and lower Tower column ends remained aligned to provide maximum resistance; AND
(2) The assumption that the Top Block columns dropped to make an impact.

Both valid assumptions for Bazant's original purpose - a "limit case" assessment. But, even tho it was correct in principle, it was misunderstood by many and the B&Z paper caused much confusion. And a lot of debate went down a false trail assuming B&Z was "what really happend". So, circa 2007-8-9 "two polarised sides" were emerging and both sides were pursuing false explanations.

Throw in the NIST report and Tony Szamboti's "Missing Jolt" and intensive discussion led to a general recognition that Bazant's hypothesis was a "limit case" - not to be interpreted literally - and that column ends did not align. That mostly disposed of the first assumption as being realistic for Twin Towers collapses.

BUT the second assumption - that the "Top Block dropped to impact" is still mostly taken as accepted wisdom. NIST did not explicitly rebut it.

External Quote:
The analysis found that the ratio of the kinetic energy of the upper building section dropping one floor to the deformation energy of plastic hinge rotation in the lower building columns was approximately a factor of eight.
"dropping" one floor? It didn't happen. And anyone thinking "dropping" really should go back to the basics of how a column actually fails.

So one of those false assumptions continues to cause misunderstanding. Then the coup-de=grace" with Bazant & Verdure's Crush Down/Crush Up which is also wrong.... That is another topic - for a more suitable time, place and audience. However @Thomas B has linked and referenced the recent paper by Nikolay Lalkovski and Uwe Starossek which still includes some sources of confusion.

And those issues are of foundation premise importance to the discussion of the OP and related topics of this thread.
And let's not forget that the core columns were 3 stories tall, the facade panels columns were also 3 stories and vertically staggered.

If by some miracle the entire core's columns were destroyed... it would involve 3 stories! Conceptualizing a one story collapse indicates complete ignorance of the structure.

+++

To "revisit" the columns "destroyed" by the plane impacts.... They were either severed or severely bent and subject to buckling from the service loads. It's likely that MOST of the column would remain and braced.

North Tower Impact Damage_page1.jpg
 
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