How Buckling Led to "Free Fall" acceleration for part of WTC7's Collapse.

Mendel

Senior Member.
If a politician refuses to release their tax records, we don't assume that there's probably nothing to see.
We are talking about scientists and engineers, not about the MAGA crowd and Trump.


In science, it's disturbingly common to hear, long after a study has been widely promoted in the media ("Eat this simple thing and live to 100!"), that the data, when closely examined, doesn't justify the published conclusions (let alone the overblown hype).
No, it isn't common in science. It's extremely uncommon in engineering.

And sadly, you're again making general sweeping claims that I don't possibly see you supporting in any way except anecdotally.

Yes, if I say something surprising or implausible and claim to a have a source that backs me up but I refuse to share that source with you, you have a reason to be suspicious.
Happily, NIST did not do that.

If I say, "If you can't show me cases of people lying in the past, you have to assume I'm telling the truth," that's just weird isn't it?
Yeah, that's a weird thing to say. Happily, I didn't say it.

If you have nothing to say about NIST, could you please stop derailing the thread?
 

Thomas B

Active Member
No, it isn't common in science. It's extremely uncommon in engineering.
Did you miss the replication crisis?

The replication crisis (also called the replicability crisis and the reproducibility crisis) is an ongoing methodological crisis in which it has been found that the results of many scientific studies are difficult or impossible to reproduce. Because the reproducibility of empirical results is an essential part of the scientific method,[2] such failures undermine the credibility of theories building on them and potentially call into question substantial parts of scientific knowledge.
Content from External Source
A 2016 survey by Nature on 1,576 researchers who took a brief online questionnaire on reproducibility found that more than 70% of researchers have tried and failed to reproduce another scientist's experiment results (including 87% of chemists, 77% of biologists, 69% of physicists and engineers, 67% of medical researchers, 64% of earth and environmental scientists, and 62% of all others), and more than half have failed to reproduce their own experiments.
Content from External Source
https://en.wikipedia.org/wiki/Replication_crisis


"Why Most Published Research Findings Are False"[1]


is a 2005 essay written by John Ioannidis, a professor at the Stanford School of Medicine, and published in PLOS Medicine. It is considered foundational to the field of metascience.

In the paper, Ioannidis argued that a large number, if not the majority, of published medical research papers contain results that cannot be replicated. In simple terms, the essay states that scientists use hypothesis testing to determine whether scientific discoveries are significant. "Significance" is formalized in terms of probability, and one formalized calculation ("P value") is reported in the scientific literature as a screening mechanism. Ioannidis posited assumptions about the way people perform and report these tests; then he constructed a statistical model which indicates that most published findings are false positive results.
Content from External Source
https://en.wikipedia.org/wiki/Why_Most_Published_Research_Findings_Are_False

I really don't know what else to say. I thought this was common knowledge.
 

Jeffrey Orling

Senior Member
I have write for years and still true:

Understanding is informed by accurate observations and the technical knowledge to explain them.

You need both or you are just making things up.
 

Thomas B

Active Member
Utter nonsense. Join me and those other honest persons who refuse to accept "authorities" as the peak of truth finding.
Sorry I was imprecise in my wording. I'm not saying we have to trust them. (I agree that we should be skeptical.) I'm saying that since they won't release their data they are asking us to trust them.
 

econ41

Senior Member
Sorry I was imprecise in my wording. I'm not saying we have to trust them. (I agree that we should be skeptical.) I'm saying that since they won't release their data they are asking us to trust them.
And I'm saying we can - for most relevant discussion topics - form legitimate conclusions without needing to refer to NIST. Remember - I decided in 2007 to NEVER rely on the arguments of NIST or Bazant (subsequently extended to exclude ANY "authority") The facts stand alone in their own right. Provided you have sufficient expertise to assess the facts.

For most of the issues raised in these debates about WTC collapses, I do have sufficient expertise. The challenge is more difficult for those who do not, themselves, have enough expertise. They need a process to determine who is telling the truth. Not impossible but not as straightforward as understanding in your own right.

Most debunkers seem to accept NIST as the supreme authority. I don't.
 
Last edited:

benthamitemetric

Senior Member
Did you miss the replication crisis?

The replication crisis (also called the replicability crisis and the reproducibility crisis) is an ongoing methodological crisis in which it has been found that the results of many scientific studies are difficult or impossible to reproduce. Because the reproducibility of empirical results is an essential part of the scientific method,[2] such failures undermine the credibility of theories building on them and potentially call into question substantial parts of scientific knowledge.
Content from External Source
A 2016 survey by Nature on 1,576 researchers who took a brief online questionnaire on reproducibility found that more than 70% of researchers have tried and failed to reproduce another scientist's experiment results (including 87% of chemists, 77% of biologists, 69% of physicists and engineers, 67% of medical researchers, 64% of earth and environmental scientists, and 62% of all others), and more than half have failed to reproduce their own experiments.
Content from External Source
https://en.wikipedia.org/wiki/Replication_crisis


"Why Most Published Research Findings Are False"[1]


is a 2005 essay written by John Ioannidis, a professor at the Stanford School of Medicine, and published in PLOS Medicine. It is considered foundational to the field of metascience.

In the paper, Ioannidis argued that a large number, if not the majority, of published medical research papers contain results that cannot be replicated. In simple terms, the essay states that scientists use hypothesis testing to determine whether scientific discoveries are significant. "Significance" is formalized in terms of probability, and one formalized calculation ("P value") is reported in the scientific literature as a screening mechanism. Ioannidis posited assumptions about the way people perform and report these tests; then he constructed a statistical model which indicates that most published findings are false positive results.
Content from External Source
https://en.wikipedia.org/wiki/Why_Most_Published_Research_Findings_Are_False

I really don't know what else to say. I thought this was common knowledge.

When "truthers" (but surely not you) make these fundamentally flawed arguments that are based entirely on the fallacy of faulty generalization, does it not occur to you to just point out that obvious logical error and move on?

A faulty generalization often follows the following format:

The proportion Q of the sample has attribute A.Therefore, the proportion Q of the population has attribute A.
Such a generalization proceeds from a premise about a sample (often unrepresentative or biased), to a conclusion about the population itself.

Please stop polluting this thread with this off topic nonsense. We know you don't trust NIST. Your distrust is not an argument for anything, let alone one that has any bearing on this topic.
 

Jeffrey Orling

Senior Member
My conception/perception of what NIST did was that they demonstrated how these 3 towers COULD collapse... not necessarily how the DID collapse. They assembled a lot of data, information which anyone can "use".

So... I rejected the twin tower explanation, not because the floor truss could not "behave" as NIST asserts, but that the collapse would require almost all the trusses to behave like that in the same time frame and NIST points to one location on the 1wtc as evidence... (almost contradicting their own argument). The universal simultaneous elongation and sagging of the trusses would demand that the fires were throughout the footprint over entire floor area... There is no evidence of that and more likely contrary evidence to that.

I looked to the core region as the culprit initiating the top block drops and then the runaway floor destruction. We can't see inside the core so whatever happened would have to use sound principles of engineering and fire science. One thing we do know is that steel building need fire suppression or they fail
Another thing we know is one column failure will lead to its loads being redistributed to remaining columns AND that can lead to additional column failures.
Another thing is that heat's impact on lateral steel would impact the columns by pushing or pulling them leading into mis-alignment of ends or buckling.

Note: NIST's argument for 7WTC involved the behavior of overheated beams and girders which led to the "weakening" and collapse of a critical column as well as local floor collapse of the entire NE quadrant. BUT they ignore this same process in the cores of the twin towers. Why?
 

benthamitemetric

Senior Member
My position is the rather moderate one that NIST isn't infallible.
Great. Everyone agrees with that nonspecific and uninteresting reformulation of your position (or--wait--wasn't it the position of truthers with whom you argue on other forums?). Please come back when you have something useful to add to the actual topic of this thread.
 

Jeffrey Orling

Senior Member
Doesn't matter. I don't use "data" to understand and explain.
Perhaps I should clarify... I don't perform calculations... but understand and apply concepts such as safe working load, factor of safety. So... we know that the "safe working load" for a typical twin tower slab is a static superimposed live and dead load of X pounds per sq ft. This is from code and based on deflection etc. We know that exceeding the SWL will result in failure... excessive deflection and even break up. We can assume that the connections of the slabs to the frame have a similar SWL... and share the loads of the floor (though not equally).
We know the floors were composite with the steel floor trusses and that the design intended to distribute concentrated loads.
We know that dropping mass is a dynamic load with force large than the mass as a static load.
 

econ41

Senior Member
We know you don't trust NIST.
My position is the rather moderate one that NIST isn't infallible.
Which is the sort of standoff which made me decide to never rely on the reasoning of "authorities" such as NIST or Bazant. That was back in Nov 2007. I've never regretted that strategic choice.

We don't need NIST or Bazant to either explain the 3 towers collapses OR to rebut truther claims for CD. And the distraction from the primary objective "Explain what really happened" to "Was NIST (or Bazant's ) explanation correct" still is a distraction in many discussions. Both explanation and rebuttal of most claims can be achieved without relying on either.
 
Last edited:

econ41

Senior Member
Sorry I was imprecise in my wording. I'm not saying we have to trust them. (I agree that we should be skeptical.) I'm saying that since they won't release their data they are asking us to trust them.
I understand your position. I say it is an off-track derail. We don't need NIST's data and I see no point in debating the philosophy of the place of statutory law in the US or any other democracy. So "we" don't need to trust NIST.

The topic is: "How Buckling Led to "Free Fall" acceleration for part of WTC7's Collapse." We can answer the legitimate structural engineering aspects by reasoned structural analysis - independent of whatever data the possibly evil mischievous NIST may be hiding. And the same goes for questions about CD - whether legitimate enquiry or truther deliberate mendacity.
 

Thomas B

Active Member
he has probably merely generalized it, I don't think his actual unsupported position("I think it is much more likely that NIST fudged the data") has changed.
Since you seem to be interested, I think NIST is more worried about what critics will do with the data than what terrorists might do with it.

You countered with generalized trust in NIST and science. I countered this with reasons to be generally skeptical of science and, if not NIST specifically (since I don't know much about it), then at least large government agencies engaged in science and enginerring, like NASA.

In general, I think science is fallible. Specifically, I suspect NIST failed to explain the collapses. (It was a mystery and it remained a mystery.) But failure wasn't a politically viable option. So we got a whitewash. That's disappointing, but it doesn't mean the buildings were demolished.
 

econ41

Senior Member
I think NIST is more worried about what critics will do with the data than what terrorists might do with it.

That could be the basis of a topic for another thread... "The place of truth, full truth, half-truth and "spin" in political statements about contentious issues". << Tho that version is much too far into generic philosophy. We need a much more specific NIST focussed version. :rolleyes:
 

Jeffrey Orling

Senior Member
Come on... let's be rational...
the 2.25 +/- seconds of "FF" drop corresponds to 100+ feet and that would be about 7-8 12'-9" story heights.
The shell dropped THAT many stories before meeting the resistance of the ground.
The moment frame structure started at floor 8. Floors 5,6 & 7 were mechanical space and contained the transfer trusses and transfer girders.
So it makes sense that there was a failure at these floors... and the shell dropped because "structure" from ground to floor 8 was destroyed and could no support the service loads (moment frame)
Likely suspect for destruction of structure on floors 1-7 (up to 8) was that all the interior mass... floors and super imposed loads crashed down inside the shell... and the debris exerted lateral forces which disrupted the columns below floor 5 including the 27 locations at the base which supported the entire moment frame.
It's as simple as that.
 

econ41

Senior Member
And @Jeffrey. failure of the cantilever arrangement over a 7-8 storey free fall gap is the prima facie obvious "trigger" even before we need to consider column buckling. THEN the process of rapid cascading failure of all the elements supporting the perimeter shell which had sufficient strength - much from the moment framing - to remain intact. THEREBY forcing the cascading load redistribution. AND making it look like a simultaneous failure of all supports. Because within a fraction of a second or two it was near enough "simultaneous".

And yet another reason why I keep recommending that those expressing doubts FIRST understand the mechanisms. And most of the doubts will resolve themselves.

Yes, it really is:
It's as simple as that.
Here - let's start a bit of thinking. This is the CD version of a demonstration of "cascading failure by load redistribution"
7colsA2-400-withcutsnotated.jpg

If you cut columns "A" and "B" what happens to the load on "C"? Even more interesting - what happens to "D"?

AND this is an explanation of one of the key aspects of physics need to fully understand the OP topic.

Let's have your thoughts @Thomas B . @Henkka Any others?
 
Last edited:

Jeffrey Orling

Senior Member
And @Jeffrey. failure of the cantilever arrangement over a 7-8 storey free fall gap is the prima facie obvious "trigger" even before we need to consider column buckling. THEN the process of rapid cascading failure of all the elements supporting the perimeter shell which had sufficient strength - much from the moment framing - to remain intact. THEREBY forcing the cascading load redistribution. AND making it look like a simultaneous failure of all supports. Because within a fraction of a second or two it was near enough "simultaneous".

And yet another reason why I keep recommending that those expressing doubts FIRST understand the mechanisms. And most of the doubts will resolve themselves.

Yes, it really is:

Here - let's start a bit of thinking. This is the CD version of a demonstration of "cascading failure by load redistribution"
7colsA2-400-withcutsnotated.jpg

If you cut columns "A" and "B" what happens to the load on "C"? Even more interesting - what happens to "D"?

AND this is an explanation of one of the key aspects of physics need to fully understand the OP topic.

Let's have your thoughts @Thomas B . @Henkka Any others?
Things really do or often do happen very quickly when a building is collapsing.
 

econ41

Senior Member
Things really do or often do happen very quickly when a building is collapsing.
Yes. But load redistribution is a sequential process. "Column 65 drops its load which is picked up by Column 56a" or whatever specific detail. The load goes from one to the other - however fast it is sequential.

I'm sure that if more of our members thought about the physics - "What happens" - rather than "NIST said" our discussions could be more productive.
 

econ41

Senior Member
runaway progressive destruction... one thing leads to another!
It's like toppling dominos. A "multiple path" set of dominos. EXCEPT:
1) Each domino on domino impact is a binary event - it either topples or it doesn't. Load redistribution across an array of columns is multi-factor analogue at each step.

2) If the next domino in line does not topple the progression stops. If the next column in line does not fail under increasing load any still surplus load will be "shunted" to another column. Not necessarily the next in the line.

etc etc >> there are a few more differences. The analogy is not perfect BUT "domino toppling" is a useful introduction to "load redistribution" for a layperson starting from "scratch".
 

Mendel

Senior Member.
Since you seem to be interested, I think NIST is more worried about what critics will do with the data than what terrorists might do with it.
But you don't have evidence for this thought; the available evidence points the other way.
In general, I think science is fallible. Specifically, I suspect NIST failed to explain the collapses. (It was a mystery and it remained a mystery.)
It's not "a mystery".
But failure wasn't a politically viable option. So we got a whitewash. That's disappointing, but it doesn't mean the buildings were demolished.
The NIST report is not a "whitewash".
The collapse of World Trade Center 7: revisited
November 2020
DOI:10.14264/9f81895
Conference: 11th International Conference on Structures in Fire (SiF2020)
https://www.researchgate.net/publication/347108749_The_collapse_of_World_Trade_Center_7_revisited
SmartSelect_20220609-063552_Samsung Notes.jpg
All 4 independent analyses discussed in this paper propose the same general sequence: fire leads to column 79 (and adjacent columns) buckling, the interior collapses, the perimeter collapses. The analyses differ merely in the details of that sequence, which severely limits the scope for "mystery".
 

Thomas B

Active Member
The analogy is not perfect BUT "domino toppling" is a useful introduction to "load redistribution" for a layperson starting from "scratch".
The problem is that in order to represent the building the dominos need some non-trivial lateral connection. Likewise, a house of cards would be a useful analogy only if we glued them together. The thing that is hard for the layperson to understand is the weakness of the connections between the solid/rigid elements.

We can't leave it at an analogy with no connections, in my opinion, though you're right that it may be a place to start. At the end of the day, nobody wants to imagine that the skyscraper they live or work in is as failure prone as a row of dominos or a house of cards, which are classic cases of precariousness, not of the stability we associate with construction.
 

Thomas B

Active Member
If you cut columns "A" and "B" what happens to the load on "C"? Even more interesting - what happens to "D"?
I would expect the beam to the left of C to be weaker than column C. After all, the beam will be subject to a bending moment, while the C will only fail if it buckles. And C will have been designed to support the entire load above while the beam will have been designed to support only the loads on that beam.

Also, it's my understanding (though I find it surprising) that the beam-to-column connections aren't moment connections but shear connections. So wouldn't the beam just "snap" off where it meets C (long before C buckles)? If there are lots of floors above, we'd have a Ronan Point type collapse to the left of C, but everything to right, including C, would keep standing. (But you would think that WTC7 would have been designed with the lessons of Ronan Point learned.)
 

econ41

Senior Member
The problem is that in order to represent the building the dominos need some non-trivial lateral connection.
So true but recognise that you have a different context viz "...to represent the building..." whilst my comment referred to "...a useful introduction to "load redistribution".." i.e. I refer to a subset of the whole mechanism whilst you have in mind the total mechanism.

The diagram is one step out of a step by step explanation of the"initiation" stage for the Twin Towers collapses. BUT it is also instructive for the WTC7 FFA of the perimeter shell which is the topic of this thread. Whatever the cause of the FFA - or more likely whatever balance between three "causes" - the process would involve load redistribution. Identical in principle if not in mechanical layout to the "7 Columns" example. I gave the "explosive cutting" version because it is a grade easier to visualise than the "heat did it "version - this one:
7colsA2-400-withfirenotated.jpg
Likewise, a house of cards would be a useful analogy only if we glued them together. The thing that is hard for the layperson to understand is the weakness of the connections between the solid/rigid elements.

We can't leave it at an analogy with no connections, in my opinion, though you're right that it may be a place to start. At the end of the day, nobody wants to imagine that the skyscraper they live or work in is as failure prone as a row of dominos or a house of cards, which are classic cases of precariousness, not of the stability we associate with construction.
Understood and agreed with the proviso - I did say "...a place to start". ;)
 

econ41

Senior Member
I would expect the beam to the left of C to be weaker than column C. After all, the beam will be subject to a bending moment, while the C will only fail if it buckles. And C will have been designed to support the entire load above while the beam will have been designed to support only the loads on that beam.

Also, it's my understanding (though I find it surprising) that the beam-to-column connections aren't moment connections but shear connections. So wouldn't the beam just "snap" off where it meets C (long before C buckles)? If there are lots of floors above, we'd have a Ronan Point type collapse to the left of C, but everything to right, including C, would keep standing. (But you would think that WTC7 would have been designed with the lessons of Ronan Point learned.)
Remember it is a model to help as a "training aid" for explaining a principle. Don't read too much implied context into it.

I use it to explain load redistribution between columns which was the main feature of Twin Towers "initiation" stage. Which was "a cascading sequenced failure of columns in axial compression overloading driven by load re-distribution". With that purpose in mind removing columns "A" and "B" means that the loads they were previously supporting have to be taken up by other columns. Some will be carried by bending moment in "Top Beam" but the overhang creates leverage which means that the load previously carried by A & B will be applied to "C" and increased somewhat by the overhang leverage. (Exactly how much needs full analysis - we are only looking at the broad picture at this stage) AND the load on "D" will be reduced. Since such structures commonly have 3 times FoS it is easy to see how removing A and B could result in incipient failure of "C". But once C starts to compress we need a full analysis to go any further with explanations.
 
Last edited:

Thomas B

Active Member
But once C starts to compress we need a full analysis to go any further with explanations.
This assumes that there is one continuous beam across all the columns, right? Isn't it correct that the beam is more likely to fail under bending than that the column is likely to fail under compression?
 

econ41

Senior Member
This assumes that there is one continuous beam across all the columns, right? Isn't it correct that the beam is more likely to fail under bending than that the column is likely to fail under compression?
No - and here's why. Remember I haven't put on any additional loading. IF the "Top Beam" was (say) the upper storeys of a High Rise Tower - even a WTC "Twin Tower" - no. Column failure would be the mode. (Remember - that is what happened - the impact and fire zone columns failed by whatever mix of causes - but columns failed driven by load re-distribution. The "Top Block" did not fail till much later. And THAT is the purpose of the step in the lesson - demonstrating column failure.

You could use a weaker beam - stronger column combination to create the beam breaks first scenario. But that is not the purpose of the lesson step.

ANd - let's get back on the thread topic - in the WTC7 facade/shell FFA situation the columns/cantilever beams/transfer truss arrangement is the weak link. There is no way that the facade - all whatever 30+ storeys high - would fail in bending before the columns/cantilevers/transfer trusses failed first. << And that theoretical prediction matches what we saw in reality. So there principles shown by this model should be relevant to the thread topic - ifwe ever get back to discussing it. ;)
 
Last edited:

Thomas B

Active Member
in the WTC7 facade/shell FFA situation the columns/cantilever beams/transfer truss arrangement is the weak link. There is no way that the facade - all whatever 30+ storeys high - would fail in bending before the columns/cantilevers/transfer trusses failed first. << And that theoretical prediction matches what we saw in reality.
Can you illustrate the theoretical prediction with a series diagrams at the same level of abstraction as your ABC diagram? (Just build it, say, 10 stories higher and have column C fail on the second floor instead of A and B. Then draw the process in ten comic book frames.)

I think the problem I have is that when the trusses fail I imagine they also take their load off the columns. So I'm having a hard time understanding where the weight on the facade comes from after the whole interior structure has collapsed.
 
Last edited:

FatPhil

Senior Member.
This assumes that there is one continuous beam across all the columns, right? Isn't it correct that the beam is more likely to fail under bending than that the column is likely to fail under compression?

Column C isn't just under compression. The overhang creates a counterclockwise moment at the top of the column, which means that column C is being bowed inwards. That significantly reduces its capacity for resisting buckling.
 

Henkka

Banned
Banned
All 4 independent analyses discussed in this paper propose the same general sequence: fire leads to column 79 (and adjacent columns) buckling, the interior collapses, the perimeter collapses. The analyses differ merely in the details of that sequence, which severely limits the scope for "mystery".
I mean, it's not particularly surprising they would have the same basic explanation. They have to match their explanation to the videos, where we first see the penthouse fall, then seven seconds later the interior falls, and a fraction of a second later the perimeter. And what was under the penthouse that could make it fall as observed? Column 79, in the northeast corner of the building. And what was the only known thing going on in the building that could damage a column in the northeast corner? Fires. It's logical enough, but also carries the danger of being a predetermined conclusion.

Any other explanation would be basically implying a massive conspiracy involving all the events of 9/11. I could see the investigators thinking that even though fires causing column 79 to fail is a bit farfetched and unprecedented, it's still far more likely than some massive plot to hide explosive or incendiary devices in the building.
 

econ41

Senior Member
Does this depend on the connection between the beam and column C?
Yes. But don't lose the plot. It is a simple model to demonstrate a principle >> axial load re-distribution. I could have shown the top as "pin-jointed". The complications which lead to a reduction in axial compressive strength of a column are in separate lessons of the step by step sequence. ( loss of bracing causing problems of critical length, eccentric loading and applied bending moment are the three that come immediately to mind. Probably in that order of importance - loss of bracing >> causing longer effective length was the key trigger issuer for the extant hypotheses explaining both the Twin Towers and WTC7 collapses. i.e. the "inwards bowing" trigger for Twin Towers and Col 79 failure for WTC7 >>> both resulting from loss of bracing therefore critical length exceeded for the applied load.)
 

econ41

Senior Member
Column C isn't just under compression. The overhang creates a counterclockwise moment at the top of the column, which means that column C is being bowed inwards. That significantly reduces its capacity for resisting buckling.
I know but the example is part of a step by step explanation for laypersons. ONE issue/aspect at a time. This was also the reason why I posted the "cut columns" example first. The "weakened by fire" example is a full order more complicated to grasp.
 

Jeffrey Orling

Senior Member
One thing leads to another is not necessarily something like a row of dominios.

It could be... a wire corrodes... the pump won't function, water can't be pumped over board...water level keeps rising. shorts batteries... boat sinks.
 

Thomas B

Active Member
the example is part of a step by step explanation
I'm looking forward to the continuation. I can imagine a system where the columns C through G will buckle in rapid succession after the failure of A and B. What's the next step?
 

Jeffrey Orling

Senior Member
I'm looking forward to the continuation. I can imagine a system where the columns C through G will buckle in rapid succession after the failure of A and B. What's the next step?
The graphic was intended to illustrate the principle of load redistribution. It is not literal for the WTC

++++

In the case of 7WTC we can assume that the EPH lost axial support. It's a reasonable assumption that it was not just under the roof... as there is no evidence of fire at that level. We then turn to the area where intense fires raged for perhaps as much as 8 hrs until the collapse..

NIST demonstrates that the heated floor beams and girders framed into col 79. 80 & 81 became overheated, expanded and were pushed off of their beam seats. This likely caused two things... local collapse of the floors of the NE quadrant and the floors East of the core. It's possible/probable that the mass of floors (7-8) crashed down on the floors 5-7 where the transfer structures - trusses and girders were located. This likely caused structural havoc with the transfer structures including the 7 MG27 cantilevers spanning from the north row of core columns to the north where they supported the moment frame.
The collapse of the EPH may be a tell that all the floors and their contents (entire east side of the building) maybe have crashed down all the way to the ground.
The tower was hollowed out... the moment frame was undermined by the massive debris filling the base of the tower. The moment frame dropped... quite rigid but lacking the floor plates for lateral stiffening.

++++

The graphic is more a representation of how the twins' cores lost axial support at the plane strike zones. With inadequate support the top block's plunged downward essentially destroying the lower blocks. The collapse did not cause buckling, but rather bypassed columns and destroyed floors which were the lateral bracing for the columns. Unbraced the columns were weakened and failed.
 

econ41

Senior Member
I'm looking forward to the continuation.
Let me think about it. The introductory material I already have was targeted at truthers who had very low level of understanding of physics. you @Thomas B (plus @Henkka and @Abdullah ) are well above that level. But it may help if we review the basics that came before the "7 Columns Model")
I can imagine a system where the columns C through G will buckle in rapid succession after the failure of A and B.
Correct. And it may help if we discuss and summarise why that is so. Load redistribution is fundamental to comprehending all three WTC Tower collapses. And understanding the basics could help other members who are not primarily interested in engineering applied physics.
What's the next step?
1) A bit of revision - wait for my next post.
2) Discuss this 7 columns model; THEN
3) I'll give some thought as to how I can help all of us visualise the specific details of WTC7.. (It may help if we explore some Twin Towers details which are easier to visualise but "prove" the same principles.)

Give me a few hours >> one day. I have a real life. ;)
 

econ41

Senior Member
The graphic was intended to illustrate the principle of load redistribution. It is not literal for the WTC
Please resist the temptation to play "dog in the manger". YES, it explains a principle. That principle is directly relevant to explaining BOTH the "Twin Towers" initiation stage AND the observed FFA of the WTC7 parameter shell which is the topic of THIS thread. I am aware that it goes against some of your long held beliefs.

Whilst I did not critique your comment at Post #328 the principle which I identify specifically rebuts this claim of yours:
So... I rejected the twin tower explanation, not because the floor truss could not "behave" as NIST asserts, but that the collapse would require almost all the trusses to behave like that in the same time frame and NIST points to one location on the 1wtc as evidence... (almost contradicting their own argument). The universal simultaneous elongation and sagging of the trusses would demand that the fires were throughout the footprint over entire floor area... There is no evidence of that and more likely contrary evidence to that.
The primary mechanism of the initiation stage of the Twin Towers collapses was a sequenced cascading failure of columns losing their capacity to carry vertical loads. That process does NOT require: "...that the collapse would require almost all the trusses to behave like that in the same time frame..." NOR does it require: "...that the fires were throughout the footprint over entire floor area.." So your conclusion is moot (irrelevant) and not supported.

The principle is DIRECTLY relevant to the current topic of FFA of WTC7 perimeter shell. AND it applies independently of the current "discussion" ("dispute"??? ;) ) as to whether "buckling", "transfer truss failure" or "cantilever direct failure" caused the failure leading to FFA. Either independently, or as I contend, in some proportional mix.
 
Last edited:
Top