Bazant's model is the only one mentioned in the report that NIST did not have objections to. Since NIST does not deal with collapse progression, Bazant's collapse progression is what is officially endorsed by NIST.
That's where you fail.
Bazant's inevitability of the collapse once initiated is what is
agreed by NIST. That's not the same as promoting the limiting Bazant's collapse progression model as the explanation for the collapse. Take some minutes until you understand the difference.
From NIST:
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 study by Northwestern 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.
NCSTAR 1-6, p.323.
Why are you promoting that as if NIST endorses Bazant's progression model as if it was what happened and as if it is official, is beyond me. They discuss other models of fire effects in other studies and discuss the points of agreement just like in this one, which doesn't make these other studies official in any meaningful way either.
Of course, you're invited to provide proof that shows how NIST endorses Bazant's progression model as if it was what happened. I don't know any.
Your thinking isn't working too well. NIST agrees with Bazant's model for collapse progression. Bazant wrote subsequent papers refining it and replying to critiques, including one entitled "What Did and Did Not Cause Collapse of WTC Twin Towers". Was that just for some theoretical fun?
Possibly. What was the reason of publishing it, according to you? Do you think these are official? In what sense?
While NIST was really endorsing the pancake model the whole time? If NIST was going with the pancake model, why would they bother re-investigating the Twin Towers?
NIST does not endorse any collapse progression model whatsoever. They just didn't investigate that. It would be stupid for them to endorse something just for the sake of endorsing it.
[ETA: And they bothered re-investigating the Twin Towers because they cared about what led to collapse initiation. They didn't care about collapse progression.]
Ignoring the fact, firstly, that Bazant manufactured his so-called "inevitability",
... which is just as incorrect and misguided as the rest of your assessments...
you cannot in any case apply Bazant's "inevitability of collapse" to the FEMA pancake model.
Yes you can. From the same
paragraph section as the quote above:
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.
They are completely different models.
They aren't, in
the sense that columns are the structural elements that are most prone to arresting collapse. Floors didn't have columns supporting them, therefore Bazant's study proves that the progressive collapse of floors was inevitable, therefore FEMA's explanation is indirectly covered by Bazant as a less favorable case for collapse arrest than his limiting case.
From Bazant: "In the structural engineering community, [...]
That's from a different paper (Bazant 2007) to that which NIST discusses (Bazant 2002), and is therefore not «officially endorsed». Fail again.
But let's dig into the content:
one early speculation was that, because of a supposedly insufficient strength of the connections between the floor trusses and the columns, the floors ‘pancaked’ first, leaving an empty framed tube, which lost stability only later. This hypothesis, however, was invalidated at NIST by careful examination of the photographic record, which shows some perimeter columns to be deflected by up to 1.4 m inward. This cannot be explained by a difference in thermal expansion of the opposite flanges of column. NIST explains this deflection by a horizontal pull from catenary action of sagging floor trusses, the cause of which has already been discussed. This pull would have been impossible if the floor trusses disconnected from the perimeter columns"
That's discussing the cause of collapse
initiation, not
progression.
The only official organization I know that gave an explanation of the actual collapse sequence is FEMA. Note that NIST contended their collapse initiation mechanism, not their collapse sequence.
See above and then
please show us anywhere in the NIST reports where they endorse the FEMA pancake model.
For what I know, they don't. Again, NIST does not endorse
any collapse progression model whatsoever. They just didn't investigate that. It would be stupid for them to endorse something just for the sake of endorsing it.
However, here is a quote suggesting that they think that the floors pancaked:
Failure of the gusset plate welded to the top truss chord was again almost exclusively observed regardless of location. This may be a result of overloading the lower floors as the floors above were "pan-caking."
NCSTAR 1-3C Damage and Failure Modes p.117.
AGAIN. NIST discarded the FEMA model.
NIST discarded the FEMA model of collapse
initiation, not of collapse
progression, and your quote from Bazant explains why they discarded it. NIST didn't evaluate collapse
progression at all.
As I've already pointed out, you can't have both. You certainly can't have FEMA pancakes and Bazant's one-way-crush "limiting case" model as complementary models. They are completely different mechanistic models. Bazant is clearly talking about column and not floor failure. How is it that you don't understand this?
And Bazant proves that in the case of columns (the most favorable case to collapse arrest), the collapse could not have been avoided, which implies that in the case of floors (which is less favorable to collapse arrest) it was even more inevitable. How is it that you don't understand this?
Yes, I'm aware of this. And guess what? Just like the failure of the pancaking model, they too are not able to explain core destruction and the general absence of pancaked floors at Ground Zero. Gosh, didn't see that one coming!
That's beyond the topic, but they do explain it (as the core relies on lateral support that was stripped) and there were pancaked floors at GZ.
So I ask again: We either have a useful, realistic and officially endorsed model of the collapse progression, or we don't. Which is it?
Answer: FEMA's is the only official explanation of collapse progression, and it is useful and realistic. Therefore, we do have one.
