Merged Applicability of Bazant's model to the real world

[beachnut]

Pgimeno, many of us have been critics of the scholars and AE911T for a long time. Quite vocally to the point of being kicked out of their forums.

...

What independent researchers? Are they scenics or engineers? Are they better than Bazant? You have conspiracy theories on your conspiracy theories. Smoke and mirrors? Is that your work?

It is funny how you are stuck on NIST.

You are kicked out of forums because you post BS, which you think is engineering. It is funny as ae are do nothing cult members with thermite rot on the brain, it is amazing they can see your work as nonsense. It is ironic your BS CD delusion is kicked out from people with the same delusions and worse. Are you making up another CT?

If you have problems with Bazant publish them! It will be interesting to see the adjectives of nonsense and delusional used in a real journal when your junk is evaluated. Heiwa did it why can't you! You can always make up another CT after it goes bad.

 

[femr2]

This text addresses how and in what sense Bažant's model, initially stated in [B 2001] and [BZ], and refined in [BV] and [BLGB], with clarifications in [BL] (see below, References), can or can not apply to real world buildings.

The author welcomes any constructive criticisms aimed at addressing such inaccuracies as long as they are stated with arguments other than incredulity and disbelief

Since the author's always been not-so-good for writing closing words, please indulge him in his use of [BLGB] to do it:

These conclusions show the allegations of controlled demolition to be absurd and leave no doubt that the towers failed due to gravity-driven progressive collapse triggered by the effects of fire.​

I highlighted the inapplicability of your quoted closing remarks in the very first response to your OP.

Namely that...

The conclusion steps outside the bounds of model applicability.

Bearing in mind the specific purpose of your thread, I assume you are going to acknowledge this point shortly.

Not only is it a perfect example of the way that the model is used incorrectly, but it is a quote from the model authors themselves.

I also suggest you request that further posts from ALL members directly address the thread topic at all times.

 

[beachnut]

Since the author's always been not-so-good for writing closing words, please indulge him in his use of [BLGB] to do it:

These conclusions show the allegations of controlled demolition to be absurd and leave no doubt that the towers failed due to gravity-driven progressive collapse triggered by the effects of fire.
​

Bazant knows it was not controlled demolition, as do 99.99 percent of all engineers. Nice to see it published so 911 truth has some move evidence they can ignore.

It was also cool the OP is referenced. 911 truth pseudo-wannabe-engineers never use source or references for their made up nonsense which they use for science and evidence.

When you find 911 truth work referenced and sources, you can follow the references and sources to debunk the work. It is classic 911 truth. 911 truth cult members can't comprehend the closing statement is based on evidence, not failed paranoid conspiracy theories based on lies and hearsay. They don't do evidence, or understand Bazant does.

 

[Furcifer]

We want to know what initiated collapse, not whether the building would bounce after a 12 ft fall.

Fire.

 

[ozeco41]

No, we're not talking about the global collapse. We are talking about a mathematical model of the collapse which is an approximation of it. .....I think it's you who is missing the point. The point is that it doesn't matter - the differences in the impact behavior can still make little differences in many of the results. However, actual impact behavior is very difficult to model as there's a cloud of uncertainty surrounding it, while axial impact behavior has been modeled successfully....

Point taken that I need to be very explicit.

If we are talking about the Bazant model as a generic model then the model is valid as far as it goes.

BUT if we apply the generic model to a specific situation where the assumptions of the generic model are not valid - then the model ceases to be correct and may introduce errors which may be significant.

So you clarify that "we're not talking about the global collapse [of WTC1 and WTC2]"

Whereas I was attempting to relate the Bazant generic model to the specifics of the WTC twin towers global collapse stage.

So continue discussion of Bazant's model without referring to WTC global collapse and I have no concern.

My concern arises only when Bazant's model is taken into areas of analysis of WTC collapse where it does not fit. Where his assumptions, especially the assumptions about axial contact, are significant.

So your next comment "We are talking about a mathematical model of the [global] collapse which is an approximation of it."

So, like me you are relating to WTC global collapse. So your statement hinges on what you mean by "approximation"? I hold to my several times repeated statement. I have no doubt that Bazant was "globally" correct - there was more than enough energy to ensure complete collapse once it was initiated. I question the validity if the concept is taken to further detail given Bazant's assumption of axial column contacts in his model and the near absence of such contacts in the WTC global collapse.

 

[femr2]

PMy concern arises only when Bazant's model is taken into areas of analysis of WTC collapse where it does not fit. Where his assumptions, especially the assumptions about axial contact, are significant.

This reminds me of discussions I've had with David Benson, which arose through discussion of the roughly linear rate ejecta streams equating to the position of the primary *crush fronts*.

The velocity of the WTC 1 south-side crush front was found to reach fairly constant rate after about 5 seconds, reaching ground in roughly 14.5 seconds.

David's input to the discussion was that such details matched outputs from the model.

This is a concern imo.

The crush fronts are essentially the result of *pancaking*, with ROOSD being a more detailed description.

Why do the outputs from the model involving axial column impacts match behaviour, velocity profile and global descent time of a completely different mechanism ?

(Especially when it is clear that actual column destruction was significantly slower in propogation rate than ROOSD)

That is why, as indicated earlier, it would be useful if the form of the force function was provided, such that the model results can be replicated and parameter sensitivity tested.

 

[pgimeno]

I highlighted the inapplicability of your quoted closing remarks in the very first response to your OP.

Namely that...

The conclusion steps outside the bounds of model applicability.

Bearing in mind the specific purpose of your thread, I assume you are going to acknowledge this point shortly.

Rigorously speaking, that's true.

Certainly, Bazant doesn't deal with collapse initiation, where there is certainly room for a deliberate action against the towers. However, the amount of demolition theory believers that sustain that point of view is so low that they can be readily dismissed. Thus Bazant's comment as quoted is accurate in its context (the clear intention of dismissing claims on the merit of floor-by-floor explosive demolition) even if not scalpel-accurate. I must say, that making that much emphasis in that distinction does not seem neutral to me at all, but the contrary. It looks to me as giving last-term excuses for those who can be convinced by Bazant's arguments in order to sustain the unproven, purely faith-based deliberate destruction of the towers. It's precisely the lack of any kind of support from either evidence or rational thought (but I must put emphasis on lack of evidence), that should lead to dismiss it without giving it any serious consideration when objectively evaluated. It pertains to the realm of speculation and it's sad that faith is the only motivation for the search of evidence in that respect from people that mostly seem otherwise quite rational.

 

[bill smith]

If you want to see just how inapplicable Bazant is to the 9/11 paradigm just think about his 'upper block'.

We know that 15% or less of the columns, both core and perimeter that connected upper and lower blocks were destroyed by the plane crash. So 85% or more were intact.

So what is all this about an ' upper block ' ?

We should be talking about how those 85% apparently simultaneously ceased to exist as columns.

 

[femr2]

The conclusion steps outside the bounds of model applicability.

Rigorously speaking, that's true.

Agreed.

Response to the rest of your post is over at the911forum...
http://the911forum.freeforums.org/post12226.html?hilit=#p12226

 

[pgimeno]

Point taken that I need to be very explicit.

Yes, this is an area where misunderstandings have been and have the risk to be common.

If we are talking about the Bazant model as a generic model then the model is valid as far as it goes.

BUT if we apply the generic model to a specific situation where the assumptions of the generic model are not valid - then the model ceases to be correct and may introduce errors which may be significant.

So far, so good. That's precisely why I use this sentence:

The corollary is that it is possible to draw some conclusions even from an inexact model, just not any conclusions, and we have to be careful about which ones can be extracted and which ones won't match the real world to any sufficient degree of accuracy at all.

So your statement hinges on what you mean by "approximation"? I hold to my several times repeated statement. I have no doubt that Bazant was "globally" correct - there was more than enough energy to ensure complete collapse once it was initiated. I question the validity if the concept is taken to further detail given Bazant's assumption of axial column contacts in his model and the near absence of such contacts in the WTC global collapse.

That's a valid point that I certainly admit to have kind of handwaved because of my lack of knowledge in the field. I have a strong feeling that some of the results will apply equally to both the real case and the model, but I can't tell you precisely which ones. That's not only my sensation, though. In another forum someone made a comment from one of my sentences:

Had he modeled crush-up occuring simultaneously with crush-down, that would probably mean a factor of two deviation in some of his results.

Those results, specifically, would be count of number of members failed and the associated energy in deformation and failure until crush-up concludes. Displacement of the roofline would be considerably greater over the mixed crush interval, not necessarily a factor of two. There is strong reason to believe most other dynamic quantities of interest would not be affected much, at the level of detail of the model.

(Emphasis in original).

Wish I could be any more precise. Sorry, I can't. I have ventured an assumption regarding e.g. this quote from [BV] (p.312):

Detailed finite element analysis simulating plasticity and break-up of all columns and beams, and the flight and collisions of broken pieces, would be extremely difficult, as well as unsuited for extracting the basic general trends. Thus it appears reasonable to make four simplifying hypotheses: [...]
​

I assume that he knows how the simplifications he makes affect the obtained results and that he knows that they won't have a very significant effect on the results he intends to obtain.

But then, I guess I would need to be an engineer to be able to actually make an evaluation about that.

 

[ergo]

The Bazant Zhao argument of 12 ft freefall before the first collision has been a total red herring.

We want to know what initiated collapse, not whether the building would bounce after a 12 ft fall.

Metamars writes in post #12: "If you just gently rested the top block on the bottom block, but 'off-center' (columns resting on floors, except when outside the footprint of the base), then I expect the building to collapse. You wouldn't even need to drop it by one storey height. "

Exactly. If this is true why would anyone argue for a big bounce after 12 ft? It's an argument for suckers.

The demo would initiate collapse and once those columns are displaced is there any reason to expect the building to fare well?

If I may be allowed to comment in this more technical discussion... Showing that a jolt or bounce back accompanies any collision demonstrates that the lower portion is sufficiently providing resistance, as would be predicted. Which in turn shows that crush down would not occur first.

As for "gently resting the upper block" off-centre on the lower, how and why would two floors of off-centre columns precipitate a global collapse of the entire rest of a building whose columns are intact? This makes no sense. And if you're further suggesting that it would be a crush down, this makes even less sense.

 

[pgimeno]

Agreed.

Response to the rest of your post is over at the911forum...
http://the911forum.freeforums.org/post12226.html?hilit=#p12226

Despite this clear sentence I added to the beginning and end?

It is taking quite a good amount of time to follow one forum and I didn't have any plans to follow two.

[...]

As a final word, as outlined above, I will probably not comment much or at all to any responses.

femr2, the titles of your videos speak lots, and your attitude does too. I have already discussed some personal aspects of this with you, so I won't extend in that direction.

 

[metamars]

There has been much discussion of the model there of course, but the main problem, as far as I am aware, is the omission of the form of the force function used in B&L.

I'd like to see the function provided, and the model implemented with those handy computer things, such that it is possible to:

a) regenerate and replicate the published results
b) test parameter sensitivity

I was referring specifically to BZ.

Subsequent papers looked more relevant to a real collapse. (Which is a good thing since, as noted, BZ is illogical, and can't prove anything about a real world collapse.) Though I vaguely recall deriving an unbelievable prediction from one of them (I think it was BV; I may have posted results at physorg), I'm not really competent to analyze the 'definitive' BLGB, as it involved theorizing of a sort that I'm not familiar with. (I can't remember the term, but it wasn't theories based on first principles, or derivations like one makes in a dynamics class, but rather a theory, such as hooke's law, that follows from observation, and has some sort of statistical validity.)

I don't trust such theorizing, because in the case of the WTC, it couldn't be tested. (Unlike Hooke's Law, which is readily tested, as much as we please.) But maybe I'm just showing my ignorance. I never had time to study the references that Benson suggested.

My general impression of the BLGB paper (for whatever it's worth), is that it shows that a collapse in the time frame observed was possible given the assumptions of the theory (many of which were reasonable; perhaps all were somewhat reasonable, though IIRC, it didn't take into account transport of elastic energy into the ground, nor any possible dampening effect of floors oscillating like membranes, nor plastic waves that exceeded the collapse speed* ).

I vaguely recall concluding that their model was probably very good for when the collapse really got going, something like halfway done. However, that's the part of a collapse where you really don't need explosives, even to make sure that there's no chance of toppling over.

Sorry, I don't remember more clearly. Again, I don't have the technical background to understand the later works, fully, anyway.


BTW, have you ever looked at the papers of Charles M. Beck, posted at arxiv? They are way over my head. His analysis suggested CD:

We examine four WTC 7 descent curves, labeled "C," "E," "N," and "O," either anonymously published, or confidentially communicated to us. Descent curve describes apparent height of a collapsing building as a function of time. The set "C" suggests that there are three active phases of collapse. Phase I is a free fall for the first $H_1\simeq28$m or $T_1\simeq2.3$s, during which the acceleration $a$ is that of the gravity, $a=g=9.8$m/s$^2$. In Phase II, which continues until drop $H_2\simeq68$m, or $T_2\simeq3.8$s, the acceleration is $a\simeq5$m/s$^2$, while in Phase III which continues for the remaining of the data set, $a \simeq -1$m/s$^2$. We propose that the collapse of WTC 7 is initiated by a total and sudden annihilation of the base (section of the building from the ground level to $H_1$), which then allows the top section (building above $H_1$) to free fall during Phase I, and then collide with the ground in Phase II and III. The total duration of the collapse, assuming that Phase III continues to the end, is in the range $7.8-8.6$s. We derive a physical model for collision of the building with the ground, in which we correct the "crush-up" model of Ba\v{z}ant and Verdure, J. Engr. Mech. ASCE, {\bf 133} (2006) 308, and estimate the magnitude of the resistive force in the top section. We compare our findings to those of NIST investigators and find an agreement with respect to the distribution of damage in the primary zone. We conclude that the building was destroyed in a highly controlled fashion.

(emphasis mine)

His paper on WTC 1/2 is here.


* Even a plastic wave traveling at 1/10 of 5,000 m/s or so is much faster than the collapse

 

[pgimeno]

Subsequent papers looked more relevant to a real collapse. (Which is a good thing since, as noted, BZ is illogical, and can't prove anything about a real world collapse.)

Care to explain what makes it illogical? It proves that in the most favorable scenario for collapse arrest, the building could not arrest the collapse, thus proving it was unstoppable once started, which was the point and is perfectly logical, so I'd like to see an explanation on why you think otherwise.

 

[femr2]

it would be useful if the form of the force function was provided, such that the model results can be replicated and parameter sensitivity tested.

I have been informed that the form of the force function was provided. My bad.

 

[ozeco41]

Yes, this is an area where misunderstandings have been and have the risk to be common.


So far, so good. That's precisely why I use this sentence:

​

That's a valid point that I certainly admit to have kind of handwaved because of my lack of knowledge in the field. I have a strong feeling that some of the results will apply equally to both the real case and the model, but I can't tell you precisely which ones. That's not only my sensation, though. In another forum someone made a comment from one of my sentences:

​

(Emphasis in original).

Wish I could be any more precise. Sorry, I can't. I have ventured an assumption regarding e.g. this quote from [BV] (p.312):

Detailed finite element analysis simulating plasticity and break-up of all columns and beams, and the flight and collisions of broken pieces, would be extremely difficult, as well as unsuited for extracting the basic general trends. Thus it appears reasonable to make four simplifying hypotheses: [...]
​

I assume that he knows how the simplifications he makes affect the obtained results and that he knows that they won't have a very significant effect on the results he intends to obtain.

But then, I guess I would need to be an engineer to be able to actually make an evaluation about that.

Comments noted - we are in broad agreement.

As for "...I would need to be an engineer to be able..." my experience as both a practising engineer and (for much longer) a manager of practising engineers is that many engineers "lose the plot". Whether you call it the "technical context" or the "big picture" they can get too close to detail. Somewhat parallel to the old adage "when you are up to your arse in alligators it's easy to forget that the objective was to drain the swamp". The need is to ask "why are we here and why are we doing this?" Another sub-set of the problem is the tendency to rush into intense maths and calcs without first working out where you are going and what you are trying to clarify by the maths.

Take the question of "crush up" of the top block. It is clear that most of the "top block" mass of both towers fell inside the outer tube of the lower tower. It's not clear how because of the dust clouds.

However think about how this falling top block landed on the lower and get past the confused tangle of bent and broken bits so we are really in the "global collapse".

Ask this question "Where did the oputer tube columns of the top block fall?"

There are three possibilities - viz:
(1) inside the lower tower tube so, in effect the top block was wedged inside the lower tower outer tube and still more or less intact;
(2) The top block outer tube columns fell outside the lower tower - which means that those top block columns were sheared of in the first stage of the global collapse; OR
(3) Some inside and some outside.

For several reasons I discount (3) and prefer (1) out of the remaining two options.

But let's pursue both a little.

Think only of one wall for simplicity. If the top block outer tube fell outside the lower tower outer tube THEN the top of the lower block outer wall of columns would act as a "knife blade" and shear the top block floors off their outer columns as almost the first stage of global collapse.

Conversely if the top block outer tube fell inside the lower tower outer tube THEN the underside of the top block outer wall of columns would act as a "knife blade" and shear the floors of the lower tower off their outer columns, again as almost the first stage of global collapse.

Now whichever of these it was the first impact of the outer floor area and outer tube columns lands on a floor and has only the shear strength of the floor joist to column connections to overcome. AND the only significant load transferred to the columns is the force resulting from that shearing.

So much for any forces of column buckling magnitude whether "crush up" or "crush down".

The third option takes a bit more explaining but the engineers should see that it changes little.

So I am dubious of any "crush up" style explanation which relies on column buckling forces. Including some papers which IIRC claim there was not sufficient upwards force to buckle columns. So what? There was no need for such high magnitude forces when the only force required was to shear one floor at a time off the columns.

(And dealing with the core is nearly as straightforward but no need to complicate this post further)

Suffice that Bazant's model is limiting case valid for the global collapse of WTC1 and WTC2.

It does not address collapse initiation.

It is not valid in detail to explain the global collapse of the twin towers.

 

[ozeco41]

....This is a concern imo.

...a concern which I have shared for some years.

....The crush fronts are essentially the result of *pancaking*, with ROOSD being a more detailed description...

..agreed!!!

...Why do the outputs from the model involving axial column impacts match behaviour, velocity profile and global descent time of a completely different mechanism ?

...the world of engineering has many examples of approximations giving correct answers for wrong reasons.

...(Especially when it is clear that actual column destruction was significantly slower in propogation rate than ROOSD)

...presumably column "destruction" for the core columns --- the outer columns were simply peeled off.

 

[femr2]

...presumably column "destruction" for the core columns --- the outer columns were simply peeled off.

In general, yes.

 

[metamars]

Care to explain what makes it illogical? It proves that in the most favorable scenario for collapse arrest, the building could not arrest the collapse, thus proving it was unstoppable once started, which was the point and is perfectly logical, so I'd like to see an explanation on why you think otherwise.

Use the search function, please. Here, at physorg, and the911forum.

It can't be "the most favorable scenario for collapse arrest" if it incorporates assumptions that both favor collapse, and that favor survival....

 

[femr2]

It can't be "the most favorable scenario for collapse arrest" if it incorporates assumptions that both favor collapse, and that favor survival....

Must be worth noting that core column destruction did arrest for significant portions of the core of both WTC 1 & 2.