Bazant's crush-down/crush-up model

[pgimeno]

Can the Bazant concept of crush down, then crush up be applied to WTC1?

Sure it can, as long as noone pretends that it's a description of what actually happened to WTC1. I'd say it in reverse though: it's possible to use the WTC1 data and apply it to Bazant's ideal model (no tilt, column-to-column impacts, etc). A quick reading of the fragments you cite indicates that that's what he is doing.

Oysten already explained it quite clearly, but I felt it was a good idea to clarify the difference between applying the WTC data to Bazant's model, and assuming it's a description of how things happened.

 

[Furcifer]

Of course. That is why I asked you to clarify *It's clear that it adequately describes the actual behaviour.*, and pointed out the actual behaviour was very different.

That's what the qualifier "adequately" does.

Not a whole lot different in that sense to other simplified models kicking around.

Do you mean other than the one being worked out here in this thread?

Not at all. I'm simply making sure that the model is not used incorrectly. As there is enough energy in the limiting case for complete destruction, does that mean the model can be used to state there is enough energy for alternate modes of destruction...sure, but does it mean that the behaviour matches alternate modes of destruction (such as the actual real world event) ? No.

Perhaps you could highlight a number of real world behaviours that do match the behaviour of the Bazant model ?

To what extent? You seem to be saying yah it's good but it's not perfect. To which everyone is saying yah we never said it was.

edit: I'm not sure this is on topic for this thread. It's not constructive to the OP so feel free to report it if it's distracting.

 

[femr2]

That's what the qualifier "adequately" does.

Clearly I do not agree, and again I ask...Perhaps you could highlight a number of real world behaviours that do match the behaviour of the Bazant model ?

Do you mean other than the one being worked out here in this thread?

I mean other than Bazants'. I don't think the reframing suggested in the OP helps anyones understanding of the model, and only a few posts have referred to it other than modify it's definition to bring it closer to the actual Bazant model system definition.

You seem to be saying yah it's good but it's not perfect.

Again, no. I'm saying that the Bazant model was never intended to match real world behaviours, nor is it appropriate to make assertions that it matches the real world behaviour of the towers descent, adequately in one persons opinion or otherwise. It does not. The real world behaviour was very different. It's correct usage scope is in terms of energy availability for the limiting case.

 

[Oystein]

Okay, then...

Do you agree that in the real world there was no real semblance of *top block* shortly after initiation ?

I don't know - the descending top was soon hidden behind dust clouds.

Do you agree that core destruction and floor *pancaking* propogation was separated by considerable distance ?

Not sure what you mean. I guess different episodes of core destruction were separated by considerable distance. Some along the pancaking front, some leading as shock waves propagated downwards, some trailing as some columns survived for some seconds.

Agreed, and imo the primary valid result of the model. Other behavioural properties of the model simply don't match the real world events.

Yes. Like I also said, the crush-up-crush-down model would be worthy of interest somewhat independently of the degree to which it happened at either tower. I am sure that the principles invoked in this thread and by Bazant did apply, but more or loss imperfectly due to the peculiarities of the tube-in-tube design and the asymmetries and chaos of any real world event.

Floor destruction propogation (ROOSD) attained a fairly constant velocity after about 4s. Core destruction arrested.

Hmm you seem to have more information there than I do

Are you sure you're not inadvertently applying model behaviour to the real world inappropriately ?

No

 

[beachnut]

...
Again, no. I'm saying that the Bazant model was never intended to match real world behaviours, nor is it appropriate to make assertions that it matches the real world behaviour of the towers descent, adequately in one persons opinion or otherwise. It does not. The real world behaviour was very different. It's correct usage scope is in terms of energy availability for the limiting case.

Nonsense; this shows a lack of understanding models. What engineering degree to you have?

Any expertise at the level Bazant is at?

You fail to help the OP; this is not a, "show you don't understand models" thread.

I'm trying to understand Bazant's crush-down/crush-up model, which I know is widely accepted. I am not questioning it, I merely want to understand it, and hopefully the explanation will be useful for someone else too.

..."?

 

[ergo]

Can the Bazant concept of crush down, then crush up be applied to WTC1?

Sure it can, as long as no one pretends that it's a description of what actually happened to WTC1.

This is an invalid statement. If it applies, then it is a reasonable description of what actually happened. If it doesn't apply, then it is not a reasonable description. Which is it? Much as your "debunker" theories need that ambiguity, you can't have both.

 

[bill smith]

Without the 'rigid upper block' the theory of Bazant is as dead as the Dodo. Now that we see more and more debunkers coming around to the notion that this 'upper block' was in fact a load of falling rubble is it not time to put Bazant out to pasture and get on with the real business ?

After all if we waste oodles of time and finally even succeed in proving Bazant irrevocably wrong then the debunkers will just smile and say 'well, it was only ever a hypothesis anyway'

 

[beachnut]

Without the 'rigid upper block' the theory of Bazant is as dead as the Dodo. Now that we see more and more debunkers coming around to the notion that this 'upper block' was in fact a load of falling rubble is it not time to put Bazant out to pasture and get on with the real business ?

After all if we waste oodles of time and finally even succeed in irrevocably proving Bazant wrong then the debunkers will only smile and say 'well, it was only ever a hypothesis anyway'

You could have made a rational post if you had invested the last 8 years in college instead of wallowing in moronic delusions.

Prove it! Heiwa tried and found his work was nonsense and delusional.

 

[Furcifer]

Clearly I do not agree, and again I ask...Perhaps you could highlight a number of real world behaviours that do match the behaviour of the Bazant model ?

pg.14 Conclusions. (is this a trick question?)

Again, no. I'm saying that the Bazant model was never intended to match real world behaviours, nor is it appropriate to make assertions that it matches the real world behaviour of the towers descent, adequately in one persons opinion or otherwise. It does not. The real world behaviour was very different. It's correct usage scope is in terms of energy availability for the limiting case.

I'm sorry, are you being serious?

 

[femr2]

pg.14 Conclusions. (is this a trick question?)

What specific document and version (link) are you referring to ? No, it's not a trick question. Why not simply post a number of real world behaviours that do match the behaviour of the Bazant model ?

One reason I ask you this again is to clarify whether we are interpreting *behaviour* differently.

I'm sorry, are you being serious?

Of course.

 

[Furcifer]

What specific document and version (link) are you referring to ? No, it's not a trick question. Why not simply post a number of real world behaviours that do match the behaviour of the Bazant model ?
One reason I ask you this again is to clarify whether we are interpreting *behaviour* differently.

One and the same mathematical model, with one and the same set of parameters, is shown to be capable of matching all of the observations, including: 1 the video records of the first few seconds of motion of both towers; 2 the seismic records for both towers; 3 the mass and size distributions of the comminuted particles of concrete; 4 the energy requirement for the comminution that occurred; 5 the wide spread of the fine dust around the tower; 6 the loud booms heard during collapse; 7 the fast expansion of dust clouds during collapse; and 8 the dust content of the cloud implied by its size.

Catfish?

 

[femr2]

One and the same mathematical model, with one and the same set of parameters, is shown to be capable of matching all of the observations, including:

I see we do indeed have a different view of *behaviours*...

1 the video records of the first few seconds of motion of both towers;

No tilt. No upper block deformation. No *crush-up*. Axial column impacts. No perimeter peeling. No floor region separation leading to separated *pancaking*. etc. This, and through to ground, is where I look at the behaviour comparisons.

2 the seismic records for both towers

Seismic signatures between 1 & 2 quite different to one another. Would be interested in seeing the output seismic record from the Bazant model...

3 the mass and size distributions of the comminuted particles of concrete

Was that not part of the parameter definition rather than output ? Not sure top of head.

4 the energy requirement for the comminution that occurred

How was that observed ?

5 the wide spread of the fine dust around the tower; 6 the loud booms heard during collapse; 7 the fast expansion of dust clouds during collapse; and 8 the dust content of the cloud implied by its size.

Oookay.

Yes, we have quite a different viewpoint on what *collapse mechanics behaviours* are.

 

[ozeco41]

...Again, no. I'm saying that the Bazant model was never intended to match real world behaviours, nor is it appropriate to make assertions that it matches the real world behaviour of the towers descent, adequately in one persons opinion or otherwise. It does not. The real world behaviour was very different. It's correct usage scope is in terms of energy availability for the limiting case.

Well said.

The Bazant model is a global overview which shows that there was sufficient available energy.

It does not seek to explain the actual collapse mechanism and therefore it cannot assist when the question under discussion moves below the "global overview" and starts to address the detail, for one example only, the detail of how the outer tube columns were peeled off. The very terminology of "Crush up/crush down" begs the question of "what actually was crushed?" Certainly the majority of those outer tube columns did not suffer from damage such as we would normally associate with the word "crush".

Bazant showed that there was enough energy. The assumption of "crushing" without defining what was meant by "crushed" and what was crushed gave a conservative and correct answer.

And the way the towers actually collapsed needed a lot less energy didn't it?

 

[Furcifer]

Yes, we have quite a different viewpoint on what *collapse mechanics behaviours* are.

"We" as in you and 150 years of combined experience?

Benson and Greening used to be regular members of phys.org, feel free to take it up with them. I'll warn though, their "viewpoint" will most likely trump your "viewpoint" and you may want to approach the subject with a little more tact. Benson is pretty approachable, Greening perhaps a little less so and a heap more quirky. Best of Luck

 

[femr2]

"We" as in you and 150 years of combined experience?

I made clear what kind of behaviours being referred to, and I assume you agree that none of those listed are included within the bazant model.

Benson and Greening used to be regular members of phys.org, feel free to take it up with them.

David and Frank are both long-term members *back home* at the911forum. There's various useful threads related to this topic there...
b-l-revisited-rigidity-and-crush-direction-s

 

[Furcifer]

I made clear what kind of behaviours being referred to, and I assume you agree that none of those listed are included within the bazant model.

Not exactly. Your "behaviours" seem to be, as I mentioned before, inconsequential to the overall collapse progression. "Where'd the truss hat go? I dunno", "How far could an exterior panel be thrown outside the foot print?" "What's the biggest section left intact?" those sort of "observations on the behaviour" if you will.

Forgive me if I've misinterpreted this. It's a default position I take when I hear people question widely held theory. They tend to focus on inane aspects of the theory instead of the overall picture. It's the chip in the windshield you can't stop looking at

 

[pgimeno]

The Bazant model is a global overview which shows that there was sufficient available energy.

It does not seek to explain the actual collapse mechanism and therefore it cannot assist when the question under discussion moves below the "global overview" and starts to address the detail, for one example only, the detail of how the outer tube columns were peeled off.

After taking a look at what 3bodyproblem has cited (I think he is referring to the BLGB paper, "What did and did not cause collapse of WTC Twin Towers in New York", p.14 "Conclusions") I'd say that that is "mostly true".

It seems to me that in that paper, Bazant's simplified model is indeed applied to the actual collapse of the towers, but that's done with full knowledge of its limitations as a simplified version it is, in order to try to explain some accessory happenings that would probably be less affected by the precision of the model with respect to reality.

 

[Major_Tom]

In my last post I showed 3 examples of Bazant applying his concept of crush down, then crush up to WTC1 and 2. We agree that he is wrong when he does this, no?

if so, we have at least 3 examples of incorrect arguments in the Bazant papers.
>>>>>>>>>>>>>>

If we understand under what conditions Bazant claims crush down happens before crush up, we will see if and how it can be applied to real buildings.

In Bazant and Verdure (BV) Bazant first introduces his crush down, crush up mechanics. he did so by deriving equations of motion for a 1-D stick model which undergoers repeated axial column impacts downwards and upwards from the collapse initiation point.

He first introduced the idea that significant crush up will not occur before crush down is complete because, according to his reasoning, there is insufficient upward force to buckle the columns upwards.
In the real world we would think the upper columns simply stab and puncture the lower flooring like spears and there is no reason to believe that the column buckling strength of the upper portion will allow it to escape destruction.

If we try to claim that for WTC1 the upper portion was not destroyed because there was insufficient upward force to buckle the upper columns, we would rightly be called crazy. YET THAT IS WHAT WE ARE DOING IF WE BELIEVE THE CONCEPT OF CRUSH DOWN, THEN CRUSH UP APPLIES TO REAL BUILDINGS.
In truth, Bazant is claiming that significant crush up cannot occur until crush down is complete because the strength of the columns of the upper portion cannot be overcome until it makes contact with the earth.

Bazant makes a mistake when he applies the 1-D model to claim that crush down, then crush up applies to WTC1 and 2.
\
There is no doubt that Bazant uses the concept of crush down, then crush up when describing WTC1 and 2.

This is a mistake and it would be nice if at least one regular poster at JREF would be honest enough to admit it.

 

[sheeplesnshills]

This is a mistake and it would be nice if at least one regular poster at JREF would be honest enough to admit it.

You are arguing about a simplified model not matching exactly a very much more complex situation. Whats the point? Who has stated that the Bazant model is exactly what happed on 911? You are counting the number of angels that can dance on the head a a pin............

To me it simply a way of showing that the smaller top part of a building could completely destroy the lower part. Nothing more.

 

[pgimeno]

In my last post I showed 3 examples of Bazant applying his concept of crush down, then crush up to WTC1 and 2. We agree that he is wrong when he does this, no?

if so, we have at least 3 examples of incorrect arguments in the Bazant papers.

Who is "we"? I definitely didn't agree to that and indeed I opposed that view. See post #41 and post #57. Using a limited model with full knowledge of its limitations certainly doesn't make him wrong. Therefore your conclusion doesn't follow.

In the real world we would think the upper columns simply stab and puncture the lower flooring like spears and there is no reason to believe that the column buckling strength of the upper portion will allow it to escape destruction.

No. In the real world there are many possible cases. The french vérinage demolition technique, based on load-bearing walls with a jacking system designed to make them give way all at the same time, makes load-bearing-wall to load-bearing-wall impacts possible. Load-bearing walls are just like columns with respect to Bazant's model.

If we try to claim that for WTC1 the upper portion was not destroyed because there was insufficient upward force to buckle the upper columns, we would rightly be called crazy. YET THAT IS WHAT WE ARE DOING IF WE BELIEVE THE CONCEPT OF CRUSH DOWN, THEN CRUSH UP APPLIES TO REAL BUILDINGS.

Wrong again. THAT IS WHAT WE ARE DOING IF WE BELIEVE THE CONCEPT OF CRUSH DOWN, THEN CRUSH UP APPLIES LITERALLY TO WTC1 AS A DESCRIPTION OF THE OBSERVED BEHAVIOR WITH RESPECT TO CRUSHING.

Bazant doesn't make that mistake. For example, he doesn't assume that the top fell vertically despite what his model says, and in BLGB p.901 (p.10 of PDF) the paper goes into a certain length to calculate the tilt angle to adjust the calculation for certain observations. That's what you do when you know the limitations of your model and still want to draw conclusions from it.

Bazant makes a mistake when he applies the 1-D model to claim that crush down, then crush up applies to WTC1 and 2.

It can be applied under certain assumptions to get to certain results. Bazant does it right. His results must be understood within the limitations of his model.

There is no doubt that Bazant uses the concept of crush down, then crush up when describing WTC1 and 2.

There is no doubt for someone obsessed with making Bazant look wrong. There are strong reasons to doubt your claim after reading and assimilating the papers, their context and their meaning, and knowing that models have limitations.

I suggest you to read a basic text on models and their limitations, e.g. here:
http://www.learner.org/courses/essential/physicalsci/session2/closer1.html