Merged Applicability of Bazant's model to the real world

[ozeco41]

...


Colour change mine.

I'd need to look at the force function again to state anything specific.

Note that it is "...see how the source of Fc could have much effect..." and whether the columns were in line and buckling or stripped off taking little load is the main difference between the theoretical collapse of the model and WTC Twin Towers real world actually happened collapse.

 

[femr2]

Perhaps you can understand why I am not disinclined to acquiesce to your incomplete assurances.

ftfy

Never knew you were nowt but a humble pirate.

To argue that a mathematical/scientific/engineering model does not apply to a real situation, you need to identify an error in the model's mathematics, science, or engineering, or you need to identify an assumption of the model that is violated by the real situation.

And nothing you know about the mode of destruction conflicts with any of the assumptions of the limiting case 1D model when applied to real world behaviours ?

The limiting case would tend to result in the upper-bound in descent time, yes ?

The actual descent time would clearly be expected to be significantly below that time, yes ?

 

[Dave Rogers]

The limiting case would tend to result in the upper-bound in descent time, yes ?

Sounds reasonable.

ETA: Actually, I'm not even sure of that. The limiting case would involved simultaneous destruction of the cores, rather than the delayed fall of the core spires, which increased the descent time.

The actual descent time would clearly be expected to be significantly below that time, yes ?

The issue is in both quantifying and justifying "significantly".

Dave

 

[femr2]

ETA: Actually, I'm not even sure of that. The limiting case would involved simultaneous destruction of the cores, rather than the delayed fall of the core spires, which increased the descent time.

No. Any sensible descent time metric relates directly to the primary crush front propogation-to-ground timing.

The core remnants remained due to partial arrest of the primary (well, secondary) mechanism of destruction (with the primary core destruction being via a different mode again, which does trail the primary ROOSD mechanism). Their subsequent descent would be more correctly termed as a teritiary descent, with an entirely different mode of destruction again.

Some perimeter sections remained standing for weeks. I assume you wouldn't extend the descent time to include their eventual descent time ?


The Bazant et al model(s) relate only to the primary mode of destruction.


Also, you highlight one of the important factors, namely that different parts of the real tower suffered different modes of destruction, which are not incorporated into the single mode model(s).

 

[ozeco41]

...The Bazant et al model(s) apply only to the primary mode of destruction.


Also, you highlight one of the important factors, namely that different parts of the real tower suffered different modes of destruction, which are not incorporated into the single mode model(s).

Yes.
It is conceptually possible to 'run' two distinct and separate models viz OOS followed by core. Since the outer tube peel off and the open office space pancake failure appears to have run slightly ahead of the core strip down. The OOS collapse is similar to an 'all the way round' version of Ronan Point in that it involved failure by shearing of floor joist connectors off a still standing core. Granted that the WTC core only lasted a fraction of a second longer.

BV commented on Ronan Point

For example, in Ronan Point apartments, energy was dissipated not only by vertical crushing of stories, but also by shearing successive floor slabs from their attachments to columns on the side of the collapsing stack of rooms. The present model seems usable if the energy dissipated by shearing is added to the crushing energy Fc,....

...which hints at the sort of thing I have suggested in earlier posts. For the OOS floors replace the column crushing force with the floor joist shear off force and tidy up any loose ends. Then separately look at the core strip down.

Beyond my analytical skills at my age but the concept is simple.

 

[W.D.Clinger]

As for your complaints about the columns, I know Bažant and Verdure attempt to motivate their model by talking about the columns, but it looks to me as though simplifying hypothesis (4) folds all effects of the column impacts into F_c. With that abstraction, I don't see how the source of F_c could have much effect on their mathematical model. That impression would seem to be confirmed by their short sections on Usefulness of Varying Demolition Mode and Analogous Problem---Crushing of Foam.

...

If F(c) wasn't based on buckling, no "crush down, then crush up" concept would exist in his writing. The "proof" of no early crush up involves comparing the "upward force" to the capacity of the upper columns to resist buckling. He concludes that because the upward force isn't sufficient to overcome the upper columns, no early crush up is possible.

Colour change mine.

I'd need to look at the force function again to state anything specific.

What you wrote above supports your stated belief that reading your posts should be left to those who "have FAR too much time on your hands."

I understand why "snapthrough" would increase the preponderance of crush-down over crush-up during most of a progressive collapse that starts on an upper floor, but I also understand the physical argument for that preponderance even without snapthrough. That much of Bažant and Verdure's argument is easy to understand and uncontroversial.

Quoting Major_Tom as your authority on this subject tells me you don't understand the physics any better than he does.

 

[Dave Rogers]

No. Any sensible descent time metric relates directly to the primary crush front propogation-to-ground timing.

Fair enough. It's still not clear to me that the descent time is necessarily maximised for the scenario that provides the maximum average retarding force on the upper block, because in principle less energetic collapse scenarios could involve progressive stages of partial collapse. In any case, the claim that any other mechanism would have resulted in a significantly smaller collapse time is pure speculation.

Dave

 

[femr2]

Granted that the WTC core only lasted a fraction of a second longer.

I'd suggest a larger margin...

BV commented on Ronan Point ...which hints at the sort of thing I have suggested in earlier posts. For the OOS floors replace the column crushing force with the floor joist shear off force and tidy up any loose ends. Then separately look at the core strip down.

Yes. I have a couple of simple models that have been configured to use similar metrics...

(Async model with varying CR)

My spreadsheet (slab) model can also be configured to ignore everything but floor connections, so might get around to graphing response to varying that strength.

Beyond my analytical skills at my age but the concept is simple.

The ol' spreadsheet model is here if you're curious...
http://femr2.ucoz.com/load/3-1-0-9


I think it would be better for the ROOSD outline to be implemented as a functional model though.

 

[pgimeno]

Is this conclusion by Bazant valid?

....(Quoting Bazant)...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 say 'No!'

It is valid within its context. That claim, by Bazant, Le, Greening and Benson, was directed to counter the allegations of CD that were in use by the time the article was written. Some background information can be found in the JONES and other truther sites, deriving CD out of PE, dust size, panels stuck in other buildings, behavior of the flying debris, etc.

And it's also easy to see that what a C(ontrolled)D(emolition) means is just nonsense when applied to the towers. Even if we assumed it was a purposeful tear down of the buildings at all, that hardly can be called "controlled" and I even cast doubts about it being able to be called "demolition" at all. Yes, I know that when you say CD you're stretching the meaning of the term to mean intentional tear-down, but that's not necessarily the authors' purpose.

There's just one bit that is really wrong in the quoted paragraph:

... leave no doubt that the towers failed due to gravity-driven progressive collapse triggered by the effects of fire.​

That part specifically, certainly falls out of the scope of the paper and there's no justification within the paper to hold it. However, I'd say that, given that allegations of tearing down the building by inducing an apparently natural collapse were not widely known by the time they wrote that (nor are they now, anyway), it's still pretty justified in its context as the only competing popular alternative.

 

[femr2]

It is valid within its context. That claim, by Bazant, Le, Greening and Benson, was directed to counter the allegations of CD that were in use by the time the article was written.

The quote is BLGB March 2008.

ETA: Your statement implies other (newer?) allegations which the BLGB claim would not counter. What are you referring to ?

 

[Dave Rogers]

The quote is BLGB March 2008.

A quick look at the Journal of 9/11 Studies shows that they had by that date published at least twenty articles that claimed either explosives or thermite as the cause of the collapses of WTC1, 2 and/or 7, so I think it's fair to claim that allegations of CD had been made by that time.

Dave

 

[pgimeno]

The quote is BLGB March 2008.

ETA: Your statement implies other (newer?) allegations which the BLGB claim would not counter. What are you referring to ?

Do you even read what you reply to?

However, I'd say that, given that allegations of tearing down the building by inducing an apparently natural collapse were not widely known by the time they wrote that (nor are they now, anyway), it's still pretty justified in its context as the only competing popular alternative.

 

[femr2]

Do you even read what you reply to?

Of course. I was after specifics, but if allegations of tearing down the building by inducing an apparently natural collapse is as specific as you wish to state, okay.

Perhaps you should relax a little

 

[pgimeno]

Of course. I was after specifics, but if allegations of tearing down the building by inducing an apparently natural collapse is as specific as you wish to state, okay.

Yes, it is, because there's a non-specific range of allegations that fall into that category. For example, since you ask about specifics, the paper doesn't disprove the allegations that a team explicitly unscrewed some relevant bolts in advance.

 

[Major_Tom]

Pgimeno post 1534: "Yes, it is, because there's a non-specific range of allegations that fall into that category. For example, since you ask about specifics, the paper doesn't disprove the allegations that a team explicitly unscrewed some relevant bolts in advance. "


BLGB was published in 2008. In the forum page linked below I was having a conversation with two of the authors over the idea of OOS collapse propagation:

http://the911forum.freeforums.org/p...-twin-towers-and-collapse-mechanisms-t62.html

Notice how the thread was started by Frank Greening. Notice how most everyone agrees with something which sounds just like the collapse mechanism described in the OOS collapse propagation study. They just use different words. Notice how I use the term "open office space flooring" a few years ago, and neither of the authors disagrees with me.

Notice how the posters do not insult each other. The only person posting on that thread who had a difficult time with the concept of OOS collapse propagation was Dr Benson, who was insisting that "crush down, then crush up" is a real concept applicable to WTC1.

Notice the posts were made in 2008.


Frank Greening knew the main problem was the initiation sequence a few years ago. Many of the posters in that forum knew that in 2008, including two of the authors of BLGB. (Le was a grad student at NW U, so of the 3 PhD authors of BLGB, 2 were talking about OOS progression as the probable propagation mechanism with me in 2008.


It is interesting that everyone posting seems to agree on the same model of collapse (like ROOSD), except David Benson was quite convinced that the "upper block" survived and was actually "punctured" by the "spire". He really believed this.


Also, I asked Frank Greening why BLGB claims to "prove" demolition did not happen. He told me that it was not his idea to include the claim of "proof" in the paper. He never defended the claim like many here. He simply said it was not his choice to include it, meaning he doesn't agree with such a sweeping statement.

Later, David Benson also gave up on the solid upper block idea.

 

[Major_Tom]

At that link, Frank Greening, one of the authors of BLGB, says to me:

"Major Tom:

I agree!

In fact, after an upper block has dropped a few floors, a "natural" collapse is essentially indistinguishable from a controlled demolition.

So yes, it is all about collapse initiation....."

He knew in 2008. And he never defended BLGB as being "proof" like many of you here. Frank Greening seemed quite honest in contrast to many posters here.

 

[Major_Tom]

In fact, my conversations with Frank Greening, David Benson, Greg Urich, OneWhiteEye and others on that forum resulted in my version of the ROOSD idea.

(Ozeco and probably others coming up with essentially the same idea independently.)


Later, femr and achmispok discovered the whole width of the core survived, removing all doubt.

 

[newton3376]

Quoting Major_Tom as your authority on this subject tells me you don't understand the physics any better than he does.

And THAT is the heart of the issue.

You are arguing physics and math with people who do not have a very good understanding of either and make very large errors when talking about either topic.

This is why most engineers and scientists simply ignore them.

 

[alienentity]

At that link, Frank Greening, one of the authors of BLGB, says to me:

"Major Tom:

I agree!

In fact, after an upper block has dropped a few floors, a "natural" collapse is essentially indistinguishable from a controlled demolition.

So yes, it is all about collapse initiation....."

He knew in 2008. And he never defended BLGB as being "proof" like many of you here.

I don't think your conclusion is supported by the quotation. Greening himself refers to the 'upper block' explicitly, something you guys are arguing against, in fact.

All the quotation says is that there is no evidence of Controlled Demolition per se in the collapse. That a 'natural' collapse looks the same as a CD.

So really I think a fair, unbiased view is that the CD argument, if there ever was one, would be confined to the initiation, and I think that someone who is seriously pushing for that idea in 2011 is essentially joking or has profound judgment impairment.
Not to just leave it there - my opinion is based on the very important high-speed airplane impacts, the structural damage, and the fires.

Since this is a 9/11 conspiracy forum, let's focus on the conspiracy aspect: the only conspiracy that has any evidence is the one involving hijacked planes. The others are sheer speculation.

 

[alienentity]

In fact, my conversations with Frank Greening, David Benson, Greg Urich, OneWhiteEye and others on that forum was where my version of the ROOSD idea was developed.

(Ozeco and probably others coming up with essentially the same idea independently.)


Later, femr and achmispok discovered the whole width of the core survived, removing all doubt.

Whatever you believe, your concept needs to be properly published if it is ever to have a meaningful impact (that is what you desire, is it not?), and the physics discussion really doesn't belong on a 9/11 conspiracy forum, unless it is directly related to the issue of the controlled demolition hypothesis, IMO.

Why not discuss this on a regular engineering forum in the US? You could elicit the responses of dozens of engineers, maybe even from a few experts on tall buildings.