Merged Applicability of Bazant's model to the real world

[tfk]

If you still don't understand why calculating the terminal velocity of a hypothetical apple to 4 decimal places set tom off, I'm afraid that's your fault.

Why don't you input some parameters into the ROOSD model and see how it works in the real world?

My point about the apple fall model was not the 6 significant figures. Although that was a historical point between femr & me.

My point was femr & MT's evident belief that finding a couple of aspects of reality that don't match up to a simplified model do not necessarily negate the whole model.

femr & MT appear to believe (they can speak for themselves) that any breakup (or even major breakup) of the upper block invalidate Bazant's model.

I disagree.

They appear to believe that a factor of 2 difference in the calculated descent speed invalidate BLGB's model.

I disagree.

MT states explicitly that the lack of bent & buckled columns negates Bazant's model.

I disagree.

In BZ & BV, Bazant constructs "continuum" models. This means that, in his model, there are no more columns, or air spaces, or concrete floors. There is a mysterious, non-defined substance that absorbs, continuously, the same average crush energy per floor that the towers (with their real columns, office contents, floors, trusses & air space) did.

Bazant explicitly states that he would not be the slightest surprised if his numbers were off by considerable factors. In one of his papers, he explicitly addressed the issue of "non-buckled columns" in the debris, and showed an idealized force vs. collapse curve that had about 1/10th the energy absorption as his "buckled column" limiting case.

So that was my point. Even with numeric errors in specific assumptions or in conclusions, there are valuable insights to be gained by his type of models.
___

I pointed out that the apple falling model required a radius of the falling object for its calculation. Not being a sphere, apples have no radius.

This is not a weakness of the model. The non-spherical variation is lost in the other uncertainties. Especially the drag coefficient of 0.5, which may be off by 20%.

(And anyone who posts 4, 5, or 6 significant digits as a result of a calculation, when one of your principle factors has a 20% error, is innumerate, i.e., numerically illiterate. An illiteracy of which femr adamantly stands proud)

But if I kept up a Johnnie-one-note tirade of "the falling apple is not valid because the apples aren't round", then I'd be the moron who didn't appreciate the value & the limits of the model.

Models are tools. They are also pieces of art.

Some people know how to use them. Some don't.
___

By the way, I've asked MT repeatedly what he thinks that Bazant proved. Exactly.

He's never replied.

Bazant did not prove that the buildings were not CD'd.
Bazant did prove that CD was not required for the crush down, once started, to propagate to the ground.

He proved that this one claim of the truthers (that in order for it to collapse completely without CD) was false.

 

[tsig]

Correct, a cartoon extreme case of a single collision. Correct, no attempt to derive real roof-line movement in BZ.



Exactly. Please explain this difference to Myriad.




The intention is to map the movement of real buildings in the case of 4 simplifying assumptions. The aim of the paper was to derive eqs of motion that can be fitted to real buildings.

So I agree, except for the word "can" in the last sentence. I'd replace it with "should". BV is trying to predict and match movement of real buildings.






I agree. Correct.



This is not true, but you have given the best summary outside of Ozeco from the debunker camp on this forum.

David Benson and poster OneWhiteEye of the 9/11 forum have studied that last point in detail over a couple of years.

It is important to realize that data is extracted from WTC1 using roof-line measurements and antenna measurements. If buffer system "zone B" does not effectively separate the top "block" from the lower "block" as Bazant describes, then his assumptions about roofline movement in his equations have no meaning.

His equations over the first 3 seconds of motion are totally reliant on "zone B" shielding the "upper block" from the "lower block". Great idea in 1-D. But in a world where columns can spear floor slabs and the two "blocks" can penetrate one another through column spearing and perimeter sheets can bypass one another, the predictions of roofline measurement from his equations have no meaning.


Leaving one last question: How did Dr Bazant get his equations to match data for the first 3 seconds of motion and seismic records? We were asking the same question 2 years ago.

You really don't understand what a 'limiting condition' is do you?

 

[tfk]

femr,

You know full well that is not the reason for the statement Tom. Try and recall the ever-increasing stack of...

's

Yup. I remember them well.

They appeared after multiple attempts by me to get you to answer those simple questions. You know, the ones that you have still not answered.

ozeco41, tfk is very prone to adjusting the scope of his statements at a latter date in the futile hope of appearing all *hard done-by*. I tend to track back through discussions quoting the full to-and-fro to ansure the context is kept accurate.


Here, tfk, have you forgotten a couple of responses ? ...

http://www.internationalskeptics.com/forums/showpost.php?p=6819759&postcount=1707
http://www.internationalskeptics.com/forums/showpost.php?p=6816588&postcount=1639


ROFL.

ROFL, indeed.

Thank you for making my point for me.

No, I didn't "forget" any responses.

You are now lying about them.

In your first link:
There is not one work about how you identify that ejecta as the collapse front versus a pressure pulse.

There is not one word about the external wall of the building being intact above your claimed collapse front.

In your second link:
There is not one work about how you identify that ejecta as the collapse front versus a pressure pulse.

There is not one word about the external wall of the building being intact above your claimed collapse front.

ROFL for me some more.

Please point to where you have explained how you demonstrate or argue or prove (not merely assert) that these images are the collapse front & not pressure pulses.

I'll reconstruct the entire recent discussion if you feel like harping-on

Reconstruct anything you want. It's all you do. Sit & type.

While you're at it, please show where you answered my 2 simple questions that started all your drama-queen theatrics.

The ONLY reply that I'm interested from you is a link to your sentences that start:

"The way that I distinguish the collapse front from a pressure wave is ..."

and

"My explanation for the ability of the external wall to remain standing while the collapse front passes it by, inside the building, is ..."

Anything else is just more of your blather.

 

[rwguinn]

I'm not an engineer, but I can answer that. By "Bazant's limiting case", you probably mean Bažant and Zhou 2002:

You should note, however, that Bažant and Zhou 2002 considers only the first impact, treating the entire lower section as a single unit. Their calculations show that some failure must occur within that lower section, from which an inductive argument would suffice to show that some kind of progressive collapse would follow, but Bažant and Zhou 2002 makes no attempt to model anything beyond that first impact.

That implies, of course, that any assumptions made in Bažant and Zhou 2002 are irrelevant to "the timing of the rest of the collapse". If someone tries to tell you otherwise, you can mark them down as an unreliable source.

(ETA: Let me qualify that. One paragraph of BZ contains a back-of-the-envelope calculation for collapse duration, but that calculation is superseded by later observations and papers (not just Bažant's), and I wouldn't trust that paragraph's conclusions. For present purposes, the interesting thing about that paragraph is that BZ's optimistic assumption of column-on-column impact makes the collapse faster, not slower, which may run counter to naive intuition.)

Bažant's subsequent papers and a closure, popularly known here as BV, BL, and BLGB (in chronological order), attempt to model the rest of the collapse by generalizing and extending the BZ model. The generalized and extended model is described in BV, defended against criticism by the closure known as BL, and refined further in BLGB. One of the generalizations made in BV (and continued in the subsequent BL and BLGB) is that BZ's optimistic assumption is no longer necessary. The BZ model remains a special case of the BV model, but the BV model can be applied even without that optimistic assumption.

Because the BV model attempts to describe the rest of the collapse, you could use it to discuss the timing. BLGB actually does that. I don't have the journal version of BLGB, but I have two different preprints, both designated as Structural Engineering Report No. 07-05/C605c. In the version dated 15 December 2007, the model's timing is compared with the seismic record in Figure 7; in the version dated 31 March 2008, that comparison is in Figure 8. That figure, however labelled, shows agreement for both towers to within the seismic and calculation errors.

That argues in favor of the model's applicability. Those who are arguing against the model's applicability tend to dismiss that result on various grounds, but I don't understand their objections well enough to summarize them.

Bull's eye.
Especially the bold red part.

 

[femr2]

your CD theory

What CD theory ?

Where is your math to go with your model

What model ?

The math with your 28 m/s visual stuff. The terminal velocity stuff?

Very little *math* required. Fature trace from video. Derived velocity plotted. Straight line around the 28m/s mark from about 4s after release.

You seem a little confused Beachnut, but, of course...

Have a nice day.

 

[tfk]

Oz,

YES and it's not just femr2 who has that bit right. It is something which I thought was known and taken for granted as the mainstream understanding of the 'collapse progression'.

What I have called 'global collapse' and described since 2008 as three parallel but staggered in time processes. Office space pancaking, ahead of and leaving the outer columns unbraced to fall later - not much later but definitely later - whilst the core failed mostly by strip down of the horizontal beams as indicated by the 'spires' which remained standing briefly after the main part of collapse was over.

Could you cite any authoritative figure who has offered this view. I'm not being chippy. I'm simply asking.

It is absolutely, utterly impossible that one could take a 50,000 ton block of scrap metal & debris, tilt it slightly, and drop it 5', 20', 50', 100' onto another lattice-work block of the same size, and expect the upper block to slide down inside the [ETA upper] lower one.

This applies REGARDLESS of whether the upper block stays together or is ripped apart in the collision with the lower part.

And anyone who has built a vertical fence, and then dumped a bunch of debris on one side of it, without bracing it on the other side, knows what happens to the fence: it get pushed over. If you dump the debris on top of the fence, it fails even faster.

There were, obviously, no diagonal bracing for those columns that prevented them from being pried outward, away from the building.

Those vertical walls were pathetically weak in the lateral (outward) direction compared to the loads that would have occurred.

Large segments of them stayed together precisely because the weakest links (connections to the floor trusses) fractured, and then they could flex outward, out of the way of the descending debris.

As the mass of compacted debris between the upper & lower portions of the building gathered, it HAD to get bigger & bigger. Not only vertically, but horizontally too. Very quickly, there would have been no way for it to fit inside the outer walls. (As I said at the start, there was really no way for it to fit inside from the very beginning.)

So, I disagree with the contention that somehow the crushing occurred within the building, leaving (even temporarily) a vertical wall or shell to collapse later.

If you (or anyone else) has any evidence of this happening, I'm all ears.

If your evidence holds up, I'll freely admit that I was wrong & change my mind.


Tom

 

[pgimeno]

I don't have the journal version of BLGB, but I have two different preprints, both designated as Structural Engineering Report No. 07-05/C605c. In the version dated 15 December 2007, the model's timing is compared with the seismic record in Figure 7; in the version dated 31 March 2008, that comparison is in Figure 8. That figure, however labelled, shows agreement for both towers to within the seismic and calculation errors.

I think that the following is the journal version; at least it's the one I think everyone here is using:

http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/476 WTC collapse.pdf

07-05/C605c is mentioned in the references. I think it's the one referenced in the part that says this (p.892, 1 of the PDF):

The objective of this paper, based on the report by Bažant et al. (2007) [...]​

 

[femr2]

Of the falling rubble layer.

Multiple crush fronts are evident, and estimating the effective *height* of the internal rubble layer(s) is likely very rough. Add to that the *upper block* (or what bits of it may remain) trailing behind (including the hat truss) possibly acting as a kind of wedge down through the core, pushing core masses and columns outwards...

All manner of *stuff* trailing behind the primary leading crush front.

I'd hazard a speculative suggestion that peeling is focussed on pivot points around the upper and lower mechanical regions.

 

[tfk]

Bump for femr,

...

The ONLY reply that I'm interested from you is a link to your sentences that start:

"The way that I distinguish the collapse front from a pressure wave is ..."

and

"My explanation for the ability of the external wall to remain standing while the collapse front passes it by, inside the building, is ..."

Anything else is just more of your blather.

"Have a nice day."

 

[pgimeno]

multiple crush ejection fronts are evident

ftfy.

 

[femr2]

But that's not what you did. You made a video on the subject. From your video, we can see the precision with which you measured things.

Ye gads man. The video took about 10 minutes. The values sourced from documentation of an *industry standard apple* (yeah there is such a thing). SI units used otherwise.

The point in posting was...

using a simplified model that doesn't incorporate the (highly chaotic) effects of wind, just Newton's laws, and that therefore predicts that the apple falls straight down, and gives a decent approximation to the speed of the fall.

For *an apple*, unless you include "the (highly chaotic) effects of wind" (and air resistance) you will not get "a decent approximation to the speed of the fall.".

The rest is irrelevant, but hey ho.

Have a nice day.

 

[femr2]

Beachnut, you misrepresented my quote and then totally supported the ROOSD concept.

Could you explain it to TFK? He is the last poster to not see what you've described.

What boggles me at the moment is tfk demanding an explanation of progressive collapse mechanics from yourself and I.

How can the perimeter POSSIBLY survive for a bit after a crush front or two wafts-on by ?!!11!1

Would you Christmas Eve it eh ?

 

[Major_Tom]

What boggles me at the moment is tfk demanding an explanation of progressive collapse mechanics from yourself and I.

How can the perimeter POSSIBLY survive for a bit after a crush front or two wafts-on by ?!!11!1

Would you Christmas Eve it eh ?

It's confusing.

Beachnut could actually teach TFK about the OOS collapse model. WD Clinger could teach Myriad about the difference between BV and BZ.

Ozeco could teach the other posters about how BV, BL and BLGB don't make much sense considering ROOSD. He has tried, but people start insulting him, too.



They don't really need us to see some basic contradictions, but keep accusing us various things....

Confusing.

 

[tfk]

Bump for femr,

The ONLY reply that I'm interested from you is a link to your sentences that start:

"The way that I distinguish the collapse front from a pressure wave is ..."

and

"My explanation for the ability of the external wall to remain standing while the collapse front passes it by, inside the building, is ..."

Anything else is just more of your blather.

 

[femr2]

One paragraph of BZ contains a back-of-the-envelope calculation for collapse duration, but that calculation is superseded by later observations and papers (not just Bažant's), and I wouldn't trust that paragraph's conclusions. For present purposes, the interesting thing about that paragraph is that BZ's optimistic assumption of column-on-column impact makes the collapse faster, not slower, which may run counter to naive intuition.)

Eh ? Can you quote that paragraph please ?

Carlitos was after a yes/no I imagine. I assume your basic response is yes (as any use of any flavour of the model by definition applies same parameters to all points in the continuum).

 

[femr2]

My point was femr & MT's evident belief that finding a couple of aspects of reality that don't match up to a simplified model do not necessarily negate the whole model.

Your inept assessment of *evident belief* is your problem.

Irrelevant waffle snipped.

Have a nice day.

 

[GlennB]

femr2, Major_Tom (et al) - let's suppose that the NISTian view of collapse initiation is flawed. What are you proposing to take its place, for all 3 buildings?

Detailed analysis of the actual behaviour and sequence of the actual events individually for all three buildings.

Something real rather than imaginary. Detailed observation and measurements can be put together in a list.

It's confusing.

It's certainly confusing to me that after 24 hours you aren't able to articulate your idea of WTC collapse initiation, even after all your research and thought. Maybe my question was unclear, so let me rephrase it ...

What do you believe led to collapse initiation in WTC1,2+7?

 

[femr2]

The ONLY reply that I'm interested from you is a link to your sentences that start:

ROFL.

I'm not here to pander to your whims tom. You can pick up the phone for services like that.

Don't start spamming now though, that would be bad.

(You can respond to the baby-step posts step-by-step if you like, and are free to word them however you please.)

Have a nice day.

 

[ozeco41]

Oz,
Could you cite any authoritative figure who has offered this view. I'm not being chippy. I'm simply asking...

Believe it or not "No I cannot." There are two main reasons. Briefly those are:

1. I have always taken the main mechanism as self evident - put a bit simplistically the top block fell down inside the outer tube of the lower tower causing the outer wall columns to peel off. Then add explanation of what happened to the core.
2. I have been explaining WTC collapse since late 2007 on a forum where the membership was biased towards the biological sciences. (the now defunct Richard Dawkins Net forum.) I was the only civil and military engineering qualified person taking part in debate. And, from my side, most of the debate was explanatory rather than rigorous with all the references to evidence you would put into hard science writing. I never kept copies of my work nor indexes to the supporting evidence.

Now the next part of your post is a description of how you think it happened.

...It is absolutely, utterly impossible that one could take a 50,000 ton block of scrap metal & debris, tilt it slightly, and drop it 5', 20', 50', 100' onto another lattice-work block of the same size, and expect the upper block to slide down inside the [ETA upper] lower one.

This applies REGARDLESS of whether the upper block stays together or is ripped apart in the collision with the lower part.

And anyone who has built a vertical fence, and then dumped a bunch of debris on one side of it, without bracing it on the other side, knows what happens to the fence: it get pushed over. If you dump the debris on top of the fence, it fails even faster.

There were, obviously, no diagonal bracing for those columns that prevented them from being pried outward, away from the building.

Those vertical walls were pathetically weak in the lateral (outward) direction compared to the loads that would have occurred.

Large segments of them stayed together precisely because the weakest links (connections to the floor trusses) fractured, and then they could flex outward, out of the way of the descending debris.

As the mass of compacted debris between the upper & lower portions of the building gathered, it HAD to get bigger & bigger. Not only vertically, but horizontally too. Very quickly, there would have been no way for it to fit inside the outer walls. (As I said at the start, there was really no way for it to fit inside from the very beginning.)...

At this stage why don't you read the latest version of my explanation. The history is that I lost access to all my explanatory posts when the Richard Dawkins Net forum closed - a lot of the refugees from Dawkins forum formed rationalskepticism forum and I re-wrote my explanation "off the top of my head" for the newcomers who wanted to discuss 9/11 and WTC collapse. On the surface it is different to yours but many of your points we agree on. Be warned it is not a scientific paper and will horrify you with the number of bald assertions. There is also one significant missing factor. Warts and all it is here.
http://www.rationalskepticism.org/c...-obligatory-9-11-thread-t515-680.html#p135852

Now we part company at your conclusion:

...So, I disagree with the contention that somehow the crushing occurred within the building, leaving (even temporarily) a vertical wall or shell to collapse later....

Again I cannot give the references - it is a point I have taken as given from late 2007 on. Memory tells me that I regularly used one of David S Chandlers early 'truther' videos which clearly shows the collapse front leaving outer wall standing behind it and a corner section remaining several stories after the internal collapse wave had passed.

...If you (or anyone else) has any evidence of this happening, I'm all ears...

I would appreciate any links also.

...If your evidence holds up, I'll freely admit that I was wrong & change my mind...

Understood.

 

[femr2]

Bull's eye.
Especially the bold red part.

Er...