Cherepanov's "fracture wave" theory

[Kryptos]

I'm looking for Cherepanov's paper on the WTC collapse, which suggest a "fracture wave" theory rather than progressive collapse. Is it posted anywhere online?

* Mechanics of the WTC collapse. Author: Cherepanov, G.1. Source: International Journal of Fracture, Volume 141, Numbers 1-2, September 2006 , pp. 287-289(3)

In his comments to NIST, he says that Bazant's explanation, progressive collapse, does not explain "free fall", "sound of explosions produced by each collapse", "pulverization of the buildings collapsed". And that WTC7 should not have collapsed. I have seen Bazant's rebuttal. Besides that, has anyone else written a response to Cherepanov's paper?

[cmcaulif]

its available at his website (http://www.genadycherepanov.com/), here is the full text:
http://www.genadycherepanov.com/OnTheWTC_PDF.pdf

I haven't looked into it a whole lot, and its hard to read a paper objectively since I have already read the rebuttal.

[Kryptos]

its available at his website (http://www.genadycherepanov.com/), here is the full text:
http://www.genadycherepanov.com/OnTheWTC_PDF.pdf

I haven't looked into it a whole lot, and its hard to read a paper objectively since I have already read the rebuttal.

I'm not sure that's the same version of the paper that was submitted to the journal. The first few pages were going on about politics, David Ray Griffin, and other topics. I'm not sure that would all be acceptable for the "International Journal of Fracture".

I'd like to get the 3 page version that was in the journal, preferably an electronic copy. Otherwise, I have take the better part of a Saturday (or Sunday) afternoon and go to the nearest university library that would have this journal and photocopy the 3 pages.

The reason that I ask is that someone on Wikipedia is citing Cherepanov, as criticizing Bazant and progressive collapse "for ignoring the resistance of the underlying structure, which may have slowed a progressive collapse much more dramatically and even prevented it altogether." I need to go in there and fix that section. I'm not sure if that is an accurate characterization of Cherepanov's paper, or how better to explain his "fracture wave" theory. And then add mention of Bazant's rebuttal.

[cmcaulif]

I'm not sure that's the same version of the paper that was submitted to the journal. The first few pages were going on about politics, David Ray Griffin, and other topics. I'm not sure that would all be acceptable for the "International Journal of Fracture".

I'd like to get the 3 page version that was in the journal, preferably an electronic copy. Otherwise, I have take the better part of a Saturday (or Sunday) afternoon and go to the nearest university library that would have this journal and photocopy the 3 pages.

sorry, I can't help you there. I don't have access to that journal.

The reason that I ask is that someone on Wikipedia is citing Cherepanov, as criticizing Bazant and progressive collapse "for ignoring the resistance of the underlying structure, which may have slowed a progressive collapse much more dramatically and even prevented it altogether." I need to go in there and fix that section. I'm not sure if that is an accurate characterization of Cherepanov's paper, or how better to explain his "fracture wave" theory. And then add mention of Bazant's rebuttal.

In Bazant's critique, he says that Cherapanov ignores dynamic snap through, meaning he is basically considering static and dynamic buckling as the same, which is erroneous. You can check out the the force displacement curve in figure 3 of Bazant and Verdure, which show that peak resistance of the columns is reached quickly before snapthrough buckling occurs, so its clear from this that the columns in the lower structure will not have a significant ability to cause large decelerations on the upper block. Figure 4 shows this as well, deceleration of the crushing front only occurs for a very small portion of one story height.

link to B&V (http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf)

I'm sure some of the pros could give a better explaination as well.

[bofors]

its available at his website (http://www.genadycherepanov.com/), here is the full text:
http://www.genadycherepanov.com/OnTheWTC_PDF.pdf


That is a different paper:

Cherepanov, G.P. (2006). On the collapse of the World
Trade Center on September 11, 2002. J. of Applied
Physics, in print.

Kryptos asked for this:

2. Cherepanov, G.P. (2006). September 1 and fracture
mechanics. Int.J. of Fracture, Vol 132 (2), pp. L25--
L26



I haven't looked into it a whole lot, and its hard to read a paper objectively since I have already read the rebuttal.

Regarding, the rebuttal, I assume you mean this by Bazant: http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/Progre-RebutCherepanovCritiqueOfBazZhouWTC-06.pdf

[bofors]

I'd like to get the 3 page version that was in the journal, preferably an electronic copy. Otherwise, I have take the better part of a Saturday (or Sunday) afternoon and go to the nearest university library that would have this journal and photocopy the 3 pages.

If you get this, can you post a copy here?

[bofors]

You can check out the the force displacement curve in figure 3 of Bazant and Verdure, which show that peak resistance of the columns is reached quickly before snapthrough buckling occurs, so its clear from this that the columns in the lower structure will not have a significant ability to cause large decelerations on the upper block.


I have some questions about B&V 2007, Figure 3.

(1) Where is the experimental data that proves this hypothetical curve F(u) is correct even for a one story building?

(2) Why do B&V work with a one story diagram, when the WTC towers were much higher?

(3) While I can understand "snapping through" a floor, how is it possible to "snap though" a column?

(4) How is Wc calculated in terms of elastic and inelastic energy dissipation?

(5) How does Wc scale with the number of stories considered?

(6) Why are only three (or four) "hinges" considered?

(7) How was it determined that Uc was above Uf in the case of the WTC towers?

(8) How is tilting, bending or tipping over accounted for in such a one-dimensional analysis?

[cmcaulif]

are you serious bofors? ALL of your questions can be answered by

1) reading the references provided in Bazant and Verdure

and

2) reading Bazant and Verdure itself

I'm not going to do your homework for you, or spoon feed you information. This kind of trolling is ridiculous.

[bofors]

ALL of your questions can be answered by...

No, they can't and as you know I have read at least part of B&Z 2002.

Now, if eight questions is too much for you to handle, then just try this one:

(3) How is it possible to "snap though" a (one-dimensional) column?

[cmcaulif]

So you are indeed trolling, you do indeed fail to recognize that your questions can be answered by the textbooks and other references in B&V, since they are conceptual, and do not necessarily pertain to B&V specifically, and you have not actually read the paper(becoming your trademark) which answers the rest of your questions?

got it.

Not to mention that question 7 is stundie material

If you don't know what snap through is, research dynamic buckling. If you are not willing to do basic research on these topics, there is no point in bothering with you.

[Kryptos]

sorry, I can't help you there. I don't have access to that journal.



In Bazant's critique, he says that Cherapanov ignores dynamic snap through, meaning he is basically considering static and dynamic buckling as the same, which is erroneous. You can check out the the force displacement curve in figure 3 of Bazant and Verdure, which show that peak resistance of the columns is reached quickly before snapthrough buckling occurs, so its clear from this that the columns in the lower structure will not have a significant ability to cause large decelerations on the upper block. Figure 4 shows this as well, deceleration of the crushing front only occurs for a very small portion of one story height.

link to B&V (http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf)

I'm sure some of the pros could give a better explaination as well.

I think I understand "dynamic buckling" (applied suddenly) versus "static buckling" (slowly applied). There is something about this on Wikipedia, which is helpful, for a layman to understand.

Looking through B&V (2006) in detail, I notice they mention "Fracture Wave" theory twice. They explain that theory does not account for kinetic energy combined with the weight of the above structure. Including that, the energy is 8.4 times larger than what the floor beneath can withstand.

The 2007 Bazant et al paper also addresses the "fracture wave" theory, which is helpful. Though, I need to think about how to best to explain this.

[bofors]

If you don't know what snap through is, research dynamic buckling. If you are not willing to do basic research on these topics, there is no point in bothering with you.

If you refuse to answer some simple questions about the theories you advocate, why should people believe that you even begin understand what you are talking about?

[bofors]

I think I understand "dynamic buckling" (applied suddenly) versus "static buckling" (slowly applied). There is something about this on Wikipedia, which is helpful, for a layman to understand.


Stress under "static buckling" would not be slowly applied because even that it dynamic.

No, "static buckling" would mean something like "creep buckling" where heat is applied under constant load and buckles develop.



Looking through B&V (2006) in detail, I notice they mention "Fracture Wave" theory twice. They explain that theory does not account for kinetic energy combined with the weight of the above structure.


This part is actually true, Cherepanov 2006 Equation 13 is wrong this way, it fails to add the weight of the above structure.


Including that, the energy is 8.4 times larger than what the floor beneath can withstand.


This is just one place that Bazant's analysis is absurd. Every floor below the critical floor elastically absorbs the supposed impact energy, not just one floor. So, in terms of elastic analysis Bazant is off by a factor of 80 or so (how many floors there were below the first supposed impact floor).


The 2007 Bazant et al paper also addresses the "fracture wave" theory, which is helpful. Though, I need to think about how to best to explain this.

Cheerepanov's "fracture wave" theory is probably more absurb than the crap Bazant is promoting. Cheerepanov seems to think steal is a brittle material like glass, indeed his 1979 book is titled "Mechanics of Brittle Fracture".

Cheerepanov's ridiculous theory is that... uh... tensile... fractures from thermal stresses developed in the WTC towers because of the fire and then... some how... propagate all the way down.

Cheerepanov seems to propose that residual thermal stresses exist in a ductile material like steal just like they do in a glass. This should be quite easy to prove false.

[bofors]

I'm looking for Cherepanov's paper on the WTC collapse, which suggest a "fracture wave" theory rather than progressive collapse. Is it posted anywhere online?

* Mechanics of the WTC collapse. Author: Cherepanov, G.1. Source: International Journal of Fracture, Volume 141, Numbers 1-2, September 2006 , pp. 287-289(3)

Here is the abstract:

Two theories of the WTC collapse are examined. The first one is the theory of progressive failure, and the other one is the theory of fracture waves. The collapse in the regime of progressive failure is shown to occur at an acceleration, which is several times less than the gravitational acceleration and, hence, this theory contradicts to the observed free fall. Evidently, the WTC towers were disintegrated at the very beginning of each collapse. To explain this fact an alternative model based on the theory of failure waves is proposed.
http://www.springerlink.com/content/m12508qnr8205172/?p=69d060c2f5a34fb6aea38456791fd479&pi=20

It is also worth noting, because it shows that Cherepanov is thinking about glass (indeed he references "Batavian" tears in his WTC paper linked above), that Cherepanov published this in the same journal this:

On Self-Sustaining Fracture Waves

The breakage of a tiny tail on a head of solid glass just removed from a glass bath and treated by fluoric acid (a “Batavian tear") makes the tear explode into a cloud of dust with the sound like that of a shot. This explosion reminds that of TNT but TNT disintegrates into molecules of the order of 10?9 m while the glass particles of dust are of the order of 10?6 m and have the same chemical composition as the solid glass. Rock bursts in deep mines of South Africa and Russia represent another example of the sudden, explosive self-destruction. To explain this phenomenon the theory of self-sustaining fracture waves was suggested earlier by Galin and Cherepanov (1966). This theory was based on the analogy with detonation waves later criticized as insufficiently substantiated. The approach presented below is based only on the conservation laws and does not use any analogies. It proves that the self-sustaining fracture wave can propagate only in compressed structures at the speed of longitudinal elastic waves.

This clearly shows how warped Cherepanov's thinking is.

[cmcaulif]

If you refuse to answer some simple questions about the theories you advocate, why should people believe that you even begin understand what you are talking about?

Your questions were not meant to provoke discussion or critical thinking, they are all answered by reading the paper or by reading bazants references, or perhaps other references on background info if you prefer.

You are either asking me to spoon feed you info which you should know or can easily find, or jump through hoops for no reason, since your questions are all conceptual, and do not involve a criticism. I wont do either of those things.

Read the paper, post criticisms where you have them, but this behavior is absurd.

[cmcaulif]

This is just one place that Bazant's analysis is absurd. Every floor below the critical floor elastically absorbs the supposed impact energy, not just one floor. So, in terms of elastic analysis Bazant is off by a factor of 80 or so (how many floors there were below the first supposed impact floor).


Why are you considering elastic energy dissipation when they state explicitly that Wp is the plastically dissipated energy?

There will be energy elastically dissipated, but in order for them to be off by a factor of 80 like you say, the entire building would have to buckle at the same time, since you can't count this type of energy dissipation until after buckling has occurred, and you cant use a combined hinge rotation of 2pi until buckling has occurred completely. This is stated quite clearly in the paper by the way

[bofors]

Why are you considering elastic energy dissipation when they state explicitly that Wp is the plastically dissipated energy?


A proper analysis would consider elastic (We) and plastic (Wp) dissipation in relation to the potential energy (Wg).

Basically, Bazant seems to be arguing that:

Wg >> (We + Wp)

However, Bazant's analysis of all three fractors is obviously wrong.


There will be energy elastically dissipated, but in order for them to be off by a factor of 80 like you say, the entire building would have to buckle at the same time, since you can't count this type of energy dissipation until after buckling has occurred,


No... elastic deformation proceeds plastic deformation. A rubber band elastically stretches before it breaks, right?

The same is true with metals:

http://www.auf.asn.au/const_images/stress_strain3.jpg

As indicated at the bottom of the diagram in green, the "elastic zone" is on the left so it is first, then the "plastic zone" is on the right, as it is last.

Understand?

[cmcaulif]

A proper analysis would consider elastic (We) and plastic (Wp) dissipation in relation to the potential energy (Wg).

Basically, Bazant seems to be arguing that:

Wg >> (We + Wp)

However, Bazant's analysis of all three fractors is obviously wrong.

he is not arguing that in Bazant and Zhou equation 3, he is referring to the energy dissipated plastically.



No... elastic deformation proceeds plastic deformation. A rubber band elastically stretches before it breaks, right?

The same is true with metals:

http://www.auf.asn.au/const_images/stress_strain3.jpg

As indicated at the bottom of the diagram in green, the "elastic zone" is on the left so it is first, then the "plastic zone" is on the right, as it is last.

Understand?

LOL, so you started out by not reading the NIST report, then you moved on to not reading Bazants papers, now you have moved on to not reading posts on this forum.

I realize this, and acknowledge it in the above post. The point is that you cannot include any members in the Wp calculation unless they have buckled completely, and if you want to include We, you have to realize it is tiny in comparison to Wp especially given the fact that B&Z use the very generous 2pi as the sum of rotation angles, and We is not absorbed over 80 floors, making your criticism that they are off by a factor of 80 completely wrong.

[Mangoose]

Kryptos....I have both articles from the journal....PM me and I will give you my email.

[bofors]

he is not arguing that in Bazant and Zhou equation 3, he is referring to the energy dissipated plastically.


Since the Cherepanov paper is quite obviously ridiculous (it is based on the application of a demolition wave equation to etched glass) unless one introduces explosive charges, I am going back to the related topic: B&Z 2002.


The point is that you cannot include any members in the Wp calculation unless they have buckled completely...


Any plastic deformation, whether it represents a "complete buckle" or not, absorbs energy and should be included in a proper Wp calculation.


We is not absorbed over 80 floors.

You mean: all 80 some floors do not contribute to We.

In a simple one-dimensional analysis, which is what Bazant limits himself to, they certainly do.

A long spring can elastically absorb more energy in compression (before it plastically deforms) than a short one, just like the fact that you can strench a longer rubber band farther than a short one before it breaks.

Elastic energy is dispersed across all the atomic bonds, not just a few of them.

[rwguinn]

Since the Cherepanov paper is quite obviously ridiculous (it is based on the application of a demolition wave equation to etched glass), I am going back to the related topic: B&Z 2002.



Any plastic deformation, whether it represents a "complete buckle" or not, absorbs energy and should be included in a proper Wp calculation.



You mean: all 80 some floors do not contribute to We.

In a simple one-dimensional analysis, which is what Bazant limits himself to, they certainly do.

A long spring can elastically absorb more energy in compression than a short one, just like the fact that you can strench a longer rubber band farther than a short one before it breaks. Elastic energy is dispersed across all the atomic bonds, not just a few of them.
This is my last reponse to you, buit because it is important, I'm going to respond on this one.
The 80-odd floors are NOT a "Long Spring". They form 80-odd SHORT springs. For the appropriate analogy, take your rubber band and tie lots of short rubberbands to it at regular intervals, then tie the short ones to ground at their other end.

[cmcaulif]

plastic deformation below the crushing front in the B&V model is highly unlikely, a column cant transmit a load larger than it can bear itself.

I have no idea why you think 80 floors would act as ONE spring by the way, plenty on that in this thread (http://forums.randi.org/showthread.php?t=97584) especially the appendices.

[bofors]

The 80-odd floors are NOT a "Long Spring". They form 80-odd SHORT springs.


Come on now, this is basic physics.

One 80-floor spring or 80 one-floor springs, it makes no differnce, my point still stands.

See how the entire springs contracts (not just the part of it near the mass block):

http://upload.wikimedia.org/wikipedia/commons/9/9d/Simple_harmonic_oscillator.gif

[cmcaulif]

there is already a thread, which YOU started, for discussing B&Z by the way

[bofors]

plastic deformation below the crushing front in the B&V model is highly unlikely...


Sure... but the exact length of the crushing front would is an important question, something Bazant seems to ignore (or rather just assumes is a floor or two).


...a column cant transmit a load larger than it can bear itself.


Sure... but that does not mean that no energy is elastically transferred either. Basically, the amount of energy that can be transferred elastically is transferred elastically. This is not zero as Bazant proposes and under his simple (and absurd) impact model, the amount of energy that can be transferred in elastically is 100%. See B&Z 2002, pape 2, Figure 2(a).


I have no idea why you think 80 floors would act as ONE spring by the way, plenty on that in this thread (http://forums.randi.org/showthread.php?t=97584) especially the appendices.

Thanks for reference, I will look at the thread and hopefully find the appendices.

[cmcaulif]

the lenght of the crushing front will be short because as I said, a column can't transmit a load larger than it can bear itself. In order for 'crushing' to occur you need plastic deformation. If you have a column with a Pcr of X on top of a column with a Pcr of X+A, the column on top will fail first.

Sure... but that does not mean that no energy is elastically transferred either. Basically, the amoung of energy that can be transferred elastically is transferred elastically. This is not zero as Bazant proposes and under his simple (and absurd) impact model, the amount of energy that can be transferred in elastically is 100%. See B&Z 2002, pape 2, Figure 2(a).

I never said that no elastic deformation would occur, I said plastic deformation is unlikely, then I linked you to a post, with links in the op which calculates the elastic deformation below the crushing front.

FFS, it helps to read what I post don't you think?

[bofors]

... then I linked you to a post, with links in the op which calculates the elastic deformation below the crushing front.

I am looking at Newton Bit's work now, thank you.

[Dave Rogers]

A proper analysis would consider elastic (We) and plastic (Wp) dissipation in relation to the potential energy (Wg).

Basically, Bazant seems to be arguing that:

Wg >> (We + Wp)

Actually, I'd question that, although the engineers round here may be able to set me straight. Consider the sequence:

1) Initial impact. All the energy is kinetic, equal to Wg.
2) Elastic compression phase. Elastic energy increases to We, kinetic decreases to Wg-We. If Wg>We, we have progression to:
3) Plastic deformation phase. This progresses to the failure point, where plastic deformation energy is Wp. Kinetic energy is now Wg-We-Wp.

The failed columns have now fractured, so can not be under elastic strain. The total energy of the system is therefore the sum of kinetic + plastic, i.e. E(total) = Wg-We-Wp+Wp = Wg-We.

Where did We go? (Wrong?)

Doesn't the elastic energy dissipate into the plastic deformation phase as the failing columns unload, hence effectively being recovered and reducing the energy requirement to Wg > MAX(We, Wp) ?

Dave

[einsteen]

Come on now, this is basic physics.

One 80-floor spring or 80 one-floor springs, it makes no differnce, my point still stands.

See how the entire springs contracts (not just the part of it near the mass block):


I agree that one spring can be thought of as connected sub-springs. But the problem is that we have 110 point masses in this model. That makes it different, in two springs the force balance out very quickly but with a mass between it is different. In order to prove global collapse one should setup a model with n springs falling on 110-n springs, but not real springs but springs that have the property they are elastic (kx) at a small range in the beginning for example, then a plastic range and then a drop-down.

The "'springs" should become stronger when you go to the bottom, which implies that those of the impacting top section are weaker, but then the mass distribution is also highly relevant. Although the solution might be impossible to find the collapse could be substituted into it in order to check if it fits the equations. Major job.