Has anyone seen a realistic explanation for "Progressive Collapse"

William Rea said:
I didn't say that at all!

The subject of progressive failure (or as we have it specifically for buildings progressive collapse) is fundamental for designers. I studied progressive failure from crack propogation and growth 20 years ago.

My point was that it appears to now be a cause of so much concern when engineers have known about this type of failure for years. I drew back from saying it in my post but I will say it now, the NIST "Best Practice" also looks like a publicity exercise to make it look like something is being done when it always has been!
Click to expand...
Publicity? For what audience? Structural engineers?
 
DHR said:
Steel weakons with heat.
Click to expand...

That must be why all these years the UK Building Regulations have had requirements for fire protection to steel members!

How could I have been so stoopid?

I thought they insisted on it just for fun!
 
Gravy said:
einsteen, you keep pointing out that in papers such as Greening's, the upper "block" of the towers is assumed to be infinitely strong. ...etc...
Click to expand...

I will be the first one to say that the energy required to crush a floor is hard or impossible to calculate from first principles (as Greening says) therefore he uses some estimates, one of them that gave no derivation and the second has to do with the plane crash. If you count 39 frames with an ntsf framerate the collapse of the first material (block goes down 3.8 meter, at that moment still a solid block) then you will empirically notice that it requires an energy of 1.3GJ, ok let's remove some frames due to error margins and we get the order of 1GJ for the weakest link, if the damage is enormous then the energy to crush the intact material will be much higher, that is a matter of finding a ratio.

I'm glad that the pancake theory is dead, it is the progressive collapse now, but Greening's article is more an article that shows that the energy picture is theoretically correct, of course 1000GJ is a lot, it doesn't give a realistic explanation of the process, the upper block will indeed crush in at least the same rate as the building if there is a collapse at all, which cannot be the case IMO (only assuming gravity driven, check the video and count frames). But I'm not the one assuming an infinitely strong upper block, I'm the messenger, it is Dr. Greening that uses this to calculate a collapse time, without this assumption there will be no collapse at all, no doubt about it.
 
einsteen said:
I will be the first one to say that the energy required to crush a floor is hard or impossible to calculate from first principles (as Greening says) therefore he uses some estimates, one of them that gave no derivation and the second has to do with the plane crash. If you count 39 frames with an ntsf framerate the collapse of the first material (block goes down 3.8 meter, at that moment still a solid block) then you will empirically notice that it requires an energy of 1.3GJ, ok let's remove some frames due to error margins and we get the order of 1GJ for the weakest link, if the damage is enormous then the energy to crush the intact material will be much higher, that is a matter of finding a ratio.

I'm glad that the pancake theory is dead, it is the progressive collapse now, but Greening's article is more an article that shows that the energy picture is theoretically correct, of course 1000GJ is a lot, it doesn't give a realistic explanation of the process, the upper block will indeed crush in at least the same rate as the building if there is a collapse at all, which cannot be the case IMO (only assuming gravity driven, check the video and count frames). But I'm not the one assuming an infinitely strong upper block, I'm the messenger, it is Dr. Greening that uses this to calculate a collapse time, without this assumption there will be no collapse at all, no doubt about it.
Click to expand...
:jaw-dropp
Well, I see that my ASCII art had no effect whatsoever. Nada. Niente. Zilch. The search for my true medium continues.
Sigh.
 
einsteen said:
But I'm not the one assuming an infinitely strong upper block, I'm the messenger, it is Dr. Greening that uses this to calculate a collapse time, without this assumption there will be no collapse at all, no doubt about it.
Click to expand...
For the last time, einsteen, Dr. Greening does not assume an infinitely strong upper block. He makes no assumptions about its state whatsoever.

Try reading his paper. It's found here. Next time you criticize his paper, I want to see you quote the part you're criticizing, and give a page number. No excuses.
 
For the last time: I've read it, I've reproduced his collapse times (not posted) and he does. The 1st stage of collapse assumes it keeps its height (n-1)h_floor. Infinitely strong is not the right word but it will not disintegrate during the 1st stage of collapse, RTFP. I'm going to contact him soon. There is no constructive discussion possible about this paper, I've tried it for a month I think, it's better to leave here for me and search an other critics forum.
 
Last edited:
Bazant

Before I wade through his other papers in detail can someone tell me is Bazant considered and authority on the WTC collapse?
 
Dr. Bazant does consider the upper impacting part of the towers to behave as a rigid body in the derivation of his equations.

Dr. Bazant has published a few papers on the World Trade Center. I have his book Stability of Structures: Elastic, Inelastic, Fracture, and Damage Theories, and I will tell you it is not for the faint of heart.

Interestingly, there is a bit of a p-ssing contest going on between Dr. Bazant and Dr. Cherepanov of Harvard University...Dr. Cherepanov being the proponent of the "fracture wave" theory of collapse, which is far less popular. Dr. Cherepanov's 18-page paper starts off with a 4-page political "rant" (possibly not the most accurate description, or the most apropos, but first thing I thought) in which he criticizes the War in Iraq and Afghanistan, recounts watching David Ray Griffin on Larry King, and rails against millionaires and billionaires and "money is power"...not hard to figure out why that didn't get accepted into engineering journals...(however I should point out that Dr. Cherepanov does not buy into the explosive or CD theory)
 
Last edited:
einsteen said:
For the last time: I've read it, I've reproduced his collapse times (not posted) and he does. The 1st stage of collapse assumes it keeps its height (n-1)h_floor. Infinitely strong is not the right word but it will not disintegrate during the 1st stage of collapse, RTFP. I'm going to contact him soon. There is no constructive discussion possible about this paper, I've tried it for a month I think, it's better to leave here for me and search an other critics forum.
Click to expand...

Dude, READ BEFORE YOU POST:

Next time you criticize his paper, I want to see you quote the part you're criticizing, and give a page number. No excuses.
Click to expand...

If you can't do that, you're making stuff up. You did it again. See??
 
Augustine said:
Dr. Bazant does consider the upper impacting part of the towers to behave as a rigid body in the derivation of his equations.

Dr. Bazant has published a few papers on the World Trade Center. I have his book Stability of Structures: Elastic, Inelastic, Fracture, and Damage Theories, and I will tell you it is not for the faint of heart.

Interestingly, there is a bit of a p-ssing contest going on between Dr. Bazant and Dr. Cherepanov of Harvard University...Dr. Cherepanov being the proponent of the "fracture wave" theory of collapse, which is far less popular. Dr. Cherepanov's 18-page paper starts off with a 4-page political "rant" (possibly not the most accurate description, or the most apropos, but first thing I thought) in which he criticizes the War in Iraq and Afghanistan, recounts watching David Ray Griffin on Larry King, and rails against millionaires and billionaires and "money is power"...not hard to figure out why that didn't get accepted into engineering journals...(however I should point out that Dr. Cherepanov does not buy into the explosive or CD theory)
Click to expand...

Welcome.
Ah I wondered who he was talking about in his newer paper.
Under PDF's called ProgressiveCollapseWTC-6-23-2006.pdf
http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/

Edit....Ah and then his newest paper from 10/9 Progre-RebutCherepanovCritiqueOfBazZhouWTC-06.pdf

Looks like I'll have to track down Cherepanov's paper.
Ah nevermind, here it is
http://www.genadycherepanov.com/More911.asp
 
Last edited:
Correction: It appears I was inaccurate...Dr. Cherepanov left Harvard some 15 years ago, taught at Florida International University until 1998, and apparently is publishing his latest critiques from his living room (?) (although it certainly explains why there is no graduate student co-author)...needless to say, I think Dr. Bazant gets the nod...
 
Last edited:
Einsteen, if I may try:

Drs. Greening and Bazant do not imply that the failure propagation front does not move upward as well as downward. Clearly it does. However, the mistake is to assume that it propagates upward at the same rate as it propagates downward. It is clearly impossible to have 29 floors fall, equal failure propagation fronts, and at floor 52, collapse stops with 58 floors worth of rubble sitting on top. That fails floor 52, etc., etc.

The failure propagation front progresses downward much faster than it progresses upward, because the "disintegrated" floors will continue to impel the downward propagating front, while actually reducing the upward propagating front. Capiche?

(Just to add to the confusion, if it exists: I do believe that implicit in Dr. Greening's paper is an "essentially rigid" upper block; however this is definitely not the same as infinitely strong, and only implies that the upper block, because of dimensions, collapsed essentially planar, i.e. with minimal warping. It certainly simplifies the analysis to 2-D, and is a justifiable and valid assumption.)
 
Augustine said:
Correction: It appears I was inaccurate...Dr. Cherepanov left Harvard some 15 years ago, taught at Florida International University until 1998, and apparently is publishing his latest critiques from his living room (?) (although it certainly explains why there is no graduate student co-author)...needless to say, I think Dr. Bazant gets the nod...
Click to expand...

Without doubt. Thanks again for some of the new info. PLEASE stick around!
 
William Rea said:
So we just proved that your analogy and mine were both worthless and entertained huntsman enough for him to make another hopeless attempt at undermining my argument using that used razor blunt wit of his.
Click to expand...
I was offering an illustration, not a scale analogue. However, the detailed work by a variety of far sharper folks than I have been linked to, and offer a better discussion of the matter than I can. I will let their comments be a better reference than a 9th grade level illustration of an impact load on a box lattice structure.

DR
 
William Rea said:
You think an Engineer would be fooled by that?
Click to expand...
William, it's a paper written by engineers, for engineers. It's not intended for the general public. It's not on Oprah's book list. You'll have to ask engineers what they think of it.
 
Augustine said:
Einsteen, if I may try:

Drs. Greening and Bazant do not imply that the failure propagation front does not move upward as well as downward. Clearly it does. However, the mistake is to assume that it propagates upward at the same rate as it propagates downward. It is clearly impossible to have 29 floors fall, equal failure propagation fronts, and at floor 52, collapse stops with 58 floors worth of rubble sitting on top. That fails floor 52, etc., etc.

The failure propagation front progresses downward much faster than it progresses upward, because the "disintegrated" floors will continue to impel the downward propagating front, while actually reducing the upward propagating front. Capiche?

(Just to add to the confusion, if it exists: I do believe that implicit in Dr. Greening's paper is an "essentially rigid" upper block; however this is definitely not the same as infinitely strong, and only implies that the upper block, because of dimensions, collapsed essentially planar, i.e. with minimal warping. It certainly simplifies the analysis to 2-D, and is a justifiable and valid assumption.)
Click to expand...
Excellent summary, thanks.

I'd like to reiterate, criticism of papers is welcome. But just firing off an accusation about them is not, because we may not know what one is referring to. If you would criticise a point, please show us the part of the paper you are criticizing. Extract the quote, give a page number, explain your concern. It makes the discussion much easier to follow. Thanks!
 
You must log in or register to reply here.

Back
Top Bottom