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 International Skeptics Forum Merged: Applicability of Bazant's model to the real world

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 Tags collapse model , Zdenek Bazant

 28th August 2010, 01:57 PM #2 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by pgimeno the author welcomes any constructive criticisms aimed at addressing such inaccuracies as long as they are stated with arguments other than incredulity and disbelief, and preferably with sound engineering arguments. Firstly, it's good to see additional attempts at clarifying scope. A couple of points, which I hope you will not take as nit-picks... Quote: there's a new wave of 9/11 deniers who are misinterpreting them for discrediting purposes 9/11 deniers ? Strange turn of phrase. I've commented that there are folk who apply the model too literally, but the purpose is clarity, not *discrediting purposes*. Quote: Since the author's always been not-so-good for writing closing words, please indulge him in his use of [BLGB] to do it: 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. Ah. Not a great closure in my opinion. The model does not include initiation, and so does not deal with what caused failure. It proves that it is possible, post initiation, for gravity to drive progressive collapse. (ROOSD is imo a good description of that process) It does not disprove. To illustrate, and to illustrate only... If *evidence* arose tomorrow, which *proved* that *space aliens* *made it happen on purpose*, then the scope of the model does not change at all. The conclusion steps outside the bounds of model applicability. __________________ http://the911forum.freeforums.org
 28th August 2010, 02:06 PM #3 Major_Tom Graduate Poster   Join Date: Oct 2007 Posts: 1,960 Here is an excellent example of somebody applying the concept of crush down then crush up to the description of a 3-D building: Originally Posted by R.Mackey This is not the only factor, but it too is partially correct. Think of it in terms of impulse -- the total change of momentum at a particular impact. Impulse is equal and opposite, by conservation of momentum. Impulse is equal to F delta-T (force times the time over which the force is applied), or M delta-V (the raw change of momentum in its familiar definition P = m V). When we look at the "upper block," it's delta-V is smaller than the delta-V experienced by the newly broken part of the lower block. As you say, the upper block decelerates by an average 1/3 g, while the lower block accelerates by an average 2/3 g. This is because the participating part of the lower block masses less than the participating part of the upper block -- it really is the compacted mass and upper block versus a small number of floors at a time, not the entire lower block. The reason only part of the lower block participates at any given time is because the lower block is still a mostly intact sparse structure of braced columns. When it's hit, the columns lose bracing, get loaded eccentrically, shear their welds and bolts, and in some cases are totally overwhelmed and fracture entirely. These pieces break at a stress much too low to actually support the descending mass. This also has nothing to do with the strength of the perfectly intact building -- the descending rubble heap isn't contacting the lower structure at its strongest points, and it's introducing brand new failure modes, so the effective opposing strength of the lower structure is far lower than its ideal carrying capacity. Furthermore, where the lower structure does resist at or near its ideal strength, it can only do so for a very brief delta-T -- until reaching its failure strain, which takes only about ten milliseconds at the speeds of collapse -- and this is not enough to amount to all that much total impulse. The upper chunk, in contrast, is cushioned by a thick layer of rubble. This is compacted about as far as it can, thus it doesn't have those complex failure modes and it doesn't suffer much more "damage" even at much higher stresses. So the rubble pile remains, and the lower structure gives way. This is for the same reason you don't sink into the ground, even though you can push your finger easily through a cupful of soil. The "upper block," what remains of it, rides on top of this cushion of debris. It is supported pretty well. It also only decelerates at that lower rate, thanks to the much greater inertia of the upper block + debris. So the only real force it suffers is the inertial force, i.e. its own self-weight times its deceleration, again about 1/3 g. It can be expected to survive this deceleration. It's only when the rubble pile has nowhere else to go and the upper block has to suddenly stop, dissipating all of its momentum in mere milliseconds, that it totally fails. Again, this is slightly idealized, but you get the point. Unless you're a Truther. He calls this discription based on a literal interpretation of the 1-D stick model introduced in BV "slightly idealized". He clearly believes in the magic zone B rubble layer and the upper block that rides the rubble to earth like the Virgin Mother descending from the clouds. Honestly, pgimeno, is not R Mackey taking the 1-D concept of crush down, then crush up quite literally in his description? He seriously believes that this upper block exists, just like Bazant. Last edited by Major_Tom; 28th August 2010 at 02:10 PM.
 28th August 2010, 02:26 PM #4 pgimeno Illuminator     Join Date: Feb 2009 Location: Spain Posts: 3,343 Originally Posted by femr2 9/11 deniers ? Strange turn of phrase. I've commented that there are folk who apply the model too literally, but the purpose is clarity, not *discrediting purposes*. See below your post. Originally Posted by femr2 Ah. Not a great closure in my opinion. The model does not include initiation, and so does not deal with what caused failure. Ah, but that's because you're looking for the philosopher's stone, that thing which will make you rich and famous once you find any evidence of it and that you keep looking for because you know it must exist somewhere. That paragraph addresses the theories that were into fashion by then. But belief currents wear off too, e.g. nobody is pushing for thermate or freefall of the towers these days. __________________ Ask questions. Demand answers. But be prepared to accept the answers, or don't ask questions in the first place. Last edited by pgimeno; 28th August 2010 at 02:27 PM.
 28th August 2010, 03:11 PM #5 beachnut Penultimate Amazing     Join Date: Oct 2006 Location: Dog House Posts: 25,080 It is cool Bazant and company are able to do on a napkin what 911 truth can't do at all given all the answers and 8 years! Funny, 911 truth CD delusion cult members attack Bazant's model and fail to understand their attacks prove they don't understand models, engineering, and more. Where do their idiotic CD delusions come from? Bazant's model is like a trap to catch people with idiotic claims as they attack and comment on Bazant's work to expose their incompetence and ignorance. Why do they not have a clue. Kind of makes it clear they are not engineers, only a tiny fraction of engineers are prey to delusions like the lies 911 truth pushes. What level do you have to be at to understand without effort why the WTC Towers were doomed by impacts 7 to 11 times greater than design, and fires set with 66,000 pounds of accelerant! http://www.nae.edu/Publications/TheB...adeCenter.aspx Robertson, the first expert on the WTC towers structure The answer is easy, and can be found with google! Amazing Google can be used to support reality if you are capable of critical thinking and logical skills to weed out the lies, hearsay and delusions of 911 truth. Robertson calls the CD delusions nonsense. Google "lead structural engineer reflects, fall of the World Trade Center towers", and you find someone uniquely qualified to say the WTC towers fell due to impacts and fire. And he is proved correct by many independent studies, and he calls 911 truth claims nonsense. How many 911 truth failed idea believers will show up to attack Bazant and try to twist things so they can back in their favorite fantasy on 911? People should not attack Bazant's work, they need to do what it takes to complete their own work and see if it floats; publish it in a real journal. 911 truth can't do that, they can only attack NIST, Bazant's, and if they could do research I suppose they would attack the hundreds of other studies, papers and research showing impacts and fires did it. 911 truth are challenged researchers who can't find evidence or other work and understand those efforts to understand their claims are idiotic delusions. How many loyal 911 truth cult members will show up to battle Bazant and fail faster than free-fall? Last edited by beachnut; 28th August 2010 at 03:26 PM.
 28th August 2010, 03:59 PM #6 bill smith Philosopher     Join Date: Feb 2009 Posts: 8,408 Readers whould check out what Major Tom has to say in the link that pgimeno has distanced himself from. Is Bazant worthwhile ? Was Bazant ever worthwhile really ? http://www.internationalskeptics.com...3&postcount=83 __________________ *Think WTC7 - You cannot make the four corners of a table fall together unless you cut the four legs together *A kitchen table judgement on a world scale is enough * To Citizens: 'There comes a time when silence is betrayal'
 28th August 2010, 11:09 PM #8 ozeco41 Philosopher     Join Date: Mar 2009 Location: Moss Vale, NSW, Australia Posts: 7,422 Originally Posted by femr2 ...The model does not include initiation, and so does not deal with what caused failure. It proves that it is possible, post initiation, for gravity to drive progressive collapse... Good points. In extended discussion on another forum I tried to "nail down" CTs and truthers to which stage of collapse they were describing. For purposes of my own explanation the two critical stages were: 1) the progressive deterioration leading to the cascading failure of the "initial collapse"; AND 2) The global collapse. ..with the line between the two being the brief period when the top block first started its descent. At that point the columns of the lower tower were carrying less load than the full weight of the top block AND there was little if any axial contact of top block columns on lower tower columns AND such axial contact as may have existed was in a process of rapid buckling failure of said columns. Which gives a reliably defined boundary between the two stages. Then your point restated - the "initial collapse" caused failure - once that initial collapse started the top block descending then the "global collapse" was inevitable. This latter point as claimed by NIST, demonstrated in a limiting case analysis by Bazant AND independently determined by many others of us using our own variations of explnation.
 29th August 2010, 02:03 AM #9 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by ozeco41 Which gives a reliably defined boundary between the two stages. The more relvant point in the context of this thread is the erronious closure... Originally Posted by pgimeno 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. As I said, the model does not include initiation, and so does not deal with what caused initial failure. It does prove that, if the simplified initial state of the model is attained, post initiation, that it is possible for gravity alone to drive global collapse. (with a few caveats) It does not disprove. The conclusion steps outside the bounds of model applicability. (Clarification of bounds and scope being the entire point of this thread, this point should be made clear, and acknowledged by all.) __________________ http://the911forum.freeforums.org
 29th August 2010, 03:01 AM #10 ozeco41 Philosopher     Join Date: Mar 2009 Location: Moss Vale, NSW, Australia Posts: 7,422 Originally Posted by femr2 The more relvant point in the context of this thread is the erronious closure... As I said, the model does not include initiation, and so does not deal with what caused initial failure. It does prove that, if the simplified initial state of the model is attained, post initiation, that it is possible for gravity alone to drive global collapse. (with a few caveats).. Agreed all three points - sorry if it was not explicit enough in my previous. Quote: ...The conclusion steps outside the bounds of model applicability. ... ...it sure does.
 29th August 2010, 07:36 AM #11 pgimeno Illuminator     Join Date: Feb 2009 Location: Spain Posts: 3,343 Originally Posted by ozeco41 So "the column impacts would always be axial"?? Could anything be further from what actually happened with the twin towers on 9/11? Remember we are talking about the global collapse - the top block has started to fall - a point most people seem comfortable with. No, we're not talking about the global collapse. We are talking about a mathematical model of the collapse which is an approximation of it. That in itself makes it irrelevant how the impacts actually happened, just as the fact that greater than light speed is not contemplated or prevented by Newtonian physics. Despite the differences between model's behavior and real behavior which affects things like the way the columns impacted, the model still has many resemblances to real world and it can be used for that purpose, just not e.g. for how the column impacts actually happened, just as Newtonian physics can still be used to obtain very good approximations of how objects behave, just not for cases where the speed approaches light speed. Originally Posted by ozeco41 So what "axial load transfer" are all these papers talking of when they miss this point? I think it's you who is missing the point. The point is that it doesn't matter - the differences in the impact behavior can still make little differences in many of the results. However, actual impact behavior is very difficult to model as there's a cloud of uncertainty surrounding it, while axial impact behavior has been modeled successfully. Granted, there's still the concern that the results making big differences and the ones making little differences need to be separated. In that sense, [BLGB] is a good reference as it compares the model against several real-world parameters. __________________ Ask questions. Demand answers. But be prepared to accept the answers, or don't ask questions in the first place.
 29th August 2010, 09:10 AM #13 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by metamars If anybody ever does this, it'll probably be an open-minded member of the911forum.freeforums.org, not ae911truth or a serial debunker member of JREF. There has been much discussion of the model there of course, but the main problem, as far as I am aware, is the omission of the form of the force function used in B&L. I'd like to see the function provided, and the model implemented with those handy computer things, such that it is possible to: a) regenerate and replicate the published results b) test parameter sensitivity __________________ http://the911forum.freeforums.org
 29th August 2010, 10:18 AM #16 Major_Tom Graduate Poster   Join Date: Oct 2007 Posts: 1,960 The Bazant Zhao argument of 12 ft freefall before the first collision has been a total red herring. We want to know what initiated collapse, not whether the building would bounce after a 12 ft fall. Metamars writes in post #12: "If you just gently rested the top block on the bottom block, but 'off-center' (columns resting on floors, except when outside the footprint of the base), then I expect the building to collapse. You wouldn't even need to drop it by one storey height. " Exactly. If this is true why would anyone argue for a big bounce after 12 ft? It's an argument for suckers. The demo would initiate collapse and once those columns are displaced is there any reason to expect the building to fare well? I don't care if buildings were designed to survive a good bounce. I care about what initiated collapse. It's a total red herring as both Bazant and the NIST skip over the real issue of the initial column failure sequence.
 29th August 2010, 10:24 AM #17 Major_Tom Graduate Poster   Join Date: Oct 2007 Posts: 1,960 Pgimeno, you seem to be very impressed by the publication process. We are debating here, now, on this forum. If you cannot tell the difference between a 1-D stick model and the real towers here, now, how will it help you if you see our arguments in print? Last edited by Major_Tom; 29th August 2010 at 10:25 AM.
 29th August 2010, 10:34 AM #18 Major_Tom Graduate Poster   Join Date: Oct 2007 Posts: 1,960 Pgimeno, many of us have been critics of the scholars and AE911T for a long time. Quite vocally to the point of being kicked out of their forums. The best research I have seen has been done by independent researchers not associated with either group. In my opinion the standard debunker vs AE911T back and forth arguments have been mostly fake. Fake arguments and equally fake counter-arguments. Tweedle-dee vs Tweedle-dum, while the better independent researchers go largely ignored in all the smoke and mirrors.
 29th August 2010, 10:39 AM #19 TexasJack Penultimate Amazing     Join Date: May 2008 Posts: 10,906 Originally Posted by Major_Tom The best research I have seen has been done by independent researchers not associated with either group. You mean by independent research those with unpublished work and a degree from Google University.
 29th August 2010, 10:45 AM #20 pgimeno Illuminator     Join Date: Feb 2009 Location: Spain Posts: 3,343 Originally Posted by Major_Tom I don't care if buildings were designed to survive a good bounce. I care about what initiated collapse. That's fine, but speak for yourself. Dedicating efforts to the study of collapse progression instead of your object of interest doesn't make the resulting engineering studies such as Bazant's a "red herring", no matter how much you try to smear them. That's quite an egocentric point of view. Along time, people have studied what has concerned them instead of what has concerned you. Face it. Originally Posted by Major_Tom Pgimeno, you seem to be very impressed by the publication process. We are debating here, now. No, I'm confident of it as a guarantee of competence, of which you have shown quite little here so far. Plus, that tends to be the excuse of those who know they can't get published. But my point stands. Even Björkman's incompetence was exposed to the engineering world in an engineering journal. If you have a good point, you should have no problem to be published there as Björkman was. I just hope that, in case you don't even pass even the most basic threshold to get published there, you won't come crying about "the establishment" or a standard excuse like that. __________________ Ask questions. Demand answers. But be prepared to accept the answers, or don't ask questions in the first place.
 29th August 2010, 11:12 AM #21 beachnut Penultimate Amazing     Join Date: Oct 2006 Location: Dog House Posts: 25,080 Originally Posted by Major_Tom Pgimeno, many of us have been critics of the scholars and AE911T for a long time. Quite vocally to the point of being kicked out of their forums. ... What independent researchers? Are they scenics or engineers? Are they better than Bazant? You have conspiracy theories on your conspiracy theories. Smoke and mirrors? Is that your work? It is funny how you are stuck on NIST. You are kicked out of forums because you post BS, which you think is engineering. It is funny as ae are do nothing cult members with thermite rot on the brain, it is amazing they can see your work as nonsense. It is ironic your BS CD delusion is kicked out from people with the same delusions and worse. Are you making up another CT? If you have problems with Bazant publish them! It will be interesting to see the adjectives of nonsense and delusional used in a real journal when your junk is evaluated. Heiwa did it why can't you! You can always make up another CT after it goes bad.
 29th August 2010, 11:55 AM #22 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by pgimeno This text addresses how and in what sense Bažant's model, initially stated in [B 2001] and [BZ], and refined in [BV] and [BLGB], with clarifications in [BL] (see below, References), can or can not apply to real world buildings. Quote: The author welcomes any constructive criticisms aimed at addressing such inaccuracies as long as they are stated with arguments other than incredulity and disbelief Quote: Since the author's always been not-so-good for writing closing words, please indulge him in his use of [BLGB] to do it: 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 highlighted the inapplicability of your quoted closing remarks in the very first response to your OP. Namely that... The conclusion steps outside the bounds of model applicability. Bearing in mind the specific purpose of your thread, I assume you are going to acknowledge this point shortly. Not only is it a perfect example of the way that the model is used incorrectly, but it is a quote from the model authors themselves. I also suggest you request that further posts from ALL members directly address the thread topic at all times. __________________ http://the911forum.freeforums.org
 29th August 2010, 12:06 PM #23 beachnut Penultimate Amazing     Join Date: Oct 2006 Location: Dog House Posts: 25,080 Originally Posted by pgimeno Since the author's always been not-so-good for writing closing words, please indulge him in his use of [BLGB] to do it: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. Bazant knows it was not controlled demolition, as do 99.99 percent of all engineers. Nice to see it published so 911 truth has some move evidence they can ignore. It was also cool the OP is referenced. 911 truth pseudo-wannabe-engineers never use source or references for their made up nonsense which they use for science and evidence. When you find 911 truth work referenced and sources, you can follow the references and sources to debunk the work. It is classic 911 truth. 911 truth cult members can't comprehend the closing statement is based on evidence, not failed paranoid conspiracy theories based on lies and hearsay. They don't do evidence, or understand Bazant does. Last edited by beachnut; 29th August 2010 at 12:08 PM.
 29th August 2010, 01:06 PM #24 Furcifer Guest   Join Date: Apr 2007 Posts: 13,796 Originally Posted by Major_Tom We want to know what initiated collapse, not whether the building would bounce after a 12 ft fall. Fire.
 29th August 2010, 01:47 PM #25 ozeco41 Philosopher     Join Date: Mar 2009 Location: Moss Vale, NSW, Australia Posts: 7,422 Originally Posted by pgimeno No, we're not talking about the global collapse. We are talking about a mathematical model of the collapse which is an approximation of it. .....I think it's you who is missing the point. The point is that it doesn't matter - the differences in the impact behavior can still make little differences in many of the results. However, actual impact behavior is very difficult to model as there's a cloud of uncertainty surrounding it, while axial impact behavior has been modeled successfully.... Point taken that I need to be very explicit. If we are talking about the Bazant model as a generic model then the model is valid as far as it goes. BUT if we apply the generic model to a specific situation where the assumptions of the generic model are not valid - then the model ceases to be correct and may introduce errors which may be significant. So you clarify that "we're not talking about the global collapse [of WTC1 and WTC2]" Whereas I was attempting to relate the Bazant generic model to the specifics of the WTC twin towers global collapse stage. So continue discussion of Bazant's model without referring to WTC global collapse and I have no concern. My concern arises only when Bazant's model is taken into areas of analysis of WTC collapse where it does not fit. Where his assumptions, especially the assumptions about axial contact, are significant. So your next comment "We are talking about a mathematical model of the [global] collapse which is an approximation of it." So, like me you are relating to WTC global collapse. So your statement hinges on what you mean by "approximation"? I hold to my several times repeated statement. I have no doubt that Bazant was "globally" correct - there was more than enough energy to ensure complete collapse once it was initiated. I question the validity if the concept is taken to further detail given Bazant's assumption of axial column contacts in his model and the near absence of such contacts in the WTC global collapse.
 29th August 2010, 02:43 PM #26 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by ozeco41 PMy concern arises only when Bazant's model is taken into areas of analysis of WTC collapse where it does not fit. Where his assumptions, especially the assumptions about axial contact, are significant. This reminds me of discussions I've had with David Benson, which arose through discussion of the roughly linear rate ejecta streams equating to the position of the primary *crush fronts*. The velocity of the WTC 1 south-side crush front was found to reach fairly constant rate after about 5 seconds, reaching ground in roughly 14.5 seconds. David's input to the discussion was that such details matched outputs from the model. This is a concern imo. The crush fronts are essentially the result of *pancaking*, with ROOSD being a more detailed description. Why do the outputs from the model involving axial column impacts match behaviour, velocity profile and global descent time of a completely different mechanism ? (Especially when it is clear that actual column destruction was significantly slower in propogation rate than ROOSD) That is why, as indicated earlier, it would be useful if the form of the force function was provided, such that the model results can be replicated and parameter sensitivity tested. __________________ http://the911forum.freeforums.org
 29th August 2010, 03:18 PM #28 bill smith Philosopher     Join Date: Feb 2009 Posts: 8,408 If you want to see just how inapplicable Bazant is to the 9/11 paradigm just think about his 'upper block'. We know that 15% or less of the columns, both core and perimeter that connected upper and lower blocks were destroyed by the plane crash. So 85% or more were intact. So what is all this about an ' upper block ' ? We should be talking about how those 85% apparently simultaneously ceased to exist as columns. __________________ *Think WTC7 - You cannot make the four corners of a table fall together unless you cut the four legs together *A kitchen table judgement on a world scale is enough * To Citizens: 'There comes a time when silence is betrayal' Last edited by bill smith; 29th August 2010 at 03:23 PM.
 29th August 2010, 03:26 PM #29 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by pgimeno Originally Posted by femr2 The conclusion steps outside the bounds of model applicability. Rigorously speaking, that's true. Agreed. Response to the rest of your post is over at the911forum... http://the911forum.freeforums.org/po...?hilit=#p12226 __________________ http://the911forum.freeforums.org
 29th August 2010, 03:51 PM #31 ergo Illuminator     Join Date: Aug 2010 Posts: 4,339 Originally Posted by Major_Tom The Bazant Zhao argument of 12 ft freefall before the first collision has been a total red herring. We want to know what initiated collapse, not whether the building would bounce after a 12 ft fall. Metamars writes in post #12: "If you just gently rested the top block on the bottom block, but 'off-center' (columns resting on floors, except when outside the footprint of the base), then I expect the building to collapse. You wouldn't even need to drop it by one storey height. " Exactly. If this is true why would anyone argue for a big bounce after 12 ft? It's an argument for suckers. The demo would initiate collapse and once those columns are displaced is there any reason to expect the building to fare well? If I may be allowed to comment in this more technical discussion... Showing that a jolt or bounce back accompanies any collision demonstrates that the lower portion is sufficiently providing resistance, as would be predicted. Which in turn shows that crush down would not occur first. As for "gently resting the upper block" off-centre on the lower, how and why would two floors of off-centre columns precipitate a global collapse of the entire rest of a building whose columns are intact? This makes no sense. And if you're further suggesting that it would be a crush down, this makes even less sense.
 29th August 2010, 04:22 PM #33 metamars Graduate Poster   Join Date: Apr 2007 Posts: 1,207 Originally Posted by femr2 There has been much discussion of the model there of course, but the main problem, as far as I am aware, is the omission of the form of the force function used in B&L. I'd like to see the function provided, and the model implemented with those handy computer things, such that it is possible to: a) regenerate and replicate the published results b) test parameter sensitivity I was referring specifically to BZ. Subsequent papers looked more relevant to a real collapse. (Which is a good thing since, as noted, BZ is illogical, and can't prove anything about a real world collapse.) Though I vaguely recall deriving an unbelievable prediction from one of them (I think it was BV; I may have posted results at physorg), I'm not really competent to analyze the 'definitive' BLGB, as it involved theorizing of a sort that I'm not familiar with. (I can't remember the term, but it wasn't theories based on first principles, or derivations like one makes in a dynamics class, but rather a theory, such as hooke's law, that follows from observation, and has some sort of statistical validity.) I don't trust such theorizing, because in the case of the WTC, it couldn't be tested. (Unlike Hooke's Law, which is readily tested, as much as we please.) But maybe I'm just showing my ignorance. I never had time to study the references that Benson suggested. My general impression of the BLGB paper (for whatever it's worth), is that it shows that a collapse in the time frame observed was possible given the assumptions of the theory (many of which were reasonable; perhaps all were somewhat reasonable, though IIRC, it didn't take into account transport of elastic energy into the ground, nor any possible dampening effect of floors oscillating like membranes, nor plastic waves that exceeded the collapse speed* ). I vaguely recall concluding that their model was probably very good for when the collapse really got going, something like halfway done. However, that's the part of a collapse where you really don't need explosives, even to make sure that there's no chance of toppling over. Sorry, I don't remember more clearly. Again, I don't have the technical background to understand the later works, fully, anyway. BTW, have you ever looked at the papers of Charles M. Beck, posted at arxiv? They are way over my head. His analysis suggested CD: Quote: We examine four WTC 7 descent curves, labeled "C," "E," "N," and "O," either anonymously published, or confidentially communicated to us. Descent curve describes apparent height of a collapsing building as a function of time. The set "C" suggests that there are three active phases of collapse. Phase I is a free fall for the first $H_1\simeq28$m or $T_1\simeq2.3$s, during which the acceleration $a$ is that of the gravity, $a=g=9.8$m/s$^2$. In Phase II, which continues until drop $H_2\simeq68$m, or $T_2\simeq3.8$s, the acceleration is $a\simeq5$m/s$^2$, while in Phase III which continues for the remaining of the data set, $a \simeq -1$m/s$^2$. We propose that the collapse of WTC 7 is initiated by a total and sudden annihilation of the base (section of the building from the ground level to $H_1$), which then allows the top section (building above $H_1$) to free fall during Phase I, and then collide with the ground in Phase II and III. The total duration of the collapse, assuming that Phase III continues to the end, is in the range $7.8-8.6$s. We derive a physical model for collision of the building with the ground, in which we correct the "crush-up" model of Ba\v{z}ant and Verdure, J. Engr. Mech. ASCE, {\bf 133} (2006) 308, and estimate the magnitude of the resistive force in the top section. We compare our findings to those of NIST investigators and find an agreement with respect to the distribution of damage in the primary zone. We conclude that the building was destroyed in a highly controlled fashion. (emphasis mine) His paper on WTC 1/2 is here. * Even a plastic wave traveling at 1/10 of 5,000 m/s or so is much faster than the collapse
 29th August 2010, 05:13 PM #34 pgimeno Illuminator     Join Date: Feb 2009 Location: Spain Posts: 3,343 Originally Posted by metamars Subsequent papers looked more relevant to a real collapse. (Which is a good thing since, as noted, BZ is illogical, and can't prove anything about a real world collapse.) Care to explain what makes it illogical? It proves that in the most favorable scenario for collapse arrest, the building could not arrest the collapse, thus proving it was unstoppable once started, which was the point and is perfectly logical, so I'd like to see an explanation on why you think otherwise. __________________ Ask questions. Demand answers. But be prepared to accept the answers, or don't ask questions in the first place.
 29th August 2010, 07:29 PM #35 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by femr2 it would be useful if the form of the force function was provided, such that the model results can be replicated and parameter sensitivity tested. I have been informed that the form of the force function was provided. My bad. __________________ http://the911forum.freeforums.org
 30th August 2010, 01:38 AM #37 ozeco41 Philosopher     Join Date: Mar 2009 Location: Moss Vale, NSW, Australia Posts: 7,422 Originally Posted by femr2 ....This is a concern imo. ...a concern which I have shared for some years. Originally Posted by femr2 ....The crush fronts are essentially the result of *pancaking*, with ROOSD being a more detailed description... ..agreed!!! Originally Posted by femr2 ...Why do the outputs from the model involving axial column impacts match behaviour, velocity profile and global descent time of a completely different mechanism ? ...the world of engineering has many examples of approximations giving correct answers for wrong reasons. Originally Posted by femr2 ...(Especially when it is clear that actual column destruction was significantly slower in propogation rate than ROOSD) ...presumably column "destruction" for the core columns --- the outer columns were simply peeled off.
 30th August 2010, 03:16 AM #38 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by ozeco41 ...presumably column "destruction" for the core columns --- the outer columns were simply peeled off. In general, yes. __________________ http://the911forum.freeforums.org
 30th August 2010, 03:25 AM #39 metamars Graduate Poster   Join Date: Apr 2007 Posts: 1,207 Originally Posted by pgimeno Care to explain what makes it illogical? It proves that in the most favorable scenario for collapse arrest, the building could not arrest the collapse, thus proving it was unstoppable once started, which was the point and is perfectly logical, so I'd like to see an explanation on why you think otherwise. Use the search function, please. Here, at physorg, and the911forum. It can't be "the most favorable scenario for collapse arrest" if it incorporates assumptions that both favor collapse, and that favor survival....
 30th August 2010, 08:13 AM #40 femr2 Illuminator   Join Date: Apr 2009 Posts: 3,859 Originally Posted by metamars It can't be "the most favorable scenario for collapse arrest" if it incorporates assumptions that both favor collapse, and that favor survival.... Must be worth noting that core column destruction did arrest for significant portions of the core of both WTC 1 & 2. __________________ http://the911forum.freeforums.org

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