The 9/11 Forum

OneWhiteEye wrote:

Heiwa wrote:Well, ... sideways.

Uh huh.

The average speed of the ejected material is 25 m/s according G, which means that it was 50 m/s when ejected

That wasn't what he meant by 'average', he meant average over the interval of travel. Maybe it started at 27 and ended at 23. You're getting a lot of very simple stuff wrong.

Maybe you are right, BUT, it seems, watching videos of the WTC 1 destruction, that the sideways, horizontal, velocity of the objects ejected is reduced pretty fast, due to friction in air, and is virtually 0 before the object hits ground, i.e. the object ejected hits ground vertically = 0 horizontal velocity. So I conclude it started at 50 and ended at 0 with an average 25 m/s. Maybe G can clarify what he means with average? The object evidently displaces 150 m sideways during 6 seconds, average 25 m/s, but it must have been much faster at beginning and much slower, 0?, at end. Anyway, what kind of force or IMPULSE can eject objects sideways?

Major_Tom wrote:For me basic, fatal flaws in BV are not difficult to see.

Obviously your understanding of physics is incorrect.

DBB has been fitting data to equations of motion

True.

... which are fundamentally based on floor by floor column buckling, ...

False. I explained this already and am not going to repeat.

My problem is this: ...

That you don't understand, properly, B&V, BLGB and my early posts here.

DBB has no response to evidence that upper and lower blocks destroy each other in practice, ...

I did respond earlier. Go back and read, with some comprehension this time, my earlier posts.

... this overwhelming evidence ...

There is none beyond the indirect evidence supplied by OneWhiteEye.

... understanding of resistance force F ...

I already explained it. Do attempt to understand the explanation. If you have questions, ask.

Heiwa wrote:Maybe you are right, BUT, it seems, watching videos of the WTC 1 destruction, that the sideways, horizontal, velocity of the objects ejected is reduced pretty fast, due to friction in air, and is virtually 0 before the object hits ground, i.e. the object ejected hits ground vertically = 0 horizontal velocity.

I think the actual numbers would quite be a bit different, given the velocity dependence in air resistance, but I'll grant you the point. Good recovery. The truth is probably somewhere between our off-the-cuff figures.

You've examined collisions but I have to ask: have you blown anything up?

David, in the interest of not wasting more time I'll be frank (no, not the poster).

To me, some of you posts appear dishonest. I think you are a master in circular logic.

I think your ability to be even slightly realistic about questions concerning zone C destruction and it's consequences wastes the time of people on this forum.

You cannot be bothered to watch videos of the crush-up, crush down process tested via a special type of demo (verinage) highly informative to us, but you have no problem repeating the same mistakes through hundreds of posts.

This wastes a lot of time for us. It is obstinate at best, intentionally manipulative at worst.


In some of your posts I see an almost artistic effort to avoid issues and spin circular logic.


An excellent case of this has been your inability to provide anything of substance to explain the most glaring contradictions in paper you constantly cite on other threads (BV).

You claim to have validated BV despite my comments in your last couple of posts.

In truth, you've provided nothing of substance while avoiding the issue using a confusing type of circular logic.

This is provable, but only if you stop trying to "squirm" your way out of addressing the concerns and push the last few pages of posts down the memory hole.



So let's all take a deep breath and start the BV exchange from scratch:

David, could you please just copy and paste your answers to my two complaints in your next post. I know you claim to have already answered them but just to be clear for some of the slower posters that don't understand physics like myself, can you restate your answers so we can see them explicitly?


David, I can see that fitting WTC1 data to BV is important to you. It is a constant theme through hundreds of you posts. Could you please tell us why? What do you think it tells us about WTC1. Why is fitting data points to BV important to you and what should it teach us? How can we understand that the buildings fell naturally using BV?

OneWhiteEye wrote:You've examined collisions but I have to ask: have you blown anything up?

Answer is YES (part of Swedish Navy training) but off topic.

Major_Tom wrote:David, could you please just copy and paste your answers to my two complaints in your next post. I know you claim to have already answered them but just to be clear for some of the slower posters that don't understand physics like myself, can you restate your answers so we can see them explicitly?

Go back and read my post David B. Benson on Wed Oct 14, 2009 1:35 am on the previous page. Then there is a quiz question for you from a yet earlier post: what did statistician G.E.R. Box say? Why is that important to mention?

David, I can see that fitting WTC1 data to BV is important to you. It is a constant theme through hundreds of you posts. Could you please tell us why?

This is how science is done. The model provides a decent, not perfect, understanding of the progressive collapse of large structures.

How can we understand that the buildings fell naturally using BV?

We can't. Or at least I can't alone although BLGB offers another approach to state the naturality of the progression. I just do parameter estimation. So I can tell you, quite precisely, how and how much WTC 1 resisted, but I don't claim anything more than that.

I'll repeat my long standing offer. Devise a one dimensional model of progressive collapse starting from Newton's laws and using any material properties you desire. You are not allowed more than six parameters for me to fit. I'll code it up and run it against OneWhiteEye's data, then apply AIC to detrmine whether it is substantially better than BV+vaf (seemingly impossible), a little better, the same explanatory power, a little worse or much worse. May the best model win!

How can we understand that the buildings fell naturally using BV?

yes. how can guessing what force was available/expended based on timing show that that was the actual force available/expended?

"the buildings offered little resistance" is not intuitive for a giant steel mesh. JENGA, sure, but not supertowers.

even NIST's computer models show the steel deforming, but HOLDING TOGETHER.

amazing how those computer models are far more accurate, being in 3D and all, yet show NOTHING like the BV one dimensional hand wave. they show what one would EXPECT, ie. a folding deformation. even more amazing, that THOSE computer models look NOTHING like the actual demolitions, er, "collapses". and, more amazing still, is the continued defence of these obviously flawed "explanations".

newton wrote:how can guessing what force was available/expended based on timing show that that was the actual force available/expended?

Science proceeds by inductive logic. Vaf is significantly better at agreeing with the data than B&V's orginal constant force with constant stretch. So the latter has essentially no support. The statistics of all this was complete by 1972 CE and in textbook form by 1977 CE.

"the buildings offered little resistance" is not intuitive for a giant steel mesh.

WTC 1 offereed essentially no resistance of the sort which kept it standing when intact; see above. Enough resistance of another form, vaf, sufficed to keep the collapse from progressing faster than about 0.68g.

even NIST's computer models show the steel deforming, but HOLDING TOGETHER.

NIST stopped their simulation of WTC 1 two minutes before collapse initiation. They made no attempt to model progressive collapse. AFAIK Frank Greening was the first to do so, following by B&V (completely independently) and later by Kieth Seffen. All three papers set up essentially the same model for the collapse of the towers.

Thanks DBB. It's too bad NIST never even tried to model the collapse itself.....

I always said my first WTC collapse model was an approximation, or let's say a starting point.... But it showed, (at least to my satisfaction - but I am open to debate on this), that a self-propagating collapse is energetically possible.

And by the way, I made my first drop distance measurements with a ruler on a TV screen. However, even today's computer-based measurements run into all the same problems such as establishing a vertical scaling of the drop distance and defining a meaningful t(0).

About 5 pages ago I posted two fundamental problems concerning BV. Hate to repeat but it seems to me nobody addressed them.

DBB claims to so I'll repost my complaints followed by what seems to be his replies.


Formal complaint #1:

It is impossible to describe motion of both upper block and lower block using only one generalized coordinate.

The illustration below shows how BV attempts to explain the system motion using only one generalized coordinate.



How do they describe a system with 2 inherent degrees of freedom with only one coordinate?

They fix the distance Zo and do not allow it to vary during what they call "crush down phase".

The authors do this by claiming that crush-up of upper block C begins to occur only after the lower block A is completely crushed.

This claim is provably invalid for the following reasons:

a) WTC1 upper block was toast early on
b) The outside walls of the upper block actually fell out and over the lower walls on the E, N and W sides (probably on the S side too, but that is top secret). This means the upper block was milktoast (there was very little structure left early on).
c) Demos we have observed that use an upper and lower block see both their upper and lower blocks consumed in the collapse.


These observations invalidate the claim and means eq 12 in the paper cannot be used to describe crush-down.

There is in fact no single differential equation which can describe crush-down.

Even using only 1 physical dimension there must be at least 2 differential equations used with 2 variables to describe crush-up, crush-down motion.


Note: If I were to give this problem of crush-up crush-down to an undergraduate class of pretty advanced mechanics students and even give them the form that building resistance F(z) takes, very few of them would try to solve it using only one generalized coordinate (and the ones that do would be wrong). If I gave this problem for homework to a decent graduate class of physics students, I'd bet that nobody in the class would even attempt to solve it using only one degree of freedom.



To which DDB seemed to answer:

First of all, this crush-down equation is simply the continuous analogue of Frank Greening's floor-by-floor model; simply continue to refine that into millifloors, microfloors and so to the continuos limit. As a matter of practice, using Runge-Kutta to solve the ODE means passing back into the discrete domain once again.

B&V make four simplifying assumptions:
(1) one dimensional;
(2) energy dissipated only at the crushing front;
(3) known resisting force;
(4) homogeneous.

Major_Tom objects to (2), implying, I think, two crushing fronts. Obviously Frank Greening does not think so and indeed Bazant & Le thoroughly remove that possiblity in the idealized, analytic case being considered just now.

and

OneWhiteEye --- I've been thorugh all this before. Homogenization is fine when the tilt is taken into account; crushing proceeded on 3+ floors simultaneaously which is surely better represented by homogenization that by stepwise floor-by-floor model. However, both give essentially ythe same results; shagster actually went to the effort of running his own version of Greening's ideas using minifloors to demonstrate this; although, after some study, this is analytically obvious.

The issue of early crush-up never seems to die, does it? The problem is that it would have to proceed against the force of gravity, not with it. Instead what you seem to have noticed in frame 1007 is a lack of one dimensionality, with zone C west perimeter wall going outside the lower portion, yes? That actually does not trouble me, yet.

Major_Tom --- Kieth Seffen also uses one coordinate; his paper is also in ASCE J. Engg. Mechanics. I opine you need to rethink your position. The question is simply the extent to which the four simplifying assumptions are adequate to describe the evolution of position of the uppermost parts. Works d**n well for WTC 1 all the way to the bottom; not so for WTC 2 where it seems zone C fell off.

Assuming homogeneity, Bazaant & Le show thaqt zone C is almost industrucible. That's mechincs for you. The sturcture obviiously was not homogeneous and you have, in other threads, shown some distruction along the west and north walls. In of itself that mass loss is not important, but it does mean the floor trusses in those areas have been weakened. So an average of about 4--6 stories above floor 98 do not come close to satisfying the homogeneity condition. Fine. consider then that zone C is from floor, say, 102 up. To keep the equation simple, assume crush-down begins from there. As I mentiioned in this thread yesterday, this works well enough to match the additional observations by OneWhiteEye.

That is his answer. Sorry for posting it in a scattered way, but that is just how he presented it to us over the last few pages.

Dearest impartial reader, did DBB actually answer the complaint or did he avoid doing so? Does his answer satisfy you? Please remember:

DBB believes in the indestructible upper block based on a theory even though demolition planners have been smashing upper blocks against lower blocks for a few years now and even have a special name for this style of demolition.

We can see the upper block take quite a beating in every one of these cases http://www.youtube.com/watch?v=NwFHEoiUZ7o&NR=1 and crush itself with the lower block in what appears to be a 1:1 ratio. Every case.

Reader, you can see that upper blocks are far from indestructible yet DBB cannot because he "doesn't watch videos".


So do you think he refuted this first complaint?

(I think he just bullsh*tted past answering it). Watch carefully to see how artistically he avoids addressing the issue again....

i can answer for him.
"some stuff is just too complicated. i mean, here it is the 21st century, and i can't even watch videos that are inherently prerequisite in this discussion. obviously a one dimensional model that has no coherence with the observed reality is the best we can do, and we must assume that if the observed reality doesn't match the one dimensional calculations, then the observed reality must be inaccurate, because math is flawless."

he may use different words, but that's the general trend.

Major_Tom wrote:
They fix the distance Zo and do not allow it to vary during what they call "crush down phase".

The authors do this by claiming that crush-up of upper block C begins to occur only after the lower block A is completely crushed.

This claim is provably invalid for the following reasons:

a) WTC1 upper block was toast early on
b) The outside walls of the upper block actually fell out and over the lower walls on the E, N and W sides (probably on the S side too, but that is top secret). This means the upper block was milktoast (there was very little structure left early on).
c) Demos we have observed that use an upper and lower block see both their upper and lower blocks consumed in the collapse.

Zo = 53 meters during crush-down! Then there is also the mast on top!
Only air (and debris/fragments) is ejected 200 m in all directions below the 53 m tall part C during crush-down.
At the end of crush-down lower part A has been compressed into a 92 m tall box of compressed rubble. Part C remains intact!!
Then air ejection stops and part C is finally crushed-up! Zo suddenly becomes smaller!
Finally the mast should also be crushed-up, which Bazant & Co forget.

Figure is from an early Bazant paper with colors and mast added by me.
An alleged crush-down (C crushing A) by gravity is only possible, if C and B can continuously apply a constant or increasing force on A. For that C must remain intact and B must be able to break/crush intact A structure all the time. How compacted rubble B can break/crush intact structure at all is ??? We are also told separately (by DB) that 20°% of B spills out or is ejected at high speed all the time so much energy/force is used for that.
But let's face it and keep it simple! Part C incl. B cannot apply the required force on A, as A incl. B apply the same force on C, that is always decelerated, locally damaged and arrested at once! Reason is of course that you cannot destroy a big structural part A by dropping a small part C of same structure on it.

All this is described in my scientific paper at http://heiwaco.tripod.com/nist3.htm - to be added to the list. I await ASCE/Journal of Engineering Mechanics to publish another paper of mine soon.

Dr. G wrote:... run into all the same problems such as establishing a vertical scaling of the drop distance and defining a meaningful t(0).

Vertical scaling does not appear to be a problem. In some sence there was no t0. I resolve this by letting the program choose t0 so as to provide the best fit by assuming that in the earliest stages the resistance is a high fraction of mg, chosen according to the best fit, followed by the B&V crush-down equation with whatever resistive force is under study. So the t0 for that study is the moment of transition between the two stages.

Major_Tom wrote:Formal complaint #1:

Addressed by Bazant & Le.

a) WTC1 upper block was toast early on

Not demonstrated for WTC 1. Demonstrated for WTC 2.

b) The outside walls of the upper block actually fell out and over the lower walls on the E, N and W sides

I accept this for W. Provide stills demonstrating this for E and N.

This means the upper block was milktoast (there was very little structure left early on).

Neither demonstrated nor likely true. All that matters is that the mass remain on top.

c) Demos we have observed that use an upper and lower block see both their upper and lower blocks consumed in the collapse.

Irrelevant as far from homogeneous.

Using only 1 physical dimension there must be at least 2 differential equations used with 2 variables to describe crush-up, crush-down motion.

Bazant & Le do so and under the assumptions they use that crush-up is negligble. However, produce your own system of ODEs with not more than 6 parameters to estimate and I'll compare --- as I already wrote.

That is his answer.

You missed the most important part by failing to answer the quiz question posed to you.

... and crush itself with the lower block in what appears to be a 1:1 ratio. Every case.

You can't both have the upper wall going over the lower wall and also actually see such crushing. Make up your mind which it is. Better, post as careful analyses, with stills, as you did for the early detachement of four large wall sections.

I see good points on both sides of this argument. Don't think there's any bullshitting here, Major_Tom, just a disconnect.

Bazant & Le do so and under the assumptions they use that crush-up is negligble. However, produce your own system of ODEs with not more than 6 parameters to estimate and I'll compare --- as I already wrote.

No need, just adjust one parameter of B&L. Drop the capacity of the lowest story of the upper block until there is some non-trivial crush-up. Then see if, within the bounds of what's known currently, it is possible to justify that reduction through the asymmetrical action between upper and lower due to tilting. If it is, carry through. Carry through, anyway, since it's quite difficult to say what a legitimate reduction would be.

Only the one story gets reduced capacity. However, if crush up proceeds through the first story (and it most surely will), you'll have to toss out the B&L assumption that the rest of the block is rigid. Instead, you'd have to repeat with new initial conditions and a debris layer, which frankly is not yet thick enough to call rigid or cushiony, IMO, but call it rigid to keep two DOF.

See how long crush-up continues. See how fast the roofline falls. Notice if the results for the lower coordinate are much different (wager: not much). See if it works.

You can't both have the upper wall going over the lower wall and also actually see such crushing. Make up your mind which it is.

He's talking about the rash of verinage videos appearing on YouTube. I don't agree that they all show 1:1, but there's definitely a mix of up/down crushing. Sure, the parameters of the structure are different, but it is an awesome testbed for a nearly homogeneous crushing situation, and the upper blocks do suffer. Badly.