The 9/11 Forum

Yes, I believe it's all about the (weak) column connectors in WTC 1 & 2.

Bazant considers the worst possible case; truth is, the perimeter column connectors were quite weak.

IF THE STRUCTURE WAS KNOCKED OUT OF VERTICAL ALIGNMENT. (which it was by the aircraft impacts and fires), ...... then throw in a bit of column creep, liquid metal embrittlement, accelerated corrosion from S/Cl-rich atmospheres, molten aluminum reactions with iron oxide and gypsum, etc, .... you have no need for pre-planted explosives.

And, YES!, Major_Tom, YES!, ....... WTC 7 COULD BE ANOTHER STORY!

IF THE STRUCTURE WAS KNOCKED OUT OF VERTICAL ALIGNMENT. (which it was by the aircraft impacts and fires), ...... then throw in a bit of column creep, liquid metal embrittlement, accelerated corrosion from S/Cl-rich atmospheres, molten aluminum reactions with iron oxide and gypsum, etc, .... you have no need for pre-planted explosives.

And, YES!, Major_Tom, YES!, ....... WTC 7 COULD BE ANOTHER STORY!

accelerated corrosion from S/Cl-rich atmospheres

Whoa, how much? Musta be some pretty rich atmosphere with massive corrosion rate to attack the steel in a few minutes, no wonder the jumpers jumped out of the towers, the hydrogen chloride was eating their lungs alive!

molten aluminum reactions with iron oxide

Any proof of such a reactions taking part on a massive scale?

btw.such a reaction should be really slow, as Jones showed

you have no need for pre-planted explosives

Great.

And, YES!, Major_Tom, YES!, ....... WTC 7 COULD BE ANOTHER STORY!

????

What if some of the red chips don't ignite because of greater oxidation of the Al platelets....? Nah, can't be thermite.

OneWhiteEye wrote:If the lower structure were capable of supporting this randomly imposed load which has no integrity, then it might be possible for the progressive resistance provided by entanglement to arrest the upper portion without exceeding the overall peak capacity of the lower portion.

But I don't believe that. Not for a minute, not in these towers.

Most composite structures are mainly air; the primary and secondary elements just make up a fraction of the volume. So there is plenty space for failed elements of both upper and lower parts in contact to get entangled and friction (heat production) to take place. Bazant and & recognize this but talk about stretch or compaction - in a 1-D model - that takes place in the lower part only with no energy involved. Lower part is compressed to 25% of its original volume according Bazant & Co. In these towers there is no possibility that the upper, smaller part can one-way crush down/compress the lower part at increasing velocity corresponding to abt 0.7 g. You are invited to describe a structure (apart from these towers) that behaves like that!

Bazant considers the worst possible case;

BV is not about the worst possible case but about derivation of equations of motion for the WTC cases and demos in general. DBB has used it many times to justify the actual trajectory of WTC1.

BV no longer exists as a usable paper. "Best case scenario" has nothing to do with it, as BV is not based on that argument. BZ is but BV isn't. I hope we can absorb this fact as a group.


Are we all, including Dr G and DBB, beyond BV? Can we admit it's derivations are useless? Please let's settle this before moving on.

In Bazant's 1-D theory the lower part, A, has uniform density 0.25 prior impact by upper part, C, that has also uniform density 0.25! Like wool! Or cotton.

After impact Bazant suggest the upper section - one floor - of lower part A is compacted/compressed/stretched to uniform density 1 (like water or four times wool) and Bazant suggests that this compacted part becomes a part B that accelerates (??) and assists part C to continue to destroy lower part A, floor by floor.

Actually, using the NWO physical terms of Bazant, part A should infact start to compact part C at impact in any 1-D world.

But we are in 3-D. No compacting of anything takes place in 3-D. In 3-D weak elements are broken by strong elements and then the structural layout changes and elements start to rub against each other ... and the destruction stops ... at once. Happens everytime you drop a small piece of structure on a bigger piece of same structure.

NIST has of course issued standards for the opposite. Little part C then applies energy on lower part, that lower part cannot absorb = it collapses. Only problem is that little part C cannot apply that energy!

Are we all, including Dr G and DBB, beyond BV? Can we admit it's derivations are useless? Please let's settle this before moving on.

?

In the meantime I want to offer feedback on Charles Beck's "Descent curve and the phases of collapse of WTC 7"


The paper is linked at http://arxiv.org/abs/0806.4792

People on this forum have commented on the paper at
http://the911forum.freeforums.org/beck-descent-curve-and-the-phases-of-collapse-of-wtc-7-
and at
http://the911forum.freeforums.org/technical-notes-on-video-motion-analysis-t55-90.html#p944


His whole argument depends on his data of the WTC7 roofline measurement. If he is using unreliable data the points in his paper fall to pieces.

But if his interpretation of the data is correct his paper is pretty cool.


Lets review his argument. In his words:

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. While all
sets are mutually consistent, it is set “C” which suggests that there are three active
phases of collapse. Phase I is a free fall for the first H1 ≃ 28 m or T1 ≃ 2.3 s, during
which the acceleration a is that of the gravity, a = g = 9.8 m/s2. In Phase II, which
continues until drop H2 ≃ 68 m, or T2 ≃ 3.8 s, the acceleration is a ≃ 5 m/s2, while
in Phase III which continues for the remaining of the data set, a ≃ −1 m/s2.

He says the roofline position data suggests you can divide the collapse into three distinct phases. Each phase shows a distinct acceleration, markedly different from the other phases.


Phase 1: From t=0 to t=2.3 sec or the first 28m fall when a=g (or pretty close)

Phase 2: from t=2.3 to 3.8 sec or from 28m roofline fall to 68m when a= about 5m/s2

Phase 3: from t=3.8 sec onward or after a 68m roofline fall when a= -1m/s2


These 3 acceleration "steps" are shown in figure 3, pg 10 of the paper.



If this is true, it is pretty interesting.


So the big question is: Does/can the data he uses show 3 different phases of acceleration as he claims?

On the "Technical notes on video motion" thread we were discussing piece-wise fitting functions to the data. OWE suggested fitting three different pieces to phases of the fall. From the thread:

Yes! I feel vindicated (not that anyone was objecting) for expressing the need to do piecewise fits. I'd wager, if we could get the last 2.5 seconds of the fall, you'd need a third segment to complete the fit. NIST should have done piecewise fits.

Hmmmm

I think Charles Beck's idea of a multi-phase collapse model is pretty good.

Multi phase, meaning two or three phase, physical models of collapse makes sense in the case of WTC7, and probably for WTC1 also (not the useless crush down then up phases but something real.)

In the case of WTC7 one can argue that empirically it would be smart to view the descent curve as consisting of different phases (two or three of them).


Piecewise fitting: If we model the fall of WTC7 as consisting of 3 phases, it is natural that you will use different functions in each region.

Of course the transitions between phases is not instantaneous but it could be quite rapid.


Why consider 3 different phases like Charles Beck? If we consider major damage to be done on the 6th and 13th floors, we could consider first 28m movement to possibly be subject to one type of force (hence acceleration), base destruction to earth as a second type of force and crush up destruction and a third.

Beck's 3 phases are:

Phase 1: From t=0 to t=2.3 sec or the first 28m fall when a=g (or pretty close)

Phase 2: from t=2.3 to 3.8 sec or from 28m roofline fall to 68m when a= about 5m/s2

Phase 3: from t=3.8 sec onward or after a 68m roofline fall when a= -1m/s2


Maybe his guess isn't too bad? It would mean:

Phase 1: fl 13 falls to fl 6 (with virtually no resistance, hence very high acceleration).

Phase 2: Destruction of base to earth's surface.

Phase 3: Crush up: Earth vs building.


Think about it , guys. Three different types of resistance to destruction depending upon crush mode. Acceleration transition points after a 28m fall and a 68m fall. Transitions between phases could be smooth or quick.

And how would you fit a function to the drop data? 3 piecewise fits. Why not?

Major_Tom wrote:If he is using unreliable data the points in his paper fall to pieces.

I don't think it's unreliable, but it undoubtedly could be better. If very accurate results are important, more samples plus perspective correction are highly recommended. He does use some of my (so-so) data but it doesn't really contribute significantly, and that's good, because it's not from the NW corner like the rest of the datasets. It's the lower left corner of the big dark rectangle which begins dropping at least a half second earlier and doesn't have as high an acceleration. This is how it really compares to einsteen's data, having synchronized the different source videos.

So the big question is: Does/can the data he uses show 3 different phases of acceleration as he claims?

Obviously, I think so. Three is better than one, unless one or two happens to fit really well, seems one doesn't. einsteen's simple model could roughly be separated into high nearly-constant acceleration early on with a decrease in acceleration becoming increasingly prominent later, eventually leading to rapid deceleration. Apparently Beck gets a good fit but I don't know about his resulting numbers. Dr. G's two-piece fit WITH tilt correction of this data is probably the best fit so far of the early portion, demonstrating the importance of a tilt correction. Unfortunately the video may have conversion errors.

I'd split the NW motion into:

1) a very early phase of very low acceleration lasting about 0.75s, shown here



generally overlooked and certainly so by Beck.


2) the near freefall phase, constant a until the fit wanes

3) ??? (one or more unknown segments)

Pieces, yes, what kind and over what periods, not so sure. Probably four would be a minimum unless the last were cubic. Anyone have good copies of these videos?

More on BV:

There were a few follow-up papers on BV which include criticism by Gregory Szuladzinski and more criticism by James R. Gourley. This is followed up by "Closure to “Mechanics of Progressive
Collapse: Learning from World Trade Center and Building Demolitions” by Zdene˘k P. Bažant and Mathieu Verdure which was written by Bazant and Le.

Link to the three papers http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/D25%20WTC%20Discussions%20Replies.pdf

Here, Bazant again justifies the use of a single variable to describe the crush-up, crush-down process.

From the paper

So it must be concluded that the simplifying hypothesis of
one-way crushing
i.e., of absence of simultaneous crush-up,
made in the original paper, was perfectly justified and caused
only an imperceptible difference in the results. The crush-up
simultaneous with the crush down is found to have advanced
into the overlying story by only 37 mm for the North Tower
and 26 mm for the South Tower. This means that the initial
crush-up phase terminates when the axial displacement of
columns is only about 10 times larger than their maximum
elastic deformation. Hence, simplifying the analysis by neglecting
the initial two-way crushing phase was correct and
accurate.

Recall the title of BV is "Mechanics of Progressive
Collapse: Learning from World Trade
Center and Building Demolitions”.

People have been demolishing buildings for a long time. You only need to look at some examples to see crush-up does happen along with crush down. And yet, the authors are telling you that this cannot happen on theoretical grounds.


The topic is handled analytically rather than experimentally because apparently WTC1 was obscured by too much dust to make observations about the crush-up, crush-down process and none of the hundreds of demos already performed can provide them with useful data?

When some members of this forum looked a bit more carefully we noticed that the upper block fell to pieces early in the collapse and it's outer walls popped off in large unbuckled chunks.


BV is proven wrong by observing known crush-up crush down demolitions and by observing the fate of the upper block of WTC1 carefully. It is also proven wrong by observing the state of core and perimeter columns within the rubble which show their derivations of resistive force F based on floor by floor buckling cannot be correct.


Please remember that the topic is building demolitions and crushing, not astrophysics. We have examples of the physical processes under discussion right here on earth. So why are these papers (BV and closure to BV) written with only analytical arguments with no observation of actual demos to back them up?

If actual demos contradict the claims in the paper and we can see that the WTC1 upper block did not remain intact very long at all.......why cannot the authors recognize this?

Why would anyone derive equations of motion of a crush-up, crush-down building demolition without observing a crush-up, crush-down building demolition? (They are not all "obscured by smoke", you know).


If I were to show them that the sides of the WTC1 upper block kicked away from the building early on and the upper block structure was destroyed early into the collapse, do you think these facts could....penetrate their minds?

(Yes, OWE, the derivation of these equations show a talent for mathematics. But what about their powers of observation (like those of NIST for WTC7)? Without the ability to carefully observe the events, what good is the misapplication of physics? Their insistence on crush-up occuring for a few millimeters make them look silly to the very few people who can even follow the argument.)

I'd like to see Dr Bazant tackle WTC7 so I can use my bullsh*t-o-meter to see where he really stands.

Major_Tom wrote:And yet, the authors are telling you that this cannot happen on theoretical grounds.

This is one of the ways I feel the papers have overreached. Properly disclaimed, and with reference to the manner in which exceptions can occur, the analysis has merit. It is a non-intuitive result for me, so is illuminating (there may be error but I'm assuming not). The way it's packaged, though, leaves little room for interpretation. While the understood context is the simple model, unquestionably the authors conflate the model with the real thing. To this day, and after several reads, I come away with the impression that Bazant believes this is how it went down, in accordance with his analysis which shows it must be so. The analysis, I'm afraid, is purely academic and actually has no bearing whatsoever on what happened.

This of course, doesn't knock the leg out from under the 'conventional wisdom' that collapse can and will proceed once initiated. It just makes the analysis a bit of an educational sideshow, and leaves the real mechanics unaddressed.

Please remember that the topic is building demolitions and crushing, not astrophysics. We have examples of the physical processes under discussion right here on earth. So why are these papers (BV and closure to BV) written with only analytical arguments with no observation of actual demos to back them up?

This is a very good question. Scientific literature is brimming with in-depth exploration of idle academic curiousities. For the most part, Bazant has spelled out differences between theory and reality but, in this one case, the lines are far more ambiguous, and there is some indication that he personally crossed the line, confusing simplified explanation with reality.

Why would anyone derive equations of motion of a crush-up, crush-down building demolition without observing a crush-up, crush-down building demolition? (They are not all "obscured by smoke", you know).

Another good question.

Their insistence on crush-up occuring for a few millimeters make them look silly to the very few people who can even follow the argument.)

Yes, I have to agree with that.

OneWhiteEye --- Not to further clutter Major_Tom's thread, I have moved over here (to a thread I didn't even knew existed).

Southwest corner: I assume this explusion is early on, being the same as reported by the NYPD helicopter observer. So I can neglect at at just being more of the results of early buckling.

MOre interesting, it occurred to me there is a way to verify that no (significant) early cush-up of sone C happened. It was about 14 stories tall. Using B&V, I find that the crushing front reached floor 84 in about 3.35 seconds after a formal t0 set at frame 907. So check a video. Either the crushing front has progressed this far or else it has not. If crush-up was progresssing as fast as crush-down, then the lower crushing front would be at only floor 91. (The program computes that floor 91 was crushed by 2.36 seconds. It seems the difference is enough to be readible discernable.)

David B. Benson wrote:OneWhiteEye --- Not to further clutter Major_Tom's thread, I have moved over here (to a thread I didn't even knew existed).

Don't worry, it's not clutter, it's right on track.

MOre interesting, it occurred to me there is a way to verify that no (significant) early cush-up of sone C happened. It was about 14 stories tall. Using B&V, I find that the crushing front reached floor 84 in about 3.35 seconds after a formal t0 set at frame 907. So check a video. Either the crushing front has progressed this far or else it has not. If crush-up was progresssing as fast as crush-down, then the lower crushing front would be at only floor 91. (The program computes that floor 91 was crushed by 2.36 seconds. It seems the difference is enough to be readible discernable.)

Good idea. Let me see what I can come up with.

OneWhiteEye --- The computer program matches data down to floor 80.8 at 3.7678 seconds. After that, I can set two times for reports of the extrapolated drop. Easy to do and you may find a later time at which it is easier to determine the floor number for the initial explusion of air about 2 stories below the actual crushing front.

Major_Tom offered two criticisms of the B&V crush-down equation. Neither hits the mark. 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. Also Major_Tom takes some sort of objection to (3) as B&V make it appear to depend upon column buckling. However, using parameter estimation and OneWhiteEye's data, my computer program uses just a known force function and computes the required force parameter which gives the best fit. I explained this on the WTC 1 offered no resistance thread. The whole point of both the exposition in B&V and Major_Tom's objections is rendered moot by the homogenization assumption; there is then nothing left to discuss except the validity of these four assumptions in the case of WTC 1 and separately, WTC 2.

For WTC 2 I used Greening's model some time ago. The fit during the interval of measurements is rather good, although not as good as for WTC 1. However, at some later time zone C fell off, determined so by shagster's analysis of a ABC(?) video of the crushiing front passing the Marriot Hotel. So for a short while, the four B&V assumptions apply to WTC 2 as well.

As best as I can tell, the lowest extent of debris at f907+3.35s = f1007, is located at or towards the SW corner, and appears thick at floor 87, possibly some penetration into 86. The exigent circumstances:

- this is the lowest ejection seen in the Sauret video and another
- this is the horizontal location of the advanced front we've also been discussing
- it's not necessarily all coming out in the form of an expulsion, stuff is also falling from above
- from the other video, most of the west wall - north side - is intact and expelling nothing up to at least floor 92 at the equivalent of frame 996 of the Sauret video
- this same video shows the upper north wall, west corner, slipping outside the lower perimeter which continued to stand after the block passed
- if there is any gas expulsion leading the crush front, as assumed for later times, then that must be subtracted from the 86-87 story marker

It's a very good match for part of the collapse. BUT... most of what's visible, perimeter-wise, is nowhere near that advanced in terms of seeing any external effect. No expulsion, no deformation or translation. This is part of the argument, there's a faster part and a slower part. So far, the faster part is just about where you expect it to be, but at least half of the perimeter, and perhaps more, is well behind.

I'll post more information in a bit, need to review what's been posted recently.