Acceleration of the falling top blocks.

[WTC Dust]

You didn't answer the question. What destroyed the columns?

The support columns fell last, after the floors surrounding them had collapsed. They are called "spires" for the brief time they tottered, before collapsing themselves (no support).

 

[WTC Dust]

Oh that is easy: Gravity.

Nope.

 

[WTC Dust]

Not very satisfying. A cascade has to begin somewhere. Talking about a cascade is talking about a process that has already begun. I want to know what, in your mind, began the process of destruction at 9:59 and 10:26AM.

So have I. It was a feature of a cascade failure in the impact and fire zone which reduced the strength of that part of the tower to less than was needed to support the top storeys above that level.* You may be asking the wrong question here. The answer to the question as written is "Gravity" as Oystein has already said. Possibly you are looking for details of the mechanism which initiated collapse?





* Note: That statement is neutral to any claims of CD by explosives, incendiaries, energy beams or any other technology. If there was CD it must have formed part of the cascade failure which was observed.

 

[WTC Dust]

Since you apparently have some reading comprehension issues, why not take a few minutes and just watch the YouTube version? After all, "YouTube" = "Published" in the truther fantasy world, yes?

CAn you tell me what's in the video? I almost never click a link to a video unless I know what I'm going to see.

 

[WTC Dust]

There are many failures in the model shown above, but the biggest one is that it doesn't address the cause of the failure. Your model is entirely devoid of an explanation as to why this happened.

I've published notes on my model here.

[qimg]http://www.csicop.org/uploads/images/si/thomas-figure.png[/qimg]

Of course, it's a very simplified model, but it does convey the essence of what happened. Quite different from truthiness, in which the only thing of importance is to express dubiousness with the last word.

 

[WTC Dust]

Why didn't you apply the concept of conservation of momentum to the material that was moving horizontally during the destruction of the WTC? First of all, if gravity was the culprit (the strongest force on Earth haha), explain how momentum is conserved by horizontal movement of debris and building materials.

Second, since there was significant horizontal movement of material, and since this material could not have contributed to any downward force on the remaining floors of the building, the downward force would have been reduced. Where were these calculations? How are you planning to estimate the amount of material that fell outside the footprint?

By the way, in reality, no floors fell on any floors. The building was destroyed as it was sitting there, not by successive impacts. But I'm still listening to what you have to say about the horizontal movement of material and how you calculate its conservation of momentum into your model.

In other words, "Don't forget the dust!"

I'm not "back substituting", I am applying conservation of momentum. Your description is pure strawman, as anyone who reads my detailed calculations knows.

Kindly don't put words in my mouth.

 

[Tony Szamboti]

[qimg]http://www.nmsr.org/strawman.jpg[/qimg]

I'm not "back substituting", I am applying conservation of momentum. Your description is pure strawman, as anyone who reads my detailed calculations knows.

Kindly don't put words in my mouth.

Nonsense. You can't just use conservation of momentum and account for the column energy dissipation. The resistance was a combination of inertial resistance and coumn resistance. You are competely ignoring column resistance, which is also the much more significant of the two.

Sorry to burst your bubble publicly, but you have been told this privately several times and should have withdrawn what you were saying and amended it for column resistance.

 

[Tony Szamboti]

Had you actually read my article (I am not Zdenek Bazant, BTW), you might have noticed this:



So, I posited an upper section of 14 floors (WTC1), 28 million kg total, around half of what Bazant used.

So with 28 million kg and 19.3 mph (8.63 m/s) your kinetic energy at first impact = (0.5) x (28 x 10e6 kg) x (8.63 m/s)^2 = 1.04 GNm. Zdenek Bazant's estimate for column energy disipation is 0.5 GNm. So your model would lose at least 0.5/1.04 = 48% of its kinetic energy, just due to Bazant's column energy dissipation, and with inertial resistance another 7%, given (V1M1 = V2(M1 + 2/28 M1), for a total of 55%.

Now if we take away your freefall during the first story drop, which you have no basis for and measurements show not to be true, the kinetic energy with your mass figure = (0.5) x (28 x 10e6 kg) x (6.13 m/s)^2 = 0.53 GNm and your loss is 0.5/0.53 = 94% just for column resistance, even using Bazant's low estimate. When the inertial loss of 7% is added in your collapse arrests at the first impact.

Your analysis is meaningless without considering the column resistance, and the above shows people here that your analysis doesn't match Bazant's by your own admission.

 

[Oystein]

Nonsense. You can't just use conservation of momentum and account for the column energy dissipation. The resistance was a combination of inertial resistance and cumn resistance. You are competely ignoring column resistance which is also the much more significant of the two.

Sorry to burst your bubble publicly, but you have been told this privately several times and should have withdrew what you were saying and amended it for column resistance.

I again highlighted the parts where your argument requires a bit of refinement.

 

[Oystein]

So with 28 million kg and 19.3 mph (8.63 m/s) your kinetic energy at first impact is 104 GNm. Zdenek Bazant's estimate for column energy disipation is 0.5 GNm. So your model would lose at least 48% of its kinetic energy just due to using Bazant's column energy dissipation and with inertial resistance another 7% given (V1M1 = V2(M1 + 2/28 M1) for a total of 55%.

Now if we take away your freefall during the first story drop, which you provideno basis for, the kinetic energy with your mass figure = (0.5) x (28 x 10e6 kg) x (6.13 m/s)^2 = 0.53 GNm and your loss is 0.5/0.53 = 94% just for column resistance even using Bazant's low estimate. When the inertial loss of 7% is added in your collapse arrests at the first impact.

Your analysis is meaningless without considering the column resistance, and the above shows people here that your analysis doesn't match Bazant's by your own admission.

...and again

 

[ozeco41]

Not very satisfying. A cascade has to begin somewhere. Talking about a cascade is talking about a process that has already begun....

1) Wasn't intended to be a fully detailed explanation.
2) Yes
3) Actually I was describing the overall process. So where it began AND "has already started" are subsets of what I used the term for.

... I want to know what, in your mind, began the process of destruction at 9:59 and 10:26AM.

"began" is a confused term to use in that context. The key about those two times is that they are the times at which the collapses entered a stage of "visible in macro to a human observer". Draw up some better words if you don't like those ones.

The guts of the issue is "what event started the obvious to macro observation rapid collapse at those times." Again change the words if they don't convey the meaning.

So to your question "...what, in [my] mind, caused..."

To my mind the cascade failure had been progressing for some time prior to each of those two times. That process had reached the stage where the "last straw" would "break the camels back". OR, slightly less colloquially, the next bit of failure triggered the fall of the top block.

There were three main processes which I have regarded as possibilities as trigger mechanisms:

1) Inwards bowing of perimeter columns as identified by NIST;
2) Core failure which certain researchers on the 911Forum claim occurred before perimeter failure. I find much of the work of those researchers is persuasive as to technical facts. BTW they are generally on this forum regarded as "truthers".

Those two often referred to as "perimeter led initiation" and "core led initiation". I am agnostic on whether I prefer either of those or some other variant which would still become those two categories. Column failure was critical and there were only two groups of columns. Collapse initiation at the observed times you refer to involved failure of both sets of columns. And, to my mind, it matters not which went first.

3) Assistance by some malicious human intervention. I discount this possibility totally for a wide range of reasons - coming down from the strategic level of "Why do it" down through all levels of "How" - and resting on two premises 1) I cannot conceive of any reason or method AND 2) No-one of those claiming nefarious activity have ever, to my knowledge, put forward a comprehensive reasoned and supportable claim.

I have posted fuller explanations of the progress of a cascade failure on other forums - not all now still on line. It is a process which many engineers don't comprehend at much detail in my experience. And there is no way that we can say "Colum234 went first then column567 followed by column789 etc etc"

 

[ozeco41]

I again highlighted the parts where your argument requires a bit of refinement.

...and again

Sure...BUT....

...we need to get some agreement on what we are calling by what names...

....and, of course, to decide whether we are discussing the real event OR the Bazant academic exercise.

Otherwise we are in "cloud cuckoo land" if that colloquialism is understood.

 

[Oystein]

Sure...BUT....

...we need to get some agreement on what we are calling by what names...

....and, of course, to decide whether we are discussing the real event OR the Bazant academic exercise.

Both actually, with the goal being to gain an understanding what most likely happened in real world. This sort of understanding can, for the most part, not be directly observed: There are no observations available from which we can measure how much energy was dissipated by this crushing of concrete, that fracturing of bolted connection or that bending of a steel beam.

That's where models come in, and Bazant's successively refined models can provide some good guidance. As you know, he started out with a limiting case most geared towards building survival, and we KNOW that this case did not (or only to a small, if not insignificant part) play out in the real world, and that IS observable.
The real world played out a complicated mix of interactions of all sorts of components, weak and strong, but preferably week.

What I am highlighting, and you understand this, is that Tony clings to Bazant's unrealistic limiting case, and thus his calculations and conclusions cannot be validly applied to the real world. In fact, he needs to substitute for assumptions that introduce very significantly different values with a significant influence on the results.

Dave's (and my, and OWE's) model involves a process that is quite independent of WHAT deformed and was destroyed; so you could say it does not describe the real event to any level of detail at all, BUT we know that, in summary, that model MUST have been close to reality. Some corrections introduced by real world properties, such as mass shedding and elastic wave propagation away from the collapse front, need to be applied, but these can be hedged; Dave's / my / OWE's estimates from a simple "conservation of momentum" model are in the right ballpark; Tony's estimates from "column dissipation" are not. His method however I think is "good enough". So I really think he needs to correct the assumptions implied in the phrases I highligthed, substitute them for more realistic values, re-calculate, and then he will find what you have said all along: As soon as collapse is underway, all structure must get "overwhelmed"
Energy available >> energy necessary to break connections
Force needed to arrest collapse >> Resistance offered by disaligned assembly

Otherwise we are in "cloud cuckoo land" if that colloquialism is understood.

Is that an actual English phrase? We do have a "Wolkenkuckucksheim" in our language ("home of the cloud cuckoo")

 

[DaveThomasNMSR]

Nonsense. You can't just use conservation of momentum and account for the column energy dissipation. The resistance was a combination of inertial resistance and coumn [sic]resistance. You are competely [sic]ignoring column resistance, which is also the much more significant of the two.

Sorry to burst your bubble publicly, but you have been told this privately several times and should have withdrawn what you were saying and amended it for column resistance.

Yes, you have been misunderstanding and misrepresenting my model for several years. My post above is not the first time I've called you on this specific strawman distortion of my analysis.

 

[GlennB]

I again highlighted the parts where your argument requires a bit of refinement.

It was highlighted 627 times during the "Missing jolt" thread. He took no notice then, either

 

[DaveThomasNMSR]

You didn't answer the question. What destroyed the columns?

An experiment: take several drinking straws, and wedge the end of one into the other until you have an assembly that looks like a yard-long straw.

Take this long straw, and see you long it will stand upright without you providing any support to keep it from tipping over.

That force that makes the straw tip over - the same force that made the "spires" collapse once their lateral supports (the floors) had fallen away - is called

Gravity.

 

[Tony Szamboti]

An experiment: take several drinking straws, and wedge the end of one into the other until you have an assembly that looks like a yard-long straw.

Take this long straw, and see (how) you long it will stand upright without you providing any support to keep it from tipping over.

That force that makes the straw tip over - the same force that made the "spires" collapse once their lateral supports (the floors) had fallen away - is called

Gravity.

Dave, I fixed your sentence, just like you fixed the two words in one of my posts where a letter was left out inadvertently.

With that aside, let's just say you have one of two legitimate ways forward. Either you go back and include the column resistance, or simply accept that your attempt to explain the constant acceleration as being possible due to natural circumstances didn't work out, and leave it at that.

No harm done unless you continue to claim a fatally flawed explanation, which does not include the most significant resistance, is still viable.

 

[ozeco41]

What column resistance are we disagreeing over?

From post 2 of this thread:

...Once the top block had started to fall all the support columns had already failed. some of them the top bit already falling past the bottom bit. Others still plastic bending before breaking. But all had failed. And none of them landed top bit on bottom bit and stayed there. (Several points in that paragraph which need careful thinking to understand why they must be true... )...

Are we talking about the real collapse given that is what D Chandler and others have measured?

Or are we extending a Bazantian theoretical model?

...And taking it outside the validity of its assumptions?

 

[Oystein]

Dave, I fixed your sentence, just like you fixed the two words in one of my posts where a letter was left out inadvertently.

With that aside, let's just say you have one of two legitimate ways forward. Either you go back and include the column resistance, or simply accept that your attempt to explain the constant acceleration as being possible due to natural circumstances didn't work out, and leave it at that.

No harm done unless you continue to claim a fatally flawed explanation, which does not include the most significant resistance, is still viable.

Tony! Argh!

I now not only highlighted but also boldfaced, italicised, underlined, magnified and colored the parts of your post that not just need reconsideration or improvement, but where you are
plain and fatally WRONG!!!

Tony, it is wrong, mistaken, erroneous, stupid to claim that column resistance slowed the collapse front. It didn't! The columns were largely bypassed,and that is easily observable at least in the case of the perimeter columns, which peeled off in large unbuckled sheets as the floors were sheared off on their insides.

The most important structural resistance to the avalanching floors was that of column-to-floor connections, which were orders of magnitude weaker than as-built (laterally fully braced) column strength.

Columns mainly suffered self-buckling subsequent to their loss of lateral bracing. All your values and claims about column resistance are wrong and do not apply.

Open your eyes, man!

 

[ozeco41]

...plain and fatally WRONG!!!...

I thought my version was slightly more subtle.

Let's see if your version is more effective.



BTW Why do both "sides" of this discussion mix up Bazantian bits with Real World bits???