Merged Applicability of Bazant's model to the real world

[enik]

What is your reason?

 

[DGM]

What is your reason?

My reason for what?

 

[tfk]

Excuse the terseness. I really don't have the time for this, and I'm not going to get drawn into trying to figure out your "analysis".

If you feel it "disproves" NIST's, publish it. Somewhere meaningful. Not the Interwebz.

Let’s see the model. Post a few jpgs, I know you have that ability.

OK. Here: http://wtc.nist.gov/

For the constraint for the truss to the vertical column, I constrained rotation at the nodes. I ran both analyses, with and without rotation; the non-rotational made the model more rigid and it kept its rectangular shape longer and more representative of the videos. I felt this was more conservative. Both failed in similar fashion though.

I presume you read NIST's model details. Feel free to detail what you think they got wrong. Remember to post what is the RIGHT answer that they should have used.

If you “feel” it should not be rigid, then I can model it that way (see above). If I ever perform analysis of failures at the truss/seat connection, I don’t see any reason not to use NIST’s results. I used their material/ temperature curves in other models.

Your model. You are responsible for the assumptions you make. That's how it works. If you make reasonable assumptions, then informed people will look favorably on you & your analysis.

If you make unreasonable assumptions, then informed people will look unfavorably on you & your analysis.

Who gives a flying fig what uninformed people think?

As for the question of the truss seat angles, obviously, the ¼” truss seat angle was rigid enough to allow pulling in the perimeter walls. Anything beyond that, I’ll assume NIST is correct unless I can prove otherwise.

Bending != Tension.

If my model doesn’t match reality then what should it have looked like?

Wrong question. Should be "If my model doesn’t match reality, then what should I do." Answer: if the differences are significant, change the model.

"what should it look like?" Answer: Like the real thing.

"How do you get there?" Answer: That's your job.

However, in its report, NIST gives you a WHOLE BUNCH of clues...

Should I change the entire upper part into a rigid assembly? Should I change the upper part into a solid block of steel? Both of these changes will suffice the Bazant hypothesis.

This is just silly.

And, by "silly", I mean "wrong".

As to your question of the sagging floors and the ‘S’ shaped external column, it’s beyond the scope of this thread topic and more detailed than your simplified description.

It wasn't my simplified description. It was yours.

I asked for you (in another forum) to demonstrate that heating a truss will cause sufficient pull in forces to pull in the perimeter wall. Let me know when you are able to do it and not just reiterate the NIST report.

I presume that you don't need it explained that heating a truss to the point that it sags will generate catenary pull-in forces that aren't in place at room temp. I presume that your problem is with the work "sufficient".

NIST came up with 14,000 pounds per truss. (NCSTAR1, pg 100, pdf pg. 150) What number did you get?

Let me ask you this: "What makes you think that the column deflection comes entirely from the truss sag?" Just as a matter of "feel", it seems clear to me that some percent of the inward bowing is due to the compressive loads in the columns. Which leads to more sag, and more deflection. A positive feedback loop.

Damage would not change the overall results of my model. In fact, it would make the collapse happen quicker. The model is more conservative without damage. Prove me wrong though.

No my yob, mon.

I didn’t count the number of my connections; maybe the NIST does have more.

I didn't ask about connections. I asked about elements. You know, as in "FEA".

To answer your final questions in a summary, the details in the NIST report are pretty much fine for me (unless I can prove otherwise). It’s the conclusions they draw by not connecting the dots by using FEA. They did not model the truss sag pulling in perimeter columns,

Uh, yeah, they did.
NCSTAR1, section 6.6.4
They specifically state that the thermal expansion initially pushed the external columns outward, but that floor sag reversed this, resulting in significant pull-in.
They also came up with the sag produced about 14,000 pounds of inward pull on each exterior column.

They got these from their models.

they did not demonstrate the initiating sequence with respect to perimeter column buckling,

I don't know what you're saying here. They went into great detail explaining the changes in loads & creep leading up to the collapse initiation, including the role played by inward buckling. They describe in detail what they concluded was the collapse sequence.

and obviously they did not model progressive collapse.

They didn't see this as their job. Neither do I.

They saw their job as to answer the questions: "what caused it?" and "how do we improve other buildings to reduce the chance of it happening again?"

Let me ask you two final ones:
Which is better:
1. Performing an FEA and backing it up with hand calculations or
2. Performing hand calculations and backing it up with an FEA

Neither is "better".
Each has its place. Hand calcs are quick & easy. And, in the hands of an experienced engineer, can be really useful. For simple systems.

For complex systems, FEA is the way to go.

The asymmetry is that you can use FEA to check hand calculations.
You generally don't use hand calculations to check FEA. (Unless someone has done something wildly inappropriate.)

tk

PS. I asked you what exactly has been your specific job description in your career. Care to answer?

 

[Major_Tom]

Ozeco post 1061: "But it does get boring seeing M_T and enik and femr2 repeatedly subjected to abuse and false claims which have no basis in fact. For example the ridicule poured on M_T for correctly identifying the limits in BZ and also commenting on the other papers. Such is the topic of this thread so the discussion and conclusions are spot on topic - contrast some of the criticisms which are both off topic and wrong. Same goes for M_T's OOS modelling of collapse progression or 'global collapse' which just happens to be a mainstream accepted explanation for global collapse other than the "ROOSD" title."


Contrast this post with

R Mackey post 1062: "uh, no. If worthless, why would they bother to publish it? Why would reviewers and editors accept and publish it?

The assumptions are called "simplifying assumptions" and not "worthlessing assumptions" because they simplify the problem -- in this case, as in Dr. Bazant's other works on the subject, providing a bounding envelope of likely outcomes. This result is not precise, but it's hardly worthless. Those assumptions are not guesses about what actually happened. They describe the model that the researchers applied to the problem.

All of science uses models. All of it. And some models are better than others. Some models only apply in certain situations and require some care before relying on them. If we took such a hardline, black-or-white view as you did, there would be no such thing as science. Nothing is 100% precise. Everything, every prediction, every estimation, every calculation relies upon sampling and assumptions and simplifications. Some fields like economics are so abstracted it's sometimes hard to even draw similarity between the simplifications and reality.

The only way the Bazant & Verdure model and result are "worthless" is if there exists a plausible case that lies outside its bounding envelope. Well, we're still waiting for such a solution. "


This is all BS and a lie. R Mackey is still selling the same snake oil even today.

Contrast this yet again with a more intelligent poster earlier in the thread

Dave Rogers, post 898

'There is a rather broader validity to Bazant's model, though. I agree that the collapse was not sufficiently homogeneous and well-behaved to follow Bazant's differential equations accurately. However, when faced by the wilful misapplication of Newton's Third Law by the "Net Force=0" idiots, it's worth pointing out that there were three components to the collapse, not two."

post http://www.internationalskeptics.com/forums/showpost.php?p=6415092&postcount=901

How about the "crush down, then crush up" idiots, Dave? You justify you position by contrasting them with the hallucinations of AE911T? How about the correct answer instead?


Dave Rogers, post 902:

'I think Bazant's later statements appear over-dogmatic in claiming that his model is a complete analysis of the collapses; it's clearly far too idealised to give any significant understanding of the detailed processes. It's useful, though, as a limiting case - as has been repeated ad nauseam to truthers on this forum - to refute the uninformed opinion that global collapse was in any way unexpected or implausible."

Post http://www.internationalskeptics.com/forums/showpost.php?p=6415103&postcount=902

This statement, outside of the fact that BV eqs 12 and 17, as the concepts of "crush down, then crush up", cannot be applied to WTC1, is wrong.

BZ is useful as a limiting case. The papers BV, BL and BLGB use a different model than BZ, based on eqs of motion for collapse progression.

Bazant has 2 models: One in BZ and the other through BV, BL and BLGB. If you confuse them or blur them as Dave does, you begin to speak jabberwockey.


>>>>>>>>>>>>>>>>>>>.
>>>>>>>>>>>>>>>>>

I told you all this in my OP for the OOS collapse progression model in May. I received about 14 pages of insults and poor, poor interpretations at the beginning of that thread.


It is now December. This forum is still selling the same lie. This is the perfect example of why I call JREF a propaganda forum. The crap is so piled so high that no real, fair debate is even possible.

If Albert Einstein himself rose from the dead and explained to you what is wrong with the BV, BL and BLGB papers, he would be shouted down in this environment and called an idiot.

R Mackey feeds you incorrect garbage even today.

 

[tfk]

If Albert Einstein himself rose from the dead and explained to you what is wrong with the BV, BL and BLGB papers, he would be shouted down in this environment and called an idiot.

R Mackey feeds you incorrect garbage even today.

LoL.

Old Al was a physicist. His opinion on the matter wouldn't matter squat. I feel pretty sure that he was humble enough that, if he were here, he'd reply "go ask an experienced structural engineer."

You know, guys like Leslie Robertson, John Gross, Therese MacAllister, Thomas Wiezbecki, etc.

Oh, yeah, and Zdenek Bazant.

Guys like that.

tk

PS.

The assumptions are called "simplifying assumptions" and not "worthlessing assumptions" because they simplify the problem -- in this case, as in Dr. Bazant's other works on the subject, providing a bounding envelope of likely outcomes. This result is not precise, but it's hardly worthless. Those assumptions are not guesses about what actually happened. They describe the model that the researchers applied to the problem.

All of science uses models. All of it. And some models are better than others. Some models only apply in certain situations and require some care before relying on them. If we took such a hardline, black-or-white view as you did, there would be no such thing as science. Nothing is 100% precise. Everything, every prediction, every estimation, every calculation relies upon sampling and assumptions and simplifications. Some fields like economics are so abstracted it's sometimes hard to even draw similarity between the simplifications and reality.

The only way the Bazant & Verdure model and result are "worthless" is if there exists a plausible case that lies outside its bounding envelope. Well, we're still waiting for such a solution. "

This is all BS and a lie.

Each sentence seems both reasonable and correct.

Which ones do you feel are "BS & a lie"?
Why don't you elaborate...

 

[DGM]

Major Tom:
This is just a friendly suggestion,
CHANGE YOUR FORMAT.


Your post border on the un-readable. You may think what you say is significant but, until you show us why your not just some nothing with the most confusing posting style in history no one is listening.

A couple points you should consider:

(1) Why do you think we should listen to you?

(2) Why should we put up with your odd style to listen to you?

(I had more but, frankly none of them need to be considered until you can answer the above)

 

[enik]

Excuse the terseness. I really don't have the time for this, and I'm not going to get drawn into trying to figure out your "analysis".
...

No problem, I don't have the time to teach you FEA.

 

[excaza]

It is now December. This forum is still selling the same lie. This is the perfect example of why I call JREF a propaganda forum. The crap is so piled so high that no real, fair debate is even possible.

If Albert Einstein himself rose from the dead and explained to you what is wrong with the BV, BL and BLGB papers, he would be shouted down in this environment and called an idiot.

R Mackey feeds you incorrect garbage even today.

And yet, you restrict your work to JREF instead of going somewhere real.

 

[Major_Tom]

3 JREF posters hallucinating an "upper block" and "crush up, then crush down": (I could find many, many examples of this fantasy projection of Bazant's BV eqs 12 and 17 onto the "real world")


R Mackey, physics expert, hallucinating an "upper block":

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.

Dave Rogers provides another example of applying the concept of crush down, then crush up to the "real world" here:

If you were to actually read Bazant's papers for comprehension, rather than deciding what strawman you want to attribute to them, you would see that the analysis predicts that crush-up and crush-down will initially both occur, but that the rate of crush-up will quickly decay to zero while the rate of crush-down increases. This is an idealised case, and the presence of damage to the structure above or below the collapse initiation zone will modify the precise amount of crush-up initially observed, but at no point is Bazant claiming that there is no crush-up until crush-down is complete; he's determining that a very small amount of initial crush-up occurs, but that it self-terminates until the upper block contacts the ground. As a result, a small proportion of the rubble comes from the upper block, and the majority from the lower.

We once again have an upper block being destroyed by crush up only after it hits the earth.

The upper block once again preserved by the strength of it's columns and the magic zone B. Bazant proved it in BL, no?

with no awareness of the irony, Dave concluded:

Funnily enough, no, the rest of us can't see that, because the dust ejected by the collapse obscures vision of the upper block part way into the collapse. Since we can't tell what happens to things we can't see, we can either make up something that fits our prejudices or model the physics of the collapse mathematically and draw provisional conclusions. The first approach seems to be working very nicely for you, to the extent that you've convinced yourself you can see something that's hidden in a dust cloud. For the rest of us, we'd rather start from what we can see then decide on a conclusion, than start from a conclusion then decide what we can see.

Here is an example of Newton's Bit conjuring up a surviving upper block and the magic zone B in his description of how real buildings would collapse.

From page 2 of the OOS model thread

I asked him:

"1) In BL, can you explain why Dr Bazant insists that crush down must be complete before crush up occurs. Does he mean this literally?

2) Do you consider the equations of motion in BV, equations 12 and 17, to be accurate considering the information in the ROOSD study?"

He answered:

ffs Read the paper. Here, let me explain it to you:

The upper block is accelerating at near g. This means that there is very little force being applied to it. We can imply that the absolute maximum height of destruction occurring through the upper block will happen at a rate equal to (g - a). However the upper block has some residual strength. This force is much less than the original capacity upper block which is somewhere in the neighborhood of 3*m*g.

There will be, during the initial stages of the collapse that forms the rubble layer, destruction on both the upper block and lower block. But once it gets moving? Not so much.

You've provided no information on how this is incorrect.

>>>>>>>>>>>>>>>>>>>>>>.
>>>>>>>>>>>>>>>>>>>>>

To me, this is the perfect example of being gullible while pretending you know all the answers. All these comments are not based on physics or the physical world at all, but on a deep-seated belief that whatever Bazant says and whatever passes peer revioew is the "God's truth".

All three posters are hallucinating an "upper block" and a "crush down, then crush up" process wherein the the top part rides a magic carpet of debris to the earth like sweet Jesus descending from a cloud.

Why? Gullible belief in a perceived authority figure with no actual fact checking whatsoever.

Belief hidden in the guise of physics.

Notice the irony of R Mackey's and Dave's insults toward those who do not share the same hallucination.

Edited by Locknar: 

Edited to correct quoted material; when quoting please ensure such material is clearly noted (use of the QUOTE tags is the preferred method).

 

[TheRedWorm]

Major Tom:
This is just a friendly suggestion,
CHANGE YOUR FORMAT.


Your post border on the un-readable. You may think what you say is significant but, until you show us why your not just some nothing with the most confusing posting style in history no one is listening.

A couple points you should consider:

(1) Why do you think we should listen to you?

(2) Why should we put up with your odd style to listen to you?

(I had more but, frankly none of them need to be considered until you can answer the above)

It's probably deliberate. He has the ability to use the quote feature to cut down on confusions and increase readability, he just chooses no to. The purpose is not clear, concise communication; it is obfuscation by means of formatting.

 

[twinstead]

The purpose is not clear, concise communication; it is obfuscation by means of formatting.

Would that be obfumatting, or formafuscation?

 

[beachnut]

Engineers would not attack Bazant's paper...

Engineers would do their own papers and not make up lies of CD based on nonsense.

Where in this thread has anyone "attacked" Bazant. The thread is simply an attempt to identify the limits that Bazant built in to his work. ...
Suggesting that anyone identifying these assumptions and limits is somehow attacking Bazant is bizarre to say the least.

The whole Bazant Zhou thing is a bit of a red herring,

It's a total red herring as both Bazant and the NIST skip over the real issue of the initial column failure sequence.

tell the difference between a 1-D stick model and the real towers here

The conclusion steps outside the bounds of model applicability.

It's such a relief to throw Bazant out the window..

On the question of applicability, we need to honestly recognize examples of people clearly crossing the line by applying the results of the Bazant 1-D stick model to real 3-D buildings.

It's a pleasure to see the Bazant distraction being frogmarched out of the real-world event.

That is one of Bazant's mistakes.

you see any traces of Bazantian pollution of real world thinking in the attached video ?

Bazant was only right to initially believe there would have to be a jolt since that is what it would take for a natural collapse to occur. However, he never measured the descent to see if there was one. It turns out there isn't one and it means the collapse of that building was not due to natural causes.

believe it has something to do with a man named Bazant and this supernatural source of kinetic energy he discovered two days after 9/11.

Posting nonsense about Bazant's work; for me that is an attack.

... Notice the irony of R Mackey's and Dave's insults toward those who do not share the same hallucination.

Major Tom does not understand models with each off topic post of nonsense. How can he attack Bazant's work; something with math in it?

911 truth, the CD believers think facts are insults.

 

[pgimeno]

Unwarranted personal attacks aside, there is a very basic misunderstanding of the scientific method here.

Once you have a model, you go back to the real world to see if it works. In other words, you run experiments to see if the model agrees with reality, or in this case, to see if the simplifying assumptions are actually "reasonable" and the model works.

Two ways I see of validating the B&V model would be (1) build scale models of buildings, initiate collapses, (2) build FEA models of buildings, initiate collapses; then see whether - and under what conditions - the B&V equations are valid. As this work has not been done, the model remains unproven. I suspect that the B&V assumptions are wrong, and therefore that the model is worthless, but I am willing to be proven otherwise. Enik's model is the first attempt in this direction I have seen, and it doesn't appear to support the model.

May I recommend a reading of the OP here?

Same goes for Major_Tom.

 

[TheRedWorm]

Would that be obfumatting, or formafuscation?

That one sounds more like a word. Or a dark ages torture.

 

[Major_Tom]

Closure to Mechanics of Progressive Collapse, Bazant and Le, 2007

http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/D25.pdf

Sections 2 through 6 written by Bazant are meaningless considering what we now know.

This is a dinosaur. I challenge anyone to find meaningful, applicable information is sections 2 through 6.

This is one of the easiest papers in the series to rip apart.

WIth the advantage of hindsight, it amazes me that anyone took this crap seriously.

 

[pgimeno]

It's déjà vu all over again...

http://www.internationalskeptics.com/forums/showpost.php?p=6274286&postcount=84

MT keeps ignoring the answers already given and keeps ignoring the context of the texts he criticizes, distorting their meaning. An excerpt of my response:

Let's add context to that quotation. It's a response to a criticism raised by chemical engineer James R. Gourley. Here's an excerpt of Gourley's words:

The physical reality for each tower, which any instructive collapse analysis must take into account, can be summarized as follows: for a particular tower, the upper part (Part C), lower section (Part A), and the crushing section (Part B) were all very similar to one another from a materials, engineering, and construction standpoint. Therefore, the only reasonable qualitative assumption to make when analyzing the ability of each section of the building to deform when the upper part (Part C) impacts the lower structure is that the plastic deformation and yield strengths, (as well as any other energy absorptive properties, such as elastic strain values) of the components of the lower structure (Part B and Part A) are roughly equivalent to the deformation and yield strengths of the components of the upper Part C. This qualitative assumption is required regardless of the quantitative assumptions that are made regarding the magnitude of such deformation and yield strengths or the mode of deformation used in the collapse analysis. Furthermore, this unavoidable qualitative assumption leads to the conclusion that when Part C impacts the lower structure Part B or Part A , the damage or deformation caused by the impact must be shared roughly equally between Part C and the lower structure. The justification for this conclusion lies in the application of Newton's Third Law.
​

From this, it should be clear that Gourley is criticizing the principle behind Bazant's crush direction model, and that is what the closure addresses. It is still a theoretical point of view, no matter how you try to push the contrary. Again, Bazant is not claiming anywhere that the crush-up did not happen in reality in either WTC.

I agree with you, however, in the irony in Bazant's closing comments. Your very attempts to discredit him are the very proof of how true they are.

Highlighting added.

 

[twinstead]

That one sounds more like a word. Or a dark ages torture.

Or something the Dark Ages Church would have burned you at the stake for. "You stand accused of formafuscating with the Devil. How do you plead?"

 

[ozeco41]

May I recommend a reading of the OP here?

Same goes for Major_Tom.

The OP is "Applicability of Bazant's model to the real world" and I am clear where the assumptions lie for Bazant and Zhou.

I am not clear where the assumptions apply to limit applicability of Bazant's later work with other collaborators. I had been hoping that someone could clarify things for me but it looks like I will have to do the hard mental graft of working through all the papers.

The truth - if I dare to use that word - lies somewhere in the middle ground between the two polarised 'sides' engaged in this thread. And both 'sides' seem to be overstating their claims and derailing into not relevant matters rather than focussing on the topic.

 

[Major_Tom]

Pgimeno, you make up the meaning of these papers yourself.

You have no clue how to read them. Bacially everything your wrote is incorrect, but you prefer your own dream of what these papers mean.

I have been informing you of this for months.

Do you realize that your famous "upper block" survives until it collides with the earth in this fantasy scenario?

 

[ergo]

This is a good thread. Finally something to read again on JREF.

I am wondering why tfk did not address enik's post #1075 wherein he asks tfk to post some jpegs of his catheter design. TFK posted instead a link to the NIST WTC FAQ. -- ??? WTF? I know that bee dunkers have a tendency not to answer simple, straightforward questions, but such a response that is so blatantly fake is shocking, even by bee dunker standards.