Merged Applicability of Bazant's model to the real world

[ozeco41]

Would you happen to have a quick link to these equations (save an old guy a lot of looking-up)?

Anyone else want to "catch me up" (although I vaguely remember being here before)?

I cannot help there. Part of the reason also being "retired old fart". (The '41' in the username should decode easily. )

It is pure hard work reading all the Bazant stuff after BZ to see where the limiting assumptions are. And a thankless task on this forum where anyone daring to look at the bounding assumptions is cast into the outer darkness of trutherdom.

With BZ it is easy to see the assumptions but the other papers are harder and I haven't really spent the intellectual energy to work through the obtuseness of the academic style. They all clearly start from a theoretical model so the applicability to the specifics of WTC collapse must be sus but at this stage I cannot say exactly where the limits are. Doesn't bother me all that much - I simply don't rely on Bazant et al as authorities. Neither do I confront those who do see Bazant et al as holy writ - I won't do that until and if ever I get a handle on where the limits are.

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.

Still this thread is about "Applicability of Bazant's model to the real world" not about opposing members qualifications or any supposed interest in CD which has not been raised in this thread.

 

[R.Mackey]

Read Bazant & Verdure if you haven't already:

If any of these "simplifying hypotheses" are wrong, than their 1-dimensional mathematical model is worthless.

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.

I understand enik might claim he has one, but like the Great Oz he keeps it well hidden, behind a curtain. This is silly. If anyone has such a result, it should be examined, verified, and published, at the very least in a conference setting.

None of this has happened. Ergo, there is no validity to claims that Bazant & Verdure is worthless. QED.

---

For the tl;dr crowd: The quoted poster knows precisely zip about science.

 

[Carll68]

Still this thread is about "Applicability of Bazant's model to the real world" not about opposing members qualifications or any supposed interest in CD which has not been raised in this thread.

Supposed? Really? Supposed interest in CD by Femr2?

This is the same kid who:
*Argued endlessly that there was a 'pod' on the underneath of the flight 11
*That there were two FL175's and thus a flyover
*That there was not enough energy in the collapse to 'throw' the debris from the trade centers to the roof of the winter gardens unless there were 'explosives' involved
*That the fires would be 'wicked away' with the' heat sinking' of the towers construction and thus would never collapse without explosives
*That built a faulty collapse simulator (that later when called on his errors by TFK was no longer a "simulator" but a "visual aid")
*That arrested all the energy from collapse into an energy sink to 'crush' the concrete thus concluding that the only way the towers would collapse was through a CD.....on and on...

Supposed? Phhhlease.

This is just another way for the kid who can't answer high school level physics questions or understand conservation of momentum to try to back in his delusions of CD.....

Point. Blank. End.

Oh, and ENIK..where is the answer to that simple physics question? Cat got your tongue?

 

[enik]

...crickets.

Thanks TFK, you gave me my 50th post and a signature, dedicated to you.

 

[Carll68]

...crickets.

Thanks TFK, you gave me my 50th post and a signature, dedicated to you.

We all know why it is crickets kid.....

To bad that why is because - with all your, uh-hum 'degrees', in reality, ya don't know a darn thing about physics....

Fact is..you could have answered that simple question (as opposed to running from it) in the time it took you to type that reply and make that signature you seem proud of.....


I think we are done here, and you have been exposed .. for all to see

sur-prise sur-prise..another twoofer with made up credentials...

Crickets indeed...

 

[ozeco41]

Supposed? Really? Supposed interest in CD by Femr2?

Bit of a quote mine there Carll.

I am aware of some of femr2's other interests. They are not under discussion in this thread.

That does not legitimise snide comments about those interests as tricks to evade responding to what is actually posted and on topic for this thread.

Legal practitioner's maxim "If you have no case attack the witnesses"

Corollary "If they are attacking the witnesses they have no case."

Why not simply address the topic. End of my comments.

 

[lozenge124]

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.

I understand enik might claim he has one, but like the Great Oz he keeps it well hidden, behind a curtain. This is silly. If anyone has such a result, it should be examined, verified, and published, at the very least in a conference setting.

None of this has happened. Ergo, there is no validity to claims that Bazant & Verdure is worthless. QED.

---

For the tl;dr crowd: The quoted poster knows precisely zip about science.

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.

 

[beachnut]

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.

Your post exposes you don't understand the scientific method attacking a paper you don't understand. You have talk and failed claims. You will not be publishing anything rational on Bazant, or 911. Where is your model?

Pointing out your ignorance in science and engineering is not a personal attack, it is a fact. I suggest you take some physics courses and engineering courses, or consult an engineer who is not a crazy CT nut; this may help you become rational on 911 issues and stop supporting attacks on a paper you don't understand. Engineers would not attack Bazant's paper, they would publish their own paper. By attacking Bazant, people expose their ignorance and the fact they are paranoid conspiracy theorists on 911 issue, not engineers, not scientists, only people with delusions on 911.

 

[Grizzly Bear]

I'd rather they actually read the papers they critique... this misreading of the B&Z models is exactly the reason why I've grown tired of exchanging posts with their critics. :\

 

[triforcharity]

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

You must not come around these parts often.....

 

[ozeco41]

... Engineers would not attack Bazant's paper, they would publish their own paper...

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. There is nothing wrong with putting bounding assumptions on an explanatory method which is what Bazant and Zhou did in their paper and a practice which Bazant correctly continued into his later work with other collaborators. I am an engineer and I choose to recognise the work of Bazant and Zhou in full recognition of the assumptions which they openly identify.

Suggesting that anyone identifying these assumptions and limits is somehow attacking Bazant is bizarre to say the least.

 

[ozeco41]

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

In some ways the problem is even deeper than that.

The test of a claim about anything - say WTC Collapse here - is "Is the claim right?" NOT "Has it been published in a peer reviewed journal?"

Granted that peer reviewed publication is one good test of the probable veracity of the material in a paper.

Then again the "scientific method" is not the only approach to analysis of WTC Collapses. It is not a perfect fit on what is essentially a one off exercise in engineering forensic assessment.

And both those two claims could start threads of their own. I merely post them as thought starters.

 

[tfk]

MSME, BSME, PE, 20 years in Nuclear Construction, Automotive, and now oil and gas.

"... in nuclear construction, automotive & oil & gas."

Doing what, exactly?

Mine: BSME, 36 years as a project engineer & new product design engineer.

You know, enik, you remind me of our late, unlamented Derek Johnson. The guy that ran for state representative &, when word got out that he was a truther, got about 700 out of about 28,000 votes.

TFK, can you demonstrate your abilities using FEA?

Yup. Several thousand people's heart arrhythmias cured by a catheter that I designed using FEA. Had to push the limits of the material in order to get the catheter down to a size that was introduceable. The fact that the design worked proves it.

Now, two comments on your model.

You asserted that the proper constraint for the truss to vertical column is a fixed constraint.

Here's the connection, according to NIST's model. (NCSTAR1, p 98, pdf pg 148)

First, engineering "feel":
Do you really think that a 1/4" thick (IIRC) seat angle will be rigid compared to the 14" box column & 34' long moment arm of the floor trusses?

Second: the evidence.
If feel doesn't work for you, you might want to look at the hard data of the failure modes of the "column support / truss seat / truss" assemblies. Just to see what failed, and how they failed.

Finally, a little engineering common sense.
The first rule of modeling: if your model doesn't match reality, change your model.

You correctly asserted that, if the connections were rigid, the external columns would have been bent into "S" shapes as the floors sagged. The floors DID sag & the outer walls did not bend into "s" shapes.

Gee, enik. What do you think that might say about your assumption …?
___

BTW, I didn't notice any physical damage captured in any of your models. I'm sure it was just an oversight on my part. Surely, you weren't drawing your conclusions based upon a model of the towers the did not have any impact damage…?
___

NIST went thru a detailed description of their analysis of the floors.

They did not "assume the connections were rigid". They modeled them. (see figure 6-10 above. Looks to me like it's got about 500 or so elements in just the stand-off plate, seat angle & bolts. Looks like it's gonna have about 20,000 or more elements in just one truss. How many did your model have?)

The models were developed by Leslie Robertson's company (LERA), and checked by Skidmore, Owings & Merrill & by NIST (NCSTAR1, pg 92, 93).

Rather than discuss your model, please explain:

1. what you think is wrong with the LERA / NIST FEA model.
2. what changes would correct NIST's "errors".
3. why you think that I should reject the careful analyses of dozens, perhaps hundreds of recognized world class experts in structural engineering of skyscrapers, and accept the contradictory assertions of some anonymous guy on the internet who, by his own admission, has never designed or analyzed a skyscraper in his life?

tom

PS. Perhaps someone else will be able to engage you in this discussion. I'm afraid that my schedule is packed full at the moment. And this nonsense is, well, just plain nonsense.

 

[twinstead]

3. why you think that I should reject the careful analyses of dozens, perhaps hundreds of recognized world class experts in structural engineering of skyscrapers, and accept the contradictory assertions of some anonymous guy on the internet who, by his own admission, has never designed or analyzed a skyscraper in his life?

This is, and has been since I started paying attention to the 9-11 conspiracies, the 64 thousand dollar question.

 

[enik]

"...a catheter that I designed using FEA...

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

As for your questions, you’ll forgive me if I don’t answer point by point but I should be able to cover everything.

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.

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.

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.

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

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. 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.

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.

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

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, they did not demonstrate the initiating sequence with respect to perimeter column buckling, and obviously they did not model progressive collapse.

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

 

[DGM]

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

I would say #2 if there was some legitimate reason to doubt the analysis. So far no one has produced this reason.

How about you? What exactly did they get wrong?

 

[enik]

How about if we exclude everything having to do with 9-11, WTC, NIST, truss sag, column buckling, etc.
1 or 2?

 

[DGM]

How about if we exclude everything having to do with 9-11, WTC, NIST, truss sag, column buckling, etc.
1 or 2?

Exactly the answer I expected. Thanks.

 

[enik]

Your welcome.

 

[DGM]

Your welcome.

So, do you plan to tell us (or the engineering community) why we should pay you any attention?