Analysis of Bazant & Zhou (2002)

[Minadin]

Normally I would agree but bofors is so obviously spamming . Nothing can kill off a messageboard then a constant diet of spam. IF would bother to put the information in his own words I would be a lot more tolerent.

I would tend to agree that I prefer original content when I can get it, but in this case, perhaps the lack thereof is equally educational.

The Conspiracy Theorists in the so-called "Truth Movement" have been reduced, with very few exceptions, to broken-record status. All of the "points" any of them have brought up, in recent memory, have just been mindless parroting and unthinking mimicry of the same absurdities we've seen time and time again. At least in this case it's a little more honest, the author isn't pretending to think for himself, and isn't trying to pass someone else's work as his own.

So while I would personally format his argument a little bit differently (by citing my source and then expanding on the points on my own, perhaps responding to posts made in opposition, etc) at least the chap is giving us new insight into how some conspiracy theorists work, with his transparency, if not actually providing any new worthwhile analysis into the subject matter he's attempting to tackle.

 

[GregoryUrich]

Valid criticism of B and Z

cut...Valid criticisms so far - 0

I'll await the remaining points with more resignation than anticipation.

Dave

There remains valid criticism of B and Z:

According to B and Z "Po = mg = design load capacity".

They are using mg for two different things that are not equal: First as a component of the gravitational potential energy and then as the design load capacity.

The proper equation is Pdyn/Po = (1/2 + sqrt(1 + 2Ch/mg)) x mg/Po.

B and Z assumed mg = Po, which is untrue. In fact mg = Po/5 (approx).

Since they didn't know what design load capacity was, they guessed it was 55,000 tons. Oops! The actual load capacity was around 155,000 tons at the collapse area, based on Newton's total cross-sectional area and 36 ksi steel. Since they didn't know what the service mass of the upper part was they guessed it was 55,000 tons. Oops! A more realistic mass is 32,000 tons.

One has to ask, where they got the value for C. If it is as far off as the other values, the conclusion may not be valid.

 

[Gravy]

Gregory, keep in mind this statement in the paper:

Once accurate computer calculations are carried out, various details of the failure mechanism will doubtless be found to differ from the present simplifying hypotheses. Errors by a factor of 2 would not be terribly surprising, but that would hardly matter since the present analysis reveals order-of-magnitude differences between the dynamic loads and the structural resistance.

And keep in mind the simplifying assumptions that are grossly in favor of global collapse prevention.

 

[beachnut]

There remains valid criticism of B and Z:

According to B and Z "Po = mg = design load capacity".

They are using mg for two different things that are not equal: First as a component of the gravitational potential energy and then as the design load capacity.

The proper equation is Pdyn/Po = (1/2 + sqrt(1 + 2Ch/mg)) x mg/Po.

B and Z assumed mg = Po, which is untrue. In fact mg = Po/5 (approx).

Since they didn't know what design load capacity was, they guessed it was 55,000 tons. Oops! The actual load capacity was around 155,000 tons at the collapse area, based on Newton's total cross-sectional area and 36 ksi steel. Since they didn't know what the service mass of the upper part was they guessed it was 55,000 tons. Oops! A more realistic mass is 32,000 tons.

One has to ask, where they got the value for C. If it is as far off as the other values, the conclusion may not be valid.

Funny stuff; as you attack this work making gross errors, you in effect make Ross's work totally worthless. But all is not lost since you are off by a factor of two. You still have not found the errors in your weight. So which is it. All your work is error filed as is this post, I only have to look at the things you sign to see how bias you are, and at this post and other to see the bias at work.

 

[cmcaulif]

There remains valid criticism of B and Z:

According to B and Z "Po = mg = design load capacity".

They are using mg for two different things that are not equal: First as a component of the gravitational potential energy and then as the design load capacity.

The proper equation is Pdyn/Po = (1/2 + sqrt(1 + 2Ch/mg)) x mg/Po.

B and Z assumed mg = Po, which is untrue. In fact mg = Po/5 (approx).

Since they didn't know what design load capacity was, they guessed it was 55,000 tons. Oops! The actual load capacity was around 155,000 tons at the collapse area, based on Newton's total cross-sectional area and 36 ksi steel. Since they didn't know what the service mass of the upper part was they guessed it was 55,000 tons. Oops! A more realistic mass is 32,000 tons.

One has to ask, where they got the value for C. If it is as far off as the other values, the conclusion may not be valid.

I really don't see how that would change his conclusion that progressive collapse occurs. Even if the result of equation one showed that the the dynamic load was the minimum of two times the static load, as long as Wg/Wp is greater than one collapse will occur.

Plugging in your new mass still causes progressive collapse, though you could still check the blueprints and find or calculate the Zx for the several different sections used to see if his estimate was accurate. I think using 2pi for the sum of the rotation of the three hinges was quite a lot, though in favor of survival, perhaps other posters can comment on that.

 

[Dave Rogers]

One has to ask, where they got the value for C. If it is as far off as the other values, the conclusion may not be valid.

So the correct way forward is for other workers to examine their conclusions based on evidence arising subsequently, and determine whether that conclusion remains valid. As far as I understand, you've done so and verified it, based on the assumptions of no damage to the columns immediately below the point of initiation (which is not only biased, but unreasonably so, in favour of survival, given that the damage to the perimeter columns at the very minimum is indisputable), and of symmetrical column-on column impact (which is biased to the limit of physical possibility in favour of survival), and still found that only in the limit of crush-up/crush-down (which takes as a starting assumption that the lower block survives the impacts of all but the last floor to strike it, and hence is biased heavily in favour of survival) does collapse self-terminate. Please correct me if I'm wrong, but that's how I understand your earlier posts.

I really have no idea what bofors is trying to prove here. If he's trying to prove that Bazant and Zhou published quickly derived interim results, the clue is in the title, "Rapid Communications", which any scientist should recognise as a format for publishing quickly derived interim results. If he's trying to show that global collapse shouldn't have ensued, he needs to show his calculations that lead to an arrested collapse, rather than try to nitpick the first ever paper to address the issue and ignore the large body of subsequent analysis that's been done. And if he's trying to show that collapse shouldn't have initiated, he needs to actually read the NIST report before he can show where it's wrong.

Dave

 

[DGM]

Bump for Bofor.

You didn't forget this did you?

 

[boloboffin]

I don't think he's forgotten it. He's going to write the whole thing out and then post it.

Of course, he does seem to post an awful lot in other threads for someone who's cracking down on their analysis.

 

[Dave Rogers]

Edited by chillzero: 

This post moved from:
http://www.internationalskeptics.com/forums/showthread.php?t=98081
Please do not ignore mod warnings to stay on topic.

I have not even looked at thread since my last post in it.

Instead, I am preparing a written critique of Bazant & Zhou 2002, which of course will detail the problems with their Equation 1 and their "Elastic Dynamic Analysis", among other things.

I will post a copy in this forum when my paper is done.

Bofors, I am doing you a favour here. Don't post your critique. You'll only embarrass yourself even more. Let me explain.

Bazant and Zhou's Equation 1 is derived from the equation of motion of a weight constrained to move vertically, acted on by gravity, connected to a perfectly elastic spring, and subject to the boundary condition that the vertical speed at the point where the spring is in zero compression is sqrt(2gh). This is a very good first approximation to the behaviour of a weight dropped on to a steel structure from a height h above the top surface of that structure from the moment of impact to the moment when the structure reaches maximum compression. The two roots of equation 1 correspond to the force exerted by the mass on the spring at the two extremes of its oscillation. The negative root corresponds to the point when, after rebounding from the initial fall, the weight rises to the point where the spring is now in tension, at which point (because there is no connection between the weight and the spring in the situation being modelled) the model becomes inappropriate; however, this is not a concern because the analysis does not require the motion to be projected this far. The positive root corresponds to the force exerted on the spring at maximum compression, and is hence the maximum force that can be exerted on the spring by the falling weight. This value is known as the dynamic loading. You observed that the dynamic loading is twice the static loading when h=0; this is correct, and is a consequence of the fact that the weight is above the equilibrium position at h=0 because the spring has not compressed at this point, so it will fall and compress the spring, falling past the equilibrium point in its harmonic motion and hence, by Hooke's law, exerting a force greater than its weight. All this has been pointed out to you.

The above analysis is roughly at the level of a reasonably able high school student who has taken a mechanics course. The fact that you're unable, despite having this explained to you, of following this analysis should be a major warning sign to you. Your criticism stems not from any error in Bazant and Zhou, but from the fact that you do not understand simple mechanics even at the most elementary level. Your critique will do nothing but highlight this ignorance, and several posters, myself included, will show no mercy in exposing that ignorance should you go ahead and choose to attack Bazant, whose understanding is so much greater than yours that you seem unable to comprehend the gap between you. And the end result of this is that it will be clearly shown that ignorance is at the root of your beliefs about 9-11.

For the good of your self-respect and of the movement you attempt to represent, I suggest you withdraw from this debate altogether. You can do yourself, and it, nothing but harm.

Dave

 

[westprog]

I don't think he's going to read this even with the abnormally large text size

Try a different font and colour.

It's an important point that even if there are flaws to be found in a given analysis, that doesn't imply that the conclusions of the analysis are wrong, or that some alternate theory is necessarily right, or even plausible.

There are ample non-engineering reasons to conclude that the WTC collapse was caused by aircraft impact and subsequent fires. If an engineering document that supports this turns out to use an incorrect analysis, that doesn't mean that it's conclusions are false, or even in doubt.

In order to rebut such an analysis, it's necessary to provide a plausible alternate mechanism for collapse. It would then be desirable to provide a detailed engineering document describing how such an alternate collapse mechanism might have occurred.

This is not to imply that there are necessarily any such flaws in any of the standard documents describing the collapse initiation - merely that any such flaws don't lead to an automatic conclusion that the collapse could not have occurred from impact and fire alone.

 

[GregoryUrich]

Funny stuff; as you attack this work making gross errors, you in effect make Ross's work totally worthless. But all is not lost since you are off by a factor of two. You still have not found the errors in your weight. So which is it. All your work is error filed as is this post, I only have to look at the things you sign to see how bias you are, and at this post and other to see the bias at work.

Nothing funny here. I have no interest in Ross being correct.

Based on your 50 ton clue, I guess you are talking about the airplane wreckage which is not part of the building. We can add that in the collapse analysis. Nonetheless, I am aware that I don't include elevators and aluminum cladding. I will add this before publication.

You can't say what the error in my post is because there is none. The errors are all B and Z's, and your's too if you believe them.

 

[GregoryUrich]

Gregory, keep in mind this statement in the paper:

And keep in mind the simplifying assumptions that are grossly in favor of global collapse prevention.

Many people here point to the B and Z paper as proof that the building should have failed as they describe. It's just not valid to make simplfying assumptions in favor of collapse prevention, have an erroneous result and claim the hypthesis still holds.

The problems with B and Z's paper are:

• mg is not equal to Po
• C is probably as far off as Po (since it is based on it)
• that upper part is also a spring which is not taken into account
• the upper part is also weaker structurally and would (and did) fail first

All the problems together could reduce Pdyn/Po to less than one. Unfortunately, no one tried to solve this problem correctly yet. One day it may be shown that the building should have collapsed, but it hasn't been proven yet.

 

[GregoryUrich]

So the correct way forward is for other workers to examine their conclusions based on evidence arising subsequently, and determine whether that conclusion remains valid. As far as I understand, you've done so and verified it, based on the assumptions of no damage to the columns immediately below the point of initiation (which is not only biased, but unreasonably so, in favour of survival, given that the damage to the perimeter columns at the very minimum is indisputable), and of symmetrical column-on column impact (which is biased to the limit of physical possibility in favour of survival), and still found that only in the limit of crush-up/crush-down (which takes as a starting assumption that the lower block survives the impacts of all but the last floor to strike it, and hence is biased heavily in favour of survival) does collapse self-terminate. Please correct me if I'm wrong, but that's how I understand your earlier posts.

I really have no idea what bofors is trying to prove here. If he's trying to prove that Bazant and Zhou published quickly derived interim results, the clue is in the title, "Rapid Communications", which any scientist should recognise as a format for publishing quickly derived interim results. If he's trying to show that global collapse shouldn't have ensued, he needs to show his calculations that lead to an arrested collapse, rather than try to nitpick the first ever paper to address the issue and ignore the large body of subsequent analysis that's been done. And if he's trying to show that collapse shouldn't have initiated, he needs to actually read the NIST report before he can show where it's wrong.

Dave

No, I haven't gotten around to verifying C or done any serious collapse analysis yet, so I haven't made any assumptions about damage or reached any conclusion. A good collapse analysis would include the points you mention.

My intuition tells me that probably a few floors in the upper block failed first and then both blocks failed simultaneously with the slight possibility of the hat truss floors riding most of the way down.

I think bofors is focussing on this paper because many people point to it as proof that global collapse was inevitable. I think critcizing the paper in this regard is useful. It would be even more useful to do a better analysis that actually proves something one way or the other, but most people don't have the knowledge or tenacity. I am impressed by Newton's work in this regard.

 

[Dave Rogers]

The problems with B and Z's paper are:

• mg is not equal to Po

That's probably not what you mean, as the paper contains the definition mg=P0. Do you mean that the yield point of the lower block is not equal to P0? If so, it isn't asserted in the paper that it is.

• C is probably as far off as Po (since it is based on it)

"Probably as far off" could do with a little quantification, I think. B&Z's values are certainly open to debate, and your work makes some valid points about them.

• that upper part is also a spring which is not taken into account

As far as I understand it, elastic deformation of the upper block will have no effect whatsoever on the dynamic loading exerted on the lower block. Work it out for yourself; it can be modelled as a second spring attached to the upper block and to the spring representing the lower block. Since the tension or compression in a spring is invariant with length, the dynamic loading is unchanged.

• the upper part is also weaker structurally and would (and did) fail first

Nowhere in the analysis is it required that the upper block is structurally intact, only that it's capable of exerting force on the lower block. Loss of mass should be considered, of course, but what mechanism exists for significant loss of mass prior to the initial impact?

Overall I think you're right in that this paper falls short of conclusive proof that global collapse ensues, but I suspect the aim of the paper was rather to explain the mechanisms assuming that the observation of global collapse was valid; like so many other sources cited, Bazant and Zhou was written as an analysis of engineering phenomena rather than as a rebuttal of controlled demolition theories. It's trivial to demonstrate that there must exist a level of collapse initiation at which global collapse ensues, otherwise conventional controlled demolitions would be impossible. There is therefore a reasonable presumption that global collapse is possible. Given the absence of evidence of any other cause of collapse, I would say that the burden of proof is on demonstrating that the building could not possibly have collapsed.

Dave

 

[GregoryUrich]

That's probably not what you mean, as the paper contains the definition mg=P0. Do you mean that the yield point of the lower block is not equal to P0? If so, it isn't asserted in the paper that it is.

B&Z define Po as the design load capacity which is not mg either. They should be using yield point.

"Probably as far off" could do with a little quantification, I think. B&Z's values are certainly open to debate, and your work makes some valid points about them.

Definitely needs quantification.

As far as I understand it, elastic deformation of the upper block will have no effect whatsoever on the dynamic loading exerted on the lower block. Work it out for yourself; it can be modelled as a second spring attached to the upper block and to the spring representing the lower block. Since the tension or compression in a spring is invariant with length, the dynamic loading is unchanged.

This is valid up until the upper structure fails, and it probably fails first.

Nowhere in the analysis is it required that the upper block is structurally intact, only that it's capable of exerting force on the lower block. Loss of mass should be considered, of course, but what mechanism exists for significant loss of mass prior to the initial impact?

This affects the dynamic loading as stated above.

Overall I think you're right in that this paper falls short of conclusive proof that global collapse ensues, but I suspect the aim of the paper was rather to explain the mechanisms assuming that the observation of global collapse was valid; like so many other sources cited, Bazant and Zhou was written as an analysis of engineering phenomena rather than as a rebuttal of controlled demolition theories. It's trivial to demonstrate that there must exist a level of collapse initiation at which global collapse ensues, otherwise conventional controlled demolitions would be impossible. There is therefore a reasonable presumption that global collapse is possible. Given the absence of evidence of any other cause of collapse, I would say that the burden of proof is on demonstrating that the building could not possibly have collapsed.

Dave

Personally, I would be thankful if someone could prove either hypothesis.

 

[Dave Rogers]

Personally, I would be thankful if someone could prove either hypothesis.

Given that there are still three competing theories of the cause of the Tay Bridge disaster, don't hold your breath.

Dave

 

[cmcaulif]

Many people here point to the B and Z paper as proof that the building should have failed as they describe. It's just not valid to make simplfying assumptions in favor of collapse prevention, have an erroneous result and claim the hypthesis still holds.

The problems with B and Z's paper are:

• mg is not equal to Po
• C is probably as far off as Po (since it is based on it)
• that upper part is also a spring which is not taken into account
• the upper part is also weaker structurally and would (and did) fail first

All the problems together could reduce Pdyn/Po to less than one. Unfortunately, no one tried to solve this problem correctly yet. One day it may be shown that the building should have collapsed, but it hasn't been proven yet.

again, eq. 1 is just the load magnification, it does not predict collapse or arrest.

Eq. three does this however.

 

[rwguinn]

again, eq. 1 is just the load magnification, it does not predict collapse or arrest.

Eq. three does this however.

[ct mode]Don't you understand yet?
Variables have to have exact values. Abstract equations prove absolutely nothing! How can you solve the equation if you don't already know the answer?[/ct mode]

Yoou will never get across to Gregoryurich, or any other truther "engineer" that you can use equations to indicate a trend, in addition to their occasional usefulness toward giving numerical answers.

note that

Definitely needs quantification.

from his post...

and

B&Z define Po as the design load capacity which is not mg either. They should be using yield point

he will never believe that a definition defines the thing, for that particular issue. He will never get it through his head that B &Z are demonstrating a magnification factor, not a collapse, and he will NEVER understand that "design load" is the expected, everyday load at which the building is safe, and still has a Safety Factor available. It is NOT the Yiel;d point. Yield is design load *SF.
SF is above and beyond Design Load.
"B&Z define Po as the design load capacity which is not mg either. They should be using yield point"

 

[GregoryUrich]

[ct mode]Don't you understand yet?
Variables have to have exact values. Abstract equations prove absolutely nothing! How can you solve the equation if you don't already know the answer?[/ct mode]

Yoou will never get across to Gregoryurich, or any other truther "engineer" that you can use equations to indicate a trend, in addition to their occasional usefulness toward giving numerical answers.

note that from his post...

and

he will never believe that a definition defines the thing, for that particular issue. He will never get it through his head that B &Z are demonstrating a magnification factor, not a collapse, and he will NEVER understand that "design load" is the expected, everyday load at which the building is safe, and still has a Safety Factor available. It is NOT the Yiel;d point. Yield is design load *SF.
SF is above and beyond Design Load.
"B&Z define Po as the design load capacity which is not mg either. They should be using yield point"

Nevermind, I see that I am not using the terminology correctly.

Added:

OK, now I see we are talking about two different things. You are following B&Z's argument and I am saying what they should have done. I see your point about the definitions. Please bear with me. This is not my area of expertise.

As cmcaulif mentions above, eq (1) does not govern failure. However, B&Z move on to plastic buckling without showing that failure will occur in the first impact. Plastic buckling will not occur unless the columns fail so eq (3) does not necessarily apply.

I thought they were trying to demonstrate failure in eq (1), which would be necessary for the rest of the paper to make sense. To prove column failure they would need to apply my version of the equation, with the correct values for C and m and use the yield capacity. They would also need to take the upper spring (which fails first) into account.

To prove collapse continuation they would first need to prove failure in the lower columns at the first impact and then eq(3) would have to hold, which it clearly would.

 

[beachnut]

Nothing funny here. I have no interest in Ross being correct.

Based on your 50 ton clue, I guess you are talking about the airplane wreckage which is not part of the building. We can add that in the collapse analysis. Nonetheless, I am aware that I don't include elevators and aluminum cladding. I will add this before publication.

You can't say what the error in my post is because there is none. The errors are all B and Z's, and your's too if you believe them.

No, not the plane. Oops, did you add the elevator stuff, motor, cables. You left out more, but you will not find it. And no matter how light you make the building steel still fails fast in fires. It is a know fact your bias whittling at the weight can not change the failure of the WTC. No explosives were used, you have hooked up with idiots.

I think your CT bias is showing. You have signed a petition of fools, and your bias is seen by others in your errors. Your petition is a sham, made up by idiots in 9/11 truth. What a sham. The only thing missing in your posts are your motives for trying to back in your conclusions to support your 9/11 truth movement of fools.