Merged Applicability of Bazant's model to the real world

[enik]

It sure has.

 

[TheRedWorm]

Got any, enik?

 

[tfk]

enik,

Feel free to jump in here.

Do you agree with MT's assertion that Bazant's analyses in BZ & BV are fundamentally different? That there are "2 distinct models"?

Do you agree with MT that Bazant has made errors (simple or otherwise) in his "crush down / crush up" analysis?

MT said that "it is easiest to rip apart … sections 2 thru 6" of his "D25 Closure to the Mechanics of Progressive Collapse" paper with Le. Yet he hasn't provided the first snip. Do you agree with MT's assessment?

A simple "yes or no" will suffice for now, please. Explanations can come shortly. We wouldn't want to deny Major T the opportunity - that he's avoided for about a week - to strut his engineering stuff…


tk

 

[rwguinn]

It sure has.

I see that you are apparently a firm believer that if you are the last poster on a thread, your position must be true, and everyone is afraid to try and refute it.
Even if you haven't actually shown your position, any evidence for your position, or even any logic that your position is true.

 

[ozeco41]

enik,

Feel free to jump in here.

Do you agree with MT's assertion that Bazant's analyses in BZ & BV are fundamentally different? That there are "2 distinct models"?...

Crazy though it may seem you can interpret either way. It depends whether or not you want to apply the two models to WTC Twin Tower collapse.

The BZ model is a limiting case model built on assumptions that make it the most optimistic for survival or least optimistic for collapse. (Pause whilst I make sure that is the right way around. )

The three assumptions are:

1. assume that all the impact forces go into the columns and
2. are distributed among them equally. AND
3. the upper part may be assumed to move through distance h almost in a free fall.

Of those 1 & 2 are valid assumptions in the same 'direction' of conservatism as the framing of the limiting case. 3 seems to be in the opposite 'direction' i.e. 'most optimistic for collapse'.

So BZ takes no cognisance of how the towers actually collapsed, makes some conservative assumptions, and concludes that there is far more energy available than is needed for progression into global collapse.

Despite my reservations about the third assumption its effect, if my concern is valid, would still be completely overridden by the order of magnitude surplus of available energy. Bazant addresses the same point in BV which states "was sufficient for Bažant and Zhou 2002a to conclude, purely on energy grounds, that the tower was doomed once the top part of the tower dropped through the height of one story or even 0.5 m". (My emphasis)


So BZ 'fits' the real world of WTC1 and WTC2 collapse despite assumptions which do not model the real collapse BUT are valid for a limiting case assessment.

Now the real global collapse can be analysed further and with validity by recognising that the collapse acted as four main components of structural effects:

1. The outer tube columns which were 'peeled off' and took little part in resisting collapse other than the relatively small forces resulting from resisting failure of the floor joist connectors.
2. The pancaking collapse of the open office space floors which placed the additional load on the core and outer tube columns as each floor was sheared off at its joist to column connection;
3. The core where the top block section fell beam on beam onto the lower section, with failure of the beams shearing off the columns would be probably the main failure mode. AND
4. A little bit of adjustment because the "top bits' did not fall 100% aligned with the corresponding bottom bits and the hat truss and upper structure would do some 'load balancing'.

Recalling also that once the top block started to fall no column was in axial end for end full load bearing relationship.

Call that description of what actually happened 'my scenario' for convenience AND note that the situation which actually happened bears no resemblance to the assumptions under BZ but it matters not given that BZ is a limiting case.

Not so for BV which is modelled on a floor by floor crushing collapse where the columns are the main elements resisting collapse.

That is not what happened. But Bazant et al erect some numeric modelling on that foundation which is not the foundation of what actually happened.

So I have identified two paths which are available from here to progress analysis.

'My scenario' which does further analysis based on the foundation of the collapse which actually happened; OR

The BV et al modelling which takes no account of what actually happened and builds on a generic set of assumptions.

'My scenario' lends to order of magnitude assessments which support explanation of the global collapse. I have not done the fancy maths.

BV is built on a foundation which does not apply to the actual WTC collapses unless some one can show me that it doesn't matter that the model is wrong. Maybe the fancy maths cover up the lack of fit of the assumptions to real world WTC 9/11.

So, as I said at the start in response to the question 'Do you agree...that Bazant's analyses in BZ & BV are fundamentally different? That there are "2 distinct models"?..'

You can go either way. The models are not fundamentally different if you go with the progression of Bazant's thinking and don't apply it to WTC collapse. But if you want to apply to WTC collapse the assumptions which are acceptable as a limiting case for BZ and can legitimately be applied to WTC as a limiting case cease to be valid when taken beyond 'limiting case' which is what BV does.

As I said in my first post on the Internet and first post on this topic on another forum - 13/14 Nov 2007:

Re: World Trade Center? What Really Happened?

The paper referenced as Engineering Reality by Tony Szamboti is typical of many which look impressive in detail to the non-engineer. The complex calculations may even be correct but the base premises are faulty and the resulting conclusions can readily be demonstrated to be totally wrong.

So for me there is a prima facie case that BV does not validly apply to WTC1 or WTC2 collapse.

 

[tfk]

Oz,

I'm going to send Major Tom a PM, requesting that he respond here. Then I'll give him a couple of days.

Then I'll get into the above with you.

This will also allow me to finish up some work before quitting time tonite.

Happy New Year, all.


Tom

 

[ozeco41]

Oz,

I'm going to send Major Tom a PM, requesting that he respond here. Then I'll give him a couple of days.

Then I'll get into the above with you.

This will also allow me to finish up some work before quitting time tonite.

Happy New Year, all.


Tom

 

[enik]

enik,

Feel free to jump in here.

Do you agree with MT's assertion that Bazant's analyses in BZ & BV are fundamentally different? That there are "2 distinct models"?

Do you agree with MT that Bazant has made errors (simple or otherwise) in his "crush down / crush up" analysis?

MT said that "it is easiest to rip apart … sections 2 thru 6" of his "D25 Closure to the Mechanics of Progressive Collapse" paper with Le. Yet he hasn't provided the first snip. Do you agree with MT's assessment?

A simple "yes or no" will suffice for now, please. Explanations can come shortly. We wouldn't want to deny Major T the opportunity - that he's avoided for about a week - to strut his engineering stuff…


tk

I agree that Bazant is wrong in his initial paper that the upper structure is rigid.

 

[Newtons Bit]

I agree that Bazant is wrong in his initial paper that the upper structure is rigid.

Are you trying to say that a rigid upper block is not a "simplifying assumptions most optimistic in regard to survival are made"? That's pathologically insane.

A rigid upper block is an assumption that favors collapse prevention. This is because a rigid upper block may apply forces directly to the columns below. An upper block that is capable of deforming will ultimately be broken up into smaller pieces and those smaller pieces will bear on floors. The floors, having a small fraction of the capacity of the columns will collapse without the strongest element ever being engaged in any meaningful capacity.

Weren't you just demanding other people prove their qualifications? I think you need to start looking at your own again. You obviously have no 'ing clue as to what you're talking about.

 

[ozeco41]

I agree that Bazant is wrong in his initial paper that the upper structure is rigid.

Are you trying to say that a rigid upper block is not a "simplifying assumptions most optimistic in regard to survival are made"? That's pathologically insane.

Just a couple of cautionary comments:

• Remember that the term 'rigid' can be ambiguous in this context viz:
  • Literally rigid meaning no deflections of the structural members or changes of relative positions of those members; OR
  • 'Rigid' in the structural sense of all the members of the top part remaining joined together in an integral whole structure BUT subject to all the elastic and/or plastic deformations which would result from the imposed loadings.
  
  BUT - and this one is more important for this immediate discussion:
• Remember the context set by Bazant's assumptions which, as I see it, would over-ride any consideration of 'rigidity' including the consequences outlined by NewtonsBit.

So, although I don't see where Bazant set 'rigid' as an explicit assumtion, it doesn't change the applicability of BZ to WTC collapse which is the relevant aspect within this topic.

 

[Newtons Bit]

So, although I don't see where Bazant set 'rigid' as an explicit assumtion, it doesn't change the applicability of BZ to WTC collapse which is the relevant aspect within this topic.

Read the beginning of the section "elastic dynamic analysis" again.

However, a computer is not necessary to conclude that the collapse of the majority of columns of one floor must have caused the whole tower to collapse. This may be demonstrated by the following elementary calculations, in which simplifying assumptions most optimistic in regard to survival are made

 

[ozeco41]

Read the beginning of the section "elastic dynamic analysis" again.

Your point being what? Are you disagreeing with what I said? If so which bit - the fact that I do not see Bazant claiming rigidity OR my conclusion that it would not invalidate the application to a limiting case if he did?

Remember that Bazant's main assumption "...For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally...." over-rides any consideration of 'rigidity'. That assumption artificially constrains the presumed behaviour of the 'top block' in order to set up the limiting case.

 

[Newtons Bit]

Your point being what? Are you disagreeing with what I said? If so which bit - the fact that I do not see Bazant claiming rigidity OR my conclusion that it would not invalidate the application to a limiting case if he did?

The upper block is rigid in Bazant and Zhou as seen in the impact equations. They lack a variable for the stiffness of the upper block. It would ultimately be a very minor difference, however.

Remember that Bazant's main assumption "...For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally...." over-rides any consideration of 'rigidity'. That assumption artificially constrains the presumed behaviour of the 'top block' in order to set up the limiting case.

The fact that all the forces go into the columns equally is part of the top block being rigid. Bazant doesn't explicitly state that the upper block is rigid, but his statements and the math show that it is.

Edit: actually he does state that the upper block is rigid in the Addendum:

Second, note that the analysis that led to Eq. ~1! implies the hypothesis that the impacting upper part of the tower behaves
essentially as a rigid body. This is undoubtedly reasonable if the upper part has the height of 20 stories, in which case the
ratio of its horizontal and vertical dimensions is about 52.8/2033.7'0.7. But if the upper part had the height of only
3 stories, then this ratio would be about 5. In that case, the upper part would be slender enough to act essentially as a
flexible horizontal plate in which different column groups of the upper part could move down separately at different times.
Instead of one powerful jolt, this could lead to a series of many small vertical impacts, none of them fatal.

 

[ozeco41]

The upper block is rigid in Bazant and Zhou as seen in the impact equations. They lack a variable for the stiffness of the upper block. It would ultimately be a very minor difference, however.

...yes - that is why I said explicit in the post "...I don't see where Bazant set 'rigid' as an explicit assumtion[sic], it doesn't change the applicability..." (complete with the spelling error )

...The fact that all the forces go into the columns equally is part of the top block being rigid. Bazant doesn't explicitly state that the upper block is rigid, but his statements and the math show that it is....

It is also a logical consequence of his first explicitly stated objective. "...For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally. Unlikely though such a distribution may be,..." etc

So we are saying the same thing but getting to it from slightly different directions.

...Edit: actually he does state that the upper block is rigid in the Addendum:

...true. And he postulates "one powerful jolt" but I have no wish to go down that track at this stage.

 

[Major_Tom]

TFK post 1158:
"Here it is, simply & plainly: I don't believe that you have the slightest clue what you are talking about. I believe that you are blowing smoke & bluffing.

I think that you're a fraud.

Now, I invite you to prove me wrong.

Don't explain to Oz. Explain to me.

And when you get it completely & utterly wrong, then I'll explain it to you.

Clear enough?

tk"
link: http://www.internationalskeptics.com/forums/showpost.php?p=6701638&postcount=1158


My post before his was considered in violation of rule 12. It was a pretty gentle post compared with the fraud comment above.

How can TFK be allowed to speak to people like this? I am in breach of the rules for attacking the arguer, not the argument. People are allowed to openly insult me from my first thread in May.

The first comment on that thread is an insult, but that not considered attacking the arguer.

Tom, since you've been wrong so many times before, why are you so confident you understand the contents of these papers?

 

[enik]

Are you trying to say that a rigid upper block is not a "simplifying assumptions most optimistic in regard to survival are made"? That's pathologically insane.

A rigid upper block is an assumption that favors collapse prevention. This is because a rigid upper block may apply forces directly to the columns below. An upper block that is capable of deforming will ultimately be broken up into smaller pieces and those smaller pieces will bear on floors. The floors, having a small fraction of the capacity of the columns will collapse without the strongest element ever being engaged in any meaningful capacity.

Weren't you just demanding other people prove their qualifications? I think you need to start looking at your own again. You obviously have no 'ing clue as to what you're talking about.

Do an FEA. Then you'll see who has the clue.

Literally rigid meaning no deflections of the structural members or changes of relative positions of those members

Yes.

 

[Dog Town]

Tom, since you've been wrong so many times before, why are you so confident you understand the contents of these papers?

 

[triforcharity]

TFK post 1158:
"Here it is, simply & plainly: I don't believe that you have the slightest clue what you are talking about. I believe that you are blowing smoke & bluffing.

I think that you're a fraud.

Now, I invite you to prove me wrong.

Don't explain to Oz. Explain to me.

And when you get it completely & utterly wrong, then I'll explain it to you.

Clear enough?

tk"
link: http://www.internationalskeptics.com/forums/showpost.php?p=6701638&postcount=1158


My post before his was considered in violation of rule 12. It was a pretty gentle post compared with the fraud comment above.

How can TFK be allowed to speak to people like this? I am in breach of the rules for attacking the arguer, not the argument. People are allowed to openly insult me from my first thread in May.

The first comment on that thread is an insult, but that not considered attacking the arguer.

Tom, since you've been wrong so many times before, why are you so confident you understand the contents of these papers?

Blah blah blah.....

Hey MT,

When do you plan on writing your paper and submitting it to a respectable journal?

Maybe you could make that your New Years resolution.....

 

[ozeco41]

Literally rigid meaning no deflections of the structural members or changes of relative positions of those members...

Yes

Thanks. That is how I read it but I thought it best to identify the ambiguity in case it caused confusion in future discussion - if any.

And, in the context set by Bazant and Zhou, it is overridden by their first assumption:
"...For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally. Unlikely though such a distribution may be..."
Which has a similar but not identical effect - 'rigidity' does not mean and is unlikely to result in 'distributed among them equally'.

...and that raises additional questions which I have no interest in pursuing. I am content to go along with the accepted status of BZ as a valid limiting case.

 

[tfk]

TFK post 1158:

"Here it is, simply & plainly: I don't believe that you have the slightest clue what you are talking about. I believe that you are blowing smoke & bluffing.

I think that you're a fraud.

Now, I invite you to prove me wrong.

Don't explain to Oz. Explain to me.

And when you get it completely & utterly wrong, then I'll explain it to you.

Clear enough?

tk"

link: http://www.internationalskeptics.com/forums/showpost.php?p=6701638&postcount=1158

My post before his was considered in violation of rule 12. It was a pretty gentle post compared with the fraud comment above.

How can TFK be allowed to speak to people like this? I am in breach of the rules for attacking the arguer, not the argument. People are allowed to openly insult me from my first thread in May.

YOU claimed that you could explain the "simple errors" that Bazant made, but that you didn't think that anyone here could understand.

I invited you to explain those simple errors multiple times.

You refused to reply.
___

YOU claimed that the analyses in BZ & BV were fundamentally different.

I disagreed & invited you to explain yourself.

You refused to reply.
___

YOU make claims. When challenged to defend your claims, you shut up.

In debating circles, that's considered a fraud.

YOUR words, and YOUR subsequent refusal to defend them when challenged, make me believe that you are a bluffer & a fraud.

There is ONE SIMPLE way to prove my beliefs wrong.

Whining about the fact that I ACCURATELY quoted your text, then challenged you to defend your own words, then ACCURATELY observed your silence is NOT the way to prove that you are not a bluffer & a fraud.