Merged Applicability of Bazant's model to the real world

[Disbelief]

Unless there is a decrease in mass.

MM

How exactly would this happen?

 

[Miragememories]

How exactly would this happen?

Chaos theory.

MM

 

[BigAl]

Unless there is a decrease in mass.

MM

Where did it go?

In the meantime, with each floor V is increasing and as a result momentum is increasing.

 

[femr2]

Where did it go?

In the meantime, with each floor V is increasing and as a result momentum is increasing.

No. *crush front* traversal rate was linear 4/5 seconds after initiation. ~27m/s.

 

[ozeco41]

Loose rubble does not deliver the same type of load as an intact structure.

A disarming truism Tony.

As it relates to dynamic impacts - not static - "loose rubble" could be "better", it could be "worse" than an intact structure. It depends on the manner of contact when the impact load is applied.

And, in the case of WTC1 and WTC2, that goes to the whole complex area of analysis where Gage's boxes and Heiwa's blocks represent one extreme of the possibilities.

...my "cut wire baskets" are towards the other end of that range and being just one attempt at analogy for what really happened.

...and I don't think anyone could detail analyse the actualities of WTC1 and 2 on 9/11 - the "which beam hit which beam" and "which column did what" level of detail will never be available. And the task is probably too complex even if that detail was available. (But then I come from the slide rule generation... )

Which is why modelling approximations such as Bazant's are valuable.

...provided they are not taken outside the range of validity set by the assumptions.

 

[ozeco41]

No. *crush front* traversal rate was linear 4/5 seconds after initiation. ~27m/s.

Which implies an interesting "balance" between:
1) the increasing total falling mass; AND
2) the more or less constant shear failure limited impact resistance of successive floors.

 

[pgimeno]

Seymour again: "The crush up/down thing STILL refers to the idealized case of the strength of the columns, not the floors, being the determining factor in his equations. "

It does. That is one of Bazant's mistakes. This is how the concept of crush down, then crush up was born.

One of Bazant's mistakes, you say? Why is it a mistake to build a model based on that? You can claim to have a mathematical model based on better assumptions, if you do (do you, perchance?) but to say that it's a mistake without any reason is merely baseless smearing.

Now please read the quotes I gave from Dave Rogers, R Mackey and Newtons Bit again.

I've read them again, and in my opinion, only Dave Rogers is making the mistake you attribute to all three.

Mackey's quote is an explanation in reply to this question:

This has come into my mind when thinking about this before and I have no idea if it's right so can someone explain why it's wrong.

The forces acting on the upper and lower blocks are equal but opposite, the force acting on the lower block does not accelerate the lower block downwards but the force on the upper block does accelerate the upper block upwards so there is more destructive force acting on the lower block.

Obviously, alexi_drago's question (why it's wrong) is purely theoretical, as is Mackey's reply, as evidenced by his ending phrase: "Again, this is slightly idealized, but you get the point. Unless you're a Truther".

Newton's Bit, as ozeco41 already noted, merely explained Bazant's words to you, throwing the burden of proof to you again. Prior to your quote, he already wrote the following:

Bazant and Verdue sets out to model and understand progressive collapse. Not prove how the WTC collapsed. It uses the WTC only as a paradigm. I.e. an example, a model, a pattern, etc etc. It then applies the conclusions of this model to other buildings, as that is the stated purpose of this model.

Crystal clear to those who don't have a smearing agenda: he doesn't believe that Bazant's model should be taken literally as a description of how the collapse happened.

They make this mistake. In BLGB Bazant makes the same mistake. They apply crush down, then crush up to real buildings and believe that some upper block survives until colliding with the earth.

Your repeated claim that it's a mistake won't make it a mistake. It's valid engineering because predictions can be extracted out of it. These predictions turn out to be quite accurate, therefore supporting the applicability of the model to real buildings for the purpose of measuring the speed of fall.

What you seem to fail to see again and again, is that the model can be applied to the real world to obtain approximations for some purposes but not for all purposes and not for no purpose. In particular, it can't be applied to the measurement of the crush direction for the WTC, but it can be applied to the measurement of the speed of fall.

 

[pgimeno]

Even to the degree this is true, so what? Momentum increases with each floor.

Unless there is a decrease in mass.

MM

Wrong.

Unless the decrease in mass of the rubble layer equals or exceeds the gain of mass due to the ongoing crushing.

Which is quite ridiculous itself.

[Edited to add: Forgot to specify that that applies to an assumption of constant velocity.]

 

[bill smith]

A disarming truism Tony.

As it relates to dynamic impacts - not static - "loose rubble" could be "better", it could be "worse" than an intact structure. It depends on the manner of contact when the impact load is applied.

And, in the case of WTC1 and WTC2, that goes to the whole complex area of analysis where Gage's boxes and Heiwa's blocks represent one extreme of the possibilities.

...my "cut wire baskets" are towards the other end of that range and being just one attempt at analogy for what really happened.

...and I don't think anyone could detail analyse the actualities of WTC1 and 2 on 9/11 - the "which beam hit which beam" and "which column did what" level of detail will never be available. And the task is probably too complex even if that detail was available. (But then I come from the slide rule generation... )

Which is why modelling approximations such as Bazant's are valuable.

...provided they are not taken outside the range of validity set by the assumptions.

How soon after 9/11 did Bazant's first model appear ?

 

[ozeco41]

How soon after 9/11 did Bazant's first model appear ?

From the footnotes to Bazant and Zhou:

The original version with Eqs. 1 and 2 was originally submitted to ASCE on September 13, 2001, and an expanded version with Eq. 3 was submitted to ASCE on September 22, 2001. The appendices were added between September 28 and October 5, 2001; The preliminary report Bazant and Zhou 2001 on which this article is based was posted on September 14, 2001...

Didn't waste any time did they?

 

[ozeco41]

...What you seem to fail to see again and again, is that the model can be applied to the real world to obtain approximations for some purposes but not for all purposes and not for no purpose. In particular, it can't be applied to the measurement of the crush direction for the WTC, but it can be applied to the measurement of the speed of fall.

Whilst I am in broad agreement with what you say I am nervous about one aspect.

We know that "... it can be applied to the measurement of the speed of fall [for WTC1 or 2]" because we can measure that speed of fall by other methods and those do in fact confirm the model.

My concern is that it may happen to be right for WTC for wrong reasons AND that, if applied to other buildings may give wrong answers.

Not that I can see any practical consequences arising but.....

 

[pgimeno]

My concern is that it may happen to be right for WTC for wrong reasons AND that, if applied to other buildings may give wrong answers.

I know, but I think I've already seen, maybe in this thread, a justification for the little sensitivity of the model to the assumptions with regards to the speed of fall. If so (sorry to be so vague, I'd have to find who said it and what it was exactly), then the application would be for right reasons.

 

[Tony Szamboti]

A disarming truism Tony.

As it relates to dynamic impacts - not static - "loose rubble" could be "better", it could be "worse" than an intact structure. It depends on the manner of contact when the impact load is applied.

And, in the case of WTC1 and WTC2, that goes to the whole complex area of analysis where Gage's boxes and Heiwa's blocks represent one extreme of the possibilities.

...my "cut wire baskets" are towards the other end of that range and being just one attempt at analogy for what really happened.

...and I don't think anyone could detail analyse the actualities of WTC1 and 2 on 9/11 - the "which beam hit which beam" and "which column did what" level of detail will never be available. And the task is probably too complex even if that detail was available. (But then I come from the slide rule generation... )

Which is why modelling approximations such as Bazant's are valuable.

...provided they are not taken outside the range of validity set by the assumptions.

Any legitimate statistical analysis would show that a random chaotic process would have produced a definitive deceleration if the structure below and above had been intact when they impacted after the initial fall. WTC 1 would be a severe exception to the rule if it were somehow able to collapse without this occurring.

 

[ozeco41]

Any legitimate statistical analysis would show that a random chaotic process would have produced a definitive deceleration if the structure below and above had been intact when they impacted after the initial fall. WTC 1 would be a severe exception to the rule if it were somehow able to collapse without this occurring.

Whether right or wrong the key issue is the size of the "definitive deceleration".

And as I said "It depends on the manner of contact when the impact load is applied."

..specifically the lack of column on column axial contact which means no easily measured jolt of large magnitude.

 

[Tony Szamboti]

Whether right or wrong the key issue is the size of the "definitive deceleration".

And as I said "It depends on the manner of contact when the impact load is applied."

..specifically the lack of column on column axial contact which means no easily measured jolt of large magnitude.

You are arguing for a severe exception or an extraordinary event without providing extraordinary evidence for it.

 

[twinstead]

You are arguing for a severe exception or an extraordinary event without providing extraordinary evidence for it.

Indeed. And we mustn't do that, must we Tony?

 

[carlitos]

Am I reading this right? Does Tony think that there should have been "column on column axial impact" in the WTC tower collapses? That seems impossible, given the twisting and turning the upper sections showed. Is it only the idealized model by Bazant that gave people this idea?

 

[ozeco41]

You are arguing for a severe exception or an extraordinary event without providing extraordinary evidence for it.

Whether your statement is applicable or not it does not call for extraordinary thinking.
Recalling that the precursor condition for your lost jolt is that the top block is falling.

Therefore no column on column contact at that time.

(And, yes, I am aware of where the next step of logic goes.)

Indeed. And we mustn't do that, must we Tony?

Am I reading this right? Does Tony think that there should have been "column on column axial impact" in the WTC tower collapses? That seems impossible, given the twisting and turning the upper sections showed. Is it only the idealized model by Bazant that gave people this idea?

Not only "should have been" - his hypothesis relies on it.

Tony's "Missing Jolt" paper is premised on "column on column axial impact" where columns are the only structural elements capable of developing sufficient resistance in one isolated sub-event which would be identifiable as a "jolt". Quoting from Graeme MacQueen & Tony Szamboti "The Missing Jolt: A Simple Refutation of the NIST-Bazant Collapse Hypothesis"

...any impulse at the impact zone between the 98th and 99th story floor slabs capable of causing collapse continuation would have had to cause the columns on at least the first stories on either side of the impact to deform elastically, and plastically, and then to buckle...

...so he takes the extreme case allowed by the assumptions in Bazant & Zhou and builds on it.
That extreme has column on column axial contact. It is valid for B & Z to use it as an approximation - it is on the "safe" side when it finds that there was sufficient energy to allow propagation of the global collapse. It is not valid for Tony to assume it. In fact, properly interpreted, the lack of a jolt is confirmation that there was not (significant if any) column on column axial contact.

And that goes right to the core of this topic "Applicability of Bazant's model to the real world" and previous discussion where I and others have agreed that Bazant and Zhou's model is valid within the limits of validity of the assumptions.

And, yes, there are steps of logic needed to complete the picture.
And, ironic though it may be, to that extent Tony's paper would seem to present part of "A Simple Refutation of the NIST-Bazant Collapse Hypothesis"

 

[Miragememories]

Am I reading this right? Does Tony think that there should have been "column on column axial impact" in the WTC tower collapses? That seems impossible, given the twisting and turning the upper sections showed. Is it only the idealized model by Bazant that gave people this idea?

You make it sound like the upper sections had a life of their own.

MM

 

[ozeco41]

You make it sound like the upper sections had a life of their own.

MM

To the extent that the top block was falling it did have a life of its own.

And that much is common to both sides of the "argument":
1) It had sufficient life of its own to fall due to natural consequences of damage; OR
2) It had sufficient life of its own to fall because some naughty demolition had helped it.

Cheers.