Some Calculations requested regarding why the towers upper portion did not slide off

[Furcifer]

NIST made this kind of confusion inevitable by deciding not to cover the collapse beyond initiation in any detail in their report. Whatever side of the fence you are setting, clearly they did not satisfy their mandate to explain "how and why WTC1 and WTC2 collapsed" (NISTNCSTAR1 p.xxix).

I think you are misinterpreting the mandate. But I wish they would have had the time and money to explain the global collapse as well.

Of course had they done this I think I would just be in another forum debating with you about recreating the sinking of the Titanic.

 

[TruthSeeker1234]

Lol, we were talking about the picture, not the mass in the foot prints.

TS could you please try and incorporate what you think happened when you ask questions? I'd hate to spend 10 minutes explaining something to you, only for you to say "But it was dustified by a space beam..."

I think you have been directed to Bazant's work on how they arrived at the 80% figure.

I know how Greening and Bazant arrived at the 80% figure. If any more than 20% of the mass went outside the footprint, then there is no longer enough accumulating mass to sustain the "collapse". The problem is, sir, there is no evidence to support the position.

They calculate the force of the accelerating mass at each story. They notice that for collapse to continue, at least 80% of the mass above the collapse front must accumulate, and contribute to the force applied to the subsequent story. If any more than 20% goes over the side, the "collapse" will halt. So they "conclude" that >80% must have stayed inside.


Greening/Bazant is thus circular reasoning. Assume collapse. For collapse to continue, >80% must stay inside. The collapse continued. Therefore, >80% stayed inside.

That is how they "arrived" at the figure. Only by assuming a "collapse" can one "arrive" at that figure.

Circular reasoning is not evidence.

Scientists require evidence.

 

[lozenge124]

Lozenge: No one said the floors pancaked and left an "empty framed tube" here. This is why you are mistaken.

I am not saying this, Bazant/Le/Greening/Benson are:

In the structural engineering community, one early speculation was that, because of a supposedly insufficient strength of the connections between the floor trusses and the columns, the floors ‘pancaked’ first, leaving an empty framed tube, which later lost stability.

But I believe they are referring to the 2002 FEMA "World Trade Center Building Performance Study" popularized in the NOVA PBS program.

 

[pomeroo]

I think you are misinterpreting the mandate. But I wish they would have had the time and money to explain the global collapse as well.

Of course had they done this I think I would just be in another forum debating with you about recreating the sinking of the Titanic.

I often wonder how the loons would have reacted if the Impossibly Vast Conspiracy really did fly planes into the Twin Towers and claimed that the ensuing collapses were the result of explosives planted by Arab terrorists.

Let's see: you'd have the gubmint arguing that the planes had nothing to do with the buildings falling down, and the other side would be demanding to see proof that explosives had been planted.

I also wonder how, if the evildoers argued that there were no planes, that all those witnesses were deluded, our imaginative friend Ace would have demonstrated the reality of the planes.

Makes you kinda dizzy.

 

[lozenge124]

For the record, I never said "The Pancake Theory". So why the [rule8] are you quoting it?

Please enlighten us all to the differences between "pancake collapse" and "'pancake theory' of collapse". One is an event, the other is a theory? Splitting hairs a little?

 

[Furcifer]

No, they collapsed, and debris was spread quite widely due to the chaotic way it collapsed. Where is the problem?

There is some debate as to how much was in the footprint and how much was out of the footprint and why what was in was in and what was out was out. Oh, and how much that was in the footprint contributed to the collapse, how much that was out of the footprint didn't contribute and how much was in the footprint didn't contribute to the collapse. Oh, and how much was dust and how much was thermite and how much was spherules. And how much was melted and how much was molten. There's probably more, but these are the major ones.

 

[lozenge124]

I think you are misinterpreting the mandate. But I wish they would have had the time and money to explain the global collapse as well.

Of course had they done this I think I would just be in another forum debating with you about recreating the sinking of the Titanic.

Again, I am quoting directly from the Preface to NISTNCSTAR1:

The specific objectives were:

1. Determine why and how WTC 1 and WTC 2 collapsed following the initial impacts of the aircraft and why and how WTC 7 collapsed;
(...)

I think it's clear enough.

If someone were to produce a WTC style total "progressive" collapse in an FEA model, or even as a scale model, that would go a long way towards changing my mind about the plausibility of a gravity driven only collapse. "Global collapse ensues" just doesn't do it for me, sorry.

 

[Dave Rogers]

There is some debate as to how much was in the footprint and how much was out of the footprint and why what was in was in and what was out was out. Oh, and how much that was in the footprint contributed to the collapse, how much that was out of the footprint didn't contribute and how much was in the footprint didn't contribute to the collapse. Oh, and how much was dust and how much was thermite and how much was spherules. And how much was melted and how much was molten. There's probably more, but these are the major ones.

Or, to summarise, "We don't know how much fell in the footprint, or how much should have fallen in the footprint, but it definitely wasn't the right amount."

Dave

 

[Furcifer]

I know how Greening and Bazant arrived at the 80% figure. If any more than 20% of the mass went outside the footprint, then there is no longer enough accumulating mass to sustain the "collapse". The problem is, sir, there is no evidence to support the position.

They calculate the force of the accelerating mass at each story. They notice that for collapse to continue, at least 80% of the mass above the collapse front must accumulate, and contribute to the force applied to the subsequent story. If any more than 20% goes over the side, the "collapse" will halt. So they "conclude" that >80% must have stayed inside.


Greening/Bazant is thus circular reasoning. Assume collapse. For collapse to continue, >80% must stay inside. The collapse continued. Therefore, >80% stayed inside.

That is how they "arrived" at the figure. Only by assuming a "collapse" can one "arrive" at that figure.

Circular reasoning is not evidence.

Scientists require evidence.

Ugh, TS you butchered that one badly. You hardly need 80% of the mass to sustain the collapse.

I've got a cup of coffee and some free time. You give me an estimate of how much you think stayed in the footprint, I'll give you my counter offer, and we will see if we can arrive at a reasonable estimate of how much was in and how much was out. Then I will post it over at PhysOrg and see what happens. I don't like the 80% either, but I'm not sure what the exact number is.

 

[Dave Rogers]

If someone were to produce a WTC style total "progressive" collapse in an FEA model, or even as a scale model, that would go a long way towards changing my mind about the plausibility of a gravity driven only collapse.

For at least the third time, forget the scale model. All the properties scale differently with size, so a scale model will behave nothing like the full size building, and if the experimenters change the proportions of the model so it does behave like the full size building then you won't believe the results because they may have changed them so as to weaken the model too much.

Dave

 

[lozenge124]

For at least the third time, forget the scale model. All the properties scale differently with size, so a scale model will behave nothing like the full size building, and if the experimenters change the proportions of the model so it does behave like the full size building then you won't believe the results because they may have changed them so as to weaken the model too much.

Dave

Agreed, an FEA model would be better.
But a scale model of something, anything, undergoing a total progressive collapse would be a start - to show that it's possible at least. (and preferably without gimmicks like angle cut connections between the support columns and the like)

 

[Corsair 115]

But a scale model of something, anything, undergoing a total progressive collapse would be a start - to show that it's possible at least.

Wait, let's back up a step. Are you saying you think a progressive collapse of a building is not possible at all except when explosives or something similar are used to weaken the structure?

 

[Furcifer]

I am not saying this, Bazant/Le/Greening/Benson are:
.

Just to clarify, there is a huge difference in pancake theory and pancaking. The NIST pancake theory was the one that left a hollowed out tube, which then collapsed. That's way different than if the floors fell on top of one another during the collapse. You either get this or you don't.
If I had a telestrator I could clarify it for you even better. If you want to make a fortune on the internet, make an online, real time telestrator that would work in the forums. Rich I tell yah, rich!!!

 

[lozenge124]

Wait, let's back up a step. Are you saying you think a progressive collapse of a building is not possible at all except when explosives or something similar are used to weaken the structure?

I am careful to say "total progressive collapse" and not simply "progressive collapse" meaning I am looking for a building that collapses totally - not a Ronan Point Apartment style partial collapse:

Do you have any examples of such a total progressive collapse?

To answer your question, I have trouble seeing how a structure with vertical support columns can fail "floor by floor" because the vertical impact force of a falling "upper block" will be absorbed by the columns as a whole - not on a "floor by floor", progressive basis. But any examples would be appreciated.

 

[DavidJames]

II have trouble seeing how a structure with vertical support columns can fail "floor by floor" because the vertical impact force of a falling "upper block" will be absorbed by the columns as a whole - not on a "floor by floor", progressive basis.

Have you read the NIST report, it provides the science behind what you "have trouble seeing"

 

[Furcifer]

Wait, let's back up a step. Are you saying you think a progressive collapse of a building is not possible at all except when explosives or something similar are used to weaken the structure?

The funny thing is building codes around the World already consider progressive or cascade collapses and how to prevent them. I'm pretty sure this is why NIST says, "...and then global collpase ensues" It's just understood by those who deal in a world where this "phenomenom" is very real.

 

[lozenge124]

Just to clarify, there is a huge difference in pancake theory and pancaking. The NIST pancake theory was the one that left a hollowed out tube, which then collapsed. That's way different than if the floors fell on top of one another during the collapse. You either get this or you don't.
If I had a telestrator I could clarify it for you even better. If you want to make a fortune on the internet, make an online, real time telestrator that would work in the forums. Rich I tell yah, rich!!!

I think you mean FEMA instead of NIST there.

But when the term "pancake" is invoked, to me it implies the failure of the truss connectors to the support columns, which causes each floor to fail in turn.

In the "pile driver" or crush down theory with the upper block crushing the lower block, floors from the upper block are hitting floors in the lower block certainly. But the main impetus in the collapse is the buckling and failing of the vertical core and perimeter support columns as they are hit from above by the upper block. So I don't think the term pancake is appropriate here - especially not if we are to distinguish it from the original theory.

 

[lozenge124]

Have you read the NIST report, it provides the science behind what you "have trouble seeing"

Yes I have.
And no it doesn't.

 

[Furcifer]

Do you have any examples of such a total progressive collapse?

To answer your question, I have trouble seeing how a structure with vertical support columns can fail "floor by floor" because the vertical impact force of a falling "upper block" will be absorbed by the columns as a whole - not on a "floor by floor", progressive basis. But any examples would be appreciated.

Dang, no I don't. I know it has happened, here in Vancouver I believe. I just don't have "proof". I will tell you it is a very real concern during construction, and I believe the case to which I am referring happened at just this time.

It would in the static case, but not in the dynamic case lozenge. Once the upper section started moving you need to consider how the energy is being transmitted componentwise.

 

[Newtons Bit]

Please enlighten us all to the differences between "pancake collapse" and "'pancake theory' of collapse". One is an event, the other is a theory? Splitting hairs a little?

Well, let's see. The Pancake Theory, as described by Fema, is a description of how collapse STARTED. Particularly, that the thermal expansion of the floors caused them to disconnect from their connections.

Pancake collapse, in context with what I said, is a collapse driven by a large upper block pancaking the lower block one floor at a time. This couldn't be more simple. "Pancake Theory" is how the collapse initiated. I was talking about something a great deal of time AFTER collapse initiated. But you didn't get that, you just honed right into the word "pancake", not realizing it just might have a meaning not directly associated with the "pancake theory". Do you really think the word pancake, as relating to structural terms, was never used before 2001?