Merged Applicability of Bazant's model to the real world

[femr2]

As we all know, femr2 likes to eat his "pie" one pixel at a time. It's all good.

I'm currently eating 0.01 pixels at a time. Progress

 

[ergo]

I keep asking you questions which should help you to *get there* without me being rude to you. I'll continue to try...

What EXACTLY do you think is *holding up the upper block* ?

a) Core columns.
b) Perimeter columns
c) Floor truss assembly connected to core and perimeter (with connections which do not change throughout the height of the tower, excepting a few special floors).

The core structure comprised the central 25% of the total horizontal area of the towers.

Furthermore, the floor spaces were not simply empty. There were furnishings, large filing systems (for which floor support enhancements had to be made), machinery, partition walls, some made of cement--as well as people, as we know. Some walls in fancy offices had marble slabs. There was material in each floor. Maybe this material could not really be considered as supporting any significant weight, but neither can we imply that these are empty metal-with-concrete-slab pans stacking on top of each other. And even if this is what you're implying, this is not the Bazant/NIST hypothesis, which is what we are discussing in this thread.

The floor assembly is *stuck onto* the core and perimeter columns. You have previously included the probability that the core columns *punched through* the floor slab. Same applies to perimeter.

The floor assemby is only designed to hold a small multiple of its own weight. It is the core and perimeter columns that support the mass. The floors were always simply hanging off of them, like a hammock.

Nothing you've said here has anything to do with your "one floor" theory.

Furthermore, a 20' x 60' WTC floor panel apparently can weigh 7 tons, if we go by the story of the floor panel that fell into Kill van Kull. Likening these panels to "hammocks" is a tad misleading. The floor panels further are supported by a column arrangement, 25% of which is covered by the inner core. These are not flimsy assemblies. And even if they were, if the columns in your model are "piercing" the floor panels, then they are doing so on both sides of the crush front. You're still going to have to explain Newton's Third Law in your model.

 

[GlennB]

.... You're still going to have to explain Newton's Third Law in your model.

Just for laffs, why don't you explain Newton's Third Law? You could use Newton's own illustration .. that of a horse hauling a stone via a rope.

There was a poster called Heiwa here once upon a time. He took Newton's 3rd to mean that all falling things must invariably be stopped by the thing they hit. Action = reaction, right? He was a funny guy. Mad, but funny.

 

[femr2]

The core structure comprised the central 25% of the total horizontal area of the towers.

Tower Core Width 26.52m
Tower Core Length 41.15m

However, the vertical support is simply the columns themselves.

Again, please say exactly what you think the upper mass would be arresting upon.

Furthermore, the floor spaces were not simply empty.

Indeed.

There were furnishings, large filing systems (for which floor support enhancements had to be made), machinery, partition walls, some made of cement--as well as people, as we know. Some walls in fancy offices had marble slabs. There was material in each floor.

Absolutely. Live load. Part of the mass each floor was designed to carry. Again, it's important to understand that the OOS flooring (open office space) was only designed to support it's own vertical load, plus a safety factor, NOT the mass of the tower above. That was borne by the core and perimeter columns.

Maybe this material could not really be considered as supporting any significant weight

Agreed.

but neither can we imply that these are empty metal-with-concrete-slab pans stacking on top of each other.

Indeed, and am implying no such thing.

And even if this is what you're implying

It is not.

this is not the Bazant/NIST hypothesis, which is what we are discussing in this thread.

Seems like a side-track, but regardless...

As far as I'm concerned the scope of applicability of the Bazant et al model is quite simple.

It confirms that there is enough energy available, given the initial state assumptions, for the (semi) optimal limiting case of perfect axial column impact.

That's not what happened though, of course.

Nothing you've said here has anything to do with your "one floor" theory.

Incorrect, and you are spending little time actually looking at what I'm saying.

Do you understand why I suggested the analogy of the *hammock* ?

If so, and instead of putting one person in the thing, you put five in there, what do you expect to happen ?

a) Strings holding the hammock to the tree break and five people fall to the ground.

b) The two trees holding up the hammock break and the lot falls to the ground ?

Furthermore, a 20' x 60' WTC floor panel apparently can weigh 7 tons, if we go by the story of the floor panel that fell into Kill van Kull. Likening these panels to "hammocks" is a tad misleading.

As I hope you see now, no, it's actually pretty good.

A full single storey of WTC 1 weighed around 1.58E6Kg (Floor 92)

The floor panels further are supported by a column arrangement

No, they are not. They are attached to the sides of the columns, and *hang* from them.

These are not flimsy assemblies.

They are compared to a more standard steel beam grid type floor structure, with more regular evenly space vertical support columns.

And even if they were, if the columns in your model are "piercing" the floor panels, then they are doing so on both sides of the crush front.

Agreed. Why is that a problem ?

You're still going to have to explain Newton's Third Law in your model.

The upper block ends up rapidly being fragmented. What's the problem ?

The Bazant model is a mathematical limiting case. It doesn't say what happened, and it can't.

It says that once the top section had fallen a certain distance there was no way the remaining structure could stop it, regardless of how that initial drop ocurred.

I have issues with elements of the descent, but I have no problem agreeing with the validity of the underlying energetics based limiting case.

 

[ergo]

Just for laffs, why don't you explain Newton's Third Law? You could use Newton's own illustration .. that of a horse hauling a stone via a rope.

There was a poster called Heiwa here once upon a time. He took Newton's 3rd to mean that all falling things must invariably be stopped by the thing they hit. Action = reaction, right? He was a funny guy. Mad, but funny.

Just for laughs, I already have. Newton's Third Law applied to the collapse of the WTC towers says that the impact on the upper block of 30 floors "hitting" 80 floors is like 80 floors hitting 30, which is why we see the upper block crushing up before any crushing down could possibly begin.

Newton's Third Law explains why, in any collision, the larger and/or stronger and/or denser object or structure is going to affect the smaller one disproportionately, and the smaller one loses. Every time.

 

[Newtons Bit]

Just for laughs, I already have. Newton's Third Law applied to the collapse of the WTC towers says that the impact on the upper block of 30 floors "hitting" 80 floors is like 80 floors hitting 30, which is why we see the upper block crushing up before any crushing down could possibly begin.

And this is why understanding load paths matters.

 

[ergo]

Absolutely. Live load. Part of the mass each floor was designed to carry. Again, it's important to understand that the OOS flooring (open office space) was only designed to support it's own vertical load, plus a safety factor, NOT the mass of the tower above. That was borne by the core and perimeter columns.

Fortunately the floors don't ever have to support the mass of the tower above, since they are supported by columns below. Same with the floors of the upper block, which are the ceilings coming down. Columns on the other side of those, too.

As far as I'm concerned the scope of applicability of the Bazant et al model is quite simple.

It confirms that there is enough energy available, given the initial state assumptions, for the (semi) optimal limiting case of perfect axial column impact.

I don't think this is the case of a "limiting case". I think it is the case of an erroneous model, with therefore inherently erroneous calculations.

I will read the rest of your post later.

 

[femr2]

Fortunately the floors don't ever have to support the mass of the tower above, since they are supported by columns below.

Again, no. The floors outside of the core *hang* from the core and perimeter columns.

If the upper *block* descends, and the columns don't align perfectly, it's the floors that do end up having to support that mass. They can't.

Same with the floors of the upper block, which are the ceilings coming down. Columns on the other side of those, too.

Nope. Still hangin'

I don't think this is the case of a "limiting case". I think it is the case of an erroneous model, with therefore inherently erroneous calculations.

You think incorrectly. Read this thread from the beginning to see why it was started. It's about the applicability of the model to the real world.

It's not perfect, but the premise holds.

I will read the rest of your post later.

Please do. Take your time.

 

[W.D.Clinger]

To cause failure in a column which can support 3 times the load above it requires more than 3 times the load, meaning at least a 3g deceleration (jolt) would be required.

The highlighted text is incorrect.

The static load is 1mg, where m is the mass of the supported structure. At the static load of 1mg, the acceleration is zero, hence the deceleration is also zero. For a dynamic jolt of three times the static load, the deceleration would be 2g, not 3g: The first 1mg of force offsets the force of gravity and reduces the acceleration to zero but does not change the velocity. The remaining 2mg of the 3mg force is available to reduce the acceleration further (causing the 2g of deceleration).

Tony has made this mistake many times before, and has been corrected by many different people, but appears to have learned nothing from those corrections. It's almost as though Tony is deliberately exaggerating the magnitude of the jolt he expects.

What's more, my correction of Tony's miscalculation does not fix all of the errors he made in that brief statement I quoted above. Tony is misapplying an engineering rule of thumb that suffices for static situations but is grossly inappropriate for the dynamic situation he is pretending to model. For a correct calculation, see pages 308-311 of the Bažant and Verdure (2007) paper I cited earlier in this thread.

As Bažant and Verdure explain, detailed modelling of the force F(u) "is a formidable problem", but the kinetic energy of the falling upper section is easier to estimate, as is the energy dissipation obtained by integrating F(u) over distance. The kinetic energy of the falling section is roughly one decimal order of magnitude larger than the energy needed to initiate the accelerated collapse seen on 11 September 2001.

Tony Szamboti can't be expected to understand that, because he's still comparing impulses and accelerations.

Estimation of F(u) and its integration with respect to distance is complicated by the phenomenon described below by Dave Rogers. First, though, let's pay our respects to the comedy of Tony's argument:

1. It doesn't look like any deliberate demolition Tony has ever seen.
2. Conclusion: It was "unnatural".

In Tony-speak, "unnatural" evidently means collapses that don't look like deliberate demolitions must have been deliberate demolitions.

Someone who hasn't been paying attention might think I'm kidding or giving Tony an unnecessarily hard time. Sadly, no:

Every single Verinage demolition shows a significant deceleration at impact between the upper and lower sections of the building and I haven't seen a good explanation as to why there wouldn't have been one in the measured fall of WTC 1, other than that the structural integrity was being removed in an unnatural way.

Yes you have. I've offered you one several times. You've simply chosen not to read it. A simple tilt of the upper block, as observed in videos of the collapse, reduces the jolt below -1g, because the upper block is impacting sequentially rather than simultaneously. This doesn't happen in verinage demolitions because the collapse is controlled such that the supports are all removed over an equal length, and the upper block falls without tilting. It happened in the WTC collapses because they were uncontrolled.

I don't know why I'm bothering to post this, though. You've demonstrated beyond any possible doubt that you're either disinclined, or unable, to understand it.

 

[ergo]

The upper block ends up rapidly being fragmented. What's the problem ?

Well, for one, broken up matter will not have the ability to "pop out" floors at a rate of 95 floors in under 15 seconds, for example, which then are supposed to pulverize everything in their path and somehow also destroy the core structure at the same time.

Nor would the floor-column connections be as flimsy as you seem to want to suggest. I've read some da bunkers calling them "clips". This is ridiculous. They had enormous static loads to carry. They are not all going to fail at the rate of 6 floors per second because a few floors above have lost 15% of their columns, and then also have nothing to show for it at Ground Zero. If this is the collapse mode you're suggesting, we would see much more whole pieces of furnishings, machinery, bodies, and all the stuff that was in between these supposedly compacting floor panels, at Ground Zero. We don't.

You seem to want to have both your pancaking and your pulverization happening without a plausible scenario for either.

The Bazant model is a mathematical limiting case. It doesn't say what happened, and it can't.

It says that once the top section had fallen a certain distance there was no way the remaining structure could stop it, regardless of how that initial drop ocurred.

We know what it says. That's the "inevitability" argument. The problem is that's not what will occur in real life. In the video of WTC1 we clearly see the upper block crushing up before any crush-down could begin. It is crushing up as an integrate body. We are not seeing the sides peeling off and then an exposed core, which might suggest your mode of collapse. It is crushing up as a complete unit. Then the bottom portion begins to descend, apparently independently from whatever the upper block is doing.

http://www.plaguepuppy.net/public_html/collapse update/close-up_north_tower.mpg

By the way, what is 1.58E6Kg in tonnes?

 

[excaza]

http://lmgtfy.com/?q=1.58E6Kg+in+tonnes

 

[ergo]

http://lmgtfy.com/?q=1.58E6Kg+in+tonnes

http://www.google.com/search?btnG=1&pws=0&q=1.58E6Kg+in+tonnes

 

[excaza]

cool

 

[ergo]

Oops. Didn't see the calculator at first.

 

[femr2]

Well, for one, broken up matter will not have the ability to "pop out" floors at a rate of 95 floors in under 15 seconds

Explain why not. *Pop out* is not a great description. Strip them from the core and perimeter, sure.

which then are supposed to pulverize everything in their path

Significant pulverisation occurs when mass with enourmous KE impacts the *ground*.

and somehow also destroy the core structure at the same time.

Multiple modes of destruction were occurring. ROOSD for the OOS flooring, resulting in perimeter peeling, with slower, more chaotic and less understood (personally) core region destruction trailing behind, which did eventually arrest for a significant portion of each tower as debris was funnelled quickly into the OOS regions bypassing the remaining core remants, but stripping them even more cleanly along the way (imo).

Nor would the floor-column connections be as flimsy as you seem to want to suggest.

I'm not saying they are flimsy. If compared to the load bearing capacity of all of the core and perimeter columns, yes, flimsy, very flimsy. Relative. Simplistic estimations put the energy requirement to shear the connections for one OOS floor assembly under 100MJ.

and then also have nothing to show for it at Ground Zero

The huge dust clouds seen AFTER descent (not during) are the result of the chunks of tower hitting the ground with enourmous KE. That is where a good deal of the fine scale fragmentation occurred.

If this is the collapse mode you're suggesting, we would see much more whole pieces of furnishings, machinery, bodies, and all the stuff that was in between these supposedly compacting floor panels, at Ground Zero. We don't.

See previous ground impact KE response.

You seem to want to have both your pancaking and your pulverization happening

Correct.

without a plausible scenario for either.

Incorrect.

We know what it says. That's the "inevitability" argument. The problem is that's not what will occur in real life.

Correct, as it's the limiting case.

In the video of WTC1 we clearly see the upper block crushing up before any crush-down could begin.

You seem to be getting hung-up on one-way crush.

In the real world crush of course occurred in both directions, to varying degrees, and as the upper section tipped over we could even add crushed sideways if you like.

Again, read the full thread if you still don't understand the context and applicability of the Bazant one-way-crush thing.

It is crushing up as an integrate body.

Not really. More like it's being skinned, separating the perimeter and dumping the OOS flooring.

We are not seeing the sides peeling off

Yes, we are.

and then an exposed core

Eventually we do, but who knows what was happening behind the smoke early on ?

I'm not sure you're actually answering any of my questions. I think you should. They are there to help you.

 

[femr2]

I note a few of your posts on other threads.

You really need to go and spend some time getting to grips with the actual structure you are talking about.

That'll take you a couple of weeks I imagine.

I suggest you don't dig yourself in further until you've done so.

 

[ergo]

Significant pulverisation occurs when mass with enourmous KE impacts the *ground*.

Multiple modes of destruction were occurring. ROOSD for the OOS flooring, resulting in perimeter peeling, with slower, more chaotic and less understood (personally) core region destruction trailing behind, which did eventually arrest for a significant portion of each tower as debris was funnelled quickly into the OOS regions bypassing the remaining core remants, but stripping them even more cleanly along the way (imo).

Not evidenced in the videos or photos and not actually what the Bazant/NIST hypothesis describes, which is what we are discussing in this thread.

 

[femr2]

Not evidenced in the videos or photos and not actually what the Bazant/NIST hypothesis describes, which is what we are discussing in this thread.

Well, I've tried to get you to look. You're not listening. Suggest you go back through the discussion a few times, carefully. Start of the thread is not a bad place to start to get to grips with applicability of the Bazant model to the real world.

Have fun.

 

[ergo]

Not really. More like it's being skinned, separating the perimeter and dumping the OOS flooring.

This is not what we see in the video I posted.

Yes, we are.

No, we are not. Look at the video.

Eventually we do, but who knows what was happening behind the smoke early on ?

You know full well the core remnant disappears seconds after it appears. This is not something we can say "remains standing".

If this is the collapse mode you're suggesting, we would see much more whole pieces of furnishings, machinery, bodies, and all the stuff that was in between these supposedly compacting floor panels, at Ground Zero. We don't.

See previous ground impact KE response.

No. This doesn't follow from your model.

 

[beachnut]

Not evidenced in the videos or photos and not actually what the Bazant/NIST hypothesis describes, which is what we are discussing in this thread.

Your post exposes your complete ignorance on models.