I would imagine it to be mostly the spandrel which supported the ends of the floor trusses
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Question for Apollo20
- Thread starter Golden Bear
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I would imagine it to be mostly the spandrel which supported the ends of the floor trusses
Golden Bear
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Let me say it in terms you may be able to understand. I was asking Dr. Greening to go through a thought experiment with me. Taking into account the factors I have described, what did he think would happen during an FEA if it were possible to run one. Is it unreasonable to ask the powerful computers in our heads to think about something that can't be handled by the silicon based computers on our desks?
Your little stundie nominations make you all sound like 3rd graders, by the way.
Golden Bear
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Wait a minute, earlier you said the lower structure has more "give" to it, and now you are saying it is more rigid than the upper floors. Which is it?
Also, rotating, moving and tilting the massive upper block of floors would consume a huge amount of energy. Bazant's mathematical model does not take this into account either. But it is convenient for you to rely on it for reducing the damage to the upper floors, so go for it!
I know you're just regurgitating what has been explained to you by the other, shall we say, more articulate members here, so I'll let you off the hook on this one.
It gives when each storey is destroyed. What happens if you jump from a high ledge onto a pile of empty cardboard boxes? If there's enough boxes you don't die, but the boxes are destroyed, right?
Why shouldn't the upper block tilt or rotate? The damage is already asymetrical, the upper block is not falling perfectly aligned onto the lower block, so therefore some parts of the lower block my provide slightly more resistance than others. But the upper block doesn't have to move in one path if it encounters a bit of resistance. I'm not talking huge deviations over a long period of time, but enough deviation to enable the falling block to avoid the sort of damage a rigid, unmoveable block cannot avoid.
So, you really don't have any imagination then? Shame
uk Dave writes of the "leading edge" of the upper part of the building:
That would explain the perimeter of the 207ft x 207 ft "leading surface".
The rest would consist of open floor space and their trusses, and 47 "spears" (core columns).
Don't you see that you have no leading, rigid surface of the "block" whatsoever?
As for the core columns, those of the lower portion will spear the flooring of the upper portion and penetrate the flooring. The core columns of the upper portion will likewise spear the floor panelling of the lower portion.
So where is the direct transfer of kinetic energy that the Bazant equations rely upon?
Bazant "imagines" an upper "block".
And his analysis would fall to pieces without this imaginary block.
That would explain the perimeter of the 207ft x 207 ft "leading surface".
The rest would consist of open floor space and their trusses, and 47 "spears" (core columns).
Don't you see that you have no leading, rigid surface of the "block" whatsoever?
As for the core columns, those of the lower portion will spear the flooring of the upper portion and penetrate the flooring. The core columns of the upper portion will likewise spear the floor panelling of the lower portion.
So where is the direct transfer of kinetic energy that the Bazant equations rely upon?
Bazant "imagines" an upper "block".
And his analysis would fall to pieces without this imaginary block.
So you're unable to imagine that the 'leading edge' of the upper block might not be perfectly aligned with the lower block? You can't imagine the leading edge smashing through the floor pans as the still mostly intact perimeter columns of the upper block push the lower perimeter columns outwards (or pulls them inwards)?
Can you imagine floor assemblies in the lower block becoming detached by this 'crush down' and themselves falling onto the floor below, punching through this and disconnecting it from the perimeter columns?
Can you imagine the release of material, so great that it overflows the collapse front and beats the collapse front to the ground?
You seem to be only capable of imagining a clean, perfectly aligned scenario where the damage inflicted by the upper block is mirrored by the damage inflicted by the lower block. Somehow I suspect it is much dirtier than that.
Can you imagine floor assemblies in the lower block becoming detached by this 'crush down' and themselves falling onto the floor below, punching through this and disconnecting it from the perimeter columns?
Can you imagine the release of material, so great that it overflows the collapse front and beats the collapse front to the ground?
You seem to be only capable of imagining a clean, perfectly aligned scenario where the damage inflicted by the upper block is mirrored by the damage inflicted by the lower block. Somehow I suspect it is much dirtier than that.
I think with a PhD in Physics, Dave Rogers can understand it anyway you wish to explain it.
TAM
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Golden Bear
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I've been through this here before but you may have missed the discussion. The proper analogy is not a human being jumping onto a pile of cardboard boxes. The proper analogy is dumping cardboard boxes onto a pile of cardboard boxes.
Your analogy isn't quite as bad as the rock falling onto the house of cards analogy that your cohorts here at JREF like to rely on, but it still misses the mark.
If you're dropping a rock onto something else, it has to be made of rock. If you're dropping something onto a house of cards, it has to be made out of cards and structurally similar to the lower structure.
The analogy is meaningless unless whatever you are dropping is similar in construction, materials and engineering to whatever you dropping it onto.
Also, I never said the upper block wouldn't rotate. I just said that any rotation or tilting (ie. any change in angular momentum) would consume a large amount of energy, certainly enough energy that Bazant shouldn't neglect it in his analysis.
Golden Bear:
You are incorrect about the magnitude of the angular momentum vis a vis Bazant's analysis. It's actually the INCREASE in rotational kinetic energy of the upper section that must be compared to the DECREASE in potential energy.
The change in the energy of the upper section of a tower is given by:
Delta{E} = Delta {Rotational KE + Potential Energy}
And, approximately, for a rigid upper section:
E = 1/6Mh^2.[d(theta)/dt]^2 + 1/2Mgh.cos(theta)
where M is the mass and h the height of the upper section and theta is the tilt angle.
This must be evaluated for an initial and a final tilt angle.
For WTC 2, the rate of change of theta in the first few seconds is less that 10 deg per second. Now after converting to rads per second and taking h as 111 meters you will find that the increase in rotational KE is considerably smaller than the loss in PE and can be neglected to a first approximation.
You know sometimes I think you are the one who is handwaving......
You are incorrect about the magnitude of the angular momentum vis a vis Bazant's analysis. It's actually the INCREASE in rotational kinetic energy of the upper section that must be compared to the DECREASE in potential energy.
The change in the energy of the upper section of a tower is given by:
Delta{E} = Delta {Rotational KE + Potential Energy}
And, approximately, for a rigid upper section:
E = 1/6Mh^2.[d(theta)/dt]^2 + 1/2Mgh.cos(theta)
where M is the mass and h the height of the upper section and theta is the tilt angle.
This must be evaluated for an initial and a final tilt angle.
For WTC 2, the rate of change of theta in the first few seconds is less that 10 deg per second. Now after converting to rads per second and taking h as 111 meters you will find that the increase in rotational KE is considerably smaller than the loss in PE and can be neglected to a first approximation.
You know sometimes I think you are the one who is handwaving......
Golden Bear
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You are talking about something completely different than UK Dave. He seems to think the upper block will kind of bounce around as it descends. You are talking about it rotating in one direction. In UK Dave's case, where the upper block is constantly changing angular momentum, I stand by my remarks. That change in angular momentum must be accounted for. In any case, he's obviously confused about what he thinks really happened during collapse.
In your case, you have yet to provide any legitimate reason why the upper block of floors would remain a rigid block and not be damaged when it impacts the lower structure.
Dave Rogers
Bandaged ice that stampedes inexpensively through
It's still a stupid question. Let's assume an infinite amount of computing power and a perfect specification of the starting structure and its condition; in that case what would ideally be expected is a perfect simulation of the collapse that actually occurred (although in practice chaos theory suggests that even this is impossible). If we then assume limited computing power and imperfect specification of the structure, we'll see a progressively less accurate simulation. The inaccuracy of such a simulation tells us nothing whatsoever about the collapse because it has nothing to do with the collapse, but arises only from the limitations of the system carrying out the simulation. By saying that an FEA is not feasible, Dr. Greening is in effect saying that if one were carried out then the results would be so inaccurate as to be completely useless. That's the answer to your question, and you could easily have figured that out before you even bothered to ask it. And that's why your question merits ridicule rather than a sensible answer.
Dave
Dave Rogers
Bandaged ice that stampedes inexpensively through
Your scenario seems perfectly reasonable, and I'm sure has more in common with how the collapse actually progressed than Bazant's model. However, Bazant's model still represents a valid proof that global collapse would be expected to follow. Why? Because Bazant is using a limiting case. In Bazant's analysis, it's implicitly assumed that the impact is column-on-column, so buckling failure of the columns is required for collapse propagation. In the column-on-floor and floor-on-column scenario, the impact of the columns will easily overload the floors, which will break up and fall on the floors below, as the columns also continue to fall and spear the lower floors. There is therefore a progressive collapse of the floors progressing ahead of the column collapse, and this will remove the bracing between the core and perimeter columns. With this bracing removed, the columns alone cannot support their own weight and will simply fall away. The energy requirements of this collapse mechanism are very much less than those of Bazant's model, so in this scenario collapse is even more energetically favourable. And that is why Bazant's model is valid; he's biased the analysis as strongly against global collapse as he can, and found that collapse still ensues. Your scenario only makes that collapse even more energetically favourable.
Dave
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Well put. Short but accurate explanation to all the Bazant critics.
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Golden Bear asks:
The FEA problem or collapse "visualation" problem become much simpler if we take advantage of the 2 following verifiable facts:
1) The large, large majority of core box column sections seen in the rubble are totally straight.
2) The large, large majority of core box column sections seen in the rubble have squared-off ends with clean breaks that are right along the original weld surfaces.
There is a third rather interesting fact about the locations of all core column-to-column welds in WTC 1, 2 that will probably be new to most all readers:
All 47 core columns had welds about every 38 feet along their entire 1400 ft lengths.
The welds of each column were located at the exact same elevations as all the other columns.
In other words, there are distinct 2-D horizontal planes separated by about 38 feet all the way up each building on which ALL CORE COLUMN-TO-COLUMN WELDS are located. In fact, this was the origin of the term "weld plane" that Max Photon used before.
Or, to visualize it simply, If all core column-to-column welds were treated as "points", then all WTC 1, 2 core column-to-column welds would form a "rectangular lattice structure".
If we incorporate the "matchstick" model to the core box columns before, during, and after the "progressive collapses" (demolitions), we can begin to see some absurdities in the Bazant (and Steven Jones, and Gordon Ross, and Judy Wood....) "collapse" scenarios.
After all, we know the exact locations of the "plastic hinges" (to the foot) all throughout the core
Anyway, do you see how "matchstick" visualization of the core structure (matchsticks are 38 feet long and typically span 3 floors) greatly simplifies the FEA?
The FEA problem or collapse "visualation" problem become much simpler if we take advantage of the 2 following verifiable facts:
1) The large, large majority of core box column sections seen in the rubble are totally straight.
2) The large, large majority of core box column sections seen in the rubble have squared-off ends with clean breaks that are right along the original weld surfaces.
There is a third rather interesting fact about the locations of all core column-to-column welds in WTC 1, 2 that will probably be new to most all readers:
All 47 core columns had welds about every 38 feet along their entire 1400 ft lengths.
The welds of each column were located at the exact same elevations as all the other columns.
In other words, there are distinct 2-D horizontal planes separated by about 38 feet all the way up each building on which ALL CORE COLUMN-TO-COLUMN WELDS are located. In fact, this was the origin of the term "weld plane" that Max Photon used before.
Or, to visualize it simply, If all core column-to-column welds were treated as "points", then all WTC 1, 2 core column-to-column welds would form a "rectangular lattice structure".
If we incorporate the "matchstick" model to the core box columns before, during, and after the "progressive collapses" (demolitions), we can begin to see some absurdities in the Bazant (and Steven Jones, and Gordon Ross, and Judy Wood....) "collapse" scenarios.
After all, we know the exact locations of the "plastic hinges" (to the foot) all throughout the core
Anyway, do you see how "matchstick" visualization of the core structure (matchsticks are 38 feet long and typically span 3 floors) greatly simplifies the FEA?
Of course there is a way around it, you just don't see it. I will explain to you where the key error in your reasoning is.
You are imagining the following situation: You take two crushable objects, place them on the floor, brace one of them against the wall, and push the other against it. Let's call this case 1. You conclude that whatever destruction occurs should be shared roughly equally between the two objects. If both objects are destroyed, they should be destroyed about simultaneously. And you are correct in that conclusion.
Now, you place one crushable object on the ground, and drop another one on top of it. Let's call this case 2. Again, you conclude that the destruction should be shared roughly equally. And you are wrong - if both objects are completely destroyed, the bottom object will be destroyed first.
I will now explain to you why.
In case 1, the situation is symmetrical. The force that you apply to the edge of the crushing object is matched by equal force exerted by the wall on the edge of the crushed object. Ignoring the floor, there is no significant difference between the two objects, destruction-wise.
In case 2, the situation is not symmetrical. The floor exerts force on the bottom edge of the bottom object, but this force is not matched by equal force applied to the top of the top object. Instead, gravity exerts force throughout the entire mass of both objects: equal force on any two parts of equal mass. This is very important.
As the top object begins to crush against the bottom object, the situation is initally symmetrical, and indeed, some part of the top object will initially be destroyed. But the symmetry is broken as crushing continues.
While in case 1, in the collision zone, the mass of crushed debris experiences the same force from both sides - therefore, zero net force - in case 2, gravity also accelerates the mass of crushed debris. As crushed debris in the collision zone gains more and more mass, the downward force exerted on this mass increases. This is because force exerted by gravity is proportional to mass.
As the falling mass of crushed debris and the remains of the top object continue to accelerate as the collapse progresses, the bottom object continues to be crushed by the mass of crushed debris with ever increasing ease. The forces between the collision zone and the bottom object are ever greater.
But not the forces between the collision zone and the top object! Initially they are the same, yes, but as the mass of crushed debris builds up, the momentum imparted by each crushed "floor" of the bottom object will be increasingly more "absorbed" by the mass of crushed debris. This is because forces between the top object and the collision zone result only from the difference between free fall and actual acceleration of the crushed debris.
Another way to look at it is to realize that the remains of the top object effectively rest upon the collision zone, which is not only moving downwards, but is actually accelerating downwards. This means that the forces between the collision zone and the remains of the top object are actually less than if the remains of the top object were resting on the ground. If you ever experienced the apparent decrease in your weight while standing in an elevator accelerating downwards, you will know what I am talking about.
To sum up: the error in your reasoning is that you do not realize that the situation is not symmetrical. While inertia of the ground exerts force only on the bottom of the WTC tower, gravity does not exert force only on the top of the WTC tower, but throughout its entire mass, and as the collapse progresses, increasingly more on the collision zone.
Thanks for paying attention.
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Golden Bear: Bazant has never argued "crush down THEN crush up"; the collapse front propagates in both directions, but at different rates. See below - this was discussed over a year ago.
Regarding finite element modeling - no engineer will advise continuing a forensic collapse model past the point of multiple member failure, or once progressive or global collapse is imminent. What's the point?
To attempt to create a model which covers the linear elastic response, through the nonlinear plastic stage, to fracture, with impact, fire, vertical collapse, then run the results through a post-processor to obtain some kind of graphic (because god knows the output is going to look like a metropolitan phone book) would take a disproportionate amount of time versus the accuracy gained.
Of course, no one in the truth movement really wants any modeling done.
Why do you think, after all these years, they have not hired a single engineer to run any models for them?
Regarding finite element modeling - no engineer will advise continuing a forensic collapse model past the point of multiple member failure, or once progressive or global collapse is imminent. What's the point?
To attempt to create a model which covers the linear elastic response, through the nonlinear plastic stage, to fracture, with impact, fire, vertical collapse, then run the results through a post-processor to obtain some kind of graphic (because god knows the output is going to look like a metropolitan phone book) would take a disproportionate amount of time versus the accuracy gained.
Of course, no one in the truth movement really wants any modeling done.
Why do you think, after all these years, they have not hired a single engineer to run any models for them?
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Golden Bear
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I see exactly what you are saying, and you're simply wrong. Basically you are arguing that Newton's Third Law applies in your case 2 only at the initial impact. And that's where you're wrong. Any force imparted in a downward direction on the lower structure will be accompanied by an equal force in the upward direction. Newton's Third Law dictates this result. You deny the existence of this opposite force, but it does exist. Several others on here have proposed different ways this force will express itself, but you have gone one step further into fantasy land to deny its very existence.
Even if there is a "collapse zone" of crushed debris between the upper block of floors and the lower structure, I'll say it again, any force that is imparted onto the lower structure will be accompanied by an equal but opposite force on whatever is imparting that force. Prove me wrong if you like, but you will be proving Sir Newton wrong, and I would love to see that proof. In fact, please submit it to a technical journal.
You can talk about gravity and where the forces come from all day long, but in the end, from a basic physical standpoint, it comes down to a destructive downward force being imparted into the lower structure which deforms the lower structure. This downward force is being exherted onto the lower structure by something (the upper block of floors or crushed zone of debris). This downward force must be accompanied by an equal and opposite upward force on whatever is exherting the downward force, and the upward force must express itself somehow. We can have a legitimate debate on how this force is expressed during the collapse, but what is not debatable is the existence of the equal but opposite force.
I understand you are merely regurgitating Bazant's theory, but he is ignoring Newton's Third Law as well. That's his main problem.
DGM
Skeptic not Atheist
The wouldn't the opposing force be the earth.
Golden Bear
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I don't think "the earth" is a force....
But, Newton's Third Law applies when two bodies interact. When a first body interacts with a second body, the first body imparts a force onto the second body. However, Newton's Third Law says the second body also imparts a force right back onto the first body, equal in magnitude but opposite in direction.
Bazant models the WTC as basically two interacting bodies. The rigid upper block of floors, and the lower block of floors. I know there is a "crushing zone" in there, but that's really just a subset of the body comprising the lower block of floors that's being destroyed. When these two bodies interact (ie. impact), there will be equal and opposite forces at the moment of impact.
Then Bazant says this destroyed floor becomes part of the rigid upper block of floors. This, Bazant says, gives the upper floors even more destructive power. His error of ignoring Newton's Third Law just propagates throughout his model because the upper body never experiences this equal but opposite upward force when it impacts the lower structure.
It's really a simple concept you should be able to understand. As long as the falling upper block of floors is physically interacting with the lower structure, Newton's Third Law applies and there will be an equal but opposite force applied to the falling body comprising the upper floors. I'll say it again, there is no way around this.
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No, sir, I'm sorry, but it is you who are wrong. You apparently do not understand what I am saying.
I am not saying any such thing. Newton's Third Law applies all the time.
That is correct.
No, sorry. I am fully aware of the existence of this opposite force. It is this very force that slows down the fall of the crushed debris+upper part of the tower, making the acceleration slower than free fall.
What you do not understand is that this equal and opposite force is exerted on the crushed debris. Please pay attention to this, because this is very important. It is not the same as the force exerted by the crushed debris on the upper part of the tower.
I will attempt to explain this to you through a simple example. Imagine a person standing on the roof of a building. The building exerts a huge force on the ground. The ground exerts equally huge and opposite force on the building. Does this mean that the building exerts equally huge force on the person standing on the roof? Of course not. Force exerted by the building on the person is of very different magnitude than force exerted by the ground on the building.
For the very same reason, force exerted by the crushed debris on the upper part of the tower is not the same as the force exerted by the bottom part of the tower on the crushed debris.
Yes. Force on the crushed debris. Please pay attention to this important distinction.
If you read what I have written above, you will realize that by the example of a person standing on the roof of a building, I have proven you wrong, without proving Sir Newton wrong.
Because this is basic mechanics that is readily apparent to any competent physicist, I will of course not submit this to any technical journal.
You are correct. But if you have read and comprehended what I have written above, you now understand that the conclusion you draw - that the upper part of the tower will be crushed in the same way as the bottom part of the tower - is wrong.
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