WTC collapses - Layman's terms again

btw, Architect, someone asked for your assistance to take a look at my claim and explenation.
why dont you help him?
 
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Dictator Cheney said:
a chain, would be exactly the opposite,
in the tower example , that would be like after the failure of the remaining columns. the top part would go into the other direction.
would that have happened, we all would agree that law of physics was violated or have to be reconsidered. :)
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Sorry that I was unclear. What I meant was not that the chain was a good illustration of the tower, only an example to illustrate that the energy released in the collapse of the upper block would not be distributed amongst the different floors, but would hit every single point in the tower with the full energy, and therefore any point in the tower that was exposed to this energy that couldn't withstand it would fail. From your reasoning it sounded like you suggested that the floors below the impact zone would act like a "cushion" (for lack of better words, meaning that each floor would take their part of the imapct energy absorbing it). THAT was what I questioned, and the chain only served as a badly worded example.
 
padragan said:
Sorry that I was unclear. What I meant was not that the chain was a good illustration of the tower, only an example to illustrate that the energy released in the collapse of the upper block would not be distributed amongst the different floors, but would hit every single point in the tower with the full energy, and therefore any point in the tower that was exposed to this energy that couldn't withstand it would fail. From your reasoning it sounded like you suggested that the floors below the impact zone would act like a "cushion" (for lack of better words, meaning that each floor would take their part of the imapct energy absorbing it). THAT was what I questioned, and the chain only served as a badly worded example.
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i think that is wrong.
 
Architect said:
I would be interested to see ANY computer programme which could model a non-linear collapse such as occured at WTC.
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Such software does not exist. What you have to do is to first model the complete structure with FEM/beams and then decide the local failures step by step and redo the FEM analysis at every step. An iteration of kind.
If at a certain step you find that something free falls you have to include that in the analysis and apply the relevant loads (where they start again).

Many (10?) years ago the the Japanese did this with two bodies; one (A) a very solid bow of a ship (shell plates, strong horizontal webs, transverse frames) driven by a constant force, the other (B) the vertical plate side of another vessel and its internal structure. When A hit B, A penetrated a fair distance into B causing plenty of structural damages but A was finally arrested a bit into B. The whole thing maybe took 7 seconds full scale. In order to analyse this very non-linear collapse the Japanese split it into 700 steps, analysed the damage at every step, adjusted the FEM model + loads accordingly, and calculated the next step, etc. It took them 3 weeks with plenty of PCs running in parallell to do the analysis. And then a full scale test was done (real ship bow A hitting real ship side B) for comparison. It was quite good comparison. The vertical side of B lacked initially resistance to withstand the solid bow structure of A but after a while the assembly ran out of energy.
With today's better PCs the electronic analysis will go faster but every intermediate step needs some human input to adjust the model. But it can be done. And should be done for WTC1.
I am still curious about the 0.8-0.9 seconds free fall or near free fall of the upper block (or what remained of it) and then the alleged impact - what bottom parts of the upper block (verticalal columns or the lowest horizontal floor?) contacted the lower structure when and where (vertical columns? or just the uppermost horizontal floor?), etc. so that further damage could take place locally in the upper block and the lower structure.

Evidently the lower structure will cause serious damages to the upper block structure at once, when the former makes contact with the latter = the Bazant, Seffen, NIST assumption of an undamaged upper block during the whole collapse is proven wrong ... at once.

To me this strange assumption - the upper block remains intact - is suspicious. Very suspicious. Has nothing to do with reality.

It is in fact the destruction by the lower structure of the upper block dropping down that will result in complete collapse arrest very quickly.

And there is no reason to get upset about it and shoot the pianist because the music is what it is.
 
padragan said:
Sorry that I was unclear. What I meant was not that the chain was a good illustration of the tower, only an example to illustrate that the energy released in the collapse of the upper block would not be distributed amongst the different floors, but would hit every single point in the tower with the full energy, and therefore any point in the tower that was exposed to this energy that couldn't withstand it would fail. From your reasoning it sounded like you suggested that the floors below the impact zone would act like a "cushion" (for lack of better words, meaning that each floor would take their part of the imapct energy absorbing it). THAT was what I questioned, and the chain only served as a badly worded example.
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but wait, somehow you are right when you say, " any point in the tower that was exposed to this energy that couldn't withstand it would fail."

but that is wrong.
that the energy released in the collapse of the upper block would not be distributed amongst the different floors.
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i think you better ask the experts here on the forum if your assumption is correct.

but would hit every single point in the tower with the full energy
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do you mean that shock pulse wave that was "distributed true all the floors"?
 
Dictator Cheney said:
do you mean that shock pulse wave that was "distributed true all the floors"?
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Well, sort of. If you hit the head of a nail with a hammer the entire nail will be exposed to the impact. That was the reason for my hypothetical WTC tower with different floors made out of different material.

So, just as an illustrative example. If we imagine WTC1 the way it was, but we replace floor 25 with a special floor made entirely out of glass or plastic (of such dimensions that it can just about hold up the weight of the floors above it (ok, that may not be possible even with a sollide block, but bare with me, it's just an example anyway). Now, let's move to where the upper block collapse and comes down on the lower part of the building what would happen? I imagine that floor 25 would collapse since it's the weakest link in the chain, but the only way it can do that is if the impact energy is distributed through all the floors via the steel structure, since floor 25 was not hit directly.

Do you agree?

Now, of course floor 25 was just an ordinary floor, but for the sake of the argument I hope you understand where I'm going?
 
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padragan said:
Well, sort of. If you hit the head of a nail with a hammer the entire nail will be exposed to the impact. That was the reason for my hypothetical WTC tower with different floors made out of different material.

So, just as an illustrative example. If we imagine WTC1 the way it was, but we replace floor 25 with a special floor made entirely out of glass or plastic (of such dimensions that it can just about hold up the weight of the floors above it (ok, that may not be possible even with a sollide block, but bare with me, it's just an example anyway). Now, let's move to where the upper block collapse and comes down on the lower part of the building what would happen? I imagine that floor 25 would collapse since it's the weakest link in the chain, but the only way it can do that is if the impact energy is distributed through all the floors via the steel structure, since floor 25 was not hit directly.

Do you agree?

Now, of course floor 25 was just an ordinary floor, but for the sake of the argument I hope you understand where I'm going?
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i dont ignore your post, i am still thinking about it, i have some troubles with it :)

but i will come with an answer :)
 
Dictator Cheney said:
i dont ignore your post, i am still thinking about it, i have some troubles with it :)

but i will come with an answer :)
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No worries, take your time. My guess is that you are better educated than I am in terms of building integrity (most people are), I'm just a simple computer geek who tries to translate my understandings to layman terms so that people with more knowledge than I can slap my hands... :)

And if I'm wrong in my assumption that the glass floor would be the first to break I'm very interested in knowing where my reasoning is flawed.
 
Dictator Cheney said:
but wait, somehow you are right when you say, " any point in the tower that was exposed to this energy that couldn't withstand it would fail."

but that is wrong.


i think you better ask the experts here on the forum if your assumption is correct.


do you mean that shock pulse wave that was "distributed true all the floors"?
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padragan said:
Well, sort of. If you hit the head of a nail with a hammer the entire nail will be exposed to the impact. That was the reason for my hypothetical WTC tower with different floors made out of different material.

Now, of course floor 25 was just an ordinary floor, but for the sake of the argument I hope you understand where I'm going?
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May I try to clarify this?

In short, the way the WTC Towers were constructed was not monolithic. Even though they looked "solid" from the outside, there was a great deal of tension and compression on the inside that kept them standing. An out-of-control fire, alone, could have yielded the same result :( A critical element in the design was vulnerable to extreme heat.

Different from the more anthropomorphic endoskeleton design, these were held in the air by an exoskeleton, whose rigidity was maintained by horizontally arrayed members. Thus, the integrity of the structure depended on the integrity of the dimensional stability of the horizontal members; such that if the floor should not maintain its proper size, the columns--the vertical load-bearing members--would become so deformed, such that they would break, the structural integrity would be compromised. (Such as it was :( )

For a number of design considerations, light-weight prefabricated truss joists were chosen for this design, supplemented by more robust joists. Both were designed not only to provide direct support for the flooring, but also as horizontal members that participated in the structural integrity. There were also fully load-bearing beams, although these were minimized, for the same design considerations.

Because of extreme heat, the horizontal shape of a significant number of joists was warped, bending vertical columns beyond their limits of endurance. That was the initial failure. As the fall of that topmost structure continued to breach the integrity of the next layer of horizontal members, subsequent columns failed, and the entire structure collapsed.

This is not to say that other structures do not behave as you believe they do.
 
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leonAzul said:
May I try to clarify this?
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Thanks for the help! Should I interpret that when applying it to my hypothetical example that the floors between floor 25 and the impact zone would probably "soak up" the impact energy (like a spring) and prevent it from hitting floor 25 so that it would collapse? If so I understand, otherwise I'm probably just to uneducated to grasp your explanation.

(of course, it would collapse anyway once the destruction would have travelled down the building)
 
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padragan said:
Thanks for the help! Should I interpret that when applying it to my hypothetical example that the floors between floor 25 and the impact zone would probably "soak up" the impact energy (like a spring)
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That's not how the building was designed, nor constructed; so that's not how the building behaved.

;)
 
leonAzul said:
That's not how the building was designed, nor constructed; so that's not how the building behaved.

;)
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But the key question I'm going after, would floor 25 experience the same level of impact in the moment of collapse as the impact zone? The way I see it, when you apply force to some thingies that are connected they will either absorb energy (like foam rubber for instance) or simply transport it (like a nail), or some combination of the two (most materials have some degree of flexibility).

The reason for my lenghty and clumpsy examples was the DC explanation (with the nifty animation that's been so disresepcted) of impact affecting several of the floors below the impact zone. It felt as if his point was that the floors below the impact zone would absorb some of the energy from the impact (like a spring), and I thought that would also imply that a much higher tower would not collapse as easy (more floors = bigger spring = more impact energy absorbed). That didn't sound right in my head, which was my reason to ask for some clarification in the first case on how the building at large would react to the sudden impact.


(for the record, in my layman opinion global collapse was to expect once the impact zone couldn't hold the upper block in place. I have a hard time grasping how the lower part of the building would be able to withstand the momentum of all those floor coming down. But like I've said before, I have no relevant education or knowledge to back that up)
 
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padragan said:
But the key question I'm going after, would floor 25 experience the same level of impact in the moment of collapse as the impact zone? The way I see it, when you apply force to some thingies that are connected they will either absorb energy (like foam rubber for instance) or simply transport it (like a nail), or some combination of the two (most materials have some degree of flexibility).

The reason for my lenghty and clumpsy examples was the DC explanation (with the nifty animation that's been so disresepcted) of impact affecting several of the floors below the impact zone. It felt as if his point was that the floors below the impact zone would absorb some of the energy from the impact (like a spring), and I thought that would also imply that a much higher tower would not collapse as easy (more floors = bigger spring = more impact energy absorbed). That didn't sound right in my head, which was my reason to ask for some clarification in the first case on how the building at large would react to the sudden impact.


(for the record, in my layman opinion global collapse was to expect once the impact zone couldn't hold the upper block in place. I have a hard time grasping how the lower part of the building should be able to withstand the momentum of all those floor coming down. But like I've said before, I have no relevant education or knowledge to back that up)
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i think i get what you mean.

what i have more trouble with in the collapses. is the uppwer tower part.

it was the same spring/tower. but for some reason, the uppwer parts lowest floor was able to destroy all the other floors below it, and after that the upper part destroyed itself.
in reality, the upper part would start destroying tself when it hits the lower tower, oc also the lower towers upper floors will be destroyed.

but my point is in layman terms. actually we have 2 big energy "consumers" lower tower and upper tower. but mr Bazant only uses the lower tower. the upper tower is for some magical reason undestructable in the crush down phase.
and when you take a look to videos, you can clearly see that the lowest floor of the upper falling tower was in no way undestructable, it was one of the first things that was destroyed.
 
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