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Fairbanks Video stabilized with horizontal charges.

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posted on Aug, 20 2007 @ 04:51 PM
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reply to post by Griff
 





How would pressurized air act diferently?


And you're a structural engineer? Worrying.

Note the differences between explosions and fluid dynamics.




posted on Aug, 20 2007 @ 07:27 PM
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Originally posted by himselfe
reply to post by gottago
 





True. Instead it disintegrated explosively barely a second after collapse began. Twenty-odd floors, dropping in a coherent mass--for it was still a coherent structure--simply exploded in mid-air. Big grey flower-bloom of destruction with structural members flying outward, some for hundreds of yards.


Disintegrated explosively? Hardly:



Watch your own video please. What is going on in the last 2-3 seconds? How is that building mass disintegrating and flying out at the bottom right corner of the screen? Why is it roiling and moving outward?



posted on Aug, 20 2007 @ 07:37 PM
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Originally posted by Griff


How would pressurized air act diferently?

it would have waved out. Explosions ARE air. the entire poit of an explosion is to generate enough air pressure in a small area so that the energy waves out a shockwave to kill. Everything from grenades to nukes are based on this. To build enough air to destroy.



posted on Aug, 20 2007 @ 11:21 PM
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reply to post by gottago
 





Watch your own video please. What is going on in the last 2-3 seconds? How is that building mass disintegrating and flying out at the bottom right corner of the screen? Why is it roiling and moving outward?


It's collapsing



posted on Aug, 21 2007 @ 08:34 AM
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Originally posted by himselfe

And you're a structural engineer? Worrying.

Note the differences between explosions and fluid dynamics.


What do either have to do with structural engineering?

[edit on 8/21/2007 by Griff]



posted on Aug, 21 2007 @ 09:07 AM
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Originally posted by himselfe
Perhaps since you are a structural engineer (and hopefully a competent one) you would care to back up what you state by showing us laymen, using scientific proof and data, how you arrive at such conclusions?


I will try. I am not very elequant with words though.


Given your expertise hopefully you can describe in unambiguous terms the process which you claim transfers the stress of gravity and mass from the bottom of the building (which has to bear 110 stories of weight) to the upper sections.


I'm not saying the loads would transfer up. The transfer truss transfers the loading from the exterior to the interior and vice versa. That's horizontal.


Granted beams and columns are used and designed to distribute loads, however like any scientific process, this distribution is not perfect, also the load must be transferred somewhere. While my understanding of structural design is basic, I always thought the desire with columns and vertical beams was to transfer the upper load downwards?


You're understanding is correct.


What benefit would there be to designing systems that transfer loads upwards?


This is why I believe you are not understanding what I'm saying. The loads are acting down on the columns correct? The core and perimeter held up the weight of the building correct? Without the core, the exterior would be overstressed (because of load transfer) and fail at it's weakest part. It is not rocket science.


The outer frame of the two towers was not designed to bear the full gravitational load of the tower, if you were to remove the load bearing capacity of the central support system that load would be transferred to the outer frame.


That is what I'm saying. Why are you arguing with me? Because you have a preconcieved notion that I'm a CTer?


The outer frame on the lower part of the building could not transfer the load away and would collapse from the stress. Transferring the load upwards does nothing to reduce the effects of mass and gravity.


Since the loads are acting throughout the entire length of the columns, there would be no transfer upward. Again, I believe it is you that is not understanding what I say. No offense. The transfer is horizontal (from the interior to the exterior) not up and down.



Well from what I've been reading you have been trying to assert that there was a conspiracy to place bombs in the basement, is that not right?


I believe the core had to be taken out first for what we see yes.


Since as yet there is no element of truth in the theory, what else could be the point?


One man's lie is another man's truth.



I was talking about the lower parts that are attached to the ground holding the building up.


And I'm telling you that columns hold up vertical load and moments. There would be no transfer upwards, just that the vertical load becomes greater. And given that the exterior is damaged, it would tend to fail in the damaged part.




Care to cite?


Look into NIST's computer models and fire models.




Don't know where toilet seats come into it.


Sorry to go off on the toilet seat thing. It is an inside joke here at my office. BTW, I work for architects.




I'm sure as a structural engineer you understand the importance of the scientific process and proving your work or theory.


I'm not here to write a disertation. I'm just here to tell people that the core failing below the impact zones would still fail the exterior at the impact zones .




Are you claiming that the point of greatest stress would not fail when loaded beyond it's capacity?


And the point of greatest stress would be the impact zones on the exterior.

You could be correct in that just taking the core out in the bottom would fail the exterior there also. I haven't done any calculations. But the point is, it would also fail at the impact zones first.



posted on Aug, 21 2007 @ 09:13 AM
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BTW. To clarify something. The exterior columns were the same dimension the entire length. Except for the tree design where 3 columns became 1 at the base. So, where would they tend to fail when over stressed? Undamaged stronger parts or damaged weaker parts?

[edit on 8/21/2007 by Griff]



posted on Aug, 21 2007 @ 10:11 AM
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reply to post by Griff
 





What do either have to do with structural engineering?


Nothing directly I guess, however I would hope that any structural engineer has a competent understanding of science.
In relation to fluid dynamics I believe they would be somewhat important to a structural engineer since you have to design structures with tolerance for various stresses including air, and in the case of bridges, water.


reply to post by Griff
 


Since we both agree that the loads would be transferred to the outer structure, and that the outer structure was not designed to bear the full gravitational load of the building, and we agree that the load would not be transferred upwards, how do you propose that that the outer structure at the base of the building could withstand the entire gravitational load and the extra stress provided by the momentum of the upper collapsing sections for the entire duration of the collapse sequence?

I am not disputing the fact that taking out the core structure at the base of the building could initiate the collapse sequence at the site of impact, what I am disputing is the idea that the outer structure at the base of the building could bear the entire gravitational load without failing prior to the upper collapse sequence reaching that point, especially considering the extra energy imposed on the support structure by the momentum of the upper collapsing sections.




I believe the core had to be taken out first for what we see yes.


But can you prove that the core had to be taken out first?




One man's lie is another man's truth.


That does not answer the question of what other point there could be in asserting something for which there is no evidence other than alluding to conspiracy.




And the point of greatest stress would be the impact zones on the exterior.


As far as I understand it when the entirety of a structure is concerned, the weakest point is not synonymous with the point of greatest stress, especially considering the comparably lesser forces the damaged upper section has to contend with as compared to the base of the structure.



posted on Aug, 21 2007 @ 10:33 AM
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Originally posted by himselfe
Nothing directly I guess, however I would hope that any structural engineer has a competent understanding of science.
In relation to fluid dynamics I believe they would be somewhat important to a structural engineer since you have to design structures with tolerance for various stresses including air, and in the case of bridges, water.


Yes and no. Structural engineers just have to consider wind load. We do study fluid dynamics and is what I have been studying the last 5 weeks for my PE. (Thank God I don't have to study that anymore...now onto environmental, geotechnical, structural and transportation). I don't know enough about fluid dynamics to say either way, but what would be the flow rate of explosive gas as oppossed to gas being compressed and flowing out the core and out the exterior? I don't know.



I am not disputing the fact that taking out the core structure at the base of the building could initiate the collapse sequence at the site of impact, what I am disputing is the idea that the outer structure at the base of the building could bear the entire gravitational load without failing prior to the upper collapse sequence reaching that point, especially considering the extra energy imposed on the support structure by the momentum of the upper collapsing sections.


Ok. We can agree. I see your point and is really why I believe they would have had to do it in at least three parts. Severing the core at the mechanical floors. This would give the base more stability until that portion of core was severed.




But can you prove that the core had to be taken out first?


No, but all evidence points to it. Even NIST. How would floor trusses pull inward on exterior columns that were already designed to carry that load? Other than the core not being there anymore? That would certainly place an enormous moment on the exterior plus vertical load. Only way IMO that it could have happened because a sagging floor truss still weighs the same as it did at start (so no added load just from sagging). If you want, I can look up how much the moments would increase without the core. I believe they would be on the order of 8 times more without checking. That alone might be enough to fail the exterior without even considering the loss of interior load strength. Again, without calculations, I'd just be speculating.




That does not answer the question of what other point there could be in asserting something for which there is no evidence other than alluding to conspiracy.


The only conspiracy I'm alluding to is the cover-up of the failure (incompetence) to stop the terrorists from placing a few bombs in the building. Either that or the cover-up that the buildings were built shoddy. IMO it's the former.




As far as I understand it when the entirety of a structure is concerned, the weakest point is not synonymous with the point of greatest stress, especially considering the comparably lesser forces the damaged upper section has to contend with as compared to the base of the structure.


And I've already said that you could be correct. Without doing any calculations, I'd say you might be, just with Euler's buckling formula. But, if the core was taken out in more precise pieces instead of just at the base, this affect would be less.

I think we are arguing the same thing just from different standpoints.



posted on Aug, 21 2007 @ 07:04 PM
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reply to post by Griff
 





what would be the flow rate of explosive gas as oppossed to gas being compressed and flowing out the core and out the exterior?


I haven't formally studied either subject so I couldn't give you a qualified answer, but as I understand it explosions cause a sudden, short but very intense blast wave that extends almost equally in all directions, while fluid dynamics does come into play to some extent with any fluid that interacts with the blast wave, the pressure caused by the blast wave is far greater than most materials can withstand and is much much more intense than the pressure caused by a collapsing building. It's to do with the rate and intensity of the compression caused by the blast wave. You can push any volume of fluid through a small hole and so long as the pressure is low enough the fluid will jet out from the hole at a sustained rate, if you increase the pressure beyond the capacity of the material the hole is in, the material will lose integrity and tear apart. With an explosion you get a very intense pressure for a very short period of time. If you watch the video posted by 11 11 earlier on in this post, you can see where they show one of the dust jets in slow motion that it is a sustained jet, while it is still a short period of time for us, the length in which the jet is sustained is much longer than would be caused by an explosion. A very easy experiment can be done to prove this: take a balloon and fill it with dust and air, seal it up and then place a strip of sticky tape on it, place it on the floor and use a small pin to poke a hole through the sticky tape, if you leave it like that all the dust and air will jet out of the small hole and the balloon will eventually deflate, if you stamp on the balloon while there is still a significant volume of air in it the balloon will pop and send dust everywhere, like an explosion. The same sort of thing can be achieved using water if you don't have dust and don't mind getting wet.

I hope none of this sounds patronising, I'm just trying to explain it the best I can.




Only way IMO that it could have happened because a sagging floor truss still weighs the same as it did at start (so no added load just from sagging).


I think the extra load comes from the intense energy provided by the momentum of the upper collapsing section. Under normal conditions the floors below can bear the weight of the floors above because the forces are pretty static, when the upper sections collapsed on to the lower sections the force they had to bear was much greater because of the extra energy provided by the momentum. It's kid of like if you rest a weight on the palm of your hand you can hold your hand pretty steady, but if you drop the weight on to the palm of your hand (even from a short distance) your hand will momentarily drop because of the momentum of the weight, an object in motion has greater energy than an object at rest, and since in a closed system energy is always conserved, that energy must go somewhere. While you can raise your hand back into position, that takes extra energy to apply a greater force than gravity in the opposite direction, energy that a building does not have. While beams and trusses do have a certain amount of elasticity, giving the building the energy to stabilize itself and restore it's natural form under relatively small loads like wind, the energy provided by the momentum of the collapsing section is far greater than the tensile strength of the supporting material. The process of the support material breaking would actually absorb some of that energy, however with each floor the total mass of the collapsing section would increase and thus so would the total energy.

(continued)...



posted on Aug, 21 2007 @ 07:39 PM
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reply to post by Griff
 





If you want, I can look up how much the moments would increase without the core. I believe they would be on the order of 8 times more without checking. That alone might be enough to fail the exterior without even considering the loss of interior load strength.


I would appreciate it if you could do some sort of calculations, it would help us determine the magnitude of the forces involved.




The only conspiracy I'm alluding to is the cover-up of the failure (incompetence) to stop the terrorists from placing a few bombs in the building. Either that or the cover-up that the buildings were built shoddy. IMO it's the former.


I apologise for implying otherwise, on this thread most people are trying to prove that the government undertook some sort of covert op to plant explosives them selves, so I misinterpreted what you were trying to say.

I'd like to thank you for making the effort to back up your reasoning and helping to . the debate in a more rational direction. I know you might already understand most of what I've said in this post, so I hope you don't take offence to my attempt at simplifying it, I'm doing so to try and help people who might not understand what's going on grasp the processes involved. I might be wrong on some of my facts so please correct me on any mistakes I've made.

To summarise what I understand of the official explanation is, it's not that the floors below the damage could not cope with the upper loads at rest, it's that they could not cope with the extra energy provided by the upper section collapsing, and the upper section collapsed due to the damage caused to vital support structure by the force of the impact and the resulting fire. While the fire was not intense enough to melt the steel, steel does soften under intense heat, and while under normal circumstances with all the support structure intact the steel might not have softened enough to fail even with a fire of that intensity, the impact of the plane would have taken out a proportion of the core support structure at the site of impact, thus transferring the load and increasing the stress beyond the capacity that the remaining structure could handle when exposed to intense heat.

[edit on 21-8-2007 by himselfe]



posted on Aug, 21 2007 @ 08:12 PM
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Originally posted by himselfe
To summarise what I understand of the official explanation is, it's not that the floors below the damage could not cope with the upper loads at rest, it's that they could not cope with the extra energy provided by the upper section collapsing, and the upper section collapsed due to the damage caused to vital support structure by the force of the impact and the resulting fire. While the fire was not intense enough to melt the steel, steel does soften under intense heat, and while under normal circumstances with all the support structure intact the steel might not have softened enough to fail even with a fire of that intensity, the impact of the plane would have taken out a proportion of the core support structure at the site of impact, thus transferring the load and increasing the stress beyond the capacity that the remaining structure could handle when exposed to intense heat.


What you fail to understand, is how fast the WTC collapsed. There is no possible way the weight of the upper section, and the "extra energy" from the upper section falling, could fall through the rest of the building WITH ZERO RESISTANCE. The building was so strong, that all of the people who understand physics and reality are dumbfounded by the fact that the rest of the building did not slow down the upper section's collapse.

The upper section of building should have slowed down drastically while collapsing downward through the undamaged sections of the building.

We know why the upper section collapsed, we DON'T know why the upper section fell through the rest of the undamaged building without slowing down AT ALL. The only plausible explanation for the upper section to fall so quickly through the undamaged part of the building is if the "undamaged" part of the building was actually being "damaged" by explosives before the upper section could crash into it.

Nobody, not even NIST or FEMA or ASCE or whoever, has given us a REAL reason why the upper section fell with no resistance.

[edit on 21-8-2007 by 11 11]



posted on Aug, 21 2007 @ 09:19 PM
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Just to clarify a few things to people who don't understand where this extra energy comes from:

An object at rest requires energy from an external force to attain velocity, here on earth all objects are subject to the force of gravity, including us standing on the ground. While objects are normally at rest (relatively speaking) due to resistance provided by other objects such as earth for us and structural support for buildings and their contents, when that resistance falls bellow equilibrium with gravity, such as when support structures fail, the object accelerates by acquiring the extra energy provided by gravity, and due to momentum the object's potential energy is converted into kinetic energy. The the object only stops accelerating when an opposite force, such as friction, achieves equilibrium with gravity, the only way the object can slow down is by an opposite force increasing beyond equilibrium with gravity, and the only way the opposite force can stop an object is by achieving equilibrium with the total kinetic energy of the object. This works by the opposite force absorbing the object's energy and/or acquiring sufficient energy to oppose the object's momentum. In the case of friction, energy is lost through radiation as each object's kinetic energy is converted into heat. That is at least roughly how it works.



posted on Aug, 21 2007 @ 09:46 PM
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reply to post by 11 11
 





What you fail to understand, is how fast the WTC collapsed. There is no possible way the weight of the upper section, and the "extra energy" from the upper section falling, could fall through the rest of the building WITH ZERO RESISTANCE.


Nobody other than you and other conspiracy theorists is claiming that the upper section fell through the rest of the building with zero resistance. Even if the rest of the building wasn't there the upper section would not have fallen with zero resistance due to friction from air.




The building was so strong, that all of the people who understand physics and reality are dumbfounded by the fact that the rest of the building did not slow down the upper section's collapse.


Nobody with a competent understanding of physics disputes that the rest of the building absorbed energy from the collapsing section, however as I have explained in a previous post, as it reached each floor the collapsing section also gained energy from the extra mass. Finding out to what degree each action affected the collapsing section's velocity requires knowing the quantities of the various variables involved.

When a snowball rolls down a snow laden hill, does it slow down or speed up?



The upper section of building should have slowed down drastically while collapsing downward through the undamaged sections of the building.


Can you prove this?




The only plausible explanation for the upper section to fall so quickly through the undamaged part of the building is if the "undamaged" part of the building was actually being "damaged" by explosives before the upper section could crash into it.


Once again, can you back your assertions up with proof/evidence?




Nobody, not even NIST or FEMA or ASCE or whoever, has given us a REAL reason why the upper section fell with no resistance.


That's because it didn't. Since you are the one asserting that it did fall with zero resistance perhaps you can explain to us how?

[edit on 21-8-2007 by himselfe]



posted on Aug, 21 2007 @ 09:50 PM
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Originally posted by IgnoranceIsntBlisss

Negative. Those "dark bands" are the mechanical (AC unit) floors. Instead of there being windows they were some sort of ventilation panels, that I still haven't seen any high resolutio images of to better understand what those window replacements were.

Um, so do you WANT! for it to have been explosives used?


So uh, if those dark bands are ventilation panels, wouldnt it make sense that all those floors falling down on each other would produce enough force to blow debris out of them?



posted on Aug, 22 2007 @ 08:05 AM
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Originally posted by himselfe
I think the extra load comes from the intense energy provided by the momentum of the upper collapsing section. Under normal conditions the floors below can bear the weight of the floors above because the forces are pretty static, when the upper sections collapsed on to the lower sections the force they had to bear was much greater because of the extra energy provided by the momentum.


I'm actually talking about the initial collapse. NIST says that the sagging floor trusses pulled the outer columns in. There was no momentum at this point.

BTW, I wasn't looking for a verbatum of the pancake theory. NIST has already thrown that out. But thanks anyway.



posted on Aug, 22 2007 @ 08:16 AM
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Originally posted by himselfe
To summarise what I understand of the official explanation is, it's not that the floors below the damage could not cope with the upper loads at rest, it's that they could not cope with the extra energy provided by the upper section collapsing, and the upper section collapsed due to the damage caused to vital support structure by the force of the impact and the resulting fire. While the fire was not intense enough to melt the steel, steel does soften under intense heat, and while under normal circumstances with all the support structure intact the steel might not have softened enough to fail even with a fire of that intensity, the impact of the plane would have taken out a proportion of the core support structure at the site of impact, thus transferring the load and increasing the stress beyond the capacity that the remaining structure could handle when exposed to intense heat.


Actually, you make more sense than NIST does. I can see partial failures and such. That's a given with the type of composite steel floor decking. It's the core and to a lesser degree the exterior that bothers me about the whole collapse. And I'll admit that I'm not a structural god so some of that is even over my ..

As far as calculations. I'll see what I can come up with. I do know that changing a beam's support (the floor) from attatched at both ends to a cantilever would increase the moment on the beam (and thus transferring the moment to the column) by a degree of 8. I'm going from memory but I looked it up not long ago. Plus, the added weight of the plane would increase both shear and moment on the members.

All I was trying to get at was that even if the core was taken out at the bottom we would still see the collapse at the impact zones from the outsides.



posted on Aug, 22 2007 @ 08:31 AM
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Originally posted by himselfe
To summarise what I understand of the official explanation is, it's not that the floors below the damage could not cope with the upper loads at rest, it's that they could not cope with the extra energy provided by the upper section collapsing, and the upper section collapsed due to the damage caused to vital support structure by the force of the impact and the resulting fire.


Not according to NIST, if you've read their report.

According to NIST, there was not significant heating to any support columns, as to cause softening and loss of yield strength. In reality, and in real fires in steel-framed structures (I can post links to a particular study completed in 2000, after ~20 years of research, from the University of Edinburgh), the deformations caused during fires are caused by additional internal stresses induced between members from thermal expansion.

According to NIST, the exact opposite occurred, and instead of deflections from expanding beams/trusses, NIST says that the trusses were heated to the point of softening, sagged, and that somehow this sagging created a force pulling inwards on the exterior columns and causing them to buckle inward. Apparently, when a truss sags, it also becomes heavier? I don't understand the logic, and the only thing that really changes is the angle at which the force is applied to the columns. Anyone familiar with the construction of the towers would also realize that the connection to the perimeter columns would fail long before the perimeter columns themselves would be jerked out of place.

NIST also did no particular lab tests or models to verify the above, which is their major hypothesis. They submitted a replica composite floor from the WTC to fire for about two hours, for both fireproofed and unfireproofed steel, but couldn't get any failures whatsoever, let alone anything resembling their hypothesis.



While the fire was not intense enough to melt the steel, steel does soften under intense heat


Again, this is a misconception. Steel warps in framed structures during fires, because it tries to expand in place and this creates all sorts of additional stress between structural members. The steel has to be uniformly heated to much too high of a temperature to lose significant yield strength, especially in a redundant structure.

Here's a PDF of the University of Edinburgh study:

www.studyof911.com...


A couple of excerpts, remembering that it was released in 2000 independently:


Steel beams in standard fire tests reach a state of deflections and runaway well below temperatures achieved in real fires. In a composite steel frame structure these beams are designed to support the composite deck slab. It is therefore quite understandable that they are fire protected to avoid runaway failures. The fire at Broadgate showed that this didn't actually happen in a real structure. Subsequently, six full-scale fire tests on a real composite frame structure at Cardington showed that despite large deflections of structural members affected by fire, runaway type failures did not occur in real frame structures when subjected to realistic fires in a variety of compartments.

This project was the first major effort to understand this behaviour using computational models of the Cardington fire tests. A full explanation of the mechanics that are responsible for the robust behaviour of unprotected composite frames in fire has been achieved and will be presented in detail in this report. Reaching this new understanding has been a laborious process, and numerous blind alleys had to be investigated along the way, however obvious the answer may now seem to the researchers involved in this project. It is possible that the conclusions will not seem obvious to others who have not been directly involved, however considerable effort has gone in to presenting the results of the project to provide as much detail as possible. Approximately 40 supplementary reports and over 10 technical papers have been written and appear as an appendix to this report. This amount of work has ensured that the conclusions presented have been verified by a number of independent approaches. Mutually reinforcing arguments were developed from the results of different computational models, application of fundamental mechanics and the analysis of test data. It is therefore with a great deal of confidence that these findings have been presented for close scrutiny by the profession. Once this new understanding of structural behaviour in fire is widely disseminated, discussed and understood, the way will be clear for completing all the other tasks which are necessary for full exploitation of the knowledge gained. This will lead to safer, more economic and rational design of steel frame structures for fire resistance.


Also, specific to the mechanism by which steel "fails" (note: the definition of "fail" is NOT catastrophic, runaway failure in these structures):



The question may now be asked, what about the large deflections seen in real structures? Are those not a clear sign that ‘runaway’ was occuring? Figure 3.36 clearly shows that for temperatures below 300 °C, the deflections for the restrained beam are much larger than that for the simply supported beam, however they have nothing to do with ‘runaway’. These deflections are caused entirely by the increased length of the beam through thermal expansion and are not a sign of loss of ‘strength’ or ‘stiffness’ in the beam until much later. In fact approximately 90% of the defelection at 500°C and 75% at 600°C is explained by thermal expansion alone. Most of the rest is explained by increased strains due to reduced modulus of elasticity. However the behaviour remains stable until about 700°C when the first signs of runaway begin to appear.


That paragraph is from page 41 of the PDF, 34 of the report itself.


The dynamic loading of the building involves steel impact loading. No one has considered it. Not even NIST. It's a severely under-studied phenomena.



posted on Aug, 22 2007 @ 11:20 AM
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reply to post by Griff
 





I'm actually talking about the initial collapse. NIST says that the sagging floor trusses pulled the outer columns in. There was no momentum at this point.


Sorry I misinterpreted that part of your post thinking you were referring to the lower undamaged parts of the building. The mechanism I was trying to explain was how the upper collapsing section could load the lower undamaged sections beyond their capacity, as the structural integrity of the lower undamaged sections is not important up until that point. I don't think we are arguing the same points because I was taking it as a given that the upper section would initiate some sort of collapse.




BTW, I wasn't looking for a verbatum of the pancake theory. NIST has already thrown that out. But thanks anyway.


I made no assertions about a pancake collapse theory, or even to what degree the above section came into contact with the lower section. I simply explained how the above section could provide load beyond the capacity of the lower section and how, as the collapse sequence progresses, each floor would contribute to the energies involved. As the collapse sequence reaches each floor, parts of the structure on that floor does break, and thus each floor would absorb some of the energy (regardless of whether or not the upper section makes contact with that floor or not). And as each floor joins the collapse sequence, each floor's mass is added to the momentum of the collapsing section and thus increasing it's total kinetic energy, regardless of the degree to which that floor interacts with the upper section. Do you disagree with this?

In fact, given that that the pancake theory is not in effect, each floor would absorb far less energy as the sequence progressed than it would in a pancake collapse, since full contact collision absorbs far more energy.




All I was trying to get at was that even if the core was taken out at the bottom we would still see the collapse at the impact zones from the outsides.


That part is not disputed.



posted on Aug, 22 2007 @ 12:05 PM
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reply to post by bsbray11
 






Originally posted by himselfe
To summarise what I understand of the official explanation is, it's not that the floors below the damage could not cope with the upper loads at rest, it's that they could not cope with the extra energy provided by the upper section collapsing, and the upper section collapsed due to the damage caused to vital support structure by the force of the impact and the resulting fire.


Not according to NIST, if you've read their report.

According to NIST, there was not significant heating to any support columns, as to cause softening and loss of yield strength.


Citation


Based on this comprehensive investigation, NIST concluded that the WTC towers collapsed because: (1) the impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns, and widely dispersed jet fuel over multiple floors; and (2) the subsequent unusually large jet-fuel ignited multi-floor fires (which reached temperatures as high as 1,000 degrees Celsius) significantly weakened the floors and columns with dislodged fireproofing to the point where floors sagged and pulled inward on the perimeter columns. This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1 and the east face of WTC 2, initiating the collapse of each of the towers.





In reality, and in real fires in steel-framed structures (I can post links to a particular study completed in 2000, after ~20 years of research, from the University of Edinburgh), the deformations caused during fires are caused by additional internal stresses induced between members from thermal expansion.


Comparing what happened in the two towers to any normal building fire is ridiculous. That study fails to take into account all the variables in effect in the two towers.




According to NIST, the exact opposite occurred, and instead of deflections from expanding beams/trusses, NIST says that the trusses were heated to the point of softening, sagged, and that somehow this sagging created a force pulling inwards on the exterior columns and causing them to buckle inward. Apparently, when a truss sags, it also becomes heavier?


No, when a truss sags it provides torque and loses it's ability to distribute loads.




Anyone familiar with the construction of the towers would also realize that the connection to the perimeter columns would fail long before the perimeter columns themselves would be jerked out of place.

NIST also did no particular lab tests or models to verify the above, which is their major hypothesis. They submitted a replica composite floor from the WTC to fire for about two hours, for both fireproofed and unfireproofed steel, but couldn't get any failures whatsoever, let alone anything resembling their hypothesis.


Citation


NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel “trusses” integrated with a concrete slab; see diagram below). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.


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