9-11 Conspiracy Theories thread

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Why did WTC 7 collapse?

 

I believe the official line is something about impacts from debris from the destruction of the other towers.  Surprising, considering those towers fell cleaner than most controlled demolitions hope to achieve.  That and I would assume some fires, which you have to think weren't very engulfing.

 

Oh, and Giuliani's central control/police/whatever it was center that for some reason he knew better than to report to that day, along with Enron and WorldCom files which are now forever lost...  Hmmmmmmmmm....

 

 

WTC 7 was certainly brought down in a very skilled demolition job but this one was a carefully controlled implosion. Whereas WTC 1 and 2 combined both an implosive and an explosive collapse. Implosive since the central core of the building was totally pulverised and not a single core column remained standing, but explosive to since a huge explosion erupted from the floors were the planes had crashed, and it was huge because curtain walls were blasted hundreds of feet away. So while an implosion took care of the central core and dragged down floors from within, explosions blasted out every curtain walls in a symmetrical fashion.

 

You can see it in the footage, while the top part of WTC 1 (and the same happened with WTC 2) was collapsing into floors below, several floors down curtain walls were exploding outwards and this happened for the duration of the collapse. This needed to happen otherwise the central core would be totally obliterated while large portions of the curtain walls, and parts of floors attached to them, would still be standing hundreds of feet high. Huge portions of curtain walls, weighing hundreds if not thousands of tonnes, were blasted hundreds of feet away.

 

I can accept that maybe, just maybe, the twin towers did just collapse from structural failure caused by a plane crash and extensive fires. But what I can't accept is how that resulted in so much concrete being pulverised, curtain walls being blasted outwards as if they were large projectiles, and the lack of a mountain of debris twenty or so stories high from the collapsed floors (and core structure) as the pancake theory alleges. Where did the remains of the twin towers go? In the basements, that huge multi-story underground complex? But if the basements collapsed so would the streets nearby and what was left of the twin towers.

 

Another thing I can't accept is how a hot pyroclastic flow was generated from a pancake collapse, a flow so hot it burnt the outsides of cars and gave hundreds of people third degree burns and respiratory burns. How was the dust heated to hundreds of degrees centigrade in such a short period of time?

[dazza262 133]

Don't know how credible this is, but it's quite compelling.

 

http://neonnettle.com/news/211-ex-cia-pilot-gives-sworn-testimony-that-no-planes-hit-the-twin-towers

 

Just putting this out there, but one thing that's always bothered me about the Pentagon attack is the lack of any aircraft wreckage in the aftermath. Anyone want to clear that one up for me?

 

[Meg 368]

Don't know how credible this is, but it's quite compelling.

 

http://neonnettle.com/news/211-ex-cia-pilot-gives-sworn-testimony-that-no-planes-hit-the-twin-towers

 

Just putting this out there, but one thing that's always bothered me about the Pentagon attack is the lack of any aircraft wreckage in the aftermath. Anyone want to clear that one up for me?

 

 

 

Don't know who wrote that article but I don't find it compelling at all because there is amateur footage of a plane crashing into a tower.

 

As for the Pentagon plane, there was aircraft wreckage.   The rescue crews dug through the rubble and announced when they reached the plane.   A lot of local kids on a field trip were on that plane and were found burned in their seats.

 

I was living and working in Arlington, VA at the time and knew the Pentagon had been hit long before it was announced on any news program.   (I don't know how long it was but it seemed to take forever.  I was wondering what else was going on that they weren't telling us.)

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Don't know how credible this is, but it's quite compelling.

 

http://neonnettle.com/news/211-ex-cia-pilot-gives-sworn-testimony-that-no-planes-hit-the-twin-towers

 

Just putting this out there, but one thing that's always bothered me about the Pentagon attack is the lack of any aircraft wreckage in the aftermath. Anyone want to clear that one up for me?

 

 

 

Don't know who wrote that article but I don't find it compelling at all because there is amateur footage of a plane crashing into a tower.

 

As for the Pentagon plane, there was aircraft wreckage.   The rescue crews dug through the rubble and announced when they reached the plane.   A lot of local kids on a field trip were on that plane and were found burned in their seats.

 

I was living and working in Arlington, VA at the time and knew the Pentagon had been hit long before it was announced on any news program.   (I don't know how long it was but it seemed to take forever.  I was wondering what else was going on that they weren't telling us.)

 

 

Yep, planes did crash into the twin towers. But it highly unlikely that a Boeing 747 crashed into the Pentagon. The wings did not impact ring E and there are no substantial debris of the wings around the lawn.

 

 

Just look at that lawn it is almost pristine. And again no sign of the plane wings cracking in two the outer façade of ring E. Also no sign of plane debris or debris which rebounded off of the outer wall.

 

Next if the plane had struck horizontally that would be impossible since the plane would have to make contact with the ground, but there is not enough space to actually land the plane and even if did land and impact it would be pointed upwards. Also if the plane struck the Pentagon at a downwards angle, then it would take highly precise flying to impact the building's outer wall but not smash into the lawn or impact inner rings first. Remember these hijacker's only flight experience was flying small fixed-wing aircraft, not only did they figure out how to fly the plane -- which allegedly struck the Pentagon -- but they performed flight manoeuvres even highly trained pilots would find difficult to execute.

 

And, as shown in this picture, the plane did not make contact with the ground as there are no tyre marks or any indication whatsoever that any part of the plane made contact with the lawn. Given there are no signs of the wings striking this building, very little plane debris and an almost unblemished lawn. Some kind of missile must have struck the building. A missile would be far more precise than a crashing airplane - whether civilian or military -- ever could be. Cruise missiles can strike a target the size of a garage and still precisely hit after travelling hundreds of miles, cruise missiles can also carry a warhead packed with one ton of high explosives...

[Meg 368]

So . . . my co-workers who saw a plane go down and a fireball go up were all hallucinating it?

[elavery 1,013]

This thread is pathetic. No plane crashed into the pentagon? What the hell did all those eye-witnesses see then? Or are they in on it too? Perhaps the all the passengers on the plane were in on the conspiracy too and are in fact living on Diego Garcia along with the MH 370 passengers?

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So . . . my co-workers who saw a plane go down and a fireball go up were all hallucinating it?

 

Some kind of plane, or missile, hit the Pentagon. But it must have been a small plane due to the lack of debris. The only live footage of the Pentagon attack was the one released by the Pentagon itself a few years later. As far as I know there are no other videos out there showing the moment of impact from a different angle. There is only this video.

 

https://www.youtube.com/watch?v=vwzT0QnwtTE

 

 

In one of the frames you can just see a plane to the very centre right of the frame, it is seen pointing slightly downwards towards the lawn. From this angle a part of it must have struck the lawn and left behind numerous debris. But see the picture in my post above, a near pristine lawn and very few debris.

 

Were your co-workers actually working in the Pentagon?

[APSMS 1,893]

This thread is pathetic. No plane crashed into the pentagon? What the hell did all those eye-witnesses see then? Or are they in on it too? Perhaps the all the passengers on the plane were in on the conspiracy too and are in fact living on Diego Garcia along with the MH 370 passengers?

That would be a nice thought. If it's really a government conspiracy, then they're all dead like they're supposed to be, regardless of who's responsible.

 

Also, that's a small hole for a 125ft wingspan, even if canted at an angle for impact.

[Meg 368]

 

So . . . my co-workers who saw a plane go down and a fireball go up were all hallucinating it?

 

Some kind of plane, or missile, hit the Pentagon. But it must have been a small plane due to the lack of debris. The only live footage of the Pentagon attack was the one released by the Pentagon itself a few years later. As far as I know there are no other videos out there showing the moment of impact from a different angle. There is only this video.

 

https://www.youtube.com/watch?v=vwzT0QnwtTE

 

 

In one of the frames you can just see a plane to the very centre right of the frame, it is seen pointing slightly downwards towards the lawn. From this angle a part of it must have struck the lawn and left behind numerous debris. But see the picture in my post above, a near pristine lawn and very few debris.

 

Were your co-workers actually working in the Pentagon?

 

 

No, we were in a building along the flight path.

 

I don't understand your point about the debris field.   The Pentagon is huge.   A jet that size could easily fit into it.  Why would there have to be debris on the ground outside?

 

There is a cabbie who saw the plane clip a streetlight pole.   He swerved to keep the pole from hitting his cab.   There are rescue workers who found the burnt bodies in their seats.  There were a lot of local stories that apparently didn't make it into the nation-wide news.

 

[elavery 1,013]

I love how most 9/11 truthers also seem to be experts on engineering, explosions, and aviation.

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So . . . my co-workers who saw a plane go down and a fireball go up were all hallucinating it?

 

Some kind of plane, or missile, hit the Pentagon. But it must have been a small plane due to the lack of debris. The only live footage of the Pentagon attack was the one released by the Pentagon itself a few years later. As far as I know there are no other videos out there showing the moment of impact from a different angle. There is only this video.

 

https://www.youtube.com/watch?v=vwzT0QnwtTE

 

 

In one of the frames you can just see a plane to the very centre right of the frame, it is seen pointing slightly downwards towards the lawn. From this angle a part of it must have struck the lawn and left behind numerous debris. But see the picture in my post above, a near pristine lawn and very few debris.

 

Were your co-workers actually working in the Pentagon?

 

 

No, we were in a building along the flight path.

 

I don't understand your point about the debris field.   The Pentagon is huge.   A jet that size could easily fit into it.  Why would there have to be debris on the ground outside?

 

There is a cabbie who saw the plane clip a streetlight pole.   He swerved to keep the pole from hitting his cab.   There are rescue workers who found the burnt bodies in their seats.  There were a lot of local stories that apparently didn't make it into the nation-wide news.

 

 

 

Witnesses who saw this plane all said it flew more or less horizontally into the building. If all of the plane hit the Pentagon where is the imprint made by the wings? That question has always foxed me. Did the wings fold inwards as the cockpit crashed into E ring, while in the process, the rest of the plane had not yet been engulfed by the building.

 

It's just puzzling that is all.

[47ply 1,100]

I don't clam to know what happened I saw planes smash into the building while watching the Today show.  I have been a Mechanic and welder my whole life and there is now way possible for office furniture and #2 kerosene (jet fuel) to burn hot enough in one hour or so it took for the towers to fall.

 

My theory is that the planes were full of explosives and that the government was told by binladin it was going to happen but did believe he could pull it off and still cant to this day. The cover up is not being ready

[Meg 368]

 

 

Witnesses who saw this plane all said it flew more or less horizontally into the building. If all of the plane hit the Pentagon where is the imprint made by the wings? That question has always foxed me. Did the wings fold inwards as the cockpit crashed into E ring, while in the process, the rest of the plane had not yet been engulfed by the building.

 

It's just puzzling that is all.

 

 

 

The wingspan of a 757 is only 124 feet.   The section of the Pentagon that collapsed is larger than that.

 

What's so puzzling?

[elavery 1,013]

I guess the absence of a hole in the pentagon that is the perfect outline of a plane is what puzzles the conspiracy nuts.

[Meg 368]

I guess the absence of a hole in the pentagon that is the perfect outline of a plane is what puzzles the conspiracy nuts.

 

 

I think people underestimate the size of the building.

 

One side is over 920 feet (280 meters)in length.   The building itself covers 29 acres.   Plenty of room to fit an airplane.

 

[CapTon 592]

I'm just glad that there's no one in this thread saying that 9/11 never happened.

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I guess the absence of a hole in the pentagon that is the perfect outline of a plane is what puzzles the conspiracy nuts.

 

 

I think people underestimate the size of the building.

 

One side is over 920 feet (280 meters)in length.   The building itself covers 29 acres.   Plenty of room to fit an airplane.

 

 

 

It is indeed a huge building and to be honest I spent more of my time investigating the twin towers and WTC 7. But after reading witness testimony I now definitely believe a plane hit the building. I think the collapsed portion of the Pentagon is at most the extent of this plane's impact profile, since it was travelling diagonally it impacted a larger portion of the outer wall.

 

Given the dimensions of the collapse though it may have been a somewhat smaller plane than a Boeing 757.

 

[Duke87 1,070]

Alright, fair warning: the person making this post has a college degree in civil engineering and has studied this particular matter quite a bit. There's a lot here, let's get to work poking holes in all these nutty arguments, shall we?

 

Fire does not cause complete structural failure in steel-framed buildings.

 

Normally, no, it does not. Do you know why not? Because structural steel in buildings is covered with fireproofing material that protects it from the heat if a fire breaks out. The World Trade Center was no exception, its steel was covered in fireproofing material. Problem with that, though, is that fireproofing material is designed to be fireproof, not explosionproof. The shrapnel resulting from a forceful explosion (such as, say, a commercial airliner hitting the building) can easily dislodge chunks of this fireproofing material from the beams, leaving them exposed and susceptible to being weakened by fire.

 

As a comparison, look at stories of tanker truck fires erupting on highway overpasses. In these situations it is quite typical for the blaze to leave the steel structure of the overpass (which is NOT covered in fireproofing material) permanently deformed and unfit to drive over, requiring it to be replaced.

 

 

Other gems of implausibility include a collapse where both buildings fell with an acceleration various close to a large fraction of g (=9.81m/s). If it was a pancake collapse, where the floors collapsed on top of each other and then the core columns followed afterwards, then the velocity of every coalesced floor -- and those above it -- increased in speed.

Basic conservation of momentum equations (assuming the coefficient of restitution = 1, i.e. perfect conservation of mechanical energy) tells you that when a moving object strikes a stationary object, and the two coalesce (behave as one joined object in motion) the energy in this system before and after remains the same. But the speed of the two coalesced objects is less than the speed of the first moving object.

So if the steel supports kept simultaneously failing on floors from the collapse above, the collapse would have slowed down even more so given that mechanical energy would be lost due to friction, the floors intertia and the normal reaction exerted upwards. Nevertheless, the collapse of the twin towers was a big screw you to Newtonian mechanics and the rules of momentum if you believe the official explanation for the collapse. It can only make sense if a floor -- below the collapsing one above -- itself collapsed BEFORE the one above impacted. This would account for the lack of resistance, building redundancy and rapid collapse. How else can you explain a collapse where the buildings fell down with an acceleration of a rather large fraction of g?

 

There is a glaring flaw with this argument: when you talk about conservation of momentum between two colliding objects, you assume that there are no external forces acting on the system and it's simply one object in an inertial state striking another object in an inertial state. This is not the case in a collapsing building, since you have this force called gravity pulling down on the building as it falls, causing it to continually accelerate so long as the force of gravity on the falling floors exceeds the supporting force of the floors below them.

 

All the fact that the collapse of the building accelerated tells you is that when the top fell, it fell with far more force than the structure underneath it could withstand. Which, given that one floor of building isn't designed to withstand the force of 20+ stories worth of weight (only the columns are designed for that) is to be expected!

 

 

It was also a horrible blemish to the engineers and architects who built the twin towers. Yeah those aeroplanes made a big dent, yes the plane wings cut through a quarter of the outer columns (on several floors) before disintegrating, and yes the the passenger part cut through a tiny part of several out of 50 core columns. But both buildings were a grid-like mesh of steel girders and columns, a frame which could flex and thus absorb impacts (wind and sadly hijacked planes), and such a design gives a LOT of redundancy.

Redundancy is that magic word of engineers which means a structure has several or more ways of supporting itself if parts of the structure are damaged or destroyed. Heck, the architects designed the twin towers to withstand an impact from a Boeing 747, a plane whose weight and size is about the same as a Boeing 777. An impact at ANY level of the building. The twin towers should have remained standing. What should have happened was that the fires would have burnt all through the day and all through the night. They would not have spread further since every floor was hermetically sealed, thus every floor not damaged by the plane would have been devoid of fire.

And even in the worse case scenario, had the fires spread downwards and burnt every floor. The core structure of the twin towers would still be standing; the steel-frame would be largely intact and most of the concrete would still be in place. You would be left with two horrible blackened eyesores of buildings but they would be standing. That is what always happens after a major skyscraper fire, you see it in the news all the time.

 

Okay, first of all, the Boeing 747 was not in production (1968 in factory, flying in 1970) until after construction on the World Trade Center had already broken ground (1966). The twin towers were designed to withstand the impact of a Boeing 707, which is a substantially smaller plane.

 

Secondly, in this regard the buildings performed as designed. Both buildings were hit by 757s and neither collapsed from the impact. What the engineering team never considered was what effect the ensuing fires from the impacts might have (which is ultimately what actually brought the buildings down). In an era before computer modeling, this would not have been possible. It should also be noted that they assumed a plane hitting the building would likely be near landing and relatively low on fuel, not fresh from takeoff and near fully gassed up.

 

Yes, the structure had plenty of redundancy. But even the most redundant structure in the world will collapse if you knock enough of it out. The impacts themselves took a LOT of columns out, and the fires afterward gradually made matters worse... interestingly though (at least in the case of the south tower), it was fires weakening the floor trusses and thus leaving the columns unbraced which led to the collapse, not weakening of the columns themselves. There is a rather fascinating Nova episode on this subject:

https://www.youtube.com/watch?v=KPqxJpykW00

 

The twin towers were steel framed buildings supported by both the curtain walls (outer steel columns) and core columns in the centre. The core columns were all braced together with horizontal steel beams that connected to the floor struts which connected to the outer columns. The very centre formed a grid-like lattice of columns and steel beams. So even when the airplane hit only a small fraction of core columns, which were cut in two from the central part of the plane. While the wings completely disintegrated the moment they hit the curtain walls.

 

So if a large part of the curtain wall was missing on one side of the floor, the floor struts would still have support from the core columns. The floor struts had considerable support from both the core columns and the curtain walls, this was a rather hollow steel-framed design and gave further structural integrity and redundancy. Curtain walls were never the key support to the twin towers, if they were they would buckle and collapse from high winds while carrying the weight of floors above.

 

Even by your argument, if all the floors did come down the core columns and the central lattice structure would still be standing. Think of the twin towers as a structure (curtain walls and floors) built within a structure (core columns and horizontal beams).

 

 

"Curtain walls" do not support anything except themselves - a "curtain wall" describes a means of supporting the facade of a building, by hanging the outer wall of each story from the floor above it. The World Trade Center did not have a curtain wall, what it had was structural columns integrated with (and defining) the facade.

 

Semantics aside, the floor trusses in the twin towers were only supported at two points - the outer wall and the edge of the core. Remove the outer wall and naturally the floor trusses connected to it go crash since they weren't designed to hang from just one end. And yes, the outer wall was key to the building's support. The reason wind did not make it buckle was because those floor trusses braced it. Hence, also, why knocking out floor trusses in turn can cause columns in the outer wall to fail.

 

It would in theory be possible for the core of the twin towers to have remained standing without the rest of the building around it (this is true of most buildings with a "core"), but that would require somehow for only the outer section of the building to fall and for those destructive forces to not act on the core. Given the mechanism of collapse for each tower (failure of the core for the north, uneven failure of the outer wall causing the top to lean over for the south), the cores were not going to be left unaffected.

 

Consider the Windsor Tower in Madrid. In 2005 the entire building caught fire, a bright ferocious fire full of bright yellows.

 

Though gutted it survived with nearly all of the steel structure intact and most of the concrete intact to, there were a couple of minor collapses but the core structure was still standing.

 

That is clearly a concrete frame building, which the twin towers were not. Also, as I said before... no explosion/impact would mean any steel members would retain their fireproofing, unlike with the twin towers. That stuff is there for a reason, it works!

 

 

 

Why did WTC 7 collapse?

 

I believe the official line is something about impacts from debris from the destruction of the other towers.  Surprising, considering those towers fell cleaner than most controlled demolitions hope to achieve.  That and I would assume some fires, which you have to think weren't very engulfing.

 

7 WTC is not as clean cut and obvious an explanation as 1 and 2 WTC. But there is a lengthy report on it. It ultimately comes back to the fires. There were fires burning throughout the building (more engulfing than you assert). To the point of fireproofing addressed above, it should be noted that most of the structure was not compromised by the fires. That said, unfortunately a key piece of it was. Whether the fireproofing in this area was damaged or deficient, who knows.

 

It is entirely possible that it was neither but due to the length of the blaze (7 WTC burned out of control for seven hours before collapsing), that at some point even the best thermal insulating material will allow enough heat through to weaken the steel it protects. Fireproofing is very effective at preventing transmission of heat to the steel underneath it by radiation (which is generally the means by which fire heats things up), but it is only so effective at preventing conduction. If the air outside the beam heats up to a temperature that will weaken the steel, it is only a matter of time before thermal conduction causes the steel to heat up to that temperature as well.

Normally this doesn't happen either because the fire naturally burns out before it has a chance to, or because sprinkler systems prevent it from happening by putting the fires out or at least introducing a lot of water, which is a wonderful heat sink. But the sprinkler systems in 7 WTC were poorly designed and failed to work properly.

 

 

Just look at that lawn it is almost pristine. And again no sign of the plane wings cracking in two the outer façade of ring E. Also no sign of plane debris or debris which rebounded off of the outer wall.

But it highly unlikely that a Boeing 747 crashed into the Pentagon. The wings did not impact ring E and there are no substantial debris of the wings around the lawn.

 

Well, you're right about this: a 747 did not hit the Pentagon. It was a 757. Also, no debris, you say?

 

There's plenty of debris, just no big pieces because, well, a plane crashing kinda breaks it up into little bits.

 

Witnesses who saw this plane all said it flew more or less horizontally into the building. If all of the plane hit the Pentagon where is the imprint made by the wings?

 

Right here:

 

Closer up:

 

Didn't penetrate very deep, but then the outer wall of The Pentagon I am sure was designed to be somewhat robust against attack, it being a military facility and all.

 

This image is also a bit informative:

 

The collapse was only in the area where the fuselage hit, which is where the most damage was done. The plane being bigger than the collapse is not a flaw in the story, it just means the wings and engines didn't do enough damage to cause collapse.

.

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Why did WTC 7 collapse?

 

I believe the official line is something about impacts from debris from the destruction of the other towers.  Surprising, considering those towers fell cleaner than most controlled demolitions hope to achieve.  That and I would assume some fires, which you have to think weren't very engulfing.

 

7 WTC is not as clean cut and obvious an explanation as 1 and 2 WTC. But there is a lengthy report on it. It ultimately comes back to the fires. There were fires burning throughout the building (more engulfing than you assert). To the point of fireproofing addressed above, it should be noted that most of the structure was not compromised by the fires. That said, unfortunately a key piece of it was. Whether the fireproofing in this area was damaged or deficient, who knows.

 

It is entirely possible that it was neither but due to the length of the blaze (7 WTC burned out of control for seven hours before collapsing), that at some point even the best thermal insulating material will allow enough heat through to weaken the steel it protects. Fireproofing is very effective at preventing transmission of heat to the steel underneath it by radiation (which is generally the means by which fire heats things up), but it is only so effective at preventing conduction. If the air outside the beam heats up to a temperature that will weaken the steel, it is only a matter of time before thermal conduction causes the steel to heat up to that temperature as well.

Normally this doesn't happen either because the fire naturally burns out before it has a chance to, or because sprinkler systems prevent it from happening by putting the fires out or at least introducing a lot of water, which is a wonderful heat sink. But the sprinkler systems in 7 WTC were poorly designed and failed to work properly.

 

Thanks a lot for the time taking to construct such a lengthy reply, it's been a couple of years since I studied any mechanics since I'm now studying pure mathematics. So my understanding of the basics is a bit flaky now. I do have a few questions, since you have a degree in civil engineering, that maybe you answer.

 

1. In the case of WTC 7, whose collapse was caused by fires weakening steel supports on certain floors, why should the collapse be so uniform?

 

2. Are there any other large steel-framed buildings which have been engulfed in fire and completely, and rapidly, collapsed?

 

 

Also, what do you make of the Architects & Engineers for 9/11 Truth?

 

 

Edit: I've been reading a few of the articles from engineers on the Architects & Engineers for 9/11 Truth ( http://www.ae911truth.org/en/home.html ), and it's stuff which I kind of half followed. There is one article that caught my eye about the momentum transfer analysis of the upper stories in WTC 1.

 

http://www.journalof911studies.com/articles/Journal_5_PTransferRoss.pdf

 

Given your background Duke87, I wonder what you make of this analysis?

[A Nonny Moose 8,262]

And if the fourth plane's passengers had been as complacent as the rest, the target was the Capitol complex in DC.  This was probably the real target.  What would the drones do if the queen bee was destroyed?

[LexusInfernus 908]

Why did WTC 7 collapse?

Because it was also on  fire. And most defintely struck by debris. You can check the photos yourself. 

[Danny50205 71]

4 words "the illuminati card Game"

[elavery 1,013]

The biggest problem with 9-11 truthers is the huge amount of evidence they ignore. You can cherry-pick evidence to prove almost anything. If this was all really conspiracy there is no way it could have been kept quiet. There would have been all sorts of people coming out of the woodwork, not just a few guys with foil helmets who live in their parents basement.

[Duke87 1,070]

In the case of WTC 7, whose collapse was caused by fires weakening steel supports on certain floors, why should the collapse be so uniform?

 

In order to cause a collapse to be "non-uniform", you would have to have a significant imbalance between compromised structure in one area and intact structure in other areas. The building was, in effect, compromised throughout. It is also difficult in a structure that is much taller than it is wide or long to create a meaningful horizontal imbalance unless you do so near the base. Note how even in the case of the south tower, which fell when the east wall suddenly failed, the top of the building leaned towards the east but the overall tower still fell straight down. This is because when you work on this sort of scale, gravity is the overwhelmingly predominant force involved, so down is going to be the overwhelmingly predominant direction involved.

 

Meanwhile, if you take a building such as 7 WTC and compromise it at various points throughout the structure, you end up with the weakness being fairly evenly distributed. So a "uniform" collapse is what you'd expect.

 

Are there any other large steel-framed buildings which have been engulfed in fire and completely, and rapidly, collapsed?

 

Not that I know of, but on the other hand I can't think of any other instance where a tall building has burned in an analagous fashion, where the interior of a skyscraper which has already suffered some debris damage is burning throughout. There are certainly other stories out there of skyscrapers burning (like this one, this one, and this one), but these cases are all different. In the first story, it is just the facade of the building that burned, not the interior. In the second story it was only a few stories that burned, not the whole thing, and since the building was still under construction it wasn't fully loaded and there wasn't as much potential fuel around. In the third story, again, it was only a few stories that burned, and the building was noted in the incident report to have unusually good fireproofing.

 

So yes, the collapse of 7 WTC is unique, but so are the circumstances that led to it.

 

I've been reading a few of the articles from engineers on the Architects & Engineers for 9/11 Truth ( http://www.ae911truth.org/en/home.html ), and it's stuff which I kind of half followed. There is one article that caught my eye about the momentum transfer analysis of the upper stories in WTC 1.

 

http://www.journalof911studies.com/articles/Journal_5_PTransferRoss.pdf

 

Given your background Duke87, I wonder what you make of this analysis?

 

Three things which come to mind as flaws here:

1) The author is making the same mistake I pointed out previously by neglecting gravity and assuming it is merely the kinetic energy in the inertia of the collapsed floors acting on the floors below them. The columns in the building would already be loaded to some significant portion of their capacity supporting the weight of the building above them. The amount of additional force necessary to buckle them is therefore far less than if you had a column in a lab with no weight on it and wanted to make it buckle.

2) The author is assuming that the shockwave moving down ahead of the collapse is purely a dissipation of energy, and fails to account for the fact that it weakens the columns it affects, thus reducing the force required to buckle them.

3) The author is assuming that the columns are the only important structural members in the collapse, and neglects to consider that falling stories will place loads on the floor trusses far above what they can handle, thus causing them to fail, which in turn will cause the columns in the outer wall to fail by virtue of being suddenly unbraced even if those columns are not caused to fail directly. Indeed, there was likely some of this involved in the collapse - consider the fact that a few stories of the bottom of the core of each tower survived. This points to the pancaking below the impact zone involving the outer wall failing (perhaps due to sudden lack of bracing) before the core did.

[A Nonny Moose 8,262]

"Three people can keep a secret if two of them are dead"

-- Ben Franklin.