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World Trade Center on 9-11

2M views 4K replies 255 participants last post by  luchkovtim 
#1 ·
So people like Kon133 can post 9-11 pics to their heart's content instead of on the THE MEGA WTC Picture Thread.
 
#340 ·
Yeah, they were sloppy. I think if they indented the windows, it would have looked much better, also. They should have included the originally planned logo on the blank wall to distract from the poor facade.

At least the red brick adds some balance to the glassy area (It looks much better than that beige and grey building to the right)
 
#342 ·
I think that's the 98th floor on fire. If that is, we had at least 1,000 computers on that floor, not to mention tons of cubicles, a library where paper files were stored, among other combustable materials. All of it would have combusted, and started a massive conflagration.

Here's the floor plan for the 98th floor, you can see the cubicles (and their contents) that would have provided fuel.

 
#346 · (Edited)
I just hope it was quick and painless for them, but judging from the fire, I'm inclined to think it probably wasn't :eek:hno:

It would appear that most of the office contents that survived the initial impact were hurled across the floor from the force of the impact, and piled up on the southside of the tower. Those office contents, plane parts, among other things burned for the next hour and a half, and I think it's on the south face of the tower, where that stuff had been burning, where the collapse initiated.

The worst part is pictures and video of the fire on the south face of the North Tower are rare and hard to find. Especially the 104th floor fire in the SW corner, which probably spread upwards from the impact floors through shafts in the core, and then burned its way across those floors.

And for the record, the new Fiterman Hall is a turd compared the original 1959 Fiterman. So out of place.
 
#352 ·
Windows on the World, kudos for actually having an open mind and not just buying what others tell you to believe.
Its funny how as soon as you question the events of that day, in a realistic and unbiased way, you must be some sort of deranged nut. Just as quick as that.

An architecture forum is a good place to bring this up:
The North Tower was hit on the 92-98 floors (being generous, other reports 94-98).
The tower was 110 stories tall.
Therefore, 18 stories of building collapsed the entire rest of the building (92 floors). All the way down to the bottom.
The problem is, those 92 floors were undamaged, meaning they were fully ready for the weight of 18 stories.

So on 9/11, the weight of 18 stories totally destroyed the lower 92 floors in about 15-20 seconds.

And they say the 'crazy conspiracy theorists' are the ones who make things up
 
#354 ·
Ritazzo, This is just senior school level physics. The motion of bodies is governed by Newton's Laws of Motion and the third law states:

'Rate of change of momentum is proportional to the impressed force'.

That is not a particularly complicated idea. If you push a car along a level road, it will move very slowly at first but speed up as you push it until you would have to run to catch up with it. If someone else then tried to stop the car, by standing in front of it and holding their arms out, they might well find that they would be run over by the car as they would need superhuman strength to stop it in an arms length (depending on the size and weight of the car).

That is because, your pushing the car increases its momentum and, if you push it over a length of several metres, it will get so much momentum that your friend, trying to stop it, would have to run backwards while pushing the car for a similar distance.

That is basically what happened with the World Trade Center tower. The supporting structure failed at the point of the plane impact and the tower would have fallen by a distance of ten feet (one storey height) - not a great distance but it would build up so much momentum by the time it hit the floor beneath that the force required to stop it would be many times the weight those storeys imposed when intact.

It is just the same as the car analogy, momentum built up over a distance of ten feet would have to be resisted in a distance of some few inches. Ironically, it would be the rigidity of the steel structure of the tower that would be against it. A steel structure (even one hundreds of feet tall) can only give a few inches due to the natural 'give' in the steel. The uppermost storey beneath the impact zone would collapse and the mass of that storey would then add to that of the eighteen storeys above and so increase the load on the storey beneath - and so on until the tower collapsed completely. That is known as a progressive collapse.

It is probably true that the WTC was very vulnerable to progressive collapse. Although the external closely spaced columns and the core columns would have been very strong, the floors, which held the structure together were of relatively flimsy construction (six inches of concrete supported on lightweight steel trusses). The loss of the floors removed the restraint to the main columns meaning that they became destabilised.
 
#353 ·
^^ And it can be solved by just factoring in the energy gained when the 18 floors fell that massive height of just 1 floor, easily gaining enough energy to rip through the rest of the floors (which were made of thin trusses, sheet metal, and 4 inch bolts)
It was not a concrete block. It was a massive bundle of interconnected beams that aren't capable of holding so much extra energy.

Conspiracy theorists are known to edit out certain parts of quotes to fit their agenda, as well as lying (molten steel theory) so yes, they are making things up. They also take many other events out of context and make easily explained events turn into 'mysteries.' Don't believe everything the 911 truth movement wants you to believe, I learned that the hard way.

You can quyestion, but be sure to listen to the answers given to you. Truthers don't usually do that.
 
#355 ·
I appreciate your responses. Too often this conversation turns into someone getting angry for some reason, I never understood that.

While I am not an engineer, I feel as if we aren't giving the WTC structure enough credit. This is not a fragile structure, ready to collapse the moment an extra force is added to it.
This was a beast of a building, with 59 steel beams on each side, and large steel beams in the core. It is a disservice to the architect to assume the whole building would collapse because of some damage to the top of the structure.

I just have to add, about the car analogy. That car would pick up speed, yes. However, in the case of the WTC, as soon as the falling floors hit the undamaged floors, it would encounter resistance. Now, this resistance might not stop it at once..but we seem to be assuming this resistance adds up to..nothing? Take a moment to think about the resistance these floors would have encountered. This 18 story section is encountering a massive, undamaged beast.

Also, lets see if we can demolish a building in such a way. Go down 16% from top of building. Cut all exterior steel and core columns at this spot. We should see the top 16% fall one story downward, and then continue to demolish the rest of the structure. Lets ask some demolition experts about this.
 
#359 ·
Rizzato,
I too hate it when these conversations descend into angry ranting. That's why I am assuming that you are open to the idea that the WTC collapsed for no other reason than that it was hit by two hijacked planes and aren't wedded to the idea of a conspiracy.

I don't think that I am doing the 'architect' (actually the structural engineer, Leslie Robertson) any disservice by assuming that the tower collapsed due to the reasons I have described. Your use of the terms 'fragile' and 'extra force' shows that you have completely underestimated what we are talking about here.

Let me try another analogy. I am writing this on a laptop on a glass-topped table. The table isn't fragile and has no problem supporting the weight of not just one laptop but probably twenty or more. However, should I have a fit of pique and decide to drop my laptop from a height of ten feet onto the table, I wouldn't be surprised if the glass were to break.

That is because of g - the acceleration due to gravity which is 9.81m/sec/sec (or in imperial units 32 ft/sec/sec). That is a constant on the Earth's surface and is irrespective of the mass of the object falling.

Now, I understand that each tower of the WTC weighed about half a million tonnes, which means that 16% would be 80,000 tonnes. Imagine the impact loading that would cause on the structure underneath. (You can work this out using the equations of motion but it is safe to assume that it would be many times that which the structure was designed to take).

There are other factors at work here. This was not a simple case of one whole storey suddenly disappearing and the tower above dropping ten feet onto the columns of the storey below. In practice, the collapse would have been very uneven. One weakened column would fail leading to overloading of its neighbours that would also fail and so on. So the mass of the tower above would descend very unevenly onto the storey beneath, with a large part impacting onto the lightweight floor structure rather than the perimeter columns (just see the floor plan posted by Chapelo and you can see the small proportion of the total area occupied by the main vertical columns).

I fully agree with you that the collapsing tower would encounter resistance from the structure beneath but that resistance would be less than the force from the collapsing structure. That is not the same thing as saying that the resistance amounted to 'nothing'. Going back to the car analogy, if your friend tried to stop the car that you had been pushing for a while, he would succeed in slowing it down but it would push him off his feet. (However, where this analogy falls down is that the speed of the WTC collapse would be constantly increasing due to the effect of gravity - as if you kept on pushing the car even after your friend had been run over by it).

I am not a demolition expert but I don't see that there is anything that difficult in understanding how the collapse of the upper section would lead to the total collapse of the tower. The very large momentum of the upper storeys collapsing would easily collapse the first undamaged storey that they encountered, then the weight of that storey would be added to the mass of the collapsing structure, so that when the next storey down was encountered, the mass would be greater and the speed of collapse would be greater due to the acceleration due to gravity. So, the storey below would collapse even more quickly and so on until the whole tower was demolished. The speed of collapse would be very close to freefall.

(I suggest that you Google the Ronan Point disaster. This was a 20 plus storey tower block in London of which a whole corner fell down back in 1968 due to progressive collapse. The cause of this collapse was an old lady lighting the gas in her flat where there had been a gas leak. The resulting explosion was so weak that the lady survived but it resulted in a massive structural failure).
 
#356 · (Edited)
To be fair, Rizzato has a point. By undamaged beast i'm guessing you mean the acre in size floor and all of it's trusses which would in fact be a load bearing beast because they all worked together to cary the load. However, the moment the building started collapsing (before it's total collapse) the floors were collapsing unevenly, and some trusses were exposed to heavier loads than other trusses. Even the tower's total collapse occurred unevenly.



It would make sense that the tower could collapse in such a way. What i still don't understand to this day is the total disappearance of the core.
 
#360 ·
To be fair, Rizzato has a point. By undamaged beast i'm guessing you mean the acre in size floor and all of it's trusses which would in fact be a load bearing beast because they all worked together to cary the load. However, the moment the building started collapsing (before it's total collapse) the floors were collapsing unevenly, and some trusses were exposed to heavier loads than other trusses. Even the tower's total collapse occurred unevenly.

It would make sense that the tower could collapse in such a way. What i still don't understand to this day is the total disappearance of the core.
The floors were the weak points in the building. If you go back to earlier designs of skyscraper such as the ESB, the floors would have been heavy steel supported at regular intervals by a grid of columns over the whole plan area of the building.

By the 70s, firms favoured open plan offices with large unobstructed areas of floor space so the floors had to span a long distance from the outer columns to the central core. To save on weight, the floors were constructed from lightweight trusses topped with about 150mm (6") of concrete. These floors would be perfectly adequate to take the loading from people and furniture but not the impact loading from the collapse.

The failure of the floor trusses is probably the key to understanding the collapse of the whole building including the core. What each floor did was to ensure that the building kept its shape - much the same way that the diaphragms in an aircraft wing make it rigid. With the floors collapsing, the external and central columns would no longer be propped and would no longer be capable of supporting the weight of the storeys above.

Although the central core had a large number of very strong steel column sections what it probably lacked was sufficient diagonal bracing to enable it to stand up when the propping effects of the floors were removed. (Even with a well-braced core the shear slenderness of the structure would make it very unstable over the height of the WTC and it would probably have collapsed within seconds of the external structure collapsing). (If you see videos of Tower 1 collapsing, you can see some of the core columns projecting above the top of the smoke and dust cloud - but these would not have sufficient stability to remain in place).
 
#362 ·
Martin, thanks. It may surprise you that yes, I am ready to accept that 2 planes were the reason for the collapse. There is no reason to violently defend myself, and quite to the contrary; I strongly question my own ideas constantly.
Im not with the truthers; to call yourself a Truther would imply that you "know" the truth. This is just not the case with me, that would be far too arrogant.

This is an architecture forum, and I felt it would be a good place to bring up the structure of the WTC itself, and explain why I feel that the structure should have held up that day.

I have researched Verinage demolition, and yes, a top-down collapse is possible. The weight of the upper floors crushes the lower floors down to the ground. The problem is, I have not seen a steel-framed building brought down in such a way. The documents I have seen on Verinage report that this demolition is done on concrete buildings.

The upper 18 floors would have incurred a large amount of energy on the lower floors. Rather than crash through these undamaged floors without resistance, I feel that the energy would have been absorbed by the lower floors, since this was a steel building, and quite strong. The momentum of these 18 floors must have weakened when it encountered Floor 91. That leaves less momentum to act on Floor 90, Floor 89, and so on.
Cheers, and hope you don't find it offensive that I am looking for evidence that a steel-framed building will progressively collapse because of 16% of the floors being dropped onto the undamaged 84%.
 
#366 ·
Rizzato,

I think that you have hit the nail on the head with your understanding of how the collapse might have been prevented. Everything is down to energy.

The 18 floors of the WTC structure that collapsed contained a huge amount of potential energy that was accumulated as it was constructed thirty years prior to the collapse. All the energy expended by the cranes that lifted up the steel sections and hoppers of concrete over the course of many months would have been released as kinetic energy in a matter of seconds.

The only way that the steel structure could have arrested that collapse would have been by absorbing that energy in the bending and breaking of beams and columns as the structure fell. In effect, the steel structure would have acted as a cushion and would have slowed down the collapse until it stopped. Maybe three or four storeys would have been lost in the process but the remainder of the tower would have been left intact. The energy of collapse would be converted into heat and dispersed harmlessly.

In effect, that is what happened to the Marriott hotel that was hit by falling debris when Tower 2 collapsed. Photos show a large area of collapse of the upper storeys but this did not extend down to ground level.

What prevented that from happening in the case of the WTC was the structural arrangement. With the columns on the perimeter, the mass of building simply pushed them out of the way as it fell. In many photos and videos you can see these otherwise undamaged columns falling away from the path of the collapsing structure. Their strength was useless in preventing the collapse.

Whilst it is not right to say that there was no resistance to the collapse, the amount of resistance would have been minimal as it was only provided by the lightweight floors designed only to take people and furniture loading - not 18,000 tonnes of building moving at speed.

Remember that whilst the WTC was a steel building, it was not technically a steel framed building as there was no frame of beams and columns as would have been found in a more conventional building. The structural arrangement was innovative in a building of that height and allowed large areas of unobstructed floor space. Also the steel structure was very efficient in providing both support to the building and lateral resistance to hurricane force winds. Unfortunately, it was not designed to resist the extreme loading condition that it experienced on September 11th 2001.

I am not at all offended that you want to find out more about how the structure collapsed. There have been so many conspiracy theories around and so much misinformation that it is good to find somebody who is not taken in by all of that.
 
#365 ·
One thing I often wonder is if the towers had been constructed differently would they still be standing? Would a concrete core (reinforced, or not) or heavy steel beams supporting the floor diaphragm, as opposed to the lightweight trusses and drywall-lined core have saved the buildings? Or at least arrested the collapse long enough for the fire to be put out?
 
#368 ·
I think that would be very difficult to answer Chapelo. Shortly after 9/11 somebody made the claim that the Canary Wharf tower in London (almost identical to one of the World Financial Center towers near to the WTC) would have survived a similar attack but many structural engineers did not agree.

I think that the towers might have survived had their fire-proofing been better. The brittle spray-on fire-proofing was blasted off by the exploding jet fuel leaving the small section truss members exposed to the full heat of the fire. Also, sprinkler systems might have contained the fire until such time as the fire-fighters could have reached it and begun to tackle it.

I think the structural system was against it as well, as I have pointed out in the earlier posts, a more conventional steel frame might have redistributed the load and cushioned the collapse.

However, the towers did survive long enough for almost everybody below the point of impact (and some above) to escape, so they obviously had a lot of structural redundancy given the amount of damage that they received.

Conspiracy theorists often point to the fact that the towers were designed to resist aircraft impact and so presumably should not have collapsed as they did. That conveniently misses the point that very few people, when the towers were designed, would consider it to be a significant risk that an aircraft full of jet fuel would be deliberately crashed at 400mph into them.

What was seen as a conceivable accident would be that a Boeing 707 (the largest jet passenger plane at the time the towers were designed) would have got lost when coming into land at a New York airport and hit a tower. In that case its speed would be much lower (the energy contained varies with the square of the speed) and there would be little fuel load.

I think it was the shear amount of fuel on board the planes that was the ultimate killer. In a conventional office fire, paper, furniture, carpets etc would be involved and those parts of the steel frame exposed to the heat would lose strength. However, other parts of the structure would be unaffected and would act to relieve some of the loading on the weakened columns. As the fuel was used up and the fire died down, the affected columns would regain their strength and be able to relieve the loading from other columns now at the centre of the fire.

In the case of the WTC, some four floors were engulfed in flames for a prolonged period and the columns already weakened by the impact would lose their strength without being able to redistribute their loading elsewhere.
 
#370 ·
Thanks Martin, very illuminating, and answered my questions.

About cross-bracing, our datacentre was located on the eastern face of the 95th floor. If memory serves correctly, some of the core-columns, as well as the floor diaphragm, had to be reinforced because of the sheer weight of all the equipment that was in the datacentre; servers, networking hardware, cabling, UPS (battery backup) systems. I seem to also remember part of the concrete slab on that floor being re-poured to support the weight.

The 95th floor. The datacentre is the walled-off area on the eastern side of the floor.

 
#372 ·
Thanks Martin, very illuminating, and answered my questions.

About cross-bracing, our datacentre was located on the eastern face of the 95th floor. If memory serves correctly, some of the core-columns, as well as the floor diaphragm, had to be reinforced because of the sheer weight of all the equipment that was in the datacentre; servers, networking hardware, cabling, UPS (battery backup) systems. I seem to also remember part of the concrete slab on that floor being re-poured to support the weight.

The 95th floor. The datacentre is the walled-off area on the eastern side of the floor.
I have read that various building tenants would carry out work to the structure such as cutting staircases through where they occupied more than one floor. Interesting that they would need to reconstruct the floor to support all the loading. I find it odd though that they would need to beef up the core columns as the weight of your datacentre would be only a small part of all the loading that a core column would be designed to take.
 
#371 ·
This thread is very interesting ! It's refreshing that people are discussing a sensible and tragic subject like this one , in a composed and organized way .

I admit that i' m still dubious about the whole thing . A few questions are still unanswered , and i think that this is the right place to get some " closure ".

Now first , just like some of you pointed out earlier , how can 16 % of the building , cause the collapse of the other ( Undamaged ) 84 % ? Not only that , but the whole structure collapsed at a " free - fall " speed . Wouldn't the more massive bottom part be strong enough to resist the pressure , and stop or at least slow down the collapse ?

The only way the building could've collapsed that fast is if the main beams were weakened by heat ( Or like some would claim , explosives ) , but this leads us to a cul-de-sac as we all know , Jet fuel doesn't melt steel .

Plus , there have been pictures of victims , standing outside of the damaged areas to avoid being suffocated by toxic gases , so you can be sure it wasn't hot enough to melt steel or weaken the building .

Finally , what the hell happened to Building N 7 ?

Since some of you seem to have advanced knowledge in physics and architecture , any clarification would be appreciated !

Cheers ,
 
#374 ·
Hi AceOfSpades,

I wouldn't claim to have 'advanced knowledge' in physics or architecture but I do work as a civil and structural engineer so I am familiar with some of the issues here.

Quite honestly, so much research has been done into the collapse of the WTC that I doubt that there are many unanswered questions. Nobody will ever be 100% sure but the advanced computer techniques that have been used to get a handle on the precise method of collapse get us as close as we are ever likely to get.

I am sure that if there were reasonable suspicion of the use of explosives to bring the towers down then it would be structural engineers who would be the first to announce the fact. After all, they need to reassure their clients that their buildings aren't going to collapse in a similar fashion.

I discussed this issue of '16% of the building demolishing the other 84%' with Rizzato a couple of nights ago. It was a simple case of progressive collapse. As the upper floors descended, they demolished the floors below them and the weight of the floors added to the collapsing mass, which meant that the floors below would collapse even faster.

The towers did collapse almost at freefall - not quite - the reason being that the only resistance was offered by the lightweight floors - the structural columns were simply pushed out of the way.

The best description that I ever heard about the collapse of the WTC towers was that the building simply 'unzipped'. The central core and perimeter columns were immensely strong but were ineffective in stopping the collapse of the floors that simply detached from them as the building fell.

I have to admit that over twelve years after the disaster it is odd to me that people are still repeating that old story about the steel not melting because burning jet fuel is not hot enough. I guess that was exploded within a few days of the disaster.

Whilst it is true that steel will not melt at the temperature of burning jet fuel, what it will do is lose around half its strength and that, combined with the major damage to the structural columns and the loss of the propping action of the floors, is enough to account for the collapse of the steel structure.

Of course, you would still need very high temperatures to weaken steel but the evidence of people surviving at the crash site does not prove those temperatures did not occur in other parts of the building. After all, it was the burning jet fuel that caused the high temperatures and that would not have spread everywhere. As heat travels upwards, people just a few floors below the crash site would have been relatively unaffected whilst those many floors above would have unbearably hot conditions, as evidenced by the high number of people who chose to jump from the towers.

The collapse of World Trade Center 7 was a mystery for some time after the disaster and, obviously led to many conspiracy theories.

The problem is that the extent of the damage to the building caused by the collapse of the adjacent towers was hidden from sight due to the smoke and ash clouds. So, it had to be assumed that the collapse was caused by fire alone and it is rare for a skyscraper to collapse in that way.

WTC7 was built on top of an existing substation and, to carry the weight of the building, large beams were required to span across this structure to supports either side. The disaster investigation engineers concluded that the intense heat of the fire, which was not tackled by firefighters, would have resulted in the long span steel members expanding to such a large extent that they broke away from their bearings at each end and initiated the collapse.

What is known is that WTC7 unlike the twin towers collapsed from the bottom up rather than top down.
 
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