General Question

Zen's avatar

9/11 question concerning the Towers' collapse?

Asked by Zen (7743points) September 11th, 2009

Could someone (not an engineer or architect – I don’t understand them) please explain in simple English why the buildings collapsed?

Watched it live, seen the tapes many times over, heard the explanations and theories (and even the controversy) but still can’t wrap my brain around it. The plane hit some of the top floors. There was a fire and a lot of damage. Why did the building just collapse – like in the demolitions when they blow them up setting the devices at the bottom to perfection, causing the building to implode and collapse upon itself (thus causing less damage to the immediate vicinity). I just don’t get it.

Observing members: 0 Composing members: 0

29 Answers

drdoombot's avatar

The upper floors heated up to such high temperatures (from the jet fuel) that the steel beams of the buildings became weakened. Once they were weak enough, they couldn’t support the buildings any longer and they collapsed.

The_Compassionate_Heretic's avatar

That’s what buildings look like when they fall down. Gravity pulled the structure down, not off to the side. They don’t fall like trees.

The fire didn’t need to disintegrate the steel supports, it only needed to weaken them. Then when the upper floors started to fall, the resulting force caused the rest of the structure to fail.

SuperMouse's avatar

Here is a great thread discussing this very question. After reading it all, following all the links, and doing tons of looking on my own, I have some serious questions.

The_Compassionate_Heretic's avatar

@SuperMouse What questions? Let’s talk about these questions.

kevbo's avatar

Hollywood put out all these movies with exploding buildings, and it focused the collective consciousness to the point that the towers’ skeletons got the equivalent of osteoporosis, so they were very fragile when the planes hit them and exploded.

Hence all the dust.

sandystrachan's avatar

The collapsed cause they got blown up , it’s simple to see when you watch them fall .

kevbo's avatar

@The_Compassionate_Heretic, that’s not accurate. Structures collapse in the direction of least resistance. Some do fall
like trees. Link

It would especially seem fitting that the tower with the pronounced lean would crack at the break and topple in the direction of the lean.

Even if it did pancake as originally suggested, it would
seem true that the floors would not fall towards the core and that more of the core would remain standing. Even PBS’s Frontline demonstrates this while simultaneously floating the official explanation. I’m on the iPhone and can’t find the clip, but perhaps someone else can.

dalepetrie's avatar

Essentially, and this is the version of the story I find to be the most credible, because jet fuel doesn’t burn at a rate high enough to melt the interior steel structure, it wasn’t that the structure melted. Basically, however…when the planes hit, they did structural damage to certain parts of the steel frame….those parts had a slightly lower melting point and were at the site of the highest heat flames. Enough heat was generated in the weak spots that one high up floor eventually collapsed on just one side….it was the weight of an entire floor caving in on one side that brought down the other side of that floor….then as each floor fell on top of the floor below it, the force of gravity exerted by all the floors above it caused each subsequent floor to collapse under the weight of the falling floors above it. Basically, it pancaked, and one area giving way completely was all it really took to set off something akin to a chain of dominos. But of course, there are a lot of other theories, that just seems to hold the most water unless you want to start buying into the idea that bombs were planted to implode the building, which seems pretty far fetched to me. As I’ve explained elsewhere, I believe Bush and co may well have let 9/11 happen, but I don’t think they forced it to happen…I’m sure they realized that the risks of getting caught doing something like that were a) too high and b) completely unnecessary as all they had to do was let their guard down one Tueday morning and it would happen anyway.

PandoraBoxx's avatar

The building was designed to withstand wind pressure, and being hit by small airplanes, as had happened in the past. The floors in the building had no interior supports; they were only attached to the exterior walls, where the beams were hollow tubes to allow the building to move in the wind. It is the pins that attached the floors to the beams that failed due to the heat, causing a change in the tension that held the building together. It’s pretty much agreed that the lack of interior support pillars, which most buildings have, caused the pancaking.

hiphiphopflipflapflop's avatar

Both those planes were fueled for a transcontinental trip. When they impacted the towers, a significant portion of their mass was jet fuel which was spilled throughout the impact/blow-through zone and ignited. The impact/explosion/carry-through of debris would have stripped off an appreciable amount of the spray-on fireproofing insulation protecting structural members. The fires burned out of control. Steel loses strength with heat like any other material – it isn’t a constant that then drops to zero as it melts, it’s a downward slopping curve. Add to that what @PandoraBoxx said about the nature of the WTC’s construction. FWIW, I’m a metallurgical engineer/materials scientist with a masters’ degree (which, along with four dollars gets me a coffee at Starbuck’s like everyone else).

sandystrachan's avatar

For all the fuel in those planes what a lack of raging flames, plane 2 had more fuel only cause they hit too early off the plan thats why more flames on crash 2

Darbio16's avatar

Even if you buy into the whole jet fuel theory making the beams weaken, how the hell can you explain WTC building 7 falling down all at once at free-fall rate having never even been hit by a plane? The National Geographic Channel had a special on the other night about 9/11. They didn’t even mention building 7, no one ever does. It is the one thing that NO ONE in the government can or want to explain. Check out the link on WTC 7. The 9/11 commission didn’t touch WTC 7 in their report either. WTC 7 held all sorts of investigation records for the SEC and FBI, one strong reason for the need to demolish the building.

It seems that most of America has been brainwashed in regard to the Twin Towers. No jet fuel in wtc 7 though. No plane hit it, the twin towers didn’t fall onto it. So how did it fall?

hiphiphopflipflapflop's avatar

Wikipedia on 7 WTC collapse doesn’t wave a red flag saying OMG INSIDE JOBZ at me. But if then I’m probably one of the brainwashed anyway, having “bought into the whole jet fuel theory making beams weaken”.

kevbo's avatar

@hiphiphopflipflapflop, props
for bringing your expert perspective.

@Darbio16, the official explanation for WTC7 is “thermal expansion,” which is (if I remember correctly) unique in history to WTC7.

hiphiphopflipflapflop's avatar

NIST FAQ on 7 WTC. I will admit that this quote from the Wikipedia article raises my level of attention: “The collapse of 7 World Trade Center is remarkable because it was the first known instance of a tall building collapsing primarily as a result of uncontrolled fires.”

kevbo's avatar

@hiphiphopflipflapflop, I don’t know how much this interests you, but it would be interesting to hear your perspective on this article published in the Journal of Metallurgy. (If you’re not interested, no biggie.) I glaze over at the core science, but have a few issues with the article as a whole.

hiphiphopflipflapflop's avatar

@kevbo Thanks! I may have seen this soon after 9/11 but had forgotten about it. This brings up buckling due to thermal expansion from the heating as a critical contributor.

Darbio16's avatar

For anyone listening to Alex Jones, like me as of yesterday, Don’t do it anymore! He’s a liar, a traitor and he’s in on the conspiracy too.

Bill Cooper is who we should have been listening to all along. Sadly, he got killed 2 months after 9/11 by police. He accurately predicted the Osama Bin Laden would attack America. The truth was spoken by bill cooper, not alex jones.

kevbo's avatar

@hiphiphopflipflapflop, hey, no problem. So obviously it makes sense to you. While admittedly not able to comment on the heat vs. temp distinction, it doesn’t give me confidence that they first claim the plane is loaded with 90,000 L gallons, nor that it doesn’t subtract 1,500 or so liters due to ascent and flight time. I also think the “black smoke” pic is photoshopped. If you look at other photos at that moment of impact, the smoke is not nearly so dark.

Those are minor nitpicks, but not below expectation for a peer review article in an academic journal.

hiphiphopflipflapflop's avatar

JOM is actually something sort of between a trade/prof. society magazine and an academic journal. “Acta Met” and “Scripta Met.” are among the “sexy” ones to get your work published in, JOM not so much. Also this looks like something the editorial staff put emphasis on getting out quickly (“Feature: Special Report”).

This the more substantive article JOM published in 2007 based on NIST’s work is linked to at the top of the page:

kevbo's avatar

Ahhh… thanks for the clarification.

hiphiphopflipflapflop's avatar

Going back to the original JOM article there is this quote attributed to Lord Kelvin that I find chastening:

“I often say . . . that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be.”

Not having poured over the data, done tests, run simulations, etc.. my own knowledge of the situation is exactly of that “meager and unsatisfactory kind”.

SquirrelEStuff's avatar


I couldn’t agree more with listening to William Cooper. After reading Behold A Pale Horse, all the missing pieces come together. The scariest part is, the book was written in 1991.

sandystrachan's avatar

The news channels made WTC 7 collapse , they reported it an hour or so before hand . Blame teh news people . Explosions and thermite made the other two fall

PandoraBoxx's avatar

One of the things that I find interesting and would like to understand more about is the stability of the ground on which the WTC was built. If I remember correctly, one factor that hampered the removal of debris from the site was that the Army Corps of Engineers had to shore up the land edge on the harbor as they removed debris from the whole in order to stop the pressure of the water from causing the excavation to collapse into itself.

Kraigmo's avatar

@Darbio16 How can I trust anything that website said when this following sentence is in there:

“I am not even saying that the Jesuits are at the top of the Pyramid, but they are the Gatekeepers between higher dimensional forces and the people on Earth, and it certainly looks as if Alex Jones is one of those Gatekeepers”

That’s a bunch of mishmush compared to the things Jones himself talks about.

jamjar's avatar

There has only ever been 3 steel frame buildings to collapse due to fire. WTC 1, 2 and 7…

PandoraBoxx's avatar

I believe those are also the only steel frame buildings of that height built without interior floor supports.

sandystrachan's avatar

Let Charlie Sheen speak to Obama , he will get the answers :) until then its all speculation

Answer this question




to answer.

This question is in the General Section. Responses must be helpful and on-topic.

Your answer will be saved while you login or join.

Have a question? Ask Fluther!

What do you know more about?
Knowledge Networking @ Fluther