to believe some if not all of the 9/11 conspiracy theories

[mrsunreasonable]

NOTE: This is not meant to be offensive and if you suffered as a result of 9/11 you have my deepest sympathies it was a terrible event however it was caused.

Having watched a few documentaries on the conspiracy theories I am partially if not completely convinced all was not as it seemed. The fact that many witnesses that saw/heard things that didn't tie in with the official version have since died in suspicious circumstances doesn't help!

Yes, that last post of yours sounded sarcastic - "tail between legs", "no hope of getting it", etc. Sorry if I have misunderstood.

No reason why you shouldn't be able yo "get it" if you read the answers to your questions, and not just from anonymous conspiracy theorists.. It is not that complicated.

God, Cote, you credit me with a capacity for extended sarcasm, that would have been quite an achievement...I have AS so am usually a bit too straightforward, if anything!

Wow - just seen your post Tokyo. I am going to have a read. Really, really nice of you to do that...and that isn't sarcasm either!

Be back in a minute when I've had a look.

'Unlike a cathedral, where the walls are thick at the bottom to support the weight of the thinner walls above, the walls are a constant thickness, because the wall of each floor is supported by the floor. There isn't a continuous wall running from the top to the bottom of the building; rather, each floor has its own wall, which is the same weight be it the bottom floor or the top floor. So you can remove the wall around the 20th floor, and the 21st floor walls don't move, and no load is removed from the 19th floor walls.'

So how do they do that? Is there like a little gap between the top of one wall and the floor above it? That's really clever.

How are the floors attached to the lift shaft, as well? Can you do that/ I mean some kind of bracket or whatever that extends all the way out from the central shaft thing, to hold up the floor? That is amazing...I had no idea. I thought the outer walls held up the edges of the floors iyswim.

Ok, so far so good. But the bit I have the most trouble with in the collapse is the lift shaft bit. The floors, all very well, but this central thing which is how wide across? and how thick? I don't know, I can't remember. But it looked really strong when they were building it.

I get how the concrete got blown off the bit in the middle when the plane went through. (and I have no doubt there were actual planes!) so this made the steel vulnerable, right, and it bent or buckled or something, and the floors above came down like a huge weight on everything below.

But the central shaft below still had almost 100% strength - yes? Was the weight of the top bit seriously enough to make all those 47 columns of steel, and the concrete around them, just shatter instantly into little sections, or dust, at the same rate as the floors (which were not that strong)? If so then that's Ok. But it seems so odd.

(Sorry missed top bit of post off! Should begin like this:)

Thankyou so much, Tokyo - I now have a good idea how skyscrapers are formed, and why in photos of damaged ones you have no walls but the floors are intact. That makes sense.

A couple of things if I might ask?

"So how do they do that? Is there like a little gap between the top of one wall and the floor above it? That's really clever."

Whether you can literally do it, like the panels on a car, will depend on the design. But there will be little gaps: imagine what happens when the building heats up or cools down. You need the walls to be able to flex slightly, because otherwise they'll buckle.

"How are the floors attached to the lift shaft, as well? Can you do that/ I mean some kind of bracket or whatever that extends all the way out from the central shaft thing, to hold up the floor? That is amazing...I had no idea. I thought the outer walls held up the edges of the floors iyswim."

It depends on the design how they're fastened.

"But the central shaft below still had almost 100% strength - yes? Was the weight of the top bit seriously enough to make all those 47 columns of steel, and the concrete around them, just shatter instantly into little sections, or dust, at the same rate as the floors "

I was trying to explain why it drops onto its own footprint. As to the collapse of the central structure, you need to remember that (as has been pointed out before) steel is not magical, and if you bend it quickly it fractures. I don't know the design of the WTC buildings, but one way that you can fasten the floors to the core is to project girders outwards, with one end set into the core and the other end projecting out as part of the floor.

Picture a game of "Kerplunk". If you run your hand down the plastic straws slowly, they'll flex and spring back. If you run it down faster, they'll break. Now, replace the plastic straws with something stiffer: if you know what carbon fibre feels like, that, otherwise imagine a stiff piece of wire. If you run your hand down slowly, they'll flex slightly and spring back (and your hand will hurt). Now, imagine running your hand down that quickly: what will happen to the plastic column in the middle?

That's my understanding of what happened. The floors were keyed into the structure, and when they fell, the structure couldn't deform fast enough to absorb the energy, so broke. As the first floor to fail wasn't the top floor, rather wherever the fire was, as soon as that disrupted the core at that point, the entire mass of the core above the initial fracture was dropping onto what was left. Shazam.

You need to remember that no-one designs massive safety factors into buildings. They used to, because they didn't know how not to: either it fell down, or it stayed up, and conservative engineering preserved the things that made buildings stay up so they became stronger and stronger. The Empire State Building was hit by a B25 bomber (twin engined: not that big) in the 1940s, and not much happened. But once you have got computer analysis, and once you want big windows, buildings are only as strong as they need to be. Extra mass has to be carried, and has to be paid for.

Thankyou very much Tokyo. Sorry I didn't come back last night; I had to put ds2 to bed and fell asleep myself.

I am now picturing it a bit more like 'kerplunk', which does help a bit. So, maybe the floors and whatever held them up (trusses?) snapped at the outer walls, then the place where they were attached on the inner core didn't just snap at the join, it pulled some of the cetral core off sideways? All around the core.

It is fascinating about the separate floors, I had never imagined buildings were made that way. I do appreciate your explaining so patiently.

I am a little bit worried when you say you don't know the design of the WTC buildings though!! Perhaps that's not necessary to know, though. If you have a decent enough general concept of how things fail, I guess it just seems plausible.

Thanks again.

Hang on though. I am certain I have seen documentaries (BBC etc) that explain that the outer walls of the WTC were structurally relevant - ie trusses attached at each floor, to the inner and outer sections. And a 'hat truss' on the top? So there was like an exo-skeleton type of thing.

Or is that not relevant anyway? I mean if that wasn't very strong.

I've just read a description of the WTC structure, and my account of single core buildings is a reasonable model. The WTC uses perimeter trusses as well, which on the one hand means the floors are supported at both ends, but on the other hand means that the floors are in tension (they keep the perimeter and the core from pulling apart) rather than in shear (any line drawn from the core to the perimeter is supported at both ends, rather than one).

You can visualise a cross-section of the structure as two kerplunk sets side by side, with extra long sticks threaded through both. Again, gentle forces will flex the sticks, sharp forces will break the towers. When a floor fails it loads the floor below, and the structure of the building will experience unexpected shear just as in the single-column example, but now half the load at the core, half at the perimeter. But the core and the perimeter are half the strength they would be in a single-code version, so the same thing happens: unable to flex, they snap.

But I suspect this design makes the failure even more rapid. I am speculating now, but here goes (any real structural engineers?)

In a single column design, the floors only need to support their own weight. They don't act to tie the structure of the building together. In a WTC design, the floors are what stop the core and the perimeter from moving relative to each other. That means that when the loads increase, the core and the perimeter are held in the correct relationship to each other. They can't bend while the floor is intact, because the floor is acting as a truss. So the columns may fail before the floors: they can't flex, because they're tied together by the floors, and at the point the floor joins the column they're supporting 2/3/4/5/etc times the intended load.

It's not easy to think of analogies for how steel fails when subjected to rapid loads, because steel is, well, steel. If you clamp a piece of steel in a vice and push it slowly, it'll bend, and either spring back or stay there when the load is released, depending on a variety of factors. If you clamp a piece of steel in a vice and hit it with a sufficiently heavy and fast moving hammer, it'll just snap off. Steel is better than iron in this regard (indeed, this is why steel was developed): cast iron will always just snap. It's further complicated if, as in a girder, rather than simply having a straight piece of steel it's an I/T/L section for rigidity: when that fails, the webs of the girder will usually tear straight through (you can demonstrate this with dexion strip, but you need a bloody big vice).

Steel has some useful properties, but it isn't strong in shear (it snaps) and it isn't ductile at high speed (you can bend it, but you have to do it slowly). Materials "flow" as they bend (if you think about the region of a bend, material is being compressed on the inside and stretched on the outside) and if it doesn't have time to do that, it snaps.

Yes, I can see how it would snap if whacked hard from above. But a force like that would send the steel flying off to one side, surely? Not downwards. Many a time I have hit a nail only for the top bit to fly off because there is resistance from the piece of wood or whatever it's refusing to go into.

And in the WTC surely there was no sideways option? The steel was encased in concrete all the way down to the ground - how could it shear off when it's protected from going sideways? Or would the concrete just shear into sections with it? Just 'boom-boom-boom' like that?

I think we would really benefit from a model which shows this happening in a different context.

Just exploring the fire-causing-structural-failure theory a bit more - this is very dumbed down obviously but it is interesting.

"Yes, I can see how it would snap if whacked hard from above. But a force like that would send the steel flying off to one side"

No, it wouldn't. Where does the lateral force come from? Try it. Put a piece of hard, plain chocolate on a worktop so that half of it sticks out. Hold the supported end firmly, and drop an apple on it from a few feet above (to make sure the force is directly downwards). Where does the chocolate first hit the ground?

"And in the WTC surely there was no sideways option? "

Precisely. It can't flex.

"Or would the concrete just shear into sections with it?"

It would indeed. Although it would be fracturing, rather than shearing.

A lot of people believe that concrete and steel is very strong. They are, but they're not infinitely strong. They're strong enough. You don't build buildings out of any more material than you need, because very kilo you add is a kilo that has to be carried on the foundations, and foundations are expensive. Steel behaves in all sorts of counter-intuitive ways under immense, rapid force, which is what happened here.

"obviously but it is interesting."

So, since you've been asking questions about "the government" account, deploy the same scepticism to that. Ask yourself how a fire that started in an office space might differ from the fire on 9/11 in terms of its ability to cause structural damage.

That site is classic troofer distraction (it's over there). It makes endless "it's a conspiracy" asides (for example, "For some strange reason, the modifications failed to perform on September 11, 2001 and again the fires spread from floor to floor."). It isn't a strange reason. See if you can work out what it is.

I can see it's a dodgy site...that's fairly obvious isn't it! I was trying to ignore the obvious weirdness and just wondering why that fire didn't cause the buildings to fall, when it burnt for much longer and apparently it was the length of time the smallish fires on 911 burnt, not their constant magnitude (which I think I'm right in saying diminished as the hours/minutes went on) which brought the buildings down.

was it the kerosene in the mix that made the difference?

Flighttattendant, this is a response from the Architects and Engineers for 911 Truth to the paper that tokyo linked to earlier on
heiwaco.tripod.com/blgb.htm

I haven't read it, don't know if there is anything interesting in there

claig, the first claim made by the page you link to is that all the video of the collapses has been faked by the government in order to conceal the truth.

"The ABC video is fake

Actually, the ABC video is a 100% falsification! It is a pre-made movie or video with simulations of an alleged 'live' event on TV that doesn't take place in reality!

It starts with a 'live' interview with plenty of cats and dogs popping in but later things get really serious - the 'crush-downs' of both WTC 1 and 2!"

I don't think it's worth reading any further. Is this what passes for a serious response in troofer land?

"was it the kerosene in the mix that made the difference?"

Probably. Air is a very good insulator, so you can have a very high temperature that doesn't transfer much energy. Heat your oven to 100C, which will probably be the lowest setting you can find (gas mark half is 120C, gas mark 1 is 140C). Open the door and put your hand in. Wiggle it about. It's a bit warm, isn't it? Wiggle it a bit more. OK? Now, either cook some meringues in the nice cool oven, or turn it off.

Now, pop a pan of water on, and wait until it's boiling. 100C, yes? Take the lid off and, no, don't put your hand in. Because it's a lot more than warm, isn't it? You'll burn yourself very badly.

Second example. Find a piece of steel bar several feet long, and cut about an inch off it. Play a blow torch onto the small piece, and see how long it takes to glow a dull red. Now, play the same blow torch on the end of the remaining length of bar and see if you can get it red before the gas runs out. You'll find that the thicker the bar is, the less chance you have.

Heat is conducted through metal, fairly efficiently. So if you heat one part of a piece of metal, it will tend to even out through the whole structure. In order to get it hot, you have to be able to pour heat in faster than it conducts away from the heat and then radiates away. As the rate of transfer is proportional to the square of the difference in temperature, as the metal heats up the transfer of heat in becomes slower, but the transfer of heat away to the cooler surroundings becomes faster, so you need a progressively larger source of heat.

A fire burning in a building will transfer very little heat into the structure itself. That's why there's no paint on the walls of the fire escape stairs in concrete buildings: with nothing terribly flammable against the concrete, the air acts as a powerful insulator and the structure will be secure. The floor surface and the ceiling above where the fire is burning may get very hot, but once the concrete is hot heat will be carried away by the steel reinforcement and radiated through the whole structure. A fire involving furniture, curtains, carpets and so on in a sky scraper is dangerous for people, and damaging, but probably won't even get the structure warm. All that steel and concrete is a massive heat sink. Hot air will convect through the building and will ignite other material, but it won't be able to transfer significant heat into the structure. You've seen pictures of "burnt out" buildings, yes? The structure is intact, because the fire ran out of combustible materials (for the purposes at hand, concrete and steel won't burn) before it managed to get the structure hot enough to cause damage. Houses don't "burn down", usually; the common scenario is that they are gutted, but the walls are still standing.

Now, consider 9/11. It's not a fire starting in one point and spreading by consuming flammable materials. It's the addition of several hundred tonnes of kerosene. Note the attackers knew this: that's why they hi-jacked aircraft bound for the west coast, not local commuter shuttles. Once that's burning straight onto the concrete and penetrating the structure, the heat is transferring much more quickly (cf. your hand in the pan). Kerosene isn't like petrol, it's like diesel: it takes quite a lot to get it ignited, but once it is burning it delivers immense heat for a long time (petrol engines are power by explosion, diesel engines by burning). 300 tonnes spread over the upper floors means that conduction through the steel frame doesn't help dissipate the energy, because it's hot all along its length. And there's enough heat, as opposed to temperature to heat the whole lot up faster than it can radiate it away.

The paper you quote both ignores the effect of kerosene, and confuses heat with temperature with energy transfer.

OMG toy did u jsut know all that stuff or did you google it??

Nope, just typed it top to bottom. Remember that when your daughter's talking about dropping physics.

well i am very impressed x

oh and no dd here just a ds!!

tokyo you obviously know a lot about it. The guy who wrote that article is offering 10,000 Euros to anyone who can prove him wrong that a building can't collapse from the top downwards due to damage at the top. I think you stand a good chance of winning the prize

heiwaco.tripod.com/chall.htm

"The guy who wrote that article is offering 10,000 Euros to anyone who can prove him wrong"

See the crackpot index. That's point 13. It would be fair to say that it fails on many other fronts, too.

claig, you obviously have a keen interest in this subject. What, in your opinion, is the most likely explanation for WTC7's collapse?

Tokyonambu, snorbs, et al:

How do you explain the fact that numerous governments have admitted to carrying out false flag attacks (staged terrorist attrocities intended to demonize an enemy)?

www.washingtonsblog.com/2010/02/governments-have-admitted-that-they.html

* The CIA admits  that it hired Iranians in the 1950's to pose as Communists and stage bombings in Iran in order to turn the country against its democratically-elected president

* Israel admits that an Israeli terrorist cell operating in Egypt planted bombs in several buildings, including U.S. diplomatic facilities, then left behind "evidence" implicating the Arabs as the culprits (one of the bombs detonated prematurely, allowing the Egyptians to identify the bombers, and several of the Israelis later confessed) 

* The well-respected former Indonesian president admits that the government probably had a role in the Bali bombings

* The former Italian Prime Minister, an Italian judge, and the former head of Italian counterintelligence admit that NATO, with the help of the Pentagon and CIA, carried out terror bombings in Italy and blamed the communists, in order to rally people?s support for their governments in Europe in their fight against communism. As one participant in this formerly-secret program stated: "You had to attack civilians, people, women, children, innocent people, unknown people far removed from any political game. The reason was quite simple. They were supposed to force these people, the Italian public, to turn to the state to ask for greater security" (and see this)(Italy joined NATO in 1949, years before the bombings occurred)

* As admitted by the U.S. government, recently declassified documents show that in the 1960's, the American Joint Chiefs of Staff signed off on a plan to blow up AMERICAN airplanes (using an elaborate plan involving the switching of airplanes), and also to commit terrorist acts on American soil, and then to blame it on the Cubans in order to justify an invasion of Cuba.

Kurkum, I don't think it comes as any surprise to anyone that the CIA has played some very dirty tricks in the past (and, with things like "extraordinary rendition, aka kidnapping, continue to do so) in non-US countries. They have behaved appallingly at times and, sadly, they're likely to continue to do so. They need some decent oversight.

It's a fact. It doesn't need to be "explained" and I don't believe anyone has ever tried to deny it.

What's your point? Or are you trying to imply that, because the US has been involved in very shady operations outside of the US, that they were involved in the 9/11 attacks?

Let me ask you the same question that I asked claig. What do you think is the most likely explanation for the 9/11 attacks? Who do you think were behind it? What were their motives? And how did WTC7 fall? You don't have to provide loads more links to other websites; I'd just love to hear what your own opinions are.