Wonder About 9/11

[The Outsider]

To quote from the article, all of it what makes perfect logical sense :

As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour. If it had been free fall, with no restraint, the collapse would have only taken eight seconds and would have impacted at 300 km/h.1 It has been suggested that it was fortunate that the WTC did not tip over onto other buildings surrounding the area. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure. Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a 500,000 t structure has too much inertia to fall in any direction other than nearly straight down.

[CC1981]

The force that one is going to require for a controlled demolition is going to be based upon the strength of the building, correct?

Strength of the building ? eh ?!? There are many different ways of measuring strength- tensile strength/compressional strength, mohr scale, etc. But even then, strength is only part of the equation - shape, size and total weight of building are the other equally important factors.

After an impact with a jet moving at hundreds of miles per hour it is plain obvious that the internal columns will be broken

Internal columns of ONE floor. That too, it obviously wernt shattered immediately for if it were, it'd mean instant collapse. but if say you denotate charges through the other 90 floors, starting 2-3 floors below impact site, it'd still go according to plan because the shape/size/mass of building overall hasnt changed significantly.

Let us see some examples.

Let us see examples of what ?!? I am saying that buildings hit by planes arnt supposed to collapse like that because the physics of it (as explained by the US govt. explanations) doesnt make sense. How am i supposed to provide example for this ?!? How many incidents of planes flying into buildings exist for cross-reference ?!?

all of it what makes perfect logical sense

I've already explained to you why this 'collapsing into its own footprints' doesnt make sense. That'd only happen if there is linear collapse. Which is extremely improbable in an uncontrolled demolition ( ie, it means ALL the non-redundant pillars on the impacted floor failed at the same time so the floor has zero 'tilt' to its collapse. If you have any science background, you can straightaway see the absurdity of that scenario because in an uncontrolled impact site, pillars damaged due to impact/heat etc. wont all snap away at the same time ! Thus without controlled demolition, i fail to see how the building doesnt develop a 'lean' in the collapse (ie, leaning on whichever side of the floor that initiates collapse, ie, fraction of a second earlier) and topple over the side as the weight differential picks up. Incidentally, this is how buildings with compromised foundations/support pillars collapse - they break off or explode outwards near the end. This is widely documented because buildings falling apart after big earthquakes have been seen most recently in the last great Turkish earthquake which really hit Ankara badly.

[CC1981]

First, the building is not solid; it is 95 percent air and, hence, can implode onto itself.

doesn't matter if your building is 95 % air or 95% solid. Whether it implodes inwards or not is completely dependent on the linearity of the collapse.

Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure.

If the aircraft's added mass was enough to shift the c.o.g by 100 feet ( ie, 30m or so, relatively huge inside a building) then it obviously means that the aircraft weight would've been a significant factor. Which means that when the floors collapse( assuming collapse is due to the structural damage caused by the aircraft), the side that is closer to the c.o.g. will go first...ie, fraction of a second faster. Ie, develop a leading edge and the top chunk of building topples over at some point.

Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity.

Okay this guy officially doesnt know his arse from his elbow on this topic then. What causes a building to break and fall outwards has got nothing to do with lateral speed, its got everything to do with c.o.g. and moments of inertia. Buildings fall outwards because in uncontrolled fashion, it is really unlikely for a floor to collapse uniformly, almost always one side goes first and that side develops a 'lean' in the falling sequence..which leads the 'portion of the building on top' to eventually fall over as the rubble under it increases and the lean becomes more and more pronounced.

[The Outsider]

But even then, strength is only part of the equation - shape, size and total weight of building are the other equally important factors.

Agreed. I never said that strength is the ONLY factor. But I know this much if you change one of the important parameters in an equation the result is bound to be affected, something which could not have been accurately factored in the calcuations. Okay, so we dont have any precedence to go by.

I've already explained to you why this 'collapsing into its own footprints' doesnt make sense. That'd only happen if there is linear collapse. Which is extremely improbable in an uncontrolled demolition ( ie, it means ALL the non-redundant pillars on the impacted floor failed at the same time so the floor has zero 'tilt' to its collapse.

Not according to the article, it does not have to be the case. The author's premise is that there was very little time between the begining of the collapse and the end for the effect you are talking about to take effect. He has also pointed out that there would need to be a 100 feet lateral displacement for the building to have tipped over because only that amount of displacement would have made it go beyond base of the building. Can you propose a mechanism for the building to have attained such a large lateral velocity in the short time frame of 10 seconds to have moved its center of gravity by more than 100 feet?

[CC1981]

But I know this much if you change one of the important parameters in an equation the result is bound to be affected, something which could not have been accurately factored in the calcuations.

One/two floor's wallside/non-load bearing structure damaged by initial impact( as i said, it cannot be significant # of load bearing structures damaged because it'd mean instant or collapse right after impact) for a building with 100+ floors (multiplied by four..four sides) is not a significant change in the strength parameter...around 1% if that and engineers usually keep a leeway of 10-15% for this 'strength factor' since it can never be known exactly.

. The author's premise is that there was very little time between the begining of the collapse and the end for the effect you are talking about to take effect.

False premise. This was one of the tallest buildings collapsing the world has seen. And rate of collapse is uniform, irrespective of height- since it is acceleration due to gravity that is doing all the work. a.o.g. is constant. So therefore, if 15-20 storey buildings have enough time to keel over because of m.o.i, WTC 1 & 2 had more than sufficient time.

He has also pointed out that there would need to be a 100 feet lateral displacement for the building to have tipped over because only that amount of displacement would have made it go beyond base of the building.

Again, guy either doesnt know what he is talking about or he is doing good job misleading people. I am not talking about the entire building toppling over. I am talking about the part of the building ABOVE the impact floor ( thats gotto be a contiguous structure of 5-10 floors ? i know there were atleast that many floors to the top from the floor(s) of impact) that will topple over as it rides the cushion of unstable rubble below it on its way down. Therefore, c.o.g of whole building = irrelevant. What now matters is that whether the c.o.g. of this 5-10 floor 'chunk' is gonna fall outside its base or not... Now, instinctively you can say that 'hang on a minute, if you are shortening the height ( by considering the part that is 5-10 floors tall, as its the relevant part) then c.o.g. is gonna be surely harder to disturb ? THe answer to that would be yes, true, c.o.g. needs to shift far more but the torque experienced by the '5-10 floor chunk' is far greater and thus will help a LOT in tipping over that side.

[The Outsider]

One/two floor's wallside/non-load bearing structure damaged by initial impact( as i said, it cannot be significant # of load bearing structures damaged because it'd mean instant or collapse right after impact) for a building with 100+ floors (multiplied by four..four sides) is not a significant change in the strength parameter...around 1% if that and engineers usually keep a leeway of 10-15% for this 'strength factor' since it can never be known exactly.

You are ignoring the damage which was caused by the fire and the gradual weakening of the internal columns of the structure. Not a prudent assumption. And, CC you keep on coming up with these numbers without any basis. Has there been study which is leading you to quote the 1% figure, say one hour after the impact?

False premise. This was one of the tallest buildings collapsing the world has seen. And rate of collapse is uniform, irrespective of height- since it is acceleration due to gravity that is doing all the work. a.o.g. is constant. So therefore, if 15-20 storey buildings have enough time to keel over because of m.o.i, WTC 1 & 2 had more than sufficient time.

In controlled demolitions the support structure above a certain point in the building is taken off which causes the top portion to fall on whats below and make the collapse due to gravity. Tell me how it is different from the support structure of the top floors in the WTC being taken away by the impact of the jet and in the mean time the structure beneath has also become weaker unlike in a controlled demolition. That will make the collapse faster, correct?

THe answer to that would be yes, true, c.o.g. needs to shift far more but the torque experienced by the '5-10 floor chunk' is far greater and thus will help a LOT in tipping over that side.

Can we see some numbers in support of this?

doesn't matter if your building is 95 % air or 95% solid. Whether it implodes inwards or not is completely dependent on the linearity of the collapse.

BTW, this is important because of air resistance reasons.

[King]

Shwetabh, there was another building that came crashing down in similar fashion too. The two towers came yes but how about the 7th building? It didn't catch fire nor did a commercial airliner hit that. The official report said it came down because of the pressure created by the other two bulidings. The 7th buliding ( need to double check the name) hosted CIA, Ministry of defence and lot other sensitive ministries. You may want to check that out too.

[The Outsider]

Yeah, Ravi I am including that in the argument as well. There was seismic activity detected due to the collapse of the big towers which might have brought the third building down. There was also large amounts of debris which fell on it. BTW, I am not saying that everything concerned with 9/11 is overboard. There are irregularities to be seen all over, specially with regards to how long it took the F16s to take flight, and how long it took for the air traffic to be brought down, also how the occupants of the South tower were instructed to stay calm and not vacate the building after the North tower was struck, the dilly dallying in forming the commission etc. But controlled demolition of the towers is difficult to explain for many reasons : 1. The logistics involved in setting up such an operation without any leaks 2. The motive behind having controlled collapse as opposed to uncontrolled 3. The difficulty associated with ensuring that the collapse would be controlled AFTER the buildings had been violently disturbed If the argument is that the US govt knew this was going to happen and allowed it to happen like Pearl Harbor, I can buy it. But the controlled demolition theory has many holes in it while the theory of the towers having been brought down by the planes has been reasonably well explained by many unbiased and recognized scientists.