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9/11 silly question

rwguinn said:
Thanks--I will take a look.
Quick perusal indicates that there is not a simple failure mode, as I suspected---But I will take the time to read it in depth and get back to you!
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You could probably find a briefer summary. I'm not interested enough to search further.
 
Rob Lister said:
You could probably find a briefer summary. I'm not interested enough to search further.
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I have read most of the detail description, and I pretty much agree. I am going to paraphraase a lot of their stuff here:
A large number of supporting columns were destroyed by impact. There were sufficient supports left to hold up the building under normal circumstances, but these weren't normal. There was a fire.
What I found most interesting was the assertion that a "diffuse flame will usually not exceed 1000 C" (Which is 1830F), and that the temperature probably didn't exceed 750-800C (1380-1470F)---which is hot.
Steel expands when it gets hot. They point out that the heating was most likely uneven, and that beam buckling probably occurred in the floors, which would start failing the floor beams.
Now, column strength is a function of length. In the Towers, the length of the support columns was reduced by having the floors in there. As a beam doubles in length, the column's ability to resist buckling is 1/4 what it was. Lose 1 floor, and you now have 1/4 the weight bearing capability you had. 2 floors, 1/9th--and you are in over your head very quickly- and the collumns start buckling and the building comes down.
The way I read it, softening of the fasteners may have been a contributer, but it was thermal loading (Elongation of the trusses due to thermal expansion) which overloaded the fasteners holding the floor/ceiling trusses to the columns. And by failing enough floor trusses, you get a high load on the floor where this debris all accumulates, as well as a buckling failure in the vertical supports. When this collapses, you get an impulse loading on the lower part of the system, which it wasn't designed for (who could forsee this! Or if he/she could, that engineer would be eligible for a $1000000 reward--and would need a new job) and the whole thing collapses just like you had cut the supports with explosives.
Now, that is over-simplification to many, I'm sure, and probably clear as the Rio Grande to others. But anyway--Thank you for the interesting link. I do appreciate it.

Edited for speling...a'hm a injuneer, not anglish majer...
 
Steel trusses similar to what was used in the WTC are rather common in building construction these days. Next time you're in a Wall Mart, Sam's Club or similar Big Box store take a look up at the roof. This type of construction has killed more firefighters over the years than you could imagine: Fire in the building and firefighters working on the roof to ventilate. When the steel gets heated it softens and sags. Down comes the roof...and often the firefighters. Hard to believe, but laminated wood generally holds up longer and better in fire conditions.
Check out some of Francis Brannigan's books on building construction for more on this.
 
Hamradioguy said:
Steel trusses similar to what was used in the WTC are rather common in building construction these days. Next time you're in a Wall Mart, Sam's Club or similar Big Box store take a look up at the roof. This type of construction has killed more firefighters over the years than you could imagine: Fire in the building and firefighters working on the roof to ventilate. When the steel gets heated it softens and sags. Down comes the roof...and often the firefighters. Hard to believe, but laminated wood generally holds up longer and better in fire conditions.
Check out some of Francis Brannigan's books on building construction for more on this.
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And yet another reason why evidence trumps conjecture and faith.
 
Well thank you for all the replies.

I must say I would have thought 'common sense' would dictate that you could heat something to a higher temp than the heat source by containing the heat. I guess that is the problem with common sense.
 
MetalPig said:
No. You can't make stuff hotter than the heat source.

According to the conspiracy-debunkers, the jet fuel was spent within a very short time. After that, it was the building and the stuff in it that was burning. And apparently, that burned at a temperature high enough to weaken the steel in the central columns of the towers.
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The central columns may or may have not been weaked. But as I understand it, that isn't what cause the collapse. The trusses were weakened and collapsed (due to the fire). That removed the ability of the central columns and the external steel structure to support each other. The external structure gave way.
 
valis,

I lived in NYC at the time. I visited the Towers on several occasions. I saw them fall. Not, as most other people, on TV, but for real. If you didn't get a chance to see them, you would simply not believe how huge these constructions were. They were not "towers", but mountains of steel. They dominated the Manhattan Skyline, a view that is filled with the most awesome buildings in the world.

But big passenger planes, fully loaded with jet fuel, hammering mercilessly into these structures?

Instant hell.

Fireballs the size of football fields. Everything burned: Paper, carpets, inventory, people. The temperatures were immense. What could burn, did. What could melt, did.

I am a great admirer of the scientific endeavours of mankind, but I cannot see how any structure could have withstood the attack of such huge planes. It is ludicrous to even consider building megastructures that can withstand a big passenger plane hitting it at full speed, with full tanks.

To cast doubt on how these buildings fell is to piss on the victims and their families.

That makes me mad.
 
Ririon said:
Newton says so. :) If a skyscraper was weakened at the base AND there was a very strong wind, then it might fall to one side while collapsing.
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In a TV special shortly after the collapse, I remember hearing about an engineering principle that explained why the towers went straight down. When a tall building is designed, it is engineered to take vertical stresses from gravity -- NOT diagonal stresses. It is designed to sway a certain amount, but never over a certain limit. Thus, if a tower leans more than a certain number of degrees, it is no longer able to support its weight and drops straight down. If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.

I only heard this explanation once, and its never been mentioned since then, as far as I know.
 
A few years ago my brother slipped on the floor of a public restroom and broke his leg. It was a brutal tib-fib fracture that required surgery and sent several small emboli into his lungs. To this day I can't imagine how a healthy adult in the prime of his life could injure himself so badly by slipping on a bathroom floor -- yet it did happen. I'm sure if I was there, I would understand in an instant how it could happen.

My point is, there are many things that happen that seem to defy common sense. That is simply because common sense is often wrong. It only applies to predictable, commonplace events. Something that is totally outside our experience does not always conform to our expectations. The conspiracy theorists don't seem to understand this.

Would they also cry "foul" when told that Japanese torpedoes in Pearl Harbor were able to sink ships ACROSS THE HARBOR from the ships that they hit, just from the shock wave of the explosion? It seems impossible to me, but then, I wasn't there, nor am I an explosives expert. So I trust those with more experience when they tell me what happened.
 
aggle-rithm said:
In a TV special shortly after the collapse, I remember hearing about an engineering principle that explained why the towers went straight down. When a tall building is designed, it is engineered to take vertical stresses from gravity -- NOT diagonal stresses. It is designed to sway a certain amount, but never over a certain limit. Thus, if a tower leans more than a certain number of degrees, it is no longer able to support its weight and drops straight down. If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.

I only heard this explanation once, and its never been mentioned since then, as far as I know.
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Actually, that's not the way things happened. It would take a LOT of lean--It's in that report linked elsewhere, so I don't know haw far, but we're talking BIG lean...
To demonstrate what happened, go get a beverage-of-your choice in acan, and drink it.
Set the can on the floor with the opening up. very carefully, place one foot on the can, and gently transfer all your weight to the can, so you are standing on it. If you are less than 225 lb weight, it will hold you up.
Now, get off the can, and do it again, only this time, transfer your weight all at once-or, if you are small, start with your foot 2" above the can and step on to it.
No difference in weight--just that the same weight impacting the can casuse collapse. That's what happened when the collumns bowed, and several floors worth of debris dropped onto a single floor.
 
rwguinn said:
Actually, that's not the way things happened. It would take a LOT of lean--It's in that report linked elsewhere, so I don't know haw far, but we're talking BIG lean...
To demonstrate what happened, go get a beverage-of-your choice in acan, and drink it.
Set the can on the floor with the opening up. very carefully, place one foot on the can, and gently transfer all your weight to the can, so you are standing on it. If you are less than 225 lb weight, it will hold you up.
Now, get off the can, and do it again, only this time, transfer your weight all at once-or, if you are small, start with your foot 2" above the can and step on to it.
No difference in weight--just that the same weight impacting the can casuse collapse. That's what happened when the collumns bowed, and several floors worth of debris dropped onto a single floor.
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Even better, stand on the can as you first indicated, then have a friend tap the side of the can with a pencil while you're standing on it. Only a slight deformation of the aluminum, but it will instantaneously crumple (and straight downward, even though the force that initiated the collapse came from the side).
 
aggle-rithm said:
If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.
Click to expand...
This is true with the second tower that was struck (the South tower I think), and the first to fall. You can see the section of the building above the impact start to tilt as a single unit, before the area around the impact suddenly stops supporting it. This was the tower that the plane hit more on one side, and that side was the one to give way.

With the North tower, it fell straight down, and you can actually see the TV tower on its top begin falling well before the outer walls. It collapsed from the middle. This tower was struck in the middle, so its center supports were likely more damaged.
 
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