On 17/09/18 19:51, juan wrote:
On Mon, 17 Sep 2018 03:24:39 +0100 Peter Fairbrother <peter@tsto.co.uk> wrote:
But it didn't need any explosives, hand-positioned thermate, or the like - the burning jet fuel would do that to a building like WTC.
sure - because when the buildings were designed to withstand a plane crash, nobody was aware that planes have 'fuel' in them.
The designers simply never considered the combination of impact and fire. It wasn't required in the 70's when WTC was built - still isn't generally required. I don't know if you remember, but at the time it was built there was a whole lot of safety criticism and safety politicking of the design. That all seems to have been conveniently forgotten after 9/11. Architects don't consider every possible disaster scenario - in general they just do what the building regulations tell them to do.
nobody realized that "burning jet fuel would do that to a building like WTC"
Oh yes they realised. Look closely: WTC was rated for 3 hours major fire resistance. Put that another way - *it was rated so that it _would_ collapse after 3 (or so) hours of major conflagration*. It's in the design docs. The reason it didn't last even that long is that the 3-hour rating relied on insulation applied to the interior steelwork, and that insulation was disrupted by the impact. I guess WTC7 was designed the same way - it lasted 7 hours because the fire was less intense, there was no damage to the insulation, and the 3 hours is a minimum rating. But I'm only guessing. As to why a 3-hour rating was considered acceptable: I don't know, but speculating, I expect they didn't consider it likely that there would be 80 tons of JP-4 to fuel the blaze, so a blaze lasting longer than 3 hours would be unlikely. Speculating again, if it had burned for 3 hours it would be so badly damaged that it would have to be knocked down anyway; and everybody was supposed to be out after 3 hours, so it wouldn't matter if it collapsed. And again, if they wanted any more fire resistance, it would have been too expensive to build.
...You can see a huge ball of fire when one of the planes(?) hit. Guess what was that fireball? Well it must have been fuel no? Oops, so it didn't burn inside the building.
That's maybe 50 gallons of fuel actually burning. See movie special effects. The rest - the fuel still in the tanks, and liquid fuel inside the fireball which didn't have air to burn it - mostly went into the building, though some fell all the way to the ground while still on fire (and burned some people). The thick black smoke which came from the building for about 1/2 hour is jet fuel burning badly, ie where there isn't enough oxygen. After a while the smoke thins, the fuel/air ratio has become more favourable, carbon burns to carbon dioxide rather than carbon monoxide giving off more heat, and the temperature rises even more. NIST (I'm a cryptographer, a real one, got paid for it before I retired, been a cypherpunks subscriber for 16 years, you can guess what I think of NIST) - anyway NIST reckoned that the flame temperature in the center where the inner steel supports were got to 1000C. It could have done, but the yield stress of A36 steel at 1000C is 6% of it's RT yield stress, it would have been like cooked spaghetti. I don't think the steel got that hot, more like 650-800C.
So how is it that you "know a lot about metal"? Does your knowledge come from teh US military PSYOPS department?
10 years of designing alloys. Mostly for rocket engines. :) Plus a lot of explosion theory, analyses of several hundred actual unintended explosions, and occasionally actually blowing stuff up ...
you mean the thermal protection was 'shattered' im the 200 floors of the two towers? OR at best it may have been damaged in PARTS of a COUPLE of floors?
The latter. The rest of the steelwork in the building was unaffected by the impact or the fire.
The steel never melted, nor did it come close to melting - but there was a lot of fuel, and the whole of two or so floors was on fire. That's a lot of heat in one place. The word "inferno" comes to mind.
so the whole building collapsed because a couple of floors burned.
Yup. That's how it was designed, and that's what it did. Was the design crap? With hindsight, frankly, yes. -- Peter Fairbrother