erp… I pasted the URLs in the wrong order… the first one is the one I consider better, though the Trib article has more history on planes and buildings.
Well, I taped the news and got a few good quality clips of the second 767 impact. By counting frames, and looking at the various lengths of the 767 family, I can say that the most conservative estimate for speed was about 540 mph, which is the 767-300 cruising speed. And I feel like that’s probably a little low–that it was closer to 600 mph.
I saw the chief architect of the WTC and you guys are right. He said that the building was design to withstand fires of up to 1200 degrees for 1 to 2 hours.
He said the steel melted and the rest was a domino effect.
This is evident if you watch closely the footage of the south tower collapsing; you can see it going down floor by floor.
For a somber laugh, Charlie Gibson on Good Morning America just reported that the fires were “15,000 to 16,000 degrees F”, which means that the steel was likely plasma…right.
They also reported on the “specialized knowledge” required to know how to bring a building down in this manner. That same specialized knowledge is also possessed by or available to most Sophomore Civil Engineering students, and anyone who reads an book on famous building fires. When I saw the fire live on TV, within 5 minutes of the crash I knew the Towers were going to be coming down, based on the level of fire - although I predicted it would take another hour.
It was horrific, and I pray I never see it again.
I know that you were talking about the ESB. The odds are much higher that the walls are load bearing in the ESB than in the WTC. The white stone exterior of the WTC was just a facade, not load bearing. The earliest sky scrapers were limited by the fact that the walls had to be load bearing, that is why they were limited in height. THe higher they went, the larger the exterior walls would have to be at the base. Once improvements were made in concrete and in construction methods were truly large buildings able to be constructed. The structural load of the WTC was almost certainly supported by the core of the building.
I saw Peter Jennings interview this guy, too. At the end of the interview, Peter asked him if there was anything else that could have been done to keep the buildings from collapsing, the guy was at a loss for words, obviously trying to find a tactful way to say, “Well, if we can keep people from flying airplanes into them, that’d help a lot…”
A third bldg also fell & wasn’t hit by any planes. What about that one? Wasnt it like 45 stories?
#7 WTC was 47 stories high. Even though it wasn’t hit by either plane, it was hit by a tremendous amount of debris when the towers collapsed, and there were also reports of fires fueled by gas leaks. Other buildings in the general area are also reported to have been severely damaged by falling debris and fires.
I’ve seen articles that stae there was around 200 thousnad tons of concrete in the WTC, add to that the steelwork and everything else.
Even a grazing blow from a collapsing structure like this would flatten or seriously damage any other nearby building, and that is aside from the airwave shock which will have impacted much of the vicinity.
I just read a really interesting book called “Why Buildings Stand Up.” What a timely read, eh?
The author explains that when buildings are designed, 3 types of loads are taken into account (Hopefully I have the terminology correct). The building is built to withstand the following types of loads:
Dead loads: This is the weight of the building itself, and of its permanent systems and features.
Live loads: These are loads that do move around in the building, but relatively slowly: People, goods, furniture, non-load bearing walls. Based on the intended use for the building, you can make a good estimate of what the live loads will be.
Active loads: These are the loads that build up very very quickly, and they are much more stressful to the structure than live loads, because their force is so great and so sudden. Wind is the big one that is always taken into account with tall buildings. Many buildings are also built to withstand earthquakes. And I suppose buildings are designed to withstand any expectable impacts from the outside. Buildings are built as sturdily as they are to withstand this third type of load.
The big planes hitting the buildings were certainly in the third category–an enormous sudden force. It seems that the buidings actually initially survived these impacts! But when the top floors collapsed, they produced a humongous active load that the rest of the building could not withstand.
After the first one fell, the shared foundations were probably so damaged that the whole load-bearing capability of the other building was really messed up. The vibrations and debris of the main towers falling were surely enough to cause major structural damage to surrounding buildings.
So, yes, is it easy to see that the plane crashes alone were enough to topple the towers.
One of the (many) news reports I watched last night mentioned that the WTC towers were “tube” buildings, with the outer surface being the load-bearing structure. Apparently, this saves weight and allows for taller buildings.
From the Discovery Channel web site:
And
The absence of load bearing walls is what allowed for the modern skyscraper.
adam yax, read the link Ino provided. In it they say
and (emphasis mine)
Kinetic energy = 1/2 * mass * velocity^2
200 mph = 320 km/h = 90 m/s (approx.)
So (using metric) 1/2 * 186,880 kg [liftoff weight] * (90 m/s)^2 = approximately 750,000,000 Joules.
A ton of TNT releases 2,977,789,639.02084 Joules.
So you ave about 500 lbs of TNT in one plane crash. So the WTC had a half-ton of TNT smash into it between the two planes.
Now the fuel calculations based on the values from Chevron:
The Jet fully fueled carries 90,770,000 mL. Assuming some was lost, I’ll round down to 90,000,000 mL. So choosing 42 MJ/Kg and 0.8 g/mL (based on the middle of the boiling point spectrum for Kerosene-type fuels), we have 42,000 J/g * 0.8 g/mL * 90,000,000 mL = approx. 3E12 Joules. Which is about 3000 tons of TNT per plane. That’s much higer than the original 700 calculated. (Although someone might want to recheck my calculations in case I screwed up somewhere.)
According to http://www.ymp.gov/documents/rpb536m3_b/main.htm: The specific heat of carbon steel (grade 1025) for temperatures of 50 to 200°C range from 486 to 519 J/kg. Now I don’t know what grade of steel was used in the WTC, but with a potential energy of 3E12 Joules, it only takes a small percentage of that to melt a kilogram of steel.
So there was plenty of energy in one plane to melt the steel.
Thanks to all for your responses.
I saw an interview with one of the guys from Controlled Demolitions Incorporated and he said that it was a known fact that this type of thing was going to happen sooner or later. And like the chief architect for the WTC, he basically said that there’s not much you can do, other than preventing people from crashing planes into buildings.
I saw a brief note on the news that the WTC was built to withstand the impact of a Boeing jet.
See above how I concluded that the collision speed was closer to 600 mph.
Also, you have that energy being delivered to the fuel. Quite a lot of ignition energy.
We calculated the same number of Joules, but we apparantly disagree on the energy in one ton of TNT. Every reference I’ve seen pegs it at 4.1810[sup]9[/sup] Joules, whereas you’re quoting 2.9810[sup]9[/sup] Joules. Furthermore, even if I use your numbers I get 1000 tons of TNT, not 3000.
Yes, I heard/saw the same thing (CNN I think).
But the reference was to a smaller jet. 727 I think.
I don’t know much about aircraft, but I looked at the Boeing site and found the 727 could hold about 8000-9000 gal of fuel.