# Would a plane crash be enough to take out a WTC tower? **URL:** \ **Category:** Factual Questions\ **Created:** [September 11, 2001, 6:07pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890 "2001-09-11T18:07:33Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![bughunter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bughunter](https://boards.straightdope.com/u/bughunter)\ **Post date:** [September 12, 2001, 12:35am UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/21 "2001-09-12T00:35:17Z")
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. ---
**Author:** ![emarkp](https://avatars.discourse-cdn.com/v4/letter/e/3be4f8/32.png) [@emarkp](https://boards.straightdope.com/u/emarkp)\ **Post date:** [September 12, 2001, 3:38am UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/22 "2001-09-12T03:38:19Z")
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. ---
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [September 12, 2001, 6:30am UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/23 "2001-09-12T06:30:48Z")
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. ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [September 12, 2001, 12:38pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/24 "2001-09-12T12:38:28Z")
> [@](#): > > \*Originally posted by Markxxx \* > \*\*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. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [September 12, 2001, 1:06pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/25 "2001-09-12T13:06:52Z")
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. ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [September 12, 2001, 1:22pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/26 "2001-09-12T13:22:49Z")
> [@](#): > > \*Originally posted by RealityChuck \* > \*\* > > > [@](#): > > > > Originally posted by RealityChuck > > The load on the ESB is carried by the inner framework and, from a structural point of view, the outer walls are just there to keep the wind out. > > I think that you have this backwards. > > No. I was talking about the Empire State Building, which is different from the World Trade Center. \*\* 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. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [September 12, 2001, 1:23pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/27 "2001-09-12T13:23:30Z")
> [@](#): > > \*Originally posted by Markxxx \* > \*\*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. \*\* 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…” ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [September 12, 2001, 3:21pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/28 "2001-09-12T15:21:51Z")
A third bldg also fell & wasn’t hit by any planes. What about that one? Wasnt it like 45 stories? ---
**Author:** ![Fillet](https://avatars.discourse-cdn.com/v4/letter/f/2acd7d/32.png) [@Fillet](https://boards.straightdope.com/u/Fillet)\ **Post date:** [September 12, 2001, 3:43pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/29 "2001-09-12T15:43:55Z")
> [@](#): > > \*Originally posted by handy \* > \*\* > 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. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [September 12, 2001, 4:44pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/30 "2001-09-12T16:44:43Z")
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. ---
**Author:** ![Green\_Bean](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/green_bean/32/1760_2.png) [@Green\_Bean](https://boards.straightdope.com/u/Green_Bean)\ **Post date:** [September 12, 2001, 5:02pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/31 "2001-09-12T17:02:27Z")
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. ---
**Author:** ![Kilt-wearin\_man](https://avatars.discourse-cdn.com/v4/letter/k/82dd89/32.png) [@Kilt-wearin\_man](https://boards.straightdope.com/u/Kilt-wearin_man)\ **Post date:** [September 12, 2001, 5:02pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/32 "2001-09-12T17:02:49Z")
> [@](#): > > \*Originally posted by adam yax \* > \*\* > > > [@](#): > > > > \*Originally posted by RealityChuck \* > > \*\* > > > > > [@](#): > > > > > > Originally posted by RealityChuck > > > The load on the ESB is carried by the inner framework and, from a structural point of view, the outer walls are just there to keep the wind out. > > > I think that you have this backwards. > > > > No. I was talking about the Empire State Building, which is different from the World Trade Center. \*\* > > 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. \*\* 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. ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [September 12, 2001, 6:07pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/33 "2001-09-12T18:07:34Z")
From the [Discovery Channel](http://www.discovery.com/stories/technology/buildings/buildings.html) web site: > [@](#): > > Before the inventions of steel and elevators, a building with useable interior space could only go so high before its stone and brick facade would collapse on itself. The Egyptians managed to take the Great Pyramid of Cheops to a whopping 482 feet in 2600 B.C., but in order to support its height, the pyramid had to be built almost entirely of solid rock, leaving little interior space. And > [@](#): > > The World Trade Center’s tube-like towers were the first of the modern glass boxes to reach true skyscraper proportions, although their reign as tallest lasted only one year. After the age of ornate handmade structures like the Empire State Building came to an end, architects became enamored with the modern glass-box high-rise. These buildings were flimsier than the earlier skyscrapers and required different structural reinforcements to bring them to similar heights The absence of load bearing walls is what allowed for the modern skyscraper. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 12, 2001, 6:15pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/34 "2001-09-12T18:15:08Z")
**adam yax** , read the link **Ino** provided. In it they say > [@](#): > > “The World Trade Center was designed as a very large tube with steel columns on the perimeter of the building,” said John Cryan, president of Severud Associates, a structural engineering firm that provides consulting to skyscraper architects. and (emphasis mine) > [@](#): > > Built by the Port Authority of New York and New Jersey in 1973, the World Trade Center towers were the best examples of tube buildings of their time. Tube buildings are reinforced by closely spaced columns and beams **in their outer walls** , forming a steel tube. A series of glass windows fill in the space between the beams. And an internal core beam adds to the stability of tube structures. ---
**Author:** ![Hoopy\_Frood](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hoopy_frood/32/8452_2.png) [@Hoopy\_Frood](https://boards.straightdope.com/u/Hoopy_Frood)\ **Post date:** [September 15, 2001, 8:40pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/35 "2001-09-15T20:40:50Z")
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:](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. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [September 15, 2001, 9:13pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/36 "2001-09-15T21:13:38Z")
Thanks to all for your responses. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [September 15, 2001, 9:59pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/37 "2001-09-15T21:59:13Z")
I saw an interview with one of the guys from [Controlled Demolitions Incorporated](http://www.controlled-demolition.com/index.html) 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. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [September 15, 2001, 10:30pm UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/38 "2001-09-15T22:30:08Z")
I saw a brief note on the news that the WTC was built to withstand the impact of a Boeing jet. ---
**Author:** ![emarkp](https://avatars.discourse-cdn.com/v4/letter/e/3be4f8/32.png) [@emarkp](https://boards.straightdope.com/u/emarkp)\ **Post date:** [September 16, 2001, 6:20am UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/39 "2001-09-16T06:20:22Z")
> [@](#): > > \*Originally posted by Hoopy Frood \* > 200 mph = 320 km/h = 90 m/s (approx.) See above how I concluded that the collision speed was closer to 600 mph. > [@](#): > > 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. Also, you have that energy being delivered to the fuel. Quite a lot of ignition energy. > [@](#): > > 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. We calculated the same number of Joules, but we apparantly disagree on the energy in one ton of TNT. [Every reference I’ve seen](http://www.google.com/search?q=ton+tnt+joule) pegs it at 4.18_10[sup]9[/sup] Joules, whereas you’re quoting 2.98_10[sup]9[/sup] Joules. Furthermore, even if I use your numbers I get 1000 tons of TNT, not 3000. ---
**Author:** ![Seven](https://avatars.discourse-cdn.com/v4/letter/s/3d9bf3/32.png) [@Seven](https://boards.straightdope.com/u/Seven)\ **Post date:** [September 16, 2001, 7:05am UTC](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890/40 "2001-09-16T07:05:33Z")
> [@](#): > > \*Originally posted by handy \* > \*\* > I saw a brief note on the news that the WTC was built to withstand the impact of a Boeing jet. \*\* 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. [Previous page](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890.md?page=1) [Next page](https://boards.straightdope.com/t/would-a-plane-crash-be-enough-to-take-out-a-wtc-tower/80890.md?page=3)