A tip of the hat to the designers of the WTC.

Miscellaneous and Personal Stuff I Must Share
1

I’ve been present when a section of curtainwall decided to drop. Thankfully, that was on the third floor and nobody got hurt, but it was only pushed off by ice jacking. Did anybody notice that none of the curtainwall on the WTC sheared off until the final, catastrophic failure? Except, of course, that directly affected by the jets. But I expected that to start a chain reaction, shearing off the sections below.

Those guys did a terrific job of overengineering those buildings and deserve lots of credit for the survival of as many people as did survive. The final failure was as predictable as it was unavoidable, although my immediate reaction was, “Had that been framed with wood you’d have gotten another half hour out of it.”

“And you wouldn’t have gotten it a hundred stories tall, either,” said a coworker.

2

What impressed me was that the fall was vertical. If the towers had toppled horizontally, the disaster could have been much worse.

3

As the floors pancaked I think they would have forced the trend of the fall to be vertical. But it was fortunate.

4

The architects were Minoru Yamasaki and the firm of Emery Roth and Sons. The latter firm was also responsible for the Ritz Tower and the Pan Am Building. Information from Skyscrapers, author Judith Dupre, copyright 1996 by Black Dog and Leventhal Publishers, Inc.

5

Thanks, Baker.

6

From what I recall, Yamasaki was primarily a sculptor who had never before done a project of anywhere near the magnitude of the WTC. When he saw that the cost was going to be $270 million, he thought they meant to say $27 million.

Emery Roth and Sons, on the other hand, had many skyscrapers under their belt by that point. I’m not sure that anything of their design for the Pan Am building was actually used. Their plans weren’t grand enough, and they were replaced by Walter Gropius. (Source: same book, a few pages earlier)

7

Uhm, architects design what buildings look like. It’s the structural engineers who are responsible for making the architect’s designs actually “work.” In this case, that would be the engineering firm of Skilling, Helle, Chrstiansen, Robertson.

And unfortunately, dropzone, it wasn’t predictable in this case. The principle engineer, Les Robertson addressed a conference just the week before the tragedy and said that “their steel columns could remain standing if they were hit by a 707.” :frowning:

Cite: http://chicagotribune.com/news/nationworld/chi-010911kamin-towers.story

Jeg elsker dig, Thomas

8

It was predictable. They could (and did) survive the impacts, but it was the fire that did 'em in. It was well known that a major fire, especially that high up*, would soften the structural steel and drop the towers.
[sub]*–The asbestos coating on the structural steel was phased out around the 64th floor, making anything above that point more susceptible to fire.[/sub]

9

You know, that’s been confusing me all week. I read one article that said “the buildings were designed to withstand a hit by a 707, but that no one could have anticipated this.”

Isn’t that pretty much what this was? Were these planes that much larger than a 707? Also, as Gunslinger pointed out, it was the fire more than the crash. But I’ve got to ask … can you ever really have a crash without a fire? What would be the point of being able to take a crash if the building can’t tolerate the subsequent fire?

And one more point which will probably further demonstrate my ignorance of large buildings – I’m not sure the WTC had a curtainwall to begin with. One of the reasons it is unique is that the exterior wall is actually a supporting wall.

10

Shayna

Damn straight. Preach it sister.

And, seeing as how he beat me to the post, um, what Gunslinger said, about the jet fuel fire. Not only that, but the buildings survived the initial impact of a 767, which is larger and heavier than a 707. The 757* and 707 appear pretty comparable, based on the limited information given about the 707.

[sup]*The 757-200 link wouldn’t work, so I linked to the 757-300 instead[/sup]

11

The “impact of a 707” spec is pretty vague. I’m willing to bet the requirement was along the lines of a mass having the same mass and similar dimensions to the 707 impacting the building. Where? The corner? The center? Top? Bottom? Also, the temperature requirement would most likely be an entirely different spec, i.e. a flame and/or temperature requirement (IANACE, but I’m basing this guess on my knowledge of aerospace specs). Who knows if the potential heat resulting from burning jet fuel was given the same consideration as the stresses in the supports due to impact.

12

Sounds like we have some experts here… does anyone know if concrete burns when subjected to intense fires like in the WTC? ISTR reading something about that. Obviously no architect could possibly envision a situation where tons of jet fuel were injected into the top floors.

13

I know I’m going on and on about this, and I do believe the WTC was designed remarkably well, but I’m still annoyed about the claim that it could hold up to a jet crash. If the designer said (and he did) the building could survive a jet crashing into it, then he should have remembered that most jets do, in fact, come with jet fuel. Also, that if a jet were to accidentally crash into the building, the point of impact would most likely be more toward the top than toward the bottom.

I’m not quibbling that anyone should have planned or anticpated such a horrible attack when the WTC was built. I’m just peeved because that quote keeps popping up in the media as if there was something special (in terms of the laws of physics) about these planes that made this an exception to the otherwise true statement that the Towers could survive a jet.

Just so you all know I’m not an absolute maniac about this issue, I do see Strainger’s point that perhaps the reference was to “something as massive as a 707” as opposed to an actual plane crash.

And now for the non-obsessive part of this post:
According to my Newsweek, much of the concrete was incinerated by the high temperature of the fire.

14

They were built to withstand the impact of an passenger jet, but maybe not a passenger jet full of highly flammable fuel. It was the fire that did the towers in.

15

Concrete does not burn pre se, but under extreme heat flux (possibly greater than what you would see in the crash, I’m not certain) it can crack and spall as the temperature differential becomes too high. Due to its granular nature, the cracks sometimes don’t propagate fast enough to cause a problem, but sometimes they do. And I’ve read of occurances where the fire was so hot the steel in the reinforced concrete melted completely, and of course when the steel in the reinforced concrete either softens or melts, the overall beam/pillar loses a huge proportion of its strength, and is likely to give.

Certainly though, steel-reinforced conrete is far more fire resistant under normal conditions than steel.

16

Yes, concrete can burn under extremely hot temperatures. Here is a link to a bit on thermal lances. These operate in the temperature range of 1800 C to 4430 C, depending on which source you look at on the page.

Typical temperatures given for concrete’s breakdown point (different than burning) are in the range of 2000 F. So, Newsweek could be misquoting, or misunderstanding. Breakdown and burning are not the same thing, but as far as the WTC was concerned it may as well have been.

17

How about the dehydrating effect of the heat? Would it drive off the water and reduce the cement to powder?

18

The first thing that I thought when I saw the first tower got down was “Oh my god!”

My second thought (several seconds later) was a very fervent “Thank God for engineers!”

19

Our Architecture school is sponsoring some talks about this. This Friday they’re discussing the structural failure, but in future weeks they’re going to talk about the role of architecture and urban planning in this sort of thing.

I’m furious that a conflict keeps me from attending, but Mr. Cranky (a degreed architect, though not a practicing one) hopes to make it.

20

The 707-320
Maximum Fuel Capacity ~23,000 gal
Maximum Takeoff Weight 328,060 lb (149,118 kg)

The 757-200 and 757-300
-200
Maximum Fuel Capacity 11,276 gal (42,680 l)
Maximum Takeoff Weight 255,000 lb (115,680 kg)
-300
Maximum Fuel Capacity 11,466 gal (43,400 l)
Maximum Takeoff Weight 272,500 lb (123,600 kg)

The 767-200, 767-300 and 767-400ER:
-200
Maximum Fuel Capacity 23,980 U.S. gal (90,770 l)
Maximum Takeoff Weight 395,000 lb (179,170 kg)
-300
Maximum Fuel Capacity 23,980 U.S. gal (90,770 l)
Maximum Takeoff Weight 412,000 lb (186,880 kg)
-400
Maximum Fuel Capacity 23,980 U.S. gal (90,770 l)
Maximum Takeoff Weight 450,000 lb (204,120 kg)

(Source: Boeing)

So, on the face of it, the 707 fell somewhere between the 75 and 76, fuel and weight-wise. It was a four-engine aircraft while the others were two, but the top operating speeds were fairly similar (though efficiency was a different matter.)

I think, all things considered, saying that the buildings could withstand a strike from a 707 was more of a thought experiment than a fully factual statement and dealt more with sustaining the impact of the crash and perhaps a small fire than it did with the impact of the crash, slicing the supporting wall and spewing a nearly full load of fuel throughout a number of floors.

That said, I’m still amazed that they fell and am surely glad that they stood for as long as they did.