ADVISORY: "Nova" to air "Why The Towers Fell" Tuesday, April 30

PBS ^ | April 29, 2002

[areafiftyone]

Thanks for posting this reminder. I just clicked on the website and read Brian Clark's story. It brought that day right back into my mind. I will never forget! WE MUST NEVER FORGET!

[epluribus_2]

it had better not be about why we need to understand why they hate us...yada yada... or the "Bush administrations lack of engagement in the mideast peace process..." or ANYTHING having to due with palestinians. They fell because of the islamic hatred of a group of subhuman maggots who have no place in this millenium - or the last one for that matter.

[pikachu]

Any Freeper know if there is any thruth the urban legand that the hijackers, due to their lack of real flying experience, ran the port tank nearly dry before crashing into the WTC? Supposedly the out of balance aircraft caused more damage because shift the kinetic energy into the starboard wing actually, for a fraction of a second, caused the right side to expand!! They are calling it the 'vast right wing conspiracy'.

</groan> :-)

[epluribus_2]

(I know it's about the engineering but you know how PBS likes to slip the knife into the ribs of the Right when they can...)

[dead]

Thanks for the ping.

Nova does great work (when they stick to non-political things like astronomy or engineering.)

[Harrison Bergeron]

This was published only weeks after the attack. It's still the most comprehensive explanation out there. I'd be surprised if Nova has anything more believable or accurate.

[JoeGar]

I'm interested in knowing if they air the fact that there was no asbestos insulation on the steel piers (to keep them from melting). (I've read that the asbestos was not used to satisfy the environmental wack-os of the time.)

[ao98]

I just read the linked interview with Dr. Thomas Eagar, a professor of materials engineering and engineering systems at MIT. It's a very interesting interview where he concludes that the first parts to fail were the clips that connected the floor to the outer structure.

He makes no mention of the fire proofing. I hope it's mentioned in the show but I doubt it.

[Pyro7480]

I saw a documentary on the History Channel or the Learning Channel along these lines sometime over the past couple of months. It quoted a fireman saying an old rule of thumb amongst firemen is "Never trust a truss." If I remember correctly, the documentary went over how the floors of the Towers consisted of trusses lined up next to each other. The reason why the Towers rose so quickly during construction is because the walls and the floors were prefab, and all that needed to be done at the site was the raise them into place and attach them (oversimplifying the process, of course). When the jet fuel was ignited in the areas affected by the impact of the planes, it weakened the trusses of the floors in these areas, causing them to sag in the center, until the weight of the material on each floor became too much for the sagging trusses to hold, causing the floors to pancake one on top of the other. I think the footage of the Towers' collapse and the evidence from the rubble supports this theory.

[gridlock]

The towers fell because Islamic terrorists flew fully fueled airliners into them. At the moment of impact, the result was inevitable. The exact mode of failure may be interesting from an engineering point of view, but is not relevant otherwise. The forensic studies of this structure will be used to design the next-generation hardened structures. But to suggest that there was any negligence in the design or construction of the towers mitigates the culpability of the evil men who perpetrated these attacks.

From everything I have seen, the towers were a marvel of innovative and intelligent design. Unfortunately, there are some parameters which are beyond the scope of what is designed for. Airliners smashing into the upper floors at 600 mph is one of those things. If every design were require to withstand every concievable event, we would all be living in holes in the ground, and there would be no skyscrapers (and precious few two story buildings).

[geaux]

According to post #8 on this thread, there was no asbestos; crews were prohibited from using it.

[ao98]

Here is a link to the original story about the lack of asbestos in the upper floors. I have been looking for confirmation of this story, but engineering studies on the collapse of the WTC that I've seen have not mentioned asbestos.

[Kay Soze]

Clinton already told us why they fell:

"This country once looked the other way when a significant number of native Americans were dispossessed and killed to get their land or their mineral rights or because they were thought of as less than fully human.

"And we are still paying a price today,"

The Washington Times

www.washtimes.com

Clinton calls terror a U.S. debt to past Joseph Curl

Published 11/8/01

[Jay W]

I'm interested in knowing if they air the fact that there was no asbestos insulation on the steel piers (to keep them from melting). (I've read that the asbestos was not used to satisfy the environmental wack-os of the time.)

As the links posted by others indicate, asbestos was used in the construction of the building, up to about halfway up. Then, during the time the towers were still under construction, asbestos was outlawed, and the remaining stories were built with some "substitute."

It's an open question whether the towers would still be standing if asbestos had been used all the way up. Possibly they may have stood. Alternatly, maybe they would have still fallen, but stood for a longer period of time, thus enabling more people to escape.

Either way, the decision to not continue to use asbestos was a political decision, not an engineering one.

[supercat]

It's an open question whether the towers would still be standing if asbestos had been used all the way up. Possibly they may have stood. Alternatly, maybe they would have still fallen, but stood for a longer period of time, thus enabling more people to escape.

I doubt it would have made that much difference. From what I've read, most of the people killed were either above the initial point of impact or were rescue workers who were not, at the time of collapse, trying to leave the building.

When trying to fireproof a structure, there's a tricky design issue of whether it's better to have the insulation over the structure as a whole (in which case heat from a fire in one part of the structure can dissipate into other parts, preventing localized meltdown), or whether it's better to have individual parts insulated separetly (in which case heating effects will be localized, but there's more likely to be a localized failure).

I don't know which design approach was used in the WTC, but both would have been problematical. My guess would be from the pictures I've seen that the former approach was used. Such an approach would be best in case of a fire which was not accompanied by much structural damage (most fires would probably fall into this category). In such a case, all that is necessary for the structure to survive is that the metal-to-metal heat tranfer away from the fire through the ends of the involved beams be fast enough compared to the air-through-insulation-to-metal heat transfer from the fire. Given that the frame of the building as a whole has a very large thermal mass, this would normally not be a problem.

The plane crash, however, created a problem: many structural members were ripped apart. The loss of structural support from such members would not have been a problem, but unfortunately the ends of such members would have had substantial areas of exposed metal. While heat damage to these elements themselves would not have been a problem (they were structurally useless at that point anyway) they provided a means by which heat could be conducted to the elements that had up to that point not failed but which now had to bear substantially greater than design loads.

BTW, I forget the exact figures, but I calculated the amount of potential energy unleashed with the collapse of that building. That was a pretty darned big number.

[X-FID]

It's an open question whether the towers would still be standing if asbestos had been used all the way up. Possibly they may have stood. Alternatly, maybe they would have still fallen, but stood for a longer period of time, thus enabling more people to escape

In the south tower, that plane cut through it like a hot knife through butter before it exploded, I don't remember what floor area it hit at but it was much lower than the first. It was basically like having a 20 or 30 story building with very little support left sitting on top of the rest of the building, I doubt having more asbestos would have made any difference.

The heat at that point had to be tremendous, but even without it I think both towers were doomed and would've collapsed anyway, asbestos wasn't the problem IMHO

[dr_who]

Fire. Insufficient insulation to prevent the fire from melting the girders. There you have it.

[supercat]

Insufficient insulation to prevent the fire from melting the girders.

I think there's another important ingredient: structural members which had no insulation because of impact damage.

[Timesink]

late night bump