Why the WTC Towers Fell - on PBS

[Focht3]

For U.S. (and perhaps some Canadian) members of [green]Eng-Tips[/green] members: here is an interesting program on the collapse of the World Trade Center towers. It is based on the ASCE investigation and report. It's a good place to direct your curious non-engineer friends who want to understand why the towers fell. Here's the link for additional information as well as the press release I received by email:

http://www.pbs.org/nova/wtc/

_____________________________________________________________________
NEXT ON NOVA: "WHY THE TOWERS FELL"

http://www.pbs.org/nova/wtc/

Broadcast: September 9, 2003
(NOVA airs Tuesdays on PBS at 8 p.m. Check your local listings as
dates and times may vary.)

For most Americans, the image of the collapse of the World Trade Center
towers was not only a scene of unforgettable horror, it was a moment of
unimaginable consequence. Who could have guessed that a steel behemoth
of such size and strength -- a building so massive that it had its own
zip code -- could actually be reduced to 150 feet of dust and rubble? In
the Emmy-Award winning "Why the Towers Fell," NOVA reports on the
findings of the government-mandated American Society of Civil Engineers
(ASCE) investigation.

Here's what you'll find online:

Towers of Innovation
A basement like a bathtub. A building like a tube. An
elevator system like a subway system. These are just some
of the engineering marvels that made the quarter-mile-tall
World Trade Center possible.

The Collapse: An Engineer's Perspective
In this interview, Dr. Thomas Eagar, a professor of materials
engineering and engineering systems at MIT, explains how and
why the Twin Towers survived the initial impact -- and how
and why they likely failed in the end.

Above the Impact: A Survivor's Story
Brian Clark was one of only four individuals to escape either
tower from above the floors where the planes struck. Here, Clark
tells his riveting, vividly personal tale.

Outfitting Firefighters
The firefighters that raced up the stairwells of the doomed
towers carried several dozen pounds of equipment, everything
from axes and turnout gear to thermal imaging cameras and self-
contained breathing apparatuses. In this feature, equip fire-
fighters for a high-rise response.

The Structure of Metal
Explore metal at the atomic level and discover how it's structured,
why it bends, and what happens when it heats up.

NOVA News Minutes
Watch news clips related to the program.

Plus Resources.

http://www.pbs.org/nova/wtc/

_____________________________________________________________________
_____________________________________________________________________

Thank you for visiting NOVA Online. We welcome your questions, comments,
and feedback. You can send a message directly to nova@wgbh.org, or use
our feedback form at

http://www.pbs.org/nova/feedback/

You are subscribed to the NOVA Online mailing list. To unsubscribe, go
to

http://www.pbs.org/nova/mailing/unsubscribe.html

-- or send an e-mail
to majordomo@franz.wgbh.org and, on a line by itself in the message,
type: unsubscribe nova-online

Major funding for NOVA is provided by the Park Foundation, Sprint, and
Microsoft.
_____________________________________________________________________





Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[IRstuff]

Is that a re-run?

I remember seeing a Nova on the WTC towers either much earlier this year or late last year.

TTFN

 

[Focht3]

I'm pretty sure it is a re-run; but I'm not certain -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[AJUK]

We have had several documentaries in the UK covering this subject. No doubt some of the material used in the program is from the same source. In the documentary over here they had an interview with Mr Robertson, the structural engineer who lead the design team, and I really felt for him. He seemed to be devestated at the fact that he couldnt forsee such a terrible act - who could!

As a structural engineer myself, I consider the solution for the buildings to have been an elegant and clever design and the engineer did absolutely nothing wrong.

Perhaps when the program has aired Focht3 and others could post with a summary of the findings and we could discuss the facts and compare with the documentaries others have seen.

Regards

 

[Bbird]

On the day I saw the news I had this idea that Binadin's plane killed less than a hundred with the initial plane impact. It was the engineering design that kill the thousands.

I fully agree with some of the posters here that it was not in the scope of design of the towers to include terrorism provision at that time. The structural engineer is therefore not to blame. We now live in a world different to the designer of the twin tower and we have to think of the terrorist risks.

I have been puzzled by only one feature on the collapse of the twin tower. Are the terrorists really that clever or it was down to pure luck? They had to have to access to world experts on structural engineering, tall buildings design, material science, aeroplane design, daynamics and combustion engineering to pull it off as they did. I know Binadin is just a huge civil engineering contractor in Saudi but I am not convinced he had the necessary know how. Seems to me it was Binadin's own mistake because of his lack of engineering appreciation to understand the consequence. That action led to thousands of his followers died and his base uprooted in Afganstan. He can no longer openly exists anywhere in this world and his religion suffers a bad name for generations to come.

 

[dik]

There was an earlier discussion on the collapse of the towers in one of the eng-tips fora... I've tried searching for it without avail... If anyone can dig up the thread, it would be appreciated...

 

[Focht3]

I can't quote the source, but I recall hearing that OBL (Osama bin Laden) was surprised that the towers fell. He had not anticipated that outcome; many others (myself included) were surprised as well. I think it was the prolonged heat from the fuel that was the unexpected factor.

I suspect we all have a much healthier respect for the potential consequences of fire, particularly where a large pool of accelerant is involved -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[EnglishMuffin]

Focht3:
My recollection is the exact opposite. I remember a private videotape made in Afghanistan and recovered from there after the war, in which OBL was seen sitting around with some other guys and saying (according to the translation) that he had predicted that the towers would fall after the impacts, and that his expertise in the family construction business enabled him to do this. Of course, whether he had actually made such a prediction, or was just being wise after the event, is a debatable point.

 

[Bbird]

It was easy for OBL or any or his guys to claim credits but any educated person will know his head would be on the line thereafter with the full might of the world after his ass. Can anybody be stupid enough to sign his own death warrant by risking the hatred of the whole world?

I was surprised by the collapse too. I think it would be right to say if the planes had very little or no fuel left then the two towers should have stood because the fire risk would be low.

The progressive collapse within the central core, pulling the outer shell neatly to the inner is unseen and unheard before the disaster. I doubt if any structural engineer has set out to engineer a collapse intentionally, for all intents and purposes, within the footprint of such a tall building.

 

[Focht3]

[blue]EnglishMuffin[/blue]:

We are both right - and wrong...

I found the following link to NPR's web site (after a Google search for 'Osama world trade center collapse videotape'):

http://www.npr.org/news/specials/response/investigation/011213.binladen.tape.html

An excerpt from that site says,

According to a translated transcript issued by the Pentagon, bin Laden says the attacks on the World Trade Center did more damage than expected. "...we calculated in advance the number of casualties from the enemy, who would be killed based on the position of the tower," he says, according to the transcript. "We calculated that the floors that would be hit would be three or four floors. I was the most optimistic of them all. (...Inaudible...) due to my experience in this field, I was thinking that the fire from the gas in the plane would melt the iron structure of the building and collapse the area where the plane hit and all the floors above it only. This is all that we had hoped for."

I can't wait until we catch that guy -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[IRstuff]

The PBS documentary is a re-broadcast. The structural engineers that performed the post-mortem concluded that the high heat from the fuel load weakened the structure.

In any case, the collapse was un-anticipated, since the structure was designed to handle a 707 impact with margin. Had OBL thought that the towers could be brought down and or thought through the amount of potential damage, he would have designed for a lower strike point on the tower, i.e., down to possibly the 40th floor. This would have been above the capabilities of any ground-based fire-fighting equipment, while maximizing the possibility of causing the towers to weaken and fall sideways, which would have increased the potential damage.

It's more likely that OBL thought that the towers would pancake down to the impact site and no further, which would have left two damaged towers as a constant reminder of his power. It would have taken much more than 8 months to clean up and would have taken many more months to repair or rebuild. I suspect that a full collapse was undesirable, since that would have meant a relatively quick clean up and no obvious reminder of his deed in the skyline.

TTFN

 

[EnglishMuffin]

Focht3:
Well, if he was really smart enough to figure out that it was definitely going to collapse "all the floors above", he should have been able to deduce that the whole tower would subsequently collapse - it would seem to me that this would be the simpler part of the analysis. Perhaps he was just referring to the local part of the floors directly above the impact - you'd have to be a real expert in Arabic translation to know.

 

[Focht3]

Perhaps. And perhaps we are giving him too much credit for his intelligence. After all, any fool can be an anarchist...



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[EnglishMuffin]

Focht3
When I first glanced at your reply I thought it said "any fool can be an architect" .... perhaps something deep and Freudian there ....

 

[msajjadh_imported]

Please read this as well

http://www.sumeria.net/politics/bushknew/ghostriders2.html

 

[redhead]

Just a thought that occurred to me immediately after the collapse. If the Towers had had a slip-formed concrete core, they might have survived.

 

[Bbird]

Reading msajjadh's suggested website confirms me that there is a lot of misinformation around.

Good job we engineers base everything on facts and experience.

 

[unclesyd]

Both the History Channel and PBS ran documentaries on the WTC last evening.
One thing that occurs in the videos of the WTC after the planes hit is that one can see the floors failing. This hasn’t been mentioned in any of the commentary on the collapse that I’ve seen.
The failure of the floors can be readily ascertained by the “jets” of dust and debris being ejected from the tower at a point that appears to 20 to 30 floors below the mass of the failed section above the impact.

I think the plan was to duplicate the plane crashing into the Empire State Building and as mentioned above leave a symbol in the sky. But one still has to wonder as Osama had a lot experience in construction and probaly engineering help. Atta was an Architectural student. What type projects did he work on in school.

 

[Bbird]

From my own experience I rarely meet a knowledgeable engineer from Osama's country. With due respect I have come into contact with some excellent local engineers out there but they are few and far in between. The trouble is that Osama and his educated countrymen seldom do technical work which is left to the guest workers (employees) recruited outside the kingdom. Many of his senior managers are other Midle East nationals. Like other contractors in his own country Osama hired cheap labour from the Indian subcontinents and the far east. At the peak of his activities he was probably one of the biggest overseas employers for Pakistan. He gave employment to many islamic workers outside his country and enjoyed their support. The guy has connections at high places and made a fortune out of the situation. His outfit can only be regarded as low tech and will have great difficulty in competing construction work internationally, especially on projects where Arabic architecture is not needed.

 

[msajjadh_imported]

Thanks Bbird for your response to my posting. I am a Pakistani and working in Osama's COUNTRY. I do agree with you that it is difficult to find a really knowledgeable structural engineer over here. In my opinion it is a technical forum and our discussion should be within the boundries defined by the authorities of this web site. One thing you misunderstood is that OBL company hired people from Pakistan and he was one of the largest employers for Pakistanies. There were lot of Pakistanies working in his company during the construction of the HOLY MASJID in Madina. But I am very much doubtful that they had any structural design section in their company.

Besides that, if someone is capable enough to design such an intelligent move, don't you think he would be wise enough to forsee the post-accident effects. See this event in a bigger prospective. Regards