Engineering Analysis of WTC Destruction

“I couldn't find the thread this topic was discussed on, so I started a new one. I received this analysis (pdf file) that gives one engineering professor's analysis of what happened.

In summary, he estimates that much of the fuel did not explode in the initial impact but burned after creating immense heat. The temperature generated was more than the steel supports could handle. The "impact" (more than the weight) of the upper floors dropping on the lower floors was more than any structure could stand.

His ultimate conclusion was that it is impossible to design a high rise structure to withstand such an attack.

I am not a structural engineer and did not check his calculations, but they seem plausable. Kinda scary when you think about it.”

“What I think is most amazing is how the towers fell. They were designed so that in the case of a collapse, that the interior would fall first and cause the building to fall in on itself. That is exactly what happened. It looks like the engineers who designed it could not prevent against that kind of act, but they did stop the towerd from hitting surrounding buildings and killing countless others.”

“I am a professional engineer IRL. When this happened there were about eight like me (scary enough)standing in the lobby watching and all agreed the heat would cause the steel columns to deflect and bring them down. Once the mass of 20 stories of building starts moving, nothing can stop it but the ground. Its easier to burn down a steel building than a wooden one for that reason. Yes, its very scary. Here's another analyis that reached the same conclusion.http://www.civil.usyd.edu.au/wtc.htm”

“Yeah, it pretty much looked like the columns buckled once the heat got through the fireproofing. Hey mtnman, whay kind of engineer are ya. There are a few of us techies on this board, but not many. I'm structural.”

“It looks like there are a lot of us engineers around here. My field is more industrial, manufacturing, and quality (P.E. in Manufacturing). Mozark and Solitary Hiker are engineers also.”

“I thought that if the towers were knocked off plumb even a small percentage of a degree that they would be become very unstable as well.”

“Design factor of 30?!? I've never heard of anything that overbuilt. It sounds like even without the damage from the initial impact, it would have been fatal for the building.

Phil, you can add one more engineer to the list. Just got my BSME from San Diego State.”

“Markar - Congratulations. (Hope you weren't around when they had their problem with the psycho grad student. I remember that well because I was having a problem with a psycho undergrad student.)”

“I came in the year after that incident, thankfully. The most we ever had problems with was the %^&*head that kept stealing the coin box (in the age old battle between armor and warhead...)”

“I'm a materials engineer but for some reason a lot of people think I'm a stripper???

Phil, I was wondering what aiplane black boxes could possibly be made out of to be able to withstand such high temps (2000 deg F?)...even if they are made out of high temp ceramics, wouldn't the electronics inside be fried? What kind of polymer adhesive could possibly withstand that temp?..maybe silicone). I am just a little leary about info 'reportably' obtained from the WTC black boxes..

Has anyone heard if they have found them or if they are still looking for them? Is there a tracking device on those things so they can even locate them?”

“Those black boxes are tough as nails that's for sure.

Here's a link to answer some of your questions:

Black Box Construction”

“Great link regarding the black boxes!

I haven't heard of them recovering any black boxes from the towers. If they ever do, I think it will be a miracle.”

“i am an engineer too. i drive for the BNSF”

“what's the BNSF?”

“burlington northern santa fe
operates one of the largest rail
networks in north america, with
33,500 route miles covering 28
states and two canadian provinces.”

“"Is there a tracker device on those things so they can even locate them?"
One of the network talking heads mentioned that they have a "pinger" but it's only activated when the box is immersed in liquid.”

“hmm interesting”

“GearSlut, I believe the WTC was designed to have up to a 2 degree sway during wind loads. Thats just what I heard, so it may not be accurate. Steel building are very flexible and can remain stable with "drift". I usually design building up to about 5 floors using height/500 as the maximum drift. A 50' building would be allowed to move about 1 1/4" at the top. This is about .11 deg. Tall buildings go way beyond that because you couldn't afford to build them otherwise. 2 deg. sound pretty high.”

“Dayhiker- I'm not smart enough to be a Structural, I a civil.”

“Did any of you see the article on foxnews.com's "junk science " section about Asbestos use in WTC?
Link to the article on Foxnews
Essentially the writer stated that if they allowed the WTC's steel structure to be treatd completely with asbestos then there might have been enought time to get everyone out. Asbestos use was banned halfway through the construction of the WTC.

Waddayathink?”

“Asbestos is a darned effective insulator. I think there's truth tho the article, maybe that's why the planes hit high up. I originally thought they would have been more effective at killing people to have hit lower. Do terrorists do that kind of research? I believe the heat was far greater than the normal type of fire due to the full load of Jet-A and that the buildings would have colapsed anyway. Glad to hear lots of engineers are here, Hmm, during lunch hour I suppose..”

“Another civil here. I'm wondering how much the ground is going to rebound after they get all that weight off of it. Do you think the upward ground movement would buckle the subway lines below it?”

“I saw a show on PBS about New York that focused on the infrastructure and engineering that went into building the city. One of the interesting things that they mentioned was that the entire island is solid granite. They went on to mention that possibly no other place in north America would be able to provide as firm a foundation to support as many large buildings as in New York. New foundations usually need to be blasted out. I think it was an episode of NOVA.”

“I don't deal with glacial till in the southeast where all my work experience is but I doubt it. Does the line actually run beneath it? I'm guessing it was pretty well surcharged so who knows, I bet it does rebound some in the upper 10 feet.”

“I thought the entire island was a terminal morraine.”

“I've read a couple of structural analyses of the collapse. The towers were an interesting tubular structural design. I had two years of architecture classes in high school, and we went up into the towers when they were under construction. It was well overdesigned. I believe that I remember hearing that each tower was designed to sway 6-8 feet.

Large timber construction will definitely resist fire better than steel but I don't know of any material that would have withstood what must have been an incredible inferno. Even the concrete would have buckled and spalled. I also read that the fire sprinkler system probably failed. I can't imagine any fireproofing that would have helped.

I'm certainly not going to start designing my buildings to stand up to airplane impact. Unless, of course, I get a contract to design a new military headquarters. I can't imagine that the people at the pentagon aren't seriously thinking about relocating.”

“Uh, Phil? Has anybody double checked the numbers on that report. 19.7 m/s is only 44 mph. It seems a little slow for an aircraft the size of a 767.”

“I haven't double checked anything. Sturctural is not my area. As far as I am concerned the calculations are subject to examination.

Regardless, it seems like the key was inferno caused by the burning fuel. The sprinkler system would be destroyed by the impact and rendered mostly ineffective...unable to blanket the area. You would almost have to be able to flood three or four floors with foam or something very quickly to have any chance at extinguishing the fuel...and sacrifice everyone who is in the way. Even then, the fuel could still flow down into shafts, vaporize, and burn or explode.

A quicker escape than stairs would be nice also, say a slide or something.

A stinger missle launcher on topof the tower with an early warning system and guidance capability might work.”

“An antiaircraft/antiship battery for an island city like Manhatten(sp?) might be feasible. But, the legal and ethical aspects are damn cloudy.

The rapid evacuation system sounds interesting. Maybe give it to one of the students as a senior project.”

“I am a construction supervisor and often have the fire chief visit the site to investigate fire fighting requirements and the ability to place a fire engine down the driveway and next to the building. It's really good education for the fire department and me.

BTW, I often trade a tour of my building for a ride in their fire engine. I think it's a fair trade, and my daughter is jealous! LOL

Back to the subject. They tell me that in a fire, they prefer a wood stucture, as it retains it's shape and strength better than steel, which melts and weakens and deforms too fast.I was surprised that one department only allows men on a steel deck for the first 5 minutes of the fire. Yes, I did ask. They generally get there after 5 minutes of fire, which effectivly means they won't walk on a steel deck while the fire is raging. Many of the department stores we all frequent have these roofs. After the fire is stopped and the steel has had a chance to cool and harden, they'll inspect the roof.

One building I had was 100 feet square, with a 20 foot meatl stuture roof perimeter, and a second story about 60 foot square. That means in a fire, they would have to climb a ladder up to the roof, walk the 20 foot steel roof, and procede to the windows. They had a provision added to the building permit that there were to be no offices there as they would not walk the roof.

I remembered that when the towers were hit. I suggested to Skinny Dip that those towers could melt and collapse. She nearly freaked when I told her that.I was surprised at how soon they fell, having seen Towering inferno. In that movie, the building seemed to burn for days and stand. Interesting the difference from hollywood and reality.”

“Just a couple of years ago I could not even spell Enguyneer to-day I are one.
I am an Electrical Engineer and with my limited knowledge of structural I was very worried about those buildings. I have a friend that is on a fire response crew in the Air Force and he has told me stories of just how hot this kind of thing can be. When I second plane crashed I looked to a friend I work with and told him I was very concerned. Well we know the rest of the story. I have seen this material that has a very high heat resistance. During a demonstration this guy would place this woven material on his bare hand and heat with a torch with out a problem. I wonder if this would have promise”

“Nah, grunt. Nobody would want to pay for it.”

“Grunt, he didn't mention the critical temperature for the material did he?”

“I understand that the steel was covered with a temperature resistant material, butthat the impact of the jet probably knocked a lot of it off exposing the steel. That shortened the failure time from 2 or 4 hours to a lot less. I only heard this once, however.”

“I think that at 2000 degrees, most fire proofing fails. Pretty much, few buildings are built to withstand an aircraft and tons of jet fuel burning. If things get hot enough, even rocks burn. (see: lava)”