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Leaked FEMA/ASCE Draft Report On WTC Collapse 562

Posted by Hemos
from the structure-integrity-good dept.
securitas writes "The New York Times obtained a copy of the World Trade Center draft report by the Federal Emergency Management Agency and the American Society of Civil Engineers about the engineering failures that caused the towers to collapse. Among the findings: 'Fireproofing, sprinkler systems and the water supply for hoses were all disabled and the fires generated heat equivalent to the energy output of a nuclear power plant' reports the NYT (Yahoo link). Amazingly, if it wasn't for the fire (or another secondary catastrophic force), the towers would have remained standing."
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Leaked FEMA/ASCE Draft Report On WTC Collapse

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  • Amazingly (Score:5, Funny)

    by Anonymous Coward on Saturday March 30, 2002 @05:52PM (#3256029)
    if it weren't for the 767s, massive fires, tens of thousands of gallons of burning jet fuel, and the abliteration of the several floors worth of the buildings' structural cores, the towers would have remained standing. But, shhh, this is leaked info. Don't tell anyone.
    • Re:Amazingly (Score:3, Interesting)

      by Grech (106925)
      I understand that you were being sarcastic, but the point is a good one. These buildings were designed with short-duration catastrophes in mind. A missile wouldn't have succeeded, but a 767 did. Whether this speaks well of a design that can withstand a heavy impact, or whether it speaks poorly of a design that cannot withstand a kerosene fire, I don't know.

      However, now that a 'proof of concept' attack has been performed, it will be interesting to see what engineering tricks can be used to keep a tower standing when a barely sub-nuclear blaze is allowed to burn inside it for an hour or two.

      • Re:Amazingly (Score:5, Informative)

        by Fishstick (150821) on Saturday March 30, 2002 @06:31PM (#3256312) Journal
        TLC ran an interesting program about a month ago that went into detail about why the structures collapsed (beyond the obvious, crash, fire, etc).

        The looked at factors like the blast having blown the fire protective coating off the steel and the way the building was designed with the majority of the load being carried by the steel skeleton on the perimeter of the buildings, as opposed to columns within. The achilles heel was reported to be the steel trusses running under the floors connecting the outer steel to the core.

        The heat from the fire caused these trusses to weaken and fail, leaving the outer steel frame without the stabilizing and load-transfering benefit. By the time the first floor had begun to collapse, there was so much inertia in the falling portion of the structure that it was inevitable that the each floor below would fail under the crushing pressure.

        They interviewed the cheif structural engineer and he said that they had designed the structure to withstand an impact from the largest airliner of the day, the 707... flying at low speed and lost in the fog. They didn't anticipate a modern widebody, loaded with enough fuel for a coast-to-coast flight crashing into the buildings at full speed.

        He said that even if they took all that into account, he doesn't think there could have been any way to design the buildings to withstand that. The fact that the structures stood as long as they did is actually a testament to the good overall design (so the program said, anyway).
        • My personal opinion is that enough has been said - and we should move on - talking about how the Twin Towers collapsed isn't going to bring them back - and dwelling on the past too much is bad as well - it was over six months ago and if Americans should move on - it was a terrible tragedy yes - but enough's been said about it already.
          • Re:Amazingly (Score:5, Insightful)

            by oni (41625) on Saturday March 30, 2002 @09:26PM (#3257352) Homepage
            it was over six months ago and if Americans should move on - it was a terrible tragedy yes - but enough's been said about it already.

            would it be ok if we try to prevent it from happening again first? like maybe by going after people who plan terrorist attacks against us... would that be ok?

            I got beat up in school once - my dad told me I shouldn't harp on it for too long - I should just get over it. I remember thinking "wtf! Does he realize I have to go back to school tomorrow?" It's kinda hard to get over it when they're still out there.
          • Re:Amazingly (Score:4, Insightful)

            by Wyatt Earp (1029) on Saturday March 30, 2002 @11:01PM (#3257790)
            My opinion is that anytime a large structure or construct fails, no matter what the reason, it should be seriously studied so that we know what works and what doesn't so that future structures can incorperate the helpful features and remove the extra features so that stucture can be build cheaper, faster, better and quicker.

            Reports like this may lead to better fire systems in tall buildings, better alloys and all around safer buildings. Because the next tall building disaster could be in London, Paris, KL, Osaka, Shanghi or Mexico City. It's not an America exclusive danger.

            It's not about lingering on the event, or saying enough about it, because it would be wrong to forget events like 9-11, Hiroshima, Dresden, the Death Camps, and the list goes on and on, because if we forget, the horrible things will happen again.

            It can happen in the US, it could happen anywhere, tall buildings, wealth and crazy people willing to kill anyone isn't just and American thing.
            • Re:Amazingly (Score:3, Interesting)

              by Pig Hogger (10379)
              My opinion is that anytime a large structure or construct fails, no matter what the reason, it should be seriously studied so that we know what works and what doesn't so that future structures can incorperate the helpful features and remove the extra features so that stucture can be build cheaper, faster, better and quicker.
              The obvious answer, in the case of the WTC, is that feeding the sprinkler systems from standpipes located in the thick building skin would have made a hell of a difference, as they would not have been concentrated in the building core.

              Let's bet that future design guidelines, if not advocating such a design, will definitely promote a wider distribution of emergency gear throughout the building.

              * * *

              When one looks at the structural design of the Twin Towers (one could build an argument about them NOT being a skyscraper by the mere fact that the outer walls were load-bearing - a definition of a skyscraper is that the walls are not load-bearing), with it's thick walls and a center core (no intermediate columns), one wonder why the express elevator (that whisked people to the two "sky lobbies") could not have been situated, say, on each corner (or in the middle of the outer-wall, to preserve the sacrosanct "corner offices"), for a panoramic view when going up, à la Hyatt-Regency/Bonaventure hotels.

              Such a configuration would definitely have withstood the blaze much better than the central-core-with-all-the-vitals; for it is certain that designers would have ran the standpipes along the exterior elevator shafts, if only because of the blazingly obvious reduntancy it offered.

              It would have taken more than one direct aircraft hit to sever all standpipe systems.

        • Re:Amazingly (Score:3, Interesting)

          by Reziac (43301)
          I was rather impressed that the design let the towers collapse coherently (almost as tidy as a commercial demolition), rather than keeling over sideways in any which direction and taking out the entire neighbourhood.

  • UK Horizon program (Score:3, Interesting)

    by Matts (1628) on Saturday March 30, 2002 @05:59PM (#3256071) Homepage
    I recently watched a well known (in the UK) documentary series called "Horizon" on the WTC disaster. It basically stated in no uncertain terms that the disaster was caused by the use of drywall for all the fireproof walling. The theory was that the explosions caused by the planes basically blew away the drywalling and so the heat from the flames which would have otherwise been slowed down by the drywall, would have been dramatically slowed down.

    I wasn't sure whether to entirely believe the program or not, but it seemed fairly plausible. However I came away asking only one question: "So what would have been better?"
    • If I am not incorrect, that drywall you are talking of would not be able to withstand the heat of burning jet fuel.

      So, sadly, the drywall would have been useless even if it stayed.
    • I think you're referring not to drywall, but to the spray-on fireproofing that protected the steel columns. The alternative would be fireproofing tiles, used in older buildings, which are expensive and heavy. Without the spray-on material, the twin towers probably would never have been built.
    • by cprael (215426)
      They're stuffed. Drywall had exactly nothing to do with this one.

      However, I find interesting the fact that the lack of asbestos coating for the structural steel above the, what was it, 60th floor is being ignored. That was the insulation that was supposed to reduce the heat impact on the structural elements in just such a fire for ~8-10 hours. And application of which was stopped midway through construction, after NYC passed their "no asbestos" laws.
  • by beebware (149208) on Saturday March 30, 2002 @06:02PM (#3256103) Homepage
    Recently on British television (on Discovery channel) they had the programme "How The Twin Towers Collapsed" which detailed that the towers probably fell because they impact shock the poor fire-proofing covering off the support beams under each floor which then allowed the fire to reach them. This then caused the to bend under the now extreme stress and heat they were subject to causing the towers structual intregety to fail. It didn't help that the towers were designed that the outside of the building (especially the corners) were the main support sections: the "core" of the building wasn't made to support the whole building as this would have meant reducing the floorspace available to the offices...
    IIRC the person that designed it has an office that overlooks Ground Zero...
  • Fuzzy thinking... (Score:2, Insightful)

    by xeniten (550128)
    "If it wasn't for the fires the towers would have remained standing.."

    That follows similar logic like...

    if it wasn't for the iceberg, the Titanic wouldn't have sunk...or... If it wasn't for the fact that the Hindenberg used hydrogen instead of helium the Hindenberg might not have erupted in flame...or...if it wasn't for Microsoft, there would be nothing but Unix.

    • Re:Fuzzy thinking... (Score:3, Informative)

      by mindstrm (20013)
      It is now thought that the Hindenberg did not go down as a result of it's hydrgogen.

      Yes, obviously the Hydrogen burned... but that was not what did it in.

      It was the coating on the outer shell, made chiefly of the yet-undiscovered ingredients for dry rocket fuel.
      • If it had been filled with helium, though, would the entire airship have been destroyed? Could the outer cover have burned off leaving the inner helium balloons and support framework relatively intact, allowing it to hit the ground a little more gently?
  • by crystalplague (547876) on Saturday March 30, 2002 @06:03PM (#3256112)
    there was an excellent documentary on TLC/Discovery called World Trade Center: Anatomy of a Collapse.

    They explained that most of the WTC towers' strenth was in the outer steel "shell" and the brackets connecting the floor to that were found in the wreckage badly warped. They think the floors collapsed and there was nothing to keep the 4 outer walls from buckling without the floors.

    The most amazing part was in the beginning when they were lifting a huge piece of steel off of a tractor trailer truck. It was as long as the trailer, 4 feet wide, and a foot thick. A bit grabber backhoe thing couldn't even lift it, it sort of slid it off the truck. They made the point that this piece of metal falling just a foot to the ground, shook the ground and the camera 30 feet away. Then they said there was 5,000,000 or some large tonnage falling to the ground at 120mph at the time of the collapse. quite amazing
    • by Billly Gates (198444) on Saturday March 30, 2002 @07:13PM (#3256600) Journal
      "They made the point that this piece of metal falling just a foot to the ground, shook the ground and the camera 30 feet away. Then they said there was 5,000,000 or some large tonnage falling to the ground at 120mph at the time of the collapse. quite amazing "

      Actually, I was unfortunately at ground zero on that horrific day. I was in a hallway in a nearby building about maybe only a block away at the most and it shook like a big earthquake with loud explosions as those beams you described fell. It sounded like a bunch of cannons going off that then turned into a loud hum as 5,000,000 of those suckers fell. Some of the beams and parts of the wall stayed together in very large chunks that sounded like bombs going off when they fell. I really thought that the building I was in was actually collapsing on top of me because it was so loud and the vibrations were so intense. I also thought one of the wings actually did fall of and was crushed from the sound of the large chunks of the wall falling. It turns out the beams that fell were over a block away but I really did think it was gone for at least a few hours until I could get outside. Another thing you may find interesting is one of the long steel beams fell on an adjacent building and it actually bent in a 45 degree angle from the intense force. It looked like a wet noodle just hangling all warped. THe beam was at least 3 to 4 feet thick. Absolutely astounding indeed!
      • Hmm.. Makes me wonder if the USGS registered the event on their earthquake sensors. I'd guess it's probably likely they did.. I know they had some interesting stuff show up when the Oklahoma City bombing happened, though that explosion was felt by people many miles away..
        • Hell yeah. (Score:3, Informative)

          by Convergence (64135)
          In fact, the most accurate timestamps for all of the collissions and the collapse (all 3 planes, and both collapses) are from seismometers.)

          They detected WTC 270 miles away!

          http://www.volcanolive.com/wtc.html

          Both planes hitting, and again, both collapses.

  • by digitect (217483) <digitect@dancingpape[ ]om ['r.c' in gap]> on Saturday March 30, 2002 @06:06PM (#3256136) Homepage

    I think most of us in the construction industry (architecture) were concerned about this as events were unfolding, even before the first tower collapsed. But the saddest part was finding out later that concessions had been made during design/construction in the sizing and configuration of sprinkler systems including the abscense of a rooftop water supply.

    Who knows if it really would have helped, but having to second guess now is hardly comforting. As in most things, those that focus on stupid quantitative evaluations of design (cost per square foot for example) are doomed to come up short when all the chips are really down.

  • SkyScrapers.com [skyscrapers.com]

    On this site there was an Interview done with an engineer who had some knowledge on the World Trade Center. He stated that the airplanes could have not brought them down seeing that buildings of a lesser, equal, or greater size get the same sort of impact daily with the force of winds.

    It is said that the airplanes caused an impact of equal or lesser force than what it would experience from day-to-day wind.
    • by Benley (102665) on Saturday March 30, 2002 @06:24PM (#3256259) Journal

      He stated that the airplanes could have not brought them down seeing that buildings of a lesser, equal, or greater size get the same sort of impact daily with the force of winds.

      Well, this may be true, but when you consider that the airplanes *did* down the two buildings, one must realise that there is something flawed about that statement. I would accept that most skyscrapers are pummeled with the strength of an airplane crash daily, except that the force is spread across the entire structure, or at least one entire face, of the building. Consider what it might feel like if you were walking down the street and suddenly the entire energy of the ~50mph wind gusts that you normally can easily withstand were channeled at a 1cm^2 section of your chest, or even your skull. Wouldn't that at least completely knock the wind out of you? I haven't the time to properly do the math myself right now, but it may work out that such an energy release over such a small space would be enough force to pierce skin and possibly break bones.

      And that is what made the difference, aside from the fire and explosions that are discussed elsewhere in the thread.

      • How's this. You know that a 5 inch magnifing glass can easily burn you in the sun.

        Imagine a magnifier that had the same surface area as your exposed skin, focusing that energy on you, it would quickly burn you to the bone.

        A more easily quantifiable analogy for your argument.
    • Problem is though, all that force was concentrated into a very tight area, only a few floors, thus putting the building under great stress. Plus the floors were ripped apart by the impact, a thing that would not happen with wind.
    • It is said that the airplanes caused an impact of equal or lesser force than what it would experience from day-to-day wind.

      Keep in mind that when calculations are done to measure the force of wind on a building, it is measured as the wind force distributed against the ENTIRE surface of the building.

      The airplanes caused an equivalent force to a much smaller area on the side of the building. Thus, this smaller area experienced an impulse far greater than it would normally feel from wind. Compare apples to apples, people. Please.

      Common sense: If in fact you really think that wind force did equal plane force on the WTC's over the same area, then tell me this: how come those windows aren't caving in and a huge hole ripped due to wind? They did cave in under force of the plane.
  • by Alien54 (180860)
    PBS is supposed to have a special on this sometime later this month.

    I don't recall if it is supposed ot be NOVA or Frontline, and will have to wait a few days for the promo to show up on the websites. The are still in the march schedul

  • Asbestos (Score:4, Informative)

    by Picass0 (147474) on Saturday March 30, 2002 @06:12PM (#3256168) Homepage Journal
    One of the contributing factors is the lack of Asbestos fireproofing above the 70th floors. New EPA laws were enacted during the construction of WTC that prohibited the spray-on fireproofing that was applied to the I-beams. With the fireproofing, the I-beams could withstand an esimated 2000 degree fire, and without they would lose temper and bend at approx. 1200 degrees.

    The jet fuel burned at an excess of 2000 degrees,
    so it's likely the towers still would have collapsed, but some extra time would have allowed further evacuation efforts.
    • Didnt the article say that there was spray on fireproofing on the steel columns?
    • Re:Asbestos (Score:5, Informative)

      by PeterClark (324270) on Saturday March 30, 2002 @06:23PM (#3256246) Journal
      Except that if you consider that the first tower to come down was the second hit, and that it was hit below the 70th floor, it becomes quite clear that the asbestos that was there did little to help.


      Face it, no building could have survived a planeload of burning jet fuel that was busy eating its way through the building, with dozens of floors above adding weight to the weakening structure. And for all those people bemoaning the lack of a rooftop water supply for the sprinklers: consider the fact that the fire trucks at airports are not loaded with water, but with foam. You need foam, not water, to effectively put out burning jet fuel. Otherwise, the water would evaporate into steam before it had a chance to extinguish the flames.


      Really, it's amazing that they stood as long as they did. Of course, knowing the limitless bounds of greed, people are still going to try to find someone to sue. "I want a bazillion dollars because the contractor didn't design the building to resist the destructive impact of a 767 and a plane-load of burning fuel!" Sheesh.


      :Peter

      • Of course, knowing the limitless bounds of greed, people are still going to try to find someone to sue. "I want a bazillion dollars because the contractor didn't design the building to resist the destructive impact of a 767 and a plane-load of burning fuel!" Sheesh.

        You're aware that people are suing both United and American for failing to adequately protect the passengers on the four doomed flights, aren't you? Like you said, "limitless bounds of greed."
      • Re:Asbestos (Score:5, Informative)

        by istartedi (132515) on Saturday March 30, 2002 @09:05PM (#3257286) Journal

        Except that if you consider that the first tower to come down was the second hit, and that it was hit below the 70th floor, it becomes quite clear that the asbestos that was there did little to help.

        I don't think you can make a rational statement one way or the other, since we are dealing with two different crashes which probably cut different beams and spilled fuel in different patterns. Also, the beams on the 70th floor were bearing a lot more weight. So, they required less heat before they lost their cohesion.

        As for all the people slinging accusations of greed, I agree that's bollox.

        The WTC was designed to withstand an 8.0 earthquake. It handled the impact of the planes just fine. This hardly seems like the work of companies that were cutting corners. That the slurry wall holding back the Hudson river held is simply amazing considering it contained the epicenter of a minor earthquake. If that had broken, we would be looking at a huge lake there today. No recovery efforts would have been possible until a new slurry wall was built, and that would have taken months.

        That said, I do have to question the use of "trusses". On the Discovery Channel they quoted a fireman who said that they always say "don't trust the truss" because they have a tendancy to melt quickly. Perhaps there should be a review of what types of trusses can be used in all new construction. Would it have been possible to build the WTC's wide-open design with heavier cross beams instead of trusses?

        As bad as all this is, I'm sure we can learn from it. What will buildings of the future use for fire suppression? How about active cooling systems for structural components? Perhaps insulation can be coated with a material that is resistant to blast waves so that the material will be retained. From now on, architects will be thinking more about explosions and huge incendiary bombs. Perhaps they will improve design, thus resulting in safer buildings for everyone.

    • One of the contributing factors is the lack of Asbestos fireproofing above the 70th floors
      Please offer a citation from a reputable source that:
      1. This is factually correct.
      2. It had any relevance on the disaster.

      • [foxnews.com]
        Link.

        As I state elsewhere in this thread, I was mistaken about the EPA's role in this, that it was ultimately The City of New York that choose not to use asbestos above fl. 64.

        Is it relevant? Well, it might have kept the towers standing a bit longer. Some more people might have escaped during that time. Of course, we'll never know 100%. But it makes sense to me.

        • The CATO's Institute's pet Steve Milloy writing for Fox "News" 3 days after the incident doesn't meet most folks standards of legitimate or informed reportage.
          • You don't have to like the source.

            But I think you are mistaken in your implied argument that the building not having fireproofing is a non-issue.

            You're not going to convince many people that no asbestos is safer when there is an inferno.
  • putting out fires (Score:4, Informative)

    by Ozan (176854) on Saturday March 30, 2002 @06:12PM (#3256172) Homepage
    Burning kerosine swims on water. No sprinkler system would have put out that fire. Halon would have been needed, but this surely would have been too expensive for the whole building to be equipped with. Nevertheless it surely would have delayed the colapse for a certain time if the sprinklers had worked and cooled the fire.
    The report seems not to say anything about the fact that the WTC was a steel construction and thus rather unprotected against fire as opposed to ferroconcrete which is safer but would have needed the buildings to be smaller. This is the cause why there are not similar high buildings in Europe where regulations demand ferroconcrete.
    • Burning kerosene swims on water. No sprinkler system would have put out that fire.

      True, however a sprinkler system would have reduced the temperatures reached inside the building, quite possibly enough to have saved more people. Also a sprinkler system would've reduced the number and intensity of secondary fires; office furniture and the like.
      Smaller buildings using 'feroconcrete' may well be safer, but this is irrelevant to the WTC terrorist attack, the towers weren't smaller or built using this concrete.

      Working sprinklers would've made a difference. Your comment on halon is well received; probably halon would be more effective, assuming the delivery system was operating.

      Overall I see this report as optimistic, better protected fire escapes, better fireproofing and more redundancy in the fire fighting capability may have saved, not only more people, but the buildings themselves. Applying the knowledge gained, will result in even studier building.
      • Of course we all know that the buildings built with extroardinary fire fighting capabilities are going to have the occupants drown when terrorists seal all windows, doors and turn on the system full blast.
    • The kerosine burned out mostly within the first 10 minutes. It served as the lighter fluid for the major fuel mass of the building: furniture, paper, etc. Sprinklers might very well have been able to cool or extinguish this secondary fire which in fact was what finally brought the buildings down.
      • by Ozan (176854)
        10 minutes, Where did you get that figure from?
        The report says there were appr. 10000gallons of fuel in the plane of which two third flew into the building. With an energy density of 34 MJ/L this is a total energy of about 900 GJ just from the kerosine. The specific heat capacity of water is 4200 J/kgK, so it was enough to vaporize 2.6 million litres of water, a cube with side lenghts of 140 meters. Plus the secondary fire of the furniture.
        This event was just too much for any security system. It was only a matter of time.
    • Re:putting out fires (Score:3, Informative)

      by elmegil (12001)
      Halon relies on a closed container like room to smother the fire. As soon as the jets broke through the building, any chance for Halon to have put out the resulting fire was gone.
  • by Yoda2 (522522) on Saturday March 30, 2002 @06:20PM (#3256232)
    In the future, we'll just have to build all really tall buildings underwater. Maybe Kevin Costner could offer up some good advice.
    • Sure, why not build under water? Well have you ever watched Deep Blue Sea? That is the answer to your question - terrorist controlled sharks would love to have a bite on your average marketroid. Wait, maybe this is not such a bad idea after all!
  • by pgrote (68235) on Saturday March 30, 2002 @06:26PM (#3256274) Homepage
    They ran an hour long program where they interviewed two key people ... the mechanical engineer who built the towers and a forensic mechanical engineer who was looking at the wreckage.

    Each had unique viewpoints. The designing mechanical engineer is haunted to the core over this. Most of his sentances trailed off as he was reliving what happened.

    The forensic scientist identified the fact that the fireproofing material was blown off from the original impact. This hastened the collapse. He also commented that the support structures for the floors were the first things to fail.

    My question is did anyone really think they were going to fall? Remembering back to the day no one in the media raised the question. None of my friends or family I was talking to that day even thought of it as a remote possibility.

    This raises a very interesting question about our expectations vs. reality. After the shuttle disaster I think this stands as one of the most shocking slaps in the face to us concerning technology.

    Of course the buildings weren't going to survive, but our faith in technology made us think that day that the buildings collapsing wasn't a possibility.
    • The designing mechanical engineer is haunted to the core over this.

      Yeah, that was disturbingly apparent. The poor bastard looked like Death in those interviews. I remember wondering the first time I saw it if we'd be hearing about his suicide in the near future-- he obviously (and wrongly, IMHO) feels incredibly responsible for nearly 3,000 deaths.

      ~Philly
  • WTC & Respect (Score:5, Insightful)

    by maggard (5579) <michael@michaelmaggard.com> on Saturday March 30, 2002 @06:26PM (#3256276) Homepage Journal
    Lots of folks are posting-from-the-hip how "obviously" the towers had sub-standard sprinklers or fire protection or should of held up to the impact or the fire...

    Think for a few moments before posting.

    1. These buildings received Certificates of Occupancy, had been tested in the prior attack, their systems and procedures were as good as any other in the world.
    2. There is NO evidence of cost-cutting, sub-standard materials or equipment, etc. This was a public building owned until recently by the Port Authority of NY & NJ and by all reports kept in exemplary condition.
    3. These were not slip-shod towers built overnight in some 3rd-world country without reviews, standards, or regular inspections.
    4. Aside from their unusual tube-design (which appears to have been their greatest asset) and height there is nothing special about WTC towers that would separate them from tall buildings around the world. This includes materials.
    Finally, before you post realize that 3,000 humans died horribly in this disaster. Perhaps before you post your Monday-morning-quarterbacking, rumor-spreading & conspiracy theories you might show a bit of respect for those folks and the ones they left behind.

    A little courtesy and respect is appreciated.

    • by nagora (177841)
      A little courtesy and respect is appreciated.

      Didn't stop Cameron making up details (and lots of them) for "Titanic"; how long does something have to be in the past before no one cares I wonder. Probably a question Yassir Arafat is asking himself about now...

      TWW

    • Re:WTC & Respect (Score:3, Insightful)

      by gad_zuki! (70830)
      These buildings received Certificates of Occupancy, had been tested in the prior attack, their systems and procedures were as good as any other in the world.

      World? Try New York. There are different standards in every city and vary a bit from country to country.
  • The TLC special about the collapse of the WTC was really interesting. One of the things the engineers found was that the fireproofing was gone....either incinerated or had crumbled away. Also, the primary reason for the collapse was the method of using flimsy truss-platforms for the floors and using the exterior for all the support. What happens is that the steel is much thinner than it would be normally is softens much faster. This leads to the pancaking of the floors.


    Apparently this type of construction is despised by firefighters because when they're inside a building during a fire the floors are likely to collapse at any moment.

  • by dshelt (234834) on Saturday March 30, 2002 @06:52PM (#3256453)
    Another famous New York Landmark also suffered an airplane collision. Now granted the airplane that hit the side of the Empire State Building was not the same size as the two that hit the World Trade Center, the B25 did quite a bit of structural damage. Enough damage in fact, that if simply the collision caused the Trade Center collapse, then the Empire STate (the plane did hit somewhere between the 78th and 79th floors)building should have also collapsed. In actuality the reason that the Trade Center collapsed and the Empire State building did not, is one of metallurgy. The thousands of gallons of jet fuel that were burning in the Trade Centers got hot enough to anneal the structural steel. When that happened the sheer mass of the floors above the impact zone collapsed triggering the chain reaction. Had the Jets that hit the Trade centers been nearly empty of fuel (ie. getting ready to land, instead of just taking off) the buildings would have survived the impact.



    The following excerpt is from "Empire: A Tale of Obsession, Betrayal, and the Battle for an American Icon", copyright © 2001, available from John Wiley & Sons. It describes the impact of the B25 that hit the Empire State Building in 1945.

    "Army Lieutenant Colonel William Smith Jr., a 27-year-old veteran of 34 bombing missions over Germany, had been flying a twin-engine B-25 bomber from Bedford, Massachusetts, to New York's LaGuardia Airport, and had secured permission to continue to Newark, New Jersey.

    The fog was blinding. When he dropped down out of the clouds, he found himself approaching a forest of skyscrapers. In a panic, he banked away from the Grand Central Building, then from another tower on Fifth Avenue, only to find himself bearing down on the biggest one of all.

    In desperation, he pulled up hard, twisting. The 10-ton (9-tonne) bomber plowed into the office of War Relief Services of the National Catholic Welfare Conference on the 78th and 79th floors, 913 feet (278 meters) off the street, tearing a gaping hole in the Empire State Building's north side."

    The full article describing the impact in 1945 can be found here: Empire State Building Collision [architectureweek.com].
  • by HardCase (14757) on Saturday March 30, 2002 @06:55PM (#3256471)
    The WTC was designed to withstand the impact of the largest airliner of its time, a Boeing 707. A 757/767 isn't much more massive than a 707, but obviously the real problem is the tremendous amount of fuel that a cross-country flight carries.

    In fact, it probably wouldn't have mattered what fire suppression system the building used...jet fuel is basically kerosene and it is much lighter than water. You can't effectively extinguish a kerosene fire with water. That's why you see aviation firefighers using something called aqueous film-forming foam. It floats on the kerosene.

    Maybe to the layman the fact that the buildings survived the impact was amazing, but in fact it was simply a matter of good, purposeful design. Unfortunately, it's asking an awful lot to expect structural steel to survive the kind of intense temperature that is generated by an aviation fuel fire, particularly when the fuel supply is effectively limitless.

    -h-
    • by Nelson (1275)
      A 707 has a max takeoff weight of 328,000lbs. A 767 has a max takeoff weight of 450,000lbs. They have similar max velocities. Now I don't remember the physics off the top of my head but isn't force proportional to the square of mass and velocity? There is nearly a 50% difference and I think that's substantial, substantial enough that it should fall outside what the building was speced to do, essentially it's twice the impact.


      Personally, I think the engineers and architects who built those buildings should be awarded and applauded. The buildings were made on budget and schedule. Only 3000-4000 people died, when they could easily hold close to 100,000 between the two of them. Neither building fell over and crashed other buildings, they pretty much imploded, which is remarkable. And despite the huge trauma, they stood for nearly an hour. It's amazing if you ask me.


      This security second guessing crap is what's going to cause the next recession and put a minor stop to modern engineering. Money and time are really the difference between academia and engineering. Do you have any idea what it will cost to start engineering all of our buildings to withstand the worst? The WTC was over engineered as it was and we're talking about making it able to withstand twice what it was speced to. If it's possible and there are steel makers that don't think it is, I'm guessing we're talking about a 10x hit to the costs. That's crazy. The same thing can be said about all the security checks everywhere else. It'll work for a year or two and then the bills will start adding up and people will be astounded.

  • by FallLine (12211) <fallline@oper a m a i l .com> on Saturday March 30, 2002 @06:58PM (#3256498)
    Calling the WTC's collapse an engineering failure is kind of like taking C4 to slashdot's servers and saying that the code failed somehow. You just can't reasonably have expected them to anticipate this. Expecting a building of similar requirements (e.g., height, usable space, windows, etc) to withstand both the impact of a modern airliner and the jet fuel may well be an impossible task, especially when trying to do it within any reasonable budget. Please think about what you are saying and try to be a little less arrogant. Thank You
  • At least this time the emergency lighting worked. In the 1991 truck bombing of the Twin Towers, the emergency lighting went out. That bomb, in the parking garage between the towers, knocked out the primary power transformers and the cooling water plumbing for the emergency generators. The WTC didn't have battery backups on the emergency lighting in 1991. It did in 2001, and that saved many lives.

    The Twin Towers had large emergency water tanks as high as the 110th floor. But they were damaged in the explosion, and water dumped uselessly down the stairwells and elevator shafts. Even if the firefighters had reached the fire floor, they wouldn't have had water. We're probably going to see more redundancy required in high-rise standpipe systems because of this. Extra pipes and one-way check valves are needed, but that's not a big deal.

    It's not impossible to put out a fire that big with water, if you start early. Aircraft hangars and aircraft carriers have deluge systems that can do the job. We may see systems like that required in skyscrapers. A big problem is making sure they don't go off because of a smoky wastebasket or something.

  • by Raetsel (34442) on Saturday March 30, 2002 @07:14PM (#3256605)

    16 days after Sept 11th, I received this in an email from my father, (who happens to be a Mechanical Engineer):
    • Professor Thomas Mackin, who currently teaches Failure Mechanisms in Engineering Materials class, made this short presentation (attached) after the World Trade Tower tragedy. This presentation was made in response to the Chancellor's request for teachers to discuss with their classes the recent events. Mackin was clearly as shaken up about the events as were the rest of us. He only had a short response to his final question: "As engineers, what can we do to prevent this from happening. - Nothing."

      Attached was a .PDF file, "ME 346 - Engineering Analysis of Tragedy at WTC." [uiuc.edu]

    There was simply too much energy put into the buildings. bin Laden knew that, the engineers know that... it's a damn shame we're back to the accusations, finger-pointing, and blame-placing that so much plagues our culture.

    The engineers did their job. They did it well. World Trade Center 1 & 2 were good buildings -- I stood on top of one just over 10 years ago. I can hardly believe I never will again.

    Osama bin Laden and his cronies are the ones -- the ONLY ones -- responsible for this outrage. Please, let's try to remember that.

  • To sum up.... (Score:3, Interesting)

    by phillymjs (234426) <slashdot&stango,org> on Saturday March 30, 2002 @08:02PM (#3256933) Homepage Journal
    ...the report more or less concludes that the buildings collapsed because of the way they were designed, but withstood the damage for as long as they did before collapsing because of the way they were designed. Talk about, "Damned if you do, damned it you don't."

    The worst-case disaster scenario for those towers was a 707 accidentally blundering into one, not a bunch of crazy religious-zealot, martyr-wannabe motherfuckers purposely plowing a much larger, fully-fueled aircraft into it at full speed.

    If anyone who lost someone in the collapse even thinks of trying to sue anyone involved in the design or construction of the twin towers, they ought to be drawn and quartered. Sure, they could build a building that could stand up to worse than the WTC got, but proofing it against everything would cost a mint and leave a few phone booths' worth of usable space per floor. Don't forget that there wouldn't be any windows. The rent would be so expensive that nobody would be able to afford to put an office in it.

    IMHO, when you step back and look at the big picture, you simply cannot fault the design of the buildings for the fact that they catastrophically failed in the face of an unprecedented, unimagined, deliberate action that was well beyond the scope of their design.

    ~Philly

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