loubetti
Pays to fly
I'd have to check that out, but as a much smaller building, maybe they all got out in time? I mean, it did not collapse until 5:21 PM!!! So, maybe they just all hung out there watching as debris from the two towers hit them?
United 93 - Accident Investigation
- Thread starter hambone
- Start date
I'd have to check that out, but as a much smaller building, maybe they all got out in time? I mean, it did not collapse until 5:21 PM!!! So, maybe they just all hung out there watching as debris from the two towers hit them?
darrenf
resident denizen
opcorn:
[video=youtube;R5kPUFxXYLs]http://www.youtube.com/watch?v=R5kPUFxXYLs[/video]
Cazadores
Well-Known Member
I think they had enough time to evacuate, and the firefighters I think gave up the building to fire as it was evacuated and all the water pressure had been used or was gone. I think I remember hearing they made a decision to just cordon off the area and let it go more or less.
loubetti
Pays to fly
Yes, indeed. I was being sarcastic in my remarks about ATC 7 above.
NickH
Uber Driver
I think that the conspiracy is a conspiracy.
There are far easier ways of destroying a building than shooting missiles from a 757. How about convincing a bunch of Saudi Arabians to hijack an airplane and fly it into the building?
All these conspiracies focus on why the building collapsed and sound so ridiculous that it draws attention away from more plausible theories, which range from simple foreknowledge to actual complicity.
There are far easier ways of destroying a building than shooting missiles from a 757. How about convincing a bunch of Saudi Arabians to hijack an airplane and fly it into the building?
All these conspiracies focus on why the building collapsed and sound so ridiculous that it draws attention away from more plausible theories, which range from simple foreknowledge to actual complicity.
inigo88
Composite-lover
Well it's simple middle school physics that when a structure weakens enough, it fails. Maybe this massive gash through the middle of the building has something to do with it.
...
First of all, the building was completely evacuated so nobody died. Please leave all the WTC tower and Pentagon conspiracy theories out of this conversation, and check the emotion at the door. Having a casual and objective discussion about structural engineering and building methods is not going to dishonor anyone's memory if nobody died, and the building only coincidentally collapsed 7 hours after the worst terrorist attacks this country has ever seen. I am genuinely curious about your photo because I would like to take a look at the "massive gash," but it's so small and pixilated all I see are some broken windows and smoke from the fires. Please find me a bigger one.
It's funny you mention that. I just took a final exam today in a college physics course at one of the top ten public universities in the country, that covered thermodynamics and the conduction of heat through metals. I guess I better go back to middle school though. In the mean time would you mind looking up the melting temperature of steel for me in your middle school physics textbook? Nevermind I'll help you...
wikipedia: Structural Steel said:
The fire resistance section is also really interesting reading, because there are set standards on acceptable critical temperature. The critical temperature is defined as the temperature which it can no longer safely support its load. It is more technically defined as the point where the Yield Stress (denoted by sigma y in the relevant equations) has been reduced to 60% of its original value, meaning even with a 40% softening and weakening of the steel, the building should still stay up.
Wikipedia: Structural Steel: Fire Resistance said:
I'm having a hard time finding hard numbers on how hot general structural materials burn (i.e. desks, computers, stuff you would find in an office building), but I recall a majority of the fires were diesel-fueled anyway from the generators in the basement. Diesel is a hard one to find hard numbers on too since at regular pressures and room temperature it doesn't burn easily, but its autoignition temperature (the temperature at which it will vaporize and burn without an external flame applied) is ~400 C (752 deg F), which happens to be in the same for gasoline and kerosene as well. Since jet fuel is basically kerosene, the temperature of an open air Jet A fire is more easily obtainable:
Edit: I guess my post was too long so it's continued below...
inigo88
Composite-lover
Continued from the previous post:
Since jet fuel is basically kerosene, the temperature of an open air Jet A fire is more easily obtainable:
This is only one fourth the temperature needed to melt steel. It is also only half the Critical Temperature, meaning the yield stress of the steel should still be greater than 60% of its original value and whatever softening or weakening took place shouldn't compromise its ability to safely hold its load. Since diesel and kerosene have similar chemical properties and the same autoignition temperature, I am venturing a guess that their open air burning temperatures are at least within the same ballpark.
That's a really good point, and the most plausible reason in my opinion. However the fact that the fire doesn't reach the critical temperature for the steel (it only gets half way there in fact), which is then covered in that spray-on gypsum fireproofing insulation on top of that, is troubling to me.
I would think so too, but I haven't seen a lot of compelling photos to support this. Clearly the east side (the short side) got the brunt of the debris damage, but it covers a relatively small percentage of the building.
I don't get why that amount of damage caused the building to fall down, when we've all seen the media footage of the Oklahoma City building, with an entire side completely blown off, still standing. A lesser known example which happened during the 9/11 attacks is WTC Building 6, which got completely pelted by debris as the World Trade Center towers collapsed, but did not fall down (the top floors clearly collapsed but the rest didn't).
To put it simply, I don't get why the big building that was further away (WTC 7) fell down when less stuff landed on it, while the little building that was closer (WTC 6) that got completely pummeled by stuff falling on it, remained standing. Qualitatively we can speculate that the fires + the structural debris damage worked together to take it down, and I could buy that. But quantitatively the numbers I have quoted don't add up to support that, and that frustrates and annoys me because scientists and engineers are pretty good at figuring out how and why stuff happens and explaining it with numbers, and that hasn't happened yet.
This is an aviation website to talk about airplanes and I apologize to Doug for temporarily hijacking it and leading it astray from its intended purpose. I think engineering is interesting, and it's the degree I've chosen to pursue in college. So when someone says "THE JET FUEL MELTED THE STEEL YOU IDIOT, EVERY MIDDLE SCHOOLER KNOWS THAT!", I've gotta call BS, because that contradicts a lot of college classes (thermodynamics, solid mechanics, materials science, structural engineering, etc.) that said person probably hasn't taken. Whatever did happen was a very complicated dynamic process that has yet to be explained adequately on a quantitative level, and I wish more effort would be made to do so rather than just shrugging and saying "oh well." I think it's human nature to want to understand why stuff happens the way it does.
Since jet fuel is basically kerosene, the temperature of an open air Jet A fire is more easily obtainable:
Typical Physical Properties for Jet A/Jet A-1 said:
This is only one fourth the temperature needed to melt steel. It is also only half the Critical Temperature, meaning the yield stress of the steel should still be greater than 60% of its original value and whatever softening or weakening took place shouldn't compromise its ability to safely hold its load. Since diesel and kerosene have similar chemical properties and the same autoignition temperature, I am venturing a guess that their open air burning temperatures are at least within the same ballpark.
JordanD said:
That's a really good point, and the most plausible reason in my opinion. However the fact that the fire doesn't reach the critical temperature for the steel (it only gets half way there in fact), which is then covered in that spray-on gypsum fireproofing insulation on top of that, is troubling to me.
JordanD said:
I would think so too, but I haven't seen a lot of compelling photos to support this. Clearly the east side (the short side) got the brunt of the debris damage, but it covers a relatively small percentage of the building.
I don't get why that amount of damage caused the building to fall down, when we've all seen the media footage of the Oklahoma City building, with an entire side completely blown off, still standing. A lesser known example which happened during the 9/11 attacks is WTC Building 6, which got completely pelted by debris as the World Trade Center towers collapsed, but did not fall down (the top floors clearly collapsed but the rest didn't).
To put it simply, I don't get why the big building that was further away (WTC 7) fell down when less stuff landed on it, while the little building that was closer (WTC 6) that got completely pummeled by stuff falling on it, remained standing. Qualitatively we can speculate that the fires + the structural debris damage worked together to take it down, and I could buy that. But quantitatively the numbers I have quoted don't add up to support that, and that frustrates and annoys me because scientists and engineers are pretty good at figuring out how and why stuff happens and explaining it with numbers, and that hasn't happened yet.
This is an aviation website to talk about airplanes and I apologize to Doug for temporarily hijacking it and leading it astray from its intended purpose. I think engineering is interesting, and it's the degree I've chosen to pursue in college. So when someone says "THE JET FUEL MELTED THE STEEL YOU IDIOT, EVERY MIDDLE SCHOOLER KNOWS THAT!", I've gotta call BS, because that contradicts a lot of college classes (thermodynamics, solid mechanics, materials science, structural engineering, etc.) that said person probably hasn't taken. Whatever did happen was a very complicated dynamic process that has yet to be explained adequately on a quantitative level, and I wish more effort would be made to do so rather than just shrugging and saying "oh well." I think it's human nature to want to understand why stuff happens the way it does.
FAYEV
Well-Known Member
The nature of your initial post seemed to lean towards the fact that you were a conspiracy theorist. "Who tipped off the media" leads me to believe that you think this was an inside job. Frankly, that is disrespectful to the lives that were lost that day, regardless of the fact that none were lost in Tower 7 itself.
As for the picture I posted, it is one of very few that are available of that side of the building. Considering there was a pile of the two tallest buildings in the world on that side, that's probably why there aren't many other pictures. The gash runs vertically from the top of the building, in the center. Here is a better version:
Thanks for sharing all your wonderful knowledge. I'm so happy that you attend "one of the top ten public universities in the country". You are correct. The steel did not melt. My definition of "melting" was more of a simpleton definition. I am aware it weakened, rather than melted, but I didn't realize you were a fountain of Physics knowledge, which is why I used a broader (although incorrect) term. I shall bow down now because I have better things to do, and arguing on the Internet is not one of them. I do not have time to throw around citations to prove I know something, because I probably don't....but I did stay at a Holiday Inn Express last night.
Oh and here's the official report on the collapse of Tower 7: http://www.nist.gov/customcf/get_pdf.cfm?pub_id=861610 You can probably make more sense of it, since you go to a better school than me. Here's a summary:
Looks like we're both wrong.
I believe a lot of the fireproof insulation had been blown off the support structure by the impact of the plane, at least on the floors that were hit. As I said, those floors had the equivalent of a 30+ story building to support. A lot of conspiracy theories seem to forget about the airplanes that hit then at near cruise speed. When they claimed they designed the buildings to withstand an aircraft impact they had a plane on approach lost in the fog in mind.
Jet
Well-Known Member
That's a pretty far out assumption from somebody posting a video of the BBC reporting that a building fell before it actually fell. That is definetly not disrespectful to the fallen. What would be disrespectful is not investigating the incident which could have been an honest mixup.
loubetti
Pays to fly
Talking about WTC 1 & 2 and not 7 (I'll get to that later):
First, does anyone know how WTC 1 & 2 was constructed? Anyone, anyone? Where was it's true structural strength? Inside or outside?
As to fire insulation what the heck do you think happened to it when those jets hit at that speed? If you think it clung on on, you have another thing coming- it was blown off! Again, I get the impression that some do not know how the buildings were constructed, and that your engineering knowledge is tenuous at best.
Does anyone think that burning jet fuel in the WTC was an "open air" fire? Not to mention other things were burning with it in an enclosed environment. It was not "open air". This wasn't burning some jet fuel in your back yard. Again, tenuous knowledge.
It should be obvious that we do not need steel to fully melt in order to lose its strength; just get a bit soft. The weight of the floors above then take care of the rest.
Sadly, one can not convince those not knowledgeable. They just make up their own minds based on what little they know. Sad, but the conspiracy theorists often provide humorous entertainment. Not so much about what really happened, but about how little they know.
First, does anyone know how WTC 1 & 2 was constructed? Anyone, anyone? Where was it's true structural strength? Inside or outside?
As to fire insulation what the heck do you think happened to it when those jets hit at that speed? If you think it clung on on, you have another thing coming- it was blown off! Again, I get the impression that some do not know how the buildings were constructed, and that your engineering knowledge is tenuous at best.
Does anyone think that burning jet fuel in the WTC was an "open air" fire? Not to mention other things were burning with it in an enclosed environment. It was not "open air". This wasn't burning some jet fuel in your back yard. Again, tenuous knowledge.
It should be obvious that we do not need steel to fully melt in order to lose its strength; just get a bit soft. The weight of the floors above then take care of the rest.
Sadly, one can not convince those not knowledgeable. They just make up their own minds based on what little they know. Sad, but the conspiracy theorists often provide humorous entertainment. Not so much about what really happened, but about how little they know.
loubetti
Pays to fly
There we go, smart man above! Indeed, the insulation was blown off on the floors hit (does anyone think it was molecular attached?!!), and with the steel trusses getting soft under the heat, and the weight above, that's all you need. Not sure why some cannot grasp this. Again, learn how the buildings were built. Learn why they failed. Don't listen to those who know nothing and talk to hear themselves talk.
Jet
Well-Known Member
I find that unusual but it still doesn't prove anything and I wouldn't draw a conclusion such as an inside job, the BBC reported on it later saying that it was a mistake. Just like all of the insider trading that went on the days before 9/11, could be just a random coincidence but the details were never released to the public as to who was behind all the short sales.
flyingbum
Needz Re-Edjamacayshun
Well I'm interested in learning if you know?
I do recall hearing something about the towers being able to withstand the impact of an airliner when they were designed. I think at the time it was the 707.
BeRich
Very Special Agent
As was said earlier, they were almost certainly thinking of a plane on final lost in the soup or something, not a plane at cruise speeds.