I’m not a structural engineer but IMHO the collapse of WTC7 as portrayed in the video cannot be explained by the failure of one column.
I’m not a structural engineer either but I can guess why intuition built from the breakage of objects on a scale of several feet, as we more typically encounter, cannot apply to the demolition of a skyscraper.
First, the entire column of the skyscraper should have a lot of inertia—why would it tip horizontally in one direction or another without a significant continued force to do so?
You’re probably underestimating the cohesion of the floors, one to another. Maybe they’re not like layers of cake balanced on toothpicks. Just a few internal structures connecting the floors (like concrete staircases?) make a vertical crumbling fall seem much more reasonable.
An impact that is strong enough to break a hole in an exterior wall doesn’t just affect that wall, presumably the whole building would be agitated, shaking and wobbling at various sonic and supersonic frequencies. (Thunder during a storm is enough to cause my house to resonate and rattle the mirrors on my wall.)
I’m not saying that I would have predicted that the building would fall vertically rather than tip over. I’m just saying that I would expect that the fall of an enormous building with lots of external and internal structure to be more complex than my intuition could accommodate.
If I was worried about there being a conspiracy, and it was because the fall of this building was nagging at me, what I would do—because I know from experience this is what I do when I worry—is I would go to youtube and google “building collapse” and see if buildings typically fall in ways that I expect, and if there’s a lot of variation, etc. I would see if after watching a few buildings collapse at that scale, if my brain could extract enough information to really feel comfortable one way or another about the likelihood of identifying a ‘false’ collapse..
(Seeing what structural engineers have to say about it is not the first thing I would do, because I expect demolition models are like climate models—you have enough free parameters and undetermined assumptions to get out anything.)
When I first started back to school in 2006, I was studying Engineering. I was in a materials class when they did strength testing of various materials. I remember the noise that the breaking I-Beam made when it snapped. It did not just go “Ping” like many people think, but rather sounded like a combination of an explosion and a breaking mirror (a BIG mirror).
We had a short discussion at this point about 9/11 and the reported “explosions” hear within the building. The professor asked what those noises might have been (nodding at the tiny I-Beam we had just broken and mentioning that the I-Beams in the WTC where hundreds of times larger).
It did not take us long to get the clue that the “explosions” hear were large structural members breaking under incredible strain, and that the stored up energy in these members was then released further along the member’s length (so, you get this recursively adding structural failure that generates louder and louder “BANGs” as the buildings falls).
The pancaking of the floors is just a part of that process. Also, as you mention below… The fire did not need to melt anything, all it needed to do was to remove just enough strength from one portion of the building to have that fail, and have the other supporting redundant members have just enough strength sapped from them as well to begin a catastrophic failure. If the fire did melt things (as is possible when you have a hot firing burning in an oxygen deprived environment, it will heap up to huge temperature and then if a hole were to suddenly appear that allowed in oxygen. It will act like a blowtorch—we got to do this in class too) then that would just make the failure all the more spectacular...
I’m not deleting this previous comment, but someone over my shoulder tells me they just read about this in Physics for Future Presidents by Richard Muller.
Accordingly, what happened was that the burning gasoline in the plane melted the metal support structure on one of the floors, so that one floor collapsed onto another (like the melting of a cake layer). When the first floor collapsed, this caused a domino effect as the lower floors failed structurally one after another.
So the building fell due to fire rather than the impact of the plane. I am told this is consistent with the time scale of the building collapse.
In any case, I’m not deleting my previous comment with all speculations because it still goes to show; the dynamical system of the building and the plane was too complex to guess what was going on.
I’m not a structural engineer either but I can guess why intuition built from the breakage of objects on a scale of several feet, as we more typically encounter, cannot apply to the demolition of a skyscraper.
First, the entire column of the skyscraper should have a lot of inertia—why would it tip horizontally in one direction or another without a significant continued force to do so?
You’re probably underestimating the cohesion of the floors, one to another. Maybe they’re not like layers of cake balanced on toothpicks. Just a few internal structures connecting the floors (like concrete staircases?) make a vertical crumbling fall seem much more reasonable.
An impact that is strong enough to break a hole in an exterior wall doesn’t just affect that wall, presumably the whole building would be agitated, shaking and wobbling at various sonic and supersonic frequencies. (Thunder during a storm is enough to cause my house to resonate and rattle the mirrors on my wall.)
I’m not saying that I would have predicted that the building would fall vertically rather than tip over. I’m just saying that I would expect that the fall of an enormous building with lots of external and internal structure to be more complex than my intuition could accommodate.
If I was worried about there being a conspiracy, and it was because the fall of this building was nagging at me, what I would do—because I know from experience this is what I do when I worry—is I would go to youtube and google “building collapse” and see if buildings typically fall in ways that I expect, and if there’s a lot of variation, etc. I would see if after watching a few buildings collapse at that scale, if my brain could extract enough information to really feel comfortable one way or another about the likelihood of identifying a ‘false’ collapse..
(Seeing what structural engineers have to say about it is not the first thing I would do, because I expect demolition models are like climate models—you have enough free parameters and undetermined assumptions to get out anything.)
When I first started back to school in 2006, I was studying Engineering. I was in a materials class when they did strength testing of various materials. I remember the noise that the breaking I-Beam made when it snapped. It did not just go “Ping” like many people think, but rather sounded like a combination of an explosion and a breaking mirror (a BIG mirror).
We had a short discussion at this point about 9/11 and the reported “explosions” hear within the building. The professor asked what those noises might have been (nodding at the tiny I-Beam we had just broken and mentioning that the I-Beams in the WTC where hundreds of times larger).
It did not take us long to get the clue that the “explosions” hear were large structural members breaking under incredible strain, and that the stored up energy in these members was then released further along the member’s length (so, you get this recursively adding structural failure that generates louder and louder “BANGs” as the buildings falls).
The pancaking of the floors is just a part of that process. Also, as you mention below… The fire did not need to melt anything, all it needed to do was to remove just enough strength from one portion of the building to have that fail, and have the other supporting redundant members have just enough strength sapped from them as well to begin a catastrophic failure. If the fire did melt things (as is possible when you have a hot firing burning in an oxygen deprived environment, it will heap up to huge temperature and then if a hole were to suddenly appear that allowed in oxygen. It will act like a blowtorch—we got to do this in class too) then that would just make the failure all the more spectacular...
I’ll shut up now...
I’m not deleting this previous comment, but someone over my shoulder tells me they just read about this in Physics for Future Presidents by Richard Muller.
Accordingly, what happened was that the burning gasoline in the plane melted the metal support structure on one of the floors, so that one floor collapsed onto another (like the melting of a cake layer). When the first floor collapsed, this caused a domino effect as the lower floors failed structurally one after another.
So the building fell due to fire rather than the impact of the plane. I am told this is consistent with the time scale of the building collapse.
In any case, I’m not deleting my previous comment with all speculations because it still goes to show; the dynamical system of the building and the plane was too complex to guess what was going on.
Well, in this thread we are discussing the collapse of WTC7 which was not hit by any plane.