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Originally posted by MikeVet
1- oh, i'm sure about it. but, now i understand your confusion. you think that a global collapse would be initiated by a floor falling. This is incorrect. as i stated before, but you decided to edit out, the floors sagging/failing/pulling the exterior columns out of vertical alignment would only make the exterior columns more prone to buckle, which lessens steel's ability to absorb compression loads.
since it must be agreed upon that the exterior columns supported some of the vertical loads - around 50%?
a global collapse would be initiated when the load capacity of the columns -both core and exterior- were exceeded, and at the point of failure, the entire mass above would fall as one onto the mass below.
we agree that a global collapse couldn't be initiated by a single floor falling onto a floor below, so that avenue of discussion is a pointless waste of bandwidth, agreed?
2- simple answer again here, even though i suspect you're looking for something much more complicated/conspiracy friendly. The core structure would "go" when their load bearing capacity was exceeded
3- actually the fires, if we accept your 15% calc, would only have to do 233% of the weakening that the planes did, not 400%. i'll ask again, do you have any idea, since i see your an engineering student, what a typical safety factor might be? i'd assume you have sources..... again, structural docs would be nice.
3- actually the fires, if we accept your 15% calc, would only have to do 233% of the weakening that the planes did
did i interpret it right and the connections are 11x as strong as necessary?
5- so then by your reasoning, if i give the angles, then we can agree that the building didn't collapse symmetrically?
Originally posted by bsbray11
Ok, but this doesn't have anything to do with (a) dynamic (impact) loading of the floors, or (b) floor connections failing. Both of these are required by "traditional theory" to progressive the global collapse downward.
Around that much but the higher perimeter columns also had much greater FoS ratings than 2.
That is incorrect. Floors may fall, theoretically, if you want to generalize and be vague and not realistic. The columns would not telescope into themselves. Nor would they just rip apart. Buckling is buckling, and that's only for the perimeter columns theoretically. Remember none of this was ever proven.
It depends on whether you want that dynamic loading or not. The buckling columns would not experience impact loading, nor loading of so many more floors than they were built for, because the columns held ALL of the floors above them on a day to day basis at just the design strength.
But how do you define "go"? Does "go" mean they just start moving downwards somehow? How does it move downwards? Do you know what the formal definitions of failures in steel structures are? Like buckling, etc.? What kind of failure would be a failure that's just "downward"? It doesn't exist. There is resistance if you try to do that, MASSIVE resistance, from the moment of inertia of the entire lower column and all of its bracing and connections to the rest of the structure. That stuff doesn't just move on a whim like you think a single floor would.
The only source I can offer is from one of the engineering teams in the 1960s suggesting the perimeter columns of the upper floors had FoS ratings of 20.
I said >15%. The real numbers are like 11% and 13% for the perimeter columns on those floors according to FEMA, and NIST did core modeling and came up with something like 7-8 core columns severed max, and this was even after changing Flight 175's impact angle.
How would I know, if I don't have the structural documents?
The angles would be like 5 degrees and I would ignore you because any discerning person familiar with anything related to engineering knows how small of a margin of error 5/180 or 5/90 is. 10% is considered a reasonable tolerance for most purposes.
Really anyone with EYES can look at WTC1 fall and see that it happens evenly, that the roof line drops pretty flat the whole way across, there is no tilting or asymmetrical loading. It's as if everything were pulled at the same instant. It's really pathetic when such an obvious fact can't be grasped, and someone tries to cloud it by turning it into semantics. There is no amount of explaining you can do to explain this to me, because I already understand it simply by looking at it. When everything falls evenly, at the same time, that means, guess what?, it must have failed at the same time. To within a very small difference, such that you can hardly even tell, if you can tell at all.
Originally posted by MikeVet
Because I'm going by what NIST says. This must be the basis of our inability to communicate.
3- again with telescoping. I thought we agreed that columns would bend , buckle, and break?
I think we agree that the core columns, regardless of their bracing, would buckle at some undefined point. So what is incorrect? that a global collapse would involve columns b, b, and b'ing? How else could it be described then? We agree that floors failing wouldn't be called a global collapse, neither would they be the cause of it. So what else is left?
A downward failure would need a combo of things, the way I imagine it. You'd need buckling, followed by bending, plastic deformation, inelastic deformation and a whole variety of things going on.
7-I disagree with 7-8 max severed. Perhaps max on 1 floor, but when all floors are taken into account, the cummulative number is higher. And there were more that were damaged, so maybe your 15% estimate is too low? Meaning that fire would have to do less weakening.
9- Remind me to not go into any building you design if you think 10 degrees is of no consequence !!!!!
But since I see you already know the angles, why did you ask me to provide them? Totally unnecessary, IMHO.
This is the nature of a global collapse, it's not semantics, as you claim.