femr2 wrote:Splendid. So do you agree that any debris falling/emerging from the footprint above that point is irrelevant, as the actual point of destruction is lower down in the tower ?
I agree that debris emerging from the footprint is irrelevant in that it is not participating with impact and crushing.
Not quite what I asked. I'd suggest debris emerging from the footprint has already
participated in impact and crushing, or it wouldn't be crushed. Agreed ?
Again, my (leading) question is to clarify with you that, regardless of the cause of the "crush front", everything you see above that is not going to be relevant to the cause of that crush front. Agreed ?
However, I feel that it is still relevant with regard to mass and energy considerations.
Why ? You're now hopefully aware of the ROOSD process in enough detail to know that numbers bandied around "out there" have very little to do with reality.
Presumably you have already done calculations and concluded that even with the amount of energy being expended pulverizing concrete and other interior materials, there is still enough energy available in the crush front to cause failure of the columns and sustain a downward acceleration of the crush front.
Correct. Also bear in mind that crushing is not a separate process. Also bear in mind that not too many columns buckled in the sense used in many calculations. Instead the OOS floor regions were stripped from the core, and the core kind of prised apart at the seams by falling mass. The core floors themselves were thicker than the OOS regions, and there was plenty of mass in there to break core beam connections once the OOS region support had gone.
the load being experienced by the columns in the lower portion of the building is decreasing; thus increasing the margin between the load that they are experiencing and the maximum load allowed by the factor of safety, and thus making buckling due to overload less likely.
Again the core columns did not buckle in any great numbers, but instead broke at the joins between 3-storey sections or fell outwards in multi-column sections.
Which raises another question: how many buckled columns, due to vertical overload conditions and not horizontal impact, were found in the debris?
A small proportion.
femr2 wrote:As long as there's enough mass acting at that crush front (which we've worked out to bo about 3 storeys worth) then the rest of the mass (many floors worth by the time of that photo) is not necessary and is quite at liberty to fall out wherever it pleases without affecting the crush front propogation. Yes ?
If the mass is "enough", then yes. Does 3 storys worth of mass apply through the entire height of the building, from top to bottom?
Yes (almost). The floor connections were pretty much constant throught the tower height, apart from the MER floors, which were stronger.
Do you have an explanation handy for what appears to be trails of white smoke coming from the ends of pieces of steel flying through the air?