ozeco41 wrote:Given that whatever hit the first floor down when the "global" or "progression" stage started was dynamic and included weight of top block rather than one or more disconnected floors
Have to disagree....
Great. I'm referring back to my own 2008 thinking - your details most likely better than mine. Could be interesting to work through it though my primary motivation here is to help illuminist14 get a handle on the basics. As you know I'm not all that driven by details unless they change the outcomes.
femr2 wrote:...Disparity between crush front "release" and propogation rate, when compared to roofline release and rate of descent, suggests that floor region(s) essentially separated from the "upper section" as part of the initiation process....
I have had in mind - with zero proof so it is a possible hypothesis only - that floor separation was initiated in two ways - one of them with two sub-sets.
1) The initiation resulting from accumulated damage in the impact and fire zone could well have separated some zones of flooring. I certainly don't envisage anything like a flat floor on flat floor interaction. And (almost??) certainly all the envisionable initiation mechanisms would cause some floor bits to break free.
2) The falling top block had its outer perimeter attached and that outer perimeter fell either inside or outside the lower perimeter - depending on which side of which tower we consider. I understand that you or Major_T know which ones went where. I don't and haven't needed the detail. However my preliminary part of an hypothesis has been that:
Sub set A - where the top block perimeter fell inside it would act as a knife edge putting a big load on the first floor it landed on and initiating disconnection of that floor. Full disconnection most likely a progressive event moving around the tower due to several factors.
Sub set B - Likewise but in reverse, where the Top Block perimeter fell outside the lower perimeter the lower perimeter moving upwards (relatively that is) to the top Block acted as a knife edge and separated floors in the top block.
All of that thinking based purely on thinking about possible mechanisms. Remember my objective has been "sufficient understanding to enable me to explain." For that objective I only need a plausible mechanism. Sure a probable mechanism is better if it is relatively easy to access.
Do you have data which proves what I say OR proves me wrong and supports and defines another mechanism?
femr2 wrote:...It may have been that after release of a floor or two upper section mass kicked ROOSD into motion, but it's a grey area in observational terms....
I would have thought very dark grey.
I continue to admire the work you and M_T have done. No way could I either be bothered or do it. but my needs have been very different also.
femr2 wrote:...ROOSD gets off too rapidly is the problem....
I may need to get to understand what that means/implies.
femr2 wrote:...We haven't looked at reduced load capacity in floor regions immediately below initiation zone.