> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Gibson Jonathan > Sent: Thursday, June 29, 2006 1:18 PM > To: Killer Bs Discussion > Subject: Re: Physics Prof Finds Thermate in WTC Physical Samples > > > I have yet to see a model - or even discussion - on how such metal is a > renowned heat wick and just how this would have mitigated total > systemic collapse... unless the argument is that this apparently > minimal heat was X-ferred down the entire skeleton structure... leading > to the "Soft Butter" support member lack of resistance that allowed the > entire building to fall at damn-near free-fall speeds - all at once. > Seems a stretch.
As Charlie pointed out, it wasn't all at once. Floor by floor, it collapsed, from multiple shocks. I discussed the physics of this at some length in an earlier post. The essence of what I am arguing is that the time to build the g forces necessary for the falling mass of floors X+1 to 110+ to build up sufficient g forces to break though floor X is very short....say ~10msec. That is not surprising. If it is traveling at only 100 feet/sec, then this is the time it takes to travel 1 foot. The floor has to give 1 foot, fairly uniformly, or break in 10 msec.** To move 1 foot in 10 msec, it has to be accelerated at a rate of 8 g's. There is some resistance to this, of course, so the force of the falling upper stories has to be greater than 8 g's. I'd have to look at stress-strain curves and the building structure to give a good number, but I have a hard time seeing the lower floors not breaking before they are displaced 1 foot downwards. Shear, as Charlie suggested, looks like a very good candidate for the failure mechanism to me. Since this is the second time I explained this, I get the feeling that I'm not being as clear as I might wish. It would be helpful for you to tell me what about the shock wave propagation that I describe is troublesome for you. Dan M. ** Well, the falling mass could also be squeezed together, with the bottom part decelerating at a higher rate than the top part. But, this doesn't buy a whole lot of time before the forces needed for further compaction are multiple g's. Not a whole lot would probably add to one or two hundred msec. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
