Alright, folks, I think I got it:
K(falling girder) = 81/2 E*I/L^3 = 48.15 kip/in
I opened a thread in the Science&Technology section of ISF, hoping to attract the attention of some engineering type of person not usually lurking "9/11 CTs". Didn't really find any and helped myself, and here is my derivation:
http://www.internationalskeptics.com/forums/showthread.php?postid=11088153#post11088153 (and following post).
Can you look at this and check whether I make sense and did my multisubplitractions right?
With that value, I get K(eff) = 47.85 kip/in and equivalent Force F = 576.5 kip.
That's within 10% of Nordenson's connection capacity (632 kip)! In other words: Deep in "
maybe" territory.
Deflection is in the vicinity of 12 inches (formula for max. deflection of an unsymmetrically loaded beam is a bit complicated, haven't bothered yet), so average deflection would be anywhere between 4 and 12 inches, adding a bit of PE to the 46 kips * 83 in = 3818 kip*in gross PE Nordensen started out with.
Also, being so close to the break point, we'd now might feel compelled to scrutinze all the values we have so far, consider that heat may ir may not have decreased shear capacity (how hot did the connection get in the various fire models?), that heat probably decreased girder stiffness (how hot did it get, on average, in the ARUP and NIST models?), and think hard about possible further energy sinks and whether or not they are significant.
My hunch is that all these effects are small in magnitude (each affects the effective force by no more than 10% - order of magnutide - and some may cancel out). The only variable that I don't have a hunch about is the connection temperature (and whether or not the connection on floor 12 was already damaged somewhat). The girders got hot, the column did not - and the connection?