It's got something I hadn't thought of for some reason: the thermal expansion of the steel beams.
Should have occurred to me before. People generally don't realize just how much a big piece of steel increases in length as heat rises. First time this whacked me was the first time I hardened & tempered a broadsword. I've got a long, narrow forge just for hardening & tempering, and the blade fit in with room to spare. Until it got up toward critical temperature; it stretched enough that I had to cut more than an inch off the tang(oversize, so not a big problem) for it to fit. Now think of a beam many feet long and weighing many, many pounds, coming up to high heat... I don't know the formula to figure it, but the increase in length would put enormous strain on that beam and anything it was connected to. Enough, unsurprisingly, to make connections fail. And that triggered a cascade of failures.
I'm sure the truthers have another explanation, probably involving a SEAL team with cutting torches on a suicide mission or something.