What exactly did NIST change their opinion on?

[Caper]

Lately I've had a few truthers us the line "NIST keeps changing their story".... Apparently from the towers had collapsed from just fire, to what ever their current position is (a compination of damage from the plane and then fires, I'm guessing.

Was there ever a change in the NIST hypothis as to why WTC1 & 2 collapsed?

[R.Mackey]

Lately I've had a few truthers us the line "NIST keeps changing their story".... Apparently from the towers had collapsed from just fire, to what ever their current position is (a compination of damage from the plane and then fires, I'm guessing.

Was there ever a change in the NIST hypothis as to why WTC1 & 2 collapsed?

The big shift is, of course, away from the "pancaking" theory floated by Dr. Eagar and others, and towards the more complex collapse initiation theory involving attached, but bowed, floor trusses, that pulled in the perimeter columns at the connections until they failed. More detailed photographs alone are enough to get us thinking in this direction, but you can also see additional details of this in NCSTAR1-6C and 1-6D as their modeling reveals, to their surprise, that the other candidate for inward wall bowing -- total failure of floors leading to longer unsupported perimeter column lengths, which would support buckling -- turns out not to work after all.

There are some other minor surprises, such as the relatively good performance of intact floor trusses in certification tests, relatively poor adhesive performance of the sprayed-on fireproofing, and the much greater influence of the hat truss than originally anticipated. But really, all it takes to appreciate the NIST theory is looking at the pictures up close. NCSTAR1-5A, alone, refutes every alternate collapse theory I've ever read. Most of these pictures were not available to the early investigations.

[Caper]

My god you do great work. Thanks.