Lateral movement of the C79-44 girder was due to the expansion and/or later the sagging of the floor beams that framed into it from the east. The axial expansion in the girder itself moves it's ends closer to the C79/44 faces and is important because the west sideplate on C79 overhangs the edge, and the girder expands to the inside of it and so cannot possibly fail to the west at the temperatures illustrated in the 3 NIST case outputs that you were shown earlier. Every ARUP simulation shows this trapping of the girder at lower temperatures than NIST claim to have observed it fail to the west at.
Even NIST's own figure shows it is trapped.
View attachment 67198957
So the girder has to contract to the inside of the sideplate to be able to fail east or west. That requires it to be in a cooling phase and it will cool slower than the beams will making it impossible for the girder to fail as per NIST's stated hypothesis. *(ETA - Should say that Case 3 ARUP shows a failure in the heating phase due to sagging at temperature hundreds of degrees in excess of NIST's estimates.)
Shyam Sunder, WTC Lead Investigator, NIST,
"And the main reason
the girder can be pushed off to the west is there is no opposing beam on this side trying to push it back to the east, because of the arrangement of the floor framing system. And, as you see in the sketch on your slides, you will see that once the bolts break, then you have essentially the girder moves off the seat and eventually falls."
