What? As the metal cooled down? For cryin' out loud this whole fiasco lasted less than an hour, steel that expands "six inches" in your "1800 degree" fire would take the friggin' day to return back to ambient size unless you quenched it with water. But then it flared up again after crashing to the ground and stayed glowing orange for another month... OK.
The more you explain the less sense it makes.
In the words of Prof. Abolhassan Astaneh-Asl himself...
"I have not been provided with the information made available to the FEMA Building Performance Assessment Team. This includes, videotapes and photographs taken on 9/11and the following days and copies of the engineering drawings. At this time, having the videotapes, photographs and copies of the drawings not only is useful, but also is essential in enabling us to conduct any analysis of the collapse and to formulate conclusions from our effort."
He may be a good investigator but arrived 8 days after the fact and was hindered in his efforts.