04-03-2014, 02:28 AM
Lauren Johnson Wrote:Peter, I really don't understand the stiffener issue. Do you understand it and mind explaining it to those of us who don't?
Hi Lauren and Peter,
I was just bouncing around on the Internet to see how much play the NIST omissions issue has gotten and saw Peter's thread here and Lauren's question.
The stiffeners are vertical plates on the girder which are welded to both the web and flanges. NIST claimed that when the girder web was pushed past its seat at the column connection that the load was too much for the .855" thick flange to take and that it would fail by bending upward. That would be true if it was only the flange involved and that is what the figures in the NIST report show.
However, the drawings for WTC 7 were finally released due to a FOIA request about three years after the WTC 7 report and when they were reviewed it was found that the girder had these 18" high x 3/4" thick web to flange stiffeners. The stiffeners make the flange about 58 times stronger in bending and make the NIST collapse initiation hypothesis impossible. The stiffened flange makes it so they can't push the girder far enough to get it to fall off the seat by causing the flange to fail.
The interesting thing is that they did not release all of the drawings and the actual girder fabrication drawing was not released. However, there was an assembly drawing which showed the girder to column connection from the side and it contained the stiffeners. David Cole found them and notified several of us about it asking if it would make a difference. I immediately knew it would and the structural engineer (Ron Brookman) who got the drawings released sent NIST a letter about it. They ignored the stiffener issue for almost two years but Cole finally got them to admit they left them out which they claimed they did as they were for web crippling and that their analysis said web crippling wasn't an issue. Of course, that is circular reasoning and they cannot get around the fact that these stiffeners strengthen the flange enormously. They will have to redo their analysis with the omitted features included. This somewhat invalidates the NIST WTC 7 report as they no longer have an initiating mechanism and they will not be able to make bare assertions any longer without review after this hit to their credibility.