14-08-2013, 09:24 AM
(This post was last modified: 14-08-2013, 09:53 AM by Tony Szamboti.)
Phil Dragoo Wrote:The hat trusses said to have weakened and sagged forty inches, in tests sagged two to six, and could not have initiated collapse absent significant weakening of core columns--likely by charges, as no other cause presents.Phil, I think you meant to say it was the floor trusses under the floor slabs between the core and perimeter which NIST claimed sagged 40+ inches and pulled in the south exterior wall of WTC 1 (North Tower) over several stories around the 98th floor. Of course, there are serious problems with this theory as they couldn't get the sagging trusses to pull the exterior columns inward in their FEA model and the trusses did not sag anywhere near what they claimed in their actual floor slab fire testing, as you state. The only legitimate mechanism to pull in the perimeter columns was a falling core and there was not enough heat to weaken the core and cause the acceleration observed over the first story of the fall.
In case you aren't aware, the hat truss was a large truss at the top three floors of the building, with A-frame outriggers connecting the core to the perimeter, intended to spread the antenna wind load induced moments out to the perimeter which cut down the vertical force required to counteract them due to the increased lever arm. Lauren put pictorials of it in post #292 of this thread.