The Truss Failure Theory According to FEMA
FEMA's BPAT gave the truss failure theory
the official stamp of legitimacy in their report.
Tall freestanding columns?
We see only short freefalling column fragments.
They say the perimeter and core columns would self-destruct
if the floor diaphragms collapsed:
As the floors collapsed, this left tall freestanding portions
of the exterior wall and possibly central core columns.
As the unsupported height of these freestanding exterior wall elements
increased, they buckled at the bolted column splice connections,
and also collapsed.
The columns were not freestanding:
- The perimeter columns were grids with horizontal spandrel
plates linking the columns.
- The core structures were lattices, densely cross-braced.
Note legalistic CYA language possibly central core columns:
Engineers knew floor failures would not destroy core structures.