Pancaking Floors Leave Unsupported Columns
Tall freestanding columns?
We see only short freefalling column fragments.
FEMA's Report authors imply that 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.