The inward bowing of the east wall, due to the inward pull
of the sagging floors, caused failure of exterior column splices
and spandrels and resulted in the east wall columns becoming unstable.
The instability progressed horizontally across the entire east face.
The east wall, now unable to bear its gravity loads, redistributed them
to the thermally weakened core through the hat truss and
to the east and west walls through the spandrels.