At 02:04 PM 03/20/2003 -0500, Steve Thompson wrote:
This seems reasonable. As a large structure topples,
the sheer stress across the long axis of the building
will inexorably increase as the upper floors retard
the downward progression of the lower floors (caused
of course by gravity). I suspect that a large
structure such as a WTC tower would cant no more than
a few degrees before loading stresses opposite to the
design of the compression structure caused a series of
gross structural failures -- which would allow the
building to fall mostly `in place'.
If the collapse starts from the upper floors,
as this one did, then perhaps the upper floors are retarding
the downward collapse, but when the damage starts on the bottom,
the upper floors aren't retarding anything - they're adding weight.
The weight might be somewhat balanced, so I'm not sure that it's
not self-aligning, but that probably also depends a lot on
how the lower floors are attached together and to the ground,
and how centralized the columns are that support the upper floors.
