From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Sun, 9 May 1999 19:56:34 -0400
Rodrigo Lema wrote:
. > Roger Turk wrote:
. > "It seems to me that the definition of what constitutes a rigid and
. > flexible diaphragm is reversed. It seems to me that a flexible diaphragm
. > would be one whose "... maximum lateral deflection is *less* than ??
. > times the average story drift ... ." (Actually, why is it even related
. > to story drift?)"
. > I think the tie between the rigid/flexible diaphragm and the story drift
. > is that, if you think of the diaphragm as a deep beam supported on lateral
. > shearwalls, the deflection at midspan compared to the story drift (that
. > is, how much the supports move) is a good parameter to see if the
. > diaphragm is rigid or not. Just a thought.
. > Rodrigo Lema.
If the supports were infinitely stiff, I can't see how that would affect
whether or not the diaphragm is flexible or rigid. A flexible diaphragm
would impart one set of forces into the infinitely stiff supports and a rigid
diaphragm would impart a different set of forces into the infinitely stiff
supports. The deflection of the diaphragm at midspan would be one distance
if the diaphragm was flexible and another distance if the diaphragm was
rigid. For a diaphragm supported on flexible supports, the total movement of
the midspan of the diaphragm would be a rigid body displacement, due to the
deflection of the supports (shear walls), plus the deflection of the
diaphragm at midspan.
A. Roger Turk, P.E.(Structural)