Ben Yousefi, S.E. stated:
"It is not clear why you claim that per 1997 the diaphragm shall be
rigid. The definition of diaphragm rigidity has not changed from the 1994 to
1997 UBC. "
This is true, but the '97 code has taken away the ability to use professional
judgement in the evaluation of the diaphragm as rigid or stiff. Specific
seminars were devoted to preparing engineers to compare the rigidity of
diaphragms and those smaller buildings with aspect ratio's converging on 1
(between shear walls) will most likely calculate to be stiffer (lower
deflection) than the code cut off.