Dennis Wish writes:<< how come we aren't considering URM retrofits with rigid
diaphragm analysis? >>
I believe the analysis approach for a typical URM building is an assumption
that the building is a single mode oscillator that moves instantaneously with
the ground. And the relative rigidity of straight or diagonal sheathing to
URM walls (13", 17" and 21" thick walls) would be great. Wouldn't these
conditions give little chance for a diaphragm to react and distribute forces
based on its rigidity?