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Re: diaphragm drift limitation

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The walls at ends of beams, perpendicular to the wall, need to be checked
for deformation compatibility of the differential rotation between the wall
and beams. Additional tension may occur in diaphragm anchors to wall,
increase moments in wall and beam, and may tear away the diaphragm from the
wall.

A reduction of seismic response, due to a high period of the flexible
diaphragm, might be considered. This is problematic because it is tinkering
with a possibly empirical code method with a dynamic analysis tool. Codes
have responded to tilt-up wall failures by increasing the forces at
mid-lengths of walls. This seems to not have addressed analytical reduction
of shear forces due to the increased period of large deflecting single story
diaphragms. The accelerations will be higher at the maximum deflections.
Does the code increase of acceleration at the maximum deflections account
for a designer reducing the base shear for a higher period? Did the observed
failures that the code responded to, occur not because of the design force
but because of the lack of deformation compatibility?

David Merrick, SE


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