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RE: Rigid Wood Diaphragm?

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A non-generic design that will increase problematic deflections is not good.

Concrete topping may act rigid but at higher shear values, the concrete may
delaminate. Rigid and flexible analysis must be considered. Gluing down the
sheathing may have the same argument. For a ductile-load-criteria, maybe one
should greatly increase the shear to the relied-on rigid/brittle diaphragm.
Maybe use the OMEGA factor.

Identifying a wood diaphragm as rigid, is only for the purposes of
distributing the shear to the walls, not to justify deformation
compatibility and not to exceed allowed cantilevered diaphragm dimensions.

All systems will deflect. Compatibility of deformation in non-shear walls is
required. Unusual engineering approaches are difficult to defend. (Drift,
Glass, and life-safety). Drift is rarely checked in wood construction but
the designs are usually accepted because they follow generic shapes with
generic expectations. I have heard arguments against checking for wood
Deformation Compatibility. Such as, structures are rarely over three stories
high and windows are usually over planted areas or non-public areas.

Is observing no movement a true test? The 500 year (or more) event has
probably yet to occur.

A generic wood frame design allows 1/2" (or more) story movement. I  do not
like to wake up, before my coffee, to see 1/2" wall cracks and broken
windows. You want to make it worse?

David Merrick, SE



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