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rigid plywood diaphragm??????

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Rigid plywood diaphragms are of code and 

Maybe something is wrong with the design if 
there is a radical difference between analysis 
for a rigid or flexible horizontal diaphragm.

Plywood stiffness is nearly directly related to 
its nailing shear capacity. The force is 
balanced by being delivered to where it can be 
resisted. Exception would be large h/t walls 
with flexible hold-downs. Replace the HD.

Tributary area methods for the flexible 
diaphragms places the rigid diaphragm shear 
center near to the mass center.

A test of rigidity is a global concern. Maybe 
the deflection test of rigidity should be from 
outside to outside wall where extreme affects 
of torsion occur.

APA publishes force deflection curves of 
wood shear walls. They are flat near their 
capacity and continue for a very large 
deflection. The walls will eventually share the 
load relative to their strength. Compare the 
results to the ductility factors of steel and see 
which is superior!

The above are issues for discussion only and 
are not to be considered as opinions.

David B. Merrick, SE