Rigid Wood Diaphragms 1

I have been researching rigid wood diaphragms for an upcoming project. i understand that it can be classified as rigid based on the big long deflection equation from IBC and AWC and comparing it to shear wall deflection.

i would ask if anyone has any tips in classifying a timber diaphragm as rigid. also, how is nail slip quantified for the deflection equation? any tips on quantifying shear wall anchorage elongation besides PL/AE?

thanks for you help in advance.