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residential plywood diaphragm gue

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Nonlinear behavior allows the tributary area 
method to work, but that doesn?t mean that the 
plywood diaphragm is flexible.

Plywood diaphragms are mostly rigid in residential 
structures. The code has made it so. Maybe the 
span of the diaphragm should have been the full 
width of the diaphragm, not the smaller spans 
between two intermediate shear walls. Torsion 
affects are of the whole diaphragm.

The ?tributary area method designs? may have 
survived earthquake events because the shear walls 
behave non-linearly. 

The floor glue does, or does not, add rigidity. 
Demolition of glued floors leaves split wood 
framing and the glue does not fail. We can?t rely on 
the glue, ?what if the wood was wet at application? 
but nor should one rely on the glue not adhering.  
The glue is there and the result is most likely a 
rigid diaphragm. Specifying that floor glue is not 
allowed could be a liability.

My bet is that the glue increases the rigidity of a 
diaphragm. Floor glue is flexible, as in a slow 
movement or creep, but probably acts rigidly under 
a seismic impact load. I would say first prove it not 
rather than assuming a ?wiggly glue?.

Tributary area methods may be reasonable for the 
initial distribution of loads; the loads may very 
well be delivered as such, in an ultimate strength 
analysis, but not because the diaphragm is flexible. 
Analysis and detailing may be misdirected by 
assuming a flexible diaphragm rather than yielding 
and performing plywood shear walls. 

David Merrick, SE