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RE: Report on Wood Diaphragm

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|~|Every house that I know of, has glued floors, how is a glued
|~|floor going to perform as a flexible diaphragm?

...turn on broken record:

For that matter, who knows how it is going to perform. Does the empirical
deflection formula consider glue? Most subfloor glue is somewhat flexible to
provide reduced sound/impact. It clearly is not a glu lam type glue. Has
there been any deflection tests to prove the glue changes the stiffness of
the diaphragm from a flexible to rigid diaphragm? How does the glue fail,
before or after nail slip? What is the effect of the glue relative to
nailing spacing and floor blocking? Does deflection formulas consider
ceiling sheetrock and partition wall effects? Roof diaphragms are usually
not glued and unblocked. Can we accurately calculate how 2:1 shearwalls or
shear walls with openings deflect? I think the real behavior of wood
diaphragms in real world applications are less understood than concrete
rigid diaphragms. For that reason why pretend that we do understand this and
impose a more complicated analysis. It's twisted logic when the premise is
flawed. Sure we could require a rigid diaphragm analysis for plywood
diaphragms, why not also do a finite element analysis for the diaphragms and
shearwalls? (I once talked to an engineer that told me he used ABAQUS to
design a wood framed residence.)

The better performing residential buildings are those that have a well
detailed load path with special consideration for continuity and anchorage
connections, low aspect ratio plywood shearwalls, with good workmanship and
a formal inspection program. The question has been asked before: has there
been any evidence of structural failure or unacceptable performance of a
residential wood framed building designed as a flexible diaphragm (that is,
properly designed, detailed and inspected) that could be attributed to
behaving as a rigid diaphragm? (Not including the improperly designed
Northridge open carports.)

I would suggest that we revise conventional construction provisions for 3
story and less wood diaphragm buildings in seismic zone 3 and 4 so that the
static force, flexible diaphragm provisions essentially take the place of
conventional construction. Unusual conditions in geometry and redundancy
would require a more detailed analysis.

Jeff Smith, S.E.