From: merrick group <merrickgroup(--nospam--at)compuserve.com>
Date: Mon, 10 Jan 2000 16:43:45 -0500
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
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