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Re: Plywood rigid diaphragms

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I consider plywood diaphragm semi-rigid. If we define a 100% flexible
diaphragm as one which distribute lateral loads to shear walls according to
the wall's tributary width and a 100% rigid diaphragm as one which distribute
lateral loads to shear walls according to the wall's relative rigidity, then,
a plywood diaphragm's distrubution of lateral load fall somewhere in between.
We don't know where because we don't have the exact formula for plywood
diaphragm and plywood shear walls. So right now we just simplify it by
assuming a 100% flexible diapragm and no relative rigidity distribution at the
shear walls.

If we use an approximate formula(derived by experiments on actual diaphragms
and walls) and consider all the physical characteristics of the diaphragm and
shear wall(such as diaphragm openings for stairs, elevators, shafts, etc and
shear wall openings such as doors and windows), we can distribute the loads to
each section of wall by relative rigidity, the same way we do it on concrete
or masonry walls. We can simplify shear wall distribution by relative rigidity
by using only walls that extend full height and neglect the effect of the part
of the wall above doors and above and below windows, OR,  we can include them
and design the appropriate straps across the corners of these openings after
the loads have been distributed and make sure the these portion of the wall
also gets a plywood shear wall, not only the full height ones. We make sure we
include the effects of holddown anchor tightening, allowances for bolt holes,
nails slippage, etc.

It can be done and it will happen. It is just a matter of time before someone
or some organization spend time, money and effort to get all the pertinent
formulas generated and accepted by the structural engineering community,
included in the codes, and required for all plywood diaphragm and shear wall
calculations. It's gonna be more work for us wood engineers but that is what
has been happening anyway every new code edition for revised seismic and wind
formulas, USD on concrete, strength design on masonry, LRFD on steel, maybe
LRFD on wood later, new provisions after earthquake and strong wind disasters
, etc.

Just my opinion on the future of wood shear wall design.

Ernie Natividad