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Re: residential plywood diaphragm glue

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Very funny.


Rob Rodgers, S.E.


> >  I understand that the
> >reason we do not use glued shearwalls is that the failure would be
brittle
> >as opposed to ductile.
> ----------------------------
> That's my understanding too, but it's still an idea to poke fun at.
>
> It's the same reason why not to "glue" steel moment frames together with
> weld metal, and besides we can't afford another SAC Project just on glued
> plywood shearwalls.
>
> It might help even more if the plywood itself weren't glued up rigidly,
but
> was mechanically laminated with zillions of little staples. Common
staples,
> that is, not box staples. Then the plywood could be nailed on with box
nails
> instead of commons, to protect the framing from brittle splitting failure.
>
> Also, glued wood products like I-joists should have nailed-on flanges,
like
> old-time riveted steel plate girders, to avoid brittle failures and obtain
> ductile ones.
>
> Concrete, being made of various sizes of stones glued together with
> water-based cement (not even real glue) is notoriously brittle, and should
> be prohibited outright.
>
> Masonry is like concrete, except the stones are precast and placed by hand
> in horizontal failure planes, and the "glue" is mixed up like batter in a
> doughnut shop that cops hang out at. Brittle behavior on the job is the
> typical result in both cases.
>
> On the other hand, if "failure" can be designed against, glued wood can
work
> and perform pretty well. The Brits and Canadians glued up many thousands
of
> wood framed and plywood veneer sheathed airplanes in the early 1940's that
> served as high performance light bombers, night fighters, and photo recon
> planes. They flew nearly 400 mph and didn't fail in a ductile manner or in
> any other way, once sorted out.
>
> The ability to sort out glued wood for elaborate load combinations was
> present at DeHavilland Aircraft for their "Mosquito" way back then, but
has
> yet to even be forseen among earthquake code engineers 60 years later. For
> airfield landing loads, they designed their "ductility" into the landing
> gear struts and tires. If not living in a life of seismic codewriting, one
> might imagine glued plywood shearwalls having external devices and
anchorage
> provisions that served similar purposes, for when the very high, very
stiff
> glued strengths might still be exceeded. But now any such attempt is
> forbidden in advance. "Chicken" comes first, so no egg.
>
> And we still call ourselves engineers.
>
> Charles O. Greenlaw
>
>
>