From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
Date: Mon, 10 Jan 2000 22:02:17 -0800
> 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
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
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