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Re: plywood glued to framing

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----- Original Message -----
From: John Rose <jrose36(--nospam--at)earthlink.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, January 11, 2000 7:15 PM
Subject: Re: plywood glued to framing


3M 5230 adhesive (a 100% solids polyurethane) was on the market for a long
time, since the early 1970s. At one time, it had ICBO ES recognition for
semi-structural gluing, even for glued diaphragms with T&G lumber decking.
It
was quite costly because of its high-tech formulation. It has been taken off
the market (so I understand), but a marine version (5200) is still
available,
also costly.


John-
I did a qucik search of the 3M web site & found.....

http://www.mmm.com/market/construction/html/products/product32_p.html
. Scotch-Grip Wood Adhesive 5230 -- The first wood adhesive to have design
strength values recognized by ICBO for structural wood bonding in
applications such as shear walls, and diaphragm construction.


Looks like they still make it...at least it's on their web site.

I agree with John that glue will only be helpful in narrow shearwalls..I'd
be very surprised if glued walls could match the even limited ductility of a
conventionally nailed shearwall of 2:1 to 1:1 aspect ratios.

Robert Kazanjy, PE  **Disclaimer: I speak for myself not UC-Irvine**
Senior Development Engineer
Civil & Environmental Engineering
UC Irvine


John rose wrote:
Glued shear walls were tested at Michigan Technological Institute back in
the
1960s or 70s. A finite element analysis was developed for their design. The
resulting structure was very stiff (linear elastic to strength limit state),
but strength was limited by "rolling shear" failures between the sheathing
and
framing at the corners of the panels, where shear forces are highest. One
way
around this would be to add extra framing at plates and panel edges to
increase
the glue contact area.  Also, fasteners such as nails or staples still would
be
required to provide some ductility if strength limit state is reached (to
avoid
brittle failure).  Such application would require a substantial amount of
adhesive around the panel perimeter; about 24 lf of adhesive per 4x8 panel,
if
only the perimeter is glued, more if panel is also adhered to interior
framing.  Say about 1/10 gal of adhesive per 4x8 panel, based on 37 lf at
1/4"
dia. bead (for 5230, this amounts to about $6-8 per panel just for adhesive,
plus labor to apply adhesive). Glued shear walls might make sense for narrow
shear walls (aspect ratio greater than 2:1), where stiffness is a concern.

APA also tested glued diaphragms (see APA Report 138). The surprising thing
is
that the diaphragms acted more like a true beam, with parabolic shear
distribution which was maximum along the horizontal axis at mid-width of the
diaphragm, rather than uniform shear in both axes with a maximum at the end
supports (shear walls).

John Rose/APA, Tacoma, WA