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Re: plywood glued to framing

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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.

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

merrick group wrote:

> Martin W. Johnson has called attention to the ?3M 5230 adhesive?, a ?break
> through?
> for shear walls!
> I was talking about whether or not glue adds rigidity to floors. I argue
> that it does,
> hence rigid diaphragms. It seems that this glue may add strength and
> rigidity but is
> not brittle. That is good.
> I like that glue! Is it the only product that behaves in this way? I
> suspect a little
> competition by other glues would get your funding. I am emailing another
> engineer
> interested in testing shear walls if he get started on a project for other
> glues, I?ll tell
> Martin.
> It would be important that if a glue was used, that the HD strengths were
> higher than
> the maximum possible strength of glued and nailed plywood. I suspect in
> using the glue
> that Martin knows of its maximum probable strength.
> There might be a difference between static tests and dynamic.  You know,
> the: more elastic
> ?gummy? thing. Its probably not what: wiggly. So I pulled out my gum to see
> if it snapped
> at different speeds. It seems to be dependant on how cold it is and if it
> is
> real bubble gum. It wasn't wiggly like jello.
> David Merrick, SE
> Recall message from Martin W. Johnson
> We often use 3M 5230 adhesive when we install new wood framing in retrofit
> work.
> It has a more elastic "gummy" hardness after it dries that allows the nails
> to
> continue to form ductile bending mechanisms.  We did some limited testing
> in
> samples using it after the Northridge EQ and were able to develop
> substantial
> strengths and ductilities.  Being more elastic, the glue tends to roll into
> tiny
> beads as the nails bend and the deformations become large.  We were even
> able to
> get significant ductility using screws in parallel with the glue.  It's too
> bad
> we didn't have the time or budget to carry through and publish the results.