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Re: Wood Adhesives

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We recently did seismic retrofitting of a condo project (retrofitting was
done after settlement of a construction defects claim), where new shear
walls and shear transfers were installed, including blocking attachments to
the underside of existing roof sheathing.  We found no reliable existing
data and therefore had test samples assembled and tested by a testing lab.
We used two beads of adhesive, 1/4-inch in diameter, applies to the blocks.
No special clamping was used, nor was there any special cleaning of either
the plywood or block surfaces.  Cyclic testing was done until failure.  Two
different types of adhesive were used:  Hilti (not epoxy) and Covert (epoxy)
adhered to 15/32" plywood (not Structural 1 material) in single shear.  For
two beads of adhesive, the lowest failure load was about 8,000#/ft, with the
Hilti not quite as strong as the Covert, but less expensive (mode of failure
for Hilti was the glue, and for Covert was tearing of the wood).  The
adhesive was approved for use on this project  by the building department
(in San Jose, CA).  Our working-level shears were only about 400#/ft, so
there was a significant factor of safety.  Testing  was cost-effective for
this project because the detail was used extensively and did not require
roofing removal.  In other words, the testing paid for itself.  For a small
residential project, this may not be true (full testing and documentation
was about $5,000).

----- Original Message -----
From: Robert Fennema, P.E. <bobfennema(--nospam--at)home.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, July 21, 1999 9:14 PM
Subject: Wood Adhesives


> I am designing a detail to correct a construction defect. The
> contractor failed to install blocking and boundary nailing at the top of
> the shear walls perpendicular to the roof rafters. This is only one of
> the many shear transfer connections omitted from this 12,000 SF home.
>
> Of course the roof covering is on. It is a two piece clay tile system
> set in mortar.  We would like to repair the defect without removing the
> roof covering to install the missing boundary nailing.
>
> Am considering gluing a 2 x 4 block flat onto the underside of the OSB
> roof sheathing and connecting it to a new block on the shear wall using
> an A35. I need help selecting the adhesive that would substitute for
> the lack of boundary nailing.  Does anyone know the shear transfer
> values of various adhesives that might be available?  I guess this would
> be expressed in # per sq in.
>
> Is this an acceptable idea?
>
>