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Structural Adhesive Wood-to-wood

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 Jeff,

Thanks for posting this interesting problem to the list server.

I personally would be very leary of using any adhesive for this shear transfer
unless it has been TESTED and APPROVED for this use by ICBO or the local
building department.  A nailed or screwed shear transfer connection capable of
non-linear behavior (such as the one originally specify) is is always a good
choice, especially in areas having significant lateral forces.  The 3M 5230
product you mentioned WAS an excellent wood adhesive.  Unfortunately, ALL
adhesives fail in a brittle manner, and thus are not the best choice for seismic
CONNECTIONS.

If you need to use wood adhesives for this purpose, I suggest that you be sure
to account for ALL eccentricities in the load path, and assess the relative
stiffness of the structural components and connections.  I would also use the
system overstrength factor (Omega zero) to scale design forces up, AND use a big
factor of safety on the adhesive to include statistical material and
construction variations.  In addition, you shouldn't ever combine ductile steel
clip angles with brittle adhesives to resist forces in a line (or for rotation
of a block) - since the adhesive connection will be so much stiffer than the
clip angle connection, it will take most of the forces, and will likely fail
before the clip angle is ever significantly loaded.

In reading your posting I had to ask myself these questions:
1. If the builder and the inspector don't know how to properly implement such a
simple shear transfer conection to plywood/OSB roof sheathing, how are they
going to correctly implement a complicated adhered connection?  --Search me.
2. If anything goes wrong with that connection over the life of the structure,
who will the owners call second (after calling an attorney)? --Probaby the
builder, who will also call an attorney.
3. Is the use of any non-ductile seismic connection really good design practice?
--In my opinion, I must say no.
4. What happens to the connection if the wood swells for some reason? --Depends
on the use, I guess, but it sounds like trouble for a block shear connection
5. Is there any nationally recognized testing-based approval for this use? --I
don't know of any.

Good luck on finding a wood adhesive for OTHER uses.  Ohio Sealants
(800-321-3578) Pro-Series SF-400 selant is a good product and is used for wood
sub-floor system adhesion.  However, I don't think it meets your cesein-based
material requirement, and I don't know which ASTM specifications it might meet.
Call them.

Regards,
Todd Erickson, S.E.



>Jeff Flansburg wrote:


  Here's the SHORT story:

  We are looking for a structural adhesive conforming to ASTM D2559 or =
D4689 for a field-constructed shear connection from plywood-to-plywood =
or OSB-to-OSB (face-to-face).



  Here's the LONG story:

  Our firm performs many Lateral-Force-Resisting System (LFRS) designs =
for single family residences in Washington and Oregon States utilizing =
the 1997 UBC.

  A standard detail that we include is a shear transfer at the roof =
eave.  This detail transfers roof diaphragm shears to the shearwalls:

    a.. Nailing through roof sheathing to bird blocking.=20
    b.. Simpson A35 clips from the bird blocking to the double top =
plate.

  Occasionally (more often than we would like) a contractor will ignore =
this detail.  Upon inspection by the local building official (always =
AFTER the roofing material has been applied) it will be discovered that =
the nailing through the roof sheathing to the bird blocking has not been =
completed, then we are contacted for a 'fix'.

  The two obvious options we come up with;

  1.)  Remove the roofing and add the nails, the replace the roofing.  =
This can be very expensive and time consuming, especially if the roofing =
is tile.
  2.)  Provide the contractor or owner with a retrofit detail.

  Obviously the client never wants to tear the roofing off.

  We would like to provide a retrofit detail to our clients for this =
shear transfer.  The retrofit detail utilizes a structural adhesive =
rather than nails to transfer the shear from the roof diaphragm to a =
retrofitted wood assembly as follows:
    a.. Roof sheathing, typically 1/2" CDX, to sheathing between =
trusses/rafters, say 1/2" x 6" x 22 1/2" CDX, via structural adhesive =
(set in place with wood screws)=20
    b.. Sheathing between trusses/rafters to 2x blocking via nail =
(assembled prior to glue application)=20
    c.. 2x blocking to bird blocking via pneumatic nailing=20
    d.. Bird blocking to double top with Simpson A35 clips.
  In the past we have specified a 3M adhesive,ScotchGrip 5230, which is =
no longer available.  According to the APA technical note Number Y391C =
Structural Adhesives for Plywood-Lumber Assemblies,  we are looking for =
a glue that would meet ASTM D4689 Standard Specification for Adhesive, =
Casein-Type or ASTM D2559 Standard Specification for Adhesives for =
Structural Laminated Wood Products for Use Under Exterior (Wet Use) =
Exposure Conditions.

  Does anyone have any recommendations of a structural adhesive that =
would meet either of these ASTM specs?



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