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RE: Diaphragm Chord Wood Roof

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I appreciate the replies, especially on a Friday night.  I wasn't expecting
answers until Monday.

I have tried to attach a JPG image of the truss to this file but the Server
kicked it out.  I have setup a web page link to a JPG image you can view to
see a schematic of the truss.

http://www.lewisengineering.com/RF_truss.jpg
 
As you can see from the image the truss is parallel chord with bottom chord
bearing.  There is also a tall parapet that kind of cantilevers up.  This is
for a chain restaurant.  It came from a Prototype design.  I assume this has
been built in several locations already but I don't see from the prototype
drawing how they accounted for the shear transfer from the diaphragm to the
shear walls and for the diaphragm chord force transfer.  There is no
discernable load path from the roof sheathing to the shear wall.  

Several have mentioned using coil strap anchors and I'm not sure I picture
what you are describing.  If I understand correctly I would put solid
blocking between the trusses at the top chord.  The sheathing would be
nailed to the blocking.  I would add a strip of coil strapping on the top of
the sheathing that would act as the tension chord member.  For the
compression chord I would consider the line of blocking between trusses as
adequate.  Due to the parapet wind and the long narrow building my chord
force is over 8,000 pounds.  I don't have a Simpson book with me now, but I
imagine this will be a hefty strap. I have not thought to use coil strapping
before, but then again I typically design top chord bearing or gable style
trusses and use the double top plate of the stud wall.

If I didn't have this parapet I could see this as being feasible.  The
additional issue I see is getting the shear from the diaphragm into the
shear wall.  Ideally the roof sheathing would stop at the inside face of
parapet wall so the sheets don't have to be cut.  To get shear transfer I
think I need to require the sheets to be notched around the vertical parapet
stud and run my top chord blocking out at the exterior face of wall.  For a
prototype, this seems to have been ignored by others.

Hopefully this JPG image will help provide additional insight and response
from the List.

Thanks again for your help.

Rich


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