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Re: Shear Transfer from roof diaphragms....

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The man who stated that I didn't need to look at shearwalls was unfortunately my boss who is a PE but not a
practicing engineer who is familiar with lateral design.

Not sure which shear walls he's saying you don't need to look at but the code requires a load path.  The extent our companies want us to detail with this is another question.  Some offices say we only need to worry about the major stuff and the little stuff can just work themselves out.  Many hope their typical details cover them but that's not always the case.  First you have to take the time to create these details and then you need to make sure they're kept up to date.  Cadd makes this a little easier than when they were hand drawn.  Of course not all situations can be solved by typical details and this is when we need to take note of them.  One issue I had when I first graduated (and still a little bit today) was when your being mentored (sp?)  with an experienced engineer I found a lot of the time I was being told not to check certain things because it was a given they wouldn't be an issue.  His experience told him this but I didn't have that.  I ended up spending personal time proving these issues to myself.  Then I would get a larger structure where this wasn't true and I would check it on company time but I've had it go both ways.  An example of this is a large wood structure with it's diaphragm chord force (the plates).  On residences this hardly ever occurs but then when you go to the large stuff it becomes a major issue.    Especially if the plate height jumps in the middle of the diaphragm. (ugh)

The Simpson A35 and LTP4 connectors look good if end blocking is present,
but I don't believe that continuous end blocking will work due to attic
ventilation requirements.  If the distance above the top plate is 18" and
the eave height is 11", what Simpson connector is available to transfer
loads out of the roof diaphragm perpendicular to the roof truss?

We either specify full height blocking or a "shear panel".  The shear panel would have a flat 2x4 around it's perimeter with sheathing applied at whatever nailing you require.  At the top would be typical diaphragm nailing from the roof sheathing and A35 at the bottom to the top plate.  As far as ventilation we allow holes to be cut thru the sheathing and have the architect tell us how much he needs and tell him where the holes can go.

Also, is it common to have roof trusses at 24" o.c. and wall studs at 16"
o.c.?  How is the double top plate analyzed for this situation?

It all depends what your comfortable with.  Normally, I would only anticipate a single plate but that it's fixed both ends.  Span 16" with point load at mid span.  Worse case but simpler to analyze is simple span.  Obviously, design to NDS with whatever factors you can use.

Seth