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RE: Wood truss as drag strut

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I’ve done it both ways before – use the truss and show the shear force on the roof plan with a note for the truss designer – or detail a balloon framed shear wall.  I don’t recall ever having a problem either way, as long as you cut a section at the wall or truss and add some clearly worded notes on the plan you should be fine.

 

The choice between the two usually comes down to coordinating with the architect and/or mechanical to see if they need openings above the ceiling to run ducts or circulation venting.

 

~~ Eli Grassley, PE

 

-----Original Message-----
From: Jason Christensen [mailto:jason.christensen(--nospam--at)es2eng.com]
Sent:
Thursday, September 01, 2005 8:30 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Wood truss as drag strut

 

In our experience it has been hard to get the truss designer to actually design the truss properly, as well as the contractor getting the proper truss at that location.  So now we take the up to the roof and create a blocking drag to the shear wall.  The truss designer has the ability to design the it correctly,  just make sure you really review their design.

 

Jason

-----Original Message-----
From: Rich Lewis [mailto:seaint03(--nospam--at)lewisengineering.com]
Sent: Thursday, September 01, 2005 8:24 AM
To: seaint(--nospam--at)seaint.org
Subject: Wood truss as drag strut

 

I haven’t seen much in design literature about this condition.  If I have an interior shear wall, perpendicular to the ridge line, with prefab metal plated wood trusses at 2’-0” on center, what is the best way to detail this as a drag strut?  Should it be used as a drag strut, or should the shear wall continue all the way up to the roof sheathing?  The walls occur for the first 11 feet from the bearing ends, with a 5:12 pitch.

 

If I detail the truss to be connected to the wall top plate, even say a double ply truss, and tell the truss designer the shear force, is it practical for them to design the truss for those loads?  Shouldn’t I also have some details of lateral bracing down from the roof diaphragm to the wall top plate?

 

As I said, I haven’t seen this discussed in design literature or text books.  If someone can point me in the direction of some discussion, I would greatly appreciate it.

 

Rich