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Re: Plywood Roof Diaphragm Connections

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Title: RE: Plywood Roof Diaphragm Connections
I always specify full height solid blocking with diaphragm boundary nailing at the heel of trusses.  The last footnote on Simpson's commentary on their H series holdowns states "Hurricane ties do not replace solid blocking."  For this reason alone, solid blocking should be installed, otherwise I think Simpson's rated loads would be considered invalid.  Relying on cross grain bending for load transfer through a critical connection of a plated wood truss seems pretty risky to me.
 
Conrad Guymon, P.E.
----- Original Message -----
Sent: Wednesday, October 17, 2001 4:12 PM
Subject: RE: Plywood Roof Diaphragm Connections

When I use a holddown anchor such as a hurricane series anchor by Simpson Strong Tie, I use the nails in each truss to transfer the shear load down through the truss and into the anchor.  I pick an anchor that can handle the forces.  If I can't get the nails to work alone, I have been placing blocking between the trusses to help transfer the load.  My next question is how big the heel depth can be before I have to provide blocking, if the nails and anchor both work?  In other words, how big can the heel depth be before I have to start considering weak axis bending of the truss and the flipping of the trusses onto their sides?

Zachary Goswick