Top plate bending and all-thread rod hold-down systems

[UcfSE]

When using an all-thread rod system for basic roof uplift, the top plate is under flexure due to the roof member uplift force. If you're using a double top plate and need both 2x members together to resist bending (as composite section), how do you splice the top plate so that you keep moment capacity at the splice? There are details and requirements in building codes for nails each side and splice lengths, but I don't think these are meant to address the top plate as a flexural member.

 

[scottiesei]

I guess it would depend on where the splice occurs in relation to the trusses and bolts. If you where really concerned, maybe spec a bolt on ea. end of the laps. I would think that the location and magnitude of the forces would vary all around the structure. Instead of calc'ing your way out of it, try finding a way around it. Go Knights!

 

[UcfSE]

Thanks scottiesei. Did you go to UCF also?

 

[scottiesei]

Yup, graduated in fall of 02'. I was working on my Masters there but took time off too study for the PE. I plan on going back to finish when I pass.

 

[scottiesei]

FYI, as a cost effective alternative to the all thread rods, I have used tight nail spacing on the sheathing and used blocking as splices to resist both the shear and uplift forces. Typically only on stucco covered walls utilizing a portion of the dead load to resist the uplift. Works pretty good and my builders love it!

 

[boo1]

Simpson recommends:
Bearing plate at double top plate. No splice in the top plate permitted within 8? of the rod.

 

[FSS]

To get true composite action for your double plate (i.e. beam depth of 3"), you must look at shear flow between the two plates. You just can't fit enough nails in there to make it work 100%.

 

[boo1]

I saw an article discussing rod systems at:

http://www.structuremag.org/

under June-2006/C-CI-Multi-story-Light-Frame-Construction.pdf>