Plywood to light gage truss connection 1

[WWTEng]

Is it possible to connect plywood diaphragm directly to light gage trusses, or would a cont. plate (2x4 or 2x6) over the truss chord be necessary to make the connection?

 

[BAretired]

It is standard practice to nail the plywood or OSB deck directly to the 1.5" face of each truss. Sometimes, framers miss a truss on the first try. With power nailing, it is not uncommon to find several nails projecting down from the deck next to a truss. When this happens, it is important for the framer to re-nail affected areas.

Inspection of this feature is difficult after the job is completed because nails in the correct position are not visible from below.

BA

 

[MiketheEngineer]

As BA stated - done all the time. Really good framers will drop a chalk line but that takes time!! The nail size and spacing is always a concern

 

[WWTEng]

BA,

Thanks. And the next question is that you obviously can’t use nails for the connection. I am assuming that screws would be the way to go but what type?

 

[MiketheEngineer]

If this is wood on wood - nails are used all the time. Just follow the IBC nailing specs

 

[AELLC]

In the 2006 IRC code, it specifies in R804.2.2

#8 self-drilling, self-tapping sheet metal screws w/ countersunk head.

 

[BAretired]

Wood screws would be fine but I have never seen them used. The usual practice is to use power nail guns.

BA

 

[Teguci]

Recommend getting AISI S213 regarding lateral design. Depending on the required shear, you will need to use #8 (or #10) self tapping screws at 2 tp 6" spacings. In addition, the edges of the 4x8 sheathing will need to be blocked and the interior panel to truss connections (at 16 to 24" spacing)will need to be made with scerws at 12" oc.

I imagine the nails reference is a misreading of your original post.

 

[hokie66]

He did say "light gage", which to me means steel.

 

[WWTEng]

Teguci, thanks for that reference. Would be possible to share that load capacity table for you here? I am going to order a copy of AISI S213 but it may take a few days to get it.

 

[Teguci]

What is your maximum, unfactored shear load (specify wind and seismic service loads) that needs to be carried by the ceiling diaphragm (lbs/ft)?

Omega-quake = 2.5, Omega-wind = 2.0

 

[WWTEng]

The maximum unfactored shear due to wind is about 500 plf (no seismic, site class B). But thats the worst case. Plywood is 3/4" str -1, typ truss top chord is 20 ga 1 3/4" wide. I am hoping to use #8 or #10 screws.

 

[BAretired]

Sorry, I thought you were asking about light wood trusses. Please ignore my earlier responses.

BA

 

[MiketheEngineer]

Me too (on the wood trusses). 500 plf seems a bit high but not unseen. Check with the truss mfg - they should be able to guide you.

 

[NewbieStruct]

I just checked the shop drawings for a light gage truss attached directly to plywood. The attachment was done using #10 screws at 6" o.c at the plywood panel edges.

 

[Teguci]

All edges must be fully blocked. Sheathing will need to be one of the following for wind loads:

3/8" thick Structural I with #8 at 4" on center around boundary edges and continuous panel edges and @ 6" for other panel edges and @ 12" for intermediate supports

7/16" C-D, C-C and other graded wood structural panels - same attachments as above

 

[WWTEng]

Teguci, thank you for the info. I was also able to get some guidance from APA and ordered the AISI book yesterday.