Straps on the inside face of sheathing at a force transfer shear wall (wood)

[smeller]

I recently went on a site visit for a project of mine and noticed that the contractor placed the force transfer shear wall straps, located at the corners of openings, on the inside face of the wall sheathing. Our drawings do not explicitly say which face of sheathing to place the straps aside from showing a shear wall elevation that suggests the straps are on the outside face. I am fairly new to force transfer shear walls and have only ever seen images of walls with strapping on the outside face of the sheathing, so I am not sure if this is okay or compliant with my analysis. I also cannot find any literature that suggests straps need to be on any particular face of the sheathing.

Before I make the contractor remove wall sheathing to adjust the strap locations, I want to make sure it's necessary. Does anyone have an opinion on this?

 

[codySTR]

To clarify, what are the FTSW straps attached to? Are the straps attached directly to wood stud framing with wood structural panels installed over the straps? Or did the straps get installed to the wood structural panels from the inside face of panel (nailing facing away from wall framing)?

 

[smeller]

codySTR, the straps are attached directly to the wood stud framing. The wall sheathing is then nailed to the wood framing over the straps.

 

[dhengr]

Smeller:
So, at these openings and opening corners the strapping is nailed directly to the studs, and then the sheathing is installed and nailed over the strapping, right? Once the strapping is applied, are they actually able the nail the sheathing to the framing properly wherever there is strapping, or does it prevent the sheathing nailing? I haven’t dug too deeply into the latest APA lit., or into Simpson and USP/MiTek lit. on this particular topic, but I suspect the strapping and the sheathing are assumed/expected to act together to keep corners from racking and to properly transfer loads around the opening. And, I suspect the codes/stds. want the sheathing and the strapping both properly nailed to the framing, and for the framing to be nicely fitted and joined. Sheathing edge nailing and nail spacing are the most important feature in making the sheathing and framing work together as a good shear wall system/panel, for a given sheathing thickness and its tabulated strength. Interior panel nailing is mostly to prevent panel buckling, and only adds a little to shear cap’y. So, this edge nailing should always be inspected and as spec’ed. and designed. The best way to accomplish the desired result would seem to be apply and nail the sheathing to the framing and then apply and nail the strapping to the sheathing and nailing through the sheathing and into the framing. Although, you do end up with some potential nail bending issues btwn. the strap and the framing as the nails pass through the sheathing. But, testing for setting tabulated values will have taken this into account. You really must read and fully understand the footnotes in these code and std. tabulations. I would want to know that the strapping was properly nailed to the framing, maybe remove a few random sheets to prove this. Then, if the strapping prevented any sheathing nailing, I would make them locate the proper nailing and predrill the strapping so proper sheathing nailing can be done. Use a fixed stop on the drill, so you don’t predrill the framing too; and a drill a few thousandths smaller than the nail dia. If they can shoot these nails without killing anyone and get proper nail head seating too that would be o.k. also.

 

[MotorCity]

Since you did not specify on your drawing where the strap goes, the burden is on you to show that it works as installed otherwise you may be asked to pay to change it (been there). How did you determine the capacity of your shear wall? Did you rely on the plywood? the strap? both? Conceptually, I would not think it makes a difference which side of the wall the strap is installed on. I would however give pause to relying on the strap and plywood for lateral resistance due to strain compatibility and stiffness concerns. I'd leave it as installed.

 

[KootK]

I've only ever seen the straps outside the sheathing and I suspect there are some good reasons for that. The normal load path goes something like this:

1) Moment at ends of horizontal panels becomes tension / compression couples at the top and bottom plates.

2) Tension forces of the couple need to be transferred across the jack/king studs to dissipate into the vertical sheath panels.

3) The strap accomplishes #2, moving load from the top and bottom plates over to the vertical panels.

4) On the vertical panel side of the joint, the strap delivers the tension to the sheathing panel directly through the nails that connect the strap to the sheathing. Here, the blocking in the wall merely provides stability to the strap and a substrate for nailing

With the straps on the inside face of sheathing, replace #4 with.

4) The straps deliver the tension to the blocking via the nails connecting the two.

5) The blocking delivers the tension back out to to the vertical sheathing panel via the nails connecting the two.

The trick is whether or not you have enough fastening for #5 and whether nailing blindly through the sheathing into the strap effectively destroys it via section loss and fastener interference. The good news is that you could add these fasteners after the fact if the sheathing is still exposed. The bad news is that there might not be much strap left when you're done.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.