How to avoid cross grain bending when anchoring balloon framed wall to diaphragm?

[MJC6125]

I have had many projects where it makes sense to balloon frame wood stud walls because the roof requires a tall parapet or the parapet is acting as a guardrail for a rooftop patio. See the attached pdf for an example wall section. I'm wondering how people deal with the anchorage of the stud wall to the diaphragm without inducing cross grain bending in the ledger? Here is a list of a few ideas I've had or used in the past. Does anybody have any recommendations on what works best (especially based on constructability)?

A. Don't worry about the cross-grain bending. I don't know how you can do this since there is no design value for cross grain bending, but I'm sure this has been done in the past and has worked fine.
B. Use a Simpson strap anchor that runs along the length of the joists and then gets wrapped around the stud. I've used this method in the past with Simpson twist straps (LTS/MTS/HTS), and put one every 4'-0". The issue is the studs need to line up properly with the joists every 4'-0" and I don't know how easy it would be to install. This is a similar solution to the joist anchors that are used with CMU walls anchored to wood diaphragms (specifically in high seismic areas).
C. One thought I had was using an OSB rim board product as the ledger. I have never done this, and I think all the commercially available OSB rim boards are too thin to get the joist hanger nailing to work. However, I assume it could solve the gross grain bending issue because you have wood grain running each direction in the different plys of the OSB board.

Does anybody have any other techniques they use for the wall anchorage in this scenario? Or do people use an entirely different framing technique in order to get these taller parapets to work without having to do kickers down to the roof structure? Redbuilt has the following technical bulletin which shows different framing techniques: Link

 

[XR250]

I usually use the LTS12 at each stud and specify in a big note that the studs have to align as needed. I am not a particular fan of this detail in general as I don't like counting on multiple screws in the skinny face of the stud. I use it sparingly.

 

[jayrod12]

I'll typically set the joists spacing to match the stud spacing. Set the joist to rest on top of the ledger for gravity loading and extend past the ledger with screws through the stud to deal with that connection.

 

[Deker]

I like jayrod's detail. We've also used Simpson H2A connectors.

 

[dhengr]

MJC6125:
I don’t really see much cross-grain bending going on in your ledger. The joists will rotate a little, on their bearing area, in the hangers without putting much torsion or cross brain bending on the ledger. They used to let the ledgers into the studs, and then follow jayrod12's detail of resting the joists on the ledger. That way the ledger is primarily supported in bearing on the stud and the screws just hold it in place. You may also need some fire blocking btwn. the studs at about this level. You can get serious cross-grain tension up at the top of the ledger, if your screws get to close to the top of the ledger (small edge distance), and that failure mechanism will be cross-grain tension/tearing. Alternatively, lower placed screws will start to fail in dowel pin bearing and be supported by sufficient wood above/around them. But then, the above causes a problem when the small parapet becomes a handrail because you have cut a notch in the edge of the stud right where the handrail canti. moment (bending tension stress) is the greatest.

 

[MJC6125]

The cross grain bending that I'm worried about is developed when the wall wants to pull away from the building (wind suction on the wall). See attached Fig. 6.1b from Breyer's wood text book that shows where the cross grain bearing occurs. The example is for a concrete wall but I think the same issue applies with my wood stud wall example.

Jayrod, do you detail this with a ledger on the face of the stud or with the let-in ledger that is flush with the studs? I would think it would create an undesirable drywall issue if you didn't do the let-in ledger?

 

[KootK]

The pic below is, of course, of a rafter connected to a wall. Suspend disbelief for a moment, however, and imagine that you're instead looking down upon your ledger board with the wall studs running out of the page. This solves another issue as well. It gives you a legitimate path for transferring your roof diaphragm shears out to the exterior wall sheathing where they belong.

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.

 

[dhengr]

MJC6125:
If those lateral loads are that high, you should probably tie the jsts. to the wall (a strap or clip of some sort). You should not usually be counting on tensile pull-out of nails or screws for significant structural loads. Alternatively, your detail shows 5 screws into each stud, and 16 or 24" o/c. Breyer’s detail shows one A.B., likely at a greater spacing, and half the height of the ledger away from (below) where the diaphragm load is taken out. This is a significant load and lever arm for that cross-grain bending to develop and then be taken out at a single fastener. Breyer’s detail would be significantly improved with a second A.B. up near the top of his ledger to take that lat. load, and reduce the bending lever arm. I’m not suggesting that you shouldn’t watch out for cross-grain bending, but there are degrees of magnitude to be considered also. Jayrod12's detail handles this better by face screwing the joists to the studs, as long as he’s careful about the screw end distance on the joists.