Shear connection from existing plywood diaphragm to new shear wall

[BPA827]

I have a scenario as follows: I have a project where we are raising up an existing single story wood framed house and building a new lower level. The owner was planning/hoping to leave the existing finishes as-is.

My question: I am detailing an interior lower plywood shearwall to the existing floor diaphragm. Ideally I would install a line of plywood edge nailing from the top of the floor diaphragm down to solid 2x blocking between to floor joists then use framing angles from joist to top plate. The edge nailing in the floor diaphragm obviously goes against the owners wishes of leaving the existing finishes as-is. Does anyone have a creative suggestion to acheive the floor diaphragm to blocking connection from the underside of the diaphragm?

 

[DaveAtkins]

I would use blocking perpendicular to the joists at a certain spacing (maybe 16" or 24"). This blocking would be nailed into the existing floor joists, and attached to the top plate of the new shear wall below.

The load path would be floor diaphragm to two joist lines, two joist lines to blocking, blocking to shear wall.

DaveAtkins

 

[msquared48]

In addition to what Dave said, I would:

1. Use glue at the top of the blocking to the underside of the plywood diaphragm.

2. I would also use Simpson LPT4 clips applied flat to the blocking and shear wall double top plate. And, finally,

3. I would go back and infill the joist spaces without the blocking with blocking, glued on top and with LPT4,s. This set of blocking could be installed flush with the other side of the plate so they could still be end nailed.

This is about as good of a connection as you will be able to get without nailing the floor diaphragm to the top of the blocking. If you want to, just alternate the blocking flush to one side of the top plate, then flush with the opposite, for the length of the wall.

Lots of options here, depending on the capacity your wall needs.

Mike McCann
McCann Engineering

 

[BPA827]

Thanks for the suggestions, I think that is about the best we can do.

MSQUARRED48: Regarding the glue, I know that it would provide some connection, but is that accepted by City plan checkers? I guess I should mention that this project is in Oakland CA, Zone 4, 5 km to Type A Hayward Fault

 

[JRESE]

I'm doing something similar just up the road from your project, in El Cerrito. I used a 1-3/4" LVL flat, ripped to 14-1/2" wide to fit between the joists. The LVL runs continuously the length of the shearwall. I used SDS screws from the shearwall top plate to the LVL, and from the existing joists to the LVL. In my case, this is a voluntary seismic upgrade with no calculated shear loads.

 

[BPA827]

JRESE: What a coincidence, I live in El Cerrito. Your project wouldn't happen to be the one on Barrett Avenue near Edwards would it?

 

[JRESE]

BPA: Nope, Poinsett Ave.

 

[msquared48]

BPA827:

No, glue is not recognized as transferring any force when applied like this, I just think that it is good practice, plus it can't hurt.

It's structural contributions can be considered though when in a tested system, as one that is ICBO tested and rated. If you note, TJI has span tables for their floor joists that are load rated both with and without glue.

Mike McCann
McCann Engineering