Creating a floor diaphragm chord at balloon framing

[ddcpe]

I am working on an apartment building (2 story home turned into 4 apts) and the second floor framing abuts & attaches to balloon framed studs. The floor diaphragm consists of 2x10 @ 16"oc and 1x T&G fir decking. Along the wall with joists parallel its easy enough to simply strap the joist breaks but at walls perpendicular I have not got a good idea how to create a chord. What I have done in the past is simply blocking and a coil strap. Anyone got any other ideas. Oh, and besides the lack of the chord, any ideas about a safe number to use for allowable diaphragm shears? For this kind of assembly I have been using 100 plf.

 

[msquared48]

I am a little confused here with the 100 plf figure, Don't compromise the structure here...

I would detail the connection, whatever it is, to meet the IRC/IBC requirements for whatever horizontal shear and chord force you need, using horizontal blocking in the wall, a 2X ledger, and appropriate nailing and strapping.

The ledger, if strapped at any splices, could be made into your chord member with no problem.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ddcpe]

The 100 plf is an approximation based upon Fema stuff done some years back (273 i think). The deal is the owner wants to keep the fir flooring so cant put ply over. The problem with the blocking straps is that it is shingled and youo know there will be lots of bent nails when the siding crew forgets the metal strap as they blow it out. Also all those blocks are kind of costly. I have never been able to think of anything else to do.

 

[msquared48]

You can hang the floor yoists off a 2X ledger that is nailed/bolted to the studs and strap the ledger at the splices. The ledger would replace the blocking for the diaphragm. However, for the shearwall nailing, you would still have to cut blocking pieces for the wall above and below the diaphragm. You are not going to be able to eliminate that requirement.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ddcpe]

Thanks Mike; that's what I thought. Like I said, I have never been able to come up with any other detail.