Minimum length % for sistered wood members

[FSUDrew99]

Have a project that needs some 2x6 CJ sistered. The Joists had some funky wall framing and now need to extend probably 6" to the new all to bear. I like to try and sister full length of the member and bear on both ends and then factor DL & LL for shear and calc fastener req.

My question is: is there somewhere in the FBC or IBC/IRC that calls out a minimum length of a sistered component when added to ends of a member? I know a lot of people for damaged existing members like to add about 3'-5' of new sistered member past the damaged area and fasten accordingly.

I would assume min. 6' for a sistered end connection....

Thanks.

 

[KootK]

I know of no code recommendation for this. As long as you can make a go of it with the fastenings, I think that it's your call. That said, I think that your 6' rule of thumb is sensible. 5D is my own which would be similar.

 

[r13]

Are you splicing, or sister the joists? The former is to extend the length of the joist, the latter is to increase load carrying capacity. The two looks similar, but function differs.

 

[FSUDrew99]

This would be (splicing) then technically as it is for just extending the member.

Thanks KootK.

I figured I could calc the applied load on the end of the existing member and then disperse that load thoughout the attached splice member.

 

[KootK]

You're most welcome.

I figured I could calc the applied load on the end of the existing member and then disperse that load thoughout the attached splice member

Kinda depends on what you mean by "disperse". You're making a connection here that will be both a shear connection and moment connection. The latter part's usually the tricky bit. For me, it means two separate connections offset by a nice lever arm to keep things simple.

 

[DaveAtkins]

I am not sure what a CJ is...but in my experience, when you splice wood joists together, the lap will be quite long, as described above, due to the low value for shear perpendicular to grain. For cold formed steel joists, the lap can be very short, like one foot, because screws have a lot higher capacity.

DaveAtkins

 

[KootK]

Ceiling joists?? Cold Jambs? Cumbersome Jeans?

 

[FSUDrew99]

Ceiling Joists.....

 

[FSUDrew99]

My thought its apply 10 D and 20L and call it 30psf x 1.33 (16" o.c.) and multiply it times the length of the CJ trib area on the spliced end.

In return like your lever arm calls for apply the same loading but distance from bearing wall to the new splice member and sum both moments.

If I call out (3) 10D nails @ 12" OC for the 6' splice I will be beyond sufficient.

 

[DaveAtkins]

You need to determine the shear and the moment at the center of the splice, and design for both. I would use an analysis program like RISA-3D, but you could also do it by hand. It will be by trial and error, because you don't know how long the splice must be, so you don't know where the center of the splice occurs relative to the support locations.

DaveAtkins

 

[dik]

I love Lepage's PL Premium adhesive... and would rely on it over actual fasteners...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

Ideally the location of splice should be kept away from the high shear region and the maximum positive moment. Don't you have full length member available?

 

[KootK]

That's a pretty tall order in that the low shear locations will usually be the max moment location and vice versa. Given that the moment is likely to be more onerous to deal with than the shear, I feel that the member end is a good place for the splice.