Sistering LVL with a 2x10

[JStructsteel]

I have a few joists that need to be reinforced, and was wondering how you guys feel about using LVL with a 2x10. Obviously different strength, What procedure would you use to check any design?

 

[jayrod12]

I've never gone so far as worry about strain compatibility with wood reinforcing. Generally when I've needed to do what you're describing, I've designed the reinforcing for the entire load and not worried about how they'll perform together.

It's likely that the size of LVL to take the entire anticipated load is not incredible.

 

[DaveAtkins]

jayrod12 is correct. If you want to be more precise, each portion of the sistered joist will take a portion of the load based on the modulus of elasticity and the moment of inertia of the portion.

DaveAtkins

 

[DETstru]

If you can't get the new LVL to take the whole load you could assume the existing 2x10 is handling the loads that are on it right now (some dead load). The new LVL will handle the load beyond what the 2x10 is taking at the time the new LVL is installed (any remaining dead load and the entire live load). It's still very much on the conservative side but it might help.

Edit: just realized I got the 2x10 and LVL backwards, fixed it

 

[jayrod12]

I'm assuming it's a deficient single 2x10 that you want to add LVL to make it work. As I said, my bet is an LVL designed to take the entire load won't be considerably more expensive from a material standpoint and would likely be less from a labour standpoint as no more than standard nailing would be required.

 

[racookpe1978]

Depends on how you mate the two sisters.

(Hmmmn. somehow that seems rather incestwous, doesn't it?)

If nailed, the two WILL slip and slide as the nails lose the grips over time, as the wood dries, and as the wood swells with humidity. the weaker of the two will take almost all of the load until the stretched joint pulls tight, then the weaker will keep its load and more of the new load will be pickked up by the stronger sister.

If firmly bolted, the two will move much less with respect to each other, and the load will be shared proportionally earlier in life. But bolts do tend to weaken (loosen) and so the load will shift a little over the rest of the life of the sisters.

Well-glued and bolted with start off with both sisters sharing the load much closer to their theoretical values. But they have to be well-glued. And firmly bolted for the theory to work.

 

[XR250]

I'm with Jayrod - I never worry about strain comapitbility or nail slip etc. It will just work!

 

[dhengr]

Jrisebo:
If the existing 2x10 isn’t broken, another 2x10 would almost double the cap’y. If you want to do something constructive, jack the existing 2x10 up so it is slightly cambered up before you install the new member. Do this jacking slowly and listen for any serious cracking sounds from above. This will make the installation easier and cause the two members to share the load in proportion to their relative flexural stiffness, once they are nailed together properly. You might hold the new member down just a bit (1/16th or 1/8"), so that it doesn’t disrupt any floor sheathing nailing to the existing joist.