Floor joists not bearing on LVL 1

[Alan CA]

Hi everyone,

We have a situation where the wood floor joists are not bearing on an LVL beam. The contractor suggested that the gap between the joists and the LVL be filled by shimming 3 plies of 2x4s. The 2x4s will be stacked one abkve the next one, where the smaller dimension (1.5 inch) will be vertical (floor joists will be supported on the larger dimension of the 2x4s.

Is this acceptable in concept? Does it need to be calculated, or it is unacceptable regardless of the numbers?

 

[milkshakelake]

I don't see anything technically wrong with it, as long as there's blocking between the joists above the LVL. It's not really different than reinforcing the depth of the LVL from the top. The 2x4 plates need to be nailed to the LVL and to each other. Preferably lap spliced to add a little residual strength to the LVL, but not strictly necessary. The joist bearing over 3.5" will probably work. I guess I'd be worried about 2x4 shrinkage a little bit, which could lead to floor joists sagging. You can easily calculate that with the NDS formulas and see if it's acceptable.

I don't see that it needs to be calculated, except for possibly the shrinkage. You can potentially calculate the bearing / compression perpendicular to grain to put your mind at ease, but since it's not a stud, it'll definitely work. The nailing pattern can be the same as typical stacked top plates.

I think it goes without saying, but there needs to be some kind of connection between the joist and the 2x4 plates.

 

[SWComposites]

What is the width of the LVL?
And how did this situation occur?
Is this at the end of the joists or midspan of the joists?

 

[KootK]

My only technical concern is that your joists need to brace your lvl laterally. And the taller you make that shim stack, the worse of a job the joists will do of that. That said, I don't feel that 3 2x4 is too tall for this purpose. Maybe run some long screws through the whole stack or something for good measure

The shrinkage issue is real. I'd be seeking to use engineered lumber plates to address that

 

[AaronMcD]

Koot, would engineered lumber really be better?

Assuming there are walls with 2-2x4 top plates, wouldn't 3-2x4 over the LVL match the shrinkage better than engineered lumber?

Edit: assuming this is new construction. If existing, I think engineered is definitely the way to go.

 

[Alan CA]

Thank you everyone for your kind responses. Regarding the lateral brace, is it because the joists are not attached by metal hangers? Cause I see joists bearing directly on beams in normal situations!

Also, how could engineered lumber plates help with the shrinkage?

 

[KootK]

Also, how could engineered lumber plates help with the shrinkage?

They don't really shrink.

Assuming there are walls with 2-2x4 top plates, wouldn't 3-2x4 over the LVL match the shrinkage better than engineered lumber?

Yup, if that's the case then it may not be a big deal. OP needs to assess his own situation, whatever that is.

 

[phamENG]

What is the LVL bearing on? It it's on a steel post or a post otherwise bearing directly on concrete, then you're right - the 3 stacked 2x4s would better approximate the surrounding shrinkage. But there are usually some plates stuck in there somewhere, and you'll end up with additional shrinkage below the LVL, too.

 

[KootK]

Regarding the lateral brace, is it because the joists are not attached by metal hangers? Cause I see joists bearing directly on beams in normal situations!

Nope, it's not that. Try this. Imagine that you had eight top plates and beam wanting to rotate over in lateral torsional buckling. We can agree that would be a problem, yes? By a similar token, I'm sure that we can also agree that zero plates is not a problem. Nor is one plate.

So everything in between zero plates and eight plates is... something in between.

It's about the aspect ratio of your shim stack and how well the stack is stitched together.

 

[Alan CA]

Thank you Kootk for the illustration.

 

[KootK]

You're most welcome Alan_CA. To clarify, I haven't a clue how one would put realistic numbers to such a concern.

 

[XR250]

I have a similar situation where we have a 5-ply girder truss that is 12" too short (in height)
The Arch. showed a 12" pony wall on top and we did not catch it during DD. Our solution is to use a 7 1/2" wide pony wall and sheath both sides of the truss and pony wall to prevent a hinge (starting at the top to avoid joints in bad places). Does anyone see any issues with this?

 

[KootK]

Does anyone see any issues with this?

I don't love that as a moment connection but, as with Alan's thing, I don't really know how to evaluate it rigorously.

I take it that it would be spacially problematic to scab a vertical strong back of sorts on to the side of the truss?

 

[XR250]

So you are talking like flat 2x4's vertical 16" O.C.?
We can prolly make that work. Deeper may be an issue.
To evaluate the sheathing idea, was thinking to determine the required force/ft to brace the truss top chord, convert to a moment as a line load acting horizontally on the assembly, 12" from the top. Then use that to figger the T/C in the sheathing.

 

[jayrod12]

To evaluate the sheathing idea, was thinking to determine the required force/ft to brace the truss top chord, convert to a moment as a line load acting horizontally on the assembly, 12" from the top. Then use that to figger the T/C in the sheathing.

I was about to propose this method.

 

[KootK]

I like the sound of those flat 2x4's. SDS screws.

 

[KootK]

Stiffness is more important than strength for something like this. That's the part that will be tough to assess reliably for the sheathed moment connection.

 

[jayrod12]

You're speaking of out of plane stiffness I assume of the 2x4 in flatwise bending versus the plywood?

Where I have concerns with the 2x4 plan, you may get what 2 screws from the 2x4 into each flange of the truss? Versus being able to put screws at whatever spacing you like from the sheathing to the truss. So although the sheathing may not be as stiff, I'd have far more confidence in the connections.

 

[KootK]

Yes to out of plane. I envisioned the 2X running the full depth of the truss. And ideally ones set over the truss verts if there are any.

With some lunch in me, I'm kinda warming up to the sheathing thing.

 

[jayrod12]

Oh I picked up what you were envisioning. But then each 2x4 becomes a cantilevered member of sorts right? Therefore the top 2 screws provide a tension connection between the vert and the truss. And although it would be nice to have them align with truss verticals, It's possible there aren't any truss verticals. So I was sort of worst-casing it in my mind.