Type III timber construction with steel flitch plates

[mfernando]

I want to connect an LVL beam to a wood built-up column inside the wall cavity. Any wood penetrating the wall assembly must be noncombustible materials (steel/ fire treated wood.) So I wan to use a 10"x10"x1/2" steel plate to connect the 2-ply lvl to a 4-ply 2X6 column (in order to stop the beam short of the wall.). The steel plate is in the center of the beam and the center of the stud pack (1/2" steel plate in order to use 1/2" osb as filler for the remaining length of the beam and column). I can transfer the shear from the beam to the plate with two rows of three bolts. I have a problem transferring the shear and eccentricity induced moment to the built-up column since I can only get one row of bolts in the 2x6. Plus, the couple in the bolts produced by the moment creates tension perpendicular to grain, which is not covered by the NDS and they recommend not doing it at all (2012 NDS Section C10.1.3). I was thinking of detailing an L-shaped flitch plate to get more bolts in the column and increase the couple distance in the column.

Any thoughts on this one?

Normally we would put a HSS4x4 column in the wall, but the architect will probably have a hernia if I do it now since construction started.

 

[EngineeringEric]

Do you have a sketch of this beam? It sounds like you accounted for most un-even loadings, eccentricties, and the fact the members will take load relative to stiffness... To be honest, you probably are better replacing all of that beam with a steel beam, and bear the steel beam on timber posts. The composite section is ugly (structurally and looking ) and the steel in the flitch plate is very inefficiently utilized, you are using a lot of steel and not getting much benefit, use a small W of two channels or double angles ?...

 

[mfernando]

Attached is what I have for a detail so far. As the shear force transferred from the wood beam to steel plate increases, I need another row of bolts in the beam side. Thus creating a problem in the wood column. I'm trying to use as much wood as possible to keep the steel costs down at this point in time, but it looks like the options are limited without going to a steel beam. Luckily the framing is covered up so no one will see the flitch plate. I could pull the column out of the wall since this is in a maintenance area.

What do you think of the detail?

 

[AELLC]

If you can pull the column out of the wall, I say do it. It will probably cost more in your time to analyze this than any additional construction cost, because construction cost estimates aren't going to take into account every fine detail.

We aren't getting any awards from anyone for most elegant solution. All we can do is get the project configured in a practical manner and wait for our next paycheck.

 

[EngineeringEric]

I see i misunderstood your intent. The detailed cleared that up right away, what i had in my mind was far more McGyvered than that. I agree with AELLC if you can move it just move it. I would assume some Jack studs would be preferred over that detail, but i don't see anything wrong as long as the column can handle that local moment/compression from the eccentricity and bolt groups can transfer the loads... Seems like a good amount of work for a few inches of clear space though.

 

[mfernando]

Thanks for the help. It is a lot of work because of the Type III construction where exterior load bearing walls and stairwells have to be made of non-combustible materials and LVL's do not have a company that will back any sort of fire-treatment. Normally we can't pull it out of the wall because of stairwells etc. and top flange hangers over gyp only give 2500 lb floor load or something small like that. This case I agree that it is better to talk the architect into pulling it out.

 

[RFreund]

I agree with the above recommendations but if you had to get something to work...
You could make that plate into L which turns down into the column. Then you can distribute your bolts along the length of the column.

EIT

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