built up column 1

[JStructsteel]

Got a girder truss that is a 5 ply member, about 15.5K of load. Was going to use (6)-2x6 column. I will specify a nail pattern to connect them all together.

At the top/bottom, do you folks call out for the built up column to be trimmed flush once connected together?

Do you run the top plate over top, or splice top plate at the column?

Thanks

 

[jayrod12]

Do you need continuity of the top plate?

Are you concerned about crushing of the top plate under that load? I don't think it's a concern based on some quick and dirty calcs on my end. If crushing isn't a concern, then I usually don't care and often would prefer to have the top plates continuous. If crushing is an issue, and I don't need continuity of the top plate, then I'll often have them interrupt the top plate.

 

[JStructsteel]

Thanks, that was my intent. I didnt check crushing, but just wondered how people handle it. I can show the top plate dead ending into the side, with some jack studs or something.

Jim

 

[dhengr]

JStructsteel:
You probably still want longitudinal continuity of the double top pl. across the built-up column.

 

[JStructsteel]

dhegr, why wouldnt the truss/beam that frames into the column not provide a load path for the interrupted top plate if the top plate frames into the side of the column?

 

[phamENG]

Depends on the load in your top plate. If it's acting as a collector element, then you'll likely have the possibility of tension or compression. How is the interrupted top plate fastened to the stud pack and/or beam? Does that connection have the capacity to transmit the force? Usually it's just a few toenails, or maybe a series of face nails that inevitably leaves a nail in withdrawal somewhere. Usually best to spec a strap across the face to handle it. Then again, there may be no "real" load and some toenails are sufficient to stabilize the assembly. Just depends on the particulars.

 

[JStructsteel]

Thanks all. Did some pencil sharpening, got the load down a bit, and checked the top plates for crushing. All works out.

phamENG, good point about a strap to span across the face. Simple and easy.

 

[KootK]

I also prefer to run the plates over top of the post if the crushing works. It's pretty common in practice to relax the crushing requirement as well as it's really just about limiting local displacement rather than a strength or stability failure. In my mind, running the plates continuously helps with:

1) Diaphragm boundary element continuity which can be addressed by tensions straps.

2) Post stability in the plane of the wall which can be addressed by tying the plates or blocking into the sides of the post.

3) Post stability out of the plane of the wall in rare cases where the load is not delivered by a framing element that would otherwise provide that.

At the top/bottom, do you folks call out for the built up column to be trimmed flush once connected together?

Nobody seems to have addressed that part. And I'm curious too. I've never said anything explicitly about trimming the ends flush. I suppose that I've unwittingly been relying upon:

a) common sense and craftsmanship which is perhaps naive and worth little in the event of a problem.

b) maybe an IRC framing standard floating around out there that I'm not aware of?

c) plate crushing helping to iron out the load distribution for small discontinuities.

 

[phamENG]

I've never mentioned it specifically, but I have seen instances where the trades have failed miserably in this regard. When I catch it, I make them at least glue a shim in the gap. But I'm usually leaning toward KootK's (c). I've never seen a minimum level of craftsmanship requirement in the IRC.

 

[jayrod12]

This is why, whenever possible, I get the architect on board with using stud length studs to frame the walls. You can easily buy 92 5/8" and 104 5/8" studs precut to exact (reasonable tolerance) length. Then I don't have to worry about some guy that is too lazy to set up a proper cutting jig to ensure his studs are all the same length. I can't say that I often see stuff egregious enough to require installing shims, but I have seen it so it's not impossible.

 

[KootK]

I have no idea what it's actually like on site but, in my head, I feel that you'd have some natural misalignment between plies as a result of the fabrication process. Even with pre-cut studs:

1) Maybe a 1/8" variation in length between them?

2) Maybe an 1/8" misalignment in the fabrication process?

Seems like you could wind up with a 1/4" elevation difference across a 4-ply stud pack pretty easily.

I've never seen a minimum level of craftsmanship requirement in the IRC.

I was hoping for something like a "finish to bear" tucked away someplace lie you have with steel etc.

 

[jayrod12]

I've framed, the stud length studs are essentially bang on. I could maybe give it to you on alignment, but I don't think you're giving framers enough credit. I thought I was being detailed, until I worked with a professional house framer, apparently the office is where I should be.

 

[KootK]

It wasn't my intent to shortchange framers on their skills. I was merely attempting to rationally discuss tolerances with respect to OP's concern which I myself had not considered Previously. There just isn't much of interest to discuss if one doesn't attempt to put numbers to things.

Most of my rough carpentry experience was in a controlled, plant environment, fabricating trusses and wall panels. There, I'd be hard pressed to cut or construct anything consistently within a tolerance of much less than 3/16". Out in elements, in can get harder still. In my opinion, the magic of wood doesn't come about because it has awesome tolerances but, rather, because it's easy to modify the situation on the ground to deal with natural tolerances as they arise. But, yeah, precut stud tolerances are pretty great. I'd be curious to know what tolerance precut stud lengths are held to when they are fabricated.

When you try to laminate a stud pack with a nail gun before installing it into a wall, the plies tend to "hop" a bit when the first nail goes in unless you're doing it in a vice or something. I believe that this may be why stud packs are often built up incrementally within the wall. That way the top and bottom plates kind of force/hold each stud into proper alignment as it's added and, then, even an 1/8" variation in length is surely tolerable.

 

[JStructsteel]

Thanks all. Ask KootK mentioned, building this thing is another issue. Nail patterns, glue? bolts?

Im using alot of LVL's, perhaps some engineered columns are in order.

 

[jayrod12]

No glue, the nail patterns are generally laid out in the code and aren't overly difficult. Bolts if necessary, for the CSA code a bolted built-up column has some additional capacity over a nailed build-up.

 

[dauwerda]

I'd be curious to know what tolerance precut stud lengths are held to when they are fabricated.

Pre-cut studs are more precisely identified as "precision-end trimmed" or PET lumber. To meet this criteria both ends must be cut square and to a uniform length with a tolerance of plus or minus 1/16" in no more than 20% of the pieces.
This can be found in the voluntary American Softwood Lumber Standard, PS 20 - available at this webisite:

https://www.nist.gov/standardsgov/voluntary-product-standards-program

or if you prefer, here is the direct pdf link:

https://www.nist.gov/document/doc-ps-20-20-american-softwood-lumber-standard

 

[KootK]

Thanks for that Dauwerda. It's amazing how much easier the Googling gets once you know the correct terminology for something. Since it's an over/under tolerance, my 1/8" guess was prescient. Although I imagine that you'd need to be rocking some serious bad luck to see it materialize one stud to the next.

 

[dhengr]

JStructsteel:
A good framer will not have any trouble with that built-up col. They will know that we expect all of the studs to be cut square and to length so that they all bear, this is a seriously loaded col. The problem is that so many builders don’t have any real, experienced (to code), framers on their crews, and their only effort is production, and get on to the next one. That’s how they make some of their profit. My note on that stud pack would be…, “All studs in this stud pack must be cut to the same length, so they all bear on the beam above and the sill pl. below.” That’s in my gen. framing notes. They shouldn’t have any trouble picking 4,5 or 6 studs out of a PET pile of lumber to meet this criteria. The +/- 1/16” in length, on less than 20%, causes few problems in the longer field of the whole stud wall. That is within normal framing tolerances. Alternatively, I’ve seen these looking like a beaver chewed the studs to approx. fit.