WF beam torsion 2

[laneng]

I’m working on two details along the same column line where there is a 12” step in the framing from inside to outside. I’m using a W21x44 in the first one and framing the exterior wood trusses into the side. For the 2nd detail, I’m using a W12x26 with a WT12x31 because the beam extends past the step so the beam needs to be lower, but the WT is needed for a portion of the span just to pick up the interior wood trusses on the right side of the detail.

I have the vertical 1/4” plate in the second detail to create a tube section with the beam flanges and the web because I think there is a torsional issue.

1) do you agree that there is a torsional issue with that detail?

2) does the first detail also have a torsional issue with the lower trusses framing into the side? Could I resolve it with an angle that gets welded to the angle supporting the trusses then to the bottom of the beam?

 

[canwesteng]

There is some torsion in the second details, though it could be resolved with a couple in the top chord of the owsj framing from either side at different elevations. At minimum ditch the upper plate and let the boxed wide flange take the torsion.
You could box the angle on the second detail if that's what you're going for, though at that point just use an HSS. Make sure the torsion has somewhere to go at the ends of the beam. I would still lean to a couple in the top chord of the oswj.

 

[laneng]

Thanks for your reply canwestng. As a point of clarity, the joists are open web wood joists, not steel, so I’m less confident in developing a couple in the top chord of the joist on the right.

As I’m writing this, I’m thinking that I could probably come up with a Simpson strap detail from the 2x nailer to the side of the top chord to take the tension. It would have to get installed before they laid down the plywood, but it could be done.

This was my initial thought:

 

[dik]

Can you extend the bottom chords of the trusses to eliminate the torsion?

 

[laneng]

I’ve done it lots of times with steel bar joists but never with wood trusses. I’ve thought about adding a kicker like what I’ve drawn below but I don’t love the detail. You really aren’t guaranteed it’s going to hit a panel point in the truss.

 

[dik]

Extend it horizontally... or have it as part of the truss design. It doesn't have to extend to the bottom flange.

 

[laneng]

Wouldn’t that be bracing it right at the center of rotation?

 

[dik]

maybe close enough...

 

[lexpatrie]

Well, at least there's a drawing on this one.

Since it's late I'll try to look at this more tomorrow.

Personally I'd doesn't look like you can eliminate that torsion, you need to design the steel beams for it. Generally ends are torsionally "free" and pinned for flexure. Unless you're welding the beam directly to the column all around.

 

[Eng16080]

For Detail #1, I would look into providing a load path into the floor sheathing to resist the torsion.

For Detail #2, I would use an alternative detail altogether. Unless I'm missing something, that detail seems way overly complicated.

See below:

 

[Eng16080]

Same image below (inline). (Not used to the new website.)

 

[laneng]

Thanks Eng16080. I do like the knee wall idea. I borrowed the WT filler from a bar joist building I had designed a while ago and didn't think twice. I'll definitely offer it up to the GC and see what he says. He has a bit of an "everything needs to happen now" aura about him, so he may actually go for the more expensive WT option so they can build both floors at the same time, but he can't say that I didn't try to save him some $...

For the other detail, I think I will give them your detail showing a Simpson H2.5T (or H8, or H-whatever works for the T) from the nailer to the side of the top chord, then possibly a flat strap on the plywood down to the top chord of the truss. If he doesn't want to wait until the H clip is in place to attach the plywood, I'll tell them that they can instead weld a vertical plate between the lower angle and the beam bottom flange.