steel beam lateral bracing top flange with wood floor joist

[Ben29]

Does the scenario depicted in the image below provide lateral bracing for the top flange of the steel beam? Imagine you are just toenailing each joist to the wood plate with 3 box nails.

If not, then is there a way to make it so? Or, how do you calculate that you are sufficiently bracing the top flange of the steel beam?

 

[structSU10]

AISC appendix 6 helps to define the strength and stiffness required to brace the beam. It really depends how heavily loaded it is for how much force is generated at the brace point. I think it could be possible but maybe you end up needing a clip from the joists to the nailer rather than toe nails.

 

[BridgeSmith]

Well, you'd need attach the wood plate to the steel beam, and then how the joists need to be attached to the wood plate.

I would say the wood plate would need to be bolted to the steel beam, and I'd want an angle bracket screwed into the joists and wood plate to attach those together. I would not trust toenailing as a secure connection, even for the low amount of restraint required. I've seen a value of 2% of the compression force in the steel beam thrown around alot as the necessary lateral restraint, but I don't know the origin of that value.

 

[dik]

I add solid blocking under the wall... a 2x something or other to match the joist depth.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[bowlingdanish]

Forget the codes. For lateral torsional buckling - just think: does it stop global rotation of the cross section?

If the timber plate isn’t bolted to the flange - it probably doesn’t so I’d not consider that braced. If it is - then is there a load path beyond the connection to stop the section rotating?

Remember that there isn’t a definitive solution for LTB (or Euler buckling) for every situation/configuration, and everything in the codes are an approximation. Sometimes a buckling analysis is ‘good idea’ and other times, it’s essential.

 

[Ben29]

Sorry for the confusion... I am showing the top flange bolted to the plate, but I wasn't calling it out. And because of the autocad layer the bolt is on, you can barely see it in this image.

Thanks, all. I will check out AISC appendix 6.

 

[JAE]

Yes - your sketch would be such that the beam is braced against lateral torsional buckling. Very common assumption.

Agree with the blocking per dik.

 

[KootK]

Agree with JAE. So long as this is a simple span beam with reasonable amounts of diaphragm tying in, this would be a "no brainer" assumption of top flange lateral LTB support for me.

 

[Ben29]

Thank you JAE and KootK!