Web Sidesway Buckling Bracing

[MegaStructures]

I am on a stability roll today.

Section J10.4 of the AISC manual deals with web sideway buckling of sections where the compression flange is restrained against rotation and where it is not. The commentary says the case where the compression flange is restrained against rotation is in situations where there is a slab or deck on the top flange, but the manual does not seem to give a definite stiffness requirement for the compression flange "rotational bracing".

The first thought is that the torsional bracing requirements from Appendix 6 would apply, but I believe those are for torsion of the section, not for one flange. Any ideas what the requirement would be to restrain rotation of the compression flange other than the situation having to be completely obvious (e.g. 6" concrete slab)

“The most successful people in life are the ones who ask questions. They’re always learning. They’re always growing. They’re always pushing.” Robert Kiyosaki

 

[KootK]

Good question, and one that I don't recall ever seeing addressed in print. Practically speaking, the cases where I'd consider the flange rotationally braced are not too exotic:

1) Slab and studs of course.

2) Beam over top of another beam with a robust connection.

3) Column over beam with a robust connection.

4) Maybe welded joist seat in combination with some desperation...

..but I believe those are for torsion of the section, not for one flange.

Agreed. I'd actually expect the demand to be higher for sidesway bracing since, in many cases, I'd expect that to be higher up the chain of buckling events, energetically speaking, than LTB.

Any ideas what the requirement would be to restrain rotation of the compression flange other than the situation having to be completely obvious (e.g. 6" concrete slab)

The basic stability model is fairly straight forward except for the fact that you're stuck having to estimate "effective" stuff on both sides of the joint.