How can you properly check for buckling in an upturned beam subjected only to flexure 2

[M.M.Q.]

How can I check an upturned beam for compression failure in the compression zone? Upturned beam is only subjected to flexure. And is there somewhere in codes that I should be following for this?

 

[driftLimiter]

A sketch and some dimensions for context would be useful.

Not sure why its any different from a compression zone in a concrete beam? Why are you worried about the stability of the section locally?

 

[M.M.Q.]

Sorry, I should have elaborated. As an example, an 8"x44" upturned beam for a residential home, tied into the floor slab, length is 40ft, takes 20ft of a 6" concrete slab (this is an example, not what I'm working on). As long as I choose the steel such that the section is tension controlled and minimums are met, there is nothing else that I currently check to ensure the beam won't fail in lateral torsional buckling, due to flexural force only (downward force, no lateral force in this hypothetical). But there must be a limit to how deep I can increase the section and/or increase the unbraced length to where out-of-plane buckling may occur. I do check deflection. In the case of an upturned beam, especially where a slab is tied into the beam and the slab and beam are poured monolithically, the tension zone is pinned in place so it can't flex like a rectangular beam would, wouldn't that cause more compression in the compression zone? All this to just ask, what types of checks should I be doing to ensure out-of-plane buckling is not an issue? I don't see any in ACI 318. Or am I thinking of this the wrong way? Any discussion or opinions welcomed

 

[KootK]

For concrete beams that are not restrained in any way torsionally, ACI deals with lateral torsional buckling by limiting the width of the beam to span/50. Such a non-fancy checking algorithm reflects the fact that rectangular concrete beams typically possess significant torsional stiffness relative to open section steel beams etc. Your beam will have torsional restraint provided to it by way of connection to the slab that ties into the bottom of the beam. This only improves matters with respect to LTB. That said, I'd be inclined to just satisfy the L/50 business and not bother trying to exploit the torsional bracing effect of the low slab.

 

[M.M.Q.]

Thank you! Would you know where in the ACI can I find the span/50 limit? ACI318?
I found it referenced in 10.4 of ACI318-11 (i found a preview and saw it in the table of contents, not the actual code), and I do have it in my CSA A23.3 (10.2), but i was just curious where its found in ACI 318 in later versions, I have 318-19 at my desk. Thanks

 

[JAE]

ACI 318-14 has it in 9.2.3.1