Determine force on bracing beam?

[StructureMan44]

A heavily loaded 30ft beam that needs a brace midspan to oppose LTB buckling. If this beam is only loaded vertically, how do I determine the required strength of the bracing beam needed for LTB buckling resistance?

 

[Leftwow]

My question is that if there is lateral torsional buckling, wouldn't there be some kind of eccentricity about the beam? B/c of wind loads, moment causing torsion, etc... And what direction of the beam are you bracing related the possible buckling? We had a similar problem here at work the other day, So we discussed using stiffener plates... That won't work. You cannot convince me that stiffener plates can reduce significant amounts of torsion. Another thing we tried is putting a bracing on the bottom section of the beam to the flange. Which doesn't make sense to me either, since bracings and their connections aren't usually used to transfer a moment onto them.

 

[Leftwow]

By the way I need this question answered as well, I am a junior engineer working under unexperienced people

 

[JAE]

AISC's specification covers the required bracing of beams and columns in Appendix 6.
Look through that and read the commentary on it and you should have your questions answered.

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[structSU10]

see attached paper for a primer on beam bracing. As JAE points out it is discussed in appendix 6 of AISC - this paper will help you understand how to apply some of those provision a little better.

 

[JeanLucPicard]

So you have lateral / transverse beam connection in the midspan? Look out so that the beams are connected in such a way that flanges cannot "dance". Not every flexural buckling support is a LTB support! (So says the EuroCode3 )

You can make a numerical model, load it, read the deflections. Make a new model of the bracing beam, feed it with the given deflections (forced deflections), or make a force using Force=stiffens×deflection...

Live long and prosper!

 

[MacGruber22]

Forget numerical models - AISC spells it out just fine. And you'll find that it is less than 5% of the normal force in the flange.