Beam lateral bracing location

[ars13]

I know lateral bracing is ineffective if it is placed near the center of the beam. I know the ideal place is to brace the compression flange. I have a situation where it would be ideal someplace in between. What works? What doesn't? Thanks

 

[Lion06]

AISC says that any bracing within the top 1/3 of the beam is effective in bracing the top flange.

 

[ars13]

StructuralEIT-
Solid! Thanks for the quick response. Do you know where it states that?

 

[Lion06]

I can't find it right now and I have to run out to pick up my suit. I'll look for it tonight or tomorrow.

 

[kelowna]

You can brace in the middle of the beam and design the connection between the brace and the beam as a moment connection, creating a portal frame effect. That will provide restraint to the compression flange. Mind you, it is expensive and the analysis not simple. I have done it once before, not recommended.

 

[GalileoG]

Kelowna (beautiful place by the way, driving there this weekend.)

How would designing the beam to beam connection as a moment connection brace the top flange of the supporting beam? What did you mean by "portal frame effect"? Can you please elaborate?

Thanks

Clansman

If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.

 

[jberg]

I believe that Kelowna is referring to the other type of bracing, where you prevent twist of the cross section.

Joel Berg

 

[WillisV]

The "one-third" rule of effective lateral bracing is not stated in the Specification or Commentary itself to my knowledge, but it is generally accepted and can be found in other locations such as here:

http://www.aisc.org/DynamicTaxonomyFAQs.aspx?id=1646

 

[kelowna]

Yes, Kelowna is a beautiful place, and yes, the bracing has rigid connections preventing twist of the cross section. In effect you are creating a single structural section with the two (or more) main girders.

As I said, it was not easy and it was complicated to satisfied ourselves it worked