Beam Bracing Questions
Beam Bracing Questions
(OP)
If you have a interior beam framing into a perimeter beam, and the interior beam is coped to be at the same level as the perimeter beam, will this be considered a point of bracing? It seems like it wouldn't because it doesn't restrain either the top or bottom flange, like it would if it were sitting on top the perimeter beam.
Also, can anyone describe or provide a link for some general methods of providing bracing for a beam when you are concerned about lateral-torsional buckling? I hear people speak of providing bracing for beams, as if it is something easy to incorporate into the framing, I just have no visual idea of how this is accomplished.
I am sure these topics have been discussed before, I just couldn't find these specific answers when I did a search... thanks.
Also, can anyone describe or provide a link for some general methods of providing bracing for a beam when you are concerned about lateral-torsional buckling? I hear people speak of providing bracing for beams, as if it is something easy to incorporate into the framing, I just have no visual idea of how this is accomplished.
I am sure these topics have been discussed before, I just couldn't find these specific answers when I did a search... thanks.






RE: Beam Bracing Questions
HTH
RE: Beam Bracing Questions
The 13th Ed. AISC Spec. Appendix 6 and its commentary are all about this subject. For more info (and it will certainly be needed to really understand what's going on), dig up a copy of the AISC bracing seminar notes by Yura and Helwig. They recycled this seminar about 4000 times, so most offices have at least one copy floating around.
For your specific case, there will usually be a diaphragm there, but let's assume there's not one. Assuming the spandrel beam has only the top flange in compression, the filler beams will be connected close enough to the top flange to count as _lateral_ braces, to use Spec. terminology. I'm sure there are weird cases in which they won't be sufficient to be lateral braces, though, but I think they'd be rare.
RE: Beam Bracing Questions
"271828" hit the nail right on the head.
best regards registeredpe in AZ
RE: Beam Bracing Questions
But I feel that this kind of filler beam is still helpful because beam buckles in a lateral-torsional mode. If the lateral displacement is restrained, Mr should be higher.
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
Your beam is fine.
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
as slickdeals asked
"Does anyone have the Yura bracing papers in PDF Format?"
RE: Beam Bracing Questions
RE: Beam Bracing Questions
You are right. The lateral translation that must be resisted is at the compression flange. I believe that 1/3 of the depth of the cross section from the compression flange is considered adequate for bracing.
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
For example, say you have a W36 girder with a filler beam shear connected to the web. The top of connection plate is 12" from top of girder. Top flange of girder in compression. I wouldn't consider that filler beam to provide a lateral brace.
RE: Beam Bracing Questions
I believe (although I'm not stating categorically) that yes, as long you connect your bracing member within 1/3 of the member depth from the compression flange, the brace is considered sufficiently "near" the compression flange.
RE: Beam Bracing Questions
RE: Beam Bracing Questions
RE: Beam Bracing Questions
Unless you or someone can point to some text, I wouldn't use the 1/3 depth guideline. I'd go more subjectively, such as:
1. Girder, top flange in compression, filler beam attached near the top in the typical manner (i.e. T/STL same for both, or nearly so) = a brace point. The connection will begin a very small distance down from the top flange.
2. Girder, top flange in compression, filler beam attached more or less in the middle or below != a brace point.
Of course, as JAE and others point out, a diaphragm will often be there. I'm typing about cases in which the filler beam is providing the braced point.
We're also typing specifically about *lateral* braces. Torsional braces are a whole different deal. Web distortional stiffness is the usually the critical item that gets left outta discussions of those.