Unbraced Length of Wood Beams
Unbraced Length of Wood Beams
(OP)
I searched the forum, but all I can find are questions about wood framing bracing steel. I'm looking for wood framing (or even GWB) bracing wood beams. AISC provides us with the very useful Appendix 6 for calculations of required strength and stiffness of bracing members for steel columns and beams. Does anyone know of a similar resource for wood beams? Would it be appropriate to go to the commentary for AISC App. 6 and use the equations there, modifying as needed for rectangular wood rather than steel beams with flanges? My thought is to to use the entire compression region as my compression "flange" and substitute the appropriate values. ho would be distance from compression centroid to tension centroid.
I realize a lot of people probably don't pay a lot of attention to this check, but I'd like to get a better understanding of it so I can establish my own judgement before calling it "good by inspection." Thanks.
I realize a lot of people probably don't pay a lot of attention to this check, but I'd like to get a better understanding of it so I can establish my own judgement before calling it "good by inspection." Thanks.






RE: Unbraced Length of Wood Beams
Generally speaking, wood members don't have buckling issues as they are typically fairly wide when compared to the depth. Also, they typically have members framing into them at a fairly small and typical spacing, 16"/24"/32", and therefore the unbraced length doesn't come into play.
If you are checking this for a specific case, perhaps you could provide a little more information and we can help more.
RE: Unbraced Length of Wood Beams
The most popular US wood text on the market still lists inflection point bracing as valid for Pete's sake. Boo.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Unbraced Length of Wood Beams
NDS tells you to consider the unbraced length, but then doesn't define the requirements to consider a point "braced" beyond saying that it must prevent lateral displacement. I'm looking for a way to quantify that. I realize that, in most cases, it's not a necessary check for the reasons you mention. I'm interested in the cases when it does become important, but if I'm unable to quantify the requirement I'm not sure how to identify those situations. Thanks again.
RE: Unbraced Length of Wood Beams
RE: Unbraced Length of Wood Beams
If the beam in question had an extraordinary amount of sweep, then I may reevaluate this approach. But for an initially straight beam a brace load of 2% seems like a conservative approach to me.
The total stress resultant could be calculated using MQ/I.
RE: Unbraced Length of Wood Beams
RE: Unbraced Length of Wood Beams
RE: Unbraced Length of Wood Beams
http://www.awc.org/pdf/codes-standards/publication...
http://www.survivorlibrary.com/library/light_and_h...
RE: Unbraced Length of Wood Beams
http://files.engineering.com/getfile.aspx?folder=e...
http://files.engineering.com/getfile.aspx?folder=d...
EIT
www.HowToEngineer.com
RE: Unbraced Length of Wood Beams
Thank you! The first document is just what I was looking for. Sadly the second still states "design of lateral and/or torsional bracing for wood beams is currently beyond the scope of the document," but it is encouraging and goes on to state that further research is being considered to "quantify and develop design provisions for lateral and torsional bracing systems." It also provides an in depth review of the code provisions and the theories used to back them up, which is always valuable.
RE: Unbraced Length of Wood Beams