Unbraced Length of Tower "X" braces with bolt at intersection

[jbuening]

What is everyone's take on unbraced lengths when modeling towers that utilize single angles forming an "X" for bracing between columns? The intersection point will have a through bolt, so my thought is the bolt will reduce the effective length for buckling vertically but the buckling will still occur horizontally/outward for the full length of the brace. Do you share this opinion? Since they have that center bolt would the "r" be for both angles since their stiffness will combine and buckling occurring near the bolt?

I've been seeing a lot of very slender angles being used for this bracing in towers and many exceed KL/r of 200 using only its on "r" value, so I'm wondering if I'm missing something basic or if there is some caveat that I'm overlooking in the AISC manual. Thanks in advance

 

[KootK]

These threads should see you through:

Link
Link

ASCE-10-97 has the provisions that govern this for towers I believe.

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.

 

[JAE]

From the second link that KootK supplied, one of the posts referenced this AISC Engineering Journal article which, after reading, appears to definitively answer your question:

AISC Engineering Journal, 3rd Quarter, 2013 - Stability Design of Cross-Bracing Systems for Frames
Author: Eric M. Lui and Xiaoran Zhang

It's only $10. Free if you are an AISC member.


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[jbuening]

Thanks for the info. I'll look into that Journal article!