Unbraced length of X-brace design

[STRCIVIL]

I am currently designing a x-braced frame. He's using W-columns and double angle x-braces. Column top to other column bottom distance is about 30-feet (corner to corner) He is providing bolted connection at the middle where the braces intersect. Apparently, he is using lu of 14.7 feet for compression bracing. Some people say the tension brace help and provide lateral stability of the compression brace at the bolted connection, thus reducing the lu of the brace to half the corner to corner distance.
What lu should i use? is there any reference which can clearly explain this issue? thank you in advance.

 

[DaveAtkins]

I would ignore the compression brace, and put all the load into the tension brace. Then your problem goes away.

DaveAtkins

 

[VoyageofDiscovery]

Hi STRCIVIL,

In Canada we have a tower structure design standard and it states for your situation:

For out-of-plane buckling where the 30ft from corner to corner is comprised of DL1+DL2, the adjusted unbraced length is ADL= DL1 + DL2*((m-0.5)*2) where m=(0.523-0.428(T/C))^0.5 but m is not less than 0.5. In your case (T/C)= 1 thus ADL = DL1 or 15ft.

Thus for angle struts L/r = the larger of ADL/ryy or DL1/rmin

See Cl. 6.2.3.3 of CSA S37-01.

Wrt tension-only system, Dave's right. Just remember to ensure that the horizontal from top corner to top corner is designed to transfer the load across in compression to the tension member. Check that corner connection as well.

Regards

VOD