Cb value for crane rail beam simply supported by hangers attached to top flange only 4

[AKM30]

Is a crane rail beam that is supported at each end by hanger connections that attach only to the top flange of the beam considered to be braced for the purposes of the calculation of the lateral-torsional buckling modification factor, Cb? With these end conditions, can you use AISC 14th Eq.(F1-1) to calculate Cb using the length between hangers as the beam length to calculate the moment values?

 

[Ingenuity]

I thought - possibly mistakenly - that the OP's situation had a diagonal brace to the top flange at the vertical hanger support location - validating the lateral restraint requirement:

Maybe the diagonal member in the photo above is part of a truss in the background.

 

[AKM30]

Ingenuity, what you have clouded in the top Photo is actually a diagonal truss element beyond the crane rail beam. This crane rail beam (left side of bottom photo) only has vertical hanger rods and no diagonal braces. In the bottom Photo, the clouded section on the right crane rail beam is a diagonal brace from the top flange to the bottom chord of the truss (hangers and brace are tube steel on this side). The arrows in the bottom photo are pointing to the a diagonal of the building truss and not associated with the crane. It seems like the original designers of the hoist system must have been counting on the bridge beam connecting the crane rails to brace the left beam.

Agent666, thank you for the explanation and spreadsheet. It is somewhat difficult for me to follow the nomenclature in the article and your spreadsheet since I am only familiar with the AISC code, but I think understand the point you are making. I will try to do a similar analysis using AISC code and the actually properties to see where I end up.