Bending capacity of steel beams - unbraced lengths

[Bigbeam]

How do I specify the unbraced length of the compression flange of a beam in bending?

I am designing a gas bar canopy with cantilevered column and beam over, forming a T. The top flange of the beam is fully braced with the bottom flange can be considered braced at both ends and at the column.

I tried locally setting the unbraced length ratio for the member but I etabs always calculates the capacity based on full bracing of the compression flange which is clearly wrong.

I should really be able to specify the unbraced lengths of both the top and bottom flanges so that positive and neg. moments can be calculated properly.

K

 

[Skicat]

Etabs by default calculates the unbraced length for each member (based on what is framing into that member, etc.). You can manually specify the LTB ratio for each object by selecting the object(s), going to design > steel frame design > view / revise overwrites, I believe. You should be able to manually input values for unbraced lengths but I'm not sure about specifying it for the bottom flange. Hope this helps.