SCBF Column Anchorage

[StructuralEngGuy]

AISC 341-05 section 8.5a requires column axial anchorage to be designed for the required strengths of the steel elements connected at the base. In the case of a SCBF, this would be the summation of the required column strength per section 8.3 and the vertical component of the brace connection force.

My question is, what if the column is in the corner of the building and has braces in both orthogonal directions? Do I design the axial anchorage for the required column strength in addition to the vertical components of both brace connection design forces?

What about a two-bay braced frame where typical elastic analysis would result in the vertical components of the brace forces canceling each other out. Would that column axial anchorage still be designed for the required column strength in addition to the vertical components of both brace connection design forces?

Thanks in advance for your help!

 

[jittles]

I just recently had a similar discussion with my local building officials regarding the corner column of an EBF system. We settled on applying the 100/30 orthogonal combination rule to the expected strengths. In my case, the expected strength was the summation of the link shear above for an EBF, but the issue was the same - summing those strengths for both orthogonal directions resulted in a pretty ridiculous column design for the corner.

As for the second question, you would consider both brace strengths, one in tension and the other in compression (if I understand the question correctly), such that they would be opposite. However, you also need to consider the effects of the compression brace buckling, i.e. also design for the controlling case of a single brace in tension while neglecting the compression brace's force in the opposite direction or determining the post-buckling strength of that brace, if you want to really nail down the design.

 

[StructuralEngGuy]

Thanks for the reply Jittles. I agree with you on both counts. I think the 100/30 combination is a good compromise, although I can see some Building Officials taking a more strict interpretation of the provisions and requiring the full brace capacity for both braces.