Box Beam Local Buckling

[BMart006]

Hopefully a quick and easy question. I have a built-up box beam with thin (vertical) webs and thick (horizontal) flanges. Using AISC to analyze the MINOR AXIS moment capacity of the beam, do you flip the local buckling equations for analyzing the different elements? In other words, where AISC F7.2 provides the “Flange Local Buckling” check, should the value b/tf be changed to h/tw and vice versa for F7.3? Thanks.

 

[Agent666]

Yes you would need to assess different local buckling criteria for each axis of bending. Not 100% familiar with AISC specifically but I'm sure someone else will confirm the exact criteria, but typically for one direction of bending the plate element is under constant tension/compression stress, under the other direction the stress might vary from tension to compression. For each of these conditions usually standards have different plate slenderness limits, and means of assessing which is critical for working out section properties/strengths for each direction of bending.

 

[Lomarandil]

Yes, or you could think of h and b being defined as for the axis of bending, not the physical orientation of the beam.

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The name is a long story -- just call me Lo.

 

[BMart006]

Thanks, that's what I was suspecting.