Beam Web Allowable Stresses

[iv63]

I am analyzing beam with knife plate welded to web and top flange using quadrilateral plate elements (see attached screen shots). The most stressed element is on beam web just below knife plate subject to both axial compression and bending stresses (fa=Sx, fby=6My/t2). Question is how to calculate beam web allowable stresses Fa and Fby? Can AISC interaction formula fa/Fa+fby/Fby<1.0 be used? As always I appreciate your help.
iv

 

[KootK]

For pure stress interaction, I'd be tempted to use Von Mises failure criterion with phi=0.9 on Fy. There will be interaction with shear as well although I imagine that would be minor.

For practical, real world design, I think that this would be best handled using a plastic design method such as the yield line method. Given my druthers, I'd also run the stiffener full depth in this application unless there's going to be ten thousand of these things.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[iv63]

Thank you KootK. We are trying to standardize/optimize this detail since there will be more than "ten thousand of these things" Would you compare Von Mises stresses to 0.9Fy?
iv

 

[KootK]

Alrighty then. I would compare to 0.9Fy. Depending on the magnitude of the load, there could be some local plate buckling issues to contend with. I'm not sure if your modelling strategy captures that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.