Get the side surface of Beam

Hello folks, I am trying to get the side surface of structural framing (The last purpose is to create stirrup for beam in Revit).
The picture below is the case, but…
For that beam it’s simple since I can get the surface area and counter-pose among each other and find the minimum surface area and get back those two surfaces.
In real practice project, we still have to deal a lot with more complex cases, e.g:
(Please see comments below)
Although I have found some packages but none of them can solve those cases. Any thought? Maybe some python script will the solve that?
Thanks you!!

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Try getting the location curve of the beam then find the faces with normals parallel to that curve.