Is there a way to consider the reduction factor km, alpha for the cut fiber according to EC5 (6.4.2) when the BSH beam is modeled as a surface and not as a bar?
Hello Adrian, 
yes, you can insert a result bar into the surface. You can easily download a BSH beam with result bar as a block from the Dlubal Center. 
Additionally, I would like to point you to the Knowledge Base article Bemessung von wandartigen Trägern in RFEM 6. It describes the use of the result bar in detail. 
Best regards,
Matthias Meyer
Good tip with the result beam, thanks for that already.
That probably works well for the normal BSH beam. But now we have a curved BSH beam (fish belly beam).
This does exist in principle as a beam type, but not when I want to define a result beam.
Modeling with surfaces is unfortunately necessary due to other factors.
Do you have any clever solutions here?
Regards,
Adrian
In this case, you can use a result line to obtain the inner forces of your beam. Here’s a step-by-step guide:
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Create your fish belly beam as a surface.
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Define an arc using 3 nodes along the center line of your surface.
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Define this arc as a result line.
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Finally, include the surface in the results of your result line.
Unfortunately, verifications for fish belly beams are not yet implemented. We understand this might be limiting, and we’re always working to improve the software. If you have any further questions or need additional help, feel free to reach out! 
