Hi, I'm wondering how Cu,y is calculated from S-prov. As I see it's about 0.6168*S-prov, but why is that? Shouldn't Cu,y = S-prov / length of the stabilized beam?
Hi and welcome! 
You can transform the shear stiffness using the following equation:
Shear Stiffness Transformation Formula
If you have any questions while applying it, feel free to ask — we’re happy to help!
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Thank you! I've tried to follow example E8.2 of ECCS - Application of Metal Sheeting Acting as Diaphragm for validation, but unfortunately Ncr and Mcr are not even close in RFEM.
Simply supported beam IPE 550, nodal compression load N = 200 kN, member gravity load q = 5.8 kN/m, L = 20, S = 1438 kN, so then Cu,y is 35,48 kN/m2. When I use lateral y support with S-prov, then I get Ncr = 342,6 kN (instead of 576 kN) and Mcr = 556,34 kNm (instead of 835 kN).
Also one more question - how is it possible to compare orthotropy surface with support via S-prov?
Hi daniel_2025,
thanks for your message!
To analyse the problem more precisely, the model file would be very helpful:
Click on File → Save as and choose the following settings to reduce the file size:
Then upload the file here (e.g. *.rf6, *.rs9) – this way, the community can also contribute to the solution.
Prefer not to share the file publicly? No problem – send it to me via direct message: click on my profile picture or user name → Message.
Best regards
Gerhard Rehm