I have designed a steel bridge on RFEM 6 with stainless steel material.
The arc section is 406.4x12.5 > 240mm (diameter), i can not have a section less than 240 due to heavy loads. Acoording to EN-1-4 th class of the section is not defined and i have to refer to EN-1-6. What can i do so I can utilize sections with diameter>240mm for examble 406.4x12.5 on RFEM6, is there any solution. Thank you.
Hello,
You're absolutely right—the standard refers to EN 1993-1-6, which addresses the stability of shells. In RFEM, this topic can be modeled using a surface model. This means the pipe should be represented using surface elements, and a buckling analysis should be performed.
For a deeper dive into this topic, I recommend checking out this webinar:
Webinar on Shell Stability
Additionally, within the 3D model, the “Surface Model” beam type can be very helpful. You can find more information about this in the following article:
Surface Model Knowledge Base
I hope this helps! If you have any further questions, feel free to reach out. 
Hello,
If I model only the arch of the bridge using surface elements, while all other structural components are modeled as members (sections), which type of analysis should be performed (e.g., linear or nonlinear)?
Additionally, is it possible in RFEM 6 to run an analysis that simultaneously evaluates both member and surface elements within the same model? If this is not possible, what would be the recommended approach in this case?
Another question that would help me a lot: I have already created the model, including the arch defined as a member with its cross-section and all applied ( Loads,Supports,Load cases / combinations,Analysis settings). Is there a fast or efficient way in RFEM 6 to convert this member into a surface element without having to delete and re-apply everything (e.g., section properties, loads, and boundary conditions)?
The member is currently defined as a single line, whereas a surface element requires a polyline. In addition, the existing line is an arc. I am unsure whether a polyline in RFEM 6 can be defined with a curved (arc) geometry.
Thank you in advance.
