The grasshopper says it’s planar, but FEM-Design says it’s not.
planar surface.gh (10.3 KB)
ehi @netsonicyxf
FEM-Design has a tight tollerance to check the planarity. It seems that your slab is not planar for a tollerance which is less than 0.0001.
Can you double check if you can make the surface planar with that tollerance?
It is a well known issue that we would like to fix in one of the future release.
One other option would be to split the quad surface in 2 triangles. Triangle are planar by definitions.
It’s planar if the tol is 0.001mm and it’s not planar if the tol is 0.0001mm.
Sap2000 can handle this type of surfaces, Is it possivle for FEM-Design to handl it in the near future?
Absolutely.
The idea is to albe able to have a less strict tolerance when checking planarity.
Is your geometry made in rhino or it comes from an import process from a different software?
The geometries are created in Rhino and meshed via a Rhino plugin called “Griddle”, which is a professional mesher for FEM analysis.
These new surfaces are planar with TOL of 0.0001m. But FEM-Design still shows they aren’t planar.
1.gh (208.3 KB)
ehi @netsonicyxf
Beautiful structure! I did send the file to support. I need to double check with the developer.
One question:
Would it be an option for you to split the quad surfaces in two triangles?
I have found out that tolerance in FEM-Design is really tight. We need to use a 0.0001 m tolerance 
However, for you case, you can recreate the middle step as shown in the script below.
Let me know if it works!