Hi GOBA,
With the help of my colleague, I've got an answer to your question. I'll try my best to explain it here:
In short, this is a limitation of ARCHICAD. The reason for that is, ARCHICAD deals with architectural models only, which means that it converts structural analysis models into architectural models as well.
The entity IfcRelConnectsWithEccentricity adds the definition of eccentricity to the connection between a structural member and a structural connection (representing either a node or support), which presents in the structural analysis but not architectural models.
In the future, we are working on connection between ARCHICAD's model and Structural Analysis Model. I hope that this feature will come soon to provide better support for communicating between the architect and structural engineer.
I hope this will answer your question. Feel free to ask me again if you have any questions!
Have a nice day!
Best regards,
Minh
Minh Nguyen
Technical Support Engineer
GRAPHISOFT