Question:
I would like to determine and consider the stiffness of a line support using a fictitious wall. Why is this option grayed out?
Answer:
The "Stiffness via fictitious wall" option is only available if you have selected the local axis system of the supported line, not the global coordinate system.
Once you select "Local xyz" under the coordinate system and activate the option, the "Stiffness via fictitious wall" tab becomes available. See also Image 01 and Image 02.