no need to worry about analytical line. it will be created automatically based on category of Structural framing.
Analytical line is based on the bounding Box.

Thank you very much for your answer... My goal is to create a tunnel junction and export it into sofistik... So, in the beginning a created a generic model face based family (in order to cut and reshape automatically the "hosting" wall) and then changed the category to Structural Framing.. when I export the model in Sofistik the void in the hosting wall is created but the analytical model of the new family is not there... In Revit I cannot see the analytical model option activated... I have the possibility to attach a structural material to the object and create its rebars though (so it works indeed as a structural object)...

I had never before read about this bounding box... I am searching about it and I hope it will get me somewhere..

Unfortunately though, the analytical model is not automatically created in my case... and I am searching for a hint for such cases... It would be really helpful... Have you ever faced a similar problem or heard anything similar?

Sorry for very late reply, many new jonnies to Revit are facing this issue. Bounding box is nothing but the outer edges of the family element.
Ex 300x300 Column , here the bounding box is 300x300. The analytical line is always at the centroid. it will automatically change in project depends on site condition. where the other element node is present with in the bounding box.

Thank you