Answer:
Yes, this is possible with the RF‑/JOINTS Timber – Steel to Timber add-on module. You can design the connection of two diagonals if they are connected with steel plates and dowels, for example. For this, it is reasonable to use the "Main member only" joint type.
After selecting the node in the program, the connection is still marked as insufficiently defined due to the steel bottom flange.
You can now deactivate both steel members to perform the design for the connection of the two diagonals only.
This design is possible in the add-on module.
