In the Steel Joints add-on, you can use not only the usual member types of "Beam", "Truss", and so on, but also the member type of "Result Beam", as well as cross-sections from surface elements. You should select a suitable cross-section for the result beam and then define any member openings in the surface model using the member editor.
Steel Joint Design on "Result Beam" Member Type and on Surface Models
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