I am trying to design a base plate connection for a Tube column using the RAM Connection interface within STAAD.Pro. I am getting a message "Unable to create Joint. Only I shapes are allowed for columns". Can the software not design base plate for tube columns ?

Most likely the tube sections in your model are defined from the TUBE database in STAAD.Pro. RAM Connection interface within STAAD.Pro is able to design base plate for tube shapes but you need to define these tubes using sections from the HSS Rectangle database in STAAD.Pro. So replace the TUBE sections with HSS Rectangle shapes and the software should be able to design base plates.