How to make double channel back to back rather face to face.This is the section image of double channel which is from uk.xml delivered by Bentley Structural.
Open uk.xml by any editors and copy the section "2C100x50x10" and rename it to "2C100x50x10BB" to create a new section in uk.xml. In the new section, set the attribute "Back2Back" = to "true" (see both sections pasted below),and load the updated uk.xml in Bentley Structural and place one of each section (see attached screen capture dcbb.jpg), please observe how the "Back2Back" attribute affects the geometry of this section type.