The DataGroup instance Steel Beam : Bar Joist Envelope is a component of the overall Joist compound cell. It has these properties:

• Linear Member – A rectangular linear member encompasses the physical space the joist occupies. Interference detection can take advantage of the joist envelope member extents.
• Section Definition – A rectangular section is named for the joist using the joist designation (e.g. 10K1)
• DataGroup Assignment – The Steel Beam : Bar Joist Envelope assignment distinguishes the joist envelope member from the detailed joist members.