In the Properties of the beam under Construction; set the Start or End Offset (Depending on what end of the beam is touching the other end; ie. Start to Start or Start to End) to be the distance you want the beams to be apart. Initially have the "Drag Structural Framing Component " dot to be the same as the other beam. This will join the two beams. Then set your offset and the beams will still be "joined" if you were to right click and select "Select Joined Elements" but graphically it shows them separate. Even with bar joists, the bottom cords do not graphically stay joined.