Gap in Deck

I am trying to model a bridge that has two abutments and five piers. I have two beam groups (one with 7 beams and the next with 8) that changes at the middle pier. At this point I need the deck to have a gap 20" wide, which is filled with a joint filler in the field but is not continuous in respect to strength. When I try to leave this gap my model fails. Any recommendations