Are fixed shelves needed for a built in book case?
I'm building a set of book cases that will be 8' tall and 16' wide. There will be a wall on both sides of the cases. Each will be roughly 27" wide, 3/4 sides, screwed together, and will have 1/4 backs. I will attach them to the wall behind them. Given this, is a fixed shelf or two needed? I've done a built in at my old house and used two fixed shelves with framing. But I'm hoping for a more open look in this set. But of course I want to make sure it's sound. Given that there are walls on both sides it seems safe to me, but I wanted to hear from the counsel first.
EDIT:
Picture 7 distinct book cases, each about 27 inches wide, screwed together. No shelf span is more than 27 inches wide. Each case is just a big open rectangle. There is one face frame to tie it all together.