@Katia and Lostcoast. The shelves are around 35-40 pounds I exaggerated a bit, but they still are freaking tanks. They are thick like that because I made a frame out of 2x2's for each shelve before I put a piece of plywood on both sides.

The reason I did that was plywood can warp with the changes in humidity, so they are screwed to a frame that's screwed to a frame (lol) AND glued! Plus It allowed me to pack the dead space inside the shelves with insulation.