I recently traveled on the lower deck of an A380 and the section where the side walls of the fuselage and its roof top meet is curved just like any single deck airplane.
Credits: Wikimedia Commons
If there is a deck above me (which there definitely is) then why does the lower deck have to be curved near the top? Shouldn't it be straight on the sides?
Shouldn't it be straight when there is one more deck above it? I'm sure that it's just the interior that is curved and the external structure is indeed straight but does it serve any important purpose?
Seat: Row 58
Here is what i saw:
Notice that even the roof is curved, is there a structural reason for that as well? On the side wall one of the rows has an extra covering on it, I'm almost sure that is to cover one of the brackets as mentioned in the answer below but even without that the whole cabin is curved.