Have you guys always wondered why Hawaii is the only place in the world that has crazy ridges or on the top of thier soda cans? Hawaii only has one can making plant, and it was too expensive to change it over to the new way, so here we are 30 some years later with ribbed top cans.
Ribbing on Tin Cans strengthens the tin. The can is curved and the ridges reduce your ability to dent the can with normal handling. Compare to a typical aluminium soda can that has thinner walls and no corrugation of the metal. It's pretty easy to dent empty soda cans with hand pressure.