This appears to be an iron barrel hoop (that would be wrapped around a barrel to hold it together), fashioned into an accordion shape for another purpose. Possibly, it was to serve as a grill top on which food and pots/pans could rest while cooking. It measures around 6.5″ x 11.5″. For source and more details, click here.
Image from: http://www.cr.nps.gov/museum/exhibits/revwar/image_gal/morrimg/broilerhoop.html