The Iron Bridge in Kingfield must be replaced within 12 months after an engineer from Calderwood Engineering of Brunswick determined the structure is in severe disrepair. Sagging planks are sectioned off from traffic and the weight limit has been reduced from 32 tons to 5 tons, preventing some fire engines, fuel trucks, ambulances and other heavy loads from crossing. Photo by Ashton F. LeCraw.KINGFIELD — A private bridge serving about 60 househo…