PURPOSE: To keep a rust preventative/anticorrosive effect for a long period by forming non-woven fabric sheets in a cap shape, coating a bolt and a nut part in a cap shape concave part filled with painting adhesives and sticking the cap shape opening ends of the sheets on splicing plates.

CONSTITUTION: The bolt and nut part 13 of structure splicing parts are covered with caps 2 formed in such a manner that cylindrical parts whose one end is closed, and other end is opened, and edge parts 3 provided to its opening end are provided thereto by using non-woven fabric sheets consisting of film/ fibril structure of flexible filament manufactured by a flash spinning method using polyolefin series resin. In this case, painting adhesives 5 consisting of inorganics and a curing agent are filled in the caps 2 so that structure wherein the bolt and the nut part 13 are sealed with the non-woven sheets is formed. Water content in the caps 2 is completely eliminated because the non-woven sheets have excellent air permeability, moisture permeability, durability and waterproofness, and further rust preventative/anticorrosive effect can be kept for a long period by sticking the edge parts 3 of the sheets to the splicing parts.