A novel approach to the protection of structural steelwork of composite bridges was proposed in 1980. Clean steel does not corrode at relative humidities up to 99 per cent if environmental contaminants are absent. The concept was therefore to enclose plate girders that are already sheltered by a concrete deck with plastic or other sheeting material. Enclosure then produces a condition in which bridge steelwork would be maintenance-free for several decades. The successful enclosure of the steelwork of three bridges is described, including the Conon River Bridge near Inverness, which has been totally enclosed with aluminium sheeting. The enclosure principle is applicable to unpainted as well as painted steelwork. The technique will also extend the life of weathering steel bridges that have been built in unfavourable environments. It is appropriate both for existing and new bridges. The permanent access that results is a major additional benefit providing built in facilities for inspection. (A)

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