Aluminium Structures in Refurbishment: Case of the Real Ferdinando Bridge on Garigliano River

The use of aluminium alloys is today an emerging activity which competes with steel in many specific fields of structural engineering. A new field of particular interest is the one of structural restoration, where aluminium and its alloys represent a new material whose properties can be exploited in a very promising way. An interesting experience has been the restoration of old suspension bridges in France during the seventies. These structures, built during the 19th century, were made of wooden deck, masonry piers, steel girders and steel suspension cables. Their bad condition required structural consolidation operations, also in view of re–using these bridges in a new improved road planning. After a national competition, in which both steel and aluminium solutions were presented, the French Road Authorities accepted to use an aluminium deck in the retrofitting project of three bridges (the Montmerle and the Trevoux bridges on the Saône river; the Groslée bridge on the Rhône river). They were completed within 1975. In the Montmerle bridge (two 80 m bays) the use of aluminium both for the two longitudinal truss beams with bolted connections and for the deck structures led to the possibility of increasing the weight of the road vehicles, while preserving both the existing cables and piers without significant strengthening (Fig. 1). In the retrofit of the Groslée bridge (a single 174 m bay) the new deck structure is made of three longitudinal aluminium truss girders, connected to a light reinforced concrete slab (Fig. 2). At the end of the eighties, a structural restoration project of the oldest Italian suspension bridge, the "Real Ferdinando" bridge on the Garigliano river (1832), had been proposed in the context of a wider rehabilitation program of that area, which wanted to re-use it for a pedestrian connection. This bridge was designed by Luigi Giura in 1828 (Fig. 3) and erected in 1831–32 under the supervision of the King-Ferdinando II. During World War 2 the deck of the bridge was completely destroyed and it was in a bad condition for many years. Considering the positive French experience, it was clear that an aluminium solution would be very appropriate for the planned purpose. But it was necessary to develop a comprehensive comparison between the more classical steel solution and the aluminium one in order to convince the public Authorities. A long procedure of about ten years followed after the first approach to the problem. In 1998 erection of the new aluminium bridge was successfully completed.