THE SAINT-NAZAIRE-SAINT-BREVIN BRIDGE AND ITS TWO ACCESS VIADUCTS

THE STRUCTURE DESCRIBED IS THE LONGEST IN FRANCE AND WILL HAVE BEEN BUILT IN 3 YEARS. IT IS FOUNDED ON VERTICAL BENCHES OF GNEISS COVERED WITH LAYERS OF SAND AND MUD. IT COMPRISES 2 PRESTRESSED CONCRETE ACCESS VIADUCTS WHICH CONNECT EACH SIDE TO THE CENTRAL METAL BRIDGE. THE LATTER HAS THREE SPANS, A STAYED GIRDER BRIDGE DECK HELD IN POSITION BY GALVANIZED CABLES ANCHORED TO THE TOP OF TWO BRIDGE TOWERS. THE BRIDGE DECK OF THE ACCESS VIADUCTS CONSISTS OF 4 PRECAST PRESTRESSED CONCRETE GIRDERS. PILED FOUNDATIONS ARE MADE OF TUBULAR REINFORCED CONCRETE. SLIDING FORMS WERE USED FOR THEIR CONSTRUCTION. THE MAIN PIERS HAVE THE SHAPE OF A HOLLOW CAISSON AND WERE ALSO BUILT WITH SLIDING FORMS. THE GIRDERS OF THE VIADUCT DECK WERE PRECAST BEHIND EACH ABUTMENT AND LAUNCHED WITH THE HELP OF TWO LATTICED GIRDERS FITTED WITH FORE- AND AFT-CUTWATERS.