Crossing motorways under traffic without intermediate piers

The European research programme SBRI attempted to reveal the costs caused during the service life of a bridge - direct costs for the bridge owner as well as indirect costs for users. The principal results of SBRI should make it possible to take better account of the true costs of a central pier by considering the risks in the construction phase and those that may threaten the highway overpass during its service life.
CEREMA has developed two economic solutions to reach the objective of avoiding the central pier:
1) The solution implemented at Ko Wé Kara in New Caledonia is a steel-concrete composite tied arch bridge with innovative and economic details:
- innovative radial hangers made of welded plates, and
- innovative reinforcement against accidental impact of over-height vehicles.
2) One other possible solution is the composite steel-concrete gantry bridge. The European research programme PRECOBEAM allowed the use of tests and experimental projects to finalize a new system of connection to lower the cost of this type of structure: a strip along which the cutting line of the steel dowels is made in a clothoid shape (CL), which improves the fatigue resistance. CEREMA introduced this innovation in its research programme.
A composite structure can take various forms. It can associate, for instance, the steel web of a beam directly with a concrete flange. It can also constitute a composite deck with a bottom plate stiffened by connecting CL-shape indented strips. An outstanding project of this type in New Caledonia is described in detail. Of course, this type of bridge is an integral bridge and the article includes some recommendations for the design and construction of integral bridges.