Extradosed bridges

Extradosed bridges with their flat/shallow stay cables and stiff decks are an economic alternative to box girder bridges and cable-stayed bridges for spans of 100 to 200 m. The structural system of extradosed bridges is considered also as a transition between the structural systems of the box girder bridges and the cable-stayed bridges. The stay cables for extradosed bridges are normally designed to carry nearly the full permanent load and the deck behaves as a continuous beam on rigid supports. The method, used usually for the determination of the stay cable forces under permanent load for cables-stayed bridges, cannot be followed for the extradosed bridges with their heavy and stiff decks. The typical configurations for such type of bridges will be presented in this paper. Further, a simple and an economic method for the determination of the stay cable forces and the corresponding bending moment distribution along the deck elements under permanent load, for extradosed bridges, will be proposed. Additionally, the arrangement of the prestressing tendons inside the concrete deck elements, to nearly eliminate the bending moments under permanent load, will be consistently handled.