Abstract:

The paper is focussed on the presentation of twin composite viaducts located at Vitoria province in Spain.

The longitudinal scheme of the deck is a continuous beam of three spans. The length of the main span is 35 meters and both lateral spans have 17.5 metres. The design of the viaduct is controlled by the necessary clearance of 5.5 metres height. That results in a very slender deck of 0.72 metres of structural depth.

In order to reduce the interaction of the construction of the viaducts with the existing traffic, an hybrid solution for the structure is adopted. The piers are designed in reinforced concrete and they are embedded into the deck.

The lateral spans are designed in prestressed concrete and the main span is a composite steel-concrete deck which is partially suspended of a central tubular truss. The adoption of this structural scheme allows control of the deflection of the slender deck designed for this viaduct. In addition, internal forces and longitudinal bending moments are significantly reduced.

Figure 1.
Elevation and a section through the central span and Elevation and plan of the tubular lattice truss

On the other hand, aesthetics of the viaducts is clearly improved. The tubular truss designed is a spatial structure consisting of two inclined Warren trusses sharing the compression chord, being the tension chords of the trusses both composite decks. For the spatial trusses, structural elements with circular hollow sections (CHS) are adopted. The structural steel used is S355.

To conclude, the use of composite structures in these structural types, extends the number of possibilities to be considered by the designer and introduces high expressive formal aspects

Figure 2.
View of the bridge and  Ground-level view of the bridge.