The Mollet Railway Interchange plays a major role in the European freight railway network. Completed in 2010, it allows freight trains travelling between Spain and France to bypass the city of Barcelona and join the high speed railway line also conceived for freight use. The interchange has a total length of 1.34 km and includes four railway viaducts: E2, E3, E7 and E8; 219.2 m, 143.7 m, 644.3 m and 333 m long, respectively.
The first three viaducts consist of a reinforced concrete deck supported by two precast concrete U-girders. Viaduct E8, spanning two major tollways with a longest span of 55 m; supports two railway branches that intersect each other, which gives it an X-shaped plan view. It is composed of a steel box girder of variable depth with a top concrete slab. The deck is designed with double composite action and includes a bottom concrete slab in negative bending moment regions. This allowed a reduction of the amount of steel used and an increase in ductility. All foundations consist of drilled piles of 1.5 m in diameter.
A detailed track-bridge interaction was performed to assess the behavior of the track-bridge system under live loads. This non-linear analysis avoided the placement of track expansion joints on the first three structures despite their length. For Structure E8, given its length and complex shape, some of the non-fixed supports were defined as elastomeric bearings and others as sliding POT bearings. The abutments are equipped with shock transmission units. This configuration allowed to optimize the distribution of horizontal forces and the design of the substructure.
The complexity of the structures’ geometry (E8 in particular) and their interaction with the heavy traffic roadways underneath required a careful approach in terms of construction planning and scheduling. These requirements were considered during the design phase in order to correctly assess the time-dependent concrete effects (creep and shrinkage).