The Mollet Railway Interchange has a major role in the European freight railway network. The interchange is 4,396 ft (1.34 km) long in total and includes four railway viaducts: E2, E3, E7 and E8. The first three structures consist of a reinforced concrete deck supported by two precast concrete U-girders. The lengths of E2, E3 and E7 structures are 719 ft (219.2 m), 471 ft (143.7 m) and 2,114 ft (644.3 m), respectively.
E8 provides the crossing of a railway intersection over two major tollways. This structure is a steel bridge with an X-shaped plan view. The bridge is 1,092 ft (333 m) long with a maximum span of 181 ft (55 m). It consists of a steel box girder with a top concrete slab of variable depth.
The superstructure E8 is designed with double composite action and includes a bottom concrete slab in negative bending moment regions. This allows for the reduction of the steel quantities and the increase in ductility.
All foundations consist of 5 ft (1.50 m) drilled piles.
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. The structure E8, given its length and complex shape, required the location of a fixed point on the substructure at the smaller abutment, in order to support the braking/acceleration and seismic loads. All non-fixed supports were defined as sliding POT bearings.
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 long time-dependent concrete effects (creep and shrinkage).