Les Cèdres footbridge. Stress ribbon

The leading idea that has presided over the formal and structural design of the footbridge, winner of the competition, has been based on a double consideration: try to offer a vision of great transparency, lightness and clarity; guarantee a construction process characterised by a very efficient execution with a very low incidence in the traffic of the lower road.

To achieve this leading idea, a stress ribbon system has been adopted with a certain originality, due to the significant width of 8 m, greater than usual.

The stress ribbon, with a total length of 13.15+35.7+13.15 m, is completed by the presence of two piers located on both sides of the motorway, longitudinally inclined to reduce the central span and composed of two slightly inclined shafts, connected at the top through a lintel. The latter incorporates the “”chair”” to support the deck, with a curvature that minimises the bending moments in the stress ribbon.

The bearing elements of the stress ribbon are composed of two steel plates with a 2000.40 cross section and in S355 weathering steel, separated 1.10 m from each other and supporting precast concrete segments with 0.22 m maximum thickness, separated longitudinally by joints of 20 mm through which the deck drainage would be realised, constituting the slab a semi-permeable element.

The equilibrium of each of the two abutments is guaranteed by the presence of the following foundation systems: compressed piles in correspondence with the piers, micropiles in the rear part of the abutment and horizontal compressed pipes, pushed below the highway and joining the two abutments.

Once the Preliminary Phase of the Project was finalised, this solution was subsequently rejected by the Federal Roads Office (Switzerland), which reconsidered its initial approval of the drainage system.