Architecture 

Two road bridges near Fribourg, Switzerland. The aim of both projects is to return to the original horizon of the landscape, not to create new landmarks. 

The first project is an 840-metre-long bridge structure with separated vehicular traffic. Over the years, the Sarine River has carved a deep furrow in the landscape around Fribourg. With our proposal we are going back in time and restoring the horizon above the canyon. No building rises above the level of the bridge deck; the intention is to remain below the horizon of the valley. The main structure of the bridge, a truss supported by piers, does not compete with the Poya Bridge, which is located near the centre of Fribourg. The cross-section of the bridge is laid out in two levels, which makes it possible to separate car traffic from cycling and pedestrian circulation. Overlooking the beautiful surrounding countryside, such a structure has the potential to become not only a new road link at the Matran motorway junction, but also part of the network of hiking and cycling trails around Fribourg.

The proposed 245-metre-long Chésalles bridge is part of the Fribourg bypass, together with the Hauterive bridge, which will allow access to the Matran motorway junction without passing through the city. The structure connects two agricultural plains separated by the Chésalles stream valley, at the bottom of which is the Ferradzo road. It creates a very simple horizontal connection between these plains: the entire support system is located under the bridge deck, with no structural elements above it. The integration of the structure into its environment is achieved by means of the bridge's four piers. Their architecture is loosely inspired by the geometry of trees: the trunk (the vertical stem) is crowned by branches (the head of the pillar), which break up into four very slender bar elements (60 cm across) inclined at an angle of 30°. These branches are directly supported by two steel box girder beams of trapezoidal cross-section. This geometry allows a perfect redistribution of the internal forces and a reduction in the size of the supports. The result is an impression of lightness: very thin, subtle columns supporting a thin concrete bridge deck, with two steel box girders in the background. With the slender bars at the top of the structure, the building thus resembles ants, whose slender legs are capable of carrying loads far in excess of their own weight.

Construction

Bridge 1

The lower level, fully integrated into the height of the truss, provides a safer and quieter pedestrian zone without the close proximity of cars. Benches along the route also encourage pedestrians to sit and enjoy the view of nature. The upper section is reserved for cars. The roadway is wide enough to accommodate one lane in each direction and two lanes with a paved shoulder. In the future, these could become a third lane. Both levels of the bridge are protected against falls. A 1.1 m high guardrail filled with stainless steel mesh with maximum openings of 4 cm was installed for the lower part of the bridge. Above the railing, the net continues to the upper bridge deck with holes of approximately 20 cm. This net is placed only between the two decks and never overhangs the top, but, thanks to its inclination of approximately 20°, it secures both levels of the bridge. The net with 20 cm holes is shaded by the landscape.

Bridge 2

The lightness of the semi-integral bridge with a main steel structure combined with a concrete slab bridge deck will guarantee the required strength and durability and ensure that the structure blends harmoniously with the site. The materials and construction methodology will also ensure rapid implementation and a lower environmental impact. The bridge deck describes a gently curved trajectory with a radius of 1.9 km. The road on the Marly side is at the same level as the natural terrain. On the Matran side, the bridge deck is at ground level and the road continues downhill with a 45° to 60° slope on the sides. The bridge is 11.7 m wide, allowing one lane of traffic in each direction, with safety space and guardrails on both sides. The colour of the steel girders will be metallic anthracite (DB 703), so that they almost disappear in the shadow of the bridge deck. The columns will be light grey metallic (DB 701) to retain their metallic character. The space between the two box girders will house and conceal all of the bridge's technical equipment, as well as any cables and pipes.

Authors: Patrick Gartmann (Ferrari Gartman AG), Petr Tej, Pavel Rak

International Architecture Competition: reward