The Comú d´Encamp (Town Council) called a competition for a pedestrian bridge on the Les Pardines road over a ravine in the middle of the Pyrenees 100 meters deep in a spectacular landscape setting.
A suspension typology footbridge is designed, in a minimalist and formal purity line mimicked by the landscape, which allows us to jump the valley without the need to locate intermediate piers, thus safeguarding the environment from any aggression due to the difficulty of existing access.
The length of the structure is 191 meters between both abutments with a useful width of 3.00 meters and a depth of 70 cm.
The deck is suspended every 3.00 meters by hangers from two the main cables. The twin plane of cables makes pedestrian traffic more pleasant by feeling more protected while structurally picking up the twists of the board. The planes generated by the hangers and the main cable fold 15 degrees outwards, making the passage through the footbridge more transparent and improving its transverse stability.
The cables of the suspension footbridge are anchored directly to the slopes of the valley, thus integrating it into the high mountain landscape and eliminating any intermediate pier that would negatively affect the final image. This generates a clean and at the same time surprising solution for the pedestrian. These cables are anchored to the rock by permanent anchorages to the ground, so common in Andorra.
The deck is made up of two steel trough girders with a 70 cm depth, braced transversely using a K-brace. This deck gives the structure sufficient rigidity, both longitudinal and transverse, as verified by the calculations.
The pavement of the walkway is formalized with a 22 mm thick synthetic wood grooved platform supported on a tramex which in turn rests on longitudinal strips placed on the deck bracing. In certain areas in the centre of the walkway, sections of glass are placed to admire the valley bottom down bellow.
Longitudinally there is an anatomical stainless steel handrail to improve traffic for people with reduced mobility, inserting in its lower part a longitudinal LED lighting throughout the entire footbridge. The side railings of the deck are solved using vertical stainless steel plates 1.50 meters high.
Masonry walls solve the abutments of the footbridge concerning the existing vernacular walls on the road.
The current difficulty of access and construction complexity have been taken into account in the design of the bridge. Light elements easy to assemble have been selected.
The following parameters condition the chosen solution:
The design of the proposed solution integrates perfectly into the serenity of the environment and the high mountain landscape. Maintaining that problematic balance between the symbolism of the structure and its formal integration.
The parabolas described by the cables harmonize with the undulating orography of the surrounding slopes, favouring landscape integration, which is why it has fled from much more aggressive cable-stayed solutions typical of more urban environments.
The width given to the deck of 3.00 free meters is in line with the length of the bridge, avoiding a feeling of narrowness or vertigo when crossing a valley of such height. At the same time, it facilitates the crossing of bicycles without risk of collision.
The bridge has been designed to ensure all service limit states,
A dynamic calculation has been made to verify this at the pedestrian crossing, checking that the vibrations produced in the structure are within the optimal comfort range, whether the pedestrian crosses on foot or running.
An aerodynamic deck with closed sections and elliptical side deflectors integrated within the section has been arranged to guarantee the aeroelastic behaviour of the footbridge.
Ease of construction with small elements subsequently assembled on site and with minimal impact on the environment.
The excellent foundation conditions in the rocky massif are used to make the anchorages on the slopes. It means a minimum effect on the terrain without earthworks.
The machinery used for construction is of reduced dimensions, especially that for the execution of ground anchors.