Interview with Romain Ricciotti, structural engineer, and Rudy Ricciotti, architect of the Pont du Diable footbridge

07.07.2016
 

Listed by Unesco as part of a World Heritage site, the Pont du Diable footbridge, designed by architect Rudy Ricciotti and engineer Romain Ricciotti, constitutes a first for Europe. A 70 meter-long, muscular girder provides discretion and lightness, thanks to the exceptional prestressing resistance of Ductal®. Welcoming nearly 600,000 visitors every year, the gorges de l'Hérault in the south of France, reveals stunning landscape, classified sites, historical monuments, a protected biotope and a state biological reserve. At the heart of this popular tourist attraction, the Pont du Diable footbridge accommodates up to 250,000 pedestrians and cyclists every year. With these excessive numbers in mind, developing the landscape and restoring natural spaces were at the core of the grand site project's design, with hight emphasis on the organization of walking trails.

As an essential element of the development project, the Pont du Diable footbridge opened in the summer of 2008, allows pedestrians to explore the area and discover its richness at an easy pace. The structure is according to Romain Ricciotti "neither an arch, nor even a suspended footbridge, but a simple beam set on two supports: the two banks, to cross the gorge"

 

Material able to withstand very high pre-stressing

Romain Ricciotti
 

"A performance that could be achieved by dividing the structure into 15 monolithical segments, cast from a single mold, which are placed on the scaffolding. No casting is carried out on site, everything was previously cast in the factory and then placed on the scaffolding.

The cables that were tensioned to place the segments under compression (up to a tenth of a millimetre of tolerance*) thereby forming the beam. This ultimately produced a "flat vault"; a conventional pre-stressing technique, which is enhanced by the performances of Ductal®. Thanks to this material, it is no longer necessary to reinforce the concrete with steel as previously the case. Therefore it is possible to build a structure with a deck just 4 cm thick. The resulting visual expression is a static height of 1.80 m for a span of 70 m."

For its designer, Rudy Ricciotti, the footbridge shows "that the difference between utopia and action is this reality of implementation. The paradox between high-level technological assertion and physical disappearance assumes its full value and meaning in an exceptional landscape. It means believing in the material and what we can get it to say. And asking one's self whether the structure's mathematical reasoning belongs to the person reasoning or whether it is already part of the material itself?" * A performance due to the quality of the mold and Bonna Sabla's precaster.

 

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