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Asymmetrical Bridge Joins Lyon’s River Rhône
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Night view rendering of the new slender, asymmetrical pedestrian bridge that crosses the river Rhône in Lyon, France
At night, the new slender, asymmetrical pedestrian bridge that crosses the river Rhône in Lyon, France, is lighted so that it appears as a sculptural element that just lightly touches down on the riverbanks. Photograph by Michael Zimmermann

A slender, asymmetrical pedestrian bridge now crosses the River Rhône in the city of Lyon, France.

April 15, 2014—Last month marked the grand opening of a new pedestrian bridge that now crosses the River Rhône, in the city of Lyon, France. The asymmetrical, curved steel-and-wood bridge is a slim-lined crossing that offers pedestrians and bicyclists the option of entering the bridge at two different heights on either side of the river, the pathways converging at a central plaza so that visitors can enjoy the views up and down the river. At night, the bridge will be lit up so that it becomes a sculptural element that appears light and elegant.

“It’s playful,” says Dietmar Feichtinger, Dipl.-Ing., an architect with Montreuil, France-based Dietmar Feichtinger Architectes and the designer of the footbridge. The design was a direct product of the desire to provide both access to the bridge from both upper and lower paths on either side of the river, according to Feichtinger. “I wanted a bridge that was able to integrate into this really beautiful landscape.” he adds.

The new pedestrian bridge is located within sight of two parallel concrete bridges located upstream, a rail bridge and a road bridge. Given that location, Feichtinger wanted the pedestrian bridge to have a strong presence of its own while remaining as slender as possible so that it did not overpower sight lines up and down the river. As a result, “it’s almost like an insect,” Feichtinger says.

The bridge has been designed so that people crossing it can see its human scale and understand how the structural elements work together. “The bridge is generous in space once you are on it [but] incredibly slender from a view toward the bridge,” Feichtinger says. 

Image of the steel elements and diagonals that form the triangular trusses for the footbridge

The steel elements and diagonals that form the triangular trusses
for the footbridge connect the offset upper and lower chords,
stiffen the bridge, and provide its lateral support. The triangular
trusses appear to rotate as they follow the curve of the lower
chord. Photograph by
Michael Zimmermann

The €9,795,500 (U.S.$13.6-million) bridge, known as the Passerelle de la Paix, has a clear span of 157 m over the river, extending 220 m in total length to reach the upper quays on either bank. The bridge offers 8 m of clearance over the typical river water height. The bridge’s steel upper and lower chords are offset from one another, linked via individually shaped triangular trusses that appear to rotate as they follow the curve of the lower chord. Both the upper and lower chords offer wood-decked crossings with wooden handrails that are in-filled with a cable net to provide security while offering maximum transparency.

“It’s not an arch bridge,” Feichtinger says. Instead, the bridge is formed from two cantilevers that meet in the middle of the river above “a slender curve,” he says.

From the beginning, the architects collaborated closely with the structural engineers, Stuttgart-based schlaich bergermann und partne (sbp), which specializes in complex bridge structures. “The structure works like a combined arch-cantilever structure,” said Michael Zimmermann, Dipl. –Ing., the director of projects in France for sbp, who responded in writing to questions posed by Civil Engineering online. Curved diaphragm walls measuring 10 m by 14 m and 20 m deep are used to create an efficient foundation on either side of the river, he explained.

The bridge was preassembled on one of the riverbanks and brought to the location on a barge. Temporary rails that had been built onto the barge enabled the bridge to be slid into its final position.

The bridge’s top chord is formed from a hollow steel box girder, and the offset lower chord is formed from two curved tube sections

The bridge’s top chord is formed from a hollow steel box girder.
The offset lower chord is formed from two curved tube sections.
Both the upper and lower chords offer wood-decked crossings
with wooden handrails. Photograph by
Michael Zimmermann

The bridge’s top chord is formed from a hollow steel box girder that offers a 5 m wide crossing with routes for both bicyclists and pedestrians. The lower chord is formed from two arched tube sections that also support a 1.5 m wide wooden stairway across the river. The steel elements and diagonals that form the triangular trusses—which connect the offset upper and lower chords—stiffen the bridge and provide lateral support, according to Zimmermann.

“The primary elements of the bridge, like the deck girder—a hollow steel box—and the two arches—tubes with [a] maximum diameter of 700 mm—are fixed in a monolithic way with the abutments,” Zimmermann said. By using a monolithic system, the bridge performs better with respect to any imperfections, eccentric loadings, and dynamic behavior than it otherwise would, Zimmermann explained.

The monolithic system also enabled the design team to keep the apex of the arch at 8 m, the height of the upper chord that connects the quays on either side of the river. “We could have done an arch structure intersecting the deck, but our aim was to clearly keep the structure underneath the deck,” Zimmermann said. This kept the profile of the bridge to a minimum.

A secondary structure consisting of transverse and longitudinal beams is located on the curved lower chord of the bridge and provides the substructure for the arch’s light, wooden deck. The steps measure just 5 cm thick and are fixed on cantilever plates that are welded directly onto the steel arch. The result is a crossing that offers visitors an experience that “feels like a walk on the water,” Zimmermann said.

“The wooden deck was selected by the architects [because] of its natural and simple character,” Zimmermann noted. “It is the opposite of the quite technical and complicated steel primary structure.”

At the apex of the arch, the two decks join together to form the 8 m wide plaza area, complete with benches. The joint plaza is the highlight of the bridge, Feichtinger says. “When you want to sit down and look around—that is in the middle of the river, which is a magic place,” he says.

The bridge will link the city’s sixth arrondissement, near the Renzo Piano-designed Cité International, to the park located at Saint Clair at Caluire et Cuire.


 

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