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February 5, 2019

France: Pont de Térénez

Pont de Térénez

Departement Road 791 from Quimper to Camaret-sur-Mer crosses over the Aulne River via the Pont de Térénez. A bridge at this place was originally constructed between 1913 and 1925. This bridge was destroyed in World War II either by an allied bombing raid or by the retreating German’s demolition crew. In 1951 the bridge was repaired. But by 1992 it was found that the bridge had contracted a terminal case of “concrete cancer”. Ultimately it was determined that the disease was fatal and a replacement span was needed. Thus in 2007 the construction of a new bridge was initiated.

We whizzed by the Terenez Bridge on our way to Camaret-sur-Mer in August of 2018. By the time we realized we might want to have a closer look we were well past the turn off. Fortunately we had a second chance. On the way back from Camaret, when the bridge appeared again in front of us, we turned off into the convenient parking lot near the bridge’s abutment.

A cable-stayed bridge

Access to see the bridge from the parking lots is easy. The stubs of the old bridge have been repurposed as observation areas allowing for a good view unblocked by the trees. The bridge itself has wide bike and pedestrian walkways on both sides that extend all of the way across the Aulne. These are useful for sightseeing access.

No matter the observation point, le pont de Térénez is striking. The bridge is attractive in both its design and geographical position. Most interesting and unusual is the bridge’s curving road deck.

Cable-stayed bridges like Terenez Bridge use steel cables to transfer loads from the bridge deck to the towers in a manner not entirely unlike the traditional suspension bridges. The primary difference is that the road deck support cables are diagonally routed rather than vertically, as in a traditional suspension design like the Golden Gate Brdige. This allows the cables of cable-stayed bridges both suspend the deck and hold the bridge together. One advantage of this design is that there is no need for massive anchorages to hold the cables on both shores. Building the massive anchor blocks seen on a traditional suspension bridge is expensive and requires the proper soil conditions. The absence of the need for heavy anchors is one of the reasons why the cable-stayed design is now often preferred medium span-length bridges, like the Pont de Térénez. A cable-stayed design can be optimal from both structural and economic perspectives.

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Given their advantages cable-stayed bridges are now common. What’s different about the Pont de Térénez is that the road deck takes a semi-circle route rather than a straight line across the gorge. Indeed it is claimed that this the first circular cable-stayed bridge that was been built.

When looking at the bridge closely it is interesting to see how the cabling has been adapted not only to limit both the end-to-end spreading of the bridge but also is angled so that it keeps the arch of the curving road deck together. It’s a clever and attractive design. Indeed the design of Pont de Térénez received the Bombay the prize from the International Concrete Federation for the finest work of art. In 2013, the structure was also given the World Infrastructure Award.

We agree with the awards: The Pont de Térénez innovatively designed bridge was well worth hitting the brakes to explore.

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