Pont de La Roche-Bernard
Coordinates: 47 ° 31 ′ 28 " N , 2 ° 18 ′ 19" W.
| Pont de La Roche-Bernard | ||
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| use | Road bridge | |
| Crossing of | Vilaine | |
| place | La Roche-Bernard | |
| overall length | 408.60 m | |
| Longest span | 244 m | |
| Clear height | 54 m | |
| completion | 1839/1911/1960 | |
| location | ||
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The Pont de La Roche-Bernard is a road bridge at La Roche-Bernard over the Vilaine in the Morbihan department in Brittany . At the same location one was 1839 suspension bridge was built in 1911 by a steel - arch bridge was again replaced and in 1960 by a suspension bridge.
location
The place La Roche-Bernard and the bridge named after him are located on the former national road between Nantes and Brest , which was the most important traffic connection in southern Brittany. Today most of the traffic flows via the N 165 national road, which bypasses the town to the north, and the Pont du Morbihan .
history
The Vilaine, which flows between steep slopes, could initially only be crossed by ferry , which was dependent on wind, weather and the tidal currents reaching far into the river . With a water depth of 5 to 9 m, a subsoil with a layer of sediment and silt at least 10 m thick and the clearance height of 30 m required by shipping, building a bridge was out of the question. Only the suspension bridge offered the opportunity to cross the river.
Suspension bridge from 1839
In 1833, the chief engineer Leblanc des Corps des ponts et chaussées drew up the plans for a suspension bridge, which was built between 1835 and 1839. It was 360 m long, including the access ramps consisting of three masonry arches, and had a span of 198 m. Only Le Grand Pont suspendu , the Zähringer bridge in Freiburg im Uechtland , had a larger span at that time. The wooden bridge deck had a 4.80 m wide, two-lane carriageway and 0.60 m wide sidewalks. The clear height was 36 m above high water and 42 m above low water.
The first ten years went without any major problems, although the bridge vibrated slightly in the wind and parts of the wooden bridge deck broke and fell into the river.
On October 26, 1852, a heavy storm caused the bridge deck to vibrate so much that it broke completely and fell into the river, above which only the suspension cables with the remains of various hangers hung. People were not harmed. The bridge was restored, but in 1866 and 1869 it suffered new storm damage, in 1870 a 20 m long section of the carriageway fell into the water and in 1871 a 35 m long section. In 1872 an attempt was made to reinforce the bridge with a footbridge, which was installed 1.60 m high above the previous carriageway, but could only be used by one vehicle at a time. This temporary solution lasted for almost 40 years - until the steel arch bridge was opened.
Steel arch bridge from 1911
In 1905 a new bridge was put out to tender, with offers for three suspension bridges and an offer for a three- hinged steel arch bridge, which was awarded the contract. The construction used the existing brick-built access ramps and the bridge deck. At the side of the ramps, fighter foundations were installed, from which arches in the form of lattice girders that tapered upwards protruded diagonally over the river to the joints in the bridge deck. The two segments of the actual steel arch, which were connected by the third joint in the apex of the arch, rose above these joints. The arch structures on both sides of the bridge were connected and stiffened by cross girders. The middle part of the deck was suspended from the arches with steel rods, while the side parts were raised on them. As before, the arch bridge had a span of 198 m between the transom foundations, while the three-hinged arch over the two joints in the bridge deck had a span of 112 m. The Pont de La Roche-Bernard was the second largest steel bridge in France after the Viaduc du Viaur . This bridge served the rail next to the road, about her ran the meter gauge railway line Vannes -La Roche Bernard of Chemins de Fer du Morbihan .
For decades the steel arch bridge provided the desired problem-free traffic connection. It survived the First and almost the Second World War . After the Allies landed in Normandy , German soldiers had prepared the bridge to be blown up, but were still waiting to see how far the American units would advance - only after the end of the war and the surrender of the areas in and around Saint, which were still occupied by German troops -Nazaire invaded the place. On August 15, 1944, however, a violent storm occurred in which a lightning strike triggered the detonation and destroyed the bridge.
One had to make do with ferry boats again until a pontoon bridge was set up in July 1948 , which consisted of parts of the floating bridges that had been used when the Allies landed between Mulberry Harbor off Arromanches and the coast on Gold Beach .
Suspension bridge from 1960
Today's suspension bridge stands a few meters downstream next to the remains of the steel arch bridge, of which only the brick ramp bridges and the fighter foundations still exist. The two-lane bridge with sidewalks on both sides, built between 1957 and 1960, is significantly higher with a clearance height of 54 m and with a total length of 408.60 m and a span of 244 m significantly longer than the two old bridges. It no longer has any ramp bridges, its bridge deck extends over the entire length of the bridge.
The pylons on the bank consist of reinforced concrete pillars , which are stiffened below the bridge deck by a concrete wall and between the tips by a wide crossbar. The bridge deck consists of three lattice girders, which are relatively high compared to previous French suspension bridges, which are supported on the concrete pillars and give it the necessary rigidity to withstand even heavy storms without damage. Stable metal railings along the sidewalks add rigidity. The suspension cables consist of 19 twisted wire ropes combined in a hexagonal profile .
Web links
- P. Leblanc: Description d'un pont suspendu ... sur la Vilaine, à La Roche-Bernard . Carilian-Gœury et V. Dalmont, Paris 1841
Individual evidence
- ↑ a b c d Marcel Prade: Ponts & Viaducs au XIXe Siècle . Brissaud, Poitiers 1988, ISBN 2-902170-59-9 .
- ↑ a b c Les Ponts Pictures and description of the bridges and their history on the website of La Roche-Bernard (French)
- ^ La Roche-Bernard, Morbihan private collection of picture postcards of the bridge.
- ↑ Pont de la Roche-Bernard - 1839 in Base d'ouvrages en service ou construits au XIXème siècle en France on art-et-histoire-com
- ↑ Amaury de la Pinsonnais: Le pont de la Roche-Bernard with a historical photo of the steel bridge; on Au hasard des archives ... (private blog).
- ↑ Bernard Marrey: Les Ponts Modern, 20e siècle . Picard, 1995, ISBN 2-7084-0484-9 , p. 171