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The Pont D'Avignon


The Pont D'avignon - original

Context:


The Pont de Saint Bénezet, popularised as the “Pont d’Avignon” by the song “Sur le Pont d’Avignon”, is a masonry arch bridge, originally with 22 arches, crossing the Rhône at Avignon. The original bridge connected Villeneuve-les-Avignon on the right bank to Avignon on the left bank. The construction of the bridge began in the 12th century, and it is thought that the bridge was never truly completed, due to segments of the bridge remaining in timber instead of stone, although most of the bridge was completed by the 14th century. The bridges true name of “Pont de Saint Bénezet” comes from the man “Benoit” nicknamed “Bénezet”, who rallied the townspeople of Avignon to build the bridge in 1177, having received a message from God, ordaining him to do so.

The Bridge was frequently destroyed due to the large political tensions in the area, with the most notable of these destructions being the burning of several arches by the Catalonians during the Catalan War in the 15th century. However the most important factor which lead to the structural undermining of the bridge was the volatile nature of the Rhône river. At 812km long, the Rhône is a formidable river, making its mark across several European countries.


The Rhône’s tendency to flood combined with its very strong current made it very difficult to sustain the bridge with economic viability. There were several attempts made to reinforce the bridge through the 15th to 17th centuries however these were eventually given up, leaving only four arches of the original twenty-two, remaining.



Structure:


Despite the eventual collapse of most of the bridge, the bridge originally had 22 arches, and 21 piers, spanning 920m . The bridge now has 4 arches and 4 piers, spanning 120m. The longest span on the remaining section of the bridge, of 35.8m is between the third and fourth piers.



Structural behaviour:


The bridge is a classic example of a masonry arch bridge, a bridge style used frequently by the Romans, exploiting the advantages of arch as oppose to beam structures. A defining feature of the Pont d’Avignon, is that the arches are not semi-circular, but segmental.


This means the radius of the arch is greater than the vertical distance between the apex of the arch and the centre point between the two piers. These types of arch bridges first appeared in China, with the ZhaoZhou bridge (605AD) being a famous example, but were uncommon in 12th Century Europe. This was caused by the need for larger abutments to support the greater horizontal force exerted, in comparison to semi-circular arches, and that it was not possible to build the bridge simply by building each arch individually back to back as was commonly done by the Romans. The arches in the Pont d’Avignon are voussoirs arches. This plays to the strengths of the material used, by putting it in compression.



Construction:


The construction of the Pont d’Avignon was conducted mainly in summer as this is when the water level of the Rhône is lowest. A layer of gravel and stone would be removed and then workers would dig 1 to 2 metres into the river bed. If the riverbed was dry they would lay a wooden foundation, to act as a stable base for the rest of the pile. They would then lay the foundations for the masonry bridge pile. The piles were built with carefully hewn stone on the outside and partially filled with rubble and mortar. Gravel and pebbles were then piled up around the base for additional strengthening.

If the water level was high, a cofferdam - a primitive type of caisson - would be placed around where the pile was to be built.


One of the original wooden piles with a protective iron tip - original

A cofferdam is a frame with thick impermeable walls of manure and earth, sunk into the river bed and then drained to create a dry space for construction. Thick wooden piles were then hammered deep into the river bed, on top of which the wooden foundation was built and construction of the masonry pile, as above, began. The arches were then built by placing the voussoirs on a wooden frame in the shape of the arch. This gave the structure support before the keystone was put in and it could become self supporting.

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