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Chrimes watch: French delight for civil engineers, pontists, historians and cyclists alike

Tourists are generally drawn to the Loire valley in France by chateaux and the wines of the region, and in the past I have been among their number. To celebrate my retirement I cycled the Loire a Velo trail - described by the British Guild of Travel as the best European tourism project and certainly one to put most other long distance cycle paths to shame.

If the appeal of cycling is not an incentive, I am sure many civil engineers will find much interest in the structural engineering of the Loire chateaux, with their use of masonry and timber in buildings built over many centuries. There is an additional attraction for pontists: a whole range of bridge crossings to view. The commemoration of the 70th anniversary of D-Day brings the history of many of these bridges into focus.

A key element of the planning for the D-Day landings was to isolate the Normandy region from intervention by German reinforcements elsewhere in France. As a consequence, allied bombers attacked bridge crossings on the Loire and Seine from D-Day minus 46. On 8 and 9 June 1944 tallboy bombs were used to attack the railway tunnel and bridge at Saumur. Aerial attacks continued through June and early July as the invasion was consolidated.

Military action

This destruction of 1944 had been preceded by less well known military action along the Loire around 18 to 20 June 1940 when a strong rearguard action by cavalry cadets and others around Saumur can be regarded as the last act of the French army before surrender or the first action of the resistance. It led to the dynamiting of the then Pont de Napoleon at Saumur and the suspension bridge at Gennes.

As a consequence, many of the bridges across the Loire were rebuilt in the late 1940s and early 1950s including some multi-span suspension bridges.

Perhaps the best documented bridge of all the Loire crossings is the multi-span arch bridge at Saumur, now known as the Pont Cessart in honour of the young 18th century engineer who recorded its constriction in a two volume work giving enormous detail of its piled foundations and cofferdams.

This generally survived the war as it was the 1808 bridge to the north that was destroyed.

French engineers designed many wire cable bridges in the early 19th century following guidelines developed by Navier and Vicat. Many were built over the Loire, and it was the fatal failure at Basse-Chaines Bridge over a tributary of the Loire at Angers that signalled the end of the widespread use of this form of bridge in France until the post war period. Crossings of the Loire included the 238m Ancenis Bridge originally built by Seguin (1838) and strengthened by Arnodin. Destroyed in 1944, it was rebuilt by Jean Courbon, an early example of design influenced by the Tacoma Narrows failure, and is now under reconstruction.

The bridge at Ingrandes, originally designed by Arnodin in 1922, had stay cables as well as catenary cables and vertical hangars, while there is an early French example of a modern cable stayed bridge at St Fleurant, and a very modern example completed in 2011 on the outskirts of Nantes at Malakoff.

There are, of course, some everyday structures such as the warren truss at Saint Mathurin (1951-1954) and interesting survivals, at least in some of its spans at Mauves sur Loire, and Thoare (1879-1882) of girder bridges - the latter with brick jack arches between the cross girders to support the deck.

It is the range of suspension crossings that justify the most attention, and provide a pleasant break from chateaux and cycling.

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