The Cance footbridge was built by Marc Seguin on the Cance, next to their cloth factory, a little upstream from the town of Annonay.
The work took place at the beginning of 1822, attested by an official letter from the city mayor dated March 24.
This very innovative test wasa intended to bea trial for the much more ambitious project, on the Rhône, between Tournon and Tain.
It was partly inspired by a temporary suspended structure at Schuylkill River, near Philadelphia (USA).
The entrepreneur expressed his satisfaction with this prototype in 1824: « The small bridge on my property, which only cost 50 francs, yet it is 55 feet long by 18 inches wide; and for more than a year it has not required the slightest repair, although it was visited and tested by more than ten thousand people /…]. It was supported by six beams of No. 8 wire, of eight strands each /…].
The Seguins’ project for a suspension bridge over the Rhône at Tournon-Tain was drawn up in throughout 1822 and 1823.
The plan was to cross the river in two spans, each around 85 meters long.
They are supported by a central pier and two massive abutments.
Above them, three monumental gates support the suspension cables, planned to be made of wire.
The spans are made of wood, supported by vertical wire ropes.
Seguin chose an intermediate deflection ratio (suspension height compared to length), close to 1/10, a good compromise compared to the Anglo-Saxon choices.
The pioneering tests in France and Switzerland (1823-1824)
After the Cance footbridge, another trial work was carried out in Chomérac (Ardèche) on the Peyre river by Plagniol, an engineer working with the Seguins for the Tournon project.
It was also achieved during the year 1822, but it was quickly swept away by a storm.
In France, to grant a private company authorization to build a bridge as innovative as the one planned at Tournon-Tain took a relatively long time to obtain, from March 1822 to November 1823, and they involved the technical agreement of the ‘Ponts et Chaussées’, long opposed to the use of wire cables ‘because the British never did it!’.
However, in the fall of 1822, the Seguin brothers met the Genevan scholars and city councilors Pictet and de Candolle. A project emerged for the city of Geneva for a public bridge to cross the double ditch of the ramparts of the time.
The affair was carried out smoothly: Marc went to Geneva at the end of December 1822, and he submitted to the Geneva city councilors a complete study for a bridge suspended by thin iron wire cables. This was carried out within the following six months by the city engineer, Guillaume-Henri Dufour.
It was the first public suspension bridge in Continental Europe.
For their part, the Seguin brothers built a test bridge in Saint-Vallier (Drôme), on the Galaure, a tributary of the Rhône where they tested their new technical ideas. The work was completed in the summer of 1824.
