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Saint Antoine Wire Cable Bridge, site of
Promenade du Pin, Geneva, Switzerland
Saint Antoine Wire Cable Bridge, site of
associated engineer
Marc Seguin
Guillaume-Henri Dufour
date  1823
era  Georgian  |  category  Bridge  |  reference  Tj286210
photo  Creative Commons BY-SA 3.0, original author B.R. Davies (1841)
The world’s first permanent bridge to be supported by wire suspension cables crossed in two spans the double ditch between the fortified heart of Geneva (pictured above in 1841) and its outlying suburbs. The structure marked a new development in bridge engineering. However, it was demolished in the mid 19th century as the city was remodelled.
Self-taught French engineer Marc Seguin (1786-1875) and his brothers pioneered wire suspension bridges in Europe. Their first construction was in mid 1822, when they built a model 600mm wide with a 19m span at Annonay, in the Ardèche départment of south west France. In 1824, it was followed by a temporary bridge over the La Galaure river at Saint Vallier, in neighbouring Drôme départment, which was 1.7m wide and had a span of 30m.
Iron wire suspension bridges had been developed elsewhere, though it's not clear whether Seguin was aware of them. In 1816, Josiah White and Erskine Hazard erected a temporary suspension footbridge spanning 124m across the Schuylkill River north of Philadelphia, USA, which was in use for one or two years. In the same year, Richard Lees built a suspension footbridge at Galashiels in south west Scotland, with a span of 33m over Gala Water. It was later strengthened with cable stays strung from larger towers to reduce movement and, in 1839, was destroyed by flood waters.
Swiss scientist Marc-Auguste Pictet (1752-1825) heard about Seguin’s work and, after visiting Annonay, thought a similar bridge would be ideal for Geneva. At the time, the city was fortified by bastions forming a star-shaped enclosure ranged around the point where the River Rhône flows into Lake Geneva. In 1822, there were only three gates, inevitably resulting in congestion.
Seguin was asked to report on the possibility of installing a pedestrian bridge to span the fortifications. His design of 21st October 1822 contained the initial drawings, calculations and specifications. It crossed the double ditch fortifications south of the river, at Bastion du Pin (in the bottom right corner of the 1841 map above), in the former Saint Antoine district, and followed approximately the route of the present-day Promenade du Pin.
Seguin discussed the design with Colonel Guillaume-Henri Dufour (1787-1875), later a General in the Swiss army and acting cantonal engineer (confirmed as such in 1828). Dufour had studied military engineering at the Ecole d’application de l’artillerie et du genie (School of Applied Artillery & Engineering) in Metz, north east France. He is believed to have reviewed Seguin’s scheme and made some small amendments.
The project began in November 1822 and construction commenced in spring 1823. As part of the work, Dufour conducted a series of tests to determine the tensile strength of iron wire — essential at the time, as production quality and material properties could vary between factories and batches. He found that strength varied considerably with diameter. He also realised there was a difference between the apparent elongation as a result of sagging under self-weight and the true extension of a wire under strain.
The overall length of the structure was some 82m. It incorporated two equal suspension spans of 40m, one over each ditch (inner ditch: 33.2m wide, outer ditch: 23m wide), with three masonry towers — on the central embankment (25m wide) and at each end. The towers were 4m high and 3.8m wide, founded on timber piles about 3.7m deep, although an 1832 drawing shows the northern tower to be deeper than the others. The openings in the towers measured 1.8m wide and 3m high.
The bridge was supported by six cables, three each side, passing over the towers side-by-side (200mm apart) but sitting one above the other over the spans. The main cables passed over the towers in smooth brass-covered stone saddles 1m long, 800mm wide and 840mm deep.
Each cable was made up of five pieces, partly because weight was a limiting factor on the length that could be manufactured at the time and partly to facilitate replacement. The lengths were connected using bound loops at the ends. Hollow cast iron cylinders (connected by looped wire links) were passed through the overlapping loops of each pair joined. Backstay cables were connected to the looped ends of iron anchorage bars by wire loops inside brass saddles. Each cable was wrapped spirally with wire, 2.1mm in diameter — with 90 wires per cable (total breaking strain 112.9 tonnes).
At the north end, the cables were fastened to vertical iron bars, 2.3m long and 35mm square, fixed to the rear of the tower and linked to horizontal bars, 1m long and 50mm by 35mm in section, laid on edge in the tower foundations. At the south end, the cables were fastened to inclined bars 35mm square, anchored in the ground.
The decks were made of timber. Set at 1.4m centres, cross joists 2.3m long were suspended from the main cables by short iron hangers composed of 12 wires. The timber for joists measured 140mm x 110mm in section. Five longitudinal beams, 160mm deep by 110mm wide, were laid on joists and planking laid on top. The decks were steadied by diagonal ties underneath, located about 7.6m from each end of each span. One end of each tie was attached to the deck and, the other to eye-bolts in the ditch retaining walls.
The parapets were 1.1m high and consisted of upright iron rods, 19mm in diameter, with top rails of the same dimension and two lower rails of flat iron, 19mm by 6mm. The parapets were located inside the hangars.
The bridge cost just over 16,000 Swiss Francs to construct. It opened to pedestrians in August 1823. Dufour apparently reported that the bridge had been modified to accommodate wheeled traffic, though it is not clear when, or indeed if, this happened.
In his 1832 book on suspension bridges, Charles Drewry writes of this bridge that it, "… vibrates very much, from the great slackness and lightness of the construction. It is well adapted for its purpose, being intended only for foot passengers, but it would be dangerous to allow it to be completely loaded, or to allow more than 50 men to march over it in step".
The Saint Antoine Bridge was demolished some time between 1853 and 1864, as the city fortifications were removed to make way for new street layouts needed for urban expansion.
Research: ECPK
bibliography
"Footbridges: Construction, Design, History" by Ursula Baus and Mike Schlaich, Walter de Gruyter, Berlin, 2008
"In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability" by Richard Scott, ASCE Publications, Reston, 2001
"Transitions In Engineering: Guillaume Henri Dufour and the Early 19th Century Cable Suspension Bridges" by Tom F. Peters, Birkhäuser Basel, 1987
"Le premier pont suspendu permanent en câbles de fer: un ouvrage de Guillaume-Henri Dufour: le pont Saint-Antoine à Genève, 1823" by Tom F. Peters, in Ingénieurs et architectes suisses, Vol.108, 1982
"A Memoir on Suspension Bridges" by Charles Stewart Drewry, Longman, Rees, Orme, Brown, Green & Longman, London, 1832
www.bridgemeister.com
Location

Saint Antoine Wire Cable Bridge, site of