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Arve Bridge, Vessy
Route de Vessy, Vessy, Geneva, Switzerland
Arve Bridge, Vessy
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  4th May 1936 - July 1937
era  Modern  |  category  Bridge  |  reference  Tj296191
photo  copyright ETH-Bibliothek Zürich, Bildarchiv
Towards the end of his career, Swiss engineer Robert Maillart developed further the three-hinge arch concrete bridge system he had been using, for a road bridge over the River Arve in south east Geneva. It features a pointed arch and unusual X-shaped cross walls. The bridge has been refurbished and is a listed structure with protected status. It remains in use.
Innovative reinforced concrete specialist Robert Maillart (1872-1940) began designing the Arve Bridge (Pont de Vessy) in 1934, sending an initial design to the Geneva authorities on 11th December. His ideas for it had evolved from the Thur Bridge (Thurbrücke, 1933) at Felsegg, north east Switzerland, where he had first used a pointed arch. At Vessy, the arch is flatter and was constructed in three parallel sections, done economically by re-use of one set of centring.
In July 1935, the city approved the concept design, possibly under the influence of his friend Maurice Braillard (1879-1965), architect and head of Geneva’s public works department 1933-6. However, Maillart must have been asked to reduce costs, as by 26th August, Ingenieurbureau Maillart's estimate had dropped from 140,000 to 91,444 Swiss Francs. The contract was put out to tender and the eight bids received in September 1935 were all well below the estimate, ranging from 74,819 to 87,637 Swiss Francs.
The total length of the bridge, between the tops of the abutments, is 79m. Its three-hinge arch spans 56m between the base hinges, with a vertical distance between central and support hinges of 4.8m. The arch supports a deck 10.1m wide overall, carrying a two-lane roadway and two footpaths.
The three upstanding longitudinal walls, or ribs, together with the arch form two hollow boxes, closed at the top in the centre of the bridge, where the walls meet the deck. At the outer ends of the span, the ribs become U-shaped channels as the walls decrease in height down to the support hinges, leaving triangular cut-outs between rib, deck and abutment.
The ribs are 630mm thick at the central hinge and 440mm thick at the support hinges, while the base of each rib is 150mm thick between hinges. The side walls of each rib are 120mm thick where the section forms a box, and 200-280mm thick where it is a channel.
Maillart also moved the support hinges from the abutments into the span. The central hinge of the arch omits the protruding block of his earlier schemes. Instead, the hinge is expressed by a vertical joint, emphasising the pointedness of the arch.
Connecting the arch to its deck are rows of three unconnected concrete cross-walls (piers almost), distinctively X-shaped in elevation, mirroring the profiles of the bending moments acting on them. This arrangement reduced the overall quantity of concrete required, an additional cost-effective benefit. The walls are 180mm thick and 1.9m wide where they meet the deck and the arch, but only 300mm wide at the 'waist'.
The bridge's hinges are reinforced with hooked steel rods crossing diagonally through the concrete, 32mm in diameter in the central hinge and 35mm in diameter in the support hinges. Slots for timber and cork pads are included, which take up any movement in the bridge.
To minimise cracking and deformation in the concrete, the construction sequence was critical. The abutments were constructed first, then the timber centring for the downstream longitudinal section of the arch. The upstream then the middle sections followed, using the same falsework, which was struck as soon as the sections hard enough to be self-supporting (7 days or so). The outer box side walls came next, then the middle wall, and lastly the deck slab.
During construction, samples were taken and tested at the Ecole des Arts et Métiers laboratory in Geneva. The results showed a high quality of concrete with average density of around 2,440kg per cu m and prism compressive strength of 320-400 kg per sq cm. The modulus of elasticity of the concrete was approximately 380,000 kg per sq cm.
On 20th- 21st July 1937, the bridge was successfully load tested, in accordance with Swiss practice, to check its elastic behaviour and to investigate its bearing capacity. The tests were carried out under the supervision of Maillart’s friend and colleague, Professor Mirko Ros (1879-1962) of the Eidgenössische Materialprüfungs- und Forschungsanstalt (Swiss Federal Laboratories for Materials Science & Technology).
A total mass of 112 tonnes was applied in the form of 10 laden trucks, parked in two rows of five at various points along the deck. The tests measured vertical deflection, rotation, movement in the hinges, stresses and strains, vertical oscillation at the apex of the arch and abutment displacement. Vibration tests were carried out with two trucks moving side by side over the bridge at about 23kph (14mph).
Despite the high loading, equivalent to about 600 kg per sq m, the bridge showed almost completely elastic behaviour and surpassed the testing criteria. For example, the maximum vertical deflection of 5.7mm, or 1/9800 of the span, was measured at the apex of the arch. Swiss regulations at the time allowed a deflection for road bridges of up to 1/700 of the unsupported length, which would have meant 80mm in this case.
The Arve Bridge opened to traffic soon after the tests were completed. The final cost was around 80,000 Swiss Francs. Historian and architectural critic Sigfried Giedion (1888-1968) described it as having the flexibility of a taut spring.
In 1968, the central hinge, outer side walls and deck were refurbished. In 1986, the bridge was listed in the Swiss inventory of buildings worthy of protection. The deck was planed and a new deck liner installed.
However, after that date, the combined effects of air pollution, road salt and water runoff caused carbonation and degradation of the deck sealing. Corrosion and swelling of reinforcement where it had insufficient concrete cover resulted in the collapse of the concrete's surface layer.
In April 1992, the city and the canton of Geneva each granted 1,450,000 Swiss Francs for repairs. Work took place in 1993 and included the removal of areas of spalled concrete, the application of a protective treatment to corroded reinforcement, restoration of the concrete surface and the installation of new safety railings.
Contractor: Ed. Favre, Geneva
Research: ECPK
bibliography
"Robert Maillart e l’emancipazione del Cemento Armato", Studio Giovannardi e Rontini, Italy, October 2007
"Robert Maillart, Beton-Virtuose" ed. Gesellschaft für Ingenieurbaukunst, VDF Hochschulverlag AG an der ETH Zürich, 1996, reprinted 2007
"Robert Maillart: Builder, Designer, and Artist" by David P. Billington, Cambridge University Press, 1997
"La Souplesse d’un Ressort Tendu: le Pont de Robert Maillart á Vessy" by Jean-Pierre Lewerer and Yves Peçon, in FACES, No.30, pp.50-55, Geneva, winter 1993-1994
"Robert Maillart and the art of reinforced concrete" by David P. Billington, Architectural History Foundation, MIT Press, 1990
"Robert Maillart: Bridges and Constructions" by Max Bill, translated by W.P.M.K. Clay, Pall Mall Press, 3rd revised edition, November 1969
"Belastungsversuche an der Eisenbeton-Bogenbrücke Champel-Vessy über die Arve bei Genf" by H.C.M. Ros, EMPA, Zürich, 1938
www.braillard.ch
Location

Arve Bridge, Vessy