The Millau Viaduct (French: le Viaduc de Millau, IPA: [vjadyk də mijo]) is a cable-stayed bridge that spans the gorge valley of the Tarn near Millau in southern France. It is the tallest bridge in the world, with one mast's summit at 343.0 metres (1,125.3 ft) above the base of the structure. In a Franco-British partnership, it was designed by the English architect Sir Norman Foster and French structural engineer Michel Virlogeux, and as of May 2017[update] it is the twenty-second highest bridge deck in the world, being 270 metres (890 ft) between the road deck and the ground below.
The Millau Viaduct is part of the A75-A71 autoroute axis from Paris to Béziers and Montpellier. The cost of construction was approximately € 394 million. It was built over three years, formally inaugurated on 14 December 2004, and opened to traffic two days later on 16 December. The bridge has been consistently ranked as one of the great engineering achievements of all time, and received the 2006 Outstanding Structure Award from the International Association for Bridge and Structural Engineering.
In the 1980s, high levels of road traffic near Millau in the Tarn valley were causing congestion, especially in the summer due to holiday traffic on the route from Paris to Spain. A method of bypassing Millau had long been considered, not only to ease the flow and reduce journey times for long distance traffic, but also to improve the quality of access to Millau for its local businesses and residents. One of the solutions considered was the construction of a road bridge to span the river and gorge valley. The first plans for a bridge were discussed in 1987 by CETE, and by October 1991 the decision was made to build a high crossing of the Tarn by a structure of around 2,500 metres (8,200 ft) in length. During 1993–1994, the government consulted with seven architects and eight structural engineers. During 1995–1996, a second definition study was made by five associated architect groups and structural engineers. In January 1995, the government issued a declaration of public interest to solicit design approaches for a competition.
In July 1996 the jury decided in favour of a cable-stayed design with multiple spans, as proposed by the Sogelerg consortium led by Michel Virlogeux and Norman Foster. The decision to proceed by grant of contract was made in May 1998; then in June 2000, the contest for the construction contract was launched, open to four consortia. In March 2001, Eiffage established the subsidiary Compagnie Eiffage du Viaduc de Millau (CEVM), and was declared winner of the contest and awarded the prime contract in August.
In initial studies, four potential options were examined:
After long construction studies by the Ministry of Public Works, the low solution was abandoned because it would have intersected the water table, had a negative impact on the town, cost more, and lengthened the driving distance. The choice of the 'high' solution was decided by ministerial decree on 29 October 1991.
After the choice of the high viaduct, five teams of architects and researchers worked on a technical solution. The concept and design for the bridge was devised by French designer and structural engineer Dr Michel Virlogeux. He worked with the Dutch engineering firm ARCADIS, responsible for the structural engineering of the bridge.
The 'high solution' required the construction of a 2,500-metre-long (8,200 ft) viaduct. From 1991 to 1993, the structures division of Sétra, directed by Michel Virlogeux, carried out preliminary studies, and examined the feasibility of a single structure spanning the valley. Taking into account technical, architectural, and financial issues, the Administration of Roads opened the question for competition among structural engineers and architects to widen the search for realistic designs. By July 1993, seventeen structural engineers and thirty-eight architects applied as candidates for the preliminary studies. With the assistance of a multidisciplinary commission, the Administration of Roads selected eight structural engineers for a technical study, and seven architects for the architectural study.
Simultaneously, a school of international experts representing a wide spectrum of expertise (technical, architectural, and landscape), chaired by Jean-François Coste, was established to clarify the choices that had to be made. In February 1995, on the basis of proposals of the architects and structural engineers, and with support of the school of experts, five general designs were identified.
The competition was relaunched: five combinations of architects and structural engineers, drawn from the best candidates of the first phase, were formed; each was to conduct in-depth studies of one of the general designs. On 15 July 1996, Bernard Pons, minister of Public Works, announced the decision of the jury, which was constituted of elected artists and experts, and chaired by Christian Leyrit, the director of highways. The solution of a multiple-span viaduct cable-stayed bridge, presented by the structural engineering group Sogelerg, Europe Etudes Gecti and Serf, and the architects Foster + Partners was declared the best.
Detailed studies were carried out by the successful consortium, steered by the highways authority until mid-1998. After undergoing wind tunnel tests, the shape of the road deck was altered, and detailed corrections were made to the design of the pylons. When the details were eventually finalised, the whole design was approved in late 1998.
Once the Ministry of Public Works had taken the decision to offer the construction and operation of the viaduct as a grant of contract, an international call for tenders was issued in 1999. Five consortia tendered:
Piers were built with Lafarge high performance cement. The pylons of the Millau Viaduct, which are the tallest elements (the tallest pylon – 244.96 metres (803.7 ft)) were produced and mounted by PAECH Construction Enterprise from Poland.
The Compagnie Eiffage du Viaduc de Millau, working with the architect Sir Norman Foster, was successful in obtaining the tender. Because the government had already taken the design work to an advanced stage, the technical uncertainties were considerably reduced. A further advantage of this process was to make negotiating the contract easier, reducing public expense, and speeding up construction, while minimising such design work as remained for the contractor.
All the member companies of the Eiffage group had some role in the construction work. The construction consortium was made up of the Eiffage TP company for the concrete part, the Eiffel company for the steel roadway (Gustave Eiffel built the Garabit viaduct in 1884, a railway bridge in the neighbouring Cantal département), and the Enerpac company for the roadway's hydraulic supports. The engineering group Setec has authority in the project, with SNCF engineering having partial control.[clarification needed] Appia (company) was responsible for the job of the bituminous road surface on the bridge deck, and Forclum (fr) for electrical installations. Management was handled by Eiffage Concessions.
The only other business that had a notable role on the building site was Freyssinet, a subsidiary of the Vinci Group specialising in prestressing. It installed the cable stays and put them under tension, while the prestress division of Eiffage was responsible for prestressing the pillar heads.
The steel road deck, and the hydraulic action of the road deck were designed by the Walloon engineering firm Greisch from Liège, Belgium, also an information and communication technologies (ICT) company of the Walloon Region. They carried out the general calculations and the resistance calculations for winds of up to 225 kilometres per hour (140 mph). They also applied the launching technology.
The bridge's construction cost up to €394 million, with a toll plaza 6 kilometres (3.7 mi) north of the viaduct, costing an additional €20 million. The builders, Eiffage, financed the construction in return for a concession to collect the tolls for 75 years, until 2080. However, if the concession yields high revenues, the French government can assume control of the bridge as early as 2044.
The project required about 127,000 cubic metres (166,000 cu yd) of concrete, 19,000 tonnes (21,000 short tons) of steel for the reinforced concrete, and 5,000 tonnes (5,500 short tons) of pre-stressed steel for the cables and shrouds. The builder claims that the lifetime of the bridge will be at least 120 years.
Numerous organisations opposed the project, including the World Wildlife Fund (WWF), France Nature Environnement, the national federation of motorway users, and Environmental Action. Opponents advanced several arguments:
Two weeks after the laying of the first stone on December 14, 2001, the workers started digging the deep shafts. There were four shafts per pylon; 15 metres (49 ft) deep and 5 metres (16 ft) in diameter, assuring the stability of the pylons. At the bottom of each pylon, a tread of 3–5 metres (10–16 ft) in thickness was installed to reinforce the effect of the deep shafts. The 2,000 cubic metres (2,600 cu yd) of concrete necessary for the treads was poured at the same time.
In March 2002, the pylons emerged from the ground. The speed of construction then rapidly increased. Every three days, each pylon increased in height by 4 metres (13 ft). This performance was mainly due to sliding shuttering. Thanks to a system of shoe anchorages and fixed rails in the heart of the pylons, a new layer of concrete could be poured every 20 minutes.
The bridge road deck was constructed on land at the ends of the Viaduct, and rolled lengthwise from one pylon to the next, with eight temporary towers providing additional support. The movement was accomplished by a computer-controlled system of pairs of wedges under the deck; the upper and lower wedges of each pair pointing in opposite directions. These were hydraulically operated, and moved repeatedly in the following sequence: the lower wedge slides under the upper wedge, raising it to the roadway above, and then forcing the upper wedge still higher to lift the roadway. Both wedges move forward together, advancing the roadway a short distance. The lower wedge retracts from under the upper wedge, lowering the roadway and allowing the upper wedge to drop away from the roadway; the lower wedge then moves back all the way to its starting position. There is now a linear distance between the two wedges equal to the distance forward the roadway has just moved. The upper wedge moves backward, placing it further back along the roadway, adjacent to the front tip of the lower wedge and ready to repeat the cycle and advance the roadway by another increment. It worked at 600 millimetres (24 in) per cycle which was roughly four minutes long.
The mast pieces were driven over the new road deck lying down horizontally. The pieces were joined to form the one complete mast, still lying horizontally. The mast was then tilted upwards, as one piece, at one time in a tricky operation. In this way, each mast was erected on top of the corresponding concrete pylon. The stays connecting the masts and the deck were then installed, and the bridge was tensioned overall, and weight tested. After this, the temporary pylons could be removed.
The construction Millau Viaduct broke several records:
Since opening in 2004, the deck height of Millau has been surpassed by several suspension bridges in China, including Sidu River Bridge, Baling River Bridge, and two spans (Beipan River Guanxing Highway Bridge and Beipan River Hukun Expressway Bridge) over the Beipan River. In 2012, Mexico's Baluarte Bridge surpassed Millau as the world's highest cable-stayed bridge. The Royal Gorge suspension bridge in the U.S. state of Colorado is also higher, with a bridge deck approximately 291 metres (955 ft) over the Arkansas River.
The Millau Viaduct is located on the territory of the communes of Millau and Creissels, France, in the département of Aveyron. Before the bridge was constructed, traffic had to descend into the Tarn valley and pass along the route nationale N9 near the town of Millau, causing heavy congestion at the beginning and end of the July and August holiday season. The bridge now traverses the Tarn valley above its lowest point, linking two limestone plateaus, the Causse du Larzac and the Causse Rouge, and is inside the perimeter of the Grands Causses regional natural park.
The Millau Viaduct forms the last link of the preexisting A75 autoroute (known as la Méridienne), from Clermont-Ferrand to Pézenas (to be extended to Béziers by 2010). The A75, with the A10 and A71, provides a continuous high-speed route south from Paris through Clermont-Ferrand to the Languedoc region, and through to Spain, considerably reducing the cost and time of vehicle traffic travelling along this route. Many tourists heading to southern France and Spain follow this route because it is direct and without tolls for the 340 kilometres (210 mi) between Clermont-Ferrand and Pézenas, except for the bridge itself.
The Eiffage group, which constructed the Viaduct, also operates it, under a government contract, which allows the company to collect tolls (Péage) for up to 75 years. The toll bridge costs €7.50 for light automobiles (€9.40 during the peak months of July and August).
|94.501 m (310 ft 0.5 in)||244.96 m (803 ft 8 in)||221.05 m (725 ft 3 in)||144.21 m (473 ft 2 in)||136.42 m (447 ft 7 in)||111.94 m (367 ft 3 in)||77.56 m (254 ft 6 in)|
The metallic road deck, which appears very light despite its total mass of around 36,000 tonnes (40,000 short tons), is 2,460 metres (8,070 ft) long and 32 metres (105 ft 0 in) wide. It comprises eight spans. The six central spans measure 342 metres (1,122 ft), and the two outer spans are 204 metres (669 ft). These are composed of 173 central box beams, the spinal column of the construction, onto which the lateral floors and the lateral box beams were welded. The central box beams have a 4 metres (13 ft 1 in) cross-section, and a length of 15–22 metres (49–72 ft) for a total weight of 90 metric tons (99 short tons). The deck has an inverse airfoil shape, providing negative lift in strong wind conditions.
The seven masts, each 87 metres (285 ft) high, and weighing around 700 tonnes (690 long tons; 770 short tons), are set on top of the concrete pylons. Between each of them, eleven stays (metal cables) are anchored, providing support for the road deck.
Each mast of the Viaduct is equipped with a monoaxial layer of eleven pairs of cable-stays; laid face to face. Depending on their length, the cable stays were made of 55 to 91 high tensile steel cables, or strands, themselves formed of seven strands of steel (a central strand with six intertwined strands). Each strand has triple protection against corrosion (galvanisation, a coating of petroleum wax, and an extruded polyethylene sheath). The exterior envelope of the stays is itself coated along its entire length with a double helical weatherstrip. The idea is to avoid running water which, in high winds, could cause vibration[dubious ] in the stays and compromise the stability of the viaduct.
The stays were installed by the Freyssinet company.
To allow for deformations of the metal road deck under traffic, a special surface of modified bitumen was installed by research teams from Appia (company). The surface is somewhat flexible to adapt to deformations in the steel deck without cracking, but it must nevertheless have sufficient strength to withstand motorway conditions (fatigue, density, texture, adherence, anti-rutting etc.). The 'ideal formula' was found after two years of research.
The electrical installations of the viaduct are large in proportion to the size of the bridge. There are 30 kilometres (19 mi) of high-current cables, 20 kilometres (12 mi) of fibre optics, 10 kilometres (6.2 mi) of low-current cables, and 357 telephone sockets; allowing maintenance teams to communicate with each other and with the command post. These are situated on the deck, on the pylons, and on the masts.
The pylons, road deck, masts, and cable stays are equipped with a multitude of sensors to enable structural health monitoring. These are designed to detect the slightest movement in the Viaduct, and measure its resistance to wear-and-tear over time. Anemometers, accelerometers, inclinometers, temperature sensors are all used for the instrumentation network.
Twelve fibre optic extensometers were installed in the base of pylon P2. Being the tallest of all, it is therefore under the most intense stress. These sensors detect movements on the order of a micrometre. Other extensometers, electrical this time, are distributed on top of P2 and P7. This apparatus is capable of taking up to 100 readings per second. In high winds, they continuously monitor the reactions of the Viaduct to extreme conditions. Accelerometers placed strategically on the road deck monitor the oscillations that can affect the metal structure. Displacements of the deck on the abutment level are measured to the nearest millimetre. The cab stays are also instrumented, and their ageing meticulously analysed. Additionally, two piezoelectric sensors gather traffic data: weight of vehicles, average speed, density of the flow of traffic, etc. This system can distinguish between fourteen different types of vehicle.
The only toll plaza (Péage) on the A75 autoroute; the bridge toll booths and the buildings for the commercial and technical management teams are situated 4 kilometres (2.5 mi) north of the viaduct. The toll plaza is protected by a canopy in the shape of a leaf, formed from tendrilled concrete, using the ceracem process. Consisting of 53 elements (voussoirs), the canopy is 100 metres (330 ft) long and 28 metres (92 ft) wide. It weighs around 2,500 tonnes (2,500 long tons; 2,800 short tons).
The toll plaza can accommodate sixteen lanes of traffic, eight in each direction. At times of low traffic volume, the central booth is capable of servicing vehicles in both directions. A car park and viewing station, equipped with public toilets, is situated at each side of the toll plaza. The total cost was €20 million.
The rest area of Brocuéjouls, named Aire du Viaduc de Millau, is situated just north of the viaduct, and is centred on an old farm building named 'Ferme de Brocuéjouls'. It was inaugurated by the prefect of Aveyron, Chantal Jourdan, on 30 June 2006, after 7 months of works. The farm and its surroundings can accommodate entertainment and tourism promotion activities.
The cost of this work amounted to € 5.8 million:
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Unusually for a bridge closed to pedestrians, a run took place in 2004, and another on 13 May 2007:
déclarant d'utilité publique les travaux de construction des sections de l'autoroute A 75 comprises entre le Engayresque et Lasparets (mise aux normes autoroutières du P.R. 23,520 au P.R. 26,580), entre Lasparets et La Cavalerie Sud (du P.R. 26,580 au P.R. 66,820) y compris les voies de raccordement à Saint-Germain (R.D. 911), à la Côte rouge (R.D. 999) et à La Cavalerie (R.N. 9), de l'échangeur d'Engayresque, des aires de repos, de la section de route à créer pour assurer la continuité de l'itinéraire de substitution d'Engayresque à Lasparets ainsi que des mesures d'accompagnement sur cet itinéraire à Aguessac et à Millau, classant dans la catégorie des autoroutes l'ensemble de la voie comprise entre l'échangeur d'Engayresque et La Cavalerie Sud (du P.R. 22,700 au P.R. 66,820) dans le département de l'Aveyron et portant mise en compatibilité des plans d'occupation des sols des communes d'Aguessac, Millau, Creissels et Saint-Georges-de-Luzençon
This French-language video illustrates the launching technique
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