Millau Viaduct Bridge PDF

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Millau Viaduct Bridge, France

Introduction: The Millau viaduct, the biggest civil engineering structure on the A75 motorway, carries the latter over the Tarn valley between the Causse Rouge to the north and the Causse of the Larzac to the south, 5 km west of the town of Millau. The concession for the financing, design, construction, operation and maintenance of the viaduct has been made by the French government to the Compagnie Eiffage du Viaduc de Millau (CEVM) by virtue of a decree published in the Official Journal of 10 October 2001. The concession is for 75 years. However, the concession contract stipulates a "useful project life" for the viaduct of 120 years.

Architecture: The viaduct, 343 m high to the top of the pylons, is the last link in the A75 Clermont Ferrand-Béziers motorway. The search for an aesthetically pleasing structure led to the choice of a multi cable-stayed viaduct with slender piers and a very light deck, touching the valley at only seven points. The precision required for each technical phase demands multiple checks, notably by GPS. A toll barrier, whose canopy will be built using CERACEM (BFUP), will be constructed approximately 6 km north of the viaduct at Saint Germain.

Structure specifications:

Elevation of Millau Viaduct 1. Type of Structure: The Millau viaduct is a multi-cable-stayed structure long of 2460m, slightly curved in plan on a radius of 20,000 m and with a constant upward slope of 3.025% from north to south. The structure is continuous along its eight cable-stayed spans: Two end spans of 24 m each and six central spans of 342 m each. 2. Piers and abutments: The high complexity of the site, which makes access difficult to those areas with steep slopes, has led to the number of piers being limited and to their position being restricted to the top or bottom of the slopes. These piers P2 (height 245 m) and P3 (height 223 m) are the two highest piers ever built in the world to date and that the top 90 m of the shafts of the piers are split into two. Each split shaft is prestressed using eight 19 T 15 super cables using the DYWIDAG procedure (DYWIDAG Bars are used for prestressing reinforced concrete elements. The anchor nut absorbs the tensioning force from the post-tensioning bar and rests on the anchor plate, which transfers tensioning

force onto the concrete). The deck rests on each pier via four spherical bearings, two on each column half, thus effectively fixing the deck to the pier. These characteristics make this structure the world record-holder for the longest multiple cable-stayed bridge with the stays arranged in a central plane over multiple spans as well as for the highest pier (pier P2). 3. Continuity of the deck: The deck consists of a trapezoidal profiled metal box girder with a maximum height of 4.20 m at the axis with an upper orthotropic decking made up of metal sheets 12-14 mm thick on the greater part of the main spans. To ensure resistance to fatigue, a thickness of 14 mm has been adopted for the whole length of the structure under the traffic lanes. This thickness is increased around the pylons. The longitudinal stiffening of the upper orthotropic decking is provided by trapezoidal stiffeners 7 mm thick and in general 600 mm apart which go through the diaphragms.

The sloping base plates of the bottoms of the side box girders consist of 12mm sheet steel on the greater part of the spans, and 14-16 mm sheets around the pylons. 6 mm thick trapezoidal stiffeners are fitted at variable centers. The bottom of the box girder consists of metal sheets of between 25 and 80 mm thick. Rigidity is provided by three trapezoidal stiffeners 14 or 16 mm thick. Two vertical webs 4 m apart and consisting of metal sheet between 20 and 40 mm thick run the entire length of the structure in order to spread out the localized forces of the temporary piers during the launching of the deck. These webs are stiffened on their lower part by two longitudinal trapezoidal stiffeners.

4. The pylons and the stay cables: The pylons are set into the deck: • Longitudinally, continuity is ensured between the metal sheets of the webs of the central box girder and those of the walls of the pylons legs. • Transversely, rigidity is provided by a frame which covers the bearings found on each pier shaft. The legs of the pylons, which are 38 m high, are composed of two stiffened metal box girders. These are surmounted by a mast 49 m high onto which the cables are anchored. The top 17 m of each pylon, whose overall height is 87 m is not structural, but purely aesthetic. The eleven pairs of cables which support each span are arranged in a single plane in a halffan pattern. They are anchored along the axis of the central reservation at regular intervals of 12.51 m following the curvature of the structure. The cables consist of T 15 strands of class 1,860 MPa which are super-galvanized, sheathed and waxed. Each cable is protected by a white, overall aerodynamic sheath made of non-injected PEHD. This acts as a barrier to UV light and has discontinuous spirals on its surface in order to combat vibration resulting from the combined effects of wind and rain. The number of strands making up each cable varies between 45 T 15s near the pylons and 91 T 15s towards the middle of each span. The cable anchors are adjustable at the deck end and fixed on the pylons. 5. The choice of materials: The deck and the pylons, entirely of metal, are made of steels of grade S355 and S460. The piers are constructed in B60 concrete. This concrete was chosen more for its durability than for its high mechanical resistance. The main objectives for the definition of the concretes were:  Protection against alkaline reaction (level C)  Protection against differential internal sulphate reactions  Frost resistance according to the GRA 2002 rules

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Durability in relation to protection of the reinforcing material.

The other concrete elements of the structure: foundation shafts, abutments and foundation slabs are made of B35.

Construction of the Viaduct: The team attempting to build this amazing freeway in the sky had to survive landslides, fight winds gusting at a 135 km/h. It’s a bridge that pushed the boundaries of engineering to the limit and then beyond. From the start the construction team faced 3 main challenges. 1. Foundations: From the geological point of view, the foundations rest on two main rock types:  Limestones beneath the abutments C0 and C8 and beneath piers P1, P2, P3 and P4  Marls beneath the other piers (P5, P6 and P7). Each pier foundation slab rests on four foundation shafts 4.50 or 5 m in diameter and between 9 and 16 m deep. The shafts of piers P4 to P7 are enlarged at the bottom to form an "elephant's foot". The foundation slabs of the piers, whose thickness varies between 3 and 5 m, contain between 1,100 and 2,100 m3 of concrete. The time taken to pour the concrete for the biggest slabs was 30 hours. The slabs are made using B35 concrete with a minimum dose of CPA-CEM 1 52.5 PM ES – CP 2 cement at 280 kg/m3.

One of the seven foundations for piers

2. Building Piers: The piers had to be constructed using an automatic rail climbing system or ACS. The system required the bottom section the pier be constructed then the climbing system attached to rail secured to the pier. Allowing the system to move up the piers independently. The ACS would pour 4 meter sections of concrete at a time allowing accurate pours and ensuring structural stability. The ACS enabled the piers to be built on schedule. The system allowed for a correct pour each time it moved up the pier. 3. Steel Road Deck: The most important part for the driver. The road deck includes all the areas people will actually move on. The designers decided to go with a steel road deck instead of a concrete because of weight and cost. The road deck if made from concrete would weigh near 200,000 metric tons and be 7 meters deep. Using steel the deck is only 36,000 metric tons and 4 meters deep. The design of the road deck is a trapezoidal box girder design. To improve strength and weight reduction. The deck was built on site and using hydraulic movers the first of eighteen 171 meter sections of the deck were slowly moved onto the piers. Using GPS satellites the decks were each moved with precision accuracy to their correct position. On May 28, 2004 the north and south sections of the deck conjoined in the middle above the Tarn River. Deck launching system

4. Masts: The masts were made out of the reinforced concrete the same as the piers. The masts are 87 meters tall and each weighs 700 metric tons. Each mast holds 11 pairs of stays which vary in length. 5. Stays: The stays are used to support the deck of the bridge. Each stay is made out of 55 to 91 high tensile steel cables. The cables are protected with three layers of galvanization, a coating of petroleum wax and an extruded polyethylene sheath to prevent from corrosion and damaging of the cables. The stays are coated with a double helix formation to prevent running water and vibration that could cause deformation and compromise the stability of the road deck. Construction statistics by Leviaducdemillau.com Length: 2460 m Breadth: 32 m Maximum height: 343 m, 19 m higher than the Eiffel Tower Slope: 3.025% uphill north-south (towards Clermont-Ferrand - Béziers) Bending radius: 20 km Height of the tallest pier (P2): 245 m Height of towers: 87 m Number of batteries: 7 Length bays: two side spans of 204 m span and 6 span current 342 m span Cable-stayed Number: 154 (pylon by 11 pairs arranged in a single piece monoaxial) Shroud tension: 900 to 1200 t. For the longest Steel deck weight: 36,000 tons, or 5 times the Eiffel Tower Volume of concrete: 85 000 m3, or 206,000 t. Construction cost: € 400 million (+ Viaduct toll gate) Duration of the concession: 78 years (3 years of construction and 75 years of operation) Warranty of the book: 120 years...