Head and shoulders above the clouds

The world's tallest bridge is recognized at the IBC in Pittsburg

Stephanie Harris Assistant Editor / July 18, 2005

High above the deep and winding gorges of the Tarn River valley stands a structure massive in size, yet beautiful and delicate in appearance. Considered to be a modern-day architectural marvel, the Millau Viaduct in Millau, France, was recently recognized as an outstanding achievement. The 885-ft-tall bridge was awarded the Gustav Lindenthal Medal on June 13, at the International Bridge Conference (IBC) in Pittsburgh.

The Millau Viaduct has earned the right of being the world’s tallest traffic bridge, standing 1,125 ft high at its tallest point—53 ft taller than the Eiffel Tower in Paris. The multi-cable-stayed bridge stretches 1.6 miles between two plateaus in the Massif Central mountain range, connecting Paris with the Mediterranean. Studies for the Millau Viaduct began in 1988 with the objective of ending congestion on the A75 motorway link between Paris and Barcelona.

Towering above clouds and the thick afternoon fog, the architectural marvel was inaugurated on Dec. 14, 2004, by French President Jacques Chirac in front of a crowd of nearly 1,000 people. The bridge was completed within the anticipated three-year schedule.

English architect Lord Norman Foster designed the bridge, while the French-based construction company Eiffage was selected to carry out the project. The $523 million structure was privately funded by Eiffage, who in exchange will collect tolls from motorists for the next 75 years. Toll fees will vary from $6.50 in the winter up to $8.60 in the summer, while trucks pay a year-round fee of $32.24.
The eye-appealing steel and cement bridge sits on seven piers and two abutments and is supported by its streamlined diagonal suspension cables. The deck of the bridge was constructed of steel, which provides better aesthetics and greater safety and was designed to withstand the most extreme meteorological and seismic conditions.

The Millau Viaduct provides motorists with a link across the Tarn River valley and its dramatic landscape. “A work of man must fuse with nature,” Foster said of his design. “The [piers] had to look almost organic, like they had grown from the earth.” Foster, who also designed the Millennium Bridge in London, described the design of the Millau Viaduct as emerging from the natural setting with the “delicacy of a butterfly.”

Pushing forward

Because of the extreme mass of the bridge—nearly 36,000 tons—the structure was assembled offsite as much as possible. Large sections of the deck were lifted by crane and slid onto the piers using hydraulic technology from Enerpac of Milwaukee, a company specializing in hydraulic system integration for large-scale construction projects.

The hydraulic system was designed to push the 27-m-wide deck from both sides onto the concrete piers and meet in the middle. During the launching process, the deck was supported by seven temporary metal piers, which were raised using a hydraulic telescopic system.

The deck of the bridge was pushed by means of a hydraulic launching device on each pier. The device first lifted and then pushed the deck. An adjustable nose structure at the end of the deck allowed it to land on the next pier as it approached.

Each system consisted of a lifting cylinder with a capacity of 250 tons that would lift the deck off of the supporting structure of the pier and two to four skates, each equipped with two 60-ton cylinders that would retract to launch the deck a maximum of 600 mm. All of this rested on a system of single-acting lock-nut cylinders supporting both the launching device and the deck.

The launching process began on the western slope with two launching devices, each consisting of two 120-ton cylinders.

In the last phase of the launch, there were 5,280 tons of pushing capacity from the southern slope (1,752 m of deck) and 2,400 tons from the northern slope (708 m of deck, making a total length of 2,460 m). Each push cycle moved the deck 600 mm and took four minutes. There were 3,280 pushes from the west and 1,540 from the east.

Each launching system rested on a system of cylinders that allowed the load of the skates to be balanced right and left on each pier, in order to compensate for the rotation of the deck during the launch phase and to correct or modify the height of the skate and of the deck where necessary.
Keep the nose up

Because of the extreme weight of the deck, as it was pushed along farther from its support, the deck would curve downward and approach the next pier below the proper level. In order to compensate for this deviation, a nose recovery system was constructed at the end of the deck. This independent system consisted of a hydraulic group of four 270-ton cylinders that would pull the nose upward to the level of the skate, while another hydraulic system allowed the nose-end to pivot.
All of the hydraulic systems for pushing the deck were operated from the control center on the bridgehead. This control center received data via a PROFI-BUS cable, where it was automatically handled so that the system could follow the parameters established when programming the cycle. Because the bridge was constructed piece by piece, Global Positioning System technology was used to precisely join the massive structures together hundreds of feet in the air.

Although the hydraulic systems installed on each pier were controlled from this center, each single hydraulic system had a local control panel that allowed for local movement of the skates to be made from that pier independently as long as it was allowed by the control center, which in turn had to receive the approval of each local control center in order to make synchronized pushing movements from all of the pushing cylinders of all the piers.

After three years of construction, the Millau Viaduct officially opened to the public on Dec. 16, 2004. According to Eiffage Construction Co., nearly 28,000 vehicles a day are expected to cross the bridge in the summer months and about 10,000 a day during the rest of the year. This year’s Tour de France will be routed under the bridge, allowing the world to get a glimpse of the magnificent structure in July.

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