Creators




The Millau Viaduct is the world’s tallest and longest bridge constructed as a cable-stay design that began construction in October of 2001. It is a bridge that marveled the world with new inventions and techniques in order to make this incredible structure exist. The Millau Viaduct is located in southern France near the city of Millau. Its purpose was to create a quicker way to cross the River Tarn between Paris and Barcelona in Spain. By constructing this bridge, it shortened the then current route by 100 km and by up to 4 hours during holiday season, especially the summertime. (3) The bridge spans 2.46 km from one high plateau near Millau to another plateau near Barcelona. (1) The bridge is often referred to as being transparent as it was designed to obstruct the view of the valley as little as possible. . (4)

The bridge is constructed as a cable-stay design massed structure. It consists of 7 piers that are 15 m deep in the ground and 5 m in diameter.  Each pier was formed as a split design as it reached the top near the bridge deck. This was more for aesthetic purposes to appeal to the design of the pylon used for the cable-stay, but also served the purpose of allowing expansion and contraction of the bridge deck. These pylons extended the height of the bridge an additional 90 m. In between each of the 7 accompanying pylons, there were 11 stay cables on either side of a pylon which consisted of different numbers of cables ranging from 55 to 91 cables. The sections of bridge deck between the piers were about 342 meters. The deck of this bridge was constructed of steel rather than the most commonly used concrete. The bridge deck was constructed in two sections spanning half the bridge each and was placed using newly developed, untested, machines which rolled the deck from land to its resting position 600 mm at a time. (Later discussed) This bridge also features a toll plaza, as it convenience is not free. (2)

Challenges of the Project



When discussing engineering projects, it is inevitable that at some point the topic of what challenges and problems had to be faced during the design, as well as construction and implementation of the project. The Millau Viaduct is not an ordinary project; in fact, it is one of the most extensive extreme projects ever tackled by the construction industry, so it comes as no surprise that the challenges and problems that the engineers, architects, and builders of the Millau Viaduct faced were of immense and critical proportion. Some challenges presented themselves as problems seen before with other cable-stayed bridges, however some were particular to the location and enormous size of the bridge.

Beginning with design, France is known for having some of the most appreciable works of artistic ability displayed through structures built throughout the country. When Civil Engineer Michel Virlogeux created his idea for the design of the Millau Viaduct he had recently finished the Normandy Bridge which was an engineering feat in itself as it was the longest cable-stayed bridge for many years. When he came up with this design for the Millau Viaduct he was attempting to push the limits of engineering and create something that had never been done before. It was then up to architect Sir Norman Foster working with Virlogeux to create a sweeping elegant design for the structure that would also be structurally sound. The final design was without a doubt one of the most appealing ever before created and proved that “big doesn’t always have to look brawny.” (8)

In 1998, waiting to hear from government officials, the approval for the construction of this massive bridge was achieved. After a staggering 14 years of planning, construction finally began on the Millau Viaduct. Challenges faced with these first steps of construction were previously discussed during the planning stages and studied intently. The solutions to these problems however were not finalized as there were a few uncertainties that would not be known until the construction began. One of the first challenges to overcome was the need to drill and bury the foundations of the massive pylons deep into the bed rock. The challenge here was that there are cavities throughout the country side that have fractured the limestone. These cavities are necessary to the survival of the local cheese industry. This terrain is responsible for containing the bacteria responsible for the blue mold necessary to make Roquefort cheese. The cracked limestone meant one thing, landslides! Not far into the project this problem became a reality, with a landslide pushing rock and dirt into the first pylon. This landslide however, did not hurt the pylon.

Another problem faced with construction was the need to eliminate error in position. The pylons were of such enormous heights that being off even the slightest at the bottom of the pylon could spell disaster at the top of the pylon in the form of meters off the intended mark. When considering the pylons, other challenges faced included: pouring the cement in a timely manner as to prevent from setting, hurricane grade winds faced by workers, and the intricate design of each pylon moving to the overall construction of the bridge. This made constructing the platform a challenge all its own. Spans of this great length in the past have spelled disaster in the form of collapse of the structure and death of workers. The road spans also would be at the highest point putting the winds at even larger velocities. Placing the 700 ton pylons atop the bridge and adding even more weight to the roadways also served as challenges that could result in the destruction and abrupt end of the Millau Viaduct.

Innovations (Moving Forward)



The Millau Viaduct is a one of a kind bridge and a great engineering feat. The bridge is the tallest vehicle bearing bridge in the world that stands taller than the Eiffel Tower and just shy of the empire state building with the tallest mast reaching 1,120 feet. (7) Many aspects of the Millau Viaduct can be termed innovations both in its construction as well as the overall bridge.

Engineers and architects made innovations in the design of this extreme structure. One of those innovations is the use of only one set of cables down the center of the bridge instead of the usual two along the sides of the bridge. Next they designed the bridge to have its pylons to split into two instead of having a solid pylon on the way up the bridge. The reasoning behind the split pylon design is not only for aesthetic purposes but also for the purpose of contraction and expansion. It was also a challenge for the engineers and designers to create a way for the Millau Viaduct to withstand the wind as well as protect the drivers of the automobiles from harsh wind conditions. To do this they came up with an aerodynamic underside to the bridge which actually looks like an airplane wing turned bottom side up. This allows the wind to cut around the bridge in a smooth manner lowering the chance of twisting. To protect the drivers they installed elegant curved wind break grates down the length of the bridge which take the brunt of the force from the wind and pushes it up and away from the roadway.

To construct such a massive never before accomplished structure, innovations had to be made in the construction phase of the project as well. One innovation formed was the use of pre-built materials coupled with self moving forms for the pylons which cut down on construction time and quite possibly other incidents as well. In order to assure that the pylons would not be off their mark by the time they reached the massive height gps systems were used in every stage of the construction on each pylon which had such great accuracy that the largest error was less than 2 cm. One other innovation brought to life was the creation of the hydraulic pushing system used to put the deck in its place.(This can be seen in the picture above-left) The deck, the height of the deck, and the incredible spans posed a problem for the construction workers. The winds were so strong that building the deck spans in the traditional way, which was to build one span at a time over the gaps between the pylons, was not an option. Instead hydraulic machines from Enerpac were invented to push the 4,000 ton deck into place. This hydraulic machine, a system which utilizes two skates and hydraulic jacks, pushed the deck 6 cm every four minutes. This means that the entire deck was able to be built on the safety of hard ground. A link to additional information on this topic is provided in the sidebar under "Pushing of the Deck."

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Engineering



The Millau Viaduct took a team of engineers to come to completion. Within the civil engineering field several disciplines had to work together in finding solutions to problems as well as initial design and planning of the extensive project. To name a few structural engineers, transportation engineers, and geotechnical engineers all played a huge role in the Millau Viaduct project. In its initial stages these engineers spent many hours together drafting, designing and planning the most efficient and cost effective as well as best for the public, ways to position and build the bridge.

The location of the bridge needed to provide optimal advantages to the public, as the tremendous traffic problem which Millau was facing had to be fixed. Transportation Engineers had to find a way to regulate this problem and develop a route and plan the roads to make the best driving experience possible. Four proposed routes were formed and each one carefully studied and the pros and cons weighed. After much consideration they decided on a route which bypassed the city of Millau in order to direct traffic and thus noise away from the city; problems the city had been criticized about for many years. This route was also found to be of best fit due to the easy link to the city of Millau and the welcoming from the citizens and local government. (6)

Next to be considered was the geotechnical aspect of this project. Geotechnical engineers had to consider the technical aspects of the route which had been favored to see if it was even feasible. The initial design of the bridge already posed a challenge and geotechnical engineers had to find solutions to many different obstructions. The limestone in the area of the Tarn River Valley is cracked due to the many tunnels and cavities in the countryside produced by the cheese industry. The geotechnical engineers, when considering the proposed route for the roads as well as for the bridge, had to make a decision by analyzing the soil and weather patterns of the area. One downfall and very important aspect to consider was the possibility of landslides. The cracked limestone made this feat of nature all the more likely to occur, which could spell disaster for the project. The technical aspects of the proposed route were considered and finally geotechnical engineers and geologists declared the route feasible in 1989. (6)

“The Millau Viaduct was designed by structural engineer Michel Virlogeux and British architect Norman Foster.”  (5) The Millau Viaduct is in every way a success by structural engineering. Beyond its record breaking height and length, the Millau Viaduct is a structural marvel through its innovations and technologies used to build it. Through various tests and collaboration with geotechnical engineers and transportation engineers, the project came down to within 1cm when the decks were placed together. An amazing accomplishment met because of the collaboration between engineering disciplines.

Structurally, the bridge took trial and error tests and 14 years of research to decide what was right for this specific project. Besides the fact of making it structurally sound, they wanted to make it almost transparent in design as to not obstruct the view of the valley in which it was crossing. The structural engineers found a perfect way to build the piers so that they could keep this transparency look and also account for expansion and contraction of the bridge deck. To begin this design however, they had to work with the geotechnical engineers who were finding a way to properly support these piers in the ground. As mentioned before the soil was a special case there so special actions had to be made to insure the piers would not fail. The way the piers accounted for expansion and contraction of the bridge deck shows how they worked closely with transportation engineers. Transportation engineers had to reveal a plan to get the best way possible for traffic on the bridge. Their ideas had to work with how the structural engineers safely needed to design the bridge allowing for what the transportation engineers wanted. So in the end, this amazing bridge and work of art could not have been possible without the combined efforts of all involved.


References 

[1] Miesvanderrohe (October 10, 2009) Millau Viaduct. Retrieved  November 30, 2011, from: http://en.urbarama.com/project/millau-viaduct

[2] Submitted by Er. Akansha (March 5, 2011) Millau Viaduct France – Extreme Engineering. Retrieved  November 30, 2011, from: http://www.cebulletin.com/archive/view/183/

[3] No author Provided (2011) Highest, longest: Viaduct de Millau. Retrieved  November 30, 2011, from: http://www.abelard.org/france/viaduct-de-millau.php

[4] No author provided (2011) The Millau Viaduct Over the River Tarn. Retrieved  November 30, 2011, from: http://midipyreneessouth.angloinfo.com/information/9/millau.asp

[5] Tarun Goel (September 7, 2011) The Engineering Story of Millau Viaduct. Retrieved  November 30, 2011, from: http://www.brighthub.com/engineering/civil/articles/57723.aspx

[6] French OMEGA team (2011) France Millau Viaduct by Bartlett School of Planning. Retrieved  November 30, 2011, from:

http://www.omegacentre.bartlett.ucl.ac.uk/studies/cases/pdf/FRANCE_MILLAU_PROFILE_201210.pdf

[7] Jennifer Gregory (January 12, 2010) Exploring the Millau Viaduct. Retrieved  November 30, 2011, from: http://www.ratestogo.com/blog/millau-viaduct/

[8] No author provided (2011) Top 10 Feats of Engineering, No. 05 - Millau Viaduct. Retrieved  November 30, 2011, from: http://science.discovery.com/top-ten/2009/feats-engineering/feats-engineering-05.html

[9] Enprac (2011) Pushing the 4000 ton deck out into space. Retrieved  November 30, 2011, from: http://www.enerpac.com/en/integrated-solutions-metric/pushing-the-4000-ton-deck-out-into-space