The Millau Viaduct Bridge : The bridge with Butterfly delicacy.

The present time has been well described as the age of bigness with people vying to create the ever largest things. What was considered the ultimate and most gigantic of its kind in the past, has in most cases been surpassed.

The Viaduc de Millau Bridge, situated in southern France across the Tarn gorge, is the final link in 210 mile A75 highway from Paris to Barcelona in Spain. Before the bridge was built the traffic had to crawl through Millau down the 2.6 k.m. valley creating a bottleneck. After decades of deliberation, the French Govt. approved a design prepared by Sir Norman Foster jointly with French bridge engineer, Micheal Virlogeux which would preserve the ecology and scenic beauty of the landscape. The work started in October 2001 by Eiffage, the company which built the world famous Eiffel Tower. It has been on seven piers each having 16 sections. Each section weighs 2453 tons and measures 56 feet (17 meters) by 13 feet (4 meters). Yet it is much lighter than similar other bridges, presenting a unique fusion of size and strength with a sense of lightness.

Spanning the huge gap from one plateau across the valley to the other end and crossing the Tarn River, was an unprecedented problem. The designers and engineers, therefore, decided to use seven piers instead of usual two or three. The piers have different heights ranging from 75 meters to 235 meters. The piers were sunk in shafts, made of reinforced concrete in a pyramidal shape. They rise to a further 90 meters above the road deck of the bridge. Below the roadway each column splits into two thinner columns forming an A – frame above the deck. This gives the bridge necessary flexibility and creates a dramatic silhouette and results into minimizing the interference with the surrounding picturesque landscape. The bridge suspended over the Tarn River faces a lot of stress. It is exposed to the hot summer sun and freezing winter winds. The split piers allow the highway deck of the bridge to expand or contract by approximately 10 feet.

Intriguingly, the Millau Viaduct Bridge is not straight. The bridge has a 20k.m. curve. The road on the bridge also has a 3 degree incline. The slope descends from the southern end of the bridge towards the north. These enable the drivers to have a better visibility and reduce the odiousness of driving. The deck of the bridge is stayed by 154 cables in a semi harp formation.

The construction design of the Millau Viaduct Bridge is such that it required for lesser materials and kept the structure lighter than other possible designs. Still the gigantic structure required 205000 tons of concrete. This included 19000 tons of steel – reinforced concrete. The total weight of Millau Viaduct Bridge has been estimated at 290000tons. It has a deck with 2 – lane road. This lane provides greater security while driving across the bridge. It prevents the drivers from seeing the deep valley while driving and from possible height – phobia.

Suspension bridges are prone to very severe adheres effects of high winds. In July 1940, when it was complicated, the design of first Tacona Narrows Bridge, built near Seattle in the U.S.A. was considered the most advanced and a trendsetter for suspension bridges, praised for its lightness, grace and flexibility. However, soon its excessive grace and flexibility gave its deck a wave like motion. It began to be called “Galloping Gertie” and became something of local dare to drive cross. On November 7, 1940, hardly four months after completion, it was hit by a moderate 45 miles per hour wind. This gave it a strong sideways twisting in addition to the usual lengthwise waves and, in a short a span of time as 45 minutes, the road deck of the bridge broke apart with sections of it plunging into the river below. The Millau Viaduct Bridge has been built on much improved designs on a much improved design tested in wind to pass through, such winds can cause the vehicles passing the bridge to sway uncontrollably. To prevent this, the road deck has been covered by a 10 feet high transparent plastic shield on both sides. This reduces the wind speed on the road to the level of that on the ground.

The Millau Viaduct Bridge was built at a cost of Euro 400 million, i.e. within the budget and in a record time of 38 months, i.e. one month before the schedule. At its 343 meters it is 43 meters higher than Japan’s Akashi Ksikyo Bridge. In the words of its designer Lord Foster, the Millau Viaduct Bridge seems “to rise out of landscape with the delicacy of a butterfly”.