The Millau marvel

When driving through France I often pass over the Millau viaduct. It is a construction of great beauty and one of the engineering marvels of the world. The interpretation centre was open today so I took the time to read the account of the bridge's construction . The bridge was opened in 2004. Comprising 8 consecutive cable stayed spans totaling 8,100 feet (2460 mtrs), the viaduct is the tallest bridge structure in the world with a pier and mast rising a lofty 1,100 feet (335 mtrs) above the ground. With a roadway 909 feet (277 mtrs) above the Tarn River, it is also the highest cable stayed bridge in the world, a record it retained until 2012 when Mexico’s Baluarte bridge opened. Despite being the highest bridge in Europe, the massive structure ranks only 13th among all high bridges of the world. The bridge has rightfully been described as beautiful, breathtaking, spectacular and awe-inspiring.

Located near the southern end of France, the bridge was the last major connection on the A75 motorway, a 4-lane highway that has been under construction in one form or another since 1975. Several routes were proposed that would have put the Tarn River crossing either east or west of the small town of Millau.

Construction began in October of 2001 and took a little over 3 years - exceptional for such a large, complicated undertaking. The 3 year construction period had many unique challenges, the most significant being the unusual launching of the roadway. Instead of cantilevering the road deck outward in small sections from each of the 7 tall pylons, the deck was constructed on flat land on the north and south sides of the bridge in two large sections. Hydraulic jacks on the tops of the piers were then synchronized to move the entire deck out over the valley in small increments of about 2 feet (600 mm). Both sides eventually met over the Tarn river. To make this method work, massive temporary intermediate piers were built to prevent bending of the thin deck since the cable stays and masts above the roadway would not be erected until the entire deck was in its final position. The only exception to this was for the two river spans where the masts and several of the stays were erected on land and went along for the ride across the piers before finally meeting 890 feet (271 mtrs) above the Tarn River.

More information can be found here.