MILLAU VIADUCT BRIDGE MAP

MILLAU VIADUCT BRIDGE MAP

Crossing Tarn Valley, Millau, France Designer/Engineer Foster + Partners Completed 2004 Span 1,148 feet (350 meters)

Materials Steel, concrete Type Cable-stayed

A span so high that its architect says crossing it is like “flying a car” The Millau Viaduct touches the earth lightly, recalling the long French tradition of audacious structures, begun more than a century ago by Gustave Eiffel, who crossed a similar windy gorge in the Massif Central with an equally astonishing viaduct (see here). The Millau crossing, designed by Foster + Partners in association with an engineering group led by Michel Virlogeux, is the tallest bridge in the world, with a deck so high that architect Norman Foster has compared driving over it to “flying a car.” Beyond its impressive height, the viaduct is admired for its sleek, aerodynamic beauty and minimal impact on the surrounding landscape. Like the best of Foster’s works, it draws on the architect’s spatial inventiveness, a hallmark that is at once completely fresh and, harkening back to England’s nineteenth-century technological innovations, peculiarly Victorian.

A mile and a half (2.5 kilometers) long, the viaduct alleviated a notorious traffic bottleneck along the A75 highway and opened a direct route between Paris and Spain; about 5 million vehicles cross it annually. Its roadway is borne by seven soaring pillars, the tallest of which is taller than the Eiffel Tower; in fact, according to Virlogeux, conceptual drawings of the new bridge included that tower and the Garabit Viaduct to convey just how tall the bridge would be. For all its staggering height, it is precisely executed, with a minimalist aesthetic that Foster compares to “butterflies’ legs.” At night, illuminated, its subtly elegant structure becomes apparent. A delicate butterfly of concrete and steel, the Viaduct of Millau soars across the sky as if eager to proclaim that no bridge on earth is taller. Yet its arrogant daring can surely be forgiven. It took a feat of engineering and a leap of the imagination to span the rough, rugged Tarn Valley.

A decade-long discussion of the best way to cross the Tarn Valley preceded the start of construction in 2001. Two routes, one low and one high, were considered, as were prestressed concrete and steel designs; the high steel solution proved the most economical. The viaduct consists of eight spans: two side spans that are 669 feet (204 meters) long and six intermediate spans that are 1,122 feet (342 meters) long. Its design is a response to extreme structural demands, primarily the need to deflect strong winds at that altitude and to balance asymmetrical live loads (people, vehicles) along multiple cable-stayed spans.

When measured to the top of its tallest pylon, the Millau Viaduct is currently the world’s tallest bridge. However, with a roadway that is 771 feet (235 meters) above the river, the Millau’s deck is lower than the deck of the Beipanjiang Bridge in southwest China, which, at a dizzying 1,854 feet (565 meters), is more than twice as high, garnering it the title of the world’s highest bridge.

A concept sketch by Norman Foster shows how the viaduct relates to the entire valley, rather than simply the river. Seven slender concrete towers, the tallest of which is 1,125 feet (343 meters), minimally impact the landscape. To accommodate the deck’s expansion and contraction, each tower splits into two thinner, more flexible columns below the roadway.

The 420-foot (128-meter) pylons honor the area’s unique contributions to the nation. One pylon houses a three-story observatory. A single vertical plane of cables supports the roadway. The cables are sheathed in pipes that are impregnated with color so their appearance remains consistent over time.