The Millau viaduct : behind the feat, a number of brilliant innovations

The technique of cable-stayed bridges goes back to the 18th century. But various accidents, usually the breaking of cables following wind-generated oscillations, put this technique in quarantine until the 1960s. A video to watch once again shows it: the collapse of the Tahoma Bridge in the United States in 1940. A few pictures available on http://thefilmvault.com/disasters/tahoma_bridge.html.

The Millau viaduct, opened yesterday, has been praised for a few feats. The height of its pillars for a start ; pillar #3 with 221 meters and pillar #2 with 245 meters (343 meters if you add the pylon holding the cables) shatter the previous record for the category (180 meters). The span between pillars is also remarkable : with 340 meters, the previous record (140 meters) for a metallic bridge almost looks short. But much interest lies in the various innovations generated during this exceptional roadwork.

One of the most important is the simultaneous management of two projects : the pillar building on one side, and the manufacturing and assembling of the parts of the metallic deck. A manager of Eiffage, the company which carried the project, yesterday assessed that this innovation amounted to a 15 month gain compared with a more traditional approach.

To prevent "Tahoma bridge" disasters, all bridges must go through aerodynamic tests. The Millau viaduct complied with this rule, but Meteo France, France’s official wether forecast agency, innovated by creating an "hydraulic tunnel": a model (1/3,000) of the valley and the bridge under construction, where engineers had water and micro-balls to understand wind trajectories. A first in France.

A last example : the use of a GPS positioning tool, with a … 1 millimeter accuracy. The result: with only two surveyors for a 500 construction site, the bridge remained within an error margin set at … 5 millimeters !

All these innovations will remain invisible for future drivers on this motorway, but they enabled Eiffage to manage this project within the initial timing (39 months against 40 forecasted) and within budget (399,5 million Euros against … 400 forecasted).

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