Millau Viaduct breaks all records

On 14 December 2004, a new viaduct was opened in Millau in Southern France. It is an amazing structure which can only be described in superlatives. And rightly so. It is the highest cable-stayed bridge in the world and was built in record time.

It relieves the Rhône Valley of a large volume of heavy traffic and means that tens of thousands of holidaymakers will no longer get stuck in miles of tailbacks on their way to the south. The Millau viaduct is also a breathtakingly beautiful and elegant construction which owes many of its outstanding technical qualities to the high quality Arcelor steel used to build it.

The negotiations leading up to the construction of this remarkable work of art took longer than the actual building process. The first preparatory studies date from 1987, but it was not until 1996 that agreement was reached on the technical and architectural approach to the project.

Then the French government took another two years to decide that the construction of the bridge should be put out to tender. In 2001 a decision to opt for a steel structure was finally taken, and from then onwards things moved rapidly.

Controlled from space

The Millau viaduct was built in just 38 months. That is a remarkably achievement, in view of the impressive dimensions of the construction. The road deck is 2,460 metres long, 32 metres wide and 4.2 metres 'thick'. The bridge rests on 7 piers. The seventh is the smallest, 77 metres high, and the second is the highest at 244.8 metres.

The road deck sections spanning the distance between the piers are also suspended by means of cable stays. The cables are attached in groups of 22 to the seven pylons standing on the piers. Each pylon rises 87 metres above the road deck.

The total height of the tallest pier together with its pylon is 340 metres: 19 metres higher than the Eiffel Tower. The road deck is 270 metres above the Tarn valley. Gorge Bridge in Colorado USA is the only bridge in the world with a slightly higher road deck, but it is a different type of bridge, without pylons. The total height of the French bridge, pylons included, beats the American bridge hands down.

The Millau viaduct weighs 242,000 tonnes. To an expert, that is very little. The reason lies in the use of steel. Over the last three years, Arcelor FCS Commercial supplied 7,000 tonnes of hot rolled steel to Profilafroid, who manufactured 173 bridge elements, which now literally form the backbone of the viaduct.

The length of the elements varies between 16 and 24 metres, but most are 23 to 24 metres long. The steel bridge elements were fixed together at the site, and then from both sides of the Tarn simultaneously, they were pushed forward over the piers into place at a speed of eight metres per hour. This had to be performed with the utmost precision, and the whole operation was monitored continuously via GPS satellites. On 28 May 2004, at twelve minutes past two in the afternoon, the two halves were finally joined together and the valley was bridged.

The advantages of steel

The steel framework of the bridge weighs 36,000 tonnes. In addition to hot rolled steel, Arcelor also supplied large amounts of heavy plate and beams for the construction of the bridge.

The Millau viaduct is a perfect illustration of the many advantages of building with steel. Virtually all steel components could be welded together, assembled and painted at ground level, and in many cases even in an indoor workshop. This had a favourable effect on the quality of the finished pieces and also on the safety of the workforce.

Moreover, it reduced costs. As we all know, steel is a recyclable material that is actually recycled on a large scale. Using steel meant that considerably less stone aggregate was used, and less water. An important advantage in a very dry region with a beautiful natural landscape.

The relatively lightweight steel structure - about half the weight of a comparable structure in concrete - also meant that fewer trucks had to drive to and from the site with material, lower fuel consumption and less pollution from exhaust emissions.

Moreover, the steel structure did not require such heavy foundations and needed fewer pylons and cables to support it, which also had a favourable effect on the total cost price.

The original idea of spanning the Tarn valley with a suspension bridge came from the French engineer Michel Virlogeux. Together with the British architect Lord Norman Foster, who is internationally acclaimed for the Reichstag in Berlin, the Millennium Bridge in London and Chek Lap Kok International Airport in Hong Kong, he has delivered an outstanding structure based on respect for both man and nature.

It is an excellent example of a sustainable solution for a transport problem in a situation where economic and ecological interests appeared to be virtually irreconcilable.

It is not surprising that steel played a part in achieving the optimum result.

Pictures:
Milau Viaduct by Norman Foster / © Daniel Jamme