Majestic and minimalist, the world’s longest bridge is also one of the most beautiful
From a distance, the seven steel masts of the record-breaking Millau Viaduct in southern France look like billowing sails of a cosmic spacecraft. Up close, the tallest bridge in the world is no less stunning, a minimalist masterpiece that resembles an Apple iPad in bridge form.
The Millau Viaduct is a cable-stayed road bridge of concrete and steel with load-bearing masts stretching 343 metres (1,125 feet) into the air. 17 years in the making – at a cost of 400 million euros – the 2,460-metre (1.52-mile) span employed the very latest construction techniques and technologies during each of its six stages of fabrication and assembly.
First came the ‘legs’ of the bridge, seven thick piers consisting of 206,000 tons of poured concrete. The smooth, seamless surface of each pier was achieved using a machine called a self-climbing framework. Powered by hydraulic lifters, the concrete framework rises upwards with the pier at a rate of three meters every three days. Pouring continuously, the piers rose from the valley fl oor, reaching their peak heights in ten months.
Next came the deck, built from 173 steel box beams forged in the Eiffel factory. Using two on-site metalworks, the steel fl oor was welded to the box beams to create 171-metre deck panels. The panels were then ‘launched’ from both sides of the bridge using 64 hydraulic conveyors positioned atop the piers and temporary steel crutches. The two sides of the deck literally slid towards each other at a rate of 60cm per push, equal to nine metres an hour. The two sides fi nally met on 28 May 2004 at 2:12pm.
The seven steel masts support 1,500 tons of steel stays attached at 11 paired points. Each stay consists of up to 91 bound steel cables and each cable is made from seven individual strands of steel. The stays are triply weatherproofed to avoid corrosion.
Before paving the road, workers used high pressure blasters to scour the steel deck with millimetre-size ball bearings. Once all traces of rust were removed, special equipment laid a four-centimetre thick layer of tar thermosealed at 400°C, offering complete corrosion protection.
The bridge construction is guaranteed for 120 years and is continuously monitored for movements as small as a micrometre by dozens of fi bre-optic sensors strung throughout the structure.