TECHKNOW: Pushing the envelope

TECHKNOW: Pushing the envelope - BRIDGES

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Last Updated: 31 Aug 2010

BRIDGES

As Simon and Garfunkel recognised in their 1970 hit Bridge over Troubled Water, getting from one river bank to the other is far less traumatic if you travel over the torrent rather than struggle through it. Such is mankind's aversion to wet feet that bridges of one form or another have been spanning rivers, streams, marshes and straits for thousands of years. The Sweet Track (a series of halved logs laid end to end) is one of the first known - it's nearly 6,000 years old and meanders a rickety 1.8km across the boggy Somerset Levels.

These days, steel and reinforced concrete replace tree trunks, and bridges are big business. Italian premier Silvio Berlusconi recently announced one of the largest public works in his country's history - a dollars 4.5 billion project to bridge the Straits of Messina between Sicily and the Italian mainland.

THE CHALLENGE

The longest bridge in the world is the 38.6km causeway on highway 90 over Lake Pontchartrain, near New Orleans, carried on 9,000 concrete piles sunk into the floor of the relatively shallow lake. But for deep-water crossings the suspension bridge is the engineers' choice. It's a simple design requiring few supports dug into river or seabed, so is both easier to build and less disruptive to shipping than other types.

For a decade or so in the '80s Britain had the longest single-span suspension bridge in the world: the 1.4km stretch crossing the Humber estuary. But in the '90s the honour passed to Japan's 1.9km Akashi Kaikyo. The title will return to Europe if Berlusconi gets his way: the Messina bridge, due for completion in 2010, will have a 3.3km span.

THE SOLUTION

As with the channel tunnel before it, plans permanently to join the Italian boot to its neighbouring football have been maturing for at least 30 years. Not least because the Straits of Messina form a very hostile environment. The combination of deep water and rip tides in the middle of an earthquake zone does not bode well for the bridge-builders, who will need high-tech materials such as carbon fibre (more usually associated with aerospace than civil engineering) to stand a chance of doing the job. The latest design features an aerodynamic deck to avoid hurricane damage, carrying a three-lane motorway and a single railway track in each direction.

More than enough traffic, say critics, to choke the island's primitive road network and consign the slow pace of life so attractive to tourists to the history books. But given that the Sicilians - a people whose ruthlessness underpins black economies the world over - are themselves pretty lukewarm about the idea, it may be another 30 years before these troubled waters are bridged.

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