Coming soon: the world’s longest bridge – Physical News

Coming soon: the world’s longest bridge – Physical News – Brief Article

Kim Y. Masibay

Rumor has it that a legendary six-headed monster lurks in the deep waters of the Tyrrhenian Sea between Italy and the island of Sicily. If true, one day you might spy the beast while zipping across the Messina Strait Bridge. When completed in 2010, the world’s longest bridge will weigh nearly 300,000 tons–equivalent to the iceberg that sank the Titanic–and stretch 5 kilometers (3 miles) long. “That’s nearly 50 percent longer than any other bridge ever built,” says structural engineer Shane Rixom in Saint Augustine, Fla.

What do the world’s longest bridges have in common? They’re suspension bridges, massive structures built to span vast water channels or gorges. A suspension bridge needs just two towers to shoulder the structure’s mammoth weight, thanks to hefty supporting cables slung between the towers and anchored firmly in deep pools of cement at each end of the bridge (see diagram, below).

When construction begins on the Messina Strait Bridge in 2005, the first job will be to erect two 370 meter (1,214 foot)-tall steel towers. Next, builders will pull two sets of steel cables across the strait–each cable a bundle of 44,352 individual steel wires. “Getting them up will be something,” says Rixom. “It’s not just their length”–totaling 5.3 km (3.3 mi)–“but their weight.” The cables will tip the scales at 166,500 tons–more than half the bridge’s total mass.

After lowering vertical “suspender” cables from the main cables, builders will erect a 60 meter (200 ft)-wide, 54,630-ton steel roadway, or deck–wide enough to accommodate 12 lanes of traffic. The deck’s weight will pull down on the cables with a force of 70,500 tons. In return, the cables yank up against their firmly rooted anchors with a force of 139,000 tons–equivalent to the weight of about 100,000 cars. “Those anchors are key,” says Rixom. “They’re what will keep the bridge from going anywhere.”

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