Cooper River Bridge

Cooper River Bridge
	Cooper River Bridge Fact file When built: 2005 Height: 175m Length: 490m Timescale: Four years Workforce: 500 Construction material: Concrete and steel Number of suspension cables: 128 Capacity: 18.2m people per year Connecting the bustling port city of Charleston and Mount Pleasant in South Carolina, the Cooper River Bridge will be the longest cable-stay bridge in America. Spanning 490 metres across a busy shipping lane, the bridge has to be built of sturdy stuff. But the biggest threat to its survival is nature.Not only is the structure standing on one of the most seismic spots on the East Coast, it also faces the frequent threat of 300kmph hurricanes. The engineers faced a very tall order – especially with a relatively low budget of $531million. The mainline structure will accommodate eight 4m-wide lanes of traffic, separated by a central barrier. The road deck itself is suspended 54m above sea level by 128 individual cables, strung in parallel from the diamond-shaped support towers. Cable-stayed bridges consist of one or more pillars located in the middle of the span, with cables supporting the roadbed. In this case, each cable is capable of holding 500 tons. To protect the cables from changing weather conditions and moisture they’re enclosed in high-density polymer pipes. Rock barrier islands have been built up around the support towers to prevent ships from careering into the bridge. Plastic hinge zones are being built into towers to allow flexibility during an 8.0 magnitude earthquake. In addition, a damping system has been developed to ensure the structure can withstand hurricane-force wind. The Cooper River Bridge is designed to remain in operation for the next 100 years.

Oakland Bay Bridge

	Oakland Bay Bridge Fact file When built: Began 2002, estimated completion 2006 Height: 161.5m Weight: Approx 1 million tons Length: 3.4km Timescale: Five plus years Construction material: Concrete and steel Number of steel piles: 160 Capacity: Approx 180 million per year The original Oakland Bay Bridge opened for traffic in 1936, opening a corridor between San Francisco and Oakland in California. One of the world’s busiest highline viaducts, it carries an average of 3.2 cars every second – that’s 280,000 vehicles a day.After the 1989 Loma Prieta earthquake, part of the bridge collapsed – clearly, it was time for a replacement. Unfortunately, planning takes time, and construction on the New Bay Bridge only commenced in January 2002. It’s estimated the project will take five years to build. However, after a series of problems, some experts suggest it might take an entire decade to complete. With a projected cost of $2.8 billion, the New Bay Bridge – known as the East Span – will incorporate two engineering disciplines; a self-anchored suspension mechanism and trestle skyway design, supported by 28 concrete platforms. As with the original, there will be five lanes of traffic in each direction. Building on top of a fault line is quite clearly a risky business, but the East Span incorporates several engineering features designed to maximise seismic safety. A shock-absorbing hinge system built into the bridge deck will make it ‘earthquake-proof. The new bridge is designed to withstand an 8.5 magnitude quake. In any eventuality, the East Span has been designed to be up and running and providing service within 48 hours of an earthquake.

Golden Gate Bridge

	Golden Gate Bridge Fact file When built: Completed 1937 Height: 227m above water Length: 2,737m Weight: 80,470 tons Workforce: Unknown, but 11 men died during construction Project timescale: Four years Construction material: Steel Number of rivets: Approximately 600,000 in each tower. Capacity: By 2002, 1.7 billion vehicles had crossed the bridge One of the world’s most recognisable structures, the Golden Gate Bridge was also the longest spanning bridge for 27 years after it was finished in 1937. It is a gravity-anchored suspension bridge, with 1,280m of open water passing beneath its two soaring steel cantilevers.Joseph Strauss is largely accredited as the project’s visionary and lead engineer, however, engineer Charles Ellis and designer Leon Moissieff played a huge role in the success of this iconic crossing. With just a slide rule and an adding machine their calculations solved the problems of compression and tension that the project faced. Slung between two elegant towers, the bridge’s two main cables each weigh 11,000 tons, made from over 25,000 individual wires. As well as holding up the suspended road, the cables also transfer compression into the towers, and the bridge’s anchors at either end of the construction. An instant success, the Golden Gate Bridge had repaid its $75m cost by 1971 – only ever charging a toll to visitors heading south into San Francisco. In the last seven decades, it’s withstood countless earthquakes, including the devastating 7.1 quake of 1989. In fact, the bridge has only been closed three times in its entire history – by high winds.