Extreme Engineering

Cooper River Bridge (2x7)

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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.