6. Wrought iron chains The bridge is made up of 3,500 load-bearing bolts and 20 km of subterranean chains. The wrought iron links on the bridge come from the Hungerford chain suspension bridge, which was dismantled in 1860. This allows modern engineers to repair or replace any link if needed.
7. Painted steel girders The bridge is made of 730 painted steel girders weighing between 22 and 44 tons each. They are all less than 10 years old and were purchased by the county council from a scrap metal dealer in 1983. The girders are held together with concrete piles that sink down into the river bed and act as support beams for the bridge.
8. Cable trams A system of cables running across the top of the bridge connects two parallel tracks (called trams) that carry road vehicles over the river. The first cable tram span to be built in Britain was designed by Sir John Rennie and opened in 1769 near his home town of Renfrew. It was used as a footbridge until it was replaced by the present-day structure in 1872.
9. Carriageways The bridge consists of two carriageways separated by a central reservation. The space inside the fence is called the "road". On one side of the river there will be residential housing, while on the other there will be industrial premises.
The suspension rods and chains are wrought iron, while the bridge deck is built of timber sleepers coated in planking and asphalt. The towers (or piers) of the bridge are composed of Pennant stone and red sandstone. The total weight of the bridge is about 7,700 tons.
Clifton Suspension Bridge was built by Richard Turner and opened to traffic in 1864. It joins Bristol to its south-western suburbs and is one of England's oldest working bridges. The original ironwork was replaced in 1901 after a fire destroyed much of it. The new suspension rods were forged from double-ribbed "clifford" steel, which is more resistant to corrosion than plain carbon steel. The bridge has been restored several times since then, most recently in 1992.
You may wonder why there aren't any warning signs on the bridge if it is such a dangerous thing to walk across. The reason is simple: nobody has ever been killed when walking across the Clifton Suspension Bridge!
The world's first vehicular road bridge, now known as the Old Bedford Road Bridge, was built by John Wolfe Lane in 1767. He also constructed Southwark Bridge and Westminster Bridge. The Old Bedford Road Bridge was used as a toll bridge until it was replaced by the present Stonebridge Road Bridge in 1872.
The steel wires that compose the cables on certain suspension bridges have been galvanized (coated with zinc). Most suspension bridge towers are composed of steel, however a handful are made of steel-reinforced concrete. Galvanized wire has several advantages over plain wire: It's more corrosion resistant, easier to work with, and less expensive. It also makes the cable stronger.
Only one other type of bridge uses galvanized cable: the Golden Gate Bridge in San Francisco. The idea came from George Selwyn, who was chief engineer on the California State Highway Commission during construction of the first section of highway across the bay in the 1940s. He had seen how well galvanized steel cable stayed up at the Canadian National Railways' Glen Canyon Dam project near Vancouver, British Columbia, and wanted to use it on a Bay Area bridge. However, since most cities won't allow bridges to be built with toxic materials like lead or zinc, which would leach into the water if they were to wear away, this solution wasn't available back then. Today, there are many different ways that bridge engineers design their cables to be as corrosion resistant as possible while still being able to withstand the stress of traffic loads.
Selwyn's idea took hold and today, most large suspension bridges use galvanized cable.
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