Primitive suspension bridges used three cables sometimes made of vines, rope or bamboo. Two acted as handrails and one was used to walk on. Some areas of the world still use this type of bridge to cross ravines. Needless to say they can be pretty scary when the wind starts to blow. In many cases the pedestrian suspension bridges have been modified by incorporating a wooden walkway to add a bit of security.
Modern suspension bridges hang from two steel cables. The cables are attached firmly at each end. They then pass over the tops of the tall towers near each end. Steel ropes are attached to the cables and the girders to support the roadway. These cables are strong enough to carry the weight of the roadway even over vast distances.
The Brooklyn Bridge was built in 1883 and was the first to use steel cables. Before this suspension bridges used iron chain.
- photos of the Brooklyn Bridge courtesy of the Brooklyn Bridge Web Site. History & more photos, old and new, can be found on the Brooklyn Bridge Web Site.
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 Lion's Gate Bridge - Vancouver, BC
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- Golden Gate Bridge - San Francisco
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Bisan Seto Bridge - one of the Seto Ohashi Bridges from Honshu Island to Shikoku Island. It is one of the first bridges in the world to allow the safe travel of heavy and rapid trains. It also provides a dual highway. Underwater foundations used steel caissons (a form for underwater concrete). The caisson was built in the shipyard then towed afloat to the site and sunk into position. The caissons were packed with coarse aggregate and mortar was injected into the aggregate for produce a very strong concrete.
photo courtesy of Dr. Loov
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Kurushima Kaikyo Bridge - one of the three suspension bridges from Oshima Island to Shikoku Island. The Kurushima Strait is a dangerous spot for seafarers because of a rapid current and unpredictable movement. The preservation of the natural environment, drivability of the bridge, and safety of ships passing through the strait all had to be studied by the engineers involved. This is the first time that three continuous suspension bridges were linearly connected by two common anchorages. The height of the towers continuously changed to allow a harmony in the overall look.
The entire bridge model was tested in a wind tunnel to accurately check aerodynamic stability.
photo courtesy of Dr. Loov
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Trivia
In 1987, 250,000 people jammed San Francisco's Golden Gate Bridge on its 50th anniversary - temporarily flattening the arched span.
