The most common type of bridge is the girder bridge, usually made of I-beams or box girders. The end of an I-beam is shaped like the letter "I." If any curves exist in the bridge's design, it could be prone to twisting forces that could cause a collapse. A box girder, which is made in the shape of a box, avoids the torque effect, but is more difficult to build. The world's longest girder bridge is the Ponte Costa e Silva bridge in Brazil, with a length of 8.25 miles.
A suspension bridge can include longer single spans than any other type. Unlike bridges that sit on piers and abutments, a suspension bridge hangs from cables. At each end of the bridge, anchors or counterweights hold the ends of the steel cables. The cables stretch from one set of anchors, over the tops of bridge towers and to the anchors on the opposite side. Smaller steel cables, called hanger cables, connect the main cables to the girder below, to help balance the bridge. The world's longest suspension bridge span is Japan's Akashi-Kaikyo Bridge; its central span, at 6,532 feet, is more than a mile long. The total bridge is about twice that long.
A truss bridge is a simple, skeletal design. Truss bridges have many small beams that, when combined, support heavy weights and can span great distances. Because of the simple design and small size of the individual parts, truss bridges are ideal for spanning areas where construction crews can't use large cranes or heavy equipment. The world's longest truss bridge is Canada's Pont de Quebec at 3,239 feet.
The arch bridge is the second oldest type after the girder bridge. It uses a curved design that does not need supporting piers in its center, eliminating obstacles for river traffic. The world's longest arch bridge, with a length of 12,870 feet, is the Lupu Bridge in Shanghai, China.
A few of the world's most famous bridges include New York City's Brooklyn Bridge, completed in 1883; San Francisco's Golden Gate Bridge, completed in 1937; Australia's Sydney Harbour Bridge, finished in 1932; and Hong Kong's Tsing Ma Bridge, completed in 1997.
