The Golden Gate Bridge in San Franscisco, California, is perhaps the best-known landmark of this remarkable era in bridge building (see Golden Gate). Completed in 1937, the Golden Gate Bridge has a main span of 1,280 m (4,200 ft).
D Introduction of Concrete
The introduction of concrete as a building material represented a major chapter in the history of bridge building. Although the ancient Romans had used concrete, the knowledge of this material virtually disappeared during the Middle Ages and was not rediscovered until the late 18th century. The first modern concrete bridge was a solid concrete bridge, 12 m (39 ft) long, built over the Garonne Canal at Grisoles, France, in 1840. All early concrete bridges used arched designs by necessity because concrete has great compressive strength but is very weak in tension. Until the invention of metal reinforcement, which adds strength in tension, the arch was the only feasible shape for structures made entirely of concrete. Reinforced concrete emerged simultaneously in Germany, the United States, England, and France between 1870 and 1900. Swiss engineer Robert Maillart became a celebrated designer of reinforced-concrete bridges in the first half of the 20th century, producing extremely innovative designs based on the unique engineering properties of reinforced concrete. The last half of the 20th century saw the construction of major reinforced-concrete structures, such as the Lake Maracaibo Bridge in Venezuela, designed by Italian engineer Riccardo Morandi. This prestressed-concrete cable-stayed bridge is 8 km (5 mi) long.
E Recent Designs
The first modern cable-stayed bridge featured a span of 183 m (600 ft). German engineers constructed this bridge in Sweden in 1956. Thereafter, Germany led the field in developing this type of bridge. Cable-stayed bridges can be constructed in an infinite variety of shapes and are one of the most popular long-span bridge designs. Notable examples include the Severn II Bridge in Bristol, England, completed in 1996 with a span of 456 m (1,496 ft), and the Sunshine Skyway Bridge in Tampa, Florida, completed in 1987 with a span of 366 m (1,200 ft).
At the end of the 20th century, construction was under way on a number of monumental bridges, most notably in Northern Europe and in Asia. Engineers are combining aspects of both suspension and cable-stayed bridges into new bridge designs that will someday span once-impossible distances of more than 3,000 m (10,000 ft).