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A bridge for cars and trains must be stronger than a simple bridge for foot travel. Question : How safe are bridges? Engineers must consider many things -- like the distance to be spanned and the types of materials available -- before determining the size, shape, and overall look of a bridge.
Since ancient times, engineers have designed three major types of bridges to withstand all forces of nature. Now that you've mastered the bridge basics, test your bridge-building skills in the Bridge Challenge! Educators' Guide Shop. Beam bridge The beam bridge The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. In later years, some were partly made of stone or metal but the trusses were usually still made of wood; in the United States, there were three styles of trusses, the Queen Post, the Burr Arch and the Town Lattice.
Hundreds of these structures still stand in North America. They were brought to the attention of the general public in the s by the novel, movie, and play The Bridges of Madison County. Bridges can be categorized in several different ways. Common categories include the type of structural elements used, by what they carry, whether they are fixed or movable, and by the materials used. Bridges may be classified by how the actions of tension , compression , bending , torsion and shear are distributed through their structure.
Beam bridges are the simplest and oldest type of bridge in use today, and are a popular type. The largest cantilever bridge is the metre 1, ft Quebec Bridge in Quebec, Canada. The world's largest arch bridge is the Chaotianmen Bridge over the Yangtze River with a length of 1, m 5, ft and a span of m 1, ft. The bridge was opened April 29, , in Chongqing , China.
The longest cable-stayed bridge since is the 1, m 3, ft Russky Bridge in Vladivostok , Russia. Most bridges are fixed bridges, meaning they have no moving parts and stay in one place until they fail or are demolished. Temporary bridges, such as Bailey bridges , are designed to be assembled, and taken apart, transported to a different site, and re-used. They are important in military engineering, and are also used to carry traffic while an old bridge is being rebuilt.
Movable bridges are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. These are generally electrically powered. Double-decked or double-decker bridges have two levels, such as the George Washington Bridge , connecting New York City to Bergen County , New Jersey , US, as the world's busiest bridge, carrying million vehicles annually; truss work between the roadway levels provided stiffness to the roadways and reduced movement of the upper level when the lower level was installed three decades after the upper level.
Some double-decked bridges only use one level for street traffic; the Washington Avenue Bridge in Minneapolis reserves its lower level for automobile and light rail traffic and its upper level for pedestrian and bicycle traffic predominantly students at the University of Minnesota. Likewise, in Toronto , the Prince Edward Viaduct has five lanes of motor traffic, bicycle lanes, and sidewalks on its upper deck; and a pair of tracks for the Bloor—Danforth subway line on its lower deck.
Robert Stephenson 's High Level Bridge across the River Tyne in Newcastle upon Tyne , completed in , is an early example of a double-decked bridge. The upper level carries a railway, and the lower level is used for road traffic.
Tower Bridge in London is different example of a double-decked bridge, with the central section consisting of a low-level bascule span and a high-level footbridge. A viaduct is made up of multiple bridges connected into one longer structure.
The longest and some of the highest bridges are viaducts, such as the Lake Pontchartrain Causeway and Millau Viaduct. A multi-way bridge has three or more separate spans which meet near the center of the bridge. Multi-way bridges with only three spans appear as a "T" or "Y" when viewed from above. Multi-way bridges are extremely rare.
A bridge can be categorized by what it is designed to carry, such as trains, pedestrian or road traffic road bridge , a pipeline or waterway for water transport or barge traffic. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height.
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