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|Jazyk:||Počet slov:||5 119|
|Referát vhodný pre:||Stredná odborná škola||Počet A4:||17.5|
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The Brooklyn Bridge, which was the world’s longest suspension bridge at the time of its completion in 1883, crosses the East River in New York City and has a main span of 486 m 31 cm (1,595 ft 6 in). The Akashi Kaikyo Bridge between Honshű and Awaji Island in Japan was completed in 1998, with a span of 1,990 m (6,529 ft). While suspension bridges can span long distances, this design has a serious drawback: It is very flexible, and traffic loading may cause large deflections, or bending, in the bridge roadway. Suspension design is rarely used for railroad bridges, because trains are heavier and can travel faster than highway traffic.
F Cable-Stayed Bridges
Cable-stayed bridges represent a variation of the suspension bridge. Cable-stayed bridges have tall towers like suspension bridges, but in a cable-stayed bridge, the roadway is attached directly to the towers by a series of diagonal cables. A cable-stayed bridge is constructed in much the same way as a suspension bridge is, but without the main cables.
Cable-stayed designs are used for intermediate-length spans. Advantages a cable-stayed bridge has over a standard suspension bridge include speed of construction and lower cost, since anchorages are not necessary. There are no massive cables, as with suspension bridges, making cable repair or replacement simpler. The Pont de Normandie (Normandy Bridge) over the Seine River near La Havre in France opened in 1995, with a span length of 856 m (2,808 ft).
G Movable Bridges
Movable bridges make up a class of bridge in which a portion of the bridge moves up or swings out to provide additional clearance beneath the bridge. Movable bridges are usually found over heavily traveled waterways. The three most common types of movable bridge are the bascule (drawbridge), vertical-lift, and swing bridges. Modern bascule bridges usually have two movable spans that rise upward, opening in the middle. A vertical-lift bridge consists of a rigid deck frame held between two tall towers. The bridge opens by hoisting the entire bridge roadway upward between the towers in an elevator-like fashion. Swing bridges are mounted on a central pier and open by swinging to one side, allowing ships to pass.
Movable bridges are generally constructed over waterways where it is either impractical or too costly to build bridges with high enough clearances for water traffic to pass underneath. Bascule bridges are used for short spans. A bascule bridge over the Black River in Lorain, Ohio, has a length of 102 m (333 ft). Vertical-lift bridges are useful for longer spans, but they must be built so they can be lifted high enough for tall ships to pass underneath.
Zdroje: Microsoft Encarta 2003