英语翻译A bridge is a structure providing passage over an obstac

英语翻译
A bridge is a structure providing passage over an obstacle without closing the way beneath.The required passage may be for a road,a railway,pedestrians,a canal or a pipeline.The obstacle to be crossed may be a river,a road,railway or a valley.
Components of a bridge
The main parts of a bridge structure are as below:
Decking,consisting of a slab,girders,trusses,etc.;
Bearings for the decking;
Abutments and piers;
Foundations for the abutments and piers,such as concrete spread footing and groups of bearing piles;
River training works,like revetment for slopes at abutments,aprons at bed level,etc.;
Approaches to the bridge to connect the bridge proper to the roads on either side;
Handrails,guard stones,etc.
Classification
Bridges may be classified in many ways,as below:
According to the material of construction of superstructure bridge is divided into timber,masonry,steel,reinforced concrete,prestressed concrete or composite bridge;
According to function of bridge,it is divided into viaduct,aqueduct,pedestrian,high-way,railway,road-cum-rail bridge.
According to the structure system of bridge,it is divided into rigid frame,arch,cable-stayed or suspension bridge.
According to the interspan relations of bridge,it is divided into simple,continuous or cantilever bridge.
According to span length of bridge,it is divided into culvert ( less than 8 m) ,minor bridge ( between 8 m and 30 m ),medium span bridge (above 30 m ),long span bridge (above 120 m ).
According to the anticipated type of service and duration of use,it is divided into permanent,temporary,military bridge.
Historical development
The history of development of bridge construction is closely linked with the history of human civilization.Form the view point of structural system,bridge structures can be classified into four basic types:beam bridges,arch bridges,rigid frames and suspension bridges.Nature fashioned the first bridges.The tree fallen accidentally across a stream was the earliest example pf a beam type bridge.Similarly,the natural rock arch formed by erosion of the loose soil below and the creepers hanging from tree allowing monkeys to cross from one bank to the other were the earliest fore-bears of the arch and suspension bridges,respectively.
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