Bridge

A bridge is a structure that is used to get from one side of an obstacle (such as a river, lake, or road) to the other side.

Importance of Bridges:

• Connects difficult terrains
• Easy trade and transportation of goods
• Reduces travelling time
• Military use
• Political and economic importance
• Less emission due to displacement

Component Of Bridge

Pier

Pier is a part of the substructure which supports the superstructure at the end of the span and which transfers loads on the superstructure to the foundations. 
Depending up on aesthetics, site, space and economic constraints various shapes of piers are adopted to suit to the requirement. 
Mostly Reinforced Concrete or prestressed concrete are adopted for the construction of piers. 
Piers are compression members. Depending on the loading and bearing articulations, piers may be subjected to bending as well.

Bearing

Bearings transfers loads from the girders to the pier caps. 
Bearing is a component which supports part of the bridge and which transmits forces from one part to another part of the structure while permitting angular and/or linear movement between parts

Grinder

Girder is the part of superstructure which is under bending along the span. 

It is the  load bearing member which supports the deck. 
Span is the distance between points of support (i.e. piers, abutment). 
Deck is bridge floor directly carrying traffic loads. 
Deck transfers loads to the Girders depending on the decking material.

Types Of Bridge

Cable stayed bridge

Cable stayed bridges are usually constructed over gorges in hilly countries where the water flow in the stream below is very fast. 
Cable stayed bridges are constructed with boulders where piers cannot be easily constructed. 
These bridges have a span of 150 meters and are usually meant for pedestrian traffic. 
The deck is supported by long cables carried over tall towers provided at their ends.

Suspension bridge

Suspension bridges are long-span bridges involving creative works and great skill on the part of the bridge engineer. 

For the stability of such long-span bridges of 600 m and above, considerations has to be given for the following parameters. 
(a) the control of aerodynamic movement, 
(b) the local angle changes in the deck and 
(c) vertical oscillations caused by serve winds

Cantilever bridge

It is so called as in a single span there are cantilever arms from each pier to the ends where the freely supported suspended span rests.
Cantilever bridges, due to their heavier weights and labor involved in construction compared to the cable stayed bridges for the same spans, are no longer popular. 

Truss bridge

For rail-road or long railway bridges of spans 100 to 200 meters, truss bridges are found suitable and expedient due to relative lightness of its component parts. 
There are various types of truss bridges like the Warren truss bridge, Pratt truss and N-truss.

Arch bridge

In case of arch bridges the abutments must be strong enough to carry the thrust exerted by the ribs.
In such cases heavy expensive abutments will be required, unless there is a gorge with rocky banks which might be strong enough to bear the load exerted by the ribs; and it is in such situations where arch bridges are most recommended. 
Arch bridges may be made of masonry or steel. For long spans, steel arch bridges are generally used.