A bridge is a support structure that allows an object to travel from one point to another by crossing over a body of water, a valley, a road or other obstacle.

The image below illustrates the key bridge components that combined maintain a safe and stable structure.

Bridge illustration

Illustration: Bridge components

Bridge photo

Photograph: Visual representation of Bridge components

A. Deck: the surface of the bridge that enables traffic crossing (pedestrian, vehicle, etc.). Decks are typically built from reinforced concrete.

B. Beam/Girder: the horizontal structure that directly supports the bridge and traffic traveling over it.

C. Cap: An intermediate support located between the bridge deck and the column. Bridge caps transfer loads from above down to the columns.

D. Column: The vertical structural member that transfers loads from caps down to the foundation and lastly the soil. Columns also provide resistance to influences such as wind and stream flow.

E. Foundation Casing: a large pipe that is assembled and inserted into a drilled section of a hole. Where water exists, the casing acts as a barrier between the water and the concrete being poured for the foundation. It is also used for stability when the soils in the ground are unstable.

F. Drilled Shaft (Foundation): designed to support structures with large loads and transfer these loads into the soil. This type of foundation is constructed by drilling equipment to excavate open shafts, then lowering a steel reinforcing cage into the shaft, to be filled with concrete.