Bridges may be classified by several factors: span, travel, form, and material. Five basic forms are arch, beam, cable-stayed, suspension, and truss. Of course, each form may serve several uses, including road vehicles, railroads, and pedestrians. Here are some examples in Maine.
The brief discussion of the basic forms below only begins to fully describe their elements and the many variations possible with combined forms. See references below for more resources. Also search “bridges” and “covered bridges” for articles referencing bridges.
This form relies on triangle-based supports of rigid materials, such as iron, steel, and wood. They include (in order below) single spans, draw, pedestrian, multi-span, wooden covered, and vertical-lift bridges. See the Kennebec Bridge.
An arch bridge gets it’s support from the arch, not from trusses and beams.
Also known as girder bridges, the simple form consists of a single beam on a vertical support at each end. A more complex version is a cantilever design, with beams anchored at one end so that they need no support at the other end. Two such beams may meet in the middle to create the span, with no vertical support in the middle.
American Institute of Architects — Cincinnati. “Five Bridge Types.” http://www.aiacincinnati.org/community/ABC/curriculum/FiveBridgeTypes.pdf (accessed March 31, 2013)
(Gale, Nellie Isabella. Some Ferries and Covered Bridges of Maine. Orono, Me. University of Maine. 1932. [Maine State Library]
“Historic Bridges of Maine:Maine Overview.” http://historicbridges.org/map_me.php (accessed July 12, 2014)
Jakeman, Adelbert M. Old Covered Bridges of Maine. Ocean Park, Me. Published at Sea Have. 1980.
Maine Covered Bridges: a collection of photographs. State Highway Commission; accompanied by an article on covered bridges from Maine Library Bulletin, April 1932; assembled 1939. [Maine State Library]
Maine Department of Transportation. “Historic Bridges in the State of Maine.” http://www.maine.gov/mdot/historicbridges/index.htm (accessed March 31, 2013)
Maine Department of Transportation. “BRIDGES AND BRIDGE COMPONENTS DEFINITIONS AND TYPES.” http://www.maine.gov/mdot/martinspointbridgedb/documents/pdf/bridgetypes9-21-10.pdf. (accessed March 31, 2013)
Old Covered Bridges of Maine, 1932-1933. Collected by Cora Parsons Watson. [Maine State Library]