Covered bridge

Covered Bridge
	Doe River Covered Bridge Elizabethton, Tennessee USA Doe River Covered Bridge; Elizabethton, Tennessee USA
Ancestor	Truss bridge, others
Related	Tubular bridge, Skyway, Jetway
Descendant	None
Carries	Pedestrians, livestock, vehicles
Span range	Short
Material	Typically wood beams with iron fittings and iron rods in tension
Movable	No
Design effort	Low
Falsework required	Determined by enclosed bridge structure, site conditions, and degree of prefabrication

A covered bridge is a bridge, often single-lane, with enclosed sides and a roof. They have typically been wooden, although some newer ones are concrete or metal with glass sides. Especially associated with the nineteenth century, covered bridges often serve as prominent local landmarks and have long attracted the attentions of historical preservationists.

Construction Details

Early bridges were made of wood, especially where it was a plentiful resource. Wooden bridges tended to deteriorate rapidly from exposure to the elements, having a useful lifespan of only nine years. Covering them protected their structural members, thus extending their life to 80 years or more. Oregon, known for its timber resources, has the largest number of historical covered bridges of any state on the west coast of the United States. ^[1]

Most wooden covered bridges employ trusses as their key structural design element. A popular design was the Brown truss, known for its simplicity, but others were also used.

Given the ready availability of steel, concrete, and other modern construction materials, most modern covered bridges are built either for the convenience of the user, rather than to protect the structure itself, or as a statement of style or design.

Covered bridges in Europe

The Western tradition of covered bridges originated in Central Europe.

Surviving or reconstructed European covered bridges include:

Bridge over the Muota river, Brunnen, near Lake Lucerne Switzerland

(picture)

Bridge over the Saane/Sarine river, near Fribourg, Switzerland (picture)
Kapellbrücke, near Lucerne, Switzerland — 650 foot long, built 1333
The Covered Bridge in Lovech, Bulgaria — built 1874
Logic Lane covered bridge in Oxford, England — built 1904

Famous stone covered bridges include the Rialto Bridge in Venice, Italy which is one of only three over the Canal Grande and a popular tourist attraction.

The Bridges of Sighs in Venice, Cambridge and Oxford are also covered bridges.

Green River bridge in Guilford, Vermont

Covered bridges in North America

Such bridges are found in rural areas throughout the United States and Canada, but are often threatened by arsonists, vandals, and flooding. In the United States, Pennsylvania has more covered bridges (more than 200) than any other state, many of which can be seen in Washington County, Pennsylvania, Chester County, Pennsylvania and Lancaster County, Pennsylvania. They are also common in places such as Elizabethton, Tennessee, Lane County, Oregon, Madison County, Iowa, and Parke County, Indiana. Parts of California, Indiana, Ohio, Michigan, Kentucky, Maryland, Minnesota, Virginia, West Virginia and the New England states also have surviving covered bridges. The U.S. state of Vermont has more covered bridges per square mile than any other place in the world, with 107 bridges located throughout the state. In Oregon, five of its 52 bridges are located along the Oregon Coast; four in Lincoln County and one in Coos County.

There are various structural designs used for covered bridges, such as the Burr arch truss.

File:HartlandCoveredBridge.jpg

The longest covered bridge in the world, at Hartland, NB, featured on a 1995 stamp.

Opened on July 4, 1901, the 1,282 foot (390 meter) Hartland Bridge, crossing the Saint John River at Hartland, New Brunswick, is currently the longest covered bridge in the world. It is a national historic site. In 1900, New Brunswick had an estimated 400 covered bridges, and Quebec more than 1000, while Ontario had only 5. As of 2006, there were 94 covered bridges still standing in Quebec, 65 in New Brunswick and at least two in Ontario.

A much longer covered bridge (5,960 feet) between Columbia and Wrightsville, Pennsylvania once spanned the mile-wide Susquehanna River, making it the longest and most versatile covered bridge in the world during its existence. It featured railroad tracks, a towpath for canal boats crossing the river between two canals on either bank, and a carriage / wagon / pedestrian road. The popular tollbridge was burned June 28, 1863, by Union militia during the American Civil War to prevent its usage by the Confederate Army of Northern Virginia during the Gettysburg Campaign. A replacement wooden covered bridge was destroyed by a windstorm a few years later. It was rebuilt as an open-air steel bridge.

As of 2006, the longest existing covered bridge in the United States is Medora Covered Bridge in Indiana, which is 458 feet in length; however, Ashtabula County, Ohio, is in the process of breaking that record. Construction is underway on a new 600-foot covered bridge, which will span the Ashtabula River near Ashtabula. The bridge should be completed before Fall 2008^[2], and will be the 5th covered bridge built in Ashtabula County since 1983.

Covered bridges are generally considered old-fashioned, and appeal to tourists, but the purpose is twofold: (1) covered bridges appear similar to barns and it is easier to transport cattle across them without startling them, and (2) to build a structure for weather protection over the working part of the bridge. A bridge built entirely out of wood, without any protective coating, may last 10 to 15 years. Builders discovered that if the bridge's underpinnings were protected with a roof, the bridge could stand for 70, or even 80 years. The existing covered bridges have been renovated using concrete footings and steel trusses to hold additional weight and to replace the original support timbers.Some covered bridges, such as the one in Newton Falls, Ohio and Elizabethton, Tennessee, also feature an integrated covered walkway.

Dong Minority Bridge, Chenyang, Guizhou, China. (2004-08-16)

Covered bridges in Asia

There are many covered bridges, called "wind and rain bridges" in the Chinese province of Guizhou. These were traditionally built by the Dong minority people. There are also many covered bridges in the Fujian province of southern China.[1]

Taishun County, in southern Zhejiang province near the border of Fujian, has more than 900 covered bridges, many of them hundreds of years old, as well as a covered bridge museum.[2]

Modern covered bridges

File:Guilford vermont bridge covered bridge interior 20040820.jpg

Plank-lattice truss interior structure of Green River bridge in Guilford, Vermont

Modern covered bridges are usually for pedestrians, for example to walk from one part of an office building to another part, to cross railway tracks at a station, or in a shopping center on an elevated level, crossing a road. See also skyway.

Glass-walled covered bridges are rather common at American airports, and some of those bridges can be found at John F. Kennedy Airport in New York City.

Also, some highway bridges, such as the George Washington Bridge, have lower decks for additional capacity, and those decks, while generally open on the sides, can be enclosed with plastic from time to time during construction, thus rendering the lower decks as partially covered bridges.

Covered bridges in fiction

Baumgardener's Covered Bridge, employing the Burr Arch Truss

North American covered bridges received much recognition as a result of the success of the novel, The Bridges of Madison County written by Robert James Waller and made into a Hollywood motion picture starring Meryl Streep and Clint Eastwood.

The fictional rural town portrayed in the 1988 film Beetlejuice features a covered bridge. It provides the early scene in which the protagonists (played by Alec Baldwin and Geena Davis) are killed when their car crashes through the wall of the bridge and plunges into the river below.

A covered bridge is featured in the 1999 film Sleepy Hollow, in a suspense-filled scene depicting an encounter between main character Ichabod Crane (played by Johnny Depp) and the main villain, The Headless Horseman (played by Christopher Walken).

A covered bridge is used for comic effect in the Jay Cronley novel (and Chevy Chase movie,) "Funny Farm," when a fully loaded delivery truck attempts to cross a rickety covered bridge.

In the early 20th century, covered bridges were sometimes nicknamed "kissing bridges", as the cover allowed seclusion for couples to kiss each other.