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A continuous truss bridge is a
truss bridge A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements, usually forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or ...
which extends without hinges or joints across three or more supports. A continuous truss bridge may use less material than a series of simple trusses because a continuous truss distributes live loads across all the spans; in a series of simple trusses, each truss must be capable of supporting the entire load. Although some continuous truss bridges resemble
cantilever bridges A cantilever bridge is a bridge built using structures that project horizontally into space, supported on only one end (called cantilevers). For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed ...
and may be constructed using cantilever techniques, there are important differences between the two forms. Cantilever bridges need not connect rigidly mid-span, as the cantilever arms are self-supporting. Although some cantilever bridges appear continuous due to decorative trusswork at the joints, these bridges will remain standing if the connections between the cantilevers are broken, or if the suspended span (if any) is removed. Conversely, continuous truss bridges rely on rigid truss connections throughout the structure for stability. Severing a continuous truss mid-span endangers the structure. However, continuous truss bridges do not experience the tipping forces that a cantilever bridge must resist, because the main span of a continuous truss bridge is supported at both ends. It is possible to convert a series of simple truss spans into a continuous truss. For example, the northern approach to the
Golden Gate Bridge The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the strait connecting San Francisco Bay and the Pacific Ocean. The structure links the U.S. city of San Francisco, California—the northern tip of the San Francisco P ...
was originally constructed as a series of five simple truss spans. In 2001, a
seismic retrofit Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent e ...
project connected the five spans into a single continuous truss bridge.


History

Continuous truss bridges started to be constructed in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
during the second half of the 19th century. Although the advantages of continuous bridges were known, there were three main engineering challenges which slowed their widespread adoption: *Continuous trusses are
statically indeterminate In statics and structural mechanics, a structure is statically indeterminate when the static equilibrium equations force and moment equilibrium conditions are insufficient for determining the internal forces and reactions on that structure. Math ...
, which made it very laborious to calculate the stresses in the bridge before computers became available. *The stresses in the truss can change significantly if one of the supports settles more than the others. *The truss is susceptible to significant stresses due to temperature gradients in the structure, such as if the upper part of the truss is in the sun and the lower part is in the shade. However, it was possible to avoid these issues to a certain extent through careful design. The early European bridges were usually lattice trusses with three to five spans. An example was the
Boyne Viaduct , native_name_lang = , image = 02 Boyne Viaduct Drogheda 2007-10-5.JPG , image_size = , alt = , caption = , official_name = , other_name = , carries = Belfast-Dublin railway ...
, built in 1855 in
Drogheda Drogheda ( , ; , meaning "bridge at the ford") is an industrial and port town in County Louth on the east coast of Ireland, north of Dublin. It is located on the Dublin–Belfast corridor on the east coast of Ireland, mostly in County Louth ...
,
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
. The first continuous truss bridge in North America was the Lachine Bridge in
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
, built in 1888, followed by the
Sciotoville Bridge The Sciotoville Bridge is a steel continuous truss bridge carrying railway tracks belonging to CSX Transportation across the Ohio River between Siloam - a junction located north of Limeville, Kentucky and east of South Shore, Kentucky - and Scioto ...
in 1916 and the Bessemer & Lake Erie Railroad Bridge in 1918. Since the development of
computer-aided engineering Computer-aided engineering (CAE) is the broad usage of computer software to aid in engineering analysis tasks. It includes , , , durability and optimization. It is included with computer-aided design (CAD) and computer-aided manufacturing (CAM) ...
, continuous truss bridges have become more common.


Examples

Some notable continuous truss bridges, with main span length

*
Ikitsuki Bridge The Ikitsuki Bridge is a continuous truss bridge that connects Ikitsuki to Hirado Island. Completed in 1991, it has a main span of . It is the longest continuous truss bridge in the world. History The bridge allows automobile access from Ikit ...
, * Astoria-Megler Bridge, *
Francis Scott Key Bridge Francis Scott Key Bridge, Key Bridge, or FSK Bridge can refer to: *Francis Scott Key Bridge (Baltimore), a bridge carrying Interstate 695 which crosses the outer harbor of Baltimore, Maryland *Francis Scott Key Bridge (Washington) The Francis Sc ...
, * Taylor-Southgate Bridge, *
Julien Dubuque Bridge The Julien Dubuque Bridge is a bridge over the Mississippi River that connects Dubuque, Iowa and East Dubuque, Illinois. The bridge is part of U.S. Route 20 (US 20). It is one of two automobile bridges over the Mississippi in the area (t ...
, *
Charles M. Braga Jr. Memorial Bridge The Charles M. Braga Jr. Memorial Bridge, also known as the Braga Bridge, is a through truss bridge that carries Interstate 195 over the Taunton River between the town of Somerset and the city of Fall River, near the mouth of the Quequechan Rive ...
, *
Governor Harry W. Nice Memorial Bridge The Governor Harry W. Nice Memorial/Senator Thomas "Mac" Middleton Bridge, also known as the Potomac River Bridge, is a , two-lane continuous truss bridge that spans the Potomac River between Newburg in Charles County, Maryland and Dahlgren in ...
, * Don N. Holt Bridge, *
Sciotoville Bridge The Sciotoville Bridge is a steel continuous truss bridge carrying railway tracks belonging to CSX Transportation across the Ohio River between Siloam - a junction located north of Limeville, Kentucky and east of South Shore, Kentucky - and Scioto ...
, *
Owensboro Bridge The Owensboro Bridge is a continuous truss bridge that spans the Ohio River between Owensboro, Kentucky and Spencer County, Indiana. Dedicated to the memory of the late U.S. Congressman Glover H. Cary (1885–1936) and often called the "Glover ...
, * Carroll C. Cropper Bridge, *
Sewickley Bridge The Sewickley Bridge is a steel continuous truss bridge spanning the Ohio River between Sewickley and Moon Township, Pennsylvania, carrying State Route 4025 and the Orange Belt. It was built by American Bridge Company and opened on October 2 ...
, *
Betsy Ross Bridge The Betsy Ross Bridge, also known as the Ross Memorial Bridge, is a continuous steel truss bridge spanning the Delaware River from Philadelphia, Pennsylvania to Pennsauken, New Jersey. It was built from 1969 to 1974, and opened in April 1976, d ...
, *
Chesapeake Bay Bridge The Chesapeake Bay Bridge (also known locally as the Bay Bridge) is a major dual-span bridge in the U.S. state of Maryland. Spanning the Chesapeake Bay, it connects the state's rural Eastern Shore region with the urban Western Shore, between ...
, , secondary spans * Cape Girardeau Bridge, (replaced in 2003 and subsequently demolished) * Champlain Bridge, (replaced in 2009 subsequently demolished) *
Kingston–Rhinecliff Bridge The George Clinton Kingston–Rhinecliff Bridge is a continuous under-deck truss toll bridge that carries NY 199 across the Hudson River in New York State north of the City of Kingston and the hamlet of Rhinecliff. It was opened to traffic o ...
, 7,793 feet (2357 m)


See also

*
List of longest continuous truss bridge spans This list of continuous bridge spans ranks the world's continuous truss bridges in two First by the length of main span (the longest length of unsupported roadway) and second by the total length of continuous truss spans. This list includes brid ...


References

{{reflist


External links


Golden Gate Bridge retrofit
Truss bridges by type