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A truss bridge is a
bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually someth ...
whose load-bearing
superstructure A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships. Aboard ships and large boats On water craft, the superstruct ...
is composed of a
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
, a structure of connected elements, usually forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. The basic types of truss bridges shown in this article have simple designs which could be easily analyzed by 19th and early 20th-century engineers. A truss bridge is economical to construct because it uses materials efficiently.


Design

The nature of a
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
allows the
analysis Analysis ( : analyses) is the process of breaking a complex topic or substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (3 ...
of its structure using a few assumptions and the application of
Newton's laws of motion Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at rest, or in mo ...
according to the branch of
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
known as
statics Statics is the branch of classical mechanics that is concerned with the analysis of force and torque (also called moment) acting on physical systems that do not experience an acceleration (''a''=0), but rather, are in static equilibrium with ...
. For purposes of analysis, trusses are assumed to be pin jointed where the straight components meet, meaning that taken alone, every joint on the structure is functionally considered to be a flexible joint as opposed to a rigid joint with strength to maintain its own shape, and the resulting shape and strength of the structure is only maintained by the interlocking of the components. This assumption means that members of the truss (chords, verticals and diagonals) will act only in tension or compression. A more complex analysis is required where rigid joints impose significant
bending In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to ...
loads upon the elements, as in a
Vierendeel truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembla ...
. In the bridge illustrated in the
infobox An infobox is a digital or physical table used to collect and present a subset of information about its subject, such as a document. It is a structured document containing a set of attribute–value pairs, and in Wikipedia represents a summa ...
at the top, vertical members are in tension, lower horizontal members in tension, shear, and bending, outer diagonal and top members are in compression, while the inner diagonals are in tension. The central vertical member stabilizes the upper compression member, preventing it from
buckling In structural engineering, buckling is the sudden change in shape ( deformation) of a structural component under load, such as the bowing of a column under compression or the wrinkling of a plate under shear. If a structure is subjected to a ...
. If the top member is sufficiently stiff then this vertical element may be eliminated. If the lower chord (a horizontal member of a truss) is sufficiently resistant to bending and shear, the outer vertical elements may be eliminated, but with additional strength added to other members in compensation. The ability to distribute the forces in various ways has led to a large variety of truss bridge types. Some types may be more advantageous when wood is employed for compression elements while other types may be easier to erect in particular site conditions, or when the balance between labor, machinery and material costs have certain favorable proportions. The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection, the availability of machinery and the cost of labor. In other cases the appearance of the structure may take on greater importance and so influence the design decisions beyond mere matters of economics. Modern materials such as
prestressed concrete Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-tensioned concreted ...
and fabrication methods, such as automated
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as b ...
, and the changing price of steel relative to that of labor have significantly influenced the design of modern bridges.


Model bridges

A pure truss can be represented as a pin-jointed structure, one where the only forces on the truss members are tension or compression, not bending. This is used in the teaching of statics, by the building of model bridges from spaghetti. Spaghetti is brittle and although it can carry a modest tension force, it breaks easily if bent. A model spaghetti bridge thus demonstrates the use of a truss structure to produce a usefully strong complete structure from individually weak elements.


History in the United States

Because wood was in abundance, early truss bridges would typically use carefully fitted timbers for members taking compression and iron rods for tension members, usually constructed as a
covered bridge A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered woo ...
to protect the structure. In 1820 a simple form of truss, Town's lattice truss, was patented, and had the advantage of requiring neither high labor skills nor much metal. Few iron truss bridges were built in the United States before 1850. Truss bridges became a common type of bridge built from the 1870s through the 1930s. Examples of these bridges still remain across the US, but their numbers are dropping rapidly as they are demolished and replaced with new structures. As metal slowly started to replace timber,
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
bridges in the US started being built on a large scale in the 1870s. Bowstring truss bridges were a common truss design during this time, with their arched top chords. Companies like the
Massillon Bridge Company The Massillon Bridge Company, most commonly abbreviated Massillon Bridge Co., was located in Massillon, Ohio and founded by Joseph Davenport in 1869. The company became incorporated in 1887 and remained in operation through the early 1900s. Steel ...
of
Massillon, Ohio Massillon is a city in Stark County, Ohio, Stark County in the U.S. state of Ohio, approximately west of Canton, Ohio, Canton, south of Akron, and south of Cleveland. The population was 32,146 at the 2020 United States Census, 2020 census. Mass ...
, and the
King Bridge Company The King Iron Bridge & Manufacturing Company was a late-19th-century bridge building company located in Cleveland, Ohio. It was founded by Zenas King (1818–1892) in 1858 and subsequently managed by his sons, James A. King and Harry W. King ...
of
Cleveland, Ohio Cleveland ( ), officially the City of Cleveland, is a city in the U.S. state of Ohio and the county seat of Cuyahoga County. Located in the northeastern part of the state, it is situated along the southern shore of Lake Erie, across the U.S ...
, became well-known, as they marketed their designs to cities and townships. The bowstring truss design fell out of favor due to a lack of durability, and gave way to the Pratt truss design, which was stronger. Again, the bridge companies marketed their designs, with the Wrought Iron Bridge Company in the lead. As the 1880s and 1890s progressed,
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
began to replace wrought iron as the preferred material. Other truss designs were used during this time, including the camel-back. By the 1910s, many states developed standard plan truss bridges, including steel Warren
pony A pony is a type of small horse ('' Equus ferus caballus''). Depending on the context, a pony may be a horse that is under an approximate or exact height at the withers, or a small horse with a specific conformation and temperament. Compared ...
truss bridges. As the 1920s and 1930s progressed, some states, such as
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, continued to build steel truss bridges, including massive steel through-truss bridges for long spans. Other states, such as
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and t ...
, used standard plan concrete girder and beam bridges, and only a limited number of truss bridges were built.


Roadbed types

The truss may carry its roadbed on top, in the middle, or at the bottom of the truss. Bridges with the roadbed at the top or the bottom are the most common as this allows both the top and bottom to be stiffened, forming a box truss. When the roadbed is atop the truss it is called a deck truss (an example of this was the
I-35W Mississippi River bridge The I-35W Mississippi River bridge (officially known as Bridge 9340) was an eight-lane, steel truss arch bridge that carried Interstate 35W across the Mississippi River one-half mile (875 m) downstream from the Saint Anthony Falls in Minne ...
). When the truss members are both above and below the roadbed it is called a through truss (an example of this application is the
Pulaski Skyway The Pulaski Skyway is a four-lane bridge-causeway in the northeastern part of the U.S. state of New Jersey, carrying an expressway designated U.S. Route 1/9 (US 1/9) for most of its length. The structure has a total length of . Its ...
), and where the sides extend above the roadbed but are not connected, a pony truss or
half-through A plate girder bridge is a bridge supported by two or more plate girders. Overview In a plate girder bridge, the plate girders are typically I-beams made up from separate structural steel plates (rather than rolled as a single cross-section), ...
truss. Sometimes both the upper and lower chords support roadbeds, forming a double-decked truss. This can be used to separate rail from road traffic or to separate the two directions of road traffic. Since through truss bridges have supports located over the bridge deck, they are susceptible to being hit by overheight loads when used on highways. The I-5 Skagit River bridge collapsed after such a strike; before the collapse, similar incidents had been common and had necessitated frequent repairs.


Gallery

Image:LittleManateeRiver.jpg, Pratt through truss of the former Seaboard Air Line Railway, located near the village of Willow,
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
; abandoned since the mid-1980s Image:ErieCanalRRBridge04 1A.jpg, Deck truss railroad bridge over the
Erie Canal The Erie Canal is a historic canal in upstate New York that runs east-west between the Hudson River and Lake Erie. Completed in 1825, the canal was the first navigable waterway connecting the Atlantic Ocean to the Great Lakes, vastly reducing ...
in
Lockport, New York Lockport is both a city and the town that surrounds it in Niagara County, New York. The city is the Niagara county seat, with a population of 21,165 according to 2010 census figures, and an estimated population of 20,305 as of 2019. Its name d ...
Image:General Hertzog Bridge over Orange River at Aliwal North.jpg, The four span through truss General Hertzog Bridge over the
Orange River The Orange River (from Afrikaans/Dutch: ''Oranjerivier'') is a river in Southern Africa. It is the longest river in South Africa. With a total length of , the Orange River Basin extends from Lesotho into South Africa and Namibia to the north ...
at Aliwal North carries vehicular traffic File:05-23-13 Skagit Bridge Collapse.jpg, The through truss Skagit River bridge on Interstate 5 collapsed after an overhead support was hit by a passing truck File:Old San Jacinto River Truss Bridge -- Humble, Texas.jpg, Old San Jacinto River truss bridge – Humble, Texas Image:Puente Tacuarembó 02.jpg, Pony truss bridge of reinforced concrete Image:Sky gate bridge01s3200.jpg, Sky Gate Bridge R at
Kansai International Airport Kansai International Airport ( ja, 関西国際空港, Kansai Kokusai Kūkō) commonly known as is the primary international airport in the Greater Osaka Area of Japan and the closest international airport to the cities of Osaka, Kyoto, and ...
,
Osaka is a designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the third most populous city in Japan, following Special wards of Tokyo and Yokohama. With a population of ...
, Japan, is the longest double-decked truss bridge in the world. It carries three lanes of automobile traffic on top and two of rail below over nine truss spans. File:Railroad Truss bridge over trinity river near Goodrich, Texas.jpg, Railroad Truss bridge over Trinity River near
Goodrich, Texas Goodrich is a city in Polk County, Texas, United States. The population was 271 at the 2010 census. Geography Goodrich is located at (30.607139, –94.946995). According to the United States Census Bureau, the city has a total area of , all o ...
Image:HartBridgeJax.jpg, The Hart Bridge spanning the St. Johns River in
Jacksonville, Florida Jacksonville is a city located on the Atlantic coast of northeast Florida, the most populous city proper in the state and is the largest city by area in the contiguous United States as of 2020. It is the seat of Duval County, with which th ...
, is a continuous, cantilevered truss bridge which combines a suspended road deck on the main span and through truss decks on the adjacent approach spans File:Columbus and Greenville Railway bridge over Yazoo River.jpg, A railway bridge with a
rail track A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleeper ...
in
Leflore County, Mississippi Leflore County is a county located in the U.S. state of Mississippi. As of the 2010 census, the population was 32,317. The county seat is Greenwood. The county is named for Choctaw leader Greenwood LeFlore, who signed a treaty to cede his p ...
File:Chevelon Creek Bridge.jpg, Chevelon Creek Warren Pony Truss Bridge,Chevelon Creek, Navajo County Arizona built 1913 File:Željeznički most, Mursko Središće.3.jpg, Side view of the iron truss railway bridge over Mura River in
Mursko Središće Mursko Središće ( hu, Muraszerdahely, Kajkavian: ''Mursko Središče'') is the northernmost town in Croatia, located at ( alt. 175 m) and one of the oldest localities in Međimurje County. Mursko Središće has a total population of 6,307, an ...
,
Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = " Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capi ...
File:Railroad Truss Drawbridge across Buffalo Bayou -- Houston.jpg, Railroad Truss Drawbridge across Buffalo Bayou—Houston


Multiple spans

Truss bridges consisting of more than one span may be either a continuous truss or a series of simple trusses. In the simple truss design, each span is supported only at the ends and is fully independent of any adjacent spans. Each span must fully support the weight of any vehicles traveling over it (the live load). In contrast, a continuous truss functions as a single rigid structure over multiple supports. This means that the live load on one span is partially supported by the other spans, and consequently it is possible to use less material in the truss. Continuous truss bridges were not very common before the mid-20th century because they are statically indeterminate, which makes them difficult to design without the use of computers. A multi-span truss bridge may also be constructed using
cantilever A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cant ...
spans, which are supported at only one end rather than both ends like other types of trusses. Unlike a continuous truss, a cantilever truss does not need to be connected rigidly, or indeed at all, at the center. Many cantilever bridges, like the Quebec Bridge shown below, have two cantilever spans supporting a simple truss in the center. The bridge would remain standing if the simple truss section were removed. File:Bally Bridge.jpg, A multi-span simple truss bridge,
Vivekananda Setu Vivekananda Setu (also called Willingdon Bridge and Bally Bridge) is a bridge over the Hooghly River in West Bengal, India. It links the city of Howrah, at Bally, to Kolkata, at Dakshineswar. Completed on 1931, it is a multispan truss bridge a ...
over the
Hooghly River The Bhagirathi Hooghly River (Anglicized alternatively spelled ''Hoogli'' or ''Hugli'') or the 'Bhāgirathi-Hooghly', called the Ganga or the Kati-Ganga in mythological texts, is the eastern distributary of the Ganges River in West Bengal, In ...
in
Kolkata Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, comme ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
. File:Kingston-Rhinecliff Bridge2.JPG, A continuous truss bridge,
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 ...
over the
Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...
in
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. File:Le pont de Québec, de l'embouchure de la rivière Chaudière.jpg, A cantilever truss bridge, Quebec Bridge over the
Saint Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connecting ...
in
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
.


Truss types used in bridges

Bridges are the most widely known examples of truss use. There are many types, some of them dating back hundreds of years. Below are some of the more common designs.


Allan truss

The Allan truss, designed by
Percy Allan Percy Allan (12 July 1861 – 7 May 1930) was a civil engineer who designed many public works in New South Wales, including the design of 583 bridges. Early life Allan was the son of Maxwell Rennie Allan, principal Under-Secretary of State ...
, is partly based on the Howe truss. The first Allan truss was completed on 13 August 1894 over Glennies Creek at Camberwell, New South Wales and the last Allan truss bridge was built over Mill Creek near Wisemans Ferry in 1929. Completed in March 1895, the Tharwa Bridge located at Tharwa, Australian Capital Territory, was the second Allan truss bridge to be built, the oldest surviving bridge in the
Australian Capital Territory The Australian Capital Territory (commonly abbreviated as ACT), known as the Federal Capital Territory (FCT) until 1938, is a landlocked federal territory of Australia containing the national capital Canberra and some surrounding township#Aust ...
and the oldest, longest continuously used Allan truss bridge. Completed in November 1895, the Hampden Bridge in
Wagga Wagga, New South Wales Wagga Wagga (; informally called Wagga) is a major regional city in the Riverina region of New South Wales, Australia. Straddling the Murrumbidgee River, with an urban population of more than 56,000 as of June 2018, Wagga Wagga is the state's ...
, Australia, the first of the Allan truss bridges with overhead bracing, was originally designed as a steel bridge but was constructed with timber to reduce cost. In his design, Allan used Australian ironbark for its strength. A similar bridge also designed by Percy Allen is the Victoria Bridge on Prince Street, Picton, New South Wales. Also constructed of ironbark, the bridge is still in use today for pedestrian and light traffic.


Bailey truss

The Bailey truss was designed by the British in 1940-1941 for military uses during World War II. A short selection of prefabricated modular components could be easily and speedily combined on land in various configurations to adapt to the needs at the site and allow rapid deployment of completed trusses. In the image, note the use of pairs of doubled trusses to adapt to the span and load requirements. In other applications the trusses may be stacked vertically, and doubled as necessary.


Baltimore truss

The Baltimore truss is a subclass of the Pratt truss. A Baltimore truss has additional bracing in the lower section of the truss to prevent buckling in the compression members and to control deflection. It is mainly used for rail bridges, showing off a simple and very strong design. In the Pratt truss the intersection of the verticals and the lower horizontal tension members are used to anchor the supports for the short-span girders under the tracks (among other things). With the Baltimore truss, there are almost twice as many points for this to happen because the short verticals will also be used to anchor the supports. Thus the short-span girders can be made lighter because their span is shorter. A good example of the Baltimore truss is the Amtrak Old Saybrook – Old Lyme Bridge in
Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the ...
, United States.


Bollman truss

The Bollman Truss Railroad Bridge at
Savage, Maryland Savage is an unincorporated community and census-designated place located in Howard County, Maryland, United States, approximately south of Baltimore and north of Washington, D.C. It is situated close to the city of Laurel and to the planne ...
, United States is the only surviving example of a revolutionary design in the history of American bridge engineering. The type was named for its inventor, Wendel Bollman, a self-educated
Baltimore Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was ...
engineer. It was the first successful all-metal bridge design (patented in 1852) to be adopted and consistently used on a railroad. The design employs
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
tension members and
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
compression members. The use of multiple independent tension elements reduces the likelihood of catastrophic failure. The structure was also easy to assemble. The
Wells Creek Bollman Bridge The Wills Creek Bollman Bridge originally served the Baltimore and Ohio Railroad's Pittsburgh Division main line. Designed by the self-taught civil engineer Wendel Bollman in 1871, this truss bridge is the last remaining span of the Pittsburgh Div ...
is the only other bridge designed by Wendel Bollman still in existence, but it is a Warren truss configuration.


Bowstring truss

The bowstring truss bridge was patented in 1841 by Squire Whipple. While similar in appearance to a
tied-arch bridge A tied-arch bridge is an arch bridge in which the outward horizontal forces of the arch(es) caused by tension at the arch ends to a foundation are countered by equal tension of its own gravity plus any element of the total deck structure such grea ...
, a bowstring truss has diagonal load-bearing members: these diagonals result in a structure that more closely matches a
Parker truss 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, o ...
or
Pratt truss 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 ...
than a true arch.


Brown truss

In the Brown truss all vertical elements are under tension, with exception of the end posts. This type of truss is particularly suited for timber structures that use iron rods as tension members.


Brunel truss

See
Lenticular truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
below.


Burr arch truss

This combines an arch with a truss to form a structure both strong and rigid.


Cantilever truss

Most trusses have the lower chord under tension and the upper chord under compression. In a cantilever truss the situation is reversed, at least over a portion of the span. The typical cantilever truss bridge is a "balanced cantilever", which enables the construction to proceed outward from a central vertical spar in each direction. Usually these are built in pairs until the outer sections may be anchored to footings. A central gap, if present, can then be filled by lifting a conventional truss into place or by building it in place using a "traveling support". In another method of construction, one outboard half of each balanced truss is built upon temporary falsework. When the outboard halves are completed and anchored the inboard halves may then be constructed and the center section completed as described above.


Fink truss

The Fink truss was designed by
Albert Fink Albert Fink (October 27, 1827 – April 3, 1897) was a German-born civil engineer who worked in the United States. He is best known for his railroad bridge designs, which helped revolutionize the use of iron for American railroad bridge constructi ...
of Germany in 1854. This type of bridge was popular with the
Baltimore and Ohio Railroad The Baltimore and Ohio Railroad was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. Merchants from Baltimore, which had benefited to some extent from the construction of ...
. The Appomattox High Bridge on the
Norfolk and Western Railway The Norfolk and Western Railway , commonly called the N&W, was a US class I railroad, formed by more than 200 railroad mergers between 1838 and 1982. It was headquartered in Roanoke, Virginia, for most of its existence. Its motto was "Precis ...
included 21 Fink deck truss spans from 1869 until their replacement in 1886. There are also inverted Fink truss bridges such as the Moody Pedestrian Bridge in Austin, Texas.


Howe truss

The Howe truss, patented in 1840 by
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millwright A millwright is a craftsperson or skilled tradesperson who installs, dismantles, maintains, repairs, reassembles, and moves machinery in factories, power plants, and construction sites. The term ''millwright'' (also known as ''industrial mecha ...
William Howe, includes vertical members and diagonals that slope up towards the center, the opposite of the
Pratt truss 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 ...
.Matsuo Bridge Company
Bridge Types – Truss
, accessed September 2007
In contrast to the Pratt truss, the diagonal web members are in compression and the vertical web members are in tension. Few of these bridges remain standing. Examples include
Jay Bridge Jay Bridge is a wooden covered bridge that spans the east branch of the Ausable River in Jay, Essex County, New York, USA. It is eligible to be listed in the National Register of Historic Places. Of the 29 covered bridges in New York State, it an ...
in
Jay, New York Jay is a town in Essex County, New York, United States. The population was 2,506 at the 2010 census. The town is named after John Jay, governor of New York when the town was formed. The town is on the northern border of Essex County and is south ...
;
McConnell's Mill Covered Bridge The McConnell's Mill Covered Bridge is an historic, wooden covered bridge that is located in Slippery Rock Township, Lawrence County, Pennsylvania, United States. It spans the Slippery Rock Creek in McConnells Mill State Park,Slippery Rock Township, Lawrence County, Pennsylvania Slippery Rock Township is a township in Lawrence County, Pennsylvania, United States. As of the 2020 census, the population was 2,913, a decline from the figure of 3,283 tabulated in 2010. History The township was linked to New Castle, Ell ...
;
Sandy Creek Covered Bridge Sandy Creek Covered Bridge State Historic Site is a publicly owned property in Jefferson County, Missouri, administered by the Missouri Department of Natural Resources, preserving the Sandy Creek Covered Bridge. The bridge is one of four remain ...
in
Jefferson County, Missouri Jefferson County is located in the eastern portion of the state of Missouri. It is a part of the St. Louis Metropolitan Area. As of the 2020 census, the population was 226,739, making it the sixth-most populous county in Missouri. Its county ...
; and Westham Island Bridge in
Delta, British Columbia Delta is a city in the Lower Mainland region of British Columbia, Canada, as part of Greater Vancouver. Located on the Fraser Lowland south of Fraser River's south arm, it is bordered by the city of Richmond on the Lulu Island to the north, N ...
, Canada. Image:Large Timber Howe Truss.jpg, A large timber Howe truss in a commercial building. Image:Jay Bridge interior.jpg,
Jay Bridge Jay Bridge is a wooden covered bridge that spans the east branch of the Ausable River in Jay, Essex County, New York, USA. It is eligible to be listed in the National Register of Historic Places. Of the 29 covered bridges in New York State, it an ...
showing the truss design. Image:Westham island bridge.jpg, Westham Island Bridge showing its wooden truss design.


K-truss

The K-truss is named after the ''K'' formed in each panel by the vertical member and two oblique members. Examples are the Südbrücke rail bridge over the River Rhine, Mainz, Germany, the bridge on I-895 (Baltimore Harbor Tunnel Thruway) in Baltimore, Maryland, the Long–Allen Bridge in
Morgan City, Louisiana Morgan City is a small Citibank, city in St. Mary Parish, Louisiana, St. Mary and lower St. Martin parishes in the U.S. state, U.S. State of Louisiana. The population was 12,404 at the 2010 United States Census, 2010 census. Known for being “rig ...
(Morgan City Bridge) with three 600-foot-long spans, and the Wax Lake Outlet bridge in Calumet, Louisiana


Kingpost truss

One of the simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support.


Lattice truss (Town's lattice truss)

This type of bridge uses a substantial number of lightweight elements, easing the task of construction. Truss elements are usually of wood, iron, or steel.


Lenticular truss

A lenticular truss bridge includes a lens-shape truss, with trusses between an upper chord (functioning as an arch) that curves up and then down to end points, and a lower chord (functioning as a suspension cable) that curves down and then up to meet at the same end points. Where the arches extend above and below the roadbed, it is called a lenticular pony truss bridge. The Pauli truss bridge is a specific variant of the lenticular truss, but the terms are not interchangeable. One type of lenticular truss consists of arcuate upper compression chords and lower
eyebar In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole ("eye") at each end for fixing to other components. Eyebars are used in structures such as bridges, in settings in which only tension, and ...
chain tension links.
Brunel Isambard Kingdom Brunel (; 9 April 1806 – 15 September 1859) was a British civil engineer who is considered "one of the most ingenious and prolific figures in engineering history," "one of the 19th-century engineering giants," and "one ...
's Royal Albert Bridge over the
River Tamar The Tamar (; kw, Dowr Tamar) is a river in south west England, that forms most of the border between Devon (to the east) and Cornwall (to the west). A part of the Tamar Valley is a World Heritage Site due to its historic mining activities. T ...
between
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devo ...
and
Cornwall Cornwall (; kw, Kernow ) is a Historic counties of England, historic county and Ceremonial counties of England, ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people ...
uses a single tubular upper chord. As the horizontal tension and compression forces are balanced these horizontal forces are not transferred to the supporting pylons (as is the case with most arch types). This in turn enables the truss to be fabricated on the ground and then to be raised by jacking as supporting masonry pylons are constructed. This truss has been used in the construction of a stadium, with the upper chords of parallel trusses supporting a roof that may be rolled back. The Smithfield Street Bridge in
Pittsburgh, Pennsylvania Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
, is another example of this type. An example of a lenticular pony truss bridge that uses regular spans of iron is the
Turn-of-River Bridge The Turn-of-River Bridge, also known as Old North Stamford Road Bridge, is a single-span lenticular pony truss bridge built by the Berlin Iron Bridge Company in 1892. It was listed on the National Register of Historic Places in 1987. It formerly ...
designed and manufactured by the Berlin Iron Bridge Co. The Pauli truss is a variant of the lenticular truss, "with the top chord carefully shaped so that it has a constant force along the entire length of the truss." It is named after , whose 1857 railway bridge (the ) spanned the
Isar The Isar is a river in Tyrol, Austria, and Bavaria, Germany, which is not navigable for watercraft above raft size. Its source is in the Karwendel range of the Alps in Tyrol; it enters Germany near Mittenwald and flows through Bad Tölz, Mu ...
near
Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the third-largest city in Germany, after Berlin and ...
. (''See also
Grosshesselohe Isartal station Großhesselohe Isartalbahn station (german: Großhesselohe Isartalbahnhof) is a station on the Isar Valley Railway from Munich to Bichl in the German state of Bavaria. Since 1981, it has been a station of the Munich S-Bahn. The station is locate ...
''.) The term Pauli truss is not interchangeable with the term lenticular truss and, according to Thomas Boothby, the casual use of the term has clouded the literature.


Long truss

The Long truss was designed by Stephen H. Long in 1830. The design resembles a Howe truss, but is entirely made of wood instead of a combination of wood and metal. The longest surviving example is the Eldean Covered Bridge north of Troy, Ohio, spanning . One of the earliest examples is the
Old Blenheim Bridge Old Blenheim Bridge was a wooden covered bridge that spanned Schoharie Creek in North Blenheim, New York, United States. With an open span of , it had the second longest span of any surviving single-span covered bridge in the world. The 1862 B ...
, which with a span of and a total length of long was the second-longest covered bridge in the United States, until its destruction from flooding in 2011. The Busching bridge, often erroneously used as an example of a Long truss, is an example of a Howe truss, as the verticals are metal rods.


Parker (camelback) truss

A Parker truss bridge is a Pratt truss design with a polygonal upper chord. A "camelback" is a subset of the Parker type, where the upper chord consists of exactly five segments. An example of a Parker truss is the
Traffic Bridge The Traffic Bridge is the name given to two truss bridges constructed across the South Saskatchewan River, connecting Victoria Avenue to 3rd Avenue South and Spadina Crescent in Saskatoon, Saskatchewan, Canada. The original bridge opened on ...
in
Saskatoon Saskatoon () is the largest city in the Provinces and territories of Canada, Canadian province of Saskatchewan. It straddles a bend in the South Saskatchewan River in the central region of the province. It is located along the Trans-Canada Hig ...
, Canada. An example of a camelback truss is the
Woolsey Bridge Woolsey Bridge (NRHP listed as Washington County Road 35 Bridge) was a truss bridge built in 1925, formerly located near West Fork, Arkansas. It carried County Route 35 over the West Fork of the White River for . It is listed on the National Reg ...
near
Woolsey, Arkansas Woolsey, Arkansas (formerly Woolseys, Arkansas) is an unincorporated community in Crawford Township, Washington County, Arkansas, United States."Feature Detail Report for: Woolsey, Arkansas." USGS. Retrieved October 5, 2010. It is located on U.S ...
.


Partridge truss

Designed and patented in 1872 by
Reuben Partridge Reuben L. Partridge (September 10, 1823 – July 17, 1900) was an American pioneer and engineer in Union County, Ohio, known locally as "The Bridge Builder". Early life Reuben Partridge was born September 10, 1823, in Wilmington, New York, to Cy ...
, after local bridge designs proved ineffective against road traffic and heavy rains.Kennedy, Willella Shearer. "Heritage: Being Little Stories of Union County". ''Union County Historical Society'', Printed by The Marysville Journal Tribune. 1963. Pg. 48. It became the standard for
covered bridge A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered woo ...
s built in central Ohio in the late 1800s and early 1900s.


Pegram truss

The Pegram truss is a hybrid between the Warren and Parker trusses where the upper chords are all of equal length and the lower chords are longer than the corresponding upper chord. Because of the difference in upper and lower chord length, each panel is not square. The members which would be vertical in a Parker truss vary from near vertical in the center of the span to diagonal near each end (like a Warren truss). George H. Pegram, while the chief engineer of Edge Moor Iron Company in Wilmington, Delaware, patented this truss design in 1885. The Pegram truss consists of a Parker type design with the vertical posts leaning towards the center at an angle between 60 and 75°. The variable post angle and constant chord length allowed steel in existing bridges to be recycled into a new span using the Pegram truss design. This design also facilitated reassembly and permitted a bridge to be adjusted to fit different span lengths. There are twelve known remaining Pegram span bridges in the United States with seven in Idaho, two in Kansas, and one each in California, Washington, and Utah.


Pennsylvania (Petit) truss

The Pennsylvania (Petit) truss is a variation on the
Pratt truss 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 ...
. The Pratt truss includes braced diagonal members in all panels; the Pennsylvania truss adds to this design half-length struts or ties in the top, bottom, or both parts of the panels. It is named after the
Pennsylvania Railroad The Pennsylvania Railroad (reporting mark PRR), legal name The Pennsylvania Railroad Company also known as the "Pennsy", was an American Class I railroad that was established in 1846 and headquartered in Philadelphia, Pennsylvania. It was named ...
, which pioneered this design. It was once used for hundreds of bridges in the United States, but fell out of favor in the 1930s, and very few bridges of this design remain. Examples of this truss type include the
Lower Trenton Bridge The Lower Trenton Toll Supported Bridge, commonly called the Lower Free Bridge, Warren Street Bridge or Trenton Makes Bridge, is a two-lane Pennsylvania (Petit) through truss bridge over the Delaware River between Trenton, New Jersey and Mor ...
in
Trenton, New Jersey Trenton is the capital city of the U.S. state of New Jersey and the county seat of Mercer County. It was the capital of the United States from November 1 to December 24, 1784. A Pratt truss includes vertical members and diagonals that slope down towards the center, the opposite of the Howe truss. The interior diagonals are under tension under balanced loading and vertical elements under compression. If pure tension elements are used in the diagonals (such as
eyebar In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole ("eye") at each end for fixing to other components. Eyebars are used in structures such as bridges, in settings in which only tension, and ...
s) then crossing elements may be needed near the center to accept concentrated live loads as they traverse the span. It can be subdivided, creating Y- and K-shaped patterns. The Pratt truss was invented in 1844 by Thomas and Caleb Pratt. This truss is practical for use with spans up to and was a common configuration for railroad bridges as truss bridges moved from wood to metal. They are Statically indeterminate, statically determinate bridges, which lend themselves well to long spans. They were common in the United States between 1844 and the early 20th century. Examples of Pratt truss bridges are the Governor's Bridge (Bowie, Maryland), Governor's Bridge in Maryland, Dearborn River High Bridge near Augusta, Montana, built in 1897, and the Fair Oaks Bridge in Fair Oaks, California, built 1907–09. The Scenic Bridge near Tarkio, Montana, is an example of a Pratt deck truss bridge, where the roadway is on top of the truss.


Queenpost truss

The queenpost truss, sometimes called "queen post" or "queenspost", is similar to a king post truss in that the outer supports are angled towards the center of the structure. The primary difference is the horizontal extension at the center which relies on Beam (structure), beam action to provide mechanical stability. This truss style is only suitable for relatively short spans.


Smith truss

The Smith truss, patented by Robert W Smith on July 16, 1867, has mostly diagonal criss-crossed supports. Smith's company used many variations of this pattern in the wooden covered bridges it built. While most all of the bridges built in the 19th century in the Jackson County, Ohio, area used the Smith truss design, the Johnson Road Covered Bridge is the last known surviving example in the state.


Thacher truss

The Thacher truss combines some of the characteristics of a
Pratt truss 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 ...
with diagonals under tension and of a Howe truss with diagonals under compression. It is quite rare.


Truss arch

A truss arch may contain all horizontal forces within the arch itself, or alternatively may be either a thrust arch consisting of a truss, or of two arcuate sections pinned at the apex. The latter form is common when the bridge is constructed as cantilever segments from each side as in the Navajo Bridge.


Vierendeel truss

The Vierendeel truss, unlike common pin-jointed trusses, imposes significant bending forces upon its members—but this in turn allows the elimination of many diagonal elements. It is a structure where the members are not triangulated but form rectangular openings, and is a frame with fixed joints that are capable of transferring and resisting bending moments. While rare as a bridge type due to higher costs compared to a triangulated truss, it is commonly employed in modern building construction as it allows the resolution of gross shear forces against the frame elements while retaining rectangular openings between columns. This is advantageous both in allowing flexibility in the use of the building space and freedom in selection of the building's outer curtain wall (architecture), curtain wall, which affects both interior and exterior styling aspects.


Waddell truss

Patented 1894 (); its simplicity eases erection at the site. It was intended to be used as a railroad bridge. One example was the Waddell "A" Truss Bridge (Parkville, Missouri).


Warren truss

The Warren truss was patented in 1848 by James Warren (engineer), James Warren and Willoughby Theobald Monzani, and consists of longitudinal members joined only by angled cross-members, forming alternately inverted Triangle, equilateral triangle-shaped spaces along its length, ensuring that no individual strut, beam, or Tie (engineering), tie is subject to bending or torsional straining forces, but only to tension or compression. Loads on the diagonals alternate between compression and tension (approaching the center), with no vertical elements, while elements near the center must support both tension and compression in response to live loads. This configuration combines strength with economy of materials and can therefore be relatively light. The girders being of equal length, it is ideal for use in prefabricated modular bridges. It is an improvement over the Neville truss which uses a spacing configuration of Triangle, isosceles triangles.


Whipple truss

A Whipple truss, named after its inventor Squire Whipple, is usually considered a subclass of the Pratt truss because the diagonal members are designed to work in tension. The main characteristic of a Whipple truss is that the tension members are elongated, usually thin, and at a shallow angle, and cross two or more bays (rectangular sections defined by the vertical members).


Wichert truss

The Wichert truss is a modified type of continuous truss which is statically determinate and helps avoid some of the other shortcomings of continuous trusses. It was patented in 1930 by Pittsburgh-based civil engineer Edward Martin Wichert (1883–1955). The defining feature of this truss type is a hinged Kite (geometry), kite-shaped section above each intermediate support. Only about ten Wichert truss bridges were ever built, mostly in Pennsylvania and Maryland. Of these, one of the best known is the Homestead Grays Bridge in Pittsburgh.


Truss bridge video

Driving across a truss bridge: The video shows the roadway perspective of a through truss bridge over the Willamette River in Harrisburg, Oregon, USA. The bridge features three simply supported Parker Truss spans.


References

*


Footnotes


External links


Bridge Basics – A Spotter's Guide to Bridge Design
– from Pghbridges.com – Illustrates many of the various types of truss arrangements used in bridges.
Historic Bridges of Michigan and Elsewhere
– Many photos of truss bridges are available on this informative and mainly truss-focused bridge website.
Historic Bridges of Iowa
– An illustrated list of different architectural bridge types found in Iowa, USA. Many of these are truss bridges.
Historic Bridges of the U.S.
– An enormous database of historic bridges. Over 17,400 truss bridges are listed here.
Iron and Early Steel Bridges of Ohio
A comprehensive inventory of all remaining truss bridges in Ohio. Includes maps, photos, and invites visitor assistance in identifying extant or demolished bridges.
Matsuo Bridge Company: Bridge Types – Truss

Management Plan for Historic Bridges in Virginia: The 2017 Update
��Virginia Department of Transportation's plan for managing its historic bridges, including metal truss bridges. The update includes sections on study findings such as "General Issues Regarding Metal and Metal Truss Bridges (Including Potential Life Span)," "Coatings Issues for Metal Truss Bridges: Painting, Metallizing, and Galvanizing," and "Truss Bridge Capacity and Overloading Potential."
structurae.de
The Structurae database on bridges. {{Authority control Bridges by structural type Truss bridges, Articles containing video clips