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, 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 and the oldest, longest continuously used Allan truss bridge. Completed in November 1895, the
Hampden Bridge in
Wagga Wagga, New South Wales, 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. in France
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, United States.
Bollman truss ; built in 1869, it was moved to Savage in 1887 and has been in continuous use since as a pedestrian bridge. The
Bollman Truss Railroad Bridge at
Savage, Maryland, United States is the only surviving example of a revolutionary design in the history of American bridge engineering. The type was named after its inventor,
Wendel Bollman, a self-educated
Baltimore 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 tension members and
cast iron compression members. The use of multiple independent tension elements reduces the likelihood of catastrophic failure. The structure was also easy to assemble.
Wells Creek Bollman Bridge is the only other bridge designed by Wendel Bollman still in existence, but it is a Warren truss configuration.
Bowstring truss , Canada The
bowstring truss bridge was patented in 1841 by
Squire Whipple. While similar in appearance to a
tied-arch bridge, a bowstring truss has diagonal load-bearing members: these diagonals result in a structure that more closely matches a
Parker truss or
Pratt truss 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 below.
Burr arch truss , a
Burr Arch Truss in
Lancaster County, Pennsylvania This combines an arch with a truss to form a structure both strong and rigid.
Cantilever truss , crossing the
Firth of Forth in eastern Scotland 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 (half span and cross section) The
Fink truss was designed by
Albert Fink of Germany in 1854. This type of bridge was popular with the
Baltimore and Ohio Railroad. The
Appomattox High Bridge on the
Norfolk and Western Railway 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 with diagonals under compression under balanced loading The
Howe truss, patented in 1840 by
Massachusetts millwright William Howe, includes vertical members and diagonals that slope up towards the center, the opposite of the
Pratt truss. 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 in
Jay, New York;
McConnell's Mill Covered Bridge in
Slippery Rock Township, Lawrence County, Pennsylvania;
Sandy Creek Covered Bridge in
Jefferson County, Missouri; and
Westham Island Bridge in
Delta, British Columbia, Canada. Image:Large Timber Howe Truss.jpg|A large timber Howe truss in a commercial building. Image:Jay Bridge interior.jpg|
Jay Bridge showing the truss design. Image:Westham island bridge.jpg|
Westham Island Bridge showing its wooden truss design.
K-truss K-truss in
Baltimore The
K-truss is named after the
K formed in each panel by the vertical member and two oblique members. Examples include 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 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. , a lattice truss
Lenticular truss , built in 1883 by
Berlin Iron Bridge Co., is the longest lenticular truss bridge in the United States with five spans, and the second-oldest lenticular truss bridge in
Massachusetts. 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. with the upper chords of parallel trusses supporting a roof that may be rolled back. The
Smithfield Street Bridge in
Pittsburgh, Pennsylvania, 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 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." The truss consists of parallel timber chords, vertical posts, and diagonal braces tightened into compression by adjustable wedges at the joints. Unlike the later
Howe truss, which employed iron vertical tension rods and mechanically defined pinned connections, the Long truss relied entirely on timber members and force transfer through bearing at shouldered joints. Historically, the Long truss represents a transitional stage in American bridge engineering between empirically proportioned timber systems such as the
Town lattice truss and the hybrid timber–iron trusses that emerged in the 1840s. Surviving examples are documented by the
Historic American Engineering Record and remain an important part of early covered-bridge preservation scholarship.
Parker (camelback) truss , a 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 in
Saskatoon, Canada. An example of a camelback truss is the
Woolsey Bridge near
Woolsey, Arkansas.
Partridge truss Designed and patented in 1872 by
Reuben Partridge, after local bridge designs proved ineffective against road traffic and heavy rains. It became the standard for
covered bridges 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, similar to 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 is an example of Pennsylvania Petit truss bridge. The
Pennsylvania (Petit) truss is a variation on the
Pratt truss. 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, 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 examples of this design remain. Examples of this truss type include the
Lower Trenton Bridge in
Trenton, New Jersey, the
Fort Wayne Street Bridge in
Goshen, Indiana, the
Schell Bridge in
Northfield, Massachusetts, the
Inclined Plane Bridge in
Johnstown, Pennsylvania, the
Easton–Phillipsburg Toll Bridge in
Easton, Pennsylvania, the Boston and Maine Connecticut River Rail Bridge in
Brattleboro, Vermont, the
Metropolis Bridge in
Metropolis, Illinois, and the
Healdsburg Memorial Bridge in
Healdsburg, California.
Post truss A
Post truss is a hybrid between a Warren truss and a double-intersection Pratt truss. Invented in 1863 by Simeon S. Post, it is occasionally referred to as a
Post patent truss although he never received a patent for it. The
Ponakin Bridge and the
Bell Ford Bridge are two examples of this truss.
Pratt truss A
Pratt truss includes vertical members and diagonals that slope down towards the center, the opposite of the
Howe truss. the
Hayden RR Bridge in
Springfield, Oregon, built in 1882; the
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 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 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. The
Pacific Bridge Company of Alameda, California was an early manufacturer of bridge kits based on the Smith design. The pre-manufactured kits were designed to be assembled on-site, and most were covered. One of the truss-bridge kits, sold in 1871 to the
California Powder Works near Santa Cruz, California, remains in use. 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 with diagonals under tension and of a
Howe truss with diagonals under compression, which is 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, 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 in
Parkville, Missouri.
Warren truss The
Warren truss was patented in 1848 by
James Warren and Willoughby Theobald Monzani, and consists of longitudinal members joined only by angled cross-members, forming alternately inverted
equilateral triangle-shaped spaces along its length, ensuring that no individual
strut, beam, or
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
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). An example of the double-intersection Whipple truss is
Bridge L-158 in
Golden's Bridge, New York. , a double-intersection Whipple rail truss over the
Muscoot Reservoir in
Golden's Bridge, New York Wichert truss over the
Monongahela River in
Pittsburgh 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-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. ==Video==