Types of trusses used in bridges
Los puentes son los ejemplos más conocidos del uso de celosías. Hay muchos tipos de celosía, algunos datados hace cientos de años atrás. A continuación se muestran algunos de los diseños más comunes.
Allan Lattice
The Allan truss was devised by the Australian civil engineer Percy Allan (1861–1930), designer of 583 bridges, mostly in New South Wales. The truss is essentially a Howe truss in which bars have been arranged in St. Andrew's crosses in the central span or spans.
The first Allan truss bridge was completed on 13 August 1894 over Glennies Creek in Camberwell, New South Wales and the last Allan Bridge was built over Mill Creek near Wisemans Ferry in 1929. Completed in March 1895, the Tharwa Bridge, located at Tharwa in the Australian Capital Territory, was the second Allan truss bridge to be built. and is the oldest surviving bridge in the Australian Capital Territory and the oldest continuously used Allan Bridge. Completed in November 1895, the Hampden Bridge in Wagga Wagga, New South Wales, the first of the air-braced Allan truss bridges, was originally designed as a bridge. steel but was built from wood to reduce cost. In his design Allan used Australian ironbark to strengthen it. A similar bridge also designed by Percy Allen is the Victoria Bridge (in Prince Street, Picton, New South Wales). Also built from ironbark, the bridge is still in use today for pedestrian and light traffic.
Bailey Bridge
A Bailey bridge is a prefabricated portable bridge designed in 1941 for military use by the English civil engineer Donald Coleman Bailey") (1901–1985) as a solution to the increased weight of new tanks that were being developed in the early phases of World War II. This invention is considered one of the best examples of military engineering during World War II. It was used to bridge spans of up to 60 meters and allowed the circulation of vehicles weighing up to 70 tons. Its assembly did not require special tools. or heavy equipment, lasted just a few hours and could be carried out even under enemy fire. The British army established itself in Italy and northern Europe.[10]
The bridge is assembled like a meccano by assembling elements about 3 m long, easily transportable by truck and moved by 1, 2, 4 (202 kg) or 6 people (272 kg). It was mounted on the shore on rails, twice the length necessary to prevent overturning, and then pushed on the rails to the intended location. The excess part was dismantled after laying. Two hours were enough for 40 sappers to install a basic structure 24 meters long. Prefabricated and standardized truss elements can be easily combined into various configurations to suit site needs.
In the images below, note the use of bent trusses to accommodate span and load requirements. In other applications, the louvers can be stacked vertically.
Baltimore Lattice
The Baltimore truss, a subclass of the Pratt truss, has additional bracing in the lower section of the truss to prevent buckling in the compression bars and to control deformation. It is mainly used for railway bridges, having proven to be a simple but very robust design. In the Pratt truss, the intersections of the vertical uprights and the lower horizontal chord are used to anchor the supports of the short joists below the rails (among other things). With the Baltimore lattice, there are almost twice as many points to anchor since short vertical bars can also be used. Therefore, short joists can be made lighter because their span is shorter.
Bollman Lattice
The Bollman truss railroad bridge at Savage, Maryland, Maryland, is the only remaining example of a revolutionary design in the history of American bridge engineering. The type was named for its inventor, Wendel Bollman, a self-taught engineer from Baltimore. It was the first successful all-metal bridge design (patented in 1852) to be adopted and used consistently to support a railroad line. The design employed wrought iron tensile members and cast iron compressed members. The use of multiple independent tensile members reduced the likelihood of a catastrophic collapse. The structure was also easy to put together.
The Bollman (Wells Creek Bridge) is the only bridge designed by Wendel Bollman that still exists, but it has a Warren truss configuration.
Arch cord lattice
The bowstring arch truss was patented in 1841[11] by Squire Whipple.[12] Although similar in appearance to a cable-stayed arch bridge, the bowstring truss is a truss as such, and therefore its diagonals are load-bearing. These diagonals result in a structure that more closely resembles a Parker lattice or a Pratt lattice than a true arch.
Brown Lattice
A Brown truss is a truss used in primarily wooden bridges with metal only in the bars in tension. It was used in the first covered bridges in the United States, notable for its economical use of materials. It is named after its inventor, Josiah Brown Jr., of Buffalo, New York ("New York (state)"), who patented it on July 7, 1857 (US patent 17,722). of Fallasburg"), Whites Bridge") and another. The design did not seem to gain wide acceptance, as modern bridges tend to be Howe, Pratt, bowstring, or Warren.
The Brown truss is a through-box design (in contrast to the board truss) and consists of compressed diagonals connected to upper and lower horizontal stays.[16] There may be vertical or near-vertical tension bars (the diagram shows these bars, whereas the patent application diagram did not) but there are no compressed vertical bars. In practice, when used on a covered bridge, the most common application, the truss is protected with an outer covering.
The floor and ceiling are also lattices, but they are horizontal and serve to give rigidity to the framework. The bottom parts of the diagonals tend to protrude below the siding. The Brown lattice is characterized by the economy of materials, since it can be built with very little metal.[17].
Brunel lattice
See Lenticular lattice below.
Burr Arch Lattice
The Burr arch truss, or simply, Burr truss or Burr arch, is a combination of an arch and a multi-truss kingpost design. It was invented in 1804 by Theodore Burr"),[18] patented on April 3, 1817,[19] and used in bridges, generally covered bridges.[20][21].
The design principle behind the Burr arch truss is that the arch must be able to support the entire load of the bridge, while the truss keeps the bridge rigid. Although the kingpost truss alone is capable of supporting a load, it is impossible to uniformly balance a dynamic load crossing the bridge between the two parts.[22] The opposite approach is also held, based on computer models, that the truss carries the majority of the load and the arch provides the stability.[18] In any case, the combination of the arch and truss provides a more stable bridge capable of supporting a greater weight than the arch or truss alone.
The state of Indiana has a large collection of Burr bridges, as of the 92 historic bridges 53 are Burr trusses, many of them in Parke County.
Bracket or cantilever lattice
Most trusses have the bottom chord under tension and the top chord under compression. In a cantilever truss, the situation is reversed, at least in part of the span. The typical cantilever truss bridge is a "balanced cantilever," which allows construction to proceed outward from a central vertical mast in each direction. These are usually built in pairs until the outer sections can be anchored to the footings. The center gap, if present, can be completed by erecting a conventional truss already manufactured or by constructing it in place using a "shift bracket." Other construction methods balance the outer half of each truss with temporary shoring. When the outer halves are completed and the inner halves are anchored, the center section can be constructed as described above.
Fink Lattice
The Fink truss was designed by German-born civil engineer Albert Fink (1827–1897) and was patented in 1854. It was commonly used in residential houses and less so in bridge architecture,[23] its origin, although its current use in bridges is rare.
Albert Fink designed his truss bridges for several American railroads, especially the Baltimore and Ohio and the Louisville and Nashville railroads. The 1865 Annual Report of the President and Directors of the Louisville and Nashville Railroad Company lists 29 Fink bridges out of a total of 66 bridges on the railroad. The first Fink Bridge was built by the Baltimore and Ohio Railroad in 1852 to span the Monongahela River at Fairmont "Fairmont (West Virginia)", Virginia (now West Virginia). It consisted of three sections, each 205 feet long. It was the longest iron railroad bridge in the United States at the time. Other Fink trusses were also world records of their time, such as the bridge over the Green River&action=edit&redlink=1 "Green River (Kentucky) (not yet written)") (circa 1858) that supported the Louisville and Nashville Railroad across the river of the same name near Munfordville, Kentucky, and the first bridge over the Ohio River, which spanned 396 feet built between 1868 and 1870.[24] Although the design is no longer used for major structures, it was widely used from 1854 to 1875.[25].
It is identified by the presence of multiple diagonal bars descending from the top of the posts at a variety of angles. These diagonal bars extend to the bottom of each of the vertical bars of the lattice, with the longest diagonal going to the central vertical bar.[26].
Many Fink trellises do not include a bottom chord. This gives the bridge an unfinished sawtooth appearance when viewed from the side or from below, and makes the design very easy to identify. If the bridge deck is arranged at the bottom of the truss (called a through truss) or has a light bottom chord, identification is made solely by the multiple diagonal bars extending from the tops of the end post.
An inverted Fink truss has a bottom chord without the top chord, like the Moody Pedestrian Bridge in Austin, Texas.
Howe Lattice
The relatively rare Howe truss, patented in 1840 by Massachusetts machinist William Howe&action=edit&redlink=1 "William Howe (architect) (not yet drafted)"), includes vertical and diagonal members that slope toward the center, the opposite of the Pratt truss.[27] In contrast to the Pratt truss, the diagonals are compressed and the vertical band members are in tension. Examples are the Jay Bridge in Jay, New York, and the Sandy Creek Covered Bridge in Jefferson County, Missouri.
Lattice K
A "K" truss derives its name because the truss forms that letter by the orientation of the vertical mullions and the two oblique diagonals in each panel. The K truss design was a variant of the Parker truss, in turn, derived from the Pratt. The idea of the K truss is to divide the vertical uprights into smaller sections, which, since they work under compression, will be able to resist more due to the significant reduction in buckling. The K lattice, probably due to its complexity, did not become very popular either in the United States or the rest of the world. Although riveted and with a curved top chord, the K truss became a familiar sight on main roads, with span lengths varying from 40 to 70 m. The builders also liked how secondary stresses were reduced and the task of erecting a large bridge in the countryside was simplified.
The K lattice allows the cords to be further distanced, which means an increase in the spans to be saved and has sometimes been used in the highest sections of complex lattices. The famous Quebec Bridge over the St. Lawrence River in 1917 first demonstrated the value and possibilities of this design.
Examples are the Südbrücke railway bridge over the Rhine in Mainz, Germany and the I-895 (Baltimore Harbor Tunnel Thruway) in Baltimore, Maryland.
Kingpost and Queenpost louvers
The Kingpost truss is used in architecture for simple deck trusses and short-span bridges (a bridge requires two trusses on each side, with the traffic platform between them). It is the simplest form of lattice that is constructed with the fewest number of bars (whether made of wood or metal). Simple triangular in shape, usually composed of wood with iron fittings, divided by a single vertical post connecting the upper and lower chords. Easy to shape and sufficiently rigid at small crossings, the type remained an option as a steel bridge well into the century.
The name "royal post" (or king post, in English: king-post, kingpost) is that of the central vertical post used in roof trusses, which works in tension to help support a beam arranged under it. (If inverted, you would have a "crown post" that although visually similar, the post works compressed). Sometimes it is called an A-shaped lattice, and in Spanish, a truss with the same shape (used on roofs) is called a simple truss, pendolón truss, pendolón scissors, par knife and pendolón or simple pendolón knife.
The queen post lattice (queen post or queenspost), is similar to a king post lattice with two vertical posts.[28] The outer bars are angled toward the center of the structure. The main difference is the horizontal extension in the center that links to the beam and provides mechanical stability. This lattice, which can span longer spans than the king post, is still only suitable for relatively short spans.[29].
Pont-y-Cafnau") (1793), the first iron railway bridge in the world, is of the Kingpost type.
Network Lattice (or Town Network Lattice)
This type of bridge uses a substantial amount of lightweight elements, which makes the construction task easier. The lattice elements are usually made of wood, iron or steel.
Lenticular lattice
A lenticular truss bridge comprises a lens-shaped truss, with trusses between an upper arch (curving up and then down to the other end), and a lower arch (curving down and then up to the other end) to meet at the same end points. When the arches extend above and below the deck, it is a lenticular pony truss bridge, as the truss is so low that top bracing cannot be used. An example of a lenticular pony bridge that uses regular iron spans is the Turn-of-River Bridge (designed and manufactured by the Berlin Iron Bridge Co.). Lenticular trusses were patented in the USA in 1878 by William Douglas, although they had already been used in Europe: the Gaunless Bridge) of 1823 can be considered the first of its kind.
A lenticular lattice consists of compression-arched top chords and tensile bottom links of eyebar chain (a vertical metal bar that has a closed loop at one or both ends). The Royal Albert Bridge (United Kingdom) uses a single tubular top strand. When the horizontal forces of tension and compression are balanced, these horizontal forces are not transferred to the supporting turrets (as is the case with most types of arches). This, in turn, allows the truss to be fabricated on the ground and then jacked up while the supporting masonry pylons are constructed. This lattice has been used in the construction of some stadiums,[30] with the upper chords of the parallel lattices supporting a retractable cover. The Smithfield Street Bridge") (1883) in Pittsburgh&action=edit&redlink=1 "Pittsburgh (Pennsylvania) (not yet redacted)"), Pennsylvania, is another example of this type.
Long Lattice
Designed by Stephen H. Long in 1830, its configuration resembles that of a Howe truss, but is made entirely of wood rather than a combination of wood and metal. The oldest surviving example is the Eldea Covered Bridge north of Troy, Ohio, which has a span of 68.2 m.
One of the earliest examples is the Old Blenheim Bridge"), which with a span of 64.0 m and a total length of 70.7 m long was the second longest covered bridge in the United States, until it was destroyed by floods in 2011. The Busching Bridge, often mistakenly used as an example of a Long truss is an example of a Howe truss, as the vertical stiles are metal profiles.[33] A Long truss has the stiles. wooden verticals.
Parker lattice (camelback)
A Parker truss bridge is a Pratt truss design with a polygonal top chord. A "camelback" is a subset of the Parker type, in which the top cord consists of exactly five segments. An example of a Parker truss is the Traffic Bridge&action=edit&redlink=1 "Traffic Bridge (Saskatoon) (not yet drafted)") in Saskatoon, Canada. An example of a camelback truss is the Woolsey Bridge") near Woolsey&action=edit&redlink=1 "Woolsey (Arkansas) (not yet redacted)"), Arkansas.
Pegram Lattice
The Pegram truss is a hybrid between the Warren and Parker trusses, in which the upper chord sections are all of equal length and the corresponding lower chord sections are longer. Due to this difference in length, the cloths are not square. The mullions that would be vertical in a Parker truss vary from nearly vertical in the center of the span, to being diagonal near each end (as in a Warren truss). George H. Pegram"), while chief engineer of the Edge Moor Iron Company in Wilmington, Delaware, patented this lattice design in 1885.
The Pegram truss consists of a Parker-type design with the vertical uprights inclined towards the center at an angle varying between 60 and 75°. The variable rear angle and constant chord length allowed the steel from the existing bridges to be recycled into a new span using the Pegram truss design. This design also facilitated reassembly and allowed a bridge to be adjusted to accommodate different span lengths. There are twelve known Pegram span bridges in the United States, seven in Idaho, two in Kansas, and one each in California, Washington, and Utah.
Pennsylvania Lattice (or Petit)
The Pennsylvania (or Petit) truss is a variation of the Pratt truss.[34] The Pratt truss includes braced diagonal bars in all spans; The Pennsylvania lattice adds half-length struts or braces to this design at the top or bottom or both sides of the panels. It is named after the Pennsylvania Railroad"), which pioneered this design. It was used on hundreds of bridges in the United States, but fell out of favor in the 1930s, and very few bridges with this truss remain today. Examples include the Lower Trenton Bridge, in Trenton, New Jersey, and the Schell Bridge, 1903, in Northfield, Massachusetts. (Massachusetts)"), the Inclined Plane Bridge") (1891), at Johnstown, Pennsylvania "Johnstown (Pennsylvania)") and the Healdsburg Memorial Bridge") (1921), at Healdsburg, California) "Healdsburg (California)").
Lattice Post
A Post truss is a hybrid between a Warren truss and a double-intersecting Pratt truss. Invented in 1863 by Simeon S. Post"), it is occasionally known as the Post patent truss, although he never received a patent for it.[36] The Ponakin Bridge") and the Bell Ford Bridge") are two examples of this truss.
Pratt Lattice
A Pratt truss includes vertical and diagonal members that slope downward and toward the center, unlike the Howe truss.[27] When the truss is subjected to balanced loads, the interior diagonals are in tension and the vertical members are in compression. If pure tension members are used on diagonals (such as eye bars), crosses may be needed near the center to support concentrated live loads as they traverse the span. They can be subdivided, creating Y-shaped and K-shaped patterns. The Pratt truss was invented in 1844 by Thomas and Caleb Pratt.[37] This truss is practical for spans of up to ones and was a common configuration for railroad bridges as truss bridges abandoned wood in favor of metal. They are statically determined bridges, which lend themselves well to long spans. They were common in the United States between 1844 and the beginning of the century.[37].
Examples of Pratt truss bridges are the Governor's Bridge &action=edit&redlink=1 "Governor's Bridge (Maryland) (not yet drafted)"), in Maryland,[37] the Dearborn River Bridge") near Augusta "Augusta (Montana)"), Montana, built in 1897, and the Fair Oaks Bridge in Fair Oaks "Fair Oaks (California)"), California, built 1907-1909.
The Scenic Bridge near Tarkio, Montana is an example of a Pratt deck truss bridge, in which the road runs along the top of the truss.
Thatcher lattice
The Thatcher truss combines some of the characteristics of a Pratt truss with tensioned diagonals and a Howe truss with compressed diagonals. It's quite rare.
Arch lattice
A lattice arch may contain all horizontal forces within the arch itself, or alternatively, it may be a thrust arch consisting of a lattice, or of two arched sections interlocking at the apex. The latter form is common when the bridge is built as segments cantilevered from each side as on the Navajo Bridge.
Vierendeel Lattice
The first characteristic of the Vierendeel lattice is that it does not have diagonal bars in its panels. The deformation of Vierendeel bridges is, as a rule, lower than that of other bridges with the same span "Span (engineering)"). It owes its name to the surname of the Belgian engineer Arthur Vierendeel who patented it. This type of bridge became very popular in the first third of the century, with numerous examples in Belgium (as well as in the Belgian Congo), either by Arthur himself or by some of his students. Vierendeel mentions his system for the first time in public at the Congrès International des Architectes held in August 1897 in Brussels. They were then applied in other countries. It is characterized by its completely rectangular mesh structure, with parallel chords (that is, without diagonal crossbars between its openings). It was initially used as a structure for railway transit.
The Vierendeel truss, unlike common articulated trusses, imposes significant bending forces on its bars, but this in turn allows the elimination of all diagonals. It is a structure without triangulations, with panels that form rectangular openings, and it is a frame with fixed joints that are capable of transferring and resisting bending moments. Although rare as a type of bridge due to higher costs compared to a triangular truss, it is commonly employed in modern building construction as it allows the resolution of gross shear forces against the frame members while preserving rectangular openings between columns. This is advantageous both in allowing flexibility in the use of building space and freedom in the selection of the building's exterior curtain wall, affecting aspects of interior and exterior style.
Waddell Lattice
Patented in 1894 (USPTO Patent No. 529220) by American civil engineer John Alexander Low Waddell" (1854 – 1938), its simplicity facilitates on-site erection. It was intended to be used as a railroad bridge.
Warren Lattice
The Warren truss consists of longitudinal bars joined only by angled transverse bars, forming equilateral triangles along the entire length, alternately supported on the base and inverted, ensuring that no individual strut, beam or brace is subject to bending or torsional stresses, but only to tension or compression. Loads on the diagonals alternate between compression and tension (approaching the center), with no vertical members, while members near the center must support both tension and compression in response to live loads. This configuration combines high rigidity with economy of materials and can therefore be relatively light. Since beams are of the same length, it is ideal to be used in prefabricated modular bridges.
The Warren lattice was patented in 1848 by English engineers James Warren "James Warren (engineer)") (1806–1908) and Willoughby Theobald Monzani. The first suspension bridge to use a Warren truss as deck support was the Manhattan Bridge (1909) in New York City.[38].
It is an improvement over the Neville lattice which uses an isosceles triangle spacing configuration.
A variant of the Warren truss has additional vertical uprights in the triangles.[39] These are used when the lengths of the upper horizontal bars would become so long as to present a risk of buckling. These vertical uprights do not carry a large proportion of loads, and act primarily to stabilize the horizontal members against buckling.
Whipple Lattice
The Whipple truss, named after its inventor Squire Whipple, an American civil engineer (1804 – 1888), is generally considered a subclass of the Pratt truss because the diagonal bars are designed to work in tension. The main feature of a Whipple truss is that the tension bars are elongated, usually thin, and at a shallow angle, and cross two or more spans (rectangular sections defined by vertical stiles).