A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch(es) are borne as tension by a chord tying the arch ends rather than by the ground or the bridge foundations. This strengthened chord may be the deck structure itself or consist of separate, independent tie-rods.
Thrusts downwards on a tied-arch bridge deck are translated, as tension, by vertical ties between the deck and the arch, tending to flatten it and thereby to push its tips outward into the abutments, like for other arch bridges. However, in a tied-arch or bowstring bridge, these movements are restrained not by the abutments but by the strengthened chord, which ties these tips together, taking the thrusts as tension, rather like the string of a bow that is being flattened. Therefore, the design is also called a bowstring-arch or bowstring-girder bridge. [1] [2]
The elimination of horizontal forces at the abutments allows tied-arch bridges to be constructed with less robust foundations; thus they can be situated atop elevated piers or in areas of unstable soil. [3] In addition, since they do not depend on horizontal compression forces for their integrity, tied-arch bridges can be prefabricated offsite, and subsequently floated, hauled or lifted into place. Notable bridges of this type include the Fremont Bridge in Portland, Oregon and the first "computer-designed" bridge of this type, the Fort Pitt Bridge in Pittsburgh, Pennsylvania. [4]
Both the tied-arch bridge and the self-anchored suspension bridge place only vertical loads on the anchorage, and so are suitable where large horizontal forces are difficult to anchor.
Some tied-arch bridges only tie a segment of the main arch directly and prolong the strengthened chord to tie to the top ends of auxiliary (half-)arches. The latter usually support the deck from below and join their bottom feet to those of the main arch(es). The supporting piers at this point may be slender, because the outward-directed horizontal forces of main and auxiliary arch ends counterbalance. The whole structure is self-anchored. Like the simple case it exclusively places vertical loads on all ground-bound supports.
An example is the Fremont Bridge in Portland, Oregon which is the second-longest tied-arch bridge in the world and also classifies as a through arch bridge. The Chaotianmen Bridge in Chongqing is a tied-arch, through arch and a truss arch bridge.
Contrarily, the Hart Bridge uses a cantilevered trussed arch, it is self-anchored, but its arch is non-tied. In particular the bridge deck is suspended, but does not tie the arch ends.
Tied arch bridges may consist of successively lined up tied arches in places where a single span is not sufficient. An example for this is the Godavari Arch Bridge in Rajahmundry, India. It has four separate supports on each pier and carries the South Central Railway Line of India. It was designed for 250 km/h rail services.
Like for multi-span continuous beam bridges the tying chord continually spans over all piers. The arches feet coincide (fuse) at the bridge piers. A good visual indication are shared supports at the piers. Dynamic loads are distributed between spans.
This type may be combined with the shouldered tied-arch design discussed above. An example for this is Dashengguan Bridge in Nanjing, China. Its two main arches are shouldered by short auxiliary arches. It is both, a (rigid) tied-arch and a cantilevered trussed arch design. Because the traffic runs through the structural envelope, it is also a through arch bridge. Guandu Bridge in New Taipei, Taiwan is a non-trussed example with three main arches augmented by two auxiliary arch segments at the bridge portals.
The Infinity Bridge uses two arches of different height and span length that both bifurcate before their apex. Above its single, middle-displaced river pier the deck lies between the arches. Contrarily each abutment on the riverbanks supports a single arch end only, in the middle of the deck. The tying chord(s) consist of a composite deck structure. Four post tensioned coil steel cables, two to each side of the walking deck, are locked in place by orthogonally run steel beams every 7.5 meters. The hangers are joined to each of these beams between each cable pair. Since the beams extend the width of the post-tensioned concrete deck, the tensing cable pairs remain visible.
A close-up of the river pier shows that the structural dead load is tied per span: The larger arch span uses thicker tensing cables and the reflex segments are not suspended from, but supported by steel beams, essentially completing the arches at the river pier. However, for dynamic and non-uniform loads the visually defining arch continuations must not be neglected. [5]
Usually, for a single span, two tied-arches are placed in parallel alongside the deck, so the deck lies in between the arches. Axial tied-arch or single tied-arch bridges have at most one tied-arch per span that is usually centered in the middle of the bridge deck. [6] An example for this is Hoge Brug in Maastricht. Since it has hinged hangers it might also classify as a Nielsen bridge who held a patent on tied-arch bridges with hinged hangers from 1926.
Some designs tilt the arches outward or inward with respect to the axis running along the bridge deck.
In analogy to twin bridges, two tied arch bridges erected side by side to increase traffic capacity, but structurally independent, may be referred to by tied arch twin bridges. Each in return may use a single- or multi-span, discrete or continuous tied-arch design.
A bowstring truss bridge is similar in appearance to a tied-arch; however, the bowstring truss behaves as truss, not an arch. The visual distinction is a tied-arch bridge will not have substantial diagonal members between the vertical members.
In a 1978 advisory issued by the Federal Highway Administration (FHWA), the FHWA noted that tied-arch bridges are susceptible to problems caused by poor welds at the connection between the arch rib and the tie girders, and at the connection between the arch and vertical ties. In addition, problems with electroslag welds, while not isolated to tied-arch bridges, resulted in costly, time-consuming and inconveniencing repairs. The structure as a whole was described as nonredundant: failure of either of the two tie girders would result in failure of the entire structure. [7]
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side, and partially into a vertical load on the arch supports. A viaduct may be made from a series of arches, although other more economical structures are typically used today.
A truss is an assembly of members such as beams, connected by nodes, that creates a rigid structure.
A cantilever bridge is a bridge built using structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete.
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 sometimes both in response to dynamic loads. There are several types of truss bridges, including some with simple designs that were among the first bridges designed in the 19th and early 20th centuries. A truss bridge is economical to construct primarily because it uses materials efficiently.
A self-anchored suspension bridge is a suspension bridge type in which the main cables attach to the ends of the deck, rather than directly to the ground or via large anchorages. The design is well-suited for construction atop elevated piers, or in areas of unstable soils where anchorages would be difficult to construct.
Beam bridges are the simplest structural forms for bridge spans supported by an abutment or pier at each end. No moments are transferred throughout the support, hence their structural type is known as simply supported.
A plate girder bridge is a bridge supported by two or more plate girders.
Hampden Bridge is a heritage-listed single-span suspension bridge that carries Moss Vale Road (B73) across the Kangaroo River, in Kangaroo Valley, in the City of Shoalhaven local government area of New South Wales, Australia. The bridge was designed by Ernest de Burgh and built by Loveridge and Hudson. The property is owned by Transport for NSW. It was added to the New South Wales State Heritage Register on 2 August 2019.
A girder bridge is a bridge that uses girders as the means of supporting its deck. The two most common types of modern steel girder bridges are plate and box.
La Vicaria Bridge is a through arch bridge that spans the Segura River, where it meets La Fuensanta Reservoir near Yeste, in the province of Albacete, Spain. It forms part of a future road that will join Yeste with Letur and the neighbouring area to the east. The bridge has 2 vehicle lanes and 2 sidewalks.
Blackfriars Bridge in London, Ontario, Canada is a wrought iron bowstring arch through truss bridge, crossing the North Thames River. The bridge was constructed in 1875 and carries single-lane vehicles, bicycles and pedestrians from Blackfriars Street to Ridout Street North.
Shaw Bridge, also known as Double-Span Whipple Bowstring Truss Bridge, is a historic bridge in Claverack, New York, United States. It carried Van Wyck Lane over Claverack Creek, but is now closed to all traffic, even pedestrians. It is "a structure of outstanding importance to the history of American engineering and transportation technology." Specifically designed by John D. Hutchinson, the bridge employs the basic design of Squire Whipple. It is the only extant "double" Whipple bowstring truss bridge in the U.S., having two identical spans placed in series over a common pier.
A deck is the surface of a bridge. A structural element of its superstructure, it may be constructed of concrete, steel, open grating, or wood. Sometimes the deck is covered by a railroad bed and track, asphalt concrete, or other form of pavement for ease of vehicle crossing. A concrete deck may be an integral part of the bridge structure or it may be supported with I-beams or steel girders.
The Hadley Parabolic Bridge, often referred to locally as the Hadley Bow Bridge, carries Corinth Road across the Sacandaga River in Hadley, New York, United States. It is an iron bridge dating from the late 19th century.
The Godavari Arch Bridge is a bowstring-girder bridge that spans the Godavari River in Rajahmundry, India. It is the latest of the three bridges that span the Godavari river at Rajahmundry. The Havelock Bridge being the earliest, was built in 1897, and having served its full utility, was decommissioned in 1997. The second bridge known as the Godavari Bridge is a truss bridge and is India's third longest road-cum-rail bridge crossing a water body.
The Adomi Bridge is a latticed steel arch suspension bridge crossing the Volta River at Atimpoku in Ghana in West Africa. It is the first permanent bridge to span the Volta River, which drains south into the Gulf of Guinea, and is Ghana's longest suspension bridge. It provides the main road passage, just south of the Akosombo Dam, between the Eastern Region and the Volta Region of Ghana. It was opened in 1957 by Kwame Nkrumah, Ghana's first president. The iconic crescent-shaped arch bridge is featured in Ghanaian stamps and currency.
Gaunless Bridge was a railway bridge on the Stockton and Darlington Railway. It was completed in 1823 and is one of the first railway bridges to be constructed of iron and the first to use an iron truss. It is also of an unusual lenticular truss design.
A balloon flange girder is a form of vertical I-beam wrought iron plate girder, where the top flange, instead of being a simple flat plate, is extended into a hollow tube. When a girder is subjected to a positive bending moment the top flange acts in compression making a flat plate flange more susceptible to local buckling than the balloon flange is.
A fracture critical bridge is a bridge or similar span that is vulnerable to collapse of one or more spans as a result of the failure in tension of a single element. While a fracture critical design is not considered unsafe, it is subject to special inspection requirements that focus on the tension elements of its structure.
Under vertical dead loads and uniform imposed loads the arches support the loads under pure axial compression with the deck edge cables acting as horizontal ties.
