Editing Through arch bridge

{{Short description|Type of bridge}}
{{BridgeTypePix
|image=File:Bayonne Bridge Collins Pk jeh-2.JPG
  |type_name=Through arch bridge
  |ancestor_names=[[Arch bridge]]
  |carries=[[Pedestrian]]s, [[vehicle]]s, [[train]]s
  |span_range=Long|material=[[Steel]]
  |movable=No
  |design=High
  |falsework=Seldom
|image_title=The [[Bayonne Bridge]], a mid-bearing through arch bridge spanning the [[Kill Van Kull]], connecting [[Bayonne, New Jersey]], with [[Staten Island]], [[New York City]]}}
A '''through arch bridge''', also known as a '''through-type arch bridge''', is a [[bridge]] that is made from materials such as steel or reinforced concrete, in which the base of an arch structure is below the deck but the top rises above it. It can either be '''lower bearing''' or '''mid-bearing'''. Thus, the deck is within the arch, and cables or beams that are in [[tension (physics)|tension]] suspend the central part of the deck from the arch.

== Function ==
For a specific construction method, especially for [[masonry]] arches, the proportions of the arch remain similar no matter what the size: wider arches are thus required to be taller arches.<ref name="Gordon, Through arch">{{Cite book |last=Gordon |first=J.E. |title=Structures |publisher=Penguin |year=1991 |isbn=978-0-14-013628-9 |pages=200–201, 203 |ref={{harvid|Gordon|Structures}} |orig-year=1978}}</ref> For a [[semi-circular arch]], the height is half of the span. Bridges across deep, narrow gorges can have their arch placed entirely beneath a flat roadway, but bridges in flatter country rise above their road approaches. A wide bridge may require an arch so tall as to become a significant obstacle and incline for the roadway. Small bridges can be [[humpback bridge|hump-backed]], but larger bridges such as the [[Old Bridge, Pontypridd]] may become so steep as to require steps, making their use for wheeled traffic difficult. Railways also find arched bridges difficult as they are even less tolerant of inclines. Where simple arched bridges are used for railways on flat terrain the cost of building long approach embankments may be considerable.

Further issues are the [[foundation (engineering)|foundations]] for the bridge. Arch bridges generate large side thrusts on their footings and so may require a solid bedrock foundation. Flattening the arch shape to avoid the humpback problem, such as for [[Maidenhead Railway Bridge|Brunel's Maidenhead bridge]], increases this side thrust. It is often impossible to achieve a flat enough arch, simply owing to the limitations of the foundations &ndash; particularly in flat country.<ref name="Gordon, Through arch" /> Historically, such bridges often became [[viaduct]]s of multiple small arches.

With the availability of iron or concrete as structural materials, it became possible to construct a ''through arch bridge'': a bridge where the deck does not have to be carried over the top of the arch.<ref name="Gordon, Through arch" /> This requires a structure that can both support the deck from the arch by tension rods, chains or cables and allow a gap in the arch, so the deck can pass through it. The first of these in particular cannot be achieved with masonry construction and requires [[wrought iron]] or steel.

The use of a through arch does not change the proportions or size of the arch: a large span will still require a tall arch, although this can now reach any height above the deck without obstructing traffic. The arch may also reach downwards at its sides, to either reach strong foundations or to place the roadway at a convenient height for spanning a deep valley from a plateau above. The [[Tyne Bridge]] demonstrates both of these advantages.

== Notable examples ==
A well-known example of this type is the [[Sydney Harbour Bridge]] in Australia, which is based on the [[Hell Gate Bridge]] in [[New York City]].<ref>{{Cite web |title=Sydney Harbour Bridge repainting |url=http://www.rta.nsw.gov.au/roadprojects/resources/documents/permanent_panels/sydney_harbour_bridge.pdf |access-date=4 February 2012 |publisher=[[Roads & Traffic Authority]]}}</ref> Other bridges include the [[Chaotianmen Bridge]] in China, the world's longest through arch bridge;<ref>CulturalChina.com, [http://news.cultural-china.com/20090430100912.html Chongqing completes world's longest arch bridge] {{webarchive|url=https://web.archive.org/web/20110708213230/http://news.cultural-china.com/20090430100912.html |date=8 July 2011 }}, 30 April 2009.</ref> [[Tyne Bridge]] of [[Newcastle upon Tyne]]; the [[Bayonne Bridge]] that connects New York City to [[New Jersey]], which is longer than the Sydney Harbour Bridge; the [[Ahwaz White Bridge]]; the [[Bourne Bridge]] and [[Sagamore Bridge]], smaller, near-twin bridges over the [[Cape Cod Canal]]; the [[Pennybacker Bridge]] in [[Austin, Texas]] and as the [[Hernando de Soto Bridge]] in [[Memphis, Tennessee]]. [[Wylam Railway Bridge]] is an early through arch bridge upstream of the Tyne Bridge.<ref>{{Cite web|url=http://tynevalleywalking.blogspot.com/2006/11/tyne-is-world-renowned-for-seven.html|title=tynevalleywalking: Wylam Railway Bridge: The first of its kind|date=November 23, 2006}}</ref>

<gallery>
File:Chaotianmen Bridge-1.jpg|The [[Chaotianmen Bridge]], China, the 2nd longest steel arch bridge in the world.
File:Hell Gate Bridge ca 1917.png|The [[Hell Gate Bridge]], New York, shortly after its completion.
File:High BB from Bayonne jeh.jpg|The [[Bayonne Bridge]], the 6th longest steel arch bridge in the world.
File:Tyne_Bridge.jpg|[[Tyne Bridge]], [[Newcastle upon Tyne]], opened in 1928.
File:AhwazWhiteBridge.jpg|The [[Ahwaz White Bridge]], built in the 1930s.
File:Sydney Harbour Bridge from Circular Quay.jpg|[[Sydney Harbour Bridge]], the 9th longest through arch bridge.
File:Douglass Bridge 090621.jpg|[[Frederick Douglass Memorial Bridge]] in [[Washington, D.C.]]
</gallery>

==Arch rib arrangements==
{{Anchor|Parallel rib arch bridge|Basket handle arch bridge}}
[[File:Pentelehíd.jpg|thumb|The [[Pentele Bridge (Hungary)|Pentele Bridge]] is an example of a basket handle arch. Seen from one end, the two arches take the form of a handle.]]
The through arch bridge usually consists of two ribs,<ref>{{Cite web |title=Concrete Arch Bridges |url=http://www.dot.state.oh.us/Divisions/Engineering/Structures/bridge%20operations%20and%20maintenance/PreventiveMaintenanceManual/BPMM/archbridges/concbridges.htm |access-date=December 16, 2015 |website=www.dot.state.oh.us |publisher=[[Ohio Department of Transportation]] |quote=The through arch (or rainbow arch) usually consists of two arch ribs that extend well above the roadway on each side of the bridge.}}</ref> although there are examples like the [[Hulme Arch Bridge]] of through arches with a single rib. When the two arches are built in [[Parallel (geometry)|parallel]] planes, the structure is a parallel rib arch bridge. When the two arch ribs lean together and shorten the distance between the arches near the top, the span is a basket handle arch bridge.<ref>{{Cite journal |last1=Zhang |first1=Xiangdong |last2=Zhang |first2=Bin |last3=Jiang |first3=Lizhong |last4=Xie |first4=Mowen |date=November 8, 2013 |title=Load test design and stability analysis of basket handle arch bridge with reinforced concrete |journal=Advanced Materials Research |volume=838-841 |pages=1009–1013 |url=http://www.scientific.net/AMR.838-841.1009 |access-date=December 16, 2015 |publisher=Trans Tech Publications, Switzerland|doi=10.4028/www.scientific.net/AMR.838-841.1009 |s2cid=109262734 |url-access=subscription }}</ref>

== Tied-arch bridges ==
[[File:Brunelwindsorbridge.jpg|thumb|[[Isambard Kingdom Brunel|Brunel]]'s wrought-iron [[Windsor Railway Bridge]]: both a tied-arch and a through-arch|alt=|left]]
[[File:StanleyFerryAqueductProfile.jpg|thumb|[[Stanley Ferry Aqueduct]], Yorkshire, opened 1839, built in [[cast iron]]. A through-arch, but not a tied-arch|alt=|left]]
Many [[tied-arch bridge]]s are also through-arch bridges. As well as tying the side-loads of the arch, the tension member is also at a convenient height to form the bridge deck, as for a through-arch.

The converse is not true: through-arch bridges do not imply that they are tied-arch bridges, unless they also provide the deliberate tension member that is the key to a tied-arch. Although ''visually'' similar, tied- and untied- through-arch bridges are quite distinct structurally and are unrelated in how they distribute their loads. In particular, [[cast iron]] bridges such as the [[Stanley Ferry Aqueduct]] may resemble tied-arch bridges, but as cast iron is weak in tension they are not structurally a tied arch.

==Construction sequence==
[[File:Frederick Douglass Bridge construction 2020b.jpg|thumb|The [[Frederick Douglass Memorial Bridge]] under construction in 2020.  The partially completed arch is supported by wires attaching it to the completed arch behind it.]]
In some locations it is not practical to support the arch from beneath during construction.

In modern construction, temporary towers are erected and supported by cables anchored in the ground. Temporary cables fly from each side to support arch segments as they are constructed. When the arches are almost complete a jacking bridge is placed over or beneath the gap to force the arches apart, whence the final section is constructed in place or lifted into position.

[[File:Runcorn-Widnes bridge - geograph.org.uk - 2784577.jpg|thumb|The [[Silver Jubilee Bridge|Runcorn–Widnes Bridge]] under construction in-between the [[Widnes–Runcorn Transporter Bridge]] and the lattice truss [[Runcorn Railway Bridge]].]]

In some cases, this type of arch has been created by constructing [[cantilever]]s from each side, with the shoreside ends bolted securely down into heavy piers. The incomplete channel ends are then constructed toward each other and either filled by construction or by lifting a prefabricated center section. This type of construction was used in the [[Sydney Harbour Bridge]] illustrated above, with the supporting cables to the higher side of the arches removed after completion.

==See also==
*[[Arch bridge]]
*[[List of the largest arch bridges]]
*[[Tied-arch bridge]]
*[[Moon bridge]]

==References==
{{Reflist}}
*{{Cite book |last1=Tonias |first1=Demetrios E. |url=https://books.google.com/books?id=B1HipIuozEQC&pg=PT40 |title=Bridge Engineering |last2=Jim J. Zhao |year=2007 |publisher=McGraw Hill Professional |isbn=978-0-07-145903-7}}

{{Bridge footer}}

[[Category:Through arch bridges| ]]
[[Category:Arch bridges|Through arch]]
[[Category:Bridges by structural type]]
[[Category:Suspended structures]]
[[Category:Suspension bridges|*]]