A tubular bridge is a
bridge
A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...
built as a rigid
box girder
A box girder or tubular girder (or box beam) is a girder that forms an enclosed tube with multiple walls, as opposed to an i-beam, - or H-beam. Originally constructed of wrought iron joined by riveting, they are now made of rolled steel, rolled ...
section within which the traffic is carried. Famous examples include the original
Britannia Bridge
Britannia Bridge () is a bridge in Wales that crosses the Menai Strait between the Isle of Anglesey and city of Bangor, Gwynedd, Bangor. It was originally designed and built by the noted railway engineer Robert Stephenson as a tubular bridge of ...
over the
Menai Strait
The Menai Strait () is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The s ...
, the
Conwy railway bridge
The Conwy Railway Bridge carries the North Wales coast railway line across the River Conwy between Llandudno Junction and the town of Conwy. The wrought iron tubular bridge, which is now Grade I listed, was built in the 19th century. It i ...
over the
River Conwy
The River Conwy (; ) is a river in north Wales. From its source to its discharge in Conwy Bay it is long and drains an area of 678 square km. "Conwy" was formerly anglicised as "Conway."
The name 'Conwy' derives from the old Welsh words ''c ...
, designed and tested by
William Fairbairn
Sir William Fairbairn, 1st Baronet of Ardwick (19 February 1789 – 18 August 1874) was a Scotland, Scottish civil engineer, structural engineer and shipbuilder. In 1854 he succeeded George Stephenson and Robert Stephenson to become the third ...
and built by
Robert Stephenson
Robert Stephenson , (honoris causa, Hon. causa) (16 October 1803 – 12 October 1859) was an English civil engineer and designer of locomotives. The only son of George Stephenson, the "Father of Railways", he built on the achievements of hi ...
between 1846 and 1850, and the original
Victoria Bridge in Montreal.
Conwy and Britannia Bridges
The Conwy railway bridge carries the
North Wales
North Wales ( ) is a Regions of Wales, region of Wales, encompassing its northernmost areas. It borders mid Wales to the south, England to the east, and the Irish Sea to the north and west. The area is highly mountainous and rural, with Snowdon ...
coast railway line across the River Conwy between
Llandudno Junction
Llandudno Junction (), once known as Tremarl, is a town in the Community (Wales), community of Conwy in Conwy County Borough, Wales. Llandudno Junction and neighbouring Deganwy are both part of the built-up area and community of Conwy.
It take ...
and the town of
Conwy
Conwy (, ), previously known in English as Conway, is a walled market town, community and the administrative centre of Conwy County Borough in North Wales. The walled town and castle stand on the west bank of the River Conwy, facing Deganwy ...
.
The wrought iron tubular bridge was built by Robert Stephenson to a design by William Fairbairn and is similar in construction to Stephenson's other famous tubular bridge, the Britannia Bridge across the
Menai Strait
The Menai Strait () is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The s ...
. It was officially opened in 1849 but had been completed in 1848. Being the first tubular bridge to be built, the design needed much testing on
prototype
A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...
s to confirm that it would be capable of carrying heavy locomotives, the testing being performed by Fairbairn. The successful result enabled the much larger Britannia bridge to be built. The current Conwy bridge has been reinforced by extra columns under the bridge into the river but is otherwise virtually unchanged since it was built.
Before the Britannia Bridge was constructed, Fairbairn conducted "the most celebrated of all engineering experiments on the grand scale",
a series of experiments "of a gigantic character".
One-sixth scale models, 78 ft long, were built at Fairbairn's
Millwall Iron Works and tested with increasing loads. By this means, although at an experimental cost of thousands of pounds, the design of the cellular girder was refined until it could carry loads of 2.4 times the original capacity.
The most significant finding was that of a thin section's susceptibility to buckling under compression loads and the cellular girder's resistance to this. Stephenson would build around a thousand other bridges using this cellular structure.
The most impressive test was performed on-site at Conwy. The 1300 ton tubular girder, deflecting 8 inches under its own weight, was loaded with a further 300 tons and the deflection measured. The effects of wind loading and asymmetric thermal expansion due to sunlight were also studied.
Chepstow and Tamar Bridges
At
Chepstow
Chepstow () is a town and community in Monmouthshire, Wales, adjoining the border with Gloucestershire, England. It is located on the tidal River Wye, about above its confluence with the River Severn, and adjoining the western end of the ...
, a tubular railway bridge was built to the instructions of
Isambard Kingdom Brunel
Isambard Kingdom Brunel ( ; 9 April 1806 – 15 September 1859) was an English civil engineer and mechanical engineer who is considered "one of the most ingenious and prolific figures in engineering history", "one of the 19th-century engi ...
in 1852. The "Great Tubular Bridge" over the
River Wye
The River Wye (; ) is the Longest rivers of the United Kingdom, fourth-longest river in the UK, stretching some from its source on Plynlimon in mid Wales to the Severn Estuary. The lower reaches of the river forms part of Wales-England bor ...
, which at that point forms the boundary between
Wales
Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...
and
England
England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
, is considered one of Brunel's major achievements, despite its appearance. It was economical in its use of materials, and would prove to be the design prototype for Brunel's
Royal Albert Bridge
The Royal Albert Bridge is a railway bridge which spans the River Tamar in England between Plymouth, Devon and Saltash, Cornwall. Its unique design consists of two lenticular iron trusses above the water, with conventional plate-girder app ...
at
Saltash
Saltash () is a town and civil parish in south Cornwall, England. It had a population of 16,184 in 2011 census. Saltash faces the city of Plymouth over the River Tamar and is popularly known as "the Gateway to Cornwall". Saltash’s landmarks ...
.
Other bridges
The unconventional nature of the tubular girder bridge was not widely accepted.
John Fowler's 1847 tubular girder design for
Torksey
__NOTOC__
Torksey is a small village in the West Lindsey district of Lincolnshire, England. The population of the civil parish at the 2011 census was 875. It is situated on the A156 road, south of Gainsborough and north-west of Lincoln, an ...
used tubes that were only 10 foot high and placed the railway deck between them, rather than inside. This is now considered as the first
box girder bridge
A box girder bridge, or box section bridge, is a bridge in which the main beam (structure), beams comprise girders in the shape of a hollow box. The box girder normally comprises prestressed concrete, structural steel, or a composite ma ...
, rather than a pure tubular bridge.
Despite this, it was initially rejected after completion by the
Board of Trade
The Board of Trade is a British government body concerned with commerce and industry, currently within the Department for Business and Trade. Its full title is The Lords of the Committee of the Privy Council appointed for the consideration of ...
’s inspector,
Captain Lintorn Simmons, and the design was also criticized by the
Institution of Civil Engineers
The Institution of Civil Engineers (ICE) is an independent professional association for civil engineers and a Charitable organization, charitable body in the United Kingdom. Based in London, ICE has over 92,000 members, of whom three-quarters ar ...
.
When the bridge was strengthened in 1897, this was done by added a central truss above the deck rather than by strengthening the box.
Legacy

Since the destruction by fire of Britannia Bridge in 1970, Conwy railway bridge remains the only surviving example of this means of construction undertaken by Stephenson.
In the case of the Britannia Bridge this technology allowed a bridge with spans up to long to be constructed, when until then the longest wrought iron span had been .
See also
*
Box girder bridge
A box girder bridge, or box section bridge, is a bridge in which the main beam (structure), beams comprise girders in the shape of a hollow box. The box girder normally comprises prestressed concrete, structural steel, or a composite ma ...
- a similar bridge that carries the traffic outside the box.
*
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 ...
- a type which may employ a variety of structures but which also encloses the traffic (for the protection of the bridge)
*
Fairbairn crane - a design of curved crane jib, with a similar doubled-walled inner face to resist compression forces.
*
Jetway
A jet bridge is an enclosed connector which most commonly extends from an airport terminal gate to an airplane, and in some instances from a port to a boat or ship, allowing passengers to board and disembark without heading outside and being exp ...
- a movable bridge that carries pedestrians from a terminal to an aircraft.
*
Skyway
A skyway, skybridge, skywalk, or sky walkway is an elevated type of pedway connecting two or more buildings in an urban area, or connecting elevated points within mountainous recreational zones. Urban skyways very often take the form of Cover ...
- a bridge connecting buildings at an elevation above the ground
References
*
*John Rapley, ''The Britannia and Other Tubular Bridges: And the Men Who Built Them'', Tempus (2003).
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Bridges by structural type