Britannia Bridge

Infobox Bridge
bridge_name = Brittania Bridge


caption = The post 1970 Britannia Bridge from the east along the Menai Strait, retains Stephenson's original piers
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carries = Automobiles
crosses = Menai Strait
locale = flag|Wales, UK
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design = two-tier steel truss arch bridge
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length = convert|1151|ft|m|abbr=on
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Britannia Bridge ("Welsh": Pont Britannia) is a bridge across the Menai Strait between the island of Anglesey and the mainland of Wales, originally a tubular bridge of wrought iron rectangular box-section spans, and now a two-tier steel truss arch bridge.

The bridge design

The opening of the Menai Bridge in 1826, a mile (1.6 km) to the east of where Britannia Bridge was later built, provided the first fixed road link between Anglesey and the mainland. The increasing popularity of rail travel necessitated a second bridge to provide a direct rail link between London and the port of Holyhead, the Chester and Holyhead Railway.

Other railway schemes were proposed, including one in 1838 to cross Telford's existing Menai Bridge. Railway pioneer George Stephenson was invited to comment on this proposal but stated his concern about re-using the suspension bridge. By 1840, a Treasury committee decided broadly in favour of Stephenson's proposals, with final consent to the route including Britannia Bridge given in 1845. Stephenson's son Robert was appointed as chief engineer.

The design required the strait to remain accessible to shipping, and to be sufficiently stiff to support the heavy loading associated with trains, so Stephenson constructed a bridge with two main spans of 460-feet (140-m) long rectangular iron tubes, each weighing convert|1500|long ton|short ton [http://www.anglesey-history.co.uk/places/bridges/] , supported by masonry piers, the centre one of which was built on the Britannia Rock. Two additional spans of 230-feet (70-m) length completed the bridge making a 1,511-feet (461-m) long continuous girder. The trains were to run inside the tubes. Up until then the longest wrought iron span had been 31 feet 6 inches (9.6 m). The bridge was decorated by four large lions sculpted in limestone by John Thomas, two at either end. These were immortalised in the following Welsh rhyme by the bard John Evans (1826 - 1888), who was born in nearby Porthaethwy :

Pedwar llew tewHeb ddim blewDau 'rochr ymaA dau 'rochr drew

Four fat lionsWithout any furTwo this sideAnd two the other side

The lions cannot be seen from the A55 although the idea of raising them to road level has been suggested from time to time.

Stephenson retained the services of two distinguished engineers as consultants. William Fairbairn was an old friend of his father. Eaton Hodgkinson was a leading theorist on strength of materials. Hodgkinson believed that it would be impractical to make the tubes stiff enough, and advised auxiliary suspension from chains. However, Fairbairn believed chains unnecessary declaring:

Provided that the parts are well-proportioned and the plates properly rivetted, you may strip off the chains and have it as a useful Monument of the enterprise and energy of the age in which it was constructed.

The consensus of received engineering opinion was with Hodgkinson, but Stephenson, rather nervously, backed Fairbairn's analysis. A convert|75|ft|m span model was constructed and tested at Fairbairn's Millwall shipyard, and used as a basis for the final design. Although Stephenson had pressed for the tubes to be elliptical in section, Fairbairn's preferred rectangular section was adopted. Fairbairn was responsible both for the cellular construction of the top part of the tubes, and for developing the stiffening of the side panels.

Construction and use

Begun in 1846, the bridge was opened on 5 March 1850. For its time, it was a bridge of "magnitude and singular novelty", far surpassing in length contemporary cast beam or plate girder iron bridges. One aspect of its method of construction was also novel; the box sections were assembled on-shore, then floated out into position before being lifted into place. In spite of the heavier loadings placed on it in its later life, the bridge was "one of the most easily maintained and successful railway bridges" in the UK, and "as the first really large wrought iron bridge of the girder type it has unique significance in civil engineering history". Stephenson went on, in short order, to design the High Level Bridge in Newcastle Upon Tyne, which can be seen as a second and more elegant version of the Britannia Bridge; and the design of the bridge and the construction techniques employed also influenced Isambard Kingdom Brunel in the design and construction of the Royal Albert Bridge across the River Tamar at Saltash.

Fire and reconstruction

During the evening of 23 May 1970 the bridge was greatly damaged when boys playing on the bridge dropped a burning torch, starting a fire (see [http://www.2d53.co.uk/britanniabridge/Fire%20Report.htm Britannia Bridge Official Fire Report] , [http://www.bbc.co.uk/wales/walesonair/database/bridgefire.shtml BBC News video] ). As a consequence the bridge was completely rebuilt and reopened in 1972 with the spans supported by archways. The deck has two levels: the lower still carries the rail line, and the upper supports a single-carriageway section of the A55 road. The new bridge was designed by Husband & Co., now part of Mott MacDonald. The Anglesey Coastal Path passes below the bridge.

Proposed Bridge Improvement

In November 2007, a Public Consultation exercise into the ‘A55 Britannia Bridge Improvement’ commenced. The perceived problems stated include:
*It is the only non dual carriageway section along the A55
*Congestion during morning and afternoon peak periods
*Congestion from seasonal and ferry traffic from Holyhead
*Queuing at the junctions at either end
*Traffic is expected to significantly increase over the next 10 years or so

In the document, four options are presented, each with their own benefits and constraints
*Do Nothing. Congestion will increase as traffic levels increase.
*Widen Existing Bridge. To do this, the towers would have to be removed to make room for the extra lanes. This is an issue as the bridge is a Grade 2 Listed Structure and also as the bridge is owned by Network Rail. The extra lanes would have to be of reduced width as the existing structure is not capable of supporting 4 full width lanes.
*New multi span concrete box bridge alongside. Building a separate bridge would allow the existing bridge to be used as normal during construction. The bridge would require support pillar(s) in the Menai Straits which is an environmental issue as the Straits is a Special Area of Conservation. Visual impact would be low as the pillars and road surface would be aligned with the current bridge.
*New Single Span Cable Stayed Bridge. This would obviate the need for pillars in the Straits, but the bridge would have a large impact on the landscape due to the height of the cable support pillars. This is also the most costly option.

Respondents were overwhelmingly in favour of seeing some improvements, with 70% favouring the solution of building a second bridge. [cite web |url=http://new.wales.gov.uk/publications/accessinfo/drnewhomepage/transportdrs2/transportdrs2008/a55britanniabridgewconsultn/?lang=en |date=2008-08-12 |accessdate=2008-08-14 |author=Welsh Assembly Government]

See also

Stephenson's only other tubular iron bridge, the Conwy railway bridge between Llandudno Junction and Conwy, remains in use, and can be seen at close quarters from another of Telford's elegant suspension bridges crossing the River Conwy.

Bibliography

* Norrie, Charles Matthew (1956) "Bridging the Years - a short history of British Civil Engineering", Edward Arnold (Publishers) Ltd
* Rolt, L.T.C. (1960) "George and Robert Stephenson: The Railway Revolution", Penguin, Ch. 15, ISBN 0-14-007646-8
* Rapley, John (2003) "The Britanna and other Tubular Bridges", Tempus, ISBN 0-7524-2753-9

External links

* [http://www.anglesey-today.com/britannia-bridge.html Britannia Bridge Video]
* [http://www.prosiectmenai.co.uk Prosiect Menai] The new site of Prosiect Menai, who aim to create a museum and education centre based on the story of the bridges over the Menai Strait.
* [http://www.anglesey-history.co.uk/places/bridges/index.html Anglesey History] History of the bridges over the Menai Strait.
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* [http://www.anglesey.info/Menai%20Bridges.htm Anglesey Information Website] High resolution photographs and in depth information about both bridges over the Menai Straits.