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Britannia Bridge
Pont Britannia
The modern Britannia Bridge.
Carries From 1850: North Wales Coast Line
From 1980:UK road A55.PNG A55 road
Crosses Menai Straits
Locale Anglesey, North Wales
Designer Robert Stephenson
Design 1850: Tubular bridge
1972: Two-tier truss arch bridge
Material 1850: Wrought Iron, Stone
1972: Steel, Concrete
Piers in water One
Total length 461 metres (1,510 ft)
Width 16 metres (52 ft)
Height 40 metres (130 ft)
Longest span 140 metres (460 ft)
Number of spans Four
Beginning date of construction 1846
Opened 5 March 1850
Design life Railway closed between: 23 May 1970 - 30 January 1972
Upper road deck opened: 1980
The original box section Britannia Bridge, circa 1852.
Postcard picture of the bridge from circa 1886 [1]
Section of the original wrought-iron tubular bridge standing in front of the modern bridge
Monumental lion, one of four guarding each corner of Britannia Bridge

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.

Contents

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 Thomas 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 the bridge 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 1,500 long tons (1,700 short tons) [2], 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).

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 75 feet (23 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.

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Lions

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 tew
Heb ddim blew
Dau 'rochr yma
A dau 'rochr drew

Four fat lions
Without any hair
Two on this side
And two over there

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

Construction and use

Commemoratory engraving of the engineers behind the Britannia Bridge, with Robert Stephenson in the center, published 1868

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.

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, setting alight the bridge's tar-coated wooden roof (see Britannia Bridge Official Fire Report, BBC News video). As a consequence the bridge was completely rebuilt by Husband & Co.. The new design had spans which were supported by additional archways. The new bridge reopened to rail traffic on 30 January, 1972.

In 1980, almost 10 years after the fire, the upper road level opened which carried a single-carriageway section of the A55 road.

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 Strait which is an environmental issue as the Strait 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 Strait, 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.[1]

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

References

External links

Coordinates: 53°12′58.5″N 4°11′9″W / 53.21625°N 4.18583°W / 53.21625; -4.18583


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