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The modern Britannia Bridge.
|Carries||From 1850: North Wales Coast Line
From 1980: A55 road
|Locale||Anglesey, North Wales|
|Design||1850: Tubular bridge
1972: Two-tier truss arch bridge
|Material||1850: Wrought Iron, Stone
1972: Steel, Concrete
|Total length||461 m (1,512 ft)|
|Width||16 m (52 ft)|
|Height||40 m (130 ft)|
|Longest span||140 metres (460 ft)|
|No. of spans||Four|
|Piers in water||One|
|Design life||Railway closed between: 23 May 1970 – 30 January 1972
Upper road deck opened: 1980
|Opened||5 March 1850|
Britannia Bridge (Welsh: Pont Britannia) is a bridge across the Menai Strait between the island of Anglesey and the mainland of Wales. It was originally designed and built by Robert Stephenson as a tubular bridge of wrought iron rectangular box-section spans for carrying rail traffic. Its importance was to connect to the port of Holyhead and facilitate a sea link to Dublin, Ireland.
Following a disastrous fire in 1970 it was rebuilt, initially as a single-tier steel truss arch bridge, carrying rail traffic. A second tier was added later and opened in 1980 to accommodate road traffic.
The opening of the Menai Bridge in 1826, one 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 a single carriageway of the suspension bridge, as bridges of this type were unsuited to locomotive use. 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.
At the Admiralty's insistence, any bridge would have to permit passage of the strait by a fully rigged man-of-war. Stephenson therefore intended to cross the strait at a high level by a bridge with two main spans of 460-foot-long (140 m), rectangular iron tubes supported by masonry piers, the centre one of which was to be built on the Britannia Rock. Two additional spans of 230 ft (70 m) length would complete the bridge, making a 1,511-foot-long (461 m) continuous girder. The trains were to run inside the tubes (inside the box girders). Up until then, the longest wrought iron span had been 31 feet 6 inches (9.60 m), barely one fifteenth of the bridge's spans of 460 ft (140 m). As originally envisaged by Stephenson, the tubular construction would give a structure sufficiently stiff to support the heavy loading associated with trains, but the tubes would not be fully self-supporting, some of their weight having to be taken by suspension chains.
For the detailed design of the girders Stephenson secured the assistance of the distinguished engineer William Fairbairn,an old friend of his father and described by Stephenson as "well known for his thorough practical knowledge in such matters". Fairbairn began a series of practical experiments on various tube shapes and enlisted the help of Eaton Hodgkinson "distinguished as the first scientific authority on the strength of iron beams":33–37 It became apparent from Fairbairn's experiments that- without special precautions - the failure mode for the tube under load would be buckling of the top plate in compression, the theoretical analysis of which gave Hodgkinson some difficulty. When Stephenson reported to the directors of the railway in February 1846, he attached reports by both Hodgkinson and Fairbairn. From his analysis of the resistance to buckling of tubes with single top plates, Hodgkinson believed that it would require an impracticably thick (and therefore heavy) top plate to make the tubes stiff enough to support their own weight, and advised auxiliary suspension from link chains.:42–47 However, Fairbairn's experiments had moved on from those covered by Hodgkinson's theory to include designs in which the top plate was stiffened by 'corrugation' (the incorporation of cylindrical tubes). The results of these later experiments he found very encouraging; whilst it was still to be determined what the optimum form of the tubular girder should be "I would venture to state that a Tubular Bridge can be constructed of such powers and dimensions as will meet, with perfect security, the requirements of railway traffic across the Straits" although it might require more materials than originally envisaged and the utmost care would be needed in its construction. He believed it would be 'highly improper' to rely upon chains as the principal support of the bridge.
Under every circumstance, I am of opinion that the tubes should be made sufficiently strong to sustain not only their own weight, but in addition to that load 2000 tons equally distributed over the surface of the platform, a load ten times greater than they will ever be called upon to support. In fact, it should be a huge sheet-iron hollow girder, of sufficient strength and stiffness to sustain those weights; and, provided that the parts are well-proportioned and the plates properly riveted, 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.:37–42
Stephenson's report drew attention to the difference of opinion between his experts, but reassured the directors that the design of the masonry piers allowed for the tubes to be given suspension support, and no view need yet be taken as to the need for it, which would be resolved by further experiments.:35 A 75-foot (23 m) span model was constructed and tested at Fairbairn's Millwall shipyard, and used as a basis for the final design. Stephenson, who had not previously attended any of Fairbairn's experiments, was present at one involving this 'model tube', and consequently was persuaded that auxiliary chains were unnecessary. 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. Each main span weighed 1830t.
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 Menai Bridge:
Pedwar llew tew
Heb ddim blew
Dau 'ochr yma
A dau 'ochr drew
Four fat lions
Without any hair
Two on this side
And two over there
The lions cannot be seen from the A55, which crosses the modern bridge on the same site, although they can be seen from trains on the North Wales Coast Line below. The idea of raising them to road level has been suggested[by whom?] from time to time[when?][clarification needed].
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 onshore, then floated out into position before being gradually lifted into place using powerful jacks.
There was originally a railway station on the east side of the bridge at the entrance to the tunnel, run by the Chester and Holyhead Railway company, which served local rail traffic in both directions. This station closed after 8 1⁄2 years in operation owing to low passenger volumes. Nothing now remains of the station other than the remnants of the lower-level station building. A new station named Menai Bridge was opened shortly afterwards.
Fire and reconstruction
During the evening of 23 May 1970 the bridge was heavily damaged when boys playing inside the bridge dropped a burning torch, setting alight the tar-coated wooden roof of the tubes. Despite the best efforts of the Caernarfonshire and Anglesey fire brigades, the bridge's height, construction, and the lack of an adequate water supply meant they were unable to control the fire, which spread all the way across from the mainland to the Anglesey side. After the fire had burned itself out the bridge was still standing, but the structural integrity of the iron tubes had been critically compromised by the intense heat. As a consequence the bridge, except for the original stone substructure, was completely rebuilt by Husband & Co.
The superstructure of the new bridge was to include two decks: a lower rail deck supported by steel arches and an upper deck constructed out of reinforced concrete, to carry a new road crossing over the straight. Concrete supports were built under the approach spans and steel archways constructed under the long spans on either side of the central Britannia Tower.
The bridge was rebuilt in stages. The first stage was to erect the new steel arches under the two original wrought-iron tubes. The arches were completed, and single-line working was restored to the railway on 30 January 1972 by reusing one of the tubes. The next stage was to dismantle and remove the other tube and replace it with a concrete deck for the other rail track. Then the single-line working was transferred to the new track. That allowed the other tube to be removed and replaced with a concrete deck and the other rail track installed. A normal two-way rail service was then restored in 1974. Finally the upper road deck was installed and by July 1980, over 10 years after the fire, the new road crossing was completed, and formally opened by HRH the Prince of Wales, carrying 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 ten years or so
In the document, four options are presented, each with their own pros and cons:
- 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 four 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 eliminate 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.
Very few other tubular iron bridges were ever built since more economical bridge designs were soon developed. The most notable of the other tubular bridges were Stephenson's Conwy railway bridge between Llandudno Junction and Conwy, the first Sainte-Anne-de-Bellevue (Québec) Grand Trunk Railway bridge, which was the prototype of the Victoria Bridge across the Saint Lawrence River at Montreal.
The Conwy railway bridge remains in use, and is the only remaining tubular bridge; however, intermediate piers have been added to strengthen it. The bridge can be seen at close quarters from Thomas Telford's adjacent 1826 Conwy Suspension Bridge.
The Victoria Bridge was the first bridge to cross the St. Lawrence River, and was the longest bridge in the world when it was completed in 1859. It was rebuilt as a truss bridge in 1898.
- Special.st-andrews.ac.uk Archived 27 September 2007 at the Wayback Machine.
- Fairbairn, William (1849). An account of the construction of the Britannia and Conway tubular bridges. London: John Weale.
- "Britannia Bridge (1850)". Engineering Timelines. Retrieved 28 October 2017.
- Baughan, P.E., 'Chester and Holyhead Railway: vol. 1' (1972), pub. David & Charles plc
- 'Disused Stations' website. Details of Britannia Bridge railway station (with pictures)
- "Britannia Bridge Official Fire Report". 2d53.co.uk. Retrieved 24 January 2013.
- "Britannia Bridge". engineering-timelines.com. Retrieved 18 November 2016.
- Welsh Assembly Government (2008-08-12). "A55 Britannia Bridge – Release of the Results of the recent Public Consultation Exercise". Retrieved 2008-08-14.
- Jones, Reg Chambers (2011). Crossing the Menai: an illustrated history of the ferries and bridges of the Menai Strait. Wrexham: Bridge Books. ISBN 9781844940745.
- Norrie, Charles Matthew (1956) Bridging the Years – a short history of British Civil Engineering, Edward Arnold (Publishers) Ltd
- Rapley, John (2003). The Britannia and other Tubular Bridges, Tempus, ISBN 0-7524-2753-9
- Richards, Robin (2004). Two Bridges over Menai (new revised ed.). Llanrwst: Gwasg Carreg Gwalch. ISBN 1845241304.
- Rolt, L. T. C. (1960). George and Robert Stephenson: The Railway Revolution, Penguin, Ch. 15, ISBN 0-14-007646-8
- Rosenberg, Nathan; Vincenti, Walter G. (1978). The Britannia Bridge: the generation and diffusion of technical knowledge. Monograph series / Society for the History of Technology, no. 10. Cambridge, Mass.: MIT Press. ISBN 0262180871.
- Mitchell, Vic; Smith, Keith (2011). Bangor to Holyhead. West Sussex: Middleton Press. figs. 18–25. ISBN 9781908174017. OCLC 795179106.
|Wikimedia Commons has media related to Britannia Bridge.|
- Britannia Bridge (1850) at Structurae
- Britannia Bridge (1905) at Grandad's Photograph Album
- Britannia Bridge, Bangor entrance showing lion (1905) at Grandad's Photograph Album
- Britannia Bridge (1971) at Structurae
- General description of the Britannia and Conway tubular bridges on the Chester and Holyhead Railway, 1849, from Google Book Search
- In 1969 the BBC show Bird's Eye View captured an aerial view of a train crossing the bridge in the episode Man on the Move. Available in the online BBC Archives, the Britannia Bridge segment appears at the 25:47 mark.
- The Night the Bridge Caught Fire BBC programme page
- Menai Heritage A community project and museum celebrating the two bridges over the Menai Strait and the town of Menai Bridge