Decades before the building of the Britannia Bridge, the Menai Suspension Bridge had been completed, but this structure carried a road rather than track; there was no rail connection to Anglesey before its construction. After many years of deliberation and proposals, on 30 June 1845, a Parliamentary Bill covering the construction of the Britannia Bridge received royal assent.[3] At the Admiralty's insistence, the bridge elements were required to be relatively high in order to permit the passage of a fully rigged man-of-war. In order to meet the diverse requirements, Stephenson, the project's chief engineer, performed in-depth studies on the concept of tubular bridges. For the detailed design of the structure's girders, Stephenson gained the assistance of distinguished engineer William Fairbairn. On 10 April 1846, the foundation stone for the Britannia Bridge was laid. The construction method used for the rivetedwrought iron tubes was derived from contemporary shipbuilding practices; the same technique as used for the Britannia Bridge was also used on the smaller Conwy Railway Bridge. On 5 March 1850, Stephenson himself fitted the last rivet of the structure, marking the bridge's official completion.
On 3 March 1966, the Britannia Bridge received Grade II listed status.[4]
A fire in May 1970 caused extensive damage to the Britannia Bridge. Subsequent investigation determined that the damage to the tubes was so extensive that they were not realistically repairable. The bridge was rebuilt in a quite different configuration, reusing the piers while employing new arches to support not one but two decks, as the new Britannia Bridge was to function as a combined road-and-rail bridge. The bridge was rebuilt in phases, initially reopening in 1972 as a single-tier steel truss arch bridge, carrying only rail traffic. Over the next eight years more of the structure was replaced, allowing for more trains to run and a second tier to be completed. The second tier was opened to accommodate road traffic in 1980. The bridge was subject to a £4 million four-month in-depth maintenance programme during 2011. Since the 1990s, there has been talk of increasing road capacity over the Menai Strait, either by extending the road deck of the existing bridge or via the construction of a third bridge.
Design
Britannia Bridge entranceThe original box section Britannia Bridge, circa 1852.Postcard picture of the bridge from circa 1902
The opening of the Menai Bridge in 1826, one mile (1.6km) 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 shortly necessitated a second bridge to provide a direct rail link between London and the port of Holyhead, the Chester and Holyhead Railway.[citation needed]
Other railway schemes were proposed, including one in 1838 to cross Thomas Telford's existing Menai Bridge.[citation needed] 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, however, final consent to the route, including Britannia Bridge, would not be granted until 30 June 1845, the date on which the corresponding Parliamentary Bill received royal assent.[3] Around the same time, Stephenson's son, Robert Stephenson, was appointed as chief engineer for the project.[citation needed]
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, over 100ft (30m), by a bridge with two main spans of 460-foot-long (140m), rectangular iron tubes, each weighing 1,500 long tons (1,500 tonnes; 1,700 short tons),[6] supported by masonry piers, the centre one of which was to be built on the Britannia Rock. Two additional spans of 230ft (70m) length would complete the bridge, making a 1,511-foot-long (461m) continuous girder.[citation needed] The trains were to run inside the tubes (inside the box girders). Up until then, the longest wrought iron span had been 31feet 6inches (9.60m), barely one fifteenth of the bridge's spans of 460ft (140m). 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.[7]:37–42
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"[7]: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.[7]: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).[citation needed] 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.[7]:37–42
A view of the entrance to the Britannia Bridge from the Bangor side, showing a steam train entering the bridge, people watching, two large stone lions and an inscription relating to the engineer, Robert Stephenson
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.[7]:35 A 75-foot (23m) 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. No chains were fitted. As the only purpose of the piers (above the level of the present road deck) was to support the chains, these piers have never had any practical use. 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.[7] Each main span weighed roughly 1,830 tonnes.[3]
Construction and use
A section of the original wrought-iron tubular bridge standing beside the modern crossing.
On 10 April 1846, the foundation stone for the Britannia Bridge was laid, marking the official commencement of construction work at the site.[3] The resident engineer for the structure's construction was civil engineerEdwin Clark, who had previously aided Stephenson in performing the complex structural stress calculations involved in its design process. The first major elements of the structure to be built were the side tubes, this work was performed in situ, using wooden platforms to support it.[3] The construction method used for the iron tubes was derived from contemporary shipbuilding practices, being composed of rivetedwrought iron plates 5⁄8 inch (16mm) thick, complete with sheeted sides and cellular roofs and bases.[3] The same technique as used for the Britannia Bridge was also used on the smaller Conwy Railway Bridge, which was built around the same time. On 10 August 1847, the first rivet was driven.[3]
Working in parallel to the onsite construction process, the two central tube sections, which weighed 1,800 long tons (1,830 tonnes) apiece, were separately built on the nearby Caernarfon shoreline. Once they had been fully assembled, each of the central tubes was floated, one at a time, into the causeway and directly below the structure.[3] The in-place sections were gradually raised into place using powerful hydraulic cylinders; they were only raised by a few inches at a time, after which supports would be built underneath the section to keep it in place. This aspect of the bridge's construction was novel at the time.[3] Reportedly, the innovative process had been responsible for costing Stephenson several nights of sleep at one stage of the project. The work did not go smoothly; at one point, one of the tubes allegedly came close to being swept out to sea before being recaptured and finally pushed back into place.[6] The tubes were manoeuvred into place between June 1849 and February 1850.[3]
Once in place, the separate lengths of tube were joined to form parallel prestressed continuous structures, each one possessing a length of 1,511 feet (460.6m) and weighing 5,270 long tons (5,350 tonnes).[3] The pre-stressing process had increased the structure's loadbearing capacity and reduced deflection. The tubes had a width of 15 feet (4.5m) and differed between 23 feet (7m) and 30 feet (9.1m) in overall depth, while also having a 10 foot (3m) gap between them; they were supported on a series of 15-foot-long (4.6m) cast iron beams that were embedded in the stonework of the towers.[3] To better protect the iron from the weather, an arched timber roof was constructed to cover both tubes; it was roughly 39 feet (12m) wide, continuous over their whole length, and covered with tarredhessian. A 12 foot (3.7m) wide central walkway was present above the roof for the purpose of producing maintenance access.[3]
On 5 March 1850, Stephenson himself fitted the last rivet of the structure, marking the bridge's official completion.[3] Altogether, the bridge had taken over three years to complete. On 18 March 1850, a single tube was opened to rail traffic. By 21 October of that year, both tubes had been opened to traffic.[3]
For its time, the Britannia Bridge was a structure of "magnitude and singular novelty", far surpassing in length both contemporary cast beam or plate girder iron bridges. The noted engineer Isambard Kingdom Brunel, a professional rival and personal friend of Stephenson's, was claimed to have remarked to him: "If your bridge succeeds, then mine have all been magnificent failures".[3] On 20 June 1849, Brunel and Stephenson had both looked on as the first of the bridge's tubes was floated out on its pontoons. The construction techniques employed on the Britannia Bridge had obviously influenced Brunel as he later made use of the same method of floating bridge sections during the construction of the Royal Albert Bridge across the River Tamar at Saltash.[3]
There was originally a railway station located 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.[8] However, this station was closed after only 8+1⁄2 years in operation owing to low passenger volumes. In the present day, little remains of this station, other than the remnants of the lower-level station building.[9] A new station named Menai Bridge was opened shortly afterwards.[citation needed]
Lions
One of four Monumental lions that stand at each corner of Britannia Bridge.
The bridge was decorated by four large lions sculpted in limestone by John Thomas, two at either end.[6] Each was constructed from 11 pieces of limestone. They are 25ft (7.6m) long, 12ft (3.7m) tall, and weigh 30 tons.[1]
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 local campaigners from time to time.[10][11][12]
Fire and reconstruction
During the evening of 23 May 1970, the bridge was heavily damaged when boys playing inside the structure dropped a burning torch, setting alight the tar-coated wooden roof of the tubes.[13][14] 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.[15] After the fire had burned itself out, the bridge was still standing. However, the structural integrity of the iron tubes had been critically compromised by the intense heat; they had visibly split open at the three towers and had begun to sag. It was recognised that there was still danger of the structure collapsing. As a consequence, the bridge was rendered unusable without the enactment of major restorative work.[15]
In light of events, the chief civil engineer of British Railways' London Midland region, W.F. Beatty, sought structural advice from consulting engineering company Husband & Co.[15] Following an in-depth investigation of the site performed by the company, it was determined that the cast iron beams inside the towers had suffered substantial cracking and tilting, meaning that the tubes required immediate support at all three towers. The Royal Engineers were quickly brought in to save the bridge, rapidly deploying vertical Bailey bridge units to fill the original jacking slots in the masonry towers. By the end of July 1970, a total of eight Bailey bridge steel towers had been erected, each being capable of bearing a vertical load of around 200 tonnes.[15]
Further analysis showed that the wrought iron tubes had been too badly damaged to be retained.[15] In light of this discovery, it was decided to dismantle the tubes in favour of replacing them with a new deck at the same level as the original tracks. With the exception of the original stone substructure, the structure was completely rebuilt by Cleveland Bridge & Engineering Company.[15] 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 strait. Concrete supports were built under the approach spans and steel archways constructed under the long spans on either side of the central Britannia Tower.[15] The two long spans are supported by arches, which had not been an option for the original structure as a result of the clearance needed for tall-masted vessels; modern navigational requirements require much less headroom.[15]
The bridge was rebuilt in stages. The first stage was to erect the new steel arches under the two original wrought-iron tubes.[15] 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 (on the west side); this allowed the other tube to be removed and replaced with a concrete deck (which is used only for service access) by 1974.[15] 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 the Prince of Wales,[15] carrying a single-carriageway section of the A5 road (now the A55).
During 2011, national railway infrastructure owner Network Rail, the Welsh Assembly Government and the English Highways Agency undertook a £4 million joint programme to strengthen the 160-year-old structure and improve its reliability.[16] The work involved the replacement of eroded steelwork, repairs to the drainage system, restoration of the parapets and stonework, and the painting of the steel approach portals of the bridge. The programme included a detailed inspection of the internal chambers of the three towers and the construction of a special walkway to enable easier and safer access to the structure for future inspections of the masonry piers; special protective efforts adopted for the work included the use of special pollution-minimising paint and the decontamination of all equipment before being brought onsite.[16]
Proposed bridge improvement
An 1868 engraving showing Robert Stephenson (seated centre) with the engineers who designed and built the Britannia Bridge.
In November 2007, a public consultation exercise into the ‘A55 Britannia Bridge Improvement’ commenced. The perceived problems stated include:[17]
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 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 per cent favouring the solution of building another bridge.[18]
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.
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 455-foot (138.7 m) lenticular iron trusses 100 feet (30.5 m) above the water, with conventional plate-girder approach spans. This gives it a total length of 2,187.5 feet (666.8 m). It carries the Cornish Main Line railway in and out of Cornwall. It is adjacent to the Tamar Bridge which opened in 1961 to carry the A38 road.
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 strait is about 25 km (16 mi) long and varies in width from 400 metres (1,300 ft) between Fort Belan and Abermenai Point to 7.5 kilometres (4.7 mi) between Puffin Island and Penmaenmawr. It contains several islands, including Church Island, on which is located St Tysilio's Church.
The Victoria Bridge, previously known as Victoria Jubilee Bridge, is a bridge over the St. Lawrence River, linking Montreal, Quebec, to the south shore city of Saint-Lambert.
The A55, also known as the North Wales Expressway, is a major road in Wales and England, connecting Cheshire and North Wales. The vast majority of its length from Chester to Holyhead is a dual carriageway primary route, with the exception of the Britannia Bridge over the Menai Strait and several short sections where there are gaps in between the two carriageways. All junctions are grade separated apart from a roundabout east of Penmaenmawr and another nearby in Llanfairfechan. Initially, the road ran from Chester to Bangor. In 2001, it was extended across Anglesey to the ferry port of Holyhead parallel to the A5. The road improvements have been part funded with European money, under the Trans-European Networks programme, as the route is designated part of Euroroute E22.
The Menai Suspension Bridge is a suspension bridge spanning the Menai Strait between the island of Anglesey and the mainland of Wales. Designed by Thomas Telford and completed in 1826, it was the world's first major suspension bridge. The bridge still carries road traffic and is a Grade I listed structure.
Sir William Fairbairn, 1st Baronet of Ardwick was a Scottish civil engineer, structural engineer and shipbuilder. In 1854 he succeeded George Stephenson and Robert Stephenson to become the third president of the Institution of Mechanical Engineers.
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 is the last surviving example of this type of design by Stephenson after the original Britannia Bridge across the Menai Strait was partially destroyed in a fire in 1970 and rebuilt as a two-tier truss arch bridge design.
The Conwy Suspension Bridge is a Grade I-listed structure and is one of the first road suspension bridges in the world. Located in the medieval town of Conwy in Conwy county borough, North Wales, it is now only passable on foot. The bridge is now in the care of the National Trust. It originally carried the A55(T) road from Chester to Bangor.
A tubular bridge is a bridge built as a rigid box girder section within which the traffic is carried. Famous examples include the original Britannia Bridge over the Menai Strait, the Conwy railway bridge over the River Conwy, designed and tested by William Fairbairn and built by Robert Stephenson between 1846 and 1850, and the original Victoria Bridge in Montreal.
Chepstow Railway Bridge was built to the instructions of Isambard Kingdom Brunel in 1852. The "Great Tubular Bridge" over the River Wye at Chepstow, which at that point forms the boundary between Wales and England, 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 at Saltash. Although the superstructure has since been replaced, Brunel's tubular iron supports are still in place. It is a Grade II listed structure.
The Chester and Holyhead Railway was an early railway company conceived to improve transmission of Government dispatches between London and Ireland, as well as ordinary railway objectives. Its construction was hugely expensive, chiefly due to the cost of building the Britannia Tubular Bridge over the Menai Strait. The company had relied on Government support in facilitating the ferry service, and this proved to be uncertain. The company opened its main line throughout in 1850. It relied on the co-operation of other railways to reach London, and in 1859 it was absorbed by the London and North Western Railway.
In mechanical engineering, stressed skin is a rigid construction in which the skin or covering takes a portion of the structural load, intermediate between monocoque, in which the skin assumes all or most of the load, and a rigid frame, which has a non-loaded covering. Typically, the main frame has a rectangular structure and is triangulated by the covering; a stressed skin structure has localized compression-taking elements and distributed tension-taking elements (skin).
A box girder or tubular girder is a girder that forms an enclosed tube with multiple walls, as opposed to an I- or H-beam. Originally constructed of wrought iron joined by riveting, they are now made of rolled or welded steel, aluminium extrusions or prestressed concrete.
The Saltwater River Rail Bridge is a large steel arch truss railway bridge completed in 1858 and crossing the Maribyrnong River on the Melbourne to Footscray railway in Melbourne, Victoria. It had the longest span of any bridge in Victoria for thirty years.
The Victoria Bridge, also known as the Victoria Bridge over the Nepean River, is a heritage-listed former railway bridge and now wrought iron box plate girder road bridge across the Nepean River on the Great Western Highway in the western Sydney suburb of Penrith in the City of Penrith local government area of New South Wales, Australia. The bridge was designed by John Whitton, the Engineer–in–Chief of New South Wales Government Railways, and built from 1862 to 1867 by William Piper, Peto Brassey and Betts (superstructure), William Watkins (piers). It is also known as Victoria Bridge, The Nepean Bridge and RTA Bridge No. 333. It was added to the New South Wales State Heritage Register on 27 May 2016.
Alexander McKenzie Ross was a British builder and engineer.
A balloon flange girder or (colloquially) balloon topper is a form of vertical I-beam wrought iron plate girder, where the top flange, instead of being a simple flat plate, is extended into a hollow tube. When a girder is subjected to a positive bending moment the top flange acts in compression making a flat plate flange more susceptible to local buckling than the balloon flange is.
The Surtees Rail Bridge is a rail bridge on the Tees Valley Line over the River Tees in the Borough of Stockton-on-Tees. The bridge is south of Stockton-on-Tees town centre and just north of the adjacent Surtees Bridge which carries the A66 road. The bridge is built on the site of a series of Tees Bridges alternating between two adjacent crossing sites.
William Heap III was an English civil engineer and industrialist who principally worked on the building of railway lines in Britain, Europe, Canada and India through his work alongside manufacturer Thomas Brassey.
The Third Menai Crossing was a proposed bridge over the Menai Strait, connecting the Isle of Anglesey with mainland Wales. The bridge was proposed to carry the A55 as a dual carriageway, and would have superseded the current A55 Britannia Bridge.
Jones, Reg Chambers (2011). Crossing the Menai: an illustrated history of the ferries and bridges of the Menai Strait. Wrexham: Bridge Books. ISBN9781844940745.
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, ISBN0-7524-2753-9
Richards, Robin (2004). Two Bridges over Menai (new reviseded.). Llanrwst: Gwasg Carreg Gwalch. ISBN1845241304.
Rolt, L. T. C. (1960). George and Robert Stephenson: The Railway Revolution, Penguin, Ch. 15, ISBN0-14-007646-8
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. ISBN0262180871.
Further reading
Mitchell, Vic; Smith, Keith (2011). Bangor to Holyhead. West Sussex: Middleton Press. figs. 18–25. ISBN9781908174017. OCLC795179106.
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.
Menai Heritage A community project and museum celebrating the two bridges over the Menai Strait and the town of Menai Bridge
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