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Report - Britannia Bridge - Menai Straights - Dec 2010 -

Discussion in 'High Stuff' started by georgie, Dec 13, 2010.

  1. georgie

    georgie He Never Even Got There
    Regular User

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    info taken from wiki

    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. Following a fire in 1970 it was rebuilt as a two-tier steel truss arch bridge, carrying both road and rail traffic.

    The etymology of the Britannia in Britannia Bridge is a corruption of the Welsh name for the rock in the middle pillar on which the bridge was built on – Carreg y Frydain. The root of the word 'Frydain' is 'brwd' meaning 'turbulence' or 'effervescence' and is a descriptive name referring to the wild nature of the Strait. As in many other cases, the name is misspelled due to unfamiliarity of some to the area or language.

    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), 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.

    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 '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 although the idea of raising them to road level has been suggested from time to time.

    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 gradually lifted into place using powerful jacks.

    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 inside the bridge dropped a burning torch, setting alight the tar-coated wooden roof of the tubes (see Britannia Bridge Official Fire Report, BBC News video). 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 fatally compromised by the intense heat. 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 (albeit with only a single line of rails rather than the twin tracks that existed prior to the fire) 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.

    visited with kevsy21

    a few old pics before the fire

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    and as the bridge and lions stand today
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    only 1 line remains today with 2 lanes of traffic wizzing overhead
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    coming to the middle section makes this a bit more interesting
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    a climb down onto a small gantry and your greeted with this sight
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    down even further and your onto the service walkways

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    looking back from the opposite end of the walkway
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    this section took you down to the bottom but you couldnt go anywhere as it was just one of the support beams (we didnt venture down here we wasnt sure if we would get spotted)
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    statue in the distance
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    one of the lions at the opposite end to where we had got in
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    looking back from the start
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    underbelly of the bridge
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    closeup of a lion
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    road level
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    #1 georgie, Dec 13, 2010
    Last edited: Dec 13, 2010

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