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 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) [1], 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.
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 :
<poem>
Pedwar llew tew Heb ddim blew Dau 'rochr yma A dau 'rochr
drew
</poem>
<poem>Four fat lions Without any hair Two on this side And two over there
</poem>
The lions cannot be seen from the A55 although the idea of raising them to road level has been suggested from time to time.
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.
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 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.
In November 2007, a Public Consultation exercise into the ‘A55 Britannia Bridge Improvement’ commenced. The perceived problems stated include:
In the document, four options are presented, each with their own benefits and constraints
Respondents were overwhelmingly in favour of seeing some improvements, with 70% favouring the solution of building a second bridge.
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.
