Britannia Bridge

Britannia Bridge Pont Britannia
The modern Britannia Bridge.
Carries	From 1850: North Wales Coast Line From 1980:A55 road
Crosses	Menai Strait
Locale	Anglesey, North Wales
Characteristics
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
History
Designer	Robert Stephenson
Construction begin	1846
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. Following a 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.

The design required the strait to remain accessible to shipping - on the Navy's insistence - and for 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-foot-long (140 m), rectangular iron tubes, each weighing 1,500 long tons (1,500 tonnes; 1,700 short tons), supported by masonry piers, the centre one of which was built on the Britannia Rock. Two additional spans of 230 ft (70 m) length completed 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).