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Britannia Bridge
Britannia Bridge (Welsh: Pont Britannia) is a bridge in Wales that crosses the Menai Strait between the Isle of Anglesey and the city of Bangor. It was originally designed and built by the noted railway engineer Robert Stephenson as a tubular bridge of wrought iron rectangular box-section spans for carrying rail traffic. Its importance was to form a critical link of the Chester and Holyhead Railway's route, enabling trains to directly travel between London and the port of Holyhead, thus facilitating a sea link to Dublin, Ireland.
Two 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 the construction of the Britannia Bridge. After many years of deliberation and proposals, on 30 June 1845, a Parliamentary Bill covering the construction of the Britannia Bridge received royal assent. 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 riveted wrought 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.
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.
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 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. 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 100 ft (30 m), by 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 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.[citation needed] 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" 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.
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Britannia Bridge
Britannia Bridge (Welsh: Pont Britannia) is a bridge in Wales that crosses the Menai Strait between the Isle of Anglesey and the city of Bangor. It was originally designed and built by the noted railway engineer Robert Stephenson as a tubular bridge of wrought iron rectangular box-section spans for carrying rail traffic. Its importance was to form a critical link of the Chester and Holyhead Railway's route, enabling trains to directly travel between London and the port of Holyhead, thus facilitating a sea link to Dublin, Ireland.
Two 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 the construction of the Britannia Bridge. After many years of deliberation and proposals, on 30 June 1845, a Parliamentary Bill covering the construction of the Britannia Bridge received royal assent. 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 riveted wrought 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.
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.
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 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. 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 100 ft (30 m), by 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 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.[citation needed] 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" 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.
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