Chepstow Bridge
Encyclopedia
Isambard Kingdom Brunel
Isambard Kingdom Brunel, FRS , was a British civil engineer who built bridges and dockyards including the construction of the first major British railway, the Great Western Railway; a series of steamships, including the first propeller-driven transatlantic steamship; and numerous important bridges...
in 1852. The "Great Tubular Bridge" over the River Wye
River Wye
The River Wye is the fifth-longest river in the UK and for parts of its length forms part of the border between England and Wales. It is important for nature conservation and recreation.-Description:...
at Chepstow
Chepstow
Chepstow is a town in Monmouthshire, Wales, adjoining the border with Gloucestershire, England. It is located on the River Wye, close to its confluence with the River Severn, and close to the western end of the Severn Bridge on the M48 motorway...
, which at that point forms the boundary between Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
and England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, 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
Royal Albert Bridge
The Royal Albert Bridge is a railway bridge that spans the River Tamar in the United Kingdom between Plymouth, on the Devon bank, and Saltash on the Cornish bank. Its unique design consists of two lenticular iron trusses above the water, with conventional plate-girder approach spans. This gives...
at Saltash
Saltash
Saltash is a town and civil parish in Cornwall, England, United Kingdom. It has a population of 14,964. It lies in the south east of Cornwall, facing Plymouth over the River Tamar. It was in the Caradon district until March 2009 and is known as "the gateway to Cornwall". Saltash means ash tree by...
.
Background
Brunel had to take the two tracks of the South Wales RailwaySouth Wales Railway
The South Wales Railway was a broad gauge railway that linked the Gloucester and Dean Forest Railway with Neyland in Wales.-History:The need for the railway was created by the need to ship coal from the South Wales Valleys to London, and secondly to complete Brunel's vision of linking London with...
across the river Wye. The Admiralty
Admiralty
The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...
had insisted on a 300 feet (91.4 m) clear span over the river, with the bridge a minimum of 50 feet (15.2 m) above high tide. The span would have to be self supporting, since although the Gloucestershire
Gloucestershire
Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....
side of the river consists of a limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
cliff, the Monmouthshire
Monmouthshire
Monmouthshire is a county in south east Wales. The name derives from the historic county of Monmouthshire which covered a much larger area. The largest town is Abergavenny. There are many castles in Monmouthshire .-Historic county:...
side is low-lying sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
ary deposit subject to regular flooding. Thus on that side, there was nowhere for an abutment
Abutment
An abutment is, generally, the point where two structures or objects meet. This word comes from the verb abut, which means adjoin or having common boundary. An abutment is an engineering term that describes a structure located at the ends of a bridge, where the bridge slab adjoins the approaching...
capable of either resisting the outward push of an arch bridge
Arch bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...
, or the inward pull of a conventional suspension bridge
Suspension bridge
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...
. In any case, neither could be used: an arch bridge would not have met the height and width restrictions imposed by the Admiralty, and suspension bridges were notoriously unfit for carrying railway trains. The concentrated weight caused the chains to deflect, allowing the bridge-deck to ride dangerously up and down. A self-supporting truss bridge
Truss bridge
A truss bridge is a bridge composed of connected elements which may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges...
was the only option.
Robert Stephenson
Robert Stephenson
Robert Stephenson FRS was an English civil engineer. He was the only son of George Stephenson, the famed locomotive builder and railway engineer; many of the achievements popularly credited to his father were actually the joint efforts of father and son.-Early life :He was born on the 16th of...
had bridged the River Conwy
River Conwy
The River Conwy is a river in north Wales. From its source to its discharge in Conwy Bay it is a little over long. "Conwy" is sometimes Anglicized as "Conway."...
(1848) and the Menai Strait
Menai Strait
The Menai Strait is a narrow stretch of shallow tidal water about long, which separates the island of Anglesey from the mainland of Wales.The strait is bridged in two places - the main A5 road is carried over the strait by Thomas Telford's elegant iron suspension bridge, the first of its kind,...
s (1850) with spans of 400 and 450 feet (137.2 m) respectively, using large box-girder sections of riveted wrought iron. Conwy-like box-girders would have been very expensive to use at Chepstow as well as being heavy (problematic, since the spans had to be lifted much higher than at Conwy). Brunel, characteristically, sought a radical solution. He had already built a bowstring or tied arch bridge
Tied arch bridge
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch, or top chord, are borne as tension by the bottom chord , rather than by the ground or the bridge foundations...
at Windsor
Windsor Railway Bridge
Windsor Railway Bridge is a wrought iron 'bow and string' bridge in Windsor, Berkshire, designed by Isambard Kingdom Brunel. It carries the ex-GWR branch line from Slough to Windsor into Windsor and Eton Central station...
(1849) consisting of three triangular cross-section cellular arch ribs "strung" by wrought iron deck girders supported by vertical hangers from the arches. This was the same year as Stephenson's tied arch High Level Bridge
High Level Bridge
The High Level Bridge is a road and railway bridge spanning the River Tyne between Newcastle upon Tyne and Gateshead in North East England.-Design:...
at Newcastle upon Tyne
Newcastle upon Tyne
Newcastle upon Tyne is a city and metropolitan borough of Tyne and Wear, in North East England. Historically a part of Northumberland, it is situated on the north bank of the River Tyne...
, which was supposed to have influenced Brunel at Chepstow. However, Brunel's solution for the latter was to make a leap forward, based, nevertheless, on sound engineering principles and a variation of the tied-arch theme.
The experiments of William Fairbairn
William Fairbairn
Sir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...
, and the mathematical analysis of Eaton Hodgkinson
Eaton Hodgkinson
Eaton A. Hodgkinson was an English engineer, a pioneer of the application of mathematics to problems of structural design.-Early life:...
had shown by a series of experiments that an enclosed box girder
Box girder
A box or tubular girder is a girder that forms an enclosed tube with multiple walls, rather than an or H-beam. Originally constructed of riveted wrought iron, they are now found in rolled or welded steel, aluminium extrusions or pre-stressed concrete....
, made of riveted wrought iron, combined relative lightness with great strength. The tubular wrought-iron girder – be the cross-section rectangular, triangular or circular – formed a most efficient truss component. If the cross-section was large enough it could be self-supporting. It was Fairbairn's experiments that led to the design of the Menai
Britannia Bridge
Britannia Bridge 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...
and Conwy
Conwy Railway Bridge
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 was built by Robert Stephenson to a design by William Fairbairn, and is similar in construction to Stephenson's other famous...
bridges. Stephenson had originally proposed using a box-girder section suspended from chains. The box section would, he argued, be stiff enough to overcome the conventional problems of the bridge-decks of suspension bridges. In the event, Fairbairn showed that a properly constructed box girder would be strong enough so that the chains could be dispensed with. Nevertheless, the decision (not to use chains) was taken late in the project, so the Britannia bridge support towers were still built with holes for the chains. Stephenson's box-girders were a great innovation, and using steel or pre-stressed concrete instead of wrought iron, box-girder construction is the standard today for large bridges. But as Berridge has observed, "Brunel was never one to follow fashion for fashion's sake... (at Chepstow)... Here was the real engineer at work, designing the bridge to suit the site and the best way of getting it into position".
The bridge filled a gap in the main rail line between Gloucester
Gloucester
Gloucester is a city, district and county town of Gloucestershire in the South West region of England. Gloucester lies close to the Welsh border, and on the River Severn, approximately north-east of Bristol, and south-southwest of Birmingham....
and Swansea
Swansea
Swansea is a coastal city and county in Wales. Swansea is in the historic county boundaries of Glamorgan. Situated on the sandy South West Wales coast, the county area includes the Gower Peninsula and the Lliw uplands...
. The line between Chepstow railway station
Chepstow railway station
Chepstow railway station is a part of the British railway system owned by Network Rail and is operated by Arriva Trains Wales. Chepstow station is on the Gloucester to Newport Line. It is located within of the town centre, at Station Road, Chepstow...
and Swansea was opened on 18 June 1850, and on 19 September 1851 the line was completed between Gloucester and a station east of the river, known as Chepstow East
Chepstow East railway station
Chepstow East railway station was a station on the South Wales Railway . It was about a mile east of Chepstow railway station, at the road bridge close to the future junction of the Wye Valley line...
. Until the bridge was completed and opened, through passengers were carried from one station to the other by coach
Coach (carriage)
A coach was originally a large, usually closed, four-wheeled carriage with two or more horses harnessed as a team, controlled by a coachman and/or one or more postilions. It had doors in the sides, with generally a front and a back seat inside and, for the driver, a small, usually elevated seat in...
, using the 1816 road bridge across the River Wye. The railway bridge was opened to public use for the first time on 19 July 1852; Chepstow East station closed at the same time as redundant. Originally there was only one line of railway over the bridge; a second was brought into use on 18 April 1853. The new railway line, and bridge, had the effect of reducing the journey time between London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
and Swansea from 15 hours, by rail, road and ferry
Aust Ferry
Aust Ferry or Beachley Ferry was a ferry service that operated across the River Severn between Aust and Beachley both in Gloucestershire, England. Before the Severn Bridge opened in 1966, it provided a daily service for road traffic crossing between the West Country and South Wales...
, to 5 hours by rail.
The Chepstow Bridge design
Brunel recognised that a circular cross-section tubular girder — a shallow “bow”, excellent in compression and tension — could be strung by suspension chains to form a stiff, self-supporting structure very much lighter (thus less expensive) than a Stephenson-type box girder. Instead of hanging the chains from towers and suspending the bridge deck from them, Brunel used the chains to stress and slightly bow the tubes, which were braced against the chains using struts. The bridge deck was rigid, because it was effectively clamped against the tubes by the chains. Brunel solved the problem in his own way, and for more than 100 years, the Chepstow and subsequently the Royal Albert BridgeRoyal Albert Bridge
The Royal Albert Bridge is a railway bridge that spans the River Tamar in the United Kingdom between Plymouth, on the Devon bank, and Saltash on the Cornish bank. Its unique design consists of two lenticular iron trusses above the water, with conventional plate-girder approach spans. This gives...
were the only suspension bridges on the British railway system.
In spite of their apparent rivalry, Brunel and Stephenson were great personal friends, to the extent that they supported each other professionally. When Stephenson was under pressure during the enquiry following the collapse of his cast-iron girder bridge over the River Dee
River Dee, Wales
The River Dee is a long river in the United Kingdom. It travels through Wales and England and also forms part of the border between the two countries....
killing several people, Brunel did not desert him. In spite of his extreme distrust of the use of cast-iron girders for such purposes, Brunel refused to condemn them when cross-examined as an expert witness. He was also present to provide Stephenson moral support, when the great Britannia box-girders were floated across the river prior to being jacked up to their final positions. So when it came to the revolutionary design at Chepstow, The Times of 24 February 1852, reported that “Mr Stephenson, the eminent engineer, has examined the (great railway) bridge (at Chepstow) and concurred in the plan adopted by Mr Brunel...”.
The bridge was a triumph of the application of a radical design to a specific problem using available materials. The total cost (£77,000) was half what the Conwy bridge cost (£145,190 18s 0d) — admittedly with a main span of only 300 feet (91.4 m) compared with Conwy's 400 feet (121.9 m), but there were no deep-water foundations needed at Conwy, and at Chepstow, the cost included a further 300 feet (91.4 m) of land spans.
With regard to the appearance of the bridge, the Illustrated London News
Illustrated London News
The Illustrated London News was the world's first illustrated weekly newspaper; the first issue appeared on Saturday 14 May 1842. It was published weekly until 1971 and then increasingly less frequently until publication ceased in 2003.-History:...
stated that "the peculiarity of the site did not permit any display of 'Art' - that is, of architectural embellishment; indeed, a pure taste rejects any attempt to decorate a large mechanical work with sham columns, pilasters, and small ornamental details."
The bridge was constructed on site for Brunel by Edward Finch of Liverpool
Liverpool
Liverpool is a city and metropolitan borough of Merseyside, England, along the eastern side of the Mersey Estuary. It was founded as a borough in 1207 and was granted city status in 1880...
as partner in the firm Finch & Willey. After it was completed, Finch remained in Chepstow, and developed a major engineering and, later, shipbuilding business on the site, beside the river. The adjoining site, now occupied by the engineering firm Mabey Bridge
Mabey Group
The Mabey Group is a British-based group of engineering companies, which specialises in bridging, steel fabrication, plant hire and construction products...
(formerly Fairfield Mabey), is still (as of 2010) engaged in prefabricated bridge construction, and in 1987 was responsible for building the A48 road
A48 road
The A48 is a major trunk road in Great Britain. It runs from the A40 at Highnam west of Gloucester to the A40 at Carmarthen. Before the construction of the M4 motorway and the first Severn Bridge in the mid 1960s it was the principal route into South Wales. For most of its journey through Wales,...
bridge which now runs alongside the railway bridge.
Epilogue
However, even Brunel was not infallible, and his foresight in allowing for slight movement of the suspension chains against supports on the bridge-deck to relieve stress, led to a weakening of the structure. In the 1950s, the speed of trains using the bridge was restricted to 15 miles per hour (6.7 m/s), because some of the girders had become distorted. In 1962, a new structure to support the bridge beneath the main span was put in place. Nevertheless, Brunel's Chepstow bridge was a watershed, leading to a final refinement of the design in his great masterpiece, the Royal Albert BridgeRoyal Albert Bridge
The Royal Albert Bridge is a railway bridge that spans the River Tamar in the United Kingdom between Plymouth, on the Devon bank, and Saltash on the Cornish bank. Its unique design consists of two lenticular iron trusses above the water, with conventional plate-girder approach spans. This gives...
over the River Tamar
River Tamar
The Tamar is a river in South West England, that forms most of the border between Devon and Cornwall . It is one of several British rivers whose ancient name is assumed to be derived from a prehistoric river word apparently meaning "dark flowing" and which it shares with the River Thames.The...
at Saltash.
Of the bridges mentioned here, the Windsor and Conwy bridges are still standing and in use, although the Conwy spans have been shortened using intermediate supports. The Britannia bridge sadly had to be replaced when some boys, bird-nesting, managed to set fire to the bridge lining. The Chepstow bridge also had to be replaced. But Brunel's brilliant and economical design concept lives on in the Royal Albert Bridge, which continues to carry the former Cornwall Railway
Cornwall Railway
The Cornwall Railway was a broad gauge railway from Plymouth in Devon to Falmouth in Cornwall, United Kingdom. The section from Plymouth to Truro opened in 1859, the extension to Falmouth in 1863...
main line into Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
.