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Chepstow Railway Bridge
River Wye, Chepstow, Monmouthshire, UK
Chepstow Railway Bridge
associated engineer
Isambard Kingdom Brunel
Percy Stuart Attwood Berridge
date  1849 - 19th July 1852, 1948, 1962
UK era  Victorian  |  category  Bridge  |  reference  ST538941
ICE reference number  HEW 1179
photo  Chris Morris
Brunel’s iron bridge across the River Wye at Chepstow completed the South Wales Railway between Gloucester and Swansea. Its functional and economical design — suspending the tracks from wrought iron tubes — was the forerunner of his Royal Albert Bridge at Saltash in Cornwall. The piers of Brunel’s bridge remain, and though its superstructure has been replaced, it continues to carry rail traffic.
The Act of Parliament for construction of the South Wales Railway was passed on 4th August 1845. The railway opened from Chepstow West to Swansea on 18th June 1850, and from Grange Court, near Gloucester, to Chepstow East on 19th September 1851. The final link, crossing the Wye at Chepstow, was the iron bridge designed by Isambard Kingdom Brunel (1806-59).
The Lords of the Admiralty stipulated that there should be a clear span of not less than 91.4m over the river channel, with navigable headway of 15.2m above the highest tide — and Chepstow has one of the highest tidal ranges in the world, at around 14m. At the bridge site, the east bank of the river is a rocky cliff and the west bank is an alluvial slope.
Brunel began designing the bridge in 1849. At this time, the design and construction of suspension-type bridges was becoming more popular. He had already designed road suspension bridges in Bristol (Clifton Bridge, designed 1831, completed in 1864 after his death) and in London (Hungerford Bridge, opened 1845, now demolished) — with main spans of 214m and 206m respectively.
So Brunel knew that a suspension bridge could easily span the Wye. However, the flexible nature of this type structure was unsuitable on its own for the carriage of fixed rail tracks and heavy steam locomotives.
The longest railway spans then constructed (122m or more) were Robert Stephenson's (1803-59) wrought iron box girder tubes over the River Conwy (1848) and Britannia Bridge over the Menai Strait (1850). Brunel had watched with Stephenson the first tube for the latter bridge being floated out to its piers. By combining the iron tube idea with suspension techniques, Brunel had a rigid ‘semi-suspension’ design he could use at Chepstow — using far less raw materials (and so cheaper) than Stephenson's bridges.
The 183m long Chepstow Railway Bridge had two distinct parts. The south-west side had three plate girder spans of 30.5m, supported on 1.8m diameter cast iron cylinders 32mm thick. Three cylinders support each of the first two spans and six the north-east end of the third span — all remain in place. They are founded on limestone bedrock and were sunk an average of 14.5m through bands of clay, quicksand and marl before being backfilled with concrete.
The north-east side of the bridge, spanning 91.4m, appeared to be a parallel pair of tall trusses. At the river end of the main span was a cast iron tower 15.2m high, with a similar tower of masonry at the east end, abutting the cliff. Each 'truss' consisted of a curved circular wrought iron tube 94.2m long and 2.7m in diameter, spanning between towers, with suspension chains to carry the rail tracks and iron bridge deck.
The towers straddled the rail tracks and the tubes rested on wrought iron cross-girders at the tops of the towers. The ends of the tubes were fixed at the iron tower but free to move on rollers at the masonry tower. Vertical A-frame wrought iron girders at the third points of each tube connected the tubes to the deck. Diagonal chains ran between the towers and the A-frames. The suspension chains were kept rigid by vertical inserts. Disc-shaped diaphragms stiffened the tubes internally at 9m intervals.
The tubes were made using the riveted plate construction common to shipbuilding and steam boilers. They were fabricated on the river foreshore, floated into position on barges and jacked into position. Sir William Fairburn (1789-1874) and Stephenson had developed the hydraulic jacking system for the construction of Conwy Bridge.
The two-railtrack bridge contained a total of 1,300 tonnes of wrought iron and 1,080 tonnes of cast iron, with 2,480 cu m of masonry in the abutments, piers and tower. It cost between £65,430 [Taylor, 1854] and £77,000 [NCE] to construct.
Brunel’s bridge opened on 19th July 1852 with one track operational. The other was in use on 18th April 1853. Before it opened, South Wales Railway passengers travelled over the 1816 road bridge (ST535944) by coach between stations on either side of the Wye.
Over the years, small movements of the suspension chains against supports on the bridge's deck weakened the structure. In 1948, the three plate-girder approach spans were replaced. During the 1950s, some of the girders were found to be distorted and train speeds were restricted to 24kph (15mph).
In 1962, the successors of the firm that built the original bridge replaced the main span with welded underline Warren girders. Percy Stuart Attwood Berridge (1901-80) designed the trusses.
All that survives of Brunel's distinctive iron bridge are the cylindrical bridge piers and the south west abutment. However, an annular section of one of the wrought iron tubes is on display (ST537937) at the Mabey Bridge headquarters (formerly Fairfield, descended from Finch & Willey, the original ironwork contractor).
Ironwork: Finch & Willey, Windsor Foundry, Liverpool
Masonry: Robert Sharpe
Steelwork (1962): Fairfield, Chepstowe
Research: ECPK
"Taylor’s Illustrated Guide to the Banks of the Wye"
by Robert Taylor, Chepstow, 1854
reference sources   CEH W&W

Chepstow Railway Bridge