Forth Bridge (railway)

For the nearby road bridge, see Forth Road Bridge.

The Forth Bridge is a railway bridge over the Firth of Forth in the east of Scotland, to the east of the Forth Road Bridge, and 14 km (9 miles) west of Edinburgh. It is often called the "Forth Rail Bridge" to distinguish it from the Forth Road Bridge. The bridge connects Scotland's capital Edinburgh with Fife, and acts as a major artery connecting the north-east and south-east of the country.

History

Construction of an earlier bridge, designed by Sir Thomas Bouch, got as far as the laying of the foundation stone, but was stopped after the failure of another of his works, the Tay Bridge. On Bouch's death the project was handed over to Sir John Fowler and Sir Benjamin Baker, who designed a structure that was built by Sir William Arrol's company between 1883 and 1890. Baker - "one of the most remarkable civil engineers Britain ever produced" - and his colleague Allan Stewart received the major credit for design and overseeing construction work.

Construction

The bridge is, even today, regarded as an engineering marvel. It is 2.5 km (1.5 miles) in length, and the double track is elevated 46 m (approx. 150 ft) above high tide. It consists of two main spans of 1,710 ft, two side spans of 675 ft, 15 approach spans of 168 ft, and five of 25 ft. Each main span comprises two 680 ft cantilever arms supporting a central 350 ft span girder bridge. The three great four-tower cantilever structures are 340 ft (104 m) tall, each 70 ft diameter foot resting on a separate foundation. The southern group of foundations had to be constructed as caissons under compressed air, to a depth of 90 ft. At its peak, approximately 4,600 workers were employed in its construction. Initially, it was recorded that 57 lives were lost; however, after extensive research by local historians, the figure has been revised upwards to 79. As well as the large number of deaths, eight more men were saved by boats positioned in the river under the working areas. Hundreds more were left crippled by serious accidents, and one log book of accidents and sickness had 26,000 entries. In 2005, a project was set up by South Queensferry Historical Society to establish a memorial to those workers who died during the bridge's construction. In North Queensferry, a decision was also made to set up memorial benches to commemorate those who died during the construction of both the rail and the road bridges, and to seek support for this project from Fife Council. More than 55,000 tons of steel were used, as well as 18,122 m³ of granite and over eight million rivets. The bridge was opened on March 4, 1890 by the Prince of Wales, later King Edward VII, who drove home the last rivet, which was gold plated and suitably inscribed. A contemporary materials analysis of the bridge, circa 2002, found that the steel in the bridge is of good quality, with little variation.

The use of a cantilever in bridge design was not a new idea, but the scale of Baker's undertaking was a real pioneering effort, afterwards extensively followed in different parts of the world. Much of the work done was without precedent, including calculations for incidence of erection stresses, provisions made for reducing future maintenance costs, calculations for wind pressures made evident by the Tay Bridge disaster, the effect of temperature stresses on the structure, and so on.

Painting the Forth Bridge

Although modern trains put fewer stresses on the bridge than the earlier steam trains, the bridge needs constant maintenance. "Painting the Forth Bridge" is a colloquial term for a never-ending task (a modern rendering of the myth of Sisyphus), coined on the erroneous belief that, at one time in the history of the bridge, repainting was required and commenced immediately upon completion of the previous repaint. According to a 2004 New Civil Engineer report on contemporary maintenance, such a practice never existed, although it is the case that under British Rail management, and before, the bridge had a permanent maintenance crew.

A contemporary repainting of the bridge commenced with a contract award in 2002, for a schedule of work expected to continue until March 2009, involving the application of 20,000 m² of paint at a cost estimate of £10M a year. This new coat of paint is expected to have a life of 20 years, which should see the bridge free from painters for a good few years.

References

Charles Matthew Norrie (1956). Bridging the Years - a short history of British Civil Engineering. Edward Arnold (Publishers) Ltd.
New Civil Engineer 5th February 2004, page 18.
McKean, Charles, Battle for the North: The Tay and Forth Bridges and the 19th Century Railway Wars, Granta Books, (August 7, 2006), ISBN 1862078521.

Popular culture

The bridge is featured prominently in a scene in Alfred Hitchcock's 1935 film The 39 Steps and even more so in the 1959 remake.
The bridge long featured in posters advertising the soft drink Barr's Irn Bru, with the slogan: Made in Scotland, from girders
The bridge was lit up red for BBC's Comic Relief in 2005
A countdown clock to the millennium was placed on the bridge in 1998.
The Bridge, a novel by Iain Banks, is mainly set on a fictionalised version of the bridge.
In Alan Turing's most famous paper about artificial intelligence, one of the challenges put to the subject of an imagined Turing test is "Please write me a sonnet on the subject of the Forth Bridge". The test subject in Turing's paper answers, "Count me out on this one. I never could write poetry". ^*
The Kincaid Rail bridge in the video game San Andreas is based on this bridge, perhaps because of the Scottish office of the programmers..
"Painting the Forth Bridge" is an expression used to indicate a never-ending (and maybe even somewhat pointless) task (see section above).