Le Jour ni l’Heure 0467 : Forth Rail Bridge, 1890, South Queensferry, West Lothian, Écosse, Royaume-Uni, samedi 14 avril 2012, 14:22:57
From Wikipedia, the free encyclopedia
For the nearby road bridge, see Forth Road Bridge.
CrossesFirth of Forth
LocaleEdinburgh, Inchgarvie and Fife, Scotland
Maintained byBalfour Beatty under contract to Network Rail
DesignerSir John Fowler and
Sir Benjamin Baker
Total length2,528.7 m (8,296 ft)
Longest span2 of 521.3 m (1710 ft)
Clearance below46 metres (151 ft)
Opened4 March 1890
Daily traffic190–200 trains per day
Coordinates56.000421°N 3.388726°WCoordinates: 56.000421°N 3.388726°W
The Forth Bridge is a cantilever railway bridge over the Firth of Forth in the east of Scotland, to the east of the Forth Road Bridge, and 14 kilometres (9 mi) west of central Edinburgh. It was opened on 4 March 1890, and spans a total length of 2,528.7 metres (8,296 ft). It is often called the Forth Rail Bridge or Forth Railway Bridge to distinguish it from the Forth Road Bridge, although it has been called the "Forth Bridge" since its construction, and was for over seventy years the sole claimant to this name.
The bridge connects Scotland's capital city, Edinburgh, with Fife, leaving the Lothians at Dalmeny and arriving in Fife at North Queensferry; it acts as a major artery connecting the north-east and south-east of the country. Described by the Collins Encyclopaedia of Scotland as "the one immediately and internationally recognised Scottish landmark", it is a Category A listed building and was nominated by the British government in May 2011 for addition to the UNESCO World Heritage Sites in Scotland.
Until 1917, when the Quebec Bridge was completed, the Forth Bridge had the longest single cantilever bridge span in the world. It still has the world's second-longest single span. The bridge and its associated railway infrastructure is owned by Network Rail Infrastructure Limited.
Construction of an earlier bridge, a suspension bridge designed by Sir Thomas Bouch, got as far as the laying of the foundation stone, but was stopped after the collapse of another of his works, the Tay Bridge. The public inquiry into the Tay bridge disaster declared the Tay Bridge "poorly designed, poorly constructed and poorly maintained". Bouch was disgraced, and the project was subsequently taken over by Sir John Fowler and Sir Benjamin Baker. who designed a structure that was built by Glasgow based company Sir William Arrol & Co. between 1883 and 1890. Baker and his colleague Allan Stewart received the major credit for design and overseeing building work.
First steel structure in United Kingdom
The bridge was the first major structure in Britain to be constructed of steel; its contemporary, the Eiffel Tower was built of wrought iron.
Large amounts of steel had become available only after the invention of the Bessemer process in 1855. Until 1877 the British Board of Trade had limited the use of steel in structural engineering because the process produced steel of unpredictable strength. Only the Siemens-Martin open-hearth process developed by 1875 yielded steel of consistent quality. The 64,800 tons[clarification needed] of steel needed for the bridge was provided by two steel works in Scotland and one in Wales.
The bridge is, even today, regarded as an engineering marvel. It is 2.5 kilometres (1.6 mi) in length, and the double track is elevated 46 metres (151 ft) above the water level at high tide. It consists of two main spans of 521.3 metres (1,710 ft), two side spans of 207.3 metres (680 ft), and 15 approach spans of 51.2 metres (168 ft). Each main span comprises two 207.3 metres (680 ft) cantilever arms supporting a central 106.7 metres (350 ft) span truss. The weight of the bridge superstructure was 51,324 tonnes (50,513 long tons), including the 6.5 million rivets used. The bridge also used 18,122 cubic metres (640,000 cu ft) of granite.
The three great four-tower cantilever structures are 100.6 metres (330 ft) tall, each tower resting on a separate granite pier. These were constructed using 21 metres (70 ft) diameter caissons, those for the north cantilever and two on Inchgrvie acting as coffer dams while the remaining two on Inchgarvie and those for the south cantilever, where the river bed was 28 m (91 ft) below high-water level used compressed air to keep water out of the working chamber at the base.
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 was increased to 63. Eight men were saved from drowning by boats positioned in the river under the working areas. Hundreds of workers 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 the Queensferry History Group 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.
Work at the site began at the end of 1882, with the construction at South Queensferry of the extensive workshops where the steelwork was to be fabricated. These eventually occupied more than 50 acres. Work on the foundations of the bridge began in February 1883, and the first of the caissons was launched on 26 May 1884. The bridge was completed in December 1889, and load testing of the completed bridge was carried out on 21 January 1890. Two trains, each consisting of three heavy locomotives and 50 wagons loaded with coal, totalling 1,880 tons in weight, were driven slowly from South Queensferry to the middle of the north cantilever, stopping frequently to measure the deflection of the bridge. This represented more than twice the design load of the bridge: the deflection under load was as expected. A few days previously there had been a violent storm, producing the higest wind pressure recorded to date at Inchgarvie, and the deflection of the cantilevers had been less than 25 mm (1 in). The first complete crossing took place on 24 February, when a train consisting of two carriages carrying the chairmen of the various railway companies involved made several crossings. The bridge was opened on 4 March 1890 by the Prince of Wales, later King Edward VII, who drove home the last rivet, which was gold plated and suitably inscribed. The key for the official opening was made by Edinburgh silversmith John Finlayson Bain. There is a plaque on the bridge commemorating this.
The use of a cantilever in bridge design was not a new idea, but the scale of Baker's undertaking was unprecedented. Much of the work done was without precedent, including calculations for incidence of erection stresses[clarification needed], provisions made for reducing future maintenance costs, calculations for wind pressures made evident by the Tay Bridge disaster and the effect of temperature stresses on the structure.
Where possible, the bridge used natural features such as Inchgarvie, an island, the promontories on either side of the firth at this point, and also the high banks on either side.
The bridge has a speed limit of 50 miles per hour (80 km/h) for passenger trains and 20 miles per hour (32 km/h) for freight trains. The weight limit for any train on the bridge is 1,422 tonnes (1,400 long tons; 1,567 short tons) although this was waived for the frequent coal trains which used the bridge prior to the reopening of the Stirling-Alloa-Kincardine railway, provided two such trains did not simultaneously occupy the bridge. The route availability code is RA8, meaning any current UK locomotive can use the bridge, which was designed to accommodate heavier steam locomotives.
Up to 190–200 trains per day crossed the bridge in 2006.
Prior to the opening of the bridge, the North British Railway (NBR) had lines on both sides of the Firth of Forth between which trains could not pass except by running at least as far west as Alloa and using the lines of a rival company. The only alternative route between Edinburgh and Fife involved the ferry at Queensferry, which was purchased by the NBR in 1867. Accordingly, the NBR sponsored the Forth Bridge project which would give them a direct link independent of the Caledonian Railway; a conference at York in 1881 set up the Forth Bridge Railway Committee, to which the NBR contributed 35% of the cost. The remaining money came from three English railways, who ran trains from London over NBR tracks: the Midland Railway, to which the NBR connected at Carlisle and which owned the route to London (St Pancras), contributed 30%, whilst the remainder came equally from the North Eastern Railway and the Great Northern Railway, who between them owned the route between Berwick-upon-Tweed and London (King's Cross), via Doncaster. This body undertook to construct and maintain the bridge. In 1882 the NBR were given powers to purchase the bridge, which it never exercised. At the time of the 1923 Grouping, the bridge was still jointly owned by the same four railways, and so it became jointly owned by these companies' successors, the London Midland and Scottish Railway (30%) and the London and North Eastern Railway (70%). The Forth Bridge Railway Company was named in the Transport Act 1947 as one of the bodies to be nationalised and so became part of British Railways on 1 January 1948. Under the Act, Forth Bridge shareholders would receive £109 of British Transport stock for each £100 of Forth Bridge Debenture stock; and £104-17-6d (£104.87½) of British Transport stock for each £100 of Forth Bridge Ordinary stock.
A structure like the Forth Bridge needs constant maintenance and the ancillary works for the bridge included not only a maintenance workshop and yard but a railway "colony" of some fifty houses at Dalmeny Station. The track on the bridge is of "waybeam" construction: 12 inch square baulks of timber 6 metres long are bolted into steel troughs in the bridge deck and the rails are fixed on top of these sleepers. In 1992 the bridge was re-railed with standard BS113A rail (54 kg/m). Prior to 1992 the rails on the bridge were of a unique "Forth Bridge" section.
Although modern trains put fewer stresses on the bridge than the earlier steam trains, the bridge needs constant maintenance, and this is currently undertaken by Balfour Beatty under contract to Network Rail.
"Painting the Forth Bridge" is a colloquial expression for a never-ending task, 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 modern maintenance, such a practice never existed, although under British Rail management, and before, the bridge had a permanent maintenance crew.
A recent repainting of the bridge commenced with a contract award in 2002, for a schedule of work which was completed on 9 December 2011. It involved the application of 230,000 m2 of paint at a total cost of £130M. This new coat of paint is expected to have a life of at least 25 years, and perhaps as long as 40, thus removing the need for constant repainting. The work involved blasting all previous layers of paint off the bridge for the first time in its history, allowing repairs to be made to the steel.
In a report produced by JE Jacobs, Grant Thornton and Faber Maunsell in 2007 which reviewed the alternative options for a second road crossing, it was stated that "Network Rail has estimated the life of the bridge to be in excess of 100 years. However, this is dependant [sic] upon NR’s inspection and refurbishment works programme for the bridge