Forth Bridge

Forth Bridge
Scotland-2016-Aerial-Edinburgh-Forth Bridge.jpg
Coordinates56°00′01″N 3°23′19″W / 56°00′01″N 3°23′19″W / 56.0004; -3.3886
CarriesRail traffic
CrossesFirth of Forth
LocaleEdinburgh, Inchgarvie and Fife, Scotland
OwnerNetwork Rail
Maintained byBalfour Beatty under contract to Network Rail
Characteristics
DesignCantilever bridge
Total length8,094 feet (2,467 m)[1]
Width120 ft (37 m) at piers[1]
32 ft (9.8 m) at centre[1]
Height361 ft (110 m) above high water[1]
Longest spanTwo of 1,700 feet (520 m)[1]
Clearance below150 ft (46 m) to high water[1]
History
DesignerSir John Fowler and
Sir Benjamin Baker
Construction start1882
Construction endDecember 1889
Opened4 March 1890
Statistics
Daily traffic190–200 trains per day
Forth Bridge is located in Scotland
Forth Bridge
Forth Bridge
Location in Scotland

The Forth Bridge[2] is a cantilever railway bridge across the Firth of Forth in the east of Scotland, 9 miles (14 kilometres) west of central Edinburgh. It is considered as a symbol of Scotland (having been voted Scotland's greatest man-made wonder in 2016), and is a UNESCO World Heritage Site. It was designed by the English engineers Sir John Fowler and Sir Benjamin Baker. It is sometimes referred to as the Forth Rail Bridge (to distinguish it from the adjacent Forth Road Bridge), although this has never been its official name.

Construction of the bridge began in 1882 and it was opened on 4 March 1890 by the Duke of Rothesay, the future Edward VII. The bridge spans the Forth between the villages of South Queensferry and North Queensferry and has a total length of 8,094 feet (2,467 m). When it opened it had the longest single cantilever bridge span in the world, until 1919 when the Quebec Bridge in Canada was completed. It continues to be the world's second-longest single cantilever span, with a span of 1,709 feet (521 m).

The bridge and its associated railway infrastructure are owned by Network Rail.

Background

View of the structure

Earlier proposals

Before the construction of the bridge, ferries were used to cross the Firth.[3] In 1806, a pair of tunnels, one for each direction, was proposed, and in 1818 James Anderson produced a design for a three-span suspension bridge close to the site of the present one.[4] Calling for approximately 2,500 tonnes (2,500 long tons; 2,800 short tons) of iron, Wilhelm Westhofen said of it "and this quantity [of iron] distributed over the length would have given it a very light and slender appearance, so light indeed that on a dull day it would hardly have been visible, and after a heavy gale probably no longer to be seen on a clear day either".[5]

For the railway age, Thomas Bouch designed for the Edinburgh and Northern Railway a roll-on/roll-off ferry between Granton and Burntisland that opened in 1850, which proved so successful that another was ordered for the Tay.[6] In late 1863, a joint project between the North British Railway and Edinburgh and Glasgow Railway, which would merge in 1865, appointed Stephenson and Toner to design a bridge for the Forth, but the commission was given to Bouch around six months later.[7]

It had proven difficult to engineer a suspension bridge that was able to carry railway traffic, and Thomas Bouch, engineer to the North British Railway (NBR) and Edinburgh and Glasgow Railway, was in 1863–1864 working on a single-track girder bridge crossing the Forth near Charlestown, where the river is around 2 miles (3.2 km) wide, but mostly relatively shallow.[7][8] The promoters, however, were concerned about the ability to set foundations in the silty river bottom, as borings had gone as deep as 231 feet (70 m) into the mud without finding any rock, but Bouch conducted experiments to demonstrate that it was possible for the silt to support considerable weight.[9] Experiments in late 1864 with weighted caissons achieved a pressure of 5 t/sq ft (4.9 long ton/sq ft; 5.5 short ton/sq ft) on the silt, encouraging Bouch to continue with the design.[9] In August 1865, Richard Hodgson, chairman of the NBR, proposed that the company invest GB£18,000 to try a different kind of foundation, as the weighted caissons had not been successful.[10] Bouch proposed using a large pine platform underneath the piers, 80 by 60 by 7 feet (24.4 m × 18.3 m × 2.1 m) (the original design called for a 114 by 80 by 9 feet (34.7 m × 24.4 m × 2.7 m) platform of green beech) weighed down with 10,000 tonnes (9,800 long tons; 11,000 short tons) of pig iron which would sink the wooden platform to the level of the silt.[9] The platform was launched on 14 June 1866 after some difficulty in getting it to move down the greased planks it rested on, and then moored in the harbour for six weeks pending completion.[9][11] The bridge project was aborted just before the platform was sunk as the NBR expected to lose "through traffic" following the amalgamation of the Caledonian Railway and the Scottish North Eastern Railway.[9] In September 1866, a committee of shareholders investigating rumours of financial difficulties found that accounts had been falsified, and the chairman and the entire board had resigned by November.[12] By mid-1867 the NBR was nearly bankrupt, and all work on the Forth and Tay bridges was stopped.[13]

Bouch's proposed bridge (top) along with other proposals on the same principle

The North British Railway took over the ferry at Queensferry in 1867, and completed a rail link from Ratho in 1868, establishing a contiguous link with Fife.[14] Interest in bridging the Forth increased again, and Bouch proposed a stiffened steel suspension bridge on roughly the line of the present rail bridge in 1871, and after careful verification, work started in 1878 on a pier at Inchgarvie.[14]

After the Tay Bridge collapsed in 1879, confidence in Bouch dried up and the work stopped.[14] The public inquiry into the disaster, chaired by Henry Cadogan Rothery, found the Tay Bridge to be "badly designed, badly constructed and badly maintained", with Bouch being "mainly to blame" for the defects in construction and maintenance and "entirely responsible" for the defects in design.[15]

After the disaster, which occurred in high winds for which Bouch had not properly accounted, the Board of Trade imposed a lateral wind allowance of 56 lb/sq ft (270 kg/m2).[16] Bouch's 1871 design had taken a much lower figure of 10 lb/sq ft (49 kg/m2) on the advice of the Astronomer Royal, although contemporary analysis showed it would probably have stood, but the engineers making the analysis stated that "we do not commit ourselves to an opinion that it is the best possible" [design].[17] Bouch's design was formally abandoned on 13 January 1881, and Sir John Fowler, W. H. Barlow and T. E. Harrison, consulting engineers to the project, were invited to give proposals for a bridge.[18][19]

Other Languages
العربية: جسر فورث
asturianu: Ponte de Forth
azərbaycanca: Fort körpüsü
čeština: Forth Bridge
Deutsch: Forth Bridge
Ελληνικά: Γέφυρα Φορθ
español: Puente de Forth
euskara: Forth Bridge
français: Pont du Forth
한국어: 포스 교
հայերեն: Ֆորտ Բրիջ
hrvatski: Forth Bridge
italiano: Forth Bridge
עברית: גשר פורת'
ქართული: ფორტ-ბრიჯი
latviešu: Fortas tilts
lietuvių: Forto tiltas
magyar: Forth Bridge
Nederlands: Forth Bridge
日本語: フォース橋
norsk: Forthbroen
norsk nynorsk: Forthbrua
polski: Forth Bridge
português: Ponte do Forth
русский: Форт-Бридж
Scots: Forth Brig
Simple English: Forth Rail Bridge
slovenščina: Most čez zaliv Forth
srpskohrvatski / српскохрватски: Forth Bridge
українська: Форт-Брідж
Tiếng Việt: Cầu Forth
吴语: 福斯桥
中文: 福斯橋