The Alloa Swing Bridge was a railway

swing bridge A swing bridge (or swing span bridge) is a movable bridge that has as its primary structural support a vertical locating pin and support ring, usually at or near to its center of gravity, about which the swing span (turning span) can then pi ...

across the

River Forth The River Forth is a major river in central Scotland, long, which drains into the North Sea on the east coast of the country. Its drainage basin covers much of Stirlingshire in Scotland's Central Belt. The Gaelic name for the upper reach of t ...

that connected

Throsk Throsk (In gd, Badan Deathach, meaning the thicket among the mist) is a village in the Stirling council area of Scotland. It lies on the A905 road east of Fallin close to the River Forth. The United Kingdom Census 2001 recorded the populati ...

and

Alloa Alloa (Received Pronunciation ; educated Scottish pronunciation /ˈaloʊa/; gd, Alamhagh, possibly meaning "rock plain") is a town in Clackmannanshire in the Central Lowlands of Scotland. It is on the north bank of the Forth at the spot wher ...

as part of the

Alloa Railway The Alloa Railway was intended to bridge the River Forth linking Alloa with the south without using a ferry. History The railway was authorised on 11 August 1879, it started from a new junction, Dunmore Junction, on the South Alloa branch of ...

. The structure was in use from 1885 until 1968.

History

The

obtained authority through an Act of Parliament on 11 August 1879 to open a section of line linking the South Alloa Branch of the

Scottish Central Railway The Scottish Central Railway was formed in 1845 to link Perth and Stirling to Central Scotland, by building a railway line to join the Edinburgh and Glasgow Railway near Castlecary. The line opened in 1848 including a branch to South Alloa. The ...

. The new line was also connected to the

North British Railway The North British Railway was a British railway company, based in Edinburgh, Scotland. It was established in 1844, with the intention of linking with English railways at Berwick. The line opened in 1846, and from the outset the company followe ...

and both opened on 1 October 1885. The rail line was double track except for the bridge crossing, which was single track. The swing bridge design was necessary to allow the passage of shipping up and downstream at a time when

Stirling Stirling (; sco, Stirlin; gd, Sruighlea ) is a city in central Scotland, northeast of Glasgow and north-west of Edinburgh. The market town, surrounded by rich farmland, grew up connecting the royal citadel, the medieval old town with its me ...

was still an active port.

Design and construction

The bridge was designed by the consulting civil engineers, Crouch and Hogg, and built by contractors Watt and Wilson, both of Glasgow. The bridge was designed as a 492 metre long (1,615 feet), multi-span, wrought-iron, bow-girder structure, with a horizontal curvature of 865 metres (43

chains A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. ...

). The span of the swing bridge was 44 metres, providing a clear opening of 19 metres for river vessels on each side of a steam-powered, rotating, central pier that housed a cabin structure to allow operation of the steam engine. The central pier of the rotating span was protected by a timber cutwater that projected 43 metres up and down river. When the swing bridge was opened for river traffic, the ends of the rotating span were supported by structures at each end of the cutwater. The deck of the bridge was at a level of 7 metres above high water level and was supported on piers, each consisting of two stone columns connected by ironwork at top and base. Several aerial and deck level photographs of the bridge that illustrate the layout of the structure are available from the

Royal Commission on the Ancient and Historical Monuments of Scotland The Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) was an executive non-departmental public body of the Scottish Government that was "sponsored" inanced and with oversightthrough Historic Scotland, an executi ...

Incidents during operation

The bridge was damaged by collisions on at least three occasions. In 1899, gales drove a sailing ship against one of the piers. In October 1904, a schooner also collided with one of the piers as it passed through the swing span, displacing some girders. Rail traffic was suspended until June 1905. In August 1920, a German warship, surrendered at the end of the First World War, broke free from its moorings and crashed into the bridge. The damage was serious enough to close the bridge to rail traffic until March 1921. As a result of these incidents, three stone piers were replaced by cast iron ones and additional cross-bracing was added to all piers.

Decline, closure and demolition

Throughout its existence the bridge had carried passenger and freight traffic, but both gradually declined and in the 1960s, the passenger service was replaced by a four-wheeled railbus. Trains continued to bring coal to the swing bridge engine house until this was fixed in the open position for river traffic in May 1970. The connecting lines and the deck were dismantled in 1971, leaving only the piers and abutments, which remain as of 2021.

References

External links

{{cite web , title=Alloa Bridge , url=https://www.railscot.co.uk/locations/A/Alloa_Bridge/ , website= Railscot , accessdate=25 July 2020 Bridges completed in 1885 Swing bridges in Scotland Demolished bridges in Scotland Railway bridges in Scotland Buildings and structures demolished in 1971 1885 establishments in Scotland 1971 disestablishments in Scotland Alloa