The Alloa Swing Bridge was a railway

swing bridge A swing bridge (or swing span bridge) is a movable bridge that can be rotated horizontally around a vertical axis. It has as its primary structural support a vertical locating pin and support ring, usually at or near to its center of gravit ...

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 Scottish Gaelic, Gaelic name for the ...

that connected Throsk and

Alloa Alloa (Received Pronunciation ; Scottish pronunciation /ˈaloʊa/; , 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 where some say it ceases to ...

as part of the Alloa Railway. The structure was in use from 1885 until 1968.

History

The Alloa Railway 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 to

. The new line was also connected to the

North British Railway The North British Railway was one of the two biggest of the five major Scottish railway companies prior to the 1923 Grouping. It was established in 1844, with the intention of linking with English railways at Berwick. The line opened in 1846, ...

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 (; ; ) is a City status in the United Kingdom, city in Central Belt, central Scotland, northeast of Glasgow and north-west of Edinburgh. The market town#Scotland, market town, surrounded by rich farmland, grew up connecting the roya ...

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 The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up of ...

), 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. A ...

). 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 executive ...

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 A railbus is a lightweight passenger railcar with an automotive engine. It shares many aspects of its construction with a bus, typically having a bus (original or modified) body and four wheels (2 axles) on a fixed base instead of on bogies. O ...

. 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