Alloa Swing Bridge

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 Alloa. The new line was also connected to the North British Railway 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 was still an active port.

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). 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…