Old Alloa Bridge : Drone footage

The Alloa Swing Bridge was a railway swing bridge across the River Forth that connected Throsk and Alloa as part of the Alloa Railway. The structure was in use from 1885 until 1968.
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 as a 492 metre long , 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 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.