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near Kelso, Scottish Borders
This is an interesting wrought iron footbridge across the River Teviot, supported on extensions to the cutwaters of Roxburgh Viaduct, which was built in 1849-50. The footbridge is probably contemporary, given that the viaduct's cutwaters were built with extensions to support a footbridge.Probably made by C. D. Young and Co of Perth.
It is of a type known as a lenticular truss bridge. 'Lenticular' comes from the profile of the truss, which, with its curved top and bottom members, bears a passing resemblance to the shape of a lens. To some extent it works as a bowstring bridge, with loads inducing compression in the top chord and tension in the bottom tie bars.
Each span is practically self-contained, needing no external assistance beyond support from the main viaduct piers for the ends of upper chords, and constraints to prevent the spans from moving on the piers. Constraint against sideways movement is provided at the ends of the chords by an iron bar with 'horns' (see Photos 4 & 5).
The upper chords are of 1" x 5" rectangular section, and the tie bars are 1.5" diameter.
The quality of the blacksmiths' work is extremely high, as study of Photos 7, 8 & 9 indicates. Each triangular bracket comprises a V-shaped forging, with two forked ends to straddle the 1" x 5" flat bar of the top chord, a forked end at the bottom to locate the tie bar, while the gap in the V is skillfully filled by three curved forgings, riveted in place.
The handrail pillars are also skillfully forged. The forked ends can be seen in Photo 4. The blacksmiths would not have approved of the modern attachments which raise the height of the railings!
Also, note the way the upper chords are enlarged at the ends to accommodate the tie bars (Photos 4 & 5).
See the Happy Pontist website for more information on this type of bridge, and illustrations of an example at Maryhill House, Elgin. Another bridge of this type can be seen at Denham Country Park. The principles are the same, but the constructional details differ.