14 August 2012

Scottish Bridges: 39. Ghurka Bridge, Aberlour

A short distance to the south of Aberlour's Victoria Bridge lies another suspension footbridge, although very different in both scale and form.

I only knew of the bridge thanks to an entry at the excellent Bridgemeister website, which reports that it was built by Ghurka troops temporarily stationed nearby, as a replacement for an old railway bridge. The masonry abutments from the railway bridge have been retained.

The bridge spans a minor watercourse which empties into the River Spey nearby, and is very basic in nature. Steel portal towers support steel spiral strand rope. Steel rod hangers carry a timber deck. The saddles for the main cables are exceptionally simplistic (pictured, right).

The main cables are anchored by wrapping them around anchor pins, and then clamping the steel rope together (pictured, left). This is a straightforward, military-style detail, quite different to what you would see on a more conventional, civilian bridge. It does not lend itself to easy adjustment.

Most light suspension footbridges use trussed parapets to provide stiffness to the deck, as is the case at the Victoria Bridge. The Ghurka Bridge is unstiffened, with only slender longitudinal timber beams below the deck spanning between the hangers.

The result is unsurprising: it deflects significantly under load, and is easy to excite into movement simply by jumping up and down. Indeed, this is so much the case that I was afraid I might break it! You can get some idea of how much it moves by watching somebody run across it, although I think the video doesn't really make clear quite how shaky the bridge is.

I have to say, I really don't understand how this design was ever deemed acceptable on such a readily accessible public footpath.

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