Clunie Footbridge, Loch Faskally, Highland, Perth and Kinross

Description

Aluminium footbridge, built from 1948 to 1950, on the River Tummel at Loch Faskally by the North of Scotland Hydro Electric Board. The consulting engineers were Sir Alexander Gibb & Partners. The contractors were P. & W. McLennan Ltd, Glasgow. The aluminium alloys were supplied by James Booth & Co. Ltd. The concrete piers were constructed by William Tawse, Aberdeen.

The bridge is of a cantilevered design with a shallow-arched deck. It is 95 metres long with a centre span of around 53 metres and two side spans of 21 metres. The width of the walkway is 2 metres. The trusses, handrail, arched soffits, walkway and rivets are aluminium alloy. The trusses are braced in a mirrored 'N' formation between the soffits and the handrail. The bridge is supported by two concrete piers that taper slightly above the water level. Tapering concrete block abutments flank the entrance at either end of the bridge.

Statement of Interest

The Clunie Footbridge is the first major example of an aluminium bridge in Scotland, and is one of the earliest surviving aluminium bridges of notable design quality in the world. Its lightweight, cantilevered design is elegant and forward-thinking and effectively exploits the properties of the modern material. The footbridge is also of interest as an integral part of the Tummel Garry Hydro Electric scheme, a hugely significant feat of post-war engineering in Scotland, and takes into account the picturesque context of the nearby Pitlochry power station. The bridge also illustrates Scotland's historical associations with the early mass production of aluminium on a global scale.

Age and Rarity

This footbridge was built in 1948-50 by the North of Scotland Hydro Board as an integral part of the Tummel Garry Hydro Electric scheme (1947-51), one of the most ambitious civil engineering projects of its time in Scotland. The creation of the Pitlochry Dam and Power Station, around 1km downstream from the bridge, saw the water level at this part of the River Tummel rise by 40 feet to form Loch Faskally.

The bridge was the first aluminium bridge of notable scale in Scotland. A 1948 sketch of the proposed footbridge shows that an aluminium suspension bridge was being considered for the site at that time (Dundee Courier 1948). The slender, cantilevered design that was settled on used significantly less raw material than a suspension bridge, lowering the cost of production. The new bridge was more forward-thinking in its design and appearance, reflecting the relative modernity of its building material. The design may also have changed in line with new understanding of the structural properties of aluminium. Photographs taken in 1950 show the completed footbridge before the water level was raised. They also show the old stone bridge of 1832 being taken down as part of the Loch Faskally works (Canmore; Dundee Courier).

Until the end of the 19th century, aluminium was regarded as a precious metal due to the difficulty in extracting alumina from bauxite ore. The separation process was aided significantly by electrolysis, which required large amounts of electricity. In the UK, this was provided by hydroelectric power generated in the Scottish Highlands. The first hydroelectric powered aluminium smelter in Scotland opened at Foyers in 1896, followed by smelters at Kinlochleven in 1909 and Lochaber in 1929, all for the British Aluminium Company. Among the attributes of aluminium alloys are its lightness and strength-to-weight ratio, and its high resistance to corrosion and staining. Advances in fabrication led to its extensive use in the emerging aviation industry, and for military purposes during the world wars.

The first known use of aluminium alloy in bridge construction was in 1933 in Pittsburgh, home of the American Aluminum Company. In 1946 the first bridge with an all-aluminium span (as well as six steel spans) was constructed in Massena, New York. As production costs are around 25% to 30% higher than reinforced steel, aluminium has rarely been used for large-scale bridges. The Arvida Bridge (1948-50) in Quebec, Canada was the first all-aluminium road bridge in the world and remains the largest by some margin (2018). In more recent years, aluminium has been used for small scale bridges where a longer life-cycle is considered to justify the initial cost (Kaufman 2007).

The three earliest aluminium bridges of notable scale in Europe were built in Britain between 1948 and 1953 (Alison, 1984). The raw material for all three was produced in Scotland. Of these, the 1948 Port Hendon bascule bridge in Sunderland and the 1953 Victoria Dock bascule bridge in Aberdeen were dismantled during the 1970s, making this bridge, the Clunie Footbridge (1948-50) the only survivor. It should be noted that in 1948 a 7 metre flat-deck aluminium footbridge was constructed over the Luibeg Burn in the Cairngorms by the Cairngorm Club. Its aluminium frame was salvaged after it was thrown some distance downstream by a heavy spate in 1956 and rebuilt on higher ground. Between 1950 and 1960, at least six more aluminium bridges were erected in Europe, four of which were footbridges (Alison 1984).

Footbridges are not a rare building type in Scotland and there are many 19th and 20th century examples across rivers and streams in remote and scenic areas throughout the country. Examples near the Clunie Footbridge include the 1913 Port-Na-Craig suspension bridge (LB39858) around 2km downstream in Pitlochry, and the 1911 Coronation suspension bridge (LB47622) located at the Linn of Tummel around 2km upstream. Designed to bespoke specifications, the Clunie Footbridge is the only example of its kind. It is understood to be the earliest surviving aluminium bridge of notable scale in Europe, and is among the first in the world. The innovative and experimental use of this material makes a significant contribution to Scotland's bridge engineering legacy, and this interest is increased by the bridge's elegant architectural design and close contextual association with a nationally significant hydroelectric scheme.

Architectural or Historic Interest

Interior

N/A

Plan form

The Clunie Footbridge uses a standard linear plan form and there is no particular interest under this heading in listing terms.

Technological excellence or innovation, material or design quality

In global terms, Scotland has a long and notable history of innovation in bridge building, pioneering the early use of cast iron, wrought iron and then steel as construction materials. The Clunie footbridge is significant for its early use of aluminium as its principal building material. 'Little information on aluminium alloy riveting practice was available at the time of erection and this aspect required careful investigation' (Paxton and Shipway 2007).

While modest in scale, the cantilevered and lattice design of the footbridge is elegant. Applied to a modern material to great aesthetic effect, the design responds the picturesque context of nearby Pitlochry power station. It therefore reflects the wider design ethos of the North of Scotland Hydro Electric Board and their team of consultant architects, who favoured Modernist architectural treatments.

It is also significant, in terms of the selection of building material, that aluminium extraction in the United Kingdom largely took place in Scotland, using Highland hydropower. This factor may have contributed to the decision to construct the Clunie footbridge using aluminium. Within this context, the aluminium footbridge illustrates leading-edge technological innovation in Scotland as part of a nationally significant civil engineering project.

While aluminium has a low flexibility compared to steel and has been associated with difficulties in joining parts, the Clunie Footbridge has 'proven not to be vulnerable to deflection effects or vibration' (Paxton and Shipway 2007). The stable condition and little-altered appearance (2018) of the bridge is evidence of its technological and design quality in terms of a largely untested material within the context of bridge construction.

Sir Alexander Gibb & Partners were the engineering consultants for the Clunie Footbridge. Founded in 1922 by noted Scottish Civil Engineer Sir Alexander Gibb (1872-1958), the firm brought together architecture and mechanical services to offer clients a complete service. Earlier works in Scotland include the 1932-6 Kincardine Bridge (LB50078, listed category A) across the Firth of Forth, which was Europe's largest swing-span road bridge at the time. Their contribution here further reinforces Scotland's innovative approach to bridge building.

Setting

As noted, the Clunie Footbridge was built as an integral part of the Tummel Garry Hydro Electric power scheme. Pitlochry Dam and Power Station, at the other end of Loch Faskally, is listed at category A (LB47534). While the dam is not inter-visible with the footbridge due to a natural bend in the river, it contributes to the wider context and setting of this important post-war infrastructural project.

The footbridge is located on a tree-lined section of the river at the head of Loch Faskally, and is adjacent to a later A9 road bridge, known as the Coronation Bridge, which passes over the river at a higher level to the east. Remains of the north abutment of the older Clunie Bridge are situated on the bank to the northwest of the current footbridge, with salvaged stone used to create a small viewing platform nearby.

The setting has changed little since the road bridge was built in 1981. It is understood that an addition to the east side of the road bridge will be constructed as part of the ongoing A9 dual-carriageway project (2018) in order to 'minimise impact on the aluminium Clunie Footbridge to the west'. (A9 Dualling Programme, Pitlochry to Killiecrankie, Cultural Heritage, Chapter 15, p11).

Regional variations

There are no known regional variations.

Close Historical Associations

There are no known associations with a person or event of national importance at present (2018).

External Links

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