Statement of Special Interest
Drochaid Ceasaig / Kessock Bridge meets the criteria of special architectural or historic interest for the following reasons:
- As a major example of 20th century bridge engineering in Scotland.
- As the largest multi-cable-stayed bridge in Europe at the time of its completion in 1982.
- For its award-winning design by one of the world's leading cable-stayed bridge engineers of the period.
- For its innovative construction methods and use of hydraulic buffers to allow for geological movement in the Great Glen Fault.
- As a major and prominent coastal landmark.
By the late 1960s, it was decided that a bridge over the Beauly Firth was needed to replace the historic ferry crossing between North Kessock and Inverness in order to connect Scotland's northernmost city more directly with the towns and communities in the Highlands. This initiative led to a feasibility study by the Scottish Development Department (SDD) in 1970. Practicality, cost efficiency and structural soundness were the primary design concerns. Extreme weather conditions as well as potential seismic movement along the Great Glen Geological Fault were taken into consideration as part of the design process.
The initial design by Alasdair Cullen Wallace of Crouch and Hogg was for a multi-cable stayed bridge with an innovative A-frame tower offset towards the south side of the bridge. Excessively high estimated costings for the proposal led the SDD to change course and initiate, in 1976, the first design-and-construct competition for a major bridge project in the United Kingdom. 'The least risk in safety, time and money' was central to the design brief (Knox, 1984).
Six designs were shortlisted in March 1977. The winning bridge by the German bridge designer Hellmut Homberg was projected to be the least expensive of the six, at around 17 million pounds (Clements, 1981). Work started on site in April 1978. The completed bridge opened to traffic in July 1982.
A 2013/2014 refurbishment programme included the installation of platforms and ladders at various locations along the underside of the bridge for ease of future maintenance, as well as resurfacing the carriageway, re-stressing of the cables, and the replacement of lighting columns and safety barriers. The general appearance of the bridge has not changed from the date it was completed (2019).
Drochaid Ceasaig / Kessock Bridge was the first multi-cable-stayed bridge of its type in the United Kingdom and the largest cable-stayed bridge (total length, weight and height) in Europe at the time of its completion in 1982.
It was designed to withstand extreme weather and geological conditions. The robustness of the structure is evident in the thick, girder-like appearance of its steel towers and deck, and its substantial concrete piers and spread footings. An unusual combined welding and bolting system was used, meaning that a maximum amount of welding could be carried out in the factory (Wallace, 1984).
An innovative feature is its hydraulic protective system to allow for seismic and geological movement in the Great Glen Geological Fault. There are two piston-like hydraulic buffers at the north abutment. Under slowly applied loads the buffers are extended or retracted, so that during an earth tremor or other type of shock event, the buffers create a stabilising resistance to movement. The Kessock Bridge was among the first bridges in Europe to apply this technology.
Drochaid Ceasaig / Kessock Bridge was designed by Hellmut Homberg (1909-1990), a leading post-war German bridge engineer involved in the design and construction of many important early multi-cable-stayed road bridges (see Age and Rarity). Homberg had a major influence in establishing this type of bridge internationally, with many of his key employees going on to start their own consultancies.
Drochaid Ceasaig / Kessock Bridge won the combined design and construction Saltire Award in 1983, the year after it opened to traffic. The structural form and appearance of the bridge has not been altered since then.
The bridge is located between Inverness and North Kessock, at the narrowest point where the Moray Firth meets the Beauly Firth, and is a major coastal landmark due to its scale. The four towers are prominent on the skyline, and the bridge is a significant foreground feature when viewed from the shore at Kessock and Inverness, particularly when illuminated at night.
The bridge is visible from Thomas Telford's early 19th century ferry pier (Listed Building Number 13464) at North Kessock. The contextual relationship also adds to the interest. The general landscape setting of a wide estuary, with low hills to the north and south of the bridge, has not changed substantially since the bridge opened in 1982.
Age and rarity
While 20th century road bridges are not a rare building type, Drochaid Ceasaig / Kessock Bridge (1976-82) is a major example of its type. It was designed by an influential pioneer of multi-cable bridge engineering at a time when large multi-cable-stayed road bridges were still relatively uncommon internationally. It was the largest multi-cable-stayed road bridge (total length, weight and height) in Europe at the time of its completion in 1982, and the first to the use the balanced 'harp' arrangement of cabling in the United Kingdom.
Cable-stayed bridges, in their modern form, were pioneered during the late 1950s. This was largely a European phenomenon, with much early innovation taking place in Germany during the 1960s. The technology allows spans of 200 metres or more to be traversed without the super-structural cost associated with large suspension bridges.
The Theodor Heuss Bridge (1953-57) on the Rhine, Düsseldorf indicated the potential of the new cable-stayed technology, initiating a run of significant designs throughout the world in the decades to follow (Gimsing, 2009). The George Street Bridge at Newport, South Wales (1964, listed Grade II*) was the first cable-stayed road bridge in the United Kingdom, using a hybrid multi-cable system to support the deck.
The North Elbe Bridge in Hamburg (1962, by Hellmut Homberg) was the first bridge to align cables on a single plane through the central axis of the bridge. This hugely influential design was used on a much larger scale for the Erskine Bridge (1967-71, LB52482, Category A), the first cable-stayed road bridge in Scotland. The George Street Bridge, the Erskine Bridge over the River Clyde and the Wye Bridge (1966, listed Grade II) over the Severn estuary have been recognised as significant early cable-stayed bridges in the United Kingdom.
During the 1960s Hellmut Homberg (1909-1990) spearheaded the development of multi-cable-stayed bridges with balanced 'harp' and 'fan' shaped cable configurations. The Rees-Kalker Bridge (1965-67 by Hellmut Homberg) has paired towers with cables in a parallel 'harp' arrangement similar to Homberg's winning design for Kessock Bridge. By modelling Kessock Bridge on a successful earlier design, Homberg may have increased his chance of winning the competition, particularly as a low risk solution was part of the design brief. Homberg's largest multi-cable-stay bridge in Britain is the Queen Elizabeth II Bridge, Dartford, completed in 1991.
Around 150 cable-stayed road bridges had been constructed worldwide by 1985, rising to over 1000 bridges by 2014 (Svensson, 2014). Almost all large-scale cable-stay road bridges built after 1985 use multi-cable systems like Kessock Bridge. This is due in part to increased stability and relative ease of assembly. Individual cables can be replaced cost-effectively without compromising the strength of the structure. The Queensferry Crossing over the Firth of Forth (2017) is the most recent example of this bridge type in Scotland (2019).
Social historical interest
Drochaid Ceasaig / Kessock Bridge has historical, social, economic and cultural associations as an important part of Scotland's civil engineering and bridge-building heritage.
Before the Industrial Revolution the Highlands of Scotland had a network of communication routes along its coastline and numerous inland waterways. The north underwent numerous far-ranging and comprehensive improvement schemes during the 19th century, using bridges, canals and roads to connect remote areas with the main centres of population and industry.
After the Second World War, increasing reliance on the motor car saw major infrastructural investment in the new road and motorway networks across the United Kingdom. An integrated road network was seen as a priority in and near Scotland's largest areas of population where the use of private cars and the need for commercial road transport was most pressing. Many new bridges spanning rivers, lochs and glens were required as a result of these changes. Among them the Forth Road Bridge (1958-64, LB47778) which, when opened, was the longest suspension bridge outside of the United States of America; and the Erskine Bridge (1967-71, LB52482) which remains the longest mono-cable-stayed bridge in Britain. Drochaid Ceasaig / Kessock Bridge is the most southerly of three firth crossings on the A9 trunk road into the Highlands, the others being the Cromarty Firth Bridge (1979, not listed) and the Dornoch Firth Bridge (1991, not listed).
The replacement of ferries with road bridges in many locations across Scotland has had a significant social and economic impact on more traditional ways of life. Kessock Bridge is a good example of how a major civil engineering work can affect the economy and way of life of rural communities. Before 1982, journeying north of Inverness meant crossing the Beauly Firth via the historic (reportedly 15th century) ferry between South and North Kessock (see LB13464) or travelling more than 20 miles around the Firth. Construction of the bridge made the ferry service redundant, significantly reducing journey times between Inverness and the far northeast. The bridge also brought communities within the Black Isle area to the north of the Beauly Firth within commuting and shopping distance of Inverness. These factors have contributed to the significant growth of the city since 1982.
Canmore: http://canmore.org.uk/ CANMORE ID 68591
Clements, L (1981) Kessock Bridge, Inverness (Scotland), published in International Association for Bridge and Structural Engineering (IABSE) Periodical, Volume 1, 1981, pp.3-5.
Cullen Wallace, A. & Nissen J. (1984) Kessock Bridge: Joint Engineers' Role, paper 8745 published in Proceedings of the Institute of Civil Engineers, February 1984, pp.67.
Gifford, J (1992) Buildings of Scotland - Highland and Islands, p.195
Inverness Courier (20/07/1982) Farewell to the Ferry, p.5.
Knox, H; Homberg, H (et al) (1984) Design and Construction of Kessock Bridge, published in Proceeding of the Institute of Civil Engineers, Part 1, 1984, p.179.
Kurrer, K (2018) The History of the Theory of Structures: Searching for Equilibrium. Germany: John Wiley and Sons, p.1008.
Paxton, R and Shipway, J (2007) Civil Engineering Heritage: Scotland – Highlands and Islands. Edinburgh: Thomas Telford Publishers, p153.
Pelke, E and Kurrer, K (2012) The Art of Major Bridge-Building – Hellmut Homberg and his Contribution to Multiple Cable-Stayed Spans, Steel Construction 5, November 2012, pp.251-265.
Svensson, H (2012) Cable-Stayed Bridges: 40 Years of Experience Worldwide. Germany: John Wiley and Sons.
Gimsing, N J (2009) History of Cable-stayed Bridges. Proceedings of the International Association for Bridge and Structural Engineering (IABSE) Conference - Cable-Stayed Bridges - Past, Present and Future (2009): http://www.ce.jhu.edu/perspectives/protected/handouts/IABSE%20cable%20stayed%20bridge%20article.pdf [Accessed, 2019]
Structurae: International Database and Gallery of Structure: Hellmut Homberg at
https://structurae.net/persons/hellmut-homberg [Accessed, 2019]
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