By Neil Calver
The Clifton Suspension Bridge, spanning the picturesque Avon Gorge, is for many the symbol of the City of Bristol. It is, also, a site for the celebration of not only Victorian science, but also more contemporary innovations.
Its story begins in 1754 with the vision of a Bristol wine merchant who left a legacy to build a bridge over the Gorge. The twenty-four year old Isambard Kingdom Brunel was appointed project engineer – his first major commission. Work began in 1831 but the project was blighted by political and financial difficulties and by 1843, with only the towers completed, the project was abandoned. The Bridge was, however, completed in 1864 at a cost approaching £100,000 in memorial of Brunel who had died five years previously.
Well, that is one version of the story. Adrian Vaughan, railway historian and biographer of the engineer, claims in his recent book The Intemperate Engineer, that Brunel’s idolatry is not justified – it is shorthand, convenient history. Vaughan argues that Brunel’s reputation today stems from ‘heroic myths’ promoted in a biography from the 1950s by Lionel Thomas Caswell Rolt which glossed over not only the engineers shortcomings, but also the contribution of others. Vaughan’s analysis of Brunel’s diaries and letters at the National Archives, Kew, and at Bristol University, show that the eventual bridge design was fundamentally different from Brunel’s and was the work of William Barlow and Sir John Hawkshaw.
While Brunel’s design had two suspension chains supporting it, the final design had three, with a third more ‘hangers’ – the bard from the chains down to the road. It also had an entirely different system of attaching the ‘hangers’ to the chains, to correct the twisting effect that Brunel’s system would have had on the chains. The method of stiffening under the road was also entirely new. While Brunel had designed a system of wooden struts, these were not considered sufficient so were replaced with riveted, wrought iron, lattice work girders.
We can, however, more readily identify the workings of a more contemporary addition to the Bridge. A question for you: how many light bulbs do you think it takes to illuminate this magnificent structure at night? None. The illumination system – which was switched on at a ceremony in 2006 to mark the 200th birthday of Brunel – is comprised of four elements. Along the length of the chains from which the bridge is suspended are more than 3,000 one watt LEDs (light emitting diodes), in groups of three, each focused on a small section of the chain and throwing into relief the giant nuts which connect the links; Fluorescent tubes beneath the handrail illuminate the walkway and silhouette and emphasize the delicate design of the iron lattice running the length of the bridge; lamps concealed within the arches of the two piers at each end of the bridge, and in the spaces around the top, reinforce the three-dimensional aspects of the bridge. The two sides of each pier are washed with light, carefully directed and focused to avoid the problems associated with urban glow.
Low powered lights concealed beneath each end of the Bridge deck gently downlight the abutments so that, when viewed from the north or south, the Bridge no longer appears to ‘float’ above the Avon Gorge but can be seen to be connected to the structures which support it. The illumination system normally uses no more electricity than a detached house with its domestic appliances switched on.