Forth Road Bridge

Official Heritage Listing Information and Findings

Listed At: Category A

Discussion:

Historic Environment Scotland Number: LB47778

Canmore ID: 50549

Description
Consulting Engineers, Mott, Hay and Anderson in association with Freeman Fox & Partners; commissioned 1947; constructed 1958-64. Suspension road bridge over Forth Estuary. Twin suspension towers; main span 1006m with equal side spans of 408m (total 1822m); approach viaducts at either end supported on paired piers (10 pairs to S, 6 pairs to N), each joined at head by round arch; main deck and suspension towers of steel; approach viaducts steel box girder with concrete deck and concrete piers; suspension towers comprise twin legs (each 150m tall) connected by lattice bracing supporting cable saddles. Main cables anchored in rock below approach viaducts in concrete anchor chambers with Corennie granite transferred aggregate facing. Vertical suspender cables support main deck of bridge. Deck, containing two carriageways and flanking pedestrian cycle/pathways cantilevered out on either side (E and W); suspended deck supported by steel stiffening lattice truss. Granite transferred aggregate facing to bases of approach piers.

Statement of Special Interest
A landmark building in post-war Scotland, particularly given its location next to the famous rail bridge of 1882-90 (and as a continuation of the tradition of innovative Scottish engineering feats exemplified by the latter). In international terms it was the first spun-cable suspension bridge to challenge American designs of the period. It has an elegance deriving from the lightweight appearance of its slender construction components (American Designs of around this date eg Mackinac Bridge of 1957 and Verrazano Narrows Bridge of 1963 were far more solid and heavier in appearance). When it was completed in 1964 it was the longest suspension bridge outside the USA and the fourth longest in the world (it has a total span of 2828m). The engineers Freeman, Fox and Partners were also responsible for 3 comparable large scale suspension bridges in the UK: the Severn Bridge (1961-66), the Erskine Bridge (1967-71) and the Humber Bridge (completed 1981). Of these the Humber Bridge has the longest main span: 1410 metres, making it the longest in the world when it was built. The Forth Road Bridge and the Severn Bridge have main spans of 1006 and 988 metres respectively. The Forth Road Bridge however stands out as the earliest of all of them. Although the project was commissioned (and the Forth Road Bridge Joint Board set up) in 1947, Treasury Authority was not given until 1958 and it was in that year that construction began. The contractors were the ACD Bridge Company, a consortium comprising 3 separate firms which was set up specially to undertake construction of the Forth Road Bridge. The firms were: Sir William Arrol and Company Ltd, The Cleveland Bridge and Engineering Company and Dorman Long Ltd. Situated just to the S of the S approach is the administration building, by Giles Gilbert Scott, Son and Partners.

References
Bibliography
Plans may be viewed at National Archives, West Register House; 'The Forth Road Bridge' in THE BUILDER, 4 September 1964; Forth Road Bridge Joint Board, FORTH ROAD BRIDGE (undated, circa 1964); C McWilliam, LOTHIAN in the 'Buildings of Scotland' series (1978; this edition 1980) pp437-38; Moubray House Press and the Forth Road Bridge Joint Board, SILVER HIGHWAY -THE STORY OF THE FORTH ROAD BRIDGE (1989); notes courtesy of DOCOMOMO (1999).