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Neath River and Briton Ferry Viaducts
Briton Ferry, Swansea, Wales, UK
Neath River and Briton Ferry Viaducts
associated engineer
Rendel, Palmer & Tritton
date  1949 - October 1955
era  Modern  |  category  Road Viaduct  |  reference  SS732942
ICE reference number  HEW 1678
photo  © Lewis Clarke and licensed for reuse under this Creative Commons Licence
The contiguous viaducts over the Neath River and Briton Ferry dock area were probably the first large-scale road bridges to be constructed in Britain after World War II. They remain in use, carrying the A48 trunk road. Road traffic also uses the M4 viaduct to the south, which was constructed almost 40 years later.
Until the viaducts were completed in 1955, a ferry was the only way to cross the River Neath at Briton Ferry. Construction commenced in 1949. The two viaducts, separated by a rock outcrop known as Warren Hill, were designed by consulting engineer Rendel, Palmer & Tritton as part of the A48 Neath bypass road scheme.
The western bridge (SS733942), sometimes known as the Cleveland Bridge after the contractor (Cleveland Bridge & Engineering Co.), crosses the River Neath navigation and canal. It consists of a steel-span viaduct some 585m long, carried on concrete piers. There are 17 spans ó two approach spans at either end, 10 spans of 32.8m, two spans of 36m and one span of 91.4m.
The eastern bridge (SS738940) crosses the dock area of Briton Ferry and the South Wales Railway main line. It consists of a 296m steel viaduct with 11 spans. It has an approach span at either end, four spans of 28.5m and five spans of 25.7m. Both viaducts also overfly various minor roads, and other railway tracks and sidings. Each carries dual 6.7m wide carriageways, 2.7m cycle tracks and 1.8m footways.
Neath Viaductís piers are generally reinforced concrete portals with a pair of legs founded on reinforced concrete monoliths. For the river span, three-legged portals are used, each founded on six 2.7m cylinders sunk under compressed air. Piers on Briton Ferry Viaduct are steel portal frames with three legs, hinged at the base and supported on individual reinforced concrete pedestals. In some cases the pedestals are founded independently while others rest on a common slab footing.
The variations in levels and types of foundation reflect the differing ground conditions. Where bedrock is found, it varies in level and slope, and the overlying material is glacial deposit. By contrast, the deck of the River Neath Viaduct is almost level over the river, sloping down at 1 in 30 to each abutment. The roadway of Briton Ferry Viaduct falls west to east at a gradient of 1 in 40.
The decks are of reinforced concrete supported on three main longitudinal steel plate girder ribs at 6.1m centres. Transverse girder beams above the longitudinal girders are set at 2.8m to 3.3m centres. At the ends of the transverse beams, cantilevers with plate girder parapets (at the same centres) extend 5.2m beyond the outer ribs to carry the cycle track and footway.
Longitudinally, the arrangement is of table and suspended spans. The table spans are fixed to two support piers, each with a partial hinge at the base. Overall longitudinal expansion is carried by the links that connect suspended and table spans. Cover plates at carriageway level bridge the expansion gap at these points.
The River Neath is bridged by a 91.4m cantilever suspended span with 28.3m clearance above mean high water level. Here the viaduct is of high tensile steel, and the main girders on both the suspended river span and the adjacent table spans of 36m, project above deck level. The remainder of the girders are of mild steel. All the steelwork was painted with red lead primer and three coats of lead finishing paint when fabricated.
The viaducts opened in October 1955. At that time, Isambard Kingdom Brunel's (1806-59) Briton Ferry Dock (completed 1861) lay beneath the eastern viaduct. The dock closed in 1959 and has since silted up.
Since the viaducts were completed, the principal maintenance issues have related to fixing the expansion joint cover plates securely under the constant pounding of heavy traffic.
In 1992-3, the section of M4 motorway between Baglan and Lon Las, Junctions 41 to 44, opened. It included a new viaduct (SS735939) at Neath, east of Junction 42, situated south of the A48.
Resident engineer: A.F. Allen
Contractor: Cleveland Bridge Engineering Co Ltd
RCAHMW_NPRN 91603, 91604
Research: ECPK
"Road Paper No. 54: The Design of Neath and Briton Ferry Viaducts" by Robert Peel Mears and Ernest Edward Pool, ICE Proceedings, Volume 7, Issue 3, pp.465-490, London, July 1957
"Discussion on Road Paper No. 54: The Design of Neath and Briton Ferry Viaducts" by Robert Peel Mears et al, ICE Proceedings, Volume 7, Issue 3, pp.490-498, London, July 1957
reference sources   CEH Wales

Neath River and Briton Ferry Viaducts