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Brunel Swing Bridge
Cumberland Basin, Bristol Docks, Hotwells, Bristol, UK
Brunel Swing Bridge
associated engineer
Isambard Kingdom Brunel
date  1849, operational 29th October 1849, certified February 1850
era  Victorian  |  category  Bridge  |  reference  ST567724
ICE reference number  HEW 926
photo  © Anthony OíNeil and licensed for reuse under this Creative Commons Licence
An early Brunel swing bridge of wrought iron girders, and a rare survivor of his Bristol work before the Clifton Suspension Bridge. It was designed to span the enlarged South Entrance Lock, as part of Brunel's upgrading of Jessop's Floating Harbour. The bridge has been relocated and shortened. Long disused, conservation is imperative for its survival.
Bristolís Floating Harbour ó so called because ships using the port could remain afloat regardless of the tide level ó opened on 1st May 1809. The harbour was designed by William Jessop (1745-1814) and impounded 33.6 hectares of the River Avon between Bristol and Avonmouth. The scheme included Cumberland Basin at Hotwells, separated from the tidal river by two entrance locks.
In 1844, the Bristol Dock Company commissioned Isambard Kingdom Brunel (1806-59) to design a new lock to replace Jessopís South Entrance Lock (ST568723). The lock contract work was carried out by "Rennie & Co.", presumably the brothers George Rennie (1791-1866) and John Rennie junior (1794-1874), with bridge and gate ironwork by George Hennet (1799-1857).
In 1848, the City of Bristol authorities acquired the Bristol Dock Company and all its works under the Bristol Dock Transfer Act. The docks were managed thereafter by a committee and work was overseen by Joseph Dand Green, the Docks Superintendent of Works 1843-51.
The west end of the south lock, now known as Brunelís Lock, was to be spanned by a movable bridge. The design work was undertaken in Brunelís London office at 18 Duke Street, Westminster. Though he worked very closely with the whole project, it was probably his trusted chief assistant Robert Pearson Brereton (1818-94) who completed the detailed design.
Initially, Brunel had envisaged a rolling bridge over the lockís 23.2m opening. In January 1849, owing to foundation difficulties, he advised the committee that he now proposed a swing bridge or "swivel bridge".
An original design drawing, dated 10th March 1849, shows it as 37.1m long overall and swivelling about a pivot ó a main span of 26.75m plus 10.35m for the "tail" (counterbalance) end. The pivot is placed centrally across the width of the structure.
The bridge is of riveted wrought iron plates. It consists of two main girders with tubular flanges. The top flange is almost cylindrical, taking an inverted pear shape, the bottom one is near triangular and 394mm deep. The top flange follows an upward curve, resulting in a maximum girder depth of 1.75m over the pivot. Vertical plate web stiffeners are spaced at about 5.9m on the inner sides of the main girders.
The transverse distance between main girders is 4.05m, centre to centre. Connecting cross girders of 305mm x 6mm web and 63mm x 63mm x 10mm angles are spaced generally at 3.1m centres, set at a slight skew in plan. The cross beams support bridge decking of 127mm timber, sheathed diagonally at 38mm.
Twin wrought iron, pre-stressed tie bars run longitudinally inside the top flange, providing rigidity. They are anchored at the tail end and some 10.5m from the pivot at the opposite end. The counterbalance weights that form the tail end are of cast iron.
The wall and base of the pivot pit are of cast iron. The roller path, attached to underside of the bridge, rests on four cast iron rollers, each 762mm in diameter with 102mm cambered treads, running in bearings fixed to the pit bottom. Originally the bridge was operated by hand through vertical pinions engaging in a rack cast into the inner edge of the pivot pit wall.
The casting work was completed in summer 1849 and the structure first swung open and shut in autumn that year. On 29th October 1849, the bridge was operational, though apparently awaiting a final coat of paint. Completion was certified in February 1850.
In 1863, a similar bridge was constructed to cross Jessopís North Entrance Lock (ST567724). It was designed by Thomas Howard (1816-96), the cityís Docks Engineer 1855-82. The contract drawings show it as 23.8m long overall, 18m main span plus 5.8m tail end.
The space restrictions of the north lock led to its redesign, also by Howard. Rebuilding commenced in 1868, and the 1863 bridge was removed. Itís thought it was shortened and re-erected over the entrance to Bathurst Basin (ST586721). The present fixed bridge here is a later replacement steel girder structure.
In 1874, Howardís North Lock opened, providing the sole river entrance to the docks. Brunelís swivel bridge over the south lock was transferred to the north lock and shortened by 3.1m in the main span and by 1.2m in the tail to fit the stepped configuration of the lock entrance.
The hand-cranked swing mechanism was changed to hydraulic operation, probably at some time between 1889 and 1902, powered by fresh water from a pressurised system in Underfall Yard (ST571721) to the east. A length of one of the top flanges has been replaced with a cylindrical steel section of matching diameter, presumably to repair impact damage.
Meanwhile, on 14th April 1872, Howard had recommended closure of Brunelís Lock and obtained the committeeís authority to adapt Brunelís swivel bridge for the new north lock. The Docks Committee intended to convert the south lock into a public graving (dry) dock but changed plans after a petition from the masters of steam vessels in November 1873. In June 1874, Howard estimated the cost of repairing the lock at £3,500 and providing a new bridge as "about £4,000".
The new bridge over Brunelís Lock was a close copy of his original bridge over the north lock, measuring 32.4m overall, 23.3m main span plus 9.1m tail. Key differences include bulb-flat web stiffeners, not available in 1849, and no evidence of longitudinal tie bars within the top flange. The bridge was erected shortly after 26th July 1875, and completed before 30th April 1876, at an actual cost of £2,469.
Howardís manually operated swing bridge was in use until the 1880s, after which it was fixed in position across the south lock. The tail end was shortened by 4.3m and the counterweights removed. It remains in use for access.
In 1965, the Cumberland Basin road network rebuilding was completed and a new steel bridge ó Plimsoll Swing Bridge ó constructed over the docks and river to carry the A3029 Brunel Way. Brunelís swivel bridge became redundant and, in 1968, was fixed in an open position on the south side of the north lock entrance. It now lies partly under the span of the modern swing bridge, with a minimum clearance of about 100mm between the two. The timber decking has disappeared.
In February 1972, Brunelís bridge was Grade II* listed. It is historically significant both for its engineering innovation and for its hand-made wrought iron fabric, now a rare commodity. After the year 2000, the Brunel Swivel Bridge Project was set up to save the structure. In 2013, initial work began to survey it and remove rust.
During winter 2014-5, further surveys and investigations of the condition of the fabric, structure and hydraulic mechanism, along with some trial repairs, were undertaken with grant aid from Historic England. The projectís aim is to restore the bridge to working condition, an ambition that could take one or more years to complete and will require grant funding of around £1m.
Resident engineer: William Bell
Ironwork: George Hennet
Research: ECPK
"The A-Z of Curious Bristol" by Maurice Fells, The History Press, Stroud, 2014
" 'Brunelís Swivel Bridge', Cumberland Basin, Bristol" by David Greenfield, interim report, Brunel Swivel Bridge Group, April 2006
"The Port of Bristol 1848-1884", Bristol Record Societyís Publications, Vol.36, ed. David Large, Alan Sutton Publishing Ltd, Gloucester, 1984
reference sources   CEH W&W

Brunel Swing Bridge