18 C O N T E X T 1 3 9 : M A Y 2 0 1 5 was designed by staff in hisWestminster office in 1849. It became operational in October that year. In 1872–73 the bridge was shortened and relocated to its present position over the North Entrance Lock (also known as Howard’s Lock). There it remains, immobile, parallel to the lock it once spanned. The bridge was decommissioned in 1968 after construction of the nearby Plimsoll Bridge as part of the new Cumberland Basin road system. It narrowly avoided being scrapped when the new bridge was constructed. The Brunel Swivel Bridge is partly concealed under the new Plimsoll Bridge. When the Plimsoll Bridge is opened there is just 80mm clearance. Brunel’s Swivel Bridge, which spanned the new lock, was fabricated at the Great Western Steamship works, where the SS Great Britain had been built a few years earlier and is now displayed in splendour. Brunel came down to Bristol several times to inspect the bridge while it was under construction, and many original drawings and some correspondence from the construction period survive. The bridge is 33.7 metres long overall, with the free end overhanging 23 metres. It would weigh an estimated 68–70 tonnes with its timber decking, although this is now missing. The bridge incorporates some features which the pioneering engineer went on to develop in his future bridge designs. The main wrought-iron edge beams comprise circular and triangular riveted tubes at the top and bottom of a web, a theme developed on his much bigger ‘tubular’ bridges. Tensioned wrought-iron ties fitted inside the top tubes are similar in form to the links used on his suspension bridge.These tension bars appear to have been intended to compress the edge-beams so as to improve their structural strength and reduce the flexibility of the span in use. The rotating wrought-iron deck structure is mounted on a turntable running on four cast-iron wheels. The moving structure is held central by a large cast-iron post or pintle, its weight being carried in part by a large centring screw. It appears that this screw rusted solid early in its life, and had been abandoned by the time the bridge was moved in the 1870s. But the structure continued to operate without some of its central-bearing parts for another 90 years. The deck was originally hauled round by a manual winch mounted on the side of one of the main beams. It must have been very hard work. In 1901–2 operation was made easier when a pair of WG ArmstrongWhitworth and Co hydraulic rams were installed in pits below ground, utilising the 750psi (47 Bar) water pressure supplied by the hydraulic pumps at the dock’s nearby Underfall Yard.The pumps are still operational, but the supply pipes and rams are not, although they remain almost complete. The Swivel Bridge stands on the harbourside, adjoining a popular walking and cycling route.Those afloat see it at close quarters when passing through the entrance lock.The bridge is owned by Bristol City Council, but the restoration project is run by an alliance of local groups: Avon Industrial Buildings Trust, Clifton and Hotwells Improvement Society, and Bristol Industrial Archaeology Society. The Swivel Bridge The Swivel Bridge seen from the air in 1906
RkJQdWJsaXNoZXIy MjgyMjA=