Opening bridges are required where a railway crosses a navigable waterway without leaving sufficient headway for ships to pass underneath. There are relatively few of these in Britain, because inland navigation is mainly by small vessels, such as canal barges. Most railway bridges over navigable water are high enough to allow ships to pass below.
The most common type of opening bridge on British railways is the swing bridge. This one is at Folkestone Harbour and is the third at this site. The first bridge was constructed in 1849, when the railway was extended across the harbour basin. It was replaced in 1893. The present bridge dates from 1930 and the deck is of steel plate construction. Like its predecessors, and most railway swing bridges, it has a centre pivot. Some swing bridges are pivoted off one of the abutments.
The bridge over the River Arun at Ford is of no aesthetic merit, but is of interest on account of its former opening span. It was completed in 1862, replacing an earlier timber bridge. Rather than being a swing bridge, it had a retractable centre section, 90 feet long, which could be drawn back onto the fixed span at the eastern end. Although the bridge could be opened in eight minutes and closed in five, considerable preparatory work was necessary, disconnecting the rails and the various wires and pipes that crossed the span. Additional steel girders were added outside the wrought iron fixed spans in 1898. The Southern Railway obtained powers to fix the bridge closed prior to electrification of the railway, and it was last opened in April 1936. The new fixed span is carried on reinforced concrete piers with steel cross members, in place of the old timber ones. A Railway Magazine article about this bridge, published in August 1955, can be found here.
There was a bridge which worked on similar principles at Newport, Isle of Wight. This carried the Ryde and Sandown lines over the River Medina. The bridge had three spans of 26 feet 6 inches, with that at the Newport station end being the movable one. This was retracted into a cavity under the trackbed on the approach to the bridge.
King's Ferry bridge, onto the Isle of Sheppey, has a lifting deck.
Until the opening of the railway to Sheerness in 1860, the Isle of Sheppey had been accessible only by ferry. The Sittingbourne & Sheerness Railway provided a combined road and rail bridge at King's Ferry, with a lifting section to allow passage of shipping. Having taken responsibility for passage to the island, the railway company took the role of Wardens and Jury of the King's Ferry and were entitled to charge tolls to road users. The original bridge lasted until 1904, when it was replaced by a one to the design of the Scherzer Rolling Lift Bridge Company, with the equipment on the Sheppey side. (A similar bridge, but much larger than the King's Ferry one, remains in use carrying the Doncaster to Scunthorpe line over the River Trent). With increasing motor traffic over the bridge, Kent County Council took responsibility for the road in 1929 and the Southern Railway ceased charging tolls.
A Railway Magazine article about the Scherzer bridge, published in December 1954, can be found a here.
The Scherzer bridge survived long enough to carry electric trains, but for less than a year. Electric services to Sheerness started on 15 June 1959 and the new King's Ferry bridge was officially opened on 20 April 1960. The new bridge, built west of the old one, is a lifting bridge where the deck remains horizontal as it is raised. The lifting deck, which is 123 feet long by 50 feet wide, is suspended from four concrete towers, 103 feet 4 inches high. The mainland and island pairs of towers are each linked at the top by concrete cross-members. The towers are each built off a 32 feet diameter concrete base, founded on clay at a depth of about 50 feet. These give a navigable passage through the bridge 57 feet wide. The bridge deck comprises two longitudinal riveted steel plate girders, with welded cross members, with the railway and footpath on steel plate and the highway on concrete. The 465 tons weight of the deck is counter-balanced by a 110 ton weight in each of the towers. The deck is raised up to 95 feet above high water by two 120 horsepower direct current electric motors located below the towers. At its normal operating speed the deck can be fully lifted in 1½ minutes. On both sides of the lifting span there are three approach spans, the main members being steel plate girders. The bridge was designed by Mott, Hay & Anderson and the main contractor was John Howard. Machinery was by Sir William Arrol and steelwork by Dorman Long. A pleasing feature of King's Ferry bridge is the care taken in the design of the towers, which taper slightly and have curves on their outer corners.
Significant works were required to divert the road and railway over the new bridge, with the road being moved from east of the railway to west of it. Swale Halt, directly south of the bridge, had to be replaced, the new platform being of prefabricated reinforced concrete components to standard Southern Region d esign. There is no conductor rail on the lifting deck, due to the difficulty in providing a power supply, and electric trains coast across. The only problems with the bridge have occurred during very hot weather, when the lifting deck has expanded so that it cannot easily be closed. The bridge lost most of its road traffic following the opening of a high level road bridge to the west in 2006.
This picture shows where the lifting deck (to the left) meets the fixed mainland approach span (to the right). The four lifting cables can be seen.
There is a similar lifting bridge, but with a shorter span and steel frame towers, over Deptford Creek, between Deptford and Greenwich. The present structure was built in 1963, to replace the original bridge dating from 1838. It was designed by Southern Region engineers and constructed by Sir William Arrol & Co. The bridge is now fixed in the closed position and continuously welded rails have been laid across it.
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This page was created 10 January 2010