General arrangement of the Tay Bridge
Did you know?
The New Tay Railway Bridge is 2miles 73 yards (3286m) long. It can vary in overall length by as much as 3ft 9in (1.14m) due to thermal expansion. Temperature extremes recorded in the Dundee district since 1980 have been +29C and -17C.
A key structure in the Scottish railway route, the Tay Bridge brought increased travel and trade opportunities to the east coast of Scotland. Out of the Tay Bridge disaster of 1879 a new structure emerged which set new standards for bridge building in Britain.
By the 1860s the battle between the Scottish North British and Caledonian railway companies had taken hold. Supremacy in controlling the major routes through Scotland would depend on which company would be first to bridge the River Tay at Dundee. The original Tay Bridge was built by the North British Railway Company and designed by Thomas Bouch, a civil engineer who had built many small branch lines in the north of England and the south east of Scotland. A railway bridge across the Tay had widespread support but from the start the design of the bridge was roundly criticised, its single track particularly so on grounds of both capacity and stability. As construction began, Bouch was forced to change his plans for the bridge. The foundations and bases were redesigned, the original brick piers replaced with braced cast iron columns and the number of spans was reduced which made each significantly wider. Despite ongoing difficulties in its construction, the bridge was opened with much celebration on 31 May 1878. Within a year it had increased the fortunes of the North British Railway as well as those for Dundee and towns throughout Fife. Passenger numbers between Dundee and Fife doubled and the railway saw a 40% increase in freight traffic. However, on the night of 28 December 1879 and in a terrible storm, the thirteen central ‘high girders’ of the bridge fell down. The subsequent Court of Inquiry fundamentally blamed the design of the bridge for the collapse, and its judgement rested on Thomas Bouch.
From the ashes of the old
After the disaster both the North British Railway and supporters of the Tay Bridge were determined that it should be rebuilt. The company quickly submitted a Bill to Parliament for the rebuilding of the old bridge, but as Thomas Bouch was associated with the rebuilding project, Parliament rejected the Bill. After dispensing of the services of Thomas Bouch, William Henry Barlow, who had sat on the Court of Inquiry, was invited to report on the best course of action. After thorough investigation of the options, his recommendation was to build a new double line bridge, completely independent of the old.
Barlow’s design for the new bridge was deeply influenced by the presence of the old. To satisfy stipulations made by the Board of Trade, the bridge was to be constructed exactly parallel alongside the old in order to keep navigation channels open, and its height was to be reduced from 88ft in the old bridge to 77ft in the new. As in the old bridge, the railway line was to run on the top of the approach girders, and through the girders of the high, larger navigation spans. Barlow recommended that if the spans of the new bridge were to be kept the same, girders from the old bridge that were unaffected by the collapse of the high girders, were able to be re-used in the new. The new bridge was to be built 60ft upstream from the old, allowing the old bridge to become ‘staging’ for the men and materials in the construction of the new. The approaches onto the new bridge were altered; to the south the branch lines were joined on brick arches nearer to the shore at Wormitt, and to the North the eastwards curve into Tay Bridge Station (now called Dundee) was softened. Stringent tests on weight and wind loading in the design and construction of the new bridge were also to be undertaken. The proposals for the ‘New Tay Viaduct’ were accepted by Parliament in October 1881, and the firm William Arrol & Co of Glasgow was appointed contractor.
The new bridge took just 5 years to build, thanks in most part to special pontoon equipment with hydraulic legs which were designed by William Arrol. Various arrangements of these hydraulic pontoons were used to sink and construct the brick and concrete foundation columns, to erect the wrought iron piers, to move the old girders into position for the new bridge, and to erect the new navigation spans. The completed bridge is 10711ft in length, 8396ft of which is in a straight line running virtually north / south across the Tay until it curves eastwards towards Dundee. There are 85 piers; 1-28 forming the south approach, 28-41 the ‘navigation spans’ and 41-85 the north approach. The new Tay Bridge was opened to traffic, without ceremony on 20 June 1887.
Page first created: Tuesday, January 17, 2012
Page last updated: Saturday, February 25, 2012
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