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Building of the Month - February 2009

Thomastown Railway Viaduct, JERPOINT WEST Td./JERPOINTABBEY Td., County Kilkenny

Thomastown Railway Viaduct 01 - Representative View (2004)  

Figure 1: A view of Thomastown Railway Viaduct in 2004

Upon completion, the viaduct at Thomastown was renowned as the longest single-span railway bridge in the British Isles.  But it has also an interesting building history.

The railway line between Kilkenny and Thomastown was opened by the Waterford and Kilkenny Railway Company on the 12th of May 1848.  It was thereafter extended from Thomastown to Jerpoint Hill, opening on the 29th of May 1850.  This relatively short section required the construction of a viaduct consisting of timber lattice girders supported on heavy masonry abutments to a design by Captain William Scarth Moorsom (1804-63), engineer.  It was two hundred feet long and seventy-eight feet above the River Nore.  Twenty-five feet wide, it was designed for two lines, although only one was built.  The timber was supplied by Messrs. J.P. Graves of Waterford and New Ross at a cost of £3,300 and construction was completed by the firm of J. and R. Mallet of Dublin.

However from the start there was public unease about its safety.  Michael Sullivan MP (d. 1878) brought these concerns to the railway company.  A series of tests was carried out by a Captain Laffin in 1850; a Colonel Wynne in 1854; and finally in June 1858 by Captain Henry Whatley Tyler (1827-1908) of the Royal Engineers, appointed Inspector of Railways in 1853.  Tyler's report concluded that while it was safe, it needed constant monitoring and that the railway company should start preparing for its replacement with a more permanent structure.

Thomastown Railway Viaduct 02 - Irish Builder (1879) 

Figure 2: A rendering of the original timber construction included as an illustration to accompany an article titled "The Nore Viaduct at Thomastown" in The Irish Builder, March 15th 1879 (pp.85-6)

Finally in 1875 the directors decided to replace the timber structure with one of iron.  The contract was awarded to Messrs. Courtney, Stephens and Bailey of Dublin, with construction starting in the autumn of 1876.  On the evening of the 29th of January 1877 a violent south-westerly gale damaged the old timber superstructure.  By early the following morning the gale increased again and by daybreak all the new construction had blown down, completely blocking the bridge.

It was quickly cleared to allow passage by foot, trains stopping short on both sides.  In his paper to the Institution of Engineers in Ireland Charles Richard Galwey (1840-94), the engineer for the new viaduct, stated: "Every exertion was made to clear the line, but owing to the difficulty of handling such large masses of iron and the shortness of the days, this was not accomplished till the afternoon of the 2nd February".  Two days later engine traffic was allowed to cross the bridge once again.

On the 3rd of August 1877 the new iron structure was tested with five engines and tenders, covering the whole span of the bridge and weighing in all nearly two hundred tons.  The results were satisfactory and the dismantling of the old bridge followed, taking some three months.  Subsequent tests showed that much of the timber was rotten; ironically it was the timber which Moorsom had suggested "should be avoided in the future" which was found to be in the best condition.  Some of the original timber piles could not be extracted so were broken off at riverbed level - where presumably they still survive.

Joe Norton, Department of the Environment, Heritage and Local Government

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