The Gaunless Bridge has started its return journey to Stockton & Darlington Railway territories. This bridge captures the genius of Stephenson – his willingness to give something tricky a go – and the pioneering vision of the S&DR. If you’d like to learn more about this example of lenticular loveliness, then read on!
In 1822 George Stephenson was made Engineer to the Stockton & Darlington Railway Company (he was previously the surveyor) and construction of the line commenced under his supervision. Works were also supervised by two engineers working under him and once his son Robert had returned from a six month stint at Edinburgh University he undoubtedly had considerable involvement too.
In July 1823, George Stephenson was able to announce that twenty two miles of the line had been completed, that all the rails and chairs had been delivered and that the railway should be complete by midsummer 1824 (it wasn’t though). Stone from local quarries was to be the main building material and would be used to create boundary walls, sleepers and bridges from Witton Park at least as far as Shildon; the remaining stretch of line making use of oak for sleepers from Portsmouth and quick sets as boundaries (Jeans 1974, 59-60). The Gaunless Bridge was to be made from a combination of stone abutments and an iron deck and piers. It would span the river Gaunless on level ground between the two inclines at Etherley and Brusselton.
Despite severe weather late in 1823 when cuttings collapsed, quarry tracks became quagmires and workmen were injured, George Stephenson was able to report in December that the Gaunless had been spanned in October by the iron bridge designed by him and cast by Burrell and Company of Newcastle (Rolt 2012). Burrell and Co were located next to Robert Stephenson’s newly opened works at Forth Street in Newcastle and George was a partner in the firm until the 31st December 1824 (Tomlinson 1987, 93). Burrell and Co worked to a design submitted by George Stephenson to the directors on the 28th December 1822. There must have been some degree of confidence that the Act of Parliament altering the line to the present position of the bridge would be secured as the commissioning of the bridge and much of the line took place before assent was received in May 1823. George Stephenson himself attended a Committee before the House of Lords to answer questions on his estimates, but he seems to have had an easy visit with the process being supported by powerful friends and this may have inspired the necessary confidence.
Heavy snow followed by flooding when the thaw came, damaged the bridge and so Stephenson rebuilt it with an additional span, taking it to four spans, to allow more space for floodwater. The bridge came into use when the line was opened on 27th September 1825. From the outset it was assumed that the waggons (and later, passenger coaches) using it would be powered by horse rather than locomotive.
It is the first railway bridge to use an iron truss and its lenticular truss design is extremely unusual; indeed it has been credited as the first bridge to use the idea of lenticular construction ( J. G. James in the Transactions of the Newcomen Society vols 52 and 59 and cited in Addyman and Haworth 2005, 13). The technology of the bridge is fascinating. It used two curved girders in a lens shape (see image below), one above and one below. The upper member was for compression, as for an arch bridge, and the lower in tension, as for a suspension bridge. The idea is that this forms a balanced truss, where the sideways forces in each member cancel out, being equal but opposite in direction. This leads to a truss with no side forces on its supports and so only requiring simple piers with no need for endways stiffness. Vertical members connected the two girders and supported the load-carrying deck of the bridge. These vertical members also transfered some load between the two girders, as to maintain their lens shape. An efficient truss distributes the load of the deck between the two girders, rather than placing the majority of the load on one truss member. George Stephenson didn’t invent this technological method, but the theory was not well known. The inspiration for the design may have had its origins in the seventeenth century when a Croatian bishop, Faustus Verantius (1551-1617) produced illustrations of each type of bridge in his Machinae novae which was published in 1616 (Addyman and Haworth 2005, 13).
Stephenson’s sound grasp of engineering and his knowledge of this method resulted in him using this combination of wrought and cast iron and while this resulted in a technical symmetry between tension and compression, it also resulted in an aesthetic symmetry. It’s other claim to technological achievement was that it was built ‘entirely without bolts or rivets’ ( Holmes 1975, 135).
The bridge remained intact until 1901 when it was dismantled, so that an alternative structure could be placed on the abutments which would accommodate heavier loads of coal. The trestle legs were cut off at river level and the superstructure moved to Brusselton Colliery. The remains of the trestle legs can still be seen on the river bed when water levels are low. The two stone abutments remained on either side of the river Gaunless, but were altered by the NER in order to accommodate a new bridge structure. The alterations took the form of recesses set into the top of the abutments to accommodate plate girders. Plans produced at the time show clearly where the alterations were to be made and suggest that other modifications were made to strengthen the stonework of the abutments.
NER 1901 plan showing alterations to be made to the abutments in order to accommodate the plate girders. Stonework would be removed from the abutment cores, but the dressed stone external faces would remain (NRM 12/6 Box 147)
The original ironwork was preserved, however, and when a railway museum opened in 1926 at Queen Street, York, the bridge was one of the exhibits marking the centenary of the Stockton & Darlington Railway in 1925. A presentation model of the Gaunless Bridge was also made for the North Eastern Railway in 1875 to mark the 50th anniversary of the opening of the Stockton and Darlington Railway. It still features in the Science Museum’s web site. The original ironwork was moved to the National Railway Museum in York in 1975, which represents its fifth re-assembling.
In 2006, correspondence took place between Archaeo-Environment, Durham County Council and the NRM regarding the possible relocation of the ironwork from the NRM York to Locomotion in Shildon. Costs were obtained to carry out a feasibility study to look at the practicalities of moving the structure and this was the subject of an application for funding to English Heritage from Durham County Council. Although the application was completed on behalf of DCC it is not clear if it was ever submitted to English Heritage.
In January 2014, non-historic timberwork was removed from the iron structure at the NRM but historic timberwork was retained but was recorded as suffering from rot. Overall, the bridge condition was described as ‘poor’ and requiring remedial work in terms of cosmetic appearance and ‘fair’ in terms of structure. This is largely because of small amounts of paint loss mainly visible at the north facing end of the bridge and at the bottoms of the A-frames with associated corrosion. The wood was noted as being structurally unsound suffering from degradation in the form of rot and the growth of vegetation. Biological accretions were also visible on parts of the metal frame (NRM Conservation Record 15.7.2014).
The S.E abutment in 1974. Although overgrown, the view is still uncluttered with a clear view of the clean elegant sweep of the wing wall on the east side. The rounded column has retained its rounded cope up to this point. Photo: John Proud Collection courtesy of Win Proud.
The bridge is finally coming home – at least very close to home. First, conservation works have to take place to address those concerns highlighted in 2014. The stone abutments still survive on either side of the Gaunless river. They are prone to graffitti and the Friends of the S&DR work with Durham County Council and the parish council to try to address this. This means that the bridge is too vulnerable to be remounted on its original abutments. Further, it will no longer fit the ironwork thanks to the 1901 alterations. Instead, it is being rehoused up the road at Locomotion in Shildon where it will be accessible and free to see, 200 years after being designed and built. This will be its 6th re-assembly. Welcome home Gaunless bridge.