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Gaunless Bridge

Gaunless Bridge
File:First Iron railway bridge.jpg
Coordinates

54°38′00″N 1°42′46″W / 54.633203°N 1.712808°W / 54.633203; -1.712808Coordinates: 54°38′00″N 1°42′46″W / 54.633203°N 1.712808°W / 54.633203; -1.712808{{#coordinates:54.633203|-1.712808|type:landmark_region:GB-DUR|||||| |primary |name=

}}
Carries Witton Park branch of the Stockton and Darlington Railway, a horse-drawn mineral railway
Crosses River Gaunless
Characteristics
Design lenticular truss
Material wrought- and cast-iron
Total length Script error: No such module "convert".
Longest span Script error: No such module "convert".
Number of spans three, later four
History
Designer George Stephenson
Fabrication by John & Isaac Burrell
Opened 1823 (1823)
This article is about the 1823 bridge by George Stephenson. For the 1863 viaduct by Thomas Bouch, see Gaunless Viaduct

Gaunless Bridge was a railway bridge on the Stockton and Darlington Railway. It was completed in 1823 and is one of the first railway bridges to be constructed of iron[1] and the first to use an iron truss.[2] It is also of an unusual lenticular truss design.[3]

Location

The bridge crosses the River Gaunless at West Auckland, Co. Durham.

Although never part of the main line, it was on a branch West of Shildon serving Witton Park Colliery.[4] This branch included two rope-worked inclines at Brusselton and Etherley. Between these, wagons were pulled by horses, rather than the heavier locomotives. The bridge was only required to carry the weight of these horse-worked trains.[1] Despite this, a postcard exists showing a locomotive of the 'Director' class on the bridge, possibly during a test or demonstration.[5]

Design

It was designed in 1823 by George Stephenson, who was the chief engineer of the railway.[3]

As well as being one of the first iron railway bridges, the bridge is the first to use the lenticular truss design.[2] This design uses two curved girders in a lens shape, one above and one below. The upper member is in 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 connect the two girders and support the load-carrying deck of the bridge. These vertical members must also transfer 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, and so requiring it to be excessively strong compared to the other.

The lenticular truss design has been used for other bridges since, but has never gained popularity in use. Brunel later made use of this truss, as the Brunel truss used at Chepstow and Saltash. The Gaunless Bridge is particularly unusual, as its wooden deck is installed above the truss girders; whereas in most lenticular trusses, the deck is hung beneath the trusses on rods or cables.[3]

Although not as sceptical or rigorously investigative as Brunel,[6] Stephenson had a deep understanding of the different strengths of wrought- and cast-iron.[2][7] Both girders are formed of wrought iron tubes, Script error: No such module "convert". in diameter. The unusual feature of this bridge is that because the deck is above the truss, the vertical members are placed in compression, rather than the more normal tension. This allowed Stephenson to use cast iron for the vertical members, rather than the more expensive wrought iron needed for bridges in tension.[i][3] The truss achieves an efficient symmetry of the load distribution between the two members, giving an economical and balanced appearance that is in great contrast to Brunel's heavily unbalanced designs that (for Chepstow at least) are barely recognisable as lenticular.

Each span is Script error: No such module "convert". wide and Script error: No such module "convert". deep.[8] The piers supporting the truss spans form a trestle comprising two inward-leaning cast iron tubular pillars.[9] The pillars are braced apart by a cast iron X-frame.[3] These pillars are Script error: No such module "convert". in diameter with Script error: No such module "convert". thick walls, They are Script error: No such module "convert". apart at the base, sloping in to Script error: No such module "convert". at their top.[8]

The bridge was originally built with three spans, but was later extended to four spans, to allow more space for floodwater. Unusually, the bridge has five metal piers for its for spans, with the weight of the ends of the outer spans resting on iron pillars, rather than on the adjoining stone abutments.[10] These additional pillars make the bridge spans self-supporting, even in the absence of the stone abutments. This may have been a factor in the bridge's preservation off-site and re-display in railway museums since, as it is relatively easy to re-erect the bridge without needing expensive foundations.

History

The original three span bridge was fabricated by John & Isaac Burrell of Orchard Street, Newcastle,[3] adjacent to Stephenson's own works at Forth Street. Its erection was completed on 23 October 1823,

The winter of 1824 had heavy snows and even before the line was opened, the bridge was damaged by flooding. It was rebuilt to its later four span form in 1825, in time for the opening of the line in September.[3]

A presentation model of the Gaunless Bridge was made for the North Eastern Railway in 1875 to mark the 50th anniversary of the opening of the Stockton and Darlington Railway.[1] It may be seen today in the Science Museum, London.[11][12]

By 1901 the bridge was overloaded by the increasing weight of coal wagons. It was dismantled and removed, but kept in storage at Brusselton Colliery. The original stone abutments were kept, although with recesses cut into them to accept new plate girders.[13] When the York Railway Museum was opened at Queen Street in 1927, the bridge was re-assembled in commemoration of the centenary of the S&DR.[3][8] Since 1975, it has been on display in the car park of the National Railway Museum, York, for many years carrying a coal wagon of the original chaldron style.[3][ii][9] The bridge has now spent longer on display as a museum artefact than it did in service as a bridge.

Comparable bridges

Escomb Bridge

The lenticular truss was never a common design and Stephenson's compression truss beneath the deck even rarer. A still-extant near-contemporary example is only a couple of miles North of Gaunless Bridge. This was built in 1842 as a skewed accommodation footbridge across the Bishop Auckland and Weardale Railway near Escomb.[14][iii] Today it carries a bridleway.[15] The bridge comprises a single span pair of lenticular girders, although in this example both girders and verticals are of wrought iron.[16] The upper member is a rolled H girder, the lower chain of forged bar chain links.

Escomb bridge is Grade II listed and was refurbished in 2009, with its wooden parapet being raised for modern safety standards.[15]

See also

References

  1. ^ Cast iron is strong in compression, but weak in tension or against bending. Wrought iron is strong for both.
  2. ^ Bridge's location on display today: 53°57′39″N 1°05′50″W / 53.96088°N 1.0973°W / 53.96088; -1.0973{{#coordinates:53.96088|-1.0973|type:landmark|||||| | |name= }}
  3. ^ Escomb Bridge: 54°39′41″N 1°42′20″W / 54.661361°N 1.705424°W / 54.661361; -1.705424{{#coordinates:54.661361|-1.705424|type:landmark_region:GB-DUR|||||| | |name= }}


  1. ^ a b c Icon:Stephenson's Gaunless Bridge, 1824. Making The Modern World. 
  2. ^ a b c Chrimes, Mike (1991). Civil Engineering 1839-1889. Alan Sutton Publishing. p. 45. ISBN 1-84015-008-4. 
  3. ^ a b c d e f g h i Beckett, Derrick (1984). Stephensons' Britain. David & Charles. pp. 38,40,42–43. ISBN 0-7153-8269-1. 
  4. ^ Beckett (1984), p. 36.
  5. ^ An engine-driver of The Stockton and Darlington Railway Company. 
  6. ^ Brindle, Steven (2005). Brunel: The Man Who Built the World. Weidenfield & Nicholson. p. 164-165. ISBN 0-297-84408-3. 
  7. ^ Beckett (1984), p. 48.
  8. ^ a b c Gaunless Bridge (relocated). Engineering Timelines. 
  9. ^ a b "George Stephenson's Metal Bridge West Auckland". West Auckland Web. 2013. 
  10. ^ West Auckland, old metal bridge. Durham County Council. 
  11. ^ Model of Gaunless Bridge, Stockton & Darlington Railway. Plaque reads Stephenson's First Railway Bridge, 1824, West Auckland. Science Museum. 10460860. 
  12. ^ Model of Gaunless Bridge, Stockton & Darlington Railway. Plaque reads Stephenson's First Railway Bridge, 1824, West Auckland. Science Museum. 10460861. 
  13. ^ Gaunless Bridge, S & D Railway. Tomorrow's History. 
  14. ^ "Escomb accommodation bridge.". Tomorrow's History. 
  15. ^ a b "Weardale Railway: News Update: No.24". Weardale Railway. 3 September 2009. 
  16. ^ "Escomb Over Bridge". Structural Images of the North East.