LMS Route: Rugby to Leamington Spa (Avenue)

LMS Route: Leamington to Weedon

Marton Junction: lnwrmartj1325

Looking towards Rugby with the wrought iron bridge carrying Hunningham Hill Road in the foreground and Marton Junction behind circa 1966. The bridge carried a farm access road over the railway cutting with Marton Junction some 200 yards beyond the bridge. The signal box controlling the junction is on the up line and was sited opposite the branch to Weedon. Ken McInnes writes, 'I am currently completing a conference paper on William Thomas Doyne, and the Hunningham High Bridge is a very significant metal truss bridge, and at the time of construction was the largest lattice girder bridge in the world'. The original span of 150ft was later reduced to three 50ft spans by propping. The bridge contractors were Smith, Smith & James, of Leamington Spa who charged £3579 19s 4d. The main contractor for the then single line railway was George Knight whose bid of £260,000 was accepted in 1847.

The importance of the bridge's design can be assessed by an extract in "The Works of Isambard Kingdom Brunel”, edited by Alfred Pugsley. Although the lattice type of construction - i.e. a flanged girder with a complexity of crossed flat wrought iron bars for the web, representing a potentially physically lighter form than that with a solid plate web of the same thickness of metal-had been introduced during the early 1840s (e.g. a bridge on the Dublin and Drogheda Railway, some 3 miles from Dublin, described by GW Hemans before the Institution of Civil Engineers in the session 1843-44, during the discussion of which it was said that, according to Dr Gregory in his book Mathematics for Practical Men, the original inventor of the lattice bridge was Mr Smart), it did not seemingly find favour. Pugsley states, when referring to Doyne's calculation of the bridges' strength, 'he seems to rely on the theory of bending of beams, asserting, by comparison with a conventional plate girder: the only difference being, that the connecting link between the top and bottom whose duty it is to carry the strain from one to the other, instead of one continuous rib, has several points of distinct attachment. And as the amount of strain thrown into the top and bottom throughout the whole length, or at any point, is in both cases the same, it is evident that the whole action upon the connecting links IS the same and that the strain upon each lattice may be calculated: this strain is not uniform throughout, but depends upon the position of the load so that it is necessary to calculate the proportions of the lattices for each part, or to make them all of the maximum strength.'

Pugsley continues' It is noteworthy that Doyne does not mention shear forces specifically, and therefore his explanation of the calculations relating to the proportions of the lattice work is less than satisfactory - a matter which drew adverse criticism during the discussion from CH Wild and GP Bidder. The latter further asserted that he believed the construction was less economical than that embodied in the conventional plate girder.' Subsequently Brunel (1851) entered into discussion of a paper by WT Doyne and Professor WB Blood (1851), of University College, Galway, concerning strains on the diagonals of lattice beams. On that occasion it was the Warren girder (named after its inventor, Captain Warren) to which they addressed themselves: a very different proposition from the lattice girder formerly described by Doyne, as Brunel noted by saying, "it was necessary to draw a distinct line of demarcation between the lattice bridge and that kind of construction called Warren's girder; in the former much of the material employed was useless, whilst in the latter, if properly proportioned, every part was made to perform its duty, either bearing pressure, or in tension; he was inclined to think it might be rendered nearly the most economical, as well as the most efficient kind of girder, for spans of a certain extent."

back