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Built in 1851-4.
The original viaduct was constructed by the Dublin and Drogheda Railway to cross the River Boyne. William Evans was awarded the contract, following his successful construction of the Conwy Railway Bridge.
1851 'THE BOYNE VIADUCT
On Saturday the directors of the Dublin and Belfast Junction Railway Company let the contract for the entire of the works the Boyne Viaduct to Mr. William Evans, of Cambridgeshire. This gentleman was the contractor who executed the entire works of the Conway Tubular Bridge on the Chester and Holyhead Railway, and who is now carrying on the extensive drainage works Cambridgeshire, where has now upwards of three thousand workmen employed. It is the intention of Mr Evans to erect workshops on the ground adjacent to the site of the intended viaduct at Drogheda. The amount of his contract is sixty-eight thousand pounds. The tender of Messrs Strapp and Cowper, of Glasgow and Dumfriesshire, was next in amount, the difference between the two being 520l; and next in amount was the tender of Messrs Dickson and M'Kenzie, of Wellington, Salop. The viaduct is to be constructed on the plan of Sir John Macneill, the eminent engineer-in-chief to the line. It will consist of an approach from the Drogheda Railway Station, on the south side of the river, of 970 feet, comprising thirteen semi-circular arches, each 60 feet span, and averaging 90 feet over the surface level, springing from piers of solid wrought ashlar masonry, the plinths, imposts, strings, copings, and archstones to be of fine-dressed cut stone. The river is crossed in three spans, two of 125 feet each, and one of 250 feet, formed by massive cut stone piers, which are to founded on the solid rock, under the bed of the river, and to be raised to the height of 90 feet above high-water mark, to admit of ships sailing under the railway with their top-gallant or royal masts unstruck ; the superstructure of this portion is to be of wrought iron on the lattice principle, and will require upwards of six hundred and twenty tons of iron. From the experience now had of bridges erected both in this and other countries, it is pretty well known that there cannot be a safer better principle adopted. It was introduced into this country in 1843 Sir John Macneill in carrying the Dublin and Drogheda Railway across the canal. This bridge is 104 feet span, and when the supports were withdrawn from under it, and a load of over one hundred tons placed upon it, the deflection was but three-eights an inch ; it has never yielded since Messrs. Grendon and M'Kay, of Drogheda, erected this bridge. At the north side of the river the structure continues for 265 feet, formed by similar piers and arches before alluded to, and is met by an embankment 1,200 feet long, and averaging about 20 feet in height, at the north end of which the Newfoundwell stream and valley is to be crossed by a viaduct of five arches, each 40 feet span. The design for this structure is the castellated style, and will harmonize with the ancient gateway adjacent.— Within 300 feet of this viaduct the two railways join, forming an unbroken line of railway direct from Amiens-street, Dublin, to Belfast. The works are to be completed in twenty-two months from the date of the contract.'
1858 Controversy was aired in the newspapers over the assignment of credit for the design of the girder bridge. Professor Joseph A. Galbraith had stated that James Barton was responsible for the construction, and John Macneill took strong exception to this, writing "The whole design and the arrangement of the structure was mine, and none other had act or part in it," In response, Barton wrote a long letter, crediting Macneill with the proposal for the lattice girder bridge, but stating that he (Barton) had been made responsible for the detail design and construction, and he was assisted by Mr. Bunting. He stated that he consulted Dr. Hart of Trinity College, Dublin regarding the calculations, and worked on the detail designs for '15 to 20 hours a day' for several weeks, with his assistants and with Mr. Schaw amd Mr. Powell, and presented the drawings to Mr Macneill on 2 June 1856 (1851?), who signed them off after about half an hour's scrutiny. These were passed to William Evans with the contract. Mr. Schaw became the resident engineer for most of the duration of the contract, after which Barton took over (Schaw having left to become County Surveyor at Waterford). After William Evans becoame bankrupt, Barton was entrusted with carrying out the whole of the work, without a contractor. At this stage the the troublesome abutment work was not complete (the difficulty being the cause of Evans' business failure), and the installation of the ironwork had not been started. Barton mentioned that he had had large scale scale tests carried out on girders of 60 ft span, weighing 5 tons, made by Coates of Belfast. The test showed that the girders proposed by Macneill would not have been adequate.
c.1860 One of the piers had settled at one corner. This caused concerns lest the whole structure should fall down. This allowed engineers elsewhere to rerun the discussion about lattice construction as opposed to use of plate-iron. The cause of the failure was thought to be due to an original defect in the foundations, or perhaps from a failure to oil the rollers supporting the Structure. The also promoted an old controversy between Sir John Macneill, the former chief engineer of the Dublin and Belfast Junction Railway, and Mr. James Barton who was his assistant whilst the works were in progress, and later became engineer to the company. The directors had already called in Mr. Hawkshaw to report upon the defect in the structure and direct arrangements for its restoration.
1932 The bridge was upgraded by replacing the wrought iron spans over the river by new steel girders, the centre span having an arched girder. These were built by the Motherwell Bridge and Engineering Co with G.B. Howden as the chief engineer.