The Dee bridge after its collapse

The Dee bridge disaster was a rail accident that occurred in 1847. A new bridge across the river Dee in Chester was needed for the Chester-Holyhead railway, a project planned in the 1840s for the expanding British railway system. It was built using cast iron girders, each of which was made of three very large castings dovetailed together. Each girder was strengthened by wrought iron bars along the length. It was finished in September 1846, and opened for local traffic after approval by the first Railway Inspector, General Pasley. However, six months later, a local train fell through the bridge and five died. The bridge had been designed by Robert Stephenson, and he was accused of negligence by a local inquest. Although strong in compression, cast iron was known to be brittle in tension or bending, yet that same day, May 24th 1847, the track was covered with track ballast to prevent the oak beams supporting the track from catching fire. Ironically, Stephenson took this precaution because of a recent fire on the Great Western Railway at Uxbridge, London, where Isambard Kingdom Brunel's bridge caught fire and collapsed. The list includes some terrorist bombings. ... Old Dee Bridge, River Dee, Chester, England (2002) The River Dee (Welsh: Afon Dyfrdwy) is a 70 mile (110 km) long river, which rises in Snowdonia, Wales and discharges to the sea a few miles west of Liverpool. ... Chester is the county town of Cheshire in North West England. ... For transport in Northern Ireland, see rail transport in Ireland Class 180 Multiple Unit of First Great Western at speed near Yate, Bristol, England. ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... A wrought iron railing in Troy, New York. ... Statue of Robert Stephenson at Euston Station, London Robert Stephenson FRS (October 16, 1803–October 12, 1859) was an English civil engineer. ... Concrete sleepers laid on Ballast Track ballast, consisting of gravel, cinders or other aggregate, forms the trackbed upon which railway sleepers are laid. ... The original Bristol Temple Meads station, first terminus of the GWR, is the building to the left of this picture The Great Western Railway (GWR) was a British railway company, linking South West England, the West Country and South Wales with London. ... Brunel before the launching of the Great Eastern. ...

The accident occurred a few hours later when the locomotive reached the final girder. It cracked in the middle, allowing all the carriages to fall into the river Dee fifty feet below. The extra load of ballast undoubtedly helped cause the accident. The design of the bridge was seriously flawed, although different authors have emphasised different causes. Lewis and Gagg state that failure occurred in tension at the bottom of the girders, exacerbated by stress concentrations. However, Henry Petroski notes that the wrought iron bars would tend to exacerbate compression in the beams, and as they are eccentric they increased the tendency towards failure by lateral torsional buckling. William Fairbairn had warned Stephenson of the problem of cast iron girders only a few months before construction of the bridge at a meeting at the Institution of Civil Engineers in London, but his advice was ignored. A subsequent Royal Commission condemned the design and the use of cast iron in railway bridges. It had been used very successfully in the The Crystal Palace of 1851 and the Crumlin viaduct in south Wales (built in 1857), but the first Tay Rail Bridge of 1878 failed catastrophically due to its poor use of the material, putting the cast iron lugs on the columns into tension. The Tay disaster stimulated engineers to use steel, as exhibited by the Forth Railway Bridge of 1890. Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ... A stress concentration is a phenomenon encounterered in mechanical engineering where an object under load has higher than average local stresses due to its shape. ... Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... In engineering, buckling is a failure mode characterised by a sudden failure of a structural member that is subjected to high compressive stresses where the actual compressive stresses at failure are bigger than the ultimate compressive stresses that the material is capable of withstanding. ... Sir William Fairbairn Sir William Fairbairn (February 19, 1789 - August 18, 1874) was a Scottish engineer. ... The Institutions headquarters Founded on 2 January 1818, the Institution of Civil Engineers (ICE) is an independent professional association, based in central London, representing civil engineers. ... The Great Exhibition in Hyde Park 1851. ... Crumlin is a town in Caerphilly county borough, traditional county of Monmouthshire, south Wales, situated in the Ebbw valley, five miles west of Pontypool. ... Original Tay Bridge (from the South) The Tay Rail Bridge (properly named the Tay Bridge) is a railway bridge approximately two and a quarter miles (three and a half kilometres) long[1] that spans the Firth of Tay in Scotland, between the city of Dundee and the suburb of Wormit... The old Steel cable of a colliery winding tower Steel is sometimes described as a sea of electrons. ... ...

References

• LTC Rolt, Red for Danger, Sutton Publishing (1998).
• PR Lewis and C Gagg, Interdisciplinary Science Reviews, 45, 29, (2004).
• Roy Wilding, Death in Chester (2003) ISBN 1-872265-44-8.
• Henry Petroski, Design Paradigms (1994) ISBN 0-521-46108-1.

External links

• Reprint of paper on Dee bridge disaster at http://materials.open.ac.uk/about_us/29-2-177.pdf