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| Dee bridge disaster | |
|---|---|
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| Details | |
| Date | 24 May 1847 ~18:25 |
| Location | Chester, Cheshire |
| Coordinates | 53°10′59″N2°53′42″W / 53.183°N 2.895°W /53.183; -2.895 |
| Country | England |
| Line | North Wales Coast Line andShrewsbury–Chester line |
| Cause | Bridge fail |
| Statistics | |
| Trains | 1 |
| Passengers | 22 |
| Deaths | 5 |
| Injured | 9 |
| List of UK rail accidents by year | |
TheDee Bridge disaster was arail accident that occurred on 24 May 1847 inChester, England, that resulted in five fatalities. It revealed the weakness ofcast iron beam bridges reinforced bywrought iron tie bars, and brought criticism of its designer,Robert Stephenson, the son ofGeorge Stephenson.
A new bridge across theRiver Dee was needed for theChester and Holyhead Railway, a project planned in the 1840s for the expandingBritish railway system. It was built using cast irongirders produced by theHorseley Ironworks, each of which was made of three large castingsdovetailed together and bolted to a raised reinforcing piece. 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, GeneralCharles Pasley.
On 24 May 1847, the carriages of a local passenger train toRuabon fell through the bridge into the river. The accident resulted in five deaths (three passengers, the train guard and the locomotivefireman) and nine serious injuries.[1]
The bridge had been designed byRobert Stephenson, and a local inquest accused him of negligence. Although strong in compression, cast iron was known to be brittle in tension or bending, yet the bridge deck was covered withtrack ballast on the day of the accident,[vague] to prevent the oak beams supporting the track from catching fire. Stephenson took that precaution because of a recent fire on theGreat Western Railway atHanwell, in which a bridge designed byIsambard Kingdom Brunel had caught fire and collapsed.[2][3][4]
The investigation was one of the first major inquiries conducted by the newly formedRailway Inspectorate. The lead investigator wasCaptain Simmons of theRoyal Engineers, and his report suggested that repeated flexing of the girder weakened it substantially. He examined the broken parts of the main girder, and confirmed that it had broken in two places, with the first break occurring at the centre. He tested the remaining girders by driving alocomotive across them, and found that they deflected by several inches under the moving load. His conclusion was that the design was basically flawed, and that the wrought irontrusses fixed to the girders did not reinforce the girders at all. The same conclusion was reached by the jury at the inquest. Stephenson's design had depended on the wrought iron trusses to strengthen the final structures, but they were anchored on the cast iron girders themselves, and so deformed with any strain on the bridge.
Stephenson maintained that the locomotivederailed whilst crossing the bridge, and theimpact force against the girder caused it to fracture. However,eyewitnesses said that they saw the girder break first, and that the locomotive and tender were still on the track at the far side of the bridge. Indeed, the driver raced on to the next station to warn of the accident and prevent any traffic using the line. He then came back on the other side and drove to Chester where he gave a similar warning.
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A subsequentRoyal Commission (which reported in 1849) condemned the design and the use of trussed cast iron in railway bridges, but there were other failures of cast-iron railway underbridges in subsequent years, such as theWootton bridge collapse and theBull bridge accident. Similar failures occurred in theInverythan crash and theNorwood Junction crash. All the structures used untrussed cast iron girders, and generally failed due toblowholes or othercasting defects within the bulk material, which were often completely hidden from external view.
The Norwood accident in 1891 led to a review of all similar structures bySir John Fowler, who recommended their replacement. Cast iron had been used very successfully inthe Crystal Palace of 1851 and theCrumlin Viaduct in South Wales (built in 1857), but the firstTay Rail Bridge of 1878 failed catastrophically due to its poor use of the material, putting the cast iron lugs on the columns into tension. TheTay Bridge disaster stimulated engineers to use steel, as exemplified by theForth Bridge of 1890.
The Dee bridge was later rebuilt usingwrought iron.
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