Inverythan crash
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The Inverythan rail crash was a railway accident at Inverythan, Aberdeenshire, Scotland, which occurred on November 27th, 1882, when a train was approaching a small bridge near Inverythan on the track from Aberdeen to Banff. The bridge was about 39 ft long and about 15 feet high over a road. It was a single line track, so the bridge was only about 10 feet wide. The track was supported by wooden beams laid on the lower flanges of the massive castings used to form the main structure. Each of the two main spans were made from two castings bolted together at the centre of the bridge. Each casting was curved upwards towards the centre, so as to counteract the greatest load there, and was central joint was reinforced underneath by a wrought iron boss. It was a mixed freight and passenger train, with five loaded wagons and four carriages. As the locomotive passed over, one of the girders suddenly collapsed into the road below. Although the engine reached the far side safely, most of the train fell into the gap, instantly killing four passengers. Another passenger died soon afterwards, and 14 others were badly injured.
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[edit] Cause of accident
The casting had broken not at the centre joint, but rather just by the side. It was a simple vertical crack running up from the bottom flange to the top of the girder, and inspection showed a very large, but hidden, blowhole at the thickest part of the section, where the flanges met the web. It was also clear that this defect had cracked some time before, judging by old rust marks on the face of the crack. This region could easily be distinguished from the fresh fracture surface caused at the moment of the accident. Samples were cut from the broken girder for testing by David Kirkaldy in Southwark, who had previously tested the many samples from the Tay Rail Bridge for the Official Inquiry in Dundee. While cores were being taken by drilling holes in the sample, it suddenly fractured along the line of holes, showing that there was a considerable level of residual stress. This is commonly encountered in many products, and is usually caused by manufacturing methods. Some parts of the product will be in a dangerous tensile state, balanced by other parts in compression. In this case, with the cast iron girder, it was probably produced by uneven shrinkage in the original casting as it cooled from the melt, and will have lowered the failure stress by a considerable margin, over and above the stress raising effects of the blowhole and its slowly growing brittle crack. Kirkaldy’s tests showed a wide variation in tensile strength, the lowest of about 4.5 tsi from a sample taken near the fractured flange, the mean being 7.5 tsi. The Board of Trade investigated the disaster, and concluded that the faulty girder was the cause of the accident. It was probably a fatigue failure, the critical crack growing slowly with time.
[edit] Implications
A survey of bridges on the Great North of Scotland lines showed some 331 cast iron bridges in operation, but of variable length and structure. Only 8 were actually of similar double structure, and they were inspected and replaced as quickly as possible. There must have been considerable disruption to traffic while they were being replaced. A warning about similar cast iron under-bridges was circulated to all British railway companies, but little further action was taken until the Norwood Junction rail accident of 1891.
[edit] References
- Day, T, The Failure of Inverythan Bridge, 1882, J Railway and Canal Historical Society, 33 (107), 404-415 (2000).
