Tay Bridge disaster

The Tay Bridge disaster occurred during a violent storm on 28 December 1879 when the first Tay Rail Bridge collapsed while a train was passing over it from Wormit to Dundee, killing all aboard. The bridge—designed by Sir Thomas Bouch—used lattice girders supported by iron piers, with cast iron columns and wrought ironcross-bracing. The piers were narrower and their cross-bracing was less extensive and robust than on previous similar designs by Bouch.

Bouch had sought expert advice on "wind loading" when designing a proposed rail bridge over the Firth of Forth; as a result of that advice he had made no explicit allowance for wind loading in the design of the Tay Bridge. There were other flaws in detailed design, in maintenance, and in quality control of castings, all of which were, at least in part, Bouch's responsibility.

Bouch died within the year, with his reputation as an engineer ruined. Future British bridge designs had to allow for wind loadings of up to 56 pounds per square foot (2.7 kPa). Bouch's design for the Forth Bridge was not used.

The bridge

For more details on this topic, see Tay Rail Bridge.

Construction began in 1871 of a bridge to be supported by brick piers resting on bedrock shown by trial borings to lie at no great depth under the river. At either end of the bridge, the bridge girders weredeck trusses, the tops of which were level with the pier tops, with the single track railway running on top. However, in the centre section of the bridge (the "high girders") the bridge girders ran as through trusses above the pier tops (with the railway inside them) in order to give the required clearance to allow passage of sailing ships to Perth.

Bedrock actually lay much deeper and Bouch had to redesign the bridge, with fewer piers and correspondingly longer span girders. The pier foundations were now constructed by sinking brick-lined wrought-iron caissons onto the riverbed, and filling these with concrete. To reduce the weight these had to support, Bouch used open lattice iron skeleton piers (each pier had multiple cast-iron columns taking the weight of the bridging girders, with wrought iron horizontal braces and diagonal tiebars linking the columns of the pier to give rigidity and stability). The basic concept was well known, but for the Tay Bridge, the pier dimensions were constrained by the caisson. There were 13 high girders spans; to accommodate thermal expansion, at only 3 of their 14 piers was there a fixed connection to the girders; there were therefore 3 divisions of linked high girder spans, the spans in each division being structurally connected to each other, but not to neighbouring spans in other divisions. The southern and central divisions were nearly level but the northern division descended towards Dundee at gradients of up to 1 in 73.

The bridge was built by Hopkin Gilkes and Company, a Middlesbrough company which had worked previously with Bouch on iron viaducts. Gilkes, having first intended to produce all ironwork on Teesside, used a foundry at Wormit to produce the cast-iron components, and to carry out limited post-casting machining. Gilkes were in some financial difficulty; they ceased trading in 1880, but had begun liquidation in May 1879, before the disaster. Bouch's brother had been a director of Gilkes, and on his death in January 1876 Bouch had inherited Gilkes shares valued at £35,000 but also a guarantee of £100,000 of Gilkes borrowings and been unable to extricate himself.

The change in design increased cost and necessitated delay, intensified after two of the high girders fell when being lifted into place in February 1877, but the first engine crossed the bridge in September 1877. A Board of Trade inspection was conducted over three days of good weather in February 1878; the bridge was passed for use by passenger traffic subject to a 25 mph speed limit, but the inspection report noted:

'... When again visiting the spot I should wish, if possible, to have an opportunity of observing the effects of high wind when a train of carriages is running over the bridge ...'.

The bridge was opened for passenger services on 1 June 1878. Bouch was knighted in June 1879 soon after Queen Victoria had used the bridge.

The disaster

On the evening of 28 December 1879, a violent storm (10 to 11 on the Beaufort scale) was blowing virtually at right angles to the bridge. Witnesses said the storm was as bad as any they had seen in the 20–30 years they had lived in the area; one called it a 'hurricane', as bad as a typhoon he had seen in the China Sea. The wind speed was measured at Glasgow – 71 mph (114 km/h) (averaged over an hour) – and Aberdeen, but not at Dundee. Higher windspeeds were recorded over shorter intervals, but at the inquiry an expert witness warned of their unreliability, and declined to estimate conditions at Dundee from readings taken elsewhere. One modern interpretation of available information suggests winds were gusting to 80 mph (129 km/h).

Usage of the bridge was restricted to one train at a time by a signalling block system using a baton as a token. At 7:13 p.m. a train from the south slowed to pick up the baton from the signal cabin at the south end of the bridge, then headed out onto the bridge, picking up speed. The signalman turned away to log this and then tended the cabin fire, but a friend present in the cabin watched the train: when it got about 200 yards (183 m) from the cabin he saw sparks flying from the wheels on the east side,[note 3] this continued for no more than three minutes, by then the train was in the high girders; then "there was a sudden bright flash of light, and in an instant there was total darkness, the tail lamps of the train, the sparks and the flash of light all ... disappearing at the same instant." The signalman saw none of this and did not believe when told about it. When the train failed to appear on the line off the bridge into Dundee he tried to talk to the signal cabin at the north end of the bridge, but found that all communication with it had been lost.

Not only was the train in the river, but so were the high girders, and much of the ironwork of their supporting piers. Divers exploring the wreckage later found the train still within the girders, with the engine in the fifth span of the southern 5-span division. There were no survivors; only 46 bodies were recovered  but there were 59 known victims. Fifty-six tickets for Dundee had been collected from passengers on the train before crossing the bridge; allowing for season ticket holders, tickets for other destinations, and for railway employees, 74 or 75 people were believed to have been on the train.

Court of Inquiry – evidence

A Court of Inquiry (a judicial enquiry under Section 7 of the Regulation of Railways Act 1871 'into the causes of, and circumstances attending' the accident) was immediately set up: Henry Cadogan Rothery, Commissioner of Wrecks, presided, supported by Colonel Yolland (Inspector of Railways) and William Henry Barlow, President of the Institution of Civil Engineers. By 3 January 1880, they were taking evidence in Dundee; they then appointed Henry Law (a qualified civil engineer) to undertake detailed investigations. Whilst awaiting his report they held further hearings in Dundee (26 February – 3 March); having got it they sat at Westminster (19 April – 8 May) to consider the engineering aspects of the collapse. By then railway, contractor and designer had separate legal representation, and the NBR had sought independent advice (from James Brunlees and John Cochrane, both engineers with extensive experience of major cast-iron structures). The terms of reference did not specify the underlying purpose of the inquiry – to prevent a repetition, to allocate blame, to apportion liability or culpability, or to establish what precisely had happened. This led to difficulties (culminating in clashes) during the Westminster sessions and when the court reported their findings at the end of June, there was both an Inquiry Report signed by Barlow and Yolland and a minority report by Rothery.

Other eyewitnesses

Two witnesses, viewing the high girders from the north almost end-on, had seen the lights of the train as far as the 3rd–4th high girder, when they disappeared; this was followed by three flashes from the high girders north of the train. One witness said these advanced to the north end of the high girders with about 15 seconds between first and last; the other that they were all at the north end, with less time between. A third witness had seen 'a mass of fire fall from the bridge' at the north end of the high girders. A fourth said he had seen a girder fall into the river at the north end of the high girders, then a light had briefly appeared in the southern high girders, disappearing when another girder fell; he made no mention of fire or flashes. 'Ex-Provost' Robertson had a good view of most of the bridge from his house in Newport-on-Tay but other buildings blocked his view of the southern high girders. He had seen the train move onto the bridge; then in the northern high girders, before the train could have reached them, he saw two columns of spray illuminated with the light, first one flash and then another and could no longer see the lights on the bridge – the only inference he could draw was that the lit columns of spray – slanting from north to south at about 75 degrees – were areas of spray lit up by the bridge lights as it turned over