Tay Bridge disaster

For McGonagall's poem on this subject, see The Tay Bridge Disaster.

Tay Bridge disaster
Details
Date	28 December 1879
Time	19:13
Location	Dundee
Country	Scotland
Rail line	Edinburgh to Aberdeen Line
Cause	Structural failure
Statistics
Trains	1
Passengers	70
Deaths	75 (estimate-60 known dead)
Injuries	0
List of UK rail accidents by year

The Tay Bridge disaster occurred on 28 December 1879, when the first Tay Rail Bridge, which crossed the Firth of Tay between Dundee and Wormit in Scotland, collapsed during a violent storm while a train was passing over it. The bridge had been designed by noted railway engineer Sir Thomas Bouch, using a lattice grid that combined wrought and cast iron. Major engineering flaws were the cause of the collapse, and the disaster ruined Bouch's reputation as an engineer.

The bridge

Original Tay Bridge from the north

Proposals for constructing a bridge across the River Tay date back to at least 1854. The North British Railway (Tay Bridge) Act received the Royal Assent on 15 July 1870 and the foundation stone was laid on 22 July 1871. The original design was for a bridge 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 were deck 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 upriver (e.g. to Perth).

When it became clear that the bedrock really lay too deep to act as a foundation for the bridge piers, Bouch had to redesign the bridge. He reduced the number of piers and correspondingly increased the span of the girders. The pier foundations were no longer taken down to bedrock; instead they were constructed by sinking brick-lined wrought-iron caissons onto the riverbed, and filling these with concrete. To reduce the weight of the bridge the brick piers were replaced by 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. To accommodate thermal expansion there were few rigid connections between girders and piers; there were 13 high girders spans (from piers 28 to 41 - numbering from the south); to accommodate thermal expansion, at only 3 of these 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 first intended to produce all ironwork on Teesside, but in the event used a foundry at Wormit to produce the cast-iron components, and to carry out limited post-casting machining operations.

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. Despite this, the first engine crossed the bridge on 22 September 1877, and upon its completion in early 1878 the Tay Bridge was the longest in the world. Like all rail lines intended to carry passenger trains, the Tay Bridge had been subject to a Board of Trade inspection before it opened. The inspection was conducted over a three-day period in February 1878 during what were described as 'favourable' weather conditions. The bridge was passed for opening subject to conditions such as a speed limit and minor remedial work. 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 (logged at 10 to 11 on the Beaufort Scale by an experienced seaman) was blowing virtually at right angles to the bridge. Local witnesses described the storm 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 been in in the China Sea The wind speed was not measured at Dundee but the windspeed averaged over an hour was measured at Glasgow– 71 mph - and Aberdeen. 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 else. (One modern interpretation of available information suggests winds were gusting to 80 mph)

At 7.13 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, then attended to the cabin fire but a friend present in the cabin watched the train onto the bridge: when it had got about 200 yards from the cabin he saw sparks flying from the wheels, this continued for no more than three minutes, by which time the train was in the high girders over the navigable channel; after which “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 signal man saw (and when told believed)none of this; but when the train failed to appear on the line off the bridge into Dundee he attempted to talk to the signal cabin at the north end of the bridge, only to find 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 subsequently exploring the wreckage found the train, still within the girders, with the engine in the 5th span of the southern 5-span division. 56 tickets for Dundee had been collected from passengers on the train before crossing the bridge; after allowing for season ticket holders, tickets for other destinations properly retained, and for railway employees 74-75 people were believed to have been on the train There were no survivors; there were 60 known victims, but only 46 bodies were found, two of which were not recovered until February 1880.

Court of Inquiry

Tay Bridge after the disaster, from the south

A Court of Inquiry was immediately set up, chaired by Henry Cadogan Rothery, Commissioner of Wrecks, supported by Colonel Yolland (Inspector of Railways) and William Henry Barlow, President of the Institution of Civil Engineers. By 3rd 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 (Feb 26 – March 3); on receipt of the report the court sat at Westminster (April 19- May 8) to examine in detail the engineering aspects of the collapse. They reported their findings at the end of June; as discussed below there was both an Inquiry Report 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, and much closer in time. A third 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 south 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 another building blocked his view of the southern high girders. He had seen the train move onto the bridge, and 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.

How the bridge was used - Speed of trains and oscillation of bridge

ex-Provost Robertson had bought a season ticket between Dundee and Newport at the start of November, but had become concerned about the speed at which north-bound local trains passed through the high girders (at either end of the bridge the train was travelling slowly to pick up or hand over the baton), which had been causing perceptible vibration, both vertical and lateral. He had spoken to the bridge inspector (Mr Noble) and complained on three occasions to the stationmaster at Dundee, with no effect on train speed; consequently, from mid-December he had used his season ticket to travel south only, using the ferry to make his north-bound crossings.

He had timed the train with his pocket watch; to give the railway the benefit of the doubt he had rounded up to the nearest 5 seconds. The measured time through the girders (3149 ft) was normally 65 or 60 seconds, twice it had been 50 seconds; he had measured 80 seconds when observing from shore trains crossing the bridge, but not on any train he had travelled on. North-bound local trains were often held up to avoid delaying expresses, and then made up time over the bridge; the heavy gradient onto the bridge at the north prevented similar high speeds on south-bound locals.

The movement he observed was hard to quantify , but lateral movement was probably one or two inches; it was definitely due to the bridge, not the train, and the effect was more marked at high speed.

Four other train passengers supported his timings but only one had noticed any movement of the bridge . . The Dundee stationmaster had passed Robertson’s complaint about speed (he had been unaware of any concern about oscillation) on to the drivers and then checked times cabin to cabin; he had never checked speed through the high girders.

Painters who had worked on the bridge in the summer of 1879 said that the bridge shook when a train was on it ; when a train entered the southern high girders the bridge had shaken at the north end, both east-west and up and down, but the up-and-down motion was stronger The shaking was worse when trains were going faster, which they did: ‘ when the Fife boat was nearly over and the train had only got to the south end of the bridge it was a hard drive’ . A joiner who had worked on the bridge May-October 1879 also spoke of a lateral shaking, which he found more alarming than the up-and-down motion; it was greatest at the southern junction between the high girders and the low girders. He was unwilling to quantify the amplitude of motion; when pressed he offered 2-3 inches, when pressed further he would only say that it was distinct, large, and visible

How the bridge was maintained - chattering ties and cracked columns

Bouch was paid by NBR to supervise maintenance of the bridge, with the NBR maintaining the railway. The bridge inspector was employed by the North British Railway but (should have) reported to Bouch(for whom he had worked during construction). He was a bricklayer by trade, not an engineer. Whilst checking pier foundations to see if the river bed was being scoured from under them had become aware that some diagonal tie bars were ‘chattering’, and in October 1878 had began remedying this. Diagonal bracing was by means of flat bars running from one lug at a column section top to two sling plates bolted to a lug at the base of the equivalent section on an adjacent column. Bar and sling plates all had a matching longditudinal slot in them; the tie bar was placed between the sling plates with all three slots aligned and overlapping and a gib driven through all three slots and secured. Two cotters (metal wedges) were then positioned to fill the rest of the slot overlap, and driven in hard to put the tie under tension. On the chattering ties the cotters were loose and even if driven fully in would not fill the slot and put the bar under tension. (He had assumed the cotters were too small and hadn't been driven up hard in the first place.) By fitting an additional packing piece between loose cotters and driving the cotters in he had retightened loose ties and stopped them chattering. There were over 4,000 gib and cotter joints on the bridge, only about 100 had had to be retensioned; most in October – November 1878. On his last check (December 1879) only two ties had needed attention; both on piers north of the high girders. He had found cracks in 4 column sections; one under the high girders, three to the north of them . These had been bound with wrought iron hoops. Bouch had been consulted about the cracked columns, but not the chattering ties

Causes

The storm winds are estimated to have been gusting up to 80 mph and whilst Bouch claimed the bridge had failed as a result of the train being blown against structural members (and some reports blame waterspouts) the inquiry (and following them most subsequent analysis) take the view that the bridge was structurally faulty, and bound to fail eventually.

Investigators quickly determined many faults in design, materials, and processes that had contributed to the failure. Bouch claimed to have received faulty information regarding wind loading, but his later statements indicated that he may have made no allowance for wind load at all. Bouch had been advised for earlier designs that calculating wind loads was unnecessary for girders shorter than 200 feet (61 m), and had not implemented wind loading calculation for his new design although it used longer girders.^{[citation needed]}

The section in the middle of the bridge, where the rail ran inside high girders (through trusses), rather than on top of lower ones (deck trusses), to allow a sea lane below high enough for the masts of ships, was potentially top-heavy and very vulnerable to high winds. Neither Bouch nor the contractor appeared to have regularly visited the on-site foundry where iron from the previous half-built bridge was recycled. The cylindrical cast iron columns supporting the 13 longest spans of the bridge, each 245 ft (75 m) long, were of poor quality. Many had been cast horizontally, with the result that the walls were not of even thickness, and there was some evidence that imperfect castings were disguised from the (very inadequate) quality control inspections.

In particular, some of the lugs used as attachment points for the wrought iron bracing bars had been "burnt on" rather than cast with the columns. However, no evidence of the burnt-on lugs has survived, and the normal lugs were very weak. They were tested for the Inquiry by David Kirkaldy and proved to break at only about 20 long tons (20 t) rather than the expected load of 60 long tons (61 t). These lugs failed and destabilised the entire centre of the bridge during the storm.

Official enquiry reports

The locomotive was eventually recovered and returned to service

Yolland and Barlow signed a short report sticking to the terms of reference of the enquiry, (seeking to identify causes, but not explicitly apportion blame), but in a separate report Rothery (on his own) gave a detailed analysis supporting the apportionment of blame, and destroying Bouch's professional reputation: he concluded that the bridge was "badly designed, badly built and badly maintained, and that its downfall was due to inherent defects in the structure, which must sooner or later have brought it down. For these defects both in the design, the construction, and the maintenance, Sir Thomas Bouch is, in our opinion, mainly to blame.".

Wind Pressure (Railway Structures) Commission

The enquiry noted “..there is no requirement issued by the Board of Trade respecting wind pressure, and there does not appear to be any understood rule in the engineering profession regarding wind pressure in railway structures ; and we therefore recommend the Board of Trade should take such steps as may be necessary for the establishment of rules for that purpose.”. Rothery dissented, feeling that it was for the engineers themselves to arrive at an understood rule, such as the French rule of 55psf or the US 50 psf. The Board of Trade accordingly set up a 5-man commission (Barlow, Yolland, Sir John Hawkshaw, Sir William Armstrong and Sir George Stokes) to consider the issue.

Windspeeds were normally measured in 'miles run in hour' (i.e. windspeed averaged over one hour) so it was difficult to apply Smeaton's table" which linked wind pressure to current windspeed

$P_t = 0.005 (V_t)^2\,$

where:

P_t is the instantaneous wind pressure (pounds per square foot)

V_t is the instantaneous air velocity in miles per hour

By examination of recorded pressures and windspeeds at Bidston Observatory , the commission found that for high winds the highest wind pressure could be represented very fairly by

$P_m = 0.01 (V_h)^2\,$

where:

P_m is the maximum instantaneous wind pressure experienced (pounds per square foot)

V_h is the 'miles run in hour' (one hour average windspeed) in miles per hour

However, they recommended that structures should be designed to withstand a wind loading of 56 psf , with a safety factor of 4 (2 where only gravity was relied upon). They noted that higher wind pressures had been recorded at Bidston Observatory but these would still give loadings well within the recommended safety margins. The wind pressures reported at Bidston were probably anomalously high because of peculiarities of the site (one of the highest points on the Wirral.): a wind pressure of 30-40 psf would overturn railway carriages and such events were a rarity. (To give a subsequent, well documented example, in 1903 a stationary train was overturned on the Levens viaduct but this was by a 'terrific gale' measured at Barrow in Furness to have an average velocity of 100mph , estimated to be gusting up to 120 mph)

Aftermath

The locomotive, NBR no. 224, a 4-4-0 designed by Thomas Wheatley and built at Cowlairs Works in 1871, survived the disaster, being salvaged from the river and repaired. It remained in service until 1919, acquiring the nickname of "The Diver"; many superstitious drivers were reluctant to take it over the new bridge.

Works of literature about the disaster

The Victorian poet William Topaz McGonagall commemorated this event in his poem The Tay Bridge Disaster, widely regarded as so bad as to be comical. Likewise, German poet Theodor Fontane, shocked by the news, wrote his poem Die Brück' am Tay . It was published only ten days after the tragedy happened. Hatter's Castle, the 1931 novel of Scottish author A. J. Cronin, includes a scene involving the Tay Bridge Disaster, and the 1942 filmed version of the book dramatically recreates the bridge's catastrophic collapse. The bridge collapse figures prominently in Barbara Vine's 2002 novel The Blood Doctor.

See also

• David Kirkaldy
• Harry Watts
• List of structural failures and collapses
• List of bridge disasters
• List of wind-related railway accidents

Notes and References

Bibliography

• Prebble, John, The High Girders: The Story of the Tay Bridge Disaster, 1956 (published by Penguin Books in 1975) ISBN 0-14-004590-2.
• Thomas, John The Tay Bridge Disaster: New Light on the 1879 Tragedy, David & Charles, 1972, ISBN 0-7153-5198-2.
• Swinfen, David The Fall of the Tay Bridge, Mercat Press, 1998, ISBN 1-873644-34-5.
• McKean, Charles, Battle for the North: The Tay and Forth Bridges and the 19th-Century Railway Wars: The Building of the Tay and Forth Bridges and the 19th Century Railway Wars Granta 2007.
• Lewis, Peter R. Beautiful Railway Bridge of the Silvery Tay: Reinvestigating the Tay Bridge Disaster of 1879, Tempus, 2004, ISBN 0-7524-3160-9.
• Rapley, John Thomas Bouch : the builder of the Tay Bridge, Stroud : Tempus, 2006, ISBN 0-7524-3695-3
• Lewis, Peter R. Disaster on the Dee: Robert Stephenson's Nemesis of 1847, Tempus Publishing (2007) ISBN 978 0 7524 4266 2
• Rothery, Henry Tay Bridge Disaster: Report Of The Court of Inquiry, and Report Of Mr. Rothery, Upon the Circumstances Attending the Fall of a Portion of the Tay Bridge on the 28th December 1879. London: Her Majesty's Stationery Office, 1880 OCLC 30875567

External links

• Tom Martin's engineering analysis of the bridge disaster
• Reappraisal of the Tay Bridge disaster Open University
• Recent review of book on the disaster — go to Failure Magazine; select "Archives" & then search for Tay Bridge.
• Dundee local history centre page on the disaster
• Tay Victims listing {reference only}
• Firth of Tay Bridge Disaster 1879: Worst Structural Disaster in British History at Suburban Emergency Management Project
• Tay Bridge Disaster: Report Of The Court of Inquiry
• Tay Bridge Disaster: Appendix to the Report Of The Court of Inquiry. Includes a large number of drawings of the bridge, and calculations of the result of wind pressure on the structure
• Report from the Select Committee on the North British Railway (Tay Bridge) Bill; together with the Proceedings of the Committee and Minutes of Evidence. All the oral evidence given, reproduced verbatim - a very large file but sometimes a useful corrective to reinterpretation by secondary sources - (eg did most contemporaries feel the bridge had been shaking itself to pieces, or is that just a rattling good yarn)