Origins and concept Proposals to build a bridge across the Tay date to 1854 but it was not until 15 July 1870 that the '''''' (
33 & 34 Vict. c. cxxxv) received
royal assent. On 22 July 1871, the foundation stone of the bridge was laid. The bridge was designed by
engineer Thomas Bouch, who received a
knighthood following the bridge's completion. The bridge was a lattice-grid design, combining
cast and
wrought iron. The design had been used by Thomas W. Kennard in the
Crumlin Viaduct in South Wales in 1858, after the use of cast iron in
the Crystal Palace. The Crystal Palace was not as heavily loaded as a railway bridge. An earlier cast-iron design, the
Dee bridge collapsed in 1847, having failed because of poor use of cast-iron girders.
Gustave Eiffel used a similar design to create several large viaducts in the
Massif Central in 1867. The original design was for lattice girders supported by brick piers resting on the bedrock, shown by trial borings to lie at no great depth under the river. At either end of the bridge, the single track ran on top of the bridge girder, most of which lay below the pier tops. At the centre section of the bridge (the high girders), the railway ran inside the bridge girder, which was above the pier tops to give clearance for the passage of sailing ships. To accommodate
thermal expansion, there were non-rigid connections between girders and piers. As the bridge extended out into the river, by December 1873, it became clear that the bedrock lay much deeper, too deep to act as a foundation for the bridge piers. Bouch redesigned the bridge to reduce the number of piers and increase the span of the girders. The pier foundations were no longer resting on bedrock; instead they were constructed by sinking brick-lined wrought-iron caissons onto the riverbed, removing sand until they rested on the consolidated gravel layer which had been misreported as rock, and then filling the caissons with concrete. Bouch had used the technique for viaducts, including the
Belah Viaduct (1860) on the
South Durham & Lancashire Union Railway line over
Stainmore, but for the Tay Bridge, even with the largest practicable caissons, the pier dimensions were constrained by their size. Bouch's pier design set six columns in a hexagon maximising the pier width but not the number of diagonal braces directly resisting sideways forces.
Design details The engineering details on the Tay Bridge were considerably simpler, lighter, and cheaper than on the earlier viaducts. The machined base of each column section docked securely into a machined enlarged section of the top of the section below. The joint was then secured by bolts through matching holes on lugs (Crumlin The bottom connection was to two sling plates bolted to the base of the equivalent section on an adjacent column. The bar and sling plates all had matching longitudinal slots in them. The tie bar was placed between the sling plates with all three slots aligned and overlapping. A
gib was 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. Horizontal bracing was provided by wrought iron channel iron. The various bolt heads were too close to each other, and to the column for easy tightening up with spanners; this coupled with lack of precision in the preparation of the channel iron braces led to various on site fitting expedients (one of them described by a witness to the enquiry as "about as slovenly a piece of work as ever I saw in my life". On the Crumlin and
Belah Viaducts, however, horizontal bracing was provided by substantial fitted cast-iron girders securely attached to the columns, with the diagonal braces then being attached to the girders. The chairman of the Court of Inquiry quoted at length from a contemporary book praising the detailed engineering of the Belah viaduct piers, and describing the viaduct as one of the lightest and cheapest of the kind that had ever been erected. ... It is a distinguishing feature in this viaduct that the cross, or distance girders of the piers encircle the columns, which are turned up at that point, the girders being bored out to fit the turned part with great accuracy. No cement of any kind was used in the whole structure, and the piers when completed, and the vertical and horizontal wrought-iron bracings keyed up, are nearly as rigid as though they were one solid piece... .... The fitting was all done by machines, which were specially designed for the purpose, and finished the work with mathematical accuracy The flanges of the column were all faced up and their edges turned, and every column was stepped into the one below it with a lip of about 5/8 of an inch in depth, the lip and socket for it being actually turned and bored. That portion of the column against which the cross girders rested was also turned. The whole of these operations were performed at one time, the column being centred in a hollow mandril-lathe. After being turned the columns passed on to a drilling machine, in which all the holes in each flange were drilled out of the solid simultaneously. And as this was done with them all in the same machine, the holes of course, perfectly coincided when the columns were placed one on the other in the progress of erection. Similar care was taken with the cross-girders, which were bored out at the ends by machines designed for that purpose. Thus, when the pieces of the viaduct had to be put together at the place of erection there was literally not a tool required, and neither chipping or filing to retard the progress of the work. Either, said the chairman, the Belah viaduct had been over-engineered, or the Tay Bridge had been under engineered.
Construction Whilst Bouch was in the process of revising his design, the company which had been awarded the contract for the bridge's construction, Messrs De Bergue of
Cardiff, went out of business. During June 1874, a replacement contract for the work was issued to
Hopkin Gilkes and Company, successors to the
Middlesbrough company which had previously provided the ironwork for the Belah viaduct. Gilkes had originally intended to produce all the bridge ironwork on Teesside, but in the event continued to use 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 during the night of Friday, 3 February 1877. The fallen girders had to be removed and new ones built. and the piers to be erected again; and this threatened seriously to interfere with the expectation of having the bridge finished for the passage of a train by September. Only eight months were now available for the erection and floating out of six, and the lifting of ten spans. Five and seven respectively of the spans had yet to go through the same process. Seven large and three small piers had yet to be built. The weight of iron which had to be put in its place was , and it seemed incredible that all this could be done in eight months. A good deal would depend on the weather but this was far from favourable. by
Major General Hutchinson of the Railway Inspectorate, who measured the deflection of the bridge girders under a distributed load of 1.5 tons per foot (5 t/m) due to heavy locomotives, travelling at up to , as less than . He reported that "these results are in my opinion to be regarded as satisfactory. The lateral
oscillation [roughly, rhythmic side-to-side movement], as observed by the
theodolite when the engines ran over at speed, was slight and the structure overall showed great stiffness". Hutchinson did require some minor remedial work to be performed, and also issued a "recommendation" to impose a speed limit on traffic passing over the bridge. Subsequently, Hutchinson explained to the inquiry that he had suggested this speed limit because of the minimal taper on the piers. The inspection report added: "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". On 1 June 1878, the Tay Bridge was opened for passenger traffic, with formal opening ceremonies having taken place during the previous day, in the course of which Thomas Bouch was made a
burgess of Dundee "in respect of his meritorious services as engineer of the bridge. ..." On 20 June 1879,
Queen Victoria crossed the bridge during her return south from staying at
Balmoral; Bouch was presented to her before she did so. On 26 June 1879, he was knighted by the Queen at
Windsor Castle.
Catastrophic failure On the night of 28 December 1879 at 7:15 p.m., the bridge collapsed after its central spans gave way during high winter gales. A train with six carriages carrying seventy-five passengers and crew, crossing at the time of the collapse, plunged into the icy waters of the Tay. All seventy-five people on board were killed. The disaster stunned the whole country and sent shock waves through the Victorian engineering community. The ensuing enquiry revealed that the design of the bridge had not accommodated for high winds. At the time of the collapse, a gale estimated at force ten or eleven (Tropical Storm force winds: had been blowing down the Tay estuary at right angles to the bridge. The train engine (
North British Railway no. 224) was salvaged from the river and subsequently restored for service on the railway. It gained the nickname "The Diver" as a result of its accident and difficult recovery. The collapse of the bridge, despite opening only nineteen months earlier after being found safe by the
Board of Trade, had a long-term effect on wider society. According to some commenters, it is still regarded as having been the most notorious
bridge disaster to have ever occurred in the British Isles. The disaster was commemorated in "
The Tay Bridge Disaster", one of the best-known verse efforts of
William McGonagall. Today, the stumps of the original bridge piers are still visible above the surface of the Tay even at high tide. In 2005, Scottish playwright Mike Gibb and composer Mairi Paton premiered their musical titled
Five Pound and Twa Bairns in Dundee. It focuses on three fictional women from very different backgrounds who lose men in the disaster. The musical has had several further productions, including three separate sold-out runs at Dundee Rep Theatre. ==Second bridge==