Editing Tay Bridge (section)

== First bridge ==
===Origins and concept===
Proposals to build a bridge across the Tay date to 1854 but it was not until 15 July 1870 that the North British Railway Tay Bridge Act received [[royal assent]]. On 22 July 1871, the foundation stone of the bridge was laid.{{Citation needed|date=May 2018}}

The bridge was designed by [[engineer]] [[Thomas Bouch]], who received a [[knighthood]] following the bridge's completion.<ref name="structurae">{{Structurae |id=20000445 |title=Firth of Tay Bridge (1877)}}</ref> The bridge was a lattice-grid design, combining [[Cast iron|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 disaster|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.

[[File:Dusk on a sunny summers day across Dundee, Scotland, July 17, 2007.jpg|thumb|At dusk. One of the stumps of the original bridge is silhouetted against the sunlit Firth.]]
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.{{Citation needed|date=May 2018}}

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.<ref name="ReferenceA">Minutes of Evidence p. 402. – evidence of Sir T Bouch.</ref> 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.<ref name="Grothe" />

To reduce the weight that the ground underneath the caissons would have to support, 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 to give rigidity and stability. The basic concept was well known, having been used by Kennard in the [[Crumlin Viaduct]] in South Wales in 1858.<ref name="Maynard">Maynard, H. M. "Handbook to the Crumlin Viaduct." J M Wilson: London, 1862. retrievable via Google Books [https://books.google.com/books?id=XoEHAAAAQAAJ] Maynard claims the loading on the Crumlin viaduct foundations to be 1/5th what they would have been had brick piers been used.</ref> 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.{{Citation needed|date=May 2018}}
 {| class="wikitable"
|-
!Structure  !! Crumlin viaduct<ref name="Maynard" />   !! Belah viaduct<ref>most data from [http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=84]. Retrieved 22 January 2012 (the quoted height between joints/bracing is clearly inconsistent with the accompanying photo so the number of column sections is taken from another reference;)</ref>!! Tay Bridge<ref>all data from Annexe to Report of Court of Inquiry</ref>
|-
|Engineer (year of opening) || Kennard (1858) || Bouch (1860) || Bouch (1878)
|-
| Single span  || {{convert|120|ft|m|1|abbr=on}}|| {{convert|60|ft|m|1|abbr=on}} || {{convert|245|ft|m|1|abbr=on}})
|-
| Pier height || {{convert|170|ft|m|1|abbr=on}}|| {{convert|180|ft|m|1|abbr=on}} || {{convert|83|ft|m|1|abbr=on}}
|-
| Pier width at top || {{convert|30|ft|m|1|abbr=on}}|| {{convert|22|ft|m|1|abbr=on}} || {{convert|19|ft|10|in|m|abbr=on}}
|-
| Pier width at base || {{convert|60|ft|m|1|abbr=on}}|| {{convert|48|ft|m|1|abbr=on}} || {{convert|21|ft|10|in|m|abbr=on}}
|-
| Columns per pier || 14 (1-3-3-3-3-1) || 6 (2-2-2) || 6 (1-2-2-1)
|-
| Sections per column || 10 || 11<ref>From diagram 276 in [https://openlibrary.org/books/OL6531011M/History_of_bridge_engineering History of Bridge Engineering HG Tyrell Chicago 1911]</ref> || 7
|-
| Diagonal tiebars giving lateral bracing (per pier)<ref>calculable from previous 2 rows</ref> || 180 || 88 || 28
|-
| Fate||Demolished 1966-7<ref>{{cite web|url=http://www.caerphilly.gov.uk/chronicle/english/onthemove/crumlinviaduct.htm|title=Crumlin Viaduct|work=caerphilly.gov.uk}}</ref>|| Demolished 1963|| Failed in service 1879
|}

=== Design details ===
[[File:The Tay Rail Bridge from Wormit on the south bank.jpg|thumb|The second (current) Tay Rail Bridge from Wormit on the south bank]]
[[File:The Tay Rail Bridge as seen across the Tay Estuary from Newport-on-Tay.jpg|thumb|upright|The current Tay Rail Bridge as seen across the Tay Estuary from Newport-on-Tay]]
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.<ref>"like the spigot and faucet of a domestic water pipe" was felt be a useful analogy at the Tay Bridge Court of Inquiry but would probably baffle modern householders</ref> The joint was then secured by bolts through matching holes on lugs (Crumlin<ref name="Maynard" />) or flanges (Belah) on the two sections. This 'spigot and faucet' configuration was used, apparently without machining, on some Tay Bridge pier columns, but on some the bolts were relied upon to ensure correct alignment. In the event, the joints were made using undersized bolts, of a smaller diameter than that which would just go through the hole. This made assembling the column easier, as the bolt holes would not need to align exactly before inserting the bolt. However, this allowed the two members, so joined, to move relative to each other under load, weakening the column.

On the Tay Bridge the diagonal bracing was by means of flat bars running from the top of one column-section diagonally down to the bottom of the adjacent column section. The top connection was to a lug that was an integral part of the column casting.<ref>"..although cast-iron lugs are peculiarly liable to fail from shock, they have been used in precisely this way successfully in tens of thousands of yards of viaduct; therefore, Sir Thomas Bouch was only following precedent in using them here. Mr Barlow will know that on the Bombay and Baroda line they were used for a great many viaducts" Minutes of Evidence – evidence of B Baker, p. 507</ref> 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 and cotter|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.<ref>Minutes of Evidence – evidence of H Law, p. 246</ref> 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".<ref>Minutes of Evidence – evidence of H Law, p. 331</ref>

On the Crumlin and [[Belah Viaduct]]s, 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.<ref>Details of the bracing of the Crumlin viaduct are given in Maynard, see also a photograph of painters at work on a pier in 1914 to be found at [http://www.crumlinviaduct.co.uk/photo.htm Crumlin Viaduct] which will probably be found of considerable assistance</ref> The Chairman of the Court of Inquiry quoted at length from a contemporary book<ref name="Humber 1870">{{cite book|last=Humber|first=William|title=Complete Treatise on Cast and Wrought Iron Bridge Construction &c Volume 1|year=1870|publisher=Longwood|location=London|pages=264|url=https://books.google.com/books?id=1SJRAAAAYAAJ}}</ref> 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.
<blockquote>...&nbsp;It is a distinguishing feature in this viaduct that the cross, or distance girders<ref>made of cast iron Minutes of Evidence – evidence of Sir T Bouch, p. 430</ref> 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...</blockquote>  <blockquote>.... 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<ref>ie c 16 mm</ref> 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.<ref>Rothery in Court of Inquiry report pp 43–44 quoting Humber op cit p 224-5</ref></blockquote>
Either, said the chairman, the Belah viaduct had been over-engineered, or the Tay Bridge had been under engineered.<ref>Rothery in Court of Inquiry report pp 43–44</ref>

=== 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.<ref>Reportedly, the company's owner, Mr De Bergue, had gone [[insanity|insane]] and then died – Minutes of Court of Inquiry.</ref> During June 1874, a replacement contract for the work was issued to [[Gilkes Wilson and Company|Hopkin Gilkes and Company]], successors to the [[Middlesbrough]] company which had previously provided the ironwork for the Belah viaduct.<ref name="ReferenceA"/><ref>Minutes of Evidence – evidence of Sir T Bouch, p. 406</ref><ref>Bouch’s brother William was Locomotive Superintendent of the [[Stockton and Darlington Railway]] and also a director of Gilkes which made locomotives for the S&D. On his brother's death in January 1876, Bouch as his sole executor effectively inherited his shares, and also his personal guarantee of the firm's borrowings. The firm was not in good enough shape for Bouch to dispose of his interest, and he lost a large amount of money when it went bankrupt during 1880. In principle, there was therefore a conflict of interest with Bouch's duty to advise the railway company on the acceptability of the contractor's work. (Minutes of Evidence – evidence of Sir T Bouch, p. 440)</ref> 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.{{Citation needed|date=May 2018}}

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.<ref name="Grothe">{{cite web|url=http://www.todayinsci.com/Events/Bridges/BridgeTay-GoodWords(1878).htm|title=The Tay Bridge|work=todayinsci.com}}</ref><ref>{{cite news|newspaper=The Dundee Courier and Argus|date=5 February 1877|title=The Tay Bridge Accident}} gives detailed accounts by those actually involved:</ref> 
<blockquote>The fallen girders had to be removed and new ones built.<ref>One of the fallen girders was recovered and reused.{{Citation needed|date=May 2018}}</ref> 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 {{convert|245|ft|adj=on|disp=sqbr}} spans. Five and seven respectively of the {{convert|145|ft|adj=on|disp=sqbr}} 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 {{cvt|2,700|LT|ST|disp=sqbr}}, 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.<ref name="Grothe"/></blockquote>

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. While visiting the city, [[Ulysses S. Grant]] commented that it was "a big bridge for a small city".

=== Inspection and opening ===
[[File:Original Tay Bridge before the 1879 collapse.jpg|thumb|The original Tay Bridge before the 1879 collapse]]
Like all UK rail lines, the Tay Bridge was subject to a [[Board of Trade]] inspection before it could carry passenger trains. The inspection was conducted 25–27 February 1878<ref>by which time ballast trains had been running over the bridge for 2 months – evidence of [[Charles Scrope Hutchinson|Major General Hutchinson]] Minutes of Evidence, p. 376</ref> by [[Charles Scrope Hutchinson|Major General Hutchinson]] of the Railway Inspectorate, who measured the deflection of the {{convert|245|ft|m|abbr=on}} bridge girders under a distributed load of 1.5 tons per foot (5 t/m) due to heavy locomotives, travelling at up to {{convert|40|mph|km/h|abbr=on}}, as less than {{convert|2|in|mm}}. 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".<ref>Hutchinson's report of 5 March 1878 annexed to evidence of Major General Hutchinson Minutes of Evidence, p. 373.</ref>

Hutchinson did require some minor remedial work to be performed, and also issued a "recommendation" to impose a {{convert|25|mph|km/h|abbr=on}} speed limit on traffic passing over the bridge.<ref>This was not a requirement -the Railway Inspectorate had no formal powers on operational matters although their views on them carried considerable weight where they did not entail significant expenditure.{{Citation needed|date=May 2018}}</ref> 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".<ref>[http://www.railwaysarchive.co.uk/documents/BoT_TayInquiryAppendix1880.pdf "Tay Bridge Disaster: Appendix to the Report Of The Court of Inquiry."] ''railwaysarchive.co.uk'', 9 April 1880. p. 42.</ref>

[[File:Tay bridge down.JPG|thumb|Tay bridge following the collapse]]
On 1 June 1878, the Tay Bridge was opened for passenger traffic,<ref>{{cite book |last=Thomas |first=John| author-link = John Thomas (author) |title=The North British Railway, vol. 1 |year=1969 |publisher=[[David & Charles]] |location=Newton Abbot |isbn=0-7153-4697-0}}</ref> with formal opening ceremonies having taken place during the previous day, in the course of which Thomas Bouch was made a [[burgess (title)|burgess]] of Dundee "in respect of his meritorious services as engineer of the bridge.&nbsp;..."<ref>Millar, A. H. 'Roll of Eminent Burgesses of Dundee 1513–1886.' Dundee, 1887. Retrievable at [https://archive.org/details/rolleminentburg00scogoog]</ref> On 20 June 1879, [[Queen Victoria]] crossed the bridge during her return south from staying at [[Balmoral Castle|Balmoral]]; Bouch was presented to her before she did so. On 26 June 1879, he was knighted by the Queen at [[Windsor Castle]].<ref>{{Cite news|title=The Queen has been graciously pleased to confer the honour of knighthood upon Thomas Bouch|date=24 June 1879|work=Aberdeen Evening Express}}</ref>

===Catastrophic failure===
[[File:Fallen_girders,_Tay_Bridge.jpg|thumb|right|Fallen girders near the Tay Bridge]]
{{main|Tay Bridge disaster}}
On the night of 28 December 1879 at 7:15&nbsp;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: {{convert|55|–|72|mph|km/h|abbr=on}} had been blowing down the Tay estuary at right angles to the bridge. The train engine ([[NBR 224 Class|North British Railway no. 224]]) was salvaged from the river and subsequently restored for service on the railway.{{sfn|SLS|1970|p=66}}{{sfn|Prebble|1959|p=164}} It gained the nickname "The Diver" as a result of its accident and difficult recovery.{{sfn|Highet|1970|p=89}}{{sfn|Prebble|1959|p=188}}

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.{{citation needed|date=April 2021}}

{{wide image|Tay Rail Bridge with pier stumps 2017-05-28.jpg|1250px|Northern segment of the second Tay Bridge, showing stumps of the original bridge's piers poking above the Tay|alt=Northern segment of the second Tay Bridge, showing stumps of the original bridge's piers poking above the Tay}}