The Court of Inquiry report (T6) concluded that, “The fall of the bridge was occasioned by the insufficiency of the cross bracing and its fastenings to sustain the force of the gale.” The Court of Inquiry indicated that if the piers, and in particular the wind bracing, had been properly constructed and maintained, the bridge may have withstood the storm that night, albeit with a lower factor of safety – 4 was the norm at the time.
The Court of Inquiry consisted of 3 commissioners: The chairman Henry Cadogan Rothery, Commissioner of Wrecks, who was trained as a lawyer with a degree in mathematics. The 2 assistant commissioners were both engineers: William Yolland, Chief Inspector of Railways and William Henry Barlow the president of the Institute of Civil Engineers. Henry Law was appointed as engineering advisor to the Board of Trade and Dr. William Pole as technical advisor to Bouch.
Two reports were produced by the Court of Inquiry, one by Rothery and the other by Barlow and Yolland. Barlow and Yolland’s report, which was only 12 pages long, addressed the disaster from a technical perspective but did not apportion blame or responsibility on any individual. Rothery’s report, which was much longer (56 pages), was more substantial although it came to the same conclusions, except it apportioned blame where appropriate. In particular, he came down heavily on Sir Thomas Bouch. Rothery concluded that:
“The conclusion then, to which we have come, is that this bridge was badly designed, badly constructed and badly maintained and that its downfall was due to inherent defects in the structure, which must 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. For the faults of design he is entirely responsible. For those of construction he is principally to blame in not having exercised that supervision over the work, which would have enabled him to detect and apply a remedy to them. And for the faults of maintenance he is also principally, if not entirely to blame in having neglected to maintain such an inspection over the structure, as its character imperatively demanded.”
Why did Yolland and Barlow see the necessity to produce a separate report from Rothery’s? Firstly, they thought that apportioning blame was outside the remit of the inquiry. Secondly, Yolland & Barlow being civil engineers they were more empathetic towards Bouch as a fellow engineer especially given the knowledge of wind loading at the time. Thirdly, Yolland had given advice to Bouch on the initial design of the bridge. Bouch had written to Yolland (Chief Inspector of Railways for the Board of Trade) on the 5th of October 1869 (G2).
“In calculating the strains of malleable iron girders will you kindly tell me what you take the live load as per running foot for spans over a hundred feet and is it necessary to take the pressure of wind into account for spans not exceeding 200 feet span, the girders being open lattice work? My own opinion is that one and a quarter tons per foot run for line loads is sufficient for spans over 100 feet, and that it is not necessary to take the force of the wind into account where open work girders are used and spans less than 200 feet. I merely ask this information that I may act in accordance with the views of the Board of Trade.”
Three days later Colonel Yolland replied: “A ton and a quarter foot run will be sufficient for spans over 100 feet, and we do not take the force of the wind into account when open lattice girders are used for spans not exceeding 200 feet.” The original design was for the 14 high girders to be 200ft, but due to the project being behind schedule and over budget, Bouch decided on increasing the span length to 11 spans of 245ft and 2 of 227ft so saving on the cost of a pier.
In a recent paper (L1) Robert Shiels looking at the disaster for a legal perspective has concluded the Court of Inquiry was procedurally in error because Yolland was one of the commissioners who had given advice on wind pressure for the design in its early stages. Other papers and articles examining the disaster from a legal viewpoint by Robert Shiels are available for download from the References section (L2, L3, L4, L5, L6, L7,L8,L9,L10).
International interest
The construction and then completion of the first Tay Bridge was of immense interest within the engineering profession and also the public both in the United Kingdom and globally. The full extent of that international interest, it would seem, has yet to be studied fully, as it perhaps ought to be if only to show how the progress and influences of the science of engineering.
One contemporary commentator was Professor Carl Wilhelm Friedrich Launhardt (1832-1918), a German mathematician and economist. He was the first Rector of the Technical School at Hanover. The professor had on an earlier occasion visited the construction site in the vicinity of Dundee where he obtained measurements and assessed the structure at the stage it had reached then. The professor presumably met with Albert Grothe (1841-1914), a fellow German and a civil engineer employed on site at Dundee.
The Scotsman newspaper, on 15 January 1880, p.5, published the views of Professor Launhardt on the collapse, taken from a German newspaper, the Hannoverscher Courier, on 6 January 1880, p.5.
The original German newspaper, a typed version of the original German article and a recent translation into English can be accessed.
Tay Bridge disaster 