16 June 2010

"Thomas Bouch: the Builder of the Tay Bridge"

I picked up a copy of John Rapley's biography "Thomas Bouch: the Builder of the Tay Bridge" (ISBN 978-0-7524-3695-1, Tempus Publishing, 2007, 192pp) [Amazon.co.uk] cheaply in a bargain book store earlier this year.

I had previously read Rapley's fascinating "The Britannia & Other Tubular Bridges" [Amazon.co.uk], which is a detailed and evenhanded account of the great joint achievement of Robert Stephenson and William Fairbairn (and some other, lesser-known structures). So his treatment of the life of the Victoria railway engineer Sir Thomas Bouch was bound to be of interest.

Bouch's name is known to posterity pretty much for one thing, and one thing only: the collapse of his Tay railway bridge on 28 December 1879, approximately 18 months after it had been officially opened to traffic. Bouch's design was discredited, as were the construction and maintenance, and he died ten months later, his reputation ruined.

Before that, he had built up a considerable reputation as a railway engineer who could build new lines for far less money than his competitors. Bouch believed that his contemporaries were often far too conservative in their designs, and his quest for economy frequently led him to build railways using secondhand rails, timber bridges which never lasted long, and single-track rather than double-track solutions. While these allowed new railway lines to be built quickly for low capital outlay, they almost invariably led to higher upgrade costs later.

His antipathy to over-design can be seen in one of his most successful bridges, the Hownes Gill Viaduct, built in 1858 (pictured left in a 1906 postcard). In his book "British Railway Bridges", David Walters suggests that "its slender grace recalls Bouch's life-long contention that contemporary engineering work was hopelessly over-designed and uneconomical, through general conservatism and a chronic underestimation of the ultimate strength of materials". Bouch's design was reviewed by Robert Stephenson, who required both the addition of invert arches at foundation level to better spread the loads, and also that the tallest piers be widened to provide greater stability in high winds.

Bouch was unafraid to innovate when required, developing roll-on-roll-off ferries for railway wagons at the Firth of Forth, and his 1871 cable-stayed Redheugh Bridge at Newcastle foreshadowed modern designs such as those of Riccardo Morandi.

Most of the book focusses on Bouch's lengthy career as a railway engineer, working generally on minor regional lines. This offers a good understanding of Bouch's finely matched strengths and weaknesses. His ability to build for a penny what others could only build for a pound seems to have been unmatched. However, as well as frequently requiring expensive rebuilding, his schemes were often blighted by initial cost over-runs, the result of inadequate advance surveys.

For my taste, there's too little offered in the book to shed light on Bouch as a person (perhaps the source material simply isn't there), and I soon tired of the endless episodes of railway woe.

The Tay Bridge, understandably, is covered in greatest detail. The difficulties of construction included the collapse of two girders during erection, blown over by the wind, but in line with Bouch's general parsinomy, one was recovered from the estuary and re-used in the finished bridge. Once open, there were problems with scour and with slackening tie bars, with inadequate repairs made on site without reference back to Bouch himself. While the civil engineer was receiving a knighthood for his achievements, the bridge was beginning to wobble alarmingly, and (with hindsight) the collapse of the bridge became inevitable.

The Court of Inquiry which investigated the failure of the bridge led to Bouch being left in disgrace. This was despite the two engineers on the Court refusing to apportion blame, and indeed disassociating themselves from the far more critical conclusions of their colleague Henry Rothery (notably, a lawyer rather than an engineer).

While Bouch was certainly responsible for many of the defects in the bridge's design and construction, his responsibility for the ultimate cause of failure, the bridge's inadequate strength against wind load, is less clear. He had sought advice from the railway inspectorate (who noted that wind load need not normally be included in design for spans only a little shorter than those adopted). He was told by the Astronomer Royal (in connection with his aborted design for the Forth Rail Bridge) that a pressure of 10 pounds per square foot was reasonable. Bouch's assistant used a pressure of 20 psf for the Tay Bridge design, despite there being in general little understanding of wind load amongst civil engineers of the period. Bouch became the fall guy, but it seems many of his peers might have made similar decisions.

Overall, I was a little disappointed by this book, although I suspect much of that is simply because Bouch was more of a designer of railways than of bridges, and hence there were large parts of the tale which were of limited interest to me. It was certainly less immediately appealing than Rapley's book on the Britannia Bridge, but that offered a more straightforward story where extensive source material is available, and with historically significant disagreements between the main protagonists to recount. To its credit, "Thomas Bouch" is well illustrated with archive photographs and diagrams, and I'd think it's likely to remain the definitive work on its unfortunate subject for a long time to come.

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