This week in 1885: The Forth Bridge

Almost 130 years after it was built it remains one of the UK’s engineering marvels.

Forth
The inner tensions and compressions of the Forth Bridge. Credit: Simon Johnston

Stretching just over 2km (1.5 miles) and rising 46m above the high tides of the Firth of Forth, its scale is such a headache for those charged with repainting it that it has become shorthand for any job without end. It is, of course, the Forth rail bridge.

READ OUR ORIGINAL ARCHIVE COVERAGE HERE

Determined not to see a repeat of the Tay Bridge disaster of 1879, no expense was spared in the construction, which cost around £3m. It’s a chastening reminder of the conditions endured by Victorian engineers that the project carried a high human cost, with more than 60 workers losing their lives. Many more became seriously ill after suffering the effects of ‘Caisson disease’, today known as the bends, brought on when they left the compressed atmosphere of watertight structures, called caissons, used to construct the bridge’s foundations.

Reporting on the early stages of the bridge’s construction, The Engineer barely hints at these problems, writing, with characteristic Victorian understatement: ‘the difficulties met with in preparing for and founding the piers of the Forth bridge have been neither few nor unimportant, and it’s patent to even the uninitiated that causes for anxiety will neither disappear nor diminish till the steel superstructure has been completed.’

READ OUR ORIGINAL ARCHIVE COVERAGE HERE

The article, the first in a number about the design of the bridge, goes on to concern itself primarily with the installation of the first part of this superstructure: the lower bed plates. ‘The whole plate is bolted on a number of short iron columns in situ and is riveted up by a special hydraulic machine. Two girders are employed, one above and one below the bed plate…on each girder slides a hydraulic cylinder, one having a more effective area than the other…the result is that when water is admitted the total pressure on one is greater than on the other, thereby holding the rivet head firmly in place.’

In a later article the magazine reports on the numerous other challenges that left us with such an enduring icon of the industrial revolution. And to think, once they’d built the thing they had to paint it…which was exactly like painting the Forth bridge.

Jon Excell