Volume Six - Pre-Victorian to the Present Day - Select Aspects - Structural Analysis of the river Ely Subway by Rota Design Limited - 2015

Three types of cast iron are commonly available to the 19th century engineer. 'Grey iron' was made from best grades of pig iron which was the most consistent in its physical properties. 'White iron' being harder and thus more brittle than grey iron but it did inhibit rust a little. Thirdly, 'Mottled iron' was high in sulphur and prone to cracking during the cooling stages of the casting process so was unreliable generally but it had a nice mix of the physical properties of white and grey irons.

Irons were produced at a variety of locations and had local names such as Blanavon, Ystalfera, Brymbo and Ynyscedwyn, whilst here in Yorkshire we had Low Moor and Bowling iron grades from Bradford. The iron segments for the Penarth subway were, to my best knowledge and as a result of the research undertaken, cast nearby Glasgow and thus I believe they would have been made from 'Clyde Iron' which was a grey iron. It was available in at least 3 grades and I would have expected it to have been a grade named 'No. 3' (providing 46.8 tons per square inch compressive strength) given its application and intended use and lifespan etc.

The British Standards organisation, of which Rota Design Limited is a member, became more closely involved in the standardisation of cast iron during the early 20th century, but by that time it was gradually falling out of favour within the construction industry. However, a standard published after WWII, BS 1452:1948, specifies seven grades of cast iron grading them by using their ultimate tensile strength (UTS), being in the range of 10 to 26 tons per square inch.

During the structural analysis of the subway we at Rota Design Limited used our discretion with regard to the physical properties applied to our finite element analysis studies and used a more conservative guesstimate of its properties. We would require a number of representative samples to be tested at an accredited test laboratory in order to obtain reliable actual physical properties if our studies were to be considered for commercial use. So our results are provided strictly without liability!