How steel measured up to Telford’s iron
I have vivid memories as a junior engineer in the 1960s of clambering through the jungle of trusses on Telford’s Craigellachie Bridge over the River Spey.
The purpose was to survey structural damage because making an arch shallow reduces its strength, contrary to John Nisbet’s analysis (Leopard, April).
Telford produced a beautiful bridge, but at the cost of some fractures of the cast iron struts as traffic weight increased.
To rectify this damage, these struts were replaced with similar ones made from steel.
Not only were they more prone to rust, however, but they were unnecessary. Just a few years later a new bridge enabled Telford’s bridge to be closed to traffic.
Douglas Stewart, BSc, PhD, MIHT, DipTE,
Benview, Peterculter, Aberdeen AB14 0NT