Cast-iron Architecture - Catastrophic Failures

Catastrophic Failures

Cast iron has some architectural advantages, and some weaknesses. It is strong in compression, but weak in tension and bending. Its strength and stiffness deteriorate when subjected to high heat, such as in a fire. In the early era of the industrial revolution cast iron was often used in factory construction, in part owing to the misconception that such structures would be fireproof. William Strutt pioneered this innovation, building a number of industrial buildings using cast iron supports. Cast iron was strong enough to support the heavy machinery but was vulnerable to the frequent fires that would occur in such factories. There were also numerous building collapses caused by fracture of brittle cast iron beams. These often occurred when the bottom side of the beam was in tension, often from defects such as blow holes within the beams. Such internal defects were common in large beams.

Cast iron was also used widely in bridge construction for the new railway system, sometimes with horrific results, especially when cast iron girders were used instead of arches. The first use was at the Water Street terminus of the Liverpool and Manchester Railway in 1830 to a design by William Fairbairn, a successful design which was demolished about 1900 owing to the widespread concern about cast iron under bridges on the rail network in Britain. Robert Stephenson built a longer bridge over the river Dee, mistakenly adding wrought iron trusses to strengthen the structure. This led to the Dee bridge disaster of 1847, which killed five when the bridge collapsed.

Following the disaster such trussed bridges were demolished and cast-iron was replaced with wrought iron composite beams formed by riveting sheets together, and then steel rolled beams when steel became available in the late 1860s and 1870s. Cast iron continued to be used in railway under bridges, and there were a number of serious failures involving loss of life. The most serious accident occurred in 1879 with the Tay Bridge disaster when the centre part of the bridge collapsed in a storm as an express train was passing over. The whole train was lost with more than 75 passengers and crew. The weakest parts of the bridge were cast iron lugs holding tie bars in place, and cast iron in new bridges was effectively abandoned after the disaster. Most small cast iron beam structures were demolished and replaced after the Norwood Junction rail accident of 1891.