THE AGE OF IRON

For millenia, the only way to create a strong, durable, and fireproof structure was to build it out of stone or brick. Needless to say, this required plenty of time, material, and effort, not to mention a lordly budget. But for most of man’s history, this tried-and-true ancient method had to suffice. 

There was finally a tantalizing glimmer of change in this situation toward the end of the 18th century, when a material long in use for other items--cast iron--began to be used in building. Pound for pound, cast iron was much stronger than stone or brick. Since it was cast in molds, it could be cheaply mass produced. And lastly, cast iron wouldn’t burn.

Among the first structural uses of cast iron was the celebrated Coalbrookdale Bridge across the river Severn in Shropshire, England, built by one Abraham Darby III in 1879, and still standing today. Darby came from a storied dynasty of English ironmongers who had cast cooking pots and like paraphenalia for generations. Darby reasoned that the same process might serve very well to produce repetitive structural members such as girders--and not incidentally create a vast new market for his products. 

Knowingly or not, Darby opened a whole new chapter in the history of building. Most of the structural innovations using cast iron came from engineers rather than architects, and most of these advances were made in Britain, the cradle of the ongoing Industrial Revolution. 

At first, cast iron appeared to be the greatest building breakthrough since ancient times. It began to be widely used in bridge structures and other civil engineering works. In architecture, cast iron columns and beams became common in factory and commercial buildings. Slender, delicately ornamented cast iron columns even appeared in a few large English manor houses. 

Alas, this promising future clouded over on May 24, 1847, when a brand new cast iron bridge across the river Dee in Chester, England collapsed. An inquiry determined that one of the cast-iron girders had snapped under the load of a crossing train.  England saw subsequent cast iron failures of the Bull Bridge in 1860, the Woolton Bridge in 1861, and finally the catastrophic collapse of the Tay Bridge in 1879, which killed sixty, including the bridge engineer’s son in law. In architecture, too, iron proved vulnerable. Unlike wood, which visibly bends when overloaded, cast iron could appear sound in one moment and shatter in the next. Most--er, ironic--it turned out that while cast iron wouldn’t burn, fire could still weaken it to the point of collapse.

After yet another bridge failure in 1891, it was determined that all cast iron bridges in the United Kingdom should be replaced. Future bridges were supposed to utilize wrought iron—a tougher, more malleable metal that unfortunately lacked cast iron’s ability to be molded. 

However, as so often happens in history, new developments soon rendered these plans moot. By the end of the 19th century, steel--a newly perfected material that was both strong and extremely malleable--was poised to revolutionize building. Cast iron continued to be used on occasion for prefabricated store fronts and the like, but engineering’s age of iron had ended.