page_title: Cast-iron architecture
section_title: Structural use
hierarchical_section_title: Cast-iron architecture / Structural use
caption_attribution_description: English: A view the The Iron Bridge by William Williams.
context_page_description: Cast-iron architecture is the use of cast iron in buildings and objects, ranging from bridges and markets to warehouses, balconies and fences. Refinements developed during the Industrial Revolution in the late 18th century made cast iron relatively cheap and suitable for a range of uses, and by the mid 19th century it was common as a structural material, and particularly for elaborately patterned architectural elements such as fences and balconies, until it fell out of fashion after 1900 as a decorative material, and was replaced by modern steel and concrete for structural purposes.
context_section_description: Cast iron is not a good structural material for handling tension or bending moments because of its brittleness and relatively low tensile strength compared to steel and wrought iron.  Cast iron has good compressive strength and was successfully used for  structural components that were largely in compression in well designed bridges and buildings. In a few instances bridges and buildings built with cast iron failed when the cast iron was used poorly.
  Cast iron was used as early as the 9th century in pagoda construction in Tang Dynasty China. Texts written by the Japanese Buddhist monk Ennin describe in detail the cast-iron pagodas and statues widespread in China at the time. Persecution of Buddhism in China led to the destruction of many of these structures. The later Song Dynasty also built cast iron pagodas, exploiting its ability to be both structural and to be cast in any shape, such as in imitation of the timber and tiles of a standard pagoda. The 22m Iron Pagoda at the Yuquan Temple (Jade Springs Temple), Dangyang, Hubei, was built during the Song Dynasty in 1061, and is the most outstanding example to survive. Cast iron pagodas were then superseded by even more elaborate bronze ones, but cast iron continued to be used for decorative items such as bowls and statues.  
  In Europe, it was in late 18th-century Britain that new production methods first allowed cast iron to be produced cheaply enough and in large enough quantities to regularly be used in large building projects. New production methods included using steam engine powered blast air, which allowed higher blast furnace temperatures, which in turn allowed the use of more limestone to be added with the iron ore charge.  The higher furnace temperatures made the slag produced with the additional lime to flow more freely. The calcium and magnesium in the lime helped tie up sulfur, which allowed the use of coke for fuel.  The higher furnace temperatures also increased the furnace capacity.
  One of the first important projects was The Iron Bridge in Shropshire, opened in 1781, a precedent-setting structure made almost entirely of cast iron. However, it was grossly over-designed, and the makers (principally Abraham Darby) suffered financially as a result. The quality of the iron used in the bridge is not high, and nearly 80 brittle cracks are visible in the present structure. Nevertheless, its success led to the use of cast iron for further bridges and structures by the Coalbrookdale foundries and others. 
  Engineer Thomas Telford improved both the design and quality of the material in bridges, for example, at Buildwas, upstream of Coalbrookdale, built in 1796, and also for aqueducts, such as the world-famous Pontcysyllte Aqueduct in North Wales, built in 1805, where both the arches and the trough are constructed of cast iron. On the continent, the 1804 Pont des Arts in Paris is an early and elegant use of cast iron for a major city river crossing (the metal work of the current bridge is a near identical copy built in 1984 due to structural decay). 
  Another notable example is the elegant Ha'penny Bridge in Dublin, cast by the Coalbrookdale foundry, and built in 1816.  
  Cast-iron columns for buildings had the advantage of being extremely slender, compared with masonry columns capable of supporting similar weight. That saved space in factories, and so after the five-storey 1795 Ditherington Flax Mill with its internal structure of cast-iron proved the concept, it became ubiquitous in the multi-level mills of northern England, and then further afield in all kinds of industrial and multi-storey structures, up until about 1900. It was also useful in other kinds of buildings, for instance enabling architects of theaters, churches and synagogues to improve sight lines when supporting balconies, by eliminating or at least making the columns that supported the roof or balconies thinner. Cast iron was used in place of timber in some buildings in the early-mid 19th century where smaller supports or larger spans were required (and where wrought iron was too expensive), notably in
caption: The Iron Bridge, Coalbrookdale, Shropshire, 1781 the first large scale use of cast iron for structural purposes.
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