Cast-iron architecture
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.
Structural use
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. However, cast iron does have 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 misused.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 in the 840's 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, 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 Cast iron pagodas were then superseded by even more elaborate bronze ones, but cast iron continued to be used for decorative items such as bowls and statues.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.
Bridges
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 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 in 1796, upstream of Coalbrookdale, 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.
Another notable example is the elegant Ha'penny Bridge in Dublin, cast by the Coalbrookdale foundry, and built in 1816. The superior performance and greater spans of wrought-iron, and later wire suspension bridges, soon superseded cast iron for bridge construction.
Early use in buildings
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 across Europe and the United States, helping to fuel the Industrial Revolution. Its usefulness for multi storey buildings ensured it remained popular for all kinds of industrial and commercial structures, as well as supports for balconies in theatres and even in churches, up until it was finally replaced by steel in about 1900.Cast iron was also taken up by some architects in the early 19th century where smaller supports or larger spans were required, notably in the Royal Pavilion in Brighton, designed by John Nash and built between 1816 and 1823, where cast iron columns were used within the walls, as well as cast iron beams, to enable the construction of the decorative domes; the columns in the kitchens were disguised as palm trees.
Roof frames
An elaborate cast iron frame was used for the dome of Saint Isaac's Cathedral in St Petersburg, and the new roof following a fire of Chartes Cathedral. Similarly large span beams were also to support the wide roofs of the Palace of Westminster.Piers
Cast iron was also used as the principle support structure for seaside piers, with multiple slender columns able to support long decks of wrought iron and wood, and later large halls and pavilions; engineer Eugenius Birch built the first, Margate Pier in 1855, followed by at least 14 piers in Britain in the 1860s–80s, and many more in Europe.Use with wrought iron
Cast iron was not useful for items in tension like beams, where the more expensive wrought iron was preferred. Improvements in production saw the costs decrease at the same time as cast iron gained popularity. The puddling process, patented in 1784, was a relatively low cost method for producing a structural grade wrought iron. Puddled wrought iron was a much better structural material, and was preferred for bridges, rails, ships and building beams, and was often used in combination with cast iron, which was better in compression.Steel
was an even better structural material than wrought iron, and new steel making processes developed in the late 19th century greatly lowered the cost of production to far below the cost of wrought iron. The widespread use of cast-and-wrought iron frames in multi-level buildings was translated into steel-frame buildings, and was an essential step in the development of the modern skyscraper.Architectural use
In Europe, cast iron had been occasionally used with architectural embellishment in the Middle Ages, such as fire backs with cast figures and scenes. The improvements in techniques in the late 18th century led to the possibilities of finer castings, allowing decorative objects such as statuary and jewelry to be mass-produced. Following the development of the material as for structural purposes, it was soon adapted for uses that were both decorative and structural in all manner of buildings, structures and objects.Early balustrades, railings and memorials
As soon as improvements in techniques led to finer castings, designers exploited the decorative possibilities. As early as 1775, noted architect Robert Adam joined with the Scottish Carron Company iron works to produce balcony railings in imitation of wrought iron, such as the railing for the Adelphi in London. Another very early large scale example is the delicate fence of the Summer Garden in Saint Petersburg, designed by Georg Von Veldten, built between 1771 and 1784, which also imitated wrought iron, and is considered the pinnacle of cast iron design in the city. Other well known architects were early adopters of the material; John Nash employed cast iron as part of the structure of his landmark 1820s Royal Pavilion in Brighton, and German architect Karl Friedrich Schinkel was an enthusiastic early adopter, using cast iron for memorials such as the 20m tall Gothic Revival Kreuzberg War Memorial in 1821, and the delightful nautical seahorses and mermaids in the balustrade of the 1820s Castle Bridge in Berlin.In Saint Petersburg, cast iron was used on the many bridges, sometimes as the supporting structure, but especially for the decorative railings and sculptural embellishments, including the chain-suspension 1826 Bank Bridge, with its distinctive cast iron griffin sculptures and elaborate balustrades, the 1840 Pevchesky Bridge, the 1842 Anichkov Bridge, and more seahorses on the 1843–1850 Annunciation Bridge.
Prefabricated and transportable buildings
Since it could be used for all the structural members that would be cast in a foundry and then transported to site for erection, it was soon realised it could just as easily be transported anywhere in the world. The Commissioner's House of the Royal Naval Dockyard, Bermuda designed by Edward Holl and built in the 1820s, is considered to be the first residence that used cast iron structure, for the verandahs, and floor and roof framing, and proved the concept of prefabrication and transportation long distances. Designers and foundries in the UK, France and Germany went on to produce all kinds of prefabricated cast iron structures and items for shipping to the colonies, from decorative elements to structural components to entire buildings. During the Victorian gold rush in Australia in the 1850s hundreds of various types of prefabricated structures were shipped out from foundries in England and Scotland, in timber, cast or wrought iron, or a combination, often with corrugated iron for the walls and roof. They included houses, stores, at least three complete churches, and an entire theatre; the most elaborate surviving structure in Australia is the completely cast iron Corio Villa, in Geelong. There are at least 100 surviving or part surviving prefabricated buildings, which in 2021 were to be nominated for World Heritage significance.Markets were a type of structure that lent themselves to prefabrication and shipping, such as the structure of the Mercado Centrale in Santiago, Chile, which was shipped out from Glasgow firm Laidlaw & Sons in 1869. The Marché en Fer in Port-au-Prince, Haiti, fabricated in Paris, was reputedly intended as a railway station for Cairo in 1891 but was purchased by the Haitian government instead.
An early type of completely prefabricated building was the large storage shed at dockyards. The Boat Shed at Sheerness Naval Dockyards, built 1856–60, is constructed entirely of a cast and wrought iron members, braced as portal frames, with extensive window and timber infill panels forming the external walls. Though not entirely of cast iron, it is the earliest large metal framed building still standing, and a pioneer in the development metal frames.
Watson's Hotel in Mumbai was prefabricated in England and built in 1867–69, using brick infill panels in a heavy and decorative cast-iron frame and is one of the largest completely cast iron framed building in the world. Possibly the largest prefabricated cast iron structure is the Bulgarian St. Stephen Church in Istanbul, shipped out from Vienna in the late 1890s.