Steel, strong and stiff, is a material of slender towers and soaring spans. Precise and predictable, light in proportion to its strength, it is also well suited to rapid construction, highly repetitive building frames, and architectural details that satisfy the eye with a clean, precise elegance. Among the metals, it is uniquely plentiful and inexpensive. If its weaknesses a tendency to corrode in certain environments and a loss of strength during severe building fires are held in check by intelligent construction measures, it offers the designer possibilities that exist with no other material.
Prior to the beginning of the 19th century, metals had little structural role in buildings except in connecting devices. The Greeks and Romans used hidden cramps of bronze to join blocks of stone, and architects of the Renaissance countered the thrust of masonr y vaults with wrought iron chains and rods. The Þ rst all-metal structure, a cast iron bridge, was built in the late 18th century in England and still carries trafÞ c across the Severn River more than two centuries after its construction. Cast iron, produced from iron ore in a blast furnace, and wrought iron, iron that has been puriÞ ed by beating it repeatedly with a hammer, were used increasingly for framing industrial buildings in Europe and North America in the Þ rst half of the 19th century, but their usefulness
Prior to the beginning of the 19th century, metals had little structural role in buildings except in connecting devices. The Greeks and Romans used hidden cramps of bronze to join blocks of stone, and architects of the Renaissance countered the thrust of masonr y vaults with wrought iron was limited by the unpredictable brittleness of cast iron and the relatively high cost of wrought iron.
Until that time, steel had been a rare and expensive material, produced only in small batches for such applications as weapons and cutler y. Plentiful, inexpensive steel Þ rst became available in the 1850s with the introduction of the Bessemer process, in which air was blown into a vessel of molten iron to burn out the impurities. By this means, a large batch of iron could be made into steel in about 20 minutes, and the structural properties of the resulting metal were vastly superior to those of cast iron. Another economical steelmaking process, the open-hearth method, was developed in Europe in 1868 and was soon adopted in America. By 1889, when the Eiffel Tower was built of wrought iron in Paris, several steel frame skyscrapers had already been erected in the United States. A new material of construction had been born.
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