Page B3.1 . 07 April 2010                     
ArchitectureWeek - Building Department
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Wrought and Cast Iron Structures

by D. Matthew Stuart

Focusing on structural engineering issues involved in the repair, restoration, or adaptive reuse of older buildings for which drawings no longer exist, this article is the seventh in a series about antiquated structural systems that can be adapted or reanalyzed for safe reuse. — Editor

Ferrous metals used in construction can be categorized into three principal iron-carbon alloys, based on approximate carbon content: wrought iron (0.020 to 0.035 percent), steel (0.06 to 2.00 percent), and cast iron (2.00 to 4.00 percent).

Wrought iron is almost pure iron and contains between one and four percent slag (iron silicate). The slag is not alloyed into the wrought iron, which gives the material its characteristic laminated (or layered) fibrous appearance. Wrought iron can also be distinguished from cast iron by its generally simpler forms and less uniform appearance.

Cast iron contains varying amounts of silicon, sulfur, manganese, and phosphorus. While molten, the cast-iron material is easily poured into sand molds, making it possible to create unlimited forms, and which also results in mold lines, flaws, and air holes. Cast-iron elements are commonly bolted or screwed together, while wrought iron is either riveted or welded.

Understanding Wrought Iron

Wrought iron refers to ferrous metals that were worked or "wrought" on an anvil or shaped and forged in rolling machines. Wrought iron is tough and stringy and has a ductility that made it conducive for use in bolts, beams, and built-up girders. Wrought iron is also easily welded.   >>>

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This article is reprinted from the March 2009 issue of STRUCTURE magazine, with permission of the publisher, the National Council of Structural Engineers Associations (NCSEA).



ArchWeek Image

The Eiffel Tower was constructed with an iron lattice structure, with components of puddled iron, a type of wrought iron.
Photo: Library of Congress Extra Large Image

ArchWeek Image

At 300 meters (984 feet) tall, the Eiffel Tower was the tallest structure in the world at the time of its completion in 1889.
Photo: Library of Congress Extra Large Image


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