Steel Frame Construction

11 Steel Frame Construction • History • Fireproofi ng of Steel • The Material Steel Framing Steel • Longer Spans in Steel FOR PRELIMINARY Improved Beams DESIGN OF A STEEL STRUCTURE Trusses Arches Steel Alloys Tensile Structures Production of Structural Shapes FABRIC STRUCTURES Cast Steel Cold-Worked Steel • Composite Columns Open-Web Steel Joists Joining Steel Members • Industrialized Systems in Steel Details of Steel Framing • CONSIDERATIONS Typical Connections OF SUSTAINABILITY IN Stabilizing the Building Frame STEEL FRAME CONSTRUCTION Shear Connections and Moment Connections • Steel and the Building Codes • The Construction Process • Uniqueness of Steel The Fabricator The Erector Floor and Roof Decking Architectural Structural Steel Ironworkers place open-web steel joists on a frame of steel wide-fl ange beams as a crane lowers bundles of joists from above. (Photo by Balthazar Korab. Courtesy Vulcraft Division of Nucor) 411 JWBK274_Ch11.indd 411 10/30/08 4:14:29 AM Steel, strong and stiff, is a material of slender towers and soaring chains and rods. The Þ rst all-metal structure, a cast iron bridge, was spans. Precise and predictable, light in proportion to its strength, built in the late 18th century in Eng- it is also well suited to rapid construction, highly repetitive build- land and still carries trafÞ c across the ing frames, and architectural details that satisfy the eye with a Severn River more than two centuries clean, precise elegance. Among the metals, it is uniquely plenti- after its construction. Cast iron, pro- ful and inexpensive. If its weaknesses—a tendency to corrode in duced from iron ore in a blast furnace, certain environments and a loss of strength during severe building and wrought iron, iron that has been puriÞ ed by beating it repeatedly with fi res—are held in check by intelligent construction measures, it a hammer, were used increasingly for offers the designer possibilities that exist with no other material. framing industrial buildings in Europe and North America in the Þ rst half of the 19th century, but their usefulness History devices. The Greeks and Romans was limited by the unpredictable brit- used hidden cramps of bronze to join tleness of cast iron and the relatively Prior to the beginning of the 19th blocks of stone, and architects of the high cost of wrought iron. century, metals had little structural Renaissance countered the thrust Until that time, steel had been role in buildings except in connecting of masonry vaults with wrought iron a rare and expensive material, Figure 11.1 Figure 11.2 Landscape architect Joseph Paxton designed the Crystal Palace, Allied Bank Plaza, designed by Architects Skidmore, an exposition hall of cast iron and glass, which was built in Owings, and Merrill. (Permission of American Institute of London in 1851. (Bettmann Archive) Steel Construction) 412 JWBK274_Ch11.indd 412 10/30/08 4:14:31 AM History / 413 JWBK274_Ch11.indd 413 10/30/08 4:14:31 AM 414 / Chapter 11 • Steel Frame Construction produced only in small batches for when the Eiffel Tower was built of of beneÞ cial elements such as manga- such applications as weapons and cut- wrought iron in Paris (Figure 11.3), nese and silicon, and of detrimental lery. Plentiful, inexpensive steel Þ rst several steel frame skyscrapers had impurities such as phosphorus, sulfur, became available in the 1850s with already been erected in the United oxygen, and nitrogen. In contrast, the introduction of the Bessemer pro- States (Figure 11.4). A new material ordinary cast iron contains 3 to 4 per- cess, in which air was blown into a ves- of construction had been born. cent carbon and greater quantities of sel of molten iron to burn out the im- impurities than steel, while wrought purities. By this means, a large batch The Material Steel iron contains even less carbon than of iron could be made into steel in most steel alloys. Carbon content is a about 20 minutes, and the structural crucial determinant of the properties properties of the resulting metal were Steel of any ferrous (iron-based) metal: Too vastly superior to those of cast iron. Steel is any of a range of alloys of iron much carbon makes a hard but brittle Another economical steelmaking that contain less than 2 percent car- metal (like cast iron), while too little process, the open-hearth method, was bon. Ordinary structural steel, called produces a malleable, relatively weak developed in Europe in 1868 and was mild steel, contains less than three- material (like wrought iron). Thus, soon adopted in America. By 1889, tenths of 1 percent carbon, plus traces mild steel is iron whose properties Figure 11.3 Engineer Gustave Eiffel’s magnifi cent tower of wrought iron was constructed in Paris from 1887 to 1889. (Photo by James Austin, Cambridge, England) The gap between stone and steel-and-glass was as great as that in the evolutionary order between the crustaceans and the vertebrates. Lewis Mumford, The Brown Decades,New York, Dover Publications, Inc., 1955, pp. 130–131. JWBK274_Ch11.indd 414 10/30/08 4:14:32 AM The Material Steel / 415 have been optimized for structural bottom of the furnace to produce into a container of molten iron and purposes by controlling the amounts carbon monoxide, which reacts with recycled steel scrap. A stream of pure of carbon and other elements in the the ore to reduce it to elemental iron. oxygen at very high pressure is blown metal. The limestone forms a slag with vari- from the lance into the metal to burn The process of converting iron ous impurities, but large amounts of off the excess carbon and impurities. ore to steel begins with the smelting carbon and other elements are inevi- A ß ux of lime and ß uorspar is added of ore into cast iron. Cast iron is pro- tably incorporated into the iron. The to the metal to react with other impu- duced in a blast furnace charged with molten iron is drawn off at the bot- rities, particularly phosphorus, and alternating layers of iron ore (oxides of tom of the furnace and held in a liq- forms a slag that is discarded. New iron), coke (coal whose volatile constit- uid state for processing into steel. metallic elements may be added to the uents have been distilled out, leaving Most steel that is converted from container at the end of the process to only carbon), and crushed limestone iron is manufactured by the basic oxy- adjust the composition of the steel as (Figure 11.6). The coke is burned by gen process (Figure 11.5), in which a desired: Manganese gives resistance large quantities of air forced into the hollow, water-cooled lance is lowered to abrasion and impact, molybdenum gives strength, vanadium imparts strength and toughness, and nickel and chromium give corrosion resistance, toughness, and stiffness. The entire process takes place with the aid of careful sampling and laboratory analysis techniques to ensure the Þ n- ished quality of the steel and takes less than an hour from start to Þ nish. Today, most structural steel for frames of buildings is produced from scrap steel in so-called Òmini-mills,Ó utilizing electric arc furnaces. These mills are miniature only in compari- son to the conventional mills that they have replaced; they are housed in enormous buildings and roll structural shapes up to 40 inches (1 m) deep. The scrap from which structural steel is made comes mostly from defunct automobiles, one mini-mill alone consuming 300,000 junk cars in an average year. Through careful met- allurgical testing and control, these are recycled into top-quality steel. Figure 11.4 The Home Insurance Company Build- ing, designed by William LeBaron Jenney and built in Chicago in 1893, was among the earliest true skyscrapers. The steel framing was fi reproofed with masonry, and the exterior masonry facings were supported on the steel frame. (Photo by Wm. T. Barnum. Courtesy of Chicago Historical Society ICHi-18293) JWBK274_Ch11.indd 415 10/30/08 4:14:33 AM 416 / Chapter 11 • Steel Frame Construction Figure 11.5 The steelmaking process, from iron ore to structural shapes. Notice particularly the steps in the evolution of a wide-fl ange shape as it progresses through the various stands in the rolling mill. Today, most structural steel in the United States is made from steel scrap in electric furnaces. (Adapted from “Steelmaking Flowlines,” by permission of the American Iron and Steel Institute) JWBK274_Ch11.indd 416 10/30/08 4:14:34 AM The Material Steel / 417 FOR PRELIMINARY DESIGN OF A STEEL STRUCTURE ¥ Estimate the depth of corrugated steel roof decking at ¥ Estimate the depth of triangular steel roof trusses at 1ր4 1 ր40 of its span. Standard depths are 1, 1½, 2, and 4 inches 1ր to 5 of their span. For rectangular trusses, the depth is (25, 38, 50, and 100 mm). 1ր 1ր typically 8 to 12 of their span. ¥ Estimate the overall depth of corrugated steel fl oor deck- ¥ To estimate the size of a steel column, add up the total 1ր ing plus concrete topping at 24 of its span. Typical overall roof and ß oor area supported by the column. A W8 column depths range from 2½ to 7 inches (65Ð180 mm). can support up to about 4000 square feet (370 m2) and ¥ Estimate the depth of open-web steel joists at 1ր20 of a W14 column 30,000 square feet (2800 m2). Very heavy their span for heavily loaded ß oors or widely spaced W14 shapes, which are substantially larger than 14 inches joists and at 1ր24 of their span for roofs, lightly loaded (355 mm) in dimension, can support up to 50,000Ð100,000 ß oors, or closely spaced joists.

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