Otis's invention of the safety elevator at mid-century heralded the end of this constraint on vertical real estate development" (495). Likewise, Masden notes that the increasingly confident use of the relatively new ' elevators' also fueled demand for more steel frame structures; such new steel-framed buildings were known during this early period as "elevator buildings" instead of skyscrapers, a term that was first coined in 1883 (Marsden 78). The underlying theory behind steel frame construction during its early use, though, fueled some well-intentioned but misguided efforts that adversely influenced future applications, selection of building materials, site selection and other salient factors involved in construction. In this regard, Mumford (1959) reports that, "Unfortunately, the skyscraper was an almost automatic response to land speculation: mechanization was subservient to the desire to achieve profitable congestion; and the architects as a profession did not oppose with any conception of public interests the private and shortsighted rapacity of the businessman" (20). The fact that most of these early steel frame projects were as effective as they were in their respective settings appears to be a matter of good fortune rather than any predetermined effort by the design team: "The architects of Chicago were technically adventurous, but socially timid: since they cheerfully accepted land speculation and congestion as if they were laws of nature, it was only by a happy accident that their site plans would turn out to be sound" (Mumford 20). By sharp contrast, steel frame applications today must take into account all of these factors as well as many more that have emerged in recent years in support of a unified building code and efforts to minimize new construction's impact on the environment continue to gain momentum and some of these initiatives are described further below.

Applications.

According to Montgomery (2003) "A revolution in building techniques was under way due to steel-frame construction methods, new fire-resistant technologies, and related innovations, paving the way for the construction of far taller buildings" (495). The development of new technologies for the construction of steel frame buildings resulted in a number of such structures in various sections of the city. Over the years, higher steel-frame buildings were built with many in Chicago; for example, the Masonic Temple (1892) of Daniel Burnham and John Root in Chicago reached 22 stories (91 meters or 302 feet); however, New York City also sported a 26-story Manhattan Life Building by 1894 (Swenson and Chang 82). The Singer Building (1907) designed by architect Ernest Flagg reached 47 stories (184 meters or 612 feet), and Cass Gilbert's Woolworth Building (1913) reached a height of 238 meters (792 feet) at 55 stories (Swenson and Chang 82). Relegated to the second-tallest building in New York until 2001, Shreve, Lamb & Harmon's 102-story steel-frame Empire State Building (1931) was an enormous 381 meters (1,250 feet) (Swenson and Chang 82). The Great Depression and World War II, though, stopped most efforts at steel frame construction until the late 1940s (Swenson and Chang 82).

Thereafter, steel frame construction applications took on some alternative configurations that no longer focused strictly on height that changed many of the structural and building component requirements. For example, in Volume 2 of his work, Encyclopedia of 20th Century Architecture, Stennott (2004) reports that the first work commissioned to Ludwig Mies van der Rohe (1886-1969) in the United States was the campus of the Illinois Institute of Technology (IIT) in Chicago. According to Stennott, this building.".. represents the fullest embodiment of modernist planning principles applied to the renovation of the city at mid-century. The campus is also notable as a site for Mies' development of industrial building techniques in the service of modernist spatial principles. Ultimately, IIT's most enduring significance is as a site for the direct architectural expression of steel-frame construction applied across scales from the individual structural member to the overall urban plan" (667). This author suggests that the entire campus and accompanying 22 original structures completed by Mies between 1939 and 1956 represent the seminal works of 20th-century architecture and planning in the Western Hemisphere (Stennott 667).

Mies' final plans for the larger campus as partially implemented by 1940 used a 24-by-24-foot steel frame planning module as an organizing element for the entire site (Stennott 667). According to Stennott, "The 24-foot dimension was selected for its economy and utility as a structural spanning dimension in steel-frame construction as well as its flexibility as an interior-planning dimension for classrooms, offices, and labs. This modular dimension system related interior and exterior spaces and ensured the integration of individual building components, such as columns and beams, with the...

The first building completed on the campus was the Minerals and Metals Research Building (1942-43); this project demonstrated Mies' focus on articulating a language of building construction that was based on the expression of the structural steel frame (Stennott 667).
According to Stennott, "The precise relation of steel column, fireproofing, representational steel mullion, brick panels, and glass curtain wall posed a series of architectonic and technical questions that Mies and architects of the Second Chicago School would work to articulate and solve for three decades" (667). Subsequent work for the unrealized Library and Administration Building Project (1944) extended this research to Mies' continuing interest in using steel frame construction techniques for spanning lengthy spaces; these first two projects developed the repertoire of regularly dimensioned steel-frame buildings that would influence the Institute Buildings (1945) as well as the exceptionally proportioned long-span structures that characterized Mies' work (Stennott 667). According to Stennott, Mies' masterpiece, Crown Hall (1950-56), was designated a National Historic Landmark in 2001 and is shown in Figure 1 below (667).

Figure 1. Crown Hall (1956), Illinois Institute of Technology.

Source: Stennett 668.

Crown Hall was conceived as a single interior volume completely enclosed by glass and devoid of any interior structural members. As an expression of direct construction, the clarity of its spatial volume and subtlety of its structural system reinforce each other to produce the site's single most powerful architectonic statement and one of Mies' most important works. In a series of significant deviations from the majority of buildings on the campus, Crown Hall was developed as a hierarchically important exception to, as well as an ultimate reinforcement of, Mies' overall strategy for the campus and has been considered his most valued commission at IIT (Stennott 667).

Following the development of the curtain wall, new forms of structure appeared in high-rise buildings in the mid-20th century that used steel frame construction to its maximum advantage; other innovations in technology and their added expense both fueled the drive toward steel frame construction as well efforts to minimize the costs associated with these techniques. For example, environmental control systems increased in cost, economic pressures worked to produce more efficient structures (Swenson and Chang 82). Likewise, the 60-story Chase Manhattan Bank Building, designed by Skidmore, Owings & Merrill and constructed in 1961, had a standard steel frame with rigid portal wind bracing, which required 275 kilograms of steel per square meter (55 pounds of steel per square foot), almost the same as the Empire State Building of about 30 years earlier (Swenson and Chang 82).

Today, the following categories in Figure 2 represent the primary steel frame applications in use throughout the United States and reflect the rapid growth in popularity of these techniques in recent years.

Figure 2. Steel Framing by Application: 1997-2002.

Source: Based on data in Fanjoy 6.

Properties.

Properties of economy of structure in tall buildings was demonstrated early on with the John Hancock Building in Chicago in 1970; this building used a system of exterior diagonal bracing to form a rigid tube devised by the engineer Fazlur Khan (Swenson and Chang 82). While the Hancock building is 100 stories, or 343 meters (1,127 feet), high, its structure is so efficient that it required only 145 kilograms of steel per square meter (29 pounds per square foot) (Swenson and Chang 82). The framed tube that Khan developed for concrete structures was also applied to other tall steel buildings; for instance, Khan used a steel system of nine bundled tubes of different heights -- "each 22.5 meters (75 feet) square with columns spaced at 4.5 meters (15 feet) -- "to form the structure of the 110-story, 442-metre (1,450-foot) Sears Tower (1973), also in Chicago (Swenson and Chang 82).

Today, unless otherwise specified to the contrary in the contract documents, the trade practices that are defined in the American Iron and Steel Institute Committee on Framing Standards Code of Standard Practice for Cold-Formed Steel Structural Framing [Code of Standard Practice] govern the design, fabrication and installation of cold-formed steel structural framing in the United States (Code of Standard Practice for Cold-Formed Steel Structural Framing 10). For example, the Code of Standard Practice codifies the requirements for lateral force resisting systems: "The design responsibilities of the structural engineer-of record include but are not limited to design of roof/floor diaphragms, lateral load transferring elements (sometimes referred to as shear transfer bracing), main lateral force resisting elements and foundations, as well as compliance…