arlier this year, the Reinforcing codification of the newly available material. The Structural Steel Institute (CRSI) published A rise of manufacturing, and the associated need for Comprehensive and Invaluable Treatise on warehousing to accommodate product distribu- all Forms of Steel Reinforcement Employed tion, brought higher floor loads and the desire for Ein the Design and Construction of bigger buildings. Likewise, fire and conflagration Forensics of Long Ago. The majority of the book is an exten- drove owners to seek “fireproof” construction, sive catalogue of no less than 47 different types of which concrete was able to provide. steel reinforcing bars (four of which fall under the Now, about 100 years later, many of these build- investigating structures category of “Miscellaneous”), seven types of welded ings are being repurposed and retrofitted for reuse, and their components wire fabric, 22 systems of beam and girder rein- a trend driven in part by state and federal tax cred- forcement, 12 systems of column reinforcement, its for historic rehabilitation. Today’s structural 11 slab systems and six bridge systems. consultants are practicing at the confluence of two The supporting sections of the book, includ- trends, each at opposite ends of the century, which ing a brief history of early concrete mix design converge on a general deficit of understanding and as well as historic ASTM bar specifications, are available information. Students of engineering secondary compared to the bar descriptions and and historic preservation,® as well as researchers images. Appendices are similar compendiums in the small but growing field of construction of reinforcing steel illustrations; for example, history, may also find useful information and Appendix E contains 31 patent drawings, references in the book. extending from Thaddeus Hyatt’s revolutionary pavement reinforcing issued in 1878 to latecomer Researching Reinforced Concrete CopyrightJ.T. Simpson’s visually interesting “deformed Developing enough understanding of an early bar” of 1922. Appendix concrete structure to analyze it for reuse can Introducing and Using F contains images of over require a substantial amount of research, unless CRSI’s New “Treatise” 30 early advertisements. assumptions are made – potentially at the ulti- Appendix G paraphrases mate expense of the project, or loss of historic the “Alphabetical List material. Certainly, knowledge of early reinforced Vintage Steel Reinforcement of the 144 Foreign Systems of Reinforced concrete does not replace investigation, analysis, in Concrete Structures Concrete Construction, with the Addresses of or engineering judgment; but effectively plan- the Inventor or Owner of Each System, and a ning and implementing a search for supporting Concise Description of Its Special Features” and relevant sources of information may result By Meghan Elliott, P.E., from Reinforcedmagazine Concrete in Europe by A. L. in the difference between a cost-effective and a Associate AIA S TColby Rin 1909. U C T Ucost-prohibitive R projectE approach. This new resource for structural engineers fits These sources can very generally be thought of in into, but is distinctly different from, the expand- two categories: primary and secondary. Primary ing collection of reference materials that have sources are those that are typically contempo- been produced by professional organizations. rary to the topic and representative of the query: First, it builds on and replaces CRSI’s earlier patents, advertisements, earlier building codes, Meghan Elliott, P.E., Associate publications: its initial reference, Evaluation of and historic newspaper or trade articles about a AIA ([email protected]), Reinforcing Steel Systems in Old Concrete Structures particular engineer, product, or analytical method is the founder and a principal (1981), and its abridged version as Engineering (Figure 1). Secondary sources are used to establish at Preservation Design Data Report No. 48, Evaluation of Reinforcing the context, and place the question within the Works (PVN), a historic Bars in Old Concrete Structures (2001). These broader research and academic understanding preservation consulting firm focused on summaries of industry trends in of the topic. Secondary sources typically include in Minneapolis, Minnesota. terms of material strength, specifications, and current books, journal articles, literature reviews, general availability of materials. This new pub- or even textbooks. Both types of sources are typi- lication is similar in function and potential use cally needed to understand a building structure. to the American Institute of Steel Construction’s While the CRSI publication might initially be (AISC) Design Guide 15, AISC Rehabilitation considered a secondary source, especially given the and Retrofit Guide: A Reference for Historic Shapes authors’ choice of the word “treatise,” it may be and Specifications. more successfully used as a collection of reprinted The need for this type of reference is a result primary sources. of the convergence of several trends in the his- A small but growing collection of second- tory and contemporary practice of structural ary sources is available to understand early engineering. First, there was an explosive devel- reinforced concrete. Some recent publications opment of reinforced concrete technology in include Donald Friedman’s Historical Building the United States during the approximate time Construction: Design, Materials & Technology period from 1890 to 1920. This proliferation of (2010), Amy Slaton’s Reinforced Concrete and the new products coincided with a rise in demand Modernization of American Building, 1900-1930 for industrial buildings, but preceded the formal (2001), and Andrew Saint’s Architect and Engineer:

10 September 2014 STRUCTURE magazine key factors. First, structural steel had a head start of several decades. For example, wrought- iron use as structural framing began before the 1870s, and the basics of steel framing were in place before 1900. The use of reinforced concrete for buildings, on the other hand, was mostly a post-1900 trend. Not coincidentally, structural engineers as a separate consulting practice and resource for architects were rapidly evolving at the same time: the introduction of reinforced concrete as a building material coincided with a new professional field of . According to Friedman, the use of steel fram- ing was not an analytical leap from traditional wood building methods. Builders and archi- ® tects could easily make a rational switch from a stick of wood to a stick of steel: while steel Figure 1. An example of a primary resource was a substantially stronger material, it fol- for researching concrete, the William lowed the same beam theory and acted the B. Hough Company advertisement for same in bending and compression. “M/B Special Open Hearth Bars” lists the Concrete, onCopyright the other hand, required an buildings in which the product was used. analytical shift to integrate the new system Image from Cement Age, December, 1911, into buildings, from a system of pieces to and digitized by Google Books. monolithic construction and the interaction of two distinct materials. Engineers and build- Figure 2. Excerpt of Ernest Ransome’s patent for A Study in Sibling Rivalry (2007). These books ers were thus using the material before it was twisted square reinforcement. The M/B Bar of can be supplemented by earlier analyses of understood. Many of the proprietary products Figure 1 uses a similar method for mechanical concrete history, such as articles and books appear as an attempt to rationalize what was adhesion of the concrete to the steel. Digitized by by Carl W. Condit, a good example of which already being built through experimentation Google Patents. is “The First Reinforced Concrete : and intuition. The Ingalls Building in Cincinnati and Its The evolution of reinforced concrete design strengthen the concrete with steel rods located Place in Structural History” (1968), pub- in themagazine United States was driven by a small to take the tensile stresses. In all cases, the steel lished in the journal TechnologyS and CultureT . Rgroup of U entrepreneurial C individuals,T U as reinforcement R wasE placed in two directions Other secondary sources are too numerous compared to the relatively consistent and and tied with wires, the rods in one direction to list here, but include journal articles and nationwide acceptance and distribution of designated as carrying rods and those in the trade publications, like the Association for steel framing products. As a result, regional other as distributing rods. For slabs poured Preservation Technology’s (APT) Bulletin and differences occurred, as well as leaps in the continuously over supports, the rods were the journal or proceedings of the American distribution of different products and sys- placed at the top of the slab; i.e., the correct Concrete Institute (ACI). tems. While there were earlier contributions reinforcing pattern for continuity. by William Ward and Thaddeus Hyatt, the In practice, the expansion of the use of Early Reinforced Concrete momentum of innovation in reinforced con- monolithic concrete in the US was substan- crete in the US began with Ernest Ransome. tially instigated by several engineers and The early history of reinforced concrete in From his practice in San Francisco, he intro- builders. In addition to Ransome, other the United States is very different from that duced two important concepts that would early innovators included Claude Allen Porter of other structural materials. The infancy of remain fundamental to reinforced concrete (C.A.P.) Turner practicing in Minneapolis, modern structural analysis, combined with design and construction: slabs and beams cast Kahn’s Trussed Concrete Steel Company of the new availability of concrete materials together monolithically, and deformed rein- Detroit, the Ferro-Concrete Construction and perhaps even the innovation and shame- forcement. Most early products in concrete Company of Cincinnati, and the Condron less salesmanship on the part of structural can be demonstrated to meet one or both Company of Chicago. These early engineer- engineers and builders, led to a prolifera- of Ransome’s tenets – monolithic behavior entrepreneurs developed a variety of systems tion of proprietary products, supported by and adhesion of concrete with steel through between 1890 and 1920. The systems ratio- vague or sometimes non-existent analytical mechanical interaction. Ransome’s own pat- nalized their inventors’ uses, understanding, methods, and a wide variety of reinforced ented steel reinforcement is easily recognized and promotion of different advantages of concrete systems – from individual bar types by its twisted square shape (Figure 2). reinforced concrete. and accessories (like formwork products) to In addition to Ransome, Carl Condit attri- For example, Turner singularly focused on nearly complete building systems of slabs, butes the understanding and development of the monolithic nature of concrete, and criti- beams, and columns. reinforced concrete behavior to the impor- cized his peers for imitating the earlier simple Friedman compares the acceptance and tation of the Monier-Wayss system to the systems of wood and steel. He conceptual- growth of the concrete industry to that of US from Germany. While applied to many ized his patented Mushroom Flat Slab floor steel, and attributes the differences to several types of concrete structures, the theory was to system, distinguished by its unique four-way

STRUCTURE magazine11 September 2014 Figure 4. Illustration of cross sectional and perspective views of the Kahn reinforcement bar, along with a diagram of the theoretical “truss action.”

CRSI resource, there is little documentation even see it, as® is the case with reinforce- as to the prevalence and distribution of these ment concealed in a slab. Often, engineers systems. Without promotion, and ultimately are asked to make conclusions about the adoption in building construction, these sys- structural integrity of reinforced concrete tems were entrepreneurial dead ends. with both of these unknowns. Ransome’s second contribution – the use of The new CRSI resource helps to alleviate deformed steelCopyright reinforcement and the analysis some of the difficulty of researching a type of its adhesion with concrete – was similar in of reinforcing by providing a visual resource Figure 3. Excerpt of C.A.P. Turner’s patent for a development to the proliferation of mono- with extensive patent images, advertisements, 4-way system of slab reinforcement using smooth lithic concrete systems. Ransome argued, and an Appendix of photographs of a 1979 round bars. Digitized by Google Patents. and proved through testing, that deformed Smithsonian exhibit to help give names to reinforcement achieved greater adhesion with some of the bars and systems encountered reinforcing and flared column capitals, as concrete compared to smooth reinforcement, in the field. However, secondary sources a series of flat slab cantilevers over the col- resulting in greater overall strength. The many are also needed to give more context and umns (“Deconstructing Bridge 92297,” types of patented bars were based on achieving potential information. CRSI’s Vintage Steel STRUCTURE magazine, January 2014). mechanical adhesion with the concrete. There Reinforcement in Concrete Structures offers The slab reinforcing plans quickly illustrate were even trademarked twisted square bars remarkable documentation of reinforced the concept, and demise, of the system with thatmagazine were referred to as “Ransome-style” bars. concrete products and systems that will its lack of reinforcing at the Scenter of theT slab RTurner disagreedU withC Ransome, T and pro-Uhopefully R stimulate E additional exploration span (Figure 3). moted the use of smooth round bars that, as of this topic. One of Turner’s competitors, particularly for he speculated, allowed the concrete to slip as It would be desirable to know, for example, industrial construction in the Midwest, was it cured. Likewise, Kahn’s Trussed Concrete which of the many concrete products and Julius Kahn who developed his Kahn System Company used different types of Kahn bars, systems were most popular, and whether of reinforcing for beams, girders and columns like the Kahn Trussed bar and the Kahn certain products have patterns of local (“The Kahn System of Reinforced Concrete,” Cup Bars. They also produced Rib Bars and or regional distribution and use. Future STRUCTURE magazine, April 2013). Kahn Square Rib Bars. Several types of bars were researchers should also assess the factors conceptualized the behavior of concrete as a produced by Carnegie Steel in Pittsburgh, and forces that influenced the standardiza- truss. His unique bar that formed the basis Pennsylvania, including Columbian Bars tion of reinforced concrete building. Were for all of his concrete construction, including (also known as Hanger Bars), Corrugated the concrete products and system we know columns, consisted of a longitudinal core with Bars, Elcannes Bars, Golding Monolith Bars, today determined to be the “best,” and if so, steel flanges that could be bent up to form Havemeyer Bars, Herringbone Bars, Jenks by whom, and according to what definitions the tension diagonals of the truss (Figure 4). Bars, Kahn Cup Bars, Kahn Trussed Bars, or parameters? Similarly, the visual illustration of the system Lug Bars, Monotype Bars, Ransome Bars, Additional research and publication will be demonstrates its concept and shortcoming: a Round Rib Bars, Scofield Bars, Slant Rib necessary to determine how factors like the deeper beam necessitates wider flange spacing. Bars, Square Rib Bars, Thacher Undulated cost of labor, ease of assembly, marketing, The truss concept also promotes a simply sup- Bars, U Bars, and Wing Bars. and the influence of professional associations ported end condition at the beams. shaped the trajectory of reinforced concrete Another system that was used during this Conclusion technology. In the meantime, a small but period of innovation, and the one that is clos- growing body of secondary sources provides est to our current conventions, is the Akme In the introduction to the new CRSI book, some clues as to which systems succeeded System of the Condron Company in Chicago. Matthew Stuart points out two of the chal- and those that may never have been built, This system, generally consisting of belts of lenges of researching historic reinforced the potential modes of failure or shortcom- two-way reinforcing at the slab and columns, concrete: it is very difficult to research ings with respect to current building codes, was constructed with or without column capi- something, like a type of reinforcing, if you and potentially the analytical methods that tals and drop panels. While there were other do not know its name; and it is even more may or may not support the continued use proprietary systems, as documented in the difficult to research something if you cannot of the building.▪

STRUCTURE magazine12 September 2014