As is well known, architects and builders rarely design the structural elements and systems within their buildings, instead engaging the services of (and, it is to be hoped, collaborating with) structural engineers, or relying upon standard practices sanctioned by building codes. Where architects or builders wish to be adventurous with their structures, some knowledge of structural behavior and the potential of structural materials is certainly useful. On the other hand, where they are content to employ generic structural systems — platform framing in wood, simple skeletal frames in steel or reinforced concrete — one can get by with little actual knowledge of structural design, relying instead on the expertise of structural consultants and the knowledge of common spans, heights, and cross-sectional dimensions around which many ordinary buildings can be planned.
The heroic stage of modernism, in which architects often sought to reconcile structural behavior and overall building form — some finding inspiration in the structural frame or the load-bearing wall — was also the heroic stage of structural education for architects: it was hardly necessary, in that context, to explain why architects needed to learn about structures. Some of the same excitement about the potential of structure in architecture still remains, but it is also true that a "mannerist" tendency has emerged, interested not necessarily in renouncing the role of structure in architecture, but rather reveling in its potential to distort, twist, fragment, and otherwise subvert modernist conventions and the architectural forms they support.
Yet all structures, whether hidden from view or boldly expressed, follow the same laws of equilibrium, are exposed to the same types of forces, and are constrained by the same material properties and manufacturing practices. It is therefore appropriate for architects and builders to study structures in such a way that the basic principles underlying all structural form become clear. This can be accomplished in three phases: first, by studying the concepts of statics and strength of materials; second, by learning how these concepts are applied to the design of common structural elements fabricated from real materials; and third, by gaining insight into the design of structural systems comprised of structural elements interconnected in a coherent pattern.
Much of the material presented in this text can be found elsewhere; the basic conditions of equilibrium, historical insights into structural behavior that form the basis for structural design, and recommendations for design procedures incorporated into building codes, are all widely disseminated through industry-published manuals, government-sanctioned codes, and academic texts. Many excellent structures texts have been written specifically for architects and builders. The question therefore naturally arises: Why write another one?
The primary motivation for writing this text is to organize the material in a manner consistent with the structures curriculum developed within the Department of Architecture at Cornell University, based on the three sequential "phases" described above — structural concepts, elements, and systems. While this text does contain a concise introduction to structural concepts (statics), it is primarily concerned with the design and analysis of structural elements: columns, beams, and tension members, and their connections. This material is organized into a single volume that is concise, comprehensive, and self-sufficient, including all necessary data for the preliminary design and analysis of these structural elements in wood, steel, and reinforced concrete.
A second motivation for writing this text is to present material in a manner consistent with my own priorities and sensibilities. Every chapter contains insight, speculation, or forms of presentation developed by the author and generally not found elsewhere. Additionally, the Appendices included at the end of the text contains numerous tables and graphs, based on material contained in industry publications, but reorganized and formatted especially for this text to improve clarity and simplicity — without sacrificing comprehensiveness.
Methods for designing structures and modeling loads are constantly being refined. Within the last several years, important changes have occurred in the design of wood, steel, and reinforced concrete structures, as well as in the modeling of loads. These changes include revised procedures for beam and column design in wood; the replacement of the standard specification for 36-ksi steel with a new standard based on 50-ksi steel for wide-flange sections; a major modification in the load factors used in reinforced concrete design, aligning them with those recommended by SEI/ASCE 7 and already used in the design of wood and steel structures; and numerous refinements in the modeling of environmental loads. These changes have all been incorporated into this text.
Finally, a disclaimer: this text is intended to be used only for the preliminary (schematic) design and understanding of structural elements. For the design of an actual structure, a competent professional should be consulted.
Unlike laws of equilibrium, which remain unchanged year after year, the application of structural concepts to the design of actual structures using real materials and accepted methods changes on a fairly regular schedule. Material-centric institutes periodically revise their suggestions for building code language; these are referenced in model building codes, and the various states of the union eventually get around to adopting these model codes, turning them into legal mandates that reflect evolving standards for structural design.
This fact alone would make it necessary to update the first edition of Structural Elements, and I have indeed incorporated recommendations from the latest versions of all four primary references (i.e., from the AF&PA/AWC, AISC, ACI, and ASCE) into this second edition, including revised values for Southern Pine lumber that became effective in 2013.
In addition, I have reorganized the material in this second edition around the idea of materials rather than based on structural actions. In other words, while the first edition considered tension, compression, and bending as the primary "subjects" (with wood, steel, and reinforced concrete discussed for each of these structural behaviors), the second edition organizes the content around wood, steel, and reinforced concrete (with the various structural actions — tension, compression, and bending — included within each "material" chapter). Doing so has allowed me to add new content concerning structural systems and material properties for each of the primary structural materials, and to integrate the discussion of connections within the particular material chapters to which they apply. In this way, the organization of the book reflects curricular changes within the building technology area of the architectural curriculum at Cornell.
J. Ochshorn, Ithaca, NY
January, 2015
This third edition has been updated to reflect the latest editions of all four primary references (i.e., those written by the AF&PA/AWC, AISC, ACI, and ASCE). The format has been enlarged, which helps accommodate more information in some of the appendices, and also reduces the page count. Most importantly, I have decided to self-publish this edition, in order to reduce its price and thereby make it more accessible to those who might find it useful.
J. Ochshorn, Ithaca, NY
August, 2020
© 2020 Jonathan Ochshorn; all rights reserved. This section first posted November 15, 2020; last updated November 15, 2020.