Structural Design for the Stage

Alys Holden, Bronislaw Sammler, Bradley Powers, Steven Schmidt

• Publisher: Routledge
• Year: 2015
• ISBN:
  9781317451099
• Edition: 2
• Topic: Media & Performing Arts
• Subtopic: Theatre

The follow-up to the 2000 Golden Pen Award-winning Structural Design for the Stage, this second edition provides the theater technician with a foundation in structural design, allowing an intuitive understanding of "why sets stand up." It introduces the basics of statics and the study of the strength of materials as they apply to typical scenery, emphasizing conservative approaches to real world examples. This is an invaluable reference for any serious theatre technician throughout their career, from the initial study of the fundamental concepts, to the day-to-day use of the techniques and reference materials.

Now in hardcover, with nearly 200 new pages of content, it has been completely revised and updated to reflect the latest recommended practices of the lumber and steel industries, while also including aluminum design for the first time.

1

Overview

PURPOSE

Theatrical technical design and carpentry are rooted in a craft-based tradition which places a high value on empirically tested techniques. Consequently, structural engineering is rarely applied to scenery construction, though it may often be relevant. Structural engineering provides a basis for improving empirical techniques by allowing technical designers to maximize efficiency, e.g., cost, thickness, weight, construction time, load-in time, and so on. In those cases where there is no empirical solution, a technical designer can feel as if he or she is attempting to design in a vacuum, with no foundation from which to work. A firm foundation in structural engineering allows a technical designer to explore viable alternatives as well as providing paradigms for thinking about structural systems.

The best argument for the value of structural engineering is to examine an example of its failure. In Why Buildings Fall Down, Matthys Levy and Mario Salvadori describe the “worst structural disaster in the United States.” In 1980, at the brand new Hyatt Regency in Kansas City, Missouri, two suspended walkways, one underneath the other, suddenly collapsed, killing 114 people and injuring 200 others (Levy, 224). After extensive investigation, the fundamental cause of the collapse is easy to understand. In the original design, both walkways were suspended from the ceiling by a series of continuous rods. The upper walkway was held up by one nut and one washer at the bottom of its box beams as illustrated in Figure 1.1.

Figure 1.1 Concept of original design, upper walkway

To simplify installation (load-in), the contractor suggested that the rod be discontinuous, and the architects and engineers stamped the change as illustrated in Figure 1.2.

Figure 1.2 Modified design of upper walkway

The modification required that the box beams of the upper walkway, originally designed to support the upper walkway and its pedestrian traffic, also support the lower walkway and its corresponding pedestrian traffic. The failure load, which was, ironically, much lower than the design load for total occupancy, caused the nut and washer to pull through the upper box beam, sending both walkways crashing to the ground. Though the original design was obviously stronger than the modification, subsequent investigations revealed that it did not meet the design load required by the Kansas City Building Code. In addition to the loss of life and suffering, the accident cost three billion dollars in settlements, and cost the principal engineer and project manager of the engineering firm their licenses. Fortunately, the consequences of most structural failures in theater are not so extreme.

As theatrical technical designers, two important lessons can be learned from the Hyatt Regency disaster. First it is easy to see how the temptation to reduce “load-in” time prompted the request to use discontinuous rods. The success or failure of a structural system is dependent on its being designed, built, and installed properly. Second, neither the original design nor the modification provided any redundancy. It is always a good idea to design a system which is single failure proof, i.e., no single failure should be able to lead to a disastrous series of failures. Accidents may happen, but a firm understanding of structural design can help prevent them.

The goal of modern structural engineering is to develop a mathematical model which can predict the success or failure of a real-life system or member. This is not, however, an inherently mathematical process, which Levy and Salvadori (Levy, 14) express best:

Structural behavior can be understood by the uninitiated on the basis of physical intuition and without appeal to physics or mathematics simply because whatever the structural system – the steel frame of an office building or the dome of a church – whatever the materials used in construction – steel, wood, reinforced concrete, or stone – and whatever the forces acting on it – caused by gravity, wind, earthquake, temperature changes, or uneven settlements of the soil – the elements of a structure can react to these forces only by being pulled or pushed.

This text will appear to emphasize mathematics, but we urge you not to lose sight of the forest for the trees. Sometimes it is more important to understand a structure than it is to analyze it. The end goal of this text is three fold: (1) to provide the basis of an intuitive understanding of “why sets stand up”; (2) to be a reference book for professional technicians who face small scale structural dilemmas; and (3) to enable informed conversations between theatrical technicians and professional engineers. It is rare to find an engineer who also understands theatrical scenery and its requirements. As theatrical technical designers, we are responsible for bridging this communication gap.

CONTENTS

This text introduces the basics of statics and the study of the strength of materials as they apply to typical theatrical scenery. To that end, the text is relatively heavy with “how-to” theatrical examples and is relatively light on theory. A large portion is devoted to explicating existing engineering specifications written by various governing agencies. Where appropriate, conservative simplifications have been incorporated.

Structural design is fundamentally a process of determining how a structure will react to external forces and then designing a structure with the capacity to resist those forces. This text is organized into the study of statics followed by an exploration of how to design with specific kinds of materials. Statics, the study of structures which are stable and are not subject to acceleration, are addressed in Chapters 2 and 3. The capacity of the cross-sectional properties of structural members, independent of the material from which they are made, is discussed in Chapter 4, Geometric Properties. Chapters 5 through 13 discuss the structural design of beams and columns with sawn lumber, steel and aluminum. The strength characteristics of plywood and the design of plywood structures, including stressed-skin panels, are explored in Chapter 14. Chapter 15 introduces a method for analyzing two-dimensional trusses, and Chapter 16 discusses the fundamentals of the structural design of cable systems, including an exploration of parabolic cable systems.

Appendices A through G provide vital data to which the reader will need to refer frequently and are organized in the same pattern as the primary text. Appendices A and B include formulas which are introduced in Chapters 3 and 4. These formulas form the foundation for material presented in every chapter thereafter. Appendices C, D, E and F contain the reference material needed in the design procedures utilizing sawn lumber, steel, aluminum, and plywood. Like the examples throughout the text, the data has been abridged to concentrate on structural members more likely to be found in theatrical scenery construction. Appendix G contains useful information that applies generally to theatrical structural design. Appendix H includes a math review. Lastly, Appendix I lists the answers to the even numbered problems in the lessons found at the end of each chapter.

Since examples are such an important component of the text, it is essential that the reader be able to verify intermediate steps as well as the final solution. Solutions which may appear to be slightly off have been calculated with the full value of intermediate numbers, though they may be shortened in the text. In short, when performing calculations necessary to solve example problems, do not round off beyond that which your calculator will do automatically.

The goal of this text is to provide graduate level theatrical technicians with a comprehensive textbook. Consequently, it is designed to be taught linearly, that is, the course begins with Chapter 1 and ends with Chapter 16, and requires approximately three semesters of class time. Because the differences in academic schedules and individual students may make such an approach inappropriate, it may be helpful to note that the text is composed of six parts. The first part is the study of statics and geometric properties, Chapters 2 through 4, and is a necessary prerequisite to all of the other chapters. Sawn lumber design, Chapters 5 through 7, can be taught independently of steel design, Chapters 8 through 10, or aluminum design, Chapters 11 through 13. Plywood design, Chapter 14, and cable design, Chapter 16, are independent of Chapters 5 through 13. Finally, truss design, Chapter 15, is best taught after sawn lumber, steel, and aluminum design. A suggested three semester course would include Chapters 1–5 in the first semester, Chapters 6–10 in the second semester, and Chapters 11–16 in the final semester.

Regardless of the order in which they are taught, each chapter includes a set of lessons. Each lesson lists the page numbers and the topic(s) indicating the material covered in it. Each lesson is built as a one hour lecture. For professors, a handbook with homework solutions is available. Contact the publisher for further details.

SCOPE

This text is designed to be a reference for students and professors as well as theatre professionals. Though extensive, it does not cover the full scope of structural engineering. For example, we do not cover every material choice or manufactured product available, such as manufactured joists and glue-laminated beams. This is not to discourage the use of such materials or products. In fact, the concepts presented in this text make it possible to understand and therefore apply the structural data provided by the manufacturers of other materials and products. In addition, although we do not specifically discuss the structural design of connections, the structural concepts presented in this text can be applied to their design. The specific requirements of connection details are quite extensive and merit an entire text of their own.

In general, the recommended practices that we present are congruent with modern building codes, though this text cannot address all regional building codes as every geographic area has its own unique challenges. For example, U.S. building codes in the West Coast are stricter than in the Northeast because of the higher probability of earthquakes. In the Midwest, the codes might be designed with floods, tornadoes, or snow loads in mind. In addition, interpreting building codes to apply to set construction is tricky at best. If you are concerned about meeting legal code, consult a professional general contractor, architect, engineer, or the appropriate code authority such as a Fire, Building, or Safety Department.

The basics included in this text can be expanded upon by reading more about structural design, taking advanced courses, and discussing structural issues with other theater professionals. The “concept boxes” which appear throughout the text are meant to highlight interesting issues which merit further thought. Learning the concepts and techniques of structural design is a lifetime endeavor; this text is simply the first step.

2

Force, Stress, and Strain

INTRODUCTION

The first step in understanding an...