Structure for Architects

A Case Study in Steel, Wood, and Reinforced Concrete Design

Ashwani Bedi, Ramsey Dabby

• Éditeur: Routledge
• Année: 2019
• ISBN:
  9781351348294
• Édition: 1
• Sujet: Architecture
• Sous-sujet: Architecture générale

Structure for Architects: A Case Study in Steel, Wood, and Reinforced Concrete Design is a sequel to the authors' first text, Structure for Architects: A Primer, emphasizing the conceptual understanding of structural design in simple language and terms. This book focuses on structural principles applied to the design of typical structural members—a beam, a girder, and a column—in a diagrammatic frame building. Through the application of a single Case Study across three key materials, the book illustrates the theory, principles, and process of structural design. The Case Study progresses step-by-step for each material, from determining tributary areas and loads through a member's selection and design.

The book addresses the frequent disparity between the way architects and engineers perceive and process information, with engineers focusing on technical aspects and architects focusing on visual concepts. Structure for Architects: A Case Study in Steel, Wood, and Reinforced Concrete Design presents readers with an understanding of fundamental engineering principles through a uniquely thematic Case Study. Focusing on the conceptual understanding of structural design, this book will be of interest to architecture students and professionals looking to understand the application of structural principles in relation to steel, wood, and concrete design.

1 Introduction to Structural Design

One of the earliest and most important engineering decisions on a project is to select a structural system that is compatible and consistent with the architectural intent. On some projects, the structural system may conform to the architectural expression and simply be a concealed means of support (Figure 1.1). On other projects, the structural system may be the actual architectural expression and be celebrated for itself (Figure 1.2). In any case, the selection of an appropriate structural system is a matter of discussion and close coordination between architect and structural engineer, keeping in mind the best interests of the project.

Figure 1.1 Apartment Building, Fort Lee - Structure as Concealed Support

Figure 1.2 Bach de Roda Bridge, Barcelona - Structure as Architectural Form

Whatever the structural system and however it may be expressed, the structure must be designed to satisfy the conditions of stability, strength, serviceability, economy, and sustainability—not only as a whole, but also for its individual components. With a good general understanding of how structural members behave under load, the Reader is ready to undertake their design.

The structural design of a member simply means the selection of an appropriate material and cross-sectional shape to safely and economically resist the load demands, to which the member will be subjected.

1.1 Removing a Bearing Wall

Let’s use a simple example to get a sense of this statement.

Say you’re renovating the basement of a house and want to open up the room, column-free, by removing a bearing wall that runs down the middle of the space (Figure 1.3). Since the bearing wall is supporting the first floor joists above, you know that with the bearing wall removed, you’ll have to support the loads from the joists with a new girder. Since the floor-to-floor height is limited, headroom clearance is a concern.

Figure 1.3 Basement Plan

Option 1

Your first instinct, for reasons of structural efficiency, practicality, and cost may be to design a deep and narrow girder in wood—but you’re concerned that the girder may be too deep for sufficient headroom.

Option 2

You realize however, that you can increase headroom by compromising structural efficiency and making the wood girder shallower and wider.

Option 3

It now occurs to you to design the girder in steel, knowing that steel has significantly greater strength than wood, thereby making it feasible to design a shallow steel girder providing the needed headroom—but is likely that this will be a more expensive solution (Figure 1.4).

Figure 1.4 Girder Options

Once you calculate the loads on the girder, and determine the moment and shear that the girder must resist, you’ll have the basic information needed to design the beam—but which option is the right choice?

This example illustrates the fundamental challenge of design—to use judgment and experience to reach a decision when there are multiple options that can satisfy the design intent. The decision of whether to design the girder in wood or steel is a matter of preference of the designer based on the availability and economy of the materials, and ease of construction—all of which may vary for any particular situation. In the end, you as the designer must evaluate the key properties of a member that will provide the strength to safely and economically carry the anticipated loads. Specifically, you must decide upon a member’s material and cross-sectional shape.

2 Structural Design Methodologies

2.1 Building Codes and Industry Organizations

Building codes are a set of rules that provide the public with a minimum acceptable level of performance for buildings and other structures. Their main purpose is to protect public health, safety, and welfare as they relate to a structure’s construction and occupancy.

The advent of building codes is generally traced to Hammurabi’s Code during the Babylonian Empire around 1700 bc (Figure 2.1). The earliest known building codes in the United States were established in the 1600s, but it wasn’t until the 1800s that larger US cities began adopting building codes, spurred largely by catastrophes like the Great Chicago Fire of 1871 (Figure 2.2). These early versions have developed into the building codes in use today.

Until recently, the United States followed various local and regional codes such as the BOCA National Building Code, the Uniform Building Code, and the Standard Building Code. Variations within these codes, along with the desire to have a unified building code, gave birth to the International Code Council (ICC) in 1994 that was comprised of officials representing all three codes. The ICC published the first edition of the International Building Code (IBC) in 2000, with updated revisions in subsequent years. Based on the IBC, cities and states develop and adopt their own ‘governing’ codes that reflect their own specific conditions and requirements.

Figure 2.1 Hammurabi’s Code

Figure 2.2 1871 Chicago Fire

Along with the development of building codes, advances in the science and behavior of various construction materials (such as steel, wood, and concrete) led to the formation of ‘Societies’, ‘Institutes’, and ‘Councils’ comprised of industry manufacturers, academic and practicing professionals. These organizations evolved into technical authorities in their fields, performing research, providing guidelines, and becoming references for the various building codes. The American Institute of Steel Construction (AISC), the American Wood Council (AWC), and the American Concrete Institute (ACI) are the recognized r...