Structural Wood Design

ASD/LRFD

Abi Aghayere, Jason Vigil

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781498749886
• Edición: 2
• Categoría: Technology & Engineering
• Categoría: Construction & Architectural Engineering

This text provides a concise and practical guide to timber design, using both the Allowable Stress Design and the Load and Resistance Factor Design methods. It suits students in civil, structural, and construction engineering programs as well as engineering technology and architecture programs, and also serves as a valuable resource for the practicing engineer. The examples based on real-world design problems reflect a holistic view of the design process that better equip the reader for timber design in practice.This new edition

• 
  
  

• now includes the LRFD method with some design examples using LRFD for joists, girders and axially load members.

• 
  
  

• is based on the 2015 NDS and 2015 IBC model code.

• 
  
  

• includes a more in-depth discussion of framing and framing systems commonly used in practice, such as, metal plate connected trusses, rafter and collar tie framing, and pre-engineered framing.

• 
  
  

• includes sample drawings, drawing notes and specifications that might typically be used in practice.

• 
  
  

• includes updated floor joist span charts that are more practical and are easy to use.

• 
  
  

• includes a chapter on practical considerations covering topics like flitch beams, wood poles used for footings, reinforcement of existing structures, and historical data on wood properties.

• 
  
  

• includes a section on long span and high rise wood structures

• 
  
  

• includes an enhanced student design project

Chapter 1

Introduction

Wood properties, species, and grades

1.1 INTRODUCTION

Wood is a sustainable, economical, and aesthetically pleasing material that has been used for a long time in civil engineering structures. Though a large proportion of low-rise buildings in the United States and Canada are built from wood, there is a dearth of textbooks for students and practitioners alike that presents wood structural design in a holistic and easy-to-understand manner. The purpose of this book is to bridge this gap by presenting the design process for wood structures in a holistic, succinct, and practical way including a detailed discussion of the use of wood as a structural material and the analysis and design of the major structural elements in typical wood buildings.

In general, building plans and details are defined by an architect and are usually given to a structural engineer for design of structural elements and to present the design in the form of structural drawings. In this book, we take a project-based approach covering the design process that a structural engineer would go through for a typical wood-framed structure.

The intended audience for this book is students taking a course in timber or structural wood design and structural engineers and similarly qualified designers of wood or timber structures looking for a simple and practical guide for design. The reader should have a working knowledge of statics, strength of materials, structural analysis (including truss analysis), and load calculations in accordance with building codes (dead, live, snow, wind, and seismic loads). Design loads are reviewed in Chapter 2. The reader must also have available:

1. National Design Specification for Wood Construction, 2015 edition, ANSI/AWC (hereafter referred to as the NDS code) [1].

2. National Design Specification Supplement: Design Values for Wood Construction, 2015 edition, ANSI/AWC (hereafter referred to as NDS-S) [2].

3. International Building Code, 2015 edition, International Code Council (ICC) (hereafter referred to as the IBC) [3].

4. Minimum Design Loads for Buildings and Other Structures, 2010 edition, American Society of Civil Engineers (ASCE) (hereafter referred to as ASCE 7) [4].

1.1.1 The project-based approach

Wood is nature’s most abundant renewable building material and a widely used structural material in the United States, where 90% of all residential buildings are of wood construction [5]. The number of building configurations and design examples that could be presented is unlimited. Some applications of wood in construction include residential buildings, retail buildings, offices, hotels, schools and colleges, healthcare and recreation facilities, senior living and retirement homes, and religious buildings. The most common wood structures are residential and multifamily dwellings as well as hotels. Residential structures are usually one to three stories in height, while multifamily and hotel structures can be up to five or six stories in height with the upper four stories framed with wood and the lower levels framed with steel or concrete. Four to five stories of wood framing is a practical upper limit for wood buildings, though a much higher number of stories are now possible for wood buildings with the introduction of cross-laminated timber. Commercial, industrial, institutional, and other structures that have higher occupancy loads and factors of safety are not typically constructed with wood, although wood may be used as a secondary structure, such as a storage mezzanine. The structures that support amusement park rides are sometimes built out of wood because of the relatively low maintenance cost of exposed wood structures and its unique ability to resist the repeated cycles of dynamic loading (fatigue) imposed on the structure by the amusement park rides. The approach taken in this text is to illustrate the design process required for each major structural element in a wood structure with proper consideration as to how the design and detailing of each element is incorporated into a typical project. In Figures 1.1 and 1.2, we identify the typical structural elements in a wood building. The elements are described in greater detail in the next section.

Figure 1.1 Perspective overview of a building section.

Figure 1.2 Overview of major structural elements.

1.2 TYPICAL STRUCTURAL COMPONENTS OF WOOD BUILDINGS

The majority of wood buildings in the United States are typically platform-framed construction, in which the vertical wall studs are built one story at a time and the floor below provides the platform to build the next level of wall that will in turn support the floor above. The walls usually span vertically between the sole or sill plates at the floor level and the top plates at the floor or roof level above. This is in contrast to the infrequently used and less economical balloon-framed construction, where the vertical studs are continuous for the entire height of the building and the floor framing is supported on brackets off the face of the wall studs. Platform-framed construction is the predominant method of framing for wood buildings in the United States. The typical structural elements in a wood-framed building system are described below.

Rafters (Figure 1.3): These are usually sloped sawn-dimension lumber roof beams spaced at fairly close intervals (e.g., 12, 16, or 24 in.) and carry lighter loads than those carried by the roof trusses, beams, or girders. They are usually supported by roof trusses, ridge beams, hip rafters, or walls. The span of rafters is limited in practice to a maximum of 14 ft. to 18 ft., with longer spans available with the use of engineered wood members such as laminated veneer lumber (LVL) and I-joists. Rafters of varying spans that are supported by hip rafters are called jack rafters (see Figure 1.6). Sloped roof rafters with a nonstructural ridge, such as a 1× ridge board, require ceiling tie joists or collar ties to resist the horizontal outward thrust at the exterior walls that is due to gravity loads on...