S T R U C T U R A L W D O O D E S I G N Structural Wood Design: A Practice-Oriented Approach Using the ASD Method. Abi Aghayere and Jason Vigil Copyright © 2007 John Wiley & Sons, Inc. S T R U C T U R A L W D O O D E S I G N A P - O A R A C T I C E R I E N T E D P P R O A C H U A S D M S I N G T H E E T H O D Abi Aghayere Jason Vigil JOHN WILEY & SONS, INC. This book is printed on acid-free paper. (cid:1)(cid:1) Copyright (cid:2) 2007 by John Wiley & Sons, Inc. All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada Wiley Bicentennial Logo: Richard J. 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Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-PublicationData: Aghayere, Abi O. Structural wood design: a practice-oriented approach using the ASD method/ by Abi Aghayere, Jason Vigil. p. cm. ISBN: 978-0-470-05678-3 1. Wood. 2. Building, Wooden. I. Vigil, Jason, 1974– II. Title. TA419.A44 2007 624.1(cid:1)84—dc22 2006033934 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 C ONTENTS Preface xi chapter one INTRODUCTION: WOOD PROPERTIES, SPECIES, AND GRADES 1 1.1 Introduction 1 The Project-based Approach 1 1.2 Typical Structural Components of Wood Buildings 2 1.3 Typical Structural Systems in Wood Buildings 8 Roof Framing 8 Floor Framing 9 Wall Framing 9 1.4 Wood Structural Properties 11 Tree Cross Section 11 Advantages and Disadvantages of Wood as a Structural Material 11 1.5 Factors Affecting Wood Strength 12 Species and Species Group 12 Moisture Content 13 Duration of Loading 14 Size Classifications of Sawn Lumber 14 Wood Defects 15 Orientation of the Wood Grain 16 Ambient Temperature 16 1.6 Lumber Grading 16 Types of Grading 17 Stress Grades 18 Grade Stamps 18 1.7 Shrinkage of Wood 19 1.8 Density of Wood 19 1.9 Units of Measurement 19 1.10 Building Codes 20 NDS Code and NDS Supplement 22 v (cid:1) vi C O N T E N T S References 23 Problems 23 chapter two INTRODUCTION TO STRUCTURAL DESIGN LOADS 25 2.1 Design Loads 25 Load Combinations 25 2.2 Dead Loads 26 Combined Dead and Live Loads on Sloped Roofs 27 Combined Dead and Live Loads on Stair Stringers 28 2.3 Tributary Widths and Areas 28 2.4 Live Loads 30 Roof Live Load 30 Snow Load 32 Floor Live Load 35 2.5 Deflection Criteria 39 2.6 Lateral Loads 42 Wind Load 43 Seismic Load 45 References 54 Problems 54 chapter three ALLOWABLE STRESS DESIGN METHOD FOR SAWN LUMBER AND GLUED LAMINATED TIMBER 57 3.1 Allowable Stress Design Method 57 NDS Tabulated Design Stresses 58 Stress Adjustment Factors 59 Procedure for Calculating Allowable Stress 66 Moduli of Elasticity for Sawn Lumber 66 3.2 Glued Laminated Timber 66 End Joints in Glulam 67 Grades of Glulam 67 Wood Species Used in Glulam 68 Stress Class System 68 3.3 Allowable Stress Calculation Examples 69 3.4 Load Combinations and the Governing Load Duration Factor 69 Normalized Load Method 69 References 78 Problems 78 chapter four DESIGN AND ANALYSIS OF BEAMS AND GIRDERS 80 4.1 Design of Joists, Beams, and Girders 80 Definition of Beam Span 80 (cid:1) C O N T E N T S vii Layout of Joists, Beams, and Girders 80 Design Procedure 80 4.2 Analysis of Joists, Beams, and Girders 86 Design Examples 100 Continuous Beams and Girders 117 Beams and Girders with Overhangs or Cantilevers 117 4.3 Sawn-Lumber Decking 118 4.4 Miscellaneous Stresses in Wood Members 121 Shear Stress in Notched Beams 121 Bearing Stress Parallel to the Grain 122 Bearing Stress at an Angle to the Grain 122 Sloped Rafter Connection 123 4.5 Preengineered Lumber Headers 126 4.6 Flitch Beams 128 4.7 Floor Vibrations 131 Floor Vibration Design Criteria 131 Remedial Measures for Controlling Floor Vibrations in Wood Framed Floors 136 References 142 Problems 143 chapter five WOOD MEMBERS UNDER AXIAL AND BENDING LOADS 145 5.1 Introduction 145 5.2 Pure Axial Tension: Case 1 146 Design of Tension Members 146 5.3 Axial Tension plus Bending: Case 2 151 Euler Critical Buckling Stress 153 5.4 Pure Axial Compression: Case 3 153 Built-up Columns 159 P–Delta Effects in Members Under Combined Axial Compression and Bending Loads 162 5.5 Axial Compression plus Bending: Case 4 162 Eccentrically Loaded Columns 178 5.6 Practical Considerations for Roof Truss Design 178 Types of Roof Trusses 179 Bracing and Bridging of Roof Trusses 179 References 180 Problems 181 chapter six ROOF AND FLOOR SHEATHING UNDER VERTICAL AND LATERAL LOADS (HORIZONTAL DIAPHRAGMS) 183 6.1 Introduction 183 Plywood Grain Orientation 183 Plywood Species and Grades 183 (cid:1) viii C O N T E N T S Span Rating 185 6.2 Roof Sheathing: Analysis and Design 186 6.3 Floor Sheathing: Analysis and Design 186 Extended Use of the IBC Tables for Gravity Loads on Sheathing 188 6.4 Panel Attachment 189 6.5 Horizontal Diaphragms 190 Horizontal Diaphragm Strength 192 Openings in Horizontal Diaphragms 197 Chords and Drag Struts 200 Nonrectangular Diaphragms 213 References 214 Problems 214 chapter seven VERTICAL DIAPHRAGMS UNDER LATERAL LOADS (SHEAR WALLS) 216 7.1 Introduction 216 Wall Sheathing Types 216 Plywood as a Shear Wall 217 7.2 Shear Wall Analysis 219 Shear Wall Aspect Ratios 219 Shear Wall Overturning Analysis 220 Shear Wall Chord Forces: Tension Case 224 Shear Wall Chord Forces: Compression Case 226 7.3 Shear Wall Design Procedure 227 7.4 Combined Shear and Uplift in Wall Sheathing 242 References 245 Problems 245 chapter eight CONNECTIONS 248 8.1 Introduction 248 8.2 Design Strength 249 8.3 Adjustment Factors for Connectors 249 8.4 Base Design Values: Laterally Loaded Connectors 257 8.5 Base Design Values: Connectors Loaded in Withdrawal 268 8.6 Combined Lateral and Withdrawal Loads 270 8.7 Preengineered Connectors 273 8.8 Practical Considerations 273 References 276 Problems 276 chapter nine BUILDING DESIGN CASE STUDY 278 9.1 Introduction 278 (cid:1) C O N T E N T S ix 9.2 Gravity Loads 279 9.3 Seismic Lateral Loads 283 9.4 Wind Loads 284 9.5 Components and Cladding Wind Pressures 287 9.6 Roof Framing Design 291 Analysis of a Roof Truss 292 Design of Truss Web Tension Members 293 Design of Truss Web Compression Members 293 Design of Truss Bottom Chord Members 295 Design of Truss Top Chord Members 297 Net Uplift Load on a Roof Truss 299 9.7 Second Floor Framing Design 299 Design of a Typical Floor Joist 300 Design of a Glulam Floor Girder 301 Design of Header Beams 307 9.8 Design of a Typical Ground Floor Column 311 9.9 Design of a Typical Exterior Wall Stud 312 9.10 Design of Roof and Floor Sheathing 317 Gravity Loads 317 Lateral Loads 317 9.11 Design of Wall Sheathing for Lateral Loads 319 9.12 Overturning Analysis of Shear Walls: Shear Wall Chord Forces 322 Maximum Force in Tension Chord 325 Maximum Force in Compression Chord 327 9.13 Forces in Horizontal Diaphragm Chords, Drag Struts, and Lap Splices 331 Design of Chords, Struts, and Splices 331 Hold-Down Anchors 337 Sill Anchors 338 9.14 Design of Shear Wall Chords 339 9.15 Construction Documents 344 References 345 appendix A Weights of Building Materials 347 appendix B Design Aids 350 Index 391 P REFACE The primary audience for this book are students of civil and architectural engineering, civiland constructionengineeringtechnology,andarchitectureinatypicalundergraduatecourseinwood or timber design. The book can be used for a one-semester course in structural wood ortimber designandshouldpreparestudentstoapplythefundamentalsofstructuralwooddesigntotypical projects that might occur in practice. The practice-oriented and easy-to-follow but thorough approachtodesignthatisadopted,andthemanypracticalexamplesapplicabletotypicaleveryday projects that are presented, should also make the book a good resource for practicingengineers, architects, and builders and those preparing for professional licensure exams. The book conforms to the 2005 National Design Specification for Wood Construction, and is intended to provide the essentials of structural design in wood from a practical perspective and to bridge the gap between the design of individual wood structural members and the complete design of a wood structure, thus providing a holistic approach to structural wood design.Other unique features of this book include a discussion and description of common wood structural elements and systems that introduce the reader to wood building structures, a complete wood building design case study, the design of wood floors for vibrations, the general analysisofshear wallsforoverturning,includingallapplicableloads,themanythree-andtwo-dimensionaldraw- ings and illustrations to assist readers’ understanding of the concepts, and the easy-to-usedesign aids for the quick design of common structural members, such as floor joists, columns, and wall studs. Chapter 1 The reader is introduced to wood design through a discussion and description of the various wood structural elements and systems that occur in wood structures as well as the properties of wood that affect its structural strength. Chapter 2 The various structural loads—dead, live, snow, wind, and seismic—are discussed and several examples are presented. This succinct treatment of structural loads gives the reader adequate information to calculate the loads acting on typical wood building structures. Chapter3 Calculationoftheallowablestressesforbothsawnlumberandglulaminaccordance with the 2005 National Design Specification as well as a discussion of the various stress adjustment factors are presented in this chapter. Glued laminated timber (glulam), the various grades of glulam, and determination of the controlling load combination in a wood building using the normalized load method are also discussed. Chapter 4 The design and analysis of joists, beams, and girders are discussed and several ex- amples are presented. The design of wood floors for vibrations, miscellaneous stresses in wood members,theselectionofpreengineeredwoodflexuralmembers,andthedesignofsawn-lumber decking are also discussed. xi