S TRUCTURAL W OOD D ESIGN

Transcription

1 S TRUCTURAL W OOD D ESIGN Structural Wood Design: A Practice-Oriented Approach Using the ASD Method. Abi Aghayere and Jason Vigil Copyright 2007 John Wiley & Sons, Inc.

2 S TRUCTURAL W OOD D ESIGN A PRACTICE-ORIENTED A PPROACH U SING THE ASD METHOD Abi Aghayere Jason Vigil JOHN WILEY & SONS, INC.

3 This book is printed on acid-free paper. Copyright 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. Pacifico No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) , fax (978) , or on the web at Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , or online at go/ permissions. Limit of Liability/ Disclaimer of Warranty: While the publisher and the author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor the author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information about our other products and services, please contact our Customer Care Department within the United States at (800) , outside the United States at (317) or fax (317) 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 Library of Congress Cataloging-in-Publication Data: Aghayere, Abi O. Structural wood design: a practice-oriented approach using the ASD method/ by Abi Aghayere, Jason Vigil. p. cm. ISBN: Wood. 2. Building, Wooden. I. Vigil, Jason, 1974 II. Title. TA419.A dc Printed in the United States of America

4 CONTENTS Preface xi chapter one INTRODUCTION: WOOD PROPERTIES, SPECIES, AND GRADES Introduction 1 The Project-based Approach Typical Structural Components of Wood Buildings Typical Structural Systems in Wood Buildings 8 Roof Framing 8 Floor Framing 9 Wall Framing Wood Structural Properties 11 Tree Cross Section 11 Advantages and Disadvantages of Wood as a Structural Material 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 Lumber Grading 16 Types of Grading 17 Stress Grades 18 Grade Stamps Shrinkage of Wood Density of Wood Units of Measurement Building Codes 20 NDS Code and NDS Supplement 22 v

5 vi C O N T E N T S References 23 Problems 23 chapter two INTRODUCTION TO STRUCTURAL DESIGN LOADS Design Loads 25 Load Combinations Dead Loads 26 Combined Dead and Live Loads on Sloped Roofs 27 Combined Dead and Live Loads on Stair Stringers Tributary Widths and Areas Live Loads 30 Roof Live Load 30 Snow Load 32 Floor Live Load Deflection Criteria 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 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 Glued Laminated Timber 66 End Joints in Glulam 67 Grades of Glulam 67 Wood Species Used in Glulam 68 Stress Class System Allowable Stress Calculation Examples 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 Design of Joists, Beams, and Girders 80 Definition of Beam Span 80

6 C O N T E N T S vii Layout of Joists, Beams, and Girders 80 Design Procedure Analysis of Joists, Beams, and Girders 86 Design Examples 100 Continuous Beams and Girders 117 Beams and Girders with Overhangs or Cantilevers Sawn-Lumber Decking 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 Preengineered Lumber Headers Flitch Beams 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 Introduction Pure Axial Tension: Case Design of Tension Members Axial Tension plus Bending: Case Euler Critical Buckling Stress Pure Axial Compression: Case Built-up Columns 159 P Delta Effects in Members Under Combined Axial Compression and Bending Loads Axial Compression plus Bending: Case Eccentrically Loaded Columns 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) Introduction 183 Plywood Grain Orientation 183 Plywood Species and Grades 183

7 viii C O N T E N T S Span Rating Roof Sheathing: Analysis and Design Floor Sheathing: Analysis and Design 186 Extended Use of the IBC Tables for Gravity Loads on Sheathing Panel Attachment 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) Introduction 216 Wall Sheathing Types 216 Plywood as a Shear Wall 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 Shear Wall Design Procedure Combined Shear and Uplift in Wall Sheathing 242 References 245 Problems 245 chapter eight CONNECTIONS Introduction Design Strength Adjustment Factors for Connectors Base Design Values: Laterally Loaded Connectors Base Design Values: Connectors Loaded in Withdrawal Combined Lateral and Withdrawal Loads Preengineered Connectors Practical Considerations 273 References 276 Problems 276 chapter nine BUILDING DESIGN CASE STUDY Introduction 278

8 C O N T E N T S ix 9.2 Gravity Loads Seismic Lateral Loads Wind Loads Components and Cladding Wind Pressures 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 Second Floor Framing Design 299 Design of a Typical Floor Joist 300 Design of a Glulam Floor Girder 301 Design of Header Beams Design of a Typical Ground Floor Column Design of a Typical Exterior Wall Stud Design of Roof and Floor Sheathing 317 Gravity Loads 317 Lateral Loads Design of Wall Sheathing for Lateral Loads Overturning Analysis of Shear Walls: Shear Wall Chord Forces 322 Maximum Force in Tension Chord 325 Maximum Force in Compression Chord Forces in Horizontal Diaphragm Chords, Drag Struts, and Lap Splices 331 Design of Chords, Struts, and Splices 331 Hold-Down Anchors 337 Sill Anchors Design of Shear Wall Chords Construction Documents 344 References 345 appendix A Weights of Building Materials 347 appendix B Design Aids 350 Index 391

9 PREFACE The primary audience for this book are students of civil and architectural engineering, civil and construction engineering technology, and architecture in a typical undergraduate course in wood or timber design. The book can be used for a one-semester course in structural wood or timber design and should prepare students to apply the fundamentals of structural wood design to typical projects that might occur in practice. The practice-oriented and easy-to-follow but thorough approach to design that is adopted, and the many practical examples applicable to typical everyday projects that are presented, should also make the book a good resource for practicing engineers, 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 analysis of shear walls for overturning, including all applicable loads, the many three- and two-dimensional drawings and illustrations to assist readers understanding of the concepts, and the easy-to-use design 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. Chapter 3 Calculation of the allowable stresses for both sawn lumber and glulam in accordance 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 examples are presented. The design of wood floors for vibrations, miscellaneous stresses in wood members, the selection of preengineered wood flexural members, and the design of sawn-lumber decking are also discussed. xi

10 xii P R E F A C E Chapter 5 The design of wood members subjected to axial and bending loads, such as truss web and chord members, solid and built-up columns, and wall studs, is discussed. Chapter 6 The design of roof and floor sheathing for gravity loads and the design of roof and floor diaphragms for lateral loads are discussed. Calculation of the forces in diaphragm chords and drag struts is also discussed, as well as the design of these axially loaded elements. Chapter 7 The design of exterior wall sheathing for wind load perpendicular to the face of a wall and the design of wood shear walls or vertical diaphragms parallel to the lateral loads are discussed. A general analysis of shear walls for overturning that takes into account all applicable lateral and gravity loads is presented. The topic of combined shear and uplift in wall sheathing is also discussed, and an example presented. Chapter 8 The design of connections is covered in this chapter in a simplified manner. Design examples are presented to show how the connection capacity tables in the NDS code are used. Several practical connections and practical connection considerations are discussed. Chapter 9 A complete building design case study is presented to help readers tie together the pieces of wood structural element design presented in earlier chapters to create a total building system design, and a realistic set of structural plans and details are also presented. This holistic and practice-oriented approach to structural wood design is the hallmark of the book. The design aids presented in Appendix B for the quick design of floor joists, columns, and wall studs subjected to axial and lateral loads are utilized in this chapter. In conclusion, we would like to offer the following personal dedications and thanksgiving: To my wife, Josie, the love of my life and the apple of my eye, and to my precious children, Osa, Itohan, Odosa, and Eghosa, for their support and encouragement. To my mother for instilling in me the discipline of hard work and excellence, and to my Lord and Savior, Jesus Christ, for His grace, wisdom, and strength. Abi Aghayere Rochester, New York For Adele and Ivy; and for Michele, who first showed me that I can do all things through Christ which strengtheneth me (Phil. 4:13) Jason Vigil Rochester, New York