Design of Wood Structures —ASD/LRFD Donald E. Breyer, P.E. Professor Emeritus Department of Engineering Technology California State Polytechnic University Pomona, California
Kelly E. Cobeen, S.E. Associate Principal Wiss, Janney, Elstner Associates, Inc. Emeryville, California
Kenneth J. Fridley, Ph.D. Professor and Head Department of Civil, Construction, and Environmental Engineering University of Alabama Tuscaloosa, Alabama
David G. Pollock, Ph.D., P.E. Professor Department of Mechanical and Civil Engineering George Fox University Newberg, Oregon
Seventh Edition
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Contents
Preface xi Nomenclature Abbreviations
xv xviii
Chapter 1. Wood Buildings and Design Criteria 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11
Introduction Types of Buildings Required and Recommended References Building Codes and Design Criteria ASD and LRFD Organization of the Text Structural Calculations Detailing Conventions Fire-Resistive Requirements Industry Organizations References
Chapter 2. Design Loads 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16
Introduction Dead Loads Live Loads Snow Loads Soil Loads and Hydrostatic Pressure Loads due to Fluids Rain Loads Flood Loads Self-Straining Loads Wind Loads—Introduction Wind Forces—Main Wind Force Resisting System Wind Forces—Components and Cladding Seismic Forces—Introduction Seismic Forces Seismic Forces—Primary System Seismic Forces—Wall Components
1 1 2 4 7 8 9 9 11 12 13 13
15 15 17 21 28 35 35 35 36 36 37 42 52 57 62 76 83 v
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2.17 2.18 2.19 2.20
Load Combinations Serviceability/Deflection Criteria References Problems
Chapter 3. Behavior of Structures under Loads and Forces 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8
Introduction Structures Subject to Vertical Loads Structures Subject to Lateral Forces Lateral Forces in Buildings with Diaphragms and Shearwalls Design Problem: Lateral Forces on One-Story Building Design Problem: Lateral Forces on Two-Story Building References Problems
Chapter 4. Properties of Wood and Lumber Grades 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27
Introduction Design Specification Methods of Grading Structural Lumber In-Grade versus Clear Wood Design Values Species and Species Groups Cellular Makeup Moisture Content and Shrinkage Effect of Moisture Content on Lumber Sizes Durability of Wood and the Need for Pressure Treatment Growth Characteristics of Wood Sizes of Structural Lumber Size Categories and Commercial Grades General Notation Wet Service Factor CM Load Duration Factor CD (ASD Only) Time Effect Factor (LRFD Only) Size Factor CF Repetitive Member Factor Cr Flat Use Factor Cfu Temperature Factor Ct Incising Factor Ci Resistance Factor (LRFD Only) Format Conversion Factor KF (LRFD Only) Design Problem: Adjusted Design Values Future Directions in Wood Design References Problems
Chapter 5. Structural Glued Laminated Timber 5.1 5.2 5.3 5.4
Introduction Sizes of Glulam Members Resawn Glulam Fabrication of Glulams
88 93 98 99
107 107 107 111 118 124 139 159 159
167 167 168 170 172 174 175 178 186 186 189 192 195 199 205 206 210 211 212 213 213 214 214 215 216 226 227 228
235 235 235 238 239
Contents
5.5 5.6 5.7 5.8 5.9
Grades of Glulam Members Adjustment Factors for Glulam Design Problem: Adjusted Design Values References Problems
Chapter 6. Beam Design 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.21
Introduction Bending Lateral Stability Adjusted Bending Design Value Summary Shear Deflection Design Summary Bearing at Supports Design Problem: Sawn Beam Design Problem: Rough-Sawn Beam Using ASD Design Problem: Notched Beam Design Problem: Sawn-Beam Analysis Design Problem: Glulam Beam with Full Lateral Support Design Problem: Glulam Beam with Lateral Support at 8 ft-0 in. Design Problem: Glulam Beam with Lateral Support at 48 ft-0 in. Design Problem: Glulam with Compression Zone Stressed in Tension Cantilever Beam Systems Lumber Roof and Floor Decking Fabricated Wood Components References Problems
Chapter 7. Axial Forces and Combined Bending and Axial Forces 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19
Introduction Axial Tension Members Design Problem: Tension Member Columns Detailed Analysis of Slenderness Ratio Design Problem: Axially Loaded Column Design Problem: Capacity of a Glulam Column Design Problem: Capacity of a Bearing Wall Built-Up Columns Combined Bending and Tension Design Problem: Combined Bending and Tension Combined Bending and Compression Design Problem: Beam-Column Design Problem: Beam-Column Action in a Stud Wall Using LRFD Design Problem: Glulam Beam-Column Using ASD Design for Minimum Eccentricity Design Problem: Column with Eccentric Load Using ASD References Problems
vii
245 250 253 257 258
261 261 262 274 283 289 296 298 300 307 314 316 318 322 328 332 335 339 343 345 354 355
367 367 368 373 377 385 391 396 402 404 408 413 418 425 430 439 446 447 453 454
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Contents
Chapter 8. Wood Structural Panels 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16
Introduction Panel Dimensions and Installation Recommendations Plywood Makeup Species Groups for Plywood Veneer Grades Exposure Durability Classifications Plywood Grades Other Wood Structural Panels Roof Sheathing Design Problem: Roof Sheathing Floor Sheathing Design Problem: Floor Sheathing Wall Sheathing and Siding Stress Calculations for Wood Structural Panels References Problems
Chapter 9. Diaphragms 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13
Introduction Basic Diaphragm Action Shear Resistance Diaphragm Chords Design Problem: Roof Diaphragm Distribution of Lateral Forces in a Shearwall Collector (Strut) Forces Diaphragm Deflections Diaphragms with Interior Shearwalls Interior Shearwalls with Collectors Diaphragm Flexibility References Problems
Chapter 10. Shearwalls 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14
Introduction Basic Shearwall Action Shearwalls Using Wood Structural Panels Other Sheathing Materials Shearwall Chord Members Design Problem: Shearwall Alternate Shearwall Design Methods Anchorage Considerations Vertical (Gravity) Loads Lateral Forces Parallel to a Wall Shearwall Deflection Lateral Forces Perpendicular to a Wall References Problems
463 463 465 467 470 473 475 476 479 482 485 489 492 494 498 508 509
513 513 514 519 527 532 540 544 549 554 559 563 566 566
573 573 574 575 581 583 585 594 605 606 607 611 616 618 619
Contents
Chapter 11. Wood Connections—Background 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9
Introduction Types of Fasteners and Connections Yield Model for Laterally Loaded Fasteners Factors Affecting Strength in Yield Model Dowel Bearing Strength Plastic Hinge in Fastener Yield Limit Mechanisms References Problems
Chapter 12. Nailed and Stapled Connections 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 12.11 12.12 12.13 12.14 12.15 12.16 12.17
Introduction Types of Nails Power-Driven Nails and Staples Yield Limit Equations for Nails Applications of Yield Limit Equations Adjustment Factors for Laterally Loaded Nails Design Problem: Nail Connection for Knee Brace Design Problem: Top Plate Splice Design Problem: Shearwall Chord Tie Design Problem: Laterally Loaded Toenail Design Problem: Laterally Loaded Connection in End Grain Nail Withdrawal Connections Combined Lateral and Withdrawal Loads Spacing Requirements Nailing Schedule References Problems
Chapter 13. Bolts, Lag Bolts, and Other Connectors 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17
Introduction Bolt Connections Bolt Yield Limit Equations for Single Shear Bolt Yield Limit Equations for Double Shear Adjustment Factors for Bolts Tension and Shear Stresses at a Multiple Fastener Connection Design Problem: Multiple-Bolt Tension Connection Design Problem: Bolted Chord Splice for Diaphragm Shear Stresses in a Beam at a Connection Design Problem: Bolt Connection for Diagonal Brace Lag Bolt Connections Yield Limit Equations for Lag Bolts Adjustment Factors for Lag Bolts in Shear Connections Design Problem: Collector (Strut) Splice with Lag Bolts Lag Bolts in Withdrawal Combined Lateral and Withdrawal Loads Split Ring and Shear Plate Connectors
ix
627 627 627 634 635 639 643 647 652 652
655 655 656 659 661 668 676 683 688 696 700 704 706 713 714 718 718 718
727 727 728 731 740 744 756 760 766 773 775 781 785 788 793 799 802 803
x
Contents
13.18 References 13.19 Problems
Chapter 14. Connection Details and Hardware 14.1 14.2 14.3 14.4 14.5 14.6
Introduction Connection Details Design Problem: Beam-to-Column Connection Cantilever Beam Hinge Connection Prefabricated Connection Hardware References
Chapter 15. Diaphragm-to-Shearwall Anchorage 15.1 15.2 15.3 15.4 15.5 15.6 15.7
Introduction Anchorage Summary Connection Details—Diaphragm to Wood-Frame Wall Connection Details—Diaphragm to Concrete or Masonry Walls Subdiaphragm Anchorage of Concrete and Masonry Walls Design Problem: Subdiaphragm References
Chapter 16. Advanced Topics in Lateral Force Design 16.1 16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 16.10 16.11
809 809
821 821 821 839 848 850 853
855 855 855 860 869 885 891 899
901
Introduction Seismic Forces—Regular Structures Seismic Forces—Irregular Structures Overturning—Background Overturning—Review Overturning—Wind Overturning—Seismic Lateral Analysis of Nonrectangular Buildings Rigid Diaphragm Analysis Additional Topics in Diaphragm Design References
901 901 903 914 914 919 923 929 934 944 944
Appendix A. Equivalent Uniform Weights of Wood Framing
945
Appendix B. Weights of Building Materials
947
Appendix C. Sl Units
951
Index
955
Preface
The purpose of this book is to introduce engineers, technologists, and architects to the design of wood structures. It is intended to serve either as a text for a course in timber design or as a reference for systematic self-study of the subject. The book will lead the reader through the complete design of a wood structure (except for the foundation). The sequence of the material follows the same general order that it would in actual design: 1. Vertical design loads and lateral forces 2. Design for vertical loads (beams and columns) 3. Design for lateral forces (horizontal diaphragms and shearwalls) 4. Connection design (including the overall tying together of the vertical- and lateral-force-resisting systems) The need for such an overall approach to the subject became clear from experience gained in teaching timber design at the undergraduate and graduate levels. This text pulls together the design of the various elements into a single reference. A large number of practical design examples are provided throughout the text. Because of their widespread usage, buildings naturally form the basis of the majority of these examples. However, the principles of member design and diaphragm design have application to other structures (such as concrete formwork and falsework). This book relies on practical, current industry literature as the basis for structural design. This includes publications of the American Wood Council (AWC), the International Code Council (ICC), the American Society of Civil Engineers (ASCE), APA—The Engineered Wood Association, and the American Institute of Timber Construction (AITC). In the writing of this text, an effort has been made to conform to the spirit and intent of the reference documents. The interpretations are those of the authors and are intended to reflect current structural design practice. The material presented is suggested as a guide only, and final design responsibility lies with the structural engineer.
xi
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Preface
The seventh edition of this book was prompted by four major developments: 1. Publication of the 2012 National Design Specification for Wood Construction (NDS). 2. Publication of the 2008 Special Design Provisions for Wind and Seismic (SDPWS) Supplement to the NDS. 3. Publication and adoption nationally of the 2012 International Building Code. 4. Publication of updated load standards in the 2010 edition of Minimum Design Loads for Buildings and Other Structures (ASCE 7-10). The National Design Specification (NDS) is published by the American Wood Council (AWC) and represents the latest structural design recommendations by the wood industry. The 2012 NDS presents both traditional allowable stress design (ASD) provisions as well as new load and resistance factor design (LRFD) provisions. LRFD provisions were first introduced to the NDS in the 2005 edition. As such, the NDS is considered a dual-format design specification. While ASD has been and may continue to be the method of choice for many designers of wood buildings, the acceptance and use of LRFD for wood design is increasing. The 2012 ASD/LRFD Manual for Engineered Wood Construction includes guidelines and provisions helpful for wood engineering design. It includes design information for sawn lumber, structural glued laminated timber, structural-use panels, shearwalls and diaphragms, poles and piles, I-joists, structural composite lumber, and structural connections (nails, bolts, screws, timber rivets, shear plate and split ring connectors). The Manual was first introduced in 1999 for the 1997 NDS, and has evolved into a useful design support document. The International Building Code (IBC) is a product of the International Code Council (ICC). The ICC brought together the three regional model building code organizations to develop and administer a single national building code. The first edition of the IBC was published in 2000, and now nearly all regions of the United States have adopted all or part of the IBC at either the state or local level. Traditionally, the NDS has been based on the principles of what is termed allowable stress design (ASD). In ASD, allowable stresses of a material are compared to calculated working stresses resulting from service loads. In the 1990s, the wood industry and design community completed the development of a load and resistance factor design (LRFD) specification for wood construction. In LRFD, adjusted nominal capacities (resistance) are compared to the effect of factored loads. The factors are developed for both resistance and loads such that uncertainty and consequence of failure are explicitly recognized. The LRFD approach to wood design is now included in the NDS. This seventh edition of Design of Wood Structures presents both ASD and LRFD guidelines as provided in the NDS. In many examples, both ASD and LRFD approaches are presented to allow the reader a direct, side-by-side comparison of the two methods.
Preface
xiii
Questions or comments about the text or examples may be addressed to any of the authors. Direct any correspondence to: Prof. Emeritus Donald E. Breyer Department of Engineering Technology California State Polytechnic University 3801 West Temple Avenue Pomona, CA 91768
Ms. Kelly E. Cobeen Wiss, Janney, Elstner Associates, Inc. 2000 Powell St., Suite 1650 Emeryville, CA 94608
Prof. Kenneth J. Fridley Department of Civil, Construction, and Environmental Engineering University of Alabama Box 870205 Tuscaloosa, AL 35487-0205
Prof. David G. Pollock Department of Mechanical and Civil Engineering George Fox University 414 N. Meridian St., #6142 Newberg, OR 97132
Acknowledgment and appreciation for help in writing this text are given to our numerous colleagues in the wood design profession. Suggestions and information were obtained from many engineers and suppliers, and their help is gratefully recognized. We express particular gratitude to Rosdinah Baharin for her extensive work in converting figures and diagrams to electronic format.We also acknowledge John Henry of the International Code Council (ICC) for reviewing the entire manuscript prior to publication. Finally, our sincere thanks to Bridget Thoreson, Michael McCabe, Joy Bramble, and Larry Hager for shepherding various editions of this textbook through the publication process at McGraw-Hill. Dedication To our families: Matthew, Kerry, Daniel, and Sarah Matthew Paula, Justin, Connor, and Alison Lynn, Sarah, and Will Donald E. Breyer, P.E. Kelly E. Cobeen, S.E. Kenneth J. Fridley, Ph.D. David G. Pollock, Ph.D., P.E.
