Table Of ContentS T R U C T U R A L
Wood Design
ASD/LRFD
SECOND EDITION
S T R U C T U R A L
Wood Design
ASD/LRFD
SEC OND EDI TI ON
Abi Aghayere
Jason Vigil
Boca Raton London New York
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Library of Congress Cataloging‑in‑Publication Data
Names: Aghayere, Abi O., author. | Vigil, Jason, 1974- author.
Title: Structural wood design / by Abi Aghayere and Jason Vigil.
Description: Second edition. | Boca Raton, FL : CRC Press, [2017] | Includes
bibliographical references and index.
Identifiers: LCCN 2016026976 | ISBN 9781498749855 (hardback) | ISBN
9781498749862 (pdf)
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We thank our colleagues in the academy and in the civil,
architectural and structural engineering fields who have provided
valuable input and feedback on this text. In the spirit of continuous
quality improvement, we always welcome your feedback.
We also thank both our families for their unflinching support that
has made it possible to complete this project. Finally and most
importantly, we thank our Lord and Savior, Jesus Christ, who granted
us the grace, strength, and wisdom to complete this project.
Contents
Preface xv
1 Introduction: Wood properties, species, and grades 1
1.1 Introduction 1
1.1.1 The project-based approach 1
1.2 Typical structural components of wood buildings 3
1.3 Typical structural systems in wood buildings 12
1.3.1 Roof framing 12
1.3.2 Floor framing 12
1.3.3 Wall framing 15
1.3.3.1 Shear walls in wood buildings 15
1.4 Wood structural properties 17
1.4.1 Tree cross section 17
1.4.2 Advantages and disadvantages of wood as a structural material 18
1.5 Factors affecting the strength of wood 18
1.5.1 Species and species group 19
1.5.2 Moisture content 19
1.5.2.1 Seasoning of lumber 20
1.5.3 Duration of loading 20
1.5.4 Size classifications of sawn lumber 20
1.5.4.1 Nominal dimension versus actual size of sawn lumber 21
1.5.5 Wood defects 21
1.5.6 Orientation of the wood grain 24
1.5.7 Ambient temperature 25
1.6 Lumber grading 26
1.6.1 Types of grading 26
1.6.1.1 Visual grading 26
1.6.1.2 Mechanical grading 26
1.6.2 Stress grades 27
1.6.3 Grade stamps 27
1.7 Shrinkage of wood 28
1.8 Density of wood 29
1.9 Units of measurement 30
1.10 Building codes 32
vii
viii Contents
1.11 NDS code and NDS supplement 33
1.12 Student design project problem 33
Project problems 36
Problems 46
References 48
2 Introduction to structural design loads 49
2.1 Design loads 49
2.1.1 Load combinations 49
2.2 Dead loads 51
2.2.1 Combined dead and live loads on sloped roofs 53
2.2.1.1 Calculation of the horizontal thrust at an exterior wall 54
2.2.2 Combined dead and live loads on stair stringers 55
2.3 Tributary widths and areas 59
2.4 Live loads 59
2.4.1 Roof live load 60
2.4.2 Snow load 63
2.4.2.1 Snow drift and sliding snow loads 64
2.4.3 Floor live load 66
2.4.3.1 Floor live-load reduction 70
2.5 Deflection criteria 73
2.6 Lateral loads 77
2.7 Wind load 80
2.7.1 Wind load calculation 80
2.7.2 Exposure category 81
2.7.3 Basic wind speed 81
2.8 Simplified wind load calculation method (ASCE 7, Chapter 28, Part 2) 81
2.9 Seismic load 84
2.9.1 Simplified design procedure for simple bearing wall
or building frame systems (ASCE 7, Section 12.14) 85
Problems 96
References 104
3 Design method for sawn lumber and glued-laminated timber 105
3.1 Allowable stress design method 105
3.2 Load and resistance factor design method 105
3.3 Allowable stress design method in wood design 106
3.4 Load and resistance factor design method in wood design 106
3.4.1 NDS tabulated design stresses 111
3.4.2 Stress adjustment factors 111
3.4.2.1 Load duration factor C 111
D
3.4.2.2 Moisture factor C 113
M
3.4.2.3 Size factor C 113
F
3.4.2.4 Repetitive member factor C 113
r
3.4.2.5 Flat-use factor C 114
fu
Contents ix
3.4.2.6 Incising factor C 115
i
3.4.2.7 Temperature factor C 115
t
3.4.2.8 Beam stability factor C 115
L
3.4.3 Calculation method for C 116
L
3.4.3.1 Column stability factor C 118
p
3.4.3.2 Volume factor C 118
V
3.4.3.3 Bearing area factor C 118
b
3.4.3.4 Curvature factor C 118
c
3.4.3.5 Buckling stiffness factor C 120
T
3.4.3.6 Shear reduction factor C 120
vr
3.4.3.7 Stress interaction factor C 120
I
3.4.3.8 Format conversion factor K 121
F
3.4.3.9 Resistance factor f 121
3.4.3.10 Time effect factor l 121
3.4.3.11 Radial tension stress perpendicular to grain, F 122
rt
3.4.3.12 Radial compression stress perpendicular to grain, F 122
rc
3.4.4 Procedure for calculating allowable stress or the
LRFD adjusted design stress 122
3.4.5 Moduli of elasticity for sawn lumber 123
3.5 Engineered wood products 123
3.5.1 Wood I-joists 123
3.5.2 Manufactured lumber products 123
3.5.3 Cross-laminated timber 123
3.6 Glued-laminated timber 124
3.6.1 End joints in glulam 125
3.6.2 Grades of glulam 125
3.6.2.1 Bending combination glulams (NDS-S
Tables 5A, 5A–Expanded, and 5C) 125
3.6.2.2 Axial combination glulams (NDS-S Tables 5B and 5D) 126
3.6.3 Appearance grades for glulam 126
3.6.4 Wood species used in glulam 126
3.6.5 Stress class system 127
3.6.5.1 NDS-S Tables 5A, 5A–Expanded, and 5B 127
3.6.6 Failure of glulam structures 128
3.7 Allowable stress and LRFD adjusted stress calculation examples 128
3.8 ASD load combinations and the governing load duration factor 129
3.8.1 Normalized load method—ASD method only 129
Problems 146
References 148
4 Design and analysis of beams and girders 151
4.1 Design of joists, beams, and girders 151
4.1.1 Definition of beam span 151
4.1.2 Layout of joists, beams, and girders 151
