00 Design of Wood Structures - Thiết kế công trình gỗ

A area in.2, ft2 a acceleration ft/s2 a length of end zone for wind pressure calculations Ag gross cross-sectional area of a tension or compression member in.2 Agroup-net net cross-secti

Design of Wood Structures—ASD/LRFD

Donald E Breyer, P.E.

Professor Emeritus Department of Engineering Technology California State Polytechnic University

Pomona, California Kenneth J Fridley, Ph.D.

Professor and Head Department of Civil, Construction, and Environmental Engineering

University of Alabama Tuscaloosa, Alabama

Kelly E Cobeen, S.E.

Principal Cobeen & Associates Structural Engineering

Lafayette, California David G Pollock, Ph.D., P.E.

Associate Professor Department of Civil and Environmental Engineering

Washington State University Pullman, Washington

Sixth Edition

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Information contained in this work has been obtained by The McGraw-Hill Companies, Inc (“McGraw-Hill”) fromsources believed to be reliable However, neither McGraw-Hill nor its authors guarantee the accuracy or completeness ofany information published herein and neither McGraw-Hill nor its authors shall be responsible for any errors, omissions,

or damages arising out of use of this information This work is published with the understanding that McGraw-Hill and itsauthors are supplying information but are not attempting to render engineering or other professional services If suchservices are required, the assistance of an appropriate professional should be sought

2.11 Wind Forces—Main Wind Force Resisting System 2.28

2.15 Seismic Forces—Primary System 2.61

2.16 Seismic Forces—Wall Components 2.68

3.4 Lateral Forces in Buildings with Diaphragms and Shearwalls 3.12 3.5 Design Problem: Lateral Forces on One-Story Building 3.18 3.6 Design Problem: Lateral Forces on Two-Story Building 3.33

4.8 Effect of Moisture Content on Lumber Sizes 4.20 4.9 Durability of Wood and the Need for Pressure Treatment 4.21

4.21 Incising Factor Ci 4.48

5.3 Resawn Glulam 5.4

6.10 Design Problem: Rough-Sawn Beam Using ASD 6.54

6.13 Design Problem: Glulam Beam with Full Lateral Support 6.62 6.14 Design Problem: Glulam Beam with Lateral Support at 8 ft-0 in 6.68 6.15 Design Problem: Glulam Beam with Lateral Support at 48 ft-0

7.3 Design Problem: Tension Member 7.7

7.7 Design Problem: Capacity of a Glulam Column 7.30 7.8 Design Problem: Capacity of a Bearing Wall 7.36

7.11 Design Problem: Combined Bending and Tension 7.47

7.14 Design Problem: Beam-Column Action in a Stud Wall Using LRFD

7.64 7.15 Design Problem: Glulam Beam-Column Using ASD 7.73

7.17 Design Problem: Column with Eccentric Load Using ASD 7.81

8.14 Stress Calculations for Wood Structural Panels 8.36

9.6 Distribution of Lateral Forces in a Shearwall 9.28

10.1 Introduction 10.1

11.3 Yield Model for Laterally Loaded Fasteners 11.7 11.4 Factors Affecting Strength in Yield Model 11.10

12.6 Adjustment Factors for Laterally Loaded Nails 12.22 12.7 Design Problem: Nail Connection for Knee Brace 12.29

12.10 Design Problem: Laterally Loaded Toenail 12.46 12.11 Design Problem: Laterally Loaded Connection in End Grain 12.50

13.3 Bolt Yield Limit Equations for Single Shear 13.5 13.4 Bolt Yield Limit Equations for Double Shear 13.14

13.6 Tension and Shear Stresses at a Multiple Fastener Connection 13.30 13.7 Design Problem: Multiple-Bolt Tension Connection 13.34 13.8 Design Problem: Bolted Chord Splice for Diaphragm 13.40 13.9 Shear Stresses in a Beam at a Connection 13.47 13.10 Design Problem: Bolt Connection for Diagonal Brace 13.49

13.13 Adjustment Factors for Lag Bolts in Shear Connections 13.62 13.14 Design Problem: Collector (Strut) Splice with Lag Bolts 13.67

14.3 Design Problem: Beam-to-Column Connection 14.19

16.8 Lateral Analysis of Nonrectangular Buildings 16.29

The purpose of this book is to introduce engineers, technologists, and architects to the design of woodstructures It is designed to serve either as a text for a course in timber design or as a reference for systematicself-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 teachingtimber design at the undergraduate and graduate levels

This text pulls together the design of the various elements into a single reference A large number ofpractical design examples are provided throughout the text Because of their widespread usage, buildingsnaturally form the basis of the majority of these examples However, the principles of member design anddiaphragm 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 includespublications of the American Forest and Paper Association (AF&PA), the International Codes Council (ICC),the American Society of Civil Engineers (ASCE), APA—The Engineered Wood Association, and theAmerican 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 referencedocuments The interpretations are those of the authors and are intended to reflect current structural designpractice The material presented is suggested as a guide only, and final design responsibility, lies with thestructural engineer

The sixth edition of this book was promoted by five major developments:

1 Publication of new dual-format (ASD/LRFD) wood design criteria in the 2005 National Design

Specification for Wood Construction (NDS).

2 Publication of the new Special Design Provisions for Wind and Seismic (SDPWS) Supplement to the

NDS

3 Publication of the comprehensive ASD/LRFD Manual for Engineered Wood Construction.

4 Publication and increased adoption nationally of the 2006 International Building Code.

5 Publication of updated load standards in the 2005 edition of Minimum Design Loads for Buildings and

Other Structures (ASCE 7-05).

The National Design Specification (NDS) is published by the American Forest & Paper Association

(AF&PA) and represents the latest structural design recommendations by the wood industry The 2005 NDSpresents both traditional allowable stress design (ASD) provisions as well as new load and resistance factordesign (LRFD) provisions The inclusion of the LRFD provisions is new to the NDS for the 2005 edition Assuch, the 2005 NDS is considered a dualformat 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 wooddesign is increasing

The 2006 ASD/LRFD Manual for Engineered Wood Construction includes design supplements, guidelines,

and manuals helpful for wood engineering design It includes design information for sawn lumber, structuralglued laminated timber, structural-use panels, shearwalls and diaphragms, poles and piles, I-joists, structuralcomposite lumber, structural connections (nails, bolts, screws), and pre-engineered metal connectors TheManual was first introduced in 1999 for the 1997 NDS, and has evolved into a comprehensive design supportdocument

The International Building Code (IBC) is a product of the International Codes Council (ICC) The ICC

brought together the three regional model building code organizations to develop and administer a singlenational building code The first edition of the IBC was published in 2000, and now nearly all regions of theU.S 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 Recently, 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 2005 edition of the NDS This sixth edition of Design of Wood Structures

presents both ASD and LRFD guidelines as provided in the NDS In many examples, both ASD and LRFDapproaches are presented to allow the reader a direct, side-by-side comparison of the two methods

If this book is used as a text for a formal course, an Instructor’s Manual is available Requests on schoolletterhead should be sent to: Civil Engineering Editor, McGraw-Hill Professional, 2 Penn Plaza, New York,

NY 10121-2298

Questions or comments about the text or examples may be addressed to any of the authors Direct anycorrespondence to:

Prof Emeritus Donald E Breyer

Department of Engineering Technology

California State Polytechnic University

3801 West Temple Avenue

Pomona, CA 91768

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 Civil and Environmental Engineering

Washington State University

P.O Box 642910

Pullman, WA 99164-2910

Ms Kelly E Cobeen

Cobeen & Associates Structural Engineering

251 Lafayette Circle, Suite 230

Lafayette, CA 94549

Acknowledgment and appreciation for help in writing this text are given to Philip Line and BradfordDouglas of the American Forest and Paper Association; Jeff Linville of the American Institute of TimberConstruction; John Rose, Thomas Skaggs, and Thomas Williamson of APA—The Engineered WoodAssociation; and Kevin Cheung of the Western Wood Products Association Numerous other individuals alsodeserve recognition for their contributions to various editions of the text, including Rosdinah Baharin, Russell

W Krivchuk, William A Baker, Michael Caldwell, Thomas P Cunningham, Jr., Mike Drorbaugh, John R.Tissell, Ken Walters, B J Yeh, Thomas E Brassell, Frank Stewart, Lisa Johnson, Edwin G Zacher, Edward

F Diekmann, Lawrence A Soltis, Robert Falk, Don Wood, William R Bloom, Frederick C Pneuman, Robert

M Powell, Sherm Nelson, Bill McAlpine, Karen Colonias, and Ronald L Carlyle Suggestions andinformation were obtained from many other engineers and suppliers, and their help is gratefully recognized

Dedication

To our families:

Matthew, Kerry, Daniel, and Sarah

Paula, Justin, Connor, and Alison

Chris and Matthew

Lynn, Sarah, and Will

Donald E Breyer, P.E Kenneth J Fridley, Ph.D Kelly E Cobeen, S.E David G Pollock, Ph.D., P.E.

Organizations

AF&PA

American Forest and Paper Association

American Wood Council (AWC)

American Institute of Timber Construction

7012 South Revere Parkway, Suite 140

American Society of Civil Engineers

1801 Alexander Bell Drive

Reston, VA 20191

www.asce.org

ATC

Applied Technology Council

201 Redwood Shores Parkway, Suite 240

Building Seismic Safety Council

National Institute of Building Sciences

1090 Vermont Avenue, N.W., Suite 700

CWC

Canadian Wood Council

99 Bank Street, Suite 400

Ottawa, Ontario, Canada K1P 6B9

www.cwc.ca

CPA–CWC

Composite Panel Association

Composite Wood Council

18922 Premiere Court

Gaithersburg, MD 20879-1574

301-670-0604

www.pbmdf.com

U.S Forest Products Laboratory

USDA Forest Service

One Gifford Pinchot Drive

International Staple, Nail and Tool Association

512 West Burlington Avenue, Suite 203

National Frame Builders Association

4840 West 15th Street, Suite 1000

National Lumber Grades Authority

#406 First Capital Place

Pacific Lumber Inspection Bureau

33442 First Way South, #300

Structural Board Association

25 Valleywood Drive, Unit 27

Markham, Ontario, Canada L3R 5L9

www.osbguide.com

Truss Plate Institute

218 N Lee Street, Suite 312

Western Red Cedar Lumber Association

1501-700 West Pender Street

Vancouver, British Columbia, Canada V6C 1G8

www.wrcla.org

WWPA

Western Wood Products Association

522 Southwest Fifth Avenue, Suite 500

Portland, OR 97204-2122

www.wwpa.org

WIJMA

Wood I-Joist Manufacturing Association

200 East Mallard Drive

Boise, ID 83706

www.i-joist.org

WTCA

Wood Truss Council of America

One WTCA Center

6300 Enterprise Lane

Madison, WI 53719

www.woodtruss.com

Publications

ASCE 7: American Society of Civil Engineers (ASCE) 2006 Minimum Design Loads for Buildings

and Other Structures (ASCE 7-05), ASCE, Reston, VA.

ASD/LRFD

Manual:

American Forest and Paper Association (AF&PA) 2006 ASD/LRFD Manual for

Engineered Wood Construction, 2005 ed., AF&PA, Washington, DC.

IBC: International Codes Council (ICC) 2006 International Building Code (IBC), 2006 ed.,

ICC, Falls Church, VA

NDS: American Forest and Paper Association (AF&PA) 2005 National Design Specification (NDS) for Wood Construction, ANSI/AF&PA NDS-2005, AF&PA, Washington, DC SDPWS: American Forest & Paper Association (AF&PA) 2005 Special Design Provisions for

Wind and Seismic (SDPWS) Supplement to the NDS, AF&PA, Washington, DC.

TCM: American Institute of Timber Construction (AITC) 2005 Timber Construction Manual, 5th

ed., John Wiley & Sons Inc., Hoboken, NJ

Additional publications given at the end of each chapter

Units

ft2 square foot, square feet

in inch, inches

in.2 square inch, square inches

k 1000 lb (kip, kilopound)ksi kips per square inch (k/in.2)mph miles per hour

pcf pounds per cubic foot (lb/ft3)plf pounds per lineal foot (lb/ft)psf pounds per square foot (lb/ft2)psi pounds per square inch (lb/in.2)

Adj adjusted

Allow allowable

ASD allowable stress design

B&S Beams and Stringers

c.-to-c center to center

FSP fiber saturation point

glulam structural glued laminated timber

IP inflection point (point of reverse curvature and point of zero moment

J&P Joists and Planks

MC moisture content based on oven-dry weight of wood

MDO medium density overlay (plywood)

MEL machine evaluated lumber

P&T Posts and Timbers

PSL parallel strand lumber

Q/A quality assurance

Req’d required

RM resisting moment

S4S dressed lumber (surfaced four sides)Sel Str Select Structural

SCL structural composite lumber

SJ&P Structural Joists and Planks

SLF Structural Light Framing

Tab tabulated

T&G tongue and groove

TL total load (lb, k, lb/ft, k/ft, psf)trib tributary

TS top of sheathing

WSD working stress design

A area (in.2, ft2)

a acceleration (ft/s2)

a length of end zone for wind pressure calculations

Ag gross cross-sectional area of a tension or compression member (in.2)

Agroup-net net cross-sectional area between outer rows of fasteners for a wood tension member (in.2)

A h projected area of hole caused by drilling or routing to accommodate bolts or other fasteners at net

section (in.2)

A m gross cross sectional area of main member (in.2)

A n cross-sectional area of member at a notch (in.2)

A n net cross-sectional area of a tension or compression member at a connection (in.2)

a p in-structure component amplification factor

A s area of reinforcing steel (in.2)

A s sum of gross cross-sectional areas of side member(s) (in.2)

A T tributary area for a structural member or connection (ft2)

Aweb cross-sectional area of the web of a steel W-shaped beam or wood I joist (in.2)

A x diaphragm area immediately above the story being considered (ft2)

b length of shearwall parallel to lateral force; distance between chords of shearwall (ft)

b width of horizontal diaphragm; distance between chords of horizontal diaphragm (ft)

b width of rectangular beam cross section (in.)

C compression force (lb, k)

c buckling and crushing interaction factor for columns

c distance between neutral axis and extreme fiber (in., ft)

C b bearing area factor

C D load duration factor (ASD only)

C d seismic deflection amplification factor

C di diaphragm factor for nail connections

C e exposure factor for snow load

C eg end grain factor for connections

C F size factor

C fu flat use factor for bending design values

C G grade and construction factor for wood structural panels

C g group action factor for multiple-fastener connections with D  1/4 in

C i incising factor for Dimension lumber

C L beam stability factor

C M wet service factor

C P column stability factor

C r repetitive-member factor for bending design values

C s roof slope factor for snow load

C s seismic response coefficient

C s panel size factor for wood structural panels

C st metal side plate factor for 4-in shear plate connections

C T buckling stiffness factor for 2 × 4 and smaller Dimension lumber in trusses

C t seismic coefficient depending on type of LFRS used to calculate period of vibration T

C t temperature factor

C t thermal factor for snow load

C tn toenail factor for nail connections

C V volume factor

C vx seismic vertical distribution factor

C geometry factor for connections with fastener D  1/4 in

D dead load (lb, k, lb/ft, k/ft, psf)

D diameter (in.)

d cross-sectional dimension of rectangular column associated with axis of column buckling (in.)

d depth of rectangular beam cross section (in.)

d dimension of wood member for shrinkage calculation (in.)

d pennyweight of nail or spike

d1 shank diameter of lag bolt (in.)

d2 pilot hole diameter for the threader portion of lag bolt (in.)

d e effective depth of member at a connection (in.)

d n effective depth of member remaining at a notch (in.)

d x width of rectangular column parallel to y axis, used to calculate column slenderness ratio about x

axis

d y width of rectangular column parallel to x axis, used to calculate column slenderness ratio about y

axis

E earthquake force (lb, k)

E length of tapered tip of lag bolt (in.)

E, E reference and adjusted modulus of elasticity (psi, ksi)

e eccentricity (in., ft)

Eaxial modulus of elasticity of glulam for axial deformation calculation (psi)

E m modulus of elasticity of main member (psi)

Emin,

Emin

reference and adjusted modulus of elasticity for ASD stability calculations (psi)

E min-n,

E min-n

nominal and adjusted modulus of elasticity for LRFD stability calculations (ksi)

E s modulus of elasticity of side member (psi)

E x modulus of elasticity about x axis (psi, ksi)

E y modulus of elasticity about y axis (psi, ksi)

EA, EA reference and adjusted axial stiffness design value for structural panels (lb/ft width, k/ft width)

EI, EI reference and adjusted bending stiffness design value for structural panels (lb-in2/ft width,

k-in2/ft width)

F fluid load (lb, k, plf, klf, psf)

F force or load (lb, k)

F roof slope in inches of rise per foot of horizontal span

f1 live load coefficient for special seismic load combinations

f1 live load coefficient in LRFD load combinations when other transient loads are dominant

f2 snow load coefficient in LRFD load combinations for various roof configurations

Fa flood load (lb, k, plf, klf, psf)

F a acceleration-based seismic site coefficient at 0.3 second period

f b actual (computed) bending stress (psi)

F b reference and adjusted ASD bending design value (psi)

F b reference ASD bending design value multiplied by all applicable adjustment factors except C L,

C V , and C fu (psi)

F b** reference ASD bending design value multiplied by all applicable adjustment factors except C V

(psi)

F bE critical ASD buckling (Euler) value for bending member (psi)

F bn , F bn nominal and adjusted LRFD bending design value (ksi)

F bn* nominal LRFD bending design value multiplied by all applicable adjustment factors except C L,

C V , and C fu (ksi)

F bn** nominal LRFD bending design value multiplied by all applicable adjustment factors except C V

(ksi)

F bEn nominal LRFD buckling (Euler) value for bending member (ksi)

f bx actual (computed) bending stress about the x-axis (psi)

F bx , F bx reference and adjusted ASD bending design value about the x-axis (psi)

F bxn , F bxn nominal and adjusted LRFD bending design value about the x-axis (ksi)

f by actual (computed) bending stress about the y-axis (psi)

F by , F by reference and adjusted ASD bending design value about the y-axis (psi)

F byn , F byn nominal and adjusted LRFD bending design value about the y-axis (ksi)

F c out-of-plane seismic forces for concrete and masonry walls (lb, k, plf, klf)

f c actual (computed) compression stress parallel to grain (psi)

F c , F c reference and adjusted ASD compression design value parallel to grain (psi)

reference ASD compression design value parallel to grain multiplied by all applicable

adjustment factors except C P (psi)

F cE critical ASD buckling (Euler) value for compression member (psi)

F cn, nominal and adjusted LRFD compression design value parallel to grain (ksi)

nominal LRFD compression design value parallel to grain multiplied by all applicable adjustment

factors except C P (ksi)

F cEn nominal LRFD buckling (Euler) value for compression member (ksi)

actual (computed) compression stress perpendicular to grain (psi)

, reference and adjusted ASD compression design value perpendicular to grain (psi)

reduced ASD compression design value perpendicular to grain at a deformation limit of 0.02 in.(psi)

, nominal and adjusted LRFD compression design value perpendicular to grain (ksi)

F e dowel bearing strength (psi)

dowel bearing strength parallel to grain for fasteners with D  1/4 in (psi)

dowel bearing strength perpendicular to grain for fasteners with D  1/4 in (psi)

F e dowel bearing strength at angle to grain  for fasteners with D  1/4 in (psi)

F em dowel bearing strength for main member (psi)

F es dowel bearing strength for side member (psi)

F p seismic force on a component of a structure (lb, k, plf, klf)

F px seismic story force at level x for designing the horizontal diaphragm (lb, k)

F adjusted ASD bearing design value at angle to grain  (psi)

F n adjusted LRFD bearing design value at angle to grain  (ksi)

f s stress in reinforcing steel (psi, ksi)

f t actual (computed) tension stress in a member parallel to grain (psi)

F t, reference and adjusted ASD tension design value parallel to grain (psi)

F tn , F tn nominal and adjusted LRFD tension design value parallel to grain (ksi)

F u ultimate tensile strength for steel (psi, ksi)

F v velocity-based seismic site coefficient at 1.0 second period

f v actual (computed) shear stress parallel to grain (horizontal shear) in a beam using full

design loads (psi)

F v , F v reference and adjusted ASD shear design value parallel to grain (horizontal shear) in a

beam (psi)

F vn , F vn nominal and adjusted LRFD shear design value parallel to grain (horizontal shear) in a

beam (ksi)actual (computed) shear stress parallel to grain (horizontal shear) in a beam obtained by

neglecting the loads within a distance d of face of support (psi)

F x seismic story force at level x for designing vertical elements (shearwalls) in LFRS (lb, k)

F y yield strength (psi, ksi)

F yb bending yield strength of fastener (psi, ksi)

F b S, F b S reference and adjusted ASD bending strength design value for structural panels (lb-in./ft

reference and adjusted ASD in-plane shear design value for structural panels (lb/ft width)

(F s Ib/Q) n, nominal and adjusted LRFD in-plane shear design value for structural panels (k/ft width)

F v t v , F v t v’ reference and adjusted ASD shear through the thickness design value for structural panels

(lb/in of shear-resisting panel length)

(F v t v)n, nominal and adjusted LRFD shear through the thickness design value for structural panels

(k/in of shear-resisting panel length)

G specific gravity of wood or a wood-based member

g acceleration of gravity (ft/s2)

G m specific gravity of main member

G s specific gravity of side member

G v t v, reference and adjusted shear rigidity through the thickness design value for structural

panels (lb/in of panel depth, k/in of panel depth)

H soil, hydrostatic pressure, or bulk material load (lb, k, plf, klf, psf)

h building height or height of wind pressure zone (ft)

h height of shearwall (ft)

h i , h x height above base to level i or level x (ft)

hmean mean roof height above ground (ft)

h n height above base to nth or uppermost level in building (ft)

h x the elevation at which a component is attached to a structure relative to grade, for design of portions

of structures (ft)

I moment of inertia (in.4)

I importance factor for seismic, snow or wind load

I p seismic component importance factor

K Code multiplier for dead load for use in beam deflection calculations to account for creep effects

k exponent for vertical distribution of seismic forces related to the building period

K D diameter coefficient for connections with fastener D < 1/4 in

K e effective length factor for column end conditions (buckling length coefficient for columns)

K F format conversion factor (LRFD only)

K f column stability coefficient for bolted and nailed built-up columns

KLL live load element factor for influence area

K  angle to grain coefficient for connections with fastener D  1/4 in

K zt topographical factor for wind pressure calculations

L live load (lb, k, lb/ft, k/ft, psf)

L beam span length (ft)

L length (ft)

l length (in.)

l length of bolt in main or side members (in.)

l length of fastener (in.)

l unbraced length of column (in.)

L0 unreduced floor or roof live load (lb, k, plf, klf, psf)

l/D bolt slenderness ratio

l b bearing length (in.)

L c cantilever length in cantilever beam system (ft)

l e effective unbraced length of column (in.)

l e /d slenderness ratio of column

(l e /d) x slenderness ratio of column for buckling about strong (x) axis

(l e /d) y slenderness ratio of column for buckling about weak (y) axis

l e effective unbraced length of compression edge of beam (in.)

l m dowel bearing length of fastener in main member (in.)

Lr roof live load (lb, k, lb/ft, k/ft, psf)

l s dowel bearing length of fastener in side member(s) (in.)

l u laterally unbraced length of compression edge of beam (in.)

l x unbraced length of column considering buckling about strong (x) axis (in.)

l y unbraced length of column considering buckling about weak (y) axis (in.)

M bending moment (in.-lb, in.-k, ft-lb, ft-k)

adjusted LRFD moment resistance (in.-k, ft-k)

M p plastic moment capacity (in.-lb, in.-k)

M u ultimate (factored) bending moment (in.-lb, in.-k, ft-lb, ft-k)

M y yield moment (in.-lb, in.-k)

N normal reaction (lb, k)

N number of fasteners in connection

N, N reference and adjusted ASD lateral design value at angle to grain  for a single split ring or shear

plate connector (lb)

n number of fasteners in row

n number of stories (seismic forces)

N n,

N n

nominal and adjusted LRFD lateral design value at angle to grain  for a single split ring or shearplate connector (k)

nrow number of rows of fasteners in a fastener group

P concentrated load or force (lb, k)

P, P reference and adjusted ASD lateral design value parallel to grain for a single split ring or shear plate

connector (lb)

p parallel-to-grain component of lateral force z on one fastener

p penetration depth of fastener in wood member (in.)

p f flat roof snow load (psf)

p g ground snow load (psf)

P n , P n nominal and adjusted LRFD lateral design value parallel to grain for a single split ring or shear plate

connector (k)

P n adjusted LRFD axial compression resistance (k)

pnet net design wind pressure for components and cladding (psf)

pnet30 net design wind pressure for components and cladding at a height of 30 ft in Exposure B conditions

(psf)

p s sloping roof snow load (psf)

p s simplified design wind pressure for main wind force-resisting systems (psf)

p s30 simplified design wind pressure for main wind force-resisting systems at a height of 30 ft in Exposure

B conditions (psf)

P u collapse load (ultimate load capacity)

P u ultimate (factored) concentrated load or force (lb, k)

Q static moment of an area about the neutral axis (in.3)

Q, Q reference and adjusted ASD lateral design value perpendicular to grain for a single split ring or shear

plate connector (lb)

q perpendicular-to-grain component of lateral force z on one fastener

QE effect of horizontal seismic forces (lb, k)

R seismic response modification factor

r radius of gyration (in.)

R 1 roof live load reduction factor for large tributary roof areas

R1 seismic force generated by mass of wall that is parallel to earthquake force being considered

R 2 roof live load reduction factor for sloped roofs

R B slenderness ratio of laterally unbraced beam

r i portion of story force resisted by a shearwall element

R p seismic response modification factor for a portion of a structure

R u ultimate (factored) reaction force (lb, k)

R u1 ultimate (factored) seismic force generated by mass of wall that is parallel to earthquake force being

considered (lb, k)

S snow load (lb, k, plf, klf, psf)

S section modulus (in.3)

S shrinkage of wood member (in.)

s center-to-center spacing between adjacent fasteners in a row (in.)

S length of unthreaded shank of lag bolt (in.)

S 1 mapped maximum considered earthquake spectral acceleration at 1 one-second period (g)

s crit critical spacing between fasteners in a row (in.)

SD1 design spectral response acceleration at a one-second period (g)

SDS design spectral response acceleration at short periods (g)

SMS maximum considered earthquake spectral response acceleration at short periods (g)

SM1 maximum considered earthquake spectral response acceleration at a one-second period (g)

SS mapped maximum considered earthquake spectral acceleration at short periods (g)

SV shrinkage value for wood due to 1 percent change in moisture content (in./in.)

t m thickness of main member (in.)

T n adjusted LRFD tension resistance (k)

T0 response spectrum period at which the SDS plateau is reached (sec)

T S response spectrum period at which the SDS and SD1/T curves meet (sec)

t s thickness of side member (in.)

T u ultimate (factored) tension force (lb, k)

twasher thickness of washer (in.)

U wind uplift resultant force (lb, k)

V basic wind speed (mph)

V seismic base shear (lb, k)

V shear force in a beam, diaphragm, or shearwall (lb, k)

v unit shear in diaphragm or shearwall (lb/ft)

V* reduced shear in beam determined by neglecting load within d from face of supports (lb, k)

v2 unit shear in second-floor diaphragm (lb/ft)

v12 unit shear in shearwall between first- and second-floor levels (lb/ft)

v 2r unit shear in shearwall between second-floor and roof levels (lb/ft)

V n adjusted LRFD shear resistance parallel to grain in a beam (k)

V px diaphragm forces created by the redistribution of forces between vertical elements

v r unit shear in roof diaphragm (lb/ft)

Vstory story shear force (lb, k)

V u ultimate (factored) shear force in a beam, diaphragm, or shearwall (lb, k)

v u ultimate (factored) unit shear in horizontal diaphragm or shearwall (lb/ft)

V u * reduced ultimate (factored) shear in beam determined by neglecting load within d from face of

supports (lb, k)

v u2 ultimate (factored) unit shear in second-floor diaphragm (lb/ft)

v u12 ultimate (factored) unit shear in shearwall between first- and second-floor levels (lb/ft)

v u2r ultimate (factored) unit shear in shearwall between second-floor and roof levels (lb/ft)

v ur ultimate (factored) unit shear in roof diaphragm (lb/ft)

Vwall wall shear force in the wall with the highest unit shear (lb, k)

W lateral force due to wind (lb, k, lb/ft, psf)

W weight of structure or total seismic dead load (lb, k)

w reference withdrawal design value for single fastener (lb/in of penetration)

w uniformly distributed load or force (lb/ft, k/ft, psf, ksf)

W, W reference and adjusted ASD withdrawal design value for single fastener (lb)

W1 dead load of 1-ft-wide strip tributary to story level in direction of seismic force (lb/ft, k/ft)

W2 total dead load tributary to second-floor level (lb, k)

W 2 that portion of W2 which generates seismic forces in second-floor diaphragm (lb, k)

w2 uniform load to second-floor diaphragm (lb/ft, k/ft)

W D dead load of structure (lb, k)

Wfoot dead load of footing or foundation (lb, k)

w i , w x tributary weight assigned to story level i or level x (lb, k)

W n,

W n

nominal and adjusted LRFD withdrawal design value for single fastener (lb, k)

W p weight of portion of structure (element or component) (lb, k, lb/ft, k/ft, psf)

w px uniform load to diaphragm at level x (lb/ft, k/ft)

W r total dead load tributary to roof level (lb, k)

w r uniform load to roof diaphragm (lb/ft, k/ft)

W r that portion of W r which generates seismic forces in roof diaphragm (lb, k)

w u ultimate (factored) uniformly distributed load or force (lb/ft, k/ft, psf, ksf)

w u2 ultimate (factored) uniform load to second-floor diaphragm (lb/ft, k/ft)

w upx ultimate (factored) uniform load to diaphragm at level x (lb/ft, k/ft)

w ur ultimate (factored) uniform load to roof diaphragm (lb/ft, k/ft)

x exponent dependent on structure type used in calculation of the approximate fundamental period

x width of triangular soil bearing pressure diagram (ft)

Z plastic section modulus (in.3)

z lateral force on one fastener in wood connection (lb)

Z, Z reference and adjusted ASD lateral design value for single fastener in a connection (lb)

Z adjusted resultant design value for lag bolt subjected to combined lateral and withdrawal loading

(lb)

Z n , Z n nominal and adjusted LRFD lateral design value for single fastener in a connection (lb, k)

ZGT adjusted ASD connection capacity due to group tear-out failure in a wood member (lb)

ZNT adjusted ASD connection capacity due to net tension failure in a wood member (lb)

ZRT adjusted ASD connection capacity due to row tear-out failure in a wood member (lb)

Z nGT adjusted LRFD connection capacity due to group tear-out failure in a wood member (lb, k)

Z nNT adjusted LRFD connection capacity due to net tension failure in a wood member (lb, k)

Z nRT adjusted LRFD connection capacity due to row tear-out failure in a wood member (lb, k)

Z’RT-1 adjusted ASD row tear-out capacity for first row of fasteners in a fastener group (lb)

ZRT-2 adjusted ASD row tear-out capacity for second row of fasteners in a fastener group (lb)

ZRT-n adjusted ASD row tear-out capacity for nth row of fasteners in a fastener group (lb)

Z nRT-1 adjusted LRFD row tear-out capacity for first row of fasteners in a fastener group (lb, k)

Z nRT-2 adjusted LRFD row tear-out capacity for second row of fasteners in a fastener group (lb, k)

Z nRT-n adjusted LRFD row tear-out capacity for nth row of fasteners in a fastener group (lb, k)

reference lateral design value for single bolt or lag bolt in connection with all wood members loadedparallel to grain (lb)

reference lateral design value for single bolt or lag bolt in wood-to-metal connection with woodmember(s) loaded perpendicular to grain (lb)

reference lateral design value for single bolt or lag bolt in wood-to-wood connection with mainmember loaded perpendicular to grain and side member loaded parallel to grain (lb)

reference lateral design value for single bolt or lag bolt in wood-to-wood connection with mainmember loaded parallel to grain and side member loaded perpendicular to grain (lb)

 deflection (in.)

 design story drift (amplified) at center of mass, x x 1 (in.)

a anchor slip contribution to shearwall deflection (in.)

b bending contribution to shearwall deflection (in.)

D deflection of diaphragm

MC change in moisture contend of wood member (percent)

n nail slip contribution to shearwall deflection (in.)

s deflection of shearwall (in.)

v sheathing shear deformation contribution to shearwall deflection (in.)

x amplified deflection at level x, determined at the center of mass at and above level x (in.)

 xe deflection at level x, determined at the center of mass at and above level x using elastic analysis (in.)

resistance factor (LRFD only)

resistance factor for bending (LRFD only)

resistance factor for compression (LRFD only)

resistance factor for stability (LRFD only)

resistance factor for tension (LRFD only)

resistance factor for shear (LRFD only)

resistance factor for connections (LRFD only)

 load/slip modulus for a connection (lb/in.)

 height and exposure factor for wind pressure calculations

 time effect factor (LRFD only)

 coefficient of static friction

 redundancy/reliability factor for seismic design

 angle between direction of load and direction of grain (longitudinal axis of member) (degrees)

 m angle of load to grain  for main member (degrees)

 s angle of load to grain  for side member (degrees)

o overstrength factor for seismic design

struc-The widespread use of wood in the construction of buildings has both an nomic and an aesthetic basis The ability to construct wood buildings with a min-imal amount of specialized equipment has kept the cost of wood-frame buildingscompetitive with other types of construction On the other hand, where archi-tectural considerations are important, the beauty and the warmth of exposedwood are difficult to match with other materials.

eco-Wood-frame construction has evolved from a method used in primitive ters into a major field of structural design However, in comparison with the timedevoted to steel and reinforced concrete design, timber design is not given suf-ficient attention in most colleges and universities

shel-This book is designed to introduce the subject of timber design as applied towood-frame building construction Although the discussion centers on buildingdesign, the concepts also apply to the design of other types of wood-frame struc-tures Final responsibility for the design of a building rests with the structuralengineer However, this book is written to introduce the subject to a broad audi-ence This includes engineers, engineering technologists, architects, and othersconcerned with building design A background in statics and strength of mate-rials is required to adequately follow the text Most wood-frame buildings arehighly redundant structures, but for design simplicity are assumed to be made

up of statically determinate members The ability to analyze simple trusses,beams, and frames is also necessary

1.2 Types of Buildings

There are various types of framing systems that can be used in wood buildings.The most common type of wood-frame construction uses a system of horizontaldiaphragms and vertical shearwalls to resist lateral forces, and this book dealsspecifically with the design of this basic type of building At one time building

codes classified a shearwall building as a box system, which was a good physical

description of the way in which the structure resists lateral forces However,building codes have dropped this terminology, and most wood-frame shearwall

buildings are now classified as bearing wall systems The distinction between the

shearwall and diaphragm system and other systems is explained in Chap 3.Other types of wood building systems, such as glulam arches and post-frame(or pole) buildings, are beyond the specific scope of this book It is felt that thedesigner should first have a firm understanding of the behavior of basic shear-wall buildings and the design procedures that are applied to them With a back-ground of this nature, the designer can acquire from currently available sources(e.g., Refs 1.4 and 1.10) the design techniques for other systems

The basic bearing wall system can be constructed entirely from wood

compo-nents See Fig 1.1 Here the roof, floors, and walls use wood framing The

cal-culations necessary to design these structural elements are illustratedthroughout the text in comprehensive examples

In addition to buildings that use only wood components, other common types

of construction make use of wood components in combination with some othertype or types of structural material Perhaps the most common mix of structural

materials is in buildings that use wood roof and floor systems and concrete

tilt-up or masonry (concrete block or brick) shearwalls See Fig 1.2 This type of

construction is common, especially in one-story commercial and industrialbuildings This construction is economical for small buildings, but its economyimproves as the size of the building increases Trained crews can erect large

areas of panelized roof systems in short periods of time See Fig 1.3.

Design procedures for the wood components used in buildings with concrete

or masonry walls are also illustrated throughout this book The connectionsbetween wood and concrete or masonry elements are particularly important andare treated in considerable detail

This book covers the complete design of wood-frame box-type buildings from the roof level down to the foundation In a complete building design, vertical

loads and lateral forces must be considered, and the design procedures for both

are covered in detail

Wind and seismic (earthquake) are the two lateral forces that are normallytaken into account in the design of a building In recent years, design for lat-eral forces has become a significant portion of the design effort The reason forthis is an increased awareness of the effects of lateral forces In addition, thebuilding codes have substantially revised the design requirements for both windand seismic forces These changes are the result of extensive research in windengineering and earthquake-resistant design

1.2 Chapter One