Wood Handbook - Wood as Engineering Material

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i-I

I

Wood Handbook Wood as an Engineering Material

The use oftrade or firm namesis for information only and does not imply endorsement by the U.S. Department ofAgriculture or the ForestProducts Society of any product or service. This publication reportsresearch involvingpesticides.It does not containrecommendations for their use, nor does it implythat the uses discussed herehave beenregistered. All uses of pesticides must be registered by appropriate Stateand/orFederal agencies beforethey can be recommended.

Reprintedfrom ForestProductsLaboratory General Technical ReportFPL-GTR-1 13 with the consentof the USDAForestService, ForestProductsLaboratory. Printedin 1999 by the ForestProductsSociety. ISBN 1-892529-02-5 Printedin the UnitedStatesofAmerica FPS catalogueno. 7269 99045000

Cover photo courtesy of the Southern Forest ProductsAssociation.

Conteiits 5

Preface v

HardwoodLumber 5—1 SoftwoodLumber 5—7 Purchase ofLumber 5—12 CommonlyUsed LumberAbbreviations 5—18

Acknowledgments vii Contributors xi

References

Characteristicsand Availability of Commercially ImportantWood Timber Resourcesand Uses SpeciesDescriptions 1—3 U.S. Wood Species 1—3 Imported Woods 1—17 References

2

Structure

Grading

2—1

7

3—7

References

4

8

Structural AnalysisEquations Deformation Equations 8—i Stress Equations 8—4 Stability Equations 8—8 References

8—11

3—23

9

Mechanical Properties of Wood

OrthotropicNatureofWood 4—1 Elastic Properties 4—2 Strength Properties 4—3

VibrationProperties

4—25

Mechanical Properties ofClearStraight-Grained

Wood

7—8

Connector Joints 7—18 Multiple-Fastener Joints 7—24 Metal Plate Connectors 7—25 Fastener Head Embedment 7—26 References 7—27

3—1

Weight,Density,and SpecificGravity 3—11 WorkingQualities 3—15 DecayResistance 3—15 Thennal Properties 3—15 ElectricalProperties 3—21 CoefficientofFriction 3—22 NuclearRadiation 3—23

Fastenings

Staples

MoistureContent 3—5 Shrinkage

6—14

Drift Bolts 7—9 WoodScrews 7—9 Lag Screws 7—il Bolts 7—14

and Moisture Relations

of Wood

6—2

Nails 7—2 Spikes 7—8

2—4

Appearance

Lumber StressGrades and Design Properties Responsibilities and Standards for Stress

References

Physical Properties

5—20

VisuallyGradedStructural Lumber 6—3 Machine-Graded Structural Lumber 6—'7 AdjustmentofProperties for DesignUs 6—il

ofWood

Bark, Wood, Branches,and Cambium Sapwoodand Heartwood 2—2 Growth Rings 2—2 Wood Cells 2—3 ChemicalComposition 2—3 SpeciesIdentification 2-4

3

6

1—2

1—34

References

Commercial Lumber

4—26

Natural Characteristics Affecting Mechanical

Adhesive Bonding ofWood Materials

Adhesionto Wood 9—1 Surface Properties ofWoodAdherends 9—2 Physical Properties ofWoodAdherend 9—6 Adhesives

9—9

BondingProcess 9—15 Bonded Joints 9—18 Testingand Performance References

9—20

9—23

Properties 4—27

Effects ofManufacturing and Service Environments 4—34 References 4—44

111

10

Wood-Based Composites and Panel Products

15

Scope 10—2 Types ofConventional Composite

Materials 10—3 AdhesiveConsiderations 10—3 Additives 10—4 GeneralManufacturing Issues 10—4 Standards for Wood—BasedPanels 10—4 Plywood 10—6 Particle and Fiber Composites 10—13 Wood—NonwoodComposites References 10—30

11

10—24

References

16

Glued Structural Members

StructuralCompositeLumber 11—1 Glulam 11—3 Glued MembersWith Lumberand Panels 11—12 Structural Sandwich Construction 11—16 References

12

17

18

13—13

14 Wood Preservation 14—12 Timberfor Treatment 14—17 Preservatives 14—19

Preparationof Applicationof Handlingand SeasoningofTimberAfter Treatment 14—24 Quality Assurancefor TreatedWood 14—25

iv

14—26

18—1

18—5

18—7

Specialty Treatments Plasticizing Wood 19—1 Modified Woods 19-4 Paper-Based PlasticLaminates References 19—14

14—2

Preservative Effectiveness 14—12 Effect ofSpecieson Penetration

References

Round Timbersand Ties Standards and Specifications MaterialRequirements 18—1

Availability 18—2 Form 18—3 Weight and Volume Durability 18-6

19

16—10

17—13

Strength Properties References 18—8

13—15

Wood Preservatives

16—9

Fire Safety FireSafetyDesignandEvaluation 17—1 FirePerformance Characteristics ofWood Flame-Retardant Treatments 17—12 References

1.3 Biodeteriorationof Wood

References

Use of Wood In Building and Bridges Light-Frame Buildings 16—1 Post-Frameand Pole Buildings 16-4 Log Buildings 16-6 Heavy Timber Buildings 16-6 Considerations for Wood Buildings References 16—14

12—20

Fungus Damageand Control 13—1 Bacteria 13—8 Insect Damageand Control 13—8 MarineBorerDamage and Control

15—36

TimberBridges

11—21

Drying and Controlof Moisture Content and Dimensional Changes DeterminationofMoisture Content• 12—1 RecommendedMoistureContent 12—3 Drying ofWood 12—5 Moisture ControlDuring Transit and Storage 12—14 DimensionalChangesin Wood 12—15 DesignFactorsAffectingDimensional Change 12—18 Wood Careand InstallationDuring Construction 12—18 References

Finishing of Wood FactorsAffecting Finish Performance 15—1 Control ofWater or Moisturein Wood 5--9 Types ofExteriorWood Finishes 15—14 Application ofWood Finishes 15—19 Finish Failure or Discoloration 15—24 Finishingof InteriorWood 15—30 Finishesfor Items Used for Food 15—32 Wood Cleaners and Brighteners 15—33 Paint Strippers 15—33 Lead-BasedPaint 15—35

Glossary

Index

1—1

G—1

19—12

17—6

Preface Efficientuseofour nation's timberresourceis a vital concern. Becausea majoruse ofwood in the UnitedStates is in construction, particularlyhousingconstruction, good practicein this endeavor can have a profound impact on the resource.This handbook is intendedas an aid to more efficientuse ofwood as a construction material. It providesengineers, architects, and otherswith a source ofinformation on the physicalandmechanical properties ofwood andhow these properties are affected by variations in the wood itself.Continuingresearchandevaluation techniques hold promisefor wider and more efficientutilization ofwood and for more advanced industrial, structural, and decorative uses. This handbookwas preparedby the Forest Products Laboratory (FPL),a unit ofthe researchorganizationofthe Forest Service, U.S. Department ofAgriculture.The Laboratory, established in 1910, is maintainedat Madison, Wisconsin, in cooperation with the UniversityofWisconsin.It was the first institution in the world to conductgeneralresearchon wood and its utilization.The accumulation of infonnationthat has resultedfrom its engineering and allied investigations ofwood and wood products over nine decades—along with knowledge ofeveryday construction practicesand problems—is the chiefbasis forthis handbook. The Wood Handbookwas first issued in 1935, and sI[ightly revised in 1939, as an unnumberedpublication.Further revisions in 1955, 1974, and 1987were publishedby theU.S. Department ofAgricultureas AgricultureHandbook No. 72. This current work is a complete revisionofthe 1987 edition. This revisionwas necessaryto reflectmore recentresearchaccomplishments and technological changes. The audienceforthe WoodHandbookis fairlybroad.Therefore, the coverage ofeach chapteris aimedat providing a general discussion ofthe topic,with references included for additional information. Past versions ofthe WoodHandbooktended to report only the findings and applications ofFPL research. Although the handbook is not intendedto be a state-of-the-art review,this approach would now leave significantgaps in some important areas. The currentedition has broadenedthe sources of information to provide bettercoverageofimportant topics. The organizationofthis version ofthe Wood Handbookis similarto previousones,with some modifications:

• Plywood(chapter 11 in thepreviousversion), insulation board,hardboard, medium-density fiberboard (part of chapter21 in thepreviousversion),and wood-based particle panelmaterials (chapter 22 in thepreviousversion) are now included in a new chapter on wood-basedcomposites and panelproducts. • Structural sandwichconstruction (chapter 12 inthepreviousversion) is now includedin thechapteron glued structural members.

• Moisture movementandthermal insulation in light-frame structures (chapter 20 in thepreviousversion) arenow part of a new chapter on use ofwood in buildingsand bridges. • Bentwood members(chapter

13 in the previousversion), modified woods, and paper-based laminates (chapter 23 in the previousversion)are now includedin a chapteron specialtytreatments.

Consistentwith movementby many U.S. standards agenciesand industry associations towarduse ofmetric units and nearuniversal implementation ofmetricusage in the international community, units ofmeasurement in this version ofthe hsndbook areprovidedprimarilyin metricunits, with customary inch—pound equivalents as secondary units. All conversions in i;his handbook to metricunits, including conversions ofempirically derived equations, are direct(or soft) conversions from previouslyderivedinch—pound values. At some futuretime, metricexpressions may needto be derived from a reevaluation

oforiginal research.

V

Page blank in original

cktww1égments We gratefully acknowledgethe extraordinary effortofthe following individuals in theirreview ofthe final draftofthis entirevolume.Theireffort has substantially enhancedthe clarity, consistency, and coverage ofthe Wood Handbook. Donald Bender WoodMaterials & Engineering Laboratory Washington StateUniversity Pullman,Washington

Thomas McLain Department ofForest Products Oregon StateUniversity Corvallis,Oregon

Arthur Brauner Forest Products Society Madison, Wisconsin

RussellMoody

Bradford Douglas American Forest & PaperAssociation Washington,DC

DavidGreen USDAForest Service, Forest ProductsLaboratory

Madison, Wisconsin Michael O'Halloran APA—The Engineered Wood Association Tacoma, Washington

ErwinSchaffer Sun City West, Arizona

Madison, Wisconsin

MichaelHunt

Department ofForestryand NaturalResources Purdue University West Lafayette, Indiana

Contributors to the Wood Handbookare indebtedto the following individuals and organizations for their early technical reviewofchapter manuscripts.

Terry Amburgey Forest Products Laboratory MississippiState University Mississippi State, Mississippi Jon Arno Troy, Minnesota B. Alan Bendtsen Madison, Wisconsin

A. WilliamBoehner Trus Joist MacMillan Boise, Idaho

R. MichaelCaldwell

AmericanInstitute ofTimber Construction Englewood,Colorado

Richard Caster Weyerhaeuser Company Tacoma, Washington

KevinCheung WesternWoodProductsAssociation Portland, Oregon

StephenClark Northeastern LumberManufacturers Association Cumberland Center, Maine

RichardCook NationalCasein Company Santa Ana,California William Crossman AtlantaWoodIndustries Savannah, Georgia

DonaldCarr NAHB—National Research Center UpperMarlboro, Maryland

vii

ThomasDaniels

Energy Products ofIdaho CoeurD'Alene, Idaho

DonaldDeVisser West Coast LumberInspectionBureau Portland,Oregon Bradford Douglas American Forest and PaperAssociation Washington,DC

Stan Elberg NationalOakFlooringManufacturers Association Memphis,Tennessee Paul Foehlich SouthernCypress Manufacturers Association Pittsburgh,Pennsylvania BarryGoodell Forest Products Laboratory UniversityofMaine Orono,Maine KevinHaile

JohnKressbach Gillette, New Jersey RobertKundrot NestleResins Corporation Springfield, Oregon Steven Lawser WoodComponent Manufacturers Association Marietta, Georgia

Phillip Line

American Forest & PaperAssociation Washington,DC Joseph Loferski Brooks ForestProductsCenter Blacksburg, Virginia

MapleFlooring Manufacturers Association Northbrook, Illinois

ThomasMcLain Department ofForest Products OregonStateUniversity Corvallis,Oregon

HP&VA

Reston, Virginia DanielHare The CompositePanel Association Gaithersburg, Maryland

R. Bruce Hoadley ForestiyDepartment UniversityofMassachusetts Amherst,Massachusetts

DavidMcLean Civil Engineering Department Washington State University Pullman, Washington RodneyMcPhee Canadian Wood Council Ottawa, Ontario, Canada

MichaelMilota Oregon StateUniversity

DavidHon

Corvallis, Oregon

ClemsonUniversity Clemson, South Carolina

JeffreyMorrell Department ofForest Products Oregon State University Corvallis, Oregon

Department ofForest Resources

Robert Hunt WesternWood ProductsAssociation Portland,Oregon

LisaJohnson SouthernPine InspectionBureau Pensacola, Florida

Tom Jones SouthernPine Inspection Bureau Pensacola, Florida

CharlesJourdain CaliforniaRedwoodAssociation Novato, California

VIII

National Hardwood LumberAssociation Memphis, Tennessee Darrel Nicholas

ForestProductsLaboratory MississippiStateUniversity Mississippi State, Mississippi Michael O'Halloran APA—The Engineered WoodAssociation Tacoma, Washington

Perry Peralta Department ofWoodandPaper Science North CarolinaState University

Raleigh,North Carolina

Ramsey Smith

Louisiana Forest ProductsLaboratory Baton Rouge,Louisiana

William Smith DavidPlackett ForintekCanadaCorporation Vancouver, British Columbia, Canada DavidPollock CivilEngineeringDepartment Washington State University Pullman, Washington RedwoodInspection Service Mill Valley, California Alan Ross

SUNY—ESF

WoodProductsEngineering Syracuse, New York Edward Starostovic PFS/TECOCorporations Madison, Wisconsin

LouisWagner American HardwoodAssociation Palatine, Illinois

Kop—CoatInc. Pittsburgh,Pennsylvania

Eugene Wengert Department ofForestry Universityof Wisconsin Madison, Wisconsin

Thomas Searles American LumberStandards Committee Germantown, Maryland

Michael Westfall

RedCedar Shingle& Handsplit ShakeBureau Bellevue, Washington

JamesShaw Weyerhaeuser Company Tacoma, Washington

Borjen Yeh APA—The Engineered WoodAssociation Tacoma, Washington

BradleyShelley West CoastLumberInspectionBureau Portland,Oregon

ix

Page blank in original

Coiitributors The following staff ofthe Forest ProductsLaboratory contributed to the writing,revision, and compilationofinformation contained inthe Wood Handbook.

MarkA. Dietenberger

Roger M. Rowell

Research General Engineer

Supervisory Research Chemist

David W. Green

William T. Simpson Research Forest Products Technologist

Supervisory Research General Engineer

David E. Kretschmann Research GeneralEngineer

Lawrence A. Soltis

RolandHernandez

Anton TenWolde

Research GeneralEngineer

Research Physicist

Terry L. Highley

Ronald W. Wolfe

Supervisory ResearchPlant Pathologist(retired)

Research General Engineer

Rebecca E. Ibach Chemist

Charles B. Vick Research Forest Products Technologist

Jen Y. Liu

Robert H. White Supervisory WoodScientist

Research General Engineer

Research General Engineer

Kent A. McDonald ResearchForest Products Technologist(retired)

R. Sam Williams

Regis B. Miller

Jerrold E. Winandy

Botanist

Research Forest Products Technologist

Russell C. Moody

John A. Youngquist

Supervisory Research GeneralEngineer(retired)

Supervisory ResearchChemist

Supervisory Research GeneralEngineer

xi

I

Chapter

.1(

I

Characteristics and Availability of Commercially Important Woods Regis B. Miller

hroughouthistory, the unique characteristic; and comparative abundance ofwood havemade ita naturalmaterial forhomesand other structures, furniture,tools,vehicles,and decorative objects. Today, for the same reasons,wood is prized fora multitudeofues.

Contents Timber Resourcesand Uses

1—2

Hardwoodsand Softwoods

Commercial SourcesofWoodProducts

Use Classes and Trends SpeciesDescriptions 1—3 U.S. Wood Species

1—3

Hardwoods 1—3 Softwoods

1—10

ImportedWoods

1—17

Hardwoods 1—17 Softwoods References

1—33

1—34

All wood is composed of cellulose, lignin,hemicelitloses, andminor amounts (5% to 10%) ofextraneous matera1s

1—2

1—3

1—2

contained in a cellular structure. Variations in the characteristics and volume ofthese components anddifferences in cellular structure makewoodsheavyor light, stiffor flexible, and hard or soft. Thepropertiesofa singlespecies are relatively constantwithinlimits;therefore, selectionofwood by species alonemay sometimes be adequate.However,to use woodto itsbestadvantage and most effectively inengineering applications, specific characteristics orphysicalproperties must be considered. Historically, somespeciesfilledmany purposes,whi [e other less available or less desirable species servedonly one or two needs. For example, becausewhite oak is tough, strong, and durable,it was highly prized for shipbuilding, bridges, cooperage, barn timbers, farmimplements, railroadc:rossties, fenceposts, and flooring. Woodssuch as black walnutand cheriywere usedprimarily forfurniture and cabinets. Hickory was manufactured into tough, hard, and resilientstriking-tool handles, and blacklocustwas prized forbarn timbers.What theearlybuilderor craftsman learned by trial and errorbecamethe basisfor deciding whichspecies were appropriate for given use in terms oftheir characteristics. Itwas commonlyaccepted that wood from treesgrown in certain locations undercertainconditions was stronger,more durable, more easily worked with tools, or fmergrainedthan 'vood fromtrees in other locations. Modernresearchon wood has substantiated that location and growth conditions do significantly affectwoodproperties. The gradualreductions in use ofold-growth forestsinthe UnitedStateshas reducedthe supplyoflargeclear logs for lumber andveneer. However, the importance ofhigh.•quality logs has diminished as new concepts ofwood use have been introduced. Second-growth wood,the remaining old-growth forests, and importscontinueto fill theneeds for wood in the qualityrequired. Wood is as valuablean engineering material as ever,and in many cases,technological advances have madeit evenmore useful.

a

1—1

I

The inherent factors that keepwood inthe forefrontofraw materials are many and varied,but a chiefattribute is its availabilityin many species, sizes, shapes, and conditions to suit almost every demand. Wood has a high ratio ofstrength toweightand a remarkable recordfor durability andperformance as a structural material.Dry wood has good insulating propertiesagainst heat, sound, and electricity. It tends to absorb and dissipatevibrationsunder some conditions of use, andyet it is an incomparable materialfor such musical instrumentsas the violin. The grain patternsand colors of wood make it an estheticallypleasingmaterial,and its appearancemay be easily enhanced by stains, varnishes, lacquers, and other finishes.It is easily shaped with tools and fastenedwith adhesives, nails, screws,bolts,and dowels. Damagedwood is easily repaired,andwood structures are easily remodeledor altered.In addition,wood resists oxidation,acid, saltwater,and other corrosiveagents, has high salvagevalue, has good shock resistance, can be treated with preservatives and fire retardants, and can be combined with almost any other materialfor both functional and estheticuses.

or sap in thetree. Typically,hardwoodsare plants with broad leavesthat, with few exceptions inthe temperateregion, lose theirleaves in autumn orwinter. Most imported

Timber Resources and Uses

Softwoodsare availabledirectlyfromthe sawmill, wholesale and retail yards, or lumberbrokers.Softwoodlumberand plywood are used in construction for forms,scaffolding, framing, sheathing, flooring, moulding,paneling, cabinets, poles and piles, and many other buildingcomponents. Softwoods may also appearinthe form ofshingles, sashes, doors, and other millwork,in addition to some rough products such as timberand round posts.

In theUnitedStates,more than 100 wood species areavailable to the prospectiveuser, but all are unlikely to be available in any one locality.About 60 nativewoodsare ofmajor commercial importance. Another30 species are commonly importedin the form oflogs, cants, lumber, and veneerfor industrialuses, the buildingtrade, and crafts.

tropicalwoods are hardwoods. Botanically, softwoods are Gymnosperms or conifers; the seedsare naked(not enclosed in theovaryoftheflower). Anatomically, softwoods are nonporousand do not containvessels. Softwoods are usually cone-bearing plants withneedle-or scale-like evergreen leaves. Some softwoods, such as larches andbaldcypress, losetheirneedles during autunm orwinter. Majorresources ofsoftwood species are spreadacrossthe UnitedStates, except forthe Great Plains whereonly small areas are forested. Softwood species are often loosely grouped hi three generalregions,as shownin Table 1—1. Hardwoods also occur in all parts ofthe UnitedStates, although most grow east ofthe Great Plains. Hardwoodspeciesare shown by region in Table 1—2.

Commercial Sources

of Wood Products

A continuing programoftimberinventoryis in effect in the United Statesthroughthe cooperation ofFederaland State agencies, andnewinformation onwood resources is published in State and Federalreports. Two ofthe most valuable sourcebooksare AnAnalysisofthe Timber Situationin the UnitedStates 1989—2040 (USDA 1990) and The 1993 RPA TimberAssessment Update(Haynesand others 1995).

Hardwoods are used in construction for flooring, architectural woodwork, interiorwoodwork, and paneling. These items areusuallyavailable from lumberyards andbuildingsupply dealers. Most hardwoodlumberand dimensionstock are remanufactured into furniture,flooring, pallets,containers, dunnage,and blocking. Hardwoodlumberand dimension

Current information on wood consumption, production, imports,and supply and demandis publishedperiodically by theForest Products Laboratory (Howard1997) andis availablefrom the SuperintendentofDocuments, U.S. GovernmentPrinting Office, Washington, DC.

Table 1—1. Major resources of U.S. softwoodsaccording

Hardwoods and Softwoods

Douglas-fir Whitefirs Western hemlock Western larch

Trees are dividedintotwo broad classes, usually referredto

as hardwoods and softwoods. These names can be confusing since some soitwoodsare actuallyharderthan somehardwoods, andconverselysomehardwoodsare softerthan some softwoods. For example,softwoods such as longleafpine and Douglas-firare typicallyharderthanthe hardwoods basswood and aspen. Botanically, hardwoodsare Angiosperms; the seedsare enclosedin the ovary ofthe flower. Anatomically, hardwoodsare porous;that is, they containvesselelements. A vessel elementis a wood cell with open ends;when vessel elementsare set one above another,they form a continuous tube (vessel),which servesas a conduitfortransporting water

1—2

to region Western

Northern

Incense-cedar Port-Orlord-cedar

Northern white-cedar Atlanticwhite-cedar Balsam fIr Baldcypress Eastern hemlock Fraserfir Fraserfir Southern Pine Jack pine Eastern redcedar

Lodgepolepine Ponderosapine Sugar pine Western white pine Western redcedar Redwood Engelmannspruce

Sitkaspruce Yellow-cedar

Redpine Eastern white pine Eastern redcedar Eastern spruces Tamarack

Southern

Table 1—2. Major resources of U.S. hardwoods according to region Southern

Ash Basswood American beech Butternut

Northernand Appalachia

Western

Ash

Redalder

Aspen Basswood Buckeye

Oregon ash

Cottonwood

Butternut

Elm Hackberry Pecan hickory True hickory Honeylocust Blacklocust

American beech Birch Black cherry American chestnuta Cottonwood Elm

Magnolia Soft maple Red oaks Whiteoaks Sassafras Sweetgum American sycamore Tupelo Black walnut

Blackwillow Yellow-poplar

Aspen

Black cottonwood Californiablackoak Oregon white oak Bigleaf maple

Paperbirch Tanoak

Hackberry

True hickory Honeylocust Black locust Hard maple Soft maple Red oaks Whiteoaks American sycamore Black walnut Yellow-poplar

chestnut isno longer harvested,but chestnut lumber fromsalvaged timbers canstillbe found on the market.

a4A,.,.erican

stockare available directlyfromthe manufacturer, through wholesalers andbrokers,and from someretail yards. Both softwoodand hardwoodproductsare distributed throughoutthe United States. Localpreferencesandthe availability ofcertainspecies may influence choice,but a wide selectionofwoodsis generallyavailable forbuilding construction, industrialuses, remanufacturing, andhome use.

Use Classes and Trends The productionand consumptionlevels ofsome ofthe many use-classifications for wood are increasing withthe overall nationaleconomy,and othersare holding aboutthe same. The most vigorouslygrowingwood-basedindustries are those that convertwood to thin slices (veneer), particles (chips, flakes),or fiberpuips andreassemble the elementsto producevarioustypes ofengineered panelssuch as plywood, particleboard, strandboard, veneerlumber, paper,paperboard, and fiberboardproducts. Another growingwood industry is theproduction of laminated wood.Foranumber ofyears,the lumberindustry has producedalmost the same volume of wood peryear.Modestincreases haveoccurred inthe productionofrailroadcrossties, cooperage, shingles, and shakes.

Species Descriptions Inthis chapter, each species or groupofspecies is described in terms ofits principallocation, characteristics, and uses. Moredetailedinformation on the properties ofthese and other species is given in various tables throughoutthis handbook. Information onhistoricaland traditionaluses is providedfor some species. Commonandbotanicalnames follow the Checklist ofUnitedStates Trees (Little 1979).

U.S. Wood Species Hardwoods Alder, Red Red alder(Alnus rubra)grows along the Pacific coastbetweenAlaskaand California. It is the principalhardwoodfor commercial manufacture ofwoodproductsin Oregon and Washington and the most abundant commercial hardwood species in these two states. The wood ofred aldervaries from almostwhite to pale pinkishbrown, and there is no visibleboundarybetween heartwoodand sapwood. Red alder is moderatelylight in weightand intermediate inmost strengthpropertiesbut low in shock resistance.It hasrelatively low shrinkage. The principaluse ofred alderis for furniture, butit i also used for sashand door panel stockand other millwork.

Ash (White Ash Group) Importantspeciesofthe white ash group are American white ash (Fraxinusamericana),green ash (F. pennsylvanica), blue ash (F. quadrangulata),and Oregon ash (F. latfo/ia).The firstthree species grow in the eastern halfofthe United States. Oregon ash grows alongthe Pacific Coast. The heartwoodofthe white ash group is brown, andthe sapwoodis light-colored ornearly white. Second-growth treesare particularly soughtafter becauseofthe inherent qualities ofthe wood from these trees: it is heavy, strong, hard, and stiff, and ithas high resistanceto shock. Oregon ash has somewhat lowerstrengthpropertiesthan American white ash, but it is used for similarpurposeson the West Coast.

American white ash is used principallyfor nonstriking tool handles,oars, baseballbats, and other sporting and athletic goods. Forhandles ofthe bestgrade, somehandle specifications call for not less than 2 nor more than 7 growthrings per centimeter(notless than 5 normore than 17 growth rings perinch). The additional weightrequirementof 690 kg/rn3(43 lbfft3) or more at 12% moisturecontent ensures high qualitymaterial.Principaluses for the white ash group are decorative veneer, cabinets, furniture,flooring, millwork, and crates.

1—3

3

Ash (Black Ash Group)

The heartwoodofbasswood is pale yellowishbrown with occasional darkerstreaks.Basswoodhas wide, creamywhite orpalebrownsapwoodthat mergesgraduallyinto heartwood. When dry, the wood is without odoror taste. It is soft and light in weight,has fme, even texture,and is straightgrainedand easy to work with tools. Shrinkage in width and thicknessduring diying is rated as high; however, basswood seldom warps in use.

The black ash group includesblack ash (F. nigra) and pumpkinash (F. profunda). Black ash grows in the Northeast and Midwest, and pumpkinash in the South.

The heartwoodofblack ash is a darkerbrownthan that of American white ash; the sapwoodis light-colored or nearly white. The wood ofthe black ash group is lighterin weight (basic specific gravity of0.45 to 0.48)than that ofthe white ash group (>0.50). Pumpkinash, American white ash, and green ash that grow in southernriverbottoms, especiallyin areas frequentlyfloodedfor long periods, produce buttresses that contain relativelylightweightand brash wood.

Basswood lumberis used mainly in venetianblinds, sashes and door frames, moulding, apiary supplies,woodenware, andboxes. Somebasswood is cut for veneer,cooperage, excelsior, andpulpwood, and it is a favoriteofwood carvers.

Principaluses forthe black ash group are decorative veneer, cabinets,millwork,furniture,cooperage, and crates.

Beech, American Only one speciesofbeech,American beech (Fagus

grandfolia),is nativeto theUnited States. It grows in the easternone-third ofthe UnitedStatesand adjacentCanadian provinces. The greatestproduction ofbeech lumberis in the

Aspen Aspen is a generallyrecognizednamethat is appliedto bigtooth(Populusgrandidentata) and quaking (P. tremuloides)aspen.Aspen does not includebalsam poplar (P. balsamfera) and the other speciesofPopulus that areincludedin thecottonwoods.In lumberstatisticsofthe U.S. Bureau ofthe Census, however, the term cottonwood includesall the preceding species. Also, the lumberofaspen and cottonwoodmay be mixed in trade and sold as either poppleor cottonwood. The name poppleshould not be

Central and Middle AtlanticStates.

In somebeechtrees, colorvaries from nearly white sapwood to reddish-brown heartwood. Sometimes there is no clear line ofdemarcation betweenheartwoodand sapwood. Sapwood may be roughly7 to 13 cm (3 to 5 in.) wide. The wood has little figureand is ofclose, uniformtexture. It has no characteristic taste or odor.The wood ofbeech is classed as heavy,hard, strong, high in resistanceto shock, and highlysuitablefor steam bending. Beech shrinks substantially and therefore requires careful drying.It machines smoothly, is an excellentwood for turning, wears well, and is rathereasily treatedwith preservatives.

confusedwith yellow-poplar(Liriodendrontulipfera), also knownin the trade as poplar. Aspen lumber is produced principally in the Northeasternand Lake States, with some production in the RockyMountainStates.

The heartwoodofaspen is grayish white to light grayish brown. The sapwoodis lightercoloredand generallymerges gradually into the heartwoodwithoutbeing clearly marked. Aspenwood is usually straightgrained with a fine, uniform texture. It is easily worked.Well-dried aspen lumber does not impartodor or flavorto foodstuffs. Thewood ofaspenis lightweight and soft. It is low in strength, moderatelystiff, andmoderatelylow in resistance to shock and has moderately high shrinkage.

Most beech is used for flooring, furniture,brush blocks, handles, veneer, woodenware, containers, and cooperage. Whentreatedwith preservative, beech is suitablefor railway ties.

Birch The threemost important speciesare yellowbirch (Betula alleghaniensis),sweetbirch (B. lenta),and paper birch (B. papyrjfera). Thesethree species are the sourceofmost birch lumberand veneer. Other birch species ofsome commercialimportance are riverbirch (B. nigra), gray birch (B. populfo1ia),and westernpaper birch (B. papyrfera var. commutata). Yellow,sweet,and paper birch grow principally in theNortheastand theLake States;yellow and sweet birch alsogrow along the Appalachian Mountainsto northern Georgia.

Aspen is cut for lumber,pallets, boxes and crating, pulpwood, particleboard, strandpanels, excelsior, matches,veneer, and miscellaneousturnedarticles. Today, aspen is one ofthepreferred species foruse in oriented strandboard, a panel productthat is increasinglybeing usedas sheathing.

Basswood Americanbasswood(Tilia americana)is the most important ofthe native basswood species;next in importance is white basswood (T. heterophylla),and no attemptis made to distinguish between these species in lumberform.In commercialusage, "whitebasswood"is used to specify the white

Yellow birch has white sapwoodand light reddish-brown heartwood. Sweetbirch has light-colored sapwoodand dark brown heartwoodtinged with red. For both yellow and sweet birch, the wood is heavy, hard, and strong, and it has good shock-resisting ability. The wood is fine and uniform in texture.Paper birch is lowerinweight, softer, and lower in strength than yellowand sweetbirch. Birch shrinks considerablyduringdrying.

wood or sapwoodofeither species.Basswoodgrowsin the eastern halfofthe UnitedStatesfrom the Canadian provinces southward. Most basswoodlumbercomesfrom the Lake, Middle Atlantic, and Central States.

1-4 [4.

Yellowand sweetbirch lumberis usedprimarilyfor the manufacture offurniture, boxes, baskets, crates, woodenware, cooperage, interiorwoodwork,and doors; veneerplywoodis used for flushdoors, furniture, paneling, cabinets, aircraft, and other specialtyuses. Paperbirch is used for toothpicks, tonguedepressors, ice creamsticks,and turnedproducts, including spools, bobbins, smallhandles, and toys.

The heartwoodofblackcherryvariesfrom light to dark reddishbrown and has a distinctive luster. The nearly white sapwoodis narrowin old-growth trees and widerin secondgrowthtrees. The wood has a fairlyuniformtexture and very good machiningproperties. It is moderatelyheavy,strong, stiff, and moderately hard; it has high shockresistance and moderately high shrinkage. Black cherryis very dimensionally stable after drying.

Buckeye

Black cheny is usedprincipally for furniture, fme veneer panels,and architectural woodwork. Otheruses include burial caskets, woodenware, novelties, patterns, and

Buckeyeconsistsoftwo species,yellowbuckeye(Aesculus octandra) and Ohiobuckeye (A. glabra). These species range from the Appalachians ofPennsylvania, Virginia, and North Carolinawestwardto Kansas, Oklahoma, and Texas. Buckeye is not customarily separated from other species whenmanufactured into lumberand can be used forthe same purposes as aspen(Populus),basswood(Tilia), and sapwood ofyellow-poplar(Lfriodendrontu1ipfera).

The white sapwoodofbuckeyemerges gradually into the creamyor yellowishwhite heartwood. The wood is uniform in texture, generallystraight grained, light in weight,weak whenused as a beam, soft, and low in shock resistance. It is rated low on machinability such as shaping,mortising, boring, and turning. Buckeyeis suitablefor pulping for paper; in lumberform,it has been usedprincipallyfor furniture, boxes and crates, food containers, woodenware, novelties, andplaningmill products.

Butternut Also calledwhitewalnut,butternut(.Juglans cinerea) grows from southernNew Brunswick and Mainewest to Minnesota. Its southernrange extendsinto northeastern Arkansas and eastwardto westernNorth Carolina. The narrow sapwoodis nearly white and heartwoodis light brown,frequentlymodifiedbypinkish tonesordarkerbrown streaks. The wood is moderatelylight in weight (aboutthe same as easternwhite pine), rather coarse textured,moderately weak in bendingand endwise compression, relatively low in stiffhess, moderatelysoft, and moderately high in shock resistance. Butternut machineseasily and finishes well.In many ways, butternutresemblesblack walnutespecially when stained, but it does not have the same strength

or hardness.

Principal uses are forlumberand veneer, whichare further manufactured into furniture, cabinets,paneling, interior woodwork, andmiscellaneousrough items.

Cherry, Black Black cherry (Prunus serotina) is sometimes knownas cherry,wild black cherry, and wild cherry. It is the only nativespecies ofthegenus Prunus ofcommercial importance for lumberproduction. Black cherryis foundfrom southeastern Canadathroughoutthe easternhalfoftheUnited States. Productionis centered chieflyin the MiddleAtlanticStates.

paneling.

Chestnut, American Americanchestnut(Castanea dentata) is also known as sweetchestnut. Before this species was attackedby ablight inthe I920s, it grewin commercial quantities from New Englandto northernGeorgia. Practically all standingchestnut has beenkilled by blight, and most suppliesofIhe lumbercomefrom salvaged timbers.Because ofthe species' naturalresistance to decay, standing deadtrees in the Appalachian Mountains continued to provide substantial luantities oflumberfor several decadesafter the blight,butthis source is now exhausted.

The heartwoodofchestnutis grayishbrownorbrown and darkenswith age. The sapwoodis very narrowand almost white. The wood is coarse in texture;growth rings are made conspicuous by severalrows of large, distinctpores st the beginningofeach year's growth. Chestnutwood is inoderately lightin weight,moderatelyhard, moderatelylow in strength, moderately low in resistance to shock, and low in stiffness. It dries well and is easy to work with tools. Chestnutwas onceused for poles,railroadcrossties, furniture, caskets, boxes, shingles, crates,and corestock f veneer panels.At present,it appearsmost frequently as wotmy chestnutfor paneling, interiorwoodwork, and pictureframes.

r

Cottonwood Cottonwoodincludesseveralspecies ofthe genus Populus. Most important are easterncottonwood (P. deltoide"and varieties), alsoknownas Carolinapoplarand whitewood; swamp cottonwood (P. heterophylla), alsoknown a; cottonwood, river cottonwood, and swamppoplar; black cottonwood (P. trichocarpa);and balsampoplar (P. ba1samfera).Easternand swamp cottonwood giow throughoutthe easternhalf ofthe UnitedStates. Greatest productionoflumberis in the SouthernandCentral States. Black cottonwood grows on the West Coast and in western Montana, northern Idaho,and westernNevada.Balsam poplargrowsfrom AlaskaacrossCanadaand in thenorthern Great Lakes States. The heartwoodofcottonwood is grayish white to light brown.The sapwoodis whitish and mergesgraduallywith theheartwood. The wood is comparatively uniformintexture andgenerallystraightgrained.It is odorlesswhen well dried. Easterncottonwood is moderatelylow in bending and 1—5

5

compressive strength, moderatelystiff, moderately soft, and moderatelylow in ability to resist shock. Most strength propertiesofblack cottonwood are slightly lowerthan those ofeasterncottonwood. Both easternand blackcottonwood have moderatelyhigh shrinkage. Some cottonwood is difficultto work with tools becauseofits fuzzy surface, which is mainly theresult oftensionwood (see discussion ofReaction Wood in Ch. 4). Cottonwood is used principallyfor lumber, veneer, pulpwood,excelsior, andfuel. Lumberand veneerare used primarilyfor boxes, crates,baskets,and pallets.

Elm Six speciesofelm grow in the easternUnitedStates: American (Ulmusamericana),slippery (U rubra), rock

(U thomasii),winged (U alata), cedar (U crassfo1ia),and September(U serotina) elm. American elm is alsoknown

as white, water, and gray elm; slipperyelm as red elm; rock elm as cork and hickory elm; wingedelm as wahoo;cedar elm as red and basket elm; and Septemberelm as red elm. Americanelm is threatenedby two diseases, DutchElm disease and phloemnecrosis,whichhave killedhundreds of thousandsoftrees.

Sapwood of elm is nearly white and heartwoodlight brown, often tinged with red. Elm may be dividedinto two general classes,soft and hard, based onthe weight and strength of thewood. Soft elm includesAmericanand slippery elm. It is moderatelyheavy, has high shockresistance,and is moderately hard and stiff. Hard elm includesrock, winged, cedar, and Septemberelm. These species are somewhat heavierthan soft elm. Elm has excellentbending qualities. Historically, elm lumberwas used forboxes, baskets, crates, and slack cooperage; furniture; agricultural supplies and implements; casketsand burial boxes; and wood components in vehicles. Today,elm lumberand veneer are used mostly for furniture and decorative panels. Hardelm is preferred for uses that require strength.

Hackberry Hackberry(Celtisoccidentalis)and sugarberiy(C. laevigata) supplythe lumberknown in the trade as hackberry. Hackberrygrowseastofthe Great Plainsfrom Alabama, Georgia, Arkansas, and Oklahoma northward, exceptalong the Canadianboundary.Sugarberry overlapsthe southern part ofthe hackberryrange and growsthroughoutthe Southernand SouthAtlantic States. Sapwoodofboth speciesvariesfrom pale yellowto greenish or grayishyellow. The heartwoodis commonly darker. The woodresembleselm in structure.Hackberrylumberis moderately heavy. It is moderatelystrong in bending, moderately weak in compressionparallelto grain, moderatelyhard to very hard, and high in shock resistance,but low in stiffliess. Hackberryhas high shrinkagebut keeps its shapewell during drying.

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Most hackberryis cut into lumber; small amounts are used for furniture parts,dimension stock, and veneer.

Hickory (Pecan Group)

Species ofthe pecan hickory group include bittemut hickory

(Carya cordformis), pecan (C. illinoen.sis), water hickory (C. aquatica), and nutmeghickory (C. myristicjformis). Bittemuthickorygrows throughoutthe eastern half ofthe UnitedStates; pecanhickory,from centralTexas and Louisiana to Missouriand Indiana; water hickory,from Texas to SouthCarolina;and nutmeg hickory, in Texas and Louisiana. The sapwoodofthis group is white ornearly white and relatively wide. The heartwoodis somewhatdarker. The wood is heavy and sometimes has very high shrinkage.

Heavy pecan hickory is usedfortool and implementhandles and flooring. The lowergrades are usedforpallets. Many highergrade logs are sliced toprovide veneerfor furniture anddecorative paneling.

Hickory (True Group) Truehickories are foundthroughoutthe easternhalfofthe

United States. The species most importantcommercially are shagbark (Carya ovata), pignut(C. glabra), shelibark (C. laciniosa), andmockernut(C. tomentosa).The greatest commercial production ofthetrue hickories for all uses is in theMiddleAtlantic and Central States,with the Southern and South Atlantic Statesrapidly expanding to handle nearly halfofall hickorylumber. The sapwoodofthe true hickory group is white and usually quite wide, exceptin old, slow-growing trees. The heartwood is reddish. The wood is exceptionally tough, heavy, hard, and strong, and shrinks considerably in drying. For some purposes, both ringsper centimeter(or inch) and weightare limitingfactorswhere strength is important. The major use for high qualityhickory is for tool handles, whichrequirehigh shock resistance. It is alsousedfor ladder rungs, athleticgoods, agriculturalimplements, dowels, gymnasium apparatuses, poles, and furniture. Lowergrade hickory is not suitablefor the special uses ofhigh quality hickorybecauseofknottiness or othergrowth features and low density.However, the lowergrade is useful for pallets and similar items. Hickory sawdust, chips, and some solid wood are usedto flavor meat by smoking.

Honeylocust The wood ofhoneylocust (Gleditsiatriacanthos) has many desirable qualities,such as attractive figureand color, hardness, and strength, but it is little usedbecauseof its scarcity. Although the naturalrange ofhoneylocust has been extended by planting,this species is foundmost commonlyin the easternUnitedStates, exceptforNew Englandand the South Atlanticand GulfCoastalPlains.

Sapwoodis generallywide and yellowish, in contrastto the light red to reddish-brown heartwood.The wood is very heavy,very hard, strong in bending,stiff, resistantto shock, and durable when in contact with the ground. Whenavailable, honeylocust is primarilyused locally for fenceposts and generalconstruction. It is occasionally used with other species in lumberforpallets and crating.

Locust, Black Black locust(Robiniapseudoacacia) is sometimes called yellow orpost locust.This species grows from Pennsylvania along the Appalachian Mountainsto northernGeorgia and Alabama. It is also nativeto westernArkansasand southern Missouri.The greatestproduction ofblack locust timberis in Tennessee,Kentucky, West Virginia,and Virginia.

Locusthas narrow, creamywhite sapwood. The heartwood, when freshlycut, varies from greenish yellow to darkbrown. Black locustis very heavy, very hard, very resistant to shock, and very strong and stiff. It has moderately low shrinkage. The heartwoodhas high decayresistance. Black locust is used for round, hewed,or splitmine timbers as well as fenceposts, poles, railroadcrossties, stakes, and fuel. Otheruses are for rough construction, crating, andmine equipment. Historically,blacklocust was importantfor the manufactureofinsulator pins andwoodenpegs used in the construction ofships, for whichthe woodwaswell adapted becauseofits strength, decayresistance, andmoderate shrinkageand swelling.

Magnolia Commercialmagnoliaconsistsofthree species:southern magnolia(Magnoliagrand/1ora), sweetbay (M virginiana), and cucumbertree (M acuminata).Othernamesfor southern magnoliaare evergreenmagnolia,big laurel, bull bay, and laurelbay. Sweetbay is sometimes called swamp magnolia.

The lumberproducedby all three speciesis simplycalled magnolia.The natural range ofsweetbay extendsalongthe Atlanticand GulfCoastsfrom Long Islandto Texas, and that ofsouthernmagnoliaextends fromNorth Carolina to Texas. Cucumbertree growsfrom the Appalachians to the Ozarksnorthwardto Ohio. Louisiana leads in the production ofmagnolialumber. Sapwoodofsouthernmagnoliais yellowishwhite, and heartwoodis light to dark brown with a tinge ofyellow or green.The wood, which has close, uniform textureand is generallystraightgrained,closelyresembles yellow-poplar (Lfriodendrontulip([era). It is moderately heavy, moderately low in shrinkage, moderatelylow in bendingand compressive strength, moderatelyhard and stiff, and moderately high in shockresistance.Sweetbay is much like southern rnagnoha. The wood of cucumbertree is similarto that ofyellowpoplar (L. tulipjfera); cucumbertree that growsin the yellowpoplarrange is notseparatedfrom that species on the market.

Magnolia lumberis usedprincipally in the manufacture of furniture,boxes, pallets, venetian blinds, sashes, doors, veneer,and miliwork.

Maple, Hard Hard mapleincludessugarmaple (Acer saccharum)and black maple(A. nigrum). Sugarmaple is also known as hard androck maple, and blackmaple as black sugarmaple. Maplelumberis manufactured principally in theMiddle Atlanticand Great Lake States, whichtogether accountfor about two-thirds ofproduction.

The heartwoodis usuallylightreddish brown but sometimes considerably darker. The sapwoodis commonlywhite with a slight reddish-brown tinge. It is roughly 7 to 13 cm ormore (3 to 5 in. or more)wide. Hardmaplehas a fine,uniform texture. It is heavy,strong, stiff, hard, and resistantto shock and has high shrinkage. The grain ofsugarmaple is generally straight,but birdseye,curly, or fiddlebackgrain is often selectedforfurniture or novelty items. Hardmaple is used principally for lumberand veneer. A largeproportionis manufactured intoflooring, furniture, cabinets,cuttingboards and blocks,pianos, billiard :ues, handles,novelties, bowlingalleys, dance and gymnasium floors, spools,and bobbins.

Maple, Soft Soft mapleincludes silver maple(Acersaccharinumj., red maple(A. rubrum),boxelder(A. negundo),andbigleaf maple (A. macrophyllum). Silvermaple is also knownas hite, river, water,and swamp maple;redmaple as soft, water, scarlet,white,and swamp maple;boxelderas ash-leaved, three-leaved, and cut-leaved maple;andbigleafmapleas Oregon maple. Soft mapleis found in the easternUnited Statesexcept for bigleafmaple, which comes from PacificCoast.

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Heartwood and sapwoodare similarin appearance to hard maple: heartwoodofsoft mapleis somewhatlighterincolor and the sapwood, somewhat wider.The wood ofsoft maple, primarily silver and red maple, resemblesthat ofhard maple but is not as heavy,hard, and strong.

Soft mapleis used forrailroadcrossties, boxes,pallets, crates,furniture, veneer, woodenware, andnovelties,

Oak (Red Oak Group) Most red oak comesfrom the EasternStates.The principal species are northern red(Quercusrubra), scarlet (Q. occinea), Shumard (Q. shumardil),pin (Q. palustris), Nuttall (Q. nuttallii),black (Q. velutina), southernred (Q.jzlcata), chenybark(Q.falcata var.pagodaefolia),water (Q. nigra), laurel (Q. laur(folia),and willow(Q. phellos) oak.

The sapwoodis nearly white and roughly2 to 5 cm (1 to 2 in.) wide. The heartwoodis brown with a tinge of red. Sawn lumberofthe red oak group cannotbe separated by species on the basis ofwood characteristics alone.

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Red oak lumbercan be separatedfrom white oak by the size and arrangementofporesin latewood and becauseit generally lacks tyloses in the pores. The open pores ofred oak makethis species group unsuitablefortightcooperage, unlessthe barrels are lined with sealer or plastic.Quartersawn lumberofthe oaks is distinguished by the broad and conspicuous rays. Wood ofthe red oaks is heavy. Rapidly grownsecond-growth wood is generallyharderandtougher than fmertexturedold-growth wood.The redoaks havefairly high shrinkagein drying.

characteristic odor of sassafras. The wood is moderately heavy, moderately hard, moderatelyweak in bendingarid endwise compression, quite high in shock resistance,anI resistantto decay.

The red oaks areprimarilycut into lumber, railroadcrossties, mine timbers,fence posts, veneer, pulpwood, and fuelwood.Ties,mine timbers,and fenceposts requirepreservative treatmentfor satisfactory service. Redoak lumberis remanufactured into flooring, furniture, general millwork, boxes, palletsand crates, agriculturalimplements, caskets, woodenware, and handles. It is alsousedin railroadcars and boats.

Sweetgum (Liquidambar

Oak (White Oak Group) White oak lumbercomes chiefly from the South, South Atlantic, and Central States, including the southernAppalachianarea. Principal species are white (Quercus alba), chestnut (Q. prinus), post (Q. stellata), overcup (Q. lyrata), swampchestnut (Q. michauxii),bur (Q. macrocarpa), chinkapin (Q. muehlenbergii), swampwhite (Q. bicolor), and live (Q. virginiana) oak.

The sapwoodofthe white oaks is nearly white and roughly 2 to 5 cm or more (1 to 2 in. or more) wide. The heartwood is generallygrayishbrown.Heartwoodporesareusually pluggedwith tyloses, whichtend to make the wood impenetrable by liquids.Consequently,most white oaks are suitable for tight cooperage. Many heartwoodporesofchestnut oak lack tyloses. The wood ofwhite oak is heavy, averaging somewhat greater in weightthanred oak wood. Theheartwood has gooddecay resistance. Whiteoaks are usuallycut into lumber, railroadcrossties, cooperage, mine timbers,fenceposts, veneer, fuelwood, and many other products. High-quality white oak is especially sought for tight cooperage. Live oak is considerably heavier and strongerthan the other oaks, and it was formerly used extensivelyforship timbers.An important use ofwhite oak is for plankingand bent parts ofships andboats; heartwood is often specified becauseofits decay resistance. Whiteoak is also used for furniture,flooring, pallets, agricultural implements,railroadcars, truck floors,furniture,doors, and millwork.

Sassafras Sassafras(Sassafras albidum)ranges throughmost ofthe

easternhalfofthe UnitedStates,from southeastern Iowaand easternTexaseastward. Sassafras is easily confusedwith blackash, whichit resembles in color, grain, and texture. Sapwoodis light yellow, and heartwoodvaries from dull grayishbrownto dark brown, sometimes with a reddishtinge. Freshly cut surfaces havethe 1—8

Sassafras was highlyprizedby the Indiansfor dugoutcanoes, and some sassafraslumberis still used for smallboats. Locally, sassafras is used for fence posts and rails and for generalmillwork.

Sweetgum styracflua) grows from southwestern Connecticut westwardinto Missouriand southward o the GulfCoast. Almost all lumberis produced in the Southern and South Atlantic States. The lumberfrom sweetgum is usuallymarkedas sap gum (the light-colored sapwood) or redgum (the reddish-brown heartwood). Sweetgum oftenhas a form ofcross grain caFled interlockedgrain, and it must be dried slowly. When quartersawn, interlocked grain producesa ribbon-type stripe that is desirable for interiorwoodworkand furniture.The wood is moderately heavy andhard. It is moderately strong,moderately stiff, and moderately high in shockresistance. Sweetgum is used principally for lumber, veneer,plywood, slack cooperage, railroad crossties, fuel,pulpwood, boxes and crates, furniture, interiormoulding,and millwork.

Sycamore, American Americansycamore(Platanusoccidentalis) is knownas sycamoreand sometimes as buttonwood, buttonball-tree, and in theUnited Kingdom,planetree.Sycamoregrows from Maineto Nebraska,southwardto Texas, and eastwardto Florida.

The heartwoodofsycamore is reddishbrown;the sapwcod is lighterin color and from 4 to 8 cm (1-1/2 to 3 in.) wide. The woodhas a fine texture and interlockedgrain. It has high shrinkagein drying; is moderatelyheavy, moderately hard, moderately stiff, and moderately strong;and has good resistance to shock.

Sycamore is used principally for lumber, veneer,railroad crossties, slack cooperage, fenceposts, and fuel. The lumber is used for furniture, boxesarticular1ysmallfood containers), pallets,flooring, handles, and butcherblocks.Veneeris used for fruitandvegetablebaskets and somedecorative panels and door skins.

Tanoak Tanoak(Lithocarpusdensflorus) has recentlygained some commercial value, primarilyin Californiaand Oregon.It is alsoknownas tanbark—oak becausehigh-grade tanninwas once obtainedfrom the bark in commercial quantities. This speciesis found in southwestern Oregonand south to Southern California,mostlynear the coast but also in the Sierra Nevadas.

Sapwood oftanoak is light reddishbrownwhenfirst cut and turns darkerwith age to becomealmost indistinguishable from heartwood,whichalso ages to dark reddishbrown. The wood is heavyand hard; exceptfor compression perpendicular to grain,the wood has roughlythe same strength properties as those ofeasternwhite oak. Tanoakhas highershrinkage duringchying than does white oak, and it has a tendency to collapse during drying. Tanoak is quite susceptible to decay, but the sapwoodtakes preservativeseasily. Tanoak has straightgrain, machinesand glues well, and takes stains readily.

Becauseofits hardness and abrasion resistance, tanoakis excellent for flooring inhomesorcommercial buildings. It is alsosuitable for industrialapplications such as truck flooring. Tanoaktreatedwith preservative has beenused for railroad crossties. The wood has beenmanufactured into baseball bats with good results, and it is also suitablefor veneer, both decorative and industrial, and for high quality

heavy, hard, strong, and stiff, andhas goodresistancto shock.Black walnutis well suitedfor naturalfinishes. Because of its goodpropertiesand interestinggrain pattern, blackwalnut is much valuedfor furniture, architectural woodwork, anddecorative panels. Otherimportantuses are gunstocks, cabinets,and interiorwoodwork.

Willow, Black Black willow (Salixnigra) is the most importantof the many willowsthat grow in the United States. It is the only willow marketedunder its own name. Most black wllow comes from the Mississippi Valley, from Louisiana 1:0 southern Missouriand Illinois.

Tupelo

The heartwoodofblack willow is grayishbrown or ight reddishbrownand frequently containsdarkerstreaks. The sapwoodis whitish to creamy yellow.The wood is miform in texture,with somewhat interlockedgrain, and light in weight.It has exceedingly low strength as a beam or post, is moderately soft, and is moderatelyhigh in shock res:Lstance. It has moderatelyhigh shrinkage.

The tupelo group includes water (Nyssaaquatica),black (N. sylvatica), swamp(N. sylvaticavar. bWora), and Ogeechee(N. ogeche)tupelo. Watertupelo is also knownas tupelo gum, swamptupelo, and sourgum; black tupelo, as blackgumand sourgum; swamp tupelo, as swampblackgum,

Black willow is principally cut into lumber. Small iLmounts are used for slack cooperage, veneer, excelsior, charcoal, pulpwood, artificial limbs,and fenceposts. The lumberis remanufactured principally into boxes,pallets,crates caskets, and furniture.

furniture.

blackgum,and sourgum;and Ogeecheetupelo, as sourtupelo, gopherplum, and Ogeecheeplum. All exceptblack tupelo grow principally in the southeasternUnitedStates. Black tupelo grows in the easternUnitedStatesfrom Maine to Texas and Missouri.About two-thirdsoftheproduction oftupelo lumberis from Southern States.

Woodofthe differenttupelo species is quite similarin appearance and properties. The heartwoodis light brownish gray and merges gradually into the lighter-colored sapwood, whichis generally many centimeterswide. The wood has fine,uniformtexture and interlocked grain. Tupelowood is moderately heavy,moderatelystrong, moderately hard and stiff, and moderatelyhigh in shock resistance. Buttressesof treesgrowing in swampsor floodedareas contain wood that is much lighterin weightthan that from upper portions of thesame trees. Becauseofinterlockedgrain, tupelo lumber requirescare in drying. Tupelo is cut principally for lumber, veneer, pulpwood, and somerailroadcrossties and slack cooperage. Lumbergoes into boxes, pallets, crates,baskets,and furniture.

Walnut, Black Black walnut(Juglans nigra), alsoknown as American black walnut,rangesfrom Vermontto the Great Plainsand southward into Louisiana and Texas. Aboutthree-quarters of walnut wood is grown in the Central States.

The heartwoodofblackwalnutvaries from lightto dark brown;the sapwoodis nearly white and up to 8 cm (3 in.) wide in open-grown trees. Black walnut is normallystraight grained,easily workedwith tools, and stable in use. It is

Yellow-Poplar Yellow-poplar (Liriodendron tulipfera) is alsoknownas poplar,tulip-poplar, and tulipwood. Sapwoodfrom yellowpoplar is sometimes calledwhite poplar or whitewood. Yellow-poplar grows from Connecticut and New York southward to Florida and westwardto Missouri.Th greatest commercial production ofyellow-poplar lumberis in the South and Southeast. Yellow-poplar sapwood is white and frequently seveialcentimeterswide. The heartwoodis yellowishbrown, sometimes streaked with purple, green,black, blue, or red. These wood. colorations do not affectthe physicalproperties of The wood is generally straight grainedand comparatively uniformin texture. Slow-grown wood is moderately light in weightand moderatelylow in bendingstrength, moderately soft, andmoderatelylow in shock resistance.The wood has moderately high shrinkage when driedfrom a green condition, but it is not difficultto dry and is stable after drying. Much ofthe second-growth wood is heavier, harder,and stronger than that ofoldertrees that have grownmore slowly.

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The lumberis used primarilyfor furniture,interior moulding, siding, cabinets,musical instruments, and structural components. Boxes,pallets,and crates are made from lowergrade stock. Yellow-poplar is also madeinto plywoodfor paneling, furniture,piano cases, and variousother special products.

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and cooling towers. Second-growth wood is used for siding and millwork, including interiorwoodworkand paneling. Peckycypress is used forpanelingin restaurants,stores, and other buildings.

Douglas-Fir Douglas-fir(Pseudotsugamenziesii) is also knownlocallyas red-fir, Douglas-spruce, andyellow-fir. Itsrange extendsfrom the RockyMountains tothe PacificCoast and from Mexico to central British Columbia. Sapwood ofDouglas-fir is narrowin old-growth treesbut maybe as much as 7 cm (3 in.) wide in second-growthtrees ofcommercial size.Youngtrees ofmoderate to rapid growth havereddishheartwood and are calledred-fir. Verynarrowringedheartwoodofold-growth trees may be yellowish

Figure 1—1. Cypress-tupelo swamp near New Orleans, LA. Species includebaldcypress (Taxodium distichum)), tupelo(Nyssa), ash (Fraxinus), willow (Salix), and elm (Ulmus). Swollenbuttressesand "knees" are typically present in cypress.

Softwoods Baldcypress Baldcypress or cypress(Taxodium distichum) is also known as southern-cypress, red-cypress, yellow-cypress, andwhite-

cypress.Commercially, the terms tidewaterred-cypress, gulfcypress,red-cypress (coasttype),and yellow-cypress (inland type) are frequently used.Abouthalf ofthe cypress lumber comesfrom the SouthernStates and about a fourthfrom the SouthAtlantic States (Fig. 1—1). Old-growth biddcypress is no longerreadily available, but second-growth wood is available.

Sapwoodofbaldcypress is narrow andnearly white.The color ofheartwoodvarieswidely,rangingfrom lightyellowish brownto dark brownishred, brown,or chocolate. The wood is moderatelyheavy,moderatelystrong, and moderatelyhard. The heartwoodofold-growth baldcypress is one ofthemost decay resistantofU.S. species, but second-growthwood is only moderatelyresistantto decay. Shrinkage is moderatelylow but somewhat higherthan that ofthecedars and lower thanthat ofSouthernPine. The wood ofcertainbaldcypress treesfrequently containspocketsor localized areas that havebeenattackedby afungus. Such wood is knownas pecky cypress.The decay causedby this fungus is stoppedwhen the wood is cut into lumberand dried.Peckycypress isthereforedurable and useful where water tightnessis unnecessary, appearance isnot important, or a novel effectis desired. When old-growth wood was available, baldcypress was used principally for buildingconstruction, especially whereresistance to decay was required. It was alsoused for caskets, sashes, doors, blinds, tanks, vats, ship and boat building,

brownand is knownonthe market as yellow-fir.The wood ofDouglas-firvarieswidelyin weightand strength. When lumberofhigh strengthis neededfor structural uses, selectioncan be improvedby selectingwood with higherdensity. Douglas-firis used mostlyforbuildingand construction purposes in the form of lumber, marine fendering(Fig. 1-2), piles, andplywood. Considerable quantitiesare used for railroad crossties, cooperagestock,mine timbers,poles, and fencing. Douglas-fir lumberis used in the manufactureof variousproducts, including sashes, doors, laminated beams, generalmillwork,railroad-carconstruction, boxes,pallets, and crates. Small amounts are used forflooring, furniture, ship and boat construction, and tanks. Douglas-firplywood has found application inconstruction, furniture,cabinets, marineuse, and other products.

Firs, True (Eastern Species) Balsam fir (Abies balsamea)growsprincipally in New England,New York,Pennsylvania, and the Great Lake States. Fraserfir (A. fraseri)growsin the Appalachian Mountainsof Virginia, North Carolina, and Tennessee. The wood ofthe easterntrue firs, as well as the westerntrue firs, is creamy white to pale brown. The heartwoodand sapwoodare generallyindistinguishable. The similarityof wood structure in the true firs makes it impossibleto distinguishthe species by examinationofthe wood alone. Balsam and Fraserfirs are lightweight, have low bendingand compressive strength, aremoderatelylow in stiffness, are soft, and have low resistance to shock. The easternfirs are used mainly for pulpwood, although some lumberis producedforstructuralproducts, especially in New Englandand the Great Lake States.

Firs, True (Western Species) Six commercial species makeupthe westerntrue firs: subalpine fir (Abies lasiocarpa),California redfir(A. magnIca), grand fir(A. grandis),noble fir (A. procera), Pacific silver fir (A. amabilis),and white fir (A. concolor).The westerntrue firs are cut for lumberprimarilyin Washington,Oregon, California. western Montana, and northernIdaho, and they aremarketedas white firthroughouttheUnitedStates.

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I

Figure 1—2.Woodis favored forwaterfrontstructures,particularly fendering, because of its shock-absorbing qualities. Thefendering on thisdock in Key West, FL, is made of creosote-treatedDouglas-fir (Pseudotsugamenziesii). Some tropical species are resistant to attackby decay fungi and marine borers and are used for marine construction without preservative treatment.

The wood ofthe westerntrue firs is similarto that ofthe easterntrue firs, whichmakes it impossible to distinguish thetrue fir speciesby examination ofthe wood alone. Western true firs are light in weightbut,with theexceptionof subalpine fir, have somewhat higher strength properties than does balsam fir. Shrinkage ofthe wood is low to moderately high.

Hemlock, Eastern Eastern hemlock(Tsugacanadensis)growsfrom NewEnglandto northernAlabamaand Georgia, and inthe Great Lake States. Othernames are Canadian hemlockandhemlock— spruce. The production ofhemlocklumberis divided,fairly evenlyamongthe NewEngland States, MiddleAtlantic States,and GreatLake States.

Lumberofthe westerntrue firs is primarilyused forbuilding construction, boxes and crates,planing-millproducts, sashes,doors, and generalmillwork.In house constru.ction, thelumberis used for framing, subflooring, and sheathing. Some westerntrue fir lumberis manufactured into boxes and crates.High-grade lumberfrom noble fir is used mainlyfor interiorwoodwork, moulding, siding, and sash and door stock. Some ofthe highestquality material is suitablefor aircraft construction. Otherspecialuses ofnoble firare venetian blinds and ladder rails.

The heartwoodofeastern hemlockispale brownwith a reddishhue. The sapwoodis not distinctlyseparated from the heartwoodbut may be lighterin color. The wood is coarseand uneven in texture(old treestend to have considerable shake); it is moderatelylightweight,moderatelyhard, moderately low in strength, moderately stiff, and moderately low in shock resistance. Easternhemlockisusedprincipally for lumberandpulpwood. The lumberis usedprimarilyin buildingconstruction (framing,sheathing, subflooring, and roofboards) an in the manufacture ofboxes,pallets,and crates.

i

1—11

Hemlock, Western and Mountain is also knownas Westernhemlock(Tsugaheterophylla) West Coast hemlock, Pacific hemlock, British Columbia hemlock,hemlock—spruce,and westernhemlock—fir. Itgrows along the Pacific coast ofOregonand Washington and in the northernRocky Mountains north to Canada and Alaska.A relativeofwesternhemlock,mountainhemlock(T. mertensiana) growsin mountainous countryfrom central California to Alaska.It is treated as a separatespecies in assigning lumberproperties. The heartwoodand sapwoodofwesternhemlockare almost white with a purplishtinge. The sapwood,which is sometimes lighterin color than the heartwood, is generallynot more than 2.5 cm (1 in.) wide. The wood often contains small, sound,black knots that are usually tight and dimensionallystable.Dark streaks are often found in the lumber; these are causedby hemlockbark maggotsand generally do not reduce strength. Westernhemlockis moderately light in weight and moderatein strength. It is alsomoderatein hardness,stiffness, and shockresistance. Shrinkage ofwestern hemlockis moderatelyhigh, aboutthe same as that of Douglas-fir(Pseudotsugamenziesii). Greenhemlocklumber contains considerably more water than does Douglas-firand requires longer kiln-dryingtime. Mountain hemlockhas approximately the same density as that ofwesternhemlock but is somewhat lower in bendingstrengthand stiffness. Westernhemlockand mountainhemlockare used principally for pulpwood, lumber, and plywood. The lumber is used primarilyforbuildingmaterial,such as sheathing, siding, subflooring,joists,studding, planking, and rafters, as well as inthemanufactureofboxes,pallets,crates,flooring, furniture, and ladders.

Incense-Cedar Incense-cedar (Calocedrusdecurrens(synonym Libocedrus

decurrens))growsin California, southwesternOregon, and extreme westernNevada.Most incense-cedar lumber comes from the northern halfofCalifornia.

Sapwoodofincense-cedar is white or cream colored,and heartwoodis lightbrown,often tinged with red. The wood has a fme,uniformtexture and a spicyodor.Incense-cedar is light in weight,moderatelylow in strength, soft, low in shock resistance,and low in stiffness. It has low shrinkage and is easy to dry, with little checkingor warping. Incense-cedar is used principally for lumberandfenceposts. Nearly all the high-grade lumber isusedforpencils and

venetianblinds; some is used for chests and toys.Much incense-cedar wood is more or less pecky; that is, it contains pocketsor areas ofdisintegratedwood causedby advanced stagesoflocalizeddecay in the livingtree. There is no further developmentofdecay once the lumberis dried. This low-quality lumberis usedlocally for rough construction where low cost and decayresistanceare important. Because of its resistance to decay,incense-cedar is well suitedfor fenceposts. Other uses are railroadcrossties, poles, and split shingles. 1—12

Larch, Western Western larch (Larix occidentalis) growsin western Montana, northern Idaho,northeastern Oregon,and on the eastern slope ofthe Cascade Mountains in Washington.About twothirds ofthe lumberofthis species is producedin Idaho and Montanaand one-thirdin Oregonand Washington. The heartwood ofwesternlarch is yellowishbrown and the sapwood, yellowishwhite. The sapwoodis generallynot more than 2.5 cm (1 in.) wide. The wood is stiff, moderately strong and hard, moderately high in shock resistance, ancl moderately heavy. It has moderatelyhigh shrinkage. The wood is usually straightgrained,splits easily, and is subject to ring shake. Knotsarecommonbut generallysmallarid tight. Western larchis used mainly for rough dimensionwood in buildingconstruction, small timbers,planks and boards,and railroadcrosstiesandmine timbers.It is used also for piles, poles, and posts. Some high-grade material is manufactured into interiorwoodwork, flooring, sashes, and doors. The properties ofwestern larch are similarto those ofDouglas-fir (Pseudotsugamenziesii), and these species are sometimes sold mixed.

Pine, Eastern White Eastern white pine (Pinus strobus) growsfrom Maineto

northern Georgiaand in the Great Lake States.It is also known as white pine,northernwhite pine, Weymouth pine, and soft pine.About one-halfthe production ofeasternwhite pine lumber occursin New England, about one-thirdin the Great Lake States, and most oftheremainder in the Middle Atlantic and South Atlantic States.

Theheartwoodofeastern white pine is lightbrown, often with a reddish tinge.It turns darker on exposureto air. The wood has comparatively uniformtexture and is straight grained.It is easily kiln dried, has low shrinkage,and ranks high in stability. It is also easy to work and can be reacily glued.Easternwhite pine is lightweight,moderatelysoft, moderately low in strength,low in shock resistance,and low in stiffness.

Practicallyall easternwhite pine is converted into lumber, which is used in a great varietyofways. A large proportion, mostly second-growth knottywood or lower grades, is used for structural lumber. High-grade lumberis used for patterns for castings. Otherimportantuses are sashes,doors, furniture, interiorwoodwork, knottypaneling, caskets, shadeand map rollers, andtoys.

Pine, Jack Jack pine (Pinus banksiana),sometimesknown as scrub,

gray, and blackpine in the United States, grows naturallyin

the GreatLake Statesand in a few scatteredareas inNew Englandand northern NewYork. Jack pine lumber is sometimesnot separated from the other pines with which it grows, including red pine (Pinus resinosa) and easternwhite pine (Pinus strobus).

Sapwoodofjackpine is nearly white; heartwoodis light brownto orange.Sapwoodmay constitute one-halformore ofthe volume ofa tree. The wood hasa rathercoarsetexture and is somewhatresinous.It is moderatelylightweight, moderatelylow in bendingstrengthand compressive strength, moderatelylow in shock resistance,and low in stiffness. It alsohas moderatelylow shrinkage. Lumberfrom jackpine is generallyknotty. Jack pine is used for pulpwood, box lumber, andpallets. Less important uses includerailroadcrossties, minetimber, slack cooperage,poles,posts, and fuel.

Pine, Jeffrey (see Pine, Ponderosa) Pine, Lodgepole Lodgepolepine (Pinus contorta), also knownas knotty, black, and sprucepine, growsin the RockyMountainand Pacific Coastregionsas far northward as Alaska. Wood for lumberand other productsis producedprimarilyin the centralRockyMountainStates;other producingregions are Idaho, Montana,Oregon,and Washington. The heartwoodoflodgepole pine varies from lightyellowto lightyellow-brown.The sapwoodis yellowor nearly white. Thewood is generallystraight grainedwith narrow growth rings. The wood is moderatelylightweight,is fairlyeasy to work, and has moderatelyhigh shrinkage. It is moderately low in strength,moderatelysoft, moderatelystiff, and moderately low in shock resistance. Lodgepole pine is used for lumber, mine timbers, railroad crossties, and poles. Less important uses includeposts and fuel.Lodgepolepine is being used increasingly for framing, siding, millwork,flooring, and cabin logs.

Pine, Pitch Pitch pine (Pinus rigida) grows from Mainealong the mountainsto easternTennessee and northernGeorgia. The heartwoodis brownishred and resinous;the sapwoodis wide and light yellow.The wood ofpitch pine is moderately heavyto heavy,moderatelystrong,stiff, and hard, and moderately high in shock resistance. Shrinkage ranges from moderatelylow to moderatelyhigh. Pitch pine is usedfor lumber, fuel, and pulpwood. The lumber is classified as a minor species in gradingrules for the Southern Pine speciesgroup.

Pine, Pond Pondpine (Pinus serotina) grows in the coastalregionfrom New Jerseyto Florida. It occursin smallgroups or singly, mixed with other pines on low flats.

Sapwoodofpondpine is wide and pale yellow;heartwoodis dark orange.The wood is heavy,coarsegrained,andresinous. Shrinkage is moderatelyhigh. The wood is moderately strong,stiff, moderatelyhard, and moderatelyhigh in shock

Figure 1—3.Ponderosa pine (Pinus ponderosa) growing in an open or park-like habitat.

Pond pine is usedfor general construction, railwaycrossties, posts,and poles. The lumberofthis speciesis also graded as aminor species in gradingrules forthe Southern Pine species group.

Pine, Ponderosa Ponderosa pine (Pinusponderosa)is also knownas Donder-

osa, westernsoft, westernyellow,bull, andblackjackpine. Jeffreypine(P.jeffieyi),whichgrowsin close association with ponderosapine in Californiaand Oregon, is usually marketedwith ponderosapine and sold underthat nme. Majorponderosa pine producing areas are in Oregon. Washington, and California (Fig. 1—3). Other importantproducing areas are in Idaho and Montana; lesseramounts come from thesouthernRockyMountainregion, the Black T4ili:; of South Dakota, and Wyoming. The heartwoodofponderosapine is light reddishbrown,and thewide sapwoodis nearly white to pale yellow.The wood oftheouterportions ofponderosapine ofsawtimber size is generallymoderatelylight in weight,moderatelylow in strength, moderately soft, moderately stiff, and mode:ately low in shock resistance. It is generally straightgrainedand has moderatelylow shrinkage. It is quite uniform in texture and has little tendency to warp and twist.

a

Ponderosa pine is used mainly for lumberand to lesser extentfor piles, poles, posts, mine timbers,veneer, and railroadcrossties. The clear wood is used for sashes, doors, blinds, moulding,paneling, interior woodwork, and built-in casesand cabinets. Low-grade lumber is used forboxes and crates. Much intermediate- orlow-grade lumberis usd for sheathing, subflooring, and roofboards. Knottyponderosa pine is used for interior woodwork.

resistance.

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Pine, Red Red pine (Pinus resinosa)is frequently calledNorwaypine and occasionallyknownas hard pine and pitch pine. This species growsin New England,New York, Pennsylvania, and the Great Lake States.

shrinkage but are dimensionallystable whenproperly dried. To obtain heavy,strong wood ofthe southernpines for structural purposes,a densityrule has been writtenthat specifies a certain percentage oflatewood and growth ratesfor structural timbers.

The heartwoodofred pine varies from pale redto reddish brown. The sapwoodis nearly white with a yellowishtinge and is generallyfrom 5 to 10 cm (2 to 4 in.) wide. The wood resemblesthe lighterweightwood ofthe Southern Pine speciesgroup. Latewoodis distinct in the growthrings. Red pine is moderatelyheavy,moderatelystrong and stiff, moderatelysoft, and moderatelyhigh in shock resistance. It is generallystraightgrained,not as uniformin texture as easternwhite pine (Pinus strobus), and somewhat resinous. The wood has moderatelyhigh shrinkage, but it is not difficultto dry and is dimensionallystable when dried.

The denserandhigher strength southernpines are extensivelyused in the form of stringers in construction offactories, warehouses, bridges,trestles, and docks, and also for rooftrusses,beams,posts,joists, and piles. Lumberoflower densityand strengthis also used for buildingmaterial,such as interiorwoodwork, sheathing, and subflooring, as well as boxes, pallets,and crates. SouthernPine is usedalso for tight and slack cooperage. Whenusedfor railroadcrossties, piles, poles,mine timbers, and exterior decking, it is usually treatedwith preservatives. The manufacture ofstructuralgrade plywoodfrom SouthernPine is a major wood-using industry, as is the production ofpreservative-treated lum ber.

Redpine is used principallyfor lumber, cabinlogs, and pulpwood,and to a lesser extent for piles, poles, posts, and fuel.The lumberis usedfor many ofthe same purposesas for easternwhite pine (Pinus strobus). Red pine lumberis used primarilyforbuildingconstruction, includingtreated lumber for decking, siding, flooring, sashes, doors,generalmillwork, and boxes, pallets, and crates.

Pine, Southern A numberofspecies are includedin the group marketedas

SouthernPine lumber. The four major SouthernPine species andtheirgrowthrangesare as follows: (a) longleafpine (Pinuspalustris), easternNorth Carolinasouthwardinto Floridaandwestwardinto easternTexas; (b) shortleafpine (P. echinata),southeasternNew York and NewJersey southwardto northernFloridaand westwardinto eastern Texas and Oklahoma;(c) loblollypine (P. taeda), Maryland southwardthrough the Atlantic CoastalPlain and Piedmont Plateau into Floridaandwestwardinto easternTexas; (d) slashpine (P. elliottii), Floridaand southernSouth Carolina, Georgia, Alabama, Mississippi,and Louisiana east of the Mississippi River. Lumberfrom these fourspecies is classified as SouthernPine by the grading standards ofthe industry. Thesestandardsalso classifylumberproducedfrom the longleafand slash pine species as longleafpine ifthe lumberconforms tothe growth-ring and latewood requirements ofsuch standards.SouthernPine lumberis produced principallyin the Southernand SouthAtlantic States. Georgia, Alabama, North Carolina, Arkansas, andLouisianalead in SouthernPine lumberproduction. The wood ofthese southernpines is quitesimilar in appearance. Sapwoodis yellowishwhite andheartwood, reddish brown. The sapwoodis usuallywide in second-growth stands. The heartwoodbeginsto form whenthe tree is about 20 years old. In old, slow-growth trees, sapwoodmay be only 2 to 5 cm (ito 2 in.) wide. Longleafand slashpine are classified as heavy,strong, stiff, hard, and moderatelyhigh in shock resistance. Shortleafand loblollypine are usually somewhat lighter in weightthan is longleaf.Allthe southernpines have moderately high 1—14

Pine, Spruce Spruce pine (Pinus glabra), also known as cedar, poor,

Walter,and bottom white pine, is classifiedas a minor species in the Southern Pine speciesgroup. Spruce pine growsmost commonly on low moist lands ofthe coastal regionsofsoutheastern SouthCarolina,Georgia, Alabama, Mississippi, and Louisiana, and northernandnorthwestern Florida.

The heartwoodofsprucepine is light brown, and the wide sapwoodis nearly white. Sprucepine wood is lower in most strengthvaluesthan the wood ofthe major SouthernPine species group. Spruce pine comparesfavorablywith the westerntrue firs in important bendingproperties,crushing strength (perpendicular and parallelto grain),and hardness. It is similarto denserspeciessuch as coast Douglas-fir (Pseudotsugamenziesii) and loblolly pine (Pinus taeda in shearparallelto grain. In the past, spruce pine was principally used locally for lumber, pulpwood, and fuelwood. The lumberreportedly was usedforsashes, doors,and interiorwoodworkbecause ofits low specific gravityand similarityofearlywoodand latewood. In recentyears,sprucepinehas been used for plywood.

Pine, Sugar Sugar pine (Pinus lambertiana),the world's largest species

ofpine, is sometimes called Californiasugarpine. Most sugarpine lumbergrows in Californiaand southwestern Oregon.

The heartwoodofsugarpine is buffor lightbrown, sometimestinged with red. The sapwoodis creamy white. The wood is straight grained,fairly uniform in texture, and easy to work with tools. It has very low shrinkage, is readily dried withoutwarpingor checking, and is dimensionally stable. Sugar pine is lightweight,moderatelylow in strength, moderatelysoft, low in shock resistance,and low in stiffness.

Sugar pine is used almost exclusively for lumberproducts. The largestvolumeis usedfor boxes and crates, sashes, doors, frames,blinds, generalmillwork,buildingconstruction, and foundrypatterns. Like easternwhitepine (Pinus strobus), sugarpine is suitable foruse in nearlyevery part ofa housebecauseofthe easewith whichit can be cut, its dimensionalstability, and its good nailing properties.

Pine, Virginia Virginiapine (Pinus virginiana),also known as Jerseyand scrubpine, growsfrom New Jerseyand Virginiathroughout theAppalachianregion to Georgia and theOhio Valley. It is classifiedas a minorspeciesin thegradingrules for the SouthernPine species group. The heartwoodis orange,and the sapwoodis nearlywhite andrelativelywide. The wood is moderately heavy,moderately strong, moderatelyhard, andmoderatelystiffandhas moderatelyhigh shrinkageandhigh shock resistance. Virginiapine is used for lumber, railroadcrossties, mine timbers,and pulpwood.

Pine, Western White Westernwhite pine (Pinus monticola) is alsoknown as Idahowhite pine or white pine. About four-fifths ofthewood for lumberfromthis species is from Idahoand Washington; smallamountsare cut inMontanaand Oregon.

weight,stiff, moderately strong and hard, and moderately resistantto shock.Port-Orford-cedar heartwoodis highly resistantto decay. The wood shrinksmoderately, has little tendencyto warp,and is stable after drying. Some high-grade Port-Orford-cedar was onceused iu the manufacture ofstorage batteryseparators, matchsticks, and specialtymillwork. Today,other uses are archery supplies, sash and door construction, stadiumseats, flooring, interior woodwork, furniture,andboats.

Redcedar, Eastern Eastern redcedar(Juniperusvirginiana)grows throughoutthe

easternhalfofthe UnitedStates,exceptin Maine, Florida, and anarrow strip along the GulfCoast, and atthe higher elevations in the Appalachian MountainRange. Commercial production is principally in the southernAppalachianand Cumberland Mountain regions. Anotherspecies,southern redcedar(.1 silicicola),growsover a limited areain the South Atlanticand GulfCoastal Plains.

The heartwoodofredcedaris bright or dull red, andthe narrowsapwoodis nearly white.The wood ismoderately heavy, moderately low in strength, hard, and high ia shock resistance, but low in stiffness. It has very low shriiikage and is dimensionally stable after drying. The texture is fine and uniform, and the wood commonly has numeroussmall knots. Eastern redcedarheartwoodis very resistantto decay.

The heartwoodofwesternwhite pine is creamcolored to light reddishbrown and darkenson exposureto air. The sapwoodis yellowishwhite and generallyfrom 2 to 8 cm (ito 3 in.) wide. The wood is straightgrained,easy to work, easily kiln-dried, and stable afterdiying. This species is moderatelylightweight,moderatelylow in strength, moderatelysoft, moderatelystiff, andmoderatelylow in shock resistance and has moderately high shrinkage.

The greatest quantity ofeasternredcedaris used for fence posts. Lumberis manufactured into chests, wardrobes, and closet lining. Otheruses include flooring, novelties pencils, scientific instruments, and smallboats. Southernredcedar is used forthesame purposes. Eastern redcedaris reDuted to repel moths, but this claim has not been supported by research.

Practically all western white pine is sawn into lumber, which is used mainly for buildingconstruction, matches,boxes, patterns, and miliworkproducts,such as sashes and door frames.In buildingconstruction, lower-grade boards are used

Western redcedar(Thujaplicata)grows in the Pacific Northwestand along the PacificCoast to Alaska. It is also calledcanoe-cedar, giantarborvitae, shinglewood, and Pacific redcedar. Western redcedarlumberis producedprincipally in Washington, followed by Oregon,Idaho, and Montana.

for sheathing, knottypaneling, and subflooring. High-grade material is made into siding ofvarious kinds, exteriorand interiorwoodwork, and millwork.Westernwhite pine has practicallythe same uses as easternwhitepine (Pinus sfrobus)and sugarpine (Pinus lambertiana).

Port-Orford-Cedar Port-Orford-cedar (Chamaecyparis lawsoniana)is sometimes knownas Lawson-cypress, Oregon-cedar, and white-cedar. It growsalong the Pacific Coast from Coos Bay, Oregon, southward to California.It does not extendmore than 64 km (40 mi) inland. The heartwoodofPort-Orford-cedar is light yellow to pale brown.The sapwoodis narrowand hard to distinguishfrom theheartwood. The wood has fme texture, generally straight grain, and a pleasantspicy odor. It is moderately light-

Redcedar,Western

The heartwood ofwestern redcedaris reddishor pinkish brownto dull brown, and the sapwoodis nearly white. The sapwoodis narrow, often not more than 2.5 cm (1 ia.) wide. The wood is generallystraightgrained andhas a unform but rather coarsetexture. It has very low shrinkage. This species is lightweight, moderatelysoft, low in strength whenused as a beam orposts, and low in shockresistance. The heartwood is very resistantto decay. Westernredcedaris usedprincipally for shingles, lumber, poles, posts,and piles. The lumberis usedfor exterior siding, decking, interiorwoodwork, greenhouse construction, ship and boat building, boxes and crates, sashes, and doors.

1—15

Redwood Redwood(Sequoiasempervirens) growson the coast of California and sometrees are amongthe tallest in the world. A closely related species, giant sequoia(Sequoiadendron giganteum),is volumetrically larger and grows in a limited area in the SierraNevadasofCalifornia, but its wood is used in very limitedquantities. Othernames for redwoodare coast redwood,Californiaredwood,and sequoia. Productionof redwoodlumber is limitedto California, but the market is nationwide.

The heartwoodofredwoodvariesfrom light "cherry"red to dark mahogany.The narrow sapwoodis almost white. Typical old-growth redwoodis moderatelylightweight, moderately strong and stiff, and moderatelyhard. The wood is easy to work, generallystraightgrained,and shrinks and swells comparatively little. The heartwoodfrom old-growth trees has high decayresistance;heartwoodfrom second-growth trees generally has low to moderatedecay resistance. Most redwood lumberis used forbuilding. It isremanufactured extensivelyinto siding, sashes, doors, blinds, millwork, casket stock, and containers. Becauseofits durability, redwood is useful for coolingtowers,decking,tanks, silos, wood-stavepipe,and outdoorfurniture.It is used in agriculturefor buildingsand equipment. Its use as timbers and large dimension in bridges and trestlesis relatively minor. Redwood splits readily and plays an important role in the manufacture ofsplitproducts,such as posts and fence material.Some redwoodveneeris producedfor decorative plywood.

Spruce, Eastern The term easternspruce includes three species: red (Picea rubens),white (P. glauca), andblack (P. mariana). White and blacksprucegrow principally in the Great LakeStates andNew England, andred sprucegrowsin New England and the AppalachianMountains.

The wood is light in color, and there is little difference betweenheartwoodand sapwood. All threespecies have about the same properties, and they are not distinguished from each other incommerce.The wood dries easily andis stable after drying, is moderatelylightweight and easily worked,has moderateshrinkage, and is moderatelystrong, stiff, tough, and hard. The greatest use ofeasternspruceis for pulpwood. Eastern spruce lumberis used for framingmaterial,generalmiliwork, boxes and crates,andpiano sounding boards.

Spruce, Engelmann

Engehnann spruce (Picea engelmannii) growsathigh eleva-

tions in the Rocky Mountainregion ofthe United States. This speciesis also known as white spruce, mountain spruce,Arizona spruce, silverspruce, and balsam. About two-thirdsofthe lumberis producedin the southernRocky MountainStatesand most ofthe remainderin the northern RockyMountainStates and Oregon.

1—16

The heartwoodofEngelmann spruce is nearly white,with a slight tinge ofred. The sapwoodvaries from 2 to 5 cm (3/4to 2 in.) in width and is often difficultto distinguish from the heartwood. The wood has mediumto fine texture and is withoutcharacteristic odor.Engelmannspruceis rated as lightweight, and it is low in strengthas a beam or post. It is also soft and low in stiffhess, shock resistance,and shrinkage. The lumbertypicallycontains many smallknots. Engelmann spruceis usedprincipally for lumberand for minetimbers,railroadcrossties, and poles. It is usedalso in buildingconstruction in the form ofdimensionlumber, flooring, and sheathing. Ithas excellent propertiesforpulp andpapermaking.

Spruce, Sitka Sitka spruce(Picea sitchensis)is a large tree that grows along the northwestern coast ofNorth Americafrom Cali forniato Alaska. It is also known as yellow,tideland,western, silver, and west coast spruce.Much Sitka spruce timber is grownin Alaska, but most logs are sawn into cants for exportto PacificRim countries. Materialfor U.S. consurnption is producedprimarilyin Washingtonand Oregon.

The heartwoodofSitka spruce is a light pinkish brown. The sapwoodis creamy white and shadesgraduallyinto the heartwood;the sapwoodmay be 7 to 15 cm (3 to 6 in.) wide oreven widerin young trees. The wood has a comparatively fme,uniformtexture, generally straightgrain, andno distinct taste or odor. It is moderately lightweight,moderatelylow in bendingand compressivestrength, moderatelystiff, moderately soft, and moderatelylow in resistance to shock. Ithas moderatelylow shrinkage. On the basis ofweight,Sitka spruce rates high in strengthproperties and can be obtained in long, clear, straight-grained pieces. Sitka spruceis used principally for lumber, pulpwood, and cooperage. Boxes and crates account for a considerable amount ofthe remanufactured lumber. Other important uses are furniture,planing-mill products, sashes,doors, blinds, miliwork, and boats. Sitka spruce has been by farthe most important wood for aircraft construction. Other specialty uses are ladderrails and sounding boards for pianos.

Tamarack Tamarack(Larixlaricina), also knownas eastern larchand locally as hackmatack, is a small to mediumtree with a straight, round, slightlytaperedtrunk. It grows from Maine to Minnesota, with thebulk ofthe stand in theGreat Lake States.

The heartwoodoftamarackis yellowishbrownto russet brown. The sapwoodis whitish, generallyless than 2.5 cm (I in.) wide. The wood is coarsein texture, withoutodor or taste, and the transitionfrom earlywoodto latewoodis abrupt. The wood is intermediate in weight and in most mechanical properties.

Tamarackis used principally for pulpwood, lumber, railroad crossties, mine timbers,fuel, fence posts, and poles. Lumber

is used for framingmaterial, tank construction, and boxes,

may be obtained ofa particular wood.The references at the end ofthis chaptercontaininformation on many species not describedin this section.

White-Cedar, Northern and Atlantic Two speciesofwhite-cedargrow in the eastern part ofthe

Hardwoods

pallets,and crates. Theproductionoftamarack lumberhas declined in recentyears.

UnitedStates: northern white-cedar(Thuja occidentalis) and

Atlantic white-cedar (Chamaecyparis thyoides). Northern white-cedar is also knownas arborvitae or simply as cedar. Atlantic white-cedaris alsoknownas southern white-cedar, swamp-cedar, and boat-cedar. Northern white-cedar grows from Mainealong the Appalachians and westwardthrough the northernpart ofthe Great LakeStates.Atlantic whitecedargrows nearthe AtlanticCoast from Maineto northern Floridaand westwardalong the GulfCoastto Louisiana. It is strictlya swamptree. Productionofnorthernwhite-cedar lumberis greatest in Maineandthe Great Lake States.Production ofAtlanticwhite-cedar centers inNorth Carolinaand along the GulfCoast.

The heartwoodofwhite-cedaris light brown,and the sapwood is white or nearly so. The sapwoodis usually narrow. The wood is lightweight,rather soft, and low in strength and shock resistance.It shrinkslittle in drying. It is easily workedand holds paint well, and the heartwoodis highly resistantto decay.Northernand Atlantic white-cedar are used for similar purposes, primarilyfor poles,cabin logs, railroad crossties, lumber, posts, and decorative fencing.White-cedar lumberis used principally wherea high degreeofdurability is needed,as in tanks andboats, and for woodenware.

Yellow-Cedar Yellow-cedar(Chamaecyparisnootkatensis) growsin the PacificCoastregionofNorth Americafrom southeastern Alaska southwardthroughWashington to southernOregon.

Theheartwoodofyellow-cedaris bright,clear yellow.The sapwoodis narrow,white to yellowish,and hardly distinguishable from theheartwood.The wood is fine textured and generallystraightgrained.It is moderatelyheavy, moderately strong and stiff, moderatelyhard, and moderatelyhigh in shock resistance.Yellow-cedar shrinks little in drying and is stable afterdrying, and the heartwoodis very resistantto decay. The wood has a mild, distinctive odor. Yellow-cedar is usedfor interiorwoodwork, furniture, small boats, cabinetwork, and novelties.

Imported Woods This sectiondoes not purport to describeall the woodsthat havebeen at one time or anotherimportedinto the United States. It includesonly those species that at presentare considered to be commercially important. The same species may be marketedin the UnitedStatesunder other common names. Because ofthe variationin commonnames,many cross-references are included. Text information is necessarily brief, but when used in conjunction with the shrinkage and strengthdata tables (Ch. 3 and 4), areasonably goodpicture

Afara (see Limba) Afrormosia Afrormosia or kokrodua (Pericopsiselata), a largeWest Africantree, is sometimes used as a substitute forteak

(Tectonagrandis). The heartwoodis fme textured,with straightto interlocked grain. The wood is brownishyellowwith darkerstreaks and moderately hard and heavy,weighingabout 700 kg/m3 (43 lb/ft3) at 15% moisture content. The wood strorLgly resembles teak inappearancebut tacks its oily nature and has a differenttexture. The wooddries readily with littk degrade and has good dimensionalstability. It is somewhatheavier and strongerthan teak. The heartwoodis highly resistantto decay fungiandtermiteattackand is extremely durable under adverseconditions. Afrormosia is often used forthe same purposesas tek, such as boat construction, joinery, flooring, furniture, interior woodwork, and decorative veneer.

Albarco Albarco, orjequitiba as it is known in Brazil, is the common nameapplied to species in the genus Cariniara. The 10 species are distributed from eastern Peru and northern BoliviathroughcentralBrazilto Venezuelaand Colombia.

The heartwoodis reddishor purplish brownand sometimes has dark streaks.It isusuallynot sharplydemarcatedfrom thepale brownsapwood. The texture is mediumand the grain straight to interlocked. Albarcocan be workedsatisfactorily with only slight bluntingoftoolcutting edgesbecause ofthe presence ofsilica. Veneer canbe cut withoutdifficulty. The wood is rather strong and moderatelyheavy,weighing about 560 kg/rn3(35 lb/ft3)at 12% moisture content. In general, the wood has about the same strengthas that ofU.S. oaks (Quercusspp.). The heartwoodis durable, particularly thedeeply colored material. It has goodresistanceto drywoodtermiteattack. Albarcois primarily used for general construction and carpentry wood, but it can alsobe used forfurniturecomponents, shipbuilding, flooring, veneerforplywood, and turnery. Amaranth (see Purpleheart) Anani (see Manni) Anaura (see Marishballi) Andiroba Because ofthe widespread distribution ofandiroba (Carapa

guianensis)in tropicalAmerica,the wood is knownundera varietyofnames,including cedro macho,carapa, crabwood,

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and tangare. Thesenames are also appliedto the related species Carapanicaraguensis,whosepropertiesare generally inferiorto those of C. guianensis. The heartwoodvaries from mediumto darkreddishbrown. The texture is like that oftrue mahogany(Swietenia macrophylla), and andirobais sometimes substituted for true mahogany.The grain is usually interlockedbut is rated easy to work, paint, and glue. The wood is rated as durableto very durable with respectto decay and insects.Andirobais heavier than true mahoganyand accordingly is markedly superior in all static bendingproperties,compression parallelto grain, hardness,shear,and durability.

whereit forms fairly densebut localizedand discontinuous timberstands. The wood is creamto pale yellow with high natural luster; it eventually darkensto a goldenyellow. The grain is sometimesstraight but more often wavyorirregularlyinterlocked, whichproducesan unusual and attractivemottledfigure whensliced or cut on the quarter. Althoughavodire weighs less than northernred oak (Quercusrubra), it has almost identicalstrengthproperties exceptthat it is lowerin shock resistance and shear. The wood worksfairlyeasily with hand andmachinetools and finishes well in most operations.

Onthebasis of its properties,andirobaappearsto be suited for suchuses as flooring, frame construction inthe tropics,

Figured material is usuallyconverted into veneerforuse in decorative work,and it is this kind ofmaterial that is chiefly imported into the United States. Otheruses includefurniture, fine joinery, cabinetwork, and paneling.

Angelin (see Sucupira)

Azobe (Ekki) Azobe or ekki (Lophiraalata) is found in West Africaand extends into the Congobasin.

furniture and cabinetwork, millwork, utilityand decorative veneer,andplywood.

Angelique comesfromFrench Angelique(Dicoryniaguianensis) Guiana and Suriname.

Becauseofthe variability inheartwoodcolorbetweendifferent frees,two forms are commonly recognizedby producers. Theheartwoodthat isrusset-coloredwhenfreshlycut and becomessuperficiallydull brownwith a purplish cast is referredto as "gris." The heartwoodthat is more distinctly reddish and frequentlyshows widepurplishbands is called "angeliquerouge." The texture ofthe wood is somewhat coarserthan that ofblack walnut(Juglans nigra), and the grain is generallystraightor slightlyinterlocked. In strength, angeliqueis superior to teak(Tectonagrandis) and white oak (Quercus alba), when green or air dry, in all properties excepttensionperpendicular to grain.Angelique is ratedas highlyresistant to decay and resistantto marineborer attack. Machining properties vary andmaybe due to differences in density, moisturecontent,and silica content. After the wood is thoroughlyair or kiln dried, itcanbe workedeffectively only with carbide-tippedtools. The strength and durabilityofangelique make it especially suitableforheavy construction, harborinstallations, bridges, heavyplankingforpierand platformdecking,andrailroad bridge ties. The wood is also suitable for ship decking, planking, boat frames, industrial flooring, andparquetblocks and strips.

Apa (see Wallaba) Apamate (see Roble)

Apitong (see Keruing) Avodire Avodire(Turraeanthusafricanus)has a rather extensive range in Africa,from SierraLeonewestwardto the Congo region and southward to Zaire and Angola.It is most common in the easternregion ofthe IvoryCoast and is scattered elsewhere. Avodire is amedium-size tree ofthe rainforest

The heartwoodis dark red, chocolate-brown, or purple-brown with conspicuous white deposits in the pores (vessels).The texture is coarse, and the grain is usually interlocked. The wood is strong, and its densityaverages about 1,120 kg/rn3 (70 lb/ft3) at 12% moisture content. It is very difficult to work with hand and machinetools, and tools areseverelyblunted ifthewood is machinedwhen dry. Azobecan be dressedto a smoothfinish, and gluingproperties are usually good. Dryingis very difficultwithout excessive degrade. The heartwoodis rated as very durable against decay but only moderatelyresistantto termiteattack.Azobe is very resistantto acid and has good weatheringproperties. It is alsoresistantto teredo attack.Theheartwoodis extremely resistantto preservative treatment. Azobe is excellent forheavy construction work, harborconstruction, heavy-duty flooring, and railroadcrossties.

Bagtikan (see Seraya, White) Balata Balataor bulletwood(Manilkarabidentata) is widelydistributedthroughoutthe West Indies, Central America,and northern South America.

The heartwoodofbalata is light to dark reddish brownand not sharplydemarcatedfrom the pale brown sapwood. Texture is fine and uniform, and the grain is straightto occasionally wavyor interlocked. Balata is a strong and very heavy wood; density ofair-driedwood is 1,060 kg/m3 (66 lb/tI3). It is generallydifficultto air dry, with a tendencyto develop severe checkingand warp.The wood is moderatelyeasy to work despite its high density, and it is rated good to excellent in all machiningoperations. Balata is very resistant to attackby decay fungi and highlyresistantto subterranean termitesbut only moderatelyresistant to dry-woodtermites.

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Balatais suitable for heavy construction, textile and pulpmill equipment, furnitureparts, turnery, tool handles, flooring, boat framesand other bentwork,railroadcrossties, violin bows, billiardcues, and other specialtyuses.

generally mixed in the trade.The main commercial supplyof cuangare comes from Colombia andEcuador. Banak and cuangare are common in swamp andmarshforestsandmay occur in almostpure stands in someareas.

Balau

The heartwoodofboth banak and cuangare is usually pinkish or grayishbrownand is generally not differentiated from the sapwood. The wood is straightgrainedand is ofa medium to coarsetexture.The various species arenonresistant to decay and insectattackbut can be readilytreatedwith preservatives. Machining propertiesare very good,but when zones oftensionwoodare present,machiningmay result in surface fuzziness. The woodfinishesreadily and is easily glued. Strength properties ofbanakand cuangareare similar to those ofyellow-poplar (Liriodendrontulip(fera).

Balau, red balau, and selanganbatu constitute a group of species that are the heaviestofthe 200 Shorea species. About 45 species ofthis group grow from Sri Lankaand southern India through southeastAsia to the Philippines.

The heartwoodis light to deep red or purple—brown,and it is fairly distinctfrom thelighterand yellowish-to reddishor purplish-brown sapwood. The textureis moderatelyfine to coarse,andthegrain is often interlocked. The wood weighsmore than 750 kg/rn3(47 lb/fl3) at 12% moisture content. Balau is a heavy, hard, and strong timberthat dries slowly with moderateto severeend checksand splits. The heartwoodis durableto moderately durable and very resistant

to preservative treatments.

Balau is used forheavy construction, framesofboats,decking, flooring, and utility furniture. Balau, Red (see Balau) Balsa Balsa(Ochroma pyramidale)is widelydistributedthroughout tropicalAmericafrom southern Mexicoto southern Brazil and Bolivia,butEcuadorhas been the principalsource ofsupplysince thewood gained commercial importance. It is usuallyfoundat lower elevations,especiallyon bottomland soils along streamsand in clearings and cutover forests. Today, it is often cultivated in plantations. Several characteristics makebalsa suitable fora wide variety

ofuses.It is the lightestand softestof all woodson the

market. The lumber selectedfor use in the United States weighs, on the average,about 180 kg/rn3 (11 lb/fl3)when dry and often as little as 100 kg/rn3 (6 Ib/ft3). The wood is read-

ily recognizedby its lightweight;nearly white oroatmeal color, often with a yellowishor pinkishhue; and unique

Banakis considered a generalutilitywood for lumber, veneer, and plywood. It is also used for moulding, mi [lwork, and furniture components.

Benge (Ehie, Bubinga) Although benge (Guibourtiaarnoldiana), ehie or ovangkol (Guibourtiaehie),andbubinga (Guibourtiaspp.)belong to thesame West Africangenus, theydifferrathermarkedly in color andsomewhat in texture.

The heartwoodofbenge is pale yellowishbrownto medium brownwith gray to almostblack stripes. Ehie heartwood tends to be more golden brown to dark brown with gray to almostblack stripes. Bubingaheartwoodis pink, vivid red, or red—brown with purplestreaks,and it becomes yellowor medium brownwith a reddishtint upon exposureto air. The textureofehie is moderately coarse, whereas that ofbenge and bubingais fme tomoderatelyfine. All three wocds are moderately hard and heavy,but they can be workedwell with hand and machinetools. They are listed as moderately durable and resistantto preservative treatment.Dryingmay be difficult, butwith care,thewood dries well. Thesewoodsare used in turnexy, flooring, furniturecomponents, cabinetwork, and decorative veneers.

velvety feel.

Brown Silverbaul (see Kaneelhart)

Because ofits light weightand exceedingly porousccmposition, balsa is highlyefficient in useswhere buoyancy, insulationagainstheator cold, or low propagationofsound and vibration are important. Principal uses are for life-saving equipment, floats,rafts, corestock, insulation, cushioning, soundmodifiers,models,and novelties.

Bubinga (see Benge)

Banak (Cuangare) Variousspeciesofbanak(Virola)occur intropicalAmerica,

fromBelize and Guatemala southward to Venezuela, the Guianas, the Amazonregionofnorthern Brazil, and southern Brazil, and onthe Pacific Coastto Peru and Bolivia.Most of the woodknownas banak is V. koschnyi ofCentralAmerica and V. surinamensisand V. sebfera ofnorthern South America.Botanically, cuangare(Dialyanthera)is closely relatedto banak,andthe woodsare so similarthat they are

Bulletwood (see Balata) Carapa (see Andiroba) Cativo Cativo(Prioriacopafera)is one ofthe few tropical American species that occur in abundance and often innear]ypure stands. Commercial stands are found in Nicaragua, Costa Rica, Panama, and Colombia. Sapwoodmay be very palepink or distinctlyreddish, and it is usuallywide. In trees up to 76 cm (30 in.) in diameter, heartwoodmay be only 18 cm (7 in.) in diameter.The grain is straight andthetextureofthewood is uniform, comparablewith that oftrue mahogany (Swietenia macrophy/la). On flat-sawn surfaces, the figureis rather subduedas a result of -

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exposureofthe narrow bands ofparenchymatissue.The wood can be dried rapidly and easily with very little degrade. Dimensionalstability is very good—practically equalto that oftrue mahogany. Cativo is classifiedas a nondurable wood with respectto decay and insects.It may containappreciable quantities ofgum. In wood that has been properlydried, however, the aromaticsin the gum are removedand there is no difficulty in finishing. Considerable quantitiesofcativoare used for interiorwoodwork, and resin-stabilized veneer is an important pattern material. Cativo is widelyusedfor furniture and cabinet parts, lumber core forplywood, pictureframes,edgebanding for doors,joinery, and millwork.

Cedro (see Spanish-Cedar) Cedro Macho (see Andiroba) Cedro-Rana (see Tornhllo) Ceiba Ceiba(Ce/bapentandra)is a largetree, whichgrowsto 66 m (200 ft) in height with a straight cylindrical bole 13 to 20 m (40 to 60 ft) long. Trunkdiametersof2 m (6 ft) or more are common. Ceiba growsin West Africa,fromthe IvoryCoast and SierraLeone to Liberia,Nigeria,and the Congoregion.A related species is lupuna(Ceiba samauma) from SouthAmerica. Sapwoodand heartwoodare not clearlydemarcated. The wood is whitish,palebrown, or pinkishbrown, often with yellowishor grayish streaks. The texture is coarse, and the grain is interlockedor occasionallyirregular. Ceiba is very soft and light; density ofair-driedwood is 320 kg/rn3 (20 lb/ft3). In strength,the wood is comparable with basswood (Tilia americana). Ceiba dries rapidlywithout marked deterioration. It is difficult to saw cleanly and dress smoothly becauseofthe high percentage oftensionwood.Itprovides goodveneer and is easy to nail and glue. Ceiba is very susceptible to attack by decay fungi and insects.It requires rapid harvestand conversionto preventdeterioration. Treatability, however, is rated as good. Ceiba is availablein large sizes,and its low density combined with arather high degreeofdimensionalstability make it ideal forpattern and corestock.Otheruses includeblockboard,boxes and crates,joineiy, and furniturecomponents. Chewstick (see Manni) Courbaril (Jatoba) ThegenusHymenaea consistsofabout 25 species that occur in theWest Indiesand from southernMexico through Central Americainto the Amazonbasin ofSouthAmerica. The best-knownand most importantspeciesis H. courbaril, whichoccursthroughoutthe range ofthe genus. Courbaril is often calledjatoba in Brazil. Sapwood of courbarilis gray—whiteand usuallyquitewide. The heartwood, whichis sharplydifferentiated from the

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sapwood, is salmonred to orange—brownwhen freshly cut andbecomesrusset or reddishbrown whendried. The heartwood is often markedwith dark streaks.The texture is medium to rather coarse, and the grain is mostly interlocked. The wood is hard and heavy (about 800 kg/rn3(50 lb/ft3)at 12% moisture content). The strengthpropertiesofcourbaril arequitehigh andvery similarto those ofshagbarkhickory (Carya ovata), a species oflowerspecificgravity. Courbaril is rated as moderatelyto very resistantto attackby decay fungi and dry-wood termites. The heartwoodis nottreatable, but the sapwoodis treatablewith preservatives. Courbarilis moderately difficultto saw andmachinebecauseofits high density,but it canbe machinedto a smooth surface. Turning, gluing, and finishingpropertiesare satisfactory. Planing, however, is somewhat difficult becauseofthe interlocked grain. Courbaril comparesfavorablywith white oak (Quercus alba) in steam bendingbehavior. Courbaril is used for tool handles and other applications that requiregood shock resistance. It is also used for steam-bent parts, flooring, tumery, furniture and cabinetwork, veneerand plywood, railroadcrossties, and other specialtyitems.

Crabwood (see Andiroba)

Cristobal (see Macawood) Cuangare (see Banak) Degame

Degameor lemonwood (Calycophyllum candidissimum) growsin Cuba and ranges from southernMexicothrough Central Americato Colombia and Venezuela. It may grcw in pure stands and is common on shadedhillsidesand along waterways. The heartwood ofdegame rangesfrom light brownto oatmeal-colored and is sometimesgrayish. The sapwoodis lighter in color and mergesgradually with the heartwood. The texture is fine and uniform. The grain is usually straight or infrequently shows shallow interlocking, whichmay produce a narrowand indistinct stripe on quarteredfaces.In strength, degame is above the averagefor woodsofsimilar density;density ofair-driedwood is 817 kg/rn3(51 lb/ft). Tests show degame superior to persimmon(Diospyros

virginiana)in all respectsbut hardness.Natural durabilityis low whendegame is used under conditions favorableto stain, decay, and insect attack. However,degame is reported to be highlyresistantto marineborers. Degameis moderately difficult to machine becauseof its densityand hardness, althoughit does not dull cutting tools to any extent. Machinedsurfaces arevery smooth. Degameis little usedin the United States,but its characteristics havemade it particularly adaptablefor shuttles,picker sticks, and other textile industry items that requireresilience and strength. 1)egame was onceprizedforthe manufacture of archery bows and fishingrods. It is also suitablefor tool handlesand turnely.

Determa Determa(Ocotea rubra)is native to the Guianas,Trinidad, and the lowerAmazonregion ofBrazil.

The heartwoodis light reddishbrown with agolden sheen and distinctfrom the dull gray or pale yellowish brown sapwood. The texture is rather coarse, and the grain is interlockedto straight.Determais a moderatelystrong and heavy wood (density ofair-driedwood is 640 to 720 kg/rn3(40 to 45 lb/ft3));this wood is moderatelydifficultto air dry. Itcan be workedreadily with hand and machinetools with little dulling effect. It can be glued readily andpolishedfairlywell. Theheartwoodis durable to very durable in resistance to decay fungi and moderatelyresistantto dry-woodtermites. Weatheringcharacteristics are excellent, andthe wood is highly resistant to moisture absorption. Uses for detennâincludefurniture,general construction, boat planking,tanks and cooperage, heavy marineconstruction, turnery,andparquetflooring. Ehie (see Benge) Ekki (see Azobe) Ekop Ekopor gola (Tetraberlinia tubmaniana)grows only in Liberia.

The heartwoodis light reddish brown and is distinct from the lightercoloredsapwood,whichmaybe up to 5 cm (2 in.) wide. The wood is mediumto coarsetextured,and thegrain is interlocked, with anarrow stripedpatternon

quarteredsurfaces. The wood weighsabout 735 kg/rn3 (46 lb/ft3) at 12% moisturecontent.It dries fairlywell but with amarkedtendencyto end and surface checks.Ekop workswell with hand and machinetools and is an excellent wood forturnery. It also slices well into veneerand has good gluingproperties.The heartwoodis only moderatelydurable and is moderatelyresistant to impregnation with preservative treatments.

Ekop is ageneral utility wood that is used for veneer, plywood, and furniture components.

Encino (see Oak) Gola (see Ekop) Goncalo Alves Mostimportsofgoncaloalves (Astronium graveolensand A.fraxinjfolium)have beenfrom Brazil. These species range from southern Mexico throughCentralAmericainto the Amazonbasin. Freshly cut heartwoodis russet brown, orange—brown, or reddishbrown to red with narrowto wide, irregular, medium-to very-darkbrown stripes. After exposure to air, the heartwoodbecomesbrown,red, or dark reddishbrownwith nearly black stripes. The sapwoodis grayishwhite and sharply demarcatedfrom the heartwood. The textureis fme to

mediumand uniform. The grain variesfrom straightto interlockedand wavy. Goncaloalves turnsreadily,finishesvery smoothly, and takes a high natural polish. The heartwoodis highly resistant to moistureabsorption; pigmentedareas may present some difficulties in gluingbecauseoftheir high density. The heartwoodis very durable and resistantto both white- and brown-rotorganisms. The high density(1,010 kg/rn3 (63 lb/ft3)) ofthe air-dried wood is accompaniedby equally high strengthvalues, which are considerably higher in most respectsthan those ofany U.S. species. Despite its s'rength, however, goncaloalves is imported primarilyfor its beauty.

In theUnitedStates, goncaloalves has the greatest vahiefor specialtyitemssuch as archery bows,billiardcue butts, brushbacks, and cutleryhandles,and in turneryand carving applications.

Greenheart Greenheart (Chiorocardium

rodiei [ Ocotea rodiei]) is

essentiallya Guyanatree although small stands alsooccur in Suriname.

The heartwoodvariesfrom light to dark olive green or nearly black. The texture is fine and uniform, and the grain .s straightto wavy. Greenheart is stronger and stifferthanwhite oak (Quercusalba)and generally more difficultto work with tools becauseofits high density;densityofair-driedwood is more than 960 kg/rn3(60 lb/ft3). The heartwoodis ratd as very resistantto decay fungiandtermites.It is also very resistantto marineborers in temperatewaters but much less so in warmtropicalwaters. Greenheart isused principally wherestrengthandresistance to wear arerequired. Uses includeship and dock building, lock gates, wharves, piers,jetties, vats, piling, plank.ng, industrial flooring, bridges, and some specialtyitems (fishingrods and billiard cue butts).

Guatambu (see Pau Marfim) Guayacan (see Ipe) Hura Hura (Hura crepitans)growsthroughoutthe West Indies from CentralAmericato northernBrazil andBolivia.

It is a large tree, commonly reachinga height of30 to 43 m (90 to 130 ft), with clear boles of 12 to 23 m (40 to 75 fi). The diameteroftenreaches ito 1.5 m (3 to 5 ft) and occasionallyto 3 m (9 ft).

The pale yellowish-brown or pale olive-gray heartwocdis indistinctfrom the yellowish-white sapwood. The texaire is fine to medium and the grain straightto interlocked. Hurais a low-strength and low-density wood (densityofair-dried wood is 240 to 448 kg/rn3(15 to 28 lb/ft3)); the wood is moderately difficult to air dry. Warping is variableand sometimessevere. The wood usuallymachineseasily, but green material is somewhat difficult to work becauseoftension

1—21

ft

wood, whichresultsin a fuzzy surface. The woodfinishes well and is easy to glue and nail. Hura is variablein resistance to attack by decay fungi,but it is highlysusceptible to blue stainandvery susceptibleto wood termites. However, thewood is easy to treat with preservative. Hura is often used in generalcarpentry, boxes and crates,and lowergrade furniture. Otherimportant uses are veneerand plywood, fiberboard,and particleboard.

Ilomba Ilomba (Pycnanthusangolensis)is atree ofthe rainforestand rangesfrom Guineaand SierraLeonethroughtropical West AfricatoUganda and Angola. Commonnames include pycnanthus,walele, and otie.

The wood is grayish white to pinkish brown and, in some trees, auniform light brown. There is generallyno distinction betweenheartwoodand sapwood. The texture is medium to coarse, and the grain is generallystraight. This species is generallysimilarto banak (Virola) but has a coarsertexture. Air-drydensityis about 512 kg/rn3 (31 lb/ft3), and thewood is about as strong as yellow-poplar (Liriodendrontulipjfera). Ilombadries rapidlybut is prone to collapse,warp, and splits. It is easily sawn and can be workedwell with hand and machine tools. It is excellentfor veneerand has goodgluing and nailingcharacteristics. Green wood is subjectto insect and fungal attack. Logsrequire rapid extractionand conversionto avoid degrade. Both sapwood andheartwoodarepermeable and can be treated with preservatives.

Ipe is used almostexclusively for heavy-dutyand durable construction. Becauseofits hardness and good dimensional stability, it is particularlywell suited forheavy-dutyflooring intrucks and boxcars. It is also used for decks,railroad crossties, turnely,tool handles,decorativeveneers,and some specialty itemsin textile mills.

Ipil (see Merbau) Iroko Irokoconsistsoftwo species(Miliciaexcelsa [= Chiorophora excelsa] and M. regia[ C. regia]). Miliciaexceisa growsacross the entirewidthoftropicalAfricafrom the Ivory Coast southward to Angolaand eastwardto EastAfrica. Miliciaregia, however, is limitedto extremeWest Africa from Gambiato Ghana; it is less resistant to droughtthan is

M excelsa.

The heartwoodvariesfrom a pale yellowishbrownto dark chocolatebrownwith lightmarkingsoccurringmost conspicuously on flat-sawnsurfaces;the sapwoodis yellowish white. The texture is mediumto coarse,and the grain is typically interlocked. Iroko can be workedeasily with hand ormachinetools butwith some tearing ofinterlockedgrain. Occasional deposits ofcalciumcarbonate severelydamage cutting edges. The wood dries rapidly with little or no degrade. The strengthis similar to that ofred male (Acer rubrum),andthe weight is about 688 kg/m (43 lb/ft3) at 12% moisture content. The heartwoodis very resistantto decay fungi and resistant totermite andmarine borer attack.

In the United States, this species is used only in the form of plywood for generalutility purposes.However, ilombais defmitelysuited for furniturecomponents, interiorjoinery, andgeneral utility purposes.

Because ofits color anddurability, iroko has been suggested as a substitutefor teak(Tectonagrandis). Its durability makes it suitablefor boat building, piles, other marine work, andrailroadcrossties. Otheruses includejoinery,flooring, furniture, veneer, and cabinetwork.

Ipe

Jacaranda (see Rosewood, Brazilian)

Ipe, the commonnameforthe lapachogroup ofthe genus Tabebuia, consistsofabout 20 species oftrees and occurs in practicallyevery Latin Americacountryexcept Chile. Other commonly usednames are guayacan and lapacho.

Jarrah

Sapwoodis relativelywide, yellowishgray orgray—brown, and sharplydifferentiated from heartwood, whichis light to dark olive brown. The texture is fme to medium.The grain is straight to very irregularand oftennarrowlyinterlocked. The wood is very heavy and averages about 1,025 kg/rn3 (64 lb/ft3)at 12% moisture content. Thoroughly air-dried heartwoodspecimensgenerallysink in water. Because ofits high densityand hardness,ipe is moderatelydifficultto machine,but glassy smooth surfaces can be produced. Ipe is very strong; in the air-driedcondition,it is comparable with greenheart(Chlorocardiumrodiel).Hardnessis two tothree timesthat ofwhite oak(Quercus alba) orkeruing (Dipterocarpus). The wood is highly resistant to decay and insects, includingboth subterranean and dry-wood termites, but susceptibleto marine borer attack.The heartwoodis impermeable,but the sapwoodcan be readilytreatedwith

The heartwoodis a uniform pink to dark red, often turning to deepbrownishred with age and exposureto air. The sapwoodis pale and usually very narrow in old trees. The texture is evenandmoderatelycoarse,and the grain is frequently interlockedor wavy. The wood weighs about 865 kg/rn3 (54 lb/fl3) at 12% moisture content.The common defects ofjarrah include gum veins orpockets,which in extreme instances, separatethe log into concentricshells. Jarrah is a heavy, hard timberpossessingcorrespondingly high strengthproperties. It is resistant to attack by termites andrated as very durablewith respectto decay.The wood is difficult to work with hand and machine tools becauseofits high density and irregulargrain.

preservatives. 1—22

Jarrah(Eucalyptusmarginata) is nativeto the coastalbelt of southwestern Australiaand is one ofthe principalspeciesfor that country's sawmillindustry.

Jarrah is used for deckingand underframing ofpiers,jetties, and bridges, as well as pilesand fendersfor docks and

harbors.As flooring, jarrahhas high resistance to wear,but it is inclinedto splinterunderheavy traffic. Itis also used for railroadcrossties and other heavyconstruction. Jatoba (see Courbaril) Jelutong Jelutong(Dyeracostulata)is an important species in Malaysia where it is bestknown for its latex production in the manufacture ofchewinggum ratherthan for itswood. The wood iswhite or strawcolored,and there is no differentiationbetween heartwoodand sapwood. The texture is moderatelyfine and even. The grain is straight,and luster is low. The wood weighs about 465 kg/rn3 (28 lb/fl3) at 12% moisture content. The wood is very easy to dry with little tendencyto split or warp,but stainingmay cause trouble. It is easy to work in all operations,finisheswell, and glues satisfactorily. The wood is rated as nondurablebut readily permeable to preservatives.

Becauseofits low density and easeofworking, jelutong is well suited for sculptureand patternmaking,woodenshoes, pictureframes,and drawing boards.

Jequitiba (see Albarco) Kakaralli (see Manbarkiak) Kaneelhart Kaneelhartor brownsilverballiare names appliedto the genus Licaria. Species ofthis genus grow mostly in New GuineaandPapauNew Guinea and are found in association with greenheart(Chiorocardiumrodiei) on hilly terrain and wallaba(Eperua)in forests. The orangeor brownishyellowheartwooddarkensto yellowishorcoffee brown on exposureto air. Thewood is sometimestinged with red or violet. The texture is fine to medium, and the grain is straightto slightly interlocked. The wood has a fragrantodor, which is lost in drying. Kaneelhartis a very strong and very heavywood (densityof air-driedwood is 833 to 1,153 kg/rn3 (52 to 72 lb/fl3));the wood is difficultto work. It cuts smoothlyand takes an excellentfinishbut requfres care in gluing. Kaneelharthas excellentresistance to both brown- andwhite-rotfungi andis also rated very high in resistanceto dry-wood termites. Uses ofkaneelhartinclude furniture, turnery,boat building, heavy construction, andparquetflooring.

Kapur The genus Dryobalanopsconsistsofnine species distributed over parts ofMalaysiaand Indonesia. For the exporttrade, thespecies arecombined under the namekapur.

The heartwoodis reddishbrownand clearly demarcatedfrom thepale sapwood.The wood is fairly coarsetextured but uniform. In general,the wood resembles keruing (Dipterocarpus),but on the whole, kapur is straighter grainedand not quiteas coarse in texture. Densityofthe wood averages about 720 to 800 kglm3 (45 to 50 lb/fl3) at

12% moisturecontent. Strength propertiesare simiIar to those ofkeruingatcomparable specificgravity. The heartwood is rated resistantto attack by decay fungi;it i:; reported to be vulnerable to termites. Kapur is extremelyresistantto preservative treatment.The woodworks with moderateease in most hand and machineoperations,but bluntingofcutters may be severe becauseofsilicacontent, particularly whenthe dry woodis machined. A goodsurfacecan be obtainedfrom variousmachiningoperations, but there is atendencytoward raisedgrain ifdull cuttersare used.Kapur takes nail[s and screws satisfactorily. The wood glueswell with ureaformaldehyde but not with phenolicadhesives.

Kapurprovidesgood and very durable construction wood and is suitable for all purposesfor whichkeruing (Dipterocarpus)is used in the United States.In addition, kapur is extensively used in plywoodeitheralone or with species ofShorea (lauan—meranti). Karri Karri (Eucalyptus diversicolor) is a very large tree limited to southwestern Australia.

Karriresembles jarrah (E. marginata)in structure ard general appearance. It is usually paler in color and, on average, slightly heavier (913 kg/rn3(57 lb/fl3)) at 12% moisture content. Karri is a heavyhardwoodwith mechanicalproperties ofa correspondingly high order, evensomewhai higher thanthat ofjarrah. The heartwoodis rated as moderately durable,though less so than that ofjarrah. It is extremely difficulttotreat with preservatives. The wood is fairLy hard to machineand difficultto cut with hand tools. It is generally more resistantto cutting than isjarrahand has a slightly more dulling effecton tool edges. Karriis inferior tojarrah forunderground use and waterworks. However, where flexural strength is required, such as in bridges, floors, rafters, and beams, karri is an excellent wood. Karri is popularin heavy construction becauseofits strengthand availabilityin large sizes and long lengths that arefree ofdefects. Kauta (see Marishballi) Kempas Kempas (Koompassiamalaccensis)is distributedthroughout the lowlandforestin rather swampyareas ofMalaysiaand Indonesia.

Whenexposed to air, the freshlycutbrick-redheartwood darkens to an orange—red orred—brown with numerous yellow—brown streaks as aresult ofthe soft tissue(axialparenchyma) associatedwith the pores. The texture is rather coarse, and the grain is typicallyinterlocked. Kempasis a hard, heavy wood (densityofair-driedwood is 880 kg/rn3 (55 lb/ft3));the wood is difficultto work with hand and machine tools. The wood dries well, with some tendencyto warp and check. The heartwoodis resistant to attack by decay fungibut vulnerable to termiteactivity.However, it treatsreadilywith preservative retentionas high as 320 kg/rn3 (20 lb/ft3). 1—23

Kempasis ideal for heavyconstruction work, railroad crossties, and flooring.

Keruing (Apitong) Keruing or apitong(Dipterocarpus)is widely scattered throughoutthe Indo-Malaysian region.Most ofthe more than 70 speciesin this genus are marketedunderthe name keruing.Other importantspeciesare marketedas apitong in the PhilippineIslands and yang in Thailand. The heartwoodvaries from light to dark red—brownor brown to dark brown,sometimeswith apurple tint; theheartwood is usually well defined from thegray orbuff-colored sapwood. Similarto kapur (Dryobalanops),the texture of keruing is moderatelycoarseand the grain is straight or shallowly interlocked. The wood is strong,hard, and heavy (density ofair-driedwood is 720 to 800 kg/rn3 (45 to 50 lbfft3));thiswood is characterized by the presenceofresin ducts, whichoccur singlyor in short arcs as seen on endgrain surfaces. This resinous condition andthe presence of silicacan presenttroublesome problems.Sapwood and heartwoodare moderatelyresistantto preservative treatments. However,the wood should be treatedwith preservatives when it is used in contactwith the ground. Durability varies with species,butthe wood is generallyclassified as moderately durable.Keruing generallytakes to sawingand machining, particularlywhen green, but saws and cutters dull easily as a result ofhigh silica content in thewood.Resin adheres to machineryand tools and may be troublesome. Also, resin may cause gluingandfmishingdifficulties. Keruing is used forgeneralconstruction work,framework for boats, flooring, pallets, chemicalprocessing equipment, veneerand plywood, railroadcrossties(iftreated), truck floors,and boardwalks.

Khaya (see Mahogany, African) Kokrodua(see Afrormosia)

Korina(see Limba) Krabak (see Mersawa) KwiIa (see Merbau) Lapacho (see Ipe) Lapuna (see Ceiba) Lauan (see Meranti Groups) Lemonwood (see Degame) Lignumvitae Formany years, the only speciesoflignumvitaeused on a large scalewas Gualacumofficinale, whichis nativeto the West Indies, northernVenezuela,northernColombia, and Panama. Withthe near exhaustion ofG. officinale, harvesters turnedto G. sanctum,which is nowthe principalcommercialspecies.Guaiacumsanctum occupies the same range as G. officinalebut is more extensiveand includesthe Pacific side ofCentralAmericaas well as southern Mexico.

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Lignumvitae is one ofthe heaviestand hardestwoodson the market. The wood is characterizedby its unique green color and oily orwaxy feel. The wood has a fine uniformtexture and closelyinterlockedgrain. Its resin contentmay constitute upto one-fourth ofthe air-driedweightofthe heartwood. Lignumvitae wood is used chiefly for bearingor bushing blocks for ship propellershafts.The greatstrengthand tenacity oflignumvitae, combined with self-lubricating properties resulting from the high resin content,make it especially adaptable for underwater use. It is also used for such articles as mallets, pulley sheaves, caster wheels, stencil and chisel blocks, and turnedproducts.

Limba Limba (Terminaliasuperba), alsoreferredto as afara,is widely distributedfrom SierraLeone to Angolaand Zaire in

the rainforestandsavannaforest.Limbais alsofavored as a plantation species in West Africa.

The heartwoodvariesfrom gray—whiteto creamyor yellow brownandmay containdark streaksthat are nearly black, producing an attractive figurethat is valuedfor decorative veneer. The light color ofthe wood is consideredan important asset forthe manufacture ofblond furniture. The wood is generally straight grained and ofuniformbut coarsetexture.

The wood is easy to dry and shrinkageis reported to be rather low. Limbais not resistantto decay, insects,or termites. It is easy to work with all types oftools and is made into veneerwithoutdifficulty. Principaluses includeplywood, furniture,interiorjoinery, and sliced decorative veneer. Macacauba (see Macawood) Macawood (Trebol) Macawood and trebol are common names appliedto species inthe genus Platymiscium. Other common names include cristobaland macacauba. This genus is distributedacross continental tropicalAmericafrom southernMexicotothe Brazilian Amazonregion and Trinidad. The bright red to reddish or purplish brown heartwoodis more or less striped.Darker specimenslook waxy, and the sapwoodis sharplydemarcatedfrom the heartwood. The texture is mediumto fine, and the grain is straightto curly or striped.The wood is not very difficultto work, and it finishessmoothlyand takes on a high polish. Generally, macawood air dries slowlywith a slight tendencyto warp and check. Strength is quitehigh, and densityof air-dried wood rangesfrom 880 to 1,170kg/rn3 (55 to 73 lb/ft3). The heartwoodis reportedto be highly resistantto attack by decay fungi, insects, and dry-woodtermites. Althoughthe sapwoodabsorbspreservatives well,the heartwoodis resistant to treatment. Macawood is a fine furniture and cabinet wood. It is also used in decorative veneers, musical instruments, turnery, joinery, and specialtyitems such as violin bows and billiardcues.

Machinmango (see Manbarkiak) Mahogany The namemahoganyis presently applied to severaldistinct kindsofcommercial wood. The original mahoganywood, producedbySwieteniamahagoni,camefromthe American West Indies. This was the premierwood for fine furniture cabinetwork and shipbuilding in Europeas earlyas the 1600s. Becausethe good reputationassociatedwith the name mahoganyis based on this wood, American mahoganyis sometimes referredto as truemahogany. A relatedAfrican wood, ofthe genus Khaya, has long been marketedas "Africanmahogany"and isusedformuch the same purposes as American mahoganybecauseofits similarproperties and overallappearance. A thirdkind ofwood calledmahogany, and the one most commonlyencounteredin the market,is "Philippinemahogany."This name is appliedto a group of Asian woodsbelongingto the genus Shorea. In this chapter, information on the "Philippinemahoganies"is given under lauanand meranti groups. Mahogany, African—Thebulk of"Africanmahogany" shipped from west—central Africais Khayaivorensis, the most widely distributedandplentiful species ofthe genus found in the coastalbelt ofthe so-called high forest. The closely allied species K anthothecahas amore restricted range and is found farther inlandinregionsoflowerrainfall but well withinthearea now being used fortheexporttrade. The heartwoodvariesfrom pale pink to dark reddish brown. The grain is frequentlyinterlocked, andthe texture is medium to coarse, comparablewith that ofAmerican mahogany (Swieteniamacrophylla).The wood is easy to thy, but machiningproperties are rather variable. Nailingand gluing propertiesare good, and an excellentfinish is readilyobtained. The wood is easy to slice and peel. In decay resistance, African mahogany is generally ratedas moderately durable,whichis belowthe durabilityrating for American mahogany. Principal usesforAfricanmahogany include furniture and cabinetwork, interiorwoodwork, boat construction, and veneer.

Mahogany, American—True,American,or Honduras mahogany(Swietenia macrophylla)rangesfrom southern Mexico through CentralAmericainto South Americaas far southas Bolivia. Plantations have been established within its natural range and elsewherethroughoutthe tropics. Theheartwoodvaries from palepink or salmon colored to dark reddishbrown.The grain is generallystraighterthan that ofAfricanmahogany(Khciyaivorensis); however, a wide varietyofgrain patternsare obtainedfrom American mahogany. The texture is rather fine to coarse. American mahogany is easily air orkilndried withoutappreciablewarp or checks, and it has excellentdimensional stability. It is rated as durablein resistance to decay fungiand moderately resistant to dry-wood termites. Both heartwoodand sapwoodare resistantto treatment with preservatives. The wood is very easy to work with hand and machinetools, and it slices and

rotarycutsinto fme veneerwithout difficulty. It alsois easy

to finishandtakes an excellentpolish. The air-driedstrength ofAmerican mahogany is similarto that ofAmerican elm (Ulmus americana).Density ofair-driedwood varies from 480 to 833 kg/rn3(30 to 52 lb/fl3). The principal uses formahogany are fine furniture and cabinets, interiorwoodwork, pattern woodwork, boat construction, fancy veneers, musicalinstruments, precision instruments, paneling, turnery,carving,and many other uses that call for an attractive and dimensionallystable wood.

Mahogany, Philippine (see MerantiGroups) Manbarkiak Manbarklak is a commonnameappliedto species in the genus Eschweilera. Othernamesincludekakarallimachinmango,and mata—mata. About 80 species ofthis genus are distributed from easternBrazilthroughthe Amazonbasin,to the Guianas,Trinidad,and Costa Rica.

The heartwoodofmost species is light,grayish,reddish brown,or brownish buff. The textureis fine and uniibrm, and the grain is typically straight. Manbarklak is a very hard and heavywood (density ofair-driedwoodrangesfrom 768 to 1,185 kg/rn3 (48 to 74 lb/fl3))that is rated as fairlydifficultto dry. Most species are difficultto work becauseofthe high density and high silica content. Most speciesare highly resistantto attackby decay fungi. Also, most specieshave gainedwide recognition for their high degreeofresisLanceto marineborer attack. Resistance to dry-woodtermite attack is variabledepending on species. Manbarklak is an ideal wood for marineand other hetvy construction uses. It is also used for industrial flooring, mill equipment, railroad crossties, piles, and turnery.

Manni Manni (Symphoniaglobul([era) is nativeto the West Indies, Mexico, and Central, North, and South America. It lso occurs in tropicalWest Africa.Othernames include ossol (Gabon), anani (Brazil), waika(Africa), and chewstick (Belize), anameacquiredbecauseofits use as aprimitive toothbrush and flossingtool.

The heartwoodis yellowish, grayish,orgreenishbrown and is distinctfrom the whitish sapwood. The texture is coarse andthe grain straightto irregular. The wood is very easy to work with both hand andmachinetoots, but surfaces tend to roughenin planingand shaping.Manniair-driesrapidlywith only moderatewarpand checking. Its strengthis similarto that ofhickory(Carya),and the density ofair-driedwood is 704 kg/rn3 (44 lb/ft3). The heartwoodis durable in ground contactbut only moderatelyresistantto dry-woodand subterraneantermites. The wood is rated as resistantto treatmentwith preservatives. Manniis a general purposewood that is used forrailroad ties, general construction, cooperage, furniturecomponents, flooring, and utility plywood.

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is

Marishballi Marishballi is the commonname appliedto species ofthe

genus Licania. Othernames includekautaand anaura. Species ofLicania are widelydistributedin tropical Americabut most abundant inthe Guianas andthe lowerAmazonregion

ofBrazil.

The heartwoodis generallya yellowishto dark brown, sometimeswith areddish tinge. The texture is fme and close, and the grain is usually straight. Marishballiis strong and very heavy;densityofair-driedwood is 833 to 1,153 kg/rn3 (52 to 72 lb/ft3). The wood is rated as easy to moderatelydifficultto air dry. Becauseofits high density and silica content, marishballiis difficultto work. The use of hardenedcutters is suggested to obtain smoothsurfaces. Durabilityvaries with species,but marishballi is generally consideredto have low to moderately low resistance to attack by decayfungi. However,it is knownfor its high resistance to attack bymarine borers. Permeability also varies, but the heartwoodis generallymoderately responsiveto treatment. Marishballiis ideal for underwatermarine construction, heavy construction above ground, andrailroadcrossties (treated).

Mayflower (see Roble) Melapi (see Meranti Groups) Meranti Groups Merantiis acommonname appliedcommercially to four groupsofspecies ofShorea from southeast Asia,most commonly Malaysia,Indonesia,and the Philippines. There are thousandsofcommonnames for the various species of Shorea, but the names Philippinemahoganyand lauan are often substituted for meranti. The four groups ofmerantiare separated onthe basis ofheartwoodcolor and weight(Table 1—3). About 70 species ofShorea belongto the light and dark red meranti groups,22 speciesto the white meranti group, and 33 speciesto the yellowmeranti group. Merantispecies as awholehave a coarser texturethanthat of mahogany (Swieteniamacrophylla) and do nothave darkcoloreddeposits in pores. The grain is usuallyinterlocked. 1—3.

keruing(Dipterocarpus)species that resemblemeranti. All themerantigroups are machinedeasilyexceptwhite meranti, which dulls cuttersas a result ofhigh silica content in the wood. The light red and white merantisdry easily without degrade,but dark red and yellowmerantisdry more slowly with atendencyto warp.The strengthand shrinkageproperties ofthe merantigroupscompare favorably with that of northernred oak (Quercus rubra). The light red, white, and yellowmerantisare not durablein exposedconditions or in groundcontact, whereas darkred merantiis moderately durable.Generally, heartwoodis extremelyresistantto moderatelyresistantto preservativetreatments. Species ofmeranticonstitute a large percentage ofthe total hardwoodplywoodimportedinto the UnitedStates. Other uses includejoinery,furnitureand cabinetwork, moulding and millwork,flooring, andgeneral construction. Some dark red meranti is usedfor decking.

Merbau Merbau(Malaysia),ipil (Philippines), and kwila (New Guinea)are names appliedto species ofthe genus Intsic, most commonlyI. b/uga. Intsia is distributedthroughout the Indo—Malaysianregion,Indonesia,Philippines,and many westernPacificislands,as well as Australia.

Mata—Mata (see Manbarklak)

Table

All merantishave axial resin ducts alignedin long, continuous, tangential linesas seen on the end surfaceofthe wood. These ducts sometimes containwhite depositsthat are visibleto thenaked eye, butthe wood is notresinous like some

Freshly cut yellowish to orange—brownheartwoodturns brown or dark red—brown on exposureto air. Thetexture is rather coarse, and the grain is straight to interlockedor wavy. The strength ofair-driedmerbauis comparablewith that of hickory (Carva), but density is somewhatlower (800 kg/rn3 (50 lb/ft3) at 12% moisturecontent).The wood dries well with little degradebut stainsblack in the presenceofiron andmoisture. Merbauis rather difficultto saw because it sticksto saw teeth and dulls cutting edges.However,the wood dresses smoothly in most operations and finisheswell. Merbau has gooddurabilityand high resistanceto termite attack. The heartwoodresists treatment,but the sapwoodcan be treatedwith preservatives.

Woods belonging to Shorea and Parashoreagenera

Name

Color

Density of air-dried wood

Dark red meranti (also called tanguile and dark red seraya)

Dark brown; medium to deep red, sometimes with a purplishtinge

640+ kg/rn3 (40+ lbIft3)

Light red meranti (also called red seraya)

Variable—from almost white to pale pink, dark red, pale brown, ordeep brown

400 to 640 kg/rn3, averaging 512 kg/rn3 (25 to 40 lb/fl3, averaging 32 lb/fl3)

White meranti (also called rnelapi) Whitishwhen freshly cut, becoming light yellow-brownon exposureto air Yellow meranti (also called yellow Light yelloworyellow-brown, sometimes with a greenish tinge; darkens on exposure to air seraya)

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480 to 870 kg/rn3 (30 to 54 lb/ft3) 480 to 640 kg/rn3 (30 to 40 lb/fl3)

Merbauis used in furniture,finejoinery,turnery,cabinets, flooring,musical instruments, and specialtyitems.

Mersawa Mersawais one ofthe common namesappliedto the genus

Anisoptera,which has about 15 species distributedfromthe PhilippineIslands and Malaysiato east Pakistan. Names appliedtothis wood vary with the source, and threenames are generallyused inthe lumbertrade:krabak(Thailand), mersawa(Malaysia), and palosapis(Philippines). Mersawa wood is light in color andhas amoderatelycoarse texture. Freshlysawn heartwoodis pale yellowor yellowish

brown and darkens on exposureto air. Somewoodmay show a pinkish cast or pink streaks, butthese eventually disappearon exposure to air. The wood weighsbetween544 and 752 kg/rn3(34 and 47 lb/ft3) at 12% moisturecontent and about 945 kg/rn3 (59 lb/ft3)when green.The sapwoodis susceptible to attack bypowderpostbeetles,and the heartwood is not resistant to termites. The heartwoodis ratedas moderatelyresistantto fiurgal decay and shouldnot be used under conditions that favor decay.The heartwooddoes not absorb preservativesolutionsreadily. The wood machines easily,but becauseofthe presence ofsilica,the wood severely dulls the cuttingedges ofordinary tools and is very hard on saws. Themajor volumeofmersawawill probablybe used as plywoodbecauseconversioninthis form presents considerably less difficultythan does theproduction oflumber. Mora Mora (Mora excelsaand M gonggr/pii) is widely distributedinthe Guianas andalso occursin theOrinoco Deltaof Venezuela.

Theyellowishred—brown,reddishbrown, or dark red heartwood with pale streaksis distinctfrom the yellowishto pale brown sapwood. The texture is moderatelyfmeto rather coarse,and the grain is straight to interlocked. Mora is a strong and heavy wood (densityofair-driedwood is 945 to 1,040 kg/rn3 (59 to65 lb/fl3)); this wood is moderately difficultto work but yields smoothsurfaces in sawing, planing, turning, and boring. The wood is generally rated as moderatelydifficultto dry. Mora isratedas durable to very durablein resistance to brown- and white-rot fungi.Mbra gonggrjjpiiis rated very resistantto dry-woodtermites, but M excelsais considerablyless resistant. The sapwoodrespondsreadily to preservativetreatments,but the heartwood resists treatment.

Mora is used for industrialflooring, railroadcrossties, shipbuilding,and heavy construction.

Oak (Tropical) The oaks (Quercus)are abundantly representedin Mexico

and CentralAmericawith about 150 species,whichare nearly equallydividedbetweenthe red andwhite oak groups. Morethan 100 species occur in Mexicoand about25 in

Guatemala; the number diminishes southwardto Colombia, whichhas two species. The usual Spanishname appliedto the oaks is encino or roble,and both namesareused.interchangeably irrespective ofspecies oruse ofthe wood.

In heartwoodcolor, texture, andgrain characteristics, tropical oaks are similarto the oaks in the UnitedStates, especially live oak (Quercusvirginiana).In most cases,tropical oaks are heavier(densityofair-driedwood is 704 to 993 kg/rn3 (44 to 62 lb/fl3))than the U.S. species.Strengthdataare available foronly four species, and the valuesfall between those ofwhite oak (Q. alba) and live oak(Q. virginana)or are equaltothose oflive oak. Average specific gravilyfor the tropical oaks is 0.72 basedon volumewhengreen and ovendry weight, with an observedmaximumaverage of0.86 for one species from Guatemala. Theheartwoodis rated as very resistantto decay fungianddifficultto treat with preservatives.

Utilizationofthe tropical oaks is very limitedat present becauseofdifficulties encountered in the drying ofthe wood. Themajorvolumeis used in theform ofcharcoal,bit the wood is used for flooring, railroadcrossties, mine timbers, tight cooperage, boat and ship construction, and decorative veneers.

Obeche Obeche (TrIplochitonscieroxylon) treesofwest—central Africa

reacha height of50 m (150 ft) or more and a diameter ofup to 2 m (5 ft). The trunk is usuallyfree ofbranchesfor a considerable height so that clear lumberofconsiderable size can be obtained.

The wood is creamywhite to pale yellowwith little or no difference betweensapwood and heartwood. The wocd is fairlysoft, ofuniformmedium to coarsetexture, and the grain is usually interlockedbut sometimes straight. Air-drywood weighsabout 385 kg/rn3(24 lb/ft3). Obeche dries readily with little degrade.It is not resistantto decay, and green sapwoodis subjectto blue stain. The wood is easy to work and machine, veneers and glues well,and takes nails and screwswithout splitting. The characteristics ofobeche make it especiallysuitable for veneerand corestock. Otherusesincludefurniture,components,millwork, blockboard, boxes and crates,partic[eboard and fiberboard, patterns, and artificial limbs. Ofram (see Limba) Okoume Thenaturaldistributionofokourne (Aucoumea klaineana)is ratherrestricted; the species is found only in west—central Africa and Guinea. However, okoumeis extensively planted throughout its natural range. The heartwoodis salmon-pink in color,and the narrow sapwoodis whitish or pale gray. The wood has a high luster and uniform texture.The texture is slightly coarserthan that ofbirch (Betula). The nondurableheartwooddries readily with little degrade. Sawn lumber is somewhat difficu't to

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machinebecauseofthe silica content, but the wood glues, nails, and peels into veneereasily. Okoumeoffers unusual flexibility in fmishingbecausethe color,which is ofmedium intensity, permitstoning to eitherlighter or darkershades. In the UnitedStates,okoume is generallyusedfor decorative plywood paneling,general utility plywood,and doors. Otheruses include furniture components, joinery, and light construction.

Opepe Opepe (Nauclea diderrichii)is widelydistributed inAfrica from SierraLeone to the Congoregionand eastwardto Uganda.It is often found in pure stands. The orangeor goldenyellowheartwooddarkens on exposure to air and is clearlydefmed from thewhitishor pale yellow sapwood. The texture is rather coarse, and thegrain is usually interlocked or irregular.The density ofair-driedwood (752 kg/rn3(47 lb/ft3)) is about the same as that oftrue hickory (Carya),but strengthpropertiesare somewhat lower. Quartersawn stock dries rapidlywith little checking or warp, but flat-sawnlumbermaydevelopconsiderable degrade. The wood worksmoderatelywellwith hand and machine tools. It also glues and finishes satisfactorily. The heartwoodis ratedas very resistantto decay andmoderatelyresistantto termite attacks. The sapwoodis permeable to preservatives, but the heartwoodis moderatelyresistantto preservative treatment. Opepe is a general constructionwood that is used in dock and marine work, boat building, railroadcrossties, flooring, andfurniture.

Ossol (see Manni)

Otie (see Ilomba) Ovangkol (see Benge) Palosapis (see Mersawa) Para—Angetim (see Sucupira)

Pau Marfim Therangeofpau marfim(Balfourodendron riedelianum) is rather limited,extendingfrom the State ofSao Paulo, Brazil, into Paraguayand the provincesofCorrientes and Missiones ofnorthernArgentina. In Brazil, it is generallyknown as pau marfimand in Argentinaand Paraguay, as guatambu.

In color andgeneral appearance, pau marfimwood is very similarto birch (Betula)or sugarmaple(Acersaccharum) sapwood.Althoughgrowth rings are present,they do not show as distinctlyas those in birch and maple. There is no apparentdifference in color between heartwood and sapwood.

The wood is straightgrained and easy to work and finish, but it is not consideredresistantto decay.In Brazil, average specific gravityofpau marfimis about 0.73 basedon volume ofgreenwood and ovendiyweight.Averagedensity ofairdried wood is about 802 kg/rn3(50 lb/ft3). On the basis of

specific gravity, strength valuesarehigher thanthose ofsugar maple, whichhas anaveragespecific gravityof0.56.

In its areas of growth, paumarfirnis used for much thesame purposesas are sugarmaple and birch inthe United States. Introduced to the U.S. market in the late 1960s, pau martirn has beenvery wellreceived and is especially esteemedfor tumery.

Peroba, White (see Peroba de Campos) Peroba de Campos Perobade campos (Paratecomaperoba),also referredto as white peroba, grows inthe coastalforests ofeasternBrazil, ranging from Bahia to Rio de Janeiro. It is the only species in the genusParatecoma. The heartwoodvariesin color but is generallyshadesof brownwith tendenciestoward olive and red. The sapwoodis a yellowish gray and is clearly definedfrom theheartwood. The textureis relatively fme andapproximates that ofbirch (Betula).The grain is commonly interlocked, with a narrow stripe orwavy figure. The wood machineseasily; howeer, particularcaremust betaken in planingto preventexcessive grain tearing ofquartered surfaces. There is some evidence that the fme dust from machiningoperations may produce allergic responses in certain individuals.Densityofair-dried wood averages about 738 kg/m3 (46 lb/ft3). Perobade campos is heavierthan teak (Tectonagrandis) or white oak (Quercusalba), and it is proportionately stronger than either ofthese species. The heartwoodofperobade campos is rated as very durable with respectto decayand difficult totreat with preservatives.

In Brazil, perobade camposis used in themanufacture offme

furniture,flooring, and decorative paneling. The principaluse in theUnitedStatesis shipbuilding, where perobade campos servesas substitute forwhite oak (Quercusalba)for all purposesexceptbent members.

Peroba Rosa Peroba rosais the common name appliedto anumber of

similar species in the genusAspidosperma.Thesespecies occur in southeastern Braziland parts ofArgentina. The heartwoodis a distinctive rose-redto yellowish, often variegated or streakedwith purpleor brown, andbecomes brownishyellowto dark brownupon exposureto air; the heartwoodis oftennot demarcated from the yellowish sapwood. The texture is fme and uniform, and the grain is straight to irregular. The wood is moderatelyheavy; weight ofair-driedwood is 752 kg/rn3(47 lb/ft3). Strengthproperties are comparable with those ofU.S. oak (Quercus).Thewood dries with little checkingor splitting. It works with moderate ease,and it gluesandfmishessatisfactorily. The heartwood is resistantto decay fungi but susceptible to dry-wood termite attack. Although the sapwoodtakes preservative treatment moderatelywell, theheartwoodresists treatment.

1—28

at

Perobais suitedfor generalconstruction work and is favored for fine furniture and cabinetwork and decorative veneers. Otheruses include flooring, interiorwoodwork, sashesand doors, and turneiy.

Pilon The two main speciesofpilon are Hyeronimaalchorneoides and H. lax?flora, also referredto as suradan. These species range from southernMexicoto southernBrazilincluding the Guianas,Peru, and Colombia. Pilon species are also found throughoutthe West Indies.

The heartwoodis a lightreddish brownto chocolatebrown or sometimesdark red; thesapwoodis pinkish white. The textureismoderatelycoarseandthe grain interlocked. The wood air-driesrapidlywith only amoderateamountofwarp and checking. It has good workingpropertiesin all operations exceptplaning,whichis ratedpooras a result ofthe characteristic interlocked grain. The strengthofpilon is comparable with that oftrue hickory(Carya), andthe density ofair-driedwood rangesfrom 736 to 849 kglm3 (46to 53 lbIft3).Pilon is rated moderatelyto very durable in groundcontactand resistantto moderatelyresistantto subterraneanand dry-woodtermites. Both heartwoodand sapwood arereportedto be treatablewith preservativesby both open tank andpressure vacuumprocesses. Pilon is especially suited forheavy construction, railway crossties, marinework, and flooring. Itis alsoused for furniture, cabinetwork, decorativeveneers,tumery,andjoinery,

Piquia Piquia is the commonname generallyappliedto species in thegenus Caryocar. This genus is distributedfrom Costa Rica southwardinto northernColombia andfrom the upland forestofthe Amazon valleyto easternBrazilandthe Guianas.

The yellowishto light grayishbrown heartwoodis hardly distinguishablefrom the sapwood.The texture is medium to rather coarse, and the grain is generallyinterlocked. The wood dries at a slowrate; warpingand checking may develop, but only to a minor extent. Piquia is reportedto be easy to moderatelydifficultto saw; cutting edgesdull rapidly. The heartwoodis very durable and resistantto decay fungi and dry-woodtermitesbut only moderatelyresistantto marineborers. Piquia is recommended forgeneraland marineconstruction, heavy flooring, railwaycrossties, boat parts,and furniture components. It is especiallysuitablewherehardness and high wearresistance are needed.

Primavera The naturaldistributionofprimavera(Tabebuiadonnell— smithii [—Cybistaxdonnell-smithii]) is restrictedto southwesternMexico, the Pacific coastofGuatemala and El Salvador,and north-central Honduras. Priniaverais regardedas one ofthe primarylight-coloredwoods,but its use has been

limitedbecauseofits rather restrictedrange and relative scarcity ofnaturally growntrees. Recentplantations have increased the availability ofthis species andhave provideda more constantsource ofsupply.The quality ofthe rilantation-grown wood is equal in all respectsto the wood obtainedfrom naturallygrowntrees. The heartwoodis whitish to straw-yellow, and in some logs, it may be tinted with pale brown or pinkishstreaks, The texture ismediumto rather coarse,andthe grain is straight to wavy, whichproducesawide varietyoffigurepatterns. The wood also has a very high luster. Shrinkage is rather low, and the wood shows ahigh degree ofdimensional stability. Despiteconsiderable grain variation,primtvera machines remarkably well. The density ofair-driedwood is 465 kg/rn3(29 lb/ft3), and the wood is comparablein strength with watertupelo (Nyssaaquatica). Resistanceto both brown- and white-rot fungivaries. Weathering characteristics

aregood.

The dimensional stability, ease ofworking, and pleasing appearance makeprimavera asuitable choice for solid furniture, paneling, interiorwoodwork, and specialexter.oruses.

Purpleheart Purpleheart, alsoreferredto as amaranth, is the namoapplied to species in thegenusPeltogyne. The centerofdistribution is in the north-central partofthe Brazilian Amazonregion, butthecombined range ofall species is from Mexicothrough CentralAmericaand southwardto southernBrazil.

Freshlycut heartwoodis brown. It turns a deeppurple upon exposureto air and eventually dark brownupon exposure to light. The texture is medium to fine, and the grain i usually straight.This strong and heavy wood (densityofair..dried wood is 800 to 1,057 kg/rn3 (50 to 66 lb/It3)) is rated as easy tomoderatelydifficult to air dry. It is moderately difficult to work with using eitherhand or machinetools, and it dulls cutters rather quickly.Gummyresin exudeswhenth wood is heatedby dull tools.A slow feedrate and specially hardenedcuttersare suggested for optimalcutting. The wood turns easily, is easy to glue, and takes finisheswell. The heartwoodis rated as highlyresistantto attack by decay fungiand very resistantto dry-wood termites. It is extremely resistantto treatmentwith preservatives. The unusual and uniquecolor ofpurpleheart makesthis wood desirable forturnery,marquetry, cabinets, fine :['urnitare,parquetflooring, and many specialtyitems, such as billiardcue butts andcarvings.Otheruses includeheavy construction, shipbuilding, and chemicalvats.

Pycnanthus (see Ilomba) Ramin Ramin(Gonyslylus bancanus)is native to southeastAsia from the Malaysian Peninsulato Sumatraand Borneo. Boththe heartwoodand sapwoodare the color ofpals straw, yellow,or whitish. The grain is straightor shallowly

1—29

interlocked. The texture is even, moderatelyfme,and similar

to that ofAmerican mahogany(Swietenia macrophylla). The wood is without figure or luster.Ramin is moderatelyhard and heavy,weighingabout 672 kg/rn3 (42 lb/fl3) in the airdried condition.The wood is easy to work, finisheswell, and glues satisfactorily. Ramin is rated as not resistantto decay but permeable with respectto preservative treatment.

Ramin is used forplywood,interiorwoodwork, furniture, turnery,joinery, moulding,flooring, dowels, and handlesof nonstrikingtools (brooms),and as a generalutility wood.

Roble

a species in theroble group ofTabebuía (generally T rosea), rangesfrom southernMexicothroughCentral

Forexample, Brazilian rosewoodis harder than any U.S. native hardwoodspecies used forfurnitureand veneer. The wood machines andveneerswell. It canbe glued satisfactorily, providedthe necessary precautionsare takento ensure good glue bonds, with respect to oily wood. Brazilianrosewoodhas an excellentreputationfor durabilitywith respect to fungal and insectattack,includingtermites,althoughthe wood is not used for purposeswhere durability is necessary. Brazilian rosewoodis used primarilyin the form ofveneer for decorative plywood. Limitedquantitiesare usedin the solid form for specialty items such as cutleryhandles,brush backs, billiardcue butts, and fancy turnery.

Roble,

Rosewood, Indian

Americato Venezuelaand Ecuador. The nameroble comes from the Spanishword for oak (Quercus). In addition, T. rosea is calledroble becausethe wood superficially resembles U.S. oak. Othernames for T. rosea are mayflower and

Indian rosewood(Dalbergia latjfolia) is native to most provincesofIndia exceptin the northwest. The heartwoodvaries in color from goldenbrownto dark purplishbrownwith denserblackishstreaks atthe end of growthzones, giving rise to an attractivefigureon flat-sawn surfaces. The narrow sapwoodis yellowish. The average weight is about 849 kg/rn3 (53 lb/fl3) at 12% moisture content. The texture is uniformand moderatelycoarse. Indian rosewoodis quite similarin appearanceto Brazilian (Dalbergianigra) and Honduran (Dalbergiastevensonhi) rosewood. The wood is reported to kiln-drywell though slowly, and the color improves duringdrying. Indianrosewood is a heavywood with high strengthproperties;afler drying, it is particularlyhard for its weight.The wood is moderately hard to work with hand tools and offers a fair resistance in machine operations. Lumberwith calcareous depositstends to dull tools rapidly. The wood turns well and has high screw-holding properties. If a very smooth surface isrequiredfor certain purposes, pores(vessels) may needto be filled.

apamate.

The sapwoodbecomesapalebrownupon exposureto air. The heartwoodvaries from goldenbrownto dark brown,and it has no distinctiveodor or taste. The texture is medium andthe grain narrowlyinterlocked. The wood weighsabout 642 kg/rn3 (40 lb/fl3) at 12% moisturecontent. Roble has excellent working propertiesin all machine operations. It finishesattractivelyin natural color and takes fmishes with good results. It weighs less than the average ofU.S. white oaks (Quercus)but is comparablewith respectto bending and compressionparallelto grain. The heartwoodofroble is generallyrated as moderatelyto very durablewith respectto decay; the darkerandheavierwood is regarded as more resistantthan the lighter-colored woods. Roble is used extensively for furniture,interiorwoodwork, doors, flooring, boat building, ax handles,and generalconstruction. The wood veneerswell and producesattractive paneling. For some applications, roble is suggestedas a substituteforAmericanwhite ash (Fraxinusamericana)and oak (Quercus).

Rosewood, Brazilian Brazilian rosewood(Dalbergianigra), also referredto as jacaranda,occurs in eastern Brazilian forestsfrom the Stateof Bahia to Rio de Janeiro. Since it was exploitedfor a long time, Brazilianrosewoodis no longer abundant.

The heartwoodvarieswith respectto color,through shades ofbrown,red, andviolet, and it is irregularlyand conspicuouslystreakedwith black. It is sharplydemarcatedfromthe white sapwood. Many kinds ofrosewoodare distinguished locallyonthe basis ofprevailingcolor. The texture is coarse, and the grain is generallystraight. The heartwoodhas an oily or waxyappearance and feel, and its odor is fragrant and distinctive.The wood is hard andheavy (weightofairdried wood is 752 to 897 kg/rn3 (47 to 56 lb/fl3)); thoroughly air-driedwood will barely float in water.Strength properties ofBrazilianrosewood arehigh and are more than adequateforthe purposesforwhichthis wood is used. 1—30

Indianrosewood is essentiallya decorative wood forhighquality furniture and cabinetwork. In the UnitedStates, it is used primarily in the form ofveneer.

Sande Practicallyall commercially availablesande (mostly Brosimum utile)comesfrom PacificEcuadorand Colombia. However, the group ofspecies ranges from the AtlanticCoast in Costa Rica southwardto Colombiaand Ecuador.

The sapwoodand heartwoodshowno distinction;the wood is uniformlyyellowishwhite to yellowish or light brown. The texture ismediumto moderatelycoarse and even, and thegrain can be widelyand narrowlyinterlocked. The density ofair-driedwood rangesfrom 384 to 608 kg/rn3 (24 to 38 lb/fl3), and the strengthis comparable with that ofU.S. oak (Quercus).The lumberair dries rapidlywith little orno degrade. However, materialcontainingtensionwood is subjectto warp,and the tension wood may cause fuzzy grain aswell as overheating ofsaws as aresult ofpinching.The wood is not durable with respect to stain, decay, and insect attack, and care must be exercised to prevent degradefrom these agents. The wood stainsand fmishes easily and presents no gluingproblems.

Sandeis used for plywood, particleboard, fiberboard, carpentry, light construction, furniture components, and moulding.

Santa Maria Santa Maria (Calophyllum brasiliense)ranges from the West

Indiesto southernMexicoand southward throughCentral Americainto northernSouthAmerica.

The heartwoodis pinkishto brick red or rich reddishbrown andmarkedby fme and slightly darkerstripingon flat-sawn surfaces. The sapwoodis lighterin color and generallydistinct from the heartwood. The texture is medium and fairly uniform,and the grain is generallyinterlocked. Theheartwood is rather similarin appearanceto dark red meranti Shorea). The wood is moderatelyeasy to work and good surfaces can be obtainedwhenattentionis paidto machining operations. The wood averagesabout 608 kg/rn3(38 lb/fl3)at 12% moisture content. Santa Maria is in the density class of sugarmaple (Acersaccharum),and its strength properties are generallysimilar;the hardness ofsugarmaple is superior to that ofSanta Maria. The heartwoodis generallyratedas moderatelydurableto durable in contactwith the ground, but it apparentlyhas no resistance againsttermitesand marineborers. The inherent natural durability, color, and figureon the quarter-sawn face suggestthat SantaMaria could be used as veneerforplywoodinboat construction. Otherusesare flooring, furniture,cabinetwork, miliwork,and decorative plywood.

Sapele Sapele (Entandrophrag,nacylindricum) is a largeAfricantree

that occursfrom SierraLeonetoAngolaand eastward throughthe Congoto Uganda.

The heartwoodranges in color from that ofAmerican mahogany (Swieteniamacrophylla)to a dark reddish orpurplish brown. The lighter-coloredand distinctsapwoodmay be up to 10 cm(4 in.) wide. The texture is rather fine. The grain is interlockedandproducesnarrowand uniform striping on quarter-sawn surfaces.The wood averages about 674 kg/rn3 (42 lb/fl3)at 12% moisture content, and its mechanical propertiesare in generalhigherthanthose ofwhite oak(Quercus a/ba). The wood works fairlyeasily with machinetools, althoughthe interlockedgrain makesit difficultto plane. Sapelefmishesand glueswell. The heartwoodis rated as moderately durableandis resistantto preservative treatment. As lumber, sapeleis used for furniture and cabinetwork, joinery,and flooring. As veneer,it is used for decoratiive plywood.

Selangan Batu (see Balau) Sepetir Thenamesepetirappliesto species in the genus Sindoraand to Pseudosindorapalustris. These species aredistributed throughoutMalaysia,Indochina, and the Philippines.

The heartwoodis brownwith a pink or goldentinge that darkens on exposure to air. Darkbrownorblack streaks are sometimes present. The sapwoodis light gray, brown, or straw-colored. The textureis moderatelyfine and even, andthe grain is narrowlyinterlocked. The strengthof sepetir is similarto that ofsheilbark hickory (Carya laciniosa), and the density ofthe air-driedwood is also similar(640 to 720 kg/m3 (40 to 45 lb/fl3)). The wood dries well but rather slowly, with a tendencyto end-split. The wood is difficultto workwith handtools and has a rather rapid dullingeffecton cutters. Gumsfrom the wood tend to accumulate on saw teeth,whichcausesadditionalproblems. Sepetiris rated as nondurablein groundcontactunder Malaysian exposure. The heartwoodis extremely resistantto preservative treatment; however,the sapwoodis only moderatelyresistant. Sepetiris ageneralcarpentry wood that is alsousedfor furniture and cabinetwork, joinely, flooring (especially truck flooring), plywood, and decorative veneers.

Seraya, Red and Dark Red (see Meranti Groups) Seraya, White White serayaor bagtikan,as it is called in the Philippines, is aname appliedto the 14 species ofParashorea, which grow in Sabahand the Philippines. The heartwoodis light brownor straw-colored, sometimes with a pinkishtint. The texture is moderatelycoarse and the grain interlocked. White serayais very similar in appearance and strength propertiesto light redmeranti,and sometimes thetwo are mixed in themarket. Whiteserayadries easily with little degrade,and works fairly wellwith hand and machine tools. The heartwoodis not durable to moderately durablein groundcontact,and it is extremelyresistantto preservative treatments.

Whiteseraya is usedforjoinery, light construction, mouldingand millwork,flooring, plywood,furniture,and cabinet work.

Seraya, Yellow (see Meranti Groups) Silverballi,Brown (see Kaneelhart) Spanish-Cedar Spanish-cedar or cedro consists ofa group ofabout seven species inthe genus Cedrela that are widelydistributed in tropicalAmericafrom southernMexicoto northern Argentina. Spanish-cedar is one ofonly a few tropicalspecies that are ring-porous. The heartwoodvaries from light to dark reddish brown, and the sapwoodis pinkishto white. The texture is rather fme and uniform to coarseanduneven. The grain is not interlocked. The heartwoodis characterizedby a distinctive odor. The wood dries easily. Although Spanish-cedar is not high in strength, most other propertiesare similarto those ofAmerican mahogany (Swietenia macrophylla), except forhardnessandcompression perpendicular to the

1—31

grain,wheremahoganyis defmitelysuperior. Spanish-cedar is considereddecayresistant;it works and glues well.

ofLatinAmerica and Africa, andmany ofthese arenow

Spanish-cedaris used locallyfor all purposesthat requirean easily worked,light but straightgrained,and durablewood. In the UnitedStates,thewood is favored for miliwork, cabinets, fme furniture,boat building, cigar wrappers and boxes, humidores,and decorative and utility plywood.

The heartwoodvaries fromyellow—brownto dark golden— brownand eventually turns a rich brownupon exposureto air. Teakwoodhas a coarseuneventexture (ring porous), is usually straight grained,andhas a distinctlyoily feel. The heartwoodhas excellent dimensionalstabilityand avery high degreeofnatural durability. Althoughteakis not gerlerally used in the UnitedStateswhere strengthis ofprime importance, its propertiesare generallyonpar with those of U.S. oaks (Quercus).Teak is generallyworked with moderate easewith hand andmachinetools.However,the presence ofsilica often dulls tools. Finishingand gluing aresatisfactory, although pretreatmentmay be necessaryto ensure good

Sucupira (Angelin, Para-Angelim)

Sucupira,angelin,and para-angelimapply to species in four generaoflegumesfrom SouthAmerica. Sucupiraapplies to Bowdichia nitida from northernBrazil, B. virgilioides from Venezuela,the Guianas,and Brazil, andDiplotropispurpureafrom theGuianasand southernBrazil. Angelin (Andirainermis)is awidespreadspecies that occurs throughoutthe West Indies and from southernMexico throughCentralAmericato northern SouthAmericaand Brazil. Para-angelim (Hymenolobium excelsum) is generally restrictedto Brazil.

The heartwoodofsucupirais chocolate-brown, red—brown, or light brown (especially in Diplotropispurpurea). Angelin heartwoodis yellowishbrown to dark reddishbrown;paraangelimheartwoodturns palebrownupon exposure to air. The sapwoodis generallyyellowishto whitish and is sharplydemarcatedfrom the heartwood. The textureofall threewoods is coarseanduneven, andthe grain can be interlocked. The density ofair-driedwood ofthese species ranges from 720 to 960 kg/rn3 (45 to 60 lb/ft3), whichmakesthem generallyheavierthan true hickory (Carya). Theirstrength properties are also higher than those oftruehickory.The heartwoodis rated very durable to durable in resistance to decay fungibut only moderatelyresistantto attack by drywood termites. Angelinis reportedtobe difficultto treat with preservatives, butpara-angelimand sucupira treat adequately. Angelincan be sawn and workedfairlywell, except that it is difficultto planeto a smoothsurface becauseof alternating hard (fibers)andsoft (parenchyma) tissue. Paraangelimworks well in all operations.Sucupirais difficultto moderatelydifficultto work becauseofits high density, irregulargrain, andcoarsetexture. Sucupfra, angelin,and para-angelim are ideal forheavy construction, railroad crossties,and other uses that do not requiremuch fabrication. Other suggested uses include flooring, boat building, furniture,turnely,tool handles, and decorative veneer.

Suradan (see Pilon) Tangare (see Andiroba) Tanguile (see Lauan—Meranti Groups) Teak Teak(Tectonagrandis)occursin commercial quantities in India, Burma,Thailand,Laos, Cambodia, North and South Vietnam, and the East Indies. Numerousplantations have been developedwithinits natural range and in tropicalareas

1—32

producing teakwood.

bonding offinishes and glues.

Teak is one ofthe most valuable woods, but its use is limited by scarcityandhigh cost. Because teak does not cause rust orcorrosionwhen in contactwith metal, it is extremely usefulin the shipbuilding industry, fortanks and vats, and for fixtures that require high acid resistance. Teakis currently used inthe construction ofboats, furniture, flooring, decorative objects, and decorative veneer.

Torn1110 Tornillo (Cedrelingacatenformis), also referredto as cedrorana,growsin the LoretonHuanucoprovinces ofPeru and in thehumidterra firmaoftheBrazilian Amazonregion. Tornillo can grow up to 52.5 m (160 ft) tall, with trunk diameters of 1.5 to 3 m (5 to 9 ft). Trees in Peru are often smallerin diameter,with merchantable heights of 15 m (45 ft)or more.

The heartwoodis pale brownwith a golden luster and prominently markedwith red vessellines; the heartwood gradually merges into the lighter-coloredsapwood. The textureis coarse.The densityofair-driedmaterial collected in Brazilaverages 640 kg/in3 (40 lb/fl3); for Peruvianstock, average density is about 480 kg/rn3 (30 lb/fl3). The wood is comparable in strength with American elm (Ulmus americana). Tornillocuts easily and can be finishedsmoothly, but areas oftensionwood may result in woollysurfaces. The heartwoodis fairlydurable andreported to have goodresistance to weathering. Tomillo is a general construction wood that can be used for furniture components in lower-grade furniture.

Trebol (see Macawood) Virola (see Banak) Waika (see Manni) Walele (see Ilomba) Wallaba Wallabais a commonnameapplied to the speciesin the genus Eperua. Othernames includewapa and apa. The centerofdistributionis in the Guianas,but the species

extends into Venezuela and theAmazonregionofnorthern Brazil. Wallabagenerallyoccurs inpure stands or as the dominant tree in the forest.

Theheartwoodrangesfrom light to dark redto reddishor purplishbrownwith characteristically dark, gummystreaks. The texture is rather coarse and the grain typicallystraight. Wallabais a hard, heavywood; density ofair-driedwood is 928 kg/rn3 (58 lb/fl3). Its strengthis higher than thatof shagbarkhickory (Carya ovata). The wood dries very slowly with a markedtendencyto check,split, and warp. Although thewood has high density, it is easy to work with hand and machinetools. However,the high gum contentclogs sawteeth and cutters. Oncethe wood has beenkiln dried,gum exudates are not a seriousproblem in machining. The heartwood is reportedto be very durable and resistantto subterraneantermitesand fairlyresistantto dry-wood termites. Wallabais well suitedforheavy construction, railroad crossties, poles,industrial flooring, and tank staves. It is alsohighly favored for charcoal.

Wapa (see Wallaba) Yang (see Keruing)

Softwoods Cypress, Mexican Native to Mexico and Guatemala, Mexican cypress

(Cupressuslusitanica) isnow widelyplantedat high elevations throughoutthe tropical world. The heartwoodis yellowish, pale brown, or pinkish, with occasionalstreaking or variegation. The textureis fine and uniform, and the grain is usuallystraight.The wood is fragrantly scented. The density ofair-driedwood is 512 kg/rn3 (32 lb/fl3), and the strengthis comparable with that ofyellow-cedar (Chamaecyparis nootkatensis) or western hemlock(Tsuga heterophylla).The wood is easy to work with hand and machine tools, and it nails, stains, and polisheswell. Mexicancypressair dries very rapidlywith little orno end- or surface-checking. Reports on durability are conflicting. The heartwoodis nottreatableby the open tank processand seemsto havean irregular response to pressure— vacuumsystems. Mexicancypressis used mainlyforposts and poles, furniture components, and generalconstruction.

Parana Pine The wood commonlycalled paranapine (AraucariaangustiJolla) is a softwoodbut not a true pine. It grows in southeasternBrazil and adjacentareas ofParaguay andArgentina.

Paranapine has many desirable characteristics. It is available in large-size clear boardswith uniformtexture.The small pinheadknots(leaftraces)that appearon flat-sawn surfaces and the lightorreddish-brown heartwoodprovidea desirable figureformatchinginpanelingand interiorwoodwork.

Growthrings are fairlydistinctand similartothose ofeastern white pine (Pinusstrobus). The grain is not interlocked, and thewoodtakes paint well,glues easily, and is free from resin ducts,pitchpockets,and:pitch streaks. Densityofair-dried woodaverages545 kg/rn (34 lb/fl3). The strengthofparana pine compares favorably with that ofU.S. softwoodspecies ofsimilardensity and, in somecases, approaches that of species with higherdensity. Paranapine is especiallystrong in shear strength, hardness,and nail-holding ability, but it is notably deficientin strengthin compressionacross the grain. The tendency ofthe kiln-driedwood to splitandwarp is caused by the presence ofcompression wood, an abnormal type ofwood with intrinsicallylarge shrinkage along the grain.Boardscontainingcompressionwood shouldbe excluded from exacting uses.

The principaluses ofparanapine includeframinglumber, interiorwoodwork, sashes and door stock,furniture case goods,and veneer.

Pine, Caribbean Caribbean pine (Pinuscaribaea) occurs along the Caribbean

side ofCentral Americafrom Belizeto northeastern Nicaragua. It is also nativeto the Bahamas and Cuba. This low-elevation tree is widelyintroduced as a plantation species throughoutthe world tropics.

The heartwoodis golden-to red-brownand distinctfrom the sapwood, which is light yellow and roughly2 to 5 m (ito 2 in.) wide.This softwoodspecieshas a strong resinous odor anda greasy feel. The weightvariesconsiderably and mayrange from 416 to 817 kg/m3 (26 to 51 ib/ft3) at 12% moisture content. Caribbean pine maybe appreciably heavier than slash pine (P. elliottii), but the mechanical propertiesof these two species are rather similar.The lumbercan be kiln driedsatisfactorily.Caribbeanpine is easy to work in all machiningoperations,but its high resin contentmay cause resin to accumulate on the equipment. Durabilityand resistance to insect attackvary with resin content; in general, the heartwoodis rated as moderatelydurable.The sapwoodis highlypermeable andis easily treatedby open tank orpressure—vacuum systems. Theheartwoodis ratedas moderately resistantto preservative treatment,depending on resin content.

Caribbeanpine is used for the same purposesas are the southernpines (Pinus spp.).

Pine, Ocote Ocote pine (Pinus oocarpa) is a high-elevation species that

occurs from northwestern Mexicosouthward through Guatemala intoNicaragua. The largestand most extensive stands occur in Guatemala, Nicaragua, and Honduras.

The sapwoodis a pale yellowishbrown and generallyup to 7 cm (3 in.) wide. The heartwoodis a light reddish brown. The grain is not interlocked. The wood has a resinous odor, and it weighsabout 656 kg/rn3 (41 lb/ft3) at 12% moisture content. The strength properties ofocotepine are comparable

in most respectswith those oflongleafpine(P. palustris).

1—33

Decayresistancestudieshave shown ocote pine heartwoodto be very durable with respectto white-rot fungalattackand moderately durablewith respectto brown rot.

Building Research Establishment, Departmentof Environment. 1977. A handbook of sofiwoods. London: H. M. Stationery Office.

Ocotepine is comparablewith the southernpines (Pinus) in workability and machiningcharacteristics. It is a general construction wood suited for the same uses as are the southernpines.

Building Research Establishment, PrincesRisborough Laboratory;Farmer,R.H. 1972. Handbookofhardwoods. Rev., 2d ed. London: H. M. Stationery Office. Chudnoff, Martin. 1984. Tropicaltimbers of the world. Agric.Handb. 607. Washington DC: U.S. Departmentof

Pine,

Radiata

Agriculture.

Radiatapine (Pinus radkzta),also known as Monterey pine,

is planted extensively in the southernhemisphere, mainly in

Chile, New Zealand,Australia,and SouthAfrica.Plantationgrowntrees may reach height of26 to 30 m (80 to 90 ft) in 20 years.

a

The heartwoodfrom plantation-grown trees is light brownto pinkishbrown and is distinctfrom the paler cream-colored sapwood.Growth rings are primarilywide and distinct. False rings may be common. The texture is moderatelyeven and fme, and the grain is not interlocked. Plantation-grown radiatapine averagesabout 480 kg/rn3 (30 lb/ft3)at 12% moisture content. Its strength is comparable with that ofred pine (P. resinosa), although locationand growthrate may cause considerablevariationin strengthproperties. The wood air or kiln dries rapidly with little degrade. The wood machineseasily althoughthe grain tends to tear aroundlarge knots. Radiatapine nails and glues easily, and it takes paint and fmisheswell. The sapwoodis prone to attackby stain fungi and vulnerabletoboring insects. However, plantationgrown stock is mostly sapwood,whichtreats readily with preservatives. The heartwoodis rated as durable above groundand is moderatelyresistantto preservativetreatment. Radiatapine canbe used for the samepurposesas are the other pines grown in the United States. Theseuses include veneer,plywood,pulp, fiberboard,construction, boxes,and millwork.

References Alden,H.A. 1995. HardwoodsofNorth America. (len. Tech. Rep. FPL—GTR—83. Madison, WI: U.S. Department ofAgriculture, Forest Service,Forest Products Laboratory. Alden, H.A. 1997. SofiwoodsofNorth America. Gen. Tech. Rep. FPL—GTR—102. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest ProductsLaboratory. Berni, C.A.; Boiza, E.; Christensen, F.J. 1979. South American timbers—characteristics, properties, and uses of 190 species.Melbourne,Australia: Commonwealth Scientificand IndustrialResearchOrganization, Division ofBuildingResearch. Boiza, E.; Keating,W.G. 1972. Africantimbers—the properties, uses, and characteristics of700 species. Melbourne,Australia: Commonwealth Scientificand Industrial ResearchOrganization, DivisionofBuildingResearch.

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Hardwood MarketReport: LumberNewsLetter. [Current edition]. Memphis,Th. Haynes, Richard W.; Adams, Darius M.; Mills, John R. 1993. The 1993 RPA timber assessmentupdate. Gen. Tech. Rep. RM—GTR—259. Fort Collins, Colorado:U.S. Department ofAgriculture, Forest Service, RockyMountainForest and RangeExperimentStation. Howard, James L. 1997. U.S. timber production,trade, consumption, and price statistics, 1965—1994. (len. Tech. Rep. FPL—GTR—98. Madison, Wisconsin:U.S. Department ofAgriculture, Forest Service, Forest ProductsLaboratory. Keating, W.G.;Boiza, E. 1982. Characteristics, properties, and uses oftimbers: Vol. 1. SoutheastAsia, NorthernAitstralia, and the Pacific. Melbourne, Australia: Inkata Press. Kukachka, B.F. 1970. Propertiesof importedtropical woods. Res. Pap. FPL 125. Madison, WI: U.S. Department ofAgriculture, Forest Service,Forest Products Laboratory. LittleE.L. 1979. Checklist ofUnited Statestrees (nati\e and naturalized). Agric.Handb. 541. Washington, DC: U.S. Department ofAgriculture.

Markwardt,L.J. 1930. Comparative strengthpropertiesof woods grown in the United States. Tech. Bull. 158. Washington, DC: U.S. Department ofAgriculture. Panshin, A.J.; deZeeuw, C. 1980. Textbookofwood technology. 4th ed. New York: McGraw—Hill.

Record, S.J.; Hess, R.W. 1949. Timbers ofthe new world. New Haven, CT: YaleUniversityPress. Ulrich, Alice H. 1981. U.S. timberproduction,trade, consumption, and price statistics, 1950—1980. Misc. Pub. 1408. Washington, DC: U.S. DepartmentofAgriculture. USDA. 1990. An analysisofthe timber situationin the United States: 1989—2040. Gen. Tech. Rep. RM—199. Fort Collins,CO: U.S. Department ofAgriculture, Forest Service, Rocky Mountain Forest and Range ExperimentStation.

I

Cfiapter

Structure of Wood Regis B. Miller

Contents Bark, Wood, Branches, and Cambium

Sapwoodand Heartwood 2—2 Growth Rings Wood Cells

2—3

ChemicalComposition 2—3

References

2—4

these fibrous cells andtheir arrangement affectsuchproperties

as strengthandshrinkageas well as thegrain pattern ofthe wood.This chapterbrieflydescribessome elements ofwood structure.

2—2

SpeciesIdentification

2—1

he fibrous nature ofwood strongly influences how it is used. Wood is primarilycomposed ofhollow, elongate, spindle-shaped cellsthat are arranged parallelto each other along the trunk ofa tree. Whenlumber and otherproductsare cut from the tree, the characteristics of

2—4

Bark, Wood, Branches, and Cambium A cross sectionofatree (Fig. 2—1)showsthe following welldefmed features (from outside to center): bark, which maybe dividedinto an outer corkydeadpart (A), whosethikness variesgreatlywith species and age oftrees, and an inner thin livingpart (B), whichcarriesfood from the leaves tc growing parts ofthe tree; wood,whichin merchantable trees ofmost species is clearly differentiated into sapwood(D) and heartwood (E); and pith (F), a smallcore oftissue locatedatthe centeroftree stems, branches, and twigsabout whichinitial wood growthtakes place. Sapwoodcontainsboth livingand deadtissue and carriessap from the roots to the leaves. Heartwood is formed by agradualchange in the sapwoodand is inactive. The wood rays (G), horizontallyorientedtissue throughthe radialplaneofthe tree, vary in size fromonecell wide and a few cells high to more than 15 cells wide and several centimeters high. The rays connectvariouslayers from pithtobark for storage and transferoffood.Th cambium layer(C), whichis insidethe inner bark and forms wood and bark cells,can be seen only with a microscope.

As thetree growsin height, branching is initiated by lateral

bud development. The lateral branchesare intergrown with thewood ofthetrunk as long as they arealive.After a branch dies, the trunk continuesto increase in diameterand. surrounds that portionofthe branchprojectingfrom the trunk whenthebranchdied. Ifthe deadbranches drop from thetree, thedeadstubs become overgrown and clear wood is formed.

2—1

In general, heartwoodconsistsofinactivecells that do not functionin eitherwater conduction or food storage.The transition from sapwoodto heartwoodis accompaniedby an increase in extractive content. Frequently, these extractives darken the heartwood and give species such as black walnut

Figure 2—1. Cross sectionofwhite oaktree trunk: (A) outer bark (dry dead tissue), (B) inner bark (living tissue),(C) cambium, (D) sapwood, (E) heartwood, (F) pith, and (0) wood rays.

Most growth in thicknessofbark andwood is causedby cell division in the cambium(Fig. 2—iC).No growthin diameter takes place in wood outsidethe cambialzone;new growthis purelythe addition and growthofnew cells,not thefurtherdevelopmentofold ones.New woodcells are formedon the insideofthe cambiumand new bark cells on the outside. Thus,newwood is laid down to theoutsideof old wood and the diameterofthe woodytrunk increases. In most species, the existingbark is pushed outward by the formation ofnew bark, andthe outer bark layersbecome stretched, cracked, andridged and are fmally sloughed off.

Sapwood and Heartwood Sapwood is located betweenthe cambium and heartwood (Fig. 2—iD). Sapwoodcontainsboth living and dead cells and functionsprimarilyin the storage offood; in the outer layersnearthe cambium, sapwoodhandlesthe transportof water or sap. The sapwoodmay vary in thicknessand number ofgrowthrings. Sapwoodcommonlyranges from 4 to 6 cm(1-1/2 to 2 in.) in radial thickness. In certainspecies, such as catalpaand blacklocust,the sapwoodcontains few growthrings and usuallydoes not exceed 1 cm (1/2 in.) in thickness. The maples,hickories,ashes, some southern pines,and ponderosapine ofNorth Americaand cativo (Prioriacopafera),ehie (Guibourtiaehie),and courbaril (Hymenaeacourbaril) oftropicaloriginmayhave sapwood 8 to 15 cm (3 to 6 in.) or more in thickness,especiallyin second-growth trees. As a rule,the more vigorously growing treeshave wider sapwood. Many second-growth treesof merchantable size consistmostly ofsapwood.

2—2

andcherrytheircharacteristic color.Lightercoloredheartwood occurs inNorth Americanspecies such as the spruces (exceptSitka spruce), hemlocks, true firs, basswood,cottonwood,and buckeye, and intropical species such as ceiba (Ce/bapentandra), obeche(Triplochitonscieroxylon), and ramirt (Gonyslylus bancanus).In some species, suchas black locust, western redcedar, andredwood,beartwoodextractyes makethe woodresistantto fungi or insect attack. All darKcoloredheartwoodis not resistantto decay,andsome nearly colorlessheartwoodis decay resistant, as in northernwhitecedar. However, none ofthe sapwoodofany species is resistant to decay.Heartwood extractives may also affectwood by (a) reducing permeability, making theheartwoodslowerto dry andmore difficult to impregnate with chemicalpreservatives, (b) increasingstabilityin changing moistureconditions, and (c) increasingweight (slightly). However,as sapwood changesto heartwood, no cells are addedor taken away, nor do any cells changeshape. The basic strengthof the wood is essentially not affectedby the transition from sapwoodcells to heartwoodcells. In some species, such as the ashes, hickories,and certain oaks,the pores(vessels) becomepluggedto a greateror lesser extentwith ingrowthsknownas tyloses. Heartwocdin whichthe pores are tightlypluggedby tyloses, as in white oak, is suitable fortight cooperage, becausethe tyloses preventthe passage ofliquid throughthe pores. Tyloses slso make impregnation ofthe wood with liquidpreservatives difficult

Growth Rings Inmost species in temperate climates, thedifference between woodthat is formed early in a growingseason and that formed later is sufficient to produce well-marked annual growthrings (Fig. 2—2).The age ofa tree at the stumpor the age at any cross sectionofthe trunk may be determinedby countingthese rings.However,ifthe growth in diameteris interrupted, by drought or defoliation by insectsfor example, more than one ring maybe formed in the same season. In such an event, the inner ringsusually do not have sharply defmedboundaries andaretermed falserings.Trees that have only very small crowns or that have accidentally lostmost of theirfoliagemay form an incomplete growthlayer,sometimes calleda discontinuous ring.

The inner part ofthe growthring formedfirst in the growing seasonis called earlywoodand the outer part formed later in thegrowingseason, latewood. Actualtime offormation of these two parts ofa ringmay vary with environmental and weatherconditions. Earlywood is characterized by cells with relativelylargecavitiesandthinwalls. Lateweodcells have smallercavities and thickerwalls. The transitionfrom earlywoodto latewood may be gradualor abrupt, depending on

within atree and among species. Hardwood fibersaverage about 1 mm (1/25 in.) in length; softwood fibers range from 3 to 8 mm (1/8 to 1/3 in.) in length.

In addition to fibers, hardwoods havecells ofrelatieIy large diameterknown as vesselsor pores. Thesecells form the main conduits in the movementofsap. Sofiwoods do not containvesselsforconducting sap longitudinally in the tree; this functionis performedby the tracheids. Both hardwoods and softwoodshavecells (usuallygrouped into structures ortissues)that are oriented horizontally in the directionfrom pith towardbark. Thesegroupsofcells conduct sap radiallyacrossthe grain and are calledrays orwood rays (Fig. 2—1G). The rays are most easily seen on dgegrained orquartersawn surfaces, and theyvary greatly in size in different species. In oaks and sycamores, therays are conspicuous and addtothe decorative featuresofthi wood. Raysalsorepresent planes ofweaknessalongwhich seasoning checks readily develop. Figure 2—2. Cross sectionofponderosa pine tog showing growth rings. Lightbands are earlywoodE, dark bands latewood. An annual (growth) ring is composed of an innerearlywood zone andouter latewoodzone.

thekind ofwood and thegrowingconditionsat the time it was formed.

Growthrings are most readily seen in species with sharp contrastbetweenlatewood formed in oneyear and ea:rlywood formedin the followingyear, such as in the nativeringporoushardwoodsash andoak, and in softwoods like southern pines. In some other species, such as water tupelo, aspen, and sweetgum, differentiation ofearlywood and latewood is slight andthe annual growthrings are difficultto recognize. Inmany tropical regions, growthmay be practicallycontinuous throughoutthe year,andno well-defmedgrowthrings are formed. Whengrowth rings are prominent, as in most softwoods and ring-porous hardwoods, earlywood differs markedly from latewood in physical properties. Earlywoodis lighterin weight, softer, andweakerthan latewood. Becauseofthe greater density of latewood, the proportionoflatewood is sometimes usedtojudge the strength ofthewood. This methodis usefulwith such species as the southernpines,Douglas-fir, andthe ring-porous hardwoods(ash, hickory, andoak).

Wood Cells Woodcells—thestructuralelementsofwood tissue——are of various sizes and shapes andare quite firmly cementedto-

gether. Dry wood cells may be empty or partly filledwith deposits,such as gums and resins, or with tyloses. The majorityofwood cells areconsiderably elongated and pointedat the ends; these cells are customarily called fibers or tracheids. The length ofwood fibers is highlyvariable

Another type ofwood cells,knownas longitudinal oraxial parenchymacells, function mainlyinthe storage of Food.

Chemical Composition Dry woodis primarilycomposed of cellulose, lignio,hemicelluloses, andminor amounts (5% to 10%) ofextruneous materials. Cellulose, the major component,constitutes approximately 50% ofwood substanceby weight. It is a high-molecular-weight linearpolymerconsisting ofchains of 1 to more than 4 3-linked glucose monomers. During growthofthetree,the celldlosemolecules are arranged into orderedstrands called fibrils, whichin turnare orgaiized into thelargerstructural elementsthat makeupthecell wall of wood fibers. Most ofthe cell wall celluloseis crystalline. Delignified wood fibers, whichconsistmostlyofcellulose, havegreatcommercial valuewhenformed into paper.Delignifiedfibersmay alsobe chemically alteredto form textiles, films, lacquers, and explosives. Ligninconstitutes 23% to 33% ofthe wood substance in softwoods and 16% to 25% in hardwoods. Although lignin occurs in wood throughout the cell wall, it is concentrated towardthe outside ofthe cells and betweencells. L:Lgninis often calledthe cementing agentthat binds individual cells together. Lignin is a three-dimensional phenylpropanol polymer,and its structure and distributionin wood are still not fullyunderstood. Ona commercial scale,it is necessary toremoveligninfrom wood to make high-grade paper or other paperproducts. Theoretically, lignin might be converted to a variety of chemical products, but in commercial practicea largepercentage ofthe lignin removedfrom wood during pulping operations is atroublesomebyproduct,which is often burned forheat and recovery ofpulpingchemicals. One sizable commercial use for lignin is in the formulation ofoil-well drillingmuds. Lignin is also used in rubber compoitnding and concrete mixes. Lesser amounts are processed toyield

2—3

vanillin for flavoringpurposesand to produce solvents. Currentresearch is examiningthe potential ofusinglignin in themanufacture ofwood adhesives. The hemicelluloses are associated with celluloseand are branched, low-molecular-weight polymerscomposed of several different kindsofpentoseandhexosesugarmonomers.The relative amounts ofthese sugarsvary markedly with species. Hemicelluloses play an important role in fiberto-fiberbonding in the papermaking process.The component sugarsofhemicellulose are ofpotential interestfor conversion into chemicalproducts. Unlikethe major constituentsofwood,extraneous materials arenot structural components.Both organicand inorganic extraneous materialsare found in wood.The organic component takes the form ofextractives, whichcontribute to such wood propertiesas color,odor, taste,decay resistance, density, hygroscopicity, and flammability. Extractives include tanninsand other polyphenolics,coloringmatter, essential oils, fats, resins, waxes, gum starch, and simplemetabolic intermediates. This component is termed extractives because it can be removed from wood by extractionwith solvents, such as water, alcohol, acetone, benzene,or ether. Extractives may constitute roughly5% to 30% ofthe wood substance, depending on such factorsas species,growthconditions,and time ofyearwhen the tree is cut. The inorganic component ofextraneous material generally constitutes 0.2%to 1.0% ofthe wood substance, although greatervaluesare occasionallyreported. Calcium, potassium, and magnesiumare the more abundantelemental constituents. Trace amounts (0.3, temperaturesaround 24°C (75°F), and moisture contentvalues 25%, measurements have been few innumber and generally lackingin accuracy.

c,

= (co+0.01Mc)I(l + 0.OlM)+A

(3—9)

where Mis moisturecontent(%). The heat capacityofwater is about 4.19 kJ/kgK(I BtuJlb.°F). The adjustnientfactor can be derived from

A=M(b+b2t+b,M)

i0,

with b1 = —0.06191, b, = 2.36 x and b3 —1.33 x 10 with temperature in kelvins (b1 = —4.23 x and b3 —3.17 x 10 with temperaturein b2= 3.12 x °F). Theseformulas are valid forwood belowfiber saturation at temperatures between7°C (45°F)and 147°C (297°F). Representative values forheat capacity canbe found in Table 3—12. The moisture above fiber saturation contributes to specific heat according to thesimplerule ofmixtures.

l0,

Thermal Diffusivity Thermaldiffusivity is a measureofhow quickly material canabsorb heat from its surroundings; it is theral:ioofthermal conductivity to the product ofdensity and heatcapacity. Diffusivity is defmedas the ratio ofconductivity 1:0 the productofheat capacity and density;therefore, conclu;ionsregardingits variation with temperature and density are often basedon calculating the effectofthese variables o:i heat capacityand conductivity. Becauseofthe low thermal conductivity and moderatedensity andheatcapac[ty of

wood,the thermaldiffusivityofwood is much lowerthan that ofother structural materials,such as metal, brick, and stone. A typicalvalue for wood is 0.161 x l0_6m2/s (0.00025 in2/s) compared with 12.9 x lO_6m2/s (102 in2/s) for steel and 0.645 x 10_6m2/s (0.001 in2/s) for mineral wool. For this reason,wood does not feel extremelyhot or cold to the touch as do some other materials.

3—17

Table 3—10. Grouping of some domestic and imported woods according to average heartwood decay resistance Resistant orvery resistant

ornonresistant

Moderatelyresistant

Slightly

Baldcypress,young growth Douglas-fir Larch, western Pine, longleaf, old growth Pine, slash,oldgrowth Redwood,younggrowth Tamarack

Alder, red

Domestic Baldcypress,old growth Catalpa Cedar Atlantic white Eastern redcedar Incense Northern white Port-Orford Western redcedar Yellow Cherry, black Chestnut Cypress, Arizona

Ashes Aspens Beech

Birches Buckeye Butternut Cottonwood

Elms Pine,eastern white, oldgrowth

Junipers Locust, Black°

Basswood Firs, true Hackberry Hemlocks Hickories Magnolia Maples

Pines (other than thoselisted)b Spruces Sweetgum Sycamore Tanoak

Honeylocust Mesquite Mulberry, red8 Oaks, whiteb Osage orange8 Redwood, oldgrowth Sassafras Walnut, black

Willows Yellow-poplar

Yew,Pacific8 Imported Aflotmosia (Kokrodua)

Andiroba Avodire

Balsa

Benge Bubinga Ehie

Cativo Ceiba Hura

Balau" Courbaril Determa Goncalo alves8 Greenheart°

Ekop

Jelutong

Keruingb

Limba Meranti, light redb

Ipe (lapacho)8

Sapele

Iroko Jarrah8 Kapur

Teak, younggrowth

Obeche Okoume

Tornillo

Parana pine

Angelique8 Apamate (Roble) Azobe8 Balata8

Mahogany,African Meranti, dark redb Mersawab

Banak

Meranti, yellowb Meranti, whiteb

Ramin

Karri

Sande

Kempas Lignurnvitae8 Mahogany, American Manni Purpleheart° Spanish-cedar Sucupira Teak, old growth8 Wallaba

Sepitir Seraya, white

8Exceptionallyhigh decay resistance. bMore thanone speciesinduded, someofwhich mayvaryin resistance fromthat indicated.

3—18

Table 3—11. Thermal conductivity

ofselected hardwoodsand softWoodsa Conductivity

(W/mK (Btuin/hft2°F)) Species

Specific gravity

Ovendry

12% MC

Resistivity

(Km/W (hft2•°F/Btu•in)) Ovendry

—

12% MC

Hardwoods Ash Black

0.53

White

0.63

0.12(0.84) 0.14 (0.98)

0.15(1.0)

8.2(1.2)

6.8 (0.98)

0.17 (1.2)

7.1 (1.0)

5.8 (0.84)

0.12 (0.82) 0.12 (0.80)

10(1.5)

8.5(1.2) 8.6(1.2)

0.38

0.10(0.68) 0.10 (0.67) 0.092(0.64)

0.68

0.15(1.0)

0.18(1.3)

0.71

0.16 (1.1)

0.66

0.15(1.0)

Aspen

Btooth

Quaking Basswood,American Beech,American Birch Sweet Yellow

Cherry, black Chestnut, American Cottonwood Black Eastern

0.41

040

0.11 (0.77)

10(1.5) 11(1.6) 6.6 (0.96)

9.0(1.3) 5.4(0.78)

5.2(0.75)

0.53

0.12

(0.84)

0.19(1.3) 0.18(1.2) 0.15 (1.0)

0.45

0.11(0.73)

0.13(0.89)

6.4(0.92) 6.8(0.98) 8.2(1.2) 9.4(1.4)

0.35

0.087(0.60) 0.10(0.71)

0.10(0.72) 0.12(0.85)

12(1.7) 9.8(1.4)

9.6 (1.4)

0.12(0.86) 0.15(1.0)

0.15 (1.0) 0.18 (1.3)

8.1 (1.2)

6.7(0.93)

6.7 (0.97)

0.15(1.1) 0.16(1.1) 0.19 (1.3)

7.9(1.1) 7.7(1.1) 6.6 (0.95)

5.5 (0.80) 6.5 (0.9:3)

0.69

0.13(0.88) 0.13(0.90) 0.15 (1.1)

0.43

Elm

5.6(0.81)

6.8 (0.93) 7.8(1.1)

8.1 (1.2)

American Rock

0.54

Slippery Hackberry Hickory, pecan Hickory, true Mockemut

0.56

0.78

0.17 (1.2)

0.21 (1.4)

5.9 (0.85)

Shagbark

0.77

0.17(1.2)

0.21 (1.4)

5.9(0.86)

4.8(0.69) 4.9(0.70)

0.12 (0.83)

0.14(1.0)

8.4(1.2)

6.9(1.0)

Magnolia, southern

0.67

0.57

0.52

6.4(0.92) 5.4(0.77)

Maple

Black Red Silver Sugar Oak, red Black Northern red Southern red Oak, white Bur White

0.60

0.14(0.94)

0.16(1.1)

7.4(1.1)

6.1 (0.813)

0.56 0.50 0.66

0.13(0.88) 0.12 (0.80) 0.15 (1.0)

0.15(1.1) 0.14(0.97) 0.18(1.2)

7.9(1.1)

8.6 (1.2)

6.5(0.93) 7.1 (1.1))

6.8(0.98)

5.6(0.81)

0.66 0.65

0.15 (1.0) 0.14 (1.0)

6.8(0.98)

5.6 (0.81)

0.14(0.96)

6.9(1.0) 7.2(1.0)

5.7(0.82)

0.62

0.18(1.2) 0.18 (12) 0.17 (12)

0.66

0.18(12)

6.8(0.98)

0.19 (1.3) 0.15 (1.1)

6.3(0.91)

5.6(0.81) 5.2(0Th) 6.6(0.9t5 6.7(0.96)

Sweetgum Sycamore, American Tupelo Black Water

0.55

0.15(1.0) 0.16 (1.1) 0.13(0.87

0.54

0.12(0.86)

0.15(1.0)

8.0(1.2) 8.1 (1.2)

0.54

0.12 (0.86)

0.15(1.0)

8.1 (1.2)

0.53

0.12(0.84)

Yellow-poplar

0.46

0.11 (0.75)

0.15(1.0) 0.13(0.90)

8.2(1.2) 9.3(1.3)

0.72

5.9 (0.85)

6.7(0.96) 6.8(0.98)

7.7(1:)

3—19

Table 3—Il. Thermal conductivity of selected hardwoods and softwOodsa_con. Conductivity

Resistivity

(W/mK (Btuin/hft2°F)) Species

-

Ovendry

12% MC

0.47

0.11(0.76)

0.34

0.46

0.085(0.59) 0.11 (0.77) 0.079(0.55) 0.10(0.71) 0.083(0.57) 0.11 (0.75)

0.51

0.12 (0.82)

0.14(0.99)

0.50 0.52

0.12(0.80) 0.12(0.83)

0.14(0.97) 0.14(1.0)

0.37

0.090 (0.63)

0.11 (0.75'

0.41

0.10(0.68)

0.42 0.48

0.10(0.69) 0.11 (0.77)

0.56

0.13(0.88)

0.37 0.45 0.54 0.43 0.62 0.53

0.090(0.63) 0.11 (0.73)

Specific gravity

(W/rnK(hft2°F/Btuin)) Ovendry

12% MC

0.13(0.92)

9.1 (1.3)

7.5(1.1)

0.10 (0.70;

12(1.7) 8.9(1.3) 13(1.8) 9.8(1.4) 12(1.7) 9.3(1.3)

9.9(1.4) 7.4(1.1) 11(1.5) 8.1 (1.2) 10(1.5) 7.7(1.1)

8.5(1.2) 8.6(1.2) 8.4(1.2)

7.0(1.0) 7.1 (1.0) 6.91.0)

0.12(0.82;

11(1.6) 10(1.5)

9.2(1.3) 8.5(1.2)

0.12(0.84; 0.14(0.94) 0.15 (1.1)

10(1.4) 8.9(1.3) 7.9(1.1)

8.3(1.2) 7.4(1.1) 6.5(0.93)

0.11 (0.75)

11(1.6) 9.4(1.4) 8.1 (1.2) 9.8(1.4) 7.2(1.0)

9.2(1.3) 7.8(1.1)

Softwoods Baldcypress Cedar Atlantic white Eastern red Northern white Port-Orford Western red Yellow Douglas-fir Coast Interior north Interior west

0.48 0.31 0.43 0.33

0.14(0.94) 0.094(0.65) 0.12 (0.85 0.10(0.68) 0.13(0.90)

Fir Balsam White Hemlock Eastern Western Larch,western Pine

Eastern white Jack Loblolly Lodgepole

Longleaf Pitch Ponderosa Red Shortleaf Slash

0.42 0.46 0.54 0.61

Sugar Western white Redwood Old growth

0.37

Young growth Spruce Black

0.37

Engelmann Red

0.37

Sitlca

0.42 0.37

White

0.40

0.41

0.43

0.42

0.12(0.86) 0.14(0.95) 0.090(0.63) 0.10(0.67)

0.13(0.89) 0.15(1.0) 0.12(0.85) 0.17 (1.2) 0.15(1.0) 0.12(0.84) 0.13(0.90) 0.15(1.0) 0.17(1.2) 0.11 (0.75) 0.12(0.80)

0.10(0.68) 0.090(0.63)

0.12(0.82) 0.11(0.75)

10(1.5) 11(1.6)

8.5(1.2) 9.2(1.3)

0.10(0.71) 0.090 (0.63)

0.12 (0.85) 0.11 (0.75)

8.1 (1.2)

0.10(0.69) 0.10(0.69) 0.090 (0.63)

0.12(0.84) 0.12 (0.84) 0.11 (0.75)

9.8(1.4) 11(1.6) 10(1.4) 10(1.4) 11(1.6)

0.12(0.86) 0.10(0.71) 0.14(0.96) 0.12(0.84) 0.10(0.69) 0.11 (0.75)

8.2(1.2) 10(1.4) 9.3(1.3) 8.1 (1.2) 7.3(1.1) 11(1.6) 10(1.5)

6.7 (0.96) 8.1 (1.2) 5.9(0.85) 6.8(0.98) 8.3(1.2) 7.7(1.1)

6.7 (0.96) 6.0 (0.86)

Values inthistable are approximateand should be used with caution;actual conductivitiesmay vary byasmuchas20%. Thespecific gravitiesalso do not representspecies averages.

3—20

9.2(1.3) 8.6(1.2)

9.2(1.3) 8.3(1.2) 8.3(1.2) 9.2(1.3)

Table 3—12. Heatcapacity of solid wood at selected temperatures and ma isture contents Specific heat (kJ/kgK(Btullb°F))

Temperature (K)

(°C

(°F))

Ovendry

5% MC

12% MC

20% MC

1.2(0.28) 1.2(029)

1.3(0.32) 1.4(0.33)

1.5 (0.37)

1.7(0.41) 1.8 (0.43)

1.4 (0.34)

1.7 (0.40)

1.9 (0.45)

1.5 (0.37)

1.8 (0.43)

2.0(0.49)

1.6 (0.39)

1.9 (0.46)

2.2 (0.52)

1.7(0.41)

2.0(0.49)

2.3(0.56)

280

7

(45)

290

17

(75)

3(X)

27

(80)

320

47

(116)

340

67

(152)

1.3(0.30) 1.3(0.32) 1.4(0.34)

360

87

(188)

1.5(0.36)

Thermal Expansion Coefficient The coefficientofthermalexpansion is ameasureofthe

changeofdimension causedby temperature change. The thermalexpansion coefficients ofcompletely dry wood are positivein all directions;that is, wood expands on heating and contracts on cooling. Limitedresearchhas been carried out to explorethe influence ofwood propertyvariability on thermalexpansion. The thermalexpansion coefficient of ovendry wood parallelto the grain appearsto be independent ofspecific gravityand species. In tests ofboth hardwoods and softwoods, the parallel-to-grain values haverangedfrom about 0.000031 to 0.0000045 per K (0.0000017 to 0.0000025 per °F). The thermalexpansion coefficients acrossthegrain (radial andtangential)are proportionalto wood specific gravity. Thesecoefficients range from about 5 to morethan10 times greater thantheparallel-to-grain coefficients and are ofmore practicalinterest. The radial andtangentialthermal expansion coefficients for ovendrywood, CLr and x,, can be approximatedby the followingequations, over an ovendry specific gravityrange ofabout 0.1 to 0.8: cz,.= (32.4G+ 9.9)10_6per K

(3—11a)

a= (18G + 5.5)10_6 per °F

(31lb)

a,= (32.4G + 18.4)10_6 per K

(3—12a)

a= (18G + 10.2)l0_6 per °F

(312b)

Thermal expansion coefficients can be considered independentoftemperature over the temperaturerange of—51.1°C to 54.4°C (—60°F to 130°F).

Woodthat containsmoisturereacts differently to varying temperaturethan does dry wood. Whenmoist wood is heated,it tendsto expandbecauseofnormalthermalexpansion and to shrink becauseofloss in moisturecontent. Unless the wood is very dry initially (perhaps3% or 4% moisture contentor less), shrinkage causedby moistureloss on heatingwill be greater than thermalexpansion,so thenet dimensionalchangeon heatingwillbe negative.Woodat intermediate moisture levels (about8% to 20%) will expand when firstheated, then gradually shrink to a volume smaller thanthe initial volume as the wood graduallyloseswater while in the heated condition.

1.6 (0.38)

Even in the longitudinal (grain) direction, where dimensional changecausedby moisturechange is very small, such changes will still predominateover corresponding dimensional changes as aresult ofthermal expansion unless the wood is very dry initially.For wood at usual mcisture levels,net dimensional changes will generallybe negative afterprolonged heating.

Electrical Properties The most important electrical propertiesofwood are conductivity,dielectric constant, and dielectric power fa:tor. The conductivity ofa material determines the electric currentthat will flow whenthe material is placed under a given voltage gradient. The dielectricconstantofanonconducting material determines the amountofpotential electricenergy, in the form ofinducedpolarization, that is storedin a given volume ofthematerial whenthat materialisplacedin an electric field. The powerfactorofa nonconducting matethl determinesthe fractionofstoredenergy that is dissipai:edas heat whenthe material experiences a complete polarizc—depo1arize cycle. Examples ofindustrial wood processesand applications in whichelectrical properties ofwood are importantinclude crossarms andpoles forhigh voltagepowerlines, utility worker's tools,andthe heat-curing ofadhesivesin wood productsby high frequency electric fields. Moisturemeters forwoodutilize therelationship betweenelectrical properties and moisture contentto estimate the moisturecontent.

Conductivity The electrical conductivity ofwood varies slightly with appliedvoltageandapproximately doubles for each temperature increase of10°C (18°F). The electrical conductivity of wood (or its reciprocal, resistivity)varies greatlywith moisture content, especiallybelowthe fibersaturation point. As the moisture content ofwoodincreases fromnear zeroto fiber saturation, electrical conductivity increases (resistivitydetimes. Resistivityis about to creases) by 1010to 1016 for ovendry wood and iø to i04 for wood at fibersaturation. As the moisture contentincreases from fiber saturation to complete saturation ofthe wood structure, the

m

i'

m i0

3—21

6

E

The dielectric constantofovendry wood ranges from ab6ut 2 to 5 at room temperature and decreasesslowly but steadily with increasing frequency ofthe appliedelectric field. It increases as eithertemperature or moisture contentincreases. with a moderate positiveinteraction betweentemperatureand moisture. There is an intensenegativeinteractionbetween moisture and frequency. At20 Hz, the dielectricconstant mayrange from about 4 for dry wood to near 1,000,000 for wet wood; at 1 kHz, from about 4 when dry to about 5,000 whenwet; and at 1 MHz, from about 3 when dry to about 100 whenwet. The dielectric constant is larger for polarization parallelto the grain than acrossthe grain.

0

Dielectric Power Factor

w C-) (I) U, G)

Ce

2 C-)

a)

0. -J

-

-2 6

8

10

14 16 18 Moisture content

12

20

22 24

26

(%)

Figure 3—7. Change in electrical resistance of wood with varying moisturecontentlevelsfor many U.S. species; 90%of testvalues are represented by the shaded area. furtherincreasein conductivity is smallerand erratic, generally amountingto less than a hundredfold.

Figure3—7illustratesthe change in resistance along the grain with moisturecontent, based on tests ofmany domestic species. Variability between test specimens is illustrated by theshadedarea.Ninetypercent oftheexperimental data pointsfall within this area.The resistancevalueswere obtainedusing a standardmoisturemeter electrode at27°C (80°F). Conductivityis greater along the grain than across thegrain and slightlygreater in theradial directionthan in thetangentialdirection.Relativeconductivity values in the longitudinal, radial, and tangential directions are relatedby the approximateratio of 1.0:0.55:0.50. Whenwood containsabnormalquantities ofwater-soluble salts or other electrolyticsubstances, such as preservative or fire-retardant treatment,or is inprolongedcontact with

seawater, electrical conductivity can be substantially increased.The increaseis smallwhenthe moisture content of thewood is less thanabout 8% but quicklyincreases as the moisture contentexceeds 10% to 12%.

Dielectric Constant The dielectricconstant is the ratio ofthe dielectricpermittivity ofthe materialto that offree space;it is essentially a measureofthe potentialenergyperunitvolume stored in the material in the form ofelectricpolarization whenthe material is in agiven electricfield. As measuredby practicaltests, the dielectric constantofa material is the ratio ofthe capacitance ofa capacitorusingthematerialas thedielectric tothe capacitance ofthe same capacitor usingfree spaceas the dielectric.

3—22

Whenanonconductor is placedin an electric field, it absorbs and stores potential energy.The amountofenergy storedper unit volumedepends upon the dielectricconstant and the magnitudeofthe appliedfield. An ideal dielectric releasesall this energy tothe external electriccircuitwhen the field is removed,but practicaldielectrics dissipate some ofthe energy as heat. The powerfactoris ameasureofthat portion of thestored energy converted to heat. Powerfactorvalues alwaysfall betweenzero and unity. Whenthe powerfactor does not exceedabout 0.1, the fractionofthe stored energy that is lost in one charge—dischargecycle is approximately equalto 2it timesthe power factor ofthe dielectric; for larger power factors, this fractionis approximated simplyby the powerfactor itself The powerfactor ofwood is large compared with that ofinert plasticinsulating materials, but somematerials,for example some formulations ofrubber,haveequallylargepowerfactors. Thepower factor ofwood variesfrom about 0.01 for dry, low density woods to as largeas 0.95 for dense woods at high moisture levels. The power factor is usually, but not always, greaterforelectricfields along the grain than across

thegrain.

The powerfactor ofwood is affected by several factors,including frequency, moisture content, and temperature. These factors interact in complexways to cause the power factor to have maximum andminimumvaluesat various combinations ofthese factors.

Coefficient of Friction The coefficient offrictiondepends on the moisture contentof the wood and the roughnessofthe surface. It varies little with species except forthose species, such as lignumvitae, that contain abundantoily or waxyextraôtives.

Onmost materials, thecoefficients offrictionfor wood increase continuously as the moisturecontentofthe wood increases from ovendry to fibersaturation, then remain about constantas the moisture contentincreases furtheruntil considerable free water is present. Whenthe surface is flooded withwater,the coefficient offriction decreases.

Static coefficients offriction are generally greaterthan sliding coefficients, andthe latter depend somewhat on the speedof sliding. Sliding coefficientsoffrictionvary only slightly

with speedwhen the wood moisture contentis less than about 20%;at high moisture content, the coefficient offriction decreasessubstantially as the speedincreases.

Coefficients ofslidingfriction for smooth, dry wood against hard, smoothsurfaces commonly range from 0.3 to 0.5; at intermediatemoisture content, 0.5 to 0.7; and near fiber saturation,0.7 to 0.9.

Nuclear Radiation Radiationpassingthrough matter is reducedin intensity according tothe relationship

I = Joexp(—px)

(3—i3)

I

where is the reducedintensityofthe beamat depthx in the material,jo is the incident intensity ofa beamofradiation, and t, the linearabsorptioncoefficient ofthe material,is the fraction ofenergy removedfrom the beamper unitdepth traversed. Whendensity is a factorofinterestin energy absorption, the linear absorption coefficient is divided by the density ofthe materialto derivethe massabsorptioncoefficient.The absorptioncoefficient ofamaterialvaries withthe type and energyofradiation. The linearabsorptioncoefficient ofwood for 'yradiationis knownto vary directlywith moisturecontent and density and inversely with the yray energy.As an example,the irradiation ofovendry yellow-poplar with 0.047-MeV 'yrays yields linearabsorptioncoefficients rangingfrom about 0.065 to about 0.11 cm1over theovendryspecific gravityrange of about 0.33 to 0.62.An increase in the linear absorption coefficient ofabout 0.01 cm4occurs with an increase in moisture contentfrom ovendry to fiber saturation. Absorption ofyrays in wood is ofpracticalinterest,in part for measuringthe densityofwood.

J

The interaction ofwood with radiation is similar in characterto that with yradiation, exceptthat the absorption coefficients are larger. The linearabsorption coefficient of woodwith a specific gravityof0.5 for a 0.5-MeVJ3ray is about 3.0 cm'. The result ofthelargercoefficient is that evenvery thin wood productsare virtuallyopaque to rays. The interaction ofneutronswith wood is ofinterestbecause wood andthe water itcontainsare compoundsofhydrogen, andhydrogenhas a relatively largeprobabilityofinteraction with neutrons. Higherenergyneutronsloseenergy much more quickly throughinteractionwith hydrogenthan with other elementsfound in wood.Lowerenergyneutronsthat result from this interaction are thus a measureofthe hydrogen densityofthe specimen. Measurement ofthe lower energylevel neutronscan be relatedto the moisture content

ofthewood.

When neutronsinteractwith wood, an additional result is theproduction ofradioactive isotopes oftheelementspresent in thewood. The radioisotopes producedcan be identifiedby thetype, energy, andhalf-lifeoftheir emissions, and the specific activity ofeach indicatesthe amountofisotope present. This procedure, called neutronactivation analysis, provides asensitive nondestructive methodofanalysisfor trace elements.

In the previousdiscussions, moderateradiationlevels that leavethe wood physically unchanged havebeen ansumed. Verylargedoses ofyraysorneutronscan cause substantial degradation ofwood. The effectoflargeradiationdoses on themechanical properties ofwood is discussedin Chapter4.

References ASHIRAE. 1981. American Society ofHeating, Refrigeration, and Air-Conditioning Engineershandbook, [.981 fundamentals. Atlanta, GA:American Society ofHeating, Refrigeration, and Air-Conditioning Engineers. ASTM. 1997. Standard methods for testing smallclear specimens oftimber.ASTM D143. West Consh&iocken, PA: American Society for Testing and Materials.

Beall,F.C. 1968. Specific heat ofwood—further rsearch requiredto obtain meaningful data. Res. Note FPL—RIN-0184. Madison, WI: U.S. DepartmentofAgriculture, Forest Service, Forest Products Laboratory.

James,W.L. 1975. Electricmoisturemeters for wood. Gen. Tech. Rep. FPL—GTR—6.Madison WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Kleuters, W. 1964. Determining local density of'woodby betaray method.Forest ProductsJournal. 14(9): 414. Kollman, F.F.P.; Côté, W.A., Jr. 1968. Principlesof wood scienceandtechnologyI—solid wood.New York, Springer—Verlag NewYork, Inc.

Kubler, H.; Liang, L.; Chang, L.S. 1973. Thermal ex-

pansionofmoist wood. Wood and Fiber. 5(3): 257—267. Kukaehka, B.F. 1970. Properties ofimportedtropical woods. Res. Pap. FPL—RP—125. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory. Lin,R.T. 1967. Reviewofdielectricproperties cellulose. Forest Products Journal. 17(7): 61.

of wood and

McKenzie,W.M.; Karpovich, H. 1968. Frictional behavior ofwood. Munich: WoodScience and Technology. 2(2): 138.

Murase, Y. 1980. Frictional properties ofwood at high sliding speed. Journal oftheJapanese WoodResearch Society. 26(2):

61—65.

Panshin,A.J.; deZeeuw, C. 1980. Textbookofwood technology. New York: McGraw—Hill.Vol. 1, 4th ed.

3—23

Simpson, W.T., ed. 1991. Dry kiln operator's manual. Agric. Handb. 188. Washington,DC: U.S. Department of Agriculture,Forest Service. Simpson, W.T. 1993. Speciflc gravity, moisturecontent, and density relationships for wood. U.S. Department of AgricultureGen. Tech. Rep. FPL—GTR—76.Madison, WI: U.S. Department ofAgriculture,Forest Service,Forest ProductsLaboratory.

Skaar, C. 1988. Wood—waterrelations. New York: Springer—Verlag.New York, Inc.

Stamm,A.J.; Loughborough, W.K. 1935. Thermodynamicsofthe swellingofwood.Journal ofPhysical Chemistry.39(1): 121.

3—24

Steinhagen, H.P. 1977. Thermal conductivepropertiesof wood, green or dry, from —40° to +100°C: a literaturereview. Gen. Tech. Rep. FPL—GTR—9. Madison, WI: U.S. Department ofAgriculture, Forest Service, ForestProducts Laboratory.

TenWolde, A., McNatt, J.D., Krahn, L. 1988. Thermal propertiesofwood panelproductsfor use in buildings. ORNLISub/87—21697/l. Oak Ridge, TN: Oak Ridge NationalLaboratory. Weatherwax, R.C.; Stamm, A.J. 1947. The coefficientscf thermalexpansion ofwood and wood products.Transactions

ofAmerican Society ofMechanical Engineers. 69(44): 421—432.

I

Cfiapterl4

Mechanical Properties of Wood David W. Green, JerroldE. Winandy,and David E. Kretschmann

Contents OrthotropicNatureofWood Elastic Properties 4—2

i

4—1

ModulusofElasticity 4—2 Poisson's Ratio 4--2 Modulusof Rigidity 4—3 StrengthProperties 4—3 CommonProperties 4—3 Less CommonProperties 4—24 VibrationProperties 4—25 Speedof Sound 4—25 InternalFriction 4—26 Mechanical Properties ofClearStraight-Grained Wood 4—26 Natural Characteristics AffectingMechanical Properties 4—27 Specific Gravity 4—27 Knots 4—27 Slope ofGrain 4—28 Annual Ring Orientation 4—30 ReactionWood 4—31 Juvenile Wood 4—32 CompressionFailures 4—33 Pitch Pockets 4—33 Bird Peck 4—33 Extractives 4—33 Properties ofTimberFrom Dead Trees 4—33 Effects ofManufacturing and Service Environments

MoistureContent 4—34 Temperature

4—35

Time Under Load 4—37 Aging 4—41 Exposureto Chemicals 4—41 ChemicalTreatment 4—41 NuclearRadiation 4—43 Mold and Stain Fungi 4—43 Decay 4—43 InsectDamage 4—43 References 4—44

he mechanical properties presentedin this chapter were obtainedfromtests ofsmallpieces ofwood termed"clear" and "straightgrained"becausethey did not containcharacteristics such as knots, cross grain, checks,and splits. Thesetest pieces did have anatomical characteristics such as growthrings that occurred in consistent patternswithineach piece.Clearwood specimens are usually considered "homogeneous" in wood mechanics.

4—34

Many ofthe mechanical properties ofwood tabulated in this chapterwere derivedfrom extensive sampling and analysis procedures. Theseproperties are represented as the average mechanical properties ofthe species. Some properties, such as tension parallelto thegrain, and all propertiesfor some importedspecies arebased on a more limited numberof specimens that were not subjected to the same sampling and analysis procedures. The appropriateness ofthese latter propertiesto represent the average properties ofa species is uncertain; nevertheless, the properties represent the best ioformation available. Variability, or variationin properties, is common to all materials. Because wood is a natural material andthe tree is subjectto many constantly changing influences (suchas moisture, soil conditions, andgrowing space), wood properties vary considerably, evenin clearmaterial.This chapter providesinformation, wherepossible,on the nature and magnitudeofvariability inproperties.

This chapteralsoincludes a discussion ofthe effect ofgrowth features, such as knotsand slope ofgrain,on clearwood properties. The effects ofmanufacturing and service environments on mechanical properties are discussed,andtheir effectson clearwood and material containing growthfeatures are compared. Chapter6 discusses howthese researchresults have beenimplemented in engineering standards.

Orthotropic Nature of Wooci

i

Wood may be describedas an orthotropic material;that is, it has uniqueand independent mechanical properties the directions ofthreemutuallyperpendicular axes: longitudinal, radial, and tangential.The longitudinal axis L is parallelto thefiber (grain); theradialaxis R is normaltothe growth rings(perpendicular to the grain inthe radial direction); and

4—1

.

Rathal,

e

Table 4—I. Elastic ratios for various species at approximately 12%moisturecontenta ED'EL

Ash,white Balsa

0.080 0.015

Basswood Birch, yellow Cherry, black Cottonwood,eastern Mahogany,African Mahogany,Honduras Maple, sugar Maple, red Oak, red Oak, white Sweetgum Walnut, black Yellow-poplar

0.027

Baldcypress Cedar, northernwhite Cedar,western red Douglas-fir Fir, subalpine Hemlock, western Larch, western

0.039

ER/EL

GLRIEL

GL7/EL

GR7/Et

0.109 0.054 0.056 0.074 0.147 0.076 0.088

0.077 0.037

0.005

Hardwoods

Tangential

V

Longitudinal

Figure 4—1. Threeprincipalaxes of wood with respect to grain direction and growth rings. the tangentialaxis T is perpendicularto the grain but tangent to thegrowth rings. These axes are shownin Figure 4—1.

Elastic Properties Twelve constants(nine are independent) are neededto describethe elasticbehaviorofwood: threemoduliofelasticity

E, three moduli ofrigidity G, and six Poisson's ratios t.

The moduli ofelasticityand Poisson's ratios are relatedby expressions ofthe form

(4—1)

Generalrelationsbetweenstress and strain for a homogeneousorthotropic materialcanbe foundintexts on anisotropic elasticity.

Modulus of Elasticity Elasticity impliesthat deformations producedby low stress are completely recoverable after loadsare removed. When loadedtohigher stress levels,plasticdeformationorfailure occurs. The three moduliof elasticity, whichare denotedby EL,ER, and respectively,are the elastic modulialong the longitudinal, radial, andtangentialaxes ofwood.These moduli are usually obtainedfrom compression tests; however,data for ER and are not extensive. Average values of ER andETfor samples from a few species are presented in Table4—1 as ratios with EL; the Poisson's ratios are shown in Table4—2. The elasticratios, as well as the elasticconstantsthemselves,vary within and between species and with moisture content and specificgravity.

E

E

The modulusofelasticitydeterminedfrom bending, EL, rather than from an axial test, may be the only modulusof elasticity available for a species. Average EL values obtained from bending tests are given in Tables4—3 to4—5. Representative coefficients ofvariationofEL determined with bending tests for clear wood are reportedin Table4—6. As tabulated, EL includes an effectofshear deflection; EL frombendingcan be increased by 10% to removethis effectapproximately.

0.050 0.086 0.047 0.050 0.064 0.065 0.067 0.082 0.072

0.050 0.056 0.043

0.125 0.046 0.066 0.078 0.197 0.083 0.111

0.107 0.132 0.140 0.154 0.163 0.115 0.106 0.092

0.066 0.111 0.133 0.089 0.086 0.089 0.085 0.075

—

0.046

—

0.068 0.097 0.052

0.017

0.059 0.086 0.063

0.021

0.081

—

— —

0.028

— — — —

0.061

0.062 0.069

0.011

0.054

0.007

Softwoods 0.081 0.055 0.050 0.039 0.031 0.065

0.084 0.183 0.081 0.068 0.102 0.058

0.079

0.063

0210 0.087 0.064 0.070 0.038 0.063

0.086 0.078 0.058 0.032

0.082 0.049 0.071 0.050 0.138 0.096 0.055 0.124

0.081

0.007

Pine

Longleaf

0.055

0.113 0.102 0.102

Pond Ponderosa

0.041

0.071

0.083 0.044 0.045

0.122 0.088

Loblolly Lodgepole

i,j=L,R,T

4—2

Species

Red Slash Sugar

Western white Redwood Spruce, Sitka Spruce, Engelmann

0.078 0.068

0.087 0.038 0.089 0.043 0.059

0.074 0.131 0.078 0.087 0.078 0.128

0.066 0.064 0.124

0.013

0.046 0.115 0.081 0.053 0.113 0.048 0.077 0.061 0.120

0.012 0.009 0.017 0.011 0.010 0.019 0.005 0.011

0.003

°EL maybe approximatedbyincreasing modulus ofelasticity values inTable 4—3by 10%.

This adjustedbendingEL can be used to determineER and E:r based on the ratios in Table 4—1.

Poisson's Ratio When a member is loadedaxially,the deformationperpen-

dicularto the directionofthe load is proportionalto the deformation parallelto the directionofthe load. The ratio of the transverse to axial strain is called Poisson's ratio. The Poisson's ratios are denotedby I-LLR, lILT, /-LTL, JIRT, and The firstletter ofthe subscript refers to directionof appliedstress andthe secondletter to directionoflateral deformation. For example,Jil.]?is the Poisson's ratio for deformationalong the radial axiscausedby stress along the longitudinal axis. Averagevalues ofPoisson's ratios for samples ofa few species are given in Table4—2. Values for 4Ujuand1Um are less preciselydeterminedthan are those for the other Poisson's ratios. Poisson's ratios vary within and between species andare affected by moisturecontent and

u,

specific gravity.

Table 4—2. Poisson's ratiosforvarious species at approximately 12% moisture content Species

ILR

l.IRT

l.LLT

I.LTR

l.LRL

l.LTL

0.360 0.496 0.231 0.346 0.426

0.059 0.054 0.018 0.034 0.043 0.086 0.043 0.033 0.033 0.065 0.063 0.064 0.074 0.044 0.052 0.030

0.051 0.022

Hardwoods Ash, white Aspen,quaking Balsa Basswood Birch, yellow Cherry, black Cottonwood,eastern Mahogany,African Mahogany,Honduras Maple,sugar Maple, red Oak,red Oak,white Sweet gum Walnut, black Yellow-poplar

0.371

0.489 0.229 0.364 0.426

0.440 0.374 0.488 0.406 0.451

0.344

0.428 0.420

0297

0.641

0.314 0.424 0.434 0.350 0.369 0.325 0.495

0.533 0.476 0.509

0.318

0.392

0.392

0.4.48

0.428 0.403 0.632

0.684

—

0.665 0.912 0.697 0.695 0.875 0.604 0.600 0.774 0.762 0.560 0.618 0.682 0.718 0.703

0282 0.292 0.264 0.326 0.349 0.354 0.292 0.300 0.309 0.378

0.329

0.009 0.022 0.024 0.048

0.018 0.032 0.034 0.037 0.044 0.033 0.036 0.023 0.035 0.019

Softwoods Baldcypress Cedar, northernwhite Cedar, western red Douglas-fir Fir, subalpine Hemlock, western Larch, western Pine Loblolly Lodgepole Longleaf Pond

Ponderosa Red Slash Sugar Western white Reciwood

Spruce, Sitka Spruce, Engelmann

0.338 0.337 0.378 0.292 0.341 0.485 0.355

0.326 0.340 0.296

0.328 0.316 0.332 0.280 0.337 0.347 0.392 0.356 0.329 0.360 0.372 0.422

0.292

0449 0.332

0.423 0.276 0.347 0.365 0.364 0.400 0.315 0.444 0.349 0.344 0.346 0.467 0.462

0.411 0.458 0.484 0.390

0.437 0.442 0.389

0.382 0.469 0.384 0.389 0.426 0.408 0.447 0.428 0.410 0.373 0.435 0.530

0.356 0.345 0A03 0.374 0.336 0.382 0.352 0.362 0.381

0.342 0.320 0.359 0.308 0.387 0.358 0.334 0.400 0.245 0.255

— — —

— — —

0.036 0.029

— — —

— — —

— — — — — — — — — —

— — — — — — — — — —

0.040 0.025 0.083 0.058

Modulus of Rigidity The modulus of rigidity, also called shear modulus, indicatesthe resistance todeflectionofa member caused by shear stresses. The three moduli ofrigidity denotedby GLT, and GRTare the elastic constantsin the LR,LT, arid RT is themodulusof planes, respectively.For example, based on shear strain in the LR rigidity planeand shear stressesinthe LTandRTplanes.Averagevalues ofshear modulifor samples ofa few species expressed as ratioswith EL are given in Table4—1. As with moduliof elasticity, the moduliofrigidity vary within and betweenspecies and with moisture contentand specific gravity.

G,

G

Strength Properties Common Properties Mechanical properties most commonly measuredandrepre-

sentedas "strengthproperties"for designincludemodulusof rupture in bending,maximumstress in compression parallel to grain, compressivestressperpendicularto grain,and shear strengthparallelto grain.Additionalmeasurements are often

made to evaluate work to maximumload in bending, impact bendingstrength, tensilestrengthperpendicularto grain, and hardness.Theseproperties, grouped according to the broad forest tree categories ofhardwood andsoftwood(riotconelatedwith hardness or softness), are given in Tables4—3 to 4—5 for many ofthe commercially important species. Average coefficients ofvariation forthese properties from alimited sampling of specimens are reported in Table4—6. Modulus of rupture—Reflectsthe maximum loadcanying capacity ofa member inbendingand is proportional to maximum momentborne by the specimen. Modulusofrupture is an accepted criterionofstrength, although it is not a true stress becausethe formulaby which it is computed is valid only to the elastic limjt. Work to maximum load in bending—Abilityto absorb shock with some permanentdeformationand more or less injury to a specimen. Workto maximum load is a measure ofthe combined strength and toughness ofwood under bendingstresses. Compressive strengthparallel to grain—Maximum stress sustained by a compression parallel-to-grain specimen havinga ratio oflengthto least dimensionofless than 11. Compressive stress perpendicular to grain——Reported as stress at proportional limit. There is no clearlydefmed ultimate stress for this property. Shear strengthparallel to grain—Abilityto resist internalslippingofone part upon anotheralongthe grain. Valuespresented are average strength in radialand tangential shearplanes. Impact bending—In theimpactbendingtest, a hammer ofgiven weightis droppedupon abeam from successively increased heights untilruptureoccurs or thebeam deflects 152 mm (6 in.) or more. The height ofthe maximum drop, or the drop that causes failure, is a comparative value that represents the abilityofwood to absorb shocks that cause stressesbeyondthe proportionallimit. Tensile strengthperpendicularto grain—Rsistance of wood to forcesactingacross the grain that tend to splita member. Valuespresented are the average ofradialand tangential observations. Hardness—Generallydefined as resistance to indentation using modifiedJankahardnesstest, measuredbythe load requiredto embed a 11.28-mm (0.444-in.) bal] to one-half its diameter. Valuespresentedare the averageofradialand tangential penetrations. Tensile strength parallelto grain—Maximumtensile stress sustainedin directionparallelto grain. Relatively few dataare available on thetensilestrengthofvarious species ofclear wood parallelto grain. Table4—7lists averagetensile strengthvaluesfor a limited numberof specimens ofafew species. Inthe absenceofsufficient tension test data,modulusofrupturevalues are sometimes substituted for tensile strength ofsmall, clear, straightgrainedpieces ofwood.The modulusofruptureis consideredto be a low or conservative estimate oftensilestrength for clear specimens (this is not true forlumber'i.

a

4—3

Table 4-3a. Strength properties of some commercially important woods grown in the United States (metric)a Static bending Work to

Common species

names

Corn-

Corn- pression Shear Tension Modulus Modulus maxipression perpen- parallel perpenof of mum Impact parallel dicular to dicular Moisture Specific rupture elasticityc load bending to grain to grain grain to grain content gravityb (kPa) (MPa) (kJ/rn3) (mm) (kPa) (kPa) (kPa) (kPa)

Side hard-

ness (N)

Hardwoods

Alder, red Ash Black

Blue Green Oregon

White Aspen Bigtooth Quaking

Basswood,American Beech, American Birch Paper Sweet Yellow

Butternut Cherry, black Chestnut, American Cottonwood Balsam poplar Black Eastern

Green 12%

0.37 0.41

45,000 68,000

Green 12% Green 12% Green 12% Green 12% Green 12%

0.45 0.49 0.53 0.58 0.53 0.56 0.50 0.55 0.55 0.60

41,000 87,000 66,000 95,000 66,000 97,000 52,000 88,000 66,000 103,000

Green 12% Green 12% Green 12% Green 12%

0.36 0.39 0.35 0.38 0.32 0.37 0.56

064

37,000 63,000 35,000 58,000 34,000 60,000 59,000 103,000

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

0.48 0.55 0.60 0.65 0.55 0.62 0.36 0.38 0.47 0.50 0.40 0.43

44,000 85,000 65,000 117,000 57,000 114,000 37,000 56,000 55,000 85,000 39,000 59,000

8,100 11,000

Green 12% Green 12% Green 12%

0.31 0.34 0.31 0.35 0.37 0.40

Green 12% Green 12% Green 12% Green

0.46 0.50 0.57

8,100 9,500

55 58

7,200

83

11,000

103 101

8,500 9,700 9,700

99

560 510

20,400

40100

3,000

840 890

15,900 41,200 24,800 48,100 29,000 48,800 24,200 41,600 27,500 51,100

2,400 5,900 3,400 5,200 10,800 4,800 5,600 10,600 — 9,800 14,000 — 5,000 8,700 4,100 9,000 13,200 4,800 3,700 8,200 4,100 8,600 12,300 5,000 4,600 9,300 4,100 8,000 13,200 6,500

17,200 36,500 14,800 29,300 15,300 32,600 24,500 50,300

1,400 3,100 1,200

16,300 39,200 25,800 58,900 23,300 56,300 16,700 36,200 24,400 49,000 17,000 36,700

1,900 5,800 2,600 2,500 4,100 8,300 — 4,000 3,200 8,500 3,000 4,300 7,400 15,400 6,600 6,500 3,000 7,700 3,000 3,600 6,700 13,000 6,300 5,600 1,500 5,200 3,000 1,700 3,200 8,100 3,000 2,200 2,500 7,800 3,900 2,900 4,800 11,700 3,900 4,200 2,100 5,500 3,000 1,900 4,300 7,400 3,200 2,400

— —

108 115

890 810 990 840 970 1,090

7,700 9,900 5,900

39 53

— —

44

8,100 7,200

52 37

10,100 9,500 11,900

82 104

560 530 410 410 1,090 1,040

11,400

7,800 9,400 9,900

12,000

81

92

84 99

50

112 110 108

1,700

5,300 2,700 2,000 7,400 2,900 2,600

— — 4,600 1,600 2,600 5,900 1,800 1,200 4,100 1,900 2,600 6,800 2,400 3,700 8,900 5,000 7,000 13,900 7,000 5,000 7,400

10,300

79

6,400 8,500

48

1,240 860 1,220 1,190 1,220 1,400 610 610 840 740 610

45

480

27,000 47,000 34,000 59,000 37,000 59,000

5,200 7,600 7,400 8,800 7,000 9,400

29 34 34 46 50

— — 510 560 530 510

11,700 27,700 15,200

1,000

3400

2,100

5,400

31,000

2,100

50,000 81,000 66,000 0.63 102,000

7,700 9,200 8,200

81

970 990

11,400 15,000 10,300

13,900 6,700 8,100 9,000

124 111

143 57

57 88

51

— —

2,300 3,800 — — 3,900 5,300 3,500 5,200 4,300 5,900 — — 1,300 1,600 1,100 1,800

3,800 5,800

— —

15,700

1,400

33,900

2,600

4,200 1,900 7,200 2,300 4,700 2,800 6,400 4,000

1,100 1,600 1,500 1,900

20,100 38,100 26,100 48,600

2,500 6,900 4,100 4,800 10,400 4,600 4,200 8,800 — 8,500 13,200 — 2,900 7,700 4,400 5,700 11,200 3,700 2,800 7,400 4,300 6,100 11,000 4,000

2,800 3,700

1,100

Elm

American Rock Slippery Hackberry

12%

4-4

0.48 0.53 0.49 0.53

55,000 90,000 45,000 76,000

10,600

8,500 10,300

6,600 8,200

90 137 132 106 117 100

88

1,370 1,420 1,190 1,140 1,220 1,090

22,900

43,900 18,300 37,500

— — 2,900 3,800 3,100 3,900

Table 4—3a. Strength properties of some commercially important woods grown in the United States (metric)a._con. Static bending Work to

Common species names

Hickory, pecan Bitternut

Nutmeg Pecan Water

Green 12% Green 12% Green 12% Green

0.60 0.66 0.56 0.60 0.60 0.66

71,000 118,000

0.61

12%

0.62

74,000 123,000

Green

0.64 0.72 0.66 0.75 0.64

Hickory,true Mockernut

Honeylocust Locust, black Magnolia

Cucumbertree Southern

Maple

Bigleaf Black Red Silver Sugar

0.66 0.69

Green 12% Green 12%

0.44 0.48 0.46 0.50

51,000 85,000 47,000 77,000

10,800 12,500 7,700 9,700

69 84 106 88

760 890 1,370 740

Green 12% Green 12% Green 12% Green 12% Green 12%

0.44 0.48 0.52 0.57 0.49 0.54 0.44 0.47 0.56

51,000 74,000 54,000 92,000 53,000 92,000

7,600 10,000 9,200 11,200 9,600 11,300 6,500 7,900 10,700 12,600

60 54 88 86 79 86 76 57 92 114

580

Green

0.56

57,000

12%

0.61 0.61

96,000

8,100 11,300 12,300 15,700 9,600 11,700

84 94

Green 12% Green 12% Green 12%

Cherrybark

Green

Laurel

Green

12% 12%

Northern red Pin

95 130 133

—

1,350 1,120 1,420 1,350

125,000 70,01)0 101,000 95,000 134,000

Green

0.72 0.62 0.69 0.60

—

063

Oak, red Black

77,000

1.73 101

1,680 1,680 1,370

219 210 163 178 206 163 87 92 106 127

Green

12%

Shellbark

68,000 94,000

138 125 157

2,240 1,960 2,260 1,880 1,880 1,700 2,640 2,240 1,190 1,190 1,120 1,450

12%

Shagbark

63,000 114,000

9700 12,300 8,900 11,700 9,400 11,900 10,800 13,900 10,800 15,300 11,400 15,600 10,800 14,900 9,200 13,000 8,900 11,200 12,800 14,100

12%

Pignut

Corn-

Corn- pression Shear Tension Modulus Modulus maxipression perpen- parallel perpen- Side of of mum Impact parallel dicular to dicular hardMoisture Specific rupture elasticityc load bending to grain to grain grain to grain ness content gravityb (kPa) (MPa) (kJ/m3) (mm) (kPa) (kPa) (kPa) (kPa) (N)

Green .12% Green 12%

Scarlet

Green

Southern red

Green

Water

Green

12% 12% 12%

0.68 0.56 0.63 0.56 0.63 0.58

0.63 0.60 0.67 0.52 0.59 0.56 0.63

132,000

81,000 139,000

76,000 139,000

72,000

40,000 61,000 65,01)0 109,000

74,000 125,000

54,000 87,000 57,000 99,000 57,000 97,000 72,000 120,000

48,000 75,000 61,000 106,000

180 156

101

126

77

12,500

81 91 100

9,100

97

11,900 10,200 13,200 7,900 10,300 10,700 13,900

102 103 141

9,300

55 65 77 148

710

1,220 1,020 810 810 740 640 1,020 990 1,020 1,040 1,370 1,240 990 990 1,120 1,090 1,220 1,140 1,370 1,350 740 660 990 1,120

— 31,500 5,500 8,500 — — — — 62,300 11,600 — 27,400 5,200 7,100 — — — — 47,600 10,800 27,500 5,400 10,200 4,701) 5,800 54,100 11,900 14,300 — 8,100 — 32,100 6,100 9,900 — — — — 59,300 10,700 5600 61,600 11,900 30,900 33,200

6,300

63,400 13,700 31,600

5,800

63,500 12,100 27,000

5,600

55,200 12,400 30,500

7,900

51,700 12,700 46,900 8,000 70,200 12,600

8,800 12,000 9,400 14,800 10,500 16,800 8,200 14,500

— — — — — — — —

— — — — — — — —

11,400 6,400 6,200 15,500 6,200 7,000 12,100 5,301) 7,000

17100 4,400 7,600

21,600 2,300 43,500 3,900

6,800 9,200 18,600 3,200 7,200 37,600 5,900 10,500 22,300 41,000 22,500 46,100 22,600 45,100

3,000 2,300

4,600 3,100 4,200 3,300 5,100 4,500

3,100 7,700 5,200 11,900 4,100 7,800 7,000 12,500 2,800 7,900 6,900 12,800 17,200 2,600 7,200 36,000 5,100 10,200 27,700 4,400 10,100 54,000 10,100 16,100

4,100 3,700 5,000 4,600 — — 3,900 3,400 — —

2,800

23,900

— — 5,500 5,800 5,300 5,400 5,200 5,500 5,500 7,200

4,700

6,000 3,300 3,500 5,700 6,300

6,200 3,800 4,700 4,500 5,300

45,000 31,900 60,300 21,900 48,100 23,700 46,600 25,400 47,000 28,200 57,400 20,900 42,000 25,800

46,700

4,900 6,400 5,200 8,600

8,400 13,200

7,000 5,000 7,000 5,700 7,700 3,800 6,000 4,300 7,000

12,300

9,100 13,800 3,900 8,100 7,300 12,600 4,200 8,300 8,900 14,300 9,700 13,000 6,400 9,600 8,500 13,900

3,800 3,700 5,200 3,100

4,200 2,600 3,100 4,300 6,400

5,400 5,500 6,600 4,400 5,400 4,400 5,700 4,800 6,700 4,800 5,300

4—5

Table 4—3a. Strength properties of some commercially important woods grown in the United States (metric)a_con. Static bending Work to

Common species names

Oak, red—con.

CornCorn- pression Shear Tension Modulus Modulus maxipression perpen- parallel perpenof of mum Impact parallel dicular to dicular Moisture Specific rupture elasticityc load bending to grain to grain grain to grain content gravityb (kPa) (kJIm3) (mm) (kPa) (kPa) (kPa) (kPa) (MPa) Green 12%

0.56

51,000

8,900

0.69

100,000

13,100

0.58 0.64 0.57 0.66 0.80 0.88 0.57 0.63 0.60 0.67 0.60

50,000

6,100 7,100 9,400 11,000 10,900 13,700 7,900 9,800 7,500 10,400 9,300 12,200 11,000 14,100 8,600 12,300

Sweetgum

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green

Sycamore,American

Green

Tanoak

Green 12%

WIlow

Oak, white

Bur

Chestnut Live

Overcup Post Swamp chestnut Swamp white

White Sassafras

12% 12%

Tupelo Black

Willow, black

Green 12% Green 12% Green 12% Green

Yellow-poplar

Green

Water Walnut, black

12% 12%

Baldcypress Cedar Atlanticwhite Eastern redcedar

Incense Northern white

4—6

71,000 55,000 92,000 82,000 127,000 55,000 87,000 56,000 91,000 59,000 0.67 96,000 0.64 68,000 0.72 122,000

0.60 57,000 0.68 105,000 0.42 41,000 0.46 62,000 0.46 49,000 0.52 86,000 0.46 45,000 0.49 69,000 0.58 72,000 — — 0.46 0.50 0.46 0.50 0.51

48,000 66,000 50,000 66,000 66,000 0.55 101,000 0.36 33,000 0.39 54,000

0.40 0.42

11,300 7,300

0.31 0.32 0.44

12% 12%

0.47 0.35 0.37

32,000 47,000 48,000 61,000

Green 12%

0.29 0.31

43,000 55,000

29,000 45,000

1,120 740 890 1,020

22,700 41,800 24,300 47,100 37,400 61,400

130 87 108 76 91

88 83 100 132

80 102

49 60 70 82 52

55 43 57 48

9,800

101

11,600

—

74 76

— —

1,120 970 1,120 1,170 1,140 1,040 1,270 1,240 1,070 940

— — 910 810 660 660 — — 760 560 760 580 940 860

61

— — 660 610

Softwoods 46 8,100

10,900

Green 12% Green

74 68 65 76 85

7,100 8,300 7,200 8,700

—

70,000 46,000 73,000

20,700

59 92

9,800

41,000

0.42 0.46

890 1,070

10,700

5,400 7,000 8,400

Green 12%

Green

6,300 7,700 8,300

4,200 8,100 48,500 7,800 11,400

61 101

61

52

4,700 9,300 8,300 12,500

3,700 5,800 14,100 19,600 23,200 3,700 42,700 5,600 24,000 5,900 45,300 9,900 24,400 3,900 50,100 7,700 30,100 5,200 59,300 8,200 24,500 4,600

51,300 7,400 18,800 2,600 32,800 5,900 21,000 2,600 43,600 4,300 20,100 2,500 37,100 4,800 32,100

—

— —

3,300 6,400 3,300 6,000

2,800

640

24,700

57

610

43,900 5,000

5,200 6,400 4,500 6,100 5,800

41

460 330 890 560

16,500 32,400 24,600

7,200 4,400 5,500

103

57 44 37

39 33

430 430 380 300

ness (N)

5,200 4,400 — 6,500 5,500 4,700 4,800 — — —

4,900 6,100

4,000 5,000

— —

9,100 5,000 4,300 6,500 5,300 8,800 5,400 5,000

13,800 12,700

5,400

6,000

8,700 4,600 4,900 13,700 4,800 5,500 9,000 5,900 5,200 13,800

5,700

8,600 5,300 13,800 5,500 6,600 — — 8,500 6,800 3,700 11000 5,200 6,900 4,300 10,100 5,000 — — — —

7,200

4700 6,000 — — 2,700 3,800

2,700 3,400

— —

7,600 3,900 2,800 9,200 3,400 3,600 8,200 4,100 3,200 11,000 4,800 3,900 3,400 8,400 3,900 4,000 7,000 9,400 4,800 4,500 — 1,200 4,700 — — 28,300 3,000 8,600 — 18,300 1,900 5,400 3,500 2,000 38,200 3,400 8,200 3,700 2,400 21,000 38,100 23,200 40,800 29,600 52,300 14,100

9,900

28

8,300 10,300 15,200 18,300

Side hard-

1,700

2,800 4,800 41,500 6,300 21,700 2,600 35,900 4,100 13,700

27,300

1,600 2,100

5,600 2,100 1,700 6,900 1,900 2,300 4,800 5,500

1,200 1,500

7,000

2,300 2,900 — 4,000

5,700

1,900

—

1,300 1,600 1,700

6,100 1,900 2,100 4,300 1,700 1,000 5,900 1,700 1,400

Table 4—3a. Strength properties of some commercially important woods grown in the United States (metric)a_con. Static bending Work to

Common species names Cedar—con. Port-Orford

Western redcedar Yellow

CornCorn- pression Shear Tension Modulus Modulus maxipression perpen- parallel perpen- Side of of mum Impact parallel dicular to dicular hardMoisture Specific rupture elasticityc load bending to grain to grain grain to grain ness content gravityb (kPa) (MPa) (kJ/m3) (mm) (kPa) (kPa) (kPa) (kPa) (N) Green 12% Green 12% Green 12%

Douglasfird Coast

0.39 0.43 0.31

0.32 0.42 0.44

45,000 88,000 35,900 51,700

9,000 11,700

6,500

44,000 77,000

9,800

53,000 85,000 53,000

10,800 13,400 10,400 12,600 9,700 12,300 8,000 10,300

52 68 50 73 56 72 55 62

8,600 10,000 8,100 10,300 8,600 10,800 9,500 11,900 9,800 12,100 7,200 8,900 8,000 10,300

32 35 44

Interior North

Green 12%

0.48

Interior South

Green

0.43 0.46 0.33 0.35 0.36 0.38 0.35 0.37 0.37 0.39 0.40 0.43 0.31 0.32 0.37 0.39

38,000 63,000 40,000 72,400 40,000 61,400 43,000 74,000 44,000 75,800 34,000 59,000 41,000 68,000

0.38 0.40 0.42 0.45 0.42 0.45

44,000

7,400

61,000

8,300

Interior West

Green 12%

12%

Fir Balsam

Green 12%

Californiared Grand Noble

Pacific silver Subalpine

White Hemlock Eastern Mountain

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

Western

Green 12%

Larch, western

Green 12%

Pine Easternwhite

Green 12%

Jack

Green 12%

Loblolly

Green 12%

Lodgepole Longleaf

Pitch

Green 12% Green 12% Green 12%

0.48 0.52 0.34 0.35 0.40 0.43 0.47 0.51 0.38 0.41

0.54 0.59 0.47 0.52

710 430 430 690 740

40 63 72

87,000 51,000 90,000 47,000 82,000

12%

530

63 34

7,700 7,900

0.45 0.48 0.46 0.50 0.45

Green

51

43,000

7,200

79,000

46,000

9,200 9,000

78,000 53,000 90,000

11,300 10,100 12,900

34,000

6,800 8,500 7,400 9,300 9,700 12,300 7,400 9,200 11,000 13,700 8,300 9,900

59,000 41,000 68,000 50,000 88,000 38,000 65,0C)0 59,0C)0 100,0C)0 47,0C)0 74,OC)0

61

39 52 41 61

41 64

— —

39 50

46 47 76

72 48 57 71

87 36 47 50 57 57 72 39 47 61 81

63 63

21,600 2,100 43,100 5,000 19,100

1,700

31,400 3,200

5,800 1,2)0 1,700 9,400 2,8)0 2,800 5,300 1,6)0 1,200 6,800 1,5)0 1,600 5,800 2,300 2,000 7,800 2,500 2,600

21,000 43,500

2,400 4,300

660 790 660 810 560 660 380 510

26,100 49,900 26,700 51,200 23,900 47,600 21,400 43,000

2,600 5,500 2,900 5,200 2,500 5,300 2,300

410 510 530 610 560 710

18,100 36,400 19,000 37,600 20,300 36,500

1,300 2,800 2,300 4,200 1,900 3,400 1,900 3,600 1,500 3,100 1,300

4,800

33,500 2,700 20,000 1900 40,000 3,700.

5,200 7,600

480 580 530

610 — — 560 510

20,800 42,100 21,600 44,200 15,900

5100

530 530 810 810 560 580 740 890

21,200 2,500 37,300 4,500 19,900 2,600 44,400 23,200 49,000 25,900 52,500

5,900 1,900 3,800 2,800 6,400

430

16,800 33,100 20,300 39,000 24,200 49,200 18,000 37,000 29,800 58,400 20,300 41,000

1,500 3,000 2,100 4,000 2,700 5,400 1,700 4,200 3,300 6,600 2,500 5,600

460 660 690 760 760 510 510 890 860

— —

6,200 7,800 6,500 8,900 6,600

2,100 2,200

2300 3,200

9,700

2,000 2,300 2,400 2,900 2,300 1,900 2,700 2,700

6,600 10,400

2,300 2,300

4,600 6,500 5,300 7,200 5,100 6,200 5,500 7,200 5,200 8,400 7,400

1,700

1,300 1,800 1,600 2,700 2,200 1,700 1,600 1,700 2,200 1,600 1,300 1,500 1,800 1,700 1,400 — 1,900 — 1,200 — 1,600 2,100 1,500 2,100 2,100 1,21)0 1,21)0 2,61)0

5,900 1,600 7,300 — 6,400 2,300 — 10,600 5,900 2,000 8,600 2,300 6,000 2,300 9,400 3,000 4,700 6,200 5,200 8,100 5,900 9,600 4,700 6,100 7,200 10,400 5,900 9,400

1,600

1,700

1,800 2,200 2,100 3,000 1,800 2,400 2,300 3,700 1,300

2,100 1,700 2,500 1,800 2,900 2,500 1,800

2,000

3,200 3,100 1,500

1,500

2,000 2100 2,300 2,600 3,200 3,900 — — — —

4—7

.

Table 4—3a. Strength properties of some commercially important woods grown in the United States (metric)a_con. Static bending CornWork to Corn- pression Shear Tension Modulus Modulus maxipression perpen- parallel perpen- Side to dicular hardof of mum Impact parallel dicular load to to Moisture Common species bending grain grain grain to grain ness Specific rupture elasticityc names content gravityb (kPa) (MPa) (kJ/m3) (mm) (kPa) (kPa) (kPa) (kPa) (N) Pine—con. Pond Ponderosa Red Sand

Shortleaf Slash

Green 12% Green 12% Green 12% Green 12% Green

0.51 0.56 0.38

12%

0.51 0.54 0.59 0.41 0.44 0.34 0.36 0.45 0.48 0.36 0.38

Green 12%

Spruce

Green

Sugar

Green 12% Green 12% Green 12%

Virginia

Westernwhite Redwood Old-growth Young-growth

Spruce Black

12%

Green

12%

0.38 0.46 0.33 0.35 0.37 0.40 0.33 0.36

Green 12% Green 12%

0.37 0.40 0.49 0.53

Green

Red

Green

12% 12%

Tamarack

0.46 0.46 0.48 0.47

0.38 0.40 0.34

Engelmann

White

0.41

Green 12% Green 12% 12%

Sitka

0.40

Green

0.35

51,000 80,000 35,000

65,000 40,000 76,000 52,000 80,000 51,000 90,000 60,000

8,800 12,100 6,900 8,900 8,800 11,200 7,000

9,700 9,600

112,000

12,100 10,500 13,700

41,000

6,900

72,000 34,000 57,000 50,000 90,000 32,000 67,000

8,500 7,100 8,200 8,400 10,500 8,200 10,100

52,000 69,000 41,000 54,000 42,000 74,000

66 66 57 76

66

— —

530 480 660 660

— —

760

840 — — — — 430 460

25,200 52,000 16,900 36,700 18,800 41,900

3,000 6,500 6,300 9,500 1,900 4,800 4,000 7,800 1,800 4,800 4,100 8,400

23,700 47,700 24,300 50,100 26,300

3,100 5,800

61

580

56,100 19,600 39,000 17,000 30,800 23,600 46,300 16,800 34,700

8,100 9,200 6,600 7,600

51

530 480 410 380

29,000 42,400 21,400 36,000

9,500

51

11,100

64,000 41,000

7,100 8,900 9,200

74,000 34,000 65,000 39,000 68,000 50,000 80,000

11,100 7,900 9,900 7,400 9,200 8,500 11,300

32,000

52 59 36 49 42 68

91

— —

37 38 75 94 34

48 39 36

72 35 44 48 58 43 65 41 53 50 49

860 810

480

610 580 410 460 460 640 610 640 560 510 710 580

2,400 5,700 3,700

7,900

— 6,300 9,600 6,600 11,600 6,200 10,300 5,000 7,800 6,100 9,300 4,700

7,000

2,900 5,500 4,800 6,500 1,900 6,100 3,600 7,600

1,900

5,000 1,400 3,400 2,700 6,300 1,300 3,200

19,600

1,700

41,100

3,800

15,000

1,400

30,900

2,800

18,800 38,200 16,200 35,700 17,700 37,700 24,000 49,400

1,800 3,800 1,400 3,000 1,700 3,200

7,200

— — 2,100 2,900 2,100 3,200 — — 2,200 3,200 — —-

— — 1,400

2,000 1,500

2,500 — — 2,000 3,100 —

—

— —

2,000 2,900 1,900 1,200 2,400 1,700 2,800 2,400 2,600 3,300 1,800 1,200

—

1,900

1,800 1,700 2,100 1,700

2,100

1,800 1,600 1,900

700 1,600 5,100 — 2,300 8,500 4,400 1,700 1,150 8,300 2,400 1,750 5,200 1,500 1,600 8,900 2,400 2,200 4,400 1,700 1,600 6,700 2,600 2,300 4,800 1,500 1,400 7,400 2,500 2,100 5,900 1,800 1,700

2,700 5,500 8,800 2,800 2,600

of tests on small clear specimensin the green and air-dried conditions, convertedto metric units directly from Table 4—3b. Definition of properties: impact bending is height of drop that causes complete failure, using 0.71-kg (50-Ib) hammer; compression parallel to grain is also called maximum crushing strength; compression perpendicularto grain is fiber stress at proportional limit; shear is maximum shearing strength;tension is maximum tensile strength; and side hardnessis hardnessmeasured when load is perpendicularto grain. bSpeciflc gravity is based on weight when ovendry and volume when green or at 12% moisturecontent. cModulus of elasticity measuredfrom a simply supported, center-loaded beam, on a span depth ratio of 14/1. To correct for shear deflection, the moduluscan be increasedby 10%. dCoast Douglas-firis definedas Douglas-firgrowingin Oregon and Washington State west of the Cascade Mountains summit. InteriorWest includes Californiaand all counties in Oregon and Washington east of, but adjacentto, the Cascade summit; Interior North, the remainderof Oregon and Washington plus Idaho, Montana, and Wyoming; and Interior South, Utah, Colorado,Arizona, and New Mexico.

aResults

4—8

Table 4—3b. Strength properties ofsome commercially important woods grown in the United States (inch_pound)a Static bending

Common species names

CornCorn- pression Modulus Modulus Work to pression perpenof of maximum Impact parallel dicular load Moisture Specific rupture elasticityc bending to grain to grain content gravityb (Ibf/in2) (xlO6lbfIin2) (in-Ibflin3) (in.) (lbf/in2) (Ibf/in2)

Shear Tension parallel perpen- Side to dic'jlar hardgrain to grain ness (lbf/in2) (lbf'1n2) (lbt)

Hardwoods

Alder, red

1.17 1.38

8.0 8.4

22 20

2,960

6,000 12,600 9,600 13,800 9,500 14,100 7,600 12,700 9,500 15,000

1.04 1.60 1.24 1.40

12.1 14.9 14.7

2,300

1.40

11.8

33 35 — — 35

1.66 1.13

13.4

32 39

7,080 3,510 6,040 3,990 7,410

1,310

0.36 0.39 0.35

5,400 9,100

1.12 1.43 0.86

210 450

0.38

8,400 5,000

1.18 1.04 1.46 1.38

2,500 5,300 2,140 4,250

5.3 7.2 11.9

43

3,550

370 540

1.72

15.1

41

7,300

1,010

6,400

1.17

16.2

49

12,300 9,400 16,900 8,300 16,600 5,400 8,100 8,000 12,300 5,600 8,600

1.59 1.65

16.0

34

15.7 18.0

48

2,360 5,690 3,740

270 600 470

Green 12%

0.37

6,500

0.41

9,800

Green 12% Green 12% Green 12% Green 12% Green 12%

0.45 0.49 0.53 0.58 0.53 0.56 0.50 0.55

Green 12% Green 12% Green

Ash Black Blue Green Oregon White Aspen Bigtooth Quaking

Basswood,American

Birch Paper

Green 12%

0.64

Green

0.48 0.55 0.60

12%

Sweet Yellow Butternut

Green 12% Green 12% Green 12%

Cherry,black Chestnut, American Cottonwood Balsam, poplar Black Eastern Elm American Rock Slippery Hackberry

0.60

0.32 0.37 0.56

12%

Beech, American

0.55

Green 12% Green 12%

0.65 0.55 0.62 0.36 0.38 0.47 0.50 0.40 0.43

Green 12% Green 12% Green 12%

0.31 0.34 0.31

Green

0.46

12%

0.50 0.57 0.63 0.48 0.53 0.49 0.53

Green 12% Green 12%

Green 12%

0.35 0.37 0.40

5,100 8,700 8,600 14,900

3,900

6800

4,900 8,500 5,300 8,500

1.36 1.44 1.74

2.17 1.50 2.01 0.97 1.18 1.31

1.49

0.93 1.23 0.75 1.10 1.08 1.27 1.01

1.37

14.4

12.2 14.4 15.7 16.6

38

43

5.7 7.7

— —

6.4 7.6

22 21 16 16

7.0

47 48 55 24 24 33 29 24

6.5

19

4.2

— — 20

16.1

20.8

8.2 8.2 12.8 11.4

5.0 5.0 6.7 7.3 7.4

7,200

1.11

11,800

1.34

11.8 13.0

9,500

1.19

19.8

14,800

1.54

8,000

1.23 1.49 0.95 1.19

19.2 15.4

13,000 6,500 11,000

33

16.9

14.5 12.8

22 21

5,820 5,970

4,180 6,980 4,200

2,220 4,730

250 440

770 390

440

1,080 420

590

350 760

860 490

1570 700

520 850

810 1,420

730 530

1,250 670 1,160

38 39 54 56 47 45 48 43

2,910 5,520 3,780 7,050

3,320 6,360 2,650 5,440

960 1,320

— —

180

660 230 850

260

300 350

600 280 990 350

250 410

1,290 720 2,0101,010

850 1,300

140 300 160 300 200 380

4,910

1,160

370 170

1,690

20

1,910 94')

870 1,200 790

—. —.

1,080

2,200 4,500 2,280

1,790 72) 1,350 59')

— —

730 1,080

8,540 3,380 8,170 2,420 5,110 3,540 7,110 2,470 5,320 4,020

1,540 —. 2,030 —. 1,260 59) 1,910 70) 1,190 59)

430 970 220 460 360

690 310 620

360

690 610 1,230

420 820 400 890

840

381)

1,210

—

1,240 2,240 1,110

431) 951)

431)

1,880 921) 760 430

560 910 970 1,470 780 1,260

1,170 441)

390 490

'1,130

571)

660

1,700

561)

950 420

800 441) 1,080 460 500

790

—

—

610 270 1,040 330 680 410 930 580

1,000 590 1,510 660

1,270 1,920

540

— —

250 350 340 430 620 830 940 1,320

1,110 640 1,630 530 1,070 630

660

1,590 580

880

860 700

4—9

Table 4—3b. Strength properties ofsome commerclally important woods grown in the United States (inch_pound)a_con. Static bending CornCorn- pression Shear Tension Modulus Modulus Work to pression perpen- parallel perpen- Side to dicular hardof maximum Impact parallel dicular of load Moisture Specific rupture elasticityc Common species bending to grain to grain grain to grain ness names content gravity" (lbf/in2) (x106 bf/in2) (in-lbf/in3) (in.) (lbf/in2) (lbf/in2) (lbf/in2) (lbf/in2) (lbf Hickory, pecan Nutmeg

Green 12% Green

Pecan

Green

Bitternut

12%

Green 12%

0.66 0.61 0.62

Green 12% Green 12% Green 12% Green

0.64 0.72 0.66 0.75 0.64 0.72 0.62

12%

Water Hickory, true Mockernut

Pignut Shagbark Shelibark

0.60 0.66 0.56 0.60 0.60

1.40 1.79 1.29 1.70 1.37 1.73 1.56 2.02

20.0

1.57 2.22 1.65 2.26 1.57

26.1 22.6 31.7

20,200

2.16

25.8

1.34 1.89 1.29 1.63 1.85 2.05

29.9 23.6 12.6 13.3 15.4 18.4

47 47 44

10,300 17,100

9,100 16,600 9,800 13,700 10,700 17,800 11,100 19,200 11,700

20,100 11,000

18.2 22.8 25.1 14.6 13.8 18.8 19.3

30.4 23.7

66 66 54

—

53

44 56 53 88 77 89 74 74 67 104 88

4,570 9,040 3,980 6,910 3,990 7,850 4,660 8,600 4,480

Honeylocust

Green

Locust, black

Green

0.69 0.60 — 0.66

12%

0.69

Green 12% Green 12%

0.44 0.48 0.46 0.50

7,400 12,300 6,800 11,200

1.56 1.82 1.11 1.40

10.0 12.2 15.4 12.8

30 35 54 29

3,140 6,310 2,700 5,460

Green 12% Green 12% Green 12% Green

0.44 0.48 0.52

7,400

12%

Green 12%

0.56 0.63

13,300 7,700 13,400 5,800 8,900 9,400 15,800

8.7 7.8 12.8 12.5 11.4 12.5 11.0 8.3 13.3 16.5

23 28 48

0.57 0.49 0.54 0.44 0.47

1.10 1.45 1.33 1.62 1.39 1.64

3240

10,700

Green 12% Green 12% Green

0.56 0.61 0.61 0.68

8,200 13,900 10,800 18,100

12.2 13.7 14.7 18.3 11.2 11.8 13.2 14.5 14.0 14.8 15.0 20.5 8.0

40

12%

Magnolia

Cucumbertree Southern

Maple

Bigleaf Black Red Silver Sugar

Oak, red Black Cherrybark Laurel

12%

Northernred

Green 12%

Pin

Green

Scarlet

Green

Southern red

Green 12%

12% 12%

4—10

0.56 0.63 0.56 0.63 0.58 0.63 0.60 0.67 0.52 0.59

7,900

7900

12,600

8300

14,300 8300 14000 10,400 17400 6,900 10,900

0.94 1.14 1.55 1.83 1.18 1.64 1.79 2.28 1.39 1.69 1.35 1.82 1.32 1.73 1.48 1.91

1.14 1.49

gA

57

40 32 32 29 25 40 39 41

54 49 39 39

44 43 48 45 54 53 29 26

— —

—

— — — —

1,480

680

1,310 1,820 — —

1,240

—

1,030

2,080

880 1,440 — 1,550 810

8,940 1,730 4,810 920 9,190 1,980 4,580 840 9,210 1,760 3,920 810

10,500 18,100 10,200 14,700 13,800 19,400

12%

800 1,680 760 1,570 780 1,720

8,000 1,800 4,420 1,150 7,500 1,840 6,800 1,160 10,180 1,830

— — —

— — — — — — — 2,110 — 1,660 930 2,250 900 1,280 1,740 1,370 2,150 1,520 2,430 1,190

1,760

770

330

990

440

570 460 860

1,340 1,040 1,530

660 610 740

450 5,950 750 3,270 600 6,680 1,020 3,280 400 6,540 1,000 2,490 370

1,110 1,730

600 540 720 670 — —

740 4,020 640 7,830 1,470 5,220

3,470 710 6,520 930 4,620 760 8,740 1,250 3,170 570 6,980 1,060

610 3,440 6,760 1,010 720 3,680 6,820 1,020 830 4,090 8,330 1,120 550 3,030 6,090 870

2,480 640

1,130 1,820 1,150 1,850 1,050 1,480 1,460

2,330

560 500

— —

— — 800 2,000 840 1,180 770 1,830 790 1,220 1,910 1,320

1,210 1,780 1,290

750 800 800

2,080 1,050 1,410 700 1,890 870 930 480 1,390 510

— —

— — — — — — —.

1,390 1,580 1,570 1,700 520 700 740 1,020

620 850 840 1,180 700 950 590 700 970 1,450 1,060 1,210 1,240 1,480 1,000 1,210 1,000 1,290 1,070 1,510 1,200 1,400 860 1,060

Table 4—3b. Strength properties ofsome commercially important woods grown in the United States (inch_pouIld)a—con. Static bending

Common species

names

Oak, red—con. Water Wllow Oak, white Bur

CornCorn- pression Shear Tension Modulus Modulus Work to pression perpen- parallel perpen- Side of of maximum Impact parallel dicular to dicular hardMoisture Specific rupture elasticityc load bending to grain to grain grain to grain ness content gravityb (lbf/in2) (xl 06 lbf/in2) (in-lbf/in3) (in.) (lbf/in2) (lbf/in2) (lbf/1n2) (lbf/in2) (lbt) Green 12% Green 12%

0.56 0.63 0.56 0.69

8,900 15,400 7400 14,500

1.55 2.02 1.29 1.90

Green

0.58 0.64

7,200 10,300 8,000 13,300 11,900 18,400

0.88 1.03 1.37 1.59 1.58 1.98 1.15 1.42 1.09

12%

Chestnut

Green 12%

Live

Green 12%

Overcup

Green 12%

Post Swamp chestnut Swamp white

White

Green 12% Green 12% Green 12% Green 12%

Sassafras

Green 12%

Sweetgum

Green 12%

Sycamore,American

Green 12%

Tanoak

Green 12%

Tupelo Black

Walnut, Black

Green 12% Green 12% Green

Willow, Black

Green

Water

12%

Baldcypress Cedar Atlanticwhite Eastern redcedar Incense

NorthernWhite

0.60 0.67 0.64 0.72 0.60 0.68 0.42 0.46

0.46 0.52 0.46 0.49 0.58 — 0.46 0.50 0.46 0.50 0.51 0.55

8,000 12,600

8,100 13,200 8,500 13,900 9,900 17,700 8,300 15,200 6,000 9,000 7,100 12,500

6,500 10,000 10,500

—

7,000 9,600 7,300 9,600 9,500 14,600

1.51

1.35 1.77 1.59 2.05 1.25 1.78 0.91 1.12 1.20 1.64 1.06 1.42 1.55 1.03 1.20 1.05 1.26 1.42 1.68 0.79 1.01 1.22 1.58

12%

0.36 0.39 0.40 0.42

Green

0.42

12%

0.46

10,600

1.18 1.44

Green 12% Green 12% Green 12% Green 12%

0.31 0.32 0.44 0.47 0.35 0.37 0.29 0.31

4,700 6,800 7,000 8,800 6,200 8,000 4,200 6,500

0.75 0.93 0.65 0.88 0.84 1.04 0.64 0.80

12%

Yellow-poplar

0.57 0.66 0.80 0.88 0.57 0.63 0.60 0.67

Green

4,800 7,800

6,000 10,100

6,600

11.1

21.5 8.8 14.6 10.7

9.8 9.4 11.0 12.3 18.9 12.6 15.7 11.0 13.2 12.8 12.0 14.5 19.2 11.6 14.8 7.1 8.7 10.1 11.9 7.5

8.5

39 44 35 42

3,740 6,770 3,000 7,040

44 29 35 40 — — 44 38 44 46

45 41 50

49 42 37 — — 36 32

26 26

13.4

—

8.0 6.2 8.3 6.9 14.6 10.7 11.0

30 22 30 23 37

8.8 7.5 8.8

Softwoods 6.6 8.2 5.9 4.1 15.0 8.3 6.4 5.4 5.7

4.8

34 26 24

620

1,240

820

1,020

2,020

1,130

1,180 1,650

920 760

3,290

680

1,350

6,060 3,520 6,830 5,430 8,900 3,370 6,200 3,480 6,600 3,540 7,270

1,200

4,360 8,600

3,560 7,440

2,730 4,760 3,040 6,320 2,920 5,380 4,650 3,040 5,520 3,370 5,920

4,300 7,580 2,040 4,100 2,660 5,540

25 24

3,580

18

2,390 4,700 3,570 6,020 3,150 5,200 1,990 3,960

13 35 22 17 17 15 12

6,360

610

530 840 2,040 2,840 540 810 860 1,430 570 1,110 760 1,190

670

1,070 370

850 370 620 360 700

480 930

480 870

490 1,010

1820

1,210 1,490

2,210 2,660

980

—

1,460

800 680 690 — — —

1,110 1,370 890 1,130

1,320 2,000 1,280 1,840 1,260 1,990 1,300 2,000 1,250

730 940 790 780 670 690

2,000

8D0

950 1,240 990 1,600 1,000 1,470

540 730

1,100 1,340 1,190 1,590 1,220 1,370

1,010 1,190

850 830 770

630 720

570 500 600 700 570 690

— — 960

1,190 1,130 1,360 1,110 1,240 1,160 1,620 1,060 1,360

— —

600 850 610 770

640 810 710 880 900 1,010

— —

180

680

430 270 500

1,250

-— .—

1,190

510 540

440 540

1,000

300 270

390 510

690 800

1130

220

290 350

1,010

330

400 730 240 410 700 920 370 590

230 310

790

810

—

830 880 620

850

-—

280 270 240 240

650 — 390 470 230 320

4—Il

Table 4—3b. Strength properties of some commercially important woods grown in the United States (inch_pound)a__con. Static bending

Common species names Cedar—con. Port-Orford

Western redcedar Yellow Douglas_fird

Coast

Interior West

CornCorn- pression Shear Tension Modulus Modulus Work to pression perpen- parallelperpen- Side to dicular hardof of maximum Impact parallel dicular load Moisture Specific rupture elasticityc bending to grain to grain grain to grain ness content gravityb (lbf/in2) (x106 lbf/in2) (in-lbf/in3) (in.) (lbf/in2) (lbf/in2) (lbf/in2) (lbf/in2) (lb1 Green 12% Green 12% Green

0.39 0.43

6,400

12%

11,100

1.14 1.42

Green

0.45

12%

0.48 0.46 0.50 0.45 0.48 0.43 0.46

7,700 12,400 7,700 12,600 7,400 13,100 6,800 11,900

1.56 1.95 1.51 1.83 1.41 1.79 1.16 1.49

7.2 10.6 8.1 10.5 8.0 9.0

26

0.33 0.35 0.36 0.38 0.35 0.37 0.37 0.39 0.40

5,500 9,200 5,800 10,500 5,800 8,900 6,200 10,700

1.25

4.7

145

5.1 6.4 8.9 5.6 7.5 6.0 8.8

16 20

0.43

11,000

0.31

4,900 8,600 5,900 9,800

Green

12%

Fir Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

White

Green 12%

Hemlock Eastern Mountain

Larch, western

0.32 0.37 0.39

12%

Green 12%

0.48 0.52

7,700 13,000

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

0.34 0.35

4900

0.40 0.43 0.47

6,000 9,900 7,300

Green

Pine Eastern white

Jack LobloIly Lodgepole Longleaf

Pitch

4—12

6400

0.38 0.40 0.42 0.45 0.42 0.45

Green 12% Green 12%

Western

17 17

1.11

12%

Subalpine

5.0 5.8 9.2

0.94

Green

Pacific silver

28

7,500

Interior South

Noble

21

9.1

5200

Green

Grand

7.4

0.32 0.42 0.44

Interior North

California red

1.30 1.70

0.31

12%

Balsam

6,600 12,700

0.51

0.38 0.41

6,400 8,900 6,300 11,500 6,600

11300

8,600

12,800

5,500 9,400 8,500

0.554 0.59 14,500 0.47 6,800 0.52 10,800

1.17 1.50 1.25 1.57 1.38 1.72 1.42 1.76 1.05 1.29 1.16 1.50 1.07 1.20 1.04 1.33 1.31 1.63 1.46 1.87 0.99 1.24 1.07 1.35 1.40 1.79 1.08 1.34 1.59 1.98 1.20 1.43

10.4

27 29

7.6

26

9.9

31 32

22 26 15

20

21

24 22 28 19

23

6.0 9.3 — — 5.6 7.2

21

6.7 6.8 11.0 10.4 6.9 8.3 10.3 12.6 5.2 6.8 7.2

8.3 8.2 10.4

5.6 6.8

8.9 11.8 9.2 9.2

24 — — 22 20

3,140 6,250 2,770 4,560 3,050

300 720 240

460

6310

350 620

3,780 7,230 3,870 7,430 3,470 6,900 3,110 6,230

380 800 420 760 360 770 340 740

2,630 5,280 2,760 5,460 2,940 5,290 3,010

404 330 610 270 500 270

6,100 3,140 6,410 2,300 4,860 2,900

190

520 220

450

840

180

380

1,370

400 230

630 260

220 330 360

440

770 990 840

1,130

900 1,130

940

1,290

950

1,400

950

1,510

662 944 770 1,040 740 900 800 1,050 750 1,220 700 1,070 760 1,100

5,800

190 390 280 530

21 21 32 32 22 23 29 35

3,080 5,410 2,880 6,440 3,360 7,200 3,760 7,620

360 650 370 860 280 550 400 930

17 18

2,440 4,800 2,950 5,660

220 440 300

680 900 750

580 390 790 250 610 480 960 360 820

1,170 860

26 27 30

30 20 20 35 34

— —

3,510 7,130 2,610 5,370 4,320 8,470 2,950 5,940

850 1,060

930

500

180

290 400 360 500 360 490 290 410

180

380 390 240 240 230 220

240 — — — 300 300 230 — 330

—

1,290 870 1,360

290 340 330 430

1,390

680 880

1,040 1,510 860 1,360

580

300 340 290 350 340 390 250 330

1,540

860

350

250 310 360 420 260 470 220 290 330 470

— —

710

510 660 420 600 360 510

310

430 260 350 340

480 400 500 470 630 410 540

510 830 290 380 400 570 450 690 330 480

590 870 — —

Table 4—3b. Strength properties of some commercially important woods grown in the United States (inch.pound)a_con. Static bending Modulus

of Common species names Pine—con. Pond Ponderosa

Moisture Specific rupture content gravityb (lbf/in2) Green

0.51

7,401)

12%

0.56 0.38 0.40

11,600

Green 12%

Red Sand

Shortleaf Slash Spruce Sugar Virginia

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

Westernwhite

Green 12%

Redwood Old-growth

Green 12%

Young-growth

Green 12%

Spruce

Black Engelmann Red Sitka White

Tamarack

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

0.41

0.46 0.46 0.48 0.47 0.51 0.54 0.59 0.41 0.44 0.34 0.36 0.45 0.48

0.35 0.38 0.38 0.40 0.34 0.35 0.38 0.42

0.33 0.35 0.37 0.40 0.37 0.40 0.33 0.36 0.49 0.53

5,100 9,400 5,800 11,001)

7,500 11,600 7,400 13,100 8,700 16,300 6,000 10,400 4,900 8,200 7,300 13,000

Modulus

of

elasticityc (xlO6lbfTin2)

1.28 1.75 1.00 1.29 1.28 1.63 1.02 1.41

CornCorn- pression Shear Tension Work to pression perpen- parallel perpenmaximum Impact parallel dicular to dicular load bending to grain to grain grain to grain (in-lbf/in3) (in.) (lbf/in2) (lbf/in2) (lbf/in2) (lbf/in2) 7.5

8.6 5.2 7.1 6.1 9.9 9.6 9.6 8.2 11.0 9.6 13.2

9,700

1.39 1.75 1.53 1.98 1.00 1.23 1.03 1.19 1.22 1.52 1.19 1.46

7,500 10,000

1.18 1.34

5,900

0.96

7.4 6.9 5.7

7,900

1.10

5.2 7.4 10.5 5.1 6.4 6.9 8.4 6.3 9.4 6.0 7.7 7.2 7.1

4,700

6,100

1.38

10,800

1.61

4,70(1

1.03 1.30 1.33 1.61 1.23 1.57 1.14 1.43 1.24 1.64

9,300 6,00(1

10,80() 5,700 10,200 5,000 9,40(1

7,200 11,60(1

— —

— — 21 19

26 26

— —

30 33

— — — —

5.4 5.5 10.9 13.7

17 18

34 32

5.0 8.8

23

19

3,660 7,540 2,450 5,320 2,730 6,070 3,440 6,920 3,530 7,270 3,820

8,140 2,840 5,650 2,460 4,460 3,420 6,710 2,430 5,040

Side hard-

ness (lb1

— 440 940 — 910 1,380 280 700 310 580 1,130 420 260 690 300 600 1,210 460 — 450 1,140 — — 836 350 910 320 820 1,390 530 960 1020 1,680 280 900 730 1,490 210 720 500 1,130 390 890 910 1,350 190 680 470 1,040

— — 320

460 340

560 — — 440

470

690

— — — —

— —

450 660 270 380 540 740

270 350 400 380 260

260 420

—

19 16 15

4,200 6,150 3,110 5,220

420 700

800 260 940 240 270 890 300 520 1,110 250

410 480

24 23 16 18 18 25

2,840 5,960 2,180 4,480 2,720 5,540

240 739 550 1,230 200 640 410 1,200 260 750 550 1,290 280 760 580 1,150 210 640 430 970 390 860 800 1,280

100

— 240 350 220

370 520 260 390 350

350 250 370 220 360 260 400

490 350 510 320 480 380 590

21

24 25 22 20 28 23

2,670 5,610 2,350 5,180 3,480 7,160

350

420

of tests on small clear specimensin the green and air-driedconditions.Definition of properties: impact bending is height of drop that causes complete failure, using 0.71-kg (50-Ib) hammer; compression parallel to grain is also called maximum crushing strength; compressionperpendicularto grain is fiber stress at proportional limit; shear is maximum shearing strength; tension is maximumtensile strength; and side hardnessis hardnessmeasured when load is perpendicularto grain. bSpecjfic gravity is based on weightwhen ovendryand volume when green or at 12% moisture content. cModulus of elasticity measured from a simply supported, center-loaded beam, on a span depth ratio of 14/1. To correct for shear deflection,the moduluscan be increasedby 10%. dCoast Douglas-firis definedas Douglas-fir growingin Oregon and WashingtonState west of the Cascade Mountainssummit. Interior West includes Californiaand all counties in Oregon and Washingtoneast of, but adjacentto, the Cascade summit; Interior North, the remainderof Oregon and Washington plus Idaho, Montana, and Wyoming; and Interior South, Utah, Colorado, Arizona, and New Mexico. aResults

4—13

Table 4—4a. Mechanical properties of some commercially important woods grown in Canada and imported into

the United States (metric)a Common species names

Moisture content

Specific gravity

Staticbending Modulusof Modulus of rupture (kPa) elasticity (MPa)

Compression parallel to grain (kPa)

Compression perpendicular tograin(kPa)

Shear parallel to grain (kPa)

1,400

5,000

3,500

6,800 5,400 7,600

Hardwoods Aspen Quaking

Green

0.37

38000

0.39

68,000 36,000 66,000

9,000 11,200 7,400 8,700

16,200 36,300 16,500 32,800

28,000 49,000 32,000 52,000 34,000 70,000

6,700 8,800 6,000 7,800 7,900 11,500

12,800 27,700 13,600 26,500 14,600 34,600

12%

Big-toothed

Green 12%

Cottonwood Black

Green

0.30

12%

Eastem

Green

0.35

12%

Balsam, poplar

Green

0.37

12%

1,400

3,200 700 1,800 1,400 3,200 1,200

2,900

3,900

5900 5,300 8,000 4,600 6,100

Softwoods Cedar Northern white

Green

0.30

Western redcedar

Green

0.31

36,000 54,000

0.42

46,000

0.45

80,000 52,000 88,000

12%

Yellow

Green 12%

Douglas-fir

Green 12%

Fir Subalpine

Green

0.33

36,000

0.36

56,000 38,000 69,000

12%

Pacific silver

Green 12%

Balsam

Green

0.34

12%

Hemlock Eastern

Green

0.40

12%

Western

Green Green

36,000 59,000

47,000 67,000

0.41

48,000

0.55

81,000 60,000 107,000

12%

Larch, western

27,000

42,000

12%

12%

3,600 4,300 7,200 8,200 9,200 11,000 11,100 13,600

13,000 24,800 19,200 29,600 22,300 45,800 24,900 50,000

8,700 10,200 9,300 11,300 7,800 9,600

17,200 36,400 19,100 40,900 16,800 34,300

8,800 9,700 10,200 12,300

23,600 41,200

2,800 4,300

24,700 46,700

2,600

11400 14,300

30,500 61,000

1,400

2,700 1,900 3,400 2,400 4,800

3,200 6,000

1800 3,700 1,600

3,600 1,600 3,200

4,600 3,600 7,300

4,600 6,900 4,800 5,600 6,100 9,200 6,300 9,500 4,700 6,800

4,900 7,500 4,700

6,300 6,300 8,700 5,200 6,500 6,300 9,200

Pine

Eastern white

Green

0.36

35,000

0.42

66,000 43,000

12°/a

Jack

Green 12%

Lodgepole

Green

0.40

Ponderosa

Green

0.44

12%

Red

Green

0.39

12%

Western white Spruce Black

Green Green

0.36

0.41

12%

Green

0.38

78,000 39,000 76,000 39,000 73,000 34,000 70,000 33,000 64,100 41,000 79,000 39,000 70,000 41,000 71,000 37,000

8,100 9,400 8,100 10,200 8,800 10,900 7,800 9,500 7,400 9,500 8,200 10,100 9,100 10,500 8,600 10,700 9,100 11,000

17,900 36,000 20,300 40,500 19,700 43,200 19,600

42,300 16,300 37,900 17,400 36,100 19,000

41600

1,600

1,900

4,400 6,100 5,600 8,200 5,000 8,500 5,000 7,000 4,900

5,200

7,500

1,600

4,500 6,300

3,400 2,300 5,700 1,900 3,600

2,400 5,200

3,200 2,100 4,300

5,500 8,600

4,800 7,600 Red Green 0.38 1,900 5,600 12% 3,800 9,200 Sitka Green 0.35 9,400 2,000 4,300 12°/a 70,000 11,200 4,100 6,800 White Green 0.35 35,000 7,900 1,600 4,600 12% 63,000 10,000 3,400 6,800 Tamarack Green 0.48 47,000 8,600 2,800 6,300 12% 76,000 9,400 44,900 6,200 9,000 aResuftoftestson small, dear, straight-grainedspecimens. Property values basedonASTMStandard D2555—88. Informationon additional properties can be obtained fromDepartmentof Forestry,Canada, PublicationNo. 1104. Foreach species, values in thefirst line are from testsofgreen material; those in the second line are adjustedfromthe green conditionto 12% moisture content using dryto green clearwood property ratios as reportedinASTMD2555—88. Specificgravity is based on weightwhen ovendry and volumewhen green. Engelmann

12%

4—14

19,400 42,400 19,400 38,500 17,600 37,800 17,000 37,000 21,600

1,900

3,700

Table 4—4b. Mechanical properties ofsome commercially important woods grown in Canada and imported iiito the UnitedStates (inch_pound)a Common species names

Moisture content

Specific gravity

Staticbending Modulusof Modulus ofelasrupture (tbflin2) ticity(xl06lbf/in2)

Compression parallel to

Shear parallelto

grain (lbf/in2)

Compression perpendicular to grain (lbf/1n2)

grain(Ibf/in2)

Hardwoods Aspen Quaking

Green

0.37

12% Bigtooth

Green

0.39

Green

0.37

5,500 9,800 5,300 9,500

1.31 1.63 1.08 1.26

2,350 5,260 2,390 4,760

200 510 210 470

720 980 790 1,100

5,000

1.15 1.67 0.97

2,110 5,020 1,860 4,020 1,970 3,840

180 420 100 260 210 470

670

1,890 3,590 2,780

200 390

4,290 6,640

500 350 690

3,610

460

1,340 920

7,260

870

1380

240 460 230 520 260

680 910 710 1,190

Cottonwood

Balsam,poplar

12%

Black

Green

Eastern

Green

0.30

12%

0.35

12%

10,100

4,100 7,100 4,700

128 0.87 1.13

7,500

890

560 860 770 1,160

Softwoods Cedar Northern white

Green

0.30

12%

Western redcedar

Green

0.31

12%

Yellow

Green

Douglas-fir

Green

0.42

12% 0.45

12%

3,900 6,100 5,300 7,800 6,600 11,600 7,500 12,800

0.52 0.63 1.05 1.19 1.34 1.59 1.61 1.97

5,300 8,500 5,500 10,000 5,200

1.13 1.40 1.35 1.64 1.26 1.48

2,440

127

3,430 5,970 3,580 6,770 4,420 8,840 2,590 5,230

490

Fir Balsam

Green

0.34

12%

Pacific silver

Green

0.36

12% Subalpine

Green

0.33

12°/a

8,200

Hemlock Eastern

Green

0.40

12%

Western

Green

0.41

12%

Larch, western

Green

11,800

0.55

12%

Pine Eastern white

Green Green

0.36 0.42

12% Lodgepole Ponderosa

Green Green

0.40 0.44

12%

Red

Green

Western white

Green

0.39 0.36

Green

0.41

12%

Spruce Black

12%

Engelmann

Green

0.38

12%

Red

Green

0.38

12%

Sitka

Green

White

Green

0.35

12%

0.35

12%

Tamarack

Green 12%

8,700 15,500

12%

Jack

6,800 9,700 7,000

0.48

5,100 9,500 6,300 11,300 5,600 11,000

5700 10,600 5,000 10,100 4,800 9,300 5,900 11,400 5,700 10,100 5,900 10,300 5,400 10,100 5,100 9,100

6,800 11,000

1.41 1.48 1.79 1.65 2.08 1.18 1.36 1.17 1.48

127 1.58 1.13 1.38 1.07 1.38 1.19 1.46 1.32 1.52

125 1.55 1.32 1.60 1.37 1.63 1.15 1.45 1.24 1.36

3,240

4,980 2,770 5,930 2,500 5,280

2,950 5,870

2,860 6,260 2,840 6,130 2,370 5,500 2,520 5,240 2,760 6,040 2,810 6,150 2,810 5,590 2,560 5,480 2,470 5,360 3,130 6,510

280 .

540

660 1,000 700 810 880

680 980

400

910

630 370 660 520

1,260

1,060

1,340

240

640 880 820 1,190 720 1,240 720 1,020 710 1,090 650 920

340 830 280 530 350

760 280 720

240 470 300 620 270 540

270 550

290 590 240 500 410 900

750 940

920

800 1,250 700 1,100 810 1,330 630 980 670 960 920 1,300

°Resultsoftests onsmall, clear, straight-grainedspecimens.Propertyvalues basedonASTM StandarlD2555—88. Informationon additional propertiescan beobtained fromDepartmentofForestry,Canada, PublicationNo. 1104. Foreach species,values inthe firstline are from testsofgreen material; those inthe second line are adjustedfromthe green conditionto 12% moisture contentusing dryto green clearwood propertyratios as reportedinASTMD2555—88. Specificgravity is basedonweight when ovendry and volume when green.

4—15

Table 4—5a. Mechanical properties of some woods imported intothe United States otherthan Canadian

imports (metric)a

Common and botanical names of species Afrormosia (Pericopsis elata)

Static bending CornModulus Modulus Work to pression Shear maximum parallel parallel of of load to grain to grain Moisture Specific rupture elasticity content gravity (kPa) (kPa) (kPa) (MPa) (kJ/m3) Green -

0.61

12%

Green 12% Green Andiroba(Carapaguianensis) 12% Green Angelin (Andira inermis) 12% Green Angelique(Dicotynia 12% guianensis) Green Avodire(Turraeanthus 12% africanus) Green Azobe(Lophiraalata)

Albarco (Carinianaspp.)

0.48 0.54

— 0.65 0.6

— 0.48

0.87

12%

Balsa(Ochromapyramidale)

Green

Benge(Guibourtiaamoldiana) Bubinga (Gu!bourtia spp.) Bulletwood(Manilkara bidentata)

Cativo (Prioria copaifera)

Green 12% Green 12% Green 12% Green

12%

Ceiba (Ceiba pentandra)

0.42 — 0.65 0.71 0.85

12%

Green Green

0.4

— 0.25

12%

Courbaril(Hymenaea courbaril) Cuangare (Dialyantheraspp.) Cypress, Mexican (Cupressus lustianica) Degame (Calycophyllum candidissimum) Determa (Ocotea rubra)

Ekop(Tetraberlinia tubmaniana) Goncalo alves (Astronium graveolens) Greenheart(Chiorocardium rodie,) Hura (Hura crepitans)

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12%

4—16

11,500 14,400

7,100 6,900

AF

4,500

100,000 10,300 71,000 11,700 106,900 13,800

95 68

47,000 15,900 33,000 8,400

97

56,000

—

—

AM

—

124,100 17,200 78,600 12,700 120,000 15,100 — —

10,400

0.71

— 0.31 0.93 0.67 0.52

0.6 0.84

— 0.8 0.38

3,900 5,000

AM AF

63,400 12,700 83 105

38,500 60,500

9,200 11,400

87,600 10,300 116,500 14,900 168,900 17,000

65 83

49,300 65,600 86,900

14,000 14,100

21,600 3,400 38,600 11,300

14

7,800 4,900 5,700

AM AF

20,400

4,800 12,900 14,900

AF AM

0.16

12%

Banak (Virolaspp.)

originb

135 127

—

ness Sample (N)

102,000 12,200 126,900 13,400

51,600 68,500

Side hard-

—

2,100

28

14,900 16,500

75,200 14,100

69

35,400

6,800

1,400 2,300

147,500 14,100

—

78,600

14,400

7,800

—

72,400 59,900 80,300 17,000

21,400

12,000

13,100 17,200

14,200

—

—

— 17100 155,800

29,600 3,700 88,900 12,700 133,800 14,900 27,600 7,000 50,300 10,500 42,700 6,300 71,000 7,000 98,600 13,300 153,800 15,700 53,800 10,100 72,400 12,500

—

115,100 83,400 114,500 133,100 171,700 43,400

AF 94 197 37 50 8 19 101 121

— — — —

29,600 7,300 16,400

5,900 7,300 2,400 3,800

40,000 12,200 65,600 17,000 14,300 32,800 19,900 37,100

4,100 5,700 6,600 10,900 11,400 14,600

9,900

AM

1,000

AM

1,100 8,800

AM

10,500 1,000 1,700 1,500

AM AF

2,000

128 186

42,700

33

44

25,900 40,000

5,900 6,800

2,300 2,900

46

— 62,100 45,400 12,100

— 8,500 9,600 8,400

66,700

AM

2,000 2,800

7,300

AM

8,600

—

15,200 13,400 15,400 17,000 22,400 7,200 60,000 8,100

AM

AF

—

119,300 18,600 188,200 23,800 40,700 6,500 59,300 7,700 15,200 2,800

5,000

AM

AF

72 72 175 41

71,200 64,700 86,300 19,200

46

33,100

13,500 13,300 18,100

5,700 7,400

10,500 2,000 2,400

AM AM AM

Table 4—5a. Mechanical properties ofsomewoods imported into the United States otherthan Canadian imports (metric)a_con. Static bending CornModulus Modulus Work to pression Shear Side of of maximum parallel parallel hardMoisture Specific rupture elasticity load to grain to grain ness Sample Common and botanical names of species content gravity (kPa) (MPa) (kJlm3) (kPa) (kPa) (N) origin Ilomba (Pycnanthus Geen 0.4 37900 7,900 20,000 5,800 2,100 AF angolensis)

(Tabebuiaspp., lapachogroup) Iroko (Chiorophora spp.) Ipe

Jarrah (Eucalyptus marginata) Jelutong (Dyera costulata) Kaneelhart (Licana spp.)

Kapur (Dryobalanopsspp.) Karri (Eucalyptusdiversico!o,) Kempas (Koompassia malaccensis) Keruing (Dipterocarpusspp.)

Lignumvitae(Guaiacumspp.) Limba(Terminaliasuperba) Macawood (Platymiscium spp.)

12% Green 12% Green 12% Green 12% Green 15% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green

0.92 0.54 0.67

—

0.36 0.96

(Khaya spp.) Mahogany, true (Swieteniamacrophylla) Manbarkiak (Eschweilera spp.)

Green

Mersawa (Anisoptera spp.)

41,400 60,700 153,800 190,300 51,000 73,800 62,100 79,300 117,900 182,700 77,200 116,500 117,900

5,300 7,000 20,800 22,100 7,900 9,700 9,200 10,300 18,600 21,600 13,500 17,000 20,200 23,000 13,900 15,400 12,200 15,700 16,100 20,400

53

0.94 0.42 0.45

12%

—

Green

0.87 0.58 0.88

191,000 0.64

15%

—

Green

0.52

55,200

0.78

95,100 86,900

Green

scleroxylon)

Green 12%

108 130 80 175 84 106 96 162

- 61

—

— 49 57 63 52 120

230 77 114 92 98 88 102

— — 93

0.3

158,600 20,800 35,200 5,000 51,000 5,900

38,300 8,900 71,400 14,600 89,700 14,200 33,900 9,000 52,300 12,400 35,800 9,100 61,200 14,700 21,000 5,200 27,000 5,800 92,300 11,600 120,000 13,600 42,900 8,100 69,600 13,700 37,600 10,400 74,500 16,700 54,700 10,100 65,600 12,300 39,200 8,100 72,400 14,300

-

78,600 19,200 32,600 72,700 111,000 25,700 44,500 29,900 46,700 50,600 77,300 35,600 60,800

52300 92,300 46,700 58,200

27,300 50,800

128

44,100 81,600

114

—

0.76

12%

Obeche(Thplochiton

88,900 115,800

152,400

12%

Oak (Quercus spp.)

-

Green

Green

121

0.38

12%

Mora (Moraspp.)

153,800 26,300

39 44 94

—

1.05

12%

Merbau (lntsia spp.)

10,100 10,200 13,000 8,000 8,100

62

—

0.69

Green

Green

8,900

—

0.71

12%

Marishballi(Lincania spp.)

21,600

—

0.82

12%

Green

20,100

190 152 72

28,000 11,000 13,000 13,400 17,900 16,600 18,500 11,800 14,300

12%

Manni (Symphonia globulifera)

11,000

206,200 88,300 126,200 77,200 139,000 100,000 122,000 82,000 137,200

0.64

12%

Mahogany, African

68,300 155,800 175,100 70,300 85,500 68,300 111,700 38,600 50,300

43 48

-

2,700 13,600 16,400

AM

4,800

AF

5,600 5,700 8,500 1,500 1,700 9,800 12,900 4,400 5,500 6,000 9,100 6,600 7,600 4,700 5,600

- —

600 9,700 12,700 17,500 6,400 10,300 8,500 8,500 11,200 14,300 7,900 9,800 11,200 12,100 10,800 12,500 5,100

6,100 9,700 13100

-

— 17,700 4,600 27,100 6,800

20,000 1,800 2,200 14,800 14000 2,800

AS AS AM AS AS AS AS AM AF AM AF

3,700 3,300

AM

3,600 10,100

AM

15,500 4,200 5,000

AM

10,000 15,900

AM

6,100 6,700

AS

3,900

AS

5,700 6,400

AM

-

10,200 11,100 1,900 1,900

AM

AF

4—17

Table 4—5a. Mechanical properties of some woods imported into the United States otherthan Canadian

imports(metric)a__con.

Common and botanical names of species Okoume (Aucoumea kiaineana) Opepe (Nauclea diderrichi:)

Static bending CornModulus Modulus Work to pression of of maximum parallel Moisture Specific rupture elasticity load to grain content gravity (kPa) (MPa) (kJ/m3) (kPa) Green

0.33

12%

Green

0.63

12%

Ovangkol (Guibourtiaehie)

Green Green

Parana-pine(Araucaria

Green

augustifolia)

Pau marfim (Balfourodendron riedellanum) Peroba de campos

Green

(Paratecoma peroba) Peroba rosa (Aspidosperma spp., peroba group)

Green

Pilon (Hyeronimaspp.)

Green

Pine, Caribbean(Pinus caribaca) Pine, ocote (Pinus oocarpa) Pine, radiata (Pinus radiata) Piquia (Ca,yocarspp.)

donnell—smithi:)

Purpleheart(Peltogynespp.) Ramin (Gonystylusbancanus)

Robe (Tabebuiaspp., roble group) Rosewood, Brazilian (Dalbergianigra) Rosewood, Indian(Dalbergia latifolia) Sande (Brosimumspp., utile group)

84

99,300 11,400 — — —

— — —

0.66 0.65 —

Green

0.55

12%

—

Green

0.42

12%

—

Green

0.72 0.4 0.67 0.52

— 0.52 0.8

— 0.75 0.49

12%

brasiliense) Sapele (Entandrophragma cylindricum)

12%

0.52 —

Green

0.55

palustris)

4—18

—

57,200

—

— —

— — —

— — —

AF

AM AM AM

12,200

70

61,200

14,700

7,100

75,200

8,900

72 63 57

13,000 17,200 8,300 11,900

7,000 7,700 5,400 7,600

AM

83

38,200 54,600 34,200 66,300

10,500 73,800 13,000 125,500 15,700

AM

77,200 115,100

13,000 15,400

74 119

33,800 58,900

8,100 14,400

4,400 5,500

AM

55,200 102,700 42,100 80,700

12,000

48

11900

8,100

— —

2,600 4,000

AM

75

25,400 53,000

7,200

15,500

19,200 41,900

5,200 11,000

2,100

AS

58 109 50 44

43,400 58,000 24,200

11,300 13,700 7,100

38600

9,600

102 121

48,400 71,200 37,200 69,500 33,900 50,600

10,200

85,500 12,500 117,200 14,900 49,600 6,800 65,500 7,200 9,400 13,800 132,400 15,700 67,600 10,800 127,600 15,000 74,500 10,000 95,100 11,000 97,200 12,700 131,000

13,000

62 117 81

86 91

— 80 90 — —

38,000 66,200

3300 7,700 7,700 3,100

AM

6,800

2,800

AS

10,500

5,800 4,000 4,300 10,900 12,100

8,600 10,000 16,300 14,500 9,700 14,400 7,200 8,900

72,400 11,000

88

31,400

8700

12,600

47,600 34,500 56,300 37,600 61,200

14,300 8,600 15,600 9,000 14,000

5,100 4,500 6,700 4,200 6,300

16,500

10,300

111 72

12%

—

105,500

12,500

108

Green 12%

0.56

77,200 118,600

10,800 13,600

92 92

31,200 63,600

31,000 56,700

AM

11,300 15,300

100,700 70,300

8,200 12,300 58,600 13,400

AM

2,900 8,100 8,300

6,900 14,100 2,700 4,000 4,000

63,400 116,500

98,600

Green

71,700

106,200

83,400

Santa Maria(Calophyllum

Sepetir (Pseudosindora

3,500

67

11,100

0.68

Green 12% Green

2,500

11,900

9,300

93,100

12%

12%

6,700

52,800 41,900 56,500

49,600

12% Green

Green 12% Green 12% Green 12% Green 12% Green

27,600

62,000

12%

Primavera (Tabebuia

AM

110

12%

AF

1,700

7,700

51,400

14,100

12%

—

— 6,700 13,100 17,100

7,700

88

121,300

0.62

Sample originb

13,900

17,700 13,400

130,300

(N)

11,000

0.63

116,500 100,700

0.46 — 0.73

(kPa)

AF

—

—

to grain

Side hardness

6,800 7,300 — —

0.67

15%

Green

— 27,400 51,600

13,400

12% 12%

— — 84 99 — —

120,000

12%

Para-angelim (Hymenolobium excelsum)

— — 51,000 7,900 93,800 11,900

Shear parallel

AM AM

AS AM AM

AF AS

Table 4—5a. Mechanical properties ofsome woods imported intothe United States otherthan Canadian imports (metric)a_con. Static bending CornShear Modulus Modulus Work to pression Side of of maximum parallel parallel hardCommon and botanical Moisture Specific rupture elasticity load to grain to grain ness Sample names of species content gravity (kPa) (MPa) (kJ/m3) (kPa) (kPa) (N) orginb — Shorea (Shorea spp., Green 0.68 80,700 14,500 37,100 9,900 6,000 AS — 12% baulaugroup) 129,600 18,000 70,200 15,100 7,900 Shorea, lauan—merantigroup Dark red meranti

Light red meranti White meranti Yellow meranti Spanish-cedar (Cedrelaspp.) Sucupira (Bowdichiaspp.) Sucupira (Dipiotropispurpurea)

Teak (Tectona grandis) Tornillo(Cedrelinga cateniformis)

Wallaba (Eperua spp.)

Green 12% Green 12% Green 15% Green 12% Green 12% Green 15% Green 12% Green 12% Green 12% Green 12%

0.46 0.34 0.55 0.46 0.41

— 0.74 0.78 0.55 0.45

— 0.78

—

64,800 10,300 87,600 12,200 45,500 7,200

65,500

8,500

67,600 85,500 55,200 78,600 51,700 79,300 118,600 133,800 120,000 142,000 80,000 100,700 57,900

9,000 10,300 9,000 10,700

—

9,000 9,900 15,700

—

18,500 19,800 9,400 10,700

— —

98,600 16,100 131,700 15,700

59 95 43 59 57 79 56 70 49 65 — — 90 102

92 83 — — — —

32,500 50,700 23,000 40,800 37,900 43,800 26,800 40,700 23,200 42,800 67,100 76,500

7,700 10,000

3,100 3,500

AS

4,900 6,700

2,000 2,000 4,400 5,100

AS

3,300

AS

9,100 10,600 7,100 10,500

6,800 7,600

— —

55,300 83,700 41,100

12,400 13,500

58,000

13,000 8,100

28,300 — 55,400 74,200

8,900 — — —

3,400 2,400 2,700 — — 8,800 9,500 4,100 4,400 3,900

— 6,900 9,100

AS

iM

PM

AS PM PM

8Results of tests on small, clear, straight-grained specimens. Propertyvalues were taken from world literature (not obtained from experimentsconducted at the Forest Products Laboratory). Otherspecies may be reported in the world literature, as well as additional data on many of these species. Some propertyvalues have been adjustedto 12% moisture content. bAF is Africa; AM, America; AS, Asia.

4—19

Table 4—Sb. Mechanical properties ofsome woods imported into the United States otherthan Canadian imports (jnc._pOund)a

Static bending Modulus

of

Common and botanical names

of species

Afrormosia (Pericopsiselata) Albarco(Carinianaspp.) Andiroba(Carapaguianensis) Angelin(Andira inermis) Angelique(Dico,ynia guianensis) Avodire(Turraeanthus

africanus) Azobe (Lophira alata)

Green 12% Green 12% Green 12% Green 12% Green 12% Green

0.61

14,800 18,400

1.77 1.94

0.48

—

0.54

14,500 10,300 15,500

1.5 1.69 2

0.65

—

0.6 —

18,000 11,400 17,400

2.49 1.84 2.19

—

—

12,700 16,900 24,500

1.49 2.16

9.4

2.47 —

—

3,140

0.49 1.64 2.04

2.1 4.1

—

0.48

12%

Green

0.87

Green

0.16

12%

Banak (Virola spp.) Benge (Guibourtiaamoidiana)

12%

0.42 —

Green

0.65

Green

12%

Bubinga (Guibourtia spp.) Bulletwood (Manllkara bidentata)

Cativo (Prioria copaifera) Ceiba (Ceiba pentandra) Courbaril (Hymenaea courbari!) Cuangare (Dialyantheraspp.) Cypress, Mexican (Cupressus lustianica) Degame(Calycophyllum candidissimum) Determa (Ocotea rubra)

Ekop(Tetraberlinia

Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green 12% Green

12% tubmaniana) Green Goncalo alves (Astronium 12% graveolens) Greenheart (Chlorocardium rodie,) Green

0.71

0.85 0.4 — 0.25 0.71

Green 12%

4—20

—

—

5,600 10,900

—

2.04 —

22,600 17,300

2.48

27,300 5,900 8,600 2,200 4,300

3.45

—

0.52 0.6

10500 —

0.31 0.93 0.67

0.84 — 0.8 0.38

16,700 12,100 16,600 19,300

24,900 6,300 8,700

2.7 0.94 1.11 0.41

0.54 1.84 2.16 1.01 1.52 0.92 1.02 1.93 2.27 1.46 1.82

— 2.21 1.94

2.23 2.47 3.25 1.04 1.17

Side hard-

ness Sample

(lbl

19.5 18.4

7,490 9,940

2,090 1,560

13.8 9.8

6,820

2,310 1,020

4,780

14

8,120

—

880 1,220 1,510 1,130 — —

9,200 5,590 8,770

1,840 1,750 1,340 1,100 1,660 1,290

—

21,400

12,900 19,400 4,000 7,300 6,200 10,300 14,300 22,300 7,800

—

12%

Hura (Hura crepitans)

of

Corn-

Work to pression Shear

maximum parallel parallel Moisture Specific rupture load to grain to grain elasticity content gravity (lbfliri2) (x106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2)

12%

Balsa (Ochromapyramidale)

Modulus

— — 12

15.2

12

10

— — — — 13.6 28.5 5.4 7.2 1.2 2.8 14.6 17.6

— — — — 18.6 27 4.8 6.4

— 6.7 10.4 10.5

- - -

— 7,150 9,520

— — 2,030 1,080 2,040 2,890 2,960 3,350

- - -

12,600

2,160 2,390 5,140 —

300

—

720 980

320

AF AM AM

AF AM

AF AF AM AM

510

— — 2,090 1,750 — — 3,110 2,690

AF

8,690

1,900 2,230

AM

11,640

2,500 3,190 860 440 630 1,060 350 220 550 240

11,400

—

10,500

2,460 4,290 1,060 2,380 5,800 9,510 2,080 4,760 2,880 5,380 6,200 9,670

3,760 5,800 — 9,010 6,580

5.9

10,320 9,380 12,510 2,790

6.7

4,800

25.3

1,670 1,600

orjginb

AF

AM AM

1,770 1,970 2,470 2,350

AM

590 830 950 1,580

230

AM

380 340

AF

460

1,660 1,630 2,120 1,940 860 520 980 660

AM

—

AF

— — 1,760 1,960 1,930 2,620 830 1,080

AM

— 1,910

AM

2,160 1,880

AM

2,350 440 550

AM

Table 4—5b. Mechanical properties ofsome woods imported into the United States otherthan Canadian imports (inch_pound)a__con.

Static bending Common and botanical names of species

Ilomba (Pycnanthus angolensis Ipe (Tabebuia spp., lapachogroup) lroko(Chlorophoraspp.)

Jelutong (Dyera costulata) Kaneelhart (Licaria spp.)

Kapur (Diyobaianopsspp.) Karri (Eucalyptusdiversicolot) Kempas (Koompassia malaccensis Keruing (Dipterocarpusspp.)

content gravity Geen 0.4 12% Green

0.92

12%

Green

0.54

Green

0.67

12%

—-

Green 15% Green 12% Green 12% Green 12% Green

0.36 0.96 0.64 0.82

Limba (Terminaliasuperba) Macawood (Platymiscium spp.) Mahogany, African (Khaya spp.) Mahogany, true (Swieteniamacrophylla) Manbarkiak(Eschweilera spp.)

0.71

12%

Green

0.69

Green 12% Green 12% Green 12% Green 12% Green 12% Green

1 .C)5

--

0.38 0.94 0.42 0.45 —-

0.87

12%

Manni(Symphonia globuilfera)

Green

0.58

12%

Marishballi (Lincaniaspp.)

Green

0.88

12%

Merbau (lntsia spp.) Mersawa (Anisoptera spp.) Mora (Moraspp.)

Oak (Quercus spp.)

Green 15% Green 12% Green 12% Green

0.64 —-

0.52 0.78 0.76

12%

Obeche(Triplochiton scieroxylon)

of

of

Green 12%

(lbf/in2)

5,500 9,900 22,600 25,400 10,200 12,400 9,900 16,200 5,600 7,300

22,300 29,900 12,800 18,300 11,200

20,160

12%

Lignumvitae (Guaiacumspp.)

Modulus

Moisture Specific rupture

12%

Jarrah (Eucalyptusmarginata)

Modulus

0.3

14,500 17,700 11,900 19,900

—

— 6,000 8,800 22,300 27,600 7,400 10,700 9,000 11,500 17,100

maximum parallel load to grain elasticity (x106 lbf/in2) (in-lbf/in3) (lbf/in2) 1.14 1.59 2.92 3.14 1.29 1.46 1.48 1.88 1.16 1.18 3.82

4.06 1.6 1.88 1.94 2.6 2.41 2.69 1.71

-

2.07

— 0.77 1.01

3.02 3.2 1.15 1.4 1.34 1.5 2.7

26,500

3.14

11,200 16,900 17,100 27,700 12,900 16,800 8,000 13,800 12,600

1.96 2.46 2.93 3.34 2.02 2.23 1.77 2.28 2.33 2.96

22,100 — 23,000 5,100 7,400

Corn-

Work to pression Shear

-

3.02

0.72 0.86

— — 27.6 22 10.5 9

Side parallel hard-

to grain ness (lbflin2)

2,900

840

5,550 10,350 13,010

1,290

4,910 7,590

2,120 2,060

(lbf)

470 610

AF

3,060 3,680 1,080

AM

5,450

1,310 1,800 1,320 2,130 760 840 1,680 1,970 1,170 1,990 1,510

25.4

10,800

2,420

2,040

12.2 15.3 13.9 23.5

7,930 9,520 5,680 10,500

1,460 1,790 1,170 2,070

1,480 1,710 1,060 1,270

—

11,400

—

7.7

2,780 4,730

4,500 400 490 3,320 3,150 640 830 740 800

— — 5.6 6.4 13.6 17.5 15.7 18.8 11.6

-

8.9 — — 7.1 8.3 9.1 7.5 17.4 33.3 11.2 16.5 13.4 14.2 12.8 14.8

5,190 8,870 3,050 3,920 13,390 17,400

6,220 10,090

10,540 16,100

88

2,540

— —

4,340 6,780 7,340 11,210 5,160 8,820 7,580 13,390 6,770 8,440 3,960 7,370

13.5 18.5

11,840

931 1,500 1,240 1,230 1,630 2,070 1,140 1,420 1,620 1,750 1,560 1,810 740 890 1,400 1,900

16.5 6.2 6.9

— 2,570 3,930

— 660 990

-

3,730 6,460

6,400

AF

1,261)

1,290 1,910 330 390 2,210 2,900 980 1,230 1,360

- - 1,410 1,840

Sample originb

AS AS AM AS AS

AS AS AM AF AM AF AM

2,280 AM 3,480 94C

1,120 2,250 3,570 1,380 1,500 880 1,290 1,450 2,300

- - -

2,500 420

AM AM

AS AS AM AM AF

430

4—21

Table 4—5b. Mechanical properties ofsome woods imported intothe United States otherthan Canadian imports (inch.pound)a_con. Static bending Common and botanical

names of species Okoume (Aucoumea klaineana) Opepe (Naucleadiderrichi,) Ovangkol (Guibourtiaehie) Para-angelim (Hyrnenolobium excelsum) Parana-pine (Araucaria augustifolia) Pau marfim (Balfourodendron nedelianum) Peroba de campos (Paratecomaperoba) Peroba rosa (Aspidosperma spp., peroba group) Pilon (Hyeronima spp.)

Pine, Caribbean(Pinus canbaea) Pine, ocote (Pinus oocarpa) Pine, radiata (Pinus radiata) Piquia (Cwyocarspp.)

Green 12% Green 12% Green 12% Green 12% Green 12% Green 15% Green 12% Green 12% Green 12% Green

of

0.63

7,400 13,600 17,400

1.14 1.73 1.94

16,900 14,600 17,600 7,200 13,500 14,400 18,900

2.56 1.95 2.05 1.35

12.8 15.9

8,300 7,460 8,990

9.7

4,010

1.61

12.2

1.66

— — —

6,070

15,400 10,900 12,100 10,700 18,200 11,200 16,700 8,000 14,900 6,100 11,700 12,400

1.77 1.29 1.53 1.88

10.1

8,880 5,540 7,920

2.27

12.1

9,620

1.88

10.7 17.3 6.9 10.9

4,900 8,540 3,690 7,680 2,790 6,080

0.67

0.63 0.46 — 0.73 0.62 0.66

0.65 0.68

Green

0.55

12%

—

Green

0.42

12%

—

Green

0.72

donnell—smithil)

12%

—

—

17000 0.4

12%

—

7,200 9,500 1,370 19,200 9,800 18,500 10,800 13,800 14,100 19,000 9,200 16,900 8,500 14,300 10,500 14,600

Green

0.55

—

10,200

12%

Green

0.67

12%

Green

0.52

12%

—

Robe (Tabebuiaspp., roble group)

Green

0.52

Rosewood, Brazilian (Dalbergianigra) Rosewood, Indian (Dalbergia latifolia) Sande (Brosimumspp., utile group) Santa Maria (Calophylium brasillense) Sapele(Entandrophragma cylindricum)

Green

12%

0.8

12%

—

Green 12% Green

0.75 0.49

12%

Green

Sepetir (Pseudosindorapalustris) Green 12%

—

—

—

Green

4—22

of

CornWork to pression Shear Side maximum para to parallel hardload grain Ilel to grain ness Sample

0.33

12%

Primavera(Tabebuia

Ramin (Gonystylus bancanus)

Modulus

Moisture Specific rupture elasticity content gravity (lbflin2) (x106 lbf/in2) (in-lbf/in3) (lbu/in2)

12%

Purpleheart(Peltogynespp.)

Modulus

0.52

0.56

15,300 11,200 17,200

—

— —

2.24 1.74

2.25 1.18 1.48 1.82 2.16 0.99 1.04 2 2.27 1.57 2.17 1.45 1.6 1.84 1.88 1.19 1.78 1.94 2.39 1.59 1.83 1.49 1.82 1.57 1.97

— — 12.2 14.4

— —

10.5

9.2 8.3

— —

8.4 15.8 7.2 6.4 14.8 17.6 9 17

11.7 12.5 13.2

— 3,970 7,480 10,400

—

7,660 8,190

—

4,960

6,290

8,410 3,510 5,600 7,020 10,320 5,390 10,080 4,910

(lbf/in2)

— 970

(lbf)

originb

—

AF

380

1,900 1,520 2,480 1,630

— —

— — 1720 1,600

2,010 1,720 970 560 780 1,730

— — —

— — —

2,130 1,880 2,490 1,200 1,720 1,170

1,600 1,580 1,730 1,220 1,700

980

580 1,040 910 1,720 750 480 750 1,600 1,640 1,720 1,990 1,720 700 1,030 660 1,390 1,640 1,810 2,220 1,860 990 640 1,520 1,300 910 1,250 960 1,450 2,360 2,440

— 11.5

4,530

1,400

13.1

9,220 4,490 8,220

2,090 3,170

12.7 16.1

10.5 15.7 13.3 13.3

4,560 6,910 5,010 8,160 5,460 8,880

AF AM AM AM AM AM AM AM

2,090 1,240

7,340 5,510 9,600

— —

AF

AM AS AM AM AM AS AM AM

2,110 2,720

1,040 1,290 1,260

1,560

AS

600

AM

900 890

AM

2,080 1,150 1,250

1,020 2,260 1,510 950 1,310 2,030 1,410

AF AS

Table4—5b. Mechanical properties ofsome woods imported into the United States otherthan Canadianimports (inch_pound)a__con.

Static bending Modulus

Common and botanical names of species Shorea (Shorea spp., bullau group)

Shorea,lauan—meranti group Dark red meranti Light red meranti White meranti Yellow meranti Spanish-cedar (Cedrelaspp.)

Sucupira(Bowdichiaspp.) Sucupira (Diplotropispurpurea)

Teak(Tectonagrandis)

CornWork to

pression Shear Side of of maximum parallel parallel hardMoisture Specific rupture elasticity load to grain to grain ness Sample content gravity (lbf/in2) (x106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2) (lbf) originb — Green 0.68 2.1 11,700 5,380 1,440 1,350 AS — 12% 18,800 2.61 10,180 2,190 1,780 Green 12% Green 12% Green 15% Green 12% Green 12% Green 15% Green 12% Green

0.46 0.34 0.55 0.46 0.41 -—

0.74

0.78

9,400 12,700 6,600 9,500 9,800 12,400 8,000 11,400 7,500 11,500 17,200 19,400 17,400

0.55

Tornillo(Cedrelinga

Green

0.45

cateniformi.s)

12%

-—

Green

0.78

12%

-—

1.5 1.77 1.04 1.23 1.3 1.49 1.3 1.55

8.6 13.8 6.2 8.6 8.3 11.4 8.1

1.31

7.1

1.44

9.4 — —

2.27 —

11,600 14,600

2.68 2.87 1.37 1.55

8,400 —

—

14,300 19,100

2.33 2.28

20,600

12%

Wallaba(Eperua spp.)

Modulus

—

10.1

13 14.8 13.4 12

— — — —

4,720 7,360 3,330 5,920 5,490

6,350 3,880

5,900 3,370 6,210 9,730 11,100

8,020 12,140 5,960 8,410 4,100

—

8,040 10,760

700 1,110 780 1,450 710 440 970 460 1,320 1,000 1,540 1,140 750 1,030 770 1,520 990 550 600 1,100

— —

— —

1,800 1,980 1,960 2,140 930 1,290 1,890 1,000 870 1,170

—

— —

—

1,540

AS AS AS AS AM AM AM

AS AM AM

2,040

aResults of tests on small, clear, straight-grained specimens. Propertyvalues were taken from world literature (not obtained from experimentsconducted at the Forest Products Laboratory). Other speciesmay be reported in the world literature, as well as additional data on many of these species. Some property values have been adjustedto 12% moisture content. bAF is Africa; AM, America; AS, Asia.

Table 4—6. Average coefficients of variation for some mechanical properties

ofclearwood

Coefficientof variationa Property Static bending Modulusof rupture Modulusof elasticity Work to maximum load Impact bending Compression parallel to grain Compression perpendicularto grain Shear parallel to grain, maximumshearing strength Tension parallelto grain Side hardness Toughness

(%) 16

22 34 25 18 28 14 25 20 34

Specific gravity rn °Values based on results cf tests of green wood from approximately50 species. Values for wood adjustedto 12% moisture content may be assumed to be approximatelyof the same magnitude.

4—23

Table 4—7. Average parallel-to-grain tensile strengthof some wood speciesa

Table 4—8. Averagetoughnessvalues fora few hardwood speciesa

Tensilestrength (kPa (lb/in2))

Species

Hardwoods Beech,American Elm, cedar Maple, sugar Oak Overcup Pin Poplar, balsam Sweetgum Willow, black Yellow-poplar

Species 86,200 120,700 108,200

(12,500) (17,500) (15,700)

77,900 112,400 51,000 93,800 73,100 109,600

(11300) (16,300) (7,400) (13,600) (10,600) (15,900)

58,600

(8,500)

Softwoods Baldcypress Cedar Port-Orford Western redcedar Douglas-fir, interior north

Toughness

78,600

45,500 107,600

(11,400) (6,600) (15,600)

77,900

(11,300)

95,100 89,600

(13,800) (13,000)

111,700

Radial (J (in-lbf))

Tangential (J (in-lbf))

12%

0.65

8,100 (500)

Green 12%

0.64 0.71

11,400 (700) 10,100 (620)

10,100 (620) 11,700 (720) 10,700 (660)

Maple,sugar

14%

0.64

6,000 (370)

5,900 (360)

Oak, red Pin Scarlet

12%

0.64

11%

0.66

7,000 (430) 8,300 (510)

7,000 (430) 7,200 (440)

Green

0.56 0.62

11,900 (730) 5,500 (340)

11,100 (680)

13%

Green

0.48

13%

0.51

5,500 (340) 4,200 (260)

5,400 (330) 4,200 (260)

Green

0.38

11%

0.4

5,000 (310) 3,400 (210)

5,900 (360) 3,700 (230)

Green

0.43

12%

0.45

5,200 (320) 3,600 (220)

4,900 (3C0) 3,400 (210)

Birch, yellow Hickory (mockernut, pignut,sancO

Oak,white Overcup Sweetgum

Willow,black

Fir California red Pacific silver Hemlock, western Larch, western

Moisture Specific content gravity

Yellow-poplar

5,000 (310)

(16,200)

Pine

Eastern white Loblolly Ponderosa Virginia Redwood Virgin Young growth Spruce Engelmann Sitka

73,100 80,000 57,900 94,500

(10,600) (11,600) (8,400) (13,700)

64,800 62,700

(9,400) (9,100)

84,800 59,300

(12,300) (8,600)

aResultsoftestsonsmall, dear, straight-grained specimens tested green. Forhardwood species, strength ofspecimenstested at 12% moisture content averagesabout 32% higher:forsofiwoods, about 13% higher.

Less Common Properties Strength propertiesless commonlymeasuredin clear wood

include torsion, tougimess,rollingshear, and fracturetoughness. Otherpropertiesinvolvingtime under load include creep, creeprupture ordurationofload,and fatiguestrength.

Torsionstrength—Resistanceto twistingabout a longitudinal axis. For solid wood members,torsionalshear strengthmay be taken as shear strengthparallelto grain. Two-thirdsofthe valuefortorsionalshear strength may be usedas an estimateofthetorsionalshear stress at theproportional limit. Toughness—Energyrequired to cause rapid complete failure in a centrallyloaded bendingspecimen. Tables4—8 and4—9give averagetoughnessvaluesfor samples ofa few hardwoodand softwoodspecies. Average coefficients of variationfortoughnessas determinedfrom approximately 50 species are shownin Table4—6. 4—24

Creep and durationofload—Time-dependentdeformationofwood under load. Ifthe load is sufficiently high and thedurationof loadis long, failure (creep—rupture)will eventuallyoccur. The time requiredto reachruptureis commonly calleddurationofload. Durationofload is an important factor in settingdesignvalues forwood. Creep and durationofloadare describedin later sections ofthis chapter.

Fatigue—Resistance to failure under specific combinations ofcyclicloading conditions: frequency andnumber of cycles, maximum stress,ratio ofmaximumto minimum stress, andother less-important factors. The main factors affecting fatiguein wood are discussedlater in this chapter. The discussionalso includesinterpretation offatiguedata and information on fatigueas a function ofthe service environment. Rolling shear strength—Shearstrength ofwood where shearing force is in alongitudinal plane and is acting perpendicularto the grain. Few test values ofrolling shear in

solid wood havebeen reported.In limitedtests, rolling shearstrength averaged 18% to 28% ofparallel-to-grain shearvalues. Rollingshear strength is about the same in thelongitudinal—radialand longitudinal—tangentialplanes. Fracturetoughness—Abilityofwood to withstandflaws that initiate failure. Measurement offracture toughness helps identif'the length ofcriticalflawsthat initiatefailure

in materials.

To date there is no standardtestmethod for determining fracturetoughness in wood. Threetypes ofstress fields, and associated stress intensity factors, canbe definedat a crack tip: openingmode (I), forwardshearmode (II), and transverse shearmode (III) (Fig.4—2a). A crackmay lie in one ofthese

Table4—9. Average toughness values for a fewsoftwood

(a) Failuremodes

specie?

Toughness

Spees Cedar Western red Yellow Douglas-fir Coast

Moisture Specific content gravity 9% 10%

Green 12%

Interior west

Green

Interior north

Green

13% 14%

Interiorsouth

Green 14%

Radial

Tangential

(J (in-lbt))

(J (in-Ibf))

0.33 0.48

1,500

(90) 3,400 (210)

2,100 3,700

(130) (230)

0.44 0.47

3,400 3,300 3,300 3,400 2,800 2,600 2,100 2,000

5,900 5,900

(360) (360)

0.48 0.51 0.43 0.46

0.38 0.4

(210) (200) (200) (210) (170) (160) (130) (120)

Fir California red

Green 12%

Noble

Green 12%

0.36 0.39 0.36 0.39 0.37

Pacific silver

Green 13%

0.4

White

Green

0.36 0.38

13%

Hemlock Mountain

Green 14%

Western

Green 12%

Larch, western

Green 12%

0.41 0.44

2,100 (130) 2,000 (120)

2,400 2,800

(150) (170) 2,300 (140) 2,100 (130) 4,100

4,900 (300) 5,500

(340)

3,900

(240)

4,100 (250) 2,900 (180) 2,900 (180) 2,900 (180) 2,800 (170) 3,900 (240) 3,600 (220) 3,700 (230) 4,200 (260) 3,600 (220) 3,300 (200) 4,600 2,800

3,400

(250) (140) (150) (140) (270) (210)

6,500 5,500

(280) (170) (170) (210) (400) (340)

2,000

(120)

1,800

(110)

2,600 2,000

(160) (120)

3,300 0.42 2,300 0.48 5,000 0.51 2,600 0.38 2,600

(200) (140)

6,200 (380) 3,900

(240)

(310) (160)

6,200 4,200 3,400 4,400 3,100 5,700 4,700 6,500 3,700

(380) (260)

0.38 0.41 0.51 0.55

2,300 2,400

2,300 4,400

2,800 3,400

Pine

Eastern white Jack

Green 12%

0.33 0.34

Green

0.41

12%

Loblolly

Green 12%

Ponderosa

Green Green

Red

Green

Lodgepole

11% 12%

Shortleaf

Green 13%

Slash

Green 12%

Virginia

Green 12%

Redwood Old-growth

Green 11%

Young-growth

Green 12%

Spruco, Enelmann

Green 12%

0.38 0.43

3,100 2,400

0.4 0.43

3,400 2,600

0.47 0.5

4,700 2,400

0.55 0.59 0.45 0.49

5,700 3,400

0.39 0.39

1,800 1,500

0.33

1,800

5,500 2,800

0.34 1,500 0.34 2,400 0.35 1,800

(160) (190) (150) (210) (160) (290) (150) (350) (210) (340) (170) (110) (90) (110) (90) (150) (110)

ts

>

0)0

OC ()U)— ;U)

flffl ) cL'5 .:

Maturewood

a>

COOO)Ol-Q

be desirableto eliminatethis wood from raw material, hi logs, compression wood is characterized by eccentric growth about the pith and the large proportionoflatewood at the point ofgreatest eccentricity (Fig.4—8A). Fortunately, pronouncedcompression wood in lumbercan generallybe detectedby ordinary visualexamination.

Compressionand tensionwood undergo extensive longitudinal shrinkagewhen subjectedto moistureloss below the fiber saturation point. Longitudinalshrinkagein compression wood may be up to 10 times that in normalwood and in tension wood, perhaps up to 5 timesthat in normal wood. Whenreactionwood and normalwood are present inthe same board,unequallongitudinal shrinkagecauses internal stressesthat result in warping.In extremecases,unequal longitudinal shrinkageresults in axial tensionfailure over a portion ofthe cross sectionofthe lumber(Fig.4—8B). Warp sometimes occurs in rough lumberbut more often in planed, ripped, or resawn lumber (Fig. 4—8C).

Juvenile Wood Juvenilewood is the wood producednearthe pith ofthe tree; for softwoods, it is usuallydefmedas thematerial 5 to 20 rings from thepith dependingon species.Juvenilewood has considerably differentphysicaland anatomical properties

than that ofmature wood (Fig. 4—9). In clear wood,the propertiesthat havebeen foundto influence mechanical behavior includefibril angle, cell length, and specific gravity, the latter acompositeofpercentage oflatewood, cell wall thickness,and lumen diameter.Juvenile wood has a high fibril angle(angle between longitudinal axis ofwood cell

4—32

Pith

5-20 rings

Bark

Figure 4—9. Properties ofjuvenilewood.

and cellulosefibrils),whichcauseslongitudinal shrinkage that may be more than 10 timesthat ofmature wood.Cornpressionwood and spiral grain are also more prevalentin juvenile wood than in mature wood and contributeto longitudinal shrinkage.In structural lumber, the ratioofmodulus ofrupture, ultimate tensile stress,and modulusofelasticity forjuvenile to maturewood ranges from 0.5 to 0.9, 0.5 to

0.95, and 0.45 to 0.75,respectively.Changesin shear strengthresultingfrom increases injuvenile wood content can be adequately predicted by monitoring changes in density alonefor all annualring orientations. The same is true for perpendicular-to-grain compressive strengthwhenthe load is applied in thetangential direction. Compressivestrength perpendicular-to-grain for loadsappliedin the radial direction,however, is more sensitive to changes in juvenile wood contentand may be up to eight times less than that suggestedby changesin density alone. The juvenile wood to maturewoodratio is lowerforhigher grades of lumberthan for lowergrades,whichindicatesthat juvenile wood has greaterinfluence in reducing themechanical properties of high-grade structural lumber. Only a limitedamountof research has beendone onjuvenilewood in hardwood species.

Products containingvisiblecompression failureshavelow strength properties, especially in tensile strengthand shock resistance. The tensile strength ofwood containingcompression failures may be as low as one-third the strengthof matched clear wood. Even slight compression fail[ures,visible only under a microscope, may seriously reduce strength and cause brittlefracture. Because ofthe low strerLgth associated with compression failures, many safetycodesrequire certain structural members, such as ladderrails and scaffold planks, tobe entirely free ofsuch failures.

Pitch Pockets Apitch pocketis a well-defmed openingthat containsfree

resin. The pocket extendsparallelto the annualrings; it is almostflat on the pith side and curvedon the barc side. Pitch pocketsare confined to such species as thepines, spruces, Douglas-fir, tamarack, and western larch. The effectofpitch pocketson strength depends upontheir number, size,and location in the piece.A large numberof pitchpockets indicates a lack ofbondbetweenannualgrowth layers, and a piecewith pitchpocketsshould be inspected for shake orseparationalongthe grain.

Bird Peck Maple, hickory, white ash, and a numberofother species are often damaged by smallholes madebywoodpeckers. Thesebirdpecks often occur in horizontal rows, ometimes encircling thetree, and brown orblack discoloration known as a mineralstreakoriginates from each hole. Holes fortapping mapletrees are alsoa sourceofmineral streaks. The streaks are causedby oxidation and other chemical changes in thewood.Bird pecks and mineralstreaks are not generally important in regardto strengthofstructural lumber, although theydo impair the appearance ofthe wood.

a

Figure 4—10. Compression failures.A, compression failureshown by irregularlines acrossgrain; B, fiber breakage in end-grain surfaces ofspruce lumber caused by compression failures below dark line.

Compression Failures Excessive compressive stresses along the grain that produce

minutecompression failures can be caused by excessive bendingofstanding trees from wind orsnow; felling oftrees across boulders,logs, or irregularities in the ground;or roughhandlingoflogs orlumber. Compressionfailures shouldnotbe confusedwith compression wood. In some instances, compression failures are visibleon the surface of a boardas minutelines or zones formed by crumpling or buckling of cells (Fig.4—1OA), althoughthe failuresusually appearas white lines ormay evenbe invisibleto thenaked eye. The presenceofcompression failures may be indicated by fiberbreakage on end grain (Fig.4—lOB). Since compression failures are often difficult to detectwith theunaidedeye, specialefforts, including optimum lighting,may be required for detection. The most difficult cases are detectedonly by microscopic examination.

Extractives Many wood species containremovable extraneous materials or extractives that do not degradethe cellulose—ligninstruc tare ofthe wood.These extractives are especially abundant in species such as larch,redwood, westernredcedar, and black locust.

A smalldecreasein modulusofruptureand strengthin

compression parallelto grain has been measuredfor some species after the extractives have beenremoved.The extentto whichextractives influence strengthis apparently a function oftheamount ofextractives, the moisturecontentofthe piece,and the mechanical property underconsideration.

Properties of Timber From Dead Trees Timber from treeskilled by insects,blight, wind, or fire may be as good for any structural purposeas that from live trees, providedfurtherinsect attack, staining, decay, or drying degrade has not occurred. In a living tree, the heactwood is entirely deadand only a comparatively few sapwoodcells are alive. Therefore, most wood is deadwhencut, regardless of

4—33

whetherthe tree itselfis livingor not. However, ifatree stands on the stumptoo long afterits death, the sapwoodis likelyto decay orto be attacked severely by wood-boring insects,and eventuallythe heartwoodwill be similarly affected. Such deterioration also occurs in logs that havebeen cutfrom live trees andimproperly caredforafterwards. Because ofvariations in climatic and other factors that affect deterioration,the time that deadtimbermay stand or lie in theforestwithout seriousdeterioration varies.

Table 4—13. Intersection moisture content values selected speciesa

Tests on wood from trees that had stood as long as 15 years after being killed by fire demonstrated that this woodwas as sound and strong as wood from live trees. Also, the heartwood oflogs ofsome more durablespecies has been foundto be thoroughlysound after lying in theforestfor manyyears. Ontheother hand, in nonresistantspecies, decay may cause great loss ofstrengthwithin a very brieftime, both in trees standingdead on the stumpand in logs cut from live trees and allowedto lie on the ground. The importantconsideration is not whetherthe trees from whichwoodproductsare cutarealive or dead, butwhethertheproductsthemselves are free from decay or otherdegrading factors that would render them unsuitableforuse.

Larch, western

28

Pine, loblolly Pine, longleaf Pine, red

21 21

24

Redwood Spruce, red

21

Tamarack

24

Effects of Manufacturing and

white ash at 8% moisturecontent. Using informationfrom

Moisture Content

Ash, white

24 27 24 24

Birch, yellow Chestnut, American

Douglas-fir Hemlock, western

Spruce, Sitka

I

27

alntersection moisture content is point at which mechanical propertiesbegin to changewhen wood is dried from the green condition.

example, suppose you want to fmd the modulusofruptureof

P8

Many mechanicalpropertiesare affected by changes in moisturecontentbelowthe fiber saturation point.Most properties reportedinTables 4—3, 4—4, and 4—5 increase with decrease in moisture content.The relationshipthat describesthese changesin clear wood propertyat about 21°C (70°F) is 12—M

(4-3)

[P]MP_12 whereP is the property atmoisture contentM (%), P12 the same propertyat 12% MC,Pgthe same property for green wood, and M moisturecontentat the intersection ofa horizontal line representingthe strengthofgreen wood and an inclinedline representingthe logarithm ofthestrength—

moisture contentrelationship fordry wood.This assumed linearrelationshipresults in an M value that is slightlyless than the fiber saturationpoint. Table4—13 gives valuesofM for afew species;for other species,M = 25 may be assumed. Average property valuesofP12 andPg are given formany species in Tables 4—3 to 4—5. The formulaformoisture contentadjustmentis not recommendedforwork to maximum load,impact bending, and tensionperpendicular to grain. Thesepropertiesareknown to be erratic in their responseto moisturecontentchange. The formulacan be usedto estimate apropertyat anymoisture contentbelowM from the species datagiven. For

4—34

(%)

Tables4—3a and 4—13,

Service Environments

P

M Species

=119,500kPa

Careshouldbe exercised whenadjustingpropertiesbelow 12% moisture. Although most propertieswill continueto increase while wood is dried to very low moisture content levels,for most species somepropertiesmay reach a maximum valueandthen decreasewith furtherdrying (Fig. 4—11). For clear SouthernPine, the moisture content at whicha maximum propertyhas been observedis given in Table 4—14. This increase in mechanical properties with dryingassumes small, clear specimens in a dryingprocess in whichno deterioration ofthe product(degrade) occurs.For 51-mm(2-in.-)thick lumbercontainingknots, the increasein property with decreasingmoisturecontent is dependentupon lumberquality.Clear, straight-grained lumbermay show increases in properties with decreasingmoisture contentthat approximate those ofsmall, clear specimens. However,as the frequency and size ofknots increase, the reductionin strength resultingfrom theknots beginsto negatethe increasein propertyin the clear wood portion ofthe lumber.Very low qualitylumber, whichhas many large knots, may be insensitive to changes in moisturecontent.Figures4-12 and 4-13 illustrate the effectofmoisturecontenton the properties of lumberas afunctionofinitiallumberstrength(Greenand others 1989). Application ofthese results in adjustingallowable propertiesoflumberis discussedin Chapter6. Additional information on influencesofmoisture content on dimensionalstability is includedin Chapter 12.

22.0

120 16

(0

16.5

0)

ii.o.>.

a-

0. 0

o

Z80

t

a, =

0)

0

0. 5.5 2 a-

Figure 4—11. Effectof moisture content on wood strength properties. A, tension parallel to grain.; B, bending; C, compression parallel to grain; D, compression perpendicular to grain; and E, tension perpendicular to grain. Table 4—14. Moisture content formaximum property value in drying clearSouthern Pinefrom green to 4% moisture content Moisture content at which peak

Ultimate tensile stress parallelto grain Ultimate tensile stress perpendicularto grain MOEtension perpendicularto grain MOEcompressionparallelto grain Modulusof rigidity, GRT

—_----------------. _______________________

5

10 15 20 Moisture content (%)

Property

4O-

property occurs (%)

I

I

0

4

; E

—0

12 16 20 24 Moisturecontent (%) Figure 4—12. Effect ofmoisturecontent on tensile strengthof lumberparallel to grain.

0

8

90 -

12 (\1

0

OD

C

a)

x

60

8c

a)

>

C 0) (0

(0 (0 a,

4

12.6

(0

10.2 4.3 4.3 10.0

Ternperature

Q.

E

0 C,

J30 0

a, ce

8

12

16 Moisturecontent

20

24

E

(%)

Figure 4-13. Effect of moisture contenton compressive strengthof lumberparallel to grain.

Reversible Effects

In general, themechanical properties ofwood decrease when heatedand increase when cooled. At a constantmoisture contentandbelow approximately 150°C (302°F), mechanical properties are approximately linearlyrelatedtotemperature. The changein propertiesthat occurswhenwood is quickly heatedor cooled and then tested at that condition is termed an immediateeffect. Attemperaturesbelow 100°C(212°F), theimmediateeffectis essentially reversible;that is, the propertywill returnto the valueat the original temperature ifthe temperature changeis rapid. Figure 4—14 illustrates the immediate effectoftemperature on modulusofelasticityparallelto grain,modulusofrupture, and compressionparallelto grain, 20°C(68°F), based on a composite ofresults forclear,defect-free wood. Thisfigure represents an interpretation ofdata from several investigators.

The width ofthe bands illustratesvariabilitybetweenand withinreportedtrends. Table 4—15 lists changesin clear wood propertiesat —50°C (—58°F) and 50°C (122°F) relativeto those at 20°C (68°F) for a numberofmoisture conditions.The largechangesat —50°C (—58°F) for green wood (at fiber saturation point or wetter) reflectthe presence ofice. in the wood cell cavities. The strengthofdry lumber, at about 12% moisturecontent, maychangelittleas temperature increases from —29°C (—20°F) to 38°C (100°F). For green lumber,strengthgenerally decreases with increasing temperature. However, for temperaturesbetweenabout 7°C (45°F) and 38°C (100°F), thechanges may not differsignificantly from thoseat room temperature. Table4-16 providesequationsthat havebeen

4—35

Table 4—15. Approximate middle-trend effects of temperature on mechanical properties of clearwood atvariousmoisture conditions

200 (a)

12%moisture content

0

Relativechange in mechanical property from20°C(68°F) at

150

U)

(5

a)

0 (0

0% moisture content

100

Property

0

MOE parallel tograin

E

—50°C

+50°C

(—58°F)

(%)

(%)

(+122°F (%) —

0 >FSP

+11 +17 +50

6

—

12

50

(5

Moisture conditiona

a)

MOE perpendicularto grain

12

-200

-100

0

200

100

300

250 (b)

20 Shear modulus

>FSP

Bendingstrength

4

(/)

•0 0 100 E

-

ci)

a)

—25

Tensile strength paralleltograin

—4

Compressive strength parallel to grain Shear strengthparallelto grain Tensilestrength perpendicular tograin

0

+20 +50

—10 —25

Compressive strength perpendicular to grain atproportional

50

-38

—

> (5

—35

0—12

18—20

0% moisture content

12%moisture content

— —20

>FSP

11—15

0 150

—7

+18 +35 +60 +110

18%moisture content

200

— — —

—6

12-45 >FSP 4—6 11—16

18 0-6

10

— — —

—10 —20

—25 —25

—25 —10

—

—20 —30

— —

—20 —35

limit

0

I

-200 -150

-100

-50

U

0

50

100

150

300 -

used to adjust some lumber propertiesforthe reversible

effects oftemperature.

(0)

250

12%moisture content

II)

200 Cl)

150

E

0 0

0% moisture content

a)

>

50 -200

-100

0 100 Temperature (°C)

200

300

4—14. Immediate effectof temperature at two moisturecontentlevels relative to valueat 20°C (68°F) for clear, defect-free wood: (a) modulus of elasticity parallel to grain, (b) modulus of rupturein bending, (c) compressive strengthparallel to grain. Theplot is a composite of results from several studies.Variability in reported trends is illustratedby width of bands.

Figure

4—36

aFSp indicates moisture content greaterthanfibersaturation point.

Irreversible Effects In addition tothereversible effectoftemperature onwood, there is an irreversible effectat elevated temperature. This permanent effectis one ofdegradation ofwood substance, whichresults in loss ofweightand strength. The loss depends on factors that includemoisturecontent, heatingmedium,temperature, exposureperiod, and to some extent,

species and size ofpiece involved. Thepermanentdecrease ofmodulus ofrupturecaused by heatingin steam andwater is shownas a functionoftempera-

ture and heatingtime in Figure4—i5, based on tests ofclear pieces ofDouglas-firand Sitka spruce.In the same studies, heatingin water affected work to maximumloadmore than modulusofrupture (Fig.4—16). The effect ofheatingdry wood (0% moisturecontent) on modulusofrupture and modulusofelasticityis shown in Figures4—17 and 4—18, respectively, as derivedfrom testsonfoursoftwoods andtw hardwoods.

Table

4—16.

Property MOE

Percentagechange in bending properties of lumber with change in temperaturea Lumber gradeb

Moisture

All

Green Green

SS

No. 2 or less

I

content

12%

MOR

((P—P70) F'70) 100 = A + BT + CT2

Green Green 12% Green Green

Dry

A

B

C

22.0350 13.1215 7.8553

—0.4578 —0.1793 —0.1108

0 0 0

34.13 0 0 56.89 0 0

—0.937

0.0043 0 0 0.0072

aFor equation, P is property at temperature bSS is Select Structural.

0 0 —1.562

0 0

Temperature range

0 0

Tmi,

0 32 —15 —20

46 —20 —20

46 —20

Tmax

32 150 150 46 100 100

46

100 100

T in °F; P70, propertyat 21°C (70°F).

Figure4—19 illustratesthe permanentloss in bending strengthofSpruce—Pine—Fir standard38- by 89-mm (nominal2- by 4-in.) lumber heatedat 66°C (150F) and about 12% moisture content. Duringthis same,period, modulusofelasticitybarely changed. Most in-service exposures at 66°C(150°F)would be expectedto result in much lowermoisturecontentlevels. Additionalresults for other lumberproductsandexposureconditions wilil be reportedas ForestProducts Laboratory studiesprogress. The permanentpropertylosses discussed here arebased on tests conducted after the specimens were cooledto room temperatureand conditioned to arange of7% to 12% moisture content. Ifspecimens are tested hot,the percentage of strength reductionresultingfrom permanenteffects is based on values alreadyreducedby theimmediate effects. Repeated exposure to elevatedtemperature has a cumulative effecton wood properties. For example,at a given temperature the propertyloss will be aboutthe same after six 1-month exposure as itwould be aftera single6-monthexposure.

The shapeand size ofwoodpieces are important in analyzing the influenceoftemperature. Ifexposure is for only a short time, so that the inner parts ofa largepiece do notreach the temperatureofthe surrounding medium,the immediate effect on strengthofthe inner parts will be less than that for the outer parts.However,thetype ofloading must be considered. Ifthe memberis to be stressedin bending, the outer fibersofapiece will be subjectedto the greateststress and willordinarily govern theultimatestrengthofthepiece; hence,under this loadingcondition,the fact that the inner part is at alowertemperaturemay be oflittle significance. For extendednoncyclicexposures, it can be assumedthat the entire piece reaches the temperature oftheheatingmedium andwill thereforebe subjectto permanent strengthlosses throughoutthe volume ofthe piece, regardless of size and mode ofstress application. However,in ordinary construction wood often will notreach the dailytemperature extremes oftheair aroundit; thus, long-term effectsshouldbebased

Time Under Load Rate of Loading Mechanicalpropertyvalues, as given in Tables4—3, 4—4, and 4—5, are usuallyreferredto as staticstrengthvalues. Staticstrengthtests are typicallyconductedata rate ofloading or rate ofdeformationto attain maximum loadin about 5 min.Higher valuesofstrengthareobtainedfor wood loadedat a more rapid rate and lowervalues are obtainedat slowerrates. For example, the loadrequiredto produce failure in awood memberin 1 s is approximately 10% higher thanthat obtainedin a standardstatic strengthtest. Over several ordersofmagnitudeofrate ofloading, strength is approximately an exponential function ofrate. See Chapter6 for application to treatedwoods. Figure4—20 illustrates how strengthdecreaseswith time to maximum load. The variabilityin the trend sho'wn is based onresultsfrom several studiespertainingto bend:Lng, compression, andshear.

Creep and Relaxation When initially loaded,a wood member deformselastically. Ifthe loadis maintained, additional time-dependent deformation occurs. This is called creep. Creepoccursat evenvery low stresses, and it will continueover a period ofyears. For sufficiently high stresses, failure eventually occurs.This failure phenomenon, calleddurationofload (or creep rupture), is discussedin the next section.

At typical design levels and use environments, after several years the additional deformation caused by creepnay approximately equalthe initial, instantaneous elastic

deformation. For illustration, a creepcurve basedon creep as a function ofinitial deflection (relative creep)at several stress levels is shown in Figure4—21; creepis greater underhigher stresses than underlowerones.

ontheaccumulated temperature experience ofcritical structural parts.

4—37

100

0

0

a)

a) c,) a)

90

C— ed)

03

15°C (240°F)

IN

0. C .— 0

ccci

•V 70

.

80

eQ

2

2> 00

-o 0

175°C (350°F)

(275°F)

60 155°C(310°F)

50

175°C (350°F) I

I

50

100

I

——

—

I

—

•3 100 0

0

C

0 C.) a) a) a)

C

9OT80

0 0) 70

(ace

C

C)

a)

0. >'

0 0 a)

60 50

I

I

D 0

— ——

I

I

I

50

100 150 200 250 300 aHeating period (days) Figure 4—16. Permanent effectof heating in wateron work to maximum loadand modulus of ruptureof clear, defect-freewood.All data based on tests of Douglas-fir and Sitka spruceat roomtemperature. 0

Ordinary climaticvariations in temperature andhumidity will cause creepto increase. An increase ofabout 28°C (50°F) in temperature cancause two- to threefoldincrease in creep. Greenwoodmay creepfourto six timesthe initial deforma-

a

tion as it dries under load.

Unloadinga memberresults in immediateand complete recovery ofthe original elastic deformation and aftertime, a recovery ofapproximately one-halfthe creep at deformation as well. Fluctuations in temperatureand humidityincreasethe magnitudeofthe recovereddeformation.

4—38

96 94 92

— Modulus of rupture ———Work

135°C (275°F)

98

a) a)

C(240°F)

102 C a)—.100

.2i

-

a)

104

Cd

93°C

200

250

300 Time of exposure (days) Figure 4—17. Permanenteffectof oven heating at four temperatures on modulus of rupture, based on clear pieces offour softwood and two hardwood species. All tests conducted at room temperature. 0

150

I

16 24 32 Heating period (h) Figure 4—15. Permanent effectof heating in water (solidline)and steam (dashed tine) on modulus of rupture of clear, defect-free wood.All data based on tests of Douglas-fir and Sitka spruce at roomtemperature.

90 88 13'5°C 0

(350°F)

50

I

I

I

100 150 200 250 Time of exposure (days)

300

Figure 4—18. Permanenteffectof oven heating atfour temperatures on modulus ofelasticity,based on clear pieces of foursoftwood and two hardwood species. All tests conducted at roomtemperature. Relative creepat low stress levels is similar in bending, tension, or compression parallelto grain, although itmay be somewhat less intensionthan in bending or compression undervaryingmoistureconditions. Relativecreepacross the grain is qualitatively similar to, but likely to be greater than, creepparallel to the grain.The creep behaviorofall species studiedis approximately the same. Ifinsteadofcontrollingload or stress, a constantdeformation is imposed and maintainedon a wood member,theinitial stress relaxesat decreasingrate to about 60% to 70% ofits originalvaluewithin a few months. This reduction of stress with time is commonly called relaxation.

a

2

Ci)

0 C 0 C) 0

0

Stress

0

MPa 3.4 6.9 13.8 — — 27.6

C) C).

—

..—0

0.8

C)

——

1650f-1 5E

U)

0 0.7 C)-

C) .0 C

><

C) C) CC

0

C)C)

a)

0.6

0

0.5

0

12

24 36 48 Exposure time(months)

60

0

72

Figure 4—19. Permanenteffect of heating at 66°C (150°F) on modulus of rupturefortwo grades of machine-stressrated Spruce—Pine—Firlumberat 12%moisturecontent. Alt tests conducted at roomtemperature.

200

300

400

500

Figure 4—21. Influence of four levels of stresson creep (Kingston 1962).

120

12% moisture content

120

6% and 12% moisture content

0 C)

100

0) CC

100

C

0

80

280

C) 60

CC

C

100

Timeunder load (days)

140

0

x103 lbf/in 0.5 1.0 2.0 4.0

60

C)0

C,

40 C).

40 (C U)

(I, C,

a,

.

C

00

20

20

(C

0

io-

0 100

102

106

108

Timeto ultimate stress (s) 4—20. Figure Relationship of ultimate stressat shorttimeloadingto that at 5-mm loading, based on composite of results from rate-of-loadstudieson bending, compression, and shear parallel to grain. Variability in reported trends is indicated by width of band.

In limitedbendingtests carriedoutbetweenapproximately 18°C (64°F) and 49°C (120°F)over 2 to 3 months, the curve

ofstress as afunctionoftime that expressesrelaxationis approximately themirror image ofthe creepcurve (deformation as a functionoftime).Thesetests were carried out at initialstresses up to about 50% ofthe bending strengthofthe wood.As with creep, relaxationis markedly affectedby fluctuations intemperature and humidity. Duration of Load

The duration ofload, orthe time duringwhich a load acts on a wood membereither continuouslyor intermittently, is an

1 0-6

b-4

10-2

100

102

Timeto failure (h)

10

106

Figure 4—22. Relationship betweenstressdue to constant load and time to failure forsmall clearwood specimens, based on 28 s at 100% stress. The figure is a composite oftrendsfrom several studies; moststudiesinvolved bending but some involved compression parallel to grain and bending perpendicular to grain. Variability in reported trendsis indicated by width of band. important factorin determining the load that the membercan safelycarry. The duration ofloadmaybeaffectedby changes in temperatureand relative humidity.

The constant stress that a wood membercan sustainis approximately an exponential functionoftime to failure,as illustratedin Figure4—22. This relationshipis a composite ofresults ofstudieson small, clearwood specimens, conductedat constanttemperatureandrelativehumidity.

4—39

Foramemberthat continuouslycarriesa load for a long period,the load requiredtoproduce failure is much lessthan that determinedfrom the strengthproperties in Tables4—3 to 4—5. Based on Figure 4—22, a wood memberunderthe

continuous actionofbendingstress for 10 years maycany only 60% (orperhaps less) ofthe load requiredtoproduce failure in the same specimenloadedin a standardbending strengthtest ofonly a few minutesduration. Conversely, if the duration ofloadis very short,theload-carrying capacity maybe higherthan that determined from strengthproperties

given in the tables.

Timeunder intermittentloadinghas a cumulative effect. In tests wherea constant loadwas periodically placedon a beam andthen removed,the cumulativetime the load was actuallyappliedtothe beambefore failure was essentially equalto the time to failurefor a similarbeam underthe same load applied continuously. The time to failure under continuous or intermittent loading is lookedupon as a creep—ruptureprocess; amemberhasto undergo substantial deformation before failure. Deformation at failure is approximately the same for durationofload tests as for standard strengthtests. Changes in climaticconditions increase the rate ofcreepand

shortenthe durationduringwhich a membercan supporta given load. This effect can be substantial for very smallwood specimens under largecyclic changes in temperature and relativehumidity. Fortunately,changesin temperatureand relativehumidityare moderatefor wood in the typicalservice enviromnent.

Fatigue In engineering, the term fatigueis defined as the progressive damagethat occursin amaterial subjected to cyclic loading. This loadingmay be repeated(stressesofthe same sign; that is, always compressionoralways tension)orreversed (stressesofalternatingcompression and tension). When sufficiently high and repetitious, cyclicloadingstresses can result in fatiguefailure.

Fatiguelife is a term used to definethe numberofcyclesthat are sustainedbeforefailure.Fatiguestrength, the maximum stress attainedin the stress cycle usedto determine fatigue life, is approximately exponentially relatedto fatiguelife; that is, fatiguestrengthdecreasesapproximately linearlyas thelogarithm ofnumber ofcyclesincreases. Fatigue strength andfatiguelife also depend on several other factors: frequency ofcycling; repetition or reversalofloading; range factor (ratio ofminimumto maximumstress per cycle); and otherfactors such as temperature,moisturecontent, and specimen size. Negativerange factorsimplyrepeatedreversing loads, whereaspositiverange factors implynonreversing loads. Results from severalfatigue studieson wood are given in Table 4—17.Most ofthese resultsare forrepeatedloading with a range ratioof 0.1, meaningthat the minimumstress per cycle is 10% ofthemaximum stress.The maximum stress per cycle,expressedas a percentage ofestimatedstatic

4—40

Table 4—17. Summary of reported results on cyclic fatiguea Cyclic

Property Bending,dear, straightgrain Cantilever Cantilever Cantilever Center-point Rotational Third-point Bending,third-point Small knots Clear, 1:12 slope

ofgrain

Small knots, 1:12 slope ofgrain Tension parallel tograin Clear, straight grain Clear, straight grain Scarfjoint Fingerjoint

Range

ratio

frequency (Hz)

0.45 0

3) 3) 30

Approximate

Maximum stressper cycleb (%)

life (x106cycles)

45 40 30 30 28

30 30 30 4 30

fatigue

—1.0 —1.0 —1.0 0.1

8-1/3

0.1 0.1

8-1/3 8-1/3

50

2 2

0.1

8-1/3

40

2

40

—

)

2

3)

0.1

15

0

40

0.1 0.1

15 15

50

Compression parallel tograin Clear, straight grain

0.1

40

75

Shear paralleltograin Glue-laminated

0.1

15

45

3.E

30 30

40

3.5

30

alnial moisture contentabout 12%to15%. bPercontageofestimatedstaticstrength.

strength,

is associatedwith the fatigue life given in millions

ofcycles.The firstthree lines ofdata,which listthesame cyclicfrequency (30 Hz), demonstrate the effectofrangeratio on fatiguestrength (maximumfatiguestress that can be

maintained for a given fatiguelife); fatiguebendingstrength decreases as rangeratio decreases. Third-pointbending re-

sults showthe effectofsmallknots orslope ofgrain on fatiguestrength ata range ratio of0.1 and frequency of 8.33 Hz. Fatiguestrengthis lowerfor wood containingsmall knotsor a 1-in-12 slopeofgrainthan for clear straightgrainedwood and evenlowerforwood containinga combination ofsmallknotsand a 1-in-i2 slope ofgrain. Fatigue strengthis the same for a scarfjoint in tensionas for tension parallelto the grain, but alittle lowerfor a fmgerjointin tension. Fatigue strengthis slightlylower in shear than in tensionparallel to the grain. Othercomparisonsdo not have muchmeaningbecauserangeratios or cyclicfrequency differ; however,fatiguestrengthis high in compressionparallelto thegrain compared with other properties. Little is known about otherfactorsthat may affectfatigue strength inwood. Creep,temperature rise, and loss ofmoisturecontentoccur in tests ofwood for fatiguestrength. At stressesthat cause failurein about 106 cyclesat40 Hz, a temperature rise of

15°C (27°F) has beenreportedforparallel-to-grain compression fatigue (range ratio slightlygreaterthan zero),parallelto-graintensionfatigue(rangeratio = 0), and reversed bending fatigue(rangeratio = —1). The rate oftemperature rise is high initially but then diminishes to moderate; a moderate rate oftemperaturerise remainsmore or less constantduring a largepercentage offatiguelife. During the latter stages of fatigue life, the rate oftemperature rise increases until failure occurs. Smaller rises in temperature wouldbe expectedfor slowercyclicloadingor lowerstresses. Decreases in moisture contentare probablyrelatedto temperature rise.

Aging In relatively dry and moderatetemperature conditions where wood is protectedfrom deteriorating influences such as decay, the mechanical propertiesofwoodshow little change with time. Test results for very old timbers suggest that significant losses in clearwood strength occur only after several centuries ofnormal aging conditions. The soundness ofcenturies-old wood in some standing trees(redwood, for example) also attests to the durabilityofwood.

Exposure to Chemicals The effectofchemicalsolutions on mechanical properties depends onthe specific type ofchemical. Nonswel]Ling liquids,such as petroleumoils andcreosote, haveno appreciable effectonproperties. Properties are loweredin the presence ofwater, alcohol, or other wood-swelling organicliquids eventhough these liquids do not chemically degradethe wood substance. The loss in properties depends largelyon the amountofswelling,and this loss is regainedupon removal ofthe swellingliquid.Anhydrousammoniamarkedly reduces the strength and stiffness ofwood,but these proper-

ties are regainedto a great extentwhen the ammoniais removed. Heartwoodgenerallyis less affected thanapwood becauseit ismore impermeable. Accordingly, wood treatments that retard liquidpenetrationusually enhance natural resistance to chemicals.

Chemicalsolutions that decompose wood substance (by hydrolysis or oxidation)havea permanenteffecton strength. The following generalizations summarize the effectof chemicals:

• •

•

Somespecies are quiteresistant to attack by dilute mineral and organic acids. Oxidizing acids such as nitric acid degradewood more than do nonoxidizingacids. Alkalinesolutions are more destructivethanare acidic solutions.

•

Hardwoods are more susceptible to attackby both acids and alkalis than are softwoods.

• Heartwood is lesssusceptible to attack by both acidsand alkalis than is sapwood.

Because both species and application are extremely important, referenceto industrial sources with a specific historyof

use is recommended wherepossible. Forexample,large cypress tanks havesurvivedlong continuous use where exposureconditions involved mixed acids at the boiling point. Woodis also used extensively in cooling 1:owers becauseofits superiorresistance to mild acids and solutions ofacidicsalts.

Chemical Treatment Woodis often treatedwith chemicals to enhance its fire performance or decay resistance in service. Eachset of treatment chemicals andprocesses has a unique effectonthe mechanical properties ofthe treatedwood. Fire-retardant treatments andtreatmentmethods distinctly reducethe mechanical properties ofwood. Somefireretardant-treated products haveexperienced significant inservice degradation on exposure to elevated temperatures whenused as plywood roofsheathingor roof-truss lumber. New performance requirements withinstandards setbythe American Standards forTestingand Materials (A:STM)and American WoodPreservers'Association (AWPA) preclude commercializationofinadequatelyperforming fire-retardanttreated products. Although preservative treatments and treatment methods generally reducethe mechanical properties ofwool,any initial loss in strength from treatmentmust be balanced againstthe progressive loss ofstrength from decay when untreated wood is placed inwetconditions. The effectsof preservative treatments on mechanical propertiesare directly related to wood quality, size, and various pretreatment, treatment, and post-treatment processingfactors.The key factors include preservative chemistry or chemical type, preservative retention, initialkiln-dryingtemperature, posttreatment drying temperature, and pretreatment incising(if required). North American design guidelinesaddress the effects ofincising onmechanical properties ofrefratory wood species andthe short-term duration-of-load adjustments for all treatedlumber. These guidelines are describedin

Chapter6.

Oil-Type Preservatives cause no appreciablestrenglh loss Oil-type preservatives becausethey do not chemically react with wood cell wall components. However,treatment with oil-typepreservatives can adversely affectstrength ifextreme in-retort seasoning parameters are used (for example,Boultonizing, steaming, or vapordryingconditions) or ifexcessivetemperaturesor pressuresare usedduringthetreating process. To preclude strength loss,the usershould follow specific treatment processing requirements as describedin the treatmentstandards.

Waterborne Preservatives Waterbome preservative treatments can reducethe mechanical

properties ofwood. Treatment standards includespecific processingrequirements intendedto preventor liniit strength reductions resulting fromthe chemicals andthe wai;erborne preservative treatment process. The effects ofwaterborne preservative treatmenton mechanical properties are relatedto

4—41

species,mechanical properties, preservative chemistry or type,preservativeretention,post-treatment dryingtemperature, size and grade ofmaterial,producttype, initialkilndryingtemperature, incising, and both temperature and moisturein service. Species—Themagnitude ofthe effectofvarious waterbornepreservativeson mechanical propertiesdoes not appearto vary greatlybetweendifferentspecies. Mechanicalproperty—Waterbornepreservatives affect eachmechanical property differently. Iftreatedaccording to AWPAstandards,the effectsare as follows: modulusof elasticity(MOE), compressivestrengthparallel to grain, and compressive stress perpendicular to grain areunaffected or slightlyincreased; modulusofrupture (MOR) and tensile strengthparallelto grain are reducedfrom 0% to 20%, dependingon chemicalretentionand severityofrediying temperature; andenergy-related properties (for example, work to maximumload and impact strength)are reduced from l0%toSO%. Preservative chemistry ortype—Waterbornepreservative chemical systemsdiffer in regardto their effecton strength, but the magnitudeofthese differences is slight compared with the effectsoftreatmentprocessing factors. Chemistryrelated differences seem to be related tothe reactivity ofthe waterborne preservativeandthe temperature during the fixation/precipitation reactionwith wood. Retention—Waterbomepreservative retention levels of 6 kg/rn3 ( 1.0 lb/fl3)have no effecton MOE or compressive strengthparallelto grain and a slight negative effect (—5% to —10%) on tensile or bending strength. However, energy-related properties are often reducedfrom 15% to 30%.At a retentionlevel of40 kg/rn3(2.5 lb/ft3), MORand energy-related properties are further reduced.

l

Post-treatment drying temperature—Air drying after treatmentcausesno significantreductionin the static strengthofwood treatedwith waterbome preservative at a retentionlevel of 16 kg/rn3(1.0 lb/fl3). However, energyrelatedproperties are reduced. Thepost-treatment redrying temperature used formaterial treatedwith waterborne preservative has been found to be criticalwhentemperatures exceed 75°C (167°F). Redryinglimitationsin treatment standards haveprecluded the need foran across-the-board designadjustment factorfor waterborne-preservative-treated lumberin engineeringdesignstandards.The limitationon post-treatmentkiln-dryingtemperature is setat 74°C (165°F).

Size ofmaterial—Generally,largermaterial, specifically thicker, appearsto undergo less reductionin strengththan does smallermaterial.Recallingthat preservative treatmentsusuallypenetratethe treatedmaterial to adepth of only 6 to 51 mm (0.25 to 2.0 in.), dependingon species and other factors, the difference in size effect appears to be afunctionoftheproduct's surface-to-volume ratio,which

4—42

affects the relative ratio oftreatment-induced weightgain to originalwood weight.

Gradeofmaterial—Theeffectofwaterbome preservative treatment is aquality-dependent phenomenon. Higher grades ofwood are more affected thanlowergrades. When viewed over a range ofquality levels,higher qualitylumber is reducedin strength to aproportionately greater extentthan is lower qualitylumber.

Producttype—The magnitudeofthetreatmenteffecton strength for laminated veneerlumberconfonns closely to

effects noted forhighergradesofsolid-sawn lumber. The effects ofwaterbome preservative treatment onplywood seem comparable to that on lumber. Fiber-basedcomposite productsmay be reducedin strength to a greater extent than is lumber. This additional effecton fiber-basedcompositesmaybe more functionofinternalbond damage caused by waterborne-treatment-induced swelling rather than actualchemical hydrolysis.

a

Initial kiln-drying temperatnre—Although initialkiln dryingofsome lumberspecies at 100°Cto 116°C (212°F to 240°F) for short durations has little effect on structural properties, such drying resultsin more hydrolyticdegradation ofthe cell wall than does dryingat lowertemperature kiln schedules. Subsequent preservativetreatment and redrying ofmaterial initially dried at high temperatures causes additional hydrolyticdegradation. Whenthe material is subsequently treated,initialkilndrying at 113°C (235°F) has been shown to result in greaterreductionsover the entirebendingand tensile strengthdistributions than does initialkiln drying at 91°C (196°F). Because Southern Pine lumber, the most widelytreated product,is most ofteninitially kiln dried at dry-bulbtemperatures near or above 113°C (235°F),treatmentstandardshave imposed a maximum redrying temperaturelimitof74°C (165°F) to preclude the cumulative effectofthermalprocessing. Incising—Incising, a pretreatment mechanical process in whichsmallslits(incisions) arepunchedin the surface of thewood product,is used to improvepreservativepenetration and distributionin difficult-to-treat species. Incising mayreducestrength; however, becausethe increase in treatability providesa substantial increase in biological performance, this strengthloss must be balancedagainst theprogressiveloss in strengthofuntreatedwood from the incidence ofdecay.Most incisingpatternsinducesome strengthloss,and the magnitudeofthis effect is relatedto thesize ofmaterial being incisedandthe incisiondepth and density(that is, number ofincisionsperunitarea). In less than 50 mm(2 in.) thick, dry lumber, incisingand preservative treatmentinduces lossesin MOE of5% to 15% and in staticstrengthpropertiesof20% to 30%. Incising and treatingtimbersortie stock at an incisiondensity of ,500 incisions/rn2 140 incisions/fl2) andto a depth of 19 mm (0.75 in.) reduces strengthby 5% to 10%.

l

(

In-serviceternperature—Both fire-retardantand preservative treatments accelerate thethermaldegradation of bendingstrengthoflumberwhenexposedtotemperatures above 54°C (130°F). In-servicemoisturecontent—Currentdesignvalues apply

to material dried to 19% maximum(15%average)mois-

ture content or to green material. No differences in strength havebeen found betweentreatedanduntreatedmaterial whentested green or atmoisture contents above 12%. Whenvery dry treatedlumberofhigh gradewas tested at 10% moisturecontent,its bending strength was reduced compared with that ofmatched dry untreatedlumber. Durationof load—Whensubjectedto impact loads, wood treated with chromated copperarsenate (CCA)does not exhibitthe same increase in strengthas that exhibited by untreatedwood. However, whenloadedover along period, treatedanduntreatedwood behavesimilarly.

Polymerization Wood is also sometimesimpregnatedwith monomers, such as methyl methacrylate, which are subsequently polymerized. Many ofthemechanicalpropertiesofthe resultantwood— plasticcompositeare higherthan those ofthe originalwood, generallyas a result offillingthe void spaces inthe wood structure with plastic. The polymerization process andboth thechemical nature andquantity ofmonomersinfluence compositeproperties.

Nuclear Radiation Wood is occasionallysubjected to nuclear radiation. Examplesare woodenstructures closely associatedwith nuclear reactors, the polymerizationofwood with plasticusing nuclearradiation,and nondestructive estimation ofwood density and moisturecontent. Verylarge doses ofgamma rays orneutronscan cause substantial degradation ofwood. In general, irradiation with gammarays in doses UI) to about 1 megaradhas little effect on the strength properties ofwood. As dosageexceeds 1 megarad,tensilestrength parallelto grain and toughnessdecrease. At a dosageof300 megarads,

tensilestrengthis reducedabout 90%. Gammarays also affectcompressive strengthparallel to grainat a dosageabove 1 megarad, but higherdosagehas agreatereffectontensile strengththan on compressivestrength; only approximately one-thirdofcompressivestrengthis lost whenthe total dose is 300 megarads. Effectsofgammarays on bendingand shear strengthare intermediate between the effects on tensile and compressivestrength.

Mold and Stain Fungi Moldandstainfungidonot seriously affectmost mechanical properties ofwoodbecausesuch fungifeedon substances withinthe cell cavityor attachedto the cell wall rather than on the structural wall itself.The durationofinfection and the species offungi involved are important factors in determining theextentofdegradation.

Although low levels ofbiologicalstaincause little loss in strength, heavystainingmayreduce specificgravty by 1% to 2%, surfacehardnessby 2% to 10%, bending and crushing strength by 1% to 5%, and toughnessor shock resistanceby 15% to 30%.Althoughmolds and stainsusually do not have amajor effecton strength, conditions that favorthese organismsalsopromotethe development ofwood-destroying (decay) fungiand soft-rotfungi (Ch. 13). Pieceswith mold and stainshouldbe examined closely for decay ifthey are used for structural purposes.

Decay Unlike mold and stain fungi, wood-destroying (decay) fungi seriously reduce strength by metabolizing the cellulose fraction ofwood that gives wood its strength.

Earlystages ofdecay are virtuallyimpossible to detect.For example, brown-rot fungimayreducemechanical properties in excess of 10% beforea measurable weightloss is observed andbefore decay is visible.Whenweight loss reaches5% to 10%, mechanical properties arereducedfrom 2O% to 80%. Decayhas the greatesteffect on toughness, impact bending, and work tomaximumload in bending, the least effecton shear and hardness, and an intermediate effecton etherproperties. Thus,when strengthis important, adequate measures shouldbe takento (a) preventdecay beforeit occurs, (b) controlincipientdecay by remedialmeasures(Ch. 13), or (c)replaceany wood memberin whichdecayis evidentor believed to existin a criticalsection. Decay can be prevented from starting or progressing ifwood is kept dry (below20% moisture content).

Nomethodis knownfor estimatingthe amount ofreduction in strength from the appearance ofdecayed wood. Therefore, whenstrength is an importantconsideration, the sLfeprocedure is to discardevery piece that contains evena small amount ofdecay.An exception may be piecesinwhichdecay occurs in a knot but does not extend into the surrounding

wood.

Insect Damage Insect damage may occur in standingtrees, logs, and undried (unseasoned) ordried (seasoned) lumber. Althoughdamage is difficultto controlin thestandingtree, insectdamage can be eliminatedto agreat extentby propercontrolmethods. Insectholesare generallyclassified as pinholes,giub holes, andpowderpost holes.Becauseoftheirirregularburrows, powderpost larvae may destroymost ofa piece's interior while only smallholes appearon the surface,andthe strength ofthe piece may be reducedvirtually to zero. No methodis known for estimating the reductionin strength from the appearance ofinsect-damaged wood.Whenstrength is an important consideration, the safeprocedureis to eliminate pieces containing insectholes.

4—43

References ASTM. [Current edition}. Standardmethods for testing small clear specimensoftimber. ASTM D143-94.West Conshohocken, PA: American Society for Testing and Materials.

Bendtsen, B.A. 1976.Rollingshear characteristics ofnine structuralsoftwoods. Forest ProductsJournal. 26(11): 51—56. Bendtsen, B.A.; Freese, F.; Ethington,R.L. 1970. Methods for sampling clear, straight-grained woodfrom the forest. Forest Products Journal. 20(11): 38—47. Bodig, J.; Goodman, J.R. 1973. Predictionofelastic parametersfor wood. WoodScience.5(4): 249—264. Bodig, J.; Jayne, BA. 1982. Mechanics of wood and wood composites. New York: Van NostrandReinhold Company. Boiler, K.H. 1954. Wood at low temperatures. Modem Packaging.28(1): 153—157. Chudnoff, M. 1987. Tropicaltimbers of the world. Agric. Handb. 607. WashingtonDC: U.S. Department of Agriculture.

Coffey, D.J. 1962. Effects ofknots and holes on the fatigue strengthofquarter-scale timberbridgestringers. Madison, WI: UniversityofWisconsin,DepartmentofCivil Engineering.M.S. Thesis. Gerhards,C.C. 1968. Effectsoftype oftesting equipment and specimen size on toughnessofwood. Res. Pap. FPL— RP—97. Madison, WI: U.S. Department ofAgriculture, Forest Service,Forest Products Laboratory.

Gerhards,C.C. 1977. Effect ofduration and rate ofloading on strengthofwood and wood based materials.Res. Pap. WI: U.S. Department ofAgriculture, Forest Service,Forest ProductsLaboratory. Gerhards,C.C. 1979. Effectofhigh-temperature drying on tensile strengthofDouglas-fir2 by 4's. Forest Products Journal. 29(3): 39—46. FPL—RP—283. Madison,

Gerhards,C.C. 1982. Effectofmoisturecontentand temperature on themechanicalpropertiesofwood: an analysis of immediateeffects. WoodandFiber. 14(1): 4—36. Green,D.W.; Evans,J.W. 1994. Effectofambienttemperatureson the flexural propertiesoflumber. In: PTEC94 Timbershapingthe future: Proceedings, Pacifictimberengi-

Green,D.W.; Shelley,B.E.; Vokey, H.P. (eds). 1989. In-grade testingofstructural lumber. Proceedings 47363. Madison, WI: Forest ProductsSociety.

Hearmon, R.F.S. 1948. The elasticityofwood and plywood. Special Rep. 7. London,England: Department of Scientific and Industrial Research, ForestProductsResearch. Hearmon, R.F.S. 1961. An introductionto applied anisotropic elasticity. London, England: OxfordUniversityPress. Kingston, R.S.T. 1962. Creep, relaxation,and failure of wood.ResearchAppliedin Industry. 15(4). Kollmann, F.F.P.; Cote, W.A., Jr. 1968. Principlesof woodscienceand technology. New York: SpringerVerlag. Koslik, C.J. 1967. Effect ofkiln conditions on the strength ofDouglas-firand westernhemlock. Rep. D—9. Corvallis, OR: OregonState University, SchoolofForestry,Forestry Research Laboratory.

Little, E.L., Jr. 1979. Checklist of United States trees (nativeand naturalized). Agric. Handb. 541. Washington, DC: U.S. Department ofAgriculture. Kretschmann, D.E.; Bendtsen, B.A. 1992. Ultimate tensile stress and modulusofelasticityoffast-grown plantationloblollypine lumber. Woodand Fiber Science. 24(2): 189—203.

Kretschmann, D.E.; Green, D.W. 1996. Modelingmoisture content—mechanicalproperty relationships for clear Southern Pine. Wood and Fiber Science.28(3): 320—337. Kretschmann, D.E.; Green, D.W.; Malinauskas, V. 1991. Effect ofmoisture content on stress intensity factors in SouthernPine. In: Proceedings, 1991 international timber engineering conference; 1991 September 2—5; London. London: TRADA: 3.391—3.398. Vol. 3.

LeVan, S.L.; Winandy, J.E. 1990. Effects offire-retardant treatments on wood strength: a review. Wood and Fiber Science.22(1): 113—13 1. MacLean, J.D. 1953. Effectofsteamingon the strength or wood.AmericanWood-Preservers' Association. 49: 88—112. MacLean, J.D. 1954. Effectofheatingin water on the strengthpropertiesofwood.AmericanWood-Preservers' Association.50: 253—281. Mallory, M.P.; Cramer S. 1987. Fracture mechanics: a tool

forpredicting ood component strength. Forest Products

neeringconference; 1994 July 11—15; GoldCoast,Australia. FortitudeValley MAC, Queensland,Australia: Timber ResearchDevelopment andAdvisoryCouncil: 190—197. Vol. 2.

Journal. 37(7/8): 39—47.

Green, D.W.; Rosales, A. 1996. Propertyrelationships for tropical hardwoods. In: Proceedings, international wood engineering conference; 1996October21—3 1; New Orleans, LA. Madison, WI: Forest Products Society: 3-516—3-521.

McDonald,K.A.; Bendtsen, B.A. 1986. Measuringlocalized slopeofgrain by electrical capacitance. Forest Products

4—44

Mark, R.E.; Adams, S.F.; Tang, R.C. 1970. Moduli of rigidity of Virginiapine and tulip poplar relatedto moisture content. WoodScience.2(4): 203—211.

Journal. 36(10): 75—78.

McDonald, K.A.; Hennon,P.E.; Stevens, J.H,.; Green, D.W. 1997. Mechanicalpropertiesofsalvaged yellow-cedar in southeasternAlaska—Phase I. Res. Pap. FPL—RP---565.Madison,WI: U.S. Department ofAgriculture, Forest Service,Forest ProductsLaboratory. Millett, M.A.; Gerhards,C.C. 1972. Acceleratedaging: residualweightand flexuralpropertiesofwood heatedin air at 115°C to 175°C. Wood Science. 4(4): 193—201. Nicholas,D.D. 1973. Wood deterioration and its prevention by preservativetreatments. Vol. I. Degradation and protectionofWood. Syracuse,NY: SyracuseUniversityPress. Pillow, M.Y. 1949. Studiesofcompressionfailures and their detection in ladder rails. Rep. D 1733. Madison, WI: U.S. Department ofAgriculture,Forest Service,Forest Products Laboratory.

Sliker, A.; Yu, Y. 1993. Elastic constants for hardwoods measuredfrom plate and tensiontests. Woodand Fiber Science.25(1): 8—22. Sliker, A.; Yu, Y.; Weigel, T.; Zhang,W. 1994. Orthotropic elasticconstantsfor easternhardwood species. Wood and Fiber Science.26(1): 107—121. Soltis, L.A.; WinandyJ.E. 1989. Long-termstrength of CCA-treatedlumber. Forest Products Journal. 39(5): 64—68. Timell, T.E. 1986. Compressionwood in gymncsperms. Vol. I—Ill. Berlin: Springer—Verlag. U. S. DepartmentofDefense. 1951. Design ofwood aircraft structures. ANC—l8 Bull. Subcommittee on Air Force— Navy CivilAircraft,Design CriteriaAircraftCommission. 2d ed. MunitionsBoard AircraftCommittee.

Wangaard,F.F. 1966. Resistanceofwood to chemical degradation.Forest Products Journal. 16(2): 53—64.

Wilcox,W.W. 1978. Reviewofliterature on the effects of earlystagesofdecay onwood strength. Woodand Fiber. 9(4): 252—257.

Wilson, T.R.C. 1921. The effectof spiral grain onthe strength ofwood. Journal ofForestry. 19(7): 740—747. Wilson, T.R.C. 1932. Strength-moisture relationsfor wood. Tech. Bull. 282. Washington,DC: U.S. Department of Agriculture.

Winandy, J.E. 1995a. Effects ofwaterborne preservative treatment on mechanical properties: A review.In: Proceedings,91st annualmeetingofAmerican WoodPreservers' Association; 1995, May 21—24; New York, NY. Woodstock,MD: American WoodPreservers'Association. 91: 17—33. Winandy, J.E. I995b. The Influenceoftime-to-failure on thestrength ofCCA-treated lumber. Forest Products Journal. 45(2): 82—85.

Winandy, J.E. 1995c. Effectsofmoisturecontent on strengthofCCA-treated lumber. Woodand Fiber Science. 27(2): 168—177.

Winandy, J.E. 1994. Effectsoflong-term elevatedtemperature on CCA-treated SouthernPine lumber. Forest Products Journal. 44(6): 49—55.

Winandy, J.E.; Morrell, J.J. 1993. Relationshipbetween incipientdecay,strength, and chemical composition of Douglas-firheartwood. WoodandFiber Science. 25(3):278—288. Woodfin, R.O.; Estep, E.M. (eds). 1978. In: The dead timberresource. Proceedings, 1978May 22—24, Spokane, WA. Pullman, WA: EngineeringExtensionService, Washington State University.

4—45

I

Chapter

5

Commercial Lumber Kent A. McDonald and David W. Green

n a broadsense, commercial lumberis any lumber

Contents HardwoodLumber 5—1

Factory Lumber 5—2 Dimensionand ComponentParts

5—2

FinishedMarketProducts 5—6 Lumber Species 5—7

SoftwoodLumber 5—7 LumberGrades 5—7 LumberManufacture

5—10

SoftwoodLumberSpecies

5—12

SoftwoodLumberGrading 5—12 Purchase ofLumber 5—12

Retail Yard Inventory

5—16

ImportantPurchaseConsiderations 5—17 CommonlyUsed LumberAbbreviations 5—18 Reference

5—20

that is bought or sold in the normalchannelsof commerce. Commercial lumbermay be found in a variety offorms,species,and types,and in various commercial establishments, both wholesaleand retail. Most commerciallumberis gradedby standardized rules that make purchasingmore or less uniformthroughout the country. When sawn, a logyields lumberofvarying quaLity.To enableusers to buy the quality that best suits their purposes, lumberis gradedintouse categories, each havingan appropriate range in quality. Generally, the grade ofa pieceoflumberis basedonthe number, character, and location offeaturesthat may lowerthe strength, durability, orutility valueofthe lumber. Among themore common visual featuresare knots, checks,pitch pockets, shake, and stain, some ofwhichare a naturalpart of thetree. Somegrades arefree orpractically free fromthese features. Other grades, whichconstitute the greatbulk of lumber, containfairlynumerous knotsand other features. With proper grading,lumbercontaining these featuresis entirelysatisfactory formanyuses.

The gradingoperationformost lumbertakes place at the sawmill. Establishment ofgradingprocedures is largelythe responsibility ofmanufacturers' associations. Beause ofthe wide varietyofwoodspecies,industrial practices,and customer needs, differentlumbergradingpracticescoexist. The gradingpractices ofmost interestare considered in the sections that follow,underthe major categories ofhardwood lumberand softwood lumber.

Hardwood Lumber The principaluse ofhardwoodlumberis forremanufacture into furniture,cabinetwork, andpallets, or directuse as flooring, paneling, moulding,and miliwork.Hardwood lumberis gradedandmarketedin three main categories: Factorylumber, dimension parts, and fmishedniarketproducts. Several hardwood species are gradedunderthe AmericanSoftwood LumberStandardand sold as structural lumber

(Ch. 6). Also, speciallygradedhardwoodlumbercan be used

forstructural glued-laminated lumber.

5—1

Prior to 1898, hardwoodswere gradedby individual mills for local markets. In 1898, manufacturers and users formed theNationalHardwoodLumberAssociation to standardize grading for hardwoodlumber. Between 1898and 1932, gradingwasbased onthe number and size ofvisualfeatures. In 1932, the basis for gradingwas changed to standard clearcutting sizes. Both Factory lumberand dimensionparts are intended to servethe industrialcustomer. The important difference is that forFactorylumber, the gradesreflectthe proportion ofapiece that can be cut into useful smallerpieces,whereas the grades fordimensionparts are based on use ofthe entirepiece. Finishedmarket productsare graded fortheir unique end-use with little orno remanufacture. Examples offmished products include moulding, stair treads, and hardwoodflooring.

Factory Lumber Grades Therulesadopted by theNationalHardwoodLumberAssociation are considered standardin gradinghardwoodlumber intendedfor cutting into smallerpiecesto make furniture or other fabricatedproducts.In these rules,the grade ofapiece ofhardwoodlumber is determined by theproportionofa piece that can be cut into a certainnumberofsmallerpieces ofmaterial,commonlycalled cuttings, which are generally clearon one side, havethe reverseface sound, and arenot smallerthan a specifiedsize. The best grade in the Factory lumbercategoryis termed FAS. The second grade is F1F. The third grade is Selects, which is followedby No. 1 Common, No. 2A Common, No. 2B Common,Sound Wormy, No. 3A Common,and No. 3B Common. Except for FiF and Selects, the poorer sideofa piece is inspectedforgrade assignment. Standard hardwoodlumbergradesare describedin Table 5—1. This table illustrates, for example,that FAS includespiecesthat will allow at least 83-1/3% oftheirsurface measure to be cut into clear face material.Except for SoundWormy, the minimum acceptable length,width,surface measure, and percentage ofpiece that must work into acutting decreasewith decreasing grade.Figure5—1 is anexampleofgrading for cuttings.

This briefsummaryofgrades for Factorylumbershouldnot beregardedas a complete set ofgradingrules becausemany details, exceptions, and specialrules for certainspecies are not included. The complete official rules ofthe National HardwoodLumberAssociation (NHLA)shouldbe followed as theonly fulldescriptionofexistinggrades(see Table5—2 foraddressesofNHLA and other U.S. hardwoodgrading associations). Table 5—3 lists names ofcommercial domestic hardwoodspecies that are gradedby NHLArules.

Standard Dimensions Standard lengthsofhardwoodlumberare in 300-mm (1-ft) increments from 1.2 to 4.8 m (4 to 16 ft). Standardthickness

valuesforhardwoodlumber, rough and surfaced on two sides (S2S), are given in Table 5—4. The thicknessof SiS lumber

5—2

is subject to contractagreement. Abbreviations commonly used in contracts and other documents forthe purchaseand sale oflumberare listedatthe end ofthis chapter. Hardwoodlumberis usually manufacturedto randomwidth. The hardwoodlumbergradesdo not specify standardwidths; however, the grades do specify minimumwidthforeach grade as follows: Grade FAS

F1F Selects No. 1, 2A, 2B, 3A, 3B Common

Minimum width (mm(in.)) 150 (6) 150 (6) 100 (4) 80 (3)

Ifthewidthis specifiedby purchaseagreement, SiE or S2E

lumber is 10 mm (3/8 in.) scant ofnominal size in lumber less than 200 mm (8 in.) wide and 13 mm (1/2 in.) scant in lumber 200 mm in.) wide.

Dimension and Component Parts The term "dimensionparts" for hardwoodssignifies stock

that is processedin specificthickness,width, and length,or multiples thereofand ranges from semi-machined to completelymachinedcomponentproducts. This stock is sometimesreferredto as "hardwooddimension stock"or "hardwoodlumberfor dimension parts." This stock should not be confusedwith "dimensionlumber," a term used in thestructural lumbermarketto meanlumber standard 38 mm to less than 114 mm thick (nominal2 in. to less than 5 in. thick). Dimensioncomponent parts are normallykilndried and generallygradedundertherules ofthe WoodComponents Manufacturers Association (WCMA). These rules encompass three classes ofmaterial, each ofwhichis classifiedinto variousgrades: Hardwood dimension parts (flat stock) Clear two faces Clearone face Paint Core

Solid kilndried squares (rough) Clear Select Sound

Solid kiln-dried squares (surfaced)

Clear Select

Paint Second

Sound

Eachclassmaybe further definedas semifabricated (roughor surfaced) orcompletely fabricated, including edge-glued panels. The rough wood component parts are blank-sawn and rippedto size. Surfaced semifabricated parts havebeen throughone ormore manufacturingstages. Completely fabricated parts havebeencompletely processed fortheir end use.

Table 5—i. Standardhardwood lumbergrades Minimum Allowable

surface Grade and allowable lengths

Allowable width (in.)

amount of piece in

measure of pieces

clearface

(ft2)

(%)

cuttings

I

4to9 FASC

6+

10 to 14

83-1/3

2 3 1

16+

83-1/3 91-2/3 83-1/3 91-2/3 83-1/2 91-2/3 83-1/3

2 and 3

91-2/3

15+

4to7 6and7

8toll F1FC

6+

Selects

6tol6ft(willadniit30%of6tollIt)

4+

8 to 11 12to15 12to15

4+

1

2

No.

I Common

4to l6ft(willadmit 10%of4to7ft,

100 75

66-2/3 50 66-2/3 50 66-2/3 50 66-2/3 50 50

1 1

50 50

6

14+

3+

1+

33l/3

3÷

1+

25h

1

No. 2 Common

3+

1/3 of which may be 4 and 5 It)

2and3 2 and 3 4and5 4 and 5 6and7 6 and 7 8and9

lOandlI l2andl3 Sound Wormye No. 3A Common

Sound Wormye No. 3B Common

3 in. by 7 ft

4 in. by 5 ft, or

3tn.by7ft

by5ft,or

3 in. by 7 ft

0 2 2 3 3 4 5

5to7 5to7 8tolO

41n.by5ft,or

. 1

75 66-2/3 75 66-2/3 66-2/3 66-2/3

3+

14+

4 to 16 ft (will admit 50% of4 to 7 It, 1/2 ofwhich may be 4 and 5 It)

3 4 4

1 1

lltol3

4to 16 ft(will admit 50% of4 to 7ft, 1/2 of which may be 4 and Sit)

2 2

66-2/3

3 and4 3 and 4

1/2ofwhichmaybe4and5ft)

4to l6ft(willadmit30%of4to7ft,

Allowable cuttings Maximum no. Minimum size

2 2 3 3 4 4 5

in. by2ft, or

3in.by3ft

3m. by2ft

7

3 in. by2 ft

—

1-1/2 in. by 2 ft

acurrent grading rules are written only in the inch—pound system of measurement. binspection made on poorer side of piece, except in Selectsgrade. CFAS is a grade that designatesFirsts and Seconds. F1F is a grade that designates FAS one face. dSame as Fl F, with reverse side of board not below No. Common or reverse side of sound cuttings. eSame requirementsas those for No. I Common and better except that wormholesand limited sound knots and other imperfectionsare allowed in cuttings. Also admits pieces that grade not below No. 2 Common on the good face and reverse side of sound cuttings.

I

9Unlimited.

hcuttings must be Sound; clear face not required.

5—3

CuttingNo. 1 —3-1/2 in. by 4-1/2ft = 15-3/4 units I—

Cuthng No. 2—8-1/2 in. by 4-1/2 It

38-1/4 units

t'

Cutting No. 3—4-1/2 in. by 4-1/2ft

= 20-1/4 units ---—----._—f = 34 units

CuttingNo. 4—6in. by 5-2/3 ft

12ft.

1. DetermineSurfaceMeasure(S.M.)using lumber scale stick or from formula: Width in inchesx length in feet 12 in. 2ft

xl

12

12

5. Determine clear-facecuttingunits needed. For No. 1 Common grade S.M. x8 = 12x8

96 units

6. Determine total area of permitted clear-face

12ft2S.M.

cutting in units. Width in inches and fractionsof inches x length in feetand fractionsof feet Cutting #1—3½in. x 41/21t= l5¾units

2. No. 1 Common is assumed grade of board. Percentof clear-cutting area required for No.1 Common—66213%or 8/12. 3. Determine maximumnumberof cuttings permitted. For No. 1 Common grade (S.M. + 1) . (12 + 1) = 13 4 cuttings. 3

—

Cutting#2—81/2 Ifl.X 41,2 ft =38 UflitS Cutting#3_41/2in. x 41,2 ft = 20',d units Cutting#4—61n. x 53ft=34__units 108 Total Units Unitsrequiredfor No. 1 Common—96.

.3

3 4. DetermIne minimumsizeof cuttings.

x2 ft or 3 in.x3 ft.

For No. 1 Commongrade 4 in.

7. Conclusion: Board meets requirementsfor No. 1 Common grade.

I

Figure 5—1. Example of hardwood gradingforcuttingsusingNo. Common lumbergrade. Current grading rules are written only in the inch—pound systemofmeasurement.

Table 5—2. Hardwood gradingassociations in UnitedState? Name and address

Species covered by grading rules (products)

National HardwoodLumberAssociation P.O. Box 34518 Memphis,TN 38184—0518

All hardwood species (furniturecuttings, constructionlumber,

Wood Components ManufacturersAssociation 1000 Johnson Ferry Rd., SuiteA-130 Marietta, GA 30068

All hardwood species(hardwood furnituredimension, squares,

Maple Flooring ManufacturersAssociation 60 Revere Dr., Suite 500

Maple, beech, birch (flooring)

Northbrook,

siding, panels)

laminated stock, interior trim, stair treads and risers)

IL 60062

National Oak Flooring Manufacturers Association P.O. Box 3009 Memphis,TN 38173—0009

Oak, ash, pecan, hickory, pecan, beech, birch, hard maple (flooring,including prefinished)

www.nofma.org

aorading associationsthat include hardwood species in structuralgrades are listed in Table 5—5.

5-4

Table 5—3. Nomenclature of commercial hardwood lumber Commercial namefor lumber Alder, Red Ash, Black Ash,Oregon Ash, White

Aspen (popple)

Basswood Beech

Birch

Box Elder Buckeye Butternut

Cherry Chestnut Cottonwood

Cucumber Dogwood

Elm, Rock

Elm, Soft Gum Hackberry Hickory

Holly lronwood Locust

Madrone Magnolia Maple, Hard

Common tree name

Botanicalname

Redalder

Alnusrubra

Black ash

Fraxinus nigra Fraxinus Jatifolia Fraxinus quadrangulafa Fraxinus pennsyivanica Fraxinus americana Populusgrandklèntata

Oregon ash Blue ash Green ash Whiteash Bigtoothaspen Quakingaspen American basswood Whitebasswood American beech Graybirch Paper birch Riverbirch Sweet birch Yellow birch Boxelder Ohiobuckeye Yellow buckeye Butternut Black cherry American chestnut Balsam poplar Easterncottonwood Black cottonwood Cucumbertree Flowering dogwood Pacific dogwood Cedar elm

Commercial namefor lumber

Common tree name

Botanicalname

Maple,Oregon Maple,Soft

Bigleafmaple Red maple

Acer macrophyllum Acer nibrum Acer sacchannurn

Oak, Red

Popu/us tremuloides Ti/ia americana Ti/iaheterophylla Fagusgrandifolia Betula popu/ifolia Betula papyrifera Betula n/gm Betulalenta Beta/aalleghanier?sis

Acernegur,do

Aesculus glabra Aesculus octandra ,Juglanscinema Prunus semtina Castaneadentafa Populus balsamifera Populusdeltoides Populus trichocaipa Magnolia acum/nata Comus florida Comus nut/al/il U!mus crassifolia U/mus thomas/i Rockelm Ulmus serotina September elm Ulmus alata elm Winged Ulmus americana American elm Ulrnus rubra Slippery elm Sweetgum Liquidambar syracfflua Ce/f/soccidentalis Hackberry Ce/f/slaevigata Sugarberry Mockernut hickory Carya tomentosa Pignut hickory Car'a glabra Shagbark hickory Car/aovata Sheilbark hickory Can/a Iacinosa hexopaca American holly Eastern hophombeam Ostrya virginiana Robiniapseudoacacia Blacklocust Gleditsia triacanthos Honeylocust Arbutus menziesii Pacific madrone Southern magnolia Magnolia grand/flora Sweetbay Magnolia virginiana Blackmaple Acer nigrum Acer saccharum Sugar maple

Oak, White

Oregon Myrtle Osage Orange

Pecan

Silver maple Black oak Blackjackoak Califomia blackoak Cherrybark oak Laurel oak Northern pin oak Northern red oak Nuttall oak Pinoak Scarlet oak Shumard oak Southern red oak Turkeyoak Willowoak Arizona whiteoak Blueoak Bur oak Valley oak Chestnutoak Chinkapinoak Emory oak Gambel oak Mexicanblue oak Liveoak Oregon whiteoak Overcup oak Postoak Swamp chestnutoak Swamp whiteoak Whiteoak California-laurel Osage-orange Bitternut hickory Nutmeg hickory Waterhickory

Pecan Persimmon Poplar Sassafras Sycamore

Common persimmon Yellow-poplar Sassafras Sycamore

Tanoak

Tanoak

Tupelo

Walnut

Black tupelo, blackgum Ogeectieetupelo Water tupelo Black walnut

Willow

Blackwillow Peachleaf willow

Quercus ye/ut/na Quercus marl/andica Quercus kelloggi Querousfalcaf&var. pagodaefolia Quercus laurifo'ia Quemus el/ipsoida/is Quercusrubra Quercus nuttalli Quercuspalustris Quercuscoccinea Queivus shumadii Queicus falcata Quemus laevis Quercusphellos Quercus arizonka QUe1tJSdoug!aü Quercus macmcaipa Querous !obata Quercusprinus Quercusmuehlenbergii Queivus emotyi Quercus gambeil Quercusoblongifo/ia Quercus virginians Quercusgariyana Quemus lyrata Querous ste/late Quercus michauxä Quercus bicoior Quercusa/ba Urnbellularia califcmica Maclura pomifera Cwya cordiformis Can/amyristiciformis Can/a aquatica Can/a illlnoensis Diospyros virgin/era Liriodendron tu/ipifera Sassafras albidum Platanus occidentaifS Lithocarpusdensiflorus Nyssasylvatica Nyssa ogethe Nyssa aquafica Juglans nigra Salixn/gre Sa/ixamygdaloides

5—5

Table 5—4. Standard thickness values for roughand surfaced (S2S) hardwoodlumber Rough

(mm 9.5 12.7 15.9 19.0

25.4 31.8 38.1

44.4 50.8 63.5 76.2 88.9 101.6 114.3 127.0

139.7 152.4

(in.)) (3/8) (1/2) (5/8) (3/4) (1) (1-1/4) (1-1/2) (1-3/4) (2) (2-1/2) (3) (3-1/2) (4) (4-1/2) (5) (5-1/2) (6)

Surfaced (mm (in.)) 4.8

7.9 9.4 14.3

20.6 27.0 33.3 38.1

44.4 57.2 69.8

82.8 95.2

(3/16) (5/16) (7/16) (9/16) (13/16) (1-1/16) (1-5/16) (1-1/2) (1-3/4) (2-1/4) (2-3/4) (3-1/4) (3-3/4) a

8Finished size not specified in rules. Thickness subject to special contract.

•

Secondgrade—tight, soundknots (except on edges or ends)and other slight imperfections allowed;must be possibleto lay flooringwithoutwaste

•

Third grade—may contain all visual featurescommonto hard maple, beech, and birch; willnot admit voids on edgesor ends, or holes over 9.5-mm (3/8-in.)in diameter;must permitproperlaying offloor andprovide a serviceable floor; few restrictions on imperfections; must be possibleto lay flooringproperly

•

Fourth grade—may containall visual features,butmust be possibleto laya serviceablefloor, with some cutting

Combination grades of"Secondand Better" and "Third and Better" are sometimes specified. There are also specialgrades based on color and species.

The standardthicknessofMFMA hard maple, beech, and birch flooringis 19.8 mm (25/32 in.). Face widths are 3S, 51, 57, and 83 mm (1-1/2, 2, 2-1/4, and 3-1/4 in.). Standard lengths are 610 mm (2 ft) and longer in First- and Secondgrade flooringand 381 mm(1-1/4ft) and longer in Thirdgrade flooring.

The Official FlooringGradingRules ofNOFMAcoveroak (unfinished and prefmished), beech,birch, hard maple, ash, and hickory/pecan. Flooringgrades are determinedby the appearanceofthe face surface.

Oakis separated as red oak and white oak andby grain

Finished Market Products Some hardwoodlumberproductsare gradedinrelatively

fmishedform, with little orno furtherprocessing anticipated. Flooringis probablythe finishedmarket productwith the highest volume.Other examplesare lath, siding, ties, planks, carstock, constructionboards,timbers,trim, moulding,stair treads, and risers. Gradingrules promulgated for flooringanticipate final consumeruse andare summarized in this section. Detailson gradesofother finishedproductsare found in appropriate association gradingrules. Hardwoodflooring generallyis gradedunderthe rules ofthe MapleFlooringManufacturers Association (MFMA)orthe NationalOak FlooringManufacturers Association (NOFMA). Tongued-and-grooved, end-matched hardwood flooring is commonlyfurnished. Square-edge, square-endstrip flooringis also availableas well as parquetflooring suitable for laying with mastic.

The gradingrules oftheMaple FlooringManufacturers Association cover flooring that is manufactured from hard maple, beech, and birch. Each species is gradedinto four

direction:plainsawn (all cuts),quartersawn(50%quartered character), rift sawn(75%riftcharacter), and quarter/rift sawn (acombination). Oak flooring has four maingrade separations—Clear,Select, No. 1 Common,and No. 2 Common. Clearis mostlyheartwoodand acceptsa 10-mm (3/8-in.) strip ofbright sapwoodor an equivalent amountnot more than 25 mm (1 in.) wide along the edge and a minimum numberofcharacter marksand discoloration, allowingfor all naturalheartwoodcolor variations.Selectallows all color variations ofnaturalheartwoodand sapwoodalongwith characters such as smallknots, pinwormholes, and brown streaks. No. 1 Commoncontainsprominentvariationsin coloration,which include heavy streaks,sticker stains, open checks,knots, and small knot holes that fill. No. 2 Common contains soundnaturalvariationofthe forestproduct and manufacturing imperfections to provideaserviceablefloor. Average lengths for unfinished oakgradesare as follows: Grade

Standard packaging

Shorter packaging

Clear

1.14m

(3-3/4ft)

1.07m

(3-1/2ft)

Select

0.99 m

(3-114ft)

0.91m

(3 ft)

categories:

No. 1 Common

0.84m (2-3/4 ft)

0.76m

(2-11/2 ft)

• First grade—one face practically free ofall imperfections;

No.2Common

0.69m

0.61 m

(2 ft)

variations innatural color ofwood allowed

5—6

(2-1/4 It)

Standardpackagingreferstonominal2.4-rn (8-fl)pallets or nestedbundles.Shorterpackagingrefersto nominal 2.13-rn (7-fl)and shorterpalletsornestedbundles. Standardand specialNOFMAgradesfor species otherthan oak are as follows: Grade

Species

Standard grades Beech, birch, and hard maple

First,Second, Third, Second &Better,Third

Hickory and pecan

First,Second, Third, Second &Better,Third

Ash

Clear,Select,No. I Common, No. 2 Common

& Better & Better

Beech and birch

Special grades First GradeRed

Hard maple

First GradeWhite

Hickoryand pecan

First GradeWhite,First GradeRed,Second Grade Red

To minimize unnecessary differences inthe gradingrules of softwood lumberand to improveand simplifythese rules, a number ofconferences were organized bythe U.S. Department ofCommerce from 1919to 1925. These meetingswere attended by representatives oflumber manufacturers, distributors, wholesalers, retailers, engineers, architects, and contractors. The result was arelativestandardization ofsize3, definitions, andprocedures for deriving allowable design properties, formulated as avoluntaryAmerican Lumber Standard. This standard has been modifiedseveraltimes, including addition ofhardwoodspecies tothe standard beginning in 1970. The currentedition is the American Softwood LumberStandardPS—20. LumbercannotiDe graded as American Standardlumberunless the grade rules havebeen approved by the American LumberStandard Committee (ALSC), Inc., Board ofReview. Softwood lumber is classified formarketuse by form of manufacture, species,and grade.For many products, the American Softwood LumberStandardandthe gradingrules certified throughitserveas a basic reference. For specific information on other products, referencemust be madeto grade rules, industry marketingaids, and tradejournals.

Lumber Grades

Lumber Species

Softwoodlumbergradescanbe classified into threemajor categories ofuse: (a) yard lumber, (b) structural lumber, and (c)Factory and Shop lumber. Yard lumberand structural lumberrelate principally to lumberexpectedto function as gradedand sized afterprimaryprocessing (sawingandplaning). Factoryand Shop referto lumberthat willundergo a numberoffurther manufacturing stepsandreachthe consumer in a significantly different form.

The names usedby the trade to describecommercial lumber

Yard Lumber

Softwood Lumber

The gradingrequirements ofyard lumberare specifically relatedto the constructionuses intended,and little orno furthergrading occurs once the piece leavesthe sawmill. Yard lumber can be placedinto two basic classifications, Select and Common. Select and Commonlumber. as categorizedhere, encompass those lumberproductsin which appearance is ofprimaryimportance; structural intogrity, while sometimes important, is a secondary feature,

Standardthicknessvaluesfor NOFMAtongueandgroove flooring are 19, 12, 9.5 (3/4, 1/2, 3/8 in.), with 19.8, and 26.2 mm (25/32 and 33/32 in.) formaple flooring. Standard face widths are 38, 51, 57, and 83 mm (1-1/2,2, 2-1/4, and 3-1/4 in.). Strips are random length from minimum 0.23 m to maximum2.59m (9 to 102 in.).

in theUnitedStates arenot alwaysthesame as thenamesof treesadoptedas officialby the USDAForest Service. Table 5—3 shows the commontrade name, the USDAForest Servicetree name, andthe botanicalname. UnitedStates agenciesand associations that preparerulesfor andsupervise grading ofhardwoodsare given in Table5—2.

Formanyyears,softwoodlumberhasdemonstrated the for versatility ofwood by servingas aprimaryrawmaterial construction andmanufacture. In this role, softwoodlumber has beenproducedina wide varietyofproductsfrom many different species. The firstindustry-sponsored gradingrules (product descriptions) for sofiwoods, whichwere established before 1900, were comparatively simplebecausesawmills marketedtheirlumberlocallyand gradeshad only local significance. As new timbersources were developed and lumberwas transportedto distantpoints, each producing region continuedto establishits own gradingrules; thus, lumberfrom variousregionsdifferedin size,grade name, and allowable grade characteristics. Whendifferentspecies were graded underdifferentrules and competed in the same consuming areas, confusion and dissatisfaction were inevitable.

Select Lumber—Selectlumberis generallynon-sressgraded,but it forms aseparate categorybecauseofthe distinct importance ofappearance in the gradingprocss. Select lumberis intended fornatural and paintfinishes.This category oflumberincludeslumberthat has been machinedto a patternand S4S lumber. Secondary manufacture ofthese itemsis usually restrictedto on-site fittingsuch as cutting to length and mitering.The Selectcategoryinclude trim, siding, flooring, ceiling,paneling, casing, base, stepping, andfinishboards. Most Selectlumbergrades are generallydescribedby letters and combinations ofletters (B&BTR, C&BTR,ID) or names (Superior, Prime) depending uponthe species and the gradingrules under whichthe lumberis graded.(See list of

5—7

commonly usedlumberabbreviations at the end ofthis chapter.) The specifications FG (flat grain),VG (vertical grain), and MG (mixedgrain) are offeredas a purchase option for some Selectlumberproducts.

In cedarand redwood, there is a pronounced difference in colorbetweenheartwoodand sapwood. Heartwood alsohas high natural resistanceto decay, so some grades are denoted as "heart."Because Selectlumbergrades emphasize the qualityofone face, the reverse sidemay be lowerinquality. Selectlumbergradesare not uniformacrossspecies and products,so certifiedgrade rules for the species must be used fordetailed reference.

No.1

Common Lumber—Commonlumber isnormallya nonstress-graded product.The gradesofCommon lumberare suitable for constructionand utility purposes.Common lumber is generallyseparated intothreeto five different grades dependinguponthe species and gradingrules involved. Gradesmay be describedby number(No. I, No. 2, No. I Common,No. 2 Common)or descriptive term (Select Merchantable, Construction, Standard).

No.2

Because there are differences in the inherent properties of various species andtheircorresponding names, the grades fordifferentspecies arenot alwaysinterchangeable. The topgrade boards (No. I, No. 1 Common, SelectMerchantable) are usually gradedfor serviceability, but appearance is also considered. Thesegradesareusedfor such purposesas siding, cornice, shelving,and paneling. Features such as knots and knotholesare permittedto be larger and more frequentas the gradelevel becomes lower. Intermediate-grade boardsare often used for suchpurposesas subfloors, roofand wall sheathing,and rough concretework. The lowergrade boardsare selectedforadequatestrength, not appearance. They are usedforroofandwall sheathing, subfloor, and

No.3

rough concretefonnwork (Fig.5—2).

Grading provisionsfor other non-stress-graded products vary by species,product,and applicablegradingrules.For detaileddescriptions, consult the appropriate grade rule forthese products(see Table 5—5 for softwoodgrading organizations).

StructuralLumber—Almostall softwoodlumberstandard 38 to 89 mmthick(nominal2 to 4 in. thick, actual 1-1/2 to 3-1/2 in. thick) is producedas dimensionlumber. Dimension lumberis stress gradedand assignedallowable properties under theNationalGradingRule, apart ofthe American Softwood LumberStandard. For dimensionlumber, a single setofgrade names and descriptionsis used throughoutthe UnitedStates, althoughthe allowable properties vary with species. Timbers (lumberstandard 114 mm (nominal5 in.) ormore in least dimension)are alsostructurally gradedunder ALSCprocedures. Unlikegrade descriptions fordimension lumber, grade descriptions for structural timbers are not standardized across species.For most species,timbergrades are classifiedaccording to intendeduse. Beams and stringers aremembers standard 114 mm (nominal5 in.) ormore in thicknesswith a width more than 51 mm (2 in.) greaterthan

5—8

No.4

0 Figure 5—2. Typical examplesofsoftwoodboards in the lowergrades. the thickness.Beamsand stringersare primarilyused to resist bendingstresses, and the grade descriptionfor the

middlethird ofthe length ofthe beam is more stringentthan that for the outer two-thirds. Posts and timbers are members standard 114 by 114 mm (nominal5 by 5 in.) and larger. wherethe width is not more than 51 mm(2 in.) greater than thethickness. Post andtimbers areprimarilyused to resist axial stresses. Structural timbersofSouthern Pine are graded without regardto anticipateduse, as with dimensionlumber. Other stress-graded products include deckingand some boards.Stress-graded lumbermay be gradedvisuallyor mechanically. Stressgradesandthe NationalGrading Rule are discussedin Chapter6.

StructuralLaminations—Structurallaminatinggrades describe the characteristics used to segregatelumberto be usedin structuralglued-laminated (glulam)timbers. Generally, allowable properties are not assignedseparately to laminating grades; rather,the rules for laminating grades are based on the expectedeffectofthat grade oflamination on the combined glularntimber.

Table 5—5. Organizations promulgating softwoodgrades Name and address

Species covered by grading rules

Cedar Shingle& Shake Bureau 515 116thAvenue NE, Suite 275 Bellevue,WA 98004—5294

Western redcedar (shinglesand shakes)

National HardwoodLumberAssociation P.O. Box 34518

Baldcypress, eastern redcedar

Memphis,

TN 38184—0518

National Lumber GradesAuthority8 406 First Capital Place 960 QuamsideDrive New Westminister,BC, CanadaV3M6G2

Northern white cedar, westernred cedar, yellow cedar, alpine fir, amabilis fir, balsam fir, Douglas-fir, grand fir, eastern hemlock, westernhemlock, westernlarch, easternwhite pine, jack pine, lodgepolepine, ponderosa pine, red pine, westernwhite pine, black spruce, sitka spruce,red spruce, Engelmann spruce, white spruce, tamarack, aspen, black cottonwood,balsam poplar, red alder, white birch

NortheasternLumber Manufacturers Association,Inc. 272 Tuttle Road, P.O. Box 87A Cumberland Center, ME 04021

Balsam fir, eastern white pine, red pine, eastern hemlock, black spruce,white spruce, red spruce, pitch pine, tamarack, jack pine, northern white cedar, aspen, red maple, mixed maple, beech, birch, hickory, mixed oaks, red oak, northern red oak, white oak,yellow poplar Eastern white pine, jack pine, red pine, pitch pine, eastern spruce (red, white, and black), balsam fir, eastern hemlock, tamarack, eastern cottonwood, aspen (bigtoothand quaking),

NorthernSoftwood LumberBureaua 272 Tuttle Road, P.O. Box 87A Cumberland Center, ME 04021

yellow poplar

Redwood InspectionService 405 EnfrenteDrive, Suite 200 Novato, CA 94949

Redwood

Southern Cypress ManufacturersAssociation 400 Penn Center Boulevard Suite 530 Pittsburgh,PA 15235

Batdcypress

Southern Pine Inspection Bureaua 4709 Scenic Highway Pensacola, FL 32504

Longleafpine, slash pine, shortleafpine, loblolly pine, Virginia pine, pond pine, pitch pine

West Coast Lumber Inspection Bureaua

Douglas-fir, western hemlock, western redcedar, incense-cedar, Port-Orford-cedar, yellow-cedar, westerntrue firs, mountain hemlock, Sitka spruce,western larch

Box 23145

6980 SW. Varns Road Portland, OR 97223 Western Wood Products Association8 Yeon Building, 522 SW Fifth Avenue Portland, OR 97204—2122

Ponderosa pine, westernwhite pine, Douglas-fir, sugar pine, western true firs, western larch, Engelmann spruce, incensecedar, westernhemlock, lodgepolepine, western redcedar, mountain hemlock,red alder, aspen, alpine fir, Idahowhite pine

apublishesgrading rules certified by the Board of Reviewof the AmericanLumberStandard Committee as conformingto the American Softwood LumberStandard PS—20.

There are two kinds ofgradedmaterial: visuallygradedand E-rated. Visuallygradedmaterialis gradedaccording to one ofthree sets ofgrading rules: (1) thefirst set is basedon the grading rules certifiedas meeting the requirements ofthe American Softwood LumberStandardwith additionalrequirements forlaminating;(2) the secondset involves laminating grades typicallyused forvisuallygradedwestern species and includesthree basic categories (LI, L2, L3); and (3) the thirdset includesspecialrequirements for tension

membersand outer tensionlaminationson bendingmembers. The visualgrades have provisions for dense, closegrain, medium-grain, or coarsegrain lumber. TheE-ratedgrades are categorized by a combination ofvisual grading criteriaand lumberstiffness. Thesegraths are expressedin terms ofthe size ofmaximum edge characteristic permitted(as a fraction ofthewidth)along with a specified long-span modulusofelasticity(for example,l'6—2.2E).

5—9

Factory and Shop Lumber A wide variety ofspecies, grades, andsizes ofsoftwood lumberis suppliedto industrial accountsfor cutting to specific smallersizes, whichbecome integralparts ofother products. In the secondatymanufacturing process,grade descriptions, sizes, andoften the entireappearance ofthe wood piece are changed. Thus, forFactory and Shop lumber, therole ofthegradingprocessis to reflectas accurately as possiblethe yield to be obtainedin the subsequent cutting operation. Typicaloflumberforsecondary manufacture are thefactorygrades, industrialclears,box lumber, moulding stock,and ladderstock. The varietyofspecies availablefor these purposeshas ledto a varietyofgrade namesand grade definitions. The followingsectionsbrieflyoutline someof themore common classifications. Fordetails,referencemust be made to industrysources,such as certified gradingrules. Availability and grade designationoften vary by regionand

woodsupplyhave led to different grade descriptions and terminology. For example,in West Coast species, the ladder industtycanchoose from one "ladderand pole stock"grade plus two ladderrail grades and one ladder rail stock grade.In SouthernPine, ladder stock is availableas Selectand Industrial. Moulding stock, tank stock, pole stock, stave stock, stadiumseat stock,box lumber, and pencil stock are other typicalclassesorientedto the final product.Some product classeshaveonlyone grade level; a few offertwo or three levels.Special features ofthese grades may includearestriction on sapwoodrelatedto desired decay resistance, specific requirements for slopeofgrain and growthring orientation forhigh-stress use such as ladders, andparticularcutting requirements as inpencil stock. All referencesto these grades shouldbe madedirectlyto currentcertifiedgrading rules.

species.

Size Lumberlength is recordedin actual dimensions,whereas width and thicknessare traditionallyrecorded in "nominal" dimensions—actual dimensions are somewhatless.

Factory(Shop) Grades—Traditionally,softwoodlumber usedfor cuttingshas been calledFactory or Shop. This lumberforms the basicraw material formany secondary manufacturing operations. Somegradingrules referto these grades as Factory, while othersrefer to them as Shop. All impose asomewhatsimilar nomenclature inthe grade structure. Shop lumberis gradedon the basis ofcharacteristics that affect its use forgeneral cut-uppurposesoronthe basis ofsize ofcutting,such as for sashand doors.Factory Select and Select Shop are typicalhigh grades, followedby No. I Shop, No. 2 Shop, and No. 3 Shop. Gradecharacteristics ofboardsare influenced by the width, length, andthicknessofthe basic piece and are based on the amountofhigh-qualitymaterialthat can be removed by cutting. Typically,Factory Selectand Select Shop lumber would be requiredto contain70% ofcuttingsofspecified size,clear on both sides.No. I Shop would be required to have 50% cuttings and No. 2 Shop,33-1/3%.Becauseof differentcharacteristics assignedto grades with similarnomenclature,the gradesofFactory and Shop lumbermust be referencedto the appropriate certified gradingrules.

IndustrialClears—Thesegrades are used fortrim, cabinet

stock,garage door stock, and other product components whereexcellent appearance, mechanical andphysical properties, and fmishingcharacteristics are important. Theprincipal grades are B&BTR,C, and D industrial.Grading is primarily based on the best face,althoughthe influence ofedge characteristics is importantandvaries depending uponpiece width andthickness.In redwood,the IndustrialClear All Heart grade includesan"allheart" requirement fordecay resistancein the manufactureofcoolingtowers,tanks,pipe, and similar products. Moulding, Ladder, Pole, Tank, and Pencil Stock— Withinproducingregions,grading rules delineatethe requirements for avariety oflumberclassesorientedto specific consumerproducts.Customandthe characteristics ofthe

5—10

Lumber Manufacture

in lengthmultiplesof 300 mm (1 ft) as specifiedin variousgradingrules. In practice, 600-mm(2-ft)multiples(in evennumbers)are common for most construction lumber. Width ofsoftwoodlumber varies,commonlyfrom standard38 to 387 mm(nominal 2 to 16 in.). The thicknessoflumber can be generally categorized as follows: Softwood lumberis manufactured

• Boards—lumber lessthan standard 38 mm(nominal 2 in.) in thickness

• •

Dimension—lumber from standard38 mm (nominal2 in.) to, but not including, 114 mm (5 in.) in thickness Timbers—lumber standard 114 mm (nominal5 in.) or morein thicknessin least dimension

To standardizeand clarifj nominalto actual sizes, the American Softwood LumberStandardPS—20 specifies the actualthicknessand widthfor lumberthat falls underthe standard. The standard sizes for yard and structural lumber aregiven in Table 5—6. Timbersare usually surfacedwhile "green"(unseasoned); therefore, only green sizes are given. Becausedimension lumber and boardsmay be surfaced green or dry at theprerogative ofthe manufacturer, both green and dry standard sizes are given. The sizes are such that a piece ofgreen lumber, surfaced to thestandardgreen size, will shrink to approximately the standarddry size as it dries to about 15% moisture content.The defmitionofdry is lumber that has been seasonedor dried to a maximummoisture contentof 19%. Lumbermay alsobe designatedas kiln dried (KD),meaningthe lumberhas been seasonedin a chamberto a predetermined moisturecontentby applyingheat.

Table 5—6. American Standard Lumber sizes for yard and structurallumberforconstruction

Nominal Item Boards

(in.)

Thickness Minimum dressed Green Dry (mm (in.)) (mm (in.))

1

19

1-1/4 1-1/2

25 32

(3/4) (1) (1-1/4)

20 26 33

(25/32) (1-1/32) (1-9/32)

Face width Nominal (in.)

2 3 4 5 6

114 140

7

165

8 9

184

10 .

11

12 14 16 Dimension

2

(3-1/16)

102

(4

103

(4-1/16

5 6 8 10 12 14 16

38

2-1/2

51

3

64

3-1/2

4 4-1/2

Timbers

40 52 65 78 90

(1-9/16) (2-1/16) (2-9/16)

76 89

(1-1/2) (2) (2-1/2) (3) (3-1/2)

2

5

13 mm oif

(1/2 in. 13 mm off off)

(3-9/16)

(1/2 in. off)

Factory and Shoplumberfor remanufacture is offered in specifiedsizes to fit end-product requirements. Factory (Shop) grades forgeneralcuttings are offered inthickness from standard 19 to 89 mm(nominal ito 4 in.). Thicknesses ofdoor cuttingsstart at 35mm (nominal1-3/8 in.). Cuttings are ofvarious lengths and widths. Laminatingstock is sometimes offered oversize, compared with standard dimensionsizes,to permitresurfacingprior to laminating. Industrial Clearscan be offered rough or surfaced ina variety ofsizes, startingfrom standard38 mm (nominal2 in.) and thinner and as narrow as standard 64 mm (nominal 3 in.). Sizesfor special productgrades such as mouldingstock and ladderstockare specified in appropriate gradingrules or handledbypurchaseagreements.

Surfacing Lumbercan be producedeitherrough orsurfaced (dressed). Roughlumberhas surface imperfections causedby the primary sawing operations. Itmay be greaterthan target size by variableamountsin both thicknessand width, depending

Minimum dressed Green (mm (in.))

Dry (mm (in.))

3

4

5

38 64 89

210 235 260 286 337 387

(1-1/2)

2-l/2) (3-1/2) (4—1/2)

(5-1/2) (6-1/2) (7-1/4) (8-1/4)

—

—

40 65 90

(1-91W) (2-9/16)

117 143

(4—5/8)

168

(6-5/8) (7-1/2)

190

216

(3-9116)

(5-5/8)

(9-1/4) (10-1/4)

241

(11—1/4)

(15-1/4)

292 343 394

(8-1/2) (9-1/2) (10-1/2) (11-1/2) (13-1/2) (15-1/2)

38 64 89

(1-1/2) (2-1/2) (3-1/2)

40 65 90

(1-9/16) (2-9/16) (3-9/16)

114 140 184

(4—1/2)

117 143 190 241 292 343 394

(4—5/8)

235 286 337 387 13 mm off

(13-1/4)

(5-1/2) (7-1/4) (9-1/4) (11-1/4) (13-1/4) (15-1/4) (1/2 in.

off)

267

13 mm off

(5-5/8) (7-112)

(9-1/2) (11-1/2) (13-1/2) (15-1/2)

(1/2 in. off)

uponthe type ofsawmillequipment. Rough lumberserves as a raw material for further manufacture and alsofor some decorative purposes. A roughsawnsurface is common in post andtimberproducts. Because ofsurface roughness, gradingof rough lumber is generally more difficult. Surfacedlumberhas beensurfaced by a machine on one side (SIS), two sides (S2S), one edge(S1E), two edges S2E), or combinations of sides and edges (S1S1E, S2S1E, S1S2, S4S).Lumberis surfaced to attain smoothness and uniformity ofsize. Imperfections or blemishes definedinthe gradingrules and causedby machining are classified as "manufacturing imperfections." For example, chippedand torn grain are surface irregularities inwhichsurface fibershavebeentorn cut bythe surfacingoperation. Chippedgrain is a "barelyperceptible" characteristic, while torn grain is classified by depth. Raised grain, skip, machine burn and gouge, chipmarks, and wavy surfacingare other manufacturing imperfections. Manrfacturing imperfections are defmed in the American Softwood

5—Il

LumberStandardand furtherdetailedin the gradingrules.

Classifications ofmanufacturing imperfections (combinations ofimperfections allowed)are established in therules as StandardA, StandardB, and so on. For example, Standard A admits very light torn grain, occasionalslight chip marks, and very slightknife marks. These classifications areusedas part ofthe grade rule description ofsome lumberproductsto specify the allowable surface quality.

Flooring (standard match) C

Ceiling (edge beading)

Patterns Lumberthat has been matched,shiplapped, or otherwise patterned, in addition to being surfaced, is often classified as "worked lumber." Figure 5—3 showstypicalpatterns.

Softwood Lumber Species The names oflumberspecies adoptedby the trade as standard may vary from the namesoftreesadoptedas official by theUSDAForest Service. Table 5—7 shows theAmerican SoftwoodLumberStandardcommercial namesfor lumber, the USDAForest Servicetree names,and the botanical names. Somesoftwoodspeciesare marketed primarilyin combinations. Designationssuch as Southern Pine and Hem—Fir representtypicalcombinations. Gradingrule agencies (Table5—5)shouldbe contactedforquestionsregarding combination names and speciesnot listed in Table5—7.

Decking

Species groupsare discussedfurtherin Chapter6.

Softwood Lumber Grading Most lumber is gradedunder the supervisionofinspection bureaus and gradingagencies. Theseorganizations supervise lumbermill grading and providere-inspection services to resolvedisputes concerning lumber shipments. Some of these agenciesalso write gradingrulesthat reflectthe species and productsin the geographic regionsthey represent. These gradingrules followthe American Softwood LumberStan-

Heavy decking

dard (PS—20). This is importantbecauseit providesfor recognized uniform gradingprocedures. Names andaddresses ofrules-writingorganizations in theUnited Statesandthe species with whichthey are concernedare listed in Table 5—5. Canadian softwoodlumber imported into the UnitedStates and gradedby inspectionagenciesin Canada also follows the PS—20 standard. Names and addressesof accreditedCanadiangradingagencies may be obtained from theAmerican LumberStandardCommittee, P.O. Box 210, Germantown,Maryland20874.

Drop siding (shiplapped)

Bevel siding

Purchase of Lumber Afterprimarymanufacture, most lumber products aremarketedthroughwholesalers to remanufacturing plantsor retail outlets.Becauseofthe extremely wide variety oflumber products,wholesaling is very specialized—some organizations deal with only a limitednumberofspecies or products. Where the primarymanufacturer canreadily identify the customers, direct salesmay be made. Primarymanufacturers oftensell directlyto largeretail-chain contractors, manufacturers ofmobile and modularhousing,and truss fabricators.

5—12

\\ II

Dressed and matched (center matched)

H

Shiplap

Figure 5—3. Typical patterns of worked lumber.

Table 5—7. Nomenclatureof commercial softwood lumber Commercial species orspecies group names under American SoftwoodLumber Standard

Tree name used in this handbook

Botanicalname

yellow-cedar eastern redcedar incense-cedar northernwhite-cedar Port-Orford-cedar Atlantic white-cedar western redcedar

Chamaecypansnootkatensis Juniperus virginiana Libocednjs decurrens Thuja occidentalis ChamaecyparisIawsoniana Chamaecyparisthyoides Thujaplicata

Baldcypress Pond cypress

baldcypress pond cypress

Taxodium distichum Taxodiumdistichum var. nutans

Alpine

subalpine fir (alpinefir) balsam fir California red fir Douglas-fir Fraserfir grand fir noble fir Pacific silverfir whitefir

Abies Iasiocaipa Abies balsamea Abies magnifica Pseudotsugamenziesii

Carolina hemlock eastern hemlock mountainhemlock western hemlock

Tsuga caroliniana Tsugacanadensis Tsugamertensiana Tsugaheterophylla

alligator juniper Rocky Mountainjuniper Utahjuniper western juniper

Juniperusdeppeana Juniperus scopulorum Juniperus osteosperrna Juniperus occidentalls

western larch

Larixoccidentalis

bishoppine Coulter pine Digger pine knobconepine western white pine jack pine Jeffrey pine limber pine lodgepolepine longleafpine slash pine eastern white pine red pine pitch pine pcnderosapine loblolly pine longleafpine

Pinusmuricata

Cedar Alaska Eastern Red Incense

Northem White Port Orford SouthernWhite Western Red

Cypress Fir

Balsam California Red Douglas Fir Fraser Grand Noble Fir Pacific Grand White

Abiesfraseri

Abies grand/s Abies procera Abiesamabills Abies concolor

Hemlock Carolina Eastern

Mountain Western

Juniper Western

Larch Western Pine Bishop Coulter

Digger

Knobcone IdahoWhite Jack Jeffrey Limber Lodgepole

Longleaf Northern White Norway Pitch Ponderosa

Southern Pine Major

shortleafpine Southern Pine Minor

Southern PineMixed

RadiataiMontereyPine

slash pine pondpine sand pine spruce pine Virginia pine lobIollypine longleafpine pondpine shortleaf pine slash pine Virginia pine Monterey pine

Pinus coulteri Pinus sabibiana Pinusaltenuata Pinus montico!a Pinus banksiana Pinusjeffreyi Pinus flexilis Pinus conto,ta Pinuspalustris Pinuselliott/i Pinus strobus Pinus resinosa Pinus rigida Pinuspondesosa Pinustaeda Pinus palustris Pinusechinata Pinus elliottli Pinus serotina Pinusciausa Pinus glabra Pinus virginiana Pinustaeda Pinus palustris Pinus serotina Pinusechinata Pinus elliottii Pinus virginiana Pinusradiata

5—13

Table 5—7. Nomenclatureofcommercial softwoodlumber—con. Commercial species orspecies group names under American Softwood LumberStandard

Treename used in this handbook

Botanicalname

sugar pine whitebark pine

Pinus lambertiana Pinus albicaulis

redwood

Sequoia sempe,virens

blue spruce blackspruce redspruce whitespruce Engelmannspruce Sitka spruce

Piceapungens Picea mariana Picea rubens Picea glauca Picea engelmannhi Picea sitchensis

tamarack

Lanx larcinia

Pacific yew

Taxus bravifolia

Douglas-fir western larch black spruce red spruce white spruce balsam fir easternwhitepine jackpine pitch pine red pine eastern hemlock tamarack

Pseudotsugamenziesii Larix occidentalls Picea mariana Piceaivbens Piceaglausa Abies balsamea Pinus strobus Pinusbanksiana Pinus rigida Pinus resinosa Tsugacanadensis Larixoccidentalis

Hem—Fir

western hemlock California red fir grand fir noble fir Pacific silverfir whitefir

Tsugaheterophylla Abies magnifica Abies grandis Abies procera Abies amabilis Abies concolor

Hem—Fir (North)

western hemlock Pacific silverfir

Tsugaheterophylla Abies amabilis

Northern Pine

jack pine pitchpine red pine

Pinusbanksiana

northemwhitecedar western redcedar yellow-cedar eastern hemlock western hemlock Douglas-fir balsam fir grand fir Pacific silverfir subalpine (alpine) fir western larch tamarack eastern white pine

Thujaoccidentalls Thujaplicanta Charnaecyparisnootkatensis Tsugacanadensis Tsugaheterophylla Pseudofsuga menziesii Abies balsamea Abies grandis Abies amabilis Abies Iasiocarpa Larix occidentalls Larix laricina Pinus strobus Pinus banksiana Pinus contorta Pinusporidemsa Pinus resinosa Pinus monticola Pinus albicau/is Picea mariana Picea engelmannii Picea rubens Picea sitchensis

Pine—con. Sugar Whitebark

Redwood Redwood Spruce Blue

Eastern

Engelmann Sitka Tamarack Tamarack Yew Pacific

CoastSpecies EasternSoftwoods

North Species

jack pine lodgepolepine ponderosapine red pine westernwhitepine whitebark pine black spruce Engelmannspruce red spruce Sitka spruce

5—14

Pinus rigicla Pinus resinosa

Table 5—7. Nomenclatureof commercial softwoodlumber—con. Commercial species orspecies group names under American Softwood LumberStandard

Treename used inthis handbook

Botanicalname

North Species—con.

white spruce

Pkaglauca

btoothaspen

Populusgrandidentata Populus tremuloides Populus trichocarpa Populus balsamifera

Southern Pine

Spruce—Pine—Fir

quakingaspen black cottonwood balsampoplar lobloitly pine longloafpine shortleaf pine slash pine black spruce Engelmannspruce red spruce balsam fir subalpine (alpine) fir

jack Dine Spruce—Pine—Fir(South)

WesternCedars

Western Cedar (North) Western Woods

lodgepolepine black spruce Engelmannspruce red spruce Sitka spruce whitespruce balsam fir jackpine lodgepolepine red pine incense cedar western redcedar Port-Orford-cedar yellow-cedar western redcedar yellow-cedar Douglas-fir California red fir grand fir noble fir Pacific silverfir subalpinefir

whitefir Hemlock

White Woods

.

Pinustaeda Pinus palustris Pinus echinata

Pinuseliottii

Picearnariana Piceaengelmannii Picea rubens Abies balsamea Abies lasiocarpa Pinus banksiana Pinus contorta

Picea mariaria Picea engelmannii Picearubens Picea sitchensis Piceaglauca Abies balsamea Pinusbanksiana Pinuscontorta Pinusresinosa Ubocedrusdecuirens Thujaplicata Chamaecypanslawsoniana Chamaecypadsnootkatensis Thujapilcata Chamaecypansnootkatensis Pseudotsugamenziesii Abiesmagnifica Abiesgrandis Abiesprocera Abiesamabilis Abieslasiocarpa Abiesconcolor

mountain western hemlock wesl:emlarch Engelmannspruce Sitka spruce lodgepolepine ponderosapine sugar pine westernwhitepine

Tsugamertensiana Tsuga hetemphylla La,ixoccidentalis Piceaengelmannii Picea sitchensis Pinuscontorta

California redfir grand fir noble fir Pacific silverfir subalpinefir whitefir mouintainhemlock western hemlock Engelmannspruce Sitka spruce lodgepolepine ponderosapine sugar pine western white pine

Abies magnifica Abies graridis Abies procera Abies emabilis Abies lasiocarpa Abies concolor Tsugamertensiana Tsugaheferophyifa Picea engelmannhi Picea sitchensis Pinus contorta Pinusponderosa Pinus Iambertiana Pinusmonficola

Pinusponderosa

Pinus lambertiana Pinus monticola

5—15

Someprimarymanufacturersandwholesalers set up distribution yards in lumber-consuming areas to distributeboth hardwood and softwoodproducts more effectively. Retail yards thaw inventoryfrom distributionyardsand, in woodproducingareas, from local lumberproducers. The wide range ofgrades and species coveredin the grade rules may not be readily availablein most retail outlets. Transportation is a vital factor in lumberdistribution. Often, the lumbershippedby water is green becauseweight is not a major factor in this type ofshipping. On the other hand, lumberreachingthe East Coastfrom the PacificCoastby rail is usually kiln-driedbecauserail shippingratesare basedon

weight.A shorterrail haul places southemand northeastern speciesin a favorableeconomicposition in regardto shipping costs in this market.

Changingtransportationcosts have influenced shiftsin marketdistributionof species and products. Truckshave become a majorfactorin lumbertransportfor regional remanufacture plants,forretail supply from distributionyards, and for much constructionlumber distribution. The increased production capacity offoreign hardwoodand softwood manufacturing and the availability ofwatertransporthas broughtforeign lumberproductsto the U.S. market, particularlyin coastal areas.

Retail Yard Inventory The smallretail yards throughoutthe United Statescarry softwoodsfor construction purposesand often carry small stocks ofone ortwo hardwoodsin gradessuitable forfinishing or cabinetwork. Specialordersmust be made for other hardwoods. Trim items such as mouldingin either softwood or hardwoodare available cutto standard size and pattern. Millworkplants usuallymakeready-for-installation cabinets, and retail yards carry or catalogmany common styles and

sizes. Hardwoodflooring is availableto the buyer only in standardpatterns.Most retail yards carry stress gradesof lumber.

The assortment ofspecies in generalconstruction items carriedby retail yardsdependsto agreat extentupongeographiclocation, and both transportationcosts and tradition are importantfactors.Retail yardswithin,or close to, a major lumber-producing region commonly emphasize local timber. For example,a local retail yard on the Pacific NorthwestCoast may stock only green DouglasFir and cedar in dimensiongrades, thy pine and hemlockin boards andmoulding,and assortedspecial items such as redwood posts, cedarshinglesand shakes, and rough cedar siding. The only hardwoodsmay be walnutand "Philippinemahogany"(the commonmarket nameencompassing many species, includingtanguile, red meranti, and white lauan). Retailyards locatedfarther from amajor softwoodsupply, such as inthe Midwest, may draw from severalgrowing areas andmay stock spruce and Southern Pine, forexample. Becausethey are locatedin a major hardwoodproduction

5—16

area, these yardsmay stock,orhave availableto them,a different and widervariety ofhardwoods. Geography has less influence where consumer demands are more specific. Forexathple,wherelong construction lurriber (6 to 8 m (20 to 26 ft)) is required, West Coast species are often marketedbecausetheheight ofthe trees in several species makeslong lengths apracticalmarket item. Ease of preservative treatability makestreatedSouthernPine construction lumberavailablein wide geographic area.

a

StructuralLumber for Construction Dimensionlumberis the principalstress-gradedlumber available in a retail yard. It is primarilyframinglumberfor joists, rafters,and studs. Strength,stiffness,and uniformity ofsize are essential requirements. Dimensionlumberis stockedin almostall yards, frequently in only one or two of thegeneral purposeconstruction woods such as pine,fir, hemlock, or spruce.Standard38- by 89-mm (nominal2- by 4-in.) andwider dimension lumberis found in SelectSructural,No. 1, No. 2, and No. 3 grades. Standard38- by 89-mm (nominal 2- by 4-in.) dimension lumbermay also be available as Construction, Standard,Utility, and STUD grades. STUDgrade is also available in widerwidths. Dimension lumberis often found in standard38-, 89-, 140-, 184-, 235-, and 286-mm (nominal2-, 4-, 6-, 8-, 10-, and 12-in.) widths and 2.4- to 5.4-m (8- to 18-ft) lengths in multiplesof0.6 m (2 ft). Dimensionlumberformedby structural end-jointingproceduresmay be available. Diinen-

sion lumberthicker than standard38 mm (nominal2 in) and longerthan 5.4 m (18 ft) is not commonlyavailable in many retail yards.

Otherstress-graded products generally available are posts and timbers; some beamsand stringersmay also be in stock. Typicalgrades in these productsare Select Structural, No. I, and No. 2.

Yard Lumber for Construction Boards are the mostcommonnon-stress-graded general purposeconstruction lumberin the retail yard. Boardsare stockedin one or more species, usuallyin standard 19 mm (nominal1 in.) thickness.Commonwidths are standard 38, 64, 89, 140, 184, 235, and 286 mm (nominal2, 3, 4, 6, 8, 10, and 12 in.). Gradesgenerallyavailablein retail yardsare No. 1 Common, No. 2 Common, and No. 3 Common (Construction, Standard, No. 1, No. 2, etc.). Boards are sold

square edged, dressed (surfaced) and matched (tonguedand grooved), or with a shiplapped joint.Boards formedby endjointing ofshorter sections may constitute an appreciable portionofthe inventory.

Select Lumber

a

Completionof construction projectusually depends on the availability oflumberitemsin fmishedorsemi-fmished

form.The followingitemsoften may be stocked in only a few species, finishes, or sizes depending on the lumberyard.

Finish—Finishboards usuallyare availablein a local yard in one or two species,principallyin grade C&BTR.Cedar and redwoodhave different grade designations: grades such as Clear Heart,A, or B are used in cedar;ClearAll Heart, Clear, and B grade are typicalin redwood.Finish boardsare usually standard 19 mm (nominal 1 in.) thick, surfaced on two sides to 19mm (3/4 in.); 38- to 286-mm (2- to 12-in.) widths are usually stocked, in even increments. Siding—Sidingis specifically intendedto cover exterior walls. Beveledsiding is ordinarilystocked only in white pine,ponderosapine,westernredcedar, cypress, or redwood. Drop siding, also known as rustic or barn siding, is usually stocked in the same speciesas is beveledsiding. Sidingmay be stockedas B&BTR or C&BTRexceptin cedar, where Clear, A, and B gradesmay be available, and redwood, whereClear All Heart, Clear, and B gradesmay be found. Verticalgrain (VG) is sometimes part ofthe grade designation. Drop siding is also sometimesstockedin sound knottedC and D gradesof Southern Pine, DouglasFir, and hemlock. Drop sidingmay be surfaced andmatched,or shiplapped. Knottygrades ofcedar (SelectTightKnot (STK) andredwood (Rustic)are commonly available. Flooring—Flooringis made chieflyfrom hardwoods, such as oak and maple, andtheharder softwoodspecies, such as Douglas-fir, western larch, and Southern Pine. Often, at least one softwoodand one hardwoodare stocked. Flooringis usually 19 mm (3/4 in.) thick. Thicker flooring is available for heavy-dutyfloors. Thinnerflooringis available, especially for re-covering old floors. Vertical- and flat-grained (also calledquartersawn andplainsawn) flooring is manufactured from both softwoods andhardwoods. Vertical-grained flooringshrinks and swells less than flat-grained flooring, is more uniformin texture,andwears more uniformly, and the edgejoints have less tendencyto open. Softwoodflooring is usuallyavailablein B&BTR,C Select, or D Selectgrades. Inmaple, thechiefgradesare Clear, No. 1, and No. 2. The gradesin quartersawn oak are Clear and Select, and in plainsawn,Clear, Select, and No. I Common. Quartersawn hardwoodflooring has the same advantages as does vertical-grained softwoodflooring. In addition, the silveror flaked grainofquartersawn flooringis frequently preferred to the figure ofplainsawn flooring.

Casing and Base—Casingand base are standard items in themore importantsoftwoodsand arestocked in mostyards in at least one species. The chiefgrade, B&BTR,is designed to meetthe requirements ofinteriortrim for dwellings. Many casingand base patternsare surfaced to 17.5 by 57 mm (11/16by 2-1/4 in.); other sizes include 14.3 mm (9/16 in.) by 76 mm (3 in.), by 83 mm (3-1/4 in.), and by 89mm(3-1/2 in.).Hardwoodsfor thesame purposes,such as oak and birch, may be carriedin stock in theretail yard or obtainedon specialorder. Shingles and Shakes—Commonlyavailableshingles are sawn from westernredcedarand northern white-cedar. For westernredcedar,the shingle gradesare No. 1, No. 2, and

No. 3; for northern white-cedar, Extra, Clear, 2nd Clear, Clearwall, and Utility. Shingles that containonly heartwoodare more resistantto decay thanare shingles that containsapwoOd. Edge-grained shingles are less likelyto warp and split than flat-grained shingles, thick-butted shingles less likelythan thin-butted shingles,and narrow shingles less likelythan wide shingles. The standardthicknessvalues ofthin-buttedshinglesare describedas 4/2, 5/2-1/4, and 5/2 (four shingles to 51 mm (2 in.) ofbutt thickness,five shingles to 57 mm (2-1/4in.) ofbuttthickness,and five shingles to 51 mm (2 in.) ofbutt thickness). Lengths may be 406, 457, or 610mm (16, 18, or 24 in.). Random widths and specified("dimension"thingle) widthsare available in western redcedar, redwood,and cypress. Shingles are usually packedfour bundlesto a square.A square ofshingles will coverroughly9 m2 (100 ft2) o:roof area whenthe shingles are appliedat standard weather exposures. Shakes are hand splitor hand split and resawnfromwestern redcedar. Shakes are ofa singlegrade and mustbe 100% clear.In the caseofhand split andresawnmaterial,shakes aregraded from thesplitface.Hand-splitshakes aregraded from thebest face. Shakesmust be 100% heartwood.The standardthicknessof shakes rangesfrom 9.5 to 32 mm (3/8 to 1-1/4 in.). Lengthsare 457 and 610 mm (18 and24 in.), with a special"Starter—FinishCourse" length of381 mm (15 in.).

Important Purchase Considerations Some pointsto considerwhenorderinglumberortimbers

arethefollowing:

1. Quantity—Lineal measure, boardmeasure, surface measure, numberofpieces ofdefmitesize and length.Consider that the boardmeasuredependson the thicknessand widthnomenclature usedand that the interpretation of these must be clearlydelineated. In other words, such featuresasnominalor actualdimensions and pattrnsize must be considered.

2. Size—Thickness in millimetersor inches—nominal or actualifsurfaced on faces; widthin millimeters or inches—nominal or actualifsurfaced on edges; length in metersor feet—maybenominalaveragelength,limiting length, or a singleuniformlength.Oftenatrade cLesignation, "random"Jength, is used to denote a nonspccified assortment oflengths. Suchan assortmentshould contain critical lengths as well as a range. The limits allowedin makingthe assortmentrandom can be establishedatthe time ofpurchase.

3. Grade—As indicated in gradingrules oflumbermanufacturing associations. In softwoods that are in compliance with the American Softwood LumberStandard, each piece oflumbermay be grade stamped with its official

grade species identification, aname or numberidentif'ing

5—17

theproducingmill, thedrynessat thetime ofsurfacing, and a symbol identifjingthe inspectionagencysupervising the grading inspection. The grade designation stampedon a piece indicatesthe quality at the time the piecewas graded.Subsequent exposure to unfavorable storage conditions,improperdrying,or carelesshandling may cause the materialto fall belowits originalgrade. Workingorrecuttinga gradedproduct to a patternmay changeor invalidate the originalgrade.The purchase specification shouldbe clear inregardto regrading or acceptance ofworkedlumber. In softwood lumber, grades for dry lumbergenerallyare determined after kiln drying and surfacing. However, this practiceis notgeneralfor hardwoodFactorylumber, wherethe grade is generally based on quality and size prior to kiln drying. To be certain the product grade is correct, refertothe gradingrule by number and paragraph. 4. Speciesor speciesgroup ofwood—Suchas DouglasFir, SouthernPine, Hem—Fir. Somespecieshave been grouped for marketing convenience; othersare sold under a varietyofnames.Be sure thespecies or species group is correctlyand clearlydescribedon the purchase 5.

6.

7.

8.

9.

specification. Product—Suchas flooring, siding, timbers,boards. Nomenclaturevariesby species,region, andgrading association. To be certain the nomenclature is correctfor theproduct,referto thegradingruleby numberand paragraph. Conditionof seasoning—Such as air dry, kiln dry. Softwood lumber less than 114 mm (nominal5 in.) in thickness dried to 19% moisturecontentor less is defmedas dry by the AmericanSoftwoodLumberStandard. Kilndried lumber is lumberthat has been seasonedin a chamberto a predetermined moisturecontentby applyingheat. Green lumberis lumberless than 114 mm (nominal 5 in.) in thickness,which has a moisturecontent in excess of 19%.Ifthe moisturerequirement is critical, the level ofmoisturecontent and the methodby whichit will be achievedmust be specified. Surfacing and working—Rough (unpianed), surfaced (dressed, planed),or patternedstock. Specif,'condition. Ifsurfaced, indicatecode (S4S, SiS1E). Ifpatterned, list patternnumberwith referenceto appropriate grade rules. Grading rules—Official gradingagency nameand nameof officialrules under whichproductis graded,productidentification, paragraphandpage numberofrules, and date of rules or official rule edition may be specified by the buyer. Manufacturer—Name ofmanufacturer ortradenameof specific product or both. Most lumberproducts are sold withoutreference to a specific manufacturer. Ifproprietaiy namesor qualityfeatures ofa manufacturer are required, this must be stipulatedclearlyon the purchaseagreement.

5—18

10. Reinspection—Procedures forresolution ofpurchase disputes. The AmericanSoftwoodLumberStandardprovidesfor procedures to be followedin resolutionof manufacturer—wholesaler—consumer conflicts over quality or quantity ofALS lumbergrades. The dispute maybe resolved by reinspectingthe shipment.Time limits, liability, costs, and complaintproceduresare outlinedin the grade rules ofboth softwoodandhardwoodagencies underwhichthe disputed shipment was graded and purchased.

Commonly Used Lumber

Abbreviations

The following standardlumberabbreviations are commonly used incontractsand other documents forpurchaseand sale

oflumber.

AAR

Association ofAmericanRailroads

AD

air dried

ADF AF

after deducting freight

ALS

American LumberStandard

AST

B&B, B&BTR B&S

antistaintreated;at shiptackle (westernsoftwoods) average all widths and lengths see EB1S, CB1S, andE&CB1S see EB2S, CB2S, andE&CB2S B and Better beamsand stringers

BD

board

BDFT BDL

board feet

BEV

bevel or beveled boxed heart billoflading board measure

AV or avg AW&L B1S B2S

BH B/L, BL BM BSND BTR CB

CBIS CB2S

cc cftorCu. ft. CIF CIFE CG2E

alpinefir

bundle

bright sapwood, no defect better center beaded center bead on one side centerbead ontwo sides cubicalcontent cubic foot or feet cost and freight cost, insurance, and freight cost, insurance,freight, and exchange center grooveon two edges

C/L

carload

CLG

ceiling

CLR

clear

CM

center matched

Corn

Common

CONST

construction caulking seam

CSG

casing

CV CV1S

center V center V on one side

CV2S

DB Cig DBPart DET DF

Douglas-fir Douglas-fir plus larch

DF-L DIM DKG D/S,DS,D/Sdg D1S,D2S D&M D&CM D&SM D2S&CM D2S&SM E EB1S EB2S, SB2S

EE EM EV1S, SV1S EV2S, SV2S E&CB1S E&CB2S, DB2S, BC&2S E&CViS, DV1S,V&CV1S

FOHC FOK FRT, Frt FT, ft

flooring

free on board (named point) free ofheart center free ofknots freight

FT. SM

foot,feet feet surface measure

center V ontwo sides

G

girth

double-beaded ceiling (E&CB1S) double-beaded partition(E&CB2S)

GM

double end-trimmed

HB,H.B. HEM

grade marked groovedroofing hollowback

G/R

hemlock

dimension

Hrt

decking drop siding see S1S and S2S dressedand matched dressedand center matched dressedand standardmatched

H&M

mixedhemlockand fir (Hem—Fir) heart hitand miss

H orM

hitor miss

IC

incense cedar

IN, in.

inch, inches

md

industrial

Iwp

dressedtwo sides and centermatched dressedtwo sides and standard matched

J&p

Idaho whitepine joists andplanks

edge edge bead one side edge beadon two sides eased edges edge (verticalor rift) grain end matched

EG

FLU, Fig FOB

edge V one side edge V two sides edge and centerbead one side edge and centerbead two sides edge and centerV one side

H-F

JTD KD KDAT

L

jointed kiln dried kiln-driedafter treatment western larch

LBR, Lbr LCL

lumber

LGR

longer

LGTH

length

Lft, Lf

linealfoot, feet

LIN, Lin LL

lineal

LNG,Lng

lining

LP

lodgepole pine thousand

less than carload

longleaf

E&CV2S, DV2S, V&CV2S

edge and centerV two sides

M MBM, MBF, M.BM

thousand(feet) board measure

ES

Engelmannspruce allowable stress(MPa (lb/in2)) in bending; tension, compressionand shearparallelto grain; and incompressionperpendicular to grain, respectively facial area

MC,M.C.

moisture content

MERCH, Merch

merchantable

MLDG, Mldg

moulding

Mft

PG

factory free alongside (vessel) Firstsand Seconds Firsts and Seconds one face feet board measure flat orslash grain

FJ

fingerjoint; end-jointed lumber usingfinger-joint

NOFMA No.

thousandfeet mixed species machinestress rated nosed net board measure National Oak Flooring Manufacturers Assoiiation number

Fb,F,

F, F,F

FA Fac FAS FAS FASIF FBM, FtBM

configuration

MG MR

M-S MSR

N NBM

MapleFlooring Manufacturers Association medium grain ormixedgrain mountain hemlock

5—19

N1E or N2E

nosed one or two edges order

S&E

partially air-dried paragraph

S2E SIS

side and edge (surfacedon) surfacedone edge surfacedtwo edges surfacedone side

partition

S2S

surfaced two sides

pattern

545

Pcs.

pieces

S1S&CM

PE

plainend

S2S&CM

PET

precision end-trimmed

S4S&CS

W

ponderosapine posts andtimbers see S1S and S2S

SIS1E

random

S2S&SL

Ord PAD

PAR,Par PART, Part PAT, Pat

S1E

REG,Reg

regular

S2S&SM

surfacedfour sides surfacedone side and center matched surfaced two sides and center matched surfaced four sidesand caulkingseam surfaced one side, one edge surfaced one side, two edges surfaced two sides, one edge surfaced two sides and shiplapped surfaced two sides and standard matched

Rig.

roofing

TBR

timber

rough

T&G

randomlengths randomwidths

TSO

tonguedand grooved treating service only (nonconforming to standard)

P&T PIS,P2S RDM

RGH, Rgh R/L, RL RJW, RW RES

singlebeadoneside

SDG, Sdg S-DRY

siding

surfaceddry; lumber ALS for softwood

SEL, Se! SE&S SG S-GRN SGSSND

Sitka spruce

S/L, SL, S/Lap SM

shiplap

Specs

specifications

SP

sugar pine

SQ

square

SRB

squares stress-ratedboard standard

STD, Std

Std.lgths. STD. M SS SSE SSND STK STK STPG

standardlengths standard matched Sitka spruce sound square edge sap stain, no defect (stained) Selecttight knot stock stepping structural

SYP

SouthernPine

utility

WCH WCW

vertical (edge) grain see EVIS, CV1S,andE&CV1S see EV2S, CV2S,andE&CV2S western cedar WestCoast hemlock WestCoastwoods

WDR, wdr

wider

WF WHAD

whitefir wormholes (defect) wormholes (no defect)

V2S 19% moisture contentper

surface measure

STR,STRUCT

5—20

UTIL VU VIS

square edge Selector Select grade square edge and sound slashorflat grain surfaced green; lumber unseasoned, >19% moisturecontent per ALS for softwood sapwood, gum spots and streaks,no defect

SIT. SPR

ss

S2S1E

resawn

SB1S

SE

SIS2E

WC

WHND WT WTH WRC WW

weight width

western redcedar whitewoods (Engelmann spruce, any true firs, any hemlocks, any pines)

Reference USDC. [Current edition].American softwoodlumber

standard.Prod. Stand. PS—20—94.Washington,DC: U.S. Department ofCommerce.

I

Chapter

Lumber Stress Grades and Design Properties David E. Kretschmann and David W. Green

Contents Responsibilitiesand Standards for StressGrading 6—2

AmericanLumberStandardCommittee

6—2

NationalGradingRule 6—3 Standards

6—3

VisuallyGraded Structural Lumber 6—3 Visual Sorting Criteria 6—3 Procedures forDerivingDesignProperties

6—5

Machine-Graded Structural Lumber 6—7

Machine SortingCriteria

6—7

Procedures for DerivingDesignProperties

6—8

QualityControl 6-10 AdjustmentofProperties forDesignUse 6—il Shrinkage 6-11

SizeFactor 6-11 MoistureAdjustments 6—12 DurationofLoad

6—12

Treatment Effects 6-13 Temperature Effects 6-14 References

6—14

umbersawn from a log,regardless ofspecies and size, is quitevariablein mechanical properties. Piecesmaydiffer in strength by several hundred For simplicity and economyin use, pieces oflumber percent. ofsimilarmechanical properties are placedin categories calledstress grades,whichare characterized by (a) one or more sortingcriteria, (b) a set ofproperties for engineering design,and(c) a unique grade name. This chapterbriefly discusses the U.S. Department oC CommerceAmerican Softwood LumberStandardPS2O(1994) sorting criteria fortwo stress-grading methods, and the philosophyofhowproperties forengineering design are derived. The derivedproperties are then used in one oftwo design formats: (a) the loadand resistance factor design (LRFD), whichis basedon areferencestrength at the 5th percentile 5-mm bendingstress (AF&PA 1996), or (b) the allowable stress design(ASD), which is based on a design stress at the lower5th percentile 10-year bendingstress. The properties depend on the particularsortingcriteriaand on additional factors that are independent ofthe sortingcriteria. De sign properties are lowerthanthe average properties ofclear, straight-grained wood tabulated in Chapter4. From oneto six designproperties are associatedwith a stress grade: bending modulus ofelasticity foran edgewiseloading orientation and stress in tension and compression parallelto thegrain, stress in compression perpendicular tothe grain, stress in shearparallelto the grain, and extreme fiber stress in bending. As istrueofthepropertiesofany structurai material,the allowable engineering designpropertiesmust be eitherinferredor measurednondestructively. Inwood, the propertiesare inferredthroughvisualgrading criteria, nondestructive measurement suchas flatwisebendingstiffnass or density, or a combination ofthese properties. These nondestructive tests provideboth a sortingcriterionand a means

ofcalculating appropriate mechanical properties.

The philosophies containedin this chapterare used by a numberoforganizations to developvisual andmachinestress grades. References are madeto exactprocedures and the resultingdesignstresses,but these are not presentedin detail.

6—1

Responsibilities and Standards for Stress Grading

American LumberStandard. Under the auspices ofthe ALSC is theNationalGrading Rule, whichspecifiesgradingcharacteristics for different gradespecifications.

Anorderly, voluntary, but circuitous system ofresponsibilitieshas evolvedin theUnited States for the development,

Organizations that write and publishgrading rule books containing stress-grade descriptions are calledrules-writing agencies. Grading rules that specify American Softwood LumberStandard PS 20—94 must be certifiedby the ALSC BoardofReviewfor conformance with this standard. Organizations that write gradingrules, as well as independentagencies, can be accreditedbytheALSC Boardof Reviewto providegradingand grade-marking supervision and reinspection services to individual lumbermanufacturers. Accredited rules-writing and independentagenciesare listed in Table 6—1. The continued accreditation ofthese organizations is under the scrutinyofthe ALSCBoard ofReview.

manufacture, and merchandising ofmost stress-graded lumber. The system is shown schematically in Figure 6—I. Stress-grading principles are developed from research fmdings and engineering concepts,often withincommittees and subcommittees ofthe American Society forTestingand Materials.

American Lumber Standard Committee Voluntaryproduct standards are developed underprocedures publishedby the U.S. DepartmentofCommerce. The DepartmentofCommerce NationalInstitute ofStandards and Technology (NIST),working with rules-writingagencies, lumberinspectionagencies,lumberproducers, distributors andwholesalers,retailers, end users,and members ofFederal agencies, work throughthe American LumberStandard Committee (ALSC) to maintaina voluntaryconsensus softwood standard, calledthe American Softwood Lumber Standard(PS 20—94). The PS 20—94 Standardprescribes the ways in which stress-grading principles canbe used to formulate gradingrules designatedas conforming to the

Most commercial softwood species manufactured in the UnitedStates are stress graded underAmericanLumber Standardpractice. Distinctive grade marksforeach species or species groupingare providedby accredited agencies. The principles ofstress gradingare alsoappliedto several hardwood species underprovisions ofthe American Softwood LumberStandard. Lumberfound in the marketplacema be stress graded undergrading rules developedin accordance Table 6—1.Sawn lumber grading agenciesa Rules-writing agencies Northeastern LumberManufacturersAssociation

(1) Formulation of stress grading principles University staffmembers Government researchers Industry R&Dstaff Consumer representatives '1r

1(2) Product standards American LumberStandard Committee I and its Board of Review __1 I

National Grading Rule Committee National Institute of Standards and Technology

Review and adoption (3) Formulation and publication of stress-grading rules Rules-writing agencies - _______ (4) Grading agency accreditation American LumberStandard Committee

(5)Grademarksupervision and reinspection Rules-writing agencies Independent inspection agencies

(6) Manufactureand marketing of American standard stress-graded lumber Sawmills

Figure 6—1. Voluntarysystem of responsibilities for stressgrading under the American Softwood Lumber Standard.

6—2

(NELMA) Northern Softwood LumberBureau (NSLB) Redwood Inspection Service (RIS) Southern Pine Inspection Bureau (SPIB) West Coast Lumber Inspection Bureau (WCLIB) Western Wood Products Association (WWPA) National LumberGradesAuthority (NLGA)

Independentagencies California LumberInspection Service Pacific Lumber Inspection Bureau, Inc. Renewable Resource Associates, Inc. Timber Products Inspection Alberta Forest Products Association Canadian Lumbermen'sAssociation Canadian Mill Services Association Canadian Softwood Inspection Agency, Inc. Cariboo Lumber Manufacturers Association Central Forest Products Association ConiferousLumber Inspection Bureau

Council of Forest Industriesof British Columbia Interior LumberManufacturers Association MacDonald Inspection Maritime LumberBureau Newfoundland LumberProducersAssociation Northern Forest Products Association Ontario LumberManufacturers Association Pacific LumberInspection Bureau QuebecLumber Manufacturers Association aFor updatedinformation, contact American Lumber Standard Committee, P.O. Box 210, Germantown, MD 20874.

with methods approvedby the ALSC orby someother stress-grading rule, or itmay not be stress graded. Only those stress gradesthat meet the requirements ofthe voluntary American SoftwoodLumberStandardsystem are discussed in this chapter.

National Grading Rule Stress grading underthe auspices ofthe ALSC is appliedto

many sizes and several patternsoflumberthat meet the American Softwood LumberStandard provision. However, most stress-gradedlumberis dimensionlumber(standard38 to 89 mm (nominal2 to 4 in.) thick)and is governedby uniformspecifications underthe NationalGrading Rule. The NationalGrading Ruleprovidesguidelinesforwritinggradingrules for lumberin this thicknessrange and specifies gradingcharacteristics fordifferent grade specifications. American Softwood LumberStandarddimension lumberin this thicknessrange is requiredto conform to the National Grading Rule, except forspecialproductssuch as scaffold planks. Graderules for other sizes, such as nominal5-in. (standard1 14-mm) or larger structural timbers may vary betweenrules-writing agencies orspecies. The NationalGrading Rule establishes the lumberclassifications and grade namesforvisuallystress-graded dimension lumber(Table6—2)and alsoprovidesforthe gradingof dimensionlumberby a combination ofmachine and visual methods.Visualrequirements for this type oflumber are developedby therespective rules-writing agencies for particularspecies grades.

Table 6—2. Visual grades described in National Grading Rule

Bending

strength

Lumber classificationa

Grade name

Light framingb

Construction

34

Standard

19

Utility Select Structural

9

Structurallight framingb

3

67 55 45 26

Stud

26

Select Structural

65

1

2 Studc Structural joists and planksd

ratio (%)

1

2 3

55 45

26

2Contact rules-writing agenciesfor additional information. bStandard 38 to 89 mm (nominal 2 to 4 in.) thick and wide. Widths narrower than 89 mm (4 in.) may have different strength ratio than shown. CStandard 38 to 89 mm (nominal 2 to 4 in.) thick, 38 mm in.) wide. dStandard 38 to 89 mm (nominal 2 to 4 in.) thick, 140 mm in.) wide.

Standards Table6—2 also shows associatedminimumbending strength ratios to providea comparative index ofquality.The strength ratio is the hypothetical ratio ofthe strengthofa piece oflumber with visiblestrength-reducing growthcharacteristicsto its strengthifthose characteristics were absent. Formulas for calculating strengthratios are given in American Society of Testing and Materials (ASTM)standard D245. The corresponding visual description ofthe c.imension lumbergradescan be found in the gradingrule booksof therules-writingagencieslisted in Table 6—1. Designproperties will vary by species.The designproperties for each species and grade are publishedin the appropriate rule books and in the NationalDesignSpecfIcationfor Wood Construction(AF&PA 1997).

Grouping of Species Most speciesare grouped togetherand the lumberfromthem treatedas equivalent. Speciesare usually groupedwhenthey have about the same mechanical properties, when th wood oftwo or more species is very similarin appearance, or for marketing convenience. Forvisual stress grades, ASTM D2555 contains procedures forcalculating clear wood properties for groups ofspecies to be usedwith ASTM 1)245.

ASTMD1990contains proceduresfor calculating design properties for groups ofspecies tested as full-sized members. The propertiesassignedto a group by such procedureswill often be different from those ofany species that makeupthe group. The group willhave a unique identity, with nomenclatureapprovedbythe Board ofReview ofthe ALSC. The identities, properties, and characteristics ofindividual species ofthe group arefound in thegrade rules for anyparticular species or species grouping. In the case ofmachine tress grading, the inspectionagencythat supervises the grading certifies by testingthat the design propertiesin that grade areappropriate forthe species or species groupingarLdthe gradingprocess.

Foreign species Currently,the importation ofstructurallumberis governed by two ALSCguidelinesthat describe the application ofthe American LumberStandardand ASTM Dl990 procedures to foreign species. The approval process is outlinedin Table 6—3.

Visually Graded Structural Lumber Visual Sorting Criteria Visual gradingis the originalmethodfor stress grading. It is basedon the premisethat mechanical properties oflumber differ from mechanical properties ofclearwoodbecausemany growth characteristicsaffectproperties andthese characteristics canbe seen andjudgedby eye. Growthcharacteristics are used to sort lumberinto stress grades. The typicalvisual sortingcriteriadiscussedhere are knots, slope ofgrain,

6-3

Table 6—3. Approval process for acceptance of design values forforeign species

I 2 3 4

Rules-writing agency seeks approval to include speciesin grade-rulebook. Agency developssamplingand testing plan, followingAmerican LumberStandard Committee (ALSC) foreign importation guidelines,which must then be approved by ALSC Board of Review. Lumberis sampledand tested in accordancewith approved sampling and testing plan. Agency analyzes data by ALSC Board of Reviewand ASTM D1990 procedures and other appropriatecriteria

(if needed). 5 6 7 8 9

Agency submits proposed design valuesto ALSC Board of Review. Submission is reviewedby ALSC Board of Reviewand USDA Forest Service, Forest Products Laboratory. Submission is available for comment by other agenciesand interested parties. ALSC Board of Reviewapproves(or disapproves) design values,with modification (if needed) based on all available information. Agency publishesnew design values for species.

checksand splits, shake,density, decay,heartwoodand sapwood, pitch pockets,and wane. Knots Knotscauselocalizedcrossgrainwith steepslopes.A very damaging aspect ofknots in sawn lumberisthat the continuity ofthe grain around the knot is interruptedby the sawing process.

In general, knotshave a greatereffecton strength in tension than compression; in bending, the effectdepends on whether a knot is in thetensionor compression sideofa beam (knots alongthe centerline have little or no effect).Intergrown (or live) knots resist (or transmit)some kindsof stress,but encasedknots (unlessvery tight) or knotholes resist (or transmit)little or no stress. On the other hand, distortionof grain is greater around an intergrown knot than aroundan encased(ordead) knot ofequivalent size. As a result,overall strength effectsare roughly equalized, and often no distinction is made in stress gradingbetween intergrownknots, dead knots, and knotholes. The zone ofdistortedgrain (cross grain)around aknot has less "parallelto piece" stiffness than does straight-grained wood; thus, localizedareas oflow stifThessare often associatedwith knots. However,such zonesgenerallyconstitute only a minorpart ofthe total volumeofa piece oflumber. Because overallstiffness ofa piecereflects the character of all parts, stiffnessis not greatly influencedby knots.

Thepresenceofaknot has agreater effecton most strength propertiesthan on stiffness. The effecton strength depends approximately on the proportionofthe cross section ofthe piece oflumberoccupiedby the knot, knot location, and distributionofstress in the piece.Limits on knot sizes are thereforemadeinrelationto the widthofthe face and locationonthe face in whichtheknot appears. Compression

members are stressedabout equallythroughout, and no limitationrelated to location ofknots is imposed. In tension, knots alongthe edgeofa membercause an eccentricity that inducesbendingstresses, and they shouldtherefore be more

6-4

restrictedthan knotsaway from the edge. In simplysupported structural members subjectedto bending, stresses are greaterin the middle ofthe length and at the top and bottom edgesthan at rriidheight. Thesefacts are recognizedin some grades by differing limitationson the sizes ofknots in different locations.

Knotsin glued-laminated structural membersare not continuous as in sawn structural lumber, and differentmethods are used for evaluating their effecton strength(Ch. 11).

Slope of Grain Slope ofgrain (crossgrain)reducesthe mechanicalproperties oflumberbecausethe fibersarenot parallelto theedges.

Severely cross-grained piecesare also undesirable because they tendto warp with changes in moisture content. Stresses causedby shrinkage during dryingare greaterin structural lumberthan in small, clear straight-grained specimensarid areincreased in zones ofslopingor distortedgrain. To provide a margin ofsafety, the reductionin designproperties resulting from cross grain in visuallygradedstructural lumberis considerably greaterthan that observedin small, clear specimens that containsimilar cross grain.

Checks and Splits Checksareseparations ofthe wood that normallyoccur across or through the annual rings,usuallyas a result of seasoning. Splitsare a separationofthe wood throughthe piecetothe opposite surface or to an adjoining surface caused by tearingapart ofthe wood cells.As opposedto shakes, checks and splitsare ratedby only the areaofactualopening. Anend-splitis considered equalto an end-checkthat extends throughthe full thickness ofthe piece.The effectsofchecks and splits on strength and the principlesoftheirlimitation are the same as those for shake.

Shake Shake is aseparation

or a weaknessoffiberbond,betweenor

throughthe annualrings,that is presumedto extend lengthwise without limit. Because shakereducesresistanceto shear

in memberssubjected to bending, gradingrules therefore restrict shakemost closelyin those parts ofa bendingmemberwhere shearstresses are highest. In memberswith limited cross grain,which are subjectedonly totensionor compression, shakedoes not affectstrengthgreatly. Shake maybe limitedin a grade becauseofappearance and becauseit permits entrance ofmoisture, whichresultsin decay.

Density Strengthis relatedto the mass perunit volume (density)of

clear wood.Propertiesassignedto lumberare sometimes modifiedbyusingthe rate ofgrowthand percentage oflatewood as measuresofdensity.Typically, selectionfor density requires that the rings per unit lengthandthe percentage of latewood be within a specifiedrange. It is possible to eliminate somevery low-strength pieces from agrade by excluding those that are exceptionally low in density.

Decay Decayin most forms shouldbe prohibitedorseverelyrestrictedin stress grades becausethe extentofdecay is difficult to determine and its effecton strength is often greaterthan visualobservation would indicate.Decayofthepockettype (for example,Fomespini) can be permittedto someextentin stress grades, as can decay that occursin knots but does not extendinto the surroundingwood.

Heartwood and Sapwood Heartwooddoes not needto be takeninto account in stress gradingbecauseheartwoodand sapwoodhavebeen assumed to have equalmechanical properties. However, heathvood is sometimes specifiedin avisual grade becausethe heartwood ofsome speciesis more resistantto decaythan is thesapwood; heartwoodmayberequired ifuntreatedwood will be exposed to a decay hazard.On the otherhand, sapwoodtakes preservativetreatmentmore readily thanheartwoodand it is preferable for lumberthat will betreatedwith preservatives.

Pitch Pockets Pitch pockets ordinarily have so little effect on structural lumberthat they can be disregarded in stress gradingifthey are smalland limitedin number.The presenceofa large number ofpitch pockets,however, may indicateshake or weaknessofbondbetweenannualrings.

Wane Wanerefersto bark or lack ofwood onthe edgeor corner of a pieceoflumber, regardless ofcause (excepteasededges). Requirements ofappearance, fabrication, or ample bearing or nailing surfaces generallyimpose stricterlimitations onwane than does strength. Wane is thereforelimited in structural lumberon those bases.

Procedures for Deriving Design Properties

members (ASTM Dl990 in-gradetestingprocedure) or (b) appropriate modification oftest resultsconductedon smallclear specimens (ASTM D245 procedure for small clearwood). Design properties for the major commerial softwooddimension lumberspeciesgiven in currentdesign specification and codesin theUnitedStates havebeen derived from full-size membertestresults. However, design properties for most hardwooddimension and structuraltimbers (largerthan standard 89-mm-(nominal 4-in.-,actual 3-1/2-in.-) thick"timbers")ofall species are still derived usingresultsoftests on smallclear samples.

Procedurefor Small Clear Wood The derivationofmechanical propertiesofvisuallygraded

lumberwas historicallybasedon clear woodpropertieswith appropriate modifications for the lumber characteristics allowedby visual sortingcriteria. Sortingcriteriathat influence mechanical properties are handledwith "strengthratios" forthe strengthproperties and with "quality factors" for the modulusofelasticity. From pieceto piece,there is variationin both the clear wood properties andthe occurrence ofgrowth characteristic:. The influence ofthis variability, on lumberproperties. is handleddifferently for strength properties thanformodulusof elasticity.

Strength Properties—Eachstrength property ofapiece of lumber is derivedfrom the productofthe clear wood strength for the species andthe limitingstrength ratio. The strength ratio is thehypothetical ratio ofthe strength ofa piec of lumberwith visiblestrength-reducing growthcharacteristics to its strength ifthose characteristics were absent. Tlie true strengthratio ofapiece oflumberis neverknown and must be estimated. Therefore, thestrengthratio assignedto a growthcharacteristic servesas a predictor oflumberstrength. Strength ratio is expressed as a percentage, rangingflom

0 to 100.

Estimatedstrength ratios for cross grain and density]iave been obtained empirically; strength ratios forother growth characteristics havebeen derived theoretically. For example, to account fortheweakening effectofknots, theassumption is made that the knot is effectivelyahole throughthe piece, reducingthe cross section, as shownin Figure6—2. For a beamcontainingan edgeknot, the bendingstrengthratiocan be idealizedas theratio ofthebendingmomentthat can be resistedby abeam with a reducedcross sectionto that ofa beamwith a full cross section:

SR=l_(k/h)2 whereSRis strengthratio,kknot size, and hwidth cfface containingthe knot. This is the basic expression for the effect ofa knot at theedgeofthevertical face ofabeamthat is deflected vertically. Figure 6—3 shows how strength ratio changeswith knot size according to the formula.

The mechanical propertiesofvisuallygradedlumbermay be established by (a)tests ofarepresentative sample offull-size 6—5

safety) assignedto that grade.In visual grading,according to ASTM D245, this is handledby using a near-minimum clear wood strength as abase value arid multiplyingit by the minimumstrengthratio permittedin the grade to obtain the grade strengthproperty. The near-minimumvalue is called the 5% exclusionlimit. ASTM D2555 providesclear wood strength dataandgives amethodfor estimating the 5% exclusionlimit.

k

B

Figure 6—2. Effectof edge knot:A, edge knotin lumber and B, assumed loss of crosssection(cross-hatched area). 100

80

0 Dl a) Ci)

60 40 20 0

0.2

0.4

0.6

0.8

1.0

k/h

Figure 6—3. Relation between bending strengthratio and size of edge knot expressed as fraction of face width. k is knotsize; h, width of facecontaining the knot. Strengthratios for all knots, shakes,checks, and splits are derivedusing similar concepts.Strength ratio formulas are given in ASTM D245. The same referencecontains guidelines formeasuringvariousgrowthcharacteristics.

For example,supposea 5% exclusionlimit for the clear wood bendingstrengthofa species in the green condition is 48 MPa (7,000 lb/in2). Supposealso that amongthe characteristics allowedin a grade oflumber, one characteristic (a knot, for example)providestheloweststrengthratio iii bending—assumed in this example as 40%. Using the numbers,the bendingstrengthfor the grade is estimatedby multiplying the strengthratio (0.40) by 48 MPa (7,000 lb/in2), equaling 19 MPa (2,800 lb/in2) (Fig. 6—4). The bendingstrength in thç green conditionof95% ofthe pieces in this species in a grade that has a strengthratio of 40% is expectedto be l9 MPa lb/in2). Similar procedures are followedfor other strength properties, using theappropriate clear wood property value and strengthratio. Additional multiplyingfactors are then appliedto produce properties for design, as summarized later in this chapter. Modulus ofElasticity—ModulusofelasticityE is a measure ofthe ability ofa beamto resist deflectionor ofa column to resist buckling. The assignedE is an estimateofthe average modulus, adjustedfor sheardeflection, ofthe lumber grade whentested in staticbending. The averagemodulusof elasticityfor clear woodofthe species,as recordedin ASTM D2555,is used as abase. The clear wood average is multiplied by empirically derived "qualityfactors"to representthe reductionin modulusofelasticity that occurs by lumber grade forpieces tested in an edgewiseorientation.This procedure is outlined in ASTM D245.

Forexample, assume aclear wood average modulusofelasticity of 12.4 GPa(1.8 x 1 lb/in2) for the example shown earlier. The limitingbending strengthratio was 40%.

6

Anindividual pieceoflumberwill oftenhave several characteristicsthat can affectany particularstrength property. Only thecharacteristicthat gives theloweststrengthratio is used to derivethe estimatedstrengthofthepiece. In theory, a

ASTM D245 assigns a quality multiplyingfactor of0.80 for lumberwith this bending strengthratio. The modulus ofelasticity for that gradewould be theproduct oftheclear wood modulusand the quality factor; that is, 12.4 x 0.8 9.9 GPa (1.8 x 0.8 1.44 x 106 lb/in2).

affect strength.

Actualmodulusofelasticity ofindividual pieces ofa grade varies from the averageassumedfordesign(Fig. 6—5). Small individual lots oflumbercanbe expectedto deviatefrom the distributionshown by this histogram. The additionalmultiplyingfactors used to derive final designvalues ofmodulus ofelasticity arediscussedlater in this chapter.

visual stress grade containslumberranging from pieceswith the minimum strength ratio permittedin the grade up to pieceswith the strengthratiojustbelow the next higher grade, Inpractice,there are often pieces in agrade with strengthratios ofa highergrade. This is a resultofgrade reduction for appearance factors such aswanethat do not The range ofstrengthratios in agrade andthe natural variation in clear wood strength give rise to variationin strength betweenpieces in the grade. To accountforthis variationand to ensuresafety in design, it is intendedthat theactual strength ofat least 95% ofthe pieces in agrade exceedthe design properties(before reduction for duration ofloadand 6-6

In-Grade Procedure Toestablish themechanical properties ofspecified grades of lumberfrom tests offull-size specimens, a representative sampleofthe lumberpopulationis obtainedfollowingprocedures in ASTMD2915 and D1990.The specimens are tested using appropriate proceduresgiven in ASTM Dl98

oc"J UC

Clear wood 5% exclusion limit

50

0

C,)

C) C)

6.'.

40

C) C

4

3ç

C)

C) C

C) C

C 0)

C

2.

ci)

0 ci)

C)

0

xQ. uJ

C)

20

0

40

60 Strengthratio (%)

OxW

80

100

Machine-Graded Structural Lumber Machine-graded lumberis lumberevaluatedby a machine

using a nondestructive test followedby visual gradingto evaluate certain characteristics that the machinecannotor may not properly evaluate. Machine-stress-rated (MSR), machine-evaluated-lumber (MEL), and E-rated lumberare threetypesofmachine-graded lumber. Machine-graddlumber allows for bettersortingofmaterial for specific açplications in engineeredstructures. The basic components ofa machine-grading systemare as follows: 1.

sortingand prediction ofstrengththroughmachine-

measured nondestructive determination ofproperties coupledwith visualassessment ofgrowthcharacteristics,

Figure 6—4. Example of relation betweenstrength and strengthratio. 20 16

2.

assignment ofdesignpropertiesbasedon strength prediction, and

3.

qualitycontrol to ensurethat assignedproperties are being obtained. The qualitycontrolproceduresensure

a. proper operation ofthemachineusedto makethe nondestructive measurements,

> (.) C

b.

C)

C-

a) U-

8

appropriatenessofthe predictive parameter—bending strength relationship,and

c. appropriateness ofproperties assignedforten;ion

4

and compression.

0

4.13 (0.6)

6.89 (1.0) Modulus

9.65 (1.4)

12.41 (1.8)

15.17

17.93

(2.2)

(2.6)

of elasticity in edgewisebending (GPa(x106 lb/in2))

Figure 6—5. Histogram of modulus of elasticity observed in a single visualgrade, from pieces selected over a broad geographical range.

or D476 1. Becausethe range ofquality with any one specific grade may be large, it is necessary to assessthe grade quality index (GQI)ofthe sampledmaterial in relationto the assumedGQI. In the North American In-GradeProgram, GQI was the strengthratio calculatedaccording to formulas in ASTMD245. The sampleGQI and theassumedGQI are comparedto see ifadjustmentto the test data is necessary. Anaverage valuefortheedgewise modulusofelasticity or a near-minimum estimateof strength propertiesis obtained using ASTM D1990 procedures. The grade GQI is also used as a scalingperimeterthat allowsfor modeling ofstrength and modulusofelasticity with respectto grade. Thesepropertiesare furthermodifiedfor design use by consideration of service moisture content, durationofload, and safety.

The MSRandMEL systemsdiffer in grade names, quality control, and coefficient ofvariation (COV)forE values. Gradenamesfor MSRlumberare a combination ofthe design bending stress and averagemodulusofelasticity, whereas grade namesfor MELlumberstart with an M designation. For quality control, MSR requirespieces to be tested daily for at least one strength propertyand bendingmodulus ofelasticity in an edgewise orientation, whereas MELrequires dailytension qualitycontroland edgewisebending strengthand stiffnesstesting. Finally, MSRgrades are assigneda COV = 11%on E, whereas MELgradesare assigneda COy 15% on E. Grade namesfor awide range ofmachine-graded lumber commonly available acrossNorth Americaare given in Table6—4. Notall grades are available in all sizes or species.

Machine Sorting Criteria The most commonmethod of sortingmachine-gradedlumber is modulusofelasticityE. Whenused as a sortingcriterionfor mechanical properties oflumber, E can be measured in a varietyofways.Usually,theapparentE, ordeflection relatedto stiffuess, is actuallymeasured. Becauselumberis heterogeneous, the apparentE depends on span, orientation (edge- or flatwise inbending), load speedoftest (staticor dynamic), andmethodofloading(tension, bending, concentrated,or uniform). Any ofthe apparentE values canbe used, as long as the gradingmachineis properly calibrated,to 6—7

Table 6—4. Common grades for machine-gradedlumbera Grade name

Fb

E

(MPa (lb/in2))

(GPa(x106 lb/in2))

F

F11

(MPa (lb/in2))

(MPa (lb/in2))

5.2

14.5 (2.1)

(750) (800) 7.0 (1,020) 8.1 (1,175) 9.5 (1,375) 10.9 (1,575) 12.1 (1,750) 13.3 (1,925) 14.1 (2,050)

11.0 11.2 11.7 12.1 12.4 12.9 13.3 13.6 14.0

15.2

14.8 (2,150)

14.4 (2,100)

15.9

(2,300)

14.8

MSR

9.3 (1,350)

9.0 9.0 10.3 11.0 11.7 12.4 13.1

(1.3) (1.3) (1.5) (1.6) (1.7) (1.8) (1.9)

16.5 (2,400) 17.6 (2,550) 18.6 (2,700)

13.8

(2.0)

19.7

(2,850)

15.9 (2.3)

M—10

9.7

(1,400)

5.5

(800)

10.7 12.4 13.8 15.9 16.5 18.6

(1,550) (1,800)

8.3 10.3 11.7

(1.2)

M—11

(1.5)

5.9 6.9

(2,000) (2,300) (2,400) (2,700)

11.0 13.1 12.4 13.1

(1.6)

(850) (1,000) (1,300) (1,400) (1,900) (1,800)

1350f—1.3E 1450f—1.3E 1650f—1.5E 1800f—1.6E 1950f—1.7E

2100f—1.8E 2250f—1.9E 2400f—2.OE 2550f—2.IE

2700F—

10.0 11.4 12.4 13.4 14.5 15.5

(1,450) (1,650) (1,800) (1,950) (2,100) (2,250)

(2.2)

5.5

(1,600) (1,625) (1,700) (1,750) (1,800) (1,875) (1,925) (1,975) (2,025)

2.2E

2850f—2.3E

(2,150)

MEL M—14 M—19 M—21 M—23 M—24

(1.7) (1.9) (1.8) (1.9)

9.0 9.7 13.1 12.4

11.0 (1,600) 11.5 12.1 12.6

(1,675) (1,750) (1,825) 13.4 (1,950) 13.6 (1,975) 14.5 (2,100)

aForestProducts Society 1997. Other grades are available and permitted. Fb is allowable 10-yearload durationbending stress parallel to grain. E is modulus of elasticity. to grain. F is allowable 10-yearload durationtensile stress parallel F11 is allowable 10-yearload durationcompressivestress parallelto grain.

assign the gradedpiece to a "not to exceed"grade category. Most grading machinesin the United States are designed to detectthe lowestflatwisebendingEthat occursin any approximately 1.2-rn (4-ft)span and the average flatwiseEfor the entirelength ofthe piece.

Anothermethodof sortingmachine-gradedlumberis using density measurementsto estimateknot sizes and frequency. X-ray sources in conjunction with a seriesofdetectors are used to determine density information.Densityinformation is thenused to assign thegradedpiece to a "not to exceed" grade category.

In the United States and Canada,MSR and MEL lumberare alsosubjectedto a visual override becausethe size ofedge knots in combination with E is abetter predictorofstrength than is E alone. Maximumedge knots are limitedto a specified proportionofthe cross section, depending on grade level.Other visual restrictions, whichare primarily appearance ratherthan strengthcriteria, are placedon checks, shake,skips (portionsofboard "skipped"by the planer), splits, wane, and warp.

Procedures for Deriving Design Properties Allowable Stress for Bending A stressgrade derived formachine-graded lumberrelates design strength to a nondestructive parameter. For this example, it will be considered to be E. Because E is an imperfect predictorofstrength, lumbersortedsolelyby average E falls into one offour categories, one ofwhichis sortedcorrectlyand three incorrectly (Fig. 6—6).

Consider, for example, themost simple case (sometimes referredto as "go" or "no go") where lumberis sortedinto two groups: one with sufficient strengthand stiffness for a specific application, the other without.In Figure 6—6a,a regressionline relatingE andstrength is used as the prediction model.The "accept—reject"groups identifiedby theregression sort canbeclassifiedinto four categories:

• Category 1—Material that hasbeen acceptedcorrectly,

that is, pieceshave sufficient strength and stiffliess as defined

• Category 2—Material thathas beenacceptedincorrectly, that is, pieces do not have sufficientstrength

6—8

To minimizethe materialthat falls into category2, adjustments are madeto the propertyassignmentclaimsmade aboutthe sortedmaterial.An appropriate model is one that minimizes the material in category2 or at least reduces itto a lowerrisk level. Additionalgradingcriteria(edge-knot limitations, for example) are also addedto improve1;he efficiency ofthe sortingsystemrelative to the resource and the claimedproperties.

C

0 Cl)

Accept———*.

Commonly, a lowerconfidenceline isusedas the prediction model (Fig. 6—6b). The numberofpiecesthat fall into category 2 is now low compared with the regressionline model. Furthermore, the probabilityofapiece (and thus thenumber ofpieces)falling into category2 is controlled by the confidence line selected.

In actualMSR systems,the lumberis sorted (graded) into E classes. In the UnitedStatesandCanada,the number of grades has increased as specific marketneedshave developed

for MSR lumber. Today, individual grading agencieslist as many as 13 Eclassifications and morethan 20 different grades.The grades are designatedbythe recommended extreme fiberstress in bendingFb and edgewisemodulusof elasticity E. For example,"21OOF—1 .8E" designates an MSR grade with a designstress Fb = 14 MPa (2,100 lb/in2) and E 12.4 GPa (1.8 x 106 lb/in2).

E sort Figure 6—6. Schematic E sort:(a) using a regression line as the predictorshowing four categories: 1—acceptedcorrectly; 2—accepted incorrectly; 3—rejected correctly; and 4—rejected correctly; (b) usinga lowerconfidence line as the predictorand showingthe relatively low proportionof material un the accepted incorrectlycategory (lower right).

•

Category 3—Material that has beenrejectedcorrectly becauseit does not havesufficient strength

• Category 4—Materialthathas beenrejectedcorrectly becauseit doesnothave sufficient stiffliess

Thus, the sort shown in Figure6—6ahas workedcorrectlyfor categories 1, 3, and 4 but incorrectly for category2. Piecesin category2 presenta problem. Thesepieces are accepted as having sufficient strengthbut in reality they do not, and they are mixed with the acceptedpieces ofcategory 1. The numberofproblempieces that fallin category2 depends Oflthe variabilityin the prediction model.

Intheory,any F—Ecombination canbe marketedthat canbe supported by test data. In practice, a mill will usuallyproduceonly a few ofthepossibleexistingF—Eclassifications depending on the potentialofthe timberbeing harvested, mill production capabilities,andproduct or market demand. When a mill has determined the grades it would like to produce(based ontheirlumberresource and marketiagissues),grade boundary machinesettings are used to separate thelumberinto F—E classifications. A qualification ample oflumberis testedby a gradingagency for strength and stiffliess, to verif'that the propermachine settingsaiebeing used. After initial qualification, additionalqualitycontrol tests are performed duringproduction.

Figure6—7 illustrates how Fb—E classifications have been developedhistorically for species groups. Datafor a particular species group are collected, the relationship ofE and MOR is evaluated, and a lowerconfidence line is established forthe species, as illustratedin Figure 6—6b. Usingthe lower confidence line ofthis relationship, an MORvaluecorresponding to the "minimumE" assignedto the grade is determined. The "minimumE"' assignedto the grade representsthe 5th percentile ofthe E distribution. The 5th percentile value is expectedtobe exceededby 95% ofthe riecesin agrade or class.In this example,for a grade withan assigned E of 13.8 GPa (2.0 x 10 lb/in2), the "minimumE" is 11.3 GPa (1.64 x 10 lb/in2). The correspondingMOR value from the lowerconfidence line prediction model,approximatelya 5th percentile MORvalue, is 34.8 MPa (5.04 x i03 lb/in2). This value is then adjusted by a factor (2.1) for assumed 10-year durationofloadand safetyto obtain Fb. This factor appliedto an estimated5th percentile

6—9

Modulus

ofelasticity(xl 06lb/in2) 2.0

48.26(7)

2.2

Quality controlproceduresare necessary to ensure that stresses assigned by amachine-grading systemreflectthe actualproperties ofthe lumbergraded.Theseprocedures must check for correctmachine operation. Verification ofthe relationships betweenbending and other propertiesmay also be requiredby therules-writing agency, particularlyfor fber

nj

C

41.37

c)

0 0c

stress in tensionF1.

34.47

27.58

20.68(3) 13.79 (2)

12 13 14 15 Modulus of elasticity (GPa)

Figure 6—7. Typicalassignment of Fb—E values for MSR lumberin United States (solid lines are minimum E for the Fb—E classification and bending strengths predicted by minimum Evalues).

MOR valueof34.8 MPa (5.04 x i03 lb/in2)yields an Fbof 16.5 MPa (2.40x i03 lb/in2) for the 2.OE grade; in other words, a 2400f—2.OEMSR grade.

Design Stresses for Other Properties in tensionand compression arecommonly develProperties

oped from relationshipswith bendingrather than estimated directly by the nondestructive parameterE. In Canada and theUnited States, therelationships betweenthe5th percentile 10-yearbending stress andthose intensionand compression are baseduponlimitedlumbertesting for thethree properties but supported by yearsofsuccessful experience in construction with visual stress gradesoflumber. For tension, it is assumedthat the ratio ofdesignbendingstress Fbto designtensile stress is between0.5 and 0.8, dependingon thegrade,whereas therelationship between Fb andfiber stressin design compressivestress is assumedto be

F

F

F= [0.338 (2.lFb) + 2060.7]/1.9 Strength in shear parallelto the grain and in compression perpendicular to the grain is poorlyrelatedto modulusof elasticity. Therefore,inmachine stress gradingthese properties are assumedto be grade-independent and are assignedthe same valuesas those for visual lumber grades, exceptwhen predictedfrom specificgravity on amill-by-mill basis. It is permissibleto assign higher allowable stress for shear parallel to grain and compression perpendicular to grain to specific gradesbasedon additional specific gravity research.

6—10

Quality Control

Daily oreven more frequentcalibration ofmachine operation may be necessary. Depending uponmachineprinciple,calibrationmay involveoperating the machineon a calibrat:on bar ofknownstiffuess, comparing gradingmachine E values to those obtained on thesame pieces oflumberby calibrated laboratory test equipment, determining ifmachine-predicted density matchesa calibrationsample density,or in some instances, usingtwo or more procedures. Machineoperation shouldbe certified for all sizes oflumberbeingproducec. Machine settingsmay needto be adjustedto producethe same grade material from different widths. Qualitycontrolproceduresofthe MSR prediction model (E—bending strength relationship) have beenadoptedin Canada and the UnitedStates. Daily,ormore frequently, lumber production is representatively sampledand proofloaded, usually in bending,with supplementary testing in tension.The pieces are proof-loadedto at least twicethe design stress (Fb or F1) forthe assignedFb —Eclassification. Inbending,the piecesareloaded on a random edgewith the maximum-edge defectwithinthe maximummoment area (middleone-third span in third-pointloading)or as near to that point as possible.In tension,the pieces are tested pith a 2.4-rn (8-ft) gaugelength.

Ifthenumberofpiecesin thesamplefailing theproof-test

load indicates ahigh probabilitythat the populationfrom whichthe pieces came does not meet the minimumgrade criteria, a secondsampling and prooftest are conducted immediately. Ifthe second sample confirmsthe resultsofthe first sample, the MSR grading system is declared"out of control"and the operation is shut down to isolateand c:rrect the problem. The lumberthat was incorrectly labeled is then correctly labeled.

Cumulative machine calibration recordsare usefulfor detectingtrends or gradual changein machine operation that might coincide with use and wear ofmachine parts. The proof-test results are also accumulated. Standardstatisticalquality control procedures (such as controlcharts)are used to monitortheproduction processso that it can be modifiedas neededin response to changein the timberresource,andto makethe output fit the assumedmodel.

Too many failures in one, or evenconsecutive,samples do not necessarily indicatethat the systemis out of control. Iftheprediction line is based on 95% confidence, it carl be expectedby chance alonethat 1 samplein 20 will not meet the proof-load requirements. One or more out-of-control samples may alsorepresent a temporaryaberration in

materialproperties(E—strength relationship). In any event, this situation would call for inspectionofthe cumulative qualitycontrolrecordsfor trendsto determine ifmachine adjustmentmightbe needed. A "clean" record(ape;riod whenthe system does not go out ofcontrol)rectifiesthe evaluation ofa systemthought to be out ofcontrol.

Table 6—5. Coefficients for equations to determine dimensional changeswith moisture content change in dimension lumber

Adjustment of Properties

westernred-

for Design

Use

The mechanicalproperties associated with lumber qualityare adjustedto give designunitstressesandamodulusofelasticity suitableforengineering uses.First, a lowerconfidence level is determinedfor the material,andthis valueis then adjusted for shrinkage, size, durationofload, and in ASD,an additional factor ofsafety. Theseadjustment factors are discussed inthe followingtext (specific adjustments are given in ASTM designations D245 and D1990).

Shrinkage As describedin Chapter3, lumber shrinks and swells with changesin moisture content. The amountofdimensional change depends on a numberoffactors, such as species and ring angle. The AmericanSoftwoodLumberStandard, PS 20, lists specificshrinkage factorsfrom green to :15% moisture contentthatwere usedhistoricallyto setgreen lumberdimensions formost species (2.35%forthicknessand 2.80% for width). The standarddoes not providea meansof adjusting lumberdimensions to any other moisture content. The standardalsodoes notprovide specific shrinkage factors for species such as redwood and thecedars, whichshrink less than most species.Using the PS 20 recommendations and an assumedgreen moisturecontentMg, we derive equations that canbe usedwith most speciesto calculatetheshrinkage of lumberas afunctionofpercentage ofmoisture contentM Theequationis applicableto lumberofall annualring orientations. For dimensionlumber, the dimensionsat different moisturecontentscan be estimatedwith the following equation:

d2 =d 1—(a—bM2)/100 l—(a—bM1)I100

whered1 is dimension(mm, in.) at moisture contentM1, d2 dimension(mm, in.) at moisture contentM2, M1 moisture content(%) at d1, M2 moisturecontent (%) at d2, and

a and b are variablesfrom Table6—5.

Size Factor In general, a size effectcauses small members to havea

greaterunitstrengththan that oflargemembers. There are two proceduresfor calculating size-adjustment factors, small clear and In-grade.

WIdth Species Redwood,

Thick ness

a

b

a

b

pa

3.454

0.157

2.816

0.128

22

6.031

0.215

5.062

0.181

28

cedar, and northern white cedar

Other species

°Mg is assumed green moisture content.

Table 6—6. Exponentsfor adjustment ofdimension lumber mechanical properties with change in sizea Exponent

MOR

UTS

UCS

w I

0.29 0.14

0.29

0.13

0.14

0

aMOR is modulus of rupture; UTS, ultimatetensile stress; and

UCS, ultimate compressivestress.

Small Clear Procedure ASTM D245 providesonly a formulafor adjusting bending strength. The bendingstrengthfor lumberis adjustedto a new depthF,, other than2 in. (51 mm) usingthe fo:mula

F;

=LJ

whered0 is original depth (51 mm, 2 in.), d,, newdepth, and F0 originalbendingstrength.

This formulais based on an assumedcenterloadand a span-todepth ratio of 14. A depth effectformula fortwo equalconcentrated loads applied symmetrical to the midspanpointsis given in Chapter8. In—Grade Test Procedures ASTMDI 990 providesa formulafor adjustingbending, tension, and compression parallelto grain. No size adjustments are made tomodulusofelasticity orforthicknesseffectsin bending, tension, and compression. The size adjustmentsto dimension lumber are basedon volumeusingthe formula

= LW2) LL2)

wherePi is property value(MPa, lb/in2) at volume 1, P2propertyvalue (MPa,lb/in2) at volume2, W1 width (mm, in.) at P1, W2width (mm, in.) at P2, L1 length (mm, in.) at P1, andL2length (mm, in.) at P2. Exponentsare defined in Table 6—6.

6—11

40

-

—6

Ce

aC)

30

Table 6—7. Coefficients for moistureadjustment of dimension lumbermechanical properties with change in moisture content8

—

Property (MPa (lb/in2))

Coefficients

MOR

UTS

U)

B1

16.6 (2,415)

21.7 (3,150)

9.6 (1,430)

V 10 0

B2

0.276 (40)

0.552 (80)

0.2 34 (24)

I.-

0

-

20

I

0 7

9

11

I

I

I

110 0

I

14 16 18 20 Moisture content(%)

23

25

Figure 6—B. Modulus of ruptureas a function of moisturecontentfor dimension lumber. Open dots represent the ASTM DI990 model, and solid dots represent the moreprecisequadratic surface model on which the ASTM Dl990 model was based.

Moisture Adjustments For lumber102 mm in) thick that has been dried, have been shownto be relatedquadratistrength properties cally to moisture content. Two relationships for modulusof rupture at any moisturecontent are shown in Figure6—8. Both models start with the modulusofelasticityofgreen lumber. The curveswith solid dots representa precisequadratic model fit to experimental results. In typical practice, adjustments are made to correspondto average moisture contents of 15% and 12% with expectedmaximum moisture contents of19% and 15%, respectively,usingsimplified expressionsrepresentedby the open dot curves.Belowabout 8% moisturecontent,some properties may decrease with decreasing moisture contentvalues,and care shouldbe exercised in these situations. Equationsapplicable to adjusting propertiesto other moisturelevelsbetweengreen and 10% moisture contentare as follows: For MOR,ultimate tensile stress (UTS), and ultimate compressivestress (UCS),the following ASTMD1990 equationsapply: For MOR 16.7 MPa (2,415 lb/in2) UTS 21.7MPa (3,150 lb/in2) UCS

9.7 MPa (1,400 lb/in2) P1

=P2

Thus, there is no adjustmentfor stresses belowthese levels. For MOR> 16.6 MPa (2,415 lb/in2) UTS UCS

6—12

> 21.7 MPa (3,150 lb/in2) > 9.7 MPa (1,400 lb/in2)

UCS

aMOR is modulusof rupture; UTS, ultimate tensile stress; and UCS, ultimate compressivestress.

P2=+I_B1(M_M2) B2_M1) I

whereM1 is moisturecontent 1 (%), M2 is moisture content 2 (%), and B1, B2areconstantsfrom Table6—7.

ForE, thefollowingequationapplies: E1 11.857_(O.0237M2) ).857—(0.0237M1)

whereE1 is property(MPa, lb/in2) at moisturecontent I and £2 is property(MPa, lb/in2) at moisturecontent 2.

For lumberthicker than 102 mm (4 in.), often no adjustment for moisture contentis madebecausepropertiesare assigned on the basis ofwood in the green condition.This lumber is usually put in place without drying, and it is assumedthat drying degradeoffsetsthe increase in strength normally associatedwith loss in moisture.

Duration of Load Designmay be based on either design stressesand a durition ofload factoror on ultimatelimit state designstressesand a time effectsfactor. Both the duration ofloadand time effects factor describethe same phenomenon. In allowable stress design,design stressesare basedon an assumed10-year loading period(callednormalloading). Ifdurationofloading, either continuously or cumulatively, is expectedto exceed 10 years, design stressesarereduced 10%. Ifthe expecteddurationof loading is for shorterperiods, published designstressescan be increasedusing Figure6—9. Ultimate limit-state design stressesare based on a 5-mm loading period. Ifthe durationofloading is expectedto exceed 5 min, limit-state designstresses are reducedby applyingthe time effects factor. Intermittent loading causescumulative effects on strength and shouldbe treatedas continuousload ofequivalent duration. The effectsofcyclicloads ofshort

durationmust alsobe consideredin design(see discussionof fatiguein Ch. 4). These durationofload modifications are not applicableto modulusofelasticity.

0.50 0.53

0

0.56

C))

o

0.59 o 0.62 01.67

ceE

0.71

0(5

5' : .

650 0.77 0.83 .2

00

v

0.91 0 .2 1.00 1.11

0>0, >'>' ,- 00

a)

0

0

E

(3,

1.8

0 C) 0

1.6

0 0

1.4

0

1.2

10 minutes day

VUntreated

ATreated

(5

0

-J

1.0 0.8

(5(5

0

2

4

6

8

10

log load duration (s)

,-

Duration of load

Figure 6—9. Relation ofstrength to duration of load.

Figure 6—10. Load duration factor for material treated with waterborne preservative.

In many design circumstances there areseveral loadson the

Treatment Effects

structure,some actingsimultaneously andeach with a differentduration. When loadsofdifferenttime duration areapplied,the load durationfactor corresponding to the shortest time duration is used. Each increment oftime during which thetotal load is constantshould be treatedseparately, and themost severe condition governsthedesign.Eitherthe design stress or the total designload (but not both) can be adjusted using Figure 6—9. For example,suppose a structure is expectedto support a load of4.8kPa(100 lb/ft2)on and offfor a cumulative durationof 1 year. Also, it is expectedto support its own dead load of0.96 kPa (20 lb/fl2)for the anticipated 50-year life of thestructure.The adjustments to be madeto arriveat an equivalent10-yeardesignload are listedin Table6-8. The more severe designload is 5.36 kPa (112 lb/ft2'), and this load and the designstress for lumberwouldbe used to select members ofsuitablesize. Inthis case,it was convenient to adjust the loads on the structure,althoughthe same result can be obtainedby adjusting the design stress.

Table

6—8. Example of duration

Treatments havebeen shown to affectthe fmal strength of

wood (Ch. 4 for detaileddiscussion). There is a 5°,b reduction in E and a 15% reductionin strengthpropertiesof incisedand treateddimension lumberfor both dry- and wetuse conditions in the United States. In Canada,a 10% reduction in E and a 30% reduction in all strength properties from incisingis appliedto dry-use conditions whereas 5D/ and 15% reductions are used for wet-use conditions. Tlie wet-use factors are appliedin addition to the traditionalwet-use

service factor. Reductions in energy-related properties are about 1.5 to 2 timesthose reportedfor staticstrengthproperties. There is no difference in long-term durationof load behaviorbetween treatedanduntreatedmaterial (Fig. 6—10). Currentdesignstandards prohibitincreases in design stresses beyondthe 1.6 factor for short-term duration ofloadwhen considering impact-type loading formaterial treatedwith waterbome preservative.

of load adjustments

(kPa (lblft2))

Load adjustmenta

Equivalent 10-year design load (kPa (lb/ft2))

1

4.8 (100) + 0.96 (20) = 5.7 (120)

0.93

5.36 (112)

50

0.96 (20)

1.04

1.0 (21)

.

Time (year)

.

Total load

aFigure 6—9.

6-13

Table 6—9. Property adjustment factorsfor in-service temperature exposures Factor In-service Design values

moisture content

F, E Fb,FV,FC,FCI

T

(T

3TC lOOT)

3TC < T

(lOOT <

T

52CC

125T)

52CC < (125F <

T 65CC T 15OF)

Wet or dry

1.0

Dry Wet

1.0

0.9 0.8

0.9 0.7

1.0

0.7

0.5

Temperature Effects As woodis cooledbelow normaltemperatures, its properties increase. Whenheated, its properties decrease. The magnitude ofthe change depends upon moisturecontent. Up to 65°C (150°F), the effectoftemperature is assumedby design codestobe reversible.For structural membersthat will be exposedto temperaturesup to 65°C(150°F), designvalues are multipliedby the factorsgiven in Table 6—9 (AF&PA 1997).Prolongedexposureto heat can lead to a permanent loss in strength (see Ch. 4).

References AF&PA. 1997. Washington,DC: AmericanForest & Paper Association.

Galligan, W.L.; Green, D.W.; Gromala,D.S.; Haskell, J.H. 1980. Evaluation of lumberpropertiesin theUnited States andtheirapplication to structural research.Forest ProductsJournal. 30(10): 45—5 1.

Gerhards,C.C. 1977. Effectofdurationand rate ofloading on strengthofwood and wood based materials.Res. Pap. FPL—RP—283. Madison, WI: U.S. Department

ofAgricul-

ture, Forest Service,Forest Products Laboratory.

Green,D.W. 1989. Moisturecontent and theshrinkageof lumber. Res. Pap. FPL—RP—489. Madison, WI: U.S. Department ofAgriculture, Forest Service, ForestProducts Laboratory.

Green,D.W.; Evans, J.W. 1987. Mechanicalproperties

ofvisuallygradeddimensionlumber. Vol. 1—Vol. 7.

Springfield VA: NationalTechnical Information Service.

Nationaldesign specification forwood construction.

PB—88—l 59—371.

Design valuesforwood construction—a supplementto the national design specification for wood construction.

Green,D.W.; Kretschmann, D.E. 1992. Properties and

AF&PA. 1996. Load and resistance factor design manualfor engineeredwood construction. Washington, DC: American Forest & Paper Association. ASTM. 1998. West Conshohocken,PA: American Society for Testingand Materials. ASTM D198—97. Standardmethods ofstatic tests oftim-

grading ofSouthern Pine timbers.Forest ProductsJournal. 47(9): 78—85. Green,D.W.; Shelley,B.E. 1992. Guidelinesfor assigning allowable properties to visuallygrade foreignspecies based on test data from full sized specimens. Germantown, MD: American LumberStandards Committee.

bersin structural sizes.

Green,D.W.; Shelley,B.E. 1993. Guidelines for assigning allowable properties to mechanically gradedforeign species.

ASTMD245—93. Standard methodsfor establishing structural gradesforvisuallygradedlumber. ASTMD1990—97.Standardmethods for establishingallowableproperties for visually-graded dimension lumber from Tn-gradetests offull-size specimens.

Green, D.W.; Shelley, D.E.; and Vokey, H.P. 1989. In-grade testingofstructural lumber. In: Proceedings of workshop sponsored by In-gradeTesting Committee and Forest Products Society. Proceedings47363. Madison,WI: Forest Products Society.

ASTMD2555—96.Standard methodsfor establishing clear wood strengthvalues. ASTMD2915—94. Standardmethodfor evaluating properties forstress gradesofstructural lumber. ASTMD4761—96. Standardmethods for mechanical propertiesoflumberand wood-base structural materials.

Kretschmann, D.E.; GreenD.W. 1996. Modelingmoisture content—mechanicalproperty relationships for clear SouthernPine. Wood and Fiber Science. 28(3): 320—337.

ForestProductsSociety. 1997. Machine-graded lumber.

Germantown, MD: American LumberStandards Committee.

U.S. Department ofCommerce. 1994. American softwood lumber standard. Prod. Stand. PS2O—94. Washington,DC: U.S. Department ofCommerce. Winandy, J.E. 1995. The influenceoftime—to—failure on

Madison, WI: Forest Products Society. WoodDesign

the strength of CCA-treated lumber. Forest ProductsJournal.

Focus. 8(2): 1—24.

45(2): 82—85.

6—14

I

Chaptei

7I

Fastenings LawrenceA. Soltis

he strengthand stability ofany structure cepend heavilyon the fastenings that hold its parts

Contents Nails 7—2 Withdrawal Resistance7—2

LateralResistance 7—5 Spikes 7—8 Staples

7—8

Drift Bolts 7—9 Wood Screws 7—9 Withdrawal Resistance

7—9

LateralResistance 7—10 Lag Screws 7—11 Withdrawal Resistance 7—11 Lateral Resistance 7—12

Bolts 7—14 Bearing Stress of WoodUnder Bolts 7—14 Loadsat an Angle to the Gram 7—14 Steel Side Plates 7—15 Bolt Quality 7—15 Effect ofMemberThickness 7—15 Two-Member, Multiple-MemberJoints 7—15 Spacing, Edge, and End Distance 7—16 EffectofBolt Holes 7—16 Pre-1991 AllowableLoads 7—17 Post-1991 Yield Model 7—18 ConnectorJoints 7—18 Parallel-to-Grain Loading 7—18 Perpendicular-to-Grain Loading 7—18 DesignLoads 7—20 Modifications 7—21 Net Section 7—23 End Distanceand Spacing

7—23

PlacementofMultipleConnectors 7—23 Cross Bolts 7—24 Multiple-FastenerJoints 7—24 Metal Plate Connectors 7—25 FastenerHead Embedment 7—26 References 7—27

together, One prime advantage ofwood as a structural material is the ease with whichwood structural parts can bejoined together with a wide varietyoffastenings—nails, spikes, screws, bolts, lag screws, drift pins, staples,and metal connectors ofvarioustypes. Forutmost rigidity, strength, and service, each type offastening requires jointdesignsadaptedto thestrength properties ofwood along and acrossthe grain and to dimensionalchangesthat may occur with changes in moisture content. Maximum lateralresistance andsafe design load values for small-diameter (nails, spikes, and wood screws)and largediameter dowel-type fasteners (bolts, lag screws,and drift

9

pins) were based on an empiricalmethodprior to 1 1. Research conducted during the 1980s resultedin lateral resistance valuesthat are currentlybasedon ayield model theory.This theoreticalmethodwas adaptedfor the 1991 editionofthe NationalDesignSpec/Icationfor Wood Construction (NDS). Becauseliteratureand design proceduresexistthat are relatedto both the empiricaland theoretical methods, werefer to the empirical methodas pre-1991 and the theoreticalmethod as post-1991 throughoul: this chapter. Withdrawal resistance methods have notchanged, so thepre- and post-1991 refer onlyto lateralresistance. The information inthis chapterrepresents primarilyForest Products Laboratory research results.A more comprehensive discussion offastenings is given in the American Sccietyof Civil Engineers Manualsand Reportson Engineering Practice No. 84, MechanicalConnections in Wood Structures. Theresearchresultsofthis chapterare often modified for structural safety, basedonjudgmentor experience, and thus information presentedin design documents may differ from information presentedin this chapter. Additionally, researchby others servesas abasis for somecurrentdesign criteria. Allowable stress designcriteriaare presentedinthe NationalDesign Spec/icationfor Wood Constructwnpublishedby the AmericanForest and PaperAssociation; limit states designcriteriaare presented in the Standardfor Load andResistance Factor Design (LRFD)for EngineeredWood Constructionpublishedby the American Society of Civil Engineers.

7—1

Table 7—1. Sizes of bright common wire nails

Nails Nails are themost commonmechanicalfastenings usedin wood construction. There are many types, sizes,and forms of nails (Fig. 7—1).The load equationspresentedin this chapter apply for bright, smooth, commonsteel wire nails driven into wood when there is no visible splitting.For nails other than commonwire nails, the loads can be adjusted by factors given later in the chapter.

Nails in use resist withdrawalloads, lateral loads,or acombination ofthe two. Both withdrawaland lateralresistance areaffectedby thewood, thenail,andthe condition ofuse. In general, however, any variationin these factors has a more pronounced effecton withdrawal resistance thanon lateral resistance.The serviceability ofjointswith nailslaterally loadeddoes not dependgreatlyon withdrawalresistance unless largejointdistortion is tolerable. The diametersofvariouspenny or gauge sizes ofbright common nails are given in Table 7—1. The pennysize designationshould be used cautiously. International nail producerssometimesdo not adhereto the dimensions of Table 7—1. Thus penny sizes, although still widely used, are obsolete. Specifyingnail sizes by length and diameter dimensionsis recommended. Brightbox nailsare generallyof the same length but slightly smallerdiameter(Table7—2), while cement-coatednailssuch as coolers,sinkers, and coatedbox nails are slightlyshorter (3.2 mm(1/8 in.)) and ofsmallerdiameterthan commonnailsofthesame penny size.Helicallyand annularly threadednails generally have smallerdiametersthan commonnails for the samepenny size (Table 7—3).

Withdrawal Resistance The resistanceofanail shank to directwithdrawalfrom a

piece ofwood depends on the density ofthe wood, the diameterofthe nail, andthe depth ofpenetration. The surface conditionofthe nail atthe time ofdrivingalsoinfluencesthe initialwithdrawalresistance.

Gauge

(mm (in.))

6d 8d 10d

11-1/2 10-1/4

50.8 (2) 63.5 (2-1/2)

9

76.2 (3)

12d

9

16d

8

82.6 (3-1/4) 88.9 (3-1/2)

20d 30d 40d 50d 60d

6 5

4 3 2

Figure 7—1. Various types

Length (mm (in.))

3d 4d

14-1/2

31.8 (1-1/4)

14

38.1

Sd

14

6d 7d 8d lOd 16d 20d

12-1/2 12-1/2 11-1/2 10-1/2

44.5 50.8 57.2 63.5 76.2 88.9 101.6

10

9

7—2

4.11 (0.162) 4.88 (0.192) 5.26 (0.207) 5.72 (0.225) 6.20 (0.244) 6.65 (0.262)

(1-1/2) (1-3/4) (2) (2-1/4) (2-1/2) (3)

(3-1/2) (4)

Diameter (mm (in.)) — 1.93 2.03 2.03 2.49 2.49 2.87 3.25 3.43 3.76

(0.076) (0.080) (0.080) (0.098) (0.098) (0.113) (0.128) (0.135) (0.148)

Table 7—3. Sizes of helicallyand annularly threaded nails

16d

20d 30d

smoothwire nail, cement coated, zinc-coated, annularly threaded, helicallythreaded, helicallythreaded and barbed,and barbed.

(4-1/2) (5) (5-1/2) (6)

Gauge

12d

of nails: (left to right) bright

(4)

Size

6d 8d lOd

I

101.6 114.3 127.0 139.7 152.4

2.87 (0.113) 3.33 (0.131) 3.76 (0.148) 3.76 (0.148)

Table 7—2. Sizes of smooth box nails

Size

iJ

Diameter (mm (in.))

Length

Size

Length (mm (in.))

50.8 (2) 63.5 (2-1/2) 76.2 (3) 82.6 (3-1/4) 88.9 (3-1/2) (4) (4-1/2) (5) (5-1/2)

70d 80d

101.6 114.3 127.0 139.7 152.4 177.8

203.2

(8)

90d

228.6 (9)

40d 50d

60d

(6)

(7)

Dia meter (mm (in.))

3.05 3.05 3.43 3.43 3.76 4.50 4.50 4.50 4.50 4.50 5.26 5.26 5.26

(0.120) (0.120) (0.135) (0.135) (0.148) (0.177) (0.177) (0.177) (0.177) (0.177) (0.207) (0.207) (0.207)

Forbright commonwire nails driven into theside grain of seasoned wood or unseasonedwood that remainswet, the results ofmany tests have shownthat the maximum withdrawal load is given by the empiricalequation p=54.12G512DL

(metric)

(7—la)

p=7,850G512DL

(inch—pound)

(7—ib)

wherep is maximum load (N, lb), L depth (mm, in.) of penetrationofthe nail in the memberholding the nail point, G specific gravity ofthewood basedon ovendiyweight and volume at 12% moisture content (see Ch. 4, Tables 4—2 to 4—5), andD diameterofthe nail (mm, in.). (TheNDS and LRFD use ovendryweightand volume as a basis.) The loadsexpressed by Equation (7—1)represent average data.Certainwood species give test valuesthat are somewhat greateror less than the equationvalues.A typical load— displacement curve fornail withdrawal(Fig.7—2)shows that maximumload occurs atrelativelysmall values of displacement. Althoughthe equationfornail-withdrawal resistance indicatesthat the dense, heavywoods offergreaterresistance to nail withdrawalthan do the lowerdensityones, lighter species shouldnot be disqualified for uses requiring high resistanceto withdrawal. As a rule, the less dense species do not split asreadily as thedenserones,thus offering an opportunity for increasingthe diameter, length,and numberofthe nails to compensate for the wood's lowerresistance to nail withdrawal.

The withdrawal resistance ofnail shanks is greatlyaffected by such factorsas type ofnail point, type of shank, time the nail remainsinthe wood, surfacecoatings, and moisturecontent changesinthe wood. Displacement (in.) 0

0.01

0.02

0.03

0.04

0.05

160

700

600 500

-

120

6d smoothbox nail

400 300

diameter

-

penetration depth

200

—

100

—

Douglas-fir 12% moisture content

40

0.54 specific gravity

_-mm(0.O98-in.) I

0

80

31.Bmm(1-1/4in.)

0.3

I

0.9 0.6 Displacement (mm)

1.2

Figure 7—2. Typicalload—displacementcurvefor directwithdrawal of a nail.

0

f

Effect of Seasoning With practicallyall species,nailsdrivenintogreenwood and pulled before any seasoning takes place offeraboutthe same withdrawal resistance asnails driven into seasoned wood and pulled soon afterdriving.However, ifcommon smooth-shank nailsare driven into green wood that is allowedto season, or into seasoned wood that is subjectedto cycles ofwettingand dryingbefore the nails arepulled,they losea major part oftheirinitial withdrawalresistance.The withdrawalresistance for nailsdriveninto wood that is subjected to changesin moisturecontentmay be as low as 25% ofthe valuesfornails tested soonafter driving. On the other hand, ifthe wood fibersdeteriorate orthe nail corrodes undersome conditions ofmoisturevariationand time, withdrawal resistance is erratic; resistance maybe regainedor evenincreased over the immediate withdrawalresistance. However, such sustained performance shouldnot reliedon in thedesignofa nailedjoint.

b

In seasoned wood that is not subjected to appreciablemoisture content changes, the withdrawalresistance ofnails may also diminish due to relaxationofthe wood fibers'vithtime. Underall these conditions ofuse, the withdrawal resistance ofnailsdiffers among species and shows variation within individual species.

Effect of Nail Form The surface condition ofnails is frequentlymodifiedduring

the manufacturing process to improve withdrawalresistance. Suchmodification is usually done by surface coatin,, surface roughening, ormechanical deformation ofthe shank.Other factors that affectthe surface condition ofthe nail arethe oil filmremaining on the shank aftermanufacture or corrosion resulting from storage underadverseconditions; butthese factors are so variable that their influence on withdrawal resistance cannotbe adequately evaluated. Surface Modifications—Acommon surface treatmentfor nails is the so-called cement coating. Cementcoatings, contraryto what the name implies, do not includecementas an ingredient; they generally area composition ofresin appliedto the nail to increase theresistanceto withdrawal by increasing the frictionbetween the nail and the wood. If properly applied, they increase theresistance ofnailsto withdrawal immediately after the nailsare driveninto the softerwoods.However, in the denserwoods(suchas hard maple, birch, or oak), cement-coated nailshave practically no advantage over plain nails, becausemost ofthe coalingis removedin driving. Some ofthe coatingmay also be removedin the sidememberbeforethe nail penetrates the main member. Good-quality cementcoatings are uniform,not stickyto the touch,andcannotbe rubbedoffeasily. Different techniques of applying the cement coatingand variations in its ingredients may cause largedifferences in the relative resistance to withdrawal ofdifferentlots ofcement-coated nails. Some nails may showonly a slight initial advantage over plain nails. In the softerwoods, the increase in withdrawal resistance of

7—3

cement-coatednails is not permanentbut drops offsignificantlyafter amonth or so. Cement-coated nailsare used primarilyin constructionofboxes, crates, and other containersusuallybuiltfor rough handlingandrelatively short service.

Nails with deformedshanks are sometimeshardened by heat treatments for use where drivingconditions are difficultorto obtain improvedperformance, such as in pallet assembly. Hardenednails are brittle and care shouldbe exercised to avoid injuries from fragments ofnails broken during driving.

Nails that have galvanized coatings,such as zinc, are intendedprimarilyforuses where corrosion and stainingresistanceare important factors in pennanence and appearance. If thezinc coatingis evenly applied, withdrawalresistance may be increased,but extreme irregularities ofthe coatingmay actuallyreduce it. The advantage that uniformly coated galvanized nailsmay have over nongalvanized nails in resistance to initial withdrawalis usuallyreducedby repeated cycles ofwettingand drying.

Nail Point—A smooth, round shank nail with a long, sharp point will usually have a greaterwithdrawalresistance, particularlyin the softerwoods, than the commonwire nail (which usually has a diamond point). However,sharppoints accentuatesplitting in certainspecies, which may reduce withdrawalresistance. A blunt or flat point withouttaper reduces splitting, but its destruction ofthe wood fibers%hen drivenreduceswithdrawal resistance to less than that ofthe commonwire nail. A nail tapered at the end and terminating in a blunt pointwillcause less splitting.In heavier woods, such a tapered,blunt-pointed nail will provide about the same withdrawalresistance,but in less densewoods, its resistance to withdrawalis less than that ofthe common nail.

Nails have also been madewith plasticcoatings. Theusefulness and characteristics ofthese coatings are influenced by the qualityandtype ofcoating, the effectiveness ofthe bond betweenthe coatingand base fastener, and the effectiveness of thebond betweenthecoating and wood fibers. Someplastic coatings appearto resist corrosionor improve resistance to withdrawal, while othersoffer little improvement. Fastenerswith properlyappliednylon coatingtend to retain theirinitialresistanceto withdrawal compared with other coatings, whichexhibit amarked decrease in withdrawal resistance within the first monthafter driving.

A chemically etchednail has somewhat greaterwithdrawal

resistancethan some coatednails, as the minutelypitted surfaceis an integralpart ofthe nail shank.Underimpact loading,however,the withdrawalresistance ofetched nails is little differentfromthat ofplain or cement-coated nailsunder various moisture conditions. Sand-blastednails perform inmuch the same manneras chemicallyetchednails.

ShapeModifications—Nailshanks may be varied from a smooth, circularform togive an increase in surface area without an increasein nail weight.Specialnails with barbed, helicallyor annularly threaded, andother irregular shanks (Fig. 7.-i) are commercially available. The form and magnitudeofthe deformations along the shank influencethe performanceofthe nailsin various wood species. In wood remainingat a uniform moisture content, the withdrawalresistanceofthese nailsis generally somewhat greaterthan that ofcommonwire nails ofthe same diameter. Forinstance, annular-shanknails haveabout 40% greater

resistance to withdrawalthan commonnails. However, under conditionsinvolvingchanges in moisture contentofthe wood, some specialnail forms provide considerably greater withdrawalresistance than the common wire nail—about four timesgreater for annularly and helicallythreadednails ofthe same diameter.This is especiallytrue ofnails driveninto greenwood that subsequentlydries.In general,annularly threadednails sustainlarger withdrawalloads,and helically threadednailssustain greaterimpactwithdrawal work values than do the other nail forms.

7—4

Nail Head—Nailheadclassificationsincludeflat, oval, countersunk, deep-countersunk, andbrad. Nails with all types ofheads,exceptthe deep-countersunk, brad, and some ofthe thin flathead nails, are sufficiently strong to withstmd theforce requiredto pull them from most woods in direct withdrawal. The deep-countersunk and brad nails are usually drivenbelow the wood surface and are not intendedto carry largewithdrawalloads.In general, the thicknessand diameter ofthe headsofthe common wire nails increase as the size ofthe nail increases. The development ofsomepneumaticallyoperatedportable nailershas introduced nailswith speciallyconfigured heath, such as T-nailsand nailswith a segmentofthe head cut off.

Corrosion and Staining In the presenceofmoisture, metalsused for nails may corrode when in contact with woodtreatedwith certain preservative orfife-retardant salts (Chs. 14 and 17). Use ofcertain metalsor metal alloyswill reduce the amountofcorrosion. Nails ofcopper,siliconbronze,and 304 and 316 stainless steel haveperformed wellin wood treatedwith ammoniacal copperarsenate and chromated copper arsenate. The choice of metals for use with fire-retardant-treated woodsdepends upon

theparticular fire-retardant chemical.

Staining causedby the reactionofcertainwood extractives (Ch. 3) and steel in the presenceofmoistureis a problem if appearanceis important, such as with naturallyfmished siding. Use ofstainless steel, aluminum,or hot-dipped galvanized nails can alleviate staining.

In general, thewithdrawalresistance ofcopperand other alloy nails is comparable with that ofcommonsteel wire nails whenpulled soonafter driving. Driving The resistance ofnailsto withdrawal

is generallygreatest whenthey are drivenperpendicular to the grain ofthe wood. Whenthe nail is driven parallelto the wood fibers (that is,

intothe endofthe piece)withdrawal resistance inthe softer woodsdrops to 75% or even50% oftheresistance obtained whenthe nail is drivenperpendiculartothe grain. The difference betweenside- and end-grainwithdrawal loadsis less for densewoodsthan for softerwoods. Withmost species, the ratio betweenthe end- and side-grain withdrawal loads of nailspulled aftera time interval, or after moisture content changeshave occurred, is usually somewhat greaterthanthat ofnailspulled immediately after driving. Toe nailing, a commonmethodofjoining wood framework, involves slantdrivinganail orgroup ofnailsthroughthe end or edge ofan attachedmemberand into a mainmember. Toe nailing requires greater skill in assembly than does ordinaryend nailing but providesjoints ofgreater strength and stability. Tests show thatthe maximum strengthof toenailedjoints under lateral and upliftloads is obtainedby (a) usingthe largestnail that will not cause excessivesplitting, (b) allowing an end distance (distance from the endof theattachedmembertothepoint ofinitial nail entry)of approximately one-thirdthe length ofthe nail, (c) drivingthe nail at a slope of30° with the attachedmember,and (d) buryingthe full shank ofthe nail but avoiding excessive mutilationofthe wood from hammerblows. The results ofwithdrawaltests with multiplenail joints in whichthe piece attachedis pulleddirectlyaway from the main member showthat slant driving is usuallysuperiorto straight drivingwhen nails are driven into chywood and pulled immediately, and decidedly superior whennailsare driven into green or partiallydry wood that is allowedto season for a monthormore. However,the loss in depth of penetrationdue to slant driving may, in sometypes of joints, offsetthe advantagesofslantnailing.Cross slant drivingofgroupsofnails throughthe side grain is usually somewhat more effectivethanparallelslantdriving through theend grain.

However, this improvedstrengthofa clinched-nail jointdoes notjustify the useofgreen lumber, becausethejointsmay loosen as the lumberseasons. Furthermore, laboratorytests

were madewith singlenails, and the effectsofdrying, such as warping,twisting, and splitting, may reducethe efficiency ofajoint that has more than one nail. Clinching ofnails is generallyconfined to such construction as boxes and crates and other containerapplications. Nails clinched acrossthe grain haveapproximately 20% more resistance to withdrawalthan nailsclinchedalongthe grain.

Fastening of Plywood The nailingcharacteristics ofplywood arenot greatlydifferentfromthose ofsolid wood exceptforplywood'sgreater resistance to splitting whennails are drivennearan edge. The nail withdrawalresistanceofplywoodis 15% to 30% less than that ofsolid wood ofthe same thickness.The

reasonis that fiber distortionis less uniformin plywoodthan in solid wood. Forplywood less than 12.5 mm (1/2-in.) thick,the greatersplitting resistance tends to offsetthe lower withdrawalresistance compared with solid wood. The withdrawal resistance per unit length ofpenetration decreasesas thenumberofplies perunitlength increases.The direction ofthegrainofthefaceply has little influenceon thewithdrawal resistance fromthe face nearthe endor edgecfapiece ofplywood. The directionofthegrain ofthe face ply may influence the pull-through resistance ofstaples ornails with severely modifiedheads,such as T-heads. Fastenerdesign information forplywoodis available from APA—The EngineeredWood Association.

Allowable Loads

Nails driven into lead holes with a diameterslightlysmaller (approximately 90%)thanthe nail shank havesomewhat greaterwithdrawalresistance than nailsdrivenwithoutlead holes.Leadholes also preventor reducesplittingofthe wood,particularlyfor densespecies.

Theprecedingdiscussion dealt with maximum withdrawal loads obtainedin short-timetest conditions.For design, these loads mustbe reducedto accountfor variability, duration-of-load effects, andsafety. A valueofone-sixth tie averagemaximum loadhas usually been acceptedas theallowable load for long-time loadingconditions.For normal durationofload,this valuemay be increasedby 10%. Normal duration ofloadis defined as a loadof 10-year duration.

Clinching

Lateral Resistance

The withdrawalresistance ofsmooth-shank, clinchednails is considerably greater than that ofunclinchednails. The point ofa clinched nail is bent over wherethenail protrudes throughthe side member.The ratio betweenthe loadsfor clinchedand unclinchednails varies enormously, depending

upon the moisturecontent ofthe wood whenthe nail is driven and withdrawn, the species ofwood,the size ofnail, and the directionofclinchwith respecttothe grain ofthe wood.

In dryorgreen wood, a clinchednail provides 45% to 170% more withdrawalresistance than an unclinchednail when withdrawn soonafter driving.In green woodthat seasons after a nail is driven,a clinched nail gives 250% to 460% greaterwithdrawalresistance than an unclinched nail.

Pre-1991

Test loads atjoint slips of 0.38 mm (0.015 in.) (approximate proportional limit load) for bright common wire nails in lateralresistance driveninto the side grain (perpendicular to the woodfibers) ofseasoned woodare expressed by the empirical equation p=KD3'2

(7—2)

wherep is lateralloadpernail, K a coefficient, and D diameter ofthe nail. Valuesofcoefficient Kare listedin Table 7—4 for ranges ofspecific gravity ofhardwoods and softwoods. The loads given by the equationapply only wherethe side member and the member holdingthe nail point are of

7—5

Table 7—4. Coefficients for computing test loads for fasteners in seasoned wood8 (pre-1991) Specific gravity

Lateral load coefficientK (metric

rangeb

Nailsc

Screws

0

0.24

1.80

0.36 400

(inch—pound))

Lag screws

Hardwoods 0.33—047 50.04 (1,440) 23.17 (3,360) 26.34 (3,820) 0.48—0.56 69.50 (2,000) 31.99 (4640) 29.51 (4,280) 0.57—0.74 94.52 (2,720) 44.13 (6,400) 34.13 (4,950)

z

50.04 (1,440) 23.17 (3,360) 23.30 (3,380) 0.43—0.47 62.55 (1,800) 29.79 (4,320) 26.34 (3,820) 0.48—0.52 76.45 (2,200) 36.40 (5,280) 2951 (4,280)

240 0.90

0

bSpecifjc gravity based on ovendry weight and volume at 12% moisture content. eCoefficients based on load at joint slip of 0.38 mm (0.015 in.)

approximatelythe same density. The thicknessofthe side membershouldbe about one-halfthe depth ofpenetration of

thenail in the memberholding thepoint.

The ultimatelateralnail loads forsoftwoodsmay approach 3.5 times the loads expressedby the equation, and for hardwoodsthey may be 7 times as great. The joint slip at maximum load, however, is more than 20 times 0.38 mm (0.015in.). This is demonstratedby the typical load—slip curve shown in Figure 7—3. To maintaina sufficient ratio betweenultimate load and the load at 0.38 mm (0.015 in.), thenail shouldpenetrate into thememberholding the point by not less than 10 times the nail diameterfor densewoods (specificgravitygreaterthan 0.61) and 14 timesthe diameter for low density woods (specificgravity less than 0.42). For species having densities betweenthese two ranges,the penetrationmay be found by straightline interpolation.

Post-1991 The yield model theory selects the worst case ofyield modes based on differentpossibilitiesofwood bearing and nail bending. It does not accountfor nail headeffects. A descriptionofthevarious combinations is given in Figure 7—4.

Mode I is a wood bearingfailurein either the mainorside member;mode II is a rotationofthe fastenerinthejoint without bending; modesIll andIV are a combination of wood bearingfailureand one or more plastichingeyield formations in the fastener. Modes Im and II havenot been observedin nail and spike connections. The yieldmodel theoryis applicableto all types ofdowelfasteners(nails, screws,bolts, lag screws), and thus the wood bearingcapacity is describedby amaterialpropertycalledthe dowel bearingstrength.

.

160

-J

0.45

80

.

0

6 -C.05x in Slip joint (mm) fastener

0.29—0.42

Wood with a moisture content of 15%.

320

1.35

Softwoods

7—6

Slip in joint (in.) 0.12

diameter

Figure 7—3. Typicalrelation between lateral load and slip in the jointand 5% offset definition. Theyield mode equations(Table7—5) are enteredwith the dowel bearingstrengthand dimensions ofthe wood members andthe bendingyield strengthanddiameterofthe fastener.

The dowelbearing strength ofthe wood is experimentally determinedby compressing a dowelinto a wood member. The strengthbasis is the load representing a 5% diameter offseton the load—deformationcurve (Fig. 7—3).Dowel bearingstrengthFe (Pa, lb/in2) is empiricallyrelatedto specific gravityG by

= 1l4.5G'84

(metric)

(7—3a)

= 16,600G184

(inch—pound)

(7—3b)

wherespecific gravityis basedon ovendry weightand volume.

Spacing Enddistance,edge distance, and spacingofnails shouldbe such as to preventunusualsplitting.As a general rule,nails shouldbe drivenno closerto the edge ofthe side member than one-halfits thicknessand no closerto the end than the thickness ofthe piece. Smaller nails can be driven closerto theedgesor ends than largerones becausethey areless iikely to split the wood.

Grain Direction Effects The lateral loadfor side-grain nailingapplieswhetherthe load is in a directionparallel to the grain ofthe piecesjoined or at rightangles to it. When nails are drivenintothe end grain (parallel with the wood fibers),limited data on softwood species indicatethat their maximum resistance to lateraldisplacementis abouttwo-thirdsthat for nails driven into the side grain. Although the averageproportionallimit loadsappearto be aboutthe same for end- and side-grain nailing, the individual results are more erraticfor end-grain nailing, and the minimumloads approachonly 75% of corresponding valuesforside-grainnailing.

________

________

I

HI

H IMode'm

-I

I

(a)

I-

ModeIs

-I ..:..

__

Mode

I

m

ModeIlls

(Not applicable) Mode

Mode II

__ \ __I-I__ •t

(b)

L}

______

•-I 1.

I

1

(Notapplicable)

ModeIV

ModeWm

Mode Ills

ModeIV

Figure 7—4. Various combinations ofwood-bearing and fastener-bendingyieldsfor (a) two-member connections and (b) three-memberconnections.

Moisture ContentEffects Nails driveninto the side grain ofunseasonedwood give maximum lateral resistance loads approximately equalto those obtainedin seasonedwood, but the lateralresistance loads at 0.38 mm (0.015 in.)joint slip are somewhat less. To preventexcessivedeformation, lateral loadsobtainedfor seasonedwood shouldbe reducedby 25%forunseasoned wood that will remain wet or be loadedbeforeseasoning takes place.

Whennails are driven into greenwood, their lateralproportional limitloads afterthe wood has seasonedare alsoless thanwhen they are driven into seasonedwood andloaded. The erraticbehaviorofa nailedjointthat has undergoneone or more moisturecontentchangesmakesit difficult to establish a lateral load for a nailedjointunder these conditions. Structural joints should be inspectedat intervals, and if it is apparentthatthe jointhas loosenedduring drying, thejoint shouldbe reinforcedwith additionalnails.

Deformed-Shank Nails nailscarry somewhat highermaximum lateralloads than do the same pennyweight common wire nails, but both perform similarlyat smalldistortionsin the joint. It should be noted that the same pennyweightdeformed-shank nail has adifferentdiameter than that ofthe common wire nail. These nails often havehigherbending yield strengththan commonwire nails, resultingin higher lateral strengthin modesIII and IV. Deformed-shank

Lateral Load—Slip Models A considerable amount ofwork has been done to describe, by mathematical models, the lateral load—slip curve ofnails. Thesemodels have become important becauseoftheir need

as input parameters for advanced methods ofstructural analysis.

One theoretical model, whichconsiders the nail to be a beam supported on an elasticfoundation (thewood),describesthe initialslopeofthe curve: 5=

+L2)—

(J1

J)2]

(7-4)

(K1

P[2(L1

whereP is the lateral load and S is thejoint slip. The factors L1, L2, J1, .12, K1, and K2 (Table 7—6) are combinationsof hyperbolic and trigonometric functionsofthe quantities ?a and A2b in whicha and b are the depth ofpenetraticnofthe nail in members 1 and 2, respectively.For smooth round nails, 4!

?=2

J

r 1

(7—5)

irED3

wherek0 is elasticbearingconstant, Dnail diameter,andE modulusofelasticityofthe nail. For seasonedwood,the elasticbearingconstantk0(N/mm3, lb/in3) has been shown to be relatedto average species specific gravity G ifno lead hole is used by k0 = 582G

=2,144,000G

(metric)

(7—6a)

(inch—pound

(7—6b)

Ifapreboredleadhole equalto 90% ofthe nail diameteris used, Ic =869G Ic0

= 3,200, 00(Xi

(metric)

(7—7a)

(inch—pound)

(7—7b)

Otherempirically derived models attemptto describethe entireload—slip curve.One such expressionis

P = A 1og10(1+B5)

(7—8)

where the parameters A and Bare empirically fitted.

7—7

Table 7—5. The5% offset lateral yield strength (Z)

for nailsand screwsfora two-member joint Z value for nails Z value for screws Mode

DtF

Is

Table 7—6. Expressions for factors in Equation (7—4) Factor

DteFm L1

Ills,

Ills

smh2 ?1a— sm

l+2Re

?sinh22b cosh?.2b—sin72b cos2b

k2DcPm

k3DçF

2+R

2+Re

'

D2 /l.75IP'Yb

3(1+R)

sinh2?2b—sin2?2b

,I 2

D nail,spike, or screw diameter,mm (in.) (for annularlythreadednails, D isthread-rootdiameter; for screws,D is eitherthe shank diameterorthe root diameterifthe threadedportionofthe screw is in the shearplane) Fern dowelbearingstress ofmain member (memberholding point), kPa (lb/in2) Fe, dowelbearingstress ofside member, kPa (lb/in2) Fyb bending yield stress ofnail, spike, or screw,kPa (lb/in2)

penetrationofnail or spike in main member,mm (in.) thicknessofside member,mm (in.) Z offsetlateral yield strength t,

= Fem/Fes

2b(1+2Re)D2

k1

=—l+2(1+Re)÷ k2

Ic3

3I;;p2

I2(l+R) + 2Jjb(2+Re)D2 =—l+.j

Re

31mt

12(l+Re) + P,,b(2+Re)D2

=_l+iI

Re

2Femt2s

Spikes Commonwire spikes are manufactured inthe same manner as commonwire nails. They have either a chiselpoint or a diamondpoint and are made in lengthsof 76 to 305 mm (3 to 12 in.). For correspondinglengthsin the range of76 to 152 (3 to 6 in.),they have larger diameters(Table7—7)than common wire nails, and beyondthe 60d size they are usually designated by diameter.

7—8

s21a+Sin21a k1

sinh2?1a —sin2 ?a

?sinh2?2b+sin22b k2

sinh2?2b —sin2 A.2b

K1

?sinh1a coshAa + sin1a cos1a

K2

? sirih2b

Definitions

Re

? sinhA.1acoshA,1a—sthA1a cos?1a •2

kiDpFem

D2 T2FmF,b

p

Expression8

sinh2?.1a —sin2 ?c1a

Ic2

cosh?%2b + sin ?2b cos?2b sinh2?2b —sin2 22b

= kdand k2 = k02d, wherek and 1c2 are the foundation moduliofmembers I and 2, respectively. The withdrawaland lateralresistanceequationsand limitations given forcommonwire nails are also applicableto spikes, except that in calculatingthe withdrawalloadfor spikes, the depth ofpenetrationis taken as the length ofthe spike in the memberreceivingthe point, minustwo-thirds thelength ofthepoint.

Staples

Differenttypesofstaples havebeen developed with various modifications in points, shank treatment and coatings, gauge,crownwidth,and length. Thesefastenersare available in clipsormagazinesfor use inpneumaticallyoperated portable staplers. Most factors that affectthe withdrawal and lateralloadsofnails similarlyaffectthe loads on staples.The withdrawal resistance, for example, varies almostdirectly with the circumference anddepth ofpenetrationwhenthe type ofpoint and shank are similar to nails. Thus, Equation (7—1)has been usedtopredict the withdrawalloadfor one legof astaple,but no verificationtests have been done.

The load in lateralresistance variesapproximately asthe 3/2 powerofthe diameterwhenother factors,such as qualityof metal,type ofshank, anddepth ofpenetration,are similar to nails. The diameterofeach leg ofa two-leggedstaple must therefore be about two-thirds the diameterofanail to provide acomparable load. Equation (7—2) has beenusedto predict thelateralresistance ofstaples.However,yieldmodel theoryequations havenot yetbeen experimentally verified

forstaples.

Table

7—7. Sizes

of common wire spikes Length

Diameter

Size

(mm (in.))

(mm (in.))

lOd

4.88 (0.192) 4.88 (0.192) 5.26 (0.207)

40d

76.2 (3) 82.6 (3-1/4) 88.9 (3-1/2) 101.6 (4) 114.3 (4-1/2) 127.0 (5)

50d

139.7 (5-1/2)

7.19 (0.283)

60d

152.4 (6)

7.19 (0283)

5/16 in.

177.8 (7)

7.92 (0.312)

3/8 in.

215.9 (8-1/2)

9.53 (0.375)

12d 16d

20d 30d

Core or

•root

5.72 (0.225)

diameter

6.20 (0.244) 6.68 (0.263)

A

C

Figure 7—5. Common typesof wood screws: A, flathead; B, roundhead; and C, ovaihead.

In addition to theimmediateperformance capability ofstaples andnails as determinedby test, factors such as corro-

sion, sustainedperformanceunderserviceconditions, and durabilityin varioususes shouldbe considered in evaluating therelative usefulness ofa stapledconnection.

Drift Bolts A drift bolt(or drift pin) is a long pin ofiron or steel,with or without head or point. It is driven into a bored hole

through one timber and into an adjacent one, to preventthe separationofthe timbersconnected andto transmitlateral load. The hole in the secondmemberis drilledsufficiently deep to preventthe pin from hittingthe bottom. The ultimatewithdrawalload ofa round driftboltorpin from the side grain ofseasonedwood is given by

p= 45.5 1G2DL p =6, 600G2DL

B

(metric)

(7—9a)

(inch—pound)

(7—9b)

wherep is the ultimate withdrawalload (N, lb), G specific gravitybased onthe ovendry weight andvolumeat 12% moisturecontentofthe wood,D diameterofthe driftbolt (mm, in.), and L length ofpenetrationofthe bolt (mm, in.). (TheNDS and LRFDuse ovendry weightand volume as a basis.) This equation providesan average relationship forall species, andthe withdrawalloadfor some species may be above or below the equationvalues. It also presumesthat thebolts aredriven into preboredholes havinga diameter3.2 mm (1/8 in.) less than the boltdiameter. Data are not available on lateralresistance ofdriftbolts. The yield model should provide lateral strengthprediction,but themodelhas not beenexperimentally verified fordrift bolts. Designershave used bolt dataand designmethodsbased on experience. This suggests that the load for a driftbolt driven into the sidegrain ofwood shouldnot exceed, and o:rdinarily

shouldbe taken as less than, that for aboltofthe sme diameter. Bolt design values are based on the thicknessof themain member in ajoint. Thusthe depth ofpenetration ofthe driftbolt must be greater than or equalto themainmemberthicknesson whichthe boltdesignvalue is based. However,the drift bolt shouldnot fully penetrate its joint.

Wood Screws

i

The commontypesofwood screwshaveflat, oval, or round heads. The flathead screw is most commonly used a flush surface is desired. Ovaihead and roundhead screws are used for appearance, and roundhead screws are usedwhencountersinkingis objectionable. The principalparts of a screw are thehead, shank, thread, and core (Fig. 7—5).The root diameter for most sizes ofscrews averages about two-thirds the shank diameter. Woodscrews are usually made ofsteel, brass, othermetals, oralloys,and may have specific finishes such as nickel, blued, chromium, or cadmium. They are classified according to material,type, fmish,shapeofhead, and diameter orgauge ofthe shank.

Currenttrendsin fastenings for wood also include tapping screws.Tappingscrews havethreadsthe full length ofthe shank and mayhave someadvantage for certain specific uses.

Withdrawal Resistance Experimental Loads Theresistance ofwood screw shanks to withdrawal from the side grainofseasonedwood variesdirectlywith the square of thespecificgravityofthewood. Within limits,thewithdrawalloadvariesdirectlywith the depth ofpenetration of the threaded portion and the diameter ofthe screw,provided the screw does not fail in tension. The screw will fail in tension when its strength is exceededby the withdrawal strengthfrom the wood. The limitinglength to cause a tension failure decreases as the density ofthewood increases since the withdrawal strength ofthe wood increases with density. The longer lengths ofstandard screws are therefore superfluous in densehardwoods.

7—9

The withdrawalresistance oftype A tapping screws,commonlycalled sheet metal screws,is in general about 10% greaterthan that forwood screwsofcomparable diameter and length ofthreadedportion.The ratio betweenthe withdrawal resistance oftappingscrewsandwood screws variesfrom 1.16 in denser woods, such as oak, to 1.05 in lighter woods, such as redwood.

Fastening of Particleboard Tappingscrewsare commonly used in particleboardwhere withdrawal strength is important. Care must be taken when tightening screwsin particleboardto avoid strippingthe threads.The maximumamountoftorquethat can be applied

to a screw before thethreads in theparticleboard arestripped is given by

Ultimatetest values for withdrawal loadsofwood screws insertedinto the side grain of seasoned wood may be expressed as

p= l08.2SG2DL

(metric)

(7—1Oa)

p= 15,700G2DL

(inch—pound)

(7—lob)

wherep is maximumwithdrawalload (N, lb), G specific gravitybased on ovendiy weightandvolumeat 12% moistare content,D shank diameterofthe screw (mm, in.),and L length ofpeneirationofthe threadedpart ofthe screw (mm, in.). (TheNDS and LRFD use ovendiy weightand volume as a basis.) Thesevalues are basedon reachingultimate load

in 5- to 10-mm.

This equationis applicablewhen screw lead holeshave a diameter ofabout 70% ofthe root diameter ofthe threads in softwoods, and about 90% in hardwoods. The equationvalues are applicable to the screw sizes listed in Table7—8. (Shankdiametersarerelatedto screwgauges.)

Forlengthsand gauges outside these limits, theactual values are likelyto be less than the equationvalues. The withdrawalloads ofscrewsinsertedin the end grain of wood are somewhaterratic, but when splitting is avoided, they shouldaverage75% ofthe load sustainedby screws insertedin the side grain. Lubricating the surfaceofa screw with soap or similarlubricant is recommendedto facilitateinsertion, especially in densewoods, and it will have little effect on ultimate withdrawal resistance.

Table 7—8. Screw sizes appropriate for Equation (7—10) Screw length (mm (in.))

ito 6

19.0 (3/4)

2toll

25.4 (1) 38.1 (1-1/2)

3to12 5to14

50.8 (2)

7to16

63.5(2-1/2)

9 to 18

7—10

(3)

(metric)

(7--Ila)

T 27.98+1.36X

(inch—pound)

(7-1Ib)

where T is torque(N—m, in—lb) andXis density ofthe particleboard (kg/rn3,lb/ft3). Equation(7—11) is for 8-gauge screws with a depth ofpenetrationof 15.9 mm (5/8 in.). The maximum torqueis fairlyconstant for lead holes of0 to 90% oftherootdiameterofthescrew. Ultimate withdrawal loadsP (N, ib) ofscrewsfrom particleboardcan bepredictedby

P= KD"2(L—D/3)514G2 where D is shank diameter ofthe screw (mm, in.),L depth of embedment ofthethreadedportion ofthe screw (mm, in.), and G specific gravityofthe boardbased on ovendrywe:ght and volumeat currentmoisture content. For metricmeasurements, K= 41.1 forwithdrawal from the face ofthe board and K= 31.8 forwithdrawalfrom the edge; for inch—pound measurements, K = 2,655 for withdrawal from the face and K= 2,055 for withdrawal from theedge. Equation(7—12) applieswhenthe settingtorque is between 60% to 90% ofT

(Eq. (7—11)). Withdrawal resistance ofscrewsfrom particleboardis not significantly different for leadholes of50% to 90% ofthe root diameter.A highersettingtorque will produce a somewhat higherwithdrawal load,butthere is only a slight differerce (3%) in valuesbetween60% to 90% settingtorques (Eq. (7—11)).A modesttightening of screws in many cases provides an effective compromise betweenoptimizing withdrawal resistance and strippingthreads. Equation (7—12) can alsopredictthe withdrawalofscrews from fiberboard with K= 57.3 (metric)or 3,700(inch— pound) forthe face and K = 44.3 (metric)or 2,860 (inch— pound)for the edge oftheboard.

Lateral Resistance Gauge limits

12.7 (1/2)

76.2

T= 3.16+0.0096X

12 to 20

Pre-1991 The proportional limit loads obtainedin tests of lateral resistance for wood screws in the sidegrain ofseasonedwood aregivenby theempirical equation

p=KD2

(7—13)

wherep is lateral load, D diameter ofthe screw shank, and Ka coefficient depending on theinherent characteristics ofthe wood species. Valuesofscrew shank diameters for various screw gauges are listedin Table 7—9.

Table 7—9. Screwshankdiameters for various screw gauges Screwnumber or gauge 4 5 6 7 8

9 10 11

12 14 16 18 20 24

Diameter

(mm (in.)) 2.84 (0.112) 3.18 (0.125) 3.51 (0.138) 3.84 (0.151) 4.17 (0.164) 4.50 (0.177) 4.83 (0.190) 5.16 (0.203) 5.49 (0.216) 6.15 (0.242) 6.81 (0.268) 7.47 (0.294) 8.13 (0.320)

9.45 (0.372)

ValuesofKare basedonrangesofspecific gravity ofhardwoods and soflwoodsand are given in Table 7—4. They apply to wood at about 15% moisturecontent. Loadscomputed by substitutingthese constantsin the equationare expectedto have a slip of0.18 to 0.25 mm (0.007 to 0.010 in.), dependingsomewhat on the species and density

ofthewood.

Equation(7—13) applieswhen the depth ofpenetration ofthe screw into the block receivingthe point is not less than seventimes the shank diameterand whenthe sidemember and the main member are approximately ofthe same density. The thicknessofthe side membershouldbe about one-half thedepth ofpenetrationofthescrewin thememberholding thepoint. The end distanceshould be no less than the side member thickness, and the edge distances no less than onehalfthe sidememberthickness. This depth ofpenetration(seventimesshank diameter)gives an ultimate load ofabout four timestheload obtainedbythe equation. For a depth ofpenetrationofless than seventimes theshankdiameter,theultimateload is reducedabout in proportionto the reductioninpenetration,and the load at the proportionallimit is reducedsomewhatless rapidly. When thedepth ofpenetrationofthescrewin theholdingblock is fourtimesthe shankdiameter,themaximum load will be less than three timesthe load expressed bythe equation, and theproportionallimitloadwillbe approximately equal to that given by the equation. When thescrewholds metal to wood,the load canbe increasedby about 25%. Forthese lateralloads, the partoftheleadhole receivingthe shank should be the same diameteras the shank or slightly smaller; that part receivingthe threadedportion shouldbe thesame diameteras theroot ofthethread in dense species or slightly smallerthan the root in low-density species.

Screws should alwaysbe turned in. They shouldnever be startedordrivenwith a hammerbecausethis practicetears the wood fibersand injures the screw threads,seriously reducing the load carrying capacity ofthe screw.

Post-I 991 Screw lateral strength is determinedby the yield mcdel theory(Table 7—5). Modes I, III, and IV failuresmay occur (Fig. 7—4).The dowelbearingstrengthvaluesare based on thesame specific gravityequationusedto establish valuesfor nails (Eq. (7—3)). Furtherdiscussion ofscrew lateral strength is found in ASCEManualNo. 84, Mechanical Conections

in Wood Structures.

Lag Screws Lag screwsare commonly usedbecauseoftheirconvenience, particularly whereitwould be difficultto fastena bolt or whereanut on the surface wouldbe objectionable. Commonlyavailablelag screws range from about 5.1 to 25.4 mm (0.2 to 1 in.) in diameter and from 25.4 to 406 mm (I to 16 in.) in length. The length ofthe threadedpart varieswith thelength ofthescrewand rangesfrom 19.0 mm (3/4 in.) with the 25.4-and 31.8-mm(1- and 1-1/4-in.) screws to half thelength for all lengths greaterthan 254 mm (10 in.). Lag screws have ahexagonal-shaped headandaretightenedby a wrench(as opposed towood screws, whichhave aslotted headand are tightenedby a screw driver).The following equations for withdrawal and lateralloads are based on lag screws havingabase metal average tensile yield strength of about 310.3 MPa (45,000 lb/in2) and an averageultimate tensile strengthof530.9 MPa (77,000 lb/in2).

Withdrawal Resistance The resultsofwithdrawal tests have shownthat the maximum directwithdrawal load oflag screws from the side grain ofseasonedwood maybe computed as

p= 125.4G312D314L p= 8,100G312D314L

(metric)

(7—14a)

(inch—pound)

(7—14b)

wherep is maximum withdrawalload (N, lb), D shank diameter(mm, in.), G specific gravity ofthe wood basedon ovendiyweight and volume at 12% moisture content, andL length (mm, in.) ofpenetrationofthethreadedpart. (The NDS and LRFDuse ovendryweightand volume a; abasis.) Equation(7—14)was developedindependently ofEquation (7—10) but gives approximately the same results. Lagscrews, like wood screws,requirepreboredholes ofthe propersize (Fig. 7—6). The leadhole for the shank shouldbe the same diameteras theshank. The diameterofthelead hole forthe threadedpart varieswith the densityofthe wood: Forlow-density softwoods, such as the cedarsand white pines, 40% to 70% ofthe shank diameter; forDouglas-firand SouthernPine, 60% to 75%; and for densehardwoods,such as oaks,65% to 85%. The smallerpercentage in each range appliesto lag screws ofthe smallerdiameters andthe larger 7—11

Table 7—10. Multiplication factors for loads computed fromEquation (7—15) Ratio of thickness of side member to shank diameterof lag screw Factor 2 2.5 3 3.5

4 4.5 5 5.5 6 6.5

Figure 7—6. A, Clean-cut, deep penetration ofthread made by lag screw turned into a lead holeof proper size, and B, rough, shallowpenetration ofthread made by lag screwturned into oversized lead hole.

Table 7—11. Multiplication factorsfor loads applied perpendicular to grain computed fromEquation (7—15) with lagscrewin side grain ofwood

percentage to lag screwsoflarger diameters. Soap orsimilar lubricants shouldbe usedon the screw to facilitate turning, and lead holes slightlylarger thanthose recommended for maximum efficiencyshould be usedwith long screws.

In determining thewithdrawalresistance, the allowable tensilestrengthofthe lag screw atthe net (root) section shouldnotbe exceeded. Penetrationofthe threadedpart to a distance abOut seventimesthe shank diameterin the denser

species (specificgravitygreater than 0.61)and 10 to 12 times theshankdiameterin the less dense species (specificgravity less than 0.42) will developapproximately the ultimate tensilestrengthofthe lag screw.Penetrations at intermediate densitiesmay be found by straight-line interpolation.

The resistance to withdrawalofa lag screw from the endgrain surface ofa piece ofwood is about three-fourths as great as itsresistance towithdrawalfromtheside-grain surface of thesame piece.

Lateral Resistance Pre-1991 Theexperimentally determinedlateralloadsfor lag screws insertedin the side grain and loadedparallel to the grain ofa piece ofseasonedwood can be computed as

p=KD2

'

17—15'

wherep is proportionallimit lateral load (N, lb) parallel to thegrain,K a coefficient depending on thespecies'specific gravity,andD shank diameterofthe lag screw (mm, in.). Values ofKfora numberofspecific gravity ranges can be foundin Table 7—4. Thesecoefficients are basedon average results for several ranges ofspecific gravity for hardwoods and softwoods. The loads given by this equationapply whenthe thicknessofthe side memberis 3.5 times the shank diameter ofthelagscrew, and thedepth ofpenetration inthemain 7—12

0.62 0.77 0.93 1.00 1.07 1.13 1.18 1.21 1.22 1.22

Shank diameter of lag screw (mm (in.))

Factor

4.8 (3/16) 3.4 (1/4) 7.9 (5/16) 9.5 (3/8) 11.1 (7/16) 12.7 (1/2) 15.9 (5/8) 19.0 (3/4) 22.2 (7/8) 25.4 (1)

0.97 0.85 0.76 0.70 0.65 0.60 0.55 0.52 0.50

1.00

memberis seventimesthe diameterin the harder woodsand 11 times the diameterin the softer woods.For other thicknesses, the computed loads should be multipliedby the factors listed in Table 7—i 0.

The thicknessofa solid wood side membershould be about one-halfthe depth ofpenetrationin the main member. Whenthe lag screw is insertedin the sidegrain ofwood and theload is appliedperpendicular to thegrain, theload given by the lateralresistance equationshould be multipliedby the factorslisted in Table 7—11.

Forother anglesofloading,theloads may be computed from theparallel and perpendicular valuesby theuse ofthe Scholten nomograph for determining the bearingstrength of wood at various anglesto the grain (Fig. 7—7).

Y

P Load or stress parallelto grain

Q Loador stress perpendicularto grain

N

0

Load of stress at inclination 0 withdirection of grain

6

3 4 5 7 8 9 for Allowable load or stress /9 Q, and N in units, tens, hundreds, or thousands 2

1

10

Figure 7—7. Scholten nomograph for determining the bearing stressofwoodat various anglesto the grain. Thedashed lime ab refers to the example givenin the text.

The nomographprovidesvalues as given by the Hankinson equation,

N=

PQ Psin2 0+Qcos20

(7—16)

whereP is load or stress parallelto the grain, Q load or stress perpendicular to the grain, andNload or stress at an inclination9with the directionofthe grain. Example: P, the load parallelto grain, is 6,000 lb, and Q, the load perpendicularto the grain, is 2,000lb. The load at an angle of40°to grain,N, is foundas follows: Connect with a straightline 6,000lb (a) on line OXofthe nomograph with the intersection (b) on line Yofa verticalline through 2,000lb. The point where line ab intersectsthe line representingthe given angle 40° is directly abovethe load, 3,300 lb.

0

Valuesfor lateralresistance as computed by the preceding methods are basedon complete penetration ofthe unthreaded shank into the side memberbut not intothe main member. Whenthe shank penetrates the main member,the permitted increasesin loads are given in Table 7—12. When lag screws are usedwith metal plates,the lateral loads parallelto the grain may be increased 25%, providedthe plate thicknessis sufficientso that the bearing capacity ofthe steel is not exceeded. No increase shouldbe madewhenthe appliedload is perpendicular to the grain.

Lagscrews shouldnot be used in end grain,becausesplitting may developunder lateralload. Iflagscrewsare so used, however, the loads shouldbe takenas two-thirdsthose forlateral resistance whenlag screws are insertedinto side grain andthe loads actperpendiculartothe grain.

The spacings, endandedge distances, and net sectionfor lag screwjoints shouldbe the same as those forjoints with bolts (discussed later) ofa diameterequaltothe shank diameter of thelag screw. Lag screws shouldalwaysbe insertedby turningwith a wrench, not by driving with a hammer.Soap, beeswax, or other lubricants appliedto the screw,particularlywith the denser wood species, will facilitateinsertion and prvent damage to the threads but willnot affect performance ofthe

lagscrew. Post-1991 Lag screw lateral strength is determinedbythe yield model theorytable similarto theprocedurefor bolts.ModesI, III,

and IV yield may occur (Fig. 7—4).The dowelbearing Table 7—12. Permitted increases in loads when lagscrew unthreaded

shank penetratesfoundation member Ratio of penetration of shank into foundation memberto shank diameter

Increase

in load (%)

1

8

2

17

3

26

4

33

5

36

6

38

7

39

7—13

strengthvalues are based on the same parallel-andperpendicular-to-grain specific gravityequationsusedto establish valuesforbolts.

Bolts Bearing Stress of Wood Under Bolts The bearing stress under a bolt is computed by dividingthe load on a bolt by the productLD, whereL is the length ofa

boltin the main member and D is thebolt diameter. Basic

100 -

0

0

0 Cl)

o.

The bearingstress at proportionallimit load is largestwhen theboltdoes not bend, that is, forjoints with smallLID values. The curves ofFigures 7—8 and 7—9showthe reduction in proportionallimit bolt-bearingstress as LID increases.Thebearing stress at maximum loaddoes not decrease as LID increases, but remainsfairlyconstant, which meansthat the ratio ofmaximumload to proportional limit load increases as LID increases. To maintaina fairly constant ratio betweenmaximumload and design load for bolts,the relationsbetweenbearingstress andL/D ratio have been adjustedas indicated in Figures 7—8 and 7—9. The proportionallimit bolt-bearingstress parallelto grain for smallLIDratios is approximately 50% ofthe smallclear crushingstrength for softwoods and approximately 60% for hardwoods.Forbearing stress perpendicular to the grain,the ratio between bearingstress at proportionallimitload and the small clear proportionallimit stress in compression perpendicular to grain dependsuponboltdiameter (Fig. 7—10) for small LID ratios. Species compressive strengthalsoaffectsthe LID ratio relationship, as indicated in Figure 7—9. Relatively higher bolt proportional-limitstress perpendicular to grain is obtained with wood low in strength (proportionallimit stress of 3,930kPa (570 lb/in2)than with material ofhigh strength (proportionallimit stress of 7,860 kPa (1,140 lb/in2)). This effectalsooccursfor bolt-bearing stressparallel tograin, but not to thesame extentas forperpendicular-to-grain loading.

The proportionallimitboltload for a three-member joint with sidemembershalfthe thicknessofthe mainmember may be estimatedby the followingprocedures.

Forparallel-to-grainloading,(a) multiplythespecies small clear compressive parallelstrength(Tables 4—3, 4—4, or 4—5) by 0.50for softwoodsor 0.60 for hardwoods, (b) multiply this productby the appropriate factorfrom Figure 7—8 for the LID ratio ofthe bolt, and (c) multiply this product by LD.

7-44

60 -

C)C)

o • 40

-

—C)j

OW

0

20 -

Ce

parallel-to-grain and perpendicular-to-grain bearing stresses have beenobtainedfrom tests ofthree-member wood joints

whereeach side memberis halfthe thicknessofthe main member.The sidememberswere loadedparallelto grain for both parallel-and perpendicular-to-grain tests. Priorto 1991, bearing stress was based on test resultsat the proportional limit; since 1991, bearingstress is based on test results at a yield limit state, which is defmed as the 5% diameteroffset on the load—deformationcurve (similarto Fig. 7—3).

80 -

0

I

I

2

4

I

I

I

6

8

10

12

LID ratio Figure 7—8.Variation in bolt-bearing stress at the proportionallimit parallel to grain with LID ratio. CurveA, relation obtained from experimental evaluation; curve B, modified relation used forestablishing designloads. 100

0 .0_

—

.

80

(l) CI)(I)

60

o

40 -

.22

-

N

A-i

o

A-2

-

N

B-i

B-2

00)

o Ce

20 -

0

2

I

I

I

I

4

6 LID ratio

8

10

12

Figure 7—9. Variation in bolt-bearing stress at the proportiona''imitperpendicular to grain with LID ratio. Relations obtained from experimental evaluation for materials with average compression perpendicular stress of 7,860 kPa (1,140lb/in2) (curveA—I) and 3,930 kPa (570lb/in2) (curveA—2). Curves B—I and B—2, modified relations used for establishing design loads.

Forperpendicular-to-grain loading,(a) multiplythe species compression perpendicular-to-grain proportional limit stress (Tables 4—3, 4—4, or4—5)by the appropriate factor from Figure7—10, (b) multiplythis product by the appropriate factor from Figure7—9, and (c) multiplythis productby LD.

Loads at an Angle to the Grain For loadsappliedat an angleintermediatebetweenthose parallelto the grain and perpendicular to the grain, the boltbearingstress may be obtainedfrom the nomographin Figure 7—7.

0

Cl)

0

0.5

Bolt diameter (in.) 1.0 1.5

2.0

2.5

0 CO

C)....

oc 0CC

0) C Ce

C) .0

80

2.2

0 .0—

2.0

0 U) .C 00)

60

0) C

40

0

20

•V5 1.8

o

1.6 0) 00

0 0

CCC

o.

100

1.4

Ce

1.2 .2

•E a) 1.0 0 0.

0 32

16

48

2

4

Bolt diameter (mm)

Bearing stress perpendicular to the grain as affected by bolt diameter. Figure 7—10.

6

8

iD

12

UD ratio

64

Figure 7—11. Variation in the proportional limit boltbearing stress parallel to grain with LID ratio. Curve A, bolts with yield stress of 861.84 MPa (125,000lb/in2); curveB, bolts with yield stress of 310.26 MPa (45,000lb/in2).

Steel Side Plates When steel side plates are used, thebolt-bearingstress parallel to grain atjointproportionallimit is approximately 25% greaterthan that forwood side plates. The jointdeformation at proportionallimit is much smallerwith steel side plates. Ifloads at equivalent jointdeformation are compared, the load forjoints with steel side plates is approximately 75% greaterthan that for wood sideplates. Pre-1991 design criteria includedincreases in connection strengthwith steel side plates;post-1991 designcriteriaincludesteel side plate behaviorin theyieldmodel equations.

Forperpendicular-to-grain loading,thesame loads are obtainedforwood and steel sideplates.

Bolt Quality Both the propertiesofthe wood and the quality ofthe bolt arefactorsin determiningthestrengthofa bolted joint. The percentages given in Figures7—8 and7—9for calculating bearingstress apply to steel machinebolts with a yield stress of 310 MPa (45,000lb/in2). Figure 7—11 indicatestheincrease in bearingstress parallel to grain forbolts wiith ayield stress of862 MPa (125,00 lb/in2).

5.0

1.6 1.2

-

UD=2.67

___

UD ____ 4.00

1

C)

.C 0 0.8 C) •. CC

.2.o

0.4

-

cr

I

0

0.25

0.50

I

0.75

1.00 1.25 1.50 Side member thickness/main member thickness

Figure 7—12. Proportional limit load related to side member thickness forthree-memberjoints. Center member thickness was 50.8 mm (2 in.). load for a mainmemberthat is twicethe thicknessofthe side memberis used.Post-1991 design values includemember thicknessdirectly in the yield model equations.

Effect of Member Thickness

Two-Member, Multiple-Member Joints

The proportionallimitload is affectedbythe ratio ofthe

In pre-1991 design,theproportional limitload was taken as halftheloadfor a three-member jointwith a main member thesame thicknessas the thinnestmember for two-member

sidememberthicknesstothe mainmemberthickness (Fig. 7—12).

Pre-1991 designvaluesforbolts are based onjoints with the sidememberhalf thethicknessofthe main member. The usual practicein designofboltedjoints is to takeno increase in designloadwhen thesidemembers aregreaterthanhalf thethicknessofthemain member.When thesidemembers are less than halfthe thicknessofthe mainmember, a design

joints.

Forfour or more membersin ajoint, theproportionallimit load was takenas the sum ofthe loadsforthe individual shearplanesby treatingeach shearplaneas an equivalent two-member joint.

7—15

Post-1991 designforjoints with four or more members also resultsin values per shear plane. Connectionstrength forany number ofmembersis conservatively foundby multiplying

thevalueforthe weakestshear planeby thenumberof shearplanes.

Spacing, Edge, and End Distance The center-to-centerdistance along the grain shouldbe at least fourtimes thebolt diameter for parallel-to-grain load-

ing. The minimumcenter-to-centerspacingofbolts in the

across-the-grain directionfor loadsactingthroughmetal side plates andparallelto the grain need only be sufficient to

permitthe tighteningofthe nuts. For wood side plates,the spacing is controlled by the rules applyingto loadsacting parallelto grain ifthe designload approaches the boltbearingcapacity ofthe sideplates. When the design loadis less than thebolt-bearingcapacityofthe sideplates, the spacingmay be reducedbelowthat requiredto develop their maximumcapacity.

When ajoint is in tension, the bolt nearest the end ofa timbershouldbe at a distancefrom the end ofat least seven timesthe bolt diameterfor softwoods and five timesfor hardwoods. When thejoint is in compression, the end margin may be fourtimes the bolt diameterfor both softwoods and hardwoods. Any decreasein these spacings and margins willdecreasethe load in about thesame ratio.

Forbolts bearingparallelto thegrain,the distance from the edge ofa timberto the centerofaboltshouldbe at least 1.5 times the bolt diameter.This margin, however, will usually be controlledby (a)the common practiceofhaving an edge marginequalto one-halfthe distance betweenbolt rows and (b)the arearequirementsat thecriticalsection. (The critical section is that sectionofthe member taken at right anglesto thedirectionof load, which gives themaximum stress in the memberbasedon thenet arearemaining afterreductions are madeforboltholes at that section.) For parallel-to-grain loadingin softwoods,the net arearemainingat the critical sectionshouldbe at least 80% ofthetotal areain bearing under all the bolts in the particularjointunder consideration; in hardwoodsit should be 100%. Forbolts bearingperpendicularto thegrain,themargin betweenthe edgetoward whichthe boltpressureis acting and the center ofthe boltor bolts nearestthis edgeshouldbe at least fourtimes theboltdiameter. The margin at the oppositeedge is relatively unimportant.

Figure 7—13. Effect of rate offeed and drill speed on the surface conditionof bolt holesdrilled in Sitka spruce.

A, holewas boredwith a twistdrill rotatingat a peripheral speed of 7.62 mlmin (300 inlmin); feed rate was 1.52 mlmin (60 in/mm). B, holewas bored with the same drill at a peripheral speed of 31.75 rn/mm (1,250 in/mm); feed rate was 50.8 mmlmin (2 in/mm).

0

20

Deformation (in.)

0.010

0.020

0.030 4.5

16

3.0 12

0

C,,

x

(5

0 —'8 1.5

10

4

0

3.0 4.5 Deformation (mm)

0

Figure 7—14. Typical load—deformationcurves showing the effectof surface conditionof bolt holes, resulting from a slow feed rate and a fast feed rate, on the deformation in ajointwhensubjected to loading under bolts.Thesurface conditionsofthe bolt holes were similarto those illustratedin Figure7—13.

Effect of Bolt Holes The bearingstrengthofwood underbolts is affectedconsid-

erablyby the size and type ofboltholes into whichthe bolts are inserted. A bolt hole that is too largecauses nonuniformbearingofthe bolt; ifthe bolt hole is too small, the wood will split when theboltis driven.Normally,bolts shouldfit so that they can be insertedby tappinglightly with a wood mallet. In general,the smootherthe hole, the higherthe bearingvalues will be (Fig. 7—13). Deformations

7—16

accompanying the loadare also less with a smootherbolthole surface (Fig. 7—14).

Rough holes are caused by using dull bits and improperrates offeed and drill speed. A twist drill operatedat a peripheral speedofapproximately 38 rn/mm (1,500 inlmin)produces uniformlysmooth holes at moderatefeed rates. The rate of feed depends upon the diameter ofthe drill and the speedof

rotationbut should enable the drill to cut rather thantear the wood. The drill should produce shavings, not chips. Proportional limit loads forjoints with boltholes the same

diameteras the bolt willbe slightlyhigher than forjoints with a 1.6-mm(1/16-in.) oversizedhole. However, ifdrying takes place after assemblyofthejoint, the proportional limit load for snug-fitting bolts willbe considerably less dueto the effects ofshrinkage.

Pre-1991 Allowable Loads The following proceduresare used to calculateallowable bolt loads forjoints with wood sidemembers,each halfthe thicknessofthe main member.

Table

7—13.

Ratio

Parallelto Grain—Thestartingpoint forparallel-to-grain bolt valuesis the maximum green crushingstrengthfor the species or group of species. Procedures outlined inASTM D2555 are used to establish a 5% exclusionvalue. The exclusionvalue is dividedby a factor of 1.9 to adju to a

t

10-year normalduration ofloadandprovidea factor ofsafety. This value is multipliedby 1.20 to adjustto seasoned strength. The resulting value is called the basic bolt-bearing stress parallel to grain.

a

The basicbolt-bearing stress isthen adjustedfor the effects of L/Dratio.Table 7—13 givesthe percentage ofbasic stress for three classes ofspecies. Theparticularclass for the species is determined from the basic bolt-bearing stress as indicated in Table 7—14. The adjustedbearing stress is furthermultiplied

Percentageof basic bolt-bearing stressused for calculating allowable bolt loads LID adjustmentfactor by classa

of bolt length to diameter (UD) 1

2

3 4 5 6 7 8

9 10 11

12 13

Parallel 1

100.0 100.0 100.0 99.5

Perpendicularto grain

to grain

2

3

100.0

100.0 100.0 99.0 92.5

100.0 100.0 100.0 100.0

80.0 67.2

100.0 100.0

57.6 50.4 44.8 40.3 36.6 33.6 31.0

100.0 100.0

95.4 85.6

100.0 100.0 97.4 88.3 75.8

73.4 64.2 57.1 51.4 46.7 42.8 39.5

65.0 56.9 50.6 45.5 41.4 37.9 35.0

2

3

100.0

100.0

100.0 100.0 100.0 100.0 100.0 100.0 96.1 86.3 76.2

100.0 100.0 100.0

100.0 100.0 100.0 100.0

100.0 100.0

100.0 96.3

97.3

86.9 75.0 64.6 55.4 48.4 42.5 37.5

1

94.6 85.0 76.1

88.1

76.7 67.2 59.3 52.0

67.6

68.6 62.2

aClass determinedfrom basic bolt-bearingstress according

61.0 55.3

4

45.9

to Table 7—14.

Table 7—14. LiD adjustment classassociated with basic bolt-bearing stress Basic bolt-bearing stress for speciesgroup (MPa (lblin2)) Loading direction Parallel

Perpendicular

Softwoocls

Hardwoods

LID adjustment (Table7—13)

1,389)

2 3

412)

4

1

7—17

by a factor of0.80to adjust to wood side plates. The allowable bolt load in poundsis then determinedby multiplying by theprojectedbolt area,LD.

Perpendicularto Grain—The startingpoint for perpendicular-to-grainboltvalues is the average green proportional limit stress in compressionperpendicular to grain. Procedures in ASTM D2555 are used to establish compression perpendicular valuesforgroupsofspecies. The average proportionallimit stress is dividedby 1.5 for ring position

(growthrings neitherparallelnor perpendicular to loadduringtest) and a factor ofsafety. This value is then multiplied by 1.20 to adjustto a seasonedstrengthand by 1.10 to adjust to a normalduration of load. The resultingvalue is calledthe basic bolt-bearingstress perpendicular to grain. Thebasic bolt-bearingstress is then adjusted for the effects of bolt diameter (Table 7—15) and L/Dratio (Table 7—13). The allowablebolt load is then determinedby multiplying the adjustedbasic bolt-bearingstress by theprojectedbolt area, LD.

Post-1991 Yield Model The empiricaldesign approach used prior to 1991 was based on a tabularvalue for single bolt in awood-to-wood, threememberconnectionwherethe sidemembers are each a minimumofone-halfthe thicknessofthe mainmember.The single-boltvaluemust then be modifiedfor any variation from these referenceconditions. The theoretical approach, after 1991, is more generaland is not limited to these reference conditions.

a

Thetheoreticalapproachis based on work done in Europe (Johansen 1949) and is referredto as the European Yield Model (EYM). The EYM describes a number ofpossible yield modesthat can occur in a dowel-type connection (Fig. 7—4). The yield strengthofthese differentmodesis determinedfrom a static analysis that assumes the wood and thebolt are both perfectlyplastic. The yieldmode that results in the lowestyield load for a given geometry is the theoreticalconnectionyield load. Equationscorrespondingto the yieldmodesfor a threememberjoint are given in Table 7—16.(Equations for twomemberallowablevalues are given inthe AF&PANational Design Spec?fIcationfor Wood Construction) The nominal single-boltvalue is dependenton thejointgeometry (thickness ofmain and sidemembers),bolt diameterand bendingyield strength, dowel bearing strength, and direction ofloadto thegrain. The equations are equallyvalidfor wood or steel side members,which is taken into account by thicknessand dowelbearingstrengthparameters. Theequations are also valid for variousload-to-grain directions, whichare taken into account by the K9 and Feparameter. The dowelbearingstrength is amaterialproperty not generally familiarto structuraldesigners.The dowelbearing strength ofthe wood members is determinedfrom tests that relate species specificgravityand doweldiameter to bearing

7—18

strength. Empirical equations for these relationships are as follows:

Parallelto grain

= 77.2G

F =ll,200G

(metric)

(7— l7a)

(inch—pound)

(7—17b)

Perpendicular tograin

= 2l2.OG5D°5

(metric)

(7--18a)

= 6,1 00G145D°5

(inch—pound) (7—18b) where Fe is dowelbearingstrength(MPa, lb/in2), G specific gravity basedon ovendry weight and volume,and D bolt diameter(mm, in.).

Connector Joints Several types ofconnectors havebeen devisedthat increase

jointbearingand shear areasby utilizingrings or plates around bolts holdingjointmembers together.The primary

load-carrying portions ofthesejoints are the connectors;tie bolts usually serveto prevent transverse separationofthe members but do contribute some load-carrying capacity. The strengthofthe connector jointdependsonthe type and size ofthe connector, the species ofwood, the thicknessand widthofthe member, the distance ofthe connector from the endofthe member, the spacingofthe connectors, the dfretionofapplication oftheload with respectto thedirectionof

thegrain ofthe wood,and other factors.Loads forwood joints with steel connectors—split ring (Fig. 7—15) and shear plate (Fig. 7—16)—are discussedin this section.These connectors require closelyfittingmachinedgroovesin the wood members.

Parallel-to-Grain Loading Tests have demonstrated that the densityofthe wood is a controlling factor inthe strength ofconnectorjoints. For split-ring connectors, both maximum load and proportional limit loadparallelto grain vary linearlywith specificgravity (Figs. 7—17 and 7—18). For shear plates, the maximum load and proportional limit loadvary linearlywith specificgravity for the less densespecies (Figs. 7—19 and 7—20). In the higherdensity species,the shear strengthofthe bolts becomesthe controlling factor.Theserelationswere obtained for seasonedmembers,approximately 12% moisture content.

Perpendicular-to-Grain Loading Loads forperpendicular-to-grain loading havebeen estab-

lishedusing three-member joints with the side members loadedparallel to grain. Specific gravityis agoodindicator ofperpendicular-to-grain strength oftimberconnector joints. Forsplit-ring connectors, theproportionallimit loads perpendicularto grain are 58% ofthe parallel-to-grain proportional limit loads. Thejoint deformationat proportional limit is 30% to 50% more than for parallel-to-grainloading.

Table 7—15. Factors for adjusting basic boltbearing stressperpendicular to grain for bolt diameter when calculating allowable bolt loads Bolt diameter (mm (in.))

Adjustment factor

6.35 (1/4) 9.53 (3/8) 12.70 (1/2) 15.88 (5/8) 19.05 (3/4) 22.23 (7/8) 25.40 (1) 31.75 (1-1/4)

2.50 1.95 1.68 1.52

38.10 44.45 50.80 63.50

1.41

1.33 1.27 1.19 1.14 1.10 1.07 1.03

(1-1/2)

(1-3/4) (2)

(2-1/2) >76.20 (>3 or over)

1.00

—

Figure 7—15. Joint with split-ring connector showing connector, precutgroove, bolt,washer, and nut.

Table 7—16. The5% offset yield lateral strength (Z) forthree-member boltedjoints — ZvalueforthreeMode memberboltedjoint

DtmF

Mode Irn

K9

2DtF,

Mode I,

K9 2k4Dts1m

Mode Ills

(2+R)K9 2D2 J2JmF,b

Mode IV

K9 3(1+Re) Definitions

D nominalbolt diameter,mm(in.) Fern dowelbearing strenthofmain (center) kPa member, (lb/in) Fes dowelbearingstrengthofside members, kPa (lb/in2) Fb bending yield strength ofbolt, kPa (lb/in2)

K trn

t9

Z 9 Re

1+9/360

thickness

ofmain (center)member,mm (in.)

thicknessofside member,mm (in.) nominal single bolt design value angleofloadto grain (degrees)

= Fern/Fee

2P,b(2+Re)D2

k4 = —1+ Re 112(l+Re)

Figure 7—16. Jointswith shear-plate connectors with (A) woodside plates and (B) steelside plates.

3Fem s

7—19

30

—

150

25 120

z

0 F

z

0 -J

0 60 -J

C')

78

..

15

0 52 -J

10

26

35

Bolt diameter(mm(in.)) 19.0 (3/4)

30

15.9(5/8)

25 .0

90

20

0

C')

x

15

0 10 -J

5 30

0

0.1

0.3 0.4 0.5 0.6 0. Specificgravity 7—17. Relation between load bearing parallel Figure to grain and specificgravity (ovendry weight, volumeat test) for two 63.5-mm (2-1/2-in.) split rings with a single 12.7-mm (1/2-in.) bolt in air-dry material. Center member was thickness101.6 mm (4 in.) and side member thicknesswas 50.8 mm (2 in.).

40

150

0

C')

20

50 0.1

0.2

0.3

0.4 0.5 Specificgravity

0.6

z

40(

0 -J

V 20 3

50

maximum loads vary linearlywith specific gravity (Figs. 7—21 and 7—22). The wood strength controls thejoint strength for all species.

Design Loads Designloads for parallel-to-grain loadinghave beenestablished by dividingultimate test loads by an average factor of 4. This gives valuesthat do not exceed five-eighths ofthe proportionallimit loads.The reductionaccountsforvariability inmaterial,a reduction to long-timeloading,and a factor ofsafety. Designloads fornormaldurationofloadare 10% higher.

Forperpendicular-to-grain loading,ultimate load is given

less consideration and greaterdependence placed on loadat

50

15.9 (5/8)

30

0

Forshear-plateconnectors,theproportionallimitand

19.0 (3/4)

150

100

0.7

60

Bolt diameter(mm(in.))

200

10

Figure 7—18. Relation between loadbearing parallel to grain and specificgravity (ovendry weight, volume at test) for two 101.6-mm(4-in.) split rings and a single 19.1-mm-(314-in.-) diameter bolt in air-dry material. Center member thickness was 127.0 mm (5 in.) and side member thickness was 63.5 mm (2-1/2 in.).

7—20

0.1

250

30

0 100 -J

0

0

0.2

0.3 0.4 0.5 0.6 0.7 Specificgravity Figure 7—19. Relation between load bearing parallel to grain and specificgravity (ovendry weight, volume at test) for two 66.7-mm (2-5/8-in.)shear plates in air-dry material with steel side plates. Center member thickness was 76.2 mm (3 in.).

50

200

V

0

60

250

z

5

0.2

0 Figure

10 0.1

0.2

0.3

0.4 0.5 Specific gravity

0.6

7—20. Relation between load bearing

0

0.7

parallel

to grain and specificgravity(ovendry weight,volume at test) for two 101.6-mm (4-in.) shear plates in air-dry material with steel side plates. Center member thickness was 88.9 mm (3-1/2 in.).

proportionallimit. For split rings, the proportionallimit load is reducedby approximately half. For shearplates, the design loadsare approximately five-eighths ofthe proportional limit test loads. Thesereductionsagain accountfor materialvariability, areductionto long-timeloading,and a factor ofsafety.

Design loads are presentedin Figures7—17 to 7—22. In practice, fourwood species groupshavebeen established, based primarily on specific gravity, and designloads assigned for each group. Speciesgroupings for connectors are presentedin Table 7—17. The corresponding design loads (for long-continued load) are given in Table 7—18.The NationalDesign Specflcationfor Wood Construction gives design valuesfor normal-duration load for these and additional species.

50 40

z

Bolt diameter (mm(in.)) 19.0 (3/4) 15.9 (5/8) 19.0 or 15.9 (3/4or 5/8)

— ———

30

//

/ //

12

8

10

0

C.)

0 20 -J

72

z

2 0.1

0.2

0.3

0.4

0.5

0.6

0 0.7

Group2

—— —

—15.9(5/8) 19.0or 15.9 (3/4 or 5/8)

Group3

.0

12%

0 36

o o

18

4

-J

0.1

0.2

0.5 0.4 Specificgravity 0.3

Group4

16

0

0.6

Aspen Western redcedar Eastern hemlock

Chestnut

Yellow-cedar

20

Bolt diameter(mm(in.)) 19.0 (3/4)

54

0

Group 1

S pecies orspecies group

Sugarpine

Specificgravity Figure 7—21. Relation between load bearing perpendicular to grain and specific gravity (ovendry weight,volumeat test) fortwo 66.7-mm (2-5/8-in.) shear plates in air-dry material with steel side plates. Center memberthickness was 76.2 mm (3 in.). 90

Connector

4o

10 0

Table7—17. Species groupingsfor connector loadsa

1

0 -J

0

0.7

Figure 7—22. Relation between loadbearing perpendicularto grain and specificgravity (ovendry weight,volume attest) fortwo 101.6-mm (4-in.) shear plates in air-dry material with steel side plates. Center member thickness was 88.9 mm (3-112 un.).

Modifications Somefactors that affectthe loadsofconnectors weretaken into accountin derivingthe tabular values. Other varied and extreme conditions requiremodification ofthe values.

Steel Side Plates Steel side plates are often used with shear-plate connectors.

The loadsparallelto grain havebeen found to be approximately 10% higher than those with wood side plates.The perpendicular-to-grain loadsareunchanged.

Exposureand Moisture Condition of Wood Theloadslistedin Table 7—18 apply to seasonedmembers

used wherethey will remain dry. Ifthe wood will be more or less continuouslydamp or wet in use, two-thirdsofthe

Basswood Balsam fir

Cottonwood

Eastern white pine Western whitepine

PondErasapine

Yellow-poplar Port-Orlord-cedar

Baldcypress Western hemlock Red spruce

Whitefir

Engelrnann sprtJce

Red pine

Redwood

Sitka spruce

Whitespruce

Elm, American

Elm,slippery

Sweetgum Douglas-fir

Sycamore Larch, western

Maple, soft Tupelo SouthernPine

Ash, white Elm,rock Oak

Beed,

Birch

Hickory

Maple, hard

aGroup 1 woods provide theweakest connectorjoints;

group 4woods, thestrongest.

tabulated valuesshouldbe used. The amountby whichthe loads shouldbe reducedto adaptthem to other conditions of use depends uponthe extentto whichthe exposure favors decay,the requiredlife ofthe structure orpart,the frequency and thoroughness ofinspection, the original costand the cost ofreplacements, the proportionofsapwoodanddurability of theheartwoodofthe species (ifuntreated), andthe tharacter and efficiency ofanytreatment. Thesefactors shouEdbe evaluatedforeach individual design.Industryreco:rnmendations for theuse ofconnectors whenthe conditionofthe lumberis other than continuously wet or continucuslydry aregiven intheNationalDesign Spec(flcation for Wood Construction. Ordinarily, before fabrication ofconnector joints, members shouldbe seasoned to moisturecontentcorresponding as nearly as practicalto that whichthey will attain it. service. This is particularly desirable for lumberforrooftnissesand other structural units usedin dry locations and in which shrinkage is an important factor.Urgentconstruction needs sometimes result inthe erection ofstructures andstructural units employing green orinadequately seasonedlumber with connectors. Becausesuch lumbersubsequently dries out in most buildings, causing shrinkage and opening thejoints, adequate maintenance measures must be adopted. The maintenance forconnector joints in green lumber should include inspection ofthe structural units andtighteningof all bolts as needed during the time the units are coming to moistureequilibrium, whichis normallyduring the firstyear.

a

7—21

Table 7—18. Design loadsfor one connector in a jointa Load (N (Ib)) Minimum thickness of wood member (mm(in.))

Group 1 woods

Group 2woods

Group 3woods

Group 4woods

At90° angle to grain

AtO° angle to grain

At90°

At0°

At90°

angle to grain

angle to

angle to grain

5,471

11,032

6,561

Withtwo Withone Connector

connector only

connectors in opposite ces,one boftb

Minimum widthall members (mm (in.))

51(2)

89 (3-1/2)

AtO°

A190°

AtO°

angle

angle

angle to

to grain

to grain

grain

grain

Split ring 63.5-mm (2-1/2-in.) diameter, 19.0mm (3/4 in.) wide, with 12.7-mm (1/2-in.) bolt

25(1)

101.6-mm (4-in.) diameter, 25.4 mm (1 in.) wide, with 19.0-mm (3/4-in.) bolt

38 (1-1/2)

76(3)

140 (5-1/2)

12,769 7,673 (2,875) (1,725)

7,940

4,693

9,274

(1,785)

(1,055)

(2,085)

(1,230) (2,480) (1,475)

10,275 21262 12,344 24,821 14,390 (2,310) (4,780) (2,775) (5,580) (3,235)

15,324

8,874

17,726

(3,445)

(1,995)

(3,985)

Shear plate 66.7-mm (2-5/8-in.) diameter, 10.7mm (0.42 in.)wide,with 19.0-mm (3/4-in.) bolt

38(1-1/2)

101.6-mm (4-in.) diameter,16.2mm (0.64 in.)wide,with 19.0-mm or22.2-mm (3/4- or 7/8-in.) bolt

44(1-314)

67(2-5/8)

92(3-518)

89(3-1/2)

140 (5-1/2)

8,407

4,871

9,742

(1,890)

(1,095)

(2,190)

(1,270) (2,630) (1,525) (2,665) (1,780)

5,649

8,518 (1,915)

12,677

7,362

14,701

(2,850)

(1,655)

(3,305)

11,699

17,637

6,784

10,231

11,854

7,918

20,573 11,943

(3,965 (2,300) (4,625)

(2,685)

alheloads apply to seasoned timbers indry, inside locationsfora long-continuedload. It is also assumedthatthejointsare properlydesigned withrespecttosuchfeatures as centeringofconnectors,adequateend dIstance,and suitable spacing.Group 1 woods providethe weakest connectorjoints, group4woods the strongest.Species groupingsare given inTable 7—17.

bA three-member assembly withtwo connectorstakes double the loads indicated.

Grade and Quality of Lumber The lumberforwhichthe loadsfor connectors are applicable shouldconform tothe generalrequirements in regardto qualityofstructural lumbergiven in the gradingrule books oflumbermanufacturers'associations for various commercial species.

The loads for connectors were obtainedfrom tests ofjoints whosemembers were clear and free from checks, shakes, and splits. Cross grain at the jointshould not be steeperthan I in 10, and knots in theconnectorarea shouldbe accounted for as explainedunderNet Section.

Loads at Angle with Grain The loadsfor the split-ring and shear-plate connectors for anglesof00 to 900 between directionofloadand grain may be obtainedby theHankinson equation(Eq. (7—16)) or by the nomographin Figure7—7.

7—22

Thickness

of Member

The relationshipbetweenthe loads for the differentthick-

nessesoflumberis basedontest resultsfor connectorjoints. The least thicknessofmembergiven in Table7—18 forthe various sizes ofconnectors is the minimumto obtain optimum load. The loadslistedfor eachtype and size ofconnector arethe maximum loads to be usedfor all thicker lumber. The loads forwood members ofthicknesses less than those listed canbe obtained by the percentage reductionsindicated in Figure7—23.Thicknessesbelow those indicatedby the curvesshould not be used. When one member contains a connector in only one face, loadsforthicknessesless than those listed in Table 7—18 can be obtainedby thepercentage reductionsindicatedin Figure 7—23 usingan assumedthicknessequalto twice the actual memberthickness.

.

.C)

o0) 0

0 o

. D

.2 E

100

0

Thickness of woodmember with connector in each face (in.) 1 2 3 4 5 I

63.5-mm (2-1/2 rn) diameter,

80 12.9-mm(1/2 bolt

? 1) a)

I

I

diameter, 19-mm (3/4-in.)

Splitring

60 100 66.7-mm

0

I_mm —. 101 .6 (4 in)

80 60 0

(25/8,/2 /

diameter,

19-mm (3/4-in.) bolt

diameter, 19- or 22.2-mm (7/8- or3/4-in.)bolt

Shear plate

104 26 52 78 130 Thickness of woodmemberwith connector in each face (mm)

Figure 7—23. Effect of thickness ofwood member on the optimum load capacity ofa timber connector.

Width of Member The widthofmemberlistedfor each type and size ofconnector is theminimumthat shouldbe used. Whenthe connectors arebearingparallelto the grain,no increase in load occurs with an increase in width. Whenthey are bearing perpendicular to the grain,the load increases about 10% for each 25-mm(1-in.)increase in widthofmemberoverthe minimumwidthsrequiredfor eachtype and size ofconnector, up to twicethe diameterofthe connectors. Whenthe connector isplacedoffcenterand the loadis appliedcontinuouslyin one directiononly, the properload can be determined by consideringthe widthofmemberas equalto twice theedge distance (the distance betweenthe centerofthe connector andthe edge ofthe membertowardwhichthe load is acting). The distance betweenthe centeroftheconnector and the oppositeedge should not, however, be less than halfthepermissibleminimumwidth ofthe member.

Net Section The net sectionis the area remaining at the criticalsection after subtracting the projectedarea ofthe connectors and bolt from the full cross-sectional area ofthe member. For sawn timbers,the stress in the net area (whetherin tension or compression) shouldnot exceedthe stress for clearwood in

there are noknots at or near the connector. In laminated construction, therefore, the stress atthe net sectionis limited to thecompressive stress for the member,accounting forthe effect ofknots.

End Distance and Spacing The loadvalues in Table 7—18 apply when the distance of theconnector from the end ofthemember(end distance e) and the spacings between connectors in multiplejoints are not factors affectingthestrengthofthejoint(Fig. —24A). Whenthe end distance orspacingforconnectors bearing parallelto the grain is less than that requiredto developthe full load,the properreducedloadmay be obtainedby multiplying the loads in Table 7—18 by the appropriate strength ratio given in Table 7—19. For example,the load f r a 102-mm (4-in.) split-ring connector bearing parallelto the grain,whenplaced 178 mmor more (7 in. or more) fromthe end of a Douglas-firtension memberthat is 38 mm (1-1/2 in.) thick is 21.3 kN (4,780 ib). When the end distance is only 133 mm (5-1/4 in.), the strength ratio obtained by direct interpolation between 178 and 89 mm (7 and 3-1/2 in.) in Table 7—19 is 0.81, and the load equals 0.81 times 21.3 (4,780) or 17.2 kN (3,870 ib).

compressionparallelto the grain. In usingthis stress, it is assumedthat knots do not occurwithin a length ofhalfthe diameterofthe connector from thenet section. Ifknotsare presentin the longitudinal projectionofthe net section withina length from the criticalsectionofone-halfthe diameterofthe connector, the area ofthe knotsshouldbe subtractedfrom the area ofthe criticalsection.

Placement of Multiple Connectors

In laminatedtimbers,knots may occur in the inner laminations at the connector locationwithoutbeing apparentfrom theoutside ofthemember.It is impracticalto assure that

Whentwo or more connectors inthe same face ofa member are in a line atright anglesto the grain ofthe memberand

Preliminaryinvestigationsofthe placementofconnectors in a multiple-connector joint, togetherwith theobservedbehavior ofsingle-connector joints testedwith variables that simulate those in a multiple-connector joint, are the basis for somesuggested designpractices.

7—23

Cross Bofts Crossbolts or stitchbolts placedat or near the end ofmembersjoined with connectors orat pointsbetween connectors willprovide additional safety. They may alsobe used to reinforce members that have, throughchangein moisture contentin service, developed splits to anundesirabledegree.

Multiple-FastenerJoints A

B

When fastenersare used in rows parallelto the directionof loading,total joint load is unequally distributedamong fastenersin the row. Simplifiedmethods ofanalysishave been developed to predict the load distributionamongthe fastenersin a row. Theseanalysesindicatethat the load distribution is a function of(a) the extensionalstiffliess EA of thejointmembers,whereE is modulusofelasticityandA is grosscross-sectional area,(b) the fastenerspacing, (c) the numberoffasteners, and (d) the single-fastener loaddefonnation characteristics. Theoretically, the two end fasteners carry amajorityofthe load. For example, in a row ofsix bolts, the two end bolts will carry more than 50% ofthe total jointload. Adding

C

D

Figure 7—24. Types ofmultiple-connector joints:

A, jointstrengthdepends on end distance eand connectorspacings; B,joint strength depends on e, clearc, and edge a distances; C, jointstrengthdepends on end e and clear c distances; D, jointstrength depends on end e, clearc, and edge a distances. are bearingparalleltothe grain (Fig. 7—24C), the clear distance c betweenthe connectors shouldnotbe less than 12.7 mm (1/2 in.). Whentwo or more connectors are acting perpendicularto the grain and are spacedon aline at right anglestothe length ofthe member(Fig. 7—24B), the rules for the width ofmemberand edgedistances used with one connector are applicabletothe edgedistances formultiple connectors. The clear distance cbetweenthe connectors shouldbe equaltothe clear distance fromthe edge ofthe membertoward which theload is actingto the connector nearestthis edge.

In ajointwith two or more connectors spacedon a line parallelto the grain and with the load actingperpendicular to thegrain (Fig. 7—24D), theavailabledata indicatethat the load for multipleconnectors isnot equalto the sum ofthe loads for individual connectors. Somewhatmore favorable resultscan be obtainedifthe connectors are staggeredso that they do not act along the same line with respectto the grain ofthetransverse member.Industryrecommendations for variousangle-to-grainloadingsand spacingsare given in the National Design Spec/Icationfor Wood Construction.

7—24

bolts to a row tends to reduce the load on the less heavily loaded interiorbolts. The most even distributionofbolt loadsoccursin ajointwherethe extensional stiffliess ofthe mainmemberis equaltothat ofboth splice plates. Increasing the fastenerspacingtends to put more ofthejointload ontheend fasteners. Load distributiontends to be worse for stifferfasteners.

The actualload distribution in field-fabricated joints is difficult to predict. Small misalignmentoffasteners,variations in spacingbetweenside and mainmembers,and variationsin single-fastener load—deformation characteristics can cause the load distribution tobe differentthan predictedby the theoretical analyses.

Fordesign purposes, modification factorsfor application to arow ofbolts, lagscrews,or timberconnectors have been developed basedon the theoreticalanalyses. Tables aregiven inthe NationalDesignSpecflcationfor Wood Construction.

A designequationwas developedto replace thedoubleently required in the NationalDesignSpecificationfor Wood Constructiontables. This equationwas obtainedby algebraic simplification ofthe Lantos analysis that these tables are basedon

=

rn(l—m2")

n[(1+RMrnn)(1+m)_1÷rn2nJ

____ 1—rn

(7—19)

where C8 is modification factor, n numberoffastenersin a

/

row,RMthe lesserof(E,A) / (E4m) or(EmAm) (E,A,), Em

Table 7—19. Strength ratiofor connectors forvariouslongitudinal spacings and end distancesa Connector diameter (mm (in.))

Spacing

End distanceb (mm (in.)) Tension Compression

member

member

End distance strength ratin

100

139.7+ (5-1/2+)

101 .6+ (4+)

100

Spacingc

strength

(mm (in.))

ratio

Split-ring

63.5 (2-1/2)

171 .4+ (6-3/4+)

63.5 (2-1/2)

85.7 (3-3/8)

50

69.8 (2-3/4)

63.5 (2-1/2)

62

101.6 (4)

228.6+ (9+)

100

177.8+ (7+)

139.7+ (5-1/2+)

100

101.6(4)

123.8 (4-7/8)

50

88.9 (3-1/2)

82.6 (3-1/4)

62

66.7 (2-5/8)

171.4+ (6-3/4+)

100

139.7+(5-1 /2+)

101.6+ (4÷)

100

66.7 (2-5/8)

85.7 (3-3/8)

50

69.8 (2-3/4)

63.5 (2-1/2)

62

101.6 (4)

228.6+ (9+)

100

177.8+ (7+)

139.7+ (5-112+)

100

101.6 (4)

114.3 (4-1/2)

50

88.9 (3-1/2)

82.6 (3-1/4)

Shear-plate

62

aStrength ratio for spacings and end distancesintermediate

to those listed may be obtained by interpolation and multipliedby the loads in Table 7—18 to obtain design load. The strengthratio applies only to those connectorunits affected by the respectivespacings or end distances. The spacings and end distances should not be less than the minimum shown. bEnd distance is distance from center of connectorto end of member (Fig. 7—24A). eSpacing is distance from centerto center of connectors(Fig. 7—24A).

E

modulusofelasticityofmainmember, modulusofelasticity ofsidemembers,Am gross cross-sectional area ofmain member, A. sum ofgrosscross-sectional areas ofsidemembers, m = u —Vu2—1, u = 1 + y(s/2)(liEmAm + 1/ EA), s center-to-center spacingbetween adjacentfastenersin arow, and 'y load/slipmodulusforasingle fastenerconnection. For102-mm (4-in.)split-ringor shear-plate connectors,

= 87,560 kN/m (500,000 lb/in) For64-mm (2-1/2-in.)split ring or 67-mm(2-5/8-in.) split ring or shearplate connectors,

= 70,050 kN/m (400,000 lb/in) Forbolts or lagscrewsinwood-to-woodconnections, = 246.25 D'5 = 180,000D'5

(metric) (inch—pound)

Forbolts or lagscrewsinwood-to-metalconnections, = 369.37 D'5 (metric)

= 270,000D15

(inch—pound)

whereD is diameterofboltor lag screw.

Metal Plate Connectors Metal plate connectors,commonlycalledtrussplates, have become a popularmeansofjoining, especially in trussed raftersandjoists. These connectors transmitloads by means ofteeth,plugs, or nails, whichvary frommanufacturerto manufacturer. Examples ofsuchplates are shown in Figure 7—25.Plates are usually madeoflight-gauge galvanizedsteeland havean area and shapenecessary totransmit theforces on the joint. Installationofplatesusuallyrequires a hydraulic pressor otherheavy equipment, althoughsome plates can be installed by hand. Basic strengthvaluesfor plate connectors are deteimined from load—slip curves from tensiontests oftwo btLtted wood members joined with two plates. Sometypicalcurves are shownin Figure 7—26. Designvaluesare expressed as load pertooth, nail, plug, or unit area ofplate. The sinallestvalue as determined by two different meansis thedesign load for normal duration of load: (1)the averageloadofat least five specimens at 0.38-mm(0.015-in.) slip from plate to wood member or0.76-mm(0.030-in.) slip from memberto member is divided by 1.6; (2) theaverage ultimate load of at least five specimens is dividedby 3.0.

The strength ofa metal platejoint may alsobe controlled by thetensileor shear strengthoftheplate.

7—25

Figure 7—25. Some typical metal plate connectors.

Slip, member to member (in.)

The bearingstrengthofwood underfastenerheadsis important in such applications as the anchorageofbuildingframework to foundation structures. When pressuretends to pull theframing member awayfrom thefoundation, thefastening loadscould cause tensile failureofthe fastenings,withdrawal ofthe fastenings from the framingmember,or embedment of thefastenerheadsinthemember.The fastenerheadcould evenbe pulledcompletelythrough.

40

'30 20

0 -J

10

0

0.5

1.0 1.5 Slip, member to member(mm)

curvesfor two Figure loaded in tension. of metal connectors types plate 7—26. Typicalload—slip

7—26

Fastener Head Embedment

The maximum load for fastenerhead embedment is relatedto thefastenerheadperimeter, while loads at low embedments (1.27 mm (0.05 in.)) are relatedto the fastenerhead bearing

area.Theserelationsfor severalspecies at 10% moisture contentare shownin Figures 7—27 and 7—28.

. .

Fastener perimeter(in.)

0

.0

0 x 0

60

0

0

45

a)

E E

ASTM D5652—95. Standardtestmethodsfor bolted connectionsin wood and wood-base products.

.2 30

0E

a)

.0 a)

J150

spiker, staples.

E

C

E

ASTMFl667. Specification for drivenfasteners:nails, ASTMD2555—96. Standardmethodsfor establLshingclear wood strengthvalues. ASTMF547. Standardterminologyofnails for use with wood and wood-base materials.

E

0

ASTM. (currentedition). Philadelphia, PA: American Society for Testing and Materials.

x

ASTMD1761—88. Standardtest methods for mechanical fasteners inwood.

Fastener perimeter (mm)

Anderson, L.O. 1959. Nailingbetter wood boxes and crates. Agric. Handb. 160. Washington,DC: U.S DepartmentofAgriculture.

Figure 7—27. Relation between maximum embedment loadand fastener perimeter for several species ofwood.

Anderson, L.O. 1970. Wood-frame house construction. Agric.Handb. 73 (rev.). Washington,DC: U.S. I)epartment

z

Fastenerheadbearingarea (in2)

.0

0

C.)

35

x

30

C

25

a,

E

V a)

E a, 20 E 15 E

C%

.0 E

a)

Cramer, C.O. 1968. Load distributionin multiple-bolt

tensionjoints. Proc. Pap. 5939. Journalof Structural Division,American Society ofCivilEngineers. 94(ST5): 11011117.

Doyle, D.V.; Scholten, J.A. 1963. Performance ofbolted joints in Douglas-fir. Res. Pap. FPL 2. Madison. WI: U.S. Department ofAgriculture, Forest Service,Forest Products Laboratory.

10

q 0

0

(a

Cs

0 -jO

ofAgriculture.

5

10

15 Fastener head bearing area (cm2)

0(a 0

Figure 7—28. Relation between loadat 1.27-mm (0.05-in.)embedment and fastener bearing area for several species.

Eckelman,C.A. 1975. Screwholdingperformancein hardwoodsandparticleboard. Forest Products Journal. 25(6): 30—35. Fairchild, I.J. 1926. Holdingpower ofwood screws. Technol.Pap. 319. Washington, DC: U.S. NationalBureau

ofStandards.

ForestProductsLaboratory. 1962. Generalobservations on the nailing ofwood. FPL Tech.Note 243. Madison, WI: U.S. Department ofAgriculture, Forest Service,Forest Products Laboratory.

References

ForestProductsLaboratory. 1964. Nailingdensehard-

AF&PA. 1997. Nationaldesignspecification forwood construction. Washington, DC: American Forest & Paper

Laboratory.

Association.

ASCE. 1995. Standardfor loadand resistance factor design (LRFD) for engineeredwood construction. Washington, DC: American Society ofCivilEngineers. ASCE. 1996. Mechanicalconnections in wood structures. Washington, DC: AmericanSocietyofCivil Engineers.

woods. Res. Note FPL—037. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products

Forest ProductsLaboratory. 1965. Nail withdrswal resistance ofAmerican woods. Res. Note FPL—RN---033. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory. Goodell, H.R.; Philipps, R.S. 1944. Bolt-bearing strength ofwood andmodified wood: effectofdifferent methods of drillingboltholes in wood and plywood. FPL Rep. 1523. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory.

7—27

Johansen,K.W. 1949. Theory oftimber connections. Zurich, Switzerland: Publications ofInternational AssociationforBridge and Structural Engineering. 9: 249—262.

Scholten, J.A.; Molander, E. G. 1950. Strength ofnailed joints in frame walls. Agricultural Engineering. 31(11):

Jordan, CA. 1963. Responseoftimberjoints with metal

Soltis, L.A.; Wilkinson, T.L. 1987. Bolted connection design. Gen. Tech. Rep. FPL—GTR—54. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest

fastenersto lateral impactloads. FPL Rep. 2263. Madison, WI: U.S. DepartmentAgriculture,Forest Service,Forest

Products Laboratory. Kuénzi, E.W. 1951. Theoretical designofa nailed orbolted jointunderlateral load. FPL Rep. 1951. Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory. Kurtenacker, R.S. 1965. Performance ofcontainer fasteners subjectedto static and dynamicwithdrawal. Res. Pap. FPL 29. Madison,WI: U.S. DepartmentofAgriculture, Forest Service,Forest ProductsLaboratory. Lantos,G. 1969. Load distributionin a row offasteners subjectedto lateral load. Madison, WI: Wood Science. 1(3): 129—136. Markwardt,L.J. 1952. How surface condition ofnails

affects their holding power in wood. FPL Rep. D1927. Madison,WI: U.S. DepartmentofAgriculture,Forest Service, ForestProducts Laboratory. Markwardt,L.J.; Gahagan, J.M. 1930. Effect ofnail points on resistanceto withdrawal.FPL Rep. 1226. Madison,WI: U.S. Department ofAgriculture,Forest Service, ForestProducts Laboratory. Markwardt, L.J.; Gahagan, J.M. 1952. Slant drivingof nails. Does it pay? Packing and Shipping. 56(10): 7—9,23,25.

McLain, T.E. 1975. Curvilinearload-slip relationsin laterally-loaded nailedjoints. Fort Collins, CO: Department ofForestryand WoodScience,ColoradoState University. Thesis. NPA. 1968. Screw holding ofparticleboard.Tech. Bull.3. Washington, DC: NationalParticleboard Association. Newlin, J.A.; Gahagan, J.M. 1938. Lag screw joints: their behavior and design. Tech. Bull. 597. Washington, DC: U.S. Department ofAgriculture. Perkins, N.S.; Landsem, P.; Trayer, G.W. 1933. Modem connectors for timber construction. Washington, DC: U.S. DepartmentofCommerce, NationalCommittee on Wood Utilization, and U.S. Department ofAgriculture,Forest Service.

Scholten, J.A. 1944. Timber-connector joints, theirstrength and design. Tech. Bull. 865. Washington,DC: U.S.

Department ofAgriculture. Scholten, J.A. 1946. Strength ofbolted timberjoints. FPL Rep. R1202. Madison, WI: U.S. Department of Agriculture, Forest Service,Forest ProductsLaboratory. Scholten, J.A. 1950. Nail-holdingproperties ofsouthern hardwoods. SouthernLumberman. 181(2273): 208—210.

7—28

551—555.

Products Laboratory.

Stern, E.G. 1940. A study of lumberand plywoodjoints with metal split-ringconnectors.Bull. 53. State College, PA: Pennsylvania EngineeringExperimentStation.

Stern, E.G. 1950. Nails in end-grainlumber. Timber News and Machine Woodworker. 58(2138): 490—492.

Trayer, G.W. 1932. Bearingstrengthofwood under bolts. Tech. Bull. 332. Washington, DC: U.S. Departmentof Agriculture.

TrussPlateInstitute. {n.d.]Design specification for metal

plate connected wood trusses. TPI—78. Madison, WI: Truss Plate Institute. Wilkinson, T.L. 1971. Bearingstrength ofwood under embedment loading offasteners.Res. Pap. FPL 163. Madison, WI: U.S. Department ofAgriculture,Forest Service, Forest Products Laboratory. Wilkinson, T.L. 1971. Theoreticallateral resistanceof nailedjoints. ProceedingsofAmerican SocietyofCivil Engineering. Journal ofStructural Division. ST5(97): (Pap. 8121): 1381—1398. Wilkinson, T.L. 1978. Strength of bolted wood joints wfth variousratios memberthicknesses.Res.Pap. FPL 314. Madison, WI: U.S. Department ofAgriculture,Forest

o

Service, Forest Products Laboratory.

Wilkinson, T.L. 1980. Assessmentofmodification factors for a row of bolts or timberconnectors.Res. Pap. FPL 37o. Madison, WI: U.S. Department ofAgriculture,Forest Service, Forest ProductsLaboratory. Wilkinson, T.L. 1991. Dowel bearing strength. Res. Paper FPL—RP—505.Madison, WI: U.S. DepartmentofAgriculture, Forest Service,Forest ProductsLaboratory. Wilkinson, T.L. 1991. Bolted connectionallowableloads based on the Europeanyield model.Madison, WI: U.S. Department ofAgriculture, Forest Service, Forest Products Laboratory.

Wilkinson, T.L.; Laatsch, T.R. 1970. Lateral and withdrawalresistance oftapping screws inthree densities of wood. Forest ProductsJournal.20(7): 34—41.

Zahn,J.J. 1991. Designequationfor multiple-fastener wood connections. NewYork,NY: JournalofStructural Engineering, American Society ofCivil Engineers. Vol. 117(11): 3477—3485.

Nov.

ter'8 I Chap

I

Structural Analysis Equations LawrenceA. Soltis

Contents DeformationEquations 8—1

Axial Load

8—1

Bending 8—1 CombinedBendingand Axial Load Torsion

8—3

8—4

Stress Equations 8—4 Axial Load

Deformation Equations

8—4

Bending 8—4 CombinedBendingandAxial Load Torsion

8—8

StabilityEquations 8—8 Axial Compression 8—8 Bending 8—9 InteractionofBucklingModes References 8—il

quations for deformation and stress, whichare the basisfor tensionmembersand beamand column design,are discussedin this chapter. The firsttwo sections cover taperedmembers,straightmembem, and specialconsiderations such as notches,slits, and size effect. A third sectionpresentsstability criteria formemberssubject to bucklingand for members subjectto special conditions. The equationsare basedon mechanicsprinciples and arenot given in the designcode formatfound in Allowable Stress DesignorLoad and Resistance FactorDesignspecifications.

Equations fordeformation ofwood members are presented as 8—7

functions ofappliedloads,moduliofelasticityand rigidity, and memberdimensions. They may be solvedto determine minimum requiredcross-sectionaldimensions to nieet deformation limitations imposed in design.Averagemoduliof elasticityand rigidityare given in Chapter4. Consideration must be given to variabilityin materialpropertiesand uncertaintiesin applied loadsto controlreliabilityofthe design.

Axial Load 8—10

The deformation ofan axiallyloadedmemberis notusually an importantdesignconsideration. More important considerationswill be presentedin later sections dealingwith combined loads or stability. Axial loadproducesachangeof length given by AE

is changeoflength,L length, A cross-sectionalarea, E modulusofelasticity (EL whengrain runs parallelto member axis), andP axial forceparallelto grain. where

Bending Straight Beam Deflection The deflectionof straight beamsthat are elastically stressed and havea constantcross sectionthroughouttheirlength is given by

8—1

kWL3

El

+

kWL (8—2)

GA'

is deflection, Wtotal beamload actingperpendicular

where

to beamneutral axis, L beam span, kband k, constantsde-

pendentupon beam loading,supportconditions, and locationofpoint whose deflection is to be calculated, beam moment ofinertia,A' modifiedbeamarea, Ebeam modulus ofelasticity(for beams havinggrain directionparallelto their axis, E = EL), and G beam shear modulus(for beamswith flat-grained verticalfaces,G GLT, and for beamswith edgegrained verticalfaces,G = Gm). Elasticpropertyvaluesare given in Tables 4—1 and 4—2 (Ch. 4).

I

Tapered Beam Deflection Figures 8—1 and 8—2 are usefulin the design oftapered beams. The ordinates are based on designcriteriasuch as span, loading, difference inbeam height (h— ho) as required by roofslopeor architectural effect, and maximum allowable deflection, togetherwith materialproperties. Fromthis, the valueofthe abscissacan be determinedand the smallest beamdepth h0 can be calculated for comparison with that given by the design criteria. Conversely, the deflectionofa beamcan be calculated ifthe value ofthe abscissais known. Tapered beams deflect as aresult ofshear deflection in addition to bending deflections (Figs. 8—1 and 8—2), and this shear deflection A, can be closelyapproximated by

The first term on the right side ofEquation(8—2)gives the bending deflectionand the secondterm the shear deflection. Valuesof/c and Ic, forseveralcasesofloading and support are given in Table 8—i.

3WL A= for uniformly distnbutedload 2OGbh0

(8-5) 3PL

I

The momentofinertia ofthe beamsis given by

I=

12

lOGbh0

forbeamofrectangular cross section (8-3)

= 64

for beamofcircularcross section

whereb is beam width, h beam depth, and dbeam diameter. The modifiedarea A' is given by 5

A = bh for beamofrectangular cross section (8

= 40

ird2 forbeamofcircularcross section

formidspan-concentrated load

The final beamdesignshould consider the total deflection as the sum oftheshear and bendingdeflection, and itmay be necessaryto iterateto arrive at final beamdimensions. Equations (8—5) are applicable to eithersingle-taperedordoubletapered beams. As with straight beams, lateral or torsional restraintmaybenecessary.

Effect of Notches and Holes The deflection ofbeamsis increased ifreductionsin crosssectiondimensions occur,such as by holes or notches.The deflection ofsuch beamscan be determined by considering them ofvariable cross section along their length and appropriately solving thc generaldifferential equationsofthe elastic curves, EI(d2y/dx2) to obtain deflectionexpressions or by the application ofCastigliano'stheorem.(Theseproceduresare given in most texts on strengthofmaterials.)

i,

Ifthebeamhas initial deformationssuch as bow (lateral

bend) ortwist, these deformationswill be increasedby the bendingloads. It may be necessaryto providelateral or torsionalrestraintsto hold such membersin line. (See Interaction ofBucklingModessection.)

Table 8—1. Values of kb and k5 for several beam loadings Loading

Uniformly distributed Concentratedat midspan Concentratedat outer quarter span points Uniformly distributed Concentratedat free end

8—2

Beam ends

Deflection at

kb

k

Both simply supported

Midspan

5/384

1/8

Both clamped

Midspan

1/384

1/8

Both simply supported

Midspan

1/48

1/4

Both clamped

Midspan

1/192

1/4

Both simply supported

Midspan

11/768

1/8

Both simply supported

Load point

1/96

1/8

Cantilever,one free, one clamped Cantilever,one free, one clamped

Free end

1/8

1/2

Free end

1/3

1

0.9 ho

0.8 ho 0.7

11 ti

0.8

L

k

L,2

0.7

'I

L,2

0.6

W=Total loadon beam 0.6 -

C,)

0.5

I(

<

0.5

E= Elastic modulus of beam

Lu

-

(uniformly distributed)

= Maximum bending deflection

b= Beam width U.'

hh0

C,)

.? Single taper

0.4 -

V

0.3 0.2 -

0.3

0.2

Double taper

P= Concentrated midspari load

0.1

0.1

0

0.4

1

2

I

I

I

3

4

5

0

= Maximum bending deflection E= Elastic modulus of beam 1

2

3

5

4

1

Figure 8—1. Graph for determining tapered beam size based on deflection under uniformly distributedi load.

Figure 8—2. Graph for determining tapered be2m size on deflection under concentrated midspan loaci.

Effect of Time: Creep Deflections In addition to the elasticdeflectionspreviously discussed, wood beams usuallysag in time; that is, the deflection increases beyond what it was immediately after the loadwas first applied.(See the discussionofcreepin TimeUnder Load in Ch. 4.)

Water Ponding Pondingofwateron roofs alreadydeflected by other loads cancause largeincreases in deflection. The total deflection due to design load plus ponded watercan be closlyestimatedby

Greentimbers,in particular, willsag ifallowedto dry under load, although partiallydried material will also sag to some extent. In thoroughlydried beams,smallchangesin deflection occur with changesin moisture contentbut with little permanent increase in deflection. Ifdeflection underlongtime load with initially green timber is to be limited, it has been customary to designfor an initial deflectionofabout halfthe valuepermittedfor longtimedeflection. Ifdeflection under longtimeload with initially dry timber is to be limited, it has been customary to design foran initialdeflection ofabout two-thirds the valuepermittedfor longtimedeflection.

i

A= where

lSIScr

(8-6)

A is deflectiondue to design load alone, S beam

spacing, and Ser critical beam spacing(Eq. (8—31)).

Combined Bending and Axial L.oad Concentric Load Additionofaconcentric axial loadto abeam underloads acting perpendicular to the beamneutralaxiscauses increase in bending deflection for added axial compression and decrease in bendingdeflectionfor addedaxial tension.

8—3

The deflectionunder combined loading at midspanfor pin-endedmembers can be estimatedcloselyby A=

8

7

A0

(8—7)

1±P/P01

wherethe plus sign is chosenifthe axial loadis tensionand theminus sign ifthe axial load is compression, A is midspan deflectionunder combined loading, A0 beam midspan deflectionwithout axial load,P axial load, and aconstant equalto the bucklingload ofthe beam underaxial compressive load only (see Axial Compressionin StabilityEquations section.) based on flexuralrigidityabout the neutral axis perpendicularto the directionofbending loads.This constantappearsregardlessofwhetherP is tension or compression.IfP is compression, it must be less than Pcr to avoid collapse. When the axial load is tension, it is conservativeto ignore the PIP1,-term. (Ifthe beam is not supported against lateraldeflection, itsbuckling loadshouldbe checked using Eq. (8—35).)

6 5

P

Eccentric Load

Ifan axial loadis eccentrically appliedto apin-endedmember, it will inducebending deflections and change in length given by Equation(8—1). Equation(8—7)can be appliedto find the bendingdeflectionby writing the equationinthe form

+60 where

1±

(8—8)

bis theinducedbendingdeflection at midspan and

o theeccentricityofP from thecentroid ofthecross section. Torsion

4

3

0

GK

(8—9)

where 0 is angle oftwist in radians, Tapplied_torque, L memberlength, G shear modulus(use ...JGLRGLT , or approximateG by ELI16 ifmeasuredG is not available), and K across-section shape factor. For a circularcrosssection, K is thepolar momentofinertia:

K=— 32

(8—10)

whereD is diameter.For arectangularcross section,

K=!!b_

0.6

0.8

1.0

Figure 8—3. Coefficient for determining torsional rigidity of rectangular member (Eq. (8 —11)).

Stress Equations

The equationspresentedhere are limitedby the assumption that stress and strain are directly proportional (Hooke's law)

and by the fact that local stresses inthe vicinityofpoints of supportorpointsofload application are correct only to the extentofbeing statically equivalent to the true stress distri bution(St. Venant's principle). Local stress concentrations mustbe separately accounted for ifthey are to be limitedit. design.

Axial Load Tensile Stress Concentricaxial load(alongthe linejoining the centroidsof thecross sections) producesa uniformstress:

P A

(8—12)

J

where is tensilestress, P axial load, andA cross-sectional area.

Short-Block CompressiveStress Equation(8—12) can also be used in compression ifthe memberis short enoughto fail by simple crushingwithout

deflecting laterally. Suchfibercrushingproducesa local "wrinkle"causedby microstructuralinstability. The member as a wholeremainsstructurally stable and able to bear load.

Bending The strengthofbeams is determined by flexuralstresses

(8_il)

whereh is larger cross-sectiondimension, b is smallercrosssection dimension,and ci is given in Figure 8—3.

8-4

0.4 b/h

The angleoftwist ofwood members aboutthe longitudinal axis can be computed by TL

0.2

causedby bendingmoment,shear stressescausedby shear load, and compression acrossthe grain atthe end bearings and load points.

Straight Beam Stresses

Thestressdueto bendingmomentfor a simpiy supported pin-endedbeam is a maximum at the top and bottomedges. The concaveedge is compressed, and the convex edge is under tension. The maximum stress is given by fb

M

(8—13)

wherefiis bendingstress, Mbendingmoment,and=Zbeam sectionmodulus(for a rectangularcross section, Z bh2/6; for a circularcross section, Z = nD3/32).

This equationis also used beyond the limits ofHooke's law with M as the ultimate moment at failure. The resulting pseudo-stress is calledthe "modulusofrupture,"valuesof which are tabulated in Chapter4. The modulusofrupture has beenfound to decreasewith increasingsize ofmember. (See SizeEffectsection.) The shear stress due to bending is a maximum at the centroidalaxis ofthe beam, wherethe bendingstress happens to be zero.(This statementis nottrueifthe beam is tapered— see followingsection.)In wood beamsthis shear stress may producea failurecracknearmid-depthrunningalongthe axis ofthemember.Unlessthebeamis sufficiently shortand deep, itwill fail inbendingbeforeshearfailurecan develop; but wood beamsarerelatively weak in shear,and shear strengthcan sometimesgovern a design. The maximum shear stress is (8:14)

A

wheref, is shear stress, Vverticalshearforce on cross section,A cross-sectional area,and k= 3/2 for arectangular cross sectionork=4/3 for a circularcross section.

1

7/8

3/4

Tapered Beam Stresses Forbeams ofconstantwidththat taper in depth at a slope less than 25°, the bendingstress can be obtainedfium Equation (8—13) with an error ofless than 5%. The shear stress, however, differs markedly from that found inunifo:rmbeams. It can be determined fromthebasic theorypresentedby Maki and Kuenzi (1965). The shear stress atthe taperededge can reach amaximum value as greatas that atthe neutral axisat

a reaction.

Considerthe exampleshownin Figure 8—4, in which concentrated loads farther to the righthaveproduceda support reaction Vatthe left end. In this casethe maximumstresses occur at the cross sectionthat is doublethe depth ofthe beam atthe reaction. For other loadings, the locationofthe cross section with maximumshear stress at the taperededge will be different. For the beam depicted in Figure8—4, the bendingstress is alsoa maximum at the same cross sectionwherethe shear stress is maximumat the tapered edge. This stress situation alsocausesa stress inthe directionperpendicular1:othe neutralaxisthat is maximum atthe taperededge. The effect ofcombined stressesat apointcanbe approximately accountedforby an interaction equationbasedonthe ilenky— von Misestheory ofenergy due to the change ofshape. This theoryappliedby Norris(1950)to wood resultsin 2

f2

(8—15)

wheref is bending stress,f, stress perpendiculartD the neutral axis, andf, shear stress. Values ofF, F,, and F, are corresponding stresseschosenat designvaluesor maximum valuesin accordance with allowable or maximum values being determined for the taperedbeam. Maximumstressesin

Values of h0/h 1/2

2/3

j.2

114

—x

8/9cr Particular taperedbeam where

M= h= ÷ xtan e

—x1

—

2bh0

Figure 8—4. Shear stress distributionfor a tapered beam.

8—5

thebeam depictedin Figure8—4 are given by

1/rn

[ 361.29 1 —=1 I R2 [h1Li(1+mai/L1)J rI 11/rn 56 I R1

3M

ff

2bh

=

=

tanO

R2

tan28

Substitutionofthese equationsinto the interactionEquation (8—15) will result in an expression forthe momentcapacity Mofthebeam. Ifthetaper is on thebeamtensionedge, the values ofj andfare tensilestresses. capacity (newton-meters) Example: Determine the moment of atapered beam ofwidthb = 100mm, depth = h0 200 mm, and taper tan 8 1/10. Substitutingthese dimensionsintoEquation(8—16) (with stresses in pascals) results in

fr =375M

= 37.5M

f=3.75M Substituting these into Equation(8—15) and solving for M results in

=

I

Lh1L1(1+mai/Li)J

R1=10000[

Size Effect The modulusofrupture(maximumbendingstress)ofwood beams depends on beam size and methodofloading,and the strength ofclear, straight-grained beamsdecreases as size increases. These effects were foundtobedescribable by statistical strengththeory involving"weakestlink" hypotheses and can be summarizedas follows: For two beams under two equal concentrated loads appliedsymmetrical to the midspan points, the ratioofthe modulusofrupture ofbeam 1 to the modulusofruptureofbeam 2 is given by

= [h2L2(1+ma2/L2)li/rn R2

[h1L1(1+mai/Li)]

(8—17)

where subscripts I and 2 refer to beam 1 andbeam 2, R is modulusofrupture, h beamdepth, L beam span,a distance between loadsplaceda/2 each sideofmidspan,and m a constant. For clear, straight-grained Douglas-firbeams, m 18. IfEquation(8—17) is used forbeam 2 size (Ch. 4) loaded at midspan,then h2 = 5.08 mm (2 in.), L2 = 71.112 mm (28 in.), and a2 0 and Equation(8—17)

(8—I 8b)

56 11/18

7,330 lb/in2 Application ofthe statistical strengththeory to beams under uniformlydistributed loadresultedin the followingrelationship betweenmodulus ofruptureofbeamsunder uniformly distributedloadand modulusofrupture ofbeams under concentrated loads: 1/18

R

whereappropriate allowableor maximum values ofthe F stresses(pascals)are chosen.

(mch—pound)

[2, 160(1+ 6)]

R

+ + 3.75[104/ 1O2/ l/F]

(8—18a)

Example:Determinemodulusofrupture for a beam 10 in deep, spanning18 fi, and loadedat one-third span points compared with a beam 2 in. deep, spanning28 in., and loadedatmidspanthat had amodulusofruptureof 10,000 lb/in2. Assume m = 18. Substitutingthe dimensions into Equation(8—18) produces

I

M=

becomes

R1

(8—16)

(metric)

(l+l8a/ic)kLç 3.876kL

(8—19)

where subscripts u and c referto beamsunderuniformly distributed and concentrated loads, respectively, and other terms are aspreviouslydefined.

Shearstrengthfor non-split, non-checked, solid-sawn, and glulambeamsalso decreases asbeam size increases. A relationshipbetweenbeam shear andASTM shear block strength¶ASTh4, including astress concentration factorforthe re-entrant cornerofthe shearblock,Cf. andthe sheararea A,

t

is

= 1.9CfrAs A"5

= L3Ct

(metric)

(8—20a)

(inch—pound)

(8—20b)

t

where is beamshear(MPa,lb/in2), Cf stress concentration factor,¶ASTM ASTM shear block strength (MPa, lb/in2), and A sheararea (cm2, in2) This relationship was determinedby empiricalfit to test data. The shearblock re-entrant cornerconcentration factor is approximately 2; the shear area is defmedas beam width multipliedby the length ofbeam subjectedto shear force.

Effect of Notches, Slits, and Holes In beamshavingnotches,slits, or holes with sharp interior corners, large stress concentrationsexist at the corners. The local stressesincludeshearparallelto grain and tension

8—6

1a

-

______________

IE

T

a-

•

0.007

Combined Bending and Axial Load

0.006

Concentric Load Equation (8—7)givesthe effecton deflection ofadding an end load to a simplysupported pin-endedbeamalreadybent by transverse loads. The bendingstress in the memberis modifiedbythe same factor as the deflection:

0.005 0.004

0003

0 x

I

0,002 •

0 0

0.1

0.2

0.3

0.4

0.5

a/h Figure 8—5. Coefficients A andB for crack-

0 0.6

initiation criterion (Eq. (8—21)).

perpendicularto grain. As a result,even moderately low loads can cause a crackto initiate at the sharp cornerand propagate along the grain.An estimateofthe crack-initiation load canbe obtainedbythe fracture mechanicsanalysis of Murphy(1979) for a beam with a slit, but it is generally

more economicalto avoid sharpnotchesentirelyinwood beams, especially largewood beams, since thereis a size effect: sharpnotches cause greaterreductions in strength for larger beams. A conservative criterion for crackinitiation for a beamwith a slit is

+

fb = 1

0••001

(8—22)

±P/F

wherethe plus sign is chosenifthe axial load is tensionand theminus sign is choseniftheaxial load is compression,fi is net bendingstress from combined bending and axial load, fbo bending stress without axial load, P axial load, and Pcr the buckling load ofthe beamunder axial compressive load only (see Axial Compression in the StabilityEquations section), basedon flexural rigidityabout the neutralaxis perpendicular to the directionofthe bending loads. This is not necessarily theminimum buckling load ofthe member. IfP is compressive, the possibility ofbucklingunder combined loading must be checked. (See Interaction of Buckling Modes.)

The total stress under combined bending and axial loadis obtainedby superposition ofthe stresses given by Equations(8—12) and (8—22). Example: Suppose transverse loadsproducea bending stress

B(2J]

=1

(8—21)

where h is beam depth, b beam width,M bending moment, and Vvertical shearforce,and coefficients A and Barepresented in Figure 8—5 as functions ofa/h, where is slit

a

depth. The value ofA dependson whetherthe slitis on the tension edge orthe compressionedge. Therefore,use either A or A as appropriate.The valuesofA andB aredependent upon species; however,the valuesgiven inFigure8—5 are conservative formost softwood species.

Effects of Time: Creep Rupture, Fatigue, and Aging See Chapter4 fora discussion offatigueand aging.Creep ruptureis accounted for byduration-of-load adjustment in the setting ofallowablestresses, as discussedin Chapters4

fibtensileonthe convex edge and compressive on the concave edgeofthe beam. Then the additionofatensileaxial force P at the centroids ofthe end sections willproducea maximum tensilestress on the convex edge of

-

ftmLx —

fbo

l÷P/P

and amaximum compressive stress onthe concave edgeof fcmax

fbO

P

1+P/PrA

where a negative resultwould indicatethat the stress was in facttensile.

Eccentric Load

and 6.

Iftheaxial load is eccentrically applied, thenthebending

Water Ponding

eccentricityofthe axial load.

Pondingofwater on roofs can cause increasesinbending stressesthat can be computedby the same amplification factor (Eq. (8—6))used with deflection. (See WaterPonding in theDeformation Equationssection.)

Example: Inthe preceding example, let the axial load be eccentric towardthe concave edge ofthe beam. Then the

stressfbo should be augmentedby ±PE0/Z,where Co is

maximum stresses become

f

tmax

fcmax

fbO1O/Z÷1' H-P/P

- fbo

A

Pc0/Z P

i÷pp

8—7

5

Torsion For a circularcross section, the shearstress inducedby torsion is

4 (8—23)

where Tis appliedtorque and D diameter.For a rectangular cross section, (8-24)

fS1Jth2

3

2 0

0.6

0.8

1.0

b/h

where T is appliedtorque,h larger cross-section dimension, in and b smaller cross-section dimension,and f3 is presented Figure 8—6.

Stability Equations

I

Figure 8—6. Coefficient for computing maximum shear stressin torsion of rectangular member (Eq. (8 —24)). 1.0

FPL fourth-powerformula

0.8 -

Axial Compression

0.667—

underaxialcompression, stability is For slendermembers theprincipaldesign criterion. The following equationsare for concentrically loadedmembers. For eccentrically loaded columns,see InteractionofBuckling Modes section.

j

Eulesforrna

::

Long Columns A columnlong enoughtobuckle beforethe compressive stress P/A exceedsthe proportional limitstress is called a "long column." The critical stress at bucklingis calculated by Euler's formula:

fcr

0.4

0.2

(/2

(8—25)

whereEL is elasticmodulusparallelto the axis ofthe member, L unbracedlength,and leastradiusofgyration (for a rectangularcross section with b as its least dimension, r=b and for a circular cross section, r = d/4). Equation(8—25) is based on apinned-endcondition but may be used conservatively for square ends as well.

r

/Ji,

Short Columns Columnsthat buckle at a compressivestress P/A beyondthe proportional limit stress are called "short columns."Usually theshort column range is exploredempirically, and appropriatedesignequationsare proposed.Material ofthis nature is presentedin USDA Technical Bulletin 167 (Newlin and Gahagan1930). The fmal equationis a fourth-power para-

bolic functionthat can be writtenas

3.85

Lj

r

12

EL

Figure 8—7. Graph for determining critical buckling stress ofwoodcolumns.

F

is compressive strength andremainingterms are defmedas in Equation (8—25).Figure 8—7 is agraphical representation ofEquations (8—25) and (8—26). where

Short columns can be analyzedby fitting anonlinearfunction

to compressivestress—strain dataand using it in place of Hooke's law. One such nonlinearfunctionproposedby Ylinen(1956) is

c=

f[c

—(1—c)

—

-J]

iog[i

(8—27)

whereE is compressivestrain,fcompressive stress,c a constantbetween0 and 1, and EL and are as previously defmed. Usingthe slopeofEquation(8—27) in place ofE. in Euler's formula(Eq. (8—25)) leads to Ylinen's buckling

F

equation fcr

(8—26) cr

8—8

- F +fe 2c

+fe 2c

)

-

c

(8-28)

F

where is compressivestrengthandfe buckling stress given by Euler's formula(Eq. (8—25)). Equation(8—28) can be made to agree closelywith Figure 8—7 by choosing c = 0.957. Comparing the fourth-power parabolicfunction Equation(8—26) to experimental dataindicates the function is nonconservative forintermediateL/rrange columns.Using Ylinen's buckling equationwith c = 0.8 results in a better approximation ofthe solid-sawn and glued-laminated data.

Built-Up and Spaced Columns Built-up columnsofnearly square cross sectionwith the lumbernailed or bolted togetherwill not supportloads as great as ifthe lumberwere gluedtogether.The reasonis that shear distortionscan occur in the mechanical joints.

Ifbuilt-upcolumns areadequately connected and theaxial

load isnearthe geometriccenterofthe cross section, Equation (8—28) is reducedwith a factorthat depends on the type ofmechanicalconnection. The built-upcolumn capacityis fcr =Kf

F +fe 2c

I

frF +fe2 — fe ill 2c )

—

(8—29)

whereF, fe, andc are as defmedfor Equation(8—28).K is thebuilt-upstabilityfactor,whichaccounts forthe efficiency

ofthe connection; for bolts, Kf = 0.75, and for nails, Kf = 0.6, providedboltand nail spacing requirements meet design specification approval.

Ifthebuilt-upcolumn is ofseveralspacedpieces,the spacer

blocksshouldbe placedclose enoughtogether,lengthwise in the column,so that the unsupportedportionofthe spaced memberwillnot buckle at the same orlower stress thanthat ofthecompletemember."Spacedcolumns" aredesigned with previouslypresentedcolumn equations, considering each compression memberas anunsupportedsimplecolumn; the sum ofcolumnloads for all the membersis taken as the column load for the spacedcolumn.

Bending Beams are subjectto two kindsofinstability: lateral— torsional buckling and progressive deflection underwater ponding, both ofwhichare determined by member;tiffness.

Water Ponding Roofbeamsthatareinsufficiently stiffor spaced too farapart fortheirgiven stiffness canfail by progressive deflection underthe weight ofwaterfrom steadyrain oranothercontinuoussource. The criticalbeam spacingS. is given by mit4Ei pL4

I

whereE is beammodulusofelasticity, beammomentof inertia, p density ofwater (1,000kg/rn3, 0.0361 lbIin3), L beamlength, and m = 1 for simplesupportor m 16/3 for fixed-end condition.To preventponding, the beam spacing must be less than SCr. Lateral—TorsionalBuckling Since beamsare compressed on the concave edge whenbent underload,they can buckleby acombination oflateral deflection andtwist.Becausemost woodbeams are rectangular in cross section, the equations presentedhere are for rectangularmembers only. BeamsofT, H, or other built-up cross section exhibita more complexresistanceto :wisting andare more stable thanthe followingequations would predict.

Long Beams—Longslender beamsthat are restrained against axial rotationat theirpoints ofsupportbut are otherwise free to twist and to deflectlaterally will bucklewhenthe maximum bendingstressJ equals or exceedsthe following critical value:

fbcr

a

(8—30)

t

where Eis columnmodulusofelasticity, thickness ofthe outstandingflange, and b widthofthe outstanding flange. If thejoints betweenthecolumnmembers aregluedandreinforcedwith glued fillets,the instability stress increases to as much as 1.6 times that given by Equation(8—30).

a

a=j

Columns

fcr = 0.044E

— 7C2EL

(8—32)

where is the slenderness factorgiven by

Columns With Flanges with thin, outstandingflangescan fail by elastic instabilityofthe outstandingflange,causingwrinkling ofthe flangeand twisting ofthe columnat stressesless than those for generalcolumninstabilityas given by Equations(8—25) and (8—26).For outstanding flangesofcross sections such as I, H, +, andL, the flange instability stress can be estimated by

(8—31)

Cr

where

(8—33)

EI is lateralflexuralrigidityequal to EL h//12,

h is beam depth,b beam width, GKtorsionalrigidfty de-

fmed in Equation(8—9), and Leeffective length determined by type ofloadingand supportas given in Table 8—2. Equation (8—32) is validfor bendingstressesbelowthe proportional limit.

Short Beams—Short beamscan buckle atstresses beyond theproportional limit. In view ofthe similarityof Equation (8—32) toEuler's formula(Eq. (8—25)) forcolumn buckling, it is recommendedthat short-beam bucklingbe analyzedby usingthe column bucklingcriterionin Figure8—7 appliedwith in place ofLir on the abscissa

a

8—9

Table 8—2. Effective length for checking lateral—

10

torsionalstability of beamsa

Effective Support

Load

length Le

Concentratedforce at center Uniformly distributed force

0.742L

l—2h/L o.887L 1—2JilL

Concentratedforce at end Uniformly distributed force

0.489L 1—2JilL

aThese values are conservativefor beamswith a

in placeof fcr/Fon the ordinate.Here Fb is

beam modulusofrupture.

Effect of Deck Support—The most common form ofsupportagainst lateraldeflectionis a deckcontinuously attached to thetop edge ofthe beam. Ifthis deck is rigidagainstshear in theplane ofthe deckand is attachedto thecompression edgeofthe beam, the beam cannotbuckle. In regionswhere the deckis attachedto the tensionedgeofthe beam, as where a beam is continuousover a support,the deckcannotbe countedon to preventbucklingand restraintagainst axial rotation shouldbe providedat the support point.

Ifthedeck isnot very rigid againstin-plane shear, as for

examplestandard38-mm(nominal2-in.) wood decking, Equation(8—32) and Figure 8—7 can still be used to check stability exceptthat now the effective length is modified by dividingby 0, as given in Figure 8—8. The abscissa ofthis figureis a deck shearstiffness parameter givenby

r

EJ

(8—34)

flexural rigidityas in Equation (8—33), EI is lateral shear ofdeck(ratioof Sbeam GD where

in-plane rigidity spacing, shearforce per unit length ofedgeto shear strain), and L actual beam length. This figure appliesonly to simply supportedbeams. Cantileverswith the deckon top havetheir tensionedge supportedand do not derivemuch supportfrom

thedeck.

8—10

2

0

100

200

300

400

t

500

600 700 800

Figure 8—8. Increase in buckling stress resultingfrom attached deck; simplysupported beams.To apply this graph, divide theeffective length by 9.

Interaction

width-to-depthratio of less than 0.4. The load is assumed to act at the top edge of the beam.

= SGDL2

4

0781 1—2JilL

and fbcr/Fb

6

L

Simple support Equal end moments

Cantilever

8

of Buckling Modes

Whentwo ormore loadsare actingand each ofthemhas a criticalvalueassociatedwith a mode ofbuckling, the cortibination can producebucklingeven though each load is less than its own critical value.

The generalcaseofa beamofunbracedlength le includes a primary(edgewise) moment M1, alateral (flatwise) moment M2, and axial loadP. The axial load creates a secondary momenton both edgewise and flatwisemoments due to the deflectionundercombined loadinggiven by Equation(8--7). In addition,theedgewisemomenthas an effect like the secondary moment effectonthe flatwise moment. The following equationcontains two momentmodification factors,one on the edgewise bendingstress and one onthe flatwisebending stress that includes the interactionofbiaxial bending. The equationalso containsa squaredterm for axial loadtobetter predictexperimental data:

c)

J6

(e1/ d1)f(1.234 — 0.234O) (8--35)

Jj+6(e2/d2)f(1.234—0.23402) 21

3,450 2,400 2,400

670

0.30

34.5 31.0

3,450 3,100

0.90 0.70

1,445 1,335

1,110 1,000

0.30

Interior MDF HD MD LD

Screw-holding (N)

Formaldehyde emissionc

0.30 0.30

Exterior MDF MD—Exterior adhesive

21 >21

0.30

aFrom NPA (1994). Metric property values shall be primary in determining product performance requirements. bMD_Exterior adhesivepanels shall maintain at least 50% of listed MOR after ASTM D1037—1991, accelerated HD = density> 800 kg/rn3 (> 50 lb/fl3), MD = density640 to 800 kg/rn3 aging (3.3.4). (40 to 50 lb/ft), LD = density 0.451

Nail-head pull-through

Lateral nail resistance Modulusof rupture

667 N (150 lb) (mm avg/panel) 667 N (150 Ib) (mm avg/panel) 12.4 MPa (1,800 lb/in2) for 9.5, 11, and 12.7 mm (3/8, 7/16, and 1/2 in.) thick (mm

Hardness Impact Moisture contentc

0.36 0.38 0.40 0.40

avg/panel)

20.7 MPa (3,000 lb/in2) for 6.4 mm (1/4 in.) thick (mm avg/panel) 2002 N (450 Ib) (mm avg/panel) 229 mm (9 in.) (mm avg/panel) 4% to 9% included,and not morethan 3% variancebetweenany two boards in any one shipment or order

aFrom Youngquistand others 1992. bRefer to ANSI/AHA A135.6 1—1990 for test method for determining informationon properties. csince hardboard is a wood-basedmaterial, its moisture contentvaries with environmental humidity conditions.When the environmental humidityconditionsin the area of intended use are a critical factor, the purchaser should specify a moisture content range more restrictivethan 4% to 9% so that fluctuation in the moisture contentof the siding will be kept to a minimum.

propertiesofhardboardsiding. Hardboardsidingproducts comein a greatvariety offinishes andtextures(smoothor embossed) and in differentsizes. For application purposes, theAHA sidingclassifies into three basic types:

Lapsiding—boardsapplied horizontally, with each board overlappingthe board belowit Squareedgepanels—siding intendedfor vertical application in fullsheets Shiplap edgepanelsiding—sidingintendedfor vertical application,with the long edges incorporating shiplap joints The type ofpanel dictatesthe application method. The AHA administers a qualityconformance programforhardboard for both panel and lap siding. Participationin this programis voluntaiy and is open to all (not restrictedto AHAmembers).Under this program,hardboardsidingproductsare testedby an independent laboratoryin accordance with productstandardANSI/AHAA135.6.Figure l0—13a providesan

10—22

example ofa grade stampfor a sidingproduct meetingthis standard.

Insulation Board—Physicaland mechanicalproperties of insulation board are publishedin the ASTM C208 standard specification for cellulosic fiberinsulation board.Physical (a)

(b)

CONFORMS

ZiL\oo

CONFORMS

ANSJ/AHA 135.6

ANSI/AHA 194.1

ofgrade stamps: (a) grade Figure stamp for siding conforming toANSI/AHA Al35.6 standard, and (b) grade markstampfor cellulosic 10—13. Examples

fiberboard productsconforming to ANSIIAHAAl94.1 standard.

properties are also includedin the ANSI standard for cellulosicfiberboard, ANSJIAHA A194.1 (AHA 1985). Insulationboardproductscan be dividedinto three categories (Suchslandand Woodson1986): exterior,interior, and industrial.

Exteriorproducts

•

Sheathing—board used in exteriorconstruction because of its insulationand noise controlqualities,bracingstrength,

and low price

• Roofdecking—three-in-one component that provides roof deck, insulation, and afmishedinteriorceilingsurface; in-

sulationboardsheetsare laminated together with waterproofadhesive Roofinsulation—insulation boarddesigned foruse on flat roofdecks

•

Aluminum sidingbackerboard—fabricated insulation board for improvinginsulation ofaluminum-sided houses

Interiorproducts

•

Buildingboard—general purposeproductfor interior

Surface treatment—Surface treatments improvethe appearance andperformance ofboards. Boardsare cleaned by sprayingwith water and then dried at about 240°C: (464°F) for 30 seconds. Boardsurfaces are then modifiedwith paper overlay, paint, or stainor are printed directlyon the panel. Punching—Punchingchangesboardsinto the perforated sheets used as peg board. Most punchingmachine: punch three rows ofholes simultaneously whilethe board advances. Embossing—Embossingconsistsofpressingthe unconsolidated mat offiberswith a texturedform. This processresults in a slightly contoured boardsurface that can enhance the resemblance ofthe boardto that ofsawn or weathe red wood, brick, and other materials.

Specialty Composites Special-purpose composites are producedto obtain desirable properties like water resistance, mechanical strenglh, acidity control, and decay and insect resistance. Overlays and yeneers can alsobe addedto enhance both structural ]Droperties and appearance (Fig. 10—14).

construction

• Ceilingtile—insulationboard embossed and decorated for interioruse; valuedfor acoustical qualities; also decorative, nonacousticaltiles

•

Sound-deadening board—special productdesignedto

control noise levels in buildings

Industrialproducts • Mobilehome board•

• Expansionjoint strips • Boardsfor automotive andfurniture industries The AHAadministers a qualityconformance program for cellulosic fiberboardproductsincludingsound-deadening board, roofinsulation boards,structuralandnonstruLctural sheathings, backerboard,androofdeckingin variousthicknesses. Theseproductsare tested by an independent laboratory in accordancewith productstandardANSIIAI-IA A194.1. An exampleofthe grade mark stamp forthese productsis shown in Figure l0—13b.

Moisture-Resistant Composites Sizingagents,wax, and asphaltcan be used to make compositesresistantto moisture. Sizingagentscover the surface

offibers, reducesurface energy, andrenderthe fibeis relatively hydrophobic. Sizingagents can be applied in two ways.In thefirstmethod,water is used as a medium to ensurethor-

oughmixing ofsizingand fiber. The sizingis forcedto precipitate from thewater and is fixedto the fibersurface. In the secondmethod,the sizing is applieddirectlyto the fibers. Rosin is acommonsizing agentthat is obtainedfrom livingpinetrees, from pine stumps, and as a by-prDduct of kraftpulping ofpines. Rosinsizing is added in amountsof less than 3% solidsbased on dry fiberweight. Waxes arehigh molecularweighthydrocarbons derived from crude oil. Waxsizing is used in dry-process fiberboardproduction; for wet processes, waxis added in solid form or as

Finishing Techniques Several techniquesare usedto fmishfiberboard: trimming, sanding,surfacetreatment,punching, and embossing.

Trimming—Trimmingconsistsofreducingproductsinto standardsizes and shapes.Generally, double-saw trimmers areusedto saw theboards. Trimmers consistofoverheadmountedsaws ormultiplesaw drives. Trimmedboards are stacked in piles for futureprocessing. Sanding—Ifthicknesstolerance is critical,hardboard is sandedprior to fmishing. S1S (smooth on one side;)boards requirethis process.Sanding reducesthicknessvariationand improves surfacepaintability.Single-head, wide-beltsanders are usedwith 24- to 36-grit abrasive.

Figure 10—14. Medium-densityfiberboardwith veneer overlay. Edges canbe shaped and finishedas required by end product.

10—23

an emulsion.Wax sizing tends to lower strengthproperties

to a greater extentthan does rosin.

Asphaltis also used to increase water resistance, especially in low-density wet-processinsulation board.Asphaltis a black—brownsolid or semi-solid materialthat liquefies when heated. The predominantcomponent ofasphalt is bitumen. Asphaltis precipitated onto fiberby the additionofalum.

Flame-Retardant Composites Twogeneralapplication methodsare available for improving thefireperformance ofcomposites with fire-retardantchemicals. One methodconsistsofpressureimpregnating the wood with waterborneororganicsolventbome chemicals. The secondmethodconsistsofapplyingfire-retardant chemical coatingsto the wood surface, The impregnation methodis usually more effective and longerlasting; however, this techniquesometimes causes damageto the wood—adhesive bonds in the compositeand resultsin the degradation of some physicaland mechanicalpropertiesofthe composite. Forwood in existingconstructions, surface application of fire-retardant paintsor other finishes offers apractical method to reduceflamespread.

Preservative-TreatedCornposites Wood is highly susceptibleto attack by fungi and insects; thus, treatmentis essentialfor maximum durability in adverse conditions. Composites canbeprotectedfrom the attackofdecay fungi andharmful insects by applyingselectedchemicalsas wood preservatives. The degreeofprotection obtaineddepends on thekind ofpreservativeused and the ability to achieveproper penetration andretentionofthe chemicals. Woodpreservative chemicalscanbe appliedusingpressureornonpressure processes. As in the application offire-retardant chemicals, the application ofwood preservatives can sometimes cause damageto wood—adhesivebonds,thus reducingphysicaland mechanicalpropertiesofthe composite. Commonpreservative treatments includechromatedcopperarsenate (CCA) and boron compounds.

Wood—Nonwood Composites Interesthas burgeonedin combining wood and otherraw materials,such as plastics,gypsum,and concrete, into compositeproductswith uniquepropertiesand cost benefits (Youngquist and others 1993a, 1993b, 1994;Rowelland others 1997). The primaryimpetusfor developing such productshas comefrom one or more ofthe following research and developmentgoals:

• Reducematerialcostsby combininga lowercost material • •

(actingas a filler or extender) with an expensive material Develop productsthatcanutilize recycledmaterials andbe recyclable inthemselves Produce compositeproductsthat exhibitspecific properties that are superiorto those ofthe component materials

10—24

Figure 10—15. Laboratory-producedlow-density, cement-bondedcomposite panel. Full-scale panels suchas these are used in construction. alone(for example, increased strength-to-weight ratio,improvedabrasion resistance) Composites madefrom wood and othermaterialscreate enormous opportunities tomatchproductperformanceto end-use requirements (Youngquist 1995).

Inorganic—BondedComposites Inorganic-bonded wood composites havea long and varied history that startedwith commercial productionin Austriain 1914. A plethoraofbuilding materials can be made using inorganic bindersand lignocellulosics, and they run the normal gamut ofpanelproducts, siding, roofing tiles, and precast buildingmembers (Fig. 10—15).

Inorganic-bonded wood compositesare moldedproductsor boardsthat containbetween 10% and 70% by weightwood particles orfibersand conversely 90%to 30% inorganic binder. Acceptable properties ofan inorganic-bonded wood composite can be obtained only when the wood particlesare fullyencasedwith the binderto makeacoherentmaterial. This differs considerably from thetechniqueusedtomanufacture thermosetting-resin-bonded boardswhereflakesor particles are "spot welded"by a binderappliedas a fmely distributedsprayorpowder.Because ofthis difference and becausehardened inorganic binders have ahigherdensity than that ofmost thermosetting resins, the required amount ofinorganic binder per unit volumeofcompositematerialis much higherthan that ofresin-bondedwood composites. The propertiesofinorganic-bonded wood compositesare significantly influenced by the amountandnature ofthe inorganic binderand the woodymaterialas well as the density ofthe composites. Inorganic bindersfall into three main categories: gypsum, magnesia cement,and Portlandcement.Gypsumand magnesia cement aresensitiveto moisture, andtheiruse is

generally restrictedto interior applications. Composites bondedwith Portland cement are more durable than those bondedwith gypsumormagnesia cement and are used in both interiorand exteriorapplications. Inorganic-bonded composites are made by blending proportionate amounts of lignocellulosic fiberwith inorganic materials in the presence ofwater and allowingtheinorganic materialto cure or "set up" to make a rigid composite. All inorganic-bonded composites are very resistantto deterioration, particularly by insects,vermin,and fire.

A unique featureofinorganic-bonded composites is that their manufacture is adaptable to eitherendofthe costand tech-

nology spectrum. This is facilitatedby the fact that no heat is requiredto cure theinorganic material. Forexample, in thePhilippines, Portlandcement-bonded composites are mostlyfabricatedusing manuallabor and are used in lowcost housing. In Japan, the fabrication ofthese composites is automated,and they are used in very expensive modular housing.

The versatility ofmanufacture makesinorganic-bonded composites ideally suitedto a variety oflignocellulosic materials. With a very small capital investmentand the most rudimentary oftools,satisfactoryinorganic-bonded lignocellulosiccompositebuildingmaterials can be producedon a small scaleusing mostly unskilledlabor. Ifthe market for such composites increases, technologycan be introcLuced to increase manufacturing throughput. The laborforce can be trainedconcurrently with the gradual introduction ofmore sophisticated technology.

Magnesia-Cement-BondedComposites Fewerboardsbondedwith magnesia cementhave beenproducedthan cement- or gypsum-bonded panels, mainlybecause ofprice. However, magnesia cement does offersome manufacturing advantages over Portland cement.First,the various sugars in lignocellulosics apparentlydo not have as much effecton the curingand bonding ofthebinder.Second, magnesia cement is reportedto be more tolerantof high water contentduringproduction.This opens up possibilities to use lignocellulosics not amenableto Portlandcement composites, without leachingor other modification, and to use alternative manufacturing processes andproducts. Although composites bondedwith magnesiacemer.tare considered water-sensitive, they are much less so than gypsum-bonded composites. One successful application ofmagnesia cement is a lowdensity panel madefor interior ceiling and wall applications. In theproduction ofthis panelproduct,wood wool (excelsior) is laid out in a low-density mat. The mat is then sprayed with an aqueous solutionofmagnesia cemnt, pressed,and cut into panels.

In Finland, magnesia-cement-bonded particleboard is manu-

factured usinga converted conventional particleboard plant. Magnesiaoxide is appliedto the lignocellulosic pLrticles in a batchblenderalong with otherchemicals and water. Depending on application and otherfactors,boardsmay be cold- or hot-pressed.

Gypsum-Bonded Composites Gypsumcan be derivedby miningfrom natural sources or

Other processes havebeensuggested for manufacturing magnesia-cement-bonded composites. One application may be to spray a slurry ofmagnesiacement,water,and lignocellulosic fiber onto existingstructures as fireproofmg. Extrusion into a pipe-type profileor other profilesis also possible.

gypsum.

The most apparentand widely usedinorganic-bonded composites are those bonded with Portlandcement. Portland cement,whencombined with water, immediately eactsin a process calledhydrationto eventually solidify into a solid stone-like mass. Successfully marketedPortland-cementbondedcompositesconsist ofboth low-density products madewith excelsior andhigh-density productsmide with particles and fibers. General mechanical property valuesfor a low density cement—woodexcelsiorproduct are given in

obtainedas abyproductofflue gas neutralization. Flue gas gypsum, now being producedin very large quantities in the UnitedStatesbecauseofClean Air Act regulations, is the result ofintroducinglime into the combustion processto reducesulfur dioxide emissions. In 1995, more than 100 powerplants throughoutthe UnitedStates were producing gypsum. Flue gas gypsum can be usedin lieu ofmined Gypsum panels are frequently used to finishinteriorwall and ceiling surfaces. Inthe UnitedStates,these productsare generically called"dry wall" becausetheyreplace wet plaster systems. To increase the bending strength and stiffness, gypsumpanelsare frequently wrappedin paper,whichpro-

vides atensionsurface.An alternativeto wrappinggypsum with fiber is to place the fiberwithinthe panel, as several U.S. and Europeanfirms are doingwith recycledpaper fiber. There is no technicalreasonthat other lignocellulosics cannotbe used in this way. Gypsumis widely available and does not have the highlyalkalineenvironment ofcement.

Gypsum panels are normally made from a slurry ofgypsum, water,andlignocellulosic fiber. In large-scale production, the slurry is extruded onto a belt, whichcarriesthe slurry through dryingoven to evaporate water and facilitate cureof thegypsum. The panel is then cutto length and trimmedif necessary.

a

Portland-Cement-Bonded Composites

Table 10—13.

The low-density productsmay be used as interior ceiling and wall panels in commercial buildings. In addition to the advantages describedfor low-density magnesia-bonded composites,low-density composites bondedwith Portland cement offer soundcontrol and can be quitedecorative. In someparts ofthe world,these panels function as complete wall and roofdeckingsystems. The exteriorofthe panels is stuccoed, and the interioris plastered. High-density panels can be used as flooring, roofsheathing, fire doors, loadbearing walls, and cement forms. Fairly complexmolded shapes can be moldedor extruded,such as decoraive roofmg tiles or non-pressure pipes. 10—25

Table 10—13. General properties of low-density cement—wood composites fabricated usingan excelsior-type particle Property

From

To

Bending strength

1.7 MPa (250 lb/in2)

Modulusof elasticity

621 MPa (0.9 x

Tensile strength

0.69 MPa (100 bun2)

4.1 MPa (600 lb/in2)

Compression strength

0.69 MPa (100 lb/in2) 0.69 MPa (100 lb/in2) 40

5.5 MPa (800 lb/in2) 1.4 MPa (200 lb/in2)

Shearc E/Gd

io lb/in2)

5.5 MPa (800 lb/in2) 1,241 MPa (1.8 x

io lb/in2)

100

aData represent compilationof raw data from variety of sourcesfor range of board properties. Variables include cement—wood mix, particle configuration, board density, and the forming and curing methods. bSpecific gravity range, 0.5 to 1.0. cShear strength data are limited to a small sample of excelsior boards having a specific gravity of 0.5 to 0.65. dE/G is ratio of bending modulusof elasticityto modulusof rigidity or shear modulus. For wood, this ratio is often assumed to be around 16.

Problems and Solutions Although the entiresphere ofinorganic-bonded lignocellulosic compositesis attractive, and cement-bonded composites are especiallyso, the use ofcementinvolves limitations and tradeoffs. Markedembrittlement ofthe lignocellulosic component is known to occur and is causedby the alkaline environment providedby the cement matrix. In addition, hemicellulose, starch, sugar, tannins, and lignin, all to a varyingdegree, affectthe curerate and ultimate strength of these composites. To make strong and durable composites, measuresmust be takento ensurelong-term stabilityofthe lignocellulosic in the cement matrix. To overcome these problems,various schemes have been developed. The most commonis leaching,wherebythe lignocellulosic is soaked in water for 1 or 2 days to extractsome ofthe detrimental components. However,in someparts oftheworld, the water containingthe leachate is difficultto dispose of. Low water— cement ratios are helpful, as is the use ofcuringaccelerators like calciumcarbonate. Conversely, low alkali cements have been developed, but they are not readily available throughout theworld. Two other strategiesarenaturalpozzolansand carbondioxidetreatment. Natural Pozzolans—Pozzolans are defmedas siliceous or siliceousand aluminousmaterials that can react chemically with calciumhydroxide(lime)at normaltemperatures in the presenceofwater to form cement compounds (ASTM 1988). Somecommonpozzolanicmaterials include volcanicash, fly ash, rice husk ash, and condensedsilicafume. All these materials can react with lime at normaltemperatures tomake a naturalwater-resistant cement. In general, when pozzolansare blendedwith Portland cement,they increase the strength ofthe cement but slowthe curetime. More important, pozzolansdecreasethe alkalinity ofPortlandcement,which indicatesthat addinglignocellulosic-based material (rice husk ash) to cement-bonded lignocellulosiccompositesmay be advantageous.

10—26

CarbonDioxideTreatment—In themanufacture ofa cement-bondedlignocellulosic composite,the cementhydration processnormallyrequires from 8 to 24 h to develop

sufficient board strength and cohesiveness to permitthe release ofconsolidation pressure. By exposingthe cementto carbondioxide,the initialhardeningstage can bereducedto less than 5 mm. This phenomenonresults from the chemical reactionofcarbondioxide with calciumhydroxide to form calciumcarbonate and water.

Reductionofinitial cure time ofthe cement-bonded lignocellulosic composite is not the only advantage ofusingcarbon dioxideinjection. Certainspecies ofwood have varying amounts ofsugars and tannins that interfere with the hydration or settingofPortland cement. Research has shown that theuse ofcarbon dioxide injection reducesthe likelihood of these compounds to inhibit the hydrationprocess,thus allowing the use ofawiderrange ofspecies in these composites. In addition,researchhas demonstrated that composites treatedwith carbon dioxide can be twiceas stiffand strongas untreatedcomposites (Geimerand others 1992). Finally, carbon-dioxide-treatedcomposites do notexperience efflorescence(migration ofcalciumhydroxide to surface ofmaterial), so the appearance ofthe surface ofthe fmal productis not changedover time.

Wood Fiber—Thermoplastic Composites As described else'where in this chapter,the use oflignocellulosic materials with thermosetting polymericmaterials,like phenol-orurea-formaldehyde, in the production ofcomposites has a long history. The use oflignocellulosics with thermoplastics, however, is a more recent innovation. Broadlydefined, a thermoplastic softenswhenheatedand hardens whencooled. Thermoplastics selected for use with lignocellulosics must melt or softenat or belowthe degradation point ofthe lignocellulosic component,normally 200°C to 220°C(392°Fto 428°F). These thermoplastics

include polypropylene, polystyrene, vinyls, and low- and high-density polyethylenes.

Woodflour is a readilyavailableresource that can be used as a filler in thermoplastic composites. Woodflour is processed commercially, often frompost-industrial materials such as planer shavings, chips, and sawdust. Severalgrades are availabledepending upon wood species and particle size. Woodfibers, although more difficult to process compared with wood flour, can leadto superiorcomposite properties and act more as areinforcement than as afiller.A wide varietyofwood fibersareavailable fromboth virginand recycled resources.

Othermaterials can be addedto affectprocessing andproduct performance ofwood—thermoplasticcomposites. Theseadditives can improvebondingbetweenthe thermoplastic and wood component (for example, coupling agents),product performance (impactmodifiers, UV stabilizers, flame retardants), andprocessability(lubricants).

Figure 10—16. Theuseof lignocelulosics as reinforcing fillers allowsthermoplastics to be molded into a wide variety of shapes and forms.

inpellet form havebulk densityin therange

Several considerations must be kept in mind when processing wood with thermoplastics.Moisturecan disrupt many thermoplastic processes,resulting in poor surface quality, voids, and unacceptable parts.Materialsmust either be predriedor vented equipmentmust be used to remove moisture. The low degradation temperatureofwood must alsobe considered. As a generalrule, melt temperatures shouldbe kept below200°C(392°F),exceptfor short periods. Higher temperatures canresult in the releaseofvolatiles, discoloration, odor, and embrittlementofthe wood component.

Thermoplastics

There are two mainstrategies for processing thermoplastics in lignocellulosic composites (Youngquist and others 1993b).In the first, the lignocellulosic component serves as areinforcingagentor filler in a continuous thermoplastic matrix. In the second,the thermoplasticserves as a binderto the majority lignocellulosic component. The presence or absenceofa continuous thermoplasticmatrixmay alsodeterminethe processabilityofthe composite material. In general, ifthe matrixis continuous, conventional thermoplasticprocessingequipmentmay be usedto process composites; however, ifthe matrixis not continuous, other processesmay be required.For thepurposeofdiscussion, we presentthese two scenariosfor composites with h:igh and low thermoplasticcontent.

The manufacture ofthermoplastic composites is usuallya two-stepprocess.The raw materialsare firstmixed together, and the composite blend is then formedinto a product. The combination ofthese steps is called in-line processing, and theresult is a singleprocessing stepthat convertsraw materials to endproducts.In-lineprocessingcan be very difficult becauseofcontrol demands andprocessing trade-offs. As a result,it is often easier and more economicalto separate theprocessingsteps. Compounding is the feedingand dispersingofthe lignocellulosiccomponent in a moltenthermoplastic to produce a homogeneous material.Variousadditives are added and moisture is removedduringcompounding. Compounding may be accomplished usingeitherbatchmixers(:forexample, internaland thermokinetic mixers)or continuous mixers(for example, extruders and kneaders). Batchsystemsallow closercontrol ofresidence time, shear,and temperature than do continuous systems. Batch systemsare also more appropriate for operations consisting ofshortruns and frequent changeofmaterials. On the other hand, coitinuous systems are less operator-dependent than are batch systems and haveless batch-to-batch differences (Anon. 1997).

CompositesWith High Thermoplastic Content In composites with high thermoplasticcontent, thethermoplasticcomponentis in a continuousmatrix andthe lignocellulosic component servesas areinforcement or filler (Fig. 10—16).In the greatmajorityofreinforcedthermoplastic compositesavailable commercially, inorganic materials (for example,glass,clays, andminerals)areused as rein-

forcements or fillers. Lignocellulosic materials offer some advantages over inorganic materials; they are lighter, much less abrasive, and renewable. As areinforcement, lignocellulosicscan stiffenand strengthen the thermoplastic and can improvethermal stabilityofthe productcompared with that ofunfilledmaterial.

of500 to 600 kg/rn3(31 to 37 lb/ft3). Lignocellulosicstypically have an uncompactedbulk densityof25 to 250 kg/rn3 (1.6 to 16 lb/ft3).Wood fibersare atthe low end ofthe hgnocellulosic bulk densitycontinuum and wood flours at the high end. Althoughprocessing ofwood flour in thermoplas-

tics is relatively easy, the low bulk density and difficultyof dispersing fibrous materials makethermoplastics more difficult to compound. More intensivemixingand the use of specialfeeding equipment may be necessary to handlelonger fibers.

The compounded materialcanbe immediately pressedor shapedinto an end product while still in its moli;en state or pelletizedinto small, regularpellets for futurereheatingand forming. The most common types ofproduct-forming methods forwood—thermoplasticcompositesinvolve forcing

10—27

molten materialthrougha die (sheet orprofile extrusion) into a cold mold(injectionmolding)or pressingin calenders (calendering) or betweenmold halves(thermoforming and compression molding). Properties ofwood—plasticcomposites can vary greatly depending upon such variablesas type, form,and weight fractions ofconstituents, types ofadditives, and processing history.Table 10—14shows someofthe properties for severalunfilledpolypropylene and wood—polypropylene composites. Composites with high thermoplasticcontent are not without tradeoffs. Impactresistance ofsuch composites decreases compared with that ofunfilledthermoplastics, and these composites are also more sensitive to moisture thanunfilled material orcompositesfilled with inorganic material. Froma practicalstandpoint,however,the thermoplastic component usuallymakesthe temperaturesensitivity ofthe composite more significantthan any changein propertiesbroughtabout by moisture absorption.

CompositesWith Low Thermoplastic Content with low thermoplastic contentcan be made in a variety ofways. In the simplestform, the thermoplastic componentacts much the same wayas a thermosetting resin; that is, as a binder to the lignocellulosic component. An alternativeis to use the thermoplasticin the form ofa textile fiber. The thermoplastic textile fiberenablesa variety of lignocellulosics to be incorporatedinto a low-density, nonwoven, textile-like mat. The mat may be a product in itself, or it may be consolidatedinto a high-density product. Composites

Experimentally, low-thermoplastic-content composites have beenmadethatare very similarto conventional lignocellulosiccomposites inmany performance characteristics (Youngquist and others 1993b).In their simplestform, lignocellulosic particlesor fiberscan be dry-blended with

thermoplastic granules,flakes,or fibersand pressedinto panel products.

Becausethe thermoplastic component remainsmoltenwhen hot, differentpressingstrategies must be used than when thermosetting bindersare used. Two options havebeen developedto accommodate these types ofcomposites. In the first, the materialis placed in the hot press at ambientternperature.The press then closesand consolidates the material, and heat is transferred through conduction to melt thethermoplastic component, whichflows around the lignocellulosic component. The press is then cooled,"freezing"the thermoplastic so that the composite can be removedfrom the press.Alternatively, the material can be firstheated in an oven or hot press. The hot material is then transferred to a coolpress whereit is quickly consolidatedand cooledto makea rigidpanel. Somecommercial nonstructurallignocellulosic—thermoplasticcomposites are made in this way.

Nonwoven Textile-Type Composites In contrastto high-thermoplastic-content and conventional low-thermoplastic-content composites, nonwoventextiletype composites typically require long fibrous materials for their manufacture. These fibers mightbe treatedjute or kenaf, butmore typicallythey aresyntheticthermoplasticmaterials. Nonwoven processes allow and tolerateawider range of lignocellulosic materials and synthetic fibers, depending on productapplications. Afterfibersare dry-blended, theyare air-laidinto a continuous, loosely consolidatedmat. The mat is thenpassed through a secondary operation in which the fibersare mechanically entangled or otherwise bonded together. This low-density mat may be a product in itself, or the mat maybe shapedand densified in athermoformingstep (Youngquist and others 1993b).

Ifleft as low density andused withoutsignificant modification by post-processing, the mats have a bulk density of

Table 10—14. Mechanical properties of wood—polypropylenecomposites Tensile Strength (MPa (lb/in2))

Modulus (GPa (lb/in2))

Elongation (%)

28.5 (4,130)

1.53 (221,000)

5.9

(56.2) 1.05 (65.5)

25.4 (3,680)

3.87

1.9

(561,000)

1.03 (64.3)

28.2 (4,090)

1.03 (64.3)

52.3 (7,580)

Density Compositec Polypropylene

PP + 40% woodflour PP + 40% hardwood fiber

PP+40% hardwood fiber + 3% coupling agent aUnpublished data.

(g/cm (lb/ft3))

0.9

4.20 (609,000) 4.23 (613,000)

bpropeies measured accordingto ASTM standards Cpp is polypropylene; percentagesbased on weight. 10—28

Flexural

2.0 3.2

for plastics.

Izod impact energy Heat Unnotched deflection (J/m temperature

Strength (MPa

Modulus (CPa

Notched

(lb/in2))

(lb/in2))

(ft—lbf/in))

(ft—lbf/in))

( C ( F))

38.3

1.19 (173,000)

20.9

(5,550)

(0.39)

656 (12.3)

57 (135)

44.2 (6,410)

3.03

22.2

(439,000)

(0.42)

73 (1.4)

89 (192)

47.9 (6,950)

3.25 (471,000)

26.2 (0.49)

91

100

(1.7)

(212)

72.4 (10,500)

3.22 (467,000)

21.6 (0.41)

162

105

(3.0)

(221)

(J/m

50 to 250 kg/rn3 (3 to 16 lb/ft3). These productsare particularly well knowninthe consumerproductsindustry, where nonwoven technology is used to make avariety ofabsorbent personal care products,wipes, and other disposableitems. The productsare made from high-qualitypuipsin conjunction with additivesto increase absorptiveproperties. A much wider varietyoflignocellulosics canbe used for other applications, as describedin the following text. One interestingapplication forlow-density nonwoven mats is formulch aroundnewly plantedseedlings. The mats provide thebenefitsofnaturalmulch; in addition, controlledrelease fertilizers, repellents, insecticides, andherbicides can be added to themats. The additionofsuch chemicalscould bebased on silviculturalprescriptions to ensure seedling survivaland early development on planting sites where severenutritionaldeficiencies, animaldamage,insect attack, andweeds are anticipated. Table

10—15. Properties

Low-density nonwoven matscan alsobe usedto replace dirt or sod for grass seedingaround newhome sites or along highway embankments. Grassseed can be incorporated directlyinto the mat. Thesemats promote seed germination and goodmoistureretention.Low-density mats can also be

used for filters.The densitycan be varied,dependingon the material being filteredandthe volumeofmaterialthat passes throughthe mat per unitoftime. High-density fibermats can be defmed as composites that are madeusingthe nonwoven mat process and then formed into rigid shapes by heatand pressure. To ensuregood bonding, the lignocellulosic can be precoatedwith a thermDsetting resin such as phenol—formaldehyde,or it can be blendedwith synthetic fibers, thermoplastic granules,orany combination ofthese materials.High-density fiber matscantypicallybe pressedinto productshavinga specificgravityof 0.60 to 1.40. Table 10—15 presents mechanicalandphysicalproperty

of nonwoven web composite panels with specificgravity of 1.oa Formulationb 90H/IOPE

90H/1OPP

80H/IOPE/PR

Static bending MOR, MPa (lb/in2)

23.3 (3,380)

25.5 (3,700)

49.3 (7150)

Cantileverbending MOR, MPa (lb/in2) Static bending MOE, GPa (x103 lb/in2)

21.1 (3,060)

27.1 (3,930)

45.6 (6,610)

2.82 (409)

2.99 (434)

3.57 (518)

4.75 (689)

5.27 (764)

5.52 (800)

13.5 (1,960)

12.5 (1,810)

27.7 (4,020)

Tensile MOE, GPa (xlO3lbTin2)

3.87 (561)

420 (609)

5.07 (735)

Internal bond, MPa (lb/in2)

0.14 (20)

0.28 (41)

0.81 (120)

26.7 (19.7)

21.5 (15.9)

34.3 (25.3)

60.8 85.0

40.3 54.7

21.8

260.1 301.6

77.5 99.5

28.2 55.7

0.13 0.38

0.55 0.76

0.81

0.00 0.25 0.78

3.4

3.4

3.4

Property

DynamicMOE, GPa (xl lb/in2) Tensile strength,MPa (lb/in2)

Impact energy, J (ftlbf) Water-soak,24 h Thicknessswell, % Water absorption, % Water boil, 2 h Thicknessswell, % Water absorption, % Linearexpansionc Ovendryto 30% RH, % 65% RH, % 90% RH, % EquilibriumMC at 30% RH, % 65% RH, % 90% RH, %

45.1

0.93

6.4

6.2

6.3

15.6

14.9

14.1

aFrom Youngquistand others 1992. bValues connectedby solid line are not statisticallydifferent at 0.05 significance, level. 90H/1OPE, 90% hemlockand 10°A polyester; 90H/1OPP, 90% hemlockand 10% polypropylene; 80H/IOPE/IOPR, 80% hemlock, 10% polyester, and 10% phenolic resin. CRH = relative humidity.

10—29

data for nonwoven webcompositepanelswith a specific gravityof 1.0 for threedifferentformulations ofwood,synthetic fibers,and phenolicresin. Afterthermoforming, the productspossess goodtemperatureresistance.Becauselonger fibersare used,these productsexhibitbettermechanical propertiesthan those obtainedwith high-thermoplasticcontentcomposites;however, the high lignocellulosic contentleads to increasedmoisture sensitivity.

References Abourezk,J. 1977. Statements on introducedbills andjoint resolutions. Congressional Record—U.S. Senate Mar. 1 S3156-S3179.

AHA. 1985. Cellulosicfiberboard,ANSI/AHAA194.1— 1985. Palatine, IL: AmericanHardboardAssociation. AHA. 1990. Hardboardsiding, ANSI/AHAAl35.6—1990. Palatine,IL: American HardboardAssociation. AHA. 1995a. Basic hardboard,ANSI/AHAA135.4—1995. Palatine, IL: American HardboardAssociation. AHA. 1995b. Prefmished hardboardpaneling, ANSI/AHA

A135.5—1995. Palatine, IL: American HardboardAssociation.

Anon. 1997. Machineryand equipment. Plastics Compounding: 1996/97 Redbook. AdvanstarCommunications, Inc. 19: 58—70. APA. 1981. Performance standards andpoliciesfor APA structural use panels. Tacoma,WA: AmericanPlywood Association. APA—The Engineered Wood Association. 1991. Performance standards andpoliciesfor structural use panels. APA PRP—108. Tacoma, WA: APA—The EngineeredWood Association. APA—The Engineered Wood Association. l995a. Design capacities ofAPA performance-rated structural-use panels. Technical Note N375 B. Tacoma, WA: APA—The Engineered Wood Association. APA—The Engineered Wood Association. 1995b. Plywood design specification. Tacoma, WA: APA—The EngineeredWood Association.

ASTM. 1988. Concreteand mineralaggregates. 1988. Annual Book ofASTM Standards,Sec. 4, Vol. 4.02, 4.03. Philadelphia, PA: American Society for Testing and Materials.

ASTM. (Current edition).AnnualBook ofASTM Standards. Philadelphia,PA: AmericanSociety for Testing and Materials.

ASTM C208—94. Standardspecification for cellulosic fiber insulatingboard. ASTM Dl037—94. Standardtest methods for evaluating thepropertiesofwood-based fiberand particle panelmaterials.

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ASTMD2718—90. Standardtestmethod for structural panelsin planarshear (rollingshear). ASTMD2719—89. Standardtest methods for structural panels in shearthrougb-the-thickness. ASTM D3043—87. Standardmethods oftesting structural panels in flexure. ASTMD3044—76. Standardtest method for shear modulus ofplywood. ASTM D3500—90. Standardtest methods for structural panels in tension. ASTM D3501—76. Standardmethods oftesting plywood

in compression.

ASTM E1333—90. Standardtest method for determining formaldehyde levels from woodproductsunder defined test conditions usinga largechamber. English, B.; Chow, P.; Bajwa,D.S. 1997. Processing into composites. In: Rowell, Roger M.; Young, RaymondA.; Rowell, JudithK., eds. Paper and compositesfrom agrobased resources.Boca Raton, FL: CRC Lewis Publishers: 269—299. Chapter8. Geimer, R.L.; Souza, M.R.; Moslemi, A.A.; Simatupang, M.H. 1992. Carbondioxideapplication for rapid production ofcementparticleboard. In: Proceedings, inorganicbonded wood and fibercomposite materials conference; 1992 September 27—30; Spokane, WA. HPVA. 1994. American nationalstandardfor hardwoodand decorative plywood, ANSIIHPVA—1—1994. Reston, VA: HardwoodPlywood& VeneerAssociation. Maloney, T.M. 1986. Terminologyand products definitions—A suggested approach to uniformity worldwide. In: Proceedings, 18th international unionofforestresearch organization world congress; 1986 September; Ljubljana, Yugoslavia. IUFRO WorldCongressOrganizing Committee.

Maloney,T.M. 1993. Modernparticleboardand dry-process fiberboard manufacturing. San Francisco, CA: Miller Freeman Publications.

Marra, G. 1979. Overview ofwood as material. Journalof

Educational Modules for Materials Science and Engineering. 1(4): 699—710. McKay, M. 1997. Plywood. In: Smulski,S., ed.. Engineeredwood products—A guide for specifiers, designersand users. Madison, WI: PFS ResearchFoundation. NIST. 1992. Voluntaryproduct standardPS 2—92. Performance standard forwood-base structural-use panels. National Institute of Standards and Technology. Gaithersburg, MD: UnitedStatesDepartment ofCommerce.

NIST. 1995. Voluntaryproduct standard PS 1—95 Construction and industrial plywood. NationalInstituteof Standards and Technology. Gaithersburg, MD: UnitedStates Department ofCommerce.

NPA. 1993. Particleboard, ANSI A208.1—1993.Gaithersburg,MD: NationalParticleboardAssociation. NPA. 1994. Mediumdensityfiberboard (MDF), ANSI A208.2—1994.Gaithersburg,MD:NationalParticleboard

Youngquist, J.A. 1988. Wood-based composites:The panelandbuildingcomponents ofthe future. In: Proceedings, IUFRO Division5, Forest Products subjeci group 5.03: Woodprotection; 1987 May 16—17; Honey Harbour,

Association.

Canada: 5—22.

O'Halloran, M.R. 1979. Development ofperformance specifications for structural panelsinresidential markets. Forest Products Journal.29(12): 21—26. O'Halloran, M.R. 1980. The performanceapproach to acceptance ofbuildingproducts. In: Proceedings, 14th WashingtonStateUniversity international symposium on particleboard.Pullman, WA: 77—84.

Youngquist, J,A. 1995. Unlikely partners? The marriageofwood and nonwoodmaterials. Forest Products Journal. 45(10): 25—30.

O'Halloran, M.R.; Youngquist, J.A. 1984. Anoverview

ofstructural panelsand structural compositeproducts. In: Rafik, Y. Itani; Faherty, Keith F., eds. Structural wood

research. State-of-the-art and research needs. Proceedings, American Society ofCivil Engineers; 1983 October5—6; Milwaukee, WI.New York, NY: American Society of

Civil Engineers: 133—147.

Rowell, R.M.; Young, R.A.; Rowell, J.K. eds. 1997. Paperand composites from agro-based resources. IBoca Raton, FL: CRC Lewis Publishers. Suchsland, 0.; Woodson, G.E. 1986. Fiberboardmanufacturingpracticesin the UnitedStates,Agric.Handb. 640. Washington,DC: U. S. DepartmentofAgriculture. TECO. 1991. TECO PRP—133 Performance standards and policiesfor structural-use panels. Madison, WI: TECO. U.S. DepartmentofDefense. 1951. Designofwood aircraft structures. ANC—18 Bull. (Issuedby Subcommittee on Air Force—Navy—Civil AircraftDesignCriteria. AircraftComm.) 2d ed. Washington,DC: MunitionsBoard. Youngquist, J.A. 1987. Wood-basedpanels,their properties anduses—Areview. In: Proceedings, Technical consultationon wood-based panel. ExpertConsultation, Food and AgricultureOrganization oftheUnitedNations; 1987 September28—October1; Rome, Italy: 11&—124.

Youngquist, J.A.; Krzysik, A.M.; Muehi, J.H.; Caril, C. 1992. Mechanical and physicalproperties ofair-formed wood-fiber/polymer—fibercomposites. ForestProducts Journal. 42(6): 42—48. Youngquist, J.A.; English, B.E.; Spélter, H.; Chow, P. 1993a. Agriculture fibers in composition panels, In: Maloney,Thomas M., ed. Proceedings,27th international particleboard/composite materialssymposium; 1993 March 30—April 1; Pullman, WA. Pullman, WA: Washington StateUniversity: 133—152. Youngquist, J.A.; Myers, G.E.; Muehi, J.M. land others]. 1993b. Composites from recycledwood and plastics.Final Rep., U.S. EnvironmentalProtecl:ion Agency, Project JAG DW12934608—2.Madison, WI: U.S. Department ofAgriculture, Forest Service, ForestProducts Laboratory.

Youngquist, J.A.; English, B.E.; Scharmer, R.C. [and others]. 1994. Literature review on use ofnon-wood plants fibers for buildingmaterials and panels. Gen. Tech.Rep. FPL—GTR—80.Madison, WI: U.S. Departmentof Agriculture, Forest Service,Forest ProductsLaboratory. Youngquist, J.A.; Krzysik, A.M.; Chow, P.; ['Ieimban, R. 1997. Properties ofcomposite panels. In: Rowell, Roger M., Young,RaymondA.; Rowell, Judith K., eds. Paper and composites from agro-based resources.Boca Raton, FL: CRC Lewis Publishers.

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I

Chapter

UI

Glued Structural Members Russell C. Moody, Roland Hernandez,and Jen Y. Liu

luedstructural members are manufactured in a varietyofconfigurations.Structural composite lumber(SCL) productsconsist ofsmallpieces of woodglued togetherinto sizes commonfor solid-sawn lumber. Glued-laminated timber(glulam)is an engineered stress-rated productthat consists oftwo ormore layersof lumberin whichthe grain ofall layersis oriented parallelto thelength ofthe lumber. Gluedstructuralmembersalso includelumberthat is glued to panelproducts, such as box beamsand I-beams, and structural sandwich comtruction.

Contents StructuralCompositeLumber

11—1

Types 11—2

Advantages and Uses 11—2 Standards and Specifications

11—3

Glulam 11—3

Advantages

History

11—3

Structural Composite Lumber

11—4

Structuralcompositelumberwas developedin response to the increasing demandforhigh quality lumberat atime whenit was becoming difficultto obtain this type oflumber from the forestresource. Structural composite lumber productsare characterized by smallerpieces ofwood glued together into sizes commonfor solid-sawn lumber

Typesof GlulamCombinations 11—4 Standards and Specifications 11—6 Manufacture

11—6

Development ofDesignValues 11—9 Designs for Glued-Laminated Timber 11—10

GluedMembersWith Lumberand Panels Box Beams and I-Beams

11—12

Prefabricated WoodI-Joists Stressed-Skin Panels

11—1:2

11—13

11—14

Structural Sandwich Construction 11—16 Fabrication

11—16

Structural Design

11—17

Dimensional Stability,Durability,and Bowing Thermal Insulation 11—20

Fire Resistance 11—21 References

11—21

11—20

One type ofSCL productis manufactured by laminating veneerwith all plies parallel to the length. This product is calledlaminated veneerlumber(LVL) and consistsofspeciallygradedveneer. Another type ofSCL product consists ofstrands ofwood or strips ofveneerglued together under high pressures andtemperatures. Dependingupcn the componentmaterial, thisproduct is called laminated strand lumber(LSL), parallelstrandlumber(PSL), or oriented strandlumber(OSL)(Fig. 11—1). These types ofSCL productscan be manufactured from raw materials,such as aspen or other underutilized species, that arenot commonly used for structural applications. Different widthsoflumber can be rippedfrom SCL forvarioususes. Structural composite lumberis a growingsegmentofthe engineered wood productsindustry. It isusedas areplacement forlumberin variousapplications and in the manufactare ofother engineered woodproducts, such as prefabricated woodI-joists,whichtake advantage ofengineering design valuesthat can be greaterthan those commonlyassignedto sawn lumber.

11—1

along the length ofthe member. The least dimension ofthe strandsmust not exceed 6.4 mm (0.25 in.), and the average length ofthe strandsmust be a minimumof 150 times the least dimension. In 1997, one commercial product in the UnitedStateswas classified as PSL. Parallel strand lumberis manufactured using veneerabout 3 mm (1/8 in.) thick, whichis then clipped into strands about 19 mm (3/4 in.) wide. These strands are commonly least 0.6 m (24 in.) long. The manufacturing process was designedto use the material from roundup ofthe log in the veneercuttingoperation as well as other less than full-width veneer. Thus, the process can utilize wastematerialfrom a plywoodorLVL operation.Speciescommonlyused for PSL include Douglas-fir, southernpines, westernhemlock, and

t

Figure 11—1. Examples ofthreetypesofSCL (topto bottom): laminated veneer lumber (LVL), parallel strand lumber(PSL), and oriented strand lumber(OSL).

Types Laminated VeneerLumber Work in the 1940s on LVL targeted the production ofhigh strength parts for aircraft structures usingSitka spruce veneer. Research on LVL in the 1970s was aimedat defmingthe effectsofprocessing variablesfor veneerupto 12.7 mm (1/2 in.) thick. In the 1990s, production ofLVL uses veneers 3.2 to 2.5 mm (1/8 to 1/10 in.) thick, whichare hot pressed with phenol-formaldehyde adhesive into lengths from 2.4 to 18.3 m (8 to 60 ft) or more.

The veneerforthe manufacture ofLVL mustbe carefully selected forthe productto achieve the desired engineering properties. The visual grading criteriaofPS 1—95 (NIST 1995) are sometimes used but are generallynot adequate withoutadditionalgrading. Veneers are often sortedusing ultrasonic testing to ensure that the fmishedproductwill havethe desiredengineering properties. Endjoints between individual veneersmaybe staggered along the productto minimize their effecton strength. These endjoints may be buttjoints, or the veneer ends may overlapfor some distance to provide loadtransfer. Someproducers provide structural endjoints in the veneers usingeither scarf or fmgerjoints. Laminated veneerlumbermay alsobe made in 2.4-m(8-ft) lengths,havingno endjoints in the veneer;longerpieces are then formed by endjointingthese pieces to create the desired length. SheetsofLVL are commonly producedin 0.6- to I .2-m (2- to 4-ft) widths in a thicknessof38 mm(1.5 in.). Continuouspressescan be used to form apotentiallyendless sheet, which is cut to the desiredlength. Variouswidths of lumbercan be manufactured at the plant orthe retail facility.

Parallel Strand Lumber Parallelstrand lumber(PSL) is defined as a compositeof wood strandelementswith wood fibersprimarilyoriented

11—2

yellow-poplar,but there are no restrictionson usingother species.

The strands are coated with a waterproofstructural adhesive, commonly phenol-resorcinol formaldehyde, and oriented in a press using specialequipmentto ensure properorientation and distribution. The pressing operation results in densification ofthe material,and the adhesive is curedusing microwavetechnology. Billetslargerthan thoseofLVL are commonlyproduced; atypical size is 0.28 by 0.48 m (11 by 19 in.).This productcan then be sawn into smallerpieces, if desired. As with LVL, a continuous press is usedso that the length ofthe product is limitedby handlingrestrictions.

Laminated Strand Lumber and Oriented Strand Lumber Laminatedstrandlumber(LSL) and oriented strand lumber (OSL) products are an extensionofthe technology used to produceoriented strandboard (OSB) structural panels.One type ofLSL uses strandsthat are about 0.3 m (12 in.) long, which is somewhat longerthan the strands commonly used forOSB. Waterproof adhesives are used in themanufactureof LSL. One type ofproductuses an isocyanatetype ofadhesive that is sprayed on the strandsand cured by steam injection. This productneeds greaterdegreeofalignmentofthe strands than does OSB and higherpressures,which result in increased densification.

a

Advantages and Uses In contrastwith sawnlumber, the strength-reducing characteristicsofSCL are dispersedwithinthe veneer or strands andhave much less ofan effecton strength properties. Thus, relatively high design values can be assignedto strength properties for both LVL and PSL.Whereasboth LSL and OSLhave somewhat lowerdesignvalues, they have the advantage ofbeing produced from a raw material that need not be in a log size large enoughforpeeling into veneer. All SCL products are madewith structural adhesivesand are dependent upon a minimum level ofstrength in these bonds. All SCL products are madefrom veneers or strands that are dried to a moisturecontentthat is slightlyless than that for most service conditions. Thus, little change in moisture contentwill occur in many protectedservice conditions.

When usedindoors,this results in a productthat is less likely to warp or shrink in service. However,the rorous nature ofboth LVL and PSLmeans that these products can quicklyabsorbwater unless they are providedwith some protection.

Alltypes ofSCL productscanbe substituted for sawn lumberproductsin many applications. Laminated veneerlumber is used extensively for scaffold planks and in theflanges of prefabricated I-joists, whichtakes advantage ofthe relatively high designproperties. Both LVL and PSL beamsare used as headersand majorload-carrying elementsin construction. The LSL and OSL productsare used for bandjoists in floor constructionand as substitutes for studs and raftersin wall androofconstruction. Varioustypes ofSCL are alsoused in a numberofnonstructural applications, such as themanufacture ofwindowsand doors.

Standards and Specifications TheASTM D5456(ASTM 1997a) standardprovidesmethodsto developdesignpropertiesfor SCL productsas well as requirements for quality assurance during production. Each manufacturer ofSCL productsis responsible for developing therequiredinformation on properties and ensuringthat the minimumlevels ofquality are maintainedduringproduction. Anindependentinspectionagency is requiredto monitorthe quality assurance program. Unlikelumber,no standardgradesor designstresseshave been established forSCL.Each manufacturer mayhave unique designpropertiesand procedures. Thus,the designer shouldconsult information providedbythe manufacturer.

Glulam Structuralglued-laminatedtimber(glulam)is one ofthe oldest gluedengineeredwoodproducts. Glulam is an engineered, stress-rated product that consistsoftwo ormore

layersoflumberthat are glued togetherwith the grain ofall layers,whicharereferredto as laminations, parallelto the length.Glulamis definedas a materialthat is made from suitablyselectedandpreparedpiecesofwood eitherin a straightor curved form, with the grain ofall pieces essentially parallelto the longitudinal axis ofthe member.The maximum laminationthicknesspermitted is 50 mm (2 in.), andthe laminations are typicallymadeofstandard 25- or 50-mm-(nominal1- or 2-in.-)thick lumber. North American standards requirethat glulambemanufactured in an approved manufacturing plant. Becausethe lumberisjoined endto end, edgeto edge, and face to face,the size ofglulamis limitedonly by the capabilities ofthe manufacturingplant and the transportationsystem. Douglas Fir—Larch, Southern Pine, Hem—Fir, and Spruce— Pine—Fir (SPF) are commonlyused for glulam in the United States. Nearlyany speciescan be used for glularn timber, providedits mechanicaland physical propertiesare suitable andit canbe properly glued.Industrystandards cover many softwoods and hardwoods, andprocedures are in placefor including other species.

Advantages Comparedwith sawn timbers as well as other structural materials,glulamhas severaldistinct advantages in size capability, architectural effects, seasoning, vanationofcross sections, grades,and effecton the environment.

Size Capabilities—Glulam offers the advantage ofthe manufacture ofstructural timbers that are much larger than thetreesfrom whichthe componentlumberwassawn. In thepast, theUnitedStateshad accessto largetrees that could produce relatively largesawn timbers.However,the presenttrend is to harvestsmallerdiametertrees on much shorterrotations, and nearly all new sawmillsare built to accommodate relatively small logs. By combiningthe lumber in glulam,the production oflarge structural elementsis possible.Straightmembersup to 30 m (100 ft) long are not uncommonand some span up to 43 m (140 ft. Sections deeperthan 2 m (7 ft) have beenused. Thus, glulamoffers thepotentialto producelargetimbersfrom small trees. Architectural Effects—Bycurvingthe lumber(luring the manufacturingprocess, avarietyofarchitectural effects can be obtainedthat are impossible or very difficult with other materials.The degreeofcurvature is controlled by the thickness ofthe laminations. Thus, glulamwith moderatecurvature is generally manufactured with standard 19-mm(nominal 1-in.-) thick lumber. Low curvatures aie possible with standard38-mm (nominal2-in.) lumber, whereas 13 mm (1/2 in.) or thinnermaterial may be requiredforvery sharpcurves. Asnoted later in this chapter,the radiusof curvature is limitedto between 100 and 125 times the lamination thickness.

SeasoningAdvantages—Thelumberused in the manufacture ofglulammust be seasonedor dried prior to use, so the effects ofchecking and other drying defects are minimized. In addition, design can be on the basis ofseasonedwood, whichpermitsgreater design valuesthan canbe assignedto unseasoned timber.

Varying CrossSections—Structural elementscan be designedwith varying cross sectionsalong their length as determined by strength andstiffnessrequirements. The beamsinFigure 11—2 showhow the centralseciion ofthe beamcan bemadedeeperto account for increased structural requirements in this region ofthe beam. Similarly, arches often havevaryingcross sectionsas determined by design requirements.

Varying Grades—Onemajor advantage ofglulam is that a largequantity oflowergrade lumbercan be used withinthe less highly stressedlaminations ofthe beams. Grades are often variedwithinthe beams so that the highestgradesare used in the highlystressedlaminations near the top and bottomandthe lowergrade for the iimerhalf or more ofthe beams. Speciescan also be varied to matchthe structural requirements ofthe laminations.

11—3

adhesivesduringand followingWorldWar I stimulated additionalinterest in Europe in regardto using glulam in aircraft andbuilding frames.

(a)

(b)

In theUnitedStates, one ofthefirst examplesofglulam

p

(c)

p

(d) C)

Figure 11—2. Glulamtimbers may be (a) singletapered, (b) double tapered, (c) tapered at both ends, or (d) tapered atone end.

archesdesignedand built usingengineeringprinciples is in a buildingerectedin 1934at the USDA Forest Service,Forest ProductsLaboratory,Madison, Wisconsin(Fig. 11—3). The founder ofa company that producedmany ofthese initial buildings in the United States was a Germanimmigrantwho transferred the technology to his manufacturing facility in Peshtigo, Wisconsin. Applicationsincludedgymnasiums, churches, halls, factories, and barns. Several other companies based on the same technology were soon established. World WarII stimulated additional interestand the developmentofsynthetic resin adhesives that were waterproof. This permittedthe use ofglulam timber in bridges and other exteriorapplications that requiredpreservativetreatment.By the early 1950s, therewere at least a dozenmanufacturers of glulamtimber in the UnitedStates,whojoined togetherto form the American Institute ofTimber Construction(AITC. In 1963, this association producedthefirstnationalmanufacturing standard. The AITC continuesto prepare,update, and distribute industry standards for manufacture and design of glulam. By the mid-i990s, about 30 manufacturingplants acrossthe UnitedStatesand Canadawere qualifiedto produce glulam, according to the requirements ofthe AITC standard.

EnvironmentallyFriendly—Muchis being written and discussedregardingthe relative environmental effects of variousmaterials.Several analyseshave shown that the renewabilityofwood, its relatively low requirement for energyduring manufacture, its carbonstorage capabilities, and itsrecyclabilityofferpotentiallong-term environmental advantages over other materials. Although aesthetics and economic considerations usuallyare the majorfactorsinfluencingmaterialselection,these environmental advantages may increasingly influence materialselection. The advantages ofglulamare temperedby certain factors that are not encounteredin the production ofsawn timber. In instances wheresolid timbersareavailable intherequired size, the extra processingin makingglulamtimberusually increases its cost abovethat ofsawn timbers. The manufacture ofglulam requiresspecial equipment, adhesives, plant facilities,and manufacturingskills,whicharenot neededto producesawn timbers.All steps in the manufacturing process requfre care to ensurethe high qualityofthe fmishedproduct. One factorthat must be considered early in the design of large straight or curvedtimbersis handlingand shipping.

History Glulam was first used in Europe in the construction ofan auditoriumin Basel, Switzerland, in 1893, which is often cited as the first knownsignificantuse ofthis product. Itwas patentedas the "Hertzer System"and used adhesivesthat, by today'sstandards,arenot waterproof.Thus, applications were limitedto dry-use conditions. Improvements in

11-4

From the mid-l930s throughthe 1980s, nearly all glulam production was used domestically. During the 1990s, the exportmarketwas developed and significantquantities of material were shipped to PacificRim countries,mainly Japan.

Types of Glulam Combinations Bending Members The configuring ofvariousgrades oflumberto form a glulam cross section is commonly referredto as a glulamcombination. Glulamcombinations subjectedto flexural loads, calleti bending combinations, were developedto providethe most efficient andeconomicalsection for resisting bendingstress caused by loadsappliedperpendicular to the wide faces ofthe laminations. This type ofglulam is commonlyreferredto as ahorizontally laminated member.Lowergradesoflaminating lumberare commonly used forthe centerportionofthe combination, or core, where bendingstress is low, while a highergrade ofmaterial is placed onthe outside faces where bending stress is relativelyhigh. To optimize the bending stiffnessofthis type ofglulam member, equalamounts of high qualitylaminationson the outside faces shouldbe includedto producea "balanced"combination.To optimize bendingstrength, the combination can be "unbalanced"with more high quality laminations placedon the tension side of themember compared with thequalityusedon the compression side. For high quality lumberplaced on the tension side ofthe glulam combination, stringentrequirements are

Figure 11—3. Erected in 1934at the Forest Products Laboratory in Madison, Wisconsin, this buildingis one of the first constructed with glued-laminated timbers arched, designed, and builtusingengineering principles.

placedon knot size, slope ofgrain, and lumberstiffness. Forcompression-side laminations, however,knot size and slope-of-grainrequirements are less stringent and only lumber stiffness is givenhigh priority.In thecasewherethe glulam memberis usedover continuous supports,the combinationwouldneed to be designedas a balancedmember for strengthand stiffness becauseofthe exposure ofboth the top and bottomofthebeam to tensilestresses.The knot and slope-of-grain requirements forthis typeofcombination are generallyapplied equallytoboth the top and bottom laminations.

Axial Members Glulam axial combinations were developedto providethe most efficient andeconomicalsectionfor resisting axial forces and flexural loadsappliedparallel to thewide faces ofthe laminations. Members havingloads appliedparallelto the wide faces ofthe laminations are commonly referredto as vertically laminated members. Unlikethepracticeforbending combinations, the same grade oflaminationis used throughoutthe axial combination. Axial combinations may alsobe loadedperpendicular to the wide face ofthe lamina-

tions,but the nonselectiveplacementofmaterialoften results in aless efficient and less economical memberthan does the bending combination. As with bending combinations, knot and slope-of-grain requirements apply basedonthe intended use ofthe axial memberas atensionor compression member.

Curved Members Efficient use oflumberin cross sections ofcurved glulam combinations is similarto that in cross sections ofstraight, horizontally-laminated combinations. Tensionand compression stresses are analyzedas tangential stressesin the curved portionofthe member.A unique behavior in these curved members is the formation ofradialstressesperpendicular to thewide faces ofthelaminations. As theradiuscfcurvature oftheglulammemberdecreases, theradialstreses formedin thecurved portion ofthebeamincrease. Becauseoftherelatively low strengthof lumber in tensionperpendicular-to-thegrain compared with tension parallel-to-the-grain, these radial stresses becomea criticalfactor in designing curvedglulam combinations. Curvedmembers are commonly manufactured with standard 19- and 38-mm-(nominal 1- and 2-in.-)thick lumber. Naturally,the curvature that is obtainable with the 11—s

standard 19-mm- (nominal1-in.-) thick lumberwill be sharperthan that for the standard38-mm- (nominal 2-in.-) thick lumber. Recommended practicespecifies that the ratio oflaminationthicknesst to theradius of curvature R should not exceed 1/100 for hardwoods and Southern Pine and 1/125 forother sofiwoods(AF&PA 1997). For example, a curved Southern Pine beam (t/R 1/100) manufactured with standard 38-mm- (nominal2-in.-)thick lumber(t= 1.5 in.) shouldhave a radiusofcurvature greaterthan or equalto 3.81 m (150 in.)

Tapered Straight Members Glulam beams are often taperedto meet architectural requirements, provide pitchedroofs,facilitate drainage, and lower wall height requirementsat the end supports.The taper is achievedby sawingthe memberacross one ormore laminations at the desired slope.It is recommendedthat the taper cut be made only on the compression sideofthe glulam member,becauseviolatingthe continuity ofthe tensionside laminations would decreasethe overall strength ofthe member.Commonforms ofstraight,taperedglulam combinations include(a) single tapered, amemberhaving a continuous slope from end to end on the compression side; (b) doubletapered,a memberhavingtwo separate slopes

sawn on the compressionside; (c) taperedat both ends, a memberwith slopes sawn on the ends, but the middleportion remainsstraight; and (d) tapered at one end, similarto (c) with only one end havinga slope. Thesefourexamples areillustratedin Figure 11—2.

Standards and Specifications Manufacture The ANSI/AITCA190.1 standardofthe American National Standards Institute(ANSI 1992) contains requirements for theproduction,testing,and certificationofstructural glulam timber in the UnitedStates. Additionaldetailsand commentaly on the requirements specifiedin ANSI A190.1 are provided in AITC 200 (AITC 1993a), whichis part ofANSI A190.1 by reference. A standard for glulampoles,ANSI 05.2 (ANSI 1996),addressesspecialrequirements for utility uses.Requirements for the manufacture ofstructural glulam in Canadaare given in CAN/CSA 0122 (CSA 1989).

Derivation of Design Values ASTM D3737 (ASTM 1997b) covers the procedures to establishdesignvaluesfor structural glulam timber. Properties considered includebending, tension,compression parallel to grain, modulusofelasticity, horizontal shear,radial tension,and compressionperpendicularto grain.

Design Values and Procedures

ofglulam timber havestandardized thetarget designvalues in bending for beams. For softwoods, these designvalues are given in AITC 117, "Standard Specifications for Structural Glued-Laminated TimberofSoftwood Species"(AITC 1993b). This specification containsdesign valuesandrecommendedmodification ofstresses for the Manufacturers

11-6

designofglulam timbermembers in the United States. A comparable specification forhardwoodsis AITC 119, "Standard Specifications for Structural Glued-Laminated Timber ofHardwood Species" (AITC 1996). The National DesignSpecflcationfor Wood Construction(NDS) summarizes the design information in AITC 117 and 119 and defmes the practicetobe followedin structural designofglulam timbers(AF&PA 1997). For additionaldesign information, see the Timber Construction Manual (AITC 1994). APA—The EngineeredWoodAssociationhas also developeddesignvalues for glulamunderNationalEvaluation Report486, whichis recognizedby all the model building codes. In Canada,CAN/CSA 086, thecode for engineering design in wood,providesdesign criteriafor structural glulam timbers (CSA 1994).

Manufacture The manufactureofglulam timbermust follow recognized nationalstandards tojustif'the specifiedengineering design values. Whenglulam is properly manufactured,both the quality ofthe wood andthe adhesive bonds should demonstrateabalancein structural performance.

The ANSI A190.1 standard (ANSI 1992) has a two-phase approach to all phasesofmanufacturing. First is the qualification phase in which all equipmentand personnelcritical to theproduction of a qualityproduct arethoroughlyexamined by athird-party agency and thestrengthofsamples ofglued joints is determined. In the secondphase, aftersuccessful qualification, dailyqualityassurance procedures and criteria areestablished, whicharetargeted to keep each ofthe critical phases ofthe process under control. An employeeis assigned responsibility for supervisingthe dailytesting and inspection. The third-partyagencymakes unannouncedvisits to theplants to monitorthemanufacturing processandthe finishedproductandto examine the dailyrecords ofthe qualityassurance testing. The manufacturing processcanbe dividedinto fourmajor parts: (a) dryingand grading the lumber, (b) endjointing the lumber, (c) face bonding, and (d) fmishingand fabrication. In instances wherethe glulam will be used in high moisture contentconditions, it is also necessaryto pressuretreat the memberwith preservative. A final criticalstep in ensuring thequality ofglulam is protection ofthe glulam timber during transit and storage.

Lumber Drying and Grading To minimize dimensionalchangesfollowingmanufacture and to take advantage ofthe increased structural properties assignedto lumbercompared with large sawn timbers,it is criticalthat the lumberbe properlydried. This generally means kiln drying. For most applications,the maximum moisturecontentpermittedin the ANSI standard is 16% (ANSI 1992). Also, the maximumrange in moisture content is 5% amonglaminations to minimizedifferential changes in dimension followingmanufacture. Many plantsuse lumber at

or slightlybelow 12% moisturecontent fortwo reasons.One reasonis that the materialis more easily endjointed at 12%

moisturecontent than at higher levels.The other reason is that 12% is an overallaverageequilibrium moisturecontent for many interiorapplicationsin the UnitedStates (seeCh. 12, Tables 12—1 and 12—2). Exceptions are some areas in the southwestUnited States. Matchingthe moisturecontentof theglulamtimber at the time ofmanufactureto that whichit will attain in application minimizes shrinkage and swelling, whichare the causes ofchecking. The moisturecontent oflumbercan be determinedby sampling from the lumber supplyand usinga moisturemeter. Alternatively, most manufacturers use a continuous in-line moisturemeterto check the moisturecontentofeach pieceof lumberas it enters the manufacturingprocess.Pieces with greaterthan a given moisture level are removed and redried. Grading standardspublishedby the regional lumber grading associations describethe characteristics that are permittedin various grades oflumber. Manufacturing standards forglulam

timberdescribe the combination oflumbergrades necessary for specific design values(AITC 117) (AITC 1993b). Two types oflumbergradingare used for laminating: visual gradingandE-rating. The rules for visuallygradedlumberare based entirelyupon thecharacteristics that arereadily apparent. The lumbergrade description consistsoflimitingcharacteristics forknot sizes, slopeofgrain,wane,and several other characteristics. An exampleofthe knot size limitationfor visuallygraded westernspecies is as follows: Laminatinggrade

Maximumknot size

Li

1/4 ofwidth

L2

1/3 ofwidth

L3

1/2 ofwidth

E-ratedlumberis gradedby a combination oflumberstiffness determination and visual characteristics. Eachpiece oflumber isevaluatedforstiffness by one ofseveral acceptable procedures, and thosepiecesthat qualifyfor a specific grade are then visuallyinspectedto ensurethat they meet the requirement formaximumallowableedgeknot size.The grades are expressed in terms oftheirmodulusofelasticity followedby their limitingedge knot size. Thus, a 2.OE—i/6 grade has a modulusofelasticityof 13.8 GPa (2 x 106 lb/in2)and a maximum edge knot size of 1/6 the width. Manufacturers generally purchase gradedlumberand verify thegradesthroughvisualinspectionofeach piece and, if E-rated, testing ofa sample. To qualifythe materialfor some ofthehigherdesignstresses forglulamtimber,manufacturers must also conductadditionalgrading for material to be used in thetensionzone ofcertainbeams. Highqualilymaterialis requiredfor the outer 5% ofthe beam on the tension size,and thegradingcriteriaforthese "tension laminations" are given in AITC 117 (AITC 1993b). Special criteriaare appliedto providematerialofhigh tensilestrength. Anotheroptionis

Figure 11—4. Typicalfingerjointusedin the manufacture of glulam.

to purchasespeciallumberthat ismanufactured undera quality assurance systemto providethe requiredtensile strength. Another optionpracticed by at least one manufacturerhas been to use LVL to providethe requiredtensile strength.

End Jointing To manufactureglulamtimberin lengths beyondthose commonly available for lumber, laminations mrst be made by endjointing lumberto theproperlength. Themost common end joint, a fingerjoint, is about 28 mm (1.1 in.) long (Fig. 11—4). Otherconfigurations are also acceptable, providedtheymeet specific strength and durability requirements.The advantages offingerjointsare that they require only short length oflumberto manufacture (thus reducing waste)and continuous production equipmentis readily available. Well-made joints are criticalto ensure adequate performance ofglulamtimber.Careful control ateach stage of theprocess—determining lumber quality, cuttingthejoint, applying the adhesive,mating, applying endpressure, and curing—is necessary to produce consistenthigh strength

a

joints. Justprior tomanufacture, the ends ofthe lumber are inspected to ensure that there are no knotsor other featuresthat would impairjointstrength.Then, joints are cut on both ends ofthe lumberwith specialknives. Adhesiwe is applied. The joints in adjacentpieces oflumberare mated, and the adhesive is cured underend pressure. Most manufacturing equipment featuresa continuous radio-frequency curingsystem that providesheat to partiallyset the adhesivein a matterofa few seconds. Fingerjoints obtain most oftheir strength duringthis process,andresidualheatpermits the jointto reachits fullstrengthwithina few hours.

11—7

Fingerjoints havethe potentialto reach at least 75% ofthe strength ofclear wood in many species ifproperly manufactured, Thesejoints are adequatefor most applications because most lumbergradesused in the manufacture ofglulam timberpermitnatural characteristics that result in strength reductions ofat least 25% less thanthat ofclear wood.

The ANSI standard requiresthat manufacturers qualit' their production joints to meet the requiredstrength level ofthe highest grade glulam timber they wish to produce. This requires that the resultsoftensiletests ofend-jointed lumber meet certain strengthcriteriaand that durabilitymeets certain criteria. When these criteriaare met, daily qualitycontrol testing in tensionis required to ensurethat the strength level is being maintained.Durabilitytests are alsorequired.

A continuingchallengein theglulamproductionprocess is to eliminate theoccurrence ofan occasional low-strength end

joint. Visual inspectionand other nondestructive techniques have beenshownto be only partially effective in detecting low-strength joints. An approachused by manymanufacturers to ensure endjointquality is the use ofa proofloading system for critical endjoints. This equipmentappliesa specifiedbendingor tensionload to check thejointstrength for critical laminations on the tension sideofbeams. By applyingloadsthat are related to the strengthdesired,lowstrength joints can be detectedand eliminated. The qualification proceduresforthis equipmentmust provethat the applied loadsdo not cause damageto laminations that are accepted.

Face Bonding Theassembly of laminations into full-depth members is anothercriticalstage in manufacture. To obtain clear,parallel, and gluable surfaces,laminationsmust be planed to strict tolerances.The best procedureis toplane the two wide faces ofthelaminationsjust prior to thegluing process.This ensures that the final assemblywill be rectangularandthat thepressurewillbe applied evenly. Adhesives that havebeen prequalifiedare then spread,usuallywith a glue extruder. Phenolresorcinolis the most commonlyused adhesivefor facegluing,but other adhesives that havebeenadequately evaluated and provento meet performance and durability requirements may also be used. The laminationsare then assembledinto the required layup; after the adhesive is given the properopen assembly time, pressureis applied.The most commonmethodfor applying pressureis with clampingbeds; the pressureis appliedwith either a mechanical or hydraulic system(Fig. 11—5). This resultsin a batch-typeprocess,and the adhesiveis allowed to cure at room temperaturefrom 6 to 24 h. Somenewer automatedclampingsystemsincludecontinuoushydraulic presses and radio-frequency curingto shorten the facegluing processfromhours to minutes.Upon completion ofthe face bondingprocess,the adhesiveis expectedto haveattained 90% or more ofits bond strength. Duringthe next few days, curing continues, but at amuch slowerrate. The facebondingprocessis monitoredby controlsin the lumberplaning,adhesivemixing,and adhesivespreading

11—8

Figure 11—5. After beingplaced in the clamping bed, the laminations of these arches are forcedtogether with an air-driven screw clamp.

andclamping processes. Performance is evaluatedby conductingsheartests on samples cut offas end trim from the

finishedglulamtimber. The target shear strengthofsmall specimens is prescribed inANSI A190.1 (ANSI 1992) and equalsabout 90% ofthe average shear strength forthe species. Thus, the adhesivebonds are expectedto develop nearlythe full strength ofthe wood soonaftermanufacture.

Finishing and Fabrication Afterthe glulamtimberis removedfrom the clampingsystem, the wide faces are planedto remove the adhesivethat

has squeezed out betweenadjacentlaminations and to smooth out any slight irregularities between the edges of adjacent laminations. As aresult, the finished glulamtimber is slightly narrowerthan nominal dimensionlumber. The remainingtwo faces ofthe membercan be lightlyplaned or sandedusingportableequipment. Theappearance requirements ofthe beamdictatethe additional finishingnecessaryat this point. Historically, three classifications offinishinghave beenincludedin the industry standard, AITC 110: Industrial, Architectural, and Premium (AITC 1984). Industrial appearanceis generallyapplicable whenappearance is not aprimaryconcern, such as industrial plants andwarehouses. Architectural appearance is suitable for most applications whereappearanceis an importantrequirement. Premium appearanceis the highestclassification. The primary difference among these classifications is the

amountofknot holes and occasionalplaner skips that are permitted. A recentlyintroducedclassification, calledFraming,consistsofhit-and-miss planingand permitsa significantamountofadhesive to remainonthe surface. This fmishingis intendedfor uses that requireone member to have thesamewidth asthelumberused in manufacture for framing into walls.These members are often coveredin the finished

depthto whichthe chemicals penetrate into the lumber. Different processes are quite effective for somespecies but not for others. In addition,the treatedlumberis gener1ly more difficult to bondeffectively and requires special manufacturing procedures. Thus, it is recommendedthat the manufacturer

structure.

The major advantage ofa waterbome treatmentis that the surface ofthe timberappears little changedby thetreatment. Different chemicals can leavea green,gray, or brown color; all result in a surface.that is easily finishedwith sains or paints. To avoidthe potentialof corrosive interactions with thechemical treatments, specialcare must be given when selectingthe connection hardware. In addition, wa,terbornepreservative-treated glulamtimberis muchmore subjectto moisture contentcyclingthan is creosote-treated or oilbornepreservative-treated glulam timber. A major consideration in selectingapreservativetreatment is the localregulations dealingwith the use and disposal of wastefrom preservative-treated timber. Recommended retention levels for applications ofvarious preservatives are given in AITC 109 (AITC 1990) along with appropriatequality

The next step in themanufacturingprocess is fabrication, wherethe fmal cuts are made, holes are drilled,connectors are added, and afinish or sealer is applied, ifspecified. For various members, different degrees ofprefabrication are done at this point. Trussesmay be partiallyor fully assembled. Moment splicescan be fullyfabricated, then disconnected for transportationanderection. End sealers,surface sealers, primercoats, andwrappingwith waterproofpaper orplastic all help to stabilizethe moisturecontent ofthe glulamtimberbetweenthetime it is manufactured and installed. The extentofprotectionnecessarydepends upon the end use and mustbe specified.

Preservative Treatment In instances wherethemoisturecontentofthe finished glulam timberwillapproach or exceed20% (in most exterior and some interioruses), the glulamtimber shouldbe pre-

servativetreatedfollowingAITC (1990)and AWPA (1997b). Three main typesofpreservatives are available: creosote, oilbome,and waterborne. Creosoteand oilborne preservatives are applied to the finishedglulamtimbers. Some light oil solventtreatments can be appliedto the lumberprior to gluing, but the suitabilitymust be verified with the manufacturer. Waterborne preservatives are best appliedto the lumberprior to the laminating and manufacturing process becausethey can leadto excessive checking if appliedto large finishedglulamtimbers. Creosote Solutions—Treatmentwith creosotesolutionsis suitablefor the most severe outdoorexposure. Itresultsin a dark, oily surface appearancethat is difficult to alter. This, coupledwith a distinct odor, restrictscreosotesolutionsto structures, such as bridges,that do not comein directcontact with humans.Creosotesolutions are an extremely effective preservative as proven by their continued use formilway structures. Anotheradvantage is that the creosotetreatment rendersthe timbersmuch less susceptible to moisturecontent changes than are untreatedtimbers.Creosotesolutions areoftenusedas a preservative treatmenton bridgestringers. Oilborne Treatments—Pentachlorophenol and copper napthanate are the most commonoilbornepreservatives. The solvents are classifiedin AWPA StandardP9 as Type A, Type C, and Type D (AWPA 1997a). Type A results in an oily finishand shouldnotbe usedwhen aplain table surface is needed.Type B or C canbe stainedor painted. More details are given in AITC (1990) and AWPA(1997a). Waterborne Treatments—Waterborne preservative treatmentsconformto AWPAP5 (AWPA 1997b) and use watersoluble preservative chemicalsthat becomefixed inthe wood.The effectiveness ofthis treatmentdepends uponthe

be contacted to determine thecapabilities ofwaterbomepreservative-treatedproducts.

assurance procedures.

Development

of Design Values

The basic approach to determine the engineered design valuesofglulammembers is throughthe use ofstress index values and stress modification factors.

Stress Index Values clearofwood that is free ofdefects and otherstrength-reducing characteristics. Stressindex values for several commonly used species and E-ratedgrades oflumberare given inASTM D3737 (ASTM 1997b). Procedures are also given for developing these values for visualgrades ofother species. Stress indexvaluesarerelatedto the properties

Stress Modification Factors Stressmodification factors are relatedto strength-reducing

characteristics and are multipliedby the stress indexvalues to obtainallowabledesign properties. Detailedinformation on determination ofthese factors for bending, tension, compression, andmodulusofelasticityare given in ASTM D3737 (1997b).

Other Considerations Effect of End Joints on Strength—Both finge:rjoints and scarfjointscan be manufactured with adequatestrength for use in structural glulam. Adequacyis determinedby physical testingprocedures and requirements in ANSI A190.1 (ANSI 1992). Joints shouldbe well scatteredin portionsofstructural glulamthat is highly stressedin tension. Requird spacings ofendjoints aregiven in ANSI A190.1. Endjoints oftwo qualities can be used in a glulammember,deperLding upon strength requirements at variousdepths ofthe cross section.

11—9

However,laminatorsusuallyuse the samejointthroughout the members for easein manufacture. The higheststrength valuesare obtainedwith well-made plain scarfjoints; the lowestvalues are obtainedwith butt joints. This is becausescarfjoints with flat slopes have essentially side-grain surfaces that can bewell bondedto develophigh strength, andbuttjoints have end-grainsurfaces that cannotbe bondedeffectively. Structural fmgerjoints (eithervertical orhorizontal)are a compromise between scarf and buttjoints; the strengthofstructural fingerjoints varies with joint design.

Nostatementcan be maderegardingthe specific joint

strength factor offingerjoints, becausefmgerjoint strength depends on the type and configuration ofthejointandthe manufacturing process.However, thejointfactor ofcommonlyused fmgerjointsin high-qualitylumberused for laminating can be about 75%. High-strength fmgerjoints can be made whenthedesignis such that thefmgershaverelatively flat slopes and sharp tips. Tips are essentiallya series ofbuttjoints that reducetheeffectiveness offmgerjoints as well as creating sources ofstress concentration.

Generally,buttjoints cannot transmittensilestress and can transmit compressive stress only after considerable deformation or ifa metal bearingplate is tightlyfittedbetweenthe abutting ends. In normal assembly operations, such fitting would not be done. Therefore, it is necessaryto assumethat buttjoints areineffectivein transmittingboth tensileand compressive stresses. Because ofthis ineffectiveness and becausebuttjoints cause concentration ofboth shearstress and longitudinal stress,buttjoints are not permittedfor use in structural glued-laminatedtimbers.

Effectof Edge Joints on Strength—It is sometimesnecessary to place laminations edge-to-edge to provideglulam

members ofsufficient width. Because ofdifficulties in fabrication, structuraledgejointbondingmay not be readily available, and the designershould investigate the availability of suchbondingprior to specifying.

For tension, compression, and horizontally laminated bending members,the strength ofedgejoints is of little importanceto the overall strength ofthe member. Therefore, from the standpoint ofstrength, it is unnecessarythat edgejoints be glued ifthey are not in the same location in adjacent laminations. However,for maximum strength, edgejoints shouldbe glued where torsional loading is involved. Other considerations, such as the appearance offace laminations or thepossibilitythat water willenter theungluedjoints and promotedecay, should also dictateifedgejoints are glued.

Ifedgejoints in vertically laminated beamsarenot glued,

shear strengthcouldbe reduced. The amount ofreduction can be determinedby engineering analysis. Using standardlaminating procedureswith edgejoints staggeredin adjacent laminations by at least one lamination thickness, shear strength ofverticallylaminatedbeams with ungluededge joints is approximately halfthat ofbeams with adhesivebonded edgejoints.

11—10

Effectof Shake, Checks, and Splits on Shear Strength— In general, checks and splits havelittle effecton theshear strengthofglulam. Shake occurs infrequently and shouldbe excluded from material for laminations. Most laminated timbers are madefrom laminationsthat are thin enoughto seasonreadily withoutdeveloping significantchecks and splits.

Designs for Glued-Laminated Timber Most basic engineering equationsused for sawn lumberalso apply to glulam beamsand columns.The designofglulam in this chapteris only applicable to glulam combinations that conformto AITC 117 (AITC 1993b) for softwoodspecies and AITC 119 (AITC 1996) for hardwoodspecies and are manufactured in accordance with ANSIJAITC A190.1 (ANSI 1992). The AITC 117 standard is madeup oftwo parts: (a) manufacturing, whichprovidesdetailsfor the many configurations ofglulam made from visuallygradedand E-ratedsoftwoodlumber; and (b) design, whichprovides tabulardesign valuesofstrength and stiffness forthese glulam combinations. The AITC 119 standardprovides similar information for glulammadefrom hardwoodspecies oflumber. Thesestandards are based on laterally-braced straight members with an average moisture contentof 12%. For bendingmembers,the designvaluesare based on an assumed referencesize of305mm deep, 130mm wide, and 6.4 m long (12 in. deep, 5.125 in. wide, and 21 ft long).

Tabular Design Values Tabular designvaluesgiven in AITC 117 and AITC 119 includethe following: Fb allowablebendingdesignvalue,

F

allowable tensiondesignvalue parallelto grain,

F

allowable shear design valueparallel

Fc.perp

F

to grain,

allowable compression designvalueperpendicular

to grain,

allowable compression design valueparallel

to grain,

E allowablemodulusofelasticity, and

F,

allowable radial tension design value perpendicular to grain.

Because glulammembers canhave differentproperties when loadedperpendicular or paralleltothe wide faces ofthe laminations,a commonnamingconventionis usedto specify the design valuesthat correspondto a particulartype oforientation. For glulam members loaded perpendicularto the wide faces ofthe laminations, designvaluesare commonlydenoted with a subscriptx. For glulam membersloaded parallel to the wide faces ofthe laminations, designvaluesare commonly denotedwith a subscripty. Some examples includeFb and fordesignbending stress and design modulusofelasticity, respectively.

E

End-Use Adjustment Factors Whenglulam members are exposed to conditions other than the describedreference condition, the published allowable design values requireadjustment. The following text describeseach ofthe adjustmentfactors that account forthe enduse condition ofglulam members.

derivedassuming a uniform load. This methodof loading factor CL is recommendedin theNational Design Specj/Ication for Wood Construction(AF&PA 1997). CL = 1.00 foruniform loading on a simplespan

=

C

Volume—The volumefactor accounts for an observed reductionin strengthwhen length, width, and depth of struc-

tural glulammembersincrease.This strengthreductionis due to the higherprobability ofoccurrence ofstrengthreducingcharacteristics, such as knots and slope ofgrain, in higher volume beams. This volume factor adjustmentis given in the NationalDesign Specj/Ication for Wood Construction(AF&PA 1997) in the form 0.10 0.10, 0.10, 1 305 l30" 6.4 C =1—H I—I I—I

d) w) L) 0.10

0.10

c [.J _5J =

\

0.05

305'

C =1—I

d)

I—I I—I

w) L)

0.05

C=11

0.05

(.d) (

w

)

(1 l—2a)

0.05

1±

L

(inch—pound)

(1l—2b)

for southernpines, whered is depth (mm, in.), w width (mm, in.), andL length (m, ft). (Eqs. (11—la)and (11—2a) in metric, Eqs. (1 1—ib) and (1 l—2b) in inch—pound system.) Moisture Content—Themoisturecontentfactor CM accounts forthe reductionin strengthas moisture content increases. A moisture contentadjustmentis listed in both ASTM D3737 (ASTM 199Th) and AITC 117—Design (AITC 1993b). CM

= 0.85 withouttensionlaminations and for depth 380 mm in.) = 0.75 withouttensionlaminations and for depth >380 mm (>15 in.).

th

Curvature—Thecurvature factor accounts for increased stressesin the curvedportion ofcurvedglulambeams. This factor does not apply to design values in the straightportion ofa member, regardless ofthe curvature elsewhere. The curvature factor C, whichcan be found in the Ntional Design Specflcation(AF&PA 1997), has the following relation:

C=

Formoisture content>16%, as in ground contact andmany other exteriorconditions,use the followingMvalues:

CM

= 1.00 for specialtensionlaminationsperAITC 117

= 1.0 for moisturecontent 16%

Fb

F1

0.8

0.8

(11—3)

CT

0.05

6.4

'1

CL =

(metric)

0.10

0.05,

1130

Forother loadingconditions, valuesofCL canbe estimated usingthe proportionofthe beam length subjectedto 80% or more ofthe maximum stressL0 and

(inch—pound) (1 1—Ib)

(11—la)

for Douglas-fir and other species, and /

= 0.92 forconstantstress over the full length

Tension Lamination—Pastresearchhas shownthat special provisions are requiredfor thetensionlamination ofa glulam beamto achieve the specifieddesignbendingstrengthlevels. Properties listedin AITC 117 and 119 are applicableto beamswith these specialtensionlaminations. Ifa special tension lamination is not includedin the beam combination, strength reduction factorsmust be applied. Tensionlamination factors Cr, whichcan be found in ASTMD3737 (ASTM 1997b), have the followingvalues:

(metric)

(1J

1.08 for centerpoint loading on a 5imple span

F

'c-perp

F

E

0.875

0.53

0.73

0.833

Loading—Anadjustmentforthe type of loading onthe member is alsonecessary becausethe volume factors are

(11—4)

1_2000(LJ

t

where is thickness of lamination andR is radius ofcurvatureon insideface oflamination. The value t/F 1/100 for hardwoods and southernpines;t/R 1/125 for other sofiwoods.

FlatUse—Theflat use factoris appliedto bendingdesign values whenmembers are loadedparalleltowide faces of laminations and are less than 305 mm (12 in.) in depth. Flat use factors C, whichcan be found in theNationalDesign Spec/ication (AF&PA 1997), have the followingvalues:

il—Il

Memberdimensionparallel to wide faces oflaminations

Cf

273 or 267mm(10-3/4 or 10-1/2 in.)

1.01

222 or 216mm(8-3/4 or 8-1/2 in.)

1.04

171

mm (6-3/4 in.)

1.07

130 or 127mm (5-1/8 or 5 in.) 79 or 76mm (3-1/8 or 3 in.)

1.10

64mm (2-1/2 in)

1.19

1.16

I beam

LateralStability—The lateral stabilityfactoris appliedto bendingdesignvaluesto accountfor the amountoflateral support applied to bending members. Deep bendingmembers that are unsupported along the top surfuce are subjectto lateraltorsionalbucklingand would have lowerbending designvalues. Members that are fully supported would have no adjustments(CL = 1.0).

Glued Members With Lumber and Panels Highlyefficientstructural components can be produced by combininglumber with panel productsthroughgluing. These components,including box beams, I-beams, "stressed-skin" panels,and foldedplate roofs, are discussed in detail in technicalpublicationsoftheAPA—The EngineeredWoodAssociation(APA 1980). One type ofmember, prefabricatedwood I-joists, discussedin detail. Detailson structural designare given in the followingportion ofthis chapterforbeams with webs ofstructural panelproducts and stressed-skin panels whereinthe parts are glued together with a rigid, durableadhesive.

s

Thesehighly efficientdesigns, although adequatestructurally, can suffer from lack ofresistance to fire and decay unless treatmentor protectionis provided.The rather thinportions ofthecross section (the panelmaterials) are more vulnerable to fire damage than arethelarger, solid cross sections.

Box Beams and I-Beams BoxbeamsandI-beamswith lumberor laminated flanges and structural panel webs can be designedto providethe desired stiffness, bending,momentresistance, and shear resistance. The flangesresist bendingmoment,and the webs provideprimaryshear resistance. Properdesign requires that thewebs must notbuckle under designloads.Iflateral stability is a problem,the box beam design shouldbe chosen becauseit is stiffer in lateral bendingand torsionthan is the I-beam. In contrast,the I-beam shouldbe chosenifbuckling oftheweb is ofconcernbecauseits singleweb, double the thickness ofthatofa box beam, will offer greaterbuckling resistance.

11—12

Figure 11—6. Beams with structural panel webs.

Designdetails forbeam cross sections (includingdefinitions ofterms inthefollowing equations) are presentedin Figure 11—6. Both flanges in these beamsare the same thickness becausea construction symmetrical about the neutral planeprovidesthe greatest momentofinertiafor the amount ofmaterial used. The following equationswere derived by basic principles ofengineering mechanics. Thesemethods can be extended to derivedesignsfor unsymmetrical constructions, ifnecessary.

Beam Deflections Beam deflections can be computed using Equation(8—2)in

Chapter8. The following equations for bending stiffness (El)1 and shearstiffnessGA' apply to thebox and I-beamshown In Figure 11-6. The bendingstiffness is given by (El)1 =-[E(d —c3)b+2EWd3}

(11—5)

E

whereE is flange modulusofelasticity and is webmodu• lus ofelasticity. For plywood, valuesof forthe appropriate structural panel construction and grain directioncan be computedfrom Equations (11—1), (11—2), and (11—3).

E

Anapproximate expression fortheshearstifThessis GA'= 2WcG

(11-6)

whereG is shearmodulus forthe structural panel for appropriatedirectionandA' is the effective areaofthe web.An improvement in shear stiffness can be madeby properly orientingthe web, dependingupon its directionalproperties. Equation(11-6) is conservative becauseit ignoresthe shear stiffness ofthe flange. This contribution can be includedby use ofAPA design methodsthat are based on Orosz (1970). (Forfurtherinformation on APA design methods,contact APA—TheEngineeredWoodAssociationin Tacoma, Washington.)

Flange Stresses Flangecompressiveandtensilestressesat outer beamfibers aregiven by

6M (d3

d

(11—7)

modulusofelasticity EL. The resultanttorsionalstifthess GK will be slightly low ifbeam webs have plywoodgrain at 45° to theneutral axis. The lateral bucklingofI-beamswill also be slightly conservative becausebendingrigidityofthe flangehas been neglected inwritingthe equations given here. IfbucklingoftheI-beamseemspossibleat desigi loads,the more accurate analysis ofForest Products Laboral:oryReport 1318B (Lewisand others 1943) shouldbe used before

E

where M is bending moment.

Web Shear Stress Web shear stress at the beamneutral planeis givenby —

3V E(d2—c2)b4-2E,Wd2 4W E(d3 —c3)b+2EWd3

(11—8)

where Vis shearload. The shear stress must not exceed allowablevalues.To avoid webbuckling, eitherthe web shouldbe increased inthicknessorthe clear length ofthe webshouldbe brokenby stiffenersgluedto the web. Web edgewise bendingstresses at the insideoftheflanges

canbe computed by

6M fxw

d3 E(d3 c3b )—÷2—W

(11—9)

of Timoshenko (1961).

Lateral Buckling Possiblelateral bucklingofthe entire beamshou]Ld be checkedby calculatingthe criticalbendingstress (Ch. 8, Lateral—TorsionalBuckling section).The slenderness factor p, requiredto calculatethis stress, includesterms for lateral flexuralrigidityEI andtorsionalrigidityGKthat are defmed

as follows: Forbox beams,

'

(11—10)

÷E[(b+2W)3 —b3}d — GK =[(d÷ c)(d2 c2)(b+W)2W1G

[

(d2—c2)+4(b+W)W

j

(Il_il)

11 " I—12\ /

+E(2W)3d} GK=

E

where

[(d_c)3b+d(2W)3]G is flexuralelasticmodulusoftheweb.

Stiffeners and Load Blocks Determinationofthe numberand sizes ofstiffeners and load blocks neededin aparticularconstruction does not lend itself to arationalprocedure, but certaingeneralrules can be given that willhelp the designer ofa structure obtain a satisfactory structural member. Stiffeners servea dualpurpos in a struc-

tural memberofthis type. One functionis to limitthe size of theunsupported panel in theweb, and theother [5 to restrain the flanges frommovingtoward each other as the beamis Stiffeners shouldbe gluedto thewebs and in contactwith both flanges. A rationalway ofdetermining howthick the stiffenershouldbe is not available, but tests ofbox beams made at the Forest Products Laboratory indicatethat a thickness ofat least six timesthe thicknessofthewet is sufficient.Becausestiffeners must alsoresistthe tendencyofthe flanges to movetoward each other,the stiffenersshouldbe as wide as (extend tothe edgeof) the flanges. Forplywoodwebs containing plies with thegrain ofthe wood oriented both parallel and perpendicular to the axisof themember, thespacingofthestiffeners isrelativelyunimportantfor thewebshearstressesthat are allowed.Maximum allowable stresses are less than thosethat will producebuckling. A clear distance betweenstiffeners equalto or less than two timesthe clear distance betweenflanges is adequate. Load blocks are specialstiffeners placedalongthe member at points ofconcentrated load.Load blocksshouldbe designed sothat stresses caused by a loadthatbears againstthe sidegrain material in the flanges donot exceedthe alLiowable designforthe flangematerial in compression perpendicular

to grain.

For i-beams,

El = —'{E[(b-,-2W) —(2W)3}(d—c)

redesigning.

stressed.

Althoughit is not likely,the web can buckle as a result of bendingstresses. Shouldbucklingas aresult ofedgewise bendingappearpossible,the interaction ofshearand edgewise bendingbuckling can be examinedusingthe principles

El =—E(d—c)b 12

In Equations (11—11) and (11—13), theshear modulusG can be assumedwithoutgreaterror to be about 1/16 oCthe flange

(11—13)

Prefabricated Wood I-Joists In recentyears,thedevelopment ofimprovedadhesives and manufacturing techniqueshas led to the development ofthe prefabricatedI-joist industry. This productis a unique type ofI-beamthat is replacingwider lumbersizes in floor and roof applications forboth residential and commercial buildings (Fig. 11—7).

Significant savings in materials are possible with prefabricatedI-joiststhat use eitherplywoodororientedstrandboard (OSB) forthe web materialand smalldimensionlumberor structural composite lumber(SCL) for the flanges,The high quality lumberneededforthese flanges has beendifficultto obtain using visualgrading methods,andboth mechanically

11—13

Recently, a performance standard for prefabricted I-joists has beenpromulgated forproductsused in residentialfloor construction (APA 1997).

Stressed-Skin Panels Constructions consisting ofstructuralpanel "skins" glued to wood stringersare often called stressed-skin panels. These panels offer efficient structural constructions for floor, wall, androofcomponents. They can be designedto provide desired stiffness, bending moment resistance,and shear resistance.The skins resist bendingmoment,and the wood stringers provideshearresistance. The details ofdesignfor a panelcross section are given in Figure 11—8. The following equationswere derivedby basic principles ofengineering mechanics. A more rigorousdesign procedure that includes the effects ofshear lag is available in Kuenzi and Zahn (1975).

A Figure 11—7. Prefabricated I-joists with laminated veneer lumberflanges and structuralpanel webs. (A) One experimental producthasa hardboard web. The othertwo commercial productshave (B) oriented strandboard and (C) plywood webs. graded lumberand SCL are being used by several manufac-

turers.The detailsoffasteningthe flanges to the webs vary betweenmanufacturers; all must be glued with awaterproof adhesive.Prefabricated I-joistsare becoming popularwith buildersbecauseoftheirlight weight,dimensionalstability and ease ofconstruction. Theiraccurate and consistent dimensions,as well as uniformdepth, allowthe rapid creation ofa level floor. Utilitylines pass easilythroughopeningsin thewebs. The ASTM standardD5055(ASTM 1997d) gives procedures for establishing, monitoring,and reevaluating structural capacities ofprefabricated I-joists. Eachmanufacturer of prefabricated I-joists is responsible fordeveloping the requiredproperty information and ensuringthat the minimum levels of qualityare maintainedduring production. An independentinspectionagencyis required to monitorthe quality assurance program.

Standardgrades,sizes, and span tables have not been establishedfor all prefabricatedI-joists. The production ofeach manufacturer mayhave unique design properties andprocedures. Thus,the designermust consult information provided by the manufacturer. Manyengineering equationspresented in theprevioussection also apply to prefabricated I-joists. Duringthe 1980s, the prefabricatedwoodI-joists industry was one ofthe fastestgrowing segments ofthewood products industry. Prefabricated I-joistsare manufactured by about 15 companies in the United Statesand Canadaand are often distributedthroughbuildingmaterialsuppliers. Each manufacturerhas developedits buildingcodeacceptance andprovides catalogs with span tables and designinfonnation.

11—14

Panel deflections can be computedusing Equation(8—2)in Chapter8. The bendingstiffness Eland shearstiffnessGA' are given by the following equationsfor the stressed-skin

panelshown in Figure 11—8.

EI=

b (E1t,+E2t +Et0(s/b))

{1iz2 [(t1 + t) +(t2 + + E1t1Et(s / b)(t1 + t)2 + E2t2Et(s / b)(t2 + tj2} +

{EfIt+Ef2t

+Et (11—14)

whereE1 and E2aremodulusofelasticityvalues for skins 1 and 2, and En flexural modulusofelasticityvaluesfor skins 1 and 2, E stringermodulusof elasticity, and s total width ofall stringersin a panel. Anapproximate expression for shearstiffness is

E

GA'—Gst

(11—15)

whereG is stringer shearmodulus.

Skin Stresses Skin tensileand compressive stressesare given by

Li-- ME1y1 (11—16)

Jr2

— —

ME2y2

El

where El is given by Equation(11—14), Mis bending moment, and

L

J

1,

Figure 11—8. Stressed-skinpanel cross section.

E2t2[(t1 +

t) + (t2+t)} + Et

(t1 +

Glue Shear Stress Glue shear stress in thejointbetweenthe skins and stringers is given by

t)

y1

2E1t1

=

E1t1[(t1+

+E2t2 + Et

t)+ (t2+ ta)]+ Et

2[Eiti

,

+ t)

V(EQ)

sEl

(11—19)

whereEQ = Eitiby. Thisstress

+E2t2 + Et

Either the skins shouldbe thick enoughor the stringers spacedclosely enough so that buckling does not occur in the compression skin. Bucklingstress canbe analyzedby the principles in Ding and Hou (1995). The designstress for the structural panel in tensionandcompressionstrengthshould

notbe exceeded.

shouldnot exceeivalues for theglue and species. It shouldalso not exceedthewood stress fn ("rolling" shear)for solidwoodbecause, forplywood, the thin plies allow the glue shear stresses to be transmittedto adjacentplies and could cause rolling shear failurein thewood.

Buckling Buckling ofthe stressed-skin panelofunsupported length

under end loadappliedin a directionparallel to the length of thestringerscan be computed by

StringerBending Stress The stringerbending stress is the larger value given by —

ME(y1

(11—20)

—;/2)

El

— ME(y2—t2/2) fsr2 El

(11—17)

andthese shouldnot exceedappropriate valuesfo:r the

whereL is unsupported panel length and El is bending stiffness givenby Equation (11—14). Compressive stress in the skins is given by

-L -

species.

EA

The stringer shear stress is given by

- V(EQ) sEl

fxc2

(11—21)

PE2

(11—18)

whereEQ = (E1t1b + Esy2)y. This also shouldnot exceed appropriate valuesforthe species.

and in the stringers by

PE f=.

(11—22)

11—15

resistant facingcanbeused for the top facingofa floorpanel; anddecorative effectscan be obtainedby usingpanelswith plasticfacings forwalls, doors,tables, and other furnishings. Core materialcan be chosento provide thermal insulation, fireresistance, and decay resistance. Becauseofthe light weightofstructural sandwich construction, soundtransmission problems must also be considered in choosingsandwich component parts. Methods ofjoining sandwich panelsto each other and other structures must be plannedso that thejoints functionproperly andallow for possible dimensionalchangeas a resultof temperatureand moisture variations.Both structuraland nonstructural advantages need to be analyzedin light ofthe strength and service requirements for the sandwich construction. Moisture-resistant facings, cores, and adhesivesshould be used iftheconstruction is to be exposedto adverse moisture conditions. Similarly, heat-resistantor decay-resistant facings, cores,and adhesives shouldbe usedifexposureto elevated temperatures ordecay organisms is expected.

Fabrication Figure 11—9. Cutaway sectionofsandwich construction with plywood facingsand a paper honeycombcore.

whereEA E1t1b + E2t2b + Et,s. These compressivestresses shouldnot exceed stress valuesforthe structural panelor stringermaterial.For plywood, compressivestress should also be less than the critical buckling stress.

Structural Sandwich Construction a

Structural sandwichconstruction is layered construction formedby bondingtwo thinfacings to a thickcore (Fig. 11—9). The thin facings are usuallymade ofa strong and densematerialbecausethey resistnearly allthe applied edgewiseloads and flatwisebendingmoments.The core, whichis made ofa weak and low densitymaterial,separates and stabilizesthe thinfacings andprovidesmost ofthe shear rigidityofthe sandwichconstruction. Byproperchoiceof materials for facings andcore, constructions with high ratios ofstiffnessto weightcanbe achieved. As a crude guide to the materialproportions, an efficientsandwich is obtainedwhen

theweightofthecore is roughlyequalto the total weightof thefacings. Sandwich construction is also economical becausethe relativelyexpensive facingmaterials are usedin much smaller quantities than are the usuallyinexpensive core materials.The materialsare positionedso that each is used to its best advantage. Specific nonstructuraladvantages canbe incorporated in a sandwich construction byproperselectionoffacing and core materials.An impermeable facing can act as amoisture barrierfora wall or roofpanel in ahouse; an abrasion-

11—16

Facing Materials

One advantage ofsandwich construction is the great latitude it providesin choice offacingsand theopportunityto use thinsheetmaterials becauseofthenearly continuoussupport by thecore. The stiffliess, stability, andto a largeextent, the strength ofthe sandwich are determined by the characteristics ofthefacings. Facingmaterialsincludeplywood, single

veneers, orplywoodoverlaid with a resin-treatedpaper, oriented strandboard, hardboard, particleboard, glass—fiberreinforcedpolymers or laminates, veneerbonded to metal, and metals,such as aluminum, enameledsteel,stainless steel, magnesium, and titanium.

Core Materials Many lightweight materials,such as balsa wood, rubber foam,resin-impregnated paper, reinforcedplastics, perforated chipboard, expandedplastics,foamedglass, lightweight concrete and clay products, and formedsheetsofcloth,metal, orpaperhave beenused as a core for sandwich construction. New materials and new combinations ofoldmaterialsare constantly beingproposedandused. Cores offormedsheet materials are often calledhoneycomb cores. By varyingthe sheet material, sheet thickness, cell size, and cell shape, coresofa wide range in density can be produced. Various core configurations are shown in Figures 11—10 and 11—11. The core cell configurations showninFigure 11—10 can be formed to moderateamounts ofsinglecurvature,but cores shownin Figure 11—11 as configurations A, B, and C can be formed to severesingle curvature and mild compound curvature (spherical).

Fourtypes ofreadilyformable coresareshownas configurations D, E, F, and G in Figure 11—11. The type D and F cores form to a cylindrical shape, the type D and E cores to a sphericalshape, andthe type D and G cores tovarious compoundcurvatures.

-',.

I- I-

IIlitSt! —J'.

B

_. — D

F

E

—1ii G

Figure 11—10. Honeycomb core cell configurations.

A

— E

— D

F

Figure 11—11. Cellconfigurationsfor formable paper honeycomb cores.

Ifthe sandwich panelsare likelyto be subjectedto damp or wet conditions, a core ofpaper honeycomb shouldcontaina synthetic resin. Whenwet, paper with 15% phenclic resin provides goodstrength, decay resistance, and desirablehandling characteristics during fabrication. Resin amounts in excess ofabout 15% do not seem to produce again in strength commensurate with the increased quantity ofresin required. Smaller amounts ofresin may be combiuedwith fungicides to offerprimaryprotection againstdecay.

Manufacturing Operations Theprincipaloperation in themanufactureofsandwich panelsis bonding the facings to the core. Special presses are neededfor sandwich panelmanufacture to avoid crushing lightweight cores, becausethe pressures requiredare usually lowerthan can be obtainedinthe range ofgoodp:ressure controlon presses ordinarily used for structural panelsor plastic products. Becausepressurerequirements are low, simpleand perhapsless costly presses could be used.Continuousrollerpresses or hydraulic pressureequipmentmay alsobe suitable. Inthe pressing ofsandwichpanels, special problems can occur,but the manufacturing processis basically not complicated.

Adhesives must be selectedand appliedto providethe necessaryjointstrengthandpermanence.The facingmaterials, especially ifmetallic, mayneed special surface treatment beforethe adhesive is applied.

In certainsandwich panels, loading rails or edgings are placedbetween the facings atthe time of assembly. Special fittings or equipment, such as heating coils, plumbing,or electrical wiringconduit,can easily be installed:Ln the panel beforeits components are fittedtogether. Someofthe most persistentdifficulties in the use ofsandwich panelsare caused by the necessity ofintroducingedges, inserts, and connectors. In some cases,the problem involves tying togetherthinfacingmaterials withoutcausing severe stress concentrations. In othercases, such as furniture manufacture, the problemis "showthrough"ofcore or inserts throughdecorative facings. These difficulties are minimized by achoice ofmaterials in whichtherate and degreeofdifferential dimensional movementbetween core and insert are at a minimum.

Structural Design The structural design ofsandwichconstruction can be compared with the design ofan I-beam. The facings and coreof thesandwich are analogous to theflanges and wb ofthe I-beam, respectively. The two thin and stifffacings,separated by a thick and light core,carry thebending loads. The functions ofthe core are to supportthe facings againstlateral wrinklingcausedby in-plane compressive loads and to carry, throughthe bondingadhesive,shear loads.When the strength requirements forthe facings and core in aparticular design are met, the construction shouldalsobe checked for possible buckling, as for a columnor panel in compression, and forpossible wrinklingofthe facings.

11—17

wherey is deflection, x distance along the beam, Mbending momentper unit widthat point x, and shear force per unit width at pointx.

The contribution ofthe core material to the stiffnessofthe sandwich construction can generallybeneglectedbecause of thecore's low modulusofelasticity;when that is thecase, the shearstress can be assumedconstantover the depth ofthe core.The facing moduliofelasticityare usuallymore than 100 times as great as the coremodulusofelasticity. The core material may also have a small shear modulus. This small shearmodulus causes increased deflections ofsandwich construction subjectedto bendingand decreased buckling loadsofcolumnsand edge-loadedpanels,compared with constructions in which the core shearmodulusis high. The effectofthis low shearmodulusis greaterforshortbeamsand columns and small panelsthan it is for long beams and columns and largepanels. Withoutconsideringthe contributionofcore material, the bendingstifihess ofsandwich beamshavingfacings ofequal or unequalthicknessis given by

D= h2t1t2(E1t2+E2t1) (t1÷t2)2

1(Et '' +E22t3) 12

£

Integration ofEquation (11—25) leads to the following generalexpression for deflection ofa sandwich beam:

kPa

D

U

(11—2(5)

whereP is total loadper unit width ofbeam, a is span, and kb and k,are constantsdependentupon the loadingcondition. The firstterm in the rightside ofEquation(11—26) givesthe bendingdeflection and the secondterm the sheardeflection. Valuesofkb and Ic3 forseveralloadings are given in Table 11—1.

Forsandwich panelssupported on all edges, the theoryof plates must be appliedto obtain analyticalsolutions. A

comprehensive treatment ofsandwich plates undervarious loadingand boundary conditions can be found in the books by Allen (1969), Whitney(1987),and Vinson and Sierakowski(1986). Many extensive studies ofsandwich construc tionperformed atthe Forest Products Laboratory are referenced in those books. In addition,somehigh-orderanalyses ofsandwich construction that considergeneral materialpropertiesfor component parts in specifiedapplications can be foundin the references at the endofthis chapter.

(11—23)

whereD is the stiffnessperunit widthofsandwich construction (productofmodulusofelasticity and momentofinertia ofthecross section),E, and P22 moduli ofelasticityoffacings 1 and 2, t1 and t2 facing thickness,and h distance between facingcentroids. The shear stiffness perunitwidth is given by

U=—G

kPa3

The bucklingload per unit width ofa sandwich panel with no edge members and loadedas a simplysupportedcolumn

isgivenby

(11—24)

tc

N—

whereG0is the core shear modulusassociated with distortion ofthe plane perpendicular to the facings and parallel to thesandwich length and is thethickness ofthecore.

t

D

U1c/x

(11—27)

where criticalload

The bendingstiffness D and shear stiffness Uare used to computedeflections andbucklingloads ofsandwich beams. The general expression forthe deflection offlat sandwich beams is given by

2

NE

1+ NE/U

it2n2D

N= a

(11—28

2

in whichn is thenumber ofhalf-wavesinto whichthe column buckles and a is the panel length. The minimum value of NE is obtainedfor n = 1 and is called theEuler load.

(11—25)

Table11—1. Valuesof kb and k8 for several beam loadings Beam ends

Deflection at

Uniformly distributed

Both simply supported Both clamped Both simply supported Both clamped Both simply supported Both simply supported Cantilever,1 free, 1 clamped Cantilever,I free, clamped

Midspan

5/384

1/8

Midspan Midspan

1/384 1/48

1/8 1/4

Midspan

1/192

1/4

Midspan

11/76 1/96

1/8

118

1/2

Concentratedat midspan Concentrated at outer quarter points

Uniformly distributed Concentratedat free end

11—18

k

Loading

I

Load point Free end Free end

kb

1/3

1/8

1

Atthis load,thebuckling form is often called "general buckling,"as illustratedin Figure 1 1—12A. The bucklingload N is often expressedin the equivalent form 1 —

N

(11—29)

NEU

When U is finite, N