1996 LRFD Manual for Engineered Wood Construction

1996 EDITIONLRFDLOAD AND RESISTANCE FACTOR DESIGNMANUAL FOR ENGINEEREDWOOD CONSTRUCTIONCopyright © 1996American Forest & Paper Association

FOREWORDThis manual represents the beginning of a new era inthe design of wood structures. It is the first wood designmanual in the U.S. presented in the modern Load andResistance Factor Design (LRFD) format. It is also thefirst design manual to provide guidance for selection ofmost wood-based structural products used in the constructionof wood buildings.The complete wood LRFD package includes thismanual and its design supplements and guidelines. Themanual contains the consensus-based AF&PA/ASCE 16-95 standard, its commentary and examples ofits use. Design supplements and guidelines are organizedalong product lines and contain design information forspecific products and details of design specific to thoseproducts.The modular format of the complete package is essentialfor a design package that covers such a broad rangeof products. This format provides the ability to quicklylocate specific design information in one of the wellmarkeddesign supplement or guideline documents.PREFACEThe American Forest & Paper Association (AF&PA)has developed this manual for design professionals.AF&PA and its predecessor organizations have providedengineering design information to users of structural woodproducts for over 50 years, first in the form of the WoodStructural Design Data series and then in the NationalDesign Specification ® (NDS ® ) for Wood Construction.This manual represents the culmination of 10 yearsof development of LRFD procedures for wood products,which in turn is built on 20 years of research on this topic.The basis of this Manual can be directly traced to a prestandardactivity of the American Society of CivilEngineers (ASCE), a wood-industry sponsored LRFDspecification development project and the consensus adoptionof the specification through a joint AF&PA/ASCEcommittee. Without the dedication of the many technicalexperts who contributed to these projects and the broadsupport of virtually the entire North American forest productsindustry, this Manual could not have become a reality.Every effort has been made to ensure that the dataand information in the Manual are as accurate and completeas possible. AF&PA does not, however, assume anyresponsibility for errors or omissions in the Manual norfor engineering designs or plans prepared from it.This Manual was written by David S. Gromala, P.E.,under contract to AF&PA, with the guidance and assistanceof AF&PA staff and numerous industry technicalexperts who participated on the AF&PA LRFD committee.AF&PA/ASCE 16-95 NOTATION AND GLOSSARYAF&PA/ASCE 16-95, Standard for Load and ResistanceFactor Design (LRFD) for Engineered WoodConstruction, is contained in its entirety in the final sectionof this Manual. For the convenience of the designengineer, the notation and glossary sections of AF&PA/ASCE 16-95 are duplicated in this section.AMERICAN WOOD COUNCIL

TABLE OF CONTENTSChapter/TitlePageChapter/TitlePageNotation ......................................................................................................... iGlossary ...................................................................................................... v1 Introduction .................................................................................. 11.1 General Information1.2 Design Responsibilities1.3 Other Design Considerations1.4 Products Covered in This Manual2 Project Profiles:Case Studies ......................................................................... 112.1 General Information2.2 Commercial/Industrial2.3 Residential/Retail3. Tension Members .......................................................313.1 General3.2 Design3.3 Special Considerations3.4 Checklist: Using Tension MemberSelection Tables3.5 Design Examples4. Compression Members ........................... 354.1 General Information4.2 Design4.3 Special Considerations4.4 Checklist: Using CompressionMember Selection Tables4.5 Design Examples5. Bending Members ................................................... 415.1 General Information5.2 Design for Moment5.3 Design for Shear5.4 Special Considerations5.5 Checklist: Using Joist and BeamSelection Tables7. Mechanical Connectors ........................ 537.1 General Information7.2 Nails, Spikes and Wood Screws7.3 Bolts, Lag screws, Drift Pins, Dowels7.4 Shear Plates and Split Rings7.5 Typical Connection Details7.6 Checklist: Using Connection SelectionTables7.7 Design Examples8. Structural Panels .....................................................798.1 General Information8.2 Design for Moment8.3 Design for Shear8.4 Checklist: Using Structural PanelSelection Tables8.5 Design Examples9. Shear Walls andDiaphragms .............................................................................. 839.1 General Information9.2 Design9.3 Checklist: Using Shear Wall andDiaphragm Selection Tables9.4 Design Examples10. Reference Information .......................... 8910.1 General Information10.2 Applications-Related Information10.3 Other Design InformationAF&PA/ASCE Standard 16-95 ..... 1116. Bending Plus Axial Loads ................476.1 General Information6.2 Design for Moment6.3 Checklist: Using Combined Bendingand Axial Member Selection Tables6.4 Design ExamplesAMERICAN FOREST & PAPER ASSOCIATION

AMERICAN WOOD COUNCIL

iNotationAGross areaA nNet area, net bearing areaA min , B min Minimum spacing permitted for shear plates and split rings, parallel and perpendicular to grain,respectivelyA opt , B opt Required spacing of shear plates and split rings to achieve reference connection resistance, paralleland perpendicular to grain, respectivelyB bx , B by Moment magnification factor for loads that result in no appreciable sidesway (strong and weakaxes, respectively)B sx , B sy Moment magnification factor for loads that result in sidesway (strong and weak axes, respectively)C EComposite action factorC FSize factorC GGrade/construction factor for structural panelsC HShear stress factorC IStress interaction factorC LBeam stability factorC MWet service factorC PColumn stability factorC TBuckling stiffness factor for dimension lumberC VVolume effect factor for structural glued laminated timberC bBearing area factorC bBending coefficient dependent on moment gradientC cCurvature factor for structural glued laminated timberC csCritical section factor for round timber pilesC dPenetration depth factor for connectionsC diDiaphragm factorC egEnd-grain factor for connectionsC fForm factorC fuFlat-use factorC gGroup action factor for connectionsC m , C mx , C my Moment shape factor for biaxial bending (general, strong, and weak axes, respectively)C ptPreservative treatment factorC rLoad-sharing factorC rtFire-retardant treatment factorC spSingle pile factorC stMetal side plate factor for 4 in. shear plate connectionsC tTemperature factorC tnToe-nail factor for nailed connectionsC uUntreated factor for round timber pilesC wWidth factor for structural panelsC ∆Geometry factor for connectionsDDiameterDDead loadD, D′ Reference and adjusted diaphragm shear resistance per unit lengthD uDiaphragm shear force per unit length due to factored loadsD 1 , D 2 Minimum and maximum diameters in round tapered membersEEarthquake loadE, E′ Reference and adjusted mean modulus of elasticityE 05 , E 05 ′ Reference and adjusted fifth percentile modulus of elasticityEAAxial stiffnessEIFlexural stiffnessAMERICAN FOREST & PAPER ASSOCIATION

iiF b , F b ′ Reference and adjusted bending strengthF bx *Bending strength for strong (x-x) axis bending multiplied by all applicable adjustment factorsexcept C fu , C V , and C LF c , F c ′ Reference and adjusted compression strength parallel to grainF c *Compression strength parallel to grain multiplied by all applicable adjustment factors except C PF cz , F cz ′ Reference and adjusted compression strength perpendicular to grainF eDowel bearing strengthF em , F es Dowel bearing strength of main and side members, respectivelyF e2 , F ez , F eθ Dowel bearing strength parallel, perpendicular, and at an angle to the grain, respectivelyF g , F g ′ Reference and adjusted bearing strength parallel to grainF r ′, F rc ′, F rt ′ Adjusted radial strength (general, compression, and tension, respectively)F s , F s ′ Reference and adjusted rolling shear strength for structural panelsF t , F t ′Reference and adjusted tensile strength parallel to grainF tv ′Adjusted torsional shear strengthF v , F v ′ Reference and adjusted shear strength parallel to grain (horizontal shear)F v , F v ′ Reference and adjusted through-thickness shear strength for structural panelsF ybBending yield strength of fastenerGSpecific gravityG, G′ Reference and adjusted shear modulusG v , G v ′ Reference and adjusted shear modulus for structural panelsIMoment of inertiaJTorsional constant for a sectionK MMoisture content coefficient for sawn lumber truss compression chordsK TTruss compression chord coefficient for sawn lumberK eEffective length factor for compression membersLDesign span of bending member or compression memberLLive load caused by storage, occupancy, or impactL rRoof live loadM, M′ Reference and adjusted moment resistanceM 1 , M 2 Smaller and larger end moment in a beam or segmentM bx , M by Factored moment from loads that result in no appreciable sidesway (strong and weak axes,respectively)M eElastic lateral buckling momentM mx , M my Factored moment, including magnification for second-order effects (strong and weak axes,respectively)M s ′ Adjusted moment resistance computed with C L = 1.0M sx , M sy Factored moment from loads that result in sidesway (strong and weak axes, respectively)M t , M t ′ Reference and adjusted torsion resistanceM tuTorsion due to factored loadsM u , M ux , M uy Moment due to factored loads (general, strong and weak axes, respectively)M x ′, M y ′ Adjusted moment resistance (strong and weak axes, respectively)M x *Moment resistance for strong (x-x) axis bending multiplied by all applicable adjustment factorsexcept C fu , C V , and C LP, P′ Reference and adjusted compression resistance parallel to grainP 0 ′Adjusted member axial parallel to grain resistance of a zero length column (i.e., the limit obtainedas length approaches zero)P aAssumed axial load acting on a side bracketP eEuler buckling resistanceP g , P g ′ Reference and adjusted bearing resistanceP z , P z ′ Reference and adjusted compression resistance perpendicular to grainP θ , P θ ′ Reference and adjusted compression resistance in bearing at angle θAssumed horizontal side load placed at center of height of columnP sAMERICAN WOOD COUNCIL

iiiP uCompressive or bearing force due to factored loadsQStatical moment of an area about the neutral axisRLoad caused by initial rain water and/or iceR, R′ Reference and adjusted resistanceR BSlenderness ratio of bending memberR EARatio of minimum to maximum member axial stiffness in a connectionR eRatio of main to side member embedment strength in a connectionR tRatio of main to side member thickness in a connectionR f , R m Radius of curvature at the inside face and at mid-depth, respectivelyR uForce due to factored loadsSSection modulusSSnow loadT, T′ Reference and adjusted tension resistance parallel to grainT uTensile force due to factored loadsV, V′ Reference and adjusted shear resistanceV uShear force due to factored loadsWWind loadZ, Z′, Reference and adjusted connection lateral resistanceZ u ,Connection force due to factored loadsZ w , Z w ′ Reference and adjusted connection withdrawal resistanceZ α ′Adjusted resistance of a fastener loaded at an angle to the surface of the wood memberZ 2 ′, Z z ′, Z θ ′ Adjusted resistance of a fastener loaded parallel, perpendicular, and at an angle to thegrain,respectivelyaEnd distance for a connectiona iEffective number of fasteners for row ia minMinimum end distance permitted for connectionsa optRequired end distance to achieve reference connection resistancebMember widthbEdge distance for connectionb minMinimum edge distance permitted for connectionsb optRequired edge distance to achieve reference connection resistancecCoefficient in column stability factor equationc bCoefficient in beam stability factor equationdMember depthd 1 , d 2Minimum and maximum depth for a uniform width, linearly tapered memberd eEffective depth of member at a connectiond nDepth of member remaining at a notcheEccentricityhHeightRDesign span of bending member or compression memberRDistance between points of lateral support of a compression memberRSpan length, clear span of arch between hingesR bBearing lengthR brDistance from the bottom of the column or column segment to the top of the column bracket, in.R cClear spanR eEffective lengthR mLength of dowel-type fastener in main memberR PDistance measured vertically from point of application of load on bracket to farther end of columnR uLaterally unsupported span length of bending or compression membern fTotal number of fasteners in a connectionn iNumber of equally spaced fasteners in row iNumber of serial rows of fasteners in a connectionn rAMERICAN FOREST & PAPER ASSOCIATION

ivprss mins opttt m , t swααα bα cγ∆λφφ bφ cφ sφ tφ vφ zθθθ bDepth of fastener penetration into wood memberRadius of gyrationSpacing of fasteners in a connection (also called pitch spacing)Minimum spacing for adjusted connection resistanceRequired spacing for reference connection resistanceThicknessThickness of main and side members, respectively, in a connectionUniform loadAngle between applied force vector and the surface of the wood memberAngle of connector axis with respect to member longitudinal axisFactor in design of flexural membersFactor in design of columnsLoad/slip constant for a single fastenerDeflectionTime-effect factorResistance factorResistance factor for flexureResistance factor for compressionResistance factor for stabilityResistance factor for tensionResistance factor for shear/torsionResistance factor for connectionsAngle of cut taper or cut notch from the grain directionAngle of force vector with respect to a direction parallel to grainAngle between bearing force and the direction of grainAMERICAN WOOD COUNCIL

vGlossaryAdjusted resistance. The reference resistance adjustedto include the effects of all applicable adjustment factorsresulting from end use and other modifying factors. Timeeffectadjustments are not included because they areconsidered separately.American Softwood Lumber Standard. A voluntaryproduct standard developed by the National Institute ofStandards and Technology, U.S. Department of Commerce,in cooperation with wood producers, distributors,and users. The standard establishes the dimensions forvarious types of lumber products, the technical requirementsand the methods of testing, grading and marking,and is designated PS 20-94 (Product Standard 20 issuedin 1994).American Lumber Standard Committee (ALSC). Astanding committee composed of representatives of producers,distributors, specifiers, and consumers of lumber.The primary function of the committee is to review andconsider revisions to the American Softwood LumberStandard, PS 20-94. ALSC inspectors conduct field checkson certified grading agencies and the committee’s independentBoard of Review has the power to discipline underthe aegis of the Commerce Department, National Instituteof Standards and Technology.Aspect ratio. In any rectangular configuration, the ratioof the long side’s length to the short side’s length.Assembly. A collection of parallel structural membersand/or components connected in a manner such that loadapplied to any one component will affect the stress conditionsof adjacent parallel components.Assembly effects. Component interactions that affect theway stress is distributed within an individual componentand/or the way loads are distributed to other componentsin an assembly.Boundary elements. Shear wall and diaphragm membersto which sheathing transfers forces. Boundaryelements include chords and drag struts at shear wall anddiaphragm perimeters, interior openings, discontinuitiesand reentrant comers.Built-up member. A member made of structural woodelements that are glued or mechanically connected.Clear span. Inside distance between the faces of supports.Composite action. Interaction between elements connectedin such a way that the resulting member strengthand stiffness is greater than the sum of the strength andstiffness of the individual elements.Composite member. A member composed of multipleelements connected so as to achieve composite action.Composite panel. A structural-use panel comprised ofwood veneer and reconstituted woodbased material andbonded with waterproof adhesive.Connection. An attachment used to transmit forces betweentwo or more members by means of a fastener, anassembly of fasteners, or adhesive, acting alone or in combinationwith member bearing.Connector. Synonym for fastener.Decay. Decomposition of wood substance caused by actionof wood-destroying fungi; the word “rot” means thesame as decay.Decking. Solid sawn lumber or glued laminated deckingexpressed in nominal terms as being “2 in. to 4 in.” thickand “4 in. and wider.” Decking is usually surfaced to singletongue and groove in 2 in. (51 mm) nominal thickness. In3 in. (76 mm) and 4 in. (102 mm) nominal thickness, itmay be double tongue and groove and worked withrounded or V edges, striated, or grooved.Design resistance. Resistance (force or moment as appropriate)provided by member or connection; the productof adjusted resistance, the resistance factor, and time-effectfactor.Design span. For simple, continuous, and cantileverbeams, the design span is the clear span plus one-half therequired bearing length at each support.Design strength. Material strength (tensile, compressive,etc.) derived in accordance with ASTM 5457-93 proceduresand adjusted to reflect end-use conditions.Diaphragm. A sheathed horizontal or nearly horizontalsystem (e.g., roof, floor) acting to transfer lateral forcesto the vertical resisting elements.AMERICAN FOREST & PAPER ASSOCIATION

viDiaphragm boundary. A location where shear is transferredinto or out of the diaphragm sheathing. Transfer iseither to a boundary element or to another force resistingelement. Also applied to shear walls.Diaphragm chord. A diaphragm boundary element perpendicularto the applied load which is assumed to takeaxial stresses analogous to the flanges of a beam. Alsoapplied to shear walls.Dowel bearing strength. The maximum compressionstrength of wood or wood-based products when subjectedto bearing by a steel dowel of specific diameter.Dowel-type fasteners. Includes bolts, lag screws, woodscrews, nails, and spikes.Drag strut (collector, tie, diaphragm strut). A shearwall or diaphragm boundary element parallel to the appliedload which collects and transfers diaphragm shearforces to the vertical resisting elements or distributes forceswithin the diaphragm.Dry service. Structures wherein the maximum equilibriummoisture content does not exceed 19%.Edge distance. The distance from the edge of the memberto the center of the nearest fastener, measuredperpendicular to grain. When a member is loaded perpendicularto grain, the loaded edge shall be defined asthe edge in the direction toward which the fastener is acting.Edgewise bending. Bending about the strong axis.Effective width. In sheathing, the reduced width that,with an assumed uniform stress distribution, produces thesame effect on the behavior of a structural member as theactual plate width with its nonuniform stress distribution.End distance. In the case of square-cut ends, the distancemeasured parallel to grain from the end of themember to the center of the nearest fastener.Equilibrium moisture content. A moisture content atwhich wood neither gains nor loses moisture to the surroundingair.Exposure durability. A classification of panels basedon raw material composition and adhesive bond durability.Exposure 1 - Panels suitable for protected constructionand industrial uses. Exposure 1 panels have adequate durabilityto resist moisture exposure due to long constructiondelays, or other conditions of similar severity.Exposure 2 or IMG (intermediate glue) - Panels suitablefor protected applications that are not continuouslyexposed to high humidity conditions.Exterior - Panels suitable for permanent exposure toweather or moisture.Interior - Panels suitable for permanently protected interiorapplications.Factored load. The product of the nominal load and anapplicable load factor.Fastener. Generic term for individual mechanical devicessuch as bolts, nails, metal plates, etc., used in a connection.Synonymous with connector.Fiber saturation point. The moisture content at whichthe cell walls are saturated with water (bound water) andno water is held in the cell cavities by capillary forces. Itis species dependent and usually is taken as 25% to 30%moisture content, based on weight when ovendry.Fire-retardant treated wood. Any lumber or wood productimpregnated with chemicals by a pressure process, orby other means, meeting prescribed requirements for resistanceto flame spread and resistance to progressivecombustion.Flatwise bending. Bending about the weak axis.Gage or row spacing. The center-to-center distance betweenfastener rows or gage lines.Glued laminated timber (glulam). See structural gluedlaminated timber.Grade. The classification of structural wood productswith regard to strength and utility in accordance with thegrading rules of an approved agency.Grading rules. Requirements and specifications for themanufacture, inspection, and grading of designated speciesof lumber.Green lumber. Lumber of less than nominal 5-in. (127mm) thickness that has a moisture content in excess of19%. For lumber of nominal 5-in. (127 mm) or greaterAMERICAN WOOD COUNCIL

viithickness (timbers), green shall be defined in accordancewith the provision of the applicable lumber grading rulescertified by the ALSC Board of Review.Horizontal diaphragm. A sheathed horizontal or nearlyhorizontal element (roof, floor) acting to transfer lateralforces to the vertical resisting elements.I-beams. Wood I-beams are custom designed and fabricatedfor specific applications. Lumber flanges and panelwebs are bonded with adhesives to form “I”, multiweb, orbox sections. The design of wood I-beams is in accordancewith App. A6 of this standard.I-joists (prefabricated). Structural members manufacturedusing sawn or structural composite lumber flangesand structural panel webs, bonded together with waterproofadhesives, forming an “I” cross-sectional shape. Thedesign of I-joists is in accordance with ASTM D5055-94.Joist (lumber). Pieces (nominal dimensions 2 to 4 in.(51 to 102 mm) in thickness by 5 in. (127mm) and widerwith rectangular cross-section graded primarily with respectto strength in bending when loaded on the narrowface. Typically used as framing members for floor or ceilings.Kiln dried. Lumber that has been seasoned in a chamberto a predetermined moisture content by applying heat.Laminated veneer lumber (LVL). A composite of woodveneer sheet elements with wood fibers primarily extendedalong the length of the member. Veneer thickness doesnot exceed 0.25 in. (6.4 mm).Limit state. A condition in which a structure or componentis judged either to be no longer useful for its intendedfunction (serviceability limit state) or to be unsafe (strengthlimit state).Load duration (time-effect). The period of continuousapplication of a given load, or the cumulative period ofintermittent applications of the maximum load.Load factor. A factor that accounts for unavoidable deviationsof the actual load from the nominal value and foruncertainties in the analysis that transforms the load intoa load effect.Load sharing. The load redistribution mechanism amongparallel components constrained to deflect together orjoined by crossing members such as sheathing or decking.Load/slip constant. The ratio of the applied load to aconnection and the resulting lateral deformation of the connectionin the direction of the applied load.LRFD (Load and Resistance Factor Design). A methodof proportioning structural components (members, connectors,connecting elements, and assemblages) using loadand resistance factors such that no applicable limit stateis reached when the structure is subjected to all appropriateload combinations.Lumber. The product of the sawmill and planing millusually not further manufactured other than by sawing,resawing, passing lengthwise through a standard planingmachine, cross-cutting to length, and matching.Lumber Sizes. Lumber is typically referred to by sizeclassifications. Two of the frequently used size classificationsare dimension and timbers. Additionally, lumberis specified by manufacturing classification. Rough lumberand dressed lumber are two of the routinely usedmanufacturing classifications.Boards. Lumber of less than nominal 2 in. (51 mm) thicknessand of nominal 2 in. (51 mm) or greater width.Dimension. Lumber from nominal 2 in. through 4 in. (51mm through 102 mm) thick and nominal 2 or more in. (51or more mm) wide.Dressed size. The dimensions of lumber after surfacingwith a planing machine. Usually 1/2 to 3/4 in. (12.7 to19.0 mm) less than nominal size. The American SoftwoodLumber Standard lists standard dressed sizes.Rough lumber. Lumber that has not been dressed (surfaced)but that has been sawed, edged, and trimmed atleast to the extent of showing saw or other primary manufacturingmarks in the wood on the four longitudinalsurfaces of each piece for its overall length. Lumber surfacedon one edge (S1E), two edges (S2E), one side (S1S),or two sides (S2S) is classified as rough lumber in theunsurfaced width or thickness.Timbers. Lumber of nominal 5 in. (127 mm) or greaterin least dimension.Stress-graded lumber. Lumber graded for its mechanicalproperties.AMERICAN FOREST & PAPER ASSOCIATION

viiiMachine evaluated lumber (MEL). Lumber that hasbeen nondestructively evaluated by mechanical gradingequipment. Each piece is evaluated and marked to indicateits strength classification. MEL lumber is alsorequired to meet certain visual requirements.Machine stress-rated (MSR) lumber. Lumber that hasbeen evaluated by mechanical stress-rating equipment.Each piece is nondestructively tested and grademarked toindicate the assigned bending strength and modulus ofelasticity. MSR lumber is also required to meet certainvisual requirements.Main member. In three-member connections, the centermember. In two-member connections, the thicker member.Mat-formed panel. A structural-use panel designationrepresenting panels manufactured in a matformed process,such as oriented strand board and wafer board.Moisture content. The weight of the water in wood expressedas a percentage of the weight of the wood fromwhich all water has been removed (ovendry).Nominal loads. The loads specified by the applicablecode.Nominal size. The approximate commercial size by whichlumber products are known and sold in the market. Thenominal size is generally greater than the actual dimensions,i.e., a dry 2 x 4 is surfaced to 1½ in. by 3½ in. (38mm by 89 mm).Oriented strandboard. A mat-formed structural-usepanel comprised of thin rectangular wood strands arrangedin cross-aligned layers with surface layers normally arrangedin the long panel direction and bonded withwaterproof adhesive.Ovendry wood. Wood dried until it is free of any moisture.Panel. A sheet-type wood product.Panel rigidity. Shear rigidity of a panel, the product ofpanel thickness and modulus of rigidity.Panel shear. Shear developed in a structural-use paneldue to in-plane loads, commonly called “shear throughthe thickness and is developed in shear walls, diaphragms,and webs of I-joists.Panel stiffness. Flexural or axial stiffness of a panel.The product of panel section property and modulus of elasticity.Parallel strand lumber (PSL). A composite of woodstrandelements with wood fibers primarily oriented alongthe length of the member. The least dimension of thestrands is not greater than 0.25 in. (6.4 mm) and the averagelength is not less than 150 times the least dimension.Performance rating. A classification designating enduseapplications for which specific performance testprocedures and criteria have been established.Performance standard. A standard for trademarkedproducts based on performance. Performance is measuredby tests that approximate end-use conditions.Pile. Round timber structural element of any size or length,that is driven or otherwise introduced into the soil for thepurpose of providing vertical or lateral support.Pitch or spacing. The longitudinal center-to-center distancebetween any two consecutive holes or fasteners in arow.Planar shear. The shear developed in structural-use panelsdue to flatwise bending, commonly referred to as“rolling shear” in plywood.Plank. A piece of lumber, from 2 to 4 in. (51 to 102 mm)thick, used with the wide face placed horizontally (differsfrom joist only that latter is used on edge).Ply. A single sheet of veneer, or several strips laid withadjoining edges that form one veneer lamina in a gluedplywood panel.Plywood. A structural-use panel comprised of plies ofwood veneer arranged in cross-aligned layers. The pliesare bonded with an adhesive that cures on application ofheat and pressure.Pole. A round timber of any size or length, usually usedwith the larger end in the ground.Pole construction. A form of construction in which theprincipal vertical members are round poles or sawn timbers(post-frame construction) embedded in the groundand extending vertically above ground to provide bothfoundation and vertical framing for the structure.AMERICAN WOOD COUNCIL

ixPrefabricated wood I-joists. Pre-engineered proprietarystructural members that are mass produced to establishedspecifications. An “I” cross-section is formed from sawnor structural composite lumber flanges and structural panelwebs, bonded together with exterior exposure adhesives.These are used primarily as joists in floor and roof constructionwith their engineering properties determined inaccordance with ASTM D5055-94.Preservative. A chemical that, when suitably applied towood, makes the wood resistant to attack by fungi, insects,marine borers, or weather conditions.Pressure-preservative treated wood. Wood productspressure-treated by an approved process and preservative.Primary panel (strong) axis. The axis correspondingwith the primary strength direction of structural use panels.Unless otherwise indicated (marked) on the panel,the primary strength axis is in the panel length direction.Punched metal plate. A light steel plate fastening havingpunched teeth of various shapes and configurationswhich are pressed into wood members to effect shear transfer.Used with structural lumber assemblies.Purlin. A roof framing member, perpendicular to thetrusses or rafter members, which supports the roof sheathingor other common rafter members.Rated panel. A panel rated for conventional floor, roof,and wall applications.Reference end use conditions (reference conditions).Assume standard end-use conditions. Adjustments to resistancesare required if design end-use conditions differfrom the reference end-use conditions.Reference resistance. The resistance (force or momentas appropriate) of a member or connection computed atthe reference end-use conditions prescribed by this standard.Reference strength. Material strength (tensile, compressive,etc.) derived in accordance with ASTM D5457-93procedures.Repetitive member assembly. A system of closelyspaced parallel framing members, which exhibits loadsharingbehavior.Required member resistance. Load effect (force, moment,or stress, as appropriate) acting on an element orconnection, determined by structural analysis from the factoredloads and the critical load combinations.Resistance. The capacity of a structure, component, orconnection to resist the effects of loads. It is determinedby computations using specified material strengths, dimensions,and formulas derived from accepted principles ofstructural mechanics, or by field or laboratory tests ofscaled models, allowing for modeling effects and differencesbetween laboratory and field conditions.Resistance factor. A factor that accounts for unavoidabledeviations of the actual strength from the nominalvalue and the manner and consequences of failure.Row of fasteners. Two or more fasteners aligned withthe direction of load.Scarf joint. A slope overlapping joint bonded with anadhesive.Seasoned lumber. Lumber that has been dried. Seasoningtakes place by open-air drying within the limits ofmoisture contents attainable by this method, or by controlledair drying (i.e., kiln drying).Secondary panel (weak) axis. The axis correspondingwith the secondary strength direction of structural-use panels.Unless otherwise indicated (marked) on the panel,the secondary strength axis is in the panel width direction.Serviceability limit state. A limiting condition affectingthe ability of a structure to preserve its appearance, maintainability,durability, or the comfort of its occupants orfunction of machinery under normal usage.Shear plate. A circular metal plate that, by being embeddedin adjacent wood faces, or in one wood face, acts inshear to transmit loads from one timber to a bolt and, inturn, to a steel plate or another shear plate.Shear wall (vertical diaphragm). A sheathed wall elementthat transfers in-plane lateral forces to the base ofthe wall.Sheathing. Lumber or panel products that are attached toparallel framing members, typically forming wall, floor,ceiling, or roof surfaces.AMERICAN FOREST & PAPER ASSOCIATION

xShrinkage. The decrease in the dimensions of woodcaused by a decrease of moisture content.Side member. The member or connection element adjacentto the main member.Slenderness ratio for beams. The ratio used in lateralstability calculations for bending members.Slenderness ratio for compression members. The ratioof the effective length of a compression member to itsradius of gyration.Spaced column. A column with two or more individualmembers, usually rectangular and with their wide facesparallel, placed with their longitudinal axes parallel, spacedat their ends and in the midlength region by blocking, andjoined at their ends by the end blocks with split rings orshear plates of sufficient shear stiffness to effectively restrainthe column ends.Span rating. A panel index number identifying the recommendedmaximum center-to-center support spacing ininches for roof, floor, and wall applications under normaluse conditions.Specific gravity. The ratio of the ovendry weight of asample to the weight of a volume of water equal to thevolume of the sample at some specified moisture content,as green, air-dry, or ovendry.Split ring. A metal ring that, by being embedded intoadjacent faces of two wood members, acts in shear to transmitforce between the members.Stiffener (web). A piece of wood that is glued or otherwisefastened to the webs between the inner surfaces ofthe top and bottom flanges of a built-up beam.Strength limit state. A limiting condition affecting thesafety of a structure, a structural component, or a mechanicalconnection.Stress grades. Lumber grades having assigned designstress and modulus of elasticity values in accordance withaccepted basic principles of strength grading.Stressed skin panel. A form of construction in which theouter skin, in addition to its normal function of providinga surface covering, acts integrally with the frame memberscontributing to the strength of the unit as a whole.Structural composite lumber (SCL). In this standard,structural composite lumber is either laminated veneerlumber (LVL) or parallel strand lumber (PSL). These materialsare intended for structural use and are bonded withan exterior adhesive.Structural glued laminated timber. An engineered,stress-rated product of a timber-laminating plant comprisingassemblies of specially selected and prepared woodlaminations securely bonded together with adhesives. Thegrain of all laminations is approximately parallel longitudinally.They comprise pieces end joined to form anylength, pieces placed or glued edge-to-edge to make widerones, or pieces bent to curved form during gluing.Structural-use panel. A wood-based panel productbonded with a waterproof adhesive. Included under thisdesignation are plywood, oriented strand board, and compositepanels. These panel products meet the requirementsof PS 1-94 or PS 2-92 and are intended for structural usein residential, commercial, and industrial applications.Stud. Used for vertical framing members in interior orexterior walls of a building, usually 2 x 4 or 2 x 6 sizesand precision end trimmed.Time-effect factor. A factor applied to adjusted resistanceto account for effects of duration of load (refer toload duration).Tie down. An anchoring device for a shear wall boundaryelement that resists overturning of the wall.Unbraced length. The distance between braced pointsof a member, measured between the centers of gravity ofthe bracing members.Veneer. Thin wood sheet (ply) from which plywood orother wood products are manufactured, referred to as pliesin the glued panel.Visually stress-graded lumber. Structural lumber thathas been graded visually to limit strength-reducing andappearance characteristics. Assigned design values arebased on the effect of the strength limiting visual characteristics.Wet service. Structures wherein the maximum equilibriummoisture content exceeds 19%.AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION11INTRODUCTION1.1 General Information 21.1.1 Load and Resistance FactorDesign 21.1.2 Load Combinations and LoadFactors 31.1.3 Resistance Factors 31.1.4 Time Effect Factors 31.1.5 Reference Conditions 31.2 Design Responsibilities 41.2.1 Bracing 41.3 Other Design Considerations 41.3.1 Serviceability 41.3.2 Designing for Permanence 41.3.3 Designing for Fire Safety 51.4 Products Covered in This Manual 91.4.1 Products Included 9AMERICAN FOREST & PAPER ASSOCIATION

2 INTRODUCTION1.1 General InformationThis manual is organized as a multi-part package formaximum flexibility for the design engineer. All generaldesign information, design equations, specification language,and commentary are organized by member type(tension, bending, etc.) and are included in this volume.Actual design values and design aids are packaged separatelyon a product-specific basis in a complete set ofdesign supplements and guideline documents.Each chapter in this manual follows certain conventions.Each chapter starts with a section entitled “GeneralInformation” that prepares the reader for the type of informationto be expected within that chapter. After thechapter-specific information, the chapter ends with achecklist section that is used to identify reference conditionsfor this case, followed by one or more designexamples.The numbering of Chapters 3 through 9 correspondto chapters of the same numbers in AF&PA/ASCE 16-95,Standard for Load and Resistance Factor Design (LRFD)for Engineered Wood Construction.Chapter 10, Reference Information, includes not onlythe typical reference information for a handbook of thistype, but also includes flowcharts of the design processesand alternatives in Chapters 3 through 9.AF&PA/ASCE 16-95 along with its Commentary isreproduced in its entirety following Chapter 10 of thisManual. This is provided for convenience to the user.The user will note that design values throughout thisLRFD package are stated in ksi or kips per square inchrather than in the more familiar psi or pounds per squareinch. The reason for this departure from current units isto minimize confusion of design values between AllowableStress Design (ASD) and LRFD. The developers ofthe LRFD format debated other solutions, such as introducingcompletely different notation for LRFD-relateddata. However, the other solutions all proved to be muchless “user-friendly” for designers than the simple restatementof units.The user will also note that this design package definesseveral widely-used LRFD terms as follows:Resistance refers to the capacity of the member. Examplesinclude moment resistance (kip-ft), tensionresistance (kips), etc. Tabulated resistances are found inthe selection tables in the supplements, and are tabulatedas factored resistances (specific time effect factors, 8, andresistance factors, N, are included).Strength refers to the material property value -- thestrength values are the LRFD-equivalent of an allowablestress value. Example reference strengths (i.e., based onreference conditions) include bending strength (ksi), connectionlateral strength (kips), etc. Reference strengthvalues are also found in the supplements.1.1.1 Load and Resistance FactorDesignLoad and Resistance Factor Design (LRFD) hasevolved to become the preferred format for convertingstructural design standards to a so-called limit states approach.This section provides a brief discussion of LRFDand reassures engineers that this technique is simply analternative way of quantifying the concepts of safety factors.Although the underlying mathematics are fairlycomplex, none of these complexities are required in thedesign procedures. In fact, many of the design equationsare actually simpler to use than their Allowable StressDesign counterparts.Reliability-Based DesignTheoretical reliability-based analysis has been usedfor many years in the electronics and aerospace industries.In both of these industries the relative ease ofcomponent reliability assessment and reasonably low costof design redundancy made reliability-based design ahighly successful product development strategy.The extension of theoretical reliability concepts tobuilding applications has proven to be somewhat moredifficult. The primary source of this difficulty lies in therelatively uncontrolled nature of so many facets of constructedfacilities. The electronics engineer designs andbuilds a specific system out of precisely manufactured andassembled components that face well-defined bounds of“loading” over the product’s lifetime. Compare this withthe building designer who designs a facility for only theinitial occupancy type, using materials supplied by outsidemanufacturers and constructed by a broad range ofsubcontractors. The mathematics of reliability are thesame for both designers. However, many engineers believethat unknown and unknowable factors dominate theactual “in-place” reliability of a building more than thosefactors that can be quantified.With these thoughts in mind, the writers of AF&PA/ASCE 16-95 deliberately chose to develop a design procedurethat mixes some elements of theoretical reliabilitywith large quantities of engineering judgment.Specifically, AF&PA/ASCE 16-95 and its supportingASTM standards completely adopt the reliability refinementsembodied in the load factors of ASCE 7-93,Minimum Design Loads for Buildings and Other Structures.The procedures in ASTM D5457-93, StandardAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 3Specification for Computing the Reference Resistance ofWood-Based Materials and Structural Connections forLoad and Resistance Factor Design, are consistent withother standards in their use of reliability concepts only inthe background calculations. The design equations includethe end result of these calculations in the load factorsand the resistance factors.Nearly all of today’s (i.e., ASD) standard design formulaeand adjustment factors are directly applicable foruse in LRFD, leading to maximum consistency betweenthe familiar design concepts of Allowable Stress Designand the new LRFD procedures.Basic LRFD EquationsThe basic design equation for LRFD, as with all engineeringsafety checking equations, requires that thespecified product strength or resistance meet or exceedthe stress or other effect imposed by the specified loads.In ASD, the permissible stress levels are set very low andthe load magnitudes are set at once in a lifetime levels.This combination produces designs that maintain highsafety levels yet remain economically feasible. In LRFDthe basic design equation follows a similar format, in whichthe factored resistance must be greater than or equal to thefactored load effects.From a user’s standpoint, the design process is similarto ASD. The most obvious difference between LRFDand ASD is that both the resistance and load effect valuesin LRFD will be numerically much higher than in ASD.The resistance values are higher because they are verynear test magnitudes rather than being reduced by a significantinternal safety factor.The load effects are higher because they are multipliedby load factors in the range of 1.2 to 1.6.1.1.2 Load Combinations and LoadFactorsThe load combination equations for use with LRFDare given in AF&PA/ASCE 16-95 Sec. 1.3.2:1.4 D (1.3-1)1.2 D + 1.6 L + 0.5 (L ror S or R) (1.3-2)1.2 D + 1.6 (L ror S or R) + (0.5 L or 0.8 W) (1.3-3)1.2 D + 1.3 W + 0.5 L + 0.5 (L ror S or R) (1.3-4)1.2 D + 1.0 E + 0.5 L + 0.2 S (1.3-5)0.9 D - (1.3 W or 1.0 E) (1.3-6)Refer to AF&PA/ASCE 16-95 and its commentary foradditional details about application of these equations.The load factors in these equations are intended toprovide a consistent level of reliability across a range ofratios of the various load types.1.1.3 Resistance FactorsTo provide additional flexibility in achieving consistentreliability across a range of product applications,resistance factors are applied to the reference resistancevalues. Resistance factors (N) are always less than unity.The magnitude of a resistance factor represents the relativereduction required to achieve comparable reliabilitylevels.AF&PA/ASCE 16-95 provides the following resistancefactors for wood-based products and connections:Compression φ c= 0.90Flexure φ b= 0.85Stability φ s= 0.85Tension φ t= 0.80Shear/Torsion φ v= 0.75Connections φ z= 0.65These factors provide roughly equivalent reliabilityamong different stress modes for a given product type.1.1.4 Time Effect FactorsThe time effect factor (8) is the LRFD-equivalent ofthe load duration factor in Allowable Stress Design. Timeeffect factors are tabulated in Table 1.4-2 for each loadcombination equation. The factors were derived based onreliability analysis that considered variability in strengthproperties, stochastic load process modeling and cumulativedamage effects. Because reference strengths are basedon short-term test values, time effect factors equal unityfor load combinations in which no cumulative damageoccurs. Time effect factors range in value from 1.25 for aload combination controlled by impact loading to 0.6 fora load combination controlled by permanent dead load.Examination of Table 1.4-2 from AF&PA/ASCE 16-95reveals that common building applications will likely bedesigned for time effect factors of 0.80 for gravity loaddesign (AF&PA/ASCE 16-95 Eq. 1.3-2 under occupancyfloor load and 1.3-3) and 1.0 for lateral load design(AF&PA/ASCE 16-95 Eq. 1.3-4, 1.3-5 and 1.3-6).1.1.5 Reference ConditionsReference conditions have been defined such that amajority of wood products used in interior or in protected1INTRODUCTIONAMERICAN FOREST & PAPER ASSOCIATION

4 INTRODUCTIONenvironments will require no adjustment for moisture, temperatureor treatment effects.Moisture reference conditions are identical to thosein Allowable Stress Design. These include moisture contents19% or less for sawn lumber products. Theequivalent limit for glued products (glulam, structural compositelumber, I-joists, panel products) is defined as 16%MC or less.Temperature reference conditions are also identicalto those in Allowable Stress Design. These include sustainedtemperatures up to 100 o F. Note that it has beentraditionally assumed that these reference conditions alsoinclude common building applications in desert locationswhere daytime temperatures will often exceed 100 o F.Examples of applications that may exceed the referencetemperature range include food processing or other industrialbuildings.1.2 Design ResponsibilitiesStructural wood products are provided to serve a widerange of end uses. Some products are marketed throughcommodity channels where the products meet specificstandards and the selection of the appropriate product isthe responsibility of the user.Other products are custom manufactured to meet thespecific needs of a given project. Products that often fallinto this category are prefabricated trusses and customglulam members. Design of the individual members isbased on criteria specified by the architect or engineer ofrecord on the project. Manufacture of these products isperformed in accordance with the product’s manufacturingstandards. Engineering of these products normallyonly extends to the design of the products themselves.Construction-related issues such as load path analysis anderection bracing remain the responsibility of the professionalof record for the project.1.2.1 BracingDesign considerations related to both temporary andpermanent bracing differ among product types. Specificdiscussion of bracing is included in the product supplementor guideline.1.3 Other Design ConsiderationsMuch of this manual focuses on building design fromthe perspective of structural engineering design. Whiledesign against structural collapse remains the primarypurpose of structural design, engineers must also considerhow their design will perform from the perspective of serviceability,durability and fire safety. While each of thesetopics could easily fill a book themselves, this section providesan introduction to each topic and some brief guidancefor the designer.1.3.1 ServiceabilityIn addition to designing buildings for strength limitstates, designers must determine whether any special serviceabilitylimit states must be considered for a givenapplication. The most common serviceability limit usedin the design of typical wood-framed buildings is a limitationon the deflection of roof or floor members. Thebuilding codes have traditionally defined these limits as aratio of the member span. For example, limits of R/360computed under live load or R/240 under total load arecommon for floors.While the traditional static deflection limits were originallyintended to limit cracking of brittle finish materials,they have served equally well in short span applicationsto limit vibration problems. As engineered wood productshave evolved to span longer distances with lighterweight members, it has become increasingly common formanufacturers to recommend more stringent deflectioncriteria. The user is directed to the product supplementsand guidelines for additional information on specific products.For applications that might be particularly sensitiveto vibration considerations, the user is directed to AF&PA/ASCE 16-95 Chapter 10 Commentary.1.3.2 Designing for PermanenceWood has a feature that is unique among constructionmaterials. It retains its structural integrity indefinitelywhen maintained in a dry condition, and becomes com-AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 5pletely biodegradable (over time) when exposed to wetconditions. It is the goal of designers to detail their structureso that the wood remains serviceable for the life ofthat structure.Good construction details prevent deterioration ofwood frame structures. When such details are ignored,decay or termite damage may occur. Naturally durable orpressure treated wood assures satisfactory performanceunder adverse conditions.Decay is caused by fungi which are low forms of plantlife that feed on wood. For fungi to attack wood in serviceall the following conditions must be present: (1)temperature in the range of 35 to 100 o F, (2) adequate supplyof oxygen, and (3) wood moisture content in excess of20%.The foregoing requirements for growth of fungi indicatea method to prevent decay in structures. Temperature,except in arctic climates, is impractical to control. Lackof sufficient oxygen to support decay occurs only whenwood is completely below the ground water line or continuouslysubmerged in fresh water. Control of moisturecontent of wood is a practical and effective method forprevention of decay.The subterranean termite is an insect which attacks incolonies and derives its nourishment from cellulosic materialssuch as wood, fabric, paper and fiber board. Thetermite may attack wood frame structures above the groundby means of shelter tubes attached to foundation walls,piers and other members in contact with the ground. However,only under conditions which permit the insect toestablish and maintain contact with soil moisture, is acolony able to penetrate and consume wood in service.Thus, a barrier separating wood from earth, supplementedby inspection, is a practical and effective method for preventingdamage by termites.Principles of Good ConstructionProtection of wood frame structures to provide maximumservice-life involves three methods of control whichcan be handled by proper design and construction. Oneor more of the following methods may be employed: (1)control moisture content of wood, (2) provide effectivetermite barriers, (3) use naturally durable or preservativelytreated wood.Wood construction maintained at a moisture contentof 20% or less will not decay. Optimum conditions fordecay occur when the moisture content is above 25%. Itshould be stressed that when wood is protected from wateror from vapor condensation, and exposed to normalatmospheric conditions such as exist inside buildings andoutdoors, its moisture content rarely exceeds 15%. Therefore,moisture content control by means of accepted designand construction details is a simple and practical methodof providing protection against decay.While moisture control also contributes to preventionof subterranean termite attack, the primary control methodrequires use of effective barriers supplemented by periodicinspection. Termite barriers are provided by the useof accepted construction practices which drive termitesinto the open where shelter tubes can be detected by inspectionand destroyed.Wood frame structures provided with a recognizedbarrier supplemented by periodic inspection can be permanentlyensured against subterranean termite attack.Architectural consideration or use exposures (swimmingpools, marine structures, wet process industries,ground contact, unusual climatic conditions) may not permitmoisture or termite control by design and construction techniquesalone. Also, experience in certain geographicalregions may indicate the need for greater protection. Underthese circumstances naturally durable wood of certainspecies may be used, or wood may be pressure treatedwith preservatives to prevent decay and termite damage.General Recommendations for Good ConstructionRecommendations provided for good construction willassure basic resistance to decay. Due to climatic conditionsor geographical location, additional control measuresmay be required in some buildings or structures.Control of decay or termite attack is accomplishedprimarily through application of four fundamental constructionpractices:1. Positive site and building drainage.2. Adequate separation of wood elements from knownmoisture sources to (a) prevent excessive absorption,(b) allow for periodic inspection, and (c) provide thenecessary physical barrier for termite protection.3. Use of naturally durable or pressure treated wood whereindicated. See product-specific recommendations regardingproper procedures for preservative treatmentof that product.4. Ventilation and condensation control in enclosed spaces.These construction practices eliminate the danger ofdecay or subterranean termite damage. They also serveto control damage from other insects present in limitedgeographical areas.1.3.3 Designing for Fire SafetyThe model building codes in the U.S. cover virtuallyevery safety-related topic related to the construction ofbuildings, and fire-related issues comprise a surprisingly1INTRODUCTIONAMERICAN FOREST & PAPER ASSOCIATION

6 INTRODUCTIONlarge portion of the model codes. Designing for fire safetyis a complex and multifaceted issue. The following informationprovides an overview of the subject:To provide fire safety in any structure, many approachesare considered. This involves a combination of(1) preventing fire occurrence, (2) controlling fire growth,and (3) providing protection to life and property. All needsystematic attention to provide a high degree of economicalfire safety. The building design professional can controlfire growth within the structure by generating plans thatinclude features such as protecting occupants, confiningfire in compartment areas, and incorporating fire suppressionand smoke or heat venting devices at critical locations.Controlling construction features to facilitate rapidegress, protection of occupants in given areas, and preventingfire growth or spread are regulated by codes as afunction of building occupancy. If the design professionalrationally blends protection solutions for these items withthe potential use of a fire-suppression system (sprinklers,for example), economical fire protection can be achieved.Although attention could be given to all protectiontechniques available to the building design professional,the scope here is limited to the provisions that prevent firegrowth and limit the fire to compartments of origin.PlanningGenerating the plans for a building of prescribed occupancyis a challenge because of the varying requirementsof three major regional building codes: Building OfficialsConference of America (BOCA), International Conferenceof Building Officials (ICBO), and Southern Building CodeCongress International, Inc. (SBCCI). As a first step, theauthority having jurisdiction where a proposed buildingis to be constructed must be consulted for the requirementsof the specific design project. This normallyconcerns the type of construction desired as well as allowablebuilding areas and heights for each constructiontype.Building construction is generally classified into typessuch as wood frame, noncombustible wall-wood joist, andheavy timber. Wood frame construction is defined as havingexterior walls, bearing walls, partitions, floors androofs of wood stud and joist framing of 2-in. nominal dimension.These are divided into two subclasses that areeither protected or unprotected construction. Protectedconstruction calls for having load-bearing assemblies ofone-hour fire endurance.Noncombustible wall-wood joist types of constructionhave exterior walls of noncombustible materials androofs, floors, and interior walls and partitions of woodframe. As in wood frame construction, these are dividedinto two subclasses that are either protected or unprotected.Heavy timber construction includes exterior walls ofnoncombustible materials and columns, floors, roofs, andinterior partitions of wood of a minimum size, as follows:Table 1.3-1. Minimum Sizes to Qualifyas Heavy Timber ConstructionMaterialRoof decking:Lumberor wood structuralpanelsFloor decking:Lumberor flooringor wood structuralpanelsRoof framing:Floor framing:Columns:Minimum size(nominal size or thickness)2 in. thicknessl-l/8 in. thickness3 in. thickness1 in. thickness1/2 in. thickness4 by 6 in.6 by 10 in.8 by 8 in. (supporting floors)6 by 8 in. (supporting roofs)Noncombustible construction is generally required tobe of noncombustible materials having fire-endurance ratingsof up to 4 hours, depending on the size and locationof the building. Some circumstances provide for the useof wood in the walls of noncombustible wall-wood joistand noncombustible types of construction. For example,the Uniform Building Code allows the use of fire-retardanttreated wood framing for nonbearing walls if such wallsare more than 5 feet from the property line. Exceptions to theuse of noncombustible materials in the noncombustible-typebuildings are sometimes made for heavy timber members.Heavy timber members can often be used for roof membersmore than 25 feet above the floor, balcony, or galleryin one-story noncombustible-type buildings.Besides having protected and unprotected subclassesfor each building type, increases in floor area and heightof the building are allowed when sprinkler protection systemsare included. For example, protected wood frameeducational occupancies can be increased from two to threestories in height because of the presence of sprinklers.Also, the floor area in the first two stories may be doubledor even tripled under some conditions.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 7Fire-rated AssembliesThe previous section explained that some occupanciesrequire the use of fire-rated assemblies or membersto prevent collapse or fire spread from one compartmentof a building to another or from one building to another.Members and assemblies are rated for their abilityeither to continue to carry design loads during fire exposureor to prevent the passage of fire through them. Suchratings are arrived at either by calculation or experimentfor both members and assemblies. The fire exposure isdefined as that given in ASTM E119. A one-hourfire-resistance rating for wall, floor, and floor-ceiling assembliesincorporating nominal two-inch structural lumbercan be accomplished through the use of noncombustiblesurfaces (such as gypsum wallboard). However, fasteningof these surface materials is critical for ceilingmembranes and is carefully specified. For some woodassemblies, two-hour ratings have been achieved.Experimental ratings are also obtained independentlyon assemblies and members by materials and structuralmember producers. For a given assembly type incorporatingproprietary components, the company supplying thecomponent can be contacted to obtain the fire rating ofthe assembly. Typically rated floor-ceiling assemblies forvarious products are provided in the product supplementsor guidelines.Analytically RatedIn lieu of experimentally rating the fire endurance ofmembers and assemblies, major building codes will acceptengineering calculations of the expected fireendurance, based upon engineering principles and materialproperties. This applies to the rating of previously1INTRODUCTIONAMERICAN FOREST & PAPER ASSOCIATION

8 INTRODUCTIONuntested members or assemblies, or in cases where it isdesired to substitute one material or component for another.Although calculation procedures may be conservative,they have the advantage of quickly rating an assembly ormember and allowing interpolation or some extrapolationof expected performance. Additional details regardingthe analytical approach are provided in AF&PA’s DCANo. 4 - CAM for Calculating and Demonstrating AssemblyFire Endurance.Beams and ColumnsHeavy timber construction has traditionally been recognizedto provide a fire-resistant building. This isprimarily due to the large size of the members, the connectiondetails, and the lack of concealed spaces. Such aconstruction type has often satisfied the fire-resistive requirementin all building codes by simple prescription.Although heavy timber construction has not been “rated”in the United States, Canada has assigned it a 45-minutefire-endurance rating.Using calculations, glulam timber columns and beamscan be designed for desired fire-endurance ratings. Additionaldetails regarding the analytical approach areprovided in AF&PA’s DCA No. 2 - Design of Fire-ResistiveExposed Wood Members.Fire and Draft StoppingIn all construction types, no greater emphasis can beplaced on the control of construction to reduce the firegrowth hazard than the emplacement of fire and draft stopsin concealed spaces. The spread of fire and smoke throughthese concealed openings within large rooms or betweenrooms is a continuous cause of major life and propertyloss. As a result, most building codes enforce detailing offire blocking and draft stopping within building plans. Fireblocking considered acceptable are (1) two-inch nominallumber, (2) two thicknesses of two-inch nominal lumber,and (3) one thickness of 3/4-inch plywood, with jointsbacked with 3/4-inch plywood.Draft stopping does not require fire resistance of fireblocking. Therefore, draft stopping material is not requiredto be as thick. Typical draft stop materials and their minimumthicknesses are (1) l/2-inch gypsum wallboard and(2) 3/8-inch plywood. Building codes consider an areabetween draft stops of 1,000 square feet as reasonable.Concealed spaces consisting of open-web floor truss componentsin protected floor-ceiling assemblies are animportant location to draft-stop parallel to the component.Areas of 500 square feet in single-family dwellings and1,000 square feet in other buildings are recommended,and areas between family compartments are absolutelynecessary. Critical draft stop locations are in the concealedspaces in floor-ceiling assemblies and in attics of multifamilydwellings when separation walls do not extend tothe roof sheathing above.Other important locations to fire block in wood frameconstruction are in the following concealed spaces:1. Stud walls and partitions at ceiling and floor levels.2. Intersections between concealed horizontal and verticalspaces such as soffits.3. Top and bottom of stairs between stair stringers.4. Openings around vents, pipes, ducts, chimneys (and fireplacesat ceiling and floor levels) with noncombustiblefire stops.Flame SpreadRegulation of materials used on interior building surfaces(and sometimes exterior surfaces) of other than oneandtwo-family structures is provided to minimize thedanger of rapid flame spread. ASTM E84 gives the methodused to obtain the flame-spread property for regulatorypurposes of paneling materials. Materials are classifiedas having a flame spread of more or less than that of redoak, which has an assigned flame spread of 100. A noncombustibleinorganic reinforced cement board has anassigned flame spread of zero. A list of accreditedflame-spread ratings for various commercial woods andwood products is given in AF&PA’s DCA No. 1 - FlameSpread Performance of Wood Products.Fire-Retardant TreatmentsIt is possible to make wood highly resistant to thespread of fire by pressure impregnating it with an approvedchemical formulation. Wood will char if exposed to fireor fire temperatures, even if it is treated with a fire-retardantsolution, but the rate of its destruction and the transmissionof heat can be retarded by chemicals. However, themost significant contribution of chemicals is reducing thespread of fire. Wood that has absorbed adequate amountsof a fire-retardant solution will not support combustion orcontribute fuel, and will cease to burn as soon as the sourceof ignition is removed.Two general methods of improving resistance of woodto fire are (1) impregnation with an effective chemical,and (2) coating the surface with a layer of intumescentpaint. The first method is more effective. For interiors orlocations protected from weather, impregnation treatmentscan be considered permanent and have considerable valuein preventing ignition. These surface applications offerthe principal means of increasing fire-retardant propertiesof existing structures. However, these coatings mayrequire periodic renewal if their effectiveness is to be maintained.In the past, the only effective chemicals were waterAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9This manual was developed with the intent of coveringall structural applications of wood-based products andtheir connections that meet the requirements of the referencedstandards. Other primary referenced standards are:ASCE 7-93, Minimum Design Loads for Buildings andOther Structures: This standard is the basic reference forload factors and load combinations that should be checkedin design of buildings and other structures. Use of therequirements in this standard for applications other thanbuildings (and the other special structures that it covers)is beyond the scope of ASCE 7-93.For example, ASCE 7-93 provides no guidance onthe appropriate load factors to design a bridge, or on theproper load combinations to check. The same difficultyarises when designing a scaffold or a concrete form system— neither of these applications have loading criteriathat have been derived in a manner consistent withASCE 7.ASTM D5457-93, Standard Specification for Computingthe Reference Resistance of Wood-based Materials andStructural Connections for Load and Resistance FactorDesign: This specification provides the link betweenmaterial specifications or product manufacturing standardsand LRFD reference resistance values. This ASTM specificationdefines two alternative routes for deriving designvalues:• Format conversion: Code-accepted ASD values arepermitted to form the basis for conversion into referenceresistance values. Conversion factors have beenchosen such that designs retain roughly the same levelof safety as found in ASD. Format conversion facsoluble,making fire-retardant treatments unadaptable toweather exposure. Impregnated fire retardants that areresistant to both high humidity and exterior exposures arebecoming increasingly available on the market for treatedlumber and plywood products. See product-specific recommendationsregarding proper procedures forpreservative treatment of that product.11.4 Products Covered in This Manualtors are addressed in ASTM D5457 and are discussedfurther in the product supplement and guideline documents.• Reliability-based conversion: ASTM D5457 providesprocedures for deriving LRFD reference resistancevalues directly from test data.1.4.1 Products IncludedDesign information for LRFD is available for productsin the following list. The designation of Supplementindicates a document that contains a complete set of designvalues plus other information for use with this manualand AF&PA/ASCE 16-95. The designation of Guidelineindicates a document that does not contain design values,but includes other information required to design the productsusing LRFD.Supplements• Structural Lumber Supplement• Structural Glued Laminated Timber Supplement• Timber Pole and Pile Supplement• Structural-Use Panel Supplement• Structural Connections SupplementGuidelines• Metal Plate Connected Wood Truss Guideline• Wood I-Joist Guideline• Structural Composite Lumber Guideline• Pre-engineered Metal Connectors GuidelineINTRODUCTIONAMERICAN FOREST & PAPER ASSOCIATION

PBINTRODUCTIONAMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION11PROJECTPROFILES:CASE STUDIES22.1 General Information 122.2 Commercial/Industrial 122.3 Residential/Retail 12Projects:Fast Food Restaurants 13TYCO Warehouse 16Reservoir Cover 19Marriott Courtyard Hotels 22Delancey Street Foundation Triangle 24Pine Square/Pacific Court 28AMERICAN FOREST & PAPER ASSOCIATION

12 PROJECT PROFILES: CASE STUDIES2.1 General InformationThis chapter presents six project profiles. Each projectrepresents a type of construction with needs that wereuniquely filled by wood-based structural products. Theproject profiles present an overview of each project.2.2 Commercial/IndustrialThree projects are presented. The fast food restaurantshighlight the nationwide use of structural woodproducts in buildings that demand economy, fast installationand long-term dependability.The Tyco warehouse represents a construction systemin which the economics regularly lead to the choiceof a structural wood roof system.The LA reservoir cover illustrates the use of engineeredwood products in a unique project in which wood’s provenseismic performance, coupled with its ability to withstanda corrosive environment, lead to its use.Projects:• Fast food restaurants: McDonalds, Wendys, Hardeesand Taco Bell are several of the restaurant chains thatregularly use wood construction.• Tyco Warehouse: 250,000 square feet warehouse useda panelized wood roof system.• City of Los Angeles Reservoir Cover: 600,000 squarefoot (14 acre) roof used glulam beams and wood-flange,steel-web trusses for this unique application in a highseismic area.2.3 Residential/RetailThree projects are presented. Each represents the useof engineered wood products in a multifamily residentialproject. However, each also illustrates a feature of engineeredwood construction that makes it the system ofchoice for the project. The Marriott Courtyards illustratea use in which the owners want an economical, reliablesystem that can be duplicated throughout the country withoutconcern about material availability or specialized laborrequirements. The Delancy project showcases the architecturalflexibility that is available when using woodproducts. Finally, the Pine Square project provides aglimpse of creative genius for high density housing —erecting an entire wood-framed residential community ontop of a reinforced concrete retail center.Projects:• Marriott Courtyard Hotels: Marriott regularly uses engineeredwood construction in these hotels across thecountry.• Delancy Street Triangle: Architecturally interestingproject combines residential and retail areas in this complex.• Pine Square/Pacific Court: Urban revitalization project— a residential community atop a retail center atop aparking garage.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER1313CommercialFast Food Restaurants2PROJECT PROFILES: CASE STUDIESProject DescriptionFast food restaurants in the United States are a multibilliondollar business. New restaurants are being builtalmost daily across the U.S. The design and constructionof such facilities has been a major portion of Ozark Structures’business for many years. McDonalds, Wendys,Hardees, and Taco Bell are several of the chains that utilizeOzark’s design/build capability.Design ConsiderationsWith the exception of architectural details that distinguishone chain from the next, these structures are quitesimilar. In general this type of restaurant is a rectangularfootprint approximately 24 feet high and 35-40 feet widewith the front or street side walls of the building being a“window wall.” Building length is determined by the sitesize and the desired dining room capacity.meet the desired footprint and appearance requirementssupplied by the owner.These restaurants are typically designed as Type II,one-hour buildings. Fire and wind considerations are mostoften the critical design criteria. This is particularly truefor urban areas.Depending on the local zoning restrictions, fire safetyconsiderations vary. The use of fire retardant treated lumberand gypsum wallboard are often a suitable, costeffective alternative to steel construction.Code ConformanceSubject to local jurisdiction modifications, the modelcode (ICBO, BOCA, or SBCCI) governs design. Typicallythe owner of the building (e.g., Wendys, etc.)develops architectural plans for a given site that are sentout for bid. The building is designed by the bidder toAMERICAN FOREST & PAPER ASSOCIATION

14 PROJECT PROFILES: CASE STUDIESRoof dead loads are usually 10 psf. Roof live loadscan vary from 45 psf snow loads in the northern states to20 psf “sun loads” in the southwestern U.S.Due to the amount of glass desired in many of thestore fronts, it is often difficult to achieve the proper horizontalshear resistance. The use of deep plywoodbox-beams has been found effective in developing the necessaryshear strength.Materials SpecificationsThe primary structural system is most often comprisedof either steel or wood columns supporting glulam beams.The beams spans can be as large as 40-feet requiring 24Fgrade glulam.Wall framing is typically 2x6 stud grade lumber (fireretardant treated when necessary). In the building shownin the photos the roof structure uses parallel chord, metalplateconnected trusses. Where the mansard roofappearance is specified, parallel chord trusses are manufacturedwith mansard ends (see lower right figure.) Somepitched, metal-plate connected roof trusses are also usedin this building.Exterior sheathing is typically 7/16 in. OSB or 1/2 in.to 5/8 in. plywood, Rated Sheathing grade. Where firecodes dictate, fire retardant treated plywood is used.Exteriors are commonly stucco or brick with paintedwood trim.After the foundation and slab are poured, the materials,crane, and crew arrive on the site. No metal workersare required to erect these buildings.Within 16 hours the structural frame is to a point whereroofing can begin.The roof structure allows for great interior wall flexibility.Few, if any, internal columns are needed. Kitchenlocation, service counters and seating arrangements arefully at the discretion of the interior designer.Construction ProcedureWood framed structures have been selected for thesefast food restaurant chains primarily because of their overalleconomy, material and labor availability, andconstruction speed.Many of the components are pre-manufactured in aplant. They include; trusses, wall panels, and to somedegree roof panels.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER1515Contact ListOwner/ArchitectMajor fast food chains across the United States such asMcDonalds, Wendys, Hardees, and Taco Bell.Structural Engineer/ContractorOzark StructuresP.O. Box 4246Springfield, MO 658082PROJECT PROFILES: CASE STUDIESAMERICAN FOREST & PAPER ASSOCIATION

16 PROJECT PROFILES: CASE STUDIESIndustrialTYCO WarehouseProject DescriptionDuring the spring of 1992 TYCO Corporation, a majorproducer of children’s toys, completed 250,000 squarefeet of warehouse space for product storage and distributionnear Portland, Oregon.Two tilt-up concrete buildings with panelized woodroof systems, each measuring 250x500 feet, were erectedparallel to one another creating nearly six acres of storage/distributionfacility.The total cost of these buildings, including site workand lighting, was $11/square foot.Design ConsiderationsTilt-up concrete walls with panelized wood roof systemsare quite common, particularly in the western UnitedStates. What makes this project unique is that instead ofusing 4'x8' structural panels in the roof, 8'x8' panels wereused. This nearly doubled the roof installation speed.SiteThe site was level but wet. Even with wet soil theexpected loading did not require any special foundationdesign. Of greater significance was the fact that thesebuildings were located directly in line with a major runwayof Portland International Airport resulting in enhancedfire protection system requirements.Code ConformanceAs a storage facility in the Portland area the UBCspecifies a Type VN, B-2 Occupancy class. Due to itslocation and type of storage, fire considerations were extremelyimportant. These buildings were considered Class4 high pile commodity storage facilities. In addition, theflammability of the materials stored and their location inthe flight path of a major airport required sprinklers to bespaced at nearly twice the typical density along with specialsmoke removal equipment. Actual fire tests wereconducted in the buildings to convince the Fire Marshallthat a fire and its resultant smoke would not conflict withair traffic control.The buildings were designed as a box system(250x500-feet) in a Zone 3 seismic area. Factory MutualI-90 psf wind uplift forces were specified. In addition,the engineer designed for a condition between ExposureClass B and C, 95 mph wind speeds. These wind speedsAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 1717were higher than required by the UBC. Roof live loadwas 25 psf, governed by snow loading. Roof dead loadwas 10 psf.Materials SpecificationsThe materials list for this panelized wood roof systemis rather simple. 24F glulam girders and purlins wereused. Sub-purlins were No. 1&Btr. Douglas Fir - Larch2x4s and the panels were 1/2 in. Rated Sheathing OSB.Simpson metal hangers were used to connect purlins togirders and sub-purlins to purlins. For OSB connectionsto the perimeter walls 16d nails were used. For other panelnailing, 8d nails were used. R-11 ceiling insulation wasinstalled. All materials were readily available at localbuilding supply dealers with the exception of the 8x8-footOSB which was special ordered from the factory througha local building materials supplier.The roofing was a hot mop asphalt and the exteriorwalls of the buildings were painted.Construction ProcessThe engineering firm for this project has been involvedin the design of over 40 million square feet of panelizedwood roof systems. The reason for the proliferation ofthis system has simply been its erection speed, efficiency,and availability of materials.Reinforced concrete walls, twenty-eight feet long,were poured on the ground and tilted into position. Theconcrete formwork utilized a double 2x4 lumber framewhich became the top plate of the wall. Steel columns,placed in a 25x50-foot grid, were connected with glulambeams to form the primary structural network. Split-lamconnections were used wherever glulam beam sizechanged.The 8x25-foot “panels” were fabricated on the groundby a two man crew. The unique feature of this panel systemwas the use of 8' x 8' OSB (Oriented Strand Board)structural panels. The OSB was nailed with its strongaxis aligned parallel to the 2x4 sub-purlins spaced twofeet on center. Because of the panel orientation with thesub-purlins, a 1/2 in. thick, Rated Sheathing grade of OSBwas required. With the OSB nailed to the 25-foot glulampurlin and sub-purlins, the assembly was ready to be liftedinto position.2PROJECT PROFILES: CASE STUDIESAMERICAN FOREST & PAPER ASSOCIATION

18 PROJECT PROFILES: CASE STUDIESContact ListOwnerTyco Corporation15745 N. LombardPortland, ORThis type of system requires only one person to be onthe roof at any given time to fasten the panels in place. Apneumatic nailer is used for the connection of the panelizedassembly to both the interior purlins, as well as to the outsidewalls. Within ten days an entire 125,000 square feetof roof can be installed.Typically steel roof systems require periodic expansionjoints to account for temperature effect. With a woodroof system no expansion joints were needed.Structural EngineerVanDomelen/Looijenga/McGarrigle/Knauf3933 Kelly AvenuePortland, OR 97201ContractorGrady, Harper, Carlson, Inc.2945 N.E. Argyle StreetPortland, OR 97211AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 1919CommercialReservoir Cover2PROJECT PROFILES: CASE STUDIESProject DescriptionDuring 1992 the City of Los Angeles, Department ofWater and Power erected a reservoir cover over the VanNorman Bypass Reservoir in San Fernando, California,part of the Los Angeles drinking water supply system. Acovered reservoir offers several advantages. The mostobvious reasons include the minimization of both waterevaporation and contaminants (e.g., airborne pollutants,bird feces, etc.). The secondary benefits of a reservoircover include: reduced chemical usage (i.e., primarilychlorine) and improved safety and security. An enclosedreservoir assists in keeping people and animals from enteringthe area.The reservoir cover is a dome-like structure. Thecenter of the roof is approximately eight feet higher thanthe perimeter. Total roof area exceeds 600,000 squarefeet, or approximately 14 acres. The roof stands 44 feetabove the reservoir floor, and is supported by glulambeams and metal web wood trusses on a 60 x 60-foot concretecolumn grid. On top of the wood structural systemare 3 x 20-foot aluminum roof panels, installed to minimizetotal dead load and provide a continuous, water-tightbarrier.Design ConsiderationsPrimary engineering design considerations for thecover included both seismic activity and wind uplift wherethe Uniform Building Code was used. However, with theexception of seismic and wind consideration, the primarydesign issues were not governed by the UBC, but ratherby the end-use specification and defined by the Departmentof Water and Power. Because this water was actualdrinking water, the primary issues were: strict maintenanceof water quality and roof structure longevity/durability.Materials SpecificationsIt was essential that the roof protect the water fromcontamination for the specified design lifetime. But itwas equally important that the building materials themselvesdid not contribute any contamination. To this end,Alaskan yellow cedar was selected as the wood species tobe used in both the primary and secondary structural members.This species was used because of its balance betweennatural durability and strength characteristics.Alaskan yellow cedar is not commonly used in glulambeams, therefore, a series of tests were conducted by theAPA-EWS to verify their performance capability.AMERICAN FOREST & PAPER ASSOCIATION

20 PROJECT PROFILES: CASE STUDIESFor the 60-foot TJH trusses, a proprietary 1.65E MSRgrade of yellow cedar lumber was specified by Trus JoistMacMillan. The TJH trusses were 51-inches deep withdouble 2x6 top and bottom chords.The primary structural system was composed ofglulam beams connecting the columns in the 60 by 60-foot matrix. Two sizes of 20F glulam were used. Thegirders oriented parallel with the TJH trusses were 6 3/4-inches wide by 39-inches deep. The other beams were 103/4-inches wide by 39-inches deep, 60-feet long.Reports from the Los Angeles Department of Water andPower describe no adverse effect on the structure.Even through the roof structure is in close proximityto water, the consistently low relative humidity conditionsreduce moisture as a design consideration. However, as aprecautionary measure, wet use design values were usedin the engineering calculations for the glulam and trusses.Again, because of the proximity of the roof to water,all connections and hold-downs were designed with hotdipped galvanized bolts, hangers, nails, etc.Construction ProcedureThe construction procedure was straightforward. Theregularly spaced columns and simple structural matrix leadto rapid installation of the roof. Although the roof elevationwas minimal, the beams and trusses needed to be liftedmore than 40 feet laterally into position. For this purposea small (14 ton) hydraulic crane was used. Corrugatedaluminum roof panels, 3 x 20-feet, were caulked andscrewed to the wood members.More than 60,000 square feet of roofing was installedper week. Even at this rate the process took ten weeks.Around the entire perimeter of the cover, a stem wall2 to 4 feet high was used to connect the roof system to theground which served as a barrier to keep people from enteringthe reservoir. This lumber was locally availabletwo-inch framing lumber.Engineering DesignThe roof cover was designed for a 20 psf live load.The dead load was negligible. The aluminum roof panelscontributed just slightly over 1 psf. Earthquake resistanceand wind uplift were more important design considerations.For seismic design both lateral and verticalaccelerations were considered.On January 17, 1994 the Northridge earthquake, measuring6.8 on the Richter scale, struck close to the reservoir.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 2121Contact ListOwnerLos Angeles Dept. of Water and PowerCity of Los Angeles111 N. Hope St., Room 1334Los Angeles, CA 900512Project ManagerS. J. Amoroso Construction Co.1516-B Brookhollow DriveSanta Ana, CA 92705-5426Roof InstallationAnning Johnson Co.13250 TempleCity of Industry, CA 91749PROJECT PROFILES: CASE STUDIESAMERICAN FOREST & PAPER ASSOCIATION

22 PROJECT PROFILES: CASE STUDIESResidential/CommercialMarriott Courtyard HotelsProject DescriptionBeginning in 1987, Marriott Corporation began buildinga series of Courtyard Hotels across the country utilizingengineered wood systems. To date 22 hotels have beencompleted with numerous others in various stages of planning.The Marriott Courtyard pictured above is 78,600square feet with 150 rooms situated on 1.6 acres. A majorityof the hotels will be smaller, approximately 45,000square feet with 48 rooms.These structures are typically three stories of woodframe construction built on a concrete slab. Each facilitycontains a small restaurant and lounge with meeting roomfacilities for group sizes up to 30.The selection of engineered wood construction wasdriven primarily by cost. Wood frame construction averaged$1200 to $1500 per room less than the otherconstruction systems. Total project costs for the 150-roomfacility was $5 million.These buildings are fully sprinklered, one-hour fireresistive construction carrying a R-1 Occupancy Class.From a code standpoint, these structures are viewed simplyas a “large house.”Materials SpecificationsLocally available, conventional dimension lumber wasused for most wall framing. A sound transmission classof 52 was achieved with either a staggered 2x4 stud wallor a 2x6 with resilient metal clips. 5/8 in. gypsum wallboardwas used throughout.Engineering ConsiderationsBecause the Marriott Corporation franchises thesehotels nationwide, all model building codes have beenconsidered (e.g., ICBO, BOCA, & SBCCI) in the designs.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 2323and freezing weather. The only time a crane was neededon the jobsite was to deposit bundles of engineered woodroof trusses on the third floor. Some panelization tookplace on site.2Wall and roof sheathing materials were either plywoodor OSB depending upon availability. Wood trusses, glulamand I-joists were used where longer spans were required.Laminated veneer lumber has replaced some of the glulamin subsequent structures.A stucco exterior finish is used most often on thesebuildings.Contact ListOwnerMarriott Corporation1500 Research Blvd. Suite 200Rockville, MD 20850PROJECT PROFILES: CASE STUDIESEngineerL. S. Mason & Associates935 Moraga Rd. Suite 202Lafayette, CA 94549ArchitectBucher, Meyers,Polniaszek, and Silkey8777 First AvenueSilver Spring, MD 20910ContractorBell Construction CompanyBox 363Brentwood, TN 37027Construction ProcedureBecause the engineered wood system for the hotel isno more complicated than that of any platform framedhouse, the number of trades required on the job was minimized.Construction materials were readily availablelocally, and the job was able to continue through rainyAMERICAN FOREST & PAPER ASSOCIATION

24 PROJECT PROFILES: CASE STUDIESResidential/RetailDelancey Street Foundation TriangleProject DescriptionThe Delancey Street Foundation Triangle is a three-storywood-frame residential structure over one story of posttensionedconcrete commercial and retail space. It islocated in the South Beach area of San Francisco, California,one quarter of a mile from the San Francisco Baybridge.The site is a relatively flat 2.95 acre triangular parcelzoned for mixed residential/retail use. The property isbeing leased by the Delancey Street Foundation from thePort of San Francisco. Several other condominium, apartment,and retail complexes share the surrounding area.The Delancey Street Foundation is a unique organizationthat provides a highly successful rehabilitationprogram for drug abusers and alcoholics. The Foundationteaches trade skills to program participants. Its successcan be measured by the fact that the primary method ofsupport for the Foundation results from enterprises operatedby program participants.Design ConsiderationsThe Delancey Street project, completed in 1989, is atotal of seven buildings representing 325,000 square feetof floor area. To provide workspace and housing for severalhundred people, the architects creatively maximizedthe use of the triangular parcel and designed a multi-usecomplex that includes 177 apartments (approximately 900square feet each), group dining facilities, classrooms, acentral courtyard, health club, pool, 500-seat assembly hall,AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 2525and a recreational building with a 150-seat screening room.In addition, 138 covered parking spaces were providedalong with the commercial and retail space.The commercial functions included a dry cleaner, autorepair shop with an antique car museum, wood shops, anda 400-seat restaurant.Larch at a maximum moisture content of 12% was used.Lumber at 12% or less moisture content is in equilibriumwith the local environment so there was no need to performshrinkage calculations.For higher stress locations, glulam beams rated at F b= 2 ksi, E = 1500 ksi were used, and in some cases wideflange steel beams were needed to maintain a nominal 10in. floor depth.No. 1&Btr Douglas Fir - Larch Beams and Stringers(nominal 6 in. and larger) were used in several beam andcolumn applications.Wall and roof sheathing included 15/32 in. C-C Exteriorand C-D Structural II plywood. Interior corridorsheathing walls used 3/8 in. plywood.The building’s exterior used a cement-based plaster to harmonizewith the terra cotta roof tile used on the pyramid-shapedroof caps. Control joints were placed at each level to minimizeshrinkage problems with the exterior finish and todelineate window openings.2PROJECT PROFILES: CASE STUDIESMaterials SpecificationsWood framing was selected over other systems becauseof its economy, availability, and speed ofconstruction. This decision was also influenced by woodframing’s ease of construction with relatively unskilledlabor. The Foundation was able to utilize this project asvaluable job skills training for some of its program participants.Because much of the labor was supplied by theFoundation members and the fact that much of the materialwas donated by various agencies, the actual costsavings cannot be documented.For the exterior walls, the engineers specified 2x6 in.studs to accommodate thermal insulation. The framingmaterial was No. 2&Btr Douglas Fir - Larch. For the interiorwalls of the bottom story, 3x4 in. lumber was used toprovide additional nailing area, while the two upper storiesused 2x4s 16-inches on center. The framing lumberwas specified to be dry, that is, moisture content not toexceed 19%. Some 1350f-1.3E Machine Stress Rated 2x4framing lumber was substituted when availability of theNo. 2&Btr. became difficult.Floor joists included a variety of materials. Joist spansranged from 13 to 18 feet. Spans over 15 feet requireddouble joists where solid sawn lumber was used. Forlonger spans fingerjointed No. 2&Btr 2x10 Douglas Fir -A 6x6 in. wood bracket outrigger eave detail, constructedby Delancey Street members, is carried throughoutthe buildings. Similar brackets support planter boxes onthe lower floors.Sound TransmissionAs with any residential project, sound transmission iscritical. Group R occupancies are required to have a soundtransmission class (STC) of 50. STC ratings of 45 to 55are commonly cited as good sound barriers. To reducesound transmission between units, the architect staggeredthe 2x4 studs to the front and back of the wall cavity on a2x6 plate, while maintaining a 16 in. on center spacing oneach side. One face of the wall is covered with 5/8 in.gypsum wallboard; the other side has 3/8 in. plywood witha 5/8 in. gypsum overlay. The plywood also provides shearload resistance. Within the wall cavity, 3-1/2 in. acousticbatting was woven between the staggered studs. The entireassembly provides an STC rating of approximatelyAMERICAN FOREST & PAPER ASSOCIATION

26 PROJECT PROFILES: CASE STUDIES53. For more information on sound control, the WesternWood Products Association in Portland, Oregon providesa design manual published by the Gypsum Association.Code ConformanceThe ICBO Uniform Building Code (UBC), as acceptedand modified by the City of San Francisco, was used. Thehousing portion of the complex, which includes four woodframe buildings, is classified as a Group R-1 Occupancy,which covers hotels, apartments, and condominiums.In addition, the housing portion is a Type V, one-hourprotected assembly. Under the UBC, the building’s structuralframework, interior stairways, and exterior walls maybe constructed of wood as long as the assembly meets theone-hour fire resistive requirement. Furthermore, the complexis located in San Francisco’s fire zone, and, therefore,must be sprinklered throughout (San Francisco BuildingCode, 1603(a) Exception 1).The restaurant portion was designed as a Group A2.1, Type II one-hour building.Height and Area AllowancesThe site complexity offered some design challenges.To accommodate 177 units, allowable height and area increaseswere utilized. The UBC (Chapter 5, Table 5-C)specifies the basic allowable area at 10,500 square feetfor a one-story, Group R-1 Occupancy, Type V one-hourbuilding. For multi-story buildings, however, this areamay be doubled, provided that the floor area of any singlestory does not exceed the limits of Table 5-C, Section505(b). This increases the size to 21,000 square feet foreach building.Because the buildings are fully sprinklered, the floorarea may again be doubled (UBC Section 506(b)). Thusthe resulting 42,000 square feet is the maximum for twoof the buildings. For two other buildings an additionalarea increase was allowed due to open spaces greater than20 feet on two and three sides of the buildings.In addition, the maximum height (in stories) for R-1Occupancy, Type V unprotected buildings is three stories.The maximum allowable height (in feet) for Type V onehourconstruction is 50 feet. The Delancey Streetresidential buildings were a maximum overall height of40 feet.Design LoadsCommon code specified design loads were used. Floorlive loads included: 100 psf for public areas such as stairs,exits, and corridors required, 40 psf for living units, and60 psf for balconies. Roof dead load was 10 psf to allowfor the terra cotta tile.Seismic and Lateral ForcesThe Delancey Street complex is located in SeismicZone 4. Zone 4 includes areas that are in close proximityto a major fault system where extensive damage may occurin the event of an earthquake (UBC Chapter 23, Figure2 Seismic Zone Map). Table 23-I of the UBC permits a Kvalue of 1.0 for “Buildings not more than three stories inheight with stud wall framing and using plywood horizontaldiaphragms and plywood vertical shear panels forthe lateral force system.”The upper floor of the residences were designed touse a combination of gypsum wallboard and 3/8 in. plywoodfor shear restraint. Half of the party wall separationsused gypsum, while the other half used 3/8 in. plywood.Corridors and unit walls relied on 3/8 in. plywood.Exterior walls on the top floor were sheathed witheither 1/2 in. gypsum or 1/2 in. C-D exterior plywood.The lower two floors used either 1/2 in. C-D exterior orStructural II plywood. Shear wall nailing schedules were8d nails on two-inch centers. Although the exterior sheath-Figure 2.1 Hold-down detail.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER2727ing provides significant shear strength, most of the exteriorwalls were not relied upon in the shear wallcalculations.Metal straps were used to tie the top floor to the secondfloor. Standard hold-downs were used in the lowertwo stories (Figure 1).It is interesting to note that well into the constructionprocess, the Loma Prieta earthquake struck San Franciscoon October 17, 1989. This quake measured 7.1 on theRichter scale and caused no damage to the structure. Evenplastered exterior walls sustained no damage.FoundationThe geotechnical report showed that the site was locatedon an artificial fill over bay mud. The bay mudcovers sands and clays, which overlay sloping bedrock.To compensate for the poor bearing strength of baymud, pre-stressed, 117 ton 14 in. square concrete pileswere driven 60 to 90 feet to bedrock.The three-story wood-frame apartments were supportedby one-story post-tensioned concrete first level thatwas 12.5 feet high.Contact ListOwnerDelancey Street Foundation, Inc.2563 Divisadero StreetSan Francisco, CA 94115ArchitectBacken, Arrigoni & Ross, Inc.1660 Bush StreetSan Francisco, CA 94133Structural EngineerR.M.J. & Associates103 Linden AvenueS. San Francisco, CA 94980Geotechnical ConsultantHarding Lawson Associates666 Howard StreetSan Francisco, CA 94105Project CoordinatorJack Scott & Associates75 Lansing StreetSan Francisco, CA 941052PROJECT PROFILES: CASE STUDIESAMERICAN FOREST & PAPER ASSOCIATION

28 PROJECT PROFILES: CASE STUDIESUrban Residential/RetailPine Square/Pacific CourtProject DescriptionThe Pine Square/Pacific Court project is a residential,retail/entertainment facility situated on one full cityblock in the heart of downtown Long Beach, California.It was designed as an inner-city revitalization project, andis comprised of four stories (with a loft) of wood frameresidential construction, forty feet above street level atopseveral levels of reinforced concrete and steel constructioncontaining retail and entertainment components.Pacific Court, the housing component of the project,was added to reinforce an active “living/work” environmentwithin an urban setting. One hundred forty-twoapartments, situated forty feet above the street, allow uninterruptedviews of the surrounding city. Quietlandscaped courtyards provide a suburban tranquillitywithin Long Beach’s urban core.Overall, the project contains 35,000 square feet of restaurant/retailspace, a 16-plex cinema, 142 apartment units,and parking for 400 cars.The residents of Pacific Court have two levels of dedicatedunderground parking with a separate entrance andsecurity gate. There is also a separate street entrance forfoot traffic located on the opposite side of the block fromthe retail entrance. Two high-speed traction elevators areprovided for residents, servicing both parking and livingareas.Retail parking is located on the first level, close to theshopping and entertainment areas.The Pine Square/Pacific Court project is a total of385,000 square feet. The retail portion represents 120,000square feet and the residential portion 125,000 square feet.The parking structure comprises the remainder.Design ConsiderationsThe Pine Square/Pacific Court project is essentiallythree structures stacked vertically; a residential communityon top of a retail center, supported by a three-levelparking structure. Other than the uniqueness of the designconcept, the engineering complexity was minimal.The following discussion will focus on the residentialstructure Pacific Court.Code ConformanceWith the exception of an innovative hold-down system,and a three-hour separation floor, the Pine Square/Pacific Court project was typical Type I steel and concreteconstruction on the lower levels (Pine Square)capped with four levels and a loft (Pacific Court) of Type3,AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 2929one-hour protected residential construction, Group R-1 Occupancyall in a seismic Zone 4.To meet the fire code requirements all levels of theproject were fully sprinklered and fire retardant treatedlumber and sheathing was required for all exterior wallframing. The footprint of the retail portion of the projectwas much larger than the residential portion allowing balconiesand courtyards to be easily included in the design.wall of the apartments, steel beams were placed. Thisbeam network acted as a foundation system supportingthe 3-hour floor and apartments above.The 3-hour floor system is composed of a 7-1/4 in.concrete deck, covered by a 7/8 in. sound insulating board.The sound board was then covered with three more inchesof concrete. Special attention was given to waterproofingbetween slabs to assure proper drainage.On the bottom of the 7-1/4 in. concrete deck, two layersof 5/8 in. gypsum wallboard were hung from metalhanger clips.2PROJECT PROFILES: CASE STUDIESFigure 2.2 Three-hour floor separation system.Three-Hour Floor SeparationMany of the apartments were located above the theaters.For both safety and privacy reasons, a three-hourfloor separation was provided between the two occupancyzones. Figure 2.2 shows the separation detail. Under eachHold-Down SystemThreaded rod hold-downs were spaced every ten feetaround the perimeter of the apartment complex and weldedto the steel beams below. These threaded rods ran the fullheight of the apartment complex, securing all residentiallevels to the retail space below. For all interior walls, soleplate hold-down bolts were welded to the steel beam foundationnetwork as well.Design LoadsCommon code specified design loads were used. Floorlive loads included: 100 psf for public areas such as stairs,exits, and corridors, 40 psf for living units, and 60 psf forbalconies. Roof dead load was 10 psf to allow for cementtile, and roof live load was 20 psf. UBC specified windloads were used for the height and location of the building.Materials SpecificationsThe original design was a Type I steel frame high-risewith concrete floor slabs. The preliminary cost estimatesAMERICAN FOREST & PAPER ASSOCIATION

30 PROJECT PROFILES: CASE STUDIESdrove a search for a more cost-effective solution. RTKLArchitects of Los Angeles, California redesigned the structureto a height just inches below the Type I high-rise limitwhich allowed wood frame construction to be used.Common grades and sizes of dimension lumber wereused throughout. For exterior walls, fire retardant treatedstud grade lumber 16 inches on center was specified tomeet the Type III construction requirements. On lowerfloors 2x6 in. studs were used, and on upper floors andloft 2x4 lumber was used. Interior walls used staggered2x4s with sound insulation woven between studs for apartmentseparation walls. The remainder of the framingmaterial (floor joists and rafters) was No. 2&Btr DouglasFir - Larch. All joists and rafters were specified to be MC15lumber. This is lumber that is dried to an average of 12%moisture content with no piece to exceed 15% moisturecontent. This is common practice in multi-story buildingsto avoid vertical shrinkage considerations. Wall studswere specified to be SDRY meaning moisture content isnot to exceed 19%.Exterior wall and roof sheathing was fire retardanttreated plywood. Interior shear walls were sheathed with3/8 in. Oriented Stand Board (OSB).The exterior surface of the building was covered witha cement-based stucco and painted to complement the colorof the lower retail levels. Cement roof tile was used onall residences.Contact ListOwnerJanss Corporation1453 Third StreetSanta Monica, CA 90401ArchitectRTKL Architects818 W. 7th Street, Suite 300Los Angeles, CA 90017Structural EngineerRobert EnglekirkConsulting Structural Engineers, Inc.2116 Arlington Ave.Los Angeles, CA 90018-1398ContractorBenchmark Contractors, Inc.2901 28th Street, Suite 150Santa Monica, CA 90405AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION31TENSIONMEMBERS33.1 General 323.2 Design 323.2.1 Adjustment Factors 323.3 Special Considerations 333.3.1 Net Section Calculation 333.3.2 Radial Tension in CurvedMembers 333.4 Checklist: Using Tension MemberSelection Tables 333.5 Design Examples 33Example 3-1: Truss Bottom Chord 33Example 3-2: Bolted Truss BottomChord 34AMERICAN FOREST & PAPER ASSOCIATION

32 TENSION MEMBERS3.1 General InformationThis chapter covers design of members stressed primarilyin tension parallel to grain. Examples of suchmembers include truss members and diaphragm chords.See specific product supplements for factored tensionresistance values (tension member selection tables) andreference tension strengths.The designer is advised that use of wood members inapplications that induce tension perpendicular to grainstresses should be avoided.3.2 DesignThe basic equation for design of tension members(AF&PA/ASCE 16-95 Eq. 3.1-1) is:whereλφ tT′ $ T uλ = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)φ t= 0.80T′ = adjusted tension resistance parallel to grain= factored tensile forceT uThe factored tension resistance is tabulated in the tensionmember selection tables of individual productsupplements. The tabulated values are suitable for membersthat conform to all conditions of the checklist inSection 3.4.3.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting the tabulated tensionresistance values or by applying all applicable adjustmentfactors to the reference tension strength for the product.The complete equation for calculation of factored tensionresistance is:λφ tT′ = λφ tF t′AC MC tC FC ptC rtis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the product supplement orguideline.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100°F on a sustained basis. For higher temperatureconditions, use the value of C t given in the productsupplement or guideline.is the size factor for visually graded sawn lumberor round timber members. Tabulated resistancesalready include the size factor. For calculationsstarting from reference tension strengths, use thevalue of C F given in the Structural Lumber Supplementor Timber Pole and Pile Supplement.is the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the product supplement orguideline.is the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the product supplement orguideline.whereA = area (in 2 )F t′ = F tC MC tC FC ptC rtFor untreated members used in a normal building environment(meeting the reference conditions of Sec. 1.1.5)the general equation for F t ′ reduces to:F t= reference tension strength (ksi)F t′ = F tC FAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER33333.3 Special Considerations3.3.1 Net Section CalculationDesign of tension members is often controlled by theability to provide connections to develop tensile forceswithin the member. In the area of connections, one mustdesign not only the connection itself (described in detailin Chapter 7) but also the transfer of force across the netsection of the member.3.3.2 Radial Tension in CurvedMembersStresses induced in curved members under load includea component of stress in the direction of the radiusof curvature. This stress is traditionally called radial tension.Radial tension is a specialized design considerationthat is covered in AF&PA/ASCE 16-95 App. A2 and isexplained in detail in the American Institute of TimberConstruction (AITC) Timber Construction Manual.3.4 Checklist: Using Tension Member Selection TablesTension member selection tables provide values for factored tension resistances (λφ t T′) for common gradesand sizes of tension members. Tabulated values apply to tension members that satisfy the following conditions:3TENSION MEMBERS√ “dry” service condition (C M = 1.0)√ “normal” temperature range (C t = 1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (λ = 0.80)For members that do not satisfy all of these conditions, review the design equations in this chapter andmodify tabulated values as necessary.To compute the factored resistance for a specific condition, apply the design equations directly (productspecificdesign adjustment factors and reference resistance values are provided in each supplement).3.5 Design ExamplesExample 3-1: Truss Bottom ChordDesign the bottom chord of a sawn lumber commercial/industrialtruss to support a factored tensile force (T u )of 36.0 kips. Assume a dry moisture service condition,untreated material and a time effect factor of 0.80.Practical ConsiderationsEfficient choice of a trial section requires practical,as well as engineering, considerations. For example,choice of lumber species, grade and even commonly avail-able sizes may differ among geographic regions of thecountry. Consult your local supplier for assistance. Inaddition, other considerations include dimensional compatibilitywith the other members of the truss or minimumsizes required to adequately connect the truss members(while meeting fastener edge distance requirements).Engineering CalculationsUsing Selection Tables: Select a member from thetension member selection tables in the Structural LumberSupplement that is adequate to resist 36.0 kips factoredtensile force (T u ).AMERICAN FOREST & PAPER ASSOCIATION

34 TENSION MEMBERSA double chord of nominal 2x12’s meets practical considerations.Try No. 1 Douglas Fir-Larch:8N tT′ = (19.7 kips) (2 plies)= 39.4 kipsUsing Reference Strength Tables: Calculate factoredtension resistance using reference resistance values andadjustment factors.Try a nominal 4x12 No. 1 Hem-Fir. From the StructuralLumber Supplement, obtain F t from the referencestrength tables from Chapter 3 and applicable adjustmentfactors from Chapter 4.8N tT′ = 8N tF t′A= 8N t(F tC F) AExample 3-2: Bolted Truss BottomChordSame as Example 3-1, but the chord includes connectionswith one row of 3/4 inch bolts (in a 1/16 inchoversized hole). Check the net section to verify the selectionof a 4x12 No. 1 Hem-Fir.Engineering CalculationsCalculations follow those of Example 3-1, but the netarea of (3.5) (11.25-0.8125) = 36.53 replaces the grossarea (39.38) in the calculation:8N tT’ = 41.7 kipsThe design is still acceptable.From the supplement, F t is 1.62 ksi and C F equals 1.10.The area of a 4x12 is 39.38 square inches. Thus the factoredtension resistance is:8N tT′ = (0.80)(0.80)(1.62)(1.10)(39.38)= 44.9 kipsThis member satisfies the strength limit state for atension member.AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION35COMPRESSIONMEMBERS44.1 General Information 364.1.1 Types of Columns 364.2 Design 364.2.1 Adjustment Factors 364.3 Special Considerations 374.3.1 Slenderness Considerations andStability 374.3.2 Net Section Calculation 374.3.3 Bearing Capacity Checks 374.3.4 Radial Compression in CurvedMembers 374.4 Checklist: Using Compression MemberSelection Tables 384.5 Design Examples 38Example 4-1: Glulam Column 38AMERICAN FOREST & PAPER ASSOCIATION

36 COMPRESSION MEMBERS4.1 General InformationThis chapter covers design of members stressed primarilyin compression parallel to grain. Examples of suchmembers include columns, truss members, and diaphragmchords.Information in this chapter is limited to the case inwhich loads are applied concentrically to the column. Provisionsof Chapter 6 should be used if loads are eccentricor if the compressive forces are applied in addition to bendingforces.See specific product supplements for factored compressionresistance values (column selection tables) andreference compression strengths.built-up columns are assembled from multiple pieces ofsimilar members connected in accordance with the NationalDesign Specification ® for Wood Construction.A composite column may have some elements with asufficiently different stiffness such that transformed sectionconcepts are required to accurately apportion the stressamong elements of the column.A spaced column must comply with provisions ofAF&PA/ASCE 16-95 Appendix A1. Note that this definitionincludes main column elements, spacer blocks withtheir connectors and end blocks with shear plate or splitring connectors.4.1.1 Types of ColumnsAF&PA/ASCE 16-95 differentiates between solid,built-up, composite and spaced columns. In this context4.2 DesignThe basic equation for design of compression members(AF&PA/ASCE 16-95, Eq. 4.1-1) is:where8N cP′ $ P u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N c= 0.90P′ = adjusted compression resistance parallel tograinP u= factored compressive forceThe factored compression resistance is tabulated inthe column selection tables of individual product supplements.The tabulated values are suitable for members thatconform to all conditions in the checklist in Section 4.4.whereC MC t8N cP′ = 8N cF c′AA = area (in 2 )F c′ = F cC MC tC FC PC ptC rt= reference compression strength (ksi)F cis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the product supplement orguideline.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For higher temperatureconditions, use the value of C t given in the productsupplement or guideline.4.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting tabulated compressionresistance values or by applying all applicable adjustmentfactors to the reference compression strength for the product.The complete equation for calculation of factoredcompression resistance is:C Fis the size factor for visually graded sawn lumberor round timber members. Tabulated resistancesalready include the size factor. For calculationsstarting from reference compression strengths, usethe value of C F given in the Structural LumberSupplement or Timber Pole and Pile Supplement.AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION37C P is the column stability factor. Tabulated referencestrength is based on crushing strength. Structuralcolumns of any appreciable length must be adjustedby C P (Eq. 4.3-1 of AF&PA/ASCE 16-95) to accountfor slenderness effects.C rtis the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the product supplement orguideline.C ptis the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the product supplement orguideline.For untreated columns used in a normal building environment(meeting the reference conditions of Sec. 1.1.5)the general equation for F c ′ reduces to:F c′ = F cC FC P44.3 Special Considerations4.3.1 Slenderness Considerationsand StabilityAs stated above, the factor C P is used to compute thereduction in column capacity due to slenderness effects.The user is cautioned that stability calculations are highlydependent upon boundary conditions assumed in the analysis.For example, the common assumption of apinned-pinned column is only accurate or conservative ifthe member is restrained against sidesway. If sidesway ispossible and a pinned-free condition exists, the value ofK e in AF&PA/ASCE 16-95 Sec. 4.3-4 doubles and thecomputed critical buckling resistance decreases by a factorof 4.4.3.2 Net Section CalculationAs in design of tension members, compression membersshould be checked both on a gross section and a netsection basis (see AF&PA/ASCE 16-95 Sec. 4.3.3).4.3.3 Bearing Capacity ChecksColumns often transfer large forces within a structuralsystem. While satisfaction of the column strengthlimit state is usually the primary concern, the designershould also check the force transfer at the column bearing.For cases in which the column is bearing on anotherwood member, especially if bearing is perpendicular tograin, this calculation will often control the design.4.3.4 Radial Compression inCurved MembersStresses induced in curved members under load includea component of stress in the direction of the radiusof curvature. Radial compression is a specialized designconsideration that is addressed AF&PA/ASCE 16-95, Sec.4.6.COMPRESSION MEMBERSAMERICAN FOREST & PAPER ASSOCIATION

38 COMPRESSION MEMBERS4.4 Checklist: Using Compression Member SelectionTablesColumn selection tables provide values for factored compression resistance (8N c P′) for common gradesand sizes of columns. Tabulated values apply to members that satisfy the following conditions:√ “dry” service condition (C M = 1.0)√ “normal” temperature range (C t = 1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (8 = 0.80)√ end conditions pin-pinFor members that do not satisfy all of these conditions, review design equations in this chapter and modifytabulated values as necessary.To compute the factored resistance for a specific condition, apply the design equations directly (productspecificdesign adjustment factors and reference resistance values are provided in each supplement).4.5 Design ExamplesExample 4-1: Glulam ColumnDesign a glulam column, 16 feet long, to support afactored compressive force (P u ) of 57 kips. Assume a drymoisture service condition, untreated material and a timeeffect factor of 0.80. The column may be assumed to bepinned at the top and bottom and is not laterally supportedalong its length.Practical considerationsRelatively square shapes are generally chosen for exposedcolumns — being equally strong along both axes ofbuckling and also providing an aesthetically pleasing appearance.As with other types of members, choice ofmember size will be based on size availability and compatibilitywith the rest of the structural system.Compute C P from Eq. 4.3-2 through 4.3-4 of AF&PA/ASCE 16-95.PαFirst, compute P e :e2π E05Iy= =2(K λ)e= 80.28 kipsNext, compute α c :cφsPe= =λ φ P ′co= 0.419(9.87) (1300) (230.7)[( 1.0 )( 16)( 12)](0.85) (80.28)(0.80) (0.90) (226.0)2Engineering calculationsUsing Reference Strength Tables: Calculate factoredcompression resistance.Try a 6-3/4 x 9 inch section from the Structural GluedLaminated Timber Supplement with F c = 3.72 ksi and E 05= 1300 ksi (first entry on page 14, Table 3.2).8N cP′ = 8N cC PF c∗ AwhereP 0= F∗ c A= (3.72) (60.75)= 226.0AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION39CNext, compute C P :Pcc c= 1+ α ⎛ 1+ α ⎞ α⎜ ⎟ −2c ⎝ 2c ⎠ c= 0.3932So, the factored compression resistance, 8N c P′ equals(0.80) (0.90) (F c* C P ) A8N cP′ = 63.95 kipsUsing Selection Tables: As an alternate to the glulamcolumn, select a member from Table 5.3 of the StructuralLumber Supplement that meets the compression requirements(P u ) shown above for an effective length of 16 feet.A 10x10 inch No. 2 Douglas Fir-Larch timber has afactored compression resistance, λφ c P′, of 61.5 kips. Thisvalue already incorporates the column stability factor, C P ,so no additional calculations are necessary.With its R/d ratio of 20.2, this column is wellbelow the maximum slenderness ratio permitted byAF&PA/ASCE 16-95.4COMPRESSION MEMBERSAMERICAN FOREST & PAPER ASSOCIATION

40COMPRESSION MEMBERSAMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION41BENDINGMEMBERS55.1 General Information 425.2 Design for Moment 425.2.1 Adjustment factors 425.3 Design for Shear 435.3.1 Adjustment factors 435.4 Special Considerations 445.4.1 Stability 445.4.2 Torsion 445.4.3 Curved members 445.4.4 Ponding 445.5 Checklist: Using Joist and BeamSelection Tables 455.6 Design Examples 45Example 5-1: Simple Span I-joist 45Example 5-2: Glulam Beam 46Example 5-3: Notched Beam 46Example 5-4: Beam with PartialLateral Support 46AMERICAN FOREST & PAPER ASSOCIATION

42 BENDING MEMBERS5.1 General InformationThis chapter covers design of members stressed primarilyin flexure (bending). Examples of such membersinclude primary framing members (beams) and secondaryframing members (purlins, joists). Products commonlyused in these applications include glulam, solid sawn lumber,structural composite lumber, and prefabricated I-joists.Bending members are designed so that no applicablelimit state is exceeded under factored loads. Strength limitstates for bending members include bending moment,shear, local buckling, lateral torsional buckling, and bearing.See specific product supplements for factored momentand shear resistance values (joist and beam selectiontables) and reference bending and shear strengths.Users should note that design of bending members isoften controlled by serviceability limitations rather thanstrength. These considerations are discussed in detail inChapter 1 of this Manual and in the Commentary toAF&PA/ASCE 16-95. Serviceability limit states such asdeflection and vibration are often designated by the authorityhaving jurisdiction. Users are cautioned thatserviceability limit states are generally checked underunfactored, rather than factored, loads.5.2 Design for MomentThe basic equation for moment design of bendingmembers (AF&PA/ASCE 16-95, Eq. 5.1-1) is:whereS = section modulus (in 3 )8N bM′ $ M uF b′ = F bC MC tC LC FC VC fuC rC cC fC ptC rtwhere8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N b= 0.85M′ = adjusted moment resistanceC MF b= reference bending strength (ksi)is the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the product supplement orguideline.M u= factored momentFactored moment resistance (8N b M) is tabulated inbeam selection tables and joist selection tables for manycommon products. Tabulated values are suitable for membersthat conform to all conditions in the checklist inSection 5.5.5.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting the tabulated momentresistance values or by applying all applicable adjustmentfactors to the reference bending strength for the product.The complete equation for calculation of factored momentresistance is:8N bM′ = 8N bF b′ SC tC LC Fis the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100°F on a sustained basis. For higher temperatureconditions, use the value of C t given in the productsupplement or guideline.is the beam stability factor. Tabulated resistancesassume full lateral support and torsional restraint atpoints of support. For bending members that arenot fully laterally supported, use the value of C Lgiven in Sec. 5.2.3 of AF&PA/ASCE 16-95. Thebeam stability factor shall not be applied cumulativelywith the volume factor for glulam members.See the Wood I-Joists Guideline for special considerationsrelated to stability analysis of theseproducts.is the size factor. Tabulated resistances already includethe size factor. For calculations starting fromAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 4343C VC fuC rC creference bending strengths, use the value of C Fgiven in the product supplement or guideline.is the volume factor for glulam bending memberswith the load applied perpendicular to the wide face.Tabulated resistances do not include the volumefactor. Use the value of C V given in the StructuralGlued Laminated Timber Supplement.is the flat use factor for sawn lumber and glulam.None of the selection tables include bending membersused flatwise. Thus, calculations must startfrom reference bending strengths. Use the value ofC fu given in the Structural Lumber or StructuralGlued Laminated Timber Supplement. For glulamapplications with the load applied parallel to thewide face, use the flat use factor defined in the StructuralGlued Laminated Timber Supplement.is the load sharing factor for members in systemsthat qualify as load sharing assemblies, as definedin AF&PA/ASCE 16-95, Sec. 5.3.2.2.is the curvature factor for glulam beams. None ofthe selection tables include curved bending members.Thus, calculations must start from referencebending strengths. Use the value of C c given inAF&PA/ASCE 16-95, Sec. 5.6.1.C f is the form factor. For circular members other thanpoles and piles or for square members bent aboutthe diagonal, use the value of C f given in AF&PA/ASCE 16-95, Sec. 5.1.7.C ptC rtis the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the product supplement orguideline.is the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the product supplement orguideline.For untreated straight, rectangular, laterally supportedbeams stressed in edgewise bending in single member useand used in a normal building environment (meeting thereference conditions of Sec. 1.1.5), the general equationfor F b ′ reduces to:F b′ = F b(C For C V)5BENDING MEMBERS5.3 Design for ShearThe basic equation for shear design of bending members(AF&PA/ASCE 16-95, Eq. 5.1-2) is:where8N vV′ $ V u8 = time effect factor (seeAF&PA/ ASCE 16-95Table 1.4-2)N v= 0.75V′ = adjusted shear resistance parallel to grain= factored shearV uFactored shear resistance (8N v V) is tabulated in beamselection tables and joist selection tables for many commonproducts. Tabulated values are suitable for membersthat conform to all conditions in the checklist in Section5.5.5.3.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting tabulated shearresistance values or by applying all applicable adjustmentfactors to the reference shear strength for the product. Thecomplete equation for calculation of factored shear resistanceis:8N vV′ = 8N vF v′Ib/Qwhich, for rectangular unnotched bending members, reducesto:where8N vV′ = 2/3 (8N vF v′) AI = moment of inertia (in 4 )AMERICAN FOREST & PAPER ASSOCIATION

44 BENDING MEMBERSC MC tC HF v′ = F vC MC tC HC ptC rtF v= reference shear strength (ksi)is the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, multiplyby the value of C M given in the productsupplement or guideline.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For high temperatureconditions, multiply by the value of C t given in theproduct supplement or guideline.C ptC rtis the shear stress factor for sawn lumber. Tabulatedresistances have been reduced to allow for theoccurrence of splits, checks and shakes. For bendingmembers in which the length of split or size ofcheck or shake is known and no increase in them isanticipated, multiply by the value of C H given inthe Structural Lumber Supplement.is the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the product supplement orguideline.is the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the product supplement orguideline.5.4 Special Considerations5.4.1 Stability ConsiderationsBeams are often tied into the structural system eitherby sheathing or connection to a series of closely spacedsecondary framing members. For flexural members notfully laterally supported, the beam stability factor, C L , isused to compute the reduction in flexural capacity (seeAF&PA/ASCE 16-95, Sec. 5.2.3).As with columns, designers should note that the beamstability factor is highly dependent upon assumed boundaryconditions.5.4.2 TorsionFlexural members subjected to torsion should bechecked using AF&PA/ASCE 16-95 Eq. 5.5-1. As notedin AF&PA/ASCE 16-95, the material property to be usedwhen checking torsional resistance is two-thirds of theadjusted horizontal shear strength for sawn lumber andthe adjusted radial tension strength for glulam. To determinedthe appropriate property for use with other products,contact the manufacturer.5.4.4 PondingFlat or near-flat roof systems have the potential foraccumulation of load due to ponding. Appendix A3 ofAF&PA/ASCE 16-95 provides guidance for checking theminimum slope for which ponding must be considered. Italso provides a design procedure for calculation of pondingloads.As with stability considerations, ponding has the potentialto cause sudden collapse of portions of the structure.While adequate slope is the first preference, experiencedengineers designing near-flat roofs take extensive precautionsto guard against ponding. These precautions includeprimary and secondary drain systems and design of structuralsystems with adequate buffers of strength andstiffness.5.4.3 Radial TensionStresses induced in curved members under load includea component of stress in the direction of the radiusof curvature. Radial tension is a specialized design considerationthat is addressed in AF&PA/ASCE 16-95, Sec.5.6.2.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 45455.5 Checklist: Using Joist and Beam Selection TablesJoist and beam selection tables provide values for factored moment and shear resistance (8N b M′, 8N v V′) forcommon grades and sizes of straight bending members. Tabulated values apply to beams that satisfy the followingconditions:√ “dry” service condition (C M = 1.0)√ “normal” temperature range (C t = 1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (8 = 0.80)√ fully laterally supported (C L = 1.0)5√ rectangular member bent about its principal axis (C f = 1.0)For beams that do not satisfy all of these conditions, review the design equations in this chapter and modifytabulated values as necessary.To compute the factored resistance for a specific condition, apply the design equations directly (productspecificdesign adjustment factors and reference resistance values are provided in each supplement).BENDING MEMBERS5.6 Design ExamplesExample 5-1: Simple Span I-joistDesign a simple span I-joist to resist a factored moment(M u ) of 16.6 kip-feet and a factored shear (V u ) of 2.5kips over a span of 26 feet. Assume dry moisture servicecondition, untreated material, full lateral support, adequatebearing and a time effect factor of 0.80.Practical ConsiderationsEfficient choice of a trial section requires practical,as well as engineering, considerations. For example,choice of joist depth is often controlled by architectural,rather than structural, considerations. Consult your localsupplier for assistance.Engineering CalculationsUsing Selection Tables: Select a member from theI-joist selection tables provided by the joist manufacturerthat meets the requirements of moment (M u ) and shear(V u ) shown above.An I-joist, 16-inches deep has a tabulated momentresistance (8N b M′) of 17.0 kip-feet and tabulated shearresistance (8N v V′) of 4.6 kips. This joist is acceptable ona strength basis.In addition to the strength calculation, one must checkdeflection relative to code-prescribed limits ormanufacturer’s recommendations. Assume that the manufacturerrecommends a maximum deflection of L/480(where L is the design span) under live load for this joist.If the tabulated stiffness (EI) of this joist is 5600 kip-ft 2 ,the computed deflection of the joist is computed underthe unfactored live load of 0.1 klf on the design span of 26feet would be 1.28 inches or approximately L/240. Tomeet the L/480 deflection limit would require a stiffness,EI of 11,200 kip-ft 2 , 100% stiffer than provided by thisjoist. Thus, the deflection criteria can only be satisfied bydecreasing the spacing of the joists or by choosing a stifferjoist.Note that shear deflection must also be computed forthis design. Refer to the manufacturer’s design literaturefor guidance on including the effects of shear deflectioninto the calculations.AMERICAN FOREST & PAPER ASSOCIATION

46 BENDING MEMBERSExample 5-2: Glulam BeamAssuming conditions from Example 5-1, try a 3-1/8 x10-1/2 inch glulam beam (24F-V4, Douglas-Fir). Fromthe Structural Glued Laminated Timber Supplement, obtainF b and F v from the reference resistance tables andapplicable adjustment factors.λ φ v8N bM′ = 8N bF b′ S= 8N b(F b@ C V) S= (0.80) (0.85) (6.1) (1.00) (57.42)= 238 kip-in = 19.8 kip-ft8N vV′ = 8N vF v′ Ib/Q⎛⎜⎝23=F ′ Av⎞⎟⎠(for a rectangular member)= (0.80) (0.75) (2/3) (0.545) (32.8)= 7.2 kipsThis beam also satisfies the strength limit states for abending member. Once again, the member stiffness mustbe greater than or equal to EI req’d to meet serviceabilitycriteria for the member design.Example 5-3: Notched BeamAssuming the same conditions and material from Example5-2, check to see if shear resistance is still adequateif both ends are notched to a depth of 1 inch.Practical ConsiderationsNotches should be avoided in design whenever possible.In this case, AF&PA/ASCE 16-95 Section 5.1.4limits notch depth to 10% of beam depth. Even the smallestnotch designed into a member can lead to problems inthe field (overcutting of the notch requiring reinforcement,red tags from building inspectors requiring special calculations,etc.).Unfortunately, notches sometimes occur in application,and engineers must calculate the structural adequacyof the installed condition. AF&PA/ASCE 16-95 provisionsin Section 5.4.3 are useful for these instances.Engineering Calculations⎛ 2λφ V′= λφ⎜F′b d⎝ 3( )v n v n=⎛ dn⎞⎞⎜ ⎟⎟⎝ d ⎠⎠⎛( ) ( )( )( )( ) ( )060 . ⎜ 067 . 0545 . 3125 . 95 .95 .⎜⎝= 59 . kips⎞10.5 ⎟⎠This beam still satisfies the shear strength limit state.Example 5-4: Beam with PartialLateral SupportCheck the glulam beam from Example 5.2, assumingthat it is laterally supported only by a crossing beam at itsmid-span.From AF&PA/ASCE 16-95, Sec. 5.2.1.3, the effectivelaterally unsupported length, R e , of this 26-foot longmember is the distance between points of compressionedge bracing, or 13 feet. Using the tabulated E 05y of 1400ksi and a computed weak axis moment of inertia, I y , of26.7 in 4 , the elastic lateral buckling moment, M e , is computedfrom AF&PA/ASCE 16-95, Eq. 5.2-7:M e= 2.40 E y05(I y/R e)= 47.9 kip-ftThis value is used to compute α b , which in turn isused to compute the beam stability factor C L :C=Lαb=φλ φMs ebSxFbx′(0.85)(47.9)(12)(0.80)(0.85)(57.42)(6.1)= 2.05bb= 1+ α ⎛-1+ α ⎞ α⎜ ⎟ -2c⎝ 2c⎠ cb= 1+2.05(2)(0.95) - ⎛ 1+2.05 ⎞⎜ ⎟⎝ (2)(0.95) ⎠= 0.958b22bb2.05-0.95Thus, when full lateral support is not provided, thefactored moment resistance of this member decreases from19.8 kip-ft (above) to (19.8) (0.958) = 18.97 kip-ft. Thus,the beam still satisfies the strength limit state.AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION47BENDING PLUSAXIAL LOADS6.1 General Information 486.2 Design 4866.2.1 Adjustment Factors 486.2.2 Design Techniques 486.3 Checklist: Using Combined Bendingand Axial Member Selection Tables 496.4 Design Examples 49Example 6-1: Stud Wall 49Example 6-2: Truss Chord UnderCombined Bendingand Tension 50Example 6-3: Glulam Truss ChordUnder Biaxial Bending 50AMERICAN FOREST & PAPER ASSOCIATION

48 BENDING PLUS AXIAL LOADS6.1 General InformationThis chapter covers design of members stressed undercombined bending and axial loads. Examples of suchmembers include truss chords and wall studs. The discussionfocuses on axial loads in compression. For designsin which the axial load is in tension rather than compression,the designer should use AF&PA/ASCE 16-95Eqs. 6.2-1 and 6.2-2.The applicable strength limit state for these membersis explicit in AF&PA/ASCE 16-95 equations — limitingthe sum of various stress ratios to less than or equal tounity.See the Structural Lumber Supplement for factoredmember resistance values (wall stud, combined loadingselection tables) under combined bending and axial loads.6.2 DesignThe equation for design of members under bendingplus compression loads (AF&PA/ASCE 16-95, Eq. 6.3-1)is:whereuc2⎛ P ⎞ MMmy⎜ ⎟ + + ≤ 1.0⎝ λφ P′⎠ λ φ ′ λ φ M′mxbMxb8 = time effect factor (AF&PA/ASCE 16-95, Table1.4-2)N c= 0.90P′ = adjusted compression resistance= factored compression forceP uN b= 0.85M x′ = adjusted moment resistance (strong axis)M mx= factored moment (strong axis)M y′ = adjusted moment resistance (weak axis)M my= factored moment (weak axis)Adjusted moments and compression resistances aretabulated in appropriate selection tables in product supplements.Tabulated values are suitable for members thatconform to all conditions of the checklist in Section 6.3.y6.2.1 Adjustment FactorsMembers that do not meet all conditions in the Section6.3 checklist must be designed by adjusting tabulatedresistance values or by applying all applicable adjustmentfactors to the reference strength for the product. See Chapters4 and 5 for discussion of applicable adjustment factorsfor bending or compression.6.2.2 Design TechniquesA key to understanding design of members under combinedbending and axial loads is the insight thatcomponents of the design equation are simple ratios offactored compressive force (or moment) to factored compressionresistance (or moment resistance). One differencebetween this equation and others familiar to engineers isthe fact that the compression term is squared. This is theresult of empirical fitting to test data. As a result, moderatecompressive stresses do not have as large an impacton strength (under combined loads) as previously thought.It is thought that this is the result of compressive “reinforcing”of what would otherwise be a tensile failure modein bending.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 49496.3 Checklist: Using Combined Bending and AxialMember Selection TablesCombined bending/axial selection tables in the Structural Lumber Supplement provide values for maximumfactored moment (M u ) for common grades and sizes of wall studs. Separate tables are provided for wall studsunder compression load ratios (defined as P u / 8N c P′) of 0.20, 0.40, 0.60 and 0.80. Tabulated values apply tomembers that satisfy the following conditions:√ “dry” service condition (C M = 1.0)√ “normal” temperature range (C t = 1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (8 = 0.80)For members that do not satisfy all of these conditions, review the design equations in this chapter andmodify tabulated values as necessary.To compute the factored resistance for a specific condition, apply the design equations directly (productspecificdesign adjustment factors and reference resistance values are provided in each supplement).6.4 Design ExamplesExample 6-1: Stud wallDesign a stud wall, 10 feet high, in which the factoredcompressive force (P u ) equals 4.5 kips per stud and thefactored moment (M u ) equals 8.3 kip-inch per stud. Assumestandard conditions of load duration, dry moistureservice condition, untreated material. The studs are assumedto be pinned at each end and are laterally supportedin the plane of the wall by sheathing.Practical ConsiderationsAs this is a reasonably high wall, one would likelychoose a larger stud cross section to provide substantialstiffness. Code requirements are not always clear in thisarea. Engineering judgment should be used to considerthe absolute deflections that might be tolerated by, forexample, windows in this wall. For a deflection sensitiveapplication, experienced engineers will often design thestuds to a stringent deflection limit such as that used forfloors.The remainder of this example will compute only thestrength limit states for this stud wall.Engineering CalculationsUsing Selection Tables: Select a member from thestud wall selection tables (Structural Lumber SupplementTable 5.6) that meets the compression (P u ) and moment(M u ) requirements shown above for an effective length of10 feet.Try nominal 2X4, Select Structural Southern Pine lumber.The factored column resistance, λφ c P′, is 3.3 kipsfrom Table 5.2 of the Structural Lumber Supplement. Sincethis is less than the 4.5 kips compressive force, this memberis not adequate from a compression strength standpointalone.Increase the size to 2X6 and use No. 2 grade. Thecapacity would be computed from the table with a compressionload ratio of 0.40 (4.5/10.1) and would have amaximum factored moment, M u , of 10.7 kip-in. This exceedsthe design requirement. Note that the choice of aratio from the table that is less than the actual ratio (in thiscase, 0.45) is not conservative, however, by inspection itis clear that the tabulated M u of 10.7 kip-in exceeds theactual factored moment of 8.3 kip-in considerably. Whileinterpolation within these tables is permissible, the usershould note that underlying equations are nonlinear —thus, interpolated values would only be approximate.6BENDING PLUS AXIAL LOADSAMERICAN FOREST & PAPER ASSOCIATION

50 BENDING PLUS AXIAL LOADSUsing Reference Strength and Selection Tables: Calculatecompression and bending resistance.The design equation for member resistance under combinedbending and compression is Eq. 6.3-1 in AF&PA/ASCE 16-95:⎛ P ⎞⎜⎝ λ φ P ′⎟⎠uc2+MλφmxbMx′≤ 1.0Try a nominal 2X6 No. 2 Southern Pine member. Fromthe Structural Lumber Supplement, the factored compressionresistance (8N c P′) is 10.1 kips. Likewise, the factoredmoment resistance (8N b C r M′) is 18.8 kip-in. E 05 = 970ksi.AF&PA/ASCE 16-95 Section 6.3 shows that calculationof M mx will require computation of the criticalbuckling resistance (P ex ) and moment magnification factor(B bx ).To determine P ex , use AF&PA/ASCE 16-95 Equation4.3-4:P =e2π E 05′ I2(K λ)eSolving this equation for the selected member resultsin P ex equal to 13.8 kips.The magnified moment can now be computed usingAF&PA/ASCE 16-95 Eq. 6.3-2:M mx = B bx M bx + B sx M sxSince this stud will not exhibit appreciable sidesway,the second term (B sx ) is equal to zero.Compute B bx using AF&PA/ASCE 16-95 Eq. 6.3-4:Bbx=Cmx⎛ Pu⎜ 1 -⎝ φ Pcex⎞⎟⎠≥ 1.0For this case, C mx equals 1.00. The parameter B bxequals 1.566, therefore, M mx equals 8.3(1.566) = 13 kipin.Substituting back into Eq. 6.3-1 we compute thecombined strength equation to be equal to 0.20 + 0.69 =0.89. Thus, the design satisfies the strength limit state.Example 6-2: Truss Chord underCombined Bending and TensionDesign a truss bottom chord subjected to a factoredtensile force (T u ) of 26.9 kips and a factored moment (M u )of 1.6 kip-ft. Assume standard conditions of load duration,dry moisture service condition, untreated materialand full lateral support.Engineering CalculationsUsing Selection Tables: No selection tables are providedfor members under combined bending and tension.Using Reference Strength Tables: Calculate combinedtension and bending resistance.Try a 3-1/8X6 inch Western Species 24F-V10 DF/HFglulam member. From the Structural Glued LaminatedTimber Supplement: F t = 3.11 ksi and F b = 6.10 ksi8N tT′ = 37.32 kips8N bM′ = 6.48 kip-ftSubstituting these values into AF&PA/ASCE 16-95Equation 6.2-1:⎛ T ⎞uMux⎜λ φ T ′⎟ + ≤ 1.0⎝ ⎠ λ φ bM x ′tyields (0.72 + 0.25) = 0.97 and satisfies the strengthlimit state.Example 6-3: Glulam Truss ChordUnder Biaxial BendingDesign a glulam truss chord with a 40 foot effectivelength, subjected to factored moments (M bx , M by ) of4.5 kip-ft and 2.6 kip-ft, respectively, and a factored compressionforce (P u ) of 3.8 kips. Assume standard conditionsof load duration, dry moisture service condition, and untreatedmaterial. The chord segment has lateral supportat its ends.Engineering CalculationsUsing Selection Tables: No selection tables are providedfor specialized cases such as members under biaxialbending and compression.Using Reference Strength Tables: Calculate the memberresistance relative to the limit state imposed byAF&PA/ASCE 16-95 Eq. 6.3-1.Try a 5-1/8x13-3/4 inch 24F-V4 Southern Pine glulammember. From the Structural Glued Laminated TimberSupplement: F c = 2.52 ksi, F bx = 6.10 ksi, F by = 3.18 ksi,E 05x = 1500 ksi, and E 05y = 1200 ksi8N bM x′ = (0.80)(0.85)(6.10)(161.5) = 669.9 kip-in8N bM y′ = (0.80)(0.85)(3.18)(60.19) = 130.2 kip-in(E 05I) x= 1665 x 10 3 kip-in 2(E 05I) y= 185 x 10 3 kip-in 2AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER5151The design equation for member resistance under biaxialbending and compression is Eq. 6.3-1 in AF&PA/ASCE 16-95:Magnified moments can now be computed usingAF&PA/ASCE 16-95 Eq. 6.3-2 and 6.3-3:uc2⎛ P ⎞ M Mmy⎜λ φ P ′⎟ + + ≤ 1.0⎝ ⎠ λ φ ′ λ φ M ′mxbMxbAF&PA/ASCE 16-95 Section 6.3 shows that the calculationwill require computation of the critical bucklingresistances (M e , P ex , P ey ) and moment magnification factors(B bx , B by ).To determine P′, use AF&PA/ASCE 16-95 section4.3.2. From Eq. 4.3-4:yM mxM my= B bxM bx+B sxM sx= B byM by+B syM sySince this beam will not exhibit appreciable sidesway,the second terms (B sx , B sy ) are equal to zero.Compute B bx and B by using AF&PA/ASCE 16-95 Eq.6.3-4 and 6.3-5:Bbx=Cmx⎛ Pu⎜ 1 -⎝ φ Pcex⎞⎟⎠≥1.0P =e2π E 05′ I2(K λ)eSolving this equation for the selected member resultsin P ex equal to 71.3 kips and P ey equal to 7.9 kips.Since P ey < P ex , the weak axis will control in compressionbuckling. Therefore, calculate C p from Equation 4.3-2using P ey . This yields:P′ = C pF c* A = (0.05)(2.52)(70.47) = 8.88 kips8N cP′ = (0.8)(0.9)(8.88) = 6.4 kipsFrom AF&PA/ASCE 16-95 Eq. 5.2-7:MeE ′= 2.40 05IyReThis yields M e = 925 kip-in.Bby=Cmy⎛⎜ Pu1 - -⎜ φcP⎝ey2⎛ M ⎞ ⎞ux⎜ ⎟ ⎟⎝ φbMe⎠ ⎟⎠For this case, C mx and C my are equal to 0.85 and B bxequals 1.0 (computed as 0.9, but set by equation to a minimumof 1.0.) Similarly, B by equals 1.84, M mx equals 4.5kip-ft and M my equals 4.8 kip-ft. Substituting back intoEq. 6.3-1:ucPo′2uxbMxby≥1.0⎛ P ⎞ M Muy⎜λ φ⎟ + + ≤ 1.0⎝ ⎠ λ φ ′ λ φ M ′yields (0.35 + 0.08 + 0.44) = 0.88 # 1.0. This membersatisfies the strength limit state.6BENDING PLUS AXIAL LOADSAMERICAN FOREST & PAPER ASSOCIATION

52BENDING PLUS AXIAL LOADSAMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION53MECHANICALCONNECTORS7.1 General Information 547.2 Nails, Spikes and Wood Screws 547.3 Bolts, Lag screws, Drift Pins, Dowels 567.4 Shear Plates and Split Rings 577.5 Typical Connection Details 587.6 Checklist: Using ConnectionSelection Tables 667.7 Design Examples 661.1 Nails - Top Plate Splice 661.2 Nails - Shear Wall Chords Ties 672.1 Lag Screws - Drag Strut toShear Wall 682.2 Lag Screw - Suspended Loads(withdrawal) 703.1 Bolts - Bowstring Roof TrussSplice 703.2 Bolts - Eccentric BoltedConnection 724.1 Split-Ring Connection 757AMERICAN FOREST & PAPER ASSOCIATION

54 MECHANICAL CONNECTORS7.1 General InformationThis chapter covers design of connections betweenwood members using metal fasteners. Several commonconnection types are outlined below.7.1.1 Dowel-type (nails, bolts,screws, pins)These connectors rely on metal-to-wood bearing fortransfer of lateral loads and on friction or mechanical interfacesfor transfer of axial (withdrawal) loads. They arecommonly available in a wide range of diameters andlengths.7.1.2 Shear Plates and Split RingsThese connectors rely on their geometry to providelarger metal-to-wood bearing areas per connector. Bothare installed into precut grooves or daps in the members.7.1.3 Metal Connector PlatesMetal connector plates provide dual functions in whichprotruding teeth are the connecting elements and theunpunched portions of the plates act as splice members.Metal connector plates are proprietary connectors. Seethe manufacturer’s literature for more information regardingdesign of metal connector plates using LRFD.7.1.4 Structural FramingConnectionsStructural framing connections provide a single-piececonnection between two framing members. They generallyconsist of bent or welded steel, carrying load fromthe supported member (through direct bearing) into thesupporting member (by hanger flange bearing, fastenershear, or a combination of the two). Structural framingconnections are proprietary connectors. See themanufacturer’s literature or the Guideline for Pre-EngineeredMetal Connectors for more information regardingdesign of structural framing connections using LRFD.7.1.5 Other ConnectorsJust as the number of possible building geometries ispotentially limitless, so too is the number of possible connectiongeometries. In addition to providing customfabrication of connectors to meet virtually any geometrythat can be designed, metal connector manufacturers haveseveral categories of connectors that do not fit the categoriesabove, including:• framing anchors• hold-down devices• straps and tiesThese connectors are also generally proprietary connectors.See the manufacturer’s literature or the Guidelinefor Pre-Engineered Metal Connectors for more informationregarding design using LRFD.Connections are designed so that no applicable limitstate is exceeded under factored loads. Strength limit statesfor connections include lateral or withdrawal of the fastener,and tension or shear in the metal. Some types ofconnections also include compression perpendicular tograin as a limit state.See the Structural Connections Supplement for factoredlateral (8N z Z) and factored withdrawal (8N z Z w )resistance values.Users should note that design of connections may alsobe controlled by serviceability limitations. These limitationsare product specific and are discussed in specificproduct supplement or guideline documents. Users arecautioned that serviceability limit states are generallychecked under unfactored, rather than factored, loads.7.2 Nails, Spikes and Wood Screws7.2.1 Design for Lateral LoadThe basic equation for design of these fasteners underlateral load (AF&PA/ASCE 16-95, Eq. 7.1-1) is:where8N zZ′ $ Z u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N z= 0.65Z′ = adjusted lateral resistanceZ u= factored lateral forceAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER5555Factored lateral resistance is tabulated in the nail/spikeand wood screw selection tables in the Structural ConnectionsSupplement. Tabulated values are suitable forconnections that conform to all conditions of the checklistin section 7.6.For most nails, spikes or wood screws with adequatepenetration and used in a normal building environmentthe general equation for Z′ reduces to Z′ = Z.7.2.2 Design for or Withdrawal al Load7.2.1.1 Adjustment FactorsConnections that do not meet all conditions in thechecklist must be designed by adjusting tabulated lateralresistance values or by applying all applicable adjustmentfactors to the reference lateral strength for the connection.The complete equation for calculation of factoredlateral resistance is:whereC MC tC dC egC diC tn8N zZ′ = 8N zZ (C MC tC dC egC diC tn)Z = reference lateral strength tabulated in theStructural Connections Supplementis the wet service factor. Tabulated resistances arebased on dry fabrication and dry use. For other moistureconditions, use the value of C M given in theStructural Connections Supplement.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For higher temperatureconditions, use the value of C t given in the StructuralConnections Supplement.is the penetration depth factor. Tabulated resistancesassume penetration into the main member of at least12D (nails/spikes) or 7D (wood screws). For connectionsthat do not meet this requirement, use thevalue of C d given in the Structural ConnectionsSupplement.is the end grain factor. For connectors driven intothe end grain of the member, use the value of C eggiven in the Structural Connections Supplement.is the diaphragm factor. For nails used in diaphragms,use the value of C di given in the StructuralConnections Supplement.is the toe nail factor. For nails driven into the jointat an angle to the members (“toe nailed”), use thevalue of C tn given in the Structural ConnectionsSupplement.The basic design equation for these fasteners underwithdrawal loads is similar to that used for lateral loads,substituting Z w for Z:where8N zZ w′ $ Z uZ w′ = adjusted withdrawal resistanceZ u= factored axial (withdrawal) forceAs for lateral resistance, factored withdrawal resistancesare tabulated in selection tables and are suitablefor connections that conform to all conditions of the checklistin section 7.6.7.2.2.1 Adjustment FactorsThe list of adjustment factors for withdrawal resistanceis similar to that for lateral resistance. Thedifferences are as follows:C dC egC diC tndoes not apply.does not apply. These connectors may not be loadedin withdrawal if driven into the end grain of themember.does not apply.does not apply.7.2.3 Installation RequirementsTo achieve stated design values, connectors must complywith installation requirements such as spacing ofconnectors, minimum edge and end distances, proper drillingof lead holes and minimum fastener penetration.AF&PA/ASCE 16-95 requirements for these items aresummarized in the Structural Connections Supplement.7.2.4 Load at an Angle to GrainAnother consideration of interest to the designer isload at an angle to grain (AF&PA/ASCE 16-95 section7.2.3).7MECHANICAL CONNECTORSAMERICAN FOREST & PAPER ASSOCIATION

56 MECHANICAL CONNECTORS7.3 Bolts, Lag Screws, Pins, Dowels7.3.1 Design for Lateral LoadThe basic equation for design of these connectorsunder lateral load (AF&PA/ASCE 16-95, Eq. 7.1-1) is:where8N zZ′ $ Z u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N z= 0.65Z′ = adjusted lateral resistanceZ u= factored lateral forceFactored lateral resistance is tabulated in bolt and lagscrew selection tables in the Structural ConnectionsSupplement. Tabulated values are suitable for connectionsthat conform to all conditions of the checklist insection 7.6.7.3.1.1 Adjustment FactorsConnections that do not meet all conditions in thechecklist must be designed by adjusting tabulated lateralresistance values or by applying all applicable adjustmentfactors to the reference lateral strength for the connection.The complete equation for calculation of factoredlateral resistance is:8N zZ′ = 8N zZ (C MC tC gC )C dC eg)C gC )C dC egis the group action factor. For connections usingmore than one fastener, multiply by the value of C ggiven in the Structural Connections Supplement.is the geometry factor. For connections that do notmeet the minimum requirements of spacing or edge/end distance, multiply by the value of C ) given inthe Structural Connections Supplement.is the penetration depth factor. Tabulated resistancesassume penetration into the main member of at least8D for lag screws. For connections that do not meetthis requirement, multiply by the value of C d givenin the Structural Connections Supplement.is the end grain factor. For connectors driven intothe end grain of the member, multiply by the valueof C eg given in the Structural Connections Supplement.For most bolts and lag screws with adequate penetrationand spacing, and used in a normal buildingenvironment the general equation for Z′ reduces to Z′ = ZC g .7.3.2 Design for Withdrawal LoadThe basic design equation for these fasteners underwithdrawal loads is similar to that used for lateral loads,substituting Z w for Z:where:Z = minimum of equations in AF&PA/ASCE 16-95Table 7.5-2(a) through 7.5-2(c) (kips)where:8N zZ w′ $ Z uZ w′ = adjusted withdrawal resistanceC MC tis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, multiplyby the value of C M given in the StructuralConnections Supplement.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100EF on a sustained basis. For high temperatureconditions, multiply by the value of C t given in theStructural Connections Supplement.Z u= factored axial (withdrawal) forceAs for lateral resistance, factored withdrawal resistancesare tabulated in the selection tables and are suitablefor connections that conform to all conditions of the checklistin section 7.6.7.3.2.1 Adjustment FactorsThe list of adjustment factors for withdrawal resistanceis similar to that for lateral resistance. Thedifferences are as follows:AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER5757C gdoes not apply.7.3.3 Installation RequirementsC )C dC egdoes not apply.does not apply.is different for withdrawal load than for lateral load.Multiply by the proper value from the StructuralConnections Supplement.To achieve the stated design values, connectors mustcomply with installation requirements such as spacing ofconnectors, minimum edge and end distances, proper drillingof lead holes and minimum fastener penetration.AF&PA/ASCE 16-95 requirements for these items aresummarized in the Structural Connections Supplement.7.4 Shear Plates and Split Rings7.4.1 Design for Lateral LoadThe basic equation for design of these connectorsunder lateral load (AF&PA/ASCE 16-95, Eq. 7.1-1) is:C Mis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, multiplyby the value of C M given in the StructuralConnections Supplement.where8N zZ′ $ Z u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N z= 0.65Z′ = adjusted lateral resistanceZ u= factored lateral forceFactored lateral resistance is tabulated in the split ringand shear plate selection tables in the Structural ConnectionsSupplement. Tabulated values are suitable forconnections that conform to all conditions of the checklistin section 7.6.7.4.1.2 Adjustment FactorsConnections that do not meet all conditions in thechecklist must be designed by adjusting tabulated lateralresistance values or by applying all applicable adjustmentfactors to the reference lateral strength for the connection.The complete equation for calculation of factoredlateral resistance is:where8N zZ′ = 8N zZ (C MC tC gC )C dC st)Z = reference lateral strength tabulated in theStructural Connections SupplementC tC gC )C dC stis the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100EF on a sustained basis. For high temperatureconditions, multiply by the value of C t given in theStructural Connections Supplement.is the group action factor. For connections usingmore than one fastener, multiply by the value of C ggiven in the Structural Connections Supplement.is the geometry factor. For connections that do notmeet the minimum requirements of spacing or edge/end distance, multiply by the value of C ) given inthe Structural Connections Supplement.is the penetration depth factor. When lag screwsare used rather than bolts, the tabulated resistancesassume penetration into the main member of at least8D. For connections that do not meet this requirement,multiply by the value of C d given in theStructural Connections Supplement.metal side plate factor. For 4-inch shear plates usingmetal side plates, multiply by the value of C stgiven in the Structural Connections Supplement.For most shear plate and split ring connections withadequate spacing, and used in a normal building environmentthe general equation for Z′ reduces to Z′ = Z C g .7.4.2 Installation Requirements7MECHANICAL CONNECTORSTo achieve stated design values, connectors must complywith installation requirements such as spacing ofAMERICAN FOREST & PAPER ASSOCIATION

58 MECHANICAL CONNECTORSconnectors, minimum edge and end distances, properdapping and grooving, drilling of lead holes and minimumfastener penetration. AF&PA/ASCE 16-95 requirementsfor these items are summarized in the Structural ConnectionsSupplement.7.5 Typical Connection Details7.5.1 General Concepts of Well-Designed ConnectionsConnections must obviously provide the structuralstrength necessary to transfer loads. Well-designed connectionshold the wood members in such a manner thatshrinkage/swelling cycles do not induce splitting acrossthe grain. Well-designed connections also minimize regionswhich might collect moisture — providing adequateclearance for air movement to keep the wood dry. Finally,well-designed connections minimize the potentialfor tension perpendicular to grain stresses — either underdesign conditions or under unusual loading conditions.The following connection details are organized intonine groups:2. Similar to detail 1 with steel bearing plate only underthe beam.1. Beam to concrete or masonry wall connections2. Beam to column connections3. Column to base connections4. Beam to beam connections5. Cantilever beam connections6. Arch peak connections7. Arch base support8. Moment splice9. Problem connectionsMany of the detail groups begin with a brief discussionof the design challenges pertinent to this specific typeof connection. Focusing on the key design concepts of abroad class of connections often leads to insights regardinga specific detail of interest.Group 1. Beam to Concrete or Masonry WallConnectionsDesign concepts. Concrete is porous and “wicks”moisture. Good detailing permits wood to be in directcontact with concrete.3. Similar to detail 1 with slotted holes to accommodateslight lateral movement of the beam under load. This detailis more commonly used when the beam is sloped, ratherthan flat.1. Beam on shelf in wall. The bearing plate distributesload and keeps the beam from direct contact with the concrete.Steel angles provide uplift resistance and can alsoprovide some lateral resistance. The end of the beamshould not be in direct contact with the concrete.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 5959Group 2. Beam to Column ConnectionsDesign concepts. All connections in the group musthold the beam in place on top of the column. This sheartransfer is reasonably easy to achieve. Some connectionsmust also resist some beam uplift. Finally, for cases inwhich the beam is spliced, rather than continuous overthe column, transfer of forces across the splice may berequired.6. Custom welded column caps can be designed to transfershear, uplift, and splice forces. Note design variationsto provide sufficient bearing area for each of the beamsand differing plate widths to accommodate differencesbetween the column and the beam widths.4. Simple steel dowel for shear transfer.7. Combinations of steel angles and straps, bolted andscrewed, to transfer forces.75. Concealed connection in which a steel plate is insertedinto a kerf in both beam and column. Transverse pins orbolts complete the connection.8. A very common connection — beam seat welded tothe top of a steel column.MECHANICAL CONNECTORSAMERICAN FOREST & PAPER ASSOCIATION

60 MECHANICAL CONNECTORS9. When both beams and columns are continuous and theconnection must remain in-plane, either the beam or thecolumn must be spliced at the connection. In this detailthe column continuity is maintained. Optional shear platesmay be used to transfer higher loads. Note that, unlessthe bolt heads are completely recessed into the back ofthe bracket, the beam end will likely require slotting. In abuilding with many bays, it may be difficult to maintaindimensions in the beam direction when using this connection.11. Similar to details 1 and 2.11B. Alternate to detail 11.Group 3. Column to Base ConnectionsDesign Concepts. Since this is the bottom of the structure,it is conceivable that moisture from some sourcemight run down the column. Experience has shown thatbase plate details in which a steel “shoe” is present cancollect moisture that leads to decay in the column.12. Similar to detail 3.10. Similar to detail 4, with a bearing plate added.Group 4. Beam to Beam ConnectionsDesign concepts. Many variations of this type of connectionare possible. When all members are flat and theirtops are flush, the connection is fairly straightforward.Slopes and skews require special attention to fabricationdimensions — well-designed connections provide adequateclearance to insert bolts or other connectors andalso provide room to grip and tighten with a wrench. Especiallyfor sloped members, special attention is requiredto visualize the stresses induced as the members deflectunder load — some connections will induce large perpendicularto grain stresses in this mode.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 616113. Bucket-style welded bracket at a “cross” junction.The top of the support beam is sometimes dapped to accommodatethe thickness of the steel.the pin is installed. Note that the kerf in the suspendedbeam must accommodate not only the width of the steelplate, but also the increased width at the fillet welds.14. Face-mounted hangers are commonly used in beamto beam connections. In a “cross” junction special attentionis required to fastener penetration length into thecarrying beam (to avoid interference from other side).17. Similar to detail 13, with somewhat lower loadcapacity.715. Deep members may be supported by fairly shallowhangers — in this case, through-bolted with shear plates.Clip angles are used to prevent rotation of the top of thesuspended beam. Note that the clip angles are not connectedto the suspended beam — doing so would restraina deep beam from its natural across-the-grain shrinkingand swelling cycles and would lead to splits.18. Clip angle to connect crossing beam.MECHANICAL CONNECTORS19. Special detail to connect the ridge purlin to slopedmembers or to the beak of arch members.16. Concealed connections similar to detail 5. The suspendedbeam may be dapped on the bottom for a flushconnection. The pin may be slightly narrower than thesuspended beam, permitting plugging of the holes afterAMERICAN FOREST & PAPER ASSOCIATION

62 MECHANICAL CONNECTORS20. Similar to detail 19, but with the segments of the ridgepurlin set flush with the other framing.23. Similar to detail 22, with added shear plate.20B. Alternate to detail 20.24. Similar to detail 22 for low slope arches. Side platesreplace the threaded rod.Group 5. Cantilever Beam Connections21. Hinge connector transfers load without need to slopecut member ends. Beams are often dapped top and bottomfor a flush fit.Group 6. Arch Peak ConnectionsGroup 7. Arch Base to SupportDesign concepts. Arches transmit thrust into the supportingstructure. The foundation may be designed to resistthis thrust or tie rods may be used. The base detail shouldbe designed to accommodate the amount of rotation anticipatedin the arch base under various loading conditions.Elastomeric bearing pads can assist somewhat in distributingstresses. As noted earlier, the connection should bedesigned to minimize any perpendicular to grain stressesduring the deformation of the structure under load.25. Welded shoe transmits thrust from arch to support.Note that inside edge of shoe is left open to prevent collectionof moisture.22. Steep arches connected with a rod and shear plates.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 636326. Arch base fastened directly to a steel tie beam in ashoe-type connection.Group 8. Moment SpliceDesign concepts. Moment splices must transmit axialtension, axial compression, and shear. They must servethese functions in an area of the structure where structuralmovement may be significant — thus, they must notintroduce cross-grain forces if they are to function properly.29. Separate pieces of steel each provide a specific function.Top and bottom plate transfer axial force, pressureplates transfer direct thrust, and shear plates transmit shear.27. Similar to detail 25. This more rigid connection issuitable for spans where arch rotation at the base is smallenough to not require the rotational movement permittedin detail 25. Note that, although the shoe is “boxed” aweep slot is provided at the inside face.30. Similar to detail 29. Connectors on side faces may beeasier to install, but forces are higher because momentarm between steel straps is less than in detail 29.7MECHANICAL CONNECTORS28. For very long spans or other cases where large rotationsmust be accommodated, a true hinge connection maybe required.Group 9. Problem ConnectionsHidden column base. It is sometimes preferable architecturallyto conceal the connection at the base of thecolumn. In any case it is crucial to detail this connectionto minimize decay potential.AMERICAN FOREST & PAPER ASSOCIATION

64 MECHANICAL CONNECTORS31. Similar to detail 11, but with floor slab poured overthe top of the connection. THIS WILL CAUSE DECAYAND IS NOT A RECOMMENDED DETAIL!32B. As an alternative to detail 32, smaller plates willtransmit forces, but they do not restrain the woodfrom its natural movements.31B. Alternate to detail 31.Notched beam bearing. Depth limitations sometimescause detailing difficulties at the beam supports. A simplesolution is to notch the beam at the bearing. This induceslarge tension perpendicular to grain stresses and leads tosplitting of the beam at the root of the notch.33. Notching a beam at its bearing may cause splits. THISDETAIL IS NOT RECOMMENDED!Full-depth side plates. It is sometimes easier to fabricateconnections for deep beams from large steel platesrather than having to keep track of more pieces. Lack ofattention to wood’s dimensional changes as it “breathes”may lead to splits.32. Full-depth side plates may appear to be a good connectionoption. Unfortunately, the side plates will remainfastened while the wood shrinks over the first heating season.Since it is restrained by the side plates, the beammay split. THIS IS NOT A RECOMMENDED DETAIL!Split33B. Alternate to detail 33.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 656534. This sloped bearing with a beam that is not fully supportedmay also split under load. THIS DETAIL IS NOTRECOMMENDED!35B. As an alternative to detail 35, the plates may beextended and the connection made to the upper half of thebeam.Split S p lit34B. Alternate to detail 34.Hanger to side of beam. See full-depth side platesdiscussion.36. Deep beam hangers that have fasteners installed inthe side plates toward the top of the supported beam maypromote splits at the fastener group should the wood membershrink and lift from the bottom of the beam hangerbecause of the support provided by the fastener group.THIS DETAIL IS NOT RECOMMENDED!7Hanging to underside of beam. Sometimes it is advantageousto hang a load from the underside of a beam.This is acceptable as long as the hanger is fastened to theupper half of the beam. Fastening to the lower half of thebeam may induce splits.35. Connecting a hanger to the lower half of a beam thatpulls downward may cause splits. THIS DETAIL IS NOTRECOMMENDED!36B. Alternate to detail 36.SplitSplitGap underbeamGapunder beamMECHANICAL CONNECTORSSplitAMERICAN FOREST & PAPER ASSOCIATION

66 MECHANICAL CONNECTORS7.6 Checklist: Using Connection Selection TablesConnection selection tables provide values for factored lateral strength (8N b Z′) for common configurations ofconnectors. Tabulated values apply to connections that satisfy the following conditions:√ “dry” service condition (C M = 1.0)√ “normal” temperature range (C t = 1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (8 = 0.80)√ compliance with spacing and penetration requirements as stated in the Structural Connections SupplementFor connections that do not satisfy all of these conditions, review the design equations in this chapter andmodify tabulated values as necessary.To compute factored resistance for a specific condition, apply the design equations directly (product-specificdesign adjustment factors and reference resistance values are provided in each supplement.)7.7 Design ExamplesExample 7.7-1.1: Nails - Top PlateSpliceDesign a splice connection in the top plate of a studwall of a light commercial building. The top plate resistsa factored horizontal diaphragm chord force of 1.575 kips.The top plate is a double 2x6, No.1 Douglas Fir-Larch.Practical ConsiderationsThe first practical decision faced by the designer inthis case is to choose a fastener type. In this case theproject is primarily “stick framed,” with virtually all connectionsconsisting of nails. Quickly dividing the factoredload by a typical nail strength indicates that the requirednumber of nails will not be excessive. Thus, nails are agood first choice.Engineering CalculationsOption 1. Try 16d common nails. Factored referencestrength = 0.243 kips per nail, (Table 12.3B of the StructuralConnections Supplement). If spacing criteria ismaintained, only the penetration depth factor is requiredfor this case (p/12D). Thus, the number of nails requiredis:n = 1.575/0.243/(1.5/12/0.162) = 8.4= 9 nailsOption 2. Calculate factored nail strengtht s= 1.5"D = 0.162"F ybF em= F esR e= 90 ksi= 4.65 ksi= F em/F es= 4.65/4.65= 1.0Design equations of chapter 7 require calculation ofall four yield mode equations to determine the controllingmode. However, tabulated design values are provided inTable 12.3B.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 6767The simplification guidelines cannot be used in thisdesign, since the nail penetration is less than 12D. Calculationsusing the yield mode equations reveal that modeIV controls. Only mode IV calculations are shown forconvenience.Calculating the factored lateral strength, 8N Z Z formode IV (AF&PA/ASCE 16-95 equation 7.1-1 and 7.4-4):8N ZZ′ = 8N Z(Z@C d)2( 0162 . ) ( 465 . )( 90)3.3 2Z =22 .Z = 0.465 kipsC d3( 2)= p/12D= 1.5/12/(0.162)= 0.778N ZZ′ = 0.465(0.80)(0.65)(0.77)= 0.186 kips3.3Z =DKD22FemFyb3(1+ R )en = 1.575/0.186 = 8.47= 9 nails5 @ 1-3/4" o.c. 2-1/2" 2-1/2"5 @ 1-3/4" o.c.7Figure 7- 1.1Example 7.7-1.2: Nails - Shear WallChords TiesDesign connection ties between first and second floorshear wall chords. Floor framing consists of 9.5" deeppre-fabricated wood I-joists. Walls are 2x6, dry DouglasFir-Larch studs spaced at 16" o.c. The unfactored windoverturning force is 2.4 kips.Actual R p= 3.0 in. > 12D, C d= 1.0t s= 0.06"D = 0.148"l p= 3.0"F ybF em= 90 ksi= 4.65 ksi1-3/4".2"1-3/4".MECHANICAL CONNECTORSPractical ConsiderationsThe first practical decision faced by the designer inthis case is to choose a fastener type. Many proprietarypre-fabricated metal connectors are available to make thisconnection, (see Guideline for Pre-Engineered Metal Connectors).However, a connection can be designed that willuse commonly available, non-proprietary components.Engineering CalculationsTry an ASTM A446 Grade A metal strap, 16 gage x2.5", assuming 2 rows of staggered 10d common nails.Adjustment factor for penetration, R p : (nailed into 2-2x6 chords)F esR e= 45 ksi= F em/F es= 4.65/45= 0.103Design equations of chapter 7 require calculation ofall four yield mode equations to determine the controllingmode.The simplification guidelines cannot be used in thisdesign, since both members are not the same species.Calculations using the yield mode equations reveal thatAMERICAN FOREST & PAPER ASSOCIATION

68 MECHANICAL CONNECTORSmode III s controls. Only mode III s calculations are shownfor convenience.Calculating the factored lateral strength, 8N Z Z formode III s (AF&PA/ASCE 16-95 equation 7.1-1 and 7.4-3):2-1/4"k2=− 1+( + Re) Fyb( + e)21 2 2 R D+R 3F te2em s216 gage x 2-1/2"ASTM A446 Grade AMetal Strap8-10d CommonNails @ 3/4" o.c.( . ) 2( 90 )( 2. 103)( 0.148 )20103 .3465 ( . )( 006 . )221103k 21=− + +2-1/4"k 2= 12.669-1/2"8N ZZ′ = 8N Z(Z@C d)33 . kDtF2Z =KDs em( 2 + Re)Double Stud( )( )( )( )222103 . ( . )3. 3 12. 66 0. 148 0. 06 4.65Z =Z = 0.373 kipsC d= 1.08N ZZ′ = 1.0(0.65)(0.373)Factored load:= 0.242 kipsZ u= 2.4(1.5)= 3.6 kipsn = 3.6 / 0.242 = 14.9= 15 nailsNumber of nails required:Use 15-10d nails per side or 2 rows of 8 each.Figure 7-1.23"Example 7.7-2.1: Lag Screws- DragStrutDesign a connection to transfer a factored seismicforce of 3.430 kips into the adjoining shear wall, assuminga 2x6 No. 1 Douglas Fir-Larch double top plate. Thedrag strut is a 6x10, No.1 Douglas Fir-Larch member.Practical ConsiderationsBecause forces are higher in this example than in 7.7-1.1, lag screws are likely a better choice. Due to thephysical dimensions of this connection, bolts are not apractical alternative.Engineering CalculationsTry 1/2 inch diameter lag screws. Since the doubletop plate is acting together as a unit, assume a single shearAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER6969connection with side member thickness equal to 3". Factoredreference strength tables do not include values for3" side members. Factored lag screw strength must becalculated using yield mode equations.t s= 3"D = 0.5"F yb= 45 ksi8N ZZ′ = 8N Z(Z@C g)⎛0.6⎞ZK D 2= ⎜ ⎟ FF⎝ ⎠θe yb⎛ 0.6 ⎞ 2Z = ⎜ ⎟ . .⎝ 1 ⎠( 05) 5645 ( )F em= F es= 5.60 ksiZ = 2.38 kipsR e= F em/F es= 4.65/4.65= 1.0Design equations of chapter 7 require calculation ofthree yield mode equations to determine the controllingmode. However, the Appendix of the Structural ConnectionsSupplement provides simplification guidelines toeliminate some calculations, if the use of yield mode equationsis required.Given parameters for this design allow the use of thesimplification guidelines. Calculations using the three simplifiedequations reveal that mode IV controls. Only modeIV calculations are shown for convenience.Calculating the factored lateral strength, 8N Z Z formode IV (Appendix of the Structural Connections Supplement):3-1/2" Min.to End of Beam8N ZZ′ = (1.0)(0.65)(2.38)= 1.5 kipsIgnoring group action factor initially:n = 3.43/1.5 = 2.29= 3 lag screwsAccounting for group action factor, C g :C g= 0.92 (Table 3.6A of the Structural ConnectionsSupplement)n = 3.43/1.5/0.92 = 2.49= 3 lag screwsHorizontalPlywood Diaphragm7MECHANICAL CONNECTORSPu = 3.43 kips2-2x6 No. 1Douglas Fir-LarchTop Plates6x10 No. 1Douglas Fir-LarchBeam3 @ 2" o.c. 3-1/2" Min.Figure 7-2.1AMERICAN FOREST & PAPER ASSOCIATION

70 MECHANICAL CONNECTORSExample 7.7-2.2: Lag Screw -Suspended Load (withdrawal)Small air handling units will be suspended from3-1/8"x7-1/2" 22F-V4 Douglas Fir-Larch glued laminatedbeams spaced 8' on-center. Each unit weighs 1.5 kips andis supported by two crossing members attached to two ofthe glulam beams. Design a lag screw connection for theproposed support frame. The lumber is dry and will remainso.Practical ConsiderationsWhile structural framing hangers could be used toconnect the crossing members to the glulam members,assume that conditions dictate withdrawal type connectors.Vibration might also need to be considered dependingon the type of isolation devices used with air handlingunits. See AITC Technical Note 9 for recommendations.Z u= 0.525 kipsReference withdrawal resistance of one screw in unitsof k/in.Penetration length required for one screw:Zw( ) ( )= 5980375 . . 05 .Z w= 1.013 k/in.075 . 15 .8N ZZ′ = 0.6(0.65)(1.013)= 0.395 k/in.P = Z u/8N ZZ′= 0.525/0.395= 1.33 in.pnfEngineering CalculationsTry 3/8 inch diameter lag screws loaded in withdrawal.Factored Load, Z u :Length:R = 1.5" (side plate thickness) + 1.5" (penetration) +7/32" (tip length)( )( )15 . 14 .Z u =22= 3.22 in.Use 3/8" x 4" lag screws8'-0"2x Douglas-FirSide Plate22F-V4 3-1/8" x 7-1/2"Glued Laminated Beams1-3/8" Dia. x 4"Lag Screw with WasherFigure 7-2.21.5 kipsExample 7.7-3.1: Bolts - BowstringRoof Truss SpliceDesign the splice for the bottom tension chord of atypical bowstring roof truss intended for use over a swimmingpool. Tension splice occurs at centerline of the 80ft. long truss. Center to center depth at peak of truss is 9'-0". Trusses are spaced at 8'-0" o.c. and nominal loads are:19 psf dead load, 16 psf roof live load, and 40 psf snowload. Use Douglas Fir-Larch Select Structural material.Trusses will be fabricated from wet material, but it is anticipatedthat in-service moisture content will exceed 19%.Practical ConsiderationsWet service conditions must be considered. The potentialfor corrosion due to chlorine mist may necessitatecoatings to protect steel.Engineering CalculationsAssume an 8x8 Douglas Fir-Larch Select Structuralmember with 1/4 in. thick ASTM A36 steel side plates.Use 1 in. diameter bolts with punched holes oversized by1/16 in., and 1.25 in. required edge distance. Use 1/4 in. x4 in. ASTM A36 steel side plates for 1 row of bolts orAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 71712-1/4 in. x 2.5 in. for 2 rows of bolts. Required tensileand connection resistance (Factored load) = 61.7 kips.t m= 7.5"t S= 0.25"D = 1.0"F yb= 45 ksi8N ZZ′ = 8N Z(Z@C g)208 . kDtF3Z =s em( 2 + RK e θ)( )( )( )( )208 . 1323 . 1 025 . 56 .Z =20966 .F emF esR e= 5.60 ksi= 58 ksi= F em/F es= 5.6/58= 0.0966Design equations of chapter 7 require calculation ofall four yield mode equations to determine the controllingmode.The simplification guidelines cannot be used in thisdesign, since all members are not the same thickness.Calculations using the yield mode equations reveal thatmode III s controls. Only mode III s calculations are shownfor convenience.Calculating the factored lateral strength, 8N Z Z formode III s (AF&PA/ASCE 16-95 equation 7.1-1 and 7.5-9):k3=− 1+( + Re) Fyb( + e)21 2 2+R 3FeR D2tem s( . ) 245 ( )( 20966 . )( 1)200966 .356 ( . )( 025 . )2210966k 3=− 1 + +k 3= 13.23Estimate number of bolts required:C M = 0.7, estimate C g = 0.92Z = 18.4 kips8N ZZ′ = 18.4(0.8)(0.65)(0.7)(0.9)= 6.03 kipsn = 61.7 / 6.03 = 10.2= 11 bolts - Use 2 rows of 6 boltsAccount for group action factor, C g :Refine: use 2 rows of 5 - 1 in. diameter boltsC g= 0.94 (Table 3.6A of the Sturctural ConnectionsSupplement)8N ZZ′ = 18.4(0.8)(0.65)(0.7)(0.94)= 6.79n = 61.7/6.79 = 9.09= 10 bolts - Use 2 rows of 5 boltsConnection Dimensioning:WoodPitch spacing, s = 4D:Minimum gage, g = 1.5DEdge distance: R/D = 7.7/1Edge distance:End distance:SteelPitch required = 3 in.End distance = 1.5 in.s = 4 in.g = 1.5 in.R/D = 7.7 in.b c= max (1.5 or g/2)a ct= 7 in.7MECHANICAL CONNECTORSTo avoid large reductions in capacity due to small C gtry 2 rows of 6 - 1 in. diameter boltsEdge distance = 1.25 in.3/4"2-1/2"1"2-1/2"3/4"2" 5 @ 4" 7" 7" 5 @ 4" 2"Figure 7-3.1AMERICAN FOREST & PAPER ASSOCIATION

72 MECHANICAL CONNECTORSExample 7.7-3.2: Bolts - EccentricBolted ConnectionDesign a moment splice using steel side plates forhorizontal loads and a shear plate for vertical loads. Splicea 5-1/8" x 12" 22F-V4 glued laminated beam onto existingbeam of same size and grade. Requires: (1) design ashear plate connection to resist vertical reaction, R u = 1.056kips; (2) provide a steel plate between beams to transferaxial compressive forces, and; (3) design ties to resist tensionforce due to M u = 1.940 ft-kips. Consider possibilityof load reversal.Practical ConsiderationsDesign of eccentric connections requires engineeringjudgement. Principles of engineering mechanics are usedto determine axial forces due to the moment beingtransfered.Engineering CalculationsOption 1. Existing overhang - 5-1/8" x 12" 22F-V4glued laminated beam. Factored load (dead plus roof live)w = 0.224 klf. Factored fascia dead load = 0.496 kips.Select side members given vertical reaction of 1.056 kipsand moment of 1.94 ft-kips.2'-6"Existing5-1/8"x12" 22F-V4Glued Laminated Beam2x ExtensionFactored Load;Dead plus Roof Live: w = 0.224 klfFactored FasciaDead Load = 0.496 kipsFigure 7-3.2APreliminary sizing:Estimate gage and spacing as 5" for 2 rows.Therefore: mode III s controls.Estimated couple force = 1.94(12)/5 = 4.656 kipsZ **= 8.0 kipsTotal force parallel to grain = 4.656 kipsTotal force perpendicular to grain = 4.656 + 1.056 = 5.712kipsEstimated Z 2= 7.37 kips, 2 = 50.8EResistance:Using simplification guidelines of the Structural ConnectionSupplement AppendixParallel to grain:1.45 < t s/D < 3.95t m/D > 2.92Perpendicular to graint s/D < 2.14t m/t s> 2.0Therefore: mode I s controls, c= 1.25Z z= 3.88 kipsEstimated resistance at 2 = 51ETry 2 rows of 3 - 3/4" diameter boltsDimensioning requirements:AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 7373Parallel to grain:Pitch spacing, s = 4D:Minimum gage, g = 1.5D:Edge distance:Edge distance:End distance, a c= 7D:Perpendicular to grain:Minimum gage, g = 5D:s = 3 in.g = 1.125 in.R/D = 6.83 in.b c= 3.75 in.a c= 5.25 in.g = 3.75 in.Check capacity using traditional vector analysis:(based on simple strength of materials concepts)Polar moment of inertia: J =160 in 2Horizontal force due to moment:Vertical force due to moment:=0.582 kips=0.582 kipsVertical force due to Pu: Z py=1.056/6 = 0.176 kipsAngle to grain 2 = 52.5End distance, a c= 4D:a c= 3 in.Edge distance, b c= 4D: b c= 3 in.Spacing between rows of bolts and bolts in a row is 4".Group action factor, C g= 0.993Adjusted resistance = 5.09 kipsP u= 1.056 kips acting through centroid ofCheck Figure 7-3.2B connection capacityM uconnection.= 1.940 ft-kips at centroid of connection.5-1/4'1.85 kips > 0.956 kips4" 4" 5-1/4'7Figure 7-3.2B5-1/8"x12"3/4" Dia. ASTM A307 Bolt, typ.Option 2. Try shear plate connection with dowels inend grain: (Table 10.2B of the Structural Connections3-3/4"4"3-3/4"2x12 Each SideSupplement) to transfer shear, plus steel side plates to transfertension loads.MECHANICAL CONNECTORSFactored FasciaDead Load = 0.496 kipsFactored Load;Dead plus Roof Live: w = 0.224 klf5-1/8"x12" 22F-V4Glued Laminated Beamspliced onto existing5-1/8"x12" 22F-V4 BeamFigure 7-3.2CAMERICAN FOREST & PAPER ASSOCIATION

74 MECHANICAL CONNECTORSShear PlateZ u= 1.056 kipsSizing and number:Try one 2 - 5/8" shear plate with 3/4" dowel.Reference resistance:Since member is square cut, Eq. A6.3-1 (AF&PA/ASCE 16-95) applies.(Note: metal side plate adjustment is not applicable,C st and C g taken as 1.0)Z z= 6.181(0.7)(0.6)= 2.6 > 2.03 okTherefore use one 2-5/8" shear plate on each side ofconnection with one 3/4" diameter by 10-1/2" steel dowel.Note: used lag screw length of penetration requirementsto determine length of dowel. (R p = 5" for full design value).Shear plate to be installed at the center of connection.Z n90= 0.6Z nqFor one 2-5/8" shear plate:Z u= 1.056Z nreqd= 1.056/(0.8)(0.65)= 2.035-1/8"6"6"1/4"x5-1/8"x12"ASTM A36 Steel PlateFigure 7-3.2DTension TiesEstimated gage between rows:b c= 1.5"G = 12 - 2(1.5) = 9"Bolts:Try 1/2" diameter bolts in double shear, parallel tograin loading.Reference resistance:Metal side plates per AISC-LRFDZ u= 2.59 kipsUsing 1/4" ASTM A36 plates, net depth required =0.24 in.Therefore, width of side plate controlled by edge dimensioningper AISC LRFD, minimum edge distance

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER7575Accounting for group action factor, C g :C g= 1.992/2s = 4D = 2"= 0.9968N ZZ′ = 0.8(0.65)(0.7)(0.996)(5.01) = 1.82(2)a cb c= 7D = 3-1/2"= R m/D = 10.25b c= 1.5D = 3/4"= 3.6 kips > Z uDimensioning:1-1/2"1/4"x2" ASTM A36 Plate, typ.1/4"x5-1/8"x12"ASTM A36 Steel Plate2"9"1-1/2"1/2" Bolts, typ.2"Figure 7-3.2E4-1/2" 4" 4-1/2" 4-1/2" 4" 4-1/2"7Example 7.7-4.1: Split-RingConnectionDetermine the capacity in terms of a factored load forthe given knee-brace design. The knee-brace supportslateral loads due to wind in a wood frame system. Using2x6 MSR 1650f-1.5E Douglas Fir-Larch, 6x8 No. 1 DouglasFir-Larch, 2 - 2-1/2" split rings with 1/2" bolts.Practical ConsiderationsPost frame building design typically provides guidancefor design of the moment resisting frame. Someadjustment to required capacity may be permitted due todiaphragm action of the roof system. The American Societyof Agricultural Engineers has more information onthis subject.4.7"30°Pu2-1/2" Split Ringswith 1/2" Dia. Bolts2x6 1650f-1.5E MSRKnee Brace, 5'-0" LongMECHANICAL CONNECTORSEngineering CalculationsCheck Brace:Load is parallel to grain, assume Group B species.Geometry adjustment factor, C ) is the minimum ofC ) determined from spacing, end distance, and edge distance.See Table 7.6-3 of AF&PA/ASCE 16-95 forspacing and edge distance requirements.6x8 Douglas Fir-Larch Post, No.13-3/8"2-1/16" 2-1/16"Figure 7-4.1AAMERICAN FOREST & PAPER ASSOCIATION

76 MECHANICAL CONNECTORSSpacing:For full design value: A opt= 5-1/8"End distance, a c :a opt**= 4"Edge distance, b c :B opt= 3-7/8"a cb cC Lb min**= b opt**= 1-3/4"C )= 1.030°Ea m= 66 x 10 3Ea s= 14.85 x 10 34-1/8"Accounting for group action factor (2 split rings), C g :D/2C g= 0.94 (Table 3.6B of the Structural ConnectionsSupplement)Determine Z u for connection in brace:Figure 7-4.1B8N ZZ′ = 8N Z(Z@C g)= 1.0(0.65)(0.94)(9.07)= 11.08 kips30°Check Post:Load is at a 30 degree angle to grain, Group B speciesZ **Z z= 9.07 kips= 6.45 kipsZuGeometry adjustment factorEdge distance, b c :b c= 2-1/2"2-1/2"Consider both edges as being loaded due to changing loaddirection (Table 7.6-1)b optz= 2-3/4"b minz= 1-3/4"2-5/8"C )= 0.96Figure 7-4.1CAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 7777End distance: not applicableEdge distance: not applicableMultiple fastener adjustment (as previously calculated):C g= 0.94Determine Z u for connection in brace:8N ZZ′ = 8N Z(Z@C g)= 1.0(0.65)(0.94)(14.84)= 9.07 kipsReference resistance, Z 2 :Z 2= 14.84 kips7MECHANICAL CONNECTORSAMERICAN FOREST & PAPER ASSOCIATION

78MECHANICAL CONNECTORSAMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION79STRUCTURALPANELS8.1 General Information 808.1.1 Selecting Structural Panels 808.2 Design for Moment 808.2.1 Adjustment Factors 808.3 Design for Shear 818.3.1 Adjustment Factors 818.4 Checklist: Using Structural PanelSelection Tables 828.5 Design Examples 82Example 8-1 Sheathing in a SpecialtyApplication 828AMERICAN FOREST & PAPER ASSOCIATION

80 STRUCTURAL PANELS8.1 General InformationThis chapter covers selection of structural panels thatmeet a given design requirement. Note that the specializedtopics of panels used in shear walls and diaphragmsare covered in chapter 9. Wood-based structural panelsare produced, graded and marketed in a fundamentallydifferent manner than the structural framing products referencedin chapters 3 through 6. The manufacturingprocess permits a wide range of raw materials, layup configurationsand pressing variables. This wide range ofvariables led to adoption of performance based productstandards and to a type of “stress-class” panel rating system.The current system of grade marking, based primarilyon span ratings, provides broad distribution of panel gradesthat meet most common building requirements.8.1.1 Selecting Structural PanelsEngineers will select panels by two distinctly differentmethods, depending on the structural application. Forthe majority of building applications, panels are used assheathing, primarily to transfer loads to the framing members.For these cases, panels are selected according totheir span rating. In a small number of cases, engineerswill find it necessary to select panels according to theirfactored flexure or axial resistances.8.1.1.1 Span ratingsStructures may be subjected to many types of loads,some of which are not covered in minimum code require-ments. In addition, consumers may have performanceexpectations that may not be satisfied by minimum coderequirements. Sheathing products, being the structural“layer” that directly supports the loads, are more affectedby these concerns than other products. For this reason,structural panels used as sheathing must be designed toaccount for loads and consumer acceptance criteria.Sheathing panels are span rated to meet these requirements.Across a range of span ratings, some individual productsmay have spans controlled by deflection limits. Othersmay be controlled by impact load considerations or otherlimit states.Selecting structural panels by span rating has provento be a safe and efficient design option in allowable stressdesign. This option is equally applicable to LRFD.8.1.1.2 Using factored resistance valuesFor special applications, designers may opt to select apanel by engineering calculations. Selection tables areprovided for this purpose. For the majority of buildingapplications, panels are used as sheathing, primarily totransfer loads to the framing members. For these cases,panels are selected according to their span rating. In asmall number of cases, engineers will find it necessary toselect panels according to their factored flexure or axialresistances.8.2 Design for MomentThe basic equation for moment design of structuralpanels is similar to that for other bending members(AF&PA/ASCE 16-95, Eq. 5.1-1):where8N bM′ $ M u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N b= 0.85M′ = adjusted moment resistance= factored momentM uFactored moment resistance is tabulated in the structuralpanel selection tables. Tabulated values are suitablefor members that conform to all conditions in the checklistin Section 8.4.8.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting tabulated momentresistance values or by applying all applicable adjustmentfactors to the reference bending strength for the product.The complete equation for calculation of factored momentresistance is:8N bM′ = 8N bM (C MC tC GC swC ptC rt)AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 8181where M is the reference bending resistance of the panel(kip-in) and:C MC tC Gis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the Structural-Use PanelSupplement.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For higher temperatureconditions, multiply by the value of C t given in theStructural-Use Panel Supplement.is the grade construction factor. Tabulated referenceresistances are for a baseline panelconfiguration. For panel constructions that are differentfrom the baseline configuration, use the valueof C G given in the Structural-Use Panel Supplement.C WC ptC rtis the width effect factor. Use this factor, as specifiedin the Structural-Use Panel Supplement, forpanel widths less than 24 inches.is the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the Structural-Use PanelSupplement.is the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the Structural-Use PanelSupplement.For untreated structural panels 24 inches or wider, usedin a normal building environment (meeting the referenceconditions of Sec. 1.1.5), the general equation for M′ reducesto:M′ = M (C ) G8.3 Design for ShearThe basic equation for shear design of structural panels(AF&PA/ASCE 16-95, Eq. 5.1-2) is:where8N vV′ $ V u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N v= 0.75V′ = adjusted shear resistance= factored shearV uFactored shear resistance is tabulated in the panel selectiontables. Tabulated values are suitable for membersthat conform to all conditions in the checklist in Section8.4.C MC tC ptis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the Structural-Use PanelSupplement.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For higher temperatureconditions, use the value of C t given in the Structural-UsePanel Supplement.is the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the Structural-Use PanelSupplement.8STRUCTURAL PANELS8.3.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting tabulated shearresistance values. The complete equation for calculationof factored shear resistance is:C rtis the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the Structural-Use PanelSupplement.8N vV′ = 8N vV (C MC tC ptC rt)where V is the reference shear resistance (kips) and:AMERICAN FOREST & PAPER ASSOCIATION

82 STRUCTURAL PANELS8.4 Checklist: Using Structural Panel Selection TablesTwo types of structural panel selection tables are provided. Flexure selection tables provide values for factoredmoment and shear resistance (8N b M′, 8N v V′) for various span ratings and panel constructions. Axial forceselection tables provide factored tensile and compressive resistance (8N t T′, 8N c P′) for the baseline case only.Tabulated values apply to panels that satisfy the following conditions:√ “dry” service condition (C M =1.0)√ “normal” temperature range (C t =1.0)√ untreated material (C pt = 1.0 ; C rt = 1.0)√ time effect factor based on “live” (L or L r ) or “snow” (S) load combination (8=0.80)For panels that do not satisfy all of these conditions, review design equations in this chapter and modifytabulated values as necessary.8.5 Design ExamplesExample 8-1: Sheathing in aSpecialty ApplicationDesign a structural panel to resist a factored moment(M u ) of 2.5 kip-in per foot of panel width. Assume a 4x8ft. sheet, standard conditions of load duration, dry moistureservice condition, untreated material.Practical ConsiderationsFor normal building construction, consideration ofsimple span moments and shears under code-specifieduniform loads would ignore several significant limit statesfor structural sheathing. Among these are the strengthlimit state of impact resistance under realistic falling objectsin a building and the serviceability limit states relatedto deflection and vibration. While these limits are notexplicitly addressed in this design example, the designeris reminded that span ratings for panels DO account forthese types of considerations.Engineering CalculationsUsing Selection Tables: Select a member from thestructural panel selection tables that meets the momentrequirement (M u ) shown above.A baseline construction rated structural-use panel witha span rating of 48 oc has a tabulated factored momentresistance of 2.8 kip-in/ft. Thus, this configuration is acceptable.Using Reference Strength Tables: Calculate the factoredmoment resistance for a specific panel constructionby using the baseline configuration values and multiplyingby the grade construction factors.Try a 5-ply plywood or an oriented strand board constructionof a 32 oc structural-use panel.8N bM′ = 8N bM C GTry a 48 oc:= (0.80) (0.85) (2.2) (1.2)= 1.8 kip-in/ft < 2.5 kip-in/ft= (0.80) (0.85) (4.1) (1.2)= 3.3 kip-in/ftThis panel satisfies the strength limit state of moment.Full design must also check other applicable limitstates. Note that panel selection tables also include valuesfor panel stiffness (EI). This value must be greaterthan or equal to EI req’d to meet serviceability criteria forthe panel design.AMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION83SHEAR WALLSANDDIAPHRAGMS9.1 General Information 849.2 Design 849.2.1 Adjustment Factors 849.3 Checklist: Using Shear Wall andDiaphragm Selection Tables 849.4 Design Examples 85Example 9-1 Horizontal RoofDiaphragm inIndustrial Warehouse 85Example 9-2 Shear wall inSingle-Story Residence 879AMERICAN FOREST & PAPER ASSOCIATION

84 SHEAR WALLS AND DIAPHRAGMS9.1 General InformationThis chapter pertains to design of shear walls and diaphragms.These assemblies, which transfer lateral forces(wind and seismic) within the structure, are commonlydesigned using panel products fastened to framing members.The use of bracing systems to transfer these forcesis not within the scope of this Chapter.9.2 DesignShear walls and diaphragms transfer in-plane forces.Textbooks provide in depth coverage of this topic. Forpurposes of this chapter, note the following:where8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)• These assemblies act as deep beams• In-plane shear resistance is provided by the structuralsheathing (web action)• Axial tension and compression resistance is providedby the chord members (flange action)• Nailed assemblies as shown in selection tables exhibitductile, energy absorbing behaviorWhile shear resistance of these assemblies can be computedby principles of engineering mechanics, it isrecommended that designers use selection tables for thispurpose. In addition to eliminating laborious calculations,these tables limit configurations to those that will exhibitthe aforementioned ductile behavior.The basic equation for shear design of shear wallsand diaphragms (similar to AF&PA/ASCE 16-95, Eq. 9.2-1) is:D u# 8N ZD′N Z= 0.65 (fastener-limited shear resistance)D′ = adjusted shear wall / diaphragm shearD uresistance= factored shear wall / diaphragm shear forceFactored shear wall / diaphragm shear resistance istabulated in the Structural-Use Panel Supplement. Tabulatedvalues are suitable for assemblies that conform toall conditions of the checklist in section 9.3.9.2.1 Adjustment FactorsShear walls and diaphragms that do not meet all conditionsin the checklist must be designed by adjustingtabulated shear resistance values. A listing of applicableadjustment factors is provided in the Structural-Use PanelSupplement.9.3 Checklist: Using Shear Wall and DiaphragmSelection TablesShear wall / diaphragm selection tables provide values for factored shear resistances (8N z D′) for most applications.Tabulated values apply to assemblies that satisfy the following conditions√ “dry” service condition (C M =1.0)√ “normal” temperature range (C t =1.0)√untreated material√ time effect factor based on “live” (L or L r ) or “snow” (S) combination (8=0.80)For assemblies that do not satisfy all of these conditions, review the design equations in this chapter andmodify tabulated values as necessary.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 85859.4 Design ExamplesTransverse ForceW = 0.385 kips/ft (Factored Load)4' x 8' Structural Panel110'VVPurlins Spaced 8' o.c.240'2 x Framing, 24" o.c.Figure 9.1AFigure 9.1BExample 9-1: Horizontal RoofDiaphragm in Industrial WarehouseSelect a structural panel layout, nailing and blockingplan, and determine the maximum chord force for a 110 x240 foot warehouse roof diaphragm based on loadingshown in Figure 9.1A. Shear walls of equal strength andstiffness are located around the perimeter of the diaphragm.It is important to note that this example only considers afactored uniform lateral load on the 240' dimension of theroof diaphragm. Design for dead load as well as lateralload on the 110' dimension of the roof diaphragm mayalso control design. For this example it is assumed thatdiaphragm framing members and sheathing have alreadybeen designed to resist gravity loads.Maximum unit shear in diaphragmThe diaphragm acts as a deep beam spanning betweenshear walls. This beam is assumed to span L feet betweenshear walls and have a depth b. The maximum shear force,V, occurs at the reactions and is equal to wL/2 where w isthe load in units of force per unit length.The maximum unit shear in the diaphragm, D u is computedas the maximum shear force divided by the beamdepth:( 0385 . )( 240)( 2)( 110)V wLDu = = = = 042 . kip/ftb 2bPanel layout and fastener scheduleChoice of diaphragm materials and construction issimplified by the use of the diaphragm selection tables.Appropriate panel layouts, thickness, and fastener schedulescan be determined, based on maximum unit shear,using Table 5.5 in the Structural-Use Panel Supplement.A review of the table shows that the “Case 2” panellayout is appropriate with recommended constructionmeeting the following requirements:• Blocked construction (blocking is not required whenshear reduces to 0.23 klf).• 15/32" structural panel sheathing.• 8d 4" o.c. - nailing for all diphragm boundaries (reducenailing when shear reduces to 0.35 klf).• 8d 6" o.c. - perimeter nailing of all interior panel edges.• 8d 12" o.c. - nailing at panel intermediate supports.• Nominal 2 inch thick Douglas-Fir, Larch, or SouthernPine framing members.Figure 9.1B shows a possible framing plan and panellayout. Note that the direction of framing versus the directionof blocking does not affect identification as Case 2.Diaphragm nailing and blocking planThe framing system provides blocked construction forthe entire diaphragm since the panel’s edges coincide withsupports. In some cases, however, blocking is not requiredor provided towards the center of the diaphragm (regionaway from shear wall reactions) due to reduced unit shears.The unit shear diagram in Figure 9.1C shows the regionof the diaphragm where blocking is not required.Similarly, a unit shear diagram can be used to determineregions where increased nail spacing is permittedbased on reduced unit shears. For this example, nail spac-9SHEAR WALLS AND DIAPHRAGMSAMERICAN FOREST & PAPER ASSOCIATION

86 SHEAR WALLS AND DIAPHRAGMS0.42 klf0.35 klf0.23 klfNailing reducedBlocking not required20'55'120'0.23 klf0.35 klf0.42 klf(Blocking)8d 4" o.c.Panel edges(Blocking)8d 6" o.c.Panel edges(No Blocking Required)8d 6" o.c.Panel edges110'240'8d 6" o.c. perimeter nailing on all interior panel edges4' x 8' structural panel8d 12" o.c. at panel intermediate supportsFigure 9.1CAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 8787ing can be increased based on reduced unit shears towardsthe center of the diaphragm. See Figure 9.1C for regionswhere increased nail spacing is permitted. Additionally,specified changes in nail spacing should occur over a framingmember.4.0 kips= Factoredlateral force12'Practical considerationsAs this example shows, some diaphragms requiredense nailing patterns in high shear locations. Efficientdesign requires a reduction in the number of nails in areaswhere the shear is lower. Practical design requires thatthe designer limit the number of “nailing regions” to minimizeconfusion on the jobsite.Chord forceThe chords of a diaphragm resist axial tension andcompression. The chord axial force is obtained by resolvingthe diaphragm moment into a force couple. Forthis example, chords are located at the perimeter of thediaphragm and are accordingly assumed to be a distance,b, away from each other. Therefore, maximum axial forceswhich occur at mid-span are equal to:( 0385 . )( 240)( 8)( 110)C T M 2WL= = = = = 25.2 kipsb 8bAxial chord forces are commonly resisted by the useof two or more layers of lumber spliced together to formthe chord. The chord member and its splice must resistthe tensile and compressive forces resulting from resolvingthe diaphragm moment into a force couple. Tensioncompression member design involves considering the reducednet section of the chord due to fastener holesnecessary in the splice region. Splices must be designedto transfer a proportionate share of the chord force to continuousmembers. Continuity of chords must bemaintained.Other considerationsRecall that this example only considers transverseforce on the 240' dimension of the roof diaphragm. Loadingin the longitudinal direction (110' dimension of thediaphragm) may alter nailing and blocking requirements.Transverse as well as longitudinal loads must be consideredfor attaching the diaphragm and the shearwall. Inthe overall design of the roof, resistance to gravity load isalso a design consideration. Gravity load often controlspanel layout.2Figure 9.2AExample 9-2: Shear Wall in Single-Story ResidenceDetermine the appropriate panel thickness, nailingschedule, and anchorage requirements for the 8 x 12 footshearwall shown in Figure 9.2A. Assume that dead loadis negligible, overturning restraint is provided by mechanicalanchors, shear is resisted by 5/8" anchor bolts, and allframing members are 2 inch nominal thickness Douglasfir.Design for shearIt is assumed that the shear wall behaves as a deepcantilever beam with end members acting as “flanges” or“chords” to resist axial forces and the panels acting as a“web” to resist shear.When designing for shear, the controlling design equation(AF&PA/ASCE 16-95 Eq. 9.2-1) is:D≤λφ Du z nFrom Figure 1, the factored lateral force is 4 kips.The factored unit shear force, D u , equals:( 40 . )D u= =( 033)12T. kip/ftv = Shear at base ofshearwallPanel thickness and fastener scheduleChoice of shear wall materials and construction is simplifiedby the use of the shear wall selection tables. Panelthickness and fastener schedule can be determined, basedC8'9SHEAR WALLS AND DIAPHRAGMSAMERICAN FOREST & PAPER ASSOCIATION

88 SHEAR WALLS AND DIAPHRAGMSon factored unit shear force, using Table 5.4 in the Structural-UsePanel Supplement.A review of the table shows that the recommendedwall construction meets the following requirements:• Blocked construction.• 15/32" structural panel sheathing.• 8d 6" o.c. nailing at panel edges with common or galvanizedbox nails with a minimum penetration intoframing of 1-1/2".• 8d 12" o.c. nailing on intermediate supports.Note that panels may be oriented horizontally or verticallyfor this case. A possible layout with panels orientedvertically is shown in Figure 9.2B.Chord forceThe end members act as chords to resist axial forces.This force can be obtained by resolving the wall overturningmoment into a force couple:8d 6" o.c. nailing at panel edgesAnchor boltHold down connectorFigure 9.2B8d 12" o.c. at panelIntermediate supports4' x 8' structuralpanel( 4)( 8)C = T = M = = 27. kipsb 12The chord member must resist resulting axial forces.Chord design for tension and compression must considerthe reduced net section due to fastener holes when necessaryfor the attachment of hold down devices.Hold down requirementHold downs are required to prevent overturning ofthe wall. The required hold down force can be obtainedby resolving the wall overturning moment into a forcecouple. In this case, the required hold down must providefactored uplift resistance of 2.7 kips.for a 5/8 inch diameter anchor bolt connection betweennominal 2" thick Douglas-Fir and concrete. Three anchorbolts are required.Other considerationsThis example does not consider dead load in calculationof overturning forces. It is recommended that thedesigner refer to applicable building code provisions todetermine proper treatment of overturning forces. Theseprovisions vary based on the type of lateral force underconsideration and by building code. In addition, buildingcode provisions concerning minimum spacing and placementof anchor bolts should be consulted.Anchor boltsThe factored lateral load of 4 kips must be resisted byanchor bolts in shear. The Structural Connections Supplementcan be used to determine a bolt capacity of 1.9 kipsAMERICAN WOOD COUNCIL

LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION89REFERENCEINFORMATION10.1 General Information 9010.2 Applications-Related Information 9010.2.1 Dry vs. Wet Service Conditions 9010.2.2 Dimensional Changes in Wood 9010.2.3 Chemical Treatments 9110.3 Other Design Information 9110.3.1 Beam Formula Figures 9110.3.2 Weights of Materials 9110.3.3 Metric Conversions 9110AMERICAN FOREST & PAPER ASSOCIATION

90 REFERENCE INFORMATION10.1 General InformationThis chapter provides typical reference information(general applications information, beam formulas, weightsof materials, metric conversions) found in engineeringdesign handbooks. Product specific information (productdimensions and section calculations, product weights) areprovided in the supplements and guidelines.This chapter also includes flowcharts of the designprocess for chapters 3 through 7. This provides not only apicture of the design process for a given member type, butalso serves as a guide to development of software applicationsfor LRFD.10.2 Applications-Related Information10.2.1 Dry vs. Wet Use ConditionsWood used in most structural building applications isprotected from direct exposure to water. These applicationsgenerally have relatively low humidity conditions.These cases are called dry use conditions. AF&PA/ASCE16-95 defines dry use conditions in terms of the equilibriummoisture content (EMC) of the wood. The upperlimit of a dry use condition is a 15 percent average or a 19percent maximum EMC for sawn lumber. Table 10A relatesEMC to relative humidity for the range of temperaturefrom 30 o to 110 o F. If EMC’s for higher temperatures ormore precise information is required, the user is directedto any wood products textbook.Key to the designer’s judgment regarding the appropriateEMC for use in design is the fact that wood fibersgain or lose moisture gradually, rather than immediately.For example, a bunk of 2x4’s will take several weeks tochange moisture content by roughly plus or minus 5 percentin a controlled conditioning room. Thus, from aTable 10A.Relative Humidity(RH)RangeEquilibrium Moisture Contentof Wood 1EquilibriumMoisture Content(EMC) Range< 30% < 6%3 0 - 40% 6 - 8 %40 - 60% 8 - 11%60 - 75% 11 - 15 %75 - 85% 15 - 19%> 85% > 19%1Note that glued products (such as glulam, SCL and panel products) tend toequilibrate to moisture contents slightly lower than sawn lumber.practical standpoint, structural products that are generallydry can be designed for dry use — even if they wouldoccasionally come in contact with water.Conversely, as the table indicates, extremely highhumidity conditions over extended periods will push theEMC above the threshold for dry use. While these conditionswill not generally prevail within the buildingenvelope, the designer must be aware that high humidityareas are potentially troublesome, both from the perspectiveof strength reduction (wet use) and from theperspective of decay hazards.10.2.2 Dimensional Changes inWoodWood shrinks as it loses moisture and swells as it gainsmoisture. While dimensional changes along the grain arenegligible, changes across the grain are significant enoughto be important from a building detailing standpoint. Froma design perspective changes in moisture content are moresignificant due to dimensional changes than due to changesin strength properties. Experienced designers review allbuilding details asking “How would shrinking or swellingaffect this detail?”As a rule of thumb, wood members will shrink roughly4 to 8 percent across the grain as they dry from a saturatedcondition (about 24 percent MC) to an oven dry condition(0 percent MC). Designers are advised to either detail thestructure to minimize effects of shrinkage or to specifywood products that will be installed at a moisture contentthat is close to the long-term EMC of the structure. Forexample, modern kiln drying removes about half of themoisture content (and half of the shrinkage). Kiln driedwood at about 12 to 15 percent MC is only slightly higherthan the 8 to 12 percent EMC one might expect in buildings.Discussion of dimensional changes in wood wouldnot be complete without a brief word about checking.Surface checking in wood is caused by differential shrink-AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9191age — the drier surface of a wood member shrinks morequickly than the center of the member. Checking is minimizedby slow or controlled drying of the member. Surfacechecks have little, if any, impact on structural strength intypical applications. Larger checks under unusual stressconditions should be investigated for their possible impacton strength.10.2.3 Chemical Treatmentscommon classes of chemicals used to impregnate woodproducts are preservatives and fire retardants. The effectsof treatment on the structural properties of wooddepend upon the chemicals used and the process variablesemployed. Because many treatments are applied in proprietaryprocesses their impacts cannot be assessed in acomprehensive manner in this Manual. Contact your woodproduct supplier or the treater for more information.Wood products are sometimes treated with chemicalsto modify certain properties of the wood. The two most10.3 Other Design Information10.3.1 Beam Formula Figures10.3.2 Weights of MaterialsFigures 10.1 through 10.32 provide a series of shearand moment diagrams with accompanying formulas forbeams under various static loading conditions.Shear and moment diagrams and formulas are excerptedfrom the Western Woods Use Book, 4th edition,and are provided herein as a courtesy of Western WoodProducts Association.Notations Relative to “Shear and Moment Diagrams”E = modulus of elasticity, psiI = moment of inertia, inches 4L = span length of the bending member, feetR = span length of the bending member, inchesM = maximum bending moment, inch-poundsP = total concentrated load, poundsR = reaction load at bearing point, poundsV = shear force, poundsW = total uniform load, poundsw = load per lineal inch, pounds∆ = deflection or deformation, inchesx = horizontal distance from reaction to point onbeam, inchesTable10.33 contains minimum design dead loads formany common construction materials excerpted fromAmerican Society of Civil Engineers, ASCE 7-95, MinimumDesign Loads for Buildings and Other Structures.Many of the tabulated values appear to overestimatethe dead loads of wood products. For more accurate estimationof dead loads consult other recognized industrystandards.10.3.3 Metric ConversionsTable10.34 contains metric conversion factors for variousengineering units excerpted from AF&PA’s WoodProducts Metric Planning Package. For additional unitsnot shown, see ASTM E 380-92, Standard Practice forUse of the International System of Units (SI) (the ModernizedMetric System). More information on metricconversion for wood products is available in AF&PA’sWood Products Metric Planning Package.10REFERENCE INFORMATIONAMERICAN FOREST & PAPER ASSOCIATION

92 REFERENCE INFORMATIONFigure 10.1Simple Beam – Uniformly Distributed LoadxwRRV2 2ShearVM maxMomentFigure 10.27-36 ASimple Beam – Uniform Load Partially Distributeda b cwbR 1R 2xV 1ShearV 2a + — R 1wM maxMoment7-36 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9393Figure 10.3Simple Beam – Uniform Load Partially Distributed at One EndawaR 1R 2xShearV 2R —w 1V 1M maxMomentFigure 10.47-37 ASimple Beam – Uniform Load Partially Distributed at Each Enda b cw 1 aw 2 c10R 1 R 2xV 1V 2R 1 —w1ShearREFERENCE INFORMATIONM maxMoment7-37 BAMERICAN FOREST & PAPER ASSOCIATION

94 REFERENCE INFORMATIONFigure 10.5Simple Beam – Load Increasing Uniformly to One EndxWR 1 R 2.57741V 1ShearV 2M maxMomentFigure 10.67-38 ASimple Beam – Load Increasing Uniformly to CenterxWR22RVShearVM maxMoment7-38 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9595Figure 10.7Simple Beam – Concentrated Load at CenterxPRR22VShearVM maxMomentFigure 10.87-39 ASimple Beam – Concentrated Load at Any PointxP10R 1 R 2abV 1V 2ShearREFERENCE INFORMATIONM maxMoment7-39-bAMERICAN FOREST & PAPER ASSOCIATION

96 REFERENCE INFORMATIONFigure 10.9Simple Beam – Two Equal Concentrated Loads Symmetrically PlacedxPPRRaaVShearVM maxMomentFigure 10.107-40 ASimple Beam – Two Equal Concentrated Loads UnsymmetricallyPlacedxPPR 1 R 2abV 1ShearV 2M 1M 2Moment7-40 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9797Figure 10.11 Simple Beam – Two Unequal Concentrated Loads UnsymmetricallyPlacedxP 1P 2R 1R 2abV 1ShearV 2M 1M 2MomentFigure 10.12 Cantilever Beam – Uniformly Distributed Loadw7-41-a10xShearRVREFERENCE INFORMATIONMomentM max7-41- BAMERICAN FOREST & PAPER ASSOCIATION

98 REFERENCE INFORMATIONFigure 10.13 Cantilever Beam – Concentrated Load at Free EndPRxShearVMomentM maxFigure 10.14 Cantilever Beam – Concentrated Load at Any Point7-42 AxPRabShearVMomentM max7-42-bAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9999Figure 10.15 Beam Fixed at One End, Supported at Other – Uniformly DistributedLoadwR 2R 1xV 1ShearV 238—4M 1M maxFigure 10.16 Beam Fixed at One End, Supported at Other – Concentrated Load atCenter7-43 A10xR 1R 2V 21M 122ShearVPREFERENCE INFORMATIONM 23— 117-43 BAMERICAN FOREST & PAPER ASSOCIATION

100 REFERENCE INFORMATIONFigure 10.17 Beam Fixed at One End, Supported at Other – Concentrated Load atAny PointxPR 2R 1V 2abV 1ShearM 1MomentPa—R2M 2Figure 10.18 Beam Overhanging One Support – Uniformly Distributed load7-44 Aaxw( + a)x 1R 2(1– a2 )22V 1V 2ShearV 3M 1R 1(1–Momenta 2 )2M 27-44 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 101101Figure 10.19 Beam Overhanging One Support – Uniformly Distributed load onOverhangaxx 1waR 1R 2V 2V 1ShearMomentM max7-45 AFigure 10.20 Beam Overhanging One Support – Concentrated Load at End ofOverhangxx 1aP10V 1R 1R 2ShearV 2REFERENCE INFORMATIONMomentM max7-45 BAMERICAN FOREST & PAPER ASSOCIATION

102 REFERENCE INFORMATIONFigure 10.21 Beam Overhanging One Support – Concentrated Load at Any PointBetween Supportsxx 1R 1R 2abV 1V 2ShearM maxMomentFigure 10.227-46 Beam A Overhanging Both Supports – Unequal Overhangs – UniformlyDistributed LoadwR 1 R 2a b cV 2V 1V 4X 1XV 3M x1M 2M 1M 37-46 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 103103Figure 10.23 Beam Fixed at Both Ends – Uniformly Distributed loadxwRR2 2VShearV.2113 M 1MomentM max7-47 AFigure 10.24 Beam Fixed at Both Ends – Concentrated Load at CenterxP10RV2 2Shear4RVREFERENCE INFORMATIONM maxMomentM max7-47 BAMERICAN FOREST & PAPER ASSOCIATION

104 REFERENCE INFORMATIONFigure 10.25 Beam Fixed at Both Ends – Concentrated Load at Any PointxPR 1R 2abV 1ShearV 2M 1MomentM aM 27-48 AFigure 10.26 Continuous Beam – Two Equal Spans – Uniform Load on One spanxwR 1 R 3R 2V 1Shear V 3716M maxM 1V 2Moment7-48 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 105105Figure 10.27 Continuous Beam – Two Equal Spans – Concentrated Load at Centerof One Span2 2PR 1 R 2R 3V 1V 2ShearM max V 3M 1Moment7-49 AFigure 10.28 Continuous Beam – Two Equal Spans – Concentrated Load at AnyPointa bPR 1R 2R 3V 1V 2M maxM 1ShearMomentV 310REFERENCE INFORMATION7-49 BAMERICAN FOREST & PAPER ASSOCIATION

106 REFERENCE INFORMATIONFigure 10.29 Continuous Beam – Two Equal Spans – Uniformly Distributed LoadwwR 1R 2R 3V 2V 2xxx 1M 2M 2M x1M 12V32.46 .46∆ max7-50 AFigure 10.30 Continuous Beam – Two Equal Spans – Two Equal Concentrated LoadsSymmetrically PlacedPPR 1R 3a a a aV 1R 2V 2V 3 V 2M 1M 2xM 2M x7-50 BAMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 107107Figure 10.31 Continuous Beam – Two Unequal Spans – Uniformly Distributed Loadww1 2R 1 R 2 R 31 2V 1V 4V 3V 2x 1 x 2M x2M 1M x17-51 AFigure 10.32 Continuous Beam – Two Unequal Spans – Concentrated Load on EachSpan Symmetrically PlacedP 1 P 2R 1R 2 R 3P12a a b bV 1V 2V 3V 4M m1 M m2M 110REFERENCE INFORMATION7-51 BAMERICAN FOREST & PAPER ASSOCIATION

108 REFERENCE INFORMATIONTable 10.33 Minimum Design Dead Loads*, 11Source: This material is reproduced with permission from the American Society of Civil Engineers, ASCE 7-95, Minimum Design Loads for Buildings and Other Structures, copyright 1996 by theAmerican Society of Civil Engineers. Copies of this standard may be purchased from the American Society of Civil Engineers at 345 East 47th Street, New York, NY 10017-2398.AMERICAN WOOD COUNCIL

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 109109Table 10.34Metric Conversion FactorsQuantityFrom Inch-PoundUnitsTo Metric UnitsMultiply byLength ft mm 304.8inmm25.4Masslbkip (1000 lb)kgmetric ton (1000 kg)0.453 5920.453 592Mass density pcf kg/m 3 16.018 5ForcelbkipNkN4.448 224.448 22Force/unit lengthplfklfN/mkN/m14.593 914.593 9Force/unit areapsfksfN/m 247.880 26kN/m 2 47.880 26Pressure, stress, modulus ofelasticitypsfksfpsiksiPa (N/m 2 )kPakPaMPa (N/mm 2 )47.880 2647.880 266.894 766.894 76Bending moment, torque,moment of forceft-lbft-kipN@mkN@m1.355 821.355 82Moment of Inertia in 4 mm 4 416 231Section Modulus in 3 mm 3 16 387.064Temperature EF EC (t EF - 32)/1.8Specific Heat Capacity Btu/lb-EF kJ/kg-K 4.1868Thermal Conductivity Btu-in/h-ft 2 -EF W/m-K 0.144227910REFERENCE INFORMATIONAMERICAN FOREST & PAPER ASSOCIATION

REFERENCE INFORMATIONAMERICAN WOOD COUNCIL