2012 ASD/LRFD Manual for Engineered Wood Construction

ASD/LRFDMANUALNational Design Specification ®for Wood Construction2012 EDITION

Updates and ErrataWhile every precaution has been taken toensure the accuracy of this document, errorsmay have occurred during development.Updates or Errata are posted to the AmericanWood Council website at www.awc.org.Technical inquiries may be addressed toinfo@awc.org.The American Wood Council (AWC) is the voice of North American traditional and engineered woodproducts. From a renewable resource that absorbs and sequesters carbon, the wood products industrymakes products that are essential to everyday life. AWC’s engineers, technologists, scientists, andbuilding code experts develop state-of-the-art engineering data, technology, and standards on structuralwood products for use by design professionals, building officials, and wood products manufacturers toassure the safe and efficient design and use of wood structural components.

iASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONASD/LRFDMANUALfor Engineered Wood Construction2012 EDITIONCopyright © 2012American Wood CouncilAMERICAN WOOD COUNCIL

iiASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONASD/LRFD Manual for Engineered Wood Construction 2012 EditionFirst Web Version: October 2012First Printing: October 2012ISBN 978-0-9827380-5-4 (Volume 3)ISBN 978-0-9827380-6-1 (5 Volume Set)Copyright © 2012 by American Wood CouncilAll rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by anymeans, including, without limitation, electronic, optical, or mechanical means (by way of example and not limitation,photocopying, or recording by or in an information storage retrieval system) without express written permission of theAmerican Wood Council. For information on permission to copy material, please contact:Copyright PermissionAmerican Wood Council222 Catoctin Circle, SE, Suite 201Leesburg, VA 20175info@awc.orgPrinted in the United States of AmericaAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONiiiFOREWORDThis Allowable Stress Design/Load and ResistanceFactor Design Manual for Engineered Wood Construction(ASD/LRFD Manual) provides guidance for design of mostwood-based structural products used in the constructionof wood buildings. The complete Wood Design Packageincludes this ASD/LRFD Manual and the following:• ANSI/AF&PA NDS-2012 National Design Specification® (NDS ® ) for Wood Construction – withCommentary,• NDS Supplement – Design Values for Wood Construction,2012 Edition,• ANSI/AF&PA SDPWS-08 – Special Design Provisionsfor Wind and Seismic (SDPWS) – withCommentary,• ASD/LRFD Structural Wood Design Solved ExampleProblems, 2012 Edition.The American Wood Council (AWC) has developedthis manual for design professionals. AWC and its predecessororganizations have provided engineering designinformation to users of structural wood products for over75 years, first in the form of the Wood Structural DesignData series and then in the National Design Specification(NDS) for Wood Construction.It is intended that this document be used in conjunctionwith competent engineering design, accurate fabrication,and adequate supervision of construction. AWC does notassume any responsibility for errors or omissions in thedocument, nor for engineering designs, plans, or constructionprepared from it.Those using this standard assume all liability arisingfrom its use. The design of engineered structures is withinthe scope of expertise of licensed engineers, architects, orother licensed professionals for applications to a particularstructure.American Wood CouncilAMERICAN WOOD COUNCIL

ivASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONvTABLE OF CONTENTSPart/Title Page Part/Title PageM1M2M3General Requirements forStructural Design...........................1M1.1 Products Covered in This ManualM1.2 General RequirementsM1.3 Design ProceduresDesign Values for StructuralMembers...............................................3M2.1 General InformationM2.2 Reference Design ValuesM2.3 Adjustment of Design ValuesDesign Provisions andEquations.............................................5M3.1 GeneralM3.2 Bending Members - GeneralM3.3 Bending Members - FlexureM3.4 Bending Members - ShearM3.5 Bending Members - DeflectionM3.6 Compression MembersM3.7 Solid ColumnsM3.8 Tension MembersM3.9 Combined Bending and AxialLoadingM3.10 Design for BearingM4 Sawn Lumber................................... 11M4.1 GeneralM4.2 Reference Design ValuesM4.3 Adjustment of Reference DesignValuesM4.4 Special Design ConsiderationsM5M6Structural Glued LaminatedTimber.................................................. 17M5.1 GeneralM5.2 Reference Design ValuesM5.3 Adjustment of Reference DesignValuesM5.4 Special Design ConsiderationsRound Timber Poles andPiles......................................................23M6.1 GeneralM6.2 Reference Design ValuesM6.3 Adjustment of Reference DesignValuesM6.4 Special Design ConsiderationsM7M8M9Prefabricated WoodI-Joists................................................ 27M7.1 GeneralM7.2 Reference Design ValuesM7.3 Adjustment of Reference DesignValuesM7.4 Special Design ConsiderationsStructural CompositeLumber.................................................43M8.1 GeneralM8.2 Reference Design ValuesM8.3 Adjustment of Reference DesignValuesM8.4 Special Design ConsiderationsWood Structural Panels..........49M9.1 GeneralM9.2 Reference Design ValuesM9.3 Adjustment of Reference DesignValuesM9.4 Design ConsiderationsM10 Mechanical Connections ........59M10.1 GeneralM10.2 Reference Design ValuesM10.3 Adjustment of Reference DesignValuesM10.4 Typical Connection DetailsM10.5 Pre-Engineered Metal ConnectorsM11 Dowel-Type Fasteners.............75M11.1 GeneralM11.2 Reference Withdrawal DesignValuesM11.3 Reference Lateral Design ValuesM11.4 Combined Lateral and WithdrawalLoadsM11.5 Adjustment of Reference DesignValuesM11.6 Multiple FastenersM12 Split Ring and Shear PlateConnectors....................................... 79M12.1 GeneralM12.2 Reference Design ValuesM12.3 Placement of Split Ring andShear Plate ConnectorsAMERICAN WOOD COUNCIL

viASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONPart/Title Page Part/Title PageM13 Timber Rivets.................................81M13.1 GeneralM13.2 Reference Design ValuesM13.3 Placement of Timber RivetsM14 Shear Walls andDiaphragms......................................83M14.1 GeneralM15 Special LoadingConditions........................................85M15.1 Lateral Distribution ofConcentrated LoadsM15.2 Spaced ColumnsM15.3 Built-Up ColumnsM15.4 Wood Columns with Side Loadsand EccentricityM16 Fire Design.......................................87M16.1 GeneralM16.2 Design Procedures for ExposedWood MembersM16.3 Wood ConnectionsLIST OF TABLESM4.3-1M4.4-1Applicability of Adjustment Factors forSawn Lumber.............................................. 13Approximate Moisture and ThermalDimensional Changes................................. 14M4.4-2 Coefficient of Moisture Expansion, e ME ,and Fiber Saturation Point, FSP, for SolidWoods.......................................................... 15M4.4-3M5.1-1M5.3-1M5.4-1M6.3-1M7.3-1M8.3-1Coefficient of Thermal Expansion, e TE , forSolid Woods................................................ 16Economical Spans for Structural GluedLaminated Timber Framing Systems.......... 19Applicability of Adjustment Factors forStructural Glued Laminated Timber........... 21Average Specific Gravity and WeightFactor.......................................................... 22Applicability of Adjustment Factors forRound Timber Poles and Piles.................... 25Applicability of Adjustment Factors forPrefabricated Wood I-Joists........................ 30Applicability of Adjustment Factors forStructural Composite Lumber..................... 46M9.1-1 Guide to Panel Use...................................... 51M9.2-1Wood Structural Panel Bending Stiffnessand Strength Capacities............................... 52M9.2-2M9.2-3M9.2-4M9.3-1Wood Structural Panel Axial Stiffness,Tension, and Compression Capacities......... 53Wood Structural Panel Shear-in-the-PlaneCapacities.................................................... 55Wood Structural Panel Rigidity and ShearThrough-the-Thickness Capacities............. 55Applicability of Adjustment Factors forWood Structural Panels............................... 56M9.4-1 Panel Edge Support..................................... 57M9.4-2Minimum Nailing for Wood StructuralPanel Applications....................................... 58M10.3-1 Applicability of Adjustment Factors forMechanical Connections............................. 61M11.3-1Applicability of Adjustment Factors forDowel-Type Fasteners................................. 77M12.2-1 Applicability of Adjustment Factors forSplit Ring and Shear Plate Connectors....... 80M13.2-1 Applicability of Adjustment Factors forTimber Rivets.............................................. 82M16.1-1 Minimum Sizes to Qualify as HeavyTimber Construction................................... 88M16.1-2Privacy Afforded According to STCRating.......................................................... 95AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTIONviiLIST OF FIGURESM5.1-1M5.2-1Unbalanced and Balanced LayupCombinations.............................................. 18Structural Glued Laminated Timber AxesOrientations................................................. 20M7.4-1 Design Span Determination........................ 31M7.4-2 Load Case Evaluations................................ 33M7.4-3End Bearing Web Stiffeners(Bearing Block)........................................... 35M7.4-4 Web Stiffener Bearing Interface.................. 36M7.4-5 Beveled End Cut......................................... 36M7.4-6 Sloped Bearing Conditions (Low End)....... 37M7.4-7 Sloped Bearing Conditions (High End)...... 38M7.4-8Lateral Support Requirements for Joistsin Hangers .................................................. 39M7.4-9 Top Flange Hanger Support........................ 39M7.4-10 Connection Requirements for Face NailHangers....................................................... 40M7.4-11 Details for Vertical Load Transfer.............. 41M9.2-1Structural Panel with Strength DirectionAcross Supports.......................................... 50M9.2-2 Example of Structural Panel in Bending..... 51M9.2-3M9.2-4M9.2-5Structural Panel with Axial CompressionLoad in the Plane of the Panel.................... 54Shear-in-the-Plane for Wood StructuralPanels.......................................................... 54Through-the-Thickness Shear for WoodStructural Panels.................................................. 54M16.1-1 Cross Sections of Possible One-HourArea Separations......................................... 94M16.3-1 Beam to Column Connection -Connection Not Exposed to Fire................. 97M16.3-2 Beam to Column Connection -Connection Exposed to Fire WhereAppearance is a Factor................................ 97M16.3-3 Ceiling Construction .................................. 97M16.3-4 Beam to Column Connection -Connection Exposed to Fire WhereAppearance is Not a Factor......................... 97M16.3-5 Column Connections Covered ................... 98M16.3-6 Beam to Girder - Concealed Connection.... 98AMERICAN WOOD COUNCIL

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ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION1M1: GENERALREQUIREMENTSFORSTRUCTURALDESIGN1M1.1 Products Covered in This Manual 2M1.2 General Requirements 2M1.2.1 Bracing 2M1.3 Design Procedures 2AMERICAN WOOD COUNCIL

2 M1: GENERAL REQUIREMENTS FOR STRUCTURAL DESIGNM1.1 Products Covered in This ManualThis Manual was developed with the intention of coveringall structural applications of wood-based productsand their connections that meet the requirements of thereferenced standards. The Manual is a dual format documentincorporating design provisions for both allowablestress design (ASD) and load and resistance factor design(LRFD). Design information is available for the followinglist of products. Each product chapter contains informationfor use with this Manual and the National DesignSpecification® (NDS®) for Wood Construction. Chaptersare organized to parallel the chapter format of the NDS.• Sawn Lumber Chapter 4• Structural Glued Laminated Timber Chapter 5• Round Timber Poles and Piles Chapter 6• Prefabricated Wood I-Joists Chapter 7• Structural Composite Lumber Chapter 8• Wood Structural Panels Chapter 9• Mechanical Connections Chapter 10• Dowel-Type Fasteners Chapter 11• Split Ring and Shear Plate Connectors Chapter 12• Timber Rivets Chapter 13• Shear Walls and Diaphragms Chapter 14An additional Standard, titled Special Design Provisionsfor Wind and Seismic (SDPWS), has been developedto cover materials, design, and construction of woodmembers, fasteners, and assemblies to resist wind andseismic forces.M1.2 General RequirementsThis Manual is organized as a multi-part package formaximum flexibility for the design engineer. Included inthis package are:• NDS and Commentary;• NDS Supplement: Design Values for WoodConstruction,• Special Design Provisions for Wind and Seismic(SDPWS) and Commentary,• Structural Wood Design Solved Example Problems.M1.2.1 BracingDesign considerations related to both temporary andpermanent bracing differ among product types. Specificdiscussion of bracing is included in the product chapter.M1.3 Design ProceduresThe NDS is a dual format specification incorporatingdesign provisions for ASD and LRFD. Behavioral equations,such as those for member and connection design, arethe same for both ASD and LRFD. Adjustment factor tablesinclude applicable factors for determining an adjustedASD design value or an adjusted LRFD design value. NDSAppendix N – (Mandatory) Load and Resistance FactorDesign (LRFD) and product chapters outline requirementsthat are unique to LRFD and adjustment factors for LRFD.The basic design equations for ASD or LRFD requirethat the specified product adjusted design value meet orexceed the actual (applied) stress or other effect imposedby the specified loads. Load combination equations foruse with ASD and LRFD are given in the model buildingcodes.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION3M2: DESIGNVALUES FORSTRUCTURALMEMBERS2M2.1 General Information 4M2.2 Reference Design Values 4M2.3 Adjustment of Design Values 4AMERICAN WOOD COUNCIL

4 M2: DESIGN VALUES FOR STRUCTURAL MEMBERSM2.1 General InformationStructural 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 in this categoryare metal plate connected wood trusses and custom structuralglued laminated timbers. Design of the individualmembers is based on criteria specified by the architect orengineer of record on the project. Manufacture of theseproducts is performed in accordance with the product’smanufacturing standards. Engineering of these productsnormally only extends to the design of the productsthemselves. Construction-related issues, such as load pathanalysis and erection bracing, remain the responsibility ofthe professional of record for the project.M2.2 Reference Design ValuesReference design value designates the allowablestress design value based on normal load duration. Toavoid confusion, the descriptor “reference” is used andserves as a reminder that design value adjustment factorsare applicable for design values in accordance with referencedconditions specified in the NDS – such as normalload duration.Reference design values for sawn lumber, structuralglued laminated timber, and round timber poles and pilesare contained in the NDS Supplement: Design Values forWood Construction. Reference design values for doweltypefasteners, split ring and shear plate connectors, andtimber rivets are contained in the NDS. Reference designvalues for all other products are typically contained in themanufacturer’s code evaluation report.M2.3 Adjustment of Reference Design ValuesAdjusted design value designates reference designvalues which have been multiplied by adjustment factors.Basic requirements for design use terminology applicableto both ASD and LRFD. In equation format, this takes thestandard form f b ≤ F b ′ which is applicable to either ASD orLRFD. Reference design values (F b , F t , F v , F c , F c , E, E min )are multiplied by adjustment factors to determine adjusteddesign values (F b ′, F t ′, F v ′, F c ′, F c ′, E′, E min ′).Reference conditions have been defined such that amajority of wood products used in interior or in protectedenvironments will require no adjustment for moisture,temperature, or treatment effects.Moisture content (MC) reference conditions are 19%or less for sawn lumber products. The equivalent limitfor glued products (structural glued laminated timber,structural composite lumber, prefabricated wood I-joists,and wood structural panels) is defined as 16% MC or less.Temperature reference conditions include sustainedtemperatures up to 100ºF. Note that it has been traditionallyassumed that these reference conditions also includecommon building applications in desert locations wheredaytime temperatures will often exceed 100ºF. Examplesof applications that may exceed the reference temperaturerange include food processing or other industrial buildings.Tabulated design values and capacities are for untreatedmembers. Tabulated design values and capacitiesalso apply to wood products pressure treated by an approvedprocess and preservative except as specified forload duration factors.An unincised reference condition is assumed. Formembers that are incised to increase penetration of preservativechemicals, use the incising adjustment factorsgiven in the product chapter.The effects of fire retardant chemical treatment onstrength shall be accounted for in the design. Referencedesign values, including connection design values, forlumber and structural glued laminated timber pressuretreatedwith fire retardant chemicals shall be obtained fromthe company providing the treatment and redrying service.The impact load duration factor shall not apply to structuralmembers pressure-treated with fire retardant chemicals.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION5M3: DESIGNPROVISIONSAND EQUATIONS3M3.1 General 6M3.2 Bending Members - General 6M3.3 Bending Members - Flexure 6M3.4 Bending Members - Shear 6M3.5 Bending Members - Deflection 7M3.6 Compression Members 7M3.7 Solid Columns 8M3.8 Tension Members 8M3.8.1 Tension Parallel to Grain 8M3.8.2 Tension Perpendicular to Grain 8M3.9 Combined Bending and Axial Loading 8M3.10 Design for Bearing 9AMERICAN WOOD COUNCIL

6 M3: DESIGN PROVISIONS AND EQUATIONSM3.1 GeneralThis Chapter covers design of members for bending,compression, tension, combined bending and axial loads,and bearing.M3.2 Bending Members - GeneralThis section 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 design capacityis exceeded under applied loads. Strength criteriafor bending members include bending moment, shear, localbuckling, lateral torsional buckling, and bearing.See specific product chapters for moment and shearcapacities (joist and beam selection tables) and referencebending and shear design values.M3.3 Bending Members - FlexureThe basic equation for moment design of bendingmembers is:M′ ≥ M (M3.3-1)The equation for calculation of adjusted momentcapacity is:M′ = F b ′ S (M3.3-2)where:M′ = adjusted moment capacitywhere:S = section modulus, in. 3M = bending momentF b ′ = adjusted bending design value, psi.See product chapters for applicableadjustment factors.M3.4 Bending Members - ShearThe basic equation for shear design of bending membersis:V′ ≥ V (M3.4-1)where:V′ = adjusted shear capacity parallel tograin, lbsV = shear force, lbsThe equation for calculation of shear capacity is:V′ = F v ′ Ib/Q (M3.4-2)which, for rectangular unnotched bending members,reduces to:V′ = 2/3 (F v ′) A (M3.4-3)where:I = moment of inertia, in. 4A = area, in. 2F v ′ = adjusted shear design value, psi.See product chapters for applicableadjustment factors.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION7M3.5 Bending Members - DeflectionUsers should note that design of bending members isoften controlled by serviceability limitations rather thanstrength. Serviceability considerations, such as deflectionand vibration, are often designated by the authority havingjurisdiction.For a simple span uniformly loaded rectangular member,the equation used for calculating mid-span deflection is:∆= 5 4wl (M3.5-1)384EIwhere:∆ = deflection, in.w = uniform load, lb/in.M3.6 Compression MembersThis section covers design of members stressed primarilyin compression parallel to grain. Examples of suchmembers include columns, truss members, and diaphragmchords.Information in this section is limited to the case inwhich loads are applied concentrically to the member.Provisions of NDS 3.9 or NDS Chapter 15 should be usedif loads are eccentric or if the compressive forces are appliedin addition to bending forces.The NDS differentiates between solid, built-up, andspaced columns. In this context built-up columns areassembled from multiple pieces of similar members connectedin accordance with NDS 15.3.A spaced column must comply with provisions ofNDS 15.2. Note that this definition includes main columnelements, spacer blocks with their connectors, and endblocks with shear plate or split ring connectors.Compression Parallel to GrainThe basic equation for design of compression membersis:P′ ≥ P (M3.6-1)where:P′ = adjusted compression parallel to graincapacity, lbsP = compressive force, lbs = span, in.E I = stiffness of beam section, lb-in. 2Values of modulus of elasticity, E, and moment ofinertia, I, for lumber and structural glued laminated timberfor use in the preceding equation can be found in the NDSSupplement. Engineered wood products such as I-joists andstructural composite lumber will have EI values publishedin individual manufacturer’s product literature or evaluationreports. Some manufacturers might publish “true” Ewhich would require additional computations to accountfor shear deflection. See NDS Appendix F for informationon shear deflection. See product chapters for more detailsabout deflection calculations.The complete equation for calculation of adjustedcompression capacity is:P′ = F c ′ A (M3.6-2)where:A = area, in. 2F c ′ = adjusted compression parallel to graindesign value, psi. See product chaptersfor applicable adjustment factors.Special ConsiderationsNet Section CalculationAs in design of tension members, compression membersshould be checked both on a gross section and a netsection basis (see NDS 3.6.3).Bearing Capacity ChecksDesign for bearing is addressed in NDS 3.10.Radial Compression in Curved 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 in NDS 5.4.1.3M3: DESIGN PROVISIONS AND EQUATIONSAMERICAN WOOD COUNCIL

8 M3: DESIGN PROVISIONS AND EQUATIONSM3.7 Solid ColumnsSlenderness Considerations andStabilityThe user is cautioned that stability calculations arehighly dependent upon boundary conditions assumed inthe 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 NDS 3.7.1.2 doubles (see NDS Appendix Table G1for recommended buckling length coefficients, K e ) and thecomputed adjusted compression parallel to grain capacitydecreases.M3.8 Tension MembersThis section covers design of members stressedprimarily in tension parallel to grain. Examples of suchmembers include shear wall end posts, truss members, anddiaphragm chords.The designer is advised that use of wood membersin applications that induce tension perpendicular to grainstresses should be avoided.M3.8.1 Tension Parallel to GrainThe basic equation for design of tension members is:T′ ≥ T (M3.8-1)where:T′ = adjusted tension parallel to graincapacity, lbsT = tensile force, lbsThe equation for calculation of adjusted tension capacityis:T′ = F t ′A (M3.8-2)where:A = area, in. 2F t ′ = adjusted tension design value, psi.See product chapters for applicableadjustment factors.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 M10) but also the transfer of force across thenet section of the member. One method for determiningthese stresses is provided in NDS Appendix E.M3.8.2 Tension Perpendicular toGrainRadial Stress in Curved MembersStresses 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 stress design is a specialized considerationthat is covered in NDS 5.4.1 and is explained in detail inthe American Institute of Timber Construction (AITC)Timber Construction Manual.M3.9 Combined Bending and Axial LoadingThis section covers design of members stressed undercombined bending and axial loads. The applicable strengthcriteria for these members is explicit in the NDS equations– limiting the sum of various stress ratios to less than orequal to unity.Bending and Axial TensionFor designs in which the axial load is in tension ratherthan compression, the designer should use NDS Equations3.9-1 and 3.9-2.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION9Bending and Axial CompressionThe equation for design of members under bendingplus compression loads is given below in terms of loadand moment ratios:2⎛ P ⎞ MM⎜P′⎟⎝ ⎠+ 12+≤10 .PM ′ ⎛ ⎞−P M⎜ ⎟PM ′ − − ⎛ 2⎡⎝ E ⎠ PE⎝ ⎜ ⎞ ⎤11 12⎢1 ⎟ ⎥ (M3.9-1)1M⎣⎢2 E ⎠ ⎥ ⎦where:P′ = adjusted compression capacitydetermined per M3.6, lbsP = compressive force determined perM3.6, lbsM 1 ′ = adjusted moment capacity (strong axis)determined per M3.3, in.-lbsM 1 = bending moment (strong axis)determined per M3.3, in.-lbsM 2 ′ = adjusted moment capacity (weak axis)determined per M3.3, in.-lbsM 2 = bending moment (weak axis)determined per M3.3, in.-lbsP E1 = F cE1 A = critical column buckling capacity(strong axis) determined per NDS 3.9.2,lbsP E2 = F cE2 A = critical column buckling capacity(weak axis) determined per NDS 3.9.2,lbsM E = F bE S = critical beam buckling capacitydetermined per NDS 3.9.2, in.-lbsMembers must be designed by multiplying all applicableadjustment factors by the reference design values forthe product. See M3.3 and M3.6 for discussion of applicableadjustment factors for bending or compression, respectively.Equation 3.9-4 in the NDS is used to check the intermediatecalculation for members subjected to flatwisebending in combination with axial compression, with orwithout edgewise bending. When a flatwise bending loadis checked with the third term of the stress interaction equation(NDS Equation 3.9-3), the axial and edgewise bendinginteraction in the denominator can become a negativevalue. The occurrence of the negative value indicates anoverstress. However, use of this negative term in the stressinteraction equation (NDS Equation 3.9-3) overlooks theoverstress in flatwise bending and incorrectly reduces theoverall interaction.Design TechniquesA key to understanding design of members undercombined bending and axial loads is that componentsof the design equation are simple ratios of compressiveforce (or moment) to compression capacity (or momentcapacity). Note that the compression term in this equationis squared. This is the result of empirical test data. Moderatecompressive forces do not have as large an impact oncapacity (under combined loads) as previously thought. Itis believed that this is the result of compressive “reinforcing”of what would otherwise be a tensile failure modein bending.3M3: DESIGN PROVISIONS AND EQUATIONSM3.10 Design for BearingColumns often transfer large forces within a structuralsystem. While satisfaction of column strength criteria isusually the primary concern, the designer should alsocheck 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.The basic equation for bearing design is:R′ ≥ R (M3.10-1)where:R′ = adjusted compression perpendicular tograin capacity, lbsR = compressive force or reaction, lbsThe equation for calculation of adjusted compressionperpendicular to grain capacity is:R′ = F c⊥ ′ A (M3.10-2)where:A = area, in. 2F c⊥ ′ = adjusted compression perpendicularto grain design value, psi. See productchapters for applicable adjustmentfactors.AMERICAN WOOD COUNCIL

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ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION11M4: SAWNLUMBER4M4.1 General 12M4.2 Reference Design Values 12M4.3 Adjustment of ReferenceDesign Values 13M4.4 Special Design Considerations 14AMERICAN WOOD COUNCIL

12 M4: SAWN LUMBERM4.1 GeneralProduct InformationStructural lumber products are well-known throughoutthe construction industry. The economic advantagesof lumber often dictate its choice as a preferred buildingmaterial.Lumber is available in a wide range of species, grades,sizes, and moisture contents. Structural lumber productsare typically specified by either the stress level requiredor by the species, grade, and size required.This Chapter provides information for designingstructural lumber products in accordance with the NDS.Common UsesStructural lumber and timbers have been a primaryconstruction material throughout the world for many centuries.They are the most widely used framing material forhousing in North America.In addition to use in housing, structural lumber findsbroad use in commercial and industrial construction. Itshigh strength, universal availability, and cost saving attributesmake it a viable option in most low- and mid-riseconstruction projects.Structural lumber is used as beams, columns, headers,joists, rafters, studs, and plates in conventional construction.In addition to its use in lumber form, structural lumberis used to manufacture structural glued laminated beams,trusses, and wood I-joists.AvailabilityStructural lumber is a widely available constructionmaterial. However, to efficiently specify structural lumberfor individual construction projects, the specifier should beaware of the species, grades, and sizes available locally.The best source of this information is your local lumbersupplier.M4.2 Reference Design ValuesGeneralThe NDS Supplement provides reference design valuesfor design of sawn lumber members. These design valuesare used when manual calculation of member capacity isrequired and must be used in conjunction with the adjustmentfactors specified in NDS 4.3.Reference Design ValuesReference design values are provided in the NDSSupplement as follows:NDSSupplementTable Number4A and 4B4C4D4E4FVisually graded dimension lumberMechanically graded dimension lumberVisually graded timbersVisually graded deckingNon-North American visually gradeddimension lumberAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION13M4.3 Adjustment of Reference Design ValuesTo generate member design capacities, reference designvalues for sawn lumber are multiplied by adjustmentfactors and section properties per Chapter M3. Applicableadjustment factors for sawn lumber are defined in NDS4.3. Table M4.3-1 shows the applicability of adjustmentfactors for sawn lumber in a slightly different format forthe designer.Table M4.3-1Applicability of Adjustment Factors for Sawn Lumber4Allowable Stress DesignLoad and Resistance Factor DesignF b ′ = F b C D C M C t C L C F C fu C i C rF b ′ = F b C M C t C L C F C fu C i C r (2.54)(0.85) λF t ′ = F t C D C M C t C F C iF t ′ = F t C M C t C F C i (2.70)(0.80) λF v ′ = F v C D C M C t C iF v ′ = F v C M C t C i (2.88)(0.75) λF c⊥ ′ = F c⊥ C M C t C i C b F c⊥ ′ = F c⊥ C M C t C i C b (1.67)(0.90)F c ′ = F c C D C M C t C F C i C PF c ′ = F c C M C t C F C i C P (2.40)(0.90) λM4: SAWN LUMBERE′ = E C M C t C i E′ = E C M C t C iE min ′ = E min C M C t C i C T E min ′ = E min C M C t C i C T (1.76)(0.85)Bending Member ExampleFor unincised, straight, laterally supported bendingmembers stressed in edgewise bending in single memberuse and used in a normal building environment (meetingthe reference conditions of NDS 2.3 and 4.3), the adjusteddesign values reduce to:For ASD:F b ′ = F b C D C FF v ′ = F v C DF c⊥ ′ = F c⊥ C bE′ = EFor LRFD:F b ′ = F b C F (2.54)(0.85) λF v ′ = F v (2.88)(0.75) λAxially Loaded Member ExampleFor unincised axially loaded members used in a normalbuilding environment (meeting the reference conditions ofNDS 2.3 and 4.3) designed to resist tension or compressionloads, the adjusted tension or compression design valuesreduce to:For ASD:F c ′ = F c C D C F C PF t ′ = F t C D C FE min ′ = E minFor LRFD:F c ′ = F c C F C P (2.40)(0.90) λF t ′ = F t C F (2.70)(0.80) λE min ′ = E min (1.76)(0.85)F c⊥ ′ = F c⊥ C b (1.67)(0.90)E′ = EAMERICAN WOOD COUNCIL

14 M4: SAWN LUMBERM4.4 Special Design ConsiderationsGeneralWith proper detailing and protection, structural lumbercan perform well in a variety of environments. One key toproper detailing is planning for the natural shrinkage andswelling of wood members as they are subjected to variousdrying and wetting cycles. While moisture changes havethe largest impact on lumber dimensions, some designsmust also check the effects of temperature on dimensionsas well.Dimensional ChangesTable M4.4-1 is extracted from more precise scientificand research reports on these topics. The coefficients areconservative (yielding more shrinkage and expansionthan one might expect for most species). This level ofinformation should be adequate for common structuralapplications. Equations are provided in this section forthose designers who require more precise calculations.Design of wood members and assemblies for fireresistance is discussed in Chapter M16.Table M4.4-1Approximate Moisture and Thermal Dimensional ChangesDescriptionDimensional change due to moisture content change 1Dimensional change due to temperature change 2Radial or Tangential Direction1% change in dimension per 4% change in MC20 × 10 -6 in./in. per degree F1. Corresponding longitudinal direction shrinkage/expansion is about 1% to 5% of that in radial and tangential directions.2. Corresponding longitudinal direction coefficient is about 1/10 as large as radial and tangential.Equations for Computing Moistureand Thermal Shrinkage/ExpansionDue to Moisture ChangesFor more precise computation of dimensional changesdue to changes in moisture, the change in radial (R), tangential(T), and volumetric (V) dimensions due to changesin moisture content can be calculated as:X X ∆ MC e(M4.4-1)= ( )oMEwhere:X 0 = initial dimension or volumeand:X = dimension or volume change∆MC = moisture content change (%)e ME = coefficient of moisture expansion:linear (in./in./%MC) orvolumetric (in. 3 /in. 3 /%MC)∆MC = M − M o(M4.4-2)where:M o = initial moisture content % (M o ≤ FSP)M = new moisture content % (M ≤ FSP)FSP = fiber saturation pointValues for e ME and FSP are shown in Table M4.4-2.Due to Temperature ChangesFor more precise calculation of dimensional changesdue to changes in temperature, the shrinkage/expansionof solid wood including lumber and timbers can be calculatedas:X X ∆ T e(M4.4-3)= ( )oTEwhere:X 0 = reference dimension at T 0and:where:X = computed dimension at TT 0 = reference temperature (°F)T = temperature at which the newdimension is calculated (°F)e TE = coefficient of thermal expansion(in./in./°F)∆T = T − T o(M4.4-4)−60°F ≤ T o ≤ 130°FThe coefficient of thermal expansion of ovendry woodparallel to grain ranges from about 1.7 × 10 -6 to 2.5 × 10 -6per °F.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION15The linear expansion coefficients across the grain(radial and tangential) are proportional to wood density.These coefficients are about five to ten times greater thanthe parallel-to-the-grain coefficients and are given as:Radial:e = ⎡ ( TEG )+−⎣18 55 . ⎤ ⎦ 10 6 in./in. / ° F (M4.4-5)Tangential:Table M4.4-2Species( )e = ⎡ ( TEG )+−⎣18 10. 2⎤ ⎦ 10 6 in./in. / ° F (M4.4-6)where:( )G = tabulated specific gravity for thespecies.Coefficient of Moisture Expansion, e ME , and Fiber SaturationPoint, FSP, for Solid WoodsRadial(in./in./%)Tangential(in./in./%)e MEVolumetric(in. 3 /in. 3 /%)Alaska Cedar 0.0010 0.0021 0.0033 28Douglas Fir-Larch 0.0018 0.0033 0.0050 28Englemann Spruce 0.0013 0.0024 0.0037 30Redwood 0.0012 0.0022 0.0032 22Red Oak 0.0017 0.0038 0.0063 30Southern Pine 0.0020 0.0030 0.0047 26Western Hemlock 0.0015 0.0028 0.0044 28Yellow Poplar 0.0015 0.0026 0.0041 31FSP(%)4M4: SAWN LUMBERTable M4.4-3 provides the numerical values for e TEfor the most commonly used commercial species or speciesgroups.Wood that contains moisture reacts to varying temperaturedifferently than does dry wood. When moist woodis heated, it tends to expand because of normal thermalexpansion and to shrink because of loss in moisture content.Unless the wood is very dry initially (perhaps 3%or 4% MC or less), the shrinkage due to moisture losson heating will be greater than the thermal expansion, sothe net dimensional change on heating will be negative.Wood at intermediate moisture levels (about 8% to 20%)will expand when first heated, then gradually shrink to avolume smaller than the initial volume, as the wood graduallyloses water while in the heated condition.Even in the longitudinal (grain) direction, where dimensionalchange due to moisture change is very small,such changes will still predominate over correspondingdimensional changes due to thermal expansion unlessthe wood is very dry initially. For wood at usual moisturelevels, net dimensional changes will generally be negativeafter prolonged heating.Calculation of actual changes in dimensions can beaccomplished by determining the equilibrium moisturecontent of wood at the temperature value and relative humidityof interest. Then the relative dimensional changesdue to temperature change alone and moisture contentchange alone are calculated. By combining these twochanges the final dimension of lumber and timber can beestablished.AMERICAN WOOD COUNCIL

16 M4: SAWN LUMBERTable M4.4-3Coefficient of Thermal Expansion, e TE , for Solid Woodse TESpecies Radial (10 -6 in./in./°F) Tangential (10 -6 in./in./°F)California Redwood 13 18Douglas Fir-Larch 1 15 19Douglas Fir-South 14 19Eastern Spruce 13 18Hem-Fir 1 13 18Red Oak 18 22Southern Pine 15 20Spruce-Pine-Fir 13 18Yellow Poplar 14 181. Also applies when species name includes the designation “North.”DurabilityDesigning for durability is a key part of the architecturaland engineering design of the building. This issue isparticularly important in the design of buildings that usepoles and piles. Many design conditions can be detailedto minimize the potential for decay; for other problemconditions, preservative-treated wood or naturally durablespecies should be specified.This section does not cover the topic of designing fordurability in detail. There are many excellent texts on thetopic, including AWC’s Design of Wood Structures forPermanence, WCD No. 6. Designers are advised to use thistype of information to assist in designing for “difficult”design areas, such as:• structures in moist or humid conditions• where wood comes in contact with concreteor masonry• where wood members are supported in steelhangers or connectors in which condensationcould collect• anywhere that wood is directly or indirectlyexposed to the elements• where wood, if it should ever become wet,could not naturally dry out.This list is not intended to be all-inclusive – it ismerely an attempt to alert designers to special conditionsthat may cause problems when durability is not consideredin the design.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION17M5: STRUCTURALGLUEDLAMINATEDTIMBER5M5.1 General 18M5.2 Reference Design Values 20M5.3 Adjustment of ReferenceDesign Values 21M5.4 Special Design Considerations 22AMERICAN WOOD COUNCIL

18 M5: STRUCTURAL GLUED LAMINATED TIMBERM5.1 GeneralProducts DescriptionStructural glued laminated timber (glulam) is a structuralmember glued up from suitably selected and preparedpieces of wood either in a straight or curved form with thegrain of all of the pieces parallel to the longitudinal axisof the member. The reference design values given in theNDS Supplement are applicable only to structural gluedlaminated timber members produced in accordance withAmerican National Standard for Wood Products — StructuralGlued Laminated Timber, ANSI/AITC A190.1.Structural glued laminated timber members are producedin laminating plants by gluing together dry lumber,normally of 2-inch or 1-inch nominal thickness, undercontrolled temperature and pressure conditions. Memberswith a wide variety of sizes, profiles, and lengths canbe produced having superior characteristics of strength,serviceability, and appearance. Structural glued laminatedtimber beams are manufactured with the strongestlaminations on the bottom and top of the beam, where thegreatest tension and compression stresses occur in bending.This allows a more efficient use of the lumber resourceby placing higher grade lumber in zones that have higherstresses and lumber with less structural quality in lowerstressed zones.Structural glued laminated timber members aremanufactured from several softwood species, primarilyDouglas fir-larch, southern pine, hem-fir, spruce-pine-fir,eastern spruce, and Alaska cedar. Other species includingredwood and various hardwoods are occasionally used.Standard structural glued laminated timber sizes are givenin the NDS Supplement. Any length, up to the maximumlength permitted by transportation and handling restrictions,is available.A structural glued laminated timber member can bemanufactured using a single grade or multiple grades oflumber, depending on intended use. In addition, a mixedspeciesstructural glued laminated timber member is alsopossible. When the member is intended to be primarilyloaded either axially or in bending with the loads actingparallel to the wide faces of the laminations, a single gradecombination is recommended. On the other hand, a multiplegrade combination provides better cost-effectivenesswhen the member is primarily loaded in bending dueto loads applied perpendicular to the wide faces of thelaminations.On a multiple grade combination, a structural gluedlaminated timber member can be produced as either abalanced or unbalanced combination, depending on thegeometrical arrangement of the laminations about themid-depth of the member. As shown in Figure M5.1-1, abalanced combination is symmetrical about the mid-depth,so it has the same reference bending design values forboth positive and negative bending. Unbalanced combinationsare asymmetrical about the mid-depth, so theyhave lower reference design values for negative bendingthan for positive bending. The top face of an unbalancedmember is required to be marked “TOP” by the manufacturer.The balanced combinations are intended for use incontinuous or cantilevered applications to provide equalcapacity in both positive and negative bending. Whereasunbalanced combinations are primarily for use in simplespan applications, they can also be used for short cantileverapplications (cantilever less than 20% of the back span)or for continuous span applications when the design iscontrolled by shear or deflection.Figure M5.1-1BCBAUnbalancedUnbalanced andBalanced LayupCombinationsABCBABalancedStructural glued laminated timber members can beused as primary or secondary load-carrying componentsin structures. Table M5.1-1 lists economical spans forselected timber framing systems using structural gluedlaminated timber members in buildings. Other commonuses of structural glued laminated timber members arefor utility structures, pedestrian bridges, highway bridges,railroad bridges, marine structures, noise barriers, andtowers. Table M5.1-1 may be used for preliminary designpurposes to determine the economical span ranges for theselected framing systems. However, all systems require amore extensive analysis for final design.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION19Table M5.1-1Economical Spansfor Structural GluedLaminated TimberFraming SystemsType of Framing SystemEconomicalSpans (ft)ROOFSimple Span BeamsStraight or slightly cambered 10 to 100Tapered, double tapered-pitched, or 25 to 105curvedCantilevered Beams (Main span) up to 90Continuous Beams (Interior spans) 10 to 50Girders 40 to 100Three-Hinged ArchesGothic 40 to 100Tudor 40 to 140A-Frame 20 to 100Three-centered, Parabolic, or Radial 40 to 250Two-Hinged ArchesRadial or Parabolic 50 to 200Trusses (Four or more ply chords)Flat or parallel chord 50 to 150Triangular or pitched 50 to 150Bowstring (Continuous chord) 50 to 200Trusses (Two or three ply chords)Flat or parallel chord 20 to 75Triangular or pitched 20 to 75Tied arches 50 to 200Dome structures 200 to 500+FLOORSimple Span Beams 10 to 40Continuous Beams (Individual spans) 10 to 40HEADERSWindows and Doors < 10Garage Doors 9 to 18Appearance ClassificationsStructural glued laminated timber members aretypically produced in four appearance classifications:Premium, Architectural, Industrial, and Framing. Premiumand Architectural beams are higher in appearance qualitiesand are surfaced for a smooth finish ready for staining orpainting. Industrial classification beams are normally usedin concealed applications or in construction where appearanceis not important. Framing classification beams aretypically used for headers and other concealed applicationsin residential construction. Design values for structuralglued laminated timber members are independent of theappearance classifications.For more information and detailed descriptions of theseappearance classifications and their typical uses, refer toAPA EWS Technical Note Y110 or AITC Standard 110.AvailabilityStructural glued laminated timber members are availablein both custom and stock sizes. Custom beams aremanufactured to the specifications of a specific project,while stock beams are made in common dimensions,shipped to distribution yards, and cut to length when thebeam is ordered. Stock beams are available in virtuallyevery major metropolitan area. Although structural gluedlaminated timber members can be custom fabricated toprovide a nearly infinite variety of forms and sizes, thebest economy is generally realized by using standard-sizemembers as noted in the NDS Supplement. When in doubt,the designer is advised to check with the structural gluedlaminated timber supplier or manufacturer concerning theavailability of a specific size prior to specification.5M5: STRUCTURAL GLUED LAMINATED TIMBERAMERICAN WOOD COUNCIL

20 M5: STRUCTURAL GLUED LAMINATED TIMBERM5.2 Reference Design ValuesReference design values of structural glued laminatedtimber are affected by the layup of members composedof various grades of lumber, as well as the orientationof the laminations relative to the applied loads. As aresult, different design values are assigned for structuralglued laminated timber used primarily in bending (NDSSupplement Table 5A) and primarily in axial loading(NDS Supplement Table 5B). The reference design valuesare used in conjunction with the dimensions provided inTable 1C (western species) and Table 1D (southern pine)of the NDS Supplement, but are applicable to any size ofstructural glued laminated timber when the appropriatemodification factors discussed in M5.3 are applied.Reference design values are given in NDS SupplementTable 5A for bending about the X-X axis (see FigureM5.2‐1). Although permitted, axial loading or bendingabout the Y-Y axis (also see Figure M5.2-1) is not efficientin using the structural glued laminated timber combinationsgiven in NDS Supplement Table 5A. In such cases, thedesigner should select structural glued laminated timberfrom NDS Supplement Table 5B. Similarly, structural gluedlaminated timber combinations in NDS Supplement Table5B are inefficiently utilized if the primary use is bendingabout the X-X axis.The reference design values given in NDS SupplementTables 5A and 5B are based on use under normal durationof load (10 years) and dry conditions (less than 16%moisture content). When used under other conditions,see NDS Chapter 5 for adjustment factors. The referencebending design values are based on members loaded assimple beams. When structural glued laminated timber isused in continuous or cantilevered beams, the referencebending design values given in NDS Supplement Table 5Afor top of beam stressed in tension should be used for thedesign of stress reversal.Figure M5.2-1XYYX-X Axis LoadingStructural GluedLaminated TimberAxes OrientationsXYXXY-Y Axis LoadingYAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION21M5.3 Adjustment of Reference Design ValuesThe adjustment factors provided in the NDS are fornon-reference end-use conditions and material modificationeffects. These factors are used to modify the referencedesign values when one or more of the specific end usesor material modification conditions are beyond the limitsof the reference conditions given in the NDS.Adjustment factors unique to structural glued laminatedtimber include the volume factor, C V , the curvaturefactor, C c ,stress interaction factor, C I , and the shear reductionfactor, C vr . All are defined in Chapter 5 of the NDS.To generate member design capacities, referencedesign values for structural glued laminated timber aremultiplied by adjustment factors and section properties perChapter M3. Applicable adjustment factors for structuralglued laminated timber are defined in NDS 5.3. TableM5.3-1 shows the applicability of adjustment factors forstructural glued laminated timber in a slightly differentformat for the designer.Table M5.3-1Applicability of Adjustment Factors for Structural GluedLaminated Timber 15Allowable Stress DesignLoad and Resistance Factor DesignF b ′ = F b C D C M C t C L C V C fu C c C IF b ′ = F b C M C t C L C V C fu C c C I (2.54)(0.85) λF t ′ = F t C D C M C tF t ′ = F t C M C t (2.70)(0.80) λF v ′ = F v C D C M C t C vr F v ′ = F v C M C t C vr (2.88)(0.75)F rt ' = F rt C D C M C tF rt ' = F rt C M C t (2.88)(0.75) λF c ′ = F c C D C M C t C PF c ′ = F c C M C t C P (2.40)(0.90) λF c⊥ ′ = F c⊥ C M C t C b F c⊥ ′ = F c⊥ C M C t C b (1.67)(0.90)E′ = E C M C t E′ = E C M C tE min ′ = E min C M C t E min ′ = E min C M C t (1.76)(0.85)1. The beam stability factor, C L , shall not apply simultaneously with the volume factor, C V , for structural glued laminated timber bending members (see NDS 5.3.6).Therefore, the lesser of these adjustment factors shall apply.Bending Member ExampleFor straight, prismatic, untapered, laterally supportedbending members loaded perpendicular to the wide face ofthe laminations and used in a normal building environment(meeting the reference conditions of NDS 2.3 and 5.3), theadjusted design values reduce to:Axially Loaded Member ExampleFor axially loaded members used in a normal buildingenvironment (meeting the reference conditions of NDS2.3 and 5.3) designed to resist tension or compressionloads, the adjusted tension or compression design valuesreduce to:M5: STRUCTURAL GLUED LAMINATED TIMBERFor ASD:F b ′ = F b C D C VF v ′ = F v C DF c⊥ ′ = F c⊥ C bE′ = EFor LRFD:F b ′ = F b C V (2.54)(0.85) λF v ′ = F v (2.88)(0.75) λF c⊥ ′ = F c⊥ C b (2.40)(0.90)E′ = EFor ASD:F c ′ = F c C D C PF t ′ = F t C DE min ′ = E minFor LRFD:F c ′ = F c C P (2.40)(0.90) λF t ′ = F t (2.70)(0.80) λE min ′ = E min (1.76)(0.85)AMERICAN WOOD COUNCIL

22 M5: STRUCTURAL GLUED LAMINATED TIMBERM5.4 Special Design ConsiderationsGeneralThis section contains information concerning physicalproperties of structural glued laminated timber membersincluding specific gravity and response to moisture ortemperature.In addition to designing to accommodate dimensionalchanges and detailing for durability, another significantdesign consideration is that of fire performance, which isdiscussed in Chapter M16.Note that the information contained in this sectionaddresses design considerations separate from those describedin NDS 5.4.Specific GravityTable M5.4-1 provides specific gravity values for someof the most common wood species used for structural gluedlaminated timber. These values are used in determiningvarious physical and connection properties. Further, weightfactors are provided at four moisture contents. When thecross-sectional area (in. 2 ) is multiplied by the appropriateweight factor, it provides the weight of the structural gluedlaminated timber member per linear foot of length. Forother moisture contents, the tabulated weight factors canbe interpolated or extrapolated.Structural glued laminated timber members often aremanufactured using different species at different portionsof the cross section. In this case the weight of the structuralglued laminated timber may be computed by the sum ofthe products of the cross-sectional area and the weightfactor for each species.Dimensional ChangesSee M4.4 for information on calculating dimensionalchanges due to moisture or temperature.DurabilitySee M4.4 for information on detailing for durability.Table M5.4-1Average Specific Gravity and Weight FactorWeight Factor 2Species Combination Specific Gravity 1 12% 15% 19% 25%California Redwood (close grain) 0.44 0.195 0.198 0.202 0.208Douglas Fir-Larch 0.50 0.235 0.238 0.242 0.248Douglas Fir (South) 0.46 0.221 0.225 0.229 0.235Eastern Spruce 0.41 0.191 0.194 0.198 0.203Hem-Fir 0.43 0.195 0.198 0.202 0.208Red Maple 0.58 0.261 0.264 0.268 0.274Red Oak 0.67 0.307 0.310 0.314 0.319Southern Pine 0.55 0.252 0.255 0.259 0.265Spruce-Pine-Fir (North) 0.42 0.195 0.198 0.202 0.208Yellow Poplar 0.43 0.213 0.216 0.220 0.2261. Specific gravity is based on weight and volume when ovendry.2. Weight factor shall be multiplied by net cross-sectional area in in. 2 to obtain weight in pounds per lineal foot.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION23M6: ROUNDTIMBER POLESAND PILESM6.1 General 24M6.2 Reference Design Values 24M6.3 Adjustment of ReferenceDesign Values 25M6.4 Special Design Considerations 266AMERICAN WOOD COUNCIL

24 M6: ROUND TIMBER POLES AND PILESM6.1 GeneralProduct InformationTimber poles and piles offer many advantages relativeto competing materials. As with other wood products,timber poles and piles offer the unique advantage of beingthe only major construction material that is a renewableresource.Common UsesTimber poles are used extensively in post-frame constructionand are also used architecturally. This Chapteris not for use with poles used in the support of utilitylines. Timber piles are generally used as part of foundationsystems.AvailabilityTimber poles are supplied to the utility industry ina variety of grades and species. Because these poles aregraded according to ANSI 05.1, Specifications and Dimensionsfor Wood Poles, they must be regraded according toASTM D3200 if they are to be used with the NDS.Timber piles are typically available in three species:Pacific Coast Douglas-fir, southern pine, and red pine.However, local pile suppliers should be contacted becauseavailability is dependent upon geographic location.M6.2 Reference Design ValuesGeneralThe tables in the NDS Supplement provide referencedesign values for timber pole and pile members. These referencedesign values are used when manual calculation ofmember strength is required and shall be used in conjunctionwith adjustment factors specified in NDS Chapter 6.These values, with the exception of F c , are applicable forall locations in the pole or pile. The F c values can be increasedat other locations in accordance with NDS 6.3.9.Reference design values for poles and piles are basedon air dried conditioning. Kiln-drying, steam conditioning,or boultonizing prior to treatment will have the effect ofreducing the reference design value per NDS 6.3.5.Pole and Pile Reference DesignValuesReference design values for piles and poles are providedin NDS Supplement Tables 6A and 6B, respectively.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION25M6.3 Adjustment of Reference Design ValuesTo generate member design capacities, referencedesign values are multiplied by adjustment factors and sectionproperties. Adjustment factors unique to round timberpoles and piles include the condition treatment factor, C ct ,the critical section factor, C cs , and the load sharing factor,C ls . All are defined in Chapter 6 of the NDS.To generate member design capacities, reference designvalues for round timber poles and piles are multipliedby adjustment factors and section properties per ChapterM3. Applicable adjustment factors for round timber polesand piles are defined in NDS 6.3. Table M6.3-1 shows theapplicability of adjustment factors for round timber polesand piles in a slightly different format for the designer.Table M6.3-1Applicability of Adjustment Factors for Round Timber Poles andPilesAllowable Stress DesignLoad and Resistance Factor DesignF c ′ = F c C D C t C ct C P C cs C lsF c ′ = F c C t C ct C P C cs C ls (2.40)(0.90) λF b ′ = F b C D C t C ct C F C lsF b ′ = F b C t C ct C F C ls (2.54)(0.85) λF v ′ = F v C D C t C ctF v ′ = F v C t C ct (2.88)(0.75) λF c⊥ ′ = F c⊥ C t C ct C b F c⊥ ′ = F c⊥ C t C ct C b (1.67)(0.90)E′ = E C t E′ = E C tE min ′ = E min C t E min ′ = E min C t (1.76)(0.85)Axially Loaded Pole or PileExampleFor single, axially loaded, air dried poles or piles, fullylaterally supported in two orthogonal directions, used ina normal environment (meeting the reference conditionsof NDS 2.3 and 6.3), designed to resist compression loadsonly, and less than 13.5" in diameter, the adjusted compressiondesign values reduce to:6M6: ROUND TIMBER POLES AND PILESFor ASD:F c ′ = F c C DFor LRFD:F c ′ = F c (2.40)(0.90) λAMERICAN WOOD COUNCIL

26 M6: ROUND TIMBER POLES AND PILESM6.4 Special Design ConsiderationsWith proper detailing and protection, timber poles andpiles can perform well in a variety of environments. Onekey to proper detailing is planning for the natural shrinkageand swelling of wood products as they are subjectedto various drying and wetting cycles. While moisturechanges have the largest impact on product dimensions,some designs must also check the effects of temperature.See M4.4 for design information on dimensional changesdue to moisture and temperature.Durability issues related to piles are generally bothmore critical and more easily accommodated. Since pilesare in constant ground contact, they cannot be “insulated”from contact with moisture – thus, the standard conditionfor piles is preservatively treated. The importance of propertreatment processing of piles cannot be overemphasized.See M4.4 for more information about durability.In addition to designing to accommodate dimensionalchanges and detailing for durability, another significantissue in the planning of wood structures is that of fireperformance, which is discussed in Chapter M16.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION27M7:PREFABRICATEDWOOD I-JOISTSM7.1 General 28M7.2 Reference Design Values 28M7.3 Adjustment of ReferenceDesign Values 30M7.4 Special Design Considerations 317AMERICAN WOOD COUNCIL

28 M7: PREFABRICATED WOOD I-JOISTSM7.1 GeneralProduct InformationPrefabricated wood I-joists are exceptionally stiff,lightweight, and capable of long spans. Holes may beeasily cut in the web according to manufacturer’s recommendations,allowing ducts and utilities to be run throughthe joist. I-joists are dimensionally stable and uniform insize, with no crown. This keeps floors quieter, reducesfield modifications, and eliminates rejects in the field. I-joists may be field cut to proper length using conventionalmethods and tools.Manufacturing of I-joists utilizes the geometry of thecross section and high strength components to maximizethe strength and stiffness of the wood fiber. Flanges aremanufactured from solid sawn lumber or structural compositelumber, while webs typically consist of plywoodor oriented strand board. The efficient utilization of rawmaterials, along with high-quality exterior adhesives andstate of the art quality control procedures, result in an extremelyconsistent product that maximizes environmentalbenefits as well.Prefabricated wood I-joists are produced as proprietaryproducts which are covered by code evaluation reports.Evaluation reports and product literature should be consultedfor current design information.Common UsesPrefabricated wood I-joists are widely used as a framingmaterial for housing in North America. I-joists aremade in different grades and with various processes andcan be utilized in various applications. Proper design isrequired to optimize performance and economics.In addition to use in housing, I-joists find increasinguse in commercial and industrial construction. The highstrength, stiffness, wide availability, and cost saving attributesmake them a viable alternative in most low-riseconstruction projects.Prefabricated wood I-joists are typically used as floorand roof joists in conventional construction. In addition,I-joists are used as studs where long lengths and highstrengths are required.AvailabilityTo efficiently specify I-joists for individual constructionprojects, consideration should be given to the size andthe required strength of the I-joist. Sizes vary with eachindividual product. The best source of this information isyour local lumber supplier, distribution center, or I-joistmanufacturer. Proper design is facilitated through the useof manufacturer’s literature and specification softwareavailable from I-joist manufacturers.M7.2 Reference Design ValuesIntroduction to Design ValuesAs stated in NDS 7.2, each wood I-joist manufacturerdevelops its own proprietary design values. The derivationof these values is reviewed by the applicable buildingcode authority. Since materials, manufacturing processes,and product evaluations may differ between the variousmanufacturers, selected design values are only appropriatefor the specific product and application.To generate the design capacity of a given product,the manufacturer of that product evaluates test data. Thedesign capacity is then determined per ASTM D5055.The latest model building code agency evaluation reportsare a reliable source for wood I-joist design values.These reports list accepted design values for shear, moment,stiffness, and reaction capacity based on minimumbearing. In addition, evaluation reports note the limitationson web holes, concentrated loads, and requirements forweb stiffeners.Bearing/Reaction DesignTabulated design capacities reflect standard conditionsand must be modified as discussed in NDS Chapter 7 toobtain adjusted design values.Bearing lengths at supports often control the designcapacity of an I-joist. Typically minimum bearing lengthsare used to establish design parameters. In some casesadditional bearing is available and can be verified in aninstallation. Increased bearing length means that the joistcan support additional loading, up to the value limited bythe shear capacity of the web material and web joint. Bothinterior and exterior reactions must be evaluated.Use of web stiffeners may be required and typicallyincrease the bearing capacity of the joist. CorrectAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION29installation is required to obtain the specified capacities.Additional loading from walls above will load the joist inbearing, further limiting the capacity of the joist if properend detailing is not followed. Additional informationregarding design considerations for joist bearing can befound in M7.4.Adjusted design reactions (bearing capacities), R r ′,are determined in the same empirical fashion as is allowableshear.Deflection DesignWood I-joists, due to their optimized web materials,are susceptible to the effects of shear deflection. This componentof deflection can account for as much as 15% to30% of the total deflection. For this reason, both bendingand shear deflection are considered in deflection design. Atypical deflection calculation for simple span wood I-joistsunder uniform load is shown in Equation M7.2-1.Shear DesignAt end bearing locations, critical shear is the verticalshear at the ends of the design span. The practice ofneglecting all uniform loads within a distance from theend support equal to the joist depth, commonly used forother wood materials, is not applicable to end supports forwood I-joists. At locations of continuity, such as interiorsupports of multi-span I-joists, the critical shear locationfor several wood I-joist types is located a distance equalto the depth of the joist from the centerline of bearing(uniform loads only). A cantilevered portion of a woodI-joist is generally not considered a location of continuity(unless the cantilever length exceeds the joist depth) andvertical shear at the cantilever bearing is the critical shear.Individual manufacturers, or the appropriate evaluationreports, should be consulted for reference to shear designat locations of continuity.Often, the adjusted shear design values, V r ', are basedon other considerations such as bottom flange bearinglength or the installation of web stiffeners or bearingblocks.Moment DesignReference moment design values, M r ′, of prefabricatedwood I-joists are determined from empirical testing of acompletely assembled joist or by engineering analysissupplemented by tension testing the flange component.If the flange contains end jointed material, the allowabletension value is the lesser of the joint capacity or the materialcapacity.Because flanges of a wood I-joist can be highlystressed, field notching of the flanges is not allowed. Similarly,excessive nailing or the use of improper nail sizescan cause flange splitting that will also reduce capacity.The manufacturer should be contacted when evaluating adamaged flange.Deflection = Bending Component + Shear Component5wlwl∆= +384EIk4 2(M7.2-1)where:w = uniform load in pounds per lineal inch = design span, in.E I = joist moment of inertia times flangemodulus of elasticityk = shear deflection coefficientIndividual manufacturers provide equations in a similarformat. Values for use in the preceding equation can befound in the individual manufacturer’s evaluation reports.For other load and span conditions, an approximate answercan be found by using conventional bending deflectionequations adjusted as follows:⎛Deflection = Bending Deflection 1+384 EI ⎞⎜ ⎟⎝ 5l 2 k ⎠Since wood I-joists can have long spans, the modelbuilding code maximum live load deflection criteria maynot be appropriate for many floor applications. Many woodI-joist manufacturers recommend using stiffer criteria, suchas L/480 for residential floor construction and L/600 forpublic access commercial applications such as office floors.The minimum code required criteria for storage floors androof applications is normally adequate.7M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

30 M7: PREFABRICATED WOOD I-JOISTSM7.3 Adjustment of Reference Design ValuesGeneralMember design capacity is the product of referencedesign values and adjustment factors. Reference designvalues for I-joists are discussed in M7.2.The design values listed in the evaluation reports aregenerally applicable to dry use conditions. Less typicalconditions, such as high moisture, high temperatures, orpressure impregnated chemical treatments, typically resultin strength and stiffness adjustments different from thoseused for sawn lumber. NDS 7.3 outlines adjustments toreference design values for I-joists; however, individualwood I-joist manufacturers should be consulted to verifyappropriate adjustments. Table M7.3-1 shows the applicabilityof adjustment factors for prefabricated wood I-joistsin a slightly different format for the designer.The user is cautioned that manufacturers may notpermit the use of some applications and/or treatments.Unauthorized treatments can void a manufacturer’s warrantyand may result in structural deficiencies.Table M7.3-1Applicability of Adjustment Factors for Prefabricated WoodI-JoistsAllowable Stress DesignM r ′ = M r C D C M C t C L C rV r ′ = V r C D C M C tR r ′ = R r C D C M C tLoad and Resistance Factor DesignM r ′ = M r C M C t C L C r K F (0.85) λV r ′ = V r C D C M C t K F (0.75) λR r ′ = R r C M C t K F (0.75) λEI′ = EI C M C tEI′ = EI C M C tEI min ′ = EI min C M C t EI min ′ = EI min C M C t K F (0.85)K′ = K C M C t K′ = K C M C tBending Member ExampleFor fully laterally supported bending members loadedin strong axis bending and used in a normal building environment(meeting the reference conditions of NDS 2.3and 7.3), the adjusted design values reduce to:For ASD:M r ′ = M r C DV r ′ = V r C DR r ′ = R r C DE I ′ = E IK′ = KFor LRFD:M r ′ = M r K F (0.85) λV r ′ = V r K F (0.75) λR r ′ = R r K F (0.75) λEI′ = EIK′ = KLateral StabilityThe design values contained in the evaluation reportsfor prefabricated wood I-joists assume the compressionflange is supported throughout its length to prevent lateraldisplacement, and the ends at points of bearing have lateralsupport to prevent rotation (twisting). Lateral restraint isgenerally provided by diaphragm sheathing or bracingspaced at 16" on center or less (based on 1½" width joistflanges) nailed to the joist’s compression flange.Applications without continuous lateral bracing willgenerally have reduced moment design capacities. Thereduced capacity results from the increased potential forlateral buckling of the joist’s compression flange. NDS7.3.5.3 provides guidance for design of an unbraced I-joistcompression flange.Special Loads or ApplicationsWood I-joists are configured and optimized to actprimarily as joists to resist bending loads supported atthe bearing by the bottom flange. Applications that resultin significant axial tension or compression loads, requireweb holes, special connections, or other unusual conditionsshould be evaluated only with the assistance of theindividual wood I-joist manufacturers.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION31M7.4 Special Design ConsiderationsIntroductionThe wood I-joist is similar to conventional lumber inthat it is based on the same raw materials, but differs in howthe material is composed. For this reason, conventionallumber design practices are not always compatible withthe unique configuration and wood fiber orientation of thewood I-joist. Designers using wood I-joists should developsolutions in accordance with the following guidelines.Durability issues cannot be overemphasized. See M4.4for more information about durability.In addition to detailing for durability, another significantissue in the planning of wood structures is that of fireperformance, which is discussed in Chapter M16.Design SpanThe design span used for determining critical shearsand moments is defined as the clear span between thefaces of support plus one-half the minimum requiredbearing on each end (see Figure M7.4-1). For most woodI-joists, the minimum required end bearing length variesfrom 1½" to 3½" (adding 2" to the clear span dimensionis a good estimate for most applications). At locations ofcontinuity over intermediate bearings, the design span ismeasured from the centerline of the intermediate supportto the face of the bearing at the end support, plus one-halfthe minimum required bearing length. For interior spans ofa continuous joist, the design span extends from centerlineto centerline of the intermediate bearings.Figure M7.4-1Design Span Determination7M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

32 M7: PREFABRICATED WOOD I-JOISTSLoad CasesMost building codes require consideration of a criticaldistribution of loads. Due to the long length and continuousspan capabilities of the wood I-joist, these code provisionshave particular meaning. Considering a multiplespan member, the following design load cases should beconsidered:• All spans with total loads• Alternate span loading• Adjacent span loading• Partial span loading (joists with holes)• Concentrated load provisions (as occurs)A basic description of each of these load cases follows:All spans with total loads – This load case involvesplacing all live and dead design loads on all spans simultaneously.Alternate span loading – This load case places the L,L R , S, or R load portion of the design loads on every otherspan and can involve two loading patterns. The first patternresults in the removal of the live loads from all evennumbered spans. The second pattern removes live loadsfrom all odd numbered spans. For roof applications, somebuilding codes require removal of only a portion of thelive loads from odd or even numbered spans. The alternatespan load case usually generates maximum end reactions,mid-span moments, and mid-span deflections. Illustrationsof this type of loading are shown in Figure M7.4-2.Adjacent span loading – This load case (see FigureM7.4-2) removes L, L R , S or R loads from all but twoadjoining spans. All other spans, if they exist, are loadedwith dead loads only. Depending on the number of spansinvolved, this load case can lead to a number of load patterns.All combinations of adjacent spans become separateloadings. This load case is used to develop maximumshears and reactions at internal bearing locations.Partial span loading – This load case involves applyingL, L R , S or R loads to less than the full length ofa span (see Figure M7.4-2). For wood I-joists with webholes, this case is used to develop shear at hole locations.When this load case applies, uniform L, L R , S, R load isapplied only from an adjacent bearing to the opposite edgeof a rectangular hole (centerline of a circular hole). Foreach hole within a given span, there are two correspondingload cases. Live loads other than the uniform applicationload, located within the span containing the hole, are alsoapplied simultaneously. This includes all special loads suchas point or tapered loads.Concentrated load provisions – Most building codeshave a concentrated load (live load) provision in additionto standard application design loads. This load case considersthis concentrated load to act in combination withthe system dead loads on an otherwise unloaded floor orroof. Usually, this provision applies to non-residentialconstruction. An example is the “safe” load applied overa 2½ square foot area for office floors. This load casehelps insure the product being evaluated has the requiredshear and moment capacity throughout it’s entire lengthand should be considered when analyzing the effect ofweb holes.A properly designed multiple span member requiresnumerous load case evaluations. Most wood I-joist manufacturershave developed computer programs, load andspan tables, or both that take these various load cases intoconsideration.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION33Figure M7.4-2Load Case Evaluations7M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

34 M7: PREFABRICATED WOOD I-JOISTSFloor PerformanceDesigning a floor system to meet the minimum requirementsof a building code may not always provideacceptable performance to the end user. Although minimumcriteria help assure a floor system can safely supportthe imposed loads, the system ultimately must perform tothe satisfaction of the end user. Since expectancy levelsmay vary from one person to another, designing a floorsystem becomes a subjective issue requiring judgment asto the sensitivity of the intended occupant.Joist deflection is often used as the primary meansfor designing floor performance. Although deflection is afactor, there are other equally important variables that caninfluence the performance of a floor system. A glue-nailedfloor system will generally have better deflection performancethan a nailed only system. Selection of the deckingmaterial is also an important consideration. Deflection ofthe sheathing material between joists can be reduced byplacing the joists at a closer on center spacing or increasingthe sheathing thickness.Proper installation and job site storage are importantconsiderations. All building materials, including woodI-joists, need to be kept dry and protected from exposureto the elements. Proper installation includes correct spacingof sheathing joints, care in fastening of the joists andsheathing, and providing adequate and level supports. Allof these considerations are essential for proper systemperformance.Vibration may be a design consideration for floorsystems that are stiff and where very little dead load (i.e.,partition walls, ceilings, furniture, etc.) exists. Vibrationcan generally be damped with a ceiling system directlyattached to the bottom flange of the wood I-joists. Effectivebridging or continuous bottom flange nailers (i.e., 2x4nailed flat-wise and perpendicular to the joist and tied offto the end walls) can also help minimize the potential forvibration in the absence of a direct applied ceiling. Limitingthe span/depth ratio of the I-joist may also improvefloor performance.Joist BearingBearing design for wood I-joists requires more thanconsideration of perpendicular to grain bearing values.Minimum required bearing lengths take into account anumber of considerations. These include: cross grainbending and tensile forces in the flanges, web stiffenerconnection to the joist web, adhesive joint locations andstrength, and perpendicular to grain bearing stresses. Themodel building code evaluation reports provide a sourcefor bearing design information, usually in the form ofminimum required bearing lengths.Usually, published bearing lengths are based on themaximum allowable shear capacity of the particularproduct and depth or allowable reactions are related tospecific bearing lengths. Bearing lengths for wood I-joistsare most often based on empirical test results rather than acalculated approach. Each specific manufacturer should beconsulted for information when deviations from publishedcriteria are desired.To better understand the variables involved in a woodI-joist bearing, it’s convenient to visualize the member asa composition of pieces, each serving a specific task. Fora typical simple span joist, the top flange is a compressionmember, the bottom flange is a tension member, and theweb resists the vertical shear forces. Using this concept,shear forces accumulate in the web member at the bearinglocations and must be transferred through the flanges tothe support structure. This transfer involves two criticalinterfaces: between the flange and support member andbetween the web and flange materials.Starting with the support member, flange to supportbearing involves perpendicular to grain stresses. The lowestdesign value for either the support member or flangematerial is usually used to develop the minimum requiredbearing area.The second interface to be checked is between thelower joist flange and the bottom edge of the joist web,assuming a bottom flange bearing condition. This connection,usually a routed groove in the flange and a matchingshaped profile on the web, is a glued joint secured witha waterproof structural adhesive. The contact surfacesinclude the sides and bottom of the routed flange.In most cases, the adhesive line stresses at this jointcontrol the bearing length design. The effective bearinglength of the web into the flange is approximately thelength of flange bearing onto the support plus an incrementallength related to the thickness and stiffness of theflange material.Since most wood I-joists have web shear capacityin excess of the flange to web joint strength, connectionreinforcement is sometimes utilized. The most commonmethod of reinforcement is the addition of web stiffeners(also commonly referred to as bearing blocks). Webstiffeners are vertically oriented wood blocks positionedon both sides of the web. Web stiffeners should be cut sothat a gap of at least 1/8" is between the stiffener and theflange to avoid a force fit. Stiffeners are positioned tightto the bottom flange at bearing locations and snug to thebottom of the top flange beneath heavy point loads withina span. Figure M7.4-3 provides an illustration of a typicalend bearing assembly.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION35Figure M7.4-3End Bearing Web Stiffeners (Bearing Block)7Web StiffenersWhen correctly fastened to the joist web, web stiffenerstransfer some of the load from the web into the top ofthe bottom flange. This reduces the loads on the web toflange joint. A pair of web stiffeners (one on each side)is usually mechanically connected to the web with nailsor staples loaded in double shear. For some of the highercapacity wood I-joists, nailing and supplemental gluingwith a structural adhesive is required. The added bearingcapacity achievable with web stiffeners is limited by theallowable bearing stresses where the stiffeners contactthe bearing flange and by their mechanical connection tothe web.Web stiffeners also serve the implied function ofreinforcing the web against buckling. Since shear capacityusually increases proportionately with the depth, webstiffeners are very important for deep wood I-joists. Forexample, a 30" deep wood I-joist may only develop 20%to 30% of its shear and bearing capacity without properlyattached web stiffeners at the bearing locations. This isespecially important at continuous span bearing locations,where reaction magnitudes can exceed simple span reactionsby an additional 25%.Web stiffeners should be cut so that a gap of at least1/8" is between the stiffener and the top or bottom of theflange to avoid a force fit. Web stiffeners should be installedsnug to the bottom flange for bearing reinforcement or snugto the top flange if under concentrated load from above.For shallow depth joists, where relatively low shearcapacities are required, web stiffeners may not be needed.When larger reaction capacities are required, web stiffenerreinforcement may be needed, especially where shortbearing lengths are desired. Figure M7.4-4 illustrates thebearing interfaces.M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

36 M7: PREFABRICATED WOOD I-JOISTSFigure M7.4-4Web Stiffener Bearing InterfaceBeveled End CutsBeveled end cuts, where the end of the joist is cut on anangle (top flange does not project over the bearing, muchlike a fire cut), also requires special design consideration.Again the severity of the angle, web material, location ofweb section joints, and web stiffener application criteria effectthe performance of this type of bearing condition. Thespecific wood I-joist manufacturers should be consulted forlimits on this type of end cut.It is generally accepted that if a wood I-joist has theminimum required bearing length, and the top flange of thejoist is not cut beyond the face of bearing (measured froma line perpendicular to the joist’s bottom flange), there isno reduction in shear or reaction capacity. This differs fromthe conventional lumber provision that suggests there isno decrease in shear strength for beveled cuts of up to anangle of 45 o . The reason involves the composite nature ofthe wood I-joist and how the member fails in shear andor bearing. Figure M7.4-5 provides an illustration of thebeveled end cut limitation.Figure M7.4-5Beveled End CutAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION37Sloped Bearing ConditionsSloped bearing conditions require design considerationsdifferent from conventional lumber. An example isa birdsmouth bearing cut (notches in the bottom flange,see Figure M7.4-6). This type of bearing should only beused on the low end bearing for wood I-joists. Anotherexample is the use of metal joist support connectors thatattach only to the web area of the joist and do not providea bottom seat in which to bear. In general, this type ofconnector is not recommended for use with wood I-joistswithout consideration for the resulting reduced capacity.The birdsmouth cut is a good solution for the low endbearing when the slope is steep and the tangential loadsare high (loads along the axis of the joist member). Thisassumes the quality of construction is good and the cutsare made correctly and at the right locations. This type ofbearing cut requires some skill and is not easy to make,particularly with the wider flange joists. The bearing capacity,especially with high shear capacity members, maybe reduced as a result of the cut since the effective flangebearing area is reduced. The notched cut will also reducethe member’s shear and moment capacity at a cantileverlocation.An alternative to a birdsmouth cut is a beveled bearingplate matching the joist slope or special sloped seatbearing hardware manufactured by some metal connectorsuppliers. These alternatives also have special design considerationswith steep slope applications. As the memberslope increases, so does the tangential component ofreaction, sometimes requiring additional flange to bearingnailing or straps to provide resistance. Figure M7.4-6shows some examples of acceptable low end bearingconditions.Figure M7.4-6Sloped Bearing Conditions (Low End)7M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION39Figure M7.4-8Lateral Support Requirements for Joists in HangersFigure M7.4-9Top Flange Hanger SupportWhen top flange style hangers are used to support oneI-joist from another, especially the wider flange I-joists,web stiffeners need to be installed tight to the bottom sideof the support joist’s top flanges. This prevents cross grainbending and rotation of the top flange (see Figure M7.4-9).When face nail hangers are used for joist to joistconnections, nails into the support joist should extendthrough and beyond the web element (Figure M7.4-10).Filler blocks should also be attached sufficiently to providesupport for the hanger. Again, nail diameter shouldbe considered to avoid splitting the filler block material.Multiple I-joists need to be adequately connectedtogether to achieve desired performance. This requiresproper selection of a nailing or bolting pattern and attentionto web stiffener and blocking needs. Connectionsshould be made through the webs of the I-joists and neverthrough the flanges.7M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

40 M7: PREFABRICATED WOOD I-JOISTSFor a double I-joist member loaded from one sideonly, the minimum connection between members shouldbe capable of transferring at least 50% of the appliedload. Likewise, for a triple member loaded from one sideonly, the minimum connection between members mustbe capable of transferring at least 2/3 of the applied load.The actual connection design should consider the potentialslip and differential member stiffness. Many manufacturersrecommend limiting multiple members to three joists.Multiple I-joists with 3½" wide flanges may be furtherlimited to two members.The low torsional resistance of most wood I-joists isalso a design consideration for joist to joist connections.Eccentrically applied side loads, such as a top flangehanger hung from the side of a double joist, create thepotential for joist rotation. Bottom flange restrainingstraps, blocking, or directly applied ceiling systems maybe needed on heavily loaded eccentric connections toresist rotation. Figure M7.4-10 shows additional I-joistconnection considerations for use with face nail hangers.Figure M7.4-10 Connection Requirements for Face Nail HangersVertical Load TransferBearing loads originating above the joists at the bearinglocation require blocking to transfer these loads aroundthe wood I-joist to the supporting wall or foundation. Thisis typically the case in a multi-story structure where bearingwalls stack and platform framing is used. Usually, theavailable bearing capacity of the joist is needed to supportits reaction, leaving little if any excess capacity to supportadditional bearing wall loads from above.The most common type of blocking uses short piecesof wood I-joist, often referred to as blocking panels,positioned directly over the lower bearing and cut to fitin between the joists. These panels also provide lateralsupport for the joists and an easy means to transfer lateraldiaphragm shears.The ability to transfer lateral loads (due to wind, seismic,construction loads, etc.) to shear walls or foundationsbelow is important to the integrity of the building design.Compared with dimension lumber blocking, which usuallyis toe-nailed to the bearing below, wood I-joist blockingcan develop higher diaphragm transfer values because ofa wider member width and better nail values.Specialty products designed specifically for rim boardsare pre-cut in strips equal to the joist depth and providesupport for the loads from above. This solution may alsoprovide diaphragm boundary nailing for lateral loads.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION41A third method uses vertically oriented short studs,often called squash blocks or cripple blocks, on each sideof the joist and cut to a length slightly longer than the depthof the joist. This method should be used in combinationwith some type of rim joist or blocking material whenlateral stability or diaphragm transfer is required.The use of horizontally oriented sawn lumber as ablocking material is unacceptable. Wood I-joists generallydo not shrink in the vertical direction due to their paneltype web, creating the potential for a mismatch in heightas sawn lumber shrinks to achieve equilibrium. Whenconventional lumber is used in the vertical orientation,shrinkage problems are not a problem because changes inelongation due to moisture changes are minimal. FigureM7.4-11 shows a few common methods for developingvertical load transfer.Figure M7.4-11 Details for Vertical Load Transfer7Web HolesHoles cut in the web area of a wood I-joist affect themember’s shear capacity. Usually, the larger the hole, thegreater the reduction in shear capacity. For this reason,holes are generally located in areas where shear stressesare low. This explains why the largest holes are generallypermitted near mid-span of a member. The requiredspacing between holes and from the end of the member isdependent upon the specific materials and processes usedduring manufacturing.The allowable shear capacity of a wood I-joist ata hole location is influenced by a number of variables.These include: percentage of web removed, proximity toa vertical joint between web segments, the strength of theweb to flange glue joint, the stiffness of the flange, andthe shear strength of the web material. Since wood I-joistsare manufactured using different processes and materials,each manufacturer should be consulted for the proper webhole design.The methodology used to analyze application loads isimportant in the evaluation of web holes. All load casesthat will develop the highest shear at the hole locationshould be considered. Usually, for members resistingsimple uniform design loads, the loading condition thatdevelops the highest shear loads in the center area of ajoist span involves partial span loading.Web holes contribute somewhat to increased deflection.The larger the hole the larger the contribution.Provided not too many holes are involved, the contributionis negligible. In most cases, if the manufacturer’s holecriteria are followed and the number of holes is limited tothree or less per span, the additional deflection does notwarrant consideration.M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

42M7: PREFABRICATED WOOD I-JOISTSAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION43M8: STRUCTURALCOMPOSITELUMBERM8.1 General 44M8.2 Reference Design Values 45M8.3 Adjustment of ReferenceDesign Values 46M8.4 Special Design Considerations 478AMERICAN WOOD COUNCIL

44 M8: STRUCTURAL COMPOSITE LUMBERM8.1 GeneralProduct InformationStructural composite lumber (SCL) products are wellknown throughout the construction industry. The advantagesof SCL include environmental benefits from betterwood fiber utilization along with higher strength, stiffness,and consistency from fiber orientation and manufacturingprocess control.SCL is manufactured from strips or full sheets ofveneer. The process typically includes alignment of stressgraded fiber, application of adhesive, and pressing the materialtogether under heat and pressure. By redistributingnatural defects and through state of the art quality controlprocedures, the resulting material is extremely consistentand maximizes the strength and stiffness of the wood fiber.The material is typically produced in a long lengthcontinuous or fixed press in a billet form. This is thenresawn into required dimensions for use. Material is currentlyavailable in a variety of depths from 4-3/8" to 24"and thicknesses from 3/4" to 7".SCL is available in a wide range of sizes and grades.When specifying SCL products, a customer may specifyon the basis of size, stress (strength), or appearance.SCL products are proprietary and are covered by codeevaluation reports. Such reports should be consulted forcurrent design information while manufacturer’s literaturecan be consulted for design information, sizing tables, andinstallation recommendations.Common UsesSCL is widely used as a framing material for housing.SCL is made in different grades and with various processesand can be utilized in numerous applications. Proper designis required to optimize performance and economics.In addition to use in housing, SCL finds increasinguse in commercial and industrial construction. Its highstrength, stiffness, universal availability, and cost savingattributes make it a viable alternative in most low-riseconstruction projects.SCL is used as beams, headers, joists, rafters, studs,and plates in conventional construction. In addition, SCL isused to fabricate structural glued laminated beams, trusses,and prefabricated wood I-joists.AvailabilitySCL is regarded as a premium construction materialand is widely available. To efficiently specify SCL forindividual projects, the customer should be aware of thespecies and strength availability. Sizes vary with eachindividual product. The best source of this informationis your local lumber supplier, distribution center, or SCLmanufacturer. Proper design is facilitated through the useof manufacturer’s literature, code reports, and softwareavailable from SCL manufacturers.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION45M8.2 Reference Design ValuesGeneralBendingAs stated in NDS 8.2, SCL products are proprietaryand each manufacturer develops design values appropriatefor their products. These values are reviewed by themodel building codes and published in evaluation reportsand manufacturer’s literature.Reference design values are used in conjunction withthe adjustment factors in M8.3.Shear DesignSCL is typically designed and installed as a rectangularsection. Loads near supports may be reduced per NDS3.4.3.1. However, such load must be included in bearingcalculations. Shear values for SCL products often changewith member orientation.BearingSCL typically has high F c and F c⊥ properties. Withthe higher shear and bending capacities, shorter or continuousspans are often controlled by bearing. The user iscautioned to ensure the design accounts for compressionof the support material (i.e., plate) as well as the beammaterial. Often the plate material is of softer species andwill control the design.Published bending capacities of SCL beams are determinedfrom testing of production specimens. Adjustmentfor the size of the member is also determined by test.Field notching or drilling of holes is typically not allowed.Similarly, excessive nailing or the use of impropernail sizes can cause splitting that will also reduce capacity.The manufacturer should be contacted when evaluating adamaged beam.Deflection DesignDeflection calculations for SCL typically are similar toprovisions for other rectangular wood products (see M3.5).Values for use in deflection equations can be found in theindividual manufacturer’s product literature or evaluationreports. Some manufacturers might publish “true” E valueswhich would require additional calculations to account forshear deflection (see NDS Appendix F).8M8: STRUCTURAL COMPOSITE LUMBERAMERICAN WOOD COUNCIL

46 M8: STRUCTURAL COMPOSITE LUMBERM8.3 Adjustment of Reference Design ValuesMember design capacity is the product of referencedesign values, adjustment factors, and section properties.Reference design values for SCL are discussed in M8.2.Adjustment factors are provided for applicationsoutside the reference end-use conditions and for memberconfiguration effects as specified in NDS 8.3. When oneor more of the specific end use or member configurationconditions are beyond the range of the reference conditions,these adjustment factors shall be used to modify theappropriate property. Adjustment factors for the effects ofmoisture, temperature, member configuration, and size areprovided in NDS 8.3. Additional adjustment factors canbe found in the manufacturer’s product literature or codeevaluation report. Table M8.3-1 shows the applicability ofadjustment factors for SCL in a slightly different formatfor the designer.Certain products may not be suitable for use in someapplications or with certain treatments. Such conditionscan result in structural deficiencies and may void manufacturerwarranties. The manufacturer or code evaluationreport should be consulted for specific information.Table M8.3-1Applicability of Adjustment Factors for Structural CompositeLumber 1Allowable Stress DesignLoad and Resistance Factor DesignF b ′ = F b C D C M C t C L C V C rF b ′ = F b C M C t C L C V C r (2.54)(0.85) λF t ′ = F t C D C M C tF t ′ = F t C M C t (2.70)(0.80) λF v ′ = F v C D C M C tF v ′ = F v C M C t (2.88)(0.75) λF c ′ = F c C D C M C t C PF c ′ = F c C M C t C P (2.40)(0.90) λF c⊥ ′ = F c⊥ C M C t C b F c⊥ ′ = F c⊥ C M C t C b (1.67)(0.90)E′ = E C M C t E′ = E C M C tE min ′ = E min C M C t E min ′ = E min C M C t (1.76)(0.85)1. See NDS 8.3.6 for information on simultaneous application of the volume factor, C V , and the beam stability factor, C L .Bending Member ExampleFor fully laterally supported members stressed instrong axis bending and used in a normal building environment(meeting the reference conditions of NDS 2.3 and8.3), the adjusted design values reduce to:For ASD:F b ′ = F b C D C VF v ′ = F v C DF c⊥ ′ = F c⊥ C bE′ = EFor LRFD:F b ′ = F b C V (2.54)(0.85) λF v ′ = F v (2.88)(0.75) λF c⊥ ′ = F c⊥ C b (1.67)(0.90)Axially Loaded Member ExampleFor axially loaded members used in a normal buildingenvironment (meeting the reference conditions of NDS 2.3and 8.3) designed to resist tension or compression loads,the adjusted tension or compression design values reduceto:For ASD:F c ′ = F c C D C PF t ′ = F t C DE min ′ = E minFor LRFD:F c ′ = F c C P (2.40)(0.90) λF t ′ = F t (2.70)(0.80) λE min ′ = E min (1.76)(0.85)E′ = EAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION47M8.4 Special Design ConsiderationsGeneralWith proper detailing and protection, SCL can performwell in a variety of environments. One key to proper detailingis planning for the natural shrinkage and swellingof wood members as they are subjected to various dryingand wetting cycles. While moisture changes have the largestimpact on lumber dimensions, some designs must alsocheck the effects of temperature. While SCL is typicallyproduced using dry veneer, some moisture accumulationmay occur during storage. If the product varies significantlyfrom specified dimensions, the user is cautionedfrom using such product as it will “shrink” as it dries.In addition to designing to accommodate dimensionalchanges and detailing for durability, another significantissue in the planning of wood structures is that of fireperformance, which is covered in Chapter M16.Dimensional ChangesDurabilityDesigning for durability is a key part of the architecturaland engineering design of the building. Woodexposed to high levels of moisture can decay over time.While there are exceptions – such as naturally durable species,preservative-treated wood, and those locations thatcan completely air-dry between moisture cycles – prudentdesign calls for a continuing awareness of the possibility ofmoisture accumulation. Awareness of the potential for decayis the key – many design conditions can be detailed tominimize the accumulation of moisture; for other problemconditions, preservative-treated wood or naturally durablespecies should be specified.This section cannot cover the topic of designing fordurability in detail. There are many excellent texts that devoteentire chapters to the topic, and designers are advisedto use this information to assist in designing “difficult”design areas, such as:The dimensional stability and response to temperatureeffects of engineered lumber is similar to that of solid sawnlumber of the same species.Some densification of the wood fiber can occur invarious manufacturing processes. SCL that is densifiedwill result in a product that has more wood fiber in a givenvolume and can, therefore, hold more water than a solidsawn equivalent. When soaked these products expand anddimensional changes can occur.Adhesive applied during certain processes tends toform a barrier to moisture penetration. Therefore, thematerial will typically take longer to reach equilibriumthan its solid sawn counterpart.For given temperatures and applications, differentlevels of relative humidity are present. This will cause thematerial to move toward an equilibrium moisture content(EMC). Eventually all wood products will reach their EMCfor a given environment. SCL will typically equilibrate ata lower EMC (typically 3% to 4% lower) than solid sawnlumber and will take longer to reach an ambient EMC.Normal swings in humidity during the service life ofthe structure should not produce noticeable dimensionalchanges in SCL members.More information on designing for moisture and temperaturechange is included in M4.4.• structures in high moisture or humid conditions,• where wood comes in contact with concreteor masonry,• where wood members are supported in steelhangers or connectors in which condensationcould collect,• anywhere that wood is directly or indirectlyexposed to the elements,• where wood, if it should ever become wet,could not naturally dry out.This list is not intended to be all-inclusive – it ismerely an attempt to alert designers to special conditionsthat may cause problems when durability is not consideredin the design.More information on detailing for durability is includedin M4.4.8M8: STRUCTURAL COMPOSITE LUMBERAMERICAN WOOD COUNCIL

48M8: STRUCTURAL COMPOSITE LUMBERAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION49M9: WOODSTRUCTURALPANELSM9.1 General 50M9.2 Reference Design Values 50M9.3 Adjustment of ReferenceDesign Values 56M9.4 Design Considerations 579AMERICAN WOOD COUNCIL

50 M9: WOOD STRUCTURAL PANELSM9.1 GeneralProduct DescriptionWood structural panels are wood-based panel productsthat have been rated for use in structural applications. Commonapplications for wood structural panels include roofsheathing, wall sheathing, subflooring, and single-layerflooring (combination subfloor-underlayment). Structuralplywood is also manufactured in various sanded grades.Wood structural panels are classified by span ratings.Panel span ratings identify the maximum recommendedsupport spacings in inches for specific end uses. The spanrating applies when the long panel dimension or strengthaxis is across supports, unless the strength axis is otherwiseidentified. Design capacities are provided on the basis ofspan ratings.Sanded grades are classed according to grade andperformance category and design capacities are providedon that basis.Designers must specify wood structural panels by thespan ratings, performance category, grades, and constructionsassociated with tabulated design recommendations.Exposure durability classification must also be identified.Wood structural panel adhesive bond classificationrelates to moisture resistance of the glue bond, and thus tostructural integrity of the panel. Bond classification of thepanel does not relate to physical (erosion, ultraviolet, etc.)or biological (mold, fungal decay, insect, etc.) resistanceof the panel. Exposure 1 panels may be used for applicationswhere construction delays may be expected prior toproviding protection or where exposure to the outdoors ison the underside only. Exterior bond classification indicatesthe glue bond is suitable for applications subject tolong-term exposure to weather or moisture.Single-floor panels typically have tongue-and-grooveedges. If square edge panels are specified for single-floorapplications, the specification shall require lumber blockingbetween supports.Table M9.1-1 provides descriptions and typical usesfor various panel grades and types.M9.2 Reference Design ValuesGeneralWood structural panel design capacities listed in TablesM9.2-1 and M9.2-2 are minimum for grade and span rating.Multipliers shown in each table provide adjustments incapacity for Structural I panel grades. To take advantage ofthese multipliers, the specifier must insure that the correctpanel is used in construction.The tabulated capacities and adjustment factors arebased on data from tests of panels manufactured in accordancewith industry standards and which bear thetrademark of a qualified inspection and testing agency.Structural panels have a strength axis direction and across panel direction. The direction of the strength axis isdefined as the axis parallel to the orientation of OSB facestrands or plywood face veneer grain and is typically thelong dimension of the panel unless otherwise indicatedby the manufacturer. This is illustrated in Figure M9.2-1.Figure M9.2-14-ft TypicalStructural Panel withStrength DirectionAcross SupportsStrengthDirection8-ft TypicalPanel Stiffness and StrengthPanel design capacities listed in Table M9.2-1 are basedon flat panel bending (Figure M9.2-2) as measured bytesting according to principles of ASTM D3043 MethodC (large panel testing).Stiffness (EI)Panel bending stiffness is the capacity to resist deflectionand is represented as EI. E is the reference modulusof elasticity of the material, and I is the moment of inertiaAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION51of the cross section. The units of EI are lbf-in. 2 per footof panel width.Strength (F b S)Bending strength capacity is the design maximummoment, represented as F b S. F b is the reference extremefiber bending stress of the material, and S is the sectionmodulus of the cross section. The units of F b S are lbf-in.per foot of panel width.Figure M9.2-2Example of StructuralPanel in BendingTable M9.1-1Guide to Panel UsePanel Gradeand BondClassificationSheathingEXP 1Description & UseUnsanded sheathing grade for wall, roof,subflooring, and industrial applications such aspallets and for engineering design with propercapacities.CommonPerformanceCategory(in.)5/16, 3/8, 15/32,1/2, 19/32, 5/8,23/32, 3/4OSBPanel ConstructionPlywood MinimumVeneer GradeYes YesStructural ISheathingEXP 1Single FloorEXP 1UnderlaymentEXP 1 or EXTC-D-PluggedEXP 1Panel grades to use where shear and crosspanelstrength properties are of maximumimportance. Plywood Structural I is made fromall Group 1 woods.Combination subfloor-underlayment. Providessmooth surface for application of carpetand pad. Possesses high concentrated andimpact load resistance during constructionand occupancy. Touch-sanded. Available withtongue-and-groove edges.For underlayment under carpet and pad.Available with exterior glue. Touch-sanded orsanded. Panels with performance category of19/32 or greater may be available with tongueand-grooveedges.For built-ins, wall and ceiling tile backing. Notfor underlayment. Touch-sanded.3/8, 7/16, 15/32,1/2, 19/32, 5/8,23/32, 3/419/32, 5/8, 23/32,3/4, 7/8, 1, 1-3/32,1-1/81/4, 11/32, 3/8,15/32, 1/2, 19/32,5/8, 23/32, 3/41/2, 19/32,5/8, 23/32,3/4Yes YesYes YesNo Yes, faceC-Plugged, back D,inner DNo Yes, faceC-Plugged, back D,inner D9M9: WOOD STRUCTURAL PANELSSanded GradesEXP 1 or EXTMarine EXTGenerally applied where a high-quality surfaceis required. Includes APA A-A, A-C, A-D, B-B,B-C, and B-D grades.Superior Exterior-type plywood made only withDouglas-fir or western larch. Special solid-coreconstruction. Available with medium densityoverlay (MDO) or high density overlay (HDO)face. Ideal for boat hull construction.1/4, 11/32, 3/8,15/32, 1/2, 19/32,5/8, 23/32, 3/41/4, 11/32, 3/8,15/32, 1/2, 19/32,5/8, 23/32, 3/4No Yes, face B orbetter, back D orbetter, inner C & DNo Yes, face A orface B, back A orinner BAMERICAN WOOD COUNCIL

52 M9: WOOD STRUCTURAL PANELSTable M9.2-1Wood Structural Panel Bending Stiffness and StrengthCapacitiesSpanRatingStress Parallel to Strength Axis 1 Stress Perpendicular to Strength Axis 1PlywoodPlywood3-ply 4-ply 5-ply OSB 3-ply 4-ply 5-ply OSBPANEL BENDING STIFFNESS, EI (lbf-in. 2 /ft of panel width)24/0 66,000 66,000 66,000 60,000 3,600 7,900 11,000 11,00024/16 86,000 86,000 86,000 78,000 5,200 11,500 16,000 16,00032/16 125,000 125,000 125,000 115,000 8,100 18,000 25,000 25,00040/20 250,000 250,000 250,000 225,000 18,000 39,500 56,000 56,00048/24 NA 440,000 440,000 400,000 NA 65,000 91,500 91,50016oc 165,000 165,000 165,000 150,000 11,000 24,000 34,000 34,00020oc 230,000 230,000 230,000 210,000 13,000 28,500 40,500 40,50024oc NA 330,000 330,000 300,000 NA 57,000 80,500 80,50032oc NA NA 715,000 650,000 NA NA 235,000 235,00048oc NA NA 1,265,000 1,150,000 NA NA 495,000 495,000Multiplier forStructural I Panels 1.0 1.0 1.0 1.0 1.5 1.5 1.6 1.6PANEL BENDING STRENGTH, F b S (lbf-in./ft of panel width)24/0 250 275 300 300 54 65 97 9724/16 320 350 385 385 64 77 115 11532/16 370 405 445 445 92 110 165 16540/20 625 690 750 750 150 180 270 27048/24 NA 930 1,000 1,000 NA 270 405 40516oc 415 455 500 500 100 120 180 18020oc 480 530 575 575 140 170 250 25024oc NA 705 770 770 NA 260 385 38532oc NA NA 1,050 1,050 NA NA 685 68548oc NA NA 1,900 1,900 NA NA 1,200 1,200Multiplier forStructural I Panels 1.0 1.0 1.0 1.0 1.3 1.4 1.5 1.51. Strength axis is defined as the axis parallel to the face and back orientation of the flakes or the grain (veneer), which is generally the long panel direction, unlessotherwise marked.NA - Not applicable. Atypical panel construction.Axial CapacitiesAxial Stiffness (EA)Panel axial stiffnesses listed in Table M9.2-2 are basedon testing according to the principles of ASTM D3501Method B. Axial stiffness is the capacity to resist axialstrain and is represented as EA. E is the reference axialmodulus of elasticity of the material, and A is the area ofthe cross section. The units of EA are pounds force perfoot of panel width.Tension (F t A)Tension capacities listed in Table M9.2-2 are basedon testing according to the principles of ASTM D3500Method B. Tension capacity is given as F t A. F t is the referenceaxial tensile stress of the material, and A is the areaof the cross section. The units of F t A are pounds force perfoot of panel width.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION53Table M9.2-2Wood Structural Panel Axial Stiffness, Tension, andCompression CapacitiesSpanRatingStress Parallel to Strength Axis 1 Stress Perpendicular to Strength Axis 1PlywoodPlywood3-ply 4-ply 5-ply OSB 3-ply 4-ply 5-ply OSBPANEL TENSION, F t A (lbf/ft of panel width)24/0 2,300 2,300 3,000 2,300 600 600 780 78024/16 2,600 2,600 3,400 2,600 990 990 1,300 1,30032/16 2,800 2,800 3,650 2,800 1,250 1,250 1,650 1,65040/20 2,900 2,900 3,750 2,900 1,600 1,600 2,100 2,10048/24 NA 4,000 5,200 4,000 NA 1,950 2,550 2,55016oc 2,600 2,600 3,400 2,600 1,450 1,450 1,900 1,90020oc 2,900 2,900 3,750 2,900 1,600 1,600 2,100 2,10024oc NA 3,350 4,350 3,350 NA 1,950 2,550 2,55032oc NA NA 5,200 4,000 NA NA 3,250 3,25048oc NA NA 7,300 5,600 NA NA 4,750 4,750Multiplier forStructural I Panels 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0PANEL COMPRESSION, F c A (lbf/ft of panel width)24/0 2,850 4,300 4,300 2,850 2,500 3,750 3,750 2,50024/16 3,250 4,900 4,900 3,250 2,500 3,750 3,750 2,50032/16 3,550 5,350 5,350 3,550 3,100 4,650 4,650 3,10040/20 4,200 6,300 6,300 4,200 4,000 6,000 6,000 4,00048/24 NA 7,500 7,500 5,000 NA 7,200 7,200 4,30016oc 4,000 6,000 6,000 4,000 3,600 5,400 5,400 3,60020oc 4,200 6,300 6,300 4,200 4,000 6,000 6,000 4,00024oc NA 7,500 7,500 5,000 NA 7,200 7,200 4,30032oc NA NA 9,450 6,300 NA NA 9,300 6,20048oc NA NA 12,150 8,100 NA NA 10,800 6,750Multiplier forStructural I Panels 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0PANEL AXIAL STIFFNESS, EA (lbf/ft of panel width)24/0 3,350,000 3,350,000 3,350,000 3,350,000 2,900,000 2,900,000 2,900,000 2,500,000 224/16 3,800,000 3,800,000 3,800,000 3,800,000 2,900,000 2,900,000 2,900,000 2,700,000 232/16 4,150,000 4,150,000 4,150,000 4,150,000 3,600,000 3,600,000 3,600,000 2,700,00040/20 5,000,000 5,000,000 5,000,000 5,000,000 4,500,000 4,500,000 4,500,000 2,900,000 348/24 NA 5,850,000 5,850,000 5,850,000 NA 5,000,000 5,000,000 3,300,000 316oc 4,500,000 4,500,000 4,500,000 4,500,000 4,200,000 4,200,000 4,200,000 2,700,00020oc 5,000,000 5,000,000 5,000,000 5,000,000 4,500,000 4,500,000 4,500,000 2,900,000 324oc NA 5,850,000 5,850,000 5,850,000 NA 5,000,000 5,000,000 3,300,000 332oc NA NA 7,500,000 7,500,000 NA NA 7,300,000 4,200,00048oc NA NA 8,200,000 8,200,000 NA NA 7,300,000 4,600,0009M9: WOOD STRUCTURAL PANELSMultiplier forStructural I Panels 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.01. Strength axis is defined as the axis parallel to the face and back orientation of the flakes or the grain (veneer), which is generally the long panel direction, unlessotherwise marked.2. The values shall be permitted to be increased to 2,900,000 lbf/ft for the calculation of the bending stiffness (EI joist ) of prefabricated wood I-joists.3. The values shall be permitted to be increased to 4,500,000 lbf/ft for the calculation of the composite floor bending stiffness (EI composite ) of prefabricated woodI-joists.NA - Not applicable. Atypical panel construction.AMERICAN WOOD COUNCIL

54 M9: WOOD STRUCTURAL PANELSCompression (F c A)Compression (Figure M9.2-3) capacities listed inTable M9.2-2 are based on testing according to the principlesof ASTM D3501 Method B. Compression capacityis given as F c A. F c is the reference axial compression stressof the material, and A is the area of the cross section. Theunits of F c A are pounds force per foot of panel width.Shear CapacitiesFigure M9.2-3Structural Panel withAxial CompressionLoad in the Plane ofthe PanelShear-in-the-Plane of the Panel (F s [Ib/Q])Shear-in-the-plane of the panel (innerlaminer or rollingshear) capacities listed in Table M9.2-3 are based ontesting according to the principles of ASTM D2718. Shearstrength in the plane of the panel is the capacity to resisthorizontal shear breaking loads when loads are applied ordeveloped on opposite faces of the panel (Figure M9.2-4),as in flat panel bending. Planar shear capacity is given asF s [Ib/Q]. F s is the reference material innerlaminar shearstress, and Ib/Q is the panel cross-sectional shear constant.The units of F s [Ib/Q] are pounds force per foot of panelwidth.Panel Rigidity Through-the-Thickness (G v t v )Panel rigidities listed in Table M9.2-4 are based ontesting according to the principles of ASTM D2719. Panelrigidity is the capacity to resist deformation under shearthrough the thickness stress (Figure M9.2-5). Rigidity isgiven as G v t v . G v is the reference modulus of rigidity, andt v is the effective panel thickness for shear. The units ofG v t v are pounds force per inch of panel depth (for verticalapplications). Multiplication of G v t v by panel depth givesGA, used by designers for some applications.Panel Shear Through-the-Thickness (F v t v )Through-the-thickness shear capacities listed in TableM9.2-4 are based on testing according to the principles ofASTM D2719. Allowable shear through-the-thickness isthe capacity to resist horizontal shear breaking loads whenloads are applied or developed on opposite edges of thepanel (Figure M9.2-5), such as in an I-joist web. Whereadditional support is not provided to prevent buckling,design capacities in Table M9.2-4 are limited to sections 2ft or less in depth. Deeper sections may require additionalreductions. F v is the reference shear through-the-thicknessstress of the material, and t v is the effective panel thicknessfor shear. The units of F v t v are pounds force per inch ofshear resisting panel length.Figure M9.2-4Shear-in-the-Planefor Wood StructuralPanelsPlanar (Rolling) ShearShear AreaFigure M9.2-5 Through-the-ThicknessShear for WoodStructural PanelsAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION55Table M9.2-3Wood Structural Panel Shear-in-the-Plane CapacitiesStress Parallel to Strength AxisSpan Plywood PlywoodStress Perpendicular to Strength AxisRating 3-ply 4-ply 5-ply OSB 3-ply 4-ply 5-ply OSBPANEL SHEAR-IN-THE-PLANE, F s (Ibf/Q) (lbf/ft of panel width)24/0 155 155 170 130 275 375 130 13024/16 180 180 195 150 315 435 150 15032/16 200 200 215 165 345 480 165 16540/20 245 245 265 205 430 595 205 20548/24 NA 300 325 250 NA 725 250 25016oc 245 245 265 205 430 595 205 20520oc 245 245 265 205 430 595 205 20524oc NA 300 325 250 NA 725 250 25032oc NA NA 390 300 NA NA 300 30048oc NA NA 500 385 NA NA 385 385Multiplier forStructural I Panels 1.4 1.4 1.4 1.0 1.4 1.4 1.0 1.0NA - Not applicable. Atypical panel constructionTable M9.2-4Wood Structural Panel Rigidity and Shear Through-the-Thickness CapacitiesStress Parallel to Strength AxisStress Perpendicular to Strength AxisSpanPlywoodPlywoodRating3-ply 4-ply 5-ply 1 OSB 3-ply 4-ply 5-ply 1 OSBPANEL RIGIDITY THROUGH-THE-THICKNESS, G v t v (lbf/in. of panel depth)24/0 25,000 32,500 37,500 77,500 25,000 32,500 37,500 77,50024/16 27,000 35,000 40,500 83,500 27,000 35,000 40,500 83,50032/16 27,000 35,000 40,500 83,500 27,000 35,000 40,500 83,50040/20 28,500 37,000 43,000 88,500 28,500 37,000 43,000 88,50048/24 NA 40,500 46,500 96,000 NA 40,500 46,500 96,00016oc 27,000 35,000 40,500 83,500 27,000 35,000 40,500 83,50020oc 28,000 36,500 42,000 87,000 28,000 36,500 42,000 87,00024oc NA 39,000 45,000 93,000 NA 39,000 45,000 93,00032oc NA NA 54,000 110,000 NA NA 54,000 110,00048oc NA NA 76,000 155,000 NA NA 76,000 155,000Multiplier forStructural I Panels 1.3 1.3 1.1 1.0 1.3 1.3 1.1 1.0PANEL SHEAR THROUGH-THE-THICKNESS, F v t v (lbf/in. of shear-resisting panel length)24/0 53 69 80 155 53 69 80 15524/16 57 74 86 165 57 74 86 16532/16 62 81 93 180 62 81 93 18040/20 68 88 100 195 68 88 100 19548/24 NA 98 115 220 NA 98 115 22016oc 58 75 87 170 58 75 87 17020oc 67 87 100 195 67 87 100 19524oc NA 96 110 215 NA 96 110 21532oc NA NA 120 230 NA NA 120 23048oc NA NA 160 305 NA NA 160 305Multiplier forStructural I Panels 1.3 1.3 1.1 1.0 1.3 1.3 1.1 1.09M9: WOOD STRUCTURAL PANELS1. 5-ply applies to plywood with five or more layers. For 5-ply plywood with three layers, use G n t n values for 4-ply panels.NA - Not applicable. Atypical panel construction.AMERICAN WOOD COUNCIL

56 M9: WOOD STRUCTURAL PANELSM9.3 Adjustment of Reference Design ValuesGeneralAdjusted panel design capacities are determined bymultiplying reference capacities, as given in Tables M9.2-1 through M9.2-4, by the adjustment factors in NDS 9.3.Some adjustment factors should be obtained from themanufacturer or other approved source. In the NDS Commentary,C9.3 provides additional information on typicaladjustment factors.Tabulated capacities provided in this Chapter aresuitable for reference end-use conditions. Referenceend-use conditions are consistent with conditions typicallyassociated with light-frame construction. For woodstructural panels, these typical conditions involve the useof full-sized untreated panels in moderate temperature andmoisture exposures.Appropriate adjustment factors are provided for applicationsin which the conditions of use are inconsistentwith reference conditions. In addition to temperature andmoisture, this includes consideration of panel treatmentand size effects.NDS Table 9.3.1 lists applicability of adjustment factorsfor wood structural panels. Table M9.3-1 shows theapplicability of adjustment factors for wood structuralpanels in a slightly different format for the designer.Table M9.3-1Applicability of Adjustment Factors for Wood Structural PanelsAllowable Stress DesignLoad and Resistance Factor DesignF b S′ = F b S C D C M C t C sF b S′ = F b S C M C t C s (2.54)(0.85) λF t A′ = F t A C D C M C t C sF t A′ = F t A C M C t C s (2.70)(0.80) λF v t v ′ = F v t v C D C M C tF v t v ′ = F v t v C M C t (2.88)(0.75) λF s (Ib/Q)′ = F s (Ib/Q) C D C M C tF s (Ib/Q)′ = F s (Ib/Q) C M C t (2.88)(0.75) λF c A′ = F c A C D C M C tF c A′ = F c A C M C t (2.40)(0.90) λF c⊥ ′ = F c⊥ C M C t F c⊥ ′ = F c⊥ C M C t (1.67)(0.90)EI′ = EI C M C tEA′ = EA C M C tG v t v ′ = G v t v C M C tBending Member ExampleFor non-Structural I grade wood structural panels,greater than 24" in width, loaded in bending, and usedin a normal building environment (meeting the referenceconditions of NDS 2.3 and 9.3), the adjusted design valuesreduce to:For ASD:F b S′ = F b S C DEI′ = EIFor LRFD:F b S′ = F b S (2.54)(0.85) λEI′ = EIEI′ = EI C M C tEA′ = EA C M C tG v t v ′ = G v t v C M C tAxially Loaded Member ExampleFor non-Structural I grade wood structural panels,greater than 24" in width, axially loaded, and used in anormal building environment (meeting the reference conditionsof NDS 2.3 and 4.3) designed to resist tension orcompression loads, the adjusted tension or compressiondesign values reduce to:For ASD:F c A′ = F c A C DF t A′ = F t A C DEA′ = EAFor LRFD:F c A′ = F c A (2.40)(0.90) λF t A′ = F t A (2.70)(0.80) λEA′ = EAAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION57Preservative TreatmentCapacities given in Tables M9.2-1 through M9.2-4apply, without adjustment, to plywood pressure-impregnatedwith preservatives and redried in accordance withAmerican Wood Protection Association (AWPA) StandardU1. OSB panels are currently recommended only for nonpressureapplications of preservative treating in accordancewith AWPA Standard T1.Fire Retardant TreatmentThe information provided in this Chapter does notapply to fire retardant treated panels. All capacities andend-use conditions for fire retardant treated panels shall bein accordance with the recommendations of the companyproviding the treating and redrying service.M9.4 Design ConsiderationsPanel Edge SupportPanel SpacingFor certain span ratings, the maximum recommendedroof span for sheathing panels is dependent upon panel edgesupport. Edge support may be provided by lumber blocking,tongue and groove, or panel clips when edge support is required.Table M9.4-1 summarizes the relationship betweenpanel edge support and maximum recommended spans.Table M9.4-1 Panel Edge Support 2SheathingSpan RatingMaximum Recommended Span (in.)WithEdge SupportWithoutEdge Support24/0 24 19.2 124/16 24 2432/16 32 2840/20 40 3248/24 48 361. 20 in. for 3/8 and 7/16 performance category panels, 24 in. for 15/32 and1/2 performance category panels.2. Additional edge support is recommended when panel widths are lessthan 24 inches. Edge support requirements should be obtained from themanufacturer.Long-Term LoadingWood structural panels under constant load will creep(deflection will increase) over time. Where total deflectionunder long-term loading must be limited, provisionsof NDS 3.5.2 are applicable. For wood structural panelsin dry-service conditions, the immediate deflection due tolong term loading is increased by a factor of 2.0 to accountfor deformation under long-term loading. For long-termloading under high moisture and/or high temperature,appropriate adjustments should be obtained from themanufacturer or an approved source.Wood-based panel products expand and contractslightly as a natural response to changes in panel moisturecontent. To provide for in-plane dimensional changes,panels should be installed with a 1/8" spacing at all panelend and edge joints at the time of installation. A standard10d box nail may be used to check panel edge and panelend spacing.Minimum NailingMinimum nailing for wood structural panel applicationsis shown in Table M9.4-2.9M9: WOOD STRUCTURAL PANELSAMERICAN WOOD COUNCIL

58 M9: WOOD STRUCTURAL PANELSTable M9.4-2 Minimum Nailing for Wood Structural Panel ApplicationsNail Spacing (in.)RecommendedPanel IntermediateApplication Nail Size & TypeEdges SupportsSingle Floor–Glue-nailed installation 5Ring- or screw-shank16, 20, 24 oc, 3/4 performance category or less 6d 1 6 1224 oc, 7/8 or 1 performance category 8d 1 6 1232, 48 oc, (32-in. span (c-c) application) 8d 1 6 1248 oc, (48-in. span (c-c) application) 8d 2 6 6Single Floor–Nailed-only installationRing- or screw-shank16, 20, 24 oc, 3/4 performance category or less 6d 6 1224 oc, 7/8 or 1 performance category 8d 6 1232, 48 oc, (32-in. span application) 8d 6 1248 oc, (48-in. span application) 8d 2 6 6Sheathing–Subflooring 3Common smooth, ring- or screw-shank7/16 to 1/2 thick performance category 6d 6 127/8 performance category or less 8d 6 12Thicker panels 10d 6 6Sheathing–Wall sheathing Common smooth, ring- or screw-shank or galvanized box 37/16 performance category or less 6d 6 12Over 7/16 performance category 8d 6 12Sheathing–Roof sheathing Common smooth, ring- or screw-shank 35/16 to 1 performance category 8d 6 12 4Thicker panels 8d ring- or screw-shank 6 12 4or 10d common smooth1. 8d common nails may be substituted if ring- or screw-shank nails are not available.2. 10d ring-shank, screw-shank, or common nails may be substituted if supports are dry in accordance with NDS.3. Other code-approved fasteners may be used.4. For spans 48 in. or greater, space nails 6 in. at all supports.5. Use only adhesives conforming to ASTM D3498.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION59M10:MECHANICALCONNECTIONSM10.1 General 60M10.2 Reference Design Values 61M10.3 Adjustment of Reference DesignValues 61M10.4 Typical Connection Details 62M10.5 Pre-Engineered Metal Connectors 7010AMERICAN WOOD COUNCIL

60 M10: MECHANICAL CONNECTIONSM10.1 GeneralThis Chapter covers design of connections betweenwood members using metal fasteners. Several commonconnection types are outlined below.Dowel-Type (Nails, Bolts, Screws,Pins)These connectors rely on metal-to-wood bearing fortransfer of lateral loads and on friction or mechanicalinterfaces for transfer of axial (withdrawal) loads. Theyare commonly available in a wide range of diameters andlengths. More information is provided in Chapter M11.Split Rings and Shear PlatesThese connectors rely on their geometry to providelarger metal-to-wood bearing areas per connector. Bothare installed into precut grooves or daps in the members.More information is provided in Chapter M12.Timber RivetsTimber rivets are a dowel-type connection, however,because the ultimate load capacity of such connectionsare limited by rivet bending and localized crushing ofwood at the rivets or by the tension or shear strength ofthe wood at the perimeter of the rivet group, a specificdesign procedure is required. Timber rivet design loadsare based on the lower of the maximum rivet bending loadand the maximum load based on wood strength. ChapterM13 contains more information on timber rivet design.designed, metal connector manufacturers have severalcategories 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 M10.4 formore information regarding design.Connections are designed so that no applicable capacityis exceeded under loads. Strength criteria includelateral or withdrawal capacity of the connection, andtension or shear in the metal components. Some types ofconnections also include compression perpendicular tograin as a design criteria.Users should note that design of connections may alsobe controlled by serviceability limitations. These limitationsare product specific and are discussed in specificproduct chapters.Stresses in Members atConnectionsLocal stresses in connections using multiple fastenerscan be evaluated in accordance with NDS Appendix E.Structural Framing ConnectionsStructural 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 and are discussedin more detail in M10.4.Other ConnectorsJust as the number of possible building geometriesis limitless, so too is the number of possible connectiongeometries. In addition to providing custom fabricationof connectors to meet virtually any geometry that can beAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION61M10.2 Reference Design ValuesReference design values for mechanical connectionsare provided in various sources. The NDS contains referencedesign values for dowel-type connections such asnails, bolts, lag screws, wood screws, split rings, shearplates, drift bolts, drift pins, and timber rivets.Pre-engineered metal connectors are proprietary andreference design values are provided in code evaluation reports.More information on their use is provided in M10.5.Metal connector plates are proprietary connectors fortrusses, and reference design values are provided in codeevaluation reports.Staples and many power-driven fasteners are proprietary,and reference design values are provided in codeevaluation reports.M10.3 Adjustment of Reference Design ValuesTo generate connection design capacities, referencedesign values for connections are multiplied by adjustmentfactors per NDS 10.3. Applicable adjustment factorsfor connections are defined in NDS Table 10.3.1. TableM10.3-1 shows the applicability of adjustment factors forconnections in a slightly different format for the designer.Table M10.3-1 Applicability of Adjustment Factors for Mechanical Connections 1Allowable Stress Design Load and Resistance Factor DesignLateral LoadsDowel-Type Fasteners Z′ = Z C D C M C t C g C ∆ C eg C di C tn Z′ = Z C M C t C g C ∆ C eg C di C tn (3.32)(0.65) λSplit Ring and Shear P′ = P C D C M C t C g C ∆ C d C st P′ = P C M C t C g C ∆ C d C st (3.32)(0.65) λPlate ConnectorsQ′ = Q C D C M C t C g C ∆ C d Q′ = Q C M C t C g C ∆ C d (3.32)(0.65) λTimber RivetsP′ = P C D C M C t C st P′ = P C M C t C st (3.32)(0.65) λQ′ = Q C D C M C t C ∆ C st Q′ = Q C M C t C ∆ C st (3.32)(0.65) λSpike Grids Z′ = Z C D C M C t C ∆ Z′ = Z C M C t C ∆ (3.32)(0.65) λWithdrawal LoadsNails, Spikes, Lag Screws,Wood Screws, and Drift PinsW′ = W C D C M C t C eg C tn Z′ = Z C M C t C eg C tn (3.32)(0.65) λ1. See NDS Table 10.3.1 footnotes for additional guidance on application of adjustment factors for mechanical connections.The following connection product chapters containexamples of the application of adjustment factors to referencedesign values:Chapter M11 – dowel-type fasteners,Chapter M12 – split ring and shear plate connectors,Chapter M13 – timber rivets.10M10: MECHANICAL CONNECTIONSAMERICAN WOOD COUNCIL

62 M10: MECHANICAL CONNECTIONSM10.4 Typical Connection DetailsGeneral 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 regionsthat might collect moisture – providing adequateclearance for air movement to keep the wood dry. Finally,well-designed connections minimize the potential for tensionperpendicular to grain stresses – either under designconditions or under unusual loading conditions.The following connection details (courtesy of theCanadian Wood Council) are organized into nine groups: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 to support8. Moment splice9. Problem connections1. Beam on shelf in wall. The bearing plate distributesthe load and keeps the beam from direct contact with theconcrete. Steel angles provide uplift resistance and canalso provide some lateral resistance. The end of the beamshould not be in direct contact with the concrete.2. Similar to detail 1 with a steel bearing plate only underthe beam.Many of the detail groups begin with a brief discussionof the design challenges pertinent to the 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 never permits wood to be indirect contact 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.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION63Group 2. Beam to Column ConnectionsDesign concepts. All connections in the group musthold the beam in place on top of the column. Shear transferis reasonably easy to achieve. Some connections must alsoresist some beam uplift. Finally, for cases in which thebeam is spliced, rather than continuous over the column,transfer of forces across the splice may be required.6. Custom welded column caps can be designed to transfershear, uplift, and splice forces. Note design variations toprovide sufficient bearing area for each of the beams anddiffering plate widths to accommodate differences betweenthe column and the beam widths.4. Simple steel dowel for shear transfer.7. Combinations of steel angles and straps, bolted andscrewed, to transfer forces.5. Concealed connection in which a steel plate is insertedinto a kerf in both the beam and the column. Transversepins or bolts complete the connection.108. A very common connection – beam seat welded to thetop of a steel column.M10: MECHANICAL CONNECTIONSAMERICAN WOOD COUNCIL

64 M10: MECHANICAL CONNECTIONS9. 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 detail thecolumn continuity is maintained. Optional shear plates maybe used to transfer higher loads. Note that, unless the boltheads are completely recessed into the back of the bracket,the beam end will likely require slotting. In a building withmany bays, it may be difficult to maintain dimensions inthe beam direction when using this connection.11A. Similar to details 1 and 2.11B. Alternate to detail 11A.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 and also provideroom to grip and tighten with a wrench. Especially forsloped members, special attention is required to visualizethe stresses induced as the members deflect under load –some connections will induce large perpendicular to grainstresses in this mode.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION6513. Bucket-style welded bracket at a “cross” junction. Thetop of the support beam is sometimes dapped to accommodatethe thickness of the steel.suspended beam, permitting plugging of the holes after thepin is installed. Note that the kerf in the suspended beammust accommodate not only the width of the steel plate,but also the increased width at the fillet welds.14. Face-mounted hangers are commonly used in beam tobeam connections. In a “cross” junction special attentionis required to fastener penetration length into the carryingbeam (to avoid interference from other side).17. Similar to detail 13, with somewhat lower loadcapacity.18. Clip angle to connect crossing beam.15. 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 restrain adeep beam from its natural across-the-grain shrinking andswelling cycles and would lead to splits.19. Special detail to connect the ridge purlin to slopedmembers or to the peak of arch members.10M10: MECHANICAL CONNECTIONS16. Concealed connections similar to detail 5. The suspendedbeam may be dapped on the bottom for a flushconnection. The pin may be slightly narrower than theAMERICAN WOOD COUNCIL

66 M10: MECHANICAL CONNECTIONS20A. Similar to detail 19, but with the segments of theridge purlin set flush with the other framing.23. Similar to detail 22, with added shear plate.20B. Alternate to detail 20A.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 toresist this thrust or tie rods may be used. The base detailshould be designed to accommodate the amount of rotationanticipated in the arch base under various loadingconditions. Elastomeric bearing pads can assist somewhatin distributing stresses. As noted earlier, the connectionshould be designed to minimize any perpendicular to grainstresses during 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

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION6726. 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 not introducecross-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 moment armbetween steel straps is less than in detail 29.1028. For very long spans or other cases where large rotationsmust be accommodated, a true hinge connectionmay be 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.M10: MECHANICAL CONNECTIONSAMERICAN WOOD COUNCIL

68 M10: MECHANICAL CONNECTIONS31A. 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 32A, smaller plates willtransmit forces, but they do not restrain the wood from itsnatural movements.31B. Alternate to detail 31A.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.33A. Notching a beam at its bearing may cause splits.THIS DETAIL 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.32A. Full-depth side plates may appear to be a good connectionoption. Unfortunately, the side plates will remainfastened while the wood shrinks over the first heatingseason. Since it is restrained by the side plates, the beammay split. THIS DETAIL IS NOT RECOMMENDED!33B. Alternate to detail 33A.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION6934A. This sloped bearing with a beam that is not fullysupported may also split under load. THIS DETAIL ISNOT RECOMMENDED!35B. As an alternative to detail 35A, the plates may beextended and the connection made to the upper half ofthe beam.34B. Alternate to detail 34A.Hanger to side of beam. See full-depth side platesdiscussion.36A. Deep beam hangers that have fasteners installedin the side plates toward the top of the supported beammay promote splits at the fastener group should the woodmember shrink and lift from the bottom of the beam hangerbecause of the support provided by the fastener group.THIS DETAIL IS NOT RECOMMENDED!Hanging 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.35A. Connecting a hanger to the lower half of a beam thatpulls downward may cause splits. THIS DETAIL IS NOTRECOMMENDED!36B. Alternate to detail 36A.10M10: MECHANICAL CONNECTIONSAMERICAN WOOD COUNCIL

70 M10: MECHANICAL CONNECTIONSM10.5 Pre-Engineered Metal ConnectorsProduct InformationPre-engineered metal connectors for wood constructionare commonly used in all types of wood construction.There are numerous reasons for their widespread use.Connectors often make wood members easier and fasterto install. They increase the safety of wood construction,not only from normal loads, but also from natural disasterssuch as earthquakes and high winds. Connectors makewood structures easier to design by providing simpler connectionsof known load capacity. They also allow for theuse of more cost-effective engineered wood members byproviding the higher capacity connections often requiredby the use of such members. In certain locations, modelbuilding codes specifically require connectors or hangers.Metal connectors are usually manufactured by stampingsheets or strips of steel, although some heavy hangersare welded together. Different thicknesses and grades ofsteel are used, depending on the required capacity of theconnector.Some metal connectors are produced as proprietaryproducts which are covered by evaluation reports. Suchreports should be consulted for current design information,while the manufacturer’s literature can be consultedfor additional design information and detailed installationinstructions.Common UsesPre-engineered metal connectors for wood constructionare used throughout the world. Connectors are usedto resist vertical dead, live, and snow loads; uplift loadsfrom wind; and lateral loads from ground motion or wind.Almost any type of wood member may be fastened toanother using a connector. Connectors may also be usedto fasten wood to other materials, such as concrete, masonry,or steel.AvailabilityConnectors are manufactured in varying load capacities,sizes, and configurations to fit a wide range ofapplications. A variety of connectors are widely availablethrough lumber suppliers.Because of the wide variety of available connectors,a generic design document such as this must be limited inits scope for simplicity’s sake. Design values for specificconnectors are available from the connector manufacturer.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION71Types of ConnectorsThere are many different types of connectors, due tothe many different applications in which connectors maybe used. The following sections list the most commontypes of connectors.Face Mount Joist HangersFace mount joist hangers install on the face of thesupporting member, and rely on the shear capacity of thenails to provide holding power. Although referred to as joisthangers, these connectors may support other horizontalmembers subject to vertical loads, such as beams or purlins.Top Flange Joist HangersTop flange joist, beam, and purlin hangers rely onbearing of the top flange onto the top of the supportingmember, along with the shear capacity of any fastenersthat are present in the face. Although referred to as joisthangers, these connectors may support other horizontalmembers subject to vertical loads, such as beams or purlins.Bent-style Joist, Beam,and Purlin Hanger*Top FlangeI-joist Hanger*Face MountJoist HangerHeavy Face MountJoist Hanger10S tr ong- TieSIMPSONWelded-type Purlin, Heavy Welded BeamBeam, and Joist Hanger* Hanger (Saddle Type)Slope- and Skew-Face MountAdjustable Joist Hanger I-Joist Hanger** Joists shall be provided with lateral support at points of bearing to prevent rotation. Sometimes this restraint can be provided by the hangers.M10: MECHANICAL CONNECTIONSAMERICAN WOOD COUNCIL

@72 M10: MECHANICAL CONNECTIONSAdjustable Style HangerAdjustable style joist and truss hangers have strapswhich can be either fastened to the face of a supportingmember, similar to a face mount hanger, or wrapped overthe top of a supporting member, similar to a top flangehanger.Seismic and Hurricane TiesSeismic and hurricane ties are typically used to connecttwo members that are oriented 90º from each other. Theseties resist forces through the shear capacity of the nails inthe members. These connectors may provide resistance inthree dimensions.Adjustable Style Truss HangersSeismic and Hurricane TiesConnecting Roof Framing to Top PlatesFlat StrapsFlat straps rely on the shear capacity of the nails in thewood members to transfer load.Hold Downs and Tension TiesHold downs and tension ties usually bolt to concreteor masonry, and connect wood members to the concreteor masonry through the shear resistance of either nails,screws, or bolts. They may also be used to connect twowood members together.Strap Used toTransfer Uplift ForcesStrap Used toTransfer Lateral ForcesHold DownTension TieAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION73Embedded Type AnchorsEmbedded anchors connect a wood member to concreteor masonry. One end of the connector embeds in theconcrete or masonry, and the other end connects to thewood through the shear resistance of the nails or bolts.• type of fasteners to be used• corrosion resistance desired• appearance desiredOnce the listed information is known, proper selectionis facilitated through the use of manufacturer’s literature,code evaluation reports, and software available from connectormanufacturers.This Manual provides guidance for specifying preengineeredmetal connectors to satisfy specific designcriteria for a given application.Embedded Truss AnchorEmbedded NailedHold Down StrapConnection DetailsConnections, including pre-engineered metal connections,must provide the structural strength necessaryto transfer loads. Well-designed connections hold woodmembers in such a manner that shrinkage/swelling cyclesdo not induce splitting across the grain. Well-designed connectionsalso minimize collection of moisture – providingadequate clearance 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.Section M10.4 contains general concepts of well-designedconnections, including over 40 details showing acceptableand unacceptable practice.Product SelectionPurlin AnchorProper choice of connectors is required to optimizeperformance and economics. The selection of a connectorwill depend on several variables. These include thefollowing:Other ConsiderationsWith proper selection and installation, structural connectorswill perform as they were designed. However, properselection and installation involves a variety of items thatboth the designer and the installer must consider includingthe general topics of: the wood members being connected;the fasteners used; and the connectors themselves. Theseitems are discussed in the following sections. This Manualdoes not purport to address these topics in an all-inclusivemanner – it is merely an attempt to alert designers to theimportance of selection and installation details for achievingthe published capacity of the connector.Wood MembersThe wood members being connected have an impacton the capacity of the connection. The following are importantitems regarding the wood members themselves:10M10: MECHANICAL CONNECTIONS• capacity required• size and type of members being connected• species of wood being connected• slope and/or skew of member• connector type preference• The species of wood must be the same as that for whichthe connector was rated by the manufacturer. Manufacturerstest and publish allowable design values only forcertain species of wood. For other species, consult withthe connector manufacturer.AMERICAN WOOD COUNCIL

74 M10: MECHANICAL CONNECTIONS• The wood must not split when the fastener is installed.A fastener that splits the wood will not take the designload. If wood tends to split, consider pre-boring holesusing a diameter not exceeding 3/4 of the nail diameter.Pre-boring requirements for screws and bolts are providedin the NDS.• Wood can shrink and expand as it loses and gains moisture.Most connectors are manufactured to fit commondry lumber dimensions. Other dimensions may be availablefrom the manufacturer.• Where built-up lumber (multiple members) is installedin a connector, the members must be fastened togetherprior to installation of the connector so that the membersact as a single unit.• The dimensions of the supporting member must besufficient to receive the specified fasteners. Most connectorsare rated based on full penetration of all specifiedfasteners. Refer to the connector manufacturer for othersituations.• Bearing capacity of the joist or beam should also beevaluated to ensure adequate capacity.FastenersMost wood connectors rely on the fasteners to transferthe load from one member to the other. Therefore, thechoice and installation of the fasteners is critical to theperformance of the connector.The following are important items regarding the fastenersused in the connector:ConnectorsFinally, the condition of the connector itself is criticalto how it will perform. The following are important itemsregarding the connector itself:• Connectors may not be modified in the field unlessnoted by the manufacturer. Bending steel in the fieldmay cause fractures at the bend line, and fractured steelwill not carry the rated load.• Modified connectors may be available from the manufacturer.Not all modifications are tested by all manufacturers.Contact the manufacturer to verify loads onmodified connectors.• In general, all holes in connectors should be filled withthe nails specified by the manufacturer. Contact themanufacturer regarding optional nail holes and optionalloads.• Different environments can cause corrosion of steelconnectors. Always evaluate the environment wherethe connector will be installed. Connectors are availablewith differing corrosion resistances. Contact themanufacturer for availability. Fasteners must be at leastthe same corrosion resistance as that chosen for theconnector.• All fasteners specified by the manufacturer must beinstalled to achieve the published value.• The size of fastener specified by the manufacturer mustbe installed. Most manufacturers specify common nails,unless otherwise noted.• The fastener must have at least the same corrosionresistance as the connector.• Bolts must generally be structural quality bolts, equalto or better than ANSI/ASME Standard B18.2.1.• Bolt holes must be a minimum of 1/32" and a maximumof 1/16" larger than the bolt diameter.• Fasteners must be installed prior to loading the connection.• Power-driven fasteners may deflect and injure theoperator or others. Nail tools may be used to install connectors,provided the correct quantity and type of nailsare properly installed in the manufacturer’s nail holes.Nail tools with nail hole-locating mechanisms should beused. Follow the nail tool manufacturer’s instructionsand use the appropriate safety equipment.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION75M11: DOWEL-TYPE FASTENERSM11.1 General 76M11.2 Reference Withdrawal Design Values 76M11.3 Reference Lateral Design Values 76M11.4 Combined Lateral and WithdrawalLoads 76M11.5 Adjustment of Reference DesignValues 77M11.6 Multiple Fasteners 7711AMERICAN WOOD COUNCIL

76 M11: DOWEL-TYPE FASTENERSM11.1 GeneralThis Chapter covers design of connections betweenwood members using metal dowel-type (nails, bolts, lagscrews, wood screws, drift pins) fasteners.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 and lengths.M11.2 Reference Withdrawal Design ValuesThe basic design equation for dowel-type fastenersunder withdrawal loads is:W′p ≥ R Wwhere:W′ = adjusted withdrawal design valueR W = axial (withdrawal) forcep = depth of fastener penetration intowood memberReference withdrawal design values are tabulated inNDS Chapter 11.M11.3 Reference Lateral Design ValuesThe basic equation for design of dowel-type fastenersunder lateral load is:Z′ ≥ R Zwhere:Z′ = adjusted lateral design valueR Z = lateral forceReference lateral design values are tabulated in NDSChapter 11.M11.4 Combined Lateral and Withdrawal LoadsLag screws, wood screws, nails, and spikes resistingcombined lateral and withdrawal loads shall be designedin accordance with NDS 11.4.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION77M11.5 Adjustment of Reference Design ValuesDowel-type connections must be designed by applyingall applicable adjustment factors to the referencewithdrawal design value or reference lateral design valuefor the connection. NDS Table 10.3-1 lists all applicableadjustment factors for dowel-type connectors. TableM11.3-1 shows the applicability of adjustment factorsfor dowel-type fasteners in a slightly different format forthe designer.Table M11.3-1 Applicability of Adjustment Factors for Dowel-Type Fasteners 1Allowable Stress Design Load and Resistance Factor DesignLateral LoadsDowel-Type Fasteners Z′ = Z C D C M C t C g C ∆ C eg C di C tn Z′ = Z C M C t C g C ∆ C eg C di C tn (3.32)(0.65) λWithdrawal LoadsNails, Spikes, Lag Screws,Wood Screws, and Drift PinsW′ = W C D C M C t C eg C tn Z′ = Z C M C t C eg C tn (3.32)(0.65) λ1. See NDS Table 10.3.1 footnotes for additional guidance on application of adjustment factors for dowel-type fasteners.Example of a Dowel-Type FastenerLoaded LaterallyFor a single dowel-type fastener installed in side grainperpendicular to the length of the wood member, meetingthe end and edge distance and spacing requirements of NDS11.5.1, used in a normal building environment (meeting thereference conditions of NDS 2.3 and 10.3), and not a nailor spike in diaphragm construction, the general equationfor Z′ reduces to:Example of a Dowel-Type FastenerLoaded in WithdrawalFor a single dowel-type fastener installed in side grainperpendicular to the length of the wood member, used ina normal building environment (meeting the referenceconditions of NDS 2.3 and 10.3), the general equation forW′ reduces to:for ASD:for ASD:Z′ = Z C Dfor LRFD:Z′ = Z (3.32)(0.65) λM11.6 Multiple FastenersW′ = W C Dfor LRFD:W′ = W (3.32)(0.65) λInstallation RequirementsTo achieve stated design values, connectors mustcomply with installation requirements such as spacingof connectors, minimum edge and end distances, properdrilling of lead holes, and minimum fastener penetration.11M11: DOWEL-TYPE FASTENERSLocal stresses in connections using multiple fastenerscan be evaluated in accordance with NDS Appendix E.AMERICAN WOOD COUNCIL

78M11: DOWEL-TYPE FASTENERSAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION79M12: SPLITRING ANDSHEAR PLATECONNECTORSM12.1 General 80M12.2 Reference Design Values 80M12.3 Placement of Split Ring andShear Plate Connectors 8012AMERICAN WOOD COUNCIL

80 M12: SPLIT RING AND SHEAR PLATE CONNECTORSM12.1 GeneralThis Chapter covers design for split rings and shearplates. These connectors rely on their geometry to providelarger metal-to-wood bearing areas per connector. Bothare installed into precut grooves or daps in the members.M12.2 Reference Design ValuesReference lateral design values (P, Q) are tabulated inthe split ring and shear plate tables in NDS 12.2.Design Adjustment FactorsSplit ring and shear plate connections must be designedby applying all applicable adjustment factors to the referencelateral design value for the connection. NDS Table10.3.1 provides all applicable adjustment factors for splitring and shear plate connectors. Table M12.2-1 shows theapplicability of adjustment factors for dowel-type fastenersin a slightly different format for the designer.Table M12.2-1Applicability of Adjustment Factors for Split Ring and ShearPlate Connectors 1Split Ring andShear Plate ConnectorsAllowable Stress Design Load and Resistance Factor DesignP′ = P C D C M C t C g C ∆ C d C st P′ = P C M C t C g C ∆ C d C st (3.32)(0.65) λQ′ = Q C D C M C t C g C ∆ C d Q′ = Q C M C t C g C ∆ C d (3.32)(0.65) λ1. See NDS Table 10.3.1 footnotes for additional guidance on application of adjustment factors for split ring and shear plate connectors.For a single split ring or shear plate connection installedin side grain perpendicular to the length of the woodmembers, meeting the end and edge distance and spacingrequirements of NDS 12.3, used in a normal building environment(meeting the reference conditions of NDS 2.3and 10.3), and meeting the penetration requirements ofNDS 12.2.3, the general equations for P′ and Q′ reduce to:for ASD:P′ = P C DQ′ = Q C Dfor LRFD:P′ = P (3.32)(0.65) λQ′ = Q (3.32)(0.65) λM12.3 Placement of Split Ring and Shear PlateConnectorsInstallation RequirementsTo achieve stated design values, connectors mustcomply with installation requirements such as spacingof connectors, minimum edge and end distances, properdapping and grooving, drilling of lead holes, and minimumfastener penetration as specified in NDS 12.3.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION81M13: TIMBERRIVETSM13.1 General 82M13.2 Reference Design Values 82M13.3 Placement of Timber Rivets 8213AMERICAN WOOD COUNCIL

82 M13: TIMBER RIVETSM13.1 GeneralThis Chapter covers design for timber rivets. Timberrivets are hardened steel nails that are driven through predrilledholes in steel side plates (typically 1/4" thickness)to form an integrated connection where the plate and rivetswork together to transfer load to the wood member.M13.2 Reference Design ValuesReference wood capacity design values parallel tograin, P w , are tabulated in the timber rivet Tables 13.2.1Athrough 13.2.1F in the NDS.Reference design values perpendicular to grain arecalculated per NDS 13.2.2.Design Adjustment FactorsConnections must be designed by applying all applicableadjustment factors to the reference lateral design valuefor the connection. NDS Table 10.3-1 lists all applicableadjustment factors for timber rivets. Table M13.2-1 showsthe applicability of adjustment factors for timber rivets ina slightly different format for the designer.Table M13.2-1 Applicability of Adjustment Factors for Timber Rivets 1Timber RivetsAllowable Stress Design Load and Resistance Factor DesignP′ = P C D C M C t C st P′ = P C M C t C st (3.32)(0.65) λQ′ = Q C D C M C t C D C st Q′ = Q C M C t C D C st (3.32)(0.65) λ1. See NDS Table 10.3.1 footnotes for additional guidance on application of adjustment factors for timber rivets.For a timber rivet connection installed in side grainperpendicular to the length of the wood members, withmetal side plates 1/4" or greater, used in a normal buildingenvironment (meeting the reference conditions of NDS2.3 and 10.3), and where wood capacity perpendicular tograin, Q w , does not control, the general equations for P′and Q′ reduce to:for ASD:P′ = P C DQ′ = Q C Dfor LRFD:P′ = P (3.32)(0.65) λQ′ = Q (3.32)(0.65) λM13.3 Placement of Timber RivetsInstallation RequirementsTo achieve stated design values, connectors mustcomply with installation requirements such as spacing ofconnectors, minimum edge and end distances per NDS13.3; and drilling of lead holes, minimum fastener penetration,and other fabrication requirements per NDS 13.1.2.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION83M14: SHEARWALLS ANDDIAPHRAGMSM14.1 General 8414AMERICAN WOOD COUNCIL

84 M14: SHEAR WALLS AND DIAPHRAGMSM14.1 GeneralThis Chapter pertains to design of shear walls and diaphragms.These assemblies, which transfer lateral forces(wind and seismic) within the structure, are commonlydesigned using wood structural panel products fastenedto wood framing members. The use of bracing systems totransfer these forces is not within the scope of this Chapter.Shear wall/diaphragm shear capacity is tabulated inthe ANSI/AWC Special Design Provisions for Wind andSeismic (SDPWS).AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION85M15: SPECIALLOADINGCONDITIONSM15.1 Lateral Distribution ofConcentrated Loads 86M15.1.1 Lateral Distribution of aConcentrated Load for Moment 86M15.1.2 Lateral Distribution of aConcentrated Load forShear 86M15.2 Spaced Columns 86M15.3 Built-Up Columns 86M15.4 Wood Columns with Side Loadsand Eccentricity 8615AMERICAN WOOD COUNCIL

86 M15: SPECIAL LOADING CONDITIONSM15.1 Lateral Distribution of Concentrated LoadsM15.1.1 Lateral Distribution of aConcentrated Load for MomentThe lateral distribution factors for moment in NDSTable 15.1.1 are keyed to the nominal thickness of theflooring or decking involved (2" to 6" thick). Spacing ofthe stringers or beams is based on recommendations of theAmerican Association of State Highway and TransportationOfficials.Lateral distribution factors determined in accordancewith NDS Table 15.1.1 can be used for any type of fixedor moving concentrated load.M15.1.2 Lateral Distribution of aConcentrated Load for ShearThe lateral distribution factors for shear in NDS Table15.1.2 relate the lateral distribution of concentrated loadat the center of the beam or stringer span as determinedunder NDS 15.1.1, or by other means, to the distributionof load at the quarter points of the span. The quarter pointsare considered to be near the points of maximum shear inthe stringers for timber bridge design.M15.2 Spaced ColumnsAs used in the NDS, spaced columns refer to two ormore individual members oriented with their longitudinalaxis parallel, separated at the ends and in the middle portionof their length by blocking and joined at the ends bysplit ring or shear plate connectors capable of developingrequired shear resistance.The end fixity developed by the connectors and endblocks increases the load-carrying capacity in compressionparallel to grain of the individual members only inthe direction perpendicular to their wide faces.AWC’s Wood Structural Design Data (WSDD) providesload tables for spaced columns.M15.3 Built-Up ColumnsAs with spaced columns, built-up columns obtaintheir efficiency by increasing the buckling resistance ofindividual laminations. The closer the laminations of a mechanicallyfastened built-up column deform together (thesmaller the amount of slip occurring between laminations)under compressive load, the greater the relative capacity ofthat column compared to a simple solid column of the sameslenderness ratio made with the same quality of material.M15.4 Wood Columns with Side Loads and EccentricityThe eccentric load design provisions of NDS 15.4.1are not generally applied to columns supporting beamloads where the end of the beam bears on the entire crosssection of the column. It is standard practice to considersuch loads to be concentrically applied to the supportingcolumn. This practice reflects the fact that the end fixityprovided by the end of the column is ignored when theusual pinned end condition is assumed in column design.In applications where the end of the beam does not bearon the full cross section of the supporting column, or inspecial critical loading cases, use of the eccentric columnloading provisions of NDS 15.4.1 may be considered appropriateby the designer.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION87M16: FIREDESIGNM16.1 General 88Lumber 89Structural Glued LaminatedTimber 90Poles and Piles 91Structural Composite Lumber 91Wood I-Joists 92Metal Plate Connected WoodTrusses 92M16.2 Design Procedures for ExposedWood Members 96M16.3 Wood Connections 9716AMERICAN WOOD COUNCIL

88 M16: FIRE DESIGNM16.1 GeneralThis Chapter outlines fire considerations includingdesign requirements and fire-rated assemblies for variouswood products. Lumber, glued laminated timber, polesand piles, wood I-joists, structural composite lumber, andmetal plate connected wood trusses are discussed.PlanningAs a first step, the authority having jurisdiction wherea proposed building is to be constructed must be consultedfor the requirements of the specific design project. Thisnormally concerns the type of construction desired as wellas allowable building areas and heights for each constructiontype.Wood building construction is generally classified intotypes such as wood frame (Type V), noncombustible orfire-retardant-treated wood wall-wood joist (Type III), andheavy timber (Type IV). Type V construction is definedas having exterior walls, bearing walls, partitions, floorsand roofs of wood stud and joist framing of 2" nominaldimension. These are divided into two subclasses that areeither protected or unprotected construction. Protectedconstruction calls for having load‐bearing assemblies of1‐hour fire endurance.Type III construction has exterior walls of noncombustiblematerials and roofs, floors, and interior walls andpartitions of wood frame. As in Type V construction, theseare divided into two subclasses that are either protectedor unprotected.Type IV construction includes exterior walls of noncombustiblematerials or fire-retardant-treated wood andcolumns, floors, roofs, and interior partitions of wood ofa minimum size, as shown in Table M16.1-1.In addition to having protected and unprotected subclassesfor each building type, increases in floor area andheight of the building are allowed when active fire protection,such as sprinkler protection systems, are included. Forexample, protected wood-frame business occupancies canbe increased from three to four stories in height becauseof the presence of sprinklers. Also, the floor area maybe further increased under some conditions. Additionalinformation is available at www.awc.org.Table M16.1-1MaterialRoof decking:Lumber or structuralusepanelsFloor decking:Lumberor flooringor structural-usepanelsRoof framing:Floor framing:Columns:Minimum Sizes toQualify as HeavyTimber ConstructionMinimum 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)AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION89LumberBuilding Code RequirementsFor occupancies such as stores, apartments, offices,and other commercial and industrial uses, building codescommonly require floor/ceiling and wall assemblies to befire-resistance rated in accordance with standard fire tests.Depending on the application, wall assemblies mayneed to be rated either from one side or both sides. Forspecific exterior wall applications, the International BuildingCode (IBC) allows wood-frame, wood-sided walls to betested for exposure to fire from the inside only. Rating forboth interior and exterior exposure is only required when thewall has a fire separation distance of less than 5 feet. Coderecognition of 1- and 2-hour wood-frame wall systems isalso predicated on successful fire and hose stream testing inaccordance with ASTM E119, Standard Test Methods forFire Tests of Building Construction Materials.Fire Tested AssembliesFire-rated wood-frame assemblies can be found ina number of sources including the IBC, UnderwritersLaboratories (UL) Fire Resistance Directory, IntertekTesting Services’ Directory of Listed Products, and theGypsum Association’s Fire Resistance Design Manual.The American Wood Council (AWC) and its membershave tested a number of wood-frame fire-rated assemblies.Descriptions of these successfully tested assemblies areprovided in AWC’s Design for Code Acceptance (DCA)No. 3, Fire Rated Wood Floor and Wall Assemblies whichis available at www.awc.org.M16: FIRE DESIGN16AMERICAN WOOD COUNCIL

90 M16: FIRE DESIGNStructural Glued Laminated TimberFires do not normally start in structural framing, butrather in the building’s contents. These fires generallyreach temperatures of between 1,290°F and 1,650°F. Gluedlaminated timber members perform very well under theseconditions. Unprotected steel members typically suffersevere buckling and twisting during fires, often collapsingcatastrophically.Wood ignites at about 480°F, but charring may beginas low as 300°F. Wood typically chars at 1/40 in. perminute. Thus, after 30 minutes of fire exposure, only theouter 3/4 in. of the structural glued laminated timber willbe damaged. Char insulates a wood member and henceraises the temperature it can withstand. Most of the crosssection will remain intact, and the member will continuesupporting loads during a typical building fire.It is important to note that neither building materialsalone, nor building features alone, nor detection andfire extinguishing equipment alone can provide adequatesafety from fire in buildings. To ensure a safe structure inthe event of fire, authorities base fire and building coderequirements on research and testing, as well as fire histories.The model building codes classify heavy timber as aspecific type of construction and give minimum sizes forroof and floor beams.The requirements set out for heavy timber constructionin model building codes do not constitute 1-hour fireresistance. However, procedures are available to calculatethe structural glued laminated timber size required forprojects in which 1-hour fire resistance is required (seeNDS 16.2 and AWC’s Technical Report 10 available atwww.awc.org).To achieve a 1-hour fire rating for beams whose dimensionsqualify them for this rating, the basic layup must bemodified – one core lamination must be removed from thecenter and the tension face augmented with the addition ofa tension lamination. For more information concerning theeffects of fire on structural glued laminated timber, referto APA EWS Technical Note Y245 or AITC TechnicalNote 7. For determining fire resistance other than 1 hour,see NDS 16.2 and AWC’s Technical Report 10 availableat www.awc.org.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION91Poles and PilesVery few elements of modern structures can be called“fire proof.” Even in buildings where the major structuralmembers are noncombustible, most of the furnishings areflammable. It is for this reason that much of the attention inmodern building codes addresses issues related to containingand limiting fires, rather than simply calling materialscombustible and noncombustible.While this topic is fairly complex for other types ofproducts, fire performance is relatively straightforward forpoles and piles. Poles are generally used in cross-sectionalsizes that qualify as heavy timber construction in the modelbuilding codes. On this basis, timber poles compare favorablywith other construction materials in their performanceunder fire conditions. Piles are generally not exposed tofire conditions unless they extend substantially above thegroundline.Structural Composite LumberEngineered wood products have fire resistive characteristicsvery similar to conventional wood frame members.Since many engineered wood products are proprietary,they are usually recognized in a code evaluation reportpublished by an evaluation service. Each evaluation reportusually contains fire resistance information.Very few elements of modern structures can be called“fire proof.” Even in buildings where the major structuralmembers are noncombustible, most of the furnishings areflammable. It is for this reason that much of the attention inmodel building codes addresses issues related to containingand limiting fires, rather than simply calling materialscombustible and noncombustible. The primary intent ofthe building codes is to ensure structural stability to allowexiting, evacuation, and fire fighting.As with the previous topic of durability, this Manualcannot cover the topic of designing for optimal structuralperformance in fire conditions in detail. There are manyexcellent texts on the topic, and designers are advised touse this information early in the design process. To assistthe designer in understanding several ways in which fireperformance can be addressed, the following overview isprovided.Fire sprinklers are probably the most effective methodto enhance fire resistance of engineered wood systems (aswell as other systems). They are designed to control thefire while protecting the occupants and the building untilthe fire department arrives. They are the ultimate way toimprove fire safety.Heavy timber construction has proven to be acceptablein many areas where fire safety is of utmost concern.These applications have proven to be not only reliable, buteconomical in certain structures – many wider width SCLproducts can be used in heavy timber construction. Consultmanufacturer’s literature or code evaluation reports forspecific information.The fire performance of wood structures can be enhancedin the same ways as that of structures of steel,concrete, or masonry:• Fire sprinkler systems have proven to be effectivein a variety of structures, both large and small• Protection of the structural members with materialssuch as properly attached gypsum sheathing canprovide greatly improved fire performance. Fireratings, as established from test procedures specifiedin ASTM E-119, of up to 2 hours can be achievedthrough the use of gypsum sheathing• Where surface burning characteristics are critical,fire-retardant treatments can be used to reduce theflamespread for some productsTo reiterate, this Manual does not purport to addressthis topic in an all-inclusive manner – it is merely anattempt to alert designers to the need to address fire performanceissues in the design of the structure.M16: FIRE DESIGN16AMERICAN WOOD COUNCIL

92 M16: FIRE DESIGNWood I-JoistsThe wood I-joist industry has actively supported thefollowing projects to establish fire performance of systemsusing wood I-joist products:• ASTM E-119 fire tests have been conducted by thewood I-joist industry to establish fire resistanceratings for generic I-joist systems. Detailed descriptionsof these systems are shown in AWC’s Designfor Code Acceptance (DCA) No. 3, Fire Rated WoodFloor and Wall Assemblies available at www.awc.org.• ASTM E-119 fire tests have been conducted bywood I-joist manufacturers to establish fire resistanceratings for proprietary I-joist systems. Detaileddescriptions of these systems are available from theindividual I‐joist manufacturer.• National Fire Protection Research FoundationReport titled “National Engineered LightweightConstruction Fire Research Project.” This reportdocuments an extensive literature search of the fireperformance of engineered lightweight construction.• A video, I-JOISTS:FACTS ABOUT PROGRESS, hasbeen produced by the Wood I-Joist Manufacturer’sAssociation (WIJMA). This video describes somebasic facts about changes taking place within theconstruction industry and the fire service. Alongwith this video is a document that provides greaterdetails on fire performance issues.• Industry research in fire endurance modeling forI-joist systems.Metal Plate Connected Wood TrussesGenerally, a fire endurance rating of 1 hour is mandatedby code for many of the applications where trussescould be used. All testing on these assemblies is performedin accordance with the ASTM’s Standard Methods forFire Tests of Building Construction and Materials (ASTME119).The two primary source documents for fire enduranceassembly results are the Fire Resistance Design Manual,published by the Gypsum Association (GA), and theFire Resistance Directory, published by Underwriters’Laboratories, Inc. (UL). Warnock Hersey (WH) assembliesare now listed in the ITS Directory of Listed Products.These tested assemblies are available for specification byarchitects or building designers, and for use by all trussmanufacturers where a rated assembly is required, andcan generally be applied to both floor and roof assemblyapplications.According to the UL Directory’s Design InformationSection: “Ratings shown on individual designs apply toequal or greater height or thickness of the assembly, and tolarger structural members, when both size and weight areequal or larger than specified, and when the thickness ofthe flanges, web or diameter of chords is equal or greater.”Thus, larger and deeper trusses can be used under the auspicesof the same design number. This approach has oftenbeen used in roof truss applications since roof trusses areusually much deeper than the tested assemblies.Thermal and/or acoustical considerations at timesmay require the installation of insulation in a floor-ceilingor roof-ceiling assembly that has been tested withoutinsulation. As a general ‘rule,’ experience indicates thatit is allowable to add insulation to an assembly, providedthat the depth of the truss is increased by the depth of theinsulation. And as a general ‘rule,’ assemblies that weretested with insulation may have the insulation removed.To make a rational assessment of any modificationto a tested assembly, one must look at the properties ofthe insulation and the impact that its placement inside theassembly will have on the fire endurance performanceof the assembly. Insulation retards the transfer of heat, isused to retain heat in warm places, and reduces the flowof heat into colder areas. As a result, its addition to a fireendurance assembly will affect the flow of heat throughand within an assembly. One potential effect of insulationplaced directly on the gypsum board is to retard the dissipationof heat through the assembly, concentrating heatin the protective gypsum board.In some cases specific branded products are listed inthe test specifications. Modifications or substitutions tofire endurance assemblies should be reviewed with thebuilding designer and code official, preferably with the assistanceof a professional engineer. This review is requiredbecause the final performance of the assembly is a resultof the composite of the materials used in the constructionof the assembly.The Structural Building Components Association providessummaries of wood truss fire endurance assembliesand sound transmission ratings. For more information, visitAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION93www.sbcindustry.com. Also, several truss plate manufacturershave developed proprietary fire resistant assemblies.These results apply only to the specific manufacturer’struss plates and referenced fire endurance assembly system.For more detailed information on these assemblies, theindividual truss plate manufacturer should be contacted.Complete specifications on the UL, GA, and WH assembliesare available on their respective websites.Area Separation AssembliesIt is of great concern when fire-rated assemblies aredesigned and specified without consideration of soundstructural principles. Should a fire develop, these structuralinadequacies could cause the assemblies to fail unexpectedly,increasing the risk of loss of life. There are a numberof ways to provide sound structural and fire endurance detailsthat maintain 1-hour rated area separation assemblies.Figure M16.1-1 shows several possible assembliesthat can be used to make up the 1-hour rated system forseparation between occupancies for a) floor trusses parallelto the wall assembly; and b) perpendicular to the wallassembly. A 2x4 firestop is used between the walls next tothe wall top plates. This effectively prevents the spread offire inside the wall cavity. A minimum 1/2-inch gypsumwallboard attached to one side of the floor truss system, andlocated between the floor trusses, also provides a draftstopand fire protection barrier between occupancy spaces if afire starts in the floor truss concealed space, which is a rareoccurrence. The tenant separation in the roof is maintainedthrough the use of a 1/2-inch gypsum wallboard draftstopattached to the ends of one side of the monopitch trussesand provided for the full truss height. Figure M16.1-1effectively provides 1-hour compart mentation for all theoccupied spaces using listed 1-hour rated assemblies andthe appropriate draftstops for the concealed spaces asprescribed by the model building codes.If a fire-resistive assembly, rather than draftstopping,is required within concealed attic spaces, UL U338, U339,and U377, provide approved 1-hour and 2-hour rated assembliesthat may be used within the roof cavity and thatmay be constructed with gable end frames.The critical aspects for fire endurance assembliesinclude:• Ensuring that the wall and ceiling assemblies ofthe room use 1-hour rated assemblies. These areindependent assemblies. The wall assembly doesnot have to be continuous from the floor to the roofto meet the intent of the code or the fire enduranceperformance of the structure. The intent of the codeis that the building be broken into compartmentsto contain a fire to a given area. Fire resistanceassemblies are tested to provide code-complyingfire endurance to meet the intent of the code. Theforegoing details meet the intent of the code.• Properly fastening the gypsum wallboard to the wallstuds and trusses. This is critical for achieving thedesired fire performance from a UL or GA assembly.• Ensuring that the detail being used is structurallysound, particularly the bearing details. All connectiondetails are critical to assembly performance.When a fire begins, if the structural detail is poor,the system will fail at the poor connection detailearlier than expected.• Accommodating both sound structural details withappropriate fire endurance details. Since all conceivablefield conditions have not been and cannot betested, rational engineering judgment needs to beused.The foregoing principles could also be applied to structuresrequiring 2-hour rated area separation assemblies.In this case, acceptable 2-hour wall assemblies wouldbe used in conjunction with the 2-hour floor-ceiling androof-ceiling fire endurance assemblies.Through-Penetration Fire StopsBecause walls and floors are penetrated for a varietyof plumbing, ventilation, electrical, and communicationpurposes, ASTM E814 Standard Method of Fire Testsof Through-Penetration Fire Stops uses fire-resistiveassemblies (rated per ASTM E119) and penetrates themwith cables, pipes, and ducts, etc., before subjecting theassembly to ASTM E119’s fire endurance tests.Despite the penetrations, firestop assemblies testedaccording to ASTM E814 must not significantly lose theirfire containment properties in order to be considered acceptable.Properties are measured according to the passageof any heat, flame, hot gases, or combustion through thefire stop to the test assembly’s unexposed surface.Upon successful completion of fire endurance tests,fire stop systems are given F&T ratings. These ratings areexpressed in hourly terms, in much the same fashion asfire-resistive barriers.To obtain an F-Rating, a fire stop must remain in theopening during the fire and hose stream test, withstandingthe fire test for a prescribed rating period without permittingthe passage of flame on any element of its unexposedside. During the hose stream test, a fire stop must not developany opening that would permit a projection of waterfrom the stream beyond the unexposed side.To obtain a T-Rating, a fire stop must meet the requirementsof the F-Rating. In addition, the fire stop mustprevent the transmission of heat during the prescribed ratingperiod which would increase the temperature of anyM16: FIRE DESIGN16AMERICAN WOOD COUNCIL

94 M16: FIRE DESIGNFigure M16.1-1 Cross Sections of Possible One-Hour Area SeparationsAMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION95thermocouple on its unexposed surface, or any penetratingitems, by more than 325°F.The UL Fire Resistance Directory lists literally thousandsof tested systems. They have organized the systemswith an alpha-alpha-numeric identification number. Thefirst alpha is either a F, W, or C. These letters signify thetype of assembly being penetrated: F signifies a floor, Wsignifies a wall, and C signifies a ceiling. The second alphasignifies a limiting description, for example: C signifies aframed floor, and L signifies a framed wall. The numericportion is also significant: 0000-0999 signifies no penetratingitems, 1000-1999 signifies metallic pipe, 2000-2999signifies nonmetallic pipe, 3000-3999 signifies electricalcable, 4000-4999 signifies cable trays, 5000-5999 signifiesinsulated pipes, 6000-6999 signifies miscellaneouselectrical penetrants, 7000-7999 signifies miscellaneousmechanical penetrants, and 8000-8999 signifies a combinationof penetrants.Transitory Floor Vibration and SoundTransmissionSound TransmissionSound transmission ratings are closely aligned withfire endurance ratings for assemblies. This is due to thefact that flame and sound penetrations follow similar pathsof least resistance.Sound striking a wall or ceiling surface is transmittedthrough the air in the wall or ceiling cavity. It thenstrikes the opposite wall surface, causing it to vibrate andtransmit the sound into the adjoining room. Sound also istransmitted through any openings into the room, such asair ducts, electrical outlets, window openings, and doors.This is airborne sound transmission. The Sound TransmissionClass (STC) method of rating airborne soundsevaluates the comfort ability of a particular living space.The higher the STC, the better the airborne noise controlperformance of the structure. An STC of 50 or above isgenerally considered a good airborne noise control rating.Table M16.1-2 describes the privacy afforded accordingto the STC rating.Impact Sound Transmission is produced when astructural element is set into vibration by direct impact– someone walking, for example. The vibrating surfacegenerates sound waves on both sides of the element. TheImpact Insulation Class (IIC) is a method of rating theimpact sound transmission performance of an assembly.The higher the IIC, the better the impact noise control ofthe element. An IIC of 55 is generally considered a goodimpact noise control.Table M16.1-2Privacy AffordedAccording to STCRatingSTC RatingPrivacy Afforded25 Normal speech easily understood30 Normal speech audible, but not intelligible35 Loud speech audible and fairly understandable40 Loud speech barely audible, but not intelligible45 Loud speech barely audible50 Shouting barely audible55 Shouting inaudibleM16: FIRE DESIGN16AMERICAN WOOD COUNCIL

96 M16: FIRE DESIGNM16.2 Design Procedures for Exposed Wood MembersFor members stressed in one principle direction, simplificationscan be made which allow the tabulation of loadfactor tables for fire design. These load factor tables canbe used to determine the structural design load ratio, R s , atwhich the member has sufficient capacity for a given fireendurance time. AWC’s Technical Report 10 Calculatingthe Fire Resistance of Exposed Wood Members providesderivation of load ratios and load ratio tables for bending,compression, and tension members. TR10 is available atwww.awc.org.AMERICAN WOOD COUNCIL

ASD/LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION97M16.3 Wood ConnectionsWhere 1-hour fire endurance is required, connectorsand fasteners must be protected from fire exposure by 1.5"of wood, fire-rated gypsum board, or any coating approvedfor a 1-hour rating. Typical details for commonly usedfasteners and connectors in timber framing are shown inFigure M16.3-1 through Figure M16.3-6.Figure M16.3-3 Ceiling ConstructionFigure M16.3-1 Beam to ColumnConnection - ConnectionNot Exposed to FireFigure M16.3-4 Beam to ColumnConnection - ConnectionExposed to Fire WhereAppearance is Not a FactorFigure M16.3-2 Beam to ColumnConnection - ConnectionExposed to Fire WhereAppearance is a FactorM16: FIRE DESIGN16AMERICAN WOOD COUNCIL

98 M16: FIRE DESIGNFigure M16.3-5 Column ConnectionsCoveredFigure M16.3-6 Beam to Girder -Concealed ConnectionAMERICAN WOOD COUNCIL

American Wood CouncilAWC Mission StatementTo increase the use of wood by assuring the broadregulatory acceptance of wood products, developingdesign tools and guidelines for wood construction,and influencing the development of public policiesaffecting the use and manufacture of wood products.

American Wood Council222 Catoctin Circle, SESuite 201Leesburg, VA 20175www.awc.orginfo@awc.orgISBN 978-0-9827380-5-49 780982 73805410-12