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2005 NDS:
LRFD Provisions
Paul W. McMullin, P.E., Ph.D.Paul W. McMullin, P.E., Ph.D.
Sr. Project EngineerSr. Project Engineer
Dunn Associates, Inc.Dunn Associates, Inc.
Philosophy
““decisions not to utilize specific practices decisions not to utilize specific practices
require the same background require the same background
knowledge as those which lead to the knowledge as those which lead to the
utilization of fractureutilization of fracture--safe design safe design
practicespractices”” ((PelliniPellini 1969, p. 1)1969, p. 1)
Outline
�� Development of Development of
Wood Design CodesWood Design Codes
�� Why LRFDWhy LRFD
�� What is LRFD Wood What is LRFD Wood
DesignDesign
�� General Terminology General Terminology
and Requirementsand Requirements
�� Beam and Column Beam and Column
ProvisionsProvisions
�� Lateral SupplementLateral Supplement
�� Mechanical Mechanical
ConnectorsConnectors
�� Proprietary Proprietary
ConnectorsConnectors
�� ResourcesResources
Last Decade of Wood
Design
�� 1991 NDS1991 NDS
�� 1996 LRFD1996 LRFD-- New state of the artNew state of the art
�� 1997 NDS1997 NDS-- Based on 1991Based on 1991
�� 2001 NDS (ASD)2001 NDS (ASD)-- Updated to Updated to
technology of 1996 LRFDtechnology of 1996 LRFD
�� 2005 NDS (ASD/LRFD)2005 NDS (ASD/LRFD)
2005 NDS
2005 NDS
�� Combined ASD/ LRFD provisionsCombined ASD/ LRFD provisions
�� LRFD in same format as ASD, LRFD in same format as ASD, except:except:
�� Behavioral equations sameBehavioral equations same
�� 3 LRFD based adjustment 3 LRFD based adjustment factorsfactors
�� KKFF——Format Conversion Format Conversion FactorFactor
�� φφ——Strength Reduction Strength Reduction FactorFactor
�� λλ——Time Effect FactorTime Effect Factor
�� No CNo CDD——Load Duration FactorLoad Duration Factor
�� Consistent with ASCE 7Consistent with ASCE 7--02 02 and 7and 7--0505
NDS 2005:
Chapter Layout
1)1) General Requirements for General Requirements for Structural DesignStructural Design
2)2) Design Values for Structural Design Values for Structural MembersMembers
3)3) Design Provisions and Design Provisions and EquationsEquations
4)4) Sawn LumberSawn Lumber
5)5) Structural Glue Laminated Structural Glue Laminated TimberTimber
6)6) Round Timber Poles and PilesRound Timber Poles and Piles
7)7) Prefabricated Wood IPrefabricated Wood I-- JoistsJoists
8)8) Structural Composite LumberStructural Composite Lumber
NDS 2005:
Chapter Layout (cont.)
9)9) Wood Structural PanelsWood Structural Panels
10)10)Mechanical ConnectionsMechanical Connections
11)11)DowelDowel--Type FastenersType Fasteners
12)12)Split Ring and Shear Plate Split Ring and Shear Plate
ConnectorsConnectors
13)13)Timber RivetsTimber Rivets
14)14)Shear Walls and Shear Walls and
DiaphragmsDiaphragms
15)15)Special Loading ConditionsSpecial Loading Conditions
16)16)Fire Design of Wood Fire Design of Wood
MembersMembers
NDS 2005: Appendix
Layout
a)a) Construction and Design Construction and Design
PracticesPractices
b)b) Load Duration (ASD)Load Duration (ASD)
c)c) Temperature EffectsTemperature Effects
d)d) Lateral Stability of BeamsLateral Stability of Beams
e)e) Local Stresses in Fastener Local Stresses in Fastener
Groups (New 2001 NDS)Groups (New 2001 NDS)
f)f) Design for Creep and Critical Design for Creep and Critical
Deflection ApplicationsDeflection Applications
g)g) Effective Column LengthEffective Column Length
h)h) Lateral Stability of ColumnsLateral Stability of Columns
i)i) Yield Limit Equations for Yield Limit Equations for ConnectionsConnections
j)j) Solution of Hankinson Solution of Hankinson FormulaFormula
k)k) Typical Dimensions for Split Typical Dimensions for Split Ring and Shear Plate Ring and Shear Plate ConnectorsConnectors
l)l) Typical Dimensions for Typical Dimensions for DowelDowel--Type FastenersType Fasteners
m)m)MFG Tolerances for Rivets MFG Tolerances for Rivets and Steel Side Plates for and Steel Side Plates for Timber Rivet Conn.Timber Rivet Conn.
n)n) Load and Resistance Load and Resistance Factor Design (LRFD)Factor Design (LRFD)
NDS 2005: Appendix
Layout
Design Value Supplement:
Chapter Layout
1)1) Sawn Lumber Grading Sawn Lumber Grading
AgenciesAgencies
2)2) Species CombinationsSpecies Combinations
3)3) Section PropertiesSection Properties
4)4) Reference Design Reference Design
ValuesValues
Why Use LRFD?
�� StateState--ofof--thethe--art art
�� More rational treatment of loadsMore rational treatment of loads
�� ASDASD——Deterministic (inconsistent safety Deterministic (inconsistent safety factors)factors)
�� LRFDLRFD——Reliability based Reliability based
�� ASD load combinations not maintainedASD load combinations not maintained
�� Ease of designing with multiple materials that Ease of designing with multiple materials that use LRFDuse LRFD
�� Size benefits with multiple transient loadsSize benefits with multiple transient loads
�� Consistent with FEMA 356 (performance based Consistent with FEMA 356 (performance based design codes)design codes)
LRFD Design Concepts
�� Safety Limit StateSafety Limit State
�� Factored Loads Factored Loads
(Demand)(Demand)——LargerLarger
�� Reduced Nominal Reduced Nominal
StrengthStrength–– φφRRnn
(Capacity)(Capacity)——LargerLarger
�� Serviceability Limit Serviceability Limit
StateState
�� Unfactored Unfactored
LoadsLoads——samesame
�� Mean material Mean material
strength and strength and
stiffnessstiffness——samesame
LRFD Statistical
Methodology
AF & PA, 2005 NDS e-course
LRFD Nuts and Bolts
�� SpecificSpecific
�� ff——demand stress (e.g. demand stress (e.g. PPuu/A)/A)
�� FF’’nn——LRFD level adjusted stress LRFD level adjusted stress
(capacity)(capacity)
nFf '≤
�� Example (Sawn Lumber in Bending)Example (Sawn Lumber in Bending)
�� FF’’bb==FFbbCCMMCCttCCLLCCFFCCfufuCCiiCCrrKKFFφφbbλλ
nRQ φλα ≤�� Basic RelationshipBasic Relationship
LRFD Adjustment
Factors
2005 NDS
LRFD Nuts and Bolts
(Cont.)
�� ““AdjustedAdjusted”” strength, rather than strength, rather than ““allowableallowable””
�� Three new adjustment factorsThree new adjustment factors
�� KKFF——Format Conversion Factor Format Conversion Factor (ASTM D 5457)(ASTM D 5457)
�� Generally 2.16/Generally 2.16/φφ�� Rearranged Rearranged φφKKFF=2.16=2.16
�� φφ——Strength Reduction FactorStrength Reduction Factor
�� λλ——Time Effect FactorTime Effect Factor
�� Essentially only one additional adjustment Essentially only one additional adjustment factorfactor
LRFD Specific Adjustment
Factors
2005 NDS
2005 NDS
LRFD Specific Adjustment
Factors (Cont.)
2005 NDS
Beams and Columns
�� Behavioral equations typically sameBehavioral equations typically same
�� Very minor adjustments to FVery minor adjustments to FbEbE and and FFcEcE
�� Shear increase from 2001 NDS maintainedShear increase from 2001 NDS maintained
2
'min20.1
BR
E
bEF =��
( )2'min822.0
dl
E
cEe
F =��
�� EE’’minmin——for stability, 5for stability, 5thth percentile, App Dpercentile, App D
�� Use EUse E’’ for deflectionfor deflection
Wind and Seismic
Supplement
�� Design guidance for lateral loadsDesign guidance for lateral loads
�� ChaptersChapters
1)1) Designer FlowchartDesigner Flowchart
2)2) General Design RequirementsGeneral Design Requirements
3)3) Members and ConnectionsMembers and Connections
4)4) Lateral ForceLateral Force--Resisting Resisting
SystemsSystems
�� GeneralGeneral
�� Wood DiaphragmsWood Diaphragms
�� Wood Shear WallsWood Shear Walls
�� Appendix A (Plywood tables)Appendix A (Plywood tables)
Diaphragms
�� Rigid/Flexible definedRigid/Flexible defined
�� Based on relative deflectionBased on relative deflection
�� Deflection equationsDeflection equations
�� Limits on diaphragms resisting load Limits on diaphragms resisting load
from concrete and masonry wallsfrom concrete and masonry walls
�� 33--sided diaphragms discussedsided diaphragms discussed
�� Cantilevered diaphragms permittedCantilevered diaphragms permitted
Diaphragms (Cont.)
�� Capacities for structural sheathingCapacities for structural sheathing
�� Wind and Seismic values differentWind and Seismic values different
�� Values for lumber diaphragmsValues for lumber diaphragms
�� Tables contain GTables contain Gaa (shear stiffness)(shear stiffness)
�� GGaa includes nail slip termincludes nail slip term
�� Multiply table values by Multiply table values by φφDD=0.8 =0.8
Diaphragm Table
2005 NDS
Diaphragm Table
2005 NDS
Shear Walls
�� Deflection equationDeflection equation
�� Guidelines for double sheathed wallsGuidelines for double sheathed walls
�� Aspect ratio criteria remains same as IBC Aspect ratio criteria remains same as IBC 20032003
�� Perforated shear wall valuesPerforated shear wall values
�� TablesTables
�� Structural Panels [Tab 4.3A]Structural Panels [Tab 4.3A]
�� Gypsum and Cement Plaster [Tab 4.3B]Gypsum and Cement Plaster [Tab 4.3B]
�� Lumber [Tab 4.3C]Lumber [Tab 4.3C]
�� Plywood [Tab A.4.3A]Plywood [Tab A.4.3A]
Shear Walls (Cont.)
�� Shear Wall FramingShear Wall Framing
�� 22”” NominalNominal——TypicalTypical
�� 33”” WhenWhen
�� Nails 2Nails 2”” O.C. or lessO.C. or less
�� 10d @ 310d @ 3”” O.C.O.C.
�� Nominal Capacity (vNominal Capacity (vss)>700 lb/ft)>700 lb/ft
•• For seismic design category D, E, FFor seismic design category D, E, F
�� Requirements irrespective of ASD or LRFDRequirements irrespective of ASD or LRFD
Shear Wall Table
2005 NDS
Shear Wall Table
2005 NDS
Mechanical Connectors
�� Same behavioral Same behavioral
equationsequations
�� Check Local Wood Check Local Wood
StressesStresses
�� Multiple FastenersMultiple Fasteners
�� Based on Based on
Mechanics ORMechanics OR
�� Appendix EAppendix E
�� For both ASD & For both ASD &
LRFDLRFD
2005 NDS
Mechanical Fastener:
Local Wood Failure Modes
2005 NDS
�� Local Wood Stress Local Wood Stress
ModesModes
�� Net Section Net Section
Tension Tension
�� Row TearRow Tear--outout
�� Group TearGroup Tear--outout
Mechanical Fastener
Adjustment Factors
2005 NDS
Pre-Engineered
Connectors
�� Convert using ASTM D5457Convert using ASTM D5457--93 (1998)93 (1998)
�� Multiply ASD value by Multiply ASD value by φφ and and λ (λ (CCMM, C, Ct)t)
�� KKFF
1996 LRFD Manual- Pre-Engineered Metal
Connectors, Supplement
2005 NDS Learning
�� AF&PA eAF&PA e--coursecourse
�� http://www.awc.org/Helhttp://www.awc.org/HelpOutreach/eCourses/SpOutreach/eCourses/STD104/NDS2005.pdfTD104/NDS2005.pdf
�� AWC and AF&PA web AWC and AF&PA web sitessites——misc. papersmisc. papers
�� Structural Wood Design Structural Wood Design Using ASD and LRFD Using ASD and LRFD (Workbook)(Workbook)
�� ASD/LRFD Manual for ASD/LRFD Manual for Engineered Wood Engineered Wood Construction 2005 Construction 2005 EditionEdition
�� 2005 NDS2005 NDS
�� 2005 Design Value 2005 Design Value
SupplementSupplement
�� 2005 Wind & Seismic 2005 Wind & Seismic
SupplementSupplement
�� ASD/LRFD Manual ASD/LRFD Manual
for Engineered Wood for Engineered Wood
Construction 2005 Construction 2005
EditionEdition——Available Available
December 2005?December 2005?
2005 NDS Design Aids
Summary
�� 2005 NDS2005 NDS——dual formatdual format
�� LRFD advantageous LRFD advantageous
because:because:
�� StateState--ofof--thethe--art art
�� Reliability basedReliability based
�� Consistent with other Consistent with other
material codesmaterial codes
�� Size benefitsSize benefits
�� Consistent with FEMA Consistent with FEMA
356356
�� LRFD adds essentially 1 LRFD adds essentially 1
adjustment factoradjustment factor
�� Behavioral equations Behavioral equations
same as ASDsame as ASD
�� Design guide not Design guide not
availableavailable
�� Code currently availableCode currently available
�� Adopted in 2006 IBCAdopted in 2006 IBC