2005 nds- lrfd

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


�� 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


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

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

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