designing with awc’s 2012 national design specification

Copyright © American Wood Council 1

Designing with AWC’s 2012 National Design Specification® (NDS®) for Wood ConstructionJohn “Buddy” Showalter, PEVice President, Technology TransferAmerican Wood Council

Michelle Kam-Biron, PE, SE, SECBDirector of EducationAmerican Wood Council

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© American Wood Council 2014


Description

AWC's National Design Specification (NDS) for WoodConstruction 2012 is the dual format Allowable StressConstruction 2012 is the dual format Allowable StressDesign (ASD) and Load and Resistance Factor Design(LRFD) document referenced in US building codes andused to design wood structures worldwide. Participants willlearn about changes in the 2012 NDS and Supplementrelative to previous editions and gain an overview of thestandardstandard.

Learning Objectives

On completion of this course, participants will:

• Be able to understand Load and Resistance Factor Design• Be able to understand Load and Resistance Factor Design (LRFD) and how it applies to wood structural design.

• Be familiar with the significant changes between the 2005 and 2012 NDS and supplement.

• Be able to identify the similarities and differences with respect to ASD, design values, and behavioral equations

• Be able to analyze format and content within the 2012 e ab e to a a y e o at a d co te t t t e 0NDS.


Polling Question

1. What is your profession?

a) Architect

b) Engineer

c) Code Official

d) Building Designer

e) Other

Outline

• Overview• LRFD Primer• LRFD Primer • NDS

• Chapter-by-chapter discussion

• Changes from previous editions

• Summary

M I f• More Info.


Outline

• Overview • LRFD Primer• LRFD Primer• NDS



• Summary

M I f• More Info.

NDS History

1944 1973 1991

1962

1968

1977

1982

1997

2001

1971 1986 2005


NDS History

International Building Code

• SECTION 2306 ALLOWABLE STRESS DESIGN

2306 1 Allowable stress design The structural• 2306.1 Allowable stress design. The structural analysis and construction of wood elements in structures using allowable stress design shall be in accordance with the following applicable standards:

• American Forest & Paper Association.

• NDS National Design Specification for Wood Constructionfor Wood Construction

• 2307.1 Load and resistance factor design.

• The structural analysis and construction of wood elements and structures using load and resistance factor design shall be in accordance with AF&PA NDS.


NDS and Supplement

• 2005• 16 Chapters• 16 Chapters• 14 Appendices

NDS 2012 Approval

• ANSI approval

• August 15, 2011

• 2012 IBC Reference


NDS and Supplement

2012• 16 Chapters• 14 Appendices

2005• 16 Chapters• 14 Appendices

Wood Design Package

2005 Wood Design Package

2012 Wood Design Package


Addenda/Errata

• Publications Addenda/Errata

• Comprehensive List

• http://awc org/publications/update/index html• http://awc.org/publications/update/index.html

• Free download

Outline




• Summary

M I f• More Info.


Design Process

Demand Capacity

Design Process

LoadSupport Conditions DemandDemandSupport ConditionsGeometryMaterialsMaterialsPerformancePerformanceFireEconomics

DemandDemand

CapacityCapacity

EconomicsAesthetics….


Design Concepts

Two Limit State concerns:

• Serviceability (performance in-service)

• Safety against failure or collapse

Serviceability

• Unfactored loads• Mean (avg) material strength values


LRFD - Safety

• Factored loads• Material strengthMaterial strength values - modified

xx = standard deviation

x

xx = mean

SCL

Structural Property VariabilityNormal Distribution Curves

COVx =x

x

Vi ll G d dVi ll G d d

MSR Lumber

Glulam

I-Joist

SCL

Load

Rel

ativ

e F

req

uen

cy

Coefficient of variation

Material Property Values

Visually Graded Visually Graded LumberLumber

R


Engineered Wood Design

S > RFailure

Statistical Model

• Normal Distribution Curves for Safety Function, Z

fZ = fR - fS

22SRz

mZ = mR - mS

Probability of

Safety (or reliability ) Index

z

zm

Probability of failure of structure

Performance Distribution (Z)


Probability of Failure

• Pf = one failure expected for x number

Pfof structures designed and built with a given

• Safety (or reliability index) Ex. = 3.2 represents 1 failure for every 1 000 structures

Pf

5.2 1 : 10,000,000

4.7 1 : 1,000,000

4.2 1 : 100,000

3.7 1 : 10,000

3.2 1 : 1,000

2.7 1 : 100 every 1,000 structures or members designed.

2.2 1 : 10

LRFD - Range on

• Structural Design • Range for Strength Various Materials• Range for Strength Various Materials

Low Typical High 2.4 2.6 2.9 Pf 1 : 25 1 : 63 1 : 251


LRFD Design Equation

Demand Capacityp y

Q Q RRnn

n

i=1

b b = = Safety or Reliability Index = = Load Factor = = Reliability Index == Time effect factor (replaces LDF)

Allowable Stress Design

• What stays the same?• Same basic equation format• Same basic equation format• Same adjustment factors• Same behavioral equations


LRFD vs. ASD

• Three new notations - , , and KF• Design loads (factored) for safety are g ( ) y

bigger• Design loads (unfactored) for

serviceability are the same• Material resistance values

are biggerd h• Load Duration Factor changes

to Time Effect Factor

LRFD vs. ASD

Theoretical safety

•ASD•applied stress allowable stress

Theoretical safety margin applied to material stresses

Tested material strengthEstimated

LoadsDesign Load

Adjusted Resistance

Design values


LRFD vs. ASD

•LRFD•factored load factored resistance

Member performance factorfactor

Load factors to account for variations in loads

Tested member resistance

Estimated loads

Factored Design Load

Factored Design Resistance

Design values

2012 NDS

• Factored Load Combinations ASCE 7-10


•Format Conversion Factor KF:

NDS 2012 LRFD Specification

R C RRN = CDRASDASD

RN = KF RASD

LRFD

RASD reference strengths

2012 NDS

Reliability indices or data confidence factors


• tied to ASCE 7 Factored Loads:

2012 NDSBaseline 10 minutes (ASD uses 10 years)

Long term

Permanent

Short term

2012 NDS

RN = KF RASD

KF converts reference design values (ASD normal load duration) to LRFD reference resistance


Why use LRFD?

• Ease of designing with multiple materials

• Does not penalize material strength for unknowns on loads

• Realize efficiencies with

• Multiple transient live loads

• Extreme event loads

• ASD load combinations have notASD load combinations have not been maintained in deference to LRFD load combinations

Polling Question

2. Format Conversion Factor, KFa) is only used with ASD

b) is not necessary when calculating shear strengthb) is not necessary when calculating shear strength using LRFD

c) converts ASD material reference design values from the 2012 NDS Supplement for use with LRFD

d) converts LRFD material reference design values from the 2012 NDS Supplement for use with ASD


Outline




• Summary

M I f• More Info.

NDS 2012 Chapters1. General Requirements for Building Design2. Design Values for Structural Members3. Design Provisions and Equations4. Sawn LumberSa u be5. Structural Glued Laminated Timber6. Round Timber Poles and Piles7. Prefabricated Wood I-Joists8. Structural Composite Lumber9. Wood Structural Panels10. Mechanical Connections11. Dowel-Type Fasteners12. Split Ring and Shear Plate Connectors13. Timber Rivets14. Shear Walls and Diaphragms15. Special Loading Conditions16. Fire Design of Wood Members

Commentary!!!


NDS 2012 Supplement

1. Sawn Lumber Grading Agencies2. Species Combinations3. Section Properties4. Reference Design Values

• Lumber and Timber• Non-North American Sawn

LumberStructural Glued Laminated• Structural Glued Laminated Timber

• MSR and MEL• Timber Poles and Piles

A. Construction and Design PracticesB. Load Duration (ASD Only)C. Temperature EffectsD. Lateral Stability of BeamsE L l St i F t G

NDS 2012 Appendices

E. Local Stresses in Fastener GroupsF. Design for Creep and Critical Deflection

ApplicationsG. Effective Column LengthH. Lateral Stability of ColumnsI. Yield Limit Equations for ConnectionsJ. Solution of Hankinson EquationK. Typical Dimensions for Split Ring and Shear

Plate ConnectorsL Typical Dimensions for Standard Hex BoltsL. Typical Dimensions for Standard Hex Bolts,

Hex Lag Screws, Wood Screws, Common, Box, and Sinker Nails

M. Manufacturing Tolerances for Rivets and Steel Side Plates for Timber Rivet Connections

N. Appendix for Load and Resistance Factor Design (LRFD) – Mandatory


NDS – Chapter 1

Chapter 1 - Terminology

fb ≤ Fb'

Reference design values (Fb, Ft, Fv, Fc, Fc, E, Emin)

Adjusted design values (Fb', Ft', Fv', Fc', Fc', E', Emin')Allowable (changed in the 2005)


Chapter 1 – Design Loads

• Reference loads

Minimum load standards• Minimum load standards

• ASCE 7 – 10

NDS – Chapter 2


Chapter 2 – Adjustment Factors

Reliability indices or data confidence factors

tied to ASCE 7 Factored Loads: Baseline 10 minutes (ASD uses 10 years)

Appendix N – Adjustment Factors

Sh t t

Long term

Permanent

Short term



Revised ASTM D5457-10

RN = KF RASD

KF converts reference design values (ASD normal load duration) to LRFD reference resistance


• Adjusts from reference to site conditions• CD time-dependentCD t e depe de t

Baseline 10 years



• Adjusts from reference to site conditions• Ct temperature factorCt te pe atu e acto

Exposed for “sustained” period


• Wet Service Factor, CM


Wet Service Conditions

25

30

%

0

5

10

15

20

Wo

od

EM

C %

Temp 30 deg F

Temp 70 deg F

Temp 130 deg F

0 20 40 60 80 100

Relative Humidity %

100

110

e C

on

ten

t

Wet Service Conditions

40

50

60

70

80

90

%S

tre

ng

th a

t 1

2%

Mo

istu

re

Impact Strength

Modulus of Elasticity

Modulus of Rupture

Crushing Strength

40

12 14 16 18 20 22 24 26 28 30

Moisture Content of Wood (%)

%


Wet Service Factor, CM

• Sawn lumber MC < 19% considered dry• Otherwise, NDS Supplement for lumberOtherwise, NDS Supplement for lumber

Polling Question3. Temperature Factor Ct applies to conditions

where the wood temperatures exceed:a) 100 degrees F for sustained periods of timea) 100 degrees F for sustained periods of time

b) 100 degrees F for short period of time

c) 100 degrees F at any time

d) 100 degrees C at any time


NDS – Chapter 3

Chapter 3 – Behavioral Equations

ASD vs LRFD – adjusted stresses from reference

• ASD F′n = Fn CD x adjustment factors

• LRFD F′n = Fn KF n x adjustment factors



• Beams • CL beam stabilityy

•

Critical Buckling Design Value for bending members


• Beams

FbE Equivalence

• Emin adjusted for safety for both ASD and LRFD processes

RB Slende ness Ratio

2b

'bE

2b

'min

bE REK

RE20.1F

2012/2005 NDS

2001 NDS

• RB = Slenderness Ratio



• Columns• CP column stability

Critical Buckling Design Value for compression members

Chapter 3 – Behavioral Equations• Columns

• FcE equivalence

2e

'cE

2e

'min

cE

dl

EK

dl

E822.0F

2001 NDS

2012/2005 NDS



66.1/))(645.11(03.1min ECOVEE E = reference MOE

OREmin values published in NDS Supplement

E = reference MOE1.03 = adjustment factor to convert E to a pure bending

basis (shear-free) (use 1.05 for glulam)1.66 = factor of safetyCOVE = coefficient of variation in MOE (NDS Appendix F)


Tension members (tension parallel to grain)

• ASD F′t = Ft CD x adjustment factors

• LRFD F′t = Ft KF t x adjustment factors



• Wood and tension perpendicular to grain

• Not recommended per NDS 3.8.2

initiators:• notches

• moment connections

• hanging loads


• Combined bi-axial bending and axial compression


• Combined bi-axial bending and axial compression


New

Added to account for possible negative value in denonimator of third term of equation 3.9-3


• Bearing perpendicular to grain• F′c = Fc CM Ct Ci Cb (ASD)c c M t i b

• F′c = Fc CM Ct Ci Cb Kf c (LRFD)


NDS – Chapter 4

Chapter 4 – Lumber

•Design valuesVisually graded lumber• Visually graded lumber

• MSR / MEL

• Timber

• Decking



•Lumber adjustmentadjustment factors• KF and


•Lumber adjustmentadjustment factors• KF and


Chapter 4 – Lumber• Lumber adjustment factors

• CF - size factor

Chapter 4 – Lumber• Lumber adjustment factors



• Lumber adjustment factors

• repetitive member

• Cr = 1.15

• 2” – 4” lumber

• < 24” o.c.

• 3 or more

• Load distributingLoad distributing

element

NDS – Chapter 5


• Significant changes

• New adjustment factors

St i t ti

Chapter 5 – Glulam

• Stress interaction

• Shear reduction

• Clarified or added

• Curved members

• Double-taperedp

• Tapered straight


• New adjustment factors

• Stress interactiond• Tapered

• Timber Construction

manual

• Shear reduction• NDS footnote• Non-prismaticNon-prismatic



• Clarified or added

• Curved membersCurved members

• Double-tapered

• Tapered straight


• Adjustment factors

• CV Volume Factor

C B St bilit F t• CL Beam Stability Factor

• Not cumulative with CL

• Min (Cv, CL)


Polling Question4. The two new adjustment factors were added

to glued laminated timber design are stress interaction and shear reduction factors. T/Finteraction and shear reduction factors. T/F

True

NDS – Chapter 6


Chapter 6 – Poles & Piles

• Poles - post-framePil f d ti• Piles - foundations

Chapter 6 – Timber Piles• Design values

• Significant changes from 2005 NDS

Design values moved to NDS Supplement• Design values moved to NDS Supplement

2005 NDS

2012 NDS


Chapter 6 – Timber Poles

2005 NDS

2012 NDS

Chapter 6 – Poles & Piles


• Cct – condition treatment

• Cls – load sharing

• Ccs – critical section


NDS – Chapter 7

Chapter 7 – I-joists

• Design values

• M, V, EI, K – no changes

• Evaluation Reports

• Contain proprietary design


Chapter 7 – I-Joists

•Beam stability factor

• Braced compression flangeBraced compression flange

• CL = 1.0

• Unbraced compression flange

• Design as unbraced column

NDS – Chapter 8


Chapter 8 – Structural Composite Lumber

• No changes from 2005 NDS• Evaluation Reports

Contain proprietary design

x

x = mean

COVx =xx

MSR Lumber

Glulam

I-JoistSCL

ativ

e F

req

uen

cy

• Contain proprietary design

Material Property Values

Visually Graded Visually Graded LumberLumber

Load

Rel

a



• CV – volumeC 1 0 N l i i h b bili f C h i (C C )Cv < 1.0 Not cumulative with beam stability factor, CL - then min. (Cv, CL)

Cv > 1.0 Cumulative with beam stability factor, CL




• C Repetitive Member Factor= 1 04Cr Repetitive Member Factor 1.04• Cr is different than lumber (Cr lumber = 1.15)

• Applies to Fb only

NDS – Chapter 9


Chapter 9 – Wood Structural Panels

• Design values – obtain from an approved source

• FbSb

• FtA

• Fvtv

• Fs

• FcA

EI• EI

• EA

• Gvtv

• Fc


• Adjustment factors apply Fb & Ft

• CG - grade & construction

• Removed (no longer used by wsp industry)

• Cs - panel size

• Clarified

• Moved from commentary




• CM - wet serviceCM wet service

• Ct - temperature

NDS – Chapter 10


Chapter 10 – Mechanical Connections

• Design issues

• Reference design values

Ch t 11 d l t t ( il b lt l / d )• Chapter 11 – dowel-type connectors (nails, bolts, lag/wood screws)

• Chapter 12 – split rings and shear plates

• Chapter 13 – timber rivets


• No significant changes

Connections session• Connections session

NDS – Chapter 11


Chapter 11 - Tabulated Values• Consistent titles and footnotes• Penetration assumptions in titles

Chapter 11-Dowels


Chapter 11-Dowels

Chapter 11-Dowels


Chapter 11-Dowels

Threaded length < lm/4 lm

Dia. Fastener = D

Dia. Fastener = D

Threaded length < lm/4

lm

Chapter 11-Dowels

lm

Dia. Fastener = Dr


Chapter 11 - Dowels

Provide tools for the analysis• gaps between members• gaps between members• various fastener moment resistance

configurations• fasteners through hollow members• fasteners with tapered tips

http://www.awc.org/publications/TR/index.php

Chapter 11 - Tabulated Values

• New post frame ring shank tables• Based on ASTM F1667


Chapter 11 - Dowel Bearing Length

Fastener Type Tip Length, E

Lag Screws Appendix LLag Screws Appendix L

Wood Screws 2D

Nails & Spikes 2D

E, ℓs, ℓm < p – E / 2, s, m p /

Chapter 11 - Dowel Bearing Strength • Wood Structural Panels

• D < ¼


Chapter 11 - Perp to Grain Distance

• Glulam only

• Moisture content

• Glulam only

• Moisture content

Polling Question

5. TR 12 includes general dowel equations and provides tools for the analysis of:

a) gaps between membersa) gaps between members

b) fasteners through hollow members

c) fasteners with tapered tips

d) All of the above

e) None of the above


NDS – Chapter 12

Chapter 12 – Split Rings and Shear Plates

• Geometry factor, CD

• Side Grain


Chapter 12 – Split Rings and Shear Plates

• Geometry factor, CD

• End Grain

NDS – Chapter 13


Chapter 13 – Timber Rivets

• Many applications




• Parallel to grain

• Timber rivet capacity

• Proper application of CD

Timber Rivets – Design 2005 NDS


Timber Rivets – Design 2012 NDS

Chapter 13 – Timber Rivets• Timber rivet capacity

• Proper application of CD

Parallel to grain timber rivet capacity• Parallel to grain timber rivet capacity

• Pr = 280 p0.32 nR nC (13.2-1)

• Perpendicular to grain timber rivet capacity

• Qr = 160 p0.32 nR nC

188 2012 NDS

108 2012 NDS



• Maximum distance perpendicular to grain between outermost rows of rivets shall be 12

• Consistent with glulam

NDS – Chapter 14


NDS – Chapter 14

• ANSI / AWC SDPWS

2008 standard

Chapter 14 – Shear Walls and Diaphragms

• Recorded Webinar

•Online course 2005/2008

SDPWS

•Diaphragm Deflection

•www.awc.org


NDS – Chapter 15

Chapter 15 – Special Loading

• Built-up columns

• Flatwise bending check

• Consistent with Chapter 3

New


NDS – Chapter 16

Chapter 16 – Fire (ASD)• Fire resistance up to two hours

• Columns• Beams

T i M b

…

• Tension Members• ASD only

• Products• Lumber• Glulam• SCL

D ki• Decking


Chapter 16 – Calculated Resistance

• Fire resistance of exposed wood members may be calculated usingmay be calculated using the provisions of NDS Chapter 16

Fire Resistance

Glulam SteelGlulam Steel


Performance of Wood vs. Steel

T h i l R t N 10

Chapter 16 – Fire (ASD)

Technical Report No. 10


Code Updates -Design of Fire

Chapter 16 – Fire (ASD)

Design of Fire-Resistive Exposed Wood Members

http://www.awc.org/publications/download phpblications/download.php

Polling Question

6. The IBC includes provisions for calculating fire resistance of exposed wood members and wood decking for up to two hoursand wood decking for up to two hours. True/False

True


NDS – Appendices

2012A Construction and Design PracticesB Load DurationC Temperature EffectsD Lateral Stability of Beams

NDS 2012 Appendices

ate a Stab ty o ea sE Local Stresses in Fastener GroupsF Design for Creep and Critical Deflection

ApplicationsG Effective Column LengthH Lateral Stability of ColumnsI Yield Limit Equations for ConnectionsJ Solution of Hankinson EquationK Typical Dimensions for Split Ring and

Shear Plate Connectorsi l i i f d dL Typical Dimensions for Standard Hex

Bolts, Hex Lag Screws, Wood Screws, Common, Box, and Sinker Nails

M Manufacturing Tolerances for Rivets and Steel Side Plates for Timber Rivet Connections

N Appendix for Load and Resistance Factor Design (LRFD)


Appendix E

• Example E.8• Acritical checkAcritical check

Appendix L


Appendix N

NDS – Commentary


Outline

• Overview• LRFD Primer • NDS


• Changes from previous editionsSummary• Summary

• More Info.

2012 NDS – Notable Changes

• Chapter 5 – GlulamChapter 6 Poles and Piles• Chapter 6 – Poles and Piles

• Chapter 12 – Split Rings & Shear Plates


NDS 2012 Supplement

• New nominal and minimum Timber sizes per PS 20-10

• Section properties distinguish lumber, P&T, B&S

• New Coast Sitka Spruce & Yellow Cedar values

• Revised Northern Species bending and tension values

• Clarify Timber size factor adjustments

• New and revised values for several foreign species

• Revised glulam values - primary changes to shear

• New Tables 6A & 6B for Timber Poles and Piles

Southern Pine Design Values

• ALSC approves design values

• June 1, 2013

• AWC compiles them

• NDS Supplement

• More information

• www.spib.org

• www.southernpine.com


Wood Design Package

• Wood Design Package

• NDS + Commentary

MANUAL

Supplement: Design Values for Wood Construction

• NDS Supplement

• ASD/LRFD Manual

• Example Problems

• Almost complete

MANUAL

Future

2015


Coming in 2015 NDS/SDPWS

• NDS

• CLT Provisions

Franklin Elementary School

Franklin, West VirginiaArchitect: MSES Architects, Fairmont, WV Source: LignaTerra



Franklin, West Virginia46,200 sq. ft.8 week assembly

Source: LignaTerra


Source: LignaTerra



Scheduled completion date: Winter 2015

Coming in 2015 NDS/SDPWS

• NDS

• CLT Provisions

• SDPWS

• Design Flexible and Open Front/Cantilever Diaphragms


2015 Special Design Provisions for Wind and Seismic

2015 SDPWS

Overview

• Ch. 2

• Removes definition of flexible and rigid diaphragms• Defines “Open-Front Structure” & “Subdiaphragm”

• Ch. 4

• Clarification of concrete and masonry wall anchorage• Revised Horizontal Distribution of Shear• Clarification of shear wall Aspect ratio adjustments


2015 SDPWS

2015 SDPWS


More Details

• White paper - www.awc.org

• Comprehensive table

• Section-by-section changes

• Structure Magazine• January 2012

Resources


Resources

Questions?

www.awc.org

[email protected]

designing with awc’s 2012 national design specification

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