Designing with AWC’s National Design Specification®  (NDS®) for Wood Construction (NDS 2012)

Presented by:

Michelle Kam-Biron, PE, SE, SECB Director of Education Copyright © 2013 American Wood Council

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American Wood Council

The American Wood Council (AWC) provides wood design and construction information to assist building industry professionals, develops structural and fire performance data on a wide range of traditional and engineered wood products, and engages in long-term research.

American Wood Council

AWC provides technical expertise, education, and support on building codes, standards, and wood engineering challenges. www.awc.org [email protected]

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American Wood Council

American Wood Council Design Professional Membership: • Optional listing in AF&PA Design Professional Services Directory with description of professional services. • Member discounts on Technical Publications. • AWC IMPACT newsletter. • Wood Design Focus, the Forest Products Society quarterly journal of contemporary wood engineering. • Wood Design & Building, a quarterly North American magazine on design and construction of modern wood buildings. • Frequent updates on wood industry developments, association activity, new publications, and special reports on engineering, building codes, standards, fire technology, and research projects. • Access to technical information with a direct 800 phone number to AWC.

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American Wood Council

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Copyright Material This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission from AWC is prohibited.

© American Wood Council 2013

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Learning Objectives On completion of this course, participants will: 1. Be able to understand Load Resistance Factor Design (LRFD)  and how it applies to wood structural design. 2. Be familiar with the significant changes between the 2005  and 2012 NDS and supplement. 3. Be able to identify the similarities and differences with  respect to ASD, design values, and behavioral equations 4. Be able to analyze format and content within the 2012 NDS.

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Outline  Overview  LRFD Primer   NDS  Chapter‐by‐chapter discussion  Changes from previous editions  Summary  More Info.

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Outline  Overview   LRFD Primer  NDS  Chapter‐by‐chapter discussion  Changes from previous editions  Summary  More Info.

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NDS History 1991 1944

1973 1997

1962

1977 2001

1968

1982 2005

1971

1986

2012

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NDS History

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IBC 2006

 SECTION 2305  GENERAL DESIGN REQUIREMENTS FOR LATERAL‐ FORCE‐RESISTING SYSTEMS 2305.1 General.  Structures using wood shear walls and  diaphragms to resist wind, seismic and other lateral loads shall be  designed and constructed in accordance with the provisions of this  section. Alternatively, compliance with the AF&PA SDPWS shall be  permitted subject to the limitations therein and the limitations of  this code.  SECTION 2306  ALLOWABLE STRESS DESIGN 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 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. Copyright © 2013 American Wood Council

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NDS and Supplement

2005  16 Chapters  14 Appendices

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Governing Codes for Engineered Wood Design 2005 SDPWS (Special Design Provisions for  Wind and Seismic)  http://www.awc.org/Standards/SDPWS.html  Free download

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Future for Engineered Wood Design 2009 IBC  (International  Building Code)

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IBC 2009  SECTION 2305  GENERAL DESIGN REQUIREMENTS FOR LATERAL‐FORCE‐RESISTING SYSTEMS 2305.1 General. Structures using wood shear walls and diaphragms to resist wind, seismic  and other lateral loads shall be designed and constructed in accordance with the provisions  of this section. Alternatively, compliance with the AF&PA SDPWS shall be permitted subject  to the limitations therein and the limitations of this code. and the provisions of Sections  2305, 2306 and 2307.  SECTION 2306  ALLOWABLE STRESS DESIGN 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 Construction  SDPWS Special Design Provisions for Wind and Seismic  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 and AF&PA SDPWS.

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NDS and Supplement

2005 16 Chapters 14 Appendices

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Engineered Wood Design 2008 SDPWS (Special Design Provisions for  Wind and Seismic) mandatory  http://www.awc.org/pdf/2008WindSeismic.pdf  Free download

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NDS 2012 Approval ANSI approval  August 15, 2011

2012 IBC Reference

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IBC 2012  SECTION 2305  GENERAL DESIGN REQUIREMENTS FOR        LATERAL‐FORCE‐RESISTING  SYSTEMS 2305.1 General. Structures using wood – frame shear walls and or wood – frame  diaphragms to resist wind, seismic and or other lateral loads shall be designed and  constructed in accordance with AF&PA SDPWS and the applicable provisions of Sections  2305, 2306 and 2307.  SECTION 2306  ALLOWABLE STRESS DESIGN 2306.1 Allowable stress design. The design 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 Construction SDPWS Special Design Provisions  for Wind and Seismic  2307.1 Load and resistance factor design. The structural analysis design and construction  of wood elements and structures using load and resistance factor design shall be in  accordance with AF&PA NDS and AF&PA SDPWS.

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Engineered Wood Design 2008 SDPWS (Special Design Provisions for  Wind and Seismic) mandatory  http://www.awc.org/pdf/2008WindSeismic.pdf  Free download

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NDS and Supplement

2005  16 Chapters  14 Appendices

2012  16 Chapters  14 Appendices www.awc.org

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NDS & SDPWS

2005 NDS & SDPWS

2012 NDS & 2008 SDPWS

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Engineered Wood Design  Publications Updates/Errata  Comprehensive List  http://awc.org/publications/update/index.html  Free download

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Outline  Overview   LRFD Primer  NDS  Chapter‐by‐chapter discussion  Changes from previous editions  Summary  More Info.

Design Process

Demand  Capacity

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Design Process Load Support Conditions Geometry Materials Performance Fire Economics Aesthetics ….

Demand Capacity

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Design Concepts Two Limit State concerns:  Safety against failure or collapse  Serviceability (performance in service)

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Serviceability

Unfactored loads Mean (avg) material  strength values

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LRFD ‐ Safety  Factored loads  Material strength  values ‐ modified

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Property Variability Normal Distribution Curves x = mean x = standard deviation

x x

x

Relative Frequency

SCL x COVx =

I-Joist

x

Coefficient of variation

Load

Glulam MSR Lumber Visually Graded Lumber

Material Property Values Copyright © 2013 American Wood Council

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Engineered Wood Design

S>R Failure

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Statistical Model Normal Distribution Curves for Safety Function, Z fZ = fR - fS mZ = mR - mS

 z   R2   S2 Safety (or reliability ) Index



mz z

Probability of failure of structure

Performance Distribution (Z) www.awc.org

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Probability of Failure Pf  =  one failure expected for x number of structures  designed and built with a  given  Ex.  = 2.7 represents 1 failure for  every 100 structures or  members designed.

 5.2 4.7 4.2 3.7 3.2 2.7 2.2

Pf 1 : 10,000,000 1 : 1,000,000 1 : 100,000 1 : 10,000 1 : 1,000 1 : 100 1 : 10

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LRFD ‐ Range on  Structural Design   Range for Strength Various Materials   Pf

Low 2.4 1 : 25

Typical 2.6 1 : 63

High 2.9 1 : 251

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LRFD Design Equation Demand   Capacity n

  Q    Rn i=1   = Load Factor  = Reliability Index  = Time effect factor (replaces LDF) Copyright © 2013 American Wood Council

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Allowable Stress Design  What stays the same?  Same basic equation format  Same adjustment factors  Same behavioral equations

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LRFD vs. ASD Three new notations ‐ , , and KF Design loads (factored) for safety are  bigger Design loads (unfactored) for  serviceability are the same Material resistance values  are  bigger Load Duration Factor changes      to  Time Effect Factor Copyright © 2013 American Wood Council

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LRFD vs. ASD ASD

applied stress  allowable stress Theoretical safety margin applied to material stresses

Estimated Loads



Design Load

Adjusted Resistance

Tested material strength

Design values www.awc.org

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LRFD vs. ASD LRFD

factored load  factored resistance Member performance factor Load factors to account for variations in loads

 Estimated loads

Factored Design Load

Factored Design Resistance

Tested member resistance

Design values www.awc.org

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2012 NDS Factored Load Combinations ASCE 7‐10

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Chapter 2 – Adjustment Factors

Reliability indices or data confidence factors

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Appendix N – Adjustment Factors  tied to ASCE 7 Factored Loads:10 years)

Baseline 10 minutes (ASD uses 

Permanent

Long term Short term

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Chapter 2 – Adjustment Factors

RN = KF RASD KF converts reference design values (ASD normal load duration) to LRFD reference resistance

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NDS LRFD Specification Format Conversion Factor KF: RN = RASD

ASD

LRFD

RN = KF RASD

RASD reference strengths www.awc.org

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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 not been maintained in deference to LRFD load combinations www.awc.org

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Outline  Overview   LRFD Primer  NDS  Chapter‐by‐chapter discussion  Changes from previous editions  Summary  More Info.

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NDS 2012 Chapters 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

General Requirements for Building Design Design Values for Structural Members Design Provisions and Equations Sawn Lumber Structural Glued Laminated Timber Round Timber Poles and Piles Prefabricated Wood I-Joists Structural Composite Lumber Wood Structural Panels Mechanical Connections Dowel-Type Fasteners Split Ring and Shear Plate Connectors Timber Rivets Shear Walls and Diaphragms Special Loading Conditions Fire Design of Wood Members Commentary!!! www.awc.org

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NDS 2012 Supplement

1 2 3 4

Sawn Lumber Grading Agencies Species Combinations Section Properties Reference Design Values - Lumber and Timber - Non-North American Sawn Lumber - Structural Glued Laminated Timber - MSR and MEL

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NDS 2012 Appendices A. B. C. D. E. F. G. H. I. J. K. L.

M. N.

Construction and Design Practices Load Duration (ASD Only) Temperature Effects Lateral Stability of Beams Local Stresses in Fastener Groups Design for Creep and Critical Deflection Applications Effective Column Length Lateral Stability of Columns Yield Limit Equations for Connections Solution of Hankinson Equation Typical Dimensions for Split Ring and Shear Plate Connectors Typical Dimensions for Standard Hex Bolts, Hex Lag Screws, Wood Screws, Common, Box, and Sinker Nails Manufacturing Tolerances for Rivets and Steel Side Plates for Timber Rivet Connections Appendix for Load and Resistance Factor Design (LRFD) – Mandatory

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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)

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Chapter 1 – Design Loads Reference loads  Minimum load  standards ASCE 7 – 10

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NDS – Chapter 2

Chapter 2 – Adjustment Factors

Reliability indices or data confidence factors

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Appendix N – Adjustment Factors  tied to ASCE 7 Factored Loads:10 years)

Baseline 10 minutes (ASD uses 

Permanent

Long term Short term

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Chapter 2 – Adjustment Factors

Revised ASTM D5457-10

RN = KF RASD KF converts reference design values (ASD normal load duration) to LRFD reference resistance

Chapter 2 – Adjustment Factors Adjusts from reference to site conditions  CD time‐dependent

Baseline 10 years

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Chapter 2 – Adjustment Factors Adjusts from reference to site conditions  Ct

temperature

61

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Chapter 2 – Adjustment Factors Wet Service Factor, CM

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Wet Service Conditions 30

Wood EMC %

25 20

Temp 30 deg F

15

Temp 70 deg F Temp 130 deg F

10 5 0 0

20

40

60

80

100

Relative Humidity %

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%Strength at 12% Moisture Content

Wet Service Conditions 110 100 90

Impact Strength

80

Modulus of Elasticity

70

Modulus of Rupture Crushing Strength

60 50 40 12

14

16

18

20

22

24

26

28

30

Moisture Content of Wood (%)

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Wet Service Factor, CM NDS Supplement for lumber

NDS – Chapter 3

Chapter 3 – Behavioral Equations ASD vs LRFD – adjusted stresses from reference ASD

F′n = Fn CD

LRFD F′n = Fn KF n 

x adjustment factors

x adjustment factors

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Chapter 3 – Behavioral Equations Beams   CL beam stability

Critical Buckling Design Value for bending members

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Chapter 3 – Behavioral Equations  Beams   FbE Equivalence 

FbE 

1.20E'min K bEE'  R b2 R b2 2012/2005 NDS

2001 NDS

‐ Emin adjusted for safety for both ASD and LRFD processes ‐ RB = Slenderness Ratio

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Chapter 3 – Behavioral Equations Columns  CP  column stability

Critical Buckling Design Value for compression members Copyright © 2013 American Wood Council

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Chapter 3 – Behavioral Equations Columns   FcE equivalence FcE 

0.822E'min  le    d

2



2012/2005 NDS

K cEE'  le    d

2

2001 NDS

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Chapter 3 – Behavioral Equations Emin  1.03E(1  1.645(COVE )) / 1.66 E 1.03 1.66 COVE

= reference MOE = adjustment factor to convert E to a pure bending basis (shear-free) (use 1.05 for glulam) = factor of safety = coefficient of variation in MOE (NDS Appendix F)

OR Emin values published in NDS Supplement

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Chapter 3 – Behavioral Equations Tension members (tension parallel to grain) ASD

F′t = Ft CD

LRFD F′t = Ft KF t 

x adjustment factors

x adjustment factors

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Chapter 3 – Behavioral Equations Wood and tension perpendicular to grain    Not recommended per NDS 3.8.2

initiators: • notches • moment connections • hanging loads

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Chapter 3 – Behavioral Equations Combined bi‐axial bending and  axial compression (* if this  new third term is negative see  C 15.4)

New *

Chapter 3 – Behavioral Equations Bearing perpendicular to grain  F′c = Fc CM Ct Ci Cb (ASD)  F′c = Fc CM Ct Ci Cb Kf c (LRFD)

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NDS – Chapter 4

Chapter 4 – Lumber Design values    

Visually graded lumber MSR / MEL Timber Decking

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Chapter 4 – Lumber Lumber adjustment  factors  KF and 

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Chapter 4 – Lumber Lumber adjustment  factors  New KF and 

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Chapter 4 – Lumber Lumber adjustment  factors  CF ‐ size factor

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Chapter 4 – Lumber Lumber adjustment  factors

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Chapter 4 – Lumber Lumber adjustment  factors      

repetitive member Cr = 1.15 2” – 4” lumber < 24” o.c. 3 or more Load distributing element

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NDS – Chapter 5

Chapter 5 – Glued Laminated Timber Significant changes  New adjustment factors • Stress interaction • Shear reduction

 Clarified or added • Curved members • Double‐tapered • Tapered straight

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Chapter 5 – Glulam New adjustment  factors  Stress  interaction • Tapered • Timber Construction  manual

 Shear reduction • •

NDS footnote Non-prismatic

Chapter 5 – Glulam Clarified or added  Curved members  Double‐tapered  Tapered straight

Chapter 5 – Glulam Adjustment factors    

CV Volume Factor CL Beam Stability Factor Not cumulative with CL Min (Cv, CL)

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29

NDS – Chapter 6

Chapter 6 – Poles & Piles Poles ‐ post‐ frame Piles ‐ foundations

Chapter 6 – Timber Piles Design values  Significant changes from 2005 NDS  Design values moved to NDS Supplement

2005 NDS 2012 NDS

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Chapter 6 – Timber Poles 2005 NDS

2012 NDS

Chapter 6 – Poles & Piles Adjustment factors  Cct – condition treatment  Cls – load sharing  Ccs – critical section

untreated

single pile

NDS – Chapter 7

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31

Chapter 7 – I‐joists Design values  I‐joist conforming to ASTM D5055  M, V, EI, K – no changes

Evaluation Reports  Contain proprietary design

Chapter 7 – I‐Joists Beam stability factor  Braced compression flange • CL = 1.0

 Unbraced compression flange • Design as unbraced column

NDS – Chapter 8

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32

Chapter 8 – Structural Composite Lumber  • No changes from 2005 NDS • Evaluation Reports – Contain proprietary design



Relative Frequency

x = mean

x

 COVxx= x

SCL I-Joist Glulam MSR Lumber

Load

Visually Graded Lumber Material Property Values

Chapter 8 – Structural Composite Lumber   Adjustment factors

 CV – Volume Factor • Cv < 1.0 Not cumulative with lateral stability factor, CL  then (Cv, CL) • Cv > 1.0 Cumulative with lateral stability factor, CL

min. 

Chapter 8 – Structural Composite Lumber  Adjustment factors  Cr Repetitive Member Factor= 1.04  Cr is different  than lumber • Applies to Fb only

(Cr lumber = 1.15) 

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NDS – Chapter 9

Chapter 9 – Wood Structural Panels  Design values – obtain from an approved source         

FbS FtA Fvtv Fs FcA EI EA Gvtv Fc

Chapter 9 – Wood Structural Panels Adjustment factors  apply Fb & Ft  CG ‐ grade & construction • Removed (no longer used  by wsp industry)

 Cs ‐ panel size • Clarified • Moved from commentary

Copyright © 2013 American Wood Council. All rights reserved.

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Chapter 9 – Wood Structural Panels Adjustment factors  CM ‐ wet service  Ct ‐ temperature

NDS – Chapter 10

Chapter 10 – Mechanical Connections Design issues Reference design values • Chapter 11 – dowel‐type connectors (nails, bolts, lag/wood screws) • Chapter 12 – split rings and shear plates • Chapter 13 – timber rivets

Adjustment factors No significant changes Connections session

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35

NDS – Chapter 11

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

Chapter 11 - Dowels

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Chapter 11 - Dowels

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 L

Wood Screws

2D

Nails & Spikes

2D

E, ℓs, ℓm < p – E / 2

Copyright © 2013 American Wood Council. All rights reserved.

37

Chapter 11 ‐ Dowel Bearing Strength  Wood Structural Panels  D < ¼

Chapter 11 ‐ Perp to Grain Distance Glulam only  Moisture content

NDS – Chapter 12

Copyright © 2013 American Wood Council. All rights reserved.

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Chapter 12 – Split Rings and Shear Plates Geometry factor, C  Side Grain

Chapter 12 – Split Rings and Shear Plates Geometry factor, C  End Grain

NDS – Chapter 13

Copyright © 2013 American Wood Council. All rights reserved.

39

Chapter 13 – Timber Rivets Many applications

Chapter 13 – Timber Rivets Parallel to grain Timber rivet capacity  Proper application of CD

Timber Rivets – Design  2005 NDS

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40

Timber Rivets – Design  2012 NDS

Chapter 13 – Timber Rivets Timber rivet capacity  Proper application of CD  Parallel to grain timber rivet capacity • Pr = 280 p0.32 nR nC (13.2‐1) 188 2012 NDS

 Perpendicular to grain timber rivet capacity • Qr = 160 p0.32 nR nC 108 2012 NDS

NDS – Chapter 14

Copyright © 2013 American Wood Council. All rights reserved.

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NDS – Chapter 14

Chapter 14 – Shear Walls and Diaphragms ANSI / AWC SDPWS  2008 standard Recorded Webinar •2005/2008 SDPWS •Diaphragm Deflection •www.woodworks.org

Copyright © 2013 American Wood Council

www.awc.org

NDS – Chapter 15

Copyright © 2013 American Wood Council. All rights reserved.

42

Chapter 15 – Special Loading Built‐up columns  Flatwise bending check  Consistent with Chapter 3

Copyright © 2013 American Wood Council

www.awc.org

NDS – Chapter 16

Chapter 16 – Fire Design No significant changes

Copyright © 2013 American Wood Council

Copyright © 2013 American Wood Council. All rights reserved.

www.awc.org

43

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

Columns Beams  Tension Members ASD only

 Products    

Lumber Glulam SCL Decking

…

Copyright © 2013 American Wood Council

www.awc.org

Chapter 16 – Fire (ASD) DCA 2 Design of Fire-Resistive Exposed Wood Members

•Limited to 1-Hour – IBC 721.6.1.1 approach •Simplified •Beams/Columns Copyright © 2013 American Wood Council

www.awc.org

NDS – Appendices

Copyright © 2013 American Wood Council. All rights reserved.

44

NDS 2012 Appendices 2012 A Construction and Design Practices B Load Duration C Temperature Effects D Lateral Stability of Beams E Local Stresses in Fastener Groups F Design for Creep and Critical Deflection Applications G Effective Column Length H Lateral Stability of Columns I Yield Limit Equations for Connections J Solution of Hankinson Equation K Typical Dimensions for Split Ring and Shear Plate Connectors L 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) Copyright © 2013 American Wood Council

www.awc.org

Appendix E Example E.8  Acritical check

Copyright © 2013 American Wood Council

www.awc.org

Appendix L

Copyright © 2013 American Wood Council

Copyright © 2013 American Wood Council. All rights reserved.

www.awc.org

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Appendix N

Copyright © 2013 American Wood Council

www.awc.org

NDS – Commentary

2012 NDS – Notable Changes Chapter 5 – Glulam Chapter 6 – Poles and Piles Chapter 12 – Split Rings &  Shear Plates

Copyright © 2013 American Wood Council. All rights reserved.

46

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

Outline  Overview   LRFD Primer  NDS  Chapter‐by‐chapter discussion  Changes from previous editions  Summary  More Info.

Southern Pine Design Values  ALSC approves design values  June 1, 2012  AWC compiles them

 NDS Supplement  More information  Ww.spib.org  www.southernpine.com

Copyright © 2013 American Wood Council

Copyright © 2013 American Wood Council. All rights reserved.

www.awc.org

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Wood Design Package

Support Documents 2nd Quarter 2012

Wood Design Package NDS + Commentary NDS Supplement ASD/LRFD Manual

Supplement:

Design Values for Wood Construction

Print copies available 

MANUAL

then Copyright © 2013 American Wood Council

www.awc.org

More Details

White paper ‐ www.awc.org Comprehensive table Section‐by‐section changes Structure Magazine January 2012

Copyright © 2013 American Wood Council

www.awc.org

Engineered Wood Design NDS Changes  http://awc.org/pdf/2012‐NDS‐Changes‐Web.pdf  Free download

Copyright © 2013 American Wood Council

Copyright © 2013 American Wood Council. All rights reserved.

www.awc.org

48

More Details 2008 SDPWS (Special Design Provisions for  Wind and Seismic) Changes  http://awc.org/pdf/WDF18‐3_SDPWS‐08.pdf  Free download

www.awc.org

Copyright © 2013 American Wood Council

More Details

http://www.awc.org/technic al/LRFDStrucEng.pdf White paper LRFD

www.awc.org

Copyright © 2013 American Wood Council

Questions? This concludes The  American Institute of  Architects Continuing  Education Systems  Course

www.awc.org [email protected] Copyright © 2013 American Wood Council

Copyright © 2013 American Wood Council. All rights reserved.

www.awc.org

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