National Design Specification for Wood Construction ... - WoodWorks

National Design Specification for Wood Construction

“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

Presented by:

Michelle Kam-Biron, PE, SE

Director, Education

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

© American Wood Council 2012

Learning Objectives At the end of this program, participants will be knowledgeable of:

1. Load Resistance Factor Design (LRFD) and how it applies to wood structural design. 2. Similarities and differences with respect to ASD, design values, and behavioral equations. 3. Format and content within the 2005 NDS. 4. Changes in the 2012 NDS and Supplement relative to previous editions.

1

NDS History

Outline • Overview • LRFD Primer • Chapter-by-chapter discussion

1944

1991

1973 1997

– Changes from previous editions

• Summary

1962

1977

2001

1968

1982

2005

1971

1986

– More information

2012

IBC 2006

NDS History •

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.

2

Governing Codes for Engineered Wood Design

NDS and Supplement

• 2005 SDPWS (Special Design Provisions for Wind and Seismic) – http://www.awc.org/Standards/SDPWS. html – Free download

2005 • 16 Chapters • 14 Appendices

IBC 2009

Future for Engineered Wood Design

• 2009 IBC (International Building Code)

•

•

•

SECTION 2305 GENERAL DESIGN REQUIREMENTS FOR LATERALFORCE-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.

3

NDS and Supplement

Engineered Wood Design • 2008 SDPWS (Special Design Provisions for Wind and Seismic) mandatory – http://www.awc.org/pdf/2008WindSeis mic.pdf – Free download


IBC 2009

NDS 2012 Approval • ANSI approval

•

SECTION 2305 GENERAL DESIGN REQUIREMENTS FOR LATERALFORCE-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.

– August 15, 2011

• 2012 IBC Reference

•

4

Engineered Wood Design

NDS and Supplement

• 2008 SDPWS (Special Design Provisions for Wind and Seismic) mandatory – http://www.awc.org/pdf/2008WindSeis mic.pdf – Free download 2005 • 16 Chapters • 14 Appendices

NDS & SDPWS


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

2005 NDS & SDPWS

2012 NDS & 2008 SDPWS

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Outline

Design Process • Overview • LRFD Primer • Chapter-by-chapter discussion – Changes from previous editions

• Summary – More information

Demand  Capacity

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

Design Concepts Two Limit State concerns: Demand Capacity

• safety against failure or collapse • Serviceability (performance in service)

6

Serviceability

LRFD - Safety

• Unfactored loads • Mean (avg) material strength values

• Factored loads • Material strength values - modified

Property Variability

Engineered Wood Design

Normal Distribution Curves x = standard deviation Relative Frequency

x x

x = mean

x

SCL

x COVx =

x

I-Joist

Coefficient of variation

Load

Glulam

S>R Failure

MSR Lumber Visually Graded Lumber

Material Property Values

7

Statistical Model

Probability of Failure

Normal Distribution Curves for Safety Function, Z fZ = fR - fS m Z = mR - m S

 z   R2   S2

Ex.  = 2.7 represents 1 failure for every 100 structures or members designed.

Safety (or reliability ) Index



mz z

Pf = one failure expected for x number of structures designed and built with a given 

 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

Probability of failure of structure

Performance Distribution (Z)

LRFD Design Equation

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

Low 2.4 1 : 25

Typical 2.6 1 : 63

Demand  Capacity High 2.9 1 : 251

n

  Q    Rn i=1   = Load Factor  = Reliability Index  = time effect factor (replaces LDF)

8

Allowable Stress Design

LRFD vs. ASD

• What stays the same?

• 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

• Same basic equation format • Same adjustment factors • Same behavioral equations

LRFD vs. ASD

LRFD vs. ASD

ASD

LRFD

applied stress  allowable stress

Estimated loads

Design Load



Adjusted Resistance

Design values

Member performance factor

factored load  factored resistance

Theoretical safety margin applied to material stresses

Load factors to account for variations in loads

Tested material strength

Estimated loads

Factored Design Load



Factored Design Resistance

Tested member resistance

Design values

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2012 NDS

2012 NDS  tied to ASCE 7 Factored Loads:

Factored Load Combinations ASCE 7-10

Baseline 10 minutes (ASD uses 10 years)

Permanent

Long term Short term

2012 NDS

NDS 2012 LRFD Specification Format Conversion Factor KF: ASD

Reliability indices or data confidence factors

RN = RASD

LRFD

RN = KF RASD

RASD reference strengths

10

2012 NDS

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

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

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

NDS 2012 Chapters

Outline • Overview • LRFD Primer • Chapter-by-chapter discussion – Changes from previous editions


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!!!

11

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

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

M. N.

NDS – Chapter 1

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

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)

12

Chapter 1 – Design Loads

NDS – Chapter 2

• Reference loads • Minimum load standards ASCE 7 – 10

Chapter 2 – Adjustment Factors


• Adjusts from reference to site conditions

• Adjust from reference conditions

– CD,  time-dependent – CM wet service – Ct temperature

KF LRFD format conversion factor  LRFD resistance factor

Revised

13


Wet Service Conditions

• Wet Service Factor, CM

30

Wood EMC %

25 20

Temp 30 deg F Temp 70 deg F

15

Temp 130 deg F

10 5 0 0

20

40

60

80

100

Relative Humidity %

%Strength at 12% Moisture Content

Wet Service Conditions

Wet Service Factor, CM • NDS Supplement for lumber

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 (%)

14

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 


Chapter 3 – Behavioral Equations


• Beams

• Beams

– FbE Equivalence

– CL beam stability

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

Critical Buckling Design Value for bending members

15



• Columns

• Columns – FcE equivalence

– CP column stability

FcE 

0.822E'min  le    d

2



2012/2005 NDS

K cEE'  le    d

2

2001 NDS

Critical Buckling Design Value for compression members

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

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

F′t = Ft CD


LRFD

F′t = Ft KF t 


16



• Wood and tension perpendicular to grain

• Combined bi-axial bending and axial compression

– Not recommended per NDS 3.8.2

initiators: • notches • moment connections • hanging loads

Chapter 3 – Behavioral Equations • Combined bi-axial bending and axial compression

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)

New

17

NDS – Chapter 4

Chapter 4 – Lumber • Design values – – – –

Visually graded lumber MSR / MEL Timber Decking

Chapter 4 – Lumber


• Lumber adjustment factors


– KF and 

– New KF and 

18





– CF - size factor


NDS – Chapter 5

• Lumber adjustment factors – – – – – –

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

19

Chapter 5 – Glued Laminated Timber

Chapter 5 – Glulam

• Significant changes

• New adjustment factors – Stress interaction – Shear reduction

– New adjustment factors • Stress interaction • Shear reduction

– Clarified or added • Curved members • Double-tapered • Tapered straight



• Clarified or added

• Adjustment factors

– Curved members – Double-tapered – Tapered straight

– CV volume – Not cumulative with CL – Min (Cv, CL)

20

NDS – Chapter 6

Chapter 6 – Poles & Piles • Poles - post-frame • Piles - foundations

Chapter 6 – Timber Piles

Chapter 6 – Timber Poles

• Design values – Significant changes from 2005 NDS – Design values moved to NDS Supplement

2005 NDS

2005 NDS 2012 NDS

2012 NDS

21

Chapter 6 – Poles & Piles

NDS – Chapter 7

• Adjustment factors – Cct – condition treatment – Cls – load sharing – Ccs – critical section

Chapter 7 – I-joists

Chapter 7 – I-Joists

• Design values

• Beam stability factor

– M, V, EI, K – no changes

• Evaluation Reports – Contain proprietary design

– Braced compression flange • CL = 1.0

– Unbraced compression flange • Design as unbraced column

22

NDS – Chapter 8

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

Relative Frequency

x = mean



 x

SCL I-Joist Glulam

COVxx= x

MSR Lumber

Load

Visually Graded Lumber Material Property Values

Chapter 8 – Structural Composite Lumber

Chapter 8 – Structural Composite Lumber



– CV – volume

• Cv < 1.0 Not cumulative with lateral stability factor, CL then min. (Cv, CL) • Cv > 1.0 Cumulative with lateral stability factor, CL

– Cr Repetitive Member Factor= 1.04 – Cr is different than lumber • Applies to Fb only

(Cr lumber = 1.15)

23

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

Chapter 9 – Wood Structural Panels



– CG - grade & construction • Removed

– Cs - panel size

– CM - wet service – Ct - temperature

• Clarified • Moved from commentary

24

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

NDS – Chapter 11

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

25

Chapter 11 - Tabulated Values

Chapter 11 - Dowel Bearing Length

• New post frame ring shank tables Based on ASTM F1667

Fastener Type

Tip Length, E

Lag Screws

Appendix L

Wood Screws

2D

Nails & Spikes

2D

E, ℓs, ℓm < p – E / 2

Chapter 11 - Dowel Bearing Strength • Wood Structural Panels – D < ¼

Chapter 11 - Perp to Grain Distance • Glulam only – Moisture content

26

NDS – Chapter 12

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

Chapter 12 – Split Rings and Shear Plates

NDS – Chapter 13

• Geometry factor, C – End Grain

27

Chapter 13 – Timber Rivets


• Many applications


Timber Rivets – Design 2005 NDS

• Parallel to grain • Timber rivet capacity – Proper application of CD

28

Timber Rivets – Design 2012 NDS

Chapter 13 – Timber Rivets • Maximum distance perpendicular to grain between outermost rows of rivets shall be 12 – Consistent with glulam

NDS – Chapter 14

NDS – Chapter 14

29

Chapter 14 – Shear Walls and Diaphragms

NDS – Chapter 15

• ANSI / AWC SDPWS 2008 standard • Recorded Webinar

•2005/2008 SDPWS •Diaphragm Deflection •www.woodworks.org

Chapter 15 – Special Loading

NDS – Chapter 16

• Built-up columns – Flatwise bending check – Consistent with Chapter 3

30

Chapter 16 – Fire Design

Chapter 16 – Fire (ASD)

• No significant changes

• Fire resistance up to two hours • • • •

Columns Beams Tension Members ASD only

• Products • • • •

Chapter 16 – Fire (ASD)

…

Lumber Glulam SCL Decking

NDS – Appendices

DCA 2 Design of Fire-Resistive Exposed Wood Members

•Limited to 1-Hour – IBC 721.6.1.1 approach •Simplified Beams/Columns •

31

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)

Appendix L

Appendix E • Example E.8 • Acritical check

Appendix N

32

NDS – Commentary

Outline • Overview • LRFD Primer • Chapter-by-chapter discussion – Changes from previous editions


2012 NDS – Notable Changes • Chapter 5 – Glulam • 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

33

Southern Pine Design Values

Wood Design Package

• ALSC approves design values

• Support Documents

– June 1, 2012

• AWC compiles them – NDS Supplement

• More information – Ww.spib.org – www.southernpine.com

• 2nd Quarter 2012

• Wood Design Package • NDS + Commentary • NDS Supplement • ASD/LRFD Manual

• Print copies available then

More Details

• White paper - www.awc.org • Comprehensive table • Section-by-section changes • Structure Magazine

Supplement:

Design Values for Wood Construction

MANUAL

Engineered Wood Design • NDS Changes – http://awc.org/pdf/2012-NDS-ChangesWeb.pdf – Free download

• January 2012

34

More Details

More Details • 2008 SDPWS (Special Design Provisions for Wind and Seismic) Changes – http://awc.org/pdf/WDF18-3_SDPWS08.pdf – Free download

• http://www.awc.org/technical/L RFDStrucEng.pdf • White paper LRFD

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

www.awc.org [email protected]

35