John Buddy Showalter, PE Vice President, Technology Transfer American Wood Council

Transcription

1 2015 NDS Changes John Buddy Showalter, PE Vice President, Technology Transfer American Wood Council Michelle Kam-Biron, PE, SE, SECB Director of Education American Wood Council Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of AWC is prohibited. American Wood Council rights reserved. 1

2 Course Description AWC's National Design Specification (NDS) for Wood Construction 2015 is the dual format Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) document referenced in US building codes and used to design wood structures worldwide. Participants will learn about changes in the 2015 NDS and Supplement relative to previous editions and gain an overview of the standard. 4 Objectives Upon completion, participants will be: 1. Able to understand the load and material resistance design process and how it applies to wood structural design. 2. Familiar with the significant changes between the 2012 and 2015 NDS and supplement. 3. Able to identify the similarities and differences with respect to ASD, design values, and behavioral equations. 4. Able to analyze format and content within the 2015 NDS. 5 rights reserved. 2

3 Outline Overview Design Process Overview NDS Chapter-by-chapter discussion Changes from previous editions Summary More Info 6 NDS History rights reserved. 3

4 Governing Codes for Wood Design 2015 NDS referenced in 2015 IBC 8 ANSI Accreditation AWC ANSI-accredited standards developer Consensus Body Wood Design Standards Committee 9 rights reserved. 4

5 2015 NDS Primary Change New Provisions to Address CLT Charging Language Design Values Design Equations Product Chapter Connection Design Fire Design NDS Chapter Reorganization 2012 NDS 1-3 General 4-9 Products Connections 14 Shear Walls & Diaphragms 15 Special Loading 16 Fire 2015 NDS 1-3 General 4-10 Products +CLT Connections Shear Walls & Diaphragms 15 Special Loading 16 Fire 11 rights reserved. 5

6 Outline Overview Design Process Overview NDS Chapter-by-chapter discussion Changes from previous editions Summary More Info 12 Design Process Demand Capacity 13 rights reserved. 6

7 Design Process Load Support Conditions Geometry Materials Performance Fire Economics Aesthetics. Demand Capacity 14 Design Concepts Two Limit State concerns Serviceability (performance in-service) Safety against failure or collapse 15 rights reserved. 7

8 Serviceability ASD and LRFD Unfactored loads Mean (avg) material strength values 16 Safety ASD Unfactored loads Material strength values - modified LRFD Factored loads Material strength values modified less 17 rights reserved. 8

9 Structural Property Variability Normal Distribution Curves x = mean x = standard deviation x x x SCL Relative Frequency COV x = x x Coefficient of variation Load I-Joist Glulam MSR Lumber Visually Graded d Lumber Material Property Values 18 Engineered Wood Design S > R Failure 19 rights reserved. 9

10 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 26 LRFD vs ASD LRFD factored load factored resistance Load factors to account for variations in loads Member performance factor Estimated loads Factored Design Load Factored Design Resistanc e Tested member resistance Design values 27 rights reserved. 10

11 2015 NDS LRFD Basic Load Combinations ASCE NDS ASD Basic Load Combinations ASCE rights reserved. 11

12 2005 NDS & ASCE 7-02 LRFD vs. ASD Load Combinations LRFDvASD.pdf NDS Format Conversion Factor K F ASD R N = C D R ASD LRFD R N = K F R ASD R ASD reference strengths 31 rights reserved. 12

13 2015 NDS Reliability indices or data confidence factors NDS tied to ASCE 7 Factored Loads Baseline 10 min (ASD uses 10 yrs) Permanent Long term Short term 33 rights reserved. 13

14 2015 NDS R N = K F R ASD K F converts reference design values (ASD normal load duration) to LRFD reference resistance 34 Outline Overview Design Process Overview NDS Chapter-by-chapter discussion Changes from previous editions Summary More Info 36 rights reserved. 14

15 NDS 2015 Chapters 1. General Requirements for Building Design 2. Design Values for Structural Members 3. Design Provisions and Equations 4. Sawn Lumber 5. Structural Glued Laminated Timber 6. Round Timber Poles and Piles 7. Prefabricated Wood I-Joists 8. Structural Composite Lumber 9. Wood Structural Panels 10. Cross-Laminated Timber 11. Mechanical Connections 12. Dowel-Type Fasteners 13. Split Ring and Shear Plate Connectors 14. Timber Rivets 15. Special Loading Conditions 16. Fire Design of Wood Members 37 NDS 2015 Supplement 1. Sawn Lumber Grading Agencies 2. Species Combinations 3. Section Properties 4. Reference Design Values Sawn Lumber and Timber MSR and MEL Decking Non-North American Sawn Lumber Structural Glued Laminated Timber Timber Poles and Piles 38 rights reserved. 15

16 NDS 2015 Appendices A. Construction and Design Practices B. Load Duration (ASD Only) 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) Mandatory 39 NDS Chapter 1 40 rights reserved. 16

17 Chapter 1 - Terminology f b F b ' Reference design values (F b, F t, F v, F c, F c, E, E min ) Adjusted design values (F b ', F t ', F v ', F c ', F c ', E', E min ') 41 Chapter 1 Design Loads Reference loads Minimum load standards ASCE rights reserved. 17

18 Chapter 1 CLT Charging Language 43 NDS Chapter 2 44 rights reserved. 18

19 Chapter 2 Adjustment Factors Reliability indices or data confidence factors 45 Chapter 2 Adjustment Factors R N = K F R ASD K F converts reference design values (ASD normal load duration) to LRFD reference resistance 46 rights reserved. 19

20 Appendix N Adjustment Factors tied to ASCE 7 Factored Loads: Baseline 10 minutes (ASD uses 10 years) Permanent Long term Short term 47 Chapter 2 Adjustment Factors Adjusts from reference to site conditions C D time-dependent t Baseline 10 years 48 rights reserved. 20

21 Chapter 2 Adjustment Factors Adjusts from reference to site conditions C t temperature e Exposed for sustained period 49 Chapter 2 Adjustment Factors Adjusts from reference to site conditions C M wet service factor 50 rights reserved. 21

22 Wet Service Conditions Wood EMC % Temp Temp Temp Wet Service Conditions %Strength at 12% Moisture Content Moisture Content of Wood (%) Impact Strength Modulus of Elasticity Modulus of Rupture Crushing Strength 52 rights reserved. 22

23 Wet Service Factor, C M Sawn lumber MC < 19% considered dry Otherwise, NDS Supplement for lumber 53 Chapter 2 CLT Design Values 54 rights reserved. 23

24 NDS Chapter 3 55 Chapter 3 Behavioral Equations ASD vs LRFD adjusted stresses from reference ASD F n = F n C D x adjustment factors LRFD F n = F n K F n x adjustment factors 56 rights reserved. 24

25 Chapter 3 Behavioral Equations Beams C L beam stability Critical Buckling Design Value for bending members 57 Chapter 3 Behavioral Equations Columns C P column stability Critical Buckling Design Value for compression members 58 rights reserved. 25

26 Chapter 3 Behavioral Equations E min 1.03E( ( COV E )) /1.66 E = reference MOE 1.03 = adjustment factor to convert E to a pure bending basis (shear-free) (use 1.05 for glulam) 1.66 = factor of safety COV E = coefficient of variation in MOE (NDS Appendix F) OR E min values published in NDS Supplement 59 Chapter 3 Behavioral Equations Tension members (tension parallel to grain) ASD F t = F t C D x adjustment factors LRFD F t = F t K F t x adjustment factors 60 rights reserved. 26

27 Chapter 3 Behavioral Equations Tension perpendicular to grain Not recommended per NDS initiators: notches moment connections hanging loads 61 Chapter 3 Behavioral Equations Combined bi-axial bending and axial compression 62 rights reserved. 27

28 Chapter 3 Behavioral Equations Combined bi-axial bending and axial compression 63 Chapter 3 Behavioral Equations Bearing perpendicular to grain F c = F c C M C t C i C b (ASD) c c M t i b F c = F c C M C t C i C b K f c (LRFD) 64 rights reserved. 28

29 Chapter 3 CLT Design Equations New 65 Chapter 3 CLT Design Equations New NDS Commentary guidance on C P 66 rights reserved. 29

30 NDS Chapter 4 67 Chapter 4 Lumber Design values Visually graded lumber MSR / MEL Timber Decking 68 rights reserved. 30

31 Chapter 4 Lumber Lumber adjustment factors 69 Chapter 4 Lumber Lumber adjustment factors C F - size factor 70 rights reserved. 31

32 Chapter 4 Lumber Lumber adjustment factors 71 Chapter 4 Lumber Lumber adjustment factors Repetitive member C r = lumber < 24 o.c. 3 or more members Load distributing element 72 rights reserved. 32

33 NDS Chapter 5 73 Chapter 5 Glulam Adjustment factors 74 rights reserved. 33

34 Chapter 5 Glulam Adjustment factors C V Volume Factor C L Beam Stability Factor Not cumulative with C L Min (C v, C L ) 75 NDS Chapter 6 76 rights reserved. 34

35 Chapter 6 Poles & Piles Poles - post-frame Piles - foundations 77 Chapter 6 Timber Piles Design values NDS Supplement 78 rights reserved. 35

36 Chapter 6 Poles & Piles Adjustment factors 79 NDS Chapter 7 80 rights reserved. 36

37 Chapter 7 I-joists Design values M, V, EI, K no changes Evaluation Reports Contain proprietary design 81 Chapter 7 I-Joists Adjustment factors 82 rights reserved. 37

38 NDS Chapter 8 83 Chapter 8 Structural Composite Lumber Design Values Evaluation Reports Contain proprietary design Frequency Relative x = mean COV x x = x Load x SCL I-Joist Glulam MSR Lumber Visually Graded Lumber Material Property Values 84 rights reserved. 38

39 Chapter 8 Structural Composite Lumber New products Laminated Strand Lumber (LSL) Oriented Strand Lumber (OSL) ASTM D Chapter 8 Structural Composite Lumber Adjustment factors C V volume C v < 1.0 Not cumulative with lateral stability factor, C L, then min. (C v, C L ) C v > 1.0 Cumulative with lateral stability factor, C L 86 rights reserved. 39

40 Chapter 8 Structural Composite Lumber Adjustment factors C r Repetitive Member Factor = 1.04 C r is different than lumber (C r lumber = 1.15) Applies to F b only 87 NDS Chapter 9 88 rights reserved. 40

41 Chapter 9 Wood Structural Panels Design values obtain from an approved source F b S F t A F v t v F s F c A EI EA G v t v F c 89 Chapter 9 Wood Structural Panels Adjustment factors 90 rights reserved. 41

42 Chapter 9 Wood Structural Panels Adjustment factors C M -wet service C t - temperature 91 NDS Chapter 10 New 92 rights reserved. 42

43 Chapter 10 Cross-Laminated Timber New 93 Chapter 10 Cross-Laminated Timber New 94 rights reserved. 43

44 NDS Chapter 11 Ch 10 Ch Chapter 11 Mechanical Connections Design issues Reference design values Chapter 12 dowel-type connectors (nails, bolts, lag/wood screws) Chapter 13 split rings and shear plates Chapter 14 timber rivets Adjustment factors No significant changes Connections session 96 rights reserved. 44

45 NDS Chapter 12 Ch 11 Ch Yield Limit Equations 4 Yield Modes 6 Yield Equations Single & Double Shear Wood-to-Wood Wood-to-Steel Wood-to-Concrete 98 rights reserved. 45

46 Yield Modes MODE I bearing-dominated b i d i d yield of wood fibers MODE II pivoting of fastener with localized crushing of wood fibers 99 Yield Modes MODE III fastener yield in bending at one plastic hinge and bearing dominated yield of wood fibers MODE IV fastener yield in bending at two plastic hinges and bearing dominated yield of wood fibers 100 rights reserved. 46

47 Dowel Bearing Strength 101 Fastener Bending Yield Strength Load 102 rights reserved. 47

48 Fastener Bending Yield Strength 103 Chapter 12 Dowel-type Fasteners New 104 rights reserved. 48

49 Chapter 12 Dowel-type Fasteners New 105 Chapter 12 Dowel-type Fasteners New 106 rights reserved. 49

50 Chapter 12 Dowel-type Fasteners New Non-uniform for CLT 107 Chapter 12 Dowel-type Fasteners Adjust l m or l s to compensate for orthogonal grain orientations in adjacent layers Parallel to grain: F e /F eǁ ǁ Example: ½ bolt in southern pine 3-ply CLT with 1-½ laminations l m = t 1ǁ +t 2 +t 3ǁ = 3(1.5) = 4.5 l m-adj = t 1ǁ +t 2 (F e /F eǁ )+t 3ǁ = (3650/6150) +1.5 = rights reserved. 50

51 Chapter 12 Dowel-type Fasteners New 109 Chapter 12 Dowel-type Fasteners Lateral any end grain D<1/4 C eg =0.67 Lateral any CLT edge D>1/4 C eg =0.67 New 110 rights reserved. 51

52 Chapter 12-Dowels 111 Chapter 12-Dowels 112 rights reserved. 52

53 Chapter 12-Dowels Threaded length < lm/4 lm Dia. Fastener = D Threaded length < lm/4 lm Dia. Fastener = D 113 Chapter 12-Dowels lm Dia. Fastener = D r 114 rights reserved. 53

54 Chapter 12 - Dowels Provide tools for the analysis of gaps between members various fastener bending moment configurations fasteners through hollow members fasteners with tapered tips NDS Chapter 13 Ch 12 Ch rights reserved. 54

55 Chapter 13 Split Rings and Shear Plates Design Values 117 NDS Chapter 14 Ch 13 Ch rights reserved. 55

56 Chapter 14 Timber Rivets Many applications 119 Chapter 14 Timber Rivets Design Values Capacities > 100 kips Ch 13 Ch rights reserved. 56

57 NDS Chapter Chapter 15 Special Loading 122 rights reserved. 57

58 NDS Chapter Chapter 16 Fire (ASD) Fire resistance up to two hours Columns Beams Tension Members ASD only Products Lumber Glulam SCL Decking CLT - NEW 124 rights reserved. 58

59 Chapter 16 Calculated Resistance Fire resistance of exposed wood members may be calculated using the provisions of NDS Chapter Fire Resistance Glulam Steel 126 rights reserved. 59

60 Performance of Wood vs. Steel 127 Chapter 16 Fire Design - CLT New 128 rights reserved. 60

61 Chapter 16 Fire (ASD) Technical Report No. 10 Background gou don NDS Spo provisions so s Design examples Floor assembly lumber joist provisions 129 Chapter 16 Fire (ASD) Code Updates - Design of Fire- Resistive Exposed Wood Members /download.php p 130 rights reserved. 61

62 NDS Appendices 131 NDS 2015 Appendices A Construction and Design Practices B Load Duration C Temperature Effects D Lateral Stability of Beams E Local Stresses in Fastener e 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) 132 rights reserved. 62

63 2015 NDS Summary New Provisions to Address CLT Charging Language Design Values Design Equations Product Chapter Connection Design Fire Design 133 What s Missing for CLT? Seismic Design! ASCE 7 Minimum Design Loads for Buildings and Other Structures Response Modification Coefficient, R CLT not recognized system in ASCE 7 Table Options Performance-based design procedure per ASCE 7 Demonstrating equivalence to an existing ASCE 7 system ASCE 7-10, FEMA P695, and FEMA P795 Quantification of Building Seismic Performance Factors; Component Equivalency Methodology 134 rights reserved. 63

64 Outline Overview Design Process Overview NDS Chapter-by-chapter discussion Changes from previous editions Summary More Info NDS Supplement New Southern Pine Design Values ALSC approves design values June 1, 2013 AWC compiles them NDS Supplement More information rights reserved. 64

65 Availability PDF versions Free view-only Buy a printable PDF Spring 2015 Commentary Printed version 137 Technical Articles Structure Magazine 2015 NDS January SDPWS July rights reserved. 65

66 Questions? 140 rights reserved. 66