Strength & Loading. Of Wood Utility Poles. Webinar

Transcription

1 Strength & Loading Of Wood Utility Poles. Webinar

2 Overview Benefits of Wood as a Utility Pole Material Defining Wood Pole Strength Loading Criteria In-Service Analysis Upcoming NESC 2017 Changes

3 Pole Material Choices Wood

4 Pole Material Choices Metal (Steel, Aluminum) Concrete Composite (Fiber Reinforced Polymer)

5 Benefits of Wood as a Utility Pole Material Long-Life Span o ~45 years national average without remedial treatment Lowest Cost o Both initial and full life-cycle costs Proven Performance o Go to overhead line construction material since the early 1900 s Climb-ability o Ability to service attachments without heavy equipment

6 Benefits of Wood as a Utility Pole Material Supply Chain is Proven o Even in natural disaster events where demand is high, it has met the challenge of providing the necessary poles in required timeline. Beneficial Physical Properties o Good electrical insulator, resilience to wind and mechanical impacts Easy Maintenance and Modification in Service Green o a treated wood pole have a reduced environmental impact when competed to other utility pole materials. o A renewable and plentiful resource 10 Features Often Overlooked About the Extraordinary Wood Pole. North American Wood Pole Council.

7 Strength and Loading of Wood Poles Wire with Ice Bending Capacity > Bending Load 7

8 Strength and Loading of Wood Poles Wire with Ice Defines: Wood Strength Wood Quality Defines: Loading Criteria Strength Requirements 8

9 ANSI O5.1 Wood Pole Specification ASC O5 Accredited Standards Committee O5: Standards for Wood Utility Structures Secretariat: AWPA Revised: 5 year cycle Founded in

10 ASC O5 Standards Poles Glu-Lam Crossarms O Naturally Durable Hardwood Poles O Wood Ground Wire Moulding O Solid Sawn Naturally Durable Hardwood Crossarms & Braces O5.TR Photographic Manual of Wood Pole Characteristics 10

11 Scope Simple Cantilever Transverse Single Pole Groundline 11

12 Maximum Stress Point Solid, Round, Tapered, Cantilever Load (Wind Force on Wires, Equip., etc.) Max 1.5 Diameter Load Point Distribution Usually Groundline 12

13 ANSI O5.1 Wood Poles Wood Quality Class Loads Fiber Strength Pole Dimensions 13

14 Wood Quality Allowable knots 14

15 Wood Quality Sweep 15

16 Wood Quality Growth Rings 16

17 Class Loads 2 ft L c Horizontal Class Load (lb) , , , , , , ,500 H1 5,400 H2 6,400 H3 7,500 H4 8,700 H5 10,000 H6 11,400 17

18 Class Loads 2 ft L c L c Horizontal Class Load (lb) Telco 7 1, , , ,400 Distribution 3 3, , ,500 H1 5,400 H2 6,400 H3 7,500 Transmission H4 8,700 H5 10,000 H6 11,400 18

19 Fiber Strength L c Bending Capacity = k x fiber strength x C3 (ft-lb) Tension (psi) Compression (psi) Fiber Strength 19

20 Designated Fiber Strength: Pole Species Distribution: Douglas fir Transmission Douglas fir Western red cedar Distribution: Southern Yellow Pine Transmission: Douglas fir Western red cedar Southern Pine Southern Yellow Pine Douglas fir Western red cedar 8,000 psi 8,000 psi 6,000 psi 20

21 Strengths are Average Values COV = Coefficient of Variance COV= Approx (20%) for Southern Pine, Douglas Fir and Western Red Cedar #40 COV

22 Steel Poles Wood Poles 22

23 Applied Bending Load 2 ft D L c Applied Bending Load = L c x D (ft-lb) Class 1 4,500 lb Class 2 3,700 lb Class 3 3,000 lb Class 4 2,400 lb Class 5 1,900 lb 23

24 L x D = Bending Moment (ft-lb) 50 ft Class 4 40 ft Class lb 2400 lb 41 ft 32 ft 76,800 ft-lb 98,400 ft-lb 24

25 Pole Dimensions: Circumference 6ft G/L TIP Bending Capacity = k x fiber strength x C3 (ft-lb) 25

26 Pole Dimension Table Southern Pine and Douglas Fir 1. Circumference (in) 6ft from butt 1) The figures in this column are not recommended embedment depths; rather, these values are intended for use only when a definition of groundline is necessary in order to apply requirements relating to scars, straightness, etc. 26

27 Annex B: Groundline Stresses Minimum circumferences specified at 6 feet from the butt Were calculated so each species in a given class Can support the class horizontal load applied 2 ft from the tip Applied Bending Load = L c x D (ft-lb) Bending Capacity = k x fiber strength x C3 (ft-lb) 27

28 Pole Dimension Table Southern Pine and Douglas Fir Applied Bending Load= Class Load * Distance 76,800 ft-lbs= 2,400 lbs* 32ft (in) Bending Capacity = k x fiber strength x C 3 79,401 ft-lbs= x 8000x

29 40 ft Class 4 Poles 2400 lb Douglas fir (8000 psi) Western Red Cedar (6000 psi) 33 1/2 36 1/2 29

30 Circumference 3 Effect M G/L = x Fiber Stress x Circumference ,120 ft-lb % Pole s Bending Strength In The Outer 2-3 Of Shell! 83,010 ft-lb Circumference Increase - 30% Bending Capacity Increase - 123% 30

31 ANSI O5.1 Summary 2 ft L c All Species Same Length & Class Similar Load Capacity Bending Capacity = k x fiber strength x C3 (ft-lb) 31

32 Loading Criteria: National Overhead Line Standard NESC ANSI C2: National Electrical Safety Code Secretariat: IEEE (Institute of Electrical and Electronics Engineers) Revised: 5 year cycle Founded in

33 Loading Criteria: CA Overhead Line Standard GO95 CPUC: California Public Utilities Commission General Order 95: Overhead Line Construction Revised: As Needed Founded in 1941 From GO 64 est

34 National Electric Safety Code (NESC) Electric Supply and Communication Facilities Basic Safety Standard 34

35 Topics of the NESC Topics Covered Grounding Wood Poles Substations Overhead Electric Supply and Communication Lines Underground Electric Supply and Communication Lines Work Rules 35

36 NESC - Committees Main Committee SC 1 Sections 1, 2 & 3 (Scope/Purpose, Definitions, References) SC 2 Grounding SC 3 Substations SC 4 Overhead Lines - Clearances SC 5 Overhead Lines Strength and Loading SC 7 Underground Lines SC 8 Work Rules 36

37 Overhead Lines Subcommittee Section 24 Grades of Construction Grades of construction Grades include B, C & N (B being the highest) Section 25 Loading for Grade B&C Loads to apply Rule 250B: Combined ice and Wind District loading Rule 250C: Extreme wind Loading Rule 250D: Extreme Ice with concurrent wind loading Section 26 Strength requirements Strength utilization Section 27 Insulators Electrical Strength Mechanical Strength 37

38 Section 24: Grades of Construction Grade B: Crossing Limited Access Highways Crossing Railways Crossing Navigable Waterways Grade C: All other standard construction Grade N: Mainly used for temporary and emergency construction Defined as the strength shall exceed the expected loads 38

39 Section 25: Loading for Grade B & C Deterministic Loads Rule 250B: Combined Ice and Wind District loading Probabilistic Loads Rule 250C: Extreme wind Loading (Applies only to Structures 60ft above ground and taller) Rule 250D: Extreme Ice with concurrent wind loading (Applies only to Structures 60ft above ground and taller) 39

40 NESC District Loading ¼ Ice 40 mph ½ Ice 40 mph 0 Ice 60 mph 40 mph = 4 lbs/sqft 60 mph = 9 lbs/sqft 40

41 GO95 District Loading Heavy Loading District >3000ft elevation ½ Ice - 48 MPH Light Loading District <3000ft elevation 0 Ice - 56 MPH 41

42 Extreme Wind Rule 250C Summer Storm 85 mph = 18.5 lbs/sqft 90 mph = 21 lbs/sqft 130 mph = 43 lbs/sqft 150 mph = 58 lbs/sqft 42

43 Ice with Concurrent Wind Rule 250D Winter Storm Wind Speeds 30 mph 40 mph 50 mph 60 mph Radial Ice

44 250D 250C Rule 250B Section 25: Table Load Factors Grade B Grade Cx Grade C Vertical Loads Transverse Loads (wind) Longitudinal Loads 1.10 No Req. No Req. Wind Loads Ice and Wind loads

45 250C & 250D Rule 250B Section 26: Strength Factors Table Grade B Grade C Metal Structures Wood Structures Fiber Strength (ANSI) Strength Factor (NESC)= Allowable Stress of Pole Metal Structures Wood Structures

46 Restore or Replace Thresholds When to restore or replace: NESC Table 261-1: 2Wood and reinforced structures shall be replaced or rehabilitated when deterioration reduces the structure strength to 2/3 of that required when installed. When to restore or replace: GO95 Section 44.3: Lines or parts thereof shall be replaced or reinforced before safety factors have been reduced (due to factors such as deterioration and/or installation of additional facilities) to less than two-thirds of the safety factors specified Strength required when installed, NOT original strength of wood pole used. 46

47 Load and Strength Factors Rule 250B: District Loading Grade B Grade C Load Factor Strength Factor Effective Overall Safety Factor Effective Restore or Replace Threshold (2/3 )

48 At Replacement At Installation GO95: Table 4- Safety Factors Grade A Grade B Grade C Wood Pole Safety Factor Wood Pole Safety Factor

49 In Service Analysis Wire with Ice Bending Capacity > Bending Load 49

50 In Service Analysis Class is determined by the load on the pole Length is determined by required clearance Bending Capacity 50

51 In Service Analysis Load types acting on the pole: o Wind o Ice o Line Tension o Guy Tension Wire with Ice o Weight (equipment, conductors, etc) Bending Load 51

52 Loading Directions TRANSVERSE V E R T I C A L 52

53 Longitudinal Loading Balanced Unequal 53

54 Longitudinal Loading - Guys Balanced 54

55 NESC Guying Requirements 261.A.2 c. Strength of guyed poles Guyed poles shall be designed as columns, resisting the vertical component of the tension in the guy plus any other vertical loads. 261.A.5.C 2. Wood structures Guys add to VERTICAL loads, Balance LONGITUDINAL loads/ wire tensions When guys are used to meet the strength requirements, they shall be considered as taking the entire load in the direction in which they act, the structure acting as a strut only, 55

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59 Vertical Pole Loading V E R T I C A L 59

60 Vertical Pole Loading STRUCTURE MUST RESIST BUCKLING Weight of Conductor 57lb/ft 3 ) Equipment Weight Pole Weight Down Guy Vertical Load 60

61 Transverse Load Dictates Design TRANSVERSE Wire with Ice 61

62 Calculating Transverse Loads Wind Bending Loads On: Wires Ice Pole Equipment Offset Bending Loads Wire Tension 62

63 Transverse Wind Load on Conductors Height (ft) Diameter C x Span x Wind Pressure x Height x Load Factor = ft-lb Groundline Bending Moment 63

64 Wind Effects on Wire Sizes X 2X double wire diameter, double the load 64

65 Wind Effects: Wire Sizes Radial Ice Wire.25 Ice % +33% +17% 65

66 All Moments Added Together Moment from Wind on Conductors + Moment from Wind on Pole + Moment from Wind on Equipment + Moment from Equipment Offset = Total Groundline bending Moment 66

67 Evaluating Existing Structures 67

68 Existing Structures Efficient Pole Loading Pole Strength Characteristics: Pole Length and Class Groundline Circumference Pole Construction Details: Span Lengths Span Bearings Attachment Heights Wire Diameters Additional Details: Equipment Details Guying Details 68

69 Evaluating an In-Service Pole - By Hand Moment from Wind on Conductors + Moment from Wind on Pole + Moment from Wind on Equipment + Moment from Equipment Offset = Total Groundline bending Moment 69

70 Pole Loading Analysis Software Reports 70

71 Corrective Actions After Evaluation Proper clearances not maintained o Suggested corrective actions: Re-route attachment Move attachments to satisfy clearance needs Re-tension attachments Replace with appropriate pole length Load exceeds pole s rated capacity o Suggested corrective actions: Re-route attachment Replace with appropriate pole Class Increase pole s load carrying capacity 71

72 Determining In-Service Strength 72

73 Restore or Replace Thresholds When to restore or replace: NESC Table 261-1: 2Wood and reinforced structures shall be replaced or rehabilitated when deterioration reduces the structure strength to 2/3 of that required when installed. When to restore or replace: GO95 Section 44.3: Lines or parts thereof shall be replaced or reinforced before safety factors have been reduced (due to factors such as deterioration and/or installation of additional facilities) to less than two-thirds of the safety factors specified Strength required when installed, NOT original strength of wood pole used. 73

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75 Circumference 3 Effect M G/L = x Fiber Stress x Circumference % Pole s Bending Strength In The Outer 2-3 Of Shell! 37,120 ft-lb 83,010 ft-lb Circumference Increase - 30% Bending Capacity Increase - 123% 75

76 Circumference 3 Effect M G/L = x Fiber Stress x Circumference ,010 ft-lb 37,120 ft-lb Circumference Decrease - 24% Bending Capacity Reduction - 55% 76

77 SYP Southern Yellow Pine Thick Sapwood Species Southern Yellow Pine 77

78 Advanced Shell Rot 78

79 External Decay Pockets 79

80 Df - Douglas fir WC - Western red cedar Thin Sapwood Species Douglas Fir Western Red Cedar 80

81 Early Stage of Decay/ Enclosed Decay Pocket 81

82 Advanced Internal Decay 82

83 Circumference Calculator Limited Variables Measured Decay Circumference Reduction Results in Effective Circumference Effective Circumference Allowable Table Reject Decision Effective Circumference

84 Slide Rule Reject Criteria External Decay & Internal Pockets o Effective circumference Hollow Heart o Minimum average shell 84

85 Bending Stress 83% Wind on Wires 88% Line of Lead 99% 85

86 2005 Electronic Strength Calculator 86

87 Electronic Strength Calculator Inspector no longer averages measurements Orientation of decay is considered Reject decision based on remaining strength Reject criteria consistent for all circumferences Reject criteria can be adjusted 87

88 Common Reject Threshold 100% Serviceable Remaining Effective Circumference 87% 69% 50% 33% Reject 100% 67% 33% Bending Strength 13% 4% 40 Class 4 34in Circumference = 29.5in ¾ Reduction of shell

89 100 Years Old

90 Inaugural NESC Summit 90

91 Keynote Speakers & Bios 91

92 High Powered Speakers Bob W. Bradish AEP Vice President Transmission Grid Development Daniel K. Glover Southern Company Vice President Power Delivery - Distributioin Robert Woods Southern California Edison Managing Director of Asset Management and Operations Support Stephen A. Cauffman NIST-National Institute of Standards & Tech Manager, Community Resilience Program Jorge A. Camacho,PE PSC District of Columbia Chief, Infrastructure and System Planning 92

93 NESC 100 Years Old presented by Don Hooper 93

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99 Schedule for 2017 NESC Submit change proposals: Jan Months - July 2013 First Subcommittees Votes: Sept-Oct 2013 Preprint Distributed: 13 September Months 2014 Public Comments Until: 9 May Months 2015 Subcommittees Vote on Comments: 6 Sept-Oct Months 2015 Draft Submitted for Letter Ballot: January 3 Months 2016 Revisions Submitted to ANSI: May 4 Months 2016 Published: August 3 Months 2016 Effective: January

100 2017 NESC 100

101 Re-format Rule 241.C. At Crossings 241. Application of grades of construction to different situations 2012 version 101

102 Re-format Rule 241.C. At Crossings 241. Application of grades of construction to different situations 2012 version 2017 version 102

103 Re-format Rule 241.C. At Crossings 241. Application of grades of construction to different situations 2012 version 2017 version Same Words Easier to Comprehend 103

104 Revised Table Intention: Improve logical layout and format Columns sequence from low to high voltage Rows sequence from low to high voltage 104

105 2012 Table

106 2012 Table

107 2017 Table

108 2017 Table

109 Revise Table Grades of Construction Applications CP Intention: Improve logical layout and format Columns sequence from low to high voltage Rows sequence from low to high voltage FN 3 reversed; higher grade in the table 3 Grade B C construction shall may be used if the supply circuits will not be promptly de-energized, both initially and following subsequent breaker operations, in the event of a contact with lower supply conductors or other grounded objects. 109

110 Revise Table Grades of Construction Applications CP Intention: Improve logical layout and format Columns sequence from low to high voltage Rows sequence from low to high voltage FN 3 reversed; higher grade in the table Add FN 11 Grade N for dielectric fiber-optic supply cables 110

111 Revise Table Grades of Construction Applications CP Intention: Improve logical layout and format Meet Rule 230F1b Insulated Comm Cables in Supply Space Columns sequence and from low to high voltage Rows sequence from low to high voltage Supported by effectively grounded messenger FN 3 reversed; higher grade in the table or Add FN 11 Grade N for dielectric fiber-optic supply cables Bonded at intervals specified in Rule 092C to Supply messengers supporting cable meeting Rule 230C1 111

112 Revise Table Grades of Construction Applications CP Intention: Improve logical layout and format Columns sequence from low to high voltage Rows sequence from low to high voltage FN 3 reversed; higher grade in the table Add FN 11 Grade N for dielectric fiber-optic supply cables 112

113 Clarify when ice is applied Rule 250D 113

114 Clarify when ice is applied Rule 250D Add ice to: Wires Conductors Cables Messengers Do not add ice to: Structure Other supported facilities 114

115 Aeolian Vibration Rule 261H.1.b 115

116 Aeolian Vibration Rule 261H.1.b 116

117 Aeolian Vibration Rule 261H.1.b Final Action: Accept 117

118 Insulators New Rating System Old Line Post ratings: Rating equal to average Lowest not less than 85% of average New Line Post ratings: Rating = Minimum of all insulators 118

119 Insulators New Rating System Old Transmission Suspension ratings: 1.2 standard deviations New Transmission Suspension ratings: 3.0 standard deviations 119

120 Insulators CP Intention: Introduce Load factors (LRFD) Adjust allowable stresses Mostly equivalent insulator applications Introduce Classes: Distribution & Trans Different allowables for Rule 250B vs 250C, D 120

121 Insulators Table

122 Insulators Table

123 Insulators Table

124 Insulators Table

125 Nonceramic Table cont d 125

126 Table cont d 126

127 Table cont d 127

128 Table cont d 128

129 Table cont d Final Action: Accept FN 3: This percentage shall be supplied by the manufacturer. 129

130 Table cont d Final Action: Accept FN 3: This percentage shall be supplied by the manufacturer. 130

131 NESC Visioning Sessions Future of the NESC Safety Reliability Resiliency 131

132 NIST-National Institute of Standards & Technology 132

133 NIST Disaster Resilience Framework 133

134 NIST - NESC While this is truly a safety code, it is applied for use as a design code in lieu of other guidance. the question that exists is whether the baseline set forth in the NESC addresses the performance desired for resiliency when considering all hazards (flood, wind, seismic, ice.) 134

135 NIST NESC Rule 250C Rule 250C The ASCE 7-10 wind maps were revised to better represent the wind hazard.. However, these maps are currently not used by the NESC based on a decision by their code committee to retain the use of the ASCE 7-05 wind maps. Rule 250C Most distribution structures are lower than the 60 ft height limitation, therefore, most utilities will not design their distribution lines to the ASCE 7 criteria (something that may want to be reconsidered depending upon performance of these systems during hurricanes and tornadoes over the past 2 decades). 135

136 NESC Workshop October 18-19, 2016 San Antonio, TX 2017 NESC Changes The Future of the NESC

137 Thank you Name Nelson Bingel Phone Chad Newton