Strength & Loading Webinar - Osmose Utilities Services, Inc. and Loading Webinar_4.pdf · Overview •Benefits of Wood as a Utility Pole Material •Defining Wood Pole Strength •Loading

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Strength & Loading Of Wood Utility Poles

Webinar

Overview

• Benefits of Wood as a Utility Pole Material

• Defining Wood Pole Strength

• Loading Criteria

• In-Service Analysis

• Upcoming NESC 2017 Changes

Pole Material Choices

Wood

Pole Material Choices

Metal (Steel, Aluminum)

Concrete

Composite (Fiber Reinforced Polymer)

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

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. www.woodpoles.org

Bending Load Bending Capacity >

Strength and Loading of Wood Poles

Wire with Ice

7

Defines:

• Loading Criteria

• Strength Requirements

Defines:

• Wood Strength

• Wood Quality

Strength and Loading of Wood Poles

Wire with Ice

8

ASC O5

Accredited Standards

Committee O5:

Standards for Wood

Utility Structures

• Secretariat: AWPA

• Revised: 5 year cycle

• Founded in 1924

ANSI O5.1 Wood Pole Specification

9

http://asco5.org/standards/

ASC O5 Standards http://asco5.org/standards/

O5.4 - 2009 Naturally Durable Hardwood Poles

O5.5 - 2010 Wood Ground Wire Moulding

O5.6 - 2010 Solid Sawn Naturally Durable Hardwood Crossarms & Braces

O5.TR.01-2004 Photographic Manual of Wood Pole Characteristics

Poles Glu-Lam Crossarms

10

Scope

Single Pole

Simple Cantilever

Transverse

Groundline

11

Maximum Stress Point

Max Stress @ 1.5 Diameter Load Point

Solid, Round, Tapered, Cantilever

Distribution Usually Groundline

Load (Wind Force on Wires, Equip., etc.)

12

ANSI O5.1 – Wood Poles

Wood

Quality

Class

Loads

Pole

Dimensions

Fiber

Strength

13

Wood Quality

• Allowable knots

14

Wood Quality

• Sweep

15

Wood Quality

• Growth Rings

16

Class Loads

2 ft Lc

Horizontal

Class Load (lb)

10 370

9 740

7 1,200

6 1,500

5 1,900

4 2,400

3 3,000

2 3,700

1 4,500

H1 5,400

H2 6,400

H3 7,500

H4 8,700

H5 10,000

H6 11,400

17

Class Loads

2 ft Lc

Telco

Distribution

Transmission

Horizontal

Class Load (lb)

10 370

9 740

7 1,200

6 1,500

5 1,900

4 2,400

3 3,000

2 3,700

1 4,500

H1 5,400

H2 6,400

H3 7,500

H4 8,700

H5 10,000

H6 11,400

2 ft Lc

18

Lc

Fiber Strength

Compression

(psi)

Tension

(psi) Fiber Strength

Bending Capacity =

k x fiber strength x C3 (ft-lb)

19

Designated Fiber Strength: Pole Species

20

Distribution: Southern Yellow Pine

Transmission: Douglas fir

Western red cedar

Southern Pine

Distribution: Douglas fir

Transmission Douglas fir

Western red cedar

Southern Yellow Pine 8,000 psi

Douglas fir 8,000 psi

Western red cedar 6,000 psi

#40

COV

Strengths are Average Values

COV = Coefficient of Variance COV= Approx. 0.20 (20%)

for Southern Pine, Douglas

Fir and Western Red Cedar

Wood Poles

Steel Poles

22

Lc

D

2 ft

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

Applied Bending Load

Applied Bending Load =

Lc x D (ft-lb)

23

L x D = Bending Moment (ft-lb)

76,800 ft-lb

2400 lb

32 ft

40 ft Class 4

41 ft

98,400 ft-lb

2400 lb

50 ft Class 4

24

Pole Dimensions: Circumference

TIP

6ft

G/L

Bending Capacity =


25

Pole Dimension Table

(in) 1. Circumference 6ft from butt

Southern Pine and Douglas Fir

26

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.

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

Bending Capacity =


Applied Bending Load =

Lc x D (ft-lb)

27

Pole Dimension Table

(in)

Southern Pine and Douglas Fir

28

Applied Bending Load=

Class Load * Distance

Bending Capacity =

k x fiber strength x C3

79,401 ft-lbs=

.000264 x 8000x 33.53

76,800 ft-lbs=

2,400 lbs* 32ft

40 ft Class 4 Poles

Douglas fir

(8000 psi)

36 1/2”

Western Red Cedar

(6000 psi)

33 1/2”

2400 lb

29

Circumference3 Effect

MG/L = .000264 x Fiber Stress x Circumference 3

26” 34”

37,120 ft-lb 83,010 ft-lb

Circumference Increase - 30%

Bending Capacity Increase - 123%

80-90%

Pole’s Bending Strength

In The Outer 2-3” Of Shell!

30

ANSI O5.1 Summary

2 ft Lc

Bending

Capacity = k x fiber strength x C3 (ft-lb)

All Species

Same Length & Class

Similar Load Capacity

31

Loading Criteria: National Overhead Line Standard

ANSI C2:

National Electrical

Safety Code

• Secretariat: IEEE (Institute of Electrical and

Electronics Engineers)

• Revised: 5 year cycle

• Founded in 1918

NESC

32

Loading Criteria: CA Overhead Line Standard

CPUC:

California Public Utilities Commission

General Order 95:

Overhead Line Construction

• Revised: As Needed

• Founded in 1941

From GO 64 est. 1922

GO95

33

Basic Safety Standard

Electric Supply and Communication Facilities

National Electric Safety Code (NESC)

34

Topics of the NESC

Topics Covered

Grounding

Substations

Overhead Electric Supply and

Communication Lines

Underground Electric Supply and

Communication Lines

Work Rules

Wood Poles

35

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

Section 24 Grades of Construction

Section 25 Loading for Grade B&C

Section 26 Strength requirements

• Grades of construction

• Grades include B, C &

N

(B being the highest)

• Loads to apply

• Rule 250B:

Combined ice and Wind

District loading

• Rule 250C:

Extreme wind Loading

• Rule 250D:

Extreme Ice with concurrent

wind loading

• Strength utilization

Overhead Lines Subcommittee

Section 27 Insulators

• Electrical Strength

• Mechanical Strength

37

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

Section 25: Loading for Grade B & C

• Rule 250B: Combined Ice and Wind District loading

• 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)

Deterministic Loads

Probabilistic Loads

39

NESC District Loading

½” Ice – 40 mph

¼” Ice – 40 mph

0” Ice – 60 mph

40 mph = 4 lbs/sqft

60 mph = 9 lbs/sqft

40

GO95 District Loading

>3000ft elevation

½” Ice - 48 MPH

<3000ft elevation

0” Ice - 56 MPH

Heavy Loading District

Light Loading District

41

Extreme Wind– Rule 250C

Summer Storm

85 mph = 18.5 lbs/sqft

90 mph = 21 lbs/sqft



42

Ice with Concurrent Wind –Rule 250D

Winter Storm

Wind Speeds

30 mph

40 mph

50 mph

60 mph

Radial Ice

0”

0.25”

0.5”

0.75”

1.0”

43

Grade B Grade Cx Grade C

Ru

le 2

50

B

Vertical Loads 1.50 1.90 1.90

Transverse Loads

(wind) 2.50 2.20 1.75

Longitudinal

Loads 1.10 No Req. No Req.

25

0C

Wind Loads 1.00 1.00 1.00

25

0D

Ice and Wind

loads 1.00 1.00 1.00

Section 25: Table 253.1-Load Factors

44

Section 26: Strength Factors

Fiber Strength (ANSI)

× Strength Factor (NESC)=

Allowable Stress of Pole

Grade B Grade C R

ule

25

0B

Metal Structures 1.0 1.0

Wood Structures 0.65 0.85

25

0C

& 2

50

D

Metal Structures 1.00 1.00

Wood Structures 0.75 0.75

Table 261-1

45

Restore or Replace Thresholds

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.

Strength required when installed, NOT original strength of wood pole used.

When to restore or replace: NESC

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…

46

Load and Strength Factors

Grade B Grade C

Load Factor 2.5 1.75

Strength Factor 0.65 0.85 Effective Overall

Safety Factor 3.85 2.06

Rule 250B: District Loading

Effective Restore

or Replace

Threshold (2/3 ) 2.57 1.37

47

Grade A Grade B Grade C A

t

Inst

all

ati

on

Wood Pole Safety

Factor 4 3 2

At

Rep

lacem

en

t

Wood Pole Safety

Factor 2.67 2 1.33

GO95: Table 4- Safety Factors

48

Bending Load Bending Capacity >

In Service Analysis

Wire with Ice

49

Bending Capacity

In Service Analysis

•Class is determined by the load on the pole

• Length is determined by required clearance

50

Bending Load

In Service Analysis

Wire with Ice

Load types acting on the pole:

o Wind

o Ice

o Line Tension

o Guy Tension

o Weight (equipment, conductors, etc)

51

TRANSVERSE

V

E

R

T

I

C

A

L

Loading Directions

52

Balanced

Unequal

Longitudinal Loading

53

Balanced

Longitudinal Loading - Guys

54

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

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, …

Guys add to VERTICAL loads,

Balance LONGITUDINAL loads/ wire

tensions

55

56

57

V

E

R

T

I

C

A

L

Vertical Pole Loading

59

•Weight of Conductor

(+ice @ 57lb/ft3)

•Equipment Weight

•Pole Weight

•Down Guy Vertical Load

STRUCTURE MUST RESIST BUCKLING

Vertical Pole Loading

60

Transverse Load Dictates Design

Wire with Ice

61

TRANSVERSE

Wind Bending Loads On:

Wires

Ice

Pole

Equipment

Offset Bending Loads

Wire Tension

Calculating Transverse Loads

62

Height (ft)

DiameterC

x Load Factor

x Span x Wind Pressure

x Height = ft-lb

Groundline Bending Moment

Transverse Wind Load on Conductors

63

0.75” 1.50” 3.00”

Wind Effects on Wire Sizes

2X 2X

double wire diameter, double the load

64

0.75” 1.50” 3.00”

1.25” 2.00” 3.50”

+67% +33% +17%

Wind Effects: Wire Sizes + 0.25” Radial Ice

.25” Ice

.75” Wire

65

All Moments Added Together

66

Moment from Wind on Conductors

+ Moment from Wind on Pole

+ Moment from Wind on Equipment

+ Moment from Equipment Offset

= Total Groundline bending Moment

Evaluating Existing Structures

67

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

Moment from Wind on Conductors

+ Moment from Wind on Pole

+ Moment from Wind on Equipment

+ Moment from Equipment Offset

= Total Groundline bending Moment

Evaluating an In-Service Pole - By Hand

69

Pole Loading Analysis Software Reports

70

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

Determining In-Service Strength

72

Restore or Replace Thresholds

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.

Strength required when installed, NOT original strength of wood pole used.

When to restore or replace: NESC

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…

73


75


26” 34”

37,120 ft-lb 83,010 ft-lb

Circumference Increase - 30%

Bending Capacity Increase - 123%

80-90%

Pole’s Bending Strength

In The Outer 2-3” Of Shell!


76


26” 34”

37,120 ft-lb 83,010 ft-lb

Circumference Decrease - 24%

Bending Capacity Reduction - 55%

SYP – Southern Yellow Pine

77

Thick Sapwood Species

Southern Yellow Pine

Advanced Shell Rot

78

External Decay Pockets

79

Df - Douglas fir

WC - Western red cedar

www.osmoseutilities.com 80

Thin Sapwood Species

Douglas Fir

Western Red Cedar

Early Stage of Decay/

Enclosed Decay Pocket

81

Advanced Internal Decay

82

Circumference Calculator

• Limited Variables

• Measured Decay Circumference Reduction

• Results in Effective Circumference

• Effective Circumference Allowable Table

Reject Decision

Effective Circumference

Slide Rule Reject Criteria

• External Decay & Internal Pockets o Effective circumference

• Hollow Heart o Minimum average shell

84

Bending Stress

Line of

Lead

Wind on Wires 83%

99%

85

88%

2005 – Electronic Strength Calculator

86

Electronic Strength Calculator

87

Inspector no longer averages measurements

Reject criteria consistent for all circumferences

Reject decision based on remaining strength

Reject criteria can be adjusted

Orientation of decay is considered

Common Reject Threshold

Bending Strength

Remaining Effective Circumference

13%

50% 33% 100%

Reject

87%

67%

Serviceable

4% 100% 33%

69%

40 Class 4 34in Circumference = Reject @ 29.5in

¾” Reduction of shell

100 Years Old

Inaugural NESC Summit

90

Keynote Speakers & Bios

91

High Powered Speakers

92

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

NESC 100 Years Old

presented by Don Hooper

93

94

95

96

97

98

Schedule for 2017 NESC

Submit change proposals: Jan 2012 - July 2013

First Subcommittees Votes: Sept-Oct 2013

Preprint Distributed: September 2014

Public Comments Until: May 2015

Subcommittees Vote on Comments: Sept-Oct 2015

Draft Submitted for Letter Ballot: January 2016

Revisions Submitted to ANSI: May 2016

Published: August 2016

Effective: January 2017

99

19 Months

13 Months

9 Months

6 Months

3 Months

4 Months

3 Months

2017 NESC

100

Re-format Rule 241.C. At Crossings

101

241. Application of grades of construction to different situations

2012 version


102


2012 version

2017 version


103


2012 version

2017 version

Same Words

Easier to Comprehend

Revised Table 242-1

104

Intention:

Improve logical layout and format

Columns sequence from low to high voltage

Rows sequence from low to high voltage

105

2012

Table 242-1

106

2012

Table 242-1

107

2017 Table 242-1

108

2017 Table 242-1

Revise Table 242-1

Grades of Construction Applications

109

CP Intention:




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.

Revise Table 242-1


110

CP Intention:





Add FN 11 – Grade N for dielectric fiber-optic

supply cables

Revise Table 242-1


111

CP Intention:






supply cables

Meet Rule 230F1b – Insulated Comm Cables in

Supply Space

and

Supported by effectively grounded messenger

or

Bonded at intervals specified in Rule 092C to

Supply messengers supporting cable meeting

Rule 230C1

Revise Table 242-1


112

CP Intention:






supply cables

Clarify when ice is applied

Rule 250D

113

…………

Clarify when ice is applied

Rule 250D

114

…………

Add ice to:

Wires

Conductors

Cables

Messengers

Do not add ice to:

Structure

Other supported facilities

Aeolian Vibration – Rule 261H.1.b

115


116


117

Final Action: Accept

Insulators – New Rating System

118

Old Line Post ratings:

Rating equal to average

Lowest not less than 85% of average

New Line Post ratings:

Rating = Minimum of all insulators

Insulators – New Rating System

119

Old Transmission Suspension ratings:

1.2 standard deviations

New Transmission Suspension ratings:

3.0 standard deviations

Insulators

120

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

Insulators Table 277-1

121


122


123


124

Nonceramic Table 277-1 cont’d

125

Table 277-1 cont’d

126


127


128


129

FN 3: This percentage shall be supplied by the manufacturer.



130

FN 3: This percentage shall be supplied by the manufacturer.


NESC Visioning Sessions

131

Future of the NESC

Safety

Reliability

Resiliency

NIST-National Institute of

Standards & Technology

132

NIST – Disaster Resilience Framework

133

NIST - NESC

134

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 …….)

NIST – NESC Rule 250C

135

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).

NESC Workshop

October 18-19, 2016

San Antonio, TX

2017 NESC Changes

The Future of the NESC

Thank you Name Nelson Bingel

Phone 770-632-6703

Email [email protected]

Chad Newton

770-632-6777

[email protected]

Documents

Strength & Loading Webinar - Osmose Utilities Services, Inc. and Loading Webinar_4.pdf · Overview •Benefits of Wood as a Utility Pole Material •Defining Wood Pole Strength •Loading