Manual Asce 111 Postes

ASCE Manual and Reports of Engineering ASCE Manual and Reports of Engineering

Practice 111 Practice 111

Reliability Based Design of Reliability Based Design of

Utility Pole Structures Utility Pole Structures Birmingham, Alabama Birmingham, Alabama

October 15, 2006 October 15, 2006

Short Course Coordinated by: Short Course Coordinated by:

Dr. H. J. Dr. H. J. Dagher Dagher, P.E. , P.E.

[email protected] [email protected]

10/15/06 10/15/06 ASCE Manual 111 Workshop ASCE Manual 111 Workshop 2 2

Order from ASCE website: Order from ASCE website: https:// https://www.asce.org/bookstore/book.cfm?book www.asce.org/bookstore/book.cfm?book=6366 =6366


Session Outline Session Outline u u 1:00 Overview of course 1:00 Overview of course (Dr. H. (Dr. H. Dagher Dagher, P.E., 5 minutes) , P.E., 5 minutes) u u 1:05 1:05 Utility Perspective Utility Perspective (Mike (Mike Voda Voda, P.E., 10 minutes) , P.E., 10 minutes) u u 1:15 NESC History 1:15 NESC History (Nelson (Nelson Bingel Bingel, P.E., 20 minutes) , P.E., 20 minutes) u u 1:35 RBD Methodology 1:35 RBD Methodology (Dr. H. (Dr. H. Dagher Dagher, P.E. 35 minutes) , P.E. 35 minutes)

2:10 Break (15 minutes) 2:10 Break (15 minutes)

u u 2:25 Reliability Calibration 2:25 Reliability Calibration (Michael (Michael Voda Voda, P.E., 25 minutes) , P.E., 25 minutes) u u 2:45 Loads 2:45 Loads (Dr. Jerry Wong, P.E. 20 minutes) (Dr. Jerry Wong, P.E. 20 minutes) u u 3:05 Nominal Resistance 3:05 Nominal Resistance (Dr. H. (Dr. H. Dagher Dagher, P.E., 25 minutes) , P.E., 25 minutes)

3:35 Break refreshments served 3:35 Break refreshments served (15 minutes) (15 minutes)

u u 3:50 Design Examples 3:50 Design Examples (Ron Randle, P.E., 70 minutes) (Ron Randle, P.E., 70 minutes)

5:00 adjourn 5:00 adjourn

Earns a total of 3.5 Earns a total of 3.5 PDH's PDH's Please sign form once in back of room! Please sign form once in back of room!


Thank You Committee Members! Thank You Committee Members!

u u Dr. Jerry Wong Dr. Jerry Wong FPL FPL u u Magdi Magdi Ishac Ishac Hydro 1 Hydro 1 u u Brian Brian Lacoursiere Lacoursiere IUSI IUSI u u Camille Camille Rubeiz Rubeiz AISI AISI u u Dr. James Davidson Dr. James Davidson Shakespeare Shakespeare u u Wes Oliphant Wes Oliphant Newmark Newmark u u David West David West Duke Energy Duke Energy u u Martin Rollins Martin Rollins HM Rollins HM Rollins u u Gary Bowles Gary Bowles Electrical Consultants Electrical Consultants u u Larry Slavin Larry Slavin Outside Cons. Outside Cons. u u Alec Alec Zoltoochin Zoltoochin BC Hydro BC Hydro


The Utility Perspective The Utility Perspective

presented by presented by

Michael Voda, P.E. Michael Voda, P.E. – – Principal Civil Engineer Principal Civil Engineer

Salt River Project Salt River Project



RBD? RBD?

We don We don’ ’t need no t need no stink stink’ ’n n RBD! RBD!


u u The NESC has been in used for design The NESC has been in used for design for a number of years for a number of years

“ “This code is not intended as a design This code is not intended as a design specification or as an instruction specification or as an instruction manual. manual.” ”

u u But It works But It works

u u Why do we need something new? Why do we need something new?



Challenge #1 Challenge #1 NESC NESC Loads Loads “ “Old Method Old Method” ”: : Different Load Depending On Pole Material Different Load Depending On Pole Material

♦ ♦ Economical engineered alternatives to wood Economical engineered alternatives to wood are available. are available.

♦ ♦ Different factored loads Different factored loads depending on depending on material material of pole. of pole.

♦ ♦ Do actual wind and ice loads vary if the pole Do actual wind and ice loads vary if the pole material is different? material is different?


Challenge #2 Challenge #2 NESC Strength: NESC Strength: Defined Differently Depending Defined Differently Depending

On Pole Material On Pole Material

♦ ♦ Natural wood poles use Natural wood poles use mean strength mean strength

♦ ♦ Engineered materials use Engineered materials use minimum minimum strength strength

♦ ♦ What is the What is the relative measure relative measure of strength to of strength to insure equivalent reliability across materials? insure equivalent reliability across materials?


Challenge #3 Challenge #3 Loading Loading On On Distribution Distribution Poles: Poles:

♦ ♦ Historically, design controlled by clearances; Historically, design controlled by clearances; not loads. not loads.

♦ ♦ Poles are loading up to NESC limits with Poles are loading up to NESC limits with communications; communications; how is reliability impacted? how is reliability impacted?

♦ ♦ NESC Load Districts: Load NESC Load Districts: Load boundaries boundaries follow follow political political boundaries >> boundaries >>


Weather Related Loads Weather Related Loads

u u Do they differ across Do they differ across political political boundaries??? boundaries???


Needs Needs

u u Load Definition Load Definition – – A method of defining line loading that is independent of A method of defining line loading that is independent of the material used for the supporting structure. the material used for the supporting structure.

– – Weather loads that reflect actual measured events to Weather loads that reflect actual measured events to insure consistent structural reliability across the insure consistent structural reliability across the country. country.

u u Nominal Pole Strength Nominal Pole Strength – – A consistent method for comparing relative strengths of A consistent method for comparing relative strengths of poles made of differing materials. poles made of differing materials.

– – A method that will result in similar structural reliability A method that will result in similar structural reliability across the various materials across the various materials


Next: Next:

NESC NESC A Historical Perspective A Historical Perspective


Nelson Bingel Nelson Bingel – – VP VP Engineering Engineering Osmose Utilities Services Osmose Utilities Services




National Electrical Safety Code National Electrical Safety Code


National Electrical Safety Code National Electrical Safety Code Section 1.

Introduction to the National Electrical Safety Code ®

010. Purpose The purpose of these rules is the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment.

These rules contain the basic provisions that are considered necessary for the safety of employees and the public under the specified conditions. This code is not intended as a design specification or as an instruction manual.

















National Electrical Safety Code National Electrical Safety Code

safety of employees and the public under the specified conditions.


NESC Editions NESC Editions u u 1914 1914 First Edition First Edition

u u 1916+ 1916+ 2 2 nd nd Edition, 3 Edition, 3 rd rd Edition Edition

u u 1926 1926 4 4 th th Edition Edition



u u 1977,1980,1984 1977,1980,1984

u u 1987,1990,1993,1997, 2002 1987,1990,1993,1997, 2002


NESC Loads, LF & SF NESC Loads, LF & SF

1 1 0.85 0.65 1.75 2.5 1.75 2.5 9 psf 4 psf 4 psf 2002

1 1 0.85 0.65 2.2 2.5 1.75 2.5 9 psf 4 psf 4 psf 1987

2.2 2.5 2 4 9 psf 4 psf 4 psf 1977

0.5 0.25 2.2 2.54 9 psf 4 psf 4 psf 5th

0.909 0.788 0.658 0.439 12 psf 8 psf 8 psf 4th

C B C B C B C B L M H Editon

Steel SF Steel LF Wood LF Wood SF


LONGINTUDINAL

TRANSVERSE

V E R T I C A L


L L c c

D D

2 ft 2 ft

Class 1 4,500 lb Class 1 4,500 lb Class 2 3,700 lb Class 2 3,700 lb Class 3 3,000 lb Class 3 3,000 lb Class 4 2,400 lb Class 4 2,400 lb Class 5 1,900 lb Class 5 1,900 lb

ANSI O5.1 ANSI O5.1

Applied Applied Bending Load = Bending Load = L L c c x x D (ft D (ft lb) lb)


L L c c

Compression (psi) Tension (psi)

Bending Capacity = Bending Capacity = k k x x fiber strength fiber strength x x C C 3 3 (ft (ft lb) lb)

Fiber Strength

ANSI O5.1 ANSI O5.1


L L c c

k k x x fiber strength fiber strength x x C C 3 3 (ft (ft lb) lb)

ANSI O5.1

Bending Bending Capacity Capacity

= = k k x x fiber strength fiber strength x x C C 3 3 (ft (ft lb) lb) k k x x fiber strength fiber strength x x C C 3 3 (ft (ft lb) lb)

L L c c


HEAVY HEAVY

HAWAII LIGHT ALASKA HEAVY

MEDIUM MEDIUM

LIGHT LIGHT

Deterministic Loads Deterministic Loads

Light Medium Heavy

Ice 0" .25" .5" (radial thickness)

Wind 9 lb 4 lb 4 lb (per sq. ft.)

NESC

RADIAL ICE ON CONDUCTOR


HEAVY HEAVY


MEDIUM MEDIUM

LIGHT LIGHT


Light Medium Heavy



NESC


HEAVY HEAVY


MEDIUM MEDIUM

LIGHT LIGHT


Light Medium Heavy



NESC


4 lb. Transverse Wind

.25” ICE

Working Load Working Load

Medium Loading District


Durability Durability

Grade of Grade of Construction Construction

NESC NESC B C

4 2


GRADE B

900 lb Working Load

x 4

Class 1 4500 lb Class 2 3700 lb Class 3 3000 lb Class 4 2400 lb Class 5 1900 lb = 3600 lb

NESC ANSI O5.1


GRADE C

900 lb Working Load

x 2


NESC ANSI O5.1


NESC Loads, LF & SF NESC Loads, LF & SF

1 1 0.85 0.65 1.75 2.5 1.75 2.5 9 psf 4 psf 4 psf 2002

1 1 0.85 0.65 2.2 2.5 1.75 2.5 9 psf 4 psf 4 psf 1987

2.2 2.5 2 4 9 psf 4 psf 4 psf 1977

0.5 0.25 2.2 2.54 9 psf 4 psf 4 psf 5th

0.909 0.788 0.658 0.439 12 psf 8 psf 8 psf 4th

C B C B C B C B L M H Editon

Steel SF Steel LF Wood LF Wood SF


Load Resistance Factored Design Load Resistance Factored Design

Load * Factor < Resistance * Factor Load * Factor < Resistance * Factor (Strength) (Strength)

LRFD LRFD


Overload Strength Overload Strength Alternate Factor Factor Factor Factor Method

Wood B Wood B 2.50 ÷ .65 = 3.85 4.0 Wood C Wood C 1.75 ÷ .85 = 2.06 2.0

Standard vs. Alternate Standard vs. Alternate Overload Factors Overload Factors


GRADE B

900 lb Working Load

x 4




Load * Factor < Resistance * Factor (Strength)

900 lb * 2.5 < 3700 lb * .65

2250 lb < 2405 lb

LRFD LRFD



Load * Factor < Resistance * Factor (Strength)

LRFD LRFD



Load * Factor < Resistance * Factor Load * Factor < Resistance * Factor (Strength) (Strength)

LRFD LRFD Reliability Reliability Based Based

Load Load RP RP < 5% < 5% LEL LEL



RBD Methodology RBD Methodology presented by presented by

Dr. H. J. Dagher, P.E. Dr. H. J. Dagher, P.E.

Director, Advanced Structures and Director, Advanced Structures and

Composites Laboratory Composites Laboratory

University of Maine University of Maine

Next: Next:


Objective of Talk Objective of Talk

Describe work of Describe work of

ASCE/SEI Committee on Pole RBD ASCE/SEI Committee on Pole RBD

Oct 00 Oct 00 present present


Committee Charter Committee Charter

Write: Write:

ASCE/SEI Manual of Engineering Practice: ASCE/SEI Manual of Engineering Practice:

Structural Reliability Based Design Structural Reliability Based Design

of Utility Poles of Utility Poles

Goal: Goal:

Achieve relatively consistent Achieve relatively consistent structural structural reliabilities across materials & locations reliabilities across materials & locations


18 Active Committee Members 18 Active Committee Members

u u Producers (wood, steel, concrete, FRP) Producers (wood, steel, concrete, FRP) u u University faculty University faculty u u Utility engineers Utility engineers u u 8 meetings 8 meetings

• • 2 2 3 days each 3 days each • • over 1.5 yrs over 1.5 yrs

♦ Regular conference calls Regular conference calls


Official Committee Roster (27) Official Committee Roster (27) Aichinger, Richard Valmont Industries Bingel, Nelson Osmose, Inc. Bowles, Gary Electrical Consultants

Brewer, William A. Rochester Gas and Electric Co.

Costa, Richard National Grid Dagher, Habib UMaine Davidson, James Shakespeare Slavin, Larry OCS Fouad, Fouad U of Alabama Birm. Garcia, Michael C. Tampa Electric Co. Goodwin, Tip Entergy Gromala, David Weyerhaeuser Ishac, Magdi Hydro 1 Networks Inc.

Lacoursiere, Brian IUSI Martirossian, Robert PEPCO Moritz, Terence Arizona Public Service Co.

Oliphant, Wes Newmark International, Inc.

Randle, Ron EDM Rollins, Martin H. M. Rollins Rubeiz, Camile AISI Snyder, Dan AISI Vandergriend, Larry Hughes Brothers Voda, Michael Salt River Project West, David Duke Energy Wolfe, Ron Forest Products Lab Wong, Jerry Florida Power & Light Zolotoochin, Alec BC Hydro


Outline Outline 1. Why was the RBD Committee formed? Why was the RBD Committee formed?

2. 2. What is RBD? What is RBD?

3. 3. Are all strength guides created equal? Are all strength guides created equal?

4. 4. What is the probability of failure of a What is the probability of failure of a pole and why should we care? pole and why should we care?

5. 5. What is reliability calibration? What is reliability calibration?

6. 6. Outline of Pole RBD Manual Outline of Pole RBD Manual

7. 7. What will RBD do for the industry? What will RBD do for the industry?


1. Why was the ASCE RBD 1. Why was the ASCE RBD Committee Formed? Committee Formed?

u u Pole industry controversies Pole industry controversies

u u NESC factors not reliability NESC factors not reliability based based

u u Strength guides inconsistent Strength guides inconsistent

u u New materials cannot be included New materials cannot be included

u u How much How much “ “fat fat” ” is there in today is there in today’ ’s s designs? designs?

u u How reliable are today How reliable are today’ ’s designs? s designs?

u u ASCE/SEI to provide guidance ASCE/SEI to provide guidance


’ ’97 97, , ’ ’02 & 02 & ’ ’07 07 NESC Load & Strength Factors NESC Load & Strength Factors Wind Wind Rule 250B Rule 250B District loading District loading – – Not crossing Not crossing

Grade C LF for steel reduced in 2002 Grade C LF for steel reduced in 2002

53% 53% 88% 88% 70% 70%

C/B C/B

2.06 2.06 0.85 0.85 1.75 1.75 2.2 2.2 1.75 1.75

1 1 2.2 2.2 1.75 1.75

C C

3.85 3.85 0.65 0.65 2.5 2.5 2.5 2.5 1 1 2.5 2.5 B B

LF/SF LF/SF SF SF LF LF LF/SF LF/SF SF SF LF LF

Wood Wood Steel Steel

GRADE GRADE


2. What is Reliability 2. What is Reliability Based Based Design (RBD)? Design (RBD)?

u u Each pole has a probability of failure Each pole has a probability of failure u u RBD gives consistent target reliability RBD gives consistent target reliability u u Uses multiple partial safety factors rather Uses multiple partial safety factors rather than one than one

u u Partial safety factors depend on load and Partial safety factors depend on load and strength statistics & target reliability strength statistics & target reliability


LRFD versus LRFD versus Reliability Reliability Based LRFD? Based LRFD?

u u L Load and oad and R Resistance esistance F Factor actor D Design esign

R R 5 5 > Q > Q RP RP

φ φ R R n n > > Σ Σ γ γ i i Q Q i i

0.9 0.9 M M n n > > 1.2 1.2 M M DL DL + + 1.6 1.6 M M LL LL

u u φ φ’ ’s and s and γ’ ’s judgement based, soft s judgement based, soft

calibrated, or reliability calibrated, or reliability based based


Is it Harder to Design with RBD? Is it Harder to Design with RBD?

u u No, you won No, you won’ ’t need a Ph.D. in statistics! t need a Ph.D. in statistics!

u u Everyday design effort will be the same Everyday design effort will be the same

u u We have done all the hard work: We have done all the hard work:

The ASCE Manual will provide load and The ASCE Manual will provide load and

strength factors strength factors


Will RBD Require More Will RBD Require More Expensive Poles? Expensive Poles?

u u No, on the average, designs will be No, on the average, designs will be

equivalent to NESC grades B and C equivalent to NESC grades B and C


Manual 72 for steel poles Manual 72 for steel poles

PCI guide for P/C poles PCI guide for P/C poles ANSI 05.1 for wood poles ANSI 05.1 for wood poles

…… ……

3. Are all Strength Guides Created 3. Are all Strength Guides Created Equal? Equal?


Strength Strength u u Experiment: Test 100 identical poles Experiment: Test 100 identical poles

to failure (cantilever test) to failure (cantilever test)

Mean = average strength Mean = average strength

STD = standard deviation STD = standard deviation

COV COV = standard deviation/mean = standard deviation/mean

– – If STD = 20; mean= 100; If STD = 20; mean= 100; COV=20/100=0.2 COV=20/100=0.2

– – If STD = 40; mean= 200; If STD = 40; mean= 200; COV=40/200=0.2 COV=40/200=0.2


Nominal Strength Nominal Strength R R n n

u u Predicted strength using a code Predicted strength using a code

procedure: procedure:

– – Manual 72 for steel poles Manual 72 for steel poles

– – PCI guide for P/C poles PCI guide for P/C poles

– – ANSI 05.1 for wood poles ANSI 05.1 for wood poles


Lower Exclusion Limit (LEL) Lower Exclusion Limit (LEL)

1.645 STD 1.645 STD

5% LEL = 5th weakest in 100 identical poles

If the pole COV=20%, then 5% LEL = m1.645 (0.2 m)

= 0.67 m

Strength Strength

Mean Mean


Nominal Strength Nominal Strength in Current Design Guides? in Current Design Guides?

1.645 m V 1.645 m V

5% LEL 5% LEL Manual Manual 72? 72? FRP? FRP?

Mean Mean

ANSI ANSI 05.1? 05.1?

1 % LEL 1 % LEL

Manual Manual 72? 72?

Strength Strength


Where is the Nominal Strength in ANSI 05.1?

Strength Strength

71% LEL 71% LEL =1.2 x Mean =1.2 x Mean SP > 50 SP > 50’ ’

82% LEL 82% LEL =1.13 x Mean =1.13 x Mean DF > 50 DF > 50’ ’

33% LEL 33% LEL =0.92 x Mean =0.92 x Mean SP < 50 SP < 50’ ’


ASCE Manual Recommendation: ASCE Manual Recommendation: All Strength Values at 5% LEL All Strength Values at 5% LEL

Strength Strength

1.645 m V 1.645 m V

5% LEL 5% LEL

Manual Manual 72 72

5% LEL 5% LEL

ANSI 05.1 ANSI 05.1

5 % LEL 5 % LEL

PCI P/C PCI P/C


Strength Factor Strength Factor φ φ Manual 111 LRFD Manual 111 LRFD Eq Eq. 2.1 . 2.1 a a

φ φ R R n n > Effect of [1.1 DL + > Effect of [1.1 DL + γ γ Q Q 50 50 ] ]

50 year RP wind

50year RP Ice+wind

Load factor

5% LEL

Q RP


Strength factor Strength factor φ φ

Nominal Nominal Strength Strength Exclusion Exclusion limit , e(%) limit , e(%)

COV COV R R

0.05 0.05 0.1 0.1 0.2 0.2

1.01 1.01 0.97 0.97 0.96 0.96 0.94 0.94 0.92 0.92 0.90 0.90 0.87 0.87

1.16 1.16 1.07 1.07 1.04 1.04 1.00 1.00 0.96 0.96 0.92 0.92 0.85 0.85

1.44 1.44 1.23 1.23 1.17 1.17 1.08 1.08 1.00 1.00 0.92 0.92 0.78 0.78

1.71 1.71 1.37 1.37 1.26 1.26 1.12 1.12 1.01 1.01 .89 .89 .69 .69

0.3 0.3

0.1 0.11 1 2 2 5 5 10 1020 2050 50


Example Example Convert Wood Pole Strength to 5% LEL Convert Wood Pole Strength to 5% LEL

Strength Strength

ANSI 05.1 Annex C, ANSI 05.1 Annex C, SP Pole < 50ft SP Pole < 50ft Mean = 8,661 Mean = 8,661 psi psi COV = 0.17 COV = 0.17

ASCE Pole RBD ASCE Pole RBD Manual Manual

R R n n = 6,250 = 6,250 psi psi LEL = 5% LEL = 5%

6,250/8,661= 0.80

ANSI 05.1 ANSI 05.1 SP Pole < 50ft SP Pole < 50ft R R n n = 8,000 = 8,000 psi psi LEL = 32.6% LEL = 32.6%


4. What is Probability of Failure ? 4. What is Probability of Failure ?

Region where Load > Strength

∫ ∫ f RQ [r,q] dr dq

Strength R Strength R

Mean Mean

Load Q Load Q

Mean Mean Difficult to predict accurately! Use beta β


What Loads are Included in a What Loads are Included in a Reliability Analysis? Reliability Analysis?

Four load categories: Four load categories: u u Category I Category I: : Load produced by climatic phenomena Load produced by climatic phenomena

– – ice, wind, temperature, combinations ice, wind, temperature, combinations

u u Category II: Category II: Load produced by natural/accidental Load produced by natural/accidental events that cannot be described statistically events that cannot be described statistically – – defects, wear, landslides, sabotage, etc. defects, wear, landslides, sabotage, etc.

u u Category III: Category III: Loads produced from construction and Loads produced from construction and maintenance maintenance applications applications

u u Category IV: Category IV: Legislated Loads Legislated Loads


Challenges Challenges In Estimating Failure Probability In Estimating Failure Probability

u u Pole Strength PDF Pole Strength PDF – – Lack of test data FRP, P/C Lack of test data FRP, P/C – – No standard nominal strength equations for FRP Poles No standard nominal strength equations for FRP Poles – – Interpretations of ANSI 05.1? Interpretations of ANSI 05.1?

u u Loads PDF Loads PDF – – 50 50 year Wind on Ice Loads ? year Wind on Ice Loads ? – – Uncertainty in wind profiles < 60 ft ? Uncertainty in wind profiles < 60 ft ? – – 60 ft exemption ( 60 ft exemption (if highest part of pole is below 60 ft, if highest part of pole is below 60 ft, do not design for wind on wires do not design for wind on wires

u u Transfer functions from wind speed to force Transfer functions from wind speed to force – – Shape factor (drag coefficient) Shape factor (drag coefficient) – – Gust response factors Gust response factors – – Velocity pressure coefficient Velocity pressure coefficient


Conventional Reliability Index Conventional Reliability Index β β

Strength R

m R

Load Q

m Q

m R m Q (σ R 2 + σ Q 2 ) 0.5 β =


5. Reliability Calibration? 5. Reliability Calibration?

u u Establish minimum target pole reliability: Establish minimum target pole reliability: How reliable have designs been over the How reliable have designs been over the past 50 years that meet only minimum past 50 years that meet only minimum NESC requirements? NESC requirements?

u u Develop load factors Develop load factors to achieve this to achieve this minimum reliability minimum reliability


40 ft Grade B SP 40 ft Grade B SP NESC NESC’ ’77 77

Annual Prob. Failr. Extreme Wind

0.0397 to 0.0493 (1) 0.0299 to 0.0397 (1) 0.0201 to 0.0299 (1) 0.0103 to 0.0201 (3) 0.0005 to 0.0103 (29)


40 ft Grade C SP 40 ft Grade C SP NESC NESC’ ’77 77

Annual Prob. of failure Extreme Wind 0.09086 to 0.23112 (12) 0.05722 to 0.09086 (1) 0.05512 to 0.05722 (1) 0.0432 to 0.05512 (1) 0.02687 to 0.0432 (2) 0.02044 to 0.02687 (2) 0.0201 to 0.02044 (1) 0.0196 to 0.0201 (15)


How Were Calibration How Were Calibration Results Used? Results Used?

u u Selecting target betas Selecting target betas

– – Grade B, Grade C Grade B, Grade C

u u What have we learned from the reliability What have we learned from the reliability

calibrations? calibrations?

– – Does reliability change geographically? Does reliability change geographically?

– – How reliable is Grade B versus C? How reliable is Grade B versus C?

– – What does the 60 ft exemption really do? What does the 60 ft exemption really do?


Grade Factor γ for ASCE 74 Loads

Extreme Wind Ice+Wind

B Wind Force: 1.0 Wind Force: 1.0 Ice Thickness: 1.0

C Wind Force: 0.5 * Wind Force: 1.0 Ice Thickness: 0.5

* If any portion of the structure or its supported facilities exceeds 60 ft, Use 1

Load Factor Load Factor γ γ φ φ R R n n > Effect of [1.1 DL + > Effect of [1.1 DL + γ γ Q Q 50 50 ] ]


6. Outline of Manual 111 6. Outline of Manual 111 1. Introduction 1. Introduction 2. RBD Format: 2. RBD Format: LRFD equations, load and LRFD equations, load and strength factors to achieve relatively strength factors to achieve relatively consistent reliabilities across materials consistent reliabilities across materials

3. Loads: 3. Loads: ASCE 7, Manual 74 ASCE 7, Manual 74 4. Strength: 4. Strength: 3 methods to obtain pole 3 methods to obtain pole strength statistics strength statistics

Appendices: Appendices: A A Design examples Design examples B B Examples to obtain Examples to obtain R R n n


7. What will RBD do for the 7. What will RBD do for the

Industry? Industry?


Benefits of RBD Benefits of RBD

1. 1. More consistent reliabilities across More consistent reliabilities across materials. materials.

2. 2. More consistent reliabilities across More consistent reliabilities across geographical regions geographical regions

3. 3. Opens door for using new materials Opens door for using new materials

4. 4. Uniform definition of nominal strength Uniform definition of nominal strength

5. 5. Defines reliability levels for Grade B & C Defines reliability levels for Grade B & C


Benefits of RBD Benefits of RBD 6. 6. Allows utilities to select desired reliability Allows utilities to select desired reliability

level (which may be different from Grade level (which may be different from Grade B or C) B or C)

7. 7. Encourages manufacturers to improve Encourages manufacturers to improve their products by providing incentives for their products by providing incentives for smaller smaller COVs COVs and more strength data. and more strength data.

8. 8. Brings pole structural design in line with Brings pole structural design in line with well well established Reliability established Reliability Based Design Based Design codes such as AASHTO, AISC, IEC, the codes such as AASHTO, AISC, IEC, the NDS. NDS.


The Future The Future … … Tying the Pieces Together Tying the Pieces Together

Loads: Manual 74, NESC

ASCE RBD Standard

ASCE Manual 72 steel Pole

ASCE Steel Lattice Standard

PCI Guide ASCE Concrete Pole

ASCE FRP Pole Guide

ASCE Substation

Guide

ASCE Distribution Pole Standard

ANSI 05.1 Wood Poles


Two Points to Remember Two Points to Remember

u u Nominal Strength at 5% LEL Nominal Strength at 5% LEL u u Same loads and load factors for all Same loads and load factors for all materials materials


Quiz: Quiz: What strength should we use? What strength should we use? What load should we use? What load should we use?

Load Q

m Q Q 50

Strength R

m R R 5


Quiz: How do we achieve relatively Quiz: How do we achieve relatively consistent reliability across consistent reliability across materials and locations? materials and locations? Load Q

m Q Q 50

Strength R

m R R 5


Next Steps Next Steps ASCE Manual 111 Development ASCE Manual 111 Development

u u User feedback User feedback u u Start work on second edition in 2008 Start work on second edition in 2008

Calibration of Reliability Based Calibration of Reliability Based Design Method Design Method

Next:


Michael Voda, P.E. Michael Voda, P.E. – – Principal Civil Engineer Principal Civil Engineer Salt River Project Salt River Project


RBD Calibration: RBD Calibration:

RBD RBD ≈ ≈ NESC NESC


Reliability Calibration Reliability Calibration

Develop Strength PDFs 960 poles

Develop Load PDFs 40 locations: Wind Ice+Wind

Load and Strength Factors for RBD

Target Reliability Levels Grade B, Grade C

Annual Prob. of Failure: Wind, Ice+wind Monte Carlo Simulations

Best Pole Analysis Techniques: Transfer functions

Nonlinear Structural Analysis

Design 960 Poles Using NESC: 40 locations x 4 types (40', 65', 70', 110')

x 2 Grades x 3 Materials

Design 240 Wood Poles Using NESC 77: 40 locations x 3 types (40’, 65’, 70’)

X 2 grades

960 poles


Distribution 1 Distribution 1

u u 40 ft pole 40 ft pole u u 3 Phase 336 ACSR 3 Phase 336 ACSR u u Neutral 3/0 AAAC Neutral 3/0 AAAC u u 2 Communication 2 Communication u u 250 ft span 250 ft span u u L L M M H Districts H Districts u u Grade B & C Grade B & C

Design Poles Per Current Practice Design Poles Per Current Practice


Distribution 2 Distribution 2

u u 65 ft pole 65 ft pole u u 556 ACSR Phases 556 ACSR Phases u u 3/0 Neutral 3/0 Neutral u u 2 Communication 2 Communication u u 350 ft span 350 ft span u u L L M M H Districts H Districts u u Grade B & C Grade B & C



Transmission 1 Transmission 1

u u 70 ft pole 70 ft pole u u 3/8 3/8” ” steel static steel static u u 795 ACSR Phases 795 ACSR Phases u u 2 Communication 2 Communication u u 450 ft span 450 ft span u u L L M M H Districts & Ext Wind H Districts & Ext Wind u u Grade B & C Grade B & C



Design Poles Per Current Practice Design Poles Per Current Practice NESC 1977: Grade C NESC 1977: Grade C

Pole Class: Load District

Light Medium Heavy

Dist 1 40ft 4 6 5

Dist 2 65ft 2 4 3

Trans 1 70ft 1 3 2


Design Poles Per Current Practice Design Poles Per Current Practice NESC 1977: Grade B NESC 1977: Grade B

Pole Class: Load District

Light Medium Heavy

Dist 1 40ft 1 3 2

Dist 2 65ft H2 1 H1

Trans 1 70ft H4 H1 H3


Strength PDF Strength PDF ANSI 05.1 2002 ANSI 05.1 2002

§ § Dist 1 Dist 1 SYP 40ft poles SYP 40ft poles mean = mean = 8000 psi COV= 0.20

§ § Dist 2 Dist 2 SYP 65ft poles SYP 65ft poles mean = mean = 8000 psi COV = 0.20

§ § Trans 1 Trans 1 DF 70ft poles DF 70ft poles mean = mean = 8000 psi COV = 0.20

§ § Normal Distribution Normal Distribution used for Fiber Strength used for Fiber Strength


Load PDF Load PDF

u u Wind Wind Extreme Type I Distribution Extreme Type I Distribution ( (Peterka Peterka, , 1998). One PDF for Continental US and 1998). One PDF for Continental US and another for Hurricane zones. another for Hurricane zones.

u u Ice with concurrent wind Ice with concurrent wind Modified Pareto Distribution Modified Pareto Distribution (Jones) (Jones)


u u Monte Carlo Simulation Monte Carlo Simulation

u u 200,000 simulations per pole per location 200,000 simulations per pole per location

u u Results = Results = Annual Probability of Failure Annual Probability of Failure (P (P f f ) ) P Pf f = No. Failures/ No. Simulations = No. Failures/ No. Simulations

u u Relationship between Relationship between ß ß and Pf and Pf P P f f = =Ф Ф [ [ ß ß] ]

Calculate Annual Reliability ( Calculate Annual Reliability (ß ß) )


Monte Carlo Simulation Monte Carlo Simulation


Mean Mean

Load Q Load Q

Mean Mean PASS!! PASS!!


Monte Carlo Simulation Monte Carlo Simulation


Mean Mean

Load Q Load Q

Mean Mean FAIL!! FAIL!!


Dist. 1 40ft Wind Grade B Dist. 1 40ft Wind Grade B

0

1

2

3

4 Reliability Index Beta

ND CO MN IN NE IL OR TX CO WY UT NV MS FL

Location

Heavy Heavy Medium Medium Light Light



0

1

2

3



Location



Trans. 1 70ft Wind Grade B Trans. 1 70ft Wind Grade B

0

1

2

3



Location



Select Target Select Target ß ß

0

1

2

3

Dist 1 Dist 2 Trans 1


Establish Load Factor Establish Load Factor

P P f f = 1 = 1 Ф Ф [ [ ß ß] ]

When Strength R When Strength R5 5 = Load Q = Load QRP RP, ,

1/RP < 1/RP < P P f f < 1/2RP < 1/2RP

LF = LF = ƒ ƒ(Return (Return Period Period) )


0.0

0.5

1.0

1.5

0 100 200 300 400

Return Period (yrs)

Load Factor

Return Period vs Load Factor Return Period vs Load Factor Extreme Type I Distribution Extreme Type I Distribution

50 50

1.0 1.0


Load Factor Load Factor Extreme Wind Grade B Extreme Wind Grade B

0.0

0.5

1.0

1.5

2.0

1/RP 1/2RP


Extreme Wind Grade B Extreme Wind Grade B

u u Selected Selected ß ß ≈ ≈ 2.0 2.0

u u Wind Force Wind Force Load Factor = Load Factor =1.0 1.0


How does a 1977 NESC pole fare How does a 1977 NESC pole fare when evaluated using RBD? when evaluated using RBD?

u u ASCE 7 Wind Map: 50yr 3 sec gust ASCE 7 Wind Map: 50yr 3 sec gust

u u ASCE 74 Loading Methods ASCE 74 Loading Methods

u u RBD Load Factor = 1.0 RBD Load Factor = 1.0 Wind Grade B Wind Grade B



0

0.5

1

1.5

2

ND VT IA MN SD

MI NE PA ME OR WA ID

CO TN AK UT CA AZ MS GA

Location

Utilization




0.0

0.5

1.0

1.5

2.0 Utilization

ND

CO

MN IN

NE

IL

OR

TX

CO

WY UT

NV

MS FL

Location



Trans. 1 70ft Wind Grade B Trans. 1 70ft Wind Grade B

0.0

0.5

1.0

1.5

2.0 Utilization

ND

CO

MN IN

NE

IL

OR

TX

CO WY UT

NV

MS FL

Location



RBD Load Factors: RBD Load Factors: Grade B Grade C

Extreme Wind Load Factor

1.0 .5 (a)

Ice Thickness Factor 1.0 .5 Concurrent Wind Load Factor

1.0 1.0

(a) For Poles/wires with any portion greater than 60 ft above ground, use 1.0

Loads Loads

Next:


Dr. Jerry Wong, P.E. Dr. Jerry Wong, P.E. – – Staff Engineer, Staff Engineer, Florida Power and Light Florida Power and Light


Loads Loads & & Load Effects Load Effects Section 3 Section 3

u u Load Types Load Types (ASCE Manual #74) (ASCE Manual #74)

– – Weather Related Loads Weather Related Loads (Reliability) (Reliability)

u u Extreme Wind, Combined Ice and Wind, High Intensity Wind Extreme Wind, Combined Ice and Wind, High Intensity Wind u u Spatial Influences Spatial Influences u u Alternative Sources Alternative Sources

– – Construction and Maintenance Construction and Maintenance (Safety) (Safety)

– – Failure Containment Failure Containment (Security) (Security)

u u Load Factors Load Factors – – Line System Characteristics Line System Characteristics – – Return Period Adjustments Return Period Adjustments


Extreme Wind Extreme Wind Section 3.1.1 Section 3.1.1

3second Gust Wind


u u Air Density Air Density u u Basic Wind Speed Basic Wind Speed u u Terrain Roughness Terrain Roughness u u Gust Response Factor Gust Response Factor u u Force Coefficient Force Coefficient u u Topography Effects Topography Effects u u Structure and Line Characteristics Structure and Line Characteristics

Extreme Wind Extreme Wind Section 3.1.1 Section 3.1.1


Extreme Ice and Concurrent Wind Extreme Ice and Concurrent Wind Section 3.1.1 Section 3.1.1


u u Vertical Weight Vertical Weight u u Ice Buildup Ice Buildup

– – Projected Area Projected Area – – Force coefficient Force coefficient

u u Tension Tension – – Higher Tension Higher Tension – – Unbalanced Tension Unbalanced Tension

Extreme Ice and Concurrent Wind Extreme Ice and Concurrent Wind Section 3.1.1 Section 3.1.1

♦ ♦ Freezing Rain Freezing Rain

♦ ♦ In In Cloud Icing Cloud Icing

♦ ♦ Wet Snow Wet Snow

♦ ♦ Hoarfrost Hoarfrost


High Intensity Wind High Intensity Wind Section 3.1.1 Section 3.1.1

From ASCE 7


u u Short Short Lived Lived u u Randomly Occurring Randomly Occurring u u High Intensity High Intensity u u Small Impacted Area Small Impacted Area

ASCE #74 recommends, ASCE #74 recommends, when justified and required, when justified and required, “ “F2 F2” ” scale tornado scale tornado (157 mph, 86%) (157 mph, 86%)

High Intensity Wind High Intensity Wind Section 3.1.1 Section 3.1.1


Loads Loads & & Load Effects Load Effects Section 3 Section 3

u u Load Types Load Types (ASCE Manual #74) (ASCE Manual #74)

– – Weather Related Loads Weather Related Loads (Reliability) (Reliability)

u u Extreme Wind, Combined Ice and Wind, High Intensity Wind Extreme Wind, Combined Ice and Wind, High Intensity Wind u u Spatial Influences Spatial Influences u u Alternative Sources Alternative Sources

– – Construction and Maintenance Construction and Maintenance (Safety) (Safety)

– – Failure Containment Failure Containment (Security) (Security)

u u Load Factors Load Factors – – Line System Characteristics Line System Characteristics – – Return Period Adjustments Return Period Adjustments


Line System Characteristics Line System Characteristics Section 3 Section 3

u u Transmission System Transmission System – – Covers larger service territory and could have Covers larger service territory and could have substantial effects when system is not available substantial effects when system is not available

– – Structure supports longer span and higher physical Structure supports longer span and higher physical profile and is more difficult to rebuild or repair when profile and is more difficult to rebuild or repair when damaged damaged

– – The stability of electrical grid could be disturbed by a The stability of electrical grid could be disturbed by a single unplanned failure event single unplanned failure event



u u Distribution System Distribution System – – Limited impact in a relatively small area Limited impact in a relatively small area – – Does not need significant resources to rebuild or Does not need significant resources to rebuild or repair when damaged repair when damaged

– – Electrical grid stability is not dependent upon the Electrical grid stability is not dependent upon the availability of one particular distribution structure availability of one particular distribution structure event event



u u Distribution System Distribution System – – Low profile wind turbulence is more severe and less Low profile wind turbulence is more severe and less predictable predictable

– – Impacts for ice Impacts for ice covered broken tree branches are covered broken tree branches are more significant more significant

– – Debris induced damages occur more often and may Debris induced damages occur more often and may carry higher energy carry higher energy

– – Failure Containment Loads Failure Containment Loads typically typically NOT NOT considered considered


Return Period Adjustment Return Period Adjustment Section 3.4 Section 3.4

Table 3.4 Table 3.4 1 1 Probability of Exceeding Design Load During Reference Period Probability of Exceeding Design Load During Reference Period

0.39 0.39 0.22 0.22 0.10 0.10 0.05 0.05 0.02 0.02 0.005 0.005 0.005 0.005 200 200

0.64 0.64 0.40 0.40 0.22 0.22 0.10 0.10 0.05 0.05 0.01 0.01 0.010 0.010 100 100

0.87 0.87 0.64 0.64 0.40 0.40 0.18 0.18 0.10 0.10 0.02 0.02 0.020 0.020 50 50

0.98 0.98 0.87 0.87 0.64 0.64 0.34 0.34 0.18 0.18 0.04 0.04 0.040 0.040 25 25

100 100 50 50 25 25 10 10 5 5 1 1

Reference Period, n (years) Reference Period, n (years) Annual Annual Probability Probability

Return Return Period Period (years) (years)



1.45 1.45 400 400

1.30 1.30 200 200

1.15 1.15 100 100

1.00 1.00 50 50

0.85 0.85 25 25

Wind Load Factor Wind Load Factor Return Period (year) Return Period (year)

Table 3.4 Table 3.4 2 Approximate Load Factors 2 Approximate Load Factors (Extreme Wind Load (Extreme Wind Load – – 2% annual Probability) 2% annual Probability)



1.00 1.00 1.85 1.85 400 400

1.00 1.00 1.50 1.50 200 200

1.00 1.00 1.25 1.25 100 100

1.00 1.00 1.00 1.00 50 50

1.00 1.00 0.80 0.80 25 25

Current Wind Load Factor Current Wind Load Factor Ice Thickness Factor Ice Thickness Factor Return Period (year) Return Period (year)

Table 3.4 Table 3.4 3 Approximate Load Factors 3 Approximate Load Factors (Combined Ice and Wind Load (Combined Ice and Wind Load – – 2% annual Probability) 2% annual Probability)

Single Pole LRFD Single Pole LRFD Nominal Resistance Nominal Resistance


Ron Wolfe Ron Wolfe Research Engineer Research Engineer

US Forest Products Laboratory US Forest Products Laboratory

Next: Next:


Nominal Resistance ( Nominal Resistance (R R n n ) )

q q Definition Definition – – 5% tolerance 5% tolerance

q q Purpose Purpose – – equitable reliability equitable reliability assessment across pole types. assessment across pole types.

q q Responsibility Responsibility – –

q q Industry Associations Industry Associations

q q individual pole produces individual pole produces


Objective Objective

q q Discuss three options for the evaluation of Discuss three options for the evaluation of nominal resistance for LRFD (Section 4) nominal resistance for LRFD (Section 4)

q q Relate options to material being used Relate options to material being used


Pole Loads and Boundary Pole Loads and Boundary Conditions Conditions

1. Cantilever bending + axial load

2. Tapered beam/column

3. Anchorage fixed

4. Centroid of load variable

5. Solid section for wood

6. Hollow section for fabricated poles


Pole Strength Values Pole Strength Values q q Test Data Test Data

– – Standard Material Property Tests Standard Material Property Tests

– – Full Full scale Pole Test scale Pole Test q q Theoretically Derived Theoretically Derived

– – Solid Wood Solid Wood – – ANSI standard: linear ANSI standard: linear static analysis static analysis – – probability theory probability theory

– – Tubular (Concrete, steel, FRP) Tubular (Concrete, steel, FRP) – – vary vary with manufacturer: often based on with manufacturer: often based on nonlinear FEA. nonlinear FEA.


Options to Determine Options to Determine Nominal Resistance Nominal Resistance

q q Full Scale Tests Full Scale Tests

q q Monte Carlo Simulation with Monte Carlo Simulation with limited full scale tests limited full scale tests

q q Default Values Default Values


Full Scale Tests Full Scale Tests

qProvides reliable estimates of mean strength and strength variability of wood poles

qFailure location may vary with boundary conditions


Empirical Derivation of Empirical Derivation of R R n n

R n = R (1– k * COV)

R = mean strength

k = factors dependent on sample size

Derived to give 50% confidence in 5% LTL.

COV = Mean / standard deviation


5% LTL

1.65 1.65 200 200

1.65 1.65 120 120

1.65 1.65 100 100

1.66 1.66 40 40

1.78 1.78 5 5

k k 50% Conf 50% Conf

Sample Size Sample Size

1.72 1.72

1.75 1.75

1.76 1.76

1.83 1.83

2.46 2.46

k k 75% Conf 75% Conf

R n = R (1– k * COV)


Examples, Method 1, Examples, Method 1, 50% confidence 50% confidence

5,460 5,460 1.649 1.649 120 120 20.6% 20.6% 7165 7165 Doug Fir Treated >50 Doug Fir Treated >50’ ’

3,550 3,550 1.650 1.650 100 100 19.2% 19.2% 5200 5200 W.R.Cedar>50 W.R.Cedar>50’ ’

6,732 6,732 1.649 1.649 118 118 13.5% 13.5% 8660 8660 SP Treated <50 SP Treated <50’ ’

6,233 6,233 6,039 6,039

1.649 1.649 1.78 1.78

143 143 5 5

17% 17% 17% 17%

8660 8660 8660 8660

Doug Fir Treated <50 Doug Fir Treated <50’ ’

5% LTL 5% LTL K K N N COV COV MOR MOR Species Species

From ANSI 05.1 Annex C


Examples, Method 1, Examples, Method 1, 75% confidence 75% confidence

4,582 4,582 1.75 1.75 120 120 20.6% 20.6% 7165 7165 Doug Fir Treated >50 Doug Fir Treated >50’ ’

3,443 3,443 1.76 1.76 100 100 19.2% 19.2% 5200 5200 W.R.Cedar>50 W.R.Cedar>50’ ’

6,614 6,614 1.75 1.75 118 118 13.5% 13.5% 8660 8660 SP Treated <50 SP Treated <50’ ’

6,098 6,098 5,032 5,032

1.74 1.74 2.464 2.464

143 143 5 5

17% 17% 17% 17%

8660 8660 8660 8660

Doug Fir Treated <50 Doug Fir Treated <50’ ’

5% LTL 5% LTL K K N N COV COV MOR MOR Species Species

From ANSI 05.1 Annex C


Monte Carlo Simulation


Test Model Accuracy

q Assess model sensitivity to each variable

qEvaluate covariance matrix for important variables

qVerify model by testing extremes of influencing variables.

q Evaluate Model Adjustment Factor


Variable effects on strength

Dodecagonal Tubes

0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40

100 150 200 250 300 350 400

Sqrt(Fy)*w/t

Fcr/F

y

test

1.45Fy(1.00129sqrt(Fy)w/t)

From ASCE Manual No 72


Assess Accuracy of Model Assess Accuracy of Model

1.02 1.02 65.0 65.0 63.9 63.9 .377 .377 8.67 8.67 65.2 65.2 5 5

1.03 1.03 66.1 66.1 64.3 64.3 .311 .311 8.04 8.04 70.9 70.9 4 4

1.05 1.05 67.0 67.0 63.7 63.7 .252 .252 8.03 8.03 72.1 72.1 3 3

1.04 1.04 64.1 64.1 61.7 61.7 .224 .224 7.95 7.95 71.4 71.4 2 2

1.01 1.01 59 59 58.3 58.3 .189 .189 8.10 8.10 69.3 69.3 1 1

Ratio Ratio tst/pred tst/pred

Test Test ( (ksi ksi) )

Pred Pred ( (ksi ksi) )

t t(in) (in)

w w (in) (in)

Fy Fy ( (ksi ksi) )

# #


Evaluate Model Adjustment Evaluate Model Adjustment Factor Factor

1.005 1.01 1.015 1.02 1.025 1.03 1.035 1.04 1.045 1.05 1.055 1.06

100 150 200 250 300 350 400

Sqrt(Fy)*w/t

Ratio pred/test


Monte Carlo Simulation Result Monte Carlo Simulation Result


Default Default 1. 1. Pre Pre established values (NBS 577) established values (NBS 577)

2. 2. Use analytical model to estimate mean and use the Use analytical model to estimate mean and use the following model to predict variability following model to predict variability

V V R R 2 2 =V =V M M 2 2 +V +V P P 2 2 + V + V F F 2 2 + V + V O O 2 2

M=material , P=model (professional), M=material , P=model (professional), F=fabrication, O = other effects F=fabrication, O = other effects


Conclusions Conclusions u u Empirical derivations require repetitive testing and Empirical derivations require repetitive testing and analysis following standardized procedures. analysis following standardized procedures.

u u Monte Carlo simulation is most appropriate for Monte Carlo simulation is most appropriate for manufactured poles. manufactured poles.

u u Default values should be conservatively derived to Default values should be conservatively derived to encourage more rigorous model development and encourage more rigorous model development and test verification. test verification.

u u Time and experience provide the ultimate test of Time and experience provide the ultimate test of structural reliability. structural reliability.






Load Q

m Q Q 50

Strength R

m R R 5



m Q Q 50

Strength R

m R R 5

Appendix B Appendix B

Design Examples Design Examples

Next: Next:


Ron Randle Ron Randle – – EDM International EDM International

Ft. Collins, Colorado Ft. Collins, Colorado


Design Examples Design Examples u u Load Load – – “ “Q Q” ” – – Load Calculation: Load Calculation:

u u Extreme Wind Loading Extreme Wind Loading u u Combined Ice and Wind Loading Combined Ice and Wind Loading

– – Differences in Grades of Construction Differences in Grades of Construction – – Pole Configurations Pole Configurations

u u Transmission Pole Transmission Pole u u Distribution Pole Distribution Pole

u u Strength Strength – – “ “R R” ” – – Pole Materials Pole Materials

u u Wood Wood u u Steel Steel u u Concrete Concrete u u FRP FRP

All Examples use English Units


LOAD


Wind Load Calculation Wind Load Calculation

F = Q ∗ Kz ∗ (V) 2 ∗ G ∗ Cf ∗ A where,

u Q = air density factor u Kz = velocity pressure exposure coefficient u V = 3 second gust wind velocity u G = gust response factor u Cf = shape factor u A = projected wind area


Load Design Example Load Design Example

u u Wire: Wire: “ “Linnet Linnet” ” ACSR 336.4 (26/7) ACSR 336.4 (26/7) – – Dia = 0.721 Dia = 0.721” ” – – Wt = .463#/ft Wt = .463#/ft – – Conductor Height: H = 60 ft; Conductor Height: H = 60 ft; – – Span = 500 ft Span = 500 ft (wind & weight) (wind & weight)

u u Structure: 80 Structure: 80 ft Round Pole ft Round Pole ( embedment = 10 ft) ( embedment = 10 ft)

u u Loading: Loading: – – Case A: Extreme Wind: 90 mph Case A: Extreme Wind: 90 mph – – Exposure Exposure “ “C C” ” – – Case B: Combined Ice & Wind: 50mph + 1 Case B: Combined Ice & Wind: 50mph + 1 1 1 / /4 4” ” ice ice


Velocity Pressure Exposure Coefficient Velocity Pressure Exposure Coefficient

F = Q ∗ Kz ∗ (V) 2 ∗ G ∗ Cf ∗ A

K Kz z = Velocity Pressure Exposure Coefficient = Velocity Pressure Exposure Coefficient For Wires: For Wires: K Kz z = 2.01 (h/900) = 2.01 (h/900) (2/9.5) (2/9.5)

For Structure: For Structure: K Kz z = 2.01 (0.67h/900) = 2.01 (0.67h/900) (2/9.5) (2/9.5)

where, where, h = structure or wire height h = structure or wire height

Wire: K Kz z = 2.01 (60/900) = 2.01 (60/900) (2/9.5) (2/9.5) = = 1.137 1.137

Structure: K Kz z = 2.01 (0.67 * 70/900) = 2.01 (0.67 * 70/900) (2/9.5) (2/9.5) = = 1.079 1.079


Gust Response Factor Gust Response Factor F = Q ∗ Kz ∗ (V)2 ∗ G ∗ Cf ∗ A

G = Gust Response Factor G = Gust Response Factor For Wires: For Wires: G = [1 + (2.7 G = [1 + (2.7 E Ew w B Bw w 0.5 0.5 )] / k )] / kv v 2 2

For Structure: For Structure: G = [1 + (2.7 E G = [1 + (2.7 Es s B Bs s 0.5 0.5 )] / k )] / kv v 2 2 where, where, h = structure or wire height, L = span length, h = structure or wire height, L = span length, k kv v = 1.43 = 1.43 E Ew w = = 0.346 0.346∗(33 / h) (33 / h) 1/7 1/7 = = 0.346 0.346∗(33 / 60) (33 / 60) 1/7 1/7 = .318 = .318 E Es s = 0.346 = 0.346∗[33/(0.67h)] [33/(0.67h)] 1/7 1/7 = 0.346 = 0.346∗[33/(0.67 [33/(0.67∗70)] )] 1/7 1/7 = .329 = .329 B Bw w = = 1 / (1 + 0.8L / 220) = 1 / (1 + 0.8 1 / (1 + 0.8L / 220) = 1 / (1 + 0.8 ∗500 / 220) = .355 / 220) = .355 B Bs s = = 1 / (1 + 0.375h / 220) = 1 / (1 + 0.375 1 / (1 + 0.375h / 220) = 1 / (1 + 0.375 ∗ 70 / 220) = .893 70 / 220) = .893

Wire: Gw w = = [1 + (2.7 [1 + (2.7 * * .318 .318 * .355 * .355 0.5 0.5 )] / 1.43 ] / 1.43 2 2 = = 0.739 0.739

Structure: G Gs s = = [1 + (2.7 [1 + (2.7 * * .329 .329 * .893 * .893 0.5 0.5 )] / 1.43 ] / 1.43 2 2 = = 0.851 0.851


Shape Factor Shape Factor

F = Q ∗ Kz ∗ (V) 2 ∗ G ∗ Cf ∗ A Cf = Shape Factor: • For Wires – Cf = 1.0 • For Members – Cf = 0.9 for circular and 16sided shapes 1.0 for 12sided shapes 1.4 for 8 and 6sided shapes 2.0 for square and rectangular shapes

Wires: Cf = 1.0 and Round Pole: Cf = 0.9


Summary of Wind Load Factors Summary of Wind Load Factors u u Extreme Wind: 90 mph Extreme Wind: 90 mph – – Exposure Exposure “ “C C” ”

Wire Structure Q = 0.00256 same Kz = 1.137 1.079 V = 90 mph same G = 0.739 0.851 Cf = 1.0 0.9 (ASCE Manual 741991 – Table 2.63)

u Combined Ice & Wind V = 50 mph same


Load Calculations Load Calculations

F = Q ∗ Kz ∗ (V) 2 ∗ G ∗ Cf ∗ A uExtreme Wind:

– Tw = .00256 ∗ 1.137 ∗ (90) 2 ∗ 0.739 ∗ 1.0 ∗ A = 17.4 ∗ A – Ts = .00256 ∗ 1.079 ∗ (90) 2 ∗ 0.851 ∗ 0.9 ∗ A = 17.1 ∗ A

uCombined Ice and Wind: – Tw = .00256 ∗ 1.137 ∗ (50) 2 ∗ 0.739 ∗ 1.0 ∗ A = 5.37 ∗ A – Ts = .00256 ∗ 1.079 ∗ (50) 2 ∗ 0.851 ∗ 0.9 ∗ A = 5.29 ∗ A


Load Factors ( Load Factors (γ γ) )

u u NESC Grade NESC Grade “ “B B” ” Construction; Construction; β β = 2.0 = 2.0 u u NESC Grade NESC Grade “ “C C” ” Construction; Construction; β β = 1.5 = 1.5

Reference: RBD Manual 111 – Table 2.3

Load Factors (γ) Load Case: Extreme Wind Ice + Wind

Reliability Index: β = 2.0 β = 1.5 β = 2.0 β = 1.5 Wind Force 1.0 0.5 a 1.0 1.0 Ice Thickness na na 1.0 b 0.5 b

Dead Load (Wires + Str. Weight) 1.1 1.1 1.1 1.1 a If any portion of the structure or its supported facilities exceed 60 ft above ground , a load factor of 1.0 should be used. b The load factor for the ice thickness is to be applied to the thickness of the ice prior to calculating the associated load.


Example: Extreme Wind Example: Extreme Wind

u Wind Velocity = 90 mph u Wire: ACSR 336.4 (26/7)

Dia = 0.721 Dia = 0.721” ”; Wt = .463#/ft; Span = 500 ft ; Wt = .463#/ft; Span = 500 ft – Tw = γw ∗ 17.4 ∗ A = 1.0 ∗ 17.4 ∗ (0.721/12) ∗ 500 = 523 lbs

u Structure: Round Pole (70ft above GL) Dia top = 9.0 in.; Dia gl = 19.5 in.;

– Ts = γw ∗ 17.1 ∗ A = 1.0 ∗ 17.1 ∗ [(9.0 + 19.5)/(2 ∗ 12)] ∗ 70 = 1421 lbs

u Grade of Construction (taller than 60ft above GL) – Grade B: γw = 1.0; γdl = 1.1 – Grade C: γw = 1.0; γdl = 1.1


Shorter Pole Shorter Pole Extreme Wind Extreme Wind

uGrade of Construction (60ft or less above GL) – Grade B: γw = 1.0; γdl = 1.1 – Grade C: γw = 0.5; γdl = 1.1

Load Factors (γ) Load Case: Extreme Wind Ice + Wind

Reliability Index: β = 2.0 β = 1.5 β = 2.0 β = 1.5 Wind Force 1.0 0.5 a 1.0 1.0 Ice Thickness na na 1.0 b 0.5 b

Dead Load (Wires + Str. Weight) 1.1 1.1 1.1 1.1 a If any portion of the structure or its supported facilities exceed 60 ft above ground , a load factor of 1.0 should be used. b The load factor for the ice thickness is to be applied to the thickness of the ice prior to calculating the associated load.


Example: Ice + Wind Example: Ice + Wind u Wire: ACSR 336.4 (26/7)

Dia = 0.721 Dia = 0.721” ”; Wt = .463#/ft; Span = 500 ft ; Wt = .463#/ft; Span = 500 ft – T50 = γwind ∗ 5.37 ∗ A = γwind ∗ 5.37 ∗ [(γice ∗ 2.5 + 0.721)/12] ∗ 500 = – Grade “B” Construction (γwind = 1.0; γice = 1.0): T50 = 721 lbs – Grade “C” Construction (γwind = 1.0; γice = 0.5): T50 = 441 lbs

u Structure: Round Pole Dia top = 9.0 in.; Dia gl = 19.5 in.;

– T50 = γwind ∗ 5.29 ∗ A = 5.29 ∗ [(9.0 + 19.5)/(2 ∗ 12)] ∗ 70 = – Grade “B” Construction (γwind = 1.0): T50 = 440 lbs – Grade “C” Construction (γwind = 1.0): T50 = 440 lbs

u Vertical Loads (except ice) – Grade B: γdl = 1.1 – Grade C: γdl = 1.1


STRENGTH


Example #1 Example #1 Transmission Pole Transmission Pole

u u Length: 75 ft Length: 75 ft

u u Shape: Varies Shape: Varies

u u Embedment: 10% + 2 Embedment: 10% + 2 ft ft

u u Wind/Wt Span: 500 ft Wind/Wt Span: 500 ft

u u Wires: Wires:

– – Cond Cond: Drake : Drake ACSR 795 (26/7) ACSR 795 (26/7)

– – OHGW: OHGW: 3/8 3/8 inch EHS inch EHS

– – Comm. Wire: Comm. Wire: (1) 2.0 (1) 2.0 in. dia. in. dia. 75 ft

5’

5’

5’

1’

9.5’

35.5’

14’

Conductors

OHGW

Comm. Wire

5’6”’

75 ft

5’

5’

5’

1’

9.5’

35.5’

14’

Conductors

OHGW

Comm. Wire

5’6”’


ASCE Manual 74: Extreme Wind F = Q ∗ K z ∗ (V) 2 ∗ G ∗ C f ∗ A , where

Q = air density factor: Kz = velocity pressure exposure coefficient:

for conductors = for shield wire = for comm. wire = and, for pole =

V = 3 second gust wind velocity: G = gust response factor = (1 + 2.7 x E x B 0.5 ) / kv 2 , where E = exposure

factor and B = response term

for conductors = for shield wire =

for comm. wire = and, for pole =

Cf = shape factor: for wires = and for pole =

A = projected wind area (ft 2 )

0.00256

0.906 0.759

0.737 0.743

1.063 1.018

1.154 1.114

varies 1.0

90 mph


Extreme Wind Forces Extreme Wind Forces

Extreme Wind – Over 60ft above GL

Grade B & Grade C are the same

Line Component

Wind Pressure (psf)

Wind Area (ft 2 )

Wind Force (lbs)

Wind on Conductors (ea) 17.16 46.17 792 Wind on Shield Wire 17.64 15.00 265 Wind on Comm Wire 16.01 83.33 1334 Wind on Pole 19.97 * Cf Varies with pole geometry


Steel Pole Design Steel Pole Design

u u Pole Properties: ( Pole Properties: (D D top top = 8.00 in., = 8.00 in., D D gl gl = 18.76 in., 12 = 18.76 in., 12 sided sided t = 3/16 in., t = 3/16 in., F F y y = 65 ksi) = 65 ksi)

C Cf f = 1.0 = 1.0 (wind pressure =19.97 psf) (wind pressure =19.97 psf)

u u Strength values: 5% LEL & 10% COV Strength values: 5% LEL & 10% COV ⇒ ⇒ ( (RBD Manual RBD Manual Section 2.6.2) Section 2.6.2)

u u Using non Using non linear analysis techniques: linear analysis techniques: GLM = 250,851 ft GLM = 250,851 ft lbs lbs ⇒ ⇒ F F b b = 57.2 ksi = 57.2 ksi

φ φ = 1.0 = 1.0

< 65 ksi < 65 ksi ⇒ ⇒ Pole is OK Pole is OK

Note !!! Note !!! Stresses also need to be checked at points above groundline Stresses also need to be checked at points above groundline


Wood Pole Design Wood Pole Design

u u Pole Properties: Class H2 Pole Properties: Class H2 Douglass Fir Douglass Fir D Dtop top = 9.87 in., = 9.87 in., D Dgl gl = 18.33 in., = 18.33 in., C Cf f = 0.9 = 0.9 (wind pressure =17.97 psf) (wind pressure =17.97 psf)

u u Strength values: Strength values: Designated Fiber Stress (Mean Strength) Designated Fiber Stress (Mean Strength)

= 8,000 = 8,000 psi psi and COV = 20% and COV = 20% ⇒ ⇒

( (RBD Manual 111 RBD Manual 111 – – Table 2 Table 2 2) 2)

φ φ = 0.79 = 0.79

F Fb b = 0.79 = 0.79 ∗ 8,000 = 6,320 psi


Wood Pole Design Wood Pole Design (cont (cont’ ’d) d)

u u Using linear analysis techniques: GLM = Using linear analysis techniques: GLM =

Wind on pole = 17.97 ∗ [(9.87 + 18.33)/(2 ∗ 12) ∗ 65.5] ∗ 29.47 = = 40,758 ftlbs

Total GLM = 197,242 + 40,758 = 238,000 ftlbs

Line Component

Force (lbs)

Distance (ft)

γ GLM (ftlbs)

Wind on Top Conductor 792 59.5 1.0 47,124 Wind on Middle Conductor 792 54.5 1.0 43,164 Wind on Bottom Conductor 792 49.5 1.0 39,204 Wind on Shield Wire 265 64.5 1.0 17,093 Wind on Communication Wire 1334 35.5 1.0 47,357 Conductor Eccentricity 546 5.5 1.1 3,300 Subtotal (without pole wind force) 197,242


Wood Pole Design Wood Pole Design (cont (cont’ ’d) d)

Total Linear GLM = 197,242 + 40,758 = 238,000 ftlbs

Plus P∆ Effect – Using GereCarter Method: Amplification Factor = 1.112

GLM = 1.112 ∗ 238,000 = 264,656 ftlbs

Sreq’d = 264,656 ∗ 12 / 6320 psi = 502.5 in 3 ⇒ ⇒ CH2 = 57.58 in. Class H2 DF Pole is OK Class H2 DF Pole is OK


Creq’d =

54.14 in.

[Note CH1 = 54.16 in, but P∆ Effect would be greater]


Example #2 Example #2 Distribution Pole Distribution Pole

u u Length: 45 Length: 45 ft ft

u u Shape: Varies Shape: Varies

u u Embedment: 10% + 2 Embedment: 10% + 2 ft ft

u u Wind/Wt Span: 275 ft Wind/Wt Span: 275 ft

u u Wires: Wires: – – Cond Cond: (3) ACSR 336.5 (26/7) : (3) ACSR 336.5 (26/7)

– – Neutral: (1) ACSR 3/0 (6/1) Neutral: (1) ACSR 3/0 (6/1)

– – Comm. Wire: (1) 1.5 Comm. Wire: (1) 1.5 in. in. 45 ft

4’

4.5’

1’

6.5’

29’

Conductors

Neutral

Comm. Wire

2’ 2’ 2’

45 ft

4’

4.5’

1’

6.5’

29’

Conductors

Neutral

Comm. Wire

2’ 2’ 2’


ASCE Manual 74: Ice + Wind ASCE Manual 74: Ice + Wind F = Q F = Q ∗ ∗ K Kz z ∗ ∗ (V) (V) 2 2 ∗ ∗ G G ∗ ∗ C Cf f ∗ ∗ A , where A , where

Q = air density factor = Q = air density factor =

K Kz z = velocity pressure exposure coefficient: = velocity pressure exposure coefficient:

for conductors = for conductors = for neutral wire = for neutral wire =

for comm. wire = for comm. wire = for pole = for pole =

V = 3 second gust wind velocity = 50 mph V = 3 second gust wind velocity = 50 mph u G = gust response factor = (1 + 2.7 x E x B 0.5 ) / kv 2 , where E = exposure

factor and B = response term u for conductors = for shield wire = u for comm. wire = and, for pole = u Cf = shape factor: for wires = and for pole = u A = projected wind area (ft 2 )

1.029 1.005

0.807

0.951 0.975

0.00256

0.812

0.819 0.948

1.0 varies


Combined Ice & Wind Forces Combined Ice & Wind Forces

Wind area for wires = Length ∗ [(Wire Dia. + γ ∗ (2 ∗ Ice Tk)]

EG For Comm. Wire:

Grade B: A = 275’ ∗ [1.5” + 1.0 ∗ (2 ∗ 1.25”)]/12 = 91.67 sf

Grade C: A = 275’ ∗ [1.5” + 0.5 ∗ (2 ∗ 1.25”)]/12 = 63.02 sf

Grade B Grade C Component

Wind Pressure (psf)

Wind Area (ft 2 )

Wind Force (lbs)

Wind Area (ft 2 )

Wind Force (lbs)

Wind on Conductors (ea) 5.31 73.79 392 45.15 240 Wind on Neutral Wire 5.22 67.93 355 39.28 205 Wind on Comm. Wire 5.11 91.67 468 63.02 322 Wind on Crossarm 5.31 0.36 2 0.36 2 Wind on Pole 5.77* Cf varies varies varies varies


Calculation of Groundline Moment Using manual methods to calculate linear moment:

Subtotals: Grade B = 73,097 ftlbs

(w/o pole) Grade C = 45,162 ftlbs

Grade B Grade C Component γ Distance

(ft) Force (lbs)

GLM (ftlbs)

Force (lbs)

GLM (ftlbs)

Wind on all Conds. 1.0 37.5 1176 44,100 720 27,000 Wind on Neutral 1.0 33.5 355 11,892 205 6,868 Wind on Comm. 1.0 29 468 13,572 322 9,338 Eccentricity: Conds. 1.1 4.3 137 648 137 648 Eccentricity: Cond. Ice 1.0 4.3 842 3,621 287 1,234 Wind on Crossarm 1.0 37.0 2 74 2 74 Wind on Pole 1.0 varies varies varies varies varies


Extreme Wind Load Extreme Wind Load

Wind Pressure (psf) Component Grade B Grade C

Wind on Conductors (ea) 17.20 8.60 Wind on Neutral Wire 16.91 8.46 Wind on Comm. Wire 16.55 8.28 Wind on Crossarm 17.20 8.60 Wind on Pole 18.69 Cf 9.35 Cf

u u Per NESC Per NESC : : If If pole is shorter than 60 ft pole is shorter than 60 ft

⇒ ⇒ Design for wind on Design for wind on pole only pole only (no wires) (no wires)

u u Per Manual 111 Per Manual 111: : If If pole is shorter than 60 ft pole is shorter than 60 ft

⇒ ⇒ Design for wind on Design for wind on pole and wires pole and wires

u u Load factor ( Load factor (γ γ): ): Dependent on Grade of Construction Dependent on Grade of Construction

Grade B: Grade B: γ γ = 1.0 = 1.0 and and Grade C: Grade C: γ γ = 0.5 = 0.5


Wood Pole Design Wood Pole Design – – Grade B Grade B u u Assume Class 2 Pole Assume Class 2 Pole ( (D Dt t = 7.96 in., D = 7.96 in., Dg g = 12.83 in.) = 12.83 in.) A = 33.35 A = 33.35 sf sf

u u Linear GLM = 76,171 ft Linear GLM = 76,171 ft lbs lbs [ [73,097+ 73,097+ 1.0 1.0 * * (0.9 * (0.9 * 5.77) 5.77) * 33.35 * 17.75] * 33.35 * 17.75]

u u P P ∆ ∆ = 1.312 Amplification Factor (Gere = 1.312 Amplification Factor (Gere Carter) Carter)

Ground Line Design Moment = 99,936 ft Ground Line Design Moment = 99,936 ft lbs lbs

u u DF Pole: 8,000 DF Pole: 8,000 psi psi and COV = 20% and COV = 20% ⇒ ⇒

u u F Fallow allow = 8,000 = 8,000 * 0.79 = 6,320 psi * 0.79 = 6,320 psi (ANSI O5.1 (ANSI O5.1 2002 & RBD Manual 111 2002 & RBD Manual 111 Table 2 Table 2 2) 2)

u u S Sreq req’’d d = 99,936 * 12 / 6,320 = 189.8 in = 99,936 * 12 / 6,320 = 189.8 in 3 3

u u S Sfurn furn = 207.3 in = 207.3 in Note !!! Note !!!

Stresses also need to be checked at points above groundline Stresses also need to be checked at points above groundline

⇒ ⇒ Class 2 DF Pole is OK Class 2 DF Pole is OK

φ φ = 0.79 = 0.79


Wood Pole Design Wood Pole Design – – Grade C Grade C u u Assume Class 4 Pole Assume Class 4 Pole ( (D Dt t = 6.68 in., D = 6.68 in., Dg g = 11.08 in.) = 11.08 in.) A = 28.49 A = 28.49 sf sf

u u Linear GLM = 47,775 ft Linear GLM = 47,775 ft lbs lbs [ [45,162+ 45,162+ 1.0 1.0 * * (0.9 * (0.9 * 5.77) 5.77) * 28.49 * 17.66] * 28.49 * 17.66]



u u SP Pole: 8,000 SP Pole: 8,000 psi psi and COV = 20% and COV = 20% ⇒ ⇒

u u F Fallow allow = 8,000 = 8,000 * 0.79 = 6,320 psi * 0.79 = 6,320 psi (ANSI O5.1 (ANSI O5.1 2002 & RBD Manual 111 2002 & RBD Manual 111 Table 2 Table 2 2) 2)

u u S Sreq req’’d d = 58,333 * 12 / 6,320 = 110.8 in = 58,333 * 12 / 6,320 = 110.8 in 3 3

u u S Sfurn furn = 133.8 in = 133.8 in


⇒ ⇒ Class 4 DF Pole is OK Class 4 DF Pole is OK

φ φ = 0.79 = 0.79


FRP Pole Design FRP Pole Design – – Grade C Grade C u u FRP Pole: FRP Pole: D Dt t = 12 in., Non = 12 in., Non tapered Square Pole tapered Square Pole A = 38.50 A = 38.50 sf sf

u u Strength data based on a test sample of 5 poles: Strength data based on a test sample of 5 poles:

– – Mean Strength = 111,550 ft Mean Strength = 111,550 ft lbs & COV = 15.5% lbs & COV = 15.5% (Std Dev = 17,228 ft (Std Dev = 17,228 ft lbs) lbs)

– – Assuming Assuming “ “Normal Normal” ” Distribution with a 50% Distribution with a 50% “ “Confidence Confidence” ”: :

5% LTL = 111,550 5% LTL = 111,550 – – 1.78 1.78 * 17,228 = 80,884 * 17,228 = 80,884

(Ref. RBD Manual 111 (Ref. RBD Manual 111 – – Table 4 Table 4 1) 1)

u u Linear GLM = 52004 ft Linear GLM = 52004 ft lbs lbs [ [45,162+ 45,162+ 1.0 1.0 * * (1.6 * (1.6 * 5.77) 5.77) * 38.5 * 19.25] * 38.5 * 19.25]



u u 75,406 ft 75,406 ft lbs < 80,884 ft lbs < 80,884 ft lbs lbs ⇒ ⇒ FRP Pole is OK FRP Pole is OK






Load Q

m Q Q 50

Strength R

m R R 5



m Q Q 50

Strength R

m R R 5


Documents

Manual Asce 111 Postes