ASCE Manual and Reports of Engineering Practice 111 Practice 111
Reliability Based Design of Utility Pole Structures Birmingham, Alabama October 15, 2006 Short Course Coordinated by: Dr. H. J. Dagher Dagher , P.E.
[email protected] [email protected]
Order from ASCE website: https:// https:// www.asce.org/bookstore/book.cfm?book www.asce.org/bookstore/book.cfm?book =6366 =6366
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Session Outline u u u u u u u u
1:00 Overview of course 1:05 Utility Perspective 1:15 NESC History 1:35 RBD Methodology
(Dr. H. Dagher Dagher , P.E., 5 minutes) (Mike Voda Voda , P.E., 10 minutes) (Nelson Bingel Bingel , P.E., 20 minutes) (Dr. H. Dagher Dagher , P.E. 35 minutes)
2:10 Break (15 minutes) u u u u u u
2:25 Reliability Calibration (Michael Voda Voda , P.E., 25 minutes) 2:45 Loads (Dr. Jerry Wong, P.E. 20 minutes) 3:05 Nominal Resistance (Dr. H. Dagher Dagher , P.E., 25 minutes)
3:35 Break refreshments served u u
3:50 Design Examples
(15 minutes)
(Ron Randle, P.E., 70 minutes)
5:00 adjourn Earns a total of 3.5 PDH's ASCE Manual 111 Workshop Please sign form once in back of room! Please sign form once in back of room! 10/15/06
3
Thank You Committee Members! u u Dr. Jerry Wong
FPL u Hydro 1 u Magdi Ishac u IUSI u Brian Lacoursiere u AISI u Camille Rubeiz u u Dr. James Davidson Shakespeare u Newmark u Wes Oliphant u Duke Energy u David West u HM Rollins u Martin Rollins u Electrical Consultants u Gary Bowles u Outside Cons. u Larry Slavin u BC Hydro u Alec Zoltoochin BC Hydro 10/15/06
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The Utility Perspective The Utility Perspective presented by presented by
Michael Voda, P.E. – Principal Civil Engineer Salt River Project Salt River Project
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The Utility Perspective RBD? We don We don ’’ t need no stink stink ’’ n RBD! RBD!
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The Utility Perspective The Utility Perspective u u
The NESC has been in used for design for a number of years
““ This code is not intended as a design specification or as an instruction manual. manual. ” u u
But It works
u u
Why do we need something new?
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Challenge #1 NESC Loads ““ Old Method Old Method ”” ::
Different Load Depending On Pole Material Different Load Depending On Pole Material ¨
¨
¨
Economical engineered alternatives to wood are available. are available. Different factored loads depending on material of pole. of pole. Do actual wind and ice loads vary if the pole material is different? material is different?
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Challenge #2 NESC Strength: NESC Strength: 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
strength strength ¨
What is the What is the relative measure relative measure of strength to insure equivalent reliability across materials? insure equivalent reliability across materials?
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Challenge #3 Loading On 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 communications; communications; how is reliability impacted? how is reliability impacted? NESC Load Districts: Load boundaries follow follow political political boundaries >> boundaries >>
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Weather Related Loads
u u
Do they differ across Do they differ across political political boundaries??? boundaries???
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Needs u u
u u
Load Definition – A method of defining line loading that is independent of the material used for the supporting structure. – Weather loads that reflect actual measured events to insure consistent structural reliability across the country. Nominal Pole Strength – A consistent method for comparing relative strengths of poles made of differing materials. – A method that will result in similar structural reliability across the various materials across the various materials 10/15/06
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Next: Next:
NESC A Historical Perspective presented by
Nelson Bingel – VP VP Engineering Osmose Utilities Services Osmose Utilities Services
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National Electrical Safety Code National Electrical Safety Code
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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. 10/15/06
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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. 10/15/06
ASCE Manual 111 Workshop
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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. 10/15/06
ASCE Manual 111 Workshop
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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. 10/15/06
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National Electrical Safety Code National Electrical Safety Code
safety of employees and the public under the specified conditions.
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NESC Editions u u 1914
First Edition
u u 1916+
2 nd Edition, 3 rd Edition
u u 1926
4 th Edition
u u 1948
5 th Edition
u u 1962
6 th Edition
u u 1977,1980,1984 u u 1987,1990,1993,1997, 2002 1987,1990,1993,1997, 2002 10/15/06
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NESC Loads, LF & SF Wood LF Editon
H
M
L
Steel LF
B
C
B
C
Wood SF B
C
Steel SF B
C
4th
8 psf 8 psf 12 psf
5th
4 psf 4 psf
9 psf
2.54
2.2
0.25
0.5
1977
4 psf 4 psf
9 psf
4
2
2.5
2.2
1987
4 psf 4 psf
9 psf
2.5
1.75
2.5
2.2
0.65
0.85
1
1
2002
4 psf 4 psf
9 psf
2.5
1.75
2.5
1.75
0.65
0.85
1
1
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0.439 0.658 0.788 0.909
23
TRANSVERSE
LO
NG
IN T
UD
IN
AL V E R T I C A L
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ANSI O5.1 2 ft
L c Applied Bending Load = L c x D (ft D (ft lb) lb)
D 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 Class 5 1,900 lb 10/15/06
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ANSI O5.1 L c
k x
Bending Capacity = fiber strength x C 3 (ft (ft lb)
Tension (psi) 10/15/06
Compression (psi) ASCE Manual 111 Workshop
Fiber Strength 26
ANSI O5.1 L cc
Bending = Capacity 10/15/06
k x fiber strength x C 3 (ft (ft lb) ASCE Manual 111 Workshop
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Deterministic Loads NESC RADIAL ICE ON CONDUCTOR Light Medium Heavy
HEAVY
Ice (radial thickness)
0" .25" .5"
MEDIUM
LIGHT lb
Wind 9 lb 4
4 lb
(per sq. ft.)
HAWAII LIGHT ALASKA HEAVY 10/15/06
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Deterministic Loads NESC Light Medium Heavy HEAVY
Ice (radial thickness)
0" .25" .5"
MEDIUM
LIGHT
Wind 9 lb 4 lb 4 lb (per sq. ft.)
HAWAII LIGHT ALASKA HEAVY 10/15/06
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Deterministic Loads NESC Light Medium Heavy HEAVY
Ice (radial thickness)
0" .25" .5"
MEDIUM
LIGHT
Wind 9 lb 4 lb 4 lb (per sq. ft.)
HAWAII LIGHT ALASKA HEAVY 10/15/06
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Working Load Working Load 4 lb. Transverse Wind
.25” ICE
Medium Loading District
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Durability Grade of Construction NESC
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B
C
4
2
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GRADE B ANSI O5.1
NESC
900 lb Working Load
Class 1 Class 2 Class 3 Class 4 Class 5
x4 = 3600 lb
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4500 lb 3700 lb 3000 lb 2400 lb 1900 lb
33 33
GRADE C ANSI O5.1
NESC
900 lb Working Load
Class 1 Class 2 Class 3 Class 4 Class 5
x2 = 1800 lb
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4500 lb 3700 lb 3000 lb 2400 lb 1900 lb
34 34
NESC Loads, LF & SF Wood LF Editon
H
M
L
Steel LF
B
C
B
C
Wood SF B
C
Steel SF B
C
4th
8 psf 8 psf 12 psf
5th
4 psf 4 psf
9 psf
2.54
2.2
0.25
0.5
1977
4 psf 4 psf
9 psf
4
2
2.5
2.2
1987
4 psf 4 psf
9 psf
2.5
1.75
2.5
2.2
0.65
0.85
1
1
2002
4 psf 4 psf
9 psf
2.5
1.75
2.5
1.75
0.65
0.85
1
1
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0.439 0.658 0.788 0.909
35
LRFD LRFD Load Resistance Factored Design Load * Factor < Resistance * Factor (Strength)
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Standard vs. Alternate Overload Factors Overload Factors Overload Strength Factor Factor
Wood B Wood C
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2.50 1.75
¸ ¸
.65 .85
Alternate Method
= 3.85 = 2.06
ASCE Manual 111 Workshop
4.0 2.0
37 37
GRADE B 900 lb Working Load
Class 1 Class 2 Class 3 Class 4 Class 5
x4 = 3600 lb
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4500 lb 3700 lb 3000 lb 2400 lb 1900 lb
38 38
LRFD LRFD Load Resistance Factored Design Load * Factor < Resistance * Factor (Strength)
900 lb * 2.5 2250 lb 10/15/06
<
3700 lb
< ASCE Manual 111 Workshop
* .65
2405 lb 39 39
LRFD LRFD Load Resistance Factored Design Load * Factor < Resistance * Factor (Strength)
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LRFD Reliability Reliability Based
Load Resistance Factored Design Load * Factor < Resistance * Factor (Strength)
Load RP Q RP RP f R n > > S gi Q i 0.9 M n > 1.2 M DL + 1.6 M LL
u
f’’ s and s and g’’ s judgement based, soft s judgement based, soft calibrated, or reliability calibrated, or reliability based based
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Is it Harder to Design with RBD? u u
No, you won No, you won ’’ t need a Ph.D. in statistics!
u u
Everyday design effort will be the same
u u
We have done all the hard work: The ASCE Manual will provide load and strength factors strength factors
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Will RBD Require More Expensive Poles? u u
No, on the average, designs will be equivalent to NESC grades B and C equivalent to NESC grades B and C
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3. Are all Strength Guides Created Equal? Equal? Manual 72 for steel poles PCI guide for P/C poles ANSI 05.1 for wood poles
……
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Strength u u
Experiment: Test 100 identical poles to failure (cantilever test) Mean = average strength STD = standard deviation COV –
–
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= standard deviation/mean If STD = 20; mean= 100; COV=20/100=0.2 If STD = 40; mean= 200; COV=40/200=0.2 COV=40/200=0.2 ASCE Manual 111 Workshop
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Nominal Strength R n u u
Predicted strength using a code procedure: – Manual 72 for steel poles – PCI guide for P/C poles – ANSI 05.1 for wood poles ANSI 05.1 for wood poles
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Lower Exclusion Limit (LEL) 1.645 STD
Strength Mean Mean
5% LEL = 5th weakest in 100 identical poles If the pole COV=20%, then 5% LEL = m1.645 (0.2 m) 10/15/06
= 0.67 m
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Nominal Strength in Current Design Guides? 1.645 m V 1.645 m V
Strength Strength
1 % LEL Manual 72? 10/15/06
Mean 5% LEL Manual ANSI 72? 05.1? FRP? ASCE Manual 111 Workshop
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Where is the Nominal Strength in ANSI 05.1?
Strength
33% LEL =0.92 x Mean SP 50 ’ ASCE Manual 111 Workshop
82% LEL =1.13 x Mean DF > 50 DF > 50 ’ 61
ASCE Manual Recommendation: All Strength Values at 5% LEL 1.645 m V
Strength
5 % LEL
5% LEL
5% LEL
PCI P/C PCI P/C
Manual 72
ANSI 05.1
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Strength Factor Strength Factor f Manual 111 LRFD Eq Eq . 2.1 . 2.1 aa
Q RP
f R n > Effect of [1.1 DL + > Effect of [1.1 DL + g Q 50 ]
5% LEL
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Load factor
50 year RP 50year RP Ice+wind wind
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Strength factor Strength factor f COV R
Nominal Strength Exclusion limit , e(%)
0.05
0.1
0.2
0.3
0.1 0.1 1 2 5 10 10 20 20 50 50
1.01 0.97 0.96 0.94 0.92 0.90 0.87
1.16 1.07 1.04 1.00 0.96 0.92 0.85
1.44 1.23 1.17 1.08 1.00 0.92 0.78
1.71 1.37 1.26 1.12 1.01 .89 .69
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Example Convert Wood Pole Strength to 5% LEL 6,250/8,661= 0.80
Strength
ASCE Pole RBD Manual R n = 6,250 psi LEL = 5%
ANSI 05.1 SP Pole Effect of [1.1 DL + g Q 50 ]] Factor g for ASCE 74 Loads Grade
B
C
Extreme Wind Wind Force: 1.0
Wind Force: 0.5 *
Ice+Wind Wind Force: 1.0 Ice Thickness: 1.0 Wind Force: 1.0 Ice Thickness: 0.5
* If any portion of the structure or its supported facilities exceeds 60 ft, Use 1 10/15/06
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6. Outline of Manual 111 1. Introduction 2. RBD Format: LRFD equations, load and strength factors to achieve relatively consistent reliabilities across materials 3. Loads: ASCE 7, Manual 74 4. Strength: 3 methods to obtain pole strength statistics Appendices: A A Design examples B B Examples to obtain R 10/15/06
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7. What will RBD do for the Industry? Industry?
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Benefits of RBD 1. More consistent reliabilities across materials. 2. More consistent reliabilities across geographical regions 3. Opens door for using new materials 4. Uniform definition of nominal strength 5. Defines reliability levels for Grade B & C Defines reliability levels for Grade B & C 10/15/06
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Benefits of RBD 6. Allows utilities to select desired reliability level (which may be different from Grade B or C) 7. Encourages manufacturers to improve their products by providing incentives for smaller COVs and more strength data. 8. Brings pole structural design in line with well well established Reliability established Reliability Based Design codes such as AASHTO, AISC, IEC, the NDS. NDS. 10/15/06
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The Future … Tying the Pieces Together Loads: Manual 74, NESC ASCE Manual 72 steel Pole PCI Guide ASCE Concrete Pole
ASCE Substation Guide 10/15/06
ASCE Steel Lattice Standard ASCE RBD Standard ASCE FRP Pole Guide ANSI 05.1 Wood Poles
ASCE Manual 111 Workshop
ASCE Distribution Pole Standard
79
Two Points to Remember Nominal Strength at 5% LEL u u Same loads and load factors for all materials materials u u
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Quiz: What strength should we use? What load should we use? Strength R
Load Q
m Q
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Q 50
ASCE Manual 111 Workshop
R 5
m R
81
Quiz: How do we achieve relatively consistent reliability across materials and locations? Strength R
Load Q
m Q
10/15/06
R Q 5 50
m R
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Next Steps ASCE Manual 111 Development User feedback u u Start work on second edition in 2008 Start work on second edition in 2008 u u
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Next: Calibration of Reliability Based Design Method Design Method presented by
Michael Voda, P.E. – Principal Civil Engineer Salt River Project Salt River Project
RBD Calibration:
RBD NESC RBD » NESC
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Reliability Calibration Design 240 Wood Poles Using NESC 77: Design 960 Poles Using NESC: 40 locations x 3 types (40’, 65’, 70’) 40 locations x 4 types (40', 65', 70', 110') X 2 grades x 2 Grades x 3 Materials
Develop Strength PDFs 960 poles 960 poles
Develop Load PDFs 40 locations: Wind Ice+Wind
Best Pole Analysis Techniques: Transfer functions Nonlinear Structural Analysis Annual Prob. of Failure: Wind, Ice+wind Monte Carlo Simulations Target Reliability Levels Grade B, Grade C Load and Strength Factors for RBD 10/15/06
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Design Poles Per Current Practice Design Poles Per Current Practice Distribution 1 u u u u u u u u u u u u u u
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40 ft pole 3 Phase 336 ACSR Neutral 3/0 AAAC 2 Communication 250 ft span LL M M H Districts Grade B & C ASCE Manual 111 Workshop
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Design Poles Per Current Practice Design Poles Per Current Practice Distribution 2 65 ft pole u u 556 ACSR Phases u u 3/0 Neutral u u 2 Communication u u
u u u u u u 10/15/06
350 ft span LL M M H Districts Grade B & C ASCE Manual 111 Workshop
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Design Poles Per Current Practice Design Poles Per Current Practice Transmission 1
u u
70 ft pole 3/8 3/8 ” steel static 795 ACSR Phases 2 Communication 450 ft span LL M M H Districts & Ext Wind Grade B & C
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u u u u u u u u u u u u
89
Design Poles Per Current Practice 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
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Design Poles Per Current Practice 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
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Strength PDF ANSI 05.1 2002 § § Dist 1 SYP 40ft poles mean = 8000 psi COV= 0.20 mean = § § Dist 2 SYP 65ft poles mean = 8000 psi COV = 0.20 mean = § § Trans 1 DF 70ft poles mean = 8000 psi COV = 0.20 mean = § § Normal Distribution used for Fiber Strength used for Fiber Strength 10/15/06
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Load PDF u u Wind
Extreme Type I Distribution (( Peterka Peterka , 1998). One PDF for Continental US and another for Hurricane zones. u u Ice with concurrent wind
Modified Pareto Distribution (Jones) (Jones)
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Calculate Annual Reliability ( Calculate Annual Reliability ( ß ß )) u u Monte Carlo Simulation u u 200,000 simulations per pole per location u u Results = Annual Probability of Failure (P f )
P P f = No. Failures/ No. Simulations u u Relationship between ß
and Pf P f = = Ф [[ ß ß ]
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Monte Carlo Simulation Load Q
Mean 10/15/06
Strength R
Mean ASCE Manual 111 Workshop
PASS!! PASS!! 95
Monte Carlo Simulation Load Q
Mean 10/15/06
Strength R
Mean ASCE Manual 111 Workshop
FAIL!! FAIL!!
96
Dist. 1 40ft Wind Grade B Reliability Index Beta
4 Heavy
Medium
Light Light
3
2
1
0 ND
CO
MN
IN
NE
IL
OR
TX
CO
WY
UT
NV
MS
FL
Location 10/15/06
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Dist. 2 65ft Wind Grade B Reliability Index Beta
4 Heavy
Light Light
3
2
1
0 10/15/06
Medium
ND
CO
MN
IN
NE
IL
OR
TX
CO
WY
Location ASCE Manual 111 Workshop
UT
NV
MS
FL
98
Trans. 1 70ft Wind Grade B Reliability Index Beta
4 Heavy
Light Light
3
2
1
0 10/15/06
Medium
ND
CO
MN
IN
NE
IL
OR
TX
CO
WY
Location ASCE Manual 111 Workshop
UT
NV
MS
FL
99
Select Target ß 3
2
1
0 10/15/06
Dist 1
Dist 2
ASCE Manual 111 Workshop
Trans 1
100
Establish Load Factor P f = 1 = 1 Ф [ ß ß ] When Strength R RP , When Strength R 5 = Load Q = Load Q RP 1/RP
