linda1'ppt

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NESC 2002 Overhead Lines-Strength Loading
IEEE
Larry Slavin Telcordia Technologies, Inc. July
18, 2001
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NESC 2002Strength Loading Review

• NESC 1997
• NESC 2002 (Resolved/Final)
• Comparison

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NESC 1997Winter Storm

• Combined Ice and Wind Loading (Rule 250B)
• Heavy (0.5-in. radial ice, 40 mph wind, 0F)
• Medium (0.25-in. radial ice, 40 mph wind, 15F)
• Light (0-in. radial ice, 60 mph wind, 30F)

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(No Transcript)
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NESC 1997Summer Storm

• Extreme Wind (Structures gt60 ft Height) (Rule
  250C)
• 50 year recurrence (0.02 annual probability)
• Fastest-mile average speed
• Exposure C (open terrain)
• 33 ft. elevation

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Extreme Wind Map Rule 250C
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Conductor Loading

• Combined Ice and Wind, or Extreme Wind
• Vertical weight of bare conductor plus ice
• Horizontal force of wind on conductor plus ice
• Added constant to resultant (for tension, not
  sag)
• Corresponding temperature (0F, 15F, 30F 60F)

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Conductor Loading
ice
wind force
conductor
weight
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Loads on Line Supports

• Vertical Loads
• Dead weight of bare supports and conductors, ...
• Ice load on conductors and wires (not supports)
• Transverse Loads
• Wind force on bare structures (without ice)
• Wind force on ice-covered conductors and wires

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Loads on Line Supports
Tension
Transverse
Vertical
TOP VIEW
Tension
Angle Pull
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Loads on Line Supports

• Angles
• Unbalanced tension at corners
• Longitudinal Loads
• Unbalanced pulls
• Unequal spans
• Deadends
• ..
• Simultaneous Application of Loads

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Strength Overload FactorsSupports (Structures,
Guys, )

• Load x Overload Factor ? Strength x Strength
  Reduction Factor
• Overload Factor (typ.) ? 1
• Strength Reduction Factor (typ.) ? 1
• e.g., 1.0 for 50 year extreme event loadings,
  or some components (conductors, )
• e.g., 1.0 for metal

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Overload Factors

• Grade of Construction
• Grade B
• Grade C
• Combined Ice-Wind vs. Extreme Wind
• Loads
• Vertical
• Transverse Loads
• Longitudinal
• Materials
• Wood
• Metal

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Strength (Reduction) Factors

• Grade of Construction
• Grade B
• Grade C
• ..
• Combined Ice-Wind vs. Extreme Wind
• Materials
• Wood
• Metal
• Concrete

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Conductor/Messenger Tension

• Combined Ice-Wind (60 rated strength)
• Extreme Wind (80 rated strength)
• Criteria applied with Overload Factor 1.0
• Initial unloaded tension (60F) ? 35 rated
  strength
• Final unloaded tension (60F) ? 24 rated
  strength

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Insulators

• Combined Ice and Wind
• Cantilever (40 rated strength)
• Compression (50 rated strength)
• Tension (50 rated strength)
• Criteria applied without overload factors
• Extreme Wind
• Proper allowance should be made

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NESC 2002
Strength and Loading Requirements (Modifications)
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Status of MajorChange Proposals

• Eliminate 60 ft. exemption for Extreme Wind (CP
  2151)
• Rejected (WG 5.8 to study for 2007)
• Introduce New Combined Ice and Wind Map as
  alternative to present Storm Loading Map, Rule
  250B (CP 2309)
• Rejected (map incomplete, premature, inaccurate?)

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Status of MajorChange Proposals (Contd)

• New Materials Fiber-Reinforced Composite Poles
  (CP 2219, )
• Rejected (insufficient material data)
• Major Revision of Strength Loading Sections 25
  - 27 (CP 2372)
• Rejected (WG 5.2 to continue developing for 2007)

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Status of MajorChange Proposals (Contd)

• Uniform Treatment of Wood, Metal, Concrete
  (Reinforced, Prestressed)
• Consistent Overload Factors (CP 2233)
• Accepted
• All structures without conductors subject
• to Extreme Wind (CP 2306)
• Accepted

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Consistent Overload Factors(Wood, Metal,
Concrete)
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Status of MajorChange Proposals (Contd)

• New Extreme Wind Map (CP 2363)
• Accepted
• New Calculation Procedure

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New Extreme Wind Map Calculation Procedure

• ASCE 7-98 Extreme Wind Map
• 50 year recurrence (0.02 annual probability)
• Gusts (3-second average)
• Open terrain
• 33 ft. elevation
• Includes Gust Response Factors
• Height
• Span length

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New Extreme Wind Map Calculation Procedure

• Retains 60 ft. Exemption (Distribution)

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1997 Extreme Wind Map Rule 250C
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New (2002) Extreme Wind Map(3 Second Gusts)
Nominal speed, 33 ft. above ground, Exposure C
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New Extreme Wind Map Calculation Procedure

• NESC-1997
• load (lbs) 0.00256 (Vmph)2 x shape factor x
  projected area (ft2)
• where Vmph fastest-mile (Figure 250-2, 1997)
• NESC-2002
• load (lbs) 0.00256 (Vmph)2 x shape factor x
  projected area (ft2)
• x kz x GRF x I
• where Vmph 3-sec. gust (New Extreme Wind
  Map),
• kz velocity pressure exposure coefficient,
• GRF gust response factor, and
• I importance factor (1.0)

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New Extreme Wind Map Calculation Procedure
(Contd)

• Structure kz 2.01 x (0.67h/900)(2/9.5), 60 ft
  ? h ? 900 ft
• where h height structure (ft)
• Wire kz 2.01 x (h/900)(2/9.5), 33 ft ? h
  ? 900 ft
• where h height attachment point (ft)
• minimum kz 0.85

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New Extreme Wind Map Calculation Procedure
(Contd)

• Structure GRF 1 2.7Es(Bs)0.5/kv2
• Wire GRF 1 2.7Ew(Bw)0.5/kv2
• where
• Es 0.346 x 33/(0.67h)1/7
• Ew 0.346 x 33/h1/7
• Bs 1/1 0.375h/220
• Bw 1/1 0.8L/220
• kv 1.43
• L Design Wind Span (ft)

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New Extreme Wind Map Calculation Procedure
(Contd)
Gust Response Factor, GRF Tabulated Values
(Structure and Wire)

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NESC
NESC 2002 vs. NESC 1997 (Comparison)
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NESC 2002 vs. NESC 1997 Comparison

• Reduced Overload Factor for Metal,
  Prestressed-Concrete
• Rule 250B (Combined Ice Wind)
• Transverse wind
• Grade C (not crossing)
• 1.75 vs. previous 2.20
• Affects distribution and transmission
• Extreme Wind Loading (Rule 250C)
• 3-sec. gust map calculation procedure
• Affects transmission design only (gt60 ft.)

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NESC 2002 vs. NESC 1997 Comparison (Contd)

• Distribution Lines (Combined Ice-Wind)
• Wood, Reinforced-Concrete
• no change
• Metal, Prestressed-Concrete
• reduced design load (transverse, Grade C, )

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NESC 2002 vs. NESC 1997 Comparison (Contd)

• Transmission Lines
• Wood, Reinforced-Concrete
• no change in Combined Ice/Wind design loads
• new Extreme Wind design loads
• Metal, Prestressed-Concrete
• reduced Combined Ice/Wind design loads
  (transverse, Grade C, ) -- 0.80 factor
• new Extreme Wind design loads

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Transmission LinesStructures - Combined Ice
Wind
Transverse Wind Load
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Transmission LinesStructures - Extreme Wind
Transverse Wind Load
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Transmission LinesStructures - Extreme Wind
Transverse Wind Load
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Transmission LinesConductors - Combined Ice
Wind
Transverse Wind Load
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Transmission Lines Conductors - Extreme Wind
Transverse Wind Load
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Transmission LinesConductors

• Examples
• (Transverse Wind Load)

Woo
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Transmission Lines - ExamplesStorm Loadings
Selected
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Transmission LinesConductors

• Heavy Storm District
• (Wood)

Woo
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Wood Transmission Heavy Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Heavy Storm Area, Grade B,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Heavy Storm Area, Grade B, 50
x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Heavy Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Heavy Storm Area, Grade C,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Heavy Storm Area, Grade C, 50
x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Transmission LinesConductors

• Heavy Storm District
• (Steel)

Woo
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Steel Transmission Heavy Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Heavy Storm Area, Grade B,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Heavy Storm Area, Grade B,
50 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Heavy Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Heavy Storm Area, Grade C,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Heavy Storm Area, Grade C,
50 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Transmission LinesConductors

• Medium Storm District
• (Wood)

Woo
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Wood Transmission Medium Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Medium Storm Area, Grade B,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Medium Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Medium Storm Area, Grade C,
100x2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Transmission LinesConductors

• Medium Storm District
• (Steel)

Woo
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Steel Transmission Medium Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Medium Storm Area, Grade B,
100x2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Medium Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Medium Storm Area, Grade C,
100x2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Transmission LinesConductors

• Light Storm District
• (Wood)

Woo
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Wood Transmission Light Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Light Storm Area, Grade B,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Light Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Wood Transmission Light Storm Area, Grade C,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Transmission LinesConductors

• Light Storm District
• (Steel)

Woo
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Steel Transmission Light Storm Area, Grade B,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Light Storm Area, Grade B,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Light Storm Area, Grade C,
250 x 500
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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Steel Transmission Light Storm Area, Grade C,
100 x 2000
250B (ice wind) -1997
250B (ice wind) -2002
250C (extreme wind) -1997
250C (extreme wind) -2002
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NESC
NESC 2002 vs. NESC 1997 (Conclusions)
77
NESC 2002 vs. NESC 1997 Conclusions

• Distribution Design Loads
• Wood ? Same
• Reinforced-concrete ? Same
• Metal (Grade C) ? Reduced in Grade C
• Prestressed-concrete (Grade C) ?Reduced
  in Grade C

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NESC 2002 vs. NESC 1997 Conclusions

• Transmission design loads depend upon combination
  of parameters
• - geographic area
• - grade of construction
• - material
• - conductor diameter
• - attachment height
• - span length

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NESC
NESC 2007 (?) Integrated Re-Write of Strength
Loading
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Integrated Re-Write of Strength Loading

• Based upon CP 2372 (Rejected for NESC-2002)
• Sags and Clearances also impacted
• Modified version proposed for NESC-2007 Edition
• To be available on NESC website (when?)
• Response form provided for reporting results of
  application to actual cases!

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Integrated Re-Write of Strength Loading

• New Extreme Wind Map and wind pressure
  calculation procedure
• (Rule 250C, NESC-2002)
• Upgraded ASCE 7-98 Combined Ice and Wind Map
• Replaces Fig.250-1 Loading Districts
• Construction and Maintenance Loads

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Integrated Re-Write of Strength Loading

• All loads apply to all structures independent of
  height, but ...
• Possible wind reduction if urban/suburban and ?
  60 ft. (Ref Working Group 5.8)
• Ice thickness reduction for Grade C
• Velocity pressure exposure coefficient kz and
  gust response factor GRF (functions of height and
  span length) applied to wind pressure for both
  storm loads

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Integrated Re-Write of Strength Loading

• Consistent Overload and Strength Factors
• Alternative (Option) to Present (NESC-2002)
  Method ?

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Integrated Re-write of Strength Loading (Contd)

• Results from actual applications (as reported on
  response forms) will be considered in developing
  final proposal for 2007 Edition