linda1.ppt

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Component Strength Issues
IEEE
Robert Kluge Alliant Energy February 6, 2000
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Component Strength Issues

• Robert Kluge
• Alliant Energy
• Sunday, Feb. 6, 2000

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Component Strength Issues

• Fiber-reinforced Composites CP 2219, 2220, 2221,
  2222
• Grade C LoadStrength Factors CP 2384, 2233
• Reference for Wood Properties CP 2241
• Deterioration Limits CP 2238, 2368, 2400
• Hardware CP 2300
• Insulators CP 2402

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Fiber-reinforced Composites

• Four Change Proposals
• Load Factors CP 2219
• Strength Factors CP 2220, 2222
• Guyed Poles CP 2221

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Fiber-Reinforced CompositesLoad Factors

• CP 2219 Overload Factor for Wire Tension
• Grade B
• Ref. Table 253-1 (Same as other materials)
• Grade C
• Wood is 1.3 (Table 253-1 value)
• Metal is 1.1 (reduced via footnote 5)
• Composites 1.1 (proposed in CP)
• Composites 1.5 (modified by subcommittee)

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Fiber-reinforced CompositesStrength Factors

• CP 2220 CP 2222 Strength Factors for
  Composites
• Proposal Include with Metal Structures (1.0)
• Subcommittee recommendsNew Rule 261A3 (similar
  to wood)
• Grade B Grade C
• Rule 250B Loads 65 85
• Rule 250C Loads 75 75

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Fiber-reinforced CompositesGuyed Poles

• CP 2221 Strength of Guyed FRC Poles
• Options
• Integral Part of Structure - (Proposal)
• Strut only - (Subcommittee recommends)
• Consider relative stiffness.

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Relative Load Strength Factorsfor Various
Materials

• CP 2384 Grade C Factors
• Current Rules
• Grade B Load factors are the same for all
  materials.
• Proposal
• Revise Grade C Load Factors Make all Load
  factors the same for all types of materials.
• Revise the Strength reduction factors for wood.
• Recommend
• Revise only certain overload factors.
• (See CP 2233)

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Grade C Load Factors

• CP 2233 (Subcommittee accepts)
• Table 253-1, footnote 4 should apply to all
  materials.
• Grade C
• Transverse Loads
• Wind 2.2 1.75 (not at crossings)
• Wire Tension 1.3 1.1 (metal)
• Longitudinal Loads
• At Deadends 1.3 1.1 (metal)

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Grade C Strength Factors

• Subcommittee recommends No change to Strength
  Factors for various materials.
• Grade B Grade C
• Rule 250B Loads
• Metal 1.0 1.0
• Wood 0.65 0.85
• Rule250C Loads
• Metal 1.0 1.0
• Wood 0.75 0.75
• Note Wood strength factors vary between Grade.

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Material Strength FactorsTable 253-1

• Is it appropriate for strength factors to vary
  with Grades of Construction?
• Yes. Materials have different strength
  distributions. (Coefficients of Variation)
• See paper by H. M. Rollins. www.awpi.org

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Strength DistributionsSteel vs. Wood

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Material Strength FactorsTable 253-1

• Subcommittee ConclusionIt is OK for strength
  factors to vary with Grades of Construction.
• Grade B Grade C
• Metal 1.0 1.0
• Wood 0.65 0.85

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Reference for Wood Strengths

• CP 2241Refer to ANSI O5 for Strength Factors (or
  Design Values) for Wood Products.
• Includes
• Poles
• Crossarms
• Laminated Wood

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Strength Values for Wood

• Currently
• NESC refers to ANSI O5, Table 1
• NESC specifies strength factors
• Grade B Grade C
• Rule 250B Loads 0.65 0.85
• Rule 250C Loads 0.75 0.75
• Proposed
• ANSI O5 will publish wood design strengths.

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Strength Values for Wood ANSI O5, Table 1

• Group A (Air Seasoned)
• Western Red Cedar 6000
• Yellow Cedar 7400
• Group B (Boulton Dried)
• Douglas Fir (coastal) 8000
• Group C (Steam Conditioned)
• Southern Pine 8000
• Group D (Kiln Dried)
• Western Red Cedar 6000
• Douglas Fir (coastal) 8000
• Southern Pine 8000

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Strength Values for Wood

• Currently
• NESC refers to ANSI O5, Table 1
• NESC specifies strength factors
• Grade B Grade C
• Rule 250B Loads 0.65 0.85
• Rule 250C Loads 0.75 0.75
• Proposed
• ANSI O5 will publish wood design strengths.

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Strength Values for Wood ANSI O5, Table 1

• New Table 1 Fiber Stress Values
• Lower 5 exclusion limit of the strength of a
  single pole.
• Conditioning methods.
• Include all test data.
• Size affects.
• Load duration adjustments.

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ANSI O5 IssuesWill circumferences change?
Strength Regression with Size
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Factored Strength Values for Wood ANSI O5, Table
1

• 100 65 85
• Group A (Air Seasoned)
• Western Red Cedar 6000 3900 5100
• Yellow Cedar 7400 4800 6300
• Group B (Boulton Dried)
• Douglas Fir (coastal) 8000 5200 6800
• Group C (Steam Conditioned)
• Southern Pine 8000 5200 6800
• Group D (Kiln Dried)
• Western Red Cedar 6000 3900 5100
• Douglas Fir (coastal) 8000 5200 6800
• Southern Pine 8000 5200 6800

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Strength Deterioration Limits

• CP 2238
• Limits deterioration of any structure buried in
  earth (Same limits as wood has.)
• CP 2368 (subcommittee accepted)
• Limits deterioration of all non-wood structures.
  (No deterioration permitted.)
• CP 2400
• Clarifies - required when installed

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Components

• Hardware
• Insulators

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Hardware

• CP 2300 (subcommittee accepted)
• All hardware must support Grade B loads.
• (Grade C overloads will no longer apply to
  hardware, not even on a Grade C structure.)
• When evaluating Rule 250C Loads, utilize 80 of
  hardware strength.
• LRFD ApproachUtilize 80 of hardware strength.

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Rule 277 Strength of Insulators

• CP 2402
• Specify Loads w/o Overloads.
• Excluded Rule 250C Loads.
• Option
• Adjust strength factors in Rule 277 (Consistent
  with LRFD format) (Applicable to all loads in
  section 25)

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LRFD Load Resistance Factor Design

• Load Factors
• v.s.
• Strength Factors

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LRFD

• Loads and load factors
• should be equal for all materials and all
  components. Factored loads should be what the
  entire system is able to withstand.
• Strength factors ormanufacturers nominal
  strength
• should account for uncertainties of strengths or
  desired sequences of failures.

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LRFD Load Resistance Factor Design

• It is conceptually wrong to use load factors to
  deal with different behaviors of components.

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Load and Strength Factors NESC 1997
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Load and Strength Factors NESC 1997
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Load and Strength Factors Proposed NESC 2002
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Load and Strength Factors Proposed NESC 2002