American Iron and Steel Institute’s Technical Session
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American Iron and Steel Institute’s Technical Session. Steel Distribution Poles - The Material of the Future. Design & Testing of Steel Poles. - presented by - Richard F. Aichinger, PE Manager of Engineering, Utility Products Valmont Industries, Inc. Designing For “Equivalency”.

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American Iron and Steel Institute’s Technical Session

Steel Distribution Poles - The Material of the Future

Design & Testing of Steel Poles

- presented by -

Richard F. Aichinger, PE

Manager of Engineering, Utility Products

Valmont Industries, Inc.


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Designing For “Equivalency”

“Equivalency” to what?

  • Expected Strength

  • Expected Life

  • Expected Performance

    • Deflection

    • Handling

    • Field Use


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Designing For “Equivalency”

  • Most pole used to date have been wood

  • How do you design a “Steel wood pole”?

    • You can’t … but you don’t want to

    • Instead you design a pole that meets minimum strength and performance requirements every time


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Designing For “Equivalency”

  • How do you design a “Steel Distribution Pole”?

    • ANSI Standards:

      • ANSI 05.1

      • National Electric Safety Code (ANSI C-2)

    • ASCE Manual 72

    • Material & Manufacturing Proven Reliability

    • Testing and Proven Product Experience


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ANSI 05.1

  • Provides performance and quality criteria for wood poles of various species

  • Provides strength requirements which define the various pole Class definition (Class 6 to H-6)

    • Defined by a Capacity Loading to be applied 2 feet from the pole top

  • Provides direct embedment depth


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National Electrical Safety Code (ANSI C-2)

  • A Safety Code

  • By default, also a Design Code

    • Provides for Design considerations for various line conditions (ice, wind + ice, wind)

    • Provides for Construction Grades to differentiate the allowable risk accepted in the design


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National Electrical Safety Code (ANSI C-2)

A Little History:

  • Provided for loading and strength since the early 1900’s to present

  • Early editions were based on ultimate strength of materials

  • Steel was first to be changed to Load Factor in 1941


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National Electrical Safety Code (ANSI C-2)

  • 1941 Summary:

    • Material Grade B Grade C

      • Steel 2.54 2.2

      • wood 25% 37.5%

        • (equiv. OLF) (4.0) (2.67)


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National Electrical Safety Code (ANSI C-2)

  • 1973 Wood was modified:

    • Material Grade B Grade C

      • Steel 2.54 2.2

      • wood 25% 50%

        • (equiv. OLF) (4.0) (2.0)

    • Familiar?

    • wood is now lower than steel in Grade C.

  • 1997 Edition introduced Strength Factors


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National Electrical Safety Code (ANSI C-2)

1997 Edition Grade B:

Strength Factor Equiv. O.L.F.

Load TypeOverloadSteelWoodSteelWoodRatio

Vertical 1.5 1.0 0.651.5 2.31 0.65

Transverse

Wind 2.5 1.0 0.652.5 3.85 0.65

Tension 1.65 1.0 0.651.65 2.54 0.65


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National Electrical Safety Code (ANSI C-2)

1997 Edition Grade C:

Strength Factor Equiv. O.L.F. Ratio

Load Type Overload Steel Wood Steel Wood

Vertical 1.5 1.0 0.851.5 1.76 0.85

Transverse

Wind 2.2 (steel) 1.0 0.852.2 2.06 1.07

1.75(wood)

Tension 1.1 (steel) 1.0 0.851.1 1.53 0.72

1.3 (wood)


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ASCE Manual 72

  • “The Steel Pole Design Guide”

  • Provides for the best practices of the industry

  • Provides for the Design Requirements equated to:

    • AISC

    • ACI

    • AWS


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Designing For “Equivalency”

  • “Equivalent Wood Pole” Loading (B):

    • ANSI Load x 2.5/4.0

      ANSI 05.1 Working “Equivalent”

      Pole ClassLoadingLoadSteel Load

      2 3700 # 925 # 2313 #

      3 3000 750 1875

      4 2400 600 1500

      5 1900 475 1188


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Designing For “Equivalency”

  • CLASS 4 Pole has ANSI rated capacity of 2400#.

    • GRADE B CONSTRUCTION:

      • WOOD O.L.F. 4.0

      • STEEL O.L.F. 2.5

      • STEEL RATED LOAD BECOMES 2400# x 2.5/4.0 = 1500#

    • GRADE C CONSTRUCTION:

      • WOOD O.L.F. 2.0

      • STEEL O.L.F. 2.2

      • STEEL RATED LOAD BECOMES 2400# x 2.2/2.0 = 2640#


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Designing For “Equivalency”

  • CLASS 4 Pole has ANSI rated capacity of 2400#.

    • GRADE B CONSTRUCTION:

      • WOOD O.L.F. 4.0

      • STEEL O.L.F. 2.5

      • STEEL RATED LOAD BECOMES 2400# x 2.5/4.0 = 1500#

    • GRADE C (Expected NESC Change for 2002)

      • WOOD O.L.F. 2.06

      • STEEL O.L.F. 1.75

      • STEEL RATED LOAD BECOMES 2400# x 1.75/2.06 =2039# (vs. 2640#)


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Designing For “Equivalency”

  • Steel Allows for Designs that Consistently meet strength requirements by varying diameter and thickness

  • ASCE Manual 72 provides criteria for Local Buckling of Tubular Steel

    • Proven through years of use in other products

    • Verified by EPRI and manufacturer testing

  • Provides a pole that is consistent “by design”


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Designing For “Life”

  • Steel Allows for the Design of a Product that can be protected against deterioration

    • Galvanizing provides a proven inside/out protection for most environments

    • An additional groundline barrier coating provides extra protection at the most corrosive location

    • When damaged by overload conditions, Steel will tend to locally yield rather than “break” or “collapse”, often times allowing the line to remain in service


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Designing For “Performance”

  • Deflection of steel poles are normally less than the “equivalent wood pole” based on the pole size defined by ANSI 05.1

  • The following graph shows a representative comparison indicating the deflection of a Steel versus wood poles


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Load Deflection of Steel vs. Wood Poles(40’ Class 4, NESC Grade “B”)


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Designing For “Performance”

  • Weight of steel poles are normally much less than the “equivalent wood pole” providing added savings for field handling and maneuvering

  • The following chart is a representative comparison of the weight of wood poles versus Steel Poles



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Designing For “Performance”

  • Additionally, Steel can be Designed for true design applications wood is seldom correctly considered for:

    • Guyed angles and corners

      • NESC requirements:

    • Unguyed angles and corners

      • Steel provides the necessary strength and flexibility of size and application


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Designing For “Reliability”

  • Steel Poles have been successfully used:

    • for over 30 years for the Electric Utility industry

    • for over 40 years with the same product in other industries (lighting and traffic)

  • Fabrication and Quality systems have evolved to keep up with customer demand, technology, and increasing Design sophistication


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Designing Proven by “Testing”

  • Steel Poles have been tested for as long as Steel Poles have been fabricated. But there is a difference:

    • Steel Poles are tested to Verify Design strength is attained as a Minimum

    • wood poles are tested to determine the mean rupture strength


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Designing Proven by “Testing”

  • Steel Distribution Poles have been tested by independent firms (EDM in Fort Collins) and by the manufacturers using controlled conditions and sophisticated systems.

    • Strength / Buckling tests to verify design acceptance for conditions including:

      • full tube sections

      • tube sections with many cut holes to verify that condition

      • attachment and guy hardware loading

    • All showing the Strength and Reliability of Steel







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Steel Distribution Poles - The Material of the Future

In Conclusion:

  • Steel Distribution Poles Provide

    • Expected Strength

    • Expected Life

    • Expected Performance in

      • Deflection

      • Handling

      • Field Use


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