Post on 17-Jul-2016
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American Iron and Steel Institute
American Iron and Steel Institute’s Technical Session
Steel Distribution Poles - The Material of the Future
- presented by -
Richard F. Aichinger, PEManager of Engineering, Utility Products
Valmont Industries, Inc.
Design & Testing of Steel Poles
American Iron and Steel Institute
Designing For “Equivalency”
“Equivalency” to what?– Expected Strength– Expected Life– Expected Performance
• Deflection • Handling• Field Use
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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)
American Iron and Steel Institute
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
American Iron and Steel Institute
National Electrical Safety Code (ANSI C-2)
1997 Edition Grade B:
Strength Factor Equiv. O.L.F. Load Type Overload Steel Wood Steel Wood Ratio Vertical 1.5 1.0 0.65 1.5 2.31 0.65Transverse Wind 2.5 1.0 0.65 2.5 3.85 0.65 Tension 1.65 1.0 0.65 1.65 2.54 0.65
American Iron and Steel Institute
National Electrical Safety Code (ANSI C-2)
1997 Edition Grade C: Strength Factor Equiv. O.L.F. Ratio
Load Type Overload Steel Wood Steel WoodVertical 1.5 1.0 0.85 1.5 1.76 0.85Transverse Wind 2.2 (steel) 1.0 0.85 2.2 2.06 1.07 1.75(wood) Tension 1.1 (steel) 1.0 0.85 1.1 1.53 0.72 1.3 (wood)
American Iron and Steel Institute
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
American Iron and Steel Institute
Designing For “Equivalency”
• “Equivalent Wood Pole” Loading (B):– ANSI Load x 2.5/4.0
ANSI 05.1 Working “Equivalent”Pole Class Loading Load Steel Load
2 3700 # 925 # 2313 #3 3000 750 18754 2400 600 15005 1900 475 1188
American Iron and Steel Institute
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#
American Iron and Steel Institute
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#)
American Iron and Steel Institute
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”
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
Load Deflection of Steel vs. Wood Poles (40’ Class 4, NESC Grade “B”)
Deflection of 40 ft. Class 4(Treatment Adjustments per Table C4)
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs.
600 700 800 900 1000 1100 1200 1300 1400 1500 1700 1900 2100 2300 2400
Loading (lbs.)
Def
lect
ion
(in.)
Western Red CedarSo. Yellow PineSteel PoleDouglas Fir
American Iron and Steel Institute
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
American Iron and Steel Institute
Weight Comparison of Wood to Steel
0
500
1000
1500
2000
2500
5 4 3 5 4 3 5 4 3 2
40 40 40 45 45 45 50 50 50 50
CLASS and WEIGHT
POLE
WEI
GH
T, lb
Douglas Fir Weight, lbs.Steel Pole Weight, lbs.
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
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
American Iron and Steel Institute
Post Insulator Test On Steel Pole
American Iron and Steel Institute
Guy Attachment Test On Steel Pole
American Iron and Steel Institute
EPRI Test On 70’ Class 2 Steel Pole
American Iron and Steel Institute
Testing at EPRI (Class 2) and EDM (Class 3 & 5)
American Iron and Steel Institute
Steel Distribution Poles - The Material of the Future
American Iron and Steel Institute
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