Pole Guying
More Complicated Than Meets the Eye
NRECA TechAdvantage 2014
Presented by
Jason Settle, P.E.
jason.settle@gdsassociates.com
Pole Guying
•
•
•
•
Strength of components
NESC vs. RUS
Guy Factor
Grounding
2
Pole Guying
• Purpose
– Support fully loaded design tension of conductors
– Applied wind and ice load
3
The Components of a Guyed Structure
Guy
Attachment
Guy
Guy
Attachment
Height
Pole
Anchor
Guy Lead
4
The strength of the guy-anchor
assembly is dependent on:
• Strength of the guy wire de-rated to 90% of the
RBS (NESC Table 261-1)
• Strength of the guy attachment including the
bolt and washer
• Strength of the anchor and rod
• Holding power of the soil in which the anchor is
installed
• Only as Strong as the Weakest component
5
Guy Hardware
6
Thimble-eye Bolt
7
Johnny Ball & Guy Strain Insulator
8
Guy Wire Strength Data
9
RUS Guy Assemblies & Strength
Assembly
Item
Material
E1.1
E1.1L
E1.2
b
Bolt, machine
5/8”
(12,400 lbs)
3/4”
(18,350 lbs)
None
d
Washer, curved
3” square
(7,800 lbs)
4” square
(14,200 lbs)
None
v
Guy attachment
Standard
(6,600 lbs)
Heavy Duty
(8,500 lbs)
90% of guy
wire
y
Guy wire
3/8” SM
(6,255 lbs)
3/8” HS steel
(9,720 lbs)
7/16” SM
(8,415 lbs)
Total Guy Strength
6,255 lbs
8,500 lbs
8,415 lbs
10
11
RUS Standard Washer Allowed Load
• RUS standards allow no more than 910 pounds per
square inch of compression for washers on wood poles
and crossarms.
12
13
14
RUS Standard Distribution Anchor Assemblies
RUS
Maximum Holding
Designation Power (lbs)*
F1.8
8,000
F1.10
10,000
Expanding
F1.12
12,000
F2.8
8,000
Screw (Power
F2.10
10,000
Installed)
F2.12
12,000
Anchor Type
• *Maximum Holding Power based on installation in Class 5 Soil
15
Types of Soils for Anchor Placement
Soil Class Descriptions
Class Description
1
Solid rock
2
Dense sand, hard silts, course gravel
3
Compact clay & gravel mixed, shale, hardpan
4
Compacted sand, clay-pan, compacted gravel
5
Loose sand, gravel & clay, compacted course sand
6
Clay loam, damp clay, compacted fine sand, loose course sand
7
Silt loam, loose sand fines, wet clay, miscellaneous fill
8
Swamp, saturated loam, marshland
16
Expansion Anchors
Rating (pounds)
6,000
8,000
10,000
12,000
Item Anchor Rod
F1.6
F1.8
F1.10
F1.4
x
x
z
Anchor Rod
5/8” x 7’ 5/8” x 7’
N/A
N/A
Thimble Eye
Anchor Rod
N/A
N/A
3/4” x 8’ 3/4” x 8’
Twin Eye
Anchor (sq. in.)
90
100
120
135
17
Expansion (Bust) Anchors
Expansion
Tool
Un-expanded Anchor
Illustration courtesy of Hubble Power Systems (Chance)
18
Screw Anchors
Single Helix
Double Helix
Illustration courtesy of Hubble Power Systems (Chance)
19
20
Spacing of Anchors
5 feet
5-ft for standard duty
8-ft for heavy duty
21
Guying Situations
•
•
•
•
•
•
•
Change in conductor size
New wire sagged against old wire
Line angles
Dead-ends
Grade B Crossings
Spans that exceed the ruling span by 150%
Long crossings
22
Guy & Anchor Selection Depend on:
•
•
•
•
Horizontal pull at the guy attachment
Guy resultant tension in the down guy
Soil type in which the anchor is installed
Available materials and assemblies
23
Standard Guy and Anchor Assemblies
Guys
Anchors
E1.1 ( 6,255 lbs)
F1.6 (6,000 lbs)
E1.1L (8,500 lbs)*
F1.8 (8,000 lbs)
E1.2 (9,720 lbs)*
F1.10 (10,000 lbs)
* 3/8” HS steel
24
Guy & Anchor Grade of Construction
• RUS requires Minimum Grade C on distribution
• Must match highest Grade of construction on pole
– Transmission underbuild – Grade B
– Railroad, Limited Access Hwy – Grade B
25
Type of Guy Loads
• Transverse
– Forces acting perpendicular to the line
• Wind blowing on ice loaded conductors
• Tension in the wire
• Longitudinal
– Forces acting parallel to the line
• Maximum loaded design tension
26
Deadend Guying Calculations
Guy Height (Hg)
Neutral Height
A,B,CΦ Height
Tension
Guy Lead (Lg)
27
Dead-end guying
Gh = Mt/Hg
Gh = Horizontal pull at guy attachment
Mt = Sum of moments due to tension in the wire
Hg = Average guy attachment height
NESC construction grade = C NESC loading district = Light
Primary cond. = 1/0 ACSR 6/1, Neutral cond. = 2 ACSR 7/1
Pole height and class = 40 ft, Class 4, SYP
Pole-top assembly = C5.71L (RUS Assembly)
28
*NESC Load factors for deadend guyed
structures defined in Rule 250B
Grade C
Type of Loading
Grade B
Transverse wind
2.50
2.20
1.75
Transverse wire
tension
1.65
1.10
1.10
Longitudinal load at
dead-ends
1.65
1.10
1.10
Crossing Elsewhere
*Adapted from NESC Table 253-1, 2012 Edition
29
*NESC Load factors for Extreme Weather when
applicable
Type Loading
Grade B
Grade C
Crossing
Elsewhere
Rule 250 C Extreme Wind
Wind Loads
1.00
0.87
0.87
All other loads
1.00
1.00
1.00
1.00
1.00
1.00
Rule 250D Extreme ice with
concurrent wind
*Adapted from NESC Table 253-1, 2012 Edition
Applied to NESC 250B load if a structure or its supported facilities exceed 60
feet above ground or water.
30
Transverse Wind Load for 1-ft of
Conductor
Conductor Physical Data
Transverse Wind
Name
Size/Strand
Dia.
(in)
RBS
(lb)
Light
(lb/ft)
Medium
(lb/ft)
Heavy
(lb/ft)
Sparate
2 ACSR
7/1
0.325
3640
0.2438
0.2750
0.4417
Raven
1/0 ACSR
6/1
0.398
4380
0.2985
0.2993
0.4660
Penguin
4/0 ACSR
6/1
0.563
8350
0.4223
0.3543
0.5210
Merlin
336 ACSR
18/1
0.684
8680
0.5130
0.3947
0.5613
31
Step 1: Moment Due to Tension
(Mt)
Mt = Σ(Dt • Hc • Ft)
Mt = Moment due to tension in the wire
DT = Fully loaded design tension
DT = 50% RBS
1/0 ACSR = 0.50(4,380 lbs) = 2,190 lbs
2 ACSR = 0.50(3,640 lbs) = 1,820 lbs
Hc = Height of conductor above grade (RUS C5.71L)
Ft = NESC wire tension load factor = 1.10 (grade C)
32
Step 1: Moment due to tension
(Mt)
Wire
DT(lb)
x
Hc (ft)
x Ft (ft) = Mt(ft-lb)
A-phase
2190
x
32.5
x
1.10
=
78,293
B-phase
2190
x
32.5
x
1.10
=
78,293
C-phase
2190
x
32.5
x
1.10
=
78,293
Neutral
1,820
x
28.5
x
1.10
=
57,057
Σ(Dt • Hc • Ft) = 291,936
Mt = 291,936 ft-lbs
33
Step 2: Horizontal Pull (Gh)
Mt
Gh 
Hg
Hg = Height of guy attachment =
31.75-ft (RUS drawing C5.71L)
Mt = 291,936 ft-lbs
Gh = 291,936/31.75 = 9,195
Gh = 9,195 lbs
34
Guy Resultant or Total Guy Load
(Gr)
 Lg 2  Hg 2 

Gr  Gh 
Lg


Gr = Guy resultant tension (lbs)
Gh = Horizontal pull at guy attachment (lbs)
Hg = Height of guy attachment (ft)
Lg = Guy lead length (ft)
35
Guy Resultant for Example 1
(Equation Method for 1:1 Guy Lead)
 Lg 2  Hg 2
Gr  Gh 
Lg




 31.752  31.752
Gr  9,195
31.75


  13003.69 lbs

Total Guy Load (Gr) = 13,004 lbs
36
Guy Factors







Lg2  Hg2
Gf 
Lg







Hg
Gf = Guy Factor
Lg = Guy lead length
Hg = Guy attachment height
Lg
37
Guy Factors
30
30
30
1 to 1






30
20
15
2 to 3
1 to 2






2
2


2
2

2
2
Gf  30  30  1.414 Gf   20  30  1.803 Gf   15  30   2.236


30
20
15










38
Guy Resultant for Example 1
(Guy Factor Method)
Gr  Gh * Gf
1:1 Guy Lead
Gr  9,195*1.414  13,001 lbs
2:3 Guy Lead
Gr  9,195*1.803  16,579 lbs
1:2 Guy Lead
Gr  9,195* 2.236  20,560 lbs
39
Guy Leads
• Specify and stake adequate guy leads
– Not based on truck setup
• Short guy leads can cause
– Significant increase in total guy load
– Pole buckling due to the vertical component of guy
tension
Buckling
Guy Lead
40
Pole Buckling
• Short Guy Leads
• Small Pole Class
• Heavy Wire
Tension
Specify a larger
class pole
41
Guy Factors
Guy Lead
(ft)
Guy Attachment Height (ft)
30
32
34
36
38
40
42
10
3.16
3.35
3.54
3.74
3.93
4.12
4.32
15
2.24
2.36
2.48
2.60
2.72
2.85
2.97
20
1.80
1.89
1.97
2.06
2.15
2.24
2.33
25
1.56
1.62
1.69
1.75
1.82
1.89
1.96
30
1.41
1.46
1.51
1.56
1.61
1.67
1.72
35
#
#
#
1.43
1.48
1.52
1.56
40
#
#
#
#
#
1.41
1.45
42
43
Clearance from Guys to Other
Conductors
Adapted from NESC Table 235-6
Secondary and Neutral
Bare Guy
Wire
6 inches
Insulator
Link
4.5 inches
12 kV Primary
25 kV Primary
6 inches
10 inches
4.5 inches
7.5 inches
44
Code Violation!
45
Grounding Anchor Guys and Span Guys
• Rule 215C2 “All anchor guys and span guys shall be
effectively grounded.”
• Only EXCEPTION is to use a guy insulator
– Fiberglass guy strain insulators
– Johnny Balls used in the past
• Eliminated EXCEPTION for triplex service conductors
– Guys on secondary poles must be grounded
– Big change for many utilities
– Per Bulletin 1724E-153 “RUS considers it to be nonstandard construction when guy wires are not effectively
grounded.”
46
RUS Use of Insulator Links
•
•
•
RUS calls for insulator links on 12 kV systems when
there is less than 15 inches of wood separating guy
attachment and phase associated hardware.
RUS also calls for the lower portion of the guy to be
grounded. Thus it meets the requirements of 215C2
Insulator link used for two reasons
1. Increase BIL on the structure
2. Provide for increased spacing between phase
conductors and ground conductors as one means of
providing safety to lineman.
47
Guy on secondary pole
must be grounded
Guy must be
grounded or have guy
strain insulator
48
Grounded Guy
• Grounded guy near to
phase associated
hardware
• Susceptible to flashover
from lightning
• Solution
Guy
Attachment
1. Lower guy
• RUS says 18 inches
2. Install guy insulator
• Still ground the lower
part of the guy
49
Guy Insulator Link
• Common mistake is to
assume the guy insulator link
must extend past lower
conductors
– Not a NESC requirement
• To achieve BIL goals
– 18 inches is long enough
• To achieve working space
– Some use 36 inches
50
Span Guys
• Span guy is grounded at structure
• At stub pole
– Grounding jumper from span guy to down guy
RUS requires
grounding nut
in anchor eye
51
52
Pole Guying
• Verify/Know your material/inventory.
• Be careful of short guy leads
• RUS - insulate and ground
• Questions?
53