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PAGE NO. 2 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
TABLE OF CONTENTS
1.0 SCOPE
2.0 MATERIALS
2.1 Structural Steel
2.2 Bolts and Nuts
2.3 Galvanizing
2.4 Other Materials
3.0 CLASSIFICATION OF LOADS
3.1 Climatic Loads
3.2 Longitudinal and Torsional Loads
3.3 Construction and Maintenance Loads
4.0 APPLICATION OF WIND LOADS ON POLES
5.0 OVERLOAD CAPACITY FACTORS
6.0 TYPES OF STEEL POLES
7.0 BROKEN WIRE CONDITIONS
7.1 Single Circuit Pole
7.2 Double Circuit Pole
8.0 COMPUTATION OF LOADS
8.1 Types of Loads
8.2 Sag and Tension
8.3 Tabulation of Loads and Loading Trees
8.4 Transverse Loads
8.5 Vertical Loads
8.6 Longitudinal Loads
9.0 PERMISSIBLE STRESSES
9.1 Tension
9.2 Compression
9.3 Shear
9.4 Bending
9.5 Combined Stresses
PAGE NO. 3 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
10.0 STRESSES IN BOLTS/NUTS
10.1 Tension
10.2 Shear
10.3 Bearing
10.4 Combined Stress
11.0 ANCHOR BOLTS
11.1 Diameter
11.2 Length of Embedment
11.3 Nuts for Anchor Bolts
12.0 WELDMENTS
12.1 Material Properties
12.2 Allowable Stresses in Weldments
13.0 CONNECTION PLATES
13.1 Pin Connections
13.2 Other Bolted Connections
14.0 SPLICES
14.1 Slip Splices
14.2 Circumferential Welded Splices
14.3 Welded T Joint Connections
15.0 HOLE SIZE
16.0 ADDITIONAL REQUIREMENTS
APPENDIX 1
17.0 BIBLIOGRAPHY
PAGE NO. 4 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
1.0 SCOPE
This standard stipulates various design considerations to be adopted in the design of
galvanized steel poles self supporting structures for use in the overhead transmission
line system of Saudi Electricity Company (SEC), Saudi Arabia.
This standard covers classification of loads, loading conditions, combination of loads,
overload factors and permissible stresses.
2.0 MATERIALS
2.1 Structural Steel
The pole body, brackets, cross arms and accessories/fittings shall be fabricated
from structural steel made by either open hearth, basic oxygen or electric
furnace process and shall conform to the provisions of latest
revision/amendments of any combination of the following standards or
equivalent:
ASTM A36M 250 MPa minimum yield stress
ASTM A242M 315 MPa minimum yield stress
ASTM A572M 345 MPa minimum yield stress
ASTM A572M 450 MPa minimum yield stress
ASTM A588M 345 MPa minimum yield stress
Base plates shall be fabricated from structural steel conforming either to
ASTM A36M, ASTM A572M, ASTM A588M and ASTM A633M or
equivalent.
Anchor bolts shall conform to steel per ASTM A615M (Grade 420 MPa or 520
MPa) or equivalent, and nuts shall conform to ASTM A563M Grade C
minimum or equivalent.
Steel tubes used as components of tubular pole shall conform to ASTM A595
or equivalent.
2.2 Bolts and Nuts
Bolts, nuts and locknuts shall conform to latest revision of ASTM A307,
ASTM A325M, ASTM A354, ASTM A490 and ASTM A563M or equivalent.
PAGE NO. 5 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
2.3 Galvanizing
The poles shall be hot-dip-galvanized after fabrication in accordance with the
requirements of 01-TMSS-01 to a galvanizing thickness as specified in SEC
Material Standard 20-TMSS-02. The poles, which are too large or difficult to
galvanize, may be metalized in accordance with the acceptable industry
practice/standard.
Bolts and other fasteners shall be galvanized in accordance with ASTM
A153M or ISO 1461 to a galvanizing thickness specified in 01-TMSS-01.
2.4 Other Materials
Other materials used in the construction of steel poles shall conform to
20-TMSS-02.
3.0 CLASSIFICATION OF LOADS
Transmission lines are subjected to various types of loads during their lifetime. These
loads are broadly classified into three distinct categories:
- Climatic loads - Loads imposed on line supports and line components by the
action of wind and coincident temperature
- Longitudinal and Torsion Loads - Loads imposed on line supports due to
breakage of line components, sabotage, etc
- Construction and maintenance loads - Loads imposed on line supports during
construction and maintenance activities. Checking the strength of poles for
these loads ensures safety of workmen during construction and maintenance
activities.
Poles shall be designed to withstand factored loads arising out of above loading
conditions, per details given below for each category:
3.1 Climatic Loads
These are random loads imposed on poles, insulator strings, hardware,
conductors and ground wires due to action of wind and do not act
continuously. Loads due to climatic effects shall be considered for the
following wind and coincident temperature conditions and applied on poles
and line components (conductors, ground wires, hardware, insulators, etc.):
- Standard wind - A wind pressure of 430 N/mm² at minus 1°C (-1°C)
- High wind - A wind pressure of 1064 N/mm² at 27°C
PAGE NO. 6 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
3.1.1 Standard Wind Loading
Under this condition of loading, the following shall be assumed:
a. All wires intact
b. Direction of wind normal to the conductors (for zero deviation) or
perpendicular to the bisector of the angle of deviation at angle
locations
c. A wind pressure of 430 N/mm² acting on the projected area of
poles multiplied by the shape factor as given in Clause 4.0
d. A wind pressure of 430 N/mm² acting on the projected area of
ground wire(s) and conductors and on effective projected area of
insulator strings
e. Wire (conductor, ground wire) tensions corresponding to 430
N/mm² wind at minus 1°C (-1°C), final condition
3.1.2 High Wind Loading
Under this condition of loading, the following shall be assumed:
a. All wires intact
b. Direction of wind as in Clause 3.1.1.b above
c. A wind pressure of 1064 N/mm² acting on the projected area of
poles multiplied by the shape factor as given in Clause 4.0 for
heights up to 10m above ground level. For steel pole heights
above 10m, the wind pressure values shall be increased as per the
procedure given in Clause 4.0 multiplied by the shape factor.
Basic wind pressure values and wind pressure values inclusive of
shape factors for heights above 10m are given in Table 05-1 for
guidance.
d. A wind pressure of 1064 N/mm² acting on full projected area of
ground wires and conductors and on effective projected area of
insulator strings
e. Wire tensions corresponding to 1064 N/mm² wind at 27°C, final
condition
PAGE NO. 7 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Notes: i. The word “wire” shall mean conductor and ground wire
when used as “intact wire”, “wire tension”, “wire
loading”, etc.
ii. The word “ground wire” shall mean OHGW and OPGW.
iii. For the purpose of calculating wind load on bundled
conductors, wind pressure shall be considered acting on
full projected area of each conductor in the bundle.
iv. For the purpose of computing the wind load on insulator
strings, the effective projected area of each insulator string
shall be assumed as fifty percent (50%) of the projected
area of the cylinder with diameter equal to that of the
insulator skirt. For multi-strings, wind shall be considered
acting on each limb of multi-strings.
v. No reduction in wind span shall be considered for spans
on angle locations, i.e., full span shall be considered
instead of projected span.
3.2 Longitudinal and Torsional Loads
Designing a pole for longitudinal and torsional loads ensures adequate strength
of steel pole in longitudinal direction and provides margin for containment of
failure due to cascading effect. Longitudinal loads may be imposed on steel
poles due to failure of line components like hardware, conductors, ground
wires or reduction/removal of tension on one side.
3.2.1 Broken Wire Loading
The number of conductors and/or ground wires to be considered broken
shall be as defined in Clause 7.0 “Broken Wire Conditions”.
Under this condition of loading, the following shall be assumed:
a. Direction of wind as in 3.1.1.b
b. A wind pressure of 430 N/mm² acting on the projected area of
poles multiplied by shape factor as given in Clause 4.0
c. A wind pressure of 430 N/mm² acting on full projected area of
ground wires and conductors and on effective projected area of
insulator strings
d. Wire tension corresponding to 430 N/mm² wind at minus
1°C (-1°C), initial condition
PAGE NO. 8 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
3.3 Construction and Maintenance Loads
3.3.1 Stringing Loads
Stringing loads are imposed on poles during stringing and pulling
operations. These loads shall be assumed to act at wire
(conductors/ground wires) attachment points.
Under this condition of loading, the following shall be assumed:
a. Pulling loads due to stringing equal to tension of
conductors/ground wires at minus 1°C (-1°C), no wind, initial
condition
b. Transverse loads on account of wind on poles and line
components shall be taken as nil.
c. Transverse loads due to line deviation shall be based on wire
tensions at minus 1°C (-1°C), no wind, initial condition.
Application of stringing loads on Tangent/Suspension, Angle
(Tension) and Dead-End pole structures shall be as follows:
i. Tangent/Suspension Pole Structures
Stringing load at any one phase conductor attachment
point with remaining phase conductors and ground wires
intact.
Stringing load at any one ground wire attachment point
with other ground wire, if provided, intact Stringing of
any one phase conductor and/or ground wire when
temporarily dead-ended (anchored) at a distance such
that the angle between the traveler on the pole and
anchor on the ground is 15º to the horizontal.
ii. Angle (Tension) and Dead End pole structures
Stringing loads at all phase conductors and ground wires
attachment points simultaneously. All stringing loads
shall be considered acting in one direction only and all
wires considered intact.
PAGE NO. 9 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
3.3.2 Heavy Vertical Loads
This loading condition represents the pick up load during stringing.
The cross-arms are subjected to heavy stresses due to heavy vertical
loads during construction activities and are required to be adequately
sized for the safety of workmen.
Under this loading condition, loads shall be considered acting at any
one conductor or ground wire attachment point at a time and the
following shall be assumed:
a. A vertical load equal to twice the vertical load resulting from
intact maximum design weight span plus weight of insulator
string and 1500 Newtons to account for the weight of linemen and
tools
b. Transverse loads on account of wind on pole and line components
shall be taken as nil.
c. Transverse loads due to line deviation shall be based on wire
tensions at minus 1°C (-1°C), no wind, initial condition.
4.0 APPLICATION OF WIND LOADS ON POLES
The design wind pressure, qf
, in N/m² is given by:
q
f
= Kz·q
10
·Sf (Eq. 05-1)
Where:
Kz = Exposure coefficient, which increases with height above ground level
=
7/2
10
H
⎥⎦
⎤
⎢⎣
⎡
H = Height above ground level, in meters
q
10
= Basic wind pressure at 10 meters above ground, in N/m²
= ( )2
10V613.0 *
V10 = Wind velocity at 10 meters above ground. For high wind
loading V10 = 150 km/hr = 41.67 m/sec.
q
10
= 0.613*41.67² = 1064 N/m2
PAGE NO. 10 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Sf = Shape Factor (Pressure Coefficient)
= 0.9 Applied to circular shaped poles
= 0.9 Applied to 16-sided polygonal shaped poles
= 1.0 Applied to 12 sided polygonal shaped poles
= 1.4 Applied to 8-sided and 6-sided polygonal poles
= 2.0 Applied to square and rectangular shaped poles
The above shape factors are based on Table 2.6.3 of Guidelines for Electrical
Transmission Line Structural Loading, ASCE Manual No. 74.
Wind pressure values for high wind conditions for heights above 10 meters are given
in Table 05-1 for guidance.
Table 05-1: Wind Pressures for Heights above 10 meters
Wind Pressure (N/m2
)Height Above Ground
(m)
Exposure
Coefficient
Kz SF=0.9 SF=1.0 SF=1.4
10 1.000 958 1064 1490
20 1.219 1168 1297 1816
30 1.369 1311 1457 2040
40 1.486 1424 1582 2214
50 1.584 1517 1685 2360
5.0 OVERLOAD CAPACITY FACTORS
The overload capacity factors to be applied to various loads under different loading
conditions shall be as given in Table 05-2.
PAGE NO. 11 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Table 05-2: Overload Capacity Factors
Types of Loads
Standard
Wind
Loading
High
Wind
Loading
Broken
Wire
Loading
Stringing
Loading
Heavy
Vertical
Loading
Wind Load 2.50
Transverse
Loads Wire Tension
Load at angle
1.65
1.10 1.50 2.0 2.0
Vertical Loads 1.50 1.10 1.50 2.0 2.0
In general 1.10
Longitudinal
Loads
At dead-ends 1.65
1.10 1.50 2.0 2.0
6.0 TYPES OF STEEL POLES
The types of steel poles generally used in SEC system are listed in 20-TMSS-02. The
limitations on base dimensions have also been shown therein.
The designer shall select the design spans and wire tensions in such a way that the
loading arrived at shall not cause excessive bending moment requiring wider base
width or increase in wall thickness, which cannot be fabricated. As a guide, the plate
thickness shall not exceed 25 mm from fabrication consideration.
7.0 BROKEN WIRE CONDITIONS
The following broken wire conditions shall be assumed for the design of poles:
7.1 Single Circuit Poles - Any one phase or ground wire broken, whichever is
more stringent for a particular section
7.2 Double Circuit Tangent Poles
a. Tangent/Suspension Poles - Any one phase or ground wire broken,
whichever is more stringent for a particular section
b. Angle (Tension) and Dead End Poles - Any two phases broken on the
same side and same span or any one phase and one ground wire broken
on the same side and same span, whichever combination is more stringent
for a particular section
Notes: i. Phase shall mean all the sub-conductors in the case of bundled
conductors.
PAGE NO. 12 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
ii. Broken conductor shall mean all sub-conductors of bundle
broken.
8.0 COMPUTATION OF LOADS
8.1 Types of Loads
Three types of loads act on transmission poles, namely transverse, vertical and
longitudinal. Poles shall be designed to withstand simultaneous action of these
loads multiplied by overload factors specified in Clause 5.0, depending on
design condition.
8.2 Sag and Tension
Sag and tension values for conductors and ground wires shall be determined
for various loading conditions keeping in mind the tension limiting conditions
specified in TES-P-122 for computing steel pole loads.
8.3 Tabulation of Loads and Loading Trees
Transverse, vertical and longitudinal loads for various loading conditions
specified in this standard shall be determined in accordance with the procedure
given in Clause 8.4, 8.5 and 8.6 and tabulated, or loading trees prepared before
proceeding with stress calculations and design.
Sample loading calculations for a tangent pole is given in Appendix -1
8.4 Transverse Loads
8.4.1 Wind on Conductors and Ground Wires
Loads due to wind on wires (conductors/ground wires), FWC, in
Newtons, applied at wire attachment points, shall be determined by the
following expression:
Fwc = Pd
L·D·N (Eq. 05-2)
Where:
Pd
= Design wind pressure in N/m²
L = Wind Span, being sum of half the spans on both side of
attachment point, in meters. Values of wind spans as
specified in the Scope of Work and Technical Specifications
(SOW/TS) shall be adopted.
D = Diameter of conductor/ground wire, in meters
PAGE NO. 13 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
N = Number of sub-conductors in a bundle
Note: Wind Span for broken conductor is generally in the range of
sixty percent (60%) of intact wind span.
8.4.2 Wind on Insulator Strings
Wind loads on insulator strings, Fwi
, in Newtons, applied at attachment
points shall be determined from the following expression:
Fwi
= Pd·Ai
(Eq. 05-3)
Where:
Pd
= Design wind pressure in N/m²
Ai
= Effective projected area of insulator string in sq. m.
Effective projected area of the insulator string shall be
assumed as fifty percent (50%) of the projected area of the
cylinder with a diameter equal to that of the insulator skirt.
Note: In case of multi-strings including V-strings, wind pressure on all
strings of multi-strings shall be considered without any masking
effect.
8.4.3 Line Deviation
Loads due to line deviation, Fd, in Newtons, applied at attachment
points shall be determined by the following expressions:
Fd = 2·N·T·Sin (θ/2) Intact Spans (Eq. 05-4)
Fd = N·T·Sin (θ/2) Broken Spans (Eq. 05-5)
Where:
N = Number of sub-conductors in a bundle
T = Tension of conductor/ground wire under a given loading
condition, in Newtons
θ = Angle of line deviation, in degrees
8.4.4 Wind on Pole
Wind loads shall be distributed throughout the height of poles.
PAGE NO. 14 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Wind loads, Fwt
, in Newtons, on a section of height “H” assumed to be
acting at center of gravity of the projected area of the pole is given by
the expression:
Fwt
= Pd
·Ae
(Eq. 05-6)
Where:
Pd
= Design wind pressure in N/m²
Ae
= Projected surface area of pole section under consideration
Total transverse load at each conductor/ground wire attachment point is
the sum of Fwc, Fwi and Fd. Transverse loads due to wind of each
section, Fwt, are distributed as explained above.
8.5 Vertical Loads
8.5.1 Weight of Conductors and Ground Wires
Loads due to weight of wires, Vc, in Newtons, shall be determined as
shown below and applied at wire attachment points:
Vc = W·Wt·N (Eq. 05-7)
Where:
W = Unit weight of conductor/ground wire, in N/m
Wt = Weight Span, being the distance between the lowest points
of conductor/ground wire on the two spans adjacent to the
support under consideration, in meters
The lowest point is defined as the point at which the tangent
to the sag curve or to the extended sag curve is horizontal.
Values of weight spans as specified in SOW/TS shall be
adopted.
N = Number of sub-conductors in a bundle
In a transmission line, three types of weight spans may be encountered.
They are:
a. Minimum Weight Span
b. Maximum downward Weight Span and
PAGE NO. 15 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
c. Maximum upward Weight Span
Tangent/Suspension poles shall be designed for both minimum and
maximum downward weight spans. Minimum weight span may govern
the design of foundations under uplift. Minimum weight span also
governs the swing of suspension strings.
Tangent/Suspension type poles shall never be used at locations, which
are subjected to uplift.
8.5.2 Weight of Hardware and Insulator Strings
Loads due to weight of hardware and insulator strings, Vi, in Newtons,
shall be applied at wire attachment points. Weight of insulator strings
shall be taken as the sum of weight of all the insulators and hardware in
a string/multi-strings.
8.5.3 Weight of Linemen and Tools
Weight of Lineman and tools, VL, in Newtons, shall be applied at
ground wire and conductor attachment supports for the loading
conditions specified in Clause 3.
8.5.4 Self-Weight of Pole
Self-weight of pole is the weight of all the structural members, plates,
nuts, bolts, washers, step bolts, ladders and all other accessories
mounted on it.
Self-weight of pole is calculated on the basis of unit weight of each
component comprising the pole.
Total vertical load at each wire attachment point is the algebraic sum of
Vc, Vi and VL.
8.6 Longitudinal Loads
Longitudinal loads are caused by any of the following loading conditions:
8.6.1 Broken Wire Condition
Unbalanced pulls shall be based on wire tensions determined according
to the loading criteria specified in Clause 3.2.1.d and applied at wire
attachment points in the longitudinal direction.
Number of conductors and ground wires to be considered broken shall
be as specified in Clause 7.0.
PAGE NO. 16 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
a. Tangent/Suspension Poles
i. Longitudinal loads for broken conductors get reduced due to
swing of suspension strings. The longitudinal load shall be
calculated using tension in the broken conductor as sixty
percent (60%) of the tension in the intact conductor.
ii. Longitudinal loads for broken ground wires shall be without
any reduction in tension.
b. Angle (Tension) and Dead End Poles
i. Longitudinal loads for broken conductors/ground wires shall
be the component of tension in longitudinal direction
corresponding to minimum design angle of deviation.
ii. Longitudinal loads for broken conductors/ground wires shall
be taken as nil for Dead End pole structures.
8.6.2 Stringing Condition
Stringing loads shall be assumed equal to tension of conductors/ground
wires at minus 1°C (-1°C), no wind, initial condition and applied in the
longitudinal direction:
- at any one conductor or ground wire attachment point at a time in
case of Tangent/Suspension pole structures
- at all conductor and ground wire attachment points
simultaneously in case of Angle (Tension) and Dead End pole
structures
8.6.3 Intact Span Condition for Dead End Pole Structures
Longitudinal loads due to one sided tensions for Dead End pole
structures shall be equal to full tension of conductors and ground wires
under worst loading condition. These loads shall be applied
simultaneously at all wire attachment points in one direction only.
9.0 PERMISSIBLE STRESSES
Transmission structures are designed based on factored loads. The design approach
outlined in this standard is based on strength methods where the loads are inclusive of
desired overload capacity factors.
PAGE NO. 17 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
The equations given hereunder are applicable for determining allowable stresses in
tubular members with cross sectional shapes as described in ASCE Manual No. 72,
and for elliptical and rectangular members with cross sections that have maximum
major and minor dimension ratios of 2 to 1.
The increase in allowable design stresses due to cold working resulting from bending
of steel plates shall not be considered.
9.1 Tension
9.1.1 Planar Stress
The following conditions shall be satisfied:
yt
g
FF
A
P
=≤ (Eq. 05-8)
P
A
F F
n
t u≤ = 083. (Eq. 05-9)
F Fu y≥ 12. (Eq. 05-10)
Where
P = Factored Axial Load, Newtons
Ag = Gross Area of Cross Section, mm²
An = Net Area of Cross Section, mm²
Ft = Allowable Tensile Stress, MPa
Fy = Specified Minimum Yield Strength, MPa
Fu = Specified Minimum Tensile Strength, MPa
9.1.2 Through Thickness Stress
P
A
Ft≤ , Ft shall be limited to maximum of 248 MPa for all types of
steels.
This is applicable to plates welded perpendicular to the longitudinal
axis of members (e.g., base plate, cross-arm end plates, etc.) and takes
into consideration the possible deficiencies in the tensile strength
through the thickness of the plates.
PAGE NO. 18 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
9.2 Compression
Members subjected to compressive forces shall be checked for general stability
and local buckling tendencies. The actual compressive stresses shall not exceed
those allowed by the following criteria:
9.2.1 General Stability
a. Beam Elements (members with moments determined)
The elastic stability of tubular poles is numerically checked by
nonlinear-finite-element based analysis. The analysis takes into
account secondary moments and stress developed due to eccentric
effect of vertical loads arising out of deflections due to horizontal
loads. The computer program makes many iterations till the
difference between nth
and (n-1)th
iteration deflection is less than
10 3−
, i.e.,
y y
y
n n
n
−
<−( )
.1
0 001
Since the beam members are not permitted to yield, inelastic
buckling is not required to be checked.
b. Truss Elements (members carrying axial force only)
This is not applicable for SEC System and hence the compression
formulae for the same are not covered in this document.
9.2.2 Local Buckling
a. Polygonal Members
Formed regular polygonal tubular members for which the
combined compressive and bending stress, (
P
A
MC
I
+ ), on the
extreme fiber equals the yield stress, Fy, shall be proportioned so
that
w
t Fy
≤
683
(Octagonal Section, Bend Angle 45°) (Eq. 05-11)
w
t Fy
≤
630
(Dodecagonal Section, Bend Angle 30°) (Eq. 05-12)
w
t Fy
≤
565
(Hexdecagonal Section, Bend Angle 22.5°) (Eq. 05-13)
PAGE NO. 19 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Where:
M = Bending Moment, N mm
C = Distance from neutral axis to extreme fiber, mm
I = Moment of Inertia, mm4
w = Flat width of a side, mm
t = Wall thickness, mm
In determining w, the actual inside bend radius shall be used unless it
exceeds 4t, in which case it shall be taken as 4t. The values of w/t
obtained using the above equations 05-11, 05-12 and 05-13 may be
exceeded if the combined compressive bending stress, (
P
A
MC
I
+ ), on
the extreme fiber does not exceed the value, Fa, given by:
⎟
⎠
⎞
⎜
⎝
⎛
×−=
t
w
F000434.00.1F42.1F yya , When
683 959
F
w
t Fy y
≤ ≤
(Octagonal Section, Bend Angle 45°) (Eq. 05-14)
⎟
⎠
⎞
⎜
⎝
⎛
×−=
t
w
F000491.00.1F45.1F yya , When
630 959
F
w
t Fy y
≤ ≤
(Dodecagonal Section, Bend Angle 30°) (Eq. 05-15)
⎟
⎠
⎞
⎜
⎝
⎛
×−=
t
w
F000522.00.1F42.1F yya , When
565 959
F
w
t Fy y
≤ ≤
(Hexdecagonal Section, Bend Angle 22.5°) (Eq. 05-16)
Where:
Fa = Allowable compressive stress, MPa
Equations 05-11 and 05-14 are also applicable for polygonal shapes
with less than eight (8) sides and shall be used only when primary
loading is bending.
If the axial stress, fa, (actual compressive stress) is greater than 6.9 MPa
then the equations 05-12 and 05-15 shall be used for tubes with eight or
fewer sides.
For SEC System, the w/t ratio of regular polygonal section poles shall
not exceed
959
Fy
, where Fy is in MPa.
PAGE NO. 20 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
If a cross section with different number of sides than specified in
equations 05-11 to 05-16 is considered, the bend angle shall be used to
determine which of the above equations will apply. If the bend angle is
greater than
or falls between the values associated with above equations, the
equation for a bend angle immediately less than the required bend angle
shall be used.
If the bend angle is less than 22.5°, the equations as applicable to round
members shall be used.
b. Round Members
i. Axial Compression:
Fa = Fy, When
D
t F
o
y
≤
26180
(Eq. 05-17)
F F
D t
a y
o
= +0 75
6600
. , When
26180 82670
F
D
t Fy
o
y
< ≤ (Eq. 05-18)
ii. Bending:
Fb = Fy, When
D
t F
o
y
≤
41340
(Eq. 05-19)
F F
D t
b y
o
= +07
12450
. , When
41340 82670
F
D
t Fy
o
y
< ≤ (Eq. 05-20)
iii Axial Compression plus Bending:
f
F
f
F
a
a
b
b
+ ≤ 10. (Eq. 05-21)
Where:
Do = Outside diameter of tubular sections, across flats for
polygons, mm
Fa = Allowable compressive stress, MPa, determined
from equations 05-17 or 05-18
PAGE NO. 21 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
Fb = Allowable bending stress MPa, determined from
equations 05-19 or 05-20
fa = Actual compressive stress, MPa
fb = Actual bending stress, MPa
For any kind of round tube, the Do/t ratio shall not exceed
82670
Fy
iv. Rectangular Members
Equations 05-11 and 05-14 shall be used for rectangular
members. The flat width associated with each side shall be
treated separately. If the axial stress, fa, is greater than 6.9
MPa, then equations 05-12 and 05-15 shall be used.
v. Elliptical Members
The bend angle and flat width of elliptical cross sections are
not constant. The smallest bend angle associated with a
particular flat should be used to determine which of the
equations 05-11, 05-12, 05-13 or 05-14, 05-15, 05-16 should
be used. If the bend angle is greater than or between the
values associated with equations 05-11, 05-12, 05-13 and 05-
14, 05-15, 05-16, the equation for a bend angle immediately
less than the required bend angle shall be used. If the bend
angle is less than that for equations 05-13 or 05-16, equations
applicable to round sections shall be used.
9.3 Shear
The yield stress in shear, torsional shear or the combination of the two based
on distortion-energy yield criterion is
F
F
y
y
3
0578≈ . .
The direct and torsional shear shall satisfy the condition:
VQ
It
TC
J
F Fv y+ ≤ = 058. (Eq. 05-22)
Where:
V = Shear force, Newtons
Q = Moment of section about neutral axis, mm3
PAGE NO. 22 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
T = Torsional moment, N·mm
C = Distance from neutral axis to extreme fiber, mm
I = Moment of Inertia, mm4
t = Wall thickness, mm
J = Polar Moment of Inertia, mm4
Fv = Allowable Shear Stress, MPa
9.4 Bending
MC
I
Ft≤ , Where Ft = allowable tensile stress (Eq. 05-23)
MC
I
Fa≤ , Where Fa = allowable compressive stress (Eq. 05-24)
Fa is based on local buckling only
9.5 Combined Stresses
Combination of shear stresses and normal stresses may be evaluated by the
distortion-energy yield criterion. Normally the highest stress results from
combining the maximum normal stress with the maximum torsional shear,
since both occur at the same point.
P
A
M C
I
M C
I
VQ
It
TC
J
F
x y
x
y x
y
y+ +
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟ + +
⎛
⎝
⎜
⎞
⎠
⎟ ≤
2 2
2
3 or 2
aF
(Polygonal members) (Eq. 05-25a)
P
A
M C
I
M C
I
VQ
It
TC
J
F
x y
x
y x
y
y+ +
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟ + +
⎛
⎝
⎜
⎞
⎠
⎟ ≤
2 2
2
3 or 2
bF
(Round members) (Eq. 05-25b)
Refer to Section Properties of tubular members given in ASCE Manual 72 for
nomenclature used in the above equations.
10.0 STRESSES IN BOLTS/NUTS
10.1 Tension
P
A
F
t
t≤ =
tA
LoadProof
, (If a proof load is known) (Eq. 05-26)
PAGE NO. 23 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
OR
P
A
F F
t
t y≤ = , (If yield stress is known) (Eq. 05-27)
OR
P
A
F F
t
t u≤ = 06. , (If neither proof load nor yield stress is known) (Eq. 05-28)
Where:
P = Factored Axial Load, Newtons
Proof Load = ASTM Specified force found by the Length Measurement
Method, Newtons
At = Tensile stress area, mm².
Fy = Specified Minimum Yield Strength, MPa
Fu = Specified Minimum Tensile Strength, MPa
The proof load, tensile strength (Fu) and yield strength (Fy) shall be the
minimum specified values as per ASTM specifications of the material
involved. Any of the above equations can be used depending upon the
information available for the bolts.
10.2 Shear
Average shear stress at failure for ASTM A325M and A490 bolts is taken as
65% of the ultimate tensile stress of the bolt. Of this value, 70 % has been used
for approximating a level at which deformation rate begins to increase
significantly.
The shear stress, Fv, is given by:
A
V
≤ Fv =0.45Fu (Eq. 05-29)
Where:
V = Shear force, Newtons
A = Ag (gross area at shank of bolt) or Ar (area at root of threads), mm²
Fu = Specified Minimum Tensile Strength of the bolts, MPa
PAGE NO. 24 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
When plane of shear does not enter the threaded portion, Ag shall be used and
when threaded portion enters into plane of shear, Ar shall be used.
10.3 Bearing
Bearing stress shall be limited to the weaker of the bearing stress of bolt or
member connected by it.
10.4 Combined stress
F F fv t t= −065 2 2
. (Eq. 05-30)
Where:
Fv = Allowable shear stress, MPa
Ft = Allowable tensile stress, MPa
ft = Actual tensile stress, MPa
11.0 ANCHOR BOLTS
11.1 Diameter
The diameter of Anchor Bolts shall be such that the tension stress in the bolts
under combined bending and direct load does not exceed allowable tension
stress given by:
4M
A D N
P
A N
F
r c r
t+ ≤ (Eq. 05-31)
Where:
P = Axial load, Newtons
M = Bending moment (resultant) at base plate level, N·mm
Dc = Pitch circle diameter of anchor bolts, mm
Ar = Area of cross section of bolt at root of threads, mm²
N = Number of anchor bolts
Ft = Allowable tensile stress in anchor bolts, MPa
11.2 Length of Embedment
The length of embedment shall be determined in accordance with ACI:
PAGE NO. 25 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
L
P
d
d ≥
π σ
(Eq. 05-32)
Where:
Ld = length of embedment, mm
P = Axial load in the Anchor Bolt, Newton
d = Diameter of anchor bolt, mm
σ = Allowable bond stress between concrete and anchor bolt, MPa
11.3 Nuts for Anchor bolts
Nuts for anchor bolts shall conform to the ASTM requirements for the bolts on
which they are to be used. All nuts shall have an ASTM specified proof load
capable of developing the tensile strength of the bolt.
12.0 WELDMENTS
12.1 Material Properties
The nominal strength of weld metals shall be based on minimum values as
listed in AWS D1.1, Structural Welding Code.
12.2 Allowable Stresses in Weldments
The allowable stresses in the weldments shall be as shown in Table 2.3 of
ASCE Manual No.72. In the case of welding elements where the base metals
are of different strengths, the lowest grade of base metal shall be used as a
reference for the design of weld.
13.0 CONNECTION PLATES
Flanges, vangs and other connection plates shall be designed such that maximum
allowable stresses are not exceeded. Further, the maximum allowable stresses shall
not be increased by 33% due to “wind only” loading conditions, as transmission line
structure’s loading are primarily due to wind effect on line components and structures.
13.1 Pin Connections
All the three conditions given below shall be met for the joint/connection
PAGE NO. 26 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
( )P L d tFs h t≤ −2 05. (tension) (Eq. 05-33)
Ft = 0.75Fy
( )P L d tFe h v≤ −2 05. (shear) (Eq. 05-34)
Fv = 0.375Fu
P dtFp≤ (bearing) (Eq. 05-35)
Fp = 1.35Fu
Where:
Ls = Minimum distance, perpendicular to the load, from the center of the
hole to the member edge, mm
Le = Minimum distance, parallel to the load, from the center of the hole
to the member edge, mm
dh = Hole diameter, mm
d = Nominal diameter of bolt, mm
t = Member thickness, mm
Fu = Specified minimum tensile strength of the material or member
For the above equations to be valid, the ratio dh/d shall be less than 2.0
Pin connections are those in which the attachment is free to rotate, at least
about one axis, while under load. Single bolt framing connections and
insulator attachments are considered to be pin connections and shall be sized to
meet the above requirements.
A lower allowable stress value in bearing (Fp = 1.35Fu) has been adopted to
account for movement, which is typical of pin connections. A higher bearing
stress of 1.5Fu is recommended for other bolted connections such as multi-bolt
connections.
13.2 Other Bolted Connections
All the three following conditions shall be met:
P A Fn t≤ (tension) (Eq. 05-36)
Ft = 0.83Fu
PAGE NO. 27 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
( )P L d tFe h v≤ −2 05. (shear) (Eq. 05-37)
Fv = 0.58Fy
P dtFp≤ (bearing) (Eq. 05-38)
Fp = 1.5Fu
Minimum edge distance values have not been specified. However, the same
are taken care of by the above equations and will meet the requirements of
structural joints using ASTM A325M or A490 bolts.
14.0 SPLICES
14.1 Slip Splices
Telescoping (slip) splices for joining the sections shall be detailed for a
nominal lap of 1.5 times the largest inside diameter of the female section with a
tolerance of minus ten percent (-10%) on the final assembled lap length.
The use slip splices shall be so designed and detailed that the minimum
clearance between cross-arms and minimum height of the assembled pole is
obtained. The slip splice shall not interfere with climbing devices.
The use of slip splices is recommended only if the initial jacking force exceeds
the maximum design compressive force at the joint. Supplementary locking
devices shall be provided where relative movement of the joint is critical. Pole
subjected to uplift loads shall be provided with locking devices capable of
resisting 100% of the maximum uplift loads.
The female section longitudinal seam welds in the splice area shall be of
complete-penetration welds for at least a length equal to the maximum lap
dimension.
14.2 Circumferential Welded Splices
Complete-penetration welds shall be used for sections joined by
circumferential welds. Longitudinal welds within 300 mm of circumferential
welds shall also be complete-penetration welds.
14.3 Welded T Joint Connections
The welded joints between pole shafts and base plates, flange plates and arms
to arm brackets fall under the category of T joint connections. Where the
primary loads carried by the pole or arm are flexural in nature, a groove weld
PAGE NO. 28 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
with reinforcing fillet is recommended to satisfy the requirements for through-
thickness stresses in the attachment plate.
15.0 HOLE SIZES
Hole diameters shall be typically 3.0 mm more than the nominal diameter of bolts,
except for anchor boltholes. Anchor boltholes in the base plate shall be 10 mm
oversize.
16.0 ADDITIONAL REQUIREMENTS
For double circuit steel poles, the design shall be suitable both for single circuit and
double circuit strung conditions.
PAGE NO. 29 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
APPENDIX – 1
(Sheet 1 of 2)
Project Title:
________________________________
Contract No.:
________________
Date:
___________
Rev. No.:
_________
Code No.
________________________________
Pole Type
_________
Drawing No.
__________
Page No.
_______
Design Span (m)
Line Angle (Deg):
Wind Span (m)
Normal:
Broken:
Max. Weight Span (m)
Normal:
Broken:
Min/Uplift Weight Span (m)
Normal:
Broken:
LOADING CONDITION (Tick as Applicable)
Standard Wind High Wind Broken Wire Stringing HeavyVertical
TRANSVERSE LOADS OLF Newtons
OHGW/OPGW
Wind Load on OHG Wire…..................................................................
Wind Load on VD, SM*…..……………………………………………
Angle Pull…..........................................................................................
TOTAL
x …...
x …....
x….....
=
=
=
=
Conductor
Wind Load on Conductor…..................................................................
Wind Load on Insulators…....................................................................
Wind Load on VD, WL*….............................................................
Angle Pull…..........................................................................................
TOTAL
x …...
x …...
x …....
x….....
=
=
=
=
=
VERTICAL LOADS MAXIMUM
OHGW/OPGW
Weight of OHG Wire….........................................................................
Weight of SM, VD, HS*…......................................................................
Weight of Lineman and tools….............................................................
TOTAL
x…...
x…...
x…...
=
=
=
=
Conductor
Weight of conductor…..........................................................................
Weight of SP, VD, WL*….................................................................
Weight of Insulators…...........................................................................
Weight of Lineman & tools…..............................................................
TOTAL
x …...
x …...
x …...
x…....
=
=
=
=
=
* SM = Spherical Markers VD = Vibration Dampers
HS = Hardware Sets SP = Spacer Dampers
WL = Warning Lights
NOTE: Loads due to wind on poles shall be calculated and applied in transverse direction.
Continued on sheet 2
PAGE NO. 30 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
APPENDIX – 1
(Sheet 2 of 2)
Project Title:
________________________________
Contract No.:
________________
Contract No.:
_____________
Rev. No.:
_________
Code No.
________________________________
Pole Type
__________
Drawing No.
__________
Page No.
_______
Design Span (m)
Line Angle (Deg):
Wind Span (m)
Normal:
Broken:
Max. Weight Span (m)
Normal:
Broken:
Min./Uplift Weight Span (m)
Normal:
Broken:
LOADING CONDITION (Tick as Applicable)
Standard Wind High Wind Broken Wire Stringing HeavyVertical
VERTICAL LOADS MINIMUM OLF Newtons
OHWG/OPGW
Weight of OHG Wire…...........................
Weight of SM & VD*…..........................
Weight of Lineman and tools…............
TOTAL
x …...
x …...
x….....
=
=
=
=
Conductor
Weight of conductor…..............................................................
Weight of SP, VD, WL*…........................................................
Weight of Insulators…..............................................................
Weight of Lineman & tools…..................................................
TOTAL
x …...
x …...
x …...
x….....
=
=
=
=
=
* SM = Spherical Markers
VD = Vibration Dampers
HS = Hardware Sets
SP = Spacer Dampers
WL = Warning Lights
NOTE: Loads due to wind on poles shall be calculated and applied in transverse direction.
PAGE NO. 31 OF 31TES-P-122.05PIIR0/MAR
TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0
Date of Approval: October 17, 2006
17.0 BIBLIOGRAPHY
17.1 IEC 826: "Loading and Strength of Overhead Transmission Lines", Second edition
1991.
17.2 Holland H. Farr, "Transmission Line Design Manual", United States Department of
the Interior.
17.3 ASCE Manual - 72 "Design of Steel Transmission Pole Structures", American
Society of Civil Engineers, Second edition.
17.4 ASCE Manual – 74 “Guidelines for Electrical Transmission Line Structural Loading,
American Society of Civil Engineers.
17.5 Rural Electrification Administration (U.S. Department of Agriculture), "Design
Manual for High Voltage Transmission Lines".

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Tes p-122.05-pii-r0 (1)

  • 1.
  • 2. PAGE NO. 2 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 TABLE OF CONTENTS 1.0 SCOPE 2.0 MATERIALS 2.1 Structural Steel 2.2 Bolts and Nuts 2.3 Galvanizing 2.4 Other Materials 3.0 CLASSIFICATION OF LOADS 3.1 Climatic Loads 3.2 Longitudinal and Torsional Loads 3.3 Construction and Maintenance Loads 4.0 APPLICATION OF WIND LOADS ON POLES 5.0 OVERLOAD CAPACITY FACTORS 6.0 TYPES OF STEEL POLES 7.0 BROKEN WIRE CONDITIONS 7.1 Single Circuit Pole 7.2 Double Circuit Pole 8.0 COMPUTATION OF LOADS 8.1 Types of Loads 8.2 Sag and Tension 8.3 Tabulation of Loads and Loading Trees 8.4 Transverse Loads 8.5 Vertical Loads 8.6 Longitudinal Loads 9.0 PERMISSIBLE STRESSES 9.1 Tension 9.2 Compression 9.3 Shear 9.4 Bending 9.5 Combined Stresses
  • 3. PAGE NO. 3 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 10.0 STRESSES IN BOLTS/NUTS 10.1 Tension 10.2 Shear 10.3 Bearing 10.4 Combined Stress 11.0 ANCHOR BOLTS 11.1 Diameter 11.2 Length of Embedment 11.3 Nuts for Anchor Bolts 12.0 WELDMENTS 12.1 Material Properties 12.2 Allowable Stresses in Weldments 13.0 CONNECTION PLATES 13.1 Pin Connections 13.2 Other Bolted Connections 14.0 SPLICES 14.1 Slip Splices 14.2 Circumferential Welded Splices 14.3 Welded T Joint Connections 15.0 HOLE SIZE 16.0 ADDITIONAL REQUIREMENTS APPENDIX 1 17.0 BIBLIOGRAPHY
  • 4. PAGE NO. 4 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 1.0 SCOPE This standard stipulates various design considerations to be adopted in the design of galvanized steel poles self supporting structures for use in the overhead transmission line system of Saudi Electricity Company (SEC), Saudi Arabia. This standard covers classification of loads, loading conditions, combination of loads, overload factors and permissible stresses. 2.0 MATERIALS 2.1 Structural Steel The pole body, brackets, cross arms and accessories/fittings shall be fabricated from structural steel made by either open hearth, basic oxygen or electric furnace process and shall conform to the provisions of latest revision/amendments of any combination of the following standards or equivalent: ASTM A36M 250 MPa minimum yield stress ASTM A242M 315 MPa minimum yield stress ASTM A572M 345 MPa minimum yield stress ASTM A572M 450 MPa minimum yield stress ASTM A588M 345 MPa minimum yield stress Base plates shall be fabricated from structural steel conforming either to ASTM A36M, ASTM A572M, ASTM A588M and ASTM A633M or equivalent. Anchor bolts shall conform to steel per ASTM A615M (Grade 420 MPa or 520 MPa) or equivalent, and nuts shall conform to ASTM A563M Grade C minimum or equivalent. Steel tubes used as components of tubular pole shall conform to ASTM A595 or equivalent. 2.2 Bolts and Nuts Bolts, nuts and locknuts shall conform to latest revision of ASTM A307, ASTM A325M, ASTM A354, ASTM A490 and ASTM A563M or equivalent.
  • 5. PAGE NO. 5 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 2.3 Galvanizing The poles shall be hot-dip-galvanized after fabrication in accordance with the requirements of 01-TMSS-01 to a galvanizing thickness as specified in SEC Material Standard 20-TMSS-02. The poles, which are too large or difficult to galvanize, may be metalized in accordance with the acceptable industry practice/standard. Bolts and other fasteners shall be galvanized in accordance with ASTM A153M or ISO 1461 to a galvanizing thickness specified in 01-TMSS-01. 2.4 Other Materials Other materials used in the construction of steel poles shall conform to 20-TMSS-02. 3.0 CLASSIFICATION OF LOADS Transmission lines are subjected to various types of loads during their lifetime. These loads are broadly classified into three distinct categories: - Climatic loads - Loads imposed on line supports and line components by the action of wind and coincident temperature - Longitudinal and Torsion Loads - Loads imposed on line supports due to breakage of line components, sabotage, etc - Construction and maintenance loads - Loads imposed on line supports during construction and maintenance activities. Checking the strength of poles for these loads ensures safety of workmen during construction and maintenance activities. Poles shall be designed to withstand factored loads arising out of above loading conditions, per details given below for each category: 3.1 Climatic Loads These are random loads imposed on poles, insulator strings, hardware, conductors and ground wires due to action of wind and do not act continuously. Loads due to climatic effects shall be considered for the following wind and coincident temperature conditions and applied on poles and line components (conductors, ground wires, hardware, insulators, etc.): - Standard wind - A wind pressure of 430 N/mm² at minus 1°C (-1°C) - High wind - A wind pressure of 1064 N/mm² at 27°C
  • 6. PAGE NO. 6 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 3.1.1 Standard Wind Loading Under this condition of loading, the following shall be assumed: a. All wires intact b. Direction of wind normal to the conductors (for zero deviation) or perpendicular to the bisector of the angle of deviation at angle locations c. A wind pressure of 430 N/mm² acting on the projected area of poles multiplied by the shape factor as given in Clause 4.0 d. A wind pressure of 430 N/mm² acting on the projected area of ground wire(s) and conductors and on effective projected area of insulator strings e. Wire (conductor, ground wire) tensions corresponding to 430 N/mm² wind at minus 1°C (-1°C), final condition 3.1.2 High Wind Loading Under this condition of loading, the following shall be assumed: a. All wires intact b. Direction of wind as in Clause 3.1.1.b above c. A wind pressure of 1064 N/mm² acting on the projected area of poles multiplied by the shape factor as given in Clause 4.0 for heights up to 10m above ground level. For steel pole heights above 10m, the wind pressure values shall be increased as per the procedure given in Clause 4.0 multiplied by the shape factor. Basic wind pressure values and wind pressure values inclusive of shape factors for heights above 10m are given in Table 05-1 for guidance. d. A wind pressure of 1064 N/mm² acting on full projected area of ground wires and conductors and on effective projected area of insulator strings e. Wire tensions corresponding to 1064 N/mm² wind at 27°C, final condition
  • 7. PAGE NO. 7 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Notes: i. The word “wire” shall mean conductor and ground wire when used as “intact wire”, “wire tension”, “wire loading”, etc. ii. The word “ground wire” shall mean OHGW and OPGW. iii. For the purpose of calculating wind load on bundled conductors, wind pressure shall be considered acting on full projected area of each conductor in the bundle. iv. For the purpose of computing the wind load on insulator strings, the effective projected area of each insulator string shall be assumed as fifty percent (50%) of the projected area of the cylinder with diameter equal to that of the insulator skirt. For multi-strings, wind shall be considered acting on each limb of multi-strings. v. No reduction in wind span shall be considered for spans on angle locations, i.e., full span shall be considered instead of projected span. 3.2 Longitudinal and Torsional Loads Designing a pole for longitudinal and torsional loads ensures adequate strength of steel pole in longitudinal direction and provides margin for containment of failure due to cascading effect. Longitudinal loads may be imposed on steel poles due to failure of line components like hardware, conductors, ground wires or reduction/removal of tension on one side. 3.2.1 Broken Wire Loading The number of conductors and/or ground wires to be considered broken shall be as defined in Clause 7.0 “Broken Wire Conditions”. Under this condition of loading, the following shall be assumed: a. Direction of wind as in 3.1.1.b b. A wind pressure of 430 N/mm² acting on the projected area of poles multiplied by shape factor as given in Clause 4.0 c. A wind pressure of 430 N/mm² acting on full projected area of ground wires and conductors and on effective projected area of insulator strings d. Wire tension corresponding to 430 N/mm² wind at minus 1°C (-1°C), initial condition
  • 8. PAGE NO. 8 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 3.3 Construction and Maintenance Loads 3.3.1 Stringing Loads Stringing loads are imposed on poles during stringing and pulling operations. These loads shall be assumed to act at wire (conductors/ground wires) attachment points. Under this condition of loading, the following shall be assumed: a. Pulling loads due to stringing equal to tension of conductors/ground wires at minus 1°C (-1°C), no wind, initial condition b. Transverse loads on account of wind on poles and line components shall be taken as nil. c. Transverse loads due to line deviation shall be based on wire tensions at minus 1°C (-1°C), no wind, initial condition. Application of stringing loads on Tangent/Suspension, Angle (Tension) and Dead-End pole structures shall be as follows: i. Tangent/Suspension Pole Structures Stringing load at any one phase conductor attachment point with remaining phase conductors and ground wires intact. Stringing load at any one ground wire attachment point with other ground wire, if provided, intact Stringing of any one phase conductor and/or ground wire when temporarily dead-ended (anchored) at a distance such that the angle between the traveler on the pole and anchor on the ground is 15º to the horizontal. ii. Angle (Tension) and Dead End pole structures Stringing loads at all phase conductors and ground wires attachment points simultaneously. All stringing loads shall be considered acting in one direction only and all wires considered intact.
  • 9. PAGE NO. 9 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 3.3.2 Heavy Vertical Loads This loading condition represents the pick up load during stringing. The cross-arms are subjected to heavy stresses due to heavy vertical loads during construction activities and are required to be adequately sized for the safety of workmen. Under this loading condition, loads shall be considered acting at any one conductor or ground wire attachment point at a time and the following shall be assumed: a. A vertical load equal to twice the vertical load resulting from intact maximum design weight span plus weight of insulator string and 1500 Newtons to account for the weight of linemen and tools b. Transverse loads on account of wind on pole and line components shall be taken as nil. c. Transverse loads due to line deviation shall be based on wire tensions at minus 1°C (-1°C), no wind, initial condition. 4.0 APPLICATION OF WIND LOADS ON POLES The design wind pressure, qf , in N/m² is given by: q f = Kz·q 10 ·Sf (Eq. 05-1) Where: Kz = Exposure coefficient, which increases with height above ground level = 7/2 10 H ⎥⎦ ⎤ ⎢⎣ ⎡ H = Height above ground level, in meters q 10 = Basic wind pressure at 10 meters above ground, in N/m² = ( )2 10V613.0 * V10 = Wind velocity at 10 meters above ground. For high wind loading V10 = 150 km/hr = 41.67 m/sec. q 10 = 0.613*41.67² = 1064 N/m2
  • 10. PAGE NO. 10 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Sf = Shape Factor (Pressure Coefficient) = 0.9 Applied to circular shaped poles = 0.9 Applied to 16-sided polygonal shaped poles = 1.0 Applied to 12 sided polygonal shaped poles = 1.4 Applied to 8-sided and 6-sided polygonal poles = 2.0 Applied to square and rectangular shaped poles The above shape factors are based on Table 2.6.3 of Guidelines for Electrical Transmission Line Structural Loading, ASCE Manual No. 74. Wind pressure values for high wind conditions for heights above 10 meters are given in Table 05-1 for guidance. Table 05-1: Wind Pressures for Heights above 10 meters Wind Pressure (N/m2 )Height Above Ground (m) Exposure Coefficient Kz SF=0.9 SF=1.0 SF=1.4 10 1.000 958 1064 1490 20 1.219 1168 1297 1816 30 1.369 1311 1457 2040 40 1.486 1424 1582 2214 50 1.584 1517 1685 2360 5.0 OVERLOAD CAPACITY FACTORS The overload capacity factors to be applied to various loads under different loading conditions shall be as given in Table 05-2.
  • 11. PAGE NO. 11 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Table 05-2: Overload Capacity Factors Types of Loads Standard Wind Loading High Wind Loading Broken Wire Loading Stringing Loading Heavy Vertical Loading Wind Load 2.50 Transverse Loads Wire Tension Load at angle 1.65 1.10 1.50 2.0 2.0 Vertical Loads 1.50 1.10 1.50 2.0 2.0 In general 1.10 Longitudinal Loads At dead-ends 1.65 1.10 1.50 2.0 2.0 6.0 TYPES OF STEEL POLES The types of steel poles generally used in SEC system are listed in 20-TMSS-02. The limitations on base dimensions have also been shown therein. The designer shall select the design spans and wire tensions in such a way that the loading arrived at shall not cause excessive bending moment requiring wider base width or increase in wall thickness, which cannot be fabricated. As a guide, the plate thickness shall not exceed 25 mm from fabrication consideration. 7.0 BROKEN WIRE CONDITIONS The following broken wire conditions shall be assumed for the design of poles: 7.1 Single Circuit Poles - Any one phase or ground wire broken, whichever is more stringent for a particular section 7.2 Double Circuit Tangent Poles a. Tangent/Suspension Poles - Any one phase or ground wire broken, whichever is more stringent for a particular section b. Angle (Tension) and Dead End Poles - Any two phases broken on the same side and same span or any one phase and one ground wire broken on the same side and same span, whichever combination is more stringent for a particular section Notes: i. Phase shall mean all the sub-conductors in the case of bundled conductors.
  • 12. PAGE NO. 12 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 ii. Broken conductor shall mean all sub-conductors of bundle broken. 8.0 COMPUTATION OF LOADS 8.1 Types of Loads Three types of loads act on transmission poles, namely transverse, vertical and longitudinal. Poles shall be designed to withstand simultaneous action of these loads multiplied by overload factors specified in Clause 5.0, depending on design condition. 8.2 Sag and Tension Sag and tension values for conductors and ground wires shall be determined for various loading conditions keeping in mind the tension limiting conditions specified in TES-P-122 for computing steel pole loads. 8.3 Tabulation of Loads and Loading Trees Transverse, vertical and longitudinal loads for various loading conditions specified in this standard shall be determined in accordance with the procedure given in Clause 8.4, 8.5 and 8.6 and tabulated, or loading trees prepared before proceeding with stress calculations and design. Sample loading calculations for a tangent pole is given in Appendix -1 8.4 Transverse Loads 8.4.1 Wind on Conductors and Ground Wires Loads due to wind on wires (conductors/ground wires), FWC, in Newtons, applied at wire attachment points, shall be determined by the following expression: Fwc = Pd L·D·N (Eq. 05-2) Where: Pd = Design wind pressure in N/m² L = Wind Span, being sum of half the spans on both side of attachment point, in meters. Values of wind spans as specified in the Scope of Work and Technical Specifications (SOW/TS) shall be adopted. D = Diameter of conductor/ground wire, in meters
  • 13. PAGE NO. 13 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 N = Number of sub-conductors in a bundle Note: Wind Span for broken conductor is generally in the range of sixty percent (60%) of intact wind span. 8.4.2 Wind on Insulator Strings Wind loads on insulator strings, Fwi , in Newtons, applied at attachment points shall be determined from the following expression: Fwi = Pd·Ai (Eq. 05-3) Where: Pd = Design wind pressure in N/m² Ai = Effective projected area of insulator string in sq. m. Effective projected area of the insulator string shall be assumed as fifty percent (50%) of the projected area of the cylinder with a diameter equal to that of the insulator skirt. Note: In case of multi-strings including V-strings, wind pressure on all strings of multi-strings shall be considered without any masking effect. 8.4.3 Line Deviation Loads due to line deviation, Fd, in Newtons, applied at attachment points shall be determined by the following expressions: Fd = 2·N·T·Sin (θ/2) Intact Spans (Eq. 05-4) Fd = N·T·Sin (θ/2) Broken Spans (Eq. 05-5) Where: N = Number of sub-conductors in a bundle T = Tension of conductor/ground wire under a given loading condition, in Newtons θ = Angle of line deviation, in degrees 8.4.4 Wind on Pole Wind loads shall be distributed throughout the height of poles.
  • 14. PAGE NO. 14 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Wind loads, Fwt , in Newtons, on a section of height “H” assumed to be acting at center of gravity of the projected area of the pole is given by the expression: Fwt = Pd ·Ae (Eq. 05-6) Where: Pd = Design wind pressure in N/m² Ae = Projected surface area of pole section under consideration Total transverse load at each conductor/ground wire attachment point is the sum of Fwc, Fwi and Fd. Transverse loads due to wind of each section, Fwt, are distributed as explained above. 8.5 Vertical Loads 8.5.1 Weight of Conductors and Ground Wires Loads due to weight of wires, Vc, in Newtons, shall be determined as shown below and applied at wire attachment points: Vc = W·Wt·N (Eq. 05-7) Where: W = Unit weight of conductor/ground wire, in N/m Wt = Weight Span, being the distance between the lowest points of conductor/ground wire on the two spans adjacent to the support under consideration, in meters The lowest point is defined as the point at which the tangent to the sag curve or to the extended sag curve is horizontal. Values of weight spans as specified in SOW/TS shall be adopted. N = Number of sub-conductors in a bundle In a transmission line, three types of weight spans may be encountered. They are: a. Minimum Weight Span b. Maximum downward Weight Span and
  • 15. PAGE NO. 15 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 c. Maximum upward Weight Span Tangent/Suspension poles shall be designed for both minimum and maximum downward weight spans. Minimum weight span may govern the design of foundations under uplift. Minimum weight span also governs the swing of suspension strings. Tangent/Suspension type poles shall never be used at locations, which are subjected to uplift. 8.5.2 Weight of Hardware and Insulator Strings Loads due to weight of hardware and insulator strings, Vi, in Newtons, shall be applied at wire attachment points. Weight of insulator strings shall be taken as the sum of weight of all the insulators and hardware in a string/multi-strings. 8.5.3 Weight of Linemen and Tools Weight of Lineman and tools, VL, in Newtons, shall be applied at ground wire and conductor attachment supports for the loading conditions specified in Clause 3. 8.5.4 Self-Weight of Pole Self-weight of pole is the weight of all the structural members, plates, nuts, bolts, washers, step bolts, ladders and all other accessories mounted on it. Self-weight of pole is calculated on the basis of unit weight of each component comprising the pole. Total vertical load at each wire attachment point is the algebraic sum of Vc, Vi and VL. 8.6 Longitudinal Loads Longitudinal loads are caused by any of the following loading conditions: 8.6.1 Broken Wire Condition Unbalanced pulls shall be based on wire tensions determined according to the loading criteria specified in Clause 3.2.1.d and applied at wire attachment points in the longitudinal direction. Number of conductors and ground wires to be considered broken shall be as specified in Clause 7.0.
  • 16. PAGE NO. 16 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 a. Tangent/Suspension Poles i. Longitudinal loads for broken conductors get reduced due to swing of suspension strings. The longitudinal load shall be calculated using tension in the broken conductor as sixty percent (60%) of the tension in the intact conductor. ii. Longitudinal loads for broken ground wires shall be without any reduction in tension. b. Angle (Tension) and Dead End Poles i. Longitudinal loads for broken conductors/ground wires shall be the component of tension in longitudinal direction corresponding to minimum design angle of deviation. ii. Longitudinal loads for broken conductors/ground wires shall be taken as nil for Dead End pole structures. 8.6.2 Stringing Condition Stringing loads shall be assumed equal to tension of conductors/ground wires at minus 1°C (-1°C), no wind, initial condition and applied in the longitudinal direction: - at any one conductor or ground wire attachment point at a time in case of Tangent/Suspension pole structures - at all conductor and ground wire attachment points simultaneously in case of Angle (Tension) and Dead End pole structures 8.6.3 Intact Span Condition for Dead End Pole Structures Longitudinal loads due to one sided tensions for Dead End pole structures shall be equal to full tension of conductors and ground wires under worst loading condition. These loads shall be applied simultaneously at all wire attachment points in one direction only. 9.0 PERMISSIBLE STRESSES Transmission structures are designed based on factored loads. The design approach outlined in this standard is based on strength methods where the loads are inclusive of desired overload capacity factors.
  • 17. PAGE NO. 17 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 The equations given hereunder are applicable for determining allowable stresses in tubular members with cross sectional shapes as described in ASCE Manual No. 72, and for elliptical and rectangular members with cross sections that have maximum major and minor dimension ratios of 2 to 1. The increase in allowable design stresses due to cold working resulting from bending of steel plates shall not be considered. 9.1 Tension 9.1.1 Planar Stress The following conditions shall be satisfied: yt g FF A P =≤ (Eq. 05-8) P A F F n t u≤ = 083. (Eq. 05-9) F Fu y≥ 12. (Eq. 05-10) Where P = Factored Axial Load, Newtons Ag = Gross Area of Cross Section, mm² An = Net Area of Cross Section, mm² Ft = Allowable Tensile Stress, MPa Fy = Specified Minimum Yield Strength, MPa Fu = Specified Minimum Tensile Strength, MPa 9.1.2 Through Thickness Stress P A Ft≤ , Ft shall be limited to maximum of 248 MPa for all types of steels. This is applicable to plates welded perpendicular to the longitudinal axis of members (e.g., base plate, cross-arm end plates, etc.) and takes into consideration the possible deficiencies in the tensile strength through the thickness of the plates.
  • 18. PAGE NO. 18 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 9.2 Compression Members subjected to compressive forces shall be checked for general stability and local buckling tendencies. The actual compressive stresses shall not exceed those allowed by the following criteria: 9.2.1 General Stability a. Beam Elements (members with moments determined) The elastic stability of tubular poles is numerically checked by nonlinear-finite-element based analysis. The analysis takes into account secondary moments and stress developed due to eccentric effect of vertical loads arising out of deflections due to horizontal loads. The computer program makes many iterations till the difference between nth and (n-1)th iteration deflection is less than 10 3− , i.e., y y y n n n − <−( ) .1 0 001 Since the beam members are not permitted to yield, inelastic buckling is not required to be checked. b. Truss Elements (members carrying axial force only) This is not applicable for SEC System and hence the compression formulae for the same are not covered in this document. 9.2.2 Local Buckling a. Polygonal Members Formed regular polygonal tubular members for which the combined compressive and bending stress, ( P A MC I + ), on the extreme fiber equals the yield stress, Fy, shall be proportioned so that w t Fy ≤ 683 (Octagonal Section, Bend Angle 45°) (Eq. 05-11) w t Fy ≤ 630 (Dodecagonal Section, Bend Angle 30°) (Eq. 05-12) w t Fy ≤ 565 (Hexdecagonal Section, Bend Angle 22.5°) (Eq. 05-13)
  • 19. PAGE NO. 19 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Where: M = Bending Moment, N mm C = Distance from neutral axis to extreme fiber, mm I = Moment of Inertia, mm4 w = Flat width of a side, mm t = Wall thickness, mm In determining w, the actual inside bend radius shall be used unless it exceeds 4t, in which case it shall be taken as 4t. The values of w/t obtained using the above equations 05-11, 05-12 and 05-13 may be exceeded if the combined compressive bending stress, ( P A MC I + ), on the extreme fiber does not exceed the value, Fa, given by: ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ×−= t w F000434.00.1F42.1F yya , When 683 959 F w t Fy y ≤ ≤ (Octagonal Section, Bend Angle 45°) (Eq. 05-14) ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ×−= t w F000491.00.1F45.1F yya , When 630 959 F w t Fy y ≤ ≤ (Dodecagonal Section, Bend Angle 30°) (Eq. 05-15) ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ×−= t w F000522.00.1F42.1F yya , When 565 959 F w t Fy y ≤ ≤ (Hexdecagonal Section, Bend Angle 22.5°) (Eq. 05-16) Where: Fa = Allowable compressive stress, MPa Equations 05-11 and 05-14 are also applicable for polygonal shapes with less than eight (8) sides and shall be used only when primary loading is bending. If the axial stress, fa, (actual compressive stress) is greater than 6.9 MPa then the equations 05-12 and 05-15 shall be used for tubes with eight or fewer sides. For SEC System, the w/t ratio of regular polygonal section poles shall not exceed 959 Fy , where Fy is in MPa.
  • 20. PAGE NO. 20 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 If a cross section with different number of sides than specified in equations 05-11 to 05-16 is considered, the bend angle shall be used to determine which of the above equations will apply. If the bend angle is greater than or falls between the values associated with above equations, the equation for a bend angle immediately less than the required bend angle shall be used. If the bend angle is less than 22.5°, the equations as applicable to round members shall be used. b. Round Members i. Axial Compression: Fa = Fy, When D t F o y ≤ 26180 (Eq. 05-17) F F D t a y o = +0 75 6600 . , When 26180 82670 F D t Fy o y < ≤ (Eq. 05-18) ii. Bending: Fb = Fy, When D t F o y ≤ 41340 (Eq. 05-19) F F D t b y o = +07 12450 . , When 41340 82670 F D t Fy o y < ≤ (Eq. 05-20) iii Axial Compression plus Bending: f F f F a a b b + ≤ 10. (Eq. 05-21) Where: Do = Outside diameter of tubular sections, across flats for polygons, mm Fa = Allowable compressive stress, MPa, determined from equations 05-17 or 05-18
  • 21. PAGE NO. 21 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 Fb = Allowable bending stress MPa, determined from equations 05-19 or 05-20 fa = Actual compressive stress, MPa fb = Actual bending stress, MPa For any kind of round tube, the Do/t ratio shall not exceed 82670 Fy iv. Rectangular Members Equations 05-11 and 05-14 shall be used for rectangular members. The flat width associated with each side shall be treated separately. If the axial stress, fa, is greater than 6.9 MPa, then equations 05-12 and 05-15 shall be used. v. Elliptical Members The bend angle and flat width of elliptical cross sections are not constant. The smallest bend angle associated with a particular flat should be used to determine which of the equations 05-11, 05-12, 05-13 or 05-14, 05-15, 05-16 should be used. If the bend angle is greater than or between the values associated with equations 05-11, 05-12, 05-13 and 05- 14, 05-15, 05-16, the equation for a bend angle immediately less than the required bend angle shall be used. If the bend angle is less than that for equations 05-13 or 05-16, equations applicable to round sections shall be used. 9.3 Shear The yield stress in shear, torsional shear or the combination of the two based on distortion-energy yield criterion is F F y y 3 0578≈ . . The direct and torsional shear shall satisfy the condition: VQ It TC J F Fv y+ ≤ = 058. (Eq. 05-22) Where: V = Shear force, Newtons Q = Moment of section about neutral axis, mm3
  • 22. PAGE NO. 22 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 T = Torsional moment, N·mm C = Distance from neutral axis to extreme fiber, mm I = Moment of Inertia, mm4 t = Wall thickness, mm J = Polar Moment of Inertia, mm4 Fv = Allowable Shear Stress, MPa 9.4 Bending MC I Ft≤ , Where Ft = allowable tensile stress (Eq. 05-23) MC I Fa≤ , Where Fa = allowable compressive stress (Eq. 05-24) Fa is based on local buckling only 9.5 Combined Stresses Combination of shear stresses and normal stresses may be evaluated by the distortion-energy yield criterion. Normally the highest stress results from combining the maximum normal stress with the maximum torsional shear, since both occur at the same point. P A M C I M C I VQ It TC J F x y x y x y y+ + ⎛ ⎝ ⎜⎜ ⎞ ⎠ ⎟⎟ + + ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ≤ 2 2 2 3 or 2 aF (Polygonal members) (Eq. 05-25a) P A M C I M C I VQ It TC J F x y x y x y y+ + ⎛ ⎝ ⎜⎜ ⎞ ⎠ ⎟⎟ + + ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ≤ 2 2 2 3 or 2 bF (Round members) (Eq. 05-25b) Refer to Section Properties of tubular members given in ASCE Manual 72 for nomenclature used in the above equations. 10.0 STRESSES IN BOLTS/NUTS 10.1 Tension P A F t t≤ = tA LoadProof , (If a proof load is known) (Eq. 05-26)
  • 23. PAGE NO. 23 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 OR P A F F t t y≤ = , (If yield stress is known) (Eq. 05-27) OR P A F F t t u≤ = 06. , (If neither proof load nor yield stress is known) (Eq. 05-28) Where: P = Factored Axial Load, Newtons Proof Load = ASTM Specified force found by the Length Measurement Method, Newtons At = Tensile stress area, mm². Fy = Specified Minimum Yield Strength, MPa Fu = Specified Minimum Tensile Strength, MPa The proof load, tensile strength (Fu) and yield strength (Fy) shall be the minimum specified values as per ASTM specifications of the material involved. Any of the above equations can be used depending upon the information available for the bolts. 10.2 Shear Average shear stress at failure for ASTM A325M and A490 bolts is taken as 65% of the ultimate tensile stress of the bolt. Of this value, 70 % has been used for approximating a level at which deformation rate begins to increase significantly. The shear stress, Fv, is given by: A V ≤ Fv =0.45Fu (Eq. 05-29) Where: V = Shear force, Newtons A = Ag (gross area at shank of bolt) or Ar (area at root of threads), mm² Fu = Specified Minimum Tensile Strength of the bolts, MPa
  • 24. PAGE NO. 24 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 When plane of shear does not enter the threaded portion, Ag shall be used and when threaded portion enters into plane of shear, Ar shall be used. 10.3 Bearing Bearing stress shall be limited to the weaker of the bearing stress of bolt or member connected by it. 10.4 Combined stress F F fv t t= −065 2 2 . (Eq. 05-30) Where: Fv = Allowable shear stress, MPa Ft = Allowable tensile stress, MPa ft = Actual tensile stress, MPa 11.0 ANCHOR BOLTS 11.1 Diameter The diameter of Anchor Bolts shall be such that the tension stress in the bolts under combined bending and direct load does not exceed allowable tension stress given by: 4M A D N P A N F r c r t+ ≤ (Eq. 05-31) Where: P = Axial load, Newtons M = Bending moment (resultant) at base plate level, N·mm Dc = Pitch circle diameter of anchor bolts, mm Ar = Area of cross section of bolt at root of threads, mm² N = Number of anchor bolts Ft = Allowable tensile stress in anchor bolts, MPa 11.2 Length of Embedment The length of embedment shall be determined in accordance with ACI:
  • 25. PAGE NO. 25 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 L P d d ≥ π σ (Eq. 05-32) Where: Ld = length of embedment, mm P = Axial load in the Anchor Bolt, Newton d = Diameter of anchor bolt, mm σ = Allowable bond stress between concrete and anchor bolt, MPa 11.3 Nuts for Anchor bolts Nuts for anchor bolts shall conform to the ASTM requirements for the bolts on which they are to be used. All nuts shall have an ASTM specified proof load capable of developing the tensile strength of the bolt. 12.0 WELDMENTS 12.1 Material Properties The nominal strength of weld metals shall be based on minimum values as listed in AWS D1.1, Structural Welding Code. 12.2 Allowable Stresses in Weldments The allowable stresses in the weldments shall be as shown in Table 2.3 of ASCE Manual No.72. In the case of welding elements where the base metals are of different strengths, the lowest grade of base metal shall be used as a reference for the design of weld. 13.0 CONNECTION PLATES Flanges, vangs and other connection plates shall be designed such that maximum allowable stresses are not exceeded. Further, the maximum allowable stresses shall not be increased by 33% due to “wind only” loading conditions, as transmission line structure’s loading are primarily due to wind effect on line components and structures. 13.1 Pin Connections All the three conditions given below shall be met for the joint/connection
  • 26. PAGE NO. 26 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 ( )P L d tFs h t≤ −2 05. (tension) (Eq. 05-33) Ft = 0.75Fy ( )P L d tFe h v≤ −2 05. (shear) (Eq. 05-34) Fv = 0.375Fu P dtFp≤ (bearing) (Eq. 05-35) Fp = 1.35Fu Where: Ls = Minimum distance, perpendicular to the load, from the center of the hole to the member edge, mm Le = Minimum distance, parallel to the load, from the center of the hole to the member edge, mm dh = Hole diameter, mm d = Nominal diameter of bolt, mm t = Member thickness, mm Fu = Specified minimum tensile strength of the material or member For the above equations to be valid, the ratio dh/d shall be less than 2.0 Pin connections are those in which the attachment is free to rotate, at least about one axis, while under load. Single bolt framing connections and insulator attachments are considered to be pin connections and shall be sized to meet the above requirements. A lower allowable stress value in bearing (Fp = 1.35Fu) has been adopted to account for movement, which is typical of pin connections. A higher bearing stress of 1.5Fu is recommended for other bolted connections such as multi-bolt connections. 13.2 Other Bolted Connections All the three following conditions shall be met: P A Fn t≤ (tension) (Eq. 05-36) Ft = 0.83Fu
  • 27. PAGE NO. 27 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 ( )P L d tFe h v≤ −2 05. (shear) (Eq. 05-37) Fv = 0.58Fy P dtFp≤ (bearing) (Eq. 05-38) Fp = 1.5Fu Minimum edge distance values have not been specified. However, the same are taken care of by the above equations and will meet the requirements of structural joints using ASTM A325M or A490 bolts. 14.0 SPLICES 14.1 Slip Splices Telescoping (slip) splices for joining the sections shall be detailed for a nominal lap of 1.5 times the largest inside diameter of the female section with a tolerance of minus ten percent (-10%) on the final assembled lap length. The use slip splices shall be so designed and detailed that the minimum clearance between cross-arms and minimum height of the assembled pole is obtained. The slip splice shall not interfere with climbing devices. The use of slip splices is recommended only if the initial jacking force exceeds the maximum design compressive force at the joint. Supplementary locking devices shall be provided where relative movement of the joint is critical. Pole subjected to uplift loads shall be provided with locking devices capable of resisting 100% of the maximum uplift loads. The female section longitudinal seam welds in the splice area shall be of complete-penetration welds for at least a length equal to the maximum lap dimension. 14.2 Circumferential Welded Splices Complete-penetration welds shall be used for sections joined by circumferential welds. Longitudinal welds within 300 mm of circumferential welds shall also be complete-penetration welds. 14.3 Welded T Joint Connections The welded joints between pole shafts and base plates, flange plates and arms to arm brackets fall under the category of T joint connections. Where the primary loads carried by the pole or arm are flexural in nature, a groove weld
  • 28. PAGE NO. 28 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 with reinforcing fillet is recommended to satisfy the requirements for through- thickness stresses in the attachment plate. 15.0 HOLE SIZES Hole diameters shall be typically 3.0 mm more than the nominal diameter of bolts, except for anchor boltholes. Anchor boltholes in the base plate shall be 10 mm oversize. 16.0 ADDITIONAL REQUIREMENTS For double circuit steel poles, the design shall be suitable both for single circuit and double circuit strung conditions.
  • 29. PAGE NO. 29 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 APPENDIX – 1 (Sheet 1 of 2) Project Title: ________________________________ Contract No.: ________________ Date: ___________ Rev. No.: _________ Code No. ________________________________ Pole Type _________ Drawing No. __________ Page No. _______ Design Span (m) Line Angle (Deg): Wind Span (m) Normal: Broken: Max. Weight Span (m) Normal: Broken: Min/Uplift Weight Span (m) Normal: Broken: LOADING CONDITION (Tick as Applicable) Standard Wind High Wind Broken Wire Stringing HeavyVertical TRANSVERSE LOADS OLF Newtons OHGW/OPGW Wind Load on OHG Wire….................................................................. Wind Load on VD, SM*…..…………………………………………… Angle Pull….......................................................................................... TOTAL x …... x ….... x…..... = = = = Conductor Wind Load on Conductor….................................................................. Wind Load on Insulators….................................................................... Wind Load on VD, WL*…............................................................. Angle Pull….......................................................................................... TOTAL x …... x …... x ….... x…..... = = = = = VERTICAL LOADS MAXIMUM OHGW/OPGW Weight of OHG Wire…......................................................................... Weight of SM, VD, HS*…...................................................................... Weight of Lineman and tools…............................................................. TOTAL x…... x…... x…... = = = = Conductor Weight of conductor….......................................................................... Weight of SP, VD, WL*…................................................................. Weight of Insulators…........................................................................... Weight of Lineman & tools….............................................................. TOTAL x …... x …... x …... x….... = = = = = * SM = Spherical Markers VD = Vibration Dampers HS = Hardware Sets SP = Spacer Dampers WL = Warning Lights NOTE: Loads due to wind on poles shall be calculated and applied in transverse direction. Continued on sheet 2
  • 30. PAGE NO. 30 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 APPENDIX – 1 (Sheet 2 of 2) Project Title: ________________________________ Contract No.: ________________ Contract No.: _____________ Rev. No.: _________ Code No. ________________________________ Pole Type __________ Drawing No. __________ Page No. _______ Design Span (m) Line Angle (Deg): Wind Span (m) Normal: Broken: Max. Weight Span (m) Normal: Broken: Min./Uplift Weight Span (m) Normal: Broken: LOADING CONDITION (Tick as Applicable) Standard Wind High Wind Broken Wire Stringing HeavyVertical VERTICAL LOADS MINIMUM OLF Newtons OHWG/OPGW Weight of OHG Wire…........................... Weight of SM & VD*….......................... Weight of Lineman and tools…............ TOTAL x …... x …... x…..... = = = = Conductor Weight of conductor….............................................................. Weight of SP, VD, WL*…........................................................ Weight of Insulators….............................................................. Weight of Lineman & tools….................................................. TOTAL x …... x …... x …... x…..... = = = = = * SM = Spherical Markers VD = Vibration Dampers HS = Hardware Sets SP = Spacer Dampers WL = Warning Lights NOTE: Loads due to wind on poles shall be calculated and applied in transverse direction.
  • 31. PAGE NO. 31 OF 31TES-P-122.05PIIR0/MAR TRANSMISSION ENGINEERING STANDARD TES-P-122.05PII, Rev. 0 Date of Approval: October 17, 2006 17.0 BIBLIOGRAPHY 17.1 IEC 826: "Loading and Strength of Overhead Transmission Lines", Second edition 1991. 17.2 Holland H. Farr, "Transmission Line Design Manual", United States Department of the Interior. 17.3 ASCE Manual - 72 "Design of Steel Transmission Pole Structures", American Society of Civil Engineers, Second edition. 17.4 ASCE Manual – 74 “Guidelines for Electrical Transmission Line Structural Loading, American Society of Civil Engineers. 17.5 Rural Electrification Administration (U.S. Department of Agriculture), "Design Manual for High Voltage Transmission Lines".