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IS 802-1-1 (1995) : Code of Practice for Use of Structural
Steel In Overhead Transmission Line Towers, Part 1
Materials, Loads and Permissible Stresses, Section 1:
Materials and Loads [CED 7: Structural Engineering and
structural sections]
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Satyanarayan Gangaram Pitroda
Invent a New India Using Knowledge
Bhartrhari — Nitisatakam
"Knowledge is such a treasure which cannot be stolen"
BLANK PAGE
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PROTECTED BY COPYRIGHT
IS 802 ( Part 1/Sec 1 ) : 1995
'ijmft^ HHch ^ Reaffirmed 2006 )
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Indian Standard
USE OF STRUCTURAL STEEL IN OVERHEAD
TRANSMISSION LINE TOWERS —
CODE OF PRACTICE
PART 1 MATERIALS, LOADS AND PERMISSIBLE STRESSES
Section 1 Materials and Loads
( Third Revision )
First Reprint MAY 1997
UDC 669.14.018.29 : 621.315.668.2 : 624.042 : 006.76
© BIS 1995
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
September 1995 Price Group 8
Structural Engineering Sectional Committee, CED 7
FOREWORD
This Indian Standard ( Third Revision ) was adopted by the Bureau of Indian Standards, after
.1 1 J', r' !• ii-.xi. -i-<i i..__!T? .'„^^-;«/»c,^^4;^«->i /^^,^«^:*+/^^ u^j u ^ n».«.-m.^^ u.r-tUn
tne arail nnailZeU Oy mC lanuuiuiai X^iiyincuiiug ov^wmjuui v^mmuim^*^ nau uctu appnjy*^u ujr iu»^
Civil Engineering Division Council.
The standards under IS 802 series have been prepared with a view to establish uniform practices
for design, fabrication, inspection and testing of overhead transmission line lowers. Part 1 of the
standard covers requirements in regard to material, loads and permissible stresses apart from
other relevant design provisions. Provisions for fabrication, galvanizing, inspection and packing
have been covered in Part 2 whereas provisions for testing of these towers have been covered
in Part 3.
This standard was first published in 1967 and subsequently revised in 1973 and in 1977. In this
revision, the standard has been split in two sections, namely Section 1 Materials and loads, and
Section 2 Permissible stresses.
Some of the major modifications made in this Section are as under:
a) Concept of maximum working load multiplied by the factors of safety as per IE Rules has
been replaced by the ultimate load concept.
b) For assessing the loads on tower, concept of reliability, security and safety have been
introduced on the basis of lEC 826 : 1991 'Technical report on loading and strength of
overhead transmission lines'.
c) Basic wind speed based on peak gust velocity, averaged over 3 seconds duration, as per*
the wind map of India given in IS 875 { Part 3 ) : 1987 'Code of practice for design loads
( other than earthquake ) for buildings and structures : Part 3 Wind loads ( second revision )'
has been kept as the basis of calculating reference wind speed. Terrain and topography
characteristics of the ground have been taken into consideration in working out the design
wind speeds.
d) Wind loads on towers and conductors have been revised. These are based on the modified
wind map of the country. Reference wind speed averaged over 10 minutes duration has
been used for the determination of wind loads.
e) Provisions for the 'Temperature Effects' have been modified. In order to permit additional
current carrying capacity m the conductor the maximum temperature in the ACSR
conductor has now been permitted to be 75°C in any part of the country. For aluminium
alloy ( AAAC ) conductor, the corresponding maximum temperature has been permitted
to be 85°C.
f) Provisions for anti cascading checks have been included for angle towers.
g) Provisions for raulti circuit towers have been included.
h) Consequent to the merger of IS 226 : 1975 'Structural steel ( Standard quality )' in
IS 2062 : 1992 'Specification for weldable structural steel ( third revision )' steels conforming
to IS 2062 : 1992 and IS 8500 : 1992 'Specification for weldable structural steel { medium
and high strength qualities )' have been included.
j) With the publication of IS 12427 : 1988 'Transmission tower bolts' these bolts ( property
class 5.6 ) and bolts of property class 8.8 conforming to IS 3757 : 1985 'High strength
structural bolts ( second revision )' have been included in addition to bolts, of property class
4.6 conforming to IS 6639 : 1972 'Hixagoi bolts for steel structures'.
As transmission line towers are comparatively light structures and also that the maximum
wind pressure is the chief criterion for the design, the Sectional Committee felt that concurrence
of earthquake and maximum wind pressure is unlikely to take place. However in earthquake
prone areas the design of towers/foundations shall be checked for earthquake forces correspond-
ing to nil wind and minimum temperature . in accordance with IS 1893 : 1984 'Criteria for
( Continued on third cover )
IS 802 ( Fart 1/Sec 1 ) : 1995
Indian Standard
USE OF STRUCTURAL STEEL IN OVERHEAD
TRANSMISSION LINE TOWERS —
CODE OF PRACTICE
PART 1 MATERIALS, LOADS AND PERMISSIBLE STRESSES
Section 1 Materials and Loads
( Third Revision )
1 SCOPE
1.1 This standard ( Part 1/Sec I ) stipulates
materials and loads to be adopted in the design
of self-Nuppoiting steel lattice towers for
ovji'h^ad LraniiTiission lines.
1.1.1 Permissible stresses and other design
parameters are covered in IS 802 ( Part 1/
Sec 2 ) : 1992 of this standard.
1.1.2 Provisions on fabrication including galva-
nizing, inspection and packing, etc, and testing
of transmission line towers have been covered
in IS 802 ( Part 2 ) : 1978 and IS 802 ( Part 3 ) :
1978 respectively.
1.2 This standard does not cover river crossing
towers arid guyed towers. These will be covered
in separate standards.
2 REFERENCES
The Indian Standards listed in Annex A are
necessary adjuncts to this standard
3 STATUTORY REQUIREMENTS
3.1 Statutory requirements as laid down in the
'Indian Electricity Rules, 1956' or by any other
statutory body applicable to such structures as
covered in this standard shall be satisfied.
3.2 Compliance with this standard does not
relieve any user from the responsibility of
observing local and provincial building byelaws,
lire and safety laws and other civil aviation
requirements appilicable to such structures.
4 TERMINOLOGY
4.1 Return Period
Return period is the mean interval between
recurrences of a climatic event of defined
magnitude. The inverse of the return period
gives the probability of exceeding the event in
one year.
4.2 Reliability
Reliability of a transmission system is the
probabiity that the system would perform its
function/task under the designed load condi-
tions for a specified period . In simple terms,
the reliability may be defined as the probability
that a given item will indeed survive a given
service enviionmcnt and lo:j,ding for a prescri-
bed period of time.
4.3 Security
The ability of a system to be protected from
any major collapse such as ca-^cading ellcct, if
a failure is triggered in a given component.
Security is a deternitnistic coiicept as opposed
to reliability which is a probabilistic.
4.4 Safety
The ability of a system not to cause human
injuries or loss of life. It relates, in this code,
mainly to protection o( workers during construc-
tion and maintenance operations.
5 MATERIALS
5.1 Structural Steel
The tower member^ including cross arms shall
be of structural steel conforming to any of the
grade, as appropriate, of IS 2062 : 1992. Steel
conforming to any of the aporopriatc grade of
IS 8500 : 1992 may also be used.
5.1.1 Medium and high strength structural steels
with known properties conforming to other
national and international standards may also
be used subject to the approval of the purchaser.
5.2 Bolts
5.2.1 Bolts for tower connections shall conform
to IS 12427 : 1988 or of property class 4.6 con-
forming to IS 6639 : 1972,
1
IS 802 ( Part 1/Sec 1 ) : 1995
5.2.2 High strength bolts, if used (only with
structural steels of IS 8500 : 1992 ) shall conform
to property class 8.8 of IS 3757 : 1985.
5.2.3 Foundation bolts shall conform to IS 5624 :
1970.
5.2.4 Step bolts shall conform to IS 10238 : 1982.
5.3 Nuts
5.3.1 Nuts shall conform to IS 1363 ( Part 3 ) :
1992. The mechanical properties shall conform
to property class 4 or 5 as the case may be as
specified in IS 1367 ( Part 6 ) : 1980 except that
the proof stress for nuts of property class 5 shall
be as given in IS 12427 : 1988.
5.3.2 Nuts to be used with high strength bolts
shall conform to IS 6623 : 1985.
5.4 Washers
5.4.1 Washers shall conform to IS 2016 : 1967.
Heavy washers shall conform to IS 6610 : 1972.
Spring washers shall conform to type B of
IS 3063 : 1972.
5.<i.2 Washers to be used with high strength
bolts and nuts shall conform to IS 6649 : 1985.
5.5 Galvanization
5.5.1 Structural members of the towers, plain
and heavy washers shall be galvanized in accor-
dance with the provisions of IS 4759 : 1984.
5.5.2 Threaded fasteners shall be galvanized to
conform to the requirements of IS 1367
(Part 13) : 1983
5.5.3 Spring washers shall be hot dip galvanized
as per service grade 4 of IS 4759 ; 1984 or
electro galvanized as per service grade 3 of
IS 1573 : 1986 as specified by the purchaser.
5.6 Other Materials
Other materials used in the construction of the
tower shall conform to appropriate Indian
Standards wherever available.
6 TYPES OF TOWERS
6.1 The selection of the most suitable types of
tower for transmission lines depends on the
actual terrain through which the line traverses.
Experience has, however, shown that any com-
bination of the following types of towers are
generally suitable for most of the lines ;
i) Suspension towers ( with I or V suspension insulator strings )
a) Tangent towers ( 0'' ) with To be used on straight runs only.
suspension string
b) Intermediate towers ( 0° to 2° )
with suspension string
c) Light angle towers ( 0° to 5° )
with suspension string
To be used on straight runs and upto 2" line
deviation.
To be used on straight runs and upto 5° line
deviation.
NOTE — In the selection of suspension tower either (b) above or a combination of (a) and (c) may be
followed.
ii) Tension towers
a) Small angle towers ( 0' to 15° )
with tension string
b) Medium angle towers ( 0' to 30° )
with tension string
c) Large angle towers ( 30° to 60° )
with tension string
d) Dead-end towers with tension
string
e) Large angle and dead-end towers
with tension string
To be used for line deviation from 0° to 15°.
To be used for line deviation 0° to 30°.
To be used for line deviation from 30° to 60°
To be used as dead-end ( terminal ) tower or
anchor tower.
To be used for line deviation from 30° to 60° or
for dead-ends.
NOTE — In the selection of tension towers either (e) above or a combination of (c) and (d) maybe
followed.
IS 802 ( Part 1/Sec 1 ) : 1995
6.2 The angles of line deviation specified in 6.1
are for the design span. The span may, however,
be increased upto an optimum limit with
reducing angle of line deviation, if adequate
ground and phase clearances are available.
7 RELIABILITY CONSIDERATIONS
7.1 Transmission lines shall be designed for the
reliability levels given in Table 1 . These levels
arc expressed in terms of return periods in years
of climatic ( wind ) loads. The minimum yearly
reliability Ps, corresponding to the return
ind Zone
Basic Wind Speed, Vt, mfs
1
33
2
39
3
44
4
47
5
50
6
55
NOTE — In case the line traverses on the border of
different wind zones, the higher wind speed may be
considered.
peno
d, T, is expressed as Ps = j 1 ^f I ^-2 Meteorological Reference Wind Speed, Vk
Table 1 Reliability Levels
Transmission Lines
( Clause 7.1 )
of
Si
No
Description
(1)
Reliability Levels
1 2 r
(2)
(3) (4)
i) Return period of design
loads, in years, T
ii) Yearly reliability, Pe
50
150
500
l_10r-j i_10-«s 1-10-8
7.2 Reliability level 1 shall be adopted for EHV
transmission lines upto 400 kV class.
7.3 Reliability level 2 shall be adopted for EHV
transmission lines above 400 kV class.
7.4 Triple and quadruple circuit towers upto
400 kV lines shall be designed corresponding to
the reliability level 2.
7.5 Reliability level 3 shall be adopted for tall
river crossing towers and special towers,
although these towers are not covered in this
standard.
8 WIND EFFECTS
8.1 Basic Wind Speed, Vb
Figure 1 shows basic wind speed map of India
as applicable at 10 m height above mean ground
level for the six wind zones of the country. Basic
wind speed 'Vb is based on peak gust velocity
averaged over a short time interval of about 3
seconds, corresponds to mean heights above
ground level in an open terrain ( Category 2 )
and have been worked out for a 50 years return
period [ Refer IS 875 { Part 3 ) : 1987 for further
details ].
Basic wind speeds for the six wind zones ( see
Fig. 1 ) are :
It is extreme value of wind speed over an aver-
aging period of 10 minutes duration and is to
be cafculated from basic wind speed 'Vb by the
following relationship :
Fr = Vb/Ko
where
Ko is a factor to convert 3 seconds peak
gust speed into average speed of wind
during 10 minutes period at a level of
10 metres above ground. Ko may be taken
as 1-375.
8.3 Design Wind Speed, Vd
Reference wind speed obtained in 8.2 shall be
modified to include the following effects to get
the design wind speed:
a ) Risk coefficient, Ki', and
b ) Terrain roughness coefficient, K^.
It may be expressed as follows:
Fd = Fr X Xi X K^.
8.3.1 Risk Coefficient, K^
Table 2 gives the values of risk coefBcients ATj
for different wind zones for the three reliability
levels.
Table 2 Risk Coefficient K^ for Different
Reliability Levels and Wind Zones
( Clause 8.3.1 )
Reliability
Level
Coefficient K^ for Wind Zones
1
2
3
4
3
■ ■■■— ^
6
0)
(2)
(3)
(4)
(5)
(6)
17)
1
1-00
100
100
100
100
100
2
108
110
Ml
112
113
1-14
3
117
1-22
1-25
1-27
1-28
1-30
IS 802 ( Part l./Sec 1 ) : 1995
8.3.2 Terrain Roughness Coefficient, K^
Table 3 gives the values of coefficient Kr, for the
three categories of terrain roughness ( see
8.3.2.1 ) corresponding to 10 minutes averaged
wind speed.
Table 3 Terrain Roughness CoeflBcient, K^
( Clause 8.3.2 )
Terrain Category 12 3
Coefficient, Kx
108
100
0-85
NOTE For lines encountering hills/ridges, the
value of K% for a given terrain shall be changed to
next higher value of Kt.
8.3.2.1 Terrain categories
a) Category 1 — Exposed open terrain with
few or no obstruction and in which the
average height of any object surrounding
the structure is less than 1'5 m.
NOTE — This category includes open scacoasts,
Open stretch of water, deserts and flat treeless
plains.
b) Category 2 — Open terrain with well
scattered obstructions having height
generaily between 1-5 m to 10 m.
NOTE — This category includes normal country
lines with very few obstacles.
c) Catcgtiy 3 — Terrain with
closely spaced obstructions.
numerous
NOTE — This category
and forest areas.
includes built up areas
8.4 Design Wind Pressure, Pa
The design wind pressure on towers, conductors
and insulators shall be obtained by the following
relationship :
Pd = 0-6 V^
where
Fd ^ design wind pressure in N/m^, and
K(] = design wind speed in m/s.
8.4.1 Design wind pressures Pd for the three
reliability it vels and pertaining to six wind zones
and the three terrain categories have been
worked out and given in Table 4.
9 WIND LOADS
9.1 Wind Load on Tower
In order to determine the wind load on tower,
the tower is divided into diJRferent panels having
a height 'A'. These panels should normally be
taken between the intersections of the legs and
bracings. For a lattice tower of square cross-
section, the resultant wind load Fvn in Newtons,
for wind normal to the longitudinal face of tower,
Reliability
Level
(1)
Table 4 Design Wind Pressure Pd, in N/m''
( Clause 8.4. 1 )
Terrain
Category
(2)
Design Wind Pressure P^ for Wind Zones
r~~
1
{
2
3
4
5
6
(3)
(4)
(5)
(6)
(7)
(8)
403
563
717
818
925
1 120
346
483
614
701
793
960
250
349
444
506
573
694
470
681
883
1030
1 180
1460
403
584
757
879
1010
1 250
291
422
547
635
732
901
552
838
1 120
1320
1 520
1890
473
718
960
1 130
I 300
1 620
342
519
694
817
939
1 170
a mii rmn fstr ■ 1 r Ittf:
^K. I iB^w' V|V SMTPi [^ "ill 94iJi'''n ShViiv nr^n-m Plfea* I
As in the Original Standard, this Page is Intentionally Left Blank
IS 802 ( Part 1/Sec 1 ) : 1995
on a panel height 'A' applied at the centre of
gravity of this panel is:
where
Pa = design wind pressure, in N/m-:
Cdt = drag coefficient for panel under con-
sideration against which the wind is
blowing. Values of Cdt for different
solidity ratios are given in Table 5.
Solidity ratio is equal to the effective
area ( projected area of all the indivi-
dual elements ) of a frame normal to
the wind direction divided by the area
enclosed by the boundry of the frame
normal to the wind direction;
Ae = total net surface area of the legs,
bracings, cross arms and secondary
members of the panel projected normal
to the face in m^ ( The projections
of the bracing elements of the adjacent
faces and of the plan-and-hip bracing
bars may be neglected v\rhile determ-
ining the projected surface of a face );
and
Gt = gust response factor, peculiar to the
ground roughness and depends on the
height above ground. Values of Gr for
the three terrain categories are given
in Table 6.
Table 5 Drag Coefficient, Cdt for Tower
( Clause 9.1 )
Solidity
Ratio
(1)
Drag Coefflcient
(2)
Up to 005
01
0-2
0-3
04
0-5 and above
3-6
3-4
2.9
2-5
2-2
20
considered separately for the purposes of
calculating wind load on the tower, as shown
in Fig. 2.
Table 6 Gust Response Factor for Towers ( C/j )
and for Insulators ( Ci )
( Clauses 9.1 and 9.3 )
Height Above
Ground
Values of G r and G|
Categories
for Trerain
m
1
2
1
3
(1)
(2)
(3)
(4)
Up to 10
1-70
1-92
2-55
20
1-85
2-20
2-82
30
1-96
2-30
2-98
40
2 07
2-40
312
50
2-13
2-48
3-24
60
2-20
2-55
3-34
70
2-26
2-63
3-46
80
2-31
2-69
358
NOTE — Interm
interpolated.
lediate v
alues
may
be
linearly
NOTES
1 Intermediate values may be linearly interpolated.
2 Drag coefficient takes into account the shielding
effect of wind on the leeward face of the tower.
However, in case the bracing on the leeward face is
not shielded from the windward face, then the
projected area of the leeward face of the bracing
should also be taken into consideration.
9,1.1 In case of horizontal configuration towers,
outer and inner faces countering the wind
between the waist and beam level should be
9.2 Wind Load on Conductor and Groundwirc
The load due to wind on each conductor and
groundwire, Fy,c in Newtons applied at suppor-
ting point normal to the line shall be determined
by the following expression:
Fwc — Pd X Cdc X L X d X Gc
where
Pd = design wind pressure, in N/m';
Cdc = drag coefficient, taken as 10 for
conductor and 1-2 for groundwire;
L ~ wind span, being sum of half the span
on either side of supporting point, in
metres;
d = diameter of cable, in metres; and
Gc = gust response factor, takes into
account the turbulance of the wind
and the dynamic response of the
conductor. Values of Gc are given in
Table 7 for the three terrain catego-
ries and the average height of the
conductor/groundwire above the
ground.
NOTE — The average height of conductor/ground-
wire shall be taken up to clamping point of top
conductor/groundwire on tower less two-third the
sag at minimum temperature and no wind.
9.2.1 The total effect of wind on bundle conduc-
tors shall be taken equal to the sum of the wind
load on sub-conductors without accounting for
a possible masking effect of one ofthesubcon-
ductors on another.
IS 802 ( Part 1/Sec 1 ) : 1995
WINDWARD
FACE
Fig. 2 Horizontal Configuration Tower
IS 802 ( Part I/Sec 1 ) : 1995
Table 7 Values of Gust Response Factor Go for Conductor and Groandwire
( Clause 9.2 )
Terrain
Category
(1)
Height Above
Ground, ni
(2)
UP to
200
(3)
Values of Gc
for Ruling
Span of, in m
600
(7)
700
(8)
300
{A)
400
(5>
500
(6)
800 anT*
above
(9)
1 Up to
10
1-70
1-65
1-60
1 56
1-53
1-50
1-47
20
1-90
1-87
1-83
1-79
1-75
1-70
1-66
40
210
204
2 00
1-95
1-90
1 85
1-80
60
2-24
218
2-12
207
202
1-96
1-90
80
235
2-25
218
213
2-10
206
203
2 Up to
10
1-83
1-78
1-73
1-69
1-65
1.60
1-55
20
2-!2
204
1-95
1.88
1 84
1.80
1-80
40
2-34
2-27
2-20
2- 13
208
205
202
60
2-55
2-46
2-37
2-28
2-23
2-20
217
80
2-09
2-56
2-48
3-41
2-36
2-32
2-28
3 Up to
10
2 '05
1-98
1-93
1-88
i-83
1-77
1-73
20
2-44
2-35
2-25
2-15
2-10
206
2-03
40
2-76
2-67
2-58
2-49
2-42
2-38
2-34
60
2-97
2-87
2-77
2-67
2-60
2-56
2.52
80
319
3 04
2-93
2-85
2-78
2-73
2-69
^OlE — Intermediate values may be linearly interpolated.
9.3 Wind Load on Insolator Strings
Wind load on insulator strings 'fwi' shall be
determined from the attachment point to the
centre line of the conductor in case of suspen-
sion tower and up to the end of clamp in case
of tension tower, in the direction of the wind
as follows:
Fwi = Cdi X Pd X >4i X Gi
where
Cdi ~ drag coefficient, to be taken as 1,2;
Pi ~ design wind pressure in N/m';
A\ = 50 percent of the area of insulator
string projected on a plane which is
parallel to the longitudinal axis of the
string; and
Gi ~ gust response factor, peculiar to the
ground roughness and depends on the
height of insulator attachment point
above ground. Values of Gi for the
three terrain categories are given
in Table 6.
9.3.1 In case of multiple strings including V
strings, no masking effect shall be considered.
10 TEMPERATURE EFFECTS
10.1 General
The temperature range varies for different loca-
lities under different diurnal and seasonal
conditions. The absolute maximum and mini-
mum temperature which may be expected in
different localities in the country are indicated
on the map of India in Fig. 3 and Fig. 4 respec-
tively. The temperature indicated in these
maps are the air temperatures in shade. These
may be used for assessing the temperature
etfects.
10.2 Temperature Variations
10.2.1 The absolute maximum temperature may
be assumed as the higher adjacent isopleth
temperature shown in Fig. 3.
10.2.2 The absolute minimum temperature may
be assumed as the lower adjacent isopleth
temperature shown in Fig. 4.
10.2.3 The average everyday temperature shall
be 32°C anywhere in the country, except in
regions experiencing minimum temperature of
— 5°C or lower {see Fig. 4), where everyday
temperature may be taken as 15°C or as
specified by the power utilities.
9
IS 802 ( Part 1/Sec I ) : 1995
10.2.4 The maximum conductor temperature
may be obtained after allowing increase in
temperature due to radiation and heating effect
due to current etc over the absolute maximum
temperature given in Fig. 3. The tower may be
designed to suit the conductor temperature of
75°C ( Max ) for ACSR and 85^C ( Max) for
aluminium alloy couductor. The maximum
temperature of groundwire exposed to sun may
be taken as 53°C.
10.3 Sag Tension
Sag tension calculation for conductor and
groundwire shall be made in accordance with
the relevant provisions of IS 5613 ( Part 2/
Sec 1 ) : 1985 for the following combinations:
a) 100 percent design wind pressure after
accounting for drag coefficient and gust
response factor at everyday temperature,
and
b) 36 percent design wind pressure after
accounting for drag coefficient and gust
response factor at minimum temperature.
II LOADS ON TOWER
11.1 Classification of Loads
Transmission lines are subjected to various loads
during their lifetime. These loads are classified
into three distinct categories, namely,
a) Climatic loads — related to the reliability
requirements.
b) Failure containment loads — related to
security requirements.
c) Construction and maintenance loads — rela-
ted to safety requirements.
11.2 Climatic Loads
These are random loads imposed on tower,
insulator string, conductor and groundwire due
to action of wind on transmission line and do
not act continuously. Climatic loads shall be
determined under either of the following
climatic conditions, whichever is more strin-
gent:
i) 100 percent design wind pressure at
everyday temperature, or
ii) 36 percent design wind pressure at mini-
mum temperature.
NOTE — Condition (ii) above is normally not crucial
for tangent tower but shall be checked for angle or
dead-end towers, particularly for short spans.
11.3 Failure Containment Loads
These loads comprise of:
i) Anti cascading loads, and
ii) Torsional and longitudinal loads.
11.3.1 Anti Cascading Loads
Cascade failure may be caused by failure of
items such as insulators, hardware, joints,
failures of major components such as towers,
foundations, conductor due to defective mate-
rial or workmanship or from climatic overloads
or sometimes from casual events such as misdi-
rected aircraft, avalanches, sabotage etc. The
security measures adopted for containing
cascade failures in the line is to provide angle
towers at specific intervals which shall be
checked for anti-cascading loads ( see 14 ).
11.3.2 Torsional and Longitudinal Loads
These loads are caused by breakage of conduc-
tor(s) and/or groundwire. AH the towers
shall be designed for these loads for the number
of conductor (s) and/or groundwire considered
broken according to 16.
11.3.2.1 The mechanical tension of conductor/
groundwire is the tension corresponding to
100 percent design wind pressure at every day
temperature or 36 percent design wind pressure
at minimum temperature after accounting for
drag coefficient and gust response factor.
11.4 Construction and Maintenance Loads
These are loads
construction and
lines.
imposed on towers during
maintenance of transmission
12 COMPUTATION OF LOADS
12.1 Transverse Loads
Transverse loads shall be computed for relia-
bility, security and safety requirements.
12.1.1 Reliability Requirements
These loads shall be calculated as follows:
i) Wind action on tower structures, conduc-
tors, groundwires and insulator strings
computed according to 9.1, 9.2 and 9.3
respectively for both the climatic condi-
tions specified in 11.2.
ii) Component of mechanical tension Fwd
of conductor and groundwire due to
wind computed as per 11.3.2.1.
10
IS 802 ( Part 1/Sec 1 ) : 199S
Based upon Sufvey of India Outline map printed in 1 987.
The terfitorial waters of India extend into the sea to a distance of twelve najtical miles measured from the appropriate base line.
Responsibilitv for the correctness of infernal details shown on the map rests with the publisher.
^(GovernrTtent of India Copyright 1 995
Fig. 3 Chart Showing Highesi Maximum Temperature Isopleths
11
IS 802 ( Part 1/Sec 1 ) : 1995
MAP OF INDIA
SHOWING LOWEST MINIMUM
TEMPERATURE ISOPLETHs'c
BASED ON DATA UP TO 1958 SUPPLIED BY
INDIA METEOROLOGICAL DEPARTMENT
PROJECTION: LAMBERT CONICAL
ORTHOMORPHIC
Based upon Survey of InOia Outline map primed in 1 987.
Tlie territorial waters of India extend Into the sea to a distarice of twelve nautical miles measured from the appropriate base line.
Responsibility tor tlie correctness of internal ijeiails shown on the map rests with ttie publisher.
) .Government of Indis Copyiight 1 995
Fig. 4 Chart Showing Lowest Mnimum Temperature Isopleths
12
IS 802 ( Part 1/Sec 1 ) : 1995
Thus, total transverse load = (i) + (ii)
" Fwt + Fwc + i*wl + F-nd
where
'Fwc\ 'fwi' and 'Fwd* are to be applied on
all conductors/groundwire points and 'ivt'
to be applied on tower at groundwire peak
and cross arm levels and at any one conve-
nient level between bottom cross arm and
ground level for normal tower. In case of
tower with extensions, one more application
level shall be taken at top end of extension,
12.1.2 Security Requirements
These loads shall be taken as under:
i) Suspension towers
a) Transverse loads due to wind action
on tower structures, conductors,
groundwires and insulators shall be
taken as nil.
b) Transverse loads due to line deviation
shall be based on component of
mechanical tension of conductors
and groundwires corresponding to
everyday temperature and nil wind
condition. For broken wire spans the
component shall be corresponding to
50 percent mechanical tension of
conductor and 100 percent mechanical
tension of groundwire at everyday
temperature and nil wind.
ii) Tension and dead end towers
a) Transverse loads due to wind action
on tower structure, conductors,
groundwires and insulators shall be
computed as per 12.1.1 (i). 60 percent
wind span shall be considered for
broken wire condition and 100 percent
wind span for intact span condition.
b) Transverse loads due to line deviation
shall be the component of 100 percent
mechanical tension of conductor and
groundwire as defined in 11.3.2.1.
12.1.3 Safety Requirements
Transverse loads on account of wind on tower
structures, conductors, groundwires, and insula-
tors shall be taken as nil for normal and
brokenwire conditions. Transverse loads due to
mechanical tension of conditions and groundwire
at everyday temperature and nil wind condition
on account of line deviation shall be taken for
both normal and broken wire conditions.
12.2 Vertical Loads
Vertical loads shall be computed for reliability,
security and safety requirements.
12.2.1 Reliability Requirements
These loads comprise of:
i) Loads due to weight of conductors/
groundwire based on design weight span,
weight of insulator strings and accesso-
ries, and
ii) Self weight of tower structure up to
point/level under consideration.
The effective weight of the conductor/ground-
wire should be corresponding to the weight span
on ihe tower. The weight span is the horizontal
distance between the lowest points of the
conductor/groundwire on the two spans adjacent
to the tower under consideration. The lowest
point is defined as the point at which the
tangent to the sag curve or to the sag curve
produced, is horizontal.
12.2.2 Security Requirements
These shall be taken as:
i) Same as in 12.2.1 (i) except for broken
wire condition where the load due to
weight of conductor/groundwire shall be
considered as 60 percent of weight span,
and
ii) Same as in 12.2.1 (ii).
12.2.3 Safety Requirements
These loads comprise of:
i) Loads as computed in 12.2.2,
ii) Load of I 500 N considered acting at
each cross arm, as a provision of weight
of lineman with tools,
iii) Load of 3 500 N considered acting at
the tip of cross arms up to 220 kV and
5 000 N for 400 kV and higher voltage
for design of cross arras, and
iv) Following erection loads at lifting points,
for 400 kV and higher voltage, assumed
as acting at locations specified below:
Tension
Tower with
Vertical
Load, N
Distance,
from the
Tip of
Cross Arm,
mm
Twm bundle conductor
Multi bundle conductor
10 000
20 000
600
1 000
All bracing and redundant members of the
tewers which are horizontal or inclined up to
15° from horizontal shall be designed to with
stand an ultimate vertical loads of 1 500 N
considered acting at centre independent of all
other loads.
12.3 Longitudinal Loads
Longitudinal loads shall be computed for relia-
bility, security and safety requirements.
12.3.1 Reliability Requirements
These loads shall be taken as under:
i) Longitudinal load for dead-end towers
to be considered corresponding to
13
IS 802 ( Part 1/Sec 1 ) : 1995
mechanical tension of conductors and
gioundwire as defined in 11.3.2.1.
ii) Longitudinal loads which might be caused
on tension towers by adjacent spans of
unequal lengths can be neglected in most
cases, as the strength of the supports for
longitudinal loads is checked for security
requirements and for construction and
maintenance requirements.
iii) No longitudinal load for suspension and
tension towers.
12.3.2 Security Requirements
These loads shall be taken as under:
i) For suspension towers, the longitudinal
load corresponding to 50 percent of the
mechanical tension of conductor and
100 percent of mechanical tension of
groundwire shall be considered under
every day temperature and no wind
pressure.
ii) Horizontal loads in longitudinal direc-
tion due to mechanical tension of
conductors and groundwire shall be
taken as specified in 11.3.2.1 for broken
wires and nil for intact wires for design
of tension towers.
iii) For dead end towers, horizontal loads in
longitudinal directon due to mechanical
tension of conductor and groundwire
shall be taken as specified in 11.3.2 for
intact wires. However for broken wires,
these shall be taken as nil.
12.3.3 Safety Requirements
These loads shall be taken as under:
i) For normal conditions — These loads for
dead end towers shall be considered as
corresponding to mechanical tension of
conductor/groundwire at every day
temperature and no wind. Longitudinal
loads due to unequal spans may be
neglected.
ii) For brokenwire conditions
a) Suspension towers — Longitudinal load
per sub-conductor and groundwire
shall be considered as 10 000 N and
5 000 N respectively.
b) Tension towers — Longitudinal load
equal to twice the sagging tension
( sagging tension shall be taken as
50 percent of tension at everyday
temperature and no wind ) for wires
under strliigihg aind 1-5 tirnes the
sagging tension for all intact wires
( stringing completed ).
13 LOADING COMBINATIONS
13.1 Reliability Conditions
i) Transverse loads — as per 12.1.1.
ii) Vertical loads — as per 12.2.1.
iii) Longitudinal loads — as per 12.3.1.
13.2 Security Conditions
i) Transverse loads — as per 12.1.2.
ii) Vertical loads — as per 12.2.2.
iii) Longitudinal loads — as per 12.3.2.
13.3 Safety Conditions
i) Transverse loads — as per 12.1.3.
ii) Vertical loads — shall be the sura of;
a) Vertical loads as per 12.2.2 (i) multi-
plied by the overload factor of 2.
b) Vertical loads calculated as per
12.2.2 (ii), 12.2.3 (ii), 12.2.3 (iii) and
12.2.3 (iv).
iii) Longitudinal loads — as per 12.3.3.
14 ANTI CASCADING CHECKS
All angle towers shall be checked for the
following anti-cascading conditions with all
conductors and groundwire intact only on one
side of the tower
a) Transverse loads — These loads shall be
taken under no wind condition.
b) Vertical loads — These loads shall be the
sum of weight of conductor/groundwire
as per weight span of intact conductor/
ground wire, weight of insulator strings
and accessories.
c) Longitudinal loads — These loads shall be
the pull of conductor/groundwire a|
everyday temperature and no wind
applied simultaneously at all points on
one side with zero degree line deviation.
15 TENSION LIMITS
Conductor/groundwire tension at everyday
temperature and without external load, should
not exceed the following percentage of the
ultimate tensile strength of the conductor:
Initial unloaded tension 35 percent
Final unloaded tension 25 percent
provided that the ultimate tension under
everyday temperature and 100 percent design
wind pressure, or minimum temperature and
36 percent design wind pressure does not exceed
70 percent of the ultimate tensile strength of
the conductor/ground wire.
NOTE — Fo r 400 kV and 800 kV l ines, the fina l
unto£rde3 tension oi conductors at everyday tempe-
rature shall not exceed 22 percent of the ultimate
tensile strength of conductors and 20 percent of the
ultimate tensile strength of groundwire
J4
IS 802 ( Part l/Si'c 1 ) : 1995
16 BROKEN WlKE CONDITIUN
The following broken wire conditions shall be assumed in the design of towers:
a) Single circuit towers
b) Double, triple circuit and quad-
ruple circuit towers:
i) Suspension towers
ii) Small and medium angle
towers
iii) Large angle tcn;>ion towers/
dead end towers
Any one phase or groundwite broken; whichever is
more stringent for a particular member.
Any one phase or groundwire broken; whichever is
more stringent for a particular member.
Any two phases broken on the same side and same
span or any one phase and one groundwire broken on
the same side and same span whichever combina-
tion is more stringent for a particular member.
Any three phases broken on the same side and sanse
span or any two of the phases and one groundwire
broken on the same side and same span; whichever
combination constitutes the most stringent condition
for a particular member.
NOTE — Phase shall mean all the sub-conductors in the case of bundle conductors.
17 STRENGTH FACTORS RELATED TO
QUALITY
The design of tower shall be carried out in
accordance with the provisions covered in
IS 802 (Part 1/Sec 2 ) : 1992. However, to
account for the reduction in strength due to
dimensional tolerance of the structural sections
and yield strength of steel used, the following
strength factors shall be considered:
l\ Tf wt*»pl M/lth minimum oiio rn ?i t ap/t \/i#»lrt
Strength is used for fabrication of tower,
the estimated loads shall be increased by
a factor of 1.02.
ii) If steel of minimum guaranteed yield
strength is not used for fabrication of
tower, the estimated loads shall be
increased by a factor of 105, in addition
to the provision (i) above.
IS No,
802 r Part
Sec 2 ) :
1/
1992
875 ( Part
1987
3)
1363 ( Part 3 ) :
1992
ANNEX A
( Clause 2 )
LIST OF REFERRED INDIAN STANDARDS
Title
Code of practice for use of
structural steel in overhead
transmission line towers:
Part 1 Material, loads and
permissible stress. Section 2
Permissible stresses ( third
revision )
Code of practice for design
loads ( other than earthquake )
for buildings and structures:
Part 3 Wind loads ( second
revision )
Hexagon head boits, screws
and nuts of product Grade C :
Part 3 Hexagon nuts ( size
range M 5 to M 64 ) ( third
revision )
IS No.
Title
1367 Technical supply conditions
for threaded steel fasteners:
( Part 6 ) : 1980 Part 6 Mechanical properties
and test methods for nuts with
specified proof loads ( second
revision )
(Part 13): 1985 Part 13 Hot-dip galvanized
coatings on threaded fasteners
( second revision )
1573 : 1986
2016 : 1967
2062 : 1992
Electroplated coatings of zinc
on iron and steel ( second
Plain washers ( first revision )
Steel for general structural
purposes ( fourth revision )
15
IS 802 ( Part 1/Sec 1 ) : 1995
IS No,
3063 : 1972
3757 : 1985
4759 ; 1984
5613 ( Part 2/
Sec 1 ) : 1985
5624 : 1970
Title IS No.
Single coil rectangular section 6610 : 1972
spring washers for bolts, nuts
and screws {first revision ) ^^23 • 1985
High strength structural bolts
( second revision ) ^(^^9 : 1972
Hot-dip zinc coatings on
structural steel and other 5549 ; 1955
allied products ( third revision )
Code of practice for design,
installation and maintenance
of overhead lines: Part 2 Lines 8500 ; 1992
above 1 1 kV and up to and
including 220 kV, Section 1
Design {first revision) 10238 : 1982
Foundation bolts 12427 : 1988
Title
Heavy washers for steel
structures
High strength structural nuts
( first revision )
Hexagon
structures
bolts for steel
Hardened and tempered
washers tor high strength
structural bolts and nuts {first
revision )
Structural steel — Microalloyed
( medium and high strength
qualities) (first revision)
Step bolts for steel structures
Transmission tower bolts
Ife
IS 802 ( Part 1/Sec 1 ) : 1995
ANNEX B
( Foreword )
Composition of Slruclural Engineering Sectional Committee, CED 7
Representing
Metallurgical and Engineering Consultant ( India ) Ltd, Ranchi
Chairman
Shri M. L. Mfhia
Members
Shri S. K. Datta ( Alternate to
Shri M. L. Melita )
Shri R. N- Biswas
Shri Yogkndra Singh ( Alternate )
Shrt Ramfsh Chakraborty
Shri S. K. Suman ( Alternate )
Chief Manager ( Engineerjng )
GtNERAL Manager ( Structural )
( Alternate )
Dr p. Dayaratnam
DiRpcTOR ( Transmission )
Deputy Director ( 1 ransmission )
( Alternate )
Shri S. C. Duggal
Shri V. G. Mangrulkar ( Alternate )
Shri D. K, Datta
Shri A. K- Sen ( Alternate )
Shri S. K. Gangoppadhyay
SijRi P. BiMAL ( Alternate )
Shri S. Ganguli
Shri S. P. Garari ( Alternate )
Dr Janardan Jha
Shri S. P. Jamdar
Shri S. S. RathoRE ( Alternate )
Joint Director Standards ^ B & S )-SB-I
DiPUTY Director Standards ( B & S )-SB
( Alternate )
Dr V. Kalyanaraman
Dr J. N. Kar
Prof Saibal Ghosh ( Alternate )
Shri N. K. Majumdar
Shri DM. Srivastava ( Alternate )
Shri S. M. Munjal
Shri A. K. Verma ( Alternate )
Shri M. K. Mukherjee
Shri S. K. Sinha ( Alternate )
ShriB, B. Nag
Shri G. P. Lahiri ( Alternate )
Shri V. Narayanan
Shri A. K. Bajaj ( Alternate )
Shri P- N. Narkhade
Shri M. V. Bedekar ( Alternate )
Dr S. M. Patel
Shri D. P. Pal
Shri B. P. De ( Alternate )
Shri D. Paul
Shri N. Radhakrishnan
Shri P. Appa Rao {Alternate )
Shri M. B. Rangarao
Shri M. S. C. Nayar ( Alternate )
Shri C. S. S. Rao
Shri P- S. Ray ( Alternate )
Dr T. V. S. R. Appa Rao
Shri P- R- Natarajan { Alternate )
Indian Oil Corporation, New Delhi
Joint Plant Committee, Calcutta
RITES, New Delhi
m, Kanpur
Central Electricity Authority, New Delhi
Richardson & Cruddas ( 1972 ) Ltd, Bombay
Jessop & Co Limited, Calcutta
Braithwaite & Co Ltd, Calcutta
Projects & Development India Ltd, Dhanbad
Institution of Engineers ( India ), Calcutta
Road & Building Department, Gandhinagar
Ministry of Railways, Lucknow
IIT, Madras
Bengal Engineering College, Civil Engineering Department.
Government of West Bengal, Calcutta
Hindustan Steel Works Construction Ltd, Calcutta
DCS & D, Inspection Wing, New Delhi
Indian Roads Congress, New Delhi
Engineerslndia Limited, New Delhi
Central Water Commission, Nev/ Delhi
Bombay Port Trust, Bombay
Birla Vishvakarma Mahavidyala, Vallabb Vidyasagar, Gujarat
M. N, Dastur & Co Pvt Ltd, Calcutta
Industrial Fasteners Association of India, Calcutta
Binny Ltd, Madras
Tata Consulting Engineers, Bombay
Engiaeer-in-Chief's Branch, Ministry of Dsfence, New Delhi
Structural Engineering Research, Madras
( Continued on page 18 )
17
IS 802 ( Part 1/Sec 1 ) : 1995
( Continued from pagt 17 )
Members
Shri a. G. Roy
Shri K. B. ChakRABORTy ( Alternate )
Senior Shipping Engineer
Assistant Naval Architect ( Alternate )
Shri A. K. Sen
Shri G. Srebnivasan
Shri P. Sorva ( Alternate )
Dr C. M. Srinivasan
Shri C. R. Arvind ( Alternate )
Dr D. N. Trikha
Dr P. TS. GoDBELE ( Alternate )
Shri U. H. Vary an i
Shri J. R. Mehta
Director ( Civ Engg )
Representing
Bridge & Roof Co ( India ) Ltd, Howrah
Indian Register of Shipping, Bombay
Jessop & Co Limited, Calcutta
Bharat Heavy Electricais Ltd, Hyderabad
C. R. ISIarayana Rao, Madras
University of Roorkee, Roorkee
Kothaii Associates Private Ltd, New Delhi
Directoi General, BIS ( Ex-officio Member )
Member Secretary
Shri S, S. Sethi
Director ( Civ Engg, BIS )
Subcommittee for Use of Steel in Over-Head Line Towers and Switchyard Structures, CED 7 ; 1
Convener
Shri M. L. Sachdeva Central Electricity Authority, New Delhi
Members
Shri Rais-uddin ( Alternate to
Shri M. L. Sachdeva )
Advisor ( Power )
Shri D. K. Narsimhan (Alternate )
Shri Mustao Ahmed
Shri Y. R. Nagaraja ( Alternate )
Shri D. K. Bhattacharjee
Shri S. K. Sinha {Alternate )
Dr p. Bose
Central Board of Irrigation and Power, New Delhi
Karnataka Electricity Board, Bangalore
Damodar Valley Corporation, Calcutta
Electrical Manufacturing Ltd (Projects Construction Division ),
Calcutta
Shri L. N, Banbrjee ( Alternate )
Shri Umesh Chandra
Shri D. Chowdhury ( Alternate I )
Shri E. V. Rao ( Alternate II )
Chief Administrator-cum-Engineer-in-
Chief
Chief Engineer
Superintending Engineer ( Transmission )
( Alternate )
Shri S. Datta Gupta
Shri S, Z. Hussain
Shri Ashok Bajpai ( Alternate )
Joint Director ( Bridge and Structure )
Assistant Director ( TI ) ( Alternate )
Shri H. C. Kaushik
Shri Lal Khubchandani
Shri B. N. Pai ( Alternate )
ShriD. L. Kothari
Shri P. S. Tulsi ( Alternate )
Dr D. M. Lakhapati
Shri P. Bhattacharya ( Alternate )
Power Grid Corporation of India Ltd, New Delhi
Bihar State Electricity Board, Patna
Andhra Pradesh Electricity Board, Hyderabad
Larsen and Toubro Ltd, Madras
Madhya Pradesh Electricity Board, Jabalpur
Ministry of Railways, New Delhi
Haryana Electricity Board, Hissar
KEC International Ltd, Bombay
Bhakara Beas Management Board, Patiala
SAE ( India ) Ltd, Calcutta
( Continued on page 19)
18
( Continued from page 18 )
Members
Dr S. N. Mandal
Shri K. Mohandas { Alternate )
Shri PR- Natarajan
Shri K. Muralidharan ( Alternate )
Shri R. V, Nedkarni
Shri K. N. Awate ( Alternate )
Shri C*. D. Rathod
Shri A. D. Trivhoi ( Alternate )
Shri V. B. Singh
Shri Surendra Narain ( Alternate )
Shri B. Srinivasan
Shri M- A. Majeeth ( Alternate )
suprrintendino engineer
Shri R. Susendran
Shri N. V. Ramesh { Alternate )
Shri S. M Takhlkar
Shri D. C. Mehta ( Alternate )
IS 802 ( Part 1/Sec 1 ) : 1995
Representing
National Thermal Power Corporation Ltt!, New Delhi
Structural Engineering Research Centre, Madras
Maharashtra State Electricity Board, Bombay
Transpower Engineering Ltd, Bombay
UP State Electricity Board, Lucknovv
Tamil Nadu Electricity Board, Madras
Punjab State Eleciricity Board, Patiala
Central Power Research Institute, Bangalore
Gujarat Electricity Board, Baroda
19
( Continued from second cover )
Ice loadings on towers and conductors/ground wires for lines located in the mountaineous
regions of the country subjected to snow fail, may be taken into account on the basis of available
nieteorological data both for ice with wind and without wind. A separate Indian Standard on ice
loadings to be considered in the design of transmission line towers has been proposed to be
brought out.
Formulae and the values have been given in SI Units only.
While formulating the provisions of this code it has beea assumed that structural connections
are through bolts only.
"While preparing this code, practices prevailing in the country in this field have been kept in
view. Assistance has been derived from the following publications:
i) lEC 826 : 1991 'Technical report on loading and strength of overhead transmission lines',
issued by the International Electrotechnical Commission.
ii) Project report No. EL-643 'Longitudinal unbalanced loads on transmission line struc-
tures' issued by the Electric Power Research Institute USA.
iii) CIGRE Report No. 22-13 of 1978 'Failure containment of overhead lines design' by H. B.
White.
iv) Loading and strength of transmission line system, Part 1 to Part 6 issued by 'IEEE
Transmission and Distribution Committee Sub-Group on Line loading and strength of
transmission line structures', IEEE, PESj Summer 1977 Conference Papers.
v) 'Guide for design of steel transmission line towers' issued by American Society of Civil
Engineers, New York, 1988.
vi) 'Guide for new code for design of transmission line towers in India; Publication No. 239,
issued by the Central Board of Irrigation and Power, New Delhi.
The composition of the technical committee responsible for the forniulatioa of this standard is
given in Annex B.
For the purpose of deciding whether a particular requirement of this standard is complied with,
the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded
off in accordance with IS 2: 1960 'Rules for rounding off numerical values { revised y. The
number of significant places retained in the rounded off value should be the same as that of the
specified value in this standard.
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